Direct synthesis of multiple heteroatoms functionalized mesoporous silica adsorbents from phosphate industry mining byproducts. Decontaminating water from Pb(ii) ions as an application case

Abstract

Mesoporous silicate materials (MSMs) exhibit tremendous intrinsic characteristics suitable for diverse adsorption-based processes. However, the challenges brought on by the lack of sustainable production methods pose obstacles to large-scale synthesis and deployment of the adsorbents. Moreover, most applications require further steps to functionalize pristine MSMs with metal doping or organic moieties. Herein, we show a direct assembly strategy for transforming phosphate industry mining byproducts into heteroatom functionalized MSMs. Utilizing a one-pot synthesis, multiatomic compositions comprising diverse atoms from the waste precursors are incorporated within the adsorbents' framework. Two types of phosphate mining waste (PMWs), red-PMW (denoted PMW1) and yellow-PMW (denoted PMW2), were used as precursors to synthesize four different MSMs, namely PMW1-MSM1, PMW1-MSM2, PMW2-MSM3, and PMW2-MSM4. These materials were synthesized to emulate the characteristics of the well-known SBA-15 and MCM-41 synthetic routes. Specifically, PMW1-MSM1 and PMW2-MSM3 mimic the structure of SBA-15, while PMW1-MSM2 and PMW2-MSM4 emulate MCM-41. The synthesized sorbents were characterized using various analytical techniques, XRD, SEM-EDX, ICP-OES, TEM, FTIR, TGA, N₂ and water vapor sorption analysis. Comprehensive characterization revealed the structural features and surface properties of the synthesized adsorbents, elucidating their heteroatom compositions and mesoporous architecture. The adsorbents demonstrated remarkable Pb(II) removal efficiency from aqueous solutions. The experimental data were well fitted with the Langmuir isotherm and pseudo-second-order kinetics models with a maximum Pb(II) adsorption capacity of ∼830 mg g⁻¹ (PMW1-MSM2) and ∼870 mg g⁻¹ (PMW1-MSM2). Notably, no significant reduction in adsorption efficiency was observed after four adsorption–desorption cycles. The primary mechanisms driving Pb(II) adsorption are likely electrostatic interaction, surface complexation, and ion exchange. This study not only shows the feasibility of valorizing phosphate industry byproducts but also illustrates the potential of waste-derived hetero-functionalized MSMs as sustainable environmental remediation solutions.