Preparation And Photocatalytic Properties Of Cadmium Based Quantum Dots Composites

The endless demands of human beings on the earth’s minerals and resources have resulted in a large amount of pollution,which has caused a twin crisis of energy and environment.Photocatalytic technologies that utilize clean solar energy to directly decompose water to produce hydrogen and reduce CO₂ to fuel or organic chemicals are effective ways to solve energy and environmental issues.Based on this,a series of cadmium based quantum dots and composite photocatalysts were prepared by combining cadmium based quantum dots with different semiconductor materials.The structure and photoelectrochemical properties of the composite photocatalysts were characterized,and the mechanism of the improvement of the photocatalytic properties was studied.The research content of this thesis mainly includes:（1）Flowerlike CaMoO₄ microspheres were synthesized by ultrasonic precipitation method.Subsequently,Cd Se/CaMoO₄ composite photocatalysts were prepared by loading aqueous Cd Se quantum dots onto the surface of flowerlike CaMoO₄microspheres.The photocatalytic hydrogen production performance of Cd Se/CaMoO₄composite photocatalysts were studied.The introduction of Cd Se quantum dots improved the light absorption ability,inhibited the recombination of electrons and holes,and accelerated the transfer of electrons and holes.By adjusting the concentration of Cd Se quantum dots,the hydrogen production rate of Cd Se/CaMoO₄-2 composite photocatalyst can reach 10162.33μmol g^-1·h^-1,three times than Cd Se quantum dots.Meanwhile,the Cd Se/CaMoO₄-2 also had good cycling stability.（2）Firstly,flowerlike Mn In₂S₄ microsphere was synthesized by solvothermal method,and then calcined in air to obtain flowerlike Mn doped In₂O₃（Mn-In₂O₃）microspheres.Subsequently,Ni doped Cd S quantum dots(Cd_1-xNi_xS)were prepared and compounded with Mn doped In₂O₃ to obtain Cd_1-xNi_xS/Mn-In₂O₃ composite photocatalysts.The photocatalytic CO₂ reduction properties of Cd_1-xNi_xS/Mn-In₂O₃ with different doping amounts of nickel ion were studied.It was found that the sample of Cd_0.96Ni_0.04S/Mn-In₂O₃ has the highest photocatalytic CO₂ reduction properties,with a CO yield of 43.40μmol·g^-1 in 3 h.The constructed Z-scheme heterostructure improved the efficiency of charge separation,enhanced light absorption,thus leading to the improved photocatalytic CO₂ reduction properties.（3）The precursor of CeO₂ was first synthesized by hydrothermal method,and then calcined in air to obtain the CeO₂ nanorod.Then,an aqueous ZnSe quantum dot was synthesized,and Cd Se quantum dots were epitaxially grown on its surface to obtain ZnSe@Cd Se core-shell quantum dots.The photocatalytic hydrogen production properties of ZnSe@Cd Se/CeO₂ composite photocatalysts with different loading amounts of ZnSe@Cd Se quantum dots were studied.The ZnSe@Cd Se/CeO₂-2 sample has the highest hydrogen production rate,which was 14352.88μmol·g^-1 in 5 h.Compared to ZnSe@Cd Se and CeO₂,the sample of ZnSe@Cd Se/CeO₂-2 had the widest light absorption range,the highest photocurrent response intensity and the lowest electrochemical impedance The constructed type II heterostructure achieved spatial separation of electrons and holes,and avoided the charge recombination.