Visible light-driven methylene blue degradation by polycrystalline Li₆CuB₄O₁₀ photocatalytic compound

In this study, lithium copper pyroborate (Li₆CuB₄O₁₀) was synthesized using the conventional solid-state reaction method to explore its structural, optical, and photocatalytic properties. Rietveld refinement of X-ray diffraction (XRD) data confirms that the compound crystallizes in a triclinic structure with a P1 (1) space group. The crystallite sizes were determined to be 71 and 79 nm, based on the Debye–Scherrer and Hall-Williamson methods, respectively. Fourier-transform infrared (FTIR) spectroscopy revealed characteristic BO₃ stretching and bending modes, while X-ray photoelectron spectroscopy (XPS) confirmed the presence of all constituent elements. The bandgap energy was measured to be 2.1 and 4.4 eV, making it suitable for both UV and visible light photocatalysis. The calculated Urbach energy of 200 meV suggests that the optical bandgap is influenced by defects such as oxygen vacancies and lattice irregularities. Under optimized conditions (10 mg/L catalyst in 100 mL of 10 ppm methylene blue aqueous solution), Li₆CuB₄O₁₀ demonstrated a photocatalytic degradation efficiency of 56.7% within 40 min. Kinetic studies indicated a first-order reaction with a rate constant of 0.0213 min⁻¹. The novelty of this work lies in the first-time demonstration of Li₆CuB₄O₁₀ as an efficient visible-light-driven photocatalyst, with notable degradation efficiency and defect-mediated optical properties.