Dual-function Gd–doped BiPO₄ rods enabling durable UV photocatalysis and antifungal activity

Textile effluents contain persistent dyes that resist conventional treatment, while opportunistic fungal pathogens such as Candida tropicalis are increasingly associated with difficult-to-treat infections. Here, monoclinic BiPO₄ and 10 mol% Gd–doped BiPO₄ were synthesized by chemical precipitation and linked to UV-driven methylene blue (MB) degradation and antifungal performance. XRD confirmed phase-pure monoclinic BiPO₄, with dopant-induced crystallite refinement (≈ 37 → 34.04 nm) and no detectable secondary phases. UV–Vis/Tauc’s analysis showed a red-shifted absorption edge and band-gap narrowing from 3.93 eV (BiPO₄) to 3.78 eV (Gd–doped BiPO₄). Under UV irradiation (MB 10 mg L⁻¹; catalyst 25 mg; 500 mL; 60 min dark equilibration), Gd–doped BiPO₄ accelerated MB depletion to Ct/C0 ≈ 0.06–0.07 after 70 min (≈ 93–94% removal), compared with Ct/C0 ≈ 0.22 for BiPO₄ (≈ 78% removal), following pseudo-first-order kinetics (k = 0.0381 vs. 0.0212 min⁻¹). The catalyst retained high activity over six cycles (95% → 88%) with unchanged XRD/FESEM features. In agar well diffusion, Gd–doped BiPO₄ exhibited dose-dependent antifungal inhibition against C. tropicalis with a maximum ZOI of ~ 13 mm at 200 µg well⁻¹. Overall, Gd incorporation improves charge utilization and enables a stable dual-function photocatalytic/antifungal oxide platform.