Controllable luminescence of Li-Al layered double hydroxide used as a sensor for reversible sensing of carbonate
This investigation finds that Li-Al layered double hydroxide (Li-Al-CO3 LDH) that has no intercalated chromophore and no rare earth dopant could function as a luminescent material with controllable luminescence properties. The luminescence of the LDH can be tuned to ultraviolet (UV), blue or red simply by calcining the Li-Al-CO3 LDH at high temperatures. The LDH calcined at 300°C emitted strong blue luminescence with its blue emission intensity five times much higher than that of the Li-Al-CO3 LDH. The Li-Al-CO3 LDH and the 300 °C-calcined LDH were investigated by 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. Luminescence mechanism of the strong blue emission is mainly associated with the oxygen defect and pentahedrally-coordinated AlO5 site in the 300 °C-calcined LDH. Fourier-transform infrared spectroscopy (FT-IR) makes it a versatile technique to recognize the luminescence intensity of an LDH material. It is because there is a negative relationship between the blue emission intensity emitted from an LDH material and the FTIR intensity of the ν3 mode CO 2- adsorption band in the LDH. The functional application of the 300°C-calcined LDH material was explored to be an effective luminescent anion sensor that responds to CO32- anions in aqueous solution. The selective sensing of CO32- anions extends over a wide range of concentrations from 0 to 2500 ppm. The 300°C-calcined LDH exhibits reversibly effective in sensing CO32-. The LDH can also be used to detect the furnace temperature during post-processing heat treatment.