Reusing of wastewater emitted from thermal plasma decomposition of refrigerant for production of TiO2 nano-powders

초록

Wastewater containing large amounts of Cl-, F-, and NO3-, generated from the nitrogen thermal plasma decomposition of refrigerants, is reused for the production of TiO2 nano-powders using a rapid breakdown anodization in order to develop a sustainable and environmentally affinitive chemical engineering process. The target refrigerant, HCFC-22, can be decomposed using a thermal plasma decomposition with 99.99% DRE at a plasma operating condition of 80 A. The FT-IR spectra and ion-chromatograph confirm that a gaseous by-product, in which HF and HCl are included, are successfully adsorbed by a NaOH spraying wet scrubber system. Corrosive wastewater containing Cl-, F-, and NO3- is successfully re-used as an electrolyte for the anodization of titanium. During anodization, the growth of TiO2 nanotubes is observed on titanium substrates. Owing to a weak adhesiveness between TiO2 nanotubes and titanium substrate, the nanotubes are spontaneously detached from the substrate during anodization. Through TEM and XPS analyses, it is confirmed that the powder consists of amorphous TiO2 nanotubes and the mass production of TiO2 nano-powder increases as a function of the applied voltage and anodization time. The trace concentration of nitrate ions in wastewater, which is generated from nitrogen plasma, plays a crucial role as a catalyst accelerating the growth of the nanotubes.