Design of a porous lignocellulose-based hydrogel-Pd nanoparticles reactor system and its in-situ simultaneous adsorption-catalysis process concept for pollutant remedy

Abstract

The separation and reusability of nano-catalysts are paramount for their high-efficiency and low-cost use. Herein, lignocellulose hydrogels (LCG), were fabricated and served as the host matrix for in-situ generated palladium nanoparticles (Pd NPs), creating hydrogel-based Pd NPs reactor systems. The lignocellulose hydrogel-based Pd NPs (LCG/Pd NPs) reactor system possesses the following unique features: (1) lignin present in LCG acts as a “green” reducing agent so that Pd NPs are formed in situ; (2) the in-situ generated Pd NPs are well dispersed in the LCG structure via complexation; (3) the simultaneous adsorption-catalysis process concept is very effective for pollutant remedy: the adsorption of pollutants on the porous LCG effectively increases the pollutant concentration on the reaction sites, where the Pd NPs are co-located, enhancing the catalytic reactions; as a result, a much higher catalytic reaction rate is observed; (4) the LCG/Pd NPs reactor systems are readily reused/recycled after each use. As proof of this concept, the catalytic performance of the LCG/Pd NPs reactor system was demonstrated by the catalytic reduction of toxic heavy metal ions (Cr6+) and organic dye (methyl orange). Results showed that the novel LCG/Pd NPs reactor system exhibited much increased catalytic reduction rates: the pseudo-first-order rate constant (k) is 118 times higher (from 0.018 to 2.129 min−1 at 25 °C) for MO, and 38 times higher (from 0.008 to 0.304 min−1 at 25 °C) for Cr6+, in comparison with the control, under otherwise the same conditions.