Microwave promoted synthesis of chitosan‐graft‐poly(acrylonitrile)

Using microwave (MW) irradiation, polyacrylonitrile was grafted onto chitosan with 170% grafting yield under homogeneous conditions in 1.5 min in the absence of any radical initiator or catalyst. Under similar conditions a maximum grafting of 105% could be achieved when the K₂S₂O₈/ascorbic acid redox system was used as radical initiator in a thermostatic water bath at 35 ± 2°C. The representative graft copolymer was characterized by Fourier transform infrared spectra, thermogravimetric analysis, and X‐ray diffraction measurement, taking chitosan as a reference. The effects of such reaction variables as monomer/chitosan concentration, MW power, and exposure time on the graft co polymerization were studied. A probable mechanism for grafting without the redox system under microwaves was proposed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 820–825, 2005     

Low temperature synthesis and dielectric, ferroelectric and piezoelectric study of microwave sintered BaTiO3 ceramics

Barium titanate (BaTiO₃/BT) ferroelectric system was synthesized in single perovskite phase at low temperature by using powders derived from modified solid state reaction (MSSR) and sintered by microwave (MW) processing routes. Conventional calcination temperature was optimized at 900 °C for 4 h. MW sintering of BT samples was carried out at 1100 °C for 30 min to get dense (98% density) ceramics. Room temperature (RT) dielectric constant (?_r) and dielectric loss (tan δ) at 1 kHz frequency of MW sintered BT samples was found to be ∼2500 and 0.03, respectively. Saturated polarization vs. electric field (P-E) loops with remnant polarization (P_r) ∼6 μC/cm² and coercive field (E_c) ∼1.45 kV/cm confirmed the ferroelectric nature of MW sintered BT samples. Piezoelectric coefficient from strain vs. electric field (S-E) loops study was found to be 335 pm/V.     

Study on the rapid synthesis of LiNi1−xCoxO2 cathode material for lithium secondary battery

LiNi_1−xCo_xO₂ (x = 0, 0.1, 0.2) cathode materials were successfully synthesized by a rheological phase reaction method with calcination time of 0.5 h at 800 °C. All obtained powders are pure phase with α-NaFeO₂ structure (R-3m space group). The samples deliver an initial discharge capacity of 182, 199 and 189 mAh g⁻¹ (25 mA g⁻¹, 4.35-3.0 V), respectively. The reaction mechanism was also discussed, which consists of a series of defect reactions. As a result of these defect reactions, the reaction of forming LiNi_1−xCo_xO₂ takes place in high speed.     

Efficient microwave hydrothermal synthesis of nanocrystalline orthorhombic LiMnO2 cathodes for lithium batteries

Rod-like orthorhombic LiMnO₂ nanocrystals were successfully synthesized using temperature-controlled microwave hydrothermal route (TCMH) in a short time (30 min) at a temperature as low as 160 °C. o-LiMnO₂ obtained by two different methods was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemistry test. SEM revealed that the product obtained in case of TCMH was rod-like with a diameter of 40 nm, while the nanoparticles with 200 nm diameter were obtained by traditional hydrothermal route (TH). The dramatic formation of o-LiMnO₂ in the microwave hydrothermal field influenced the morphology and crystal structure of the final products. The formation and preferred growth orientation mechanism of o-LiMnO₂ in the microwave irradiation process was discussed. Electrochemistry performance exhibited that the as-synthesized o-LiMnO₂ nanorods reached the maximum discharge capacity of 194.2 mAh g⁻¹ at 0.1 C rate after several cycles between 2.2 and 4.4 V vs. Li⁺/Li at room temperature, which was higher than the electrochemical performance of o-LiMnO₂ obtained by TH. The experimental results showed that the TCMH method provided an effective way for preparing o-LiMnO₂ cathode material in lithium-ion batteries.     

Synthesis and characterizing a novel polymeric flocculant based on amylopectin-graft-polyacrylamide-graft-polyacrylic acid [(AP-g-PAM)-g-PAA]

The article highlights the development of a new generation of polymeric flocculant by grafting binary monomer mixture of acrylamide and acrylic acid onto a natural polymer—amylopectin [(AP-g-PAM)-g-PAA]. Primary graft copolymerization of acrylamide onto AP and binary graft copolymerization of acrylic acid onto AP-g-PAM was accomplished in 84 and 91?% grafting efficiency (% GE) using potassium persulphate as initiator. The influence of initiator concentration onto % GE was investigated. The developed binary graft copolymer was characterized using various materials characterization techniques like viscometry, elemental analysis, FTIR spectroscopy, ¹³C NMR spectroscopy, molecular weight and radius of gyration by Zimm plot using SLS analysis. Flocculation studies reveal that the synthesized binary grafted product is an efficient flocculant, which is because of its higher molecular weight and radius of gyration.     

Synthesis of amphiphilic ethyl cellulose grafting poly(acrylic acid) copolymers and their self-assembly morphologies in water

Amphiphilic ethyl cellulose (EC)-g-poly(acrylic acid) (PAA) copolymers were synthesized by atom transfer radical polymerization (ATRP). Firstly, ethyl cellulose macro-initiators with the degree of the 2-bromoisobutyryl substitution of 0.04 and 0.25 synthesized by the esterification of the hydroxyl groups remained in EC macromolecular chains and the 2-bromoisobutyryl bromides. Secondly, tert-butyl acrylate was polymerized by ATRP with the ethyl cellulose macro-initiator and EC-g-PtBA copolymers were prepared. Finally, the EC-g-PAA copolymers were prepared by hydrolyzing tert-butyl group of the EC-g-PtBA copolymers. The grafting copolymers were characterized by means of GPC, ¹H NMR and FTIR spectroscopies. The molecular weight of graft copolymers increased during the polymerization and the polydispersity was low. A kinetic study showed that the polymerization was first-order. Meanwhile, EC-g-PAA copolymers were self-assembled to micelles or particles with diameters of 5 nm and 100 nm in water (pH = 10) when the concentration was 1.0 mg/ml.     

Preparation of poly(tert-butyl acrylate-g-styrene) as precursors of amphiphilic graft copolymers. 1. Kinetic study and thermal properties

Free radical copolymerizations of tert-butyl acrylate and a polystyrene macromonomer carrying a methacryloyloxy group at the chain end have been performed in benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator at 70 °C. The estimated values of the ‘lumped’ kinetic constant, k_p/k_t^1/2, have shown a clear dependency on the macromonomer concentration in the reaction medium. The obtained poly(tert-butyl acrylate-g-polystyrene) graft copolymers were characterized by size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). In addition, the thermal behavior of these copolymers was studied by thermogravimetric analysis (TGA). Subsequently, hydrolysis of precursor graft copolymer was performed to afford an amphiphilic graft copolymer. Characterization using FT-IR confirmed total hydrolysis of the ester group.     

Synthesis and electrochemical performance of novel loose structured submicro/micro-sized NiSnx alloy composites for lithium batteries

An effective method of carbothermal reduction was employed to prepare spherical microcrystal NiSn_x alloy powders from oxides of Sn and Ni used as anode materials for Li-ion battery. According to XRD, SEM and TEM analysis, the synthesized spherical NiSn_x powders show a loose submicro/micro-sized structure and a multi-phase composition. The prepared NiSn_x alloy composite electrode exhibits a stable discharge capacity of electrode is ca. 380 mAh g⁻¹ at constant current density of 50 mA g⁻¹, and can be retained at 350 mAh g⁻¹ after 25 cycles. Moreover, NiSn_x alloys exhibit excellent high rate performance, i.e. stable discharge capacities of 300-310 mAh g⁻¹ and the coulombic efficiencies of 97.5-99.5% have been obtained at the current density of 500 mA g⁻¹. The loose submicro-sized particle structural characteristic and the Ni addition in Sn matrix should be responsible for the improvement of cycling stability of NiSn_x electrode. The carbothermal reduction method is simple, low-cost and mass-productive, which should be viable to other alloy composite materials system of rechargeable lithium ion batteries.     

Mass transfer limitations on fixed-bed reactor for Fischer-Tropsch synthesis

Mass transfer limitations on fixed-bed for Fischer-Tropsch synthesis were investigated by changing synthesis gas superficial velocity, catalyst pellet size, and catalyst amount. To study external mass transfer limitation, synthesis gas superficial velocity was changed from 8.47 × 10^− 4 m s^− 1 to 3.39 × 10^− 3 m s^− 1. As a result, the synthesis gas superficial velocity of 3.39 × 10^− 3 m s^− 1 was most suitable for hydrocarbon chain growth resulting to liquid hydrocarbon formation. In case of internal mass transfer limitations, the effects of catalyst pellet size and catalyst amount (W_cat/F) were discussed. The large catalyst pellet showed higher C₅₊ selectivity and a lower α value compared to the small pellet because of more severe internal mass transfer limitations of α-olefin and long-chained hydrocarbons in the large pellet, respectively. Catalyst amount (W_cat/F) was inversely proportional to the internal mass transfer limitation because increased catalyst amount gave more time for liquid hydrocarbon products to diffuse from the catalyst pellet and, therefore, the catalyst amount of 4.5 g (W_cat/F = 45 g_cat min L^− 1) was most appropriate for liquid hydrocarbon formation.     

One-step microwave synthesis and characterization of carbon-modified nanocrystalline LiFePO4

The precursors of LiFePO₄ were prepared by a sol-gel method using lithium acetate dihydrate, ferrous sulfate, phosphoric acid, citric acid and polyethylene glycol as raw materials, and then the carbon-modified nanocrystalline LiFePO₄ (LiFePO₄/C) cathode material was synthesized by a one-step microwave method with the domestic microwave oven. The effect of microwave time and carbon content on the performance of the resulting LiFePO₄/C material was investigated. Structural characterization by X-ray diffraction and scanning electron microscopy proved that the olivine phase LiFePO₄ was synthesized and the grain size of the samples was several hundred nanometers. Under the optimal conditions of microwave time and carbon content, the charge-discharge performance indicated that the nanosized LiFePO₄/C had a high electrochemical capacity at 0.2 C (152 mAh g⁻¹) and improved capacity retention; the exchange current density was 1.6977 mA cm⁻². Furthermore, the rate capability was improved effectively after LiFePO₄ was modified with carbon, with 59 mAh g⁻¹ being obtained at 20 C.     

The performances of higher alcohol synthesis over nickel modified K2CO3/MoS2 catalyst

Ni modified K₂CO₃/MoS₂ catalyst was prepared and the performance of higher alcohol synthesis catalyst was investigated under the conditions: T = 280–340 °C, H₂/CO (molar radio) = 2.0, GHSV = 3000 h^− 1, and P = 10.0 MPa. Compared with conventional K₂CO₃/MoS₂ catalyst, Ni/K₂CO₃/MoS₂ catalyst showed higher activity and higher selectivity to C₂⁺OH. The optimum temperature range was 320–340 °C and the maximum space-time yield (STY) of alcohol 0.30 g/ml h was obtained at 320 °C. The selectivity to hydrocarbons over Ni/K₂CO₃/MoS₂ was higher, however, it was close to that of K₂CO₃/MoS₂ catalyst as the temperature increased. The results indicated that nickel was an efficient promoter to improve the activity and selectivity of K₂CO₃/MoS₂ catalyst.     

Synthesis and electrochemical characterization of mesoporous CoxNi1−x layered double hydroxides as electrode materials for supercapacitors

A novel nanostructured mesoporous Co_xNi_1−x layered double hydroxides (Co_xNi_1−x LDHs), which both Co(OH)₂ and Ni(OH)₂ exhibit, has been successfully synthesized by a chemical co-precipitation route using polyethylene glycol as the structure-directing reagent. Structural and morphological characterizations were performed using powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The component and thermal stability of the sample were measured by energy dispersed X-ray spectrometry (EDS), FT-IR and thermal analyses, including thermogravimetry (TG) and differential thermal analysis (DTA). Cyclic voltammogram and galvanostatic charge-discharge testified that the Co_xNi_1−x LDH has a specific capacitance of 1809 F g⁻¹ at a current density of 1 A g⁻¹ and remains at about 90.2% of the initial value after 1000 cycles at a current density of 10 A g⁻¹. The relationship between the chemical composition and the capacitance is discussed.     

Synthesis and characterization of maleylated cellulose-<Emphasis Type="Italic">g</Emphasis>-polyacrylamide hydrogel using TiO<Subscript>2</Subscript> nanoparticles under sunlight

Graft polymerization onto the cellulose is one way to produce semisynthetic copolymers and semiconductors were hardly used as initiators. Maleylated cellulose (MC) with different degree of carboxyl groups was synthesized and degree of carboxyl groups was determined using titration method. Then the graft copolymers of acrylamide (AM) on MC were synthesized by titanium dioxide semiconductor photoinitiator in aqueous suspension under sunlight. The effect of different parameters, such as the degree of carboxyl groups, degassing of atmosphere, reactor type, light source, MC/AM ratio, and initiator concentration, was evaluated in the synthesis of graft copolymers. MC with a high degree of carboxyl groups about 2.8 mmol g^?1 was selected for graft photopolymerization. Maximum monomer conversion (55%) for Maleylated cellulose-g-polyacrylamide (MC-g-PAM) was achieved with 0.5 mg TiO₂, MC/AM = 0.056, argon atmosphere, sunlight source, and double quartz tube reactor. The maximum amount of equilibrium swelling (41 g g^?1) was achieved for MC-g-PAM with 34% monomer conversion. The resulting graft copolymers were characterized by FT-IR, SEM, and TGA. Synthesis of MC-g-PAM using TiO₂ nanoparticles (NPs) as the initiator was done successfully that shows the TiO₂ NPs are useable in graft polymerization of acrylamide monomers onto the MC under sunlight.     

Synthesis and characterization of a novel derivative of chitosan

The graft-copolymer of chitosan with 4-(6-methacryloxyhexyloxy)-4′-nitrobiphenyl I was synthesized by radical polymerization. Graft-copolymerization was carried out under homogeneous conditions with AIBN as initiator and 2 wt% acetic acid as solvent. Homopolymerization of I was also carried out to obtain material for comparative analysis. The resulting chitosan graft-copolymers were isolated, purified and characterized with FTIR, NMR, DSC, and TGA. Films were then prepared and characterized by X-ray diffraction, wave guide coupling and infrared dichroism techniques.     

Effect of support type and synthesis conditions on the oxygen reduction activity of RuxSey catalyst prepared by the microwave polyol method

Ru_xSe_y nanoparticles supported on different carbon substrates were synthesized by microwave heating of ethylene glycol solutions of Ru(III) chloride and sodium selenite at different pH and Ru/Se mole ratios. The resulting catalysts were used for the electrochemical oxygen reduction reaction (ORR) in acidic solution. The electrochemical activity was highest for the supported catalyst synthesized at pH 8. Increasing the Se concentration of the catalyst up to 15 mol% increased the catalytic activity for the ORR; at this Se concentration, the activity of the catalyst was considerably higher than that observed for pure Ru catalyst synthesized at exactly the same conditions. The influence of the type of carbon support on the activity of the electrocatalyst was also investigated. Among the different supports, including carbon black (Vulcan XC-72R) (C1), and nanoporous carbons synthesized from resorcinol- (C2) and phloroglucinol-formaldehyde (C3) resins, the Ru_xSe_y catalyst supported on C3 exhibited highest activity for ORR.     

Evolution of the local structure and electrochemical properties of spinel LiNixMn2−xO4 (0 ≤ x ≤ 0.5)

A series of Ni substituted spinel LiNi_xMn_2−xO₄ (0 ≤ x ≤ 0.5) have been synthesized to study the evolution of the local structure and their electrochemical properties. X-ray diffraction showed a few Ni cations moved to the 8a sites in heavily substituted LiNi_xMn_2−xO₄ (x ≥ 0.3). X-ray photoelectron spectroscopy confirmed Ni²⁺ cations were partially oxidized to Ni³⁺. The local structures of LiNi_xMn_2−xO₄ were studied by analyzing the and A_1g Raman bands. The most compact [Mn(Ni)O₆] octahedron with the highest bond energy of Mn(Ni)O was found for LiNi_0.2Mn_1.8O₄, which showed a Mn(Ni)O average bond length of 1.790 Å, and a force constant of 2.966 N cm⁻¹. Electrolyte decomposition during the electrochemical charging processes increased with Ni substitution. The discharge capacities at the 4.1 and 4.7 V plateaus obeyed the linear relationships with respect to the Ni substitution with the slopes of −1.9 and +1.9, which were smaller than the theoretical values of −2 and +2, respectively. The smaller slopes could be attributed to the electrochemical hysteresis and the presence of Ni³⁺ in the materials.     

Controllable synthesis of CaTi2O4(OH)2 nanoflakes by a facile template-free process and its properties

Serrated leaf-like CaTi₂O₄(OH)₂ nanoflake crystals were synthesized via a template-free and surfactant-free hydrothermal process. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The growth process for CaTi₂O₄(OH)₂ nanoflakes was dominated by a crystallization–dissolution–recrystallization growth mechanism. BET analysis showed that CaTi₂O₄(OH)₂ nanoflakes had mesoporous structure with an average pore size of 8.7 nm, and a large surface area of 88.4 m² g⁻¹. Cyclic voltammetry and galvanostatic charge–discharge tests revealed that the electrode synthesized from CaTi₂O₄(OH)₂ nanoflakes reached specific capacitances of 162 F g⁻¹ at the discharge current of 2 mA cm⁻², and also exhibited excellent electrochemical stability.     

Electrochemical characteristics of cobalt-substituted lithium nickel oxides synthesized from lithium hydro-oxide and nickel and cobalt oxides

LiNi_1−yCo_yO₂ (y=0.1, 0.3 and 0.5) were synthesized by solid state reaction method at 800 °C and 850 °C from LiOH·H₂O, NiO and Co₃O₄ as starting materials. The electrochemical properties of the synthesized LiNi_1−yCo_yO₂ were investigated. As the content of Co decreases, particle size decreases rapidly and particle size distribution gets more homogeneous. When the particle size is compared at the same composition, the particles synthesized at 850 °C are larger than those synthesized at 800 °C. LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest intercalated and deintercalated Li quantity Δx among LiNi_1−yCo_yO₂ (y=0.1, 0.3 and 0.5). LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest first discharge capacity (178 mAh/g), followed by LiNi_0.7Co_0.3O₂ (162 mAh/g) synthesized at 800 °C. LiNi_0.7Co_0.3O₂ synthesized at 800 °C has discharge capacities of 162 and 125 mAh/g at n=1 and n=5, respectively.     

Preparation and characterization of ramsdellite Li2Ti3O7 as an anode material for asymmetric supercapacitors

Ramsdellite Li₂Ti₃O₇ was first synthesized via sol-gel process with good crystallity of an average particle size of 0.175 μm. The product was thoroughly investigated as a lithium intercalation compound, and as an active anode material in asymmetric supercapacitors coupling with activated carbon as cathode. Lithium intercalation reactions were found occurring at 1.32 and 1.62 V versus Li/Li⁺, respectively. A reversible specific capacity of 150 mA h g⁻¹ at 1C was obtained on Li₂Ti₃O₇ electrode in a nonaqueous electrolyte. The charge current was found to strongly influence the anodic discharge capacity in the asymmetric cell. The capacity retention at 10C charge-discharge rate was found to be 75.9% in comparison with that at 1C.     

Synthesis and characterization of a novel graft copolymer with poly(n-octylallene-co-styrene) backbone and poly(?-caprolactone) side chain

A novel graft copolymer consisting of poly(n-octylallene-co-styrene) (PALST) as backbone and poly(?-caprolactone) (PCL) as side chains was synthesized with the combination of coordination copolymerization of n-octylallene and styrene and the ring-opening polymerization (ROP) of ?-caprolactone. Poly(n-octylallene-co-styrene) (PALST) backbone was prepared from the copolymerization of n-octylallene and styrene with high yield by using the coordination catalyst system composed of bis[N,N-(3,5-di-tert-butylsalicylidene)anilinato]titanium(IV) dichloride (Ti(Salen)₂Cl₂) and tri-isobutyl aluminum(Al(i-Bu)₃). The molar ratio of each segment in the copolymer, and the molecular weight of the copolymer as well as the microstructure of the copolymer could be adjusted by varying the feeding ratio of both styrene and n-octylallene. The hydroxyl functionalized copolymer PALST-OH was prepared by the reaction of mercaptoethanol with the pendant double bond of PALST in the presence of radical initiator azobisisbutyronitrile (AIBN). The target graft copolymer [poly(n-octylallene-co-styrene)-g-polycaprolactone] (PALST-g-PCL) was synthesized through a grafting-from strategy via the ring-opening polymerization using PALST-OH as macroinitiator and Sn(Oct)₂ as catalyst. Structures of resulting copolymer were characterized by means of gel permeation chromatography (GPC) with multi-angle laser light scattering (MALLS), ¹³C NMR, ¹H NMR, DSC, polarized optical microscope (POM) and contact angle measurements.