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Publication date: January 2022

Source: Nano Energy, Volume 91

Author(s): Along Zhao, Tianci Yuan, Peng Li, Changyu Liu, Hengjiang Cong, Xiangjun Pu, Zhongxue Chen, Xiping Ai, Hanxi Yang, Yuliang Cao

Reversible and cooperative photoactivation of single-atom Cu/TiO₂ photocatalysts

Reversible and cooperative photoactivation of single-atom Cu/TiO₂ photocatalysts, Published online: 22 April 2019; doi:10.1038/s41563-019-0344-1

Reversible and cooperative activation processes are important characteristics of biological enzymes and can be used in designing catalysts. Highly active TiO2 photocatalysts incorporated with site-specific single copper atoms are now shown to exhibit such a photoactivation process.

The piezotronic effect is introduced to enhance plasmonic photocatalysis by fabricating Au _x /BaTiO₃ nano‐heterostructures. Piezoelectric polarization of the BaTiO₃ nanocrystal upon sonication suppresses the recombination of photogenerated hot electron–hole pairs to enhance the localized surface plasmon resonance of Au nanoparticles to improve the photocatalysis process.

Abstract

Piezopotential‐assisted catalysis is of great significance for low cost and efficient catalysis processes. Here, Au _x /BaTiO₃ plasmonic photocatalysts are fabricated by precipitating Au nanoparticles on piezoelectric BaTiO₃ nanocubes through a chemical approach. The Au nanoparticles (<8 nm) are decorated uniformly on the surface of BaTiO₃, which endows the heterostructure with a wide light absorption from 300 to 600 nm. The photocatalytic properties of the heterostructures are investigated in detail toward methyl orange (MO) degradation. The Au content, piezoelectric potential of the BaTiO₃ substrate, and surface plasmon resonance (SPR) are confirmed to be vital to the photocatalytic activity. The Au₄/BaTiO₃ shows an optimum photocatalytic performance for a complete degradation of MO in 75 min under full spectrum light irradiation with auxiliary ultrasonic excitation. The piezoelectric field originating from the deformation of BaTiO₃ further enhances the separation of photon‐generated carriers induced by SPR and promotes the formation of hydroxyl radicals, which results in a strong oxidizing ability of organic dyes. This work introduces the piezotronic effect to enhance plasmonic photocatalysis with Au _x /BaTiO₃ heterostructures, which is ready to extend to other catalytic systems and offers a new option to design high‐performance catalysts for pollutant treatment.

Ultrathin TiO₂ nanosheets with abundant oxygen vacancies (V_O) are synthesized through a facile copper‐doping strategy, exhibiting remarkable and stable performance for the photofixation of N₂ to NH₃ at a rate of 78.9 µmol g⁻¹ h⁻¹ under ambient conditions (especially up to 700 nm). The outstanding activity can be attributed to the existence of V_O and compressive strain in the nanosheets.

Abstract

Dinitrogen reduction to ammonia using transition metal catalysts is central to both the chemical industry and the Earth's nitrogen cycle. In the Haber–Bosch process, a metallic iron catalyst and high temperatures (400 °C) and pressures (200 atm) are necessary to activate and cleave NN bonds, motivating the search for alternative catalysts that can transform N₂ to NH₃ under far milder reaction conditions. Here, the successful hydrothermal synthesis of ultrathin TiO₂ nanosheets with an abundance of oxygen vacancies and intrinsic compressive strain, achieved through a facile copper‐doping strategy, is reported. These defect‐rich ultrathin anatase nanosheets exhibit remarkable and stable performance for photocatalytic reduction of N₂ to NH₃ in water, exhibiting photoactivity up to 700 nm. The oxygen vacancies and strain effect allow strong chemisorption and activation of molecular N₂ and water, resulting in unusually high rates of NH₃ evolution under visible‐light irradiation. Therefore, this study offers a promising and sustainable route for the fixation of atmospheric N₂ using solar energy.

Semiconductor photocatalysis as a desirable technology shows huge potential in environmental remediation and renewable energy generation, but its efficiency is severely restricted by the rapid recombination of charge carriers in bulk phase and on the surface of photocatalysts. Polarization has emerged as one of the most effective strategies for conquering the above‐mentioned issues, tremendously promoting photocatalysis. Herein, this review summarizes the recent advances on improvement of photocatalytic activity by polarization promoted bulk and surface charge separation. We highlighted the recent progresses in charge separation advanced by different types of polarization, such as macroscopic polarization, piezoelectric polarization, ferroelectric polarization and surface polarization, and the related mechanisms. Finally, the strategies and challenges for polarization enhancement to further boost the charge separation and photocatalysis are discussed.

Publication date: February 2019

Source: Nano Energy, Volume 56

Author(s): Peng Zhou, Fan Lv, Na Li, Yelong Zhang, Zijie Mu, Yonghua Tang, Jianping Lai, Yuguang Chao, Mingchuan Luo, Fei Lin, Jinhui Zhou, Dong Su, Shaojun Guo

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Publication date: November 2018

Source: Nano Energy, Volume 53

Author(s): Song Bai, Ning Zhang, Chao Gao, Yujie Xiong

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Publication date: 15 December 2018

Source: Applied Catalysis B: Environmental, Volume 238

Author(s): Abolfazl Ziarati, Alireza Badiei, Rafael Luque

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Advanced Functional Materials, EarlyView.

In situ formation of catalytically active graphene in ethylene photo-epoxidation

In situ formation of catalytically active graphene in ethylene photo-epoxidation, Published online: 03 August 2018; doi:10.1038/s41467-018-05352-9

In situ studies under working conditions are important in atomic-level elucidation, design, and optimization of industrially relevant catalysts. Here, the authors report an in situ study of an Ag ethylene photo-epoxidation catalyst using surface enhanced Raman scattering, which uncovers an unconventional mechanism.

Advanced Materials, Volume 30, Issue 38, September 20, 2018.

Angewandte Chemie International Edition, EarlyView.

Publication date: 15 November 2018
Source:Applied Catalysis B: Environmental, Volume 236
Author(s): Yong Xu, Yong Chen, Wen-Fu Fu
A core-shell structured CdS@C3N4 photocatalyst with a 4 nm thick shell was prepared using self-assembly, and its structure, composition and morphology were characterized in detail. The hybrid visible-light catalyst exhibited a high photocatalytic performance for oxidative coupling of amines under atmospheric conditions, and robust product selectivity up to &gt;99% for photodriven oxidation of various amines to corresponding imines was achieved. It was confirmed using Hammett-type plots and radical trapping experiments that steric effects and the formation of ^•O2 ⁻ are critical for photocatalytic conversion of the investigated substrates, and the related catalytic mechanism is presented.

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Publication date: 15 November 2018
Source:Applied Catalysis B: Environmental, Volume 236
Author(s): Qiao Wang, Zhiquan Liu, Dongmei Liu, Guoshuai Liu, Min Yang, Fuyi Cui, Wei Wang
Photocatalysis is intensively investigated for environmental remediation, but suffering from moderate efficiency toward the colorless persistent organic contaminants, the major category of organic pollutants in water environment. Herein, a novel series of oxygen vacancy-rich ultrathin two-dimensional BiOBrxI1-x solid solution nanosheets (BBI-x) were successfully constructed via a one-step solvothermal method. Under visible light irradiation, the optimal BiOBr0.85I0.15 sample (BBI-0.85) exhibited over 90% degradation efficiency of 4-chlorophenol (4-CP) within 30 min, which was 4.4, 10.9 and 5.9 times greater than that of pure BiOI nanosheets, pure BiOBr nanosheets and oxygen vacancy-poor BiOBr0.85I0.15 nanoplates, respectively. Also, this excellent photoactivity can expand to other colorless organic contaminants, such as bisphenol analogues and sulfonamides, verifying the universal applicability of BiOBrxI1-x. The enhanced activity can be ascribed to the synergistic effect of solid solution and oxygen vacancies. Formation of solid solution promotes visible-light harvesting and photogenerated charge carriers’ separation efficiency, as well as endows photoinduced holes with sufficient oxidation capacity, unambiguously confirmed by multiple optical and photoelectrochemical characterizations. Meanwhile, the oxygen vacancies induce an intermediate level near the Fermi level, narrowing the band gap energy and impeding the recombination of photogenerated charge carriers, as evidenced by density functional theory (DFT) analyses. This work could give ideas for the design of highly active photocatalysts toward sustainable solar-to-chemical energy conversion and environmental remediation.

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Publication date: 5 October 2018
Source:Applied Catalysis B: Environmental, Volume 233
Author(s): Meng Sun, Qingquan Wei, Yu Shao, Bin Du, Tao Yan, Liangguo Yan, Danzhen Li
In this work, we report the fabrication of composition-tunable heterostructured bismuth oxyiodides photocatalysts using a facile ionic liquid-assisted precipitation method at room temperature. Through elaborately governing the reaction parameters, two groups of bismuth oxyiodide hybrids (Group 1: BiOI/Bi4O5I2, and Group 2: Bi4O5I2/Bi5O7I) with different components were prepared. The DRS spectra shows that the absorption edges of the hybrids were gradually tuned from 550 to 660 nm, which was in accordance with the color gradient from light yellow (Bi5O7I) to brick red (BiOI). The SEM images show that the products mainly exhibited 3D hierarchical architecture, which was beneficial for the adsorption of contaminants over the catalyst’s surface. The two groups of heterojunction photocatalysts all exhibited remarkably improved photocatalytic activity in decomposing o-phenylphenol (OPP) and 4-tert-butylphenol (PTBP) under visible light irradiation respect to single phase photocatalyst (BiOI, Bi4O5I2, or Bi5O7I). For BiOI/Bi4O5I2 hybrids, the S5 sample exhibited the optimal activity, which was approximately 5.35 and 1.85 times higher than that of pristine BiOI and Bi4O5I2, respectively. For the second group of Bi4O5I2/Bi5O7I, the optimal activity was observed for S9 hybrid, which was approximately 2.43 and 2.12 times higher than that of bare Bi4O5I2 and Bi5O7I under identical conditions. This activity enhancement should be attributed to the balanced band levels of the components, which facilitates the fast interfacial charge transmigration of photo-generated carriers, resulting in highly promoted charge separation efficiency. This deduction was proved by the photocurrent, electrochemical impedance spectroscopy, and photoluminescence measurements. The possible degradation mechanisms for BiOI/Bi4O5I2 and Bi4O5I2/Bi5O7I hybrids were proposed based on the band potentials and trapping experiment results.

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Publication date: 6 October 2018
Source:Applied Catalysis B: Environmental, Volume 234
Author(s): Lizhi Xu, Xiaoyu Deng, Zhaohui Li
Photoreduction of [PtCl6]²⁻ over hexagonal ZnIn2S4 led to the formation of surface deposited small PtS nanoparticles with a size of ca. 3 nm. The resultant PtS/ZnIn2S4 nanocomposites were fully characterized and their performance for photocatalytic splitting of thiols to produce disulfides and hydrogen was investigated. It was found that PtS significantly promoted the photocatalytic performance for thiols splitting to produce disulfides and quantitative hydrogen over ZnIn2S4 under visible light and no over-oxidized products of thiols were produced. An optimum performance was observed over 0.5 wt% PtS/ZnIn2S4, with a complete transformation of thiols to disulfides in 6 h. PtS/ZnIn2S4 nanocomposite is stable during the photocatalytic reaction and can be easily separated for recycling. The photocatalytic thiols splitting over PtS/ZnIn2S4 is an efficient and cost effective strategy to produce disulfides, which exhibits 100% atom economy since hydrogen is generated concomitantly. This study demonstrates that the coupling of water reduction with organics oxidation over semiconductor-based photocatalysts may find great potentials in organic syntheses.

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Publication date: May 2018
Source:Journal of Catalysis, Volume 361
Author(s): Dengke Wang, Yating Pan, Lizhi Xu, Zhaohui Li
PdAu@MIL-100(Fe), with PdAu alloy nanoparticles of ca. 1.7 nm encapsulated inside MIL-100(Fe) cavities, were prepared via a double-solvent impregnation followed by photoreduction. As compared with bare Pd@MIL-100(Fe), bimetallic PdAu@MIL-100(Fe) showed superior activities for the tandem reactions between amines and alcohols to produce N-alkyl amines under visible-light irradiation, ascribed to the promoting effect of metallic Au in the photocatalytic alcohol-to-aldehyde dehydrogenation. A Pd/Au ratio dependent N-alkylation activity was observed over PdAu@MIL-100(Fe), implying the possibility of synchronizing the reaction rates of two consecutive steps in the N-alkylation reaction, i.e., photocatalytic alcohol-to-aldehyde dehydrogenation and imines hydrogenation, to optimize the whole reaction. This study provides a highly efficient and stable catalytic system for the realization of alkylation of amines via a successful coupling of MOF-based photocatalysis and metal nanoparticle-based hydrogenation. This work also demonstrates that the reaction rates of different catalytic steps in a cascade/tandem reaction can be synchronized for an efficient overall reaction via a rational design of the multifunctional catalysts.

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Publication date: May 2018
Source:Journal of Catalysis, Volume 361
Author(s): Wanfeng Liao, Xiuyuan Ni, Yulan Zhou
The photopolymerization with important application has usually used the organic initiators sensitive to ultraviolet light. In this work, we designed a new visible-light initiator complex composed of iron doped TiO2 (TiO2:Fex%, x = 1, 5, and 10), succinic acid and iodonium salt (Ph2I⁺PF6 ⁻). The ternary complex was proved to efficiently initiate both cationic ring-opening polymerization and free radical polymerization. The mechanism studies with solid-state ¹³C-nuclear magnetic resonance (¹³C NMR) and gas chromatography-mass spectrometer (GC–MS) clearly presented that the TiO2:Fex% nanoparticles catalyzed the decarboxylation of succinic acid in the pathway of photo-Kolbe reaction. Meanwhile, Ph2I⁺PF6 ⁻ could serve as an electron acceptor. The reaction kinetics of epoxy resin and epoxy-acrylate hybrid resin were measured by the attenuated total reflection-Fourier transformation infrared (ATR-FTIR) spectroscopy.

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Publication date: 5 September 2018
Source:Applied Catalysis B: Environmental, Volume 231
Author(s): Jingling Yang, Chung-Yuan Mou
Imines are important intermediates for the synthesis of fine chemicals and pharmaceuticals. Design of a “green” oxidation catalyst to promote the direct oxidation of amines to imines by dioxygen have attracted great attention. Herein, we designed a catalyst of ordered mesoporous Au/M-TiO2 nanoparticles using a template-based approach. The as-prepared Au/M-TiO2 nanoarrays of anatase crystalline structure, with high specific surface area (222 m²/g), small pore size (∼2.1 nm) and ordered arrangements, gave dense array of ultrasmall pore-confined gold nanoparticles. The mesoporous Au/M-TiO2 exhibits particularly high visible light activity for photocatalytic selective aerobic oxidation of benzylamine to N-benzylidene benzylamine in a green approach by utilizing dioxygen as an oxidant in solvent-free conditions. The yield of N-benzylidene benzylamine can reach 1.73 mmol (TOF = 178.6 h⁻¹, based on Au) in Au/M-TiO2 system, which is 1.5 and 1.6 times higher than that of the Au/P25 and Au/Acros anatase photocatalysts, respectively. Furthermore, we can also achieve high yield of N-benzylidene benzylamine (1.30 mmol, TOF = 134.2 h⁻¹, based on Au) in air atmosphere. The confinement effect of the mesopores in Au/M-TiO2 facilitate the formation of O2 ⁻ radicals and make the bi-molecular reaction highly preferred for promoting the high selectivity and conversion in plasmonic photocatalysis. Meanwhile, the Au/M-TiO2 with mesoporous structure can facilitate the efficient contact between the solvent and the nanomaterial, while possessing sufficient interfacial area for active oxidation reactions. This work paves a promising way to develop visible light-responsive TiO2-based photocatalysts with high specific surface area for highly efficient green oxidative organic synthesis.

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Publication date: 5 September 2018
Source:Applied Catalysis B: Environmental, Volume 231
Author(s): Jianhao Qiu, Xingguang Zhang, Yi Feng, Xiongfei Zhang, Huanting Wang, Jianfeng Yao
Photocatalysis is a promising and ideal technology to utilize solar energy for energy regeneration and environmental remediation. Photocatalysis based on metal-organic frameworks (MOFs) has attracted extensive attention because of their excellent properties such as tunable structure and optical properties. This review principally summarizes the progress of various modification strategies, including decoration of organic linker or metal center, combination with semiconductors and metal nanoparticles loading. applied to different MOFs (mainly UiOs, MILs, and ZIFs), and their specific applications were summarized as well. In addition, the existing problems and the development prospect of MOFs for photocatalysis were also presented.

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Publication date: 15 September 2018
Source:Applied Catalysis B: Environmental, Volume 232
Author(s): Jiang Wu, Kai Xu, Qizhen Liu, Zheng Ji, Chenhao Qu, XuemeiQi, Hui Zhang, Yu Guan, Ping He, Liangjun Zhu
In-situ reduction method was successfully taken out to control the highly reactive (010) facets and decline band gaps in interlining-I/BiOIO3. It gave a fairly easy way to coordinate the control of bandgap engineering and structural engineering. The interlining-I provided an impurity level served as a plate for photo-generated electron to hop, which expanded the light reaction intensity and displayed excellent photocatalytic performance as well. The as-prepared samples were characterized and estimated for removing gas-phase Hg°. It demonstrated that there existed an optimization of I⁻ to construct a suitable impurity level for effectively separating and transferring electron-hole pairs. The corresponding structural engineering made the internal electric field(IEF) intensify, which was attributed to its increasing exposed surface in favor of obstructing their recombination in the bulk, generating a large number of essential species related to the larger exposed (010) facets to oxidize Hg° into Hg²⁺ under visible light. BI-1 showed the highest efficiency of 92.15%. However, because of the existence of light corrosion, a small part of the iodine ions may be oxidized to elemental iodine to volatilize, fortunately it could be regenerated to the original efficiency in the same preparation method. In addition, the samples with super photocatalytic properties and excellent electron transport properties also gave out a capacious prospect in CO2 conversion, hydrogen evolution, NO removal, degradation of organic pollutants, also the super capacitors and batteries.

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