# Functionalized Silica Fume for Efficient Cd2+ Removal from Aqueous Solutions

## TL;DR

This paper introduces a low-cost method to functionalize silica fume for efficiently removing Cd2+ ions from water.

## Contribution

A novel direct-functionalization strategy is proposed to utilize silica fume for Cd2+ adsorption without altering its structure.

## Key findings

- The functionalized silica fume (TACA-APTES-SF) effectively removes Cd2+ ions with high efficiency over five reuse cycles.
- Adsorption mechanisms involve electrostatic and coordination reactions between functional groups and Cd2+ ions.
- The adsorption process follows pseudo-second-order kinetics and the Langmuir isotherm model, indicating chemical monolayer adsorption.

## Abstract

The rapid development of the silicon industry has led to the massive production of silica fume (SF), while its improper disposal poses environmental risks and represents a waste of resources. Unlike conventional methods that require dissolution and high-pressure treatment, this study pioneers a low-cost direct-functionalization strategy that preserves the inherent microsphere structure of SF, using calcination for carbon removal and activation for surface hydroxylation. The activated SF was synthesized into TACA-APTES-SF by reacting with 3-aminopropylethoxysilane (APTES) and 1,3-Thiazole-2-carbaldehyde (TACA). SEM, FT-IR, and XPS were used to characterize these samples, revealing amino groups and sulfur groups grafted onto the SF surface successfully. The adsorbent demonstrated highly effective adsorption of Cd2+ ions. Throughout five reuse cycles, TACA-APTES-SF maintained a high removal efficiency for Cd2+ in aqueous solution. The adsorption kinetics confirmed to the pseudo-second-order model, while the adsorption isotherm results aligned with the Langmuir model, which collectively suggests that the adsorption process was chemical and monolayer in nature. Comparative XPS and FT-IR analyses of TACA-APTES-SF and TACA-APTES-SF-Cd indicated that adsorption mechanisms involved electrostatic and coordination reactions between hydroxyl-, amino-, and sulfur-containing groups and Cd2+ ions. This study therefore proposes a straightforward and cost-effective approach for the high-value utilization of SF.