Effects of surface iron hydroxyl group site densities on arsenate adsorption by iron oxide nanocomposites

Xu Chen; Xiaomin Dou; Dinesh Mohan; Charles U. Pittman; Meng Hu; Yongsik Ok

doi:10.1166/nnl.2016.2190

Effects of surface iron hydroxyl group site densities on arsenate adsorption by iron oxide nanocomposites

Xu Chen, Xiaomin Dou, Dinesh Mohan, Charles U. Pittman, Meng Hu, Yongsik Ok

Research output: Contribution to journal › Article › peer-review

13 Citations (Scopus)

Abstract

Nanocomposites containing maghemite (γ-Fe₂O₃) and hematite (αa-Fe₂O₃) were prepared by thermal decomposition (200 to 600 °C) of the products formed by reacting Fe0 with aqueous oxalic acid. The iron oxide nanocomposites were characterized by TEM, XRD, VSM, BET, FTIR, XPS and surface potential titration. Batch-type sorption experiments showed that As(V) adsorption capacities of these nanocomposites decreased as the calcination temperature increased from 200 to 600 °C. The highest As(V) adsorption capacity (0.343 mmol/g) was achieved on the nanocomposite prepared at 200 °C, which had a particle size of about 10 nm and a pHpzc value of 6.1. The quantity of iron hydroxide surface sites on these nanocomposites were determined by fitting the surface titration data using a one site 2-pK constant capacitance model (CCM). The total quantities of surface sites correlated with the corresponding As(V) adsorption capacities, but this correlation was not linear. The surface hydroxyl oxygen to the total oxygen ratios were estimated by fitting the XPS O1s envelopes of these nanocomposites. These ratios were also positively correlated with the As(V) adsorption capacities. However, these correlations were also not linear. Evidence, including the amount of titratable proton surface sites and the percentages of hydroxyl oxygens, favored AsO^3-₄ adsorption occurring through an oxygen bridge between iron and arsenic at the surface. This occurs with the loss of water (or hydroxide) when surface Fe-OH groups react with AsO^3-₄ or HAsO^2-₄ . The nonlinear nature of the correlations between the adsorption capacities and both the surface site densities and the percentages of hydroxyl oxygen indicated that these two properties are not the only governing factors responsible for As(V) adsorption. Other possibly contributing factors are proposed. More research should be carried out to further investigate the surface-property effects on As(V) adsorption in future.

Original language	English
Pages (from-to)	1020-1027
Number of pages	8
Journal	Nanoscience and Nanotechnology Letters
Volume	8
Issue number	11
DOIs	https://doi.org/10.1166/nnl.2016.2190
Publication status	Published - 2016 Nov
Externally published	Yes

Bibliographical note

Publisher Copyright:
© Copyright 2016 American Scientific Publishers.

Keywords

Adsorption
Arsenate
Hematite
Hydroxyl groups
Maghemite
Nanocomposites
Site density

ASJC Scopus subject areas

General Materials Science

Access to Document

10.1166/nnl.2016.2190

Cite this

@article{79e8164a51ab47a7837f58682c2c26a5,

title = "Effects of surface iron hydroxyl group site densities on arsenate adsorption by iron oxide nanocomposites",

abstract = "Nanocomposites containing maghemite (γ-Fe2O3) and hematite (αa-Fe2O3) were prepared by thermal decomposition (200 to 600 °C) of the products formed by reacting Fe0 with aqueous oxalic acid. The iron oxide nanocomposites were characterized by TEM, XRD, VSM, BET, FTIR, XPS and surface potential titration. Batch-type sorption experiments showed that As(V) adsorption capacities of these nanocomposites decreased as the calcination temperature increased from 200 to 600 °C. The highest As(V) adsorption capacity (0.343 mmol/g) was achieved on the nanocomposite prepared at 200 °C, which had a particle size of about 10 nm and a pHpzc value of 6.1. The quantity of iron hydroxide surface sites on these nanocomposites were determined by fitting the surface titration data using a one site 2-pK constant capacitance model (CCM). The total quantities of surface sites correlated with the corresponding As(V) adsorption capacities, but this correlation was not linear. The surface hydroxyl oxygen to the total oxygen ratios were estimated by fitting the XPS O1s envelopes of these nanocomposites. These ratios were also positively correlated with the As(V) adsorption capacities. However, these correlations were also not linear. Evidence, including the amount of titratable proton surface sites and the percentages of hydroxyl oxygens, favored AsO3-4 adsorption occurring through an oxygen bridge between iron and arsenic at the surface. This occurs with the loss of water (or hydroxide) when surface Fe-OH groups react with AsO3-4 or HAsO2-4 . The nonlinear nature of the correlations between the adsorption capacities and both the surface site densities and the percentages of hydroxyl oxygen indicated that these two properties are not the only governing factors responsible for As(V) adsorption. Other possibly contributing factors are proposed. More research should be carried out to further investigate the surface-property effects on As(V) adsorption in future.",

keywords = "Adsorption, Arsenate, Hematite, Hydroxyl groups, Maghemite, Nanocomposites, Site density",

author = "Xu Chen and Xiaomin Dou and Dinesh Mohan and Pittman, {Charles U.} and Meng Hu and Yongsik Ok",

year = "2016",

month = nov,

doi = "10.1166/nnl.2016.2190",

language = "English",

volume = "8",

pages = "1020--1027",

journal = "Nanoscience and Nanotechnology Letters",

issn = "1941-4900",

publisher = "American Scientific Publishers",

number = "11",

}

TY - JOUR

T1 - Effects of surface iron hydroxyl group site densities on arsenate adsorption by iron oxide nanocomposites

AU - Chen, Xu

AU - Dou, Xiaomin

AU - Mohan, Dinesh

AU - Pittman, Charles U.

AU - Hu, Meng

AU - Ok, Yongsik

PY - 2016/11

Y1 - 2016/11

N2 - Nanocomposites containing maghemite (γ-Fe2O3) and hematite (αa-Fe2O3) were prepared by thermal decomposition (200 to 600 °C) of the products formed by reacting Fe0 with aqueous oxalic acid. The iron oxide nanocomposites were characterized by TEM, XRD, VSM, BET, FTIR, XPS and surface potential titration. Batch-type sorption experiments showed that As(V) adsorption capacities of these nanocomposites decreased as the calcination temperature increased from 200 to 600 °C. The highest As(V) adsorption capacity (0.343 mmol/g) was achieved on the nanocomposite prepared at 200 °C, which had a particle size of about 10 nm and a pHpzc value of 6.1. The quantity of iron hydroxide surface sites on these nanocomposites were determined by fitting the surface titration data using a one site 2-pK constant capacitance model (CCM). The total quantities of surface sites correlated with the corresponding As(V) adsorption capacities, but this correlation was not linear. The surface hydroxyl oxygen to the total oxygen ratios were estimated by fitting the XPS O1s envelopes of these nanocomposites. These ratios were also positively correlated with the As(V) adsorption capacities. However, these correlations were also not linear. Evidence, including the amount of titratable proton surface sites and the percentages of hydroxyl oxygens, favored AsO3-4 adsorption occurring through an oxygen bridge between iron and arsenic at the surface. This occurs with the loss of water (or hydroxide) when surface Fe-OH groups react with AsO3-4 or HAsO2-4 . The nonlinear nature of the correlations between the adsorption capacities and both the surface site densities and the percentages of hydroxyl oxygen indicated that these two properties are not the only governing factors responsible for As(V) adsorption. Other possibly contributing factors are proposed. More research should be carried out to further investigate the surface-property effects on As(V) adsorption in future.

AB - Nanocomposites containing maghemite (γ-Fe2O3) and hematite (αa-Fe2O3) were prepared by thermal decomposition (200 to 600 °C) of the products formed by reacting Fe0 with aqueous oxalic acid. The iron oxide nanocomposites were characterized by TEM, XRD, VSM, BET, FTIR, XPS and surface potential titration. Batch-type sorption experiments showed that As(V) adsorption capacities of these nanocomposites decreased as the calcination temperature increased from 200 to 600 °C. The highest As(V) adsorption capacity (0.343 mmol/g) was achieved on the nanocomposite prepared at 200 °C, which had a particle size of about 10 nm and a pHpzc value of 6.1. The quantity of iron hydroxide surface sites on these nanocomposites were determined by fitting the surface titration data using a one site 2-pK constant capacitance model (CCM). The total quantities of surface sites correlated with the corresponding As(V) adsorption capacities, but this correlation was not linear. The surface hydroxyl oxygen to the total oxygen ratios were estimated by fitting the XPS O1s envelopes of these nanocomposites. These ratios were also positively correlated with the As(V) adsorption capacities. However, these correlations were also not linear. Evidence, including the amount of titratable proton surface sites and the percentages of hydroxyl oxygens, favored AsO3-4 adsorption occurring through an oxygen bridge between iron and arsenic at the surface. This occurs with the loss of water (or hydroxide) when surface Fe-OH groups react with AsO3-4 or HAsO2-4 . The nonlinear nature of the correlations between the adsorption capacities and both the surface site densities and the percentages of hydroxyl oxygen indicated that these two properties are not the only governing factors responsible for As(V) adsorption. Other possibly contributing factors are proposed. More research should be carried out to further investigate the surface-property effects on As(V) adsorption in future.

KW - Adsorption

KW - Arsenate

KW - Hematite

KW - Hydroxyl groups

KW - Maghemite

KW - Nanocomposites

KW - Site density

UR - http://www.scopus.com/inward/record.url?scp=84994634463&partnerID=8YFLogxK

U2 - 10.1166/nnl.2016.2190

DO - 10.1166/nnl.2016.2190

M3 - Article

AN - SCOPUS:84994634463

SN - 1941-4900

VL - 8

SP - 1020

EP - 1027

JO - Nanoscience and Nanotechnology Letters

JF - Nanoscience and Nanotechnology Letters

IS - 11

ER -

Effects of surface iron hydroxyl group site densities on arsenate adsorption by iron oxide nanocomposites

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

Access to Document

Other files and links

Fingerprint

Cite this