Controllable luminescence of a Li–Al layered double hydroxide used as a sensor for reversible sensing of carbonate

Abstract

This investigation finds that a 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 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. The luminescence mechanism of the strong blue emission is mainly associated with the oxygen defects and pentahedrally-coordinated AlO₅ sites in the 300 °C-calcined LDH. Fourier-transform infrared spectroscopy (FT-IR) is 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 from an LDH material and the FTIR intensity of the ν₃ mode CO₃²⁻ adsorption band in the LDH. The functional application of the 300 °C-calcined LDH material was explored and it was found 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 effective reversible sensing of CO₃²⁻. The LDH can also be used to detect the furnace temperature during post-processing heat treatment.