| Preparation: |
prepared by forced hydrolysis of a FeCl3 solution with a procedure quite similar to that reported by Matijevic (4, 5). A stock solution of 1.5 M FeCl3
(Merck) was prepared and filtered through a 0.45 μm Millipore membrane. Proper amounts of the FeCl3 stock solution and 1.0 M HCl were mixed and diluted with preheated, (∼98°C) doubly distilled water. The FeCl3 concentration obtained was then 0.020 M, and the HCl concentration was 0.001 M. The solution was transferred to preheated (100°C) Pyrex bottles, closed tightly, and sealed with Teflon tape. The bottles were stored in an oven at 100°C for 24 h and then cooled to room temperature. The hematite suspension obtained by this method contains considerable amounts of chloride ions. For purification the suspension was retained in dialyse membrane tubing (Spectra/Por® 2 Membrane, MWCO 12-14,000), which was bathed in 0.1 mM HNO3.
By this method the hematite sol was kept at pH 4, and aggregation and sedimentation were avoided. The bath solution was exchanged at least 10 times. A chloride ion concentration in the bath solution of less than 2E−7 M could then be established by adding 0.1 M AgNO3 |
