Special Issue "Titanium Dioxide Photocatalysis"

A special issue of Catalysts (ISSN 2073-4344).

Deadline for manuscript submissions: closed (15 July 2017)

Special Issue Editors

Guest Editor
Prof. Vladimiro Dal Santo

CNR-Istituto di Scienze e Tecnologie Molecolari, Via C. Golgi 19, 20133 Milano, Italy
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Interests: hydrogen; steam reforming; PEC water splitting; heterogeneous catalysis
Guest Editor
Dr. Alberto Naldoni

1. CNR-Istituto di Scienze e Tecnologie Molecolari, Via Golgi 19, 20133 Milano, Italy
2. Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA
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Special Issue Information

Dear Colleagues,

Dating from the seminal work of Fujishima et al. issued in 1971, titanium dioxide (TiO2) is at the center of intense research devoted to the development of efficient photocatalysts. Among the many candidates for photocatalytic applications, TiO2 is almost the only material suitable for industrial use. This is because TiO2 shows a good trade-off between efficient photoactivity, high stability, and low cost.

The principal applications deal with the use of TiO2 as photocatalyst for environmental remediation both in polluted air and waste water treatment and as a material in solar cells.

The rational design elements of interests for efficient TiO2 catalysts for this Special Issue are optical properties, nanocrystal shape and organization in superstructures.

The main drawback of TiO2 photocatalysts still remains their inability in visible light absorption and photoconversion, and most part of recent research activities are devoted to the improvement of the optical absorption properties of TiO2 nanomaterials. Strategies including doping; self-doping; realization of composites with plasmonic materials, with 2D materials, with other semiconductors, and with quantum dots are of particular interest. Black-TiO2 visible light active photocatalysts, antimicrobial materials, photoelectrochemical devices for water splitting and CO2 photo-reduction, are among the hot topics.

On the other hand, precise crystal shape (and homogeneous size) and organization in superstructure from ultrathin films to hierarchical nanostructures have been demonstrated to be critical for obtaining photocatalyst with high efficiency and selectivity. This topic is another pillar for the present Special Issue on “Titanium Dioxide Photocatalysis”, and submission on it are recommended.

The present Special Issue of Catalysts is aimed at presenting the current state-of-the-art in the use of TiO2 as photocatalyst, with a special emphasis on new TiO2 nanomaterials (both powdered catalysts and photoelectrodes) for photocatalytic water splitting, CO2 reduction and environmental remediation. In the present Special Issue, we have invited contributions from leading groups in the field with the aim of giving a balanced view of the current state-of-the-art in this discipline.

Prof. Vladimiro Dal Santo
Dr. Alberto Naldoni
Guest Editors

Manuscript Submission Information

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Keywords

  • Titanium dioxide
  • Photo-oxidation
  • Photocatalytic water splitting
  • Photoelectrochemical (PEC) water splitting
  • CO2 photoreduction
  • Solar fuels
  • nanostructures
  • multiscale modeling

Published Papers (10 papers)

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Research

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Open AccessFeature PaperArticle Using Density Functional Theory to Model Realistic TiO2 Nanoparticles, Their Photoactivation and Interaction with Water
Catalysts 2017, 7(12), 357; doi:10.3390/catal7120357
Received: 16 October 2017 / Revised: 8 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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Abstract
Computational modeling of titanium dioxide nanoparticles of realistic size is extremely relevant for the direct comparison with experiments but it is also a rather demanding task. We have recently worked on a multistep/scale procedure to obtain global optimized minimum structures for chemically stable
[...] Read more.
Computational modeling of titanium dioxide nanoparticles of realistic size is extremely relevant for the direct comparison with experiments but it is also a rather demanding task. We have recently worked on a multistep/scale procedure to obtain global optimized minimum structures for chemically stable spherical titania nanoparticles of increasing size, with diameter from 1.5 nm (~300 atoms) to 4.4 nm (~4000 atoms). We use first self-consistent-charge density functional tight-binding (SCC-DFTB) methodology to perform thermal annealing simulations to obtain globally optimized structures and then hybrid density functional theory (DFT) to refine them and to achieve high accuracy in the description of structural and electronic properties. This allows also to assess SCC-DFTB performance in comparison with DFT(B3LYP) results. As a further step, we investigate photoexcitation and photoemission processes involving electron/hole pair formation, separation, trapping and recombination in the nanosphere of medium size by hybrid DFT. Finally, we show how a recently defined new set of parameters for SCC-DFTB allows for a proper description of titania/water multilayers interface, which paves the way for modeling large realistic nanoparticles in aqueous environment. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessFeature PaperArticle Flame-Made Cu/TiO2 and Cu-Pt/TiO2 Photocatalysts for Hydrogen Production
Catalysts 2017, 7(10), 301; doi:10.3390/catal7100301
Received: 8 September 2017 / Revised: 29 September 2017 / Accepted: 11 October 2017 / Published: 16 October 2017
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Abstract
The effect of Cu or Cu-Pt nanoparticles in TiO2 photocatalysts prepared by flame spray pyrolysis in one step was investigated in hydrogen production from methanol photo-steam reforming. Two series of titanium dioxide photocatalysts were prepared, containing either (i) Cu nanoparticles (0.05–0.5 wt%)
[...] Read more.
The effect of Cu or Cu-Pt nanoparticles in TiO2 photocatalysts prepared by flame spray pyrolysis in one step was investigated in hydrogen production from methanol photo-steam reforming. Two series of titanium dioxide photocatalysts were prepared, containing either (i) Cu nanoparticles (0.05–0.5 wt%) or (ii) both Cu (0 to 0.5 wt%) and Pt (0.5 wt%) nanoparticles. In addition, three photocatalysts obtained either by grafting copper and/or by depositing platinum by wet methods on flame-made TiO2 were also investigated. High hydrogen production rates were attained with copper-containing photocatalysts, though their photoactivity decreased with increasing Cu loading, whereas the photocatalysts containing both Cu and Pt nanoparticles exhibit a bell-shaped photoactivity trend with increasing copper content, the highest hydrogen production rate being attained with the photocatalyst containing 0.05 wt% Cu. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessFeature PaperArticle Fast and Large-Scale Anodizing Synthesis of Pine-Cone TiO2 for Solar-Driven Photocatalysis
Catalysts 2017, 7(8), 229; doi:10.3390/catal7080229
Received: 6 July 2017 / Revised: 24 July 2017 / Accepted: 27 July 2017 / Published: 1 August 2017
Cited by 1 | PDF Full-text (5355 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Anodization has been widely used to synthesize nanostructured TiO2 films with promising photocatalytic performance for solar hydrogen production and pollution removal. However, it usually takes a few hours to obtain the right nanostructures even on a small scale (e.g., 10 mm ×
[...] Read more.
Anodization has been widely used to synthesize nanostructured TiO2 films with promising photocatalytic performance for solar hydrogen production and pollution removal. However, it usually takes a few hours to obtain the right nanostructures even on a small scale (e.g., 10 mm × 20 mm). In order to attract interest for industrial applications, fast and large-scale fabrication is highly desirable. Herein, we demonstrate a fast and large-scale (e.g., 300 mm × 360 mm) synthesis of pine-cone TiO2 nanostructures within two min. The formation mechanism of pine-cone TiO2 is proposed. The pine-cone TiO2 possesses a strong solar absorption, and exhibits high photocatalytic activities in photo-oxidizing organic pollutants in wastewater and producing hydrogen from water under natural sunlight. Thus, this study demonstrates a promising method for fabricating TiO2 films towards practical photocatalytic applications. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessArticle Sulfur-Doped TiO2: Structure and Surface Properties
Catalysts 2017, 7(7), 214; doi:10.3390/catal7070214
Received: 29 May 2017 / Revised: 30 June 2017 / Accepted: 11 July 2017 / Published: 18 July 2017
Cited by 2 | PDF Full-text (4092 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A comprehensive study on the sulfur doping of TiO2, by means of H2S treatment at 673 K, has been performed in order to highlight the role of sulfur in affecting the properties of the system, as compared to the
[...] Read more.
A comprehensive study on the sulfur doping of TiO2, by means of H2S treatment at 673 K, has been performed in order to highlight the role of sulfur in affecting the properties of the system, as compared to the native TiO2. The focus of this study is to find a relationship among the surface, structure, and morphology properties, by means of a detailed chemical and physical characterization of the samples. In particular, transmission electron microscopy images provide a simple tool to have a direct and immediate evidence of the effects of H2S action on the TiO2 particles structure and surface defects. Furthermore, from spectroscopy analyses, the peculiar surface, optical properties, and methylene blue photodegradation test of S-doped TiO2 samples, as compared to pure TiO2, have been investigated and explained by the effects caused by the exchange of S species with O species and by the surface defects induced by the strong H2S treatment. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessArticle Photocatalytic Graphene-TiO2 Thin Films Fabricated by Low-Temperature Ultrasonic Vibration-Assisted Spin and Spray Coating in a Sol-Gel Process
Catalysts 2017, 7(5), 136; doi:10.3390/catal7050136
Received: 29 March 2017 / Revised: 26 April 2017 / Accepted: 27 April 2017 / Published: 2 May 2017
Cited by 4 | PDF Full-text (4751 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this work, we communicate a facile and low temperature synthesis process for the fabrication of graphene-TiO2 photocatalytic composite thin films. A sol-gel chemical route is used to synthesize TiO2 from the precursor solutions and spin and spray coating are used
[...] Read more.
In this work, we communicate a facile and low temperature synthesis process for the fabrication of graphene-TiO2 photocatalytic composite thin films. A sol-gel chemical route is used to synthesize TiO2 from the precursor solutions and spin and spray coating are used to deposit the films. Excitation of the wet films during the casting process by ultrasonic vibration favorably influences both the sol-gel route and the deposition process, through the following mechanisms. The ultrasound energy imparted to the wet film breaks down the physical bonds of the gel phase. As a result, only a low-temperature post annealing process is required to eliminate the residues to complete the conversion of precursors to TiO2. In addition, ultrasonic vibration creates a nanoscale agitating motion or microstreaming in the liquid film that facilitates mixing of TiO2 and graphene nanosheets. The films made based on the above-mentioned ultrasonic vibration-assisted method and annealed at 150 °C contain both rutile and anatase phases of TiO2, which is the most favorable configuration for photocatalytic applications. The photoinduced and photocatalytic experiments demonstrate effective photocurrent generation and elimination of pollutants by graphene-TiO2 composite thin films fabricated via scalable spray coating and mild temperature processing, the results of which are comparable with those made using lab-scale and energy-intensive processes. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessArticle Novel Synthesis of Plasmonic Ag/AgCl@TiO2 Continues Fibers with Enhanced Broadband Photocatalytic Performance
Catalysts 2017, 7(4), 117; doi:10.3390/catal7040117
Received: 28 February 2017 / Revised: 2 April 2017 / Accepted: 13 April 2017 / Published: 17 April 2017
Cited by 1 | PDF Full-text (4812 KB) | HTML Full-text | XML Full-text
Abstract
The plasmonic Ag/AgCl@TiO2 fiber (S-CTF) photocatalyst was synthesized by a two-step approach, including the sol-gel and force spinning method for the preparation of TiO2 fibers (TF), and the impregnation-precipitation-photoreduction strategy for the deposition of Ag/AgCl onto the fibers. NaOH aqueous solution
[...] Read more.
The plasmonic Ag/AgCl@TiO2 fiber (S-CTF) photocatalyst was synthesized by a two-step approach, including the sol-gel and force spinning method for the preparation of TiO2 fibers (TF), and the impregnation-precipitation-photoreduction strategy for the deposition of Ag/AgCl onto the fibers. NaOH aqueous solution was utilized to hydrolyze TiCl4, to synthesize TF and remove the byproduct HCl, and the produced NaCl was recycled for the formation and deposition of Ag/AgCl. The surface morphology, specific surface area, textural properties, crystal structure, elemental compositions and optical absorption of S-CTF were characterized by a series of instruments. These results revealed that the AgCl and Ag0 species were deposited onto TF successfully, and the obtained S-CTF showed improved visible light absorption due to the surface plasmon resonance of Ag0. In the photocatalytic degradation of X-3B, S-CTF exhibited significantly enhanced activities under separate visible or UV light irradiation, in comparison to TF. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessArticle Photocatalytic TiO2 Nanorod Spheres and Arrays Compatible with Flexible Applications
Catalysts 2017, 7(2), 60; doi:10.3390/catal7020060
Received: 29 December 2016 / Revised: 31 January 2017 / Accepted: 7 February 2017 / Published: 14 February 2017
Cited by 4 | PDF Full-text (9697 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In the present study, titanium dioxide nanostructures were synthesized through microwave irradiation. In a typical microwave synthesis, nanorod spheres in the powder form were simultaneously produced with nanorod arrays grown on polyethylene terephthalate (PET) substrates. The syntheses were performed in water or ethanol
[...] Read more.
In the present study, titanium dioxide nanostructures were synthesized through microwave irradiation. In a typical microwave synthesis, nanorod spheres in the powder form were simultaneously produced with nanorod arrays grown on polyethylene terephthalate (PET) substrates. The syntheses were performed in water or ethanol with limited temperature at 80 °C and 200 °C. A simple and low-cost approach was used for the arrays growth, which involved a PET substrate with a zinc oxide seed layer deposited by spin-coating. X-ray diffraction (XRD) and Raman spectroscopy revealed that synthesis in water result in a mixture of brookite and rutile phases, while using ethanol as solvent it was only observed the rutile phase. Scanning electron microscopy (SEM) showed that the synthesized spheres were in the micrometer range appearing as aggregates of fine nanorods. The arrays maintained the sphere nanorod aggregate structures and the synthesis totally covered the flexible substrates. Transmission electron microscopy (TEM) was used to identify the brookite structure. The optical band gaps of all materials have been determined from diffuse reflectance spectroscopy. Photocatalytic activity was assessed from rhodamine B degradation with remarkable degradability performance under ultraviolet (UV) radiation. Reusability experiments were carried out for the best photocatalyst, which also revealed notable photocatalytic activity under solar radiation. The present study is an interesting and competitive alternative for the photocatalysts existing nowadays, as it simultaneously results in highly photoactive powders and flexible materials produced with low-cost synthesis routes such as microwave irradiation. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Review

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Open AccessFeature PaperReview On the Origin of Enhanced Photocatalytic Activity of Copper-Modified Titania in the Oxidative Reaction Systems
Catalysts 2017, 7(11), 317; doi:10.3390/catal7110317
Received: 12 October 2017 / Revised: 23 October 2017 / Accepted: 24 October 2017 / Published: 27 October 2017
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Abstract
Modification of titania with copper is a promising way to enhance the photocatalytic performance of TiO2. The enhancement means the significant retardation of charge carriers’ recombination ratio and the introduction of visible light activity. This review focuses on two main ways
[...] Read more.
Modification of titania with copper is a promising way to enhance the photocatalytic performance of TiO2. The enhancement means the significant retardation of charge carriers’ recombination ratio and the introduction of visible light activity. This review focuses on two main ways of performance enhancement by copper species—i.e., originated from plasmonic properties of zero-valent copper (plasmonic photocatalysis) and heterojunctions between semiconductors (titania and copper oxides). The photocatalytic performance of copper-modified titania is discussed for oxidative reaction systems due to their importance for prospective applications in environmental purification. The review consists of the correlation between copper species and corresponding variants of photocatalytic mechanisms including novel systems of cascade heterojunctions. The problem of stability of copper species on titania, and the methods of its improvement are also discussed as important factors for future applications. As a new trend in the preparation of copper-modified titania photocatalyst, the role of particle morphology (faceted particles, core-shell structures) is also described. Finally, in the conclusion section, perspectives, challenges and recommendations for future research on copper-modified titania are formulated. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessFeature PaperReview Brookite: Nothing New under the Sun?
Catalysts 2017, 7(10), 304; doi:10.3390/catal7100304
Received: 2 October 2017 / Revised: 11 October 2017 / Accepted: 11 October 2017 / Published: 13 October 2017
Cited by 1 | PDF Full-text (2104 KB) | HTML Full-text | XML Full-text
Abstract
Advances in the synthesis of pure brookite and brookite-based TiO2 materials have opened the way to fundamental and applicative studies of the once least known TiO2 polymorph. Brookite is now recognized as an active phase, in some cases showing enhanced performance
[...] Read more.
Advances in the synthesis of pure brookite and brookite-based TiO2 materials have opened the way to fundamental and applicative studies of the once least known TiO2 polymorph. Brookite is now recognized as an active phase, in some cases showing enhanced performance with respect to anatase, rutile or their mixture. The peculiar structure of brookite determines its distinct electronic properties, such as band gap, charge–carrier lifetime and mobility, trapping sites, surface energetics, surface atom arrangements and adsorption sites. Understanding the relationship between these properties and the photocatalytic performances of brookite compared to other TiO2 polymorphs is still a formidable challenge, because of the interplay of many factors contributing to the observed efficiency of a given photocatalyst. Here, the most recent advances in brookite TiO2 material synthesis and applications are summarized, focusing on structure/activity relation studies of phase and morphology-controlled materials. Many questions remain unanswered regarding brookite, but one answer is clear: Is it still worth studying such a hard-to-synthesize, elusive TiO2 polymorph? Yes. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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Open AccessReview Reactivity of Trapped and Accumulated Electrons in Titanium Dioxide Photocatalysis
Catalysts 2017, 7(10), 303; doi:10.3390/catal7100303
Received: 20 September 2017 / Revised: 5 October 2017 / Accepted: 8 October 2017 / Published: 13 October 2017
PDF Full-text (2342 KB) | HTML Full-text | XML Full-text
Abstract
Electrons, photogenerated in conduction bands (CB) and trapped in electron trap defects (Tids) in titanium dioxide (TiO2), play crucial roles in characteristic reductive reactions. This review summarizes the recent progress in the research on electron transfer in photo-excited TiO
[...] Read more.
Electrons, photogenerated in conduction bands (CB) and trapped in electron trap defects (Tids) in titanium dioxide (TiO2), play crucial roles in characteristic reductive reactions. This review summarizes the recent progress in the research on electron transfer in photo-excited TiO2. Particularly, the reactivity of electrons accumulated in CB and trapped at Tids on TiO2 is highlighted in the reduction of molecular oxygen and molecular nitrogen, and the hydrogenation and dehalogenation of organic substrates. Finally, the prospects for developing highly active TiO2 photocatalysts are discussed. Full article
(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)
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