Laser Ablated titanium Micro-Nanolayer for High-Temperature radiative cooling

Passive radiative cooling represents an energy‑free thermal management strategy with significant potential for applications requiring high thermal loads and long‑term reliability. Achieving efficient radiative cooling on metallic substrates, however, remains challenging due to the inherent trade‑offs among spectral selectivity, structural robustness, and large‑area manufacturability. Here, hierarchical micro-nano papillae (MNP) structures were directly fabricated on titanium surfaces by nanosecond pulsed laser texturing for high-temperature radiative cooling. Orthogonal optimization combined with single-factor verification identified an average laser power of 4.15 W, a scanning interval of 1 μm, and a scanning speed of 40 mm·s −1 as the optimal processing conditions, with laser power, scanning interval, and scanning speed primarily regulating surface oxidation, structural overlap, and laser–material interaction time, respectively. The resulting MNP surface exhibits a highly disordered hierarchical morphology composed of microscale grooves, papillae, secondary micro/nanoscale protrusions, and interstructural gaps. Together with the laser-induced oxide-rich surface layer, these multiscale features enhance light trapping, multiple reflection and scattering, and infrared optical interactions, resulting in an emissivity exceeding 0.9 over the 2.5–15 μm range. Under an input heating power of 17.4 W, the MNP sample exhibited temperature reductions of 27.7 °C during daytime and 35.2 °C at night relative to untreated titanium. Thermal treatment from 300 to 500 °C further demonstrated excellent morphological and emissivity stability, with a slight increase in emissivity at elevated temperatures. Notably, prolonged heating at 300 °C for 4 h preserved the enhanced radiative performance, while compositional analysis revealed the conversion of metastable Ti 3 ⁺ species into more stable Ti 4 ⁺ states, suggesting improved thermal stability of the surface chemistry. In addition, the MNP surface enables evaporation-assisted cooling and water-repellent self-cleaning functionality, demonstrating its potential as a multifunctional platform for high-temperature thermal management.