Anodized aluminum oxide (AOA) is applied in many technological areas such as formation of decorative or anticorrosive coating, hydrophobic and hydrophilic surfaces, development of functional micro- and nanomaterials. Due to unique properties of porous structure (most direct, regular and through pores with size in a narrow range) AOA films can be used for membrane separation. The morphological features of such films mainly depend on synthesis conditions. This review consists of the models of pore formation on the aluminum surface and the correlation parameters of films with anodizing conditions. Particular attention is paid to the influence of synthesis factors (electrolyte composition, voltage, temperature conditions, etc) on the porous structure of AOA and the film thickness that determines the mechanical strength of membranes. The optimal voltage values for the porous structure arraingment of anodized aluminum oxide were indicated for each electrolyte. It is noted formation of cylindrical shaped pores with controllable pore diameters, periodicity and density distribution can be produced during two-stage anodizing. The pre-treatment of the metal surface and stage of separation of the formed film from its surface are also considered. Modern research are mainly aimed to synthesis of porous AOA membranes in new anodizing electrolytes and determining pore formation factors on the aluminum surface.  The new anodizing conditions in most popular electrolytes (oxalic, sulfuric, phosphoric acids) for obtaining of porous AOA with the required morphological features is also under investigation. Such conditions include, for example, a lower voltage or higher temperature in case for a particular electrolyte. To avoid of local heating the electrolytes with additional components, for example, organic additives is also studied. Some practical aspects of AOA membrane utilization obtained under certain conditions are considered.

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Modification of polymer and ceramic mem­branes by modern one-, two- and three- di­men­sional carbon nanomaterials (carbon nano­tubes, fullerenes and their derivatives, oxi­dized and reduced graphene) is consi­dered. It is shown that carbon materials can be incorporated into membrane matrices both as independent components and as a part of multicomponent modifier. The main methods of modification are the addition of modifiers to the polymer solution with subsequent making of polymer membranes, incorporation of nanoparticles of carbon nanomaterials into the pristine membranes, deposition on the outer membrane surface, formation of nanoparticles directly in the pores of the ceramic matrix. Composite membranes containing carbon nanoparticles are used for pervaporation, gas separation, baromembrane processes and low-temperature fuel cells. The addition of carbon nanomaterials to polymers provides better mechanical strength of the membranes. Hydrophilic carbon modifiers increase the resistance of membranes to fouling by organic substan­ces and biofouling, improves their separation ability. Ion-exchange membranes modified with fullerenol and oxidized graphene maintain high proton conductivity at elevated temperatures and low humidity. Сarbon additives increase membrane productivity in baromembrane processes. This effect is especially evident for materials modified with nanotubes: their smooth surface ensures fast liquid transport. These carbon nanomaterials are characterized by antibacterial activity. Composites consisting of nanotubes and an ion-exchange biopolymer, and composites with oxidized graphene and inorganic ion exchanger, give to membranes selectivity to inorganic ions. Ceramic membranes modified with carbon nanoparticles that were formed in the pores of matrices by carbonization of synthetic polymers and polysaccharides have the same properties. Besides, these composites reject organic dyes too. The separating ability of composite membranes ocuures due to both dimensional and charge effects. Carbon or composite nano­particles block the pores of the membranes. The pores formed by the modifier prevent pene­tration of large particles of organic substances, for example, protein macromolecules. The charge effect is realized due to the functional groups of the modifier. For membranes modified with fullerenols, the retaining of low molecular weight organic substances occurs due to adsorption. Fullerene-modified gas sepa­ration and pervaporation membranes show increased permeability and selectivity.

Organo-inorganic membranes were obtained by impregnating ultrafiltration membranes with a composite modifier - zirconium (IV) hydroxide, containing oxidized graphene (0.5 wt.%). The modifier was precipitated in the active layer of the membrane, thus forming a "secondary active layer". The layer thickness calculated according to the Kozeny-Carman equation is 0.66-1.38 μm. A thinner layer is formed in the membrane with smaller pore size. The diffusion coefficients of Li+ and Na+ ions were found. The effect of the modifier on the retention ability relative to hardness ions (10-14%) and to protein compounds (95-98%) during filtration is determined. Mathematical modeling of the dependence of the permeate flux via time showed that the presence of ion exchanger particles in the polymer active layer prevents the accumulation of organic substances in the pores. Therefore, only the outer surface of the membrane is contaminated, and the precipitate can be easily removed mechanically. It was shown that insertion of a carbon component into pores of the membranes, in addition to the inorganic ion-exchangers, is advisable only in the case of a finely porous active layer. In particular, the performance of the initial polymer membrane (20 dm3/m3.h)) and the selectivity to the calibration substance with a molecular weight of 40 kDa (99%) serve as expediency criteria. In comparison with a membrane modified only with inorganic ion exchanger, selectivity is increased, the rate of filtration of protein solutions is higher, and resistance to contamination by organic substances is achieved. The results are discussed from the view of the hydrophobic-hydrophilic properties of oxidized graphene.

Purpose of the research: studying the effect of addition of carbon nanosized modifier graphene oxide on the formation of a porous film during the electrochemical oxidation of aluminum.Methods: UV-VIS spectra of graphene oxide suspension were obtained using a spectrophotometer, the thermogravimetric characteristics of anodized alumina were determined using a thermal analyzer, the surface characteristics were determined by the low-temperature nitrogen sorption-desorption method, the surface was calculated by the BET method, the morphology and ultrastructure of the surface were determined using electron microscope.Results: the possibility of using carbon materials for the electrochemical oxidation of aluminum was shown. The obtained electron micrographs indicate the effect of the inserted carbon modifier (graphene oxide) on the morphology of resulting oxide. As a result of this process we observe the formation of the cellular surface of the aluminium oxide with smaller pores compared with sample after synthesis without the modifier.It was shown that the addition of graphene oxide (0.25%) in the oxalic acid (0,3М) electrolyte effects on the stability of the anodizing process, the specific surface area of the sample of anodized aluminum synthesized with graphene oxide is determined as 35.5 m3/g, and it is three times higher than sample without modifier. According to sorption studies, it could be noted that the presence of nanosized graphene oxide in oxalic acid electrolyte leads to the formation of honey-comb pores with a smaller radius (22 nm), while the total volume of micropores increases. The obtained results allow us to conclude that graphene oxide as modifier is promising material for the preparation of anodized aluminum oxide matrices. In the future, these matrices could be used in processes of solutions and gases separation.Conclusions: The addition of graphene oxide into the electrolyte changes structure of porous anodized aluminum oxide and has shown the possibility of controlling the porosity of films.