Enhanced Photocatalytic Degradation of Organic Pollutants Using Fe-Doped Illite Clay under Visible Light

The contamination of water by persistent organic pollutants represents a critical environmental challenge, requiring efficient and sustainable remediation strategies. In this study, an Fe-doped illite clay photocatalyst (Fe@illite) was synthesized via a sol–gel-assisted impregnation method and evaluated for the degradation of phenol under visible light irradiation.

The structural and optical properties of the catalyst were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectroscopy, confirming successful iron incorporation into the illite matrix, improved crystallinity, and enhanced absorption in the visible region. Photocatalytic experiments were conducted at an initial phenol concentration of 20 mg·L⁻¹. The effects of key operational parameters were systematically investigated. Increasing catalyst dosage from 0.5 to 1.5 g·L⁻¹ enhanced degradation efficiency from 52% to 91% after 120 min, while extreme pH conditions negatively affected performance. Optimal degradation (≈93%) was achieved at neutral pH and 25 °C.

To elucidate the degradation mechanism, radical scavenger tests were performed. The addition of isopropanol and benzoquinone significantly reduced degradation efficiency to 48% and 55%, respectively, indicating that hydroxyl radicals (•OH) and superoxide radicals (O₂•⁻) are the dominant reactive species. The mechanism involves photoinduced electron–hole pair generation on the Fe-modified illite surface, followed by the formation of reactive oxygen species responsible for phenol oxidation.

Reusability tests demonstrated good catalyst stability, with only a slight decrease in efficiency from 93% to 85% after five consecutive cycles. Furthermore, total organic carbon (TOC) removal reached 68%, indicating partial mineralization and reduced environmental toxicity.

These findings demonstrate that Fe-doped illite clay is a promising, low-cost, and environmentally friendly photocatalyst for wastewater treatment under visible light irradiation.