Experimental Isotherms Research Articles

Highlighting the adsorption mechanism of a fluoroquinolone antibiotic from wastewater on carbon xerogel by experiments, characterization, modelling and DFT simulation.

The application of a synthesized carbon xerogel (RFX) for the adsorptive removal from water of ciprofloxacin (CPX), a widely used fluoroquinolones-group antibiotic for humans and animals, has been reported in this work. The carbon xerogel was characterized by N2 adsorption-desorption isotherms, FTIR, Raman spectroscopy, TPD studies, elemental analysis, determination of isoelectric point (pHIEP) and scanning electron microscopy (SEM). CPX adsorption experiments were conducted in batch mode, using results obtained with F400 commercial activated carbon for comparison purposes. CPX adsorption kinetics were well-described by the pseudo-second-order model for both adsorbents and by the Elovich model in the case of F400 activated carbon. Therefore, CPX equilibrium adsorption capacity values were of 457 and 72mgg-1 for RFX xerogel and F400 activated carbon, respectively. This significant difference can be attributed to the higher specific surface area and micropores volume values of F400 carbon; in this sense, this material led to a slower CPX kinetic adsorption. Also, the Dual-site Langmuir model best-described the experimental CPX adsorption isotherms in both cases. By the adsorption studies at different solution pH, it could be concluded that several mechanisms, e.g., hydrophobic and π-π interactions, and electrostatic forces highly influenced CPX adsorption capacity. Furthermore, adsorption tests using several environmentally relevant aqueous matrices have been accomplished. In this case, a competitive effect between the natural organic matter (NOM) and the target pollutant occurred in all the tested real matrices, decreasing CPX adsorption capacity, especially remarkable for F400 activated carbon. Finally, Density Functional Theory (DFT) has been used to elucidate the interactions between CPX and adsorbents, finding a high relevance of the π-π electron donor-acceptor interactions in which CPX acts as an acceptor.

Facile synthesis of active sites-rich magnetic adsorbent by simple one-pot hydrothermal strategy for quick and highly capable capture of female-steroid hormones

Rapid and efficient extraction is highly desired in the accurate quantification of female-steroid hormones (FSHs) in complex samples. In this context, an active sites-rich magnetic adsorbent (MAC) modified with carboxylated multiwalled carbon nanotubes and 4-vinylphenylboronic acid was facilely synthesized through one-pot hydrothermal technique for the magnetic solid phase extraction (MSPE) of FSHs in water and urine samples. Various characterizations revealed that the prepared adsorbent contained abundant functional groups, acceptable magnetic properties, high surface area and good stability. Due to the multiple interactions, the developed MAC/MSPE exhibited high isolation and preconcentration capability towards studied FSHs within 10 min. The concentration factors were 151–354 and the adsorption capacity was as high as 3.2 mg/g. Adsorption behaviors of MAC/MSPE towards FSHs were studied based on adsorption kinetics and isotherm experiments. After optimizing the extraction parameters, the MAC/MSPE was combined with HPLC to sensitive and reliable monitoring of studied FSHs in various waters and female urine samples. The limits of detection and recoveries with different spiked contents were 0.0015–0.0026 μg/L and 80.1–119 %, respectively. Accuracy of the established method was evaluated by confirmatory testing. Moreover, sample preparation greenness of the developed method was assessed. The present study uncovered the prospect of MAC/MSPE in the rapid and highly capable capture of FSHs, and also supplied a sensitive and reliable approach for the monitoring of trace FSHs in complex samples.

Development and Application of an Advanced Percolation Model for Pore Network Characterization by Physical Adsorption.

Physical adsorption is one of the most widely used techniques to characterize porous materials because it is reliable and able to assess micro- and mesopores within one approach. Challenges and open questions persist in characterizing disordered and hierarchically structured porous materials. This study introduces a pore network model aimed at enhancing the textural characterization of nanoporous materials. The model, based on percolation theory on a finite-sized Bethe lattice, includes all mechanisms known to contribute to adsorption hysteresis in mesoporous pore networks. The model accounts for delayed and initiated condensation during adsorption as well as equilibrium evaporation, pore blocking, and cavitation during desorption. Coupled with dedicated nonlocal-density functional theory kernels, the proposed method provides a unified framework for modeling the entire experimental adsorption-desorption isotherm, including desorption hysteresis scans. The applicability of the method is demonstrated on a selected set of nanoporous silica materials exhibiting distinct types of hysteresis loops (types H1, H2a, H1/H2a, and H5), including ordered mesoporous silica networks (KIT-6 and SBA-15/MCM-41 hybrid silica with plugged pores) and disordered mesoporous silica networks (hierarchical meso-macroporous monolith and porous Vycor glass). For all materials, a good correlation is found between calculated and experimental primary isotherms as well as desorption scans. The model allows us to determine key pore network characteristics such as pore connectivity and pore size distributions as well as a parameter correlated with the impact of pore network disorder on the adsorption behavior. The versatility and enriched textural insights provided by the proposed novel network model allow for a comprehensive characterization previously inaccessible and hence will contribute to further advancement in the textural characterization of novel nanoporous materials. It has the potential to provide important guidance for the design and selection of porous materials for optimizing various applications, including separation processes such as chromatography, heterogeneous catalysis and gas and energy storage.

Improving the adsorption properties of low surface area hardwood biochar for the removal of Fe+ and PO₄3- from aqueous solution.

Biochar produced from wood residues may provide a new method and material for managing the environment, particularly in terms of carbon sequestration and contaminant remediation. Additionally, biochar produced from wood residues is free of chemical fertilizers, likewise in rice straw, wheat straw, corn straw, etc. This study investigated the removal of iron from aqueous solutions by a novel low-cost and eco-friendly biochar made from hardwood trees and modified by adding MgCl2 for effective phosphate removal. Optimal adsorption conditions were determined through studies of adsorption time, pH, and adsorbent dosage. Batch equilibrium isotherm and kinetic experiments and pre/post-adsorption characterizations using FESEM-EDS, XRD, and FTIR suggested that the presence of carboxyl group elements and colloidal and nano-sized MgO (periclase) particles on the biochar surface were the main adsorption sites for aqueous iron and phosphate respectively. In this study, the HW and MgO-HW biochar showed excellent Dubinin-Radushkevich isotherm (D-R) maximum adsorption capacities of 289.45 and 828.82mg/g for iron and phosphate. The kinetic study for iron and phosphate adsorption was described well by pseudo second-order model and pseudo second-order model respectively. The HW biochar and the prepared MgO-HW biochar exhibited commendable iron adsorption (98.25%) performance at 10 pH units and phosphate (96.22%) at pH 6 respectively. Thus, this research reveals a waste-to-wealth strategy by converting hardwood waste into mineral-biomass biochar with excellent Fe and P adsorption capabilities and environmental adaptability.

Drying Kinetics and Sorption Isotherms of Biocomposite Materials: Experimental Investigation and Modeling Analysis.

Modern materials science has made significant progress in creating new materials and processes for waste recovery. One such advancement involves the development of a new porous composite material made from clay and an environmentally sustainable eggshell powder. In this study, the dynamic behavior of water vapor during desorption and adsorption processes within this composite material was investigated. The moisture diffusivity coefficient was determined within the clay/eggshell powder composite material. The drying kinetic data were analyzed using various models such as Newton, Page, and Wan and Singh. The static gravimetric vapor adsorption/desorption experiments were conducted at different temperatures (30, 40, 50, 60, and 70 °C) to depict the material's capacity for absorbing and releasing moisture over time. The experimental isotherm data were fitted using different mathematical models (Guggenheim, Anderson, and De Boer, Peleg, Adam and Shove, Oswin, and Modified Henderson). The findings suggest that integrating eggshell powder with clay can significantly influence the behavior and characteristics of the resultant material. The combination of eggshell powder and clay reduces moisture sorption and accelerates the drying process. Consequently, this affects the porosity, permeability, and response to humidity changes.

Metal-modified biochars prepared from blue algae and their ability of adsorbing phosphates from water and utilization as soil amendment

The problem of blue algae accumulation can be alleviated by utilizing blue algae as biomass for resource utilization, which can remove excess phosphates from water to alleviate eutrophication. Herein, Magnesium (Mg) and/or lanthanum (La) were used to modify biochar via high-temperature slow pyrolysis with blue algae as the raw biomass. These modified biochars exhibited abundant carbon (18.0%-50.3%), oxygen content (17.4%-49.1%), along with a high specific surface area (82.26-233.80 m2/g). The surface of metal-modified biochar was enriched with hydroxyl and carboxyl groups and metal elements were efficiently incorporated into biochars. Adsorption kinetic and isotherm experiments were conducted under the optimal pyrolysis temperature of 600 °C, pH of 6.0, and adsorbent dosage of 2.0g/L. The adsorption kinetics studies by metal-modified biochars for phosphate fitted well pseudo-second-order model Redlich-Peterson isotherm model. Biochar modified by Mg and La exhibited the highest removal efficiency (97.8%) for phosphate at adsorption equilibrium. The adsorption mechanism involved the electrostatic interaction between hydroxylated metal oxides and negatively charged phosphate ions and the precipitation of phosphate ions through chemical reactions with metal oxides in the solution. After phosphate adsorption, the pristine and metal-modified biochars derived from blue algae were applied as the soil amendment. Biochar adsorbed phosphate apparently improved the germination rate of seeds facilitated the height, width, weight, and chlorophyll content of vegetable seedlings, and induced oxidative stress, which proved that the biochar recovered after adsorption was a high-quality soil amendment. This study provides a new approach for the treatment of phosphate wastewater and the algae application.

Salt-free neutral dyeing of cotton fiber with monochlorotriazine type reactive dyes

In this paper, we present the modification of cotton with glycidyltrimethylammonium chloride (GTA), demonstrating its capability not only for salt-free dye adsorption but also for achieving fixation reactions with monochlorotriazine-type reactive dyes under neutral conditions. The results of adsorption kinetics and isotherm experiments indicate that the adsorption of reactive dyes by modified cotton is chemisorption. Color-stripping experiments conducted on modified cotton dyed with different dyes revealed that GTA-modified cotton underwent fixation reactions with monochlorotriazine-type reactive dyes under neutral conditions. The reaction sites of modified cotton with reactive dyes were determined by measuring the 1H NMR of the model reaction products. Mechanism investigation using Density Functional Theory (DFT) on the fixation reaction revealed that the hydroxyl groups on the modification agent chain exhibit a lower pKa value and carry more negative charge, resulting in a lower reaction barrier with monochlorotriazine-type reactive dyes. Our research findings demonstrate that GTA-modified cotton fiber enhance the reactivity of cotton, providing significant guidance for the development of novel modifiers.

Synthesis and characterization of a crosslinked deacetylated chitin modified chicken bone waste-derived hydroxyapatite and TiO2 biocomposite for defluoridation of drinking water

This work represents an innovative approach to the synthesis and characterization of a chitosan-based biocomposite for fluoride adsorption. The work involved the development of a biocomposite based on modified chicken bone waste-derived hydroxyapatite and TiO2. The composite was characterized using scanning electron microscopy with Energy Dispersive X-ray analysis (SEM-EDX), X-ray diffraction (XRD), Fourier-transform infrared analysis (FTIR), thermal-gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The optimum parameters for fluoride removal were determined, and the kinetic data was better fitted to the pseudo-first-order model. The Liu equations provided a better description of the experimental adsorption isotherm data. The adsorption mechanism and the interaction of the composite with fluoride were better understood using Density Functional Theory (DFT) calculations and Non-Covalent Interactions (NCI) analyses, paving the way for more effective and efficient defluoridation methods.

Enhanced Hydrophobicity and Oleophilicity of Modified Activated Carbons Derived from Agro-Wastes Biomass for the Removal of Crude Oil from Aqueous Medium

Crude oil spillage has tremendous environmental impacts and poses severe pollution problems worldwide due to the continuous activities and operations in the oil and gas sector. This has resulted in the urgent need for clean-up techniques such as the use of natural adsorbents which is considered a relatively low-cost, readily-available, efficient, eco-friendly, and easy-to-deploy mode of addressing oil spillage due to its high oil sorption capacity/efficiency, high oil selectivity, oleophilic, enduring, reusability and biodegradable properties. Empty palm fruit bunch and coconut coir were used as precursors to produce activated carbons for oil spill remediation. The influence of varying parameters was investigated using a batch experimental procedure resulting in the crude oil adsorption capacity increasing with a corresponding increase in contact time, initial oil concentration, temperature, agitation speed, and particle size but decreasing in adsorbent dosage. The combination of surface morphological modification and hydrophobicity enhancement resulted in significantly improved adsorption capacity for crude oil removal (2710.0 mg/g and 4859.5 mg/g for EPFBAC<SUB>LA</SUB> and CCAC<SUB>L.A</SUB> respectively), as evidenced by both FTIR and SEM analyses. The experimental isotherm data were analysed using various isotherm models and the best-fitted isotherm model was the Freundlich model with a correlation coefficient (R<sup>2 </sup>= 0.991 and R<sup>2 </sup>= 0.999) for EPFB<SUB>L.A</SUB> and CCAC<SUB>L.A</SUB> respectively. The kinetic behaviour of the adsorption process was best described by pseudo-second order with R<sup>2</sup> values of 0.970 and 0.999 for EPFBAC<SUB>LA</SUB> and CCAC<SUB>L.A</SUB> respectively while Boyd model revealed that the adsorption was controlled by an internal transport mechanism and film diffusion was the rate-limiting step. The crude oil adsorption was chemisorption and endothermic owing to the positive enthalpy values (ΔH<sup>o</sup> = 183.890 KJ/mol for EPFBAC<SUB>L.A </SUB>and ΔH<sup>o</sup> = 69.656 KJ/mol for CCAC<SUB>L.A</SUB>), the positive value of entropy suggested that the adsorption process was accompanied by an increase in the degree of randomness or disorder at the interface between the adsorbent and the adsorbate. A temperature rise led to a decline in Gibbs energy (ΔG<sup>o</sup>), suggesting that adsorption became more feasible and spontaneous at higher temperatures and the significant activation energies indicated the existence of a substantial energy barrier that must be overcome to initiate the reaction. The results showed the significant capability of the prepared adsorbents to be used as a low-cost, re-generable and eco-friendly adsorbent in oil spill clean-up and is recommended to exploit its usage on a large scale.

Binding mechanisms of trivalent chromium on colloidal phases from ultramafic systems: Insights from batch experiments and XAS analysis

Understanding the availability and mobility of chromium is a key factor in gaining insight into the fate of chromium and thus essential for assessing the risk of contamination and developing effective remediation strategies. In the natural environment, such as ultramafic systems, which are natural pools of chromium, chromium occurs mostly in the trivalent state (Cr(III)), which is known to have a high affinity for the solid phases such as particles and colloids. However, since Cr(VI) is more toxic, the vast majority of experimental studies focus on its reduction to Cr(III), which is often considered to form (hydr)oxide precipitates due to its poor solubility. Furthermore, while the oxidation state of Cr dictates its geochemical behavior, its interaction with particles and colloids is rarely controlled or monitored. Therefore, the interaction mechanisms between Cr(III) and particles or colloids require further attention. In this study, ten mineral phases (goethite, hematite, pyrolusite, kaolinite, montmorillonite, chlorite, serpentine, fuchsite, amphibole, and chromite) and one organic phase (humic acid), relevant to chromium bearing and carrier phases in ultramafic soils, were investigated to explore their interaction with Cr(III) species. These phases were first characterized by various techniques (including XRD, XRF, SEM, and BET). Adsorption and desorption experiments of Cr(III) on these phases were then carried out, and the distribution of Cr oxidation states in both the aqueous and solid phases was carefully monitored using UV–vis spectroscopy, geochemical speciation modeling, and Cr K-edge XAS spectroscopy. With the exception of pyrolusite, where partial oxidation of Cr(III) to Cr(VI) occurred, Cr(III) was shown to persist as a single oxidation state in all experiments. Desorption analyses showed significantly low desorbed rates, which further confirmed the prevalence of Cr(III). Experimental sorption isotherm data were interpreted using the Langmuir model and its linearized form, which provides important thermodynamic characteristics of adsorbents related to their structural and surface features. This study will provide better constraints for the understanding and prediction of Cr behavior and fate in the environment, especially in ultramafic systems.

Vertical distribution and migration of heavy metals in soil of green stormwater infrastructure receiving roof runoff

In order to achieve effective management of urban stormwater runoff, green stormwater infrastructure (GSI) has been widely used worldwide. However, the problem of heavy metal contamination in GSI soils has gradually become a limiting factor for their development. In this paper, concentrations of 6 heavy metals were detected in soils from 0 to 80 cm depth in the GSI receiving roof runoff. The total concentration of the 6 heavy metals in topsoil of the GSI was 395 mg·kg−1, which was significantly higher than that of the control site (p < 0.01). Vertically, heavy metal concentrations in GSI soils decreased with depth. The concentrations of As, Cr, Cu, Pb and Zn in the soils at different depths (0–80 cm) of GSI were higher than those in the soils at the corresponding depths at the control site. This suggests that heavy metals may have migrated below 80 cm. The decrease in Zn/Cu ratios with depth indicated that Zn has a higher initial concentration and more of Zn accumulated in upper layer soil than Cu. Finally, we simulated the vertical migration of dissolved heavy metals in GSI soils by the Hydrus-1D model. Heavy metal concentrations in runoff and soil particle size distributions were examined, while adsorption isotherm experiments were conducted to determine input parameters for the model. The simulation results showed that only dissolved Zn would accumulate in the top soil layer. A short time of infiltration (<60 min) may have little effect on the profile shape of dissolved heavy metal levels in the soil. Substantial increases in infiltration may result in the migration of dissolved heavy metals to deeper depths in the soil.

Brazilian bentonite/MgO composites for adsorption of cationic and anionic dyes.

Industrial effluents, especially those containing dyes, have become the main cause of contamination of water resources. In this context, Brazilian bentonite/MgO composites, with excellent adsorptive properties, were prepared and investigated for their effectiveness in removing cationic and anionic dyes from aqueous solutions. The new adsorbents were obtained using Brazilian bentonites and MgO using the mechanochemical method followed by heat treatment (at 700°C for 4h). Different characterization techniques were used for the chemical, mineralogical, thermal, surface, and morphological analysis of the raw clays and the composites. The experimental adsorption isotherms were quantified under different conditions of initial concentration, contact time, pH, adsorbent dosage, and temperature variation to interpret the adsorption mechanism of the crystal violet (CV) and Congo red (CR) dyes. The modeling results were obtained from the empirical Sips equation and Pseudo Second Order (PSO) kinetics, indicating that the adsorption of molecules is a heterogeneous phenomenon that occurs in a monolayer on the surface (ns > 1), with the adsorption rate determined by chemisorption. The composites showed the best removal efficiency performance compared to the raw bentonites, with an increase of 12% for the CV dye and 46% for the CR dye. In addition, the qmax values obtained were 423.02mg/g and 479.86mg/g (AM01). This research underscores the potential of Brazilian bentonite/MgO composites as a promising solution for the removal of cationic and anionic dyes from water, offering hope for future applications in the field of environmental engineering and materials science.

Assessment of the Effects of ZnO and CuO Engineered Nanoparticles on Physicochemical Properties of Volcanic Ash Soil and Phosphorus Availability

The presence of engineered nanoparticles (ENPs) in soil systems can modify their properties and the availability of nutrients. This study evaluated the effect of 1% CuO or ZnO ENPs on the physicochemical properties and on the phosphorus (P) adsorption–desorption processes of a volcanic ash soil (Lautaro; LAU). The dynamics of P were conducted through kinetic and isotherm batch experiments. The results showed that LAU soil with 1% CuO or ZnO ENPs increased pHH2O (from 5.67 to 6.03 and 6.82, respectively), electrical conductivity (from 0.119 to 0.143 and 0.150 dS m−1, respectively), Zn availability (597.7 times higher for LAU with 1% ZnO ENPs in relation to soil without ENPs), and Cu availability (41.8 times higher for LAU with 1% CuO ENPs in relation to soil without ENPs). Moreover, the presence of ENPs decreased Brunauer, Emmett, and Teller specific surface area. The adsorption kinetic studies of P on LAU soil without and with 1% ENPs fitted well to the Elovich model (r2 ≥ 0.923), which indicated a chemiadsorption mechanism, whereas the adsorption isotherms were described by Langmuir–Freundlich model (r2 ≥ 0.939). The desorption percentage was LAU &gt; LAU + 1% CuO–ENPs &gt; LAU + 1% ZnO–ENPs, demonstrating an increased stability of the P–soil surface binding with 1% ENPs. Co–existing NO3−, SeO42−, and SO42− anions did not generate a steric hindrance between P and LAU soil binding. Finally, both ENPs could alter the quality of the soil due to changes in their physicochemical properties and decrease the availability of P in volcanic ash soils.

Fabrication of a cost-effective metal oxide-based adsorbent from industrial waste slag for efficient CO2 separation under flue gas conditions

Efficient and affordable adsorbents for CO2 capture are essential in implementing carbon capture technology to mitigate the negative impact of greenhouse gas emissions. This study focuses on synthesizing new nanoporous adsorbents from industrial waste slag using a simple and cost-effective coprecipitation method. In this method, raw slag was milled for 48 h and used as a benchmark for comparing two newly synthesized adsorbents. Selectivity and pure gas isotherm experiments were conducted for all adsorbents in the 25–65°C temperature range and under harsh industrial conditions of 65°C and 15 % CO2. This study utilized the response surface methodology (RSM) to optimize the CO2 adsorption parameters. Specifically, the optimized adsorption conditions were determined for the 15/85 % CO2/N2 condition, and the optimal values for pressure and temperature were found to be 5 bar and 45°C, resulting in CO2/N2 selectivity of 5.65. The NH3-slag adsorbent was identified as the superior choice based on its selectivity and maximum adsorption capacity. The maximum adsorption capacity and cyclic efficiency were determined to be 4.15 mmol/g and 98.1 %, respectively, at a temperature, pressure, and composition of 45°C, 5 bar, and 15 % CO2. Isotherm and thermodynamic models were employed to further investigate the adsorption process. The isotherm results indicated that the adsorption of CO2 by adsorbents occurred heterogeneously in patch-wise sites. Meanwhile, the thermodynamic parameters showed that the process was exothermic and spontaneous, with ΔH° falling below 20 (kJ/mol), showing physisorption phenomena.

Efficient adsorption of sodium oleate from wastewater with graphene oxide/polyethyleneimine composite hydrogel: Performance and mechanism

Sodium oleate (NaOL) is commonly employed as a traditional organic collector during the flotation process of phosphate ore. However, the residual NaOL in mineral processing wastewater not only poses a great threat to the environment, but also reduces the qualities of subsequent flotation products. In this study, an effective adsorbent graphene oxide/polyethyleneimine (GP) composite hydrogel was prepared and applied for the adsorption of NaOL. The successful association between GO and PEI was elucidated through various characterizations. Further to that, the adsorption performance was systematically determined through adsorption isotherm, adsorption kinetics, co-existing ions and reusability experiments. The results clearly demonstrated that the adsorption behavior of NaOL could be well described by both pseudo-second-order (PSO) kinetic and Langmuir isotherm models. GP composite hydrogel was able to achieve superior NaOL adsorption with an excellent adsorption capacity (295.95 mg/g) and a quick kinetic (120 min). The existence of competitive ions, such as CO32−, SO42− and PO43−, had a negative effect on NaOL adsorption. The mechanism investigation suggested that chemical adsorption and hydrogen bonds were central and played imperative roles for the adsorption of NaOL on GP composite hydrogel. Overall, the current work provides a valuable reference for the efficient adsorption of NaOL.

Acylhydrazone-functionalized starch for efficient removal of hazardous dyes, heavy metal ion, and sulfides from wastewater: Adsorption behavior and mechanism analysis

Herein, a novel acylhydrazone biosorbent (GSL) with abundant three-dimensional porous structure was successfully prepared by using low-cost starch as raw material for water pollution remediation applications. Various analytical techniques were applied to characterize the morphological structure and chemical composition. Interestingly, the adsorption efficiency of the adsorbent towards Malachite green (MG), Safranin O (SO), Cu2+, and sulfide in the static adsorption experiment was extremely high due to presence of ample functional groups. Additionally, the adsorption isotherm and kinetic experiments revealed that the adsorption processes were based on monolayer chemisorption. The maximum sorption amounts were 2237.4961 mg/g for SO, 2101.6610 mg/g for MG, 410.7019 mg/g for Cu2+, and 483.0194 mg/g for sulfides at 298.15 k. The thermodynamic analysis also demonstrated that all adsorption processes were spontaneous heat processes. The adsorption mechanism was analyzed by FTIR, SEM-EDAX and XPS. The adsorption of SO onto GSL reached 1025.8617 mg/g in continuous adsorption experiments, and the experimental data were fitted through the Thomas model and Yoon-Nelson model. Furthermore, the GSL showed good reusability and salt resistance. Importantly, starch-based acylhydrazone as the adsorbent for the simultaneous removal of hazardous dyes, heavy metal ions and sulfhides has not yet been seen reported.

An Ultramicroporous Zinc‐Based Zeolitic Imidazolate Framework‐8 for the Adsorption of CO2, CH4, CO, N2 and H2: A Combined Experimental and Theoretical Study

AbstractAn alternative synthesis route to obtain ultramicroporous zeolitic imidazolate framework‐8 (ZIF‐8) is reported that is rapid and does not require organic solvent or heating. The polyethylene glycol‐templated ZIF‐8 nanoparticles (&lt;50 nm size) exhibited a high BET (Brunauer, Emmett and Teller) surface area of 1853 m2/g, a total pore volume of 0.73 cm3/g, and 0.54 nm ultramicropores. A new approach is introduced here to better understand gas adsorption in porous metal organic frameworks (MOFs) that combines theoretical and experimental isotherm data obtained for five gases with statistical physics modelling. The multiscale analytical model reveals that the gas molecules, irrespective of their structure, adsorb in a mixed orientation at low temperature, and a parallel multi‐molecular orientation at higher temperature. The number of gas molecules adsorbed per site ranged from 0.83–2.2 while the number of adsorbent layers ranged between 1.4–5.6, depending on the gas and the temperature. The multilayer adsorption processes involved adsorption energies from 2.85 kJ/mol–9.77 kJ/mol for all gases, consistent with physisorption via van der Waals and London dispersion forces. The initial adsorption energies were higher and therefore stronger. A particularly high capacity for CO2 of 1088 mg(CO2)/g at 298 K was observed while H2 adsorption was only 9 mg(H2)/g. The other gases adsorbed at 145 mg/g–245 mg/g at 298 K. Thermodynamic functions that governed the adsorption process such as the internal energy, the enthalpy, and Gibbs free energy, are also reported, as well as the adsorption entropies, for the 5 gases.

Comparison of Gravimetric Determination of Methane Sorption Capacities of Coals for Using Their Results in Assessing Outbursts in Mines

The gravimetric method for determining coal gas sorption has many advantages and limitations. The article presents the influence of various factors on the results of methane sorption on coal. In mining practice, in addition to sorption properties of coal, knowledge of methane sorption capacity and effective diffusion coefficient determined when assuming a unipore sorption/desorption model are crucial for predicting sudden releases of methane from coal seams to a mine ventilation environment. In Poland, determining sorption capacities of coals for methane is mandatory when starting mining operations in new parts of coal deposits threatened by outbursts. Traditionally, gravimetric microbalances, such as intelligent gravimetric analysis (IGA), are used to determine adsorption capacity and desorption rate. Recently, newer microbalances XEMIS have been introduced to the market. Two gas laboratories, AGH in Krakow and CLP-B in Jastrzebie-Zdroj, respectively, compared experimental adsorption isotherms using XEMIS microbalances with mutually exchanged coal samples. Both sorption capacity at the pressure of 1 bar (a1bar) and effective diffusion coefficient (De) were independently determined for the coal samples tested. The results obtained are comparable despite the use of different microbalance XEMIS models. The conducted studies and comparative evaluation of the results allowed for assessing procedures for determining sorption properties using XEMIS microbalances. The exchange of laboratory experiences also allowed for the identification of methodology factors crucial for the development of a uniform procedure for conducting similar studies with XEMIS microbalance. The proposed factors for testing the sorption behavior of methane in coal structures may be helpful in mining practice.

Preparation of imprinted cryogels of cellulose cross-linked ionic liquids for selective separation of Gd(III) from rare earth leachate

The development of high technology has elevated industry’s dependence on rare earth resources. The hydrometallurgical process is widely used for the separation of rare earth elements (REEs) from rare earth ores, producing acidic leachate with trace amounts of REEs. Recovery of REEs from rare earth leachate not only mitigates the negative impact of leachate on the environment, but also contributes to the realization of sustainable resource utilization. In this study, two novel imprinted cryogel adsorbents, methyltrioctylammonium chloride-derivative carboxymethylated cellulose nanocrystal imprinted cryogel (LR-ICMC) and ethylmethylimidazolium bromide-derivative carboxymethylated cellulose nanocrystal imprinted cryogel (LM-ICMC), were constructed by using carboxymethylated modified cellulose nanocrystals as a backbone structure, and successfully branched ionic liquids (ILs) methyltrioctylammonium chloride-derivative and ethylmethylimidazolium bromide-derivative, respectively, for the separation of gadolinium ions (Gd(III)) from rare earth leachate. Firstly, SEM and TEM results showed that the incorporation of ILs retained part of the pore structure of carboxymethylated cellulose nanocrystals (CMCNCs). BET and TG results illustrated that the incorporation of ILs effectively increased the specific surface area and thermal stability of LR-ICMC and LM-ICMC. FT-IR and XPS results showed that LR-ICMC and LM-ICMC could adsorb Gd(III) by electrostatic and chelating effects. Secondly, adsorption isotherm experiments demonstrated the adsorption capacities of 66.880 mg/g and 75.895 mg/g for LR-ICMC and LM-ICMC, respectively; adsorption kinetic experiments demonstrated the ability of LR-ICMC and LM-ICMC to rapidly adsorb 85.152 % and 87.989 % of the maximum adsorption capacity, respectively, within the initial first 40 min. Finally, cycling experiments demonstrated the advantages of LR-ICMC and LM-ICMC in reuse, maintaining 89.245 % and 90.734 % of the original performance after five adsorption–desorption cycles, respectively. Based on these results, LR-ICMC and LM-ICMC were demonstrated to be highly efficient and reusable adsorbents for selective recovery of Gd(III) from rare earth leachate. This study deepens the application of ILs in solid-phase adsorbents and highlights the great potential of LR-ICMC and LM-ICMC in the field of REEs recovery.

Experimental and Mathematical Investigation of Hydrogen Absorption in LaNi5 and La0.7Ce0.1Ga0.3Ni5 Compounds

In the present study, the hydrogen-absorption properties of the LaNi5 and the La0.7Ce0.1Ga0.3Ni5 compounds were determined and compared. This work is therefore divided into two parts: an experimental part that presents and discusses the kinetics and isotherms of hydrogen absorption in the two compounds at two different temperatures (298 K and 318 K). In addition, the temperature variations inside the hydride bed were determined. In the second section, the experimental isotherms were compared to a numerical model processed using statistical physics. Following that, thanks to the perfect agreement between the experimental data and the proposed model, the stereographic and energetic parameters associated with the hydrogen absorption reaction, such as the number of hydrogen atoms per receptor site (n1, n2), the densities of the sites (Nm1, Nm2), the half-saturation pressures (P1, P2) and the absorption energies (ΔE1, ΔE2) for each receptor site, were calculated. All of these parameters are acquired by making numerical adjustments to the experimental data. Thermodynamic functions, such as internal energy and Gibbs energy, which regulate the absorption process, were then identified using these parameters. For both compounds, all of the aforementioned were compared and discussed in relation to initial temperature and pressure. The results demonstrated that the hydrogen-storage properties in LaNi5 are enhanced by more than 30% of stored mass and kinetics when Ce and Ga are substituted at the La sites.