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TiO2 nanorod (TNR) arrays have been sensitized by CdS, PbS, CdS/PbS, and PbS/CdS quantum-dots (QDs). The TNR arrays were synthesized by a hydrothermal treatment, and QDs were deposited on the arrays by a successive ionic layer adsorption and reaction (SILAR) technique. The morphology, structure, composition, optical, photoelectrochemical (PEC), and photocatalytic (PC) properties were systematically investigated. The results demonstrate that TNR/QDs can effectively facilitate photoinduced carrier transport, suppress the recombination rate of electron-hole pairs, and improve the visible light absorption, PEC, and PC properties. The TNR/CdS(7)/PbS(3) sample shows the maximal photocurrent density (0.91 mA/cm2) and photodegradation efficiency (97.3%), which is nearly 37.9 and 2.89 times higher than those of bare TNR, respectively. The enhanced properties are attributed to the narrow band gaps and high absorption coefficients of QDs, and the type-II nanoheterostructures with a staggered alignment of band edges at the hetero-interface that can facilitate the spatial separation of electron-hole pairs.

Highly ordered TiO2 nanorod (TNR) arrays decorated with Cu2ZnSnS4 (CZTS) nanocrystals were prepared via a facile and effective method. The TNR arrays were synthesized using a hydrothermal treatment, and the CZTS nanocrystals were deposited by a three-step successive ionic layer adsorption and reaction (SILAR) technique followed by annealing in a sulfur atmosphere. The morphology, structure, composition, optical, and the photoelectrochemical (PEC) properties of the CZTS/TNR arrays were investigated in detail. The results demonstrate that the CZTS/TNR arrays can effectively facilitate photoinduced carrier transport, reduce the recombination rate of electron-hole pairs, and as a result demonstrate improved light absorption properties and PEC performance. The CZTS/TNR arrays sensitized with 7 SILAR cycles showed a maximal photocurrent density of 2.17 mA/cm2 at 0 V and the longest electron lifetime of 47.39 ms, which is nearly 80 and 2.03 times higher than those of pure TNR, respectively. The improvement in performance can be attributed to the high absorption coefficient and narrow bandgap of CZTS and the type-II nanoheterostructures with a staggered alignment of band edges present at the heterointerface. Surface passivation with ZnS resulted in a further improvement in PEC performance in comparison to the untreated CZTS/TNR arrays with values of 2.53 mA/cm2 and 59.77 ms for the maximal photocurrent density and longest electron lifetime, respectively.

TiO2 nanotube arrays (TiO2-NTAs) were respectively fabricated using traditional one-step oxidation and re-oxidation method on a titanium surface in fluorine-containing electrolytes. Microstructures, optical properties of specimen were characterized by X-ray diffractometer, digital microscope, field-emission scanning electron microscope and ultraviolet-visible spectroscope. Compared with the one-step oxidation, the resulted samples showed more uniform surface, longer tube length and statistical higher absorption in visible light region. Importantly, a new growth mechanism named template-induced growth model is proposed to explain the growth of TiO2-NTAs prepared by re-oxidation approach in present work. Besides, water contact angles of samples before and after irradiated by UV light were measured and discussed in detail. It is confirmed that samples obtained from re-oxidation method have more hydroxyl groups can be formed when irradiated by UV light, which lead to more sensitive light-induced hydrophilicity finally. The light-induced hydrophilic performance of TiO2-NTAs would be favorable to improve the likelihood of electrolyte contacting of the surface, which is useful in many realistic application instances.

Highly ordered TiO2 nanorod (TNR) array films decorated with Ag nanoparticles (NPs) were synthesized on fluorine-doped tin oxide (FTO) by a hydrothermal treatment and a successive ionic layer adsorption reaction (SILAR) technique. The amount of Ag NPs on the TNR can be controlled by changing the number of cycles in silver nitrate (AgNO3) solution. The morphology, structure, composition, optical, photoelectrochemical and photocatalytic properties of the Ag/TNR films were investigated in detail. The Ag/TNR films exhibit larger redshift of the absorption edges and higher absorption intensities in the visible light range. Furthermore, the Ag/TNR films sensitized with 5 SILAR cycles show the best photocurrent density (32 uA/cm2) and photodegradation efficiency (95.52%), which is 5.7 and 1.3 times higher than that of pure TNR, respectively. The excellent properties can be ascribed to localized surface plasmon resonance (LSPR) effect of Ag NPs. The stability and reusability of the Ag/TNR films were also investigated. Therefore, the Ag/TNR films with high performance and stability can be used in potential applications.

Hetero-structured TiO2 nanotree arrays on flurine-doped tin oxide (FTO) substrates were deposited by a two-step hydrothermal method, CdS/ZnS core-shell quantum dots (CdS/ZnS QDs) were deposited by a successive ionic layer absorption and reaction (SILAR) process. The TiO2 nanotree array is composed of a trunk-branch structure where the trunk is rutile TiO2 nanorod array and the branch is anatase TiO2 nanosheets standing on the trunk. Morphology, optical properties and photoelectrochemical (PEC) performances were investigated in detail. After the deposition of CdS/ZnS QDs, TiO2 nanotree array photoanode shows much better PEC performance compared to TiO2 nanorod array photoanode that sensitized nanotree array show a higher photocurrent desity (1.5 mA/cm2) at 1.0 V and almost 2-fold current density (0.29 mA/cm2) than sensitized nanorod array (1.0 mA/cm2 and 0.15 mA/cm2) in the measurement of linear sweep voltammetry (LSV) and transient photocurrent, respectively. This result is due to the enlarged surface specific area for more quantum dots loading, and also due to the rutile/anatase junctions formed on the boundary of trunks and branches, leading to an effective charge separating and transporting. It suggests that the hetero-structured TiO2 nanotree array is very promising to be applied in highly efficient photoanodes for energy devices.