Simultaneous removal of heavy metal ions using carbon dots-doped hydrogel particles

Heavy metal ions (HMI) have attracted worldwide concern due to their serious environmental pollution which led to the risk of health conditions. From Red Malus floribunda fruits, nitrogen-doped carbon dots (N-CDs) were prepared, followed by hybrid-spherical shaped hydrogel particles (CGCDs) were prepared. The prepared CGCDs were utilized as adsorbents for HMI-(Hg(II), Cd(II), Pb(II), and Cr(III)) from water. N-CDs with about 4.0 nm in diameter were characterized by various techniques such as field emission-scanning electron microscopy (FE-SEM) and attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR) that confirm the presence of nitrogen, oxygen, and carbon functionalities. The prepared spherical CGCDs were characterized very well before it was used as HMI adsorbents. The sizes of the CGCDs were ranges between 20 and 300 μm and the degree of swelling was calculated as 1320 %. ATR-FTIR and X-ray diffraction analyses reveal the presence of N-CDs in CGCDs. Further, FE-SEM confirms the spherical shape morphology of CGCDs. Three different concentrations of HMI solutions were 500 mg/L, 1000 mg/L, and 1500 mg/L. Hg(II) adsorbed proficiently by CGCDs in single metal ion systems with ~72 % and almost complete removal of Hg(II) ions (99 %) in multiple metal ion systems was observed. Moreover, all metal ions Hg(II), Cd(II), Pb(II), and Cr(III) were efficiently (>70 %) removed in multiple systems by CGCDs. After HMI adsorption experiments, the elemental mapping from FE-SEM and X-ray photoelectron spectroscopy studies conveys the presence of HMI on CGCDs. This suggests that CGCDs would be a suitable adsorbent for the simultaneous removal of multiple HMI from wastewater.