Preparation of nanostructured materials by heterocoagulation-interaction of montmorillonite with synthetic hematite particles

A nanostructured, porous material was prepared by heterocoagulation of negatively charged montmorillonite with positively charged synthetic spherical hematite particles. The process of heterocoagulation of such particles was monitored by turbidimetric titrations over the pH range 2.5-7.5. On the basis of the results of turbidimetric measurements, a series of solid materials were prepared for further characterization using ESEM, BET, XRD, and FTIR techniques. Environmental scanning electron microscopy detected isolated hematite particles or small hematite aggregates on montmorillonite surfaces (mass ratios 8:1 and 4:1). At a mass ratio of 1:1, exfoliated montmorillonite layers, covering the hematite particles as semitransparent blankets were seen. A low mass ratio led to compact hematite particle aggregates covering the montmorillonite surfaces. Nitrogen-gas-adsorption isotherms revealed the sorption properties to be gradually dependent upon mass ratios. Pore volume distributions showed that mesopores with diameter of about 10 - 20 nm were produced in the heterocoagulates with mass ratios of 4:1, 1:1, and 1:8. The sample prepared with a 4:1 mass ratio showed the greatest BET surface area, which decreased slightly upon sample calcination at 500 degreesC. X-ray diffraction measurements were used to investigate layer stacking, by comparing the integral intensities of d(001) reflection. For this purpose, samples with 4:1 mass ratios, prepared both by heterocoagulation and mechanical grinding, were used. It was found that heterocoagulation effectively diminished the stacking of the layers to about 85%; hence, a significant amount of fundamental, 1 nm thick montmorillonite layers was achieved in this sample.