Highly efficient heterogeneous photo-Fenton BiOCl/MIL-100(Fe) nanoscaled hybrid catalysts prepared by green one-step coprecipitation for degradation of organic contaminants.

An excellent heterojunction structure is vital for the improvement of photocatalytic performance. In this study, BiOCl/MIL-100(Fe) hybrid composites were prepared via a one-pot coprecipitation method for the first time. The prepared materials were characterized and then used as a photo-Fenton catalyst for the removal of organic pollutants in wastewater. The BiOCl/MIL-100(Fe) hybrid exhibited better photo-Fenton activity than MIL-100(Fe) and BiOCl for RhB degradation; in particular, the hybrid with 50% Bi molar concentration showed the highest efficiency. The excellent performance can be ascribed to the presence of coordinatively unsaturated iron centers, abundant Lewis acid sites, fast H2O2 activation, and efficient carrier separation on BiOCl nanosheets due to the high charge carrier mobility of the nanosheets. The photo-Fenton mechanism was studied, and the results indicated that ˙OH and h+ were the main active species for organic pollutant degradation. The coprecipitation-based hybridization approach presented in this paper opens up an avenue for the sustainable fabrication of photo-Fenton catalysts with abundant coordinatively unsaturated metal centers and efficient electron-hole separation capacity.

Ordered Coimmobilization of a Multienzyme Cascade System with a Metal Organic Framework in a Membrane: Reduction of CO2 to Methanol.

Enzymatic reduction of CO2 is of great significant, which involves an efficient multienzyme cascade system (MECS). In this work, formate dehydrogenase (FDH), glutamate dehydrogenase (GDH), and reduced pyridine nucleotide (NADH) (FDH&GDH&NADH), formaldehyde dehydrogenase (FalDH), GDH, and NADH (FalDH&GDH&NADH), and alcohol dehydrogenase (ADH), GDH, and NADH (ADH&GDH&NADH) were embedded in ZIF-8 (one kind of metal organic framework) to prepare three kinds of enzymes and coenzymes/ZIF-8 nanocomposites. Then by dead-end filtration these nanocomposites were sequentially located in a microporous membrane, which was combined with a pervaporation membrane to timely achieve the separation of product methanol. Incorporation of the pervaporation membrane was helpful to control reaction direction, and the methanol amount increased from 5.8 ± 0.5 to 6.7 ± 0.8 µmol. The reaction efficiency of an immobilized enzymes-ordered distribution in a membrane was higher than that disordered distribution in the membrane, and the methanol amount increased from 6.7 ± 0.8 to 12.6 ± 0.6 µmol. Moreover, it appeared that introduction of NADH into ZIF-8 enhanced the transformation of CO2 to methanol from 12.6 ± 0.6 to 13.4 ± 0.9 µmol. Over 50% of their original productivity was retained after 12 h of use. This method has wide applicability and can be used in other kinds of multienzyme systems.

Metalloporphyrin-based porous polymers prepared via click chemistry for size-selective adsorption of protein.

Zinc porphyrin-based porous polymers (PPs-Zn) with different pore sizes were prepared by controlling the reaction condition of click chemistry, and the protein adsorption in PPs-Zn and the catalytic activity of immobilized enzyme were investigated. PPs-Zn-1 with 18 nm and PPS-Zn-2 with 90 nm of pore size were characterized by FTIR, NMR and nitrogen absorption experiments. The amount of adsorbed protein in PPs-Zn-1 was more than that in PPs-Zn-2 for small size proteins, such as lysozyme, lipase and bovine serum albumin (BSA). And for large size proteins including myosin and human fibrinogen (HFg), the amount of adsorbed protein in PPs-Zn-1 was less than that in PPs-Zn-2. The result indicates that the protein adsorption is size-selective in PPs-Zn. Both the protein size and the pore size have a significant effect on the amount of adsorbed protein in the PPs-Zn. Lipase and lysozyme immobilized in PPs-Zn exhibited excellent reuse stability.

Repairable Woven Carbon Fiber Composites with Full Recyclability Enabled by Malleable Polyimine Networks.

Carbon-fiber reinforced composites are prepared using catalyst-free malleable polyimine networks as binders. An energy neutral closed-loop recycling process has been developed, enabling recovery of 100% of the imine components and carbon fibers in their original form. Polyimine films made using >21% recycled content exhibit no loss of mechanical performance, therefore indicating all of the thermoset composite material can be recycled and reused for the same purpose.

Self-decontaminating properties of fluorinated copolymers integrated with ciprofloxacin for synergistically inhibiting the growth of Escherichia coli.

In this paper, copolymers composed of antibacterial monomer containing ciprofloxacin, methyl methacrylate (MMA), and 2-perfluorooctylethyl methacrylate (FMA) were prepared, and the surface properties and antibacterial performance of the copolymers and blends-mixed PMMA were investigated. Surface characterization using dynamic contact angle measurement and X-ray photoelectron spectroscopy showed that anti-adhesive fluorinated moieties and antimicrobial moieties were highly concomitant on the material surface. All the copolymers and blends films exhibited excellent antibacterial properties. It was found that the fluorinated antibacterial copolymers showed significantly enhanced antibacterial efficiency toward Escherichia coli bacterium, and even markedly prevented the formation of biofilm for long term. The PMMA films blended with fluorinated antibacterial polymer also show similar results. In contrast, the common copolymer without fluorinated units cannot effectively resist bacterial adhesion, proliferation, and prevent biofilm formation. The desirable antibacterial polymer prohibiting the biofilm formation performance of copolymer with special push-me/pull-you structure which weaken the interaction among polymer chains resulted in the more easy segregation of ciprofloxacin on surface in real environment by the help of synergistic effect of fluorinated units, potentially enabling the design of new self-decontaminating biomaterials for control biofouling.

Effect of surface compositional heterogeneities and microphase segregation of fluorinated amphiphilic copolymers on antifouling performance.

In this paper, a series of fluorinated amphiphilic copolymers composed of 2-perfluorooctylethyl methacrylate (FMA) and 2-hydroxyethyl methacrylate (HEMA) monomers were prepared, and their surface properties and antifouling performance were investigated. Bovine serum albumin (BSA) and human plasma fibrinogen (HFg) were used as model proteins to study protein adsorption onto the fluorinated amphiphilic surfaces. All the fluorinated amphiphilic surfaces exhibit excellent resistant performance of protein adsorption measured by X-ray photoelectron spectroscopy (XPS). The surface compositional heterogeneities on the molecular scale play an important role in the antifouling properties. It was found that the copolymers exhibited better antifouling properties than the corresponding homopolymers did, when the percentage of hydrophilic hydroxyl groups is from 4% to 7% and the percentage of hydrophobic fluorinated moieties is from 4% to 14% on the surface. In addition, the protein molecular size scale and the pattern of microphase segregation domains on the surface strongly affect the protein adsorption behaviors. These results demonstrate the desirable protein-resistant performance from the fluorinated amphiphilic copolymers and provide deeper insight of the effect of surface compositional heterogeneity and microphase segregation on the protein adsorption behaviors.

Protein-resistance performance enhanced by formation of highly-ordered perfluorinated alkyls on fluorinated polymer surfaces.

In this paper, the relationship between the surface structure of fluorinated polymers and their protein-resistant property was studied by preparing films of poly(n-alkyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate (FMA) (PFMA(y)-ec-PnAMA(x)-ec-PFMA(y)) with various ordered structures of perfluorinated alkyls. These fluorinated polymers were synthesized via a controlled/living atom-transfer radical polymerization (ATRP) method. Both the surface free energy and the CF(3)/CF(2) ratio obtained by X-ray photoelectron spectroscopy (XPS) were employed to scale the ordered structures of the perfluorinated alkyls. Protein adsorption studies using fibrinogen as a test molecule were undertaken on the various films by XPS. The results show that the adsorbed mass of fibrinogen decreased linearly with increasing CF(3)/CF(2) ratio on the fluorinated polymer surfaces. When the CF(3)/CF(2) ratio reaches 0.26, there was almost no fibrinogen adsorption. This work not only demonstrates the design of a fluorinated copolymer film on glass substrate with desirable protein-resistant performance, but also provides a fundamental understanding of how the orientation of perfluoroalkyl side chains affects protein-resistant behavior on fluorinated surfaces.

Stick-slip phenomenon in measurements of dynamic contact angles and surface viscoelasticity of poly(styrene-b-isoprene-b-styrene) triblock copolymers.

In this paper, a series of poly(styrene-b-isoprene-b-styrene) triblock copolymers (SIS), with different chemical components, was synthesized by anionic polymerization. The relationships between surface structures of these block copolymers and their stick-slip phenomena were investigated. There is a transition from stick-slip to a closely smooth motion for the SIS films with increasing PS content; the patterns almost vanish and the three-phase line appears to move overall smoothly on the film surface. The results show that the observed stick-slip pattern is strongly dependent on surface viscoelasticity. The jumping angle Δθ, which is defined as θ(1) - θ(2) (when a higher limit to θ(1) is obtained, the triple line "jumps" from θ(1) to θ(2) with increases in drop volume), was employed to scale the stick-slip behavior on various SIS film surfaces. Scanning force microscopy/atomic force microscopy (AFM) and sum frequency generation methods were used to investigate the surface structures of the films and the contributions of various possible factors to the observed stick-slip behavior. It was found that there is a linear relationship between jumping angle Δθ and the slope of the approach curve obtained from AFM force measurement. This means that the stick-slip behavior may be attributed mainly to surface viscoelasticity for SIS block copolymers. The measurement of jumping angle Δθ may be a valuable method for studying surface structure relaxation of polymer films.

Enhanced surface segregation of poly(methyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate by introduction of a second block.

New fluorinated copolymers of poly(methyl methacrylate)-b-poly(butyl methacrylate) or poly(n-octadecyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate (PMMA(x)-b-PBMA(y)-ec-PFMA(z) or PMMA(x)-b-PODMA(y)-ec-PFMA(z)) were synthesized by living atom transfer radical polymerization. Thin films made of PMMA(230)-b-PODMA(y)-ec-PFMA(1) were characterized by differential scanning calorimetry, angle-resolved X-ray photoelectron spectroscopy and X-ray diffraction. These films were found to exhibit robust surface segregation of the end groups. Furthermore, the fluorine enrichment factor at the film surface was found to increase linearly with increasing degree of polymerization of poly(n-octadecyl methacrylate) and its increasing fusion enthalpy in the second block, which enhances the segregation of the fluorinated moieties.

Studies on the effects of the alkyl group on the surface segregation of poly(n-alkyl methacrylate) end-capped 2-perfluorooctylethyl methacrylate films.

The effects of the alkyl group on the surface segregation of poly(n-alkyl methacrylate) end-capped with various numbers of units of 2-perfluorooctylethyl methacrylate (FMA) (PnAMA-ec-PFMA) were investigated by differential scanning calorimetry, angle-resolved XPS analysis, contact angle measurements, and X-ray diffraction (XRD). The results show that with similar numbers of FMA units at the polymer chain end the extent of fluorine segregation (Q) increased with increasing the number of carbon atoms in the side n-alkyl chains of poly(n-alkyl methacrylate). The surface fluorine content within 5 nm deep of the film of poly(n-octadecyl methacrylate) end-capped with one FMA unit (PODMA(160)-ec-PFMA(1.0)) was 208-fold higher than that of the bulk level. These observed differences in Q values were found due to the aggregate structure of the end-capped polymers in the solution, the flexibility, and the crystallinity of the n-alkyl side chains. When the nonfluorinated block was completely amorphous, the molecular aggregate structure of the end-capped polymers in the solution played an important role in the surface segregation of the fluorinated moieties on the resulting film. However, when the nonfluorinated block was crystalline, crystallinity would enhance greatly the segregation of the fluorinated moieties.

Surface segregation of fluorinated moieties on poly(methyl methacrylate-ran-2-perfluorooctylethyl methacrylate) films during film formation: Entropic or enthalpic influences.

The effects of solvents, fluorinated monomer content and film-formation methods on the surface structures of random copolymers composed of methyl methacrylate (MMA) and 2-perfluorooctylethyl methacrylate (FMA) were investigated by contact angle goniometry, X-ray photoelectron spectroscopy, sum frequency generation (SFG) vibrational spectroscopy and surface tension measurement. It is found that, with cyclohexanone as the solvent, there is a critical FMA content of 9mol%, below which the copolymer films by spin coating have a more surface segregation extent of fluorinated moieties than those by solution casting; above which the copolymer films by solution casting have a more surface segregation extent of fluorinated moieties than those by spin coating. However, with toluene as solvent, the critical FMA content lowers down to 3mol%. We believe that the solvent nature and the content of fluorinated moieties in the random copolymer have the great effect because the combined effect of these two factors can determine the random copolymer chain conformations and their thermodynamic dominating factors in the solution and at the solution-air interface. A thermodynamic analysis combining the entropic and enthalpic effects is suggested to explain the observed phenomenon. This research is believed to obtain an enhanced understanding of the surface formation mechanism of the polymer films and thus demonstrate how to promote the segregation of fluorinated moieties at the polymer film surfaces.

Surface segregation of fluorinated moieties on random copolymer films controlled by random-coil conformation of polymer chains in solution.

The relationship between solution properties, film-forming methods, and the solid surface structures of random copolymers composed of butyl methacrylate and dodecafluorheptyl methylacrylate (DFHMA) was investigated by contact angle measurements, X-ray photoelectron spectroscopy, sum frequency generation vibrational spectroscopy, and surface tension measurements. The results, based on thermodynamic considerations, demonstrated that the random copolymer chain conformation at the solution/air interface greatly affected the surface structure of the resulting film, thereby determining the surface segregation of fluorinated moieties on films obtained by various film-forming techniques. When the fluorinated monomer content of the copolymer solution was low, entropic forces dominated the interfacial structure, with the perfluoroalkyl groups unable to migrate to the solution/air interface and thus becoming buried in a random-coil chain conformation. When employing this copolymer solution for film preparation by spin-coating, the copolymer chains in solution were likely extended due to centrifugal forces, thereby weakening the entropy effect of the polymer chains. Consequently, this resulted in the segregation of the fluorinated moieties on the film surface. For the films prepared by casting, the perfluoroalkyl groups were, similar to those in solution, incapable of segregating at the film surface and were thus buried in the random-coil chains. When the copolymers contained a high content of DFHMA, the migration of perfluoroalkyl groups at the solution/air interface was controlled by enthalpic forces, and the perfluoroalkyl groups segregated at the surface of the film regardless of the film-forming technique. The aim of the present work was to obtain an enhanced understanding of the formation mechanism of the chemical structure on the surface of the polymer film, while demonstrating that film-forming methods may be used in practice to promote the segregation of fluorinated moieties on film surfaces.

Solvent effect on the film formation and the stability of the surface properties of poly(methyl methacrylate) end-capped with fluorinated units.

The surface structure and stability (the resistance to surface reconstruction) of end-capped poly(methyl methacrylate) films were greatly affected by the solvents used for film preparation. Films of end-capped PMMA with about four 2-perfluorooctylethyl methacrylate units cast with benzotrifluoride solution exhibited excellent stability and resistance to polar environments compared with those cast with cyclohexanone and toluene solutions. The observed difference in stability between these fluorinated surfaces is attributed to their surface microstructures formed during the film formation processes, which are closely related to the associative behavior of the end-capped PMMA in the solution. A relatively perfect close-packed and well-ordered structure of the perfluoroalkyl side chains at the surface of the PMMA(857)-ec-FMA(3.3) film was formed when the film was cast with benzotrifluoride solution, in which only unimers existed. This study indicates that such a solvent effect may be used to promote the formation of a well-ordered packing structure of the fluorinated moieties at the film surface. The ordering of the packing structure is to a certain extent more important than the content of the fluorinated moieties at the surface for improving the surface stability.