Nitrogen Porosimetry Research Articles

Efficient removal of organophosphate insecticide employing magnetic chitosan-derivatives

Herein, this work reports an efficient acephate adsorption using chitosan (CS) incorporating varying amounts of magnetite. A co-precipitation methodology was employed for the functionalization of chitosan with iron nanoparticles, using Fe2+ as the sole iron source and with a low energy requirement. The adsorbents were characterized by FTIR, XRD, VSM, and nitrogen porosimetry techniques. The CS∙Fe3O4 1:1 NPs showed the highest acephate removal percentage (74.96 %) at pH 9 and ambient temperatures. The adsorption process exhibited high dependencies on pH, adsorbent dosage, initial concentration of adsorbate, and ionic strength. Sips and pseudo-second-order kinetics models best adjusted the experimental data, suggesting that the process occurs on a heterogeneous surface. Thermodynamic evaluation showed that the adsorption was exothermic, favorable, and predominately through chemical interactions. Finally, the CS∙Fe3O4 showed no significant decrease after several cycles of adsorption/desorption, avoiding centrifugation-filtration steps.

Biocatalysts engineering by varying the binary CNTs-silica composition and the physicochemical characteristics of adsorbents for the immobilization of recombinant T. lanuginosus lipase

Biocatalytic engineering was carried out by varying monotonically the binary CNTs-silica composition and, accordingly, the physicochemical characteristics of adsorbents developed for immobilization of recombinant T. lanuginosus lipase (rPichia/lip). The adsorbents based on composite carbon-silica materials (CCSMs) were produced by impregnating finely dispersed multi-walled carbon nanotubes with silica hydrosol followed by calcination in argon at 350°C; the mass ratio of the hydrophobic and the hydrophilic components varied over a wide range. Biocatalysts (BCs) for green low-temperature synthesis of various esters in a non-aqueous medium of organic solvents were prepared by adsorption of rPichia/lip with subsequent drying under ambient conditions. The characteristics of the CCSMs and BCs were characterized by thermogravimetry, nitrogen porosimetry and electron microscopy. The catalytic properties of BCs, such as enzymatic activity, substrate conversion and specificity, as well we their operational stability depending on the chemical composition of CCSMs were extensively studied in the esterification of saturated monocarboxylic acids (C4, C7, C18) and primary aliphatic alcohols (C2, C4, C16) in hexane at 20°C. It was found that the esterifying activity manyfold decreased with increasing the silica content primarily due to a decrease in adsorption ability of CCSMs toward rPichia/lip. The substrate specificity and operational stability of the lipase-active BCs did not greatly depend on the composition of CCSMs. Biocatalysts retained more than half of their initial esterifying activity after 10 reaction cycles.

The influence of hydrocarbon generation on the sealing capability of mudstone caprock rich in organic matter

To investigate the sealing capability of mudstone caprock during the evolution of organic matter (OM)-rich mudstone, a series of hydrous pyrolysis experiments were first conducted to examine the impact of hydrocarbon generation. The pore type, pore structure, porosity, and gas breakthrough pressure of pyrolytic residual samples were analyzed by field emission scanning electron microscopy, low pressure nitrogen adsorption measurements, porosimetry, and gas breakout core experiments. To model the environment at different depths, these six experiments on hydrous pyrolysis were performed at different temperatures, lithostatic pressures, and hydrodynamic pressures, while other experimental factors such as the original sample, heating time, and rate were kept constant. The results showed that during the thermal evolution process, hydrocarbons were generated from OM in mudstone, resulting in the formation of pores within the OM. Organic acids produced by hydrocarbon generation effectively dissolved minerals, leading to the creation of numerous dissolution pores. Changes in pore type led to changes in pore structure and porosity. The volume of micropores and macropores showed an increasing trend before reaching a Ro value of 1.41%. However, after passing this threshold, they began to decrease. The volume of mesopores showed a decreasing trend before reaching a Ro value of 1.32%. After 1.32%, they began to increase. The porosity was mainly affected by the pore volumes of the mesopores and macropores. The porosity exhibited two peaks: the first occurred at a Ro value of 0.72%, with a porosity level of 4.6%. The second occurred at a Ro value of 1.41% and a porosity level of 10.3%. The breakthrough pressure was a comprehensive reflection of these influences, and its trend exhibited a negative correlation with porosity (R2 = 0.886). For two high values of porosity, the breakthrough pressure corresponded to two low values. Smaller values of the breakthrough pressure indicated a poorer sealing capability of the mudstone caprock. Overall, hydrocarbon generation in the mudstone affected the sealing capability. The mudstone in the studied area exhibited good sealing at Ro below 1.32%. However, once above the 1.32% threshold, the fluctuations of the breakthrough pressure values exhibited considerable variability, requiring a comprehensive evaluation to assess its sealing capability.

Hierarchical porous SAPO-34 decorated with Mo and W oxides for concurrent transesterification-esterifications for efficient biodiesel production from acidic soybean oil

Hierarchical porous materials have gained much attention as promising heterogeneous catalyst supports due to their high efficiency of mass transfer and high exposure of active centers. In this research, the hierarchical porous SAPO-34 support with microporous, mesoporous, and macroporous hierarchical structure was initially prepared by in-situ alkali etching. Then, Mo and W oxides were incorporated into this hierarchical porous support by using the impregnation method to prepare Mo15W15/HSAPO-34/70 catalyst. This developed catalyst was applied to concurrently catalyze the oil transesterification and free fatty acid (FFA) esterification to biodiesel as the low-value oils severed as feedstocks. The textural and physicochemical properties of the nanocatalysts were evaluated by XRD, XPS, SEM, EDS, TEM, UV–vis, NH3-TPD, Py-FTIR, and nitrogen porosimetry measurement. This catalyst had hierarchical porous structure to ameliorate the large oil molecular transfer, and featured dual Brønsted-Lewis acid sites to synergistically boost the catalytic efficiency for the biodiesel production. Over this catalyst, the oil conversion of 90.1 % and full FFA conversion were achieved under optimized operation conditions, therefore imparting to one-pot conversion to biodiesel with low-value oils as feedstocks. In addition, this catalyst not only exhibited superior tolerance to moisture and FFAs, but also retained high activities after five reuse cycles, thus revealing its tremendous potential of being used in durable and efficient biodiesel production. The present work opens a new avenue for synthesizing a robust solid acid catalyst to achieve a one-pot biodiesel production from low-value oils.

Iron(III) based Metal-Organic Frameworks in cellulose acetate film preservation: Fundamental aspects and first application

Low-temperature storage to slow down degradation is accepted by the film conservation community. Still, this solution prohibits public access, is price-sensitive, has high energy costs, and there are concerns about their effects on the physical stability and material lifetime. In this research, a smart solution is developed based on the selective capture of acetic acid produced by the cellulose acetate polymer. This innovative approach is based on Metal-Organic Frameworks (MOFs) for acetic acid adsorption, specifically a highly selective porous iron(III) based MOF, MIL-100(Fe), which was synthesized using a green approach. The stability of MIL-100(Fe), under acetic acid exposure, was demonstrated by accelerated aging experiments, with no noticeable changes in crystallinity and/or porosity as deduced from powder X-ray diffraction analysis, infrared spectroscopy, thermogravimetric analysis, nitrogen porosimetry, and electron microscopy. Compatibility tests with the artefacts were performed to prove the safety of the MIL-100(Fe) to the artefacts. A field application in a demonstration prototype (smart box) was performed at Institut Valencià de Cultura. A recently developed hybrid model provided recommendations on the quantity of adsorbents to use in the smart box. Good agreement was observed between the model predictions and the in-field experimental results, which validated the model application. The model predicted that the new adsorbent (5% of the film's weight, replaced every 10 years, at 16°C or 22°C) extends the film's lifetime equivalently to cold storage (5°C). Finally, environmental impact assessment and life cycle analysis were performed to compare the two preservation approaches. The new approach based on this Fe-MOF yielded an average reduction of carbon footprint related to movie film preservation of about 50% considering the current European Union (EU) energy mix and about 40% considering the 2030 EU energy mix (where a transition towards renewable energy is expected). The proposed innovative technology represents a robust solution towards efficient and more sustainable film preservation while significantly contributing to moving toward climate transition objectives in the culture heritage sector.

Synthesis of Carboxymethylcellulose–Acrylamide–Montmorillonite Composite Hydrogels for Wastewater Purification

The three-dimensional network and ample pore structure of novel hydrogel materials enable outstanding adsorption performance for pollutants such as methylene blue (MB) and Cr6+ ions in wastewater. In order to develop an environmentally friendly hydrogel with high adsorption performance and low cost, a type of carboxymethyl cellulose (CMC) composite hydrogel was synthesised with montmorillonite (MMT) via chain radical polymerization, which gives it great potential for application in the field of wastewater purification. A series of hydrogel samples were characterised through SEM, FTIR and nitrogen porosimetry analysis, indicating the successful intercalation of MMT nanosheets into the hydrogel crosslinking network. The mass ratio of CMC to MMT, the amounts of adsorbent, the initial concentration of wastes, pH, and the adsorption temperature were investigated and optimised for hydrogel adsorption performance. When the initial concentration of MB is 60 mg/L, pH is 7, the dosage of MB is 0.5 g/L, and the adsorption temperature is 30 °C, the hydrogel sample the highest adsorption capability for MB removal, with an adsorption amount of 112.9 mg/g. When the initial concentration of Cr6+ is 10 mg/L with a pH of 7, the highest adsorption capacity of the hydrogel for Cr6+ removal is 1.35 mg/g. The fitting results of the isothermal models, the kinetic models, internal particle diffusion models and the thermodynamics of the experimental data of the adsorbate adsorption process show that the adsorption of MB by hydrogel is a spontaneous segmented process of multi-layer physical and chemical adsorption. Additionally, the adsorption of Cr6+ ions by hydrogel is a spontaneous segmented process of multi-layer physical adsorption.

Investigation of Gelation Techniques for the Fabrication of Cellulose Aerogels.

Because of the pronounced degradation of the environment, there has been an escalated demand for the fabrication of eco-friendly and highly efficient products derived from renewable sources. Cellulose aerogels have attracted significant interest attributable to their structural characteristics coupled with biodegradability and biocompatibility. The features of the molecular structure of cellulose allow for the use of various methods in the production of gels. For instance, the presence of hydroxyl groups on the cellulose surface allows for chemical crosslinking via etherification reactions. On the other hand, cellulose gel can be procured by modulating the solvent power of the solvent. In this study, we investigate the impact of the gelation methodology on the structural attributes of aerogels. We present methodologies for aerogel synthesis employing three distinct gelation techniques: chemical crosslinking, cryotropic gelation, and CO2-induced gelation. The outcomes encompass data derived from helium pycnometry, Fourier-transform infrared spectroscopy, nitrogen porosimetry, and scanning electron microscopy. The resultant specimens exhibited a mesoporous fibrous structure. It was discerned that specimens generated through cryotropic gelation and CO2-induced gelation manifested higher porosity (93-95%) and specific surface areas (199-413 m2/g) in contrast to those produced via chemical crosslinking (porosity 72-95% and specific surface area 25-133 m2/g). Hence, this research underscores the feasibility of producing cellulose-based aerogels with enhanced characteristics, circumventing the necessity of employing toxic cross-linking agents. The process of gel formation through chemical crosslinking enables the creation of gels with enhanced mechanical properties and a more resilient structure. Two alternative methodologies prove particularly advantageous in applications necessitating biocompatibility and high porosity. Notably, CO2-induced gelation has not been hitherto addressed in the literature as a means to produce cellulose gels. The distinctive feature of this approach resides in the ability to combine the stages of obtaining an aerogel in one apparatus.

Hydrogen Sulfide Removal via Sorption Process on Activated Carbon-Metal Oxide Composites Derived from Different Biomass Sources.

Biomass exploitation is a global trend due to the circular economy and the environmentally friendly spirit. Numerous applications are now based on the use of biomass-derived products. Hydrogen sulfide (H2S) is a highly toxic and environmentally hazardous gas which is emitted from various processes. Thus, the efficient removal of this toxic hazardous gas following cost-effective processes is an essential requirement. In this study, we present the synthesis and characterization of biomass-derived activated carbon/zinc oxide (ZnO@AC) composites from different biomass sources as potential candidates for H2S sorption. The synthesis involved a facile method for activated carbon production via pyrolysis and chemical activation of biomass precursors (spent coffee, Aloe-Vera waste leaves, and corncob). Activated carbon production was followed by the incorporation of zinc oxide nanoparticles into the porous carbon matrix using a simple melt impregnation method. The synthesized ZnO@AC composites were characterized using X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and nitrogen porosimetry. The H2S removal performance of the ZnO@AC composites was evaluated through sorption experiments using a handmade apparatus. Our findings demonstrate that the Aloe-Vera-, spent coffee-, and corncob-derived composites exhibit superior H2S sorption capacity up to 106 mgH2S/gads., 66 mgH2S/gads., and 47 mgH2S/gads., respectively.

Performance of Zr-Based Metal-Organic Framework Materials as In Vitro Systems for the Oral Delivery of Captopril and Ibuprofen.

Zr-based metal-organic framework materials (Zr-MOFs) with increased specific surface area and pore volume were obtained using chemical (two materials, Zr-MOF1 and Zr-MOF3) and solvothermal (Zr-MOF2) synthesis methods and investigated via FT-IR spectroscopy, TGA, SANS, PXRD, and SEM methods. The difference between Zr-MOF1 and Zr-MOF3 lies in the addition of reactants during synthesis. Nitrogen porosimetry data indicated the presence of pores with average dimensions of ~4 nm; using SANS, the average size of the Zr-MOF nanocrystals was suggested to be approximately 30 nm. The patterns obtained through PXRD were characterized by similar features that point to well-crystallized phases specific for the UIO-66 type materials; SEM also revealed that the materials were composed of small and agglomerate crystals. Thermogravimetric analysis revealed that both materials had approximately two linker deficiencies per Zr6 formula unit. Captopril and ibuprofen loading and release experiments in different buffered solutions were performed using the obtained Zr-based metal-organic frameworks as drug carriers envisaged for controlled drug release. The carriers demonstrated enhanced drug-loading capacity and showed relatively good results in drug delivery. The cumulative percentage of drug release in phosphate-buffered solution at pH 7.4 was higher than that in buffered solution at pH 1.2. The release rate could be controlled by changing the pH of the releasing solution. Different captopril release behaviors were observed when the experiments were performed using a permeable dialysis membrane.

Selective and sensitive GC-MS analysis of carcinogenic N-nitrosodimethylamine in pharmaceuticals using a magnetic coconut carbon composite as a solid-phase extraction sorbent

The aim of the present research was to develop a magnetic coconut carbon composite (Fe2O3/Fe3O4@CNC) as a solid-phase extraction (SPE) sorbent for the analysis of carcinogenic N-nitrosodimethylamine (NDMA) in pharmaceuticals. Coconut composites modified with Fe2O3 and Fe3O4 were prepared and applied as SPE sorbent for the extraction of NDMA in pharmaceuticals. The sorbent was characterized with X-Ray, infrared spectroscopy and nitrogen porosimetry. The best ions for the Gas Chromatography-Mass Spectrometry with Selected Ion Monitoring (GC-MS/SIM) analysis were m/z 74 and 42 for NDMA, and m/z 80 and 46 for NDMA-d6 internal standard. System has offered great method performance in terms of sensitivity limit of quantitation (LOQ) 16 ng kg−1. The developed sorbent has enhanced the sensitivity and speed of analysis. The developed method was applied to authenticate the presence of NDMA in various pharmaceutical samples. Among the analyzed samples, NDMA impurities were relatively identified at high amounts in nizatidine samples. Highlights NDMA was verified in ranitidine, metformin and nizatidine Fe2O3/Fe3O4@CNC composite was used for NDMA identification without pretreatment SPE sorbent enhance sensitivity, reduce analysis time, sustain accuracy & precision High level of NDMA impurity were found in nizatidine pharmaceuticals.

Bimetallic Zrx-Aly-KIT-6 modified with sulfate as acidic catalyst for biodiesel production from low-grade acidic oils

For the purpose of fabricating an efficient solid acid catalyst for biodiesel production from low-grade acidic oils, bimetallic silica mesoporous composites with different Zr/Al molar ratios were initially synthesized via a facile one-step hydrothermal method, and then sulfated with sulfuric acid at different concentrations to get a series of sulfated Zrx-Aly-KIT-6 catalysts (denoted as SZA-K, where x/y represents the molar ratio of Zr to Al). The sulfated bimetallic solid catalysts were fully characterized by using XRD, FT-IR, TEM, SEM, EDS, NH3-TPD, and nitrogen porosimetry measurements. Results showed that the remarkable amount of acidic sites in the catalysts was derived from the Zr and Al incorporation and further sulfation, and specifically, the Zr4+ and Al3+ could afford abundant weak acid sites while the inductive effect of SO42− species greatly influences the acidic strength of this solid catalyst. In combination with the enhancement in mass transfer resulting from the inherent interconnected mesoporous structure, the SZA-K catalyst could facilitate the transesterification reaction to take place efficiently. The sulfated Zr5–Al1-KIT-6 catalyst (Zr/Al molar ratio of 5/1, treated using 0.75 mol/L sulfuric acid for 12 h) exhibited enhanced acid strength with larger number of acidic sites (7.81 mmol/g), resulting in a high catalytic performance to the oil transesterification reaction. An oil conversion of 96.3% was attained for the transesterification reaction performed at 120 °C for 7 h by using a methanol/oil molar ratio of 20:1 and a catalyst dosage of 6 wt%. Further, this solid catalyst exhibited better acid and water-resistance capacity with above 80% of oil conversion even with 10% of free fatty acid (FFA) and 2% of moisture present in the low-grade acidic oils. Meanwhile, the good reusability was shown for this catalyst with 80.1% conversion even after reusing for three cycles. The good stability of the solid catalyst was resulted from the strong interactions between the acidic species and the bimetallic composite support.

Investigation of the transformation of organic matter of carbonate deposits of the Semiluksky–Mendymsky horizon under hydrothermal conditions

The paper presents the results of studies on the transformation of the organic matter of siliceous-clayey carbonate rocks of the Semiluksko–Mendymsky horizon of the Romashkino oil field in a hydrothermal fluid for an hour (with a water-to-rock ratio of 33) at 340°C and 380°C and pressures of 17 and 20 MPa. As a result of hydrothermal treatment, at 340°C and 17 MPa, based on nitrogen porosimetry and electron microscopy data, transformations of rock-forming minerals in the rock are observed. They lead to an increase in the volume and average diameter of mesopores in it and the formation of micropores, as well, which improve its filtration properties. At the same time, the amount of kerogen in the composition of the organic matter decreases and the yield of the petroleum hydrocarbon extract increases, in which, according to the SARA analysis, the content of asphaltenes increases and the content of resins, aromatic and saturated hydrocarbons decreases. In the composition of aroatic hydrocarbons, the proportion of alkyltrimethylbenzenes and dibenzothiophenes increases, phenanthrene homologues appear, and in the composition of saturated hydrocarbons, the amount of iso-structure alkanes decreases relative to the content of linear alkanes. Raising the temperature and pressure of the hydrothermal fluid to 380°С and 20 MPa increases the degree of kerogen conversion from 12.4% to 23.6%. At the same time, changes occurring in the component composition of petroleum hydrocarbon extracts remains similar to the experiments carried out at 340°C and 17 MPa; the content of naphthalenes decreases, the content of dibenzothiophenes increases and C11–C17, C19–C22 alkyltrimethylbenzenes appear. According to IR spectroscopy, with increasing temperature and pressure of the hydrothermal fluid the intensity of the absorption bands of the aromatic ring, aliphatic fragments, and oxygen-containing groups increases in resins; the structural-group composition of asphaltenes changes little: aromaticity and the content of condensed structures slightly increase. The revealed distinctive features in the composition of organic matter after hydrothermal impact on siliceous-clayey carbonate rocks confirm the concept of staged destruction of kerogen, when large structural heteroatomic blocks (asphaltenes) are split off at the initial stages. Changes occurring in the composition of petroleum hydrocarbon extracts indicate their involvement in the process of hydrothermal transformation of organic matter of siliceous-clayey carmbonate rocks with the predominant reactions of dehydrogenation of naphthenic compounds and oxidative polycondensation of aromatic structures. The data of electron microscopy and nitrogen porosimetry of rocks after hydrothermal exposure at 380°С and 20 MPa indicate a deterioration in their reservoir properties. The most optimal thermobaric conditions of the hydrothermal fluid for the generation of petroleum hydrocarbons from kerogen of siliceous-clayey carbonate deposits of the Semiluksko–Mendymsky horizon of the Romashkino field, which improve their reservoir properties, are 340°С and 17 MPa; with implication of hard-to-recover heavy hydrocarbon resources and well-established catalytic methods of in-situ conversion.

Glycerol Carbonate Solventless Synthesis Using Ethylene Carbonate, Glycerol and a Tunisian Smectite Clay: Activity, Stability and Kinetic Studies

Biodiesel is nowadays added in 5–10% v/v to diesel, and its production involves the parallel creation of a vast glycerol amount as a by-product. Despite its many applications, there is a surplus of glycerol (Gly) that has boosted the search for new applications of this compound, now transformed into an industrial synthesis intermediate or platform chemical. Its transcarbonation is a type of reaction that occurs under mild conditions, using weak or moderate basic catalysts, and allows the parallel production of glycols of industrial interest with high selectivity, such as ethylene glycol. In this research, we have studied the activity of a Tunisian clay rich in inorganic carbonates that give it a weak basic character. The raw clay (RC) has been fully characterized by XRD, FTIR, SEM-EDS and nitrogen porosimetry. Subsequently, it has been employed as a catalyst to react glycerol (G) with ethylene carbonate (EC) to obtain glycerol carbonate (GC) and ethylene glycol (EG). The main operating variables and their effects on glycerol conversion and initial reaction rate were analyzed: catalyst concentration (2–6% w/w glycerol), reagent molar ratio (EC:G 1.5:1 to 3:1), and temperature (80–110 °C). Then, an appropriate kinetic model was selected from the results obtained under various reaction conditions, including the total deactivation of order 1 of the catalyst. The kinetic constant activation energy in this reaction using Tunisian smectite was found to be around 183.3 kJ·mol−1. In the second phase of the investigation, we explored the reuse of smectite using the kinetic model to appreciate the effect of cycle-to-cycle deactivation. It can be seen that the kinetic constant of the main reaction generally decreases with the number of cycles at low temperature and goes through a maximum at high operating temperature, while the deactivation constant increases with the number of catalytic cycles. The catalyst shows more stability, in general, at higher temperatures.

Comparative Study of the U(VI) Adsorption by Hybrid Silica-Hyperbranched Poly(ethylene imine) Nanoparticles and Xerogels.

Two different silica conformations (xerogels and nanoparticles), both formed by the mediation of dendritic poly (ethylene imine), were tested at low pHs for problematic uranyl cation sorption. The effect of crucial factors, i.e., temperature, electrostatic forces, adsorbent composition, accessibility of the pollutant to the dendritic cavities, and MW of the organic matrix, was investigated to determine the optimum formulation for water purification under these conditions. This was attained with the aid of UV-visible and FTIR spectroscopy, dynamic light scattering (DLS), ζ-potential, liquid nitrogen (LN2) porosimetry, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Results highlighted that both adsorbents have extraordinary sorption capacities. Xerogels are cost-effective since they approximate the performance of nanoparticles with much less organic content. Both adsorbents could be used in the form of dispersions. The xerogels, though, are more practicable materials since they may penetrate the pores of a metal or ceramic solid substrate in the form of a precursor gel-forming solution, producing composite purification devices.

Investigation of the Pore Structure of Exfoliated Graphite Based on Highly Oriented Pyrolytic Graphite Nitrate

Graphite intercalated compounds (GICs) with different stage numbers were prepared from highly oriented pyrolytic graphite (HOPG) and nitric acid using a chemical method. Exfoliated graphite (EG-T) was synthesized from GICs by water treatment followed by thermal shock. The effects of the graphite oxidation depth on the EG-T thermal expansion coefficient, volatile content, and total porosity were examined. However, the main purpose of this work was investigation of the dependence of the inner EG-T pore structure on the level of oxidation. Thus, we studied the micro- and mesopore structure and specific surface area by nitrogen porosimetry and the modern 2D-NLDFT method to calculate the pore size distribution and pore volume. As well, we performed a mercury porosimetry experiment to determine the macropore characteristics. We examined the pore space using a number of scanning electron micrographs of EG-T particle cross-sections using an image processing technique. In this way we showed the strong correlation between the EG-T pore structure parameters and oxidation depth of graphite.

Delopment of Composite Carbon–Silicate Materials, Their Research and Testing for the Preparation of Heterogeneous Biocatalysts for Low-Temperature Synthesis of Esters

Composite carbon–silica materials (CCSM), differing in the content of carbon and silica components, were obtained using two silicon dioxide precursors (silica sol and silane) and multi-walled carbon nanotubes (MWNTs). At the initial stage of obtaining CCSM by method 1, impregnation of finely dispersed MWCNT powder with silica sol was used, method 2 was carried out using treatment of MWCNTs with tetraethoxysilane followed by hydrolysis and polycondensation. The content of silica (SiO2) in the composites varied from 3 to 60 wt %. After drying and appropriate heat treatment at 250–350°C, the composite materials were studied by various physicochemical methods: nitrogen porosimetry, electron microscopy, X-ray fluorescence analysis, and synchronous thermal analysis. Significant differences in parameters were found depending on the chemical composition of CСSM, including textural characteristics. Thus, with an increase in the SiO2 content, the specific surface area of composite materials increased (by a factor of 2), and maxima were observed on the distribution curves over pore diameters (at 20–40 nm).The composite carbon–silica materials were tested as adsorbent for the preparation of heterogeneous biocatalysts (BC) for the low-temperature synthesis of esters; the active component of these BC was lipase immobilized exclusively on the carbon surface of nanotubes. With a decrease in the content of MWCNTs in the composite materials, the enzymatic activity and operational stability of biocatalysts, measured in the reaction of esterification of heptanoic acid (C7) with butanol (C4), decreased monotonically, reaching a 2–8-fold drop in activity at the maximum content of SiO2 (58 wt %).

STUDY OF THE PRODUCTION PARAMETERS INFLUENCE OF HIGHLY POROUS CELLULOSIC MATERIALS ON THEIR STRUCTURAL CHARACTERISTICS

Highly porous materials based on natural polymers are present of particular interest in various applications. Among them, for example, biomedicine, water purification, thermal insulation. This paper describes the developed method for obtaining highly porous materials based on cellulose, which include: dissolving microcrystalline cellulose in an aqueous solution of sodium hydroxide with urea; cross-linking cellulose using epichlorohydrin; drying the resulting gels. The influence of the concentrations of cellulose and the crosslinking agent and the drying method – freeze-drying (obtaining cryogels) and supercritical drying (obtaining aerogels) – on the final structural characteristics of the obtained materials has been studied. Cryogels and aerogels based on cellulose have been characterized by helium pycnometry, nitrogen porosimetry, and scanning electron microscopy. It was found that with an increase in the concentration of cellulose and epichlorohydrin, the porosity of the samples significantly decreases (from 84% to 22% for aerogels). For samples with the highest concentration of the crosslinking agent, the porosity of cryogels is higher (63%) than that of aerogels (22%). The specific surface area and mesopore volume were determined by nitrogen porosimetry, and nitrogen adsorption-desorption isotherms were obtained. Despite the fact that aerogels have a lower porosity, they are characterized by a higher specific surface area than cryogels (162 m2/g for aerogel and 65 m2/g for cryogel containing 6 wt.% cellulose and 4 wt.% epichlorohydrin). Scanning electron microscopy images were obtained, from which it can be seen that aerogels have a porous fibrous structure, while cryogels are characterized by a layered macroporous structure. The use of supercritical drying using CO2 avoids the destruction of the mesoporous structure of the material. For citation: Fedotova O.V., Trofimova K.V., Tsygankov P.Y., Safarov R.R. Study of the production parameters influence of highly porous cellulosic materials on their structural characteristics. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 2. P. 107-113. DOI: 10.6060/ivkkt.20236602.6736.

Synthesis, Characterisation and Catalytic Evaluation of Castor Oil-Templated Mesoporous Sulfated Solid Acid Catalysts for Esterification Reaction

In bio-refinery and other catalytic reactions, heterogeneous catalysts confer advantage over homogenous catalysts due to minimized recovery and separation costs. However, templating surfactant and solid support for the synthesis of heterogeneous catalysts ought to consider their cheap sources and environmentally friendliness for their sustainable use. Thus, with the vision to make the process significantly benign, in the present work, solid acids were synthesised from renewable sources (castor oil as surfactant and rice husk as the source of silica). The synthesised castor oil-templated mesoporous sulfonic acid modified catalysts (SO3H-MTS and SO3H-MT-RHS) were characterised and evaluated for catalytic esterification of acetic acid (C2), hexanoic acid (C6), lauric acid (C12), palmitic acid (C16), and ricinoleic acid (C18) with butanol at 110 °C. Physicochemical properties of the synthesised materials were characterised by nitrogen porosimetry, X-ray powder diffraction, thermogravimetry, X-ray Photoelectron Spectroscopy (XPS), and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The porosimetric analysis of the synthesised materials revealed a type IV adsorption-desorption isotherm reminiscent of the mesoporous structures. The surface area of the synthesised materials decreased upon functionalisation by sulfonic group. The DRIFTS and XPS confirmed the attachment of sulfonic functional group on the synthesised materials. Evaluation of the catalytic performance of the synthesized materials was determined through analysis of carboxylic acid conversions using gas chromatographic technique. SO3H-MTS gave higher acid conversions compared to SO3H-MT-RHS. The sulfated solid acid catalysts showed good catalytic activity on the esterification with conversion ranging from 96-37% for C2-C18 with butanol at 110 °C within 6 h. Such castor oil-templated mesoporous sulphated solid acid catalysts can therefore be applied in biodiesel production upon process optimisation.

The Methyl Functionality of Monolithic Silica Xerogels Synthesized via the Co-Gelation Approach Combined with Surface Silylation.

The present research aims to investigate the chemical and morphological properties of the methylated silica xerogels produced via the co-gelation approach combined with surface silylation. In the sol-gel synthesis, methyltrimethoxysilane (MTMS) and tetraethylorthosilicate (TEOS) were utilized as silica precursors and trimethylchlorosilane (TMCS) served as a silylating agent. Structural changes were observed depending on the MTMS/TEOS molar ratio and on the post-synthesis-performed surface silylation of the xerogels. Post-synthesis silylation plays a critical role in the exchanging of the surface silanols with methyl groups, preserving the monolithic form. The morphological and structural changes were followed by SEM, 29Si-MAS-NMR, FTIR spectroscopy, nitrogen porosimetry, and contact angle measurements. The results have shown significant structural variations depending especially on the MTMS content. With an increasing MTMS content, the morphology of the samples has changed from a micro/mesoporous texture to a meso/macroporous texture. A higher degree of methyl substitution has been achieved for the silylated samples both confirmed by the FTIR and 29Si-NMR results. On the other hand, only the samples with a high MTMS content could preserve their structural integrity after evaporative drying, and all have exhibited a high degree of hydrophobicity with θ > 140°.

Removal of linear siloxanes and dimethyl sulfone from water using hierarchical zeolite porous carbon adsorbents

Low molecular weight linear siloxanes are problematic compounds known to occur in water bodies, especially in water reclaimed from closed volumes. Remediation was attempted using a hierarchical porous composite adsorbent containing a Faujasite zeolite imprinted in activated carbon, namely CFAU. Although CFAU was prepared using procedures reported elsewhere, it was modified also to include extra-framework Ag+ cations. The composites long-range, textural, and compositional characteristics were verified via XRD, nitrogen porosimetry, water contact angle, zeta potential, TGA, and ICP elemental analyses. Furthermore, the composites were tested for the adsorption of siloxanes (i.e., monomethylsilanetriol, dimethylsilanediol, and trimethylsilanol (TMS)) as well as dimethyl sulfone (DMSO2) from water (mg L−1 level) in single and multicomponent fashion at ambient temperature and neutral pH. DMSO2 is highly ubiquitous in reclaimed waters where these siloxanes occur. Ag+-CFAU was the superior adsorbent, with siloxane and DMSO2 loadings of up to 20 and 87 mg cm−3 (or 17 and 72 mg g−1), respectively. These are at least an order of magnitude larger than commercial alternatives like carbon and resins. FTIR data suggest that the adsorption interaction with siloxanes is of Van der Waals type, whereas interactions between Ag+-CFAU and DMSO2 plausibly involve complexation. Moreover, multicomponent adsorption tests showed that Ag+-CFAU excels probably because of the complexation with DMSO2 and a TMS-driven siloxane co-adsorption.