Electrochemical stripping of cotton fabrics dyed with Reactive Black 5 in water and wastewater.

Cotton fabrics dyed with Reactive Black 5 (RB5) was electrochemically stripped using Ti/TiO2 -RuO2 -IrO2 anode in water, pyridine and phenol solution. The results showed that RB5 dye could be easily stripped from the surface of cotton fabrics through the cleavage of chromophoric group (NN) under the attack of hydroxyl radicals (OH) and active chlorines generated in situ. Efficient stripping performance could be obtained in water and pyridine solution, whilst the stripping percent was not obviously affected by pyridine concentration and layers of dyed cotton fabrics. Whereas, phenol existing in water slowed the stripping rate due to the competition between the stripping of RB5 dye and the degradation of phenol. In the case of multi-layer dyed cotton fabrics, the stripping performance of the inner layer is superior to that of the outer layer owing to that the cotton fabrics hinder the diffusion of active chlorines and OH. The FTIR analysis of stripped cotton fabrics showed that the effect of electrochemical process and the existence of pollutant in water on the stripped cotton fabrics could be negligible. Electrochemical oxidation could also successfully strip various dyes from waste cotton fabrics in the investigated stripping solutions. Therefore, electrochemical oxidation provides an environmentally friendly alternative for color stripping of dyed cotton fabrics. The removal of dye from cotton fabrics and the degradation of pollutant in water could occur simultaneously, implying that wastewater containing chloride ions may replace the fresh water as stripping solution.