LAUSR

Four solid adsorbents namely nanohydroxyapatite (NP), cetyltrimethyl ammonium bromide modified nanohydroxyapatite (NPB), and nanohydroxyapatite/chitosan composite either in acidic (NPS1) or basic media (NPS2) were prepared based on egg shell as a biosource. Solid materials were characterized by N2 adsorption/desorption isotherms, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and point of zero charges. The thermal, textural, and chemical properties of nanohydroxyapatite/chitosan composite prepared in basic medium were found to be more enhanced than the other three solid adsorbents with surface area and pore radius of 152.5 m2/g and 5.11 nm, respectively. pHPZC for all the prepared solid samples ranged between 6.8 and 7.5. Adsorption of hexavalent chromium were studied under different application condition such as the effect of adsorbent dosage, time, pH, initial Cr(VI) concentration, and temperature. The maximum adsorption capacities of chromium onto NP, NPS1, NPS2, and NPB (119.047, 131.578, 134.048, and 85.397 mg/g, respectively) were observed at pH 6. Thermodynamic and kinetic parameters proved that adsorption of Cr(VI) onto all the investigated solid adsorbents follow pseudo-second-order kinetic model, spontaneous, and endothermic adsorption process.