# High-Capacity Adsorption of a Cationic Dye Using Alkali-Activated Geopolymers Derived from Agricultural Residues

## TL;DR

A sustainable geopolymer made from agricultural waste effectively removes a harmful dye from water, offering a low-cost and efficient solution for wastewater treatment.

## Contribution

A novel geopolymer from agricultural residues shows high adsorption capacity and chemisorption mechanism for methylene blue dye removal.

## Key findings

- The geopolymer achieved a maximum adsorption capacity of 270.58 mg/g for methylene blue.
- The adsorption process followed the pseudo-second-order kinetic model, indicating chemisorption as the rate-limiting mechanism.
- The material demonstrated an 85.20% removal efficiency under optimal conditions.

## Abstract

A geopolymer, derived from agricultural waste, was used as an efficient, sustainable, and low-cost adsorbent of methylene blue, a recurrent industrial dye contaminant. The geopolymer was synthesized via a standard alkali activation process using wheat husk ash calcinated at 1050 °C. Adsorption capabilities were evaluated through batch kinetic experiments. The removal efficiency was determined by ultraviolet–visible spectrophotometry, and the adsorption kinetics were fitted to various models. The geopolymer demonstrated a maximum adsorption capacity of 270.58 mg/g for methylene blue, achieving a removal efficiency of 85.20% under optimal conditions. Kinetic analysis confirmed that the adsorption process is best described by the pseudo-second-order model. This suggests that chemisorption, which involves chemical bonding or electron exchange between the dye and the negatively charged aluminosilicate structure of the geopolymer, is the rate-limiting mechanism. This demonstrates that geopolymers are effective and promising adsorbents, valorizing an agricultural waste stream into a functional material for the efficient treatment of dye-polluted wastewater. The competitive capacity and favorable chemisorption mechanism position the geopolymer as a promising material for the remediation of dye-contaminated industrial effluents.