Visible Light Trapping against Charge Recombination in FeOx–TiO2 Photonic Crystal Photocatalysts

Tailoring metal oxide photocatalysts in the form of heterostructured photonic crystals has spurred particular interest as an advanced route to simultaneously improve harnessing of solar light and charge separation relying on the combined effect of light trapping by macroporous periodic structures and compositional materials’ modifications. In this work, surface deposition of FeOx nanoclusters on TiO2 photonic crystals is investigated to explore the interplay of slow-photon amplification, visible light absorption, and charge separation in FeOx–TiO2 photocatalytic films. Photonic bandgap engineered TiO2 inverse opals deposited by the convective evaporation-induced co-assembly method were surface modified by successive chemisorption-calcination cycles using Fe(III) acetylacetonate, which allowed the controlled variation of FeOx loading on the photonic films. Low amounts of FeOx nanoclusters on the TiO2 inverse opals resulted in diameter-selective improvements of photocatalytic performance on salicylic acid degradation and photocurrent density under visible light, surpassing similarly modified P25 films. The observed enhancement was related to the combination of optimal light trapping and charge separation induced by the FeOx–TiO2 interfacial coupling. However, an increase of the FeOx loading resulted in severe performance deterioration, particularly prominent under UV-Vis light, attributed to persistent surface recombination via diverse defect d-states.

Contact Angle Tuning of Copper Microporous Structures

Two-phase, capillary-fed cooling devices are appealing thermal management technologies due to their potential for high heat transfer performance and ease of system-level integration. While existing evaporative wicking structures such as copper inverse opals (CIOs) and copper wire meshes (CWMs) have shown promise for achieving target heat dissipation rates of 100 Wcm−2 or greater, the reliability of these structures for long-term device operation and optimal capillary-driven boiling performance has not received much attention. To ensure proper functionality of the evaporator wick, the microporous copper structures must retain a hydrophilic contact angle during device operation. Surface oxidation of the copper is a critical degradation mechanism that must be addressed to preserve the integrity of the wick. In this study, we systematically investigate the contact angle change of untreated copper and various copper oxides under different conditions. To avoid the formation of hydrophobic Cu2O, we pre-oxidize the copper micro porous wick to form hydrophilic cupric oxide CuO and study the effect of various thermal and chemical oxidation recipes on the hydrophilicity and morphology of the resulting structures. A chemical oxidation formula is implemented for the creation of a stable superhydrophilic surface at a low temperature (70°C) for copper inverse opals (CIOs) (5 μm pore size) and copper wire meshes (CWMs) (76 μm pore opening). The recipe has been optimized to create nano CuO needles with a length of < 100 nm and keep the necks (∼1 μm diameter) open for better capillary wicking of the working fluid. The findings of this study potentially benefit the development of copper-based capillary-fed cooling devices.