Preparation And Adsorption Properties Of Hydrophobic Mesoporous Molecular Sieves

Mesoporous MCM-41, developed by Mobile researchers in1992, has superioradvantages over zeolites due to its relatively large and tunable pore size （14–100A）,highsurface area, and long range of ordered pore structure. However, the material has stronghydrophilicity, poor thermal and hydrothermal stability, it is not conducive for such materialsto adsorb organic compounds from the water-rich environment. Previous work showed thatcationic silanemodifed MCM-41material exhibited increased sorption capacity foraromatic organic compounds.In the present work, surfactant structure-directing agent was used to synthesizehydrophobic mesoporous molecular sieve （MCM-41-dry） at room temperature andhydrophilic mesoporous material （MCM-41-cal） was prepared by removing the template withcalcination. These two materials were characterized by XRD、N₂adsorption-desorptionisotherms、FTIR and so on. And its adsorption properties were inspected.The adsorption properties of these two materials toward the organic pollutants inbiologically treated coking wastewater were studied. The effects of adsorbent concentrationand pH on the adsorption process as well as the kinetics of adsorption process wereinvestigated. The adsorption capacity of MCM-41-dry was much higher than that ofMCM-41-cal, which was due to its higher hydrophobicity and the existence of the quaternaryammonium groups on the surface of MCM-41. At25℃, when the adsorbent concentrationwas2g·L^-1, the COD and TOC removal efficiencies on MCM-41-dry toward cokingwastewater were53%and66%, corresponding to the adsorption capacity of64mg.g^-1and17mg·g^-1, respectively. The kinetic data could be fitted well by second-order kinetic model. TheGC/MS data showed that the residuals of biologically treated coking wastewater werelong-chain alkanes, halides, polycyclic aromatic hydrocarbons and other refractory organiccompounds. After the adsorption by MCM-41-dry, these substances were reduced, especiallythe hydrophobic alkanes, indicating that this adsorbent could preferentially adsorb thehydrophobic substances. Meanwhile, the overall hydrophobic material still showed somehydrophilicity, which did not affect its contact with wastewater, making it a possibility for thepractical wastewater treatment.In order to prove the adsorption selectivity of MCM-41-dry, we especially used twostructurally similar phenols as target pollutants. The effects of adsorbent concentration and pH on the adsorption process as well as coexisting ions were investigated. Studies had shownthat the MCM-41-dry had a certain adsorption capacity for phenol and chlorophenol, and it ismore adsorption capacity toward chlorophenol than phenol, which may be related to thehydrophobic properties of the two substances. At the same time, it had the ability topreferentially adsorb hydrophobic organic matter.Surfactant structure-directing agent was used to synthesize molecular sieve（MCM-41-dry） at room temperature. The adsorption properties of this material towardphenanthrene were studied. The effects of adsorbent concentration and pH on the adsorptionprocess as well as the kinetics and thermodynamics of adsorption process were investigated.MCM-41-dry showed a higher adsorption rate toward phenanthrene, and equilibrium wasreached within one hour. The kinetic data could be fitted well by second-order kinetic model.The equilibrium data fitted the linear model well, and the adsorption process follows theliquid/solid phase distribution mechanism. The adsorption is spontaneous and exothermic.The regeneration of exhausted adsorbent material was carried out by0.1M NaOH solution.The regenerated material still showed high removal efficiency, and it could be used to adsorbpolycyclic aromatic hydrocarbons （PAHs）.