Revision of adsorption models of xyloglucan on microcrystalline cellulose

Gas content is currently determined using either direct measurements, such as on-site desorption canister tests, adsorption isotherm experiment, measurements of porosity and saturation used in conventional gas content tests, or via indirect prediction such as regression-based approach or calculations using measured dada and wireline logs. Generally, the free gas content can be calculated in terms of porosity, gas saturation, in-situ temperature and pore pressure. And adsorbed gas content can be calculated based on adsorption isotherm experiment. However, there are some drawbacks involved with these methods, such as high costs, limited samples. In this paper, a simple and effective method of estimating free-to-adsorbed gas content ratio is proposed for shale gas reservoirs. Firstly, the adsorption isotherm and acoustic amplitude measurement joint experiment is designed. Meanwhile we get the Langmuir isotherm, we can also get the acoustic amplitude at different pore pressures. Then the empirical relationship between gas content, acoustic amplitude attenuation coefficient and porosity can be acquired by the experimental data. And the new method is applied well in YS shale gas field, and has good agreement with the results by the traditional method.

Heavy metal pollution has become one of the most severe environmental issues. Adsorption is an effective method for removing heavy metals from aquatic environments. The adsorption isotherm and kinetics models can provide information on the adsorption process, maximal adsorption capacity, and mass transfer steps, which are essential to evaluate the performance of an adsorbent and to design an adsorption system. In this review, the adsorption kinetics and isotherms of heavy metals by various adsorbents were summarized and discussed in depth. First, the sources of heavy metal pollution and the adsorption technology to remove heavy metals were reviewed. The adsorption capacity of Cu, Cd, Zn, Ni, Cr, As, Fe, Hg, Co, Sr, and Cs by biosorbents (e.g. algae, agriculture waste biochar/activated carbon, and bacteria) and by abiotic adsorbents (e.g. metal–organic frameworks (MOFs), microtubes, polymers, clays, minerals, and coal) were systematically summarized. Second, the origins, basic assumptions, importance, physical meanings, and applications of the adsorption kinetics and isotherm models were discussed in depth. Third, the methods for selecting adsorption models in different conditions were explained, and the statistical parameters which can be applied to evaluate the performance of the models were illustrated. Finally, two Excel sheets are provided for solving the adsorption models, which are available in Supplementary Information. This review article will deepen the understanding of the interaction between heavy metals and adsorbents and facilitate the development of adsorptive technology for heavy metal removal from water and wastewater.

Soluble starch-functionalized graphene oxide composite (GO-starch) was prepared by a facile esterification reaction. And the composite was used as a novel adsorbent for the removal of Cd(II) from aqueous solution. The chemical composition and morphology of the GO-starch was investigated by fourier transform infrared spectroscopy, scanning electron microscopy and Raman spectroscopy. To evaluate the effects of the adsorption of Cd(II) by GO-starch, batch adsorption studies were performed to optimize the major parameters such as contact time, pH, initial concentration and temperature. The maximum uptake capacity of Cd(II) was 43.20 mg/g under the optimal conditions. Furthermore, the adsorption kinetics, isotherms and thermodynamics of Cd(II) on GO-starch were also investigated. The experimental data indicated that the adsorption kinetics and adsorption isotherms of Cd(II) on GO-starch were well fitted by pseudo-second-order kinetic model and Langmuir isotherm model, respectively. The adsorption thermodynamic parameters were calculated as ΔG 0 < 0, ΔH 0 > 0 and ΔS 0 > 0, respectively. The thermodynamic parameters indicated that the adsorption process was endothermic, feasible and spontaneous. Due to its high adsorption capacity for Cd(II), the GO-starch might have considerable potential for the aqueous removal of metal ions. Soluble starch-functionalized graphene oxide composite (GO-starch) was prepared and used as a novel adsorbent for the aqueous removal of Cd(II). The chemical composition and morphology of the GO-starch was characterized by fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and Raman spectroscopy. Batch adsorption experiments were performed to optimize the major parameters such as contact time, pH, initial concentration and temperature. The maximum uptake capacity of Cd(II) was 43.20 mg/g under the optimal conditions. The adsorption kinetics and adsorption isotherms were well fitted by pseudo-second-order kinetic model and Langmuir isotherm model, respectively. The adsorption thermodynamic parameters were ΔG 0 < 0, ΔH 0 > 0 and ΔS 0 > 0, indicating that the Cd(II) adsorption process was spontaneous, endothermic and feasible.

The adsorption removal of C.I Reactive Blue 21 (RB-21) dye from aqueous solution by commercial MCC was successfully modified with aminopropyltriethoxysilane. The various physiochemical attributes like initial dye concentration, contact time, solution pH, adsorbent dose and temperature were evaluated. The surface modification was characterised and confirmed with specific surface area analyser using Brunauer–Emmett–Teller, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Energy Dispersive Spectrometer and X-ray diffraction. The adsorption kinetics, isotherms, and thermodynamics were explored. The Langmuir, Frendlich and Redlich-Perterson isotherm models were studied with the Langmuir adsorption isotherm model showing the best fit with the adsorption capacity of 30 mg g− 1 at 323 K. The kinetic data was considered using pseudo-first-order and pseudo-second-order. The results indicated that the pseudo-second-order model was preferred with good correlation. The thermodynamic attributes like changes in standard enthalpy, standard entropy and standard Gibbs free energy were assessed at different operating temperatures. Hence, current research work shows efficient removal of RB-21 dye from effluent solution by modified microcrystalline cellulose.

Adsorption Kinetics describes the rate at which solute is adsorbed and the resident time of the adsorbates on the solid-liquid interface. Adsorption isotherms play important role in determining the interaction between adsorbate and adsorbent and the optimum adsorption capacity of adsorbent. This article considered selected adsorption kinetics and isotherms models. Pseudo first order, Pseudo second order, Elovich, Bhattacharya and Venkobachar, and Natarajan and Khalaf were adsorption kinetics reviewed on the assumption that the process behaves as heterogeneous reaction at solid-liquid interface. Adsorption kinetics equation presented takes the form of straight line, the slopes and intercepts of the plots are used to determine adsorption capacity of adsorbent, rate constant, rate of adsorption and intraparticle diffusion. Value of correlation coefficient obtained is used in determining the adsorption kinetics model that best describe the adsorption process. Langmuir, Freundlich, Radlich-Peterson, Temkin and Dubinin-Radushkevic adsorption isotherms were presented. Their slopes and intercepts provide insight on adsorption affinity, mean free energy, whether the adsorption is physisorption or chemisorptions, single or multilayer. Adsorption kinetics and isotherms reviewed provide essential information required for understanding adsorption process. Keywords: Adsorption; kinetics; isotherms; pseudo first order; Langmuir

The main purpose of this study was to characterize the adsorption behavior of naphthalene, one of polycyclic aromatic hydrocarbons (PAHs), on silk fabric. Typical batch reactors were used to perform adsorption kinetics and isotherm experiments. It was found in this study that the pseudo-second-order model described the sorption kinetics data well. An adsorption isotherm in the form of Linear Equation was observed, and the adsorbed capacity was influenced evidently by the enhanced temperature. In addition, the results demonstrated that silk fabric could adsorb large amounts of naphthalene from water, and the maximum exceeded 700 μg/g.

Shale needs to contain a sufficient amount of gas to make it viable for exploitation. The continental heterogeneous shale formation in the Yan-chang (YC) area is investigated by firstly measuring the shale gas content in a laboratory and then investigating use of a theoretical prediction model. Key factors controlling the shale gas content are determined, and a prediction model for free gas content is established according to the equation of gas state and a new petrophysical volume model. Application of the Langmuir volume constant and pressure constant obtained from results of adsorption isotherms is found to be limited because these constants are greatly affected by experimental temperature and pressures. Therefore, using measurements of adsorption isotherms and thermodynamic theory, the influence of temperature, total organic carbon (TOC), and mineralogy on Langmuir volume constants and pressure constants are investigated in detail. A prediction model for the Langmuir pressure constant with a correction of temperatures is then established, and a prediction model for the Langmuir volume constant with correction of temperature, TOC, and quartz contents is also proposed. Using these corrected Langmuir constants, application of the Langmuir model determined using experimental adsorption isotherms is extrapolated to reservoir temperature, pressure, and lithological conditions, and a method for the prediction of shale gas content using well logs is established. Finally, this method is successfully applied to predict the shale gas content of the continental shale formation in the YC area, and practical application is shown to deliver good results with high precision.

Hybrid super-porous hydrogel composites with high water vapor adsorption capacity – Adsorption isotherm and kinetics studies

This study aimed to develop an environmentally friendly, inexpensive, and efficient adsorbent for removing methylene blue (MB) dye from wastewater using a three-dimensional porous poly(2-Acrylamido-2-methyl-1-propanesulfonic acid-co-2-Hydroxyethyl Methacrylate), p(AMPS-co-HEMA) composite hydrogel crosslinked with vinyl-functionalized activated carbon (VAC). The surface morphology and chemical structure of the crosslinker were characterized using transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray spectroscopy (XRD) and Fourier transform-infrared spectroscopy (FT-IR) instruments. The surface morphology, chemical structure and thermal properties of the hydrogel were also characterized using scanning electron microscopy (SEM), FT-IR and thermogravimetric analyzers (TGA). Experimental parameters affecting the adsorption behavior, such as initial dye concentration, time, dosage, pH, and temperature, were systematically investigated. Hydrogel achieved optimal MB removal efficiency (69.53%) at an initial MB concentration of 250 mg/L (1 mg/mL, pH not adjusted) over 24 h. Adsorption kinetics, isotherm, thermodynamic studies, and reusability were investigated. Experimental adsorption isotherm and kinetic data followed the Langmuir model and pseudo-second-order kinetics with a maximum adsorption capacity of 284.90 mg/g hydrogel at 293 K. Thermodynamic findings proved the spontaneity and endothermic behavior of the adsorption process. After 5 adsorption-desorption cycles, the adsorption capacity of the composite hydrogel decreased by only 7.51 mg/g compared to the initial adsorption capacity.

The Kyoto Protocol, 1998, was signed by member countries to reduce greenhouse gas (GHG) emissions to a minimum acceptable level. India agreed to Kyoto Protocol since 2002 and started its research on GHG mitigation. Few researchers have carried out research work on CO2 sequestration in different rock formations. However, CO2 sequestration in abandoned mines has yet not drawn its attention largely. In the past few years or decades, a significant amount of research and development has been done on Carbon Capture and Storage (CCS) technologies, since it is a possible solution for assuring less emission of CO2 to the atmosphere from power plants and some other major industrial plants. CCS mainly involves three steps: (a) capture and compression of CO2 from source (power plants and industrial areas), (b) transportation of captured CO2 to the storage mine and (c) injecting CO2 into underground mine. CO2 is stored at an underground mine mainly in three forms: (1) adsorbed in the coals left as pillars of the mine, (2) absorbed in water through a chemical process and (3) filled in void with compressed CO2. Adsorption isotherm is a graph developed between the amounts of adsorbate adsorbed on the surface of adsorbent and the pressure at constant temperature. Various types of adsorption isotherms are available, namely, Freundlich, Langmuir and BET theory. Indian coal is different in origin from most of the international coal deposits and thus demands isotherm experiments of the same to arrive at the right adsorption isotherm. To carry out these experiments, adsorption isotherm set up is fabricated in the laboratory with a capacity to measure the adsorbed volume up to a pressure level of 100 bar. The coal samples are collected from the pillars and walls of the underground coal seam using a portable drill machine. The adsorption isotherm experiments have been carried out for the samples taken from a mine. From the adsorption isotherm experiments, Langmuir Equation is found to be more acceptable as compared to Freundlich’s and BET adsorption isotherm models. CO2 is soluble in water and is reversibly formed carbonic acid. It is a weak acid since its ionization in water is incomplete. The CO2 solubility in water is estimated from the experimental results published by Wiebe and Gaddy. In most of the cases of abandoned mines, the chances of available air filled void space is limited as the level of operation is below the water table. So it is expected that the void would be completely filled with water. During this research investigation, the practical experimentation for CO2 sequestration was not within the scope. Thus, one operating mine was considered for the feasibility study. The sequestrated quantities of CO2 in terms of adsorbed volume and soluble volume were quantified. The cost of the CO2 was taken from the standard international literature. The sealing cost of the shaft was also considered. Costs of CO2 sequestration for different pressure were estimated for the mine.

Zeolitic-imidazolate framework derived magnetic N-doped hierarchical carbons with ultrahigh indole-3-butyric acid adsorption capacities: Behavior and mechanism

Investigation of dispersion methodologies of microcrystalline and nano-fibrillated cellulose on cement pastes

Adsorption and desorption kinetics at the solid/solution interface have been monitored using attenuated total reflection infrared (ATR-IR) spectroscopy to evaluate this approach as an alternative to equilibrium (adsorption isotherm) measurements of adsorption affinity. The adsorption and desorption kinetics of oxalate ion to anatase TiO2 have been measured by using aqueous 1 x 10(-4) mol L(-1) oxalic acid solutions at pH 4 and thin films of TiO2 particles deposited on an internal reflection prism. The adsorption kinetics were obtained from the absorbance versus time behavior of major adsorbed oxalate infrared absorptions with flow of oxalic acid solution followed by flow of solution not containing oxalic acid to measure the desorption kinetics. Regression analysis of the desorption data based on Langmuir kinetics yielded three distinct pseudo-first-order rate constants with desorption half-lives of 300, 14, and 2 min, indicating the presence of three adsorbed oxalate species of different adsorption affinities. The most slowly desorbing and most strongly bound adsorbate species is likely to be a bidentate chelating oxalate ion from comparisons with the IR spectra of coordination compounds involving oxalate ligands. Regression analysis of the adsorption data was unable to yield the corresponding pseudo-first-order adsorption constants and prevented the calculation from kinetics data of Langmuir adsorption affinity constants. Measurement of adsorption and desorption kinetics by ATR-IR spectroscopy is expected to provide a relatively rapid means of assessing the presence of species of different adsorption affinities in systems in which their spectra are not well differentiated.

Adsorption to microcrystalline cellulose (Avicel) of pure cellobiohydrolase I and II (CBH I and CBH II) from Trichoderma reesei has been studied. Adsorption isotherms of the enzymes were measured at 4 degrees C using CBH I and CBH II alone and in reconstituted equimolar mixtures. Several models (Langmuir, Freundlich, Temkin, Jovanovic) were tested to describe the experimental adsorption isotherms. The isotherms did not follow the basic (one site) Langmuir equation that has often been used to describe adsorption isotherms of cellulases; correlation coefficients (R2) were only 0.926 and 0.947, for CBH I and II, respectively. The experimental isotherms were best described by a model of Langmuir type with two adsorption sites and by a combined Langmuir-Freundlich model (analogous to the Hill equation); using these models the correlation coefficients were in most cases higher than 0.995. Apparent binding parameters derived from the two sites Langmuir model indicated stronger binding of CBH II compared to CBH I; the distribution coefficients were 20.7 and 3.7 L/g for the two enzymes, respectively. The binding capacity, on the other hand, was higher for CBH I, 1.0 mumol (67 mg) per gram Avicel, compared to 0.57 mumol/g (30 mg/g) for CBH II. The isotherms when analyzed with the combined Langmuir-Freundlich model indicated presence of unequal binding sites on cellulose and/or negative cooperatively in the binding of the enzyme molecules.

Adsorption isotherms and kinetics of HFC410A onto activated carbons