The Behavior of Divalent Metals in Double-Layered Hydroxides as a Fenton Bimetallic Catalyst for Dye Decoloration: Kinetics and Experimental Design

This study investigates the influence of divalent metals—(Mg(II), Co(II), and Ni(II)) in layered double hydroxides (LDHs), with a constant trivalent Fe(III) component—on the decoloration of crystal violet and methyl blue dyes via a Fenton-type oxidation reaction. The catalysts, synthesized by co-precipitation and hydrothermal treatment, were tested in both hydroxide and oxide forms under varying agitation conditions (0 and 280 rpm). A 22 × 3 factorial design was used to analyze the effect of the divalent metal type, catalyst phase, and stirring. The Mg/Fe oxide, with the highest BET surface area (144 m2/g) and crystallite size (59.7 nm), showed superior performance—achieving up to 98% decoloration of crystal violet and 97% of methyl blue within 1 h. The kinetic analysis revealed pseudo-second-order and pseudo-first-order fits for crystal violet and methyl blue, respectively. These findings suggest that LDH-based catalysts provide a fast, low-cost, and effective option for dye removal in aqueous systems.