Selective heavy metal removal and water purification by microfluidically-generated chitosan microspheres: Characteristics, modeling and application

Many industrial wastewater streams contain heavy metals, posing serious and irreversible damage to humans and living organisms, even at low concentrations due to their high toxicity and persistence in the environment. In this study, high-performance monodispersed chitosan (CS) microspheres were prepared using a simple microfluidic method and evaluated for metal removal from contaminated water. Batch experiments were carried out to evaluate the adsorption characteristics for the removal of copper ions, one representative heavy metal, from aqueous solutions. The inherent advantages of microfluidics enabled a precise control of particle size (CV = 2.3%), while exhibiting outstanding selectivity towards target ions (adsorption capacity 75.52 mg g−1) and fair regeneration (re-adsorption efficiency 74% after 5 cycles). An integrated adsorption mechanism analytic system was developed based on different adsorption kinetics and isotherms models, providing an excellent adsorption prediction model with pseudo-second order kinetics (R2 = 0.999), while the isotherm was fitted best to the Langmuir model (R2 = 0.998). The multi-step adsorption process was revealed via quantitative measurements and schematically described. Selective adsorption performance of CS microspheres in the present of other competitive metal ions with different valence states has been demonstrated and studied by both experimental and density functional theory (DFT) analysis

Synergistic DFT-guided design and microfluidic synthesis of high-performance ion-imprinted biosorbents for selective heavy metal removal

International water security has become unprecedentedly complicated, therefore, effective and selective removal of hazardous materials, especially toxic heavy metal ions, are significant for effluent purification. In this regard, ion-imprinted polymers with special recognition cavities have received much attention. However, configuration screening and performance optimization of functional materials by trial-and-error design method is undoubtedly time- and money-consuming. In this study, high-performance ion-imprinted chitosan microspheres (ICSMs) were successfully designed via density functional theory (DFT) calculation and synthesized via facile microfluidic technology. As-synthesized ICSMs exhibited highly uniform morphology (Dav = 420.6 µm, CV = 3.6%) and ultra-high adsorption capacity (qmax = 107.12 mg g−1). The adsorption isotherm was best fitted to the Langmuir model while the kinetic data followed the pseudo-second order model, indicating a dominant role of chemisorptions. Also, ICSMs displayed satisfactory stability and reusability (95.34 mg g−1, after 5 cycles). Moreover, the selective adsorption mechanism was quantitative revealed by electronegativity, electrophilicity index, adsorption energy (Ea) and bond length. This study is expected to lay a foundation for high-performance biosorbents design and synthesis for future water remediation