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. 2018 Jan 2;23(1):96.
doi: 10.3390/molecules23010096.

Preparation of Starch-Hard Carbon Spherules From Ginkgo Seeds and Their Phenol-Adsorption Characteristics

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Free PMC article

Preparation of Starch-Hard Carbon Spherules From Ginkgo Seeds and Their Phenol-Adsorption Characteristics

Hongxia Chen et al. Molecules. .
Free PMC article

Abstract

Carbon spherules from ginkgo seed starch were prepared through stabilization and carbonization processes. The ginkgo seed starch was first stabilized at 195 °C for 18 h, then carbonized at 500 °C for 2 h under an N₂ atmosphere. The characterization results confirmed that carbon spherules were in the size range of 10-20 μm. Experimental data were also evaluated to find out the kinetic characteristics of phenols on the carbon spherules during the adsorption process. Adsorption processes for phenol, p-nitrophenol and p-chlorophenol were found to follow the pseudo-first order kinetic model with R² values of 0.995, 0.997 and 0.998, while the rate constants k₁ = 0.014, 0.009 and 0.011 min-1 showed that the adsorption is mainly controlled by adsorbate diffusion. The equilibrium data were analyzed with the Langmuir, Freundlich and Temkin-Pyzhev models and the best fit was observed with the Freundlich isotherm, suggesting the physical adsorption of phenols. From the thermodynamic functions, ∆G, ∆H, and ∆S were calculated, which showed that adsorption is more favorable at low temperature and is an exothermic process, and the adsorption of p-nitrophenol and p-chlorophenol were more advantageous than that of phenol.

Keywords: adsorption; ginkgo seeds; phenols; spherule; starch.

Conflict of interest statement

The authors have declared no conflict of interest.

Figures

Figure 1
Figure 1
(a) N2 adsorption-desorption isotherms; and (b) pore-size distributions for ginkgo seed starches.
Figure 2
Figure 2
Fourier-transform infrared (FT–IR) spectroscopies of native (a); stabilized (b); and carbonized (c) ginkgo seed starches.
Figure 3
Figure 3
Scanning-electron micrograph (SEM) images of native (a); stabilized (b); and carbonized (c) ginkgo seed starches.
Figure 4
Figure 4
X-Ray Diffraction (XRD) figurations of native, stabilized and carbonized ginkgo seed starches.
Figure 5
Figure 5
Kinetic adsorption curves of phenol compounds onto ginkgo seed starch-hard carbon spherules (a); and coal-activated carbon (b).
Figure 6
Figure 6
(a) Pseudo-first order adsorption kinetics plot; (b) pseudo-second order adsorption kinetics plot; and (c) Weber–Morris adsorption kinetics plot.
Figure 7
Figure 7
Equilibrium adsorption isotherms of phenol (a); p-nitrophenol (b); and p-chlorophenol (c) onto ginkgo seed starch-hard carbon spherules.

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