Magnetic multi-walled carbon nanotubes as an efficient sorbent for pirimicarb removal from aqueous solutions in continuous (FBAC) and batch formats: thermodynamic, kinetic, isotherm study, optimization and modeling by RSM-ANN

Abstract

In this study magnetic carbon nanotubes (CNT) were synthesized and used for the removal of pirimicarb insecticide. For characterization of CNT/Fe3O4 nanocomposite, various analyses such as FT-IR, XRD, VSM, SEM, EDX, Map, and TEM were used. The results of this analysis showed that the CNT/Fe3O4 nanocomposite was well-synthesized and had great paramagnetic properties (with Ms = 38.12 emu/g) and effective functional groups. The removal of pirimicarb process by this nanocomposite was performed in fixed bed adsorption column (FBAC) and batch format. In batch format, the effects of pH, contact time, composite dosage, and concentration of pirimicarb were studied using surface response method-central composite design (RSM-CCD) and artificial neural network (ANN). The results of response surface methodology demonstrated that the maximum efficiency of adsorption is 94.62 % while pH, contact time, composite dosage, and concentration of pirimicarb are 6.72, 47.56 min, 1.07 g/L and 43.91 ppm, respectively. Also, RSM-CCD modeling was more capable of expressing the adsorption process than artificial neural network modeling due to higher correlation coefficient and lower error. The equilibrium and kinetic studies showed that the process follows the sips model and pseudo-second-order model respectively and is physically desirable. Also, the mechanism of adsorption was best fitted in double-exponential model and is consisted of both inter and intra-particle diffusion. Thermodynamic studies suggested that pirimicarb adsorption onto CNT/Fe3O4 was a spontaneous and exothermic process. In addition, the results of FBAC showed that the breakthrough time was reduced from 365 min to 9 min by increasing temperature (25 °C, 35 °C and 45 °C) and exhaustion time was diminished by increasing in temperature.