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

Abstract

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 (Pb2+) and methylene blue (MB) was investigated. HAp was successfully synthesized on the surface of Luffa with an average length of 40–56\xa0nm and a width of 14–19\xa0nm. 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 Pb2+ concentrations were studied. The results showed that luffa/HAp composites were more effective in removal of Pb2+ ions than MB compared to Luffa without HAp, and vice versa. Kinetic and adsorption studies of MB and Pb2+ ions were well fitted with the pseudo-second-order and Langmuir models. The maximum adsorption capacity of Pb2+ was 625\xa0mg/g, 714\xa0mg/g, and 714.5\xa0mg/g for oxidized-fibers/HAp, oxidized-nanocellulose/HAp, and cellulose/HAp, respectively, at dose 4\xa0g/L, pH 5.3, 25\xa0°C. While the maximum adsorption capacity of MB was 25.2\xa0mg/g, 30.8\xa0mg/g, and 36.2\xa0mg/g for oxidized-fibers/HAp, oxidized-fibers, and cellulose, respectively, at dose 4\xa0g/L, pH 7.3, 25\xa0°C. Also, more than 95% of lead (500\xa0mg/L) and 85% of MB (25\xa0mg/L) were removed within the first 5\xa0min. Separately, cellulose sample was the most effective in removing MB while cellulose/HAp for removal of Pb2+. However, oxidized-fibers/HAp composite was the easiest to prepare and the most effective in removing both MB and Pb2+.