Polydopamine Functionalized Graphene Oxide as Membrane Nanofiller: Spectral and Structural Studies

A facile strategy for the preparation of carbon nanotubes/polybutadiene crosslinked composite membrane and its application in osmotic energy harvesting

The osmotic energy between riverine water and seawater can be converted into electricity by reverse electrodialysis (RED). However, the facile fabrication of advanced RED membranes with high energy conversion efficiencies, large areas, and excellent mechanical properties remains a challenge. Carbon nanotubes (CNTs) exhibit excellent conductivity and provide suitable channels for ion transport but cannot form membranes independently, which limits the related applications in osmotic energy conversion. Herein, a new organic-inorganic composite membrane is prepared by combining hydroxyl-terminated polybutadiene as a matrix and carbon nanotubes as transport nanochannels. The nanotubes are pre-subjected to plasma treatment to increase the surface charge density and transport capacity of the nanochannels, improving the ion selectivity and energy conversion efficiency. Under actual seawater/river water conditions, the developed membrane delivers a power density of ∼5.1 W/m2 and shows good mechanical strength (219 MPa). Our work provides a facile solution to the problem posed by the inability of ideal nanochannels to form membranes independently and paves the way for the application of RED membranes in osmotic energy conversion.

Effectively Reinforced α-Bi2O3 MPs/PDA-RGO Sensor for Selective Modality Sensing of a Hazardous Phenolic Compound

The phenolic compound trichlorophenol (TCP) is an ingredient in fungicides and herbicides. This compound's high stability, bioaccumulation, toxicity, and poor biodegradability result in severe environmental and biological health issues. Consequently, it is crucial to have an affordable and sensitive method for detecting TCP in environmental samples. In this study, α-phase bismuth oxide microplates and polydopamine-functionalized reduced graphene oxide (α-Bi2O3 MPs/PDA-RGO) were synthesized using a simple ultrasonic method and characterized with various analytical and physical characterizations. The conversion of the catechol moieties present in the resulting PDA-RGO material into quinones facilitates productive interactions with diverse functional groups, such as hydroxyl, amine, and imine. Consequently, the compounds 2,4,6-trichlorophenol (TCP) engages in electrochemical interactions with the aforementioned functional groups. As a result, TCP shows more excellent selectivity on the designed α-Bi2O3 MPs/PDA-RGO/SPCE sensor. Under the optimized conditions, the sensor demonstrated a lower detection limit (0.0042 μM), a limit of quantification (0.0078 μM), good sensitivity (2.24 μA μM-1 cm2), a wide linear range (0.019-190.7 and 212.7-1649 μM), and pinpoint specificity. The efficacy of the sensor is additionally validated through the accurate identification of TCP residues in water, soil, and food samples.

A Comprehensive Review of Performance of Polyacrylonitrile-Based Membranes for Forward Osmosis Water Separation and Purification Process

Polyacrylonitrile (PAN), with its unique chemical, electrical, mechanical, and thermal properties, has become a crucial acrylic polymer for the industry. This polymer has been widely used to fabricate ultrafiltration, nanofiltration, and reverse osmosis membranes for water treatment applications. However, it recently started to be used to fabricate thin-film composite (TFC) and fiber-based forward osmosis (FO) membranes at a lab scale. Phase inversion and electrospinning methods were the most utilized techniques to fabricate PAN-based FO membranes. The PAN substrate layer could function as a good support layer to create TFC and fiber membranes with excellent performance under FO process conditions by selecting the proper modification techniques. The various modification techniques used to enhance PAN-based FO performance include interfacial polymerization, layer-by-layer assembly, simple coating, and incorporating nanofillers. Thus, the fabrication and modification techniques of PAN-based porous FO membranes have been highlighted in this work. Also, the performance of these FO membranes was investigated. Finally, perspectives and potential directions for further study on PAN-based FO membranes are presented in light of the developments in this area. This review is expected to aid the scientific community in creating novel effective porous FO polymeric membranes based on PAN polymer for various water and wastewater treatment applications.

Bio-inspired nanocomposite coatings on orthodontic archwires with corrosion resistant and antibacterial properties

The corrosion resistance and antibacterial properties of fixed orthodontic devices are insufficient in the complex oral cavity, which delays tooth movement and causes enamel demineralization. To overcome the challenges, this research constructs a series of polydopamine-graphene oxide (PDA-GO) nanocoatings on representative NiTi archwires via self-assembly. The morphology, chemical structure, and multifunctional properties of coatings showed tunability dependent on the PDA/GO ratio. Optimized PDA-GO coatings with uniform and dense characteristics prolonged the diffusion path for the corrosive medium and reduced Ni dissolution in NiTi alloys. Meanwhile, the applied coatings endowed NiTi alloys with antibacterial activity against Streptococcus mutans due to the surface structures and inherent properties of PDA-GO. In vitro cytotoxicity tests further verified their good biocompatibility. This bio-inspired nanocomposite coating provides a practical reference for modification of dental metal surfaces to better behave in the intraoral environment.

Polyethylene glycol-grafted graphene oxide nanosheets in tailoring the structure and reverse osmosis performance of thin film composite membrane

Introducing hydrophilic polymers such as polyethylene glycol (PEG) within the polyamide (PA) layer of thin film composite (TFC) membranes helps achieve high water desalination performance. Here, PEGs of different molecular weights (X: 1500, 6000, 16,000 g/mol) are effectively introduced into the PA layer of TFC membranes utilizing PEG-grafted graphene oxide (GOPX) nanosheets and their effects on the physicochemical properties and reverse osmosis (RO) performance of the thin film nanocomposite (TFN) membranes are investigated. Among the TFNs prepared the GOP16000/TFN exhibits the best performance with 68% improvement in water flux and almost constant salt rejection compared to those of the bare TFC. The influence of PEG molecular weight on the RO performance of the membranes is interpreted by different surface and bulk hydrophilicity as well as thickness and surface roughness of PA layers of GOPX/TFNs. Furthermore, TFNs with thinner and smoother PA layers and thus higher water flux are obtained by dispersing GOPXs in the aqueous phase of the PA interfacial polymerization reaction than by dispersing them in the organic phase of the reaction. Finally, the high antifouling potential of TFNs containing PEG-grafted GOs is demonstrated.

One-step uranium extraction and brine desalination via adsorptive pervaporation by graphene-oxide scaffold membranes

The ocean reserves nearly four billion tons of uranium, providing an inexhaustible supply of nuclear energy if the limits of ultralow U(VI) concentration (3.3 µg·L^-1) are addressed. Membrane technology is promising to make this happen by simultaneous U(VI) concentration and extraction. Herein, we report a pioneering adsorption-pervaporation membrane for efficient enrichment and capture of U(VI) along with clean water production. A bifunctional poly(dopamine-ethylenediamine) and graphene oxide 2D scaffold membrane was developed and further crosslinked by glutaraldehyde, capable of recovering over 70% U(VI) and water from simulated seawater brine, which validates the feasibility of one-step water recovery, brine concentration, and uranium extraction from seawater brine. Moreover, compared with other membranes and adsorbents, this membrane exhibits fast pervaporation desalination (flux: 153.3 kg·m^-2·h^-1, rejection: >99.99%) and excellent uranium capture properties of 228.6 mg·m^-2 benefiting from plentiful functional groups provided by embedded poly(dopamine-ethylenediamine). This study aims to provide a strategy for recovering critical elements from the ocean.

Immobilized short-chain dehydrogenase/reductase on Fe3O4 particles acts as a magnetically recoverable biocatalyst component in patulin bio-detoxification system

Patulin is one of the most important mycotoxins that contaminates fruit-derived products and causes acute or chronic toxicity in humans. In the present study, a novel patulin-degrading enzyme preparation was developed by taking a short-chain dehydrogenase/reductase and covalently linking it to dopamine/polyethyleneimine co-deposited magnetic Fe₃O₄ particles. Optimum immobilization provided 63% immobilization efficiency and 62% activity recovery. Moreover, the immobilization protocol substantially improved thermal and storage stabilities, proteolysis resistance, and reusability. Using reduced nicotinamide adenine dinucleotide phosphate as a cofactor, the immobilized enzyme exhibited a detoxification rate of 100% in phosphate-buffered saline and a detoxification rate of more than 80% in apple juice. The immobilized enzyme did not cause adverse effects on juice quality and could be magnetically separated quickly after detoxification to ensure convenient recycling. Moreover, it did not exhibit cytotoxicity against a human gastric mucosal epithelial cell line at a concentration of 100 mg/L. Consequently, the immobilized enzyme as a biocatalyst had the characteristics of high efficiency, stability, safety, and easy separation, establishing the first step in building a bio-detoxification system to control patulin contamination in juice and beverage products.

Enhancement of AFB1 Removal Efficiency via Adsorption/Photocatalysis Synergy Using Surface-Modified Electrospun PCL-g-C3N4/CQDs Membranes

Aflatoxin B₁ (AFB₁) is a highly toxic mycotoxin produced by aspergillus species under specific conditions as secondary metabolites. In this study, types of PCL (Polycaprolactone) membranes anchored (or not) to g-C₃N₄/CQDs composites were prepared using electrospinning technology with (or without) the following surface modification treatment to remove AFB₁. These membranes and g-C₃N₄/CQDs composites were characterized by SEM, TEM, UV-vis, XRD, XPS and FTIR to analyze their physical and chemical properties. Among them, the modified PCL-g-C₃N₄/CQDs electrospun membranes exhibited an excellent ability to degrade AFB₁ via synergistic effects of adsorption and photocatalysis, and the degradation rate of 0.5 μg/mL AFB₁ solution was observed to be up to 96.88% in 30 min under visible light irradiation. Moreover, the modified PCL-g-C₃N₄/CQDs electrospun membranes could be removed directly after the reaction process without centrifugal or magnetic separation, and the regeneration was a green approach synchronized with the reaction under visible light avoiding physical or chemical treatment. The mechanism of adsorption by electrostatic attraction and hydrogen bonding interaction was revealed and the mechanism of photodegradation of AFB₁ was also proposed based on active species trapping experiments. This study illuminated the highly synergic adsorption and photocatalytic AFB₁ removal efficiency without side effects from the modified PCL-g-C₃N₄/CQDs electrospun membranes, thereby offering a continual and green solution to AFB₁ removal in practical application.

Composite GO/Ceramic Membranes Prepared via Chemical Attachment: Characterisation and Gas Permeance Properties

Graphene oxide (GO) oligo-layered laminates were self-assembled on porous ceramic substrates via their simple dip-coating into aqueous GO dispersions. To augment the stability of the developed composite GO/ceramic membranes and control the morphology and stacking quality of the formed laminate, short-((3-glycidoxypropyl)trimethoxy silane-GLYMO, (3-aminopropyl)triethoxy silane-APTES), and long-chain (polydopamine-PDA) molecules were involved and examined as interfacial linkers. A comparative study was performed regarding the linker's capacity to enhance the interfacial adhesion between the ceramic surface and the GO deposit and affect the orientation and assemblage characteristics of the adjacent GO nanosheets that composed the formed oligo-layered laminates. Subsequently, by post-filtrating a GO/H₂O suspension through the oligo-layered laminate membranes, the respective multi-layered ones have been developed, whereas ethylenediamine (EDA) was used in the suspension as an efficient molecular linker that strongly bonds and interlocks the GO nanosheets. The definition of the best linker and approach was conducted on macroporous α-alumina disks, due to the use of inexpensive raw materials and the ability to fabricate them in the lab with high reproducibility. To validate the concept at a larger scale, while investigating the effect of the porous substrate as regards its micrometer-scale roughness and surface chemistry, specific chemical modifications that yielded membranes with the best gas permeability/selectivity performance were replicated on a commercial single-channel monolith with a ZrO₂ microfiltration layer. XRD, Raman, ATR, FESEM, and XPS analyses were conducted to study the structural, physicochemical, surface, and morphological properties of the GO/ceramic composite membranes, whereas permeance results of several gases at various temperatures and trans-membrane pressures were interpreted to shed light on the pore structural features. Concerning the short-chain linkers, the obtained results ascertain that GLYMO causes denser and more uniform assembly of GO nanosheets within the oligo-layered laminate. PDA had the same beneficial effect, as it is a macromolecule. Overall, this study shows that the development of gas-separating membranes, by just dipping the linker-modified substrate into the GO suspension, is not straightforward. The application of post-filtration contributed significantly to this target and the quality of the superficially deposited, thick GO laminate depended on this of the chemically attached oligo-layered one.

Recent Advances in Responsive Membrane Functionalization Approaches and Applications

In recent years, significant advances have been made in the field of functionalized membranes. With the functionalization using various materials, such as polymers and enzymes, membranes can exhibit property changes in response to an environmental stimulation, such as heat, light, ionic strength, or pH. The resulting responsive nature allows for an increased breadth of membrane uses, due to the developed functionalization properties, such as smart-gating filtration for size-selective water contaminant removal, self-cleaning antifouling surfaces, increased scalability options, and highly sensitive molecular detection. In this review, new advances in both fabrication and applications of functionalized membranes are reported and summarized, including temperature-responsive, pH-responsive, light-responsive, enzyme-functionalized, and two-dimensional material-functionalized membranes. Specific emphasis was given to the most recent technological improvements, current limitations, advances in characterization techniques, and future directions for the field of functionalized membranes.

pH-Sensitive Polydopamine-La (III) Complex Decorated on Carbon Nanofiber toward On-Demand Release Functioning of Epoxy Anti-Corrosion Coating

The high aspect ratio and unique thermal and electrical characteristics of carbon nanofiber (CNF) made it an ideal physical barrier against the penetration of corrosive ions. However, the poor compatibility of the CNF with the polymer matrix and the lack of active corrosion inhibitors are the key limitations of this nanomaterial, resulting in short-term anti-corrosion resistance. An intelligent self-healing epoxy (EP) coating, including CNF modified with a polydopamine (PDA)-La³⁺ complex, was successfully fabricated to overcome these issues. Electrochemical impedance spectroscopy (EIS) evaluation implied that mild steel (MS) submerged in a 3.5 wt % NaCl solution containing the CNF-PDA-La extract had a total corrosion resistance (R_T) of 3107 Ω cm² after 24 h, which is much greater than the MS immersed in the blank solution (1378 Ω cm²). Furthermore, the potentiodynamic polarization analysis indicated a 50% reduction in the corrosion rate (CR) of the MS soaked in the solution containing released PDA and La³⁺ inhibitors compared to the blank solution. EIS and salt spray analysis were used to assess the self-healing capabilities of epoxy coatings incorporating modified CNFs. EIS assessment of scratched coatings revealed a 117% improvement in R_T of the CNF-PDA-La/EP coating compared to the Blank/EP after 10 h of immersion in the saline solution. This enhancement is due to the intelligent release of PDA and La³⁺ inhibitors at the scratch sites, which can mitigate MS corrosion by forming a PDA-Fe complex and the deposition of La(OH)₃ on the MS surface. The salt spray test results also exhibited the CNF-PDA-La/EP coating's superior anti-corrosion capabilities after 20 days. Hence, this research presents a logical approach for developing anti-corrosion coatings with improved nanofiller compatibility and self-healing characteristics.

Progress for Co-Incorporation of Polydopamine and Nanoparticles for Improving Membranes Performance

Incorporating polydopamine has become a viable method for membrane modification due to its universality and versatility. Fillers in their different categories have been confirmed as effective elements to improve the properties of membranes such as hydrophilicity, permeability, mechanical strength, and fouling resistance. Thus, this paper mainly highlights the recent studies that have been carried out using polydopamine and nanomaterial fillers simultaneously in modifying the performance of different membranes such as ultrafiltration, microfiltration, nanofiltration, reverse osmosis, and forward osmosis membranes according to the various modification methods. Graphene oxide nanoparticles have recently attracted a lot of attention among different nanoparticles used with polydopamine, due to their impressive characteristics impacts on enhancing membrane hydrophilicity, mechanical strength, and fouling resistance. Thus, the incorporation techniques of graphene oxide nanoparticles and polydopamine for enhancing membranes have been highlighted in this work. Moreover, different studies carried out on using polydopamine as a nanofiller for optimizing membrane performance have been discussed. Finally, perspectives, and possible paths of further research on mussel-inspired polydopamine and nanoparticles co-incorporation are stated according to the progress made in this field. It is anticipated that this review would provide benefits for the scientific community in designing a new generation of polymeric membranes for the treatment of different feed water and wastewater based on adhesive mussel inspired polydopamine polymer and nanomaterials combinations.

Graphene oxide and mineralized collagen-functionalized dental implant abutment with effective soft tissue seal and romotely repeatable photodisinfection

Grasping the boundary of antibacterial function may be better for the sealing of soft tissue around dental implant abutment. Inspired by ‘overdone is worse than undone’, we prepared a sandwich-structured dental implant coating on the percutaneous part using graphene oxide (GO) wrapped under mineralized collagen. Our unique coating structure ensured the high photothermal conversion capability and good photothermal stability of GO. The prepared coating not only achieved suitable inhibition on colonizing bacteria growth of Streptococcus sanguinis, Fusobacterium nucleatum and Porphyromonas gingivalis but also disrupted the wall/membrane permeability of free bacteria. Further enhancements on the antibacterial property were generally observed through the additional incorporation of dimethylaminododecyl methacrylate. Additionally, the coating with sandwich structure significantly enhanced the adhesion, cytoskeleton organization and proliferation of human gingival fibroblasts, which was effective to improve soft tissue sealing. Furthermore, cell viability was preserved when cells and bacteria were cultivated in the same environment by a coculture assay. This was attributed to the sandwich structure and mineralized collagen as the outmost layer, which would protect tissue cells from photothermal therapy and GO, as well as accelerate the recovery of cell activity. Overall, the coating design would provide a useful alternative method for dental implant abutment surface modification and functionalization.

In Situ Grown Nanohydroxyapatite Hybridized Graphene Oxide: Enhancing the Strength and Bioactivity of Polymer Scaffolds

Graphene oxide (GO) and nanohydroxyapatite (nHA) are usually used for improving the strength and bioactivity of polymer scaffolds. However, due to the nano-aggregation effect, these applications often face the problems of uneven dispersion and poor interface bonding. In this work, their hybrids (GO@nHA) were constructed by combining chemical modification and in situ growth methods, realizing the perfect combination of nHA and GO. First, the functionalization of GO was realized through oxidative self-polymerization of dopamine (DA), and the product was denoted GO@DA. Furthermore, the in situ growth of nHA on GO@DA was induced by hydrothermal reactions to prepare GO@nHA hybrids. Then, the obtained hybrid was added to the polymer matrix, and a composite scaffold was prepared through a selective laser sintering process. The results demonstrated that with the addition of GO@DA and GO@nHA, the ultimate strength was increased to 16.8 and 18.6 MPa, respectively, which is 66 and 84% higher than the 10.1 MPa of the polylactic acid (PLA) scaffold. In addition, composite scaffolds exhibited good biomineralization ability in vitro and also promoted the adhesion and proliferation of MG63 cells.

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 I_2D/I_D+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.

Development of Novel Composite Membranes in Water/Wastewater Treatment

Composite membranes have attracted significant attention due to their flexibility in having more than one layer, with many materials being used to form the membrane [...]

Functional GO-based membranes for water treatment and desalination: Fabrication methods, performance and advantages. A review

Graphene oxide (GO) and GO-based materials have gained a significant interest in the membrane synthesis and functionalization sector in the recent years. Inspired by their unique and tuneable properties, several GO-based nanomaterials have been investigated and utilized as effective nanofillers for various membranes in the water treatment, purification and desalination sectors. This paper comprehensively reviews the recent advances of GO utilization in pressure, concentration and thermal-driven membrane processes. A brief overview on GO particles, properties, synthesis and functionalization methods was provided. The conventional and the state-of-art fabrication methods of GO-based membranes were summarized and discussed, and consequently the GO-based membranes were classified into different categories. The applications, types, and the performance in terms of flux and rejection were summarized and reviewed. The advantages of GO-based membranes in terms of antifouling properties, bactericidal effects, mechanical strength and stability have been reviewed, too. The review gives insights on the future perspectives of GO functional materials and their potential use in the various membrane processes discussed herein.

A Hybrid NF-FO-RO Process for the Supply of Irrigation Water from Treated Wastewater: Simulation Study

Municipal treated wastewater could be considered as a water source for food crop irrigation purposes. Enhancing the quality of treated wastewater to meet irrigation standards has become a necessary practice. Nanofiltration (NF) was used in the first stage to produce permeate at relatively low energy consumption. In the second stage, two membrane combinations were tested for additional water extraction from the brine generated by the NF process. The simulation results showed that using a hybrid forward osmosis (FO)–reverse osmosis (RO) system is more efficient than using the RO process alone for the further extraction of water from the brine generated by the NF process. The total specific energy consumption can be reduced by 27% after using FO as an intermediate process between NF and RO. In addition, the final permeate water quality produced using the hybrid FO-RO system was within the allowable standards for food crops irrigation.