Synthesis of Cu₁₃ NCs/TiO₂ composite material and experimental design for photocatalytic CO₂ reduction

In the context of the global “dual carbon” strategy, converting carbon dioxide (CO₂) into high-value chemicals through photocatalytic reduction represents an important approach to addressing energy and environmental challenges. Titanium dioxide (TiO₂) has been widely studied as a photocatalyst owing to its good stability, low cost, and non-toxicity. However, its wide band gap and the rapid recombination of photogenerated electron–hole pairs severely limit its efficiency. Recent studies have shown that atomically precise copper nanoclusters (Cu NCs), which possess unique electronic properties and abundant active sites, can enhance charge separation and catalytic activity. This study aims to design and implement a comprehensive undergraduate experiment that combines cutting-edge scientific research with teaching practice, enabling students to gain hands-on experience in the synthesis, characterization, and application of nanomaterials while fostering their understanding of green chemistry and sustainable technologies.

The experimental design includes the following key steps: material synthesis, structural characterization, performance testing, and theoretical simulation. First, a two-dimensional sheet-like TiO₂ was prepared by a hydrothermal method. Atomically precise Cu₁₃ NCs with the formula Cu₁₃H₁₀(SR)₃(PPh₃)₇ were synthesized by a solvent-mediated precipitation method. Subsequently, Cu₁₃ NCs were loaded onto the TiO₂ surface using a low-temperature deposition strategy, followed by freeze-drying and mild thermal treatment, yielding Cu₁₃ NCs/TiO₂ composite catalysts with different loading amounts. The morphology, elemental distribution, crystal structure, surface chemistry and electronic states, surface wettability, and optical properties of the materials were analyzed using a series of characterization techniques. Photoelectrochemical performance was measured using an electrochemical workstation. Under irradiation from a 300 W xenon lamp in a gas-sealed circulation system, the photocatalytic CO₂ reduction performance was evaluated, and the gaseous products were quantitatively analyzed by gas chromatography. The electronic structure, charge transfer, and light absorption properties of the composite materials were simulated using density functional theory (DFT).

Multiple structural characterizations confirmed the successful synthesis and loading of Cu₁₃ NCs on TiO₂. X-ray photoelectron spectroscopy (XPS) analysis indicated the presence of Cu(Ⅱ), and the composite material exhibited enhanced surface oxygen species, which is beneficial for CO₂ adsorption. The ultraviolet–visible (UV–Vis) absorption spectrum showed that the light absorption capacity of the composite material in the visible light region was enhanced compared with that of pure TiO₂. The Cu₁₃ NCs/TiO₂ composite material demonstrated excellent photoelectrochemical performance. Transient photocurrent measurements showed a marked increase in the photocurrent density of the composite material, and the Nyquist plot from electrochemical impedance spectroscopy (EIS) indicated a smaller arc radius, suggesting improved charge transfer kinetics. In the photocatalytic CO₂ reduction test, the CO production rate of the Cu₁₃/TiO₂-2 composite material reached 517.23 μmol g^–1 h^–1, which was more than twice that of pristine TiO₂. DFT calculations provided theoretical insights, indicating that the formation of the Cu₁₃/TiO₂ heterojunction promoted the transfer of electrons from TiO₂ to Cu₁₃ NCs (approximately 0.88 e), creating an electron trap that facilitates charge separation.

This study successfully designed and conducted a comprehensive experiment integrating the synthesis and characterization of Cu₁₃ NCs/TiO₂ composite materials and their application in photocatalytic CO₂ reduction. The experiment demonstrated that an interface heterojunction was constructed between atomically precise Cu nanoclusters and TiO₂. This heterojunction effectively shortened the electron transmission path, inhibited charge carrier recombination, and enhanced light absorption and surface reaction activity, thereby markedly improving the photocatalytic CO₂-to-CO conversion rate. In terms of teaching, it provided a comprehensive platform for undergraduate students to learn material synthesis techniques, characterization methods, performance evaluation schemes, and basic theoretical simulations. It effectively bridges fundamental knowledge with cutting-edge research, aligns with the national “carbon neutrality” strategy, and cultivates students’ innovative thinking and practical abilities.