氨基/五氟苯基双功能化磁性三组分共价有机骨架的制备及其在氟苯甲酸类物质吸附中的应用

Preparation of an amino/pentafluorophenyl dual-functional magnetic tricomponent covalent organic framework and its application in fluorobenzoic-acids adsorption

氟苯甲酸类物质(FBAs)是合成许多药物、农用化学品和其他有机化合物的重要中间体,同时也被用作水示踪剂。FBAs作为地下水示踪剂具有环境友好、不会在地层中自然存在、性质稳定、地层吸附量小、用量少以及种类多且彼此间无干扰等优点,因此FBAs作为示踪剂的应用不断扩大。在采用FBAs追踪地层水运动时,由于地层水基质复杂且FBAs浓度低,直接分析较为困难,因此对复杂基质中FBAs进行样品预处理十分重要。本研究采用多元(MTV)策略,以2,4,6-三甲酰基间苯三酚(Tp)、3,3′-二羟基联苯胺(DHB)、3,3′-二硝基联苯胺(DNB)为构筑基元,通过希夫碱反应制备了一系列不同羟基/硝基比例的三组分共价有机骨架(COF)[Tp-DHB_(x)DNB(1-x)](x=0、0.25、0.5、0.75、1)。再通过合成后修饰,得到氨基/五氟苯基双功能化COF,即氟亲和/阴离子交换/反相混合模式吸附剂COF-PFB_(x)-NH_(2(1-x))。通过考察COF-PFB_(x)-NH_(2(1-x))对FBAs的吸附性能,筛选出COF-PFB_(0.5)-NH_(2)(0.5)用于FBAs的吸附。为了便于将材料从溶液中分离,以Fe_(3)O_(4)纳米粒子为核,采用原位生长法制备了氨基/五氟苯基双功能化磁性三组分共价有机骨架吸附剂(Fe_(3)O_(4)@COF-PFB_(0.5)-NH_(2)(0.5)),通过扫描电子显微镜、X射线光电子能谱及傅里叶变换红外光谱等表征,证明了该材料的成功制备。Fe_(3)O_(4)@COF-PFB_(0.5)-NH_(2)(0.5)对4-氟苯甲酸(4-FBA)、2,3,4-三氟苯甲酸(2,3,4-TFBA)、2,3,4,5-四氟苯甲酸(2,3,4,5-Tetra-FBA)和3,5-双三氟甲基苯甲酸(3,5-BTFMA)的最大吸附容量分别为73.5、64.9、38.4和253 mg/g。重复使用5次后,其吸附效果保持良好。在最佳吸附条件下,Fe_(3)O_(4)@COF-PFB_(0.5)-NH_(2)(0.5)对模拟地层水中4-FBA、2,3,4-TFBA、2,3,4,5-Tetra-FBA和3,5-BTFMA的吸附率分别为85.7%、86.5%、94.9%和82.4%,表明Fe_(3)O_(4)@COF-PFB_(0.5)-NH_(2)(0.5)在实际样品中FBAs的分离富集方面具有很大的应用潜力。

Fluorobenzoic acids(FBAs)are important intermediates in the synthesis of many drugs,agrochemicals,and other organic compounds,and are also used as water tracers.FBAs are environmentally friendly,unnatural,have stable properties,are poorly adsorbed in aquifers,and are used in low dosages as groundwater tracers,which are their main advantages along with non-interfering diversity;as a result,their applications scope continues to expand.While FBAs are used to trace the movement of groundwater,direct analysis is often challenging owing to their low concentrations and the complexity of the groundwater matrix.Therefore,sample pretreatment for trace and ultra-trace FBAs in complex matrices is important prior to instrumental analysis.Covalent organic frameworks(COFs)are porous crystalline polymers constructed from organic units through strong covalent bonds and are characterized by low densities,large specific surface areas,permanent porosities,excellent chemical/thermal stabilities,and ease of functionalization for required purposes.In this study,we used a multivariate(MTV)strategy to construct a series of tricomponent COFs with different hydroxy/nitro ratios from^(2),4,6-trihydroxybenzene-1,3,5-tricarbaldehyde(Tp),3,3′-dihydroxybenzidine(DHB),and 3,3′-dinitrobenzidine(DNB)as building blocks using Schiff-base reactions;these COFs are referred to as Tp-DHB_(x) DNB(1-x)(x=0,0.25,0.5,0.75,and 1).We then anchored pentafluorophenyl and amino groups to these COFs via post-synthetic modification;the adsorption performance of the COF-PFB x-NH 2(1-x)samples prepared in this manner led to the selection of COF-PFB_(0.5)-NH 2(0.5)for its FBAs-adsorbing ability.A magnetic fluorophilic/anion-exchange/reversed-phase mixed-mode COF adsorbent(Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5))was prepared via an in-situ growth method using Fe_(3)O_(4) nanoparticles as cores to facilitate separation of the material from solution.Notably,the Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)particles were very dispersible in water owing to their abundant amino groups and facilitated magnetic solid-liquid separation.In addition,Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)exhibited excellent operational stability for the magnetic solid-phase extraction(MSPE)of FBAs in aqueous samples.The structural properties of Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)were characterized using various techniques,including scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),powder X-ray diffractometry(PXRD),Fourier-transform infrared spectroscopy,and the Brunauer-Emmett-Teller method,all of which revealed that Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)had been successfully prepared;it also has uniformly distributed mesopores and a specific surface area of 107 m^(2)/g.Adsorption-mechanism studies revealed that Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)is highly adsorptive toward all four FBAs(4-fluorobenzoic acid(4-FBA),2,3,4-trifluorobenzoic acid(2,3,4-TFBA),2,3,4,5-tetrafluorobenzoic acid(2,3,4,5-tetra-FBA)and 3,5-bis(trifluoromethyl)benzoic acid(3,5-BTFMA))through electrostatic,hydrogen bonding,F-F affinity,andπ-πand hydrophobic interactions through synergy between the dual-functional fluorine and carboxyl binding sites,as well as the benzene rings in their skeletons.Isothermal FBAs-adsorption experiments involving Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)revealed maximum adsorption capacities of 73.5,64.9,38.4,and 253 mg/g for 4-FBA,2,3,4-TFBA,2,3,4,5-tetra-FBA and 3,5-BTFMA,respectively.Adsorption kinetics were also investigated,which revealed that FBAs-adsorption by Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)follows pseudo-second-order kinetics.Remarkably,no significant decrease in adsorption efficiency was observed after five adsorption-desorption cycles,highlighting good material reusability.We next optimized the factors that affect MSPE efficiency.Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)exhibited adsorption efficiencies of 85.7%,86.5%,94.9%,and 82.4%for 4-FBA,2,3,4-TFBA,2,3,4,5-tetra-FBA and 3,5-BTFMA from simulated underground water,respectively,under the optimal extraction conditions,which indicates that Fe_(3)O_(4)@COF-PFB_(0.5)-NH 2(0.5)holds significant potential for the separation and enrichment of FBAs in real samples.