“…The intensity of the PL spectra of the parent TiO 2 catalysts decreased considerably with the addition of Ag, reflecting the enhanced charge pair separation that led to the increased photoactivity of the catalysts (Fig. 5) [51]. However, sometimes this phenomenon seems to be incompatible, wherein further addition of Ag 0 may act as a recombination center that is detrimental to the photocatalytic activity [40].…”