Elsevier

Applied Clay Science

Volume 43, Issue 2, February 2009, Pages 160-163
Applied Clay Science

Adsorption of benzene derivatives on allophane

https://doi.org/10.1016/j.clay.2008.07.024Get rights and content

Abstract

The adsorption properties of benzene derivatives from water on allophane, extracted from soil, have been investigated by UV and FTIR spectroscopic measurements. Allophane adsorbs benzoic acid, phthalic acid, benzaldehyde, ethyl benzoate, and diethyl phthalate. Benzoic acid, phthalic acid, and benzaldehyde formed carboxylate anions on the positive sites of the hydrated alumina surface of allophane. In the case of adsorption from an acidic solution (pH 2), a small amount of a neutral species of benzoic acid was detected on the allophane. Ethyl benzoate and diethyl phthalate were adsorbed by an interaction between their carbonyl groups and the hydroxyl groups of the allophane. It was confirmed that allophane has an adsorption ability for the benzene derivatives that are not only ionic but also polar molecules. Allophane was found to be available as an absorbent for use in water purification by a simple procedure.

Introduction

Some clay minerals have a high activity for ion exchange, adsorption, and catalyst uses, and they are also available for water purification (Xu et al., 1998, Bergaya et al., 2006, Cea et al., 2007). Environmental water purification is a very important subject in today's world because of the serious problems resulting from the bad management of some chemicals in the past. Clay minerals in soil spontaneously purge some chemicals in the natural world. The chemicals are expected to be decomposed while they are adsorbed on the clay minerals by the biological actions reported in a paper (Fisenko, 2004).

Some benzene derivatives, such as dialkyl phthalate, have been suspected of being endocrine disruptors. Besides polluting soil and groundwater, such compounds may affect animal/human fertility and reproduction.

Allophane, a natural clay mineral distributed throughout the world, is a hydrated aluminosilicate (1  2SiO2·Al2O3·5  6H2O) having a 3.5−5.0 nm-sized hollow spherical structure with 0.3−0.5 nm-sized defects on its surface (Kitagawa, 1971, Henmi and Wada, 1976, Wada and Wada, 1977, Hall et al., 1985, van der Gaast et al., 1985). The walls in the hollow spheres consist of two layers, inner silica and outer alumina layers, and hydroxyl groups or water of hydration on their surface. Some studies suggest that these surfaces have a high ability to adsorb ionic or polar pollutants due to an amphoteric ion-exchange activity (Theng, 1972, Clark and McBride, 1984, Hanudin et al., 1999, Gustafsson, 2001, Hashizume et al., 2002, Jara et al., 2006) and high surface area (Kitagawa, 1971, Hall et al., 1985). Allophane has, in part, been applied to wall materials to control humidity in the air. However, only a small amount of allophane distributed throughout the world has been utilized, and its chemical properties have not been effectively utilized. Basic studies on the adsorption of harmful aromatic molecules are needed. However, there is no report describing the detailed structure of aromatic molecules adsorbed on allophane.

In this study, we have investigated the absorption properties for benzene derivatives, i.e., benzoic acid, phthalic acid, benzaldehyde, ethyl benzoate, and diethyl phthalate, by allophane in order to assess its utilization as an absorbent for water purification. The adsorption was quantitatively evaluated by measuring UV absorption spectra, and the adsorption structure was determined by examining the IR spectra.

Section snippets

Materials

Benzoic acid (reagent grade), phthalic acid (S, = special, grade), benzaldehyde (S grade), and ethyl benzoate (S grade), purchased from Wako Pure Chemicals, were used without further purification (Scheme 1). Diethyl phthalate (reagent grade) was purchased from Kanto Chemicals and was used without further purification. Water, which was deionized and then distilled, was used as a solvent. Hydrochloric acid (S grade) and sodium hydroxide (S grade), purchased from Wako Pure Chemicals, were used

Adsorption of esters

The spectrum of diethylphthalate exhibited two peaks at 235 and 276 nm and a strong band at less than 210 nm (Fig. 1). The intensity of these bands very slowly decreased with time and reached equilibrium after around 30 days, when the absorbance was reduced by 92%. The amounts of diethylphthalate and ethyl benzoate adsorbed per gram of allophane were 2.3 ± 0.2 and 1.6 ± 0.1 × 10 5 mol g 1. The amounts of these compounds adsorbed on allophane increased with their concentration and approached their

Conclusions

UV and IR spectroscopic measurements revealed that allophane adsorbed benzoic acid, phthalic acid, benzaldehyde, ethyl benzoate, and diethyl phthalate. Benzoic acid, phthalic acid, and benzaldehyde formed benzoate or phthalate anions on the positive sites of the hydrated alumina surface of allophane. In the case of adsorption from an acidic solution, a small amount of a neutral species of benzoic acid was detected. Ethyl benzoate and diethyl phthalate were adsorbed by interaction of the

Acknowledgments

This work was supported in part by a Grant-in-Aid for Scientific Research (A No. 14208070) from the Ministry of Education, Culture, Sports, Science and Technology of the Japanese Government. The authors thank Dr. T. Matsumoto of Tochigi Research Institute for kindly providing the allophane.

References (21)

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