# Mercury Removal Using Sulfur-Decorated Chitosan Polymer Nanocomposites: Adsorption Performance and Mechanisms

## TL;DR

This paper introduces a new nanocomposite material that efficiently removes mercury from water, offering a promising solution for environmental protection.

## Contribution

The novelty lies in the synthesis of sulfur-modified chitosan nanocomposites with enhanced mercury adsorption performance.

## Key findings

- The nanocomposites achieved over 95% mercury removal efficiency under optimized conditions.
- Adsorption followed a pseudo-second-order kinetic model and Langmuir isotherm, indicating monolayer adsorption.
- Optimal conditions varied slightly between the two nanocomposite types, with pH and contact time being critical factors.

## Abstract

In this work, pCh-MWCNTs@Ag-TiO2/S and pCh-MWCNTs@Ag-TiO2 nanocomposites were synthesized through a combined phosphorylation and cross-linked polymerization method. The materials were thoroughly characterized using several analytical techniques, including SEM/EDS, FTIR, TGA, and BET analysis. SEM images revealed that the pCh-MWCNTs@Ag-TiO2/S nanocomposite displayed a smooth, flake-like morphology with spherical, dark greenish particles. EDS analysis confirmed the presence of Si, S, P, and Ag as prominent elements, with Ti, C, and O showing the most intense peaks. The TGA curves indicated significant weight loss between 250–610 °C for pCh-MWCNTs@Ag-TiO2 and 210–630 °C for pCh-MWCNTs@Ag-TiO2/S, corresponding to the decomposition of organic components. FTIR spectra validated the existence of functional groups such as hydroxyl (-OH), carboxyl (-COOH), and carbonyl (-C=O) on the surface of the nanocomposites. Following characterization, the materials were evaluated for their capacity to adsorb Hg2+ at parts-per-billion (ppb) concentrations in contaminated water. Batch adsorption experiments identified optimal conditions for mercury removal. For pCh-MWCNTs@Ag-TiO2, the best performance was observed at pH 4, with an adsorbent dose of 4.0 mg, initial mercury concentration of 16 ppb, and a contact time of 90 min. For pCh-MWCNTs@Ag-TiO2/S, optimal conditions were at pH 6, a dosage of 3.5 mg, the same initial concentration, and a contact time of 100 min. Each parameter was optimized to determine the most effective conditions for Hg2+ removal. The nanocomposites showed high efficiency, achieving more than 95% mercury removal under these conditions. Kinetic studies indicated that the adsorption process followed a pseudo-second-order model, while the equilibrium data aligned best with the Langmuir isotherm, suggesting monolayer adsorption behavior. Overall, this research highlights the effectiveness of sulfur-modified chitosan-based nanocomposites as eco-friendly and efficient adsorbents for the removal of mercury from aqueous systems, offering a promising solution for water purification and environmental protection.