基于氟硅烷改性UIO-66-OH的疏水金属有机骨架材料的制备及在灰岩类石质文物保护中的应用.pdf

第39卷第9期2023年9月Vol.39 No.918171831无机化学学报CHINESE JOURNAL OF INORGANIC CHEMISTRY收稿日期：20221225。收修改稿日期：20230609。国家自然科学基金(No.51279073)和河南省高等学校重点科研项目(No.22B150010)资助。通信联系人。Email：wuxiu-基于氟硅烷改性UIO66OH的疏水金属有机骨架材料的制备及在灰岩类石质文物保护中的应用左天悦1张拦2王鸿毅3丁梧秀,1,3(1河南工业大学土木工程学院，郑州450001)(2洛阳理工学院环境工程与化学学院，洛阳471023)(3洛阳理工学院土木工程学院，洛阳471023)摘要：疏水材料的研制一直是石质文物保护工作中的难点问题。本工作制备了一种新型疏水金属有机骨架(MOF)材料，即采用氟硅烷修饰含有2羟基对苯二甲酸桥联配体的ZrMOF以获得UIOOFS材料，并对材料进行了FTIR、X射线衍射、N2吸附-脱附、热重、扫描电镜和透射电镜等表征分析以及抗侵蚀试验。试验结果表明，该材料具有良好的疏水性、固结性、耐酸性和耐盐性，是一种新型石质文物保护材料。关键词：金属有机骨架；UIO66OH；疏水；合成后改性；灰岩类石质文物保护中图分类号：TU45；O614.41+2文献标识码：A文章编号：10014861(2023)09181715DOI：10.11862/CJIC.2023.142Hydrophobic metalorganic framework material based on fluorosilanemodifiedUIO66OH:Preparation and application in the conservation of limestone cultural relicsZUO TianYue1ZHANG Lan2WANG HongYi3DING WuXiu,1,3(1School of Civil Engineering,Henan University of Technology,Zhengzhou 450001,China)(2School of Environmental Engineering and Chemistry,Luoyang Institute of Science and Technology,Luoyang,Henan 471023,China)(3School of Civil Engineering,Luoyang Institute of Science and Technology,Luoyang,Henan 471023,China)Abstract:The development of hydrophobic materials has always been a difficult issue in the protection of stonecultural relics.In this work,a new hydrophobic metalorganic framework material was synthesized by modifying theZrbased MOFs containing 2hydroxyterephthalic acid linkers with fluorosilane to obtain UIOOFS material,andcharacterization tests such as FTIR,Xray diffraction,N2adsorptiondesorption,thermogravimetry,scanning electron microscope,and transmission electron microscope,as well as erosion resistance tests,were carried out on thematerial.Based on the results,the material possesses good hydrophobicity,consolidation ability,acid resistance,and salt resistance,and is a new type of stone heritage conservation material.Keywords:metalorganic framework;UIO66OH;hydrophobic;postsynthetic modification;conservation of limestone heritage0IntroductionA large number of stone cultural heritages exist inthe world today,which are very precious but sufferfrom serious damage due to the long years of exposureto the natural environment and the resultant weatheringand erosion13.In recent years,global warming andenvironmental pollution have accelerated the deteriora无机化学学报第39卷tion of stone cultural relics.Therefore,the protection ofstone cultural relics has received increasing attentionand has become an important research topic.At present,several conservation methods for rocks have beenproposed by relevant researchers415.For example,Graziani,Tesser,and Shu et al.48coated differentmaterials such as calcium oxalate,alicyclic epoxy resin,and rodshaped TiO2composite on the marble surface and investigated their protective properties respectively,and the test results showed that the materialshad a certain protective effect.To protect sandstone,Shu,Tokarsky,and Aslanidou et al.911prepared modified sol gel coating,nano ZnO/poly(alkyl siloxane)coating,and nanoSiO2/alkoxysilane coating materialsrespectively,and applied them uniformly on the surface of rock samples,and the test results showed thatthe materials have good acid resistance and hydrophobicity.AlDosari et al.12prepared nanoCa(OH)2/polymer composites for the protection of carbonate rocksusing insitu emulsion polymerization method and thehydrophobicity and consolidation properties of thematerials were demonstrated by tests.Zhu et al.1617prepared nanolime/kaolin(NK)nanocomposites andpolydopamine(PDA)modified nanolime(PDANL)byinsitu growing Ca(OH)2nanoparticles on the surface ofkaolin nanosheets,respectively,which improved the stability,permeability,and consolidation of nanolime.PDANL also avoids the adverse effects of back migration and delayed carbonization on the conservationeffect of nanolime in the protection of stone artifacts.Chai et al.18introduced the synergistic effect of ZnOnanoparticlesandSiO2nanoparticles,andshowedexperimentallythatthenanocompositecoatingsobtained after modification by fluorocarbon couplingagents have excellent hydrophobicity and weatheringstability.Current protection materials can be categorized into three types,inorganic materials,organicmaterials,and new materials.Inorganic materials areresistant to weather but have low permeability.Organicmaterials are corrosionresistant but have a shorter lifespan.New materials,such as nanomaterials and bionic,have unique functions and compatibility,indicating anew development prospect in the field of stone protection.Based on the above,this work aims to researchthe application of nanomaterials in the preservation oflimestonetype stone relics of the Longmen Grottoes.Metal organic frameworks(MOFs)are nanoporous materials composed of inorganic metal nodesand organic linkers1922and have attracted much attention in the research fields of sensors2325,catalysts2627,drug delivery2830,and gas adsorption and separation3132because of their excellent properties such ashigh surface area,large pore volume,tunable pore size,favorable chemical and hydrothermal stability,andeasy postmodification.According to the standard recommendations,tone cultural relic protection materialsneed to be hydrophobic,permeable,and stable andpossess good stone adhesion and compatibility33.However,due to the high sensitivity of MOFs to moisture,their advantageous structural features are rapidly compromised,which restricts their applicability in stoneheritage conservation3435.There have been studies onthe modification of MOFs materials and using them inthe stone field.For example,Yoon et al.prepared semisiloxane Zn MOF liquid marbles using azobenzene containing dicarboxylic acids as organic linkers andinvestigated their stability under acidic conditions36.Baah et al.summarized hydrophobic metalorganicframeworks and their applications,which included theuse of MOF materials to prepare liquid marbles37.However,there are relatively few studies on the use ofMOFs materials for the conservation of limestonetypestone heritage,so this paper addresses their application in the field of limestonetype stone heritage conservation.Based on the available studies,we understandthat special functional groups can be introduced intoporous MOFs by post synthetic modification methods2425.In this work,porous fluorosilylated MOFs(UIOOFS)was synthesized from Zrbased UIO66OH containing 2hydroxyterephthalic acid linkers bymodification with dodecafluoroheptylpropylmethyldimethoxysilane(G502B).In UIOOFS,the interconnected discrete pores are covered with G502B,presenting gas channels,and the hydrophobicity induced bythe fluorosilane surface makes the material ideal for1818第9期exhibiting both good gas permeability and hydrophobicity.This work demonstrates an attempt at linkeroxonode engineering of hydrophobic MOFs for the protection of rock artifacts.The precise modification of thelinkeroxo nodes of MOFs without blocking the windows of pores maximizes the preservation of the inherent accessibility of pore textures,ensuring the uniquesuperiority of these MOFs in practical applications.According to the experimental results,it can be seenthat UIOOFS has a good protective effect in the protection of stone heritage.Therefore,a new hydrophobicMOF material for stone heritage protection is proposed.1Experimental1.1Materials2Hydroxyterephthalic acid(H2BDCOH,99%),terephthalic acid(H2BDC,99%),and N,Ndimethylformamide(DMF,99.9%)were provided by AladdinReagentCo.,Ltd.Zirconium chloride(ZrCl4,99.9%),acetic acid(CH3COOH,99.5%),absolute ethanol(C2H5OH,99.7%),sulfuric acid(H2SO4,98.3%),hydrochloric acid(HCl,36%38%),sodium chloride(NaCl,99.5%),dodecafluoroheptylmethacrylate(ActyflonG04)and dodecafluoroheptylpropylmethyldimethoxysilane(G502B)were supplied by SinopharmChemical Reagent Co.,Ltd.All reagents were used asreceived without further purification,and deionized water was used in all experiments.1.2InstrumentationThe crystallographic structures of the preparedUIO66,UIO66OH,and UIOOFS adsorbents wereanalyzed by X ray diffraction(XRD)using a MAC 18XHF diffractometer(Rigaku,Japan)with Cu Kradiation(=0.154 05 nm at 30 kV and 30 mA)in a 2range of 560.A LeoSupra 55 fieldemission scanning electron microscope(FESEM)(Carl Zeiss,Germany)was employed to survey the morphologies of samples.The BrunauerEmmettTeller(BET)specific surface areas of UIO66,UIO66OH,and UIOOFS weredetermined with a JWBK132F specific surface areaultrafine pore size analyzer(Beijing JWGB Sci.&Tech.Co.,Ltd.,China)using nitrogen sorption at 77 K.The functional groups of the adsorbents were assessedvia FTIR)spectroscopy on a Tensor 27 instrument(Bruker,Germany).A JEM2100F instrument(JEOL,Japan,200 kV)was used to obtain high resolutiontransmission electron microscopy(HRTEM)imagesandconductenergydispersiveXrayspectroscopy(EDS)for the mapping of elements of the materials.The static contact angle was measured with a DSA 100instrument(Krss,Germany)at room temperature.Thethermogravimetric analysis(TGA)of the samples wasperformed by a TG209 instrument.The tests were performed under N2protection with a N2flow rate of 20mLmin-1.The temperature was increased from 100 to800 with a rate of 10 min-1.1.3Synthesis and activation of UIO66OHTo synthesize UIO66OH1920,1 mmol each ofZrCl4and H2BDCOH were dissolved in 35 mL of DMFunder magnetic stirring(1 500 rmin-1,20 min).Then,the solution was transferred to a Teflonlined autoclaveand reacted at 120 for 12 h.After the reactor wascooled to room temperature,the resulting solid productwas isolated by centrifugation(8 000 rmin-1,10 min),washed with DMF and anhydrous ethanol,and finallydried under vacuum(12 h,60)to obtain UIO66OHas a yellow product.To perform a comparative test with UIO66OH,itis necessary to prepare UIO66 to demonstrate the successful synthesis of UIO66OH.The synthesis processof UIO66 employed H2BDC as the organic ligand andwas otherwise the same as the synthesis of UIO66OH.1.4Synthesis of crosslinked UIO66OHG502B was hydrolyzed by the following method.The fluorosilane was dropped into a mixture of deionized water and absolute ethanol(mass ratio of 1 4,andthe pH of this mixture was adjusted to three with glacial acetic acid).The hydrolysis reaction was continuedunder magnetic stirring until a clear solution wasobtained.UIO 66OH powder and the solution of hydrolyzed G502B were combined in a beaker and heated at110 until dryness.The obtained crosslinked UIO66OH was named UIOOFS,as shown in Fig.1.The flowchart of the entire experiment,as well as the structuresof UIO66OH and UIOOFS,are shown in Fig.2.左天悦等：基于氟硅烷改性UIO66OH的疏水金属有机骨架材料的制备及在灰岩类石质文物保护中的应用1819无机化学学报第39卷Fig.3 provides an artistic illustration of the UIOOFSprotective material applied to the surface of a stone artifact,demonstrating the hydrophobicity and permeability of the protective material.Fig.1Schematic illustration of the chemical reaction process of UIOOFSFig.2Schematic illustration of the synthetic process for UIOOFS compositesFig.3Effect of UIOOFS protection material in practical application1.5Samplepreparationforacidandsaltresistance testsBecause the prepared UIOOFS may be in theagglomerative state,to enable it to act directly on thesurface of stone artifacts,it was ground before use toobtain UIOOFS powder.After that,UIOOFS powderwas combined with ActyflonG04 solution under ultrasonic treatment for 30 min to obtain a mixture with amass fraction of 3%,and finally,the mixed solution ofthe protective material acting on the rock surface wasobtained.The configured mixed solution was evenlyapplied to the surface of the rock specimen with abrush,followed by drying treatment(110,2 h),andthe above operation was repeated three times after drying.ActyflonG04 contains unsaturated bonds that canundergo polymerization at high temperatures,forming a1820第9期polymer film layer on the surface of rocks.Therefore,the above drying process was performed at 110.Toverify whether ActyflonG04 underwent the polymerization reaction.,after dispersing the UIOOFS powderinto the ActyflonG04 solution in the experiment andfound that the viscosity of the solution graduallyincreased as the temperature rose,indicating that polymerization occurred in ActyflonG04.To study the acid resistance of UIOOFS,twelverock samples were divided into four groups.The firstand third groups were unprotected samples,the secondand fourth groups were protected samples,and the rocksamples of the third and fourth groups were alsoimmersed in sulfuric acid solution at pH=3 for 10 d.Similarly,to study the salt resistance of UIOOFS,therock samples were prepared in the same way as theacid resistance test,with the difference that the thirdand fourth groups of rock samples needed to beimmersed in a solution of sodium chloride at pH=3 anda concentration of 0.02 molL-1for 7 d.A hydrochloricacid solution was used to adjust the pH of the NaClsolution.2Results and discussion2.1Structure and physicochemical properties ofpristine and crosslinked UIO66OHThe FTIR spectra of three MOF samples,UIO66,UIO66OH,and UIOOFS,are provided in Fig.4a.Ascan be seen in Fig.4a,the peaks observed in a range of400 600 cm-1are attributed to the ZrO stretchingvibration in the three MOFs3840.For the UIO66 sample,the band in a range of 430700 cm-1is referred toas a combination of ZrO modes with OH and CHbending vibrations.Moreover,the bands of C=O(1 708 cm-1),C=C(1 577 cm-1),and CO(1 400cm-1)stretching vibrations had a similar position forUIO66,UIO66OH,and UIOOFS,hence a highdegree of overlapping was observed in the spectra.Inthe spectrum of UIO66OH,the band in a range of1 2601 420 cm-1is attributed to the deformation vibration peak of OH,and this absorption band was widerthan that in the UIO66 spectrum because of the addition of hydroxyl groups to the MOF framework,indicates the successful synthesis of UIO66OH.In thespectrum of UIOOFS,characteristic bands at 1 313and 867 cm-1correspond to CF and CSi stretchingvibrations,while these were not observed in the spectrum of UIO66OH,indicating that the modificationexperiment was completed,that is,the hydrophobicgroup grafted onto the UIO66OH surface,making theUIOOFS material hydrophobic.XRD analysis was used to determine the phasepurity and crystalline structures of products,and theirXRD patterns are shown in Fig.4b.For the UIO 66sample,the diffraction peaks were consistent with previously reported articles3940.The analysis demonstrated that the characteristic reflection peaks of the prepared UIO66OH and UIOOFS samples matchedFig.4(a)Infrared spectra and(b)XRD patterns of UIO66,UIO66OH,and UIOOFS左天悦等：基于氟硅烷改性UIO66OH的疏水金属有机骨架材料的制备及在灰岩类石质文物保护中的应用1821无机化学学报第39卷those of the pattern of UIO66,but the intensity of theUIOOFS peak was lower than that of UIO66,thewidth of the UIOOFS peak was wider than that ofUIO66,and the intensity and width of the UIO66OHpeak were in between.Therefore,from the Scherrer formula D=K/(Bcos),the particle size of UIO66OHwas smaller than that of UIO66 due to that the OHgroups embedded in the exoligand4142.Similarly,theparticle size of UIOOFS after hydroph