Rapid Preparation Of Photocatalysts Via Microwave-Assisted Heating Strategy For Visible-Light-Response Hydrogen Generation

Among the alternative technologies for addressing these issues,such as nuclear energy,wind energy,hydropower,and photovoltaics,photocatalytic hydrogen generation is one of most attractive and ideal routes to sovle the energy crisis and environmental pollution problems because the generated hydrogen can power the vechicles and water is the only product.Therefore,the overall photocatalytic reactions are totally green and renewable.The main mission for photocatalysis is exploring the active and stable photocatalysts.The main problem for the sun light photocatalysis technology is low utilization rate,recombination and poor stability and so on,solution generally is to increase the noble metal deposition,the specific surface area of the photocatalyst,ion doping.In comparison to conventional heat transfer by conductor or convection,the microwave heating has the advantages of rapidness,uniformity,and energy saving.Moreover,the microwave heating always endows the products with high quality owing to its high uniformity of heating.In this thesis,we have explored the microwave heating strategy to prepare CdS,g-C₃N₄,g-C₃N₄/Ni₂P,and discussed their photocatalytic hydrogen production performance.Them main content are follows:?1?Metal sulfide photocatalysts.We first prepared the the complexes of cadmium and thiourea by mixing thiourea and cadmium acetate in aqueous solution under magnetic stirring.The Cd-thiourea complexes as prepared were then thermolysis through microwave heating procedure.CuO was used the microwave absorber to convert microwave energy into heat energy.Several variables,including microwave heating time,the molar ratio of Cd/thiourea were studied on thechemical composition,morphology,optical absorption and photocatalytic hydrogen activity of products.More over,several techniques,such as steady-state fluorescence spectra,transient photocurrent were used to reveal the mechanism on increased H2 generation,.The results show that CdS can be rapidly prepared within 5 min microwave heating.Prolonging the heating time would improve 'the crystallinity of produced CdS photocatalyst,and thereby enhance the photocatalytic H2 generation rate.Na2S?0.35 mol/L?and NaSO3?0.25 mol/L?as a sacrificial agent,Pt as catalyst,the hydrogen production capacity of the sample under visible light was detected.When the molar ratio of cadmium to cadmium acetate is 6:1 and the microwave heating time is 35min,CdS has the best photocatalytic performance,and its hydrogen production rate is 70.6?mol·h-I.?2?Preparation of g-C₃N₄ with extended light absorption edge and high crystallinity.g-C₃N₄ was first prepared by thermolysis of melamine at 520? for 4 h in a muffle frnace.The g-C₃N₄ obtained was then thermally heating under microwave irradiation for various times.The as-treated g-C₃N₄ is labeled as CNX,x is the microwave heating time.The variables including microwave power and microwave heating time were investigated on the morphology,optical absorption properties,and photocatalytic H2 generation activity in detail.It is found that the g-C₃N₄ nanosheets with thickness of 30 nm were formed after microwave heating.Moreover,the absorption edge extends to near 600 nn.In addition,the corresponding diffraction peak at 27° intensifies markedly after microwave heating.The extended light absorption edge and improved crystallnitity translate into increased photocatalytic H2 generation activity.Using TEOA as a sacrificial agent,Pt as catalyst,the hydrogen production capacity of the sample under visible light was detected.When the load is 2%Ni₂P,the sample has the best performance,and its hydrogen production rate is 20.1 ?mol·h^-1.?3?Photocatalytic hydrogen production performance of g-C₃N₄/Ni₂P Composite Photocatalytic Materials.Ni₂P was facilely grown on graphitic carbon nitride?g-C₃N₄?surface.During the annealing,the formation of Ni₂P particles and the interfaces between Ni₂P and g-C₃N₄ occurred simultaneously.As a result of Ni₂P loading,the charge transfer from photoexcited g-C₃N₄ to Ni₂P was effectively improved,as evidenced by the considerable enhancement on the photocatalytic H2 production of g-C₃N₄.Impressively,Ni₂P as non-noble-metal co-catalyst shows highly stable H2 production activity.No activity loss occurs over repeated usages and 24-h long term applications.Owing to the advantages of non-toxicity,inexpensive and abundant in nature,this active g-C₃N₄/Ni₂P composite would have great promise for efficient photocatalytic H2 production in future.Using TEOA as a sacrificial agent,the hydrogen production capacity of the sample under visible light was detected.When the microwave heating time is 26min,the photocatalytic activity of the sample is the best,and its hydrogen production rate is 1.65 ?mol·h^-1.