Crystal plane directed interaction of TiO2 [101] with AgNPs [111] silver nanoparticles enhancing solar light induced photo-catalytic oxidation of ciprofloxacin: Experimental and theoretical studies

Solar light induced photo-catalysts are of great interest for environmental remediation. Thus the TiO2-Ag NPs (different content of Ag NPs deposition on TiO2) were prepared, and characterized completely by various analytical methods such as X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and photo electron spectroscopy (XPS). The results show the adhesion of AgNPs on the surface of TiO2, exhibiting absorption band around 550 nm in the solid state diffusion spectra. This is consistent with the HR-TEM where the existence of multiple zones having high crystalline TiO2 particles attached to Ag NPs is established. With XPS spectra, the oxidation state of metal (Ti4+) and nature of orbital orientation towards Ag are analyzed. Interestingly, with using Density Functional Theory (DFT), we studied how the crystal plane of anatase TiO2 [1 0 1] orients with the plane [1 1 1] of Ag NPs reducing the band gap energy altered by Density of State (DOS). The nano-hybrids (TiO2-Ag NPs) were then employed in the oxidation of ciprofloxacin (Cipro) under solar light resulting high oxidation efficiency under visible light, and analyzed the role of Ag deposition over TiO2 relating to the reduction of band gap energy. The formation of intermediates in the degradation was analyzed by HPLC-MS, corroborating excellently with DFT studies, and then proposed a possible mechanism. Meanwhile, the surface morphology of the catalysts studied by AFM shows how the surface alteration was seen after using in the reaction.