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Photocatalysis: Activity of Nanomaterials catalysts Editorial Photocatalysis: Activity of Nanomaterials Giuseppe Vitiello 1,2,* and Giuseppina Luciani 1,* 1 Department of Chemical, Materials and Production Engineering, University of Naples Federico II, 80125 Naples, Italy 2 CSGI, Center for Colloid and Surface Science, via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy * Correspondence: [email protected] (G.V.); [email protected] (G.L.) Photocatalytic processes have shown great potential as a low-cost, green-chemical, and sustainable technology able to address energy and environmental issues. Nanosized mate- rials, 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 ad- vances in the design and development of nanomaterials in photocatalysis, focusing on the description of synthesis methods and physicochemical properties, as well as on the com- prehension 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 pho- toactive nanomaterials, Tofa et al. [1] described the visible-light-induced photoactivity of Citation: Vitiello, G.; Luciani, G. platinum nanoparticles deposited on zinc oxide nanorods (ZnO-Pt) in degradation of frag- Photocatalysis: Activity of mented microplastics of low-density polyethylene (LDPE) film in water. The experimental Nanomaterials. Catalysts 2021, 11, 611. results demonstrate that the enhanced plasmonic photocatalyst is effectively able to de- https://doi.org/10.3390 grade microplastic LDPE fragments. It is confirmed following the changes in carbonyl and /catal11050611 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, Received: 6 May 2021 Lau et al. [2] proposed an eco-friendly synthesis of ZnO nanoparticles (ZnO-NPs) by using Accepted: 7 May 2021 Published: 11 May 2021 roselle flower and oil palm leaf extract as reducing agents. These nanomaterials are charac- terized in terms of structural, optical, chemical, and antioxidant properties, proposing as Publisher’s Note: MDPI stays neutral enhanced nanomaterials for the treatment of wastewater, especially to those containing with regard to jurisdictional claims in hard-to-remove organic compounds. Boaretti et al. [3] investigated the ability in volatile published maps and institutional affil- organic compounds (VOCs) abatement of electrospun (PVDF) nanofibers as support for the iations. 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 Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. semiconductor nanomaterials to obtain high-performance photocatalysts, focusing mostly This article is an open access article on modification and efficacy towards environmental pollutants, such as heavy metals, dyes, distributed under the terms and antibiotics, and pesticides. Hampel at al. [5] evaluated the photocatalytic activity under UV- conditions of the Creative Commons light of Cu/TiO2 composites with different composition in degradation of methyl orange Attribution (CC BY) license (https:// and Rhodamine B as model and ketoprofen as real pollutant. The morpho-structural prop- creativecommons.org/licenses/by/ erties are investigated by a combined physicochemical approach of different techniques in 4.0/). order to evaluate the role of copper concentration in enhancing the photocatalytic activity Catalysts 2021, 11, 611. https://doi.org/10.3390/catal11050611 https://www.mdpi.com/journal/catalysts Catalysts 2021, 11, 611 2 of 3 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 deter- mined 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 local- ized 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 supe- rior 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. Author Contributions: The manuscript was written through equal contributions of the authors. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. References 1. Tofa, T.S.; Ye, F.; Kunjali, K.L.; Dutta, J. Enhanced Visible Light Photodegradation of Microplastic Fragments with Plasmonic Platinum/Zinc Oxide Nanorod Photocatalysts. Catalysts 2019, 9, 819. [CrossRef] 2. Lau, G.E.; Che Abdullah, C.A.; Wan Ahmad, W.A.N.; Assaw, S.; Zheng, A.L.T. Eco-Friendly Photocatalysts for Degradation of Dyes. Catalysts 2020, 10, 1129. [CrossRef] 3. Boaretti, C.; Vitiello, G.; Luciani, G.; Lorenzetti, L.; Modesti, M.; Roso, M. Electrospun Active Media Based on Polyvinylidene Fluoride (PVDF)-Graphene-TiO2 Nanocomposite Materials for Methanol and Acetaldehyde Gas-Phase Abatement. Catalysts 2020, 10, 1017. [CrossRef] 4. Kaus, N.H.M.; Rithwan, A.F.; Adnan, R.; Ibrahim, M.L.; Thongmee, S.; Yusoff, S.F.M. Effective Strategies, Mechanisms, and Photocatalytic Efficiency of Semiconductor Nanomaterials Incorporating rGO for Environmental Contaminant Degradation— Review. Catalysts 2021, 11, 302. [CrossRef] 5. Hampel, B.; Pap, Z.; Sapi, A.; Szamosvolgyi, A.; Baia, L.; Hernadi, K. Application of TiO2-Cu Composites in Photocatalytic Degradation Different Pollutants and Hydrogen Production. Catalysts 2020, 10, 85. [CrossRef] 6. Li, H.; Zhang, N.; Zhao, F.; Liu, T.; Wang, Y. Facile Fabrication of a Novel Au/Phosphorus-Doped g-C3N4 Photocatalyst with Excellent Visible Light Photocatalytic Activity. Catalysts 2020, 10, 701. [CrossRef] 7. Ortiz, Y.G.D.; de la Osa, R.A.; Saiz, J.M.; González, F.; Moreno, F. Electromagnetic Effective Medium Modelling of Composites with Metal-Semiconductor Core-Shell Type Inclusions. Catalysts 2019, 9, 626. [CrossRef] 8. Kim, J.; Heo, J.N.; Do, J.Y.; Yoon, S.J.; Kim, Y.; Kang, M. Hydrogen Production Improvement on Water Decomposition Through Internal Interfacial Charge Transfer in M3(PO4)2-M2P2O7 Mixed-Phase Catalyst (M = Co, Ni, and Cu). Catalysts 2019, 9, 602. [CrossRef] Catalysts 2021, 11, 611 3 of 3 9. Peng, Y.; Kan, P.; Zhang, Q.; Zhou, Y. Oxygen Vacancy Enhanced Photoreduction Cr(VI) on Few-Layers BiOBr Nanosheets. Catalysts 2019, 9, 558. [CrossRef] 10. San Martín, S.; Rivero, M.J.; Ortiz, I. Unravelling the Mechanisms that Drive the Performance of Photocatalytic Hydrogen Production. Catalysts 2020, 10, 901. [CrossRef].
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