Challenges of photocatalytic extraction of uranium: a review

Abstract

Nuclear energy, known for its low carbon emissions and high energy density, is considered one of the most promising future energy sources. However, the generation of nuclear waste and depletion of uranium resources make the development of simple, efficient, and cost-effective uranium extraction methods critical for the sustainable development of nuclear energy and environmental recovery. Photocatalytic uranium extraction, as a straightforward, highly efficient, and low-cost technique, has attracted increasing attention from researchers. Herein, we provide a comprehensive overview of the mechanisms behind photocatalytic uranium extraction, summarizing the evolution of materials used in this process. It also evaluates the experimental progress in extracting U(VI) from real uranium-containing wastewater and seawater. Moreover, the review highlights the challenges currently faced by photocatalytic uranium extraction technologies, such as the stability and scalability of photocatalysts, and discusses future development directions. Additionally, modification strategies to enhance the photocatalytic performance of catalysts are summarized, with comparisons drawn between the strengths and limitations of various materials used for U(VI) extraction. This review concludes with an evaluation of the potential of photocatalytic technologies for large-scale applications and their role in addressing environmental concerns related to uranium extraction.

Keywords

Uranium extraction / photocatalysis / electron-hole generation/separation / structure regulation

References

[1] Sholl DS.Seven chemical separations to change the world.Nature2016;532:435-7

[2] Xie Y,Geng Y.Uranium extraction from seawater: material design, emerging technologies and marine engineering.Chem Soc Rev2023;52:97-162

[3] Ye Y,Han W.Spontaneous electrochemical uranium extraction from wastewater with net electrical energy production.Nat Water2023;1:887-98

[4] Yang L,Qian Y.Bioinspired hierarchical porous membrane for efficient uranium extraction from seawater.Nat Sustain2022;5:71-80

[5] Sun Q,Perman J.Bio-inspired nano-traps for uranium extraction from seawater and recovery from nuclear waste.Nat Commun2018;9:1644 PMCID:PMC5915388

[6] Yuan Y,Xiao J.DNA nano-pocket for ultra-selective uranyl extraction from seawater.Nat Commun2020;11:5708

[7] Liu C,Xie J.A half-wave rectified alternating current electrochemical method for uranium extraction from seawater.Nat Energy2017;2:17007

[8] Mei D,Yan B.Adsorption of uranium (VI) by metal-organic frameworks and covalent-organic frameworks from water.Coord Chem Rev2023;475:214917

[9] Tamada M. Current status of technology for collection of uranium from seawater. In International seminar on nuclear war and planetary emergencies-42nd session. 2010; pp 243-52.

[10] Yang H,Hao M.Functionalized iron-nitrogen-carbon electrocatalyst provides a reversible electron transfer platform for efficient uranium extraction from seawater.Adv Mater2021;33:e2106621

[11] Cai Y,Lv Z.Highly efficient uranium extraction by a piezo catalytic reduction-oxidation process.Appl Catal B Environ2022;310:121343

[12] Meng C,Zhang Z.Open-framework vanadate as efficient ion exchanger for uranyl removal.Environ Sci Technol2024;58:9456-65

[13] Yang J,Ye MY.Protonated imine-linked covalent organic frameworks for photocatalytic hydrogen evolution.Angew Chem Int Ed2021;60:19797-803

[14] Huang NY,Liu S.Electrostatic attraction-driven assembly of a metal-organic framework with a photosensitizer boosts photocatalytic CO₂ reduction to CO.J Am Chem Soc2021;143:17424-30

[15] Shiraishi Y,Hagi T.Resorcinol-formaldehyde resins as metal-free semiconductor photocatalysts for solar-to-hydrogen peroxide energy conversion.Nat Mater2019;18:985-93

[16] Qin C,Zhou W.Urea/thiourea imine linkages provide accessible holes in flexible covalent organic frameworks and dominates self-adaptivity and exciton dissociation.Angew Chem Int Ed2025;64:e202418830

[17] Wu Y,Liu X.Functional nanomaterials for selective uranium recovery from seawater: material design, extraction properties and mechanisms.Coord Chem Rev2023;483:215097

[18] Liu X,Liu X.Orderly porous covalent organic frameworks-based materials: superior adsorbents for pollutants removal from aqueous solutions.Innovation2021;2:100076

[19] Tang N,Niu C.Amidoxime-based materials for uranium recovery and removal.J Mater Chem A2020;8:7588-625

[20] Xie Y,Chen L.Recent progress of radionuclides separation by porous materials.Sci China Chem2024;67:3515-77

[21] Amadelli R,Sostero S.Photodeposition of uranium oxides onto TiO₂ from aqueous uranyl solutions.Faraday Trans1991;87:3267

[22] Chen T,Dong C.Advanced photocatalysts for uranium extraction: elaborate design and future perspectives.Coord Chem Rev2022;467:214615

[23] Li P,Wang Y.Photoconversion of U(VI) by TiO₂: an efficient strategy for seawater uranium extraction.Chem Eng J2019;365:231-41

[24] Lei J,Yuan C.Enhanced photoreduction of U(VI) on WO₃ nanosheets by oxygen defect engineering.Chem Eng J2021;416:129164

[25] Linsebigler AL,Yates JT.Photocatalysis on TiO₂ surfaces: principles, mechanisms, and selected results.Chem Rev1995;95:735-58

[26] Filippov TN,Chetyrin IA.Photocatalytic and photochemical processes on the surface of uranyl-modified oxides: an in situ XPS study.Appl Catal A-Gen2018;58:81-90

[27] Chen T,Li M.Efficient uranium reduction of bacterial cellulose-MoS₂ heterojunction via the synergistically effect of Schottky junction and S-vacancies engineering.Chem Eng J2021;406:126791

[28] Nosaka Y.Generation and detection of reactive oxygen species in photocatalysis.Chem Rev2017;117:11302-36

[29] Hu E,Gao Q.Cyano-functionalized graphitic carbon nitride with adsorption and photoreduction isosite achieving efficient uranium extraction from seawater.Adv Funct Materials2024;34:2312215

[30] Jiang X,Luo X.Simultaneous photoreduction of Uranium(VI) and photooxidation of Arsenic(III) in aqueous solution over g-C₃N₄/TiO₂ heterostructured catalysts under simulated sunlight irradiation.Appl Catal B Environ2018;228:29-38

[31] Li P,Wang J.Carboxyl groups on g-C₃N₄ for boosting the photocatalytic U(VI) reduction in the presence of carbonates.Chem Eng J2021;414:128810

[32] Gaya UI.Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: a review of fundamentals, progress and problems.J Photochem Photobiol C Photochem Rev2008;9:1-12

[33] Li P,Wang Y.An overview and recent progress in the heterogeneous photocatalytic reduction of U(VI).J Photochem Photobiol C Photochem Rev2019;41:100320

[34] Kim YK,Ryu J.Solar conversion of seawater uranium (VI) using TiO₂ electrodes.Appl Catal B Environ2015;163:584-90

[35] Hu L,Zhang X.Integration of adsorption and reduction for uranium uptake based on SrTiO₃/TiO₂ electrospun nanofibers.Appl Surf Sci2018;428:819-24

[36] He H,Dong F.Simultaneous removal and recovery of uranium from aqueous solution using TiO₂ photoelectrochemical reduction method.J Radioanal Nucl Chem2017;313:59-67

[37] Wu Y,Liu Y.Environmental remediation of heavy metal ions by novel-nanomaterials: a review.Environ Pollut2019;246:608-20

[38] Xu R,Zhang C.Vinylene-linked covalent organic frameworks with enhanced uranium adsorption through three synergistic mechanisms.Chem Eng J2021;419:129550

[39] Endrizzi F,Rao L.Scientific basis for efficient extraction of uranium from seawater. I: understanding the chemical speciation of uranium under seawater conditions.Ind Eng Chem Res2016;55:4249-56

[40] Endrizzi F.Chemical speciation of uranium(VI) in marine environments: complexation of calcium and magnesium ions with [(UO₂)(CO₃)₃]^4- and the effect on the extraction of uranium from seawater.Chemistry2014;20:14499-506

[41] Abney CW,Saito T.Materials for the recovery of uranium from seawater.Chem Rev2017;117:13935-4013

[42] Shi S,Mei P.Robust flexible poly(amidoxime) porous network membranes for highly efficient uranium extraction from seawater.Nano Energy2020;71:104629

[43] Hao X,Liu Q.A novel U(vi)-imprinted graphitic carbon nitride composite for the selective and efficient removal of U(vi) from simulated seawater.Inorg Chem Front2018;5:2218-26

[44] Miyake C,Sano Y.EPR study of uranium (V) species in photo-and electrolytic reduction processes of UO₂NO₃)₂-2TBP.J Nucl Sci Technol1993;30:1256-60

[45] Salomone VN,Schinelli G,Litter MI.Photochemical reduction of U(VI) in aqueous solution in the presence of 2-propanol.J Photochem Photobiol A Chem2014;277:19-26

[46] Bard AJ, Parsons R, Jordan J. Standard potentials in aqueous solution, 1st ed.; Routledge, 1985.

[47] Salomone VN,Litter MI.Heterogeneous photocatalytic removal of U(VI) in the presence of formic acid: U(III) formation.Chem Eng J2015;270:28-35

[48] Lu C,Jiang S.Photocatalytic reduction elimination of UO22+ pollutant under visible light with metal-free sulfur doped g-C₃N₄ photocatalyst.Appl Catal B Environ2017;200:378-85

[49] Li ZJ,Guo WL.Enhanced photocatalytic removal of uranium(VI) from aqueous solution by magnetic TiO₂/Fe₃O₄ and its graphene composite.Environ Sci Technol2017;51:5666-74

[50] Li H,Gui D.Powerful uranium extraction strategy with combined ligand complexation and photocatalytic reduction by postsynthetically modified photoactive metal-organic frameworks.Appl Catal B Environ2019;254:47-54

[51] Chen J,Rulkens WH.Photocatalyzed deposition and concentration of soluble uranium(VI) from TiO₂ suspensions.Colloids Surf A Physicochem Eng Asp1999;151:339-49

[52] Feng J,He S.Photocatalytic reduction of Uranium(VI) under visible light with Sn-doped In₂S₃ microspheres.Chemosphere2018;212:114-23

[53] Bonato M,Scott T.Reduction of U(VI) to U(IV) on the surface of TiO₂ anatase nanotubes.Micro Nano Lett2008;3:57-61

[54] Alhindawy IG,Youssef AO.Cobalt doped titania-carbon nanosheets with induced oxygen vacancies for photocatalytic degradation of uranium complexes in radioactive wastes.Nanoscale Adv2022;4:5330-42 PMCID:PMC9724698

[55] Lee S,Piao G,Han DS.Homogeneous photoconversion of seawater uranium using copper and iron mixed-oxide semiconductor electrodes.Appl Catal B Environ2017;207:35-41

[56] Wang G,Zhou L,Deng N.Adsorption and photocatalytic reduction of U(VI) in aqueous TiO₂ suspensions enhanced with sodium formate.J Radioanal Nucl Chem2015;304:579-85

[57] Wang Y,Wang J.Efficient recovery of uranium from saline lake brine through photocatalytic reduction.J Mol Liq2020;308:113007

[58] Wang Y,Ding Z.Light promotes the immobilization of U(VI) by ferrihydrite.Molecules2022;27:1859

[59] Yu K,Yuan H,Zhu W.Cu-based nanocrystals on ZnO for uranium photoreduction: plasmon-assisted activity and entropy-driven stability.Appl Catal B Environ2021;288:119978

[60] Wang T,Dong Z,Cheng Z.A facile synthesis of g-C₃N₄/WS₂ heterojunctions with enhanced photocatalytic reduction activity of U(VI).J Radioanal Nucl Chem2022;331:577-86

[61] Han R,Zhong Q.Perfluorooctane sulphonate induces oxidative hepatic damage via mitochondria-dependent and NF-κB/TNF-α-mediated pathway.Chemosphere2018;191:1056-64

[62] Ye Y,Chen F.Removal and recovery of aqueous U(VI) by heterogeneous photocatalysis: progress and challenges.Chem Eng J2022;450:138317

[63] Gong X,Wang R.Achieving efficient photocatalytic uranium extraction within a record short period of 3 min by Up-conversion erbium doped ZnO nanosheets.Chem Eng J2022;450:138044

[64] Liu H,Gong C.In-situ oxidized tungsten disulfide nanosheets achieve ultrafast photocatalytic extraction of uranium through hydroxyl-mediated binding and reduction.Nano Res2022;15:8810-8

[65] Zhang P,Wang Y,Huang J.Highly efficient uranium (VI) remove from aqueous solution using nano-TiO₂-anchored polymerized dopamine-wrapped magnetic photocatalyst.J Clean Prod2023;425:138796

[66] Lei J,Zhou L.Progress and perspective in enrichment and separation of radionuclide uranium by biomass functional materials.Chem Eng J2023;471:144586

[67] He P,Wu L.Synergistic effect of the sulfur vacancy and schottky heterojunction on photocatalytic uranium immobilization: the thermodynamics and kinetics.Inorg Chem2022;61:2242-50

[68] Liang P,Deng H.Photocatalytic reduction of uranium(VI) by magnetic ZnFe₂O₄ under visible light.Appl Catal B Environ2020;267:118688

[69] Lu C,Wu X.Boron doped g-C₃N₄ with enhanced photocatalytic UO₂²⁺ reduction performance.Appl Surf Sci2016;360:1016-22

[70] Fujishima A.Electrochemical photolysis of water at a semiconductor electrode.Nature1972;238:37-8

[71] Jeon J,Jang BJ,Baek J.Enhancing the photocatalytic activity of TiO₂ catalysts.Adv Sustainable Syst2020;4:2000197

[72] Evans CJ,Faith DA.Photochemical removal of uranium from a phosphate waste solution.Green Chem2004;6:196-7

[73] Liu N,Liu Q.Magnetron sputtering ultra-thin TiO₂ films for photocatalytic reduction of uranium.Desalination2022;543:116121

[74] Liu G,Wang X.Visible light responsive nitrogen doped anatase TiO₂ sheets with dominant {001} facets derived from TiN.J Am Chem Soc2009;131:12868-9

[75] Yu J,Xiao W,Jaroniec M.Enhanced photocatalytic CO₂-reduction activity of anatase TiO₂ by coexposed {001} and {101} facets.J Am Chem Soc2014;136:8839-42

[76] Yang HG,Qiao SZ.Anatase TiO₂ single crystals with a large percentage of reactive facets.Nature2008;453:638-41

[77] Zhang L,Li L,Deng W.Photocatalytic reduction of uranyl ions over anatase and rutile nanostructured TiO₂.Chem Lett2013;42:689-90

[78] Wang J,Wang W.Visible light driven Ti³⁺ self-doped TiO² for adsorption-photocatalysis of aqueous U(VI).Environ Pollut2020;262:114373

[79] Gong X,Zou J.Introduction of cation vacancies and iron doping into TiO₂ enabling efficient uranium photoreduction.J Hazard Mater2022;423:126935

[80] Dong Z,Li Z.3D structure aerogels constructed by reduced graphene oxide and hollow TiO₂ spheres for efficient visible-light-driven photoreduction of U(VI) in air-equilibrated wastewater.Environ Sci Nano2021;8:2372-85

[81] Wan H,Wang M.Boosting efficient U(VI) immobilization via synergistic Schottky heterojunction and hierarchical atomic-level injected engineering.Chem Eng J2022;430:133139

[82] Dong Z,Li Z.Biomimetic photocatalytic system designed by spatially separated cocatalysts on Z-scheme heterojunction with identified charge-transfer processes for boosting removal of U(VI).Small2023;19:e2300003

[83] Dong Z,Li Z.Novel Co₃O₄@TiO₂@CdS@Au double-shelled nanocage for high-efficient photocatalysis removal of U(VI): roles of spatial charges separation and photothermal effect.J Hazard Mater2023;452:131248

[84] Lucena R,Conesa JC.Hydrothermally synthesized nanocrystalline tin disulphide as visible light-active photocatalyst: spectral response and stability.Appl Catal A Gen2012;415-416:111-7

[85] Liu Q,Wang S.MXene as a non-metal charge mediator in 2D layered CdS@Ti₃C₂ @TiO₂ composites with superior Z-scheme visible light-driven photocatalytic activity.Environ Sci Nano2019;6:3158-69

[86] Yu J,Zhou P,Cheng B.Morphology-dependent photocatalytic H₂-production activity of CdS.Appl Catal B Environ2014;156-157:184-91

[87] Zou L,Wang X.High efficient photodegradation and photocatalytic hydrogen production of CdS/BiVO₄ Heterostructure through Z-scheme process.ACS Sustain Chem Eng2017;5:303-309

[88] Chava RK,Kang M.Enhanced photoexcited carrier separation in CdS-SnS₂ heteronanostructures: a new 1D-0D visible-light photocatalytic system for the hydrogen evolution reaction.J Mater Chem A2019;7:13614-28

[89] Zhang K,Du Y.2D/2D heterostructured CdS/WS₂ with efficient charge separation improving H₂ evolution under visible light irradiation.ACS Appl Mater Interfaces2018;10:20458-66

[90] Lin G,Xu R.Template-free synthesis of uniform CdS hollow nanospheres and their photocatalytic activities.J Phys Chem C2008;112:7363-70

[91] Han Z,Li C,Zhou Y.Preparation of 1D cubic Cd_0.8 Zn_0.2 S solid-solution nanowires using levelling effect of TGA and improved photocatalytic H₂-production activity.J Mater Chem A2015;3:1696-702

[92] Liang P,Du K.Photocatalytic reduction of uranium(VI) under visible light with 2D/1D Ti₃C₂/CdS.Chem Eng J2021;420:129831

[93] Rehman SU,Wu G,Xian J.Unraveling the photocatalytic potential of transition metal sulfide and selenide monolayers for overall water splitting and photo-corrosion inhibition.J Mater Chem A2024;12:6693-702

[94] Zhang N,Li Z.Sulfur vacancy engineering of metal sulfide photocatalysts for solar energy conversion.Chem Catalysis2023;3:100375

[95] Liu J,Antonietti M.Graphitic carbon nitride “reloaded”: emerging applications beyond (photo)catalysis.Chem Soc Rev2016;45:2308-26

[96] Cheng L,Li X,Xiang Q.Carbon-graphitic carbon nitride hybrids for heterogeneous photocatalysis.Small2021;17:e2005231

[97] Cao S,Yu J.Polymeric photocatalysts based on graphitic carbon nitride.Adv Mater2015;27:2150-76

[98] Li C,Tu W,Xu R.Metal-free photocatalysts for various applications in energy conversion and environmental purification.Green Chem2017;19:882-99

[99] Bhanderi D,Modi CK.Graphitic carbon nitride (g-C₃N₄) as an emerging photocatalyst for sustainable environmental applications: a comprehensive review.RSC Sustainability2024;2:265-87

[100] Wang L,He T,Song H.Graphitic carbon nitride-based photocatalytic materials: preparation strategy and application.ACS Sustainable Chem Eng2020;8:16048-85

[101] Yu K,Cao X.In-situ constructing amidoxime groups on metal-free g-C₃N₄ to enhance chemisorption, light absorption, and carrier separation for efficient photo-assisted uranium(VI) extraction.J Hazard Mater2023;460:132356

[102] Wei W,Liu S,Ma J.Enhancing the photocatalytic performance of g-C₃N₄ by using iron single-atom doping for the reduction of U(VI) in aqueous solutions.J Solid State Chem2022;312:123160

[103] Zhao J,Zhang R,Wu Y.Self-cleaning and regenerable nano zero-valent iron modified PCN-224 heterojunction for photo-enhanced radioactive waste reduction.J Hazard Mater2023;442:130018

[104] Wang J,Wang Y.New strategy for the persistent photocatalytic reduction of U(VI): utilization and storage of solar energy in K⁺ and cyano co-decorated poly(heptazine imide).Adv Sci2023;10:e2205542 PMCID:PMC9929247

[105] Nie Y,Lu X.Cu doped crystalline carbon nitride with increased carrier migration efficiency for uranyl photoreduction.Chem Eng J2023;477:146908

[106] Xue J,Li Z,Le Z.Bromine doped g-C₃N₄ with enhanced photocatalytic reduction in U(VI).Res Chem Intermed2022;48:49-65

[107] Chen T,Zhou L.Harmonizing the energy band between adsorbent and semiconductor enables efficient uranium extraction.Chem Eng J2021;420:127645

[108] Meng Q,Wu L.Metal-free 2D/2D C₃N₅/GO nanosheets with customized energy-level structure for radioactive nuclear wastewater treatment.J Hazard Mater2022;422:126912

[109] Ma Y,Zhao S.Molecular engineering of multivariate porous aromatic frameworks for recovery of dispersed uranium resources.Adv Funct Mater2024;34:2410778

[110] Yu F,Wang S.Tunable perylene-based donor-acceptor conjugated microporous polymer to significantly enhance photocatalytic uranium extraction from seawater.Chem Eng J2021;412:127558

[111] Yu F,Li C.Molecular engineering of biomimetic donor-acceptor conjugated microporous polymers with full-spectrum response and an unusual electronic shuttle for enhanced uranium(VI) photoreduction.Chem Eng J2023;466:143285

[112] Chen L,Kang J.The synthesis of a novel conjugated microporous polymer and application on photocatalytic removal of uranium(VI) from wastewater under visible light.Chem Eng J2022;431:133222

[113] Kumar V,Kim K,Younis SA.Metal-organic frameworks for photocatalytic detoxification of chromium and uranium in water.Coord Chem Rev2021;447:214148

[114] Zhong X,Zeng W,Hu B.Excellent photoreduction performance of U(VI) on metal organic framework/covalent organic framework heterojunction by solar-driven.Sep Purif Technol2022;285:120405

[115] Younis SA,Qasim M.Metal-organic framework as a photocatalyst: progress in modulation strategies and environmental/energy applications.Prog Energy Combust Sci2020;81:100870

[116] Qiu J,Zhang X.Constructing Cd_0.5Zn_0.5S@ZIF-8 nanocomposites through self-assembly strategy to enhance Cr(VI) photocatalytic reduction.J Hazard Mater2018;349:234-41

[117] Zhang H,Li A.Three mechanisms in one material: uranium capture by a polyoxometalate-organic framework through combined complexation, chemical reduction, and photocatalytic reduction.Angew Chem Int Ed2019;58:16110-4

[118] Liu X,Lei L.Synergistic effect of photocatalytic U(VI) reduction and chlorpyrifos degradation by bifunctional type-II heterojunction MOF525@BDMTp with high carrier migration performance.Appl Catal B Environ2024;342:123460

[119] Bi R,Lei L.Core-shell MOF@COF photocatalysts for synergistic enhanced U(VI) and tetracycline cleanup through space and carrier separation.Chem Eng J2024;485:150026

[120] Chen M,Zhang X.Photoinduced enhancement of uranium extraction from seawater by MOF/black phosphorus quantum dots heterojunction anchored on cellulose nanofiber aerogel.Adv Funct Mater2021;31:2100106

[121] Cui WR,Xu RH.Regenerable covalent organic frameworks for photo-enhanced uranium adsorption from seawater.Angew Chem Int Ed2020;59:17684-90

[122] Hao M,Liu X.Modulating uranium extraction performance of multivariate covalent organic frameworks through donor-acceptor linkers and amidoxime nanotraps.JACS Au2023;3:239-51 PMCID:PMC9875373

[123] Zhang S,Qu Z.Confining Ti-oxo clusters in covalent organic framework micropores for photocatalytic reduction of the dominant uranium species in seawater.Chem2023;9:3172-84

[124] Chen Z,Hao M.Tuning excited state electronic structure and charge transport in covalent organic frameworks for enhanced photocatalytic performance.Nat Commun2023;14:1106 PMCID:PMC9970987

[125] Yu F,Li W.Π-skeleton tailoring of olefin-linked covalent organic frameworks achieving low exciton binding energy for photo-enhanced uranium extraction from seawater.Adv Funct Mater2024;34:2307230

[126] Yang H,Xie Y.Tuning local charge distribution in multicomponent covalent organic frameworks for dramatically enhanced photocatalytic uranium extraction.Angew Chem Int Ed2023;62:e202303129

[127] Li Z,Zhang Z.Covalent organic frameworks for boosting H₂O₂ photosynthesis via the synergy of multiple charge transfer channels and polarized field.Angew Chem Int Ed2025;64:e202420218

[128] Li ZF,Zhang ZB.Covalent organic frameworks for boosting H₂O₂ photosynthesis via the synergy of multiple charge transfer channels and polarized field.Angew Chem Int Ed2024;64:e202420218

[129] Guo L,Gong L.Boosting photosynthesis of H₂O₂ using topological defects in covalent organic framework for selective extraction of uranium through an innovative mineralization strategy.CCS Chem2024;

[130] Xie Y,Rong Q.Rational design of 3D space connected donor-acceptor system in covalent organic frameworks for enhanced photocatalytic performance.Adv Funct Mater2024;34:2411077