The dependence of the degree of sorption of potassium dichromate by aerogels based on reduced graphite oxide and superparamagnetic iron oxide nanoparticles of the rGO⋅Fe3O4 composition on the mass of the sorbent, acidity, and temperature of the medium is studied. It is shown that in order to increase the degree of potassium dichromate sorption by the rGO⋅Fe3O4 magnetic aerogel, the process is best carried out at room temperature in media with low pH value lower than 5. The results obtained make it possible to propose aerogels rGO⋅Fe3O4 as environmentally friendly sorbents for water purification from the carcinogenic substance of potassium dichromate. The proposed materials after completion of the sorption process can be completely removed from the reaction medium using an external magnetic field, thereby preventing them from acting as pollutants. It is important to note that the described 3D structures based on GO and nanoparticles of superparamagnetic iron oxide Fe3O4 are of practical importance for the treatment of wastewater from enterprises using an oxidative method for removing phenols, cresols, and cyan-containing substances from impurities using potassium dichromate and sulfuric acid.

The comparative study of sorption of polar substances acetonitrile and water into powders and membranes (>10 μm thick) of modified Hummers (HGO) and Brodie (BGO) graphite oxides was performed using isopiestic method (IM) and differential scanning calorimetry (DSC). Additional sorption data were obtained for pyridine and 1-octanol. Sorption measurements were accompanied by conventional XRD and XPS control. Electron paramagnetic resonance (EPR) was additionally used to characterize ordering of the membranes. The impact on sorption of synthetic procedure (Brodie or Hummers), method of making membranes, chemical nature of the sorbent, and method of sorption was systematically examined. It was demonstrated that variations in synthetic procedures within both Hummers and Brodie methods did not lead to changes in the sorption properties of the corresponding powders. Sorption of acetonitrile and pyridine was reduced by approximately half when switching from powders to membranes at ambient temperature. DSC measurements at a lower temperature gave equal sorption of acetonitrile into HGO powder and membranes. Water has demonstrated unique sorption properties. Equal sorption of water was measured for HGO membranes and powders at T = 298 K and at T = 273 K. It was demonstrated that lowering the orientational alignment of the membranes led to the increase of sorption. In practice this could allow one to tune sorption/swelling and transport properties of the GO membranes directly by adjusting their internal ordering without the use of any composite materials.

This paper reports novel techniques for the preparation of aerogels based on graphite oxide (GO) and nanocomposites of GO and superparamagnetic iron oxide nanoparticles (GO/Fe3O4) and discusses specific features of the synthesized materials as sorbents of doxorubicin from aqueous solutions. Sorption efficiency of the aerogel based on GO and superparamagnetic iron oxide nanoparticles (GO/Fe3O4) and the GO aerogel has been determined to be about 50 and 85 W(τ ) = W(∞ )( 1 - e^ - kτ), where W is sorption efficiency, the rate constant is k = 0.042 ± 0.004 min–1 for graphite oxide and 0.0832 ± 0.018 min–1 for the GO/Fe3O4 nanocomposite. The GO/Fe3O4 composite saturates about a factor of 2 more rapidly than pure GO. Sorption by the magnetic aerogel is an exothermic process. The highest efficiency of sorption from a solution with a concentration of 40 mg/L was 95

В статье рассматриваются новые методики получения аэрогелей на основе оксида графита (GO) и его нанокомпозитов с суперпарамагнитными наночастицами оксидов железа (GO/Fe 3 O 4 ), а также обсуждаются особенности полученных материалов в качестве сорбентов доксорубицина из водных растворов. Установлено, что эффективность сорбции аэрогелем на основе GO и суперпарамагнитных наночастиц оксида железа (GO/Fe 3 O 4 ) и аэрогелем GO составляет около 50 и 85% соответственно. В то же время, к преимуществам магнитного аэрогеля следует отнести возможность извлечения сорбента при помощи внешнего магнитного поля. Показано, что при формальном описании сорбции уравнением кинетики псевдопервого порядка: \(W(\tau ) = W(\infty )\left( {1 - {{{\text{e}}}^{{ - k\tau }}}} \right),\) где W – эффективность сорбции, константы достигают значений k = 0.042 ± 0.004 мин –1 для оксида графита и 0.0832 ± 0.018 мин –1 для нанокомпозита GO/Fe 3 O 4 . Для композита GO/Fe 3 O 4 насыщение наступает примерно в 2 раза быстрее, чем для чистого GO, а процесс сорбции магнитным аэрогелем является экзотермическим, максимальная эффективность сорбции из раствора с концентрацией 40 мг/л при 25°C составила 95%, при 40°C – 60%. Полученные результаты перспективны для использования магнитных графитовых аэрогелей в качестве сорбентов и матриц для терапевтических противоопухолевых препаратов пролонгированного действия.

Reversible phase transformation in the Brodie graphite oxide-acetonitrile system, which is intercalation or release of part of the sorbed liquid from the interplanar space accompanied by an increase or a decrease in interplanar distances, is commonly observed in twice-oxidized materials. We observed this phenomenon for once-, twice- and thrice-oxidized materials using the EPR spin probe technique, DSC, and temperature programmed XRD. It was shown that all materials under study formed similar low temperature (LT) and high temperature (HT) swollen structures with acetonitrile. The phase transformation of these structures is observed for materials with different oxidation levels in the same temperature range (∼20 K). The twice- and thrice-oxidized Brodie graphite oxides form swollen structures with the same parameters, while the once-oxidized material sorbs less acetonitrile at lower temperatures, but shows the same interplanar distances as those in twice- and thrice-oxidized materials. The spin probe technique has proven its sensitivity to the appearance of small amounts of the new forming swollen structures, which makes this method useful in studies of phase transformations.

Thin films of photonic crystals with inverse opal structure were prepared from opal-type templates, using photocurable resin polymerisation. Different techniques for neatly incorporating gold nanoparticles (NPs) into inverse opal films, based on multiple infiltration of water-ethanol solution of gold NPs, were proposed. In a number of cases, a sharp deepening of the transmittance dip in the region of the photonic stop band was observed; this was presumably related to the resonant absorption of NPs. The possibility of an ordered entry of gold NPs into the structure of inverse opal and their influence on the effective refractive index are also discussed. According to the Kramers-Kronig relation, changes in the effective refractive index should be more noticeable on the long-wave side of the plasmon resonance peak. At a gold concentration of about 0.1 mu g/mm(2), a significant improvement in the properties of photonic crystals can be achieved by the ordering of NP clusters and an increase in the effective refractive index.

Описано получение гидро- и аэрогелей на основе восстановленного оксида графита и наночастиц золота, полученных методом Туркевича. Наночастицы золота, согласно данным просвечивающей электронной микроскопии, имеют сферическую форму и средний размер 16–18 нм. Для характеризации полученных 3D-структур использована сорбция растворов красителя метиленового голубого. Проведено сравнение сорбционных свойств гидро- и аэрогелей, показано, что аэрогель сорбирует более эффективно (>80%), чем композит на основе гидрогеля (~50%). Сформированная пористая 3D-структура аэрогеля эффективно сорбирует молекулы красителя, а наночастицы золота, входящие в состав аэрогеля, способствуют его разрушению под воздействием видимого света. Сорбция красителя аэрогелем чистого оксида графита проходит с наибольшей эффективностью при комнатной температуре, в нейтральной среде и без использования дополнительных восстановителей. Введение в аэрогели наночастиц золота позволяет увеличить эффективность сорбции на 15%.

Solvothermal reduction of graphene oxide performed up to a sp(2)/sp(3) ratio of 20 was demonstrated. The presence of chemical and structural defects was minimized by varying the treatment conditions and reduction agents to reduce their impact on electronic and optical properties. Using the interphase deposition technique both graphene oxide and reduced graphene oxide films were transferred onto ITO-coated glass substrates or SITAL for further analysis. The analysis of the electric characteristics of the reduced graphene oxide films showed high sheet resistance originated from grain boundary resistance. The optical transmittance of the films reached 30% for the most uniform coatings.

The preparation of hydro- and aerogels based on reduced graphite oxide and gold nanoparticles obtained by the method of Turkevich is described. According to the transmission electron microscopy data, gold nanoparticles have a spherical shape and an average size of 16‒18 nm. Sorption of methylene blue dye from water solutions was used to characterize the obtained 3D structures. The sorption properties of hydro- and aerogels were compared; it was shown that aerogels sorb the dye more efficiently (>80%) than a composite based on hydrogel (~50%). The formed porous 3D structure of the aerogel efficiently sorbs the molecules of the dye, while the gold nanoparticles facilitate its destruction under the visible light. Sorption by aerogels of pure graphite oxide is most efficient at room temperature, in a neutral medium, and in the absence of additional reducing agents. Introduction of gold nanoparticles to aerogels led to an increase of the maximal sorption by 15%.

Core-shell SiO2@Ag composite spheres with dense, complete and nanoscaled silver shell were prepared by using facile chemical reduction method. Self-assembly of the composite microspheres into 3D photonic crystals (PhCs) was carried out using the vertical deposition method. The core-shell PhCs composites were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy and energy dispersive X-ray spectroscopy (EDX). The results of amplification of Raman scattering by these composite substrates are presented.

Two-level arrays of colloidal particles have been obtained using the method based on an intermittent, "stick-slip" motion of the meniscus during colloidal suspension evaporation. The ethanol suspension of monodisperse polystyrene microspheres of about 1 pm in size was prepared by emulsifier-free emulsion polymerization of styrene with potassium persulphate as an initiator. The resulting structures consist of parallel monolayer stripes of deposited microspheres, repeated with a period of 140-150 mu m, and empty spaces between them. The microspheres are packed into a hexagonal structure inside the stripes. Laser diffraction patterns have been demonstrated for both levels of ordering, i.e., for the hexagonal structure at the first level and for the parallel stripes at the second level.

Статья посвящена созданию многофункционального нанокомпозита состава GO@Fe3O4@DOX, содержащего оксид графита, наночастицы суперпарамагнитного оксида железа и лекарственный препарат доксорубицин. Созданный материал сочетает функцию двойного магнитного и молекулярного нацеливания на опухолевые ткани. Первоначально для создания композита на поверхность оксида графита (GO) химически осаждали суперпарамагнитные наночастицы Fe 3 O 4 , при этом получали двойной композит GO@Fe 3 O 4 . Затем полученный материал связывали с противоопухолевым лекарственным препаратом доксорубицином (DOX) и получали тройной композит состава GO@Fe 3 O 4 @DOX. Для характеристики морфологии, фазового состава, магнитных и оптических свойств синтезированных в работе образцов были использованы методы термогравиметрического и рентгенофазового анализа, измерения магнитной восприимчивости, просвечивающей электронной микроскопии, УФвидимой и спектроскопии комбинационного рассеяния (КР). В результате проведенного исследования найдено оптимальное соотношение оксида графита, оксида железа и доксорубицина для создания материала, который может быть прообразом нового лекарственного препарата. В работе доказано вхождение лекарственного препарата доксорубицина и оксида железа в композит, что делает возможным использование внешнего магнитного поля для адресной доставки лекарства к пораженным тканям. Показано, что композит стабилен в течение месяца в растворах с физиологическим значением рН.

This work is dedicated to the synthesis of a GO@Fe 3 O 4 @DOX multifunctional nanocomposite composed of graphite oxide, superparamagnetic iron oxide nanoparticles, and the drug doxorubicin. The final product combines double magnetic and molecular targeting to tumor tissues. Superparamagnetic Fe 3 O 4 nanoparticles are first chemically deposited onto a surface of graphite oxide (GO) with the acquisition of a double GO@Fe 3 O 4 composite. The material is then bound with the antitumor drug doxorubicin. The morphology, phase composition, and magnetic and optical properties of synthesized samples are characterized via thermal gravimetry, X-ray diffraction, magnetic susceptibility measurements, transmission electron microscopy, and via UV-visible and Raman spectroscopy. The optimal ratio of graphite oxide, iron oxide, and doxorubicin for the creation of a potential precursor of the new drug is established. The presence of doxorubicin and iron oxide in the composite is confirmed, making it possible to use an external magnetic field for targeted drug delivery towards the affected tissues. It is also shown that the composite retains its stability for a month in solutions with physiological pH values.

La0.7Ca0.3Mn0.95M0.05O3 (M = Mn, Al, 0.5Al+0.5In, and In) perovskites (ABO3) were studied with x-ray diffraction and AC susceptibility measurements. We provide the phenomenological expressions for the electron bandwidth, W, and Curie temperature, TC, to describe the variance in these values caused by the change of the degree of doping in the A- position and of the type of dopant in the B-position. The observed decrease in TC with doping is found to be mostly related to the difference in the electron configuration of Mn3+ ions and dopant M, and partially caused by the change in the local crystal structure because of the difference in the Mn3+- and M-ion radii.

Surface-enhanced Raman scattering (RS) spectroscopy is a sensitive analytical method that makes it possible to detect individual molecules. The substantial enhancement of the intensity of the signals in this method when compared to traditional Raman scattering is associated with two mechanisms, namely, electromagnetic and chemical. The first mechanism is associated with the enhancement of both the impinging and scattered radiation (electromagnetic enhancement), while the second mechanism is explained by the electron interaction between the molecule being analyzed and metal nanoparticles, namely, by the change in the polarizability of the adsorbed molecule, which results in the displacement and broadening of the electron levels of the adsorbed molecule or in the occurrence of new levels and promotes the enhancement of the signal in the Raman scattering spectrum. Graphene and material associated with it such as graphene oxide, graphite oxide, and reduced forms of graphene and graphite oxides are advanced materials for the creation of a significant chemical enhancement. Taking into account the different nature of the enhancement of the signal from the nanoparticles of noble metals and graphene and its derivatives, it is reasonable to study the effectiveness of hybrid structures on the basis of derivatives of graphene and noble metal nanoparticles in the Raman scattering spectroscopy of the analyte molecules with an aromatic structure.

This article is devoted to studying the kinetics of formation of individual nanoparticles of noble metals and composites based on them. The effect of the concentration of the reducing agent and temperature on the rate of formation of nanoparticles of noble metals is studied. In order to characterize the morphology, phase composition, and optical properties of the synthesized nanomaterials, X-ray diffraction, transmission electron microscopy, UV–visible spectroscopy, and Raman scattering (RS) are used. It is shown that the formation of nanoparticles of noble metals and composites based on them is a three-step process consisting of an induction period, the process of nucleation, and the particle growth stage (which has an autocatalytic character). The formed nanoparticles of noble metals catalyze the further process of reduction of ions remaining in the solution. It has been confirmed that an important factor for amplifying the signal from the analyte molecules in Raman spectroscopy is the resonance absorption by nanoparticles of noble metals in a wavelength range close to the wavelength of the excitation laser.