Surface plasmon resonance effect of Ag metallized SnO2 particles: Exploration of metal induced gap states and characteristic properties of Ohmic junction

Ag metallization on the surface of SnO2 catalyst was performed by the photoreduction method, and its presence was confirmed by the (111), (200), (220), and (311) hkl planes of Ag metal by powder X-ray diffraction technique. Further lattice parameters "a" and "c" of the SnO2 tetragonal unit cell show prominent changes on metallization. Ultraiolet-visible absorption spectrum of Ag-SnO2 shows the extended adsorption in the visible region up to almost 565 nm due to the surface plasmon resonance (SPR) effect. Percentage composition of the elements present in the SnO2 and Ag-SnO2 samples were confirmed by the energy-dispersive X-ray analysis and the inductively coupled plasma-atomic emission spectroscopic analysis techniques, and the spherical morphology of these samples were confirmed by the scanning electron microscopy. The photoluminescence technique confirms the reduction of recombination of photogenerated charge carriers by 44% in the case of Ag-SnO2. The metal-metal oxide contact was found to be Ohmic rather than Schottky. The higher activity of the Ag-SnO2 nanoparticles are correlated to the SPR effect, metal-induced gap states, inherently created structural defects, the ability of Sn to show multiple oxidation states, variation in the surface oxygen concentration, and also to the Ohmic junction. Synergistic effect between electronic/intrinsic defect energy levels of Ag-SnO2 photocatalyst with the redox potential of the fast red dye leads to the higher quantum efficiency.