Oxidation Of 5-hydroxymethylfurfural Coupled With Hydrogen Production From Water Splitting Photo-catalyzed By Ni Decorated G-C₃N₄/CdS

The fast consumption of fossil energy and increserious environmental issues in the worldwide scale demands us to find clean and renewable energy.Thus,hydrogen and biomass energy have received much attention.As a renewable carbon source,biomass energy can be depolymerized and then converted into a range of platform chemicals such as 5-hydroxymethylfurfurural（HMF）,lactic acid,and biofuels.Among them,HMF is particularly important,which can produce value-added products such as 2,5-diformylfuran（DFF）etc.Based on the advantages of low cost,efficiently and environment friendly,it is a promising strategy to selectively oxidize HMF to DFF and produce hydrogen by water splitting through photocatalytic technology.Therefore,the g-C₃N₄/CdS/Ni composite was designed and synthesized.Furthermore,the Au nanoparticles was introduced and CdS/Au/g-C₃N₄/Ni composite was obtained.The properties of HMF oxidation coupled with H₂ generation from water splitting photo-catalyzed by these two materials were studied.The g-C₃N₄/CdS/Ni composite with type-Ⅱ electron transfer mechanism was prepared by high-temperature calcination method,in-situ growth method and photoreduction deposition method in three times.Firstly,the content of CdS in this composite was optimized through the photocatalytic hydrogen production test with triethanolamine（TEOA）as the electron donor.Experiments showed that the composite with 25 mass%CdS exhibited the best photocatalytic performance.The H₂ production rate was 4,134.5μmol·g^-1·h^-1,which catalyzed by g-C₃N₄/25CdS/Ni composite.Based on this,TEOA was replaced by HMF and the HMF can be selectively oxidized to DFF.When the reaction time was 1.5 h,82.3%HMF conversion,69.4%DFF selectivity and 57.2%DFF yield was obtained.At the same time,the H₂ yields in this system was 51.8μmol·g^-1.Furthermore,the DFF selectivity was no significant decrease after five consecutive cycles,which showed that the stability of this material was good.Next,Au nanoparticles were loaded between g-C₃N₄ and CdS by chemical reduction method,which can induce the recombination of e^-from conduction band of CdS and h⁺from valence band of g-C₃N₄.Thus,h⁺from valence band of CdS and e^-from conduction band of g-C₃N₄ can be effectively separated to prepare CdS/Au/g-C₃N₄/Ni composite with Z-scheme electron transfer mechanism.Furthermore,the content of Au nanoparticles and CdS in this composite was optimized through photocatalytic oxidation experiments.Experiments demonstrated that the material with 2 mass%Au and 35 mass%CdS exhibited the best photocatalytic performance.Under optimal reaction conditions,HMF conversion was 40.3%,DFF selectivity and yield were 91.6%and 36.9%respectively.And H₂ yield in this system was 22.3μmol·g^-1.In addition,this material can be reused at least five times,implying that stability of this photocatalyst was also good.