Reuse of wastewater discharged from thermal-plasma decomposition of chlorodifluoromethane: Production of titanium dioxide nanopowder

Chlorodifluoromethane, a refrigerant that will be phased out in the future, is decomposed by nitrogen thermal plasmas with a 99.99% destruction and removal efficiency discharging wastewater containing halide ions. Titanium dioxide nanotubes having a pore size less than 9 nm are produced via electrochemical anodization of titanium using wastewater containing fluoride and chloride ions generated by the decomposition of chlorodifluoromethane. Titanium dioxide spontaneously detached from the substrate into the electrolyte as the period of anodization increased due to weak adhesion between the oxide and substrate. The amount of nanopowder produced was accelerated by nitrate ions, which originated from the nitrogen plasma during the thermal decomposition process. The nitrate ions, which is naturally generated in wastewater due to nitrogen plasma act as a catalyst to accelerate the mass production of TiO2 powder by up to two-fold, compared to that in an electrolyte without nitrate ions. The basic property originated by NaOH neutralizer of the electrolyte leads to the smooth surface morphology.