Effect of thiourea addition on PMS activation by NiFe₂O₄ for dye degradation

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have attracted considerable attention as an effective method for removing refractory organic pollutants through the generation of reactive species such as SO₄^･－ and ･OH. Among the transition metal oxides used for PMS activation, NiFe₂O₄ exhibits high stability and excellent magnetic properties. In this study, thiourea was introduced during the synthesis of NiFe₂O₄, and its effect on PMS activation for the degradation of Reactive Yellow 86 (RY86) was investigated.

The catalysts were synthesized using hydrothermal and calcination methods. Ni(NO₃)₂·6H₂O, Fe(NO₃)₃·9H₂O and citric acid were dissolved in 30 mL of water, followed by the addition of thiourea. The resulting mixture was hydrothermally treated at 160 °C for 16 h, and the obtained precursor was vacuum-dried at 60 °C and calcined at 400 °C for 2 h to obtain thiourea-added NiFe₂O₄ (NFO-TU). For comparison, pristine NiFe₂O₄ (NFO) was synthesized under the same conditions without thiourea addition. The catalytic activity of the prepared catalysts was evaluated through the degradation of RY86 in the presence of PMS. After adsorption equilibrium was achieved, PMS was added to initiate the degradation reaction. The degradation of RY86 was monitored using UV-vis spectrophotometry, and the degradation efficiency was determined from the change of absorbance.

When NFO was used, the degradation efficiency of RY86 reached 18.3% after 60 min of reaction. In contrast, NFO-TU exhibited significantly enhanced catalytic activity, achieving a maximum degradation efficiency of 53.1%. These results suggest that thiourea addition modified the catalyst structure and promoted more efficient PMS activation, leading to improved degradation performance.