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Sorption and desorption of Cr(VI) ions from water by biochars in different environmental conditions.

Tytłak A, Oleszczuk P, Dobrowolski R - Environ Sci Pollut Res Int (2014)

Bottom Line: The Langmuir model has better fitting of adsorption isotherms than the Freundlich model.The sorption process can be described by the pseudo second-order equation.The results indicated that the sorption mechanism of Cr(VI) on biochar involves anionic and cationic adsorption combined with Cr(VI) species reduction.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Chemistry, Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie-Skłodowska Square 3, 20-031, Lublin, Poland.

ABSTRACT
In the present research, the potential of two biochars produced by the thermal decomposition of wheat straw (BCS) and wicker (BCW) for Cr(VI) ions removing from wastewater was investigated. The pH and the presence of chlorides and nitrates were also investigated. The Freundlich and Langmuir models were applied for the characterization of adsorption isotherms. The Langmuir model has better fitting of adsorption isotherms than the Freundlich model. The sorption process can be described by the pseudo second-order equation. The optimal adsorption capacities were obtained at pH 2 and were 24.6 and 23.6 mg/g for BCS and BCW, respectively. X-ray photoelectron spectroscopy (XPS) studies confirmed that Cr(III) ions were the most abundant chromium species on the biochars' surface. The results indicated that the sorption mechanism of Cr(VI) on biochar involves anionic and cationic adsorption combined with Cr(VI) species reduction.

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FTIR/PAS spectrum of BCs used in the study: 1 4,000–2,400 cm−1 range and 2 2,000–700 cm−1 range
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Fig1: FTIR/PAS spectrum of BCs used in the study: 1 4,000–2,400 cm−1 range and 2 2,000–700 cm−1 range

Mentions: The IR spectra of examined biochars (Fig. 1) are complicated because of the presence of multiple bands in a wide range of wavenumbers, which is also in correlation with the amount of functional groups on the surface of the biochar. At about 3,650 and 3,202 cm−1 in BCS, the spectra have centered band characteristics for stretching vibration of hydrogen-bonded hydroxyl groups of alcohols and carboxylic acids, respectively. In the same spectrum, the band being in correlation with hydroxyl groups of water at about 3,433 cm−1 can be seen. At about 3,354 and 3,358 cm−1 in the both spectra, the bands attributed to the primary amine groups’ presence on the biochars’ surface can be seen. The vibration at 3,068 cm−1 in BCW spectrum is associated with vinyl and acrylic C-H groups. The band at about 3,034 cm−1 is attributed to the =C-H stretching of aromatic compounds. The aliphatic C-H bands at the region 2,867–2,932 cm−1 can be found in the BCW spectrum, but there are no adsorption bands of those types in BCS spectrum. The bands at 1,751 and 1,685 cm−1 in the BCS spectrum and the similar band at 1,701 cm−1 in the second biochar spectra are the adsorption bands of C=O. The vibration at 1,595 cm−1 is associated with C=O in ketones, carboxylates, and quinones or with the C=C stretching in the aromatic components [30]. The bands in the range 1,400–1,050 cm−1 could be correlated with C-O and O-H presence in carboxylic acids (band at 1,356 cm−1) and phenols or C-O-C in ethers. The bands in the region of 1,200–1,000 cm−1 are attributed to the C-H deformation in the aromatic structures. The bands centered at 1,055, 957, and 783 cm−1 can be responsible for Si-O vibrations of inorganic materials in BCS [31]. The bands at 874 and 873 cm−1 in BCS and BCW spectra, respectively, can be associated with C-H bending in aromatic compounds.Fig. 1


Sorption and desorption of Cr(VI) ions from water by biochars in different environmental conditions.

Tytłak A, Oleszczuk P, Dobrowolski R - Environ Sci Pollut Res Int (2014)

FTIR/PAS spectrum of BCs used in the study: 1 4,000–2,400 cm−1 range and 2 2,000–700 cm−1 range
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4381096&req=5

Fig1: FTIR/PAS spectrum of BCs used in the study: 1 4,000–2,400 cm−1 range and 2 2,000–700 cm−1 range
Mentions: The IR spectra of examined biochars (Fig. 1) are complicated because of the presence of multiple bands in a wide range of wavenumbers, which is also in correlation with the amount of functional groups on the surface of the biochar. At about 3,650 and 3,202 cm−1 in BCS, the spectra have centered band characteristics for stretching vibration of hydrogen-bonded hydroxyl groups of alcohols and carboxylic acids, respectively. In the same spectrum, the band being in correlation with hydroxyl groups of water at about 3,433 cm−1 can be seen. At about 3,354 and 3,358 cm−1 in the both spectra, the bands attributed to the primary amine groups’ presence on the biochars’ surface can be seen. The vibration at 3,068 cm−1 in BCW spectrum is associated with vinyl and acrylic C-H groups. The band at about 3,034 cm−1 is attributed to the =C-H stretching of aromatic compounds. The aliphatic C-H bands at the region 2,867–2,932 cm−1 can be found in the BCW spectrum, but there are no adsorption bands of those types in BCS spectrum. The bands at 1,751 and 1,685 cm−1 in the BCS spectrum and the similar band at 1,701 cm−1 in the second biochar spectra are the adsorption bands of C=O. The vibration at 1,595 cm−1 is associated with C=O in ketones, carboxylates, and quinones or with the C=C stretching in the aromatic components [30]. The bands in the range 1,400–1,050 cm−1 could be correlated with C-O and O-H presence in carboxylic acids (band at 1,356 cm−1) and phenols or C-O-C in ethers. The bands in the region of 1,200–1,000 cm−1 are attributed to the C-H deformation in the aromatic structures. The bands centered at 1,055, 957, and 783 cm−1 can be responsible for Si-O vibrations of inorganic materials in BCS [31]. The bands at 874 and 873 cm−1 in BCS and BCW spectra, respectively, can be associated with C-H bending in aromatic compounds.Fig. 1

Bottom Line: The Langmuir model has better fitting of adsorption isotherms than the Freundlich model.The sorption process can be described by the pseudo second-order equation.The results indicated that the sorption mechanism of Cr(VI) on biochar involves anionic and cationic adsorption combined with Cr(VI) species reduction.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Chemistry, Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie-Skłodowska Square 3, 20-031, Lublin, Poland.

ABSTRACT
In the present research, the potential of two biochars produced by the thermal decomposition of wheat straw (BCS) and wicker (BCW) for Cr(VI) ions removing from wastewater was investigated. The pH and the presence of chlorides and nitrates were also investigated. The Freundlich and Langmuir models were applied for the characterization of adsorption isotherms. The Langmuir model has better fitting of adsorption isotherms than the Freundlich model. The sorption process can be described by the pseudo second-order equation. The optimal adsorption capacities were obtained at pH 2 and were 24.6 and 23.6 mg/g for BCS and BCW, respectively. X-ray photoelectron spectroscopy (XPS) studies confirmed that Cr(III) ions were the most abundant chromium species on the biochars' surface. The results indicated that the sorption mechanism of Cr(VI) on biochar involves anionic and cationic adsorption combined with Cr(VI) species reduction.

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