Experimental study on influence of adsorption equilibrium time on methane adsorption isotherm and Langmuir parameter

The aim of this work was to examine the impact of equilibrium judgment criteria on adsorption test of samples with different adsorption kinetics and determine how long it takes for different particle size samples to attain equilibrium adsorption data. The adsorption data of coal samples with three different particle sizes was obtained by manometric method at the different time intervals. High pressure CH₄ adsorption equilibrium measurements and low pressure N₂ and CO₂ adsorption measurements were carried out for coal samples of eight various particle sizes. The results demonstrated that both the equilibrium and disequilibrium adsorption data satisfied the Langmuir equation. The Langmuir volume (V_L) increased on the equilibrium time increase and it became more remarkable with increasing particle size. The Langmuir pressure (P_L) showed an opposite and more obvious trend. When the particle size of the coal sample decreased from 2 to 4 to <0.074 mm, the adsorption equilibrium time (AET) required for the adsorption isotherm testing declined rapidly from 389 to 5 h. This research is of some enlightening significance for comparing the adsorption characteristics of samples with different adsorption kinetics (adsorbent, temperature, particle size, etc.).     

Effect of nitric acid modification on the lead(II) adsorption of mesoporous biochars with different mesopore size distributions

Two mesoporous biochars AC-1 and AC-2 with similar chemical properties but different mesopore size distributions were prepared to study the effect of HNO₃ modification on the lead(II) adsorption. AC-2 possesses higher mesopore volume and broader pore diameter than AC-1, while their surface area and micropore volume are similar. Adsorption experiments showed that AC-2 had far better removal efficiency, indicating the important role of mesopores played in the adsorption. HNO₃ modification enhanced the adsorption capacity of lead AC-1 and AC-2 by 15 and 27 mg g^?1, respectively. In particular, the removal rate of lead for AC-1 was improved from 46 to 99 % by HNO₃ treatment at a low initial lead concentration of 10 mg L^?1. Results of Boehm’s titration demonstrated that the amounts of oxygenic acid groups of AC-1 and AC-2 increased to 2.456 and 2.705 mmol g^?1 after HNO₃ treatment, respectively. Analyses of FTIR spectrum revealed that AC-2 was more likely to graft oxygen-containing acidic functional groups than AC-1, indicating that higher mesoporosity takes advantage of grafting more oxygenic functional groups, thus forming more active adsorption sites. The above results indicate that mesoporous biochars with wider pore width are more favorable to be introduced with oxygenic groups for enhanced lead removal efficiency.     

Characterization of structural parameters of porous materials by a new adsorption isotherm

A new adsorption isotherm equation, log logP=C+n logv, has been developed which characterizes many properties of the structure of porous materials, such as monolayer capacity of isotherms of Types I, II and IV, limiting micropore volume at extremely low pressure, degree and dispersion of micropores, mesopore surface area, mean pore size, etc. The equation has been successfully extended to binary and ternary mixtures, data for which have been obtained from the individual isotherms. It is also shown that a linear plot of the new isotherm implies that the distribution of adsorption volume with adsorption potential is Gaussian. Various other well know isotherm equations have been deduced from this new equation. The equation is direct and involves fewer mathematical calculations for solving the structural parameters of porous materials.     

Mesoporous indium oxide synthesized via a nanocasting route

The synthesis of crystalline mesoporous indium oxide by using a mesoporous carbon (CMK-3) as hard template is described. Transmission electron microscopy (TEM) exhibits the presence of mesoporous structure in our sample and the corresponding wide-angle X-ray diffraction (XRD) pattern confirmed the crystalline wall of sample. N₂ adsorption measurement exhibits the synthesized crystalline mesoporous indium oxide possesses a specific surface area of 39 m²/g and the total pore volume of 0.17 cm³/g, and the corresponding pore size distribution curve reveals the presence of a mesopore of 7.0 nm in maximum. Our work demonstrates that the maintenance of the ordered structure of carbon template is very significant for obtaining high quality replicas via the nanocasting route.     

Preparation of hierarchical porous carbon by post activation

A series of hierarchical porous carbons (HPCs) have been prepared by a combination of soft-templating and post activation. As evidenced by N₂ sorption tests, the pristine mesopores were basically preserved and micropores were generated on the mesopore wall of mesoporous carbon (MC). The micropore generation on the mesoporous skeleton can be controlled by simply adjusting the KOH ratio and activation temperature. The BET surface area, mesopore surface area and total pore volume of the HPCs increase monotonously with increasing activation temperature and KOH/MC ratio. In contrast, the micropore surface area reaches the maximum at the ratio of KOH/MC of 4. Further increase of KOH/MC ratio and activation temperature reduces the micropore surface area. Structural characterizations confirm that the main mesopore channel was preserved during activation.     

Relation between biochar physicochemical characteristics on the adsorption of fluoride,nitrite, and nitrate anions from aqueous solution

This study describes how physicochemical characteristics of rice straw-based biochar, prepared at a different pyrolysis temperature (550, 650, 750°C) and treated by HNO₃ or H₂O₂ or KMnO₄, influence on its removal capacity for fluoride, nitrite, and nitrate anions from the water. Biochars exhibit broad pore size distribution from wide mesopores (5.0?nm) to narrow micropores (1.0?nm). Furthermore, all prepared biochars have both basic sites (2.8–8.13?meq/g) and acidic ones (1.8–9.3?meq/g) on their surface. The effect of biochar porosity, acidity, and basicity on anions adsorption was studied. KMnO₄- and H₂O₂-treated biochar give high nitrite and nitrate uptake in micropore range (0.03–0.05 cc/g) and mesopore range (0.01–0.06 cc/g) while HNO₃-treated ones give low uptake in both micropore range (0.02–0.021 cc/g) and mesopore range (0.01–0.05 cc/g). As a conclusion, no particular characteristics seem to be an influential essential in the removal of anionic contaminants. These observations are useful to guide the surface modification of biochars as efficient sorbents for specific application needs and removal of environmental pollutants.     

Adsorption characteristics of N-nitrosodimethylamine from aqueous solution on surface-modified activated carbons

This study investigated the removal of N-nitrosodimethylamine (NDMA) by an adsorption mechanism using commercially available activated carbons and surface-modified activated carbons. The effects of the modification on the properties of the activated carbon were studied by N₂ adsorption/desorption, Diffuse Reflectance Infrared Fourier Transmission (DRIFT) analysis and X-Ray Photoelectron Spectroscopy (XPS). Adsorption experiments revealed that the activated carbons demonstrated a greater capacity for NDMA adsorption capacity than can be achieved using zeolite. The equilibrium data was fitted to the Freundlich equation and it was found that the adsorption capacity was significantly influenced by the micropore size, relative pore volume and surface characteristics. Adsorption experiments were conducted using unmodified and modified activated carbons. The results indicated that the adsorption capacity of NDMA can be significantly improved by heat treatment and doping of TiO₂ particles. This was because the surface treatments yielded more hydrophobic sites and fewer oxygen-containing surface functional groups, and consequently an increased capacity for NDMA adsorption.     

具有不同孔结构的沥青基球状活性炭对肌酐及维生素B12吸附性能？…

主要研究了３种具有不同孔结构的沥青基球状活性炭对肌酐及ＶＢ１２的吸附性能,与ＢＥＴ比表面主孔结构进行了关联。结果表明,具有微孔结构的沥青基球状活性炭对小分子肌酐的吸附性能较好;具有中孔结构的沥青基球状活性炭对中分子物质ＶＢ１２具有较好的吸附性能;而中孔与微孔并存的沥青基球状活性炭对肌酐及ＶＢ１２都有较好的吸附性能。     

Microstructure and heavy metal adsorption mechanisms of hydrothermally synthesized Al-substituted tobermorite

Due to the properties of tobermorite as a cation exchanger and its potential applications in catalysis, and in hazardous waste disposal, attention has been drawn to the properties of tobermorite. In this study, fresh calcium oxide (CaO), fumed silica powder (SiO₂) and aluminum nitrate nonahydrate (Al(NO₃)₃·9H₂O) were used for synthesizing tobermorite with/without aluminum. The suitable synthesis condition was confirmed as 5 h in an autoclave at 180 °C and saturation vapor pressure around 1 MPa, marked as samples T and TA, respectively. The BET surface areas of T and TA were 198.83 and 80.48 m²/g, respectively. The pore sizes were mainly distributed between 100 and 300 nm, and pore volume of TA significantly lower than T. Laser scattering particle analysis indicated that the particle size of T and TA were both distributed between 1 and 100 μm, and the median diameter was 27.41 and 19.44 μm, respectively. These results indicated that the aluminum refined pore structure and particle size. The adsorption effectiveness was affected by adsorbent contents and adsorption time. For both of T and TA, the adsorption effectiveness of Cr⁶⁺, Pb²⁺, and Cu²⁺ could be higher than 97.62. 96.4, and 94.13%, respectively. The residues after adsorption were further studied by XRD, ATR-IR, and SEM. The results of XRD and ATR-IR showed that there was no other significant phase and functional group, except hydrocerussite (Pb₃(CO₃)₂(OH)₂) in T–Pb residue. The results indicate that the uptake of heavy metals (Cr⁶⁺, Pb²⁺, and Cu²⁺) by T or TA mainly through two ways which are surface complexation and uptake in the interlayer. SEM showed TA has better structural stability with the uptake of heavy metals than T. It indicated that chemical effects were the dominant factor, and physical effect took second place.     

Quick high-temperature hydrothermal synthesis of mesoporous materials with 3D cubic structure for the adsorption of lysozyme

Abstract

Three-dimensional cage-like mesoporous FDU-12 materials with large tuneable pore sizes ranging from 9.9 to 15.6 nm were prepared by varying the synthesis temperature from 100 to 200 °C for the aging time of just 2 h using a tri-block copolymer F-127(EO₁₀₆PO₇₀EO₁₀₆) as the surfactant and 1,3,5-trimethyl benzene as the swelling agent in an acidic condition. The mesoporous structure and textural features of FDU-12-HX (where H denotes the hydrothermal method and X denotes the synthesis temperature) samples were elucidated and probed using x-ray diffraction, N₂ adsorption, ²⁹Si magic angle spinning nuclear magnetic resonance, scanning electron microscopy and transmission electron microscopy. It has been demonstrated that the aging time can be significantly reduced from 72 to 2 h without affecting the structural order of the FDU-12 materials with a simple adjustment of the synthesis temperature from 100 to 200 °C. Among the materials prepared, the samples prepared at 200 °C had the highest pore volume and the largest pore diameter. Lysozyme adsorption experiments were conducted over FDU-12 samples prepared at different temperatures in order to understand their biomolecule adsorption capacity, where the FDU-12-HX samples displayed high adsorption performance of 29 μmol g^?1 in spite of shortening the actual synthesis time from 72 to 2 h. Further, the influence of surface area, pore volume and pore diameter on the adsorption capacity of FDU-12-HX samples has been investigated and results are discussed in correlation with the textural parameters of the FDU-12-HX and other mesoporous adsorbents including SBA-15, MCM-41, KIT-5, KIT-6 and CMK-3.     

Synthesis and characterization of V,Mo and Nb incorporated micro–mesoporous MCM-41 materials

Highly microporous metal-MCM-41 ordered mesoporous structure catalysts having different metal/Si (V, Mo, Nb) atomic ratios and combinations of metal sources were hydrothermally synthesized. The structural properties estimated using different techniques were found to be in agreement with each other. Metals were successfully incorporated into MCM-41 without deteriorating the ordered hexagonal structure. The metal ions in the synthesis solutions probably settled on the hydrophilic end of the template hence the metal incorporation resulted improvements in the micropore structure. Low loading of metals caused an increase in the surface area and pore volume values of the catalysts. The highest total (1310 m² g^?1) and micropore surface area values (1083 m² g^?1) were obtained by Nb incorporation. The micro- and mesopore dimensions of MCM-41 increased from 0.5 to 1.1 nm and from 2.5 to 2.8 nm, respectively, with metal incorporation. Low V/Si ratios and presence of Nb in the starting solution enhanced narrow mesopore size distribution. The pore dimension and wall thickness values estimated from nitrogen adsorption and X-ray diffraction methods were consistent with the corresponding values obtained using transmission electron microscopy.     

Characterization and adsorption properties of powders prepared from cactus pulp

Two cactaceous powders, labelled CACMM1 and CACMM2, are shown to contain calcium oxalate and to consist of globular or cubosome particles. The samples were characterized by X-ray diffractometry, spectroscopic, thermic, nitrogen and water adsorption methods and compared with other organic compounds. The pore systems have been analysed from adsorption isotherms, t-plots and pore size distribution curves. The bioadsorbents CACMM1 and CACMM2 exhibited low specific surface area values and presented pores in the mesopore range. Composite adsorption isotherms for the binary mixtures benzene-hexane and benzene-cyclohexane on cactaceous powders have been established and revealed preferential adsorption of hexane and cyclohexane in the respective system. Also the adsorption behavior of dyes from aqueous solution was studied to complete the diversity of adsorbate molecules. Linear adsorption isotherms were obtained up to 6 mM dye equilibrium concentration.     

利用核桃壳制备高比表面积活性炭电极材料的研究

以核桃壳为原料,采用KOH活化法制备活性炭,并将其用作超级电容器电极材料。利用N2吸附和扫描电镜(SEM)表征活性炭的孔结构及表面形貌,系统研究碱炭比(KOH与核桃壳炭化料的质量比)对活性炭孔结构的影响,并采用恒流充放电及循环伏安等测定核桃壳活性炭电极材料在3mol/L KOH电解液中的电化学性能。结果表明,随着碱炭比的增大,活性炭的比表面积、总孔容及中孔比例先逐渐增大后稍有减小。当活化温度为800℃,活化时间为1h,碱炭比为4时,可制备出比表面积为2404m2/g,总孔容为1.344cm3/g,中孔比例为28.6%,孔径分布在0.7~3.0nm之间的高比表面积活性炭。该活性炭用作超级电容器电极材料具有良好的大电流放电特性和优异的循环性能,电流密度由50mA/g提高到5000mA/g时,其比电容由340F/g降低到288F/g,经1000次循环后,比电容保持率为93.4%。     

Nitrogen adsorption method for determining the mesopore slit-like size distribution of expansive soils

One of the most important structural parameters involved in the characterization of the void space of soils is the pore size distribution. In this work, a nitrogen adsorption method is presented as an alternative to determine the mesopore contribution of slit-shaped pores to the abovementioned parameter in montmorillonite-containing soils. The mesopore size structural parameter obtained via this sorption method is related to montmorillonite d₀₀₁ interlayer distances proceeding from either X-ray or electron diffraction analysis, if only by assuming during sorption analysis that mesopores resident inside clay grains adopt slit-shaped geometries. Mineralogical analysis and determination of some important geotechnical properties of these montmorillonite-containing soils complement the preceding sorption and structural studies.     

Surface area, pore size distribution and microstructure of vacuum getter

An effective getter is necessary in vacuum technology. In order to obtain the adsorption mechanism of the getter, its microstructure information must be studied. Surface area, pore size distribution and microstructure of vacuum getter were studied with XRD, SEM and N₂ adsorption technique.Vacuum getter is composed of the different proportions of PdO and Ag₂O. The crystalline size of 3^# vacuum getter that includes W₂AgO = 22% and W_PdO = 78% is the maximum among all the vacuum getters. SEM images showed that vacuum getters expose a large number of nanometer-size pores. The adsorption isotherms of the vacuum getters are typical of type Ⅳ, characteristic of mesoporous material, and a type H₂ hysteresis loop is observed. Langmuir model describes N₂ adsorption at low pressure region. At the medium pressure, N₂ adsorption can be modeled by BET model. The pore size distributions of the vacuum getters are calculated by applying BJH method to the adsorption branch of N₂ isotherms at 77 K. With percentage of Ag₂O elevation, Langmuir surface area, BET specific surface area, the adsorption capacity and the pore volume become larger. But the average pore diameter becomes smaller. However, above Ag₂O content of 22%, an inverse behavior is observed. 3^# vacuum getter has the highest surface area and pore volume among all the vacuum getters. The experimental results and related analysis can be adopted in the later design of the vacuum tank.     

Facile synthesis of ordered mesoporous silica with high γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> loading via sol-gel process

A series of ordered mesoporous silica loaded with iron oxide was synthesized by facile one-step sol-gel route using Pluronic P123 as the template, tetraethylorthosilicate as the silica source, and hydrated iron nitrite as the precursor under acid conditions. The as-synthesized materials with Fe/Si molar ratio ranging from 0.1 to 0.8 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and N₂ adsorption porosimetry. All samples possess ordered hexagonal mesoporous structure similar to SBA-15, with a high surface area, large pore volume, and uniform pore size. Although higher iron content causes a distortion of hexagonal ordering structure to some extent, the materials still maintain the ordered mesopore structure even with Fe/Si molar ratio as high as 0.8. Pore structure and TEM data suggest that iron oxide nanoparticles are buried within the silica wall, and increasing the iron oxide loading has little effects on the pore structure of the mesoporous silica. VSM results show as-synthesized samples exhibit superparamagnetic behavior.     

Experimental study on geometric parameters of pore structure and quantitative evaluation of complexity of pulverized coal with different metamorphic degrees

In order to quantify pore structure complexity of coal, the low pressure argon adsorption method (LP-ArGA) was used to study geometric parameters of pore structure and quantitative evaluation of complexity of pulverized coal. The results showed that the geometric parameters of pore structure of most single-particle coals showed an obvious downward trend with the decrease of particle size, indicating that the pore structure became simpler in the pulverization process. The weight value of equivalent matrix scale is the largest, which is 0.4871, indicating that it has the greatest influence on pore structure complexity. With the decrease of particle size, the composite evaluation index of complexity of 1#, 2#, 3#, 4#, 5# and 6# samples decreased by 52.4%, 61.1%, 86.3%, 42.1%, 74.6% and 39.9%, respectively. It indicated that particle size has an extremely influence on pore complexity characteristics of single-particle coal. With the decrease of particle size, the pore complexity characteristics of coal samples tended to be simple, on the contrary, they showed medium or complex characteristics. The model has important guiding significance for evaluating the same coal sample with different particle sizes, but there are still some deficiencies for different coal samples.     

Preparation of hydrophilic mesoporous carbon and its application in dye adsorption

A hydrophilic mesoporous carbon (H-MS) has been prepared by a rapid redox reaction between mesoporous carbon (CMK-3) and an acidic potassium permanganate (KMnO₄) solution at room temperature. The obtained material has a hydrophilic surface by the modification of oxygen-containing groups, and meanwhile retains the ordered mesoporous structure. No obvious difference of pore size between H-MS and CMK-3, and the slight decrease of surface area and pore volume is due to the modification of oxygen-containing groups on the carbon surface. An improved property for adsorbing dyes in aqueous solution was observed in H-MC, and the adsorption amount at equilibrium is ~ 3 times higher than that of CMK-3.     

GCMC simulations of dynamic structural change of Cu–organic crystals with N2 adsorption

N₂ adsorption on Cu–organic crystals [Cu(bpy)₂(BF₄)₂] (bpy?=?bipyridine) at 77?K begins suddenly at P/P ₀?=?0.1. This unique adsorption is named gate adsorption. Gate adsorption is associated with the change of crystal structure from GCMC and dynamic GCMC simulations. An expansion of 10% opens internal pore spaces in the crystal, giving rise to gate adsorption. The complete filling of the internal spaces with N₂ molecules induces an expansion of 30%.     

Size-controlled synthesis of ZrO2-TiO2 nanoparticles prepared via reverse micelle method: Investigation of particle size effect on the catalytic performance in vapor phase Beckmann rearrangement

Zirconium-titanium mixed oxide nanoparticles have been synthesized using microreactors made of bis-(2-ethylhexyl) sulfosuccinate (AOT)/water/n-hexane microemulsions. The control of particle size was achieved by varying the process variables, such as water-to-surfactant molar ratio and reagent concentration. Their sizes, appearances, crystal structures, pore diameter and surface area were characterized by TEM, XRD, N₂ adsorption/desorption methods. The results revealed that samples prepared in reverse micelles had no crystalline phase. The Beckmann rearrangement of cyclohexanone oxime on ZrO₂-TiO₂ nanoparticles was carried out in a fixed-bed down flow reactor to investigate the effect of particle size on catalytic activity and selectivity. Samples synthesized in reverse micelles had better reaction performance than samples prepared via sol-gel method. A parallel relationship could be drawn between the catalytic activity and the particle size as well as the selectivity of the catalyst.