Effect of toluene, an immiscible pollutant, on the photocatalytic degradation of azo dye

•Addition of toluene affects DR80 degradation.•Toluene continuous layer form has adverse effect but PE form has supportive effect.•Highly hydrophilic and large TiO2 particles do not provide a stable PE.•A stable PE is better than an unstable PE for DR80 degradation.•Separation of nanomaterials/catalysts from the effluent is essential.

An adverse effect of a water-immiscible pollutant, toluene, on the photocatalytic degradation of Direct Red 80 (DR80) with TiO2 in an aqueous solution was observed when toluene was added as a continuous free layer. However, a more efficient photocatalytic system was obtained when toluene was added in the Pickering emulsion (PE) form with TiO2. With only UV and two different types of TiO2 (more hydrophilic and large-sized type A TiO2 and less hydrophilic and small-sized type B TiO2), 44% and 59% color removal was observed, respectively. Almost 20% decrease in color removal with toluene in the continuous free layer form was observed, however, the higher color removal was obtained when toluene was added as PE stabilized with type B TiO2 than with type A TiO2. The higher color removal was owing to the good stability of PE stabilized with type B TiO2.

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