Degradation of diclofenac sodium using Fenton-like technology based on nano-calcium peroxide.

A nano-calcium peroxide (nCaO) powder with a purity of 89.1% was prepared using an improved traditional method. Then, the as-prepared nCaO was used as the source of hydrogen peroxide (HO) for the Fenton-like degradation of diclofenac sodium (DCF). The results showed that nCaO performed better for DCF removal when compared to nCaO prepared by a conventional method and commercial calcium peroxide (CaO). Further experimental results indicated that 97.5% of DCF could be removed in 180 min at a nCaO/Fe-EDTA/DCF molar ratio of 16/8-8/1, which was more efficient than in the HO/EDTA-Fe/DCF and nCaO/Fe/DCF systems. The best removal rate of DCF was at pH 6.0, unlike previous claims that stated that the lower the pH in the buffer system, the better the degradation of DCF. In addition, the influence of water quality parameters, such as Cl, NO, SO, HCO, and humic acid (HA), on DCF removal were evaluated. A free radical masking experiment revealed the existence of hydroxyl radical (OH), superoxide radical (O) and singlet oxygen (O), and indicated that the degradation of DCF was mainly due to oxidation caused by OH. Electron paramagnetic resonance (EPR) studies for different systems and different active oxygen species were carried out, and it was further confirmed that OH radicals have high intensity in the Fenton-like system based on nCaO. EPR results also showed that the addition of EDTA can promote the production of OH. According to the identification of the dominant reactive species and GC-MS, the possible theoretical DCF degradation pathways were proposed.