Efficient mercury(II) removal by corn bract/dopamine@ZnS composites

In this study, we have utilized corn bract, a green agricultural by-product, as a carrier. It is subsequently modified with zinc sulfide to synthesize an efficient composite material termed as corn bract/polydopamine@zinc sulfide (CB/PDA@ZnS). This novel composite demonstrates significant potential for biomass removal of mercury ions (Hg(II)). The composition, structure, and morphology of CB/PDA@ZnS composites are characterized by Fourier transform infrared (FT-IR) spectrum, thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and scanning electron microscope (SEM). The effect of pH value, adsorbent dosage, initial Hg(II) concentration, adsorption time and temperature, and coexistence ions on the adsorption behavior is investigated. The results show that CB/PDA@ZnS can efficiently remove Hg(II) from water with uptake capacities of 333.03 mg/g and removal efficiency of 99.91% under an optimal conditions (pH of 3, the adsorbent dosage of 0.015 g, contact time of 90 min, and initial concentration of 100 mg/L) at room temperature. The fitting analysis of the experimental data reveals that the adsorption process of Hg(II) follows the quasi-secondary adsorption kinetic model as well as the Langmuir isothermal adsorption model, which is a spontaneous heat absorption process. In addition, the composite adsorbent obtained exhibit excellent selectivity for Hg(II) ions and anti-coexisting ion interference performance. After five cycles of adsorption-desorption experiments, the corresponding adsorption capacity is 331.11 mg/g, accounting for 93.33% of the first adsorption capacity, indicating that the adsorbent has excellent regeneration performance. The stability of the adsorbent and the adsorption mechanism of Hg(II) ion are systematically discussed using FT-IR, XRD, and X-ray photoelectron spectroscopy (XPS). Finally, this adsorbent is tested for the removal of industrial wastewater containing Hg(II), and the adsorption and removal efficiency are 331.67 mg/g and 99.50%, respectively. This study provides a very valuable information for future Hg(II) removal from aqueous solutions.