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The adsorption process using inexpensive adsorbents is one of the methods to remove contaminants from aqueous solutions. Biomass porous carbon based materials are among the most widely used adsorbents in this field. Rice husk is a bio-based adsorbent material for pollutant removal. In this study, the porous carbon material obtained from the rice husk was used for the adsorptive removal of lead (Pb) and arsenic (As) from aqueous solutions. Silica was removed from rice husk structure through the one-step reaction using PTFE. The morphological and crystallographic characteristics of the adsorbent surface were determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The removal efficiency was investigated under different conditions of pH (3–9), contact time (3–90min), adsorbent amount (0.5–6 g/l) and initially adsorbed concentration (10–100 μg/l) by changing the parameters in the adsorption reactions. The Response Surface Method (RSM), a Box-Behnken design (BBD), was used to optimize adsorption of Lead and Arsenic by Rice husk. The removal efficiency was finally calculated using analysis of variance. According to the adsorption analysis results, the removal efficiency of Pb and As in aqueous solutions increased (up to 97%, 85% for Lead and Arsenic) under optimum conditions.

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The density functional theory (DFT) has been used to simultaneously investigate physic/chemi-sorption properties of oxygen on the (5, 5) boron nitride nanotube (BNNT). Geometry optimizations were carried out at B3LYP/6-31G*level of theory using gaussian 98 suites of program. physisorption of O2outside the BNNT with a vertical orientation to the tube axis above a boron atom is the most stable state of physisorption and its binding energy is -0.775 kcal/mol. In the chemisorption of O2molecule, the most stable state is above two adjacent B and N atoms of a hexagon with a B-N bond length of 2.503 Å and the binding energy of adsorbed oxygen atoms -14.389 kcal/mol. Based on these results, We also provide the effects of O2adsorption on the electronic properties of BNNTs.