2019 Vol. 40 No 年 第 40 卷第 1 期 In This Issue Cover: Xi s group controls the synthesis of the silk-like FeS 2 /NiS 2 hybrid nanocrystal. The mat

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2 2019 Vol. 40 No 年 第 40 卷第 1 期 In This Issue Cover: Xi s group controls the synthesis of the silk-like FeS 2 /NiS 2 hybrid nanocrystal. The material has rich interfaces and defects, which is beneficial to enhance its catalytic performance. The picture shows the flexible battery assembled by this catalyst and their promising application. Read more about the article behind the cover on pages 封面 : 席聘贤课题组控制合成了丝绸状纳米结构 (FeS 2 /NiS 2 ). 该材料具有丰富的界面和缺陷, 有利于提升其催化性能. 见本期第 页. About the Journal Chinese Journal of Catalysis is an international journal published monthly by Chinese Chemical Society, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, and Elsevier. The journal publishes original, rigorous, and scholarly contributions in the fields of heterogeneous and homogeneous catalysis in English or in both English and Chinese. The scope of the journal includes: New trends in catalysis for applications in energy production, environmental protection, and production of new materials, petroleum chemicals, and fine chemicals; Scientific foundation for the preparation and activation of catalysts of commercial interest or their representative models; Spectroscopic methods for structural characterization, especially methods for in situ characterization; New theoretical methods of potential practical interest and impact in the science and applications of catalysis and catalytic reaction; Relationship between homogeneous and heterogeneous catalysis; Theoretical studies on the structure and reactivity of catalysts. The journal also accepts contributions dealing with photo-catalysis, bio-catalysis, and surface science and chemical kinetics issues related to catalysis. Types of Contributions Reviews deal with topics of current interest in the areas covered by this journal. Reviews are surveys, with entire, systematic, and important information, of recent progress in important topics of catalysis. Rather than an assemblage of detailed information or a complete literature survey, a critically selected treatment of the material is desired. Unsolved problems and possible developments should also be discussed. Authors should have published articles in the field. Reviews should have more than 80 references. Communications rapidly report studies with significant innovation and major academic value. They are limited to four Journal pages. After publication, their full-text papers can also be submitted to this or other journals. Articles are original full-text reports on innovative, systematic and completed research on catalysis. Highlights describe and comment on very important new results in the original research of a third person with a view to highlight their significance. The results should be presented clearly and concisely without the comprehensive details required for an original article. Perspectives are short reviews of recent developments in an established or developing topical field. The authors should offer a critical assessment of the trend of the field, rather than a summary of literatures. Viewpoints describe the results of original research in general in some area, with a view to highlighting the progress, analyzing the major problems, and commenting the possible research target and direction in the future. Impact Factor 2017 SCI Impact Factor: SCI 5-Year Impact Factor: Abstracting and Indexing Abstract Journals (VINITI) Cambridge Scientific Abstracts (CIG) Catalysts & Catalysed Reactions (RSC) Current Contents/Engineering, Computing and Technology (Clarivate Analytics ISI) Chemical Abstract Service/SciFinder (CAS) Chemistry Citation Index (Clarivate Analytics ISI) Japan Information Center of Science and Technology Journal Citation Reports/Science Edition (Clarivate Analytics ISI) Science Citation Index Expanded (Clarivate Analytics ISI) SCOPUS (Elsevier) Web of Science (Clarivate Analytics ISI)

3 2019 Vol. 40 No. 1 Publication Monthly (12 issues) Started in March 1980 Transaction of The Catalysis Society of China Superintended by Chinese Academy of Sciences (CAS) Sponsored by Chinese Chemical Society and Dalian Institute of Chemical Physics, CAS Editors-in-Chief Can Li, Tao Zhang Edited by Editorial Board of Chinese Journal of Catalysis Tel.: cjcatal@dicp.ac.cn Add.: Dalian Institute of Chemical Physics, CAS, 457 Zhongshan Road, Dalian , Liaoning, China Published by Science Press Distributed by Science Press, 16 Donghuangchenggen North Street, Beijing , China, Tel: sales_journal@mail.sciencep.com Subscription Agents Domestic All Local Post Offices in China Foreign China International Book Trading Corporation, P.O.Box 399, Beijing , China Printed by Dalian Haida Printing Company, Limited Price $60 月刊 SCI 收录 1980 年 3 月创刊 中国化学会催化学会会刊主管中国科学院主办中国化学会 中国科学院大连化学物理研究所主编李灿张涛编辑 催化学报 编辑委员会出版编辑部联系方式 : 地址 : 大连市沙河口区中山路 457 号 中国科学院大连化学物理研究所邮编 : 电话 : (0411) 传真 : (0411) 电子信箱 : cjcatal@dicp.ac.cn 国内统一连续出版物号 CN /O6 国际标准连续出版物号 ISSN CODEN THHPD3 广告经营许可证号 总发行北京东黄城根北街 16 号, 邮编 : 电话 : (010) sales_journal@mail.sciencep.com 国内订购全国各地邮政局邮发代号 8-93 国外订购中国国际图书贸易总公司北京 399 信箱邮编 国外发行代号 M417 印刷大连海大印刷有限公司定价 60 元 公开发行 Advisors ( 顾问 ) Alexis T. Bell ( 美国 ) Jürgen Caro ( 德国 ) Gabriele Centi ( 意大利 ) Michel Che ( 法国 ) Yi Chen ( 陈懿 ) Avelino Corma ( 西班牙 ) Zi Gao ( 高滋 ) Editors-in-Chief ( 主编 ) The Fifth Editorial Board of Chinese Journal of Catalysis 催化学报 第五届编辑委员会 Masatake Haruta ( 日本 ) Mingyuan He ( 何鸣元 ) Graham J. Hutchings ( 英国 ) Johannes A. Lercher ( 德国 ) S. Ted. Oyama ( 日本 ) Daniel E. Resasco ( 美国 ) Rutger A. van Santen ( 荷兰 ) Can Li ( 李灿 ) Tao Zhang ( 张涛 ) Associate Editors ( 副主编 ) Xingwei Li ( 李兴伟 ) Haichao Liu ( 刘海超 ) Members ( 编委 ) Xinhe Bao ( 包信和 ) Yong Cao ( 曹勇 ) De Chen ( 陈德, 挪威 ) Jingguang G. Chen ( 陈经广, 美国 ) Weiping Ding ( 丁维平 ) Yunjie Ding ( 丁云杰 ) Xianzhi Fu ( 付贤智 ) Naijia Guan ( 关乃佳 ) Xinwen Guo ( 郭新闻 ) Hongxian Han ( 韩洪宪 ) Heyong He ( 贺鹤勇 ) Hong He ( 贺泓 ) Emiel J. M. Hensen ( 荷兰 ) Jiahui Huang ( 黄家辉 ) George W. Huber ( 美国 ) Huanwang Jing ( 景欢旺 ) Alexander Katz ( 美国 ) Jinlin Li ( 李金林 ) Jun Li ( 李隽 ) Junhua Li ( 李俊华 ) Weixue Li ( 李微雪 ) Yingwei Li ( 李映伟 ) Young Members ( 青年编委 ) Bingyang Bai ( 拜冰阳 ) Shaowen Cao ( 曹少文 ) Weili Dai ( 戴卫理 ) Jiguang Deng ( 邓积光 ) Yong Ding ( 丁勇 ) Fan Dong ( 董帆 ) Pingwu Du ( 杜平武 ) Fengtao Fan ( 范峰滔 ) Yanlong Gu ( 顾彦龙 ) Yanqiang Huang ( 黄延强 ) Changzhi Li ( 李昌志 ) Fei Li ( 李斐 ) Roel Prins ( 瑞士 ) Junwang Tang ( 唐军旺, 英国 ) Yongdan Li ( 李永丹 ) Changjun Liu ( 刘昌俊 ) Jingyue Liu ( 刘景月, 美国 ) Zhongmin Liu ( 刘中民 ) An-Hui Lu ( 陆安慧 ) Marcel Schlaf ( 加拿大 ) Susannah L. Scott ( 美国 ) Jianyi Shen ( 沈俭一 ) Wenjie Shen ( 申文杰 ) Chunshan Song ( 宋春山, 美国 ) Baolian Su ( 苏宝连, 比利时 ) Dangsheng Su ( 苏党生 ) Zhiyong Tang ( 唐智勇 ) Zhijian Tian ( 田志坚 ) Ying Wan ( 万颖 ) Aiqin Wang ( 王爱琴 ) Dezheng Wang ( 王德峥 ) Feng Wang ( 王峰 ) Jianguo Wang ( 王建国 ) Ye Wang ( 王野 ) Yong Wang ( 王勇, 美国 ) Yingxu Wei ( 魏迎旭 ) Rengui Li ( 李仁贵 ) Xiang Li ( 李翔 ) Xin Li ( 李鑫 ) Zhenxing Liang ( 梁振兴 ) Gang Liu ( 刘钢 ) Gang Liu ( 刘岗 ) Mingce Long ( 龙明策 ) Kangle Lv ( 吕康乐 ) Botao Qiao ( 乔波涛 ) Yong Qin ( 覃勇 ) Feng Shi ( 石峰 ) Wei Sun ( 孙伟 ) Ferdi Schüth ( 德国 ) Huilin Wan ( 万惠霖 ) Youchang Xie ( 谢有畅 ) Qin Xin ( 辛勤 ) Xiaoming Zheng ( 郑小明 ) Peng Wu ( 吴鹏 ) Qihua Yang ( 杨启华 ) Zidong Wei ( 魏子栋 ) Zili Wu ( 吴自力, 美国 ) Chungu Xia ( 夏春谷 ) Fengshou Xiao ( 肖丰收 ) Jianliang Xiao ( 肖建良, 英国 ) Zaiku Xie ( 谢在库 ) Boqing Xu ( 徐柏庆 ) Jie Xu ( 徐杰 ) Longya Xu ( 徐龙伢 ) Yushan Yan ( 严玉山, 美国 ) Weimin Yang ( 杨为民 ) Weishen Yang ( 杨维慎 ) Shuangfeng Yin ( 尹双凤 ) Jiaguo Yu ( 余家国 ) Youzhu Yuan ( 袁友珠 ) Zongchao Zhang ( 张宗超 ) Huijun Zhao ( 赵惠军, 澳大利亚 ) Zhen Zhao ( 赵震 ) Xiao-Dong Zhou ( 周晓东, 美国 ) Yonggui Zhou ( 周永贵 ) Guoxiong Wang ( 汪国雄 ) Xiuli Wang ( 王秀丽 ) Yujie Xiong ( 熊宇杰 ) Fan Yang ( 杨帆 ) Hengquan Yang ( 杨恒权 ) Changlin Yu ( 余长林 ) Huogen Yu ( 余火根 ) Yunbo Yu ( 余运波 ) Wangcheng Zhan ( 詹望成 ) Jing Zhang ( 张静 ) Wenzhen Zhang ( 张文珍 ) Liangshu Zhong ( 钟良枢 ) Online Submission Homepage

4 Chinese Journal of Catalysis Vol. 40, No. 1, January 2019 催化学报 2019 年第 40 卷第 1 期 available at journal homepage: Chinese Journal of Catalysis Graphical Contents Academic discussion Chin. J. Catal., 2019, 40: 1 3 doi: /S (18) Comment On the correction of gas phase signals during IR operando analyses Frederic Meunier * Institut de Recherches sur la Catalyse et l'environnement, France Gas-phase or surface species? Wavenumber (cm -1 ) The accuracy of dual beam Fourier transform infrared (DB FTIR) spectrometer in eliminating the interference of gas phase molecular vibration in gas/solid heterogeneous catalysis under reaction conditions is discussed. Reviews Chin. J. Catal., 2019, 40: 4 22 doi: /S (18) Recent advances in one dimensional nanostructures for energy electrocatalysis Ping Li, Wei Chen * Changchun Institution of Applied Chemistry, Chinese Academic of Science; University of Science and Technology of China This overview summarizes the recent advances in one dimensional metal nanostructures for energy electrocatalysis, including the main reactions in direct methanol fuel cells and water splitting.

5 iv Graphical Contents / Chinese Journal of Catalysis Vol. 40, No. 1, 2019 Chin. J. Catal., 2019, 40: doi: /S (18) Transition metal nitrogen sites for electrochemical carbon dioxide reduction reaction Chengcheng Yan, Long Lin, Guoxiong Wang *, Xinhe Bao * Dalian Institute of Chemical Physics, Chinese Academy of Sciences; University of Chinese Academy of Sciences Metal nitrogen sites constituted of earth abundant elements with maximum atom utilization efficiency have emerged as promising catalysts for electrochemical CO2 reduction reaction. Communication Chin. J. Catal., 2019, 40: doi: /S (18) A hydrated amorphous iron oxide nanoparticle as active water oxidation catalyst 400 Zheng Chen, Qinge Huang, Baokun Huang, Fuxiang Zhang *, Can Li * Dalian Institute of Chemical Physics, Chinese Academy of Sciences O 2 ( mol/l) TOF: 9.3 s -1 H 2 O O 2 hydrated FeO x 2.2 nm 0 A hydrated amorphous iron oxide nanoparticle exhibits high water oxidation activity with TOF of 9.3 s 1 in the photocatalytic Ru(bpy)3 2+ Na2S2O Time (s) 2S O 8 +2H 2 O FeO x 2+ Ru(bpy), hv O 2 +4H +4SO 4 3 Articles Chin. J. Catal., 2019, 40: doi: /S (18) Synthesis of silk like FeS2/NiS2 hybrid nanocrystals with improved reversible oxygen catalytic performance in a Zn air battery Jing Jin, Jie Yin, Pinxian Xi * Lanzhou University Herein, an efficient liquid exfoliation strategy was designed for producing silk like FeS2/NiS2 hybrid nanocrystals with enhanced reversible oxygen catalytic performance that displayed excellent properties for Zn air batteries.

6 Graphical Contents / Chinese Journal of Catalysis Vol. 40, No. 1, 2019 v Chin. J. Catal., 2019, 40: doi: /S (18) Eco friendly synthesis of high silica zeolite Y with choline as green and innocent structure directing agent Dawei He, Danhua Yuan, Zhijia Song, Yunpeng Xu *, Zhongmin Liu * Dalian Institute of Chemical Physics, Chinese Academy of Sciences; University of Chinese Academy of Sciences Choline chloride or choline hydroxide was used as an eco friendly and nontoxic organic structure directing agent (OSDA) for the synthesis of high silica zeolite Y with SiO2/Al2O3 ratios of Chin. J. Catal., 2019, 40: doi: /S (18) Construction of 2D 2D TiO2 nanosheet/layered WS2 heterojunctions with enhanced visible light responsive photocatalytic activity Yongchuan Wu, Zhongmin liu, Yaru Li, Jitao Chen, Xixi Zhu, Ping Na * Tianjin University; College of Chemistry and Chemical Engineering; Shandong University of Science and Technology The 2D 2D TNS/WS2 heterojunction was successfully constructed by in situ growing the layered WS2 on the surface of TiO2 nanosheet. The 2D 2D nanointerfaces boosted the separation of photogenerated carriers, thereby resulting in a higher photocatalytic activity. Chin. J. Catal., 2019, 40: doi: /S (18) Enhanced photocatalytic Cr(VI) reduction and diclofenac sodium degradation under simulated sunlight irradiation over MIL 100(Fe)/g C3N4 heterojunctions Xuedong Du, Xiaohong Yi, Peng Wang, Jiguang Deng *, Chong chen Wang * Beijing University of Civil Engineering and Architecture; Beijing University of Technology The MIL 100(Fe)/g C3N4 hybrids show high photocatalytic activity under simulated sunlight and can reduce Cr(VI) to Cr(III) and decompose diclofenac sodium effectively.

7 vi Graphical Contents / Chinese Journal of Catalysis Vol. 40, No. 1, 2019 Chin. J. Catal., 2019, 40: doi: /S (18) Fast electron transfer and enhanced visible light photocatalytic activity by using poly o phenylenediamine modified AgCl/g C3N4 nanosheets Linlin Sun, Chongyang Liu, Jinze Li, Yaju Zhou, Huiqin Wang *, Pengwei Huo *, Changchang Ma, Yongsheng Yan Jiangsu University The degradation efficiency of tetracycline over PoPD/AgCl/CN composites synthesized by precipitation reaction and photoinitiated polymerization approach was three times higher than that over pure CN; O2 and h + are the main reactive species in the case of PoPD/AgCl/CN. Chin. J. Catal., 2019, 40: doi: /S (18) Improving the denitration performance and K poisoning resistance of the V2O5 WO3/TiO2 catalyst by Ce 4+ and Zr 4+ co doping Jun Cao, Xiaojiang Yao *, Fumo Yang, Li Chen, Min Fu *, Changjin Tang, Lin Dong Chongqing Technology and Business University; Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences; Sichuan University; Nanjing University NO + NH 3 + O 2 N 2 + H 2 O NO + NH 3 + O 2 N 2 + H 2 O K 2 O K 2 O V 2 O 5 V 2 O 5 WO 3 WO 3 TiO 2 TiO 2 TiO 2 TiO 2 TiO 2 TiO 2 TiO2 TiO 2 TiO 2 TiO 2 TiO 2 TiO 2 TiO 2 TiO 2 K 2 O V 2 O 5 V 2 O 5 WO 3 WO 3 ZrO 2 CeO 2 TiO 2 TiO 2 CeO 2 TiO TiO 2 -CeO 2 -ZrO 2 TiO 2 2 K 2 O ZrO 2 CeO 2 ZrO 2 CeO 2 TiO 2 TiO 2 CeO 2 TiO 2 TiO 2 ZrO 2 CeO 2 TiO 2 TiO 2 TiO 2 TiO2 TiO 2 TiO 2 TiO 2 ZrO 2 CeO 2 TiO 2 TiO 2 CeO 2 TiO 2 TiO 2 ZrO 2 CeO 2 Co doping of Ce 4+ and Zr 4+ enhances the denitration performance and K poisoning resistance of V2O5 WO3/TiO2 catalyst because more K atoms can be combined with Ce 4+ to yield the better protection of active vanadium species.

8 Graphical Contents / Chinese Journal of Catalysis Vol. 40, No. 1, 2019 vii Chin. J. Catal., 2019, 40: doi: /S (18)63164 X Synergistic effects of CuO and Au nanodomains on Cu2O cubes for improving photocatalytic activity and stability Denghui Jiang, Yuegang Zhang, Xinheng Li * Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences; Central South University; Suzhou Institute of Nano tech and Nano bionics, Chinese Academy of Sciences Au/CuO/Cu2O catalysts were synthesized by sequential surface oxidative and reductive deposition on Cu2O surfaces improving both the photocatalytic activity and stability of Cu2O. Chin. J. Catal., 2019, 40: doi: /S (18) A highly stable and active mesoporous ruthenium catalyst for ammonia synthesis prepared by a RuCl3/SiO2 templated approach Yaping Zhou, Yongcheng Ma, Guojun Lan, Haodong Tang, Wenfeng Han, Huazhang Liu, Ying Li * Zhejiang University of Technology; Sichuan Huadi Construction Engineering Co., Ltd. Semi embedded Ru MC has stable Ru NPs and strong interaction between Ru and C that promote the catalytic performance for ammonia synthesis.

9 中国科学院科学出版基金资助出版月刊 SCI 收录 2019 年 1 月第 40 卷第 1 期 目 次 学术讨论 1 关于双光束红外光谱在气固相多相催化反应实时原位表征中气相校正的讨论 Frederic Meunier 综 4 一维纳米材料在能源电催化中的研究进展李苹, 陈卫 23 过渡金属 - 氮活性位点在二氧化碳电化学还原反应中的应用阎程程, 林龙, 汪国雄, 包信和 快 38 水合状态的无定形氧化铁作为高效水氧化催化剂的研究陈政, 黄清娥, 黄保坤, 章福祥, 李灿 论 述 讯 文 43 可逆氧催化性能提升的 FeS 2 /NiS 2 纳米复合物的合成及其在锌空电池中的应用靳晶, 殷杰, 刘瀚文, 席聘贤 52 以胆碱为绿色无毒有机结构导向剂合成高硅 Y 型分子筛贺大威, 袁丹华, 宋智甲, 徐云鹏, 刘中民 60 构建 2D-2D TiO 2 纳米片 / 层状 WS 2 异质结用以增强可见光响应光催化活性吴勇川, 刘中敏, 李亚茹, 陈继涛, 祝熙熙, 那平 70 模拟太阳光照射下 MIL-100(Fe)/g-C 3 N 4 异质结光催化 Cr(VI) 还原和双氯芬酸钠降解杜雪冬, 衣晓虹, 王鹏, 邓积光, 王崇臣 80 聚邻苯二胺修饰 AgCl/g-C 3 N 4 纳米片复合光催化剂的制备及性能研究孙林林, 刘重阳, 李金择, 周亚举, 王会琴, 霍鹏伟, 马长畅, 闫永胜 95 Ce 4+, Zr 4+ 共掺杂提高 V 2 O 5 -WO 3 /TiO 2 催化剂脱硝性能及抗 K 中毒能力曹俊, 姚小江, 杨复沫, 陈丽, 傅敏, 汤常金, 董林 105 CuO 和 Au 纳米结构协同增强 Cu 2 O 立方体光催化活性和稳定性蒋登辉, 张跃钢, 李鑫恒 114 以 RuCl 3 /SiO 2 为模板制备的高性能镶嵌式钌基氨合成催化剂周亚萍, 马永承, 蓝国钧, 唐浩东, 韩文锋, 刘化章, 李瑛 相关信息 124 催化学报 第五届编辑委员会 128 Guide for Authors 135 催化学报 作者指南 英文全文电子版 ( 国际版 ) 由 Elsevier 出版社在 ScienceDirect 上出版 在线投审稿网址

10 Chinese Journal of Catalysis 40 (2019) 催化学报 2019 年第 40 卷第 1 期 available at journal homepage: Article Enhanced photocatalytic Cr(VI) reduction and diclofenac sodium degradation under simulated sunlight irradiation over MIL 100(Fe)/g C3N4 heterojunctions Xuedong Du a, Xiaohong Yi a, Peng Wang a, Jiguang Deng b, *, Chong chen Wang a,# a Beijing Key Laboratory of Functional Materials for Building Structure and Environment Remediation, Beijing University of Civil Engineering and Architecture, Beijing , China b Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing , China A R T I C L E I N F O A B S T R A C T Article history: Received 24 July 2018 Accepted 12 September 2018 Published 5 January 2019 Keywords: MIL 100(Fe) g C3N4 Heterojunction Cr(VI) reduction Diclofenac sodium Metal organic framework MIL 100(Fe) and g C3N4 heterojunctions (MG x, x = 5%, 10%, 20%, and 30%, x is the mass fraction of MIL 100(Fe) in the hybrids) were facilely fabricated through ball milling and annealing, and characterized by powder X ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, UV visible diffuse reflectance spectrometry, and photoluminescence emission spectrometry. The photocatalytic activities of the series of MG x heterojunctions toward Cr(VI) reduction and diclofenac sodium degradation were tested upon irradiation with simulated sunlight. The influence of different organic compounds (ethanol, citric acid, oxalic acid, and diclofenac sodium) as hole scavengers and the ph values (2, 3, 4, 6, and 8) on the photocatalytic activities of the series of MG x heterojunctions was investigated. MG 20% showed superior photocatalytic Cr(VI) reduction and diclofenac sodium degradation performance than did the individual MIL 100(Fe) and g C3N4 because of the improved separation of photoinduced electron hole charges, which was clarified via photoluminescence emission and electrochemical data. Moreover, the MG x exhibited good reusability and stability after several runs. 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved. 1. Introduction Among toxic heavy metal ions, hexavalent chromium (Cr(VI)) is a mutagenic and carcinogenic contaminant that is found in surface water and groundwater, as it is widely utilized in the electroplating, leather tanning, printing, polishing, and pigment industries [1 3]. Up to now, photocatalytic reduction of Cr(VI) to Cr(III) has been a hot topic of research [4 10], therefore, it is a great challenge to develop novel photocatalysts with efficient visible light absorption and excellent stability * Corresponding author. Tel/Fax: ; E mail: jgdeng@bjut.edu.cn # Corresponding author. Tel/Fax: ; E mail: wangchongchen@bucea.edu.cn This work was supported by the National Natural Science Foundation of China ( , ), the Great Wall Scholars Training Program Project of Beijing Municipality Universities (CIT&TCD ), the Project of Construction of Innovation Teams and Teacher Career Development for Universities and Colleges Under Beijing Municipality (IDHT ), the Beijing Talent Project (2017A38), the Fundamental Research Funds for Beijing Universities (X18075/X18076/X18124/X18125/X18276), and the Scientific Research Foundation of Beijing University of Civil Engineering and Architecture (KYJJ /KYJJ ). DOI: /S (18) Chin. J. Catal., Vol. 40, No. 1, January 2019

11 Xuedong Du et al. / Chinese Journal of Catalysis 40 (2019) [8,11]. Among the various photocatalysts, graphitic carbon nitride (g C3N4) is a good, metal free photocatalyst that possesses appealing features like π conjugated electronic structure, high chemical stability, and earth abundance [12,13]. However, g C3N4 has some disadvantages, such as high recombination probability of the photogenerated electron hole pairs due to hybridization of the N 2p and C 2p states in the conduction band (CB) and unavoidably disordered structure or defects [14 16] and low surface area resulting from the bulk structure [17 19]. These disadvantages lead to the low photocatalytic activity for Cr(VI) reduction or organic pollutant degradation. Recently, synthesis of g C3N4 composites with different materials, such as g C3N4/Bi2WO6 [20], g C3N4/SiW11 [21], g C3N4/Zn3V2O7(OH)2(H2O)2 [22], WO3/g C3N4 [23], g C3N4/Ag2O [24], and g PAN/g C3N4 [25], has been identified to be an efficient way to improve the photocatalytic reduction efficiency. Recently, the application of metal organic frameworks (MOFs) in heterogeneous photocatalysis under UV/visible/UV vis irradiation for water splitting and CO2 & Cr(VI) reduction by using photogenerated electrons as well as the degradation of organic pollutants based on holes has become widespread [8,26 30]. The photocatalytic performance of composites containing g C3N4 and MOFs has been widely reported. For example, ZIF 9(Co)/g C3N4 exhibited multiple functions in both CO2 adsorption and high photocatalytic activity for CO2 reduction [31]. UiO 66(Zr)/g C3N4 demonstrated efficient photocatalytic hydrogen production because of the heterojunctions [32]. MIL 125(Ti)/g C3N4, MIL 53(Al)/g C3N4, and MIL 100(Fe)/g C3N4 exhibited highly efficient photocatalytic performance toward rhodamine B degradation in aqueous solution under visible light irradiation [12,33,34]. ZIF 8(Zn)/g C3N4 is a bifunctional material that shows efficient adsorption and facilitates sunlight induced photocatalytic degradation of tetracycline [35]. ZIF NC/g C3N4 composites exhibit enhanced photocatalytic activity for bisphenol A degradation with peroxymonosulfate under visible light irradiation [36]. Moreover, MIL 53(Fe)/g C3N4 had improved photocatalytic efficiency for Cr(VI) reduction [37]. In this work, MIL 100(Fe)/g C3N4 hybrids were synthesized through ball milling and annealing for photocatalytic Cr(VI) reduction under different conditions. Both g C3N4 and MIL 100(Fe) showed photocatalytic performance, but each material when used individually exhibited limited photocatalytic efficiency due to the high charge recombination rate and limited light absorption ability. The MIL 100(Fe)/g C3N4 hybrids obtained by combining MIL 100(Fe) with g C3N4 demonstrated outstanding photocatalytic performance for Cr(VI) reduction under simulated sunlight, along with good stability and reusability. 2. Experimental 2.1. Materials All chemicals including urea (CH4N2O, USP grade, Amresco), iron powder (Fe, 99%, J&k Scientific Ltd.), benzene 1,3,5 tricarboxylic acid (H3BTC, C9H6O6, 99%, J&k Scientific Ltd.), nitric acid (HNO3, analytical grade, Sinopharm Chemical Reagent Co., Ltd.), hydrofluoric acid (HF, analytical grade, Sinopharm Chemical Reagent Co., Ltd.), potassium dichromate (K2Cr2O7, analytical grade, Sinopharm Chemical Reagent Co., Ltd.), diclofenac sodium (C14H10Cl2NNaO2, 98%, J&k Scientific Ltd.), hydrogen peroxide (H2O2, 30 wt%, Sinopharm Chemical Reagent Co., Ltd.), oxalic acid (H2C2O4, analytical grade, Sinopharm Chemical Reagent Co., Ltd.), citric acid monohydrate (C6H8O7 H2O, 99%, J&k Scientific Ltd.), sodium acetate (C2H3O2Na, analytical grade, Sinopharm Chemical Reagent Co., Ltd.), and acetonitrile (C2H3N H2O, LC MS grade, J&k Scientific Ltd.) were commercially available and used without further purification Preparation of MIL 100(Fe)/g C3N4 hybrids g C3N4 was prepared by calcination with urea as the precursor [33]. Briefly, 10.0 g of urea was placed in a porcelain crucible with a cover, moved into a muffle furnace, and heated at 500 C for 4 h. The obtained yellow powder was collected for further use. Crude g C3N4 powder (1.0 g) was dispersed in ml deionized H2O by sonication for 6 h. Then, pure g C3N4 was obtained by centrifuging the supernatant at 6000 rpm for 10 min and dried at 60 C for 6 h. MIL 100(Fe) was synthesized according to the procedure reported by Horcajada and coworkers [38]. A mixture of g Fe 0, g H3BTC, 0.1 ml HF, 0.1 ml HNO3, and 10.0 ml H2O with a molar ratio of 1.0:0.66:2.0:1.2:280 was sealed in a 25.0 ml Teflon lined autoclave and heated at 150 C for 6 d. The light orange MIL 100(Fe) was collected by filtration, washed with deionized water, and finally dried in an oven at 60 C for 2 h. The MIL 100(Fe)/g C3N4 heterojunctions (MG x, x = 5%, 10%, 20%, and 30%, x is the mass fraction of MIL 100 in hybrids) were fabricated by ball milling, followed by thermal treatment of the mixture of g C3N4 and MIL 100(Fe). In a typical procedure, a certain amount of MIL 100(Fe) and g C3N4 powders was mixed in a stainless steel pot and ground for 20 min using a ball mill. The ground mixture was then thermally treated at 300 C for 2 h in a tube furnace under N2 atmosphere to produce a series of MIL 100(Fe)/g C3N4 (MG x) heterojunctions. For comparison, pristine g C3N4 and MIL 100(Fe) were also thermally treated under the same conditions as those for the MG x hybrids Characterization Powder X ray diffraction (PXRD) patterns of the samples were obtained with a Dandong Haoyuan DX 2700B diffractometer in the range of 2θ = 5 50 with Cu Kα radiation. Thermogravimetric analyses (TGA) were performed in the range of C in an air stream at a heating rate of 10 C/min on a DTU 3c thermal analyzer using α Al2O3 as a reference. Fourier transform infrared (FT IR) spectra were recorded using KBr pellets on a Nicolet 6700 spectrometer in the range of cm 1. UV visible diffuse reflectance spectra (UV vis

12 72 Xuedong Du et al. / Chinese Journal of Catalysis 40 (2019) DRS) of the solid samples were measured in the range of nm on a Perkin Elmer Lambda 650S spectrophotometer, in which barium sulfate (BaSO4) was used as the standard with 100% reflectance. Photoluminescence (PL) emission spectra were recorded on a Hitachi F 7000 spectrophotometer across wavelengths ranging from 400 to 600 nm at room temperature, with an excitation wavelength of 320 nm. The surface area of the sample was calculated from N2 adsorption desorption isotherms measured on a BELSORP mini II surface area analyzer at 196 C using the Brunauer Emmett Teller (BET) nitrogen adsorption method. The morphology of the samples was observed using a Hitachi HT7700 transmission electron microscope (TEM) operating at an acceleration voltage of 120 kv. X ray photoelectron spectroscopy (XPS) measurements were performed with Thermo ESCALAB 250XI Electrochemical measurements Electrochemical measurements were conducted using a Metrohm Autolab PGSTAT204 electrochemical station in a typical three electrode mode with 0.2 mol/l Na2SO4 aqueous solution (ph = 6.8) as the electrolyte. A Pt electrode and a saturated Ag/AgCl electrode were used as the counter electrode and reference electrode, respectively. Powder samples of 5.0 mg MIL 100(Fe) or g C3N4 were mixed sufficiently with μl ethanol/nafion (v/v = 19/1) under sonication for 30 min to prepare the working electrodes. The prepared slurry (10.0 μl) was drop cast onto the conductive side of a Fluorine doped Tin Oxide (FTO) substrate (1.0 cm 1.0 cm), and then dried at 80 C for 30 min. This step was repeated five times to ensure uniform coverage of MIL 100(Fe) or g C3N4 on the FTO substrate for obtaining the desired working electrodes Photocatalytic experiment The photocatalytic Cr(VI) reduction experiment was carried out at 25 C in a 300 ml quartz reactor containing mg of the photocatalyst and ml of 10.0 ppm Cr(VI) aqueous solution, and the solution ph was adjusted to with 0.2 mol/l H2SO4 or 0.2 mol/l NaOH solution. After stirring for 60 min to achieve adsorption desorption equilibrium, the suspensions were irradiated by a 300 W xenon lamp (Beijing Aulight Co., Ltd.). The spectrum of the light source is shown in Fig. S1 (Supporting Information). During illumination, 2.5 ml of the suspension was taken from the reactor at specific time intervals and centrifuged to separate the photocatalyst. The Cr(VI) content in the supernatant was determined colorimetrically at 540 nm using the diphenylcarbazide method with a Yuanxi UV 5200PC UV vis spectrophotometer [39]. The photocatalytic degradation performance of the MG x nanocomposites toward diclofenac sodium was also tested. In a typical experiment, mg of photocatalyst powder was dispersed in ml diclofenac sodium aqueous solution (0.1 mmol/l). The suspension was stirred in the dark for 60 min to achieve adsorption desorption equilibrium, and then, hydrogen peroxide (50.0 μl) was added to the suspension before turning on the light. A 300 W xenon lamp (Beijing Aulight Co. Ltd.) was used as the light source. During the photocatalytic degradation, the samples were collected at regular time intervals using a 0.22 mm syringe filter to remove the photocatalyst particles before analysis. An Acquity UPLC H Class (Waters) system was used to detect the residual concentration of diclofenac sodium after the photocatalytic degradation. The analytes were separated on a C18 (1.7 μm, 2.1 mm 50 mm) column in a UPLC system equipped with a TUV detector. Aqueous sodium acetate solution (0.015 mol/l) and acetonitrile were used as mobile phases A and B, respectively. The gradient was programmed as follows: min, 0 0% B; min, 0 48% B; 1 2 min, 48 48% B; min, 48 0% B. The column temperature was maintained at 40 C. 3. Results and discussion 3.1. Characterization The PXRD patterns of the parent materials and heterojunctions are illustrated in Fig. 1. The PXRD patterns of MIL 100(Fe) were consistent with those reported in the literature (Fig. S2) [38,40], demonstrating that the prepared MIL 100(Fe) was pure and well crystallized. The typical interlayer stacking peak (002) at 2θ = 27.2 corresponded to an interlayer distance of ~0.32 nm for g C3N4 [41,42]. The PXRD patterns of the MG x composites matched well with the corresponding peaks of g C3N4 and MIL 100(Fe), implying their successful combination. More importantly, no sign of a new phase in the MG x hybrids was observed after annealing; the characteristic peaks at 6.2, 10.2, 11.0, and 20.0 attributed to MIL 100(Fe) became more evident with increasing mass content in the MG x samples. The unchanged backbones of g C3N4 and MIL 100(Fe) in the MG x hybrids were further revealed by the identical FTIR spectra, as shown in Fig. 2. As expected, the same characteristic absorption peaks were observed for g C3N4 and MG x hybrids, except for the low MIL 100(Fe) content in the MG x samples. The texture of MG 20% hybrids was selected for observation in the TEM and HRTEM images, as shown in Intensity (a.u.) MIL-100(Fe) MG-30% MG-20% MG-10% MG-5% g-c3n (degree) Fig. 1. XRD patterns of g C3N4, MG x (x = 5%, 10%, 20%, and 30%) hybrids, and MIL 100(Fe).

13 Xuedong Du et al. / Chinese Journal of Catalysis 40 (2019) MIL Transmittance (a.u.) MG-30% MG-20% MG-10% MG-5% Weight (%) g-c3n4 MIL-100(Fe) MG-5% MG-10% MG-20% MG-30% g-c3n Wavenumber (cm 1 ) Fig. 2. FTIR spectra of g C3N4, MG x (x = 5%, 10%, 20%, and 30%) hybrids, and MIL 100(Fe). (a) 500 nm 500 nm g-c 3 N nm MIL-100(Fe) (c) 10 nm g-c 3 N 4 Fig. 3. For comparison, the TEM images of pure MIL 100(Fe) and g C3N4 were also included. MIL 100(Fe) (Fig. 3(a)) displayed a polygonal structure [34], and g C3N4 samples (Fig. 3(b)) exhibited aggregated, slate like, and smooth particles with lamellar structures [33]. It could also be clearly observed that the g C3N4 nanosheets adhered strongly to the edges of MIL 100(Fe) (Fig. 3(c)). High resolution TEM images (Fig. 3(d)) could not be obtained as g C3N4 and MIL 100(Fe) were solids with low crystalline quality [32]. TGA revealed that the thermal stability of MG x decreased with an increase in the MIL 100(Fe) content in the MG sample, as shown in Fig. 4, and the residual weight further confirmed the different MIL 100(Fe) contents in the MG x samples. Fig. 5 presents the XPS survey spectrum and the high resolution XPS spectra of MG 20%. The XPS survey spectrum (Fig. 5(a)) shows that C, N, O, and Fe exist in MG 20%. Fig. (b) (d) MIL-100(Fe) Fig. 3. TEM images of (a) pure MIL 100(Fe), (b) pure g C3N4, and (c) MG 20%, and (d) HRTEM image of MG 20% Temperature ( o C) Fig. 4. Thermal analysis of g C3N4, MG x (x = 5%, 10%, 20%, and 30%) hybrids, and MIL 100(Fe). 5(b) shows the C 1s XPS spectrum of MG 20%, in which the peaks at ev/288.2 ev and ev can be attributed to the sp 2 bonded carbon (C C bond)/c H bond and C N present in the g C3N4, respectively [33,37], while the peaks at and ev can be ascribed to benzoic rings and C=O bonds of the H2bdc ligand in MIL 100(Fe) [43]. Four binding energies in the N 1s region (Fig. 5(c)) can be observed, which can be ascribed to the C N C (398.7 ev), N (C)3 (400.1 ev), and N H groups (401.3 ev), and the charging effects (404.9 ev), respectively [44]. The spectrum of MG 20% (Fig. 5(d)) exhibits two O 1s peaks at and ev, which are related to the Fe O bonds of MG 20% and the oxygen components of the H2bdc ligand, respectively [45]. Furthermore, the Fe 2p spectrum in Fig. 5(e) has two peaks at and ev, which can be assigned to Fe 2p3/2 and Fe 2p1/2, respectively [46]. These results clearly imply that the MG 20% photocatalyst is successfully fabricated. The UV vis DRS spectra of g C3N4, MIL 100(Fe), and MG x are shown in Fig. 6(a). The band gap energy (Eg) and band edge wavelength (λg) of g C3N4, MIL 100(Fe), and MG x can be estimated using Eqs. (1) and (2), respectively [47]. Ahv = k(hv Eg) 1/n (1) λg = 1240/Eg (2) where k represents a constant, and n is determined by the type of optical transition of a semiconductor. The results reveal that the Eg values of g C3N4, MG 5%, MG 10%, MG 20%, MG 30%, and MIL 100(Fe) are 2.96, 2.87, 2.83, 2.80, 2.77, and 2.63 ev, respectively, and the band gaps tend to become narrow with an increase in the MIL 100(Fe) content. The PL spectra of g C3N4 and MG 20% at an excitation wavelength of 320 nm are demonstrated in Fig. 7. The PL intensity of MG 20% at the 440 nm peak is weaker than that of pure g C3N4, implying that the recombination rate of photogenerated electrons and holes decreases in case of MG 20% [48,49] Photocatalytic activity Before the photocatalytic reduction experiments, the adsorption abilities of the samples were tested. As shown in Fig. 8(a), the adsorption capacity of g C3N4 and MG x hybrids toward Cr2O7 2 was about 5%, while MIL 100(Fe) showed higher

14 74 Xuedong Du et al. / Chinese Journal of Catalysis 40 (2019) Survey N 1s (a) C 1s (b) N 1s (c) Intensity (a.u.) Fe 2p O 1s C 1s Intensity (a.u.) Intensity (a.u.) Binding energy (ev) Binding energy (ev) Binding energy (ev) O 1s (d) Fe 2p Fe 2p 1/ Fe 2p 3/ (e) Intensity (a.u.) Intensity (a.u.) Binding energy (ev) Binding energy (ev) Fig. 5. XPS spectra of the MG 20% hybrid. (a) Survey scan; (b) C 1s; (c) N 1s; (d) O 1s; (e) Fe 2p (a) 25 (b) Absorbance (a.u.) g-c3n4 MIL-100(Fe) MG-5% MG-10% MG-20% MG-30% (Ahv) g-c3n4 MIL-100(Fe) MG-5% MG-10% MG-20% MG-30% Wavelength (nm) Photon energy (ev) Fig. 6. (a) UV vis spectra and (b) (Ahv) 2 versus photon energy (hv) plots for g C3N4, MG x (x = 5%, 10%, 20%, and 30%) hybrids, and MIL 100(Fe). adsorption activity toward Cr2O7 2 (~20%) because of its positive surface at ph 2.0 [50,51]. The photocatalytic Cr(VI) reduction performance over MG x (x = 5%, 10%, 20%, and 30%) under simulated sunlight irradiation was evaluated, as illustrated in Fig. 8(a). All MG x hybrids exhibited higher photocatalytic activities than those of pure g C3N4 and MIL 100(Fe) owing to the synergistic effect between g C3N4 and MIL 100(Fe). The MG 20% hybrid demonstrated the best photocatalytic activity, evidenced by its Cr(VI) reduction (97%) efficiency within 80 min. The kinetic curves for the photocatalytic reduction of Cr(VI) over MG x (5%, 10%, 20%, and 30%) photocatalysts were plotted to the pseudo first order model (ln(c/c0) = kt), and the values of k are shown in Fig. 8(b). The order of the Cr(VI) reduction rates for the as prepared photocatalysts is as follows: MG 20% (0.037 min 1 ) > MG 10% (0.028 min 1 ) > MG 30% (0.026 min 1 ) > MG 5% (0.023 min 1 ) > g C3N4 (0.016 min 1 ) > MIL 100(Fe) (0.012 min 1 ). Appropriate introduction of MIL 100(Fe) into g C3N4 will not only be beneficial for charge transfer at the heterojunction interfaces, but also improve visible light harvesting (Fig. 6(a)). However, excess g C3N4 may decrease the quality of effective heterointerfaces in MG x, which would be unfavorable for charge transfer at the heterointerfaces [32,33,52]. During the redox process, the Cr(VI) reduction rate over the photocatalyst is greatly influenced by the ph of the aqueous solution. The reduction efficiencies of Cr(VI) over MG 20% at different ph values are shown in Fig. 9(a). The reduction ratio decreased rapidly with increasing ph (98%, 79%, 29%, 15%, and 9% at ph 2, 3, 4, 6, and 8, respectively). Under acidic conditions, the photocatalytic Cr(VI) reaction follows Eq. (4), and the abundant H + further facilitates the conformation change from Cr(VI) to Cr(III) [8]. However, under alkaline conditions, CrO4 2 is predominant, leading to a reaction as expressed in Eq. (6) [8]. Moreover, the Cr(OH)3 precipitate formed at ph > 6 covers the

15 Xuedong Du et al. / Chinese Journal of Catalysis 40 (2019) Intensity (a.u.) g-c3n4 MG-5% MG-10% MG-20% MG-30% Wavelength (nm) C/C (a) ph=8 ph=6 ph=4 ph=3 ph= Time (min) Fig. 7. Photoluminescence spectra of g C3N4 and MG x (x = 5%, 10%, 20%, and 30%) hybrids. k (min 1 ) C/C No catalyst MIL-100(Fe) g-c 3 N 4 MG-5% MG-30% MG-10% MG-20% No catalyst MIL-100(Fe) g-c3n4 Time (min) MG-5% MG-10% MG-20% MG-30% active sites of MG 20%, leading to a decline in its photocatalytic activity [52]. MG x + hv MG x(h + + e ) (3) Cr2O H + + 6e 2Cr H2O (4) Organic compounds + h + CO2 + H2O + others (5) CrO H2O + 3e Cr(OH)3 + 5OH (6) The consumption of holes (h + ) will accelerate photoinduced (a) (b) Catalyst Fig. 8. (a) Cr(VI) reduction photocatalytic performance of MIL 100(Fe), g C3N4, and MG x (x = 5%, 10%, 20%, and 30%) hybrids; (b) Rate constant k of MIL 100(Fe), g C3N4, and MG x hybrids. For comparison, the photocatalytic performance in a reaction without the catalyst is also given. C/C (b) Time (min) 0 ml 0.5 ml 1 ml 2 ml Fig. 9. Photocatalytic activities of the MG 20% hybrid for the reduction of Cr(VI) in aqueous solution at (a) different ph values and (b) different ethanol concentrations. electron hole charge separation and result in achieve outstanding Cr(VI) reduction efficiency. To investigate the effect of some organic compounds as hole scavengers on the reduction efficiency, a series of experiments were carried out with the addition of different organic compounds like citric acid, oxalic acid, and diclofenac sodium at ph 2.0. As shown in Fig. 10(a), the addition of hole scavengers (citric acid and oxalic acid) increases the photocatalytic Cr(VI) reduction activity of MG 20%, which might be ascribed to the fact that citric acid and oxalic acid can consume the photoinduced holes produced by the MG 20% photocatalyst upon light irradiation (Eq. (5)) [53]. Thus, more electrons can escape from the pair recombination and become available for the reduction of Cr(VI) under acidic conditions. Ethanol can also capture photoinduced holes, and it was found that an increase in ethanol concentration led to faster Cr(VI) reduction, as shown in Fig. 9(b). However, the addition of diclofenac sodium does not increase the reduction efficiency, as it consumes the hydroxyl radicals, and not photoinduced holes. To investigate the possible mechanism of the photocatalytic Cr(VI) reduction over MG 20%, the conduction bands (CBs) of MIL 100(Fe) and g C3N4 were determined to be 0.11 and 1.12 V at ph 7.0 (Fig. 11(a) and (b)), respectively, by Mott Schottky experiments. From the UV Vis DRS spectra, the band gaps of MIL 100(Fe) and g C3N4 were calculated to be 2.63 and 2.96 ev, respectively. Based on these values, the band structures of MIL 100(Fe) and g C3N4 were determined, and a

16 76 Xuedong Du et al. / Chinese Journal of Catalysis 40 (2019) (a) 1.0 No catalyst and no H 2 O 2 H 2 O 2 (b) g-c 3 N MG-20% g-c 3 N 4 +H 2 O MG-20%+H 2 O No hole scavenger mmol/l diclofenac sodium mmol/l oxalic acid mmol/l citric acid C/C C/C Time (min) Time (min) Fig. 10. (a) Photocatalytic activities of the MG 20% hybrid for the reduction of Cr(VI) in the presence of various hole scavengers; (b) Photocatalytic degradation of diclofenac sodium under different control conditions. 4 (a) 2 (b) Hz 1000 Hz 1500 Hz 500 Hz 1000 Hz 1500 Hz C 2 /(F ) V C 2 /(F ) V Potential (V) vs. Ag/AgCl Potential (V) vs. Ag/AgCl Fig. 11. Mott Schottky plots of (a) MIL 100(Fe) and (b) g C3N4 in 0.2 mol/l aqueous Na2SO4 solution (ph 7.0). schematic diagram is shown in Fig. 12. Electron hole pairs can be produced both on MIL 100(Fe) and g C3N4. Fig. 12 illustrates the charge carrier path in the MG 20% system. The photoexcited electrons from the CB of g C3N4 move to the CB of MIL 100(Fe), which can suppress the recombination of photogenerated electron hole pairs so that more free electrons are Fig. 12. Possible mechanism of photocatalytic reduction of Cr(VI) and degradation of diclofenac sodium over MG 20%. gathered in the CB of MIL 100(Fe). Consequently, MG 20% exhibits enhanced photocatalytic activity for Cr(VI) reduction under simulated sunlight irradiation. To further evaluate the photocatalytic performance of the heterojunction structure, the MG 20% was tested for the degradation of diclofenac sodium under different conditions. In the absence of H2O2, only 65.4% diclofenac sodium was degraded within 2 h, while 100% degradation was achieved within 50 min after adding H2O2, as shown in Fig. 10(b). The above process can be summarized in Eq. (3) and Eqs. (7) (8) as a Fenton like reaction occurs [54,55]. H2O2 + H + + e H2O + OH (7) Diclofenac sodium + OH Products (8) To assess the practical application potential of the photocatalysts, the reusability and stability of MG 20% were also investigated. MG 20% was stable after a long term stability test in an aqueous solution with ph 2.0, for up to 72 h. As shown in Fig. 13(a), the photocatalytic reduction efficiency of MG 20% does not obviously decrease after five runs of Cr(VI) reduction, indicating that the photocatalyst is highly stable and can be used for repeated treatment of Cr(VI). Moreover, the XRD patterns (Fig. 13(b)) of MG 20% before and after the photocatalytic reaction indicated that the crystal structure of MG 20% was not destroyed even after five cycles of the reaction. It can be concluded that MG 20% is stable during the photocatalytic

17 Xuedong Du et al. / Chinese Journal of Catalysis 40 (2019) (a) 100 (b) Degradation efficiency (%) Intensity (a.u.) Used sample Fresh sample Number of recycling experiments (degree) Fig. 13. (a) Reusability of MG 20% in the reduction of Cr(VI); (b) XRD patterns of MG 20% before and after the photocatalytic reaction. process. 4. Conclusions The facile fabrication of a series of photocatalytically active MIL 100(Fe)/g C3N4 (MG x) hybrids was accomplished. The optimal MG 20% hybrid demonstrated excellent photocatalytic activity for Cr(VI) reduction and organic pollutant degradation under simulated sunlight irradiation, which was superior to that of pure MIL 100(Fe) and g C3N4. The results of electrochemical measurements and PL emission revealed that the enhanced Cr(VI) reduction was due to the efficient interfacial charge transfer from the photoexcited g C3N4 to MIL 100(Fe). The different hole scavengers and ph value of the reaction solution played important roles in the photocatalytic Cr(VI) reduction. In the photocatalytic system, the addition of ethanol, citric acid, or oxalic acid facilitated the photocatalytic Cr(VI) reduction as the photogenerated holes were easily consumed. Cyclic experiments also indicated the reusability and stability of MG x for the photocatalytic Cr(VI) reduction. This work further demonstrates the great potential application of versatile MOFs and economic g C3N4 for the development of active heterostructured photocatalysts for environmental remediation. References [1] R. J. Kieber, J. D. Willey, S. D. Zvalaren, Environ. Sci. Technol., 2002, 36, [2] J. J. Testa, M. A. Grela, M. I. Litter, Environ. Sci. Technol., 2004, 38, [3] S. Loyaux Lawniczak, P. Lecomte, J. J. Ehrhardt, Environ. Sci. Technol., 2001, 35, Chin. J. Catal., 2019, 40: Graphical Abstract doi: /S (18) Enhanced photocatalytic Cr(VI) reduction and diclofenac sodium degradation under simulated sunlight irradiation over MIL 100(Fe)/g C3N4 heterojunctions Xuedong Du, Xiaohong Yi, Peng Wang, Jiguang Deng *, Chong chen Wang * Beijing University of Civil Engineering and Architecture; Beijing University of Technology The MIL 100(Fe)/g C3N4 hybrids show high photocatalytic activity under simulated sunlight and can reduce Cr(VI) to Cr(III) and decompose diclofenac sodium effectively.

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