EXPERIMENTAL
Materials and characterizations
The base adsorbent used in the study was commercially available GAC made from coconut shell (A-GAC), whose mesh size ranges 12*30. The surface morphology of the GAC were analyzed by Scanning electron micrograph (SEM) using the S-4700 (Hitachi, Tokyo, Japan) and surface area and pore size distributions for the sample were measured by the Brunauer-Emmett-Teller (BET) method using Micrometrics (ASPS2020, USA). The surface functional groups of the samples were characterized by a mono-chromatized Al Kα X-ray from X-ray photoelectron spectroscopy (XPS) (VG Scientific ESCALAB 250 Spectrometer). Inductively coupled plasma-atomic emission spectroscopy (ICP) was used to analyze heavy metal absorption using OPTIMA 4300 DV (perkin elmer, USA).
Point of zero charge (PZC)9
To measure the PZC of the A-GAC sample, three different initial pH solutions were prepared using 0.1M HNO and 0.1 M NaOH; for example, pH=3.5, 6.5, and 11.5. NaNO, was used as the background electrolyte. For each initial pH, six containers were filled with 100 ml of the solution, and different amounts of carbon sample were added (0.05%, 0.1%, 0.5%, l%, 5%, and 10% by weight). The equilibrium pH was measured after 24 h.
Modification of GAC
The GACs were deposited in a three-necked flask, equipped with stirrer, condenser, dropping funnel and heating mantle. The GACs (5 g) in 20 ml distilled water were treated with 1, 2, 3 N NaOH (5 g), respectively at 80 ℃ for 1 h to increase the formation of functional groups and porosity. The modified GACs were washed with deionized water and dried overnight at 80 ℃ in vacuum oven to produce modified ACs such as NaGAC1, NaGAC2, and NaGAC3.
Adsorption measurements
Adsorption isotherms of the Pb ion were carried out in batches as follow. Salts used were Pb(NO3)2 for Pb(II) with a high degree of purity. Experiments were carried out using 250 mL of Pb ion aqueous solution containing 10 mgl-1 concentration and a constant modified GACs, in 300 mL Teflon bath at 20±1.5 ℃. At a given intervals, samples were filtered using 0.45 μm cellulose acetate filters and the content of remaining Pb ion was analyzed every 2 min by using ICP.
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