Advanced degradation of hydrocarbons without UV source: Efficiency of TiO2 and ZnO nanocatalysts

The study explores how two common metal oxides, titanium dioxide (TiO₂) and zinc oxide (ZnO), behave when used to clean drilling muds rich in petroleum hydrocarbons. Tests were carried out on a laboratory mixture of mineral oil and condensate, under visible light, using different catalyst loads (1, 5, and 10 g L⁻¹).

The outcomes were quite distinct for the two materials. TiO₂ only led to partial breakdown of the hydrocarbons, leaving behind several oxygenated fragments such as alcohols, ketones and acids. ZnO, on the other hand, showed a much stronger response: at 5 g L⁻¹ the hydrocarbon content dropped almost completely (≈99 % removal), and the carbon balance confirmed that most of the material had been converted into CO₂ and water.

Additional tests helped explain this difference. Radical trapping and oxygen purging experiments, supported by EPR and XPS analyses, indicated that ZnO contains more structural defects able to activate oxygen, which in turn leads to a higher production of reactive radicals. Microscopy also revealed clear surface changes on both materials after treatment.

From a practical point of view, the method is simple and does not involve organic solvents; the nanoparticles were recovered by centrifugation, and the overall energy requirement was modest (∼6.3 Wh per milligram of hydrocarbons removed). These results suggest that ZnO could be a reliable and sustainable option for treating oily wastes using only visible light, without the need for UV lamps.