Studies On The Photocatalytic Performance Of Ceria Quantum Dots Modified Carbon Nitride Materials

Semiconductor photocatalytic technology has attracted extensive attention in the fields of hydrogen/oxygen generation from water splitting,removal of environmental pollutants and reduction of carbon dioxide,which is recognized as an ideal way to solve the current global energy shortage and environmental pollution issues.As a metal-free polymeric semiconductor photocatalyst,graphitic carbon nitride?CN?has drawn great attention due to its low cost,simple synthesis route,structural stablility,non-toxicity and adjustable band gap.However,the severe recombination of charge carriers in CN significantly restricts its photocatalytic applications.In this paper,aimed at improving the carrier separation efficiency of CN,we synthesized ceria?CeO₂?quantum dots?QDs?decorated one-dimensional CN nanotubes and investigated the photocatalytic activity of hydrogen production from water splitting and the mechanism of enhanced performance over the zero-dimensional?0D?/One-dimensional?1D?heterojunction.The main findings of this thesis are as follows:?1?1D sulfur-doped carbon nitride nanotubes?SCN NTs?were successfully prepared by the thermal polycondensation of supramolecular aggregate,which were then decorated with CeO₂ QDs by an in situ deposition-precipitation method,forming a type II CeO₂/SCN heterojunction.The structure and morphology characterizations show that CeO₂ QDs of 2-3 nm in sizes are evenly distributed inside and outside of SCN NT,providing highly dispersed active sites and maximal contact interfaces between two semiconductors.This structure promotes the conversion of Ce⁴⁺to Ce³⁺and the formation of abundant oxygen vacancies in the CeO₂/SCN heterojunction,as evidenced by XPS.?2?The photocatalytic performance of CeO₂/SCN materials was evaluated by hydrogen production from water splitting under visible light irradiation.The results indicated that the uniform dispersion of CeO₂ QDs inside and outside of SCN nanotubes was conducive to the fast separation of photogenerated charge carriers and thus a higher photocatalytic activity.Among them,the CeO₂/SCN photocatalyst with CeO₂ loading of 10 wt%showed the optimal photocatalytic activity with a hydrogen evolution rate up to 2923.8?mol h^-1g^-1,which was much higher than that of pure SCN,pure CeO₂,and the corresponding physical mixtures.The mechanism investigation showed that the surface defect structure,large surface area and well-matched band structure play important roles in the activity enhancement of CeO₂ QDs/SCN NTs.In addition,the time-resolved fluorescence spectroscopy and photoelectrochemical experiments demonstrated that the close contact between 0D CeO₂ quantum dots and 1D SCN nanotubes can accelerate the separation and transfer of carriers,effectively inhibiting the recombination of photogenerated electron-hole pairs.Therefore,CeO₂ QDs/SCN NTs exhibit excellent activity and stability for photocatalytic hydrogen production.