Characterization and crystal violet removal of polymer inclusion membranes containing PC88A

Cationic dyes such as crystal violet pose serious environmental and biological risks in aqueous environments. These pollutants, especially those originating from industrial wastes, disrupt the natural balance of water resources, threaten life and put drinking water safety at risk. When crystal violet is dissolved in water, it disrupts the life cycle of photosynthetic organisms by reducing light transmittance; this leads to a decrease in photosynthesis, decreased oxygen production and the development of hypoxic conditions. At the same time, the long-term effects of crystal violet on human health can include toxic effects ranging from skin and eye irritation to respiratory problems and even damage to the retina. For these reasons, the effective and selective removal of such pollutants from water is of great importance in terms of sustainable water management and environmental protection. Methods such as chemical oxidation, photocatalysis, precipitation, coagulation, and ultrafiltration are among the primary methods used for dye removal. However, the water obtained from these processes still requires advanced treatment. Alternatively, solvent extraction, emulsion-type liquid membrane (ELM), supported liquid membrane (SLM), and other separation technologies have been applied for dye removal. In ELM, emulsion breakage and swelling make it difficult to optimize operating conditions. Emulsion stability is a key problem with ELMs and SLMs. Polymer inclusion membranes (PIMs), which do not have these problems and use very small amounts of expensive extractants and solvents, have increased interest in the application of PIMs due to their environmental friendliness and cost-effectiveness. The most important feature that distinguishes PIMs from other processes is the dispersion of organic carriers within the polymer structure, thereby increasing transport efficiency. Furthermore, their high selectivity, ease of application, and low energy consumption provide significant advantages in both the separation and purification of target ions. Furthermore, the reusability of membranes and their large surface area-to-volume ratio are important features that will make this process more widely used in industrial applications compared to other processes. In this study, polymeric membranes containing bis(2-ethylhexyl) phosphoric acid (PC88A) and tributyl phosphate (TBP) were developed and the the removal of crystal violet dye from aqueous solutions was investigated in detail. The use of PC88A in the literature has generally been limited to hydrometallurgical applications and solvent extraction systems. However, there is no direct study in the literature on the removal of crystal violet dye with cationic character by PC88A. TBP was preferred as a modifier that increases extraction efficiency, facilitates phase transfer and provides stability to the membrane matrix. These additives, which are generally used in hydrometallurgical processes in the literature, were evaluated together in a membrane matrix for the first time in this study and it was revealed that they can also interact selectively with organic dyes. The polymer inclusion membrane was prepared by homogeneously dispersing the support material, organic carrier, and plasticizer in the solvent. A mechanical stirrer and ultrasonic bath were used to ensure homogeneous dispersion. The membrane solution was poured into a petri dish that was cleaned and dried and placed on a flat surface. After the organic solvent evaporated and dried, it was washed with distilled water. The membrane film was removed from the petri dish. The membrane thickness was determined to be 25 μm, measured with a digital micrometer). To evaluate the performance of the membrane, crystal violet samples were measured with a UV-Vis spectrophotometer at 590 nm. The findings showed that PC88A-containing membranes provided high removal efficiency for crystal violet dye. With the increase in the amount of membrane (1cm2-3cm2), the dye retention efficiency increased from 87% to 93% in 3 hours. 93,06 % dye removal was achieved in 3 hour with 0,0610 g (2cm2) membrane. The enrichment of the membrane surface with PC88A and TBP allowed the presence of acidic functional groups on the surface and the ability of these groups to establish a strong bond with cationic pollutants through both electrostatic interactions and hydrogen bonds. As part of the characterization studies, the prepared membranes were analyzed by Differential Thermal Analysis (TG-DTA), Contact Angle Measurement, X-Ray Diffraction Spectrometry (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Field Emission Scanning Electron Microscopy (FEG-SEM). In the DTA-TGA analysis, the mass loss of the PC88A-containing membrane began around 180°C. The mass loss in 414°C was 80%. Contact angle measurements were performed by recording 10-15 measurements for a single drop, with an average duration of 10 seconds. The contact angle of the membrane was measured at approximately 78°. This value shows that the membrane surface is hydrophilic. In XRD analysis, it was determined that the membrane contained an amorphous structure. Due to the small amount of added PC88A, no crystalline structure formation was observed in XRD analysis. In FTIR analysis, the bands observed in the spectra revealed that the structures of PC88A and PVC remained intact. It was observed that physical interaction or weak intermolecular interactions were at the forefront instead of chemical bonding between the membrane components. The findings demonstrate the effectiveness of PC88A-TBP-containing membranes in environmental applications such as dye removal. Almost 100% removal of crystal violet dye was achieved with PC88A-TBP-containing membranes. FEG-SEM images following crystal violet removal revealed a change in the density and arrangement of folds on the membrane surface. The surface appears more complex and, in some cases, granular. This suggests that there is a physical interaction between the dye molecules and the membrane surface related to the adhesion of the dye to the surface. From FEG-SEM images of the membranes, the combination of PC88A's tendency to form nano-sized clusters and TBP's surface-smoothing and pore-modifying effects resulted in the formation of a more ordered and wavy nanostructure in this membrane. The presence of TBP allowed these nanostructures to integrate better and form a smoother (at the macroscale) film, in contrast to the irregular and coarse particle structure exhibited by PC88A alone. In conclusion, this study represents an innovative approach that highlights the effectiveness of polymeric membranes containing PC88A and TBP in the selective removal of organic pollutants (dyes). The high removal capacity, thermal stability and multifunctional structure of the membranes provide significant contributions to their wide application potential. Thus, it has been shown that PC88A and TBP can be used in polymer inclusion membranes outside of their traditional areas of use.