Comparative Study of the Adsorption Properties of Silicon Oxide in the Removal of Organic Pollutants and Heavy Metals

Abstract

Removal of mixed contaminants, including heavy metal ions and aromatic hydrocarbons, from water systems requires the development of efficient and selective adsorbents. This study presents a comparative investigation of the adsorption properties of silicon oxide with different purity levels (80% and 100%) toward Cu²⁺ ions and aromatic hydrocarbons (benzene, ethylbenzene, m, p-xylenes). Adsorption kinetics were examined, and the porous structure of the materials was characterized using low-temperature nitrogen adsorption-desorption analysis.
The results revealed a paradoxical advantage of technical silicon dioxide (80%) over the high-purity sample (100%) in copper ion adsorption. The maximum sorption degree reached 36.90% compared to 32.37%, while equilibrium was achieved within 10 min versus 30 min, respectively. In contrast, high-purity SiO₂ demonstrated superior selectivity toward aromatic hydrocarbons, particularly benzene, with removal efficiency increasing from 17% to 79% within 40 min, accompanied by partial desorption of bulkier molecules.
Pore structure analysis showed a 4.75-fold reduction in micropore volume after purification, together with significant redistribution of mesopores: pores in the 5-10 nm range disappeared, while a new maximum emerged at 40-60 nm. Benzene adsorption on technical SiO₂ followed a pseudo-second-order kinetic model (R² = 0.992), indicating a chemisorption mechanism. The findings establish a clear relationship between pore architecture and adsorption selectivity, enabling rational adsorbent selection depending on pollutant type and supporting cost-effective design of adsorption materials without additional feedstock purification.