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Chinese Journal of Catalysis
2019, Vol. 40, No. 3
Online: 18 March 2019


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Li and coworkers comprehensively reviewed the advances in the promising and appealing low-cost Ni-based H₂-generation cocatalysts. Specific emphasis was placed on the fundamentals, design principle, roles, challenges and mechanism insights. Especially, four kinds of modification strategies based on increased light harvesting, enhanced charge separation, strengthened interface interaction, improved electrocatalytic activity were discussed. Read more about the article behind the cover on pages 240–288.

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Table of Contents for VOL.40 No.3 2019, 40 (3):  0-0.  Abstract ( 114 )   PDF (1099KB) ( 366 )

Editorial

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Preface to Special Issue for Chinese Symposium on Photocatalytic Materials (CSPM) Jiaguo Yu, Xin Li, Zhaohui Li 2019, 40 (3):  239-239.  DOI: 10.1016/S1872-2067(19)63308-5 Abstract ( 200 )   [Full Text(HTML)] () PDF (178KB) ( 335 )

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Ni-based photocatalytic H2-production cocatalysts Rongchen Shen, Jun Xie, Quanjun Xiang, Xiaobo Chen, Jizhou Jiang, Xin Li 2019, 40 (3):  240-288.  DOI: 10.1016/S1872-2067(19)63294-8 Abstract ( 482 )   [Full Text(HTML)] () PDF (5623KB) ( 1393 )   Photocatalysis is believed to be one of the best methods to realize sustainable H2 production. However, achieving this through heterogeneous photocatalysis still remains a great challenge owing to the absence of active sites, sluggish surface reaction kinetics, insufficient charge separation, and a high thermodynamic barrier. Therefore, cocatalysts are necessary and of great significance in boosting photocatalytic H2 generation. This review will focus on the promising and appealing low-cost Ni-based H2-generation cocatalysts as the alternatives for the high-cost and low-abundance noble metal cocatalysts. Special emphasis has been placed on the design principle, modification strategies for further enhancing the activity and stability of Ni-based cocatalysts, and identification of the exact active sites and surface reaction mechanisms. Particularly, four types of modification strategies based on increased light harvesting, enhanced charge separation, strengthened interface interaction, and improved electrocatalytic activity have been thoroughly discussed and compared in detail. This review may open a new avenue for designing highly active and durable Ni-based cocatalysts for photocatalytic H2 generation.

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Interfacial engineering of graphitic carbon nitride (g-C3N4)-based metal sulfide heterojunction photocatalysts for energy conversion: A review Yijie Ren, Deqian Zeng, Wee-Jun Ong 2019, 40 (3):  289-319.  DOI: 10.1016/S1872-2067(19)63293-6 Abstract ( 605 )   [Full Text(HTML)] () PDF (7085KB) ( 1723 )   As one of the most appealing and attractive technologies, photocatalysis is widely used as a promising method to circumvent the environmental and energy problems. Due to its chemical stability and unique physicochemical, graphitic carbon nitride (g-C3N4) has become research hotspots in the community. However, g-C3N4 photocatalyst still suffers from many problems, resulting in unsatisfactory photocatalytic activity such as low specific surface area, high charge recombination and insufficient visible light utilization. Since 2009, g-C3N4-based heterostructures have attracted the attention of scientists worldwide for their greatly enhanced photocatalytic performance. Overall, this review summarizes the recent advances of g-C3N4-based nanocomposites modified with transition metal sulfide (TMS), including (1) preparation of pristine g-C3N4, (2) modification strategies of g-C3N4, (3) design principles of TMS-modified g-C3N4 heterostructured photocatalysts, and (4) applications in energy conversion. What is more, the characteristics and transfer mechanisms of each classification of the metal sulfide heterojunction system will be critically reviewed, spanning from the following categories:(1) Type I heterojunction, (2) Type Ⅱ heterojunction, (3) p-n heterojunction, (4) Schottky junction and (5) Z-scheme heterojunction. Apart from that, the application of g-C3N4-based heterostructured photocatalysts in H2 evolution, CO2 reduction, N2 fixation and pollutant degradation will also be systematically presented. Last but not least, this review will conclude with invigorating perspectives, limitations and prospects for further advancing g-C3N4-based heterostructured photocatalysts toward practical benefits for a sustainable future.

Communication

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3D flower-like heterostructured TiO2@Ni(OH)2 microspheres for solar photocatalytic hydrogen production Wei Zhang, Hongwen Zhang, Jianzhong Xu, Huaqiang Zhuang, Jinlin Long 2019, 40 (3):  320-325.  DOI: 10.1016/S1872-2067(18)63169-9 Abstract ( 193 )   [Full Text(HTML)] () PDF (553KB) ( 592 )   TiO2@Ni(OH)2 core-shell microspheres were synthesized by a facile strategy to obtain a perfect 3D flower-like nanostructure with well-arranged Ni(OH)2 nanoflakes on the surfaces of TiO2 microspheres; this arrangement led to a six-fold enhancement in photocatalytic hydrogen evolution. The unique p-n type heterostructure not only promotes the separation and transfer of photogenerated charge carriers significantly, but also offers more active sites for photocatalytic hydrogen production. A photocatalytic mechanism is proposed based on the results of electrochemical measurements and X-ray photoelectron spectroscopy.

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Preparation of Z-scheme WO3(H2O)0.333/Ag3PO4 composites with enhanced photocatalytic activity and durability Zhen Li, Xia Wang, Jinfeng Zhang, Changhao Liang, Luhua Lu, Kai Dai 2019, 40 (3):  326-334.  DOI: 10.1016/S1872-2067(18)63165-1 Abstract ( 227 )   [Full Text(HTML)] () PDF (776KB) ( 618 )   Ag3PO4 is widely used in the field of photocatalysis because of its unique activity. However, photocorrosion limits its practical application. Therefore, it is very urgent to find a solution to improve the light corrosion resistance of Ag3PO4. Herein, the Z-scheme WO3(H2O)0.333/Ag3PO4 composites are successfully prepared through microwave hydrothermal and simple stirring. The WO3(H2O)0.333/Ag3PO4 composites are characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV-Vis spectroscopy. In the degradation of organic pollutants, WO3(H2O)0.333/Ag3PO4 composites exhibit excellent performance under visible light. This is mainly attributed to the synergy of WO3(H2O)0.333 and Ag3PO4. Especially, the photocatalytic activity of 15% WO3(H2O)0.333/Ag3PO4 is the highest, and the methylene blue can be completely degraded in 4 min. In addition, the stability of the composites is also greatly enhanced. After five cycles of testing, the photocatalytic activity of 15% WO3(H2O)0.333/Ag3PO4 is not obviously decreased. However, the degradation efficiency of Ag3PO4 was only 20.2%. This indicates that adding WO3(H2O)0.333 can significantly improve the photoetching resistance of Ag3PO4. Finally, Z-scheme photocatalytic mechanism is investigated.

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Rational design of ternary NiS/CQDs/ZnIn2S4 nanocomposites as efficient noble-metal-free photocatalyst for hydrogen evolution under visible light Bingqing Wang, Yao Ding, Zirong Deng, Zhaohui Li 2019, 40 (3):  335-342.  DOI: 10.1016/S1872-2067(18)63159-6 Abstract ( 280 )   [Full Text(HTML)] () PDF (657KB) ( 1058 )   Supporting Information The NiS/CQDs nanocomposite (CQDs represents carbon quantum dots), with a mass ratio of NiS/CQDs to be 1.19:1 based on the ICP result, was obtained via a facile hydrothermal method from a mixture of CQDs, Ni(OAc)2 and Na2S. The self-assembly of ZnIn2S4 microspheres on the surface of NiS/CQDs was realized under microwave conditions to obtain a ternary NiS/CQDs/ZnIn2S4 nanocomposite. The as-obtained NiS/CQDs/ZnIn2S4 nanocomposite was fully characterized, and its photocatalytic hydrogen evolution under visible light irradiation was investigated. The ternary NiS/CQDs/ZnIn2S4 nanocomposite showed superior photocatalytic activity for hydrogen evolution than ternary CQDs/NiS/ZnIn2S4, which was obtained by deposition of NiS in the preformed CQDs/ZnIn2S4. The superior photocatalytic performance of ternary NiS/CQDs/ZnIn2S4 is ascribed to the introduction of CQDs, which act as a bridge to promote the vectorial transfer of photo-generated electrons from ZnIn2S4 to NiS. This result suggests that the rational design and fabrication of ternary CQDs-based systems are important for the efficient photocatalytic hydrogen evolution. This study provides a strategy for developing highly efficient noble-metal-free photocatalysts for hydrogen evolution using CQDs as a bridge to promote the charge transfer in the nanocomposite.

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Ni nanoparticles as electron-transfer mediators and NiSx as interfacial active sites for coordinative enhancement of H2-evolution performance of TiO2 Ping Wang, Shunqiu Xu, Feng Chen, Huogen Yu 2019, 40 (3):  343-351.  DOI: 10.1016/S1872-2067(18)63157-2 Abstract ( 206 )   [Full Text(HTML)] () PDF (964KB) ( 767 )   The development of efficient photocatalytic H2-evolution materials requires both rapid electron transfer and an effective interfacial catalysis reaction for H2 production. In addition to the well-known noble metals, low-cost and earth-abundant non-noble metals can also act as electron-transfer mediators to modify photocatalysts. However, as almost all non-noble metals lack the interfacial catalytic active sites required for the H2-evolution reaction, the enhancement of the photocatalytic performance is limited. Therefore, the development of new interfacial active sites on metal-modified photocatalysts is of considerable importance. In this study, to enhance the photocatalytic evolution of H2 by Ni-modified TiO2, the formation of NiSx as interfacial active sites was promoted on the surface of Ni nanoparticles. Specifically, the co-modified TiO2/Ni-NiSx photocatalysts were prepared via a two-step process involving the photoinduced deposition of Ni on the TiO2 surface and the subsequent formation of NiSx on the Ni surface by a hydrothermal reaction method. It was found that the TiO2/Ni-NiSx photocatalysts exhibited enhanced photocatalytic H2-evolution activity. In particular, TiO2/Ni-NiSx(30%) showed the highest photocatalytic rate (223.74 μmol h-1), which was greater than those of TiO2, TiO2/Ni, and TiO2/NiSx by factors of 22.2, 8.0, and 2.2, respectively. The improved H2-evolution performance of TiO2/Ni-NiSx could be attributed to the excellent synergistic effect of Ni and NiSx, where Ni nanoparticles function as effective mediators to transfer electrons from the TiO2 surface and NiSx serves as interfacial active sites to capture H+ ions from solution and promote the interfacial H2-evolution reaction. The synergistic effect of the non-noble metal cocatalyst and the interfacial active sites may provide new insights for the design of highly efficient photocatalytic materials.

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Novel PtPd alloy nanoparticle-decorated g-C3N4 nanosheets with enhanced photocatalytic activity for H2 evolution under visible light irradiation Nan Xiao, Songsong Li, Shuang Liu, Boran Xu, Yandong Li, Yangqin Gao, Lei Ge, Guiwu Lu 2019, 40 (3):  352-361.  DOI: 10.1016/S1872-2067(18)63180-8 Abstract ( 308 )   [Full Text(HTML)] () PDF (1030KB) ( 914 )   PtPd bimetallic alloy nanoparticle (NP)-modified graphitic carbon nitride (g-C3N4) nanosheet photocatalysts were synthesized via chemical deposition precipitation. Characterization of the photocatalytic H2 evolution of the g-C3N4 nanosheets shows that it was significantly enhanced when PtPd alloy NPs were introduced as a co-catalyst. The 0.2 wt% PtPd/g-C3N4 composite photocatalyst gave a maximum H2 production rate of 1600.8 μmol g-1 h-1. Furthermore, when K2HPO4 was added to the reaction system, the H2 production rate increased to 2885.0 μmol g-1 h-1. The PtPd/g-C3N4 photocatalyst showed satisfactory photocatalytic stability and was able to maintain most of its photocatalytic activity after four experimental photocatalytic cycles. In addition, a possible mechanism for the enhanced photocatalytic activity was proposed and verified by various photoelectric techniques. These results demonstrate that the synergistic effect between PtPd and g-C3N4 helps to greatly improve the photocatalytic activity of the composite photocatalyst.

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A Bi/BiOI/(BiO)2CO3 heterostructure for enhanced photocatalytic NO removal under visible light Yanjuan Sun, Jiazhen Liao, Fan Dong, Sujuan Wu, Lidong Sun 2019, 40 (3):  362-370.  DOI: 10.1016/S1872-2067(18)63187-0 Abstract ( 159 )   [Full Text(HTML)] () PDF (803KB) ( 681 )   Narrow-band BiOI photocatalysts usually suffer from low photocatalysis efficiency under visible light exposure because of rapid charge recombination. In this work, to overcome this deficiency of photosensitive BiOI, oxygen vacancies, Bi particles, and Bi2O2CO3 were co-induced in BiOI via a facile in situ assembly method at room temperature using NaBH4 as the reducing agent. In the synthesized ternary Bi/BiOI/(BiO)2CO3, the oxygen vacancies, dual heterojunctions (i.e., Bi/BiOI and BiOI/(BiO)2CO3), and surface plasmon resonance effect of the Bi particles contributed to efficient electron-hole separation and an increase in charge carrier concentration, thus boosting the overall visible light photocatalysis efficiency. The as-prepared catalysts were applied for the removal of NO in concentrations of parts per billion from air in continuous air flow under visible light illumination. Bi/BiOI/(BiO)2CO3 exhibited a highly enhanced NO removal ratio of 50.7%, much higher than that of the pristine BiOI (1.2%). Density functional theory calculations and experimental results revealed that the Bi/BiOI/(BiO)2CO3 composites promoted the production of reactive oxygen species for photocatalytic NO oxidation. Thus, this work provides a new strategy to modify narrow-band semiconductors and explore other bismuth-containing heterostructured visible-light-driven photocatalysts.

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One-pot hydrothermal synthesis of willow branch-shaped MoS2/CdS heterojunctions for photocatalytic H2 production under visible light irradiation Zhen-Wei Zhang, Qiu-Hao Li, Xiu-Qing Qiao, Dongfang Hou, Dong-Sheng Li 2019, 40 (3):  371-379.  DOI: 10.1016/S1872-2067(18)63178-X Abstract ( 160 )   [Full Text(HTML)] () PDF (919KB) ( 760 )   Willow branch-shaped MoS2/CdS heterojunctions are successfully synthesized for the first time by a facile one-pot hydrothermal method. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption measurements, diffuse reflectance spectroscopy, and photoelectrochemical and photoluminescence spectroscopy tests. The photocatalytic hydrogen evolution activities of the samples were evaluated under visible light irradiation. The resulting MoS2/CdS heterojunctions exhibit a much improved photocatalytic hydrogen evolution activity than that obtained with CdS and MoS2. In particular, the optimized MC-5 (5 at.% MoS2/CdS) photocatalyst achieved the highest hydrogen production rate of 250.8 μmol h-1, which is 28 times higher than that of pristine CdS. The apparent quantum efficiency (AQE) at 420 nm was 3.66%. Further detailed characterizations revealed that the enhanced photocatalytic activity of the MoS2/CdS heterojunctions could be attributed to the efficient transfer and separation of photogenerated charge carriers resulting from the core-shell structure and the close contact between MoS2 nanosheets and CdS single-crystal nanorods, as well as to increased visible light absorption. A tentative mechanism for photocatalytic H2 evolution by MoS2/CdS heterojunctions was proposed. This work will open up new opportunities for developing more efficient photocatalysts for water splitting.

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Accelerating photocatalytic hydrogen evolution and pollutant degradation by coupling organic co-catalysts with TiO2 Jun Shen, Rui Wang, Qinqin Liu, Xiaofei Yang, Hua Tang, Jin Yang 2019, 40 (3):  380-389.  DOI: 10.1016/S1872-2067(18)63166-3 Abstract ( 299 )   [Full Text(HTML)] () PDF (900KB) ( 777 )   Accelerating the separation efficiency of photoexcited electron-hole pairs with the help of highly active co-catalysts has proven to be a promising approach for improving photocatalytic activity. Thus far, the most developed co-catalysts for semiconductor-based photocatalysis are inorganic materials; the employment of a specific organic molecule as a co-catalyst for photocatalytic hydrogen evolution and pollutant photodegradation is rare and still remains a challenging task. Herein, we report on the use of an organic molecule, oxamide (OA), as a novel co-catalyst to enhance electron-hole separation, photocatalytic H2 evolution, and dye degradation over TiO2 nanosheets. OA-modified TiO2 samples were prepared by a wet chemical route and demonstrated improved light absorption in the visible-light region and more efficient charge transport. The photocatalytic performance of H2 evolution from water splitting and rhodamine B (RhB) degradation for an optimal OA-modified TiO2 photocatalyst reached 2.37 mmol g-1 h-1 and 1.43×10-2 min-1, respectively, which were 2.4 and 3.8 times higher than those of pristine TiO2, respectively. A possible mechanism is proposed, in which the specific π-conjugated structure of OA is suggested to play a key role in the enhancement of the charge transfer and catalytic capability of TiO2. This work may provide advanced insight into the development of a variety of metal-free organic molecules as functional co-catalysts for improved solar-to-fuel conversion and environmental remediation.

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Controllable design of Zn-Ni-P on g-C3N4 for efficient photocatalytic hydrogen production Yanbing Li, Zhiliang Jin, Lijun Zhang, Kai Fan 2019, 40 (3):  390-402.  DOI: 10.1016/S1872-2067(18)63173-0 Abstract ( 137 )   [Full Text(HTML)] () PDF (1192KB) ( 1042 )   Synthesizing a stable and efficient photocatalyst has been the most important research goal up to now. Owing to the dominant performance of g-C3N4 (graphitized carbonitride), an ordered assemble of a composite photocatalyst, Zn-Ni-P@g-C3N4, was successfully designed and controllably prepared for highly efficient photocatalytic H2 evolution. The electron transport routes were successfully adjusted and the H2 evolution was greatly improved. The maximum amount of H2 evolved reached about 531.2 μmol for 5 h over Zn-Ni-P@g-C3N4 photocatalyst with a molar ratio of Zn to Ni of 1:3 under illumination of 5 W LED white light (wavelength 420 nm). The H2 evolution rate was 54.7 times higher than that over pure g-C3N4. Moreover, no obvious reduction in the photocatalytic activity was observed even after 4 cycles of H2 production for 5 h. This synergistically increased effect was confirmed through the results of characterizations such as XRD, TEM, SEM, XPS, N2 adsorption, UV-vis DRS, transient photocurrent, FT-IR, transient fluorescence, and Mott-Schottky studies. These studies showed that the Zn-Ni-P nanoparticles modified on g-C3N4 provide more active sites and improve the efficiency of photogenerated charge separation. In addition, the possible mechanism of photocatalytic H2 production is proposed.

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Effects of crystallinity, {001}/{101} ratio, and Au decoration on the photocatalytic activity of anatase TiO2 crystals Jiangyan Wang, Baoshun Liu, Kazuya Nakata 2019, 40 (3):  403-412.  DOI: 10.1016/S1872-2067(18)63174-2 Abstract ( 142 )   [Full Text(HTML)] () PDF (1593KB) ( 687 )   Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800℃. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO2 samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF2 at 700 and 800℃.

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Prolonging charge-separation states by doping lanthanide-ions into {001}/{101} facets-coexposed TiO2 nanosheets for enhancing photocatalytic H2 evolution Yongan Zhu, Zhenyi Zhang, Na Lu, Ruinian Hua, Bin Dong 2019, 40 (3):  413-423.  DOI: 10.1016/S1872-2067(18)63182-1 Abstract ( 189 )   [Full Text(HTML)] () PDF (1334KB) ( 621 )   Ultrathin TiO2 nanosheets with coexposed {001}/{101} facets have attracted considerable attention because of their high photocatalytic activity. However, the charge-separated states in the TiO2 nanosheets must be extended to further enhance their photocatalytic activity for H2 evolution. Herein, we present a successful attempt to selectively dope lanthanide ions into the {101} facets of ultrathin TiO2 nanosheets with coexposed {001}/{101} facets through a facile one-step solvothermal method. The lanthanide doping slightly extended the light-harvesting region and markedly improved the charge-separated states of the TiO2 nanosheets as evidenced by UV-vis absorption and steady-state/transient photoluminescence spectra. Upon simulated sunlight irradiation, we observed a 4.2-fold enhancement in the photocatalytic H2 evolution activity of optimal Yb3+-doped TiO2 nanosheets compared to that of their undoped counterparts. Furthermore, when Pt nanoparticles were used as cocatalysts to reduce the H2 overpotential in this system, the photocatalytic activity enhancement factor increased to 8.5. By combining these results with those of control experiments, we confirmed that the extended charge-separated states play the main role in the enhancement of the photocatalytic H2 evolution activity of lanthanide-doped TiO2 nanosheets with coexposed {001}/{101} facets.

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Defect-assisted surface modification enhances the visible light photocatalytic performance of g-C3N4@C-TiO2 direct Z-scheme heterojunctions Xibao Li, Jie Xiong, Ying Xu, Zhijun Feng, Juntong Huang 2019, 40 (3):  424-433.  DOI: 10.1016/S1872-2067(18)63183-3 Abstract ( 202 )   [Full Text(HTML)] () PDF (1274KB) ( 1001 )   To increase the number of active sites and defects in TiO2 and promote rapid and efficient transfer of photogenerated charges, a g-C3N4@C-TiO2 composite photocatalyst was prepared via in situ deposition of g-C3N4 on a carbon-doped anatase TiO2 surface. The effects of carbon doping state and surface modification of g-C3N4 on the performance of g-C3N4@C-TiO2 composite photocatalysts were studied by X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible diffuse-reflectance spectroscopy, transmission electron microscopy, electrochemical impedance spectroscopy, photoluminescence, and electron paramagnetic resonance. With increasing carbon doping content, the carbon doping state in TiO2 gradually changed from gap to substitution doping. Although the number of oxygen vacancies gradually increased, the degradation efficiency of g-C3N4@C-TiO2 for RhB (phenol) initially increased and subsequently decreased with increasing carbon content. The g-C3N4@10C-TiO2 sample exhibited the highest apparent reaction rate constant of 0.036 min-1 (0.039 min-1) for RhB (phenol) degradation, which was 150 (139), 6.4 (6.8), 2.3 (3), and 1.7 (2.1) times higher than that of pure TiO2, 10C-TiO2, g-C3N4, and g-C3N4@TiO2, respectively. g-C3N4 was grown in situ on the surface of C-TiO2 by surface carbon hybridization and bonding. The resultant novel g-C3N4@C-TiO2 photocatalyst exhibited direct Z-scheme heterojunctions with non-local impurity levels. The high photocatalytic activity can be attributed to the synergistic effects of the improved visible light response ability, higher photogenerated electron transfer efficiency, and redox ability arising from Z-type heterojunctions.

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Enhanced photocatalytic H2 production over dual-cocatalyst-modified g-C3N4 heterojunctions Zong Li, Yongning Ma, Xiaoyun Hu, Enzhou Liu, Jun Fan 2019, 40 (3):  434-445.  DOI: 10.1016/S1872-2067(18)63189-4 Abstract ( 166 )   [Full Text(HTML)] () PDF (1683KB) ( 858 )   Supporting Information Ag nanoparticles (NPs) were deposited on the surface of g-C3N4 (CN) by an in situ calcination method. NiS was successfully loaded onto the composites by a hydrothermal method. The results showed that the 10 wt%-NiS/1.0 wt%-Ag/CN composite exhibits excellent photocatalytic H2 generation performance under solar-light irradiation. An H2 production rate of 9.728 mmol·g-1·h-1 was achieved, which is 10.82-, 3.45-, and 2.77-times higher than those of pure g-C3N4, 10 wt%-NiS/CN, and 1.0 wt%-Ag/CN composites, respectively. This enhanced photocatalytic H2 generation can be ascribed to the co-decoration of Ag and NiS on the surface of g-C3N4, which efficiently improves light harvesting capacity, photogenerated charge carrier separation, and photocatalytic H2 production kinetics. Thus, this study demonstrates an effective strategy for constructing excellent g-C3N4-related composite photocatalysts for H2 production by using different co-catalysts.

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Preparation of a p-n heterojunction 2D BiOI nanosheet/1DBiPO4 nanorod composite electrode for enhanced visible light photoelectrocatalysis Sen Liu, Mengyu Zhao, Zetian He, Yi Zhong, Hao Ding, Daimei Chen 2019, 40 (3):  446-457.  DOI: 10.1016/S1872-2067(18)63186-9 Abstract ( 219 )   [Full Text(HTML)] () PDF (915KB) ( 724 )   In this study, a 2D BiOI nanosheet/1D BiPO4 nanorod/fluorine-doped tin oxide (FTO) composite electrode with a p-n heterojunction structure was prepared by a two-step electrodeposition method. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-visible diffuse reflectance spectroscopy, and electrochemical testing were used to characterize its composition, crystal morphology, and optical properties. The BiOI/BiPO4/FTO composite electrode has higher photoelectrocatalytic (PEC) activity for the degradation of tetracycline than pure BiPO4 and BiOI. The PEC activity of the composite was 1.98 times and 2.46 times higher than those of the BiOI/FTO and BiPO4/FTO electrodes, respectively. The effects of the working voltage and BiOI deposition time on the degradation of tetracycline were investigated. The optimum BiOI deposition time was found to be 150 s and the optimum working voltage is 1.2 V. Trapping experiments showed that hydroxyl radicals (·OH) and superoxide radicals (·O2-) are the major reactive species in the PEC degradation process. The BiOI/BiPO4/FTO composite electrode has good stability, and the tetracycline removal efficiency remains substantially unchanged after four cycles in a static system. The reason for the PEC efficiency enhancement in the BiOI/BiPO4/FTO composite electrode is the increased visible light absorption range and the p-n heterojunction structure, which promotes the separation and migration of the photogenerated electrons and holes.

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Direct electrospinning method for the construction of Z-scheme TiO2/g-C3N4/RGO ternary heterojunction photocatalysts with remarkably ameliorated photocatalytic performance Liming Hu, Juntao Yan, Chunlei Wang, Bo Chai, Jianfen Li 2019, 40 (3):  458-469.  DOI: 10.1016/S1872-2067(18)63181-X Abstract ( 276 )   [Full Text(HTML)] () PDF (1684KB) ( 1278 )   A series of Z-scheme TiO2/g-C3N4/RGO ternary heterojunction photocatalysts are successfully constructed via a direct electrospinning technique coupled with an annealing process for the first time. They are investigated comprehensively in terms of crystal structure, morphology, composition, specific surface area, photoelectrochemical properties, photodegradation performance, etc. Compared with binary TiO2/g-C3N4 and single-component photocatalysts, ternary heterojunction photocatalysts show the best photodegradation performance for RhB under stimulated sunlight. This can be attributed to the enlarged specific surface area (111.41 m2/g), the formation of Z-scheme heterojunction, and the high separation migration efficiency of photoexcited charge carriers. A potential Z-scheme mechanism for ternary heterojunction photocatalysts is proposed to elucidate the remarkably ameliorated photocatalytic performance based on active species trapping experiments, PL detection test of hydroxyl radicals, and photoelectrochemical properties.

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Simultaneous hydrogen and peroxide production by photocatalytic water splitting Lichao Wang, Shuang Cao, Kai Guo, Zhijiao Wu, Zhi Ma, Lingyu Piao 2019, 40 (3):  470-475.  DOI: 10.1016/S1872-2067(19)63274-2 Abstract ( 1180 )   [Full Text(HTML)] () PDF (855KB) ( 1108 )   Photocatalytic oxidation of water is a promising method to realize large-scale H2O2 production without a hazardous and energy-intensive process. In this study, we introduce a Pt/TiO2(anatase) photocatalyst to construct a simple and environmentally friendly system to achieve simultaneous H2 and H2O2 production. Both H2 and H2O2 are high-value chemicals, and their separation is automatic. Even without the assistance of a sacrificial agent, the system can reach an efficiency of 7410 and 5096 μmol g-1 h-1 (first 1 h) for H2 and H2O2, respectively, which is much higher than that of a commercial Pt/TiO2(anatase) system that has a similar morphology. This exceptional activity is attributed to the more favorable two-electron oxidation of water to H2O2, compared with the four-electron oxidation of water to O2.