4. Reduction and Removal of Cr(VI) from Aqueous Solution by Microplasma

In this chapter, the reduction and removal of Cr(VI) from aqueous solution by microplasma are explained, which represents a new and fascinating realm of plasma science for the first time. The effect of various process parameters on the Cr(VI) reduction efficiency and the effect of initial pH and ethanol on the removal of Cr(VI) are systematically examined. The optimum condition for Cr(VI) reduction was initial pH at 2 with stir where the microdischarge gas was argon with the flow rate of 60 mL/min. The reduction efficiency of Cr(VI) increased with an increase in input power but decreased with an increasing initial concentration of Cr(VI). In particular, additive hydroxyl radical scavenger (ethanol) greatly improved the reduction efficiency and facilitated the removal of chromium dissolved in the solution. The best removal efficiency was obtained when the pH was 6. In addition, the energy efficiency of microplasma to reduce Cr(VI) is 2.0 × 10⁻⁴ mg/J and is comparable to that in electrolysis and other forms of glow discharge. The advantages, such as low cost, scalability, and easy operating techniques, of this approach have broad prospects in water treatment (Xiao in Removal of hexavalent chromium in water and preparation of cuprous oxide nanoparticles by microplasma. Yat–sen University, 2012, [1]; Du in Non-Thermal arc plasma technology and application. BeiJing: Chemical Industry Press, 2015, [2].