Layered Double Hydroxides as Precursors to Ti⁴⁺ Doped MgO Nanoparticles with Tunable Band Gap

TixMg1-xO solid solutions with tunable band gap are potential candidates for various applications such as photocatalysis, water splitting, dielectrics, etc. Present study reports the synthesis of TixMg1-xO (x = 0.02 to 0.5) solid solution nanoparticles via a simple sol-gel method. First, layered double hydroxides (precursors) are produced by sol-gel method, which on calcination produce the TixMg1-xO solid solutions. The effect of concentration of titanium (introduced as titanium isopropoxide during the synthesis) on the optical properties of TixMg1-xO solid solution nanoparticles has been investigated. Phase analysis of the precursors demonstrates the formation of Mg-Ti layered double hydroxides and after calcination at 500 °C and 700 °C, Ti4+ doped MgO as well as Mg2TiO4 and MgTiO3 are formed. Scanning electron microscopy images show that the TixMg1-xO samples calcined at 500 °C possess flake-like morphology and after calcination at 700 °C, small agglomerated nanoparticles are formed. In the TEM images, flakes along with nanoparticles are observed in the TixMg1-xO solid solutions prepared using lower concentration of titanium isopropoxide (0.4 and 2.0 mmol) whereas agglomerated nanoparticles are formed in the TixMg1-xO solid solution prepared using higher concentration of titanium isopropoxide (5.0 mmol). Diffuse reflectance spectroscopic studies indicate that the band gap of TixMg1-xO solid solution nanoparticles can be tuned from 3.7 eV to 4.4 eV by varying the concentration of titanium and calcination temperature. Layered double hydroxides are excellent precursors that can yield band gap tunable TixMg1-xO solid solution nanoparticles on calcination with homogeneous elemental distribution.