Improving solar thermal absorption of an anodic aluminum oxide-based photonic crystal with Cu-Ni composite nanoparticles.

In this study, an anodic aluminum oxide (AAO)-based photonic crystal, with a branched channel structure and deposited Cu-Ni composite nanoparticles, is fabricated for solar thermal absorption. The infrared-wave emission properties can be finely tuned by adjusting photonic band gap of the photonic crystal, facilitating the production of an excellent solar heat-absorbing material. Such a channel structure, as generated by anodic oxidation, possesses layers with high and low porosities, featuring a periodical change. The programmed power source (with periodically changed voltage and hence step-change current) enables sharp alteration of the porosity, forming the AAO-based photonic crystal oxidation film (with a complete photonic band gap). Subsequently, Cu-Ni composite nanoparticles are deposited into the pores of the AAO-based film at an alternating current (AC) frequency under different conditions. The optimized conditions (including periodical oxidation time, voltage, oxidation period, AC deposition voltage, time, and temperature) lead to the generation of a solar heat-absorbing composite coating that exhibits solar absorptance, thermal emissivity, and quality factor reaching values of 0.95, 0.13 and 7.3, respectively. In addition, the composite oxidation coating, with the AAO-based photonic crystal layer, shows a significantly lower thermal emissivity as compared to the counterpart in the absence of the AAO-based photonic crystal layer. [ABSTRACT FROM AUTHOR]