Facile synthesis of hollow globular Cr(VI)-adsorbents inspired from assembly to polymerization

In this work, hollow globular Cr(VI)-adsorbents were successively fabricated via the assembly of tannic acid (TA) and 1, 6-hexanediamine (HA) converting to polymerization using polyvinyl alcohol (PVA) as precursor. PVA@poly(tannic acid - 1, 6-hexanediamine) (PVA@PTHA) with hollow structure can chelate Cr on their bodies accompanying of reduction of Cr(VI) to Cr(III) caused by phenolic hydroxyl groups, which is proved by means of TEM , XPS , SEM and EDX, etc . Many factors affecting the adsorption of Cr(VI) were studied systematically, i.e. , initial Cr(VI) concentration (20–260 mg/L), contact time (0–48 h), foreign ions (Cu 2+ , Fe 3+ , Mn 2+ ), and pH value (2–7). The adsorption-reduction process followed the Langmuir isotherm model (R 2  = 0.9994) and fitted well with the pseudo-second-order kinetic model (R 2  = 0.9984). Besides, the removal capabilities of PVA@PTHA for Cr(VI) were affected insignificantly by nitrate ion (NO 3 − ) or sulfate ion (SO 4 2− ) as a competitive ion. In brief, PVA@PTHA is low-cost green adsorbent with the maximum adsorption capacity of 434.0 mg/g for Cr(VI)-sewage treatment.