A new volumetric method has now been developed for the determination of iron(III) through reduction to iron(II) with excess of hydroxylamine. The reduction is completed at the temperature of the boiling water bath in 10 min, keeping the acidity at 0.2–0.5 N sulphuric acid. The mixture is cooled and treated with enough 1 1 sulphuric acid to bring up the acidity to 6 N. It is then titrated with a standard solution of sodium vanadate, using N-phenyl anthranilic acid as inside indicator. Diphenyl benzidine, barium diphenyl sulphonate, or 1,10-phenanthroline cannot be used as indicators in this titration, because of the interference of the unreacted hydroxylamine.The method has been found to be very precise, and convenient. It has also the advantage that it is subject to fewer interferences than the existing methods.
[Show abstract][Hide abstract] ABSTRACT: Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red–orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs.
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