Development of immobilized natural adsorbent filters for one-pot removal of selected pharmaceuticals and metal ions from water

Abstract

In this work, a xerogel immobilized natural adsorbent filter system was developed for the removal of selected pharmaceuticals and toxic heavy metals from water. The filter system comprises of activated carbon from banana peels, sand/stones, and xerogel. The xerogel was synthesized using the sol-gel process. The activated carbon was obtained from banana peels by chemical activation with sulphuric acid at a temperature of 700 ºC and a time of 48 hours. The activated carbon obtained was characterized using fourier transform infrared spectroscopy which identified the presence of carbonyls, alkenes, and hydroxyls, the thermogravimetric analysis showed thermal stability to degradation, field emission scanning electron microscopy showed the gradual formation of pores due to the elimination of volatiles components. Furthermore, powder x-ray diffraction analysis indicated the appearance of broad diffraction which shows an amorphous structure, and the surface area was then determined by N2- Brunauer-Emmett-Teller isotherm with ranges between 105-253.10 (m2/g). The adsorption capacities of activated carbon, xerogel, and stones obtained were 91.4, 141.8, and 1.819 mg/g for lead, 19.3, 36.1, and 0.920 mg/g for ciprofloxacin and 19.4, 35.9 and 0.920 mg/g for caffeine respectively. The adsorption isotherms that is the Langmuir and Freundlich were carried out to determine interactions between the adsorbate and adsorbent. The Langmuir isotherm model experimental data correlated well with correlation coefficient R2 ranges between 0.9832-0.9963 and maximum adsorption capacities ranges of 25.367-42.789 mg/g for both selected pharmaceuticals and toxic heavy metal ions. Pseudo-first-order and Pseudo second-order kinetic models were also carried out to determine the mechanism of adsorption. The experimental data showed that the pseudo-second-order kinetic model fits well with the data and the coefficient of correlation R2 ranges were between 0.973-0.991 hence the mechanism of adsorption was mainly by chemisorption. The designed filter containing activated carbon, stones, xerogel, sand, and banana peel at 1, 0.55, 21.60, 10.03 and 1.52 g respectively was able to remove both the selected pharmaceuticals and toxic heavy metal ions in ranges of 95 and 98 % with initial concentrations of 2 ppm and 10 ppm within 60 minutes. This procedure is cheap, effective, and environmentally benign.