Preparation Of Nickel-based Graphene Composites And Study Of Dye-sensitized Photocatalytic H2 Evolution

So far,we have relied mainly on traditional energy sources such as oil,coal and natural gas to support our production and life.However,they themselves have many problems,such as depletion,non-renewable,and so on.At the same time,they have brought about many problems,such as serious environmental pollution,ecological damage,Greenhouse Effect,and so on.The search for a new alternative energy is imminent.Hydrogen,as an efficient,clean and green energy,appears in people’s sight.At present,the main ways to obtain hydrogen are electrolytic water,petroleum cracking,solar photocatalytic splitting water,and so on.Among them,solar energy is cheap and inexhaustible which has been favored by the majority of researchers.In the dye sensitization system,the conversion of solar energy into chemical energy has a good research significance and is therefore widely concerned.In this system,cocatalyst is very important because it can effectively separate photogenerated electrons and holes,reduce the hydrogen evolution overpotential,and thus improve the hydrogen production activity.Some precious metals including platinum,rhodium and so on are commonly used as co-catalysts.However,they are rare,difficult to obtain and expensive limiting their application.Therefore,looking for new cheap and easy-to-obtain materials as co-catalysts is important.Nickel is rich in content and low in price.Graphene has large specific surface area,good chemical and physical properties.In this paper,nickel-based graphene composites were prepared by simple heat treatment as co-catalysts for hydrogen evolution by dye sensitized.The whole work is composed of the following two parts:（1）The graphene oxide（GO）sol was obtained by the improved Hummers method,and then the Ni²⁺/GO precursor was obtained by adding NiCl₂ solution.The nickel oxide/nickel carbide/RGO（NNG）composite was obtained via thermal treatment of it in N₂ atmosphere at 400^oC.Nickel oxide plays the role of active sites for OH^-adsorption to promote dissociation of water molecule into proton in basic medium.The formed nickel carbide acts as the active sites for hydrogen atoms adsorption(H_ads).Reduced graphene oxide（RGO）enhancing the conductivity and dye adsorption amount.Meanwhile,RGO sheet as carrier to improve the dispersion of nickel oxide/nickel carbide.The obtained NNG composites exhibit good dye-sensitized photocatalytic because of the synergetic effect of nickel oxide,nickel carbide and RGO.Under the optimal experimental conditions the apparent quantum efficiency（AQY）is 39.4%when the irradiation wavelength is 420 nm.（2）The precursor Ni²⁺/GO was calcined in a N₂ atmosphere at a low temperature of 250°C to obtain an amorphous nickel oxide/nickel carbide/RGO composite NNG-250 which has superior conductivity and electron transport capability compared with the catalyst obtained at 400°C.In the dye sensitization system,NNG-250 has better hydrogen evolution performance than NNG-400.Under the optimal conditions,the concentration of eosin is 5×10^-4 M,and the pH of triethanolamine aqueous solution is10.0,the AQY of the system can reach 43.0%（λ=420 nm）.