A new greener strategy to incorporate Bi 2 S 3mercaptopropionic acid (MPA) quantum dots (QDs) onto TiO 2 nanotube (NT) films was developed, using in situ electrochemical synthesis with a graphite/sulfur powder macroelectrode (cathode) and cavity cell. Simultaneously, the obtained QDs were adsorbed on TiO 2 NTs, for the photoelectrochemical cell (PEC) assays. After the electrochemical synthesis, different thermal post-treatments were performed for growth and crystallization of obtained nanocrystals. The obtained TiO 2 −Bi 2 S 3 nanostructured composites were characterized by UV−vis, diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Photoelectrochemical tests were carried out, where TiO 2 NTs/Bi 2 S 3 QDs with 15 min post-treatment at 90 °C presented a greater photocurrent density, when irradiated with visible light (427−655 nm region, 10 mW.cm −2 ) and compared to pristine TiO 2 NTs. Such performance can be attributed to the synergetic effect caused by the good interface between TiO 2 NTs/Bi 2 S 3 QDs, promoted by the electrochemical method of synthesis employed. The proof of concept evidenced in this work can be potentially extended for the sensitization of TiO 2 NTs with other semiconductors for PEC hydrogen generation and solar cell applications.

Hydrogen fuels generated by water splitting using a photocatalyst and solar irradiation are currently gaining the strength to diversify the world energy matrix in a green way. CdS quantum dots have revealed a hydrogen generation improvement when added to TiO2 materials under visible-light irradiation. In the present paper, we investigated the performance of TiO2 nanotubes coupled with CdS quantum dots, by a molecular bifunctional linker, on photocatalytic hydrogen generation. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into the anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogeneous), while the concentration relative to the sulfate anion decreases by more than 80% with respect to the initial value after ∼100 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix seemingly protected the CdS for photocorrosion in sacrificial solution leading to good stability properties proved by long duration, stable photocurrent measurements. The effect of the size and the distribution of sizes of CdS quantum dots attached to TiO2 nanotubes on the photocatalytic hydrogen generation were investigated. The experimental results showed three different behaviors when the reaction time of CdS synthesis was increased in the sensitized samples, i.e. similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related to two populations of sizes of CdS, where the population with a shorter band gap acts as a trap for the electrons photogenerated by the population with a larger band gap. Electron transfer from CdS quantum dots to TiO2 semiconductor nanotubes was proven by the results of UPS measurements combined with optical band gap measurements. This property facilitates an improvement of the visible-light hydrogen evolution rate from zero, for TiO2 nanotubes, to approximately 0.3 μmol cm(-2) h(-1) for TiO2 nanotubes sensitized with CdS quantum dots.

Herein, we report the in situ photocatalytic deposition of cesium lead bromide (CsPbBr 3 ) perovskite quantum dots on mesoporous TiO 2 -coated fluorine-doped tin oxide (FTO/TiO 2 ) electrodes. The mesoporous TiO 2 layer is used as a photocatalyst to promote the following: (1) the Pb deposition from a Pb 2+ aqueous solution and (2) the in situ Pb conversion into CsPbBr 3 perovskite in the presence of a CsBr methanolic solution without any organic capping agent. Both steps are carried out under ultraviolet light irradiation under ambient conditions without any post-treatment. The obtained FTO/TiO 2 /CsPbBr 3 film was characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction, photoluminescence spectroscopy, scanning electron microscopy, and transmission electron microscopy. The FTO/TiO 2 /CsPbBr 3 heterojunction exhibited enhanced visible-light photodegradation activity demonstrated for the oxidation of curcumin organic dye as a model system. The novel and simple approach to fabricating a supported photocatalyst represents a scalable general method to use semiconductors as a platform to incorporate different perovskites, either all-inorganic or hybrid, for optoelectronic applications. The perovskite deposition method mediated by the UV light at room temperature could be further applied to flexible and wearable solar power electronics.

Photochemical water oxidation was carried out at a mesoporous nanoparticle film composed of indium tin-doped oxide (nanoITO). Annealing nanoITO at temperatures above 250 °C affects both conducting and semiconducting properties. Impressive photoelectrochemical activity was observed at this degenerate ntype semiconductor electrode, outperforming the traditional semiconductor titanium dioxide (TiO 2 ) under the same conditions. In a 0.1 M HNO 3 solution, the nanoITO electrode sustained photocurrents of 1.0 mA/cm 2 at an E applied = 1.5 V vs saturated calomel electrode (SCE) (η = 0.55 V) under a 90 mW/ cm 2 UV illumination (375 nm). This activity is compared to ∼0.3 mA/cm 2 with a traditional TiO 2 electrode under the same potential and conditions. Evidence for oxygen generation in the photolysis experiments was quantified using the collector−generator method, and >70% photocurrent efficiency for O 2 production was confirmed at this nanoITO photoanode.