Nitrogen Adsorption Analysis Research Articles

Removal of lead (II) and cadmium (II) cations from water using surface‐modified graphene

With its unique structure, graphene exhibits a number of outstanding mechanical, optical, and electronic properties, thus promising several potential applications. In the current work, graphene sheets were prepared from graphite and surface‐modified via an acid treatment. The synthesized material physicochemical properties were assessed using X‐ray diffraction, nitrogen adsorption and BET analysis, transmission electron microscopy, and Raman as well as X‐ray photoelectron spectroscopy techniques. The ability of the surface‐modified graphene in the adsorptive elimination of Pb(II) and Cd(II) cations from aqueous solutions was investigated batchwise under numerous experimental conditions. A pseudo‐second order kinetic model described adequately the adsorption kinetic profiles. The adsorption isotherms were compared to the Langmuir and Freundlich models. It was found that for both heavy metal cations, adsorption isotherms were reasonably described by Langmuir model equation. Maximum adsorption capacities reached 0.946 and 1.779 mmol ion/g for Pb(II) and Cd(II), respectively.

Molecularly Imprinted Solid Phase Extraction using Bismethacryloyl-β-cyclodextrin and Methacrylic Acid as Double Functional Monomers for Selective Analysis of Glycyrrhizic Acid in Aqueous Media.

In this work, a new molecularly imprinted solid phase extraction protocol was developed for the selective extraction and purification of glycyrrhizic acid from liquorice roots in aqueous media. The molecularly imprinted polymers (MIPs) for glycyrrhizic acid were prepared by using bismethacryloyl-β-cyclodextrin and methacrylic acid as double functional monomers and characterized by Fourier transform infrared spectroscopy, scanning electron microscope, thermo gravimetric analysis, nitrogen adsorption and elemental analysis. In aqueous media, the adsorption properties of MIPs including adsorption kinetics, adsorption isotherms and selectivity adsorption were investigated. The characterization of imprinted polymers indicated that the prepared MIPs had good stability and many cavity structures. The results of adsorption experiments illustrated the MIPs had high adsorption capacity of glycyrrhizic acid (69.3 mg g−1) with the imprinting factor 3.77, and it took ~5 min to get adsorption equilibrium. The MIPs could be used as an solid phase extraction sorbent absorbent for enrichment and purification of glycyrrhizic acid from the crude extraction of licorice roots, and the results showed promising practical value.

Hollow molecular imprinted polymers towards rapid, effective and selective extraction of caffeic acid from fruits

Rapid and selective extraction and enrichment of trace bioactive analytes from complex matrices were of significant importance for efficient and accurate quantification. Here, novel hollow molecular imprinted polymers (HMIPs) were prepared using caffeic acid (CA) as template, 4-vinylpyridine (4-VP) as functional monomer, and Fe3O4@SiO2 as sacrificial support. Fourier transform infrared spectrometer (FT-IR), transmission electron microscopy (TEM), nitrogen adsorption and thermo-gravimetric analysis (TGA) were used to verify the successful synthesis of HMIPs. Hollow structure with large surface area (325.8m2/g) made most recognition sites locate on the surface of HMIPs, resulting in high binding capacity (21.10mg/g) and fast kinetic binding (35min) in comparison with magnetic MIPs (MMIPs) and solid MIPs. The equilibrium data fitted well to Freundlich equation and the adsorption process could be described by pseudo-second order model. The selectivity performance of HMIPs was favorable. Finally, HMIPs were successfully used as adsorbent to rapidly and selectively extract and enrich CA from fruits with a relatively satisfactory recovery (85.6–103.5%). Coupling with high-performance liquid chromatography (HPLC), the content of CA in four kinds of fruits (kiwifruit, apple, papaya and waxberry) was determined as less than 1.0μg/g fresh fruit. Results indicated the superiority of HMIPs in the selective extraction of target compound from complex matrices.

Supersaturation of poorly soluble drugs induced by mesoporous magnesium carbonate

This work investigates whether the solubility of poorly soluble compounds can be improved by using mesoporous magnesium carbonate (MMC) as the drug delivery system. A solvent evaporation method was used to load structurally diverse model drugs (celecoxib, cinnarizine and griseofulvin) into the pores of MMC. The drug-loaded carrier system was then characterized in terms of porosity, crystallinity, and release profiles by a variety of experimental techniques, including X-ray diffraction, nitrogen adsorption analysis, differential scanning calorimetry, infrared spectroscopy, UV absorption spectroscopy, and thermogravimetric analysis. All three drugs were in a non-crystalline state after loading into the pores of MMC. The concentrations of the drugs in solution over time (a measure of the release rates from loaded MMC) were higher than the corresponding concentrations (dissolution rates) of equal amounts of the crystalline drugs. The release rates were five (celecoxib), three (cinnarizine) and two times (griseofulvin) higher than the dissolution rates of their crystalline counterparts. Supersaturation release profiles were also observed; the areas under the concentration-time curves (0–240min) were 25- (celecoxib), 5- (cinnarizine) and 2-fold (griseofulvin) greater than those of the crystalline drugs. Hence, MMC shows promise as a general drug delivery vehicle for increasing the bioavailability of compounds with dissolution rate- or solubility-limited absorption.

Preparation, characterization, and photocatalytic activity evaluation of Fe–N-codoped TiO2/fly ash cenospheres floating photocatalyst

Nitrogen-doped titanium dioxide (TiO2) and Fe-N-codoped TiO2 layers on fly ash cenospheres (FAC) as floating photocatalyst were successfully prepared through sol-gel method. Photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)-Vis diffuse reflectance spectroscopy (DRS), and nitrogen adsorption analyses for Brunauer-Emmett-Teller (BET) specific surface area. Photocatalytic efficiency of the prepared catalyst was evaluated through using the decomposition of Rhodamine B (RhB) as a model compound under visible light irradiation. Photocatalytic activity and kinetics of catalyst under visible light were detected in details from different Fe/Ti mole ratios by detecting photodegradation of RhB. Experimental results show that when the calcination temperature was 550°C, the dosage of FAC was 3.0g, and the mole ratio of Fe/Ti was 0.71%; the synthesized Fe-N-TiO2/FAC photocatalyst presented as anatase phase and that N and Fe ions were doped into TiO2 lattice. The material's specific surface area was 34.027m2/g, and UV-Vis diffuse reflectance spectroscopy shows that the edge of the photon absorption has been red shifted up to 400-500nm. Fe-N-codoped titanium dioxide on FAC had excellent photocatalytic activity during the process of photodegradation of RhB under visible light irradiation.

Mechanically Strong and Thermally Responsive Cellulose Nanofibers/Poly(N-isopropylacrylamide) Composite Aerogels

Cellulose nanofibers (CNFs)/poly(N-isopropylacrylamide) (PNIPAm) composite aerogels were successfully fabricated from a CNF aqueous suspension containing PNIPAm solute via lyophilization. PNIPAm was synthesized through free radical polymerization, and CNFs were individualized from filter paper cellulose fibers using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) mediated oxidation pretreatment followed by mechanical nanofibrillation. It was discovered that the incorporation of CNFs could remarkably improve the structural integrity of composite aerogels by preventing them from shrinking during lyophilization. The structure and properties of the obtained aerogels were comprehensively analyzed with various techniques, including infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption analysis, compression testing, and water contact angle (CA) measurements. Due to the synergistic effects from the two components, the composite aerogels exhibited attractive thermoresponsive properties with exceptionally high compressive strength. The ultimate compressive strength for the composite aerogel (A4) at 70% strain reached 0.227 MPa, more than 12 times higher than that of the neat CNF aerogel. The CA measurements demonstrated that the hydrophilicity/hydrophobicity of CNF/PNIPAm composite aerogels could be switched at a certain temperature. The CA sharply increased from 0 to 97° when the temperature was increased from 20 to 35 °C, exhibiting strong temperature-dependent water absorption behaviors.

Investigation of iron-containing powder on coal combustion behavior

Effects of iron-containing powder on coal combustion behavior were investigated using thermogravimetry (TG) and differential scanning calorimetric (DSC) analysis. The results indicated that the presence of hematite, BOF dust, and BOF sludge reduced ignition temperature, speeded up combustion rate, improved burnout behavior and enhanced the heat release rate during the coal combustion process. However, BF dust generally showed a negative effect on coal combustion behavior. Based on the results of kinetic study, XRD, SEM–EDS and nitrogen adsorption analysis, the possible mechanism of intensified or suppressed combustion by these powder was proposed. The catalytic effect of these iron-containing powder on coal combustion is related not only with the constituents but also with the surface morphology and pore structure of these powder.

Preparation of edge-nitrogenated graphene nanoplatelets as an efficient electrode material for supercapacitors

Edge-nitrogenated graphene nanoplatelets (ENGNPs) with high surface area were prepared through a simple and eco-friendly mechanochemical pin-grinding process using the flake graphite as the precursors in the presence of nitrogen and investigated as the electrode materials for supercapacitors. Nitrogen adsorption, SEM, and XPS analysis indicated that the mechanochemical pin-grinding process can effectively delaminates the pristine graphite into graphene nanoplatelets and generates the activated carbon sites that can directly react with nitrogen at the broken edge of graphite framework, leading to ENGNPs with excellent capacitive performance. Electrochemical measurements indicate that the as-prepared ENGNPs exhibits a high specific capacitance of 202.8Fg−1 in 1M H2SO4 aqueous electrolyte at the current density of 0.3Ag−1, meanwhile maintaining a good capacitance retention capability. The excellent capacitive performance of ENGNPs can be attributed to the combined effect of high surface area, edge-nitrogenated structure, and undamaged basal plane.

Thermophysical property and pore structure evolution in stressed and non-stressed neutron irradiated IG-110 nuclear graphite

The nuclear graphite, IG-110, was irradiated with and without a compressive load of 5 MPa at ∼400 °C up to 9.3 × 1025 n/m2 (E > 0.1 MeV). Following irradiation physical properties were studied to compare the effect of graphite irradiation on microstructure developed under compression and in stress-free conditions. Properties included: dimensional change, thermal conductivity, dynamic modulus, and CTE. The effect of stress on open internal porosity was determined through nitrogen adsorption. The IG-110 graphite experienced irradiation-induced creep that is differentiated from irradiation-induced swelling. Irradiation under stress resulted in somewhat greater thermal conductivity and coefficient of thermal expansion. While a significant increase in dynamic modulus occurs, no differentiation between materials irradiated with and without compressive stress was observed. Nitrogen adsorption analysis suggests a difference in pore evolution in the 0.3–40 nm range for graphite irradiated with and without stress, but this evolution is seen to be a small contributor to the overall dimensional change.

Conventional and field-assisted sintering of nanosized Gd-doped ceria synthesized by co-precipitation

Gadolinium-doped ceria is an attractive electrolyte for potential application in SOFCs operating at intermediate temperature; for such use, the fundamental compositions typically contain 10–20mol% Gd2O3. In this work, we produced nanosized 10mol% gadolinium-doped ceria powder by co-precipitation, starting from Ce and Gd nitrate solutions and using ammonia solution as precipitating agent. The co-precipitate was characterized by DTA-TG, TEM, XRD and nitrogen adsorption analyses. We studied the behavior of the nanopowder under both conventional and Flash sintering. Very different behavior was seen: the conventional sintering cycle produced a poorly densified material, while Flash sintering allowed production of a perfectly densified material, with uniform sub-micrometric grain size.

Preparation and characterization of novel thermosensitive magnetic molecularly imprinted polymers for selective recognition of norfloxacin

Novel norfloxacin (NOR) thermosensitive magnetic molecularly imprinted polymers (T-MMIPs) were prepared with functional monomer methacrylic acid (MAA), temperature-response monomer N-isopropylacrylamide (NIPAM) and cross-linking agent N,N′-methylenebisacrylamide (MBA) by the surface imprinting technique. The silica layer and imprinted polymers layer coated on the surface of Fe3O4 nanoparticles, forming double-shell structure. The morphology and composition of the thermosensitive magnetic molecularly imprinted polymers were investigated by transmission electronmicroscope (TEM), Fourier transform infrared spectrometry (FT-IR), thermogravimetic (TGA), vibrating sample magnetometer (VSM), powder X-ray diffraction (XRD) and nitrogen adsorption analysis. The phase behavior and thermosensitivity of T-MMIPs were studied by swelling experiments and adsorption tests at different temperatures. And the adsorption performance of T-MMIPs at 35 °C were evaluated by adsorption experiments, including kinetic, isotherm and selectivity tests. The maximum capacity of T-MMIPs at 35 °C was 52.85 mg g−1. In selective recognition tests, the T-MMIPs showed the highest selectivity for NOR among four components while the T-MNIPs showed similarly adsorption for all components. The prepared T-MMIPs have great potential in the detection and separation of norfloxacin due to the good temperature response, adsorption capacity, selectivity and reusability.

Photocatalytic enhancement of floating photocatalyst: Layer-by-layer hybrid carbonized chitosan and Fe-N- codoped TiO2 on fly ash cenospheres

Due to the advantage of floating on water surface, floating photocatalysts show higher rates of radical formation and collection efficiencies. And they were expected to be used for solar remediation of non-stirred and non-oxygenated reservoirs. In this research, floating fly ash cenospheres (FAC) supported layer-by- layer hybrid carbonized chitosan and Fe-N-codoped TiO2 was prepared by a simple sol-gel method. The catalysts were characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy(DRS), nitrogen adsorption analyses for Brunauer-Emmett-Teller (BET) specific surface area. It is indicated that Fe-N codoped narrowed the material’s band gap, and the layer of carbonized chitosan (Cts) increased the catalyst’s adsorption capacity and the absorption ability of visible light. Comparing with Fe-N-TiO2/FAC and N-TiO2/FAC, the composite photocatalyst show excellent performance on the degradation of RhB. Photodegradation rate of RhB by Fe-N-TiO2/FAC-Cts was 0.01018min−1, which is about 1.5 and 2.09 times higher than Fe-N-TiO2/FAC and N-TiO2/FAC under visible light irradiation in 240min, respectively. The dye photosentization, capture of holes and electrons by Fe3+ ion, and synergistic effect of adsorption and photodegradation were attributed to the results for the improvement of photocatalytic performance. The floating photocatalyst can be reused for at least three consecutive times without any significant decrease on the degradation of Rhodamin B after each reuse.

Calorimetric study of adsorption of alcohols on silicas

This work describes adsorption and wetting characterisation of hydrophobic ordered mesoporous silicas (OMSs) with the SBA-15 and SBA-16 type. A synthetic approach to prepare hydrophobic SBA-15 and SBA-16 silicas was explored grafting with covalently-attached monolayers (CAMs) of CnH2n+1Si(CH3)2N(CH3)2, labelled in this research as SBA-15H and SBA-16H, respectively. The materials prepared were characterised by nitrogen adsorption and FTIR analysis. The surface properties of the materials were assessed by BET C constants. For hydroxylated bare SBA-15 silica and SBA-16, C constants were ≈100–150 and 70–90 respectively, indicating high-energy, polar surfaces of Si–OH groups. The C constants of SBA-15H and SBA-16H grafted with CAMs of alkyldimethylsilanes were in the range of ≈15–25 and ≈35–50, demonstrating non-polar, low-energy organic surfaces of closely packed alkyl groups. The hydrophobic character in this study was evidenced by studying the adsorption of alcohols of chain lineal (C1–C5), where the modified silicas showed that the adsorption capacity of less polar alcohols increased, as in the case of pentanol, butanol and propanol. Immersion calorimetry proved to be a useful and versatile technique for analysing the structural changes of silicas.

Esterification of fatty acids using acid-activated Brazilian smectite natural clay as a catalyst

This work reports the use of an acid-activated Brazilian smectite natural clay-based catalyst in the esterification of fatty acids at atmospheric pressure and without a co-solvent. Conversion levels of 99%, 98%, 93% and 80% were reached for caprylic, lauric, stearic and oleic methyl esters, respectively, using 1:3 fatty acid/methanol molar ratio, heating bath at 100 °C after 4 h. A conversion level of 89% was achieved for methyl esters from a fatty acid residue of the palm oil refining industry in the same reaction condition. The acid-activated clay provided better performance than the commercial catalyst K-10. The effects of catalyst amount, temperature, fatty acid/alcohol molar ratio and time were investigated. The heating activation of the catalyst immediately before the catalytic test increased the conversion from 94% to 99% using 1:1.5 stearic acid/methanol molar ratio, heating bath at 100 °C after 4 h. The catalyst was reused five times. The conversion decreases less than 5% in the first three reuses. The smectite natural clay and the catalyst were characterized by X-ray fluorescence, X-ray diffraction, n-butylamine thermodesorption, nitrogen adsorption analysis, thermogravimetric analysis and differential thermal analysis.

Facile synthesis of nanostructured porous carbon/silica composite and its adsorption property

Nanostructured porous carbon/silica composite was synthesized via a novel one-step carbonization method by using metal–organic frameworks (MOFs)/silica composite as sacrificial precursor. The crystallinity and properties of the as-prepared samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and nitrogen adsorption analysis at 77 K. The obtained composite showed foam-like nanostructure with high surface area and pore volume. The adsorption results indicate that nanostructured carbon/silica composite displayed a good ability to remove Congo red pollutant from wastewater.

Treatment of Volatile Organic Compounds with Mesoporous Materials Prepared from Calcium Fluoride Sludge.

Large amount of calcium fluoride sludge was generated by semiconductor industry every year. It also needs high requirement of fuel consumption using rotor concentrator and thermal oxidizer to treat VOCs. The mesoporous catalyst prepared by calcium fluoride sludge was used for VOCs treatment in this study. Acetone is a kind of solvent and used in a large number of laboratories and factories. The serious problems will be caused when it exposed to the environmental. Economic and practical technology is needed to eliminate this kind of hazardous air pollutant. In this research, the adsorption of acetone was tested with CF-MCM (mesoporous silica materials synthesized from calcium fluoride). The raw material was mixed with cationic cetyltrimethyl ammonium bromide (CTAB) surfactants, firstly. The prepared mesoporous silica materials were characterized by nitrogen adsorption and desorption analysis, transmission electron microscope (TEM), scanning electron microscopy (SEM), X-ray powder diffractometer (XRPD) and Fourier transform infrared spectroscopy (FTIR). The results showed that the surface area, large pore volume and pore diameter could be up to 862 m2 g(-1), 0.57 cm3 g(-1) and 2.9 nm, respectively. The crystal patterns of CF-MCM were similar with MCM-41 from TEM image. The adsorption capacity of acetone with CF-MCM was 118, 190, 194 and 201 mg g(-1), respectively, under 500, 1000, 1500 and 2000 ppm. Furthermore, the adsorption capacity of MCM-41 and CF-MCM was almost the same. The effects of operation parameters, such as contact time and mixture concentration, on the performance of CF-MCM were also discussed in this study.

Preparation and Characterization of K2CO3-Activated Kraft Lignin Carbon

A series of activated carbons (ACs) were prepared by K2CO3 activation from kraft lignin (KL) that was recovered from papermaking black liquor. The effects of process parameters such as the activation temperature (AT), activated period, K2CO3 to KL mass ratio, and N2 flow rate on the characteristics of the final product were determined. The ACs were characterized using nitrogen adsorption, morphology, and fractal dimension analyses. The results showed that the AT was the main factor influencing the yield, surface area, and pore structure. The yield of ACs obviously decreased from 50.6% to 20.5% with increasing AT from 600 °C to 1000 °C, and decreased with increasing K2CO3/KL mass ratio. Activation time and N2 flow rate had slight effect on the yield of ACs. The surface area and total pore volume increased as the AT rose to 900 °C and then decreased with further increases in temperature. The maximum surface area and total pore volume were 1816.3 m2/g and 1.26 cm3/g, respectively, at a K2CO3 to KL mass ratio of 3:1, AT of 900 °C, activation time of 2 h, and N2 flow rate of 70 cm3/min. The pore structure of the ACs could be tailored by controlling the AT. As the AT was increased from 700 to 1000 °C, the mesoporosity increased from 11.6% to 95.9%. SEM images indicated that the morphology of ACs was modified by the AT. The K2CO3 was partially recycled.

Plasma Treatment of Silver Impregnated Mesoporous Aluminosilicate Nanoparticles for Adsorptive Desulfurization

We report a regenerable adsorbent for the removal of refractory organosulfur compounds from fossil fuels. The material is composed of well-dispersed silver nanoparticles confined within the mesochannels of aluminum-doped MCM-41 nanoparticles. With an average initial desulfurization capacity of 15 mg S·g–1, 79% desulfurization capacity is retained after six cycles for the removal of dibenzothiophene from n-decane. The addition of intraframework aluminum to form a mesoporous aluminosilicate nanoparticle (MASN) aids in the retention and dispersion of silver ions within the mesochannels (Ag-MASN). The nanoparticles are subsequently reduced by glow discharge plasma treatment in argon (PT-Ag-MASN). The size dispersion, surface area, and structural integrity were characterized by scanning electron microscopy, annular dark-field scanning transmission electron microscopy (ADF-STEM), nitrogen adsorption analysis (BET), and powder X-ray diffraction. Silver nanoparticle formation within the mesochannels of MASN was confirmed by ADF-STEM and diffuse reflectance UV–vis spectroscopy. Model fuel testing revealed that PT-Ag-MASN had the highest regeneration capacity after six cycles compared to non-plasma-treated (Ag-MASN) and aluminum-free materials (Ag-MSN and PT-Ag-MSN). Initial testing of the military jet fuel JP-8 also shows a high desulfurization capacity of 41 mg S·g–1.

New functionalised polymeric microspheres for multicomponent solid phase extraction of phenolic compounds

Three new porous copolymers possessing basic character were prepared by chemical modification of polymeric adsorbent (copolymer of bis[4(2-hydroxy-3-methacryloyloxypropoxy)phenyl]sulfide and glycidyl methacrylate, BES.DM + GMA). Modification was carried out by reactions of surface epoxide groups of the precursor with amines: butylenediamine, diethylenetriamine and triethylenetetramine. Next, two of the synthesized materials were chosen for further modification involving addition of HCO3 − groups to amine species. The obtained polymer adsorbents were characterised by elemental analyses, FTIR, nitrogen adsorption and thermal analyses. The prepared copolymers were studied for use as adsorbent in solid phase extraction (SPE) of multicomponent mixture of phenolic compounds consisting of: phenol, 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol. The SPE experiments were carried out in off-line mode. The influence of the chemical modification on adsorption properties of the presented materials was observed. The prepared adsorbents possessed different sorption properties towards the phenols. In addition, a competition phenomenon of the testing compounds for active sites on the polymer surface was observed. The most effective in adsorption of phenol and its chlorinated derivatives were the polymers with both amine and bicarbonate groups. The best recovery results were obtained for 2,4-dichlorophenol.

Activated Carbon from Rubber Wood Sawdust by Carbon Dioxide Activation

Activated carbon (AC) is an organic adsorbent and mostly used to adsorb volatile organic compound pollutants. In the present work, AC was produced from rubber wood sawdust via a physical activation method using CO2 gas. Prior to activation process, the biomass was carbonized under N2 gas flow of 600mL/min for 1h at a corresponding temperature to produce char. The effect of activation temperature (700, 720, 740, and 760°C) and time (60, 90, and 120min) on the mass yield and characteristics of activated carbon was investigated. In overall, the yield of AC decreased when heated at higher activation temperature and increased at longer time. Under nitrogen adsorption analysis, surface area and pore volume of AC were determined. At higher temperature, surface area and pore volume increased, but excessive heating could break the pore structure. Next, the performance of activated carbon was tested in term of adsorption capacity for gas and liquid phase adsorption represented by benzene and trichloroethylene, respectively. Preliminary results suggested that the AC could adsorb both compounds efficiently.