Fluorescent carbon dots (CDs) are inspiring intensive research interests because of their high chemical stability, low toxicity and customizable surface functionalization. However, there are still some limitations such as low quantum yield, less active sites and so on. As research continues, nitrogen-doped carbon dots (N-CDs) have recently become of great interest because it addresses the above problems of CDs to achieve promising applications for them in biochemical sensing, environmental detection and other fields. In the past five years, doping CDs with nitrogen as a principle way to tune the intrinsic properties of CDs has been considered as an effective strategy, and the procedures for preparing N-CDs have become increasingly green and facile. But the formation mechanism of N-CDs is still not clarified. To easily understand the mechanism and expand its application fields, we reviewed the discovery history, preparation methods and optical properties of N-CDs, especially in latest developments of analytical and bioanalytical applications in quantitative analysis. We also give perspectives on future opportunities and promising applications, which would provide the reference for the development of N-CDs in analytical chemistry.

Contents
1 Introduction
2 Preparation and properties of nitrogen-doped carbon dots
2.1 Preparation of nitrogen-doped carbon dots
2.2 Properties of nitrogen-doped carbon dots
3 Applications in Quantitative analysis of nitrogen-doped carbon dots
3.1 Detection of ions
3.2 Detection of molecules
4 Conclusion and outlook

Photocatalytic water splitting technology based on TiO₂ semiconductor is a promising strategy for clean, low-cost, and environmental friendly H₂ production by utilizing solar energy. The whole process includes three crucial steps:solar light harvesting to excite electron from VB to CB of TiO₂, charge separation and transportation, and the catalytic reduction of H⁺ to H₂ evolution reaction. Many progresses are achieved on the first two steps, while much less researches are concentrated on the third step to improve catalytic activity with the utilization of the cocatalysts. Noble metal Pt as cocatalyst can obviously promote the H₂-producing rate in TiO₂ photocatalytic system. However, it has been restricted seriously due to its limited sources and high cost. Thus, developing cheap, earth-abundant, and high active noble-metal-free cocatalysts is very significant for high efficient photocatalytic water splitting. This review summarizes the research progress on noble-metal-free cocatalysts for TiO₂-based H₂-evolution half reaction, including transition metals, transition metal compounds, nanocarbon materials and nanocarbon-based composites. The role of different cocatalysts in catalytic performance improving, such as, content, structure, particle size, surface area, dispersity, synthesis method of the cocatalysts, and so on, was discussed in detail. And the challenges and perspectives of the research directions are also remarked.

Contents
1 Introduction
2 Fundamentals of photocatalytic water splitting and the role of cocatalyst
2.1 Fundamental of TiO₂-based photocatalyst
2.2 Process of H₂ production from water splitting
2.3 The roles of cocatalysts for H₂-evolution
2.4 Factors influencing the performance of cocatalysts
3 Noble-metal-free cocatalyst for H₂-evolution half reactions
3.1 Transition metal cocatalysts
3.2 Transition metal compounds
3.3 Nanocarbon-based cocatalysts
3.4 Catalytic mechanism
4 Conclusion and outlook

Water-soluble conjugated polymers (WSCPs) have been applied to a wide range of fields such as chemical sensing, bio-sensing and bio-imaging. The advantages of WSCPs for these applications include their high brightness, good photo-stability, structure variety and sufficient solubility in aqueous solution. WSCPs are usually decorated with water-soluble ionic groups or polymers on their sides or end groups. Sugars are a kind of biomolecules existing naturally and most of them have the features of water-solubility, therefore in recent years researchers have introduced sugar compounds into conjugated polymers leading to water-soluble conjugated glycopolymers with the biological properties of carbonhydrates. In this review, we summarize the recent development in the synthesis of water-soluble conjugated glycopolymers and their applications in terms of lectin-sensing, bacteria-sensing and live-cell imaging. Finally, we point out the peculiarity, developing trend and the challenges of water-soluble conjugated glycopolymers.

Contents
1 Introduction
2 Water-soluble conjugated polymers with sugar side-chains
2.1 PDA-based water-soluble conjugated glycopolymers
2.2 PPE-based water-soluble conjugated glycopolymers
2.3 PT-based water-soluble conjugated glycopolymers
2.4 Others water-soluble conjugated glycopolymers
3 Amphiphilic conjugated glycopolymers
4 Conclusion

The design and synthesis of artificial receptors for sensing and recognition of anions have received considerable attention in supramolecular chemistry because of the essential roles that anions play in a wide variety of biological, clinical and environmental sciences. The usual design strategies for anion sensing are through hydrogen-bonding interaction, intermolecular proton-transfer reaction, the Lewis acid/base interactions or an irreversible specific chemical reaction. Compared to the conventional anion receptors containing the NH or OH binding sites, recently, the anion receptors based on CH group have attracted much attention. Therefore, this review summarizes the main design principles and sensing abilities of the anion receptors based on receptors which having alkyl CH groups, phenyl CH groups, triazole-based CH groups, imidazolium-based CH groups, triazolium-based CH groups, CHCN group.

Contents
1 Introduction
2 Alkyl-based CH groups
3 Phenyl-based CH groups
4 Triazole-based CH groups
5 Imidazolium-based CH groups
6 Triazolium-based CH groups
7 CHCN-based CH groups
8 Conclusion

The organic electroluminescent (EL) technology, which has been the research focus in the field of electro-optical information, holds a wide range of potential applications in domains of communication, information, display, illumination, and so on. Organic EL materials have many advantages when compared with their inorganic counterparts. As a kind of rigid plane triphenyl compound with wide band gap and high flexibility to modify the molecule skeleton, the triphenyl phosphine oxide group with triangular pyramidal configuration has attracted broad attentions. In addition, this group with electron-deficient feature can polarize the molecule framework and promote electron-transporting ability of the obtained materials, which have shown good thermal stability, high triplet energy level values and relatively good device performance. In this regard, the triphenyl phosphine oxide group has been a key bridging chromophore in the synthesis of highly efficient host materials for phosphorescent organic light-emitting diodes, organic charge-transporting materials and single molecular EL light-emitting materials. In this review, the synthetic methods of the materials based on triphenyl phosphine oxide group are introduced. The applications of triphenyl phosphine oxide group-based bridging chromophores in the synthesis of organic EL materials are discussed in detail. Finally, some issues to be addressed and hotspots to be further investigated are also pointed out.

Contents
1 Introduction
2 Unique characteristics of triphenyl phosphine oxide-based segments and their applications in electroluminescent materials
3 General synthetic route to triphenyl phosphine oxide-based segments
4 Applications of triphenyl phosphine oxide-based segments in the synthesis of host materials for PhOLEDs
4.1 Host materials for red light PhOLEDs
4.2 Host materials for green light PhOLEDs
4.3 Host materials for blue light PhOLEDs
4.4 Host materials for white light PhOLEDs
5 Charge-transporting materials based on triphenyl phosphine oxide derivatives
6 Triphenyl phosphine oxide derivative-bridged single molecular electroluminescent materials
7 Conclusion

Photocatalysis, which not only converts solar energy into storable energy but also directly employs solar energy to decompose environmental pollutants, is one of the effective ways to alleviate the shortage of energy and remediate environment. The Z-scheme photocatalysts can simulate the natural photosynthesis process with high photocatalytic activity under visible light irradiation, becoming a research hotspot in recent years. The development of emerging carbonization nitrogen and graphene-like two-dimensional nanomaterials inspire people to build Z-scheme photocatalytic systems based on two dimensional nanostructure. By this means, the optical spectrum response, carriers separation capacity, redox potentials, and stability to resist light-etch of Z-scheme photocatalysts are reinforced. This paper reviews the recent progress in the study of two dimensional Z-scheme photocatalytic materials, introduces the preparation methods, reaction mechanisms and applications of two dimensional Z-scheme photocatalysts in the field of environment purification and solar energy conversion. Finally, the research prospects of two-dimensional Z-scheme materials in the field of photocatalysis are briefly proposed.

Contents
1 Introduction
2 Study on mechanism of two dimensional Z-scheme photocatalysis
2.1 Reaction mechanism of Z-scheme photocatalysis
2.2 Characteristics and functions of two dimensional Z-scheme photocatalyst
3 Novel two-dimensional visible light catalysts and its control synthesis
3.1 Graphite-phase carbon nitride (g-C₃N₄)
3.2 Sulfide
3.3 Bismuth based photocatalyst
4 Application of two dimensional Z-scheme visible light responsive photocatalyst in the field of pollutant control
4.1 Photocatalytic degradation of dyes
4.2 Photocatalytic degradation of phenols
4.3 Photocatalytic degradation of antibiotics
5 Application of two dimensional Z-scheme visible light responsive photocatalyst in the energy conversion
5.1 Photocatalytic hydrogen production
5.2 Photocatalytic reduction of CO₂
6 Conclusion

In this paper, research progress about the utilization of non-TiO₂ photocatalysts in degradation of gaseous VOCs are reviewed. We give a concise overview of several novel non-TiO₂ photocatalysts with a focus in their structure, which affect the catalytic activities, including metal oxide, wide bandgap p-block metal oxides/hydroxides, perovskite-type, spinel-type, bismuth based compounds, vanadium based compounds, et al. In addition, the research progress of influence factors of non-TiO₂ photocatalytic purification of gaseous VOCs exhaust is summarized from photocatalytic reaction conditions (such as VOCs initial concentration, flow rate, light source, light intensity, reaction temperature and humidity). Finally, the fundamental challenges and perspectives of non-TiO₂ photocatalysts are briefly brought up.

Contents
1 Introduction
2 Non-TiO₂ photocatalytic oxidation of VOCs
2.1 Metal oxide photocatalysts
2.2 Wide bandgap p-block metal oxides/hydroxides photocatalysts
2.3 Perovskite-type oxides photocatalysts
2.4 Spinel-type photocatalysts
2.5 Bismuth based photocatalysts
2.6 Vanadium based photocatalysts
2.7 Other photocatalysts
3 The effect of process parameters on VOCs purification
3.1 The initial concentration of VOCs and flow rate
3.2 The light source and light intensity
3.3 Temperature and humidity
3.4 Other parameters
4 Conclusion and outlook

As a new type of photocatalyst, elemental bismuth has attracted wide attentions for energy conversion and environmental remediation. In this review, the photocatalytic mechanism of elemental Bi including photosensitization, photocatalysis and plasma resonance is discussed. In addition, the main preparation methods such as precipitation, solvothermal and electrochemical methods are described as well. Moreover, the influences of surface active agents, reaction temperature and pH values on the synthesis of bismuth particles are discussed in details. Generally, the optical properties of bismuth are strongly affected by its size and morphology, which is one of the key factors for photocatalytic applications. Besides, bismuth-semiconductor composites including Bi-titanium dioxide, Bi-bismuth oxides, Bi-zinc oxides and Bi-C₃N₄ are also reported as a kind of promising non-noble metal photocatalysts due to their enhanced oxygen vacancy density and increased photo-generated carriers mobility caused by the formation of heterojunction, which could be prepared by one-step hydrothermal process or reduction methods through polybasic alcohol or light irradiation. Furthermore, the narrowed band gap of the compound and the plasma resonance effect of bismuth are also demonstrated to be the reasons for the enhanced photocatalytic activities. Finally, on the basis of the above work, the development of Bi-semiconductor composite photocatalysts is discussed and the opinions on future trend are presented as well.

Contents
1 Introduction
2 Bismuth photocatalyst
2.1 The photocatalytic mechanism of bismuth
2.2 The relationship among the size, morphology, absorption of bismuth
2.3 The preparation methods of bismuth
3 Bismuth composite photocatalysts
3.1 Bi-TiO₂
3.2 Bi-bismuth oxides
3.3 Bi-other semiconductors
4 Conclusion

Energy shortage and environmental deterioration are the difficult problems now confronting us in the development of human society. As one of the best and new type energy which is clean, renewable and zero-pollution, solar energy is the best choice to achieve sustainable development, because it is an inexhaustible energy source. The issue that semiconductor photocatalysis can use solar light directly to conduct the photocatalytic reaction has aroused widely public concern. As a kind of low cost and non-metal photocatalyst, graphitic carbon nitride (g-C₃N₄) shows great application prospects in decomposition of water into hydrogen and oxygen, photocatalytic degradation of organic pollutants, carbon dioxide reduction, antibacterial, selective conversion of organic functional groups, as well as other fields, for its unique electronic band structure, thermal and chemical stability. But at present, g-C₃N₄ photocatalyst still exists some problems such as small specific surface area, low visible light utilization rate, low light quantum yield, and easy recombination of photo-generated carriers which restrict its application in the field of photocatalysis. Therefore, it has become a key subject in the field of photocatalytic research to improve the photocatalytic activity of g-C₃N₄. The first principles have the incomparable advantages over semi empirical method, which have become an important basis for the calculation and simulation in the field of photocatalytic research. The wide application of first principles based on density functional theory in the field of photocatalysis provides a clear research means to explore the method to improve the photocatalytic activity of g-C₃N₄ effectively and quickly. In this review, some important research progress in g-C₃N₄ modification in recent years is reviewed from the theoretical point of view, including element doping modification, composite modification, morphology control modification and other means of modification. The microscopic mechanism of improved photocatalytic activity of g-C₃N₄ modified photocatalyst is studied, from the point of view of electronic properties, band structure, optical properties and defect formation energy. Finally, on the basis of summarizing various of the modification research mentioned above, the future development trend of g-C₃N₄ modified photocatalyst is discussed.

Contents
1 Introduction
2 Molecular model and band structure of g-C₃N₄
2.1 Molecular model of g-C₃N₄
2.2 Band structure of g-C₃N₄
3 Modification research of g-C₃N₄
3.1 Doping modification
3.2 Composite modification
3.3 Morphology control modification
3.4 Other modification research
4 Conclusion

Nitrogen oxides (NO_x) in flue gases is an important source of air pollution. It is urgent to remove the NO_x from flue gases. In this review, the removal ways of nitrogen oxides are reviewed in terms of high-temperature and low-temperature selective catalytic reduction (SCR) De-NO_x catalysts. We discuss the high-temperature SCR De-NO_x catalysts including vanadium-based catalysts, iron-based catalysts and molecular sieve-based catalysts. Then, we highlight the low-temperature SCR De-NO_x catalysts such as noble metal-based catalysts, manganese-based catalyst, carbon-based catalysts, etc. We specifically focus on the mechanism studies of SCR De-NO_x catalysts. Finally, we summarize the recent advances in denitrification.

Contents
1 Introduction
2 Process arrangement of SCR denitrification
3 SCR catalysts
3.1 High-temperature catalysts
3.2 Low-temperature catalysts
4 Conclusion