# Polyethyleneimine Modified Expanded Vermiculite-Supported Nano Zero-Valent Iron for Cr(VI) Removal from Aqueous Solution

## TL;DR

This paper introduces a new material for removing toxic chromium from water, combining nano iron and modified clay for efficient and reusable adsorption.

## Contribution

A novel amino-modified clay-supported nano iron composite for Cr(VI) removal with high efficiency and reusability is developed.

## Key findings

- The material achieved a maximum Cr(VI) adsorption capacity of 116.2 mg/g at pH 2 and 30°C.
- The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm model.
- The composite retained 40.1 mg/g adsorption capacity after four reuse cycles.

## Abstract

In order to develop an efficient, environmentally friendly heavy metal ions adsorbent, the amino-modified expanded vermiculite-supported nano zero-valent iron (nZVI@PEI/EVMT) was prepared by using polyethyleneimine (PEI) as the functional reagent and expanded vermiculite (EVMT) as the carrier. The characterization results of nZVI@PEI/EVMT confirm that the PEI modification did not destroy the crystal configuration of EVMT, and when nano zero-valent iron (nZVI) was successfully loaded onto the PEI/EVMT surface, the value of saturation magnetic field was 41.5 emu/g, which could be separated from solution with magnet. The performance of Cr(VI) adsorption onto nZVI@PEI/EVMT was studied, showing that the ideal mass ratio for nZVI@PEI/EVMT was 1:1, and the removal capacity was largest when solution pH was 2. After four adsorption–desorption cycles, the adsorption amounts remained 40.1 mg/g. The Cr(VI) adsorption onto nZVI@PEI/EVMT was more consistent with a pseudo-second-order kinetics equation. Isotherm adsorption data accord with the Langmuir model, which suggests that the adsorption was the monolayer, the maximum adsorption amount was 116.2 mg/g at 30 °C and pH 2, and the adsorption was spontaneous and endothermic. It was inferred that the adsorption mechanisms included electrostatic attraction, reduction, chemical complexation, and co-precipitation.