Removal of heavy metal ions in wastewater and reuse as a hydrogenolysis catalyst: Multistage application of lignin-based adsorbent

Abstract

Heavy metals in industrial wastewater represent a significant threat to the ecosystem and need to be efficiently removed before discharge. However, the effective utilization of heavy metals using affordable and efficient processes still poses a sustainability challenge. Here, we report a sustainable regeneration of spent heavy metal ions from lignin-based adsorbents toward efficient reductive catalytic degradation of lignin into monophenols. A reverse suspension strategy was first used to cross-link small molecules of industrial lignin waste into long-chain macromolecules using epichlorohydrin as a crosslinking agent. The long-chain macromolecules displayed a high affinity of Cu^2 + and Pb²⁺ with maximum adsorption capacity of 393.9 mg/g and 349.2 mg/g, respectively. The adsorption isotherms and kinetics models revealed that Cu²⁺ and Pb²⁺ adsorption followed monolayer chemisorption. Notably, the regenerated carbon-loaded copper oxide (CuO/C) nanomaterial served as an effective catalyst for lignin deconstruction with a yield of monomeric phenols up to 25.9 wt%, which for the first time realized the multistage application of lignin-based adsorbents for the removal of heavy metal ions and their reuse as hydrogenolysis catalysts. This work paves a new way for the fabrication of bio-derived heterogeneous catalyst in wastewater treatment.