Preparation Of Hyper-cross-linked And Polar-modified Polystyrenes And Their Adsorption Performance For Organic Pollutants

As the porous organic polymers with good physical and chemical stability,and easy to be functionalized,polystyrenic adsorbent resins are widely used in several fields including adsorption and separation.In order to improve the adsorption performance of polystyrene resins,two strategies are adopted in structure modification of polystyrene,which include the physical structure modification to increase the specific surface area and the chemical structure modification to introduce polar functional groups.However,the carcinogenic agent of chloromethyl methyl ether or expensive monomers,toxic solvents,and complex reaction routes are often adopted in structure modification of polystyrene resins,which limits the large-scale production and industrial applications of structure modified polystyrene resins.It is a challenge to develop inexpensive and facile method for structure modification of polystyrene so as to prepare polystyrenic adsorbent resins with controllable structures.In this paper,a series of hyper-cross-linked and polar-modified polystyrene resins were prepared via the Friedel-crafts reactions by using inexpensive agents,facile synthetic routes,and mild reaction conditions,thereafter the chemical structure and pore parameters of the resins were characterized,the adsorption performances of the resins for various organic pollutants were investigated,and the interactions between the resins and the adsorbates of organic pollutants was further analyzed.The main contents of the dissertation are showed as following:（1）A series of hyper-cross-linked polystyrene networks（HPNs）were obtained from macroporous slightly cross-linked polystyrene by using inexpensive and commercial multi-chloroalkanes as external cross-linkers via a two-step Friedel-Crafts reaction,and the highest BET surface area(S_BET)of the HPNs amounted to 832.8 m²/g.Effects of reaction conditions such as crosslinking agent,catalyst,reaction time and temperature on pore structure of the HPNs were investigated.The results indicated that specific surface area and swelling behaviors of the HPNs could be regulated by varying the strut length and structure of cross-linkers via a two-step Friedel-Crafts reaction.Sorption isotherms of caffeine on the HPNs from aqueous solution were tested.The results showed that the sorption performance of HPN-DCM-DCE was best among the HPNs,and the adsorption capacity amounted 189.2 mg/g at the equilibrium concentration of 100 mg/L.（2）Sorption isotherms of phenol,p-chlorophenol,and hydroquinone onto the adsorbents of HPNs,Amberlite XAD4 and HCPSs（prepared by post-cross-linking of chloromethylated polystyrene）from aqueous solutions were tested.Among the adsorbents,HPN-DCM-DCE displayed best sorption performance toward phenol,p-chlorophenol and hydroquinone,and the adsorption capacity was 170.0 mg/g,354.7 mg/g and 57.4 mg/g at the equilibrium concentration of 200 mg/L,respectively.The adsorption data of HPNs could be well described by Freundlich,Pseudo-second-order and Micropore diffusion equation at the temperature range of 298-318 K.The adsorption mechanism study indicated that the adsorption performance of the HPNs for phenol was greatly improved due to both adsorption on the surface and absorption in the matrix through framework swelling,especially for phenols with low log K_ow.The HPN-DCM-DCE solid phase extraction column showed good effects of low concentration enrichment and separation for volatile phenols.（3）A series of hydroxylated polystyrene resins（PS-OHs）were prepared from macroporous slightly cross-linked polystyrene by nitration,reductive amination,diazotation and hydrolysis in sequence,and then a series of hyper-cross-linked hydroxylated polystyrene resins（HPN-OHs）were prepared from the PS-OHs via the Friedel-Crafts post-cross-linking reaction using dichloromethane as external cross-linker.The reaction results indicated that anhydrous FeCl₃ was more suitable to catalyze the post-cross-linking reaction of the highly hydroxylated PS-OHs.HPN-OHs showed good adsorption performance because of the reasonable pore structure and hydroxyl content(Q_OH).HPN-Al Cl₃-OH-1(S_BET:463.8 m²/g,Q_OH:1.4 mmol/g)showed the highest adsorption capacity for aniline and p-nitroaniline,and the adsorption capacity was 92.3 mg/g and 233.4 mg/L at the equilibrium concentration of 100 mg/L,respectively.HPN-FeCl₃-OH-4(S_BET:69.0 m²/g,Q_OH:5.0 mmol/g)showed the highest adsorption capacity for methylene blue,malachite green and crystal violet from aqueous solutions,and the adsorption capacity was 203.6 mg/g,268.3 mg/g and 116.3 mg/g at the equilibrium concentration of 20 mg/L,respectively.Methylene blue adsorption on HPN-FeCl₃-OH-4 was more suitable for monolayer adsorption by hydrophobic interactions,π-πstacking and hydrogen bonding,and the adsorption data could be well fitted by Redlich-Peterson,pseudo-second-order and intra-particle diffusion equations.The methylene blue adsorption on HPN-FeCl₃-OH-4 was an endothermic,spontaneous,and disorder process.Moreover,HPN-FeCl₃-OH-4 had good adsorption selectivity for methylene blue in mixed solution,and the solid phase extraction column had a good effect of the low concentration enrichment and separation of malachite green.（4）Phenol（Ph（OH））,catechol（Ph（OH）₂）,and pyrogallol（Ph（OH）₃）were employed as the hydrogen-bond donors to chemically modify the commercial adsorbent of Amberlite XAD16 via the Friedel-Crafts reaction,and a series of phenolic hydroxyl groups modified resins（XAD16-Ph（OH）_x）were prepared.XAD16-Ph（OH）_x had pore structure parameters similar to Amberlite XAD16,however the hydroxyl groups content was remarkably increased after the Friedel-Crafts reaction.XAD16-Ph（OH）₂(S_BET:751.3 m²/g,Q_OH:2.1 mmol/g)with reasonable hydrogen bond donors uploading possessed the maximum adsorption capacity toε-caprolactam.The adsorption data could be described by Freundlich,pseudo-second-order and micropore diffusion equations excellently.The recyclability of XAD16-Ph（OH）₂ was explored by repeating the adsorption-regeneration process for 10 cycles using 70%（v/v）methanol aqueous solution as desorbing solvent,and the results showed good reusability.