Supercritical CO₂ Synthesis Of Mesoporous Carbon/Oxide ?Sulfide? Composites And Their Photocatalytical Properties

Mesoporous carbon composites have been widely applied in the electrochemical energy storage,catalyst supports,adsorption,gas separation,and other important fields due to their special properties.However,from the viewpoint of green chemistry,the utilization of high cost organic templates for pososity as well as the complexity of the synthetic procedures for mesoporous C might restrict their industrial applications.As a green and sustainable technology,supercritical CO₂ has recently drawn great interest in different fields due to its environmentally friendly and unique features.The thesis aim to develope a new strategy to fabricate several mesoporous carbon composites in the supercritical CO₂ system.Advanced characterizations were applied to study the structures of the as-obtained mesoporous C composites,moreover,photocatalytic degradation of pollutants were investigated.Mesoporous carbon/bismuth oxide?mCBiO?composites were successfully fabricated through a facile and green process through a CO₂-mediated approach.The utilization of CO₂ in the synthesis has the following advantages: provided a simple physical expansion to make the carbon precursor mix and dope with the Bi precursor effectively;offer some chemical groups,such as CO₃^2-and HCO3-,which facilitate the deposition of small sized C-Bi₂O₃ completely and uniformly through the coordination to metallic cations;The chemical groups CO₃^2-and HCO3-anions acted as mesoporous templates for the formation of mesoporous carbon.For the photodegradation of RhB and phenol,the photocatalyst synthesized by the CO₂ mediated approach exhibited excellent recycling stability and incereased photodegradation rate when compared with the pure Bi₂O₃ and the reference sample synthesized in pure ethanol.Visible-light-responsive mesoporous carbon/ZnO composites were fabricated in scCO₂-expanded ethanol solution.The mC/ZnO-CE composites showed the excellent photocatalytic activity when evaluated for degrading RhB dye and phenol under visible light.In addition,the combination of Ag and semiconductors can substantially increase the separation of electron-hole pairs owing to the excellent conductivity and strong electron-trapping ability of Ag.Moreover,Ag modified semiconductor exhibits strong absorbance in the visible region owing to the localized surface plasmon resonance.Hence,Ag/mC/ZnO photocatalyst was further prepared in scCO₂-expanded ethanol solution.When utilized for the degradation of RhB and phenol,Ag/mC/ZnO exhibited excellent degradation properties and practical cycles.Magnetically separable visible-light-driven photocatalyst mesoporous C/ZnFe₂O₄composites?C/ZFO-CE?were fabricated through the CO₂-expanded ethanol route,avoiding the use of expensive organic mesoporous template and precipitants.As for degrading RhB and phenol pollutants,C/ZFO-CE in the presence of 2.0 m L 30% H₂O₂ exhibited the excellent performance and outstanding recycle activity.The saturation magnetization of C/ZFO-CE composites was determined to be 43.9 emu g^-1,which was favorable for the separation of photocatalyst from the solution after the catalytic reaction by external magnetic field and was very attractive to practical applications.Highly active and photostable visible-light-driven mesoporous C/CdS catalyst?C/CdS-CO₂?was facilely fabricated through the scCO₂-expanded ethanol medium.The high diffusivity and low surface tension of scCO₂-expanded ethanol system were beneficial to the formation of uniform carbon coating on the surface of CdS.Moreover,the pores were simultaneously introduced into the carbon layer with the help of existed CO₃^2-or HCO3-avoiding the use of additional pore-forming template.Due to the modifyication of uniform mesoporous carbon,the photocorrosion of CdS in C/CdS-CO₂ composites was inhibited,thus C/CdS-CO₂ composites exhibited excellent catalytic performances and stability.Additionally,the structure of the utilized C/CdS-CO₂ remained unchanged when compared to the freshly prepared C/CdS-CO₂,indicative the structure stability during the photoreaction process.Based on the above discussions,a possible photodegradation process for the pollutants over C/CdS-CO₂ composite was proposed.