In-Situ Preparation of Black TiO2/Cu2O/Cu Composites as an Efficient Photocatalyst for Degradation Pollutants and Hydrogen Production

Design and Preparation of Heterostructured Cu2O/TiO2 Materials for Photocatalytic Applications

The extensive use of fossil fuels has sped up the global development of the world economy and is accompanied by significant problems, such as energy shortages and environmental pollution. Solar energy, an inexhaustible and clean energy resource, has emerged as a promising sustainable alternative. Light irradiation can be transformed into electrical/chemical energy, which can be used to remove pollutants or transform contaminants into high-value-added chemicals through photocatalytic reactions. Therefore, photocatalysis is a promising strategy to overcome the increasing energy and environmental problems. As is well-known, photocatalysts are key components of photocatalytic systems. Among the widely investigated photocatalysts, titanium dioxide (TiO2) has attracted great attention owing to its excellent light-driven redox capability and photochemical stability. However, its poor solar light response and rapid recombination of electron-hole pairs limit its photocatalytic applications. Therefore, strategies to enhance the photocatalytic activity of TiO2 by narrowing its bandgap and inhibiting the recombination of charges have been widely accepted. Constructing heterojunctions with other components, including cuprous oxide (Cu2O), has especially narrowed the bandgap, providing a promising means of solving the present challenges. This paper reviews the advances in research on heterostructured Cu2O/TiO2 photocatalysts, such as their synthesis methods, mechanisms for the enhancement of photocatalytic performance, and their applications in hydrogen production, CO2 reduction, selective synthesis, and the degradation of pollutants. The mechanism of charge separation and transfer through the Cu2O/TiO2 heterojunctions and the inherent factors that lead to the enhancement of photocatalytic performance are extensively discussed. Additionally, the current challenges in and future perspectives on the use of heterostructured Cu2O/TiO2 photocatalysts are also highlighted.

Ultra-fast green synthesis of a defective TiO2 photocatalyst towards hydrogen production

An ultra-fast green synthesis of defective titanium dioxide (TiO2) photocatalysts was conducted by the microwave-assisted method using l-ascorbic acid (l-As) as a reducing agent. Effect of l-As concentrations on the chemical-, optical- and photoelectrochemical properties as well as the photocatalytic performance towards the hydrogen (H2) production was explored. The obtained TiO2 nanoparticles (NPs) illustrated the brown fine powders with different brownness levels depending on the concentrations of l-As. A high l-As concentration provided a high brownness of TiO2 NPs with a high generation of Ti3+ defects and oxygen vacancies (Ov), which can extend the light absorption towards the visible and near-infrared regions, suppress the recombination rate of electron-hole pairs, promote the photocurrent response and minimize the interface charge transfer resistance. An appropriate quantity of generated defects and good porous properties played a crucial role in photocatalytic H2 production. Under fluorescence illumination, the sample synthesized with a TiO2 and l-As weight ratio of 1 : 0.25 (PAs0.25) exhibited the highest H2 production rate (∼162 μmol g-1 h-1 in the presence of 1 wt% Au co-catalyst) with a slight drop (∼8.2%) after the 5th use (15 h). The synthesis method proposed in this work provides a new insight to an ultra-fast synthesis of defective TiO2 NPs using an eco-friendly chemical precursor under non-severe conditions.

Recent Advances in Black TiO2 Nanomaterials for Solar Energy Conversion

Titanium dioxide (TiO₂) nanomaterials have been widely used in photocatalytic energy conversion and environmental remediation due to their advantages of low cost, chemical stability, and relatively high photo-activity. However, applications of TiO₂ have been restricted in the ultraviolet range because of the wide band gap. Broadening the light absorption of TiO₂ nanomaterials is an efficient way to improve the photocatalytic activity. Thus, black TiO₂ with extended light response range in the visible light and even near infrared light has been extensively exploited as efficient photocatalysts in the last decade. This review represents an attempt to conclude the recent developments in black TiO₂ nanomaterials synthesized by modified treatment, which presented different structure, morphological features, reduced band gap, and enhanced solar energy harvesting efficiency. Special emphasis has been given to the newly developed synthetic methods, porous black TiO₂, and the approaches for further improving the photocatalytic activity of black TiO₂. Various black TiO₂, doped black TiO₂, metal-loaded black TiO₂ and black TiO₂ heterojunction photocatalysts, and their photocatalytic applications and mechanisms in the field of energy and environment are summarized in this review, to provide useful insights and new ideas in the related field.