Catalysts

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10 pages, 968 KiB

Open AccessArticle

Operando Laboratory X-ray Absorption Spectroscopy and UV–Vis Study of Pt/TiO₂ Photocatalysts during Photodeposition and Hydrogen Evolution Reactions

by Elizaveta G. Kozyr, Peter N. Njoroge, Sergei V. Chapek, Viktor V. Shapovalov, Alina A. Skorynina, Anna Yu. Pnevskaya, Alexey N. Bulgakov, Alexander V. Soldatov, Francesco Pellegrino, Elena Groppo, Silvia Bordiga, Lorenzo Mino and Aram L. Bugaev

Catalysts 2023, 13(2), 414; https://doi.org/10.3390/catal13020414 - 15 Feb 2023

Cited by 2 | Viewed by 2197

Abstract

Photocatalytic hydrogen (H₂) production is a promising route for alternative energetics. Understanding structure–activity relationships is a crucial step towards the rational design of photocatalysts, which requires the application of operando spectroscopy under relevant working conditions. We performed an operando investigation on [...] Read more.

Photocatalytic hydrogen (H₂) production is a promising route for alternative energetics. Understanding structure–activity relationships is a crucial step towards the rational design of photocatalysts, which requires the application of operando spectroscopy under relevant working conditions. We performed an operando investigation on a catalytic system during the photodeposition of Pt on TiO₂ and photostimulated H₂ production, using simultaneous laboratory X-ray absorption spectroscopy (XAS), UV–Vis spectroscopy, and mass spectrometry. XAS showed a progressive increase in Pt fluorescence for Pt deposited on TiO₂ for over an hour, which is correlated with the signal of the produced H₂. The final Pt/TiO₂ catalyst contained Pt(0) particles. The electronic features corresponding to the Pt⁴⁺ species in the UV–Vis spectrum of the solution disappear as soon as UV radiation is applied in the presence of formic acid, which acts as a hole scavenger, resulting in the presence of Pt(0) particles in solution. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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12 pages, 3421 KiB

Open AccessArticle

Pulsed-Laser Induced Photolysis of Synthesizing Magnetic Fe₃O₄ Nanoparticles for Visible-Light Photocatalysis

by Bing-Yen Wang, Sheng-Yang Huang, Ya-Shing Hsiao, Pei-Ching Wei, Chia-Man Chou and Vincent K. S. Hsiao

Catalysts 2022, 12(11), 1459; https://doi.org/10.3390/catal12111459 - 17 Nov 2022

Cited by 6 | Viewed by 1587

Abstract

Our report is the first example describing the successful synthesis of magnetic Fe₃O₄ nanoparticles (NPs), for which we used pulsed-laser induced photolysis (PLIP). Compared with the previous method of using pulsed-laser ablation of a target, or strong energy of pulsed-laser [...] Read more.

Our report is the first example describing the successful synthesis of magnetic Fe₃O₄ nanoparticles (NPs), for which we used pulsed-laser induced photolysis (PLIP). Compared with the previous method of using pulsed-laser ablation of a target, or strong energy of pulsed-laser light to decompose precursors in generating a solvated-ion reaction, the PLIP method used here is dependent on hydrogen peroxide (H₂O₂) to generate a hydrolysis reaction. Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used to demonstrate the Fe₃O₄ crystalline structure of the synthesized NPs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed that the average size of the NPs was about 20–50 nm. Regarding their magnetic characteristics, the synthesized NPs exhibited a saturation magnetization of 5.62 emu/g, remanence of 3.82 emu/g, and coercive force of 49.8 Oe. The photocatalytic experiments confirmed that the synthesized magnetic Fe₃O₄ NPs have visible light-degradation effects based on their ability to photocatalytically degrade methylene blue (MB). The MB degradation efficiency was 60–80% under white-light exposure for 180 min. This study presents a new route for synthesizing magnetic Fe₃O₄ NPs for their potential use in photocatalysis. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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12 pages, 2192 KiB

Open AccessArticle

Visible Light-Induced Photocatalyst with Au/TiO₂ Nanocomposites Fabricated through Pulsed Laser-Induced Photolysis

by Bing-Yen Wang, Ya-Shing Hsiao, Pei-Ching Wei, Yuan-Tung Liu, Chih-Chien Chu and Vincent K. S. Hsiao

Catalysts 2022, 12(5), 564; https://doi.org/10.3390/catal12050564 - 20 May 2022

Cited by 6 | Viewed by 2055

Abstract

Gold–titanium oxide nanocomposites (Au–TiO₂ NCPs) were fabricated through pulsed laser-induced photolysis (PIPS) and verified to be usable for the visible light catalytic degradation of methylene blue (MB). The PIPS method can produce a sufficient amount of NCPs quickly and has potential to [...] Read more.

Gold–titanium oxide nanocomposites (Au–TiO₂ NCPs) were fabricated through pulsed laser-induced photolysis (PIPS) and verified to be usable for the visible light catalytic degradation of methylene blue (MB). The PIPS method can produce a sufficient amount of NCPs quickly and has potential to be commercialized. In contrast to other studies, we clarified the optical spectrum of the light sources, including peak power, bandwidth, and total intensity used for photodegradation reactions and discovered that the photodegradation efficiency of the produced Au–TiO₂ NCPs in the wavelength range of 405 nm could reach 37% in 30 min due to the charge transfer between Au and TiO₂. The control experiment shows that the addition of individual Au and TiO₂ nanoparticles (NPs) to an MB solution has no enhancement of degradation ability under visible light illumination. The photodegradation of Au–TiO₂ NCPs can be further improved by increasing the concentrations of auric acid and TiO₂ NPs in a precursor under PIPS fabrication. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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9 pages, 3466 KiB

Open AccessArticle

Reduced Graphene Oxide Supported Zinc Tungstate Nanoparticles as Proficient Electro-Catalysts for Hydrogen Evolution Reactions

by Norah Alhokbany, Tansir Ahamad, Saad M. Alshehri and Jahangeer Ahmed

Catalysts 2022, 12(5), 530; https://doi.org/10.3390/catal12050530 - 09 May 2022

Cited by 2 | Viewed by 1962

Abstract

The nanocomposites of reduced graphene oxide (rGO) supported zinc tungstate nanoparticles (ZnWO₄-NPs) receive considerable attention in electro-catalytic hydrogen evolution reactions (HER) and reveal significantly higher electro-catalytic performances than pure ZnWO₄-NPs in alkaline media (i.e., 0.5 M KOH electrolyte). The [...] Read more.

The nanocomposites of reduced graphene oxide (rGO) supported zinc tungstate nanoparticles (ZnWO₄-NPs) receive considerable attention in electro-catalytic hydrogen evolution reactions (HER) and reveal significantly higher electro-catalytic performances than pure ZnWO₄-NPs in alkaline media (i.e., 0.5 M KOH electrolyte). The polarization studies show that the ZnWO₄-NPs@rGO nanocomposites exhibit low energy loss and good electrode stability during electrochemical reactions for HER. Furthermore, the Tafel slope of ZnWO₄-NPs@rGO nanocomposites is found to be approximately 149 mV/dec, which closely agrees with the reported Tafel values of the noble metal electrocatalyst. In contrast, the performance of the ZnWO₄-NPs@rGO nanocomposite is found to be approximately 1.5 times higher than that of ZnWO₄-NPs in hydrogen production efficiency. Our results emphasize the significance of the nanocomposites with enhanced electro-catalytic activities by lowering the energy loss during electro-catalysis in an alkaline medium. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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19 pages, 4640 KiB

Open AccessArticle

Tailoring g-C₃N₄ with Lanthanum and Cobalt Oxides for Enhanced Photoelectrochemical and Photocatalytic Activity

by Naseer Iqbal

Catalysts 2022, 12(1), 15; https://doi.org/10.3390/catal12010015 - 24 Dec 2021

Cited by 9 | Viewed by 3442

Abstract

Herein, the synthesis, characterization, and photoelectrochemical and photocatalytic characteristics of hydrothermally prepared La₂O₃–g-C₃N₄, CoO–g-C₃N₄, and La₂O₃–CoO–g-C₃N₄ are discussed. The XRD analysis and crystalline phases [...] Read more.

Herein, the synthesis, characterization, and photoelectrochemical and photocatalytic characteristics of hydrothermally prepared La₂O₃–g-C₃N₄, CoO–g-C₃N₄, and La₂O₃–CoO–g-C₃N₄ are discussed. The XRD analysis and crystalline phases unveiled the impregnation of La₂O₃ and CoO into g-C₃N₄. The microscopic analysis supports the formation of g-C₃N₄ nanoflakes and La₂O₃ and CoO nanoparticles embedded homogeneously in the La₂O₃–CoO–g-C₃N₄ nanocomposite, whereas the EDX comprehended their respective elemental composition and ratios. A bandgap energy of 2.38 eV for La₂O₃–CoO–g-C₃N₄ was calculated using the Tauc plot method, complementing high visible-light activity. The solar-driven water-splitting reaction exhibited significant photocurrent efficiency (~3.75 mA/cm²), augmenting the hydrogen generation by La₂O₃–CoO–g-C₃N₄ compared to that by pure g-C₃N₄, La₂O₃–g-C₃N₄, and CoO–g-C₃N₄ in 0.5 M Na₂SO₄ electrolyte. The synergistic effect of La₂O₃ and CoO impregnation with g-C₃N₄ led to effective division of the photogenerated charge transporters, enhancing the photocatalytic hydrogen generation by the photocatalysts. Furthermore, photocatalytic pollutant removal, namely greater than 90% decomposition of methylene blue (MB) from water, was investigated with a pseudo-first-order reaction kinetics under 1 sun visible-light irradiation. Thus, La₂O₃–CoO–g-C₃N₄ nanocomposite was found to be a prospective material for harnessing solar energy. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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11 pages, 7129 KiB

Open AccessArticle

Synthesis, Characterization and Enhanced Visible Light Photocatalytic Performance of ZnWO₄-NPs@rGO Nanocomposites

by Norah Alhokbany, Saad M. Alshehri and Jahangeer Ahmed

Catalysts 2021, 11(12), 1536; https://doi.org/10.3390/catal11121536 - 16 Dec 2021

Cited by 10 | Viewed by 2296

Abstract

ZnWO₄ nanoparticles on reduced graphene oxide (ZnWO₄-NPs@rGO) nanocomposites were synthesized using the hydrothermal method. Structural, morphological, optical, and photocatalytic studies of the ZnWO₄-NPs@rGO nanocomposites were successfully investigated. Photo-catalytic performances of the ZnWO₄-NPs@rGO nanocomposites were examined for [...] Read more.

ZnWO₄ nanoparticles on reduced graphene oxide (ZnWO₄-NPs@rGO) nanocomposites were synthesized using the hydrothermal method. Structural, morphological, optical, and photocatalytic studies of the ZnWO₄-NPs@rGO nanocomposites were successfully investigated. Photo-catalytic performances of the ZnWO₄-NPs@rGO nanocomposites were examined for the degradation of hazardous methylene blue dye (HMBD) in a neutral medium. ZnWO₄-NPs@rGO nanocomposites show superior photo-catalytic performances over pure ZnWO₄ nanoparticles. ZnWO₄-NPs@rGO nanocomposites degrade ~98% dye while pure ZnWO₄ nanoparticles degrade ~53% dye in 120 min. The prepared nanocomposites also show excellent recycled photo-catalytic efficiencies over multiple cycles. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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15 pages, 4570 KiB

Open AccessArticle

Oxygen-Deficient WO₃/TiO₂/CC Nanorod Arrays for Visible-Light Photocatalytic Degradation of Methylene Blue

by Liaochuan Jiang, Xingyuan Gao, Shaoling Chen, Jangam Ashok and Sibudjing Kawi

Catalysts 2021, 11(11), 1349; https://doi.org/10.3390/catal11111349 - 09 Nov 2021

Cited by 9 | Viewed by 2002

Abstract

At present, TiO₂ is one of the most widely used photocatalytic materials. However, the narrow response range to light limits the photocatalytic performance. Herein, we reported a successful construction of self-doped R-WO₃/R-TiO₂/CC nanocomposites on flexible carbon cloth (CC) [...] Read more.

At present, TiO₂ is one of the most widely used photocatalytic materials. However, the narrow response range to light limits the photocatalytic performance. Herein, we reported a successful construction of self-doped R-WO₃/R-TiO₂/CC nanocomposites on flexible carbon cloth (CC) via electrochemical reduction to increase the oxygen vacancies (O_vs), resulting in an enhanced separation efficiency of photo-induced charge carriers. The photocurrent of R-WO₃/R-TiO₂/CC at −1.6 V (vs. SCE) was 2.6 times higher than that of WO₃/TiO₂/CC, which suggested that O_vs could improve the response to sunlight. Moreover, the photocatalytic activity of R-WO₃/TiO₂/CC was explored using methylene blue (MB). The degradation rate of MB could reach 68%, which was 1.3 times and 3.8 times higher than that of WO₃/TiO₂/CC and TiO₂/CC, respectively. Furthermore, the solution resistance and charge transfer resistance of R-WO₃/R-TiO₂/CC were obviously decreased. Therefore, the electrochemical reduction of nanomaterials enabled a promoted separation of photogenerated electron–hole pairs, leading to high photocatalytic activity. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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25 pages, 7813 KiB

Open AccessFeature PaperArticle

Synthesis Design of Electronegativity Dependent WO₃ and WO₃∙0.33H₂O Materials for a Better Understanding of TiO₂/WO₃ Composites’ Photocatalytic Activity

by István Székely, Endre-Zsolt Kedves, Zsolt Pap and Monica Baia

Catalysts 2021, 11(7), 779; https://doi.org/10.3390/catal11070779 - 27 Jun 2021

Cited by 7 | Viewed by 3139

Abstract

The design of a semiconductor or a composite semiconductor system—with applications in materials science—is complex because its morphology and structure depend on several parameters. These parameters are the precursor type, solvent, pH of the solution, synthesis approach, or shaping agents. This study gives [...] Read more.

The design of a semiconductor or a composite semiconductor system—with applications in materials science—is complex because its morphology and structure depend on several parameters. These parameters are the precursor type, solvent, pH of the solution, synthesis approach, or shaping agents. This study gives meaningful insight regarding the synthesis design of such WO₃ materials. By systematically alternating the precursor (sodium tungstate dihydrate—NWH, or ammonium tungstate hydrate—AMT), subsequently shaping the agents (halide salts—NaX, KX, or hydrohalic acids—HX; X = F⁻, Cl⁻, Br⁻, I⁻), we have obtained WO₃ semiconductors by hydrothermal treatment, which in composite systems can enhance the commercial TiO₂ photocatalytic activity. We investigated three sample series: WO₃-NWH-NaX/WO₃-NWH-KX and, subsequently, WO₃-AMT-HX. The presence of W⁺⁵ centers was evidenced by Raman and X-ray photoelectron spectroscopy. W⁺⁵ and W⁺⁶ species affected the band gap values of the NaX and KX series; a higher percentage of W⁺⁵ and, subsequently, W⁺⁶ caused a redshift, while, regarding the HX series, it led to a blue shift. Increased electronegativity of the halide anions has an unfavorable effect on the composites’ photoactivity. In contrast, in the case of hydrohalic acids, it had a positive impact. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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15 pages, 2707 KiB

Open AccessFeature PaperArticle

Solvothermal Crystallization of Ag/Ag_xO-AgCl Composites: Effect of Different Chloride Sources/Shape-Tailoring Agents

by Zsejke-Réka Tóth, Saurav Kumar Maity, Tamás Gyulavári, Enikő Bárdos, Lucian Baia, Gábor Kovács, Seema Garg, Zsolt Pap and Klara Hernadi

Catalysts 2021, 11(3), 379; https://doi.org/10.3390/catal11030379 - 15 Mar 2021

Cited by 2 | Viewed by 2196

Abstract

In the present work, AgCl microcrystals were obtained by solvothermal crystallization to investigate the effect of H⁺, Na⁺, K⁺, and different shape-tailoring agents (non-ionic: polyvinylpyrrolidone vs. anionic: sodium dodecyl sulfate) on the textural and photocatalytic properties of [...] Read more.

In the present work, AgCl microcrystals were obtained by solvothermal crystallization to investigate the effect of H⁺, Na⁺, K⁺, and different shape-tailoring agents (non-ionic: polyvinylpyrrolidone vs. anionic: sodium dodecyl sulfate) on the textural and photocatalytic properties of the samples. The crystallization process resulted in secondary products, such as Ag_xO or Ag, AgClO₃, AgClO₄, which were further transformed during the photocatalytic tests. The most efficient photocatalyst (assessed for methyl orange degradation) was synthesized using HCl, as a chloride source and polyvinylpyrrolidone, as a shape-tailoring agent. Therefore, the ability of polyvinylpyrrolidone to enhance the photocatalytic activity was also investigated, and it was found that the addition of 0.6 g polyvinylpyrrolidone resulted in the most efficient photocatalyst. Moreover, Ag_xO, being a charge separator, could play a critical role in the photocatalytic process, while reversibly transforming to Ag back and forth. Full article

(This article belongs to the Special Issue The Importance of Shape-Tailoring at Nano- and Micro-Levels in Catalytic and Photocatalytic Applications)

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