Tuning the particle size, physical properties, and photocatalytic activity of Ag₃PO₄ materials by changing the Ag⁺/${\mathrm{PO}}_4^{3-}$ ratio

This study demonstrates the influence of the Ag⁺/${\mathrm{PO}}_4^{3-}$ ratio in precursor solution on the crystal structural formation, morphology, physical properties, and photocatalytic performance of a Ag₃PO₄ photocatalyst that is fabricated, using a facile precipitation method, from AgNO₃ and Na₂HPO₄⋅12H₂O. The material characterizations were carried out using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET) surface area, Fourier transform infrared (FTIR) absorption, Raman scattering, x-ray photoelectron spectroscopy (XPS), UV-vis absorption, and photoluminescence (PL). The results show that Ag₃PO₄ crystallizes better when the excess ${\mathrm{PO}}_4^{3-}$ content increases, and the lattice parameters decrease slightly, while the crystal diameter and the particle size increase. This change is also observed in the Raman scattering and FTIR spectra with the increase in the vibration frequency of the PO₄ group. The compression of the PO₄ unit was also confirmed in the XPS spectra with the shift of P 2p peaks toward higher binding energy. The photocatalytic results showed that the samples synthesized from excess ${\mathrm{PO}}_4^{3-}$ solution exhibited higher photocatalytic performance compared to the sample with a Ag⁺/${\mathrm{PO}}_4^{3-}$ ratio of 3:1. A sample prepared from the precursor solution with a Ag⁺/${\mathrm{PO}}_4^{3-}$ ratio of 3:1.5 was optimal for RhB decomposition under both visible light and natural sunlight, completely decomposing 10 ppm RhB after 15 minutes of xenon lamp irradiation and after 60 minutes under solar light irradiation. This is attributed to the high crystallinity, small particle size and low electron–hole recombination rate of the sample.