Crystal plane directed interaction of TiO2 [1 0 1] with AgNPs [1 1 1] silver nanoparticles enhancing solar light induced photo-catalytic oxidation of ciprofloxacin: Experimental and theoretical studies

Abstract

• Solar light induced ciprofloxacin oxidation by TiO 2 -Ag NPs. • TiO 2 -Ag NPs: the influence of Ag deposition in the band gap. • Band gap energy with Density of States relating to orientation of crystal. • Theoretical optimization and determination of oxidation products from ciprofloxacin by HPLC-MS. Solar light induced photo-catalysts are of great interest for environmental remediation. Thus the TiO 2 -Ag NPs (different content of Ag NPs deposition on TiO 2 ) 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 TiO 2 , 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 TiO 2 particles attached to Ag NPs is established. With XPS spectra, the oxidation state of metal (Ti 4+ ) and nature of orbital orientation towards Ag are analyzed. Interestingly, with using Density Functional Theory (DFT), we studied how the crystal plane of anatase TiO 2 [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 (TiO 2 -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 TiO 2 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.