Adsorption separation of vinyl chloride and acetylene on activated carbon modified by metal ions

This work mainly involved the adsorption separation of vinyl chloride and acetylene on modified activated carbons. Six metal ions with different hardness were loaded on activated carbon respectively. The effect of metal ions on the adsorption separation performance of vinyl chloride and acetylene was investigated. The experimental results shown that the separation factor of C₂H₃Cl to C₂H₂ over modified activated carbon followed the order: Al(III)/AC > Mg(II)/AC > Fe(III)/AC > AC > Zn(II)/AC ≈ Cu(II)/AC > Ag(I)/AC. The effect of the hardness of metal ions on the adsorption capacity of C₂H₂ was more remarkable than that of C₂H₃Cl, thus the separation factor of C₂H₃Cl to C₂H₂ increased with the rising of absolute hardness of the metal ions.     

Theoretical study of noncovalent functionalization of BN nanotubes by various aromatic molecules

The unsatisfactory stability of CNT under high temperature or subject to strong oxidants has limited the potential use of p- and n-type field-effect transistors (FETs). Promisingly, boron nitride (BN) nanotubes are known to have the excellent resistance to oxidant and thermal stability at high temperature as well as the uniform electronic properties, which rends their possible application as alternative FET device. In this paper, through the theoretical computation of the noncovalent functionalization of BN nanotube by various aromatic molecules (including C₁₀H₈, C₁₄H₁₀, porphyrin, DDQ, and TCNQ molecules), we for the first time evaluate its possibility as a candidate of stable FET device. We find that: (i) these aromatic molecules can be stably adsorbed on the studied BN with the adsorption energy ranging from ? 0.22 (C₁₀H₈) to ? 0.42 eV (porphyrin); (ii) the adsorption of electrophilic molecules on the outer sidewall of BN nanotube realizes a p-type semiconductor with a smaller band gap (~ 0.90 eV); (iii) exoherdral adsorption of nucleophilic aromatic molecules leads to an n-type semiconductor. This novel BN nanotube-based material offers great promise for molecule electronics in terms of their good stability.     

H2/D2 adsorption and desorption studies on carbon molecular sieves with different pore structures

The critical effect of confinement on the interaction of hydrogen isotopes (H₂ and D₂) with carbon surfaces was investigated through a combined low temperature adsorption/thermal desorption spectroscopy (TDS) study on three carbon molecular sieves (CMS) possessing nanopores with nominal sizes between 0.3 and 0.5 nm. The porous structure and the sorption properties of all three adsorbents were characterized by N₂ (77 K) and CO₂ (273 K), as well as H₂ and D₂ (77 K) low pressure (up to 1 bar) adsorption measurements. The interaction of the carbons with hydrogen, deuterium, and an isotopic H₂/D₂ gas mixture was further studied by means of TDS measurements, extended to temperatures down to 20 K. The differences in the H₂/D₂ adsorption/desorption profiles of the three CMS samples are correlated with the respective micropore size distributions. The presence of very narrow micropores, with size close to the kinetic diameter of the hydrogen molecule, resulted in enhanced hydrogen (both for H₂ and D₂) interactions, giving rise to a TDS maximum centered on 122 K, the highest desorption temperature ever measured for the desorption of physisorbed hydrogen. Furthermore, the quantum effects on hydrogen/deuterium adsorption on CMS adsorbents have been addressed for the first time using the TDS technique.     

Selective low temperature synthesis of carbon nanospheres via the catalytic decomposition of trichloroethylene

The catalytic growth of structured carbon from a C₂H₄ and C₂HCl₃ feed promoted by Ni/SiO₂ in the presence of H₂ over the temperature range 673 K ≤ T ≤ 1023 K has been examined. The supported Ni phase exhibited an exclusive cubic symmetry (XRD analysis) with a range of Ni particle sizes (TEM analysis) and a net shift in the distribution to larger particles with increasing reduction temperature (from 20 to 36 nm), accompanied by a decrease in H₂ chemisorption. Conversion of C₂H₄ generated hydrogenation (C₂H₆), hydrogenolysis (CH₄) and decomposition (C + H₂) products. Ethane formation was favoured at lower temperatures with C formation increasingly preferred at higher temperatures so that C₂H₄ decomposition was the predominant process at T > 723 K; significant CH₄ production was only observed at T > 900 K. Carbon yield from C₂H₄ passed through a maximum at 773 K and took the form of high aspect ratio graphitic nanofibres with a central hollow core and diameters in the range 5–180 nm. The carbonaceous product has been characterized by a combination of TEM-EDX, SEM, XRD, BET area and temperature programmed oxidation (TPO). Carbon formation from C₂HCl₃ exceeded (by a factor of up to an order of magnitude) that generated via the decomposition of C₂H₄ at the same inlet C:Ni ratio to deliver essentially a carbon yield invariance (9.1 ± 0.3 g_C g_Ni^?1) where 898 K ≤ T ≤ 1023 K, which represents a carbon efficiency (fraction of carbon in the inlet feed that is converted to a solid carbon product) in excess of 96%. Ni/SiO₂ promoted a composite dehydrochlorination/decomposition of C₂HCl₃ to HCl + C. The nature of the carbon product generated from C₂HCl₃ is strongly temperature dependent with a shift from a pseudo-fibrous product at 773 K to a predominant nanosphere formation at 923 K. These nanospheres exhibit a wide diameter range (40–700 nm), a significant Cl content (1.1–2.6%, w/w) and a conglomeration or clustering to give a less ordered carbonaceous product than that generated at the lower temperature (773 K). A tentative carbon growth rationale is presented to account for the observed dependence of carbon structure on carbon-containing precursor and reaction temperature.     

Direct synthesis of carbon nanofibers on the surface of copper powder

A novel approach to synthesize carbon nanofibers (CNFs) directly on the surface of metal μm-sized particles to evenly disperse the carbon nanomaterials in a composite material was proposed. As a metal matrix, 5–10 μm copper particles were utilized. As a carbon source, C₂H₂, CH₄ and CO were examined. The best conditions were found to be in C₂H₂ (30 cm³/min) and H₂ (260 cm³/min) atmosphere at the temperature of 750 °C. The composites based on copper and CNFs prepared by vacuum hot pressing showed the increase in hardness from 35 to 60 kg/mm² almost retaining pure copper electrical properties.     

Fabrication of high pressure hydrogen adsorption/desorption unit—Adsorption study on flame synthesized carbon nanofibers

An in-house custom made high pressure adsorption/desorption unit has been designed and fabricated to study reversible hydrogen (H₂) intake capacity, hysteresis, kinetics, plateau pressure of various nanomaterials, zeolites and metallic compounds, in the pressure range of 1 ≤ P ≤ 150 atm. The unit has been used to estimate H₂ intake capacity of carbon nanofibers prepared by flame synthesis in the absence of catalyst. H₂ adsorption studies have been carried out in the pressure range of 25–100 atm at 297 K. The maximum H₂ intake capacity has been observed to be 3.7 wt% at 100 atm.     

The effects of the surface oxidation of activated carbon,the solution pH and the temperature on adsorption of ibuprofen

A commercial microporous–mesoporous granular activated carbon was modified by oxidation with either H₂O₂ in the presence or absence of ultrasonic irradiation, or NaOCl or by a thermal treatment under nitrogen flow. Raw and modified materials were characterized by N₂ adsorption–desorption measurements at 77 K, Boehm titrations, pH measurements and X-ray photoelectron spectroscopy. Ibuprofen adsorption kinetic and isotherm studies were carried out at pH 3 and 7 on raw and modified materials. The thermodynamic parameters of adsorption were calculated from the isotherms obtained at 298, 313 and 328 K. The pore size distribution of carbon loaded with ibuprofen brought out that adsorption occurred preferentially into the ultramicropores. The adsorption of ibuprofen on pristine activated carbon was found endothermic, spontaneous (ΔG° = −1.1 kJ mol⁻¹), and promoted at acidic pH through dispersive interactions. All explored oxidative treatments led mainly to the formation of carbonyl groups and in a less extent to lactonic and carboxylic groups. This then helped to enhance the adsorption uptake while decreasing adsorption Gibbs energy (notably −7.3 kJ mol⁻¹ after sonication in H₂O₂). The decrease of the adsorption capacity after bleaching was attributed to the presence of phenolic groups.     

Effects of tungsten and aluminium on the oxidation and phase formation in mechanically alloyed Ti(C,N)–W–Al systems

The effects of milling parameters and composition of the powder mixtures on the transformations of Ti(C,N)–W–Al powders processed by high energy ball milling were investigated by XRD, SEM and TEM. The strain energy and the fine particle size contributed to the high chemical reactivity with oxygen of the powders milled for 12–24 h. Powders milled for 48 h were chemically stable. The affinity with oxygen decreased after W dissolution in Ti(C,N), and the subsequent decrease in lattice strains. Aluminium lowered the lattice strains, and subsequently the strain energy stored in the deformed crystals of Ti(C_0.5N_0.05) and W milled above 25 °C. Fracturing of hard particles dominated in the early stage of milling in the absence of Al, whereas with Al, plastic deformation of particles and cold welding of Ti(C,N) and W particles by the softer Al prevailed at the same time.     

Continuous flame aerosol synthesis of carbon-coated nano-LiFePO4 for Li-ion batteries

Core–shell, nano-sized LiFePO₄-carbon particles were made in one step by scalable flame aerosol technology at 7 g/h. Core LiFePO₄ particles were made in an enclosed flame spray pyrolysis (FSP) unit and were coated in-situ downstream by auto thermal carbonization (pyrolysis) of swirl-fed C₂H₂ in an O₂-controlled atmosphere. The formation of acetylene carbon black (ACB) shell was investigated as a function of the process fuel-oxidant equivalence ratio (EQR). The core–shell morphology was obtained at slightly fuel-rich conditions (1.0<EQR<1.07) whereas segregated ACB and LiFePO₄ particles were formed at fuel-lean conditions (0.8<EQR<1). Post-annealing of core–shell particles in reducing environment (5 vol% H₂ in argon) at 700 °C for up to 4 h established phase pure, monocrystalline LiFePO₄ with a crystal size of 65 nm and 30 wt% ACB content. Uncoated LiFePO₄ or segregated LiFePO₄–ACB grew to 250 nm at these conditions. Annealing at 800 °C induced carbothermal reduction of LiFePO₄ to Fe₂P by ACB shell consumption that resulted in cavities between carbon shell and core LiFePO₄ and even slight LiFePO₄ crystal growth but better electrochemical performance. The present carbon-coated LiFePO₄ showed superior cycle stability and higher rate capability than the benchmark, commercially available LiFePO₄.     

Thermodynamic adsorption data of CH4, C2H6, C2H4 as the OCM process hydrocarbons on SAPO-34 molecular sieve

Adsorption of CH₄, C₂H₆ and C₂H₄, the feed and main products of oxidative coupling process of methane (OCM) has been studied on silicoalumina-phosphate molecular sieve (SAPO-34) in mild conditions. The experiments were conducted in a batch system based on volumetric adsorption measurement technique for determination equilibrium adsorption capacity in the absolute pressure range of 100–1000 kPa and at the isothermal temperatures of 303, 313 and 323 K. Various isotherm equations were fitted on the adsorption equilibrium data and the model parameters were predicted as a function of temperature. Isosteric heats of adsorption were determined using Clausius–Clapeyron equation at different surface coverage. Maximum capacity of SAPO-34 was observed at 303 K and 880–900 kPa equilibrium pressure with 1.25, 2.02 and 4.67 mmol/g adsorbed amount for methane, ethane and ethylene adsorption, respectively. The adsorption selectivity of ethane and ethylene against methane were determined and the appropriate potential of SAPO-34 was observed for separation of OCM products from methane. The isotherm models and enthalpy of adsorption can be efficiently used for the simulation of the adsorption process constructed at the downstream of the OCM process for separation of ethane and ethylene from methane.     

The production of carbon particles of different shapes produced by the chlorination of Cr(C5H5)2

Carbon particles have been obtained by the chlorination of chromocene (Cr(C₅H₅)₂). Changes in their morphology and micro-nanostructure have been monitored at two different temperatures. At 400 °C, filled materials (tubes and spheres) and agglomerated round particles are formed, whereas at 900 °C closed-end tubes, hollow and solid spheres were produced. Transmission electron microscopy shows that these particles are formed of highly disordered graphene-like layers, which is confirmed by the absence of the 2D and 2G bands in the Raman spectrum. The calculated in-plane correlation length of these graphene-like layers is 1.2 ± 0.1 nm. In all the carbon particles, electron energy-loss spectroscopy shows a very similar sp² carbon bonding content (89–98%) and mass density ranging from 1.6 to 1.8 g/cm³, both below standard graphite. Textural studies performed on the sample prepared at 900 °C show Type II adsorption isotherms with a surface area of 694 m²/g.     

Preparation of superhard BxCy fibers by microvortex-flow hyperbaric laser chemical vapor deposition

A novel class of freestanding B_xC_y fibers was prepared by hyperbaric-pressure laser chemical vapor deposition. Utilizing mixtures of diborane and helium with hydrocarbons, such as methane, ethene, and pentane, B_xC_y-alloy fibers were prepared at axial rates of up to 12.2 μm/s. Regions of kinetically-limited and transport-limited growth were identified, and the activation energy for deposition from B₂H₆ + C₅H₂₀ + He mixtures (at relative concentrations of 1:25:10) was found to be 197 ± 27 kJ/mol, while the rate constant was approximately 1810 μm/s. Compositions ranged from B_0.4C_0.6 to B_0.03C_0.97 depending on the gas mixture and laser powers employed; axial and radial fiber compositions/microstructure were explored using Auger spectroscopy and electron microscopy. Glassy B_xC_y fibers with Vickers hardnesses of 42–45 GPa were grown at laser powers below 150 mW. The growth kinetics of pure boron fibers was also investigated from BCl₃ + H₂, BF₃ + H₂, and B₂H₆ + H₂ gas mixtures, producing fine-grained α-boron and large single-crystals of β-boron. Micro-scale vortices in the gas flow emanating from the reaction zone were observed using particle image velocimetry; such vortices enhance axial fiber growth rates through rapid gas mixing. Arrays of fibers were also grown in-parallel using diffractive optical elements.     

Hydrogenation of carbon monoxide to methane over mesoporous nickel-M-alumina (M = Fe,Ni, Co,Ce, and La) xerogel catalysts

Mesoporous nickel(30 wt%)-M(10 wt%)-alumina xerogel (30Ni10MAX) catalysts with different second metal (M = Fe, Ni, Co, Ce, and La) were prepared by a single-step sol–gel method for use in the methane production from carbon monoxide and hydrogen. In the methanation reaction, yield for CH₄ decreased in the order of 30Ni10FeAX > 30Ni10NiAX > 30Ni10CoAX > 30Ni10CeAX > 30Ni10LaAX. Experimental results revealed that CO dissociation energy of the catalyst and H₂ adsorption ability of the catalyst played a key role in determining the catalytic performance of 30Ni10MAX catalyst in the methanation reaction. Optimal CO dissociation energy of the catalyst and large H₂ adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 30Ni10FeAX catalyst with the most optimal CO dissociation energy and the largest H₂ adsorption ability exhibited the best catalytic performance in terms of conversion of CO and yield for CH₄ in the methanation reaction. The enhanced catalytic performance of 30Ni10FeAX was also due to a formation of nickel–iron alloy and a facile reduction.     

Development of cobalt catalysts for the steam reforming of naphthalene as a model compound of tar derived from biomass gasification

The catalytic performances of Co/MgO catalysts for the steam reforming of naphthalene were investigated. The results of characterizations (TPR, XRD, CO adsorption, and CO-TPD) showed that large-sized Co metal particles were formed over the catalysts pre-calcined at 873 K with high Co loading via reduction of Co₃O₄ and MgCo₂O₄ phases. A few Co metal particles were obtained over the catalysts pre-calcined at 1173 K with all Co loading values after reduction.The catalytic performances data showed that 12 wt.% Co/MgO catalyst pre-calcined at 873 K exhibited the best catalytic performance (conv., 23%, 3 h) for the steam reforming of naphthalene among the catalysts tested in this study, due to the existence of Co metal and the low amounts of coke deposition. On the other hand, the data also revealed that the reaction of steam reforming of naphthalene proceeds over all Co-loaded catalyst pre-calcined at 1173 K initially; however, the deposition of the polymer of C_nH_m radicals and the oxidation of catalysts by H₂O led to the decrease of activity.It should be noted that 12 wt.% Co/MgO catalyst pre-calcined at 873 K showed high and stable activity under the low steam/carbon mole ratio (0.6), with H₂ and CO₂ as main products. These two excellent advantages serve to increase the overall biomass gasification system energy efficiency and allow using the product gas for fuel cell system. Thus, Co catalyst is a promising system for the steam reforming of naphthalene derived from biomass gasification as a second fixed catalytic bed.     

Formation of three-dimensional supramolecular water architectures containing 1D water chains via dianion templating

A three-dimensional supramolecular water architectures: [Ni(phen)₃](C₁₀H₁₆O₄) · (C₁₀H₁₈O₄)_0.5 · 11H₂O (1) [phen = 1,10-Phenanthroline, C₁₀H₁₆O₄ = sebacic dianion, C₁₀H₁₈O₄ = sebacic acid] has been synthesized and characterized by IR, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffractions. 1D water chains behave as pillars to join these water sheets to make an overall three-dimensional supramolecular architecture by hydrogen-bonding interactions.     

Synthesis of electrically conducting composite adsorbents for wastewater treatment using adsorption & electrochemical regeneration

Electrically conducting adsorbent materials called Nyex™ 1000 & 2000 have already been reported with comparatively low adsorption capacity for various organic, biologically non-degradable and toxic compounds. Two composite adsorbents called CA₁ & CA₂ were synthesized using synthetic graphite-carbon black and expanded graphite-carbon black respectively. The aim of developing the new adsorbents was to increase the adsorption capacity along with good electrical properties. The developed adsorbents were characterized using N₂ adsorption for specific surface area, Boehm surface titration for surface chemistry, bed electrical conductivity, laser size analyzer for average particle size, and scanning electron microscope (SEM) for particle morphology and shape. Then both the composite adsorbents were tested for the adsorption of acid violet 17 followed by an electrochemical regeneration. The adsorption study revealed that both the adsorbents had almost similar kinetic behavior with a significant increase in adsorption capacity for acid violet 17 (300 & 26 mg g⁻¹ respectively) when compared with the adsorption capacity of previously developed electrically conducting materials called Nyex™ 1000 & 2000 (3.5 and 9 mg g⁻¹ respectively). The composite adsorbent CA₂ was successfully electrochemically regenerated by passing an electric charge of 138 C g⁻¹ at a current density of 14 mA cm⁻² for a treatment time of 60 min, whereas, the composite adsorbent CA₁ could not be regenerated successfully. The regeneration efficiencies of CA₂ were obtained at around 120% during five adsorption–regeneration cycles. The amount of actual charge passed of 138 C g⁻¹ for achieving 100% regeneration efficiency was found to be similar with stoichiometrically calculated amount of charge. The amount of electrical energy required to oxidize each mg of adsorbed acid violet onto CA₂ (24 J mg⁻¹) was found to be significantly lower to that of Nyex™ 1000 & 2000 adsorbents (52 J mg⁻¹ & 32 J mg⁻¹ respectively).     

Evidence for large hydrogen capacity in single-walled carbon nanotubes encapsulated by thin Pd layers onto a Pd substrate

We report a study of hydrogen storage and its mechanism in a novel material, representing single-walled carbon nanotubes (SWCNTs) encapsulated by thin Pd layers onto a Pd substrate. A synergetic effect resulting in combination of the Pd and the SWCNT properties with regard to hydrogen has been achieved. We showed that adding SWCNTs increases the H₂-capacity of the Pd–SWCNT composite under electrochemical loading only by up to 25% relative to the Pd metal alone. At the same time, with regard to the added SWCNTs, such synergetic approach (providing high H₂ pressure from highly H-loaded massive Pd substrate into a small fraction of deposited SWCNT) allowed us to achieve a net capacity of 8–12 wt.%. H₂, thus, bringing a unique chance to study hydrogen storage mechanism in highly H-loaded SWCNT. Using ESR technique it was established that the Pd–C_x π-complexes forming at the openings of SWCNTs could be considered as hydrogen adsorption sites, providing both high gravimetric capacity (H/C > 1) and low hydrogen binding energy in the Pd encapsulated SWCNT.     

Carbon molecular sieve dense film membranes derived from Matrimid® for ethylene/ethane separation

Development of dense film carbon molecular sieve (CMS) membranes for ethylene/ethane (C₂H₄/C₂H₆) separation is reported. A commercial polyimide, Matrimid®, was pyrolyzed under vacuum and inert argon atmosphere, and the resultant CMS films were characterized using pure C₂H₄ and C₂H₆ permeation at 35 °C, 50 psia feed pressure. The effects on C₂H₄/C₂H₆ separation caused by different final vacuum pyrolysis temperatures from 500 to 800 °C are reported. For all pyrolysis temperatures separation surpassed the estimated ‘upper bound’ solution processable polymer line for C₂H₄ permeability vs. C₂H₄/C₂H₆ selectivity. C₂H₄ permeability decreased and selectivity increased with increasing pyrolysis temperature until 650–675 °C where an optimum combination of C₂H₄ permeability ～14–15 Barrer with C₂H₄/C₂H₆ selectivity ～12 was observed. A modified heating rate protocol for 675 °C showed further increase in permeability with no selectivity loss. CMS films produced from argon pyrolysis showed results comparable to vacuum pyrolysis. Further, mixed gas (63.2 mol% C₂H₄ + 36.8 mol% C₂H₆) permeation showed a slightly lower C₂H₄ permeability with C₂H₄/C₂H₆ selectivity increase rather than a decrease that is often seen with polymers. The high selectivity of these membranes was shown to arise from a high ‘entropic selection’ indicating that the ‘slimmer’ ethylene molecule has significant advantage over ethane in passing through the rigid ‘slit-shaped’ CMS pore structure.     

Promotional effect of graphite oxide on surface properties and catalytic performance of La1 − xSrxMnO3 (x = 0,0.1) for methane combustion

The effect of graphite oxide (i.e. GO)/La_1 − xSr_xMnO₃ (x = 0,0.1) catalysts on methane combustion in CNG's (compressed natural gas) exhaust was investigated in current work. GO layer was employed to realize a surface modification. The light-off temperature of methane decreased, and reached the full conversion at 540 °C. The prepared catalysts were also characterized by TEM, surface energy, XPS and H₂-TPR techniques. SEM indicated that the La_1 − xSr_xMnO₃ particles grew dispersedly on GO layer, and surface analysis suggested that the introducing of GO can enhance the adsorption of oxygen groups on the surface of the catalysts.     

Influence of the powder dimensions on the antimicrobial properties of modified layered double hydroxide

Nano-hybrids of layered double hydroxides (LDHs), or hydrotalcite-like compounds, containing the antimicrobial anions of o-hydroxybenzoate (o-BzOH), also known as salicylate, were synthesized by a direct coprecipitation method. Elemental analysis indicated the chemical formula [Zn_0.65Al_0.35(OH)₂] (C₇H₅O₃)_0.35 1 0.7 H₂O with a value of the molar fraction x = M^III/M^III + M^II of 0.35. FT-IR spectroscopy and X-ray diffractograms confirmed the presence of o-hydroxybenzoate anions into the clay galleries, and indicated the presence of small size and disordered crystallites. The initial powder dimensions, reported as “surface weighted mean”, D[3,2], were reduced by using high energy ball milling (HEBM) technique for 1 min, 2 min, and 5 min. Also the morphology, investigated by SEM, was influenced by HEBM: big agglomerated particles were found for the pristine samples, while well-defined platelets with uniform and thinner size were present in the milled samples. The release of the o-hydroxybenzoate anion into a saline solution was measured for the initial powder with 25.0 μm of D[3,2] and for the powder with the smallest dimensions (D[3,2] = 8.2 μm). It was observed that the lower the powder dimensions the higher the percentage of active anions released into the saline solution. Also the diffusion parameter was found higher for the lower dimension powders. The antimicrobial activity against Escherichia coli was found much more effective for the sample with the lower powder dimensions, and even a slow but progressive reduction was noted after 24 h. In the presence of particles of 8.2 μm the microbial growth after 96 h of incubation is not evident.