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Special Issue "Enhancing the Photocatalytic Activity of TiO2 Photocatalysts"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials for Energy Applications".

Deadline for manuscript submissions: closed (31 July 2017)

Special Issue Editor

Guest Editor
Prof. Walid A. Daoud

School of Energy and Environment, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong
Website | E-Mail

Special Issue Information

Dear Colleagues,

Solar energy is the most abundant source of renewable energy conversion and storage. Photocatalysis has demonstrated its promising potential to convert solar energy into chemical energy, which has gained substantial attention and research interests. TiO2, owing to its abundance, nontoxicity, low-cost and good chemical stability, has been one of the most widely investigated photocatalysts in various applications, including photocatalytic self-cleaning, environmental pollutants removal, CO2 photoreduction for fuel generation and photocatalytic hydrogen production from water. However, the inherent limitation of its large bandgap confines its absorbance to the UV region and the considerable recombination of photogenerated electron-hole pairs suppresses its photocatalytic efficiency. Thus, significant efforts have been devoted to the better utilization of solar energy and the enhancement of the photocatalytic activity of TiO2. The most prominent strategies include introducing dopants or defects, dye-sensitization, and coupling with narrow bandgap semiconductors to form heterojunction structures.

This Special Issue aims to encompass original research work and reviews, which focus on tuning the optical, electronic, surface, morphological and structural properties of TiO2, as well as its size, crystallinity and surface facets for improved photocatalytic performance in self-cleaning surfaces, photodegradation of pollutants, photocatalytic water splitting for hydrogen generation and other emerging applications.

It is my pleasure to invite you to submit original papers, short communications and reviews for this Special Issue “Enhancing the Photocatalytic Activity of TiO2 Photocatalysts”.

Walid A. Daoud
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 papers will be 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 monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

• TiO2
• Photocatalysis
• Self-cleaning
• Photodegradation
• Photocatalytic water splitting
• CO2 photoreduction
• Photocatalysis-based applications

Published Papers (9 papers)

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Research

Open AccessArticle Synthesis and Characterization of TiO2 Nanoparticles for the Reduction of Water Pollutants
Materials 2017, 10(10), 1208; doi:10.3390/ma10101208
Received: 30 August 2017 / Revised: 13 October 2017 / Accepted: 18 October 2017 / Published: 20 October 2017
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Abstract
The aim of this manuscript was the optimization of the synthesis of TiO2 nanoparticles (TiO2 NPs) with conditions that could be easily reproducible at the industrial level. Several procedures were tested and those with C12H28O4Ti
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The aim of this manuscript was the optimization of the synthesis of TiO2 nanoparticles (TiO2 NPs) with conditions that could be easily reproducible at the industrial level. Several procedures were tested and those with C12H28O4Ti and CO(NH2)2 as precursors seemed the most promising and, consequently, were improved with different molar ratios, lower temperatures and the addition of NH4Cl as a secondary dopant of nitrogen. The obtained samples were studied with analytical techniques such as X-ray powder diffraction (XRPD) and field emission scanning electron microscopy (FESEM). To complete the study, dye degradation and bacteriological tests were also performed. The results indicate that it is possible to obtain TiO2 NPs at lower temperatures with respect to those used in the literature; the best candidate that could satisfy all the requirements was a sample with a molar ratio of C12H28O4Ti:CO(NH2)2 at 2:1 and obtained at 50 °C. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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Open AccessArticle Preparation and Application of Immobilized Surfactant-Modified PANi-CNT/TiO2 under Visible-Light Irradiation
Materials 2017, 10(8), 877; doi:10.3390/ma10080877
Received: 17 July 2017 / Revised: 25 July 2017 / Accepted: 25 July 2017 / Published: 29 July 2017
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Abstract
Hydrothermally and sol-gel-synthesized immobilized surfactant-modified polyaniline-carbon nanotubes/TiO2 (PANi-CNT/TiO2) photocatalysts were prepared and their application in the degradation of diethyl phthalate (DEP) under visible light at 410 nm was investigated in this sturdy. To improve the dispersion of nanoparticles and the
[...] Read more.
Hydrothermally and sol-gel-synthesized immobilized surfactant-modified polyaniline-carbon nanotubes/TiO2 (PANi-CNT/TiO2) photocatalysts were prepared and their application in the degradation of diethyl phthalate (DEP) under visible light at 410 nm was investigated in this sturdy. To improve the dispersion of nanoparticles and the transfer of electrons, the TiO2 surface was modified with both sodium dodecyl sulfate (SDS) and functionalized carbon nanotubes (CNT-COOH and CNT-COCl). With the addition of PANi, which was increased from 1%–5%, the adsorption edge of the prepared photocatalysts shifted to 442 nm. The SDS linked the PANi polymers to achieve a thickness of coating of the film of up to 314–400 nm and 1301–1600 nm for sol-gel hydrolysis and hydrothermally-synthesized photocatalysts, respectively. An appropriate film thickness would extend the transfer path of the electrons and inhibit the recombination of the electrons and the electron-holes. The photo-degradation performance of DEP by the hydrothermally-synthesized photocatalysts was better than those by sol-gel hydrolysis. The results revealed that the hydroxyl radicals were the key oxidant in the degradation of DEP using hydrothermally-synthesized PANi-CNT/TiO2 photocatalysts. The morphology and functional groups of the raw materials of photocatalysts were characterized and a comparison of photocatalytic activity with other TiO2-based photocatalysts was also provided. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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Open AccessArticle Structure and Photocatalytic Properties of Mn-Doped TiO2 Loaded on Wood-Based Activated Carbon Fiber Composites
Materials 2017, 10(6), 631; doi:10.3390/ma10060631
Received: 20 April 2017 / Revised: 24 May 2017 / Accepted: 2 June 2017 / Published: 9 June 2017
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Abstract
Mn-doped TiO2 loaded on wood-based activated carbon fiber (Mn/TiO2-WACF) was prepared by sol–gel and impregnation method using MnSO4·H2O as manganese source. The structure of Mn/TiO2–WACF was characterized by SEM, XRD, FTIR, N2 adsorption
[...] Read more.
Mn-doped TiO2 loaded on wood-based activated carbon fiber (Mn/TiO2-WACF) was prepared by sol–gel and impregnation method using MnSO4·H2O as manganese source. The structure of Mn/TiO2–WACF was characterized by SEM, XRD, FTIR, N2 adsorption and UV–Vis, and its photocatalytic activity for methylene blue degradation was investigated. Results show that Mn-doped TiO2 were loaded on the surface of wood-based activated carbon fiber with high-development pore structures. The crystallite sizes of Mn-doped TiO2 in composites were smaller than that of the undoped samples. With an increase of Mn doping content, Ti–O bending vibration intensity of Mn/TiO2–WACF increased and then decreased. Moreover, Ti–O–Ti and Ti–O–Mn absorption peaks increased upon doping of Mn. Mn/TiO2–WACF with low specific surface area, and pore volume was improved at 3.5–6.0 nm of mesopore distributions due to the Mn-doped TiO2 load. In addition, the UV–Vis showed that Mn/TiO2–WACF (photodegradation rate of 96%) has higher photocatalytic activity than the undoped samples for methylene blue degradation under visible light irradiation. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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Open AccessArticle Markedly Enhanced Surface Hydroxyl Groups of TiO2 Nanoparticles with Superior Water-Dispersibility for Photocatalysis
Materials 2017, 10(5), 566; doi:10.3390/ma10050566
Received: 17 March 2017 / Revised: 7 May 2017 / Accepted: 19 May 2017 / Published: 22 May 2017
Cited by 3 | PDF Full-text (4034 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The benefits of increasing the number of surface hydroxyls on TiO2 nanoparticles (NPs) are known for environmental and energy applications; however, the roles of the hydroxyl groups have not been characterized and distinguished. Herein, TiO2 NPs with abundant surface hydroxyl groups
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The benefits of increasing the number of surface hydroxyls on TiO2 nanoparticles (NPs) are known for environmental and energy applications; however, the roles of the hydroxyl groups have not been characterized and distinguished. Herein, TiO2 NPs with abundant surface hydroxyl groups were prepared using commercial titanium dioxide (ST-01) powder pretreated with alkaline hydrogen peroxide. Through this simple treatment, the pure anatase phase was retained with an average crystallite size of 5 nm and the surface hydroxyl group density was enhanced to 12.0 OH/nm2, estimated by thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Especially, this treatment increased the amounts of terminal hydroxyls five- to six-fold, which could raise the isoelectric point and the positive charges on the TiO2 surface in water. The photocatalytic efficiency of the obtained TiO2 NPs was investigated by the photodegradation of sulforhodamine B under visible light irradiation as a function of TiO2 content, pH of solution, and initial dye concentration. The high surface hydroxyl group density of TiO2 NPs can not only enhance water-dispersibility but also promote dye sensitization by generating more hydroxyl radicals. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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Open AccessArticle Immobilization of TiO2 Nanoparticles on Chlorella pyrenoidosa Cells for Enhanced Visible-Light-Driven Photocatalysis
Materials 2017, 10(5), 541; doi:10.3390/ma10050541
Received: 22 March 2017 / Revised: 4 May 2017 / Accepted: 9 May 2017 / Published: 17 May 2017
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Abstract
TiO2 nanoparticles are immobilized on chlorella cells using the hydrothermal method. The morphology, structure, and the visible-light-driven photocatalytic activity of the prepared chlorella/TiO2 composite are investigated by various methods. The chlorella/TiO2 composite is found to exhibit larger average sizes and
[...] Read more.
TiO2 nanoparticles are immobilized on chlorella cells using the hydrothermal method. The morphology, structure, and the visible-light-driven photocatalytic activity of the prepared chlorella/TiO2 composite are investigated by various methods. The chlorella/TiO2 composite is found to exhibit larger average sizes and higher visible-light intensities. The sensitization of the photosynthesis pigment originating from chlorella cells provides the anatase TiO2 with higher photocatalytic activities under the visible-light irradiation. The latter is linked to the highly efficient charge separation of the electron/hole pairs. The results also suggest that the photocatalytic activity of the composite remains substantial after four cycles, suggesting a good stability. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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Open AccessArticle One-Pot Route towards Active TiO2 Doped Hierarchically Porous Cellulose: Highly Efficient Photocatalysts for Methylene Blue Degradation
Materials 2017, 10(4), 373; doi:10.3390/ma10040373
Received: 19 February 2017 / Revised: 25 March 2017 / Accepted: 28 March 2017 / Published: 31 March 2017
Cited by 1 | PDF Full-text (7849 KB) | HTML Full-text | XML Full-text
Abstract
In this study, novel photocatalyst monolith materials were successfully fabricated by a non-solvent induced phase separation (NIPS) technique. By adding a certain amount of ethyl acetate (as non-solvent) into a cellulose/LiCl/N,N-dimethylacetamide (DMAc) solution, and successively adding titanium dioxide (TiO
[...] Read more.
In this study, novel photocatalyst monolith materials were successfully fabricated by a non-solvent induced phase separation (NIPS) technique. By adding a certain amount of ethyl acetate (as non-solvent) into a cellulose/LiCl/N,N-dimethylacetamide (DMAc) solution, and successively adding titanium dioxide (TiO2) nanoparticles (NPs), cellulose/TiO2 composite monoliths with hierarchically porous structures were easily formed. The obtained composite monoliths possessed mesopores, and two kinds of macropores. Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET), and Ultraviolet-visible Spectroscopy (UV-Vis) measurements were adopted to characterize the cellulose/TiO2 composite monolith. The cellulose/TiO2 composite monoliths showed high efficiency of photocatalytic activity in the decomposition of methylene blue dye, which was decomposed up to 99% within 60 min under UV light. Moreover, the composite monoliths could retain 90% of the photodegradation efficiency after 10 cycles. The novel NIPS technique has great potential for fabricating recyclable photocatalysts with highly efficiency. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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Open AccessArticle Photocatalytic Degradation of Organic Dye under UV‐A Irradiation Using TiO2‐Vetiver Multifunctional Nano Particles
Materials 2017, 10(2), 122; doi:10.3390/ma10020122
Received: 29 November 2016 / Accepted: 25 January 2017 / Published: 30 January 2017
Cited by 2 | PDF Full-text (2892 KB) | HTML Full-text | XML Full-text
Abstract
The properties and photocatalytic performance of anatase nanoparticles of pure TiO2 and a core–shell structure of TiO2 on calcined vetiver grass leaves have been compared. Samples were fabricated by sol‐gel and heating at 450 °C for 5h.The comparison was based on
[...] Read more.
The properties and photocatalytic performance of anatase nanoparticles of pure TiO2 and a core–shell structure of TiO2 on calcined vetiver grass leaves have been compared. Samples were fabricated by sol‐gel and heating at 450 °C for 5h.The comparison was based on data for X‐ray diffraction(XRD), UV‐Vis spectrophotometry, photoluminescence, transmission electron microscopy, specific surface area measurement, pore volume assessment, and methylene blue degradation testing. The results showed that the pure TiO2 consisted of agglomerated equiaxed nanoparticles of individual grain sizes in the range 10–20 nm. In contrast, the TiO2‐vetiver composite exhibited a core–shell structure consisting of a carbonaceous core and TiO2 shell of thickness 10–15nm. These features influenced the photocatalytic performance in such a way that the lower crosssectional area, greater surface area, and higher pore volume of the TiO2 shell increased the number of active sites, reduced the charge carrier diffusion distance, and reduced the recombination rate, thereby improving the photocatalytic activity. This improvement derived from morphological characteristics rather than crystallographic, semiconducting, or optical properties. The improved performance of the TiO2‐vetiver core–shell was unexpected since the X‐ray diffraction data showed that the crystallinity of the TiO2 was lower than that of the pure TiO2. These outcomes are attributed to the reducing effect of the carbon on the TiO2 during heating, thereby facilitating the formation of oxygen vacancies, which enhance charge separation and hence photocatalysis by TiO2. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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Open AccessArticle Mechanistic Characteristics of Surface Modified Organic Semiconductor g-C3N4 Nanotubes Alloyed with Titania
Materials 2017, 10(1), 28; doi:10.3390/ma10010028
Received: 8 November 2016 / Revised: 13 December 2016 / Accepted: 15 December 2016 / Published: 3 January 2017
Cited by 2 | PDF Full-text (4099 KB) | HTML Full-text | XML Full-text
Abstract
The visible-light-driven photocatalytic degradation of Bisphenol A (BPA) was investigated using the binary composite of alkaline treated g-C3N4 (HT-g-C3N4) deposited over commercial TiO2 (Evonik Degussa GmbH, Essen, Germany). The existence and contribution of both TiO
[...] Read more.
The visible-light-driven photocatalytic degradation of Bisphenol A (BPA) was investigated using the binary composite of alkaline treated g-C3N4 (HT-g-C3N4) deposited over commercial TiO2 (Evonik Degussa GmbH, Essen, Germany). The existence and contribution of both TiO2 and g-C3N4/HT-g-C3N4 in the composite was confirmed through various analytical techniques including powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectra (UV-vis-DRS), and photoluminescence (PL) analysis. The results showed that the titania in the binary composite exhibited both pure rutile and anatase phases. The morphological analysis indicated that the spongy “morel-like” structure of g-C3N4 turned to nanotube form after alkaline hydrothermal treatment and thereby decreased the specific surface area of HT-g-C3N4. The low surface area of HT-g-C3N4 dominates its promising optical property and effective charge transfer, resulting in a deprived degradation efficiency of BPA two times lower than pure g-C3N4. The binary composite of HT-g-C3N4/TiO2 exhibited excellent degradation efficiency of BPA with 2.16 times higher than the pure HT-g-C3N4. The enhanced photocatalytic activity was mainly due to the promising optical band gap structure with heterojunction interface, favorable specific surface area, and good charge separation. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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Open AccessArticle First Principles Study on the Interaction Mechanisms of Water Molecules on TiO2 Nanotubes
Materials 2016, 9(12), 1018; doi:10.3390/ma9121018
Received: 30 October 2016 / Revised: 1 December 2016 / Accepted: 8 December 2016 / Published: 16 December 2016
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Abstract
The adsorption properties of water molecules on TiO2 nanotubes (TiO2NT) and the interaction mechanisms between water molecules are studied by first principles calculations. The adsorption preferences of water molecules in molecular or dissociated states on clean and H-terminated TiO2
[...] Read more.
The adsorption properties of water molecules on TiO2 nanotubes (TiO2NT) and the interaction mechanisms between water molecules are studied by first principles calculations. The adsorption preferences of water molecules in molecular or dissociated states on clean and H-terminated TiO2NT are evaluated. Adsorption of OH clusters on (0, 6) and (9, 0) TiO2 nanotubes are first studied. The smallest adsorption energies are −1.163 eV and −1.383 eV, respectively, by examining five different adsorption sites on each type of tube. Eight and six adsorption sites were considered for OH adsorbtion on the H terminated (0, 6) and (9, 0) nanotubes. Water molecules are reformed with the smallest adsorption energy of −4.796 eV on the former and of −5.013 eV on the latter nanotube, respectively. For the adsorption of a single water molecule on TiO2NT, the molecular state shows the strongest adsorption preference with an adsorption energy of −0.660 eV. The adsorption of multiple (two and three) water molecules on TiO2NT is also studied. The calculated results show that the interactions between water molecules greatly affect their adsorption properties. Competition occurs between the molecular and dissociated states. The electronic structures are calculated to clarify the interaction mechanisms between water molecules and TiO2NT. The bonding interactions between H from water and oxygen from TiO2NT may be the reason for the dissociation of water on TiO2NT. Full article
(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)
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