Nanogeology in China: A review

Y-wn Ju, Cn Hun, Yn Sun, C-nn Zou, Hon-pn H, Qun Wn, Xu-qu Wn, Xn- Lu, Sun-n Lu, Jn-un Wu, Hon-t Co, H-n Lu, J-sn Qu, F Hun, Hon-n Zu, Jn-o C, , Yu Sun

a Key Laboratory of Computational Geodynamics, Chinese Academy of Sciences, College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049,China

b School of Earth Sciences and Engineering, State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, China

c PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China

d Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China

e State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China

f Institute of Geophysical and Geochemical Exploration, CAGS, Key Laboratory of Geochemical Exploration, Ministry of Land and Resources, Langfang 065000, China

g Research Institute of Unconventional Petroleum and Renewable Energy, Chinese University of Petroleum (East China), Qingdao 266580, China

h China United Coalbed Methane Co., Ltd., Beijing 100011, China

i Earthquake Administration of Shandong Province, Jinan 250014, China

j Key Laboratory of Marginal Sea Geology of South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China

k Carbon Research Laboratory, School of Chemical Engineering, Dalian University of Technology, Dalian 116012, China

l Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, School of Resources and Civil Engineering, Northwestern University, Shenyang 110819, China

m Institute of Geophysics and Geomatics, China University of Geosciences(Wuhan), Wuhan 430074, China

ABSTRACT

Nanogeology is a subject that is a combination of geology and nanoscale science, and it has been a frontier field in recent years. It is also a new subject with the features of intersectionality and multidisciplinary.Digging deeper into geological problems and nanoscale phenomena helps better revealing the more essential mechanisms and processes in geological science, which is also an evitable path in the development of geology. In this paper, we elaborate the concept, feature and main subdisciplines, and summarize three stages of nanogeology development from preliminary research in the 1990s to subject formation in China. After summarizing the researchers’ achievements in this field, we illustrate some primary research progresses of nanogeology in China as eight subdisciplines. On the basis of the above content, we propose the development prospect of nanogeology in China. There are many geologic problems with scientific values and economic benefits, such as research of geologic fundamental problems, resource exploration and development, mechanism study and prediction of geological activities(disasters), mechanism research and management of environmental pollution and others. Nanogeology has a great potential in China to solve all of these problems. As a result, the theories and methods of nanogeology will become enriching and advanced. It offers important theoretical basis and technological methods to deal with major issues concerning the national economy and the people's livelihoods, such as the prediction of geological activities, as well as resource distribution and its exploration and utilization.

Keywords:

Nanogeology

Nanoparticle

Nanostructure

Scientific frontier

Research progress

Research prospect

1. Introduction

Nanogeology is the combination of nanoscience and geoscience, as well as the use of nanotechnology tools and geologic tools. Solid earth materials are used as the research objects. Intensive studies are conducted on known or unknown nanoparticles and nanopores in various geologic bodies, to reveal the nanoscale information during the geological processes and the relationship of geologic phenomena, as well as the contributing factors and regularity(Ju YW et al., 2016). The subdisciplines include nanomineralogy, nano-petrology, nano-geochemistry, nanostructural geology, nano-energy geology, nano-ore deposit geology, nano-earthquake geology, nano-environmental geology and others.

The main research objective of nanogeology is to reveal the nanoscale information recorded by solid earth’s material.With the help of the rapidly developing nanoscience study means, experience and results, combined with geology, the subject studies the morphology, structure and components of solid earth materials (Ju YW et al., 2016, 2017; Wang WB et al., 2016). Conducting in-depth studies on geologic problems and phenomena on the nanoscale helps reveal mechanism and processes that is more fundamental in geology, which is an evitable path during the development of geology. Professor Hochella MF Jr, a geochemist and mineralogist, mentioned,“Nanoscience and technology: the next revolution in Earth sciences” (Hochella MF, 2002, 2008). Nanogeology has been developed by combining both geology and nanoscale science and technology, which enormously expands the multi-subject application prospect of earth science. Therefore, it brings to our understanding that the rise of nanogeology will lead to revolutionary improvement of earth science development in the 21st century, and thus major breakthroughs of earth science will be achieved on nanoscale.

Nanogeology is currently one of the most leading-edge sciences. It is a new research field with features of frontier,intersectionality and multidisciplinary. In recent years,geologists have realized the developmental potential of nanometer theory in geology. The rise of nanogeology guides the geoscience workers with new ideas and research direction to know more about the earth. The dynamic integration between nanoscale and earth also offers an opportunity to understand the microcosmic mechanism of geologic bodies and geologic activities.

Regarding the current progress of nanogeology in China(Chen JZ, 1994; Ding ZH, 1999; Zhu XQ and Zhang ZG,1996; Tong CH et al., 1998; Ye Y et al., 2002; Ju YW et al.,2005a, 2005b, 2014a, 2014b, 2016, 2017; Ju YW and Li XS,2009; Chen JH et al., 2005; Lu AH, 2005; Sun Y et al., 2005,2009; Cao JJ et al., 2011; Wang XQ et al., 2011, 2016; Wang et al., 2012, 2014; Zou CN et al., 2011, 2013; He HP et al.,2014; Yang Y et al., 2016a; Wan Q et al, 2016; Chen TH et al., 2018; Chao HT et al., 2009, 2016, 2018), we can see that experts and academicians in geological fields all realize the importance of understanding the movement processes of Earth’s materials on the nanoscale. They comprehensively apply nanoscale material observation techniques, such as electron microscope and atomic force microscope. They also adopt material nano-structural characterization methods, such as various spectra methods (Fourier transform infrared spectroscopy, Raman spectrum and others), as well as low temperature low-pressure fluids absorption and other nanoporous characterization methods. The research scope includes nano-geology features and causes of different levels of materials or structures that are in each circle of planet earth.However, the correlational loose studies of nanogeology are still sporadic, lacking the guidelines set by systematic and completed theories. At present, the study still focuses on the observation and description of nanoscale particles and structures. The knowledge of formation mechanism and the influence of macroscopic geologic processes are still quite unclear. Many follow-up works are still required in order to enrich and advance the theories and methods of nanogeology.Therefore, the studies can provide important theoretical basis to utilize minerals and carbon-based new materials, to explore and develop energy and mineral resources, and to protect the environmental and predict hazards.

2. Research development phase of nanogeology in China

Nanogeology study is still in the early phase in China.After almost thirty years of development, remarkable progresses have been achieved, and thus China has gained certain international influence. The authors believe that nanogeology has mainly experienced three following developmental stages, from the proposition of concepts to multi-direction and practical applications.

2.1. The conceptual proposal and exploratory research of nanogeology

Back in the 1990s, Chinese geologists had already introduced nanotechnology into geology, and explicitly proposed the concept of this new geologic subject. Based on their various levels of researches on nanominerals, nanogeochemistry, nano-structural geology, nano-energy geology and nano-ore deposit etc., they acquired rudimentary understanding of nanogeology (Tang XW et al., 1991; Jiang ZC, 1995; Zhang ZG and Jiang ZC, 1993; Zhu XQ and Zhang ZG, 1996). Chen JZ (1994) summarized the newly developing nanotechnology and introduced some research methods, such as nanosolid, transmission electron microscope (TEM),scanning tunneling microscope (STM), atomic force microscope (AFM) and others. He also brought up that the development of nanotechnology opened a new field of geoscientific research. Therefore, it would lead the understanding and reformation of nature into a new level, and finally take geoscience into a higher level. Tong CH et al.(1998) had already realized that geogas method was a new approach to search for deep deposits and concealed deposits.They adopted on-site geogas to measure and select geogas anomaly samples during indoor model experiments. By AFM,TEM and scanning electron microscope (SEM) etc., the observations showed that geogas materials migrated as a form of nanoparticles. Chinese geologists are the first to come up with the concept of nanogeology, and the first to propose the application prospect of combining nano-technology and geology. However, the early exploratory development is not organized and has a relatively narrow coverage.

2.2. The development of multi-research directions of nanogeology

The early study of nanogeology is restricted by its single technique, insufficient precision, and incomprehensive cognition of nanoparticles and structure. Therefore, the limited influence just only brought about sporadic results.After that, as the rapid upgrading of related instrument and equipment, more scholars realized that natural nano-size matters and nano-structure exist extensively on Earth. On the nanoscale, it is speculated that macroscopic geologic phenomena are feasible and have considerable advantages. It only takes 10 years for Chinese geologists to make a series of achievements in nano-mineralogy, nano-geochemistry, nanostructural geology, nano-ore deposit geology, nano-energy geology, nano-earthquake geology, nano-environmental geology and other fields (Ye Y et al., 2002; Chen TH et al.,2005; Ju YW et al., 2004, 2005a, 2005b; Ju YW and Li XS,2009; Lu AH, 2005; Chao HT et al., 2009; Sun Y et al., 2005,2009; Zou CN et al., 2009). Meanwhile, we must realize that relevant achievements are mainly on relevant scientific problems in nanogeology fields. Still there are no systematic researches on nanometer effects, resources disasters, and environmental problems. The theoretical system of nanogeology has not yet been established, and we are not clear on the overall understanding of nanoscale accumulation and mineralization.

2.3. Comprehensive research and preliminary subject formation of nanogeology

After 2010, Chinese geologists studied several fields of nanogeology in a deeper level and made remarkable achievements. Most of all, several large academic conferences were held, which prompted the development of comprehensive researches in nanogeology (Ju YW et al.,2014a, 2014b, 2016, 2017; Wang YX et al., 2011; Yao SP et al., 2011; Li XS et al., 2012, 2013a; Cheng HF et al., 2012;Sun Y et al., 2013, 2017; He HP et al., 2014; Yuan RM et al.,2014; Lu SF et al., 2016; Wang XQ et al., 2016; Chao HT et al., 2016, 2018; Huang F et al., 2017a; Zhao AK et al., 2017;Chen HF et al., 2017). Geological researchers not only brought nano-technological means, but also nano-thoughts into geological researches. At the same time, they promoted the initial shaping of nanogeology in China, and the following events occurred, which were of significance:

(1) November 2013, Xiangshan Science Conference was held the 476thSession in Beijing, on the subject of “frontier scientific problems of nanoscale accumulation and mineralization in nanogeology”.

(2) August 2014, Geological Society of China Nanogeology Specialized Committee was established, and then nanogeology researchers had their own research institution and academic organization, which was the first nanogeology related research organization.

(3) The following conferences included the 1stChina nano-geoscience seminar, and the 2ndChina nano-geoscience seminar and international academic conference. The conference contents contained many respects of nanogeology research, which showed and exchanged the latest research results in China, as well as confirmed the major scientific problems in the field.

(4)“Bulletin of Mineralogy Petrology and Geochemistry”(in Chinese) in 2016, “Journal of Nanoscience and Nanotechnology” in 2017, and “Earth Science” (in Chinese)which is set to publish in 2018 with a special issue on nanogeology or nanogeoscience. They all have the same purposes, which is to expand the domestic and international influence of nanogeology. To achieve that, we need to use the help of nanotechnology, as well as geological measures,experiences and achievements. In addition, we should make the most use of the achieved international academic frontier advantages. Consequently, basic and applied study can be further reinforced, with which the capability of independent innovation in nanogeology will be promoted.

Nowadays, the research of nanogeology has arisen in the field of geoscience in China, and national fund assistance has rapidly increased. For the past years relevant researches have been contained each aspect of nanogeology, and thus laid a solid foundation for the future development of this subject.

3. Research progress of nanogeology

Based on the Chinese research achievements of eight subdisciplines in nanogeology, the summary of some recent achievements are shown as follows. Research objects and research contents of each subdiscipline are sometimes overlapped but they all have their own focus (Table 1).

3.1. Nano-mineralogy

Nano-mineralogy is an integrated and combined subject of two fields, nanoscale science and technology and minerology.The subject adopts characteristics methods, such as highresolution transmission electron microscope (HRTEM),scanning tunneling microscope (STM), and atomic force microscope (AFM), to reveal the microstructure, morphology,interface relation and the formation mechanism of minerals.The focuses of nano-mineralogy study primarily revolve around mineral growth, mineral dissolution, mineral transformation, mineral evolutionary process, mineral biomineralization, the interaction between organisms and minerals, etc. (Chen TH et al., 2018)

Nanominerals include mineral grains from small crystal size to nanoscale, tubular or rodlike minerals with onedimensional nanostructure, and sheet minerals with twodimensional nanostructures. Significant differences are found between nanominerals and their corresponding large mineral grains in adsorption behavior, dissolution rate, agglomeration state, catalytic activity, electron transmission efficiency in the interface and others. Owing to the different studies between nanominerals and corresponding macroscopic mineral crystals, it helps us build comprehensive understandings about the roles of nanominerals during geological processes, which has significant implications in prompting the development of geoscience into a more microcosmic and deeper direction (Liu J et al., 2018a).

In order to reveal the structure change of microcrystalline graphite in the process of oxidation and expansion, Sun HJ et al., (2018b) studied the products by means of SEM-EDS,XRD, Raman and FTIR. The results show that the interlayer distance of microcrystalline graphite oxide is enlarged and many functional groups, like hydroxyl, carboxyl and epoxy groups are bonded on the graphene layer in the oxidation process. The “nominal anhydrous minerals” (NAMs) such as coesite in eclogites of the Shima area from Dabie Mountains were studied by (Liu WP et al., 2018c) through FTIR analysis and first-principles calculations. The study of the distribution of structural water at microscopic scale can provide important evidences for the formation environment and tectonic evolution dynamics of UHP metamorphic rocks.

The research object of nano-mineralogy includes not only inorganic minerals, but also biological minerals. Wang YY et al., (2015c) synthesized the hexagon columnar pellets aragonite successfully by bionic mineralization. In addition,he proved that the products have structural feature of mesocrystals, by means of a variety of nanoscale testing methods. Mesocrystals are the products of non-classical crystallization process with nanoparticles as the basic building units (Zhou GT et al., 2009; Li H et al., 2018). Magnetotactic bacteria (MTB) are a phylogenetically and morphologically diverse group of microorganisms that synthesize iron minerals of magnetite and/or greigite within complex subcellular structures, the magnetosomes. Magnetosomes have even distribution of granularity (35-120 nm) and usually arranged in chains (Lin W and Pan YX, 2012). Because of the linkage between magnetofossils and pore water oxygen level, organic carbon flux, and redox condition, fossil magnetosomes may also serve as potential archives of paleoenvironmental processes (Lin W and Pan YX, 2012; Chen AP et al., 2014).

The resource attribute of nanominerals has brought about great attention and cognition in the latest 10 years (Chen TH and Liu HB, 2011). Palygorskite clay and sepiolite clay are the typical nano-mineral resources, while also being China’s exclusive nonmetallic mineral resources. Palygorskite have unique properties, which are adsorptive property, colloidal property, carrier properties, strengthening property, high reaction activities and other nano-properties. These properties are well expressed in the depolymerization processing of palygorskite trabeculae, as well as during the development and utilization of new function materials (Wang WB and Wang AQ, 2016; Cai DQ et al., 2014; He HP et al., 2014;Huo CL and Yang HM, 2010). As the information carrier and recorder of all geologic processes, nanominerals not only have resource attribute, but also have environmental attribute. Xie QQ et al.(2016) studied the loess-red clay sequence components of dust depositions, and they ascertained the form, contents and distribution rule of nanominerals, like palygorskite and nano-rod calcite (Fig. 1). Among them,nano-rod calcite is an important indicator mineral of arid environment during the period of loess accumulation (Chen TH et al., 2005). In addition, the results of Xie QQ et al.(2016) have important values in studying the nanominerals in the environment, the formation cause of carbonate in the loess and the paleoclimatic. They also came up with the clay minerals responding mechanism of the paleoclimate change.

Fig. 1. TEM images of (a) morphological and microstructure of nano-rod calcite from Quaternary loess; (b) microstructures of authigenic attapulgite from Lingtai red clay sequence (after Xie QQ et al., 2016).

Limonite is a nano-mineral resource with the main mineral content being nano-mineral goethite. However, as nano-mineral resources, the values of limonite have not yet been fully explored. The iron grade will be too low to be used for iron manufacture. According to studies, limonite has distinct characteristics on physicochemical property, crystal chemistry and morphology, thermochemical reactivity,atmosphere and structure evolution of the thermal treatment,etc. Besides, limonite shows great exploiting and utilizing potential. (Zou XH and Chen TH, 2013; Liu HB et al., 2012).In addition, studying some features of nanominerals can provide theoretical foundation for the preparation,characterization and structure of nanoscale materials. For example, the graphitized molecular structure of coals gives inspiration to produce carbon nanotube. Therefore,nanominerals have a broad exploitation and utilization future.

Clay minerals are layered silicates formed by the combination of silica tetrahedron and alumina octahedron.The weak molecular bonds between layers can be used to prepare nano-clay by interlayer layering and layer separation techniques (Yang NR and Xu LL, 2003). In addition,polymer/clay composite, as a typical nano-mineral composite,was made by embedding many monomers or polymers in the interlaminar domain of the mineral (Feng AS et al., 2006).This kind of composite, on the one hand, shows good strength, dimension stability and thermal stability of clay minerals; on the other hand, it has toughness, workability and dielectric properties of polymers. Lu YP et al. (2008) made some research on the surface modification and properties of nano-kaolin. In his work, nano-kaolin was treated with titanate and silane coupling agent, and FT-IR, sedimentation experiments and bulk density were applied to investigate the modification effect on the powders. By use of modified nano-kaolin, Chen HZ et al. (2008) prepared poly (ethylene terephthalate)/kaolin nanocomposites with in situ polymerization method. The results indicated that nano-kaolin could be dispersed with poly (ethylene terephthalate), and thermal stability of the synthetic material was better. Zhang SY et al. (2015) studied the relationship between the corrosion ratio of steel bars and the nano-kaolin content at different corrosion times by the electrochemical accelerated corrosion method. The results showed that the addition of nano-kaolin can improve the bonding behavior of concrete and steel bars and reduce the stiffness of concrete specimen.

3.2. Nano-petrology

Petrology is the study of rocks and it is one of the important branches in geology. It also studies its compositions, tectonic structure, distribution, cause of formation, evolution history and the relations between rocks and minerals. Nano-petrology is a new discipline that combines both nanotechnology and petrology. Nanoscale rock particles and fluid inclusions can be found in every stage of rocks formation and development, and record many important geological information. Due to technical restrictions, people are yet to be aware of them. Nevertheless, since highresolution electron microscopy and other equipment are available, it is possible to observe nanoscale particles and fluids directly, which promotes the development of nanopetrology(Ju YW et al., 2016, 2017).

Yan EY and Wu XL (2004) adopted TEM to study the jadeite quartzite in the ultra-high-pressure metamorphic belt within Dabie Mountain Anhui Shuanghe Region and the mylonite and basic granulite in the middle of Himalayan Mountains. They analyzed the relation between fluid inclusions and structural limitation, nano-cracks, subboundary, etc., on nano and submicron scale. The results were that fluid inclusions in jadeite quartzite are isolated or in groups and formed into network distributed fluid inclusions.But in mylonite and basic granulite, discovered fluid inclusions are inside host minerals and distributed along the dislocation walls, sub-grains and closed nano-cracks. The phase stats include single phase, multiphase and melt phase.The microscopic structural defect of nanoscale fluid inclusions that are inside rocks and minerals is probably caused by the partial weakening and deep faulting of continental collision orogenic under high strain rate, which is vital for understanding the formation cause of different rocks,as well as fluid effects (Yan ZY and Wu XL, 2004, Wu XL et al., 2008).

By mapping crystal orientations of the whole thin section with EBSD method, of pyroxene exsolution from a polycrystalline garnet porphyroblast of the Western Gneiss Region garnet peridotite, Norway. Zhang JF et al. (2011)found the same basic crystallographic relationship for both clinopyroxene (Cpx) and orthopyroxene (Opx), with the host garnet. The results provide quantitative microstructural evidence demonstrating an exsolution (precipitation) origin,rather than captured inclusions, of both the intracrystalline Cpx and Opx and the small interstitial Opxcrystals. Hu S et al.(2014) measured the hydrogen isotopes and water contents of melt inclusions and apatite that locate far from shock-induced melt veins in the Martian meteorite GRV 020090, using nanoscale secondary ion mass spectrometry (nanoSIMS). This provides an evidence for past-presence of liquid water on Mars. In fact, the same method can be applied to the study of deep water in the earth, in order to reconstruct the geological process of the magma inclusion and the water content of the parent magma (Yang W et al., 2015c).

Nanoparticles and nano-structural phenomena are also common in rocks, especially in a-b fabric plane of the foliation in metamorphic rocks and narrow slip bands. Under stress effect, internal friction and dynamic differentiation may lead to changes in physical-chemical fields, and further affect the order of nanoparticles within such narrow distorting centralized areas (Sun Y et al., 2005, 2009, 2014, 2018a; Ju YW et al., 2016, 2017). The discovery of nanoparticles in the slip lane of rocks is a classic representation of nano-petrology development. By studying this type of nanoparticles and nano-structure in detail, it is not only be used to analyze the microcosmic mechanism of rock metamorphism and deformation, but also help ascertain the geologic motion during geologic historic periods.

Researches on nanoscale structure of organic rocks have been studied quite a long time. The studies primarily focus on the characterization of coal macromolecular structure (Ju YW et al., 2005a; Ju YW and Li XS, 2009), and discuss the effects of metamorphic grade and deformation degree on their structure. Especially, detailed analysis is performed in nanoscaled pores and nano-deformation coal matrix properties of physical and gas storage capacity. Some certain organic rocks can also be developed to prepare carbon materials. Carbon nanotubes with Y- or T-type junction morphologies have great application potential (Wang ZY et al., 2006). Wang ZY et al.(2006) suggested the synthesis of branched carbon nanotubes (BCNTs) from coal, the cheapest natural carbon source, by arc-discharge with copper as catalyst (Fig. 2). It has been found that BCNTs with a purity of ca. 70% can be obtained in large quantity under suitable experimental conditions.

Fig. 2. TEM images of BCNTs prepared from coal (after Wang ZY et al., 2006). (a) an image showing abundant BCNTs; (b) two Y-junctions marked as A and B by black arrows, which are circled in square in (a).

Liu QF et al.(2018b) proceeded with the test analysis of coral series graphite with different metamorphic grades, and their analysis shows that as the graphitization degree of samples increases, the interlayer spacing between carbon atoms gradually decreases, while the number of layers and the area of single layer both increase. In Raman spectrum, G band gradually increases and becomes sharp, and the intensity ratio and area ratio of D band and G band both decreases, which shows that sp2plane domain of carbon atom increases.According to the lattice images of transmission electron microscope, during the transformation from anthracite into graphite structure, first the aromatic lamella of coals forms into mini-columns with graphitic structure. Then these minicolumns join and bind together, and finally form into graphitic crystal layer that extends unlimitedly and horizontally.

Although the study on nanoscale structure and particles has already made some achievements in petrology, it is still in the preliminary phrase that requires more data and a better theoretical system to enrich and develop.

3.3. Nano-geochemistry

The development of geochemistry to the nanometer scale,is emphasized on in situ analysis with high resolution. Based on this, technological means like nano-SIMS has become an important analytical platform to determine chemical compositions of solid materials, with relatively high mass resolution, spatial resolution, sensitivity, and analytical precision (Yang W et al., 2015c). The application in nanogeochemistry include trace element distribution images in mineral zoning (Li XH et al., 2013b), high spatial resolution(2-5 μm) Pb-Pb and U-Pb dating (Yang W et al., 2012),Cisotopic analysis for diamond and graphite, Oisotopic analysis for carbonate, S isotopic analysis for sulfides (Zhang TC et al., 2014).

Nano-geochemistry aims to study the chemical composition, chemical reaction and chemical evolution law of nanomaterials that are ubiquitous in nature, as well as their effects on geochemical processes. The research fields of nanogeochemistry mainly include: geochemical processes of nanoparticle formation; information record of nano-scaled geochemical processes and geologic meaning of nano-scaled phenomena; understand the organism-mineral interaction and its limitation on biological weathering and elementary geochemical cycle from nanoscale, and then revealing the process mechanism, contents, form, structural feature and life indication of biological mineralization, as well as its relationship with mineralization, enrichment of hazardous elements, etc. (Ju YW et al., 2016, 2017; Wan Q et al., 2016;Wang WB et al., 2016).

Deep mineralization related nanoparticles can be stored in soils, gases and organisms above the ore body, and therefore,separating nanoparticles in these mediums can develop nanogeochemistry prospecting methods. Wang XQ et al.(2012,2016; Fig. 3a) aimed at metal nanoparticles and analyzed them in detail. These nanoparticles can be observed in soils,geogas, and even plants above the buried Cu-Ni deposit,hidden gold deposit and hidden multi-metal deposit of silvergold-copper. It was revealed that the nanoparticles showed consistency or similarity in particle size, morphology,components, structure and other features. Given the shape of the hexagonal crystal and ordered arrangement of internal atoms, it has been confirmed that the nanoparticles are the outcome in endogenous condition, which means the nanometal particles on Earth's surface originally came from deep ore body. After abundant observations, Cao JJ et al.(2009,2011; Fig. 3b) proposed to combine the geogas measurement and the observations of geogas particle size, structure,components and other characteristics to detect concealed ore body. They said the nanoparticles in metallogenic materials could integrate with gas molecules. The nanoparticles are used geogas current as carriers and then migrated along with upflow. Since they have large surface areas, some properties of these nanoparticles can be the same as that of gases.Therefore, they can also migrate by themselves in the form of“gas-like phase” (Wang XQ et al., 2012). These nanoparticles also have the strong ability of penetration.

Fig. 3. (a) Nanometer hexagonal crystals of Cu–Ti alloy in geogas (after Wang WB et al., 2016). (b) TEM photomicrograph of spherical Pbbearing particles (b) and cudgel Pb-bearing particle (c) (after Cao JJ et al., 2009).

Recently, extensive observational experiments of nanometal particles have been carried out on the known gold,cooper, cooper-nickel and other deposits (Cao JJ et al., 2009,2011; Wang XQ and Ye R, 2011; Ye R et al., 2015; Wang XQ et al., 2017), and the results show that abundant nanoscaled metal particles are deposited in soils, geogas and minerals within the mine lot. These particles are similar in size, morphological feature and compositional characteristic.The diameter of particles is between 5 nm and 100 nm. Most of the particles are gathered aggregates and comprised by single metal element or alloys. Besides, some particles are hexagon crystals with orderly crystal structure, suggesting that they are the outcome of endogenous condition.Nanoparticles from various mine deposits are diffident, and the most distinct part is their chemical composition. For example, particles with Au are only captured in gold deposits,while Ni and Cr are mainly stored in Cu-Ni deposits. Hence,the collected and observed nanoparticles within surface medium of the mining area are closely related to the deposit type (Wang XQ et al., 2017). Studying various physical chemical characteristics of nano-scale particles can help explain sophisticated geologic phenomena from the microscopic and mesoscopic point of view, which is meaningful in both theory and practice.

3.4. Nano-structural geology

Nano-structural geology is a subject that investigates different structural phenomena from the nanoscale, especially the microstructure, and then discusses the tectonic dynamics and mechanisms in combination with macroscopic regional structure. The main researches include: the feedback relationship between the nano-scaled coating structure of deformed geologic body and shear slip motion; the relation between nano-micron grain structure developed in faulted structural belt and the extraction behavior of supercritical fluid; and the relation between brittle-ductile deformation and metamorphism of organic rocks, like shale and coal bed, and gas storage mechanisms of these rocks etc. (Sun Y et al.,2005, 2008; 2016; Ju YW et al, 2009, 2014a, 2016, 2017;Chao HT et al., 2009, 2016; Li XS et al., 2012, 2013a; Shen BY et al., 2016; Liu HL et al., 2017; Huang QT et al., 2017b).

Nanoparticles are normally found in the slip layer of shearing motion. Rolling and slipping dominate the structural surface motion, and nano-sized layer can act as lubricant and resistance reducer, which helps accelerate the fracture movement and expand the size (Sun Y et al., 2016).Therefore, the interaction between shear slip and nanoparticles gives each other mutual feedbacks (Sun Y et al.,2008). Shen BY et al. (2016) analyzed the shear surface of three types of rocks in a ductile shear belt through SEM at nanoscale. The results show multiple nano-textures and nanostructures in all three kinds of rocks and a positive relationship between the development degree of nanoparticles and the stress of the rocks. Several possible formation mechanism of the nanoparticles were proposed, including thermal decomposition of sheet silicates under shear stress, or brittle deformation of minerals after ductile deformation, then followed by crushing and grinding of the particles to nanoscale under shear force.

Wang Y et al. (2018a) analyzed three kinds of rock samples (granite, granitic gneiss and quartz schist), which were developed in the ductile shear zone, then observed the structure and aggregation morphology of nanoparticles. Based on the development process and formation mechanism of nanoparticles in the ductile shear zone, the development phases are divided as granulation stage-alienation stagestratification accumulation stage. Similarly, observations and researches were conducted on the lubricating effect of nanoparticles in the fault surface. The results showed that nanoparticles caused the widely developed macroscopic fault mirror slips on the fault surface during the fault sliding process (Sun Y et al., 2009; Liu H et al., 2009). So far, nanoscale particles have been discovered in several ductile shear zones in China, such as Tancheng-Lujiang fault zone, South China Wugong Mountain, Red River fault zone etc.Generally, these nanoparticles are less than 100nm, and mostly in globular, rod-like, tubular and other forms (Fig. 4).Cai ZR et al.(2017) used SEM to observe the samples of mylonite, gneiss and schist in a typical ductile shear zone within the Red River fault zone. They discovered two types of nanoparticles and then analyzed their formation causes (Liu DL et al., 2004; Cai ZR et al., 2017). In the follow-up work,Cai ZR et al. (2018) recognized twelve kinds of nanoparticles aggregations, which showed obvious differences in their morphology features and development stages. The observation reflect different tectonic stress, temperature and pressure conditions that different areas have experienced in the shear process of Red River Fault.

However, tectonism has more significant influences on soft rocks and organic rocks, like coal petrography, shale etc.The change in the stacking degree of coal Basic Structure Unit (BSU) reflects the change in tectonic deformation strength, which can be used as an indicator of nanoscale deformation degree of tectonic coal structure (Ju YW et al.,2017; Fig. 5). With SEM, Ju YW et al., (2016) discovered Permo-Carboniferous shales in Southwest Fujian and Huainan region and Lower Paleozoic shales in east Sichuan Basin through their preliminary studies. After tectonic deformation,many nano-scaled pores, and large amounts of fissure were found in brittle deformation shale. While massive nano-scaled crumpling phenomena were found in ductile deformation shale samples, and the quantity of nano-scaled pores increased, which was also confirmed by liquid nitrogen absorption, carbon dioxide adsorption and other porosity character tests.

Fig. 4. SEM images of nanoparticles developed in ductile shear zones (after Liu HL et al., 2017). (a) the sample was paragneiss taken from Taroko ductile shear zone in Taiwan. The nano particles on paragneiss surface may be the products at granulating stage. (b) the sample was quartz schist taken from Xiaomei ductile shear zone in Hainan Island. Rubbed (wiped) ridge and groove (trench) constituted by nano particles in belt structure, indicating plastic flow (a-axis), where a-axis represents shear sliding direction. The small arrow represents for wiped ridge formed by accumulation of nano particles.

Fig. 5. HRTEM images of tectonically deformed coals (after Ju YW et al., 2017). Brittle deformation: (a, b) basic structure units are scattered and isolated with small diameter and no directionality; small brightness of diffraction ring (002). Ductile deformation: (c, d) basic structure units are stripy and variegated with large diameter and strong directionality; dispersed brightness of diffraction ring (002).

The observational study of Sun Y et al., (2005) is about slight creeping in Carboniferous mudstone within Well Shaancan 1 of Shaanxi Province and Permian mudstone within Yellow sea borehole NH. In the associated fault rocks,they found ductile brittle shear zone and unique symbolic ultrastructural (micro and nanometer level) spherulitic texture,rheological structure etc. The structure of fault rocks in ductile brittle shear is relatively dense, and these rocks are good blocking surfaces for capturing oil gas. Ductile shear is different from dynamic friction, and is a gradually increasing slip. Studying the mechanism of ductile shear on the nanoscale helps prompt the development of microstructure dynamics and explore new fields of structural geology.

3.5. Nano-energy geology

Nano-energy geology is a subject that studies the characteristics of nano-sized pores and fissures in unconventional or tight reservoirs, analyzes and predicts oil and gas accumulation (Ju YW et al., 2004, 2005a, 2014a,2014b, 2016, 2017; Zou CN et al., 2011, 2013; Wang GC and Ju YW, 2015; Wang GC et al., 2015a; Lu SF et al., 2016;Zhang H et al., 2016; Yang YF and Bao F, 2017; Hu QH et al., 2017; Zeng JH et al., 2017; Xiao DS et al., 2017). The main research objects are the reservoirs that contain coalbed gas, shale oil and gas, tight sandstone oil and gas, natural gas hydrate and others. The research contents include the size,type, form, formation cause, connectivity, gas bearing,lipophilicity, hydrophily and other features of pores and fissures. Besides, the hazard evaluation will be made on the coalbed activities, including mining, beneficiation, coking,gasification, liquidation, coalbed gas exploitation and gas outburst. Hence, it holds extremely vital significance on the gas accumulation mechanism of coal, shale and tight sandstone, prolific zone prediction and other aspects.

Petroleum geologists are expanding their perspective from conventional traps to unconventional continuous reservoirs,and characterization study for unconventional or tight reservoir in micrometer and nanometer scale is becoming more and more important. Nanopore is the main body of reservoir space, up to 70%–80% of the total, in tight reservoirs. Researches show that the pore size, in several representative unconventional oil and gas tight reservoirs, can be as low as several nanometers to dozens of nanometers (Zou CN et al., 2011; Yang Z et al., 2015b; Fig. 6).

Fig. 6. Diagram of pore size in several representative unconventional oil and gas tight reservoirs (after Zou CN et al., 2011; Yang Z et al., 2015b).

Shale gas will be important component of China’s energy structure in the future. In recent years, a series of researches have been conducted on microstructure of varied shale gas reservoirs (Fig.7), shale gas producing, percolation mechanism and others (Zou CN et al., 2011, 2013; Ju YW,2014b, 2016, 2017; Wang GC and Ju YW, 2015; Wang GC et al., 2015a; Zhang H et al., 2016; Yang YF and Bao F, 2017;Hu QH et al., 2017). The characteristics and influential factors of shale gas reservoirs in China are summarized from these results. They also found out feasible approaches that fit Chinese geologic condition including evolution methods, as well as exploration and development methods. Wang XZ et al.(2018b) investigated organic pores, whose size is relatively small in all kinds of pores, of Yanchang shale formation particularly by argon ion polishing and field emission scanning electron microscopy. Most of the organic pores are less than 30 nm.

Fig. 7. SEM images of pores in shale and tight sandstone. Longmaxi Formation from Fuling shale gas field in Sichuan Basin (after Yang YF and Bao F, 2017): (a) BSE image, nanopores within bitumen; (b) SE image, pore-filled bitumen with numerous nanopores. Yanchang Formation from Ordos Basin (after Zou XH et al., 2013): (c) pores in the matrix of slate chloride; (d) organic pores.

Meanwhile, researches on other unconventional oil gas also can also reach nanoscale (Zeng TH et al., 2017; Xiao DS et al., 2017). By using spectroscopic methods, like Raman spectrum, nuclear magnetic resonance spectrum and others,fluid injection methods, such as liquid nitrogen absorption,carbon dioxide absorption and others, and molecular dynamics simulation technique etc. (Ju YW et al., 2005b; Ju YW and Li XS, 2009, 2014a; Yao SD et al., 2011; Li J et al.,2015), we can characterize the nano-pore structural feature of reservoirs that contain coalbed gas and tight sandstone gas.Pan JN et al. (2015) analyzed the macromolecular and nanoscale pores of different types of tectonically deformed coals by AFM. The nanostructures of coal differed in terms of the metamorphism degree, deformation degree, and deformation properties. Zeng JH et al. (2017) discussed the influence of tight sandstone micro-nano-pore-throat structures on oil accumulation by combining casting thin section and micro-nano-CT. Tight sandstone has relatively large pores,while nano-CT has relatively low resolution among frequently-used imaging methods at nanoscale. Thus, the advantage of nano-CT, characterizing the pore structure from three-dimensional scale, can be fully exerted. The adsorption behavior of CH4and CO2in illite slit pores with different sizes under varying temperature and pressure conditions was simulated by GCMC method (Lu SF et al., 2018). The results showed that the adsorption capacities obtained from both molecular simulation and experiments can have the same connotation and be comparable only if being normalized to the surface area. Therefore, more profound understanding on associated microscopic dynamic processes can be acquired.

In recent years, researches on natural gas hydrate have gradually expanded to nanometer and mesoscopic levels. In the bottom of South China Sea, nano-scaled argillaceous siltstone has large influences on deposition rate in sea bottom and velocity of water flow. By studying the mass transfer properties of gas and water in argillaceous siltstone, it can help build hydrate accumulation dynamic model, and eventually establish the formation-evolution model of Shenhu natural gas hydrate (Su Z et al., 2014). Through research on the dynamics of methane hydrate formation in the sea sand of South China Sea, sea sand particles (average diameter around 12nm) with different water contents can have remarkable influences on the growth dynamics of methane hydrate. For sea sands in South China Sea with different water contents,nano-pore structure shows different gas-liquid contacting forms. It changes the mass transfer of hydrate that grows inside nanoparticles. Meanwhile, the research also indicates that sea sands with low water contents have better repeatability of experiments on methane hydrate than sea sands with high water contents (Zhang Y et al., 2017).

3.6. Nano-ore deposit geology

Nano-ore deposit geology is a subject that uses nanometer technology and methods to study the process formation,transferring mechanism and storage mechanisms of metallogenic materials, thus forming a new perspective to explore concealed deposits. The study of mineral deposit is multidisciplinary, including the sources, activation, migration sedimentation and mannerization mechanism of metallogenic materials. The essential problems that are involved include the physicochemical properties of metallogenic materials.Nanometer effect can cause nanometer materials , in geologic body, to have different physical and chemical behaviors from macroscopic substances. A nano-material field can develop in geologic body, especially around deposits. Upflow brings these nano-scaled materials and vertically migrates to the surface. Sometimes these nanoparticles themselves can migrate as a form of “gas-like phase” (Wang XQ et al., 2012).If nano-materials that are closely related to deposits are captured and analyzed, they can be used for exploring minerals. Therefore, a new subject is born, which is the study of nano-prospecting.

“Fine-disseminated type gold deposit”, which is Carlintype gold deposit, is the most representative nano-ore deposit.The basic characteristic of this gold deposit is that golds in this deposit are invisible to the naked eyes, and these golds primarily exist in forms of nano-scaled natural gold particles and solid solutions (Hua SG et al., 2012). As Xia Y (2005)discovered, golds in Guizhou Shuiyingdong gold deposit(Carlin-type gold deposit) are mainly nanogold. Experiencing rapid precipitation, these golds deposited in arsenopyrite bands of small pyrites that are several microns wide, as well as in small hydrothermal fluids of arsenopyrite that are dozens of microns wide. Among them, the switch of mineralization condition and the absorption of pyrites are the main factors.Researches have been carried out on the occurrence mode of rare earth elements that are accumulated in the weathered crust of rare earth deposit below the southern Jiangxin hillock.The results show that there is not only hydrate or hydroxyl hydrate ionic phase, but also large amounts of colloidal sedimentary facies or mineral adsorbed phase. Generally,these rare-earth minerals are nano-scaled (10-150nm) mineral granules that are absorbed by clay minerals, and then cemented together. TEM experiments further confirm that some rare-earth mineral granules are polycrystalline aggregations of nano-scaled cerianite (Liu R et al., 2016).

Adsorption is regarded as an important metallogenic mechanism for the supergene and epithermal ore deposits.Zhu XQ et al. (2005) found that the nano-sized native silver and gold are strongly selective to naturally occurring minerals. Silver shows a strongly selective adsorption tendency toward galena and gold toward pyrite, which is in good consistency with what is observed in nature. In the gold deposits in Hunan Province and other similar regions, most of the gold in pyrite and, especially, in arsenopyrite is invisible,as particles less than 0.1 μm. This raises divergence of views about the occurrences of gold in such minerals, i.e. ultramicro particles or isomorphs in mineral lattices. Based on experiments and ore-dressing results in related gold deposits,the invisible gold in pyrite and arsenopyrite is considered to exit as nanometer gold (mineral gold), but not lattice gold(structure gold) (Ai GD et al., 2010). In Nibao gold deposit,point analysis by EMPA and the scanning of the surface wave spectrum showed that the distribution of Au in gold-bearing minerals is not uniform. Zheng LL et al. (2017) inferred that Au mainly occurs in arsenian pyrite and arsenopyrite as an“invisible” solid solution, and probably also as small amounts of nanoparticles native gold.

The coexistence relationship between organic matters and mineral deposits, along with their complicated interaction,generally leads to the anomaly enrichment of metal elements in organic rocks. The special microscopic structural relation between organic matters and metals may restrict the scattered ultramicron occurrence mode of metal minerals, which is same with the feature where metal minerals can be separated from minerals. Recent researches showed the paragenesis and enrichment of multi-metal elements in Southern China, where the black rocks series from Sinian and Cambrian system are widely stored (Yang XL et al., 2008; Zhang FX et al., 2009).In western Guizhou province, the gold contents of upper Permian series coals are often higher than that of other crustal abundance, and higher than the average gold contents of all coal forming periods in China. For this abnormal phenomenon, Wang R (2011) systematically analyzed the geochemical behavior of gold and other associated elements in major coal-bearing stratums within this region. The discovery showed that inside the coals the gold were mainly in inorganic state, and were mostly stored in mineral carriers,such as pyrite. Besides, nanometer dispersion gold is the one with the primary occurrence.

However, the traditional meaning of ore deposits cannot fully represent nanometer deposits. This is because nanominerals generally have features like huge specific surface areas, high absorption and ion exchange capacity, high chemical reactivity, high thermal decomposition activity, etc.These features also determine that the processing and utilization of nanominerals are different from the utilization of conventional resources. In addition, the works are more focused on taking full advantage of the nanometer characteristics of nano-minerals and then using this to manufacture functional materials (Chen TH and Xu HF,2003). Nano-ore deposits are rich in resources, cheap in raw materials, and environmentally friendly. Nanoscale structuration is easy to complete due to their natural vesicular structure, and the processing technique is simple. They contain valence-variation elements, which can transform into functional materials with multi valence states and structural conditions. In addition, there are many varying methods to remove pollutants (Chen TH et al., 2018).

3.7. Nano-earthquake geology

Nano-earthquake geology is a subject that studies the development mechanism of faulting on the nanoscale and then reveals the formation process of earthquakes under micro conditions. It explains the earthquake mechanism through the nanoscale researches of friction theory, then speculates the seismic causes, and thus predicts the earthquake. In the shear slip plane, nanostructure is rub viscosity belt of nanometer and micrometer bed of particles, which is probably the narrow causative fault. Normally, the width is only from few millimeters to several centimeters.

Wenchuan earthquake occurred on May 12, 2018. In the main co-seismic surface rupture zone, the Beichuan-Yingxiu fracture zone, thin layer of fault gouge can be found with strong deformation in several dislocation surfaces. Yuan RM et al. (2014) selected several fault gouges as research objects based on the large vertical shift. With the help of lens stereoscope and SEM, they studied the morphology and structure, and found two types of particles in which nanomicrometer monomers and their complexes commonly existed in the fault frictional sliding surface. The abrasion, grind and powdering of fault frictional sliding surface are the main methods of forming (Fig. 8). The main structural features are stripped and stratified structure of plastic deformation,scattering and accumulated structure of brittle deformation, as well as loose structure formed by discontinuous dynamic friction (fault viscosity sliding). Studies confirm that the structure of nano-micrometer particles in the co-seismic dislocation surface of Wenchuan earthquake is the geologic trace caused by seismic fault slip (not pseudotachylite). The structure also witnesses the seismic fault slip, which can be used as the standard for determining the earthquake fault.Chao HT et al., 2009 conducted detailed observations and analysis on Shandong Haiyang fracture within the eastern China Tan-Lu active fault belt that formed in the Quaternary.They discovered that fault belt experienced early development stage of ductile shear foliation surface and later went through the development stage of brittle fault friction surface (Chao HT et al., 2009). It does not matter whether it is early static friction of ductile earthquake-generating or later dynamic friction of brittle earthquake generating. Nanoparticles can develop under both conditions with comparatively good roundness and sphericity. These nanoparticles both have rigid features of shaping and the flow deformation feature of stretching, which explains the deformational behavior of visco-elasticity in shear motion (Wang ZC et al., 2015b; Chao HT et al., 2016).

Fig. 8. Pictures of micro-nanometer grains on the slip surface of the Shaba fault gouge under SEM (after Yuan RM et al., 2014). (a) scattered ball-shaped grains; (b) inlaid elongated grains; (c) complexes of micro-nanometer grains with tension fractures and local tilt edge (marked by the white arrows); (d) worm-shaped (H), cake-shaped (E) and massive-shaped (G) complexes with tension fractures and local tilt edge (marked by the white arrows); loose region exited among these complexes (marked by dashed line).

During the stick-slipping process in the fault, clay minerals are mainly schistose clay minerals in directional alignment. Within the field of view, SEM can clearly observe schistose clay minerals in directional alignment, and multiple stick-slipping events can be recognized. However, the creepslipping phenomena are common in the fault gouge. Under the sight of SEM, they are presented as fold deformation, flow deformation, sliding around the gravels, entangling deformation, etc. (Chao HT et al., 2018). By now, Chinese scholars in earthquake geology have already held preliminary investigations on the nanoscale kinetic mechanism in both earthquake-generating faults by ductile creep and causative faults by brittle stick-slip, laying a foundation for solving macroscopic seismic phenomena.

3.8. Nano-environmental geology

Nano-environmental geology is a subject that studies the particulate pollutants on nanoscale and the application of nano-scale particles or pores in pollution treatment. The researches mainly include: rock and soil environmental, and aquatic environmental behavior of nano-materials, as well as the recombination behavior of nano-materials and coexisting pollutants in the environment; nano-pores of minerals are used as absorbents to solve environmental pollution; the rapid determination and characterization methods of nano-scaled materials or nano-pores in geologic environment (Wang WB et al., 2016).

Soil heavy metal contamination is one of the key environmental problems around the world. In recent years,many researchers have paid their attentions to the application of nanomaterials in soil heavy metal remediation (Cui YS et al., 2018). Yang ZM et al. (2016b) used a kind of biocharsupported nano-hydroxyapatite (nHAP@BC) material in insitu remediation of lead-contaminated soil, which greatly reduced the bioavailability of Pb in the soil. Cheng JM et al.(2014) mixed Cu contamination soil with the surfacemodified nano-scale carbon black (MCB), to examine the effect of MCB on the remediation the soils polluted by Cu and Zn. And the results showed that metal contents of exchangeable and bound to carbonates (EC-Cu or EC-Zn) in the treatments with MCB were generally lower than those without MCB, and decreased with the increasing of MCB adding amount (p＜0.05).

Perfluorinated compounds (PFCs) widely exist in aqueous because of their high solubility and stability, which has potential risk to human health due to the high bioaccumulation and potential toxicity. Compared with bulk materials, nano-materials have higher reactivity because of their special structure. Xu Q et al. (2018) discussed the issues and prospects for PFCs removal from water by nanomaterials by summarizing some nanomaterials such as carbon nanotube,modified clay minerals, nano-TiO2, In2O3, Ga2O3, etc. which have been applied in adsorption, nanofiltration,photochemistry, electrochemistry, etc. The advantages and disadvantages of aforementioned technologies were summed up here, revealing the mechanism as well.

Tracking a pollution incident of poisonous metal caused by coal ash leak, Yang Y et al.(2015a) discovered a unique Magneli phase titanium oxide, which is a typical secondary nanoparticle that is closely linked to coal-fired activities.Yang Y et al.(2016a) and Tou FY et al.(2017) recently found the coexistence of Pb nanoparticles and Sn nanoparticles in Shanghai road dust samples and excess sludges respectively.Tou FY et al. (2017) also used nanoparticles analysis technique that is single particle inductively coupled plasma mass spectrometry (SP-ICP-MS), and found that the test results of this technique were the same with transmission electron microscope images. Recent studies of Xu J et al.(2016a) show that nano-scaled abiogenic ZnS is polycrystalline, but biogenetic ZnS is single crystal. Hence, it is speculated that polycrystalline nanometer ZnS may be formed under abiogenic conditions in the sludge, which is the same case with single crystal ZnS.

Scholars used transmission electron microscope/energy spectrum (TEM/EDX) and X-ray photoelectron spectroscopy technology to observe imaging of particulate pollutants in air and analyze the distribution of the including elements. They find that most organic matters are fine particles. As main pollution resources, S, N and other elements mainly distribute in relatively larger particles with diameters of 0.56–1.8 μm(Xu P et al., 2016b; Zhou QH et al., 2016).

Atmospheric particulates, especially fine particulate matters, are carriers for poisonous and hazardous materials. In addition, atmospheric particulates have features like hygroscopicity, optical absorption, scattering ability, etc.Hence, atmospheric particulates are important to the environment and climate change. The scattering effect of atmospheric particulates depends on particle size, chemical components, surface texture feature and others. The direct radiative effect of particulate matters is different. For example, sulfate particles can increase the reflected solar radiation and thus causes decrease in the temperature, which has a certain bucking effect of greenhouse effect (Wang DD et al., 2014). Sea salt particles are important components of atmospheric particulates in coastal cities. They are rapidly aged in urban environment, and have important influences on the moisture absorption and scattering of light (Li WJ et al.,2010).

4. Research prospect of nanogeology in China

The study of nanotechnology is currently a research hotspot. It pushes human nature remaking into a new level,which is from micron size to nanometer, it also lifts geologists’ ability in understanding and remaking nature into a new level. With abundant achievements and a wild coverage, China has taken off to an early start in the study of nanogeology. It spans multiple orders of magnitude, through a combination of nano-scaled geologic body and macroscopic geologic phenomenon, structure, materials and others. Hence,by characterizing geologic behavior mechanism on Earth,many problems that have scientific values and economic benefits can be solved, such as geologic activity prediction and resource distribution.

According to the present research progress and development tendency of related subjects of nanogeology, the huge developmental potentials of nanogeology in China can be summarized as two aspects,scientific research and industrial application. Related works about scientific research cover the main areas of nanogeology research in China:

(1) Studies on basic geology issues. Based on the original disciplines, nanotechnology and theory integrated with geology refers to new research directions, including nanomineralogy, nano-petrology, nano-geochemistry, and nanostructural geology. Understating the initial conditions during the formation of geologic body on the nanoscale gives us an opportunity to re-recognize the earth. A large quantity of active nanoparticles and nano-pores are developed both on the surface of earth and in deep systems, and are important components to the whole system. Studying the nanoscale materials or structures requires more refined equipment and innovative thinking mode due to their unique physical chemical features. This has great influence on understanding the mechanism of geologic processes, no matter whether on earth surface, in deep systems or even along geologic history.

(2) Resource exploration and development. Currently,China’s consumption of resources is far greater than it has ever been. The urgent demand for resources has pushed the technological advances of exploration and development.Recently, the studying of the form, structure and chemical components of nanoscale metallic particles, metallic ions or compounds on surface soils has provided a new idea to discover and evaluate the concealed deposits. On the other hand, the enormous aggregations of nanominerals or mineral nanoparticles are mineral resources themselves. Although some mineral products cannot reach the industrial standard and have low exploration and utilization rate in the conventional sense, if we review them as nanominerals with adsorptive and colloidal property, their industrialized application-values might be discovered. The exploration and development of fossil energy, like oil and gas, also faces the thinking transformation and technological innovation. The new understanding on current massive storage capacity of nanoscale pores and fissures that are in the low porosity and low permeability reservoirs are basing on the conventional exploration thought regarding hydrocarbon source rocks or tight cap ricks. “Unconventional energy” is the national pillar industry of energy structure in some countries. At present,China’s researches on unconventional oil gas exploration and development has gradually diverted its focus on dynamics of hydrocarbon generation processes in tight reservoirs, as well as the hydrocarbon-water-rocks interaction, but still it is essential to think about the production and storage process of hydrocarbon on the nanoscale.

(3) Geologic activities (disasters) mechanism research and prediction. Among all geologic activities, geologic disasters have the biggest influences on human production and living.However, the forecasts of most geologic disasters are hardly effective due to insufficient knowledge. For activities like earthquakes, landslides, debris flow and gas outburst in coalmine, the formatting mechanism still needs to be determined. Associated studies in geologic subjects, such as nano-structural geology and nano-earthquake, not only offer methods to observe and describe the geologic body on the nanoscale, but also point out a new solution path. The causative fault in seismic activity may originally be from nano-scaled shear slip belt; gas outburst in coal mine may be resulted by tectonic deformation, thus nano-porous structure is developed inside coals that can store large amounts of gases; the studies on these nanomaterials and nanostructure may confirm the understanding about the formation mechanism of disasters.

(4) Mechanism study and treatment of environmental pollution. The air dust in the atmosphere that attaches massive pollutants and heavy metal nanoparticles aggregations in the water are essential reasons for pollution. The right solutions would be found only by analyzing the source, component,structure and migration rule of these nanoscale particles. In addition, by targeting some natural nanominerals or mineral nanoparticles that have large specific surface areas, as well as porous minerals with large porous specific surface areas, these researches can offer solutions to deal with heavy mental treatment in waste water, air pollution control, ecological restoration and underground storage of carbon dioxide.

5. Conclusions

Nanogeology is such a science that mainly studies nanoscale particles in geologic body, including the formation,migration, aggregation and existence from various geologic processes and geologic evolution mechanism. The rise of nanogeology is driven by the innovation in nanoscale science and technology, and the need for the development of geology itself. Nanogeology is an international frontier field resulting from the recent years of combined development between geology and nanotechnology, which greatly expands the application prospect of each geologic field. Predecessors adopted nanotechnology to conduct some basic studies on geologic problems, but these studies were fragmented and did not have a systematic and completed thermotical guide. We conduct systematical analysis and comprehensive studies on core topics of both nanoscience and geology. We summarize the research progress and development direction of nanomineralogy, nano-petrology, nano-geochemistry, nanostructural geology, nano-energy geology, nano-ore deposit geology, nano-earthquake geology, nano-environmental geology, etc. in China

For future nanogeology development in China, we should synthesize the research progress of each subdiscipline. Based on the international academic communication and cooperative study, we will open a new field of nanogeology by giving full play to the multi-disciplinary advantage, as well as nanoscale accumulation and mineralization. Establishing international academic organization of nanogeology and holding international large-scale academic conferences will enable us to plan and innovatively advance with a global view. To promote the independence and full innovation ability in China, we need to focus on solving major frontier questions in nano-geological fields. To make sure of high-level original research findings in nanogeology, it is necessary to recruit and foster talent teams with international influence. Therefore, our researches on nanogeology will still be the international academic frontier. Meanwhile, theses researches will provide new theoretical foundations for mineral deposit exploration,resource development, new energy utilization, environmental pollution, geological hazard prevention and management, etc.With huge developmental potential and promising prospect,China is already playing the leading role in nano-geological researches in the world. It is believed that such researches will improve even more significantly in this century.

Acknowledgments

This research was financially supported by the National Natural Science Foundation of China (41530315; 41372213),the National Science and Technology Major Project of China(2016ZX05066003; 2016ZX05066006), and the “Climate Change: Carbon Budget and Related Issues” Strategic Priority Research Program of the Chinese Academy of Sciences(XDA05030100).