Langmuir-Freundlich Model Research Articles

Efficient fluoride removal from aqueous solution by sorption using natural adsorbent - Eugenia Jambolana: Equilibrium isotherm analysis and influence of anions

Commercial industries which employ metallurgical extraction, cement manufacturing and fuel cells expulse heavy volumes of fluoride-containing wastewater into the natural environment posing grave threats to public health. In the current study, a locally available plant known as Jamun (Eugenia Jambolana), was used as an adsorbent for fluoride removal from aqueous solutions. Physico-chemical experiments were conducted to reveal the size and surface distribution of natural fluoride adsorption on the adsorbent surface using SEM, XRD, and FT- IR. Effects of different parameters such as solution pH, adsorbent dosage (m), co-ions contact time (t), fluoride concentration, and flow rates were investigated. Additionally, the adsorption efficiency of competing ions like Cl-, NO3-, SO42-, PO43-, Ca2+, and Mg2+ and their physiological effects were studied under different solution concentrations ranging from 20 – 200 mg / L at pH 6.90±0.10 for 1 hour. Results showed that the adsorption equilibrium and kinetic data were matched with the isotherm Langmuir model (R2 = 0.98) and Freundlich model (R2 = 0.97). Also, we could conclude that the adsorption process of fluoride using the natural adsorbent resu bivalve shells was an endothermic reaction and resulted in a spontaneous adsorption process. Adsorption kinetic models revealed a swift adsorption rate with minimum and maximum fluoride concentrations as 100 mg / L and 500 mg / L with contact time (t) = 60 minutes at adsorbent dosage (m) = 1 g / L.

Phenomenological‐based model of direct blue 2 adsorption on corncob in a fixed‐bed

AbstractThis work presents a phenomenologically based semi‐physical model (PBSM) for the liquid–solid adsorption process, which has been experimentally validated. Two modes of operation of adsorption of direct blue 2 dye (DB2) on corn cobs in a fixed bed are discussed by applying the PBSM. The first mode of operation is the typical continuous liquid flow, whereas the second is a semicontinuous mode with the recirculation of liquid leaving the column. These modes of operation were used to illustrate different ways in which the system reaches equilibrium conditions. The equilibrium distribution curve (EDC) for low DB2 concentration was reached with the best fit using the Langmuir–Freundlich model (). The local mass transfer coefficient for the solid phase was evaluated by the PBSM deduction, and subsequently, the diffusivity of the surface solid was experimentally evaluated through comparison in terms of the PBSM. Regardless of the mode of operation, surface diffusion is associated with only the nature of the adsorbent material rather than the concentration of the liquid phase. In addition, the PBSM exhibited liquid and solid concentration changes at different points in the column. Moreover, different operating curves of the process were constructed and validated, exhibiting similar results when comparing the predictions of the model and the experimental data. These findings support the strength of the constructed model, enabling its extension to other adsorbent–dye systems.

Modeling of Supercritical CO2 Adsorption for Low-Permeability Coal Seam of Huainan-Huaibei Coalfield, China.

Investigating the coal adsorption behavior on supercritical CO2 (ScCO2) is crucial for long-term CO2 geological storage. In this paper, low-permeability coal samples from the Huainan-Huaibei coalfields in China were selected. The high-pressure isothermal adsorption of CO2 was carried out at 36, 42, and 48 °C. The results of adsorption experiments were analyzed by fitting 9 types of modified adsorption models, including three different adsorption theories. Considering that different adsorption mechanisms may exist for CO2 in coal, 14 mixed adsorption models were established. The accuracy of the coefficient of determination (R2) and root-mean-square error (RMSE) for ScCO2 excess adsorption capacity was analyzed, mainly focusing on the accuracy of the key model parameters such as the adsorption phase density and the theoretical adsorption capacity. These parameters were discussed, combined with the predicted adsorption phase density of CO2 based on the intercept method. The results indicate that among the 9 types of modified adsorption considered, based on the adsorption phase density screening, the deviation of the predicted adsorption capacity from the experimental value was then considered. The Dubinin-Radushkevich (DR) model can effectively fit the adsorption behavior of CO2 at low pressure (<7.5 MPa). The Langmuir (L), Langmuir-Freundlich (LF), Extended-Langmuir (EL), and TOTH models can effectively fit the adsorption behavior of CO2 at high pressure (7.5-20 MPa), while the multimolecular layer models were unsuitable for fitting ScCO2 adsorption. The model fitting results showed that only the monomolecular layer and micropore-filled adsorption models were suitable for fitting the ScCO2 adsorption capacity. The DR-LF model best fits the adsorption data based on its key parameters of adsorption phase density and theoretical adsorption capacity. The established mixed model DR-LF fitting results showed that the CO2 in coal was dominated by microporous filling adsorption. The higher the temperature, the greater the contribution of microporous filling adsorption to the total adsorption. There still exists deviation in the adsorption phase density and theoretical adsorption capacity. The contribution percentage of different adsorption mechanisms of CO2 in coal needs to be further investigated.

Unleashing the dye adsorption potential of polyaminoimide homopolymer: DFT, statistical physics, site energy and pore size distribution analyses

The efficient removal of Congo Red (CR) dye from aqueous solutions is an important issue in environmental protection. This study presents the synthesis and optimization of a polyaminoimide homopolymer (PHP) adsorbent for the removal of CR dye. To optimize the synthesis of PHP, ten different compositions of maleic anhydride and ethylene diamine were tested, with PHP3 demonstrating the highest efficacy. The adsorption process was further enhanced by optimizing pH, temperature, adsorbent dose, and initial dye concentration. Isotherm and kinetic studies revealed that the Langmuir-Freundlich model and the pseudo-second-order kinetics best described the adsorption process. Moreover, PHP3 demonstrated significantly greater selectivity for CR compared to Synozol yellow, and Sulfasalazine. Advanced statistical models were used to analyze the adsorption data, and the single-layer model with single energy (M1) being the most suitable, suggesting that CR molecules were adsorbed onto PHP3 in a perpendicular position through a multimolecular process, the adsorption process is physical, endothermic, spontaneous and specific surface area of PHP3 increased from 54.31 to 115.74 m2 g−1 as temperature rose from 288 to 318 K. Site energy distribution and pore size distribution studies showed that PHP3 has a heterogeneous energy distribution on its surface, and that the adsorption of CR dye primarily takes place in the macropores of PHP3. Density Functional Theory analysis indicated that PHP3 has electron-rich amine groups that can interact with electron-deficient sulfonate groups in CR, while electron-poor amide groups in the polymer can interact with the electron-rich azo group in Congo Red. It also shows that the presence of NaF, Na2SO4, and KCl salts did not significantly affect the CR adsorption, indicating the potential affinity/selectivity of PHP3 towards CR dye. The findings suggest that PHP3 could be an effective and promising adsorbent for industrial applications in wastewater treatment.

Adsorption behaviors and mechanisms of porous hypercrosslinked polymers with adjustable functional groups toward doxycycline hydrochloride from water

AbstractImino hypercrosslinked polymers (NH‐HCPs), amino hypercrosslinked polymers (NH2‐HCPs), and carboxyl hypercrosslinked polymers (COOH‐HCPs) were synthesized through cross‐linking and Friedel‐Crafts reactions to serve as highly efficient adsorbents for doxycycline hydrochloride (DOX) in water. These polymers, NH‐HCPs, NH2‐HCPs, and COOH‐HCPs, exhibited specific surface areas measuring 450, 267.576, and 94.39 m2/g, respectively. The adsorption kinetics of DOX onto these polymers were consistent with the pseudo‐second‐order model, while the adsorption isotherms followed the Langmuir model (NH‐HCPs) and Freundlich model (NH2‐HCPs and COOH‐HCPs), respectively. The maximum DOX adsorption capacities for NH‐HCPs, NH2‐HCPs, and COOH‐HCPs were 166.82, 132.43, and 72.07 mg/g, respectively. Simulation results indicated that COOH‐HCPs exhibited the strongest adsorption capability due to a substantial presence of oxygen and nitrogen groups on its surface, enabling the formation of hydrogen bonds with DOX. However, its actual adsorption capacity was the lowest among the polymers, indicating that structural adjustments played a more significant role in improving adsorption performance compared to functional adjustments. Adsorption experiments conducted with NH‐HCPs and NH2‐HCPs further supported this hypothesis. The primary DOX adsorption mechanism of NH‐HCPs, NH2‐HCPs, and COOH‐HCPs involved the H‐bonding of oxygen and nitrogen functional groups, along with other mechanisms such as π‐π conjugated effects, pore‐filling effects, electrostatic interactions, and acid–base interactions. Overall, this study demonstrates the effectiveness of NH‐HCPs, NH2‐HCPs, and COOH‐HCPs in DOX removal from water, highlighting the significant influence of structural adjustments on adsorption performance.

Efficient Adsorption of Ammonia by Surface-Modified Activated Carbon Fiber Mesh.

In view of the characteristics and risks of ammonia, its removal is important for industrial production and environmental safety. In this study, viscose-based activated carbon fiber (ACF) was used as a substrate and chemically modified by nitric acid impregnation to enhance the adsorption capacity of the adsorbent for ammonia. A series of modified ACF-based adsorbents were prepared and characterized using BET, FTIR, XPS, and Boehm titration. Isotherm tests (293.15 K, 303.15 K, 313.15 K) and dynamic adsorption experiments were performed. The characterization results showed that impregnation with low concentrations of nitric acid not only increased the surface acidic functional group content but also increased the specific surface area, while impregnation with high concentrations of nitric acid could be able to decrease the specific surface area. ACF-N-6 significantly increased the surface functional group content without destroying the physical structure of the activated carbon fibers. The experimental results showed that the highest adsorption of ammonia by ACFs was 14.08 mmol-L-1 (ACF-N-6) at 293 K, and the adsorption capacity was increased by 165% compared with that of ACF-raw; by fitting the adsorption isotherm and calculating the equivalent heat of adsorption and thermodynamic parameters using the Langmuir-Freundlich model, the adsorption process could be found to exist simultaneously. Regarding physical adsorption and chemical adsorption, the results of the correlation analysis showed that the ammonia adsorption performance was strongly correlated with the carboxyl group content and positively correlated with the relative humidity (RH) of the inlet gas. This study contributes to the development of an efficient ammonia adsorption system with important applications in industrial production and environmental safety.

Polyaniline-coated magnetic nanoparticles to enhance removal of diclofenac from aqueous media

This study presents a straightforward and cost-effective synthesis method for producing magnetic nanoparticles coated with polyaniline. These nanoparticles are utilized for the efficient removal of diclofenac from aqueous solutions. The synthesized material underwent thorough characterization through various techniques. Additionally, the adsorbent's properties were investigated, and adsorption experiments were conducted to explore the effects of pH, contact time, and diclofenac concentration. The most favorable outcomes were achieved at pH 4, using 25 mg of adsorbent, and with a stirring time of 10 min. Under these optimized conditions, the material exhibited a diclofenac removal efficiency of approximately 90 %. The adsorption process was comprehensively studied employing the pseudo-second-order kinetic model and the isothermal Langmuir-Freundlich dual-site model. Furthermore, the adsorbent displayed exceptional regenerative capabilities, allowing for multiple reuse cycles without a noticeable decline in efficiency. Theoretical investigations suggested that the interaction between diclofenac and the polyaniline surface predominantly involves the nucleophilic groups of diclofenac (-CO, -OH, and -NH) as well as the electrophilic group of polyaniline (-NH-). Overall, these findings underscore the high potential of this adsorbent material for effectively extracting diclofenac from water sources.

Equilibrium and Kinetic Insights into the Comprehensive Investigation of CO2, CH4, and N2 Adsorption on Cation-Exchanged X and Y Faujasite Zeolites.

The adsorption equilibria and kinetic performance of CO2, CH4, and N2 on pelletized cation-exchanged faujasite zeolites (with alkali, alkaline earth, and transition metal ions) have been investigated by an innovative volumetric apparatus simultaneously. The standard instrumental analytical techniques, including X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy (EDX), and atomic absorption spectroscopy (AAS), were utilized to characterize binder-free modified zeolites. EDX and AAS analyses revealed that the ion exchange was successfully achieved. The results indicate that the type of cation present in the zeolite framework and the Si/Al ratio can have a significant impact on the adsorption capacity and kinetic performance. The obtained isotherms were determined by three isotherm models, and the Langmuir-Freundlich (Sips) model was found to show the best agreement with the experimental isotherm data for all gases. The CO2 uptakes of KX, MgX, and CaX reached 4.13, 4.79, and 5.48 mmol/g, respectively. The effective binary and kinetic selectivities of CO2/CH4 and CO2/N2 were also calculated. Among all samples, KX showed the highest CO2/CH4 and CO2/N2 selectivities of 54.46 and 91.62, respectively. Pseudo-first-, pseudo-second-order, and Avrami kinetic models were fitted to the experimental kinetic data to analyze the adsorption kinetics. Finally, the macropore diffusion coefficient (Dp) and microporous diffusional time constant (Dc/rc2) were estimated by correlating the micropore-macropore kinetic model with the experimental fractional uptake curves. Among the ion-exchanged zeolite samples, the K+ form exhibits a suitable performance in terms of kinetic behavior and adsorption capacity.

Mechanistic understanding of the enhanced adsorption of diclofenac on a heat-treated and acid-leached halloysite

ABSTRACT Diclofenac (DCF), a common nonsteroidal anti-inflammatory drug, is frequently detected in aquatic environments, causing serious threat to aquatic organisms and humans through bioaccumulation, persistence, and toxicity. Using eco-friendly clay-based adsorbents, samples of halloysite (H) processed at 600°C (H600-0N) and then HCl-leached with 3 N concentration (H600-3N) were prepared, characterised by Inductively Coupled Plasma (ICP), N2 adsorption – desorption, and infrared spectroscopy with Fourier transform (FTIR), and used in DCF adsorption. H600-3N exhibited a substantial surface area increase from 63 m2 g−1 for H to 434 m2 g−1 due to an elevated SiO₂/Al₂O₃ ratio of 23.83 against 1.72 for H. In this context, H600-3N and H adsorbed 165 mg g−1 and 37.9 mg g−1 of DCF, respectively. The isotherms of H600-xN(x = 0 or 3) were adequately adjusted to the Langmuir-Freundlich model, while the kinetic data were suitably described by the pseudo-second order equation. Through cross-checking the results of characterisation, DCF adsorption and the FTIR investigation between DCF and H600-3N, a mechanism has been suggested that includes two main components: hydrogen bonding between the silanol’s hydrogen atom and the negatively charged carboxylate anion and hydrophobic interactions between the – Si – O – Si – entities and the DCF aromatic rings. The elucidation of intermolecular interactions between organic contaminants and 1:1 clay minerals is essential to develop the application of these abundant and low-cost materials in wastewater treatment.

Phosphate recovery using activated sludge cyanophycin: Adsorption mechanism and utilization as nitrogen-phosphorus fertilizer

Recovery of biopolymers is an important way of resource recovery in wastewater treatment plants. However, their recycling and application pathways need to be further developed. This study explored the application potential of cyanophycin granule polypeptide (CGP) extracted from activated sludge in recycling phosphate from wastewater and used for nitrogen-phosphorus fertilizer. The results showed that the adsorption behavior of phosphate by CGP was well described by Elovich and Langmuir-Freundlich models, which reflects the uneven energy distribution on the surface of CGP and belongs to multimolecular layer adsorption. The maximal adsorption capacity of CGP to phosphate was 53.739 mg P/g, and the effects of anions and macromolecules on adsorption are negligible. The guanidyls in CGP were involved in binding phosphates, and the adsorption energies of CGP-HPO42– and CGP-H2PO4– calculated by DFT are –0.645 and –0.179 eV, respectively. Moreover, CGP absorbed phosphate significantly promoted the germination and growth of Brassica napus, and altered communities of rhizosphere rare species. Transcriptomic results of Brassica napus showed that nitrate uptake and arginine synthesis were down-regulated and arginine metabolism was up-regulated, which may be attributed to the degradation of CGP to arginine and ammonium in soil and uptake by plant. Nitrogen and phosphate released by CGP degradation promoted plant hormone signal transduction, thereby accelerating cell enlargement and plant growth. These results indicate that CGP can effectively recover phosphate and be utilized as a nitrogen-phosphorus fertilizer.

Development of a portable, low-cost QCM sensor-based device for detecting α-pinene in Indian cardamom

One of the key quality indicators for Indian cardamom is α-pinene. To detect α-pinene, linoleic acid, a constituent fatty acid present in rice bran oil, was found responsible for the physisorption of α-pinene through Van der Waals (vdW) interaction. For the analysis and study of the sensing behaviour of α-pinene, a portable gas measuring device incorporating the rice bran oil coated quartz crystal microbalance sensor (RB-QCM) is developed for real-time detection. The sensor offers a good sensitivity (0.367 Hz/ppm) and a rapid response/recovery time (6 s/11 s). The physical adsorption affinity of α-pinene is calculated using the Langmuir, Freundlich, and Langmuir-Freundlich isotherm models. For estimating α-pinene in cardamom samples, the sensor demonstrated a coefficient of 0.98, with the peak area (%) determined by gas chromatography-mass spectrometry (GC–MS). SEM, FTIR, and AFM are used to analyse the structure and morphology of the sensor coating. According to this study, the rice bran oil-coated QCM sensor is a promising method for detecting α-pinene.

Molecular Simulation Study Based on Adsorption of Gas (CO2,O2,CH4) on Coal

This study aimed to further explore the adsorption properties of different gases (CO2, O2, and CH4) on the coking coal surface by establishing a molecular model. Changes in the absolute adsorption capacity and the isosteric heat of adsorption of gases under different temperatures, pressures, and compositions were simulated using grand canonical Monte Carlo (GCMC) and molecular dynamics simulations. Interaction energy and energy distribution were used to analyze the adsorption behavior of gases, and the diffusion properties were investigated using the diffusion coefficient and diffusion activation energy. The absolute adsorption results fit well with the Langmuir–Freundlich model. The absolute adsorption capacity had a significant positive correlation with pressure and the corresponding mole fraction, and a significant negative correlation with temperature. The competitiveness, based on binary adsorption selectivity, was in the order of CO2 &gt; O2 &gt; CH4. The isosteric heat of adsorption of CH4 was slightly higher than that of O2, and that of CO2 was 1.49–1.64 times that of O2 and CH4. The isosteric heat of the adsorption of gases was also barely influenced by temperature and pressure. The interaction energy between CO2 and coal was greater than that of O2 or CH4, but the high pressure and high content were not conducive to the adsorption of O2 by CO2. The preferred adsorption site for CO2 was stronger than that for O2 and CH4, and its peak value negatively correlated with the molar fraction. The diffusion coefficient for single component gases initially increased and then decreased with increased pressure, showing a positive correlation with temperature. A close inverse correlation existed between diffusion activation energy and pressure. These results revealed the microscopic adsorption and diffusion regularities of CO2, O2, and CH4 in the coal model, indicating great significance in accurately predicting coal fires.

Fabrication of porous adsorbent by quinoa husk stabilized foam templates for dye adsorption and carbonization for soil remediation

In this study, a novel adsorbent with a sufficient porous structure was fabricated using a green and highly stable water-based foam template. This template was stabilized with agricultural waste quinoa husk (QH) and applied to remove dye pollutants in wastewater. The porous adsorbent exhibited a high adsorption capacity of 740.95 mg/g for methylene blue and 1022.1 mg/g for methyl violet. The adsorption process was well described by the Langmuir-Freundlich model and the pseudo second-order kinetic model. A sustainable concept for handling the spent adsorbent was also proposed, involving its conversion into biochar and safe return to the soil. An additional benefit was observed, as the biochar effectively adjusted the physicochemical properties of the soil and improved crop growth with the addition of 1 wt%. The potential application of porous adsorbent in wastewater treatment and the reference of sustainable strategy for disposing of other adsorbents are both noteworthy.

Did Salts in Seawater Play an Important Role in the Adsorption of Molecules on Minerals in the Prebiotic Earth? The Case of the Adsorption of Thiocyanate onto Forsterite-91.

Thiocyanate may have played as important a role as cyanide in the synthesis of several molecules. However, its concentrationin the seas of the prebiotic Earth could have been very low. Thiocyanate was dissolved in two different seawaters: a) a composition that comes close to the seawater of the prebiotic Earth (seawater-B, Ca2+ and Cl-) and b) a seawater (seawater-A, Mg2+ and SO42-) that could be related to the seas of Mars and other moons in the solar system. In addition, forsterite-91 was a very common mineral on the prebiotic Earth and Mars. Two important results are reported in this work: 1) thiocyanate adsorbed onto forsterite-91 and 2) the amount of thiocyanate adsorbed, adsorption thermodynamic, and adsorption kinetic depend on the composition of the artificial seawater. For all experiments, the adsorption was thermodynamically favorable (ΔG < 0). The adsorption data fitted well in the Freundlich and Langmuir-Freundlich models. When dissolving thiocyanate in seawater 4.0-A-Gy and seawater 4.0-B-Gy, the adsorption of thiocyanate onto forsterite-91 was ruled by enthalpy and entropy, respectively. As shown by n values, the thiocyanate/foraterite-91 system is heterogeneous. For all kinetic data, the pseudo-first-order model presented the best fit. The constant rate for thiocyanate dissolved in seawater 4.0-A-Gy was twice that compared to thiocyanate dissolved in seawater 4.0-B-Gy or ultrapure-water. The interaction between thiocyanate and Fe2+ of forsterite-91 was with the nitrogen atom of thiocyanate. In the presence of thiocyanate, sulfate interacts with forsterite-91 as an inner-sphere surface complex, and without thiocyanate as an outer-sphere surface complex.

Bridged EGFET Design for the Rapid Screening of Sorbents as Sensitisers in Water-Pollution Sensors.

We further simplify the most 'user-friendly' potentiometric sensor for waterborne analytes, the 'extended-gate field effect transistor' (EGFET). This is accomplished using a 'bridge' design, that links two separate water pools, a 'control gate' (CG) pool and a 'floating gate' (FG) pool, by a bridge filled with agar-agar hydrogel. We show electric communication between electrodes in the pools across the gel bridge to the gate of an LND150 FET. When loading the gel bridge with a sorbent that is known to act as a sensitiser for Cu2+ water pollution, namely, the ion exchanging zeolite 'clinoptilolite', the bridged EGFET acts as a potentiometric sensor to waterborne Cu2+. We then introduce novel sensitisers into the gel bridge, the commercially available resins PurometTM MTS9140 and MTS9200, which are sorbents for the extraction of mercury (Hg2+) pollution from water. We find a response of the bridged EGFET to Hg2+ water pollution, setting a template for the rapid screening of ion exchange resins that are readily available for a wide range of harmful (or precious) metal ions. We fit the potentiometric sensor response vs. pollutant concentration characteristics to the Langmuir-Freundlich (LF) model which is discussed in context with other ion-sensor characteristics.

Adsorption characteristics and mechanism of ammonia nitrogen and phosphate from biogas slurry by Ca2+-modified soybean straw biochar.

The utilization of biogas slurry is critical for the sustainable development of animal husbandry. Biomass carbon adsorption is a feasible method for the recycling of nutrients from biogas slurry. However, research on the co-adsorption of ammonia nitrogen and phosphate is scarce. Herein, soybean straw was utilized as the raw material to prepare Ca2+-modified biochar (CaSSB), which was investigated for its ammonia nitrogen and phosphate adsorption mechanisms. Compared with natural biochar (SSB), CaSSB possesses a high H/C ratio, larger surface area, high porosity and various functional groups. Ca2+-modified soybean straw biochar exhibited excellent adsorption performance for NH4+-N (103.18 mg/g) and PO43--P (9.75 mg/g) at pH = 6, using an adsorbent dosage of 2 g/L. The experimental adsorption data of ammonia nitrogen by CaSSB corresponded to pseudo-second-order kinetics and the Langmuir isotherm model, suggesting that the adsorption process was homogeneous and that electrostatic attraction might be the primary adsorption mechanism. Meanwhile, the adsorption of phosphate conformed to pseudo-second-order kinetics and the Langmuir-Freundlich model, whose mechanism might be attributed to ligand exchange and chemical precipitation. These results reveal the potential of CaSSBs as a cost-effective, efficient adsorbent for the recovery of ammonium and phosphate from biogas slurry.

Self-polymerization magnetic hydrogel for Cu and Pb adsorption from aqueous solutions: Theoretical insight and implication

In this work, the polyacrylic acid/carboxymethyl starch/Fe3S4 (PAA/CMS/Fe3S4) magnetic hydrogel was prepared. Pb and Cu in aqueous solution were as targeted pollutants for PAA/CMS/Fe3S4. Fe3S4 as the magnetic factor was added to the hydrogel. The hydrogel that composed by PAA and CMS can prevent Fe3S4 from oxidization. And, Fe3S4 not only had magnetic properties but also promoted the adsorption capacity of PAA/CMS/Fe3S4. In addition, the Fe(II) that in Fe3S4 served as the activator of potassium persulfate to produce SO4-· and triggered polymerization without the traditional method that need extra energy including heating and UV lighting, which can simplify the material preparation process. PAA/CMS/Fe3S4 exhibited adsorption stability in the pH from 3.0 to 6.0. The adsorption process fitted to pseudo-second-order and Langmuir-Freundlich models. The functional groups of CO/Metal-O-C and O-CO in PAA/CMS/Fe3S4 were identified by FTIR and XPS, which will adsorb Pb and Cu through complexation. The XRD results showed that the Pb and Cu can also be adsorbed by the formation of PbS and CuS, which due to the present of Fe3S4. The Density-functional theory analysis showed that the orbital hybridization between Pb and Fe3S4 was stronger than that of Cu and Fe3S4, which result in Fe3S4 had a stronger interaction with Pb than Cu. PAA/CMS/Fe3S4 magnetic hydrogel is a novel magnetic hydrogel and have a good adsorption performance for Pb and Cu from water. This work provides a new method for Fe3S4 application in magnetic adsorbent.

Influence of potential contaminants on I2 and CH3I adsorption onto zeolitic imidazolate frameworks (ZIFs) using GCMC simulations

Zeolitic imidazolate frameworks (ZIFs) are one type of promising volatile radioiodine sorbents due to their chemical/thermal stability, tunable structures, and high iodine adsorption capacity. However, the inhibiting effect of contaminants on volatile iodine adsorption onto ZIFs remains unclear. Herein, the adsorption of volatile iodine (I2 and CH3I) onto five different ZIFs (SALEM-2, ZIF-8, ZIF-Cl, ZIF-90, and ZIF-65) and adsorption selectivity over ten contaminants were investigated by using grand canonical Monte Carlo (GCMC) methods. It is found that the I2 adsorption isotherm could be accurately described by the Langmuir-Freundlich model. Furthermore, the adsorption quantity of CH3I is much smaller than that of I2 at the same partial pressure. Ten potential gaseous contaminants that existed in a reprocessing plant or nuclear reactor accident, including CO, NO, H2O, CH4, C2H6, CH3OH, CH3CH2OH, Cl2, CH3Cl, and C6H6, were considered for calculation of binary adsorption. The results show that C6H6 has the largest adsorption enthalpy among all contaminants, whereas CO, NO, H2O, and CH4 have the smallest. Moreover, CO, NO, H2O, and CH4 have negligible effects on volatile iodine adsorption onto ZIFs. In contrast, except for CH3I adsorption onto ZIF-65, C6H6 has the strongest inhibiting effect since benzene could occupy the adsorption sites of iodine in ZIFs. This work not only provided the fundamental knowledge of volatile iodine adsorption on ZIFs but also proposed a new strategy to evaluate the inhibiting effect of contaminants. It could be helpful for future screening and design of better sorbents.

The Adsorption Characteristics of Heavy Metals in Acid Mine Drainage from Abandoned Tin Mines on Lightweight Expanded Clay Aggregate (LECA)

Abandoned tin mines produce acid mine drainage in their water basin. If not treated well, it will damage environmental ecosystem by entering rivers or other water bodies. This acid mine drainage is attempted to be remediated by adsorption technique. The adsorbent used in this study is Lightweight Expanded Clay Aggregate (LECA) because its base material is natural clay. LECA is commonly used for hydroponics and constructions. LECA is made from natural clay that being heated at temperature over 1100°C. This study aims to determine how significant LECA in adsorbing metals in acid tin mine drainage. This research used two materials namely LECA and tin acid mine drainage. Both materials were contacted for two days in shaker bath. The results of this study were the adsorbing Fe(II) and Cu(II) on LECA could be approached by the Langmuir-Freundlich (LF) combined model where the Cµ,max are 0.406 and 0.020 mg/g of adsorbent, respectively. Unlike the other two metals, Sn(II) was more likely to experience precipitation instead of adsorption because of increasing of pH value. The conclusion, heavy metals in tin acid mine drainage could be remediated well by using LECA.

Biosorption of methylene blue by lentil shell on activation with sulfuric acid, formaldehyde, and calcination: kinetic, isotherm, and thermodynamic study

Lentil shell (LS) on modification with sulfuric acid (LSAC), formaldehyde (LSFM), and on calcination (LSCL) were used for the adsorption of methylene blue dye in the present study. The sulfuric acid treated LS adsorbent has shown maximum adsorption. The batch adsorption experiments were studied with the effect of adsorbent dose (10–60 mg), pH (4–10), dye concentration (10–80 mg/L), contact time (10–60 minutes), and temperature (303–333 K). The maximum removal of methylene blue was found at pH 10 with adsorption time 60 minutes. The maximum adsorption capacity is measured for LSAC, LSCL, LSFM, and LS untreated (LSUN) are 49.56, 45.79, 42.24, and 42.09 mg/g respectively for 60 mg adsorbent dose with 60 mg/L of initial methylene blue dye concentration. The biosorbents were characterized with Fourier Transform Infrared spectra, Scanning Electron Microscopy, Transmission Electron Microscopy, BET-N2 adsorption, and Energy Dispersive X-ray analysis. The adsorption isotherm was studied at the temperature of 303, 313, 323, and 333 K. It was found that the higher temperature suitable for maximum adsorption. Langmuir model and Freundlich model were studied from the obtained results for adsorption mechanism. The pseudo second order kinetic model was found suitable for the present adsorption study in comparison with pseudo first order model and intraparticle diffusion model. The data obtained from the present work showed that LS could be employed as an efficient adsorbent for the adsorption of the dye.