Application of polymer-coated Macadamiaintegrifolia nutshell biomass impregnated with palladium for chromium(VI) remediation

Malvin Moyo,Sekomeng Johannes Modise,Vusumzi Emmanuel Pakade

doi:10.1038/s41598-021-03473-8

Abstract

Freely suspended and porous basket restrained granules of palladium nanoparticles supported on polymer-grafted Macadamia nutshell biomass (Pd@Polym-MNS) composite were used for the treatment chromium(VI)-containing water. In the presence of formic acid, the Pd@Polym-MNS demonstrated its activity in the adsorption-reduction-based conversion of noxious chromium(VI) to less toxic chromium(III) with a low activation energy of 13.4 kJ mol–1, ΔH0 (+ 10.8 kJ mol–1), ΔS0 (−270.0 J mol–1 K–1), and ΔG0 (+ 91.3 to + 98.0 kJ mol–1) indicated the exothermic, endergonic and non-spontaneous nature of the catalytic redox reaction. In addition to facilitating easy recovery, rinsing, and reuse, restraining the Pd@Polym-MNS in the basket reactor helped maintain the integrity of the catalysts by preventing violent collisions of suspended granules with the mixing apparatus and the walls of the reaction vessel. Whereas the pseudo-first-order rate constant was recorded as 0.157 min–1 upon initial use, values of the mean and relative standard deviation for the second, third and fourth consecutive uses were found to be 0.219 min–1 and 1.3%, respectively. According to a response surface methodological approach to batch experimentation, the initial concentration of chromium(VI) and catalyst dosage had the greatest impact on the redox reaction rate, accounting for 85.7% and 11.6% of the variability in the value of the pseudo-first-order rate constant, respectively. Mutually beneficial effects of the combinations of high formic acid and low chromium(VI) concentration, high temperature and catalyst dosage as well as high formic acid and catalyst dosage were recorded.

Highlights

From a health perspective, the presence of hexavalent chromium [Cr(VI)] in water is of primary concern owing to its cancer-causing effects on animal c ells[1]
Following the synthesis and characterization of palladium nanoparticles dispersed on polymer-grafted Macadamia nutshell (Pd@Polym-MNS) granules in our previous work[48], we have restrained the Pd@Polym-MNS granules in a porous stainless steel basket
Zerovalent palladium impregnated in polymer-grafted Macadamia nutshell biomass packed in a porous basket reactor to enhance the ease of recovery for recurrent use provides a reactor that adsorbs aqueous Cr(VI) species and formic acid molecules

Summary

Introduction

The presence of hexavalent chromium [Cr(VI)] in water is of primary concern owing to its cancer-causing effects on animal c ells[1]. Since the use of HCOOH as the reducing only produces carbon dioxide and water, waste solutions devoid of iron(III) species can be produced. Excess HCOOH in the reaction mixture can be decomposed on the surface of the catalyst to liberate hydrogen gas (H2), an environmentally friendly fuel, in accordance with Eq (6)[37,38], and the decomposition of excess HCOOH lowers the acidity of the solution prior to the precipitation of chromium(III) hydroxide. The elevated costs associated with the precious metal-based catalysts used in the Cr(VI)-HCOOH redox system can be offset by the value of the hydrogen gas and the pure chromium(III) hydroxide that can be produced via subsequent treatment with sodium hydroxide, calcium hydroxide or magnesium o xide[39,40]. The practical implication of restraining the catalytic Pd@PolymMNS granules in a porous basket is that it enables easy application and recovery by immersion and retrieval, respectively, without the need for elaborate, time consuming steps in industrial wastewater treatment processes

Methods

Results

Conclusion