Chemiluminescence imaging of the formation and photodegradation of humic acid derived from 5-hydroxy-1,4-naphthoquinone [juglone]

A new model humic acid (HA) have been synthetized from 5-hydroxy-1,4-naphthoquinone (juglone, J), an allelopathic compound occuring in leaves, nut shells, exsudates of roots and barks of Juglans genera. Aqueous solutions of J were autooxidised at different pH 6-10 with mineral matrices: bentonite, glass and silica. The very slow autooxidation reaction was monitored by means of chemiluminescence (CL) imaging and kinetics supported by a highly sensitive CCD camera Molecular Light Imager. In the course of autooxidation that lasted three weeks, an extremely low-intensity of CL was detected The reaction liquid was further treated according to the IHSS protocol to isolate humic acid fractions. Elemental analysis, UV-VIS and FTIR absorption spectra as well as fluorescence excitation and emission spectra were measured to characterise this new HA.