Competitive Adsorption Behavior Research Articles

Competitive adsorption and selectivity of water vapor/R134a on activated carbon for indoor air purification

As an efficient tracer gas of activated carbon filter quality testing, the use of R134a is limited by relative humidity (RH) due to water vapor competitive adsorption. To analyze the competitive effect, the isosteric heats between vapor and ASZMT were calculated by C–C equation, the adsorption selectivity was predicted using the DIH method, and the binary adsorption equilibrium of water vapor and R134a on ASZMT were investigated via IAST model. Results showed that water vapor exhibited a higher isosteric heat than R134a at the same adsorption capacity, indicating a stronger interaction with ASZMT. The water vapor/R134a adsorption selectivity on ASZMT increases from 0 to 6.6, proving that the ASZMT is more selective for water vapor than R134a with water vapor pressure increasing. Besides, with water vapor pressure ratio improving, the R134a adsorption capacity on ASZMT decreases obviously, but water vapor adsorption capacity keeps increasing continuously. R134a breakthrough curves (1000 ppm) also showed that with relative humidity increasing, the R134a breakthrough times and dynamic adsorption capacities both became shorter, from 15 min to 9 min and from 6.68 mg/g to 1.49 mg/g, respectively. It proves that R134a and water vapor have obvious competitive adsorption behavior which is mainly dominated by water vapor concentration. It is necessary for ppm-level R134a to control the lower relative humidity of airflow in application.

Anaerobic environment-induced efficient degradation of chloroquine phosphate: Insights into the role of metal-free C3N4 nanotube in visible light-driven peroxymonosulfate activation

Catalytic efficiency is the main bottleneck in metal-free photocatalyst-mediated visible light-driven peroxymonosulfate (PMS) activation processes (PMS-Vis). In this study, a nanotubular carbon nitride (C3N4 NT) photocatalyst was prepared and applied to a PMS-Vis system to degrade chloroquine phosphate (CQP). The special structure and excellent photoelectrochemical properties of C3N4 NT optimized its active site exposure and charge transport performance, which in turn enabled its use as a photocatalyst for PMS activation and CQP degradation. Importantly, the anaerobic environment enhanced the degradation performance, and the degradation kinetic constant for the C3N4 NT/PMS-Vis-N2 system reached 0.0898 min−1 at a 0.2 g·L−1 catalyst dosage and 0.8 mM PMS concentration. Mechanistic studies and theoretical calculations clarified that the anaerobic environment prevented the competitive adsorption and consumption behavior of dissolved O2 and PMS on the photocatalyst surface, thus maximizing the transfer of surface photogenerated charges to PMS for PMS activation and active species generation. Thus, CQP was efficiently degraded, and its toxicity was reduced. The developed process demonstrated high catalyst utilization efficiency and overcame interference from real water matrices. This study provides a reference for improving the environmental applicability of metal-free photocatalysts and developing water treatment technologies for anaerobic environments.

Molecular simulation study on the effect of coal metamorphism on the competitive adsorption of CO2/CH4 in binary system

To explore the competitive adsorption characteristics of a CO2/CH4 binary gas in coal with different metamorphic degrees, macromolecular-structure coal models with different metamorphic degrees (anthracite coal, coking coal, and long-flame coal) were constructed based on elemental analysis, X-ray photoelectron spectroscopy (XPS), and carbon-13 nuclear magnetic resonance (13C NMR) results. Then, the competitive adsorption behaviors of CO2 and CH4 molecules in the different coal molecular models were simulated using molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) methods, and the changes of the competitive adsorption capacity, density distribution, adsorption selectivity, adsorption heat, and energy distribution were investigated. The results showed that the variation characteristics of the total adsorption of mixed gas were similar to those of pure gases, and the increase in the pressure led to an increase in the total adsorption, which also increased with the increase in the coal deterioration degree. The distribution ranges of the gas adsorption sites in coal with different metamorphic degrees were significantly different, with anthracite coal being the most widely distributed and long-flame coal being the least widely distributed. With the increase in the coal rank, the competitive adsorption selectivity of any proportion of CO2/CH4 binary mixed gas increased. The difference in the equivalent adsorption heat of single-component gases CO2 and CH4 in the mixed gas increased with the increase in the coal metamorphism and decreased with the increase in the CO2 gas proportion coefficient. This paper provides a theoretical basis for the application of CO2 enhanced coal bed methane in coal seams with different metamorphic degrees.

Competition between oxygen and water molecules on SiO2/P-doped Si surface: The electrical dipole evolution on water/oxygen-adsorbed oxide surface

The performance of gas sensors is greatly influenced under humidity environment due to the dynamic correlation between water and oxygen molecules. In this work, we utilize the charge trapping characteristic to study surface gas adsorption and demonstrate the competitive adsorption behaviors between oxygen and water vapor from the perspective of electrical dipole by observing the evolution of second harmonic generation (SHG). By analyzing the trapping time constant of time-dependent SHG spectrum, we propose a dynamic model of the way water molecules weaken oxygen adsorption and develop water adsorption layer. Results show that the electric field created by charge trapping would further align the water molecules and enhance the SHG intensity. Here, a viewpoint of analyzing the net surface dipole change due to the adsorption–desorption on SiO2 surface to realize the energy preferable state is presented and provides a pathway for solving the water–sensor interaction problems in gas sensor.

Effects of competitive adsorption on production capacity during CO2 displacement of CH4 in shale

During CO2 displacement of CH4 in shale, competitive adsorption results in reduced pore space used for gas flow in shale, which is closely associated with the production capacity of shale-gas reservoirs. Thus, the present work investigates the effects of CO2–CH4 competitive adsorption on production capacity. Herein, a slit–pore model is developed in terms of gas storage (CO2 and CH4) and graphene pores using molecular dynamics and implemented via large-scale atomic/molecular massively parallel simulator. The effects of CO2 injection pressure, temperature, and velocity and of pore size on CO2–CH4 displacement and competitive adsorption properties are simulated and examined. Hence, the displacement efficiency of CH4 and the adsorption layer thickness of the CO2–CH4 binary mixture are determined. Moreover, based on a basic seepage model of planar linear flooding, the effect of CO2–CH4 competitive adsorption on production capacity is analytically investigated. Results demonstrate that the production capacity with consideration of adsorption layer thickness is less than that without consideration of adsorption layer thickness, illustrating that CO2–CH4 competitive adsorption behaviors are closely connected with permeability, flow rate, and production capacity of shale-gas reservoirs, especially for shale-gas reservoirs containing large numbers of pores and slits.

Unraveling the Synergistic Reaction and the Deactivation Mechanism for the Catalytic Degradation of Double Components of Sulfur-Containing VOCs over ZSM-5-Based Materials.

The competitive adsorption behavior, the synergistic catalytic reaction, and deactivation mechanisms under double components of sulfur-containing volatile organic compounds (VOCs) are a bridge to solve their actual pollution problems. However, they are still unknown. Herein, simultaneous catalytic decomposition of methyl mercaptan (CH3SH) and ethyl mercaptan (C2H5SH) is investigated over lanthanum (La)-modified ZSM-5, and kinetic and thermodynamic results confirm a great difference in the adsorption property and catalytic transformation behavior. Meanwhile, the new synergistic reaction and deactivation mechanisms are revealed at the molecular level by combining with in situ diffuse reflectance infrared spectroscopy (in situ DRIFTS) and density functional theory (DFT) calculations. The CH3CH2* and SH* groups are presented in decomposing C2H5SH, while the new species of CH2*, active H* and S*, instead of CH3* and SH*, are proved as the key elementary groups in decomposing CH3SH. The competitive recombining of SH* in C2H5SH with highly active H* in dimethyl sulfide (CH3SCH3), an intermediate in decomposing CH3SH, would aggravate the deposition of carbon and sulfur. La/ZSM-5 exhibits potential environmental application due to the excellent stability of 200 h and water resistance. This work gives an understanding of the adsorption, catalysis, reaction, and deactivation mechanisms for decomposing double components of sulfur-containing VOCs.

The impact of humic acid on hydrogen adsorptive capacity of eagle ford shale: Implications for underground hydrogen storage

Hydrogen is a clean fuel that is anticipated to play a key role to phase-out fossil fuels and consequently decline the global warming challenges. Large-scale Underground Hydrogen Storage (UHS) is a critical link in hydrogen economy, but it is yet to be successfully achieved at industrial scale, and this is presently a main drawback in the hydrogen economy. Organic-rich shale pores have been suggested as promising geo-storage media for underground storage of hydrogen through the adsorption trapping mechanism. The hydrogen (H2) could be stored as an adsorbed phase on the kerogen surface or clay minerals, thus replacing methane (CH4) on adsorption sites during competitive adsorption. Moreover, methane has been suggested as a promising cushion gas for hydrogen. Experimental measurement of the H2 and CH4 adsorptive capacity of shale is essential for precise description of competitive adsorption behavior between CH4 and H2 in shale, as well as in designing of UHS in shale. Thus, adsorption capacities of methane and hydrogen were measured using a PCTpro adsorption analyzer in this study. Since organic acids are inherently present in geo-storage media, H2 and CH4 adsorption capacities in the fresh shale and shale aged with humic acid (Shale-HA) were compared to evaluate the impacts of adsorbed organic acids on their gas adsorption affinities. Our results showed that at 303 K, the adsorption of hydrogen increased by almost 170 % at 2.5 MPa and 350 % at 4.28 MPa in Shale-HA. The H2 adsorption trends on both shale samples are type IV isotherm adsorption curves that increased steeply with pressure but levelled beyond 3.5 MPa. The low-pressure N2 adsorption-desorption isotherms showed a type II adsorption isotherm. The CH4 adsorption capacity in raw shale was uniformly increased more than that of hydrogen, but there is no significant difference in CH4 adsorption capacity in shale-HA. This work provides fundamental data for hydrogen storage in shale reservoirs, thus facilitates full-scale implementation of hydrogen economy.

Competitive adsorption of water and collector molecules on sulfide mineral surfaces

To study the influence of water molecules on the adsorption behavior of flotation reagents at the solid-liquid interface system, a model of the molecule interaction between sulfide minerals and flotation reagents at the solid–liquid interface system was established based on the density functional theory (DFT). The results of the calculations show that the surfaces of the galena and pyrite are hydrophobic after the adsorption of the xanthate molecules. In addition, using molecular dynamics simulation can positively explain the competitive adsorption behavior occurring between water molecules and xanthate molecules. This study provides some theoretical basis and guidance for the study of the interaction mechanism between flotation reagents and the surface of sulfide minerals under the solid–liquid interface system.

Competitive adsorption of Cu2+, Pb2+, Cd2+, and Zn2+ onto water treatment residuals: implications for mobility in stormwater bioretention systems.

The lack of knowledge regarding competitive adsorption of heavy metal ions onto water treatment residuals has been hindering their reuse as a medium in stormwater bioretention systems. Competitive adsorption of copper(II), lead(II), cadmium(II), and zinc(II) onto polyaluminium chloride and anionic polyacrylamide water treatment residuals (PAC-APAM WTRs) was evaluated with different pH, temperature, initial concentration, and time. The competitive adsorption removal increased with the increase of pH and temperature. The analysis of the ratios of maximum adsorption capacity of a heavy metal ionic species in a multi-component system to that in a mono-component system (Qmix/Qmono) demonstrated that the coexisting ion had a negative effect on the adsorption of a metal ionic species. The Langmuir model provided a better fit, indicating that the adsorption could be a monolayer adsorption process. The modified Langmuir isotherm studies showed that the affinity order in the multi-component systems was Cu2+>Pb2+>Cd2+>Zn2+. The pseudo-second-order model better described the adsorption kinetics implying that the competitive adsorption behavior could be interpreted by diffusion-based mechanisms. This study contributed to a better understanding the mobility of those frequently occurring heavy metal ions in stormwater runoff in the PAC-APAM WTRs media layer of stormwater bioretention systems.

Highly selective adsorption of 5-hydroxymethylfurfural from multicomponent mixture by simple pH controlled in batch and fixed-bed column studies: Competitive isotherms, kinetic and breakthrough curves simulation

Fixed-bed column adsorption is one of the most promising technologies for the separation and purification of 5-hydroxymethylfurfural (5-HMF) from biomass hydrolysate from the point of view of industrial application. However, one of the most pressing issues to be resolved is how to improve the separation factor of 5-HMF and its by-product levulinic acid (LA) and formic acid (FA). In this study, we used poly (BDM-alt-DVB) resin (BD-11) as an adsorbent and a simple pH control in batch and fixed-bed column to explore the competitive adsorption behavior and mechanism of 5-HMF from multicomponent solution. Without adjustment for solution pH, the separation factors of α5-HMF/LA, α5-HMF/FA, α5-HMF/Glucose were 2.6, 11.3, and 22.2, respectively. Interestingly, the separation factors of α5-HMF/LA, α5-HMF/FA, α5-HMF/Glucose increased dramatically to 73.0, 72.2, and 49.2 by merely adjusting the solution pH to 7.02. Furthermore, when the pH was adjusted to 7.02, the equilibrium time of 5-HMF adsorption on the BD-11 resin was within 20 min, and the adsorption capacity reached 69.7 mg/g, which was 118 % of the equilibrium adsorption capacity of the unadjusted pH value. In addition, the proposed fixed-bed column multicomponent competitive adsorption model was shown to agree well with the experimental data and successfully simulated the adsorption behavior of 5-HMF under a variety of experimental conditions. In conclusion, the fixed-bed column had great potential in 5-HMF selective adsorption from an aqueous solution by simple pH control.

CO2-oil diffusion, adsorption and miscible flow in nanoporous media from pore-scale perspectives

Enhancing shale/tight oil and sequestering CO2 by CO2 huff-n-puff have gained extensive attentions in recent years. However, the fundamental understanding of CO2-oil diffusion, competitive adsorption and miscible flow behaviors are mainly limited to the single pore scale based on molecular dynamics (MD) simulations, and that in nanoporous media are still ambiguous. In this work, we propose a novel multiple relaxation time lattice Boltzmann method (MRT-LBM) to simulate CO2-oil diffusion, adsorption and miscible flow in pore-scale nanoporous media, which is successfully verified by the Fick’s second law and MD simulations. The proposed model can obtain various fluid-surface molecular interaction forces (adsorption capacities) of CO2/oil single phase and CO2-oil miscible phase, and quantify the attraction and repulsion from the pore surface to CO2 and oil. Then, the effects of CO2 and oil phase heterogeneous adsorption capacity on CO2 diffusion, storage and oil extraction are quantitatively analyzed. Additionally, based on the MD simulations, we also study the adsorption and flow behaviors of CO2-nC8 miscible adsorption and flow behaviors in calcite nanoporous media. The results show that CO2 can diffuse into the oil phase in porous media more readily from the regions that are relatively attractive to CO2 and repulsive to oil. In porous media with heterogeneous adsorption capacity, CO2 first contacts with the CO2-friendly surface which is attractive to CO2 during diffusion, beneficial to CO2 storage. With an increasing nC8 mass percentage (OMP), the proportion of adsorbed CO2 increases, and that of free CO2 decreases. That indicates that the CO2 diffusing into the oil phase is firstly adsorbed on the surface. When CO2 adsorption reaches saturation, the density of CO2 in the bulk phase begins to increase. We also observed a critical OMP equaling 81% below which CO2 can enhance nC8 flow while having a negligible enhanced impact on nC8 flow beyond 81%. Additionally, with an increasing porous media size, the proportion of adsorbed CO2 decreases, and the critical OMP increases.

Effect of oxidative aging of biochar on relative distribution of competitive adsorption mechanism of Cd2+ and Pb2+

In this study, aged biochar (CCB350 and CCB650) were obtained from pyrolysis of corn stalk biochar (CB350 and CB650) at the degree of 350 °C and 650 °C by artificial oxidation with hydrogen peroxide (H2O2). Also, the mechanism of Pb2+ and Cd2+ on fresh and aged biochars was analyzed qualitatively and quantitatively by batch adsorption experiments combined with characterization. The adsorption isotherm results showed that aging treatment decreased the adsorption capacity of Pb2+ and Cd2+ and inhibited the competitive adsorption behavior of heavy metals. In the single-metal system, precipitation and cation exchange were considered as the main adsorption mechanisms for CB350 and CB650, with a ratio of 40.07–48.23% and 38.04–57.19%, respectively. Competition between Pb2+ and Cd2+ increased the relative contribution of mineral precipitation, but decreased the contribution of cation exchange mechanism. Aging resulted in the rise of the contribution of surface complexation to the adsorption of Pb2+ and Cd2+ on biochars, especially in low-temperature biochars, but weakened the contribution of mineral precipitation to the adsorption. Further, the contribution of other adsorption mechanisms was significantly enhanced for high-temperature aged biochars. These results are important to evaluate its long-term application prospects in the natural environment.

Analysis of non competitive and competitive adsorption behaviour of ciprofloxacin hydrochloride and ofloxacin hydrochloride from aqueous solution using oryza sativa husk ash (single and binary adsorption of antibiotics)

Among various pharmaceutical pollutants, broad spectrum antibiotics of fluoroquinolones family, emerged as major water contaminants, usually occur in the form of multicomponent mixtures in the aquatic environment. Present study pertains to the adsorption of ciprofloxacin hydrochloride and ofloxacin hydrochloride as pure component and binary mixtures under dynamic and equilibrium conditions using oryza sativa husk ash as adsorbent and characterized using XRD, FTIR and SEM analyses. Single batch adsorption was carried out to study the dependence of drug concentration, time, pH and temperature and the process was found to be dependent on all the parameters investigated, with a pH of 8 for optimum removal of both drugs at which binary adsorption of [ciplox + oflox] and [oflox + ciplox] mixture was carried out for concentration ratios 1:0, 1:0.5, 1:1, 1:1.5, 1:2 to validate the effect of presence of each on the uptake of other. Applicability of Langmuir multicomponent adsorption isotherm revealed that the affinity of each drug was depressed by the presence of other; hence the effect of the mixtures seemed to be antagonistic. Also the present study highlights the oryza sativa husk ash as a viable, cost-effective and efficient bioadsorbent for the removal of antibiotics from multicomponent mixtures, specifically for small scale industries.

Effects of gas components, reservoir property and pore structure of shale gas reservoir on the competitive adsorption behavior of CO2 and CH4

CO2 injection into shale gas reservoirs is deemed as a potential scheme to enhance CH4 recovery and achieve the ambition of carbon neutral. The insufficient research of binary gas competitive adsorption behavior at in-situ conditions of shale gas reservoirs, and the coupling control of gas components, shale properties, and pore structure on CO2 adsorption affinity limit its general application. Therefore, the competitive adsorption behavior of CO2 and CH4 at in-situ conditions is simulated using high-pressure multi-component adsorption experiments, and the effects of binary gas components, shale properties and pore structure on CO2 adsorption affinity are discussed. Subsequently, the mathematical and geological models of CO2 injection into Longmaxi shale gas reservoir enhancing CH4 recovery and achieving carbon sequestration are established based on experimental parameters and reservoir geological parameters, and the feasibility and expectation benefits are discussed. The results exhibit that selectivity coefficient of CO2 relative to CH4 (Sc) decreases with higher CO2 mole fraction, whereas it increases with higher total organic carbon content (TOC) and clay content. Both pore volume (PV) and specific surface area (SSA) have clear positive correlations with Sc. Overall, TOC is a crucial controlling factor of pore structure and adsorption capacity of shale, further, affects the adsorption affinity of CO2. The injection of CO2 into shale gas reservoir shows a promising application prospect in improving CH4 recovery and carbon emission reduction in geological and mathematical models, and the leakage risk is low after CO2 sequestration.

Characteristics of Co–Ca catalyzed coal hydrogasification in a mixture of H2 and CO2 atmosphere

Coal catalytic hydrogasification (CCHG) is a promising approach for producing substituted natural gas by using pure hydrogen as a gasifying agent. If pure hydrogen could be replaced by cheaper crude gas from the coal gasifier, the economy of CCHG would be significantly improved. However, the composition of crude gas is complicated because in addition to H2, CO, CO2 and H2O are contained in it. To preliminarily investigate the influence of CO2 in the feed gas on CCHG, a mixture of H2 and CO2 with a CO2 concentration of 10% (denoted as H2 + CO2) was used for Co–Ca catalyzed coal hydrogasification at 850 °C and 3 MPa in a fluidized bed reactor. The results showed that the concurrence of coal hydrogasification with CO2 methanation produced CH4 efficiently. The CH4 yield (based on the carbon in coal) increased from 77.4% for pure H2 to 188% for H2 + CO2 within 120 min. More than 90% CO2 in situ conversion and 72.3% coal conversion were achieved. The catalytic effect of the Co–Ca loaded coal considerably improved the CH4 selectivity of CO2 methanation from 43.5% to 82.7%. The forms of Co and Ca in H2 + CO2 were consistent with those in pure hydrogen. The slow coal hydrogasification rate in H2 + CO2 was mainly attributed to the two-fold effects of CO2 methanation: the decrease in the partial hydrogen pressure and the competitive adsorption behavior of H2 and CO (a by-product of CO2 methanation) molecules on the cobalt active surface. This work provides a unique approach for simultaneously realizing the conversion of coal and the utilization of CO2.

Development and application of a predictive model for advanced wastewater treatment by adsorption onto powdered activated carbon

This work presents a mathematical method to describe adsorptive removal of organic micropollutants (OMPs) and dissolved organic carbon (DOC) from wastewater treatment plant effluent using powdered activated carbon (PAC). The developed model is based on the tracer model (TRM) as a modification of the ideal adsorbed solution theory (IAST) and uses the fictive component approach for organic matter fractionation. It enables the simulation of multisolute adsorption of OMPs considering competitive adsorption behavior of organic background compounds (OBC). Adsorption equilibrium data for DOC and seven different OMPs as well as kinetic data for DOC were derived from batch experiments performed with secondary clarifier effluent of two municipal wastewater treatment plants (WWTP 1 and WWTP 2). Two conventional PAC products were investigated as well as one biogenic PAC (BioPAC). Verification and validation of the fitting results based on operational data of WWTP 1 showed promising prediction of DOC and OMP removal efficiency. However, when applied to a static simulation of a full-scale PAC adsorption stage, the model overpredicts the removal efficiency of sulfamethoxazole and candesartan. For benzotriazole, carbamazepine or hydrochlorothiazide, predicted removal falls below operational removal. The model can be used to predict removals of good adsorbable OMPs but fails to accurately predict the removals of OMPs with variable or low PAC affinity. The model was further used for a dynamic simulation of DOC and diclofenac effluent concentrations of a full-scale PAC adsorption stage with varying operating conditions and influent concentrations. Results show that the hydraulic retention time (HRT) in the contact reactor is a decisive operational parameter for OMP removal efficiency besides the PAC dose.

Predicting Adsorption of Methane and Carbon Dioxide Mixture in Shale Using Simplified Local-Density Model: Implications for Enhanced Gas Recovery and Carbon Dioxide Sequestration

Carbon dioxide (CO2) capture and storage have attracted global focus because CO2 emissions are responsible for global warming. Recently, injecting CO2 into shale gas reservoirs is regarded as a promising technique to enhance shale gas (i.e., methane (CH4)) production while permanently storing CO2 underground. This study aims to develop a calculation workflow, which is built on the simplified local-density (SLD) model, to predict excess and absolute adsorption isotherms of gas mixture based on single-component adsorption data. Such a calculation workflow was validated by comparing the measured adsorption of CH4, CO2, and binary CH4/CO2 mixture in shale reported previously in the literature with the predicted results using the calculation workflow. The crucial steps of the calculation workflow are applying the multicomponent SLD model to conduct regression analysis on the measured adsorption isotherm of each component in the gas mixture simultaneously and using the determined key regression parameters to predict the adsorption isotherms of gas mixtures with various feed-gas mole fractions. Through the calculation workflow, the density profiles and mole fractions of the adsorbed gases can be determined, from which the absolute adsorption of the gas mixture is estimated. In addition, the CO2/CH4 adsorption selectivity larger than one is observed, illustrating the preferential adsorption of CO2 over CH4 on shale, which implies that CO2 has enormous potential to enhance CH4 production while sequestering itself in shale. Our findings demonstrate that the proposed calculation workflow depending on the multicomponent SLD model enables us to accurately predict the adsorption of gas mixtures in nanopores based on single-component adsorption results. Following the innovative calculation flow path, we could bypass the experimental difficulties of measuring the multicomponent mole fractions in the gas phase at the equilibrium during the adsorption experiments. This study also provides insight into the CO2/CH4 competitive adsorption behavior in nanopores and gives guidance to CO2-enhanced gas recovery (CO2-EGR) and CO2 sequestration in shale formations.

Molecular dynamics simulation of the competitive adsorption behavior of effluent organic matters by heated aluminum oxide particles (HAOPs)

Fouling mitigation of reverse osmosis membranes using various pre-treatment methods has received tremendous attention in the past years. The use of dynamic membranes particularly composed of heated aluminum oxide particles (HAOPs) appears to be a promising approach. Based off adsorption behaviors by individual foulants revealed by molecular dynamics (MD) simulations in an earlier study, this study targeted to understand the competitive adsorption of different constituents of effluent organic matters (EfOM) on HAOPs, which mimics the high local foulant concentration at the boundary layer. Quantitative analysis reveals that (i) EfOM constituents, except for low-molecular-weight neutrals, exhibit means to anchor onto HAOPs despite steric hindrance; (ii) adsorbed foulants exhibit significantly lower mobility and flexibility, indicating excellent adsorption capability of HAOPs before the dynamic membrane layer becoomes fully saturated with EfOM; and (iii) divalent ions and carboxylic group play critical roles in facilitating the adsorption of foulants. The MD results provide molecular-level mechanistic insights on the superior pre-treatment effectiveness by HAOPs.

Concurrent elimination and stepwise recovery of Pb(II) and bisphenol A from water using β–cyclodextrin modified magnetic cellulose: adsorption performance and mechanism investigation

Coexistence of heavy metals and endocrine disrupting compounds in polluted water with competitive adsorption behavior necessitates design of tailored adsorbents. In this work, β-cyclodextrin modified magnetic rice husk-derived cellulose (β-CD@MRHC) which can provide independent functional sites for effectively binding the above two types of contaminants was synthesized and used for Pb(II) and BPA elimination in both unit and multivariate systems. Characterizations results confirmed successful β-CD grafting and Fe3O4 loading, and the β-CD@MRHC had excellent magnetic property for its effectively recovery from water, which was not affected by the adsorption of pollutants. The β-CD@MRHC possessed superior adsorption performance with maximal Pb(II)/BPA uptake of 266.2 or 412.8 mg/g, severally, and the adsorption equilibrium was fleetly reached in 30 and 7.5 min. Moreover, the β-CD@MRHC could accomplish synergetic Pb(II) and BPA elimination through averting their competitive behaviors owing to diverse capture mechanisms for Pb(II) (ion exchange, complexation and electrostatic attraction) and BPA (hydrogen bonding and host-guest inclusion). Furthermore, after three cycles of step-wise desorption, the binding of Pb(II) as well as BPA byβ-CD@MRHC dropped slightly in dualistic condition. In summary, β-CD@MRHC was a promising tailored adsorbent to practical application for simultaneously removing heavy metals and organic matters from wastewater with high-performance magnetic recovery.

Dynamic adsorption behavior of benzene, toluene, and xylene VOCs in single- and multi-component systems by activated carbon derived from defatted black cumin (Nigella sativa L.) biowaste

In the current study, activated carbon (AC) was produced from defatted black cumin (Nigella sativa L.) biowaste (DBCB) with ZnCl2 activation by means of the response surface methodology. The optimum process conditions for the production of DBCB-AC with a high iodine number of 1055.02 mg/g were predicted as an activation time of 57 min, activation temperature of 550 °C, and impregnation ratio of 105%. The surface and textural properties of the optimal DBCB-AC were characterized by SEM, FTIR, and BET analysis techniques. The DBCB-AC exhibited a highly porous structure with a specific surface area of 1213.32 m2/g, total pore volume of 0.89 cm3/g, and micropore surface area of 787.65 m2/g. Exploring the comparative and competitive adsorption behavior of volatile organic compounds (VOCs) is of both practical and scientific interest. Therefore, the competitive adsorption of multi-component benzene, toluene, and xylene (BTX) vapors by the DBCB-AC was elucidated. In the single-component system, the adsorption capacities of the BTX vapors at inlet concentrations of 20 mg/L were determined as 495, 580, and 674 mg/g, respectively. In contrast, in the binary-component system, the adsorption capacity of the B-vapor at 20 mg/L B + 10 mg/L T and 20 mg/L B + 10 mg/L X decreased by approximately 42% and 56%, respectively. Similarly, the adsorption capacity of the T-vapor at 20 mg/L T + 10 mg/L X decreased by approximately 47%. In the ternary-component system, the adsorption capacity of the X-vapor remained consistent. The adsorption mechanism of the BTX was explained by adsorption kinetic and isotherm models. The reuse efficiency of the DBCB-AC for the BTX was assessed through five cycles of adsorption-desorption tests and was found to be 89.45%, 88.02%, and 87.25%, respectively. The DBCB-AC, which had high-performance in terms of both reuse efficiency and adsorption capacity, can be recommended as a promising adsorbent for removal of VOC pollutants.