Modeling adsorption rate of organic micropollutants present in landfill leachates onto granular activated carbon

The overall adsorption rate of single micropollutants present in landfill leachates such as phthalic acid (PA), bisphenol A (BPA), diphenolic acid (DPA), 2,4-dichlorophenoxy-acetic acid (2,4-D), and 4-chloro-2-methylphenoxyacetic acid (MCPA) on two commercial activated carbons was studied. The experimental data obtained were interpreted by using a diffusional model (PVSDM) that considers external mass transport, intraparticle diffusion, and adsorption on an active site. Furthermore, the concentration decay data were interpreted by using kinetics models. Results revealed that PVSDM model satisfactorily fitted the experimental data of adsorption rate on activated carbon. The tortuosity factor of the activated carbons used ranged from 2 to 4. The contribution of pore volume diffusion represented more than 92% of intraparticle diffusion confirming that pore volume diffusion is the controlling mechanism of the overall rate of adsorption and surface diffusion can be neglected. The experimental data were satisfactorily fitted the kinetic models. The second-order kinetic model was better fitted the experimental adsorption data than the first-order model.     

Analysis of diffusion models for protein adsorption to porous anion-exchange adsorbent

The ion-exchange adsorption kinetics of bovine serum albumin (BSA) and gamma-globulin to an anion exchanger, DEAE Spherodex M, has been studied by batch adsorption experiments. Various diffusion models, that is, pore diffusion, surface diffusion, homogeneous diffusion and parallel diffusion models, are analyzed for their suitabilities to depict the adsorption kinetics. Protein diffusivities are estimated by matching the models with the experimental data. The dependence of the diffusivities on initial protein concentration is observed and discussed. The adsorption isotherm of BSA is nearly rectangular, so there is little surface diffusion. As a result, the surface and homogeneous diffusion models do not fit to the kinetic data of BSA adsorption. The adsorption isotherm of gamma-globulin is less favorable, and the surface diffusion contributes greatly to the mass transport. Consequently, both the surface and homogeneous diffusion models fit to the kinetic data of gamma-globulin well. The adsorption kinetics of BSA and gamma-globulin can be very well fitted by parallel diffusion model, because the model reflects correctly the intraparticle mass transfer mechanism. In addition, for both the favorably bound proteins, the pore diffusion model fits the adsorption kinetics reasonably well. The results here indicate that the pore diffusion model can be used as a good approximate to depict protein adsorption kinetics for protein adsorption systems from rectangular to linear isotherms.     

ZnO/C纳米球的亚甲基蓝单吸附特性:平衡、动力学及机理

采用电弧放电法制备了ZnO/C纳米球,利用FESEM、XRD和N₂吸附/脱附测试进行了表征。在避光条件下研究了复合材料对亚甲基蓝的吸附性能。研究结果表明,随着亚甲基蓝的浓度及接触时间的增长吸附量明显上升,在吸附时间为150 min时达到吸附平衡。采用Langmuir、Freundlich及Temkin等温吸附模式对吸附平衡进行了研究。结果表明,吸附等温线符合Langmuir等温吸附模式,单层吸附饱和容量可达188.68 mg·g^-1。利用动力学模型、内扩散模型和外扩散速率控制模型拟合实验数据,拟合数据表明其动力学符合伪二级动力学模型;内扩散机理不是吸附速率的唯一限制机理,亚甲基蓝的总吸附速率受膜扩散控制。     

ZnO/C纳米球的亚甲基蓝单吸附特性:平衡、动力学及机理

采用电弧放电法制备了ZnO/C纳米球,利用FESEM、XRD和N₂吸附/脱附测试进行了表征。在避光条件下研究了复合材料对亚甲基蓝的吸附性能。研究结果表明,随着亚甲基蓝的浓度及接触时间的增长吸附量明显上升,在吸附时间为150 min时达到吸附平衡。采用Langmuir、Freundlich及Temkin等温吸附模式对吸附平衡进行了研究。结果表明,吸附等温线符合Langmuir等温吸附模式,单层吸附饱和容量可达188.68 mg·g^-1。利用动力学模型、内扩散模型和外扩散速率控制模型拟合实验数据,拟合数据表明其动力学符合伪二级动力学模型;内扩散机理不是吸附速率的唯一限制机理,亚甲基蓝的总吸附速率受膜扩散控制。     

Mesoporous activated carbon from <Emphasis Type="Italic">Pentace</Emphasis> species sawdust via microwave-induced KOH activation: optimization and methylene blue adsorption

This work studied the optimization of preparation conditions of Pentace species sawdust activated carbon (PSAC) via microwave-induced KOH activation for the adsorption of methylene blue (MB) dye from aqueous solutions. The produced activated carbon was characterised through Brunauer–Emmett–Teller (BET) surface area and pore structural analysis, proximate and ultimate, scanning electron microscopy, and Fourier transform infrared spectroscopy. Response surface methodology technique was used to optimize the radiation power, radiation time and impregnation ratio for MB removal and PSAC yield through central composite design. The optimum preparation conditions for PSAC were obtained at a radiation power of 418 W, radiation time of 6.4 min, and an impregnation ratio of 0.5, which resulted in 27% PSAC yield and 93.74% MB removal. A mesoporous structure of PSAC was formed, with a BET surface area, total pore volume and average pore diameter of 914.15 m²/g, 0.52 cm³/g, and 3.19 nm, respectively. The experimental kinetic data were well described by a pseudo-second-order model and intraparticle diffusion. Adsorption data fitted the Redlich–Peterson equation better than the Langmuir, Freundlich, Temkin, Dubinin–Radushkevich and Sips equations. However, the exponential value of Redlich–Peterson approached unity, hence, resulting in the original Langmuir equation, with adsorption capacity of 357.14 mg/g. The adsorption performance was effectively preserved even after four consecutive cycles, demonstrating good regeneration ability.     

Comparative study on composition, structure, and adsorption behavior of activated carbons derived from different synthetic waste polymers

The composition, structure, and adsorption behavior of activated carbons (ACs) derived from three different types of waste polymers, i.e., tire rubber (TR), polyvinyl chloride (PVC), and polyethyleneterephtalate (PET), by KOH activation were compared. The AC derived from PET exhibited the largest surface area (2831 m(2)/g) and pore volume (1.68 cm(3)/g) due to the homogenous aromatic composition of PET. The AC derived from PVC exhibited relatively lower surface area (2666 m(2)/g) but more narrowed pore size distribution (2-3 nm). The complex composition and high ash content of tire particles resulted in AC product with significantly lower surface area (398.5 m(2)/g) and heterogeneous pore width. Adsorption data of methylene blue (MB) were fitted well by Langmuir equation, indicating monolayer coverage on the ACs. The high oxygen content of PET-derived AC heavily affected its adsorption to MB and iodine. Due to the remarkable surface area and highly mesoporous structures, ACs based on both PET and PVC exhibited much higher adsorption capacities than that of TR and commercial coal-based AC (F400). This study demonstrates that the properties of ACs are highly dependent on their starting polymers and the potential of converting synthetic polymer waste into effective adsorbents for environmental remediation and cleanup.     

Kinetic and calorimetric study of the adsorption of dyes on mesoporous activated carbon prepared from coconut coir dust

Mesoporous activated carbon has been prepared from coconut coir dust as support for adsorption of some model dye molecules from aqueous solutions. The methylene blue (MB) and remazol yellow (RY) molecules were chosen for study of the adsorption capacity of cationic and anionic dyes onto prepared activated carbon. The adsorption kinetics was studied with the Lagergren first- and pseudo-second-order kinetic models as well as the intraparticle diffusion model. The results for both dyes suggested a multimechanism sorption process. The adsorption mechanisms in the systems dyes/AC follow pseudo-second-order kinetics with a significant contribution of intraparticle diffusion. The samples simultaneously present acidic and basic sites able to act as anchoring sites for basic and acidic dyes, respectively. Calorimetric studies reveal that dyes/AC interaction forces are correlated with the pH of the solution, which can be related to the charge distribution on the AC surface. These AC samples also exhibited very short equilibrium times for the adsorption of both dyes, which is an economically favorable requisite for the activated carbon described in this work, in addition to the local abundance of the raw material.     

Comparisons of porous and adsorption properties of carbons activated by steam and KOH

In this work, fir woods and pistachio shells were used as source materials to prepare porous carbons, which were activated by physical (steam) and chemical (KOH) methods. Pore properties of these activated carbons including the BET surface area, pore volume, pore size distribution, and pore diameter were first characterized by a t-plot method based on N(2) adsorption isotherms. Highly porous activated carbons with BET surface area up to 1009-1096 m(2)/g were obtained. The steam and KOH activation methods produced carbons with mesopore content in the range 9-15 and 33-49%, respectively. The adsorption equilibria and kinetics of tannic acid, methylene blue, 4-chlorophenol, and phenol from water on such carbons at 30 degrees C were then investigated to check their chemical characteristics. The Freundlich equation gave a better fit to all adsorption isotherms than the Langmuir equation. On the other hand, the intraparticle diffusion model could best follow all adsorption processes. In comparison with KOH-activated carbons, it was shown that the rate of external surface adsorption with steam-activated carbons was significantly higher but the rate of intraparticle diffusion was much lower.     

Liquid-phase adsorption: Characterization and use of activated carbon prepared from diosgenin production residue

The adsorption behavior of activated carbon (AC) prepared from the residue of diosgenin by-product was characterized. The adsorption capacities of AC such as iodine, phenol and methylene blue (MB) are 933.28, 145.38 and 165 mg/g, respectively. The results of MP analysis and BJH method show AC has developed micropore and mesopore volumes, which are 0.1621 and 0.2623 cm³/g respectively, with the mean pore diameter of 1.49 nm. Comparison of the liquid phase adsorption capacities of AC to the standard activated carbon (SAC) and the commercial activated carbon (CAC) for wastewater treatment showed AC was superior to SAC and CAC. Experiments on phenol and MB adsorption and COD and chroma removal from diosgenin wastewater were carried out under different conditions of contact time, temperature, concentration, adsorbent dose and pH. The removal of COD and chroma of 10-multiple wastewater is 92.46 mg/g and 88 %, respectively. Adsorption parameters for the Langmuir and Freundlich isotherm models were determined. At lower temperatures, the data for phenol and COD fitted Freundlich model better than Langmuir model and vise versa for MB and chroma. Adsorption followed second-order kinetics. The study proves that AC prepared from the residue of diosgenin by-product can be used as adsorbent for the treatment of diosogenin wastewater as a cost-effective approach of resource recycle of Discorea zingiberensis C.H. Wright.     

Adsorption of phenol by oil-palm-shell activated carbons

Steam activated carbons from oil-palm shells were prepared and used in the adsorption of phenol. The activated carbon had a well-developed mesopore structure which accounted for 45% of the total pore volume. The BET surface area of the activated carbon was 1183 m²/g and a total pore volume of 0.69 cm³/g using N₂ adsorption at 77 K. The adsorption capacity of the activated carbon for phenol was 319 mg/g of adsorbent at 298 K. The adsorption isotherms could be described by both the Langmuir-Freundlich and the Langmuir equations. The adsorption kinetics consisted of a rapid initial uptake phase, followed by a slow approach to equilibrium. A new multipore model is proposed that takes into account of a concentration dependent surface diffusion coefficient within the particle. This model is an improvement to the traditional branched pore model. The theoretical concentration versus time curve generated by the proposed model fitted the experimental data for phenol adsorption reasonably well. Phenol adsorption tests were also carried out on a commercial activated carbon known as Calgon OLC Plus 12×30 and the agreement between these adsorption data and the proposed model was equally good.     

Analysis of mass transport models for protein adsorption to cation exchanger by visualization with confocal laser scanning microscopy

The mass transfer of bovine serum albumin (BSA) to a cation exchanger, SP Sepharose FF, has been studied by finite batch adsorption experiments. The uptake curve was simulated with three mass transport models (i.e., effective pore diffusion model, surface diffusion model and Maxwell-Stefan model) incorporating the particle size distribution of the adsorbent particles. All the three models can simulate the uptake curves reasonably well. However, how well these models could simulate the real concentration profile within the adsorbent particle cannot be verified by the fitness of the models to the uptake curve. Thus, confocal laser scanning microscopy (CLSM) was used to visualize protein uptake to the porous adsorbent particles during the batch experiments. Using a fluorescent dye-labeled bovine serum albumin (BSA) for the dynamic adsorption experiments, the radial concentration profiles of the labeled BSA molecules into individual adsorbent particles at different times were obtained from the CLSM images. The protein distribution profiles within various particle diameters at different time were compared with the radial protein distributions predicted from the models. It reveals that surface diffusion model describes the intraparticle protein concentration profiles better than the other two models.     

Synthesis, characterization and adsorption performance of a novel post-crosslinked adsorbent

In this paper a post-crosslinked polymeric adsorbent PDHT-2 with high specific surface area was prepared by Friedel-Crafts reaction of the pendant vinyl groups without an externally added crosslinking agent. It was obvious that both the specific surface area and the pore volume of starting copolymer PDHT-1 increased significantly after post-crosslinking. Batch adsorption runs of phenol from aqueous solution onto adsorbent PDHT-1 and PDHT-2 were researched, and commercial macroporous resin XAD-4 was chosen for comparison purpose. Experimental results showed that the adsorption isotherms could be fitted by Langmuir model and Freundlich model and the adsorption capacity onto PDHT-2 was much larger than that onto PDHT-1 and XAD-4 with respect to phenol and phenolic compound, which possibly resulted from its larger specific surface area. The adsorption process for phenol onto the three adsorbents was proved to be exothermic and spontaneous in nature. The thermodynamic parameters such as Gibb's free energy (ΔG), change in enthalpy (ΔH) and change in entropy (ΔS) had been calculated. The adsorption kinetic curves obeyed the pseudo-second order model and the intraparticle diffusion process was the rate-controlling step.     

金属-有机骨架对苯二甲酸酯-铝吸附水中酚类化合物动力学和热力学

以吸附等温线、动力学和热力学等方法研究了金属-有机骨架对苯二甲酸酯-铝[MIL-53(Al),MIL:Materials of Institut Lavoisier]对水中邻硝基苯酚、苯酚和邻苯二酚的吸附行为。 MIL-53(Al)对上述酚类化合物的吸附符合准二级吸附动力学模型,且包含表面吸附和孔内扩散两个过程。 吸附热力学结果表明,MIL-53(Al)对酚类化合物的吸附是自发的,且为吸热和熵增加过程。 在40 ℃条件下,MIL-53(Al)对邻硝基苯酚、苯酚和邻苯二酚的吸附量分别为78.6、30.5和16.5 mg/g。     

Removal of methylene blue by seed-watermelon pulp-based low-cost adsorbent: Study of adsorption isotherms and kinetic models

Based on the abundance of seed-watermelon pulp (SWP) in Xinjiang, China, SWP was employed to prepare low-cost adsorbent toward the removal of methylene blue (MB). The effects of contact time at different initial concentration were studied. The widely used adsorption isotherm models including Langmuir, Freundlich, and Temkin isotherms were employed to depict the adsorption process. The Langmuir isotherm was best fitted to the experimental data. Batch kinetic studies showed that an equilibrium time of 300 minutes was needed for the adsorption. The adsorption properties can be well described by pseudo-second-order kinetic model and the MB uptake was not controlled by intraparticle diffusion mechanism.     

Isolation and partial characterization of a biosurfactant mixture produced by Sphingobacterium sp. isolated from soil

The concentration decay curves for the adsorption of phenol on organobentonite were obtained in an agitated tank batch adsorber. The experimental adsorption rate data were interpreted with diffusional models as well as first-order, second-order and Langmuir kinetic models. The surface diffusion model adjusted the data quite well, revealing that the overall rate of adsorption was controlled by surface diffusion. Furthermore, the surface diffusion coefficient increased raising the mass of phenol adsorbed at equilibrium and was independent of the particle diameter in the range 0.042-0.0126 cm. It was demonstrated that the overall rate of adsorption was essentially not affected by the external mass transfer. The second-order and the Langmuir kinetic models fitted the experimental data quite well; however, the kinetic constants of both models varied without any physical meaning while increasing the particle size and the mass of phenol adsorbed at equilibrium.     

Mechanism of Adsorption of Dyes and Phenols from Water Using Activated Carbons Prepared from Plum Kernels

The kinetics and mechanism of adsorption of two commercial dyes (BR22, AB25), phenol, and 3-chlorophenol from water on activated carbons were studied at 30 degrees C. The activated carbons were prepared from plum kernels, and the activation temperature and time tested were in the ranges 750-900 degrees C and 1-4 h, respectively. Three simplified kinetic models including a pseudo-first-order, a pseudo-second-order, and an intraparticle diffusion model were tested. It was shown that the adsorption of both phenols could be fitted to a pseudo-second-order rate law, and that of both dyes could be fitted to an intraparticle diffusion model. Kinetic parameters were calculated and correlated with the physical properties of the adsorbents. Copyright 2000 Academic Press.     

A Stefan-Maxwell Model of Single Pore Pressurization for Langmuir Adsorption of Gas Mixtures

A model based on the application of the Maxwell-Stefan approach has been used to describe the dynamics of intraparticle transport (pore diffusion, surface diffusion and convection) in a single pore during and after a pressurization process. The model was first compared with the model proposed by Taqvi and Levan (Adsorption, 2, 299–309 (1996)) for a linear adsorption isotherm. The effect of several parameters (pressurization rate, adsorption capacity, bulk gas-phase mole fraction, adsorption affinity and pore radius) was studied, evaluating the relative importance of each mass-transport mechanism in different conditions. A binary mixture of an inert and an adsorbable component was considered first, extending the analysis of the pore radius effect to a ternary mixture. In general, surface diffusion is dominant with very low pore radius, whereas gas-phase fluxes dominate in a large pore. However, depending on the value of the bulk gas-phase mole fraction (which is related to the surface coverage level through the adsorption equilibrium isotherm), the equilibrium and rate parameters, and the surface to volume ratio, surface diffusion cannot be always neglected for large pores. More generally, system non-linearity can switch the dominant mechanism and create fronts.     

Kinetic models applied to erbium adsorption on activated charcoal from aqueous solutions

The adsorption of erbium (Er) ions on activated charcoal (AC) is investigated at temperatures 10–40 °C from aqueous solutions to understand the kinetics behavior. The intra-particle diffusion, the pseudo-first order kinetic and pseudo-second order kinetic models were used to describe the kinetic data. Results shows that the adsorption of Er ions on AC occurs in two stages and the surface adsorption and diffusion phenomena are operative in the adsorption process. The result also reveals that intra-particle diffusion is not only the main rate determining step through out the adsorption process, but the boundary layer diffusion also play significant role in rate determination. Values of the intra-particle diffusion rate constant and the extent of the boundary layer diffusion were calculated. A comparison of the kinetics models on the overall adsorption rate indicates that the Er/AC system is best described by the pseudo-second order kinetic model than the pseudo-first order model, and the overall rate of the Er ions adsorption on AC appears to be controlled by more than one step, i.e., external mass transfer and diffusion mechanism.     

Removal of ronidazole and sulfamethoxazole from water solutions by adsorption on granular activated carbon: equilibrium and intraparticle diffusion mechanisms

The equilibrium and intraparticle diffusion of ronidazole (RNZ) and sulfamethoxazole (SMX) during the adsorption on granular activated carbon (GAC) from aqueous solution was investigated in this work. The solution pH, temperature, ionic strength and water matrix affected the adsorption capacity of GAC towards SMX, but no effect was observed for the adsorption of RNZ. This behavior was due to the different mechanism involved in the adsorption of both antibiotics. The adsorption capacity of GAC towards RNZ was greater than that towards SMX. Molecular computation allowed the estimation of the binding free energy and confirmed that the adsorption of RNZ was more favorable than the adsorption of SMX. The adsorption mechanism of both antibiotics is governed by π–π dispersive interactions, and molecular simulation demonstrated that the coulombic interactions did not affect, but the solvation and nonpolar interactions play a significant role on the adsorption of both antibiotics. The application of diffusional models revealed that the overall adsorption rate of both antibiotics is controlled by intraparticle diffusion. Moreover, the surface diffusion was more predominant than the pore volume diffusion. Besides, surface diffusion coefficient, D_s, for RNZ was not a function of the aqueous matrix, whereas D_s for SMX was highly dependent on the water matrix.     

Parallel pore and surface diffusion of levulinic acid in basic polymeric adsorbents

The equilibrium and kinetics of levulinic acid (LA) adsorption on two basic polymeric adsorbents, 335 (highly porous gel) and D315 (macroreticular), were investigated. Experimental adsorption rates in batch stirred vessels under a variety of operating conditions were described successfully by the parallel pore and surface diffusion model taking into account external mass transfer and nonlinear Toth isotherm. The film-pore diffusion model was matched with the rate data and the resulting apparent pore diffusivities were strongly concentration-dependent and approached to a constant value for 335 adsorbent. Thus, the constant value was taken as the accurate pore diffusivity, while the pore diffusivity in D315 was estimated from the particle porosity. The surface diffusivities decreased with increasing initial bulk concentration for both adsorbents. The inverse concentration dependence was correlated reasonably well to the change of isosteric heat of adsorption as amount adsorbed.