TiO₂-coated 2D photonic crystals for reflectometric determination of malachite green

A "detect and destroy" strategy is reported for the spectroscopic determination and photocatalytic degradation of Malachite Green (MG) in aqueous solutions. The intensity of the reflection peak maxima from the TiO₂-coated 2D-photonic crystal (PhC) at 633 nm wavelength undergoes a gradual decrease with increasing concentrations of MG. The determination of MG was readily achieved in the nanomolar range due to the quenching of the reflection intensity of the peak, measured using a fiber optic probe. The assay works in the 1.0 nM to 10 μM MG concentration range with a detection limit of 1.3 nM. The same TiO₂-coated 2D-PhC surface can photocatalytically degrade MG in aqueous solutions under UV irradiation. The photocatalytic degradation in the presence of TiO₂-coated 2D-PhC becomes evident as the blue color of MG changes to colorless with increasing irradiation time. The decrease in absorption is detected at 617 nm. It was found that the photocatalytic efficiency of TiO₂ was synergistically enhanced in the presence of 2D-PhCs. It is concluded that each component of the TiO₂-coated 2D-PhC system plays a key role in the detection and degradation of MG. Graphical abstractSchematic representation for reflectometric detection and photocatalytic degradation of hazardous Malachite Green dye using TiO₂-coated two-dimensional photonic crystals.