Effective and Stable Adsorptive Removal of Cadmium(Ii) and Lead(Ii) Using Selenium Nanoparticles Modified by Microbial Smta Metallothionein

The metallothionein SmtA modified selenium nanoparticles (SmtA-SeNPs), an efficient adsorbent for Cd(II) and Pb(II), were synthesized in the present work. The ligand, microbial SmtA protein, was synthesized using an engineered strain Escherichia coli , posing the benefits of simplicity, safety, and high production. Characterization experiments reveal that SmtA-SeNPs were spheres with diameters between 68.1 and 122.4 nm. The surface of SmtA-SeNPs contained amino, hydroxyl, and sulfhydryl functional groups and was negatively charged when the pH exceeded 5. Most importantly, SmtA-SeNPs displayed better adsorption performance than dissociative SmtA and SeNPs. The adsorption of Cd(II) and Pb(II) mainly depends on the electrostatic attractions and the metal chelation of abundant functional groups on the surface. Moreover, the adsorption kinetic curve was described well with the pseudo-second-order model and the thermodynamics curves fitted well to the Freundlich model. The maximum adsorption capacity was 567.3 mg/g for Cd(II) and 776.0 mg/g for Pb(II), which was higher than the values of most nanoparticles. In addition, SmtA-SeNPs were immobilized with a membrane filter to produce SmtA-SeNPs filter, and the percentage removal of Cd(II) and Pb(II) increased from 26.75% to 98.13% for Cd(II) and from 9.95% to 99.20% compared with the blank filter. Moreover, the SmtA-SeNPs filter was regenerated with an efficiency greater than 94.17% using subacid water (pH 4), and the filter exhibited a stable removal ratio of Cd(II) and Pb(II) in ten continuous cycles of Cd(II) or Pb(II) containing wastewater treatment. The residual amounts of Cd and Pb met national standard levels of wastewater discharge