聚合物半导体光催化合成过氧化氢：光氧化还原中心的空间分离和协同利用.pdf

物 理 化 学 学 报 Acta Phys.-Chim.Sin.2023,39(11),2301001(1 of 22)Received:January 1,2023;Revised:February 21,2023;Accepted:February 21,2023;Published online:March 6,2023.*Corresponding authors.Emails:qitao-(Q.Z.);(C.S.);Tel.:+86-15875517091(Q.Z.);+86-13066870440(C.S.).The project was supported by the National Natural Science Foundation of China(21972094,21805191,22102102),National Key Research and Development Program of China(2021YFA1600800),Educational Commission of Guangdong Province,China(839-0000013131),Guangdong Basic and Applied Basic Research Foundation,China(2020A1515010982),Shenzhen Science and Technology Program,China(JCYJ20190808142001745,RCJC20200714114434086),Shenzhen Stable Support Project,China(20200812160737002,20200812122947002),Shenzhen Peacock Plan,China(20180921273B,202108022524B,20210308299C).国家自然科学基金(21972094,21805191,22102102)，国家重点研发计划(2021YFA1600800)，广东省教育厅基金(839-0000013131)，广东基础和应用基础研究基金(2020A1515010982)，深圳科技计划(JCYJ2019080808142001745,RCJC2020200714114434086)，深圳稳定支持项目(20200812160737002,20200812122947002)，深圳孔雀计划(20180921273B,202108022524B,20210308299C)资助 Editorial office of Acta Physico-Chimica Sinica Review doi:10.3866/PKU.WHXB202301001 Semiconducting Polymers for Photosynthesis of H2O2:Spatial Separation and Synergistic Utilization of Photoredox Centers Yao Xie 1,Qitao Zhang 1,*,Hongli Sun 1,Zhenyuan Teng 2,3,Chenliang Su 1,*1 International Collaborative Laboratory of 2D Materials for Optoelectronic Science&Technology,Engineering Technology Research Center for 2D Materials Information Functional Devices and Systems of Guangdong Province,Institute of Microscale Optoeletronics,Shenzhen University,Shenzhen 518060,Guangdong Province,China.2 School of Chemistry,Chemical Engineering and Biotechnology,Nanyang Technological University,Singapore 637459,Singapore.3 Department of Applied Chemistry,Faculty of Engineering,Kyushu Institute of Technology,Kitakyushu 804-8550,Japan.Abstract:The photocatalytic synthesis of hydrogen peroxide using earth-abundant water and/or O2 as raw materials and solar energy as the sole energy input is an attractive route to achieving a carbon-neutral future.In particular,semiconducting polymer photocatalysts have piqued the interest of researchers working on the photocatalytic synthesis of H2O2 because their bandgap structures,reactivation sites,and components are easily tunable at the molecular level.However,there are two major challenges:1)the photoredox centers are difficult to separate and recombine easily,resulting in low reactivity in the photocatalytic production of H2O2,and 2)the low utilization rate of the redox centers.In several cases,only one side of the redox center is used for the photocatalytic synthesis of H2O2,while the other side typically reacts with a sacrificial agent.In this review,we provide a timely survey of recent advances in the spatial separation and synergistic utilization of photoredox centers for photocatalytic H2O2 production.The key aspect for achieving spatial separation of the redox centers is to engineer electron donor-acceptor(D-A)units on a single photocatalyst,such as by incorporating atomically dispersed metals into the polymer frameworks to build metal-organic D-A units or constructing all-organic D-A units.Depending on the photocatalytic behavior of the redox centers,the synergistic utilization of photoredox centers can be classified into three major reaction models:1)the oxygen reduction reaction(ORR)combined with the oxidative production of chemicals;2)the water oxidation reaction(WOR)combined with the reductive production of chemicals;and 3)the ORR combined with the WOR.Based on this,the regulation modes,characteristics,catalytic mechanisms,and reaction pathways to overcome the two challenges of efficient H2O2 production are summarized and discussed.Finally,we demonstrate efficient photocatalytic H2O2 production and provide prospects and challenges for the photocatalytic production of H2O2 using photoredox centers.Key Words:H2O2 synthesis;Photo-redox center;Spatial separation;Synergistic utilization;Polymer photocatalyst 物理化学学报 Acta Phys.-Chim.Sin.2023,39(11),2301001(2 of 22)聚合物半导体光催化合成过氧化氢：光氧化还原中心的空间分离和协同利用聚合物半导体光催化合成过氧化氢：光氧化还原中心的空间分离和协同利用 谢垚1，张启涛1,*，孙宏丽1，滕镇远2,3，苏陈良1,*1深圳大学微纳光电子学研究院，广东省二维材料信息功能器件与系统工程中心，教育部二维材料光电科技国际合作联合实验室，广东 深圳 518060 2南洋理工大学化学，化学工程与生物技术学院，新加坡 637459 3九州工业大学工学部，应用化学科，日本 北九州市 804-8550 摘要：摘要：以地表丰富的水和/或氧气为原料，以太阳能为能量来源的光催化合成过氧化氢是面向碳中和的一个颇具吸引力的路径。近年来，以能带、活性位点、组成等可调的聚合物半导体为光催化剂，开展光合成过氧化氢的研究进入了新的高峰期。当前，该研究主要面临两大关键挑战：1)由于材料性质固有的限制，光氧化还原中心通常难以分离，导致光生电荷复合严重，使得光催化合成过氧化氢的活性较差；2)氧化还原中心的利用率低，多数情况下，只有氧化端或还原端参与过氧化氢的合成，另一侧则与牺牲剂反应消耗。对此，本文聚焦光氧化还原中心的空间分离和协同利用来阐述聚合物半导体光催化合成过氧化氢的最新进展。光氧化还原中心空间分离的关键是在聚合物中设计电子给体和供体单元，例如在聚合物框架中引入原子级金属，构建金属-有机给吸电子体系，或构建全有机给吸电子体系。根据氧化还原中心的光催化行为，协同利用主要分为以下三种模型：1)氧还原耦合有机分子氧化；2)水氧化耦合有机分子还原，3)氧还原耦合水氧化。在此基础上，本文详细探讨了针对上述两个关键挑战的调控模式、特性、催化机制和反应途径。最后，我们阐述了光催化合成过氧化氢的潜在应用，并展望了光催化合成过氧化氢中理性设计氧化还原中心协同利用模式的机遇和挑战。关键词：关键词：过氧化氢合成；氧化还原中心；空间分离；协同利用；聚合物光催化剂 中图分类号：中图分类号：O643 1 Introduction Hydrogen peroxide(H2O2)was first discovered by Thenard in 1818;since then,it has become one of the most valuable chemicals 1,2.Globally,with the widespread application of H2O2(organic synthesis,wastewater treatment,disinfection,and paper bleaching)and environmentally friendly processes(the major products are clean and nontoxic),the global demand for H2O2 is expected to increase to 5.7 million tons by 2027 35.Furthermore,H2O2 is a potential green energy alternative to H2 in the fuel cell field due to its comparable energy density to H2 and more convenient storage and transportation 6.Thus,the synthesis method of H2O2 has attracted increasing attention.The oxidation of anthraquinone(AQ)was first developed in 1953 and has dominated the industrial production of H2O2 ever since 4,7.Nevertheless,it involves multiple catalytic reactions of oxygen and hydrogen,leading to a variety of side reactions,which produce a large amount of waste.This results in the waste of resources,which makes the AQ process nonenvironmentally friendly.Furthermore,the oxidation of AQ is characterized by a high energy input and explosion risks;therefore,for a carbon-neutral future,ecofriendly and safe methods for the sustainable production of H2O2 are highly desired.Photocatalysis has become a unique route that can simultaneously meet the requirements of environmental protection,energy saving,and safety since it uses water and oxygen as reactants and solar energy as the energy input,leading to zero or even negative carbon emissions.Interestingly,the photocatalytic synthesis of H2O2 can be traced back to 1927,when H2O2 was produced via photocatalytic oxidation on ZnO particles 8.Recently,research on the photocatalytic technology has become a hot spot,and many efforts have been devoted to studying the related field of photocatalysis 9.In particular,the study of polymer-based photocatalysts has become increasingly popular,making the research on the photocatalytic synthesis of H2O2 a hot topic(as shown in Fig.1)3,10,11.Notably,the classification,modification method,reaction pathway,and activity enhancement mechanism of polymer-based photocatalysts used in the photocatalytic production of H2O2 have been summarized in previous reviews 13,10,11.However,there are still two major challenges that should be faced in this aspect,which lead to a low utilization of solar energy and a poor activity.One is the poor separation of redox centers,which leads to the easy recombination of the photogenerated carriers and the low selectivity of the photocatalytic production of H2O2;the other is the low utilization rate of redox centers.In many cases,only one side of the redox centers is utilized for the photocatalytic H2O2 synthesis,with the other side being sacrificed.For the reaction to proceed,sacrificial agents are usually added to consume the unreactive photoelectrons or holes,leading to a waste of resources and energy 12,13.Accordingly,in order to enhance the utilization of solar energy and activity,the spatial separation and 物理化学学报 Acta Phys.-Chim.Sin.2023,39(11),2301001(3 of 22)synergistic utilization of the redox centers are vital for an efficient H2O2 production,and extensive research efforts have been devoted to the advancement of this technology.Furthermore,compared with traditional inorganic metal compound photocatalysts(such as TiO2 14,WO3 15,ZnO 16,CdS 17,MoS2 18,and BiVO4 19),polymer-based photocatalysts mostly consist of C,H,and N,which provide rich site structures(central atoms,coordination atoms,surface functional groups,and coordination number),a variety of bond levels(hydrogen bonds,covalent bonds,coordination bonds,and ionic bonds),intrinsic hybrid performance,highly tunable molecular and band structures 20.In the photocatalytic production of H2O2,polymer-based photocatalysts are superior over conventional inorganic semiconductor photocatalysts upon rational design;as a result,polymer-based photocatalysts are more easily designed and expanded and thus exhibit wide application prospects.Consequently,they are promising materials for low-cost and easy-to-process photocatalytic H2O2 production 21.Over the past decade,numerous polymer-based photocatalysts have been investigated for achieving the photocatalytic production of H2O2(Fig.1),including polymeric carbon nitride(denoted as C3N4 or PCN)12,2224,covalent organic frameworks(COFs)2528,metal-organic frameworks(MOFs)10,24,29,linear conjugated polymers(LCPs)30,conjugated microporous polymers(CMPs)31,32,resorcinol-formaldehyde(RF)resins 3337,and covalent triazine frameworks(CTFs)38,39.Therefore,this review focuses primarily on polymer-based photocatalysts for the spatial separation and synergistic utilization of the redox centers for efficient H2O2 production.The spatial separation of the photoexcited redox centers is an effective way to achieve efficient H2O2 production,and a promising strategy is to modify the redox centers,developing a type of photocatalyst with photoredox centers working independently.Based on this strategy,two approaches have been developed,which afford superior efficiency.Atomic metal cocatalysts and polymer frameworks 40 could be utilized to engineer electron donors and acceptors on different moieties of a single catalyst,thus achieving the spatial separation of the redox centers.These were proved to be effective methods for improving the catalytic efficiency and have thus received considerable research attention 41.For example,Co and Sb were incorporated as atomic active sites into polymer-based photocatalysts to drive the spatial separation of the redox centers 4244.Moreover,organic moieties,such as AQ 45,46,acetylene 47,diacetylene 38,48,diarylamine 26,49,triazine 39,50,thiourea 51,52,and porphyrin 53,54,which serve as reduction centers or oxidation centers,were introduced in some polymer frameworks,so as to achieve effective spatial separation of the redox centers.The synergistic utilization of photoexcited redox centers is also challenging,but it is effective in increasing the solar energy utilization rate and avoiding the use of sacrificial agents.Therefore,depending on the photocatalytic behavior of the redox centers,polymer-based photocatalysis are here classified into three reaction models,as illustrated in Table 1.Type I:Oxygen reduction reaction(ORR)combined with the oxidative production of chemicals.The photoexcited electrons reduce O2 to H2O2,while the photoexcited holes oxidize the substrates to produce valuable chemicals.Type II:Water oxidation reaction(WOR)combined with the reductive production of chemicals.The photoexcited holes oxidize water to H2O2 and hydrogen species,while the photoexcited electrons reduce the substrates to produce value-added chemicals with the hydrogen species.Type III:ORR combined with the WOR.The photoexcited electrons reduce O2 through the 2e route,while the photoexcited holes oxidize water,and eventually the redox centers couple to generate H2O2 without the utilization of sacrificial agents nor the generation of any by-products.Based on this,the regulation modes,characteristics,catalytic mechanisms,and reaction pathways for achieving the separation and full utilization of the redox centers for efficient H2O2 production are summarized and discussed.Finally,we demonstrate an efficient photocatalytic production of H2O2 and prospect the opportunities and challenges that are involved in the spatial separation and Fig.1 Timeline showing the critical polymer photocatalysts in H2O2 production.物理化学学报 Acta Phys.-Chim.Sin.2023,39(11),2301001(4 of 22)synergistic utilization of the redox centers for the photocatalytic production of H2O2.2 Spatial separation of photoexcited redox centers Generally,multiphase photocatalytic processes can be divided into four independent steps:(I)photoexciton generation;(II)photoexciton separation;(III)carrier migration to the surface catalytic center;and(IV)surface catalytic reaction 55.The four steps determine the photocatalytic efficiency.After absorbing photons,the polymer-based photocatalyst generates hot electron(e)and hole(h+)pairs,and the bound excitons form through energy relaxation,triggering the formation of photoexcited redox centers 56.Accordingly,when the organic semiconductor polymer absorbs photons with an energy higher than its forbidden band,the electrons will be excited and will migrate to the surface of the catalyst;they will then overcome the overpotentials for the subsequent redox reaction(Fig.2)1.However,the redox centers are hard to separate due to the intrinsic limitations of the photocatalysts.Furthermore,the overlapping of the redox centers often increases the recombination of the photogenerated carriers and decreases the selectivity of the photocatalytic production of H2O2 57.Thus,to achieve an efficient photocatalytic production of H2O2,the spatial separation of the redox centers is an issue that must be addressed.Notably,natural organisms can perform efficient photosynthesis and continuously convert solar energy into biological energy.This is mainly because the redox centers in organisms are physically separated,which is quite challenging to achieve in artificial photosynthesis.Generally,the Fig.2 Schematic of the processes involved in the photocatalytic production of H2O2.Table 1 Three types of synergistic utilization of photo-redox centers.Reaction modes Typical photocatalysts Reduction center products Oxidation center products Ref.Type I MIL-125-Rn H2O2 Benzaldehyde 68 TA-Por-sp2-COF H2O2 N-Benzylidenebenzylamine 53 PFBTPCBM H2O2 Formate 69 Type II PCN-10-CP-10 H2 H2O2 73 C-N-g-C3N4 H2 H2O2 74 CoP/CDs H2O2&H2 O2 75 24%-WO3-MIL-100-Fe CH4&CO H2O2 76 Type III-4e WOR NvCNCN H2O2 O2 63 g-C3N4/PDI/rGO0.05 H2O2 O2 64 MRFS-7 H2O2 O2 35 TPE-AQ H2O2 O2 31 Sb-SAPC15 H2O2 O2 43 Type III-2e WOR CTF-EDDBN H2O2 H2O2 38 CTF-BDDBN H2O2 H2O2 38 COF-TfpBpy H2O2 H2O2 66 e-h+excitationH2O2Chemicale-h+excitationH2O2Chemicale-h+excitationH2O2O2+H+e-h+excitationH2O2H2O2+H+物理化学学报 Acta Phys.-Chim.Sin.2023,39(11),2301001(5 of 22)simultan