Intraparticle Diffusion Model Research Articles

The valorization of Prunus mahaleb shell through acid modification for the sorption of Pb2+ removal from aqueous solution

AbstractThis study aimed to investigate the biosorption performance of acid-modified waste Prunus mahaleb (PMA) shells in the removal of Pb2+ ions from aqueous solutions. Changes in the morphological properties and functional components of PMA biosorbent were characterized using SEM–EDX, FT-IR, BET, and PZC analyses. The effect of various parameters such as initial Pb2+ concentration, pH, PMA dosage, contact time, and temperature on biosorption was investigated using a batch biosorption procedure. The maximum biosorption capacity, determined using the Langmuir isotherm, was calculated to be 119 mg g−1. It was found that the biosorption kinetic mechanism followed pseudo-second-order kinetics and intraparticle diffusion model. According to the determined thermodynamic parameters, the biosorption mechanism was found to be endothermic (ΔH° > 0), spontaneous (ΔS° > 0), and entropy-increasing (ΔG° < 0). The outcomes of the experiment were evaluated in comparison to other sorbents that have been previously commonly used in the literature. It was demonstrated that PMA could be a promising, environmentally friendly, cost-effective, and sustainable potential biosorbent for the removal of Pb2+ ions.

Investigation of effectiveness of KOH-activated olive pomace biochar for efficient direct air capture of CO2

The capture of CO2 directly from the air is one of the most promising methods under investigation in recent years to reduce the environmental concentration of this pollutant in order to mitigate its effects on climate change. In this work, the activation of olive pomace biochar with potassium hydroxide, KOH, has been studied for its use as a CO2 adsorbent. The effectiveness of biochar activated with KOH at 750 °C in an inert N2 atmosphere was evaluated, using different mass ratios of biochar/KOH, 1:0.5, 1:1, and 1:2. Various characterisation analyses of the biochar were performed to determine its chemical composition, specific surface area, pore size and volume, structure, morphology, and functional groups. The adsorption isotherm was determined at atmospheric pressure and a temperature of 10 °C. The experimental equilibrium results were fitted to the Langmuir, Freundlich, and Temkin models. Additionally, the kinetic behavior of biochar/KOH as an adsorbent was studied, and dynamic experiments were conducted at atmospheric pressure and 10 °C. The experimental data were fitted to various kinetic models (pseudo-first order, pseudo-second order, Avrami, and Elovich). Furthermore, the mass transfer mechanism during the adsorption process was evaluated using the intra-particle diffusion model. Finally, biochar regeneration was investigated for its subsequent reuse as an adsorbent. For this purpose, complete desorption of the captured CO2 in the biochar was easily carried out by modifying the temperature.

Design and development of rare earth elements anchored pectin/chitosan integrated magnesia hybrid composite for effective defluoridation of water

Fluoride pollution in drinking water is a worldwide concern arises from natural and human actions. The excessive fluoride present in drinking water leads to fluorosis. In this study, dual polysaccharide biopolymers namely pectin and chitosan were incorporated with magnesia followed by imprinted with lanthanum and cerium ions gives PCML (pectin/chitosan/magnesia/lanthanum) and PCMC (pectin/chitosan/magnesia/cerium) hybrid materials for fluoride adsorption investigation. The enhanced defluoridation capacities (DCs) of PCML and PCMC composites were seen as 4.976 and 4.972 mg g−1 by 30 min individually. To decide the impact of various affecting parameters viz., dosage, initial fluoride concentration, pH, contact time and challenging anions were examined in batch method. The pH results show the utmost DCs of PCML and PCMC composites was noted at pH 6 and in co-ions experiments, the significant competition found with bicarbonate ion owing to the superior electronic building of bicarbonate ion. The defluoridation equilibrium data of PCML and PCMC composites follows Langmuir, pseudo-second-order and intraparticle diffusion models. The positive ΔH° value as 3.04 kJ mol−1 for PCML composite and 2.88 kJ mol−1 for PCMC composite were exposed that the endothermic nature of fluoride adsorption occurs onto PCML and PCMC composites. The defluoridation mechanism of PCML and PCMC composites were attained by complexation, ion-exchange and electrostatic interaction. The reusability results shows that the synthesized PCML and PCMC composites can be reused upto six cycles. Field trail result demonstrates the synthesized PCML and PCMC composites were applicable at field conditions by reducing fluoride concentration below 1.5 mg/L.

Hydrophobic hypercrosslinked polymers prepared by secondary pore-forming method as excellent toluene adsorbents

In this work, inspired by molecular imprinting technology, we developed a secondary pore-forming method to chemically etch three hypercrosslinked polymers which are constructed from three novel hexapolar monomers containing imine groups, resulting in three novel hydrophobic porous hyper-crosslinked polymers (HCPs) pGly-TPA, pP-TPA and pBP-TPA. The structures were determined by FT-IR and solid-state 13C NMR spectroscopic techniques. The specific surface areas of pGly-TPA, pP-TPA and pBP-TPA are 694.1, 197.9 and 497.7 m2/g, respectively. All three porous polymers exhibit high hydrophobic properties with wetting angles of much greater than 90°. The breakthrough adsorption experiments revealed that the three prepared polymers exhibited significant adsorption capacity for toluene (322.05 mg/g for pGly-TPA, 114.43 mg/g for pP-TPA and 279.14 mg/g for pBP-TPA), but showed almost no adsorption for ethyl acetate, cyclohexane, and n-hexane, exhibiting certain molecular size and polarity selectivity. The adsorption behaviors of toluene on pGly-TPA, pP-TPA and pBP-TPA can be fit by the Boltzmann model and the Yoon-Nelson model, suggesting that the fixed bed has low mass transfer resistance. The adsorption rate is controlled by both external diffusion and intraparticle diffusion, as shown by the intraparticle diffusion model analysis. In addition, the adsorption capacity of toluene on pGly-TPA is almost unchanged under high humidity (70 %) or five adsorption–desorption processes, which demonstrates exceptional water-resistance and stability. This work is a reference for preparing novel hydrophobic HCPs using the secondary pore-forming method for removing VOCs from humid air.

Photocatalytic degradation of Direct Black 10 B dye in aqueous phase using nanophotocatalyst

ABSTRACT In this study, the photocatalytic degradation of an aqueous solution containing a mixture of Direct Black 10 B dye using titanium dioxide (TiO2) as a catalyst was investigated. The degradation of Direct Black 10 B dye was studied for several parameters, including the catalyst, dosage, initial concentration of dye, and pH. Variable catalyst quantities (0.25, 0.50, 0.75, 1, and 1.25 g), pH (3, 5, 9, and 11), and beginning dye concentration were used in the studies (62.5, 125, 250 and 500 ppm). 0.75 g/litre of catalyst was found to be the ideal dose. The ideal catalyst concentration was determined to be 0.75 g/litre, and the maximal dye decolourization rate was further studied in a basic media, i.e. at pH 9 Blue turned into grey and finally white in the acidic medium, whereas blue turned into pink and then white in the basic medium. After 3 hours 98% of the colour was completely removed at this optimal point. The Langmuir, Freundlich and Temkin isotherms were examined. The langmuier isothers with regression coefficient 0.99 is best fitted as compared to Freundlich and Temkin isotherms. The findings of the kinetic analysis suggest that the Pseudo Second order with regression coefficient 0.9923 is best suited as compared with the pseudo first order and Intra-particle diffusion model.

Hydrothermally Produced Activated Carbon Impregnated with ZnO for the Adsorptive Removal of Toxic Pharmaceutical Contaminants from Aqueous Solution

This research explores the adsorption (AD) of diclofenac sodium (DS) onto a Hydrothermally produced activated carbon impregnated with ZnO (HTC-AC/ZnO) surface, considering various factors such as initial concentration (IC), adsorbent dose, contact time, and pH. The characterization of HTC-AC/ZnO was performed using X-ray diffractometer (XRD), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), and nitrogen physisorption spectroscopy (BET). Tests were conducted with different adsorbent doses (0.5–4 g/L) at 303 K and various initial diclofenac concentrations (ranging from 50 mg/L to 250 mg/L) to observe their effects. Additionally, pH values were altered from 2 to 12 to study their influence on AD. Kinetic studies, thermodynamic studies, and AD isotherm models were examined. The Temkin isotherm model (TIM) was found to be the most accurate for DS-AD on HTC-AC/ZnO. For DS-AD on HTC-AC/ZnO, pseudo-first-order models (PFOM), intraparticle diffusion model (IPDM), and pseudo-second-order models (PSOM) were applied, with a correlation coefficient of 0.945, indicating a good fit for PFOM. The kinetics suggested rapid adsorption. Notably, the HTC-AC/ZnO composite exhibited consistent AD characteristics across four consecutive cycles, with a removal efficiency exceeding 99.38%. This suggests that HTC-AC/ZnO is an appropriate and economically viable adsorbent for the elimination of DS from water-based solutions. The investigation provides compelling evidence that HTC-AC/ZnO is a viable adsorbent for the effective elimination of DS from water sources.

The Effectiveness of Carbonized Neem Leaves Adsorbent for the Removal of Phenol from Synthesized Effluent Using the Batch Process Method

The adsorption of phenol in aqueous solution was investigated using carbonized neem leaves adsorbents. The effect of various factors such as contact time, phenol concentration, pH, temperature, and amount of adsorbent on the adsorption capacity of the adsorbents was determined. The results show that maximum adsorption was obtained at a contact time of 150 minutes, at a phenol concentration of 50 mg/L, optimum adsorption temperature of 45⁰C, pH of 2 and adsorbent dosage of 3 g/L. The equilibrium data was well described by the Freundlich isotherm equation (R2= 0.955 ). This shows a heterogenous adsorption process. The kinetics of the process were explained by the intra-particle diffusion models (R2>0.9). This fitted data indicates a degree of boundary layer control and is not limited to intra-particle diffusion.

Revealing the contribution of Cu(II) and Cu(I) inherent in MOF-199 for efficient thiophene removal at room temperature

Thiophene (C4H4S) removal from coke oven gas is critical to its subsequent high valuable utilization but remains a challenge. MOF-199 was considered as a promising candidate for C4H4S adsorption removal owing to its nature of enriched opened Cu sites. However, the presence of mixed valence of Cu(II) and Cu(I) in MOF-199 makes it puzzling to their respective contribution to the removal of C4H4S. Herein, a series of MOF-199 with different Cu(I) contents were synthesized using different methods, including hydrothermal, solution diffusion, and ultrasonic, and their C4H4S adsorption performance were investigated. The respective contributions of Cu(II) and Cu(I) to the C4H4S removal was systematically discussed. The collected results indicated that although the samples prepared with different methods present a remarkable difference in textural characters, the latter was found to have a negligible influence on the C4H4S removal owing to MOF-199(H) affording an inferior surface area and pore volumes but performing the best C4H4S removal capacity of 53.7 mg S/g. The co-adsorption results of CH3SCH3 and C4H4S indicated that the excellent performance of MOF-199(H) mainly attributed to the presence of Cu(I), which provides active sites for C4H4S adsorption through π complex coordination. Cu(II) species was also found to the C4H4S adsorption via soft-acid-base coordinated interaction, but its contribution is 8.3 mg S/g, only accounting for 15.5 %. Additionally, the adsorption of C4H4S on MOF-199(H) was found to follow the intra-particle diffusion model and the Langmuir models. Moreover, MOF-199(H) also exhibited an excellent regeneration performance due to the weak interaction between C4H4S and their opened Cu sites, the C4H4S adsorption capacity still reaches 50.6 mg S/g after three regeneration cycles, about 94 % of its initial value. The results collected in this study will provide new insights for the manipulation of performance of C4H4S adsorption on the MOF-199.

Diclofenac sodium adsorption in aqueous media by activated carbon obtained from einkorn (Triticum monococcum L.) husk

The uncontrolled release of waste diclofenac with low biodegradability is considered to be a potential threat for the environment and creatures. To find effective solution for this issue, this study reports the adsorption performance of diclofenac sodium salt (DCF) by using activated carbon (EHAC) obtained from einkorn (Triticum monococcum L.) husk in aqueous solution under various circumstances. It was found that DCF adsorption on EHAC was highly solution pH dependent, and DCF adsorption by EHAC decreased with increasing adsorption temperature. Equilibrium data showed that fitted isotherm model with the experiment results of DCF adsorption on EHAC followed the order of Langmuir > Temkin > Freundlich > Dubinin-Radushkevich. Adsorption capacity of EHAC for DCF adsorption in aqueous solution was calculated to be 147.06 mg/g at 25 °C. The adsorption kinetic of DCF adsorption on EHAC was determined to obey the pseudo-second-order kinetic model. By utilizing FTIR and pH data obtained from DCF adsorption on EHAC, DCF adsorption mechanisms with some interactions such as π-π stacking, electrostatic interactions, and hydrogen bonding were suggested at diverse pH values. Additionally, intraparticle diffusion model was applied to kinetic results to further recognize the kinetic mechanism of DCF adsorption on EHAC. Furthermore, thermodynamic parameters for DCF adsorption on EHAC were calculated and evaluated, in which DCF adsorption process by EHAC was determined to be exothermic, spontaneous, and feasible.

Atenolol uptake from pharmaceutical sources onto carbon aerogel prepared by supercritical CO2 drying

Atenolol (ATL) is a popular medication which is widely used to treat hypertension and angina. It is often found in aqueous environments, posing potential risk to human health and ecological well-being. In this study, carbon aerogel was prepared by supercritical CO2 drying of resorcinol–formaldehyde resin subsequently carbonized at 600 °C in an inert atmosphere. This porous material was characterized by SEM, BET, FTIR, and XRD and used for the first time for the removal of ATL from aqueous solutions under varying experimental conditions. Carbon aerogel in the form of microbeads exhibited a relatively high specific surface area of 376.02 m2/g and median pore radius of 9.83 nm. The isotherm models of Langmuir, Freundlich, Temkin, Redlich-Peterson and Brouers-Sotolongo were used to interpret the equilibrium data. Although most of the applied models fitted the data well, the calculated values for maximum sorption capacity (qmax) showed a huge deviation when compared to experimental value of 76.66 mg/g. The pseudo-first and pseudo-second-order kinetic models, Chrastil’s model, and the intraparticle diffusion model were employed for fitting the kinetic data. The rate of the process was rapid with most of the uptake attained in the first 20 min of the contacting. The sorption optimum was achieved at pH pH 9.0 and for sorbent’s dosage of 750 mg/L. Reusability study of the spent aerogel conducted in seven cycles evidenced slight decrease of approximately 1 % in removal efficiency across the cycles indicating that the sorbent maintained its high effectiveness and stability throughout its usage.

Synthesis of MgZnAl Layered Triple Hydroxide Nanoplates as an Efficient Adsorbent for Removing the Acid Yellow 76 Azo Dye

AbstractA simple hydrothermal method was employed for synthesizing MgZnAl layered triple hydroxide nanoplates (MgZnAl LTH) as an efficient adsorbent for removing the Acid Yellow 76 (AY76) azo dye. A batch process was used to perform adsorptions were and investigate the effects of experimental parameters including temperature, adsorbent dosage, solution pH. The best adsorption conditions obtained were pH of 4, MgZnAl LTH dosage of 20 mg and temperature of 55 °C. The kinetics of adsorption was studied using pseudo‐first‐order, pseudo‐second‐order, Elovich, and intraparticle diffusion models. To obtain equilibrium absorption data, Freundlich, Langmuir, and Temkin isotherms were utilized. The findings showed that the adsorption data based on the experiment had a good agreement with the Freundlich model. The highest capacity of adsorption equal to 277.8 mg/g was obtained for the MgZnAl LTH nanoplates toward AY76. Thermodynamic results showed that the process of adsorption of AY76 onto MgZnAl LTH nanoplates had a spontaneous and endothermic nature.

Phosphate adsorption on dried alum sludge: Modeling and application to treatment of dairy effluents

This study evaluates Alum sludge from drinking water treatment plants for the efficient and cost-effective removal of phosphates from aqueous solutions. Extensive characterization and batch experiments have established that optimal phosphate removal was achieved with a sludge dosage of 20 g L−1 (at an initial phosphate concentration of 100 mg L−1), a pH of 5, a temperature of 23 °C, and a stirring speed of 200 rpm. These conditions significantly reduced phosphate levels, ensuring compliance with legal discharge limits. The Langmuir isotherm, pseudo-second-order kinetic and intraparticle diffusion models best described the adsorption process, highlighting the spontaneous and endothermic nature of the phenomenon. The sludge effectively reduced phosphate concentrations to acceptable levels when applied to dairy effluents. This study underscores the potential of Alum sludge as a viable solution for phosphate management in environmental cleanup efforts.

Determination of water quality and efficient removal of arsenic and iron from groundwater using mahogany fruit husk and banana peduncle charcoals

The groundwater (GW) of Bangladesh is predominantly contaminated with arsenic (As) and iron (Fe) which has a bad impact on human health. We tried to remove these elements with easily available mahogany-fruit (Swietenia mahagoni) husk charcoal (MHC) and banana (Musa acuminata) peduncle charcoal (BPC). The trial was implemented with 3 replications throughout the research. The sampled GW contained 0.06 mg As L−1 and 4.83 mg Fe L−1. Firstly, the pH was 3, 5, 7, and 9 with a 250 mg L−1 dose. The MHC removed almost 91.05 % of As at pH 5.0, and BPC removed almost 86.67 % of As at pH 9. However, in the case of Fe, the MHC removed almost 100 % at pH 7 and 9; and BPC removed the same quantity at pH 5, 7, and 9. Secondly, the contact times were 0, 5, 10, 20, and 40 min with a 250 mg L−1 dose at pH 7.0. The maximum removal of As and Fe was 100 % with MHC and BPC at 5 min. The pseudo-first-order kinetic, pseudo-second-order kinetic, and intra-particle diffusion models were considered. The result showed that the rate of adsorption followed the pseudo-second-order kinetic model. Lastly, the adsorbent doses were 0, 50, 150, 250, and 350 mg L−1. At pH 7, the highest removal of As was 79.47 % and Fe removal was 100 % at 350 mg L−1 dose for MHC. Similarly, the values were 79.29 % and 100 % for the same at 350 mg L−1 dose of BPC, indicating these charcoal are good for heavy metals removal.

Sequestration of divalent heavy metal ions from aqueous environment by adsorption using biomass-bentonite composites as potential adsorbent: Equilibrium and kinetic studies

Hybrid clay adsorbents have been investigated in recent studies as cheap and effective adsorbents for eliminating micropollutants, such as heavy metal ions from aqueous solution. Here, we modified bentonite (BEN) with palm kernel shell and groundnut shell by calcination to obtain palm kernel shell-modified bentonite (BPKS) and groundnut shell-modified bentonite (BGS). We studied the batch equilibrium adsorption of Pb2+, Cd2+ and Ni2+ ions under the influence of dosage, solution pH, contact time and concentration. Under these conditions, we found that the modified adsorbents (BGS and BPKS) had a higher equilibrium adsorption (qe) for the metal ions than unmodified BEN. BEN exhibited Langmuir adsorption capacities (Qo) of 32.47, 14.04 and 14.16 mg/g for Pb2+, Cd2+ and Ni2+, respectively. BGS and BPKS had Qo values of 29.15, 14.27, 16.61 and 31.75, 17.67, 15.625 mg/g for Pb2+, Cd2+, Ni2+, respectively. Investigations revealed that the rate of adsorption on the three adsorbents is best described by a pseudo-second-order kinetic model, with R2 values ≥ 0.9; the intra-particle diffusion model establishes a surface interaction mechanism involving the exchange of electrons between the surfaces of the adsorbents and the adsorbate. Scanning electron microscopy results suggest porous and heterogeneous adsorbent surfaces, indicating a physio-sorption phenomenon. The modifications increased the surface area of BEN from 78.435 to 194.850 and 140.650 m2/g in BGS and BPKS, respectively, using BET surface area analysis. However, the average pore width of BEN reduces from 3.8 to 3.3 nm in both BGS and BPKS. Also, the modification enhanced the cation exchange capacity in BPKS only. The findings from this study offered invaluable insights into how biomass can enhance the physicochemical properties of BEN, as needed for practical environmental application and/or optimization, during the removal of Pb2+, Cd2+ and Ni2+ ions from aqueous media.

Composites of sodium alginate based - Functional materials towards sustainable adsorption of benzene phenol derivatives - Bisphenol A/Triclosan

The present study evaluates the adsorption efficiency of low-cost carbonaceous adsorbents as fly ash (FA), saw dust biochar (SDB) (untreated and alkali - treated), live/dead pulverized white rot fungus Hypocrea lixii biomass encapsulated in sodium alginate (SA) against the commercially available activated carbon (AC) and graphene oxide (GO) SA beads for removal of benzene phenol derivatives - Bisphenol A (BPA)/triclosan (TCS). Amongst bi - and tri - composites SA beads, tri-composite beads comprising of untreated flyash - dead fungal biomass - sodium alginate (UFA - DB - SA) showed at par results with commercial composite beads. The tri - composite beads with point zero charge (Ppzc) of 6.2 was characterized using FTIR, XRD, surface area BET and SEM-EDX. The batch adsorption using tri - composite beads revealed removal of 93% BPA with adsorption capacity of 16.6 mg/g (pH 6) and 83.72% TCS with adsorption capacity of 14.23 mg/g (pH 5), respectively at 50 ppm initial concentration with 6 % adsorbent dose in 5 h. Freundlich isotherm favoring multilayered adsorption provided a better fit with r2 of 0.9674 for BPA and 0.9605 for TCS respectively. Intraparticle diffusion model showed adsorption of BPA/TCS molecules to follow pseudo - second order kinetics with boundary layer diffusion governed by first step of fast adsorption and intraparticle diffusion within pores by second slow adsorption step. Thermodynamic parameters (ΔH°, ΔS°, ΔG°) revealed adsorption process as exothermic, orderly and spontaneous. Methanol showed better desorbing efficiency leading to five cycles reusability. The phytotoxicity assay revealed increased germination rate of mung bean (Vigna radiata) seeds, sprinkled with post adsorbed treated water (0 h, 5 h and 7 h) initially spiked with 50 ppm BPA/TCS. Overall, UFA - DB - SA tri - composite beads provides a cost effective and eco - friendly matrix for effective removal of hydrophobic recalcitrant compounds.

By-product Eucalyptus leaves valorization in the basic dye adsorption: kinetic equilibrium and thermodynamic study

Abstract Algerian Eucalyptus Leaves (AEL), a natural biodegradable adsorbent abundantly available, was used for the removal of methylene blue (MB) dye. The AEL properties for the removal of MB were investigated under different conditions by varying the AEL amount, MB concentration, pH of the solution and the reaction temperature. Scanning electron microscopy (SEM) and infrared spectroscopy (FTIR) techniques have been used to characterize AEL biosorbent. Experimental results showed that the adsorption of MB dye at the concentration of 50 mg L−1 reached to 91 % at pH 10 with a stirring speed of 200 rpm and after 180 min of reaction time. The experimental data were analyzed using the linear forms of different kinetic models (pseudo-first order kinetic model, pseudo-second order kinetic model, and intra-particle diffusion models). The results demonstrated that the adsorption kinetics of MB was consistent with the pseudo-second order model with R 2 value of 0.9969. The isotherm models Langmuir, Freundlich, Dubinin, Elovich, Brunaut Emmet Teller and Temkin models were also investigated to describe the adsorption equilibrium. The results show that the AEL adsorption is in accordance with Temkin isotherm. The thermodynamic study revealed that the adsorption is spontaneous and exothermic. Therefore, as a cheap green adsorbent with high MB adsorption performance, AEL is expected to become one of the best candidate materials for future industrial wastewater treatment.

Performance of removing aqueous contaminant by zirconium based adsorbents: a critical review

The studies on materials for decontamination in aqueous solutions have increasingly received greater attentions. Such contaminants as heavy metals, arsenic, fluoride and phosphate are harmful to humans and aqueous species due to higher toxicity. Zirconium based adsorbents have become more attractive due to outstanding performance in decontamination. This article provides a comprehensive review of the performance and mechanisms of five types adsorbents: zirconium (hydro)oxides, zirconium hydrogen sulfate, zirconium based multiple metal typed adsorbents and zirconium impregnated complexes. The pseudo-first order and pseudo-second order equations and the intraparticle diffusion model can be applied in describing the adsorption kinetics, while Langmuir and Freundlich equations are the most commonly used adsorption isotherms. The important mechanisms for uptake of contaminants are: ligand exchange between adsorbate and adsorbent, surface complexation formation, and Lewis acid–base and electrostatic interactions. A series of successful studies demonstrate that the adsorbents are promising for removing aqueous contaminants.

Exploring kinetic and thermodynamic insights of graphene related two dimensional materials for carbon dioxide adsorption

Graphene related two dimensional materials (GR2Ms) are promising adsorbents for CO2 capture. However, the CO2 adsorption kinetics and mechanisms on these materials remain insufficiently explored and understudied. Recognizing the pivotal role of adsorption kinetics in assessing the practical applicability, this study comprehensively evaluates the CO2 adsorption kinetics, underlying mechanisms, and thermodynamic properties via gravimetric analysis on three distinct well-characterized graphene materials (few layer graphene-FLG, graphene oxide-GO, reduced graphene oxide-rGO) across temperatures from 25 to 75 °C under atmospheric pressure. Results reveal that Avrami’s fractional model offers the most accurate fit for CO2 adsorption kinetics among the three examined models (pseudo-first, pseudo-second, and Avrami’s fractional order). The interplay between the physico-structural-chemical properties of GR2Ms and the CO2 adsorption kinetics discloses that the morphology, crystallite size, specific surface area and porosity of GR2Ms greatly influence the CO2 adsorption rate as evidenced by the largest rate constant, kA value of rGO at 25 to 75 °C under atmospheric pressure. Analysis of activation parameters including activation energy, enthalpy of activation, entropy of activation, and free energy of activation derived from Eyring, Arrhenius, and Gibbs equations indicates a greater favorability of CO2 adsorption on GR2Ms at lower temperatures. Moreover, investigation into the underlying interaction mechanisms between CO2 molecules and GR2Ms, using rate-limiting kinetic models (Boyd’s film diffusion model, interparticle diffusion model, and intraparticle diffusion model), confirms that both film diffusion resistance and intraparticle diffusion resistance predominantly govern the CO2 adsorption rate.

Investigation of boundary layer effect of intra-particle diffusion on methylene blue adsorption on activated carbon

Methylene blue (MB) is a model dye used in many adsorption studies, and it is chemisorbed on activated carbon (AC) adsorbent. The adsorption of an adsorbate by a natural adsorbent is a phenomenon where kinetics is often complex despite the necessity of having reliable information on such reactions which is much needed to predict the efficiency of industrial processes of which rate of adsorption plays an integral part. Such information is, at times, not available under different experimental conditions, limiting desired applications. The research reported herein was thus performed to investigate rate of adsorption of MB onto coconut shell activated carbon by fitting experimental data to kinetics and diffusion models. According to the regression analysis of linearized pseudo-order models applied for various experimental conditions, the pseudo first order (PFO) model is found to be best suited to describe the kinetics of the MB-AC system having rate constants in the range 0.0799 – 0.2437 min−1 under different experimental conditions at the ambient temperature. The rate constants determined through the PFO model at different solution temperatures are indicative of chemisorption of MB on AC surface. Application of the Webber and Morris intra-particle diffusion (IPD) model, which accounts for the boundary layer effect on mass transfer, indicates that adsorption kinetics may be controlled by both film diffusion and intra-particle diffusion sequentially, and that the thickness of the boundary layer on the AC surface, which is a measure of the intercept of the linearized Webber and Morris IPD model, is sensitive to experimental conditions. Consequently, experimental parameters would be able to control the adsorption behaviour of the MB-AC system, which can be investigated by monitoring the magnitude of the initial adsorption factor.

Adsorption of CO2 and H2 on the polymer-based membrane from High-density Polyethylene (HDPE) Plastic

High-density polyethylene (HDPE), a widely used polymer globally, notably found in plastic bags, presents an environmental concern due to its non-biodegradable nature. Transforming non-biodegradable HDPE waste into a valuable resource presents a formidable ecological challenge. This research aims to study CO2 and H2 gases toward HDPE-based membranes through the adsorption process with pressure and temperature variation. The highest CO2 and H2 adsorption capacities of 14.19 mmol.g−1 (62.43 %wt) and 18.04 mmol.g−1 (3.61 %wt) were obtained by pressure feeding 3 bar at 30°C. The adsorption capacity decrease as the temperature increase. At an adsorption temperature of 50°C, the adsorption capacity of CO2 and H2 decrease, respectively by 75.86 % and 69.81 %. The adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, and intraparticle diffusion models. The kinetic study shows that adsorption at 30°C follows the pseudo-second order. The adsorption at elevated temperatures reveals the intraparticle diffusion mechanism, indicating that the gas is adsorbed directly into the polymer matrix. Thermodynamic results include enthalpy of adsorption (ΔH), standard entropy of adsorption (ΔS), energy Gibbs (ΔG), and energy activation (Ea). ΔH CO2 and H2 are -22.339 and -23.654 kJ mol−1, respectively, which indicates that the process is exothermic and physisorption. The ΔS value shows that the irregularity and randomness of gas movement during the adsorption process, with the respective values for CO2 and H2 are -0.069 and -0.072 kJ mol−1K−1, respectively. ΔG for adsorption of CO2 and H2 with increasing temperature becomes less spontaneous, which results in decreased adsorption capacity. Ea of CO2 is greater than H2, so the adsorption capacity of CO2 is smaller than H2. The thermodynamic study shows that the adsorption process is preferable at lower temperatures.