| Cadmium [Cd(II)] and lead [Pb(II)] are both heavy metals and are widely present in industrial wastewater,agricultural irrigation sewage,and domestic sewage.The International Agency for Research on Cancer listed Cd(II)and Pb(II)as human carcinogens because of them are harmful to the human body.Cd(II)and Pb(II)have the characteristics of high solubility and strong transfer in water,China listed Cd(II)and Pb(II)in the “List of Toxic and Harmful Water Pollutants(First batch)” in 2019.Therefore,it is urgent to find an effective adsorbent for the removal of Cd(II)and Pb(II)from wastewater.In this study,a biosafe adsorbent,metallothionein SmtA-modified selenium nanoparticles SmtA-SeNPs with high efficient Cd(II)and Pb(II)adsorption capacity was synthesized.Ligand microbial metallothionein SmtA is derived from the cyanobacteria Synechococcus elongatus PCC 7942.Metallothionein SmtA is synthesized by the engineering strain Escherichia coli and purified by alcohol precipitation and heating,which has the advantages of simplicity,safety,and high production.The preparation of selenium nanoparticles and the loading of SmtA were carried out using the chemical reagent cysteine solution.The chemical method is simple to operate and can synthesize SeNPs of high purity and easy modification.The adsorption experiments of Cd(II)and Pb(II)showed that the adsorption efficiency of SmtA-SeNPs on Cd(II)and Pb(II)was significantly higher than that of dissociative SmtA and unloaded SeNPs.By characterizing of SmtA-SeNPs before and after the adsorption of Cd(II)and Pb(II),it was found that before the adsorption of heavy metals,the diameters of SmtA-SeNPs were between 68.1 and 122.4 nm,and an average particle size of 94.6 nm.Cd(II)and Pb(II)elements can be detected on the surface of SeNPs after adsorption of heavy metals.FTIR showed the negatively charged(p H<5)functional groups such as amine,hydroxyl,and sulfhydryl groups on the surface of SmtA-SeNPs changed,which may be involved in the adsorption of heavy metals.In addition,the Cd(II)and Pb(II)adsorption models of SmtASeNPs fit the pseudo-second-order kinetic model and the Freundlich model,indicating that the Cd(II)and Pb(II)adsorption process of SmtA-SeNPs were the complex adsorption process involved in multitype physical and chemical reactions and a heterogeneous surface multilayer adsorption.It was inferred that the adsorption of Cd(II)and Pb(II)mainly depends on the electrostatic attraction and the metal chelation of abundant functional groups.The maximum adsorption capacity of SmtA-SeNPs was 506.3 mg/g for Cd(II)and346.7 mg/g for Pb(II),which were higher than the values of most published nanoparticles.SmtA-SeNPs were immobilized with a membrane filter to produce a 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.The SmtA-SeNPs filter was regenerated using subacid deionized water,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.In this study,SmtA were synthesized by alcohol precipitation,heating.SeNPs were synthesized by cysteine reduction.SmtA-SeNPs were synthesized by adding SmtA protein at the same time as the synthesis of SeNPs.The adsorption efficiency of SmtA-SeNPs on Cd(II)and Pb(II)is remarkable,which were higher than many published nanomaterials,and can be recycled.The findings demonstrate the feasibility of Cd(II)and Pb(II)absorption by SmtA-SeNPs and provide a novel approach for the remediation of Cd(II)and Pb(II)contamination.In summary,SmtA-SeNPs are novel,highly efficient,environmentally friendly,biologically safe,and easily prepared adsorbent materials and have good prospects for application in the environmental remediation field. |
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