Study of Morphology Effect on Polydopamine-based Adsorbents for Dye Removal

Abstract

Dyes are one of the most hazardous materials in industrial wastewater, which pose severe problems to humans and the ecosystem. Adsorption is a promising dye removal technique due to its low cost, high efficiency, and facile operation. However, there are some drawbacks of current adsorbents such as low adsorption capacity, lack of capability for diverse dyes, and regeneration issues which limit their practical application. Therefore, it is important to develop high-performance adsorbents to meet the increasing demand for fresh water.

In this work, polydopamine-based adsorbents with three different morphologies including, nanotubes, hollow spheres, and mesoporous structures were developed through template-based methods and emulsion induced assembly processes. The polydopamine templates with different structure were further functionalized by attaching magnetic particles on the surface and coating with polydopamine/polyethylenimine. The introduction of polyethylenimine increases the positive charge on the surface, allowing for adsorption of anionic dyes. Moreover, the add-layer served as a protective coating immobilized magnetic particles, which contributes to the good magnetic response of these adsorbents.

The adsorption performance of the as-prepared adsorbents were evaluated. Methylene blue and methyl orange are used as model cationic and anionic dyes, respectively. Three kinetic models and five adsorption isotherm models were evaluated. The results indicated that the polydopamine-based adsorbents possessed good adsorption capacity for both cationic and anionic dyes. Adsorption kinetics fit a pseudo-second-order model, and the adsorption equilibrium data fitted well by Freundlich isotherm model. The thermodynamic evaluation indicated that the adsorption is an endothermic and spontaneous process. Moreover, the adsorbents exhibit excellent regeneration property after five adsorption-desorption cycles. The adsorption mechanism was attributed to the electrostatic interaction, π-π stacking and hydrogen bonding.