Adsorption Kinetic Models Research Articles

Study on the mechanism of lignin non-productive adsorption on cellobiohydrolase

Enzymatic hydrolysis is important for lignocellulosic biomass conversion into fermentable sugars. However, the nonproductive adsorption of enzyme on lignin was major hinderance for the enzymatic hydrolysis efficiency. In this study, non-productive adsorption mechanism of cellulase component cellobiohydrolase (CBH) onto lignin was specific investigated. Research revealed that the adsorption behavior of CBH on eucalyptus alkali lignin (EuA) was affected by reaction conditions. As study on the adsorption kinetic, it was indicated that the adsorption cellulose binding domain (CBD) of CBH onto EuA well fitted with Langmuir adsorption model and pseudo second-order adsorption kinetics model. And the tyrosine site related to the adsorption of CBD onto lignin was proved by the fluorescence and UV spectra analysis. The results of this work provide a theoretical guidance to understanding the nonproductive adsorption mechanism and building method to reduce the adsorption of cellulase on the lignin.

Reduction of nitrogen loss in runoff from sloping farmland by a ridged biochar permeable reactive barrier with vegetated filter strips

IntroductionEutrophication due to nitrogen (N) loss from sloping farmland has a high risk in the Three Gorges Reservoir. Biochar and vegetated filter strips (VFS) are used to control nutrient runoff and increase soil water-holding capacity, soil nutrient retention, and crop yield. However, surface biochar application has limited ability to control N loss, especially from sloping farmland.MethodsIn this study, different widths of ridged biochar permeable reactive barrier (RB-PRB) with VFS were employed to intercept N loss in runoff from sloping farmland. Adsorption characteristics of biochar for nitrate and ammonium N were evaluated using isothermal and kinetic adsorption models before field experiments. N index values for ammonium (NH4+), nitrate (NO3−), dissolved N (DTN), particulate N (PN), and total N (TN) lost through runoff were monitored from April 2019 to January 2020.ResultsNO3− and NH4+ sorption on biochar was predominantly physical adsorption with a maximum capacity of 4.51 and 4.12 mg g-1, respectively. During the research period, the dominant transportation pathway of N loss involved dissolved total N movement through subsurface flow, which accounted for 65.55% of the total loss. TN loss for CK was 1954 g·hm-2, while RB-PRB and VFS decreased N loss from sloping farmland by 36.7%. The interception efficiency of RB-PRB was highest at 0.3 m width. VFS successfully intercepted particulate N and reduced it by 32.75%. In terms of soil nutrients, the RB-PRB and VFS interventions led to a substantial 41.69% increase in the TN content of the soil at a 0.4 m width.DiscussionThe findings suggest that biochar has a favorable adsorption effect on NH4+ and NO3−, an appropriate width of RB-PRB with VFS could effectively reduce nitrogen loss from sloping farmland. Simultaneously, it enhances the water and fertilizer retention capacity of sloping cropland soil; however, the long-term implications necessitate further validation.

Syzygium aromaticum-mediated green synthesis of iron oxide nanoparticles for efficient heavy metal removal from aqueous solutions

The current study focused on the environmentally friendly synthesis of iron oxide nanoparticles (IONPs) using ferric nitrate Fe(NO3)3 9H2O as a precursor and aqueous Syzygium aromaticum (clove) extract as a reducing agent. Several analytical methods, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and ultraviolet–visible (UV–Vis.) spectroscopy, were used to confirm the synthesized iron oxide nanoparticles. These procedures were carried out to learn more about the surface shape and chemical composition of the produced iron oxide nanoparticles. The mean size of iron nanoparticles was determined by TEM examination to be 4.7 nm. The characterization revealed that the primary component of iron nanoparticles was magnetite when the Syzygium aromaticum extract was utilized as a reducing agent for Fe3+. For application, synthesized material was used to remove the harmful Cr (VI) ions from an aqueous solution. The batch adsorption approach was utilized to maximize the effects of significant elements such as pH, adsorbent dose, treatment duration, and initial Cr (VI) ions concentration to achieve the highest removal of Cr (VI) ions. The experimental adsorption data were fitted using various isotherm and kinetic adsorption models.

Effective and fast removal of ionic dyes from contaminated water using multi‐walled carbon nanotubes decorated with polyelectrolyte brushes

AbstractIn this work, new nanoadsorbents consisting of polymer‐modified multi‐walled carbon nanotubes (MWCNTs) were used to remove toxic ionic dyes, of methylene blue (MB) and methyl orange (MO), effectively from aqueous solutions. The MWCNTs were coated with polymer brushes of poly(potassium 3‐sulfopropyl methacrylate) (PKSPMA) and poly(2‐methacryloyloxyethyltrimethylammonium chloride) (PMETAC) via surface‐initiated atom transfer‐radical polymerization. The PKSPMA@MWCNTs and PMETAC@MWCNTs delivered removal efficiencies of ~80% at pH 7. Maximum adsorption capacity (qmax) reached 411.62 mg/g for MB using PKSPMA@MWCNTs and 224.60 mg/g for MO using PMETAC@MWCNTs, showcasing the effectiveness of these novel nanoadsorbents. The experimental results were analyzed using adsorption isotherm models (Langmuir, Freundlich, and Temkin) and kinetic models (pseudo‐first‐order, pseudo‐second‐order, and intraparticle diffusion). The Freundlich model provided an excellent fit for MB adsorption on both adsorbents, whereas the Temkin model best described MO adsorption on PKSPMA@MWCNTs and the Langmuir model on PMETAC@MWCNTs. The fitting results showed that the pseudo‐second‐order kinetic model was the most accurate fit for MB and MO adsorption on both nanoadsorbents, suggesting that the removal mechanism was chemisorption. In conclusion, PKSPMA@MWCNTs and PMETAC@MWCNTs demonstrate significant potential as effective adsorbents for dye removal from water, providing a promising approach for water treatment and environmental remediation.

Enhancing the adsorption capacity of organic and inorganic pollutants onto impregnated olive stone derived activated carbon

This study presents a sustainable approach to activated carbon production from olive stones in comparison to commercial ones, using various activating agents such as H3PO4, KOH, and ZnCl2, for enhancing the adsorption properties and versatile adsorption capability to remove a range of pollutants including copper ion, methylene blue, and 2,4-Dichlorophenoxyacetic acid from aqueous solutions. The performances of activated carbons across varying conditions such as pollutant concentrations, temperatures, pH levels, and adsorbent amounts were tested. Increased initial pollutant concentrations correlated with higher adsorption capacities. Maximum adsorption capacities were achieved at pH levels of 5, 10, and 2 for Cu, MB, and 2,4-D, respectively. For KOSAC, Cu removal rose from 27 % to 52 %, for ZOSAC, MB removal increased from 39 % to 65 %, and for ZOSAC, 2,4-D removal surged from 33 % to 99 % at varying adsorbent amounts. Model validation was carried out utilizing the kinetic models (PFO, PSO) and isotherm models (Langmuir, Redlich-Peterson). The PFO kinetic model and Langmuir isotherm model proved more suitability for Cu adsorption, whereas PFO and PSO kinetic models, along with Redlich-Peterson isotherm models, were more prominent for MB and 2,4-D adsorption. Thermodynamic analysis revealed that the adsorption of Cu and 2,4-D was exothermic, while MB adsorption was endothermic. By optimization of experimental conditions, the maximum adsorption capacities were attained at 30.34 °C and 297.65 mg L−1 for KOSAC-Cu, 48.62 °C and 269.37 mg L−1 for ZOSAC-MB, and 30.31 °C and 299.02 mg L−1 for ZOSAC-2,4-D sorption. This research highlights ZOSAC's potential as a cost-effective, eco-friendly solution for water treatment, contributing to environmental sustainability and economical feasibility.

Simultaneously enhancing toluene adsorption and regeneration process by hierarchical pore in activated coke: a combined experimental and adsorption kinetic modeling study.

Activated coke is a type of commonly used adsorbent for benzene series VOCs such as toluene, but traditional microporous activated coke usually faces the challenge of poor regeneration performance. Herein, based on self-made activated cokes with typical pore configuration, we found that adsorption and regeneration of toluene can be simultaneously enhanced by constructing hierarchical pore in activated coke. Correlations of pore configuration with toluene adsorption capacity and regeneration efficiency reveal that micropore contributes for strong toluene adsorption; meso-macropore provides mass transfer channel for toluene desorption and regeneration process. Hierarchical porous activated coke prepared from Zhundong subbituminous coal not only achieves the highest toluene adsorption capacity of 340.92mg·g-1, but also can retain more than 90% of initial adsorption capacity after five adsorption-regeneration cycles. By contrast, micropore-dominant activated cokes can only retain 70% of initial adsorption capacity. Adsorption kinetic modelling on adsorption breakthrough curves shows that hierarchical porous activated coke prepared from Zhundong subbituminous coal exhibits high adsorption and diffusion rate constants of 14.39 and 33.45min-1, respectively, much higher than those of micropore-dominant activated cokes. Due to the accelerated surface adsorption and diffusion processes induced by meso-macropore, toluene adsorption and regeneration behavior can be simultaneously improved. Results from this work validated the role of pore hierarchy in toluene adsorption-regeneration process, providing guidance for designing high-performance activated coke with synergistically improved toluene adsorption capacity and regeneration performance.

Adsorption isotherm and kinetic modeling of malachite green (MG) dye on cost-effective mesoporous material Al-MCM-41 synthesized from local clay

Adsorption isotherm and kinetic modeling of malachite green (MG) dye on cost-effective mesoporous material Al-MCM-41 synthesized from local clay

Efficient Adsorption Removal of Tetrabromobisphenol A from Water by Using a Magnetic Composite Fe3O4/GO/ZIF-67

Tetrabromobisphenol A (TBBPA) is a kind of widely used brominated flame retardant (BFR), which is proven to be harmful to ecological systems and public health. It is very important to remove TBBPA from the environment. In our study, a magnetic composite named Fe3O4/GO/ZIF-67 was synthesized by a coprecipitation method and applied in the highly efficient adsorption of TBBPA from water. Static adsorption experiments demonstrated that the adsorption capacity could reach 232 mg·g−1 within 120 min, which is much higher than those reported in the other literature. The experimental results show that the adsorption of TBBPA on Fe3O4/GO/ZIF-67 followed Langmuir and pseudo-second-order kinetic adsorption models. The main mechanisms for these adsorptions were identified as hydrogen bonds between OH groups in TBBPA and COOHs of Fe3O4/GO/ZIF-67, and π-π stacking between Fe3O4/GO/ZIF-67 and TBBPA. This study provides a method with great promise for the design and synthesis of better adsorbents for the removal of TBBPA from the water environment.

Electrospun nanofiber membrane of 14-crown-4 polyimide by in situ grafting diamino crown ether for highly selective Li+ adsorption and separation

The global demand for lithium is increasing rapidly with the blossom of the new energy field. It is imperative to develop a sustainable and efficient approach for recovering Li+ resources from salt-lake brine. In this study, diamino dibenzo-14-crown-4 ether (DAB) was chemically grafted on 14-crown-4 polyimide (14C4PI) by nucleophilic substitution to fabricate nanofiber membrane by electrospinning method. The crown ether loading of DAB-g-14C4PI membrane was increased from 1.38 up to 2.27 mmol/g, and the grafting degree reached 83.4 % by regulating the additive amount of DAB and the reaction time. The Li+ equilibrium adsorption capacity of the DAB-g-14C4PI nanofiber membrane was enlarged from 40.17 (14C4PI) to 60.71 mg/g. The adsorption for Li+ on the membrane was a monolayer chemical adsorption process proved by the adsorption kinetic and isotherm models. The separation factors of the membrane for Li+/Na+, Li+/K+, Li+/Mg2+ and Li+/Ca2+ were 69.24, 79.4, 37.46 and 67.53, respectively. DFT calculations indicated the raised Li+ adsorption capacity was also ascribed to the enhanced adsorption energy from −107.71 to −122.84 kcal/mol, owing to the relatively higher electric charge density (−0.478 vs −0.448 a.u.). In summary, this work put forward a novel method to fabricate a nanofiber membrane with a high crown ether loading for the extraction of lithium resources.

Synthesis and characterization of Novel Igepal Co-520 surfactant coated Fe3O4 Nanoparticles: An evaluation of Vanadium enrichment in spice samples

In this study, novel Fe3O4 nanoparticles coated with surfactant Igepal Co-520 (polyoxyethylene (5) nonylphenylether) as adsorbent were synthesized, and total vanadium recovery was performed by magnetic solid phase extraction (MSPE) method. Fe3O4 nanoparticles coated with Igepal Co-520 were employed in the investigation of vanadium enrichment. The synthesized nanoparticles were characterized by Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Analysis (EDX), X-Ray Diffraction Analysis (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), and Thermogravimetric Analysis (TGA), and total vanadium concentration was determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The corresponding values for the pH, adsorbent amount, and contact time were 3, 5 mg, and 120 min. Total vanadium was recovered from an aqueous solution under the optimum conditions. Langmuir and Freundlich adsorption isotherms, pseudo-first and pseudo-second order adsorption kinetics, foreign ion studies, desorption, and analytical value studies were performed. In isotherm studies, the effect on adsorption was examined by varying the vanadium concentration between 1 mg/L and 100 mg/L. The Langmuir model (R2>0.99) seems to be more compatible with vanadium adsorption than the Freundlich model (R2<0.87). Pseudo−first-order and pseudo-second-order equations were used to evaluate adsorption kinetic models. It has been observed that the pseudo-quadratic equation (R2>0.89) was more suitable for modeling than the pseudo-first-order equation (R2<0.56). The analytical performance parameters of the method were calculated as enrichment factor (EF) 114, the limit of detection (LOD) 8.3 µg/L, the limit of quantification (LOQ) 28.3 µg/L, and relative standard deviation (RSD) 1.20 %. At various molarities, the effects of acidic (HCl) and basic (NaOH) agents on the desorption of total vanadium ions adsorbed on the magnetic Fe3O4 surface were examined and compared. It was observed that the maximum recovery (100 %) was obtained using HCl as the desorption agent. The total vanadium concentration in spice samples was measured in an actual sample analysis. All the results demonstrate that the Fe3O4@Igepal Co-520 was successfully synthesized and has the potential to be a useful tool for heavy metal recovery.

Evaluation of Kinetic and Isotherm Models for Adsorption of Boron Under Different Soil Orders in Oil Palm Plantations of India

ABSTRACT Adsorption isotherm and kinetic models are essential in predicting the adsorption mechanisms, which helps in boron (B) recommendation at appropriate doses. This study is formulated with the objective of assessing different kinetic and adsorption models for the adsorption of B in different soil orders (Entisol, Alfisol, Inceptisol and Vertisol) in Oil Palm plantations in India. The B adsorption in soils followed the order: Vertisol > Alfisol > Inceptisol > Entisol. The results revealed that, the Langmuir adsorption model fitted well for alfisol (part1 R2 = 0.9912 & part2 R2 = 0.9678), entisol (R2 = 0.9862) and inceptisol (R2 = 0.9924), while the Freundlich model fitted well for vertisol (R2 = 0.9943). The soils under entisol and inceptisol showed linear isotherms whereas, the vertisol and alfisol had curvilinear isotherms and the split Langmuir isotherm was worked out. High bonding energy at the lower part of split isotherm represented stronger retention of B at lower B concentrations. The B equilibrium was attained in 24 h in alfisol and inceptisol, and 12 h in entisol, whereas in vertisol, the equilibrium was not completed until 72 h. From the correlation coefficients obtained from all models, the pseudo-second-order kinetic model explained the B sorption in a better way followed by elovich and power function kinetic models in different soil types. Desorption of B is higher in entisol in most of the added B concentrations. The study suggests a higher rate of B fertilizer application than the recommended in soils having high B adsorption capacity for optimum crop growth and yield.

Unlocking the potential of biochar: an iron-phosphorus-based composite modified adsorbent for adsorption of Pb(II) and Cd(II) in aqueous environments and response surface optimization of adsorption conditions.

In this work, iron-phosphorus based composite biochar (FPBC) was prepared by modification with potassium phosphate and iron oxides for the removal of heavy metal ions from single and mixed heavy metal (Pb and Cd) solutions. FTIR and XPS characterization experiments showed that the novel modified biochar had a greater number of surface functional groups compared to the pristine biochar. The maximum adsorption capacities of FPBC for Pb(II) and Cd(II) were 211.66mg·g-1 and 94.08mg·g-1 at 293K. The adsorption of Pb(II) and Cd(II) by FPBC followed the proposed two-step adsorption kinetic model and the Freundlich isothermal adsorption model, suggesting that the mechanism of adsorption of Pb(II) and Cd(II) by FPBC involved chemical adsorption of multiple layers. Mechanistic studies showed that the introduction of -PO4 and -PO3 chemisorbed with Pb(II) and Cd(II), and the introduction of -Fe-O increased the ion exchange with Pb(II) and Cd(II) during the adsorption process and produced precipitates such as Pb3Fe(PO4)3 and Cd5Fe2(P2O7)4. Additionally, the abundant -OH and -COOH groups also participated in the removal of Pb(II) and Cd(II). In addition, FPBC demonstrated strong selective adsorption of Pb(II) in mixed heavy metal solutions. The Response Surface Methodology(RSM) analysis determined the optimal adsorption conditions for FPBC as pH 5.31, temperature 26.01°C, and Pb(II) concentration 306.30mg·L-1 for Pb(II). Similarly, the optimal adsorption conditions for Cd(II) were found to be pH 5.66, temperature 39.34°C, and Cd(II) concentration 267.68mg·L-1. Therefore, FPBC has the potential for application as a composite-modified adsorbent for the adsorption of multiple heavy metal ions.

Mechanistic Understanding of Sieving Lithium Ions Using a Biobased Sorbent Technology for Sustainable Lithium Reclamation and Cleansing Brines.

Low-cost environmentally benign materials that can be produced in a large scale to extract lithium from brine resources could drive the lithium market toward a clean technology with high lithium recovery and production. Herein, we have investigated the utilization of a novel, environmentally benign, and low-cost biobased sorbent for the extraction of lithium from lithium-rich solutions. This biobased molecular sieving sorbent, iron(III)-tannate (Fe(III)-TA), belongs to a novel class of coordination polymer frameworks derived from a natural polyphenol-tannic acid (TA)-coordinated with iron(III) metal cations. Its lithium adsorption and kinetic isotherm studies conducted using lithium-rich aqueous solutions confirm the sorbent's dual function for lithium sieving via physisorption, chemisorption, and mass transfer diffusion processes. The adsorption equilibrium and kinetic isotherm models combined with the external and internal mass transfer diffusion models reveal a mechanistic pathway for lithium-ion adsorption. Aiding by forming a fluid film for external mass transfer diffusion of lithium ions, analytes adsorb onto the sorbent surface via physisorption and chemisorption followed by the internal mass transfer diffusion, occupying lithium ions in the sorbent's pores. The lithium adsorption efficiency studies conducted for brines with different concentrations of interference alkali and alkaline cations evidence that the sorbent's affinity for lithium ions strongly depends on the analyte concentration. The results evidence that the sorbent has the ability to lower the brine's salinity and significantly reduces the ratios of Mg/Li and Ca/Li by 4-fold and 10-fold, respectively, yielding lithium-rich solutions. Thus, implementing this innovative biobased sorbent technology as an add-in step into traditional lithium extraction and refining processes, one can design a cost-effective pathway to yield lithium-rich leachate by reducing the Mg/Li and Ca/Li ratio. Nonetheless, the present work demonstrates that Fe(III)-tannate is an effective multifunctional sorbent for sieving lithium from lithium-rich aqueous solutions as well as for desalinating brine resources to recover usable water. Thus, this biobased sorbent offers the possibility of effective application of lithium reclamation and remediation of brine, mitigating the environmental impact of brine discharge and large volume of freshwater usage for lithium extraction and refining.

Copper-Modified Iron Oxide Nanoparticles: A Novel Catalyst for Effective Congo Red Dye Degradation in Wastewater Treatment

The raising worldwide water tainting from different sources has delivered admittance to unpolluted drinking water progressively testing. The release of effluents containing colors into water bodies become as a basic ecological worry lately. Regular treatment strategies are insufficient in wiping out these steady and risky poisons, requiring the investigation of novel methodologies. In this review, Cu-doped FeO nanoparticles were easily blended by using a co-precipitation strategy, and their synthetic qualities were entirely analyzed. These nanoparticles showed extraordinary adsorption abilities in the corruption of various color compounds. In particular, manufactured acidic color was focused on for expulsion utilizing metal-doped nanoparticles. Ideal boundaries for maximal acidic color not set in stone by surveying the adsorbent portion, beginning color focus, contact time, and temperature. The pH was distinguished as a critical variable, with the best incentive for maximal adsorption of Congo Red Dye viewed as less than 7. As indicated by late discoveries, Cu/FeO nanoparticles displayed unrivalled adsorption limit with regards to Congo Red Dye color at an ideal pH of 2, a measurement of 0.5 g/500 mL, a contact season of an hour and a half, and a color centralization of 150 ppm at 35° centigrade. Pseudo second order adsorption kinetic model exhibited amazing fitting outcomes for adsorption energy and balance information.

Development of Biomass Derived Adsorbents using Wood Apple Pulp for the Removal of Contaminants

This study involves the development of biomass derived adsorbents from wood apple pulp for water and wastewater treatment. This biomass was modified by the addition of commercially available activated charcoal and copper nanoparticles. Adsorbent characterization was performed for understanding the surface morphology and surface area. These new adsorbents were further evaluated for their potentiality in removing dyes and API pollutants (Active Pharmaceutical Ingredient). All the adsorbents were highly effective in the removal of these contaminants, 96% of Malachite Green and 72% of Congo Red was removed with a high adsorption capacity of 45 mg/g. API pollutant (Ciprofloxacin) removal showed 52% removal, which is greater when compared to several modified adsorbents. Adsorption equilibrium models (Langmuir and Freundlich) and kinetic models (pseudo first order and pseudo second order) were evaluated for fit of the experimental data. In general, the isotherm studies indicated multilayer adsorption.

Removal of Azo Dyes from Water Using Natural Luffa cylindrica as a Non-Conventional Adsorbent.

Reducing high concentrations of pollutants such as heavy metals, pesticides, drugs, and dyes from water is an emerging necessity. We evaluated the use of Luffa cylindrica (Lc) as a natural non-conventional adsorbent to remove azo dye mixture (ADM) from water. The capacity of Lc at three different doses (2.5, 5.0, and 10.0 g/L) was evaluated using three concentrations of azo dyes (0.125, 0.250, and 0.500 g/L). The removal percent (R%), maximum adsorption capacity (Qm), isotherm and kinetics adsorption models, and pH influence were evaluated, and Fourier-transform infrared spectroscopy and scanning electron microscopy were performed. The maximum R% was 70.8% for 10.0 g L-1Lc and 0.125 g L-1 ADM. The Qm of Lc was 161.29 mg g-1. Adsorption by Lc obeys a Langmuir isotherm and occurs through the pseudo-second-order kinetic model. Statistical analysis showed that the adsorbent dose, the azo dye concentration, and contact time significantly influenced R% and the adsorption capacity. These findings indicate that Lc could be used as a natural non-conventional adsorbent to reduce ADM in water, and it has a potential application in the pretreatment of wastewaters.

Insight into low-grade natural Linze palygorskite for composite particles preparation towards efficient wastewater treatment

Natural clay possesses advantages such as low cost and high adsorption capacity, rendering it a promising adsorbent for wastewater treatment. In this work, low-grade Linze palygorskite (LZ), comprising 20.5% palygorskite, was utilized as a representative material to synthesize polyvinylformal-LZ (PVFM-LZ) composite particles through cross-linking polyvinyl alcohol (PVA) with formaldehyde. The raw material ratio of LZ and PVA was maintained at a high level of 20:1. Meanwhile, high-purity montmorillonite (Mt) and palygorskite (Pal) were employed as raw materials to prepare PVFM-Mt and PVFM-Pal using the same method, enabling comparative analysis with PVFM-LZ. PVFM-LZ exhibited a notable adsorption capacity of 101.92 mg·g−1 for methylene blue, which was comparable to that of PVFM-Mt and PVFM-Pal. What’s more, owing to the tightly cross-linked network structure formed by PVFM, PVFM-LZ demonstrated minimal loss (2.53%) and swelling (8.0%) rates in water, facilitating easy separation and promoting recyclability. Even after six cycles, its adsorption efficiency remained above 85%. The structure, physicochemical properties and adsorption performance of the three composite particles were meticulously examined before and after adsorption. Kinetic, thermodynamic and isotherm adsorption models revealed that PVFM-LZ exhibited spontaneous surface-controlled monolayer adsorption behavior. The possible adsorption mechanisms included electrostatic interactions, hydrogen bonding, and intermolecular forces. This work may provide an experience for the adsorption application of low-grade natural clay in composite engineering.

Polydopamine Enhanced Interactions of Graphene Nanosheets to Fabricate Graphene/Polydopamine Aerogels with Effectively Clear Organic Pollutants.

Graphene/polydopamine aerogels (GPDXAG, where X represents the weight ratio of DA·HCl to GO) were prepared by the chemical reduction of graphene oxide (GO) using dopamine (DA) and l-ascorbic acid as reducing agents. During the gelation process, DA was polymerized to form polydopamine (PDA). The introduction of PDA in the gelation of aerogels led to a deeper reduction of GO and stronger interactions between graphene nanosheets forced by covalent cross-linking and noncovalent bonding including π-π stacking and hydrogen bonding. The weight ratio of DA·HCl to GO influencing the formation and morphology of GPDXAG was explored. With the increasing content of DA in gelation, the reduction of GO and the cross-linking degree of graphene nanosheets were enhanced, and the resulting GPDXAG had a more regular pore distribution. Additionally, introducing PDA into GPDXAG improved its hydrophobicity because of the adhesion of PDA to a network of aerogels. GPDXAG exhibited a higher removal efficiency for organic pollutants than the controlled graphene aerogels (GAG). Specifically, the adsorption capacity of GPDXAG for organic solvents was superior to that of GAG, and organic solvent was completely separated from the oil/water mixture by GPDXAG. The equilibrium adsorption capacity of GPDXAG for malachite green (MG) was measured to be 768.50 mg/g, which was higher than that for methyl orange (MO). In MG/MO mixed solutions, aerogels had obvious adsorption selectivity for the cationic dye. The adsorption mechanism of aerogels for MG was also discussed by simulating adsorption kinetic models and adsorption isothermal models.

An overview on the key advantages and limitations of batch and dynamic modes of biosorption of metal ions

Water purification using adsorption is a crucial process for maintaining human life and preserving the environment. Batch and dynamic adsorption modes are two types of water purification processes that are commonly used in various countries due to their simplicity and feasibility on an industrial scale. However, it is important to understand the advantages and limitations of these two adsorption modes in industrial applications. Also, the possibility of using batch mode in industrial scale was scrutinized, along with the necessity of using dynamic mode in such applications. In addition, the reasons for the necessity of performing batch adsorption studies before starting the treatment on an industrial scale were mentioned and discussed. In fact, this review article attempts to throw light on these subjects by comparing the biosorption efficiency of some metals on utilized biosorbents, using both batch and fixed-bed (column) adsorption modes. The comparison is based on the effectiveness of the two processes and the mechanisms involved in the treatment. Parameters such as biosorption capacity, percentage removal, and isotherm models for both batch and column (fixed bed) studies are compared. The article also explains thermodynamic and kinetic models for batch adsorption and discusses breakthrough evaluations in adsorptive column systems. The review highlights the benefits of using convenient batch-wise biosorption in lab-scale studies and the key advantages of column biosorption in industrial applications.

MnFe2O4-NH2-HKUST-1, MOF magnetic composite, as a novel sorbent for efficient dye removal: fabrication, characterization and isotherm studies

Dye in industrial wastewater is one of the most serious environmental concerns due to its potentially harmful effects on human health. Many industrial dyes are carcinogenic, toxic and teratogenic. Removal and recovery of hazardous dyes from the effluents requires efficient adsorbents. In this study, magnetic adsorbent MnFe2O4-NH2-HKUST-1 was synthesized to remove methylene blue and crystal violet dyes from aqueous solutions. The synthesized adsorbent was characterized using FTIR, XRD, BET, VSM, SEM, TGA and Zeta potential techniques. The effect of different parameters such as pH, contact time, and adsorbent dosage on the removal of dyes was investigated. The dye adsorption process was investigated by UV–Vis spectrophotometry. The maximum adsorbent capacity was obtained as 149.25 mg/g for methylene blue and 135.13 mg/g for crystal violet. The adsorption equilibrium isotherm and kinetic models were plotted and results showed that the adsorption process for both dyes is a collection of physical and chemical adsorption based on langmuir and freundlich isotherm models, and follows the pseudo-second-order adsorption kinetics. This study shows that magnetic adsorbent MnFe2O4-NH2-HKUST-1 has a good potential for removal of methylene blue and crystal violet dyes from water in a short time (5 min) and it is easily separated from the solution by a magnetic field due to its magnetic property.