Tailoring the Structural and Morphological Properties of Biogenic Nano-Chlorapatite to Enhance the Capture Efficiency Towards Cr(VI)

Nano-chlorapatite (nClAP) has been widely used as an efficient and environment-benign material to remediate heavy metal-contaminated water and soil. However, the adsorption capacities of nClAP to heavy metal oxyanions such as Cr(VI) are limited, which restricts its further application in environmental remediation. Herein, a novel carboxymethyl cellulose (CMC)-modified biogenic nClAP (CMC-nClAP) adsorbent was synthesized by a facile wet chemical method and used for Cr(VI) removal from water. The obtained CMC-nClAP materials were characterized by FTIR, XRD, TEM, and TGA analyses. Then, batch experiments were conducted to explore the effects of various factors such as the ratio of CMC and nClAP, pH, adsorbent dosage, adsorption time, and temperature on the adsorption process. The results revealed that the CMC-nClAP adsorbent displayed markedly improved stability against aggregation as well as Cr(VI) adsorption capacity as compared to that of the pristine nClAP. The Cr(VI) adsorption data obeyed the Langmuir isotherm model and pseudo-second-order kinetic model. Site energy distribution analyses revealed that Cr(VI) first occupied the high-energy sites and then diffused to the low-energy adsorption sites on the CMC-nClAP surface. Our experimental results indicated that the CMC-nClAP could be a promising material for the removal of Cr(VI) from water.