Surface‐modified carbon black derived from used car tires as alternative,reusable, and regenerable catalysts for H2 release studies from sodium borohydride methanolysis

Carbon black (CB) obtained from used car tire rubbers were treated with concentrated sulfuric and nitric acids. The oxidized CB (CB‐COO‐Na⁺) is subsequently modified with epichlorohydrin (ECH) and amines including polyethylene imine (PEI). These modified CBs such as CB‐PEI are used as metal‐free catalysts in methanolysis of sodium borohydride (NaBH₄) to produce hydrogen. The hydrogen generation rate (HGR) of 3089 ± 44.69 mL.min^‐1.g^‐1 is accomplished at room temperature with CB‐PEI‐hydrochloric acid (HCl) catalyst. The resulting activation energy of 34.7 kJ/mol for the temperature range of ?20°C to +30°C compares favorably to most of alternative catalysts reported in literature while reaction catalyzing capabilities of CB‐PEI‐HCl particles extend to the subzero temperature range (?20°C‐0°C). The reuse and regeneration studies conducted for the CB‐PEI‐HCl catalyst showed that these catalysts do provide complete conversion at every use up to five consecutive runs and retain 50 ± 2.5% of the original hydrogen generation rate at the fifth consecutive reuse. The CBs‐based catalysts are fully regenerated with HCl treatment.     

The Characteristic Parameters of Ni/<Emphasis Type="Italic">n</Emphasis>-6H-SiC Devices Over a Wide Measurement Temperature Range

Ni/n-type 6H-SiC/Ni Schottky barrier diodes (SBDs) have been prepared by the DC magnetron sputtering deposition technique. Their current-voltage characteristics (I-V) have been measured in the measurement temperature range of 40-400 K with steps of 20 K under dark conditions. The barrier height (BH) values from the temperature-dependent forward and reverse bias I-V characteristics by different methods coincide with each other which indicates the elimination of the polarity between the Si and C ions. The ideality factor value remains almost unchanged in the 160-400 K range, and below 160 K, it has the values of 1.57 at 140 K, and 3.82 at 60 K. The BH has the values of 0.79 eV at 400 K, and 0.71 eV at 300 K. The decrease in the BH is due to the fact that the current will preferentially flow through the lowest BH with decreasing temperature due to barrier inhomogeneity. The value of 0.71 eV at 300 K is in close agreement with the values of 0.65 and 0.83 eV reported from the forward bias I-V characteristics for the Ni /n-type 6H-SiC in the literature. Thus, it has been concluded that the reduced barrier devices are promising for applications in devices operating at cryogenic temperatures as infrared detectors, sensors in thermal imaging and small signal zero-bias rectifiers and microwave mixers.     

Development of novel adsorbent materials for recovery and enrichment of uranium from aqueous media

A new polymeric adsorbent bearing both hydrophilic groups providing swelling in water and amidoxime groups for chelating with uranyl ions (UO₂²⁺), has been developed and its adsorptive ability for recovering uranium from aqueous media has been investigated. The polymers obtained by irradiating the solution of polyethylene glycol (PEG) in acrylonitrile (AN) are defined as interpenetrating polymer networks (IPNs) and the adsorbent has been obtained by applying the amidoximation reaction to the IPNs with a conversion ratio of ∼ 60%. Kinetics of the conversion reaction of the cyano (CN) group to the amidoxime (HONCNH₂) group has been studied by reacting with hydroxylamine (NH₂OH) solution at a molar ratio of NH₂OH/CN = 1.25 in aqueous media at three different temperatures, 30, 40, and 50°C, for 3–4 days. The degree of amidoximation ratio was determined by UO₂²⁺ ion adsorption and FTIR spectrometry and the UO₂²⁺ ion adsorption values were found by both UV and gamma spectrometry and also by gravimetry. It was found that the polymeric adsorbent has a very high adsorption ability for uranium and quite a good stability in aqueous media. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2475–2480, 1997     

In situ micro/nano-hydrogel synthesis from acrylamide derivates with lecithin organogel system

Acrylamide based hydrogel particles with variable charge were synthesized in different sizes using a biocompatible surfactant. We use microemulsion polymerization to synthesize the hydrogel particles in lecithin organogel systems. The phospholipid, lecithin, is a soybean extract that exhibits a rich phase behavior depending on various factors such as amount of water, co-solvent, additives and their concentrations. By UV irradiation of water-in-oil microemulsions of lecithin, containing different monomers, phospholipid coated hydrogels were synthesized in situ. The hydrogel particle size varies from a few hundred nanometers to tens of micrometer. The response time of these micron sized hydrogel particles, as measured by swelling experiments, is very fast (∼10⁰ s) in comparison with their corresponding bulk hydrogels (∼10¹ h). The positively charged cationic hydrogel microparticles were embedded/dispersed into another hydrogel matrix to render responsive behavior to a non-responsive matrix. Besides TEM and SEM studies, fluorescein dye absorption studies were also performed in order to visualize the hydrogel microparticles. Additionally, anionic hydrogel micro/nano-particles were also synthesized in the lecithin system.     

Degradation of Remazol Black B dye and its simulated dyebath wastewater by advanced oxidation processes in heterogeneous and homogeneous media

This study focused on the degradation of hydrolysed Remazol Black B (CI Reactive Black 5), a common diazo reactive dye, in aqueous solution. In the presence of various dye auxiliary chemicals a typical Remazol Black exhausted dyebath liquor simulated, which was then treated with homogeneous [ozonation with hydroxy ions, and Fe(II) or Fe(III) with hydrogen peroxide] and heterogeneous (titanium dioxide with UV-A irradiation) advanced oxidation processes. Treatment performance of the investigated advanced oxidation systems was comparatively assessed in terms of the environmental sum parameters total organic carbon, biochemical oxygen demand and spectrophotometric measurements. The results obtained clearly reveal that the investigated advanced oxidation processes are capable of completely decolourising and partially mineralising the dye solution and its simulated dyebath effluent under predetermined reaction conditions. During the application of alkaline ozonation at an ozone dose of 2340 mg/ml, a three-fold biodegradability enhancement was observed.     

Rheological characterization of a charged cationic hydrogel network across the gelation boundary

The in situ rheological behavior across the gelation threshold has been investigated for an affine network of a completely charged cationic monomer (3-acrylamidopropyl)-trimethylammonium chloride (APTMAC1) when it is crosslinked with a neutral crosslinker (N,N′-methylenebisacrylamide) to form a fully charged novel cationic hydrogel. The elastic moduli (G′) near the gel point (during the crosslinking or ‘curing’ process) show a power law dependence of the form G′(t)=ε^z, where ε=((t−t_c)/t_c) is the distance from the gel point (t_c). The critical exponent, z, for the hydrogel series investigated is estimated to be 1.5, slightly lower than the predictions based on percolation theory (z∼1.7-1.9). From the equilibrium (after the curing process) rheological measurements of a series of samples, it is inferred that there is a critical crosslinker mole percent (X_c) with respect to the monomer concentration, required to form a well-defined three-dimensional network with a solid-like behavior. The value of this X_c is found to be between 0.5 and 1%. The theoretically predicted value of X_c using the percolation theory (for the percolation of crosslinks, G₀(X)∝[|X−X_c|/X_c]^z) and the exponent estimated from the in situ measurements (z=1.5), is X_c∼0.6, which is in good agreement with the experiments. The results may have applicability in translating from bulk systems to the nanoscale in hydrogel design.     

Preparation of dextran cryogels for separation processes of binary dye and pesticide mixtures from aqueous solutions

We present mechanically strong macroporous, squeezable dextran cryogels as a column filling material for the removal and separation of binary organic dye and pesticide mixtures from aquatic medium. Dextran cryogels were prepared from aqueous solutions of dextran of various molecular weights (MWs) in the presence of 20 to 50 mol% divinyl sulfone (DVS) as a cross-linker at −18°C. The cryogels have interconnected irregular pores of 100 μm in sizes, and exhibit 69-84% reversible squeezability without damaging the 3D dextran network. Their total open pore volumes (6.3-10 mL g⁻¹), weight swelling ratios in water (1380%-2200%), and mechanical parameters could easily be adjusted by both DVS mol% and MW of dextran. Dextran cryogel with the highest modulus (3.8 ± 0.5 MPa), compressive stress (8 ± 2 MPa) and plateau stress (0.46 ± 0.04 MPa) was obtained at 50 mol% DVS using dextran with a MW of 15 to 25 kg·mol⁻¹. Dextran cryogels are hydrolysable at pH = 1 and 9 but stable at 7.4 independent on both the degree of cross-linking and MW of dextran. At below 50 mol% DVS, they are blood compatible and possess slight thrombogenic effect with blood clotting index value of 98% ± 5%. They are also capable to separate binary dye and pesticide mixtures from aqueous solutions via ionic interactions.     

Application of superporous magnetic cationic cryogels for persistent chromate (toxic chromate and dichromate) uptake from aqueous environments

Poly((3‐Acrylamidopropyl)trimethylammonium chloride) (p(APTMACl)) cryogels were prepared with cryopolymerization technique and employed for the removal of toxic chromate and dichromate anions from aqueous media. The maximum adsorption capacities of 94 mg/g and 135 mg/g for chromate and dichromate anions, respectively, were determined with the application of the Langmuir isotherm. These values are very close to the experimental values of about 77 and 128 mg/g from 100 mL, 100 ppm chromate, and dichromate solutions using 0.03 g cryogel. The removal efficiency of chromate and dichromate anions were increased with the increase in the amount of cryogel and the removal percentage of chromate and dichromate toxic anions were estimated as 99.21 and 93.61%, respectively, for 0.15 g of p(APTMACl) cryogels used in 100 mL, 100 ppm chromate, and dichromate solutions. Furthermore, magnetic p(APTMACl) cryogels were also prepared and used in the removal of chromate and dichromate, and the maximum adsorption capacities were 30 mg/g and 40 mg/g, respectively. Additionally, the adsorption of these anions were investigated from different media such as drinking water, tap water, seawater, and creek water; and the maximum adsorption amounts in drinking water were 65.5 ± 15, and 125.5 ± 11 mg/g for chromate and dichromate anions, respectively. The reusability of p(APTMACl) cryogels for the removal of chromate and dichromate anions was also investigated, and it was found that the adsorption capacity for chromate anions decreased to 71.23 ± 4.3 from 97.37 ± 4.5 mg/g, whereas the adsorption capacity of dichromate anions only decreased to 123.69 ± 3.5 mg/g from 129.9 ± 7 mg/g at the end of five adsorption‐desorption cycles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43438.