Ag/BiPbO₂Cl Nanosheet Composites: 3.6‑Fold Enhancement of Visible‑Light Photocatalytic Activity

Background

Environmental pollution from organic contaminants has driven the development of semiconductor photocatalysts, notably ZnO and TiO₂, which mainly absorb ultraviolet light. To harness the abundant visible spectrum, bismuth‑based semiconductors such as BiPbO₂Cl—known for a narrow band gap, internal electric fields, and hybrid band structures—are attractive, yet suffer from rapid electron–hole recombination.

Integrating noble metals or graphene with photocatalysts can mitigate recombination by acting as electron sinks. Ag, Au, and Pt have demonstrated such effects. Here, we combine Ag with BiPbO₂Cl to enhance visible‑light photocatalysis.

Methods

Preparation of Ag/BiPbO₂Cl Nanosheet Composites

BiPbO₂Cl nanosheets were synthesized via a one‑step hydrothermal route (see ref. 13). For Ag loading, 1 mmol BiPbO₂Cl was dispersed in 20 mL deionized water, then AgNO₃ was added at 0.25, 0.5, or 0.75 wt %. The mixture was irradiated with a 500‑W Xe lamp (cut‑off filter <420 nm) under stirring at room temperature for 3 h. The resulting powders were washed, dried at 80 °C, and stored for analysis.

Photocatalytic Activities

Photocatalytic performance was evaluated using a 500‑W Xe lamp (cut‑off filter >420 nm) in an XPA photochemical system. 50 mg of catalyst was dispersed in 50 mL 10 mg L⁻¹ MO solution, stirred in the dark for 1 h to reach adsorption equilibrium, then illuminated. UV‑Vis spectra were recorded with a Shimadzu UV‑2700.

Sample Characterization

XRD (Cu K_α, 1.54178 Å) was performed on a PANalytical X’Pert Pro. SEM (Hitachi S‑4800) and TEM (JEOL JEM‑2011) examined morphology. UV‑Vis diffuse‑reflection spectra were obtained on a Shimadzu UV‑2450. XPS (Pekin Elmer PHI‑5300) provided surface chemistry, and PL spectra (Shimadzu RF‑5301, 320 nm excitation) assessed charge‑carrier recombination.

Results and Discussion

MO degradation under visible light (>420 nm) showed a clear dependence on Ag content. The 0.5 wt % Ag/BiPbO₂Cl composite achieved the highest activity, with a degradation rate constant of 0.0158 min⁻¹, 3.6 times that of pristine BiPbO₂Cl (0.0044 min⁻¹) (Fig. 1a,b). Excess Ag reduces the BiPbO₂Cl surface area and thus diminishes photocatalytic sites.

a Photocatalytic degradation of MO; b Degradation kinetics.

SEM images reveal BiPbO₂Cl as ~12 nm‑thick nanosheets, while Ag nanoparticles (~10 nm) are uniformly distributed on the composite surface (Fig. 2). HRTEM confirms the presence of Ag (Fig. 2c). XRD patterns (Fig. 2d) show no new phases, indicating the low Ag content. EDS mapping (Fig. 3) confirms homogeneous Ag distribution.

SEM of BiPbO₂Cl (a) and 0.5 wt % Ag/BiPbO₂Cl (b). c HRTEM; d XRD.

EDS elemental mapping of Ag/BiPbO₂Cl.

XPS spectra (Fig. 4) confirm the presence of Bi³⁺, Pb²⁺, O²⁻, Cl⁻, and metallic Ag (Ag⁰). The Ag 3d peaks at 368.1 and 374.3 eV match the literature value for Ag⁰ (ref. 23).

The XPS spectra of Ag/BiPbO₂Cl composites: a survey; b Bi 4f; c Pb 4f; d O 1s; e Cl 2p; f Ag 3d.

UV‑Vis absorption (Fig. 5a) shows enhanced visible‑light absorption (450–800 nm) due to surface plasmon resonance of Ag, increasing the light‑harvesting range. The band gap narrows from 2.05 eV (pure BiPbO₂Cl) to 1.68 eV (0.5 wt % Ag) (Fig. 5b). PL spectra (Fig. 5c) display a marked intensity reduction, evidencing suppressed electron–hole recombination.

UV‑Vis absorption (a) and PL emission (b) of BiPbO₂Cl and 0.5 wt % Ag/BiPbO₂Cl.

Mechanistically, the Ag loading extends visible‑light response, establishes an internal electromagnetic field by aligning Fermi levels (Ag lower than BiPbO₂Cl), and enhances conductivity. Electrons excited in BiPbO₂Cl rapidly transfer to Ag, where they reduce O₂ to •O₂⁻, while holes oxidize water to •OH (Fig. 6). The combined action of these radicals drives MO decomposition into CO₂ and H₂O.

a Photocatalytic mechanism; b Band alignment at the Ag/BiPbO₂Cl interface.

Conclusions

Hydrothermal synthesis followed by photo‑reduction produced Ag/BiPbO₂Cl nanosheet composites with 0.5 wt % Ag loading that outperform pure BiPbO₂Cl by 3.6× in visible‑light photocatalytic degradation of MO. The enhanced performance stems from extended light absorption, reduced charge‑carrier recombination, and the creation of an internal electromagnetic field due to Ag’s lower Fermi level and superior conductivity.