Cold Plasma Processing of Biochar Using Corona Discharge in Atmospheric Pressure Dry Air and Helium

摘要

Cold plasma generated from a gas admixture of helium and dry air with 60-Hz ac voltage at 6.50-kV rms was utilized to process biochar. Reactive oxygen and nitrogen species (RONS) were generated in the cold plasma and these chemical radicals modified the biochar. Plasma-processed biochar samples were immersed in distilled water after which the pH of the solid/water mixture was measured. This pH test provided a quick and reliable indication that the plasma-processing modified the biochar, after which more thorough tests were applied. The pH data showed that plasma-processed biochar/water admixtures have lower pH, indicating plasma processing introduced more acidic groups onto the biochar. After pH analysis the solid biochar granules were reclaimed from solution and the leachate was evaluated for carbon content resulting from material leaching into the distilled water. Fourier-transform infrared spectroscopy (FTIR) spectra were measured for dry samples of biochar before and after immersion in the distilled water. Cold plasma processing converted recalcitrant biochar mass into labile biochar mass, resulting in an enhanced amount of water-extractable carbon. FTIR spectra showed that new oxygen- and nitrogen-containing functional groups were introduced into the labile portion of the biochar and that functionalized material leached into solution.