Modification of a polyethersulfone membrane with a block copolymer brush of poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) and a branched polypeptide chain of Arg–Glu–Asp–Val

Polyethersulfone (PES) has good thermal stability, superior pH, chlorine tolerance, and excellent chemical resistance; however, the hydrophilicity and biocompatibility of PES need to be improved for its real applications. In this study, we report a surface modification method for the preparation of a functional PES membrane with hydrophilic polymer chains (MPC and GMA) via surface-initiated electrochemically-mediated atom-transfer radical polymerization (SI-eATRP) technology, and the Arg–Glu–Asp–Val polypeptide groups (REDV) were immobilized onto the modified membrane by a ring-opening reaction. XPS and SEM were used to analyze the chemical composition and morphology of the modified membrane surfaces, confirming that the hydrophilic polymer chains MPC and GMA and the polypeptide group REDV were successfully grafted onto the PES membrane surface. The static water contact angle decreased from 89° to 50–65°, and the hydrophilic property of the modified membrane was enhanced. The water flux increased from 4.29 L m⁻² h⁻¹ for the pristine PES membrane to 25 L m⁻² h⁻¹ for the modified membrane with PGMA chains grafted on it and REDV functional groups immobilized on it; note that the antifouling tests showed that all the modified membranes had the higher flux recovery ratio values (FRR) of above 80% than the pristine PES membrane (about 60%), and the APTT for the modified membrane increased from 46 s to 93 s, indicating that these modified membranes could be applied in the separation and blood purification fields.

A block copolymer involving chains of poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) and Arg–Glu–Asp–Val was designed and used for modification of polymer membrane for applications in separation and blood purification field.     

Self-cleaning expanded polytetrafluoroethylene-based hybrid membrane for water filtration

Membrane surface fouling is a key problem for water filtration. Compositing photocatalytic substances with a base membrane is a widely used strategy, but most of the membrane will be decomposed by photocatalysis. Herein, expanded polytetrafluoroethylene (ePTFE) with extremely stable chemical properties is grafted with polyacrylic acid (PAA) and then modified with titanium dioxide (TiO₂) to realize a self-cleaning TiO₂–PAA–ePTFE filtration membrane. It can recover its flux under UV irradiation after fouling. With 20 rounds of self-cleaning, the membrane microstructure still remains intact. Moreover, in addition to retaining bovine serum albumin, TiO₂ particles on the membrane surface are capable of absorbing small organic pollutants and degrading them. Thus, this membrane is potentially used as an anti-fouling membrane for water filtration.

Herein, expanded polytetrafluoroethylene (ePTFE) with extremely stable chemical properties is grafted with titanium dioxide (TiO₂) to realize a self-cleaning and UV resistance TiO₂–PAA–ePTFE filtration membrane.      

Fabrication of a blood compatible composite membrane from chitosan nanoparticles,ethyl cellulose and bacterial cellulose sulfate

A heparin-like composite membrane was fabricated through electrospinning chitosan nanoparticles (CN) together with an ethylcellulose (EC) ethanol solution onto a bacterial cellulose sulfate membrane (BCS). Scanning electron microscopy images revealed that there were no chitosan particles in the obtained composite CN-EC/BCS membranes (CEB), indicating CN had been stretched to nanofibers. X-ray photoelectron spectroscopy verified the existence of –NH₂ from chitosan and –SO₃⁻ from BCS on the surface of CEB membranes. Positively charged CN in the electrospinning solution and negatively charged BCS on the collector increased the electrostatic force and the electrospinning ability of the EC was increased. The membrane was hydrophobic, with a water contact angle higher than 120°. CEB membranes expressed good blood compatibility according to the results of coagulation time and platelet adhesion experiments. No platelets adhered on the surface of the CEB membranes. An inflammatory response was investigated according to activation of the macrophages seeded onto the membranes. Macrophages seeded on CEB membranes are not activated after 24 h incubation.

A blood compatible membrane was fabricated through electrospinning a solution of chitosan nanoparticles and ethylcellulose onto a bacterial cellulose sulfate membrane to mimic heparin''s structure.     

A simple electrochemical immunosensor based on a chitosan/reduced graphene oxide nanocomposite for sensitive detection of biomarkers of malignant melanoma

The sensitive and specific detection of tumor biomarkers is crucial for early diagnosis and treatment of malignant melanoma. Immunoassay with a simple sensing interface and high sensitivity is highly desirable. In this work, a simple electrochemical immunosensor based on a chitosan/reduced graphene oxide (CS–rGO) nanocomposite was developed for sensitive determination of an S-100B protein, a tumor marker of malignant melanoma. CS–rGO nanocomposite were prepared by chemical reduction of graphene oxide in the presence of chitosan and modified on glassy carbon electrode (GCE) to provide a biofriendly, conductive, and easily chemically modified matrix for further immobilization of antibodies. Anti-S-100B antibodies were grafted onto the chitosan molecules to fabricate the immunorecognition interface by a simple glutaraldehyde cross-linking method. Electrochemical determination of S-100B was achieved by measuring the decreased current signal of solution phase electrochemical probes, which originated from the increased steric hindrance and insulation caused by the formation of antigen–antibody complexes at the electrode interface. Due to the good conductivity, high surface area, excellent biocompatibility, and good film-forming ability of CS–rGO, the constructed immunosensor exhibited good stability, high selectivity and sensitivity, a wide dynamic range from 10 fg mL⁻¹ to 1 ng mL⁻¹ and a low limit of detection of 1.9 pg mL⁻¹ (S/N = 3). Moreover, the sensor was also applicable for the sensitive detection of S-100B protein in real human serum samples.

Simple electrochemical immunosensor is easily fabricated based on chitosan/reduce graphene oxide nanocomposite for sensitive determination of a tumor marker of malignant melanoma.     

Sulfonated covalent triazine-based frameworks as catalysts for the hydrolysis of cellobiose to glucose

Covalent triazine-based frameworks (CTFs) were synthesized in large scale from various monomers. The materials were post-synthetically modified with acid functionalities via gas-phase sulfonation. Acid capacities of up to 0.83 mmol g⁻¹ at sulfonation degrees of up to 10.7 mol% were achieved. Sulfonated CTFs exhibit high specific surface area and porosity as well as excellent thermal stability under aerobic conditions (>300 °C). Successful functionalization was verified investigating catalytic activity in the acid-catalyzed hydrolysis of cellobiose to glucose at 150 °C in H₂O. Catalytic activity is mostly affected by porosity, indicating that mesoporosity is beneficial for hydrolysis of cellobiose. Like other sulfonated materials, S-CTFs show low stability under hydrothermal reaction conditions. Recycling of the catalyst is challenging and significant amounts of sulfur leached out of the materials. Nevertheless, gas-phase sulfonation opens a path to tailored solid acids for application in various reactions. S-CTFs form the basis for multi-functional catalysts, containing basic coordination sites for metal catalysts, tunable structural parameters and surface acidity within one sole system.

Novel post-synthetically sulfonated covalent triazine-based frameworks (S-CTFs) enable selective hydrolysis of cellobiose to glucose at rather high substrate-to-catalyst weight ratios.     

MXene potassium titanate nanowire/sulfonated polyether ether ketone (SPEEK) hybrid composite proton exchange membrane for photocatalytic water splitting

A cross-linked sulfonated polyether ether ketone (C-SPEEK) was incorporated with MXene/potassium titanate nanowire (MKT-NW) as a filler and applied as a proton exchange membrane for photocatalytic water splitting. The prepared hybrid composite PEM had proton conductivity of 0.0097 S cm⁻¹ at room temperature with an ion exchange capacity of 1.88 meq g⁻¹. The hybrid composite proton exchange membrane is a reactive membrane which was able to generate hydrogen gas under UV light irradiation. The efficiency of hydrogen gas production was 0.185066 μmol within 5 h for 12% wt of MKT-NW loading. The results indicated that the MKT-NW/C-SPEEK membrane is a promising candidate for ion exchange with hydrogen gas evolution in photocatalytic water splitting and could be applied as a renewable source of energy to use in various fields of applications.

A cross-linked sulfonated polyether ether ketone (C-SPEEK) was incorporated with MXene/potassium titanate nanowire (MKT-NW) as a filler and applied as a proton exchange membrane for photocatalytic water splitting.     

Facile synthesis and properties of a cation exchange membrane with bifunctional groups prepared by pre-irradiation graft copolymerization

A new type of a cation exchange membrane named ETFE-g-poly(AA-co-SSS) with bifunctional groups was synthesized by a one-step method. Its preparation by an electron beam-induced pre-irradiation grafting method and the effects of reaction temperature, monomer concentration, pH value of the grafting solution, storage time and temperature of the irradiated poly(ethylene-alt-tetrafluoroethylene) (ETFE) films on the grafting yield were studied. A total concentration of 2 mol L⁻¹ of monomers was found to be beneficial for acrylic acid (AA) and sodium styrene sulfonate (SSS) co-grafting onto the ETFE films. Infrared spectroscopic analysis of the grafted membrane confirmed the existence of sulfonate and carboxylic acid groups. The contact angle of the grafted membrane decreased from 94.3 to 46.7° with the increase in grafting yield. The higher the grafting yield, the faster the response and recovery rate with respect to humidity. AFM images showed that the diameter of the grafted chains on the surface of ETFE membranes was about 30 nm. The voltage of the grafted membrane was stable after 100 cycles of charge–discharge; thus, the prepared membranes have great potentials to be used as separators in secondary batteries.

Low-cost and anti-degradation ion-exchange membrane named ETFE-g-poly(AA-co-SSS) with bifunctional groups prepared by the pre-irradiation grafting method.     

The green synthesis of a palm empty fruit bunch-derived sulfonated carbon acid catalyst and its performance for cassava peel starch hydrolysis

A sulfonated carbon acid catalyst (C–SO₃H) was successfully generated from palm empty fruit bunch (PEFB) carbon via hydrothermal sulfonation via the addition of hydroxyethylsulfonic acid and citric acid. The C–SO₃H catalyst was identified as containing 1.75 mmol g⁻¹ of acid and 40.2% sulphur. The surface morphology of C–SO₃H shows pores on its surface and the crystalline index (CrI) of PEFB was decreased to 63.8% due to the change structure as it became carbon. The surface area of the carbon was increased significantly from 11.5 to 239.65 m² g⁻¹ after sulfonation via hydrothermal treatment. The identification of –SO₃H, COOH and –OH functional groups was achieved using Fourier-transform infrared spectroscopy. The optimal catalytic activity of C–SO₃H was achieved via hydrolysis reaction with a yield of 60.4% of total reducing sugar (TRS) using concentrations of 5% (w/v) of both C–SO₃H and cassava peel starch at 100 °C for 1 h. The stability of C–SO₃H shows good performance over five repeated uses, making it a good potential candidate as a green and sulfonated solid acid catalyst for use in a wide range of applications.

A sulfonated carbon acid catalyst (C–SO₃H) was successfully generated from palm empty fruit bunch (PEFB) carbon via hydrothermal sulfonation via the addition of hydroxyethylsulfonic acid and citric acid.     

Amino-functionalized magnetic chitosan beads to enhance immobilization of potassium copper hexacyanoferrate for selective Cs+ removal and facile recovery

Potassium copper hexacyanoferrate (KCuHCF)-incorporated magnetic chitosan beads (HMC) were synthesized for both selective Cs⁺ removal in aqueous solutions and facile recovery of the spent adsorbent. To disperse and immobilize large amounts of the KCuHCF, methyl acrylate and diethylenetriamine were sequentially grafted onto the one-step synthesized magnetic chitosan beads. The additional introduction of amino functionality led to the enriched Cu²⁺ ions on the bead surface to incorporate KCuHCF into the grafting matrix. Consequently, the HMC exhibited a high Cs⁺ capacity calculated to be 136.47 mg g⁻¹ from the Langmuir model, and the equilibrium was established within 4 h. Moreover, the HMC exhibited excellent stability in a wide pH range from 4 to 11 and an outstanding Cs⁺ selectivity (>97%) in seawater (1.11 mg L⁻¹ Cs⁺). From a practical point of view, the HMC was stable during five successive adsorption cycles and easily recovered by magnets, enabling continuous operation to decontaminate a large volume of wastewater.

The magnetic chitosan beads were amino-functionalized by grafting and showed an outstanding removal performance for radioactive Cs⁺.     

A graphene oxide polymer brush based cross-linked nanocomposite proton exchange membrane for direct methanol fuel cells

Functional polymer brush modified graphene oxide (FPGO) with functional linear polysiloxane brushes was synthesized via surface precipitation polymerization (sol–gel) and chemical modification. Then, FPGO was covalently cross-linked to the sulfonated polysulfone (SPSU) matrix to obtain novel SPSU/FPGO cross-linked nanocomposite membranes. Meanwhile, SPSU/GO composite membranes and a pristine SPSU membrane were fabricated as control groups. Reduced agglomeration of the inorganic filler and better interfacial interaction, which are benefit to increase diffusion resistance of methanol and to generate continuous channels for fast proton transportation at elevated temperature, were observed in SPSU/FPGO cross-linked membranes. Moreover, the enhanced membrane stability (thermal, oxidative and dimensional stability) and good mechanical performance also guaranteed their proton conducting durability. It is noteworthy that the SPSU/FPGO-1 cross-linked membrane possesses the best comprehensive properties among all the prepared membranes and Nafion®117, it acquires the highest proton conductivity of 0.462 S cm⁻¹ at 90 °C under hydrated conditions together with a low methanol permeability of 1.71 × 10⁻⁶ cm² s⁻¹ at 30 °C. The resulting high membrane selectivity displays the great potential of the SPSU/FPGO cross-linked membrane for DMFCs application.

A novel proton exchange nanocomposite which was cross-linked by functional graphene oxide polymer brushes shows interesting and comprehensive advantages for DMFCs.     

Sulfonated SnO2 nanocatalysts via a self-propagating combustion method for esterification of palm fatty acid distillate

Biodiesel derived from palm fatty acid distillate (PFAD) was produced via catalytic esterification using sulfonated tin oxide (HSO₃⁻/SnO₂) as the superacid solid catalyst. In this work, the SnO₂ catalyst was synthesised by the self-propagating combustion (SPC) method, and activated using chlorosulfonic acid. The SPC method was able to produce nano-sized particles with homogenous size and shape that were anchored with many HSO₃⁻ ions, resulting in more exceptional acid properties that effectively esterified the PFAD feedstock into FAMEs (fatty acid methyl esters). Several studies based on metal oxide-based catalysts were also included for comparison. Under the optimised conditions of 9 : 1 (methanol-to-PFAD molar ratio), 4 wt% (catalyst loading), 100 °C (reaction temperature) and 3 h (reaction time), the FFA conversion and FAME yield were 98.9% and 93.8%, respectively. Besides, the sulfonated SnO₂-spc catalyst can be reused in up to five consecutive cycles with an acceptable esterification performance and minimal sulfur leaching. It is worth mentioning that the SPC method is a greener and simpler technique to obtain the nanocatalysts. Overall, the production of FAME from low value, cheaper, abundant, and non-edible PFAD feedstock, assisted by a non-transition metal oxide of sulfonated SnO₂ catalyst, could reduce the cost of biodiesel production.

A facile SPC method gave a superacid sulfonated tin oxide nanocatalyst for the esterification of low-cost palm fatty acid distillate into biodiesel.     

Calixarene based portable sensor for the direct assay of indiscriminate ephedrine content of weight loss herbal preparations

A novel potentiometric sensor was developed and optimized for the quantitative analysis of ephedrine in non-prescribed herbal supplements used as adjunctive therapy for weight loss. An initial optimization study aimed to reach the optimum membrane composition, sensor assembly, and experimental conditions. The study evaluated the effect of several factors on the sensor performance including different ion-exchangers, plasticizers, ionophores, membrane thicknesses, soaking solution concentrations, soaking time intervals, and pH. The optimized polyvinyl chloride membrane included tungstophosphoric acid hydrate as a cation exchanger, tricresyl phosphate as a plasticizer, and calix[8]arene as an ionophore to enhance the sensitivity and selectivity of the developed sensor. The polyvinyl chloride membrane was drop-casted over a polyaniline modified glassy carbon electrode surface to form a solid-state sensor. The proposed membrane succeeded to quantify ephedrine over a linear range of 6 × 10⁻⁶ to 1 × 10⁻² M with a LOD of 3.60 × 10⁻⁶ M, acceptable selectivity, and fast response time. The IUPAC characterization of sensor response and International Conference on Harmonization validation parameters were calculated. The method successfully determined ephedrine concentration in spiked herbal mixtures and determined labeled and undeclared ephedrine content of weight loss herbal preparations.

Calixarene based solid-state potentiometric sensor for direct assay of indiscriminate ephedrine content in weight loss herbal products.     

Novel sulfonated poly(ether ether ketone)/triphenylamine hybrid membrane for vanadium redox flow battery applications

A novel sulfonated poly(ether ether ketone)/triphenylamine hybrid membrane with various triphenylamine loadings (1%, 2% and 5%) has been successfully fabricated. Optimum triphenylamine loading was confirmed by exploring the physicochemical properties and morphology of different membranes. The hybrid membrane exhibited lower vanadium permeability than pristine SPEEK membranes due to the acid–base interaction between amine groups and sulfonated groups. Introduction of triphenylamine also improved the proton conductivity because the nitrogen atom of triphenylamine can be protonated and contribute to the proton transfer. As the result, the hybrid membrane demonstrated higher ion selectivity compared with SPEEK and Nafion115 membranes. The VRFB single cell with SPEEK/TPAM-1% membrane showed better performance compared to a Nafion115 membrane at the current density of 60 mA cm⁻². The SPEEK/TPAM hybrid membrane has great potential for VRFB application.

The novel TPAM hybrid membrane exhibited both lower vanadium permeability and higher proton conductivity than pristine SPEEK membrane.     

Effect of VIPS fabrication parameters on the removal of acetic acid by supported liquid membrane using a PES–graphene membrane support

In this study, the removal of acetic acid by supported liquid membrane (SLM) using hybrid polyethersulfone (PES)–graphene membrane prepared by vapor induced phase separation (VIPS) was investigated. The effects of graphene loading, coagulation bath temperature, air exposure time, and air humidity on the morphology, mechanical strength, porosity, and contact angle of the membrane were analyzed. The performance and stability of the hybrid membrane as a SLM support for acetic acid removal were studied. The best PES–graphene membrane support was produced at a coagulation bath temperature of 50 °C, an air exposure time of 30 s and air humidity of 80%. The fabricated membrane has a symmetrical micropore cellular structure, high porosity and high contact angle. Under specific SLM conditions, almost 95% of acetic acid was successfully removed from 10 g L⁻¹ aqueous acetic acid solution. The hybrid membrane remains stable for more than 116 h without suffering any membrane breakage during the continuous SLM process.

In this study, the removal of acetic acid by supported liquid membrane (SLM) using hybrid polyethersulfone (PES)–graphene membrane prepared by vapor induced phase separation (VIPS) was investigated.     

Anhydrous proton conductivity of electrospun phosphoric acid-doped PVP-PVDF nanofibers and composite membranes containing MOF fillers

A high-temperature proton exchange membrane was fabricated based on polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP) blend polymer nanofibers. Using electrospinning method, abundant small ionic clusters can be formed and agglomerated on membrane surface, which would facilitate the proton conductivity. To further enhance the conductivity, phosphoric acid (PA) retention as well as mechanical strength, sulfamic acid (SA)-doped metal–organic framework MIL-101 was incorporated into PVP-PVDF blend nanofiber membranes. As a result, the anhydrous proton conductivity of the composite SA/MIL101@PVP-PVDF membrane reached 0.237 S cm⁻¹ at 160 °C at a moderate acid doping level (ADL) of 12.7. The construction of long-range conducting network by electrospinning method combined with hot-pressing and the synergistic effect between PVP-PVDF, SA/MIL-101 and PA all contribute to the proton conducting behaviors of this composite membrane.

A composite SA/MIL101@PVP-PVDF membrane was fabricated via electrospinning and reached a conductivity of 0.237 S cm⁻¹ at 160 °C with a moderate acid doping level (12.7).     

Chitosan-covered liposomes as a promising drug transporter: nanoscale investigations

Liposomes are small artificial vesicles spherical shaped of 50–1000 nm in diameter. They are created from natural non-toxic phospholipids membranes. Externally, they are decorated with biocompatible polymers. Chitosan, a natural polymer, demonstrates exceptional advantages in drug delivery, in particular, as liposome cover. In this paper, Molecular Dynamics simulations (MD) are performed in the coupled NPT-NPH and NVT-NVE statistical ensembles to study the static and dynamic properties of DPPC membrane-bilayer with grafted cationic chitosan chains, with added Cl⁻ anions to neutralize the environment, using the Martini coarse-grained force-field. From the NPT-NPH MD simulations we found a chitosan layer L_DM ranging from 3.2 to 6.6 nm for graft chains of a degree of polymerization n_p = 45 and different grafting molar fractions X_p = 0.005, X_p = 0.014 and X_p = 0.1. Also, the chitosan chains showed three essential grafting regimes: mushroom, critic, and brush depending on X_p. The DPPC bilayer thickness D_B and the area per lipid A_l increased proportionally to X_p. From the NVT-NVE MD simulations, the analysis of the radial distribution function showed that the increase of X_p gives a more close-packed and rigid liposome. The analysis of the mean square displacement revealed that the diffusion of lipids is anomalous. In contrast, the diffusion of chitosan chains showed a normal diffusion, just after 100 ps. The diffusion regime of ions is found to be normal and independent of time. For the three identified regimes, the chitosan showed a tendency to adhere to the membrane surface and therefore affect the properties of the liposomal membrane.

In this paper, we studied the graft chitosan conformation and its influence on the liposome membrane structure and dynamics as a function of the grafting molar-fraction.     

Durable flame retardant polyacrylonitrile fabric via UV-induced grafting polymerization and surface chemical modification

To improve the flame retardancy of polyacrylonitrile (PAN) fabric, glycidyl methacrylate (GMA) was firstly grafted onto the surface of PAN fabric. Then, the GMA grafted PAN fabric (PAN-g-GMA) was chemically modified with hydrazine hydrate and phosphorus acid in sequence to obtain ammoniated PAN-g-GMA fabric (Am-PAN-g-GMA) and flame retardant PAN fabric (FR-PAN), respectively. The structures, thermal properties and combustion characteristics of the samples were researched in detail. The results indicate that the fire retardant PAN fabric has good char-forming ability. Cone calorimeter tests show that the total heat release (THR) of FR-PAN declines by 38.4%, while the peak heat release rate (PHRR) of FR-PAN decreases by 60.2%. Moreover, the total smoke production (TSP) and the peak smoke production rate (PSPR) of FR-PAN dropped from 1.5 m² and 0.06 m² s⁻¹ for the control sample to 0.4 m² and 0.01 m² s⁻¹, respectively, indicating excellent smoke repression performance. The LOI value of FR-PAN fabric was 29.3% after 30 washing cycles showing good washing resistance and excellent flame retardant durability.

A durable flame retardant PAN fabric was prepared via UV-induced grafting polymerization and chemical modification. The flame retardant performance of the fabric was greatly improved.     

Lead (Pb2+) sorptive removal using chitosan-modified biochar: batch and fixed-bed studies

Chitosan-Modified fast pyrolysis BioChar (CMBC) was used to remove Pb²⁺ from water. CMBC was made by mixing pine wood biochar with a 2% aqueous acetic acid chitosan (85% deacylated chitin) solution followed by treatment with NaOH. The characterizations of both CMBC and Non-Modified BioChar (NMBC) were done using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), scanning electron microscopy (SEM), surface area measurements (S_BET), elemental analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and ζ-potential measurements. Elemental analysis indicated that chitosan accounts for about 25% weight of the CMBC. The Langmuir maximum adsorption capacity of CMBC at pH 5 was 134 mg g⁻¹versus 48.2 mg g⁻¹ for NMBC at 318 K. CMBC column adsorption studies resulted in a capacity of 5.8 mg g⁻¹ (Pb²⁺ conc. 150 mg L⁻¹; pH 5; column dia 1.0 cm; column length 20 cm; bed height 5.0 cm; flow rate 2.5 mL min⁻¹). CMBC removed more Pb²⁺ than NMBC suggesting that modification with chitosan generates amine groups on the biochar surface which enhance Pb²⁺ adsorption. The modes of Pb²⁺ adsorption on CMBC were studied by comparing DRIFTS and X-ray photoelectron spectroscopy spectra before and after Pb²⁺ adsorption.

Batch and fixed-bed column studies for the removal of lead (Pb²⁺) from aqueous solution by chitosan-modified pinewood biochar.     

Novel ionic polymer–metal composite actuator based on sulfonated poly(1,4-phenylene ether-ether-sulfone) and polyvinylidene fluoride/sulfonated graphene oxide

In the present work, sulfonated graphene oxide and sulfonated poly(1,4-phenylene ether-ether-sulfone) were blended with polyvinylidene fluoride to create a novel ionic polymer–metal composite actuator with enhanced performance. An ionic polymer–metal composite membrane in the protonated form was prepared by casting a composite blend of sulfonated poly(1,4-phenylene ether-ether-sulfone), polyvinylidene fluoride and sulfonated graphene oxide onto a plating of platinum metal as the electrode. The degree of sulfonation of poly(1,4-phenylene ether-ether-sulfone) was characterized using ion-exchange capacity measurements. Energy dispersive X-ray and transmittance electron microscopy analyses were carried out to analyze the chemical composition and detailed structure. Deposition of the platinum electrode and the surface morphology of the proposed ionic polymer–metal composite actuator were assessed using scanning electron microscopy analysis. The electrical properties were measured using cyclic voltammetry, linear sweep voltammetry and proton conductivity. These measurements confirmed the better actuation performance of the fabricated ionic polymer–metal composite actuator compared to other expensive ionic polymer-based actuators, in terms of its high ion-exchange capacity, good proton conductivity, high current density and large bending deflection. The robust, flexible and mechanically strong membrane actuator, fabricated via the synergistic combination of sulfonated poly(1,4-phenylene ether-ether-sulfone), polyvinylidene fluoride and sulfonated graphene oxide, has considerable potential as an actuator material for robotic, bio-mimetic and other applications.

In the present work, sulfonated graphene oxide and sulfonated poly(1,4-phenylene ether-ether-sulfone) were blended with polyvinylidene fluoride to create a novel ionic polymer–metal composite actuator with enhanced performance.     

Superoleophobic micro-nanostructure surface formation of PVDF membranes by tannin and a condensed silane coupling agent

A tannin-based hybrid coating was coated on the PVDF membrane surface through a simple one-step co-deposition of tannin and KH550. A micro/nano hierarchical structure was formed on the PVDF membrane surface through hydrolysis/condensation of KH550 and Michael addition reaction between oxidized tannin and an amino group revealed by the field-emission scanning electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy, which established a harsh surface. Abundant hydrophilic groups and high surface roughness endowed the modified membranes with high hydrophilicity and underwater superoleophobicity. The modified PVDF membranes possess excellent oil/water separation and antifouling performance due to the underwater superoleophobicity. Moreover, the modified membrane exhibited outstanding stability.

A tannin-based hybrid coating was coated on the PVDF membrane surface through a simple one-step co-deposition of tannin and KH550.

The oil/water separation process, especially for separating emulsified oil-in-water emulsions, has become an increasingly important part of water treatment as more and more oily wastewater has been produced from industrial processing and oil spills.^1–5 Among many conventional methods, polymer-dominated filtration technology has been widely applied to water treatment for its simple operation, low cost and easy control of pores.^6–10 Polyvinylidene fluoride (PVDF) is a promising membrane material owing to its excellent mechanical and chemical properties. However, the intrinsic hydrophobicity makes PVDF easily fouled during treatment of aqueous solutions containing organic matters, decreasing its service life, which has limited its application in the field of oil/water separation.^11–14 Thus, it is of great importance to improve the hydrophilicity of PVDF porous membranes for highly efficient and eco-friendly separation of oily wastewater.The concept of bio-adhesion stems from mussel adhesion protein (MAP) with broad adhesion potency. MAP rich in catechol, amino acids and 3,4-dihydroxyphenylalanine (DOPA) allows mussels to adhere to a variety of materials. Dopamine containing amine and catechol groups exhibits a molecular structure similar to that of DOPA, and has become a focus of attention as a novel bioadhesive coating.^15–19 Low-cost tannin, which has analogous polyphenols units with dopamine, has also been reported to have excellent interfacial properties and could be coated on a variety of substrates including hydrophobic polymer materials.^20–24 In our previous work,²⁵ we demonstrated that the plant tannin layer can strongly construct on the surface of the PVDF membrane and effectively improve the hydrophilicity and filtration performance of PVDF membrane. In this work, in order to further enhance the underwater superoleophobicity of PVDF membrane for oil-in-water emulsion separation, we constructed a tannin-based hybrid coating on the PVDF membrane surface through a simple one step co-deposition of tannin and (3-aminopropyl) triethoxy-silane (KH550) which is a silane coupling agent containing amino group. On the one hand, hybrid coating can coat on the PVDF membrane surface because of the existence of polyphenols tannin, on the other hand, tannin and KH550 can bond together by means of Michael addition reaction between oxidized tannin and amino of KH550, at the same time, hydrolysis and condensation of KH550 can form crosslinking agents, which can greatly enhance the adhesive ability of coating layer.The modified membranes were fabricated through a simple one step dip-coating method in plant tannin and KH550 hybrid solution in the context of a weak alkaline solution (pH 7.8) and contacting with atmosphere. Fig. 1 shows the co-deposition pathway. The phenolic group of tannin is oxidized to benzoquinone under weakly alkaline conditions and undergoes a Michael addition reaction with the amino group in KH550.^26–28 The alkoxy group of the silane coupling agent has a hydrogen bond with the phenolic hydroxyl group of the tannin after hydrolysis, and will condense with itself to form a silicon-containing oligomer. Tannin and KH550 form a strong coating on the membrane surface through this complex cross-linking structure. The silicon-containing oligomer produced by KH550 changed the surface morphology and roughness of the membrane surface, and the wettability of the membrane surface was significantly improved.Open in a separate windowFig. 1The co-deposition pathway of tannin and KH550 for membrane modification.The surface morphology of the pristine membrane (TK-0) and modified membranes with different adding contents of KH550 were observed via FESEM and AFM, which can be seen in the Fig. 2a and b. As indicated by the FESEM images in Fig. 2a, some spherical particles have formed on the all modified membranes through co-deposition process, but the size and number of particles are greatly different among various membranes. With increasing the content of KH550, the particle size and number sharply increase. Moreover, it can be seen that the top surface of TKN-0.6 is almost completely coated by the particles, which shows a micro/nano hierarchical structure. These phenomena can be rationalized by the formation of hybrid oligomer. The more the content of KH550 in the co-deposition process, the more and bigger hybrid oligomer will be formed through hydrolysis and condensation reaction of KH550. AFM images are shown in Fig. 2b, the roughness obviously increased with extending the content of KH550. This result corresponds with the FESEM and indicates the formation of micro/nano structure. Interestingly, the roughness of TK-0 are higher than TKN-0.15, it can be explained that the main part of the coating layer on the TKN-0.15 are tannin due to the less adding content of KH550, which can form a homogeneous coating with a few particles. In contrast to polydopamine, our modified membranes show a slight change in color (Fig. S1^†), which indicates that this novel process has more widely application.Open in a separate windowFig. 2Characterizations of morphology and chemical composition of the different PVDF membranes. (a) FESEM images of the membrane top surface. (b) AFM images of the membrane top surface. (c) XPS spectra and atomic ratio of the membrane surface.The deposition ratio (DR) can directly reflect the amount of coating layer which deposited on the membranes. As increasing of the content of KH550, the DR of the modified membranes are increasing linearly, which demonstrates that more hybrid oligomer was formed and anchored on the membrane surface (Fig. S2^†). The surface chemical elements and groups are critical for wettability of materials. The XPS spectrum of the membranes were shown in Fig. 2c and Table S1,^† and the elemental compositions of different modified membranes were determined. The presence of oxygen, nitrogen, and silicon elements can be confirmed in the XPS spectrum, wherein the oxygen element is derived from tannin and KH550, and the nitrogen and silicon elements are derived only from PVP. Therefore, the Si/O, Si/C and O/C ratio can illustrate the content of tannin and KH550 applied to the surface of the membrane to a certain extent. The atomic ratio about Si/O, Si/C and O/C are all raising with the increase of KH550, this shows that more silicon-containing oligomers are fixed on the membrane surface. These indicate that tannin and KH550 have co-deposited on membrane surface successfully. This result is also confirmed by ATR-FTIR measurement (Fig. S3^†). Four notably absorption peaks at 1608 cm⁻¹, 1499 cm⁻¹, 1323 cm⁻¹, and 1098 cm⁻¹ were detected, which assigned to skeletal vibration of aromatic rings, N–H bending vibrations, C–N stretching vibration and Si–O–Si stretching vibration, respectively. These imply that a lot of hydrophilic groups have coated on the hydrophobic PVDF membrane surface, which can significantly improve its hydrophilicity.As an interfacial issue, membrane surface energy and surface roughness can simultaneously affect the wettability.^29–32 According to Wenzel''s model, roughness can increase the actual contact area between droplet and substrate, thus improving the hydrophilicity and total surface energy of hydrophilic substrate.^33,34 In this work, the hybrid coating layer contains abundant hydrophilic groups, thus, the hydrophilicity of modified PVDF membranes have improved greatly. As shown in Fig. 3a, the water contact angle (WCA) of modified membranes sharply decreased comparing with TK-0, and the minimum WCA value was occurred to TKN-0.3 rather than TKN-0.6, which indicates that this modified process exists a threshold WCA with the increase of KH550. The water droplet permeation of modified membrane can be observed in Fig. 3b, the WCA rapidly decrease to 0° within 5 s, which exhibit much high hydrophilicity. Fig. 3b shows the dynamic underwater oil-adhesion property of TKN-0.6. An extremely low oil-adhesion performance was detected, it can be explained that a water barrier has formed on the modified PVDF membrane surface under water due to the high hydrophilicity, which can greatly reject the oil droplets and effectively decrease fouling. The underwater oil contact angle (OCA) directly revealed the excellent oleophobicity of our modified membranes as shown in Fig. 3c and d. The underwater chloroform contact angle of different membranes are raising with the increase of KH550. The value of TK-0 is 127°, but the modified membranes are all higher than 150°, the value of TKN-0.6 is 163° which show a outstanding oleophobicity. Therefore, underwater different oils (dichloromethane, toluene, petroleum ether and diesel) contact angle of TKN-0.6 were measured to further characterize the oil repelling performance. It can be seen that the OCA of four oils are 161°, 162°, 163° and 156° respectively, indicating a underwater superoleophobic property which is critical to oil/water separation. This underwater superoleophobicity is caused by the cooperation of high hydrophilicity and roughness of tannin and KH550 hybrid coating.Open in a separate windowFig. 3Characterizations of hydrophilicity and oleophobicity of the different PVDF membranes. (a) Water contact angle of membrane surface. (b) Water droplet permeation and dynamic underwater oil-adhesion measurements. (c) Underwater chloroform contact angle of various membranes. (d) Different oils underwater contact angle of TKN-0.6.The pure water flux, emulsion filtration flux and flux recovery ratio (FRR) were measured by a vacuum driven filtration system (Fig. S4^†) to evaluate filtration performance, as shown in Fig. 4. The pristine membrane and modified membranes were all wetted before measurement to avoid the compaction effect. The pure water flux was shown in Fig. 4a, the flux value of pristine membrane is 14 133 L m⁻² h⁻¹, however, the modified membranes are 18 982 L m⁻² h⁻¹, 19 863 L m⁻² h⁻¹ and 18 480 L m⁻² h⁻¹ respectively, which are much higher than pristine membrane. This result is triggered by the excellent hydrophilicity of coating layer on modified membranes. Meanwhile, the slightly different flux values among the modified membranes can be detected, which result in the blocking of micro/nano particles. The emulsion filtration performance is shown in Fig. 4b, the prepared emulsion had an average particle diameter of 487 nm as measured by a Malvern particle size analyzer. The flux value of pristine membrane is 782 L m⁻² h⁻¹, however, all the modified membranes exhibit high emulsion filtration flux, as the flux of 2512 L m⁻² h⁻¹, 4178 L m⁻² h⁻¹ and 4632 L m⁻² h⁻¹ for TKN-0.15, TKN-0.3 and TKN-0.6 respectively were obtained. This indicates the great emulsion separation efficiency of modified membranes. After filtration, the toluene-in-water emulsion is transformed into transparent exhibited by the inset images. The underwater superoleophobic property of modified membranes is the main reason for this outstanding filtration performance. The antifouling property was characterized by flux recovery ratio (FRR) shown in Fig. 4c. It can be seen that the FRR value of modified membranes are all higher than the pristine membrane (82%) and all more than 98%, even reaches 100% for TKN-0.3 and TKN-0.6. This excellent antifouling property should give the credit to the superoleophobic property which is aroused by the high hydrophilicity and roughness of tannin and KH550 hybrid coating. To measure the stability of modified membranes, a water rinsing experiment was taken and underwater chloroform contact angle was measured to evaluate the stability of underwater superoleophobic property of modified membrane (Fig. 5a). It is found that the underwater chloroform contact angle of TKN-0.3 stabilized at 157–160° during seven days rinsing, which disclosed the outstanding stability of hybrid coating coated PVDF membrane. As shown in Fig. 5b, the emulsion flux declines gradually with the increase of time due to the fouling of the membrane. The emulsion flux was almost completely recovered by washing with pure water after 1 hour of emulsion filtration, indicating the stability of the TKN-0.3 membrane.Open in a separate windowFig. 4Filtration performance of the different membranes. (a) Pure water flux of the wetted PVDF membranes. (b) Flux of toluene-in-water emulsion, inset images is the emulsion before (left) and after (right) filtration. (c) Flux recovery ratio after the emulsion separation.Open in a separate windowFig. 5(a) The underwater chloroform contact angle of TKN-0.3 membrane during the pure water rinsing test for 7 days. (b) Emulsion flux and flux recovery over three cycles.In summary, a hydrophilic and underwater superoleophobic PVDF membrane was fabricated through a simple one step co-deposition method, the low cost tannin and commercial KH550 hybrid coating layer was coated on PVDF membrane surface successfully. A micro/nano hierarchical structure, which can be adjusted by the adding content of KH550, was observed on the modified membrane surface. It can increase the roughness of membrane surface and obtain an excellent hydrophilic and underwater superoleophobic property. The underwater superoleophobicity endows the membrane with a superior antifouling property (underwater oil contact angle reaches 160°, FRR reaches 100%) and high oil/water separation efficiency (the emulsion flux reaches 4600 L m⁻² h⁻¹). The great performance indicates that this strategy is promising for practical applications in the field of treating oily wastewater.