Sorption of 8-hydroxyquinoline by Some Clays a N D Oxides

-The sorption of 8-hydroxyquinoline onto some clays and oxides was studied as a function of concentration, pH, and time. The sorption reaction reached equilibrium in about 5 hr, was irreversible, and reached a maximum at pH 5. The decrease in sorption on both sides of the maximum was attributed to electrostatic interactions of charged molecules with similarly charged surfaces and/or neighbors as well as solvent and proton competition. X-ray powder diffraction of dried clays showed that a one-layer complex formed in which the molecules lay flat between the clay interlayers. The sorption onto the clays included physical and exchange sorption and was accompanied by exchangeable cation hydrolysis. At high surface coverage the silicate structure deteriorated in the direction of the Z-axis due to chemical aggressiveness of the reagent. Key Words--Adsorption, Alumina, Charcoal, 8-Hydroxyquinoline, Kaolinite, Montmorillonite, Silica. I N T R O D U C T I O N In previous studies (de Bussetti et al., 1980; Ferreiro et al., 1983; Helmy et aL, 1983) the sorption reactions by clays and oxides of compounds that may have industrial and agriculture use or that could ult imately become incorporated in soils and sediments were examined. In the present work, the 8-hydroxyquinoline molecule, also known as quinolinol or oxine, was investigated. This molecule to date has received little attention despite its use in many agricultural and pharmaceutical preparations (Harris, 1979; Oladiran and Okusanya, 1980; Tinis et aL, 1978) and as an analytical reagent for chelation and precipitation. Furthermore, this molecule can exist as posit ively charged, negatively charged, and neutral species depending on the pH of the system, thereby offering aspects of sorbate-sorbent interactions o f considerable interest. In this paper, the results of a study of the sorption reaction of oxine onto clays, oxides, and charcoal are reported. Factors that affect the reaction, such as time, concentration, exchangeable cation, and pH, are also described. MATERIALS A N D METHODS The following substances were used as sorbents of 8-hydroxyquinoline: (1) montmori l loni te from Cerro Bandera, Argentina, having a cation-exchange capacity (CEC) of 0.92 meq/g and a glycerol surface area of 808 m2/g (Peinemann et al., 1972); particles <2 tzm were saturated with Na or Ca by repeated washings with 0.5 M chloride salts followed by washing out of excess salt with the help of a centrifuge; (2) kaolin from Birch Pit, Macon, Georgia, having a CEC of 0.06 meq/g and a surface area o f 7.9 m2/g as determined by paranitrophenol (PNP) adsorption from xylene (Giles and Trivedi, 1969); particles <2 /~m were saturated with Na or K as described above; (3) synthetic, noncrystalline Copyright 9 1988, The Clay Minerals Society 61 sil ica-alumina prepared in this laboratory and having the composition: SIO2, 75.6; A1203, 14.2; HzO, 10.1%; and a PNP surface area of 94.9 mVg; (4) hydrous oxide of aluminum, chromatographic grade, from Carlo Erba, Milano, Italy; this material is amorphous to X-rays and has a PNP surface area of 48 m2/g; (5) hematite (a-Fe203) from May and Baker Limited, Dagenham, England, having a surface area o f 10.3 m2/g as determined by water vapor adsorption; (6) active dry charcoal, from Merck, Darmstadt , Federal Republic o f Germany; and (7) silica gel from Davison Chemicals, Baltimore, Maryland, having a N2 surface area of 600 m2/g and an average pore diameter of 67/~,. Analytical grade 8-hydroxyquinoline (CgH6NOH) was obtained from Riedel de Hahn, Hannover, Federal Republic of Germany. It has a molecular weight o f 145.16 g, a melting point of 76~ a boiling point of 266.6~ and a water solubility of about 4 mmole/l i ter . Oxine dissociates as follows: (C9HTNOH) + Kl" C9H6NOH + H +, (1) C9H6NOH K2" (C9H6NO) -1H +, (2) where pK~ = 5.0 and pK2 = 9.85. The concentration of oxine in aqueous solutions was determined spect rophotometrical ly at 340 nm using a s tandard curve. All measurements were made in solutions adjusted to pH 12.5 with NaOH. The sorption of oxine by the above-ment ioned substances as a function of pH and oxine concentration was carried out by adding 25 ml of oxine solutions of different concentrations and pH to 0.1-0.2 g o f sorbent in 50-ml Pyrex bottles. For charcoal, the suspensions were prepared by weighing 0.05 g of material and adding 100 ml of the oxine solutions into 150-ml Pyrex bottles. The pH of the solutions was adjusted by adding 62 Ferreiro, de Bussetti, and Hclmy Clays and Clay Minerals