Study on superabsorbent composites. IX: Synthesis,characterization and swelling behaviors of polyacrylamide/clay composites based on various clays

A series of clay-based superabsorbent composite from acrylamide (AM) and various clays, such as attapulgite, kaolinite, mica, vermiculate and Na⁺-montmorillonite, was prepared by free-radical aqueous polymerization, using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator, and then saponified with sodium hydroxide solution. In this paper, the reaction mechanism and thermal stability of the superabsorbent composites incorporated with various clays were characterized by FTIR, XRD and TGA, respectively. The effects of clay kind and clay content on equilibrium water absorbency of these composites were also investigated and compared. In addition, the influences of clay kind on comprehensive swelling behaviors of the PAM/clay superabsorbent composites were studied. The results indicated that the introduced clays could influence physicochemical properties of obtained superabsorbent composites. Mica could improve thermal stability of corresponding superabsorbent composites to the highest degree comparing with the other clays. The PAM/clay superabsorbent composites incorporated with 10 wt% clay of various kinds were all endowed with equilibrium water absorbency of more than 1300 g g⁻¹. The equilibrium water absorbency decreases with increasing clay content and correlates with the kind of clay. Attapulgite-based superabsorbent composite was endowed with higher water absorbency in univalent cationic saline solution, however, the vermiculite- and the kaolinite-based ones acquired the highest water absorbency in CaCl₂ and FeCl₃ aqueous solution, respectively. Moreover, the superabsorbent composites incorporated with Na⁺-montmorillonite have higher swelling rate and that of doped with mica was endowed with higher reswelling capability.     

Promising graphene/carbon nanotube foam@π-conjugated polymer self-supporting composite cathodes for high-performance rechargeable lithium batteries

Three-dimensional (3D) graphene foam materials are highly favored due to large accessible surface and excellent conductive network, which can be commendably applied as self-supporting electrodes for advanced rechargeable lithium batteries (RLBs). Here, promising graphene nanosheets/acid-treated multi-walled carbon nanotubes (GNS/aMWCNT)-supported 1,5-diaminoanthraquinone (DAA) organic foams [oGCTF(DAA)] are prepared by organic solvent displacement method followed by solvothermal reaction. And then electrochemical polymerization is carried out to obtain 3D porous GNS/aMWCNT organic foam-supported poly(1,5-diaminoanthraquinone) (oGCTF@PDAA) nanocomposites, which achieves the ordered growth of homogeneous PDAA nanoparticles on GNS/aMWCNT surface due to the role of oGCTF(DAA). Such structure largely improves PDAA utilization, facilitates charge transportation and suppresses the dissolution of PDAA. As a result, the oGCTF@PDAA cathode for RLBs delivers a high discharge capacity of 289 mAh g⁻¹ at 30 mA g⁻¹ and still retains 122 mAh g⁻¹ at extreme 10 A g⁻¹ for rapid charging/discharging. Moreover, superior cycling stability is achieved with only 14.8% capacity loss after 2000 cycles even at a high current density of 1 A g⁻¹.     

Enhancement of Lipase-catalyzed Synthesis of Caffeic Acid Phenethyl Ester in Ionic Liquid with DMSO Co-solvent

Caffeic acid phenethyl ester (CAPE) is a natural and rare ingredient with several biological activities, but its industrial production using lipase-catalyzed esterification of caffeic acid (CA) and 2-phenylethanol (PE) in ionic liquids (ILs) is hindered by low substrate concentrations and long reaction time. To set up a high-efficiency bioprocess for production of CAPE, a novel dimethyl sulfoxide (DMSO)–IL co-solvent system was established in this study. The 2% (by volume) DMSO–[Bmim][Tf₂N] system was found to be the best medium with higher substrate solubility and conversion of CA. Under the optimum conditions, the substrate concentration of CA was raised 8-fold, the reaction time was reduced by half, and the conversion reached 96.23%. The kinetics follows a ping-pong bi-bi mechanism with inhibition by PE, with kinetic parameters as follows: V_max = 0.89 mmol · min^− 1 · g^− 1, K_m,CA = 42.9 mmol · L^− 1, K_m,PE = 165.7 mmol · L^− 1, and K_i,PE = 146.2 mmol · L^− 1. The results suggest that the DMSO co-solvent effect has great potential to enhance the enzymatic synthesis efficiency of CAPE in ILs.     

Graphitic carbon nitride nanosheet-assisted preparation of N-enriched mesoporous carbon nanofibers with improved capacitive performance

N-enriched mesoporous carbon nanofibers (NMCNFs) were prepared by an electrospinning technique using graphitic carbon nitride (g-C₃N₄) nanosheets both as sacrificial template and N-doping source. The resultant NMCNF film has a high N-doping level of 8.6 wt% and a high specific surface area of 554 m² g⁻¹. When directly used as the electrode material for supercapacitor, the free-standing NMPCNF film shows a significantly improved capacitive performance including a higher specific capacitance (220 F g⁻¹ at 0.2 A g⁻¹) and a better rate capability (∼70% retention at 20 A g⁻¹) than those of microporous carbon nanofiber film prepared using the same process without using g-C₃N₄ nanosheets (145 F g⁻¹ at 0.2 A g⁻¹ and ∼45% retention at 20 A g⁻¹). Moreover, the NMCNFs show superior stability with only a ∼3% decrease of its initial capacitance after 1000 cycles at a high current density of 10 A g⁻¹. More significantly, the energy density of a symmetrical supercapacitor (SC) based on the NMPCNF film can reach 12.5 Wh kg⁻¹ at a power density of 72 W kg⁻¹.     

Hydrazine hydrate-induced hydrothermal synthesis of MnFe2O4 nanoparticles dispersed on graphene as high-performance anode material for lithium ion batteries

Herein, a MnFe₂O₄/graphene (MnFe₂O₄/G) nanocomposite has been synthesized via a facile N₂H₄·H₂O-induced hydrothermal method. During the synthesis, N₂H₄·H₂O is employed to not only reduce graphene oxide to graphene, but also prevent the oxidation of Mn²⁺ in alkaline aqueous solution, thus ensuring the formation of MnFe₂O₄/G. Moreover, MnFe₂O₄ nanoparticles (5–20 nm) are uniformly anchored on graphene. MnFe₂O₄/G electrode delivers a large reversible capacity of 768 mA h g⁻¹ at 1 A g⁻¹ after 200 cycles and high rate capability of 517 mA h g⁻¹ at 5 A g⁻¹. MnFe₂O₄/G holds great promise as anode material in practical applications due to the outstanding electrochemical performance combined with the facile synthesis strategy.     

Porous structures in stacked,crumpled and pillared graphene-based 3D materials

Graphene, an atomically thin material with the theoretical surface area of 2600 m² g⁻¹, has great potential in the fields of catalysis, separation, and gas storage if properly assembled into functional 3D materials at large scale. In ideal non-interacting ensembles of non-porous multilayer graphene plates, the surface area can be adequately estimated using the simple geometric law ∼2600 m² g⁻¹/N, where N is the number of graphene sheets per plate. Some processing operations, however, lead to secondary plate–plate stacking, folding, crumpling or pillaring, which give rise to more complex structures. Here we show that bulk samples of multilayer graphene plates stack in an irregular fashion that preserves the 2600/N surface area and creates regular slot-like pores with sizes that are multiples of the unit plate thickness. In contrast, graphene oxide deposits into films with massive area loss (2600–40 m² g⁻¹) due to nearly perfect alignment and stacking during the drying process. Pillaring graphene oxide sheets by co-deposition of colloidal-phase particle-based spacers has the potential to partially restore the large monolayer surface. Surface areas as high as 1000 m² g⁻¹ are demonstrated here through colloidal-phase deposition of graphene oxide with water-dispersible aryl-sulfonated ultrafine carbon black as a pillaring agent.     

Selective boron extraction by polymer supported 2-hydroxylethylamino propylene glycol functions

Boron sorption ability of polymer supported 2-hydroxyethylamino propylene glycol functions was investigated. 2-hydroxyethylamino propylene glycol was prepared by reaction of glycidol with excess ethanolamine in N-methyl, 2-pyrrolidone (NMP). This was reacted with terpolymer of glycidyl metacrylate (0.4 mol) with methyl metacrylate (0.5 mol) and divinylbenzene (0.1 mol) which was prepared in spherical beads form (210–422 μm) by suspension polymerization.The resulting terpolymer having hydroxyethylamino propylene glycol functions (1.82 mmol g⁻¹) was found to be as efficient as previously reported iminodipropylene glycol functional resins in removal of trace boron from water. The resin showed a boron loading capacity of 1.6 mmol g⁻¹. Nearly second-order kinetics, with respect to the boric acid (k = 1.65 mol l⁻¹ s⁻¹, with a correlation factor of 0.99129) was determined in non-buffered conditions.It was observed that, more than 95% of boron is extracted by this resin from very dilute H₃BO₃ solution (100 ppm initial concentration) in less than 30 min of contact time. Splitting of sorbed boron can be achieved by simple acid leaching (4 M HCl) and regenerated by NaOH (0.1 M) solution.     

Multi-walled carbon nanotubes stimulate callus induction,secondary metabolites biosynthesis and antioxidant capacity in medicinal plant Satureja khuzestanica grown in vitro

The present study was carried out to explore the potential effects of multi-walled carbon nanotubes (MWCNTs) on callus induction and secondary metabolism in Satureja khuzestanica. Leaf segments were aseptically cultured in B5 basal medium with different MWCNTs concentrations (0, 25, 50, 100, 250 and 500 μg ml⁻¹). The calli morphogenic responses were measured and the contents of phenolics, flavonoids, rosmarinic acid (RA), caffeic acid (CA), and the activity of polyphenol oxidase (PPO), l-phenylalanine ammonia-lyase (PAL) and peroxidase (POD) were quantified. Moreover, antioxidant activities of calli extract were assayed. Calli growth improved significantly with the increase of MWCNTs concentration, peaked at 50 μg ml⁻¹, and then followed a rapid decrease at 500 μg ml⁻¹. However, metabolic effects observed following exposure to MWCNTs particularly at 100 μg ml⁻¹ tended to be more pronounced than all other treatments, exhibiting significant induction of antioxidant activity with the lowest IC₅₀ value. Maximum oxidative stress index (H₂O₂) and the highest PPO and POD activities were observed on the media treated with 500 μg ml⁻¹ MWCNTs. Our findings suggest for the first time that use of MWCNTs at specific levels could act as a novel elicitor for in vitro biosynthesis of valuable secondary metabolites and antioxidant drugs.     

Bioconversion of barley straw and corn stover to butanol (a biofuel) in integrated fermentation and simultaneous product recovery bioreactors

In these studies concentrated sugar solutions of barley straw and corn stover hydrolysates were fermented using Clostridium beijerinckii P260 with simultaneous product recovery and compared with the performance of a control glucose batch fermentation process. The control glucose batch fermentation resulted in the production of 23.25 g L⁻¹ ABE from 55.7 g L⁻¹ glucose solution resulting in an ABE productivity and yield of 0.33 g L⁻¹ h⁻¹ and 0.42, respectively. The control reactor (I) was started with 62.5 g L⁻¹ initial glucose and the culture left 6.8 g L⁻¹ unused sugar due to butanol toxicity resulting in incomplete sugar utilization. Barley straw (BS) hydrolysate sugars (90.3 g L⁻¹) resulted in the production of 47.20 g L⁻¹ ABE with a productivity of 0.60 g L⁻¹ h⁻¹ and a yield of 0.42. Fermentation of corn stover (CS) hydrolysate sugars (93.1 g L⁻¹) produced 50.14 g L⁻¹ ABE with a yield of 0.43 and a productivity of 0.70 g L⁻¹ h⁻¹. These productivities are 182–212% higher than the control run. The culture was able to use 99.4–100% sugars (CS & BS respectively) present in these hydrolysates and improve productivities which were possible due to simultaneous product removal. Use of >100 g L⁻¹ hydrolysate sugars was not considered as it would have been toxic to the culture in the integrated (simultaneous fermentation and recovery) process.     

Facile synthesis of sandwich-like polyaniline/boron-doped graphene nano hybrid for supercapacitors

The physicochemical property of chemically prepared graphene can be significantly changed due to the incorporating of heteroatoms into graphene. In this article, boron-doped graphene sheets are used as carbon substrates instead of graphene for loading polyaniline by in situ polymerization. Compared with the individual component and polyaniline/non-doped graphene, the sandwich-like polyaniline/boron-doped graphene exhibits remarkably enhanced electrochemical specific capacitance in both acid and alkaline electrolytes. In a three-electrode configuration, the hybrid has a specific capacitance about 406 F g⁻¹ in 1 M H₂SO₄ and 318 F g⁻¹ in 6 M KOH at 1 mV s⁻¹. In the two-electrode system of a symmetric supercapacitor, this hybrid achieves a specific capacitance about 241 and 189 F g⁻¹ at 0.5 A g⁻¹ with a specific energy density around 19.9 and 30.1 Wh kg⁻¹, in the acid and alkaline electrolytes, respectively. The as-obtained polyaniline/boron-doped graphene hybrid shows good rate performance. Notably, the obtained electrode materials exhibit long cycle stability in both acid and alkaline electrolytes (∼100% and 83% after 5000 cycles, respectively). The improved electrochemical performance of the hybrid is mainly attributed to the introduction of additional p-type carriers in carbon systems by boron-doping and the well combination of pseudocapacitive conducting polyaniline.     

Ionic liquid as an efficient promoting medium for synthesis of dimethyl carbonate by oxidative carbonylation of methanol

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol using Cu salt catalysts in the presence of various room temperature ionic liquids (RTILs) was reported. Among the ionic liquids used, N-butylpyridinium tetrafluoroborate was the most effective promoter in terms of the conversion of methanol and the selectivity to dimethyl carbonate (DMC). The influences of reaction temperature, pressure, time, molar ratio of CO/O₂, and amount of the ionic liquid on the oxidative carbonylation of methanol were investigated. The results indicated that under the reaction conditions of 120 °C and 2.4 MPa of a 2:1 mixture of CO and O₂, 17.2% conversion of methanol, 97.8% selectivity of DMC and a DMC productivity of 4.6 g g⁻¹ cat h⁻¹ were achieved. The N-butylpyridinium tetrafluoroborate-meditated CuCl catalyst system could be reused at least five recycles with the same selectivity and a slight loss of catalytic activity due to loss of the catalyst during handling and transferring the reaction mixture.     

Preparation and swelling behaviors of a high temperature resistant superabsorbent using tetraallylammonium chloride as crosslinking agent

A new high temperature resistant superabsorbent was synthesized through solution polymerization of acrylamide (AM) and partially neutralized acrylic acid (AA), using tetraallylammonium chloride (TAAC) as crosslinker, ammonium persulfate (APS) as initiator. Parameters that influence water absorbency of the superabsorbent at 25 °C and 200 °C such as molar ratios of AM to AA, TAAC to AA, APS to AA and neutralization degree, were investigated. Swelling behaviors of superabsorbent prepared at the optimum conditions in different pH and saline solutions were studied. The swelling ratios of superabsorbent in distilled water and 1 wt% NaCl solution at 250 °C reach 287 g/g and 69 g/g, respectively.     

Chitosan modified with Reactive Blue 2 dye on adsorption equilibrium of Cu(II) and Ni(II) ions

This study aimed at immobilizing Reactive Blue 2 (RB 2) dye in chitosan microspheres through nucleophilic substitution reaction. The adsorbent chemical modification was confirmed by Raman spectroscopy and thermogravimetric analysis. This adsorption study was carried out with Cu(II) and Ni(II) ions and indicated a pH dependence, while the maximum adsorption occurred around pH 7.0 and 8.5, respectively. The pseudo second-order kinetic model resulted in the best fit with experimental data obtained from Cu(II) (R = 0.997) and Ni(II) (R = 0.995), also providing a rate constant, k₂, of 4.85 × 10⁻⁴ and 3.81 × 10⁻⁴ g (mg min)⁻¹, respectively, thus suggesting that adsorption rate of metal ions by chitosan-RB 2 depends on the concentration of ions on adsorbent surface, as well as on their concentration at equilibrium. The Langmuir and Freundlich isotherm models were employed in the analysis of the experimental data for the adsorption, in the form of linearized equations. Langmuir model resulted in the best fit for both metals and maximum adsorption was 57.0 mg g⁻¹ (0.90 mmol g⁻¹) for Cu(II) and 11.2 mg g⁻¹ (0.19 mmol g⁻¹) for Ni(II). The Cu(II) and Ni(II) ions were desorbed from chitosan-RB 2 with aqueous solutions of EDTA and H₂SO₄, respectively.     

Kinetic and thermodynamic studies on the removal of Cu(II) ions from aqueous solutions by adsorption on modified sand

Studies on the removal of copper by adsorption on modified sand have been investigated. The adsorbent was characterized by XRD, FTIR and SEM. Removal of Cu was carried out in batch mode. The values of thermodynamic parameters namely ΔG⁰, ΔH⁰ and ΔS⁰ at 25 °C were found to be −0.230 kcal⁻¹ mol⁻¹, +4.73 kcal⁻¹ mol⁻¹ and +16.646 cal K⁻¹ mol⁻¹, respectively. The process of removal was governed by pseudo second order rate equation and value of k₂ was found to be 0.122 g mg⁻¹ min⁻¹ at 25 °C. The resultant data can serve as baseline data for designing treatment plants at industrial scale.     

Physical,thermal and ablative performance of CVI densified urethane-mimetic SiC preforms containing in situ grown Si3N4 whiskers

A two-step process has been developed for silicon carbide (SiC) coated polyurethane mimetic SiC preform containing silicon nitride (Si₃N₄) whiskers. SiC/Si₃N₄ preforms were prepared by pyrolysis/siliconization treatment at 1600 °C, of powder compacts containing rigid polyurethane, novolac and Si, forming a porous body with in situ grown Si₃N₄ whiskers. The properties were controlled by varying Si/C mole ratios such as 1–2.5. After densification using a chemical vapour infiltration, the resulting SiC/Si₃N₄/SiC composites showed excellent oxidation resistance, thermal conductivity of 4.32–6.62 Wm⁻¹ K⁻¹, ablation rate of 2.38 × 10⁻³ − 3.24 × 10⁻³ g cm⁻² s and a flexural strength 43.12–55.33 MPa for a final density of 1.39–1.62 gcm⁻³. The presence of a Si₃N₄ phase reduced the thermal expansion mismatch resulting in relatively small cracks and well-bonded layers even after ablation testing. This innovative two-step processing can provide opportunities for expanded design for using SiC/Si₃N₄/SiC composites being lightweight, inexpensive, homogeneous and isotropic for various high temperature applications.     

Graphene-wrapped polyaniline nanofibers as electrode materials for organic supercapacitors

Graphene-wrapped polyaniline nanofibers were prepared by assembly of negatively charged graphene oxide with positively charged aqueous dispersible polyaniline nanofibers in an aqueous dispersion, followed by the reduction of the graphene oxide. The hybrid material with a graphene oxide loading of 9.1 wt.% displayed a high specific capacitance of over 250 F g⁻¹ in a 1 M Et₄N⁺·BF₄⁻/propylene carbonate electrolyte, a 39.7% increase compared with pristine polyaniline nanofibers. A significant improvement in long-term cycle life was also realized. The hybrid exhibited an initial specific capacitance of 236 F g⁻¹, which remained as high as 173.3 F g⁻¹ over 1000 cycles, or a 26.3% decrease, much better than that for pure polyaniline nanofibers. An asymmetric supercapacitor based on this hybrid material and activated carbon was assembled. An energy density of 19.5 W h kg⁻¹ at a power density of 738.95 W kg⁻¹ was obtained for the cell under an operating voltage window of 2 V.     

Carbons with narrow pore size distribution prepared by simultaneous carbonization and self-activation of tobacco stems and their application to supercapacitors

Highly microporous carbons with narrow pore size distribution have been prepared by simultaneous carbonization and self-activation of tobacco wastes at temperatures ranging from 600 to 1000 °C. The efficiency of porosity development, without pores broadening, is attributed to well-distributed alkalis at the molecular level in the tobacco precursor. With Burley tobacco, the BET specific surface area and average micropore size L₀ increased up to 800 °C (Burley 800), where the values reached maxima of 1749 m² g⁻¹ and 1.2 nm, respectively. At temperatures higher than 800 °C, annealing of the materials dominates and provokes a decrease of S_BET and L₀. Burley carbons were implemented in supercapacitors using 1 mol L⁻¹ aqueous Li₂SO₄ or 1 mol L⁻¹ TEABF₄ in acetonitrile. In both electrolytes, the capacitance of Burley carbons followed the same trend as S_BET and L₀. Burley 800 demonstrated outstanding capacitance values of 167 F g⁻¹ (at 0.8 V limit) and 141 F g⁻¹ (at 2.3 V limit) in 1 mol L⁻¹ aqueous Li₂SO₄ and 1 mol L⁻¹ TEABF₄, respectively. Such values, about 50% higher as compared to commercially available carbons, are attributed to the narrow pore size distribution of this carbon with a maximum of pores around 1.2 nm close to the size of solvated ions in these electrolytes.     

Microwave-enhanced catalytic degradation of phenol over nickel oxide

A mix-valenced nickel oxide, NiO_x, was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Further, pure nickel oxide was obtained from the NiO_x by calcination at 300, 400 and 500 °C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), nitrogen adsorption at −196 °C and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of phenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhance catalytic degradation (MECD) of phenol have been investigated. The results indicated that the relative activity affected significantly with the oxidation state of nickel, surface area and surface acidity of nickel oxide, i.e., NiO_x (>+2 and S_BET = 201 m² g⁻¹) ≫ C300 (+2 and S_BET = 104 m² g⁻¹) > C400 (+2 and S_BET = 52 m² g⁻¹) > C500 (+2 and S_BET = 27 m² g⁻¹). The introduction of microwave irradiation could greatly shorten the time of phenol degradation.     

Three-dimensional hybrid materials of fish scale-like polyaniline nanosheet arrays on graphene oxide and carbon nanotube for high-performance ultracapacitors

Three-dimensional (3D) hybrid materials composed of 2D fish scale-like polyaniline (PANI) nanosheet arrays on graphene oxide sheets and carbon nanotubes were synthesized by a one-step process using a simplified template-free polymerization method. PANI nanosheet growth is proposed to be accomplished through electrostatic interaction, hydrogen bonding, and π–π stacking interaction. Such a material exhibits specific capacitances of 589 and 413 F g⁻¹ at 0.2 and 5 A g⁻¹, respectively, compared to pristine PANI of 397 and 180 F g⁻¹. After 1000 cycles, the composite still retains 81% of its initial capacitance, while PANI retains only 48%.     

Development of gluten-free flat bread using hydrocolloids: Xanthan and CMC

The effects of xanthan gum (XG) and (carboxymethyl cellulose (CMC) (5–20 g kg⁻¹) on the quality parameters of gluten-free flat bread, based on rice flour were investigated. Increase in CMC concentration yielded bigger gas cells, leading to better crumb porosity. Formula 3 (F3), containing 15 g kg⁻¹ XG and formula 10 (F10), containing 10 g kg⁻¹ CMC and 10 g kg⁻¹ XG resulted in the highest dough yield (P < 0.05) and bread yield, respectively, and F10 showed the lowest bread weight loss (P < 0.05). F10, followed by, F3 were the best and most acceptable (P < 0.05) formulae, compared to all the others.