Optimization Using Box-Behnken Design for Sustainable Naphthol Green Removal by Moringa Biochar-Modified Mg/Fe LDH Nanosheets

The potential of Moringa Olivera biochar-modified Mg/Fe layered double hydroxides (LDHs) nanosheets as a sustainable adsorbent for removing naphthol green (NG) has been studied. Mg/Fe-LDH modified with Moringa biochar was created using in situ co-precipitation method. The synthetic LDHs were characterized using thermogravimetric analysis (TGA), field emission scan electron microscope (FE-SEM), transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDS), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) techniques for nitrogen adsorption-desorption. Experimental design techniques are employed to optimize removal efficiency by examining factors such as pH, temperature, adsorbent dosage, and contact time. The resulting LDHs exhibits improved adsorption properties due to the combined effects of Mg/Fe LDHs and the high surface area of Moringa biochar (SBET increased from 87 to 144 m2/g after modification with biochar). Through response surface methodology, optimal conditions are determined to maximize NG removal and found to be pH 7.8, contact time 150 min, dose 380 mg, and temperature 25 degrees C. With an R2 value of 0.999, 0.998 and an adjusted R2 value of 0.997 and 0.993 in the RSM model for Mg/Fe and Mg/Fe-BC LDH, respectively, it can be concluded that the chosen model is appropriate for data analysis (quadratic model). Additionally, the adequacy precision was assessed using the signal-to-noise ratio, which was determined to be around 23 and 66 for Mg/Fe and Mg/Fe-BC LDH, respectively (significantly higher than the baseline of 4), indicating a satisfactory signal. The highest adsorption capacity of Mg/Fe and Mg/Fe-BC LDHs was determined to be 43 and 53 mg.g-1 (with removal efficiencies of 82 and 97%, respectively). The Freundlich adsorption isotherm model testing characterized the removal of NG. A comprehensive kinetic study reveals a pseudo-first order. This study finds out the potential of Moringa biochar-modified Mg/Fe LDHs nanosheets as an effective green adsorbent for naphthol green removal in comparison with Mg/Fe free of biochar.