To characterize the adsorption process, these isotherms were adjusted to Langmuir and Freundlich models Figure 8 and the results of this characterization are in Table 1.
Figure 8. Table 1. Parameters obtained from the fit to the Langmuir and Freundlich models for the gas phase adsorption isotherms of toluene and hexane on CS and CST. According to the values obtained by adjusting to the models, toluene was adsorbed in a greater proportion than hexane. While in the case of hexane-CS, this sample is the one that presents the greatest heterogeneity with respect to surface chemistry and the lowest values of surface area and micropore volume, due to this and added to the fact that hexane tends to be arranged as an elongated cylinder Wang et al.
Likewise, the results of the values obtained are shown in Table 2. Figure 9. Table 2. The effect of the samples remained the same, which showed that the sample subjected to heat treatment at For the liquid phase, the adsorbed amount tripled if the CST sample was used instead of CS and it could also be seen that when hexane was used as a solvent for toluene, the adsorbed amount of toluene decreased to one fifth for the sample CST and it was reduced practically eight times for the CS sample.
Figure The calorimetric determinations were carried out in triplicate with standard deviation values between 0. Table 3. Immersion enthalpies of pure solvents and toluene-hexane mixtures in function of the molar fraction of toluene in the mixture.
Figure 11 corresponds to the immersion enthalpies of pure solvents or toluene-hexane mixtures in function of the molar fraction of toluene in the mixture. This showed the region of the mixtures center of the figure, dark green square and the edges where the pure solvents were. For the pure solvents, the intensity of the interaction was greater with toluene than hexane it increased 2.
As for the mixtures, the above was confirmed, since by adding 0. Regarding to the samples, Figure 12 shows the immersion enthalpies of pure solvents and toluene-hexane mixtures in function of the molar fraction of toluene and the total acidity and basicity of samples. Immersion enthalpies of pure solvents and toluene-hexane mixtures in function of the molar fraction of toluene and the total acidity A and basicity B.
Whereas, if binary mixtures of these adsorbates were evaluated assuming that the process started with hexane as a pure component and different amounts of toluene were added, energetically more energy was released when the system was bicomponent regardless of the molar fraction, since the immersion enthalpies of the mixtures toluene-hexane at 0.
Finally, comparing the adsorption processes from the gas and liquid phase, it was found that the amount adsorbed was greater in the gas phase because the particles in this phase considered as ideal gases did not present adsorptive-adsorptive interaction; while in the liquid phase there was not only adsorptive-adsorptive interaction both for hexane and toluene but also solute-solvent interaction, as well as a competition between the solute and the solvent to enter the porous structure, which made difficult the entrance of the adsorbate to the porous solid; on the other hand, the high hydrophobicity of toluene generated a high affinity with hexane, so that it hindered the adsorption of the aromatic compound Goto et al.
This was corroborated with the immersion enthalpies, because it was found that the energy released was greater when toluene was the immersion liquid compared to hexane , but when toluene and hexane were together, it was seen that as toluene concentration increased, the immersion enthalpy of the mixture decreased, which probably occurred because there was displacement of hexane molecules by toluene molecules, which would require energy, causing the magnitude of the exothermic process to decrease Unnikrishnan and Srinivas, , showing that there is a competition for the adsorption sites.
Submitting the starting sample to thermal modification at When hexane was added as a solvent to the toluene adsorption process, the adsorption of the aromatic compound decreased because both molecules competed for the adsorption sites, and as the amount of C 7 H 8 increased, a possible displacement of the hexane molecules was generated, making that the energy released decreased its magnitude because the displacement of a molecule of hexane by one of toluene required energy, leading to the adsorbed toluene amount was smaller for the liquid phase than for gas phase due to the fact that in the liquid phase there was not only adsorbent-adsorbate interaction, but also solute-solute, solute-solvent and solvent-solvent, added to the fact that the high affinity between toluene and hexane hindered the adsorption of the aromatic compound.
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation. The authors know the content of the paper and have contributed equally to each of its parts. All authors contributed to the article and approved the submitted version. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors thank the Framework Agreement between the Universidad de los Andes and the Universidad Nacional de Colombia and the act of agreement established between the Chemistry Departments of the two universities.
Abd, A. Carbon dioxide removal through physical adsorption using carbonaceous and non-carbonaceous adsorbents: a review. Abdulrasheed, A. Surface modification of activated carbon for adsorption of SO2 and NOX : a review of existing and emerging technologies. Energy Rev. Anuradha, S. Adsorption of VOC on steam activated carbon derived from coconut shell charcoal. Indian J. Google Scholar.
Assadi, Y. Chromatographia 71, — Bazzini, P. Wermuth, D. Aldous, P. Raboisson, and D. Rognan London: Elsevier , — Bedolla, P. Effects of van der Waals interactions in the adsorption of isooctane and ethanol on Fe surfaces. C , — Bhatnagar, A. An overview of the modification methods of activated carbon for its water treatment applications.
Biniak, S. Influence of high-temperature treatment of granular activated carbon on its structure and electrochemical behavior in aqueous electrolyte solution. Boehm, H. Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon 32, — Molecular simulation of the adsorption and diffusion in cylindrical nanopores: effect of shape and fluid—solid interactions. Molecules Chen, X. Modeling of experimental adsorption isotherm data.
Information 6, 14— Chen, Z. Synthesis and fabrication of g-C3N4-based materials and their application in elimination of pollutants. Total Environ. Cheng, D. Adsorption behavior of p-chlorophenol on the reed wetland soils. Cheng, Y. Challenges and solutions for biofiltration of hydrophobic volatile organic compounds.
Contescu, C. Activated carbons derived from high-temperature pyrolysis of lignocellulosic biomass. C 4, 51— Surface modification of commercial activated carbon cag for the adsorption of benzene and toluene. Daud, W. Textural characteristics, surface chemistry and oxidation of activated carbon.
Gas Chem. Grumezescu London: Academic Press, Inc. Denoyel, R. Rouquerol, F. Rouquerol, P. Llewellyn, G. Maurin, and K. Sing Kidlington: Academic Press, Inc.
Diao, R. Adsorption and structure of benzene, toluene, and p-xylene in carbon slit pores: a Monte Carlo simulation study. Dubinin, M. Physical Adsorption of Gases and Vapors in Micropores. Moscow: Academic Press, Inc. Water vapor adsorption and the microporous structures of carbonaceous adsorbents. Carbon N. Figueiredo, J. Modification of the surface chemistry of activated carbons. Foo, K. Insights into the modeling of adsorption isotherm systems. Fu, X. A Gen.
Giraldo, L. Detailed information on the preparation of the WSs is shown in Table 2. Since the F-WSs contained different solvents, the calibration characteristics of the toxic compounds according to the solvent effects were assessed. The target analytes were then transferred to the Rtx-5MS column diameter: 0. The target analytes separated by the GC system were then detected by the MS system. Extracted ion chromatographic EIC mode was subsequently applied to the minimized interfaces using significant ions identified from the spectrum of each target analyte Table 1.
Detailed setting information of the analysis instrument is presented in Table 3. Notably, the RF value of each target analyte was different, depending on the solvent type. Benzene and toluene had relatively high N-RF values above 0.
The LOD values of all target analytes were below 0. Based on these results, we concluded that the instrument responsivity and reproducibility of the target compounds differed, depending on their physicochemical properties. Moreover, the responsivity and analytical reliability was found to be especially affected by the solvent type. Therefore, in order to achieve an accurate quantitation, it is important to select the solvent by considering the physicochemical properties i.
Diverse solvents have been previously used in chemical and biological analyses for the pretreatment of target samples and the preparation of standard solutions.
In this study, we confirmed that the calibration results were different depending on the solvent type, although the same target compounds were analyzed by the same analytical methods.
However, many researchers do not fully consider the solvent effect in their quantitative analyses Table 5. For example, Rezende et al. Additionally, a 0. In both of these cases, there could be a quantitative error due to the solvent difference between the standards and samples. Furthermore, there are also studies that use the same solvent for both standard and sample preparation. For instance, Lim et al.
In both of these cases, the solvent effects could be minimized by using the same solvent for the quantitative analysis. In order to conduct a toxicity testing, one needs to be able to obtain reliable quantitation data of the target toxic compounds.
In this study, we assessed the effect of the solvent type on the quantitative results by analyzing three toxic compounds using four different solvents. Benzene, toluene, and MIT, which are well-known toxic compounds, were selected as target analytes.
Liquid working standards of the target analytes were prepared using four different solvents MeOH, hexane, PBS, and DMSO , which are commonly used for extraction and dilution of sample solutions.
These working standards were analyzed using GC-MS, thereby providing the calibration results of the target compounds according to the solvent type. The solvent effect was then assessed by comparing these results Figure 3. In contrast, hexane induced a low R 2 value of MIT 0. All in all, the results of this study confirmed that the quantitative results were affected by the solvent effect.
Since quantitative results can differ depending on the solvent type, it is important to select the solvent by considering the physicochemical properties i. In addition, the use of different solvents in the quantitative analysis, such as in the extraction and dilution processes, could lead to difficulties in obtaining reliable quantitative data.
This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Journal overview. Special Issues. Academic Editor: Paolo Montuori. Received 30 Sep Accepted 24 Mar Published 30 Apr Abstract The quantitative analysis of target substances is an important part of assessing the toxicity of diverse materials. Introduction Chemical products that are generally used to clean, sanitize, and disinfect are widely employed in our living environments.
NA, not available. Table 1. Figure 1. A plot of the experimental sequence for the preparation and analysis of the working standards WSs. Table 2. Table 3. Table 4. Figure 2. Chromatograms of the three target compounds based on four different solvents. Table 5. List of the comparison of the solvent effects on chemical and biological analysis using the analytical instrument.
Figure 3. These documents generally contain a critical review of the scientific and technical information available on the prevalence of hazards, the existence of safety and health risks, and the adequacy of methods to identify and control hazards. CIBs review and evaluate new and emerging information about occupational hazards. A CIB may draw attention to a previously unrecognized hazard, report new data on a known hazard, or disseminate information about hazard controls.
Skip directly to site content Skip directly to page options Skip directly to A-Z link. Section Navigation. Facebook Twitter LinkedIn Syndicate. Organic Solvents. Minus Related Pages. On This Page. Overview Organic solvents are carbon-based substances capable of dissolving or dispersing one or more other substances. The following resources provide information about occupational exposure to organic solvents. Manual of Analytical Methods.
Health Hazard Evaluations.
0コメント