The concept of a machine can be extended to the molecular level. A molecular-level machine can be defined as an assembly of molecular components designed to perform mechanical-like movements as a consequence of appropriate external stimuli, such as chemical energy, electrical energy and light. Artificial molecular machines show potential applications in the field of nanotechnology, which attract chemists with great interest. The two basic movements of artificial molecular machines are linear motion and rotary motion. We limit our discussion to the rotary motion and describe the different types of rotary motors in this review. The structure of this rotational molecular machine consists of axis, a rotator and a stator. The rotator winds around the stator through the axis in the way of bidirectional or unidirectional rotation. We describe the designs and dynamic behaviors of single molecular rotary machines in solution, which mainly include molecular gear, motor, molecular turnstile, molecular brake and ratchet.

Contents
1 Introduction
2 Molecular gears
2.1 Bevel gear
2.2 Spur gear
3 Molecular turnstile
4 Molecular brake and ratchet
4.1 Molecular brake
4.2 Molecular ratchet
5 Molecular motor
5.1 Chemical-driven molecular motor
5.2 Light-driven molecular motor
6 Conclusion and outlook1 Introduction
2 Molecular gears
2.1 Bevel gear
2.2 Spur gear
3 Molecular turnstile
4 Molecular brake and ratchet
4.1 Molecular brake
4.2 Molecular ratchet
5 Molecular motor
5.1 Chemical-driven molecular motor
5.2 Light-driven molecular motor
6 Conclusion and outlook1 Introduction
2 Molecular gears
2.1 Bevel gear
2.2 Spur gear
3 Molecular turnstile
4 Molecular brake and ratchet
4.1 Molecular brake
4.2 Molecular ratchet
5 Molecular motor
5.1 Chemical-driven molecular motor
5.2 Light-driven molecular motor
6 Conclusion and outlook

Supramolecular gel is an important class of soft materials, in which the solvents are immobilized by the entangled three-dimensional network formed by gelator molecules via the various non-covalent interactions. Supramolecular gel can be quickly formed, self-assembled into uniform and adjustable nanostructure over a wide scale range. Thus the research of supramolecular gel is one of the important research directions among supramolecular chemistry, nanotechnology and materials science. The functional gels are applied widely in many fields, such as material templates, photoelectric switch, drug release, molecular recognition, supramolecular catalysis, etc. With solid-liquid phase transition, controlled self-assembly and other characteristics, the supramolecular gel has become an important vehicle of the reserch of supramolecular chirality and molecular chirality. In recent years, the supramolecular gel has been applied to supramolecular asymmetric catalysis and chiral molecular recognition. And a series of important breakthroughs have been achieved. The new functional application of supramolecular gels have been established, and supramolecular gels have become an important means and method for preparation of chiral nano-materials.The chiral supramolecular gels, as a kind of soft materials will have potential application in the field of asymmetric catalysis and chiral recognition. The supramolecular gels may provide a high density of recognition or catalytic sites and chiral microenvironment suitable for recognition and asymmetric reaction, thus, the study of asymmetric catalysis and enantioselective recognition in the supramolecular gels becomes a hot issue and has attracted more and more attention in recent years.In this paper,the application of supramolecular gels on asymmetric catalysis and chiral recognition are reviewed mainly.

Contents
1 Introduction
2 Application of supramolecular gels in chiral molecular recognition
2.1 Chiral molecular recognition based on gel phenomenon
2.2 Chiral molecular recognition based on fluorescence spectra
2.3 Chiral molecular recognition based on supramolecular chiral characterization
3 Application of supramolecular gels in asymmetric catalysis
3.1 Self-assembly strategies for asymmetric organocatalysis
3.2 Asymmetric catalysis in supramolecular gels
4 Conclusion and outlook

A sensor array is an artificial olfactory system based on the array analysis method. On an array, information from different sensing units could be collected simultaneously, which improves the analysis efficiency of the sensors. This high-throughput sensing mode has broad application prospect in the areas such as public safety, environmental monitoring and medical diagnosis. Among different kinds of sensor arrays, optical chemical sensor arrays have attracted much attention because of their high sensitivity and abundant output signal types. In recent years, for further improving the identification ability and sensitivity of the arrays, functional nanomaterials have been widely applied in optical chemical sensor arrays for increasing sensing materials and developing new sensing methods. The present review introduces the applications of functional nanomaterials in optical sensor arrays which can be classified into fluorescent arrays, colorimetric arrays, cataluminescence arrays and multidimensional arrays according to the type of spectroscopic detection technology.

Contents
1 Introduction
2 Fluorescent sensor array
2.1 Sensor array based on gold nanoparticles
2.2 Sensor array based on fluorescent gold nanoclusters
2.3 Sensor array based on graphene
3 Colorimetric sensor array
3.1 Sensor array based on nanoporous pigments
3.2 Sensor array based on gold nanoparticles
3.3 Sensor array based on peroxidase mimic enzyme
4 Cataluminescence sensor array
5 Multidimensional sensor array
6 Conclusion and outlook

Lithium ion batteries (LIBs) have been considered as promising energy storage devices in the past decades owing to their high operating voltage, large energy density and outstanding cycle performance. However, the currently commercial LIBs could not fulfill the demand of electric vehicles(EV) or hybrid electric vehicles(HEV) applications. Thence, superior electrode materials possessing either higher capacity or higher voltage have gained enormous interest. Taking this into account, spinel LiNi_0.5Mn_1.5O₄ which owns high operating voltage, relatively high theoretical capacity (147 mAh ·g^-1) and three-dimensional lithium ion transport channels has become one of the most excellent cathode materials. In the presented paper, the structure and synthesis of this material are reviewed, and special emphases are shown to the current research activities on LiNi_0.5Mn_1.5O₄ cathodes in ion doping along with surface coating synthesized by various synthetic techniques. Finally, the key issues and prospects of the cathode material are commented.

Contents
1 Introduction
2 Structure of LiNi_0.5Mn_1.5O₄ cathode material
3 Synthesis of LiNi_0.5Mn_1.5O₄ cathode material
4 Problems of LiNi_0.5Mn_1.5O₄ cathode material
5 Modification of LiNi_0.5Mn_1.5O₄ cathode material
5.1 Ion doping
5.2 Surface modification
5.3 Other methods
6 Conclusions and outlook

In recent years, three dimensional (3D) graphene derived from 2D graphene assemblies, is an emerging functional material in the field of graphene chemistry. Integration of graphene sheets, two-dimensional (2D) nanoscale building blocks, into 3D assemblies which have well-defined 3D architecture, is an effective way for tuning and/or controlling the electrical, optical, chemical, mechanical or catalytical properties. As a novel kind of functional materials, the methodology for preparing 3D graphene materials with micro-/nano-architectures and the potential applications have triggered tremendous interests. The rationally designed 3D graphene architecture may not only provide inherently excellent properties of 2D graphene materials, such as high electronic, optical and catalytical properties, but also exhibit micro-/nano-architectures, huge specic surface areas, strong mechanical strengths, high electron conductivity and fast mass transport kinetics. Until now, 3D graphene materials have demonstrated superior performance when applied in nanoelectronics, energy storage/conversion, chemical and biological sensing, hybrid materials and other areas. In this article, we review recent advances of 3D graphene and its composite materials in the fields of catalysis, hydrogen/gas storage, sensor fabrication, environmental protection and supercapacity. The current challenges and future perspectives in the applications of 3D graphene materials are also outlined.

Contents
1 Introduction of 3D graphene materials
2 Preparation of 3D graphene architectures
3 Applications of 3D graphene and its composite materials
3.1 Applications as catalysis
3.2 Applications in hydrogen storage and other gases adsorption
3.3 Applications in fabrication of sensor
3.4 Applications in environmental remediation
3.5 Applications in fabrication of supercapacitor
4 Conclusion and outlook

Iron-base inorganic mesoporous materials have attracted a lot of attentions recently due to their environmental-benignancy, cost-efficiency, and unique properties of magnetism and chemical activity, which allow them to find potential applications in different areas. In this paper, the recent progress in synthesis of iron-based inorganic mesoporous materials as well as their applications has been reviewed, with an emphasis on the synthetic routes and structural properties of various iron-based inorganic mesoporous materials (i.e., mesoporous iron oxyhydroxides, mesoporous iron oxides, mesoporous ferrosilicates, mesoporous iron phosphates, iron-based mesocrystals, mesoporous Fe/Si (C, Al, Ti) composites, etc.). In addition, their applications in catalysis, adsorption, gas-sensing, lithium-ion batteries, pharmacies, host-guest synthesis and other fields have been summarized and discussed. The current research problems of iron-based inorganic mesoporous materials and several future research directions have also been addressed.

Contents
1 Introduction
2 Synthesis of iron-based mesoporous materials
2.1 Mesoporous iron oxyhydroxides (MIHs)
2.2 Mesoporous iron oxides (MIOs)
2.3 Mesoporous ferrosilicates (MFSs)
2.4 Mesoporous iron phosphates (MIPs)
2.5 Iron-based mesocrytals (IMCs)
2.6 Mesoporous Fe/Si (C, Al, Ti) composites
2.7 Other iron-based mesoporous materials
3 Applications of iron-based mesoporous materials
3.1 Catalysis
3.2 Adsorption
3.3 Gas-sensing
3.4 Li-ion batteries
3.5 Pharmacies
3.6 Host-guest synthesis
3.7 Other applications
4 Summary

With high lipophicity and metabolic stability, trifluoromethyl alkyl ketones (TFMKs) act as important bioactive molecules, especially enzyme inhibitors. Besides, they are superior intermediates for pharmaceuticals and materials. Due to severe electrophilicity of trifluoromethyl, TFMKs form covalent hemiketal adducts targeting at many hydrolytic enzymes such as phospholipase A2 (PLA2) both in mammal and plant, human leukocyte elastase, oleamide hydrolase, human plasma kallikrein, pig liver esterase. TFMKs are inhibitors of human renin in the regulation of blood pressure and electrolyte homeostasis. Structure of chymotrypsin-trifluoromethyl ketone inhibitor complexes have been presented by XRD and NMR spectroscopy, this inhibition is depended on pH. TFMKs are also served as outstanding inhibitors of SARS-CoV 3CL protease. Diversity methods have been used in synthesis of TFMKs, involving the reactions of organometallic reagent like Grignard reagent or alkyl lithium with trifluoromethyl acid, acetate, or their salts, ester or amide react with TMSCF₃ or Et₃GeNa/PhSCF₃ to generate nucleophilic trifluoromethylation, treatment of carboxylic acid chlorides with pyridine and trifluoroacetic anhydride, sulfone-mediated synthesis of TFMKs from alkyl and alkenyl bromides, oxidation of trifluoromethyl carbinols, catalytic aerobic oxidative decarboxylation of trifluoromethylhydroxy acids, conversion of trifluoroethyl amines by the treatment of NBS/DBU, conversion of enolizable carboxylic acids to TFMKs via enediolate trifluoroacetylation/decarboxylation, and ring opening of alkyl 2-siloxycyclopropanecarboxylates by triethylamine trihydrofluoride. Bioactive TFMKs on enzyme inhibition are summarized and synthesis methods are discussed in this paper, trend on both application and preparation are described.

Contents
1 Introduction
2 Possible mechanism and bioactivities of TFMKs
2.1 Inhibition on phospholipase A2(PLA2)
2.2 Inhibition on FAAH hydrolases
2.3 Inhibition on AChE
2.4 Inhibition on chymotrypsin
2.5 Inhibition on SARS-CoV 3CL
2.6 Inhibition on juvenile hormone esterase
2.7 Inhibition on other hydrolases
3 Synthesis of TFMKs
3.1 Organometallic reagent with trifluoromethyl acid, acetate, or their salts
3.2 Nucleophilic trifluoromethylation with TMSCF₃ or Et₃GeNa/PhSCF₃
3.3 Carboxylic acid chlorides with pyridine and trifluoroacetic anhydride
3.4 Ethanolysis after condensation
3.5 Oxidation of trifluoromethylcarbinols
3.6 Trifluoroacetic ester/ketone exchange
3.7 Other methods
4 Conclusion and outlook

Heme proteins play various important roles in biological systems such as oxygen storage and transport, electron transfer, catalysis and signaling. Although most heme proteins exist as a monomer, homomeric complexes are also observed for some heme proteins in vitro and/or in vivo. This review summarized the progress of dimerization, oligomerization and polymerization of heme proteins, including myoglobin, cytochrome c, cytoglobin, cytochrome b₅, cytochrome b₅₆₂, nitrite reductase, heme-based sensor and heme transport proteins, etc., and focused on the resultant structures and functions, as well as the approaches for rational design of polymers and their applications. These progresses, on one hand, enhanced our knowledge of the structure-function relationship of heme proteins in biological systems, and on the other hand, endowed us an ability of regulating and utilizing heme proteins by functional protein design through polymerization.

Contents
1 Introduction
2 Dimerization of heme proteins
2.1 Structure and function of dimeric myoglobin
2.2 Structure and function of dimeric cytochrome c
2.3 Structure and function of dimeric cytoglobin
2.4 Structure and function of dimeric nitrite reductase
2.5 Structure and function of dimeric heme-based sensor protein
2.6 Structure and function of dimeric heme transport protein
3 Oligomerization of heme proteins
4 Polymerization of heme proteins
4.1 Rational design of heme protein polymer
4.2 Applications of heme protein polymer
5 Conclusion and outlook

During last several decades, organic/inorganic hybrid materials have been used widely in many fields due to their excellent structure and performance. Thiol-ene/yne click chemistry, a new type of click chemistry, is of great interest because of its mild reaction conditions, fast reaction rate, high yield, easy post-treatment and high selectivity for the obtained products. Therefore, synthesis of high-performance organic/inorganic hybrid materials via thiol-ene/yne click chemistry is one of the hot topics of novel material research. In this review, the recent research progress of organic/inorganic hybrid materials synthesized by thiol-ene/yne click chemistry is discussed. Synthesis of silicon-, carbon-, metal- and metal oxide-based organic/inorganic hybrid materials via thiol-ene/yne click chemistry is highlighted. In addition, the applications of these hybrid materials in the fields of biomedical materials, environment protection and photoelectric materials are summarized. Finally, the development trend and future prospects of organic/inorganic hybrid materials synthesized by thiol-ene/yne click chemistry are presented.

Contents
1 Introduction
2 Organic/inorganic hybrid materials synthesized by thiol-ene/yne click chemistry
2.1 Synthesis of silicon-based organic/inorganic hybrid materials
2.2 Synthesis of carbon-based organic/inorganic hybrid materials
2.3 Synthesis of metal- and metal oxide-based organic/inorganic hybrid materials
3 Application of organic/inorganic hybrid materials synthesized by thiol-ene/yne click chemistry
3.1 Biomedical materials
3.2 Environmental protection
3.3 Photoelectric materials
3.4 Other application
4 Conclusions and outlook

Single lithium-ion conductors (SLICs), which have anions covalently bonded to polymers or immobilized by anion acceptors, have been intensively studied. SLICs are generally accepted to have advantages over conventional salt-in-polymer electrolytes for application in lithium batteries due to the unity transference number and the absence of detrimental effect of anion polarization. By now, many types of SLICs have been reported, including organic polymers, organic-inorganic hybrid polymers and anion acceptors. In this paper, progresses in SLICs are reviewed, which mainly focused on their electrochemical properties, especially those with high ionic conductivity and high lithium-ion transference number. The current challenges and future perspectives in this field are also prospected.

Contents
1 Introduction
2 Organic polymer-based single lithium-ion con-ductors
2.1 Single lithium-ion conductors based on lithium salts of ionomer without ion conduction matrix
2.2 Single lithium-ion conductors based on lithium salts of ionomer with ion conduction matrix
3 Organic-inorganic hybrid polymers
3.1 The siloxane-based single lithium-ion conductors
3.2 The aluminate and borate-based hybrid polymers
4 Anion acceptor
4.1 Lewis acid-based anion acceptor
4.2 Calixarene and their derivatives
5 Conclusions and outlook

Halogen-, phosphorous- and lead-free flame-retardant epoxy-based thermosets are environmental-friendly materials and expected to be applied to the electronic materials. Nitrogen heterocyclic ring is highly efficient flame-retardant with low toxicity and has been covalently introduced into the backbone of the epoxy polymers, but so far the structure of such nitrogen heterocyclic ring and its flame-retardant property for epoxy resin has not yet closely correlated. Based on our previous works in the field, this article summarizes recent research progress for synthesis and application of the flame retarded epoxy-based thermosets containing nitrogen heterocyclic ring, including triazine, isocyanurate, azo phthalazinone, imide, benzoxazine and hydantion rings, etc. The structure-property relationships of these systems are presented in detail. Generally, introducing nitrogen heterocyclic structures into epoxy resin systems by covalent bonding can maintain the overall performance while endow the flame retardancy to the final materials. Moreover, nitrogen heterocyclic structure can improve the thermal stability of the cured epoxy resins. As a result, epoxy resin containing nitrogen heterocyclic structures might be a good choice to obtain halogen-, phosphorous- and lead-free flame retardant epoxy-based electronic materials. However, it is still a big challenge to get flame-retardant epoxy-based thermosets just depending on nitrogen heterocyclic structure in these materials. Most of the reported systems had contained low content of phosphorous for bettering the flame retardancy. As a result, it is important to intensively understand the structure-property relationship of nitrogen heterocyclic ring-containing epoxy resin. Several methods are proposed for improving the flame retardancy of nitrogen heterocyclic ring-containing epoxy resin.

Contents
1 Introduction
2 Triazine structure
2.1 Melamine modified phenol novolac
2.2 Tiazine ring introduced by sol-gel
3 Isocyanurate rings
4 Azo phthalazinone structures
5 Imide structures
6 Benzoxazine structures
7 Hydantion epoxy resins
8 Other nitrogen-containing structures
9 Conclusion

Double network hydrogels (DN gels) are unique interpenetrating polymer networks consisting of two kinds of polymer networks with strong asymmetric structure. Compared to single network hydrogels, DN gels exhibit extremely high strength (fracture tensile stress of 1 ~ 10 MPa and strain of 1000% ~ 2000%) and toughness (tearing fracture energy of 10² ~ 10³ J ·m^-2), due to their contrasting network structures where the first, brittle polyelectrolyte network is strongly entangled and interpenetrated with the second, soft, neutral polymer network. Fundamental understanding of the fracture process and toughening mechanisms of DN gels is critical for rational design of the next-generation of tough DN gels with desirable mechanical properties. Some DN gels illustrate large hysteresis, yielding/necking and softening phenomena, which can't be well interpreted by classical Lake-Thomas theory. Based on these experimental facts, Brown and Tanaka had suggested a "Damage Zone" model to explain the extraordinary high toughness of DN gels. Recently, "sacrificial bonds" theory, which proposed by Gong's group, has been well applied to design and prepare high toughness DN gels with novel nano-/microstructures. In the present of review, we focus on the toughening mechanisms of DN gels. The latest finding in this field are summarized, and the effect factors on toughness are discussed. In the end, the problems and research directions of the mechanisms of DN gels are pointed out.

Contents
1 Introduction
2 Experimental facts for toughening mechanisms of double network hydrogels
2.1 Hysteresis
2.2 Yielding and necking
2.3 Softening
3 Toughening mechanisms of double network hydrogels
3.1 Brown-tanaka model
3.2 Sacrificial bonds theory
4 Influence factors on toughness of double network
4.1 First network
4.2 Second network
4.3 Between the two network
4.4 Others
5 Conclusion and perspective

Targeted drug delivery system (TDDS) nowadays has been adopted as a superb approach to the therapies of cancer and other mortal diseases. Cyclodextrins (CDs) are chosen to take the part of a promising drug carrier due to its low toxicity and high flexibility of structure modification. They are commonly used to enhance the aqueous solubility, chemical stability, safety and bioavailability of drugs in virtue of their peculiar ability to form CD/drug inclusion complexes. Not only native and chemically modified cyclodextrins were employed as drug carriers, but also sorts of CD-based more sophisticated carrier systems such as polyrotaxanes/polypseudorotaxanes, polycations and nanoparticles emerged in recent years. Considering the fact that lots of biological receptors such as folate receptor, asialoglycoprotein receptor, hyaluronic receptor, transferrin receptor, integrin receptor are overexpressed on the surface of most cancer cells and other focal cells, design of TDDS containing matching targeting ligands (TLs) could help realize targeted therapy for those focal cells or tissues. Targeting ligands such as folic acid (FA), mono- and oligosaccharides, hyaluronic acid (HA), transferrin, RGD sequence are consequently chemically bound to CD-based carriers to form targeted carrier systems which further furnished TDDS via non-covalent complexation or bio-cleavable conjugation to drug molecules. Such TDDS are also widely applied on nucleic acid delivery in addition to chemotherapeutical drugs. As to depict the important developments, basic targeting principles and the latest progress on targeted drug delivery systems based on CDs are summarized, and also a brief prospect is given in this review.

Contents
1 Introduction
2 Folate receptor-mediated TDDS based on CDs
2.1 Targeting mechanism
2.2 Progress on folate receptor-mediated TDDS based on CDs
3 Asialoglycoprotein receptor-mediated TDDS based on CDs
3.1 Targeting mechanism
3.2 Progress on asialoglycoprotein receptor-mediated TDDS based on CDs
4 Hyaluronic receptor-mediated TDDS based on CDs
4.1 Targeting mechanism
4.2 Progress on hyaluronic receptor-mediated TDDS based on CDs
5 Transferrin receptor-mediated TDDS based on CDs
5.1 Targeting mechanism
5.2 Progress on transferrin receptor-mediated TDDS based on CDs
6 Integrin receptor-mediated TDDS based on CDs
6.1 Targeting mechanism
6.2 Progress on integrin receptor-mediated TDDS based on CDs
7 Other receptor-mediated TDDS based on CDs
8 Conclusion

Single-cell biophysical characterization has been widely employed for demonstrating the physiological activity and status of individual cells, or revealing the heterogeneity among various populations. It also plays an important role in the studies on cellular differentiation and pathology, as well as early clinical diagnosis and treatment. Compared to conventional biochemical schemes, the feature of scale compatibility between cell and microchannel makes microfluidics more suitable for precise microenvironment control, high-throughput manipulation, and multi-parameter label-free detection of individual cells. Therefore, microfluidics has become an important platform for single-cell characterization and analysis. This review covers the recent advances in microfluidics for characterizing the single-cell biophysical properties, and then focuses on the discussion of specific advantages, such as single-cell resolution level and high-throughput feature, offered by microfluidics. Finally, the challenges and future directions concerning the application of this scheme in clinical practices are also discussed, and a novel single-cell microdevice for multi-parameter characterization is proposed.

Contents
1 Introduction
2 Density(Mass) characterization
3 Electrical characterization
3.1 Microfluidic Coulter counter
3.2 Microfluidic impedance cytometer
4 Mechanical characterization
4.1 Optical stretcher
4.2 Electroporation-induced deformation
4.3 Structure-induced deformation
4.4 Fluid-induced deformation
5 Multi-parameter biophysical characterization
6 Conclusion and outlook

Following carbon monoxide and nitric oxide, hydrogen sulfide (H₂S) is found to be the third endogenous gasotransmitter, which provides the regulation significance of physiological and pathological processes in the cardiovascular and nervous systems. Therefore, the selective recognition and detection of H₂S are of importance. Fluorescent probe method, among biological detection technologies, is an indispensable technique for the biological species analysis, and that is highlighted by its good selectivity, high sensitivity, noninvasive detection, and real-time monitoring in situ. Recently, the development of fluorescent probes for intracellular H₂S detection has been becoming one of the hot topics. Herein, the progress during the last three years of fluorescent molecular probes based on the small molecules for H₂S detection are reviewed. These fluorescent probes are classified and concluded according to the different types of chemical reaction with H₂S, and then arranged specifically by the fluorophores in different type. The design concepts of molecular structures, detection mechanism and biological applications of these probes are introduced. In addition, the relationship between molecular structures and properties while testing are elucidated. Finally, the challenge and application prospects for the development of hydrogen sulfide fluorescent probes are also discussed.

Contents
1 Introduction
2 Chemical strategies to design H₂S fluorescent probes
2.1 Detection of H₂S via reduction reactions
2.2 Detection of H₂S via nucleophilic addition reactions
2.3 Detection of H₂S via copper-sulfide precipitation
2.4 Detection of H₂S via thiolysis reactions
2.5 Detection of H₂S via redox reactions
3 Fluorescent probes based on the reduction reaction
3.1 H₂S probes employ coumarin dyes as fluorophore
3.2 H₂S probes employ naphthalimide dyes as fluorophore
3.3 H₂S probes employ rhodamine dyes as fluorophore
3.4 H₂S probes employ near-infrared fluorescent (including two-photon) dyes as fluorophore
3.5 H₂S probes employ other dyes as fluorophore
4 Fluorescent probes based on the nucleophilic addition
4.1 H₂S probes employ BODIPY dyes as fluorophore
4.2 H₂S probes employ fluorescein dyes as fluorophore
4.3 H₂S probes employ benzothiazole dyes as fluorophore
4.4 H₂S probes employ cyanine dyes as fluorophore
4.5 H₂S probes employ other dyes as fluorophore
5 Fluorescent probes based on the Cu-S precipitation
5.1 H₂S probes employ fluorescein dyes as fluorophore
5.2 H₂S probes employ cyanine dyes as fluorophore
5.3 H₂S probes employ other dyes as fluorophore
6 Fluorescent probes based on the thiolysis reaction
7 Fluorescent probes based on mimics selenium enzyme
8 Fluorescent probes for other active sulfur species
8.1 Fluorescent probes for bisulfite anion
8.2 Fluorescent probes for sulfane sulfurs
9 Conclusion

Halogenated organic contaminants (HOCs), including perfluorinated or partially fluorinated chemicals (PFCs), chlorinated organic compounds (COCs) and brominated organic compounds (BOCs), show the characteristics of persistent organic pollutants after they are discharged into the environment. Optimized photochemical elimination methods, which involve the pollutant properties, light adsorption and quantum yield, interfacial interaction and environmental conditions, are promising techniques for controlling the potential risk of HOCs. The present review summarizes the mechanisms of photocatalytic degradation of perfluorooctanoic acid (PFOA), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) by photo-generated radical species (eg, h_VB⁺, e_CB^-, ·OH, e_aq^-) on photocatalyst as well as the mechanisms of direct photolysis. The photochemical degradation of HOCs can be achieved through the electron transfer between HOCs and reactive radical species or photo-induced reduction from the excited state of HOCs. Optimazation designs of photocatalyst and reaction process are important factors for the photocatalytic degradation of HOCs. Based on the currently achieved research results, some key issuses for the future are proposed from some aspects such as the interfacial electron transfer, the information of band structure, and the integration of reaction and separation.

Contents
1 Introduction
2 The mechanisms of photochemical degradation of HOCs
2.1 The photocatalytic degradation of HOCs
2.2 The direct photolysis of HOCs
3 Influencing factors on photocatalytic degradation of HOCs
3.1 Effect of photocatalytic materials
3.2 Effect of reaction condition
4 Conclusions