Catalysts

Editorial

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113 KiB

Open AccessEditorial

Photocatalysis—A Special Issue on a Unique Hybrid Area of Catalysis

by Cooper H. Langford

Catalysts 2012, 2(3), 327-329; https://doi.org/10.3390/catal2030327 - 9 Aug 2012

Cited by 6 | Viewed by 6206

Abstract

An overview of the development of photocatalysis with an identification of contemporary areas of interest. Photocatalysis is placed in the broad field of catalysis. [...] Full article

(This article belongs to the Special Issue Photocatalysts)

Research

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738 KiB

Open AccessArticle

Application of Photocatalysts and LED Light Sources in Drinking Water Treatment

by Maryam Izadifard, Gopal Achari and Cooper H. Langford

Catalysts 2013, 3(3), 726-743; https://doi.org/10.3390/catal3030726 - 12 Sep 2013

Cited by 53 | Viewed by 9818

Abstract

This study investigates a cross-section of TiO₂ compositions for which existing evidence suggests the prospect of improved performance compared to standard Degussa P25. In the context of a program aimed toward a 365 nm LED based photo-reactor, the question is whether a [...] Read more.

This study investigates a cross-section of TiO₂ compositions for which existing evidence suggests the prospect of improved performance compared to standard Degussa P25. In the context of a program aimed toward a 365 nm LED based photo-reactor, the question is whether a distinctly superior photocatalyst composition for drinking water treatment is now available that would shape design choices. An answer was sought by synthesizing several photocatalysts with reported high reactivity in some context in the literature, and by performing photocatalysts reactivity tests using common pollutants of water system including Natural Organic Matter (NOM) and Emerging Contaminants (ECs) from the pesticide and pharmaceutical classes. 365 nm Light Emitting Diodes (LEDs) were used as the irradiation source. Since LEDs are now available in the UV, we did not examine the TiO₂modifications that bring band gap excitation into the region beyond 400 nm. The results suggest that the choice of the photocatalyst should be best made to fit the reactor design and photocatalyst mounting constraints such as mass transport, reactive surface, and light field. No photocatalyst composition overall, superior for all classes emerged. Full article

(This article belongs to the Special Issue Photocatalysts)

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1287 KiB

Open AccessArticle

Photocatalytic Activity of Vis-Responsive Ag-Nanoparticles/TiO₂ Composite Thin Films Fabricated by Molecular Precursor Method (MPM)

by Likius S. Daniel, Hiroki Nagai, Naoya Yoshida and Mitsunobu Sato

Catalysts 2013, 3(3), 625-645; https://doi.org/10.3390/catal3030625 - 31 Jul 2013

Cited by 34 | Viewed by 11645

Abstract

The Ag-nanoparticles (Ag-NP)/TiO₂ composite thin films with various amounts of Ag (10 mol% ≤ n ≤ 80 mol%) were examined as a potential photocatalyst by decoloration reaction of methylene blue (MB) in an aqueous solution. These composite thin films of ca. 100 [...] Read more.

The Ag-nanoparticles (Ag-NP)/TiO₂ composite thin films with various amounts of Ag (10 mol% ≤ n ≤ 80 mol%) were examined as a potential photocatalyst by decoloration reaction of methylene blue (MB) in an aqueous solution. These composite thin films of ca. 100 nm thickness were fabricated by the MPM at 600 °C in air. The decoloration rates monitored by the absorption intensity of the MB solution indicated that the composite thin films of Ag with an amount less than 40 mol% are not effective under vis-irradiation, though they can work as a photocatalyst under UV-irradiation. Further, the UV-sensitivity of the composite thin films gradually decreased to almost half the level of that of the TiO₂ thin film fabricated under the identical conditions when the Ag amount increased from 10 to 40 mol%. Contrarily, the composite thin films of Ag content larger than 50 mol% showed the vis-responsive activity, whose level was slightly lower than the decreased UV-sensitivity. Diffuse reflectance spectra suggested that the vis-responsive activity of the composite thin films is due to the conductivity, localized surface plasmon resonance and surface plasmon resonance of Ag-NP. It was also elucidated that the vis-responsive level of the composite thin films corresponds to their electrical conductivity that depends on the Ag content. Full article

(This article belongs to the Special Issue Photocatalysts)

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530 KiB

Open AccessArticle

Dye Modification Effects on TaON for Photocatalytic Hydrogen Production from Water

by Hidehisa Hagiwara, Masakiyo Nagatomo, Chihiro Seto, Shintaro Ida and Tatsumi Ishiahara

Catalysts 2013, 3(3), 614-624; https://doi.org/10.3390/catal3030614 - 23 Jul 2013

Cited by 22 | Viewed by 8827

Abstract

Modification effects of porphyrin dyes on the photocatalytic activity of tantalum (oxy)nitride (TaON) were investigated. The nitrogen content in tantalum (oxy)nitride was increased by increasing the heat treatment period. The optimized nitridation conditions were found to be calcination at 800 °C for 14 [...] Read more.

Modification effects of porphyrin dyes on the photocatalytic activity of tantalum (oxy)nitride (TaON) were investigated. The nitrogen content in tantalum (oxy)nitride was increased by increasing the heat treatment period. The optimized nitridation conditions were found to be calcination at 800 °C for 14 h under a NH₃ gas flow (25 mL min⁻¹). Among the porphyrin dyes examined, pentamethylene bis[4-(10,15,20-triphenylporphine-5-yl) benzoate]-dizinc (II) (Zn-TPPD) showed the most positive effect on the photocatalytic activity of TaON for H₂ production from Na₂S aqueous solution. From the results of the photocatalytic reaction using various combinations of catalyst components, it was found that the modification dye and PtO_x co-catalysts were necessary to achieving photocatalytic H₂ formation. In the PtO_x/Zn-TPPD/TaON photocatalyst, the expected charge transfer mechanism was a two-step excitation of both TaON and Zn-TPPD, and the oxidation and reduction sites were TaON and PtO_x co-catalyst, respectively. These results indicate that dye modification has the potential to improve the photocatalytic activity of various (oxy)nitride photocatalysts. Full article

(This article belongs to the Special Issue Photocatalysts)

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868 KiB

Open AccessArticle

Photocatalytic Degradation of Acridine Orange over NaBiO₃ Driven by Visible Light Irradiation

by Chung-Shin Lu, Chiing-Chang Chen, Ling-Kuen Huang, Peir-An Tsai and Hsiao-Fang Lai

Catalysts 2013, 3(2), 501-516; https://doi.org/10.3390/catal3020501 - 21 May 2013

Cited by 33 | Viewed by 9460

Abstract

The photocatalytic degradation of acridine orange (AO) dye by NaBiO₃ photocatalyst under visible light irradiation was investigated systematically. The NaBiO₃ photocatalyst exhibited a higher photocatalytic activity compared to the P25 photocatalyst. After 160 min of photocatalytic reaction, the degradation rate of [...] Read more.

The photocatalytic degradation of acridine orange (AO) dye by NaBiO₃ photocatalyst under visible light irradiation was investigated systematically. The NaBiO₃ photocatalyst exhibited a higher photocatalytic activity compared to the P25 photocatalyst. After 160 min of photocatalytic reaction, the degradation rate of AO could reach to 99% in appropriate conditions. Factors, such as catalyst dosage, solution pH, initial AO concentration and the presence of anions, were found to influence the degradation rate. To scrutinize the mechanistic details of the dye photodegradation, the intermediates of the processes were separated, identified and characterized by the HPLC-ESI-MS technique. The analytical results indicated that the N-de-methylation degradation of AO dye took place in a stepwise manner to yield mono-, di-, tri- and tetra-N-de-methylated AO species generated during the processes. The probable photodegradation pathways were proposed and discussed. Full article

(This article belongs to the Special Issue Photocatalysts)

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2682 KiB

Open AccessArticle

Manganese Oxide-Surface Modified Titanium (IV) Dioxide as Environmental Catalyst

by Qiliang Jin, Hiroshi Arimoto, Musashi Fujishima and Hiroaki Tada

Catalysts 2013, 3(2), 444-454; https://doi.org/10.3390/catal3020444 - 23 Apr 2013

Cited by 37 | Viewed by 9232

Abstract

The purpose of this study is to present an “environmental catalyst” possessing both thermocatalytic activity and visible-light activity for the decomposition of organic pollutants. Molecule-sized MnO_x clusters are highly dispersed on the surface of TiO₂ (anatase/rutile = 4/1 w/w [...] Read more.

The purpose of this study is to present an “environmental catalyst” possessing both thermocatalytic activity and visible-light activity for the decomposition of organic pollutants. Molecule-sized MnO_x clusters are highly dispersed on the surface of TiO₂ (anatase/rutile = 4/1 w/w, P-25, Degussa) by the chemisorption-calcination cycle technique using Mn(acac)₃ complex as a precursor (MnO_x/TiO₂). The thermo- and photo-catalytic activities of MnO_x/TiO₂ were studied for the degradation of 2-naphthol used as a model water pollutant. In contrast to the FeO_x/TiO₂ system, MnO_x/TiO₂ exhibits high thermocatalytic activity exceeding those of bulk β-β-MnO₂ and Mn₂O₃. Also, visible-light activity is induced by the surface modification of TiO₂ with MnO_xclusters, whereas its UV-light activity decreases. Full article

(This article belongs to the Special Issue Photocatalysts)

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859 KiB

Open AccessArticle

Generation of Free OH_aq Radicals by Black Light Illumination of Degussa (Evonik) P25 TiO₂ Aqueous Suspensions

by Haidong Liao and Torbjörn Reitberger

Catalysts 2013, 3(2), 418-443; https://doi.org/10.3390/catal3020418 - 16 Apr 2013

Cited by 51 | Viewed by 12766

Abstract

This work demonstrates how formation of strongly chemiluminescent 3-hydroxyphthalic hydrazide by hydroxylation of non-chemiluminescent phthalic hydrazide can be applied as a selective reaction probe to obtain information on authentic hydroxyl radical, i.e., ^•OH_aq, formation, in black light illuminated Degussa [...] Read more.

This work demonstrates how formation of strongly chemiluminescent 3-hydroxyphthalic hydrazide by hydroxylation of non-chemiluminescent phthalic hydrazide can be applied as a selective reaction probe to obtain information on authentic hydroxyl radical, i.e., ^•OH_aq, formation, in black light illuminated Degussa P25 TiO₂ aerated suspensions in the pH range from 3 to 11. The ^•OH_aq formation was found to be strongly pH dependent. At alkaline pH, the apparent quantum efficiency of ^•OH_aq formation was estimated to be at the ~10⁻² level whereas at acidic pH it was near zero. Addition of phosphate and fluoride ions substantially enhanced the ^•OH_aq production in the acidic pH range. It is suggested that ^•OH_aq-radical formation in TiO₂ photocatalysis can occur by oxidation of hydroxyl ions in the water layer adsorbed on TiO₂ surfaces. Full article

(This article belongs to the Special Issue Photocatalysts)

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1683 KiB

Open AccessArticle

Visible Light-Photocatalytic Activity of Sulfate-Doped Titanium Dioxide Prepared by the Sol−Gel Method

by Hiromasa Nishikiori, Maki Hayashibe and Tsuneo Fujii

Catalysts 2013, 3(2), 363-377; https://doi.org/10.3390/catal3020363 - 8 Apr 2013

Cited by 40 | Viewed by 7666

Abstract

Sulfate-doped TiO2 was prepared from sol−gel systems containing titaniumalkoxide and sulfuric acid. The time needed for gelation of the systems was significantlyreduced by ultrasonic irradiation. The doped sulfate was observed by FTIR and XPSmeasurements. Some sulfate ions remained in the TiO2 even after [...] Read more.

Sulfate-doped TiO2 was prepared from sol−gel systems containing titaniumalkoxide and sulfuric acid. The time needed for gelation of the systems was significantlyreduced by ultrasonic irradiation. The doped sulfate was observed by FTIR and XPSmeasurements. Some sulfate ions remained in the TiO2 even after heating at 300−600 °C.The UV and visible photocatalytic activities of the samples were confirmed by thedegradation of trichloroethylene (TCE). The activity of the photocatalyst samples duringthe UV irradiation strongly depended on their crystallinities rather than their specificsurface areas, i.e., adsorption ability. The degradation rate during the visible irradiationdepended on both the adsorption ability and visible absorption of the photocatalystsamples. The visible absorption induced by the sulfate-doping was effective for theTCE degradation. Full article

(This article belongs to the Special Issue Photocatalysts)

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276 KiB

Open AccessArticle

Broad Spectrum Microbicidal Activity of Photocatalysis by TiO₂

by Ryuichi Nakano, Masayuki Hara, Hitoshi Ishiguro, Yanyan Yao, Tsuyoshi Ochiai, Kazuya Nakata, Taketoshi Murakami, Jitsuo Kajioka, Kayano Sunada, Kazuhito Hashimoto, Akira Fujishima and Yoshinobu Kubota

Catalysts 2013, 3(1), 310-323; https://doi.org/10.3390/catal3010310 - 21 Mar 2013

Cited by 89 | Viewed by 11711

Abstract

Photocatalytically active titanium dioxide (TiO₂) is widely used as a self-cleaning and self-disinfecting material in many applications to keep environments biologically clean. Several studies on the inactivation of bacteria and viruses by photocatalytic reactions have also been reported; however, only few [...] Read more.

Photocatalytically active titanium dioxide (TiO₂) is widely used as a self-cleaning and self-disinfecting material in many applications to keep environments biologically clean. Several studies on the inactivation of bacteria and viruses by photocatalytic reactions have also been reported; however, only few studies evaluated the spectrum of the microbicidal activity with photocatalysis for various species. There is a need to confirm the expected effectiveness of disinfection by photocatalysis against multidrug-resistant bacteria and viruses. In this study, microbicidal activity of photocatalysis was evaluated by comparing the inactivation of various species of bacteria and viruses when their suspensions were dropped on the surface of TiO₂-coated glass. Gram-positive bacteria, e.g., methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and penicillin-resistant Streptococcus pneumoniae, were easily inactivated by photocatalysis, whereas some gram-negative bacteria, e.g., Escherichia coli and multidrug-resistant Pseudomonas aeruginosa, were gradually inactivated by photocatalysis. Influenza virus, an enveloped virus, was significantly inactivated by photocatalysis compared with feline calicivirus, a non-enveloped virus. The effectiveness of microbicidal activity by photocatalysis may depend on the surface structure. However, they are effectively inactivated by photocatalysis on the surface of TiO₂-coated glass. Our data emphasize that effective cleaning and disinfection by photocatalysis in nosocomial settings prevents pathogen transmission. Full article

(This article belongs to the Special Issue Photocatalysts)

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2469 KiB

Open AccessArticle

Inactivation of E. Coli in Water Using Photocatalytic, Nanostructured Films Synthesized by Aerosol Routes

by Jinho Park, Eric Kettleson, Woo-Jin An, Yinjie J. Tang and Pratim Biswas

Catalysts 2013, 3(1), 247-260; https://doi.org/10.3390/catal3010247 - 4 Mar 2013

Cited by 14 | Viewed by 7406

Abstract

TiO₂ nanostructured films were synthesized by an aerosol chemical vapor deposition (ACVD) method with different controlled morphologies: columnar, granular, and branched structures for the photocatalytic inactivation of Escherichia coli (E. coli) in water. Effects of film morphology and external applied [...] Read more.

TiO₂ nanostructured films were synthesized by an aerosol chemical vapor deposition (ACVD) method with different controlled morphologies: columnar, granular, and branched structures for the photocatalytic inactivation of Escherichia coli (E. coli) in water. Effects of film morphology and external applied voltage on inactivation rate were investigated. As-prepared films were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and UV-VIS. Photocatalytic and photoelectrochemical inactivation of E. coli using as-prepared TiO₂ films were performed under irradiation of UVA light (note: UVA has a low efficiency to inactivate E. coli). Inactivation rate constants for each case were obtained from their respective inactivation curve through a 2 h incubation period. Photocatalytic inactivation rate constants of E. coli are 0.02/min (using columnar films), and 0.08/min (using branched films). The inactivation rate constant for the columnar film was enhanced by 330% by applied voltage on the film while that for the branched film was increased only by 30%. Photocatalytic microbial inactivation rate of the columnar and the branched films were also compared taking into account their different surface areas. Since the majority of the UV radiation that reaches the Earth’s surface is UVA, this study provides an opportunity to use sunlight to efficiently decontaminate drinking water. Full article

(This article belongs to the Special Issue Photocatalysts)

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396 KiB

Open AccessArticle

Photocatalytic Oxidation Processes for Toluene Oxidation over TiO₂ Catalysts

by Hisahiro Einaga, Keisuke Mochiduki and Yasutake Teraoka

Catalysts 2013, 3(1), 219-231; https://doi.org/10.3390/catal3010219 - 4 Mar 2013

Cited by 44 | Viewed by 9179

Abstract

Gas-solid heterogeneous photooxidation of toluene over TiO₂ catalyst was studied to investigate the factors controlling the catalytic activities. The toluene photooxidation behavior on TiO₂ was strongly affected by the formation and oxidation behavior of intermediate compounds on TiO₂, and [...] Read more.

Gas-solid heterogeneous photooxidation of toluene over TiO₂ catalyst was studied to investigate the factors controlling the catalytic activities. The toluene photooxidation behavior on TiO₂ was strongly affected by the formation and oxidation behavior of intermediate compounds on TiO₂, and their accumulation decreased the reaction rate for toluene photooxidation. The formation and oxidation behavior of the byproduct compounds depended on the initial concentration of toluene and water vapor. In situ Fourier transform infrared (FTIR) studies revealed that water vapor promoted the cleavage of the aromatic ring and facilitated CO₂ formation. At the reaction temperature of 300 K, the deposition of Pt on TiO₂ suppressed CO formation, whereas catalytic activity was decreased due to the increase in the amount of intermediate compounds. On the other hand, Pt/TiO₂ showed higher activity than TiO₂ at 353 K, in spite of the increase of the intermediate compounds. Full article

(This article belongs to the Special Issue Photocatalysts)

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703 KiB

Open AccessArticle

Microvolume TOC Analysis as Useful Tool in the Evaluation of Lab Scale Photocatalytic Processes

by Monika Kus, Stefan Ribbens, Vera Meynen and Pegie Cool

Catalysts 2013, 3(1), 74-87; https://doi.org/10.3390/catal3010074 - 22 Jan 2013

Cited by 6 | Viewed by 9118

Abstract

Analysis methods that require small volumes of aqueous samples can be of large benefit for applications when expensive chemicals are involved or available volumes are substantially small and concentrations are low. A new method is presented to allow microvolume liquid injections on TOC [...] Read more.

Analysis methods that require small volumes of aqueous samples can be of large benefit for applications when expensive chemicals are involved or available volumes are substantially small and concentrations are low. A new method is presented to allow microvolume liquid injections on TOC equipment using a special designed Shimadzu gas injection kit^® in combination with a high precision syringe and Chaney adapter. Next to details on the methodology of microvolume TOC injections, the technique is shown to be beneficial to evaluate the efficiency of photocatalytic dye degradation on titania materials in terms of CO₂ conversion simultaneously with classic UV-Vis analysis measurements within a lab scale photocatalytic test setup (volume <100 mL). The possibility to allow multiple microvolume samplings in short time intervals during several hours without a substantial decrease in volume/catalyst ratio is of particular value for the evaluation of photocatalysts. By combining both techniques at short time intervals, additional knowledge of the degradation process/mechanism, kinetics and the efficiency can be obtained in a direct way. Moreover, the developed μV-TOC analysis is specifically useful in those applications in which low sample volumes in combination with low concentrations are involved. For example, μV-TOC can similarly be put into service in a wide range of small volume setups, e.g., analytes from high-throughput screening, pharmaceutical applications and other advanced oxidation processes that formally could not be analyzed due to limited sample volumes and often low concentrations. Full article

(This article belongs to the Special Issue Photocatalysts)

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Open AccessArticle

Preparation and Photocatalytic Properties of Sr_2−xBa_xTa₃O₁₀₋_yN_zNanosheets

by Shintaro Ida, Yohei Okamoto, Hidehisa Hagiwara and Tatsumi Ishihara

Catalysts 2013, 3(1), 1-10; https://doi.org/10.3390/catal3010001 - 16 Jan 2013

Cited by 22 | Viewed by 7689

Abstract

Sr_2−xBa_xTa₃O₁₀_−yN_z (x = 0.0, 0.5, 1.0) nanosheets were prepared by exfoliating layered perovskite compounds (CsSr_2−xBa_xTa₃O₁₀_−yN_z). The Sr [...] Read more.

Sr_2−xBa_xTa₃O₁₀_−yN_z (x = 0.0, 0.5, 1.0) nanosheets were prepared by exfoliating layered perovskite compounds (CsSr_2−xBa_xTa₃O₁₀_−yN_z). The Sr_1.5Ba_0.5Ta₃O_9.7N_0.2nanosheet showed the highest photocatalytic activity for H₂ production from the water/methanol system among the Sr_2−xBa_xTa₃O_9.7N_0.2 nanosheets prepared. In addition, Rh-loaded Sr_1.5Ba_0.5Ta₃O_9.6N_0.3 nanosheet showed the photocatalytic activity for oxygen and hydrogen production from water. The ratio of hydrogen to oxygen evolved was around two. These results indicate that the Rh-loaded Sr_1.5Ba_0.5Ta₃O_9.6N_0.3 nanosheet is a potential catalyst for photocatalytic water splitting. Full article

(This article belongs to the Special Issue Photocatalysts)

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Review

Jump to: Editorial, Research

242 KiB

Open AccessReview

Titania Photocatalysis beyond Recombination: A Critical Review

by Bunsho Ohtani

Catalysts 2013, 3(4), 942-953; https://doi.org/10.3390/catal3040942 - 15 Nov 2013

Cited by 183 | Viewed by 15349

Abstract

This short review paper shows the significance of recombination of a photoexcited electron and a hole in conduction and valence bands, respectively, of a titania photocatalyst, since recombination has not yet been fully understood and has not been evaluated adequately during the past [...] Read more.

This short review paper shows the significance of recombination of a photoexcited electron and a hole in conduction and valence bands, respectively, of a titania photocatalyst, since recombination has not yet been fully understood and has not been evaluated adequately during the past several decades of research on heterogeneous photocatalysis. Full article

(This article belongs to the Special Issue Photocatalysts)

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1358 KiB

Open AccessReview

Specific Facets-Dominated Anatase TiO₂: Fluorine-Mediated Synthesis and Photoactivity

by Maria Vittoria Dozzi and Elena Selli

Catalysts 2013, 3(2), 455-485; https://doi.org/10.3390/catal3020455 - 16 May 2013

Cited by 118 | Viewed by 17557

Abstract

Semiconductors crystal facet engineering has become an important strategy for properly tuning and optimizing both the physicochemical properties and the reactivity of photocatalysts. In this review, a concise survey of recent results obtained in the field of specific surface-oriented anatase TiO₂ crystals [...] Read more.

Semiconductors crystal facet engineering has become an important strategy for properly tuning and optimizing both the physicochemical properties and the reactivity of photocatalysts. In this review, a concise survey of recent results obtained in the field of specific surface-oriented anatase TiO₂ crystals preparation is presented. The attention is mainly focused on the fluorine-mediated hydrothermal and/or solvothermal processes employed for the synthesis and the assembly of anatase micro/nanostructures with dominant {001} facets. Their peculiar photocatalytic properties and potential applications are also presented, with a particular focus on photocatalysis-based environmental clean up and solar energy conversion applications. Finally, the most promising results obtained in the engineering of TiO₂ anatase crystal facets obtained by employing alternative, possibly more environmentally friendly methods are critically compared. Full article

(This article belongs to the Special Issue Photocatalysts)

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865 KiB

Open AccessReview

The Influence of Surface Alumina and Silica on the Photocatalytic Degradation of Organic Pollutants

by Terry A. Egerton

Catalysts 2013, 3(1), 338-362; https://doi.org/10.3390/catal3010338 - 21 Mar 2013

Cited by 13 | Viewed by 7702

Abstract

Practical photocatalysis for degradation of organic pollutants must take into account the influence of other chemicals. Significant Al deposition on titania can occur at naturally occurring concentrations of dissolved Al. This paper reviews the author’s work on the influence of deliberately deposited hydrous [...] Read more.

Practical photocatalysis for degradation of organic pollutants must take into account the influence of other chemicals. Significant Al deposition on titania can occur at naturally occurring concentrations of dissolved Al. This paper reviews the author’s work on the influence of deliberately deposited hydrous oxides of aluminium on the behavior of a ~130 m² g⁻¹ rutile TiO₂, and then compares the behavior of deposited alumina with that of deposited silica. On rutile some adsorbed nitrogen is infrared-active. Alumina and silica deposited on the rutile reduce, and ultimately eliminate, this infrared-active species. They also reduce photocatalytic oxidation of both propan-2-ol and dichloroacetate ion and the photocatalytic reduction of diphenyl picryl hydrazine. The surface oxides suppress charge transfer and may also reduce reactant adsorption. Quantitative measurement of TiO₂ photogreying shows that the adsorbed inorganics also reduce photogreying, attributed to the capture of photogenerated conduction band electrons by Ti⁴⁺ to form Ti³⁺. The influence of adsorbed phosphate on photocatalysis is briefly considered, since phosphate reduces photocatalytic disinfection. In the context of classical colloid studies, it is concluded that inorganic species in water can significantly reduce photoactivity from the levels that measured in pure water. Full article

(This article belongs to the Special Issue Photocatalysts)

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1729 KiB

Open AccessReview

Heterogeneous Photocatalysis: Recent Advances and Applications

by Alex Omo Ibhadon and Paul Fitzpatrick

Catalysts 2013, 3(1), 189-218; https://doi.org/10.3390/catal3010189 - 1 Mar 2013

Cited by 1102 | Viewed by 65183

Abstract

Semiconductor heterogeneous photocatalysis, the subject of this review, is a versatile, low-cost and environmentally benign treatment technology for a host of pollutants. These may be of biological, organic and inorganic in origin within water and air. The efficient and successful application of photocatalysis [...] Read more.

Semiconductor heterogeneous photocatalysis, the subject of this review, is a versatile, low-cost and environmentally benign treatment technology for a host of pollutants. These may be of biological, organic and inorganic in origin within water and air. The efficient and successful application of photocatalysis demands that the pollutant, the catalyst and source of illumination are in close proximity or contact with each other. The ability of advanced oxidation technology to remove low levels of persistent organic pollutants as well as microorganisms in water has been widely demonstrated and, progressively, the technology is now being commercialized in many areas of the world including developing nations. This review considers recent developments in the research and application of heterogeneous semiconductor photocatalysis for the treatment of low-level concentrations of pollutants in water and air using titanium dioxide as a “model” semiconductor. The review considers charge transport characteristics on the semiconductor surface, photocatalyst reactor design and organic degradation mechanistic pathways. The effects of photoreactor operating parameters on the photocatalytic process are discussed in addition to mineralization and disinfection kinetics. Full article

(This article belongs to the Special Issue Photocatalysts)

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1949 KiB

Open AccessReview

Brookite, the Least Known TiO₂ Photocatalyst

by Agatino Di Paola, Marianna Bellardita and Leonardo Palmisano

Catalysts 2013, 3(1), 36-73; https://doi.org/10.3390/catal3010036 - 18 Jan 2013

Cited by 507 | Viewed by 30263

Abstract

Brookite is the least studied TiO₂ photocatalyst due to the difficulties usually encountered in order to obtain it as a pure phase. In this review, a comprehensive survey of the different methods available for preparing brookite powders and films is reported. Attention [...] Read more.

Brookite is the least studied TiO₂ photocatalyst due to the difficulties usually encountered in order to obtain it as a pure phase. In this review, a comprehensive survey of the different methods available for preparing brookite powders and films is reported. Attention has been paid both to the most traditional methods, such as hydrothermal processes at high temperatures and pressures, and to environmentally benign syntheses using water soluble compounds and water as the solvent. Papers reporting the photocatalytic activity of pure and brookite-based samples have been reviewed. Full article

(This article belongs to the Special Issue Photocatalysts)

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1026 KiB

Open AccessReview

Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates

by Manoj A. Lazar, Shaji Varghese and Santhosh S. Nair

Catalysts 2012, 2(4), 572-601; https://doi.org/10.3390/catal2040572 - 19 Dec 2012

Cited by 507 | Viewed by 39934

Abstract

Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products [...] Read more.

Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO. Full article

(This article belongs to the Special Issue Photocatalysts)

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556 KiB

Open AccessReview

Conversion of CO₂via Visible Light Promoted Homogeneous Redox Catalysis

by Richard Reithmeier, Christian Bruckmeier and Bernhard Rieger

Catalysts 2012, 2(4), 544-571; https://doi.org/10.3390/catal2040544 - 27 Nov 2012

Cited by 86 | Viewed by 17555

Abstract

This review gives an overview on the principles of light-promoted homogeneous redox catalysis in terms of applications in CO₂ conversion. Various chromophores and the advantages of different structures and metal centers as well as optimization strategies are discussed. All aspects of the [...] Read more.

This review gives an overview on the principles of light-promoted homogeneous redox catalysis in terms of applications in CO₂ conversion. Various chromophores and the advantages of different structures and metal centers as well as optimization strategies are discussed. All aspects of the reduction catalyst site are restricted to CO₂ conversion. An important focus of this review is the question of a replacement of the sacrificial donor which is found in most of the current publications. Furthermore, electronic parameters of supramolecular systems are reviewed with reference to the requisite of chromophores, oxidation and reduction sites. Full article

(This article belongs to the Special Issue Photocatalysts)

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Hydrogen Production from Semiconductor-based Photocatalysis via Water Splitting

by Chi-Hung Liao, Chao-Wei Huang and Jeffrey C. S. Wu

Catalysts 2012, 2(4), 490-516; https://doi.org/10.3390/catal2040490 - 17 Oct 2012

Cited by 434 | Viewed by 32999

Abstract

Hydrogen is the ideal fuel for the future because it is clean, energy efficient, and abundant in nature. While various technologies can be used to generate hydrogen, only some of them can be considered environmentally friendly. Recently, solar hydrogen generated via photocatalytic water [...] Read more.

Hydrogen is the ideal fuel for the future because it is clean, energy efficient, and abundant in nature. While various technologies can be used to generate hydrogen, only some of them can be considered environmentally friendly. Recently, solar hydrogen generated via photocatalytic water splitting has attracted tremendous attention and has been extensively studied because of its great potential for low-cost and clean hydrogen production. This paper gives a comprehensive review of the development of photocatalytic water splitting for generating hydrogen, particularly under visible-light irradiation. The topics covered include an introduction of hydrogen production technologies, a review of photocatalytic water splitting over titania and non-titania based photocatalysts, a discussion of the types of photocatalytic water-splitting approaches, and a conclusion for the current challenges and future prospects of photocatalytic water splitting. Based on the literatures reported here, the development of highly stable visible–light-active photocatalytic materials, and the design of efficient, low-cost photoreactor systems are the key for the advancement of solar-hydrogen production via photocatalytic water splitting in the future. Full article

(This article belongs to the Special Issue Photocatalysts)

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