Biopolymeric templates for green synthesis of nanoporous silica adsorbents for wastewater remediation

Porous silica nanostructures were synthesized using various polysaccharides including Tragacanth gum, Guar gum, Arabic gum, Xanthan gum, and Chitosan as environmentally friendly soft templates. The role of biopolymer chemical structure and topology of supramolecular network on the formation of porous silica structures and its effect on the heavy metal adsorption was investigated. The adsorption capacity of the synthesized materials was evaluated for the removal of Cu²⁺, Pb²⁺, Cd²⁺, and Ni²⁺ ions. Among the ions investigated, Cu²⁺ showed the highest adsorption capacity (60.55 mg g -1 ). The adsorption potential is strongly influenced by adsorbent structure and metal behavior. Guar Gum showed the enhanced adsorption capacity due to the highest specific surface area and the largest total pore volume among all synthesized materials. Adsorption equilibrium were analyzed using nonlinear Langmuir, Freundlich, Temkin, and Sips isotherm models. The Freundlich and Sips models showed the best fitting performance, suggesting heterogeneous adsorption behavior associated with structurally diverse mesoporous silica surfaces. Thermodynamic analysis shows the spontaneous endothermic adsorption process which is predominantly governed by chemisorption in Guar gum and physisorption interactions in other absorbances. Two-Way Analysis of Variance shows the selective affinities of specific adsorbents toward particular metal ions. The synthesized adsorbents also exhibited good regeneration capability, maintaining stable adsorption performance during multiple adsorption–desorption cycles. The obtained results indicate that the supramolecular organization and network topology of natural biopolymer templates play a decisive role in directing silica condensation and controlling the final porous architecture. The environmentally friendly synthesis strategy developed in this work provides an effective route for preparing high-performance mesoporous silica adsorbents for heavy metal removal from wastewater.