N2 Specific Surface Area Research Articles

Palygorskite–TiO2 nanocatalysts for photocatalytic degradation of tebuconazole in water

AbstractPalygorskite–TiO2 nanoparticles are frequently used as nanocatalysts. In the present study, two different nanocatalysts were developed based on the use of different palygorskite–TiO2 ratios: 40–60 and 10–90. The nanocomposites were investigated for the photocatalytic degradation of the common fungicide tebuconazole (TEB), under aquatic conditions. The samples were extensively characterized by X‐ray powder diffraction, attenuated total reflectance–Fourier transform infrared spectroscopy, scanning electron microscopy and N2 specific surface area (SSA) by Brunauer–Emmett–Teller (BET) analytical techniques. The TiO2 nanoparticles were successfully dispersed on the mineral's surfaces and the photocatalytic activity reached 88.4% for the palygorskite–TiO2 ratio of 40:60, where the dispersion was better as proved by the total pore volume and BET parameters (0.49 cm3/g and 258 m2/g compared to 0.33 cm3/g and 220 m2/g of the 10:90 ratio). The photocatalytic efficiency of the proposed materials was significantly higher than Degussa P25 (33.2%), and that makes the palygorskite–TiO2 nanocomposites very promising for advanced application in fungicides' degradation in aquatic environments.

Pore characterization of Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation shale gas reservoirs, Sichuan Basin, China

In order to investigate pore structure characteristics of Wufeng and Longmaxi Formations shales in the Sichuan Basin, the organic geochemical parameter and petrologic experiments, N2 and CO2 adsorptions, field emission scanning electron microscopy analysis and helium porosity measurement are carried out. Results showed that the thermal maturity of shales belong to over-maturity stage with TOC content and porosity of 1.84%–6.82% and 2.6%–5.1%, respectively. The TOC content has a good correlation with quartz, weak correlation with clay and no correlation with carbonate, indicating that the organic matter is mainly controlled by quartz content. The N2 and CO2 specific surface areas of organic-rich shale is generally 16.86–29.71 m2/g and 13.76–26.47 m2/g, respectively and the average N2 and CO2 specific surface area of organic-poor shale are 8.91 m2/g and 9.11 m2/g respectively, which indicating that the organic-rich shale has higher specific surface area, pore volume and smaller average pore diameter than that of organic-poor shale. The specific surface area in organic-rich shale is mainly contributed by micropores, while the pore volume is mainly contributed by mesopores, followed by micropores. There is a very strong correlation between TOC and CO2 and N2 specific surface area, indicating that pores were controlled by organic matter. Both porosity and specific surface have a positive relation when clay content is less than 28% for organic-rich shale, and its correlation is not obvious when clay content is more than 28% for organic-poor shale, indicating that the clay has a certain effect on reservoir.

Synthesis of natural zeolite agglomerates: clinoptilolite-based geopolymers through aluminate activation

AbstractNatural zeolite (clinoptilolite)-based geopolymers were synthesized using alkali aluminate solution, including aluminate anodizing waste solution. The effect of calcination of the clinoptilolite sample at 900°C was investigated. The samples were studied by powder X-ray diffraction, thermal analysis, scanning electron microscopy and N2-specific surface area. The alkali aluminate-activated clinoptilolite geopolymers are characterized by satisfactory compressive strength (up to 37 MPa), low density and acceptable shrinkage. The clinoptilolite geopolymer obtained contains an X-ray amorphous phase and newly formed phillipsite and zeolite NaP. The presence of zeolite phases in the geopolymer agglomerate could be beneficial in products with specific qualities and properties, such as ion exchange, passive cooling, antimicrobial activity,etc.

Synthesis and Structural Analysis of LDH-SO4-CO3 Whisker

High-quality LDH-SO4-CO3 whiskers were synthesized via liquid precipitation method using MgSO4·7H2O and Al2(SO4)3·18H2O as precursors and Na2CO3-NaHCO3 buffer solution as precipitant. The influence of buffer solution concentration on the characteristics of the samples was investigated. The as-grown whiskers were characterized by X-ray diffraction, transmission electron microscopy, and Brunauer-Emmett-Teller N2 specific surface area measurements. The results show that the buffer solution concentration has significant impact on whiskers with intercalated structure. The LDH-SO4-CO3 whiskers with well-defined geometry, distinct intercalated structure, decent quality, and excellent dispersing capability can be obtained under the following conditions: buffer solution volume ratio of 45%, reaction temperature of 83°C, and reaction time of 182 h. The obtained whiskers are well-crystallized and exhibit homogeneous morphology consisting of fber bars.

Structural and fractal characterization of adsorption pores of middle–high rank coal reservoirs in western Yunnan and eastern Guizhou: An experimental study of coals from the Panguan syncline and Laochang anticline

To better understand the structural characteristic of adsorption pores (pore diameter < 100 nm) of coal reservoirs around the coalbed methane production areas of western Yunnan and eastern Guizhou, we analyzed the structural and fractal characteristics of pore size range of 0.40–2.0 nm and 2–100 nm in middle–high rank coals ( Ro,max = 0.93–3.20%) by combining low-temperature N2/CO2 adsorption tests and surface/volume fractal theory. The results show that the coal reservoirs can be divided into three categories: type A ( Ro,max < 2.15%), type B (2.15% < Ro,max <2.50%), and type C ( Ro,max > 2.15%). The structural parameters of pores in the range from 2 to 100 nm are influenced by the degree of coal metamorphism and the compositional parameters (e.g., ash and volatile matter). The dominant diameters of the specific surface areas are 10–50 nm, 2–50 nm, and 2–10 nm, respectively. The pores in the range from <2 nm provide the largest proportion of total specific surface area (97.22%–99.96%) of the coal reservoir, and the CO2-specific surface area and CO2-total pore volume relationships show a positive linear correlation. The metamorphic degree has a much greater control on the pores (pore diameter less than 2 nm) structural parameters than those of the pore diameter ranges from 2 to 100 nm. Dv1 and Dv2 can characterize the structure of 2–100 nm adsorption pores, and Dv1 (volume heterogeneity) has a positive correlation with the pore structural parameters such as N2-specific surface area and N2-total pore volume. This parameter can be used to characterize volume heterogeneity of 2–10 nm pores. Dv2 (surface heterogeneity) showed type A > type B > type C and was mainly affected by the metamorphism degree. Ds2 can be used to characterize the pore surface heterogeneity of micropores in the range of 0.62–1.50 nm. This parameter has a good correlation with the pore parameters (CO2-total pore volume, CO2-specific surface area, and average pore size) and is expressed as type C < type B < type A. In conclusion, the heterogeneity of the micropores is less than that of the meso- and macropores (2–100 nm). Dv1, Dv2, and Ds2 can be used as effective parameters to characterize the pore structure of adsorption pores. This result can provide a theoretical basis for studying the pore structure compatibility of coal reservoirs in the region.

A novel magnesium ascorbyl phosphate graphene-based monolith and its superior adsorption capability for bisphenol A

In this study, a non-shell graphene-based monolith (GBM) with huge surface area was synthesized by chemical reduction of Graphene oxide (GO) using magnesium ascorbyl phosphate (MAP), and tested as an adsorbent for trace Bisphenol A (BPA) removal. The properties of MAP-GBM was characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller N2 specific surface area (BET), X-ray powder diffraction, Fourier transform-infrared (FTIR), Raman, and X-ray photoelectron spectroscopies. BPA adsorption was investigated in batch and column adsorption experiments. The data showed that MAP-GBM was a three-dimensional (3D) graphene material with macrostructure and most CC double bonds were recovered. Adsorption isotherms and kinetics of BPA on MAP-GBM followed the Langmuir model and fitted well with a pseudo-second-order kinetic model, respectively, and the adsorption process was endothermic. The saturated adsorption capacity of MAP-GBM was 324 mg/g for BPA, which was 2.43 times of that of ascorbic acid-GBM. A MAP-GBM adsorption column completely removed BPA from solution at low concentration (50 μg/L) for ∼450 mL.This efficiency is much higher than traditional adsorbents such as activated carbon, which could be ascribed to the unique 3D porous structure, hydrogen bonding, and π-π interaction characteristics of this MAP-GBM. The material can be easily regenerated by simply immersing in methanol for 24 h, and the adsorption efficiency remain as high as 88% after five regenerations. These findings demonstrated that MAP-GBM is a promising adsorbent for the effective and cost-efficient removal of low concentration endocrine-disrupting chemicals.

Predicting Contaminant Adsorption in Black Carbon (Biochar)-Amended Soil for the Veterinary Antimicrobial Sulfamethazine

Commercial hardwood biochars ranging in N2 specific surface area of 0.1-427 m(2) · g(-1) were added to an agricultural soil at 0, 1, or 2% levels to determine whether they would predictably reduce the pore water concentration of sulfamethazine (SMT). The soil and biochar-soil mixtures were preweathered under mild (2 d, 20 °C) or more severe (28 d, 40 °C) conditions before spiking. The carbon-normalized biochar-water distribution coefficient (KBC) of the biochars varied by a factor of up to 10(4), depending on biochar properties and SMT concentration. Except for the fast-pyrolysis biochar, KBC greatly exceeded the soil organic carbon-water distribution coefficient KOC. Sorption in the mixtures increased as expected with biochar and dose. However, sorption was dramatically overpredicted (by up to 10(2.5)) by the sum of sorption to the individual components, indicating a strong weathering effect even under the mild conditions. The soil-subtracted weathered biochar-water isotherms were more linear, and the KBC values approached or lay within the range of KOC values reported for SMT in 19 soils. Biochars both in intimate contact with soil and placed in a membrane bag suspended in the solution showed reduced N2-B.E.T. surface area after weathering, implicating fouling of the biochar surface by humic substances transferred through water. The results indicate that only highly surfaceous, carbonaceous biochars would be useful for stabilizing soil contaminated with compounds such as SMT. They also suggest that weathering may attenuate the contribution of native (environmental) black carbon to sorption of such compounds in soils and sediments.

Halloysite–TiO2 nanocomposites: Synthesis, characterization and photocatalytic activity

Two halloysite–TiO2 nanocomposites were prepared with two different tubular halloysite clays by depositing anatase-TiO2 on the halloysite surfaces using titanium isopropoxide under hydrothermal treatment at 180°C. The nanocomposites were characterized by X-Ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR), absorption properties by UV–vis spectroscopy and N2 specific surface area (SSA) analysis by BET method. Good dispersion of 3–10nm TiO2 particles on halloysite external surfaces was achieved in both the halloysite–TiO2 nanocomposites and ATR-FTIR results showed the formation of hydrogen bonding between TiO2 and the outer surfaces of halloysite tubes. After treating with TiO2, both halloysite samples largely showed interparticle mesopores of about 5.7nm. However, the macropores of halloysite (lumen or central hole in halloysite tubes) were not detected probably as a result of plugging of the lumens in halloysite tubes by TiO2 nanoparticles. These nanocomposites were tested for their photocatalytic activities in decomposing NOx gas and toluene. The halloysite–titania samples showed significantly higher activity in decomposing NOx gas under visible-light irradiation (λ>510nm) and UV–visible light irradiation (λ>290nm) compared to that of the standard commercial titania photocatalyst, P25. In addition, composite photocatalyst showed larger catalytic activity either under sunlight or pure UV irradiation in decomposing toluene compared to the commercial titania, P25. Our experimental data suggest that the enhanced photocatalytic activity is related with the good dispersion of the TiO2 nanocrystals on the surface of the clay minerals.

Comparison of Methods for Determining Specific Surface Area of Soils

The present study was undertaken to compare the capabilities of four of the known methods; more specifically, N2 adsorption, methylene blue (MB)-titration, MB-spot test, and ethylene glycol monoethyl ether (EGME) methods were evaluated to determine the specific surface area (SSA) of 16 different clayey soils. The study showed that N2 adsorption method underpredicts the SSA of soils, especially for smectitic soils. No significant differences were observed between N2 SSA, MB SSA-titration, or MB-spot test for kaolinitic soils. The SSA estimates of MB-titration and MB-spot test methods were highly correlated for all soils. The EGME method has a very different procedure from the MB methods; however, it was highly correlated with MB methods (r2=0.95). The N2 adsorption method had no correlation to other methods. The cation exchange capacity of tested soils was highly correlated to the SSA, as high as r2=0.77. No unique relationship was determined between the clay fraction and SSA.

Heavy Metal Adsorption by Functionalized Clays

Organic ligands containing the thiol (−SH) metal-chelating functionality were either grafted to the external surface silanol groups of sepiolite or introduced in the interlayers of montmorillonite, and the resulting functionalized clays were characterized and assayed as adsorbents for Hg(II), Pb(II), and Zn(II) ions from solution. Sepiolite was functionalized by covalently grafting 3-mercapto- pro-pyltrimethoxysilane (MPS) to the surface ⋮Si−OH groups of the clay, whereas montmorillonite was functionalized by replacement of the interlayer inorganic cation (Na+) by 2-mercaptoethylammonium (MEA) cations. These clay-organic ligand systems were selected to minimize the congestion of the internal porosity of the clays, which has recently been shown to be the main obstacle to heavy metal adsorption by functionalized clays. Infrared spectroscopy and elemental analyses demonstrated the presence of the organic ligands in the modified clays. X-ray diffraction analysis indicated the organic cations (MEA) occupied the interlayers of montmorillonite. N2 specific surface area measurements suggested that much of the surface area of montmorillonite and sepiolite remained accessible upon functionalization and that the organic ligand kept the montmorillonite interlayers open. The functionalized clays adsorbed most of the Hg(II) ions present in solution up to saturation and were also good adsorbents of Pb(II) at low metal ion concentrations (i.e., <0.02 mM). They were, however, less effective toward Pb(II) and Zn(II) at high metal ion concentrations. The presence of NaNO3 or Ca(NO3)2 as background electrolytes at concentra tions ranging from 0.001 to 0.1 M did not alter the great adsorption capacity of functionalized sepiolite for Hg(II). The results show that clay functionalization can be optimized by matching clay structure with a suitable reactive (i.e., fibrous clay with a graftable ligand or expandable clay with an exchangeable cationic ligand) and minimizing the gallery volume taken up by the organic ligand, thus improving the performance of the functionalized clay as adsorbent of heavy metals from solution.

Hydrophobicity of Siloxane Surfaces in Smectites as Revealed by Aromatic Hydrocarbon Adsorption from Water

AbstractThe nature of the siloxane surface in smectites was investigated by measuring the adsorption of aromatic hydrocarbons from water by organo-clays. The organo-clays were prepared by replacing the hydrophilic, inorganic exchange cations of a series of smectites with the small, hydrophobic organic cation, trimethylphenylammonium (TMPA). Smectites with a range in charge densities were used that resulted in different TMPA contents in the organo-clays. Adsorption isotherms of benzene, alkylbenzenes, and naphthalene from water by the TMPA-smectites indicated that sorption was inversely related to TMPA content. The Langmuir form of the isotherms suggests that the aromatic compounds adsorb to the clay surface. Possible adsorptive sites in TMPA-smectites are limited to the TMPA cations and the siloxane oxygen surfaces. Because sorption increased as layer charge and TMPA content decreased, the organic compounds must adsorb to the siloxane surfaces.Calculations based on an adsorbed compound monolayer, which was estimated by fitting adsorption data to the Langmuir equation, and the N2 specific surface area of each TMPA-clay, indicate that the surface area occupied by each adsorbed molecule increases as the planar area of the molecule increases. This strongly indicates that the planar surfaces of the compounds adsorb directly to the clay surface. Apparently, the TMPA cations function to keep the smectite interlayers open. Interactions between the phenyl groups of TMPA cations on opposing interlayer clay surfaces may act to increase the size of the adsorptive regions. These results show that the siloxane surfaces of smectites can effectively adsorb aromatic hydrocarbons from water if the hydrophilic, inorganic exchange cations are replaced with small, hydrophobic organic cations. The strong adsorption of hydrophobic organic molecules from water demonstrates the hydrophobicity of the siloxane surfaces in smectites.

Surface texture of strontium carbonate

AbstractTwo batches of strontium carbonate (SrCO3) prepared at temperatures ⩽333 K (A) and 373 K (B) were investigated using differential thermal analysis (DTA), thermogravimetric (TG), X‐ray diffraction (XRD) and N2 adsorption techniques. Heat treatment up to 1073 K causes no material decomposition of the carbonate and DTA and TG results indicate impurity action. XRD patterns of both samples though slightly different at low temperatures, are identical with orthorhombic SrCO3 above 773 K. The N2 specific surface area of sample B is about three times that of sample A. Thermal treatment of batch A shows two regions of area development resulting from two different types of entrapped water whereas batch B shows only one region and contains only one type of entrapped water. Both samples and their decomposition products are predominantly lyophobic towards cyclohexane adsorption. With sample A the parent material was mesoporous. These pores widen at 423 K due to growth in grain size, but narrowing commences with the evolution of area at 573 K. At temperatures ⩾ 773 K the pores widen again. Sample B contains both micro‐ and mesopores with the latter dominating at higher temperatures where sintering operates.