Parametric modelling and analysis to optimize adsorption of Atrazine by MgO/Fe3O4-synthesized porous carbons in water environment

Abstract

Abstract Background Pesticide contamination to water, continues to raise ecotoxicological and human concerns. Studying the application of green adsorbents for removing pesticides from water can significantly reduce ecotoxicological impacts and sustain reclamation of water bodies. Results The current study investigated the adsorption capacity of MgO/Fe3O4 modified coconut shell biochar (MCSB) towards Atrazine removal in water. The prepared adsorbents were structurally constricted and obtained relative amount of mesopore spaces filled by nanoparticles which equally provided active occupancy/binding sites for Atrazine molecule deposition. Equilibrium isotherm studies under temperature regimes of 300 K, 318 K and 328 K were best described by the Freundlich isotherm (R 2 = 0.95–0.97) with highest adsorption capacity corresponding to the highest temperature range (328 K) at (K F = 9.60 L mg−1). The kinetics modelling was best fitted to the pseudo second-order kinetic (R 2 = 0.90–0.98) reaction pathways revealing that Atrazine uptake and removal occurred majorly over non-homogenous surfaces and high influence of surface functional groups in the process. Atrazine uptake by the adsorbent were mostly efficient within pH ranges of 2–6. Thermodynamics values of free energy ΔG° were negative ranging (ΔG° = − 27.50 to − 29.77 kJ mol−1) across the varying reaction temperature indicating an exothermic reaction, while enthalpy (ΔH°) (34.59 kJ mol) and entropy (ΔS°) (90.88 JK−1/mol) values were positive revealing a degree of spontaneity which facilitated Atrazine uptake. The adsorbents regeneration capacities over five cycles were observed to decrease proportionally with maximum yields up to 50–60%. Optimization of the adsorption condition by response surface modelling (RSM) and Central Composite Design (CCD) could reveal optimum conditions for Atrazine removal through interaction of different variables at pH = 12, adsorbate initial concentration at 12 mg L−1, adsorbate dosage at 0.5 g and reaction temperature at 54 °C. The overall mechanisms of the adsorption could be contributed by availability of surface functional groups on the MCSB surface through increase in hydrophilicity facilitating easy Atrazine molecule attachment via hydrogen bonding and improved surface complexation. Conclusions The as-synthesized MCSB adsorbent could uptake and remove Atrazine in water. A high pH, low concentration, low adsorbent dosage and high reaction temperature could be optimized conditions to attain highest Atrazine removal by the synthesized adsorbent. Graphical Abstract

Keywords

• Atrazine
• Adsorption
• Coconut shell biochar
• Response surface methodology