Mechanisms of silver capture, reduction, and release in propyl carboxylic acid-functionalized SBA-15

The growing contamination of aquatic systems by silver pollutants necessitates the development of advanced, sustainable remediation strategies. This study investigates Ag + sequestration using propyl-carboxyl-functionalized SBA-15 (1.25–20 % COOH), focusing on how the density of functional groups governs structure, adsorption, and reduction. PALS and TEM revealed that low functionalization (1.25–5 %) enhances microporosity, whereas higher COOH contents (10 % and 20 %) expand mesopores. UV–Vis and FL-AAS confirmed that adsorption capacity depends on both surface chemistry and pore accessibility. Kinetic modeling indicated multistage sorption in highly functionalized samples, involving diffusion and surface adsorption. XPS results showed partial Ag + reduction, with metallic fractions of ∼8.5 %, 64.4 %, and 73.7 % for the 2.5 %, 10 %, and 5 % COOH samples, respectively. LAXRD showed preserved mesostructural ordering, slightly weakened at lower COOH density, while TEM confirmed in-pore nucleation of reduced Ag 0 nanoparticles. Despite having fewer COOH sites, the 2.5 % COOH material exhibited comparable sorption to higher density carboxyl-functionalized SBA-15 as a result of the presence of larger mesopores and accessible silanols that enhanced Ag + binding. Raman spectra revealed both unidentate/bidentate carboxylate coordination and silanol interactions. Desorption studies distinguished single-step surface release (10 % COOH) from dual-stage surface/pore release at lower functionalization. Overall, the results highlight the cooperative role of pore geometry and functionalization in controlling Ag + adsorption, reduction, and release, positioning COOH-modified SBA-15 as an efficient, eco-friendly adsorbent. • Engineered SBA-15 filters target silver pollutants in water. • COOH functionalization tunes adsorption: low density favors surface adsorption, high density promotes in-pore nanoparticle formation. • Tunable desorption allows sustainable silver recovery and reuse.