Characteristics and mechanisms of cadmium adsorption by Sphingopyxis sp. YF1

Abstract:

[Background] Heavy metal pollution in water is a serious environmental problem posing a severe threat to human health. Using microbial adsorbents to remediate heavy metal-contaminated water is an efficient and eco-friendly method. Sphingopyxis is capable of removing heavy metal pollution, while little is known about the mechanism of the removal of cadmium from water by Sphingopyxis. [Objective] To reveal the cadmiumadsorption efficacy and mechanisms of Sphingopyxis sp. YF1 isolated from water. [Methods] The adsorption of Cd²⁺ by live and dead cells of strain YF1 under different pH, contact time, and initial concentrations of Cd²⁺ were analyzed. Kinetic and isothermal models were fitted to investigate the cadmium adsorption characteristics of this strain. Scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) were employed to observe the accumulation of cadmium on the surface of live and dead cells. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were employed to identify the functional groups involved in the adsorption of Cd²⁺by YF1 cells, so as to elucidate the adsorption mechanism. [Results] With the rise in pH, cadmium adsorption of both live and dead cells increased within the range of pH 3.0–5.0 and did not change greatly within the range of pH 5.0–7.0. The adsorption mainly occurred in the first 10 min, and then the adsorption rate gradually decreased. The process of Cd²⁺ adsorption by live and dead cells was more in line with the pseudo-second-order kinetic model, which suggested YF1 mainly adopted chemisorption. The adsorption of Cd²⁺ by both live and dead cells was better fitted by the Langmuir model, indicating the adsorption of Cd²⁺ by YF1 was homogeneous. The maximal adsorption capacity of Cd²⁺ by live and dead cells reached 36.20 mg/g and 62.98 mg/g, respectively. Cd(II) was deposited on the surface of both live and dead cells after adsorption, and -OH, C-(O,N), and -NO₂ groups were involved in the adsorption. [Conclusion] Sphingopyxis sp. YF1 has high Cd²⁺ removal ability and is promising in the removal of Cd²⁺ from water.