Flax fiber based semicarbazide biosorbent for removal of Cr(VI) and Alizarin Red S dye from wastewater

Abstract

In the present study, flax fiber based semicarbazide biosorbent was prepared in two successive steps. In the first step, flax fibers were oxidized using potassium periodate (KIO4) to yield diadehyde cellulose (DAC). Dialdehyde cellulose was, then, refluxed with semicarbazide.HCl to produce the semicarbazide functionalized dialdehyde cellulose (DAC@SC). The prepared DAC@SC biosorbent was characterized using Brunauer, Emmett and Teller (BET) and N2 adsorption isotherm, point of zero charge (pHPZC), elemental analysis (C:H:N), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses. The DAC@SC biosorbent was applied for the removal of the hexavalent chromium (Cr(VI)) ions and the alizarin red S (ARS) anionic dye (individually and in mixture). Experimental variables such as temperature, pH, and concentrations were optimized in detail. The monolayer adsorption capacities from the Langmuir isotherm model were 97.4 mg/g and 18.84 for Cr(VI) and ARS, respectively. The adsorption kinetics of DAC@SC indicated that the adsorption process fit PSO kinetic model. The obtained negative values of ΔG and ΔH indicated that the adsorption of Cr(VI) and ARS onto DAC@SC is a spontaneous and exothermic process. The DAC@SC biocomposite was successfully applied for the removal of Cr(VI) and ARS from synthetic effluents and real wastewater samples with a recovery (R, %) more than 90%. The prepared DAC@SC was regenerated using 0.1 M K2CO3 eluent. The plausible adsorption mechanism of Cr(VI) and ARS onto the surface of DAC@SC biocomposite was elucidated.

Surfactant supported chitosan for efficient removal of Cr(VI) and anionic food stuff dyes from aquatic solutions

“…9 ). This is consistent with other batch studies which also reported maximum Cr(VI) adsorption in acidic environments 37 , 66 , 67 and can be explained by considering the surface charges of the adsorbents and the Cr(VI) adsorbate species 68 . The surface charge of an adsorbent is determined by pHpzc where an adsorbent surface is neutral at pH = pHpzc, but develops a positive charge at pH < pHpzc and a negative charge at pH > pHpzc.…”

“…Because of the strong protonation, the adsorbent surface becomes positively charged at low pH. The Cr(VI) adsorption was enhanced due to the electrostatic force between negatively charged HCrO 4 − and Cr 2 O 7 –2 and SO 3 − of (E110 and E122) and the positively charged adsorbent surface 37 . Thus, this, in turn, enhances the affinity of CS@CTAB material towards attracting positively charged metal ions and dye molecules depending on pH control, causing the improvement of Cr(VI), E110, and E122 adsorption as shown in the equations below (12) and (13), respectively.…”

“…From ΔH o values that are higher than 80kJ/mole, it was proven that the adsorption was chemisorption. The negative ΔS o ads values showed that Cr(VI) metal ion, E110, and E122 adsorption onto CS@CTAB surface leads to lower disorder and higher arrangement 37 . The plot of lnK C versus(1/T) absolute temperature for the adsorption of E122, E110 and Cr(VI) onto CS@CTAB is shown in Fig.…”