Sorption Amount Research Articles

Molecular Simulation of Diffusion and Competitive Sorption of CH4 and CO2 in Shale Nanopores

Based on the competitive adsorption of CH4 and CO2, molecular dynamics (MD) and Grand Canonical Monte Carlo (GCMC) are used to study the mechanism of increasing shale gas recovery by carbon dioxide injection. The influence of different factors on the diffusion capacity of CH4 in unrestricted space and restricted space is analyzed, and the diffusion capacities of CH4 and CO2 in shale nanopores are compared. Under different conditions, the difference in the sorption amount and sorption heat of CH4 and CO2 is studied, and the displacement simulation of CH4 and CO2 is conducted. The obtained results show that the diffusion capacity of CH4 in restricted space is much smaller than that in unrestricted space, and the difference between them is related to temperature, pressure, and pore size. When pressure exceeds 10 MPa, the difference gradually decreases. The diffusion capacity of CO2 is weaker than that of CH4 under the same conditions, which contributes to the retention of CO2. There is a competitive sorption relationship between CH4 and CO2. The sorption amount and sorption heat of CH4 and CO2 are affected by the combination of pressure, temperature, density ratio, pore size, and mineral type. The adsorption capacity of CO2 is much higher than that of CH4. When sorption conditions are more favorable, the adsorption difference between CH4 and CO2 will become larger. In shale nanopores, CO2 can replace CH4 that is adsorbed on the pore surface to improve shale gas recovery.

Removal of phosphates using eggshells and calcined eggshells in high phosphate solutions

This study was conducted to evaluate the phosphate sorption properties of eggshell (ES) and calcined ESs (C-ESs) in a high-concentration phosphate solution. The C-ESs yield decreased rapidly at 900 °C, indicating that the CaCO3 constituting the ES was converted to CaO by the high calcination temperature. The optimum calcination temperature for phosphate removal using C-ES was 900 °C. The actual sorption amount of phosphate by ES and C-ES900 was in agreement with the Langmuir isothermal sorption equation, and the maximum sorption capacities derived from this equation were 178.6 and 270.3 mg/g, respectively. The sorption rate of phosphate by ES and C-ES900 was divided into two stages: an initial fast sorption stage, followed by a slow sorption stage. The sorption of phosphate by ES was dominantly influenced by the initial pH and salt concentration, whereas C-ES900 exhibited a constant sorption capacity regardless of environmental changes. The SEM–EDS and XRD results demonstrated that phosphate was successfully adsorbed on the ES and C-SE900 surfaces. In this study, it was found that the sorption of phosphate by ES occurred via ion exchange and precipitation reactions and that the sorption of phosphate by C-ES900 was dominantly affected by precipitation. Above all, C-ES can be applied as an effective adsorbent for removing high concentrations of phosphate under a wide range of environmental conditions.

High hexane sorption capacity of loosely crosslinked PDMS rubbers at low temperatures: Macromolecular and physicochemical elucidation for VOC recovery

A series of soft polydimethylsiloxane (PDMS) rubbers was obtained by diluting reaction mixtures of a PDMS macromer and a crosslinker with an organic solvent. The degree of swelling of the softest rubber was 600 wt% when immersed in pure hexane at room temperature. From the Flory–Huggins equations, the free energy change for hexane sorption per 1 g rubber was calculated to be −7.4 J g−1 and the entropy contribution of the polymer chains was 1.6 J g−1 larger than that of the conventional PDMS rubber. The loosely crosslinked PDMS rubber could sorb 776 mg g−1 of hexane at 298 K and 606 mg g−1 at 195 K. The latter value was 4.4 times larger than that of the conventional PDMS rubber. At a low pressure of 23 Pa, the PDMS rubber sorbed a 3500-fold greater amount of hexane at 195 K, as compared with the value at 298 K. This high sorption amount is because the expansion energy of such soft PDMS rubber is small. The sorption heat of the loosely crosslinked PDMS rubber was 30.3 kJ mol−1 when calculated from the Clausius–Clapeyron equation. This value is substantially smaller than that of commercial activated carbon (75 kJ mol−1). Unlike activated carbon, PDMS rubber is insensitive to water and selectively sorbs VOCs even under a saturated humidity. Because of the large swelling potential and small sorption/desorption heat, the loosely crosslinked PDMS rubber will be an indispensable sorbent for the recovery of flammable gasses such as alkane and iso-alkane VOCs in the chemical and oil and gas industries.

Effect of calcination temperature on geopolymer for the adsorption of cesium

The effect of calcination on geopolymer for the adsorption of cesium and related change of microstructure were explored. The sorption results indicated that the cesium sorption amounts of geopolymers after calcination dramatically decreased. However, the specific surface areas of accordingly calcined geopolymers increased significantly. Aluminum tetrahedrons are the source of negative charges for the adsorption of cesium. It was found that approximately 10% of tetrahedrally coordinated aluminum was transformed to penta-coordinated aluminum and hexa-coordinated aluminum after thermal treatment. Furthermore, approximately 10% of aluminum on the surface of calcined geopolymers decreased compared to raw geopolymer. Therefore, calcination has a great influence on the cesium sorption due to the decrease of aluminum tetrahedrons on the surface of geopolymer.

Characterization of ultrasonic induced damage on multi-scale pore/fracture in coal using gas sorption and μ-CT 3D reconstruction

Ultrasonic physical stimulation is a promising approach of coalbed methane enhancement recovery. This study is devoted to quantitatively characterizing the damage of multi-scale pores and fractures in coal induced by power ultrasonic stimulation using the gas sorption and CT image-based 3D reconstruction. The gas sorption tests show that the ultrasound treatment (3 kW, 25 Hz, 2 h) increased the maximum N2 sorption quantities (by 75.44 %–111.8 %), the average pore diameter by 12.15 %–20.81 %, and the pore surface area (by 30.99 %–56.02 %) in the tested coal. The mesopore volumes increase by 16.46 %–79.15 %, and the macropore volumes increase by 2.38 %–14.82 % after the ultrasound treatment, which reveals that the ultrasound implemented in this study is more efficient for structure modification in pore with scale of 2–50 nm. The CT image-based characterization shows that fracture volume increased by 8.11 %–11.81 %, and the fracture surface increased by 13.92 % −21.63 %, and the average equivalent diameter increased by 6.76 %–10.74 %, and the porosity increased by 8.1 %–11.86 % for the tested coal subjected to ultrasound treatment. Based on the pore network model, the fracture connectivity was quantitatively analyzed, and it shows that pore throat number increased by 17.62 %–45.76 %, and the average equal radius of pore throat increased by 3.86 %–4.83 %. The proportion of connected fractures in the total fractures was increased by a maximum of 12.78 % in the tested coal after ultrasound treatment. The results show that ultrasound stimulation can significantly improve the multi-scale structure of pores and fractures of coal, which will promote gas desorption, diffusive and Darcian flow flux in coal seam, and enhance coalbed methane production.

Comparative study of divalent cation sorption on titania nanotubes using Co2+, Ni2+, Zn2+, and Sr2+

Developing environmental purification techniques for water resources is important for realising a sustainable society. Inorganic ion-exchanger is one of the research themes in technological development, particularly titania nanotubes (TNTs), which have been studied for the removal of cationic heavy metals and radionuclides. Although many studies have reported the adsorption properties of TNTs, the sorption behaviour and state of intercalated cations in the structure are still unclear. In this study, the sorption properties of Co2+, Ni2+, Zn2+, and Sr2+ on TNTs were investigated using the equilibrium isotherms, kinetics and detailed analysis of residues under simple batch conditions. The sorption isotherms of cations on TNTs were fitted with the Langmuir model, and the maximum sorption amount (Qmax) was in the order of Sr2+ (1.13 mmol/g) > Zn2+ (0.99 mmol/g) > Co2+ (0.85 mmol/g) > Ni2+ (0.78 mmol/g). The sorption kinetics data fitted well with pseudo second-order model. The X-ray analysis indicated that the Sr2+ sorption on TNTs resulted from the ion-exchange and formation of carbonate compounds. In contrast, the Co2+, Ni2+, and Zn2+ ions were estimated to be incorporated in an ionic state in the TNT interlayer by ion-exchange with Na+ and H+ via chelation with surface hydroxyl groups on TNTs. These results indicate that the crystallographic properties of TNTs, ionic size, and chemical property of the target cation, and reactivity with carbonic acid are important factors to consider in the design of water purification systems using TNTs.

Preparation of MnOx-Modified Biochar and Its Removal Mechanism for Cr(VI) in Aqueous Solution

Biochar (BC) is considered to be a great potential adsorbent to remove various contaminants, but the sorption capacity for chromium (Cr) is predominantly limited for the net negative charge. In this study, BC from rice husk was impregnated with Mn(NO3)2 solution to synthesize MnOx-modified BC (MnOBCs) for enhancing Cr(VI) removal in an aqueous solution. MnOBCs were characterized, and MnOx (manganese ore) was found to be the dominant crystal in MnOBCs. Batch sorption and kinetic experiments combined with spectral analysis were carried out to elucidate the sorption capacity and mechanisms of Cr(VI) sorption onto BC and MnOBCs. Results showed that the sorption kinetic process fitted to the Elovich model, and the modification enhanced the sorption capacity of Cr(VI) on BC. Compared to ion strength, pH is the main control factor for Cr(VI) fixed on BC and MnOBCs, and the sorption amount decreased with the pH value increasing. Moreover, X-ray photoelectron spectroscopy results showed that the proportion of Mn(II) decreased from 33.59% to 8.33%, and that of Mn(VI) increased from 30.58% to 52.72% after Cr(VI) sorption on MnOBCs. Meanwhile, the reduction reaction of Cr(VI) occurred during the sorption process on the BC and MnOBCs surface, and the reduction reaction was more obvious on the MnOBCs surface. MnOx loaded in BC can enhance the electrostatic attraction and redox capacity, which can improve the removal of Cr(VI) in an aqueous solution. This study provides information on the sorption and redox of Cr(VI) on BC, and allows us to better understand the mechanism of Cr(VI) removal in solutions by MnOBCs.

Comparison of the performance of hydrochar, raw biomass, and pyrochar as precursors to prepare porous biochar for the efficient sorption of phthalate esters

In this study, three high-performance porous biochars were synthesized by the cocarbonization of Pistia stratiotes-derived precursors (raw biomass, hydrochar and pyrochar) with potassium hydroxide and utilized for the sorption of diethyl phthalate from aqueous solution. The developed pore structure, surface functional groups, high hydrophobicity characteristic and graphene structure of porous biochars contributed to the excellent sorption quantity of up to 813 mg g−1 (Ce, 25 mg L−1). Among the three precursors, hydrochar-derived porous biochar showed better properties in terms of its specific surface area and hydrophobicity, and it displayed the highest sorption capacity. The sorption kinetics and isotherm experiments confirmed that pore filling and partitioning dominated the sorption capacity while the mass transfer, hydrogen bonding and π-π stacking in the hydrochar limited the sorption rate. This finding helped to propose a feasible method for the efficient utilization of invasive aquatic plants and provided novel insight into the selection of precursors for preparing porous biochars.

Sorption of selected pharmaceutical compounds on polyethylene microplastics: Roles of pH, aging, and competitive sorption

Microplastics (MPs) as the carrier of pharmaceuticals in aquatic environments have been concerned in recent years. However, the influences of environmental factors on the sorption of pharmaceuticals onto MPs, particularly the effect of the simultaneous sorption by MPs of different pharmaceuticals in multi-solute systems are still unclear. This study investigated the influences of pH, aging of MPs, and competition of pharmaceuticals on the sorptions of sulfamethoxazole (SMX), propranolol (PRP), and sertraline (SER) onto polyethylene MPs. In the 96 h pH-dependent experiments, the sorptions of the three pharmaceuticals were mainly driven by hydrophobic interaction. Besides, the ionization states of the three pharmaceuticals varied with the pH ranging from 2.00 to 12.00, and electrostatic interaction would affect the sorption affinities of the pharmaceuticals in different ionization states. In the aged MPs experiments, the MPs aged by UV irradiation showed a stronger sorption capacity than the pristine ones. Across the MPs under different UV irradiation durations, the 6 d aged MPs showed the highest sorption percentages of 23.0% and 17.6% for SER and PRP, respectively; for SMX, the highest sorption percentage of 5.4% was recorded with the 10 d aged MPs. In the multi-solute systems, the sorption kinetics of the three pharmaceuticals fit well with the pseudo-second-order model. The sorption quantities of the three pharmaceuticals onto MPs followed the order of SER cations (18.70 μg g−1) > SMX anions (7.83 μg g−1) > PRP cations (3.80 μg g−1) at pH 7.00. The good fitting of the Freundlich model suggested a multilayer sorption of the three pharmaceuticals onto MPs. The SER with higher hydrophobicity would preferentially be adsorbed onto MPs and influenced the subsequently sorption processes of the other pharmaceuticals via electrostatic interactions. This may change the environmental fate of the contaminants, which should be carefully considered in future work.

Assisting the carbonization of biowaste with potassium formate to fabricate oxygen-doped porous biochar sorbents for removing organic pollutant from aqueous solution

In contrast to the efforts dedicated to applying porous biochars in environmental remediation, the search for green synthesis methods, which are crucial for industrialized production, is often neglected. Herein, oxygen-doped porous biochars were prepared for the first time by the assisted carbonization of hydrochar with a novel noncorrosive activator, potassium formate, and these biochars displayed a porous structure with large amounts of micropores (surface area: 1242 ∼ 1386 m2 g−1). Interestingly, the biochars contained an abundance of oxygen element (20 ∼ 26%), which formed many functional groups. Through sorption experiments, it was demonstrated that the oxygen-doped porous biochars were excellent sorbents for diethyl phthalate, and maximum sorption quantity reached 453 mg g−1. Monolayer sorption by pore filling, hydrogen bonding, electrostatic interaction and π-π stacking was the potential mechanism. This finding indicated that potassium formate was promising as an activator to greenly convert biowaste into advanced biochars for removing organic pollutants from aqueous solutions.

Effect of Biochar Addition on Phosphorus Adsorption Characteristics of Red Soil

Phosphorus (P) sorption by red soil is strong due to its acidic pH and high content of metal oxides. Biochar addition may increase the availability of red soil P by altering P sorption characteristics. This study examined the influences of doping ratios of the biochar, phosphate concentration, solution pH, and biochar-derived dissolved black carbon (DBC) on P sorption in red soil. The specific sorption mechanisms were explored using 3D fluorescence spectroscopy, infrared spectroscopy, and zeta potential analysis. The results show that the bioavailable P content in the biochar-amended red soil increased to 1.92 mg kg−1, which is an increase of 255% compared with the original red soil. With the increase in the doping ratio of biochar, the maximum sorption amount of P initially decreased and then increased. Moreover, the pH value and the content of the dissolved organic carbon (DOC) of the red soil were effectively elevated by biochar addition. The increase in the DOC content is likely caused by the DBC released from biochar. As the soil pH value increased, the amount of P sorption was reduced due to electrostatic repulsion. P sorption by the red soil decreased with the increasing DBC concentration. The humic acid-like substances in DBC can compete with phosphate for soil sorption sites, leading to a decrease in P absorption. This study demonstrates that the addition of biochar affects P sorption of the red soil mainly by changing its physicochemical properties or by releasing DBC to occupy the sorption sites.

Contribution of different mechanisms to Pb2+ and Cd2+ sorption on magnetic wheat straw biochars: Impact of pyrolysis temperature and DOM in biochar

This work quantitatively studied the sorption of Pb2+ and Cd2+ on magnetic biochars (MBCs) pyrolyzed at temperatures of 300, 500 and 700 °C and the effect of biochar-derived dissolved organic matter (BDOM) on Pb2+ and Cd2+ sorption. Surface characteristics of the MBCs before and after sorption were analyzed using Boehm titration and various spectroscopic techniques. For Pb2+, with increasing pyrolysis temperature, the sorption amounts by precipitation and coordination with π electrons increased from 63.5 to 109.3 mg/g and from 27.0 to 84.9 mg/g, respectively. While the sorption amount by complexation decreased from 34.5 to 16.5 mg/g. The contribution of precipitation (45.9–52.5%) and coordination with π electrons (19.5–39.1%) increased with increasing pyrolysis temperature, while contribution of complexation (7.6–24.9%) decreased. Increased ash content and aromaticity with pyrolysis temperature played the key roles in the change of Pb2+ sorption. The ion exchange and precipitation mechanisms dominated Cd2+ sorption on MBCs. Their respective sorption amounts were in the ranges of 5.08–10.36 and 1.31–9.82 mg/g, accounting for 48.8–72.5% and 18.7–46.3% of the total sorption, respectively. The change of ion-exchangeable sites on minerals with pyrolysis temperature is the main reason influencing the sorption via ion exchange for Cd2+. Unlike MBC500 and MBC700, removing BDOM from pristine biochar of MBC300 enhanced the total amounts of Pb2+ and Cd2+ sorption by 1.2 and 3.6 times, respectively, which was attributed to the enhanced sorption via ion exchange, precipitation and complexation for Pb2+ and enhanced sorption via ion exchange and precipitation for Cd2+. Therefore, the DOM-removed low-temperature MBC is a promising sorbent for treating heavy metal polluted waters.

Emergent Behavior at the Calcite–Water Interface during Reactive Transport in a Simple Microfluidic Channel

Geochemical reactive transport processes in natural mineral–fluid systems may produce a wide array of emergent phenomena that are difficult to predict from basic principles and to reproduce in model systems. Here, we present experimental results obtained from a simple microfluidic system with which we explored the consequences of reacting the calcite (104) cleavage surface with an acidic Pb-bearing solution (pH = 3.5, [Pb]total = 5 mM) as a function of flow rate. This system is relevant to passive remediation systems for Pb-rich acid mine drainage. We observed periodic banding in the amounts of Pb sorption at flow velocities ≥926 μm s–1, where the band spacing was spatially correlated with the amount of calcite dissolution and the development of micropyramidal topography on the calcite (104) surface. The equivalent coverage of Pb deposited in these Pb-rich bands was at least several monolayers per unit cell, yet there was no evidence for precipitation of any secondary Pb phase implying incorporation of Pb within the near-surface calcite lattice. We also observed spatial variations in nucleation and growth of euhedral secondary Pb-carbonate minerals hydrocerusite and cerussite at flow rates ≤278 μm s–1. These findings demonstrate potential for exploiting the rich phenomenology afforded by the interplay among transport phenomena and chemical kinetics in experimental systems designed to yield deeper insights into geochemical self-organization.

Sorption behavior of Pb(II) onto polyvinyl chloride microplastics affects the formation and ecological functions of microbial biofilms

Microplastics (MPs) are regarded as transport media for heavy metals in aquatic systems, whereas the effects of the heavy metal-enriched MPs on microbial biofilms are still unclear. In this study, Pb(II) sorption onto polyvinyl chloride (PVC) MPs and its effects on the formation and ecological functions of microbial biofilms were investigated. The results showed that the interaction between Pb(II) and PVC MPs was dominated by physisorption. The maximum sorption amount reached 1.25 mg/g. Afterward, microbial biofilms were exposed to the Pb(II)-enriched PVC particles. It is suggested that Pb(II)-enriched PVC exposure reduced productivities of polysaccharides and proteins in extracellular polymeric substances, which restricted the formation of microbial biofilms. Meanwhile, microbial community structure was reassembled accompanying the decline of capacities for nitrate and phosphate removal. Therefore, this study examines the ecological risk associated with the heavy metal-enriched MPs that can adversely affect microbial biofilms.

The Impact of the Type and Concentration of Different Additives on the Water Sorption of Denture Base Resin

Aims: To evaluate the effect of incorporation of different types and concentrations of additives on water sorption denture base acrylic resin. Materials and Methods: Heat polymerized acrylic resin samples were prepared and divided into two groups; control group (without additives) and experimental group (with additives). The additives were three types of polymers (Styrene Butadiene Rubber (SBR), Poly Ethylene Glycol (PE) and Poly Urethane (PU)) being added with three concentrations 1%, 3% and 5%. SPSS Version 19 was used to analyze and to assess the results of the present study by mean of Descriptive statistics, analysis of Variance (ANOVA) and Duncan multiple range tests at p ≤0.05. Results: The results reveal that there is statistically significant reduction in the amount of water sorption of experimental group as compared to that of control group at p≤ 0.05. The reduction in the amount of water sorption of experimental group is directly proportional to the concentration of incorporate additives. Conclusions: Water sorption of experimental group is less than that of control group. The additives produce statistically significant reduction in the amount of absorbed water of denture base resin and this reduction was directly proportional to the concentration additives material being used.

Development and Characterization of Composite Desiccant Impregnated with LiCl for Thermoelectric Dehumidifier (TED)

Aqueous salt solutions (LiCl) were impregnated into a porous host matrix to create composite desiccant materials (silica gel). The authors of this paper fabricated and analyzed composite desiccant-coated aluminum sheets (DCAS) with varying LiCl mass concentrations. Nitrogen sorption results revealed that the Brunauer–Emmett–Teller (BET) surface area and pore volume of the composite desiccant-coated aluminum sheets decreased. Furthermore, composite DCAS had lower nitrogen sorption than silica-gel-coated aluminum sheets (SGCAS). According to the results, the composite DCAS had the highest thermal conductivity, measuring 6.1 Wm−1 K−1, doubling that of the SGCAS. For evaluating sorption kinetics, the linear driving force model (LDF) was used, and composite DCAS showed greater dynamic sorption quantities and sorption rate coefficients than SGCAS. Furthermore, three different moisture sorption isotherm models were used to fit the experimental results: the Brunauer–Emmett–Teller (BET) model, the Guggenheim–Anderson–Boer (GAB) model, and the double log polynomial (DLP) model. The DLP model was shown to be the best model for predicting the moisture sorption isotherms of DCAS. Additionally, the composite desiccant-coated heat sink (DCHS) of the thermoelectric dehumidifier (TED) was evaluated and compared to silica gel in terms of dehumidification capacity. According to the findings, the outlet air humidity ratio of the composite DCHS reached a minimum of 10.23 g kg−1, and the dehumidification capacity was 0.117 kg h−1 when the input electrical voltage was kept at 9 V.

SORPTION OF FERUM IONS ON NATURAL AND MODIFIED CLINOPTYLOLITE. INFLUENCE OF OXYDANTS

The health of the population depends on the state of the environment, so the study of opportunities to improve the condition of water, air and soil does not lose its actual.
 The presence of substances in waters in concentrations is higher than the maximum permissible concentration can be caused by both human economic activity and the peculiarities of the geological structure of the lithosphere of the region. For example, high iron content is observed in the natural waters of many regions of the world. Although iron is an important element in human life, its excess in the body can cause many diseases.
 Removal of iron ions from water has a high cost, so reducing the cost of this process is an urgent issue. One of the options to reduce the cost of the process is to use natural zeolites, such as clinoptilolite. One of the largest deposits of clinoptilolite in Europe is located in the village Sokyrnytsia, Transcarpatian region.
 In this work, the sorption of iron ions on the natural clinoptilolite of the Sokyrnytsia deposit and its modified forms under static conditions has been studied. Any of the proposed modification methods has a positive effect on the sorption properties of clinoptilolite with respect to iron ions, the amount of Fe ions sorption increases for hydrogen form by 30%, ammonium form by 60% and sodium form by 65% are shown.
 The influence of oxidants (hydrogen peroxide) on the sorption of iron ions on clinoptilolite of the Sokyrnytsia deposit (Ukraine) has been studied. The significant influence of iron oxidation before sorption on the growth of its extraction from water by natural clinoptilolite is shown, which is confirmed by thermodynamic calculations performed by the semi-empirical method GFN2- xTB (density functional theory), which indicate that only ion exchange reaction involving Fe3+. And if the exchange ion is a Na+ ion, ion exchange sorption can occur with both Fe3+ and Fe2+.
 Isotherms of ion-exchange sorption of iron in the range of concentrations from 0.05 mmol/l to 1 mmol/l are well described by the Langmuir equation. Sorption isotherms in the coordinates 1 / A = f (1 / C) are linear.
 Keywords: clinoptilolite; iron; ion exchange; oxydants.

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C 2 H 2 /CO 2 Separation

Fluorous Metal–Organic Frameworks with Unique Cage-in-Cage Structures Featuring Fluorophilic Pore Surfaces for Efficient C ₂ H ₂ /CO ₂ Separation

Сорбционная способность гель-пленок функционализированной бактериальной целлюлозы по отношению к хлорамфениколу

Due to unique natural characteristics such as biocompatibility, nontoxicity, mechanical stability, and high moisture content, bacterial cellulose can be efficiently used for the production of new medical materials, including various wound dressings. Bacterial cellulose can be produced by bacteria of the genera Gluconaceto-bacter, Aerobacter, Rhizobium and others. Under static cultivation conditions, the producers form gel films of bacterial cellulose, which differ in their properties. Bacterial cellulose does not possess inherent antimicrobial activity; therefore, bacterial cellulose films must be further enhanced before they are used as medical materials. In order to improve the properties of BC, researchers use various modification methods to introduce antimicrobial activity. The main attention is paid to the post-synthetic modification: in this concept, in order to impart antimicrobial properties to bacterial cellulose it is saturated with antibiotics or other antibacterial and antifungal drugs. To improve the sorption properties, successful attempts were made to oxidize BC and then to saturate it with an antibiotic. The introduction of new reactive functional groups to the surface of bacterial cellulose fibers will make it possible to better control the sorption process and increase the saturation of films with antibacterial drugs. The purpose of this work was to determine the effect of bacterial cellulose treatment during oxidation in the TEMPO/NaClO/NaBr system on the properties of oxidized samples, i.e., an increase in the sorption capacity with respect to a biologically active compound. Films were obtained under conditions of stationary cultivation of the strain Gluconacetobacter hansenii GH 1/2008 (VKPM B-10547) on glucose and fructose carbon sources. Chloramphenicol, a broad-spectrum antibiotic, was chosen as a model antibiotic with which the films were saturated. The resulting films did not differ significantly in terms of thickness, water-holding capacity, and dry weight (see Table 1). Derivatives of BC gel films were obtained without destroying the native three-dimensional gel structure using an oxidative process catalyzed by the nitroxyl radical TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxyl). Depending on the oxidation conditions, a series of gel films functionalized with carboxyl groups (COOH) were obtained with a total content of COOH groups varying in a wide range from 0.041 to 0.219 mmol/g (see Fig. 2В). It was shown for the first time that the content of COOH groups depends on the quality of films synthesized on various carbon sources: the maximum degree of carboxylation was noted for films synthesized by G. hansenii on fructose, which is apparently associated with differences in the supramolecular structure of cellulose (see Fig.2B and 3). For the obtained gel films, the sorption capacity with respect to the antibacterial drug chloramphenicol (CP) was evaluated. A direct relationship was established between the sorption value and the amount of COOH groups in the films. The amount of sorption of the antibiotic depends on the degree of carboxylation of the sample (see table 3). Thus, the functionalization of the surface of bacterial cellulose gel films with carboxyl groups leads to an increase in their sorption properties. Indeed, the amount of antibiotic absorbed by the oxidized films is several times higher as opposed to the non-oxidized gel films. The obtained results demonstrate the benefits of carrying out the process of oxidation of bacterial cellulose films, increasing the degree of their saturation with antimicrobial agents and the possibility of their further use for medical purposes as a dressing material. The article contains 7 Figures, 3 Tables and 26 References.

Experimental and simulation investigations of the impact of polyacrylamide on CBM ad-/desorption

Slickwater is commonly used during hydraulic fracturing in coalbed gas well, which is often prepared with polyacrylamide as the friction reducer. To investigate the impact of polyacrylamide on CBM ad-/desorption after a fracturing operation, slickwater with different concentrations of polyacrylamide were prepared and used to treat Illinois coal samples. Both isothermal ad-/desorption experiments and molecular simulations were conducted to investigate the impact of slickwater. Nuclear magnetic resonance measurements were performed to analyse the evolution of surface functional groups of coal during slickwater treatment. The results show that there is no significant chemical reaction between the coal component and polyacrylamide. Because of the porosity of the polyacrylamide coating adhered onto the surface of the pore, polyacrylamide has a significant sorption capacity of methane. The methane sorption amount of the ‘coal-slickwater’ system is higher than that of raw coal. However, with the increase of the amount of residue entering the pores, the porous structure of the polyacrylamide coating becomes denser, blocking some pores and the pore surface area is reduced; thus, the overall sorption capacity of the ‘coal-polyacrylamide’ system decreases.