Fractional-order Kinetic Model Research Articles

Comprehensive investigation of isotherm, RSM, and ANN modeling of CO2 capture by multi-walled carbon nanotube

Chemical vapor deposition was used to produce multi-walled carbon nanotubes (MWCNTs), which were modified by Fe–Ni/AC catalysts to enhance CO2 adsorption. In this study, a new realm of possibilities and potential advancements in CO2 capture technology is unveiled through the unique combination of cutting-edge modeling techniques and utilization of the recently synthesized Fe–Ni/AC catalyst adsorbent. SEM, BET, and FTIR were used to analyze their structure and morphology. The surface area of MWCNT was found to be 240 m2/g, but after modification, it was reduced to 11 m2/g. The modified MWCNT showed increased adsorption capacity with higher pressure and lower temperature, due to the introduction of new adsorption sites and favorable interactions at lower temperatures. At 25 °C and 10 bar, it reached a maximum adsorption capacity of 424.08 mg/g. The optimal values of the pressure, time, and temperature parameters were achieved at 7 bar, 2646 S and 313 K. The Freundlich and Hill models had the highest correlation with the experimental data. The Second-Order and Fractional Order kinetic models fit the adsorption results well. The adsorption process was found to be exothermic and spontaneous. The modified MWCNT has the potential for efficient gas adsorption in fields like gas storage or separation. The regenerated M-MWCNT adsorbent demonstrated the ability to be reused multiple times for the CO2 adsorption process, as evidenced by the study. In this study, a feed-forward MLP artificial neural network model was created using a back-propagation training approach to predict CO2 adsorption. The most suitable and efficient MLP network structure, selected for optimization, consisted of two hidden layers with 25 and 10 neurons, respectively. This network was trained using the Levenberg–Marquardt backpropagation algorithm. An MLP artificial neural network model was created, with a minimum MSE performance of 0.0004247 and an R2 value of 0.99904, indicating its accuracy. The experiment also utilized the blank spreadsheet design within the framework of response surface methodology to predict CO2 adsorption. The proximity between the Predicted R2 value of 0.8899 and the Adjusted R2 value of 0.9016, with a difference of less than 0.2, indicates a high level of similarity. This suggests that the model is exceptionally reliable in its ability to predict future observations, highlighting its robustness.

Hydrogenolysis of Glycerol by Heterogeneous Catalysis: A Fractional Order Kinetic Model with Analysis

The demand for glycerol, a by-product of biodiesel manufacturing, is anticipated to surpass supply, necessitating efficient conversion techniques for sustainability. The importance of effective conversion techniques is illustrated by the development of a system of fractional order differential equations using a literature reaction model. This study focuses on understanding and describing potential glycerol hydrogenolysis pathways by investigating the kinetics of a catalyzed hydrogenolysis model using qualitative analysis of fractional order differential equations, as there is limited research on the underlying reactions. The model is analyzed qualitatively and quantitatively using fixed point theorems. It is found to be generalized Ulam-Hyers-Rassias stable. The impact of the fractional operator is studied through computational simulations using a two-step Lagrange polynomial. Graphs at different fractional derivative orders show the significant influence of the fractional order on the model's classes. Even though the results are based on a particular kinetic model, they aim to improve comprehension and description of the process.

Application of oak charcoal-based activated carbon for the removal of methylene blue dye from aqueous solutions: kinetics, equilibrium, and reusability studies

Abstract The present study investigated the use of oak charcoal-based activated carbon (OC-AC) as an adsorbent for the removal of methylene blue (MB) dye from aqueous solutions. The study examined the effects of key operational variables, including pH, equilibrium time, adsorbent dosage, and initial dye concentration. The results showed that pH had no significant effect on MB adsorption for the initial MB concentration below 50 mg L−1 and an adsorbent dosage of 1 g L−1, but increasing the contact time and adsorbent dosage improved the removal efficiency. For instance, at an initial MB concentration of 50 mg L−1, the removal percentage increased from 76 to 99.9%, with increasing adsorbent dosage from 0.5 to 3 g L−1. In addition, with increasing contact time from 5 to 300 min, the removal percentage increased from 45.43 to 87.42%. The study also analyzed the kinetics and isotherm behavior of MB adsorption and found that the Avrami fractional order kinetic model and the Freundlich isotherm model provided the best fit for the experimental data. MB removal from real water samples showed that OC-AC could be used as an efficient and environmentally friendly adsorbent for removing MB dye from contaminated effluents with the removal percentage ranging from 83 to 97%.

Comprehensive adsorption and spectroscopic studies on the interaction of magnetic biochar from black wattle sawdust with beta-blocker metoprolol

The rise of contaminants of emerging concern in water-resources due to human activities has driven research toward wastewater treatment, specifically adsorption. The utilization of woody biomass for biochar production in adsorption has shown promise due to its high availability. This study shows the preparation of magnetic biochars (MB) from waste black wattle sawdust, utilizing ZnCl2 and NiCl2 (proportions: 1:0.5:0.5 = MB-0.5 and 1:1:1 = MB-1) as activating and magnetic agents. Synthesized via microwave-assisted-pyrolysis, MB boasts a high surface area (up to 765 m2.g−1) and functional groups, enhancing metoprolol medicine adsorption. Nonlinear kinetic and isothermal models were tested; the Avrami fractional-order kinetic model and Liu's isothermal model provided the best fits for experimental data. Thermodynamics and spectroscopic studies revealed spontaneous and exothermic adsorption processes, with physisorption magnitude and dominance of hydrogen-bond and π-π-interactions. MB can be easily extracted from an aqueous medium using magnetic fields, while adsorption capacity could be regenerated through green solvent elution.

An amine-functionalized strategy to enhance the CO2 absorption of type III porous liquids

Porous liquids (PLs) is a new material with two seemingly unrelated characteristics: porosity and liquidity. In this study, an amine functionalized strategy was proposed to enhance the CO2 absorption of Type III Porous Liquids. 2-Methylimidazole zinc salt (ZIF-8) modified by tetraethylenepentamine (TEPA) was chosen for providing porosities and the 1-Ethyl-3-methylimidazolium Bis(trifluoro-methanesulfonyl)-imide ([EMlm][NTf2]) was chosen as sterically hindered solvent, an amine-functionalized type Ⅲ porous liquids were reported. First, amine groups were successfully loaded on the ZIF-8. Then, the effect of amine loading on ZIF-8 was investigated. It was found the 30 TEPA@ZIF-8 nanoparticles were the optimum candidates based on CO2 absorption capacity and micropore analysis. Subsequently, the CO2 absorption capacity of absorbent was studied. 5-30TEPA@ZIF-8/[EMlm][NTf2] had a CO2 absorption capacity of 0.124 mmol g−1, which was 4.43 times higher than 5-0TEPA@ZIF-8/[EMlm][NTf2]. And the corresponding absorption rate increased by 745%. Three kinetics models were used for describing the absorption process, and the result showed the fractional-order kinetic model was the most accurate. Finally, the absorbent had a low heat absorption with a value of −1.38 kJ/mol. The CO2 absorption capacity lost just 4.3% after five cycles. All the results indicate the prepared porous liquids had an application potential in CO2 capture.

Green self-activating synthesis system for porous carbons: Celery biomass wastes as a typical case for CO2 uptake with kinetic, equilibrium and thermodynamic studies

Due to its rich porous structure, high specific surface area, and stable chemical characteristics, hierarchically biomass-derived porous carbon is considered to be the most potentially effective material for CO2 capture. Herein, a green self-activating synthesis system (SASS) has been introduced for the synthesis of porous carbons. In this system, there is no external reagent for the activation process, and the activating agents are the circulating gases such as CO2, CO, and H2O released during the pyrolysis treatment. As a typical case, this system was used for the synthesis of hierarchical porous carbons from celery wastes in hydroponic greenhouses. Based on the adsorption-desorption results, the optimal porous carbon was synthesized at 700 °C, providing a surface area as high as 1126 m2g−1 and a micropore volume of approximately 0.7 cm3g−1. The existence of graphitic-pyridinic nitrogen in the synthesized porous carbon structure was confirmed by X-ray photoelectron spectroscopy. The synthesized porous carbons were applied as an adsorbent for CO2 uptake. Under low pressures (0–1 bar), the synthesized carbons adsorbed 5 mmolg−1 at 0 °C and 2.03 mmolg−1 at 25 °C. The sorption capacity of the synthesized carbon at 25 °C and relatively high pressure of 9.5 bar was 9.57 mmolg−1. Based on the thermodynamic and kinetic models, it was clarified that the sorption process can be regarded as physisorption with an adsorption enthalpy of 23.2 kJmol−1. The fractional-order kinetic model was also shown to be the best fit in the kinetic curves. The presented synthesis system is a promising strategy for manufacturing green porous carbon from various waste organic precursors.

Experimental and kinetics investigations of low-concentration CO2 adsorption on several amine-functionalized adsorbents

The rapid cleanup of endogenous CO2 has become a necessity in environmental control and life support systems (ECLSSs), to ensure crew safety and long-term task execution. The extensively used non-regenerable LiOH and soda lime adsorbents, although exhibit high CO2 storage capacities and fast kinetics, can hardly fulfill the demands of reduced launch weight and storage volume in the space- and load-limited ECLSSs. New CO2 adsorbents with desirable attributes including high CO2 uptakes, good selectivity, facile regeneration, fast adsorption and desorption kinetics, and good multicycle stability are urgently needed. We developed amine-functionalized adsorbents by loading tetraethylenepentamine (TEPA) on mesoporous supports of activated carbon (AC), aluminum oxide (AO) and silica gel (SG). The adsorbents were characterized by N2 adsorption-desorption, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM) to study their microstructural properties. CO2 adsorption capacities and kinetic performance of the adsorbents with different supports and various amine loadings (10–50 wt%) were evaluated in 2%CO2 at 20 °C. The effects of support and amine loading on the structure-performance relationships of the adsorbents were demonstrated. The TEPA-SG-20 adsorbent (20 wt% TEPA loaded on silica gel support) exhibits the highest CO2 adsorption capacity of 1.90 mmol CO2/g and the maximum amine efficiency of 0.48 mmol CO2/mmol N. TEPA-SG-20 also exhibits fast CO2 adsorption kinetics, and the Avrami fractional order kinetic model provides a satisfactory correlation of the experimental CO2 uptakes. Furthermore, the TEPA-SG-20 adsorbent can be efficiently regenerated at 110 °C with a great regeneration efficacy of 97%. The desired adsorbent also exhibits good working stability with a low loss-in-capacity of 4.32% in 10 consecutive cycles. The good CO2 adsorption performance of TEPA-SG-20 is associated with the excellent microstructural properties such as high surface area, great pore volume and uniform dispersion of amine species. Overall, the desired TEPA-SG-20 adsorbent shows promise for low-concentration CO2 removal in ECLSSs.

Study of rice husk ash derived MCM-41-type materials on pore expansion, Al incorporation, PEI impregnation, and CO2 adsorption.

Conventional MCM-41 (M41), silica-pure pore-expanded MCM-41 (PM41), and Al-containing pore-expanded MCM-41 (PM41Ax) were synthesized from rice husk ash and tested as polyethyleneimine (PEI) supports for CO2 capture. Samples were characterized by small-angle X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, granulometric analysis, and nitrogen adsorption techniques. The PEI loading rate and CO2 adsorption-desorption performance were determined via thermogravimetric analysis. The effects of pore expansion, heteroatom Al incorporation, PEI loading rate, and Si/Al ratio on CO2 adsorption performance were examined. For the first time, the amount of PEI impregnated in PM41 was increased beyond 55 wt%, and the low-Si/Al-ratio PM41Ax support was used to load PEI in a novel procedure. Results show that at the same PEI loading rate, PM41 is always superior to M41 regarding adsorption capacity and adsorption rate. For a PEI loading rate >50 wt%, the superiority is amplified, reaching 15.9% and 21.3%, respectively. The use of the high-Al-containing PM41Ax support further increases adsorption capacity and adsorption rate by 13.4% and 9.6%, respectively. The presented reaction has a hybrid adsorption characteristic that includes both chemisorption and physisorption. Avrami’s fractional-order kinetic model describes the adsorption best. Over the entire time scale, the adsorption rate is determined by several kinetic diffusion-controlled processes. The intraparticle diffusion and equilibrium adsorption are two predominant rate-limiting steps, and their control ranges change with temperature. After five cycles of adsorption and desorption, the desorption ratio was as high as 99%, and the working capacity still retained 96.5% of the original capacity. In addition, the presence of water vapor increased the adsorption capacity of the adsorbents presented in this study. These advantages make them successful iin capturing CO2 in the post-combustion scenario.

Synthesis and CO2 adsorption performance of TEPA-loaded cellulose whisker/silica composite aerogel

The CO2 storage technology of abandoned coal mines has problems such as high gas separation costs and incomplete CO2 separation in the gas capture stage, which hinders the development of abandoned coal mines for CO2 storage. Regarding the issue above, a new type of carbon dioxide adsorption material has been prepared. Cellulose whiskers/silica composite aerogels were synthesized from skim cotton using tetraethyl orthosilicate (TEOs) and alkaline silica solution as silica precursors through a sol-gel process. The obtained aerogel has a rich porous structure with a specific surface area in the range of 34.7–170.1 m2/g, pore volume in the range of 0.06–1.52 cm3/g, and average pore size in the range of 4.5–11.9 nm. The sample CSA-TEPA-70% showed excellent adsorption performance, with a maximum adsorption capacity of 2.25 mmol/g. The Avrami fractional-order kinetic model can fit the CO2 adsorption process of the adsorbent well. This adsorbent has broad prospects in the CO2 capture process.

Preparation, characterization, and application of a homemade graphene for the removal of Congo red from aqueous solutions.

Ethylene diaminetetraacetic acid (EDTA)-functionalized graphene was synthesized from Nigerian coal using a chemical exfoliation method and the graphene was applied for the removal of Congo red dye from aqueous solutions. The synthesized coal graphene and the raw coal were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM)-energy-dispersive X-ray (EDX) spectroscopy, measurement of pHpzc (pH of point of zero charge), and Boehm titrations. The SEM data revealed surface roughness which is enhanced in the prepared graphene while the EDX revealed an increase in carbon content, the main constituent of graphene, from about 26% in the raw coal to about 80% in the prepared graphene. Various adsorption variables, such as pH, contact time, concentration of Congo red, and temperature, were varied for the removal of the dye using raw coal and the synthesized coal graphene. The Liu isotherm gave the best fit of the equilibrium data than the Langmuir, Freundlich, and Dubinin-Radushkevich models. The maximum adsorption capacities of the raw coal and synthesized coal graphene at 25°C are 109.1 mg/g and 129.0 mg/g, respectively. The Avrami fractional-order kinetic model was the best model for description of the kinetic data. The model had the lowest values of standard deviation than the pseudo-first-order and pseudo-second-order models. The adsorption process of the two materials occurred via two stages as proved by intraparticle diffusion model. The adsorption process of the Congo red removal was spontaneous, feasible, and endothermic. The study conclusively revealed the graphene nanomaterial to be a viable adsorbent for textile wastewater treatment.

CO2 Adsorption Capacity of Organic Alkali Sorbent CPEI from Polyethyleneimine

Support-free cross-linked polyethyleneimine sorbent (CPEI) for CO2 capture was evaluated as the regenerable sorbent. The total amines available for the CO2 capture on CPEI were determined by the polyethyleneimine/glutaraldehyde ratio for the synthesis of CPEI. The CO2 capacity of CPEI in the slurry bubble column reactor reached 4.92 mmol/g, which is 1.97 times higher than that obtained under anhydrous conditions. The adsorption kinetics of CPEI in the reactor were investigated in terms of the CPEI amount, the CO2 fraction, the gas flow rate, temperature, and the total amines available. The experimental breakthrough curves for the sorbent were well-fitted with a fractional-order kinetic model. The modeling analysis found the influence of diffusion resistance on the adsorption is more significant than that of the driving force. The CO2 capacity of CPEI remained almost constant during the temperature swing adsorption/desorption cycles.

Efficient CO2 adsorption and mechanism on nitrogen-doped porous carbons

In this work, nitrogen-doped porous carbons (NACs) were fabricated as an adsorbent by urea modification and KOH activation. The CO2 adsorption mechanism for the NACs was then explored. The NACs are found to present a large specific surface area (1920.72–3078.99 m2·g−1) and high micropore percentage (61.60%–76.23%). Under a pressure of 1 bar, sample NAC-650-650 shows the highest CO2 adsorption capacity up to 5.96 and 3.92 mmol·g−1 at 0 and 25 °C, respectively. In addition, the CO2/N2 selectivity of NAC-650-650 is 79.93, much higher than the value of 49.77 obtained for the nonnitrogen-doped carbon AC-650-650. The CO2 adsorption capacity of the NAC-650-650 sample maintains over 97% after ten cycles. Analysis of the results show that the CO2 capacity of the NACs has a linear correlation (R2 = 0.9633) with the cumulative pore volume for a pore size less than 1.02 nm. The presence of nitrogen and oxygen enhances the CO2/N2 selectivity, and pyrrole-N and hydroxy groups contribute more to the CO2 adsorption. In situ Fourier transform infrared spectra analysis indicates that CO2 is adsorbed onto the NACs as a gas. Furthermore, the physical adsorption mechanism is confirmed by adsorption kinetic models and the isosteric heat, and it is found to be controlled by CO2 diffusion. The CO2 adsorption kinetics for NACs at room temperature and in pure CO2 is in accordance with the pseudo-first-order model and Avramis fractional-order kinetic model.

K2CO3-Impregnated Al/Si Aerogel Prepared by Ambient Pressure Drying for CO2 Capture: Synthesis, Characterization and Adsorption Characteristics.

A new potassium-based adsorbent for CO2 capture with Al aerogel used as support is proposed in this work. The adsorbents with different surface modifiers (tetraethyl orthosilicate (TEOS) and trimethyl chlorosilane (TMCS)) and different K2CO3 loadings (10%, 20%, 30% and 40%) were prepared by sol-gel and iso-volume impregnation processes with ambient pressure drying. The CO2 adsorption performance of the adsorbents were tested by a fixed-bed reactor, and their adsorption mechanisms were studied by scanning electron microscopy (SEM), Brunauer Emmett Teller (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and X-ray fluorescence spectrometry (XRF). Furthermore, the adsorption kinetics and the cycling performance were investigated. The results show that using TEOS to modify the wet gel can introduce SiO2 to increase the strength of the skeleton. On the basis of TEOS modification, TMCS can further modify –OH, thus effectively avoiding the destruction of aerogel structure during ambient drying and K2CO3 impregnation. In this work, the specific surface area and specific pore volume of Al aerogel modified by TEOS + TMCS are up to 635.32 cm2/g and 2.43 cm3/g, respectively. The aerogels without modification (Al-B), TEOS modification (Al/Si) and TEOS + TMCS modification (Al/Si-TMCS) showed the best CO2 adsorption performance at 20%, 30% and 30% K2CO3 loading, respectively. In particular, the CO2 adsorption capacity and K2CO3 utilization rate of Al/Si-TMCS-30K are as high as 2.36 mmol/g and 93.2% at 70 degrees Celsius (°C). Avrami’s fractional order kinetic model can well fit the CO2 adsorption process of potassium-based adsorbents. Al-B-20K has a higher apparent activation energy and a lower adsorption rate during the adsorption process. After 15 adsorption-regeneration cycles, Al/Si-TMCS-30K maintain a stable CO2 adsorption capacity and framework structure, while the microstructure of Al/Si-30K is destroyed, resulting in a decrease in its adsorption capacity by nearly 30%. This work provides key data for the application of Al aerogel in the field of potassium-based adsorbent for CO2 capture.

Synthesis of polyethylenimine-impregnated Al-fumarate metal-organic framework and its CO<sub>2</sub> adsorption characteristics

Carbon capture and storage (CCS) can effectively reduce CO2 emissions from fossil-fuel combustion and mitigate global warming. Among the many CCS technologies, solid-amine based CO2 adsorption exhibits simple operation, great environmental sustainability, and good adsorption performance under post-combustion conditions of humidity, high temperature, and low CO2 partial pressure. Solid amine is always composed of porous solid support and organic amine. However, the disadvantages of complex preparation limit the application of traditional support materials. Therefore, the preparation of a kind of support with convenient synthesis, low cost, and high performance is of great significance for the preparation of solid-amine CO2 adsorbent. In this study, a method for the rapid preparation of an aluminum fumarate metal-organic framework (AlFu) is proposed based on sodium fumarate as the source of the organic ligand and water as the reaction solvent. Post-treatment of AlFu is not required due to the good water solubility of the reactants. The synthesized materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption, and thermogravimetric analysis (TGA) techniques. The results show that AlFu can be successfully synthesized at room temperature in 10 min. AlFu shows a typical porous morphology with a specific surface area of 828.44 m2/g. The TGA results show that AlFu is thermally stable up to 400°C. AlFu is a kind of superior solid-amine support material. Polyethylenimine (PEI) was then introduced into the AlFu support by an impregnation method to prepare solid-amine CO2 adsorbent, and the functionalized materials were characterized. The results show that the impregnation method can successfully introduce PEI into the AlFu framework. PEI modification did not destroy the crystal structure, but decreased the XRD characteristic peak intensity of AlFu. Increasing PEI loading leads to the agglomeration of the AlFu skeleton and the decrease of the specific surface area and pore volume of the samples. PEI modification will reduce the thermal stability of the material, but all samples showed good thermal stability below 200°C. Subsequently, the CO2 adsorption performance of the samples was investigated by TGA. The results showed that the optimum PEI content is 50 wt%, and the optimum adsorption temperature of PEI modified AlFu is 75°C, and that the highest CO2 adsorption capacity, 2.68 mmol/g, was obtained under optimum conditions. The CO2 adsorption kinetics onto PEI-AlFu with different PEI loadings was investigated by employing the pseudo-first/second-order kinetic models and fractional-order kinetic model. The results show the fractional-order kinetic model fitted well with the CO2 adsorption experiment data, and that the CO2 adsorption processes of PEI-AlFu were controlled by chemical reaction and physical transmission. Cyclic CO2 adsorption experiments revealed that PEI-AlFu has superior reproducibility after nine CO2 adsorption-desorption cycles. These results suggest that PEI-AlFu has high CO2 adsorption capacity and good reproducibility, and shows great potential for practical CO2 adsorption applications under post-combustion conditions.

Fast synthesis of Al fumarate metal-organic framework as a novel tetraethylenepentamine support for efficient CO2 capture

In this study, a rapid synthesis of Al fumarate metal-organic framework (AlFu) at 25 °C for 1 min has been reported. The synthesized AlFu has been impregnated by different amounts of tetraethylenepentamine (TEPA) to build novel CO2 adsorbents. AlFu before and after functionalization was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and nitrogen adsorption/desorption isotherms (BET). The results showed the introduction of TEPA into AlFu was successfully achieved by impregnation. The CO2 adsorption performances of AlFu and TEPA@AlFu were investigated by the TGA method. The effect of adsorption temperature, TEPA loading and CO2 partial pressure on the adsorption performance was studied. The results showed that the optimum adsorption temperature of TEPA@AlFu is 75 °C, and increasing the loading amount of TEPA will enhance the CO2 adsorption capacity and decrease the adsorption rate. High CO2 partial pressure is good for the adsorption process, and the highest CO2 adsorption capacity of 4.10 mmol/g was obtained at 75 °C in a pure CO2 atmosphere for the AlFu loaded with 60 wt% TEPA. The studies of adsorption kinetics show the fractional-order kinetic model fitted well with the CO2 adsorption experiment data. Moreover, the CO2 adsorption capacity of 60TEPA@AlFu sorbent declined only 2.81% after 10 adsorption-desorption cycles tested in the temperature range of CO2 adsorption (75 °C) and desorption (110 °C).

Alkali modified oak waste residues as a cost-effective adsorbent for enhanced removal of cadmium from water: Isotherm, kinetic, thermodynamic and artificial neural network modeling

Heavy metals are kind of toxic substances which are abundant in all municipal, agricultural, industrial and treated wastewaters. In this research, a comparative study was carried out for adsorptive removal of Cd2+ from aqueous solution using raw oak waste and NaOH-activated oak waste at different experimental conditions namely, pH of solution (2–8), contact time (5–240min), adsorbent dosages (0.1–10g/L) and initial Cd2+ concentrations (25–100mg/L). In addition, the experimental data of Cd2+ adsorption were fitted with different isotherm and kinetic models to determine the most appropriate model. Artificial neural network (ANN) model was also used to find the effect of each individual parameter on Cd2+ adsorptive removal. Based on the results of batch experiments, adsorbent dosages and initial Cd2+ concentrations had direct and indirect relationships with Cd2+ removal, respectively. Furthermore, among all applied isotherm and kinetic models, Langmuir isotherm model and Avrami fractional-order kinetic models could best-fitted with the experimental data of Cd2+ removal. The results of thermodynamic studies revealed that the adsorption of Cd2+ onto the surfaces of oak waste adsorbents is exothermic and spontaneous. Finally, according to the findings of ANN studies, this approach could model the role of each parameter on Cd2+ removal with high coefficient of correlation (>0.99). Accordingly, pH of solution and temperature had the highest and lowest influence on removal of Cd2+ from solution, respectively. The results implied that oak waste can be selected as a promising and environmentally friendly adsorbent for the effective remediation of water bodies containing heavy metals.

Kinetic study and breakthrough analysis of the hybrid physical/chemical CO2 adsorption/desorption behavior of a magnetite-based sorbent

The CO2 adsorption and desorption kinetics of a magnetite-based sorbent, CB-FM, obtained coating a low-cost carbon black (CB) with magnetite fine particles (FM), has been systematically and thoroughly investigated for the first time under post-combustion capture operating conditions. Experimental data of CO2 uptake (18–150 °C) and extent of CO2 desorption (200–260 °C) have been fitted to different apparent kinetic models, namely pseudo-first-order, pseudo-second-order and Avrami’s fractional-order kinetic models. The mechanism of CO2 adsorption on CB-FM in terms of controlling mass transfer resistances, interparticle diffusion, intraparticle diffusion and Boyd’s film-diffusion models has been also investigated. Finally, a two-constants deactivation model has been adopted to simulate the dynamic breakthrough curves.

Porous carbons derived from polyethylene terephthalate (PET) waste for CO2 capture studies

Oxygen augmented carbon adsorbent has been developed using polyethylene terephthalate (PET) waste by first carbonizing at different temperatures (500–800 °C) and then chemically activating using different ratios of KOH: PET (mass ratio 1 to 4). The textural characterization divulges the effect of activation in terms of the development of the high surface area and micropore volume of 1690 m2 g−1 and 0.78 cm3 g−1 respectively, for the optimum sample (PET-3-700). Elemental analysis of PET-3-700 illustrates the presence of 34.33% oxygen and XPS results confirmed the occurrence of oxygen moieties which enhance the basicity of the adsorbent and promote CO2 capture. The CO2 adsorption capacity of prepared carbons was determined thermogravimetrically under dynamic conditions, at different concentrations of CO2 (6–100%) and temperatures. The maximum CO2 uptake capacity of 2.31 mmol g−1 was exhibited by PET-3-700 at an adsorption temperature of 30 °C under 100% pure CO2 flow. Four adsorption-desorption cycles corroborate almost complete regenerability of the prepared adsorbent. Adsorption kinetics at all adsorption conditions was described best by fractional order kinetic model. Freundlich isotherm fit indicates the surface of adsorbent being heterogeneous and low values of isosteric heat shows physisorption behavior of the process. Negative values of thermodynamic parameters indicate exothermic and feasible nature of adsorption process.

Chemically activated nanoporous carbon adsorbents from waste plastic for CO2 capture: Breakthrough adsorption study

Abstract This paper describes the preparation of O-enriched porous carbonaceous adsorbents derived from low cost, abundantly available polyethylene terephthalate (PET) waste with high carbon content by directly carbonising at different temperatures (500–800 °C) and then chemically activating using variable impregnation ratios of KOH to carbon. The prepared carbon adsorbents were characterized for their textural and surface chemical properties using nitrogen sorption, CHN, FTIR, XRD, SEM, HRTEM, and XPS techniques. Further, to assess their CO2 adsorption-desorption performance under dynamic conditions, breakthrough experiments were conducted in a fixed-bed adsorption set up. Porous carbon obtained at 700 °C with KOH to carbon mass ratio of 3 (Act-3-700) exhibited best textural properties with BET surface area of 1690 m2g-1 and micropore volume of 0.78 cm3 g−1 and showed highest CO2 uptake of 1.31 mmol g−1 at 30 °C and 12.5% CO2 concentration. Four adsorption–desorption cycles establish the adsorbent's remarkable stability and regeneration. Furthermore, fractional order kinetic model explained the CO2 adsorption kinetics and Freundlich isotherm showed superior fit with the adsorption equilibrium data suggesting heterogeneous nature of the adsorbent surface. Negative values of Gibbs free energy ΔG° and adsorption enthalpy ΔH° indicate the spontaneous and exothermic nature of adsorption process.

Dynamic CO2 adsorption on activated carbon adsorbents synthesized from polyacrylonitrile (PAN): Kinetic and isotherm studies

Abstract In this research work, PAN-based activated carbon adsorbents have been synthesized by using the simple and cost-effective route of carbonization and chemical activation. The effect of different activating agents like NaNH2, NaOH, K2CO3, and KOH on the textural properties of PAN and its adsorption potential for CO2 under dynamic conditions was investigated. The KOH activated carbon adsorbent exhibited the surface area of 1890 m2 g−1 whereas, NaNH2, NaOH, and K2CO3 activated carbons showed the surface area of 833 m2 g−1, 1020 m2 g−1 and 1250 m2 g−1 respectively. The porosity of the adsorbents was affirmed by SEM and HRTEM analysis. Whereas, XPS analysis have been revealed the various types of basic functional groups which contains oxygen and nitrogen on the carbon surface. The adsorbent, PAN-KOH shows the best CO2 uptake of 1.2 mmol g−1 which is about four times the adsorption capacity of the carbonized PAN (0.32 mmol g−1) under 12.5% CO2 concentration flow. Moreover, the adsorbents showed a stable adsorption capacity over multiple sorption cycles. The best information of the adsorption at all adsorption temperatures was given by fractional order kinetic model whereas, the best fit of Freundlich isotherm model with the adsorption data and high Qst values confirms the adsorbent's surface heterogeneity. Thus, the present study provides a two-step synthesis process to produce nitrogen and oxygen-containing activated carbons from low-cost and commercially available PAN for its use in CO2 capture practical applications.