Engineering of balanites aegyptiaca-derived SrO@biochar and SrO@biomass for nitrophenol removal from wastewater

Abstract

Abstract This study reports a sustainable route for the synthesis of an eco-friendly adsorbent derived from Balanites aegyptiaca (Laloub) decorated with strontium oxide nanoparticles (SrO NPs) for the removal of ortho-nitrophenol (o-NP) from water. The plant extract was used as a reducing agent for the green synthesis of SrO-NPs, while the plant branches were used to prepare biomass (BM) and biochar (BC). The obtained composites (SrO-BM and SrO-BC) were characterized by XRD, FTIR, and SEM, that revealed that SrO NPs crystallinity, and confirmed the presence of functional oxygenated groups, with a uniform distribution of SrO-NPs on the BM and BC surfaces. A comparative study has been executed to evaluate whether converting BM into BC enhances its adsorption performance or represents wasted energy. The experimental results reflected that SrO-BC exhibited higher adsorption capacity of 335.57 mg/g toward o-NP compared with 234.74 mg/g for SrO-BM at optimum conditions of pH 5, 25 °C, and 0.5 g/L dosage. Adsorption isotherm models showed that the adsorption onto SrO-BM followed the Langmuir model, while that for SrO-BC followed Freundlich model with a pseudo-second-order behavior for both. Mechanistic insights suggested electron donor–acceptor interactions, hydrogen bonding, π–π stacking, and coordination bonding as governing pathways. Reusability tests confirmed adsorbent stability since they retained more than 80% of their removal efficiency after five cycles. These findings provide a green and eco-friendly route to fabricate efficient and reusable adsorbents derived from Balanites aegyptiaca with a superior adsorption potential of SrO-BC for sustainable wastewater treatment.