Incorporation of Fe3+ into Mg/Al layered double hydroxide framework: effects on textural properties and photocatalytic activity for H2 generation

Abstract

This present work highlights the successful preparation of the ternary series of (Mg/Al + Fe)-CO₃ layered double hydroxides with a constant ratio of Mg/(Al + Fe) = 2 : 1 and their application for photocatalytic hydrogen generation from water. At Mg/(Al + Fe) = 2 : 1, the Al : Fe ratio was varied from 1 : 4 to lower the concentration of iron in the synthetic gel, in order to get samples with different amounts of iron in the brucite layers, and to find out the role of iron in photocatalytic activity. The presence of a hydrotalcite structure in the catalysts was clearly demonstrated from the powder X-ray diffraction (PXRD) pattern. The shifting of the diffraction plane d₁₁₀ towards lower angles clearly indicated the amount of Fe³⁺ substitution in the brucite layer increases with increasing addendum (Fe³⁺) concentration up to a certain limit and thereafter shows a decreasing trend. Further characterizations like Fourier transform infrared (FTIR), thermogravimetry (TG) and differential thermal analysis (DTA) described the formation of amorphous Fe₂O₃ upon addition of a higher amount of Fe³⁺ than the optimum amount that can be accommodated in the brucite layer. Other characterizations like UV–Vis DRS, BET surface area, transmission electron microscopy (TEM), photoluminescence spectra (PL) and X-ray photoelectron spectral studies (XPS) were performed to detect the efficiency of the catalysts towards H₂ evolution. Among all the prepared photocatalysts, LDH1(Mg/Al + Fe = 10 : 4 + 1), containing the highest amount of iron in the brucite layer, was found to be the most promising towards hydrogen evolution (301 μmol g⁻¹ h⁻¹) under visible light irradiation, which was attributed to the favourable surface structure and higher crystalline nature of hydrotalcites.