Preparation And Photoelectric Property Investigation Of Quantum Dot-sensitized TiO₂Nanotube Array

Highly-ordered TiO2nanotube arrays (TNTAs) have attracted much attention in a variety of applications including energy, environment, chemical sensors, etc. However, a critical drawback of TiO2is the relatively wide band gap (3-3.2eV), which is only respond to ultraviolet light. Quantum dot (QD) sensitized TNTAs could achieve the tunable optical properties by adjusting the composition and size of the quantum dots. And the nanotube hollow tubular structure has the large specific surface area and strong adsorption capacity. It’s easier to combine the TNTAs with quantum dots which could achieve the visible light absorption and improve the photoconversion efficiency and catalytic activity.Water-soluble CdS QD covered with cetyltrimethylammonium bromide (CTAB) were deposited on TNTAs by various methods, such as direct current (DC) electrodeposition, cyclic voltammetric (CV) electrodeposition, and successive ionic layer adsorption reaction (SILAR). The morphology measurements show that CTAB capping could well control the QD size and the CV method could effectively prevent the nanoparticle aggregation and uniformly deposit QDs onto TNTAs. Among all the samples, the sample prepared by the CV method possesses superior photoelectrical properties and photocatalytic activity. A maximum photoconversion efficiency of2.81%is achieved for the CTAB/CdS/TNTAs prepared by CV deposition, which exhibits about17times enhancement over the efficiency of the sample prepared by DC electrodeposition. And the photocatalytic degradation of methyl orange under simulated sunlight irradiation demonstrates that the rate constant of the sample prepared by the CV method is almost seven times than that of the untreated TNTAs. Moreover, the underlying mechanism for the improving properties has been discussed.To enhance the light absorption properties of the material, we take ultrasound-assisted successive ionic layer deposition method (S-SILAR) to prepare CdS/PbS quantum dots co-sensitized TNTAs. The result indicated that PbS could expand the range of light absorption but the stability and corrosion resistance are poor and TNTAs/CdS/PbS had a high dark current. Changing the deposition order (TNTAs/PbS/CdS) could reduce the dark current and improve the stability of the material. For accurate analysis of the material’s optical properties and found out the optimal performance of the preparation conditions, we studied the effects of single quantum dot and hybrid quantum dots cosensited TNTAs.Experimental studies have shown that the best deposition cycle of the single QD sensitized TNTAs:CdS14cycles and PbS5cycles. The the hybrid QDs co-sensitized TNTAs shows the shorter deposition cycles that the TNTAs/PbS(2)/CdS(5)(2cycles of PbS and5cycles of CdS sensitized TNTAs) shows the synergistic effect. The compound could absorb visible and near-infrared light when PbS and CdS QDs deposited on the TNTAs. Under the illumination condition, the photocurrent density of TNTAs/PbS(2)/CdS(5) is about the sum of single’s photocurrent density. But synergistic effect disappears when continues to increase the deposition cycle. TNTAs/PbS(5)/CdS(5)(5cycles PbS and5cycles of CdS sensitized TNTAs) shows the subject-effect. The photoelectric performance is demonstrated by PbS which has strong light absorption capacity. CdS as the co-sensitized material could improve the stability, prevent photocorrosion and increase the initial value of the voltage. TNTAs/PbS(5)/CdS(5) has the maximum photoconversion efficiency14.4%at OV (vs SEC) under white light with intensity5.9mW/cm2(dominant wavelength:553nm, half intensity line width:△119nm). Based on this, increasing the deposition cycle of CdS, the photocurrent density of compound has no obvious increase, but the initial value of voltage is gradually increased. The TNTAs/PbS(5)/CdS(14) shows the maximum value-1.3V, it indicated that produce hydrogen could achieved under the lower potential. The further study will devote to improve the migrate rate of photoelectrons, reduce the potential of hydrogen evolution, reduce the recombination of electrons and holes and improve the photoconversion efficiency.