A series of La³⁺-doped Ag₁₀Si₄O₁₃ nano-photocatalysts were synthesized via the sol-gel method. The regulation mechanism of La³⁺ doping on the composition, crystal structure, microscopic morphology, and photoelectric properties of the photocatalyst was systematically investigated by characterization techniques including XRD, XPS, TEM, and paramagnetic resonance spectrometer (EPR), combined with density functional theory (DFT) calculations. Using tetracycline hydrochloride (TCH) as the target pollutant, the influence pattern and promotion mechanism of La³⁺ doping on the photocatalytic degradation performance of TCH were investigated. The results show that La³⁺ substitutes Ag⁺ into the Ag₁₀Si₄O₁₃ lattice to trigger lattice distortion (the maximum cell volume change rate is 1.06%), enhance the ferroelectric built-in electric field, and induce the generation of a small amount of Ag monomers on the Ag₁₀Si₄O₁₃ surface to form an Ag/Ag₁₀Si₄O₁₃ Schottky junction. The synergistic effect of these two factors simultaneously controls the carrier transport path from the crystal interior to the surface, driving h⁺ to accumulate on the Ag₁₀Si₄O₁₃ surface and e^- to enrich on the metallic Ag, thereby effectively improving carrier separation efficiency and achieving significant enhancements in degradation rate and photoreduction resistance. The injection of La-5d state electrons into the conduction band forms a donor level, reducing the material's band gap from 1.82 eV to 1.72 eV, lowering the work function by 0.17 eV, significantly broadening the photoresponse range to 683 nm, and increasing carrier density. The 1% (in mass) La³⁺-doped sample achieved a TCH degradation rate of 90% (k = 0.031 04 min^-1), representing a 15% improvement in efficiency and a 20% increase in rate compared to the undoped system. Furthermore, the activity retention rate remained above 90% after five cycles, and the material composition tended to stabilize. Free radical trapping experiments indicated that h⁺ is the primary active species in the photocatalytic reaction, with •O₂- and •OH playing synergistic roles.

The photocatalysts were prepared by the sol-gel method. 0.9 g of citric acid was dissolved in anhydrous ethanol, after which 9.5 mL of tetraethyl orthosilicate was added dropwise and stirred for 1 h, followed by the dropwise addition of 3 mL of distilled water and continued stirring for another hour; the mixture was then sealed and aged for one week to obtain a colorless and transparent silicic acid sol. Subsequently, 6.39 mL of a 0.38 g/mL AgNO₃ solution and a specified amount of lanthanum (III) nitrate hexahydrate were added to this silicic acid sol, stirred for 1 h, and aged for 24 h to yield the precursor sol. The precursor sol was dried, ground, and heat-treated in a muffle furnace at 400 ℃ for 5 h to produce La³⁺-doped Ag₁₀Si₄O₁₃. By varying the amount of lanthanum(III) nitrate hexahydrate added to achieve La³⁺ doping levels of x%(in mass fraction) (x = 0, 0.50, 1.00, 1.25, 1.50, 2.00) relative to the mass of Ag₁₀Si₄O₁₃, a series of La³⁺-doped Ag₁₀Si₄O₁₃ photocatalysts were prepared, labeled as ASO (for x = 0) and x L-ASO (where x represents the specific doping level).

The crystal structures of the photocatalysts were analyzed by a D8/axs type ray diffractometer (XRD), and the lattice parameters of the samples were determined by Rietveld refinement using GSAS software. The surface composition and electronic states of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) using AXISSUPRA model. A JEM-2010 transmission electron microscope (TEM) was used to observe the microscopic morphology of the samples, and the elemental distributions were analyzed by an accompanying energy spectrometer (EDS). The JW-BK100 A Specific Surface Area and Pore Size Analyzer was used to test the specific surface area and the maximum pore size of the photocatalysts.The light absorption properties of the samples were tested using a UV-Vis DRS (model U-3900H). The fluorescence intensity of the photocatalysts was tested by Fluorescence Spectrometer (PL) (model F-97). An electrochemical impedance test and Mott-Schottky curve test were performed using a CHI660D electrochemical workstation. An electron EPR (model EPR) 200M was used to detect active substances.

Weigh 0.1 g of photocatalyst in 100 mL of TCH solution (pH 6) with a concentration of 10 mg/L, dark adsorption for 30 min to reach the adsorption equilibrium and then turn on the 300 W xenon lamp for the photocatalytic reaction, and sample every 10 min, centrifuged to take the supernatant in the cuvette, and calculated the degradation rate by using UV-Vis DRS to test the concentration of TCH. The test samples were recovered and the above steps were repeated for five cycles of testing. Simulations were carried out using Materials Studio 2020 software developed by Accelrys, based on the generalized gradient approximation (GGA) plane-wave ultrasoft pseudopotential method in the DFT framework to describe the interactions between the ionic potentials and the valence electrons, and the exchange-correlation energies between electrons were described by the Perdew-Burke-Ernzerhof (PBE) generalized function. Geometry optimization and energy calculations were performed for all cell models using the GGA+U method without considering spin-polarization effects, with U_Ag-p = 6 eV, U_O-p = 4 eV, and U_Si-p = 4 eV. The valence electron groupings used to construct the pseudopotentials are Ag 4d¹⁰5s¹, O 2s²2p⁴, Si 3s²3P², and La 5p⁶6s²5d¹. The plane-wave truncation energy (E_cut) is set to 480 eV and a 2 × 2 × 2 K-point grid is used to sum the Brillouin zone.

The XRD diffraction patterns show that the characteristic diffraction peaks of Ag₁₀Si₄O₁₃ appeared in all the samples, and the doping of La³⁺ did not change the crystal structure type of ASO. The XPS test results showed that there is metallic Ag in the 1.0 L-ASO, and the La element stably exists in the ASO cell as La³⁺. The TEM photographs show that La³⁺occupies some Ag⁺ sites in the ASO lattice through substitutional doping, and the corresponding metallic Ag are polarised on the surface of the material, forming a metal-semiconductor contact interface with the L-ASO and constituting a Schottky junction. La³⁺doping showed an inverted 'V'-shaped dependence on the degradation rate of TCH, in which the 1.0 L-ASO sample showed the best degradation performance, and the degradation rate of TCH by the 1.0 L-ASO sample remained more than 90% of the initial efficiency after five cycles of testing. DFT calculation analysis of ASO before and after doping revealed that: After La³⁺ doping, the band gap is reduced; the work function decreases from 4.22 eV to 4.05 eV and the Fermi level shifts towards the conduction band, significantly enhancing the strength of the ferroelectric built-in electric field.

La³⁺-doped Ag₁₀Si₄O₁₃ nano-photocatalytic materials were successfully prepared by sol-gel method. The optimal doping site of La³⁺ was determined by combining with DFT calculations. It was confirmed that La³⁺ substitutional doping triggered lattice distortion, with a unit cell volume distortion up to 1.06%. La³⁺ doping significantly enhanced the intensity of ferroelectric built-in electric field and induced the in-situ generation of metallic Ag on the surface, forming an Ag/Ag₁₀Si₄O₁₃ Schottky heterojunctions. The injection of La 5d state electrons into the conduction band forms new electronic states near the conduction band minimum, which reduces the band gap and effectively broadens the photoresponse range to 683 nm. The synergistic effect between the optimized ferroelectric built-in electric field within the crystal and the surface Schottky junction simultaneously controls the carrier transport path from the crystal interior to the surface. This drives the accumulation of h⁺ on the Ag₁₀Si₄O₁₃ (ASO) surface and the enrichment of e- on the metallic Ag, significantly inhibiting carrier recombination, enhancing separation efficiency, and ultimately achieving a significant improvement in the degradation rate and the photoreduction resistance. h⁺ plays a dominant role in the degradation process, and La³⁺ doping can significantly enhance the h⁺ yield. When the doping amount is 1% (in mass fraction), the degradation rate of TCH reaches 90%, which represents a 15% improvement compared to the undoped system. Furthermore, after five cycles, the degradation rate remained above 90% of its initial value, demonstrating excellent service stability. This work reveals a dual-effect mechanism where the triple synergistic effects of rare-earth doping-induced band narrowing, enhanced polarization electric field, and surface Schottky junction improve both photocatalytic efficiency and photostability. It provides a new strategy for developing highly efficient and stable silver-based photocatalysts.