Influences Of Cations And Cyclodextrin On Sorption Of Norfloxacin To Zeolite

Norfloxacin in natural water has adverse effect on indigenous microorganismscommunity, growth and development of plants and animals, and even the health ofhuman beings by screening drug-resistance gene. Sorption is an efficient method toremove norfloxacin in natural water. Zeolite is a kind of sorbent being often used withadvantages such as high efficiency and low cost. To study the mechanisms and influencesof sorption of norfloxacin to zeolite has practical significance. In this study, naturalzeolite was used as sorbent to study the mechanism of sorption of norfloxacin, and theinfluences of coexisting cations. Meanwhile, cyclodextrin was selected to represent drugcarrier. The influence of coexisting cyclodextrin was studied, too. The main conclusionsare as follows:（1） When zeolite was used as sorbent, the pseudo-second-order kinetic model and theFreundlich isotherm fitted the experimental data well. This indicated that sorption ofnorfloxacin on zeolite is a chemical and inhomogeneous sorption.（2） The species of norfloxacin are not the same when values of solution pH aredifferent. Consequently, the sorption mechanisms of norfloxacin onto zeolite are different.When pH＜6.22, the main species of norfloxacin is cation, and the sorption mechanismis cation exchange; when pH is in range from6.22to8.51, the mechanisms ofzwitterionic norfloxacin include cation exchange, cation bridge, complexation andhydrophobic effect; when pH＞8.51, cation bridge is the main sorption mechanism ofanionic norfloxacin.（3） Coexisting cations brought negative influence of sorption. At pH4.5or7.5, thesorption to zeolite was mainly affected by ionic strength but not the type of coexistingNa⁺, Ca²⁺, Al³⁺or NH₄⁺. Cu²⁺has more negative effect than the other coexisting cation.The kind of cation had influence on the sorption of anionic norfloxacin when Na⁺or Ca²⁺was the main coexisting cation, respectively.（4） On one hand, the existence of cyclodextrin could hinder sorption of norfloxacin to zeolite. On the other hand, inclusion effect of cyclodextrin promoted the removal ofnorfloxacin. The removal efficiency of inclusion by cyclodextrin was lower than sorptionby zeolite when solid to solution ratio was the same. With increase of pH, zeolitesorption ability of norfloxacin hindered by cyclodextrin was enhanced. The influence ofcoexisting Na⁺and Ca²⁺in solution on sorption depends on ionic strength but not thetype of cation.