Nitrogen Gas Adsorption Research Articles

Aqueous electrochemical energy storage system based on phenanthroline- and anthraquinone-modified carbon electrodes

This manuscript reports the electrochemical behaviour of electrochemical energy storage system based on carbon-based electrodes modified with phenanthroline and anthraquinone molecules, respectively. The composite electrodes consist of activated carbon powder modified with phenanthroline or anthraquinone molecules by the diazonium chemistry. The phenanthroline-modified carbon used to prepare the composite electrode was characterized by elemental analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis coupled to infrared spectrometry, and nitrogen gas adsorption. Phenanthroline-modified carbon composite electrode exhibited redox activity in aqueous acidic electrolyte around 0.4 V vs. Ag/AgCl. Consequently, it was used as positive electrode in electrochemical energy storage system with an anthraquinone-modified carbon negative electrode. Pre-polarization of both electrodes was needed to take full advantage of the charge storage properties of the grafted species and to reach the potential range of their redox activity upon charge/discharge cycling. This pre-treatment also enabled an increase of the operating voltage cell to 1.0 V in aqueous 1 M H2SO4 electrolyte.

ГИДРОФОБИЗАЦИЯ ТОНКОДИСПЕРСНОГО МЕЛА

Natural fine chalk (calcium carbonate) is widely used functional filler for composite materials used in many industries. The development of in-depth studies of the physicochemical properties of hydrophobic chalk contributes to the expansion of its application. The analysis of scientific and technical literature has shown that at the moment there are no studies of the parameters of the porous structure and textural parameters of natural chalk of various granulometric composition, especially superficially treated (hydrophobized) with fatty carboxylic acids. Carboxylic acids of C17 to C20 fractions are practically applied for hydrophobization of calcium carbonate that is conditioned by presence of these acids with enough long hydrocarbon chains and reactive carboxyl group. The treatment of chalk with hydrophobizing additive gives it the following advantages over untreated chalk: prevention of moisture accumulation, absence of caking and improvement of technological properties (flowability, compatibility with polymer and others). The paper presents the results of chemical and mineralogical analyses of natural chalk from the Sheinsky deposit, data on the differential distribution of particles, the degree of hydrophobicity, and the study of the textural characteristics of natural and hydrophobized fine chalk. The influence of the grinding method on the granulometric composition is evaluated and the cumulative effect of the grinding method and hydrophobization on the texture characteristics of chalk is revealed. It is established that the surface treatment of chalk particles with fatty acids (C18 content not less than 65 wt%) affects the process of nitrogen gas adsorption

Pore formation and evolution of organic-rich shale during the entire hydrocarbon generation process: Examination of artificially and naturally matured samples

Shale pore type and variation have significant influences on natural gas storage and are of vital importance for shale gas resource evaluation. To better understand the formation and evolution of shale pores during hydrocarbon generation process, organic geochemistry, X-ray diffraction, field emission scanning electron microscopy (FE-SEM), and low-pressure nitrogen gas adsorption (N2GA) were applied to samples created by thermal simulation and to naturally evolved samples of the Upper Permian Dalong Formation in the northwestern Sichuan Basin. The results show that the development of organic matter (OM) pores is controlled by kerogen type and thermal maturation level and begins at equivalent vitrinite reflectance (eqvRo) value of 0.91%. Two types of OM pores are developed during OM evolution stage, as bubble pores that are formed at the oil window stage and spongy pores which occcur at the dry gas stage. Maximum pore volume, particularly mesopore volume, occurs within two opportune development periods with the corresponding eqvRo values of 1.11–1.53% and 2.5–2.9%, respectively. The periods are known to be the two peak stages of shale pore development. The first peak corresponds to the late oil generation stage, and the second corresponds to the cracking peak of extractable OM to gas, during which numerous OM micropores and mesopores are generated. OM pore generation is generally resulted from OM decomposition, and pore structure parameters exhibit significant positive correlations with OM reduction for simulated samples. For naturally matured samples, TOC content is positively correlated with pore structures. Extractable OM generated from primary kerogen fills OM pores and mineral-related pores and further reduces shale pore volume. In terms of analysis on naturally matured samples with similar maturities, OM pores in type II1 kerogen are inferior to those in type I kerogen but more developed than those in type III kerogen. Shale pore evolution is also controlled by diagenesis. Compaction and cementation have adverse effects on shale pore preservation during early and late diagenesis stages, which leads to a significant decrease in shale pore volume, particularly that of mesopores. It should be noted that OM pores are better developed and preserved even when the eqvRo value exceeds 3.25%, which is of vital importance for extending the field of shale gas exploration of over-mature shale reservoirs.

Preparation of the methyltriethoxysilane based aerogel monolith with an ultra-low density and excellent mechanical properties by ambient pressure drying

Methyltriethoxysilane based aerogel monoliths with excellent mechanical properties, an ultra-low density, and a highly efficient thermal insulating property were prepared by an improved simple and environmental-friendly ambient pressure drying process. The morphology, particle size, and nano-pore volume of aerogel monoliths were characterized by scanning electron microscope and nitrogen gas adsorption–desorption analyzer. The elastic modulus of particles in aerogel monoliths and the compressive stress–strain response of aerogel monoliths were estimated based upon experimental data obtained via atomic force microscope and materials testing machine. A structural model is proposed to estimate the critical compressive stress with a structural coefficient being introduced to manifest the microstructural integrity of aerogel monoliths. The mechanism for the low bulk density aerogel monoliths to exhibit a linear stress–strain response and a non-buckling failure mode under the uniaxial compression is discussed.

Full-scale pore size distribution features of uranium-bearing sandstone in the northwest of Xinjiang, China.

As an important nuclear fuel, uranium in sandstone uranium deposits is mainly extracted by in situ leaching. The porosity of sandstone is one of the important indexes determining in situ leaching efficiency. Moreover, the microscopic pore size distribution (PSD) of the uranium-bearing layer has an important effect on porosity. It is necessary to feature the pore structure by various techniques because of the different pore types and sizes in the uranium layer. In this paper, combined with nitrogen gas adsorption, nuclear magnetic resonance techniques and scanning electron microscopy, the full-scale PSD features of uranium-bearing sandstone in the northwest of Xinjiang are effectively characterized. The results show that pores structure of uranium-bearing sandstone include dissolution pores (d ≤ 50 nm), intergranular pores (50 nm < d ≤ 200 µm) and microfractures. Intergranular pores of 60 nm and 1 µm are the significant contributors to pore volume. The effects of the pore volume of two pore types (dissolution pores and intergranular pores) on the porosity of uranium-bearing sandstone are analysed. The results show that intergranular pores have the greater influence on the porosity and are positively correlated to the porosity. Dissolution pores have little effect on the porosity, but it is one of the key factors for improving uranium recovery. Moreover, the greater the difference of PSD between sandstones, the stronger the interlayer heterogeneity of uranium-bearing sandstone. This kind of interlayer heterogeneity leads to the change of permeability in the horizontal direction of strata. It provides a basis for a reasonable setting of well type and well spacing parameters.

Fabrication of hydrophilic and hydrophobic silica aerogel by drying‎ at ambient pressure and their structural properties

In this research, silica aerogel was made by sol-gel method with sodium silicate precursor ‎and drying at ambient temperature. The silica aerogel prepared by this method is ‎superhydrophobic. To make it hydrophilic, the sample was heated at 400 °C for 2 h. The ‎structure of the samples was studied using X-ray diffraction, scanning electron microscopy, ‎adsorption and desorption of nitrogen gas. To investigate the hydrophilicity and ‎hydrophobicity of the samples, the water droplet contact surface test was performed. The ‎chemical bonds of the prepared samples were studied using Fourier transform infrared ‎spectroscopy. The overall results showed that the size of the particles and the pores increase ‎and become smaller, respectively when the hydrophilicity of the silica aerogel sample ‎changes to the hydrophobic sample. The angle of contact of the water droplet with the ‎surface of the hydrophobic sample is 170°, while reaches to 51° for the hydrophilic sample‎.

Evaluation of Ionomer Distribution on Electrocatalysts for Polymer Electrolyte Fuel Cells by Use of a Low Acceleration Voltage Scanning Electron Microscope

The qualitative evaluation of the dispersion of prefluorosulfonic ionomer (PFSI) with different ionomer/carbon mixing ratios (I/C) using electron microscopy was carried out without the use of a stain treatment. Both low acceleration voltage transmission electron microscopy (LAV-TEM) and ultralow acceleration voltage scanning electron microscopy with a retarding method (ULV-SEM) use a characteristically low acceleration voltage, which allows the selective examination of the sensitive ionomer morphology. The high-performance charge-coupled device enables one to obtain high contrast ionomer images without the use of lead or cesium staining, which could otherwise result in morphological changes during these pre-treatments. The electrochemically active surface area of the polymer electrolyte fuel cell using Pt/GCB increased with increasing PFSI content and saturated at an ionomer/carbon weight ratio (I/C) of 1.2, where full coverage of the ionomer was detected by LAV-TEM. The ULV-SEM images showed the obvious occlusion of the primary and secondary pores of the Pt/GCB catalyst layers above I/C = 1.2. The nitrogen gas adsorption measurement, carried out by use of quenched solid-density-functional theory analysis, also supported the occlusion of the primary and secondary pores of the Pt/GCB catalyst layers above I/C = 1.2.

Pore Characteristics of Gondwana Shale of Eastern India

Abstract A complete pore characteristic of the Indian Gondwana shale is studied by combining laboratory experiments and numerical modeling. Mercury injection capillary pressure (MICP), nitrogen gas adsorption (N2GA) and scanning electron microscopy (SEM) are the primary laboratory methods used to evaluate the pore characteristics. The N2GA and MICP were coupled to estimate the pore size distribution (PSD) of Indian Gondwana shale for the first time. The estimated PSD of Gondwana shale varies between 0.5 nm to 100 µm and most of the pores of the samples fall in the micropore and mesopore category. The porosity of Gondwana shale, measured using MICP, varies from 1.13 to 8.01 %. The SEM micrographs and hysteresis pattern of isotherms reveal the presence of cylindrical, ink-bottle and slit shape pores in the samples. The BET (Brunauer-Emmett-Teller) surface area of pore for Gondwana shale varies from 3.42 m2/g to 21.5 m2/g. The FHH (Frenkel-Halsey-Hill) fractal model suggests that the Gondwana shale exhibits two types of fractal dimensions with highly complex pore geometry. The adsorption capacity of Gondwana shale is affected by the clay content. This paper attempted a different interpretation approach using experimental data and concluded that Indian Gondwana shale has high gas storage capacity.

Assessment of surface heterogeneity of lime treated kaolinites: Probed by low-pressure argon and nitrogen gas adsorption

It is a common practice to alter the undesirable behavior of clayey soils (i.e. swelling-shrinkage and high plasticity) with lime addition. However, the reaction mechanism involved in the early stage (first minute up to 24 h after mixing) of lime treatment is still not well explored. In the present work, the surface chemistry of lime ([Ca] = 22 mmol/l and pH = 12.63) treated kaolinites (Kaol) was studied using argon and nitrogen gas adsorption. The effect of pH ([Ca] = 22 mmol/l and. pH = 12.63 vs. [Ca] = 22 mmol/l and pH = 7) was also examined. The derivative low-pressure adsorption isotherms were analyzed using derivative isotherm summation (DIS), focusing on the analysis of surface heterogeneity. After the treatment with lime, the specific surface area and adsorption energy distribution of Kaol were modified. The adsorption of the calcium cation at both investigated pH (i.e. pH 7 and pH 12.63) takes place on the basal and lateral face of Kaol, however, the species of adsorbed calcium cation appeared to be different. The treatment also leads to a decrease in basal surface area due to basal face-basal face particle aggregation. The basal surface of Kaol treated with lime exhibited polar sites when probed with nitrogen molecule. These sites may have promoted linkage and flocculation of Kaol particles, which in turn play a role in the short-term modification of the macroscopic behavior of lime treated kaolins.

Activated carbon from Nauclea diderrichii agricultural waste–a promising adsorbent for ibuprofen, methylene blue and CO2

The adsorption potential of activated carbon derived from Nauclea diderrichii biomass (NDAC) was scrupulously harnessed as a low cost and ubiquitous adsorbent for the removal of greenhouse gas (CO2), and organic pollutants such as methylene blue (MB) and ibuprofen (IB) from water. NDAC was fully characterized by scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), universal attenuated total reflectance-infra red (UATR-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), solid state nuclear magnetic resonance (NMR) and nitrogen gas adsorption–desorption by Brunauer-Emmett-Teller (BET) technique. This study showed that NDAC comprises graphitic carbons that had some surface functional groups such as CC, CO, etc, which adsorbed these environmental contaminants. The adsorption equilibrium and kinetic data that the adsorption of these environmental contaminants formed multilayers (homogeneous surfaces) with the surface of NDAC. The adsorption mechanism of CO2, MB and IB onto NDAC occurred by via electrostatic attractions and π-π conjugal interactions. The adsorption capacity of NDAC for CO2 was ca. 3.2 cm3.g−1 at 298 K. The Langmuir maximum adsorption capacity, qmax of NDAC for MB and IB was obtained as 35.09 mg.g−1 and 70.92 mg.g−1 at 328 K respectively.

Removal of Pb(II) Ions from Aqueous Solution Using Modified Starch

In this study, two types of modified cassava starch samples (MCS and MWS) prepared from commercially available native cassava starch (NCS) and native cassava starch extracted using the wet method (NWS) were investigated for the removal of Pb(II) ions from aqueous solutions. MCS and MWS samples were synthesized under acidic conditions using Pluronic 123 as the structure-directing agent and tetraethylorthosilicate (TEOS) as the chemical modifying agent. Modified starch samples were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray Diffraction (XRD), and a nitrogen (N2) gas adsorption–desorption analyser. MCS and MWS showed enhanced thermal stabilities upon acid hydrolysis and chemical modification. The effects of contact time and initial Pb(II) concentration were studied through batch adsorption experiments. Adsorption kinetics followed the pseudo-second-order kinetic model. The equilibrium adsorption data were analysed and compared by the Langmuir and Freundlich adsorption models. The coefficient correlation (R2) was employed as a measure of the fit. The Langmuir model fitted well with equilibrium adsorption data, giving a maximum Pb(II) adsorption capacity of 370.37 and 294.12 mg/g for MWS and MCS, respectively. Modified samples exhibited a higher desorption efficiency of over 97%. This study demonstrated that modified starch could be utilized for Pb(II) removal from industrial wastewater.

Microwave-assisted novel one-pot synthesis and characterization of copper oxide

Copper oxide (CuO), being a transition metal oxide, finds numerous applications in current science and technology. To tailor the different properties of CuO to meet the requirements of intended applications, recent research is focused on the exploration and utilization of various synthesis routes. Hence, there is huge scope for research in the rapid facile synthesis of CuO with desirable characteristics. This work presents the synthesis of CuO in one-step using a dedicated single-mode sealed-vessel microwave reactor. The relevant properties of synthesized CuO were evaluated by characterization studies such as nitrogen gas adsorption measurement, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermal analysis.

Pd Nanoparticles-Loaded Vinyl Polymer Gels: Preparation, Structure and Catalysis

Four vinyl polymer gels (VPGs) were synthesized by free radical polymerization of divinylbenzene, ethane-1,2-diyl dimethacrylate, and copolymerization of divinylbenzene with styrene, and ethane-1,2-diyl dimethacrylate with methyl methacrylate, as supports for palladium nanoparticles. VPGs obtained from divinylbenzene and from divinylbenzene with styrene had spherical shapes while those obtained from ethane-1,2-diyl dimethacrylate and from ethane-1,2-diyl dimethacrylate with methyl methacrylate did not have any specific shapes. Pd(OAc)2 was impregnated onto VPGs and reduced to form Pd0 nanoparticles within VPGs. The structures of Pd0-loaded VPGs were analyzed by XRD, TEM, and nitrogen gas adsorption. Pd0-loaded VPGs had nanocrystals of Pd0 within and on the surface of the polymeric supports. Pd0/VPGs efficiently catalyzed the oxidation/disproportionation of benzyl alcohol into benzaldehyde/toluene, where activity and selectivity between benzaldehyde and toluene varied, depending on the structure of VPG and the weight percentage loading of Pd0. The catalysts were stable and Pd leaching to liquid phase did not occur. The catalysts were separated and reused for five times without any significant decrease in the catalytic activity.

A new application of atomic force microscopy in the characterization of pore structure and pore contribution in shale gas reservoirs

The pore structure determined by different materials is extremely significant for shale gas accumulation. Understanding how different materials contribute to the pore remains a knowledge gap. To elucidate the surface property and pore structure qualitative and quantitative characteristics of gas-bearing shales, the Atomic Force Microscopy (AFM) and low-temperature nitrogen gas adsorption (LT-N2GA) experiments were performed on shale samples selected from the Longmaxi Formation (Fm.) in the Sichuan Basin in China in this study. A new method based on AFM technique was used to calculate shale porosity, and the double-threshold discrete integration method was proposed to estimate the pore contributions of main materials. The results show that the organic-rich shale is significantly different from the organic-poor shale in material composition. The average value of mean roughness (Ra) of the organic-rich and organic-poor shale samples are 38.74 nm and 104.58 nm, respectively, indicating that the organic-poor shale has a rougher surface. The average value of mean square roughness (Rq) of the organic-rich and organic-poor shale samples are 49.91 nm and 138.80 nm, respectively, indicating that the organic-poor shale has a severer variation degree. Moreover, organic-poor shale samples also have a more concentrated height distribution. The average surface porosity of the organic-rich shale and organic-poor shale are 17.08% and 3.31% respectively. The average form factor (ff) of the organic-rich shale and organic-poor shale are respectively 0.102 and 0.386. It indicates that organic-rich shale has more pores and more complicated pore boundaries than organic-poor shale. AFM-calculated porosity is consistent with that of LT-N2GA-converted, which indicates that the porosity calculated by AFM is real porosity and reliable. The essence of the phase change on the shale surface is the difference in material composition. Shale pores are mainly contributed by organic matter, followed by chlorite, potash feldspar, and quartz. The results show that our method provides a powerful and effective tool to characterize the nanopore structure of organic rocks, obtain shale reservoir physical properties, and analyze pore contribution of shale components etc. issues, which has a wide application prospect.

Fractal characteristics of pore networks and sealing capacity of Ordovician carbonate cap rocks: A case study based on outcrop analogues from the Tarim Basin, China

Understanding and predicting the main controls on the sealing capacity of carbonate cap rocks is of great significance for ultradeep carbonate reservoir exploration and production. This study focuses on revealing the pore networks and sealing capacity of the Ordovician carbonate cap rocks in the Tarim Basin by analyzing samples from outcrop analogues using optical and scanning electron microscopy and a combination of mercury intrusion capillary pressure and nitrogen gas adsorption. Three classes of cap rocks are defined here according to their pore-throat structure, fractal dimension, and sealing capacity. These carbonate cap rocks are dominated by limestones and dolomitic limestones. Four pore types are identified: microfractures, intragranular, intercrystalline, and intracrystalline. Six pore structure types show multiscale variability from macropores to micropores. The pore structures present multiple fractal behaviors, with fractal dimensions showing an increasing trend as the pore diameter decreases. The cover coefficient, a parameter that allows characterization of the caprock sealing performance, shows an increasing trend along with increasing the fractal dimension of pore structure. The average cover coefficients of six pore structure types not only show good correlations (either exponential or linear) with certain fractal dimensions, but they also demonstrate a strong positive correlation with the average fractal dimension. These results suggest that the sealing capacity of the studied rocks increases with increasing fractal dimension. The sealing performance of cap rocks significantly decreases with an increasing amount of macropores. This work provides a relevant case study for further understanding of pore structures and sealing capacity of carbonate cap rocks.

Preparation and characterization of new adsorbents of pea and bean agricultural peels for water purification loaded with organic tryptophan compound

The aim of the study was to find alternative materials that could contribute to the protection of the environment by the elimination of organic pollutant (tryptophan). The adsorbent materials (activated carbon) were prepared from pea and bean peels which were chemically treated with phosphoric acid and then treated physically by calcination. This synthesized material was used as an adsorbent for the purification of different waters charged with organic tryptophan compound. Agricultural residues were characterized by electronic microscopy and thermogravimetric analysis. The physical characterization was determined by adsorption of nitrogen gas at 77 K (BET). The impact of some process parameters was examined and analyzed, namely the initial concentration of pollutant, the dose of activated carbon and the dilution medium. The obtained results showed a low yield between 10% and 33% in the three types of water for coagulation-flocculation with aluminum sulfate alone. However, better removal efficiency was obtained by combination of aluminum sulfate and activated carbon between 70% to 90%, and elimination efficiency between 75% to 80% in combination with aluminum sulfate and activated carbon. Specific areas of pea and bean peels respectively 735.27, 760.56 m(2)/g, and the diameter of its pores respectively 58.42 and 52.88, make these adsorbent materials efficient, economical and effective for the removal of organic matter.

The surface and bulk properties of CuO ribbons and ZnO particles mixture using physical adsorption and gamma ray attenuation techniques

AbstractIn the present work, we investigate the surface, and bulk structural properties of composite cupric oxide ribbons, and zinc oxide particles. The composites are synthesized using the technique of solution combustion. Crystallographic phases are confirmed using the x‐ray diffraction technique and proved the formation of monoclinic cupric oxide and hexagonal zinc oxide crystallites. Scanning electron microscope and high‐resolution transmission electron microscope are used to examine the morphology of the prepared materials. Composite mixtures of raw particles cupric oxide and zinc oxide are used as benchmark morphologically‐alike composite materials. The specific surface area values of the studied materials are investigated using nitrogen gas adsorption at 77 K while the spectroscopic gamma ray attenuation is used to determine the effective density of the different samples. Zinc oxide particles are dispersed on cupric oxide ribbons and cause nonlinear dependence of the specific surface area and density on the composition ratio due to the physical contact between particles, especially at the voids and the nodes of the fibrous ribbons network.

Implications of thin laminations on pore structure of marine shale reservoir: Goldwyer Formation case study from Western Australia

The pore structure of a shale reservoir is a major control on hydrocarbon potential, yet shale pore systems are complex and affected by various factors. This paper focuses on the differences in pore structure between thinly laminated and massive black shale (MBSh) beds in the Ordovician Goldwyer-III shale, Canning Basin, Western Australia. A multiscale approach included image logs, core descriptions, thin sections, scanning electron microscope and X-ray diffraction analysis with low-pressure nitrogen and carbon dioxide gas adsorption tests. The results indicate that the Goldwyer shale comprises laminated beds of quartz silt and shale with thin beds of organic-rich clay, plus minor interbedded carbonate bands or concretions. The pore types are subjected to rock type, and the thinly laminated shale (LSh) is enriched in intergranular and intragranular pores. In contrast, the MBSh mainly comprises organic matter pores. The LSh is slightly enriched in mesopores but has negligible micropores. The mesopores are wedge-shaped and associated with an inorganic matrix of clay and pyrite. In comparison, the MBSh contains both mesopores and micropores. These pores are slit-like and related to organic matter and clay. The clay content and total organic carbon fluctuations control the development of mesopores and micropores in both the laminated and MBSh beds in the Goldwyer-III shale. The MBSh layers are suggested as the most important rock types for fluid flow via pore systems due to higher total pore volume, specific surface area and gas adsorption capacity.

Nanopore Structure of Different Rank Coals and Its Quantitative Characterization.

Based on gas adsorption theory, high-pressure mercury intrusion (HPMI), low-temperature liquid nitrogen gas adsorption (LT-N₂GA), CO₂ adsorption, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and small-angle X-ray scattering (SAXS) techniques were used to analyze the pore structures of six coal samples with different metamorphisms in terms of pore volume, specific surface area (SSA), pore size distribution (PSD) and pore shape. Combined with the gas adsorption constant a, the influence and mechanism of the pore structure of different coal ranks on gas adsorption capacity were analyzed. The results show that there are obvious differences in the pore structure of coals with different ranks, which leads to different adsorption capacities. To a large extent, the pore shapes observed by SEM are consistent with the LT-N₂GA isotherm analysis. The pore morphology of coal samples with different ranks is very different, indicating the heterogeneity among the coal surfaces. Adsorption analysis revealed that mesopore size distributions are multimodal and that the pore volume is mainly composed of mesopores of 2-15 nm. The adsorption capacity of the coal body micropores depends on the 0.6-0.9 nm and 1.5-2.0 nm aperture sections. The influence of coal rank on gas desorption and diffusion is mainly related to the difference in pore structure. The medium metamorphic coal sample spectra show that the number of peaks in the high-wavenumber segment is small and that it is greater in the high metamorphic coal. The absorption intensity of the C-H stretching vibration peak of naphthenic or aliphatic hydrocarbons varies significantly among the coal samples. Over a small range of angles, as the scattering angle increases, the scattering intensity of each coal sample gradually decreases, and as the degree of metamorphism increases, the scattering intensity gradually increases. That is, the degree of metamorphism of coal samples is directly proportional to the scattering intensity. The influence of coal rank on gas adsorption capacity is mainly related to the difference in pore structure. The gas adsorption capacity shows an asymmetric U-shaped relationship with coal rank. For higher rank coals (Vdaf < 15%), the gas adsorption consistently decreases significantly with increasing Vdaf. In the middle and low rank coal stages (Vdaf > 15%), it increases slowly with the increase of Vdaf. We believe that the results of this study will provide a theoretical basis and practical reference value for effectively evaluating coal-rock gas storage capacity, revealing the law of CBM enrichment and the development and utilization of CBM resources.

Removal of methylene blue dye using nano zerovalent iron, nanoclay and iron impregnated nanoclay - a comparative study.

There has been an increasing challenge from the emission of methylene blue (MB) dye-containing wastewater and its management methods in industry. The sorption process is one conventionally used method. In this study, nanoclay, nano zero valent iron (nZVI), and iron impregnated nanoclay were prepared and studied for the removal of MB dye in batch mode. The effects of operating parameters like pH, dye concentration, sorbent dosage, and contact time were investigated and optimized. The nZVI, nanoclay, and iron impregnated nanoclay sorbents showed zeta potentials of −32.1, −53.4, and −40.7 mV, respectively. All the nano adsorbents were crystalline. The nanoclay was characterized by an average surface area, pore volume and pore diameter of 43.49 m2 g−1, 0.104 cm3 g−1 and 2.806 nm, respectively. nZVI showed a surface area of 47.125 m2 g−1, pore volume of 0.119 cm3 g−1, and pore diameter of 3.291 nm. And iron impregnated nanoclay showed a surface area of 73.110 m2 g−1 with a pore volume of 15 cm3 g−1 and a pore diameter size of 3.83 nm. A Langmuir EXT nitrogen gas adsorption isotherm (R2 ∼ 0.99) was the best fit. The thermodynamics parameters, such as ΔG° (−12.64 to −0.63 kJ mol−1), ΔH° (+0.1 to +62.15 kJ mol−1) and ΔS° (+0.10 to +0.22 kJ mol−1), confirmed that a spontaneous and endothermic adsorption process took place at a high rate of disorder. Iron impregnated nanoclay showed higher negative Gibbs free energy (−12.64 kJ mol−1), higher enthalpy change (+62.5 kJ mol−1) and entropy (+0.22 kJ mol−1) and gave a better MB removal performance. In addition, the lower negative heat of enthalpy for all adsorptions proved the dominance of physisorption. The methylene blue adsorption isotherm on nZVI and nanoclay showed the best fit with the Freundlich isotherm model with correlation coefficients (R2) ∼0.98 and 0.99, respectively. Whereas the Langmuir adsorption isotherm was the best fit for iron impregnated nanoclay (R2 ∼ 0.98). The adsorption activities of nZVI, nanoclay and iron impregnated nanoclay were fitted to a pseudo-second-order kinetic model with correlation coefficients (R2) of 0.999, 0.997 and 0.983, respectively. The optimal pH 7.0 (RE: 99.1 ± 0.73%), initial MB concentration 40 ppm (RE: 99.9 ± 0.03%), contact time 120 min (RE: 99.9 ± 0.9%), and adsorbent dose 80 (99.9 ± 0.03%) were obtained for iron impregnated nanoclay. The optimal operational parameters of nanoclay and nZVI, respectively, were pH 11.0 and 13.0, initial MB concentration 20 and 20 ppm, adsorbent dose 100 and 140 mg, and contact time 120 and 140 min. In general, iron impregnated nanoclay has shown promising cationic dye adsorbance for industrial applications; but a recyclability test is suggested before scale-up.