Preparation,characterization and antibacterial properties of cobalt doped titania nanomaterials

Cobalt-doped titania(Co-TiO_2) nanomaterials were synthesized by the sol–gel method at different calcination temperatures. Using Escherichia coli(a), Staphylococcus aureus(b) and Candida albicans(c) as target strains,the antibacterial activity in visible light of the nanomaterials were studied. Co-TiO_2 nanomaterials were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), UV–Vis diffuse reflectance spectroscopy(DRS), Fourier transform infrared spectrum(FT-IR) and X-ray photoelectron spectroscopy(XPS). The Co ions in the Co-TiO_2 nanomaterial exist in the form of CoTiO_3 phase.The antibacterial properties of Co-TiO_2 nanomaterials on E. coli(a), S. aureus(b) and C. albicans(c) were investigated with the oscillating flask method and the inhibition zone method. The nanomaterials calcined at 600 °C exhibit excellent antibacterial activity. The bacteriostatic rates for E. coli, S. aureus and C. albicans reached 99.5%,91.3% and 93.4% respectively. The diameters of the antibacterial rings were up to 36 mm, 37 mm, 30 mm respectively, and the clarity of the ring was clear. The antibacterial properties of Co-TiO_2 nanomaterials were compared with those of traditional silver sol, zinc oxide sol and Zn-doped TiO_2 nanomaterials The mechanism of the influences of Co ions doping on the antibacterial activity of TiO_2 nanomaterials was also discussed. The doping of Co ions inhibits the particle size of the antibacterial agent and extends the photocatalytic response range, thereby improving the photocatalytic performance of the antibacterial agent.     

Thermodynamic parameters of poly(lactic acid) solutions in dialkyl phthalate

Some of thermodynamic parameters for poly(lactic acid) (PLA)/dialkyl phthalate systems have been investigated. Both poly(dl-lactic acid) (PDLLA) and poly(l-lactic acid) (PLLA), which are stereoisomers of PLA, were used and a series of 1,2-dialkyl phthalates with different alkyl chain, from methyl to hexyl, was adopted as a solvent. Theta temperatures of PLA/dialkyl phthalate system were determined and subsequently the second virial coefficient and the interaction parameter were evaluated. Theta temperature was determined by the extrapolation of the highest liquid-liquid phase separation temperatures and Zimm plots were constructed by static light scattering to obtain second virial coefficient and z-average radius of gyration. Second virial coefficient and z-average radius of gyration was examined quantitatively as a function of temperature and solvent. Thermodynamic parameters that could not be obtained experimentally were calculated based on the Flory-Huggins theory.     

Studies on the preparation and dental properties of antibacterial polymeric dental restorative composites containing alkylated ammonium chloride derivatives

The preparation of antibacterial polymeric dental restorative composites (PDRC) was carried out using various alkylated ammonium chloride derivatives as the antibacterial compound. To improve the mechanical properties of PDRC, the surface of the silica filler was hydrophobically treated with γ-methacryloxypropyltrimethoxysilane. The diametral tensile strength, flexural strength, and Knoop hardness of PDRC were measured and the antibacterial effect was also investigated. The addition of alkylated ammonium chloride derivatives to the bisphenol-A glycerolate dimethacrylate/triethyleneglycol dimethacrylate resin matrix enhanced the antibacterial properties of PDRC. It was also discovered that alkylated ammonium chloride derivatives with a higher chain length between the ammonium and the acryl (or methacryl) functional groups reduced the mechanical properties of PDRC. In addition, it was found that the optimum concentration of the antibacterial compound was about 3 wt% based upon resin matrix, and the optimum chain length between functional groups of alkylated ammonium chloride derivatives was 2–3 carbons.     

Effect of hydrolysis on spatial inhomogeneity in poly(acrylamide) gels of various crosslink densities

The spatial inhomogeneity in poly(acrylamide) (PAAm) gels of various crosslink densities has been investigated with the static light scattering measurements. The gels were prepared using N,N′-methylenebis(acrylamide) (BAAm) as a crosslinker at a fixed initial monomer concentration but at various crosslink densities. Ammonium persulfate-N,N,N′,N′-tetramethylethylenediamine (TEMED) redox initiator system was used to initiate the polymerization reactions as well as to create charged groups in the aged gels. The gels were characterized by elasticity tests and by light scattering measurements at a gel state just after their preparation. Elasticity measurements show that 91-94% of the crosslinker molecules used in the hydrogel preparation were wasted in ineffective crosslinks. Debye-Bueche analysis of the light scattering data indicates frozen concentration fluctuations within the gel samples, which increase continuously with increasing crosslink density of the hydrogels. This phenomenon was explained with the multiple crosslinking reactions leading to the formation of highly crosslinked regions in the final hydrogel. The extent of concentration fluctuations was found to decrease drastically with increasing time of aging of gels in the synthesis reactor, indicating that the hydrolysis of amide groups into carboxylate anions facilitates the homogenization of the gel samples. A thermodynamic model was developed to explain the experimental observations in terms of the osmotic pressure of counterions in the aged gels.     

Effect of swelling on spatial inhomogeneity in poly(acrylamide) gels formed at various monomer concentrations

The effect of swelling on the spatial inhomogeneity in poly(acrylamide) (PAAm) gels has been investigated with the static light scattering measurements. Four sets of gels were prepared using N,N′-methylenebis(acrylamide) (BAAm) as a crosslinker at various initial monomer concentrations. The crosslinker ratio X (the mole ratio of BAAm to the monomer acrylamide) was fixed at 1/50, 1/61.5, 1/66, and 1/100 in each set of gels. The gels, both at the state of preparation and at the equilibrium swollen state in water, exhibit a maximum degree of spatial gel inhomogeneity at a critical monomer concentration (ν_2,cr⁰). ν_2,cr⁰ shifts toward smaller concentrations as X is decreased or, as the gel swells beyond its swelling degree after preparation. Swelling enhances the extent of spatial inhomogeneity in PAAm gels and, this enhancement mainly occurs at low crosslinker ratios. The theoretical prediction of the Panyukov-Rabin theory was found to be in qualitative agreement with the experimental findings. It was also shown that three different effects, namely crosslinker, concentration, and swelling effects determine the extent of inhomogeneities in gels formed at various monomer concentrations.     

Characterization and antibacterial properties of aminophenol grafted and Ag NPs decorated graphene nanocomposites

A new route for the synthesis of aminophenol grafted and Ag NPs decorated reduced graphene sheet (Ag-RGS) was developed as an effective antibacterial nanostructure. The nucleophilic substitution reaction of amine group of aminophenol with epoxy group of GO in the presence of silver nitrate and subsequent reduction with hydrazine generated Ag-RGS nanocomposite. The morphology and structure of the as-synthesized nanocomposite was characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. TEM images of Ag-RGS revealed that the silver nanoparticles were decorated on the surface of the graphene sheet. The presence of phenolic groups and silver nanoparticles on the surface of Ag-RGS showed synergistic effect on antibacterial activity against Escherichia coli and Staphylococcus aureus. This feature of the Ag-RGS nanocomposite showed that it can be a promising candidate in broad range of antibiotics.     

Synthesis and characterization of polysaccharide-maghemite composite nanoparticles and their antibacterial properties

The aim of this study was to obtain saccharide (dextran and sucrose)-coated maghemite nanoparticles with antibacterial activity. The polysaccharide-coated maghemite nanoparticles were synthesized by an adapted coprecipitation method. X-ray diffraction (XRD) studies demonstrate that the obtained polysaccharide-coated maghemite nanoparticles can be indexed into the spinel cubic lattice with a lattice parameter of 8.35 Å. The refinement of XRD spectra indicated that no other phases except the maghemite are detectable. The characterization of the polysaccharide-coated maghemite nanoparticles by various techniques is described. The antibacterial activity of these polysaccharide-coated maghemite nanoparticles (NPs) was tested against Pseudomonas aeruginosa 1397, Enterococcus faecalis ATCC 29212, Candida krusei 963, and Escherichia coli ATCC 25922 and was found to be dependent on the polysaccharide type. The antibacterial activity of dextran-coated maghemite was significantly higher than that of sucrose-coated maghemite. The antibacterial studies showed the potential of dextran-coated iron oxide NPs to be used in a wide range of medical infections.     

Studies on PVA/AgI-based polymeric membranes for exploration of antibacterial activity

In the present communication, solid polymer electrolyte films have been prepared using solution cast technique based on polyvinyl alcohol (PVA) as host polymer and silver iodide (AgI) as salt. The objective of the study is to develop PVA electrolytic films with AgI and evaluate to protect against simulants of biological warfare agents. The antibacterial activities of the films are explored against Aeromonas hydrophila, Escherichia coli, Salmonella typhii, and Shigella boydii. The antibacterial effects of the PVA/Ag⁺ hybrids were assessed by the minimum inhibitory concentration method. Polymer electrolyte films show good antibacterial activity against A. hydrophilla, S. typhii, and S. boydii. Scanning electron microscopy is used to study the surface morphology of the polymeric membranes. Complex impedance spectroscopy is used for characterizing the electrical and dielectric properties of the electrolyte samples. Frequency-dependent various dielectric properties such as dielectric constant, dielectric loss, and loss tangent have been discussed. The variations of AC conductivity gives the explanation in understanding the mechanism of the ion transport and determine power exponent value n lying in the range 1 and 1.2 which represents the trapping of ions in the polymer matrix.     

Construction of g-C3N4/TiO2/Ag composites with enhanced visible-light photocatalytic activity and antibacterial properties

In this study, the multifunctional carbon nitride based composite graphitic-C₃N₄ (g-C₃N₄)/TiO₂/Ag was prepared through a simple and efficient vacuum freeze-drying route. TiO₂ and Ag nanoparticles were demonstrated to decorate onto the surface of g-C₃N₄ sheet. In the ultraviolet–visible absorption test, a narrower band gap and red-shift of light absorption edge were observed for g-C₃N₄/TiO₂/Ag compared to pristine g-C₃N₄ and single-component modified g-C₃N₄/TiO₂. The photodegradation property of g-C₃N₄/TiO₂/Ag was investigated toward the degradation of methylene blue (abbreviated as MB) under the irradiation of visible light. These results indicated that the degradation performance of organic dyes for g-C₃N₄/TiO₂/Ag was obviously improved compared with g-C₃N₄/TiO₂ and g-C₃N₄. The reaction rate constant of MB degradation for g-C₃N₄/TiO₂/Ag was 4.24 times higher than that of pristine g-C₃N₄. In addition, such rationally constructed nanocomposite presented evidently enhanced antibacterial performance against the Gram-negative Escherichia coli. Concentration dependent antibacterial performance was systematically investigated. And 84% bacterial cell viability loss had been observed at 500 μg/mL g-C₃N₄/TiO₂/Ag within 2 h visible light irradiation.     

Plant mediated green synthesis and antibacterial activity of silver nanoparticles using Crataegus douglasii fruit extract

In this study, silver nanoparticles were synthesized using the Crataegus douglasii fruit extract as a reducing agent. The reaction process was monitored by UV–vis spectroscopy. Further characterization was carried out using scanning electron microscopy (SEM). To optimize the biosynthesis of silver nanoparticles, the effect of process variables such as extract concentrations, mixing ratio of the reactants, time and pH were also investigated. The SEM images showed silver nanoparticles with 29.28 nm size and nearly spherical shape at 24 h interaction time. The antibacterial activity of the synthesized silver nanoparticles was confirmed against Staphylococcus aureus and Escherichia coli.     

Aggregation in dilute solutions of high molar mass poly(ethylene) oxide and its effect on polymer turbulent drag reduction

We apply methods of dynamic light scattering (DLS) and fluid mechanics to quantitatively establish the role of aggregation in the turbulent drag reduction of high molar mass poly(ethylene oxide) (PEO) solutions. By means of DLS, we show that the dilute aqueous solutions of high molar mass PEO (M_w ∼ 4 × 10⁶ g/mol) are aggregated and that this aggregate structure can be manipulated by addition of the chaotropic salt guanidine sulfate (GuS) or the divalent salt magnesium sulfate (MgSO₄). In aqueous solution, we find Γ ∼ q^2.8±0.1, where Γ is the DLS correlation function relaxation rate and q is the scattering vector. This scaling is consistent with internal motions of a large coil or aggregate. Addition of salt progressively decreases the scaling to Γ ∼ q^2.0±0.1 (at 0.5 M of MgSO₄) consistent with center-of-mass diffusion of isolated coils. We further find that manipulating the aggregation state of PEO with MgSO₄ shifts the critical condition for onset of turbulent drag reduction at dilute concentrations in pipe flow by a factor of 2.5. Because this critical condition is inversely proportional to the viscoelastic relaxation time of the polymer solution, we conclude that the aggregation state and the turbulent drag reduction behavior of PEO are strongly correlated. This correlation definitively confirms prior speculation (Cox et al. Nature 1974;249; Vlachogiannis et al. Physics of Fluids 2003;15(12)) that the high molar mass PEO commonly used in literature studies of turbulent drag reduction is in a state of aggregation. Furthermore, the quantitative differences in quiescent DLS characterization and turbulent flow pressure drop measurements suggest that high molar mass PEO undergoes flow-induced de-aggregation in transport systems with shear stresses as low as 0.5 Pa.     

Solvents effect on the physical properties of semi-dilute poly(N-isopropyl acryl amide) solutions

The physical properties of 5 wt% poly(NIPAM) (M_v=3.22×10⁵) semi-dilute solutions in H₂O, D₂O, and THF (tetrahydrofuran) solvents were studied using dynamic light scattering (DLS) and dynamic shear viscosity (DSV) measurements. The DLS data showed that there were poly(NIPAM) slow mode inter-polymer chains associations in H₂O and D₂O solvents. However, no DLS slow mode was observed in poly(NIPAM)/THF solutions. The DSV data showed that there are shear thickening behavior in these three poly(NIPAM) solutions, resulting in a maximum shear viscosity η_peak in the viscosity η′(ω) versus shear frequency ω curve. The slow mode hydrodynamic radius 〈R_hs〉 of DLS measurements and the zero shear rate viscosity η₀ and maximum viscosity η_peak data of DSV measurements from poly(NIPAM)/H₂O and poly(NIPAM)/D₂O solutions show two critical transition temperatures with T_cr1=30-32 °C and T_cr2=32-34 °C. Poly(NIPASM)/D₂O has higher T_cr1 and T_cr2 than poly(NIPASM)/H₂O. However, no transition temperatures of poly(NIPAM)/THF solution were observed. The different temperature dependencies of these three solutions were attributed to the ‘solubility’ and ‘hydrogen bonding’ effects between poly(NIPAM) with H₂O, D₂O, and THF solvents. Without considering the polymer-solvent hydrogen bonding, the solubility of poly(NIPAM) in solvents decreases in the following sequence: THF>H₂O>D₂O and the degree of polymer-solvent hydrogen bonding increases in the following sequence: THF<H₂O<D₂O. The effects of the degree of ‘hydrogen bonding’ and the ‘solubility’ of polymer in solvents on the physical properties of poly(NIPAM) solutions are discussed.     

Studies on the annealing and antibacterial properties of the silver-embedded aluminum/silica nanospheres

Substantial silver-embedded aluminum/silica nanospheres with uniform diameter and morphology were successfully synthesized by sol-gel technique. After various annealing temperatures, the surface mechanisms of each sample were analyzed using scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. The chemical durability examinations and antibacterial tests of each sample were also carried out for the confirmation of its practical usage. Based on the result of the above analyses, the silver-embedded aluminum/silica nanospheres are eligible for fabricating antibacterial utensils.     

Synthesis of CuO/MXene nanocomposite to study its photocatalytic and antibacterial properties

In this work, bare copper oxide CuO nanoparticles, MXene nanosheets and their CuO/MXene nanocomposite were synthesized for enhanced photocatalytic activity. CuO nanoparticles were prepared hydrothermally, MXene was synthesized via HF etching, and their nanocomposite was formed via a simple ultrasonication route. The as-prepared materials were characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques to analyse their structural and functional group features. Scanning electron microscopy (SEM) analysis was used to evaluate the surface morphologies of all the samples. UV–visible spectroscopic analysis was used to calculate the band gap energies of CuO, MXene and CuO/MXene. The enhanced surface area of the synthesized nanocomposite supported excellent photocatalytic activity. The maximum degradation of methylene blue by CuO/MXene was recorded at approximately 1 h. The higher degradation rate of methylene blue by the nanocomposite is due to the effective intercalation of nanoparticles between the MXene nanosheets, resulting in increased electron trapping ability of the photocatalyst.     

Preparation of antibacterial poly(sulfobetaine methacrylate) grafted on poly(vinyl alcohol)-formaldehyde sponges and their properties

Conventional wound dressings cover wound surfaces and separate them from the outer environment. However, wound sites are readily infected by some bacteria during healing. To overcome these problems, a macroporous sample is designed through the grafting polymerization of hydrophilic sulfobetaine methacrylate (SBMA) on poly(vinyl alcohol)-formaldehyde (PVF) sponges. The as-prepared PVF sponges have a grafting percentage of 15–50%, an average pore size of 60–90 μm, and a high porosity of 90%. This series of PVF-g-PSBMA sponges can absorb deionized water and saline solution at approximately 16 g·g⁻¹ within 2 min because of their hydrophilic surface and macroporous structure. The antibacterial potential of PVF-g-PSBMA sponges against Escherichia coli and Staphylococcus aureus is evaluated via a shake flask test. As the grafting percentage increase from 15 to 50%, the antibacterial activities against Gram-positive S. aureus and Gram-negative E. coli gradually increase from 87 to 95% and from 94 to 99%, respectively. The biocompatibility of these sponges is confirmed through an in vitro cell viability assay. All of the survival rates of the bacterial cells relative to the control (100% of metabolic activity) exceed 90% as the extract ratio of PVF-g-PSBMA sponges increase. Thus, the as-prepared PVF-g-PSBMA sponges can be an ideal wound dressing candidate. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47047.     

氯化银纳米粒子散射光谱的应用研究

研究了氯化银纳米粒子的散射光谱及其应用,与透射光谱相比,用散射光谱法测定微量银离子,具有更好的线性关系、更宽的线性范围和更高的灵敏度。     

Construction of Er-doped ZnO/SiO2 composites with enhanced antimicrobial properties and analysis of antibacterial mechanism

Herein, silica carrier was used as underlying structure to prepare composite material loaded with rare earth element Er and Zn. Rare earth elements can improve antimicrobial effects of ZnO due to their specific electronic structure. Er–ZnO/SiO₂ hybrid antibacterial material was prepared through sol-gel method and its structure and morphology were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma emission spectroscopy and Brunauer-Emmett-Teller measurements. E. coli and S. aureus were selected as model bacteria to assess antibacterial activity of prepared hybrid material by plate coating method. Er–ZnO/SiO₂ exhibited good antibacterial activity towards E. coli and S. aureus. Increase in Er³⁺ concentration from 0.12% to 1.10% led to increase in antibacterial performance followed by subsequent decrease. Improving effect of Er relied on the molar ratio of Er doped in ZnO/SiO₂ hybrid material. The optimal sample was found to be 0.60%Er–ZnO/SiO₂, with antibacterial rates of 93.71% and 70.46% against E. coli and S. aureus, respectively. Antibacterial mechanism was assessed by fluorescence detection of reactive oxygen species. In addition, flame atomic absorption spectrometry was used to measure the amount of released Zn²⁺. Results also showed that 0.60%Er–ZnO/SiO₂ hybrid material generated more reactive oxygen species, released more Zn²⁺ ions, and had the largest surface area, which improved its antibacterial rate. Thus, Er enhanced antibacterial properties of ZnO/SiO₂, providing these composite materials with great potential as antibacterial products.     

3-氯-2-羟丙基三甲基氯化铵的合成进展与应用

介绍了3-氯-2-羟丙基三甲基氯化铵的几种合成方法———常规法、水相法和有机溶剂法,重点对以无水乙醇为溶剂、以三甲胺盐酸盐和环氧氯丙烷为原料的有机溶剂法进行了研究。综述了3-氯-2-羟丙基三甲基氯化铵在石油开采、环保和造纸中的应用。     

Activity of antibacterial compounds immobilised on montmorillonite

The activities of antibacterial compounds, such as cetylpyridinium (CP), cetyltrimethylammonium (CTA), silver ions and metallic silver, immobilised on montmorillonite (MMT), were tested in Escherichia coli and Enterococcus faecium bacteria. The results of bacterial growth tests were confirmed by determination of the minimum inhibition concentrations (MICs). Unlike CP and CTA, the intercalated silver ions were easily released from MMT by ion-exchange with Na⁺ and acted as very effective antibacterial substances in the long term. Their bactericidal and bacteriostatic effects were determined. Generally, antibacterial compounds are effective when they are released from an inorganic carrier. Metallic silver was prepared by reduction of intercalated Ag⁺ with sodium borohydride. Antibacterial effects of metallic silver were not observed.     

Solution properties of xanthan. Light scattering and viscometry on dilute and moderately concentrated solutions

Elastic and quasi-elastic light-scattering, viscometric and rheological studies are given for solutions of the microbial polysaccharide Xanthomonas campestris (xanthan) in aqueous 0.62N NaCl for polymer concentrations from 0.03 to 2.2 g kg⁻¹. The observed negative ∂ln[η]/∂ln T is interpreted as a decrease of the persistence length with increasing T. The behaviour in moderately concentrated solutions (2<[η]c<25) reveals intermolecular association, leading to gel formation in the extreme case. The effect of the association on the viscometric and light-scattering data is discussed. It is concluded that the early stages of association involve structure with the chain axes nearly parallel, but that larger, particulate-like structures develop with increasing c, eventually leading to gel formation under certain conditions.