Valorization of Sargassum wightii through biochar production: development, characterization, and potential applications

The valorization of marine biomass into functional materials offers a sustainable strategy for water purification within a circular bioeconomy framework. In this study, Sargassum wightii biomass was converted into biochar through controlled pyrolysis at 350, 500, and 600 °C, and the resulting materials were evaluated for water treatment applications. Increasing pyrolysis temperature resulted in reduced biochar yield but enhanced alkalinity and surface reactivity, driven by progressive carbonization and mineral enrichment. The biochars produced at higher temperatures exhibited favorable surface characteristics, including increased negative surface charge and mineral-associated active sites, which are advantageous for contaminant removal. The practical applicability of the biochars was demonstrated through adsorption studies using the pyrethroid pesticides cypermethrin and deltamethrin in spiked water systems. All biochars showed very high removal efficiencies, with biochar produced at 500 °C achieving the lowest residual pesticide concentrations, followed closely by biochar produced at 600 °C, while biochar produced at 350 °C showed comparatively lower performance. The enhanced adsorption at higher pyrolysis temperatures is attributed to improved pore development and aromatic carbon structures that promote strong hydrophobic and π–π interactions with pesticide molecules. Overall, S. wightii–derived biochar, particularly when produced at approximately 500 °C, demonstrates strong potential as a low-cost and sustainable adsorbent for pesticide-contaminated water treatment.