Rational Design of W-Doped Ag3PO4 as an Efficient Antibacterial Agent and Photocatalyst for Organic Pollutant Degradation

Abstract

Bacterial and organic pollutants are major problems with potential adverse impacts on human health and the environment. A promising strategy to alleviate these impacts consists in designing innovative photocatalysts with a wider spectrum of application. In this paper, we report the improved photocatalytic and antibacterial activities of chemically precipitated Ag₃PO₄ microcrystals by the incorporation of W at doping levels 0.5, 1, and 2 mol %. The presence of W directly influences the crystallization of Ag₃PO₄, affecting the morphology, particle size, and surface area of the microcrystals. Also, the characterization via experimental and theoretical approaches evidenced a high density of disordered [AgO₄], [PO₄], and [WO₄] structural clusters due to the substitution of P⁵⁺ by W⁶⁺ into the Ag₃PO₄ lattice. This leads to new defect-related energy states, which decreases the band gap energy of the materials (from 2.27 to 2.04 eV) and delays the recombination of e'-h^• pairs, leading to an enhanced degradation process. As a result of such behaviors, W-doped Ag₃PO₄ (Ag₃PO₄:W) is a better visible-light photocatalyst than Ag₃PO₄, demonstrated here by the photodegradation of potential environmental pollutants. The degradation of rhodamine B dye was 100% in 4 min for Ag₃PO₄:W 1%, and for Ag₃PO₄, the obtained result was 90% of degradation in 15 min of reaction. Ag₃PO₄:W 1% allowed the total degradation of cephalexin antibiotic in only 4 min, whereas pure Ag₃PO₄ took 20 min to achieve the same result. For the degradation of imidacloprid insecticide, Ag₃PO₄:W 1% allowed 90% of degradation, whereas Ag₃PO₄ allowed 40%, both in 20 min of reaction. Moreover, the presence of W-dopant results in a 16-fold improvement of bactericidal performance against methicillin-resistant Staphylococcus aureus. The outstanding results using the Ag₃PO₄:W material demonstrated its potential multifunctionality for the control of organic pollutants and bacteria in environmental applications.

Figure 1

XRD patterns of Ag₃PO₄, Ag₃PO₄:W 0.5%, Ag₃PO₄:W 1%, and Ag₃PO₄:W 2% samples.

Figure 2

Schematic representation of the 2 × 2 × 2 supercell periodic models built for (a) pure Ag₃PO₄ and (b) Ag₃PO₄:W.

Figure 3

(a) Raman spectra and (b) A₁ Raman mode of Ag₃PO₄, Ag₃PO₄:W 0.5%, Ag₃PO₄:W 1%, and Ag₃PO₄:W 2%.

Figure 4

(a) XPS spectra of Ag₃PO₄, Ag₃PO₄:W 0.5%, and Ag₃PO₄:W 1% samples and (b) W 4f high-resolution spectra of Ag₃PO₄:W 0.5% and Ag₃PO₄:W 1%.

Figure 5

FESEM images of (a) Ag₃PO₄, (b) Ag₃PO₄:W 0.5%, and (c) Ag₃PO₄:W 1%. TEM images of the Ag₃PO₄:W 1% sample: (d) high-angle annular dark-field (HAADF) image showing two regions comprising Ag₃PO₄:W 1% and Ag⁰ structures (yellow and red dotted circles, respectively), (e–h) EDS mapping of Ag, O, P, and W elements, (i, j) high-resolution TEM (HR-TEM) images of a border region of the Ag₃PO₄:W 1% crystal, and (k, l) HR-TEM images of Ag⁰ nanostructures.

Figure 6

(a) UV–visible absorption spectra and band-gap energies for Ag₃PO₄, Ag₃PO₄:W 0.5%, and Ag₃PO₄:W 1% samples. Calculated band structures of (b) Ag₃PO₄ and (c) Ag₃PO₄:W models.

Figure 7

UV–visible absorption spectra of RhB upon photodegradation in the presence of (a) Ag₃PO₄, (b) Ag₃PO₄:W 0.5%, and (c) Ag₃PO₄:W 1%. (d) Photocatalytic degradation of RhB (1.0 × 10^–1 mol L^–1) in the absence and in the presence of Ag₃PO₄ and Ag₃PO₄ doped with different amounts of W and (e) Langmuir–Hinshelwood plot for the determination of the rate constant.

Figure 8

(a) UV–visible absorption spectra of RhB photodegradation in the presence of Ag₃PO₄:W 1% collected in time less than 5 min and (b) run cycles of RhB degradation using Ag₃PO₄:W 1% under visible-light irradiation. (c) Influence of the scavengers on the degradation of RhB in the presence of Ag₃PO₄:W 1% under visible-light irradiation and (d) analysis of total organic carbon (TOC) for degradation of RhB in the presence of Ag₃PO₄:W 1% under 30 min of visible-light irradiation.

Figure 9

(a) Photocatalytic degradation of CFX in the presence of Ag₃PO₄ and Ag₃PO₄:W 1% in a linear plot and (b) analysis of total organic carbon for degradation of CFX in the presence of Ag₃PO₄ and Ag₃PO₄:W 1% under 30 min of visible-light irradiation. (c) Photocatalytic degradation of IMC in the presence of Ag₃PO₄ and Ag₃PO₄:W 1% in a linear plot and (d) analysis of total organic carbon for degradation of IMC in the presence of Ag₃PO₄ and Ag₃PO₄:W 1% under 30 min of visible-light irradiation.

Figure 10

Bacterial growth values (Log₁₀) as a function of the concentrations (mg mL^–1) of Ag₃PO₄ and Ag₃PO₄:W.