A polystyrene resin in situ supported PANI/Fe3O4 composite as a heterogeneous Fenton catalyst for the efficient degradation of tetracycline in water

Abstract

Tetracycline (TC) residue in water environments is a problem that needs to be solved. A heterogeneous Fenton catalyst shows excellent performance in TC degradation in water, but its use still faces challenges in terms of efficient recovery and reduction of catalyst loss. This paper reports the successful preparation of a ternary composite catalyst, polyaniline (PANI)/Fe₃O₄/ammoniated polystyrene resin (APS), by using the inexpensive and easily available polystyrene resin (PS) as a carrier after simple modification. We also used Fe₃O₄ and PANI, which were supported by coprecipitation and in situ polymerization, respectively. Under light conditions, PANI/Fe₃O₄/APS produced four active species (˙OH, ˙O₂⁻, ¹O₂, and h⁺) by activating H₂O₂. It removed 98.7% of TC (c₀ = 20 mg L⁻¹) from the solution at a rate of 0.03068 min⁻¹ within 2 h, showing exceptional catalytic activity. Compared with the catalyst Fe₃O₄/APS without PANI, the pseudo-first-order kinetic rate of PANI/Fe₃O₄/APS increased by 6.9 times. After seven cycles, the TC removal efficiency was still high (>80%), and the leaching amount of Fe was low (<0.26 mg L⁻¹). The degradation pathways of TC were analyzed by HPLC-MS and density functional theory (DFT). The degradation was found to involve a series of ring opening, oxidation, and defunctionalization reactions. We also filled a purification column with PANI/Fe₃O₄/APS to simulate an actual wastewater-application scenario. After continuous flow operation for 50 h, it can still remove 50% of TC, showing good catalytic persistence and stability. Overall, the catalyst has a very broad application prospect in the field of environmental remediation.