Significant Enhancement of the Photoelectrochemical Activity of Nanoporous TiO 2 for Environmental Applications

Nanomaterials for photo-electrochemical water splitting: a review

Over the last few decades, the global rise in energy demand has prompted researchers to investigate the energy requirements from alternative green fuels apart from the conventional fossil fuels, due to the surge in CO2 emission levels. In this context, the global demand for hydrogen is anticipated to extend by 4-5% in the next 5 years. Different production technologies like gasification of coal, partial oxidation of hydrocarbons, and reforming of natural gas are used to obtain high yields of hydrogen. In present time, 96% of hydrogen is produced by the conventional methods, and the remaining 4% is produced by the electrolysis of water. Photo-electrochemical (PEC) water splitting is a promising and progressive solar-to-hydrogen pathway with high conversion efficiency at low operating temperatures with substrate electrodes such as fluorine-doped tin oxide (FTO), incorporated with photocatalytic nanomaterials. Several semiconducting nanomaterials such as carbon nanotubes, TiO2, ZnO, graphene, alpha-Fe2O3, WO3, metal nitrides, metal phosphides, cadmium-based quantum dots, and rods have been reported for PEC water splitting. The design of photocatalytic electrodes plays a crucial role for efficient PEC water splitting process. By modifying the composition and morphology of photocatalytic nanomaterials, the overall solar-to-hydrogen (STH) energy conversion efficiency can be improved by optimizing their opto-electronic properties. The present article highlights the recent advancements in cleaner and effective photocatalysts for producing high yields of hydrogen via PEC water splitting.

Quantitative structure-property relationship of the photoelectrochemical oxidation of phenolic pollutants at modified nanoporous titanium oxide using supervised machine learning

Here we report on an advanced photoelectrochemical (PEC) oxidation of 22 phenolic pollutants based on modified nanoporous TiO2, which was directly grown on a titanium substrate electrochemically. Their degradation rate constants were experimentally determined and their physicochemical properties were computaionally calculated. The quantitative structure-property relationship (QSPR) was elucidated by employing multiple linear regression (MLR) method. A supervised machine learning approach was employed to build QSPR models. The high predictive abilities of the QSPR model were validated via leave-one-out (LOO) method and a strict regimen of statistical validation tests. The significant descriptors identified in the QSPR Model for the phenolic compounds were also assessed using a typical dye pollutant Rhodamine B, further confirming the high effectiveness and predictability of the optimized model. Our study has shown that the integrated effect of the structural, hydrophobic and topological properties along with electronic property should be considered in order to design an efficient PEC catalytic approach for environmental applications.

N/Ti3+-codoped triphasic TiO2/g-C3N4 heterojunctions as visible-light photocatalysts for the degradation of organic contaminants

N/Ti³⁺-codoped triphasic TiO₂/g-C₃N₄ heterojunctions were successfully prepared by a one-step in situ hydrothermal method, and they demonstrated considerably enhanced photocatalytic performance.

Efficient bacterial disinfection based on an integrated nanoporous titanium dioxide and ruthenium oxide bifunctional approach

The increasing lack of drinking water around the globe is of great concern. Although UV irradiation, photocatalysis, and electrocatalysis for bacterial disinfection have been widely explored, the synergistic kinetics involved in these strategies have not been reported to date. Herein, we report on an efficient and cost-effective strategy for the remediation of a model bacterium (E. coli), through the integration of photochemistry and electrochemistry based on a bifunctional electrode, which utilizes titanium (Ti) as the substrate, nanoporous titanium dioxide (TiO₂) as a photocatalyst, and ruthenium oxide (RuO₂) nanoparticles as an electrocatalyst. The nanoporous TiO₂ was grown directly onto a Ti substrate via a three-step anodization process, and its photocatalytic activity was significantly enhanced by a facile electrochemical treatment. A high disinfection rate at 0.62 min^-1, with >99.999% bacterial removal within 20 min was achieved using the novel TiO₂/Ti/RuO₂ bifunctional electrode. Complete bacterial disinfection was attained within 30 min as assessed by a spread plate method. Bacterial survival strategies, including a viable but non-culturable state of the bacteria, were also investigated during the bifunctional treatment process. The novel strategy demonstrated in this study has strong potential to be utilized for water purification and wastewater treatment as an advanced environmentally compatible technology.

Synergetic Effect of Ti3+ and Oxygen Doping on Enhancing Photoelectrochemical and Photocatalytic Properties of TiO2/g-C3N4 Heterojunctions

To improve the utilization of visible light and reduce photogenerated electron/hole recombination, Ti³⁺ self-doped TiO₂/oxygen-doped graphitic carbon nitride (Ti³⁺-TiO₂/O-g-C₃N₄) heterojunctions were prepared via hydrothermal treatment of a mixture of g-C₃N₄ and titanium oxohydride sol obtained from the reaction of TiH₂ with H₂O₂. In this way, exfoliated O-g-C₃N₄ and Ti³⁺-TiO₂ nanoparticles were obtained. Simultaneously, strong bonding was formed between Ti³⁺-TiO₂ nanoparticles and exfoliated O-g-C₃N₄ during the hydrothermal process. Charge transfer and recombination processes were characterized by transient photocurrent responses, electrochemical impedance test, and photoluminescence spectroscopy. The photocatalytic performances were investigated through rhodamine B degradation test under an irradiation source based on 30 W cold visible-light-emitting diode. The highest visible-light photoelectrochemical and photocatalytic activities were observed from the heterojunction with 1:2 mass ratio of Ti³⁺-TiO₂ to O-g-C₃N₄. The photodegradation reaction rate constant based on this heterojuction is 0.0356 min^-1, which is 3.87 and 4.56 times higher than those of pristine Ti³⁺-TiO₂ and pure g-C₃N₄, respectively. The remarkably high photoelectrochemical and photocatalytic performances of the heterojunctions are mainly attributed to the synergetic effect of efficient photogenerated electron-hole separation, decreased electron transfer resistance from interfacial chemical hydroxy residue bonds, and oxidizing groups originating from Ti³⁺-TiO₂ and O-g-C₃N₄.

Facile synthesis of mesoporous carbon nitride and titanium dioxide nanocomposites with enhanced visible light photocatalytic activity

C₃N₄–TiO₂ nanocomposites with a large surface area and strong visible light response were fabricated via a rapid solution combustion method.

Metal/TiO2 hierarchical nanocomposite arrays for the remarkable enhancement of photocatalytic activity

Metal/TiO₂ hierarchical nanocomposite arrays were assembled by the deposition of aggregated TiO₂ nanoparticles on anodic aluminum oxide templates and the subsequent loading of metal nanoparticles by electrochemical deposition.