Plasmonic Ag-decorated Bi₂WO₆ nanoflakes for photocatalytic Congo red degradation and hydrogen evolution

Silver (Ag)-decorated Bi₂WO₆ (BW) nanoflakes were developed as a visible-light-responsive plasmonic semiconductor photocatalyst for enhanced hydrogen evolution and efficient photocatalytic degradation of Congo red under natural sunlight irradiation. The Ag-Bi₂WO₆ (ABW) nanocomposites were characterized by UV-visible spectroscopy, XRD, XPS, TRPL analysis, BET analysis, Raman spectroscopy, FESEM and HRTEM. XRD showed the formation of the orthorhombic crystal phase of Bi₂WO₆ and the face-centered cubic structure of Ag. UV-visible spectroscopy showed the extended absorption of ABW composites in the visible range, whereas BW showed an absorption peak at 320 nm. Raman analysis confirmed the successful decoration of Ag onto BW, altering its vibrational mode and structural bonding. FESEM confirmed the nanoflake morphology with a densely packed and self-assembled plate/disc structure of BW and spherical Ag nanoparticles (diameter ∼6 nm) well-deposited on it. The high-resolution TEM results showed lattice fringes with interplanar spacings of ∼0.22 nm and 0.27 nm, corresponding to the (111) and (113) planes of Ag and BW, respectively. The ABW nanocomposite showed excellent photocatalytic activity, with 94% CR dye (25 ppm) degradation within 6 minutes under natural sunlight, along with a pseudo-first-order rate constant of 0.43 min^-1. The obtained cumulative hydrogen production rate using BW and the ABW nanocomposites is 8231 µmol g^-1 and 13 054 µmol g^-1, respectively, within 4 hours under a mercury vapor lamp (400 W).