Preparation of a sustainable bioadsorbent by modifying filter paper with sodium alginate, with enhanced mechanical properties and good adsorption of methylene blue from wastewaters

Treatment of dyes in wastewaters is necessary to ensure environmental protection. In this work, sodium alginate (SA) was utilized for modifying filter paper (FP) through Williamson reaction with epichlorohydrin, and its purpose was to meet global needs of sustainable development, while ensuring good mechanical properties of the adsorbent in the aqueous phase and good interaction with the dye molecules. The obtained composites were evaluated for both tensile strength and adsorbability. The results of tensile tests demonstrated that the composites prepared with 4 wt% SA exhibited outstanding wet mechanical performance with the tensile strength and elastic modulus values of 1.84 and 126 MPa, respectively, about 25 times and 10 times higher compared to original FP. Adsorption experiments showed that the maximum adsorption capacity of the composites for methylene blue (MB) was 503.8 mg g⁻¹, compared to only 88.0 mg g⁻¹ for FP. Freundlich and Scatchard model for isothermal study of the composites demonstrated that the MB adsorption occurred on a heterogeneous surface by multilayer sorption, and its kinetic study revealed that the adsorption of MB followed the pseudo-second-order kinetic model. Furthermore, the filtration performances for the composites and original FP showed that the percentage removal of MB on FP was only 36.3%, while that of the composite was 93.9%. The above results suggested that the prepared composites not only had good mechanical properties but could also adsorb the MB molecules efficiently from the aqueous phase. Therefore, the preparation of this bioadsorbent would be useful for environmental protection and sustainable development of resources.