Zeolite ‘adsorption’ capacities in aqueous acidic media; The role of acid choice and quantification method on ciprofloxacin removal

Abstract

Zeolites prepared from coal fly ash were used for the ‘adsorptive’ removal of the antibiotic, ciprofloxacin from aqueous solutions. Synthesised zeolites and other standard zeolites were characterised using XRD, FTIR and SEM analysis, to determine their formation, crystalline phase, morphology and elemental composition. The effect of acid type used for pH adjustment on the adsorption behaviour of ciprofloxacin on zeolites was investigated. Residual ciprofloxacin solutions after contact with zeolites were comparatively monitored using UV–Vis spectrometric and LC-MS TOF/DAD chromatographic methods. Results obtained, indicated formation of pure phase low silica zeolites. Removal efficiency by the synthesised zeolites for ciprofloxacin was significantly higher in acetic acid (92–94%) compared to HCl (27–61%) at pH 3 emphasising a clear dependence of results on experimental conditions. At experimental pH, the zeolites underwent chemical changes that were linked to structural changes. The presence of organic substrate during the chemical changes may probably explain side reactions, which led to by-products of organic origin reported in this contribution. FTIR and SEM images are presented after adsorption and clearly showed changes in zeolite structures. A discuss on the use of conventional UV–Vis spectroscopic, and LC-MS-TOF/DAD chromatographic method for quantification of aqueous residual ciprofloxacin after the ‘adsorption’ process is also presented and highlights the shortcomings of the former method compared to the latter. The zeolites showed promise for aqueous ciprofloxacin remediation reducing chemical oxygen demand (COD) levels, with process mechanisms supporting chemical interactions with substrate in a manner similar to degradation reactions.