Green lignocellulosic superadsorbent for superior Pd(II) removal and cascade catalytic conversion

Abstract

In this study, a lignocellulosic-based adsorbent with excellent adsorption capacity for palladium and can be used for upcycling as an eco-friendly catalyst was prepared. The palladium adsorption performance of the lignocellulosic-based adsorption material was improved by 6 times compared to that of kraft lignin before the cationization modification process using polyethyleneimine. The prepared cationized lignin was introduced into a cellulose dissolution-regeneration process to be fabricated into a bead-type adsorbent, and through a cross-linking reaction using citric acid, a natural cross-linking agent, structural stability in contaminated water was achieved and adsorbent recovery and reuse were facilitated. As a result of the adsorption isothermal study, the maximum monolayer adsorption capacity for palladium of the regenerated cellulose beads containing cationized lignin was 212.5 mg/g. Palladium was recovered and reused from the beads by reducing Pd(II) to Pd(0) using the cationized lignin-containing regenerated cellulose beads as the catalyst. After reduction, Pd(0) present on and inside the beads successfully promoted the hydrogenation reaction that reduces 4-nitrophenol to 4-aminophenol with a conversion rate of 98 %. In addition, when reused 5 times after a simple water washing process, a conversion rate of 96 % or more was maintained, and high reuse catalyst efficiency was exhibited.