Removal of Formaldehyde from Aqueous Solution by Hydrogen Peroxide

Formaldehyde (HCHO) is a common chemical raw material and one of the major constituents in wastewaters from the production of chemical products. HCHO in wastewater is mainly removed by adsorption, biodegradation, and advanced oxidation. The objective of this study is to investigate transition metal oxides (Fe2O3, Co2O3, Ni2O3, CuO, ZnO) without pretreatment for enhancing the oxidation of HCHO. The oxidation of HCHO in wastewater by hydrogen peroxide using transition metal oxides as catalysts is studied. The concentration of HCHO in waste water was measured by indirect method. HCHO reacts with 2,4-dinitrophenylhydrazine in the presence of acetic acid to produce 2,4-dinitrophenylhydrazone. 2,4-Dinitrophenylhydrazone increases in proportion to the concentration of HCHO. The HCHO removal rate is determined by quantitative analyses of 2,4-dinitrophenylhydrazone using high-performance liquid chromatography (HPLC). The catalytic oxidation experiments are performed in test tubes at 25 degrees C. The results indicate that the catalytic activity of the transition metal oxides towards HCHO oxidation is very different. The removal rate of HCHO was attributed to the number of hydroxyl radicals formed in the system. CuO shows higher catalytic activity in the oxidation of HCHO. The effect of the temperature, the mole ratios of hydrogen peroxide to HCHO, and the amount of CuO on the removal rate of HCHO were studied. Results of experiments show that the HCHO is almost wholly oxidized (>98%) at the best conditions (molar ratio of hydrogen peroxide to HCHO is 2.5, CuO is 0.06 g, 25 degrees C for 15 min). CuO also offers the advantages of simple recovery from the treated solution and repeated use. It is hypothesized that CuO can transform hydrogen peroxide into active oxygen that has higher oxidation activity. But, the rate of formation and removal of free radicals HO center dot is very fast in the presence of transition metal oxides (Fe2O3, Co2O3, Ni2O3, ZnO).