EPR Spectra of Metal Ions on Graphite Oxide

Аствацатуров, Д.А.; Воробьев, А.Х.

Авторы: Аствацатуров Д.А., Воробьев А.Х.
Сборник: Modern Developments of Magnetic Resonance. Abstracts of international conference
Тезисы
Год издания: 2021
Место издания: АО “Информационно-издательский центр” Казань
Первая страница: 160
Последняя страница: 161
Аннотация: Graphite oxide is a non-stoichiometric derivative of graphite prepared by oxidation of pure graphite in acidic conditions. Graphite oxide could be used asa precursor of graphene as well as a starting material for membrane fabrication. Today, the investigation of physico-chemical properties of graphite oxidemembranes attracts a lot of attention. Graphite oxide membranes are layeredmaterials consisted of packages of graphene oxide sheets. The thickness of themembrane and its interlayer distance are often used to characterize the material. The degree of graphene oxide sheets ordering in the membrane is also animportant characteristic of the material. The most detailed way to describe thedegree of ordering of a material is to use the order parameters, which are valuesof Legendre functions averaged over all possible orientations. It is known thatgraphite oxide membranes demonstrate selective permeation of liquids and gases.The correlation of permeating ability and separation selectivity of membraneswith the degree of layer ordering is a question of interest. However, there arefew works that employ the quantitative approach for determination the degree oflayer ordering in graphite oxide membranes [1, 2]. In work [2], the authors usethe EPR method and obtain quantitative data using TEMPOL radical as a spinprobe. The values of the second and fourth rank order parameters (P20 and P40)were obtained by computer simulation of the EPR spectra recorded at differentorientations of the sample in the magnetic field [2]. The goal of this contribution is to investigate if paramagnetic metal ions could be used as spin probes to study the degree of layer ordering in the graphite oxide membranes. Paramagneticmetal ions are known to demonstrate higher anisotropy of magnetic parametersthan nitroxide radicals and can be sorbed by graphite oxide and membranes.In our work, four samples of the graphite oxide membranes were studied.Three samples were prepared by the vacuum filtration of graphite oxide waterdispersion. The one additional sample was fabricated by evaporation of thegraphite oxide water dispersion. Mn2+, Cr3+, VO2+, Cu2+ complexes were tested asspin probes. The concentration of paramagnetic species in membranes was takento be enough for spectra recording but to avoid the dipole-dipole broadeningof the EPR spectra. EPR spectra were registered in the X-range and at 100K.We found that the most reliable results are obtained if the copper hexaammonia complex [Cu(NH3)4]2+ is used as a spin probe. EPR spectra of the membranes treated with copper ammonia solution demonstrated hyperfine structuretypical for Cu2+ ions. The typical angular dependence of the EPR spectrum of[Cu(NH3)4]2+ adsorbed on the membrane is presented in Fig 1.The numerical simulation of the spectrum angular dependence was foundto be impossible because of a complex shape of base line depending on theorientation of a sample. To overcame that trouble we used simplified methodbased on the measurement of the angular dependence of the amplitude of theparallel component (mI = –3/2) of the experimental EPR spectra (this amplitudeis marked as “Ampl” in the Fig. 1) and numerical prediction of this angulardependence for different orientation distributions. The matching of the orientation distribution satisfactory describing the experimental angular dependence ofparallel component of spectrum allows to estimate the order parameters. Thevalues of the order parameters of studied graphite oxide membranes were foundto be in range: P20 = 0.020÷0.55; P40 = 0.033÷0.30; P60 = 0.03÷0.10. It wasfound that membranes fabricated by different methods have different degree ofgraphene oxide layers ordering.
Добавил в систему: Аствацатуров Дмитрий Александрович

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