Showing papers in "Reactive & Functional Polymers in 2019"

Synthesis and performance characterization of poly(vinyl alcohol)-xanthan gum composite hydrogel

Abstract: Poly(vinyl alcohol) (PVA)-xanthan gum (XG) hydrogel, which possesses good reusable absorption properties, has been prepared by the freezing–thawing method. Hydrogels prepared with different ratios compositions are characterized using Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM), and examined in terms of their swelling behavior, mechanical, rheological and adsorption properties. The results show that a shift in the major signals of FTIR for OH absorption, and with varied intensities in the FTIR spectra andmore and more wrinkles observed in SEM indicated cross-linked interaction by the polymers. All the features of the PVA-XG hydrogel are closely related to its rheological properties. The presence of XG visibly improves the swelling ratio of PVA-XG and reduces the compression properties of PVA-XG due to the formation of hydrogen bonds between the PVA and XG. PVA-XG-4 had the best adsorption of methylene blue (MB) dye, such enhancement in adsorption can be attributed to strong electrostatic attraction between XG and MB. The adsorption conformed to the second-order kinetic model and the adsorption process conformed to the Langmuir isotherm model. In addition, PVA-XG-4 exhibits a promising cycling absorption performance. The 1st and 5th cycle of dye removal for PVA-XG-4 reached to 92 and 80%, respectively. Provides basis for application in water treatment.

Polymer inclusion membranes based on CTA/PBAT blend containing Aliquat 336 as extractant for removal of Cr(VI): Efficiency, stability and selectivity

Abstract: Cellulose triacetate (CTA) and poly(butylene adipate-co-terephthalate) (PBAT)-based polymer inclusion membranes (PIMs) containing ionic liquid (tricaprylmethylammonium chloride (Aliquat 336)) as the carrier extractant were obtained for the facilitated and selective transport of Cr(VI) ions. The composition of PIMs was optimized in terms of the CTA/PBAT ratio. The obtained membranes were investigated using different techniques in order to show the influence of the membrane composition and the ionic liquid presence on the PIM resulting properties. The infrared analysis confirmed the presence of the intermolecular interactions of the hydroxyl groups of CTA with the carboxyl groups of PBAT and of the negatively charged carboxyl groups of CTA with the positively charged ammonium groups of Aliquat 336. The water contact angle measurements highlighted that the Aliquat 336 and PBAT presence modified the membrane hydrophobic/hydrophilic character. Moreover, it was shown that PIM containing the equivalent content of CTA and PBAT (35/35 wt%/wt%) with 30 wt% of Aliquat 336 revealed the optimized composition and was used for the Cr(VI) ions transport measurements. It was found that this PIM transported >99% of Cr(VI) in only 6 h and accumulated 120 h).

Improved corrosion protection of waterborne epoxy/graphene coating by combining non-covalent and covalent bonds

Abstract: High-efficient anti-corrosive epoxy coating, containing homogeneously dispersive graphene (Gr), has been achieved by combining non-covalent and covalent bonds. Tannic acid (TA) has been used as intercalators to disperse Gr in water via π − π non-covalent bond to form Gr-TA hybrids. Consequently, γ-(2,3-epoxypropoxy)propytrimethoxysilane was used to modify the surface of Gr-TA via covalent bond to enhance the interactions between Gr-TA and epoxy. The corrosion resistance properties of the composite Gr-TA/epoxy coatings were tested by electrochemical experiment and salt spray test. The results showed that anti-corrosion properties of Gr-TA-KH560/epoxy composite coatings were hugely enhanced compared with those of the Gr-TA/epoxy and pure epoxy.

Microfluidics and hydrogel: A powerful combination

Abstract: Microfluidics is a very useful and promising technology that allowed engineering a huge variety of developments in several fields, such as biology, biomedical engineering, biotechnology, biochemistry, medicine and tissue engineering, among others. Moreover, when microfluidic is combined with hydrogel, the possibilities seem to be limitless. However, it is not found in the bibliography any report that shows the wide range of developments and application fields of this combination. In this review, the bibliography is explored by looking for these new systems that, combining microfluidics and hydrogels, substantially contribute to the state of the art. Seven large application fields are identified -from 649 papers reviewed-: 1) cell culture (out of the scope of this review), 2) biosensors, 3) gradient generator microdevices (GGMD), 4) active elements of hydrogel embedded into microfluidic devices, 5) separation devices, 6) models and 7) other uses. Most of these fields are presented and discussed in detail, the great benefits of the combination are highlighted and perspectives on future directions are exposed.

Co-encapsulation of enzyme and tricyanofuran hydrazone into alginate microcapsules incorporated onto cotton fabric as a biosensor for colorimetric recognition of urea

Abstract: One of the major consequences resulting from chronic kidney failure is a considerable increase in the level of metabolism waste products in blood, including urea that is naturally released by kidney. Herein, we report a novel practical colorimetric test gauze strip for an efficient recognition of urea in serum was developed. The prepared testing gauze strip was based on a composite composed of urease enzyme co-encapsulated in alginate biopolymer, supported on cotton gauze assay, with artificial tricyanofuran hydrazone (TCFH) receptor sites. A cross-linked calcium alginate microcapules containing tricyanofuran hydrazone molecules and urease enzyme, were successfully prepared and employed on cotton fibers creating a colorimetric cotton strip to act as a color changeable sensor for determining urea. The readout limit achieved for urea was as low as ~250 ppm at room temperature and atmospheric pressure. The sensor responded linearly relying on the urea concentration in the range from 0.1 to 250 ppm. The chromogenic cotton platform response depended on the acid-base characteristic effects of the tricyanofuran hydrazone probe. The protonated form of tricyanofuran hydrazone molecules immobilized within the alginate microcapsules (1.7–12.9 μm) were in a microenvironment demonstrating a light yellow color. When binding to ammonia produced by urease/urea reaction, the tricyanofuran hydrazone spectroscopic probe was deprotonated and exhibited higher absorption wavelength and a purple color. The simple fabrication and abovementioned characteristics of such naked-eye colorimetric cotton gauze sensor are such that they should be applicable for monitoring of urea. A thin alginate microcapsules layer was created on the surface of cotton strip using dip-coating technique. We studied the distribution of the colorimetric cross-linked alginate microcapsules onto cotton strip. Its distribution was investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) as well as Fourier-transform infrared spectroscopic (FT-IR) analysis. Colorimetric measurements of the solid state cotton gauze were applied to monitor the color changes.

Fabrication and characterization of microwave assisted carboxymethyl cellulose-gelatin silver nanoparticles imbibed hydrogel: Its evaluation as dye degradation

Abstract: The hybrid hydrogel of carboxymethyl cellulose (CMC) and gelatin was synthesized by grafting of poly(acrylic acid) chains in the presence of ammonium persulphate (APS) as initiator and N, N′–methylenebisacrylamide (MBA) as cross-linker in aqueous medium using microwave irradiation method. The hydrogel showed swelling ratio (SR) of 80 g/g at pH 10.0. FTIR of hydrogel confirmed the interaction of CMC and gelatin through cross-linker MBA to form a three-dimensional network. SEM studies further confirmed the three dimensional cross-linked porous structure of synthesized hydrogel. The addition of gelatin to CMC modified the network architecture and contributed to improved mechanical and thermal properties. The characteristic surface plasmon resonance (SPR) of nanosilver was observed at 414 nm. TEM images showed the formation of spherical nanoparticles with mean particle size of 12 nm and zeta potential value is +34.12 mV, indicated the good stability of silver nanoparticles. XRD and SAED pattern agreed with fcc crystalline structure of silver nanoparticles within porous network. The silver nanoparticles loaded hybrid hydrogel exhibited a promising catalytic activity for degradation of congo-red and rhodamine B dyes.

Novel polyphenylsulfone (PPSU)/nano tin oxide (SnO2) mixed matrix ultrafiltration hollow fiber membranes: Fabrication, characterization and toxic dyes removal from aqueous solutions

Abstract: Novel polyphenylsulfone (PPSU)/nano tin oxide (SnO2) mixed matrix hollow fiber membranes (HFMs) were fabricated by dry-wet spinning via phase separation method. In the current research, reported the contrast between neat PPSU membrane and nanocomposite membranes (PPSU/SnO2), to determine the toxic reactive dyes namely, reactive black-5 (RB-5) and reactive orange-16 (RO-16) removal ability from the aqueous media. Scanning electron microscopy (SEM) was used to observe the HFMs cross-sectional morphological changes and surface roughness parameters of membranes were analyzed using atomic force microscopy (AFM). The surface wettability ability of HFMs was examined with a contact angle, water uptake, and porosity measurements. The cross-flow filter unit was engaged to quantify the water permeability, anti-fouling ability as well as the dye rejection ability of fabricated membranes. With increasing the SnO2 NPs wt% in PPSU polymer matrix the membrane performance was enhanced continuously, it became evident that the incorporated SnO2 NPs plays main role in membrane performance. Added, water-soluble poly (vinylpyrrolidone) (PVP) can also impact the pore morphology in membranes. At the end, PS-3 membrane exhibited lower contact angle (63.7 0), higher water uptake (74.8%), porosity (84.1%), pure water flux 362.9 L/m2 h, and high potential for dyes rejection application, of about >94% for RB-5, and >73% for RO-16 dye, respectively. From the preliminary results, it can be stated that the usage of SnO2 NPs in membrane technology become effective towards wastewater treatment.

Evaluation of bioactive compounds-loaded chitosan films as a novel and potential diabetic wound dressing material

Abstract: Delayed wound healing is a major complication of diabetes and the medical treatment of such wounds still remains a challenge. Among the modern wound dressings, film dressings are considered to be one of the major advances in wound management. In the current study, the feasibility of using a previously developed and optimized bioactive compounds-loaded chitosan film formulation as a functional wound dressing material for diabetic wounds was investigated. The antioxidant capacity, as well as the effect of the chitosan films on cell viability was assessed in vitro. Furthermore, the in vivo performance of the films was further evaluated, by using a streptozotocin-induced diabetic rat model. The chitosan film formulation provided a beneficial moist wound environment, reducing the risk of dehydration and favouring the closure of the wounds. Also, it exhibited good antioxidant activity, as well as a proliferative effect and adequate biocompatibility. The in vivo evaluation of the bioactive compounds-loaded chitosan film formulation confirmed that the biofilm stimulated wound contraction and accelerated the wound healing process. The results strongly support that the above mentioned chitosan film seems to be a promising formulation, as well as a potential and novel biomaterial used for wound healing applications.

Dialdehyde carboxymethyl cellulose cross-linked chitosan for the recovery of palladium and platinum from aqueous solution

Abstract: Platinum (Pt) and palladium (Pd) have widespread applications, such as in catalysts, jewelry, fuel cells, and electronics because of their favorable physical and chemical properties. Recovery of Pt and Pd from secondary sources is of great concern due to the increased market demand and limitation of the natural reserves of these precious metals. The aim of this research is to achieve recovery of Pt and Pd ions from dilute aqueous solution using dialdehyde of carboxymethyl cellulose (DCMC) crosslinked chitosan (Ch-DCMC). The DCMC was prepared by periodate oxidation of carboxymethyl cellulose (CMC). Both the DCMC and Ch-DCMC were characterized before and after Pt or Pd adsorption using Fourier-transformed infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). The effect of cross-linking ratios of chitosan and DCMC (1:1, 1:0.8, 1:0.5, 1:0.25 and 1:0.1) on the Pt and Pd recovery was studied. The optimal cross-linking ratio was found to be 1:0.25 (chitosan: DCMC) with maximum adsorption capacity of 80.8 mg/g Pt and 89.4 mg/g Pd. High selectivity for Pt and Pd compared to base metals and common anions was achieved.

Adsorption of Hg(II) ions by PAMAM dendrimers modified attapulgite composites

Abstract: This research focused on developing a series of (G1.0, G2.0, G3.0 and G4.0) PAMAM dendrimers modified attapulgite (ATP) sorbents (G1.0-G4.0 PAMAM-ATP) to remove Hg(II) from aqueous solution. The effects of several parameters including solution pH, contacting time, temperature and initial Hg(II) ion concentration were studied. Batch sorption results showed that the adsorption process was rapid and over 90% of Hg(II) was removed within 80 min at optimal pH 5.0. The adsorption capacity of PAMAM-ATP adsorbents followed the order of G2.0 > G1.0 > G3.0 > G4.0 and the maximum adsorption capacities significantly increased from 5 mg/g (raw ATP), 90 mg/g (amine modified ATP, M-ATP), 192.5 mg/g (polyacrylamine modified ATP, PAM-ATP) by previous similar studies to 200.8 mg/g (G2.0-PAMAM-ATP). Kinetics of adsorption was suitable for pseudo-second-order and controlled by chemical adsorption over a whole sorption range. The adsorption capacities increased as temperature rise from 283 to 303 K and the thermodynamics properties implied that the adsorption processes was spontaneous and endothermic. Thus, the adsorption capacities decreased when the temperature was above 303 K. The isotherm adsorption was described by Langmuir model well with monolayer behavior. A specific coordination between Hg(II) and the N, O atoms on the functional groups of PAMAM-ATP surface was determined by XPS analysis. Furthermore, the maximum adsorption capacity of the regenerated G2.0-PAMAM-ATP sorbents could still be higher than 90% after five cycles by acid treatment. The favorable adsorption capacity compared with other adsorbents exhibited that G2.0-PAMAM-ATP was an excellent renewable sorbent for Hg(II) removal.

Evaluation of antibacterial and antifouling properties of silver-loaded GO polysulfone nanocomposite membrane against Escherichia coli, Staphylococcus aureus, and BSA protein

Abstract: Herein, the silver-loaded graphene oxide (GO-Ag) was synthesized and used as a nanoadditive to develop the antimicrobial and antifouling polysulfone (PSF) nanocomposite membrane. The antimicrobial property of the prepared membranes was tested against Escherichia coli the representative gram-negative bacteria, and Staphylococcus aureus the gram-positive bacteria. The antifouling characteristic of the membranes was studied by ultrafiltration of bovine serum albumin (BSA) a model protein foulant. The fouling mechanisms were investigated by Hermia's models and the analysis involved fitting the volumetric flux decline experimental data to models. The results revealed that GO sheets were well decorated with spherical Ag of an average ~5 nm diameter. The Ag was dispersed well throughout the outer surface of GO sheets. The antimicrobial results showed that adding GO-Ag nanoadditive into a PSF membrane inhibited the attachment, colonization, and biofilm formation of the microbial species. The fitting of experimental data showed that the all fouling mechanisms were present during the ultrafiltration for PSF membrane using BSA protein but the standard blocking and cake formation mechanisms (R2 ≥ 0.98) dominate the UF processes. The all R2 values (0.70–0.77) of PSF/GO-Ag membrane indicate that the fouling does not occur in the PSF/GO-Ag.

Carboxymethyl chitosan/carbon nanotubes mixed matrix membranes for CO2 separation

Abstract: The separation of CO2 using membranes has grabbed vast attention of researchers in the recent years. In this study, a thermally stable carboxymethyl chitosan (CMC)/multiwalled carbon nanotubes (CNTs) mixed matrix membrane (MMM) has been proposed for separation of CO2 from CO2/N2 gas mixture. Herein, the amine groups present in CMC serve as CO2 carrier and CNTs provide alternate pathway to the gas molecules. Various spectroscopic and microscopic analyses have been performed to confirm the successful wrapping of CNTs. Further, the prepared mixed matrix membranes were characterized using field emission scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and dynamic mechanical analyzer. The wrapping of CNT improves the dispersion of CNT in CMC matrix. The moisture holding ability of the membranes which is essential for the facilitated transport reaction has been measured at different humid conditions. The CMC/CNTs MMM exhibited CO2 permeance and CO2/N2 selectivity of 43 GPU and 45, respectively, at sweep/feed water supply ratio of 3 and at 80 °C temperature.

Selective adsorption of cationic dyes from colored noxious effluent using a novel N-tert-butylmaleamic acid based hydrogels

Abstract: The present research offers an innovative cyclic approach to cleaning colored water of toxic dyes due to the increased need for pure and safe water. Novel anionic hydrogels were fabricated via free radical copolymerization method in the presence of acrylamide or 2-hydroxyethyl methacrylate as neutral comonomer and N-tert-butylmaleimic acid as anionic monomer with the addition of N , N ′-methylenebisacrylamide as cross-linker. Hydrogels were examined for morphology and chemical structure using SEM and FTIR analyses. The swelling and adsorption behavior of the hydrogels with different molar ratios were examined. The parameters affecting the adsorption of the model dyes of CV and MB onto the hydrogel were investigated such as initial concentration of dye, various comonomer ratios, dose of hydrogel, and temperature. The adsorption behavior was consistent with the Langmuir isotherm model. Also, the thermodynamic analysis and Dubinin-Radushkevich isotherm model revealed that the adsorption of the dyes onto hydrogels was applicable in a wide temperature range as well as with physical and weak chemical interactions. TBMAC-based hydrogels were found to be a cost-effective prospective candidate with great regeneration efficiency and selectivity to be used as an adsorbent to effectively remove hazardous dyes from industrial waste.

Synthesis and characterization of cellulose based adsorbents for removal of Ni(II), Cu(II) and Pb(II) ions from aqueous solutions

Abstract: Functional copolymers were prepared by graft polymerization of the cellulose extracted from agricultural residue rice husk thus represent a class of highly efficient, eco-friendly and biodegradable adsorbents for water purification applications. Functionalized grafted copolymers of cellulose with N-isopropylacrylamide (NIPAM) and comonomer acrylic acid (AAc) were synthesized by free radical grafting. To ascertain the grafting, cellulose and its graft copolymers were analyzed through various characterizations techniques such as FESEM, XRD, FTIR, TGA/DTA/DTG and swelling properties. Sorption of Ni(II), Cu(II) and Pb(II) metal ions was studied as a function of time, temperature, pH and concentration of metal ions in solution. The order for metal ions uptake was Cell-g-NIPAM-co-AAc > Cell-g-NIPAM > ungrafted cellulose. The metal ions sorption was best fitted in the pseudo-second-order kinetic model and Langmuir adsorption isotherm model. At the optimized conditions, almost complete sorption of Pb(II) ions was observed for Cell-g-NIPAM-co-AAc copolymer, whereas 74.5% of Ni(II) and 77.5% of the Cu(II) metal ions were sorbed by Cell-g-NIPAM-co-AAc copolymer.

Synthesis and characterization of a novel inulin hydrogel crosslinked with pyromellitic dianhydride

Abstract: Smart hydrogels with pH and enzyme triggered release suitable for colon specific drug delivery were prepared by crosslinking inulin with pyromellitic dianhydride (PMDA) in a simple one pot synthesis. Back titration, Fourier transform infrared spectroscopy (FTIR) and ultraviolet spectrophotometry (UV) demonstrated that the hydrogel crosslinking reaction resulted in ester linkages and carboxylic acid groups and that the amount of the crosslinker in the hydrogel increased with increasing PMDA concentration in the crosslinking reaction. Thermal analysis and scanning electron microscopy (SEM) confirmed the chemical change by illustrating the hydrogels changed thermal properties and appearance compared to inulin. This hydrogel showed excellent swelling in water and the degree of swelling was inversely proportional to the cross-linking density, as determined using Flory-Rehner theory. Due to the presence of the carboxylic acid groups in the structure, the swelling was pH dependent, with significantly reduced swelling as acidity decreased from pH 7.4 to pH 1.2.

One-step hydrothermal synthesis of reduced graphene oxide/aspartic acid intercalated layered double hydroxide for enhancing barrier and self-healing properties of epoxy coating

Abstract: Self-healing coatings, possessing an “active healing” ability to repair physical damage and to prolong the life of coating without external intervention, are of current interest. Herein, a novel self-healing coating, by using aspartic acid intercalated layered double hydroxide (AA-LDH) @ reduced graphene oxide (RGO) as filler within epoxy has been demonstrated. The corrosion protection performance and self-healing ability of composites coatings have been investigated via electrochemical impedance spectroscopy (EIS) and salt spray test. The AA-LDH@RGO/epoxy exhibits excellent corrosion resistance owing to the high barrier properties of RGO for corrosive ions. Moreover, the epoxy loaded with AA-LDH@RGO shows outstanding self-healing performance, attributing to the release of AA from LDH on the basis of the ion exchange performance, thus leading to formation of AA-Fe-AA compounds at the coating/steel interface. The results clarified that the addition of AA-LDH@RGO increases the impedance of the epoxy resin from 6.437 × 106 to 2.112 × 109 Ω cm2, and effectively extends the epoxy coating failure time to 40 days.

Preparation and evaluation of an eco-friendly, reactive, and phytic acid-based flame retardant for wool

Abstract: Bio-derived phytic acid exhibits great potential to improve the flame retardancy of textile materials, but it has poor washing durability. In order to address this problem, an efficient, reactive, and phosphorus-containing flame retardant (FR) HPPHBTCA was synthesized using phytic acid, pentaerythritol and 1,2,3,4-butanetetracarboxylic acid, and the chemical structure of HPPHBTCA was characterized. HPPHBTCA was applied to develop FR functional wool fabric, and its FR efficiency and washing durability were evaluated. The wool fabric treated with 0.14 mol/L HPPHBTCA had self-extinguishing performance even after 20 washing cycles during the vertical burning test, presenting good FR ability and resistance to washing. The catalytic char-forming effect of HPPHBTCA contributed to the enhanced FR and smoke suppression properties of wool fabric, and the ester bonds formed between HPPHBTCA and wool fiber resulted in the good washing durability. The HPPHBTCA treatment had a negligible effect on the whiteness, tensile strength and handle of wool fabric. This study offers a novel route to prepare the eco-friendly and durable FR agent using natural and phosphorus-containing compound.

The rapid removal of iodide from aqueous solutions using a silica-based ion-exchange resin

Abstract: Rapid and efficient removal of radioactive iodine from nuclear accidents and effluent waste is significantly essential to protect the living environment and maintain human health. Here, we describe a novel silica-based quaternized poly(4-vinyl pyridine) ion-exchange resin (SiPyR-N4) used for the removal of iodide from aqueous solution. Adsorption experiments including the effect of pH, contact time, concentration of iodide, and influence of coexisting anions were investigated in detail. A series of experimental results showed that the composite possessed excellent adsorption performance towards I−. The removal efficiency at pH 6.0 exceeded 96% within 30 min in the solution with 0.1 mmol/L iodide. The adsorption kinetics and isotherms can be nicely described by the pseudo-second kinetic model and Redlich-Peterson model. The thermodynamic process was also evaluated, which indicated that the adsorption reaction was a spontaneous and exothermic process. Furthermore, XPS spectrum demonstrated that the adsorption of SiPyR-N4 was dominated by ion-exchange. Versus commercial resins, SiPyR-N4 in column experiment showed considerable application potential. SiPyR-N4 exhibited an excellent immobilization capability towards iodide at a flow rate of 8 mL/min with the maximum dynamic capacity reaching 124 mg/g, while the commercial products D201 and IRA-900 were immediately leaked under the same condition. Regeneration experiments suggested that SiPyR-N4 could be used repeatedly. In conclusion, this work presents a promising sorbent for capture and enrichment of iodide from waste water on a large scale.

Preparation of heat-resistant poly(amide-imide) films with ultralow coefficients of thermal expansion for optoelectronic application

Abstract: The novel poly(amide imide) (PAI) films derived from three kinds of amide-containing diamines and different aromatic dianhydrides were synthesized and characterized. These PAI films exhibited excellent mechanical and thermal properties due to the rigidity of main chains and existence of strong hydrogen bonding interactions. For PAI films based on the diamine N,N′-(1,4-phenylene)bis(4-aminobenzamide) (PABA), their tensile strength and modulus even exceeded 280 MPa and 10 GPa, accompanied with Tg and T5 values higher than 408 °C and 520 °C, respectively. The results indicated that CTE values of these PAI films were greatly affected by rigidity, orientation and packing of chains as well as hydrogen bonding interactions. PABA-based PAI films with the highest amide content and linearly rigid backbones had ultralow in-plane CTE values ranging from −4.6 to −0.8 ppm/°C in the temperature range of 30–300 °C combined with the largest ∆n values of 0.22–0.23, suggesting a remarkable negative correlation between CTE and ∆n. The hydrogen bonding interactions were proved to be maintained at high temperature, and it was crucial for the regulation and control of thermal expansion. These heat-resistant PAI films with high tensile strength and ultralow CTE can be used as flexible polymeric substrates for optoelectronic application.

Synergistic effect of carboxylated-MWCNTs on the performance of acrylic acid UV-grafted polyamide nanofiltration membranes

Abstract: Surface modification of a commercial polyamide nanofiltration membrane was achieved by UV induced graft polymerization of acrylic acid and incorporation of carboxylated-MWCNTs (COOH-MWCNTs). The grafting process was done under different monomer concentrations and UV exposure times. The modified membranes were characterized through scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle and zeta-potential analysis, and cross-flow filtration experiments. Changes in the surface hydrophilicity, negative charge and roughness of the modified membranes improved their permeability and fouling resistance significantly. The membrane grafted with 50 g/L acrylic acid under 5 min UV exposure showed the best filtration performance including pure water flux of 38.8 L/m2 h, salt rejections of 97.43% (Na2SO4) and 93.4% (NaCl), and flux recovery ratio (FRR) of 80.2% during bovine serum albumin (BSA) filtration. After optimizing grafting condition, different amounts of COOH-MWCNTs were dispersed in the monomer solution for embedding in the grafting layer. By adding 0.2 wt% COOH-MWCNTs to the grafting layer, a water flux improvement of around 30% was observed. But, excess loading of the COOH-MWCNTs led to compaction of the grafting layer and made it inflexible and subsequently, reduced the hydrophilicity and permeability of the membrane. Fouling tests with BSA aqueous solution showed that antifouling ability of the modified membranes was remarkably improved at all concentrations of the COOH-MWCNTs. Furthermore, salt rejection results displayed that simultaneous surface modification through grafting and COOH-MWCNTs embedding could effectively improve the nanofiltration performance of the membranes in the term of permeability, desalination and fouling resistance.

Efficient treatment of emulsified oily wastewater by using amphipathic chitosan-based flocculant

Abstract: A series of chitosan-based flocculants have been successfully synthesized by grafting poly(acrylamide) (PAM) or poly(dimethyl acryloyloxyethyl benzyl ammonium chloride) (PDBC) onto chitosan (CS) molecular chain and then characterized by using multiple techniques. The synthesized CS-based flocculants were subsequently used to flocculate the emulsified oil droplets in simulated oily wastewater under various conditions. It was found that the PDBC-grafted CS (CS-g-PDBC) showed better flocculation performance than those of CS and two other commonly used flocculants, i.e. cationic PAM (CPAM) and polyaluminum chloride (PAC). Moreover, the flocculation efficiency of CS-g-PDBC was gradually enhanced with increasing grafting ratio of PDBC, while declined after the introduction of grafted PAM chains. The cationic and hydrophobic groups of PDBC could significantly promote the adsorption of flocculant molecular chains on the negatively charged oil droplets via electrostatic attraction and hydrophobic interaction, thereby facilitating subsequent flocculation process. In addition to the adsorption bridging mechanism, zeta potentials measurements indicated that patching was the dominant mechanism under acidic and neutral conditions, while charge neutralization was the main mechanism under alkaline condition. On this basis, the chosen flocculant CS-g-PDBC was employed to treat the actual oily wastewater. Results showed that the removal ratio of both turbidity and oil exceeded 98%, suggesting that this newly synthesized CS-g-PDBC would be a promising flocculant for emulsified oily wastewater treatment.

An efficient pH sensitive hydrogel, with biocompatibility and high reusability for removal of methylene blue dye from aqueous solution

Abstract: An efficient method for the removal of methylene blue dye (MB) (cationic-dye) from aqueous solution under alkaline conditions was explored, by synthesizing and utilizing suitable pH sensitive poly (acrylic acid-co-vinylsulfonic acid) hydrogel (PAAVSA). The hydrogel was synthesized by free radical polymerization reaction using optimum ratio of the acrylic acid and vinylsulfonic acid monomers. The functional groups present in PAAVSA (i.e. COO− and SO3− groups) have strong affinity with positively charged (cationic) dye molecule, enabling absorption and trapping of cationic dyes from aqueous solution. Synthesized PAAVSA was characterized by Raman and Fourier-transform-infrared-spectroscopy techniques, while significant pH response of PAAVSA, was evident through swelling studies, indicating large swelling ratio, ~250, at higher pH values. Field-emission-scanning-electron-microscopy (FESEM) images of the respective freeze-dried PAAVSA samples swelled at different pH, exhibit distinct pH-responsive change in surface morphology of the hydrogel. PAAVSA shows significant efficiency as an adsorbent for the removal of cationic dyes (MB-dye) from aqueous solution at higher pH values (pH 7 and above), along with biocompatibility and excellent reusability, leading to potential application in waste-water treatment. The adsorption kinetics and isotherm analysis indicate that the overall adsorption process was governed by chemisorption through heterogeneous surfaces having different activation energies for adsorption of MB-dye.

Preparation and properties of ZrPA doped CMPSU cross-linked PBI based high temperature and low humidity proton exchange membranes

Abstract: Poly[4,4′-(diphenyl ether)-5,5′-bibenzimidazole] (oPBI) based high temperature proton exchange membranes are prepared by covalent cross-linking with chloromethylated polysulfone (CMPSU) and doping with zirconium phytate (ZrPA). ZrPA is synthesized as the proton conductor through a facile method from zirconyl chloride and phytic acid which is abundant and readily available. oPBI is cross-linked by CMPSU and that hydrogen bonds are formed between ZrPA and oPBI-CMPSU. The composite membranes are dense without through holes when doping with ZrPA. The composite membranes exhibit good thermal stability below 140 °C. Meanwhile, the composite membranes reveal good mechanical strength and methanol resistance. The oxidative stability is improved because of cross-linking and the doping of ZrPA. Conductivities of oPBI-CMPSU/ZrPA at different temperatures and relative humidity (RH) are investigated. At 100% RH, 50% RH and 0 RH, the conductivity of oPBI-CMPSU(20%)/ZrPA(30%) can reach 0.072 S/cm, 0.025 S/cm and 0.012 S/cm at 140 °C, respectively. Although the proton conductivity of the composite membrane was not particularly high at 100% RH, the composite membrane comparatively exhibited good proton conductivity at high temperature and at 50% RH and 0 RH.

Anionic polysaccharide stabilized nickel nanoparticles-coated bacterial cellulose as a highly efficient dip-catalyst for pollutants reduction

Abstract: This article presents the preparation and catalytic performance of carboxymethyl cellulose stabilized nickel nanoparticles (CMC-Ni) and bacterial cellulose coated with it (CMC-Ni-BC) in the colloidal form and dip-catalyst, respectively. Ni nanoparticles were prepared by mixing nickel chloride and CMC aqueous solutions with reductant followed by quick microwave heating treatment. In a separate experiment, BC was synthesized by Gluconacetobacter xylinum. After purification, the synthesized BC was coated with the prepared CMC-Ni. The CMC-Ni-BC catalytic efficiency was evaluated in anionic 2-nitrophenol (2-NP) and cationic methylene blue (MB) dye reduction reactions by sodium borohydride. While using the similar reaction conditions for the 2-NP reduction, the suspension form of CMC-Ni catalyst showed higher reduction reaction rate constant as compared to the dip-catalyst of CMC-Ni-BC. Similarly, high reaction rate constant was observed for the CMC-Ni in comparison with the CMC-Ni-BC while performing the MB reduction reaction. However, supported type Ni catalyst was easily applied in further reactions without the need of further processing which is needed in the case of colloidal form of the catalyst. Moreover, the CMC-Ni-BC catalyst was also tested in the complex situation using the binary solution of 2-NP and MB for their simultaneous reductions. As high as 7.89 min−1 of reaction rate constant was calculated for the reduction of cationic MB by anionic polysaccharide stabilized Ni nanoparticles-coated BC.

Hydrophilic and anti-fouling PVDF blend ultrafiltration membranes using polyacryloylmorpholine-based triblock copolymers as amphiphilic modifiers

Abstract: To fabricate hydrophilic and anti-fouling PVDF ultrafiltration membrane, a kind of tailor-made symmetrical amphiphilic triblock copolymer, polyacryloylmorpholine-b-poly (methyl methacrylate)-b-polyacryloylmorpholine (PACMO-b-PMMA-b-PACMO, termed as PAMA), was prepared via RAFT polymerization and employed as an in situ surface segregation modifier. FTIR, 1H NMR, and GPC were used to verify the well-defined chemical structure of PAMA. The hydrophilic PACMO segments of PAMA were enriched on the surface of membrane skin and interior pores as confirmed by ATR-FTIR, XPS, EDX, and water contact angle tests, endowing the blend membranes with outstanding hydrophilicity. The different cross-sectional and surface morphologies of the PVDF/PAMA blend membranes indicated that the introduction of PAMA modifiers could manipulate membrane structure due to their strong pore-forming ability. Compared with the pure PVDF membrane, PVDF/PAMA blend membranes showed higher permeability for water (28.1 times higher), excellent rejection for bovine serum albumin (up to 98.3%), and enhanced fouling resistance with a higher flux recovery ratio (up to 98.1%). Therefore, the approach of in situ surface segregation employed the RAFT mediated well-defined amphiphilic PAMA triblock copolymer modifiers for the preparation of anti-fouling PVDF membranes showed a great potential in water purification.

Free radical-mediated conjugation of chitosan with tannic acid: Characterization and antioxidant capacity

Abstract: Chitosan (CS) is a natural biopolymer with versatile applications. In this work, CS was functionalized with tannic acid (TA) by a free radical grafting procedure to improve its antioxidant capacity. The resulting TA-conjugated CS (TA-CS) showed a high TA equivalent content of 267.1 ± 5.4 mg TAE/g. The formation of TA-CS was verified by UV–vis, FTIR, and 1H NMR analyses. Moreover, TA-CS showed a lower thermal stability and crystallinity than CS and exhibited a good water-solubility of 15.0 ± 0.3 mg/mL. The DPPH radical scavenging activity of TA-CS reached a maximum of 91.6%, which was 6.4-fold higher than that of CS. Similar results were also observed in ABTS and hydroxyl radical scavenging assays. Moreover, TA-CS showed a higher superoxide radical scavenging activity and ferrous ion chelating activity than both TA and CS. These results suggest that conjugating with TA is an available way to enhance the antioxidant capacity of CS.

Polyhexamethylene guanidine functionalized chitosan nanofiber membrane with superior adsorption and antibacterial performances

Abstract: Although various nanofiber membranes have been developed for sewage treatment, only a few membranes possess antibacterial activities. Thus, poly-hexamethylene guanidine (PHMG) with broad-spectrum antimicrobial activity was used to functionalize the oxidized chitosan (OCS) nanofibers in solid state. Scanning electron microscope (SEM) investigation indicated that polyvinyl alcohol (PVA) introduced leads to the significantly improved spinnability. Fourier transform infrared spectroscopy (FTIR) and elemental analysis indicate that the as-proposed solid phase grafting strategy is successful and the graft ratio of PHMG is about 36.5%. As expected, PHMG grafted can significantly enhance the antibacterial activity of OCS-PVA nanofibers, but leads to the decrease of the specific surface area and total pore volume. Further adsorption analysis shows that the adsorption capacities of the PHMG-OCS-PVA fiber membrane for Cu(II) and Congo red are 57.0 mg g−1 and 183.3 mg g−1, respectively. Kinetic and isotherm model studies indicate that the pseudo second-order kinetic and Freundlich models can well match the adsorption process of Cu(II) and Congo red. The PHMG-OCS-PVA fiber membrane also shows excellent selectivity towards the separation of various anionic dyes from an aqueous dye mixture. In conclusion, the as-fabricated PHMG-OCS-PVA fiber membrane may be used as a new sewage treatment membrane with superior anti-biofouling performance.

Development of bioactive compounds-loaded chitosan films by using a QbD approach – A novel and potential wound dressing material

Abstract: In the present study, a Quality by Design (QbD) approach was applied in order to develop and optimize a chitosan film formulation loaded with bioactive compounds, intended for further use as an aid in the acceleration of wound healing. Chitosan was chosen as film forming polymer, polyethylene glycol was used as plasticizer, while polyvinyl alcohol was added to improve the bioadhesive properties of the films. Risk assessment strategy was applied to identify the critical formulation variables, which were further introduced as factors of a 3 level Box Behnken design of experiments. The optimal film formulation registered a film thickness of 0.09 mm, solubility in water of 44.9% and a high swelling degree of 2157.4%. The optimized formulation, as well as a placebo formulation without bioactive compounds proved to have a good antibacterial activity. We conclude that in the current study, the QbD approach was successfully applied in order to ensure a good understanding of the manufacturing process, as well as to optimize the formulation of chitosan films. To the best of our knowledge, this is the first time when a QbD approach has been applied in order to develop and optimize a film formulation as a novel wound dressing material.

Fabrication of a functional microgel-based hybrid nanofluid and its application in CO2 gas adsorption

Abstract: In this study, a novel hybrid nanofluid, composed of a composite core of poly(2-dimethylamino ethyl methacrylate) microgel and silica (PDMAEMA/SiO2) and a shell of polyetheramine (M2070), was fabricated via a combination of inversed emulsion polymerization, biomimetic silicification and grafting onto approach. Firstly, PDMAEMA microgel of ca. 300-nm diameter with good dispersity was prepared in water/cyclohexane system. Subsequently, walnut kernel-structured and solid spherical PDMAEMA/SiO2 composites were fabricated using swollen and contractive PDMAEMA microgel as catalytic template, respectively. Then 3-(2, 3-epoxypropoxy) propyl trimethoxysilane (KH560) modified M2070 was grafted on PDMAEMA/SiO2 composites to obtain two kinds of solvent-free PDMAEMA/SiO2@M2070 hybrid nanofluids with core@shell structure. Finally, the CO2 gas adsorption performance of these nanofluids was investigated under different CO2 pressure (0.5–4.5 MPa) at 25 °C. The results indicated that nanofluid with walnut kernel-structured core showed more excellent CO2 adsorption capacity than solid spherical one. Moreover, it still displayed good stability over ten adsorption-desorption cycles.