Study On Preparation And Photocatalytic Performance In Hydrogen Production Under Visible Light Of Hollow Au-ZnO/CN Nanocomposite Derived From ZIF-8

Development of high-performance catalysts for photocatalytic water splitting has been regarded as an efficient and clean solution to meet energy and environmental challenges.Recently,it is promising to prepare high-efficiency visible light-responsive photocatalysts,especially by modifying oxide semiconductors with noble metal.In this thesis,novel hollow N-doped carbon nanocages incorporating Auand ZnO nanoparticles derived from ZIF-8 were successfully synthesized.The photocatalytic hydrogen evolution performance under visible light was also studied.Hollow N-doped carbon nanocages incorporating Auand ZnO nanoparticles EE-Au-ZnO/CN derived from ZIF-8 were successfully synthesized.Firstly,ZIF-8nanocrystals were treated with tannic acid(TA)etching and NaAuCl₄ exchanging(EE)step by step to produce hollow EE-Au_X@ZIF-8.Afterwards,the EE-Au_X@ZIF-8 was converted to EE-Au_X-ZnO/CN after pyrolysis in a N₂ atmosphere.The results showed that the EE-Au_0.6-ZnO/CN prepared under optimized conditions possessed of a hollow cubic structure(?200 nm)with around 30 nm conformal shell,which incorporated uniformly dispersed nanoparticles of Auand ZnO,and Au/Zn atomic ratio was 0.329.Compared with ZnO/CN prepared by direct pyrolysis of ZIF-8,EE-Au_X-ZnO/CN had obvious absorption in the visible region,and the electron-hole separation efficiency was remarkably improved.EE-Au_0.6-ZnO/CN with hollow structre and an optimal ratio of Auand ZnO showed the highest catalytic activity,which was 8 times of that of ZnO/CN.The hydrogen production rate of EE-Au_0.6-ZnO/CN was 0.45 mmol(g·h)^-1by optimizing the reaction conditions.In addition,EE-Au_0.6-ZnO/CN performed good cycle stability.E-Au_X-ZnO/CN derived from ZIF-8 was successfully synthesized by treating with HAuCl₄ through acid etching and exchanging cation simultaneously(E)and pyrolysis.The E-Au_0.40-ZnO/CN prepared under optimized conditions presented the same structure as EE-Au_0.6-ZnO/CN,while the size of ZnO and Aunanoparticles was significantly reduced to about 5 nm,and Au/Zn atomic ratio was 0.425.E-Au_0.40-ZnO/CN could absorb visible light and the electron-hole separation efficiency was enhanced.Therefore,E-Au_0.40-ZnO/CN exhibited the highest hydrogen production rate,which is 12 times and 2.6 times of those of dense cubic ZnO/CN and hollow cubic Au/CN,respectively,indicating a unique hollow structure,and the proper coupling of Auand ZnO made the visible light absorption stronger,charge separation efficiency,electron transfer improved and eventually leading to the highly efficient hydrogen production.The hydrogen production rate could be increased to0.70 mmol(g·h)^-1 under optimized reaction conditions.In addition,E-Au_0.40-ZnO/CN displayed excellent recyclability.The photocatalytic activity of E-Au_0.40-ZnO/CN was better than that of EE-Au_0.6-ZnO/CN,attributing to the appropriate ratio of Auto ZnO,and the fine ZnO Aunanoparticles,which were more conducive to the enhancement of visible light response induced by Auplasma resonance effect.