Recently, air pollution occurs frequently in China mainly in the form of haze, which poses great risks to human health and obstacles to social and economic development. It is well known that the sources of China's air pollution are complicated and unique, and the source identification of air pollutants is one of key points in air pollution prevention. With the development of radioisotope tracer technology, its utilization in the source identification of air pollutants has attracted increasing attention. Recently, this technology has obtained great achievements in environmental science, especially in the source identification of environmental pollutants. A variety of radioactive isotopes have been used in the source identification of air pollutants. The article presents a brief overview on the development and application of isotopes of radioactive cesium, plutonium and uranium in the source apportionment of air pollutants, as well as the existing problems and their future prospect.
Contents
1 Introduction
2 Advances of radioisotope on air pollutant tracing study
2.1 Research progress of cesium isotope tracing
2.2 Research progress of plutonium isotope tracing
2.3 Research progress of uranium isotope tracing
3 Radioactive isotope fingerprints of air pollution sources
4 Conclusion and outlook

Titanium-based catalysts have been not only providing major catalyses in conventionally producing massive polyolefins with low cost as well as good properties, but also advancing the properties of new polyolefins for new plastic materials. Therefore it has been a core consideration of finely tuning the structures of titanium complexes and enhancing catalytic performances of the olefin polymerization. Besides metallocene catalysts, titanium complexes bearing multi-dentate ligands have been maintained as hot topics, in which tridentate ligands positively stabilize titanium complexes. Meanwhile variations of coordination atoms of those ligands greatly enrich the syntheses and manipulation of the catalytic activity of complexes, therefore controlling the polymerization activity as well as improving the microstructures and properties of resultant polyolefin materials. Herein the recent progress of titanium complexes bearing tridentate ligands have been reviewed toward olefin polymerization, focusing on the electronic and steric influences of substituents within ligands on their catalytic activities and properties of resultant polyolefins. The observations would be helpful to design titanium complexes and correlations between activities of complexes and structures of ligands used.
Contents
1 Introduction
2 Titanium complexes
2.1 Half-titanocene complexes
2.2 Cp-containing Schiff-base titanium complexes
2.3 Complexes based on C, N, X imine ligands
2.4 Complexes based on O, P, N imine ligands
2.5 Complexes based on O, S, N imine ligands
2.6 Complexes based on O, N, N imine ligands
2.7 Complexes based on O, N, O imine ligands
2.8 Complexes based on N, C, N imine ligands
2.9 Complexes based on N, N, S imine ligands
2.10 Bis(aryloxide)s with one additional donors
2.11 Bis(aryloxide)s with two additional donors
2.12 Complexes with other ligands
3 Conclusion

Greenhouse effect has been a pressing challenge for the mankind. The conversion and utilization of greenhouse gases become a difficult research topic with general interest all over the world. In this context, carbon dioxide (CO₂) reforming of methane, namely dry reforming has been recognized as an advanced technology with great prospect because it can convert two potent greenhouse gases (CH₄/CO₂) into valuable synthesis gas (syngas, H₂/CO). Commercialization of this technology remains unrealized mainly due to the lack of feasible catalysts. Considering the excellent activity and relatively low cost, transition metal based catalysts are regarded as the most promising candidates. The previous research mainly focuses on Ni-based catalysts. But the Ni-based catalysts are vulnerable to rapid deactivation due to carbon deposition and metal sintering. Recently, Co-based catalysts have been reported to possess excellent catalytic performance. Herein, the progress of Co-based catalysts for CO₂ reforming of methane is reviewed. The first section addresses the role of active phases, supports, promoters and synthesis methodologies on catalytic performance. The second section discusses the catalytic mechanism and the formation of coke. The last section proposes the strategies for rational design of improving Co-based reforming catalysts and the research directions of Co-based reforming catalysts in the near future.
Contents
1 Introduction
2 The study of Co-based catalysts
2.1 The role of active phases
2.2 The role of supports
2.3 The role of promoters
2.4 The role of synthesis methodologies
3 Catalytic mechanisms and the formation of coke
3.1 Catalytic mechanisms
3.2 The formation of coke
4 Conclusion and outlook

Stimuli-responsive polymers are capable of exhibiting reversible or irreversible changes in physical and/or chemical properties in response to small changes in external environment, such as pH, ions, temperature, light, etc. In recent years, stimuli-responsive polymers have been widely used in disease diagnosis, drug delivery, and sensors. Depending on the type of the external stimuli, stimuli-responsive polymers can be classified into several categories. This article reviews the synthesis methods and the mechanism of the stimuli-responsive polymers based on the chemical stimulation, physical stimulation and biological stimulation. Furthermore, the long-term prospect and the potential applications of these functional materials are introduced.
Contents
1 Introduction
2 Chemical stimulation
2.1 pH-responsive polymers
2.2 Gas-responsive polymers
2.3 Ion-responsive polymers
3 Physical stimulation
3.1 Thermo-responsive polymers
3.2 Electric-responsive polymers
3.3 Photo-responsive polymers
4 Biological stimulation
4.1 Glucose-responsive polymers
4.2 Nucleic acids-responsive polymers
4.3 Enzyme-responsive polymers
5 Conclusion

The tissue penetration limitation of excitation light and the absorption wavelength of the photosensitizer hinder the effective treatment of traditional photodynamic therapy (PDT) in deep-seated tumors. Recently, X-ray excited photodynamic therapy (XE-PDT) based on excitation or indirect excitation of photosensitizers via energy transfer by X-ray has attracted a great deal of attention. In this review, recent progress of nanoscintillators, including their rational designs, strategies of photosensitizer loading as well as effects of energy transfer and PDT are summarized. The main problems, challenges and future development in deep-seated tumor PDT are also discussed.
Contents
1 Introduction
2 Principle of X-ray excited photodynamic therapy
3 General photosensitizer loading strategies
3.1 Sol-gel method
3.2 Direct surface coating by polymer
4 X-ray excited phosphors
4.1 Rare-earth-element-based nanoparticles
4.2 Metal oxide (or sulfide) nanoparticles
4.3 Transition metal cluster compounds
5 Conclusion and outlook
Contents
1 Introduction
2 Principle of X-ray excited photodynamic therapy
3 General photosensitizer loading strategies
3.1 Sol-gel method
3.2 Direct surface coating by polymer
4 X-ray excited phosphors
4.1 Rare-earth-element-based nanoparticles
4.2 Metal oxide (or sulfide) nanoparticles
4.3 Transition metal cluster compounds
5 Conclusion and outlook

Ortho-phenylendiamine (oPD), with two adjacent -NH₂ groups in the benzene ring, is one of typical aniline derivatives. PoPD has huge advantages in the respects of post processing and modification because PoPD owns more active sites than poly-aniline. As an important conductive polymer, PoPD has attracted increasing attention due to its special conductive mechanism and important role in chemical production. Herein, the progress in preparation and applications of PoPD micro/nano related materials are summarized. The progress in the preparation of PoPD micro/nano structures by using chemical oxidation method, reprecipitation method and microfluidic methods are focused. In combination with our research results, this paper summarizes the mechanism of polymerization, the process of oxidation-reduction and the mechanism of self-assembly of PoPD materials. Their applications in the field of sensors, bio-imaging and supercapacitors are also summarized. The current issues and the future trends of the preparation of PoPD micro/nano related materials are also analyzed which will provide useful references for the new research of PoPD micro/nano related materials.
Contents
1 Introduction
2 Preparation of PoPD micro/nano materials
2.1 Chemical oxidation method
2.2 Reprecipitation method
2.3 Microfluidic method
2.4 Other methods
3 Applications of PoPD materials
3.1 Applications of PoPD materials in sensors
3.2 Applications of PoPD materials in biological imaging
3.3 Applications of PoPD materials in supercapacitors
4 Outlook

Syngas(CO, H₂) methanation is an effective route to produce synthetic nature gas (SNG), and the Ni-based catalysts are extensively used for this reaction. However, due to the high CO concentration, high reaction temperature and the presence of sulfur-containing compounds in raw gas, the Ni-based catalysts suffer from sintering, carbon deposition and sulfur poisoning during the methanation reaction. These often lead to the catalyst deactivation. How to improve the sulfur-tolerant, anti-sintering and anti-carbon deposition abilities of the Ni-based catalysts remains a great challenge. In this paper, the recent progress in solving the above issue is reviewed from the aspects of the metal-support interaction, the interface modification and the confinement effect to provide a theoretical basis for the microstructure design and the performance regulation of the Ni-based methanation catalysts.
Contents
1 Introduction
2 Metal-support interaction
3 Interface modification
4 Confinement effect
5 Conclusion

Stratum corneum, the protective barrier of the skin, is the principal obstacle for drugs to pass through the skin, especially macromolecular drugs or hydrophilic drugs. Micron-sized microneedles in transdermal drug delivery system can permeabilize the stratum corneum to promote the penetration of skin-impermeant drugs by creating reversible microchannels in the skin in a minimally invasive manner, which can overcome low permeability of traditional transdermal drug delivery system. What's more, percutaneous microneedle insertion can cause less or even no pain because it has limited insertion depth without touching nerves in the skin. Polymeric microneedles not only have sufficient strength to puncture the stratum corneum but also exhibit other outstanding performances such as biocompatibility and relatively lager drug loading capacity. It is safe even if polymeric microneedles rupture in the skin. Polymeric microneedles have so many advantages that they have an extensive prospect in transdermal drug delivery system, which has received abroad attention. In this paper, the recent advances of polymeric microneedles are reviewed in detail from the following aspects:microneedle types, manufacturing methods, and applications in transdermal drug delivery system. Challenges and prospects of polymeric microneedles are also discussed.
Contents
1 Introduction
2 Types of polymeric microneedles
3 Manufacturing methods of polymeric microneedles
4 Applications of polymeric microneedles in transdermal drug delivery system
4.1 Rapid drug release
4.2 Extended drug release
4.3 Stimuli-responsive drug release
5 Conclusion and outlook

Heavy metal pollution is an environmental and social problem that needs to be solved urgently. Heavy metal elements in nature will form a variety of minerals with different states of valence and show different physical and chemical properties, which has important implications for the treatment of heavy metal pollution. The valence state of heavy metal ions can be regulated through electron transfer and electron absorption from microbe, electrode, and semiconductor mineral photocatalysis. This review analyzes the reduction effect of heavy metal ions by microbes, microbial electrolysis system (MES), photoelectron and photoelectron-microorganism synergistic effect. The redox reaction and the energy utilization mechanism during the heavy metal ions reduction process are illustrated based on oxidation reduction potential principle. Detailed transmembrane electron transfer process and molecular networks are elaborated for direct/indirect electron transfer pathways during reduction of heavy metal ions by microorganism. The electron transfer from microorganism cells to electrode and reverse electron absorption-utilization process are also expounded for heavy metal ion valence state regulation by microbial electrolysis system and photoelectron-microorganism synergistic effect. Finally, the interaction network and energy utilization mechanism are proposed to elucidate the regulation of heavy metal ion valence state by microorganisms, electrodes, semiconductor minerals and light. This review will provide a reference for the further study regarding the microbial extracellular electron transfer, the photoelectron utilization by microorganism and the valence state regulation of heavy metal ions by microbe-photoelectron coordination as well as its environmental significance.
Contents
1 Introduction
2 Reduction and immobilization of heavy metal ions by microorganisms and electrochemical systems
2.1 Reduction of heavy metal ions by microorganisms
2.2 Reduction of heavy metal ions by microbial electrolysis system
3 Reduction of heavy metal ions by microorganism and photoelectron coordination
3.1 Reduction of heavy metal ions by photoelectron
3.2 Reduction of heavy metal ions by microorganism and photoelectron coordination
3.3 Mineralization, transformation and interface interaction during reduction of heavy metals induced by microorganisms and photoelectrons
4 Electrochemical mechanism of reduction of heavy metal ions by microorganisms, electrochemical systems and photoelectrons
5 The role of microbial electrode as well as electron transport and transfer during reduction of heavy metal ions
5.1 Electron transfer from microorganism to heavy metal ions
5.2 Electron transfer from microorganism to electrode
5.3 The reverse transfer of electrons:from electrode to microorganism
6 Conclusion and outlook