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Enhanced adsorption of trivalent arsenic from water by functionalized diatom silica shells.

Zhang J, Ding T, Zhang Z, Xu L, Zhang C - PLoS ONE (2015)

Bottom Line: The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume.X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups.Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

View Article: PubMed Central - PubMed

Affiliation: Environmental Science Institute, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China; Zhejiang Provincial Key Laboratory of Organic Pollution Process and Control, Hangzhou, Zhejiang, People's Republic of China.

ABSTRACT
The potential of porous diatom silica shells as a naturally abundant low-cost sorbent for the removal of arsenic in aqueous solutions was investigated in a batch study. The objective of this work was to chemically modify the silica shells of a diatom Melosira sp. with bifunctional (thiol and amino) groups to effectively remove arsenic in its toxic As(III) form (arsenite) predominant in the aquatic environment. Sorption experiments with this novel sorbent were conducted under varying conditions of pH, time, dosage, and As(III) concentration. A maximum adsorption capacity of 10.99 mg g-1 was achieved within 26 h for a solution containing 12 mg L-1 As(III) at pH 4 and sorbent dosage of 2 g L-1. The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume. As(III) adsorption was best fitted with the Langmuir-Freundlich model, and the adsorption kinetic data using pore surface diffusion model showed that both the external (film) and internal (intraparticle) diffusion can be rate-determining for As(III) adsorption. Fourier transform infrared spectroscopy (FTIR) indicated that the thiol and amino groups potentially responsible for As(III) adsorption were grafted on the surface of diatom silica shells. X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups. Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

No MeSH data available.


Related in: MedlinePlus

The van’t Hoff plot of lnKd vs. 1/T for the estimation of thermodynamic parameters for arsenic sorption by functionalized diatom frustules (adsorbent concentration: 2 g L-1; contact time: 26 h; pH 4).
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pone.0123395.g006: The van’t Hoff plot of lnKd vs. 1/T for the estimation of thermodynamic parameters for arsenic sorption by functionalized diatom frustules (adsorbent concentration: 2 g L-1; contact time: 26 h; pH 4).

Mentions: Several thermodynamic parameters were estimated to provide an insight into the inherent energetic changes in the process of adsorption. The changes in Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) are calculated using the following equations [11]:ΔG0=−RTlnKD(1)lnKD=ΔS0/R−ΔH0/RT(2)where R is the universal gas constant (8.314 J mol-1 K-1), T is temperature (K) and KD is the distribution coefficient equating to the ratio of the sorbed arsenic concentration (qe) to the aqueous phase arsenic concentration (Ce) at equilibrium. The ΔG° values were calculated using the lnKD given in the van’t Hoff plot (Fig 6) and found to be -7.78, -6.97, -5.91, and -5.10 kJ mol-1 for temperature at 25, 35, 45, and 55°C, respectively. The negative ΔG° values indicated the spontaneous nature of the adsorption, and the increased ΔG° values with the elevated temperature illustrate a lower adsorption efficiency at higher temperatures. It was reported that ΔG° values up to 20 kJ mol-1 were consistent with electrostatic interaction and the typical chemical bonding energy for an ion-exchange mechanism is in the range of 7.9–16 kJ mol-1 [24]. The low ΔG° values in this study (< 7.9 kJ mol-1) indicate that ion-exchange may not play a significant role in the adsorption processes. Thus, the covalent binding of arsenite to form a surface complex is possibly the major mechanism responsible for the arsenic adsorption process. In addition, the negative value of ΔS° (-92.20 ± 1.42 kJ mol-1 K-1) reveals the thermodynamically decreased randomness at the solid-solution interface during the adsorption process. Furthermore, the ΔH° was found to be -35.31± 0.44 kJ mol-1, indicating the exothermic nature of the adsorption processes at 25–55°C. It was reported that the ΔH° value in the range of 2.1–20.9 kJ mol-1 is indicative of physical adsorption, whereas chemical adsorption corresponds to ΔH° in the range from 20.9 to 418.4 kJ mol-1 [25]. These results all collectively point to chemisorption as the mechanism primarily responsible for the adsorption of arsenic by modified diatom frustules.


Enhanced adsorption of trivalent arsenic from water by functionalized diatom silica shells.

Zhang J, Ding T, Zhang Z, Xu L, Zhang C - PLoS ONE (2015)

The van’t Hoff plot of lnKd vs. 1/T for the estimation of thermodynamic parameters for arsenic sorption by functionalized diatom frustules (adsorbent concentration: 2 g L-1; contact time: 26 h; pH 4).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4383452&req=5

pone.0123395.g006: The van’t Hoff plot of lnKd vs. 1/T for the estimation of thermodynamic parameters for arsenic sorption by functionalized diatom frustules (adsorbent concentration: 2 g L-1; contact time: 26 h; pH 4).
Mentions: Several thermodynamic parameters were estimated to provide an insight into the inherent energetic changes in the process of adsorption. The changes in Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) are calculated using the following equations [11]:ΔG0=−RTlnKD(1)lnKD=ΔS0/R−ΔH0/RT(2)where R is the universal gas constant (8.314 J mol-1 K-1), T is temperature (K) and KD is the distribution coefficient equating to the ratio of the sorbed arsenic concentration (qe) to the aqueous phase arsenic concentration (Ce) at equilibrium. The ΔG° values were calculated using the lnKD given in the van’t Hoff plot (Fig 6) and found to be -7.78, -6.97, -5.91, and -5.10 kJ mol-1 for temperature at 25, 35, 45, and 55°C, respectively. The negative ΔG° values indicated the spontaneous nature of the adsorption, and the increased ΔG° values with the elevated temperature illustrate a lower adsorption efficiency at higher temperatures. It was reported that ΔG° values up to 20 kJ mol-1 were consistent with electrostatic interaction and the typical chemical bonding energy for an ion-exchange mechanism is in the range of 7.9–16 kJ mol-1 [24]. The low ΔG° values in this study (< 7.9 kJ mol-1) indicate that ion-exchange may not play a significant role in the adsorption processes. Thus, the covalent binding of arsenite to form a surface complex is possibly the major mechanism responsible for the arsenic adsorption process. In addition, the negative value of ΔS° (-92.20 ± 1.42 kJ mol-1 K-1) reveals the thermodynamically decreased randomness at the solid-solution interface during the adsorption process. Furthermore, the ΔH° was found to be -35.31± 0.44 kJ mol-1, indicating the exothermic nature of the adsorption processes at 25–55°C. It was reported that the ΔH° value in the range of 2.1–20.9 kJ mol-1 is indicative of physical adsorption, whereas chemical adsorption corresponds to ΔH° in the range from 20.9 to 418.4 kJ mol-1 [25]. These results all collectively point to chemisorption as the mechanism primarily responsible for the adsorption of arsenic by modified diatom frustules.

Bottom Line: The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume.X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups.Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

View Article: PubMed Central - PubMed

Affiliation: Environmental Science Institute, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China; Zhejiang Provincial Key Laboratory of Organic Pollution Process and Control, Hangzhou, Zhejiang, People's Republic of China.

ABSTRACT
The potential of porous diatom silica shells as a naturally abundant low-cost sorbent for the removal of arsenic in aqueous solutions was investigated in a batch study. The objective of this work was to chemically modify the silica shells of a diatom Melosira sp. with bifunctional (thiol and amino) groups to effectively remove arsenic in its toxic As(III) form (arsenite) predominant in the aquatic environment. Sorption experiments with this novel sorbent were conducted under varying conditions of pH, time, dosage, and As(III) concentration. A maximum adsorption capacity of 10.99 mg g-1 was achieved within 26 h for a solution containing 12 mg L-1 As(III) at pH 4 and sorbent dosage of 2 g L-1. The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume. As(III) adsorption was best fitted with the Langmuir-Freundlich model, and the adsorption kinetic data using pore surface diffusion model showed that both the external (film) and internal (intraparticle) diffusion can be rate-determining for As(III) adsorption. Fourier transform infrared spectroscopy (FTIR) indicated that the thiol and amino groups potentially responsible for As(III) adsorption were grafted on the surface of diatom silica shells. X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups. Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

No MeSH data available.


Related in: MedlinePlus