Photocatalysis: Activity of Nanomaterials

Photocatalytic processes have shown great potential as a low-cost, green-chemical, and sustainable technology able to address energy and environmental issues. Nanosized materials, with their superior features, including structural, optical, and size-tunable electronic properties, can endow remarkable catalytic performance and even novel functionalities. Understanding the nanoscale drives design and synthesis strategy to tailor photocatalytic and/or physicochemical properties of nanostructured materials and organic–inorganic nanocomposite semiconductor systems.

This Special Issue on “Photocatalysis: Activity of Nanomaterials” shows recent advances in the design and development of nanomaterials in photocatalysis, focusing on the description of synthesis methods and physicochemical properties, as well as on the comprehension of processing–structure–property relationships in photoactive nanomaterials proposed for different applications.

The issue includes ten papers. They focus on the synthesis, characterization, and application of different kinds of nanostructured materials, showing the relevance of their photocatalytic activity for two specific environmental and energy applications, namely pollutants degradation/abatement and H₂ production. Concerning the first class of photoactive nanomaterials, Tofa et al. [1] described the visible-light-induced photoactivity of platinum nanoparticles deposited on zinc oxide nanorods (ZnO-Pt) in degradation of fragmented microplastics of low-density polyethylene (LDPE) film in water. The experimental results demonstrate that the enhanced plasmonic photocatalyst is effectively able to degrade microplastic LDPE fragments. It is confirmed following the changes in carbonyl and vinyl indices in infrared absorption, proposing it as an effective photocatalytic material for a clean and green approach towards mitigation of microplastics in the ecosystem. Instead, Lau et al. [2] proposed an eco-friendly synthesis of ZnO nanoparticles (ZnO-NPs) by using roselle flower and oil palm leaf extract as reducing agents. These nanomaterials are characterized in terms of structural, optical, chemical, and antioxidant properties, proposing as enhanced nanomaterials for the treatment of wastewater, especially to those containing hard-to-remove organic compounds. Boaretti et al. [3] investigated the ability in volatile organic compounds (VOCs) abatement of electrospun (PVDF) nanofibers as support for the photocatalytic nanosystems obtained by coupling graphene-based materials and TiO₂ by solvothermal synthesis. Specifically, the obtained nanostructured membranes were tested for acetaldehyde and methanol degradation under UV light, showing an increase in the photocatalytic activity compared to bare TiO₂. Kaus et al. [4] proposed a brief review that illustrates the main strategies of combining reduced graphene oxide (rGO) with various semiconductor nanomaterials to obtain high-performance photocatalysts, focusing mostly on modification and efficacy towards environmental pollutants, such as heavy metals, dyes, antibiotics, and pesticides. Hampel at al. [5] evaluated the photocatalytic activity under UV-light of Cu/TiO₂ composites with different composition in degradation of methyl orange and Rhodamine B as model and ketoprofen as real pollutant. The morpho-structural properties are investigated by a combined physicochemical approach of different techniques in order to evaluate the role of copper concentration in enhancing the photocatalytic activity for methyl orange degradation. The proposed nanocomposites also show an interesting ability in hydrogen generation by using oxalic acid as a sacrificial agent.

Li et al. [6] synthetized Au/phosphorus-doped g-C₃N₄ (Au/P-g-C₃N₄) photocatalysts with high photocatalytic activity towards H₂ production, due to the synergy between gold-induced surface plasmon resonance and structural and electronic properties determined by phosphorous doping. In the continuous look for more efficient performances, metal–semiconductor core–shell nanostructures promise to combine high stability with great photocatalytic yield due plasmonic effects. In this context, Ortiz et al. [7] defined a new method to calculate effective dielectric function of metal–semiconductor core–shell nanostructures. This method proved effective in predicting spectral position of localized plasmonic resonance, a key parameter to design high-efficiency photocatalysts. Kim et al. [8] designed three compositions of Nasicon-type materials as mixed-phase catalysts for water splitting. These compositions exhibited enhanced charge separation through inter-phase electron migration. Two-dimensional nanomaterials hold huge promise for the design of high performance photocatalysts with tunable properties through surface-defect engineering. In this field, Peng et al. [9] developed few-layer BiOBr nanosheets with superior photocatalytic activity due to the presence of oxygen vacancies. These systems achieved fast and complete reduction of Cr(VI) species. Creating a semiconductor–semiconductor heterojunction appears to be the most effective strategy to address main limitations of photocatalysts, enabling their activity under visible light. As a key contribution to the efficient design of these systems, Kim et al. [10] reviewed the charge-transfer mechanisms responsible for the photocatalytic activity.

In summary, these ten papers clearly show the relevance of nanostructured materials in light-driven reactions and the key role they could exert in the widespread of this eco-sustainable technology.

We are honored to be the Guest Editors of this Special Issue. We would like to thank the reviewers for improving the quality of the papers with their comments. We are also grateful to all the staff of the Catalysts Editorial Office.