# Synthesis of Phosphorus-Modified Magnetic Chitosan and Its Application for Cr(VI) Removal from Aqueous Solution

## TL;DR

A new magnetic chitosan material was created to efficiently remove chromium from water, offering stability and reusability.

## Contribution

A novel phosphorus-modified magnetic chitosan adsorbent was synthesized for enhanced Cr(VI) removal.

## Key findings

- PCC/Fe3O4 achieved a saturated adsorption capacity of 23.6 mg/g for Cr(VI) removal.
- The material showed 86% efficiency after 5 days and over 90% after five cycles.
- Electrostatic attraction, redox reaction, and ligand exchange were identified as main removal mechanisms.

## Abstract

Traditional Fe-based materials are limited for Cr(VI) remediation due to low reactivity, oxidation, and aggregation. Although chitosan coatings improve stability, they hinder efficient liquid-solid separation. To overcome this, a novel phosphorus-modified magnetic chitosan adsorbent (PCC/Fe3O4) was synthesized using Fe3O4 as the core and tetrakis hydroxymethyl phosphonium sulfate (THPS) as a cross-linking agent. The composite exhibited a high surface area (20.67 m2/g) and superparamagnetism, enabling easy magnetic recovery. PCC/Fe3O4 demonstrated superior Cr(VI) removal capabilities compared to unmodified chitosan and raw Fe3O4, achieving a saturated adsorption capacity of 23.6 mg/g under the selected conditions (pH 6, initial Cr(VI) concentration of 1 mg/L), which were chosen to balance adsorption efficiency, adsorbent stability, and environmental relevance. The main removal mechanism includes electrostatic attraction, redox reaction, and ligand exchange. PCC/Fe3O4 maintained 86% efficiency after 5 d aging and >90% efficiency after five cycles, demonstrating excellent stability and reusability and strong potential for practical environmental remediation.