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Photocatalytic Materials

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A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (31 October 2014) | Viewed by 75999

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Dr. Klára Hernádi

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1. Institute of Physical Metallurgy, Metal Forming and Nanotechnology, University of Miskolc, C/2-5 Building 209, H-3515 Miskolc-Egyetemvaros, Hungary
2. Department of Applied and Environmental Chemistry, University of Szeged, Szeged, Hungary
Interests: heterogeneous catalysis; photocatalytic materials; carbon nanotubes; nanocomposite materials; immobilization of biologically active units
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Special Issue Information

Dear Colleagues,

Photocatalysis is one of the most frequently investigated topic in the field of advanced oxidation processes. Researchers around the world aim at developing semiconductor materials that can be effectively utilized for decomposing potentially harmful compounds in gas, liquid and solid phase. These catalysts can also be suitable for converting the energy of sunlight to chemical energy by generating hydrogen from water-based solutions. This special issue is targeted to gather quality papers about the synthesis and application of photocatalytic materials.

The collected articles will emphasize the surface and structural properties of these micro- and nanoscaled materials and focus on the applicability of the catalysts in UV or visible light irradiation. Studies concerning synthesis methods and reaction mechanisms are also welcome.

I am pleased to invite you to submit manuscripts for this special issue on Photocatalytic Materials in the form of research papers, communications, letters and review articles. We look forward to your participation in this special issue of the journal Materials.

Klara Hernadi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

photocatalytic materials
advanced oxidation processes
decomposing harmful compounds
converting of sunlight
generating hydrogen
uv or visible light irradiation

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Published Papers (10 papers)

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Research

1248 KiB

Open AccessArticle

One-Step Formation of WO₃-Loaded TiO₂ Nanotubes Composite Film for High Photocatalytic Performance

by Wai Hong Lee, Chin Wei Lai and Sharifah Bee Abd Hamid

Materials 2015, 8(5), 2139-2153; https://doi.org/10.3390/ma8052139 - 27 Apr 2015

Cited by 39 | Viewed by 7962

Abstract

High aspect ratio of WO₃-loaded TiO₂ nanotube arrays have been successfully synthesized using the electrochemical anodization method in an ethylene glycol electrolyte containing 0.5 wt% ammonium fluoride in a range of applied voltage of 10–40 V for 30 min. The novelty of this research works in the one-step formation of WO₃-loaded TiO₂ nanotube arrays composite film by using tungsten as the cathode material instead of the conventionally used platinum electrode. As compared with platinum, tungsten metal has lower stability, forming dissolved ions (W⁶⁺) in the electrolyte. The W⁶⁺ ions then move towards the titanium foil and form a coherent deposit on titanium foil. By controlling the oxidation rate and chemical dissolution rate of TiO₂ during the electrochemical anodization, the nanotubular structure of TiO₂ film could be achieved. In the present study, nanotube arrays were characterized using FESEM, EDAX, XRD, as well as Raman spectroscopy. Based on the results obtained, nanotube arrays with average pore diameter of up to 74 nm and length of 1.6 µm were produced. EDAX confirmed the presence of tungsten element within the nanotube arrays which varied in content from 1.06 at% to 3.29 at%. The photocatalytic activity of the nanotube arrays was then investigated using methyl orange degradation under TUV 96W UV-B Germicidal light irradiation. The nanotube with the highest aspect ratio, geometric surface area factor and at% of tungsten exhibited the highest photocatalytic activity due to more photo-induced electron-hole pairs generated by the larger surface area and because WO₃ improves charge separation, reduces charge carrier recombination and increases charge carrier lifetime via accumulation of electrons and holes in the two different metal oxide semiconductor components. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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900 KiB

Open AccessArticle

Photocatalytic, Morphological and Structural Properties of the TiO₂-SiO₂-Ag Porous Structures Based System

by Gábor Kovács, Zsolt Pap, Cosmin Coteț, Veronica Coșoveanu, Lucian Baia and Virginia Danciu

Materials 2015, 8(3), 1059-1073; https://doi.org/10.3390/ma8031059 - 12 Mar 2015

Cited by 24 | Viewed by 9305

Abstract

TiO₂-SiO₂-based nanocomposites with highly porous structures are gaining ever increasing attention due to their specific properties and large variability of synthesis pathways together with wide information on the impact of the synthesis on the activity of the catalyst. This thereby offers an alternative approach to traditional/commercially available photocatalysts. In our work TiO₂-SiO₂ based aerogels were obtained and modified with various amount of Ag nanoparticles, using different synthesis pathways. In the first instance their photocatalytic activity was examined in detail, by observing major differences toward salicylic acid and correlating them with their morphological and structural properties (investigating their mesoporous character, band-gap values, crystallinity grade etc.). Applying different techniques such as diffuse reflectance spectroscopy (DRS), X-ray diffraction measurements (XRD), transmission electron microscopy (TEM), Raman- and X-ray photoelectron spectroscopy (XPS) the nanoparticles and their composite morphological and structural details were successfully evaluated. Major differences were observed in the activity towards salicylic acid. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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768 KiB

Open AccessArticle

TiO₂-Mediated Photocatalytic Mineralization of a Non-Ionic Detergent: Comparison and Combination with Other Advanced Oxidation Procedures

by Péter Hegedűs, Erzsébet Szabó-Bárdos, Ottó Horváth, Krisztián Horváth and Péter Hajós

Materials 2015, 8(1), 231-250; https://doi.org/10.3390/ma8010231 - 14 Jan 2015

Cited by 17 | Viewed by 8532

Abstract

Triton X-100 is one of the most widely-applied man-made non-ionic surfactants. This detergent can hardly be degraded by biological treatment. Hence, a more efficient degradation method is indispensable for the total mineralization of this pollutant. Application of heterogeneous photocatalysis based on a TiO₂ suspension is a possible solution. Its efficiency may be improved by the addition of various reagents. We have thoroughly examined the photocatalytic degradation of Triton X-100 under various circumstances. For comparison, the efficiencies of ozonation and treatment with peroxydisulfate were also determined under the same conditions. Besides, the combination of these advanced oxidation procedures (AOPs) were also studied. The mineralization of this surfactant was monitored by following the TOC and pH values, as well as the absorption and emission spectra of the reaction mixture. An ultra-high-performance liquid chromatography (UHPLC) method was developed and optimized for monitoring the degradation of Triton X-100. Intermediates were also detected by GC-MS analysis and followed during the photocatalysis, contributing to the elucidation of the degradation mechanism. This non-ionic surfactant could be efficiently degraded by TiO₂-mediated heterogeneous photocatalysis. However, surprisingly, its combination with the AOPs applied in this study did not enhance the rate of the mineralization. Moreover, the presence of persulfate hindered the photocatalytic degradation. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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3809 KiB

Open AccessArticle

Differently Shaped Au Nanoparticles: A Case Study on the Enhancement of the Photocatalytic Activity of Commercial TiO₂

by Zsolt Pap, Zsejke Réka Tóth, Virginia Danciu, Lucian Baia and Gábor Kovács

Materials 2015, 8(1), 162-180; https://doi.org/10.3390/ma8010162 - 31 Dec 2014

Cited by 14 | Viewed by 7949

Abstract

In the present work, the influence of a gold nanoparticle’s shape was investigated on the commercially available Evonik Aeroxide P25. By the variation of specific synthesis parameters, three differently shaped Au nanoparticles were synthetized and deposited on the surface of the chosen commercial titania. The nanoparticles and their composites’ morphological and structural details were evaluated, applying different techniques such as Diffuse Reflectance Spectroscopy (DRS), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). The influence of the Au nanoparticles’ shape was discussed by evaluating their photocatalytic efficiency on phenol and oxalic acid degradation and by investigating the H₂ production efficacy of the selected composites. Major differences in their photocatalytic performance depending on the shape of the deposited noble metal were evidenced. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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1260 KiB

Open AccessArticle

Enhanced Photocatalytic Efficiency of N–F-Co-Embedded Titania under Visible Light Exposure for Removal of Indoor-Level Pollutants

by Seung-Ho Shin, Ho-Hwan Chun and Wan-Kuen Jo

Materials 2015, 8(1), 31-41; https://doi.org/10.3390/ma8010031 - 24 Dec 2014

Cited by 9 | Viewed by 5861

Abstract

N–F-co-embedded titania (N–F–TiO₂) photocatalysts with varying N:F ratios were synthesized and tested for their ability to photocatalyze the degradation of pollutants present at indoor air levels using visible light. The synthesis was achieved using a solvothermal process with tetrabutyl titanate, urea and ammonium fluoride as sources of Ti, N and F, respectively. Three selected volatile organic compounds (toluene, ethyl benzene and o-xylene) were selected as the test pollutants. The prepared composites were characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Ultra-violet (UV)-visible spectroscopy. The photocatalytic degradation efficiencies of N–F–TiO₂ composites were higher than those obtained using pure TiO₂ and N–TiO₂. Moreover, these efficiencies increased as the N:F ratio decreased from sixteen to eight, then decreased as it dropped further to three, indicating the presence of an optimal N:F ratio. Meanwhile, as retention time decreased from 12.4 to 0.62 s, the average photocatalytic efficiencies decreased from 65.4% to 21.7%, 91.5% to 37.8% and 95.8% to 44.7% for toluene, ethyl benzene and o-xylene, respectively. In contrast, the photocatalytic reaction rates increased as retention time decreased. In consideration of all of these factors, under optimized operational conditions, the prepared N–F–TiO₂ composites could be utilized for the degradation of target pollutants at indoor air levels using visible light. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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558 KiB

Open AccessArticle

Photocatalytic Water Splitting for Hydrogen Production with Gd₂MSbO₇ (M = Fe, In, Y) Photocatalysts under Visible Light Irradiation

by Jingfei Luan and Yanyan Li

Materials 2015, 8(1), 16-30; https://doi.org/10.3390/ma8010016 - 24 Dec 2014

Cited by 11 | Viewed by 6692

Abstract

Novel photocatalysts Gd₂FeSbO₇, Gd₂InSbO₇ and Gd₂YSbO₇ were synthesized by the solid state reaction method for the first time. A comparative study about the structural and photocatalytic properties of Gd₂MSbO₇ (M = Fe, In, Y) was reported. The results showed that Gd₂FeSbO₇, Gd₂InSbO₇ and Gd₂YSbO₇ crystallized with the pyrochlore-type structure, cubic crystal system and space group Fd3m. The lattice parameter a for Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ was 10.276026 Å, 10.449546 Å or 10.653651 Å. The band gap of Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ was estimated to be 2.151 eV, 2.897 eV or 2.396 eV. For the photocatalytic water-splitting reaction, H₂ or O₂ evolution was observed from pure water with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst under visible light irradiation (wavelength > 420 nm). Moreover, H₂ or O₂ also spilt by using Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ as catalyst from CH₃OH/H₂O or AgNO₃/H₂O solutions under visible light irradiation (λ > 420 nm). Gd₂FeSbO₇ showed the highest activity compared with Gd₂InSbO₇ or Gd₂YSbO₇. At the same time, Gd₂InSbO₇ showed higher activity compared with Gd₂YSbO₇. The photocatalytic activities were further improved under visible light irradiation with Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇ being loaded by Pt, NiO or RuO₂. The effect of Pt was better than that of NiO or RuO₂ for improving the photocatalytic activity of Gd₂FeSbO₇, Gd₂InSbO₇ or Gd₂YSbO₇. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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590 KiB

Open AccessArticle

Enhanced Photocatalytic Degradation of Methyl Orange Dye under the Daylight Irradiation over CN-TiO₂ Modified with OMS-2

by Mohamed Elfatih Hassan, Jing Chen, Guanglong Liu, Duanwei Zhu and Jianbo Cai

Materials 2014, 7(12), 8024-8036; https://doi.org/10.3390/ma7128024 - 12 Dec 2014

Cited by 23 | Viewed by 8635

Abstract

In this study, CN-TiO₂ was modified with cryptomelane octahedral molecular sieves (OMS-2) by the sol-gel method based on the self-assembly technique to enhance its photocatalytic activity under the daylight irradiation. The synthesized samples were characterized by X-ray diffraction (XRD), UV-vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and porosimeter analysis. The results showed that the addition of OMS-2 in the sol lead to higher Brunauer-Emmett-Teller (BET) surface area, pore volume, porosity of particle after heat treatment and the specific surface area, porosity, crystallite size and pore size distribution could be controlled by adjusting the calcination temperature. Compared to the CN-TiO₂-400 sample, CN-TiO₂/OMS-2-400 exhibited greater red shift in absorption edge of samples in visible region due to the OMS-2 coated. The enhancement of photocatalytic activity of CN-TiO₂/OMS-2 composite photocatalyst was subsequently evaluated for the degradation of the methyl orange dye under the daylight irradiation in water. The results showed that the methyl orange dye degradation rate reach to 37.8% for the CN-TiO₂/OMS-2-400 sample under the daylight irradiation for 5 h, which was higher than that of reference sample. The enhancement in daylight photocatalytic activities of the CN-TiO₂/OMS samples could be attributed to the synergistic effects of OMS-2 coated, larger surface area and red shift in adsorption edge of the prepared sample. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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1410 KiB

Open AccessArticle

Photocatalytic H₂ Evolution Using Different Commercial TiO₂ Catalysts Deposited with Finely Size-Tailored Au Nanoparticles: Critical Dependence on Au Particle Size

by Ákos Kmetykó, Károly Mogyorósi, Péter Pusztai, Teodora Radu, Zoltán Kónya, András Dombi and Klára Hernádi

Materials 2014, 7(12), 7615-7633; https://doi.org/10.3390/ma7127615 - 26 Nov 2014

Cited by 16 | Viewed by 6207

Abstract

One weight percent of differently sized Au nanoparticles were deposited on two commercially available TiO₂ photocatalysts: Aeroxide P25 and Kronos Vlp7000. The primary objective was to investigate the influence of the noble metal particle size and the deposition method on the photocatalytic activity. The developed synthesis method involves a simple approach for the preparation of finely-tuned Au particles through variation of the concentration of the stabilizing agent. Au was deposited on the TiO₂ surface by photo- or chemical reduction, using trisodium citrate as a size-tailoring agent. The Au-TiO₂ composites were synthetized by in situ reduction or by mixing the titania suspension with a previously prepared gold sol. The H₂ production activities of the samples were studied in aqueous TiO₂ suspensions irradiated with near-UV light in the absence of dissolved O₂, with oxalic acid or methanol as the sacrificial agent. The H₂ evolution rates proved to be strongly dependent on Au particle size: the highest H₂ production rate was achieved when the Au particles measured ~6 nm. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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968 KiB

Open AccessArticle

Photocatalytic H₂ Production Using Pt-TiO₂ in the Presence of Oxalic Acid: Influence of the Noble Metal Size and the Carrier Gas Flow Rate

by Ákos Kmetykó, Károly Mogyorósi, Viktória Gerse, Zoltán Kónya, Péter Pusztai, András Dombi and Klára Hernádi

Materials 2014, 7(10), 7022-7038; https://doi.org/10.3390/ma7107022 - 17 Oct 2014

Cited by 18 | Viewed by 7647

Abstract

The primary objective of the experiments was to investigate the differences in the photocatalytic performance when commercially available Aeroxide P25 TiO₂ photocatalyst was deposited with differently sized Pt nanoparticles with identical platinum content (1 wt%). The noble metal deposition onto the TiO₂ surface was achieved by in situ chemical reduction (CRIS) or by mixing chemically reduced Pt nanoparticle containing sols to the aqueous suspensions of the photocatalysts (sol-impregnated samples, CRSIM). Fine and low-scale control of the size of resulting Pt nanoparticles was obtained through variation of the trisodium citrate concentration during the syntheses. The reducing reagent was NaBH₄. Photocatalytic activity of the samples and the reaction mechanism were examined during UV irradiation (λ_max = 365 nm) in the presence of oxalic acid (50 mM) as a sacrificial hole scavenger component. The H₂ evolution rates proved to be strongly dependent on the Pt particle size, as well as the irradiation time. A significant change of H₂ formation rate during the oxalic acid transformation was observed which is unusual. It is probably regulated both by the decomposition rate of accumulated oxalic acid and the H⁺/H₂ redox potential on the surface of the catalyst. The later potential is influenced by the concentration of the dissolved H₂ gas in the reaction mixture. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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813 KiB

Open AccessArticle

Benzylpyrazinium Salts as Photo-Initiators in the Polymerization of Epoxide Monomers

by Moon Suk Kim and Sang Bong Lee

Materials 2014, 7(8), 5581-5590; https://doi.org/10.3390/ma7085581 - 31 Jul 2014

Cited by 2 | Viewed by 5635

Abstract

In order to study the capability of pyrazinium salt derivatives to act as photo-initiators of epoxide monomers, benzyl pyrazinium hexafluoroantimonate (BPH), benzyl 3,5-dimethyl pyrazine hexafluoroantimonate (BDH) and benzyl quinoxalinium hexafluoroantimonate (BQH) were synthesized by the Menschutkin reaction of benzyl bromide with pyrazine, 2,6-dimethyl pyrazine, and quinoxaline, followed by exchanging with hexafluoroantimonate (SbF₆). BPH, BDH, and BQH exhibited characteristic ultraviolet (UV) absorbance as well as exothermic peaks as a function of irradiation time in a differential photo-calorimeter (DPC). In the absence of photo-irradiation, cyclohexene oxide (CHO) underwent slow polymerization at 25 °C using BPH derivatives, but quantitative conversion was achieved even after a 5-min photo-irradiation. In addition, photo-irradiation was required for the photo-polymerization of CHO and styrene oxide (STO), which was characterized by a short induction period followed by a very rapid and exothermic polymerization. While glycidyl methyl ether (GME) required long induction periods, glycidyl phenyl ether (GPE) underwent rather slow and/or no photo-polymerization. The reactivity order of the monomers was CHO > STO >> GME >>> GPE, and the reactivity order for the photo-polymerization of CHO was BPH > BQH > BDH. It was found that BPH, BDH, and BQH could serve as photo-latent initiators for CHO, STO and GME, respectively. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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