JOURNAL OF COLLOID AND INTERFACE SCIENCE 178, 586–593 (1996) ARTICLE NO. 0155 Studies on Ferric Oxide Hydroxides II. Structural Properties of Goethite Samples ( a-FeOOH) Prepared by Homogeneous Precipitation from Fe(NO 3 ) 3 Solution in the Presence of Sulfate Ions KULAMANI PARIDA AND JASOBANTA DAS Regional Research Laboratory, Council of Scientific & Industrial Research, Bhubaneswar 751013, India Received June 5, 1995; accepted August 25, 1995 It has been observed by many researchers ( 2, 5, 19, 20 ) A series of goethite samples ( a-FeOOH) have been prepared by that for the same concentration of Fe /3 ions and for the homogeneous precipitation from Fe(NO 3 ) 3 solution in the presence same conditions of hydrolysis, the nature of the corre- of SO 02 4 ions and characterized by various techniques. Although sponding anions (Cl 01 ,F 01 , ClO 01 4 , NO 01 3 , SO 02 4 ) may the cell parameters, cell volumes, and crystallite sizes of all the change the phase composition of hydrolytic products as samples prepared under different conditions remain almost same, well as the shape of the particles. Although several reports the surface area, micropore–mesopore ratio, pore volume, pore (21–28) on the influence of sulfate ions on the formation radius, particle size, and surface acidity are influenced by of a-FeOOH are available, no systematic study has been SO 02 4 /Fe /3 ratio, initial pH, and temperature of hydrolysis. The carried out so far to find out the influence of such ions on sample prepared at SO 02 4 /Fe /3 ratio of 0.5, initial pH of 1.5, and hydrolysis temperature of 90°C has predominantly micropores and the preparation and properties of a-FeOOH. In our earlier possesses high surface area (133.5 m 2 /g) and acid sites (100 study (28) we investigated the effects of SO 02 4 on the mmol/g).  1996 Academic Press, Inc. formation and physicochemical properties of ferric oxide Key Words: structural properties;goethite;homogeneous precip- hydroxides. During this study we have found that pure itation; sulfate ion. goethite samples are formed from Fe(NO 3 ) 3 solution at an SO 02 4 to Fe /3 ratio £0.5. At high SO 02 4 /Fe /3 ratios, §1.0, the formation of FeSO / 4 complex strongly sup- INTRODUCTION presses the polymerization of hydroxy complexes and the Since the first report of Atkinson et al. (1) in 1968 on precipitation of goethite (24–28). As size, shape, and the synthesis of pure goethite ( a-FeOOH), several attempts surface properties are crucial in assessing the performance have been made to prepare material of uniform shape and of a material and the relationship among all these parame- size (2–5). All the preparation methods can be broadly ters and preparation methods is obscure, the objective of divided into two groups: (1) precipitation of ferrihydrites this paper is to prepare goethite samples with desired sur- from Fe(NO 3 ) 3 /Fe 2 (SO 4 ) 3 solution by the slow addition of face properties by controlling the preparation conditions. ammonia and transformation of these hydroxides to a- In this paper we report the preparation and physicochemi- FeOOH by storage in KOH/NaOH solution (6–9) and (ii) cal characteristics with special reference to surface prop- oxidative precipitation of FeCl 2 or FeSO 4 or ( NH 4 ) 2 Fe(SO 4 ) 2 erties of a-FeOOH samples produced by urea hydrolysis in alkaline solution (10–16). Recently Kandori et al. (17, of Fe(NO 3 ) 3 solution in presence of SO 02 4 ions. 18) have used NaOH solution as precipitating as well as storing agent during their investigation to find out the effect EXPERIMENTAL of citrate, silicate, and phosphate ions on the formation and characteristics of a-FeOOH. As both categories of methods Materials and Methods are cumbersome and time-consuming, the development of a simple and novel method for the synthesis of a-FeOOH of One dm 3 of solution containing 8.37 g Fe /3 , 50 g urea, and variable amounts of sodium sulfate (in the range 0.01 characteristic shape, size, and surface properties is very much required, taking into account the importance of the to 0.05 M ) was prepared in a 2 dm 3 round bottom flask. The pH of the solution was adjusted to a desired value with 0.1 material for the preparation of catalysts, ferrites and pig- ments. M nitric acid or 5% ammonia and the total volume was made 586 0021-9797/96 $18.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved.