Research On Photoelectrocatalytic Properties Of Synergistic Modification Of TiO₂ Nanotube Arrays By CdSe And Ag

Environmental pollution and energy shortages,as two major issues that hinder global sustainable development,have been urgently needed to be resolved.The environment-friendly photocatalytic technology utilizing solar energy is a promising approach,which has attracted considerable research interest.The construction of high performance photocatalysts to achieve efficient utilization of solar energy has become a key factor for the application of this technology.As a traditional semiconductor photocatalytic material with its advantages of low cost,non-toxicity and good stability,titanium dioxide?TiO₂?has attracted considerable interest.In this work,TiO₂ nanotube arrays grown on Ti foil acting as substrates,are modified by combination of narrower band-gap semiconductor and deposition of noble metal nanoparticles,improving its photoelectrochemical properties.Furthermore,the co-sensitization by coupling with both narrower band-gap semiconductor and noble metal nanoparticles was utilized to enhance the photocatalytic activity of the system and improve the utilization of solar energy.The composites was synthesized and studied by the following work.?1?The highly ordered TiO₂ NTs were successfully fabricated by a facile anodization process.The CdSe nanocrystal was loaded on the surface of TiO₂ NTs via in-situ deposition method.It is obvious that CdSe nanocrystals were well-distributed on TiO₂ NTs.The CdSe/TiO₂ NTs samples present obvious visible light absorption ability indicating that CdSe can extend the light adsorption range.The photocurrent density of sample 7-CdSe/TiO₂ NTs was 2.86 times than that of pure TiO₂ NTs.The higher open circuit voltage,positive shift of flat band potential and smaller charge-transfer resistance of 7-CdSe/TiO₂ NTs demonstrated that the deposition of CdSe nanocrystal can effectively enhance the generation,accumulation and transportation of photo-induced charge carriers.The results of the degradation of MB showed that the degradation efficiency of CdSe/TiO₂ NTs was higher than that of pure TiO₂ NTs,in which 7-CdSe/TiO₂ NTs exhibited excellent catalytic activity and good recycling stability.?2?Ag/TiO₂ NTs composites were synthesized by a simple microwave-assisted chemicalreduction method.The results of XRD,XPS and SEM demonstrated that Ag nanoparticles successfully deposited both on the surface and wall of TiO₂ NTs.The Ag/TiO₂ NTs shows an obvious characteristic absorption peak ranging from 400 to 500 nm because of surface plasma resonance effect of Ag nanoparticles.A champion photocurrent density of 0.0050-Ag/TiO₂ NTs sample was observed?0.185 m A/cm2?,which was 1.85 times that of TiO₂ NTs.However,with further increase of precursor concentration,the photocurrent density of the prepared samples decreased.The experimental result of degradation MB showed the same phenomenon.The 0.0050-Ag/TiO₂ NTs had the highest degradation efficiency?65.75%?,and still reached65.54% after third cyclic experiments.It also indicated that the proper loading of Ag nanoparticles can enhance the photoelectrocatalytic activity of TiO₂ NTs.?3?The already-prepared Ag/TiO₂ NTs samples were further used to grow CdSe nanocrystals on the surface by the method mentioned in?1?,so CdSe/Ag/TiO₂ NTs were synthesized for the first time.It is known by structural characterization and composition characterization that CdSe and Ag are simultaneously deposited on the surface of TiO₂ NTs.A unique microstructure was established among CdSe,Ag and TiO₂ in CdSe/Ag/TiO₂ NTs system,in which they can contact with each other.The CdSe/Ag/TiO₂ NTs heterostructure have the highest hydrogen yield?413.99 ?mol/cm2?after 2.5 h irradiation,which was 3.47 times that of TiO₂ NTs,showing excellent photoelectrochemical performance.The ternary composite not only exhibited improving visible light harvesting ability but also possessed the smallest transfer resistance of photo-induced carriers with the lowest simulated values of resistance?4679 ??.By the introduction of Ag nanoparticles,a fast carrier-transfer-channel was formed acting as a linker.Meanwhile,Ag nanoparticles donated a number of hot electrons due to its surface plasma resonance effect and further enhanced photoelectric catalytic activities.