Durable CuZnAl Layered Double Hydroxides for Robust Removal of Methyl Orange from Water

Abstract In this study, CuZnAl layered double hydroxide (LDH) adsorbents were synthesized via a facile co-precipitation method and evaluated for the removal of methyl orange (MO), a model anionic azo dye. Comprehensive characterization using XRD, FTIR, BET, and SEM confirmed the successful formation of phase-pure carbonate-type LDHs with ordered layer stacking, mesoporous texture, and plate-like morphology. Among the samples tested, CuZnAl exhibited the highest BET surface area (45 m 2 g −1 ) and the largest total pore volume (0.432 cm 3 g −1 ), facilitating superior adsorption performance. Batch experiments revealed that all adsorbents achieved maximum removal at acidic pH, with CuZnAl reaching ≈ 100% MO removal at pH 3. Adsorption kinetics followed the pseudo-second-order model ( R 2 > 0.99), indicating that chemisorption and interlayer ion exchange were the dominant mechanisms. The Langmuir isotherm model provided excellent fits ( R 2 > 0.96), with the highest maximum monolayer adsorption capacity ( qₘ ) observed for CuZnAl (392.2 mg g −1 ), followed by CuAl (293.3 mg g −1 ) and ZnAl (235.3 mg g −1 ). Reusability studies demonstrated robust cycling performance for CuZnAl, which retained ≈ 95% of its initial removal capacity after five cycles, whereas ZnAl suffered the greatest decline. Graphical Abstract