Dubinin-Radushkevich Equation Research Articles

Study of the adsorption of copper, nickel and zinc ions on a zeolite-containing sorbent synthesized from thermal power plant waste

The study investigated the possibility of using ash and slag waste from thermal power plants as an alternative raw material source to obtain an inexpensive zeolite-containing sorbent, which was synthesized by hydrothermal synthesis by adding 20% sodium hydroxide at a temperature of 120оC for 24 hours. Using X-ray diffraction, it was established that the synthesized material mainly consists of the framework aluminosilicate mineral hydrosodalite. Using the obtained material, the sorption of copper, zinc, and nickel cations from aqueous media was studied using the Langmuir, Freundlich, and Dubinin-Radushkevich models. The constants of these equations were determined, the values of the isobaric-isothermal potential and the free energy of ion adsorption were calculated. It has been established that the sorption of metal ions is of a physical nature. It was found that the Dubinin–Radushkevich equation better describes the process of adsorption of zinc and nickel, and the Langmuir equation better describes the sorption of copper ions. The decrease in the degree of affinity of sorbed ions to the surface of the synthesized zeolite-containing sorbent was determined as follows: . Thus, based on the obtained values of sorption of copper, zinc, and nickel ions, the fundamental possibility of using ash and slag waste as a raw material source for obtaining inexpensive and effective zeolite-containing sorbents for extracting the above metal ions from aqueous media was established.

The adsorption of dragon fruit (Hylocereus polyrhizus) pigments on chitin for food colorants

AbstractBACKGROUNDGrowing concern over the potential adverse health effects of synthetic colorants has led to a rising utilization of plant‐derived pigments within the food industry. Purple betacyanins from red dragon fruits (Hylocereus polyrhizus) have been subjected to an environmentally sustainable purification process for natural colorants.RESULTSThe violet‐hued pigments were absorbed onto preconditioned chitin material, a biodegraded polymer derived from shrimp shells. Liquid chromatographic–electrospray ionization–tandem mass spectrometric analysis was employed to analyze the betalain pigment composition in the raw fruit extract, making comparisons between the adsorbed supernatant and desorbed solutions. Fourier transform infrared analysis, optical microscopy, and scanning electron microscopy were conducted on the resin pre‐ and post‐adsorption stages, revealing distinctive infrared bands (RNHR, CO, CO, OH) indicative of betacyanin functional groups in the pigmented materials. The uniform adsorption of the colorant onto the adsorbents causes the intense purple color of the resin, with a maximum removal efficiency of 0.29 mg g−1. Adsorption data were subjected to various kinetic models, with the pseudo‐second‐order model demonstrating the optimal fit to the kinetic data (R2 = 0.97), while the Freundlich model proved most suitable for describing the sorption isotherm (R2 = 0.98). The adsorption energy, as determined by the Dubinin–Radushkevich equation, was 0.23 kJ mol−1, implying a physical adsorption mechanism on a heterogeneous surface.CONCLUSIONBetacyanins derived from red dragon fruits could be recovered for food colorants through chitin adsorption. This recovery mechanism is attributed to electrostatic interactions among the functional groups, including hydroxyl and carboxyl groups, and hydrogen bonds. © 2024 Society of Chemical Industry (SCI).

Applications of ion exchange resins in environmental remediation

AbstractThe presence of various types of contaminants such as heavy metals, emerging organic contaminants, pesticides, organic waste, organic dyes, radionuclide's, fluorides, etc. cause water pollution. These pollutants are of concern to engineers, environmentalists and scientists. Due to the lack of freshwater, it is very important to recycle the wastewater after treatment to remove organic contaminates and heavy metal pollutants. Chemical precipitation, ion exchange, adsorption, filtration via membranes, flocculation, coagulation, flotation, and electrochemical techniques are just a few of the methods used to eliminate contaminants from wastewater. The most popular and effective among these is the ion exchange process. New generation hybrid materials, inorganic three‐dimensional matrices and synthetic organic resins are some examples of the different types of ion exchange resins. Most investigations have found that pseudo‐first and second order kinetic studies are important in the contaminant removal process. The isotherm model, which also incorporates the Langmuir, Freundlich, Dubinin Radushkevich, and Temkin equations, proved appropriate for most of the research. For an example, orgnic polymeric materials can maximum uptake capacity of 4.28 mmolg‐1 Cr(VI) and 1.97 mmolg‐1 As(V) respectively. The effectiveness of ion exchanger and its current trends in various environmental applications have been the main topics of this review article.

Batch and Continuous Column Adsorption of p-Nitrophenol onto Activated Carbons with Different Particle Sizes

The study focused on investigating the solvent adsorption of p-Nitrophenol (PNP) onto activated carbons for wastewater treatment. It explored the influence of adsorbate concentration and adsorbent size on equilibrium isotherms and removal rates to develop efficient adsorption processes. The study examined adsorption isotherms under equilibrium conditions utilizing both the Langmuir and Double-Langmuir models and the Dubinin–Radushkevich equation. Remarkably, all the models demonstrated equally excellent fitting to the experimental data. Kinetics of PNP adsorption were investigated using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models. This provided insights into the dominant adsorption mechanism and mass transfer phenomena, aiding the design of efficient wastewater treatment processes. Strong correlations (correlation coefficients > 0.9) were found between the models and experimental data for three types of activated carbons under batch conditions. This validation enhances the reliability and applicability of the models, supporting their practical use. The study also observed a slight increase in maximum adsorption capacity (qmax) with decreasing particle size, although there is not a significant difference: 340, 350, and 365 mg·g−1, for CB-L, CB-M, and CB-S, respectively. This insight helps in selecting appropriate activated carbon for effective PNP removal, considering both adsorption capacity and particle size. Furthermore, the analysis of PNP adsorption under dynamic conditions in fixed-bed columns highlighted the significance of inlet velocity and carbon mass in determining breakthrough time, with particle size playing a secondary role. This information aids in optimizing the design and operation of fixed-bed adsorption systems for efficient PNP removal. In summary, this study’s significant contributions lie in enhancing our understanding of PNP adsorption in wastewater treatment. By investigating equilibrium isotherms, kinetics, and mass transfer phenomena, it provides validated models, insights into adsorption capacity and particle size, and practical guidance for dynamic adsorption systems. These findings contribute to the development of efficient and sustainable wastewater treatment methods.

Extraction of organic pollutants from wastewater to improve the sanitary reliability of water bodies

. The purpose of this study was to evaluate the principal possibility of increasing the adsorption of hydroxybenzene by the carbon sorbent Purolate-standard by a combination of reactive and thermal oxidative modification. The control of the hydroxybenzene concentration from the solution was determined by spectrophotometry. The possibility of increasing the adsorption capacity by means of combined oxidative modification (reagent oxidation followed by heat treatment) of carbon material was considered. The characteristics of the extraction process were established on the basis of Langmuir and Dubinin-Radushkevich models. Analysis of the porous structure and functional groups of the surface of anthracite and its modified samples showed changes in the above parameters. The processing of experimental data in the coordinates of the Langmuir and Dubinin-Radushkevich equations showed a satisfactory correlation, which allows us to calculate the values: Gibbs energy, the maximum adsorption capacity of the monolayer, the adsorption equilibrium constant, the maximum volume of the adsorption space. The obtained values allow us to establish the adsorption mechanism, both on the feedstock and on the processed samples. It was found that the oxidation of 2 % ammonium salt of peroxodiseric acid with subsequent heating at 200°C reduced the adsorption of phenol. Treatment of the adsorbent with 5 % ammonium salt of peroxodiseric acid with heating at 250°C slightly increased the adsorption of phenol. The use of the studied oxidants to increase the adsorption capacity of anthracite did not give the expected result with respect to hydroxybenzene. Sorption on macroporous carbon materials with preliminary modification can be recommended as a promising direction in relation to organic pollutants. The study of the adsorption of hydroxybenzene on anthracite of the Purolate-standard brand was carried out under static conditions. The authors have proved that reducing the sanitary reliability of reservoirs is possible by means of reducing the level of contamination of wastewater. The mechanism of adsorption of hydroxybenzene on sorbents modified by a combined method under different regimes has been studied for the first time, which is a scientific novelty of the study.

Optimization Study of the Capacity of Chlorella vulgaris as a Potential Bio-Remediator for the Bio-Adsorption of Arsenic (III) from Aquatic Environments.

This study examined the ability of the green microalgae Chlorella vulgaris to remove arsenic from aqueous solutions. A series of studies was conducted to determine the optimal conditions for biological arsenic elimination, including biomass amount, incubation time, initial arsenic level, and pH values. At 76 min, pH 6, 50 mgL-1 metal concentration, and 1 gL-1 bio-adsorbent dosage, the maximum removal of arsenic from an aqueous solution was 93%. The uptake of As (III) ions by C. vulgaris reached an equilibrium at 76 min of bio-adsorption. The maximum adsorptive rate of arsenic (III) by C. vulgaris was 55 mg/gm. The Langmuir, Freundlich, and Dubinin-Radushkevich equations were used to fit the experimental data. The best theoretical isotherm of Langmuir, Freundlich, or/and Dubinin-Radushkevich for arsenic bio-adsorption by Chlorella vulgaris was determined. To choose the best theoretical isotherm, the coefficient of correlation was used. The data on absorption appeared to be linearly consistent with the Langmuir (qmax = 45 mgg-1; R2 = 0.9894), Freundlich (kf = 1.44; R2 = 0.7227), and Dubinin-Radushkevich (qD-R = 8.7 mg/g; R2 = 0.951) isotherms. The Langmuir and Dubinin-Radushkevich isotherms were both good two-parameter isotherms. In general, Langmuir was demonstrated to be the most accurate model for As (III) bio-adsorption on the bio-adsorbent. Maximum bio-adsorption values and a good correlation coefficient were observed for the first-order kinetic model, indicating that it was the best fitting model and significant in describing the arsenic (III) adsorption process. SEM micrographs of treated and untreated algal cells revealed that ions adsorbed on the algal cell's surface. A Fourier-transform infrared spectrophotometer (FTIR) was used to analyze the functional groups in algal cells, such as the carboxyl group, hydroxyl, amines, and amides, which aided in the bio-adsorption process. Thus, C. vulgaris has great potential and can be found in eco-friendly biomaterials capable of adsorbing arsenic contaminants from water sources.

CARBON FIBERS IN THE ADSORPTION PROCESSES

The parameters of the porous structure of carbon fiber sorbents based on polyacrylonitrile fiber of different activation have been studied. Fibrous carbon sorbents for the adsorption of water-soluble organic compounds have been analyzed. Sorption isotherms were constructed in the coordinates of the Langmuir equation of the studied substances on non-activated and activated carbon fibers, as well as Brunauer-Emmett- Teller isotherms, which allow one to reliably calculate the specific surface area of a carbon fiber sorbent. The sorption isotherms are satisfactorily described by the Freundlich equation. The selectivity of adsorption with a description of adsorption isotherms from solutions of organic substances is considered. It is noted that the linear form of the dependence of the Dubinin-Radushkevich isotherms makes it possible to determine the limiting value of adsorption. The parameters of the «carbon-fiber sorbent-sorbate» systems were calculated using the Dubinin-Radushkevich and Brunauer-Emmett-Teller equations. It is shown that the Dubinin-Radushkevich equations for the analysis of adsorption in the liquid phase make it possible to describe a wider range of relative concentrations than the Langmuir, Frendlich and Brunauer-Emmett-Teller equations. It is shown that the adsorption isotherms for the studied sorbents depend on temperature, and the characteristic curves are not invariant, which does not make it impossible to use the Dubinin-Radushkevich equation to describe adsorption in the liquid phase for the analysis of experimental data on adsorption isotherms. The values of the sorption capacity for extracting organic substances using a carbon fiber sorbent are analyzed. The efficiency of using carbon sorbent based on polyacrylonitrile fiber as a sorbent of organic compounds is shown. For citation: Menshova I.I., Averina Yu.M., Zabolotnaya E. Carbon fibers in the adsorption processes. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 3. P. 52-58. DOI: 10.6060/ivkkt.20236603.6715.

Performance investigations of carbon based consolidated composite adsorbents effective for adsorption cooling systems

• Composite adsorbent with activated carbon has been developed and characterized. • Presence of metal organic framework improves surface properties of composites. • Expanded graphite powder in the composites improves thermal conductivity. • Volumetric uptake of newly composite is 24.38% more than activated carbon. This paper proposes a new composite adsorbent synthesized by employing activated carbon as the parent element with expanded natural graphite and metal organic framework as secondary elements. The binder used in the composite is polyvinylpyrrolidone. The parameters such as surface area, pore volume, thermal conductivity, and adsorption/desorption of adsorbate are studied in depth for the proposed combinations. The characteristic study suggests Composite B, having a material composition of activated carbon 70 % in weight, expanded graphite powder 10 % and metal organic framework 10 % and binder 10 % as the favourable choice for adsorption cooling system. The surface area and pore volume of the composite B is determined to be 1597 ± 26 m 2 /g and 0.93 cm 3 g −1 , respectively. The thermal conductivity of the composite B is determined to be 0.29 Wm -1 K −1 , which is 55.17 % greater than the parent material activated carbon at atmospheric temperature. The Dubinin-Radushkevich equation has been used to fit adsorption uptake measurement, and it is found that the maximum adsorption of the composite B as 0.983. A performance study of a single bed adsorption cooling system with a cooling capacity of 600 W has been conducted with activated carbon/composite B as adsorbent and ethanol as the refrigerant. The performance parameters such as the coefficient of performance and specific cooling power of the adsorption cooling system using consolidated adsorbent is obtained as 0.61 and 198 Wkg −1 , respectively. The coefficient of performance obtained by using the consolidated adsorbent/ethanol is 21.31 % higher than the system using activated carbon/ethanol as the working pair. The results shows that the suggested composite material's enhanced surface area, pore volume, and thermal conductivity can improve the performance of the adsorption cooling system and can be employed as a viable alternative for conventional adsorbents.

Synthesis, characterization, antimicrobial and photocatalytic properties of nano-silver-doped flax fibers

AbstractIn the present study, the nano-silver-doped flax fibers (NAgDFF) are prepared in two steps. In the first step, oxidation of the flax fibers is performed by potassium periodate to form dialdehyde cellulose (DAC) and the second step is the reduction of silver ions by DAC. A series of characterization techniques of the photocatalyst NAgDFF was carried out using scanning electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption isotherm, thermogravimetric analysis and energy-dispersive X-ray spectroscopy. The dye degradation potential of NAgDFF for methylene blue (MB), crystal violet (CV) and brilliant green (BG) (individually or mixture) was investigated using batch and column tests. The degradation efficiency was studied under optimized conditions such as pH (5.0), dye initial concentrations (100 ppm for MB and BG, and 150 ppm for CV), contact time (3.0 h), photocatalyst NAgDFF dose (0.08 g) and temperature (25° C). The maximum degradation efficiency of NAgDFF for MB, CV and BG is 64.75, 94.98 and 63.87 (mg/g), respectively. The kinetic studies show that the experimental data match well with the pseudo-second-order kinetic model. Furthermore, equilibrium isotherm data were analyzed according to Langmuir, Freundlich and Dubinin–Radushkevich equations. The thermodynamic parameters for the adsorption processes of cationic dyes on the NAgDFF fibers were also calculated; the negative value of ΔG° indicated the spontaneous nature of sorption. NAgDFF fibers were successfully applied for photodegradation of the investigated cationic dyes from different samples. The study was extended to investigate the biological activity of newly synthesized NAgDFF against various microorganisms.

PREPARATION AND PERFORMANCE OF MAGNETIC ZIRCONIUM-IRON OXIDE NANOPARTICLES LOADED ON PALYGORSKITE IN THE ADSORPTION OF PHOSPHATE FROM WATER

Magnetic zirconium-iron oxide nanoparticles loaded on palygorskite as a low-cost adsorbent was produced by one-step co-precipitation technique and its properties for phosphate adsorption were overall investigated. The Brunauer Emmett Teller (BET) specific surface area analysis, scanning electron microscopy (SEM), thermo gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the adsorbent and evaluate the adsorption interactions. The influences of pH, ionic strength and coexisting ions on phosphate adsorption were measured with a discussion of the adsorption mechanism. Results indicated that no very noticeable changes on the surface properties, structure and phosphate adsorption capacity be found for the magnetic zirconium-iron oxide nanoparticles loaded on palygorskite or not. The adsorption kinetics fitted to the pseudo-second-order model and adsorption isotherm followed Langmuir equation and Dubinin-Radushkevich equation. The phosphate adsorption was slightly affected by ionic strength and highly dependent on pH, i.e. increasing pH sharply restrained adsorption under neutral and alkaline conditions. The surface OH groups in the adsorbent processed an important role in adsorption and the adsorption mechanism conformed to ion exchange and complex. The adsorbent could be conveniently regenerated and effectively reused.

Adsorption of Fluoride from Water Using Aluminum Coated Sand: Kinetics, Equilibrium, Effect of pH, and Coexisting Ions

An aluminum coated sand (AlCS) was evaluated as a metal oxide adsorbent for adsorption and removal of fluoride from water using a low-cost adsorbent with potential application in continuous flow adsorber systems. Surface characterization of the AlCS sorbent was performed using TEM, SEM/EDX, XRD and BET. The AlCS sorbent contained mostly amorphous aluminum oxides based on adsorbent characterization results. Favorable adsorption of fluoride onto the AlCS sorbent occurred according to the Langmuir and Freundlich adsorption equations, while physical adsorption of fluoride onto the AlCS sorbent was observed based on results from the Dubinin-Radushkevich equation. Fluoride adsorption onto the AlCS sorbent followed pseudo-second order kinetics, while surface charge analysis indicated a pHPZC of 7.1 for the AlCS sorbent. Effective fluoride removal occurred over a broad pH range from 3 to 11 with a maximum fluoride removal observed at pH 4 to 5. The effect of co-existing ions in water resulted in a decrease in fluoride uptake in the presence of bicarbonate, while resulting in an increase in fluoride uptake in the presence of calcium. The AlCS sorbent was a low-cost and sustainable adsorbent for effective adsorption and rapid removal of fluoride from water within an hour.

Сорбционно-десорбционные свойства нанокомпозита оксид графена/полигидрохинон при извлечении редкоземельного элемента Sm (III) из уксусно-ацетатных буферных систем

The paper describes the extraction of the rare earth element Sm3+ from aqueous buffer systems by a graphene-based nanostructured composite, modified using an organic polymer – polyhydroquinone. The authors determined the important parameters of the sorption-desorption of Sm3+ ions on a new nanocomposite “graphene oxide/polyhydroquinone” during a batch test, such as: initial concentration, the sorbent weight, pH of the solution, sorption rate constants, maximum sorption capacity of the nanocomposite, percentage sorption and desorption, entropy and enthalpy of the Sm3+ extraction process. The kinetic, isothermal and thermodynamic dependences allowed to propose of the Sm3+ ions adsorption mechanisms. The kinetic data were processed by pseudo-first- and second-order, Elovich and intraparticle diffusion models, and adsorption isotherms — using the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich equations. As a result of kinetic studies, the contact time of the samarium adsorption was determined — 15 min, while the sorption capacity was 100 mg·g–1. It was found that the absorption of Sm3+ ions proceeds by a mixed diffusion mechanism and limited by the interaction “samarium ions : sorbent functional groups”. According to the Langmuir model, the maximum sorbent sorption capacity was 333.3 mg·g–1. Thus, the high efficiency of the developed graphene oxide/polyhydroquinone nanocomposite for purification of aqueous media from rare earth elements was confirmed.

Novel fluorescent microcapsules based on sporopollenin for removal and detection of Cu (II) ions in aqueous solutions: Eco-friendly design, fully characterized, photophysical&physicochemical data

Sporopollenin is a natural substance found in plant walls and is highly resistant to external factors. In this paper, we designed an eco-friendly hybrid material, Sp-EDA-BODIPY , based on sporopollenin microcapsule and BODIPY to remove and detect metal ions. The fluorescent surface was fully characterized with various methods such as XRD, SEM, FT-IR, fluorescence spectroscopy. The fluorescent microcapsule sensor showed fluorometrically a remarkable quenching effect in the presence of Cu (II) ion, via the complexation mechanism that LOD it was calculated as 0.773 μM. As a result of the competing ion experiments, Sp-EDA-BODIPY also has a high selective for Cu (II) ion toward another the studied metal ions. Otherwise, we also calculated the adsorption capacities and the maximum isotherm parameters and from the Freundlich, Langmuir, and Dubinin-Radushkevich equations for the removal of Cu (II) with Sp-EDA-BODIPY fluorescent microcapsule. The maximum adsorption capacities of Cu (II) on Sp-EDA-BODIPY were calculated to be 28.65, 31.25, 34.02, and 37.74 mg/g at different temperatures (298, 308, 318, and 328 K), respectively. The adsorption experimental results were closer to Langmuir adsorption isotherm and pseudo-second-order models. Thermodynamic data showed that the adsorption process was endothermic, possible, and spontaneous. • In this paper, we successfully obtained a fluorescent microcapsule sensor, Sp-EDA-BODIPY . • The Sp-EDA-BODIPY was used for the detection and removal of Cu (II) ions. • The Cu (II) detection limit of the Sp-EDA-BODIPY is 0.773 μM. • The maximum adsorption capacities of Cu (II) on Sp-EDA-BODIPY were calculated to be 28.65, 31.25, 34.02, and 37.74 mg/g at different temperatures (298, 308, 318, and 328 K), respectively.

Absorption capacity of hydromorphic soils in relation to heavy metal

Comparative studies of ion-exchange adsorption of Zn(II) and Cu(II) cations by hydromorphic soils of southern Russia have been performed. Various equations (Langmuir, Freundlich, and Dubinin-Radushkevich) were used and the adsorption parameters and adsorption energy were calculated to describe the obtained isotherms. A significant decrease of the distribution coefficient (Kd) with an increase of the metal concentration in an equilibrium solution was revealed. It is shown that the Langmuir equation and, to a lesser degree, the Dubinin-Radushkevich and Freundlich equations are the most suitable model to describe the adsorption processes of Zn(II) and Cu(II) by the soils in all experimental variants. The strong correlation between the parameters of the sorption of metals obtained using a particular chosen model was established. The Langmuir equation provides higher strengths of a bond than the Dubinin-Radushkevich equation. In all cases, the sorption capacity of meadow soil in relation to the studied metals is higher than for alluvial soil due to the low buffering capacity of the latter. Both types of soils characterize with higher affinity to Cu(II) than to Zn(II).

Synthesis, characterization and application of gelatine and dithiocarbamylated chitin

Introduction: Gelatin or gelatine is a translucent, colorless, flavorless, and biodegradable material obtained from collagen present in animal body parts, such as skin, bones, and connective tissues of animals, e.g., domestic cattle, chicken, pigs, and fish. It is a mixture of peptides and proteins obtained by acid and alkaline processing of collagen and is commonly used as a gelling agent in food, pharmaceuticals, photographic films and papers, and cosmetics. Dithiocarbamates (DTC) are well known adsorbents (1-2). We reported preparation and characterization of dithiocarbamylated chitin (CHDTC) in a previous communication (3). CHDTC was found to possess good adsorption capacity, but recovery of adsorbent was not convenient. Therefore, it was envisaged to blend CHDTC with gelatine to not only enhance adsorption capacity but enable reuse of adsorbent also. Methods: Gelatine was blended with CHDTC and polyvinyl alcohol (PVA) to prepare an asymmetric membrane (AMCG), which was characterized by FTIR spectral analysis, powder X-ray diffraction measurements and scanning electron microscopy. Results & Discussion: Adsorption of crystal violet dye from its aqueous solution in 5 to 30 mg/L concentration range by AMCG was investigated using ultraviolet spectrophotometric measurements. Adsorption isotherm study indicated that Langmuir equation fitted better than the Freundlich, Temkin and Dubinin-Radushkevich equations, indicating adsorption process mainly to be monolayer. Adsorption kinetics studies suggested pseudo second order kinetics. AMCG was found to be very efficient adsorbent and maximum adsorption capacity was found to be 500 mg/g for crystal violet. Adsorption was studied at pH 4, 7 and 9. Adsorption was most rapid at pH 9 and almost 95% of crystal violet was observed within 1 h. Further, four adsorption/desorption cycles were followed, which clearly indicated AMCG to be a potential adsorbent for recycling of water from industrial effluents. Conclusions: AMCG is a suitable adsorbent for recycling of wastewater especially from industrial effluents. It shows high adsorbent capacity and fast removal of crystal violet as a model pollutant. Monolayer adsorption process enables recycling of adsorbent and recovery of the valuable compounds/ materials from effluents. Keywords: Recycling of water, Gelatine, Dithiocarbamylated chitin, Dye adsorption. Acknowledgment: Authors are thankful to Central Instrumentation Facility Laboratory, Govt. Science College, Jabalpur for XRD and FTIR spectral analysis.

Control of pore-size distribution on CO2 adsorption volume and kinetics in Gondwana coals: Implications for shallow-depth CO2 sequestration potential

We report experimental CO2 adsorption isotherms and diffusion-related parameters of fresh coal samples from Jharia (350–360 m) and South Karanpura (50–60 m) coalfields, India at three different temperatures (28, 35 and 45 °C) and up to 4 MPa CO2 pressures. The results confirm that temperature possesses an inverse relationship with the excess adsorption volume. Data modelling with the Langmuir and Dubinin-Radushkevich (D-R) equations show the D-R equation better predicts the experimental excess adsorption data. A conversion of the excess adsorbed volume to absolute adsorption further reveals that the modified D-R equation is even a better model to estimate absolute adsorption than the conventional D-R equation. Adsorption kinetics data indicate that temperature has a positive influence on the adsorption rate. We determined the diffusion coefficients of CO2 in these coals using the unipore model, which suggest that it increases with pressure and temperature. Effective diffusivity and diffusion-time maintain a direct and inverse relationship, respectively, with the elevation of temperature. The experimental adsorbed volume and kinetics data are correlated with the corresponding pore-size distribution of the samples. Shallow depth South Karanpura samples have lower average pore diameter, higher volumetric proportion of micropores and surface area compared to those of higher depth Jharia coal samples. Lower adsorption volume and sluggish adsorption kinetics in Jharia coals result from a small surface area and relatively sparse distribution of semi open-ended micropores with poor interconnection. Based on our experimental observations, we discuss and suggest the potential and possible conditions for CO2 sequestration in the Permian Gondwana coalfields, India.

On the use of the Dubinin-Radushkevich equation to distinguish between physical and chemical adsorption at the solid-water interface

Defining the binding mode of ions and molecules at the solid-water interface is a key step to predict their reactivity. The Dubinin-Radushkevich (D-R) equation has been used in thousands of investigations to define if there is chemical or physical adsorption on solid surfaces from water. This paper evaluates the validity of the D-R equation to achieve this purpose. It is acknowledged that, either chemical or physical, the adsorption from solution is always an exchange of molecules or ions and thus enthalpy and free energy changes can take very small or nearly zero values. Therefore, characteristic energy values obtained from the D-R equation cannot be used as indicative of the adsorption mode. It is shown for the first time that the application of the equation always leads to “chemical” binding when molar units are used for the solute concentration in solution, and to “physical” binding when mg/L units are used.

Adsorption of hexavalent chromium from water using manganese-aluminum coated sand: Kinetics, equilibrium, effect of pH and ionic strength

Removal of hexavalent chromium [Cr(VI)] from water was evaluated using a low-cost coated sand adsorbent for potential application in a flow-through filter system using permeable adsorption media. Manganese-aluminum coated sand (MACS) was investigated as a hybrid metal oxide based adsorbent due to the potential efficacy of manganese oxide and aluminum oxide for adsorption of Cr(VI) from water. Adsorbent characterization was performed using XRD, SEM/EDX, XPS and BET. Adsorption experiments were performed to determine adsorption capacity and kinetics. The effect of pH, common co-existing ions found in natural water, and the recyclability of adsorbent were investigated. Adsorbent characterization showed that the MACS sorbent contained aluminum oxide, manganese (III) oxide and manganese (IV) oxide. Adsorption followed the Langmuir and Freundlich adsorption equations, indicating favorable adsorption of Cr(VI) onto the MACS sorbent, while results from the Dubinin–Radushkevich equation were suggestive of physical adsorption of Cr(VI). Cr(VI) adsorption onto the MACS sorbent followed pseudo-second order kinetics. The adsorbent was effective in removing Cr(VI) over a broad pH range from 3 to 9.5, while surface charge analysis confirmed the adsorption of Cr(VI) onto the acidic surface of the MACS sorbent with a pHPZC of 9.72. The presence of co-existing ions bicarbonate, sulfate and phosphate in water resulted in a decrease in Cr(VI) uptake in the following order: phosphate > bicarbonate > sulfate. The presence of calcium resulted in a slight increase in Cr(VI) uptake. The MACS sorbent is a recyclable sorbent for adsorption and removal of Cr(VI) from water within 30 minutes of contact time.

The use of semi-coke for phenol removal from aqueous solutions

The paper deals with a comparative study of equilibrium and kinetics of phenol adsorption from aqueous solutions by means of commercial activated carbons and semi-cokes, differing in the nature of feedstock, production technology and structural characteristics. The main adsorption parameters are calculated with the usage of Langmuir and Dubinin–Radushkevich equations. The change in the characteristics of the structure and state of the surface of semi-coke P2 as a result of modification is estimated. It was found that phenol adsorption kinetics is described by a pseudo-second-order model. The adsorption rate constants and the coefficient of external diffusion mass transfer are calculated. It is proved that phenol extraction from aqueous solutions presents a mixed-diffusion nature, and the process rate is limited by external mass transfer for 13 min for SKD-515 and 22 min for ABG. To increase the adsorption capacity, the oxidative modification of the semi-coke P2 was carried out. Considering the economic and technological aspects, ABG semi-coke is recognized as a promising sorbent for phenol extraction from aqueous media.

Methane Adsorption on Microporous Carbon Adsorbent Prepared from Thermochemically Activated Wood

—An EC-103 microporous carbon adsorbent was synthesized from wood using thermochemically activation with Н3РО4 as an activating agent. Methane adsorption on the EC-103 adsorbent was studied within the temperature range from 303 to 333 K and at pressures up to 40 MPa. The total volume of sorbing pores was 1.71 cm3/g. The maximum values of methane adsorption were obtained at the temperature of 303 K and pressure of 40 MPa. The differential molar isosteric heat of methane adsorption 14.5 mmol/g (23.2 wt %) was on the average of 12−14 kJ/mol. Methane adsorption on the EC-103 adsorbent was calculated based on the Dubinin theory of volume filling of micropores (TVFM). It was shown that the Dubinin-Radushkevich equation and basic TVFM pattern provided the best description of experimental data on methane adsorption with the use of only the standard structural and energy characteristics of the adsorbent.