Influence of a graphene oxide additive and the conditions of membrane formation on the morphology and separative properties of poly(vinylidene fluoride) membranes

Preparation and properties of composite cellulose fibres with the addition of graphene oxide

The paper presents the results of a study on the preparation of cellulose-based composite fibres (CEL) with graphene oxide addition (GO). Composite fibres (GO/CEL) were prepared via the wet spinning method from CEL solutions in 1-ethyl-3-methylimidazolium acetate (EMIMAc) that contained a nano-addition of GO dispersion in N,N-dimethylformamide (DMF). The GO contents of the composite fibres were 0, 0.21, 0.50, 0.98, and 1.97 % w w. The fibres were coagulated in two solvents: distilled water and methanol. The results demonstrated that the amount of GO additive and the type of coagulant significantly impact the physicochemical, mechanical and structural properties of the CEL and GO/CEL fibres. The use of distilled water in a coagulation bath causes a degree of crystallinity of 31.0-40.8 % (WAXS) and a shift in the thermal decomposition temperature (by approximately 19 °C) towards higher temperatures (TGA). The results demonstrate improvements in the mechanical properties of the GO/CEL fibres, which were at the level of 9.43-14.18 cN/tex. In addition, the GO/CEL fibres exhibit satisfactory GO dispersion throughout their volume.

The Role of the Oxidation and Reduction Parameters on the Properties of the Reduced Graphene Oxide

One of the methods of obtaining reduced graphene oxide (rGO) involves the oxidation of graphite to graphene oxide, which is then exfoliated and reduced. Each of these stages has a decisive influence on the properties of the produced nanoadditive, which determines its subsequent application. The process conditions which are examined during the oxidation stage are related to: The mixing time of the reactants before oxidation, sonication of the reaction mixture, and its composition. During reduction optimization, in turn, the form of the GO sample and the method of its purification, as well as the temperature at which this process took place, are examined. At each stage, the determined structural parameters of the produced materials (GO and rGO) are related to their morphology (SEM—scanning electron microscope), oxidation state (FTIR—Fourier transform infrared spectroscopy, EDS—energy-dispersive spectrometer), structure defect (Raman spectroscopy), as well as the number of layers and crystalline structure (WAXS—wide-angle X-ray scattering). The obtained results show that the shorter mixing time of the reactants determines the formation of more oxygen functional groups. On the basis of the obtained results, the process conditions that enable the production of multilayer, well-exfoliated reduced graphene oxide, with only a slightly defected structure, are established.

Structure-Property Relationships of Pure Cellulose and GO/CEL Membranes Regenerated from Ionic Liquid Solutions

Two types of cellulose membranes were produced by a classical wet phase inversion method from a solution of the polymer in 1-ethyl-3-methylimidazolium acetate (EMIMAc) by coagulation in water and selected primary alcohols. The first type were membranes made from pure cellulose (CEL). The second type were membranes obtained by adding nanosized graphene oxide (GO) to the cellulose solution. The process of precipitation and selection of the coagulant affected the structure of the membranes, which in turn affected their usability and applicability. The results of the presented studies show that the physicochemical properties of the coagulant used (e.g., molecular mass and dipole moment) play important roles in this process. It was found that both the content and dimensions of the pores depended on the molecular mass of the coagulant used. It was also found that the dipole moment of coagulant molecules had a large influence on the volume content of the pores (e.g., the 1-octanol (Oc) membrane had a dipole moment of 1.71 D; Φ = 1.82%). We investigated the effect of the type of coagulant on the porous structure of CEL membranes and how this affected the transport properties of the membranes (e.g., for the distilled water (W) membrane, J_v = 5.24 ± 0.39 L/m² h; for the Oc membrane, J_v = 92.19 ± 1.51 L/m² h). The paper presents the results of adding GO nanoparticles in terms of the structure, morphology, and transport properties of GO/CEL membranes (e.g., for composite membrane F (containing 20% GO), J_v = 40.20 ± 2.33 L/m² h). In particular, it describes their extremely high ability to remove heavy metal ions.

Preparation and Properties of Composite PAN/PANI Membranes

The methods of modifying PAN membranes have been known and used for many years. An interesting solution seems to be to give the sensory properties to this type of membranes. This paper presents the results of research on the method of obtaining PAN/PANI membranes using phase inversion method from a solution in DMF, following two methods: (1) dissolving both polymers (PAN and PANI) and then coagulating in water or in an aqueous solution of CSA and (2) forming the membranes from polyacrylonitrile solution and coagulation in water, followed by coating of CSA with a solution of TFE. The membranes obtained as a result of the experiment were tested for physical and chemical properties, transport properties, surface morphology, degree of dispersion of composite components, and sensitivity to the presence of dilute acids and bases. FTIR microspectroscopy and scanning electron microscopy were used to study the surface morphology. The sensory properties of membranes that are inherently colored were determined visually and by UV-Vis spectrophotometry. Furthermore, when choosing the method of membrane forming, we can obtain membranes with good physical and chemical and transport properties or ones characterized by high sensitivity to the pH of the solution.