Special Issue "Photocatalytic materials alternative to TiO2 for environmental remediation, sustainable chemistry and energy conversion"

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

Deadline for manuscript submissions: closed (31 December 2017)

Special Issue Editors

Guest Editor
Prof. Giuseppe Marcì

Department of Energy, Information engineering and Mathematical models (DEIM), University of Palermo, Italy
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Interests: CO2 reduction; water and gaseous depollution treatments; kinetics; solar photocatalysis; photocatalysis for synthesis; heterogeneous photocatalysis
Guest Editor
Prof. Elisa I. García-López

Department of Energy, Information engineering and Mathematical models (DEIM), University of Palermo, Italy
Website | E-Mail
Interests: photocatalytic water splitting; polyoxometalates; C3N4; novel photocatalysts; photocatalysis for synthesis; heterogeneous photocatalysis

Special Issue Information

Dear Colleagues,
The use of solar light to carry out chemical reactions appears to be one of the most intriguing technologies in order to solve environmental and energy problems. In this challenge, photocatalysis, as a green and sustainable technology, has been employed to improve water and air quality, maximize hydrogen gas production, reduce CO2 to fuels, synthesize organic costly products from cheaper ones, and to destroy bacteria and viruses. Current research is no longer limited to the traditional TiO2 semiconductor; indeed, significant progress has been made in the development of novel nanomaterials. TiO2 exhibits photocatalytic activity under UV light, reducing its practical applications. Therefore, the exploitation of visible light-driven photocatalysts is indispensable for the actual application of photocatalytic systems. Stability to photocorrosion and cost of emerging materials should also be considered. It is, thus, of great importance to identify and design new semiconductor materials that are efficient, stable, and abundant. Recently, a great deal of interest has been focused on research into molibdates, vanadates, phosphates, ferrites, magnetic photocatalysts, perovskites, MOFs, polyoxometalates, and metal free 2D layered materials, including graphene and g-C3N4-based photocatalysts, which have attracted more attention and have become the research hotspots. During the last few years, we have been assisting a fascinating pursuit of photocatalytic materials with improved spectral response ranges and quantum efficiencies.
The importance of this research justifies a Special Issue of Catalysts, entitled “Photocatalytic Materials Alternative to TiO2 for Environmental Remediation, Sustainable Chemistry and Energy Conversion”.
This Special Issue of Catalysts aims to present the state-of-the-art and advances in emerging materials used as heterogeneous photocatalysts for environmental remediation, conversion of solar energy to usable fuel, either by reducing CO2 to carbon-based fuels or by reducing protons to hydrogen, green synthesis, and, in general, sustainable chemistry.
The contributions should be a roundup of the best photocatalysts for solar applications and induce further interest towards a resolution of environmental and energy problems using green approaches.
We are pleased to invite you to submit manuscripts for this Special Issue in the form of research papers, communications, letters, and review articles.

We look forward to your participation in this Special Issue of Catalysts.

Prof. Dr. Eng. Giuseppe Marcì
Prof. Dr. Elisa I. García-López
Guest Editors

Manuscript Submission Information

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Keywords

  • Visible light activated photocatalysts
  • C3N4-based photocatalysts
  • Graphene-based photocatalysts
  • Perovskites-based photocatalysts
  • Photocatalytic applications for environmental remediation
  • Photocatalytic water splitting
  • Hydrogen photocatalytic production
  • Photocatalytic CO2 reduction
  • Photocatalytic selective syntheses

Published Papers (8 papers)

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Research

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Open AccessArticle Heterogeneous Catalysis by Tetraethylammonium Tetrachloroferrate of the Photooxidation of Toluene by Visible and Near-UV Light
Catalysts 2018, 8(2), 79; https://doi.org/10.3390/catal8020079
Received: 8 January 2018 / Revised: 8 February 2018 / Accepted: 11 February 2018 / Published: 13 February 2018
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Abstract
Titanium dioxide is the most extensively used heterogeneous catalyst for the photooxidation of toluene and other hydrocarbons, but it has low utility for the synthesis of benzyl alcohol, of which little is produced, or benzaldehyde, due to further oxidation to benzoic acid and
[...] Read more.
Titanium dioxide is the most extensively used heterogeneous catalyst for the photooxidation of toluene and other hydrocarbons, but it has low utility for the synthesis of benzyl alcohol, of which little is produced, or benzaldehyde, due to further oxidation to benzoic acid and cresol, among other oxidation products, and eventually complete mineralization to CO2. Et4N[FeCl4] functions as a photocatalyst through the dissociation of chlorine atoms, which abstract hydrogen from toluene, and the photooxidation of toluene proceeds only as far as benzyl alcohol and benzaldehyde. Unlike TiO2, which requires ultraviolet (UV) irradiation, Et4N[FeCl4] catalyzes the photooxidation of toluene with visible light alone. Even under predominantly UV irradiation, the yield of benzyl alcohol plus benzaldehyde is greater with Et4N[FeCl4] than with TiO2. Et4N[FeCl4] photocatalysis yields benzyl chloride as a side product, but it can be minimized by restricting irradiation to wavelengths above 360 nm and by the use of long irradiation times. The photonic efficiency of oxidation in one experiment was found to be 0.042 mol/einstein at 365 nm. The use of sunlight as the irradiation source was explored. Full article
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Open AccessArticle Relations between Structure, Activity and Stability in C3N4 Based Photocatalysts Used for Solar Hydrogen Production
Catalysts 2018, 8(2), 52; https://doi.org/10.3390/catal8020052
Received: 22 December 2017 / Revised: 19 January 2018 / Accepted: 23 January 2018 / Published: 29 January 2018
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Abstract
Solar hydrogen production from water could be a sustainable and environmentally friendly alternative to fossil energy carriers, yet so far photocatalysts active and stable enough for large-scale applications are not available, calling for advanced research efforts. In this work, H2 evolution rates
[...] Read more.
Solar hydrogen production from water could be a sustainable and environmentally friendly alternative to fossil energy carriers, yet so far photocatalysts active and stable enough for large-scale applications are not available, calling for advanced research efforts. In this work, H2 evolution rates of up to 1968 and 5188 μmol h−1 g−1 were obtained from aqueous solutions of triethanolamine (TEOA) and oxalic acid (OA), respectively, by irradiating composites of AgIn5S8 (AIS), mesoporous C3N4 (CN, surface area >150 m2/g) and ≤2 wt.% in-situ photodeposited Pt nanoparticles (NPs) with UV-vis (≥300 nm) and pure visible light (≥420 nm). Structural properties and electron transport in these materials were analyzed by XRD, STEM-HAADF, XPS, UV-vis-DRS, ATR-IR, photoluminescence and in situ-EPR spectroscopy. Initial H2 formation rates were highest for Pt/CN, yet with TEOA this catalyst deactivated by inclusion of Pt NPs in the matrix of CN (most pronounced at λ ≥ 300 nm) while it remained active with OA, since in this case Pt NPs were enriched on the outermost surface of CN. In Pt/AIS-CN catalysts, Pt NPs were preferentially deposited on the surface of the AIS phase which prevents them from inclusion in the CN phase but reduces simultaneously the initial H2 evolution rate. This suggests that AIS hinders transport of separated electrons from the CN conduction band to Pt NPs but retains the latter accessible by protons to produce H2. Full article
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Open AccessArticle EPR Investigations of G-C3N4/TiO2 Nanocomposites
Catalysts 2018, 8(2), 47; https://doi.org/10.3390/catal8020047
Received: 31 December 2017 / Revised: 19 January 2018 / Accepted: 23 January 2018 / Published: 26 January 2018
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Abstract
The g-C3N4/TiO2 nanopowders prepared by the annealing of melamine and TiO2 P25 at 550 °C were investigated under dark and upon UV or visible-light photoactivation using X- and Q-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra
[...] Read more.
The g-C3N4/TiO2 nanopowders prepared by the annealing of melamine and TiO2 P25 at 550 °C were investigated under dark and upon UV or visible-light photoactivation using X- and Q-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of powders monitored at room temperature and 100 K showed the impact of the initial loading ratio of melamine/TiO2 on the character of paramagnetic centers observed. For the photocatalysts synthesized using a lower titania content, the paramagnetic signals characteristic for the g-C3N4/TiO2 nanocomposites were already found before exposure. The samples annealed using the higher TiO2 loading revealed the photoinduced generation of paramagnetic nitrogen bulk centers (g-tensor components g1 = 2.005, g2 = 2.004, g3 = 2.003 and hyperfine couplings from the nitrogen A1 = 0.23 mT, A2 = 0.44 mT, A3 = 3.23 mT) typical for N-doped TiO2. The ability of photocatalysts to generate reactive oxygen species (ROS) upon in situ UV or visible-light photoexcitation was tested in water or dimethyl sulfoxide by EPR spin trapping using 5,5-dimethyl 1-pyrroline N-oxide. The results obtained reflect the differences in photocatalyst nanostructures caused by the differing initial ratio of melamine/TiO2; the photocatalyst prepared by the high-temperature treatment of melamine/TiO2 wt. ratio of 1:3 revealed an adequate photoactivity in both spectral regions. Full article
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Open AccessArticle Synthesis of Phase Pure Hexagonal YFeO3 Perovskite as Efficient Visible Light Active Photocatalyst
Catalysts 2017, 7(11), 326; https://doi.org/10.3390/catal7110326
Received: 10 October 2017 / Revised: 25 October 2017 / Accepted: 30 October 2017 / Published: 3 November 2017
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Abstract
Hexagonal perovskite YFeO3 was synthesized by a complex-assisted sol-gel technique allowing crystallization at calcination temperatures below 700 °C. As determined by diffuse reflectance spectroscopy (DRS) and Tauc plots, the hexagonal YFeO3 exhibits a lower optical band gap (1.81 eV) than the
[...] Read more.
Hexagonal perovskite YFeO3 was synthesized by a complex-assisted sol-gel technique allowing crystallization at calcination temperatures below 700 °C. As determined by diffuse reflectance spectroscopy (DRS) and Tauc plots, the hexagonal YFeO3 exhibits a lower optical band gap (1.81 eV) than the orthorhombic structure (about 2.1 eV or even higher) being typically obtained at elevated temperatures (>700 °C), and thus enables higher visible light photocatalysis activity. Structure and morphology of the synthesized YFeO3 perovskites were analyzed by powder X-ray diffraction (XRD) and nitrogen adsorption, proving that significantly smaller crystallite sizes and higher surface areas are obtained for YFeO3 with a hexagonal phase. The photocatalytic activity of the different YFeO3 phases was deduced via the degradation of the model pollutants methyl orange and 4-chlorophenol. Experiments under illumination with light of different wavelengths, in the presence of different trapping elements, as well as photoelectrochemical tests allow conclusions regarding band positions of YFeO3 and the photocatalytic degradation mechanism. X-ray photoelectron spectroscopy indicates that a very thin layer of Y2O3 might support the photocatalysis by improving the separation of photogenerated charge carriers. Full article
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Open AccessArticle The Preparation of a Highly Efficient Ag3PO4/Ag/Bi2O2CO3 Photo-Catalyst and the Study of Its Photo-Catalytic Organic Synthesis Reaction Driven by Visible Light
Catalysts 2017, 7(9), 276; https://doi.org/10.3390/catal7090276
Received: 18 August 2017 / Revised: 14 September 2017 / Accepted: 14 September 2017 / Published: 17 September 2017
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Abstract
Ag3PO4/Ag/Bi2O2CO3 composites were prepared by a hydrothermal and precipitation method. The morphology, structure, and valence state of the photo-catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Scanning
[...] Read more.
Ag3PO4/Ag/Bi2O2CO3 composites were prepared by a hydrothermal and precipitation method. The morphology, structure, and valence state of the photo-catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface areas, and UV-vis diffuse reflectance spectra (UV-vis DRS). They were applied as heterogeneous catalysts in the synthesis of esters from aldehydes (or alcohols) and alcohols and the synthesis of imines from alcohols and amines under visible light irradiation. The photo-catalytic activities of the esterification reactions of aldehydes and alcohols were heavily dependent on the loading of Ag3PO4/Ag/Bi2O2CO3 as well as the intensity and wavelength of the visible light. Furthermore, their conversion under visible light irradiation was superior to that in the dark. Herein a reaction mechanism from aldehydes and alcohols to esters was proposed, and the Ag3PO4/Ag/Bi2O2CO3 catalysts could be used six times without a significant decrease in activity. Using these catalysts under visible light could motivate future studies to develop efficient recyclable photo-catalysts and facilitate many synthetic organic reactions. Full article
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Open AccessArticle Structure-Dependent Photocatalytic Performance of BiOBrxI1−x Nanoplate Solid Solutions
Catalysts 2017, 7(5), 153; https://doi.org/10.3390/catal7050153
Received: 19 April 2017 / Revised: 8 May 2017 / Accepted: 9 May 2017 / Published: 13 May 2017
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Abstract
BiOXxY1−x (X, Y = Cl, Br, and I) solid solutions have been regarded as promising photocatalysts attributed to their unique layered structure, tunable band structure, and chemical and optical stability. In this study, BiOBrxI1−x nanoplate
[...] Read more.
BiOXxY1−x (X, Y = Cl, Br, and I) solid solutions have been regarded as promising photocatalysts attributed to their unique layered structure, tunable band structure, and chemical and optical stability. In this study, BiOBrxI1−x nanoplate solid solutions with a high exposure of {001} crystal facets were prepared by a facile alcoholysis method at room temperature and atmospheric pressure. X-ray diffraction (XRD) peaks exhibited a slight shift to lower diffraction angle with the increase of I content in BiOBrxI1−x samples, which resulted in a gradual increase in their cell parameters. Field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM) images revealed that BiOBrxI1−x samples exhibited 2D plate-like structure with the in-plane wrinkles. The regular changes in optical absorption threshold and Eg value seen in UV-vis diffuse reflectance spectra (UV-vis DRS) indicated that the optical absorption property and band structure could be modulated by the formation of BiOBrxI1−x solid solutions. The photocatalytic degradation of active dye Rhodamine B (RhB) over BiOBrxI1−x solid solutions showed that BiOBr0.75I0.25 had the best photocatalytic activity. The RhB photodegradation processes followed a pseudo-first-order kinetic model. The synergistic effect of structural factors (including amount of exposed {001} facets, interlayer spacing of (001) plane, and energy-level position of the valence band) determined the photocatalytic performance of BiOBrxI1−x solid solutions. Full article
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Open AccessArticle Treatment of Aqueous Bromate by Superparamagnetic BiOCl-Mediated Advanced Reduction Process
Catalysts 2017, 7(5), 131; https://doi.org/10.3390/catal7050131
Received: 22 March 2017 / Revised: 26 April 2017 / Accepted: 27 April 2017 / Published: 1 May 2017
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Abstract
Bromate (BrO3) contamination in drinking water is a growing concern. Advanced reduction processes (ARPs) are reportedly promising in relieving this concern. In this work, UV/superparamagnetic BiOCl (BiOCl loaded onto superparamagnetic hydroxyapatite) assisted with small molecule carboxylic acid (formate, citrate,
[...] Read more.
Bromate ( BrO 3 ) contamination in drinking water is a growing concern. Advanced reduction processes (ARPs) are reportedly promising in relieving this concern. In this work, UV/superparamagnetic BiOCl (BiOCl loaded onto superparamagnetic hydroxyapatite) assisted with small molecule carboxylic acid (formate, citrate, and acetate), a carboxyl anion radical ( CO 2 )-based ARP, was proposed to eliminate aqueous BrO 3 . Formate and citrate were found to be ideal CO 2 precursor, and the latter was found to be safe for practical use. BrO 3 (10 μg·L−1, WHO guideline for drinking water) can be completely degraded within 3 min under oxygen-free conditions. In this process, BrO 3 degradation was realized by the reduction of CO 2 (major role) and formyloxyl radical (minor role) in bulk solution. The formation mechanism of radicals and the transformation pathway of BrO 3 were proposed based on data on electron paramagnetic resonance monitoring, competitive kinetics, and degradation product analysis. The process provided a sustainable decontamination performance (<5% deterioration for 10 cycles) and appeared to be more resistant to common electron acceptors (O2, NO 3 , and Fe3+) than hydrated electron based-ARPs. Phosphate based-superparamagnetic hydroxyapatite, used to support BiOCl in this work, was believed to be applicable for resolving the recycling problem of other metal-containing catalyst. Full article
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Review

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Open AccessReview g-C3N4-Based Nanomaterials for Visible Light-Driven Photocatalysis
Catalysts 2018, 8(2), 74; https://doi.org/10.3390/catal8020074
Received: 2 January 2018 / Revised: 24 January 2018 / Accepted: 7 February 2018 / Published: 9 February 2018
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Abstract
Graphitic carbon nitride (g-C3N4) is a promising material for photocatalytic applications such as solar fuels production through CO2 reduction and water splitting, and environmental remediation through the degradation of organic pollutants. This promise reflects the advantageous photophysical properties
[...] Read more.
Graphitic carbon nitride (g-C3N4) is a promising material for photocatalytic applications such as solar fuels production through CO2 reduction and water splitting, and environmental remediation through the degradation of organic pollutants. This promise reflects the advantageous photophysical properties of g-C3N4 nanostructures, notably high surface area, quantum efficiency, interfacial charge separation and transport, and ease of modification through either composite formation or the incorporation of desirable surface functionalities. Here, we review recent progress in the synthesis and photocatalytic applications of diverse g-C3N4 nanostructured materials, and highlight the physical basis underpinning their performance for each application. Potential new architectures, such as hierarchical or composite g-C3N4 nanostructures, that may offer further performance enhancements in solar energy harvesting and conversion are also outlined. Full article
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