Surface Reconstruction Of Photocatalysts For Enhanced Photocatalytic Water Splitting

Photocatalysis,as a technology that converts solar energy into chemical energy directly,has potential applications in the fields of environment,energy and chemical synthesis.It has’been concerned one of the green ways to solve the energy crisis and environmental pollution.The energy conversion efficiency of photocatalytic water splitting to hydrogen is currently very low,which is one of the bottlenecks restricting its industrialization and industrial application.Therefore,most of the current research focuses on the physical and chemical modification of photocatalysts to improve their photocatalytic performance.This thesis proposes a new surface modification strategy of photocatalyst,taking the new semiconductor materials BixY1-xVO4 and SrTiO3 as research objects and using the highly active intermediate products from the decomposition of melamine and sodium hypophosphite at different temperatures to reconstruct their surfaces to improve their photocatalytic decomposition of water for hydrogen production and to investigate their mechanism of action.The details of this thesis are as follows:1.BixY1-xVO4 was synthesized using a high temperature solid phase method,and then it was thoroughly grinded and mixed with NaH2PO2 and calcined at 250℃ under nitrogen for 1 h.The surface reconstruction of BixY1-xVO4 was achieved using X-ray powder diffractometer(XRD),Raman spectrometer(Raman),X-ray photoelectron spectrometer(XPS),transmission electron microscopy(HRTEM),The effects of the initial dosage ratio and reaction temperature of BixY1-xVO4 and NaH2PO2 on their photocatalytic reaction activities were investigated.The mechanism of the improved performance of photocatalytic decomposition of water was investigated.The results showed that:(1)When the mass of BixY1-xVO4 was 0.4 g,and the mass of NaH2PO2 was 0.05 g,the treated BixY1-xVO4 not only improved the photocatalytic activity compared with the untreated BixY1-xVO4,but also achieved complete hydrolysis under visible light;(2)When the calcination temperature was 250℃ and the calcination time was 1 hour,the phosphorylation treatment of BixY1-xVO4 had the highest photocatalytic activity;(3)The surface reconstruction of BixY1-xVO4 could improve its conduction band position while narrowing the forbidden bandgap.2.BixY1-xVO4 was synthesized by high-temperature solid-phase method,and then it was thoroughly grinded and mixed with C3H6N6 and calcined at 400℃ under nitrogen for 6 h.The core-shell S-type heterojunction BixY1-xVO4@PCN was successfully synthesized.The crystal structure,microscopic morphology,and photoelectric properties of the samples were tested by characterization means;the effects of the initial dosage ratio,reaction temperature,and time on the photocatalytic reaction activity of C3H6N6 and BixY1-xVO4 were investigated,and the mechanism of the improved performance of photocatalytic decomposition of water was discussed.The results showed that:(1)When the mass of BixY1-xVO4 was 0.4 g and the mass of C3H6N6 was 0.1 g,it was found that the performance of core-shell S-type heterojunction BixY1-xVO4@PCN was improved by about 5 times in the photocatalytic complete decomposition of water test compared with pure BixY1-xVO4,and the problem of little O2 production in the decomposition of pure water by PCN was solved;(2)When the calcination temperature was 400℃,the initial dosage ratio,the reaction temperature and the time affected the photocatalytic decomposition of water.The highest photocatalytic activity of core-shell Stype heterojunction BixY1-xVO4@PCN was achieved when the calcination temperature was 400℃ and the calcination time was 6 h.(3)The core-shell S-type heterojunction BixY1xVO4@PCN has a larger contact area and tighter coupling compared with the conventional gC3N4/BiVO4 heterojunction,thus promoting the rapid migration of photogenerated carriers to the catalyst surface to participate in the reaction.3.SrTiO3 nanomaterial was synthesized by high-temperature solid-phase method,and then the blue SrTiO3 was synthesized by thoroughly grinding and mixing it with C3H6N6 and calcining it at 1100℃ under nitrogen gas for 1 h.The crystal structure,microscopic morphology,and photoelectric properties of the samples were tested by characterization means;the initial dosage ratio,reaction temperature and time of C3H6N6 and SrTiO3 were investigated on their photocatalytic reaction.The effects of the initial dosage ratio,reaction temperature,and time on the photocatalytic activity of C3H6N6 and SrTiO3 were investigated.The results showed that:(1)when the mass of SrTiO3 was 0.2 g,and the mass of C3H6N6 was 0.03 g,it was found that the treated blue SrTiO3 showed higher photocatalytic activity than the untreated SrTiO3,and was able to continuously and completely decompose water to produce H2 and O2 under simulated sunlight irradiation,in addition,it was found that the H2 production of blue SrTiO3 was decreasing under the hydrogen-producing half-reaction(2)The photocatalytic activity of blue SrTiO3 was highest when the calcination temperature was 1100℃ and the calcination time was 6 h.(3)The surface oxygen defects and bulk oxygen defects of SrTiO3 had different effects on the energy band structure,with the surface oxygen defects contributing to the rise of the conduction band energy level,thus favoring the production of H2;On the contrary,the bulk oxygen defect helps to maintain the valence band energy level,thus favoring the production of O2.