Guanidyl-functionalized graphene/polysulfone mixed matrix ultrafiltration membrane with superior permselective, antifouling and antibacterial properties for water treatment

Enhanced hydrophilicity and antibacterial efficacy of in-situ silver nanoparticles decorated Ti3C2Tx/Polylactic acid composite membrane for real hospital wastewater purification

This study investigates the integration of Ti3C2Tx (MX) and Ag/Ti3C2Tx (Ag/MX) nanocomposites into polylactic acid membranes to enhance hydrophilicity and impart antibacterial properties, targeting hospital wastewater treatment. MX and silver nanoparticles are known for their hydrophilicity and antimicrobial capabilities, were synthesized and incorporated into PLA; a green polymer. The impact of nanocomposite concentration on the membrane's chemical structure, morphology, and overall performance were characterized using various PLA membrane properties and to evaluate the nanocomposite's performance in enhancing pure water flux and antibacterial efficacy. The pure water permeability increased from 1512 L m-2 h-1 bar-1 to 3108 L m-2 h-1 bar-1 in PLA/AgMX4 compared to PLA. Furthermore, a total bacteria count (TBC) rejection of up to 97 % was obtained using the PLA/AgMX4 membrane. The results demonstrated significant improvements in PLA/AgMX membranes compared to pristine PLA, showing a large potential for hospital wastewater treatment.

Improving acid mine drainage treatment by combining treatment technologies: A review

The mining and processing of some minerals and coal result in the production of acid mine drainage (AMD) which contains elevated levels of sulfate and metals, which tend to pose serious environmental issues. There are different technologies that have been developed for the treatment of wastewater or AMD. However, there is no "one-size-fits-all" solution, hence a combination of available technologies should be considered to achieve effective treatment. In this review, AMD treatment technologies and the possible alignment in tandem of the different treatment technologies were discussed. The alignment was based on the target species of each technology and AMD composition. The choice of the technologies to combine depends on the quality of AMD and the desired quality of effluent depending on end use (e.g., drinking, industrial, irrigation or release into the environment). AMD treatment technologies targeting metals can be combined with membrane and/or ettringite precipitation technologies that focus on the removal of sulfates. Other technologies can be added to deal with the secondary waste products (e.g., sludge and brines) from the treatment processes. Moreover, some technologies such as ion exchange and adsorption can be added to target specific valuable elements in AMD. Such combinations have the potential to result in effective AMD treatment and minimum waste production, which are not easily achievable with the individual technologies. Overall, this review presents combinations of AMD treatment technologies which can work best together to produce optimal water quality and valuable products in a cost-effective manner.

Novel eco-friendly polylactic acid nanocomposite integrated membrane system for sustainable wastewater treatment: Performance evaluation and antifouling analysis

Water contamination caused by heavy metals, nutrients, and organic pollutants of varying particle sizes originating from domestic and industrial processes poses a significant global challenge. There is a growing concern, particularly regarding the presence of heavy metals in freshwater sources, as they can be toxic even at low concentrations, posing risks to human health and the environment. Currently, membrane technologies are recognized as effective and practical for treating domestic and industrial wastewater. However, these technologies are hindered by fouling issues. Furthermore, the utilization of conventional membranes leads to the accumulation of non-recyclable synthetic polymers, commonly used in their production, resulting in adverse environmental consequences. In light of our previously published studies on environmentally friendly, biodegradable polylactic acid (PLA) nanocomposite mixed matrix membranes (MMMs), we selected two top-performing PLA-based ultrafiltration nanocomposite membranes: one negatively charged (PLA-M-) and one positively charged (PLA-M+). We integrated these membranes into systems with varying arrangements to control fouling and eliminate heavy metals, organic pollutants, and nutrients from raw municipal wastewater collected by the local wastewater treatment plant in Abu Dhabi (UAE). The performance of two integrated systems (i.e., PLA-M+/PLA-M- and PLA-M-/PLA-M+) was compared in terms of permeate flux, contaminant removal efficiencies, and fouling mitigation. The PLA-M+/PLA-M- system achieved removal efficiencies of 79.6 %, 92.6 %, 88.7 %, 85.2 %, 98.9 %, 94 %, 83.3 %, and 98.3 % for chemical oxygen demand (COD), nitrate (NO3--N), phosphate (PO43--P), ammonium (NH4+-N), iron (Fe), zinc (Zn), nickel (Ni), and copper (Cu), respectively. On the other hand, the PLA-M-/PLA-M+ system recorded removal efficiencies of 85.8 %, 95.9 %, 100 %, 81.9 %, 99.3 %, 91.9 %, 72.9 %, and 98.9 % for COD, NO3--N, PO43--P, NH4+-N, Fe, Zn, Ni, and Cu, respectively. Notably, the PLA-M-/PLA-M+ system demonstrated superior antifouling resistance, making it the preferred integrated system. These findings demonstrate the potential of eco-friendly PLA nanocomposite UF-MMMs as a promising alternative to petroleum-based polymeric membranes for efficient and sustainable wastewater treatment.

New dithiocarbamate-based polymer (DTCP) as an additive to improve microporous polysulfone membrane efficiency in lead and dye removal

For fabricating a membrane with hydrophilic and complexing agent groups, a new dithiocarbamate-based polymer (DTCP) containing dithiocarbamate, thioamide, and ethereal oxygen groups was synthesized and blended in polysulfone (PSF) matrix with 1, 2, 5, and 10 wt% proportion. The membranes were produced by the nonsolvent induced phase separation method. For DTCP characterization, NMR, FTIR, TGA and GPC techniques were used. SEM images show that no morphological change can be seen even in 10 wt% blended membranes. AFM surface images show that the roughness of 5 and 10 wt% membranes extremely increased. The performance of the DTCP/PSF membranes were investigated in the separation of lead ions and Reactive Yellow 39 dye from the contaminated water. The outcomes indicated that by increasing the amount of DTCP up to 10 wt%, the pure water flux, bovine serum albumin flux, and the lead removal increased very efficiently compared to the bare one. Blending of more than 1 wt% DTCP, cause to removal of 99.6% lead ions. The water contact angle decreased by the adding of DTCP, caused to increase fouling resistance. The results of this research shows that the synthesized DTCP can be used as a good additive for improving membrane permeability, anti-fouling and especially heavy metal removal efficiency.

Lignin particles as green pore-forming agents for the fabrication of microporous polysulfone membranes

Templating polymeric membranes with micro-nano-scaled solid materials is an effective method to simultaneously improve the water flux and retention ratio. However, the fabrication of a green, recyclable, and size-controlled template material remains a challenge. Here, a new green pore-forming agent, lignin particles (LP), was developed to prepare porous polysulfone (PSF) membranes via the phase inversion technique. A series of LP have uniform sizes from ~200 nm to ~1800 nm. The performances of the templated PSF membranes cast at different sizes and contents of LP were examined for their surface and crosssection morphologies. The LP-templated PSF membranes displayed a remarkable enhancement in flux, porosity, and moisture content. Particularly, the PSF membranes cast with LP from ~200 to 1800 nm broke the traditional trade-off to a certain degree, which possessed stable retentions of bovine serum albumin (> 85 %) and significantly improved water flux (174.275 to 254.775 L m^-2 h^-1). In addition, the LP pore-forming agent is low-cost and environmentally friendly as it was prepared from industrial by-products and can be easily recycled. Overall, this study shows that lignin particles are green pore-forming agents that can be used for the fabrication of porous polymeric membranes with improved performance for water treatment.

Preparation of a CAB-GO/PES Mixed Matrix Ultrafiltration Membrane and Its Antifouling Performance

Serious membrane fouling has limited the development of ultrafiltration membrane technology for water purification. Synthesis of an ultrafiltration membrane with prominent anti-fouling ability is of vital importance. In this study, CAB-GO composite nanosheets were prepared by grafting graphene oxide (GO) with a zwitterionic material cocamidopropyl betaine (CAB) with strong antifouling properties. Anti-fouling CAB-GO/PES mixed matrix ultrafiltration membrane (CGM) was prepared by the phase inversion method with polyethersulfone (PES). Due to its electrostatic interaction, the interlayer distance between CAB-GO nanosheets was increased, and the dispersibility of GO was improved to large extent, thereby effectively avoiding the phenomenon of GO agglomeration in organic solvents. Based on the improvement of the surface porosity and surface hydrophilicity of the CAB-GO/PES mixed matrix membrane, the pure water flux of CGM-1.0 can reach 461 L/(m²·h), which was 2.5 times higher than that of the original PES membrane, and the rejection rates toward BSA and HA were above 96%. Moreover, when the content of CAB-GO was 0.1 wt%, the prepared CAB-GO/PES membrane exhibited very high BSA (99.1%) and HA (98.1%) rejection during long-term operation, indicating excellent anti-fouling ability.

Optimization of carboxylated graphene oxide (C-GO) content in polymer matrix: Synthesis, characterization, and application study

Carboxylated graphene oxide (C-GO) embedded in polysulfone (PSF) membrane composites were prepared with different wt. % (i.e., 0.2% M - 1, 0.3% M - 2, 0.4% M - 3, and 0.5% M - 4) using non-solvent induced phase separation (NIPS) method and ultrafiltration assembly was applied for the removal of dye effluents. The optimization of C-GO content into polymer matrix was found influencing factor in determining the composite membranes efficiency and application in various research fields. The membranes were characterized in terms of surface morphology (SEM), crystallinity (XRD), and functional groups identification (FTIR). The water permeability of the developed membranes was analyzed, and it is observed that increasing the content of C-GO in PSF membranes imposed a positive impact on permeation performance. M - 3 was found to be a potential candidate among all the membranes with a maximum water flux of about 183 LMH which is considerably higher as compared to the pristine PSF membrane's water flux (i.e., 27 LMH). Moreover, contact angle measurements of membranes were also checked to assess the hydrophilicity of PSF membranes. The results of contact angle also support the water permeability and efficient correlation was observed as contact angle decreases with increasing the content of C-GO. The minimum contact angle with excellent hydrophilicity was shown by the M - 3 membrane and it was found of about ±58.19° and this value is close to the M - 4 membrane having maximum C-GO content. The photocatalytic performance of the M - 3 membrane was checked under UV-254 nm using methylene blue dye and 97% dye removal was achieved within 220 min of reaction time under neutral pH conditions. The M - 3 membrane having C-GO content of 0.4% was found to be the best membrane with high pure water flux (183 LMH) and efficient dye rejection (82%) capability.

Membrane-Active Nonivamide Derivatives as Effective Broad-Spectrum Antimicrobials: Rational Design, Synthesis, and Biological Evaluation

Antibiotic resistance is emerging as a "global public health concern". To address the growing epidemic of multidrug-resistant pathogens, the development of novel antimicrobials is urgently needed. In this study, by biomimicking cationic antibacterial peptides, we designed and synthesized a series of new membrane-active nonivamide and capsaicin derivatives as peptidomimetic antimicrobials. Through modulating charge/hydrophobicity balance and rationalizing structure-activity relationships of these peptidomimetics, compound 51 was identified as the lead compound. Compound 51 exhibited potent antibacterial activity against both Gram-positive bacteria (MICs = 0.39-0.78 μg/mL) and Gram-negative bacteria (MICs = 1.56-6.25 μg/mL), with low hemolytic activity and low cytotoxicity. Compound 51 displayed a faster bactericidal action through a membrane-disruptive mechanism and avoided bacterial resistance development. Furthermore, compound 51 significantly reduced the microbial burden in a murine model of keratitis infected by Staphylococcus aureus or Pseudomonas aeruginosa. Hence, this design strategy can provide a promising and effective solution to overcome antibiotic resistance.

Next-generation graphene oxide additives composite membranes for emerging organic micropollutants removal: Separation, adsorption and degradation

In the past two decades, membrane technology has attracted considerable interest as a viable and promising method for water purification. Emerging organic micropollutants (EOMPs) in wastewater have trace, persistent, highly variable quantities and types, develop hazardous intermediates and are diffusible. These primary issues affect EOMPs polluted wastewater on an industrial scale differently than in a lab, challenging membranes-based EOMP removal. Graphene oxide (GO) promises state-of-the-art membrane synthesis technologies and use in EOMPs removal systems due to its superior physicochemical, mechanical, and electrical qualities and high oxygen content. This critical review highlights the recent advancements in the synthesis of next-generation GO membranes with diverse membrane substrates such as ceramic, polyethersulfone (PES), and polyvinylidene fluoride (PVDF). The EOMPs removal efficiencies of GO membranes in filtration, adsorption (incorporated with metal, nanomaterial in biodegradable polymer and biomimetic membranes), and degradation (in catalytic, photo-Fenton, photocatalytic and electrocatalytic membranes) and corresponding removal mechanisms of different EOMPs are also depicted. GO-assisted water treatment strategies were further assessed by various influencing factors, including applied water flow mode and membrane properties (e.g., permeability, hydrophily, mechanical stability, and fouling). GO additive membranes showed better permeability, hydrophilicity, high water flux, and fouling resistance than pristine membranes. Likewise, degradation combined with filtration is two times more effective than alone, while crossflow mode improves the photocatalytic degradation performance of the system. GO integration in polymer membranes enhances their stability, facilitates photocatalytic processes, and gravity-driven GO membranes enable filtration of pollutants at low pressure, making membrane filtration more inexpensive. However, simultaneous removal of multiple contaminants with contrasting characteristics and variable efficiencies in different systems demands further optimization in GO-mediated membranes. This review concludes with identifying future critical research directions to promote research for determining the GO-assisted OMPs removal membrane technology nexus and maximizing this technique for industrial application.

Graphene based composite membranes for environmental toxicology remediation, critical approach towards environmental management

Graphene-based composite membranes, as laminated, stacked, and assembled architectures of graphene, have surpassed other conventional membranes with their advanced and preeminent structural specialization and potential use in a wide range of sustainable and environmental applications. The characteristic membrane features such as distinct laminar morphology, tailored physicochemical properties, as well as extraordinary molecular properties have fascinated scientists. Due to remarkable mechanical properties, these membranes can be easily fabricated. Recent progress has been achieved by graphene and its derivatives-based membranes to purify water and gases for environmental remediation. This review explained the latest and groundbreaking advances in chemical design, fabrication, and application of graphene-based membranes. Special attention is paid to the recent developments on graphene-based composites into membranes with various forms: free-standing, layered, and graphene-based nanocomposite membranes. Furthermore, a unique approach on environmental management with as-fabricated membranes is provided by discussing the effect of physicochemical properties. Consequently, their full-scale use for environmental management, water purification, gas purification, and biological treatments will pave the way for their promising features and realize their future prospects.

Graphene-Based Functional Hybrid Membranes for Antimicrobial Applications: A Review

Graphene-based nanomaterials have shown wide applications in antimicrobial fields due to their accelerated rate of pathogen resistance and good antimicrobial properties. To apply graphene materials in the antimicrobial test, the graphene materials are usually fabricated as two-dimensional (2D) membranes. In addition, to improve the antimicrobial efficiency, graphene membranes are modified with various functional nanomaterials, such as nanoparticles, biomolecules, polymers, etc. In this review, we present recent advances in the fabrication, functional tailoring, and antimicrobial applications of graphene-based membranes. To implement this goal, we first introduce the synthesis of graphene materials and then the fabrication of 2D graphene-based membranes with potential techniques such as chemical vapor deposition, vacuum filtration, spin-coating, casting, and layer-by-layer self-assembly. Then, we present the functional tailoring of graphene membranes by adding metal and metal oxide nanoparticles, polymers, biopolymers, metal–organic frameworks, etc., with graphene. Finally, we focus on the antimicrobial mechanisms of graphene membranes, and demonstrate typical studies on the use of graphene membranes for antibacterial, antiviral, and antifungal applications. It is expected that this work will help readers to understand the antimicrobial mechanism of various graphene-based membranes and, further, to inspire the design and fabrication of functional graphene membranes/films for biomedical applications.

Modification strategies of membranes with enhanced Anti-biofouling properties for wastewater Treatment: A review

This review addresses composite membranes used for wastewater treatment, focusing heavily on the anti-biofouling properties of such membranes. Biofouling caused by the development of a thick biofilm on the membrane surface is a major issue that reduces water permeance and reduces its lifetime. Biofilm formation and adhesion are mitigated by modifying membranes with two-dimensional or zero-dimensional carbon-based nanomaterials or their modified substituents. In particular, nanomaterials based on graphene, including graphene oxide and carbon quantum dots, are mainly used as nanofillers in the membrane. Functionalization of the nanofillers with various organic ligands or compositing the nanofiller with other materials, such as silver nanoparticles, enhances the bactericidal ability of composite membranes. Moreover, such membrane modifications reduce biofilm adhesion while increasing water permeance and salt/dye rejection. This review discusses the recent literature on developing graphene oxide-based and carbon quantum dot-based composite membranes for biofouling-resistant wastewater treatment.

Zwitterionic hydrogel modified reduced graphene oxide/ZnO nanocomposite blended membrane with high antifouling and antibiofouling performances

Membrane fouling and biofouling are major challenges in the application of membrane technology for wastewater treatment. The synthesis of antifouling and antibiofouling dual functionality membranes is a promising approach to tackling these problems. In this work, we fabricated a high-efficiency dual functionality polyethersulfone (PES) ultrafiltration membrane by blending an antibacterial reduced graphene oxide-ZnO nanocomposite into a PES matrix (rGO/ZnO-PES) followed by surface grafting of a low-fouling polyampholyte hydrogel (rGO/ZnO-z-PES). The antibacterial activity of the blended membrane was optimized by changing the nanocomposite fraction in the PES dope solution. Surface characterizations (SEM-EDS, XPS, ATR-FTIR, contact angle, and Zeta potential) confirmed the successful grafting of the zwitterionic hydrogel on the rGO/ZnO-PES membrane surface. Contact killing assays revealed that the polyampholyte hydrogel grafting did not affect the high antibacterial activity of the rGO/ZnO-PES membrane. Dynamic filtration experiments demonstrated the very high antifouling and antibiofouling of the rGO/ZnO-z-PES membrane, and significantly higher than those of the rGO/ZnO-PES and pristine PES membranes. The measured concentration of zinc ions in the permeate was low. Overall, our results demonstrate that the rGO/ZnO-z-PES membrane has excellent antifouling and antibiofouling performance and is stable and safe, and therefore very promising for wastewater treatment.

Improved anti-organic fouling and antibacterial properties of PVDF ultrafiltration membrane by one-step grafting imidazole-functionalized graphene oxide

At present, membrane fouling is a thorny issue that limits the development of polyvinylidene fluoride (PVDF) composite membrane, which seriously affects its separation performance and service lifespan. Herein, an imidazole-functionalized graphene oxide (Im-GO) with hydrophilicity and antibacterial performance was synthesized, and it was used as a modifier to improve the anti-organic fouling and antibacterial properties of PVDF membrane. The anti-organic fouling test showed that the maximum flux recovery ratios against bovine serum albumin and humic acid were 88.9% and 94.5%, respectively. Conspicuously, the grafted imidazole groups could effectively prevent the bacteria from growing on the membrane surface. It was gratifying that the antibacterial modifier Im-GO was almost not lost from the hybrid membranes even by the ultrasonic treatment, which was different from the conventional release-killing antibacterial agents. Owing to the long-term anti-organic fouling and antibacterial properties, Im-GO/PVDF hybrid membranes exhibit a great application potential in the fields of rough separation and concentration of biomedical products.

Inner Surface Hydrophilic Modification of PVDF Membrane with Tea Polyphenols/Silica Composite Coating

The use of Polyvinylidene fluoride (PVDF) membranes is constrained in wastewater treatment because of their hydrophobic nature. Therefore, a large number of researchers have been working on the hydrophilic modification of their surfaces. In this work, a superhydrophilic tea polyphenols/silica composite coating was developed by a one-step process. The composite coating can achieve not only superhydrophilic modification of the surface, but also the inner surface of the porous PVDF membrane, which endows the modified membrane with excellent water permeability. The modified membrane possesses ultrahigh water flux (15,353 L·m⁻²·h⁻¹). Besides this, the modified membrane can realize a highly efficient separation of oil/water emulsions (above 96%).

Incorporation of Biomass-Based Carbon Nanoparticles into Polysulfone Ultrafiltration Membranes for Enhanced Separation and Anti-Fouling Performance

Functionalized carbon nanomaterials are considered to be an efficient modifier for ultrafiltration membranes with enhanced performance. However, most of the reported carbon nanomaterials are derived from unsustainable fossil fuels, while an extra modification is often essential before incorporating the nanomaterials in membranes, thus inevitably increasing the cost and complexity. In this work, novel functionalized biomass-based carbon nanoparticles were prepared successfully from agricultural wastes of corn stalks through simple one-step acid oxidation method. The obtained particles with the size of ~45 nm have excellent dispersibility in both aqueous and dimethyl formamide solutions with abundant oxygen-containing groups and negative potentials, which can endow the polysulfone ultrafiltration membranes with enhanced surface hydrophilicity, larger pore size, more finger-like pores, and lower surface roughness. Therefore, the separation and anti-fouling performance of membranes are improved simultaneously. Meanwhile, the addition of 0.4 wt% nanoparticles was proved to be the best condition for membrane preparation as excess modifiers may lead to particle aggregation and performance recession. It is expected that these biomass-based carbon nanoparticles are potential modifying materials for improving the separation performance and anti-fouling property of the membranes with great simplicity and renewability, which pave a new avenue for membrane modification and agricultural waste utilization.

Polysulfone Membranes Based Hybrid Nanocomposites for the Adsorptive Removal of Hg(II) Ions

Organic-inorganic nanoparticles, which can improve and modify the mechanical and chemical properties of polymers, have been used as fillers to prepare high-performance hybrid nanocomposite membranes. In this study, we explored whether the incorporation of organic nanofillers (graphene (G), graphene oxide (GO), carbon nanotubes (CNTs), or oxidized carbon nanotubes (CNTOxi)) into polysulfone (PSF) and montmorillonite (MMt)-modified PSF membranes could enhance membrane performance for the removal of heavy metal ions from contaminated solutions. These hybrid membranes were prepared by a phase inversion method using chloroform as the solvent. The surface morphologies of the membranes revealed good dispersibility of the organoclay and carbon nanomaterials in the PSF matrix. The hybrid nanocomposite membranes showed significantly improved thermal stability and mechanical properties as compared to the pristine PSF and PSF/MMt membranes. The adsorption efficiencies of these hybrid adsorptive membranes for Hg(II), Pb(II), Sr(II), Fe(III), Zn(II), Ni(II), Al(III), Co(II), Y(III), and Cr(III) were investigated. The PSF/MMt/CNTOxi and PSF/MMt/GO membranes exhibited the highest adsorption efficiencies. In particular, these adsorptive membranes showed selectivity toward Hg(II), and the Hg(II) extraction percentage was maximized at pH 2. The maximum Hg(II) adsorption capacities of PSF/MMt/CNTOxi and PSF/MMt/GO were 151.36 and 144.89 mg/g, respectively, and the adsorption isotherm was in approval with the Langmuir model. These hybrid nanocomposites can be used in water purification application.

Fabrication of a hybrid ultrafiltration membrane based on MoS2 modified with dopamine and polyethyleneimine

The hydrophobicity of ultrafiltration membranes is the main cause of membrane fouling and reduced permeability, so it is necessary to improve the hydrophilicity and anti-fouling performance of ultrafiltration membrane materials. MoS₂ nanoparticles that were modified with polydopamine (PDA) and polyethyleneimine (PEI), named MoS₂-PDA-PEI, were added to fabricate a polyethersulfone ultrafiltration membrane (PES/MoS₂-PDA-PEI) for the first time. The effects of modified MoS₂ nanoparticles on membrane performance were clarified. The results indicated that the permeability, rejection, and anti-fouling capability of the hybrid PES/MoS₂-PDA-PEI membrane have been improved compared with the pristine PES membrane. When the content of MoS₂-PDA-PEI nanoparticles in the membrane is 0.5%, the pure water flux of the hybrid membrane reaches 364.03 L m⁻² h⁻¹, and the rejection rate of bovine serum albumin (BSA) and humic acid (HA) is 96.5% and 93.2% respectively. The flux recovery rate of HA reached 97.06%. As expected, the addition of MoS₂-PDA-PEI nanoparticles promotes the formation of the porous structure and improves the hydrophilicity of the membrane, thereby improving its antifouling performance.

The hydrophobicity of ultrafiltration membranes is the main cause of membrane fouling and reduced permeability, so it is necessary to improve the hydrophilicity and anti-fouling performance of ultrafiltration membrane materials.

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.

Near-Infrared Photothermal/Photodynamic-in-One Agents Integrated with a Guanidinium-Based Covalent Organic Framework for Intelligent Targeted Imaging-Guided Precision Chemo/PTT/PDT Sterilization

Phototherapy holds great promise in the treatment of bacterial infections, especially the multidrug resistant bacterial infections. However, most therapeutic agents are based on the integration of individual photothermal agents and photosensitizers, always in the activated state, and generally lack bacterial specificity, resulting in uncertain pharmacokinetics and serious nonspecific damage to normal tissues. Herein, we report a pH-responsive nanoplatform with synergistic chemo-phototherapy function for smart fluorescence imaging-guided precision sterilization. pH reversible activated symmetric cyanine was designed and prepared as a bacterial-specific imaging unit and PTT/PDT-in-one agent. Meanwhile, a guanidinium-based covalent organic framework (COF) was employed as a nanocarrier and chemotherapy agent to build the intelligent nanoplatform via electrostatic self-assembly. The self-assembly of the PTT/PDT-in-one agent and the COF greatly improves the stability and blood circulation of the PTT/PDT-in-one agent and provides charge-reversed intelligent targeting ability. The developed smart nanoplatform not only enables bacterial-targeted imaging but also possesses chemo/PTT/PDT synergetic high-efficiency bactericidal effects with little side effects, showing great potential in practical applications.

Biological fixed-film systems

The technical papers published in 2019 regarding wastewater treatment and microbial films were classified into two categories: biofilm and biofilm reactors. The biofilm category includes biofilm formation, biofilm consortia, bacterial signals, biofouling, extracellular polymeric substances, and biofilm membrane bioreactors. The biofilm reactors category provides recent information on rotating biological contactors, fluidized-bed biofilm reactors, integrated fixed-film activated sludge, moving-bed biofilm reactors, packed-bed biofilm reactors, sequencing biofilm batch reactors, and trickling filters.

Coupling of Immobilized Photosynthetic Bacteria with a Graphene Oxides/PSF Composite Membrane for Textile Wastewater Treatment: Biodegradation Performance and Membrane Anti-Fouling Behavior

The membrane bioreactor (MBR), as one of the promising technologies, has been widely applied for treatments of wastewater. However, serious membrane fouling and low microbial activity have been reported as major problems hindering the development of the MBR. To overcome these drawbacks, we intend to improve the MBR process in the view of membrane surface modification and efficient granular bacteria cultivation. In the present study, immobilized photosynthetic bacteria integration with graphene oxide (GO)/polysulfone (PSF) composite membrane separation (IPMBR) was first applied for textile wastewater treatment. Due to the high activity of immobilized cells, the IPMBR system exhibited higher efficiency on the removal of color, ammonia-nitrogen, and chemical oxygen demand than the conventional MBR system. In comparison with a pure PSF membrane, GO/PSF composite membrane presented the higher hydrophilicity (water contact angles of 62.9°) and more attractive permeability (178.5 L/m²h) by reducing the adhesion of hydrophobic foulants. During the whole operation, the immobilized photobioreactor exhibited approximately seven times higher membrane permeability that that of the conventional MBR. Meanwhile, the effect of the structure and character of immobilized photosynthetic bacteria on the membrane fouling reduction was investigated in detail. The change of extracellular polymeric substance concentration, settleability and particle size of flocs was very beneficial to alleviate membrane fouling. As a result, this research will open a new avenue for developing efficient and anti-fouling MBR technology in the future.

Modifying Cellulose Acetate Mixed-Matrix Membranes for Improved Oil-Water Separation: Comparison between Sodium and Organo-Montmorillonite as Particle Additives

In this study, cellulose acetate (CA) mixed-matrix membranes were fabricated through the wet-phase inversion method. Two types of montmorillonite (MMT) nanoclay were embedded separately: sodium montmorillonite (Na-MMT) and organo-montmorillonite (O-MMT). Na-MMT was converted to O-MMT through ion exchange reaction using cationic surfactant (dialkyldimethyl ammonium chloride, DDAC). Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) compared the chemical structure and composition of the membranes. Embedding either Na-MMT and O-MMT did not change the crystallinity of the CA membrane, indicating that the nanoclays were dispersed in the CA matrix. Furthermore, nanoclays improved the membrane hydrophilicity. Compared with CA_Na-MMT membrane, CA_O-MMT membrane had a higher separation efficiency and antifouling property. At the optimum concentration of O-MMT in the CA matrix, the pure water flux reaches up to 524.63 ± 48.96 L∙m^-2∙h^-1∙bar^-1 with over 95% rejection for different oil-in-water emulsion (diesel, hexane, dodecane, and food-oil). Furthermore, the modified membrane delivered an excellent antifouling property.

Combined strategy of blending and surface modification as an effective route to prepare antifouling ultrafiltration membranes

Ultrafiltration (UF) membranes blended with hydrophilic nanomaterials usually exhibit preferable overall performance including the membrane permeability and antifouling capability. However, the improvement in antifouling performance may be not outstanding due to the small amount of nanomaterial distributed near the membrane surface and the limited improvement in membrane hydrophilicity. Notably, excess addition of nanomaterials may lead to the decline in membrane permeability. In order to solve the above problem, we integrated the strategy of blending and surface modification to construct novel hybrid UF membranes. Novel nanohybrid was prepared via tannic acid (TA) coating on hydroxyapatite nanotubes (HANTs) and the subsequent grafting of zwitterionic polyethylenimine (ZPEI). The prepared nanohybrid (HANTs@TA-ZPEI) was incorporated with the polysulfone containing tertiary amine groups to fabricate hybrid membranes via the solution blending and the subsequent immersion-precipitation phase inversion process. Then the matrix was modified with zwitterions via the reaction of tertiary amine group with 1, 3-propane sultone. UF tests were conducted using the bovine serum albumin (BSA) and humic acid (HA) as the representative foulants. Results showed that both the permeability and the antifouling performance of the membranes achieved favorable promotion. Thereinto, the water flux of M-B0.4-Z membrane (pre blended with 0.4 wt% HANTs@TA-ZPEI in the casting solution and post-surface modified) exhibited 2.6 times that of the pristine membrane and the flux recovery ratio (FRR) for BSA and HA attained 93.4% and 96.1%, respectively. By the combination of blending and surface modification, both the membrane permeability and fouling resistant properties could attain remarkable promotion, which exerted the advantages of two methods and made up the deficiency of single blending method.

Cytotoxic aquatic pollutants and their removal by nanocomposite-based sorbents

Water is an extremely essential compound for human life and, hence, accessing drinking water is very important all over the world. Nowadays, due to the urbanization and industrialization, several noxious pollutants are discharged into water. Water pollution by various cytotoxic contaminants, e.g. heavy metal ions, drugs, pesticides, dyes, residues a drastic public health issue for human beings; hence, this topic has been receiving much attention for the specific approaches and technologies to remove hazardous contaminants from water and wastewater. In the current review, the cytotoxicity of different sorts of aquatic pollutants for mammalian is presented. In addition, we will overview the recent advances in various nanocomposite-based adsorbents and different approaches of pollutants removal from water/wastewater with several examples to provide a backdrop for future research.

Bibliometric approach to the perspectives and challenges of membrane separation processes to remove emerging contaminants from water

The presence of contaminants in water is concerning due to the potential impacts on human health and the environment, and ingested contaminants cause harm in various ways. The conventional water treatment systems are not efficient to remove these contaminants. Therefore, novel techniques and materials for the removal of contaminants are increasingly being developed. The separation process using modified membranes can remove these micropollutants; therefore, they have attracted significant research attention. Among the materials used for manufacturing of these membranes, composites based on graphene oxide and reduced graphene oxide are preferred owing to their promising properties, such as mechanical resistance, thermal and chemical stability, antifouling capacity, water permeability, high thermal and electrical conductivity, high optical transmittance and high surface area. Membrane separation processes (MSP) can be used as secondary or tertiary treatment during the supply of wastewater. However, the efficient and accessible applications of these technologies are challenging. This study aims to demonstrate the main concepts of membrane separation processes and their application in the removal of emerging contaminants. This study reports bibliometric mapping, relevant data on studies using membranes as water treatment processes, and their viability in industrial applications. The main challenges and perspectives of these technologies are discussed in detail as well.

Noncovalently Functionalized Sulfated Castor Oil-Graphene Oxide-Strengthened Polyetherimide Composite Membranes for Superior Separation of Organic Pollutants and Their Fouling Mitigation

A novel sulfated castor oil (SCO)-graphene oxide (GO)-strengthened polyetherimide (PEI) membrane was prepared for the first time via phase inversion process for the efficient separation of multiple organic pollutants with superior long-term antifouling stability. X-ray diffraction, attenuated total reflectance-Fourier transfer infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and mechanical strength studies revealed that the SCO and GO were successfully incorporated into the PEI membrane with enhanced mechanical strength. The water flux of the PEI/SCO@GO membrane (410.6 L m^-2 h^-1) was about 50 times that of bare PEI (7.8 L m^-2 h^-1) and about 6 times that of PEI/SCO (64.5 L m^-2 h^-1) membranes. The surface hydrophilicity of the PEI/SCO@GO membrane was significantly increased in terms of the decrease of the water contact angle from 98.5° (bare PEI) to 40.4°. The PEI/SCO@GO membrane separation efficiency was found to be greater than 99.0%, particularly for both the oil-in-water emulsion and the humic acid solution, respectively. Because of the higher flux recovery ratio and the lower total fouling rate of the PEI/SCO@GO membrane, a comprehensive antifouling performance was observed during the long-term foulant filtration cycle analyses. Hence, the incorporation of both SCO and GO into the PEI matrix would render the highly hydrophobic PEI material as the suitable and desirable antifouling membrane toward the treatment of various organic foulants in wastewater.

Synthesis of amino-functionalized Ti3C2Tx MXene by alkalization-grafting modification for efficient lead adsorption

High-quality amino-functionalized Ti₃C₂T_x MXene (alk-MXene-NH₂) nanosheets were successfully synthesized by a facile alkalization-grafting modification for lead adsorption.

Nanofiber membrane of graphene oxide/polyacrylonitrile with highly efficient antibacterial activity

Infection from bacterial resistance to antibiotics has given rise to a grave threat to human health in the world. It is vital to developing highly efficient antibacterial materials that are safe and biocompatible with humans and without bacterial resistance. In this study, nanofiber membranes of graphene oxide/polyacrylonitrile (GO/PAN) with highly efficient antibacterial activity were fabricated via electrospinning technique. As the spindle-knot structure of membranes formed by the addition of GO sheets increased, the hydrophilicity and surface roughness increased. The antibacterial test indicated that antibacterial ratios of 3GO/PAN membranes against Escherichia coli and Staphylococcus aureus were 98.5% and 99.6%, respectively after contracting 24 h, with highly efficient antibacterial activity. Furthermore, the E. coli cell structures of adhered to the GO/PAN nanofiber surface changed significantly shrunk and deformed, and the number of S. aureus cell were obviously less contrast than the pure PAN. The main antibacterial mechanism was GO of spindle-knot in nanofiber membranes produced ROS destroyed the physiological activities of the bacteria lead to death. The fabricated GO/PAN nanofiber membrane of this study is promising to develop to a kind of novel antibacterial materials.

Cationic Polymers with Tailored Structures for Rendering Polysaccharide-Based Materials Antimicrobial: An Overview

Antimicrobial polymers have attracted substantial interest due to high demands on improving the health of human beings via reducing the infection caused by various bacteria. The review presented herein focuses on rendering polysaccharides, mainly cellulosic-based materials and starch to some extent, antimicrobial via incorporating cationic polymers, guanidine-based types in particular. Extensive review on synthetic antimicrobial materials or plastic/textile has been given in the past. However, few review reports have been presented on antimicrobial polysaccharide, cellulosic-based materials, or paper packaging, especially. The current review fills the gap between synthetic materials and natural polysaccharides (cellulose, starch, and cyclodextrin) as substrates or functional additives for different applications. Among various antimicrobial polymers, particular attention in this review is paid to guanidine-based polymers and their derivatives, including copolymers, star polymer, and nanoparticles with core-shell structures. The review has also been extended to gemini surfactants and polymers. Cationic polymers with tailored structures can be incorporated into various products via surface grafting, wet-end addition, blending, or reactive extrusion, effectively addressing the dilemma of improving substrate properties and bacterial growth. Moreover, the pre-commercial trial conducted successfully for making antimicrobial paper packaging has also been addressed.

Preparation of thermo-responsive PNIPAAm-MWCNT membranes and evaluation of its antifouling properties in dairy wastewater

A novel MWCNT-PNIPAAm nanocomposite membrane was developed with an excellent cleaning efficiency of thermo-responsive surface. The thermo-responsive N-isopropyle acryleamide (NIPAAm) monomer was polymerized on the surface of MWCNT via free radical polymerization. The prepared MWCNT-PNIPAAm nanocomposite was characterized by FTIR, SEM and TGA analyses. Various amounts of the prepared nanocomposite were incorporated into the membrane matrix by the physical blending method. The resultant membranes showed better surface wettability and pure water flux compared to pristine Polyethersulfone (PES) membrane. Furthermore, after filtration, the COD value of dairy wastewater was reduced to around 90% for all membranes. The thermo-responsive cleaning method was employed to investigate the cleaning efficiency of MWCNT-PNIPAAm membrane for dairy wastewater. The 99.9% flux recovery ratio was obtained for MWCNT-PNIPAAm-0.05% membranes. All these results confirmed that the presence of MWCNT-PNIPAAm nanocomposite in the membrane matrix improves the membrane hydrophilicity and antifouling properties.

Antibacterial Properties of Graphene-Based Nanomaterials

Bacteria mediated infections may cause various acute or chronic illnesses and antibiotic resistance in pathogenic bacteria has become a serious health problem around the world due to their excessive use or misuse. Replacement of existing antibacterial agents with a novel and efficient alternative is the immediate demand to alleviate this problem. Graphene-based materials have been exquisitely studied because of their remarkable bactericidal activity on a wide range of bacteria. Graphene-based materials provide advantages of easy preparation, renewable, unique catalytic properties, and exceptional physical properties such as a large specific surface area and mechanical strength. However, several queries related to the mechanism of action, significance of size and composition toward bacterial activity, toxicity criteria, and other issues are needed to be addressed. This review summarizes the recent efforts that have been made so far toward the development of graphene-based antibacterial materials to face current challenges to combat against the bacterial targets. This review describes the inherent antibacterial activity of graphene-family and recent advances that have been made on graphene-based antibacterial materials covering the functionalization with silver nanoparticles, other metal ions/oxides nanoparticles, polymers, antibiotics, and enzymes along with their multicomponent functionalization. Furthermore, the review describes the biosafety of the graphene-based antibacterial materials. It is hoped that this review will provide valuable current insight and excite new ideas for the further development of safe and efficient graphene-based antibacterial materials.