Synthesis and catalytic study of nano CeO2 compound

Abstract

CeO2 is a stable compound having wide band gap. Considering its high temperature stability, CeO2 samples were synthesized in water and ethanol medium. Thioglycerol (TG) was used as capping agent. The Zn-doped and (Y, Zn) co-doped CeO2 nanoparticles (NPs) were also synthesized to reduce the band gap and also to generate the oxygen vacancies. Further, their heterostructures were synthesized with CdS and ZnS. It was observed that CeO2 NPs synthesized in ethanol as reaction medium with TG as capping agent showed enhanced catalytic activity as compared to samples synthesized in water medium. The synthesized samples calcined at 300 °C have shown large catalytic activity. Moreover, doped and co-doped CeO2 NPs have shown many fold degradation efficiency towards CV dye as compared to bare CeO2 NPs. The 8% Zn-doped CeO2 NPs have shown 100 % dye degradation in 5h of UV-visible irradiation which is higher than bare CeO2 samples (100 % dye removal in 7h). While, (Y, Zn) co-doped CeO2 samples have shown 100 % dye degradation in 3 h of UV-visible irradiation. Further, the CdS and ZnS heterostructures were synthesized with Zn-doped and (Y, Zn) co-doped CeO2 NPs. It was found that CdS heterostructures have shown enhanced catalytic activity with Zn-doped CeO2 NPs. Moreover, the synthesized heterostructures degraded the CV dye in 2h of UV-visible irradiation. Further, the leaching properties of CeO2 heterostructures synthesized with CdS have been studied. No leaching of Cd atoms in the dye solution was observed which shows that the synthesized heterostructures are UV-visible resistible. The photocatalytic activity of synthesized compound was also studied with variation in catalyst concentration. The catalytic activity is found to increase with the amount of catalyst dosage upto 3 mg in 100 ml of dye solution. The optical thickness of synthesized CeO2 NPs has been calculated to check its relation with observed photocatalytic results. The optical thickness is found to increase with catalyst dosage. It was found that at optimum value of optical thickness, the rate of conversion is maximum. Beyond this value, the rate of conversion is found to decrease. The results indicated that oxygen vacancies play vital role in deciding the catalytic activity of the synthesized compound as no corelationship was observed for optical thickness and degradation rate. The work shows that CeO2-based photocatalyst can play an important role for degradation of pollutants because of its non-toxicity and formation of formation of oxygen vacancy due to transformation of Ce4+ to Ce3+. It is observed that the formation of Ce3+ by creation of O-vacancies plays important role as Ce in CeO2 has stable states of both Ce4+ and Ce3+ ions.