# Catechol-Modified Alkali Lignin for Cr (VI) Removal from Synthetic Wastewater

## TL;DR

This paper introduces a new method using modified lignin to efficiently remove and reduce toxic chromium (VI) from wastewater.

## Contribution

The novelty lies in combining catechol's redox properties with lignin's stability to create a dual-function adsorbent for Cr (VI) removal.

## Key findings

- Catechol-modified alkali lignin achieved Cr (VI) adsorption of 498.4 mg/g.
- The material reduced Cr (VI) to Cr (III) with 54.6% efficiency.
- The process follows pseudo-second-order kinetics and Langmuir isotherm models.

## Abstract

Chromium (III) ions are essential for biological functions, whereas chromium (VI) ions (Cr (VI)) pose toxicity risks to both humans and animals. Therefore, it is crucial to remove these ions from industrial sources. In this work, to remove hazardous Cr (VI) from wastewater or convert it to Cr (III), catechol-modified alkali lignin (CAL) was prepared using catechol, acetone, and alkali lignin, which is a byproduct in the paper-pulping process. The sample was characterized using a combination of techniques, including scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Various factors influencing the adsorption behavior of CAL were investigated. The adsorption behavior aligns with the pseudo-second-order kinetic model and adheres to the Langmuir isotherm model. CAL simultaneously achieves Cr (VI) adsorption (498.4 mg/g) and reduction (54.6% to Cr (III)), surpassing single-function lignin adsorbents by integrating catechol’s redox capacity with lignin’s structural stability, which is another way to efficiently utilize Cr (VI) solutions. The mechanism of adsorption and reduction is discussed, which is influenced by its functional groups. In brief, this method paves a new path for the utilization of alkali lignin and provides novel opportunities for the removal of Cr (VI) contamination.