Removal of beta-lactam antibiotic in water environment by adsorption technique using cationic surfactant functionalized nanosilica rice husk.

This study aims to investigate the adsorption characteristics of cationic surfactant, cetyltrimethylamonium bromide (CTAB) onto negatively nanosilica rice husk surface and the application for antibiotic treatment in water environment. Adsorption of CTAB onto nanosilica increased with an increase of solution pH, due to an enhancement of the electrostatic attraction between cationic methylamomethylamonium groups and negatively charged nanosilica surface enhanced at higher pH. Adsorption of CTAB decreased with a decrease of ionic strength while a common intersection point (CIP) was observed for adsorption isotherm at different ionic strengths, suggesting that hydrophobic interactions between alkyl chains in CTAB molecules significantly induced adsorption and admicelles with bilayer formation were dominant than monolayer of hemimicelles. The CTAB functionalized nanosilica (CFNS) was applied for removal of beta-lactam amoxicillin (AMX). The best conditions for AMX treatment using CFNS were selected as pH 10, contact time 60 min and CFNS dosage 10 mg/mL. Removal efficiency of AMX using CFNS reached to 100% under optimum conditions while it was only 25.01% using nanosilica without CTAB. The maximum AMX adsorption capacity using CFNS of about 25 mg/g was much higher than other adsorbents. The effects of different organics such as humic acid, anionic surfactant, and other antibiotics on AMX removal using CFNS were also studied. A two-step model can fit CTAB uptake isotherms onto nanosilica and AMX onto CFNS well at different KCl concentrations. Based on the desorption of CTAB with AMX adsorption as well as adsorption isotherms, the change in surface charge and functional vibration groups after adsorption, we indicate that AMX adsorption onto CFNS was mainly controlled by electrostatic interaction. We reveal that CFNS is an excellent adsorbent for antibiotic treatment from aqueous solution.

Adsorptive Removal of Anionic Azo Dye New Coccine Using Silica and Silica-gel with Surface Modification by Polycation.

In the present work, adsorption of anionic azo dye, new coccine (NCC) on silica and silica-gel in an aquatic environment was discovered. Effective conditions such as adsorption time, pH, the influence of dosage on NCC adsorption using strong polycation, poly-diallyl-dimethylammonium chloride (PDADMAC) modified silica (PMS) and PDADMAC modified silica-gel (PMSG) were systematically studied. The removal of NCC using PMS and PMSG were much higher than that using raw silica and silica-gel without PDADMAC in all pH ranges from 3 to 10. The adsorption of NCC onto PMS and PMSG was achieved maxima at the same conditions of contact time 30 min, pH 6. The optimum adsorbent dosages of PMS and PMSG for NCC removal were 10 and 20 mg·mL-1, respectively. Experimental results of NCC adsorption isotherms onto PMS and PMSG at different ionic strength were fitted by Langmuir and Freundlich models. The NCC removal efficiencies using PMS and PMSG were higher than 87%, indicating that PMS and PMSG are novel and reusable adsorbents for removal of anionic dye. Based on adsorption isotherms, and surface group changes after PDADMAC modification and NCC adsorption examined by Fourier transform infrared spectroscopy (FTIR), we demonstrate that electrostatic interaction between positively charged adsorbents' surfaces and negative sulfonic groups of NCC are the main driving force for anionic azo dye adsorption onto PMS and PMGS adsorbents.