Polydopamine functionalized graphene oxide as membrane nanofiller: Spectral and structural studies

High-degree functionalization of graphene oxide (GO) nanoparticles (NPs) using polydopamine (PDA) was conducted to produce polydopamine functionalized graphene oxide nanoparticles (GO-PDA NPs). Aiming to explore their potential use as nanofiller in membrane separation processes, the spectral and structural properties of GO-PDA NPs were comprehensively analyzed. GO NPs were first prepared by the oxidation of graphite via a modified Hummers method. The obtained GO NPs were then functionalized with PDA using a GO:PDA ratio of 1:2 to obtain highly aminated GO NPs. The structural change was evaluated using XRD, FTIR-UATR, Raman spectroscopy, SEM and TEM. Several bands have emerged in the FTIR spectra of GO-PDA attributed to the amine groups of PDA confirming the high functionalization degree of GO NPs. Raman spectra and XRD patterns showed different crystalline structures and defects and higher interlayer spacing of GO-PDA. The change in elemental compositions was confirmed by XPS and CHNSO elemental analysis and showed an emerging N 1s core-level in the GO-PDA survey spectra corresponding to the amine groups of PDA. GO-PDA NPs showed better dispersibility in polar and nonpolar solvents expanding their potential utilization for different purposes. Furthermore, GO and GO-PDA-coated membranes were prepared via pressure-assisted self-assembly technique (PAS) using low concentrations of NPs (1 wt. %). Contact angle measurements showed excellent hydrophilic properties of GO-PDA with an average contact angle of (27.8°).Scopu

Spectral and Structural Properties of High-Quality Reduced Graphene Oxide Produced via a Simple Approach Using Tetraethylenepentamine

A simple temperature-assisted solution interaction technique was used to functionalize and reduce graphene oxide (GO) using tetraethylenepentamine (TEPA) with less chemicals, low temperature, and without using other reducing agents. GO nanosheets, produced using a modified Hummers? method, were functionalized using two different GO:TEPA ratios (1:5 and 1:10). The reduction of GO was evaluated and confirmed by different spectroscopic and microscopic techniques. The FTIR and XPS spectra revealed that most of the oxygenated groups of GO were reduced. The emergence of amide groups in the XPS survey of the rGO-TEPA samples confirmed the successful reaction of TEPA with the carboxyl groups on the edges of GO. The replacement of the oxygenated groups increased the carbon/oxygen (C/O) ratio of GO by approximately 60%, suggesting a good reduction degree. It was found that the I2D/ID+D? ratio and the relative intensity of the D?? band clearly increased after the reduction reaction, suggesting that these bands are good estimators for the reduction degree of GO. The morphological structure of GO was also affected by the reaction with TEPA, which was confirmed by SEM and TEM images. The TEM images showed that the transparent GO sheets became denser and opaque after functionalization with TEPA, indicating an increase in the stacking level of the GO sheets. This was further confirmed by the XRD analysis, which showed a clear decrease in the d-spacing, caused by the removal of oxygenated groups during the reduction reaction.Scopu

Synthesis of High-Antifouling and Antibacterial Ultrafiltration Membranes Incorporating Low Concentrations of Graphene Oxide

Membrane treatment for wastewater treatment is one of the promising solutions to affordable clean water. It is a developing technology throughout the world and considered as the most effective and economical method available. However, the limitations of membranes’ mechanical and chemical properties restrict their industrial applications. Graphene Oxide (GO) is one of the materials that have been recently investigated in membrane water treatment sector. In this work, ultrafiltration polysulfone (PSF) membranes with high antifouling properties were synthesized by incorporating different loadings of GO. High-oxidation degree GO had been synthesized using modified Hummers’ method. The synthesized GO was characterized using different analytical techniques including (FTIR-UATR), Raman spectroscopy, and CHNSO elemental analysis that showed high oxidation degree of GO represented by the its oxygen content (50 wt.%). Morphology and hydrophilicity of membranes were investigated using SEM, AFM and contact angle analyses and showed clear effect of GO on PSF morphology and better hydrophilicity of GO-based membranes caused by the hydrophilic nature of GO and its high oxygen content. Separation properties of the prepared membranes were investigated using a cross-flow membrane system. Biofouling and organic fouling resistance of membranes were tested using bovine serum albumin (BSA) and humic acid (HA) as model foulants. It has been found that GO based membranes exhibit higher antifouling properties compared to pure PSF. When using BSA, the flux recovery ratio (FRR %) increased from 65.4 ± 0.9 % for pure PSF to 86.9 ± 0.1 % with loading of 0.1 wt.% GO in PSF. When using HA as model foulant, FRR increased from 87.8 ± 0.6 % to 95.6 ± 4.2 % with 0.1 wt.% of GO in PSF. The pure water permeability (PWP) decreased with loadings of GO from 181.7 L.m-2.h-1.bar-1 of pure PSF to 181.1 and 167.4 L.m-2.h-1.bar-1 with 0.02 and 0.1 wt.% GO respectively. Furthermore, GO based membranes exhibited effective antibacterial performance against Halomonas aquamarina compared to pristine PSF. It can be concluded from the obtained results that incorporating low loading of GO could enhance the antifouling and antibacterial properties of PSF hence improving its lifetime and reuse

Bio-Inspired Fabrication of Ultrafiltration Membranes incorporating Polydopamine Functionalized Graphene Oxide Nanoparticles

Novel PSF composite UF membranes incorporating low loadings of polydopamine-functionalized graphene oxide particles (rGO-PDA) were fabricated and investigated. The functionalization was confirmed using FTIR-UATR, Raman spectra, XPS, and SEM. Pristine PSF, PSF/GO, and PSF/rGO-PDA MMMs were then prepared using the phase inversion technique and analyzed using FTIR, SEM, AFM, and contact angle (CA). The cross-section SEM images showed better distribution of rGO-PDA particles in the pores and polymer wall whereas the pristine GO particles aggregate and partially block the pores. Thus, the pure water flux increased with the addition of rGO-PDA without affecting the rejection properties, while the flux decreased with the embedding of pristine GO particles. The highest pure water permeability (PWP) was obtained with PSF/rGO-PDA-0.1 to be approximately twice that of the pristine PSF and PSF/GO-0.1. All membranes exhibited complete rejection of BSA and HA, and showed almost similar performance against different dyes. The FRRs of the pristine PSF after three fouling cycles (FRR3) against BSA and HA were recorded to be 57.8% and 70.7% respectively. FRR3 was enhanced by around 30% with PSF/rGO-PDA composites. The MMMs prepared in this work are expected to have great potential on ultrafiltration and similar studies on other membrane processes

Synthesis of graphene oxides particle of high oxidation degree using a modified Hummers method

High-oxidation-degree graphene oxide particles were synthesized using a modified Hummers' method. Six different types of particles were synthesized by varying the operating conditions, including the temperature, the reactant ratios, and the oxidation time. The oxidation degree, represented by the oxygen content, and the atomic oxygen/carbon (O/C) ratio were determined using CHNSO elemental analysis, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy-universal attenuated total reflectance sensor (FTIR-UATR) and Raman spectroscopy. The structural morphology of graphene oxide was evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal stability of the particles was studied using thermogravimetric analysis (TGA). The SEM images showed that the prepared GO samples had different graphitic layer structures. The TEM images showed different stacking levels and transparency of GO flakes caused by the difference in oxidation level. The oxygen content and O/C ratios ranged between 34.7 and 50.0 wt% and 0.43 and 0.8, respectively. The highest oxygen content and O/C ratio were found to be 50 wt% and 0.8, respectively, for GO prepared at 95 °C with a 1-hr reaction time (GO2-a). A quantitative analysis on the FTIR-UATR spectra was performed and was in reasonable agreement with the CHNSO analysis results. The Raman spectra showed two characteristic bands (D and G) with different relative intensities, as characterized by the ID/IG ratio, suggesting that the prepared samples had different crystallite sizes and defects. The crystallite size (La) of the prepared GO particles was estimated using the Tuinstra-Koenig model and were ranging between 9 and 24 nm. The TGA results were correlated with the elemental analysis results and showed a clear dependence of the weight loss on the GO elemental compositions. GO2-a exhibited the lowest thermal stability because of a high oxygen content, whereas GO1-b exhibited the highest thermal stability.Scopu

Characterization of polysulfone/diisopropylamine 1-alkyl-3-methylimidazolium ionic liquid membranes: high pressure gas separation applications

Membrane separation is gaining great attention in many applications, especially in gas separation. Polysulfone (PSF) is the most widely studied polymeric membrane material for CO2 in its pure or modified state. Ionic liquids supported membrane technology (SILMs) are now widely applied due to their unique properties at room temperatures. In our previous study, we proved the enhanced ability of ionic liquid enhanced PSF for the separation of CO2 from gas streams. In this study, the dielectric measurements (BDS) extending up to 107 Hz for different concentrations of ionic liquid into PSF matrix, are presented. Thermogravimetric analysis measurement (TGA), differential scanning calorimeter (DSC), dynamic mechanical analysis, and the tensile properties of the membranes are studied in order to optimize the efficiency of separating CO2 from CO2/N2 mixture and CO2/CH4. TGA showed that pure PSF is a highly thermostable polymer, of which the 5% weight loss temperature is above 150 C. DSC traces show that the Tg of PSF was 149.5 C and decreases gradually for the composites. This behavior was confirmed with BDS analyses, which also revealed important information about the chain motions dynamics and the fragility index.Qatar Foundation;Qatar National Research FundScopu