Synthesis And Photocatalytic Performance Of Composites Based On Metal-organic Frameworks

Photocatalysis is a facile and environmental-friendly strategy,which can directly convert solar energy into chemical energy.The utilization of sunlight for water splitting into H₂ and CO₂ photoreduction into solar fuels?e.g.CO and CH₄?is an effective approach to alleviate the global energy crisis and environmental problems simultaneously.Many researchers have been committed to the modification of semiconductor catalysts and the development of novel photocatalysts.The construction of high-efficiency photocatalysts is imperative to improve the photocatalytic performance.Recently,metal-organic frameworks?MOFs?have been a research hotspot in the field of photocatalysis due to their high porosity,large specific surface area and tunable versatility.Since traditional semiconductor photocatalysts mostly absorb UV light due to their large band gap and the photo-induced electrons and holes are easily recombined,the utilization of sunlight and photocatalytic performance are rather inefficient.In order to address the defects of traditional semiconductor photocatalysts,MOF-based composite photocatalysts were designed and fabricated by employing NH₂-UiO-66 and ZIF-8 as raw materials.The absorption range of obtained catalysts was successfully extended to the visible light region and the electron transfer at the interface was observably accelerated,which effectively inhibited the recombination of electron-hole pairs.Thus,the photocatalytic performance was remarkably boosted.The main contents of this paper are summarized as follows:1.NH₂-UiO-66 with uniform size and octahedral shape was achieved in the mixture of anhydrous zirconium tetrachloride,2-aminoterephthalic acid and N,N-dimethylformamide with acetic acid as a regulator via solvothermal method.Cd S nanoparticles?NPs?were uniformly modified on the surface of NH₂-UiO-66octahedrons by facile in-situ method to obtain Cd S/NH₂-UiO-66 composite catalysts,and the catalytic performance of different loading amounts of Cd S NPs was examined.The experimental results of photocatalytic reduction of CO₂ under visible light showed that Cd S/NH₂-UiO-66 composites exhibited enhanced photocatalytic performance.When the content of Cd S in the composite was up to 40%,Cd S/NH₂-UiO-66 achieved the highest CO production of 105.41mmol·g^-1 within 6 h.In Cd S/NH₂-UiO-66 composite,the high specific surface area of NH₂-UiO-66promoted the dispersion of Cd S NPs,thus providing more active sites.The Cd S NPs broadened the visible light absorption range and boosted the utilization of visible light.The formation of heterojunction between NH₂-UiO-66 and Cd S accelerated the electron transfer at the interface and suppressed the recombination of light-induced holes and electrons,thereby obtaining remarkable photocatalytic CO₂ reduction performance.2.ZIF-8 with polyhedral morphology and uniform size was synthesized in a mixture of zinc acetate,2-methylimidazole and deionized water at room temperature.The C-doped Zn O material derived from ZIF-8 was obtained via calcination at high temperature and was referred to as C-Zn O.C-Zn O was further vulcanized to construct ZnS/C-ZnO heterostructure.By controlling the vulcanization temperature,composite catalysts with different Zn S contents were obtained and the effect on catalytic performance was studied.The experimental results of photocatalytic water splitting under visible light showed that the catalytic performance of ZnS/C-ZnO composite catalysts was significantly enhanced compared to the single C-Zn O and Zn S.ZnS/C-ZnO composite vulcanized at 100?exhibited the highest H₂ evolution of345.8mmol·g^-1·h^-1.Compared with ZIF-8 and pure Zn O,C-Zn O displayed good absorption in the visible light region.The formation of ZnS/C-ZnO heterojunction enhanced the synergistic effect of Zn S and C-Zn O,which increased the charge transfer at the interface and narrowed the band gap,thus enhanced the utilization of visible light,and improved the photocatalytic performance of hydrogen evolution.