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. 2024 May 10;27(6):109958.
doi: 10.1016/j.isci.2024.109958. eCollection 2024 Jun 21.

Adsorption dynamics of Cd2+(aq) on microwave-synthetized pristine biochar from cocoa pod husk: Green, experimental, and DFT approaches

Jhonny Correa-Abril  1   2 , Ullrich Stahl  1 , Elvia V Cabrera  1 , Yonathan J Parra  3 , Michael A Vega  1   3 , Sonia Taamalli  4 , Florent Louis  4 , Joan Manuel Rodríguez-Díaz  5
Affiliations

Adsorption dynamics of Cd2+(aq) on microwave-synthetized pristine biochar from cocoa pod husk: Green, experimental, and DFT approaches

Jhonny Correa-Abril et al. iScience. .

Abstract

Biochar obtained via microwave-assisted pyrolysis (MAP) at 720 W and 15 min from cocoa pod husk (CPH) is an efficient adsorbent of Cd2+(aq). Biochar of residual biomass of CPH (BCCPH) possesses favorable physicochemical and morphological properties, featuring a modest surface area yet a suitable porous structure. Adsorption, predominantly governed by physisorption, is influenced by the oxygen-containing active sites (-COOR, -C(R)O, and -CH2OR; R = H, alkyl). CdCO3 formation occurs during adsorption. Experimental data were well-fitted into various kinetic models for a broad understanding of the sorption process. Langmuir model indicates a maximum adsorption capacity of 14.694 mg/g. The thermodynamic study confirms the spontaneous and endothermic sorption. Studies at the molecular level have revealed that the Cd2+ ion tends to bind to surface aromatic carbon atoms. This sustainable approach produces BCCPH via MAP as a solution for waste transformation into water-cleaning materials.

Keywords: Environmental management; Soil chemistry; Soil science.

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Conflict of interest statement

The authors declare no competing interests.

Figures

None
Graphical abstract
Figure 1
Figure 1
A schematic overview of analytical techniques employed to understand the properties of the BCCPH
Figure 2
Figure 2
Functional group profile variations in the BCCPH during the adsorption of Cd2+(aq) (A) FTIR spectra of CPH, BCCPH, and BCCPH-Cd. (B) ssNMR spectra of BCCPH and BCCPH-Cd.
Figure 3
Figure 3
Microphotographs depict morphological and topographic properties of BCCPH, illustrating Cd adsorption (A–C) SEM images of BCCPH at (A) 100x, (B) 1,000x magnifications before adsorption, and (C) after Cd adsorption (highlighted with pink dots). See also Table S3, Figures S3 and S4. (D and E) Atomic force microscopy (AFM) images of BCCPH showing (D) phase contrast – 2D for surface homogeneity and (E) surface topography – 3D for microstructure, valleys, and peaks.
Figure 4
Figure 4
Crystalline phase analyses reveal mineralogical changes on the BCCPH surface and their potential impact on Cd adsorption (A) XRPD pattern of BCCPH at 720 W-15 min before adsorption of Cd. (B) XRPD pattern of BCCPH at 720 W-15 min after adsorption of Cd.
Figure 5
Figure 5
Exploring adsorption dynamics: using various well-fitted models to understand Cd2+(aq) adsorption onto BCCPH (A–C) (A) Boyd plot, (B) intraparticle diffusion plots, and (C) fitting curves of the adsorption kinetics of 100 mg/L Cd2+(aq) onto BCCPH. See also Figures S5–S7. (D) Adsorption isotherms of Cd2+ onto BCCPH: Langmuir, Freundlich, and Redlich-Peterson models. BCCPH = 1.5 g, Vol. Cd2+(aq) = 100 mL, T = 293 K. See also Tables S4 and S5, and Figure S8.
Figure 6
Figure 6
Theoretical surface carbon structures hint at potential Cd2+ adsorption sites (A) Carbonaceous surface models. (B) Adsorption sites of Cd2+ of each model.
Figure 7
Figure 7
Illustrating the probable mechanism of Cd2+(aq) adsorption by BCCPH
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