Lignin valorization: Facile synthesis, characterization and catalytic activity of multiwalled carbon nanotubes/kraft lignin/Pd nanocomposite for environmental remediation

Abstract

Toxic organic pollutants in wastewaters are becoming a worldwide problem, which threatens life on earth and prevents essential elements to sustain living organisms. Nitro compounds and organic dyes are the most common contaminants, which result in disturbing problems for human health and the environment. The application of heterogeneous nanocatalysts is one of the most efficient methods to overcome this challenge. In view of this, a novel nanocatalyst containing multi-walled carbon nanotubes (MWNTs), Kraft lignin, and Pd nanoparticles (NPs) was synthesized through a straightforward procedure. The synthesis of Pd NPs was performed using laser ablation, generating fine NPs without chemical agents and impurities. The morphology and structure of the prepared nanocomposite were studied by X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron (XPS) and Raman spectroscopy. The efficiency of the as-prepared nanocatalyst in the reduction of methylene blue (MB), 4-nitrophenol (4-NP), and hexavalent chromium [Cr(VI)], was investigated in an aqueous solution using sodium borohydride (NaBH4) or formic acid (HCOOH) as the reducing agents. The progress of the reactions was monitored by UV–Vis spectroscopy. The catalyst can be easily removed from the reaction media by centrifugation and reused five times without any observable decrease in the catalytic activity. Overall, the performance of MWNT/KL reported herein alludes to the prodigious practical significance of this tunable support in real world scenarios such as nanocatalysis and wastewater remediation.