Preparation And Properties Of CdTe Quantum Dot-Based Composite Photocatalytic Materials

Photocatalytic technology has important development prospects in solving energy shortage and environmental pollution,which the key to industrialization of photocatalytic technology is to develop photocatalytic materials with wide spectral response and high quantum efficiency.Unlike bulk semiconductor materials,quantum dot semiconductor materials have many advantages,such as small size,large specific surface area,wide spectral response range and adjustable energy band,and have become a research hotspot of photocatalytic materials.The bandgap of CdTe semiconductors is 1.45eV,which can efficiently utilize visible light that exhibit high activities of photocatalytic H2 evolution and photocatalytic degradation of pollutants under visible light.In this paper,CdTe quantum dots(CdTe.QDs)were used as the main research object,which are compounded with typical carbon materials,graphene oxide(GO)and graphitic carbon nitride(g-C3N4).CdTe-QDs/g-C3N4 and GO/CdTe-QDs photocatalyst were fabricated by a hydrothermal method.The photocatalytic properties and possible photocatalytic mechanism of CdTe-QDs/g-C3N4 and GO/CdTe-QDs composiye photocatalyst for hydrogen production and pollutant degradation were studied respectively.The specific research work is as follows:CdTe-QDs/g-C3N4 composite photocatalyst were fabricated by a simple one-step hydrothermal method,which using 3-mercaptopropionic acid(MPA)as stabilizer,Te and CdCl2·2.5H2O as tellurium and cadmium sources,g-C3N4 nanosheets as composite carriers.The photocatalytic hydrogen production performance of the photocatalyst under visible light was studied.The results showed that the CdTe-QDs/g-C3N4 composite photocatalyst achieved more efficient H2 production under visible light irradiation 10h as compared to pure CdTe QDs and g-CoN4 in the case of employing CoCl2 andH2A as cocatalyst and sacrificial agent,respectively.The optimal composite with 20 wt%CdTe QDs showed H2 production of 4.8 mmol,which was 1.92 times higher than that of pure CdTe QDs.The 40 h stability test showed that CdTe-QDs/g-C3N4 composite photocatalyst had good photocatalytic stability.This is because CdTe-QDs and g-C3N4 form TypeⅡ heterojunction photocatalyst.Under visible light irradiation,CdTe-QDs and g-C3N4 are stimulated by light simultaneously to produce photogenerated electron-hole pairs,in which the holes in g-C3N4 valence band transfer to CdTe-QDs valence band,while the electrons in CdTe-QDs conduction band transfer to g-C3N4 conduction band,thus inhibiting the recombination of CdTe-QDs and g-C3N4 photogenerated carriers,allowing more electrons to participate in the reduction reaction,thus enhances photocatalytic activity.GO/CdTe-QDs composite photocatalyst were synthesized by a mild hydrothermal method,which using graphene oxide(GO)as composite carrier,3-mercaptopropionic acid(MPA)as stabilizer,Te and CdCl2·2.5H2O as tellurium sources and cadmium sources.The effect of GO content on photocatalytic activity of the composite was investigated for different GO and the role of GO in photocatalytic process was explored.The microstructure,optical properties and photocatalytic activity of GO/CdTe-QDs composite photocatalyst were investigated by XRD,TEM,FTIR,DRS and PL.The results showed that the optimal GO content was found to be 2wt%,and the corresponding degradation rate of MB in 60 minutes was 74.1%,which was 2.74 times higer than that of pure CdTe-QDs.The improvement of photocatalytic performance of GO/CdTe-QDs composites is due to the fact that GO as a carrier promotes the dispersion of CdTe-QDs.GO as an electron trartsport channel is conducive to the separation and transfer of photogenerated electrons.Meanwhile,the large specific surface area of GO provides more active sites for photocatalytic reaction.