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Synthesis and CO2 absorption properties of single-phase Li2CuO2 oxide were studied by X-ray powder diffraction and thermogravimetry. Samples of Li2CuO2 were prepared in solid state using Li2CO3 and CuO as starting reagents. A mixture of Li2CO3 and CuO was heated at temperatures of 600–1000 °C and then quenched to room temperature. From XRD, it was found that single-phase Li2CuO2 can be obtained by heat treatment at 680–685 °C with the quenching operation. The single phase was never obtained without quenching; that is, quenching rate (°C s−1) seems to be an important factor which determinates whether sample is obtained as a single phase or not. From thermogravimetry, it was found that Li2CuO2 begins to absorb CO2 at around 230 °C, then drastically absorbs CO2 at over 600 °C, reaching 40.2 mass % maximum CO2 absorption, and finally emits CO2 over 900 °C. The maximum CO2 absorption (40.2 mass %) is larger than that (36.7 mass %) of Li4SiO4 CO2 absorbent.

In this study, we investigated the relationship of light output power with the optical thickness of the p-layers in AlGaN-based deep ultraviolet light-emitting diodes with a transparent high-Al-composition p-AlGaN clad layer, a thin p-GaN contact layer, and a reflective p-type electrode. By adjusting the thickness of the transparent high-Al-composition p-AlGaN clad layer, we observed a marked change in light output power. A maximum light output power of 385 mW at 1500 mA, a maximum external quantum efficiency of 15.7% at 10 mA, and a maximum wall-plug efficiency of 15.3% at 10 mA were obtained at an emission wavelength of 275 nm.

Particle size dependence of CO2 absorption rate of powdered Li4SiO4 with four kinds of particle sizes was studied by SEM observation, particle size distribution measurement, and thermogravimetry. Average particle sizes of the powdered single phase Li4SiO4 samples were estimated about 26 μm, 34 μm, 53 μm, 70 μm, respectively by the particle size distribution measurement and SEM observation. The measurement of apparent rate constant k for the CO2 absorption reaction showed that k values of all the powdered Li4SiO4 samples increase with the increasing measurement temperature T, following the Arrhenius equation in the region of 620-660°C, while the k values abruptly increase deviating the Arrhenius equation over 670°C. It was also noted that the k values seem to depend on the particle size of the powdered Li4SiO4 samples, that is, the k values increase with the decreasing particle size. Moreover, difference between the k values of all the powdered samples at same temperature was found small in the region of 620-660°C, while the difference was found large over 670°C. For Li4SiO4 with smaller particle size, Δk = k700°C -k660°C was found larger, vice versa, the Δk was found smaller for Li4SiO4 with larger particle size. The values seem to correspond with reaction mechanism for CO2 absorption of Li4SiO4 particle.

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