Removal of ammonia from aqueous solutions by catalytic oxidation with copper-based rare earth composite metal materials: catalytic performance, characterization, and cytotoxicity evaluation

Ammonia (NH3) has an important use in the chemical industry and is widely found in industrial wastewater. For this investigation of copper-based rare earth composite metal materials, aqueous solutions containing 400 mg/L of ammonia were oxidized in a batch-bed reactor with a catalyst prepared by the co-precipitation of copper nitrate, lanthanum nitrate and cerium nitrate. Barely any of the dissolved ammonia was removed by wet oxidation without a catalyst, but about 88% of the ammonia was reduced during wet oxidation over the catalysts at 423 K with an oxygen partial pressure of 4.0 MPa. The catalytic redox behavior was determined by cyclic voltammetry (CV). Furthermore, the catalysts were characterized using thermogravimetric analyzer (TGA) and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), which showed that the catalytic behavior was related to the metal oxide properties of the catalyst. In addition, the copper-lanthanum-cerium composite-induced cytotoxicity in the human lung MRC-5 cell line was tested, and the percentage cell survival was determined by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetra-zolium (MTS) analysis in vitro. No apparent cytotoxicity was observed when the human lung cells were exposed to the copper-lanthanum-cerium composite.