Chinese Journal of Catalysis

Table of Contents for VOL.38 No.2

2017, 38 (2): 0-0.

Abstract ( 143 )

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Preface to Special Issue on the International Symposium on Environmental Catalysis (ISEC 2016)

Jinlin Li, Jiaguo Yu

2017, 38 (2): 191-191. DOI: 10.1016/S1872-2067(17)62792-X

Abstract ( 266 ) [Full Text(HTML)] ()

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Photochemical oxidation mechanism of microcystin-RR by p-n heterojunction Ag/Ag₂O-BiVO₄

Chunhong Wu, Yanfen Fang, Araya Hailu Tirusew, Miaomiao Xiang, Yingping Huang, Chuncheng Chen

2017, 38 (2): 192-198. DOI: 10.1016/S1872-2067(16)62583-4

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Microcystin-RR (MC-RR), a form of microcystin with two arginine moieties, is a cyanobacterial toxin that has been detected across a wide geographic range. It is a great concern globally because of its potential liver toxicity. Herein, the abilities of BiVO₄, Ag-BiVO₄, Ag₂O-BiVO₄ and Ag/Ag₂O-BiVO₄ to photocatalytically degrade MC-RR under visible-light irradiation (λ≥420 nm) were investigated and compared. The possible degradation pathways were explored through analysis of the reaction intermediates by high-performance liquid chromatography-mass spectrometry. The results showed that the presence of Ag⁰ enhanced the photocatalytic efficiency of Ag/Ag₂O-BiVO₄ via a synergetic effect between Ag₂O and Ag⁰ at the p-n heterojunction. Moreover, the presence of Ag⁰ also greatly promoted the adsorption of MC-RR on the photocatalyst surface. Toxicological experiments on mice showed that the toxicity of MC-RR was significantly reduced after photocatalytic degradation.

Effects of hierarchical structure on the performance of tin oxide-supported platinum catalyst for room-temperature formaldehyde oxidation

Yuanyuan Duan, Shaoqing Song, Bei Cheng, Jiaguo Yu, Chuanjia Jiang

2017, 38 (2): 199-206. DOI: 10.1016/S1872-2067(16)62551-2

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Flower-like tin oxide-supported platinum (Pt/SnO_x) with a hierarchical structure was synthesized by a hydrothermal method and characterized by XRD, SEM, TEM, high resolution TEM, XPS and nitrogen adsorption. The flower-like Pt/SnO_x microspheres of 1 μm in diameter were composed of staggered petal-like nanosheets with a thickness of 20 nm. Pt nanoparticles (NPs) of 2-3 nm were well dispersed on the SnO_x nanosheets. The catalyst was tested in the catalytic oxidation of gaseous formaldehyde (HCHO) at room temperature, and exhibited enhanced activity compared to Pt NPs supported on commercial SnO and ground SnO_x. HCHO removal of 87% was achieved over the hierarchical Pt/SnO_x after 1 h of reaction, which was 1.5 times that over the ground SnO_x-supported Pt (Pt/g-SnO_x), and the high activity was maintained after six recycles, showing the high stability of this catalyst. HCHO decomposition kinetics was modeled as a second order reaction. The reaction rate constant for Pt/SnO_x was 5.6 times higher than Pt/g-SnO_x. The hierarchical pore structure was beneficial for the diffusion and adsorption of HCHO molecules, and the highly dispersed Pt NPs on the SnO_x nanosheets were the active sites for the oxidative decomposition of HCHO into CO₂ and H₂O. This study provided a promising approach for designing efficient catalysts for indoor HCHO removal at ambient temperature.

Catalytic performance of cobalt oxide-supported gold-palladium nanocatalysts for the removal of toluene and o-xylene

Zhiwei Wang, Yuxi Liu, Tao Yang, Jiguang Deng, Shaohua Xie, Hongxing Dai

2017, 38 (2): 207-216. DOI: 10.1016/S1872-2067(16)62569-X

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Using the molten salt and polyvinyl alcohol-protected reduction method, we fabricated Co₃O₄ octahedron-supported Au-Pd (x(AuPd_y)/Co₃O₄; x=(0.18, 0.47, and 0.96) wt%; y (Pd/Au molar ratio)=1.85-1.97) nanocatalysts. The molten salt-derived Co₃O₄ sample possessed well-defined octahedral morphology, with an edge length of 300 nm. The Au-Pd nanoparticles, with sizes of 2.7-3.2 nm, were uniformly dispersed on the surface of Co₃O₄. The 0.96(AuPd_1.92)/Co₃O₄ sample showed the highest catalytic activity for toluene and o-xylene oxidation, and the temperature required for achieving 90% conversion of toluene and o-xylene was 180 and 187℃, respectively, at a space velocity of 40000 mL/(g·h). The high catalytic performance of Co₃O₄ octahedron-supported Au-Pd nanocatalysts was associated with the interaction between Au-Pd nanoparticles and Co₃O₄ and high concentration of adsorbed oxygen species.

Heterostructured BiOI@La(OH)₃ nanorods with enhanced visible light photocatalytic NO removal

Yanjuan Sun, Xiang Xiao, Xing'an Dong, Fan Dong, Wei Zhang

2017, 38 (2): 217-226. DOI: 10.1016/S1872-2067(17)62753-0

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Heterostructured BiOI@La(OH)₃ nanorod photocatalysts were prepared by a facile chemical impregnation method. The enhanced visible light absorption and charge carrier separation can be simultaneously realized after the introduction of BiOI particles into La(OH)₃ nanorods. The BiOI@La(OH)₃ composites were applied for visible light photocatalytic oxidization of NO in air and exhibited an enhanced activity compared with BiOI and pure La(OH)₃ nanorods. The results show that the energy levels between the La(OH)₃ and BiOI phases matched well with each other, thus forming a heterojunctioned BiOI@La(OH)₃ structure. This band structure matching could promote the separation and transfer of photoinduced electron-hole pairs at the interface, resulting in enhanced photocatalytic performance under visible light irradiation. The photocatalytic performance of BiOI@La(OH)₃ is shown to be dependent on the mass ratio of BiOI to La(OH)₃. The highest photocatalytic performance can be achieved when the mass ratio of BiOI to La(OH)₃ is controlled at 1.5. A further increase of the mass ratio of BiOI weakened the redox abilities of the photogenerated charge carriers. A new photocatalytic mechanism for BiOI@La(OH)₃ heterostructures is proposed, which is directly related to the efficient separation of photogenerated charge carriers by the heterojunction. Importantly, the as-prepared BiOI@La(OH)₃ heterostructures exhibited a high photochemical stability after multiple reaction runs. Our findings demonstrate that BiOI is an effective component for the formation of a heterostructure with the properties of a wide bandgap semiconductor, which is of great importance for extending the light absorption and photocatalytic activity of wide bandgap semiconductors into visible light region.

Heterogeneous catalytic activation of peroxymonosulfate for efficient degradation of organic pollutants by magnetic Cu⁰/Fe₃O₄ submicron composites

Gang Nie, Jia Huang, Yezhou Hu, Yaobin Ding, Xiaoyan Ha, Heqing Tan

2017, 38 (2): 227-239. DOI: 10.1016/S1872-2067(16)62566-4

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Magnetic Cu⁰/Fe₃O₄ submicron composites were prepared using a hydrothermal method and used as heterogeneous catalysts for the activation of peroxymonosulfate (PMS) and the degradation of organic pollutants. The as-prepared magnetic Cu⁰/Fe₃O₄ submicron composites were composed of Cu⁰ and Fe₃O₄ crystals and had an average size of approximately 220 nm. The Cu⁰/Fe₃O₄ composites could efficiently catalyze the activation of PMS to generate singlet oxygen, and thus induced the rapid degradation of rhodamine B, methylene blue, orange II, phenol and 4-chlorophenol. The use of 0.1 g/L of the Cu⁰/Fe₃O₄ composites induced the complete removal of rhodamine B (20 μmol/L) in 15 min, methylene blue (20 μmol/L) in 5 min, orange II (20 μmol/L) in 10 min, phenol (0.1 mmol/L) in 30 min and 4-chlorophenol (0.1 mmol/L) in 15 min with an initial pH value of 7.0 and a PMS concentration of 0.5 mmol/L. The total organic carbon (TOC) removal higher than 85% for all of these five pollutants was obtained in 30 min when the PMS concentration was 2.5 mmol/L. The rate of degradation was considerably higher than that obtained with Cu⁰ or Fe₃O₄ particles alone. The enhanced catalytic activity of the Cu⁰/Fe₃O₄ composites in the activation of PMS was attributed to the synergistic effect of the Cu⁰ and Fe₃O₄ crystals in the composites. Singlet oxygen was identified as the primary reactive oxygen species responsible for pollutant degradation by electron spin resonance and radical quenching experiments. A possible mechanism for the activation of PMS by Cu⁰/Fe₃O₄ composites is proposed as electron transfer from the organic pollutants to PMS induces the activation of PMS to generate ¹O₂, which induces the degradation of the organic pollutants. As a magnetic catalyst, the Cu⁰/Fe₃O₄ composites were easily recovered by magnetic separation, and exhibited excellent stability over five successive degradation cycles. The present study provides a facile and green heterogeneous catalysis method for the oxidative removal of organic pollutants.

Enhanced visible light photocatalytic H₂ production over Z-scheme g-C₃N₄ nansheets/WO₃ nanorods nanocomposites loaded with Ni(OH)_x cocatalysts

Kelin He, Jun Xie, Xingyi Luo, Jiuqing Wen, Song Ma, Xin Li, Yueping Fang, Xiangchao Zhang

2017, 38 (2): 240-252. DOI: 10.1016/S1872-2067(17)62759-1

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Novel WO₃/g-C₃N₄/Ni(OH)_x hybrids have been successfully synthesized by a two-step strategy of high temperature calcination and in situ photodeposition. Their photocatalytic performance was investigated using TEOA as a hole scavenger under visible light irradiation. The loading of WO₃ and Ni(OH)_x cocatalysts boosted the photocatalytic H₂ evolution efficiency of g-C₃N₄. WO₃/g-C₃N₄/Ni(OH)_x with 20 wt% defective WO₃ and 4.8 wt% Ni(OH)_x showed the highest hydrogen production rate of 576 μmol/(g·h), which was 5.7, 10.8 and 230 times higher than those of g-C₃N₄/4.8 wt% Ni(OH)_x, 20 wt% WO₃/C₃N₄ and g-C₃N₄ photocatalysts, respectively. The remarkably enhanced H₂ evolution performance was ascribed to the combination effects of the Z-scheme heterojunction (WO₃/g-C₃N₄) and loaded cocatalysts (Ni(OH)_x), which effectively inhibited the recombination of the photoexcited electron-hole pairs of g-C₃N₄ and improved both H₂ evolution and TEOA oxidation kinetics. The electron spin resonance spectra of ·O₂^- and ·OH radicals provided evidence for the Z-scheme charge separation mechanism. The loading of easily available Ni(OH)_x cocatalysts on the Z-scheme WO₃/g-C₃N₄ nanocomposites provided insights into constructing a robust multi-ple-heterojunction material for photocatalytic applications.

Highly efficient Z-scheme WO_3-x quantum dots/TiO₂ for photocatalytic hydrogen generation

Lun Pan, Jingwen Zhang, Xu Jia, Yu-Hang Ma, Xiangwen Zhang, Li Wang, Ji-Jun Zou

2017, 38 (2): 253-259. DOI: 10.1016/S1872-2067(16)62576-7

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Z-scheme semiconductors are a promising class of photocatalysts for hydrogen generation. In this work, Z-scheme semiconductors composed of WO_3-x quantum dots supported on TiO₂ (WO_3-x QDs/TiO₂) were fabricated by solvothermal and hydrogen-reduction methods. Characterization by transmission electron microscopy and X-ray diffraction indicated that the amount and size of the WO_3-x QDs could be tuned by modulating the addition of the W precursor. Evidence from X-ray photoelectron spectroscopy and photoluminescence spectroscopy suggested that the hydrogen reduction of the composite induced the formation of oxygen vacancy (W⁵⁺/VO) defects in WO₃. These defects led to ohmic contact between WO_3-x and TiO₂, which altered the charge-transfer pathway from type II heterojunction to Z-scheme, and maintained the highly reductive and oxidative ability of TiO₂ and WO_3-x, respectively. Therefore, the Z-scheme sample showed 1.3-fold higher photoactivity than pure TiO₂ in hydrogen generation. These results suggest that the formation of W⁵⁺/VO defects at the interface is highly beneficial for the fabrication of Z-scheme photocatalysts.

Surface plasmon resonance-induced visible-light photocatalytic performance of silver/silver molybdate composites

Xianglong Yang, Ying Wang, Xiao Xu, Yang Qu, Xing Ding, Hao Chen

2017, 38 (2): 260-269. DOI: 10.1016/S1872-2067(16)62553-6

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Novel silver/silver molybdate (Ag/Ag₂MoO₄) composites with surface plasmon resonance (SPR)-enhanced photocatalytic performance were successfully fabricated via a facile one-pot hydrothermal route with the presence of sodium dodecyl sulfate (SDS) in this study. The as prepared silver/silver molybdate (Ag/Ag₂MoO₄) composites were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible diffuse reflectance absorption spectroscopy (DRS) in order to investigate their crystal structure, morphology and optical property as well. The photocatalytic activities of the composites were subsequently evaluated by their ability to degrade rhodamine B (RhB) under visible-light irradiation. Varies of controlled experiments were then carefully operated to gain a deep insight into the assembling of Ag/Ag₂MoO₄ composites. It was found that preparation conditions such as pH, reaction time, and the amount of surfactant played important roles in the formation of composites with octahedral microstructures. And the composite obtained at 160℃ using 0.5 g of sodium dodecyl sulfate exhibited the highest photocatalytic performance under visible-light irradiation. Capture experiments were also conducted to clarify the function of different active species generated on the surface of Ag/Ag₂MoO₄ during the photocatalytic process, in which both holes and ·OH radicals were found to play crucial role in photocatalytic removal of RhB under visible light irradiation. A possible photocatalytic mechanism of Ag/Ag₂MoO₄ was finally proposed on the basis of all the results to explain the higher photocatalytic activity of the octahedral Ag/Ag₂MoO₄ composites. It was inferred that the photoinduced "hot" electrons can quickly transfer from the Ag NPs to the conduction band of Ag₂MoO₄ and react with oxygen and H₂O to generate a large quality of active radicals such as ·OH and ·O₂^- because of the SPR effects. Besides, this SPR effects of Ag nanoparticles deposited on the surface of Ag₂MoO₄ can not only dramatically amplify its light absorption, especially in the visible region, but also promote the separation of photoexcited electron-hole pairs and effectively decrease electron-hole recombination.

Heterojunction between anodic TiO₂/g-C₃N₄ and cathodic WO₃/W nano-catalysts for coupled pollutant removal in a self-biased system

Tingting Yu, Lifen Liu, Fenglin Yang

2017, 38 (2): 270-277. DOI: 10.1016/S1872-2067(16)62556-1

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An anodic TiO₂/g-C₃N₄ hetero-junction and cathodic WO₃/W were used to build a self-sustained catalytic fuel cell system for oxidizing rhodamine B or triclosan and reducing NO₃^--N to N₂ simultaneously. The WO₃ nano-catalyst was formed in situ by heating and oxidizing a tungsten wire in air. Cyclic voltammetry and current-time curves were used to characterize the electrochemical properties of the electrodes and system. Aeration and activation of molecular oxygen by self-biased TiO₂/g-C₃N₄ led to the formation of reactive oxidizing species in the fuel cell. The mechanism of simultaneous anodic oxidation of pollutants and cathodic reduction of nitrate was proposed. The spontaneously formed circuit and tiny current were used simultaneously in treating two kinds of wastewater in the reactor chambers, even without light illumination or an external applied voltage. This new catalytic pollution control route can lower energy consumption and degrade many other kinds of pollutants.

Enhanced photochemical oxidation ability of carbon nitride by π-π stacking interactions with graphene

Qiang Hao, Simeng Hao, Xiuxiu Niu, Xun Li, Daimei Chen, Hao Ding

2017, 38 (2): 278-286. DOI: 10.1016/S1872-2067(16)62561-5

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A one-pot method for the preparation of g-C₃N₄/reduced graphene oxide (rGO) composite photocatalysts with controllable band structures is presented. The photocatalysts are characterized by Fouirer transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, transmission electron microscope, and Mott-Schottky analysis. The valance band (VB) of g-C₃N₄ exhibits a noticeable positive shift upon hybridizing with rGO, and thus results in a strong photo-oxidation ability. The g-C₃N₄/rGO composites show a higher photodegradation activity for 2,4-dichlorophenol (2,4-DCP) and rhodamine B (RhB) under visible light irradiation (λ≥420 nm). The g-C₃N₄/rGO-1 sample exhibits the highest photocatalytic activity, which is 1.49 and 1.52 times higher than that of bulk g-C₃N₄ for 2,4-DCP and 1.52 times degradation, respectively. The enhanced photocatalytic activity for g-C₃N₄ originates from the improved visible light usage, enhanced electronic conductivity and photo-oxidation ability by the formed strong π-π stacking interactions with rGO.

Preparation and application of g-C₃N₄-ZnS-DNA nanocomposite with enhanced electrocatalytic activity

Xin Zhou, Jing Zou, Sheng Zhang, Ming Pan, Wanyun Gong

2017, 38 (2): 287-295. DOI: 10.1016/S1872-2067(16)62582-2

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We successfully designed and prepared a g-C₃N₄-ZnS-DNA nanocomposite by a simple method and systematically investigated its morphology, microstructure, and electrocatalytic properties. The as-prepared g-C₃N₄-ZnS-DNA nanocomposite possessed the electrocatalytic activity of g-C₃N₄-ZnS and the conductivity of DNA. The presence of DNA was found to enhance the electrocatalytic response of the nanocomposite towards environmental hormones, e.g. pentachlorophenol and nonylphenol, owing to the interaction between g-C₃N₄-ZnS and DNA, indicating that a stable nanocomposite was formed. The three components showed synergistic effects during electrocatalysis. Electrochemical impedance spectra indicated that the g-C₃N₄-ZnS-DNA nanocomposite dramatically facilitated the electron transfer of a modified electrode. The co-doping of g-C₃N₄ film with ZnS and DNA doubled the electrochemical response of the modified electrode in comparison with that of unmodified g-C₃N₄ film. The detection limits (3 S/N) of pentachlorophenol and nonylphenol were 3.3×10^-9 mol L^-1. Meanwhile, we propose a possible Z-scheme mechanism for electron transfer in the g-C₃N₄-ZnS-DNA nanocomposite and the possible pentachlorophenol and nonylphenol electrocatalytic oxidation mechanism. The g-C₃N₄-ZnS-DNA nanocomposite-modified electrode was demonstrated to be effective for electrochemical sensing of trace environmental hormones in water samples.

Facile synthesis and enhanced photocatalytic H₂-evolution performance of NiS₂-modified g-C₃N₄ photocatalysts

Feng Chen, Hui Yang, Xuefei Wang, Huogen Yu

2017, 38 (2): 296-304. DOI: 10.1016/S1872-2067(16)62554-8

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NiS₂ is a promising cocatalyst to improve the photocatalytic performance of g-C₃N₄ for the production of H₂. However, the synthesis of the NiS₂ cocatalyst usually requires harsh conditions, which risks destroying the microstructures of the g-C₃N₄ photocatalysts. In this study, a facile and low-temperature (80℃) impregnation method was developed to prepare NiS₂/g-C₃N₄ photocatalysts. First, the g-C₃N₄ powders were processed by the hydrothermal method in order to introduce oxygen-containing functional groups (such as -OH and -CONH-) to the surface of g-C₃N₄. Then, the Ni²⁺ ions could be adsorbed near the g-C₃N₄ via strong electrostatic interaction between g-C₃N₄ and Ni²⁺ ions upon the addition of Ni(NO₃)₂ solution. Finally, NiS₂ nanoparticles were formed on the surface of g-C₃N₄ upon the addition of TAA. It was found that the NiS₂ nanoparticles were solidly and homogeneously grafted on the surface of g-C₃N₄, resulting in greatly improved photocatalytic H₂ production. When the amount of NiS₂ was 3 wt%, the resultant NiS₂/g-C₃N₄ photocatalyst showed the highest H₂ evolution rate (116.343 μmol h^-1 g^-1), which is significantly higher than that of the pure g-C₃N₄ (3 μmol h^-1 g^-1). Moreover, the results of a recycling test for the NiS₂/g-C₃N₄(3 wt%) sample showed that this sample could maintain a stable and effective photocatalytic H₂-evolution performance under visible-light irradiation. Based on the above results, a possible mechanism of the improved photocatalytic performance was proposed for the presented NiS₂/g-C₃N₄ photocatalysts, in which the photogenerated electrons of g-C₃N₄ can be rapidly transferred to the NiS₂ nanoparticles via the close and continuous contact between them; then, the photogenerated electrons rapidly react with H₂O adsorbed on the surface of NiS₂, which has a surficial metallic character and high catalytic activity, to produce H₂. Considering the mild and facile synthesis method, the presented low-cost and highly efficient NiS₂-modified g-C₃N₄ photocatalysts would have great potential for practical use in photocatalytic H₂ production.

Enhanced ethanol electro-oxidation on CeO₂-modified Pt/Ni catalysts in alkaline solution

Zhihua Xu, Lixia Rao, Haiyan Song, Zhaoxiong Yan, Lijun Zhang, Shuibin Yang

2017, 38 (2): 305-312. DOI: 10.1016/S1872-2067(16)62560-3

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Pt/Ni catalysts modified with CeO₂ nanoparticles were prepared by simple composite electrodeposition of Ni and CeO₂, and spontaneous Ni partial replacement by Pt processes. The as-prepared CeO₂-modified Pt/Ni catalysts showed enhanced catalytic performance for ethanol electro-oxidation compared with pure Pt/Ni, and acetate species were proposed to be the main products of the oxidation when using these catalysts. The content of CeO₂ in the as-prepared catalysts influenced their catalytic activity, with Pt/NiCe₂ (obtained from an electrolyte containing 100 mg/L CeO₂ nanoparticles) exhibiting higher activity and relatively better stability in ethanol electro-oxidation. This was mainly due to the oxygen storage capacity of CeO₂, the interaction between Pt and CeO₂/Ni, and the relatively small contact and charge transfer resistances. The results of this work thus suggest that electrocatalysts with low price and high activity can be rationally designed and produced by a simple route for use in direct ethanol fuel cells.

Three-dimensional MoS₂/reduced graphene oxide aerogel as a macroscopic visible-light photocatalyst

Ruiyang Zhang, Wenchao Wan, Dawei Li, Fan Dong, Ying Zhou

2017, 38 (2): 313-320. DOI: 10.1016/S1872-2067(16)62568-8

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Photocatalysis is regarded as an ideal technology for solving the urgent environmental and energy issues that we face today. Among the reported photocatalysts, molybdenum disulfide (MoS₂) is very promising for applications in hydrogen production and pollutant photodegradation. However, its lack of active sites and the difficulty of recovering catalysts in powder form have hindered its wide application. Here, we report the successful preparation of a macroscopic visible-light responsive MoS₂/reduced graphene oxide (MoS₂/RGO) aerogel. The obtained MoS₂/RGO aerogel exhibits enhanced photocatalytic activity towards hydrogen production and photoreduction of Cr(VI) in comparison with the MoS₂ powder. In addition, the low density (56.1 mg/cm³) of the MoS₂/RGO aerogel enables it to be used as an efficient adsorption material for organic pollutants. Our results demonstrate that this very promising multifunctional aerogel has potential applications in environmental remediation and clean energy production.

Enhanced visible-light photo-oxidation of nitric oxide using bismuth-coupled graphitic carbon nitride composite heterostructures

Yuhan Li, Kangle Lv, Wingkei Ho, Zaiwang Zhao, Yu Huang

2017, 38 (2): 321-329. DOI: 10.1016/S1872-2067(16)62573-1

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Pure bismuth (Bi) metal-modified graphitic carbon nitride (g-C₃N₄) composites (Bi-CN) with a pomegranate-like structure were prepared by an in situ method. The Bi-CN composites were used as photocatalysts for the oxidation of nitric oxide (NO) under visible-light irradiation. The inclusion of pure Bi metal in the g-C₃N₄ layers markedly improved the light absorption of the Bi-CN composites from the ultraviolet to the near-infrared region because of the typical surface plasmon resonance of Bi metal. The separation and transfer of photogenerated charge carriers were greatly accelerated by the presence of built-in Mott-Schottky effects at the interface between Bi metal and g-C₃N₄. As a result, the Bi-CN composite photocatalysts exhibited considerably enhanced efficiency in the photocatalytic removal of NO compared with that of Bi metal or g-C₃N₄ alone. The pomegranate-like structure of the Bi-CN composites and an explanation for their improved photocatalytic activity were proposed. This work not only provides a design for highly efficient g-C₃N₄-based photocatalysts through modification with Bi metal, but also offers new insights into the mechanistic understanding of g-C₃N₄-based photocatalysis.

Effect of carrier and axial ligand on the photocatalytic activity of cobalt thioporphyrazine

Yi Liu, Xuanmu Zhou, Zhehui Zhang, Bingguang Zhang, Kejian Deng

2017, 38 (2): 330-336. DOI: 10.1016/S1872-2067(16)62580-9

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The photocatalytic activity of cobalt octakis(butylthio) porphyrazine (CoPz(BuS)₈) was assessed through photodegradation of the dye rhodamine B (RhB) in water under irradiation with a Xe lamp and aerated conditions. The photocatalytic activity of CoPz(BuS)₈ loaded on Al₂O₃ or SiO₂@Fe₃O₄ nanoparticles or coordinated with an axial azide ligand was also investigated. The results demonstrated that the photocatalytic activity of CoPz(BuS)₈ loaded on Al₂O₃ was higher than that loaded on SiO₂@Fe₃O₄. The kinetic curves of RhB degradation in aqueous solutions at different pH indicated the pseudo first-order kinetics of the reaction. The highest degradation rate for CoPz(BuS)₈ loaded Al₂O₃ at pH=4 after 160 min was 84.6%. However, the advantages of easier separation and recycling as well as the ability to terminate the reaction at any time for the CoPz(BuS)₈ loaded SiO₂@Fe₃O₄ cannot be ignored. When electron-rich NaN₃ was coordinated with CoPz(BuS)₈ as an axial ligand and loaded on Al₂O₃, the resulting catalyst produced more active oxygen species such as O_2^- and HO· to promote the quicker degradation of RhB than that by the other catalysts. For the N₃-coordinated CoPz(BuS)₈ loaded on Al₂O₃, the reactions at pH=4 and 7 distinctly deviated from first-order kinetics, and the degradation rate reached 77.6% after 80 min at pH=4.

Construction of Ag₃PO₄/Ag₂MoO₄ Z-scheme heterogeneous photocatalyst for the remediation of organic pollutants

Hua Tang, Yanhui Fu, Shufang Chang, Siyu Xie, Guogang Tang

2017, 38 (2): 337-347. DOI: 10.1016/S1872-2067(16)62570-6

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Hole/electron separation and charge transfer are the key processes for enhancing the visible-light photocatalysis performance of heterogeneous photocatalytic systems. To better utilize and understand these effects, binary Ag₃PO₄/Ag₂MoO₄ hybrid materials were fabricated by a facile solution-phase reaction and characterized systematically by X-ray diffraction (XRD), energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, field-emission scanning electron microscopy and ultraviolet-visible diffuse-reflectance spectroscopy. Under visible-light illumination, a heterogeneous Ag₃PO₄/Ag/Ag₂MoO₄ photocatalyst was constructed and demonstrated enhanced photocatalytic activity and photostability compared with pristine Ag₃PO₄ toward the remediation of the organic dye rhodamine B. The Ag₃PO₄/Ag₂MoO₄ hybrid catalyst with 8% mole fraction of Ag₂MoO₄ exhibited the highest photocatalytic activity toward the removal of typical dye molecules, including methyl orange, methylene blue and phenol aqueous solution. Moreover, the mechanism of the photocatalytic enhancement was investigated via hole- and radical-trapping experiments, photocurrent measurements, electrochemical impedance spectroscopy and XRD measurements. The XRD analysis revealed that metallic Ag nanoparticles formed initially on the surface of the Ag₃PO₄/Ag₂MoO₄ composites under visible-light illumination, leading to the generation of a Ag₃PO₄/Ag/Ag₂MoO₄ Z-scheme tandem photocatalytic system. The enhanced photocatalytic activity and stability were attributed to the formation of the Ag₃PO₄/Ag/Ag₂MoO₄ Z-scheme heterojunction and surface plasmon resonance of photo-reduced Ag nanoparticles on the surface. Finally, a plasmonic Z-scheme photocatalytic mechanism was proposed. This work may provide new insights into the design and preparation of advanced visible-light photocatalytic materials and facilitate their practical application in environmental issues.

Salt-assisted Synthesis of Hollow Bi₂WO₆ Microspheres with Superior Photocatalytic Activity for NO Removal

Meijuan Chen, Yu Huang, Shun Cheng Lee

2017, 38 (2): 348-356. DOI: 10.1016/S1872-2067(16)62584-6

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Hollow Bi₂WO₆ microspheres are successfully synthesized by a facile ultrasonic spray pyrolysis (USP) method using NaCl as a salt template. The as-prepared hollow microspheres assembled as nanoplates with dimensions of approximately 41-148 nm and are dispersed with non-uniform pores on the template surface. By swapping the salt template with KCl or Na₂SO₄, different morphologies of Bi₂WO₆ are obtained. The experimental results demonstrate that NaCl plays a key role on the formation of Bi₂WO₆ with hollow structures. The specific growth mechanism of hollow microspheres was studied in detail. The Bi₂WO₆ hollow microspheres exhibit an excellent photocatalytic efficiency for NO removal under solar light irradiation, which is 1.73 times higher than for the Bi₂WO₆ obtained in the absence of any salt template. This enhancement can be ascribed to the simultaneous improvement on the surface area and visible light-harvesting ability from the hollow structures. Electron spin resonance (ESR) results suggest that both radicals of ·OH and ·O₂^- are involved in the photocatalytic process over the BWO-NaCl sample. The production of ·O₂^- radicals offers better durability for NO removal.

Enhanced photocatalytic performance of cementitious material with TiO₂@Ag modified fly ash micro-aggregates

Lu Yang, Yining Gao, Fazhou Wang, Peng Liu, Shuguang Hu

2017, 38 (2): 357-364. DOI: 10.1016/S1872-2067(16)62590-1

Abstract ( 345 ) [Full Text(HTML)] ()

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A TiO₂ photocatalyst is coated on the surface of a zeolite fly ash bead (ZFAB) to improve its dispersability and exposure degree in a cement system. The application of Ag particles in TiO₂/ZFAB modified cementitious materials is to further enhance the photocatalytic performance. Various Ag@TiO₂/ZFAB modified cementitious specimens with different Ag dosages are prepared and the characteristics and photocatalytic performance of the prepared samples are investigated. It is observed that the multi-level pore structure of ZFAB can improve the exposure degree of TiO₂ in a cement system and is also useful to enhance the photocatalytic efficiency. With an increment of the amounts of Ag particles in the TiO₂/ZFAB modified cementitious samples, the photocatalytic activities increased first and then decreased. The optimal Ag@TiO₂/ZFAB modified cementitious sample reveals the maximum reaction rate constant for degrading benzene (9.91×10^-3 min^-1), which is approximately 3 and 10 times higher than those of TiO₂/ZFAB and TiO₂ modified samples, respectively. This suggests that suitable Ag particles coupled with a ZFAB carrier could effectively enhance the photocatalytic effects and use of TiO₂ in a cement system. Thus, ZFAB as a carrier could provide a potential method for a high efficiency engineering application of TiO₂ in the construction field.

Electrodeposition of Cu₂O/g-C₃N₄ heterojunction film on an FTO substrate for enhancing visible light photoelectrochemical water splitting

Shengsen Zhang, Jie Yan, Siyuan Yang, Yuehua Xu, Xin Cai, Xin Li, Xiangchao Zhang, Feng Peng, Yueping Fang

2017, 38 (2): 365-371. DOI: 10.1016/S1872-2067(16)62588-3

Abstract ( 658 ) [Full Text(HTML)] ()

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An immobilized Cu₂O/g-C₃N₄ heterojunction film was successfully made on an FTO substrate by electrophoretic deposition of g-C₃N₄ on a Cu₂O thin film. The photoelectrochemical (PEC) performance for water splitting by the Cu₂O/g-C₃N₄ film was better than pure g-C₃N₄ and pure Cu₂O film. Under -0.4 V external bias and visible light irradiation, the photocurrent density and PEC hydrogen evolution efficiency of the optimized Cu₂O/g-C₃N₄ film was -1.38 mA/cm² and 0.48 mL h^-1 cm^-2, respectively. The enhanced PEC performance of Cu₂O/g-C₃N₄ was attributed to the synergistic effect of light coupling and a matching energy band structure between g-C₃N₄ and Cu₂O as well as the external bias.

Solvent-assisted synthesis of porous g-C₃N₄ with efficient visible-light photocatalytic performance for NO removal

Wendong Zhang, Zaiwang Zhao, Fan Dong, Yuxin Zhang

2017, 38 (2): 372-378. DOI: 10.1016/S1872-2067(16)62585-8

Abstract ( 581 ) [Full Text(HTML)] ()

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Graphitic carbon nitride (g-C₃N₄) with efficient photocatalytic activity was synthesized through thermal polymerization of thiourea with the addition of water (CN-W) or ethanol (CN-E) at 550℃ for 2 h. The physicochemical properties of the g-C₃N₄ were investigated by X-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, photoluminescence spectroscopy, diffuse-reflection spectroscopy, BET and BJH surface area characterization, and elemental analysis. The carbon content was found to have self-doped into the g-C₃N₄ matrix during the thermal polymerization of thiourea and ethanol. CN-W and CN-E showed considerably enhanced visible-light photocatalytic activity, with NO removal percentages of 37.2% and 48.3%, respectively. Compared with pure g-C₃N₄, both the short and long lifetimes of the charge carriers in CN-W and CN-E were found to be prolonged. The mechanism of improved visible-light photocatalytic activity was deduced. The present work may provide a facile route to optimize the microstructure of g-C₃N₄ photocatalysts for high-performance environmental and energy applications.

Synthesis of C-Cl-codoped titania/attapulgite composites with enhanced visible-light photocatalytic activity

Lijuan Deng, Yi Xie, Gaoke Zhang

2017, 38 (2): 379-388. DOI: 10.1016/S1872-2067(17)62774-8

Abstract ( 266 ) [Full Text(HTML)] ()

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We demonstrate the synthesis of C-Cl-codoped titania/attapulgite (TiO₂/ATT) composites containing a mixture of TiO₂ phases by a facile sol-gel method at 70℃ using titanium tetraisopropoxide as the TiO₂ precursor and ATT as a support for the TiO₂ nanoparticles. The photocatalytic activity of the C-Cl-codoped TiO₂/ATT composites with mixed anatase/brookite/rutile phases obtained at pH=3.0 was much higher than that of commercially available Degussa P25 for the photocatalytic degradation of acid red G under visible-light irradiation. The excellent photocatalytic activity of the developed composite originates from the nonmetal codoping, which extends the absorption edge of TiO₂ into visible region, and the presence of multiple phases, which slow the recombination of photoexcited electron/hole pairs. The formation of hydroxyl radicals during the photocatalytic degradation process was detected by photoluminescence probing using terephthalic acid. A mechanism for photocatalysis over the C-Cl-codoped TiO₂/ATT composites was proposed.

Selective oxidative dehydrogenation of ethane to ethylene over a hydroxylated boron nitride catalyst

Lei Shi, Bing Yan, Dan Shao, Fan Jiang, Dongqi Wang, An-Hui Lu

2017, 38 (2): 389-395. DOI: 10.1016/S1872-2067(17)62786-4

Abstract ( 551 ) [Full Text(HTML)] ()

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Boron nitride containing hydroxyl groups efficiently catalysed oxidative dehydrogenation of ethane to ethylene, offering rather high selectivity (95%) but only small amount of CO₂ formation (0.4%) at a given ethane conversion of 11%. Even at high conversion level of 63%, the selectivity of ethylene retained at 80%, which is competitive with the energy-demanding industrialized steam cracking route. A long-term test for 200 h resulted in stable conversion and product selectivity, showing the excellent catalytic stability. Both experimental and computational studies have identified that the hydrogen abstraction of B-OH groups by molecular oxygen dynamically generated the active sites and triggered ethane dehydrogenation.

High activity of a Pt decorated Ni/C nanocatalyst for hydrogen oxidation

Xiaolin Gao, Yufei Wang, Heping Xie, Tao Liu, Wei Chu

2017, 38 (2): 396-403. DOI: 10.1016/S1872-2067(17)62783-9

Abstract ( 403 ) [Full Text(HTML)] ()

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The Pt decorated Ni/C nanocatalysts were prepared for hydrogen oxidation reaction (HOR) in fuel cell. By regulating the contents of Pt and Ni in the catalyst, both the composition and the structure affected the electrochemical catalytic characteristics of the Pt-Ni/C catalysts. When the Pt mass content was 3.1% percent and that of Ni was 13.9% percent, the Pt-Ni/C-3 catalyst exhibited a larger electrochemically active surface area and a higher exchange current density toward HOR than those of pure supported platinum sample. Our study demonstrates a feasible approach for designing the more efficient catalysts with lower content of noble metal for HOR in fuel cell.

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