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•The improved method (VBS) to obtain the mesopores size distribution is explained.•The VBS method is self-consistent with the experimental isotherm data.•The procedure to apply the ...VBS method is developed in detail.•Good agreement between VBS and NLDFT methods are found.
A standard method to obtain the mesopore size distribution of adsorbents is the Barrett, Joyner and Halenda (BJH) analysis of the N2 adsorption–desorption isotherm at 77K. The availability, over the last two decades, of well-defined model adsorbents in the mesopore range, together with other forms of isotherm analysis with the help of the Density Functional Theory (DFT) has shown that the BJH method tended to underestimate the pore-width when they are smaller than 10nm. Regarding this fact, we have reported an improved BJH method, where we have remarked that the reconstruction of the adsorption–desorption isotherm from the BJH results leads to some inconsistency. We therefore proposed a simple means to cancel the mentioned discrepancy and inconsistency. This correction can be made by simply adding a corrective term to the standard BJH equation, which value is selected to meet a self-consistent criterion, i.e. the reconstructed isotherm should fit the original one. In the first article, the method was applied for some ordered mesoporous materials (OMM) synthesized in our laboratory, showing only the results without major details. In this work, we validate the test for other samples, in other pore size ranges, introducing some remarks in theoretical aspects and in the importance of obtaining and taking into account the micropore volume. Finally, a detailed procedure to apply the proposal method using only the experimental data of the analysis is presented.
Emerging contaminants in the environment have caused enormous concern in the last few decades, and among them, antibiotics have received special attention. On the other hand, adsorption has shown to ...be a useful, low-cost, and eco-friendly method for the removal of this type of contaminants from water. This work is focused on the study of ciprofloxacin (CPX) removal from water by adsorption on pillared clays (PILC) under basic pH conditions, where CPX is in its anionic form (CPX
). Four different materials were synthetized, characterized, and studied as adsorbents of CPX (Al-, Fe-, Si-, and Zr-PILC). The highest CPX adsorption capacities of 100.6 and 122.1 mg g
were obtained for the Si- and Fe-PILC (respectively), and can be related to the porous structure of the PILCs. The suggested adsorption mechanism involves inner-sphere complexes formation as well as van der Waals interactions between CPX
and the available adsorption sites on the PILC surfaces.
There is a well-known relationship between porous materials performance in a given process and their textural properties. These properties include specific surface area, among others, where the most ...widely used experimental technique to determine them is gas adsorption. Although the most used adsorptive gas is N
2
at 77 K up to atmospheric pressure, its quadrupole moment generates specific interactions with surface groups, as silanols in silica materials, causing a preferential orientation effect on the adsorbed N
2
molecule affecting the specific surface area value. In this sense, we analyzed the adsorption–desorption isotherms at 77 K of nanoporous silica materials using different adsorptives. From these data, we obtained the specific surface area (
S
BET
) values of the samples by applying the BET method with the IUPAC recommendations for each gas. The selected materials were MCM-41, MCM-48, SBA-15, and SBA-16, and the adsorptives used were Ar, O
2,
and CH
4
, along with N
2.
Among the chosen adsorptives, Ar and CH
4
do not have a quadrupole moment, whereas this value is present for N
2
and O
2
, being the latter four times smaller than nitrogen. In addition, at 77 K, both Ar and CH
4
are below their triple-point temperature, while N
2
and O
2
, which are above their triple-point temperature, are in the same thermodynamic state. Taking the
S
BET
obtained by Ar at 77 K as the referential value of each sample, the corresponding molecular transversal areas of the other adsorptives were estimated. It was found that the variation of transversal area for the N
2
molecule at 77 K on silica materials was between 0.133 and 0.149 nm
2
(below its common value of 0.162 nm
2
). In contrast, in the case of the O
2
molecule at 77 K, this value was almost constant, with an average of 0.123 nm
2
. These results showed that the quadrupole moment of the O
2
does not play an important role in the interaction with surface silanol groups present in the samples, making oxygen at 77 K a potential and reliable adsorptive to determine the specific surface area of silica materials.
It is known that the use of the Dubinin–Radushkevich method in
micro-mesoporous samples
does not give adequate values of
micropore volumes,
unlike when the samples contain only microporous. Based on ...that, in this work, we propose an easy method to calculate a reliable micropore volume (
V
μP
) of micro-mesoporous (nanopores) samples, separating the microporous region from the experimental isotherm. For this, the original isotherm is modified, estimating the thickness of the adsorbed layer (
t
) as a function of relative pressure and changing the external surface area (
S
ext
) to obtain a Type I adsorption isotherm in the microporous region; then, the DR method can be applied to the modified isotherm. This proposal, named the
DR_t method
, allows the calculation of a reliable
V
μP
of
any
nanoporous material using different adsorbates. Using this method, we analyzed adsorbents of distinct nature (i.e., carbons and silicas) with different adsorbates as N
2
and O
2
at 77 K, Ar at 87 K, and CO
2
at 273 K. We used this method to calculate
V
μP
in different samples and compare them with those obtained with the traditional DR method, highlighting that unlike the latter the DR_t method showed similar and consistent results with the different adsorbates. Therefore, the values of micropore volume calculated using the DR_t method demonstrate consistency across various adsorbates, not only for N
2
but especially for CO
2
, which is suggested to analyze narrow micropore volumes.
Ferric chloride was used as a new activating agent, to obtain activated carbons (AC) from agro industrial waste (coffee husks). This material was compared with two samples from the same raw material: ...one of them activated by using the classical activating agent, zinc chloride, and the other, activated with a mixture of the two mentioned activating agents in the same mass proportion. The carbonaceous materials obtained after the activation process showed high specific surface areas (BET), with values higher than 900 m(2)g(-1). It is interesting to observe that the activation with FeCl(3) produces smaller pores compared to the activation with ZnCl(2). An important fact to emphasize in the use of FeCl(3) as activating agent is the activation temperature at 280 degrees C, which is clearly below to the temperature commonly employed for chemical or physical activation, as described in the bibliography. All the studied materials showed different behaviors in the adsorption of methylene blue dye and phenol from aqueous solutions.
Although nowadays landspreading and incineration are the conventional disposal methods for the primary sludge (PS) and biosludge (BS) generated in the wastewater treatment plants of the pulp mill ...industry in Uruguay, their direct incineration for energy recovery is the most preferable one. Here, we propose the hydrothermal carbonization (HTC) method as a pre-treatment to improve the fuel characteristic of PS and BS. Proximate and ultimate analysis, scanning electron microscopy, and thermogravimetric analysis show that the HTC affects PS and BS differently regarding carbon fixation, energy densification and energy conversion efficiency. Moreover, ash composition measured by X-ray fluorescence indicates that the HTC effectively diminishes the slagging and fouling indexes for both feedstocks, which can increase the life expectancy of boilers. Alternative PS, BS, and their hydrochars were activated with H
3
PO
4
to produce activated carbons, i.g. the BET specific surface area was as high as 800 m
2
/g for PS-AC, and exhibits CO
2
adsorption capacity of 5 mmol/g at 10 bar at 273 K. These studies provide alternatives to direct incineration and landspreading of PS and BS in Uruguay to reduce their environmental impact, either by enhancing their fuel quality or by converting them into much more valuable products to face air pollution.
Graphical Abstract
Samples with HKUST-1-like structure were modified by the substitution of trimesic acid (BTC) by isophthalic acid (iBDC). HKUST-1-like structure was monitored by XRD, finding no changes up to a BTC ...molar fraction (X
BTC
) equal to 0.67. The substitution of BTC by iBDC produced an increase of defects observed by SEM and led to a greater specific surface area. The increase in N
2
molecules adsorption was correlated with a 10% increase in H
2
uptake at 8 bar and 77 K. Interestingly, the ligand substitution showed no effects on methane uptake up to 40 bar and 298 K. The defect engineering showed to be a useful tool to increase the uptake of polar molecules with surface.
We present a new kernel of N
2
isotherms in γ-alumina, the metastable phase of α-alumina, most used in industrial applications. The dedicated kernel proposal, existing in the literature, uses ...cylindrical pores, as well as approximate kernels of commercial adsorption characterization equipment. TEM morphology studies of γ-alumina have shown that the material has slit-like pores rather than cylindrical pores. Thus, our kernel is based on a slit pore collection of N
2
isotherms at 77 K with 10 different pores sizes, dedicated to the characterization of the micropore range. The isotherms were calculated by applying the Monte Carlo method in the grand canonical ensemble. The solid–fluid interaction parameters were validated in an α-alumina surface. The agreement between experimental and simulated isotherms, using our kernel, is superior to that obtained with cylindrical pores, confirming the experimental evidence on the nature of γ-alumina morphology. Two γ-alumina samples are investigated and we observe that 12 to 22% of the total volume consists of micropores that are not adequately characterized with approximate cylindrical kernels. We also propose an alternative approach to match the different PSDs obtained, based on hybrid kernels methodology of hierarchical adsorbents materials characterization.
In this work, the influence of degassing temperature and urea functionalization were investigated as ways to improve the CO2 adsorption performance of CPO-27-Mg. Through post-synthesis modification ...treatments, four samples with different degrees of urea functionalization were obtained, incorporating 10, 25, 50, and 100% of urea concerning the metal sites of the MOF. Alternatively, the influence of the degassing temperature of the non-functionalized MOF between 70 and 340 °C was also evaluated. The resulting compounds were characterized by N2 adsorption–desorption isotherms at −196 °C using TGA-MS, FTIR, and PXRD. Finally, the thermally treated and functionalized CPO-27-Mg was evaluated for CO2 capture.
In this study, natural and modified clays were evaluated as catalysts in an esterification reaction to obtain bio-based lubricants. The biolubricants are environmentally preferred to petroleum-based ...lubricants because they are biodegradable and non-toxic. Other advantages include very low volatility due to the high molecular weight and excellent viscosity properties with temperature variations. Modifications in natural clay were performed intending to obtain materials with different textural properties that could improve the reaction under study. The modified clays were obtained in two ways: by pillarization using Al
Keggin polyoxocations or by acid treatments with H₂SO₄, HCl and HNO₃. All samples were evaluated for the esterification reaction of fatty acids from castor oil (FACO) using 2-ethyl-hexanol. During the reaction step, a zeolite-based adsorbent was used for water removal to increase the reaction equilibrium conversion. Gas chromatography and nuclear magnetic resonance were performed to ensure the formation of the products. The highest conversion of fatty acids to esters was obtained using pillared clays. Adding adsorbent in the reaction medium (10 g of 3A zeolite to 100 g of FACO), the conversion improved from 74⁻88 wt % after 6 h at 50 °C.
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