Development of kaolinite supported ferric oxalate heterogeneous catalyst for degradation of 4-nitrophenol in photo-Fenton process

• Phosphoric acid treatment of kaolin clay
• Incorporation of ferrioxalate complex into the treated kaolin clay
• Characterization of the treated kaolin and the kaolin supported catalyst
• Degradation of 100 ppm 4-NP simulated wastewater in 4 min degradation time
• Development of kinetic model for the mineralization of 4-nitrophenol

Ferric oxalate catalyst supported on phosphoric acid treated kaolin (ATKaol) was prepared and tested on the degradation of 4-nitrophenol (4-NP). The X-ray fluorescence (XRF) and Brunauer–Emmett–Teller (BET) characterization results showed drastic distortions in the raw kaolin (Kaol) crystalline structure and an increase in specific surface area (SSA) from 18.78 to 166.12 m2 g− 1 after acid treatment. The incorporation of Fe was confirmed with Fourier transformed infra-red spectroscopy (FTIR), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) results. The degradation of 4-NP without UV was slower compared to when UV was used. There was no appreciable degradation in the absence of either catalyst or hydrogen peroxide (HP). The acid treated kaolinite catalyst (ATKaolCat) exhibits high catalytic activity without pH adjustment degrading 99% of 4-NP (100 ppm) in 4 min using 2.0 g ATKaolCat and 20% excess HP at 40 °C. The reusability study shows 9.4% decrease in efficiency after 5 rounds. The kinetic model developed showed good agreement with the experimental data. The model showed that ATKaolCat has higher selectivity for direct oxidation of 4-NP to mineralized products compared to oxidation via intermediates. These qualities make the catalyst promising in 4-NP degradation.