Revealing the Multifunctional Properties of Zn-Al Layered Double Hydroxides Intercalated with Halide Ions (Cl−, Br−, I−): Textural, Electrical, Dielectric, and Optical Properties

Herein, three phases of halide ions (chloride, bromide, and iodide) intercalated in zinc-aluminum layered double hydroxides (LDH) were synthesized by co-precipitation method at constant pH with Zn/Al = 2 (molar ratio) and characterized by X-ray diffraction, Raman spectroscopy, thermal gravimetric analysis, SEM/EDX, BET analysis, laser particle size distribution analysis, impedance spectroscopy, and diffuse reflectance spectroscopy. It was found that with increasing halide size from chloride to iodide, the interlayer distance (d₀₀₃) of the cell increased, while the inter-metallic distance (d₁₁₀) remains almost constant, confirmed by the characteristic Raman bands. However, the thermal stability of the halide intercalated LDH decreased in the order of bromide–iodide–chloride, while the BET surface area increased with increasing halide size confirmed by the opposite evolution of the particle size distribution. In addition, the electrical conductivity increased at medium frequencies and decreased at high frequencies with increasing halid size, while the bromide intercalated LDH showed an increase in the dielectric constant values at low and high frequencies. Furthermore, all the LDH phases showed an improvement in the dielectric properties by reducing the dielectric loss tangent values up to 0.01 at 1 MHz. In terms of optical properties, the chloride- and iodide-containing LDH exhibited high reflectance percentages up to 93% in the Vis–NIR region and enhanced absorption coefficients in the UV light resulting in a wide band gap energy of 5.95 eV for the chloride and two ones of 5.44 and 4.76 eV for the iodide, while the bromide-containing LDH showed an enhancement of the Vis–NIR absorption leading to gap energies of 2.49 and 1.27 eV, respectively. The findings of this study indicate that in the Vis–NIR region, the chloride- and iodid-containing LDH have potential applications in the development of innovative dielectric reflective materials as well the bromide-containing LDH as an efficient dielectric absorbing material.