p-Nitrophenol degradation by heterogeneous Fenton's oxidation over activated carbon-based catalysts

Abstract

Activated carbons with different surface chemical properties were used as adsorbents or as catalysts for p-nitrophenol (PNP, 500 mg/L) removal by adsorption or wet peroxidation processes, respectively. The surface chemical properties of the support play an important role in PNP adsorption and in the catalytic performance of the respective iron-supported catalysts. Among the series of materials prepared, which were characterized by several techniques (nitrogen adsorption at -196 degrees C, elemental analysis, temperature programmed desorption, pH at the point of zero charge and temperature programmed reduction), the support doped with melamine, as nitrogen precursor, and impregnated with iron (sample Fe/ACM), presents the best catalytic performance. This catalyst is stable during reutilization in five consecutive runs, without any iron leaching. A relationship between PNP removal after 1 h of reaction and the oxygen and nitrogen amount present in the carbon materials was established. A parametric study was carried out to evaluate the effect of the main operating conditions, namely temperature, pH, hydrogen peroxide concentration and catalyst dose in PNP and total organic carbon (TOC) removal. Under the best operating conditions, i.e., pH =3.0, T=50 degrees C, [H2O2] =1.0 g/L (concentration below the stoichiometric amount for total degradation) and [Fe/ACM] = 2.0 g/L, 94, 90 and 86% of PNP, TOC and chemical oxygen demand (COD) removals were achieved after 2 h of Fenton's reaction, respectively, generating a non-toxic effluent with enhanced biodegradability.