Tetracycline degradation in aquatic environment by highly porous MnO2 nanosheet assembly

Highly porous MnO2 nanosheets were prepared from MnCl2 and KMnO4 following a modified co-precipitation route. The material was characterized by XRD, FTIR, TEM, SEM, XPS and BET surface area analysis. The MnO2 material is microporous having surface area 301 m2/g and pore diameter 0.364 nm, and is amorphous in nature. The SEM images show the formation of spherical assembly and TEM images indicate the presence of fine nanosheets within it. The porosity and surface area, as well as the oxidizing property of the as-prepared nano MnO2 have made the material a powerful oxidant for tetracycline hydrochloride (TCH) degradation in aqueous medium under ambient condition. The degradation under various operational conditions was studied and the effects of pH, initial TCH concentration, MnO2 dose, air/O2, temperature, and scavengers were examined. At lower pH, the degradation was more favored. During the oxidative degradation of TCH, slight leaching of Mn2+ was observed. The degradation followed first order rate model in unbuffered condition and second order model under buffered media. About 55% TCH degradation and ∼44% COD removal was observed on 20-min reaction, under unbuffered condition and at initial pH ∼ 4, with 50 mg/L TCH concentration and 1.0 g/L MnO2 dose. However, under similar condition, ∼75% degradation was possible under controlled pH (∼3.48). The material could be reused for two consecutive cycles with significant efficiency. The pharmaceutical products (hostacycline and terramycine, which belongs to TC group of antibiotics) were successfully degraded by the as-prepared nano MnO2 with good performance.