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Editorial: Special Issue on Photocatalytic Nanocomposite Materials (PNMs)

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Catalysts 2021, 11(5), 587; https://doi.org/10.3390/catal11050587 - 30 Apr 2021

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Abstract

This Special Issue titled “Photocatalytic Nanocomposite Materials” (PNMs) is devoted to the research into new-generation PNMs, particularly for the processes of solar radiation energy conversion with its focus lying on the physicochemical principles of creating new materials with purposeful properties for their specific [...] Read more.

This Special Issue titled “Photocatalytic Nanocomposite Materials” (PNMs) is devoted to the research into new-generation PNMs, particularly for the processes of solar radiation energy conversion with its focus lying on the physicochemical principles of creating new materials with purposeful properties for their specific applications [...] Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Rice Crust-Like ZnO/Ti₃C₂T_x MXene Hybrid Structures for Improved Photocatalytic Activity

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Qui Thanh Hoai Ta

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Nghe My Tran

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Jin-Seo Noh

Catalysts 2020, 10(10), 1140; https://doi.org/10.3390/catal10101140 - 02 Oct 2020

Cited by 28 | Viewed by 3169

Abstract

Novel two-dimensional ZnO/Ti₃C₂T_x hybrid photocatalysts with modified surface areas were prepared using a simple calcination technique. The microstructures, crystalline features, and bonding states of the ZnO structure-covered Ti₃C₂T_x MXenes were closely characterized using [...] Read more.

Novel two-dimensional ZnO/Ti₃C₂T_x hybrid photocatalysts with modified surface areas were prepared using a simple calcination technique. The microstructures, crystalline features, and bonding states of the ZnO structure-covered Ti₃C₂T_x MXenes were closely characterized using various tools. The photoluminescence intensity of the hybrid photocatalyst was greatly reduced compared to the pristine ZnO, while its Brunauer-Emmett-Teller (BET) surface area increased by more than 100 times. Under solar light illumination, the photocatalytic degradation efficiency of the hybrid photocatalyst for organic pollutants (MO, RhB) appeared to be three-fold larger as compared to pristine ZnO. The superb photocatalytic performance of the photocatalyst was attributed to several factors, such as ideal band alignment, Schottky barrier formation, and large surface area. Moreover, the ZnO/Ti₃C₂T_x hybrid photocatalyst showed excellent cycling stability. These results suggest that the novel hybrid structure may be a potential candidate for removing organic pollutants in wastewater. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessFeature PaperArticle

Dynamics of Photogenerated Charge Carriers in TiO₂/MoO₃, TiO₂/WO₃ and TiO₂/V₂O₅ Photocatalysts with Mosaic Structure

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Alexander I. Kokorin

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Tatyana V. Sviridova

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Elizaveta A. Konstantinova

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Dmitry V. Sviridov

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Detlef W. Bahnemann

Catalysts 2020, 10(9), 1022; https://doi.org/10.3390/catal10091022 - 04 Sep 2020

Cited by 9 | Viewed by 2633

Abstract

Titania is a widely used photocatalytic material possessing such advantages as low cost and high reactivity under the ultraviolet light illumination. However, the fast recombination of photoexcited charge carriers limits its application. Herein, we have synthesized original nanomaterials with mosaic structures that exhibited [...] Read more.

Titania is a widely used photocatalytic material possessing such advantages as low cost and high reactivity under the ultraviolet light illumination. However, the fast recombination of photoexcited charge carriers limits its application. Herein, we have synthesized original nanomaterials with mosaic structures that exhibited well-defined heterojunctions and new properties. Using SEM, XRD, EPR spectroscopy, photocatalytic measurements, and photoinduced pathphysiological activity of these photocatalysts, we studied the processes of charge carrier accumulation in TiO₂/MoO₃, TiO₂/WO₃, and TiO₂/V₂O₅ under in situ UV illumination with emphasis on the charge exchange between energy levels of these nanosized semiconductors. It is shown that the accumulation of photoinduced charges occurs in two forms (i) filled electron traps corresponding to Ti⁴⁺/Ti³⁺ levels and (ii) Mo⁵⁺ centers, both forms contributing to the photoinduced biocide activity of the samples. This work demonstrates that light exposure of heterostructure photocatalysts with mosaic surfaces produces different types of charge-trapping centers capable of interacting with molecular oxygen yielding peroxo species, which provide long-life light-induced ”self-cleaning” behavior. Such photoaccumulating materials open new opportunities in developing light-driven self-sterilization structures exhibiting a prolonged bactericidal effect up to 10 h after stopping light exposure. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Examination of Photocatalyzed Chlorophenols for Sequential Photocatalytic-Biological Treatment Optimization

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Liliana Bobirică

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Constantin Bobirică

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Cristina Orbeci

Catalysts 2020, 10(9), 985; https://doi.org/10.3390/catal10090985 - 01 Sep 2020

Cited by 3 | Viewed by 1817

Abstract

Given the known adverse effect of chlorophenols for the aquatic environments which they can reach, the development of efficient methods both technically and economically to remove them has gained increasing attention over time. The combination of photocatalytic oxidation with biological treatment can lead [...] Read more.

Given the known adverse effect of chlorophenols for the aquatic environments which they can reach, the development of efficient methods both technically and economically to remove them has gained increasing attention over time. The combination of photocatalytic oxidation with biological treatment can lead to high removal efficiencies of chlorophenols, while reducing the costs associated with the need to treat large volumes of aqueous solutions. Therefore, the present paper had as its main objective the identification of the minimum photocatalytic oxidation period during which the aqueous solutions of 4-chlorophenol and 2,4-dichlorophenol can be considered as readily biodegradable. Thus, the results of photocatalytic oxidation and biodegradability tests showed that, regardless of the concentration of chlorophenol and its type, the working solutions become readily biodegradable after up to 120 min of irradiation in ultraviolet light. At this irradiation time, the maximum organic content of the aqueous solution is less than 40%, and the biochemical oxygen demand and chemical oxygen demand (BOD/COD) ratio is much higher than 0.4. The maximum specific heterotrophic growth rate of activated sludge has an average value of 4.221 d⁻¹ for 4-chlorophenol, and 3.126 d⁻¹ for 2,4-dichlorophenol. This irradiation period represents at most half of the total irradiation period necessary for the complete mineralization of the working solutions. The results obtained were correlated with the intermediates identified during the photocatalytic oxidation. It seems that, working solutions initially containing 4-chlorophenol can more easily form readily biodegradable intermediates. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Noble Metal Modification of CdS-Covered CuInS₂ Electrodes for Improved Photoelectrochemical Activity and Stability

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Toshihiro Takashima

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Yukitaka Fujishiro

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Hiroshi Irie

Catalysts 2020, 10(9), 949; https://doi.org/10.3390/catal10090949 - 20 Aug 2020

Cited by 12 | Viewed by 2518

Abstract

In this paper, efficient and stable photoelectrochemical (PEC) hydrogen (H₂) evolution using copper indium sulfide (CuInS₂) thin film electrodes was studied. Modification with a cadmium sulfide (CdS) layer led to improved charge separation at the interface between CuInS₂ [...] Read more.

In this paper, efficient and stable photoelectrochemical (PEC) hydrogen (H₂) evolution using copper indium sulfide (CuInS₂) thin film electrodes was studied. Modification with a cadmium sulfide (CdS) layer led to improved charge separation at the interface between CuInS₂ and CdS; however, the photocorrosive nature of CdS induced poor stability of the photocathode. Further surface coating with an electrodeposited Pt layer over the CdS-covered CuInS₂ photocathode prevented the CdS layer from making contact with the electrolyte solution, and enabled efficient PEC H₂ evolution without appreciable degradation. This indicates that the Pt layer functioned not only as a reaction site for H₂ evolution, but also as a protection layer. In addition, it was found that surface protection using a noble metal layer was also effective for stable PEC carbon dioxide (CO₂) reduction when appropriate noble metal cocatalysts were selected. When Au or Ag was used, carbon monoxide was obtained as a product of PEC CO₂ reduction. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Curcumin Doped SiO₂/TiO₂ Nanocomposites for Enhanced Photocatalytic Reduction of Cr (VI) under Visible Light

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Catalysts 2020, 10(8), 942; https://doi.org/10.3390/catal10080942 - 17 Aug 2020

Cited by 10 | Viewed by 2289

Abstract

In order to further improve the photocatalytic performance of the SiO₂/TiO₂ composite under visible light irradiation, curcumin-doped SiO₂/TiO₂ nanocomposites were synthesized via directly incorporating it into the structure of SiO₂/TiO₂ during the synthesis using [...] Read more.

In order to further improve the photocatalytic performance of the SiO₂/TiO₂ composite under visible light irradiation, curcumin-doped SiO₂/TiO₂ nanocomposites were synthesized via directly incorporating it into the structure of SiO₂/TiO₂ during the synthesis using an inexpensive and readily available natural pigment (curcumin) as doping agent. The physicochemical properties of SiO₂/TiO₂ nanocomposites were characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform-infrared spectroscopy, N₂ adsorption–desorption isotherms, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The results indicate that all SiO₂/TiO₂ nanocomposites exhibited an anatase phase with a typical mesoporous structure. It was found that the dope of curcumin in the SiO₂/TiO₂ composite could decrease the crystal size, slightly improve the specific surface areas, significantly enhance the visible light absorption, and effectively narrow the band gap energy from 3.04 to 10(eV). Compared with bare SiO₂/TiO₂, the curcumin-doped SiO₂/TiO₂ resulted in enhanced photocatalytic reduction activity for Cr(VI) under visible light irradiation, and the CTS (12) sample with the appropriate content of curcumin of 12 wt % shows the photocatalytic yield reaching 100% within 2.5 hours, which is larger than CT (12) without silica. This could be attributed to the curcumin doping and the synergetic effects of SiO₂ and TiO₂ in SiO₂/TiO₂ nanocomposites. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Tunable Composition Aqueous-Synthesized Mixed-Phase TiO₂ Nanocrystals for Photo-Assisted Water Decontamination: Comparison of Anatase, Brookite and Rutile Photocatalysts

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Konstantina Chalastara

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Fuqiang Guo

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Samir Elouatik

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George P. Demopoulos

Catalysts 2020, 10(4), 407; https://doi.org/10.3390/catal10040407 - 08 Apr 2020

Cited by 38 | Viewed by 3573

Abstract

Mixed-phase nanoTiO₂ materials attract a lot of attention as advanced photocatalysts for water decontamination due to their intrinsic structure that allows better photo-excited e⁻_cb-h⁺_vb charge separation, hence improved photocatalytic efficiency. Currently, the best-known mixed-phase TiO₂ photocatalyst [...] Read more.

Mixed-phase nanoTiO₂ materials attract a lot of attention as advanced photocatalysts for water decontamination due to their intrinsic structure that allows better photo-excited e⁻_cb-h⁺_vb charge separation, hence improved photocatalytic efficiency. Currently, the best-known mixed-phase TiO₂ photocatalyst is P25 with approximate composition 80% Anatase/20% Rutile (A_/r). Apart from Anatase (A) and Rutile (R) phases, there is Brookite (B) which has been evaluated less as photocatalyst in mixed-phase nanoTiO₂ systems. In this work we present a sustainable solution process to synthesize tunable composition mixed-phase nanotitania photocatalysts in a continuously stirred tank reactor (CSTR) by modulating conditions like pH, C_TiCl4 and time. In particular three mixed-phase TiO₂ nanomaterials were produced, namely one predominantly anatase with brookite as minor component (A_/b), one predominantly brookite with minor component rutile (B_/r), and one predominantly rutile with minor component brookite (R_/b) and evaluated as photocatalysts in the degradation of methyl orange. The three semiconducting nanomaterials were characterized by XRD and Raman spectroscopy to quantify the phase ratios and subjected to nano-morphological characterization by FE-SEM and TEM/HR-TEM. The new mixed-phase nanoTiO₂ materials are shown to be endowed with large specific surface area, ranging from 90–125 m² g⁻¹, double of that of P25, to be mesoporous and be surface-rich in Ti–OH molecular groups varying from 12%–20% versus 4% for P25. These properties though impact the adsorptive capacity with R_/b and B_/r removing > 50% of MO but not photocatalytic activity. The latter depends on nanograined mixed-phase structure and not mere assembly of different phase nanoparticles. First-order rate constants reveal essentially equivalent photocatalytic activity for anatase nanocrystals with either rutile (P25) or brookite (this work) domains. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessEditor’s ChoiceArticle

Enhanced Visible-Light Photocatalysis of Nanocomposites of Copper Oxide and Single-Walled Carbon Nanotubes for the Degradation of Methylene Blue

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Catalysts 2020, 10(3), 297; https://doi.org/10.3390/catal10030297 - 05 Mar 2020

Cited by 36 | Viewed by 4443

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We report enhanced catalytic action of a series of copper(II)-oxide-single-walled carbon nanotube (CuO-SWCNT) composite photocatalysts (abbreviated as CuO-SWCNT-0.5, CuO-SWCNT-2, and CuO-SWCNT-5, where 0.5, 2, and 5 represent the calcination time in hours) synthesized via recrystallization followed by calcination. The photocatalytic performance of the [...] Read more.

We report enhanced catalytic action of a series of copper(II)-oxide-single-walled carbon nanotube (CuO-SWCNT) composite photocatalysts (abbreviated as CuO-SWCNT-0.5, CuO-SWCNT-2, and CuO-SWCNT-5, where 0.5, 2, and 5 represent the calcination time in hours) synthesized via recrystallization followed by calcination. The photocatalytic performance of the fabricated nanocomposites was examined by evaluating the degradation of methylene blue (MB) under irradiation with visible light. All of the as-fabricated nanocomposites were effective photocatalysts for the photodegradation of a MB solution; however, the CuO-SWCNT-5 displayed the best photocatalytic ability among the investigated catalysts, achieving 97.33% degradation of MB in 2 h under visible-light irradiation. The photocatalytic action of the nanocomposites was remarkably higher than that of pristine CuO nanocrystals fabricated using the same route. The recyclability of the photocatalyst was also investigated; the CuO-SWCNT-5 catalyst could be reused for three cycles without substantial degradation of its catalytic performance or morphology. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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The Effect of Carbon Content on Methanol Oxidation and Photo-Oxidation at Pt-TiO₂-C Electrodes

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Athanasios Papaderakis

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Catalysts 2020, 10(2), 248; https://doi.org/10.3390/catal10020248 - 19 Feb 2020

Cited by 12 | Viewed by 3141

Abstract

The oxidation of methanol is studied at TiO₂-supported Pt electrodes of varied high surface area carbon content (in the 30-5% w/w range) and C÷Ti atom ratio (in the 3.0-0.4 ratio). The Pt-TiO₂ catalyst is prepared by a photo-deposition process and [...] Read more.

The oxidation of methanol is studied at TiO₂-supported Pt electrodes of varied high surface area carbon content (in the 30-5% w/w range) and C÷Ti atom ratio (in the 3.0-0.4 ratio). The Pt-TiO₂ catalyst is prepared by a photo-deposition process and C nanoparticles (Vulcan XC72R) are added by simple ultrasonic mixing. The optimum C÷Ti atom ratio of the prepared catalyst for methanol electro-oxidation is found to be 1.5, resulting from the interplay of C properties (increased electronic conductivity and methanol adsorption), those of TiO₂ (synergistic effect on Pt and photo-activity), as well as the catalyst film thickness. The intrinsic catalytic activity of the best Pt-TiO₂/C catalyst is better than that of a commercial Pt/C catalyst and could be further improved by nearly 25% upon UV illumination, whose periodic application can also limit current deterioration. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Preparation of Quasi-MIL-101(Cr) Loaded Ceria Catalysts for the Selective Catalytic Reduction of NO_x at Low Temperature

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Catalysts 2020, 10(1), 140; https://doi.org/10.3390/catal10010140 - 20 Jan 2020

Cited by 17 | Viewed by 2741

Abstract

At present, the development of novel catalysts with high activity Selective Catalytic Reduction (SCR) reaction at the low temperature is still a challenge. In this work, the authors prepare CeO₂/quasi-MIL-101 catalysts with various amounts of deposited ceria by a double-solvent method, [...] Read more.

At present, the development of novel catalysts with high activity Selective Catalytic Reduction (SCR) reaction at the low temperature is still a challenge. In this work, the authors prepare CeO₂/quasi-MIL-101 catalysts with various amounts of deposited ceria by a double-solvent method, which are characterized by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and so on. The results show that the increase of Ce content has a great influence on the catalytic property of the catalyst. The introduction of Ce can promote the conversion between Cr³⁺ and Cr⁵⁺ and increase the proportion of lattice oxygen, which improves the activity of the catalyst. However, the catalyst will be peroxidized when the content of Ce is too high, resulting in the decline of the catalytic activity. This experiment indicates that CeO₂/quasi-MIL-101 plays a significant role in the NH₃-SCR process at the low temperature when the loading of Ce is 0.5%. This work has proved the potential of this kind of material in NH₃-SCR process at the low temperature, providing help for subsequent studies. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Structural Evolution of Ni-Based Co-Catalysts on [Ca₂Nb₃O₁₀]⁻ Nanosheets during Heating and Their Photocatalytic Properties

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Catalysts 2020, 10(1), 13; https://doi.org/10.3390/catal10010013 - 20 Dec 2019

Cited by 5 | Viewed by 3504

Abstract

Nickel compounds are among the most frequently used co-catalysts for photocatalytic water splitting. By loading Ni(II) precursors, submonolayer Ni(OH)₂ was uniformly distributed onto photocatalytic [Ca₂Nb₃O₁₀]⁻ nanosheets. Further heating of the nanocomposite was studied both ex [...] Read more.

Nickel compounds are among the most frequently used co-catalysts for photocatalytic water splitting. By loading Ni(II) precursors, submonolayer Ni(OH)₂ was uniformly distributed onto photocatalytic [Ca₂Nb₃O₁₀]⁻ nanosheets. Further heating of the nanocomposite was studied both ex situ in various gas environments and in situ under vacuum in the scanning transmission electron microscope. During heating in non-oxidative environments including H₂, argon and vacuum, Ni nanoparticles form at ≥200 °C, and they undergo Ostwald ripening at ≥500 °C. High resolution imaging and electron energy loss spectroscopy revealed a NiO shell around the Ni core. Ni loading of up to 3 wt% was demonstrated to enhance the rates of photocatalytic hydrogen evolution. After heat treatment, a further increase in the reaction rate can be achieved thanks to the Ni core/NiO shell nanoparticles and their large separation. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessFeature PaperArticle

Photoelectrochemical Behavior of the Ternary Heterostructured Systems CdS/WO₃/TiO₂

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Catalysts 2019, 9(12), 999; https://doi.org/10.3390/catal9120999 - 27 Nov 2019

Cited by 9 | Viewed by 3335

Abstract

In this article, we report the results of comparative studies of photoelectrochemical behavior of the binary CdS/TiO₂ and WO₃/TiO₂ and ternary CdS/WO₃/TiO₂ heterostructures based on titania nanotube and planar structures. Physical–chemical characterization by XRD, XPS, and [...] Read more.

In this article, we report the results of comparative studies of photoelectrochemical behavior of the binary CdS/TiO₂ and WO₃/TiO₂ and ternary CdS/WO₃/TiO₂ heterostructures based on titania nanotube and planar structures. Physical–chemical characterization by XRD, XPS, and electron microscopy methods together with electrochemical impedance spectroscopy measurements confirm a successful formation of heterostructured electrodes, both nanotube-based and planar. The results of photoelectrochemical studies of the heterostructures demonstrate a significant difference in their behavior depending on the structure geometry and the character of the formed heterojunctions. It is concluded that nanotube-based heterostructure electrodes can be characterized by a stochastic set of different heterojunctions while planar systems demonstrate well-ordered heterojunctions with a strictly defined electron transfer direction. Particularly, we demonstrate the possibility of the realization of Z-scheme of photoexcitation and charge separation in ternary planar systems under visible light irradiation. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Hydrogen Production from Aqueous Methanol Solutions Using Ti–Zr Mixed Oxides as Photocatalysts under UV Irradiation

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Alejandro Pérez-Larios

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Jose L. Rico

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Luis M. Anaya-Esparza

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O.A. González Vargas

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Napoleón González-Silva

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Ricardo Gómez

Catalysts 2019, 9(11), 938; https://doi.org/10.3390/catal9110938 - 08 Nov 2019

Cited by 11 | Viewed by 2120

Abstract

The synthesis and characterisation of Ti–Zr mixed oxides containing 1 to 10 wt.% of Zr is herein reported. In addition, the samples were tested as photocatalysts in the generation of hydrogen from aqueous methanol solutions. The solids were prepared by sol-gel and then [...] Read more.

The synthesis and characterisation of Ti–Zr mixed oxides containing 1 to 10 wt.% of Zr is herein reported. In addition, the samples were tested as photocatalysts in the generation of hydrogen from aqueous methanol solutions. The solids were prepared by sol-gel and then characterised by X-ray diffraction, high resolution electron microscopy, X-ray photoelectron spectroscopy, physisorption of nitrogen, scanning electron microscopy, UV-vis and Raman spectroscopies. The results show the presence of anatase as a predominant structure and the oxides present larger specific surface areas than that of pure titania. A maximum value of 168 m²/g was determined for the sample with 5 wt.% of zirconium. The calculated band gap energies varied from 3.05 to 3.15 eV. It was observed that the greater the zirconium content in the solid, the higher the generation rate of hydrogen when testing the Ti–Zr solids as photocatalysts. Under our experimental conditions, the best catalyst, Ti–Zr oxide with 10 wt.% Zr, showed a production rate of 2100 μmol of H₂/h which was about tenfold higher than that observed for pure titania. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Cooperative Catalytic Behavior of SnO₂ and NiWO₄ over BiVO₄ Photoanodes for Enhanced Photoelectrochemical Water Splitting Performance

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Maged N. Shaddad

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Prabhakarn Arunachalam

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Mahmoud Hezam

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Abdullah M. Al-Mayouf

Catalysts 2019, 9(11), 879; https://doi.org/10.3390/catal9110879 - 23 Oct 2019

Cited by 11 | Viewed by 3243

Abstract

n-BiVO₄ is a favorable photoelectrode candidate for a photoelectrochemical (PEC) water splitting reaction owing to its suitable energy level edge locations for an oxygen evolution reaction. On the other hand, the sluggish water oxidation kinetics of BiVO₄ photoanodes when used individually [...] Read more.

n-BiVO₄ is a favorable photoelectrode candidate for a photoelectrochemical (PEC) water splitting reaction owing to its suitable energy level edge locations for an oxygen evolution reaction. On the other hand, the sluggish water oxidation kinetics of BiVO₄ photoanodes when used individually make it necessary to use a hole blocking layer as well as water oxidation catalysts to overcome the high kinetic barrier for the PEC water oxidation reaction. Here, we describe a very simple synthetic strategy to fabricate nanocomposite photoanodes that synergistically address both of these critical limitations. In particular, we examine the effect of a SnO₂ buffer layer over BiVO₄ films and further modify the photoanode surface with a crystalline nickel tungstate (NiWO₄) nanoparticle film to boost PEC water oxidation. When NiWO₄ is incorporated over BiVO₄/SnO₂ films, the PEC performance of the resultant triple-layer NiWO₄/BiVO₄/SnO₂ films for the oxygen evolution reaction (OER) is further improved. The enhanced performance for the PEC OER is credited to the synergetic effect of the individual layers and the introduction of a SnO₂ buffer layer over the BiVO₄ film. The optimized NiWO₄/BiVO₄/SnO₂ electrode demonstrated both enriched visible light absorption and achieves charge separation and transfer efficiencies of 23% and 30%, respectively. The photoanodic current density for the OER on optimized NiWO₄/BiVO₄/SnO₂ photoanode shows a maximum photocurrent of 0.93 mA/cm² at 1.23 V vs. RHE in a phosphate buffer solution (pH~7.5) under an AM1.5G solar simulator, which is an incredible five-fold and two-fold enhancement compared to its parent BiVO₄ photoanode and BiVO₄/SnO₂ photoanodes, respectively. Further, the incorporation of the NiWO₄ co-catalyst over the BiVO₄/SnO₂ film increases the interfacial electron transfer rate across the composite/solution interface. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Immobilized rGO/TiO₂ Photocatalyst for Decontamination of Water

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Catalysts 2019, 9(9), 708; https://doi.org/10.3390/catal9090708 - 23 Aug 2019

Cited by 25 | Viewed by 3596

Abstract

The preparation of immobilized graphene-based photocatalyst layers is highly desired for environmental applications. In this study, the preparation of an immobilized reduced graphene oxide (rGO)/TiO₂ composite by electrophoretic deposition (EPD) was optimized. It enabled quantitative deposition without sintering and without the use [...] Read more.

The preparation of immobilized graphene-based photocatalyst layers is highly desired for environmental applications. In this study, the preparation of an immobilized reduced graphene oxide (rGO)/TiO₂ composite by electrophoretic deposition (EPD) was optimized. It enabled quantitative deposition without sintering and without the use of any dispersive additive. The presence of rGO had beneficial effects on the photocatalytic degradation of 4-chlorophenol in an aqueous solution. A marked increase in the photocatalytic degradation rate was observed, even at very low concentrations of rGO. Compared with the TiO₂ and GO/TiO₂ reference layers, use of the rGO/TiO₂ composite (0.5 wt% of rGO) increased the first-order reaction rate constant by about 70%. This enhanced performance was due to the increased formation of hydroxyl radicals that attacked the 4-chlorophenol molecules. The direct charge transfer mechanism had only limited effect on the degradation. Thus, EPD-prepared rGO/TiO₂ layers appear to be suitable for environmental application. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Photodegradation of Herbicide Imazapyr and Phenol over Mesoporous Bicrystalline Phases TiO₂: A Kinetic Study

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Mohamed Faycal Atitar

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Adel. A. Ismail

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Ralf Dillert

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Detlef W. Bahnemann

Catalysts 2019, 9(8), 640; https://doi.org/10.3390/catal9080640 - 27 Jul 2019

Cited by 13 | Viewed by 2256

Abstract

Mesoporous TiO₂ nanoparticles were synthesized at different temperatures (400–800 °C). The resulting mesoporous anatase–rutile TiO₂ mixtures between 27 and 82% were found to have different structural properties (morphology, mesoporosity, crystallite phases, and sizes) affected through the calcination process. They were tested [...] Read more.

Mesoporous TiO₂ nanoparticles were synthesized at different temperatures (400–800 °C). The resulting mesoporous anatase–rutile TiO₂ mixtures between 27 and 82% were found to have different structural properties (morphology, mesoporosity, crystallite phases, and sizes) affected through the calcination process. They were tested for the photocatalytic degradation of the herbicides imazapyr and phenol, compared with the nonporous TiO₂ P-25. The present work is an extension of a previously published study discussing the influence of the rutile content on the photocatalytic performance of the nanocrystals, based on the modified first order kinetic model, where the degradation rate is a function of the specific surface area of the material. The apparent degradation rate using T-800 is 10-fold higher than in the case using TiO₂ P-25. The material with the lowest anatase content (T-800) exhibits the highest photocatalytic activity in terms of initial reaction rate per unit surface area. It is considered that mixed-phase photocatalysts with rutile–anatase exhibit enhanced photoactivity with the increase of the rutile proportion. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Facile Synthesis of Heterojunctioned ZnO/Bi₂S₃ Nanocomposites for Enhanced Photocatalytic Reduction of Aqueous Cr(VI) under Visible-Light Irradiation

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Catalysts 2019, 9(7), 624; https://doi.org/10.3390/catal9070624 - 21 Jul 2019

Cited by 27 | Viewed by 3831

Abstract

Heterojunctioned ZnO/Bi₂S₃ nanocomposites were prepared via a facile solvothermal method. The obtained photocatalysts were characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), and [...] Read more.

Heterojunctioned ZnO/Bi₂S₃ nanocomposites were prepared via a facile solvothermal method. The obtained photocatalysts were characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), and Photoelectrochemical and Photoluminescence spectroscopy (PL), respectively. The results showed that ZnO/Bi₂S₃ composites exhibited the sandwiched-like structure, where ZnO nanoparticles were randomly embedded between Bi₂S₃ nanoflakes. The performance of photocatalytic Cr(VI) reduction under visible light indicated that ZnO/Bi₂S₃ composites exhibited high-efficiency photocatalytic activity in comparison with either Bi₂S₃ or ZnO. The 5%-ZnO/Bi₂S₃ photocatalyst removed 96% of Cr(VI) within 120 min at 20 mg/L initial concentration of Cr(VI). The enhanced performance of ZnO/Bi₂S₃ photocatalysts could be ascribed to the increased light harvesting and the effective separation and transfer of the photogenerated charge carriers across the heterojunction interface of the ZnO/Bi₂S₃ composite. This work could pave the way for the design of new hetero-structured materials and has great potential in environmental remediation. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

AgBr/(Sr_0.6Bi_0.305)₂Bi₂O₇ Heterostructured Composites: Fabrication, Characterization, and Significantly Enhanced Photocatalytic Activity

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Catalysts 2019, 9(5), 394; https://doi.org/10.3390/catal9050394 - 26 Apr 2019

Cited by 5 | Viewed by 2658

Abstract

The pyrochlore-type (Sr_0.6Bi_0.305)₂Bi₂O₇ (SBO) containing Bi³⁺ and Bi⁵⁺ mixed valent states was first investigated as a photocatalyst in our very recent work. To further improve the photocatalytic performance, AgBr/SBO heterostructured composites were [...] Read more.

The pyrochlore-type (Sr_0.6Bi_0.305)₂Bi₂O₇ (SBO) containing Bi³⁺ and Bi⁵⁺ mixed valent states was first investigated as a photocatalyst in our very recent work. To further improve the photocatalytic performance, AgBr/SBO heterostructured composites were synthesized by using a deposition-precipitation method. The characterization of phase structure, morphology, microstructure, elemental composition, and optical properties of the obtained products were performed using X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM)TEM, X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (UV-vis DRS). The photocatalytic activity of samples was evaluated by degrading methylene blue under visible light illumination. AgBr/SBO composites possess high stability and significantly enhanced photocatalytic performance. The improvement of photocatalytic activity is due to the enhanced light absorption and the separation of photoinduced electrons and holes on the interface of AgBr/SBO heterostructured composites. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

MoS₂/CdS Heterostructure for Enhanced Photoelectrochemical Performance under Visible Light

by

Guannan He

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Yimin Zhang

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Qinyu He

Catalysts 2019, 9(4), 379; https://doi.org/10.3390/catal9040379 - 23 Apr 2019

Cited by 31 | Viewed by 4725

Abstract

High-rate recombination of photogenerated electron and hole pairs will lead to low photocatalytic activity. Constructing heterostructure is a way to address this problem and thus increase the photoelectrochemical performance of the photocatalysts. In this article, molybdenum sulfide (MoS₂)/cadmium sulfide (CdS) nanocomposites [...] Read more.

High-rate recombination of photogenerated electron and hole pairs will lead to low photocatalytic activity. Constructing heterostructure is a way to address this problem and thus increase the photoelectrochemical performance of the photocatalysts. In this article, molybdenum sulfide (MoS₂)/cadmium sulfide (CdS) nanocomposites were fabricated by a facile solvothermal method after sonication. The CdS nanoparticles immobilized on the MoS₂ sheet retained the original crystal structure and morphology. The composites exhibit higher photoelectrochemical properties compared with pure MoS₂ nanosheets or CdS powder. When the precursor concentration of CdS is 0.015 M, the MoS₂/CdS composites yield the highest photocurrent, which is enhanced nearly five times compared with pure CdS or MoS₂. The improved photoelectrochemical performance can be ascribed to the increase of light harvest, as well as to the heterostructure that decreases the recombination rate of the photogenerated electron and hole pairs. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Characterization and Effect of Ag(0) vs. Ag(I) Species and Their Localized Plasmon Resonance on Photochemically Inactive TiO₂

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Chanel Tri Handoko

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Nikolaos G. Moustakas

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Muhammad Djoni Bustan

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Bambang Yudono

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Fakhili Gulo

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Jennifer Strunk

Catalysts 2019, 9(4), 323; https://doi.org/10.3390/catal9040323 - 02 Apr 2019

Cited by 19 | Viewed by 3319

Abstract

Commercial TiO₂ (anatase) was successfully modified with Ag nanoparticles at different nominal loadings (1%–4%) using a liquid impregnation method. The prepared materials retained the anatase structure and contained a mixture of Ag⁰ and Ag^I species. Samples exhibited extended light absorption [...] Read more.

Commercial TiO₂ (anatase) was successfully modified with Ag nanoparticles at different nominal loadings (1%–4%) using a liquid impregnation method. The prepared materials retained the anatase structure and contained a mixture of Ag⁰ and Ag^I species. Samples exhibited extended light absorption to the visible region. The effect of Ag loading on TiO₂ is studied for the photocatalytic reduction of CO₂ to CH₄ in a gas–solid process under high-purity conditions. It is remarkable that the reference TiO₂ used in this work is entirely inactive in this reaction, but it allows for studying the effect of Ag on the photocatalytic process in more detail. Only in the case of 2% Ag/TiO₂ was the formation of CH₄ from CO₂ observed. Using different light sources, an influence of the localized surface plasmon resonance (LSPR) effect of Ag is verified. A sample in which all Ag has been reduced to the metallic state was less active than the respective sample containing both Ag⁰ and Ag⁺, indicating that a mixed oxidation state is beneficial for photocatalytic performance. These results contribute to a better understanding of the effect of metal modification of TiO₂ in photocatalytic CO₂ reduction. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Enhanced Visible Light Photocatalytic Reduction of Cr(VI) over a Novel Square Nanotube Poly(Triazine Imide)/TiO₂ Heterojunction

by

Xin Yan

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Guotao Ning

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Peng Zhao

Catalysts 2019, 9(1), 55; https://doi.org/10.3390/catal9010055 - 08 Jan 2019

Cited by 13 | Viewed by 3533

Abstract

Hexavalent chromium Cr(VI) pollution makes has a harmful impact on human health and the ecological environment. Photocatalysis reduction technology exhibits low energy consumption, high reduction efficiency and stable performance, and is playing an increasingly important role in chromium pollution control. Graphite-phase carbon nitride [...] Read more.

Hexavalent chromium Cr(VI) pollution makes has a harmful impact on human health and the ecological environment. Photocatalysis reduction technology exhibits low energy consumption, high reduction efficiency and stable performance, and is playing an increasingly important role in chromium pollution control. Graphite-phase carbon nitride has been used to reduce Cr(VI) to the less harmful Cr(III) due to its visible light catalytic activity, chemical stability and low cost. However, it has a low specific surface area and fast recombination of electron–hole pairs, which severely restrict its practical application. In this work, a TiO₂-modified poly(triazine imide) (PTI) square nanotube was prepared by the one-step molten salts method. The results showed the PTI had a square hollow nanotube morphology, with an about 100–1000 nm width and 60–70 nm thickness. During the formation of the PTI square tube, TiO₂ nanoparticles adhere to the surface of the square tube wall by strong adsorption, and eventually form a PTI/TiO₂ heterojunction. The PTI/TiO₂-7 wt% heterojunction exhibited very good Cr(VI) reduction efficiency within 120 min. The enhanced photocatalytic activity was mainly attributed to the efficient separation and transport of photo-induced electron–hole pairs and the high specific surface area in the heterojunction structure. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessArticle

Network Structured CuWO₄/BiVO₄/Co-Pi Nanocomposite for Solar Water Splitting

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Catalysts 2018, 8(12), 663; https://doi.org/10.3390/catal8120663 - 17 Dec 2018

Cited by 15 | Viewed by 5051

Abstract

A network structured CuWO₄/BiVO₄ nanocomposite with a high specific surface area was prepared from CuWO₄ nanoflake (NF) arrays via a method that combined drop-casting and thermal annealing. The obtained CuWO₄/BiVO₄ exhibited high catalytic activity toward photoelectrochemical [...] Read more.

A network structured CuWO₄/BiVO₄ nanocomposite with a high specific surface area was prepared from CuWO₄ nanoflake (NF) arrays via a method that combined drop-casting and thermal annealing. The obtained CuWO₄/BiVO₄ exhibited high catalytic activity toward photoelectrochemical (PEC) water oxidation. When cobalt phosphate (Co-Pi) was coupled with CuWO₄/BiVO₄, the activity of the resulting CuWO₄/BiVO₄/Co-Pi composite for the oxygen evolution reaction (OER) was further improved. The photocurrent density (J_ph) for OER on CuWO₄/BiVO₄/Co-Pi is among the highest reported on a CuWO₄-based photoanode in a neutral solution. The high activity for the PEC OER was attributed to the high specific surface area of the composite, the formation of a CuWO₄/BiVO₄ heterojunction that accelerated electron–hole separation, and the coupling of the Co-Pi co-catalyst with CuWO₄/BiVO₄, which improved the charge transfer rate across composite/solution interface. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Review

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Open AccessFeature PaperReview

Photoactive Heterostructures: How They Are Made and Explored

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Catalysts 2021, 11(2), 294; https://doi.org/10.3390/catal11020294 - 23 Feb 2021

Cited by 11 | Viewed by 2454

Abstract

In our review we consider the results on the development and exploration of heterostructured photoactive materials with major attention focused on what are the better ways to form this type of materials and how to explore them correctly. Regardless of what type of [...] Read more.

In our review we consider the results on the development and exploration of heterostructured photoactive materials with major attention focused on what are the better ways to form this type of materials and how to explore them correctly. Regardless of what type of heterostructure, metal–semiconductor or semiconductor–semiconductor, is formed, its functionality strongly depends on the quality of heterojunction. In turn, it depends on the selection of the heterostructure components (their chemical and physical properties) and on the proper choice of the synthesis method. Several examples of the different approaches such as in situ and ex situ, bottom-up and top-down, are reviewed. At the same time, even if the synthesis of heterostructured photoactive materials seems to be successful, strong experimental physical evidence demonstrating true heterojunction formation are required. A possibility for obtaining such evidence using different physical techniques is discussed. Particularly, it is demonstrated that the ability of optical spectroscopy to study heterostructured materials is in fact very limited. At the same time, such experimental techniques as high-resolution transmission electron microscopy (HRTEM) and electrophysical methods (work function measurements and impedance spectroscopy) present a true signature of heterojunction formation. Therefore, whatever the purpose of heterostructure formation and studies is, the application of HRTEM and electrophysical methods is necessary to confirm that formation of the heterojunction was successful. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessFeature PaperReview

Photocatalytic Nanocomposite Materials Based on Inorganic Polymers (Geopolymers): A Review

by

Mahroo Falah

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Kenneth J. D. MacKenzie

Catalysts 2020, 10(10), 1158; https://doi.org/10.3390/catal10101158 - 09 Oct 2020

Cited by 14 | Viewed by 3014

Abstract

Geopolymers are ecologically-friendly inorganic materials which can be produced at low temperatures from industrial wastes such as fly ash, blast furnace slags or mining residues. Although to date their principal applications have been seen as alternatives to Portland cement building materials, their properties [...] Read more.

Geopolymers are ecologically-friendly inorganic materials which can be produced at low temperatures from industrial wastes such as fly ash, blast furnace slags or mining residues. Although to date their principal applications have been seen as alternatives to Portland cement building materials, their properties make them suitable for a number of more advanced applications, including as photocatalytic nanocomposites for removal of hazardous pollutants from waste water or the atmosphere. For this purpose, they can be combined with photocatalytic moieties such as metal oxides with suitable bandgaps to couple with UV or visible radiation, or with carbon nanotubes or graphene. In these composites the geopolymers act as supports for the photoactive components, but geopolymers formed from wastes containing oxides such as Fe₂O₃ show intrinsic photoactive behaviour. This review discusses the structure and formation chemistry of geopolymers and the principles required for their utilisation as photocatalysts. The literature on existing photocatalytic geopolymers is reviewed, suggesting that these materials have a promising potential as inexpensive, efficient and ecologically-friendly candidates for the remediation of toxic environmental pollutants and would repay further development. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessFeature PaperReview

Recent Advances in Niobium-Based Materials for Photocatalytic Solar Fuel Production

by

Barbara Nascimento Nunes

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Osmando Ferreira Lopes

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Antonio Otavio T. Patrocinio

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Detlef W. Bahnemann

Catalysts 2020, 10(1), 126; https://doi.org/10.3390/catal10010126 - 16 Jan 2020

Cited by 53 | Viewed by 6426

Abstract

The search for renewable and clean energy sources is a key aspect for sustainable development as energy consumption has continuously increased over the years concomitantly with environmental concerns caused by the use of fossil fuels. Semiconductor materials have great potential for acting as [...] Read more.

The search for renewable and clean energy sources is a key aspect for sustainable development as energy consumption has continuously increased over the years concomitantly with environmental concerns caused by the use of fossil fuels. Semiconductor materials have great potential for acting as photocatalysts for solar fuel production, a potential energy source able to solve both energy and environmental concerns. Among the studied semiconductor materials, those based on niobium pentacation are still shallowly explored, although the number of publications and patents on Nb(V)-based photocatalysts has increased in the last years. A large variety of Nb(V)-based materials exhibit suitable electronic/morphological properties for light-driving reactions. Not only the extensive group of Nb₂O₅ polymorphs is explored, but also many types of layered niobates, mixed oxides, and Nb(V)-doped semiconductors. Therefore, the aim of this manuscript is to provide a review of the latest developments of niobium based photocatalysts for energy conversion into fuels, more specifically, CO₂ reduction to hydrocarbons or H₂ evolution from water. Additionally, the main strategies for improving the photocatalytic performance of niobium-based materials are discussed. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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Open AccessReview

Polymer Nanocomposites for Photocatalytic Applications

by

Violeta Melinte

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Lenuta Stroea

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Andreea L. Chibac-Scutaru

Catalysts 2019, 9(12), 986; https://doi.org/10.3390/catal9120986 - 24 Nov 2019

Cited by 74 | Viewed by 9150

Abstract

In the present comprehensive review we have specifically focused on polymer nanocomposites used as photocatalytic materials in fine organic reactions or in organic pollutants degradation. The selection of the polymer substrates for the immobilization of the active catalyst particles is motivated by several [...] Read more.

In the present comprehensive review we have specifically focused on polymer nanocomposites used as photocatalytic materials in fine organic reactions or in organic pollutants degradation. The selection of the polymer substrates for the immobilization of the active catalyst particles is motivated by several advantages displayed by them, such as: Environmental stability, chemical inertness and resistance to ultraviolet radiations, mechanical stability, low prices and ease availability. Additionally, the use of polymer nanocomposites as photocatalysts offers the possibility of a facile separation and reuse of the materials, eliminating thus the post-treatment separation processes and implicitly reducing the costs of the procedure. This review covers the polymer-based photocatalytic materials containing the most popular inorganic nanoparticles with good catalytic performance under UV or visible light, namely TiO₂, ZnO, CeO₂, or plasmonic (Ag, Au, Pt, Pd) NPs. The study is mainly targeted on the preparation, photocatalytic activity, strategies directed toward the increase of photocatalytic efficiency under visible light and reuse of the hybrid polymer catalysts. Full article

(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)

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