Effect of Co²⁺ Substitution in the Framework of Carbonate Intercalated Cu/Cr LDH on Structural, Electronic, Optical, and Photocatalytic Properties

Abstract

In the present work, a series of Cu–Co/Cr ternary LDHs containing CO₃^2– in the interlayer was prepared by coprecipitation method. To investigate the effect of divalent metal ions on the catalytic activity, we vaired Cu/Co atomic ratios, keeping constant the atomic ratio of Cu+Co/Cr (2:1). Several characterization tools, such as powder X-ray diffraction (PXRD), Brunauer–Emmett–Teller surface area, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy, were employed to study the phase structures, textural, and optical properties of the samples. The PXRD of all samples showed the characteristic pattern of the hydrotalcite without any detectable impurity phases. The expected cell parameter variation was calculated assuming the Vegard’s law and proved the ideal atomic arrangement for the cations in the brucite layer. The shifting of the diffraction plane “d110” toward lower angle clearly indicates that Co²⁺ is substituted in the brucite layer. The formation of the highest amount of hydroxyl radicals (OH^•) on the surface of visible-light illuminated LDHs detected by the luminescence technique using terephthalic acid as probe molecules supports the highest activity LDH-4 with Cu/Co atomic ratio 0.033 + 0.1 (i.e., 1:3) toward MG degradation. The degradation of malachite green (MG) followed pseudo-first-order kinetics. The highest photocatalytic activity of LDH4 ascribed to the oxo-bridged system was explained by UV–vis DRS and EPR study.The degradation of MG followed pseudo-first-order kinetics, and the photocatalytic degradation mechanism was also explained in detail