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Your brightly coloured clothes might have a dark story to tell. Hidden in the bright oranges, blues and reds of textile wastewater are some pretty harmful pollutants. Difficult to degrade, these compounds end up in waterways and may well outlast your outfit. Can we clean up and re-use water effluent from the textile industry? Nanotechnologists can tell a lighter side of the tale using special nano-based catalysts.

Water polluted by textile dyes is a complex issue; impacting animal and plant life in waterways, and holds safety implications for human and agricultural purposes. For dry countries like South Africa under threat of climate change, these are important questions. The answer could lie in the use of light with a little help from nanosized titanium dioxide or rather, nano-TiO2.

Nano-TiO2 acts as a photocatalyst with the ability to destroy organic contaminants from water. Scientists know this process as photocatalytic treatment, harnessing the power of light. The photocalytic properties of titanium dioxide have been known for decades and recently nanosized titanium dixiode has entered the market place. Scientists at Cape Peninsula University of Technology (CPUT) are exploring these processes, and their application in treatment of dyes such as methyl orange, methylene blue and reactive red.

An ongoing CPUT study investigated commercially available round shaped nano-TiO2 and similar such particles synthesized via a hydrothermal method. The hydrothermal method of production produces rod and ribbon-shaped particles. The effect of these nanophotocatalysts was determined in laboratory-prepared solutions of model dye compounds.

Titanium dioxide is considered for this treatment because of its availability, low cost and effectiveness as a catalyst, speeding up the removal of color from the textile wastewater. The proof is clear to see in images showing the decolourisation of methyl orange, methylene blue and reactive red. [UV irradiation of nano-TiO2 excites electrons from a filled valence band to an empty conduction band, giving rise to electron-hole pairs. These generate free radicals which attack covalent bonds in the dyes].While nano-TiO2 photocatalysis represents a striking method for breaking down these complex organic compounds to simpler compounds, scope remains for studies that can improve the efficiency of dye pollution. Measures such as these may yet lead to long-term solutions for treating textile industry wastewater.

*Nangamso Nyangiwe of the Technology Station in Clothing and Textiles at CPUT presented his findings and that of his colleagues (B. Baatjie and C. Greyling) this past week at the NanoAfrica 2014 conference at the Vaal University of Technology. Their collaborators at Chemical Engineering, CPUT, Cape Town campus, also presented a poster on the hydrothermal preparation of the rod and ribbon-shaped nano-TiO2 (J. Lind and Prof. V Fester).

Decolourisation of Methyl Orange, Methylene Blue and Reactive Red at different photodegradation times from 0 min to 420 min.

Writer: Nangamso Nyangiwe