Abstract
In this work, carbon quantum dots were first prepared through one-pot hydrothermal route of the propyl aldehyde and sodium hydroxide via an aldol condensation reaction, and a novel solid-phase extraction adsorbent of hollow calcite single crystals was prepared via the precipitation of metal nitrates by the CO2 diffusion method in the presence of CQDs and further applied for excessive Cd(II) ions removal from water. The spectra and morphologies of the etched calcite were investigated by X-ray diffraction, Fourier transform infrared spectrometry, Scanning electron microscope, and Transmission electron microscopy. The results show that the CQDs etching technique successfully furnish a strategy for manufacturing interface defects onto the calcite crystal. Bath studies were done to evaluate the effects of the major parameters onto Cd(II) adsorption by the etched calcite, such as pH, contact time, and initial Cd(II) concentration. The Cd(II) adsorption onto the new adsorbent could reach a maximum adsorption amount of 66.68 mg/g at 120 min due to the abundant exterior adsorption sites on the adsorbent. The adsorption kinetics and adsorption isotherms of Cd(II) on the etched calcite were also investigated. The experimental datum showed that the adsorption kinetics and isotherms of Cd(II) on the etched calcite were well-fitted by the pseudo-second-order kinetic model and the Freundlich isotherm model respectively. The adsorption mechanisms could be primarily explained as the formation of Cd(OH)2 and CaxCd1−xCO3 solid solution on the adsorbent surface with the help of X-ray photoelectron spectroscopy.
Highlights
Fourier transform infrared spectrometry (FT-IR), X-ray powder diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and High resolution transmission electron microscopy (HR-TEM) were characterized to the interaction of Cd(II) with the hollow calcite single crystals
In the XRD pattern of the carbon quantum dots (CQDs), a broad peak attributed to amorphous carbon, appeared near 2θ = 18°
Hollow calcite single crystals were synthesized by the etching technique with CQDs provide an extremely potential and important environmental protection material for removing cadmium ions from wastewater
Summary
The etching technology can effectively form interface lattice defects, thereby greatly increasing the specific surface area to provide more active sites and improve the adsorption capacity of heavy metal ions[42]. CQDs are non-toxic with little harm to the environment, commonly used in biological imaging, photoelectric device, sensing and other fields Taking this into account, CQDs are in prospect to turn into an alternative material for the removal of a variety of organic and inorganic pollutants owing to these oxygen-containing functional groups[44,45]. The results of this paper would provide insights to the mechanisms of the novel calcite single crystals on Cd(II) adsorption and will provide a potential and effective material for treating heavy metal ions in environment
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