Competitive Adsorption Mechanism Research Articles

Atomistic Insights into the Ionic Response and Mechanism of Antifouling Zwitterionic Polymer Brushes.

Zwitterionic polymer brushes are not a practical choice since their ionic response mechanisms are unclear, despite their great potential for surface antifouling modification. Therefore, atomic force microscopy and molecular dynamics simulations investigated the ionic response of the surface electrical properties, hydration properties, and protein adhesion of three types of zwitterionic brushes. The surface of PMPC (poly(2-methacryloyloxyethyl phosphorylcholine)) and PSBMA (poly(sulfobetaine methacrylate)) zwitterionic polymer brushes in salt solution exhibits a significant accumulation of cations, which results in a positive shift in the surface potential. In contrast, the surface of PSBMA polymer brushes demonstrates no notable change in potential. Furthermore, divalent Ca2+ enhances protein adhesion to polymer brushes by Ca2+ bridges. Conversely, monovalent Na+ diminishes the number of salt bridges between PSBMA and PCBMA (poly(carboxybetaine methacrylate)) zwitterionic polymer brushes and proteins via a competitive adsorption mechanism, thereby reducing protein adhesion. A summary of polymer brush material selection and design concepts in a salt solution environment is provided based on the salt response law of protein adhesion resistance of various zwitterionic materials. This work closes a research gap on the response mechanism of zwitterionic polymer brushes' antifouling performance in a salt solution environment, significantly advancing the practical use of these brushes.

Adsorption of Pb(II) and Cd(II) on Modified Coal Gasification Slag: Competitive Adsorption, Leaching Toxicity, and Adsorption Mechanism

AbstractTo remove heavy metals from wastewater, coal gasification slag (CGS) was prepared as an adsorbent. Five modified materials were created, including HF‐CGSC, KOH‐HCl‐CGS, and three KOH‐CGS variants with different mass ratios. The adsorption tests showed KOH‐CGS (0.25) had the best efficiency for Pb(II) and Cd(II) via spontaneous chemisorption. Kinetic, thermodynamic, and 13C NMR analyses indicated that adsorption involved pore adsorption, functional group coordination, and π‐π interactions. Competitive adsorption results showed minimal interaction between Pb and Cd. Leaching tests confirmed the process's environmental safety. This study suggests new approaches for using coal gasification slag in wastewater treatment.

Adsorption sites and interactions of pigments in molasses-based distillery effluent on starch-based composites: Ternary competitive adsorption and theoretical calculations

The pigment present in molasses-based distillery effluent constitutes a primary factor influencing its degradation. Adsorption is an effective approach to eliminate pigment from wastewater. In this study, a cationic cassava starch (CCS) magnetic composite (CCS@Fe3O4) was prepared and used as adsorbents for the removal of undesirable pigments. The adsorption behaviors of caffeic acid (CA), gallic acid (GA), and melanoidin (ME) on CCS@Fe3O4 in the wastewater were investigated using single and ternary competitive adsorption systems. The equilibrium adsorption capacities of CA, GA, and ME on CCS@Fe3O4 were 197.04, 195.55, and 623.97 mg/g at the optimized conditions (0.3 mg/mL CCS@Fe3O4 dosage, temperature of 38 °C, and pH of 7). The adsorption kinetic model showed that chemisorption accounted for most of the adsorption of CA, GA, and ME on CCS@Fe3O4. The adsorption mechanisms of pigments on CCS@Fe3O4 were explored at the molecular level through quantum chemical calculations. The electrostatic potentials (ESP), average local ionisation energy (ALIE), and Fukui indices calculation indicated that the quaternary ammonium group in CCS@Fe3O4 was more susceptible to electrophilic reactions. The CC and benzene rings in CA and GA, and the COO- in ME, represent sites of attack for quaternary ammonium during adsorption. Furthermore, the competitive adsorption results, adsorption energy, and electron transfer data demonstrated that the adsorption capacity of CCS@Fe3O4 for pigments followed the order ME>GA>CA. Overall, the competitive adsorption mechanisms of CA, GA, and ME on CCS@Fe3O4 were unveiled, with quantum chemical calculations offering crucial insights into the adsorption process.

Competitive adsorption behavior and adsorption mechanism of limestone and activated carbon in polymetallic acid mine water treatment

Acid mine water (AMD) can cause significant environmental hazards due to its high concentration of metal ions, so the development of effective treatment methods is essential to mitigate its impact. In this study, adsorption experiments were conducted using limestone (LS) and activated carbon (AC) to explore the adsorption efficiency for different concentrations of metal ions. Adsorption was evaluated by static and competitive batch tests. The adsorbent mechanism was investigated using analytical techniques such as SEM, FTIR and XRD. The efficacy of LS and AC for competitive adsorption of Fe, Mn, Zn and Cu ions from AMD was evaluated. The study analyzed the effect of environmental conditions such as initial concentration and ionic strength on the adsorption efficiency. The results showed that LS showed high adsorption capacity for Fe and Cu, but was less effective in competitive adsorption of Mn. AC showed superior adsorption performance for Fe and Cu under competitive conditions due to its high surface area and functional groups. Both adsorbents showed selective efficacy influenced by the physicochemical properties of metal ions. This study helps to guide the optimization of adsorbents in AMD treatment and highlights the importance of selecting suitable materials based on specific metal ion properties.

Competitive adsorption of oxytetracycline and sulfamethoxazole by nanosized activated carbon in aquatic environments: Experimental analysis and DFT calculations

Nanosized activated carbon (NAC) is an emerging carbonaceous nanomaterial for water treatment, while oxytetracycline (OTC) and sulfamethoxazole (SMX) coexisting in aquatic environments may undergo competitive adsorption to influence its removal efficiency. This study investigated the competitive adsorption of OTC and SMX onto NAC under different interaction sequence, pH, electrolyte, and water matrix conditions, using experimental analysis and density function theory (DFT) calculations. Adsorption kinetics show that increasing concentration of one antibiotic inhibited the adsorption of another. Faster equilibrium was attained in binary systems than single systems due to competitive adsorption, with pseudo-second-order model providing the best fit in both systems. Adsorption isotherms suggest that NAC exhibited stronger affinity towards OTC (395.26 mg/g) than SMX (232.02 mg/g), with Langmuir model showing satisfactory fitting in both single and binary systems. Sequential adsorption of [NAC + OTC] + SMX was more favored than binary adsorption, aligning with the optimum configuration of SMX--[NAC-OTC±] with binding energy of −57.25 kcal/mol from DFT calculations. Competitive adsorption was preferred within pH 3.2–5.6, where electrostatic attraction existed between NAC and cationic antibiotics. Salting-out, charge screening, and complexation effects from Na+ and Ca2+ influenced competitive adsorption. Optimal removal of OTC and SMX by NAC was achieved in wastewater effluent among four water matrices in both single and binary systems. Hydrogen bonding, π − π electron donor–acceptor interactions, electrostatic interactions, and hydrophobic interactions contributed to adsorption. Sequential change in functional groups of NAC followed − OH → C − H → C − O → C = C and C = C → C − O → C − H → − OH in single and binary systems, respectively. The findings provide valuable insights into the competitive adsorption mechanisms of antibiotics on NAC, highlighting its potential for remediating mixtures of antibiotics in complex aquatic environments.

Study on the mechanism of competitive adsorption on the surface of potassium carbonate during direct air capture process

Direct air capture carbon dioxide (DAC) technology has the potential to achieve negative carbon emissions. Alkali metal-based absorbents (the active ingredient is mainly potassium carbonate or sodium carbonate) have a broad application prospect in DAC field. There is a paucity of reports on the competitive adsorption of major components of air on adsorbent surfaces. In this paper, the competitive adsorption behaviors of CO2, H2O, N2, and O2 on the surface of K2CO3 were investigated based on first principles and density functional theory (DFT), the synergic competition mechanism of each gas during adsorption was revealed by analyzing the parameters of adsorption energy, charge transfer, weak interactions and so on. The results showed that the maximum adsorption energy of CO2 by K2CO3 was 0.557 eV, and the relationship between the maximum adsorption energies of the four gases was O2 > H2O > CO2 > N2. The interaction between H2O and CO2 during co-adsorption inhibited their adsorption on the K2CO3 surface, especially weakening the adsorption effect of the surface O atoms on the H2O. Under CO2_N2_O2 gas composition, CO2 chemisorption occurred due to the strong oxidizing property of O2, the charge transfer effect commonly existed in the adsorption process of each gas, which contributed the most to O2 adsorption. The obtained results can further deepen the decarbonization mechanism of alkali metal-based adsorbents.

Understanding the Adsorption Kinetics of Acetone in Humid Activated Carbons: Perspectives from Adsorption-Breakthrough Experiments and Molecular Simulations.

The presence of water vapor influences the adsorption equilibrium and kinetics of volatile organic compounds (VOCs) in porous materials. By combination of breakthrough experiments and molecular simulations, the competitive adsorption mechanisms of water vapor and acetone on activated carbon with different textures and surface chemical properties at different humidity levels were investigated. Adsorption capacity decreases with increasing relative humidity owing to the formation of preferential adsorption sites between water and the activated carbon surface, while the adsorption rate initially increases and then decreases with increasing relative humidity. Experimental and simulation results revealed that the existence of a small amount of water changed the pore size distributions of activated carbon, thereby promoting the diffusion of acetone molecules. As the relative humidity increased, a portion of the acetone dissolved in water, resulting in a reduction in the adsorption rate. The response of different functional groups to relative humidity was further clarified by molecular simulation. Activated carbons with a high electrostatic interaction with acetone were less affected by humidity and thus exhibit greater potential as adsorbents.

Efficient adsorptive removal of methyl green using Fe3O4/sawdust/MWCNT: Explaining sigmoidal behavior

The 4R concept (reduce, reuse, recycle and repurpose) in water management necessitates innovative adsorption techniques that utilize sustainable and natural materials. This study investigates the use of natural sawdust embedded in magnetic iron oxide to treat wastewater. The performance of the newly synthesized Fe3O4/sawdust adsorbent was also compared to the native Fe3O4 and Fe3O4/MWCNT. Methyl Green (MG) was used as a model pollutant due to its wide use and potential toxicity. The new adsorbents demonstrated a high removal efficiency that exceeds 97 % under ambient conditions. The study investigates the effect of pH on adsorption, revealing a significant shift in removal efficiency as pH increases, with an optimal pH of around 7. The pH dependence is explained based on the point-of-zero-charge of the Fe3O4 adsorbent and the structure of the dye. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) of adsorption were determined through a temperature study. The adsorption equilibrium was found to be endothermic, therefore preferring elevated temperatures. Because the adsorption data of the study exhibited S-shaped-like curves, sigmoidal models were used to describe the adsorption isotherms. This provided new insights into the competitive adsorption mechanisms acting on the heterogeneous Fe3O4/sawdust surfaces. The kinetics study indicates rapid and efficient adsorption with pseudo-second-order reaction. The half-life of the reaction was as low as 4.8 min. The findings suggest a rapid, highly efficient and sustainable method to remove organic pollutants from wastewater.

Competitive Adsorption of Moisture and SO2 for Carbon Dioxide Capture by Zeolites FAU 13X and LTA 5A

Zeolites exhibit significant potential as porous materials for selective carbon dioxide (CO2) capture, leveraging their distinctive adsorption properties. However, the presence of moisture (H2O) and sulfur dioxide (SO2) in flue gas streams can significantly affect the efficiency of CO2 capture. This study investigates the CO2 adsorption characteristics of zeolites FAU 5A and LTA 13X, revealing the competitive adsorption mechanism between H2O(g), SO2, and CO2. The zeolites exhibit CO2 adsorption capacities of 93.19 mg/g and 95.80 mg/g for 5A and 13X, respectively, and demonstrate good regeneration potential. Metal cations correlated positively with CO2 adsorption. H2O(g), SO2, and CO2 exhibit a competitive adsorption relationship, with H2O(g) having the highest adsorption capacity, followed by SO2 and CO2. Additionally, the synergistic effect of SO2 and H2O(g) on CO2 adsorption is elucidated. These findings provide valuable insights into the competitive adsorption behavior of moisture and SO2 for CO2 capture using zeolites LTA 5A and FAU 13X, contributing to the development of more efficient CO2 capture processes and the design of tailored adsorbents for industrial applications.

Dynamics of oil–CO2–water three-phase under the nanopore confinement effect: Implications for CO2 enhanced shale oil recovery and carbon storage

The widespread nanopores, diverse minerals, and varying water saturation in shale reservoirs complicate the mechanism analysis and performance prediction of CO2 enhanced oil recovery (CO2-EOR) and CO2 storage (CS) in hydrated nanopores. Therefore, molecular dynamics methods were used to simulate the process of CO2 replacing shale oil in hydrated nanopores of inorganic, organic and composite minerals. Importantly, the effects of mineral type, temperature, pressure and water content on CO2-EOR and CS performances in hydrated nanopores were analyzed, and the CO2-EOR mechanisms of dissolution, extraction, viscosity reduction, miscibility and competitive adsorption were revealed. The results show that water in illite, kerogen, and composite nanopores are distributed in the forms of water films, water clusters (films), and water columns, respectively. The replacement efficiency of shale oil in three types of nanopores is improved with increased water content but reduced in kerogen nanopores under high water content. Water is not conducive to the diffusion and viscosity reduction of oil in nanopores, but the miscibility and competitive adsorption of CO2 and oil are improved. The replacement efficiency is positively correlated with temperature and pressure. The increasing temperature promotes diffusion and viscosity reduction of oil and competitive adsorption between CO2 and oil in hydrated nanopores, and increasing pressure promotes miscibility and competitive adsorption. Water columns in kerogen and composite nanopores reduce the CS performance, while thin water films in illite nanopores improve it. Moreover, an excellent CS rate can be achieved at high temperatures and pressures, but the high temperature is not conducive to CS stability. This study provides a theoretical basis for CO2 injection to improve oil production and carbon storage performance in hydrated shale reservoirs and contributes to the optimization of CO2 injection schemes.

Efficient removal of phosphate and fluoride from phosphogypsum leachate by lanthanum-modified zeolite: Synchronous adsorption behavior and mechanism

Phosphogypsum is a common large-tonnage by–product in phosphorous chemicals industry, its stacking not only causes severe environmental problems, but also leads to a serious waste of phosphate and fluoride resources. The objective of this study was to tackle the recycling treatment of phosphogypsum leachate by using a highly efficient adsorbent lanthanum hydroxide-modified zeolite (LMZ). The adsorption behaviors of phosphate and fluoride by LMZ in the coexisting system under static and dynamic conditions were studied. And further, the competitive adsorption mechanism involved was analyzed. The results showed that LMZ possessed excellent adsorption performance toward both phosphate and fluoride in the single system, but the fluoride adsorption capacity decreased by 57.9 % in the coexisting system, with no change in phosphate adsorption. In the competitive adsorption process, ligand exchange interaction on La active sites contributed most to phosphate adsorption, while fluoride could be adsorbed onto LMZ via electrostatic attraction, surface precipitation with Al sites, and hydrogen bonds with hydroxyl groups in La−OH and P−OH. In actual phosphogypsum leachate, the removal of phosphate had priority over the removal of fluorine. Under continuous adsorption condition, the concentration of phosphorus and fluoride could be decreased to below 0.5 and 1.0 mg/L, respectively, meeting the safe concentration in drinking water. This study promotes the application of La–based adsorbents in the treatment of phosphogypsum leachate, and provides a green and sustainable strategy toward practical phosphorus and fluorine recovery.

Fabrication of fluorinated triazine-based covalent organic frameworks for selective extraction of fluoroquinolone in milk

A novel fluorinated triazine-based covalent organic frameworks (F-CTFs) was designed and synthesized by using melamine and 2,3,5,6-tetrafluoroterephthalaldehydeas as organic ligands for selective pipette tip solid-phase extraction (PT-SPE) of amphiphilic fluoroquinolones (FQs). The competitive adsorption experiment and mechanism study were carried out and verified that this F-CTFs possesses favorable adsorption affinity for FQs. The abundant fluorine affinity sites endowed the F-CTFs high selectivity to FQs extraction through F-F interactions. The adsorption capacity of F-CTFs can reach up to 109.1 mg g−1 for enrofloxacin. The detailed characterization of the F-CTFs adsorbent involved the application of various techniques to examine its morphology and structure. Under optimized conditions, a method combining F-CTF-based PT-SPE with high-performance liquid chromatography (PT-SPE-HPLC) was established, which exhibited a broad linear range, excellent precision, and an impressively low limit of detection, and could be used for the determination of six FQs in milk, with LODs as low as 0.0010 μg mL−1. The recovery rates during extraction varied between 92.1% and 111.4%, exhibiting RSDs below 6.8% at different spiked concentrations.

Competitive adsorption mechanism of SiHCl3 with BCl3 under a hydrogen atmosphere: Boron impurities introduction into polysilicon

The primary method for electronic-grade (EG) polysilicon production is the modified Siemens process. Unfortunately, the EG polysilicon produced through this method contains excessive levels of boron impurities (> 0.2 ppb), thereby diminishing the product quality. This issue impedes the large-scale production of EG polysilicon. This study establishes the structure of the Si (100) surface within a hydrogen-rich environment under the BCl3-SiHCl3-H2 system and investigates the adsorption mechanisms of BCl3 and SiHCl3, as well as the competitive adsorption mechanism of BCl3-SiHCl3, on the Si (100) surface. The results indicate that the adsorption energy barriers for BCl3 and SiHCl3 on the Si (100) surface are 7.8383 kJ·mol−1 and 229.6970 kJ·mol−1, respectively, so that the preferential adsorption of BCl3 onto the Si (100) surface over SiHCl3. The B atom and the Si atom are competing for adsorption on the Si (100) surface and creating an ab-B-Si-ab structure, and the optimal adsorption path is as follows: ab-BCl3→ab-BCl2→ab-BCl2-SiHCl3→ab-BCl-SiHCl3→ab-B-SiHCl3→ab-B-SiHCl2→ab-B-SiHCl→ab-B-SiH-ab→ab-B-Si-ab.

Coverage-dependent adsorption of n-hexane and isopropanol on silica: A density-functional study

This study delves into the adsorption behavior of both polar and non-polar molecules on silica surfaces, spanning a range from low coverage to full adsorption scenarios. Our results reveal that isopropanol exhibits a self-competitive adsorption mechanism on the surface. However, due to its thermodynamic stability, we anticipate fully covered pores under experimental conditions. In contrast, n-hexane demonstrates a substantial interaction with the hydrophilic substrate, displaying an enhanced adsorption effect whereby the adsorption gets stronger with an increasing number of molecules adhering to the pore’s surface. As a consequence, we predict a complete coverage of the pores under experimental conditions, accompanied by a discernible reduction in the mobility of these attached molecules. This observation carries significance, as alkanes are typically employed as probing molecules for measuring the geometric tortuosity of silica pores, assuming a reflective surface. Caution is advised, particularly for pores with thin diameters, in the order of a few molecular sizes.

Competitive adsorption mechanisms of multicomponent gases in kaolinite under electric fields: A molecular perspective

The investigation of the competitive adsorption mechanisms of gas mixtures within the inorganic nanopores of shale influenced by an electric field holds paramount importance for improving shale gas recovery and enhancing CO2 storage efficiency. This study employs molecular dynamics (MD) simulations to investigate the competitive adsorption mechanisms of gas mixtures on kaolinite surfaces. Subsequently, the engineering parameters governing electric field-enhanced CO2 sequestration and enhanced gas recovery (CS-EGR) are explored and optimized. In the absence of an electric field, the analysis reveals that water molecules exhibit the highest adsorption capacity in a ternary H2O–CO2–CH4 mixture, resulting in the formation of a water film of a specific thickness. CO2 displays a superior adsorption capability over CH4. As the CO2 volume injected into the reservoir increases, CH4 undergoes desorption due to the dominant adsorption effect of CO2. However, the efficiency of CO2 displacing CH4 diminishes significantly. The introduction of an electric field alters the equilibrium state of the gas mixture, leading to a further increase in CO2 adsorption and enhancing its selectivity relative to that of CH4 by 33%. These findings lay the foundation for the practical implementation of electric field-enhanced CS-EGR in shale reservoirs.

Ammonium ion removal from aqueous solutions in the presence of organic compounds, using biochar from banana leaves. Competitive isotherm models

BackgroundIndustrial, e.g. food industrial and domestic wastewaters contain huge amount of compounds causing eutrophication, and should be removed with high cost during wastewater treatment. However, these compounds could be utilized as fertilizers too. Biochar can remove a wide range of pollutants from water, such as ammonium, which can be found in relatively high concentration in dairy wastewaters. However, adsorption performance may be affected by the presence of other wastewater pollutants. Thus, this study aims to determine the efficiency of biochar as an adsorbent of ammonium in aqueous solutions in the presence of some selected organic compounds of typical dairy wastewaters such as bovine serum albumin (BSA), lactose, and acetic acid. Methods: The biochar was produced from banana leaves at 300 °C, modified with NaOH, and characterized by Scanning Electron Microscope – Energy Dispersive X-Ray Spectroscopy (SEM-EDX), Fourier-transform infrared spectra (FTIR) analysis, and specific surface area measurements. Batch experiments were carried out to investigate the ammonium adsorption capacity and the ion competitive adsorption mechanism. Significant Findings: Results show that the surface structure of the biochar derived from banana leaves is different from other biochars previously studied; although the specific surface area is not very considerable and despite having nitrogen within the elemental composition, the biochar studied is capable of adsorbing 2.60 mg NH4+/m2, the highest ammonium removal in 2 h occurs at pH 9 and 500 mg biochar dose. Langmuir model in the monolayer phase analysis fits better for all scenarios and the maximum NH4+ adsorption capacity was 0.97 mg/g without organic compounds. In the multilayer adsorption phase, the isotherm model that best fits the data obtained is the Harkins-Jura model without organic compounds. The presence of organic compounds in the aqueous solution significantly impacts the adsorption of ammonium by biochar since it improves the adsorption capacity (1.132 mg/g BSA, 0.975 mg/g lactose, and 1.874 mg/g acetic acid). The Aranovich-Donohue isotherm model fitted the data obtained during ion competitive adsorption experiments well.

Molecular simulation of competitive adsorption of CO2/N2/O2 gas in bituminous coal

The main cause of coal spontaneous combustion is the oxidation and temperature rise of coal. Injecting composite inert gas for fire prevention and extinguishing is one of the important methods to prevent coal spontaneous combustion. A large number of studies have macroscopically investigated the fire prevention and extinguishing effects of CO2/N2 and their synergistic actions. However, there is currently a lack of research at the molecular level on the competitive adsorption mechanism between mixed inert gases (CO2, N2) and O2 molecules in coal. Therefore, this study conducted adsorption experiments using Qian Yingzi(QYZ) bituminous coal and compared them with the simulation data of the Wiser coal model to verify the reliability of the Wiser model. Subsequently, employing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods, the competitive adsorption behavior of different proportions of binary mixed component gases (CO2/O2, CO2/N2, O2/N2) at a temperature of 303.15 K was investigated from five perspectives: adsorption capacity, adsorption selectivity coefficient, potential energy distribution, competitive adsorption heat, and interaction energy. The results indicate that among the competitive component gases, CO2 exhibits the strongest adsorption effect on the entire system, which is closely correlated with the distribution range of adsorption energy sites. The adsorption heat and adsorption amount of CO2 consistently exhibit a negative correlation, whereas the relationship between the adsorption heat of N2 and O2 and the adsorption amount shows a positive correlation. Their adsorption capacities depend on the pressure and the proportion of the two gases. Based on the isothermal adsorption curve of CO2/N2, it is recommended that the gas pressure during actual inert gas injection be less than 2.5 MPa. Under this pressure, the competitive adsorption effect is no longer significant, providing a certain theoretical basis for high-pressure injection. Moreover, the preliminary determination of the optimal injection ratio range is from 4:6–3:7. Furthermore, a systematic logical framework for selecting underground inert gas composition is proposed, and an underground mobile inert gas infusion process is adopted. The actual gas composition for infusion is determined based on cost factors in practical engineering. The research results can provide guidance for the selection of gas injection parameters for mixed inert gas fire prevention and extinguishing in goaf.

Competitive adsorption of copper and zinc ions by Tetradesmus obliquus under autotrophic and mixotrophic cultivation

The competitive adsorption mechanism of Tetradesmus obliquus on copper and zinc ions was explored under varied cultivation conditions. Removal efficiency of Tetradesmus obliquus for these ions was evaluated during autotrophic and mixotrophic cultivation. The results revealed that Tetradesmus obliquus demonstrated achieved removal efficiencies of 74.30 %, 86.48 %, 84.55 %, and 65.33 % for 16 mg/L of Zn2+, Cu2+, and a mixture of Cu2+ and Zn2+, respectively, under autotrophic conditions. Conversely, under mixotrophic conditions, Tetradesmus obliquus demonstrated improved removal efficiencies of 86.90 %, 92.31 %, 92.30 %, and 71.94 % for Zn2+, Cu2+, and a Cu-Zn mixture, along with adsorption capacities of 38.57 mg/g, 43.86 mg/g, 23.15 mg/g, and 15.24 mg/g, respectively. This represents an increase of 46.65 %, 31.16 %, 29.47 %, and 43.50 % compared to the autotrophic group, respectively. The second-order kinetic equation and Langmuir isotherm model, as proposed, successfully fitted the experimental data for kinetics and isotherms of Zn2+ and Cu2+ in the monometallic system. The maximum adsorption capacities were determined to be 43.22 mg/g and 69.41 mg/g, respectively, under mixotrophic cultivation conditions. The Extended Langmuir isotherm model best fit all experimental data in the mixed system. The presence of Cu2+ markedly reduced Zn2+ adsorption, whereas the presence of Zn2+ had no effect on Cu2+ adsorption. The 3D fluorescence results further confirmed that glucose addition stimulates algal cells to produce additional extracellular polymers, consequently enhancing metal adsorption by microalgae. These research findings confirm that culturing Tetradesmus obliquus in a mixed environment enhances heavy metal removal during water treatment, which is of significant importance for environmental remediation and sustainable water purification.

Respective evolution of soil and biochar on competitive adsorption mechanisms for Cd(II), Ni(II), and Cu(II) after 2-year natural ageing

To reveal the respective evolution of soil and biochar on competitive heavy metal adsorption mechanisms after natural ageing, three soils and two biochars were tested in this study. The soil-biochar interlayer samples were buried in the field for 0.5, 1, and 2 years, for which competitive adsorption characteristics and mechanisms of soils and biochars in four systems (Cd, Cd+Ni, Cd+Cu, and Cd+Ni+Cu) were investigated. Results showed that physicochemical properties, adsorption capacity and mechanisms of soils and biochars all changed the most in the first 0.5 years. The properties and adsorption capacity of biochars gradually weakened with the ageing time, meanwhile, those of soils gradually enhanced. After co-ageing with acidic soil for 0.5 years, the Cd(II) adsorption capacity of modified biochar decreased by 86.59% in the ternary system; meanwhile, that of acidic soil increased by 65.52%. The contributions of mineral mechanisms decreased significantly, while non-mineral mechanisms were slightly affected by ageing. This study highlighted that when using biochar to remediate heavy metal-contaminated soils, biochar should be applied at least half a year in advance before planting crops so that biochar can fully contact and react with the soil.

Insight into the competitive adsorption mechanism of ethylbenzene and octane on zeolite NaY with different SAR

The Si/Al molar ratio (SAR) of zeolites is crucial for separating unsaturated hydrocarbon components, but it was difficult to rule out the impact of changes in pore properties. In this work, a GCMC method was developed to investigate the effect of varying SAR (2.4, 20, and 50) using a module of NaY zeolite. The deviation of pore properties is less than 5%. When using ethylbenzene and n-octane as probe molecules, increasing the SAR is not conducive to improving the selectivity of ethylbenzene in single component adsorption, but in the two components, the selectivity increases from 76.0% to 92.6% when SAR increasing from 2.4 to 50. The increase of diffusion coefficient in two component is also significantly different. The NH3 radial distribution functions (RDF) method was used to investigate the number of acid sites and acid strength, it can be observed that the adsorption capacity of ammonia decreases with SAR increasing but slightly when the SAR exceed 50. However, the number of ammonia molecules adsorbed per site significantly increases, the II site exhibits stronger acidity than III site. To distinguish different preferences of adsorbate onto zeolites with different SAR, concentration distribution combined with RDF was used. During single-component adsorption, both ethylbenzene and n-octane could be freely adsorbed on the II and III sites, however in binary situation, ethylbenzene tended on the II sites, while n-octane on the III sites. As the SAR increased, the adsorption of ethylbenzene, which displaced the original adsorption sites occupied by n-octane and consequently improved the selectivity of ethylbenzene. To investigate the interaction between adsorbents with different polarities, different feed concentration and RDF between the adsorbates were used, which revealed that polarities may have a greater impact on selectivity. Through the Monte Carlo series of tools, the structure-performance relationship between complex adsorbates and adsorbed molecules can be studied clearly.