Adsorption Kinetic Data Research Articles

The removal of methylene blue from aqueous solutions by polyethylene microplastics: Modeling batch adsorption using random forest regression

In light of the extensive contamination of water sources by microplastics, their substantial specific surface area makes them favorable candidates as adsorbents for the simultaneous removal of coexisting contaminants in wastewater. In this regard, polyethylene microplastics were utilized to eliminate methylene blue dye from water. MB adsorption onto microplastics reached equilibrium in just 30 min at pH 7. The better fit of fractional power and Redlich-Peterson models on kinetic and equilibrium adsorption data, respectively, revealed that the MB removal process is a chemisorption in multilayer adsorption on the heterogeneous surface of the microplastics particles. The reusability of the microplastics adsorbent was confirmed based on the promising outcomes observed after five cycles. The results of the random forest regression exhibited an R2 of 97.55% for the correlation between the model-computed and measured amounts of MB reduction. The sensitivity analysis illustrated that the MB sorption process on microplastics is highly influenced by the initial MB concentration and adsorbent mass. These results show that although microplastics may pose potential risks to water environments, their adsorption potential can be utilized to simultaneously omit other pollutants from the aqueous solutions.

Performance of Mg/Al and Zn/Al Hydroxide Double Lamellar-Bentonite for Removal of Anionic Azo Dye from Aqueous Solution

This paper presents the preparation and characterization of bentonite coated with hydroxide double lamellar Mg/Al-bentonite and Zn/Al-bentonite as a potential adsorbent material. The coating process involved co-precipitation of mixed metal nitrate solution (Mg-Al) or (Zn-Al), followed by immersion of bentonite (B-Na+) dispersion. The structures and morphologies of the coated bentonites were characterized using XRD, FTIR, BET, and SEM analysis. The results of the BET analysis indicate that Mg/Al-bentonite and Zn/Al-bentonite have larger surface areas and pore volumes compared to bentonite alone. Specifically, the surface area of Mg/Al-bentonite is 209.25 m2/g with a pore volume of 0.423 cm3/g, while Zn/Al-bentonite has a surface area of 175.95 m2/g and a pore volume of 0.313 cm3/g. In contrast, the surface area and pore volume of bentonite alone are 110.43 m2/g and 0.132 cm3/g, respectively. The Mg/Al-bentonite reaches 85% uptake within 3 h (equivalent to 724.20 mg/g at 25 °C and pH 7), achieving rapid equilibrium. In contrast, the Zn/Al-bentonite achieves a maximum adsorption of 74% within 5 h under identical pH and temperature conditions, corresponding to 650.34 mg/g. The error function values, including the correlation coefficient R2, chi-square test χ2, and residual sum of squares RSS, were calculated to evaluate both kinetic and isotherm models. The kinetic adsorption data agreed well with a pseudo-second-order model. The adsorption process followed the Sips isotherm model, and the monolayer adsorption capacity of Mg/Al-bent and Zn/Al-bent composites was 872.41 (R2 = 0.974) and 678.45 mg/g (R2 = 0.983), respectively. The thermodynamic analysis of the adsorption process revealed that it occurred spontaneously with an endothermic characteristic. The parameters ΔS, ΔH, and ΔG were used to determine this.

Parametric and Kinetic Study of Nitrate Removal from Water by Modified Chitosan Composite Beads

The contamination of water bodies with harmful pollutants considers an aggravating global problem. The current research focuses on a developing efficient adsorbed for removing nitrate ions from aqueous solutions. The study proposed modified chitosan-zeolite composite beads to enhance the performance of the adsorption process. The zeolite was used to increase the surface area, and Zirconium was loaded on the beads to promote the selectivity for nitrate anions. The adsorption mechanism was assessed by characterizing the beads and sorbate adsorbed beads utilizing X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and analysis with an energy dispersive X-ray analyzer (EDX). The experiments were conducted in a batch system, and the effect of key parameters like contact time, initial nitrate anion concentration, and adsorbent dosage on the adsorption performance was investigated. The results demonstrated that the highest removal of nitrate ions was determined to be 95.42% at 0.2 g of Cs-Ze-Zr adsorbent with an initial concentration of 50 mg/L and a contact time of 120 minutes. The maximum adsorption capacity of the nitrate ions on the manufactured bead was 80.15 mg/g. In addition, among the Freundlich, Langmuir, and Temkin isotherms, the isotherm equilibrium data were consistent with a Freundlich isotherm model. The kinetic data for adsorption were satisfactorily fitted by a pseudo-first order. Subsequently, the results distinctly indicated that the proposed adsorbed (Cs-Ze-Zr) could be employed fruitfully in removing nitrate ions, demonstrated through the remarkable removal efficiency and adsorption capacity obtained in the study.

Development of an amine-impregnated polymer aerogel for CO2 capture

The synthesis and characterization of amine-impregnated polymer aerogels for CO2 capture represents a groundbreaking advancement in combating the urgent challenges of carbon dioxide (CO2) emissions and climate change mitigation. The traditional way of synthesizing aerogels for CO2 capture is to use a one-step gelation process without functionalizing the aerogel, which, to some extent, has low CO2 capture capacity and kinetics. This study finds a method of synthesizing the functionalized aerogel, which has high CO2 adsorption capacity, faster kinetic, and is more stable. The polymer aerogel was developed using an oil-water emulsion polymerization method, followed by freeze-drying. It was impregnated with a mono-ethanolamine (MEA) solution to enhance CO2 adsorption. The performance of the amine-impregnated poly (AAm-co-AAc) aerogels was tested in a continuous adsorption column filled with aerogel. The adsorption results showed the amine-impregnated aerogels having an amine equilibrium uptake value of 40% had significantly improved CO2 capture capacity up to 2.34 mmole g−1 at 1 bar pressure, 25 °C reaction temperature, and 10 ml/min flow rate. The polymeric aerogel has a very fast adsorption rate, as it can capture 90% of its maximum capacity within just 10 minutes. Then the kinetic data of the CO2 adsorption was modelled and found to best fit on both pseudo-1st and 2nd-order kinetic models, proposing that the adsorption mechanism on aerogel was controlled by surface diffusion and chemisorption. Furthermore, the isotherm data were evaluated and observed to be best represented by the Langmuir isotherm model, suggesting monolayer formation on the aerogel. After five adsorption-desorption cycles, the amine impregnated poly (AAm-co-AAc) aerogel was able to preserve the initial capacity without a significant decrease. These findings underscore the immense ability of amine-impregnated poly (AAm-co-AAc) aerogels as highly efficient adsorbents for CO2 capture, thus offering a speedy adsorption process and showing stable regeneration capacity, thereby exhibiting greater industrial application potential.

Utilizing low-cost purple coneflower (Echniacea purpurea) marc for competitive sorption of 152+154Eu(III), 60Co(II) and 134Cs(I) radionuclides

Echinacea purpurea marc (EPM), a residual of echinacea herb after the extraction process, was used as a natural low-cost sorbent for competitive sorption of 152+154Eu(III), 60Co(II) and 134Cs(I) radionuclides. The EPM was ground to prepare it for use in the sorption process. The variables influencing the sorption process were assessed, including pH, contact time, concentrations of metal ions, and temperature. EPM was characterized by different analytical instruments such as FTIR, SEM, XRD, and DTA/TGA. pH 4.0 was selected as the ideal pH value for competitive sorption of the studied ions. Adsorption kinetics data found that the sorption followed a pseudo-second-order model. The adsorption isotherm data was significantly better suited by the Langmuir isotherms in the case of Eu(III) ions while following Freundlich in the case of Co(II) and Cs(I) ions. Positive ΔHo values confirm the endothermic character of metal ion sorption onto EPM. The loading efficiencies of Eu(III), Co(II), and Cs(I) ions in the EPM column were 66.67%, 9.59%, and 4.81%, respectively. The EPM is a cost-effective and efficient separation of Eu(III) ions more than Cs(I) and Co(II) ions. Therefore, in the future, it will be a starting point for the separation of trivalent elements of lanthanide ions.

Impregnation of copper-cysteamine nanoclusters containing Cu(I) and Cu(II)-ionic species on pristine and magnetic bentonite for efficient Fenton-like catalysis and higher dye adsorption

Copper-cysteamine nanoparticles are known for their capability to produce reactive oxidation species upon light irradiation. During the synthesis of copper-cysteamine nanoparticles, many intermediate species are produced possessing Cu in variable oxidation states and herein we successfully trapped an intermediate species (CC) containing both Cu+1 and Cu+2 on bentonite (B) and magnetic bentonite (BF). The synthesized products (BCC and BFCC) were employed for the Fenton-like degradation of hazardous organic dyes and proved to be highly effective in splitting H2O2 to produce reactive ●OH radicals for carrying out the photocatalytic degradation process. Degradation data fitted with pseudo-first-order kinetics model yielded higher rate constants of 0.049 s−1 and 0.041 s−1 for Congo red (CR) degradation by BCC and BFCC respectively, with retained catalytic efficacy for three repeated cycles. Products were also tested for CR adsorption and adsorption isotherm studies conducted at optimized reaction conditions were best explained by Langmuir isotherm model exhibiting the maximum adsorption capacity of 781 mg/g and 800 mg/g for BCC and BFCC respectively. Adsorption kinetics data fitted best with the pseudo-second-order model while thermodynamics study suggested the exothermicity and spontaneity of the adsorption process. In short, CC deposition on bentonite-based materials produced excellent photocatalysts and adsorbents exhibiting the two-way benefits of our synthesized products.

Synergism between polyethyleneimine, graphene oxide, and MgFeAl-layered triple hydroxide in removing acid red 1 dye and bisphenol A from contaminated water samples

Water pollution is rapidly growing, requiring the development of effective treatment processes. In this work, a novel adsorbent (composed of polyethyleneimine, graphene oxide, MgFeAl-layered triple hydroxide, abbreviated as PEI@GO/MgFeAl-LTH) was synthesized, characterized, and applied to remove two hazardous water pollutants (i.e., acid red 1 and bisphenol A). The adsorption performance of the synthesized PEI@GO/MgFeAl-LTH nanocomposite was benchmarked to its parental materials (i.e., GO, PEI@GO, MgFeAl-LTH, and GO/MgFeAl-LTH). The results demonstrated that the adsorption capacity of bisphenol A (BPA) and acid red 1 (AR1) onto the nanocomposite are 352.0 and 155.5 mg/g, respectively, which are higher than their adsorption on GO, PEI@GO, MgFeAl-LTH, and GO/MgFeAl-LTH. The obtained adsorption isotherms and kinetics data were fitted using different models, which showed that Redlich-Peterson isotherm and Avrami kinetics models provide excellent fits for the obtained experimental data; the other models provided mixed results. The zeta potential measurements and the study of the pH effect suggest that the adsorption of BPA and AR1 onto the PEI@GO/MgFeAl-LTH nanocomposite is governed by more than a single mechanism. Furthermore, thermodynamics analysis demonstrated that the adsorption of AR1 and BPA is an exothermic (the respective ∆H values are −27.59 and −11.21 kJ/mol), spontaneous, and physical in nature. With respect to the reusability of this nanocomposite, the results revealed that it is highly stable and easily regenerable using a cheap solvent (i.e., 0.2 M NaOH). Accordingly, this study demonstrates the efficacy and superiority of the synthesized PEI@GO/MgFeAl-LTH nanocomposite in efficiently capturing toxic organic pollutants from aqueous environments.

Fast and highly efficient removal of organic dyes from aqueous solution by attapulgite modified with different amino groups

Type of functional groups of the adsorbent is crucial for an adsorption process which significantly affects adsorption rate and adsorption capacity for certain adsorbate. In this study, attapulgite (APT) was modified with different amino groups and the adsorbents obtained were used to remove toxic organic dyes from aqueous solution. Five adsorption kinetic models and three adsorption isotherm models were employed to estimate the adsorption behaviors for organic dyes methylene blue (MB) and Congo red (CR) onto the adsorbents. The results showed that adsorption behaviors of the adsorbents for MB were different from those for CR, and among the four adsorbents, APT exhibited the highest adsorption capacity for MB (307.27 mg/g) while APT modified with hyperbranched polyamide-amine (APT-(3)) had the highest adsorption capacity for CR (1277.33 mg/g) according to adsorption kinetic data, indicating the type of amino groups did have a significant impact on adsorption. It can be concluded that APT-(3) exhibited certain adsorption selectivity for CR. In addition, the adsorption of MB and CR was a fast and highly efficient process. The results indicated that the APT samples used can remove and enrich cationic and anionic dyes and can be potentially used in the wastewater treatment.

Photocatalytic activity of ZnMn2O4/TiO2 heterostructure under solar light irradiation: Experimental and theoretical study

This study focuses on the application of the hetero-junction ZnMn2O4/TiO2 as an efficient photocatalyst for the degradation of Rhodamine B (RhB), a cationic dye. ZnMn2O4 was synthesized by sol-gel auto-combustion, employing citric acid as fuel. The photocatalysts underwent characterization by X-ray diffraction, Fourier Transform infrared spectroscopy, Scanning Electronic Microscopy with integrated EDX and UV–Vis Diffuse Reflectance. Creating a p-n heterojunction could significantly boost photocatalytic efficiency. In this work, we use TiO2 as a n-type co-catalyst to enhance electron transfer efficiency. The ZnMn2O4 spinel exhibits direct optical transition at 1.97 eV, while TiO2 displays an indirectly allowed transition at 3.24 eV. Mott-Schottky plots revealed flat band potentials of -0.121 and +0.3 V/SCE for ZnMn2O4 and TiO2, respectively. Kinetic data of RhB adsorption were fitted using the pseudo-second order model. The heterojunction p-ZnMn2O4/n-TiO2 demonstrates a significant pollutant degradation rate, with 95% removal within 180 min under sunlight irradiation, surpassing the effectiveness of ZnMn2O4. To validate the experimental results, a theoretical investigation was conducted using density functional theory (DFT) and molecular dynamics (MD) simulations. Geometry optimization of the Rhodamine B molecule was studied in both gas and liquid phases, and various quantum chemical parameters were computed. Molecular dynamics simulations were additionally employed to examine the dynamic behavior of Rhodamine B adsorption on ZnMn2O4 (211) and TiO2 (101) surfaces in an aqueous environment.

Kinetics and thermodynamics of Isolan Bordeaux 2S-B dye adsorption on chemically synthesized graphene particles

Dyes in wastewater are highly toxic pollutants that have negative physical, chemical, and ecological effects on aquatic ecosystems even at low concentrations. In this study, the efficiency of chemically synthesized graphene oxide (CG) for the removal of the organic dye Isolan Bordeaux 2S-B and the principles of adsorption were investigated. Scanning electron microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) analyses were performed to characterize the CG, and the point of zero charge value was determined. The optimal conditions were found to be a pH of 2, an adsorbent dosage of 0.2 g, and a reaction time and temperature of 30 min and 25 °C, respectively. The adsorption equilibrium data fitted well with the Langmuir isotherm (R2 =0.98, RMSE = 0.38). The adsorption kinetics data followed a pseudo-second-order kinetic model (R2 = 0.99). Thermodynamic studies have shown that adsorption is exothermic and spontaneous. Desorption-regeneration studies demonstrated that CG is a highly stable adsorbent, and experiments in the presence of foreign ions show that it has a high selective affinity for anionic dyes. CG is effective not only in removing IB 2S-B but also shows promise in selectively removing anionic dyes from wastewater as a long-lasting adsorbent.

Sustainable and Circular Adsorption of Anionic Dye from Textile Wastewater Using Economical Adsorbent

ABSTRACT Dyes are significant contributors to the chemical oxygen demand of the wastewater produced by textile industries. In the current study, naturally occurring, inexpensive, non-hazardous clay was pillared and used to remove Acid Green 25 dye (AG) from aqueous solutions. The pseudo-second-order model provided a better fit to describe the adsorption kinetics data for AG, with a rate constant of 9.82 × 10−3 g/mg min. Langmuir isotherm provided a better fit for describing the adsorption isotherm of the AG dye. Thermodynamic analysis revealed that adsorption was exothermic with an enthalpy change of −48 kJ/mol. The effects of pH, adsorbent dosage, and initial concentration of AG dye on adsorption capacity were analyzed, and an empirical model was developed using the response surface methodology approach. Optimization studies revealed that a maximum adsorption capacity of 105.15 mg/g for the AG dye could be achieved at a pH of 2, an adsorbent dosage of 1.5 g/L and an initial dye concentration at its upper limit of 200 mg/L. The adsorbent could be regenerated and reused up to three adsorption cycles, and the desorbed dye and treated water may be reused in the dyeing process, thereby making the entire operation circular. Circularity reduces the cost of production and makes the process more sustainable. Mechanistic insights revealed that electrostatic interaction was the driving force for the adsorption of AG dye. In this work, it has been demonstrated that after pillaring, clay-based material may be used as an effective adsorbent for treating dye-containing wastewater.

Pseudo-Second-Order Kinetic Equation for Describing the Effect of Sorbent and Sorbate Concentrations.

The sorbent concentration (Cs) effect and sorbate initial concentration (C0) effect are common phenomena observed in the study of adsorption kinetics at solid-liquid interfaces. That is, adsorption rate constants simulated with classical kinetic equations, such as the pseudo-second-order (PSO) model, for a given system vary with Cs and C0. The classical kinetic equations cannot predict or describe the "Cs-effect" and "C0-effect" (called "C-effects" here). In the current work, the dynamic partition coefficient of sorbate between solid and liquid phases (Kt) was used to describe the adsorption kinetic processes. Based on the surface component activity (SCA) model, which assumes the activity coefficients of the surface components (fs) are not equal to unity but rather a function of Cs and the adsorption capacity (or C0) and referring to the classical PSO model, a new kinetic equation was established, called the "SCA-PSO kinetic model", and its two parameters, the intrinsic equilibrium partition coefficient (Ke0) and the intrinsic rate constant (k20), are independent of Cs and C0. In addition, the new model relates Kt and the rate constant (k2) to Cs and C0 via fs, and can thus describe the C-effects. The fs can be estimated from the change of equilibrium partition coefficient (Ke) with Cs and C0. The new model predicts that with the increase of Cs and C0, Ke decreases while k2 increases. Its rationality was confirmed by the literature-reported adsorption kinetic data of heavy metals on inorganic and biomass sorbents with the C-effects.

Adsorption of methyl ester sulfonate surfactant on Berea sandstone: Parametric optimization, kinetics, isotherm and thermodynamics studies

Anionic surfactants are utilized as an enhanced oil recovery (EOR) additive in sandstone reservoirs due to their excellent surface-activity and self-assembly behaviour. Considering the toxicity of some of the conventional surfactants and the clamour for sustainability approach for oil and gas operations, this present study focuses on application of anionic bio-based surfactant (methyl ester sulfonate, MES) synthesized from used cooking oil in EOR. Studies on MES adsorption onto sandstone reservoir rock were conducted, and the influence of static conditions on adsorption rate using Taguchi experimental design approach was explored. Adsorption data were analyzed using various isotherm and kinetics models. The obtained findings from optimization studies showed that salinity had a significant effect on the process, followed by temperature and pH. The concentration of surfactant had the least effect on the static adsorption process. At an optimum initial MES concentration of 500 ppm, salinity of 3.0 wt%, pH of 4.0, and temperature of 30 °C, the maximum extent of MES adsorbed by the sandstone was 98.9±0.69%. Langmuir isotherm and pseudo-second-order kinetics models were found to fit well with the adsorption equilibrium and kinetics data, respectively. The obtained values of thermodynamic parameters confirmed that MES adsorption onto sandstone was feasible, spontaneous, and exothermic.

Facile Preparation of Magnetic COF-on-COF for Rapid Adsorption and Determination of Sulforaphane from Cruciferous Vegetables

Sulforaphane (SFN) is a natural isothiocyanate compound widely abundant in cruciferous vegetables with multiple bioactive functions. However, traditional analytical methods for the extraction and determination of SFN are cumbersome, time-consuming, and low sensitivity with large amounts of organic solvents. Herein, novel magnetic COF-on-COFs (MB-COFs) were fabricated using Fe3O4 as a magnetic core and COFs-1 grown with COFs-2 as a shell, and they were used as efficient adsorbents of magnetic dispersive solid-phase extraction for rapid quantification of SFN in cruciferous vegetables by combining with HPLC-MS/MS. At the optimal ratio of COFs-1 to COFs-2, MB-COFs had a spherical cluster-like structure and a rough surface, with a sufficient magnetic response for rapid magnetic separation (1 min). Due to the introduction of Fe3O4 and COFs-2, MB-COFs exhibited outstanding extraction efficiencies for SFN (92.5–97.3%), which was about 18–72% higher than that of the bare COFs. Moreover, MB-COFs showed good adsorption capacity (Qm of 18.0 mg/g), rapid adsorption (5 min) and desorption (30 s) to SFN, and favorable reusability (≥7 cycles) by virtue of their unique hierarchical porous structure. The adsorption kinetic data were well fitted by the pseudo-second-order, Ritchie-second-order, intra-particle diffusion, and Elovich models, while the adsorption isotherm data were highly consistent with the Langmuir, Temkin, and Redlich–Peterson models. Finally, under the optimized conditions, the developed method showed a wide linear range (0.001–0.5 mg/L), high sensitivity (limits of quantification of 0.18–0.31 μg/L), satisfactory recoveries (82.2–96.2%) and precisions (1.8–7.9%), and a negligible matrix effect (0.82–0.97). Compared to previous methods, the proposed method is faster and more sensitive and significantly reduces the use of organic solvents, which can achieve the efficient detection of large-scale samples in practical scenarios. This work reveals the high practical potential of MB-COFs as adsorbents for efficient extraction and sensitive analysis of SFN in cruciferous vegetables.

Iodide ion-imprinted chitosan beads for highly selective adsorption for nuclear wastewater treatment applications

Iodide ions from radioactive iodine isotopes are common contaminants present in nuclear wastewater from nuclear power plants which are considered hazardous contaminants to be released in water sources even at low concentrations due to their association with metabolic disorders, therefore its removal from the nuclear wastewater effluents is necessary. Chitosan beads are natural and cost-efficient adsorbents that have been used for ion removal from wastewater. However, issues of poor selectivity persist in achieving high-efficiency iodide ion removal. In this study, ion-imprinted chitosan beads (IIC) have been synthesized using the phase-inversion method, IIC beads were modified by cross-linking with epichlorohydrin (IIC-EPI) and modified by cross-linking with epichlorohydrin and silicon dioxide nanoparticles (IIC–SiO2-EPI). Through 4 h of batch adsorption experiments, IIC beads achieved a maximum adsorption capacity (Qe) of 0.65 mmol g−1 and showed more preference for the iodide ions compared to the non-imprinted chitosan beads which achieved a maximum adsorption capacity of 0.27 mmol g−1 at pH 7. While the modified beads IIC-EPI and IIC-SiO2-EPI beads have boosted the adsorption capacities to 0.72 mmol g−1 and 0.91 mmol g−1. Scanning electron microscopic cross-sectional images have shown more pores and cavities than the surface images which agrees with the multilayer heterogeneous diffusion suggested by the Freundlich adsorption isotherm, that the experimental data has fitted. Adsorption kinetic data have fitted the Pseudo-second-order model as well as the Weber and Morris intraparticle model, which suggest an intraparticle pore diffusion adsorption mechanism, with the involvement of the physical electrostatic interactions with the cationic chitosan surface.

Adsorption kinetics of CH4 and CO2 on shale: Implication for CO2 sequestration

The adsorption kinetic behavior of CH4 and CO2 in shale is critical for design and practice the CO2 sequestration with enhanced shale gas recovery. In this study, adsorption isotherms and kinetics curves of CH4 and CO2 in two shale samples were measured by the volumetric method at the temperature of 308.15 K, 323.15 K, 338.15 K and 353.15 K with the pressures up to 12 MPa. The pseudo-first-order (PFO) model, pseudo-second-order (PSO) model and Bangham model were used to describe the adsorption kinetics data. Furthermore, the influence of pressure and temperature on the adsorption kinetic behavior of CH4 and CO2 was clarified. The results show that the adsorption kinetic curves can be classified into three stages: rapid adsorption, slow adsorption and adsorption equilibrium stage. The fitting accuracy of the three kinetic models is in the order of Bangham > PSO > PFO. Moreover, the adsorption kinetics of CH4 and CO2 are highly dependent on pressure and temperature. The adsorption rate constant (kb) of CH4 and CO2 increases first and then decreases with increasing pressure. At the pressure below the supercritical pressure of CO2, the kb of CO2 shows a decreasing trend with the increase of temperature, which is the same as that of CH4. However, after exceeding the supercritical pressure of CO2, the variations in kb of CO2 with temperature presents an opposite trend as it increased with increasing temperature. Therefore, the pressure and temperature dependent adsorption kinetic behaviors requires consideration for optimizing engineering parameters in application of CO2 enhanced shale gas recovery and sequestration.

Selectivity of modified pomegranate peel for gold, platinum, and palladium: Adsorption behavior, mechanism, and recovery

Recovery of precious metals from smelting, refining, and other industrial process effluents has received increasing attention from both industry and the scientific community. A novel bioadsorbent capable of selectively adsorbing gold, platinum, and palladium was synthesized in this study by simple modification of crushed pomegranate peel (PP). The mechanisms of adsorption and reduction of the adsorbents were mainly analyzed and characterized by Fourier transform infrared spectrometer (FTIR), Scanning electron microscope (SEM), Energy dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). The determination and modeling of the adsorption isotherms and kinetics data were also undertaken in this study. The maximum adsorption capacity for Au(III), Pt(IV), and Pd(II) in 0.1 M HCl media at room temperature was 34 mg/g, 1.16 mg/g, and 1.05 mg/g, respectively. More than 95.4 % gold ions, 85.2 % platinum ions, and 97.5 % palladium ions would be reduced to be their elemental metal after selective adsorption by the rich hydroxyl groups in the polyphenolic aromatics. In addition, the effect of pH and coexisting base metal impurity ions on the adsorption efficiency of Au(III), Pt(IV), and Pd(II) were evaluated. The Langmuir isotherm model was found to be consistent with the adsorption isotherm, and the pseudo-second-order model was more appropriate to describe the adsorption. The effectiveness of practical recovery of Au(III), Pt(IV), and Pd(II) from real industrial effluent was examined using PP gel. The present study provided a quite promising novel material, pomegranate peel adsorbent, which exhibited great potential for the recovery of precious metals from various industrial effluents.

Study on the dynamic adsorption and recycling of phosphorus by Fe–Mn oxide/mulberry branch biochar composite adsorbent

In this study, the Fe–Mn oxide/mulberry stem biochar composite adsorbent (FM-MBC) was prepared and fully characterized by SEM-EDS, XRD, BET, and XPS. The solution pH (3.0, 4.5, and 6.0), initial concentration of phosphorus (10, 20, and 30 mg L−1), adsorbent bed height (2, 3, and 4 cm), and solution flow rate (1, 2, and 3 mL min−1) were investigated to analyze the breakthrough curves. The results showed that the breakthrough time was shortened as the initial phosphorus concentration, the flow rate increased and the bed height decreased. Higher initial phosphorus concentrations, flow rates, and lower bed heights, led to a faster breakthrough of phosphate ions in the FM-MBC adsorbent. Additionally, it was observed that increasing the pH value was not conducive to the adsorption of phosphorus by the FM-MBC adsorbent. Dynamic adsorption data were fitted to four models (Yoon-Nelson, Thomas, Adams-Bohart, and Bed Depth Service Time), and the R2 values of the Thomas and Yoon-Nelson models exhibited minimal variation, suggesting that the dynamic adsorption process of FM-MBC was rather intricate. The saturated fixed-bed column (including FM-MBC) was regenerated with NaOH or HCl, and it was found that a 0.1 mol L−1 NaOH solution had the best regeneration effect. XRD analysis showed that the reaction product between the FM-MBC composite and phosphate anions was Fe3(PO4)2·H2O. Moreover, the experimental results that FM-MBC can successfully be used to remove phosphorus from actual wastewater.

Experimental investigation and modeling of mass transport properties of O2 in biomass chars

This study presents two sets of kinetic adsorption data for O2 on two different biomass chars at temperatures from (298 to 373) K and pressures from (26 to 300) kPa. Thereon, incorporating data of 21 adsorption kinetic curves on a hydrochar and 24 adsorption kinetic curves on a torrefied beechwood char, a parameterization of the pore-structure dependent kinetic adsorption (PSK) model is obtained for the two investigated chars. Extensive possibilities to predict time- and pore-structure-resolved mass transport properties using the PSK model are discussed. The mass transfer coefficient and the adsorption flow rate are direct outcomes and derivatives of the PSK model and hold for a physically sound description of the time-resolved mass transport of gaseous species in the porous structure of particles. The physical and extrapolative behavior of the modeled mass transfer coefficients and adsorption flow rates are discussed for temperatures up to 1100 K, allowing for new insights into the mass transfer.

Comparative studies on the use of activated snail (<i>Achanita fulica</i>) and periwinkle shells (<i>Typanotonus fuscatu</i>) in the removal of heavy metal ions from aqueous solutions

This study seeks to compare the application of activated snail and periwinkle shells in the removal of heavy metal ions from aqueous solution. Snail and periwinkle shells obtained from local markets in Warri, Nigeria, were carbonized, activated and characterized. Batch adsorption experiment was carried out to determine the effect of pH, concentration, adsorbent dose and contact time on the adsorption process. Data obtained were examined using adsorption isotherms. Characterization result showed that activated carbon obtained from periwinkle shells had higher values of pH, pore volume, moisture content and porosity than the values obtained for activated snail shells. The maximum pH obtained for the adsorption of Pb2+ and Cd2+ ions using activated periwinkle shell carbon (APSC) and activated snail shell carbon (ASSC) were 7 for Pb2+ and 4 – 10 for Cd 2+ . The percentage adsorption of these ions onto APSC were 96.70% Pb2+ and 100% Cd2+ while that of ASSC were 95.00% Pb+2 and 68.80% Cd2+ . The optimum adsorbent dose and contact time for the removal of these ions, using both adsorbents, were 3 g and 90 min, respectively. Results revealed that APSC had better adsorption capacity than ASSC for most parameters studied. Of the four adsorption isotherms models used for this study, Langmuir had the highest regression coefficient (R2 = 0.9852 for APSC and 0.8950 for ASSC). Data for adsorption kinetics exhibited a good compliance with pseudo-second order kinetic model