Sunlight-Operated TiO2-Based Photocatalysts

Photo-catalysis is a research field with broad applications in terms of potential technological applications related to energy production and managing, environmental protection, and chemical synthesis fields. A global goal, common to all of these fields, is to generate photo-catalytic materials able to use a renewable energy source such as the sun. As most active photocatalysts such as titanium oxides are essentially UV absorbers, they need to be upgraded in order to achieve the fruitful use of the whole solar spectrum, from UV to infrared wavelengths. A lot of different strategies have been pursued to reach this goal. Here, we selected representative examples of the most successful ones. We mainly highlighted doping and composite systems as those with higher potential in this quest. For each of these two approaches, we highlight the different possibilities explored in the literature. For doping of the main photocatalysts, we consider the use of metal and non-metals oriented to modify the band gap energy as well as to create specific localized electronic states. We also described selected cases of using up-conversion doping cations. For composite systems, we described the use of binary and ternary systems. In addition to a main photo-catalyst, these systems contain low band gap, up-conversion or plasmonic semiconductors, plasmonic and non-plasmonic metals and polymers.

Electronic and optical competence of TiO2/BiVO4 nanocomposites in the photocatalytic processes

Nanocomposites with different ratios of titanium dioxide and bismuth vanadate [TiO₂]/[BiVO₄] give rise to compatible electronic band structure alignment at their interfaces to ensure enhanced photoactivated charge transfer under visible light. The sol–gel method and suitable post-synthesis thermal treatments were used to synthesize different compositions with stabilized anatase phase of TiO₂ and monoclinic scheelite polymorph BiVO₄. Structural, electronic and optical characterizations were performed and the results were analysed as a function of the stoichiometry, in which both crystalline structures show a clear junction formation among their characteristic stacking planes. Photocatalytic and (photo) electrochemical responses of the nanocomposites were investigated and tested for the degradation of azo dyes (Acid Blue-113, AB-113) (~ 99%) under visible light radiation. The nanocomposite with a mass ratio of (1:10) shows the highest photocatalytic efficiency compared to the other compositions. HRTEM images showed marked regions in which both crystalline structures form a clear junction and their characteristic planes. However, the increase of BiVO₄ content in the network overcomes the photocatalytic activity due to the decrease in the reduction potential of the photo-generated electrons with high recombination rates.

Thermo-Photocatalysis: Environmental and Energy Applications

Catalysis is an integral part of a majority of chemical operations focused on the generation of value-added chemicals or fuels. Similarly, the extensive use of fossil-derived fuels and chemicals has led to deterioration of the environment. Catalysis currently plays a key role in mitigating such effects. Thermal catalysis and photocatalysis are two well-known catalytic approaches that were applied in both energy and environmental fields. Thermo-photocatalysis can be understood as a synergistic effect of the two catalytic processes with key importance in the use of solar energy as thermal and light source. This Review provides an update on relevant contributions about thermo-photocatalytic systems for environmental and energy applications. The reported activity data are compared with the conventional photocatalytic approach and the base of the photothermal effect is analyzed. Some of the systems based on the positive aspects of thermo- and photocatalysis could be the answer to the energy and environmental crisis when taking into account the outstanding results with regard to chemical efficiency and energy saving.

Recyclable (Fe3O4-NaYF4:Yb,Tm)@TiO2 nanocomposites with near-infrared enhanced photocatalytic activity

Herein, the design and synthesis of a multifunctional (Fe₃O₄-NaYF₄:Yb,Tm)@TiO₂ photocatalyst through a facile sol–gel process combined with electrostatic self-assembly has been reported.

Synthesis of a monoclinic BiVO4 nanorod array as the photocatalyst for efficient photoelectrochemical water oxidation

The BiVO₄ nanorod array is successfully synthesized on fluorine-doped tin oxide (FTO) glasses via a simple solution method, and the electrode is applied as the photoanode for water oxidation.

The effect of iron doping on the photocatalytic activity of a Bi2WO6–BiVO4composite

The formation of Fe-doped Bi₂WO₆–BiVO₄composites could improve the separation efficiency of photogenerated electron–hole pairs, then increasing its photocatalytic activity.

The upconversion and enhanced visible light photocatalytic activity of Er3+-doped tetragonal BiVO4

Er³⁺-doped BiVO₄ with tetragonal structure is prepared by the microwave hydrothermal method.