Two Keggin-type polyoxometalates used as adsorbents with high efficiency and selectivity toward antibiotics and heavy metals

Two Keggin-type polyoxometalates ammonium phosphomolybdate (NH 4 -PMo) and ammonium phosphotungstate (NH 4 -PW) were simply synthesized and used as adsorbents for removing various antibiotics and heavy metals from water system. The effects of adsorbent dosage, initial concentration of pollutants, temperature and pH value on the adsorption efficiencies of tetracycline (TC) and Ni 2+ over both NH 4 -PMo and NH 4 -PW were systematically investigated. The adsorption process of TC molecules can be described by the Langmuir isothermal adsorption model. In terms of kinetic model, the adsorption process of TC can be described by the pseudo first-order kinetics for NH 4 -PMo and pseudo second-order kinetic model for NH 4 -PW. The results of adsorption experiments pointed out that the adsorption efficiency of NH 4 -PMo was higher than that of NH 4 -PW toward various antibiotics, dyes and heavy metals. The more negative surface charges and higher specific surface area contributed to the superior adsorption efficiency of NH 4 -PMo.