Nitrogen Adsorption Analysis Research Articles

Microwave treatment and fluorine addition on Co-B catalyst to improve the hydrogen production rate

ABSTRACTIn this paper, microwave heating treatment process and fluorine addition over Co-B-F catalyst was applied to produce hydrogen via the hydrolysis of NaBH4. The effects of microwave heating treatment time, microwave heating treatment power, microwave inert gases and temperature on the catalyst were studied. X-ray absorption spectrometer, scanning electron microscopy coupled to energy-dispersive spectroscopy, nitrogen adsorption analyzer and infrared spectrometer were performed for the chemical characterization of the catalysts. It was found that Co-B-F and microwave-treated Co-B-F catalysts exhibited excellent catalytic activity to produce hydrogen. The rates of the maximum hydrogen production for untreated and microwave-treated Co-B-F catalysts are 1868 and 3400 mL/g/min, respectively.

Chromium(III)-salen complex nanoparticles on AlPO4: as an efficient heterogeneous and reusable nanocatalyst for mild synthesis of highly functionalized piperidines, 2-arylbenzimidazoles, and 2-arylbenzothiazoles

A simple, convenient, and highly efficient multicomponent one-pot synthesis of highly functionalized piperidines has been developed via tandem reactions of β-keto esters, aromatic aldehydes, and various amines in ethanol at room temperature using catalytic amount (10 mol%) of a chromium(III)-salen complex nanoparticles supported on AlPO4. The heterogeneous catalyst exhibited excellent activity and reusability (up to 8 times) in the synthesis of highly functionalized piperidines. Also, synthesis of 2-arylbenzimidazoles and 2-arylbenzothiazoles have been efficiently developed under mild condition from o-phenylenediamines or 2-aminothiophenol with aryl aldehydes via one-step process using catalytic amount (2.0 mol%) of nanocatalyst in air atmosphere as a green oxidant. The heterogeneous catalyst was characterized by scanning electron microscopy, atomic force microscopy, inductively coupled plasma spectrometry, thermogravimetry for analysis of nitrogen adsorption, and FT-IR spectroscopy.

Nitrogen Adsorption Analysis of Wood Saccharification Residues

The objective of this study was to examine changes in the porosity and internal structure of wood as it goes through the process of saccharification (extraction of fermentable sugars). This study also examined the use of different drying methods to prepare samples for characterization of internal pores, with particular emphasis on the partially disrupted cell wall. Aspen wood flour samples after dilute acid pretreatment followed by enzymatic hydrolysis were examined for nitrogen adsorption. The resulting isotherms were analyzed for surface area, pore size distribution, and total pore volume. Results showed that freeze drying (with sample pre-freezing) maintains the cell wall structure, allowing for examination of saccharification effects. Acid pretreatment (hemicellulose removal) doubled the surface area and tripled the total volume of pores, which were mostly 10-20 nm wide. Subsequent enzymatic hydrolysis (cellulose removal) caused a 5-fold increase in the surface area and a ~ 11-fold increase in the total volume of pores, which ranged from 5 to 100 nm in width. These results indicate that nitrogen adsorption analysis is a feasible technique to examine the internal pore structure of lignocellulosic residues after saccharification. The information on the pore structure will be useful when considering value-adding options for utilizing the solid waste for biofuel production.

Experimental Study of Montmorillonite Structure and Transformation of Its Properties under Treatment with Inorganic Acid Solutions

This paper discusses the mechanism of montmorillonite structural alteration and modification of bentonites’ properties (based on samples from clay deposits Taganskoye, Kazakhstan and Mukhortala, Buriatia) under thermochemical treatment (treatment with inorganic acid solutions at different temperatures, concentrations and reaction times). Treatment conditions were chosen according to those accepted in chemical industry for obtaining acid modified clays as catalysts or sorbents. Also, more intense treatment was carried out to simulate possible influence at the liquid radioactive site repositories. A series of methods was used: XRD, FTIR, ICP-AES, TEM, nitrogen adsorption, and particle size analysis. It allowed revealing certain processes: transformation of montmorillonite structure which appears in the leaching of interlayer and octahedral cations and protonation of the interlayer and –OH groups at octahedral sheets. In turn, changes in the structure of the 2:1 layer of montmorillonite and its interlayer result in significant alterations in the properties: reduction of cation exchange capacity and an increase of specific surface area. Acid treatment also leads to a redistribution of particle sizes and changes the pore system. The results of the work showed that bentonite clays retain a significant portion of their adsorption properties even after a prolonged and intense thermochemical treatment (1 M HNO3, 60 °C, 108 h).

Hetero-atom Decoration of Activated Carbon Without Post-treatment

In this work, we attempt to decorate heteroatoms, including nitrogen and sulphur, into activated carbon without post-treatment. These atoms can be introduced into the carbon framework by the strong acid/base reactions after the carbonisation and activation. Raw materials, which contain the desired heteroatoms, were selected so that the obtained activated carbon would have the heteroatom without the harmful chemical process. Crab and shrimp shells were used as the raw material for nitrogen-doped activated carbon since they both contain chitin, which is the organic compound containing nitrogen atom. Similarly, lignite from Mae Moh (Lampang province, Thailand) which has high sulphur content, is suitable for the preparation of sulphur-doped activated carbon. Two types of activating agents, K2CO3 and KOH, were used as the activating agents and the effect from the ratio of raw materials to activating agents were studied. The surface area and the pore structures were determined by nitrogen adsorption analysis and the elemental compositions were characterised by CHNS analysis. It is found that activated carbon prepared from shrimp shells has a higher nitrogen content (1.40 wt%) than that prepared from crab shells (0.47 wt%). The specific area of the obtained activated carbonwas as high as 2,100 m2/g with the optimal condition. Sulphur-doped activated carbon can be easily preparedfrom lignite with high sulphur contents (14.34 wt%) and commercially comparable specific surface area (650 m2/g).

Sequestration of Methylene Blue and Lead ions by MWCNT Modified with Polyconducting Polymers

Taking into consideration the perspective of green chemistry, an attempt was made to investigate regenerative material for carbon nanotubes (CNTs) with high productivity. The special properties of CNTs, such as easy functionalization ability, high surface area, and unique thermal, mechanical, and electrical properties, make them an appealing component for composite materials, which resulted in the attraction of great interest on CNT-based composites. This research work focuses mainly on multiwall carbon nanotubes (MWCNTs) synthesized from camphor over iron nitrate catalyst supported on alumina by wet impregnation method. The formation of MWCNTs and incorporation of poly conducting polymers (o- and m-Toluidine) on the surface of MWCNTs was confirmed by high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), Ultraviolet visible spectroscopy (UV-Vis), low temperature nitrogen adsorption and Thermo-Gravimetric analysis (TGA). The performance evaluation of as-synthesized MWCNTs and their nanocomposites towards adsorption of methylene blue (MB) dye and Pb(II) was also highlighted. MWCNTs and their nanocomposites pose a great potential as a promising material for application in adsorption from aqueous solution.

Adsorption properties of activated carbon from reed with a high adsorption capacity

Activated carbon with a high adsorption capacity was prepared using reed from the Yellow River Delta of China as a low-cost raw material. The adsorption-desorption behavior of methylene blue (MB) onto the reed activated carbon (RAC) was studied in detail. The structure of RAC was characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption analysis. Based on a good fitting with the Langmuir isotherm model, and pseudo second-order kinetics, the adsorption behavior of MB on RAC can be considered mainly to be the monolayer adsorption process, and is related to the chemical functional groups on the surface of carbon. The maximum adsorption capacity of RAC obtained from the Langmuir isotherm equation at 30°C is 704.23mg/g. The high adsorption capacity can be attributed to its low polarity, numerous types of surface functional groups, high surface area and pore volume, and a hierarchal porous structure. The regenerating rate of the spent RAC saturated with MB was 85.15% after one regeneration cycle, indicating a good potential for commercial applications.

Constructing novel WO3/Fe(III) nanofibers photocatalysts with enhanced visible-light-driven photocatalytic activity via interfacial charge transfer effect

In this work, we have prepared a series of efficient visible-light-driven WO3/Fe(III) nanofiber photocatalysts by electrospinning and impregnation method. The physical and optical properties of the prepared photocatalysts were characterized by field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the nitrogen adsorption analysis. Under the irradiation of visible light, all the prepared WO3/Fe(III) nanofiber photocatalysts exhibit much higher activity for degrading methyl orange (MO) solution than the pristine WO3 nanofibers, and reaches 94.6% under visible light irradiation for 3 h when the relative grafting amount of Fe(III) ions was 0.003 by mass percentage. Grafting of Fe(III) ions on the surface of WO3 nanofiber could enhance its visible-light absorption and reduce the photo-generated electron-hole pairs recombination due to the interfacial charge transfer (IFCT) effect, and thus improve its photocatalytic activity, which were further verified by the ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), photoluminescence (PL) and the ns-level time-resolved fluorescence decay spectrum measurements.

Characterization and Stability of Heteropolyacid Catalysts Supported on MCM-41 Materials Synthesized by Ultrasonic Irradiation

A series of solid acid catalyst of the Keggin-type 12-phosphotungstic acid, H3PW12O40, supported on ordered mesoporous silica MCM-41 were prepared by a simple and effective impregnation method. MCM-41 supports were synthesized in a relatively short time via a recently reported ultrasonic irradiation method. The synthesis sonication time has been systematically varied in order to investigate its influence on the structural order of the resulting materials. The prepared catalysts were characterized by nitrogen adsorption, X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. The resulting materials exhibited hexagonally ordered meso structure, with high surface area of the order of several hundreds of m2g-1,relatively large pore volumes, with the pore diameter in the range of 2.19 to 2.41 nm and a corresponding pore wall thickness of over 1.67nm. The results have demonstrated that high quality MCM-41 materials can be synthesized via the ultrasonic irradiation in few tens of minutes, much shorter than the conventional synthesis methods. Despite their relatively high loading, all synthesized materials retained the characteristic MCM-41mesoporous structure after impregnation of the heteropolyacid active phase onto the inner pore surface, without crystallization, but preserving the Keggin structure as confirmed by Raman spectroscopy.

A novel approach to prepare Ni-Al mesoporous powder using electrochemical method in one step

Abstract Here we demonstrate for the first time a novel approach based on electrochemical for production of Ni-Al alloy mesoporous powder. It can be elucidated that at first step, Al will be dissolved and is oxidized in a solution. Thus, electrons will be liberated and Ni ions with attraction these liberated electrons will be reduced. In consequence, they will deposit on the Al surface. Morphology and chemical composition of the produced powder was characterized by SEM, EDS and XRD. The processing parameters including time and the solution pH were evaluated using the nitrogen adsorption and desorption isotherms analysis. The obtained results verified that the produced powder contains mesoscale porosities with size about 16–20 nm. The results show that the processing time has no effect on the porosities size. However, changing time from 15 to 45 min increases specific surface area of the powder from 311.3 to 386.8m2/gr respectively. In contrast, increasing time beyond 45min decreases this factor. It was found that the solution pH affects both porosities size and specific surface area of the powder. Highest specific surface area and lowest porosity size is related to pH 4. Decreasing pH below 4 is caused that porosities size increases and consequently specific surface area decreases because of the high hydrogen reduction and therefore the low Ni deposition efficiency.

Change in composition and pore structure of Longmaxi black shale during oxidative dissolution

Owing to the presence of chemically unstable compositions (e.g., clay minerals, carbonate, pyrite, and organic matter (OM)) which are closely related to shale structure failures or dissolution pores, the methods to increase gas well long-term productivity from tight shale matrix need to take into account the chemical interaction of shale with injected fluid. In this study, black shale samples obtained from Lower Silurian Longmaxi formation in Sichuan basin, China were treated with 15wt% hydrogen peroxide (H2O2) for the comprehensive understanding of the change in shale composition and the associated dissolution structures. The measurements of mass loss, total organic carbon content, and mineralogical composition showed that carbonate, reductive inorganic minerals containing ferrous iron (e.g., pyrite and chlorite), and OM in samples exhibited strong dissolution; however, the other minerals behaved in a non-reactive manner at the experimental time scale. After the oxidative treatment for 240h, a large amount of oxidation-induced fractures and dissolution pores were observed by field-emission scanning electron microscopy. The fractures mainly oriented parallel to lamination were attributed to the dissolution of OM and structural alteration of clay minerals. All the dissolution pores seemed to be strongly dependent on the loss of dolomite, pyrite, and OM. Results from high-pressure mercury intrusion and low-pressure nitrogen adsorption analysis showed that these dissolution pores ranging from 10 to 500nm in diameter exhibited a significant increase in pore volume due to the removal of interconnected pore-filling OM, while the volume of pores>1μm in size exhibited a minor increase because the micrometer-size dissolved particles appeared to be discrete or unconnected. Thus the oxidative dissolution could lead to the higher porosity and better connectivity of nanometer-size pore networks in shale samples. The induced fractures reduced the size of diffusion dominant zones in shale matrix, and the dissolution pores increased the size of gas transport pathways into fractures. These results indicate that the injection of H2O2 may play an important role in shale matrix stimulation by oxidative dissolution which is likely to improve matrix diffusivity.

Cerium removal by activated carbon derived from palm kernel shell

Palm kernel shell (PKS) was utilized as a precursor for the preparation of activated carbon (AC) via different carbonization temperatures and carbon dioxide gas activation processes. The physical and chemical properties of the AC samples were studied by TGA, nitrogen adsorption analysis and SEM. The results show that the AC sample with BET surface area up to 622 m 2 g -1 and total pore volume of 0.297 cm 3 g -1 with narrow pore size of 1.2 nm were obtained. The SEM shows that more pores were revealed on the surface of AC after the carbonization and activation processes. The AC samples carbonized at 500 and 600 °C (CA-500 and CA-600) exhibited higher Ce removal percentage (99.94 %) than that of the other samples. Higher BET surface area of the CA-500 and CA-600 samples resulted in slightly more Ce ions to be adsorbed and precipitated compared to that of other samples. The result indicates that high pH value and BET surface area of AC sample has a rather strong influence on Ce removal. AC samples show excellent Ce removal capacity, thereby; the results suggest that the PKS-based AC could be a promising adsorbent for the cerium removal application.

Adsorption of Toluene and Paraxylene from Aqueous Solution Using Pure and Iron Oxide Impregnated Carbon Nanotubes: Kinetics and Isotherms Study.

Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) were investigated for the adsorption of hazardous toluene and paraxylene (p-xylene) from aqueous solution. Pure CNTs were impregnated with iron oxides nanoparticles using wet impregnation technique. Various characterization techniques including thermogravimetric analysis, scanning electron microscopy, elemental dispersion spectroscopy, X-ray diffraction, and nitrogen adsorption analysis were used to study the thermal degradation, surface morphology, purity, and surface area of the materials. Batch adsorption experiments show that iron oxide impregnated CNTs have higher degree of removal of p-xylene (i.e., 90%) compared with toluene (i.e., 70%), for soaking time 2 h, with pollutant initial concentration 100 ppm, at pH 6 and shaking speed of 200 rpm at 25°C. Pseudo-second-order model provides better fitting for the toluene and p-xylene adsorption. Langmuir and Freundlich isotherm models demonstrate good fitting for the adsorption data of toluene and p-xylene.

Porous carbons derived from hypercrosslinked porous polymers for gas adsorption and energy storage

Porous carbon materials with high surface areas were prepared using a hypercrosslinked porous organic polymer as porous precursor with potassium hydroxide activation. Nitrogen adsorption analysis revealed that the porous carbon materials have high surface area of up to 3101 m2 g-1 and high pore volume of 1.84 cm3 g-1, which can provide more accessible surface and sites for gas adsorption and electrochemical energy storage. The porous carbons with high surface area show high H2 uptake ability of up to 3.25 wt% at 77 K and 1.13 bar and CO2 uptake ability of 6.69 mmol g-1 at 273 K and 1.13 bar. The lithium ion battery fabricated from CHCPB-K-600 shows a high specific discharge capacity of 1221 mA h g−1 at 100 mA g-1, which could still retain 833 mA h g−1 after 50 cycles at 100 mA g-1. CHCPB-K-600 also exhibits a high capacitance of 379 F g-1 at 0.5 A g-1 for supercapacitor, and the capacitance retains 91.2% after 3000 cycles at 2 A g-1. Considering the high gas uptake ability, the excellent electrochemical performance, and the facile preparation strategy, these porous carbons hold a great potential for gas adsorption and energy storage.

Structural analysis of mesoporous vermiculite modified with lanthanum

Clays have demonstrated an important role in many industrial processes and its modification have been a promising line of research, such as its intercalation and pillaring. The synthesis of vermiculite modified with aluminum and aluminum-lanthanum has great relevance, since the materials obtained can be used in separation processes by adsorption and catalysis. For characterization of the crystallographic phases of the synthesized materials were obtained diffraction patterns (XRD) that confirmed the effectiveness of the methodology used, and to evaluate the morphology were carried out nitrogen adsorption analysis (BET), where the results confirmed the mesoporosity of the synthesized materials. 27Al MAS NMR spectrometry was applied to distinguish between tetrahedrally coordinated aluminum and octahedrally coordinated.

INVESTIGATION OF IMPREGNATED ACTIVATED CARBON PROPERTIES USED IN HYDROGEN SULFIDE FINE REMOVAL

Abstract - The effects of relative humidity (RH), carbon dioxide (CO 2 ), methane (CH 4 ), oxygen (O 2 ) presence and gas hourly space velocity (GHSV) on H 2 S adsorption dynamics of KOH/CaO impregnated activated carbon are investigated in this study. X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray detector (SEM-EDX), thermogravimetric analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR) techniques are applied and nitrogen adsorption characteristics are determined for characterization. The presence of water, O 2 and lower GHSV has beneficial effects on the activated carbon performance. CO 2 decreases the adsorption capacity due to its acidic characteristics. Best adsorption capacity is obtained as 13 wt % in KOH/CaO impregnated activated carbon, in a CH 4 (60%)/CO 2 (38%)/O 2 (2%) gas atmosphere, at ambient temperature, RH 90 and 5000 h -1 GHSV. Sulphur species formation was verified with the help of SEM-EDX, XRD, TGA, FTIR and nitrogen adsorption analysis on the exhausted samples.

Molecular Weight Cut-Off and Structural Analysis of Vacuum-Assisted Titania Membranes for Water Processing.

This work investigates the structural formation and analyses of titania membranes (TM) prepared using different vacuum exposure times for molecular weight (MW) cut-off performance and oil/water separation. Titania membranes were synthesized via a sol-gel method and coated on macroporous alumina tubes followed by exposure to a vacuum between 30 and 1200 s and then calcined at 400 °C. X-ray diffraction and nitrogen adsorption analyses showed that the crystallite size and particle size of titania increased as a function of vacuum time. All the TM membranes were mesoporous with an average pore diameter of ~3.6 nm with an anatase crystal morphology. Water, glucose, sucrose, and polyvinylpyrrolidone with 40 and 360 kDa (PVP-40 kDa and PVP-360 kDa) were used as feed solutions for MW cut-off and hexadecane solution for oil filtration investigation. The TM membranes were not able to separate glucose and sucrose, thus indicating the membrane pore sizes are larger than the kinetic diameter of sucrose of 0.9 nm, irrespective of vacuum exposure time. They also showed only moderate rejection (20%) of the smaller PVP-40 kDa, however, all the membranes were able to obtain an excellent rejection of near 100% for the larger PVP-360 kDa molecule. Furthermore, the TM membranes were tested for the separation of oil emulsions with a high concentration of oil (3000 ppm), reaching high oil rejections of more than 90% of oil. In general, the water fluxes increased with the vacuum exposure time indicating a pore structural tailoring effect. It is therefore proposed that a mechanism of pore size tailoring was formed by an interconnected network of Ti–O–Ti nanoparticles with inter-particle voids, which increased as TiO2 nanoparticle size increased as a function of vacuum exposure time, and thus reduced the water transport resistance through the TM membranes.

Characterization of oxidized carbon materials with photoinduced absorption response

An efficient application of fast remote diagnostics for carbon material (CM) bulk particles was demonstrated. Porous layers of CM particles with different oxidation levels were characterized by self-action of picosecond laser pulses at 1064 nm. Nitrogen adsorption, Boehm titration, and thermal analysis of the oxidized CMs revealed diverse specific surface area \(S_\mathrm {BET}\), reasonable surface acidity, and high concentration of surface oxygen-containing groups. Dense CM porous layers showed a monotonous reduction of the absorptive nonlinear optical (NLO) response efficiency versus the oxidation level with characteristic magnitude Im(\(\chi _\mathrm{C}^{(3)})\sim 10^{-10}\) esu for the carbon particles fraction. The obtained Im(\(\chi _\mathrm{C}^{(3)})/S_\mathrm {BET}\) ratio remains approximately constant, which indicates the certain proportion between the absorptive NLO response efficiency and the specific surface area. We suggest to use Im(\(\chi _\mathrm{C}^{(3)})\) as a figure of merit for carbons subjected to the oxidation—the route to enhance the CM surface reactivity.

Study on flame retarded flexible polyurethane foam/alumina aerogel composites with improved fire safety

In this article, a novel strategy has been proposed for the preparation of polyurethane/alumina aerogel (FPU/Alag) composites with homogeneous dispersion of alumina aerogel. The FPU/Alag composites have been prepared via immersing FPU foams into alumina sols followed by a freeze-drying method. Fire safety performance of the FPU composites with various Alag compositions in terms of thermal properties and flammability performance were evaluated. The composites demonstrated an earlier thermal degradation but higher thermal stability with increasing temperature and greater char yields than pure FPU. Total heat and smoke release, and rate of smoke emission of the FPU/Alag composites were found to be greatly reduced in comparison with those of FPU. Morphology and thermal conductivity (κ) properties of FPU/Alag composites and their corresponding residual char were investigated. The κ values of the composites were measured to be higher than that of FPU due to the accumulation of alumina flakes on the cell-walls of FPU. In contrast, the κ values of the char were lower than that of the calcinated alumina aerogel (C-Alag) counterpart, due to the formation of side by side, partially-opened compartments isolated by alumina flakes. Nitrogen adsorption analysis showed that C-Alag had a specific surface area of 211.5m2/g and mesoporous volume of 0.28cm3/g. The remarkable improvement in fire safety of FPU foams with the addition of Alag could be attributed to the combined effects of thermal-insulating, retention and adsorption of C-Alag that was in-situ formed inside FPU matrix during the combustion process.

Towards the hydrothermal growth of hierarchical cauliflower-like TiO2 anatase structures

TiO2 anatase nanostructure-based hierarchical spheres were synthesized by using a facile microwave-assisted hydrothermal method. H2SO4 was used as both phase inducer for the formation of anatase and capping agent to promote the self-assembly of cauliflower-like spheres. The hydrothermal synthesis was carried out at 180 °C for 2 h from an acid colloidal solution of titanium tetraisopropoxide, at pH < 2. The relationship between morphology and structure was studied by the means of X-ray diffraction, high-resolution transmision electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nitrogen adsorption and ultraviolet-visible spectroscopy analyses. The results revealed that the acid concentration is a key factor to the controlled hydrothermal aggregation of TiO2 anatase faceted-like nanoparticles, leading to hierarchical cauliflower-like structures. The microspheres consist of hierarchical structures of sheet-shaped TiO2 anatase particles with exposed {001} and {101} facets. The nanostructures grow in preferential directions to become in sheet-shaped, by an oriented attachment mechanism. The sulphate groups anchored on the surface and detected by X-ray photoelectron spectroscopy, help the hydrothermal formation of hierarchical spheres and then the cauliflower-like morphology.