Sorption enhancement of nickel(II) from wastewater by ZIF-8 modified with poly (sodium 4-styrenesulfonate): Mechanism and kinetic study

Effective removal of toxic metal Ni(II) from wastewater is essential to water safety and human health. Although zeolitic imidazolate framework-8 (ZIF-8) has demonstrated outstanding selective removal of Ni(II) in highsalinity wastewater, the practical applications of ZIF-8 are mainly limited by low active sites utilization, slow adsorption kinetics and poor reusability. In this study, we prepared a novel negatively charged poly (sodium 4-styrenesulfonate) (PSS)-modified ZIF-8 adsorbent, ZIF-8@PSS (12 h), which increased the adsorption rate of Ni (II) (kinetic constant k = 0.0299 g mg(-1) min(-1)) by nearly 10 times and the adsorption capacity (329.58 mg/g) by 1.6 times compared to pristine ZIF-8 (k = 0.0021 g mg(-1) min(-1)). ZIF-8@PSS (12 h) (0.5 g/L) could quickly decrease Ni(II) (C0 = 1.0 mg/L) to 0.1 mg/L (discharged standard) in 25 min, while 600 min for ZIF-8. Batch experiments and characterization analyses revealed PSS can improve particle dispersion, increase active sites utilization, and strengthen Ni(II) diffusion kinetics, thereby enhancing the adsorption of Ni(II). Among them, the increase in active sites utilization of ZIF-8 contributes 83.3% to capacity improvement, while the -SO3- on PSS is 16.7%. Furthermore, the enhancements of adsorption kinetics and capacity were also applicable to other heavy metals (e.g., Cu2+, Pb2+, Cr3+, Cd2+). Column experiments using real nickel plating effluent shown that 1 g ZIF-8@PSS (12 h) could produce similar to 3675 mL of clean water before breakthrough (Ni2+ < 0.1 mg/L). Moreover, a specific nickel chelator, dimethylglyoxime was used to regenerate the exhausted adsorbent and showed an insignificant capacity loss after four cycles. This study indicates the potential of ZIF-8@PSS (12 h) to remove Ni (II) from nickel plating effluent.

Automated summary

A novel negatively charged poly (sodium 4-styrenesulfonate) (PSS)-modified ZIF-8 adsorbent, ZIF-8@PSS (12 h), was prepared in this study, significantly increasing the adsorption rate and capacity of Ni(II) and quickly reducing Ni(II) levels in wastewater to below safety standards. The introduction of PSS improved particle dispersion, active sites utilization, and Ni(II) diffusion kinetics, leading to enhanced adsorption performance.