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. 2020 Mar 13;10(18):10703-10714.
doi: 10.1039/c9ra09447d. eCollection 2020 Mar 11.

Competitive adsorption of naphthalene and phenanthrene on walnut shell based activated carbon and the verification via theoretical calculation

Zhansheng Wu  1   2 , Zhonghai Sun  3 , Pengyun Liu  2 , Qing Li  1 , Renpeng Yang  1 , Xia Yang  1
Affiliations

Competitive adsorption of naphthalene and phenanthrene on walnut shell based activated carbon and the verification via theoretical calculation

Zhansheng Wu et al. RSC Adv. .

Abstract

Walnut shell based activated carbon (WAC) was prepared via microwave-assisted KOH activation. The adsorption behaviors towards naphthalene (NAP) and phenanthrene (PHE) over WAC were studied, both in single- and binary-compound systems. Characterization results reveal the excellent microporous structure of WAC, with a micropore specific surface area of 438.5 m2 g-1. The functional groups of walnut shell precursor surface were activated through microwave irradiation. In both systems, the pseudo-second-order model can better describe the adsorption kinetic data of PAHs over WAC at all experimental conditions. Mass transfer mechanism analysis shows that film diffusion was the rate-limiting step during the adsorption process. The adsorption amount of PAHs on WAC decreased as pH values increased, and the equilibrium data can be fitted by the Freundlich isotherm model well. In binary-component systems, the presence of PHE prominently restrained the adsorption towards NAP, and the Sheindorf-Rebhun-Sheintuch (SRS) model can fully fit the adsorption equilibrium experimental values of PAHs over WAC. In addition, the preferential adsorption behavior of PHE over WAC also was confirmed by theoretical calculations. The π-π complex between the active sites on the WAC surface and π-electrons of benzene rings from PAHs may play a major role in competitive adsorption. These results indicated that WAC was a potentially low-cost adsorbent for PAH elimination.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. The pore size distribution and nitrogen adsorption–desorption curve of WAC.
Fig. 2
Fig. 2. The SEM of WAC.
Fig. 3
Fig. 3. The FTIR spectra of WAC.
Fig. 4
Fig. 4. The kinetic curves of NAP and PHE onto WAC in single-component (a) and binary-component (b) systems. (Conditions: w = 0.0150 g; [NAP] = 10 mg L−1; [PHE] = 10 mg L−1; shaking speed = 170 rpm.)
Fig. 5
Fig. 5. Adsorption isotherms of NAP and PHE on WAC in single-component systems (conditions: [NAP] = [PHE] = 10 mg L−1; mass of adsorbent: 5–100 mg; contact time: 40 min; shaking rate: 170 rpm).
Fig. 6
Fig. 6. Adsorption of NAP in the presence of PHE at different pH. (a) pH 3, (b) pH 7 and (c) pH 9, and at different ratios r = [NAP/PHE] (r = 2, 1 and 0.5).
Fig. 7
Fig. 7. Adsorption of PHE in the presence of NAP at different pH: (a) pH 3, (b) pH 7 and (c) pH 9, and at different ratios r = [NAP/PHE] (r = 2, 1 and 0.5).
Fig. 8
Fig. 8. The separation factors in the different proportions of components at different pH, (a) pH 3, (b) pH 7 and (c) pH 9.
Fig. 9
Fig. 9. Intraparticle diffusion (a) and film diffusion models (b) for the single and binary component systems.
See this image and copyright information in PMC

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