Nanoporous activated carbons (ACs) were prepared from Lapsi (Choerospondias axillaris) seed powder by chemical activation with sodium hydroxide (NaOH) at different NaOH impregnation ratios. The prepared ACs were characterized by Fourier transform-infrared (FTIR) spectroscopy, Raman scattering, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Semi-quantitative information on the surface properties was obtained by estimating iodine number. FTIR spectra showed the presence of oxygenated functional groups such as hydroxyl, carbonyl, and carboxyl in the prepared ACs. Raman scattering showed clear D and G bands in the spectra. The intensity ratio of G and D band peak intensity was ca. 1.39 at lowest NaOH and Lapsi seed powder ratio 0.25:1 showing high graphitic degree. This ratio decreased with increase in the NaOH impregnation ratio and reached minimum ca. 0.94 (comparable with commercial AC) at NaOH and Lapsi seed powder ratio 1:1 demonstrating that higher NaOH impregnation reduces the graphitic structure of the carbon. XRD patterns showed two broad peaks at diffraction angles of approximately 25 and 43 degrees indicating the amorphous structure. Surface properties of the ACs (BET surface area, pore volume, and pore size distributions) were evaluated by nitrogen adsorption-desorption isotherm. Our ACs showed strong methylene blue adsorption property (maximum methylene blue is ca. 200 mg/g). Judging from the iodine number and methylene blue values, structure, and surface areas, it can be concluded that NaOH impregnation ratio is one of the key parameters to tune the surface properties of Lapsi seed stone-based activated carbons.

a b s t r a c tWe report a facile synthesis of nanoporous activated carbons (NACs) derived from Lapsi (Choerospondias axillaris) seed powder (LSP). LSP and sodium hydroxide (NaOH) are mixed in 1:1 ratio by wt. and carbonized at 400°C for different time (3, 4, and 5 h) and at different temperature (400, 500, 600, and 700°C) for 3 h under a constant flow of ultrapure nitrogen gas. The effect of the conditions during the preparation on the structures and properties of NACs is investigated carefully. Fourier transform infrared spectroscopy (FT-IR) show the presence of several functional groups (e.g., hydroxyl, carbonyl, and carboxyl groups) on the carbon surface. Irrespective of the carbonization conditions, both D and G bands are clearly observed in Raman scattering spectra. It is found that the increase in carbonization time significantly increases the G/D bands ratio, indicating an enhancement in the graphitic character. The NACs prepared by carbonization at 400°C for 3 h have the highest surface area (over 1000 m 2 g À1 ) and show high adsorption efficiency in removing methylene blue (MB) from aqueous solution (around 200 mg g À1 ).

Abstract:The possibility of Fe 2 O 3 /Areca nut activated carbon composite as an adsorbent for removal of fluoride from water is presented. Activated carbon (AC) was prepared from Areca nut by chemical activation with phosphoric acid at 400°C under nitrogen atmosphere. The resultant AC was characterized by adsorption of methylene blue and iodine. As indicated by iodine and methylene blue adsorption, the AC was highly micro and meso porous in nature. The adsorbent was prepared by compositing the AC with ferric oxide. Batch adsorption experiments were conducted to describe the effect of pH, contact time and adsorbent dose on fluoride removal from water. Percentage removal of fluoride by the adsorbent was ~75 % at contact time of 180 minutes. The maximum adsorption of fluoride was observed at pH 2 with adsorbent dose of 20 gm/L. The adsorption equilibrium data was analyzed by Langmuir and Freundlich adsorption isotherms. The adsorption data was fitted Langmuir better than Freundlich isotherm. The adsorption capacity of the Fe 2 O 3 /Areca nut activated carbon composite was found to be 4.8 mg/gm. The composite adsorbent prepared from Areca nut AC could be an efficient adsorbent for removal of fluoride from water.