TiO 2 In The Preparation And Modification Of The Nanotube Arrays And Optical Catalytic Properties

In recent years, aligned Ti_O2nanotube arrays (Ti_O2-NTs) have generatedconsiderable scientific interest owing to their remarkable properties, such as a largeinternal surface area and the special nanotubular structures, which provide lots ofreaction active sites and excellent electron percolation pathways for vectorial chargetransfer between interfaces. However, the practical application of pure Ti_O2-NTs islimited by its large band gap (3.2eV for anatase) and a fast recombination rate ofphoto-generated electron-hole pairs. Many routes have been explored to overcomesuch an impediment, such as ion doping, noble metal deposition and narrow band-gapsemiconductors coupling. Recently, photoelectrocatalysis was proved as a feasibleroute to solving the tough problem of the recombination of photo-generatedelectron-hole pairs. The research is dedicated to preparing Ti_O2-NTs by anodicoxidation method, then modifying its surface with uniformly dispersed noble metalsand semiconductor using various appropriate methods, and discussing thephotoelectrocatalytic activity towards degradating organic pollutants.In this study, different Ti_O2-NTs were prepared by an anodic oxidation processunder various experimental conditions, such as anodic voltage, anodic time andcalcination temperature. The effects of nanotubular structures including surfacestructure, tube length, and crystallinity on their photoelectrocatalytic activities ofdegradation methyl orange (MO) in aqueous solution were investigated with details.The experimental results showed that the degradation of MO in thephotoelectrocatalytic process was3times higher than that of photocatalytic process.The large specific surface area, the optimal tube length and higher degree ofcrystallinity would be three important factors to achieve good performances.Au modified Ti_O2nanotube arrays were successfully prepared byelectrochemical pulse deposition method. The effects of pulse deposition potential andtime on surface morphology of obtained materials were discussed.Photoelectrocatalytic activities of degredation rhodamine B and phenol in aqueous solutions were studied. The results showed that Au nanoparticles were highlydispersed on the surface of Ti_O2-NTs by varying pulse deposition potential and time.The obtained Au/Ti_O2-NTs samples exhibited outstanding photoelectrocatalyticperformance.Ultrafine CdS quantum dots modified Ti_O2nanotube arrays were fabricated bycathodic electro-deposition with ion-exchange (CEDIE) strategy. The effects of CdSamount and electrolyte concentration on photoelectrocatalytic performance werediscussed according to the degradation results of MO in aqueous solutions. TheCEDIE strategy resulted in CdS quantum dots highly dispersed in Ti_O2-NTs ratherthan only aggregation on the surface. Compared with CdS/Ti_O2-NTs prepared viasequential chemical bath deposition(SCBD), the as-synthesized samples exhibitedstronger visible-light absorption capability, higher photocurrent density and greatlyenhanced photoelectrocatalytic activity toward degradation of methyl orange aqueoussolutions under visible light irradiation (λ>400nm). Such enhanced visible-lightphotoelectrocatalytic activity can be ascribed to strong combination and more uniformheterojunction between CdS and Ti_O2, which are favorable for visible-light absorptionand charge separation.