Revealing the potential of functionalized FeS2 composites as efficient photocatalysts for improved removal of cationic and anionic dyes

This study investigates the enhancement of pyrite (FeS₂) through functionalization with silanol (SiO₂) and silanol-amino (SiO₂-NH₂) groups to optimize its adsorption and photocatalytic performance for removing cationic (methylene blue, MB) and anionic (methyl orange, MO) dyes. Functionalized core-shell composites, Pyrite@SiO₂ and Pyrite@SiO₂-NH₂, were synthesized via a sol-gel process using tetraethyl orthosilicate (TEOS) and 3-aminopropyl triethoxysilane (APTS). Comprehensive characterization through XRF, XRD, FT-IR, TEM, UV–vis DRS, and BET analysis revealed spherical nanoparticles with smooth surfaces and uniform SiO₂/SiO₂-NH₂ coatings (200–300 nm thick). Functionalization significantly increased the specific surface area from 0.64 m 2 /g (raw pyrite) to 3.21 m 2 /g, enhancing pollutant interaction sites. Adsorption dominated over photocatalytic degradation under both UV and dark conditions, with maximum capacities of 36.5 mg/g (MO) and 34.0 mg/g (MB) at 298 K. Kinetic studies aligned with the pseudo-second-order model, while mass transfer analysis identified intraparticle diffusion as the primary mechanism. Although UV irradiation marginally improved dye removal, surface charge modification via SiO₂-NH₂ groups notably enhanced MO adsorption through electrostatic interactions. These findings underscore pyrite's potential as a cost-effective, efficient adsorbent for wastewater treatment, with surface functionalization offering a strategic avenue to tailor affinity for target pollutants, prioritizing adsorption over photocatalytic approaches.