Design And Synthesis Of Visible-light-responsive Metal Nanocatalysts And Their Application In Hydrogen Evolution From Hydrogen Storage Materials

With the depletion of fossil resources,it is of great significance to develop green fuel using efficient energy science and technology.Hydrogen is one of ideal alternative sources,which can solve current energy crisis and environmental pollution caused by fossil fuels.In the hydrogen-based energy system,developing high-performance hydrogen storage materials with easy transportion and reposition and exploring the efficient release of hydrogen from these materials under saving classical energy,are significantly important to realize hydrogen economy in the future.Formic acid(HCOOH)and borane ammonia(NH3BH3),which contain 4.4 and 19.6 wt%of hydrogen,respectively,are promising chemical hydrogen storage materials.The key scientific problems in hydrogen evolution from HCOOH and NH3BH3 are the low catalytic activity and the expensive characteristics of catalysts.On the basis of that photocatalysis can enhance the activity of catalysts,three ways,namely,introducing inactive metals with surface plasmon resonance(SPR)effect,regulating the microstructures of semiconducting supports and using the photothermal effect of non-noble metal nanoparticles(NPs)such as Fe,Co and Ni,have been adopted to design and synthesize a series of visible-light-responsive supported metal nanocatalysts in the thesis.Moreover,we have systematically studied hydrogen evolution from HCOOH and NH3BH3 over the as-synthesized catalysts using solar energy as the driving force.The main contents are listed as following:(1)On the basis of that the special metals such as Au with SPR effect can generate free electron under the light irradiation,a series of graphene oxide(GO)supported bimetallic AuPd nanocatalysts have been designed and synthesized and then their photocatalytic room-temperature hydrogen evolution from HCOOH has been studied.The results show that AuPd NPs in the catalysts exist in the alloy state and the electrons originated from Au under visible light irradiation can be effectively transferred to the surface of Pd,resulting in that the intrinsic room-temperature activity of Pd in AuPd alloy catalyst is significantly enhanced.Among all the catalysts,the room-temperature TOF value of Au1Pd2/GO under visible light irradiation reached 954.2 h-1.In addition,adjusting the wavelength and intensity of the incident light can regulate the activity of catalysts.As a result,the activity of catalysts is obviously enhanced with increasing the wavelength range and the light intensity.(2)On the basis of that the structures of semiconductors determine their photocatalytic properties,a series of porous semiconducting carbon nitrides(C3N4)and the supported non-precious transition metal nanocatalysts containing Fe,Co and Ni have been designed and synthesized and then their catalytic performance on room-temperature hydrogen evolution from NH3BH3 under visible light irradiation has been studied.The results show that the controllable synthesis of porous lamellar carbon nitrides with different microstructures can be achieved by controlling the structure and proportion of the small molecule precursors containing nitrogen,and then their visible-light-responsive characteristics and the visible-light-driven hydrogen evolution activities of the corresponding catalysts have been achieved.Among all the catalysts,the highest TOF value of Co catalyst reaches 111.1 min-1,which was the highest among the reported non-noble metal catalysts.The change of the incident light wavelength and intensity can regulate the activites of catalysts,indicating that the visible light irradiation can indeed improve the electron density of non-precious metal NPs and then their catalytic activities for hydrogen evolution can be enhanced.Moreover,the catalysts have high stability.(3)On the basis of that specific metal NPs have photothermal effect and metal organic frameworks(MOFs)have the special interaction with metal NPs,a series of MIL-53 supported non-precious transition metal nanocatalysts containing Fe,Co and Ni have been designed and synthesized and then their photothermal catalytic performance on hydrogen evolution from NH3BH3 has been studied.The results show the catalysts have the remarkably enhanced activity under photothermal condition,indicating that the photogenerated electrons indeed participate in and promote catalytic hydrogen evolution reaction.The photothermal catalytic activity of Co/MIL-53 and Ni/MIL-53 was increased by 0.73 and 1.94 times as much as that in the dark at the same temperature,and their TOF values reach 257.1 and 529.4 min-1,respectively.