Study On The Hydrothermal Synthesis Of WO₃ And Its Photocatalytic Hydrogen Production Performance After Composited With CuCrO₂

Hydrogen production from photocatalytic decomposition of water is an environmental-friendly green process as well as one of the ideal pathways to produce hydrogen.P-n hetero-junction composite photocatalyst has broader light response range,improved separation efficiency of photo-generated electron-hole pair,and hence higher efficiency of hydrogen evolution from photocatalytic water splitting.WO₃'s precursor was synthesized by hydrothermal method using Na₂WO₄·2H₂O and?NH₄?₁₀W₁₂O₄₁·5H₂O as raw materials,and hydrochloric acid,nitric acid or sulfuric acid as acidifier,respectively.The WO₃ was abtained by certain heat treatment the precursor and then was coupled with CuCrO₂ to fabricate the CuCrO₂-WO₃ composite photocatalyst.The synthesized WO₃ samples were characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?,ultraviolet-visible diffuse reflectance?UV-vis DR?and tested with respect to the photocatalytic activity of corresponding CuCrO₂-WO₃ compound.The results showed that,the WO₃ abtained using?NH₄?₁₀W₁₂O₄₁·5H₂O as raw material was better than using Na₂WO₄·2H₂O.What's more,WO₃ synthesized using?NH₄?₁₀W₁₂O₄₁·5H₂O as raw material and sulfuric acid as acidifier had small uniform particle and CuCrO₂-WO₃ made from it showed better photocatalytic property.The influence of varying sulfuric acid amounts,hydrothermal temperature and time,as well as altering between ammonium sulfate and sulfuric acid?in equally molar amount?within the protocol of preparing WO₃(with?NH₄?₁₀W₁₂O₄₁·5H₂O as raw material,sulfuric acid as acidifier)on the properties of as-synthesized samples were investigated.The results showed that with 6.8mmol sulfuric acid,ammonium sulfate equally substituting of2.7mmol sulfuric acid,and reacting at 220?for 14h,the optimal synthesis condition was reached.The change of the phase composition,morphology,and light absorption property of WO₃'s precursor in the heat treatment process were investigated by thermogravimetry?TG?,X-ray diffraction?XRD?,scanning electron microscope,ultraviolet-visible diffuse reflectance?UV-vis DR?and photocatalytic activity test.The results showed that the precursor was hexagonal WO₃·0.33H₂O with nano-rod morphology.When the heat treatment temperature is below 400?,the crystalline type remained unchanged,slightly morphological change was abserved,and the photocatalytic activity of CuCrO2-WO3 was lower.After heat treatment the precursor at 500?,the sample transform into monoclinic WO₃.Thereafter with the increasing of heat treatment temperature,the crystalline perfection of WO3 was improved gradually as well as the photocatalytic activity of CuCrO2-WO3.But as the size grew up,especially when the calcination temperature was increased to 700?,the dispersibility and uniformity decreased seriously.Detailed study of the calcination condition experiment showed that when the precursor was first calcinated at 500?for 2h and then calcinated at 650?for 1.5h,the monoclinic WO₃ was abtained with higher crystalline perfection and smaller average particle size and the corresponding CuCrO2-WO3 compound photocatalyst exhibited the highest photocatalytic activity.The hydrogen production was 187.3?mol under the irradiation of250W mercury lamp for 1h.The effect of Ru-loading on the photocatalytic activity of CuCrO2-WO3 was investigated.The result showed that Ru-loading can improve the photocatalytic activity of CuCrO₂-WO₃ and loading on the surface of WO₃ results in even higher improvement.The hydrogen production over CuCrO2-0.5wt%Ru/WO3 was up to 311.0?mol under the irradiation of 250W mercury lamp for 1h.Furthermore,in order to investigate the stability of CuCrO2-WO3 and CuCrO2-0.5wt%Ru/WO3,the photocatalytic activity cyclic test was conducted under the irradiation of 250W mercury lamp.The results of water splitting indicated that the catalysts CuCrO2-WO3 and CuCrO2-0.5wt%Ru/WO3 have good resistance to light corrosion and that their H₂ production remain unchanged after using 7 times.The hydrogen production over CuCrO2-WO3 and CuCrO2-0.5wt%Ru/WO3 were 4.7?mol and 6.7?mol respectively for 3h under the irradiation of 300W xenon lamp.