Poly(m-phenylenediamine) functionalized Calotropis gigantea fiber for coupled adsorption reduction for Cr(VI)

Abstract The Calotropis gigantea fiber (CGF)-based adsorbent with excellent hollow tubular structure was designed and developed by using poly( m -phenylenediamine) (PmPD) as the modifier layer. The amount of monomer m -phenylenediamine (mPD) from 0.5 to 2.0 g was firstly optimized using the response surface methodology. The results indicate that the modification of PmPD enables the fiber surface to change from original smooth to coarse, in addition to attaching more N-containing functional groups. Subsequently, the adsorption behaviors of modified CGF for Cr(VI) were systematically investigated, including the influences of pH (3.0–10.0), contact time (0–5 h), initial Cr(VI) concentration (25–200 mg/L), ion strength (distilled water, tap water, 1.0 mmol/L and 5.0 mmol/L NaCl), and other co-existing metal ions such as Cu(II), Zn(II) and Ni(II). Experimental results show that > 90% adsorption can be achieved within 10 min and the adsorption capacity can reach 79.90 mg/g when an initial Cr(VI) concentration is 200 mg/L, demonstrating its fast adsorption kinetics and high adsorption capacity. Meanwhile, the as-prepared adsorbent exhibits a highly selective adsorption behavior for Cr(VI) at lower pH 3.0. During the adsorption process, an adsorption coupled reduction from Cr(VI) to Cr(III) was evidenced by XPS analysis. All the information confirm that the as-prepared material shows its potential as a low-cost and highly efficient adsorbent to be used for selective removal of Cr(VI) from contaminated water.