Preparation Of Visible-light-responsive Metal-based Catalysts And Their Application In Photocatalytic Hydrogen Evolution Reaction

Hydrogen is a kind of energy with high calorific value and environmental friendliness.In the process of realizing hydrogen economy,the efficient storage and release of hydrogen are still the challenges.Ammonia borane?NH₃BH₃?and formic acid?HCOOH?with the hydrogen content of 19.6 and 4.4 wt%,are two promising chemical hydrogen storage materials with application prospect.In order to achieve the efficient hydrogen evolution from NH₃BH₃ and HCOOH under mild conditions,the design of the new catalysts is crucial.On the basis of these considerations,we have introduced the photocatalytic method into the two hydrogen evolution systems involving NH₃BH₃ and HCOOH.Since the visible light can be used to regulate the electron density of the active centers of catalysts to enhance their catalytic activity,we synthesize three kinds of visible-light-responsive catalysts and have systematically studied their catalytic performance of hydrogen evolution from NH₃BH₃ and HCOOH under visible light irradiation.The main results are listed as following.?1?On the basis of the surface plasmon resonance?SPR?effect and non-SPR effect of some metals,we have synthesized a series of different-sized Cu spheres,which are used to support the non-precious Co and Ni nanoparticles?NPs?.Then we have studied their catalytic performance of hydrogen evolution from NH₃BH₃ under visible light irradiation.The results show that the activity of all the catalysts is improved under visible light irradiation and one catalyst containing Co NPs and Cu sphere with the size of 190 nm has the highest activity with the total TOF value of 164.8 min^-1,which exceeds the values of all the reported non-noble metal catalysts.Owing to the SPR effect of Cu spheres,the generated electrons in Cu are transferred to the catalytically active Co and Ni under visible light irradiation.At the same time,the interband electron transition happens in the Co and Ni NPs with non-SPR effect under light irradiation.Thus,the electrons originated from the two types of metals synergistically enhance the photocatalytic activity of catalysts.?2?On the basis of the non-SPR effect of some metals,we have used aminosilanes to modify SiO₂,TiO₂ and TiO₂-SiO₂ without visible light absorption,resulting in the formation of NH₂-functionalized supports,which are used to support bimetallic CoPd NPs with non-SPR effect.Then we have systematically studied the catalytic performance of hydrogen evolution from HCOOH under visible light irradiation.The results show that the activity of all the catalysts is greatly improved under visible light irradiation compared with the dark condition.This suggests that the non-SPR effect of CoPd NPs indeed promotes the photocatalytic hydrogen production.In addition,among all the catalysts,one catalyst CoPd/TiO₂-SiO₂ has the highest activity with the total TOF value of 888.9 h^-1.A series of comparative experiments show that the NH₂ groups in the catalysts can adsorb and activate HCOOH molecules in the catalytic process.When SiO₂ is combined with TiO₂,the utilization efficiency of visible light becomes much higher.These favorable factors ultimately promote the efficient catalytic hydrogen evolution from HCOOH.?3?On the basis of that the combination of different semiconductors can lead to the changed characteristics of band structures,we have synthesized a series of composite semiconductors TiO₂-CeO₂,which are used to support bimetallic CoPd NPs.Then we have systematically studied the catalytic performance of hydrogen evolution from HCOOH under visible light irradiation.The results show that compared the catalysts containing single supports,the catalysts conatining composite semiconductors exhibit the higher activity under visible light irradiation.Specially,when the amount of CeO₂is 5 wt%in TiO₂-CeO₂,one corresponding catalyst has the highest activity with the TOF value is 637.1 h^-1.The spectral characterization results show that after the combination of TiO₂ and CeO₂,the band structures of TiO₂-CeO₂ significantly change and the bandgap decreases from 3.01 to 2.16 eV,which leads to the efficient photocatalytic hydrogen evolution from HCOOH.