Unravelling the interfacial secondary electron transfer mechanism in HfO2@TiO2 core-shell nanostructures for boosted X-ray energy conversion.

The performance of X-ray radiocatalysis is fundamentally limited by the mismatch between high X-ray absorption and efficient charge utilization. Herein, we report an elaborate design of constructing HfO2@TiO2 core-shell heterostructures that synergistically integrates X-ray energy harvesting and catalytic amplification for enhanced X-ray radiocatalysis. Monte Carlo simulations map the three-dimensional energy deposition profile and display a critical TiO2 shell thickness of over 10 nm that maximizes the potential of electron-hole pair excitation by HfO2-derived secondary electrons inside the TiO2 shell. Experimental validations reveal a peak radiocatalytic activity at an optimized TiO2 shell thickness of 14.7 ± 4.6 nm, which enables effective superoxide generation and cytotoxicity under X-ray irradiation. In situ valence-to-core X-ray emission spectroscopy (vtc-XES) of Ti Kβ lines further unveiled that interfacial transfer of HfO2-derived secondary electrons enhances charge excitation from the valence band of TiO2, facilitating the rapid conversion of dissolved O2 into O2˙- for maximizing radiocatalytic performance. This work establishes a rational design principle for core-shell radiation converters to optimize radiation energy conversion and electron-hole pair excitation for efficient surface catalytic reactions, offering a pathway for advanced applications.