Removal of 4-chlorophenol by visible-light photocatalysis using ammonium iron(II) sulfate-doped nano-titania

Halogenated aromatic compounds are toxic and carcinogenic. This is the case of 4-chlorophenol (4-CP), a priority pollutant found in large amounts in industrial wastewater effluents from pharmaceutical, dye, pulp and paper industries. Long term exposure to 4-CP even at low-concentration is associated to endocrine disruption. Photocatalysis is a promising advanced oxidation process that attains complete degradation of organic pollutants. The use of UV lamps undermines actual photocatalysis application due to the electrical energy requirements. In this frame, the development of visible light photoactive catalysts can overcome these challenges allowing the implementation using affordable light sources like light emitting diodes (LEDs) or natural sunlight. This work is to present the synthesis and use of an alternative photocatalyst that provided eight-fold increase on 4-CP degradation in comparison to commercial TiO₂ Degussa P-25. Almost complete removal (99.20%) was achieved with synthesized Fe/N/S-doped TiO₂ at 1.0 g L⁻¹ of photocatalyst dose and pH 7.0 for treating 10 ppm of 4-CP.The first-order rate constant, k_LH, and Langmuir adsorption constant, K_LH, were calculated with values of 0.429 min⁻¹ and 2.326 ppm⁻¹, respectively. The Fe/N/S-TiO₂. photocatalysts showed an excellent stability maintaining their performance during four cycles of recovery/reuse.