Nanoparticles hematite

The rate law is based on a surface complexation model Liger et al. (1999) developed for the hematite nanoparticles (see Chapter 10, Surface Complexation ). The >FeOH surface sites react by protonation and deprotonation to form >FeOII2h and >FeO-, by complexation with ferrous iron to form >FeOFe+ and >FeOFeOH, and to make a complex >Fe0U020H with uranyl. Table 28.1 shows the reactions and corresponding log K values. The nanoparticles are taken to have a specific surface area of 109 m2 g-1, and a site density of 0.06 per Fe2C>3. 

To see how we can use the surface complexation model to trace the kinetics of this reaction, we simulate an experiment conducted at pH 7.5 (Liger et al, 1999, their Fig. 6). They started with a solution containing 100 mmolar NaNC>3, 0.16 mmolar FeS04, and 0.53 g l-1 of hematite nanoparticles. At t = 0, they added enough uranyl to give an initial concentration of 5 x 10-7 molar, almost all of which sorbed to the nanoparticles. They then observed how the mass of sorbed uranyl, which they recovered by NaHCC>3 extraction, varied with time. 

K. Morup, S. (2000) Magnetic properties of hematite nanoparticles. Am. Phys. Soc. 

Recently, it was shown that transient absorption decay for hematite nanoparticles was very fast, 70% of the transient absorption disappeared within 8 ps and no measurable transient absorption remained beyond 100 ps [43]. This represented a much faster decay than many other semiconductors, which is consistent with the observed poor charge transfer properties in hematite. It should be mentioned that this decay was independent of the excitation power, which suggests alternative relaxation mechanisms compared to those observed for Ti02 and ZnO for instance [43]. Since the relaxation was independent of pump power, probe wavelength, pH and surface treatment the fast decay was interpreted to be due to intrinsic mid-bandgap states and trap states rather than surface defects. This is in agreement with earlier investigations [44]. 

Bocqnet S (1996) Snperparamagnetism and the Mossbaner spectrum of goethite a comment on a recent proposal by Coey et al. J Phys Condensed Matter 8 111-113 Bodker F, Hansen MF, Bender Koch C, Lefmann K, Morap S (2000) Magnetic properties of hematite nanoparticles. Phys Rev B 61 6826-6838... 

Bodker F, Morap S (2000) Size dependence of the properties of hematite nanoparticles. EnroPhys Lett 52 217-223... 

Iron oxide nanoparticles are undoubtedly one of the most investigated nanoparticles owing to their importance in industrial and medical appUcations. Hematite nanoparticles are comparatively more stable and therefore have wider applications as well. While several methods are available for the synthesis of nanoparticles, the green synthesis routes are preferred, more so iu biological apphcations. It has beeu demoustrated that natural products such as polysaccharides can be employed as effective templates, both through sacrillcial and otherwise routes to generate mono-dispersed nanoparticles of below 20 run. Such methods are easy to adopt for other ferrite nauoparticles as well. Incidentally, some of the polysaccharide methods are facile and possibly simple for rephcation at industrial scales. 

Sreeram K. J., Nidhin M. and Nair B. U. (2009a). Synthesis of aligned hematite nanoparticles on chitosan-alginate films. Colloids and Surfaces B Biointerfaces, 71(2), 260-267. 

Corrosion resistance Gold nanoparticles (AuNPs) Hematite nanoparticles Mechanical alloying Nanocontainer Phosphomolybdate (ZMP) Polysaccharides... 

Chernyshova, I.V., Hochella, M.F., Madden, A.S. Size-dependent structural transformations of hematite nanoparticles. 1. Phase transition. Phys. Chem. Chem. Phys. 9, 1736 (2007). doi 10.1039/b618790k... 

EFFECT OF IRON OXIDE AND HEMATITE NANOPARTICLES ON ELECTRICAL PROPERTIES OF POLYMERS... 

R.D. Zysler, D. Fiorani, A.M. Testa, L. Suber, E. Agostinelli, M. Godinho, Size dependence of the spin-flop transition in hematite nanoparticles. Phys. Rev. B 68(21), 212408 (2003)... 

---