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Chinese Journal of Catalysis
2021, Vol. 42, No. 1
Online: 18 January 2021

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Cover: Special Issue for 2nd Chinese Symposium on Photocatalytic Materials (CSPM2) (2020, Vol. 42, No. 1) Guest Editor(s): Jiaguo Yu, Zhaosheng Li, Shifu Chen

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Preface to Special Issue for 2nd Chinese Symposium on Photocatalytic Materials (CSPM2) Yu Jiaguo, Li Zhaosheng, Chen Shifu 2021, 42 (1):  1-2.  DOI: 10.1016/S1872-2067(20)63664-6 Abstract ( 151 )   HTML ( 350 )   PDF (355KB) ( 229 )

Review

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MXenes as noble-metal-alternative co-catalysts in photocatalysis Kaining Li, Sushu Zhang, Yuhan Li, Jiajie Fan, Kangle Lv 2021, 42 (1):  3-14.  DOI: 10.1016/S1872-2067(20)63630-0 Abstract ( 886 )   HTML ( 37 )   PDF (2762KB) ( 1473 )   Photocatalysis has become a focal point in research as a clean and sustainable technology with the potential to solve environmental problems and energy crises. The loading of noble-metal co-catalysts can substantially improve the photocatalytic efficiency of semiconductors. Because the high cost and scarcity of noble metals markedly limit their large-scale applications, finding a noble-metal-alternative co-catalyst is crucial. MXene, a novel 2D transition metal material, has attracted considerable attention as a promising substitute for noble metal co-catalysts owing to its cost-efficiency, unique 2D layered structure, and excellent electrical, optical, and thermodynamic properties. This review focuses on the latest advancements in research on MXenes as co-catalysts in relatively popular photocatalytic applications (hydrogen production, CO2 reduction, nitrogen fixation, and organic pollutant oxidation). The synthesis methods and photocatalytic mechanisms of MXenes as co-catalysts are also summarized according to the type of MXene-based material. Finally, the crucial opportunities and challenges in the prospective development of MXene-based photocatalysts are outlined. We emphasize that modern techniques should be used to demonstrate the effects of MXenes on photocatalysis and that the photocatalytic activity of MXene-based photocatalysts can be further improved using defective engineering and recent phenomena such as the localized surface plasmon resonance effect and single-atom catalysis.

Articles

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ZnxCd1-xS quantum dot with enhanced photocatalytic H2-production performance Rongrong Gao, Bei Cheng, Jiajie Fan, Jiaguo Yu, Wingkei Ho 2021, 42 (1):  15-24.  DOI: 10.1016/S1872-2067(20)63614-2 Abstract ( 319 )   HTML ( 12 )   PDF (2980KB) ( 553 )   H2 is an important energy carrier for replacing fossil fuel in the future due to its high energy density and environmental friendliness. As a sustainable H2-generation method, photocatalytic H2 production by water splitting has attracted much interest. Here, oil-soluble ZnxCd1-xS quantum dot (ZCS QD) with a uniform particle size distribution were prepared by a hot-injection method. However, no photocatalytic H2-production activity was observed for the oil-soluble ZCS QD due to its hydrophobicity. Thus, the oil-soluble ZCS QD was converted into a water-soluble ZCS QD by a ligand-exchange method. The water-soluble ZCS QD exhibited excellent photocatalytic H2-production performance in the presence of glycerin and Ni2+, with an apparent quantum efficiency of 15.9% under irradiation of 420 nm light. Further, the photocatalytic H2-generation activity of the ZCS QD was ~10.7 times higher than that of the ZnxCd1-xS relative samples prepared by the conventional co-precipitation method. This work will inspire the design and fabrication of other semiconductor QD photocatalysts because QD exhibits excellent separation efficiency for photogenerated electron-hole pairs due to its small crystallite size.

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Constructing low-cost Ni3C/twin-crystal Zn0.5Cd0.5S heterojunction/homojunction nanohybrids for efficient photocatalytic H2 evolution Rongchen Shen, Yingna Ding, Shibang Li, Peng Zhang, Quanjun Xiang, Yun Hau Ng, Xin Li 2021, 42 (1):  25-36.  DOI: 10.1016/S1872-2067(20)63600-2 Abstract ( 203 )   HTML ( 15 )   PDF (2250KB) ( 730 )   The development of low-cost semiconductor photocatalysts for highly efficient and durable photocatalytic H2 evolution under visible light is very challenging. In this study, we combine low-cost metallic Ni3C cocatalysts with twin nanocrystal Zn0.5Cd0.5S (ZCS) solid solution homojunctions for an efficient visible-light-driven H2 production by a simple approach. As-synthesized Zn0.5Cd0.5S-1% Ni3C (ZCS-1) heterojunction/homojunction nanohybrid exhibited the highest photocatalytic H2-evolution rate of 783 μmol h-1 under visible light, which is 2.88 times higher than that of pristine twin nanocrystal ZCS solid solution. The apparent quantum efficiencies of ZCS and ZCS-1 are measured to be 6.13% and 19.25% at 420 nm, respectively. Specifically, the homojunctions between the zinc blende and wurtzite segments in twin nanocrystal ZCS solid solution can significantly improve the light absorption and separation of photogenerated electron-hole pairs. Furthermore, the heterojunction between ZCS and metallic Ni3C NP cocatalysts can efficiently trap excited electrons from ZCS solid solution and enhance the H2-evolution kinetics at the surface for improving catalytic activity. This study demonstrates a unique one-step strategy for constructing heterojunction/homojunction hybrid nanostructures for a more efficient photocatalytic H2 evolution compared to other noble metal photocatalytic systems.

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Sulfur-mediated photodeposition synthesis of NiS cocatalyst for boosting H2-evolution performance of g-C3N4 photocatalyst Min Wang, Jingjing Cheng, Xuefei Wang, Xuekun Hong, Jiajie Fan, Huogen Yu 2021, 42 (1):  37-45.  DOI: 10.1016/S1872-2067(20)63633-6 Abstract ( 240 )   HTML ( 16 )   PDF (1800KB) ( 697 )   Modification of nickel sulfide cocatalysts is considered to be a promising approach for efficient enhancement of the photocatalytic hydrogen production performance of g-C3N4. Providing more NiS cocatalyst to function as active sites of g-C3N4 is still highly desirable. To realize this goal, in this work, a facile sulfur-mediated photodeposition approach was developed. Specifically, photogenerated electrons excited by visible light reduce the S molecules absorbed on g-C3N4 surface to S2-, and subsequently NiS cocatalyst is formed in situ on the g-C3N4 surface by a combination of Ni2+ and S2- due to their small solubility product constant (Ksp = 3.2 × 10-19). This approach has several advantages. The NiS cocatalyst is clearly in situ deposited on the photogenerated electron transfer sites of g-C3N4, and thus provides more active sites for H2 production. In addition, this method utilizes solar energy with mild reaction conditions at room temperature. Consequently, the synthesized NiS/g-C3N4 photocatalyst achieves excellent hydrogen generation performance with the performance of the optimal sample (244 μmol h-1 g-1) close to that of 1 wt% Pt/g-C3N4 (316 μmol h-1 g-1, a well-known excellent photocatalyst). More importantly, the present sulfur-mediated photodeposition route is versatile and facile and can be used to deposit various metal sulfides such as CoSx, CuSx and AgSx on the g-C3N4 surface, and all the resulting metal sulfide-modified g-C3N4 photocatalysts exhibit improved H2-production performance. Our study offers a novel insight for the synthesis of high-efficiency photocatalysts.

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A novel step-scheme BiVO4/Ag3VO4 photocatalyst for enhanced photocatalytic degradation activity under visible light irradiation Lizhong Liu, Taiping Hu, Kai Dai, Jinfeng Zhang, Changhao Liang 2021, 42 (1):  46-55.  DOI: 10.1016/S1872-2067(20)63560-4 Abstract ( 196 )   HTML ( 8 )   PDF (1891KB) ( 694 )   Over the past few years, the emission of organic pollutants into the environment has increased tremendously. Therefore, various photocatalysts have been developed for the degradation of organic pollutants. In this study, a step-scheme BiVO4/Ag3VO4 composite was synthesized via a hydrothermal and chemical deposition process for the degradation of methylene blue.The composite showed strong redox ability under visible light. The 40%BiVO4/Ag3VO4 composite showed excellent photocatalytic degradation properties with a Kapp of 0.05588 min-1, which is 22.76 and 1.76 times higher than those of BiVO4 (0.00247 min-1) and Ag3VO4 (0.03167 min-1), respectively. The composite showed a stable performance and could retain 90% of its photocatalytic activity even after four cycles. The improved catalytic performance of the composite as compared to BiVO4 and Ag3VO4 can be attributed to its novel step-scheme mechanism, which facilitated the separation of the photogenerated charges and increased their lifetime. The photoluminescence measurement results and transient photocurrent response revealed that the composite showed efficient extraction of charge carriers.

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Sulfur-doped g-C3N4/TiO2 S-scheme heterojunction photocatalyst for Congo Red photodegradation Juan Wang, Guohong Wang, Bei Cheng, Jiaguo Yu, Jiajie Fan 2021, 42 (1):  56-68.  DOI: 10.1016/S1872-2067(20)63634-8 Abstract ( 287 )   HTML ( 14 )   PDF (2107KB) ( 1383 )   Constructing step-scheme (S-scheme) heterojunctions has been confirmed as a promising strategy for enhancing the photocatalytic activity of composite materials. In this work, a series of sulfur-doped g-C3N4 (SCN)/TiO2 S-scheme photocatalysts were synthesized using electrospinning and calcination methods. The as-prepared SCN/TiO2 composites showed superior photocatalytic performance than pure TiO2 and SCN in the photocatalytic degradation of Congo Red (CR) aqueous solution. The significant enhancement in photocatalytic activity benefited not only from the 1D well-distributed nanostructure, but also from the S-scheme heterojunction. Furthermore, the XPS analyses and DFT calculations demonstrated that electrons were transferred from SCN to TiO2 across the interface of the SCN/TiO2 composites. The built-in electric field, band edge bending, and Coulomb interaction synergistically facilitated the recombination of relatively useless electrons and holes in hybrid when the interface was irradiated by simulated solar light. Therefore, the remaining electrons and holes with higher reducibility and oxidizability endowed the composite with supreme redox ability. These results were adequately verified by radical trapping experiments, ESR tests, and in situ XPS analyses, suggesting that the electron immigration in the photocatalyst followed the S-scheme heterojunction mechanism. This work can enrich our knowledge of the design and fabrication of novel S-scheme heterojunction photocatalysts and provide a promising strategy for solving environmental pollution in the future.

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S-scheme Sb2WO6/g-C3N4 photocatalysts with enhanced visible-light-induced photocatalytic NO oxidation performance Yuyu Ren, Yuan Li, Xiaoyong Wu, Jinlong Wang, Gaoke Zhang 2021, 42 (1):  69-77.  DOI: 10.1016/S1872-2067(20)63631-2 Abstract ( 161 )   HTML ( 8 )   PDF (3256KB) ( 659 )   Supporting Information Normal photocatalysts cannot effectively remove low-concentration NO because of the high recombination rate of the photogenerated carriers. To overcome this problem, S-scheme composites have been developed to fabricate photocatalysts. Herein, a novel S-scheme Sb2WO6/g-C3N4 nanocomposite was fabricated by an ultrasound-assisted method, which exhibited excellent performance for photocatalytic ppb-level NO removal. Compared with the pure constituents of the nanocomposite, the as-prepared 15%-Sb2WO6/g-C3N4 photocatalyst could remove more than 68% continuous-flowing NO (initial concentration: 400 ppb) under visible-light irradiation in 30 min. The findings of the trapping experiments confirmed that •O2- and h+ were the important active species in the NO oxidation reaction. Meanwhile, the transient photocurrent response and PL spectroscopy analyses proved that the unique S-scheme structure of the samples could enhance the charge separation efficiency. In situ DRIFTS revealed that the photocatalytic reaction pathway of NO removal over the Sb2WO6/g-C3N4 nanocomposite occurred via an oxygen-induced route. The present work proposes a new concept for fabricating efficient photocatalysts for photocatalytic ppb-level NO oxidation and provides deeper insights into the mechanism of photocatalytic NO oxidation.

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Hierarchically porous S-scheme CdS/UiO-66 photocatalyst for efficient 4-nitroaniline reduction Jinxin Wei, Yawen Chen, Hongyang Zhang, Zanyong Zhuang, Yan Yu 2021, 42 (1):  78-86.  DOI: 10.1016/S1872-2067(20)63661-0 Abstract ( 178 )   HTML ( 8 )   PDF (6464KB) ( 618 )   Supporting Information Unveiling the pore-size performance of metal organic frameworks (MOFs) is imperative for controllable design of sophisticated catalysts. Herein, UiO-66 with distinct macropores and mesopores were intentionally created and served as substrates to create advanced CdS/UiO-66 catalysts. The pore size impacted the spatial distribution of CdS nanoparticles (NPs): CdS tended to deposit on the external surface of mesoporous UiO-66, but spontaneously penetrated into the large cavity of macroporous UiO-66 nanocage. Normalized to unit amount of CdS, the photocatalytic reaction constant of macroporous CdS/UiO-66 over 4-nitroaniline reduction was ~3 folds of that of mesoporous counterpart, and outperformed many other reported state-of-art CdS-based catalysts. A confinement effect of CdS NPs within UiO-66 cage could respond for its high activity, which could shorten the electron-transport distance of NPs-MOFs-reactant, and protect the active CdS NPs from photocorrosion. The finding here provides a straightforward paradigm and mechanism to rationally fabricate advance NPs/ MOFs for diverse applications.

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Construction of LSPR-enhanced 0D/2D CdS/MoO3-x S-scheme heterojunctions for visible-light-driven photocatalytic H2 evolution Jinjun Peng, Jun Shen, Xiaohui Yu, Hua Tang, Zulfiqar , Qinqin Liu 2021, 42 (1):  87-96.  DOI: 10.1016/S1872-2067(20)63595-1 Abstract ( 352 )   HTML ( 21 )   PDF (6301KB) ( 1166 )   Plasmonic nonmetal semiconductors with localized surface plasmon resonance (LSPR) effects possess extended light-response ranges and can act as highly efficient H2 generation photocatalysts. Herein, an LSPR-enhanced 0D/2D CdS/MoO3-x heterojunction has been synthesized by the growth of 0D CdS nanoparticles on 2D plasmonic MoO3-x elliptical nanosheets via a simple coprecipitation method. Taking advantage of the LSPR effect of the MoO3-x elliptical nanosheets, the light absorption of the CdS/MoO3-x heterojunction was extended from 600 nm to the near-infrared region (1400 nm). Furthermore, the introduction of 2D plasmonic MoO3-x elliptical nanosheets not only provided a platform for the growth of CdS nanoparticles, but also contributed to the construction of an LSPR-enhanced S-scheme structure due to the interface between the MoO3-x and CdS, accelerating the separation of light-induced electrons and holes. Therefore, the CdS/MoO3-x heterojunction exhibited higher photocatalytic H2 generation activity than pristine CdS under visible light irradiation, including under 420, 450, 550, and 650 nm monochromic light, as well as improved photo-corrosion performance.

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2D/2D step-scheme α-Fe2O3/Bi2WO6 photocatalyst with efficient charge transfer for enhanced photo-Fenton catalytic activity Wenliang Wang, Wenli Zhao, Haochun Zhang, Xincheng Dou, Haifeng Shi 2021, 42 (1):  97-106.  DOI: 10.1016/S1872-2067(20)63602-6 Abstract ( 165 )   HTML ( 9 )   PDF (5843KB) ( 594 )   Although the traditional Fenton reaction is considered an effective strategy for solving problems caused by environmental pollution, construction of an efficient photocatalytic system by coordinating the Fenton reaction is challenging. In this study, 2D/2D step-scheme α-Fe2O3/Bi2WO6 (FO/BWO) heterostructure photo-Fenton catalysts were successfully fabricated by a facile hydrothermal method. The as-prepared materials were characterized by XRD, FT-IR, TEM, XPS, UV-vis DRS, PL, I-t, EIS, and BET analyses. Under visible light irradiation, FO/BWO exhibited remarkably high and stable photo-Fenton catalytic activity for the degradation of methyl blue (MB) at low concentrations of H2O2. It was noted that FO/BWO (0.5) displayed a significantly enhanced photo-Fenton catalytic activity, which was 11.06 and 3.29 times those of FO nanosheets and BWO nanosheets, respectively. The notably improved photo-Fenton catalytic activity of FO/BWO was mainly due to the combination of H2O2 and FO under light illumination and the presence of the 2D/2D S-scheme heterostructure, with the large contact surface, abundant active sites, and efficient separation rate of photogenerated carriers playing contributory roles. Additionally, a possible catalytic mechanism for the FO/BWO composite was preliminarily proposed via active species trapping experiments. In summary, this study provided new insights into the synthesis of an effectively heterogeneous 2D/2D S-scheme photo-Fenton catalyst for degradation of organic pollutants in wastewater.

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In situ construction of protonated g-C3N4/Ti3C2 MXene Schottky heterojunctions for efficient photocatalytic hydrogen production Haotian Xu, Rong Xiao, Jingran Huang, Yan Jiang, Chengxiao Zhao, Xiaofei Yang 2021, 42 (1):  107-114.  DOI: 10.1016/S1872-2067(20)63559-8 Abstract ( 316 )   HTML ( 16 )   PDF (1373KB) ( 630 )   Supporting Information Abstract: Converting sustainable solar energy into hydrogen energy over semiconductor-based photocatalytic materials provides an alternative to fossil fuel consumption. However, efficient photocatalytic splitting of water to realize carbon-free hydrogen production remains a challenge. Heterojunction photocatalysts with well-defined dimensionality and perfectly matched interfaces are promising for achieving highly efficient solar-to-hydrogen conversion. Herein, we report the fabrication of a novel type of protonated graphitic carbon nitride (PCN)/Ti3C2 MXene heterojunctions with strong interfacial interactions. As expected, the two-dimensional (2D) PCN/2D Ti3C2 MXene interface heterojunction achieves a highly improved hydrogen evolution rate (2181 μmol∙g-1) in comparison with bulk g-C3N4 (393 μmol∙g-1) and protonated g-C3N4 (816 μmol∙g-1). The charge-regulated surfaces of PCN and the accelerated charge transport at the face-to-face 2D/2D Schottky heterojunction interface are the major contributors to the excellent hydrogen evolution performance of the composite photocatalyst.

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H2O molecule adsorption on s-triazine-based g-C3N4 Bicheng Zhu, Liuyang Zhang, Bei Cheng, Yan Yu, Jiaguo Yu 2021, 42 (1):  115-122.  DOI: 10.1016/S1872-2067(20)63598-7 Abstract ( 212 )   HTML ( 16 )   PDF (1958KB) ( 492 )   Supporting Information The interaction between a gas molecule and photocatalyst is vital to trigger photocatalytic reaction. The surface state of photocatalyst affects much in this interaction. Herein, adsorption of H2O molecules on s-triazine-based g-C3N4 was thoroughly studied by first-principle calculation. Although various initial adsorption models with multifarious locations of H2O molecules were built, the optimized models with strong adsorption energy pointed to the same adsorption configuration, in which the H2O molecule hold an upright orientation above the corrugated g-C3N4 monolayer. An intermolecular O-H…N hydrogen bond formed via the binding of a polar O-H bond in H2O molecule and a two-coordinated electron-rich nitrogen atom in g-C3N4. Under the bridging effect of this intermolecular hydrogen bond, electrons would transfer from g-C3N4 to the H2O molecule, thereby lowering the Fermi level and enlarging work function of g-C3N4. Interestingly, regardless of the substitute, i.e. g-C3N4 multilayer, large supercell and nanotube, this adsorption system was highly reproducible, as its geometry structure and electronic property remained unchanged. In addition, the effect of nonmetal element doping on adsorption energy was explored. This work not only disclosed a highly preferential H2O adsorbed g-C3N4 architecture established by intermolecular hydrogen bond, but also contributed to the deep understanding and optimized design in water-splitting process on g-C3N4-based photocatalysts.

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Encapsulation of Co single sites in covalent triazine frameworks for photocatalytic production of syngas Yajun He, Xin Chen, Chi Huang, Liuyi Li, Chengkai Yang, Yan Yu 2021, 42 (1):  123-130.  DOI: 10.1016/S1872-2067(20)63603-8 Abstract ( 195 )   HTML ( 9 )   PDF (3103KB) ( 403 )   Supporting Information The photocatalytic production of syngas using a noble-metal-free catalytic system is a promising approach for renewable energy and environmental sustainability. In this study, we demonstrate an efficient catalytic system formed by integrating Co single sites, which act as the active sites, in covalent triazine frameworks (CTFs), which act as the photoabsorber, for the photocatalytic production of syngas from CO2 in aqueous solution. The enhanced light absorption of the CTFs, which contain intramolecular heterojunctions, in conjunction with 0.8 mmol L-1 of the Co complex enables excellent syngas production with a yield of 3303 μmol g -1 (CO:H2 = 1.4:1) in 10 h, which is about three times greater than that achieved using CTF without a heterojunction. In the photocatalytic reaction, the coordinated single Co centers accept the photogenerated electrons from the CTF, and serve as active sites for CO2 conversion through an adsorption-activation-reaction mechanism. Theoretical calculations further reveal that the intramolecular heterojunctions highly promote photogenerated charge separation, thus boosting photocatalytic syngas production. This work reveals the promising potential of CTFs for single-metal-site-based photocatalysis.

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Structural engineering of 3D hierarchical Cd0.8Zn0.2S for selective photocatalytic CO2 reduction Lei Cheng, Dainan Zhang, Yulong Liao, Jiajie Fan, Quanjun Xiang 2021, 42 (1):  131-140.  DOI: 10.1016/S1872-2067(20)63623-3 Abstract ( 192 )   HTML ( 15 )   PDF (6587KB) ( 395 )   Supporting Information The solar-driven catalytic conversion of CO2 to useful chemical fuels is regarded as an environmentally friendly approach to reduce the consumption of fossil fuels and mitigate the greenhouse effect. However, it is highly intriguing and challenging to promote the selectivity and efficiency of visible-light-responsive photocatalysts that favor the adsorption of CO2 in photoreduction processes. In this work, three-dimensional hierarchical Cd0.8Zn0.2S flowers (C8Z2S-F) with ultrathin petals were successfully synthesized through an in-situ self-assembly growth process using sodium citrate as a morphology director. The flower-like Cd0.8Zn0.2S solid solution exhibited remarkable photocatalytic performance in the reduction of CO2, generating CO up to 41.4 μmol g-1 under visible-light illumination for 3 h; this was nearly three times greater than that of Cd0.8Zn0.2S nanoparticles (C8Z2S-NP) (14.7 μmol g-1). Particularly, a comparably high selectivity of 89.9% for the conversion of CO2 to CO, with a turnover number of 39.6, was obtained from the solar-driven C8Z2S-F system in the absence of any co-catalyst or sacrificial agent. Terahertz time-domain spectroscopy indicated that the introduction of flower structures enhanced the light-harvesting capacity of C8Z2S-F. The in situ diffuse reflectance infrared Fourier transform spectroscopy unveiled the existence of surface-adsorbed species and the conversion of photoreduction intermediates during the photocatalytic process. Empirical characterizations and predictions of the photocatalytic mechanism demonstrated that the flower-like Cd0.8Zn0.2S solid solution possessed desirable CO2 adsorption properties and an enhanced charge-transfer capability, thus providing a highly effective photocatalytic reduction of CO2.

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A novel iron-chelating polyimide network as a visible-light-driven catalyst for photoinduced radical polymerization Gang Ding, Qin Wang, Fei Liu, Yi Dan, Long Jiang 2021, 42 (1):  141-151.  DOI: 10.1016/S1872-2067(20)63610-5 Abstract ( 184 )   HTML ( 8 )   PDF (3181KB) ( 474 )   With the aim of developing a low-cost and efficient visible-light-driven photocatalyst for radical polymerization, iron-chelating polyimide networks (Fe@MPI) was fabricated by firstly synthesizing photoactive melamine-containing polyimide (MPI) networks and then incorporating Fe(III) cations into the polymer networks. Fe@MPI exhibits a wide absorption spectrum ranging from 220 to 1250 nm and 3.5 times higher photocurrent intensity as compared with the pristine MPI. Based on its excellent photo-electric properties, Fe@MPI was employed as a recyclable heterogeneous catalyst, providing sufficient activity for the visible-light driven radical polymerization to synthesize poly(methyl methacrylate) with molecular weight up to 31.3 × 10 4 g/mol. Taking advantage of the heterogeneous nature of the catalyst, Fe@MPI could be facilely regenerated from the polymerization solution by filtration without an obvious loss of its activity. This research provides a novel recyclable catalyst for visible-light driven radical polymerization.

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2D mesoporous ultrathin Cd0.5Zn0.5S nanosheet: Fabrication mechanism and application potential for photocatalytic H2 evolution Wenhua Xue, Wenxi Chang, Xiaoyun Hu, Jun Fan, Enzhou Liu 2021, 42 (1):  152-163.  DOI: 10.1016/S1872-2067(20)63593-8 Abstract ( 296 )   HTML ( 13 )   PDF (2186KB) ( 641 )   Supporting Information Two-dimensional mesoporous ultrathin Cd0.5Zn0.5S nanosheets with a thickness of ~1.5 nm were fabricated using a multistep chemical transformation strategy involving inorganic-organic hybrid ZnS-ethylenediamine (denoted as ZnS(en)0.5) as a hard template. Inorganic-organic hybrid ZnS(en)0.5, Cd0.5Zn0.5S(en)x, and Cd0.5Zn0.5S nanosheets were sequentially fabricated, and their transformation processes were analyzed in detail. The fabricated Cd0.5Zn0.5S nanosheets exhibited high photocatalytic hydrogen evolution reaction activity in the presence of a sacrificial agent. The Cd0.5Zn0.5S nanosheets exhibited remarkably high H2 production activity of ~1395 μmol∙h-1∙g-1 in pure water with no co-catalyst, which is the highest value reported thus far for bare photocatalysts, to the best of our knowledge. The high activity of these nanosheets is attributed to their distinct nanostructure (e.g., short transfer distance of photoinduced charge carriers, large number of unsaturated surface atoms, and large surface area). Moreover, ternary NiCo2S4 nanoparticles were employed to facilitate the charge separation and enhance the surface kinetics of H2 evolution. The H2 production rate reached ~62.2 and ~2436 μmol∙h-1∙g-1 in triethanolamine and pure water, respectively, over the NiCo2S4/Cd0.5Zn0.5S heterojunctions. The result indicated that the Schottky junction was critical to the enhanced activity. The proposed method can be used for fabricating other highly efficient CdZnS-based photocatalysts for solar-energy conversion or other applications.

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Z-scheme N-doped K4Nb6O17/g-C3N4 heterojunction with superior visible-light-driven photocatalytic activity for organic pollutant removal and hydrogen production Chao Liu, Yue Feng, Zitong Han, Yao Sun, Xiaoqiu Wang, Qinfang Zhang, Zhigang Zou 2021, 42 (1):  164-174.  DOI: 10.1016/S1872-2067(20)63608-7 Abstract ( 168 )   HTML ( 9 )   PDF (1337KB) ( 658 )   Supporting Information A simple calcination method was employed to prepare a Z-scheme N-doped K4Nb6O17/g-C3N4 (KCN) heterojunction photocatalyst, in which the electronic structure of K4Nb6O17 was regulated by N-doping, and g-C3N4 was formed both on the surface and within the interlayer spaces of K4Nb6O17. The KCN composite showed profoundly improved photocatalytic activity for both H2 generation and RhB degradation compared to its counterparts. This improved performance was attributed to the synergistic effects of N-doping, which broadened its light harvesting ability, and heterojunction formation, which increased the charge separation rate. The relatively low BET specific surface area of the KCN composite had little effect on its photocatalytic activity. Based on ESR spectroscopy studies, •O2-, •OH, and h + are the main active species in the photocatalytic degradation of RhB. Thus, it is reasonable to propose a Z-scheme photocatalytic mechanism over the KCN composite, which exhibits the dual advantages of efficient charge separation and high redox ability. Our work provides a simple approach for constructing large-scale Z-scheme heterojunction photocatalysts with high photocatalytic performance.

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Enhanced photocatalytic NO removal and toxic NO2 production inhibition over ZIF-8-derived ZnO nanoparticles with controllable amount of oxygen vacancies Pengfei Zhu, Xiaohe Yin, Xinhua Gao, Guohui Dong, Jingkun Xu, Chuanyi Wang 2021, 42 (1):  175-183.  DOI: 10.1016/S1872-2067(20)63592-6 Abstract ( 803 )   HTML ( 32 )   PDF (1986KB) ( 551 )   Supporting Information The controlled introduction of oxygen vacancies (OVs) in photocatalysts has been demonstrated to be an efficient approach for improving the separation of photogenerated charge carriers, and thus, for enhancing the photocatalytic performance of photocatalysts. In this study, a two-step calcination method where ZIF-8 was used as the precursor was explored for the synthesis of ZIF-8-derived ZnO nanoparticles with gradient distribution of OVs. Electron paramagnetic resonance measurements indicated that the concentration of OVs in the samples depended on the temperature treatment process. Ultraviolet-visible spectra supported that the two-step calcined samples presented excellent light-harvesting ability in the ultraviolet-to-visible light range. Moreover, it was determined that the two-step calcined samples presented superior photocatalytic performance for the removal of NO, and inhibited the generation of NO2. These properties could be attributed to the contribution of the OVs present in the two-step calcined samples to their photocatalytic performance. The electrons confined by the OVs could be transferred to O2 to generate superoxide radicals, which could oxidize NO to the final product, nitrate. In particular, the NO removal efficiency of Z 350-400 (which was a sample first calcined at 350 °C for 2 h, then at 400 °C for 1 h) was 1.5 and 4.6 times higher than that of Z 400 (which was one-step directly calcined at 400 °C) and commercial ZnO, respectively. These findings suggested that OV-containing metal oxides that derived from metal-organic framework materials hold great promise as highly efficient photocatalysts for the removal of NO.

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Design of a ZnO/Poly(vinylidene fluoride) inverse opal film for photon localization-assisted full solar spectrum photocatalysis Yukai Chen, Yu Wang, Jiaojiao Fang, Baoying Dai, Jiahui Kou, Chunhua Lu, Yuanjin Zhao 2021, 42 (1):  184-192.  DOI: 10.1016/S1872-2067(20)63588-4 Abstract ( 242 )   HTML ( 8 )   PDF (3748KB) ( 318 )   Supporting Information Owing to its photonic band gap (PBG) and slow light effects, aniline black (AB)-poly(vinylidene fluoride) (PVDF) inverse opal (IO) photonic crystal (PC) was constructed to promote the utility of light and realize photothermal synergetic catalysis. As a highly efficient reaction platform with the capability of restricting heat, a microreactor was introduced to further amplify the photothermal effects of near infrared (NIR) radiation. The photocatalytic efficiency of ZnO/0.5AB-PVDF IO (Z0.5A) increases 1.63-fold compared to that of pure ZnO film under a full solar spectrum, indicating the effectiveness of synergetic promotion by slow light and photothermal effects. Moreover, a 5.85-fold increase is achieved by combining Z0.5A with a microreactor compared to the film in a beaker. The photon localization effect of PVDF IO was further exemplified by finite-difference time-domain (FDTD) calculations. In conclusion, photonic crystal-microreactor enhanced photothermal catalysis has immense potential for alleviating the deteriorating water environment.

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MoS2/Zn3In2S6 composite photocatalysts for enhancement of visible light-driven hydrogen production from formic acid Sujuan Zhang, Shixiang Duan, Gaoli Chen, Sugang Meng, Xiuzhen Zheng, You Fan, Xianliang Fu, Shifu Chen 2021, 42 (1):  193-204.  DOI: 10.1016/S1872-2067(20)63584-7 Abstract ( 204 )   HTML ( 9 )   PDF (2469KB) ( 574 )   Enhancing the separation efficiency of photogenerated carriers is propitious for the promotion of photocatalytic hydrogen production from formic acid decomposition. Herein, MoS2/Zn3In2S6 (MoS2/ZIS6) composite photocatalysts containing varying mass percentages of MoS2 were obtained by a straightforward synthetic method. The results confirmed that MoS2, as a cocatalyst, markedly promoted the photogenerated charge separation efficiency and visible light-driven hydrogen production activity of ZIS6 (λ > 400 nm). Specifically, the as-prepared 0.5% MoS2/ZIS6 photocatalyst exhibited the highest photocatalytic hydrogen production rate (74.25 µmol·h-1), which was approximately 4.3 times higher than that of ZIS6 (17.47 µmol·h -1). The excellent performance of the 0.5% MoS2/ZIS6 photocatalyst may be due to the fact that MoS2 has a low Fermi energy level and can thus enrich photogenerated electrons from ZIS6, and furthermore reduce H+ derived from formic acid, to form hydrogen. The structure and morphology of the MoS2/ZIS6 photocatalysts and the reactive species were determined by X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy, among others; a plausible mechanistic rationale is discussed based on the results.

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Metal-doped Mo2C (metal = Fe, Co, Ni, Cu) as catalysts on TiO2 for photocatalytic hydrogen evolution in neutral solution Jing Liu, Gary Hodes, Junqing Yan, 2021, 42 (1):  205-216.  DOI: 10.1016/S1872-2067(20)63589-6 Abstract ( 285 )   HTML ( 12 )   PDF (1449KB) ( 841 )   Supporting Information The neutral hydrogen evolution reaction (HER) is vital in the chemical industry, and its efficiency depends on the interior character of the catalyst. Herein, work function (WF) engineering is introduced via 3d metal (Fe, Co, Ni, and Cu) doping for modulating the Fermi energy level of Mo2C. The defective energy level facilitates the free water molecule adsorption and, subsequently, promotes the neutral HER efficiency. Specifically, at a current density of 10 mA/cm2, Cu-Mo2C exhibits the best HER performance with an overpotential of 78 mV, followed by Ni-Mo2C, Co-Mo2C, Fe-Mo2C, and bare Mo2C with 90, 95, 100, and 173 mV, respectively, and the corresponding Tafel slope values are 40, 43, 42, 56, and 102 mV/dec. The modified WF can also lead to an enhanced photocatalytic efficiency owing to the lowered Schottky barrier and excellent carrier transition across the electrocatalyst-solution interface. When coupling the metal-doped Mo2C samples with TiO2, enhanced photocatalytic neutral HER rates are obtained in comparison to the case with bare TiO2. Typically, the HER rates are 521, 404, 275, 224, 147, and 112 μmol/h for Cu, Ni, Co, Fe, bare Mo2C, and bare TiO2, respectively. Time-resolved photoluminescence spectroscopy (TRPS) and ultrafast transient absorption (TA) measurements are carried out to confirm the recombination and migration of the photogenerated carriers. The fitted τ values from the TRPS curves are 22.6, 20.5, 10.1, 4.7, 4.0, 2.5, and 1.9 ns for TiO2, TiO2-Mo2C, TiO2-Fe-Mo2C, TiO2-Fe-Mo2C, TiO2-Fe-Mo2C, TiO2-Fe-Mo2C, and TiO2-Pt, respectively. Additionally, the fitted τ values from the TA results are 31, 73, and 105 ps for the TiO2-Mo2C, TiO2-Cu-Mo2C, and TiO2-Pt samples, respectively. This work provides in-depth insights into the WF modulation of an electrocatalyst for improving the HER performance.

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Engineering graphitic carbon nitride with expanded interlayer distance for boosting photocatalytic hydrogen evolution Qiushi Yang, Shaonian Hu, Yaxuan Yao, Xiangang Lin, Haiwei Du, Yupeng Yuan 2021, 42 (1):  217-224.  DOI: 10.1016/S1872-2067(20)63611-7 Abstract ( 528 )   HTML ( 24 )   PDF (2080KB) ( 586 )   Supporting Information Regulating interlayer distance is a crucial factor in the development of two-dimensional (2D) nanomaterials. A 2D metal-free photocatalyst, such as graphitic carbon nitride (g-C3N4), exhibits morphology- and microstructure-dependent photocatalytic activity. Herein, we report a straightforward and facile route for the preparation of unique lamellar g-C3N4, by co-firing melamine and ammonium chloride via microwave-assisted heating. Through the decomposition of NH4Cl, the evaporation of NH3 gas can effectively overcome van der Waals forces, expanding the interlayer distance of g-C3N4, thereby creating a lamellar structure consisting of nanosheets. Compared with bulk g-C3N4, the NH3-derived lamellar g-C3N4 exhibits a larger specific surface area and enhanced optical absorption capability, which increase photocatalytic hydrogen production because of the highly active structure, excellent utilization efficiency of photon energy, and low recombination efficiency of photogenerated charge carriers. This study provides a simple strategy for the regulation of the g-C3N4 microstructure toward highly efficient photocatalytic applications.

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Synthesis of core-shell nanostructured Cr2O3/C@TiO2 for photocatalytic hydrogen production Yang Chen, Guobing Mao, Yawen Tang, Heng Wu, Gang Wang, Li Zhang, Qi Liu 2021, 42 (1):  225-234.  DOI: 10.1016/S1872-2067(20)63615-4 Abstract ( 169 )   HTML ( 10 )   PDF (1535KB) ( 446 )   Supporting Information In this study, the Cr2O3/C@TiO2 composite was synthesized via the calcination of yolk-shell MIL-101@TiO2. The composite presented core-shell structure, where Cr-doped TiO2 and Cr2O3/C were the shell and core, respectively. The introduction of Cr3+ and Cr2O3/C, which were derived from the calcination of MIL-101, in the composite enhanced its visible light absorbing ability and lowered the recombination rate of the photogenerated electrons and holes. The large surface area of the Cr2O3/C@TiO2 composite provided numerous active sites for the photoreduction reaction. Consequently, the photocatalytic performance of the composite for the production of H2 was better than that of pure TiO2. Under the irradiation of a 300 W Xe arc lamp, the H2 production rate of the Cr2O3/C@TiO2 composite that was calcined at 500 °C was 446 μmol h-1 g-1, which was approximately four times higher than that of pristine TiO2 nanoparticles. Moreover, the composite exhibited the high H2 production rate of 25.5 μmol h-1 g-1 under visible light irradiation (λ > 420 nm). The high photocatalytic performance of Cr2O3/C@TiO2 could be attributed to its wide visible light photoresponse range and efficient separation of photogenerated electrons and holes. This paper offers some insights into the design of a novel efficient photocatalyst for water-splitting applications.

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Co0.85Se magnetic nanoparticles supported on carbon nanotubes as catalyst for hydrogen evolution reaction Xiaohui Sun, Nuzahat Habibul, Hong Du 2021, 42 (1):  235-243.  DOI: 10.1016/S1872-2067(20)63632-4 Abstract ( 165 )   HTML ( 9 )   PDF (1479KB) ( 496 )   Supporting Information Co0.85Se magnetic nanoparticles supported on carbon nanotubes were prepared by a one-step hydrothermal method. The saturation magnetization and coercivity of the MWCNTs/Co0.85Se nanocomposites increased due to a decrease in the Co0.85Se nanoparticle size in the MWCNTs/Co0.85Se nanocomposites and an increase in the distance between the Co0.85Se nanoparticles, which increased the specific surface area, thereby benefiting the electrocatalytic performance of the catalyst. Moreover, the MWCNTs/Co0.85Se nanocomposites exhibited an excellent hydrogen evolution reaction performance owing to the presence of MWCNTs, which enhanced the mass transport during the electrocatalytic reactions. Furthermore, in an acid solution, the 30 wt% MWCNTs/Co0.85Se composite catalyst exhibited a current density of 10 mA cm-2 at a small overpotential of 266 mV vs. RHE, a small Tafel slope of 60.5 mV dec-1, and good stability for HER.