Preparation, characterization, and evaluation of Moringa oleifera pod husk adsorbents for aqueous phase removal of norfloxacin

Chemically treated and carbonized adsorbents were prepared from Moringa oleifera pod husks (MPH) and evaluated for the aqueous phase removal of Norfloxacin (NOX), a common antibiotic. The pulverized precursor was steeped in a saturated ammonium chloride solution (24h) to give the chemically treated adsorbent (AMPH). Pyrolysis of AMPH (623K, 1/2h) yielded the carbonized adsorbent (CMPH). Both adsorbents showed favorable physicochemical attributes (pH, bulk density, attrition, iodine adsorption number/surface area, titratable surface charge, and FT-IR analysis). NOX removal was studied under the effects of initial solution pH (2-11), adsorbent dosage (0.5-2.5g), initial NOX concentration (5-25mg/L), contact time (0-240min), and temperature (298-328K). Optimal NOX uptake (mg/g) by AMPH (1.42) and CMPH (1.88) occurred at solution pH 5 and adsorbent dose of 0.5g. Equilibrium adsorption obeyed the Langmuir isotherm. Free energy change (G degrees), enthalpy change (H degrees), and entropy change (S degrees) indicated that the adsorption of NOX was feasible, spontaneous, exothermic, and physisorptive. Kinetically, NOX uptake increased rapidly within the first 10min for both adsorbents and overall, was well modeled by the Blanchard pseudo-second-order equation. The adsorbents may find use in the removal of microcontaminants of pharmaceutical origin from effluents/wastewater.