Fabrication Of NiCo₂O₄ Catalysts And Their Performance On Toluene Degradation And CO₂ Reduction

With the increasing frequency of human activities since the industrial revolution,problems of environmental pollution and climate change caused by excessive emissions of volatile organic compounds（VOCs）and CO₂ have aroused world-wide concern.Among various solutions,the photocatalytic technology has received intensive research attention for VOCs degradation and CO₂ conversion due to its features of low cost,less pollution,high catalytic ability and easy to react.However,the efficiency of photocatalysis is far from satisfactory.Recently,NiCo₂O₄ with the spinel structure is considered as a kind of promising catalysts due to its low-cost,stability and rich active sites.Aiming at enhancing the photocatalytic performance on toluene degradation and CO₂ reduction,several NiCo₂O₄ catalysts with different morphology based on the modulation of microstructure were prepared and the structure-function relationship and the reaction mechanism were further investigated.The research contents and corresponding results were introduced below briefly:（1）Uniform NiCo₂O₄ nanospheres via a facile solvothermal method based on the modulation of morphology were prepared.The physicochemical and optical properties of NiCo₂O₄nanospheres were investigated by a series of characterization techniques.Benefiting from superior sunlight absorbance,the larger surface area,and the longer lifetime of carriers,the photocatalytic degradation rate of gaseous toluene over nanospheres can reach 80%,which is significantly higher than that of NiCo₂O₄ nanoparticles.The photocatalytic mechanism of toluene degradation was further explored by in situ fourier transform infrared spectroscopy and electron paramagnetic resonance.The results indicate that photo-generated·O₂^-and h⁺were main reactive species and the intermediates（benzaldehyde）and final products（CO₂）were identified during the degradation process in the NiCo₂O₄ nanospheres catalytic system.（2）A self-templated approach to fabricate hierarchical NiCo₂O₄ hollow microspheres assembled by ultrathin nanosheets using Ni-Co-hydroxides as morphology-conserved self-template were developed for visible light-driven CO₂ reduction with a Ru-based sensitizer.A series of characterization techniques were conducted to investigate structural features of the prepared NiCo₂O₄ hollow spheres.Owing to the integration of the unique microstructure,functional Ni/Co species and oxygen vacancies,NiCo₂O₄ hollow spheres possess enhanced CO₂ adsorption ability,more active sites,and efficient transfer and separation of photoexcited electrons.The high CO-evolving rate（27.7μmol/h）and selectivity（84.4%）manifest considerable performance of NiCo₂O₄ hollow spheres for CO₂ photocatalytic reduction.The findings suggest that such spinel-structured bimetallic oxides hierarchical hollow spheres,facilely synthesized via the proposed self-templated method,are efficient for photocatalytic CO₂ reduction.