Water is essential in all aspects of life, being the defining characteristic of our planet and even our body. Regrettably, water pollution is increasingly becoming a challenge due to novel anthropogenic pollutants. Of particular concern are emerging organic contaminants (EOCs), the term used not only to cover newly developed compounds but also compounds newly discovered as contaminants in the environment. Aside from anthropogenic contamination, higher temperature and more extreme and less predictable weather conditions are projected to affect water availability and distribution. Therefore, wastewater treatment has to become a valuable water resource and its reuse is an important issue that must be carried out efficiently. Among the novel technologies considered in water remediation processes, metal-organic frameworks (MOFs) are regarded as promising materials for the elimination of EOCs since they present many properties that commend them in water treatment: large surface area, easy functionalizable cavities, some are stable in water, and synthesized at large scale, etc. This review highlights the advances in the use of MOFs in the elimination (adsorption and/or degradation) of EOCs from water, classifying them by the nature of the contaminant.

Metal-Organic Frameworks for the Removal of Emerging Organic Contaminants in Water.

Visible light-induced photocatalysis is a promising way for environmental remediation due to efficient utilization of solar energy. Recently, metal–organic frameworks (MOFs) have attracted increasing attention in the field of photocatalysis. In comparison with traditional metal oxide semiconductors, MOFs have many advantages, such as high specific surface area, rich topology and easily tunable porous structure. In this review, we aim to summarize and illustrate recent advances in MOF-based photocatalysis for environmental remediation under visible light, including wastewater treatment, air purification and disinfection. A series of strategies have been designed to modify and regulate pristine MOFs for enhanced photocatalytic performance, such as ligand functionalization, mixed-metal/linker strategy, metal ion/ligand immobilization, dye sensitization, metal nanoparticle loading, carbon material decoration, semiconductor coupling, MOF/COF coupling, carrier loading and magnetic recycling. The above modifications may result in extended visible light absorption, efficient generation, separation and transfer of photogenerated charges, as well as good recyclability. However, there are still many challenges and obstacles. In order to meet the requirements of using MOF photocatalysis as a friendly and stable technology for low-cost practical applications, its future development prospects are also discussed.

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Recent advances in MOF-based photocatalysis: environmental remediation under visible light

Quasi-polymeric construction of stable perovskite-type LaFeO3/g-C3N4 heterostructured photocatalyst for improved Z-scheme photocatalytic activity via solid p-n heterojunction interfacial effect.

A review on graphitic carbon nitride (g-C3N4) based nanocomposites: Synthesis, categories, and their application in photocatalysis

Both pristine metal-organic frameworks (MOFs) and graphitic carbon nitride (g-C3N4) displayed outstanding photocatalytic performances toward H2 production, CO2 reduction, Cr(VI) reduction and organic pollutants degradation. To further enhance their photocatalytic performances under visible light or sunlight irradiation, MOFs and g-C3N4 were combined to construct g-C3N4/MOF heterojunctions with the purpose of overcoming their individual disadvantages like fast recombination of pohotogenerated electron-hole pairs. The fabrication methods, characterizations, photocatalytic performances and the corresponding mechanism of some typical g-C3N4/MOF composites were highlighted. Also, the prospective and challenges of this research field were declared.

Powerful combination of MOFs and C3N4 for enhanced photocatalytic performance

A novel binary metal sulfide fabricated with mesoporous carbon nitride (mpg-C 3 N 4 /SnCoS 4 ) was synthesized by the simple in situ hydrothermal method. Characterizations indicate that a homogenous dispersion of SnCoS 4 nanoparticles on the ordered mesoporous structure of mpg-C 3 N 4 (248 m 2  g −1 ) with average diameter of 25 nm, providing more catalytic active sites and large contact regions for adsorption and degradation of pollutant. By taking advantage of this feature, the photocatalytic properties are evaluated systematically by degradation of rhodamine B (RhB) and methylene blue (MB) under visible light irradiation, and the photocatalyitc performance of MCN/SnCoS 4 -50 is much higher than that of pristine SnCoS 4 , mpg-C 3 N 4 , MCN/CoS 2 and MCN/SnS 2 . Moreover, mpg-C 3 N 4 /SnCoS 4 heterojunction exhibits excellent photostability after four recycles. The enhanced photo-induced oxidation and reduction activity of mpg-C 3 N 4 /SnCoS 4 can be attributed to not only the high surface area of composite, but also the formation of n-n type heterojunction. The incorporation of binary metal sulfides into mpg-C 3 N 4 can decrease the band gap, alter the CB and VB potential, enhance the photoinduced interfacial charge transfer, and therefore increase the charge separation efficiency during the photocatalytic reaction.

Construction of mesoporous carbon nitride/binary metal sulfide heterojunction photocatalysts for enhanced degradation of pollution under visible light

Fabrication of BiOI@UIO-66(NH2)@g-C3N4 ternary Z-scheme heterojunction with enhanced visible-light photocatalytic activity

A novel class of CdS@UIO-66-NH2 core shell heterojunction was fabricated by the facile in-situ solvothermal method. Characterizations show that porous UIO-66-NH2 shell not only allows the visible light to be absorbed on CdS nanorod core, but also provides abundant catalytic active sites as well as an intimate heterojunction interface between UIO-66-NH2 shell and CdS nanorod core. By taking advantage of this property, the core-shell composite presents highly solar-driven photocatalytic performance compared with pristine UIO-66-NH2 and CdS nanorod for the degradation of organic dyes including malachite green (MG) and methyl orange (MO), and displays superior photostability after four recycles. Furthermore, the photoelectrochemical performance of CdS@UIO-66-NH2 can be measured by the UV–vis spectra, Mott-Schottky plots and photocurrent. The remarkably enhanced photocatalytic activity of CdS@UIO-66-NH2 can be ascribed to high surface areas, intimate interaction on molecular scale and the formation of one-dimensional heterojunction with n-n type. What’s more, the core-shell heterostructural CdS@UIO-66-NH2 can facilitate the effective separation and transfer of the photoinduced interfacial electron-hole pairs and protect CdS nanorod core from photocorrosion.

Construction of CdS@UIO-66-NH2 core-shell nanorods for enhanced photocatalytic activity with excellent photostability.

A novel ternary heterojunction Cd0.5Zn0.5S@UIO-66@g-C3N4 (Cd0.5Zn0.5S@UCN) has been prepared by the in situ hydrothermal and precipitation approach, which exhibits superior photocatalytic activity for H2 generation and MO degradation under visible-light irradiation. The Cd0.5Zn0.5S@UCN30 composite shows the maximum photocatalytic H2 production rate (1281.1 μmol h−1 g−1) that is about 32.9 and 2.7 times higher than UIO-66@g-C3N4 and pristine Cd0.5Zn0.5S, respectively. Besides, the Cd0.5Zn0.5S@UCN30 heterojunction indicates the superior degradation efficiency of MO (82%) in 120 min. The improved photocatalytic activity of the Cd0.5Zn0.5S@UCN heterostructure can be assigned to its large surface area, enhanced visible-light absorption ability and high-efficiency separation of photogenerated electron–hole pairs, which are proved by the results of photocurrent and EIS analyses. Moreover, the photocatalytic mechanism based on the ternary heterojunction Cd0.5Zn0.5S@UCN is discussed and the transfer and separation process of photogenerated electron–hole pairs is also proposed. This work demonstrates that a novel ternary noble-metal-free photocatalytic system could provide a scientific basis for the application in the field of energy production and pollution removal.

Fabrication of the ternary heterojunction Cd0.5Zn0.5S@UIO-66@g-C3N4 for enhanced visible-light photocatalytic hydrogen evolution and degradation of organic pollutants

Chao Yao

Papers

Construction of mesoporous carbon nitride/binary metal sulfide heterojunction photocatalysts for enhanced degradation of pollution under visible light

Fabrication of BiOI@UIO-66(NH2)@g-C3N4 ternary Z-scheme heterojunction with enhanced visible-light photocatalytic activity

Construction of CdS@UIO-66-NH2 core-shell nanorods for enhanced photocatalytic activity with excellent photostability.

Fabrication of the ternary heterojunction Cd0.5Zn0.5S@UIO-66@g-C3N4 for enhanced visible-light photocatalytic hydrogen evolution and degradation of organic pollutants

Synthesis of CdS/BiOBr nanosheets composites with efficient visible-light photocatalytic activity