Sorption Of Triclosan From Aqueous Solution By Surfactant-modified Molecular Sieve And Its Mechanism Study

Triclosan [5-chloro-2-（2,4-dichlorophenoxy）-phenol]（TCS）, a widely usedantimicrobial agent in pharmaceuticals and personal care products （PPCPs）, has attractedworldwide attention due to its frequent detection in natural environment and its potentialtoxicity to ecosystem. As a simple and efficient method, adsorption has been extensivelyapplied in the removal of TCS from aqueous solution.Activated carbon and carbon nanotubes have been proven to show high effectiveness inthe removal of TCS. However, these materials are too costly to be used in practicalapplications. As a natural mineral, natural zeolite is attracting more and more attention inenvironment applications due to its worldwide availability and excellent physiochemicalproperties. However, owing to the weak affinity of natural zeolite towards hydrophobicorganic compounds, researchers try to modify its surface from hydrophilic to hydrophobiccharacter with cationic surfactants in order to increase its adsorption capacity.Organo-zeolites （OZs） were prepared by loading cetylpyridinium bromide （CPB） ontonatural zeolite （NZ） and were firstly used to remove triclosan （TCS） from aqueous solution.Surface properties of NZ and OZs were evaluated by EA, BET, contact angle, zeta-potential,FT-IR, XRD, and SEM. The results indicated that NZ surface properties were considerablyaltered with CPB modification, but its mineral structures were not significantly affected.The adsorption characteristics of OZs towards TCS were studied through batch adsorptionexperiments. Batch experiments were conducted as a function of contact time, initial TCSconcentration, temperature, and pH. The adsorption capacities of OZ0.5, OZ1.0and OZ2.5, prepared with different initial concentrations of CPB, toward TCS at298K weregreatly enhanced from0.91mg·g^-1for NZ to27.15,39.66and41.14mg·g^-1, respectively.The adsorption equilibrium data of OZs were found to follow the Freundlich isotherm better.The adsorption kinetics data could be well-described by the pseudo-second-order model.Further thermodynamic investigations indicated that TCS adsorption onto OZs was anexothermic and spontaneous process. The TCS adsorption capacities were found to bestrongly dependent on the solution pH and the nature of surface charge of OZs, which werea little higher in acidic and neutral pH conditions. The main mechanisms controlling the adsorption of TCS onto OZs were presumed to be partiton and surface adsorption. As aresult, OZ1.0could be used as a more effective adsorbent for TCS removal fromwastewater.However, since the micro pores of NZ are so small that CPB cations cannot penetrateinto them, resulting in the CPB cations can only exchange with the external cations ofzeolite. In order to increase the amounts of loaded carbon content, we synthesized thehydrophobic mesophase MCM-41material （noted as MCM-41-dry） with simple method.Surface properties of MCM-41-dry were evaluated by XRD, FT-IR, TG, N2adsorptionmeasurements, zeta-potential, EA and contact angle measurements. The results indicatedthat MCM-41-dry processes stable mesostructure. Present work also deals with theadsorption of TCS on MCM-41-dry. The effect of surfactant template in MCM-41on theremoval of TCS was investigated. It was found that MCM-41–dry shows significantadsorption for TCS because of the hydrophobicity created by surfactant template in theMCM-41-dry. Batch adsorption studies were carried out to study the effect of variousparameters like adsorbent dose, pH, initial concentration and the presence of co-existinganions. It was found that adsorption of TCS depends upon the solution pH as well asco-existing anions present in the aqueous solution. The equilibrium adsorption data for TCSwas analyzed by using Freundlich adsorption isotherm model. The adsorption kinetics datacould be well-described by the pseudo-second-order model. Further thermodynamicinvestigations indicated that TCS adsorption onto OZs was an exothermic and spontaneousprocess.The comparison of adsorption of TCS on OZs and MCM-41-dry was investigated. Itwas found that the efficiency of the use of organic contents is a key factor.