Degradation of inkjet ink by greensand and ultrasonic sonification
The study describes the degradation of inkjet ink at low frequency ultrasound (US) and greensand to compare their reactivity. Environmental sonochemistry is a rapidly growing area and an example of the advanced oxidation process (AOP) that deals with the destruction of organic species in aqueous solutions. Greensand is a granular material coated with a thin layer of manganese dioxide (MnO2) which is among the strongest natural oxidants. In our study magenta inkjet water-based printing ink was dissolved in distilled water and the solutions obtained after degradation were analysed in terms of total organic compound (TOC) and absorption curves in the visible spectra. Also used for the process monitoring was high performance liquid chromatography (HPLC). The efficiency of discoloration is significantly affected by the effluent pH. The efficiency of discolouration was higher when the pH of initial solution was 2 with respect to the initial solution pH of 5.5. In all solutions, irrespective of the initial pH value and the processing method the oxidation of polyhydric alcohols occurs. Although the decomposition is significant, surface peaks resulting from HPLC analysis are very small. Decolourization is closely related to the cleavage of the – C=C and -N=N- bonds, and oxidation of polyhydric alcohol to the formation of monosaccharides, carboxylic acids or other low molecular weight compounds with a lesser number of unsaturated double bonds. These compounds have low UV absorbance or they absorb below 200 nm and therefore their detection is impossible. Thus, the obtained total organic compound results indicate a small degree of mineralization. The effectiveness of the low-frequency ultrasound (20 kHz) oxidation is similar to the effectiveness of oxidation by greendsand.
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