Development of fast and high-efficiency sponge-gourd fibers (Luffa cylindrica)/hydroxyapatite composites for removal of lead and methylene blue

Abstract

Oxidized-fibers, cellulose, and oxidized-nanocellulose were isolated from sponge-gourd fibers ( Luffa cylindrica ) and used as natural, non-toxic, and low-cost adsorbents. The effect of three luffa forms with or without hydroxyapatite (HAp) on the removal efficiency of lead ions (Pb 2+ ) and methylene blue (MB) was investigated. HAp was successfully synthesized on the surface of Luffa with an average length of 40–56 nm and a width of 14–19 nm. Prepared materials showed differences in morphology (shape and size), chemical structure, and crystalline properties. The effect of sorbent type, contact time, and initial MB and Pb 2+ concentrations were studied. The results showed that luffa/HAp composites were more effective in removal of Pb 2+ ions than MB compared to Luffa without HAp, and vice versa. Kinetic and adsorption studies of MB and Pb 2+ ions were well fitted with the pseudo-second-order and Langmuir models. The maximum adsorption capacity of Pb 2+ was 625 mg/g, 714 mg/g, and 714.5 mg/g for oxidized-fibers/HAp, oxidized-nanocellulose/HAp, and cellulose/HAp, respectively, at dose 4 g/L, pH 5.3, 25 °C. While the maximum adsorption capacity of MB was 25.2 mg/g, 30.8 mg/g, and 36.2 mg/g for oxidized-fibers/HAp, oxidized-fibers, and cellulose, respectively, at dose 4 g/L, pH 7.3, 25 °C. Also, more than 95% of lead (500 mg/L) and 85% of MB (25 mg/L) were removed within the first 5 min. Separately, cellulose sample was the most effective in removing MB while cellulose/HAp for removal of Pb 2+ . However, oxidized-fibers/HAp composite was the easiest to prepare and the most effective in removing both MB and Pb 2+ .