Efficient removal of sulfamethoxazole antibiotic from aqueous solution using red mud/layered double hydroxide nanocomposite: Optimization, kinetic, and isotherm studies

The present work has proposed the preparation of red mud-supported CaMgAl-layered double hydroxide (LDH) as a novel adsorbent via co-precipitation method and evaluation of its ability as an adsorbent for the sequestration of sulfamethoxazole antibiotic (SMZ) from aqueous solution in a batch system. The prepared adsorbent was characterized by using X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Spectroscopy (EDS), Brunauer-Emmett-Teller (BET) Analysis and Fourier Transform Infrared Spectroscopy (FTIR) and the effects of experimental conditions: pH, adsorbent dosage, initial SMZ concentration and contact time were achieved by using response surface methodology (RSM) with a central composite design (CCD). Maximum sequestration efficiency was seen at 87.33 % under the most favorable conditions (pH = 7, dose = 0.5 g/100 ml, concentration = 70 mg/l, time = 90 min). Analysis of variance (ANOVA) based on the CCD-RSM showed a good fit between quadratic model predictions and the experimental results with an R 2 value of 0.9703. The Langmuir isotherm model fitted well with the adsorption data, indicating monolayer adsorption with a maximum adsorption capacity (q max ) of 98.183 mg/g. Additionally, the adsorption kinetics followed a pseudo-second-order kinetic model, suggesting chemisorption as the dominant mechanism. The adsorbent also exhibited good regeneration potential, retaining significant capacity after six cycles with only a 40.22 % decline in efficiency. Overall, the results confirm that the low-cost CaMgAl-LDH/RM is an excellent adsorbent for effective SMZ sequestration from wastewater.