Wheat straw-core hydrogel spheres with polypyrrole nanotubes for the removal of organic dyes

Abstract

Straw biomass is an underutilized raw material, the use of which could make a significant contribution to sustainable development. Herein, wheat straw waste was regenerated into novel porous core-shell wheat straw-polypyrrole hydrogel spheres for the removal of dyes from wastewater. Adsorption experiments demonstrated that the hydrogel spheres had long-term structural and functional stability, and a high performance for the removal of the water-soluble model anionic dye eosin Y (EY). The maximum adsorption capacity of the hybrid spheres (520.2 mg/g) was 12 times greater than that of the wheat straw hydrogel sphere. Recycling experiments showed that it the initial adsorption capacity of 75.0% could be maintained after seven adsorption-desorption cycles, and the material could be recovered by simple filtration. The results from spectroscopic (FTIR, XPS) analysis, adsorption experiments and computational quantum mechanical modelling suggested that hydrogen bonds, π-π stacking and electrostatic forces, were involved in the removal of EY from aqueous solution. Interestingly, the hydrogel sphere exhibited enhanced adsorption at elevated temperature, and this could be attributed to the dynamic breaking of crosslinked hydrogen bonds in the hydrogel sphere and release of activated –OH. The results from this study provide a basis for the development of sustainable high-performance adsorption materials from wheat straw biomass for the removal of organic dyes from wastewater. It also provides a strategy to design adsorbents that work efficiently at elevated temperatures.