Selenate adsorption on pre-coordinated Fe3+-silane complexes grafted on mesoporous silicas

Area of Science:

• Materials Science
• Environmental Chemistry
• Nanotechnology

Background:

• Developing efficient adsorbents for removing toxic selenate from water is crucial.
• Mesoporous silica materials offer high surface areas for functionalization.
• Iron-based adsorbents show promise for selenate removal.

Purpose of the Study:

• To synthesize and characterize novel iron-functionalized mesoporous silicas for selenate adsorption.
• To investigate the effect of silica type and iron loading on adsorption capacity.
• To elucidate the adsorption mechanism and structural changes upon selenate binding.

Main Methods:

• Grafting N-[2-(aminoethyl)-3-aminopropyltriethoxysilane] (AEAPTES) onto MCM-41, SBA-15, and M7D silica supports.
• Varying the AEAPTES to iron ratio (n=1, 2, 3) to create different iron coordination environments.
• Adsorption isotherm studies to determine selenate uptake capacity.
• X-ray absorption spectroscopies to analyze the structure of adsorption sites and Se-Fe bonding.

Main Results:

• Synthesized nine Fe(en)n-silica adsorbents with varying iron loadings and silica substrates.
• Fe(en)2-SBA-15 exhibited the highest selenate adsorption capacity (1.1 mmol/g).
• Adsorption capacity was influenced by silica structure and iron coordination, with M7D showing saturation at lower Se/Fe ratios.
• X-ray absorption spectroscopy confirmed distorted coordination structures and Se-Fe bond formation after adsorption.

Conclusions:

• The structure of mesoporous silica significantly impacts the adsorption of selenate by iron-functionalized materials.
• Optimized iron loading and coordination on SBA-15 yield superior selenate removal efficiency.
• The concave surface of mesoporous silicas may stabilize the coordination structure essential for adsorption.
• These findings provide insights for designing advanced materials for selenium remediation.