Highly Efficient Removal of Methylene Blue Dye from An Aqueous Solution Using Polyvinylidene Fluoride (PVDF) Membranes Modified by Graphene Oxide Nano particles/Polyvinyl Alcohol (GONs/PVA)
MohamedDawam1
MahmoudY.Zorainy1
HusseinOraby1
MohamedGobara1✉Emailm.gobara@mtc.edu.eg
1Department of Chemical EngineeringMilitary Technical CollegeCairoEgypt
Mohamed Dawam1, Mahmoud Y. Zorainy1, Hussein Oraby1, Mohamed Gobara1*
1 Department of Chemical Engineering, Military Technical College, Cairo, Egypt.
*Corresponding author: Mohamed Gobara, email: m.gobara@mtc.edu.eg
A
Funding
Declaration is STDF
Data is provided within the manuscript files
Abstract
This research fabricated polyvinylidene fluoride (PVDF) membranes through application of graphene oxide nanoparticles (GONPs)/polyvinyl alcohol (PVA) coating using dip-coating technique followed by glutaraldehyde-mediated cross-linking. Glutaraldehyde (GA) served as cross-linking reagent, enhancing membrane coating's thermal alongside chemical durability. GONPs integration within the coating increased membrane hydrophilicity plus dye separation capabilities throughout filtration processes. Membrane contact angles reduced from 85° down to 55°. GO nanoparticle layers deposited onto PVDF membranes reduced fouling phenomena relative to unmodified PVDF surfaces. PVDF/GONPs (0.5wt%) membrane fouling resistance exhibited superior flux recovery values (84.2%) versus unmodified PVDF (39.3%). Modified membrane effectiveness treating cationic dye-methylene blue (MB) pollutant underwent systematic assessment through varying GONPs concentrations. Findings revealed MB+ dye elimination rates rose from 45.3% using uncoated PVDF membranes reaching 91.8% employing GONPs-coated PVDF membranes. MB+ dye elimination rapidly escalated within initial 60-minute exposure period because GO-nanoparticles possess excellent electrical properties, functional surface groups, plus considerable surface area during initial processing stages. This investigation offers an effective approach toward improving polymeric membranes, providing a practical plus expandable method addressing cationic MB elimination within wastewater remediation systems.
Keywords:
Dyes removal
GONPs
PVDF
PVA
membrane
dip-coating
surface modification
1. Introduction
Accelerated urban expansion and industrial growth have exacerbated water shortage issues and compromised the quality of freshwater resources. Manufacturing discharge frequently contains persistent organic compounds (POCs), which represent synthetic substances that resist chemical and biological breakdown processes. These materials have a tendency to bioaccumulate within environmental systems and living entities, creating significant risks to human welfare and ecological networks, particularly at minimal concentrations during prolonged exposure periods [1].
Within this category of contaminants, artificial textile colorants are becoming increasingly problematic, especially originating from the textile sector, which ranks among the highest water-utilizing industries. Throughout dyeing and treatment operations, considerable quantities of contaminated water are produced, with substantial amounts of colorants being released through industrial discharge [2, 3]. These waste streams exhibit high complexity, incorporating colorants, cleaning agents, mineral salts, surface-active compounds, dispersing agents, petroleum products, hazardous chemicals, and numerous inhibitory substances [4]. Such pollutants, particularly artificial colorants, are recognized for causing mutagenic and fatal impacts on marine ecosystems and human wellness [5].
Methylene blue (MB), among the most frequently utilized positively-charged colorants in textile manufacturing, demonstrates considerable toxicity. Contact with this substance may result in numerous health complications, including breathing difficulties, queasiness, emesis, loose stools, stomach inflammation, abdominal and thoracic discomfort, intense headaches, profuse perspiration, cognitive disorientation, and irritating sensations upon inhalation or consumption [6].
Consequently, the urgent challenge lies in finding sustainable and cost-effective strategies to treat and remediate textile wastewater. Conventional treatment technologies are often ineffective in achieving complete dye degradation due to the high stability and resistance of these compounds [7].
Among various treatment options, membrane filtration has gained significant attention owing to its high separation efficiency, simple operation, and scalability. Membrane technology has become integral in wastewater treatment, supported by advances in materials science. Polymeric membranes, particularly those made from cellulose, polyamide, and polyvinylidene fluoride (PVDF), are widely used because of their porosity, mechanical strength, and cost-effectiveness [8, 9].
PVDF membranes are especially promising due to their excellent durability and permeability [11]. However, they face challenges such as fouling, limited water permeability, and reduced separation efficiency, which restrict their long-term use in textile wastewater treatment [10]. To address these drawbacks, incorporating nanomaterials into membranes has emerged as an innovative approach to enhance their performance.
Surface modification using nanoparticles such as carbon nanotubes, graphene oxide (GO), and other nanomaterials has shown great potential in improving membrane hydrophilicity, adsorption capacity, and mechanical strength [12, 13]. GO, in particular, has attracted remarkable attention because of its large surface area, layered structure, and abundance of oxygen-containing functional groups that facilitate strong interactions with heavy metal ions and organic dyes [14–16].
Several studies have demonstrated the effectiveness of GO-based modifications. For instance, Zhang et al. reported that cross-linking GO with isophorone diisocyanate and coating it on PVDF ultrafiltration membranes enhanced dye removal efficiency to over 96% and improved heavy metal ion rejection by up to 70% compared with unmodified membranes [17]. Similarly, Chang et al. showed that combining GO with polyvinylpyrrolidone (PVP) significantly improved hydrophilicity, antifouling properties, and rejection efficiency through hydrogen bond interactions [18]. Furthermore, cross-linking GO nanoparticles with polymers such as polyvinyl alcohol (PVA) has proven effective in reducing fouling and enhancing the mechanical, electrical, and thermal properties of nanocomposite membranes [19].
Overall, these studies highlight that integrating GO into polymeric membranes improves properties such as adsorption capacity, conductivity, hydrophilicity, and dye rejection efficiency.
The objective of this current investigation is to improve the colorant removal efficiency of thin-film composite (TFC) membranes through the integration of GO nanomaterials within a PVA matrix. This research emphasizes the optimization of GO concentration and examines its effects on surface chemical properties, structural characteristics, and water affinity. Additionally, the effectiveness of the GO/PVA-enhanced membranes for colorant separation was assessed utilizing cross-flow filtration systems, with specific focus on variables including pH levels, GO proportion, and surface charge potential to gain deeper insights into the fundamental filtration processes.
2. Materials and Methods
2.1 Materials
Every chemical employed within this research possessed analytical grade requiring no additional purification steps. Graphite powder, sodium nitrate NaNO3 (purity > 98%), potassium permanganate KMnO4 (purity > 99%), flat-sheet PVDF membrane material (0.1µm) plus polyvinyl alcohol PVA (purity > 99%), originated from Sigma Aldrich (USA). Glutaraldehyde solution (25% aqueous), came from Japan. Hydrochloric acid (HCl), sodium hydroxide (NaOH), alongside sulfuric acid (H2SO4) were purchased through Sigma Aldrich (France). MB served during separation procedures, whereas bovine serum albumin (BSA) helped prepare feed solutions when investigating membrane fouling characteristics, with these substances obtained via Sigma–Aldrich (NSW, Australia). Hydrogen peroxide (H2O2) was procured through Sigma–Aldrich (Australia).
2.2
Methods
2.3
Preparation of graphene oxide Nanoparticles.
Using an adapted version of Hummer's technique, GONPs were synthesized using graphite powder [20]. Into a flask holding 23mL concentrated H2SO4 solution, 1g graphite powder plus 0.5g NaNO3 were added, with this mixture then stirred within an ice bath. Next, 3g KMnO4 was added slowly during 2hrs.
This mixture was subsequently placed within a water bath maintained at 35°C then stirred another 30 min. Afterward, once temperature reached 98°C, 46mL DI water was gradually added, continuing reaction over 12hrs. Following cooling until room temperature, 140mL DI water was added under stirring, followed by 3ml H2O2 (30%) addition for neutralizing residual KMnO4. The color then changed between brown and bright yellow, confirming effective GONPs formation.
This mixture underwent centrifugal separation operating at 7000 rpm lasting 20 min. Collected precipitate underwent washing using 100ml ethanol before separation via nylon membrane filtration. Obtained GONPs product was then dried within vacuum oven maintained at 40°C over 24hrs. A diagrammatic illustration depicting GONPs synthesis appears within Fig. (1).
Figure (1).Schematic diagram for the synthesis of GONPs.
2.4 Surface Modification of PVDF Membranes Using GONPs/PVA Solution.
Selected membrane segments possessing 0.0042 m2 cross-sectional area underwent ethanol cleaning for removing dust particles plus impurities, then dried under ambient conditions. First, homogeneous PVA solution containing GONPs was prepared enabling thin-film deposition over PVDF membrane. PVA polymer at (3wt%) concentration dissolved within DI maintained at 100°C during 5h, then GONPs (0.1, 0.3, and 0.5wt.%) were mixed into this solution. Before coating, this solution cooled until reaching ambient temperature per Fig. (2).
Flat-sheet PVDF membrane was then dipped within PVA/GO solution lasting 10 min. Excessive solution got eliminated through membrane suspension followed by complete drying under ambient conditions. Fully dried coated layers were then immersed within cross-linking mixture having 2wt.% glutaraldehyde (GA) plus 0.5wt.% H2SO4 during 5 min under ambient conditions plus 2 min maintained at 45°C, thereby reducing membrane swelling. Here, H2SO4 acted within GA solution serving as cross-linking reaction catalyst. This entire process (coating plus cross-linking) underwent duplicate repetition per membrane, ensuring improved nanoparticle stability plus performance. Lastly, membranes underwent drying maintained at 45°C lasting 5 min, then washing using Milli-Q water, removing residual cross-linking GA plus dust contamination [21]. Figure (3) illustrates schematic representation showing PVDF membrane cross-linking PVA/GO using GA.
Figure (2).Schematic diagram for preparation of GONPs/PVA coating solution.
Figure (3).Schematic diagram of cross linking PVA/ GONPs with GA on PVDF membrane.
2.5 Graphene oxide Nano particles (GONPs) Characterization.
GONPs formation underwent initial examination using XRD employing 4deg./min scanning speed, covering diffraction angles between 5–60°. Structural properties received additional analysis through FTIR, with spectra recorded across 4000 − 400 cm⁻¹ wavenumber range utilizing 4 cm⁻¹ resolution plus minimum 32 scans/sample. Raman spectroscopy additionally supplied crucial data regarding GONPs structural characteristics. Graphite plus GONPs surface morphology underwent investigation via field emission scanning electron microscopy
2.6 Membrane Characterization.
2.6.1 Surface Features of the PVDF Membrane.
Scanning electron microscopy (SEM) helped investigate surface architecture for both pristine plus modified TFC PVDF membrane. These membranes underwent cleaning plus dehydration, then sectioning into smaller pieces before gold particle sputter-coating, improving electrical conductivity. Imaging occurred using various magnifications applying high voltage, thereby detecting GO nanoparticle presence plus distribution throughout membrane surfaces.
2.6.2 Surface Polarity Measurements.
Contact angle measurement represents an effective characterization method when investigating surface wettability. Generally, solid surfaces become classified as hydrophilic if water contact angles remain under 90° while hydrophobic above 90°. Using sessile drop methodology under ambient conditions, contact angles for pristine plus modified TFC PVDF membrane containing varying GONPs concentrations within thin-film coatings were determined. After droplet contacted dried membrane surfaces, images were taken, with water contact angles then measured. Reported contact angles represent averages from five successive measurements across identical membranes taken from various positions.
2.6.3 The Membrane's Surface Charge.
Streaming potential analyzer (Malvern surface zeta potential) helped evaluate membrane surface Zeta potential. Membrane pieces (1×1 mm²) were placed within milli-Q water adjusted to desired pH, determining membrane surface charge. Reported values represent averages from three experiments using three different membrane samples across pH ranges between 3–10.
2.6.4 Filtration Performance.
Cross-flow filtration equipment helped evaluate filtration efficiency for pristine plus modified PVDF membranes per schematic illustration Fig. (4). Every filtration test utilized cross-flow filtering equipment testing membranes containing various GONPs concentrations. Using 3.0bar operating pressure, flow rate remained at 18 l/hrs. Membranes possessing 42.0 cm² active filtration area were installed within cross-flow filtration units. DI water helped measure pure water flux (J) through Eq. (1)
1
Where A is the active membrane surface area employed for filtering and V is the total volume of permeate collected within time (t).
MB helped prepare model dye mixtures having 50 mg/L concentration. Feed solution circulated within equipment during minimum 20 min prior to reject collection enabling analysis. Every filtration test occurred under ambient conditions. Feed plus permeate samples underwent collection periodically, with MB concentration changes measured via UV-V spectrometer (Shimadzu UV 2700, Kyoto, Japan). Maximum MB absorbance wavelength identification enabled calibration curve generation plus MB concentration determination within collected samples. Removal efficiency R(%) per experiment underwent calculation through Eq. (2).
R
(2)
Where CF represents the feed concentration and CP represents the permeate concentration.
Figure (4).Schematic illustration of the cross-flow filters system.
2.6.5 Analysis of Membrane Fouling.
Fouling effects upon pristine plus TFC PVDF membranes underwent evaluation through these steps: First, cross-flow filtration using pure water operated during 30 min employing chosen membranes. Next came filtration involving 1 g/L BSA solution lasting additional 60 min. Throughout this period, feed BSA solution underwent recirculation. Then, cross-flow filtration utilizing pure water continued running another 30 min. Pure water plus BSA solution permeates underwent continuous collection for determining flux changes throughout this period. Membrane resistance calculation utilized pure water flux measured preceding plus following BSA solution filtration. For examining membrane fouling characteristics, flux recovery rate (FRR) became established then evaluated through:
FRR
(3)
WhereJ0 and J1 are the pure water flux values before and after the filtration of BSA solution.
3. Results and Discussions
3.1 Graphene oxide (GO) Characterization
3.1.1 X-Ray Diffraction
XRD analysis helped confirm effective synthesis of GONPs using natural graphite. Figure (5) shows diffraction patterns for graphite plus GONPs. Within graphite samples, a strong peak appeared near 2θ = 26.5°, matching the (002) plane reflection, representing typical crystalline graphite architecture [22, 23]. Conversely, GONPs displayed peaks near 2θ = 9.2°, matching the (001) plane reflection. This observed shift demonstrates interlayer spacing increased between 0.336 nm within graphite reaching 0.96 nm within GO. Such spacing enhancement results from oxygen-containing functional group introduction throughout graphite oxidation. Typically, GO interlayer spacing falls within 0.7–0.8 nm, though differences occur based upon oxidation degree plus functionalization extent [24, 25]. These observed XRD pattern modifications confirm effective graphite conversion toward graphene oxide nanoparticles through this employed synthesis approach.
Figure (5).XRD of graphite (blue line) and graphene oxide Nanoparticles (red line).
3.2 Fourier-Transform Infrared Spectroscopy
For examining chemical changes resulting through graphite oxidation, FTIR spectroscopy was utilized. Figure (6) displays FTIR spectra for graphite plus GONPs. Missing significant peaks within graphite spectrum validates bulk graphite's chemical inactivity [26]. Conversely, GONPs FTIR spectrum showed multiple absorption bands matching oxygen-containing functional groups. One broad, strong peak near 3428 cm⁻¹ matches –OH stretching vibrations, validating hydroxyl and/or carboxyl group existence. Minor absorption peaks near 2855 plus 2920 cm⁻¹ correspond with C–H symmetric plus asymmetric stretching vibrations, correspondingly. One distinct peak near 1732 cm⁻¹ matches C = O stretching within carbonyl groups, whereas peaks near 1632 cm⁻¹ relate with C = C stretching within remaining unoxidized graphitic regions. Other peaks near 1410 cm⁻¹ (–OH deformation), 1225 cm⁻¹ (C–O stretching within epoxy groups), plus 1050 cm⁻¹ (C–O stretching within alkoxy groups) additionally validated oxygenated functionality existence [27]. Such findings definitively indicate hydroxyl, epoxy, carboxyl, plus carbonyl group integration within GO architecture.
Figure (6).FTIR of graphite (blue line) and graphene oxide Nanoparticles (red line).
3.3 Raman Spectroscopy
Raman spectroscopy helped additionally examine structural plus electronic modifications within GONPs. This method delivers data regarding defect density (D band) plus in-plane vibrational modes (G band), essential when assessing carbon-based material quality. Figure (7) shows Raman spectra for graphite plus GO. Graphite samples exhibited minor D band near 1350 cm⁻¹, indicating structural defects, plus prominent G band near 1590 cm⁻¹, matching graphitic sp² regions [29]. Following oxidation, GO spectrum showed expanded peaks, where D band moved toward 1362 cm⁻¹ while G band reached 1605 cm⁻¹. Such G band movement results from elevated resonance frequencies within isolated double bonds throughout exfoliated GO sheets [30]. Intensity ratio (ID/IG) rose between 0.27 within graphite toward 0.97 within GO, demonstrating increased disorder plus oxygen functionality integration, validating effective graphene oxide synthesis.
Figure (7).Raman spectra of (a) graphite powder and (b) GONPs.
3.4 Scanning Electron Microscopy
SEM imaging offered understanding regarding surface morphology for graphite plus GO. Per Fig. (8a), graphite displayed dense layered architecture. Alternatively, Fig. (8b) showed GONPs comprising wrinkled plus crumpled sheets, irregularly aggregated while firmly interconnected via π–π stacking interactions [31, 32]. Such morphological variations additionally validate graphite oxidation toward GO nanoparticles.
Figure (8).SEM image of (a) graphite powder (b) graphene oxide nanoparticles (GONPs).
3.5
Characterization of the plain and TFC PVDF membranes.
3.6
The surface morphology of the plain and TFC PVDF membranes at different GONPs loading.
A
SEM analysis helped examine modified plus unmodified PVDF membranes' surface morphology. Unmodified PVDF membrane surfaces display several visible macrospores, while modified membranes exhibited GONPs/PVA layers above substrates, per Fig. 9(a). Using lower concentrations (namely 0.1wt% GONPs), GO nanoparticle distribution appeared irregular; yet, when GONPs loading rose, distribution turned uniform throughout membrane surfaces, though certain particles clustered across surfaces, visible within SEM images Fig. (10). Once GONPs loading reached 0.5 wt.%, nanoparticles possibly entered membrane pores, decreasing membrane porosity. GONPs/PVA membranes grew thicker from nanoparticle aggregation, elevating MB+ dye rejection while reducing permeate flux.Similarly, surface topography represents among the best approaches for characterizing surface morphology, roughness, plus nanoparticle adhesive characteristics upon PVDF membranes, including modified plus unmodified versions. AFM images showing GONPs/PVA-coated plus unmodified membranes appear within Fig. (9 a-d). Average roughness (Ra) across multiple membranes clearly shows modified membrane surface roughness rose from GONPs concentration. Brightest areas within individual AFM images indicate peaks, whereas darkest areas indicate valleys, revealing membrane surfaces' peak-valley-like structures. GO nanoparticle attachment onto TFC membrane surfaces becomes confirmed through rising surface roughness accompanying elevated GONPs concentration. AFM analysis demonstrated that raising graphene oxide amounts upon PVDF membrane surfaces produces increased surface roughness, enabling effective MB+ elimination within contaminated water.
Figure (9).SEM images of the PVDF membranes at different GONPs loading(a) = 0; (b) = 0.1; (c) = 0.3; and (d) = 0.5wt % GONPs and AFM images of the corresponding membrane(A) = 0; (B) = 0.1; (C) = 0.3; and (D) = 0.5wt. % GONPs.
3.6.1 The Contact Angle of the Membrane.
Polyvinylidene fluoride membranes became extensively utilized within wastewater treatment owing to their suitable chemical plus thermal alongside mechanical characteristics. Such characteristics enable PVDF membrane application within water filtration procedures. Nevertheless, a primary limitation for these membranes remains their hydrophobicity, affecting fouling characteristics plus cleaning procedures.
Contact angle measurement represents an appropriate method for investigating plus assessing water/PVDF interface characteristics namely hydrophobicity. Water droplets spread across PVDF surfaces creating contact angles changing based upon water/surface interactions. Water drop geometry plus interfacial contact undergo visual observation, determining angles formed by drop boundary tangents plus drop baselines.
Membrane wettability constitutes an essential factor during membrane water permeability assessment. Generally, hydrophilicity degree elevation enhances water permeability [33]. Modified PVDF membranes' plus unmodified membranes' contact angles appear within Fig. (10). PVDF membrane contact angles reduced when GONPs loading rose [34]. Unmodified membranes exhibited 85° contact angles, decreasing alongside rising GO% until achieving 55° using 0.5 wt.% GONPs. Such hydrophilicity enhancement relates with GONPs plus PVA presence. These materials possess numerous hydrophilic groups including hydroxyl groups developing upon membrane surfaces. Additionally, previous FTIR findings show GONPs incorporate carboxylic groups, further enhancing hydrophilicity. Therefore, PVDF surface modification using PVA/GONPs improved water-membrane surface contact.
Figure (10).Impact of GONPs concentration on the water's contact angle with the PVDF membranes.
3.7 Surface Charge of the Membrane
Surface charge significantly impacts charged ion removal efficiency. Surface charge underwent evaluation through zeta potential measurements, shown within Fig. (11). Zeta potential (ζ) varied alongside solution pH changes, indicating membrane functional group protonation plus deprotonation. Ion suspension stability becomes considerably influenced through positive plus negative values. Ion segregation explains this phenomenon, occurring when identically charged ions experience mutual repulsion [35]. Within acidic environments, GONPs display negative zeta potential increasing alongside pH. PVDF membranes coated using GONPs/PVA maintain negative charges across pH ranges [36]. Such negative charging improves modified PVDF membrane effectiveness during cationic dye-MB removal via electrostatic interaction linking negatively charged GONPs surfaces with positively charged MB.
Figure (11). Surface charge of the plain and modified PVDF membranes at GONPs (0.5wt %).
3.8 Performance and Removal Efficacy of the Membrane.
3.8.1 Effect of solution pH on the removal of MB+.
Because GONPs incorporate significant oxygen group quantities including carboxylic acid (COOH), ketone (C = O), hydroxide (OH) plus epoxy (CO), pH strongly affects their charge, thus impacting adsorption capacity via electrostatic interaction. GONPs' superior adsorption capacity stems from COO– groups' negative charge plus π–π interaction involving adsorbent molecules' aromatic groups. Given this charge plus adsorption variations, solution pH considerably affects membrane removal efficiency. Figure (12) shows MB+ solution removal efficiency using PVDF/GONPs (0.5wt%) membrane across different pH values (between 2–9), adjusted through NaOH plus HCl. Evidently, MB+ adsorption decreased within acidic plus basic environments, achieving maximum under neutral pH. Acidic solution removal efficiency dropped substantially, potentially explained through proton occupation within membrane active sites, causing GONPs charge modification plus altered adsorption characteristics. MB+ represents cationic dye containing amine groups. Thus, within dye solutions having lower pH values, hydrogen ions competing against MB+ regarding exchangeable cations upon membrane surfaces caused significant removal efficiency reduction. Within quasi-neutral pH values, complex formation linking GONs basic groups plus cationic dye molecules via electrostatic attraction would enhance GONPs adsorption, consequently improving removal efficiency. Additional pH elevation toward strongly basic values would repeatedly reduce MB+ adsorption upon GONPs through competition against elevated counter cation concentrations within solutions, producing decreased removal efficiency. Therefore, findings demonstrate optimal pH regarding MB+ removal within contaminated water through modified PVDF membrane occurred near pH = 7, displaying maximum removal efficiency, validating pH adjustment importance for achieving ideal membrane performance during water treatment applications.
Figure (12).Effect of pH on the removal of MB+ on PVDF/GONPs (0.5wt %) membrane.
3.8.2 Water flux of the plain and TFC PVDF membranes.
Pure water flux variation across membranes coated using GONPs (0.1, 0.3, plus 0.5 wt%) nanoparticles underwent evaluation under 3 bar, maintaining 18 l/h flow rate using membranes possessing 42.0 cm2 active filtration area plus 50 mg/L MB concentration during 60 min experimental period at pH 7, shown within Fig. (13). GONPs integration upon membrane surfaces causes surface pore obstruction, producing permeate flux reduction [37]. Previous SEM morphology analysis similarly indicates rising GONPs loading improves dispersions while forming GONPs/PVA membranes above PVDF membrane surfaces, causing pore size reduction. Progressive pure water flux reduction occurred when GONPs loading rose within membranes. Every membrane's pure water flux remains relatively greater versus permeate flux achieved using MB solutions. Therefore, findings demonstrate considerable permeability flux reduction within MB solutions relative to pure water flux effects across membranes results from contamination effects from dye molecules plus their accumulation upon membrane surfaces plus within pores, producing transport efficiency reduction plus hydraulic resistance elevation (fouling).
Figure (13). Average flux of the plain and modified PVDF membranes at different GONPs loading.
3.8.3 Removals of MB+ dye by TFC PVDF membranes.
MB+ dye removal using membranes coated containing different GONs concentrations (0.1, 0.3, plus 0.5 wt.%) underwent investigation under 3 bars operating pressure. MB+ dye concentration equaled 50 mg/L, with filtration continuing for 60 min. Figure (14) shows modified membranes containing GONPs/PVA enhanced MB+ dye rejection versus plain PVDF membranes. MB+ dye removal efficiency rose between 45.3% using unmodified PVDF membranes toward 91.8% using modified PVDF membranes. MB+ dye removal happened quickly throughout initial 60 min contact owing to graphene oxide nanoparticles' excellent conductivity, surface functionality, plus considerable surface area during initial processing. Findings indicate modified PVDF/GONPs membranes demonstrate superior efficiency eliminating MB+ dye within polluted water, versus unmodified PVDF membranes, validating GONPs incorporation effectiveness for enhancing membrane characteristics during polluted water treatment applications.
Figure (14). Removals of MB+ dye on modified and unmodified PVDF membranes at pH 7.
3.8.4 Fouling Study of PVA/GONPs TFC PVDF Membrane.
For assessing membrane antifouling properties, dynamic filtration tests occurred with results displayed within Fig. (15). Filtration tests included three stages. First stage contained thirty minutes pure water flow. Second stage involved 60 minutes BSA solution ultrafiltration, whereas third stage determined pure water flux across cleaned membranes washed through distilled water during extra thirty minutes. Throughout first stage, unmodified PVDF membrane initial flux exceeded others, though started declining during BSA solution filtration. Alternatively, GONPs-coated membranes showed similar flux before plus during BSA rejection. Results demonstrate GONPs/PVA-coated membrane antifouling properties became considerably improved versus unmodified PVDF membranes. Furthermore, raising GONPs concentration enhanced membrane fouling resistance properties. Polymer surfaces display increased reactivity with protein molecules versus GONPs molecules; therefore, incorporating GONPs within PVDF membranes prevents protein adsorption upon membrane surfaces [38]. GONPs nanoparticle addition enables protein molecule removal within composite membranes compared against unmodified PVDF membranes. Through measured flux, FRR underwent calculation via Eq. (3).
Higher FRR values indicate improved membrane antifouling properties. PVDF/GONPs (0.5wt%) membrane pure water flux recovery achieved 84.2% after BSA filtration, though unmodified PVDF membranes reached pure water flux recovery near 39.3%.
Figure (15). Antifouling properties of membranes, Flux versus time for membranes during three steps: water flux for 30 min, BSA solution flux for 60 min, and water flux for 30 min after 20 min washing with distilled water.
3.8.5 Mechanism of methylene blue (MB+) sorption onto PVDF/GONPs-membrane.
For the adsorption of organic dyes, electrostatic attraction, pore-filling, π–π electron-donor acceptor interaction, hydrogen (H)-bonding, hydrophobic interactions, partition uncarbonized fraction, and spectrometer exchange represent several suggested mechanisms [39]. MB+ dye may interact with GO through three potential pathways: i) electrostatic attraction, ii) π–π interaction, and iii) H-bonding [40]. Research indicates that the presence of oxygen-containing functional groups generates a negatively charged surface on GO that enables the electrostatic interaction of GONPs with positively charged MB molecules [41]. Figure (16). illustrates the proposed mechanism for MB+ dye adsorption onto GONPs. Electrostatic interaction involving the positively charged –NH2 of MB and the negatively charged oxygen-containing surface groups (-COOH, –CHO, –OH, -O-, = C–, – O, –COOR of GONPs) could serve as the primary adsorption mechanism [41]. Delocalized π electrons within the conjugated aromatic rings of GO can readily interact with the π electrons found in the C–C double bond of MB+ dye through π-π interaction [42]. H-bonding involving O or N containing groups of GONPs and H containing groups of MB+ dye molecules and conversely might participate in the adsorption process [43].
Figure (16).schematic illustration of the adsorption mechanism for MB on GONPs surface.
4. CONCLUSION
This research effectively produced GONPs through a modified Hummer's technique and integrated them into PVDF membranes using dip-coating. Analytical methods such as XRD, FTIR, Raman spectroscopy, and SEM verified the successful synthesis of GO and its incorporation into the membranes. PVA and glutaraldehyde functioned as stabilizing agents and crosslinkers, improving the chemical and mechanical stability of the modified membranes. The addition of GONPs markedly enhanced membrane hydrophilicity, minimized fouling, and improved pollutant rejection. The contact angle declined from 85° to 55°, validating enhanced wettability. Dye elimination efficiency rose substantially, with modified membranes reaching up to 91.8% MB⁺ removal versus 45.3% in unmodified PVDF. Despite pure water flux decreasing marginally because of pore obstruction, the comprehensive performance enhancements significantly exceeded this drawback. Antifouling investigations showed greater flux recovery and diminished protein adsorption in modified membranes. These observations emphasize the promise of GONPs-embedded PVDF membranes as an extremely effective and sustainable method for eliminating cationic dyes including MB+ from wastewater. The findings offer both practical approaches for water treatment and advance the progress of next-generation nanocomposite membranes for environmental uses.
A
Data Availability
Data is provided within the manuscript files
A
Acknowledgement
Thank you
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Author Contribution
MD : Conceptualization, methodology, experimental work and supervision.MZ: Data curation and formal analysis.HM: Writing—original draft, visualization, and editing.MG: Supervision, Writing – Review and Editing.
1- Mohamed Dawam < m.dawam1989@yahoo.com>.............. Main manuscript text and prepared figures
2- Mahmoud Y. Zorainy < mah.y.zorainy@gmail.com>.................. Reviewed the manuscript
3- Hussein Oraby < hussein.mohamed4544@yahoo.com>................. Reviewed the manuscript
4- Mohamed Gobara < m.gobara@mtc.edu.eg>.................... Reviewed the manuscript