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

Abstract

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.