Eco-Friendly Multifunctional (TiO₂/CoFe₂O₄)‑Biochar Nanocomposite for Arsenate Removal under Alkaline Conditions:...

Titanium dioxide-cobalt ferrite functionalized sugarcane bagasse biochar (SBC/TiO₂-CoFe₂O₄) was developed as a multifunctional adsorbent for arsenate [As-(V)] removal from water. While numerous binary TiO₂-biochar or magnetic biochar systems have been reported, limited studies have explored the synergistic integration of both TiO₂ and CoFe₂O₄ on a biochar matrix, particularly for arsenate removal under alkaline conditions. The material was synthesized via the sol-gel approach using sugarcane bagasse biochar pyrolyzed at 450 °C. Its adsorption performance toward arsenate was systematically evaluated at pH 8.5, selected due to its relevance to alkaline arsenic-contaminated groundwater and its proximity to the point of zero charge (PZC ≈7.8) of the composite. Surface and structural analyses using FTIR, SEM, and EDS provided evidence for the successful deposition of TiO₂-CoFe₂O₄ particles onto the biochar matrix. Under the optimized adsorption conditions (0.1 g adsorbent, initial As-(V) concentration of 2 mg L^-1), the composite achieved an experimental equilibrium adsorption capacity of 0.39 mg g^-1, while 87.3% arsenic removal was obtained after 24 h of contact time. The adsorption kinetics followed the pseudo-second-order model. Nonlinear isotherm fitting indicated best overall agreement with the Redlich-Peterson model (R ² = 0.669, AIC = -18.32), consistent with adsorption on an energetically heterogeneous composite surface; the Langmuir theoretical maximum capacity is reported as q _max = 0.526 mg g^-1 for isotherm characterization purposes. Thermodynamic analysis confirmed a spontaneous (ΔG° < 0), endothermic (ΔH° > 0), entropy-driven adsorption process. ICP-OES analysis of the regenerant further demonstrated minimal Fe, Co, and Ti release (≤0.055% of the nominal metal content over four regeneration cycles), confirming high structural stability during repeated reuse. Overall, the SBC/TiO₂-CoFe₂O₄ composite demonstrated promising multifunctionality by combining moderate adsorption capacity, magnetic recoverability, and reusability under environmentally relevant dilute conditions rarely tested in prior composite-biochar studies, highlighting its laboratory-scale potential as a sustainable biochar-based system for arsenate remediation in alkaline aqueous environments. Although phosphate competition experiments confirmed the expected inhibitory effect of competing oxyanions, further evaluation under complex natural groundwater conditions is warranted prior to field application.