ZIF-8 metal organic framework composites as hydrogen evolution reaction photocatalyst: A review of the current state

In the past decade, extensive research has been devoted to synthesis of ZIF-8 materials for catalytic applications. As physico-chemical properties are synthesis-dependent, this review explores different synthesis strategies based the solvent and solvent-free synthesis of zeolitic imidazole framework. Accordingly, the effect of several parameters on the ZIF-8 synthesis were discussed including solvent, deprotonating agents, precursors ratio is delivered. Additionally, the advantages and disadvantages of each synthesis have been discussed and assessed. ZIF-8 textural and structural properties justify its wide use as a stable high surface area MOF in aqueous catalytic reactions. This review includes the applicatios of ZIF-8 materials in photocatalytic hydrogen evolution reaction (HER). The efficiency of the reviewed materials was fairly assessed. Finally, Limitations, drawbacks and future challenges were fully debated to ensure the industrial viability of the ZIFs.

Improved Photocatalytic Activity via n-Type ZnO/p-Type NiO Heterojunctions

The design and construct pn heterojunction to reduce the recombination rate of photogenerated electron-hole pairs can effectively improve photocatalytic activity. In this study, ZnO/NiO heterojunctions were fabricated by annealing a Zn/Ni metal organic framework precursor synthesized via coprecipitation. The effects of the precursor annealing temperature on the microstructure, morphology, and optical properties of the ZnO/NiO nanocomposites were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis absorption spectroscopy. The results showed that the nanocomposite was composed of hexagonal wurtzite ZnO and cubic NiO, with the former being the dominant phase. Large ZnO nanoparticles were attached to small NiO nanoparticles, and a pn heterojunction interface was formed. The photodegradation performance of the nanomaterials was evaluated by monitoring the degradation of RhB under irradiation by ultraviolet light. The ZnO/NiO nanocomposites exhibited excellent photocatalytic activity when the annealing temperature was 550 °C. The photodegradation mechanism was also analyzed in detail, revealing that the heterojunction between the n-type ZnO and the p-type NiO played an important role in impeding the recombination of photogenerated electron-hole pairs and improving the photocatalytic efficiency.

Metal-organic frameworks and their composites for fuel and chemical production via CO2 conversion and water splitting

Increase in the global energy demand has been leading to major energy crises in recent years. The use of excess fossil fuels for energy production is causing severe global warming, as well as energy shortage. To overcome the global energy crisis, the design of various chemical structures as efficient models for the generation of renewable energy fuels is very much crucial, and will limit the use of fossil fuels. Current challenges involve the design of Metal-Organic Framework (MOF) materials for this purpose to diminish the energy shortage. The large surface area, tunable pore environment, unique structural property and semiconducting nature of the highly porous MOF materials enhance their potential applications towards the production of enhanced energy fuels. This review is focused on the architecture of MOFs and their composites for fuels and essential chemicals production like hydrogen, methane, ethanol, methanol, acetic acid, and carbon monoxide, which can be used as renewable fuel energy sources to limit the use of fossil fuels, thereby reducing global warming.

Recent Advances in Metal-Organic Frameworks Derived Nanocomposites for Photocatalytic Applications in Energy and Environment

Solar energy is a key sustainable energy resource, and materials with optimal properties are essential for efficient solar energy-driven applications in photocatalysis. Metal-organic frameworks (MOFs) are excellent platforms to generate different nanocomposites comprising metals, oxides, chalcogenides, phosphides, or carbides embedded in porous carbon matrix. These MOF derived nanocomposites offer symbiosis of properties like high crystallinities, inherited morphologies, controllable dimensions, and tunable textural properties. Particularly, adjustable energy band positions achieved by in situ tailored self/external doping and controllable surface functionalities make these nanocomposites promising photocatalysts. Despite some progress in this field, fundamental questions remain to be addressed to further understand the relationship between the structures, properties, and photocatalytic performance of nanocomposites. In this review, different synthesis approaches including self-template and external-template methods to produce MOF derived nanocomposites with various dimensions (0D, 1D, 2D, or 3D), morphologies, chemical compositions, energy bandgaps, and surface functionalities are comprehensively summarized and analyzed. The state-of-the-art progress in the applications of MOF derived nanocomposites in photocatalytic water splitting for H2 generation, photodegradation of organic pollutants, and photocatalytic CO2 reduction are systemically reviewed. The relationships between the nanocomposite properties and their photocatalytic performance are highlighted, and the perspectives of MOF derived nanocomposites for photocatalytic applications are also discussed.

Enhanced photocatalytic hydrogen production activity of Janus Cu1.94S-ZnS spherical nanoheterostructures

Photocatalytic hydrogen evolution is one of the most promising approaches for efficient solar energy conversion. The light-harvesting ability and interfacial structure of heterostructured catalysts regulate the processes of photon injection and transfer, which further determines their photocatalytic performances. Here, we report a Janus Cu_1.94S-ZnS nano-heterostructured photocatalyst synthesized using a facile stoichiometrically limited cation exchange reaction. Djurleite Cu_1.94S and wurtzite ZnS share the anion skeleton, and the lattice mismatch between immiscible domains is ∼1.7%. Attributing to the high-quality interfacial structure, Janus Cu_1.94S-ZnS nanoheterostructures (NHs) show an enhanced photocatalytic hydrogen evolution rate of up to 0.918 mmol h^-1 g^-1 under full-spectrum irradiation, which is ∼38-fold and 17-fold more than those of sole Cu_1.94S and ZnS nanocrystals (NCs), respectively. The results indicate that cation exchange reaction is an efficient approach to construct well-ordered interfaces in hybrid photocatalysts, and it also demonstrates that reducing lattice mismatch and interfacial defects in hybrid photocatalysts is essential for enhancing their solar energy conversion performance.

Design of earth-abundant Z-scheme g-C3N4/rGO/FeOOH ternary heterojunctions with excellent photocatalytic activity

A ternary Z-scheme g-C₃N₄/rGO/FeOOH heterostructure photocatalyst for H₂ production was designed and fabricated, which exhibited photocatalytic H₂ production of 124.9 and 869.8 μmol h⁻¹ g⁻¹ under visible and UV-Vis light irradiation, respectively.

Facile strategy for the fabrication of noble metal/ZnS composites with enhanced photocatalytic activities

The introduction of noble metal nanoparticles to photocatalysts can effectively improve the separation efficiency of the photogenerated electron-holes. Therefore, noble metal/ZnS composites were synthesized using a low-temperature solid-phase chemical method with sodium borohydride as the reducing agent. The characterization results showed that the noble metal/ZnS composites have been successfully obtained and that the noble metals were distributed on the surface of ZnS. The catalytic results suggested that the composites exhibited improved activity after introduction of noble metals, which can be attributed to the rapid migration of carriers and the enhancement of the light absorption, mainly owing to the tight combination between the ZnS and noble metals and the plasmon resonance effect of the noble metals. The catalytic mechanism was explored by using photoluminescence spectroscopy, photocurrent spectra, valence band X-ray photoelectron spectroscopy (XPS-VB) spectra and capture agent experiments, and a possible mechanism was proposed. This work provides a new strategy for the high-volume synthesis of noble metal-based composite photocatalysts, which could be helpful for sustainable development.

Controllable synthesis of a 3D ZnS@MoO3 heterojunction via a hydrothermal method towards efficient NO purification under visible light

Heterojunctions can deliver superior photocatalytic efficiency via modulating the surface-interface reaction, enhancing light absorption and hindering charge carrier recombination.

Engineering a hetero-MOF-derived TiO2–Co3O4 heterojunction decorated with nickel nanoparticles for enhanced photocatalytic activity even in pure water

A highly porous TiO₂/Co₃O₄/Ni ternary heterostructure with excellent photocatalytic activity is successfully constructed by adopting hetero-metal organic frameworks as a template and a facile photoreduction method.

A facile synthesis of a ZIF-derived ZnS/ZnIn2S4 heterojunction and enhanced photocatalytic hydrogen evolution

A novel heterostructure of ZIF-derived ZnS/ZnIn₂S₄ is formed by nano-ZnS uniformly dispersed in ZnIn₂S₄ flower, which displays enhanced photocatalytic reactions.

Versatile Functional Porous Cobalt-Nickel Phosphide-Carbon Cocatalyst Derived from a Metal-Organic Framework for Boosting the Photocatalytic Activity of Graphitic Carbon Nitride

Metal-organic framework-templated g-C₃N₄-NiCoP₂-porous carbon (PC) ternary hybrid nanomaterials were designed by taking full advantage of the metal-organic framework (MOF) derivative in the photocatalytic reaction for the first time. The MOF-templated porous structure could prevent the stacking of the carbon nitride nanosheet, and the carefully designed NiCoP₂, possessing low electrocatalytic hydrogen evolution reaction (HER) overpotential and flat-band potential, could improve the separation as well as the utilization efficiency of photogenerated electron-hole pairs. Moreover, the ligand-templated porous carbon, acting as an interface mediator between g-C₃N₄ and the NiCoP₂ cocatalyst, could boost the charge carrier transport. Consequently, the optimal ternary g-C₃N₄-NiCoP₂-PC heterostructure exhibited enhanced photocatalytic HER performance and considerable H₂ evolution performance of 5.8 μmol/h/g under UV-visible light with stoichiometric H₂O₂ production even in pure water. This work took full advantage of the MOF derivative for improving the photocatalytic reaction activity and provided a method that can hopefully help in designing a novel high-performance catalyst for solar conversion.

Phosphorus-doped molybdenum disulfide facilitating the photocatalytic hydrogen production activity of CdS nanorod

Phosphorus doping could modulate the band structure and hydrogen evolution reaction over potential, and bring about the excellent photocatalytic hydrogen evolution activity of CdS/P-MoS₂.

Hybrid VS2 cocatalyst and phosphorus dopant towards both surface and bulk modification of ZnCdS/CdS heterostructures

The bulk phosphorus doping and the surface VS₂ modification over ZnCdS–CdS show synergistic effects for improving its photocatalytic activity.