Study On The Synthesis And Photocatalytic Property Of Four P-n Junction Composite Catalyst For Water Decomposition

Hydrogen as a clean, efficient and renewable energy is considered to be one of themost promising energy sources in the future. Photocatalytic water splitting producinghydrogen is widely considered a relatively ideal way using water as raw material and solarenergy as sources, and it is environmental friendly and not consuming non-renewableenergy. However, the key of photocatalytic reaction is the development of photocatalyst.Preparation of p-n junction composite catalyst can effectively promote the separation ofphoto-generated electrons and holes, and improve the efficiency of photocatalytic watersplitting producing hydrogen.Delafossite CuAlO₂is prepared by semi-wet method using Al（NO₃）₃and Cu（NO₃）₂asmaterial, and ammonia water as precipitating agent of Al³⁺. The samples are characterizedby X-ray diffraction （XRD）, transmission electron microscope （TEM） andultraviolet-visible diffuse reflectance （UV-vis DR）, and then the photocatalytic activity ofCuAlO₂is tested. The results show that the synthesized CuAlO₂has good crystal integrity,high purity and its direct band gap is about3.48eV.WO₃is prepared by tungsten acid decomposition method, and the effects ofcalcination temperature and time on the physical performance and photocatalytic activityare investigated. The results show that WO₃obtained by calcination at700℃for3h hasgood crystal integrity, high photocatalytic activity and its direct band gap is about2.82eV.CuAlO₂-WO₃is fabricated by mechanical lapping method, and the factors of compositeratio, calcination temperature, calcination time, Ag loading content and Ru loading contentare investigated. The results show that the optimal photocatalyst is prepared withn CuAlO₂:nWO₃1:1by calcination at450℃for3.5h, and the photocatalytic activity isfurther enhanced with0.3wt%Ag or Ru loading content.ZnO is fabricated by chemical precipitation method, and the effects of calcinationtemperature and time on the physical performance and photocatalytic activity areinvestigated. The results show that ZnO obtained by calcination at400℃for3h has goodcrystal integrity, high photocatalytic activity and its direct band gap is about3.25eV.CuAlO₂-ZnO is fabricated by mechanical lapping method, and the factors of compositeratio, calcination temperature, calcination time, Ag loading content and Ru loading content are investigated. The results show that the optimal photocatalyst is prepared withn CuAlO₂:nZnO1:0.6by calcination at350℃for3h, and the photocatalytic activity isfurther enhanced with0.5wt%Ag loading content or0.1wt%Ru loading content.Delafossite CuCrO₂is prepared by semi-wet method using Cr（NO₃）₃and Cu（NO₃）₂asmaterial, and ammonia water as precipitating agent of Cr³⁺. In the calcination process ofprecursor, the phase transformation sequence of chromium-containing material is Cr（OH）₃â†'CuCrO₄â†'CuCr₂O₄â†'CuCrO₂, and it is substantiated by means of XRD andthermogravimetry-differential scanning calorimetry （TG-DSC） analysis. The compositephotocatalysts CuCrO₂-WO₃and CuCrO₂-ZnO are fabricated by mechanical lappingmethod, and then their photocatalytic performance are tested. The results show that thecomposite photocatalysts can split water to produce hydrogen.The effect of reaction liquid pH value on the photocatalytic activity of CuAlO₂-WO₃and CuAlO₂-ZnO is investigated. The results show that the activity of CuAlO₂-WO₃isenhanced in acid condition, and the optimal activity of CuAlO₂-ZnO is obtained in neutralcondition.