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Chinese Journal of Catalysis
2020, Vol. 41, No. 1
Online: 18 January 2020

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Cover: Yu and coworkers in their article on pages 9–20 reported a graphene-modified WO₃/TiO₂ step-scheme heterojunction composite photocatalyst, which was fabricated by a facile hydrothermal method. The prepared ternary WO₃/TiO₂/rGO composite photocatalyst demonstrated a remarkably enhanced photocatalytic H₂-production activity by water splitting, which was about 3.5-fold that of pure TiO₂.

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Table of Contents for VOL.41 No.1 2020, 41 (1):  0-0.  Abstract ( 27 )   PDF (5038KB) ( 70 )

Editorial

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Preface to the Special Issue on Photocatalytic H2 Production and CO2 Reduction Jiaguo Yu, Jian Ru Gong, Quanjun Xiang 2020, 41 (1):  1-1.  DOI: 10.1016/S1872-2067(19)63521-7 Abstract ( 67 )   [Full Text(HTML)] () PDF (396KB) ( 373 )

Photocatalytic H2 production

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GaP/GaPN core/shell nanowire array on silicon for enhanced photoelectrochemical hydrogen production Guancai Xie, Saad Ullah Jan, Zejian Dong, Yawen Dai, Rajender Boddula, Yuxuan Wei, Chang Zhao, Qi Xin, Jiao-Na Wang, Yinfang Du, Lan Ma, Beidou Guo, Jian Ru Gong 2020, 41 (1):  2-8.  DOI: 10.1016/S1872-2067(19)63465-0 Abstract ( 105 )   [Full Text(HTML)] () PDF (1297KB) ( 421 )   Supporting Information Simultaneously improving the efficiency and stability on a large scale is significant for the development of photoelectrochemical (PEC) water splitting systems. Here, we demonstrated a novel design of GaP/GaPN core/shell nanowire (NW) decorated p-Si photocathode for improved PEC hydrogen production performance compared to that of bare p-Si photocathode. The formation of the p-n junction between p-Si and GaP NW promotes charge separation, and the lower conduction band position of GaPN relative to that of GaP further facilitates the transfer of photogenerated electrons to the electrode surface. In addition, the NW morphology both shortens the carrier collection distance and increases the specific surface area, which result in superior reaction kinetics. Moreover, introduction of N in GaP is beneficial for enhancing the light absorption as well as stability. Our efficient and facile strategy can be applied to other solar energy conversion systems as well.

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Enhanced photocatalytic H2-production activity of WO3/TiO2 step-scheme heterojunction by graphene modification Fei He, Aiyun Meng, Bei Cheng, Wingkei Ho, Jiaguo Yu 2020, 41 (1):  9-20.  DOI: 10.1016/S1872-2067(19)63382-6 Abstract ( 206 )   [Full Text(HTML)] () PDF (2074KB) ( 1131 )   Sunlight-driven photocatalytic water-splitting for hydrogen (H2) evolution is a desirable strategy to utilize solar energy. However, this strategy is restricted by insufficient light harvesting and high photogenerated electron-hole recombination rates of TiO2-based photocatalysts. Here, a graphene-modified WO3/TiO2 step-scheme heterojunction (S-scheme heterojunction) composite photocatalyst was fabricated by a facile one-step hydrothermal method. In the ternary composite, TiO2 and WO3 nanoparticles adhered closely to reduced graphene oxide (rGO) and formed a novel S-scheme heterojunction. Moreover, rGO in the composite not only supplied abundant adsorption and catalytically active sites as an ideal support but also promoted electron separation and transfer from the conduction band of TiO2 by forming a Schottky junction between TiO2 and rGO. The positive cooperative effect of the S-scheme heterojunction formed between WO3 and TiO2 and the Schottky heterojunction formed between TiO2 and graphene sheets suppressed the recombination of relatively useful electrons and holes. This effect also enhanced the light harvesting and promoted the reduction reaction at the active sites. Thus, the novel ternary WO3/TiO2/rGO composite demonstrated a remarkably enhanced photocatalytic H2 evolution rate of 245.8 μmol g-1 h-1, which was approximately 3.5-fold that of pure TiO2. This work not only presents a low-cost graphene-based S-scheme heterojunction photocatalyst that was obtained via a feasible one-step hydrothermal approach to realize highly efficient H2 generation without using noble metals, but also provides new insights into the design of novel heterojunction photocatalysts.

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Enhanced photocatalytic hydrogen production activity of highly crystalline carbon nitride synthesized by hydrochloric acid treatment Yang Li, Dainan Zhang, Xionghan Feng, Quanjun Xiang 2020, 41 (1):  21-30.  DOI: 10.1016/S1872-2067(19)63427-3 Abstract ( 282 )   [Full Text(HTML)] () PDF (5240KB) ( 775 )   Supporting Information Crystalline carbon nitride (CCN) prepared by a molten-salt method is attracting increased attention because of its promising properties and excellent photocatalytic activity. In this work, we further improve the crystallinity of CCN through synthesis by the molten-salt method under the action of aqueous hydrochloric acid (HCl) solution. Our results showed that the crystallinity of the as-prepared samples increased with increasing HCl concentration and reached the maximum value at 0.1 mol L-1. This can be attributed to the removal of some potassium ions (K+) from the terminal amino groups of CCN by the aqueous HCl solution, which results in a release of the polymerization sites. As a result, the crystallinity of the as-prepared samples further increased. Moreover, the obtained 0.1 highly crystalline carbon nitride (0.1HCCN; treated with 0.1 mol L-1 aqueous HCl solution) exhibited an excellent photocatalytic hydrogen evolution of 683.54 µmol h-1 g-1 and a quantum efficiency of 6.6% at 420 nm with triethanolamine as the sacrificial agent. This photocatalytic hydrogen evolution was 2 and 10 times higher than those of CCN and bulk carbon nitride, respectively. The enhanced photocatalytic activity was attributed to the improved crystallinity and intercalation of K+ into the xHCCN interlayer. The improved crystallinity can decrease the number of surface defects and hydrogen bonds in the as-prepared sample, thereby increasing the mobility of the photoinduced carriers and reducing the recombination sites of the electron-hole pairs. The K+ intercalated into the xHCCN interlayer also promoted the transfer of the photoinduced electrons because these ions can increase the electronic delocalization and extend the π-conjugated systems. This study may provide new insights into the further development of the molten-salt method.

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Highly efficient visible-light photocatalytic H2 evolution over 2D-2D CdS/Cu7S4 layered heterojunctions Doudou Ren, Rongchen Shen, Zhimin Jiang, Xinyong Lu, Xin Li 2020, 41 (1):  31-40.  DOI: 10.1016/S1872-2067(19)63467-4 Abstract ( 137 )   [Full Text(HTML)] () PDF (2754KB) ( 598 )   Converting solar energy into clean and sustainable chemical fuels is a promising strategy for exploiting renewable energy. The application of photocatalytic water splitting technology in hydrogen production is important for sustainable energy development and environmental protection. In this study, for the first time, 2D Cu7S4 co-catalysts were coupled on the surface of a CdS nanosheet photocatalyst by a one-step ultrasonic-assisted electrostatic self-assembly method at room temperature. The as-fabricated 2D-2D CdS/Cu7S4 layered heterojunctions were demonstrated to be advanced composite photocatalysts that enhance the water splitting efficiency toward hydrogen production. The highest hydrogen evolution rate of the 2D-2D CdS/2%Cu7S4 binary heterojunction photocatalyst was up to 27.8 mmol g-1 h-1 under visible light irradiation, with an apparent quantum efficiency of 14.7% at 420 nm, which was almost 10.69 times and 2.65 times higher than those of pure CdS nanosheets (2.6 mmol g-1 h-1) and CdS-2%CuS (10.5 mmol g-1 h-1), respectively. The establishment of the CdS/Cu7S4 binary-layered heterojunction could not only enhance the separation of photogenerated electron-hole (e--h+) pairs, improve the transfer of photo-excited electrons, and prolong the life-span of photo-generated electrons, but also enhance the light absorption and hydrogen-evolution kinetics. All these factors are important for the enhancement of the photocatalytic activity. Expectedly, the 2D-2D interface coupling strategy based on CdS NSs can be extensively exploited to improve the hydrogen-evolution activity over various kinds of conventional semiconductor NSs.

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Step-scheme porous g-C3N4/Zn0.2Cd0.8S-DETA composites for efficient and stable photocatalytic H2 production Feifei Mei, Zhen Li, Kai Dai, Jinfeng Zhang, Changhao Liang 2020, 41 (1):  41-49.  DOI: 10.1016/S1872-2067(19)63389-9 Abstract ( 123 )   [Full Text(HTML)] () PDF (4022KB) ( 650 )   In recent years, environmental pollution and energy crisis have become increasingly serious issues owing to the burning of fossil fuels. Among the many technologies, decomposition of water to produce hydrogen has attracted much attention because of its sustainability and non-polluting characteristic. However, highly efficient decomposition of water that is driven by visible light is still a challenge. Herein, we report the large-scale preparation of step-scheme porous graphite carbon nitride/Zn0.2Cd0.8S-diethylenetriamine (Pg-C3N4/Zn0.2Cd0.8S-DETA) composite by a facile solvothermal method. It was found by UV-vis spectroscopy that 15%Pg-C3N4/Zn0.2Cd0.8S-DETA exhibited suitable visible absorption edge and band gap for water decomposition. The hydrogen production rate of 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite was 6.69 mmol g-1 h-1, which was 16.73, 1.61, and 1.44 times greater than those of Pg-C3N4, CdS-DETA, and Zn0.2Cd0.8S-DETA, respectively. In addition, 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite displayed excellent photocatalytic stability, which was maintained for seven cycles of photocatalytic water splitting test. We believe that 15%Pg-C3N4/Zn0.2Cd0.8S-DETA composite can be a valuable guide for the development of solar hydrogen production applications in the near future.

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Hydrogen producing water treatment through mesoporous TiO2 nanofibers with oriented nanocrystals Guocheng Huang, Xueyan Liu, Shuangru Shi, Sitan Li, Zhengtao Xiao, Weiqian Zhen, Shengwei Liu, Po Keung Wong 2020, 41 (1):  50-61.  DOI: 10.1016/S1872-2067(19)63424-8 Abstract ( 94 )   [Full Text(HTML)] () PDF (3046KB) ( 373 )   The development of well-defined TiO2 nanoarchitectures is a versatile strategy to achieve high-efficiency photocatalytic performance. In this study, mesoporous TiO2 nanofibers consisting of oriented nanocrystals were fabricated by a facile vapothermal-assisted topochemical transformation of preformed H-titanate nanobelts. The vapothermal temperature is crucial in tuning the microstructures and photocatalytic redox properties of the resulting mesoporous TiO2 nanofibers. The microstructures were characterized with XRD, TEM, XPS and nitrogen adsorption-desorption isotherms, etc. The photocatalytic activities were evaluated by photocatalytic oxidation of organic pollutant (Rhodamine B as an example) as well as photocatalytic reduction of water to generate hydrogen (H2). The nanofibers vapothermally treated at 150℃ showed the highest photocatalytic activity in both oxidation and reduction reactions, 2 times higher than that of P25. The oriented alignment and suitable mesoporosity in the resulting nanofiber architecture were crucial for enhancing photocatalytic performances. The oriented alignment of anisotropic anatase nanocrystals shall facilitate faster vectorial charge transportation along the nanofibers architecture. And, the suitable mesoporosity and high surface area would also effectively enhance the mass exchange during photocatalytic reactions. We also demonstrate that efficient energy-recovering photocatalytic water treatments could be accomplished by a cascading oxic-anoxic process where the dye is degraded in the oxic phase and hydrogen is generated in the successive anoxic phase. This study showcases a novel and facile method to fabricate mesoporous TiO2 nanofibers with high photocatalytic activity for both clean energy production and environmental purification.

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Carbon nanotube@silicon carbide coaxial heterojunction nanotubes as metal-free photocatalysts for enhanced hydrogen evolution Xunfu Zhou, Qiongzhi Gao, Siyuan Yang, Yueping Fang 2020, 41 (1):  62-71.  DOI: 10.1016/S1872-2067(19)63421-2 Abstract ( 80 )   [Full Text(HTML)] () PDF (13355KB) ( 337 )   Considerable research efforts have been devoted to developing novel photocatalysts with increased performances by hybridizing inorganic nanomaterials with carbon nanotubes. In this work, one-dimensional coaxial core-shell carbon nanotubes@SiC nanotubes were successfully synthesized via in situ growth of SiC coatings on carbon nanotubes by a vapor-solid reaction between silicon vapor and carbon nanotubes. High-resolution transmission electron microscope images show that SiC and carbon nanotubes link to form a robust heterojunction with intrinsic atomic contact, which results in efficient separation of the photogenerated electron-hole pairs on SiC and electron transfer from SiC to carbon nanotubes. Compared with those of similar materials such as pure SiC nanocrystals and SiC nanotubes, the metal-free carbon nanotubes@SiC exhibits an enhanced photocatalytic activity for hydrogen evolution, which is attributed to the enhanced light absorption and the efficient interfacial charge transfer/separation brought about by their one-dimensional coaxial nanoheterostructures. Moreover, the photocatalytic stability of the metal-free carbon nanotubes@SiC was tested for over 20 h without any obvious decay.

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Synergistic effect of Co(II)-hole and Pt-electron cocatalysts for enhanced photocatalytic hydrogen evolution performance of P-doped g-C3N4 Kouhua Sun, Jun Shen, Qinqin Liu, Hua Tang, Mingyi Zhang, Syed Zulfiqar, Chunsheng Lei 2020, 41 (1):  72-81.  DOI: 10.1016/S1872-2067(19)63430-3 Abstract ( 264 )   [Full Text(HTML)] () PDF (1970KB) ( 707 )   g-C3N4 is a metal-free semiconductor and a potential candidate for photocatalytic H2 production, however, the drawbacks, rapid recombination rate and limited migration efficiency of photogenerated carriers, restrict its photocatalytic activity. Herein, Co(Ⅱ) as a hole cocatalyst modified P-doped g-C3N4 were successfully prepared to ameliorate the separation efficiency of photoinduced carriers and enhance the photocatalytic hydrogen production. The photocatalytic results demonstrated that the P-doped g-C3N4 (PCN) exhibited higher photocatalytic activity compared with pure g-C3N4, while Co(Ⅱ)/PCN photocatalyst exhibited further enhancement of photocatalytic performance. The proposed possible mechanism based on various characterizations is that P-doping can modulate the electronic structure of g-C3N4 to boost the separation of photogenerated-e- and h+; while the synergistic effect of both Co(Ⅱ) (as hole cocatalyst) and Pt (as electron cocatalyst) can not only lead to the directional shunting of photogenerated e+-h- pairs, but further accelerate the photogenerated electrons transfer to Pt in order to join the photocatalytic reduction process for hydrogen evolution. As a result, the transportation and separation of photoinduced carriers were accelerated to greatest extent in the Pt/Co(Ⅱ)/PCN photocatalyst.

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Unique synergistic effects of ZIF-9(Co)-derived cobalt phosphide and CeVO4 heterojunction for efficient hydrogen evolution Lijun Zhang, Xuqiang Hao, Junke Li, Yuanpeng Wang, Zhiliang Jin 2020, 41 (1):  82-94.  DOI: 10.1016/S1872-2067(19)63454-6 Abstract ( 83 )   [Full Text(HTML)] () PDF (3020KB) ( 558 )   The photocatalytic decomposition of water to produce hydrogen is an important process, through which solar energy can be converted to chemical energy. Non-precious metal phosphides have quietly attracted attention as an emerging inexpensive photocatalyst. In this study, we reported that a CoP/CeVO4 hybrid photocatalyst exhibited high hydrogen evolution efficiency owing to EY (eosin Y) sensitization under visible light irradiation for the first time, and the amount of generated hydrogen reached 444.6 μmol in 5 h. The CoP/CeVO4 nanohybrids were synthesized by a simple chemical precipitation method. The coupling of CoP and CeVO4 with ZIF-9 as a precursor could be completed in one step. The CeVO4 particles were firmly attached to the surface of the CoP particles to form a "small point" to "big point" heterojunction. The results of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, EDX, and transmission electron microscopy showed the formation of CoP and CeVO4 nanoparticles and the structure of the composite. Based on a detailed analysis of the Mott-Schottky plot, the UV-vis diffuse reflectance spectra, photocurrent-time (it) curve, Tafel curve, Nyquist curve (EIS), linear volt-ampere curve (LSV), and steady-state fluorescence spectra were studied. The time-resolved photoluminescence measurements indicated that the reason for the high-efficiency hydrogen evolution of CoP/CeVO4 was that the bands of CoP and CeVO4 were bent due to the existence of the Schottky barrier, and a heterojunction was formed between CoP and CeVO4, which generated an internal electric field and accelerated the charge transfer. In addition, the synergistic effect between CoP and CeVO4 provided a new hydrogen-evolution activity center for each of them. The improved carrier separation efficiency and the decrease in the photo-generated recombination rate led to the excellent photocatalytic hydrogen-evolution activity of the CoP/CeVO4 composite catalyst. This work provides a new strategy for modulating the electronic structure and carrier behavior of transition metal phosphide photocatalysts.

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Nitrate-group-grafting-induced assembly of rutile TiO2 nanobundles for enhanced photocatalytic hydrogen evolution Heng Wang, Xiantao Hu, Yajuan Ma, Dajian Zhu, Tao Li, Jingyu Wang 2020, 41 (1):  95-102.  DOI: 10.1016/S1872-2067(19)63452-2 Abstract ( 75 )   [Full Text(HTML)] () PDF (2817KB) ( 323 )   Supporting Information In this study, an acid-induced assembly strategy for a rutile TiO2 photocatalyst was proposed on the basis of the treatment of lamellar protonated titanate with a concentrated HNO3 solution. Nitrate groups were successfully grafted onto a TiO2 surface and induced the assembly of rutile TiO2 nanorods into uniform spindle-like nanobundles. The resulting TiO2 product achieved a photocatalytic hydrogen evolution rate of 402.4 μmol h-1, which is 3.1 times higher than that of Degussa P25-TiO2. It was demonstrated that nitrate group grafting caused the rutile TiO2 surface to become negatively charged, which is favorable for trapping positive protons and improving charge carrier separation, thereby enhancing photocatalytic hydrogen production. Additionally, surface charges were crucial to structural stability based on electrostatic repulsion. This study not only developed a facile surface modification strategy for fabricating efficient H2 production photocatalysts but also identified an influence mechanism of inorganic acids different from that reported in the literature.

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Simultaneous visible-light-induced hydrogen production enhancement and antibiotic wastewater degradation using MoS2@ZnxCd1-xS: Solid-solution-assisted photocatalysis Zhidong Wei, Meiqi Xu, Junying Liu, Weiqi Guo, Zhi Jiang, Wenfeng Shangguan 2020, 41 (1):  103-113.  DOI: 10.1016/S1872-2067(19)63479-0 Abstract ( 82 )   [Full Text(HTML)] () PDF (4792KB) ( 423 )   In this study, a ZnxCd1-xS solid solution was successfully synthesized using a hydrothermal method. MoS2 serving as a co-catalyst for hydrogen evolution was also prepared through a one-pot hydrothermal method. The structures, morphology, chemical states, and optical properties were characterized using powder X-ray diffraction, scanning electron microscopy, high-angle annular dark field-scanning transmission electron microscopy, elemental mapping, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflection spectroscopy. Visible-light-driven photocatalytic experiments were conducted to simultaneously achieve hydrogen production and amoxicillin antibiotic wastewater degradation. The results indicated 8%MoS2/ZnxCd1-xS achieves the best photocatalytic performance. The ZnxCd1-xS samples illustrated a superior performance to that of CdS, which can be attributed to a thermodynamic improvement. Based on the results of PL and TRPL analyses, the enhancement of the hydrogen production mechanisms can be ascribed to the prolonged separation process of the photocarriers. Furthermore, the degradation results were analyzed using the HPLC method and the possible degradation pathways were determined through the HPLC-MS techniques.

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Photocatalytic H2 generation via CoP quantum-dot-modified g-C3N4 synthesized by electroless plating Kezhen Qi, Wenxiu Lv, Iltaf Khan, Shu-yuan Liu 2020, 41 (1):  114-121.  DOI: 10.1016/S1872-2067(19)63459-5 Abstract ( 120 )   [Full Text(HTML)] () PDF (1035KB) ( 513 )   Photocatalytic water splitting is a promising method for hydrogen production. Numerous efficient photocatalysts have been synthesized and utilized. However, photocatalysts without a noble metal as the co-catalyst have been rarely reported. Herein, a CoP co-catalyst-modified graphitic-C3N4 (g-C3N4/CoP) is investigated for photocatalytic water splitting to produce H2. The g-C3N4/CoP composite is synthesized in two steps. The first step is related to thermal decomposition, and the second step involves an electroless plating technique. The photocatalytic activity for hydrogen evolution reactions of g-C3N4 is distinctly increased by loading the appropriate amount of CoP quantum dots (QDs). Among the as-synthesized samples, the optimized one (g-C3N4/CoP-4%) shows exceptional photocatalytic activity as compared with pristine g-C3N4, generating H2 at a rate of 936 μ mol g-1 h-1, even higher than that of g-C3N4 with 4 wt% Pt (665 μmol g-1 h-1). The UV-visible and optical absorption behavior confirms that g-C3N4 has an absorption edge at 451 nm, but after being composited with CoP, g-C3N4/CoP-4% has an absorption edge at 497 nm. Furthermore, photoluminescence and photocurrent measurements confirm that loading CoP QDs to pristine g-C3N4 not only enhances the charge separation, but also improves the transfer of photogenerated e--h+ pairs, thus improving the photocatalytic performance of the catalyst to generate H2. This work demonstrates a feasible strategy for the synthesis of highly efficient metal phosphide-loaded g-C3N4 for hydrogen generation.

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The embedded CuInS2 into hollow-concave carbon nitride for photocatalytic H2O splitting into H2 with S-scheme principle Jinhua Luo, Zhexing Lin, Yan Zhao, Shujuan Jiang, Shaoqing Song 2020, 41 (1):  122-130.  DOI: 10.1016/S1872-2067(19)63490-X Abstract ( 72 )   [Full Text(HTML)] () PDF (2315KB) ( 467 )   It is still a great challenge to effectively optimize the electronic structure of photocatalysts for the sustainable and efficient conversion of solar energy to H2 energy. To resolve this issue, we report on the optimization of the electronic structure of hollow-concave carbon nitride (C3N4) by deviating the sp2-hybridized structure of its tri-s-triazine component from the two-dimensional plane. The embedded CuInS2 into C3N4 (CuInS2@C3N4) demonstrates an increased light-capturing capability and the promoted directional transfer of the charge carrier. Research results reveal that the hollow structure with an apparent potential difference between the concave and convex C3N4 drives the directional transfer of the photoinduced electrons from the Cu 2p orbital of CuInS2 to the N 1s orbital of C3N4 with the S-scheme principle. The H2 evolution efficiency over CuInS2@C3N4 is up to 373 µmol?h-1 g-1 under visible irradiation, which is 1.57 and 1.35 times higher than those over the bulk g-C3N4 with 1 wt% Pt (238 µmol?h-1 g-1) and g-C3N4 with 3 wt% Pd (276 µmol?h-1 g-1), respectively. This suggests that the apparent potential difference of the hollow C3N4 results in an efficient reaction between the photogenerated electrons and H2O. This work supplies a new strategy for enhancing the sustainable solar conversion performance of carbon nitride, which can also be suitable for other semiconductors.

Photocatalytic CO2 reduction

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Solar-heating boosted catalytic reduction of CO2 under full-solar spectrum Hongjia Wang, Yanjie Wang, Lingju Guo, Xuehua Zhang, Caue Ribeiro, Tao He 2020, 41 (1):  131-139.  DOI: 10.1016/S1872-2067(19)63393-0 Abstract ( 160 )   [Full Text(HTML)] () PDF (1582KB) ( 413 )   Catalytic converting CO2 into fuels with the help of solar energy is regarded as 'dream reaction', as both energy crisis and environmental issue can be mitigated simultaneously. However, it is still suffering from low efficiency due to narrow solar-spectrum utilization and sluggish heterogeneous reaction kinetics. In this work, we demonstrate that catalytic reduction of CO2 can be achieved over Au nanoparticles (NPs) deposited rutile under full solar-spectrum irradiation, boosted by solar-heating effect. We found that UV and visible light can initiate the reaction, and the heat from IR light and local surface-plasmon resonance relaxation of Au NPs can boost the reaction kinetically. The apparent activation energy is determined experimentally and is used to explain the superior catalytic activity of Au/rutile to rutile in a kinetic way. We also find the photo-thermal synergy in the Au/rutile system. We envision that this work may facilitate understanding the kinetics of CO2 reduction and developing feasible catalytic systems with full solar spectrum utilization for practical artificial photosynthesis.

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Bifunctional S-scheme g-C3N4/Bi/BiVO4 hybrid photocatalysts toward artificial carbon cycling Quan Xie, Wanmei He, Shengwei Liu, Chuanhao Li, Jinfeng Zhang, Po Keung Wong 2020, 41 (1):  140-153.  DOI: 10.1016/S1872-2067(19)63481-9 Abstract ( 110 )   [Full Text(HTML)] () PDF (5105KB) ( 754 )   Supporting Information Although both the aerobic photocatalytic oxidation of organic pollutants into CO2 and the anaerobic photocatalytic reduction of CO2 into solar fuels have been intensively studied, few efforts have been devoted to combining these carbon-involved photocatalytic oxidation-reduction processes together, by which an artificial photocatalytic carbon cycling process can be established. The key challenge lies in the exploitation of efficient bifunctional photocatalysts, capable of triggering both aerobic oxidation and anaerobic reduction reactions. In this work, a bifunctional ternary g-C3N4/Bi/BiVO4 hybrid photocatalyst is successfully constructed, which not only demonstrates superior aerobic photocatalytic oxidation performance in degrading an organic pollutant (using the dye, Rhodamine B as a model), but also exhibits impressive photocatalytic CO2 reduction performance under anaerobic conditions. Moreover, a direct conversion of Rhodamine B to solar fuels in a one-pot anaerobic reactor can be achieved with the as-prepared ternary g-C3N4/Bi/BiVO4 hybrid photocatalyst. The excellent bifunctional photocatalytic performance of the g-C3N4/Bi/BiVO4 photocatalyst is associated with the formation of efficient S-scheme hybrid junctions, which contribute to promoting the appropriate charge dynamics, and sustaining favorable charge potentials. The formation of the S-scheme heterojunction is supported by scavenger studies and density functional theory calculations. Moreover, the in-situ formed plasmonic metallic Bi nanoparticles in the S-scheme hybrid g-C3N4/Bi/BiVO4 photocatalyst enhances vectorial interfacial electron transfer. This novel bifunctional S-scheme g-C3N4/Bi/BiVO4 hybrid photocatalyst system provides new insights for the further development of an integrated aerobic-anaerobic reaction system for photocatalytic carbon cycling.

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Thermal coupled photoconductivity as a tool to understand the photothermal catalytic reduction of CO2 Dashuai Li, Yu Huang, Songmei Li, Changhua Wang, Yingying Li, Xintong Zhang, Yichun Liu 2020, 41 (1):  154-160.  DOI: 10.1016/S1872-2067(19)63475-3 Abstract ( 155 )   [Full Text(HTML)] () PDF (1246KB) ( 450 )   Photocatalysis shows great promise in the field of solar energy conversion. One of the reasons for this is because it promotes the development of multi-field-coupled catalysis. In order to explore the principles of multi-field-coupled catalytic reactions, an in situ multi-field-coupled characterization technique is required. In this study, we obtained hydrogenated ST-01 TiO2 and observed enhanced catalytic activity by thermal coupled photocatalysis. In situ photoconductivity was employed to understand the activity enhancement. The effects of the reaction temperature, reaction atmosphere, and oxygen vacancy (Ov) on the photoconductivity of TiO2 were studied. After coupling thermal into photoconductivity measurement, highly active Ov-TiO2 displayed rapid decay of photoconductivity in a CO2 atmosphere and slow decay of photoconductivity in a N2 atmosphere. These phenomena revealed that photothermal coupling assisted the detrapping of electrons at the Ov surface and promoted electron transfer to CO2, which clearly explained the high photothermal catalytic activity of Ov-TiO2. This study demonstrated that photoconductivity is a useful tool to help understand photothermal catalytic phenomena.

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Fabrication of Z-scheme MoO3/Bi2O4 heterojunction photocatalyst with enhanced photocatalytic performance under visible light irradiation Tiangui Jiang, Kai Wang, Ting Guo, Xiaoyong Wu, Gaoke Zhang 2020, 41 (1):  161-169.  DOI: 10.1016/S1872-2067(19)63391-7 Abstract ( 121 )   [Full Text(HTML)] () PDF (11012KB) ( 701 )   Supporting Information Constructing Z-scheme heterojunction to improve the separation efficiency of photogenerated carriers of photocatalysts has gained extensive attention. In this work, we fabricated a novel Z-scheme MoO3/Bi2O4 heterojunction photocatalyst by a hydrothermal method. XPS analysis results indicated that strong interaction between MoO3 and Bi2O4 is generated, which contributes to charge transfer and separation of the photogenerated carriers. This was confirmed by photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) tests. The photocatalytic performance of the as-synthesized photocatalysts was evaluated by degrading rhodamine B (RhB) in aqueous solution under visible light irradiation, showing that 15% MoO3/Bi2O4 (15-MB) composite exhibited the highest photocatalytic activity, which is 2 times higher than that of Bi2O4. Besides, the heterojunction photocatalyst can keep good photocatalytic activity and stability after five recycles. Trapping experiments demonstrated that the dominant active radicals in photocatalytic reactions are superoxide radical (·O2-) and holes (h+), indicating that the 15-MB composite is a Z-scheme photocatalyst. Finally, the mechanism of the Z-scheme MoO3/Bi2O4 composite for photo-degrading RhB in aqueous solution is proposed. This work provides a promising strategy for designing Bi-based Z-scheme heterojunction photocatalysts for highly efficient removal of environmental pollutants.

Other photocatalytic application

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In situ fabrication of CdMoO4/g-C3N4 composites with improved charge separation and photocatalytic activity under visible light irradiation Bo Chai, Juntao Yan, Guozhi Fan, Guangsen Song, Chunlei Wang 2020, 41 (1):  170-179.  DOI: 10.1016/S1872-2067(19)63383-8 Abstract ( 67 )   [Full Text(HTML)] () PDF (1976KB) ( 289 )   To further improve the charge separation and photocatalytic activities of g-C3N4 and CdMoO4 under visible light irradiation, CdMoO4/g-C3N4 composites were rationally synthesized by a facile precipitation-calcination procedure. The crystal phases, morphologies, chemical compositions, textural structures, and optical properties of the as-prepared composites were characterized by the corresponding analytical techniques. The photocatalytic activities toward degradation of rhodamine B solution were evaluated under visible light irradiation. The results revealed that integrating CdMoO4 with g-C3N4 could remarkably improve the charge separation and photocatalytic activity, compared with those of pristine g-C3N4 and CdMoO4. This would be because the CdMoO4/g-C3N4 composites could facilitate the transfer and separation of the photoexcited electron-hole pairs, which was confirmed by electrochemical impedance spectroscopy, transient photocurrent responses, and photoluminescence measurements. Moreover, active species trapping experiments demonstrated that holes (h+) and superoxide radicals (·O2-) were the main active species during the photocatalytic reaction. A possible photocatalytic mechanism was proposed on the basis of the energy band structures determined by Mott-Schottky tests. This work would provide further insights into the rational fabrication of composites for organic contaminant removal.

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MoSe2/ZnO/ZnSe hybrids for efficient Cr(VI) reduction under visible light irradiation Zhenxing Ren, Xinjuan Liu, Zhihao Zhuge, Yinyan Gong, Chang Q. Sun 2020, 41 (1):  180-187.  DOI: 10.1016/S1872-2067(19)63484-4 Abstract ( 99 )   [Full Text(HTML)] () PDF (1734KB) ( 420 )   Supporting Information Photocatalysis activated by visible light remains highly challenging. Here, we report novel MoSe2/ZnO/ZnSe (ZM) hybrids fabricated via a simple hydrothermal method for photocatalytic reduction of Cr(VI) under visible light irradiation. ZM hybrids show improved photocatalytic reduction ability under visible light irradiation compared to pure ZnO owing to good visible light absorption and rapid electron transfer and separation. The ZM hybrid shows the highest Cr(VI) reduction rate of 100%. Moreover, the photocatalytic Cr(VI) reduction process is mainly controlled by photoinduced electrons.

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Sodium dodecyl sulfate-decorated MOF-derived porous Fe2O3 nanoparticles: High performance, recyclable photocatalysts for fuel denitrification Ruowen Liang, Zhiyu Liang, Feng Chen, Danhua Xie, Yanling Wu, Xuxu Wang, Guiyang Yan, Ling Wu 2020, 41 (1):  188-199.  DOI: 10.1016/S1872-2067(19)63402-9 Abstract ( 97 )   [Full Text(HTML)] () PDF (5104KB) ( 342 )   Magnetically recyclable porous sodium dodecyl sulfate (SDS)/Fe2O3 hybrids, which combine the porous structure of Fe2O3 and hydrophobicity of SDS, have been successfully synthesized for the first time. Porous Fe2O3 has been first pyrolyzed from MIL-100(Fe) using a simple two-step calcination route. Then, the obtained porous Fe2O3 nanoparticles have been self-assembled with SDS molecules and yielded hydrophobic SDS/Fe2O3 hybrids. The porous SDS/Fe2O3 hybrids have been demonstrated to be highly efficient for the denitrification of pyridine under visible light irradiation. The pyridine removal ratio has reached values as high as 100% after irradiation for 240 min. Combining the results of a series of experimental measurements, it was concluded that the superior photocatalytic performance of SDS/Fe2O3 hybrids could be attributed to (i) the fast electron transport owing to the unique porous structure of Fe2O3, (ii) the superior visible light absorption of Fe2O3 nanoparticles, and (iii) the "bridge molecule" role of SDS efficiently improving the separation and transfer across the interfacial domain of SDS/Fe2O3 of photogenerated electron-hole pairs. More significantly, after the catalytic reaction, the SDS/Fe2O3 hybrids could be easily recovered using magnets and reused during subsequent cycles, which indicated their stability and recyclability.

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Facile fabrication of ZnIn2S4/SnS2 3D heterostructure for efficient visible-light photocatalytic reduction of Cr(VI) Jingwen Pan, Zhongjie Guan, Jianjun Yang, Qiuye Li 2020, 41 (1):  200-208.  DOI: 10.1016/S1872-2067(19)63422-4 Abstract ( 100 )   [Full Text(HTML)] () PDF (3084KB) ( 484 )   Supporting Information Photocatalytic method has been intensively explored for Cr(VI) reduction owing to its efficient and environmentally friendly natures. In order to obtain a high efficiency in practical application, efficient photocatalysts need to be developed. Here, ZnIn2S4/SnS2 with a three-dimensional (3D) heterostructure was prepared by a hydrothermal method and its photocatalytic performance in Cr(VI) reduction was investigated. When the mass ratio of SnS2 to ZnIn2S4 is 1:10, the ZnIn2S4/SnS2 composite exhibits the highest photocatalytic activity with 100% efficiency for Cr(VI) (50 mg/L) reduction within 70 min under visible-light irradiation, which is much higher than those of pure ZnIn2S4 and SnS2. The enhanced charge separation and the light absorption have been confirmed from the photoluminescence and UV-vis absorption spectra to be the two reasons for the increased activity towards photocatalytic Cr(VI) reduction. In addition, after three cycles of testing, no obvious degradation is observed with the 3D heterostructured ZnIn2S4/SnS2, which maintains a good photocatalytic stability.

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Fabrication of TiO2 nanofiber assembly from nanosheets (TiO2-NFs-NSs) by electrospinning-hydrothermal method for improved photoreactivity Yachao Lu, Xiaoyu Ou, Wenguang Wang, Jiajie Fan, Kangle Lv 2020, 41 (1):  209-218.  DOI: 10.1016/S1872-2067(19)63470-4 Abstract ( 75 )   [Full Text(HTML)] () PDF (6093KB) ( 346 )   Hierarchically structured nanomaterials have attracted much attention owing to their unique properties. In this study, TiO2 nanofibers assembled from nanosheets (TiO2-NFs-NSs) were fabricated through electrospinning technique, which was followed by hydrothermal treatment in NaOH solution. The effect of hydrothermal reaction time (0-3 h) on the structure and properties of TiO2 nanofibers (TiO2-NFs) was systematically studied, and TiO2-NFs was evaluated in terms of the photocatalytic activity toward photocatalytic oxidation of acetone and the photoelectric conversion efficiency of dye-sensitized solar cells. It was found that (1) hydrothermal treatment of TiO2-NFs in NaOH solution followed by acid washing and calcination results in the formation of TiO2-NFs-NSs; (2) upon extending the hydrothermal reaction time from 0 h to 3 h, the BET surface area of TiO2-NFs-NSs (T3.0 sample) increases 3.8 times (from 28 to 106 m2 g-1), while the pore volume increases 6.0 times (from 0.09 to 0.54 cm3 g-1); (3) when compared with those of pristine TiO2-NFs (T0 sample), the photoreactivity of the optimized TiO2-NFs-NSs toward acetone oxidation increases 3.1 times and the photoelectric conversion efficiency increases 2.3 times. The enhanced photoreactivity of TiO2-NFs-NSs is attributed to the enlarged BET surface area and increased pore volume, which facilitate the adsorption of substrate and penetration of gas, and the unique hollow structure of TiO2-NFs-NSs, which facilitates light harvesting through multiple optical reflections between the TiO2 nanosheets.

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Controllable synthesis of Au-TiO2 nanodumbbell photocatalysts with spatial redox region Ye Liu, Zhaozhong Xiao, Shuang Cao, Jinhui Li, Lingyu Piao 2020, 41 (1):  219-226.  DOI: 10.1016/S1872-2067(19)63477-7 Abstract ( 78 )   [Full Text(HTML)] () PDF (3954KB) ( 344 )   Supporting Information Photocatalytic water splitting has increasingly attracted attention as one of the most useful methods of converting solar energy into chemical fuel. However, the undesirable reverse reaction significantly limits the enhancement of efficiency. Herein, we fabricated an Au nanorods/TiO2 nanodumbbells structure photocatalyst (Au NRs/TiO2 NDs) via a facile synthetic strategy, which has spatially separated oxidation and reduction reaction zones. Owing to the unique structure, the charge separation of these photocatalysts can be significantly improved and the reverse reaction can be efficiently inhibited. The photogenerated electrons were injected from the TiO2 to the Au NRs, and a positively charged TiO2 region and negatively charged Au region were formed under UV irradiation. An enhanced hydrogen production performance was obtained compared with that seen in normal Au-TiO2 heterostructure. Under optimized conditions, the H2-production rate can reach up to 60,264 μmol/g/h, about six times higher than previously reported Au/TiO2 photocatalysts. Besides this, our work also demonstrates the key factors of precise synthesis of the Au NRs/TiO2 NDs structure, which provides a new perspective and experience for the design of similar catalysts.