Efficient photocatalytic removal of N-nitrosamines from amine washing wastewater using bismuth tungstate

Abstract

The most mature and practical technology to reduce industrial CO2 emissions, the main contributor to global warming, is amine-based post-combustion CO2 capture. However, this results in amine degradation products that pose a threat to human health as well as marine life. To reduce the impact on human health and marine life, identifying and treating carcinogenic and mutagenic compounds like N-nitrosamines is extremely important. Photocatalysis, in particular, an advanced oxidation process which uses a UV light source and semiconductor catalysts is studied for the degradation of organic and inorganic pollutants. N-Nitrosodiethylamine (NDEA) is treated with strong reactive hydroxyl radicals generated by a bismuth tungstate (Bi2WO6) semiconductor under UV/visible irradiation. The Bi2WO6 was studied both in pure form and surface-modified forms using transition metal impregnation like Ag, Fe, Cu, and La. Various catalyst characterization techniques like Brunauer–Emmett–Teller (BET), X-ray diffraction analysis (XRD), UV–visible, and scanning electron microscopy–energy-dispersive X-ray (SEM-EDS) are used to study the surface textural and morphological properties of the catalyst. Furthermore, the effect of pH of the solution, catalyst dosing, and metal impregnation (%) on the photocatalytic degradation of NDEA is analyzed. The face centred-central composite design (FC-CCD) experimental design method was used through response surface methodology (RSM) and optimization studies for removal of NDEA. The quadratic model was obtained as a functional link between NDEA concentration and three operation variables for all metal impregnated Bi2WO6. The results showed that the pH of the solution was the most significant factor compared to other variables like catalyst dosing and metal impregnation. The average degradation efficiency of NDEA was 89.2% for Fe-Bi2WO6, 87.4% Ag-Bi2WO6, 86.9% for La-Bi2WO6, and 85% for Cu-Bi2WO6.