Removal behaviors and mechanisms of hexavalent chromium from aqueous solution by cephalosporin residue and derived chars

H3PO4-Activated Cattail Carbon Production and Application in Chromium Removal from Aqueous Solution: Process Optimization and Removal Mechanism

“…The oxygen-containing functional groups on the surfaces of TAC determined the surface acidity-basicity and the adsorption performance of TAC [40]. The shift in the band positions and change of the peak area of these groups after Cr(VI) adsorption indicated the electrostatic attraction and subsequent complexation and/or ion exchange between the Cr(VI) anion or the Cr(III) cation reduced from Cr(VI) and protonated -OH, -COOH, -CH, -CHO, -NH2, and phosphate (PO4 3− ) at low solution pH [3,4]. This helped the subsequent Cr(VI) anion's reduction to the Cr(III) cation by reductive substances like CxOH (hydroxyl and carbonyl groups) on the TAC surface [4], which was proved by the following XPS results (Figure 4e,g).…”

“…The adsorption capacity and removal efficiency of Cr sharply decreased with the increase of initial solution pH ( Figure 1a). One of the main reasons was probably due to the decrease/increase of protonation/deprotonation extent of TAC surfaces over the increased solution pH [4,18]. Hence, the columbic attraction at low pH and the electrostatic repulsion at high pH between TAC surfaces and Cr(VI) oxyanions would improve or inhibit the Cr(VI) diffusion and thus removal, respectively [1].…”

“…Hence, the columbic attraction at low pH and the electrostatic repulsion at high pH between TAC surfaces and Cr(VI) oxyanions would improve or inhibit the Cr(VI) diffusion and thus removal, respectively [1]. The Cr(VI) in the aqueous solution mainly exists in forms of chromate CrO 4 2− (pH > 6.0), HCrO 4 − (pH < 6.0), dichromate Cr 2 O 7 2− (pH 4-6), or H 2 CrO 4 (pH < 1.0) [1,4,16]. The HCrO 4 − oxyanion can dimerize at pH between 2 and 6 [26].…”

“…The crystallization degree in the TAC depended on the chemical compositions of a high proportion of C in TAC [20]. The mesoporous nature was considered helpful for the accessibility of Cr(VI) to the surface of TAC, and the good physical characteristics helped the physical adsorption of Cr(VI) onto TAC, and the subsequent ion exchange, complexation, and reduction for Cr removal [4].…”

“…Recently, a wide range of techniques has been proposed to remove Cr(VI) from wastewater, including chemical precipitation [4], electrochemical treatment, membrane separation [6], reduction [1,7], ion exchange [8], and adsorption [9]. Among them, adsorption is considered as an attractive and favorable method owing to its higher cost-efficient ratio and easier operation.…”