Alternative natural dyes in water purification: anthocyanin as TiO_2-sensitizer in rhodamine B photoelectrodegradation

摘要

Natural molecular dye, anthocyanin, from mangosteen rind (Garcinia mangostana L.) is described here as the safe sensitizer for TiO_2 particles in the photodegradation of organic contaminants in water. The dye is a promising replacement for the more costly and hazardous heavy metal-based systems, such as Fe-complexes and Ru-complexes. Anthocyanin was used as a sensitizer in TiO_2/anthocyanin photoanode. Those photoanodes was effectively catalyzed the photoelectrodegradation of Rhodamine B contaminant under halogen lamp of 300 watts. The natural dye molecules showed the tendency to degrade under photoelectrodegradation conditions, just like earlier hazardous sensitizers at bias voltage about 1-2 volts. However, complete mineralization of rhodamine B as well as anthocyanin occurred leaving no traces of organic species in solution. Sensitizer degradation caused deactivation of the supported catalyst on recovery. Such a shortcoming was overcome by re-treatment of the recovered catalysts with fresh dye. It was noted that the NaCl electrolyte significantly influenced the RB photoelectron degradation by applying a positive bias. Under the 3 M NaCl electrolyte conditions, RB photoelectron degradation achieves the highest.