Adsorption of charged synthetic organic dyes by pine nut husk biochars modified with hydroxyapatite: Adsorption mechanisms and reusability
Hyeok Jin Kim, Jong Wan Han, Jin Ho Yu, Byung‐Moon Jun, Kangmin Chon
Abstract
This study examined the effect of surface modification with hydroxyapatites (HAPs) on the adsorption of positively or negatively charged synthetic dyes [i.e., methylene blue (MB) or Congo red (CR)] by pine nut husk biochars. Compared with that of pristine pine nut husk biochars (PNHB), the O/C ratio of pine nut husk biochars modified with HAPs (PNHB-H) was much larger (O/C ratio: PNHB = 0.08; PNHB-H = 0.11). This result likely indicates that HAP modification enhanced the hydrophilic functional groups on the surface of PNHB. The Q max value of PNHB-H was slightly less than that of PNHB for MB (Q max : PNHB = 6.09 mg/g, PNHB-H = 4.10 mg/g), and approximately 50-fold higher than that of PNHB for CR (Q max of CR: PNHB = 1.11 mg/g, PNHB-H = 53.42 mg/g). Such findings indicate that chemisorption plays an important role in the adsorption of MB and CR by PNHB and PNHB-H. PNHB effectively removed MB, a cationic dye, due to its negatively charged surface. In contrast, PNHB-H was able to remove both MB and CR through the phosphate and Ca components of HAPs. Thus, these results suggest that PNHB-H produced by HAP modification is effectively applicable for removing charged synthetic dyes in actual water treatment.