Investigation of methylene blue adsorption from aqueous solution onto ZnO nanoparticles: equilibrium and Box-Behnken optimisation design

Throughout this report, ZnO nanoparticles are synthesised by coprecipitation as a new adsorbent. XRD, FTIR, SEM, PL, and UV-visible spectroscopy characterise the obtained nanoparticles. Characterisation of prepared nanoparticles provided evidence of the impact of duration of calcination on particle size and morphology. The new adsorbent was used to remove cationic dye (methylene blue (MB)) from aqueous solutions by batch adsorption technique. The effect of pH, adsorbent dosage, ion strength, contact time, and the temperature was investigated. The pHPZC was approximately pH 7.2. The results revealed that an amount of 0.1 g/L ZnO-NPs showed maximum removal efficiency of each dye (50 ppm) at pH 8.5. The adsorption process of the MB followed the Langmuir model with a correlating constant (R-2) higher than 0.99 and with a maximum capacity (qm) value of 62.5 mg/g. The pseudo-second-order (R-2 > 0.9986) model was most appropriate in the description of the adsorption process. Thermodynamic parameters Delta S-0(0.0001 J/mol K), Delta H-0(- 3,692 kJ/mol), and Delta G(0)(between - 4.143 to and - 4.189 kJ/mol) were investigated at four temperatures (25, 35, 45, and 55 degrees C). The uptake process of the MB occurs spontaneously following an exothermic process and shows that the adsorption follows the physisorption mechanism. It would appear that hydrogen bonding was included in the potential mechanism governing MB adsorption on the ZnO nanoparticles at pH 8.5. In order to optimise various process parameters, e.g. pH solution (X1: 4-11), adsorbing dose (X2: 0,01-0,1 g/L), [MB] Concentration dye (X3: 50-300 mg/L), and contact time (X4: 20-120 min), Box-Behnken, design (BBD) in response surface methodology (RSM) was used. The experimental results were based on a second-order polynomial equation. Overall, the adjusted coefficient of determination (R-2) value of 0.99 indicated that the used model was quite suitable and the selected RSM was successful in optimising the decolarizations conditions of MB.