As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Metal–organic frameworks (MOFs), also known as porous coordination polymers (PCPs), synthesized by assembling metal ions with organic ligands have recently emerged as a new class of crystalline porous materials. The amenability to design as well as fine-tunable and uniform pore structures makes them promising materials for a variety of applications. Controllable integration of MOFs and functional materials is leading to the creation of new multifunctional composites/hybrids, which exhibit new properties that are superior to those of the individual components through the collective behavior of the functional units. This is a rapidly developing interdisciplinary research area. This review provides an overview of the significant advances in the development of diverse MOF composites reported till now with special emphases on the synergistic effects and applications of the composites. The most widely used and successful strategies for composite synthesis are also presented.

Metal–organic framework composites

Rapidly increasing atmospheric CO2 concentrations threaten human society, the natural environment, and the synergy between the two. In order to ameliorate the CO2 problem, carbon capture and conversion techniques have been proposed. Metal–organic framework (MOF)-based materials, a relatively new class of porous materials with unique structural features, high surface areas, chemical tunability and stability, have been extensively studied with respect to their applicability to such techniques. Recently, it has become apparent that the CO2 capture capabilities of MOF-based materials significantly boost their potential toward CO2 conversion. Furthermore, MOF-based materials’ well-defined structures greatly facilitate the understanding of structure–property relationships and their roles in CO2 capture and conversion. In this review, we provide a comprehensive account of significant progress in the design and synthesis of MOF-based materials, including MOFs, MOF composites and MOF derivatives, and their application to carbon capture and conversion. Special emphases on the relationships between CO2 capture capacities of MOF-based materials and their catalytic CO2 conversion performances are discussed.

Carbon capture and conversion using metal–organic frameworks and MOF-based materials

Metal–organic frameworks (MOFs), established as a relatively new class of crystalline porous materials with high surface area, structural diversity, and tailorability, attract extensive interest and exhibit a variety of applications, especially in catalysis. Their permanent porosity enables their inherent superiority in confining guest species, particularly small metal nanoparticles (MNPs), for improved catalytic performance and/or the expansion of reaction scope. This is a rapidly developing interdisciplinary research field. In this review, we provide an overview of significant progress in the development of MNP/MOF composites, including various preparation strategies and characterization methods as well as catalytic applications. Special emphasis is placed on synergistic effects between the two components that result in an enhanced performance in heterogeneous catalysis. Finally, the prospects of MNP/MOF composites in catalysis and remaining issues in this field have been indicated.

Metal–organic frameworks meet metal nanoparticles: synergistic effect for enhanced catalysis

Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

TiO2 based photocatalytic membranes: A review

Facile synthesis of zeolitic imidazolate framework-8 from a concentrated aqueous solution

The photoreduction of CO2 on inorganic semiconductors has been researched for several decades, but the conversion efficiency is still low due to the recombination of photo-generated electron–hole pairs, low utilization efficiency of solar energy and weak adsorption of CO2. Here we for the first time demonstrate that metal–organic frameworks such as ZIF-8 can effectively adsorb CO2 dissolved in water, and promote photocatalytic activity of a semiconductor catalyst in CO2 reduction into liquid fuels in an aqueous medium. In particular, Zn2GeO4/ZIF-8 hybrid nanorods were successfully synthesized by growing ZIF-8 nanoparticles on Zn2GeO4 nanorods. The Zn2GeO4/ZIF-8 nanocomposite inherits both high CO2 adsorption capacity of ZIF-8 nanoparticles and high crystallinity of Zn2GeO4 nanorods. The Zn2GeO4/ZIF-8 hybrid nanorods containing 25 wt% ZIF-8 exhibit 3.8 times higher dissolved CO2 adsorption capacity than the bare Zn2GeO4 nanorods, resulting in a 62% enhancement in photocatalytic conversion of CO2 into liquid CH3OH fuel. The strategy reported here is promising for developing more active photocatalysts for improving CO2 conversion efficiency by taking advantage of excellent adsorption property of metal–organic frameworks in aqueous media.

ZIF-8/Zn2GeO4 nanorods with an enhanced CO2 adsorption property in an aqueous medium for photocatalytic synthesis of liquid fuel

Fabrication of polyethersulfone-mesoporous silica nanocomposite ultrafiltration membranes with antifouling properties

We have demonstrated a new strategy for enhancing solar evaporation by using floating light-absorbing materials. Floating Fe3O4/C magnetic particles with an average size of 500 nm were synthesized by carbonization of poly(furfuryl alcohol) (PFA) incorporated with Fe3O4 nanoparticles. The Fe3O4/C particles had a BET surface area of 429 m2 g−1, and a density of 1.44 g cm−3. Because of their hydrophobicity and a bulk packing density of 0.53 g cm−3, Fe3O4/C particles were floatable on water. Our results indicated that these Fe3O4/C particles enhanced the water evaporation rate by as much as a factor of 2.3 in the solar evaporation of 3.5% salt water. In addition, Fe3O4/C particles were easily recycled using a magnet, and stable after being recycled three times. Our work provides a low-cost and highly effective way for accelerating solar evaporation for industrial applications such as solar desalination, salt production, brine management and wastewater treatment.

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Kun Wang

Papers

TiO2 based photocatalytic membranes: A review

Facile synthesis of zeolitic imidazolate framework-8 from a concentrated aqueous solution

ZIF-8/Zn2GeO4 nanorods with an enhanced CO2 adsorption property in an aqueous medium for photocatalytic synthesis of liquid fuel

Fabrication of polyethersulfone-mesoporous silica nanocomposite ultrafiltration membranes with antifouling properties

Solar evaporation enhancement using floating light-absorbing magnetic particles