Novel efficient capture of hexavalent chromium by polyethyleneimine/amyloid fibrils/polyvinyl alcohol aerogel beads: Functional design, applicability, and mechanisms

Optimization of batch and packed-bed column Cr(vi) adsorption of an amine-rich chitosan/polyethyleneimine composite: application in electroplating wastewater treatment

“…In regeneration of the adsorbent, a maximum of 62% recovery was achieved. About the same recovery percentage was reported by Zhang et al 19 when they used a PEI/amyloid fibrils/polyvinyl alcohol aerogel beads as the adsorbent. Geng et al 54 investigated the performance of a PEI–graphene oxide adsorbent for Cr( vi ) removal, but they did not investigate the regeneration of the adsorbent.…”

“…Abundant amine functional groups on the adsorbent can form complexes with Cr( iii ) cations, which were reduced from Cr( vi ), due to the presence of electron donor functional groups like hydroxyl and amine. 19,53,54 It should also be noted that the k 2 value decreased from 0.0028 to 0.0006 (g mg −1 min −1 ) when the initial concentration increased, which shows that the adsorption process highly depends on the concentration. 66 To further identify the characteristics of the adsorption process, the effects of Cr( vi ) concentration and adsorption isotherms were investigated.…”

“…Cr( vi ) can be reduced to Cr( iii ) in the presence of electron donor functional groups like hydroxyl and amine. 19,22,53,57,58 After the reduction, amine groups on CS–PEI–GLA can chelate the cations. 19,53,54,59 Another possible mechanism for Cr( iii ) removal is its precipitation as Cr(OH) 3 , especially at pH above 6.…”

“…For instance, nanoscale adsorbents are popular for chromium removal among scientists; 17,18 however, the high surface energy of these adsorbents leads to aggregation, which makes the adsorption sites unavailable for chromium removal, making the adsorbent inefficient. 19 That could be the reason why most research articles limit the evaluation of their adsorbents to batch conditions instead of continuous conditions, such as in a column reactor. To put this fact into numbers, in a review article focusing on polyethyleneimine (PEI) composites, 5 out of 136 studies on chromium adsorption, only six had studied continuous flow conditions in a column reactor.…”

“…Moreover, to improve the reusability in industrial-scale applications, large-size adsorbents are more desirable. 19–21…”