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In this study, thiolated magnetic iron oxide nanoparticles (Fe 3 O 4 -SH) were prepared and characterized in detail, which exhibited benign superparamagnetism and magnetic recoverability. And the adsorption and desorption processes for various heavy metals, including Pb 2+ , Ni 2+ , Zn 2+ and Cu 2+ , had been investigated comprehensively both in single and mixed systems using the Fe 3 O 4 -SH nanoparticles as adsorbents. The results showed that heavy metal ions could be removed rapidly depending on the complexation with the SH-groups on the Fe 3 O 4 -SH surface. Besides, the adsorption was all sensitive to pH and ionic strength while the nano-adsorbents had the highest adsorption capacity and rate for Ni 2+ according to the adsorption kinetics and thermodynamics. In addition, the corresponding competitive adsorption processes and desorption experiments reflected that Fe 3 O 4 -SH had the strongest affinity and adsorption selectivity for Pb 2+ , followed by Ni 2+ and finally by Cu 2+ and Zn 2+ . Generally, the present study might provide a serviceable direction for the future efforts towards the application of Fe 3 O 4 -SH nano-adsorbents in industrial wastewater treatments involving multiple heavy metal contaminants. [ABSTRACT FROM AUTHOR]

The vacancy defect can effectively turn off conjugated π bond shield and enhance the capacity to couple with the molecules. • Electronic behaviors between intrinsic graphene and single atom vacancy graphene. • The fragment orbital analysis of molecules adsorption to understand interaction. • Conjugated π bond shield effect causes the laminate to be inert. • The mechanism of single atom vacancy improving molecule adsorption performance. Non-metal carbon materials have been widely utilized in diversified electrocatalytic reaction in virtue of property advantages. And the defective structure has greatly affected the physicochemical properties. Thus, it is of great significance to understand the mechanism of defective effect. Herein, we constructed graphene structural model to in-depth understand the electronic characteristics of vacancy defect sites and further comprehend the molecular interaction during the adsorption process. Our results indicate that the vacancy defect can effectively turn off conjugated π bond shield and form defect state, including π state and σ state. According to the fragment orbital analysis, due to the conjugated π bond shielding effect of perfect graphene, it cannot bond to nonpolar molecule. Even polar molecules, it needs to induce polar π defect on the surface of perfect graphene firstly. However, whether it's polar or nonpolar molecular, it can easily track coupling with the defect sites where the shield is turned on. The findings point out a new avenue to understand the catalytic behavior for carbon materials. [ABSTRACT FROM AUTHOR]