Visible light induced molecularly imprinted Dawson-type heteropoly acid cobalt (II) salt modified TiO2 composites: Enhanced photocatalytic activity for the removal of ethylparaben

Visible light induced molecularly imprinted titania modified with Dawson-type Co₃P₂W₁₈O₆₂·15H₂O nanocomposites (CWMT), as a recycled visible light responsive photocatalysts, were prepared successfully by the method of impregnation, stepwise acidification and sol-gel using ethylparaben (EP) as the template. Various characterization techniques were employed for the study, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron micro-scope (TEM), diffuse reflectance spectroscopy (UV–vis DRS), nitrogen adsorption-desorption measurements (BET), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), photoluminescence (PL) spectra, and electron spin resonance (ESR) spectroscopy. The results showed that the modification of Co₃P₂W₁₈O₆₂·15H₂O resulted in not only an increase in the surface area, and the pore volume of molecular imprinted titania, but also in inhibition of recombination of photogenerated electron-hole pairs. EP molecules in aqueous solutions were chosen as the target pollutant to evaluate photocatalytic activity of the obtained samples. Photo-degradation results revealed that the modification of Co₃P₂W₁₈O₆₂·15H₂O and imprinting cave could greatly boost the photoactivity of titania in comparsion to unmodified samples, and the non-imprinting titanium dioxide by photo-degradation of EP aqueous solutions. In this experiment, modifying with Co₃P₂W₁₈O₆₂·15H₂O expresses the highest photoactivity and the optimal dosage was 0.25 wt%, which caused EP photo-degradation efficiency of 87.32 %, 89.82 % irradiation under UV for 70 min and visible light (λ = 400-700 nm) for 40 h respectively. The boosted photoactivity could be attributed to the higher specific area, good crystallinity, enhancing visible light harvesting, the reducing electron recombination of photogenerated electron-hole pairs in the catalyst.