NOTE. Separation of chlorophenols using columns of hydroxyaluminium interlayered clays

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Clay Minerals (1997) 32, 143-147 NOTE Separation of chlorophenols using columns of hydroxyaluminium interlayered clays Clay minerals play an important role in the retention, transport and chemistry

1 Clay Minerals (1997) 32, NOTE Separation of chlorophenols using columns of hydroxyaluminium interlayered clays Clay minerals play an important role in the retention, transport and chemistry of organic micropollutants in soils. There has been considerable recent interest in modelling and designing modified clays as adsorbents and catalysts for the removal of contaminants from waste waters (McBride et al., 1977; Mortland et al., 1986; Boyd et al., 1988). Organo-clays have been used as chromatographic stationary phases over the past three decades. White (1957) and Barrer & Hampton (1957) used alkylammonium montmorillonites as stationary phases and determined the selective retention of aromatic hydrocarbons relative to paraffins, naphthalenes and xylenes. Until now only organo-clays have received attention as chromatographic stationary phases (McAtee & Robbins, 1980) while their pillared variants have been totally ignored. The present work investigates adsorptiondesorption and separation of chlorophenols using a column of hydroxyaluminium interlayered montmorillonite, which was eluted with water, acetone or their mixtures. Materials and methods Hydroxyaluminium interlayered montmorillonite (Al-mont) was prepared by exchanging Na montmorillonite (Wyoming) with a hydroxy-al polycation (AlI304(OH)24(H20)7~) followed by dehydration at 350~ (Michot & Pinnavaia, 1991). The specific area was 130 m2g -1 (BET) and the interlayer distance, as determined by X-ray diffraction was 14 h,. The compounds tested were 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TrCP) and pentachlorophenol (PCP). The batch adsorption experiments were carried out in 40 cm 3 polypropylene centrifuge tubes to which 0.3 g of Al-mont and 25 cm 3 of aqueous chlorophenol mixtures (25, 50, 100, 150 and 200 p.g 1-1 of each compound) were added. After 24 h equilibration, the samples were centrifuged at 6000 g for 15 min and the supernatant was carefully sampled for determination of chlorophenol equilibrium concentration. The desorption was carried out in two steps using 25 cm 3 of distilled water for 6 h, and 15 cm 3 of acetone for 30 min. After centrifugation the amount of chlorophenol in the supernatant was determined. One gram of Al-mont was placed on a porous glass sieve in a 1 cm diameter glass column. Then 0.1 cm 3 of a chlorophenol mixture (10 ~tg of each) in acetone was placed on the Al-mont. In the first experiment the following eluents were used: 100 cm 3 of water (five portions of 20 cm 3 were collected) and 20 cm 3 of acetone (two portions of 10 cm 3) (Fig. 2a). In the second experiment, 15 cm 3 of a mixture of 20% acetone in water (three portions of 5 cm 3) was inserted between the above steps (Fig. 2b). In the final experiment, the previous step was replaced by 20 cm 3 of a mixture of 10% acetone in water (four portions of 5 cm 3) (Fig. 2c). All the aqueous phases were acidified with sulphuric acid 1:1 (v/v) to ph 2 and extracted three times with 5 cm 3 dichloromethane, evaporated to c. 0.8 cm 3, redissolved in 3 cm 3 of 0.1 M K2CO 3 solution and 2 cm 3 n-hexane and derivatized with 50 lal acetic anhydrite (Lee et al., 1984; Danis & Albanis, 1996). A Varian 3300 gas chromatograph equipped with a 63Ni electron capture detector and a 2 m length 5% OV-17+4% QF-1 column were used for chlorophenol analysis. The recoveries achieved were 94% for DCP, 98% for TrCP and 105% for PCP. Results and discussion The batch adsorption experiments (Table 1 and Fig. 1) clearly show that the adsorptive capacity of Al-mont increased with an increase in the number of chlorines in the phenolic ring (parallelling the increasing lipophilic character), reaching almost quantitative adsorption of pentachlorophenol (95.2%). In contrast, the desorption into water was The Mineralogical Society

2 144 Note // ] g ~ ~ ;~ TrCP(s) tl DCP (s...~) < ~ ~ o 2o0 Equilibrium concentration (Ixg/1) FIG. 1. The separate and simultaneous (s) adsorption isotherms of chlorophenols from aqueous solutions onto hydroxyaluminium interlayered montmorillonite. increased as the number of chlorines decreased. The use of acetone resulted in almost total desorption of the remaining adsorbed chlorophenols. Therefore, it appears that Al-mont can be used for the separation of chlorophenols. The decomposed or permanently adsorbed amount was estimated from the difference between the adsorbed amount and the sum of the amounts desorbed using water and acetone. The isotherms for the three chlorophenols show type S characteristics which implies that adsorption increases as the concentration in the liquid phase increases (Calvet, 1989). Such isotherms are characteristic of weak adsorbate-adsorbent interactions (Mortland et al., 1986). Although the binding capacity of metal oxide pillared clays was substantially smaller than that observed with organo-clays, several significant features were observed (Ziekle et al., 1989). In these systems, the clay surface has been modified by the introduction of an inorganic polymer, a hydroxy metal cation of A1. Although the adsorbent is purely inorganic, the polarity of the clay surface has been substantially modified as illustrated by the increase in adsorption capacity (PCP>2,4,6-TrCP>2,4-DCP) with decreasing water solubility of the adsorbate. This selectivity of hydroxyaluminium interlayered clays in chlorophenol adsorption shows potential for the separation of organic compounds with varying water solubilities. TABLE 1. Percentage amounts of chlorophenols adsorbed and/or desorbed simultaneously from aqueous suspensions containing hydroxyaluminium interlayered montmorillonite. Compound Free Adsorption Desorption* Desorption* Decomposed or with water with acetone permanently adsorbed* PCP (8.1) 79.5 (82.2) 9.5 (9.8) 2,4,6-TrCP (18.6) 50.0 (73.2) 5.6 (8.2) 2,4-DCP (58.4) 8.7 (33.9) 2.0 (7.6) * The figures outside the parentheses express the amounts as a percentage of the initial chlorophenol concentration whereas those inside parentheses are expressed as a percentage of the adsorbed amounts.

3 Note 145 lao_ s 120 (a) water-- "-J acetone 80 L" PCP I U 6o I~ i 9 m volume (ml) L. 0~) 20% acetone water v ~_~.. ~.~, acetone,.. im 9 TrCP DCP! 9 PCP 40 2O i I i I I i In0 160 volume (ml) J (c) water 10% ~ acet4 one ~" acetonc a 9 TrCP DCP I 9 PCP 20 I I I I volume (ml) T T I FIG. 2. Separation of 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TrCP) and pentachlorophenol (PCP) using columns of hydroxyaluminium interlayered montmorillonite. (see text for details).

4 146 Note TABLE 2. Total amounts of chlorophenols eluted by each solvent. 2,4-DCP (%) 2,4,6-TrCP (%) PCP (%) First experiment: water acetone Second experiment: water 85 20% acetone acetone Third experiment: water % acetone acetone The results for the separation of selected chlorophenols through Al-mont columns using three different elution methods are given in Fig. 2 and Table 2. In the first experiment, in which pure water and acetone were used in consecutive steps, the majority of 2,4--dichlorophenol was eluted in the water phase, whereas the major part of 2,4,6- trichlorophenol and pentachlorophenol were coeluted with acetone. In the second experiment, elution with a mixture of 20% acetone in water induced a slight separation between 2,4,6-trichlorophenol and pentachlorophenol. In the third experiment, in which water, 10% acetone in water and acetone were used as eluents, the separation between the three tested chlorophenols was almost complete. The recovery of chlorophenols reached 85% for 2,4-dichlorophenol in water, 96% for 2,4,6- trichlorophenol in 10% acetone in water and 100% for pentachlorophenol in acetone (Table 2). Conclusions Clays modified by metal oxides are too polar and too hydrophilic to adsorb substantial amounts of organic toxicants from aqueous solutions but can be used in separation techniques. The above results confirm a new application of hydroxyaluminium interlayered clays, i.e. the ability to separate mixtures of organic molecules, which could be used for analytical purposes such as clean up, liquid and gas chromatography. Future studies will focus on the improvement of the solvent systems used and the application of this technique to other organic mixtures. Department of Chemistry, T.A. ALBANIS University of Ioannina, T.G. DANIS 45110, Ioannina, P.J. POMONIS Greece. Received 11 November 1996; revised 28 June REFERENCES Barrer R.M. & Hampton M.G. (1957) Gas chromatography and mixture isotherms in alkylammonium bentonites. Trans. Faraday Soc. 53, Boyd S.A., Shaobai S., Lee J.F. & Mortland M.M. (1988) Pentachlorophenol sorption by organo-clays. Clays Clay Miner. 36, Calvet R. (1989) Adsorption of organic chemicals in soils. Environ. Health Persp. 83, Danis T.G. & Albanis T.A. (1996) Removal of chlorinated phenol from aqueous solutions by adsorption on alumina pillared clays and mesoporous alumina aluminium phosphates. Water Res. (in press). Lee B., Weng L.D. & Chau A.S.Y. (1984) Chemical derivatization analysis of pesticides residues. IX. Analysis of phenol and 21 chlorinated phenols in natural waters by formation of pentafluorobenzyl ether derivatives. J. Assoc. Anal. Chem. 67, McAtee J.L. & Robbins R.C. (1980) Gas chromatographic separation of cresols by various quaternary ammonium substituted montmorillonites. Clays Clay Miner. 28, McBride M.B., Pinnavaia T.J. & Mortland M.M. (1977) Adsorption of aromatic molecules by clays in aqueous supsension. Adv. Environ. Sci. Technol. 8, Michot L.J. & Pinnavaia T.J. (1991) Adsorption of chlorinated phenols from aqueous solutions by

surfactant-modified pillared clays. Clays Clay Miner. 39, 634-642. Mortland M.M., Shaobai S. & Boyd S.A. (1986) Clayorganic complexes as adsorbents for phenol and chlorophenol. Clays Clay Miner. 34, 581-585.

5 surfactant-modified pillared clays. Clays Clay Miner. 39, Mortland M.M., Shaobai S. & Boyd S.A. (1986) Clayorganic complexes as adsorbents for phenol and chlorophenol. Clays Clay Miner. 34, White D. (1957) Use of organic-montmorillonite compounds in gas chromatography. Nature, 179, Note Zielke R.C., Pinnavaia T.J. & Mortland M.M. (1989) Adsorption and reactions of selected organic molecules on clay mineral surfaces. In: Reactions and Movement of Organic Chemicals in Soils. (B.L. Sawhney & K. Brown, editors). SSSA Special Publ. No. 22, Soil Science Society of America.

Adsorption of phenol and chlorophenols on pure and modified sepiolite

J. Serb. Chem. Soc. 72 (5) 467 474 (2007) UDC 547.562.1+541.183:679.91 JSCS 3578 Original scientific paper Adsorption of phenol and chlorophenols on pure and modified sepiolite A. YILDIZ * and A. GÜR Department