Fabrication and characterization of cellulose nanoparticles from maize stalk pith via ultrasonic-mediated cationic etherification

In this study, parenchyma cellulose, which was extracted from maize stalk pith as an abundant source of agricultural residues, was applied for preparing cellulose nanoparticles (CNPs) via an ultrasound-assisted etherification and a subsequent sonication process. The ultrasonic-assisted treatment greatly improved the modification of the pith cellulose with glycidyltrimethylammonium chloride, leading to a partial increase in the dissolubility of the as-obtained product and thus disintegration of sheet-like cellulose into nanoparticles. While the formation of CNPs by ultrasonication was largely dependent on the cellulose consistency in the cationic-modified system. Under the condition of 25% cellulose consistency, the longer sono-treated duration yielded a more stable and dispersible suspension of CNP due to its higher zeta potential. Degree of substitution and FT-IR analyses indicated that quaternary ammonium salts were grafted onto hydroxyl groups of cellulose chain. SEM and TEM images exhibited the CNP to have spherical morphology with an average dimeter from 15 to 55 nm. XRD investigation revealed that CNPs consisted mainly of a crystalline cellulose Ι structure, and they had a lower crystallinity than the starting cellulose. Moreover, thermogravimetric results illustrated the thermal resistance of the CNPs was lower than the pith cellulose. The optimal CNP with highly cationic charges, good stability and acceptable thermostability might be considered as one of the alternatively renewable reinforcement additives for nanocomposite production.     

High-temperature proton conductivity in acceptor-doped LaNbO4

The conductivity of acceptor-doped LaNbO₄ has been investigated in the temperature range 300 to 1200 °C as a function of the oxygen pressure and water vapor pressure by means of impedance spectroscopy and EMF measurements. The conductivity is predominantly ionic below 800 °C in air and for higher temperatures under reducing conditions. Protons are the major ionic charge carrier in the presence of water vapor. A maximum in proton conductivity of ∼ 0.001 S/cm was obtained at 950 °C in atmospheres containing ca 2% H₂O. At high temperatures (> 1000 °C) under oxidizing conditions, electron hole conduction prevails. The conductivity has been modeled assuming that oxygen vacancies and protons compensate the acceptor doping. Transport coefficients describing mobility of defects and thermodynamic constants for the incorporation of protons have been derived.     

Direct electrochemistry and electrocatalysis of horseradish peroxidase immobilized in Nafion-RTIL composite film

The composite film based on Nafion and hydrophobic room-temperature ionic liquid (RTIL) 1-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim] PF₆) was explored. Here, Nafion was used as a binder to form Nafion-ionic liquids composite film and help [bmim] PF₆ effectively adhered on glassy carbon (GC) electrode. X-ray photoelectron spectroscopy (XPS), cyclic voltammtery (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize this composite film, showing that the composite film can effectively adhere on the GC electrode surface through Nafion interacting with [bmim] PF₆ and GC electrode. Meanwhile, doping [bmim] PF₆ in Nafion can also effectively reduce the electron transfer resistance of Nafion. The composite film can be readily used as an immobilization matrix to entrap horseradish peroxidase (HRP). A pair of well-defined redox peaks of HRP was obtained at the HRP/Nafion-[bmim] PF₆ composite film-modified GC electrode through direct electron transfer between the protein and the underlying electrode. HRP can still retain its biological activity and enhance electrochemical reduction towards O₂ and H₂O₂. It is expected that this composite film may find more potential applications in biosensors and biocatalysis.     

Polysaccharide-based hemostats: recent developments,challenges, and future perspectives

Cellulose - Excessive hemorrhage is a leading cause of death to trauma patients, especially in combat and civilian accidents. The main priority in the medical treatment of trauma patients is to...     

Reactions of aldehyde with collagen: a DFT study

Structural Chemistry - The reaction mechanisms of several amino acids (Asn, Gln, Arg, His, and Lys) in the collagen with aldehyde were studied using density functional theory method. Based on the...     

Synthesis of one-dimensional graphene-encapsulated TiO2 nanofibers with enhanced lithium storage capacity for lithium-ion batteries

Journal of Solid State Electrochemistry - The one-dimensional graphene/TiO2 composite nanofibers with the unique microstructures have been successfully synthesized via an efficient method and...     

Hydrothermal synthesis, crystal structure, and photoluminescence of Pb(II) and Mn(II) coordination polymers based on imidazo[4,5-f][1,10]phenanthroline

Two new coordination polymers, [Pb(IDPT)₂(NO₃)₂] (I) and [Mn(IDPT)(SO₄)(H₂O)₂] (II) (IDPT = imidazo[4,5-f][1,10]phenanthroline), were synthesized by hydrothermal method and characterized by elemental analysis and single-crystal X-ray diffraction technique. The results reveal that the complex I belongs to monoclinic crystal system, space group C2/c and complex II belongs to monoclinic crystal system, P2₁/c space group. The cell parameters are: a = 19.1970(13), b = 7.3875(5), c = 17.3825(12) Å, β = 100.47(10)°, V = 2424.0(3) ų, Z = 4, F(000) = 1488 for I; a = 10.9135(6), b = 7.0230(4), c = 19.7034(10) Å, β = 99.32(10)°, V = 1490.25(14) ų, Z = 4, F(000) = 828 for II. In the structure of complex I, the metal center Pb(II) is six-coordinated, displays an octahedral geometry. Each molecule is further connected with neighboring one via π-π interactions into 1D chain. In complex II, Mn(II) is six-coordinated to form a distorted octahedral geometry. Compound II displays 1D supramolecular chain formed through hydrogen bonds. Additionally, the fluorescent properties for the complexes were investigated. Complexes I and II exhibit strong photoluminescence with emission maximum at 583 and 529 nm at room temperature.     

α-甲基苯乙烯共聚物接枝碳纳米管超疏水表面的制备

采用自由基聚合法将共聚物接枝到多壁碳纳米管(MWCNT)上制备超疏水表面。结果表明,以α-甲基苯乙烯(AMS)与甲基丙烯酸丁酯(BMA)为单体,经自由基聚合可得到共聚物AMS-co-BMA(PAB),其热降解产物接枝到MWCNT表面可制得与水滴静态接触角为165°,滚动角小于3°的超疏水表面。SEM分析结果表明,共聚物的接枝一方面增大了管间的空隙,增加了表面粗糙度,另一方面又为降低表面能提供了条件。不同pH值液滴测试及放置时间的影响结果表明,该超疏水表面具有较好的稳定性和耐久性。     

IN SITU OBSERVATION OF MELTING AND CRYSTALLIZATION BEHAVIORS OF POLY(ε-CAPROLACTONE) ULTRA-THIN FILMS BY AFM TECHNIQUE

The melting and crystallization behaviors of poly(ε-caprolactone) (PCL) ultra-thin films with thickness from 15 nm to 8 nm were studied by AFM technique equipped with a hot-stage in real-time. It was found that melting can erase the spherulitic structure for polymer film with high thickness. However, annealing above the melting point can not completely erase the tree-like structure for the thinner polymer film. Generally, the structure formation of thin polymer films of PCL is controlled not only by melting and crystallization but also by dewetting during thermal annealing procedures, and dewetting predominates in the structure formation of ultra-thin films. However, the presence of tree-like morphology at 75 °C may be due to the strong interaction between PCL and mica surface, which may stick the PCL chains onto the mica surface during thermal annealing process. Moreover, the growth of the dendrites was investigated and it was found that crystallization is followed from a dewetted sample, and the branches did not grow with the stems. The crystallization of polymer in the ultra-thin films is a diffusion-controlled process. Both melting and crystallization behaviors of PCL in thin films are influenced by film thickness.     

Synthesis of TiO2/Bi2WO6 nanofibers with electrospinning technique for photocatalytic methyl blue degradation

TiO₂/Bi₂WO₆ composite nanofibers have been successfully synthesized by a simple electrospinning process. XRD, SEM, HR-TEM, nitrogen adsorption–desorption isotherms and UV–visible diffuse reflectance spectra were used to characterize the composite nanofibers. The composite fibers with diameters about 100 nm was composed of nanoparticles and possessed of high specific surface area (49.6 m² g^?1) and porous structure. Besides, the TiO₂/Bi₂WO₆ composite nanofibers exhibited excellent visible photocatalytic property in the photodegradation of methylene blue (MB), and over 97.2 % of MB was degraded within 5.5 h.