Decrease In Specific Surface Area Research Articles

Preparation of pozzolanic addition by mechanical treatment of kaolin clay

Batches containing 5kg of Serbian medium-quality kaolin clay were mechanically treated in a conventional ball mill for 10, 30, 60, 120, 600 and 1200min of milling time. High reactive pozzolanic addition was obtained as a result of a number of physicochemical changes induced by milling, namely particle size reduction, specific surface area increase, amorphization/dehydroxylation of kaolinite phase and homogenization of clay constituents. The main characteristics of the pozzolanic material obtained after 1200min of milling were: median particle size of 6.35μm, specific surface area of 21.75m2g−1, total pore volume of 0.0580cm3g−1, pozzolanic activity (compressive strength) of 14MPa, and reactive silica content of 33.3wt.%. Continuous increase of pozzolanic activity, despite the agglomeration of particles that was accompanied with specific surface area decrease when milling time was prolonged, could be explained by kaolinite amorphization as well as the mechanical activation of quartz.

Adsorptive Removal of Pb(II) Ions from Aqueous Solution by (NH4)2S2O8 Oxidized Activated Carbons

Abstract A commercially available activated carbon (AC) was oxidized using 1 M H2SO4 solution containing 2 M (NH4)2S2O8 oxidant with the solution to carbon ratio of 50 cm3 g−1 by changing oxidation period ranging 1 to 10 days at ambient temperatures of 20 or 30 °C to introduce carboxy groups onto the carbon surface to capture Pb(II) ions. Adsorptive removal of Pb(II) ions from aqueous solution was also examined with the oxidized ACs. The Pb(II) ion adsorption progressed via ion exchange with protons of carboxy groups bound to graphite and 2.2 mmol g−1 of Pb(II) could be accommodated at equilibrium pH above 4.0 for ACs oxidized for at least 10 days at 20 °C and 4 days at 30 °C. Decrease in specific surface area and yield and increase in oxygen and hydrogen content in ACs also observed during the (NH4)2S2O8 treatment implied that the oxidation could convert graphite sheets to smaller size by hydrolysis while many carboxy groups would be introduced to the peripherals of the graphite sheets to scavenge Pb(II) ions.

Nanostructured porous Si optical biosensors: effect of thermal oxidation on their performance and properties.

The influence of thermal oxidation conditions on the performance of porous Si optical biosensors used for label-free and real-time monitoring of enzymatic activity is studied. We compare three oxidation temperatures (400, 600, and 800 °C) and their effect on the enzyme immobilization efficiency and the intrinsic stability of the resulting oxidized porous Si (PSiO2), Fabry-Pérot thin films. Importantly, we show that the thermal oxidation profoundly affects the biosensing performance in terms of greater optical sensitivity, by monitoring the catalytic activity of horseradish peroxidase and trypsin-immobilized PSiO2. Despite the significant decrease in porous volume and specific surface area (confirmed by nitrogen gas adsorption-desorption studies) with elevating the oxidation temperature, higher content and surface coverage of the immobilized enzymes is attained. This in turn leads to greater optical stability and sensitivity of PSiO2 nanostructures. Specifically, films produced at 800 °C exhibit stable optical readout in aqueous buffers combined with superior biosensing performance. Thus, by proper control of the oxide layer formation, we can eliminate the aging effect, thus achieving efficient immobilization of different biomolecules, optical signal stability, and sensitivity.

Roles of metal/activated carbon hybridization on elemental mercury adsorption.

In this study, the elemental mercury removal behavior of metal (copper or nickel)/activated carbon hybrid materials were investigated. The pore structures and total pore volumes of the hybrid materials were analyzed using the N2/77 K adsorption isotherms. The microstructure and surface morphologies of the hybrid materials were characterized by X-ray diffraction and scanning electron microscopy, respectively. In the experimental results, the elemental mercury adsorption capacities of all copper/activated carbon hybrid materials were higher than that of the as-received material despite the decrease in specific surface areas and total pore volumes after the metal loading. All the samples containing the metal particles showed excellent elemental mercury adsorption. The Ni/ACs exhibited superior elemental mercury adsorption to those of Cu/ACs. This suggests that Ni/ACs have better elemental mercury adsorption due to the higher activity of nickel.

Simultaneous catalytic oxidation of carbon monoxide, hydrocarbons and soot with Ce–Zr–Nd mixed oxides in simulated diesel exhaust conditions

Ce0.73−xZr0.27NdxO2 mixed oxides (x≤0.3) were prepared, characterized by XRD, Raman spectroscopy, N2 adsorption isotherms and H2-TPR, and tested for simultaneous CO, propylene, benzene and soot oxidation in a gas mixture containing O2, NOx, H2O, CO2, CO, propylene (model aliphatic hydrocarbon) and benzene (model aromatic hydrocarbon) that simulates a diesel exhaust. Ce–Zr mixed oxide doping with a low atomic fraction of neodymium (0.01≤x≤0.09) promotes the creation of oxygen vacancies, has a minor effect in the BET specific surface areas of the oxides, increases the surface ceria reducibility and has a positive effect in the catalytic activity. On the contrary, higher neodymium atomic fractions (x=0.2 and 0.3) promote sintering, with a drastic decrease of the BET specific surface area, surface reducibility and catalytic activity. The Ce0.73−xZr0.27NdxO2 catalysts with x≤0.09 are able to accelerate simultaneously soot, propylene and benzene combustion, and as a general trend, the catalytic behavior of Ce0.73Zr0.27O2 is improved by low atomic fraction neodymium doping (0.01≤x≤0.09). These Ce0.73−xZr0.27NdxO2 mixed oxides with 0.01≤x≤0.09 are also able to accelerate CO oxidation in a certain extent, but there is a net production of CO during soot combustion because the oxidation capacity of these oxides is not high enough to oxidize all CO released as soot combustion product.

Iron removal by precipitate flotation

The water from several artesian wells in the metropolitan area of Recife presents high iron content, preventing its use in some industrial processes. The possibility of removing the iron by the use of precipitate flotation using sodium dodecyl sulphate (SDS) as collector was studied. The tests were carried out in a glass column 65 cm high, fed by a constant airflow. At pH 8, where the isoelectric point of colloidal iron hydroxide [Fe(OH)3] was observed, the size of the precipitate increases with conditioning time and facilitates the removal of iron ions by flotation. The results showed that an increase in conditioning time, from 5 to 20 minutes, resulted in a reduction of the residual concentration of iron from 13.2 to 0.2 ppm. The decrease in precipitate specific surface area rendered a decrease in the collector consumption possible. The iron ion removal process by flotation using SDS as collector was shown to be quite efficient. A removal of 99% of Fe3+ contained in the original solution was obtained.

Valorization of the saline slags generated during secondary aluminium melting processes as adsorbents for the removal of heavy metal ions from aqueous solutions

Abstract This work describes the surface properties of saline slags generated during secondary aluminium melting processes and the application of these materials as adsorbents for the removal of Cd(II), Cu(II), Pb(II) and Zn(II) from aqueous solutions. Saline slags were chemically treated with aqueous solutions of HNO3, H2SO4 and NaOH of varying concentrations (0, 0.5, 1, 1.5 and 2 mol/dm3) for 0.5, 4 and 24 h. Nitrogen adsorption at −196 °C was used to study the textural properties of the solids. The specific surface area and pore volume decrease as the chemical reagent concentrations and duration of the treatments increase. Solids with a surface area of up to 109 m2/g are obtained. The adsorption of heavy metal ions has been studied in terms of pseudo-first-order and pseudo-second-order kinetics, and several isotherm models have also been applied to the equilibrium adsorption data at various pH values. The adsorption capacity of the saline slags was maintained after several cycles of reuse.

Role of a waste-derived polymeric biosurfactant in the sol–gel synthesis of nanocrystalline titanium dioxide

An inexpensive polymeric biosurfactant isolated from urban bio-wastes is shown to be a useful chemical aid in the synthesis of nanostructured materials with tunable pore size and surface hydrophilicity. Photocatalytic active TiO2 powders were prepared by sol–gel reaction in the presence of variable amounts of a waste-derived polymeric biosurfactant. The products were characterized for morphology, crystal structures and surface hydrophilicity. The porosity data indicate that an increase of the biosurfactant amount in the reaction medium causes a decrease of pore size, pore volume and specific surface area in the synthesized oxide, whereas TEM and XRD data indicate that particle size decreases by increasing biosurfactant amount. These results suggest that biosurfactant molecules play a role in the nucleation step, during the formation of the titanium dioxide particles. The biosurfactant amount in the synthesis mixture affects also the hydrophilicity of the titanium dioxide surface, as demonstrated by water-adsorption microcalorimetry measurements, but the results suggest that this aspect is also connected to crystal nucleation and growth during the oxide formation.

Direct soft-templating route to crystalline mesoporous transition-metal oxides

A direct and general soft-templating method has been developed to prepare crystalline mesoporous transition metal oxides. The method was versatile and simple. Several crystalline mesoporous transition metal oxides have been successfully synthesized, such as Nb2O5, Ta2O5 and α-Fe2O3. The porous structure, and crystallinity of as-synthesized metal oxides were characterized by XRD, TG-DTA, SEM, TEM and N2 sorption techniques. The crystallization of amorphous metal oxides resulted in the decrease of specific surface area due to the condensation of related amorphous metal oxide species and crystallite growth. At the same time, the pore volume was well maintained, which means the limited volume shrinkage. The pore size increased with the increasing of calcination temperature due to the growth of grain size and small pores emerged into larger ones. The as-synthesized metal oxides not only had clear mesostructure but also high crystallinity. Notably, all the reagents were commercial available and used without any treatment. It can be easily reproduced by researchers even without any experience in sol–gel related synthesis.

Influence of ball size distribution on grinding effect in horizontal planetary ball mill

The law of ball size distribution in the horizontal planetary ball mill is studied by the discrete element method. The results show that the maximum impact energy could be acquired when filling rate is 24%, moreover the biggest mean contact force and the highest energy utilization ratio of balls could be acquired when the speed ratio is 1.5. The mean contact force increases with the proportion increasing of the large balls, which means ball size distribution has some effect on the crushing and grinding process. And according to the experimental results for comparative analysis, the specific rates of breakage Si increases with the proportion rise of large balls in ball size distribution, meanwhile Si can be determined by the mean contact force(Fmcf): Si=A·10kfmcf, where the constant A is 0.437, the gradient k is 0.0252. At last the specific surface area of the product is measured and the particle size distribution (under 80μm) is analyzed by Rosin–Rammler–Bennet equation. The results show that with the proportion increasing of the large balls, the specific surface area decreases, while the uniformity coefficient and the characteristic diameter increases.

Changing the relation between micro- and mesoporosity in porous glasses: The effect of different factors

The relation between micro- and mesoporosity in the porous glasses produced by leaching of two-phase alkali borosilicate glasses was studied by use of advanced classical nitrogen equilibrium adsorption–desorption methods and new kinetic method of diffusion diagnostics with mass spectral recording. The effect of different factors, such as chemical composition, conditions of acid and alkaline treatments on the change of morphology and pore characteristics of the micro- and mesoporous substructures in the porous glasses was revealed. The porous glasses are characterized by the polymodal size distribution of mesopores (up to 4 modes) and micropores (up to 3 modes). The shape of mesopores is not purely cylindrical; there is a contribution of conical and interglobular pores. The micropore volume decreases with the decrease of the mesopore specific surface area and increasing the globule diameters of secondary silica. The micropores in the porous glasses are generally the regions of interglobular contacts in secondary silica with 1–2 times the diameter of N2 molecules. The introducing lead oxide allows obtaining the porous glasses with the highest specific surface area, maximum micropore volume, and minimum micropore diameter. The introduction of phosphorus and fluorine in the glass matrix allows producing the porous glasses with the minimal porosity, mesopore surface area, micropore volume and with the maximal size of mesopores. When increasing the leaching concentration of hydrochloric acid from 1 to 3M and acid leaching time from 3 to 9h, the mesopore specific surface area decreases and the mesopore diameters increase. The effect of alkali leads to the monomodal pore size distribution of mesopores, significant increase in the mesopore volume, and significant reduction in the micropore volume. At this, the new micropores due to the dissolution of channel walls do not create.

Inclusion of piroxicam in mesoporous phosphate glass–ceramic and evaluation of the physiochemical characteristics

The mesoporous glass–ceramic (GC) was employed as a carrier to investigate its capability for pharmaceutical applications. Piroxicam (PX) as a model drug was loaded in the GC by using of solvent evaporation technique. The physicochemical properties and morphology of the powders were evaluated employing X-ray powder diffractometry (XRPD), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The drug adsorption isotherms were assessed as well. Drug release profiles were examined by fitting the data to the 10 common kinetic models. The specific surface area, Vm (the volume of the N2 adsorbed on the 1g of the GC when the monolayer is complete) and the average pore diameter of the GC powder before and after loading process were measured by the Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) analysis benefiting N2 adsorption/desorption isotherms. The ideal loading of PX in the GC was 41.8%. The average pore diameter for the GC was determined to be about 10nm. The Freundlich model was found to be the best adsorption isotherm. Decrease of the GC specific surface area and Vm values were observed after loading process. Drug release data were best fitted to the Weibull model with the shape factor of 0.4–0.7 signifying the Fickian diffusion of PX from the GC. Accordingly, the GC could be considered as a suitable adsorbent to develop an oral drug delivery system.

Enhanced photocatalytic activity of titanium dioxide/allophane mixed powder by acid treatment

The TiO2/allophane mixed powders at various mixing ratios were acid-treated to obtain a highly active photocatalyst. It was found that amorphous silica surrounding TiO2 particles was formed after acid treatment by selective dissolution of alumina component in the allophane. The photocatalytic activity of the mixed powder, evaluated by the photocatalytic decomposition rate for gaseous acetaldehyde, was improved by the acid treatment when the mixing ratio of allophane was higher than 5mass% in spite of the decrease of specific surface area (SSA), while that of the pure-TiO2 powder was decreased maybe because of the increase of Ti3+ defects density on its surface. As for the pure-allophane powder, SSA and adsorption rate for acetaldehyde were decreased by acid treatment. In addition, it was found that the acid treatment of allophane was needed to be performed in the presence of TiO2 to obtain a highly active photocatalyst from the result of the comparative experiments using mixed powder of acid-treated TiO2 powder and acid-treated allophane powder. Based on these results, it was concluded that the silica-dispersed microstructure of the nanocomposite was suitable for the efficient removal of acetaldehyde.

Effects of temperature and grain type on time variation of snow specific surface area

The specific surface area (SSA) of snow is of particular interest to researchers because SSA is strongly related to snow albedo and is a comparatively better indicator of snow’s complexity than grain size. The time variation of SSA for fresh snow samples was observed in the laboratory under isothermal conditions at 226 K and 254 K using the gas adsorption method and Brunauer-Emmett-Teller theory. The SSA of the snow samples decreased with time under isothermal metamorphism. The decrease in SSA was fitted with the logarithmic equation proposed by Legagneux et al. (2003), and adjustable parameters were obtained. The rate of decrease in SSA depended on the shape of the initial snow type and temperature. Dendritic snow samples exhibited large initial SSAs, and their SSAs decreased faster compared with those of fragmented (collected from drifting snow) and plate-like precipitation particles with relatively small initial SSAs. The rate of decrease in SSA was lower at 226 K than that at 254 K.

Molecular dynamics simulation of thermal conductivity of mesoporous α-Al2O3

In this paper, molecular dynamics simulation was performed to predict the thermal conductivities of ordered mesoporous α-Al2O3. A kind of porous structure was proposed to guarantee the electrical neutrality. Based on the Matsui potential, the nonequilibrium molecular dynamics method adapted by Mller-Plathe was used to calculate the lattice thermal conductivity of mesoporous alumina along the axial direction of pore at various temperatures. Effects of pore size and porosity were also investigated. It turns out that with increasing temperature the thermal conductivity of mesoporous α-Al2O3 rises first until the temperature reaches 200–400 K, then decreases almost linearly. In addition, as the pore size gets larger, the specific surface area decreases, and the thermal conductivity increases because the boundary scattering has been weakened. On the other hand, the number of phonons in the pore wall decreases greatly with increasing porosity, thus dramatically reducing the thermal conductivity of the mesoporous material. Range analysis shows that the porosity is more influential than the pore size on the thermal conductivity of mesoporous materials.

Surfactant dependent self-organization of Co3O4 nanowires on Ni foam for high performance supercapacitors: from nanowire microspheres to nanowire paddy fields

Different surfactants were used in a typical hydrothermal process for controlling the morphology of the Co3O4 nanowire superstructure on Ni foam. It is easy for the Co3O4 nanowires to self-organize into nanowire microspheres on Ni foam in the absence of surfactants. And the nanowire microspheres gradually unfold into nanowire paddy fields with the addition of nonionic, cationic and anionic surfactants, respectively. The results of BET and electrochemical measurements show that the specific surface area and capacitance first decrease and then increase with the change in the Co3O4 superstructure morphology. Among these electrodes, the Co3O4 electrode with paddy like nanowires shows an outstanding specific capacitance of 1217.4 F g(-1) and areal specific capacitance as high as 6087 mF cm(-2) at 0.7 A g(-1) with high mass loading (5 mg cm(-2)), good power capability (showing a high specific capacitance of 835.1 F g(-1) (4176 mF cm(-2)) at 5 A g(-1)), excellent cycling stability and high columbic efficiency (∼100%). This exceptional performance is benefited from the almost monodispersed nanowire morphology and high specific surface area (121.4 m(2) g(-1)). At the same time, the asymmetric supercapacitor, employing the Co3O4 electrode with paddy-like nanowires as the positive electrode and the activated carbon electrode as the negative electrode, was successfully assembled. It shows a high specific energy and good long-term electrochemical stability. All these impressive results demonstrate that the Co3O4 electrode with paddy-like nanowires is promising for practical applications in supercapacitors.

Higher Alcohol Synthesis Using K-Doped CoRhMoS2/MWCNT Catalysts: Influence of Pelletization, Particle Size and Incorporation of Binders

In this study, alkalinized MWCNT supported MoS2 catalysts have been doubly-promoted with Co and Rh. Catalysts were prepared by the conventional co-impregnation method and stabilized under argon atmosphere. Characterization of the oxidic samples by BET revealed that the mesoporosity of the pristine MWCNT support was not compromised after loading a combined total of 30 wt% metals (9 wt% K, 4.5 wt% Co, 1.5 wt% Rh, and 15 wt% Mo) on the support; however, a significant decrease in specific surface area was observed. Broad angle XRD analysis confirmed the homogenous dispersion of catalyst metals on the support. Two catalyst grain sizes were first investigated to elucidate the effect of particle size: a finely ground powder (88 μm) and a pelletized form (1,780 μm). Despite the total alcohol yield of 0.261 g/(gcat h) observed by conducting higher alcohol synthesis reaction at T = 330 °C, P = 8.3 MPa, H2/CO = 1.25, and GHSV = 3.6 m STP 3 /(kgcat h) for the fine powdered sample, the relatively higher pressure drop could be minimized by using the pelletized form of the catalyst. Finally, a systematic study of variety of selected binders was conducted to gain insight of catalyst’s applicability for industrial purposes. Three selected binders namely: bentonite clay, coal tar, and humic acid were thus investigated; taking into consideration significant factors such as melting point and binder requirement per catalyst support. The CO conversions evaluated for the two binder-free catalysts (88 and 1,700 μm) showed that the catalyst with fine particle sizes (88 μm) performed better than that in the pelletized form (binder-free, 1,700 μm); yielding a maximum ethanol selectivity of 38.5 % at steady-state reaction conditions.

Surface oxidation of activated electrospun carbon nanofibers and their adsorption performance for benzene, butanone and ethanol

Carbon nanofibers prepared by electrospinning and subsequent steam activation were oxidized by treatment in HNO3 and HNO3/H2SO4 mixture. Surface morphology and degree of graphitic structure of oxidized nanofibers are affected mildly by acid oxidation according to SEM and Raman measurement. Nitrogen adsorption/desorption isotherms demonstrate decrease in specific surface area and pore volume of carbon nanofibers after oxidation. XPS spectra exhibit that oxidized nanofibers possess higher surface oxygen content than pristine nanofibers. Higher water adsorption capacities on oxidized nanofibers determined by water adsorption isotherms suggest the improvement of surface polarity and hydrophilicity. Furthermore, adsorption isotherms of benzene, butanone and ethanol show that surface oxidation enhances the adsorption tendency for butanone and ethanol on nanofibers due to increased surface polarity, indicating that the adsorption selectivity to polar organic compounds is improved.

Influence of Chloride Contamination on the Specific Surface Area of Loess

The main chlorides that pollute soil are NaCl, KCl, MgCl2and CaCl2, who will change the physicochemical properties of soil. It takes Jiuzhoutai loess as the object, using methylene blue method and ethylene glycol monoethyl ether method to determinate the specific surface area of loess, which was immersed by chloride with different concentrations and cations to analyze the influence of chloride contamination, respectively. The specific surface area decrease with the increase of chloride concentration, while has the negative correlation with the affinity of cations to clay which immersed by different cations. Different absorbents that have lead to the difference of test results, and the results of ethylene glycol monoethyl ether method are always bigger than methylene blue method.

From platy kaolinite to aluminosilicate nanoroll via one-step delamination of kaolinite: Effect of the temperature of intercalation

Aluminosilicate nanorolls were prepared using a method of one-step delamination of kaolinite. In this method, cetyltrimethylammonium chloride (CTMACl) was intercalated into the interlayer space of methoxy-modified kaolinite, which resulted in the delamination and rolling of kaolinite layers. The reaction conditions of CTMACl intercalation significantly influenced the formation of nanorolls, as shown by characterizations using X-ray diffraction, electron microscopy, infrared spectroscopy, thermal analysis, and nitrogen adsorption. Overall, increasing the CTMACl-intercalation temperature helps to promote the transformation from platy kaolinite to nanorolls. The initial kaolinite particles were mostly transformed to nanorolls in the product prepared at 80°C, whereas considerable kaolinite particles remained untransformed in the product prepared at 30°C. At 80°C, the obtained specific surface area (SSA) and the porous volume (Vpor) values of the nanoroll product are nearly twice the values obtained at 30°C and the tubular structure exhibits higher thermal persistence. The tubular morphology and the porosity of these nanorolls obtained at 80°C, were largely retained after calcination at 600–800°C. However, a calcination at 900°C led to an obvious distortion of the nanorolls and a decrease in SSA and Vpor values. The observed structural changes of the nanorolls under calcination generally resembled that of natural halloysite but occurred at lower temperatures because the prepared nanorolls were of lower structural order with thinner tube walls.