Interplanar Space Research Articles

Hybrid organic–inorganic crystals based on ammonium dihydrogen phosphate and ammonium salicylate

ADP–NH 4Sal hybrid crystals are grown from aqueous solutions. The influence of the acidity of the mixed solution on the conditions of co-crystallization of the components is studied. The spectral and scintillation characteristics are determined. Co-crystallization of ammonium salicylate (NH 4Sal) and ammonium dihydrogen phosphate (ADP, NH 4H 2PO 4) is shown to be feasible, the structure of the doping addition being defined by the solution рН. In basic and weak acidic media the hybrid crystals ADP:NH 4Sal are formed in which salicylate anions are located in the interplanar space between the {110}-type planes in the lattice of ADP. The luminescence spectra contain an emission band maximum with λ max=360 nm. In acidic solutions there are ADP:HSal crystals in which salicylic acid molecules captured by the growth macrosteps are located in the interplanar space of the prismatic {100} and pyramidal {101} growth sectors. The luminescence band undergoes bathochromic shift to λ max=400 nm. The sensitivity of ADP:NH 4Sal scintillation crystals to fast neutrons depends on the concentration of ammonium salicylate in ADP matrix. The highest neutron sensitivity is characteristic of the co-doped ADP:NH 4Sal/Tl scintillation crystals.

Effect of Oxygen Content on Structures of Graphite Oxides

Graphite oxide was synthesized by the oxidation of graphite via a modified Hummers approach. The oxygen content of graphite oxide was tuned by changing the oxidation time. The saturated ratio of oxygen to carbon is 0.47. Furthermore, the effect of oxygen content on the structures of graphite oxide was evaluated by using SEM, TEM, XRD, Raman, FTIR, TG, TPD-MS, and nitrogen adsorption. It was found that the types of functional groups in graphite oxides, which are epoxy, hydroxyl, and carboxyl groups, were independent of oxygen content. However, the interplanar space and BET surface area of graphite oxide linearly increased with increasing O/C ratio. Furthermore, the structure of graphite can be easily and remarkably disordered even by partial oxidation.

Effects of impurities on the biodegradation behavior of pure magnesium

The corrosion behavior of pure magnesium that has different content ratio of impurities (such as Fe/Mn ratio) in Hanks’ solution was investigated in order to tailor the lifetime of biodegradable implant made of pure magnesium. Two distinct stages of corrosion were observed: a slow corrosion rate stage and a subsequent fast corrosion rate stage. The first stage was characterized by uniform corrosion that produced magnesium hydroxide and calcium phosphate film on a magnesium surface, resulting in a slow corrosion rate. The second stage with an abrupt increase in the corrosion rate was induced by Fe precipitates and was stimulated by an increase in the Fe/Mn ratio. This corrosion was developed to a preferred crystallographic pitting corrosion where the pits propagated along the preferred crystallographic plane and several layers of Mg planes with narrow interplanar space remained uncorroded. From this study, it is expected that the lifetime of the biodegradable implant made of pure Mg can be tailored by controlling the amount and ratio of the impurities.

Acceptor-type graphite intercalation compounds and new carbon materials based on them

The problems of synthesis and study of the physicochemical properties of graphite intercalation compounds (GIC) formed upon insertion of various molecules into the interplanar space of graphite are considered. Binary and ternary intercalation compounds with protonic acids (HNO3, CH3COOH, H3PO4, H2SO4, etc.) are described. The results of systematic research into graphite intercalation by potentiometry, calorimetry, powder X-ray diffraction, conductivity measurements, DTA, chemical analysis, and other methods are given. These results underlie elucidation of the characteristic and peculiar features of acid insertion into graphite. The physicochemical properties and practical applications of GIC and low-density carbon materials are analyzed.

Synthesis and crystal structure of Cu2{(UO2)3[(S,Cr)O4]5}(H2O)17

Cu2{(UO2)3[(S,Cr)O4]5}(H2O)17 crystals were prepared by evaporation of aqueous solutions. The crystal structure was solved by the direct method and refined to R1 = 0.064 (wR2 = 0.177) for 8120 reflections with ¦Fhkl¦ ≥ 4σ ¦Fhkl¦. Rhombic system, space group Pbca, a = 18.0586(8), b = 19.9898(9), c = 20.5553(8) A, V = 7420.2(6) A3. The structure is based on {(UO2)3[(S,Cr)O4]5}4− anionic layers, formed by combination of UO7 pentagonal bipyramids and TO4 tetrahedra through common vertices. The { (UO2)3 ⋅ [(S,Cr)O4]5}4− layers are parallel to the (010) plane. The Cu2+ (H2O)6 octahedra and additional water molecules are located in the interplanar space and provide binding of the layers in the structure by hydrogen bonds. Based on the occupancy of tetrahedral positions, more accurate chemical formula of the compound should be written as Cu2{(UO2)3[(S0.804 Cr0.196)O4]5} (H2O)17.

Propriedades químicas e cristalográficas da caulinita e dos óxidos de ferro em sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo

As propriedades químicas e cristalográficas detalhadas da caulinita (Ct) e dos óxidos de ferro do solo e dos sedimentos do Grupo Barreiras são pouco conhecidas. Para estudar as características desses minerais em profundidade, coletaram-se 11 amostras (0,7; 1,4; 2,1; 2,8; 3,5; 4,2; 4,9; 5,6; 7,7; 10,5 e 14m) nos horizontes Bt, BC e C de um Argissolo Amarelo no município de Aracruz (ES). As frações argila e silte foram estudadas por difração de raios-X (DRX), análise termo-diferencial (ATD) e microscopia eletrônica. Os teores totais de Fe e outros microelementos (Cr, Mn, Ni, Pb, Ti e Zn) da fração argila foram determinados por espectrometria por emissão por plasma, após digestão da amostra com HF concentrado. Nos extratos resultantes das extrações com oxalato de amônio (OA) e ditionito-citrato-bicarbonato (DCB), determinaram-se os teores de Fe, Al, Si, Cr, Mn, Ni, Pb, Ti e Zn. A composição química da Ct das frações argila (amostra desferrificada) e silte (amostra natural) foi determinada pelo tratamento com NaOH 5molL-1 e pela combinação de aquecimento e extração com NaOH 0,5molL-1 fervente, respectivamente. O teor médio de Fe2O3 da Ct da fração argila (20,7gkg-1) foi superior ao obtido para a fração silte (5,2gkg-1), verificando-se, na menor fração, aumento nos teores de Fe2O3 com a profundidade. Graças ao maior raio iônico, a presença do Fe3+ na estrutura promoveu aumento no espaço interplanar do mineral, sobretudo na direção b. O tamanho das partículas de Ct foi semelhante entre os horizontes amostrados. A Ct apresentou grau semelhante de cristalinidade com a profundidade do solo, com exceção dos horizontes mais superficiais, os quais apresentaram menores valores de índice de cristalinidade, provavelmente por interferências com compostos orgânicos. A redução dos teores de Fe2O3 extraídos pelo DCB e da participação dos teores de FeOA mais FeDCB no Fe total da fração argila com a profundidade foi atribuída à dissolução dos óxidos de ferro, provocada pela umidade nas camadas inferiores dos sedimentos. A substituição isomórfica (SI) de Fe por Al na goethita (Gt) foi cerca de três vezes superior à da hematita (Hm), com maiores valores nos horizontes mais superficiais. A Hm apresentou menor valor de superfície específica (SE) que a Gt, refletindo os maiores valores de diâmetro médio do cristal para a Hm. Baixos valores de cristalinidade e menor tamanho de partículas estão associados à maior atividade e à influência da Ct e dos óxidos de ferro sobre as propriedades físico-químicas do solo. Os óxidos de ferro apresentaram baixa associação com microelementos, sobretudo com Ni, Pb e Ti.

Melanin-like units concentration effects in melanin-like/vanadium pentoxide hybrid compounds

An intercalated material has been prepared consisting of a regular alternation of organic/inorganic layers. The films were obtained by reacting 3,4-dihydroxy-phenylalanine (dl-DOPA) with varying concentrations in a solution with freshly prepared HVO3, which suffered a oxidative polymerization/intercalation ‘in situ’ process, forming a green suspension, in which after de-hydration at room temperature produces a nanocomposite with a dark blue metallic color. Films (C8H9NO2)xV2O5·nH2O were characterized using FT–IR, ESR, powder X-ray diffraction, conductivity, and cyclic voltammetry. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved for low concentrations of melanin-like units (x<0.02), but the inter-planar space increases from 1.2 nm to ca. 1.5 nm. The FT–IR and ESR spectra confirm that the V2O5 structure is preserved, however the presence of melanin-like units induces the reduction of V(V) ions to V(IV) ions. The melanin insertion is observed to increase the stability and reproducibility of the electrochemical insertion/de-insertion of Li+. The incorporation of melanin-like structures increases the conductivity, followed by a decrease in its temperature activation energy.

Electrochromic and conductivity properties: a comparative study between melanin-like/V 2O 5[formula omitted]nH 2O and polyaniline/V 2O 5[formula omitted]nH 2O hybrid materials

In this work, we report the synthesis and some properties of melanin-like/V 2O 5 · nH 2O and polyaniline/V 2O 5 · nH 2O hybrid materials that have potential applications in optics and electronics. The hybrid materials were obtained by an oxidative polymerization/intercalation process reacting the gel with the monomers of the polymers. The optical properties of the compounds in film forms were measured using ultraviolet–visible (UV–Vis) spectroscopy. Thermogravimetric analysis, differential gravimetric analysis and dc conductivity techniques were also used to study the compounds. The X-ray diffractograms indicate that the lamellar structure of the V 2O 5 is preserved with the increase of the inter-planar space from 1.18±0.05 to 1.40±0.05 nm. The presence of the organic phase induced the reduction of V(V) ions to V(IV) and increased the dc conductivity and affected the spectroelectrochemical properties of the samples.

In Situ Intercalation/Polymerization of Melanin into Vanadium Pentoxide

ABSTRACTIn this work, intercalated material was prepared consisting of a regular interchange of organic/inorganic layers. The products were obtained by reacting 3,4-dihidroxi-fenilalanina (DL-DOPA) in a solution with V2O5.nH2O gel, which suffered an oxidative polymerization/intercalation process, forming a film with a dark blue metallic color. The films were characterized using UV\Vis transmission spectroscopy, FTLR, ESR, X-ray diffraction, dc conductivity, and cyclic voltammetry. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved but the inter-planar space increase from 1.18 nm to 1.38 nm. The FTIR and ESR spectra confirms that the V2O5 structure is preserved, however the presence of melanin induces the reduction of Vv ions to Viv. The increase in the inter-planar spacing is observed to increase the stability and reproducibility of the electrochemical insertion/de-insertion of Li+. This increase in stability is also observed in the electrochromic properties of the film, which are fully reproducible even after more than 60 oxidation-reduction cycles. The melanin affects also the activation energy of the dc conductivity which changes from 0.35 eV to 0.20 eV.

The diffusion of lithium in graphitic matrix A3-3 at low concentrations and high temperatures

The diffusion of Li into the bulk is the first step in the formation of intercalation compounds. Previously we found that Li migrates in Li doped, highly oriented pyrolytic graphite within the interplanar space, and in comparison to Poco graphite AXM-5Q1, Li is preferentially absorbed in a phenolic resin based glassy carbon. We now report on a study of Li diffusion in graphitic Matrix A3-3 which consists of graphite grains (like Poco graphite) and a phenolic resin based polymeric carbon. Specimens of Matrix A3-3 and POCO AXM-5Q1 were Li doped in a closed container at 1273 K and subsequently the Li content of the specimen was determined. The Li concentration in the binder carbon was estimated to be 10 times higher than in the graphite grains. The Li release kinetics were measured by using a mass spectrometric method and were found to conform to Fick's second law at high temperatures. At low temperatures the release rate was initially lower than expected for simple diffusion kinetics. We assume this is mainly due to a nonzero Li surface concentration. After considering the literature on the structure of polymeric carbons we conclude that micropores, and probably even more vacancies and other small defects in the graphitic layers within the bulk, are preferred Li binding sites. The temperature dependence of the diffusion coefficient of Li in graphitic Matrix A3-3 is given by D = 5.6 × 10 5 exp(−2.62/ kT) cm 2 s −1 in the temperature range 1100–1400 K at concentrations in the range 1.5 μgLi/gC to 12 μgLi/gC. The activation energy E for Li diffusion in Poco AXM-5Q1, graphitic Matrix A3-3, and glassy carbon increases in the order given.