Special Issue "New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production"

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Photocatalysis".

Deadline for manuscript submissions: 31 May 2019

Special Issue Editor

Guest Editor
Prof. Dr. Simonetta Palmas

Dipartimento Ingn Meccan Chim & Mat, Univ Cagliari, Via Marengo 3, I-09123 Cagliari, Italy
Website | E-Mail
Interests: preparation and characterization of catalysts for redox processes; synthesis and characterization of semiconductor nanostructured materials; synthesis of TiO2 nanotubes; Advanced Oxidation Processes for the demolition of biorefractory organics and wastewater treatment; application of photoelectrocatalytic processes in the energetic and environmental field

Special Issue Information

Dear Colleagues,

Remediation of wastewater, up to a level acceptable for discharge into receiving waterbodies, involves an ever-growing demand of energy, so effective and low energy use demand treatment processes that are highly desirable

Among the others, photo and photo-electrochemical treatment processes may be considered as advanced oxidation processes (AOP), which are based on the generation of OH radicals, strong oxidizing agents able to indiscriminately degrade even the most persistent organic compounds.

Photocatalysis, which exploits the semiconductor material’s ability to generate electron-hole coupling, under the irradiation of a suitable wavelength, can be considered as an effective method for organic degradation, especially when the semiconductor is active in the range of visible light.

Greater efficiencies may be obtained in photo-electrocatalytic processes, thanks to the application of an electric field, which assists the displacement of electrons within the semiconductor structure, thus reducing the recombination between photo-generated charges, which represents one of the main drawbacks of this process.

This Special Issue aims to focus on new trends in photo-electrocatalysis, not only for aspects related to possible advances in materials science, but also to new possible applications of the technology. Actually, we may consider the different philosophies that have been prevailing in these last few years: rather than considering the wastewater treatment process as just a way to destroy or remove organics from waste, the pollutants may be considered as a source of energy, so that the electrons produced by the oxidative process could be recovered and possibly used to obtain new chemicals and fuels.

Thus, research on new morphologies and structures, which allow more photoactive, visible responsive, and stable materials will be welcome, as well as studies on combined processes in which photo- or photo-electrochemistry contributes to an increase in the sustainability of the whole process, in terms of lowering costs and achieving the most valuable final products.

Prof. Simonetta Palmas
Guest Editor

Manuscript Submission Information

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Keywords

  • Photoelectrocatalytic wastewater treatment
  • Photoelectrocatalytic degradation of organics
  • Nanostructured semiconductors
  • Visible light sensitive semiconductors
  • Wastewater sustainable combined processes
  • Advanced electrochemical oxidation processes
  • Bioelectricity
  • Photoelectrosyntesis
  • H2 production

Published Papers (5 papers)

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Research

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Open AccessArticle Integrated Au/TiO2 Nanostructured Photoanodes for Photoelectrochemical Organics Degradation
Catalysts 2019, 9(4), 340; https://doi.org/10.3390/catal9040340
Received: 7 March 2019 / Revised: 27 March 2019 / Accepted: 2 April 2019 / Published: 5 April 2019
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Abstract
In this work, hierarchical Au/TiO2 nanostructures were studied as possible photoanodes for water splitting and bisphenol A (BPA) oxidation. TiO2 samples were synthetized by Pulsed Laser Deposition (PLD), while Au nanoparticles (NPs) were differently dispersed (i.e., NPs at the bottom or [...] Read more.
In this work, hierarchical Au/TiO2 nanostructures were studied as possible photoanodes for water splitting and bisphenol A (BPA) oxidation. TiO2 samples were synthetized by Pulsed Laser Deposition (PLD), while Au nanoparticles (NPs) were differently dispersed (i.e., NPs at the bottom or at the top of the TiO2, as well as integrated TiO2/Au-NPs assemblies). Voltammetric scans and electrochemical impedance spectroscopy analysis were used to correlate the morphology of samples with their electrochemical properties; the working mechanism was investigated in the dark and in the presence of a light radiation, under neutral pH conditions towards the possible oxidation of both bisphenol A (BPA) and water molecules. Different behavior of the samples was observed, which may be attributed mainly to the distributions of Au NPs and to their dimension as well. In particular, the presence of NPs at the bottom seems to be the crucial point for the working mechanism of the structure, thanks to scattering effects that likely allow to better exploit the radiation. Full article
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Open AccessArticle The Role of Mediated Oxidation on the Electro-irradiated Treatment of Amoxicillin and Ampicillin Polluted Wastewater
Catalysts 2019, 9(1), 9; https://doi.org/10.3390/catal9010009
Received: 2 November 2018 / Revised: 15 December 2018 / Accepted: 18 December 2018 / Published: 24 December 2018
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Abstract
In this work, the electrolysis, photoelectrolysis and sonoelectrolysis with diamond electrodes of amoxicillin (AMX) and ampicillin (AMP) solutions were studied in the context of the search for technologies capable of removing antibiotics from liquid wastes. Single-irradiation processes (sonolysis and photolysis) were also evaluated [...] Read more.
In this work, the electrolysis, photoelectrolysis and sonoelectrolysis with diamond electrodes of amoxicillin (AMX) and ampicillin (AMP) solutions were studied in the context of the search for technologies capable of removing antibiotics from liquid wastes. Single-irradiation processes (sonolysis and photolysis) were also evaluated for comparison. Results showed that AMX and AMP are completely degraded and mineralized by electrolysis in both chloride and sulfate media, although the efficiency is higher in the presence of chloride. The effect of the current density on mineralization efficiency is not relevant and this may be related to the role of mediated oxidation. Irradiation by ultraviolet light or ultrasound (US) waves does not produce a synergistic effect on the mineralization of AMX and AMP solutions. This indicates that the massive formation of radicals during the combined processes can favor their recombination to form stable and less reactive species. Full article
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Open AccessFeature PaperArticle Ag/Ag2O as a Co-Catalyst in TiO2 Photocatalysis: Effect of the Co-Catalyst/Photocatalyst Mass Ratio
Catalysts 2018, 8(12), 647; https://doi.org/10.3390/catal8120647
Received: 20 October 2018 / Revised: 3 December 2018 / Accepted: 4 December 2018 / Published: 10 December 2018
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Abstract
Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites [...] Read more.
Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites (TC) were prepared by a precipitation method employing TiO2 and AgNO3. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag(0) and Ag2O. The activity of the materials was determined employing methylene blue (MB) as the probe compound. Bleaching of MB was observed in the presence of all materials. The bleaching rate was found to increase with increasing amounts of TiO2 under UV/vis light. In contrast, the MB bleaching rate decreased with increasing TiO2 content upon visible light illumination. XRD and XPS data indicate that Ag2O acts as an electron acceptor in the light-induced reaction of MB and is transformed by reduction of Ag+, yielding Ag(0). As a second light-induced reaction, the evolution of molecular hydrogen from aqueous methanol was investigated. Significant H2 evolution rates were only determined in the presence of materials containing more than 50 mass% of TiO2. The experimental results suggest that Ag/Ag2O is not stable under the experimental conditions. Therefore, to address Ag/Ag2O as a (photo)catalytically active material does not seem appropriate. Full article
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Open AccessArticle TiO2-SiO2-PMMA Terpolymer Floating Device for the Photocatalytic Remediation of Water and Gas Phase Pollutants
Catalysts 2018, 8(11), 568; https://doi.org/10.3390/catal8110568
Received: 23 October 2018 / Revised: 14 November 2018 / Accepted: 16 November 2018 / Published: 21 November 2018
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Abstract
Floating photocatalytic devices are highly sought-after as they represent good candidates for practical application in pollutant remediation of large water basins. Here, we present a multilayer floating device for the photocatalytic remediation of contaminants present in water as well as of volatile species [...] Read more.
Floating photocatalytic devices are highly sought-after as they represent good candidates for practical application in pollutant remediation of large water basins. Here, we present a multilayer floating device for the photocatalytic remediation of contaminants present in water as well as of volatile species close to the water surface. The device was prepared on a novel tailored ter-polymer substrate based on methylmethacrylate, α-methylstyrene and perfluoroctyl methacrylate. The ad hoc synthesized support presents optimal characteristics in terms of buoyancy, transparency, gas permeability, mechanical, UV and thermal stability. The adhesion of the TiO2 top layer was favoured by the adopted casting procedure, followed by a corona pre-treatment and by the deposition of an intermediate SiO2 layer, the latter aimed also at protecting the polymer support from photocatalytic oxidation. The device was characterized by contact angle measurement, UV-vis transmittance and scanning electron microscopy. The final device was tested for the photocatalytic degradation of an emerging water pollutant as well as of vapors of a model volatile organic compound. Relevant activity was observed also under simulated solar irradiation and the device showed good stability and recyclability, prospecting its use for the photocatalytic degradation of pollutants in large water basins. Full article
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Review

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Open AccessReview Advanced Design and Synthesis of Composite Photocatalysts for the Remediation of Wastewater: A Review
Catalysts 2019, 9(2), 122; https://doi.org/10.3390/catal9020122
Received: 29 December 2018 / Revised: 25 January 2019 / Accepted: 28 January 2019 / Published: 30 January 2019
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Abstract
Serious water pollution and the exhausting of fossil resources have become worldwide urgent issues yet to be solved. Solar energy driving photocatalysis processes based on semiconductor catalysts is considered to be the most promising technique for the remediation of wastewater. However, the relatively [...] Read more.
Serious water pollution and the exhausting of fossil resources have become worldwide urgent issues yet to be solved. Solar energy driving photocatalysis processes based on semiconductor catalysts is considered to be the most promising technique for the remediation of wastewater. However, the relatively low photocatalytic efficiency remains a critical limitation for the practical use of the photocatalysts. To solve this problem, numerous strategies have been developed for the preparation of advanced photocatalysts. Particularly, incorporating a semiconductor with various functional components from atoms to individual semiconductors or metals to form a composite catalyst have become a facile approach for the design of high-efficiency catalysts. Herein, the recent progress in the development of novel photocatalysts for wastewater treatment via various methods in the sight of composite techniques are systematically discussed. Moreover, a brief summary of the current challenges and an outlook for the development of composite photocatalysts in the area of wastewater treatment are provided. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Integrated Au/TiO2 nanostructured photoanodes for photoelectrochemical organics degradation
Authors: Roberto Matarrese1, Isabella Nova1, Andrea Li Bassi1, Laura Mais2 et al.
Affiliation: 1Department of Energy, Politecnico di Milano, Milano, Italy; 2Dipartimento di Ingegneria Meccanica Chimica e dei Materiali, Università di Cagliari, Italy
Short Abstract: Several nanostructured TiO2 networks (e.g. tubes, rods, wires, sponges) emerged as promising materials that can be used as photoanodes for photoelectrochemical applications. In particular, extensive research has been performed on TiO2 1D nanostructures such as nanotube arrays because their ordered geometry and tunable morphologies are claimed for fast charge separation and transport, and  for electrolyte infiltration. More recently, quasi 1-D hierarchical structures prepared by reactive pulsed laser deposition (PLD) have been proposed as novel photonaodes. Besides, gold plasmonic nanoparticles (NPs) have recently attracted attention of the scientific community for the possibility to enhance light harvesting and quantum efficiency in photoconversion processes.
In this study, Pulsed Laser Deposition (PLD) technique was used to produce nanostructured TiO2 films integrated with Au NPs. A wide range of PLD process parameters were investigated to control the growth of both Au NPs and nanostructured TiO2 films. In particular, hierarchical TiO2/Au-NPs assemblies with NPs deposited at the bottom, at the top of the TiO2, as well as both on the bottom and on the top were prepared. The potential of the different Au/TiO2 nanostructures as photoanodes for the photoelectrochemical wastewater treatment was investigated. For this purpose the photoelectrochemical properties of the synthesized anode materials were characterized by using a three electrode cell in which model samples worked as working electrodes. Irradiation of the samples was made by means of both a Xe lamp, equipped with focusing lens and optical filters, and under standard solar spectrum. The reactivity towards both model molecules  (e.g. ethylene glycol) and/or real organic substrates (e.g. lindane)  was analyzed with classical electrochemical techniques such as steady-state polarization and cyclic voltammetry.


Title: Wastewater Treatment and Electricity Production in the Microbial Fuel Cell with the Cu-B Alloy as Cathode Catalyst
Authors: Paweł P. Włodarczyk 1,* and Barbara Włodarczyk 1
Affiliation: University of Opole, Institute of Technical Science, Faculty of Natural Sciences and Technology, Opole, Poland; [email protected], [email protected]
* Correspondence: [email protected]; Tel.: +48-077-401-6717
Abstract: The possibility to combine wastewater treatment and electricity production can accomplish a microbial fuel cell (MFC). The possibility of wastewater treatment and electricity production using the microbial fuel cell with the Cu-B alloy as cathode catalyst is presented in this paper. The research covered catalyst preparation, analysis of the decomposition rate of hydrogen peroxide on the Cu-B catalyst, the electricity production in a MFC (with Cu-B cathode) and comparison of changes in the concentration of COD, NH4+ and NO3– in the reactor without aeration, with aeration and with using a microbial fuel cell (with Cu-B cathode). During the measurements of electricity production equal 0,21-0,35 mA/cm2 was obtained. The reduction time for COD with the use of MFC with the Cu-B catalyst is similar to the reduction time with aeration. The measurement of NH4+ reduction shows almost no changes in cases measurement in MFC. The measurements have shown also the effectiveness (about 90%) of NO3– reduction. It has been shown that the Cu-B can be used as cathode catalyst in microbial fuel cells for wastewater treatment and electricity production.
Keywords: Cu-B catalyst; microbial fuel cell; cathode; environmental engineering; renewable energy sources: oxygen electrode

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