Recent advances in surfactant-functionalized materials as adsorbents for enhanced remediation of synthetic dyes: A review

Abstract

Background

Adsorption is one of the most commonly applied techniques for the elimination of a variety of synthetic dye pollutants to ensure a safe and healthy aquatic environment. For this purpose, different materials have been adopted as adsorbents. However, some of these materials show a low capacity against specific dyes, and the relatively high capacity of other materials needs to be further improved. Several studies have shown that the surfactant modification can be successfully applied to achieve this goal.

Method

This review article addresses the surfactant treatment and characterization of different materials like clay, zeolite, chitosan, biomass, activated carbon, and biochar. The application of surfactant-modified adsorbents against a variety of synthetic dye contaminants with a focus on the isotherm, kinetics, thermodynamics, and mechanisms, as well as the dependence of adsorbent performance on different variables including inlet dye amount, solution pH, adsorbent dosage, and temperature, is considered. The reuse of exhausted adsorbents after regeneration by different eluents is also discussed.

Significant Findings

Surfactant-modified adsorbents display enhanced performance against dyes, mainly through the enhancement of functionality and, in some cases, the development of pore characteristics. The highest uptakes of the most widely studied dyes in terms of methylene blue, followed by congo red, crystal violet, methyl orange, and malachite green are reported as 740.74, 2192.0, 956.20, 567.26, and 1972.54 mg/g, respectively. The Langmuir isotherm and pseudo-second order kinetics equation provide the best representation of the adsorption data. The adsorption mechanism primarily involves electrostatic and hydrophobic contacts. Alcohols and alkalis are both often and successfully used to renew exhausted adsorbents. This review offers insights into recent advances in surfactant modification as an eco-friendly, flexible, and efficient technique for the enhancement of adsorption performance against dyes.