Heterogeneous Adsorption Research Articles

Bridging the Adsorption Data and Adsorption Process by Introducing a Polynomial Structure To Accurately Describe IUPAC Isotherms, Stepwise Isotherms, and Stepwise Breakthrough Curves.

Porous heterogeneous adsorbents, those composed of multiple pore structures and surface chemical adsorption sites, can result in various gas or vapor adsorption isotherms, including five types of IUPAC adsorption isotherms and stepwise adsorption isotherms that have been difficult to model using a single adsorption equilibrium model. The limitation of the above equilibrium model further restricts the calculations of complex stepwise breakthrough curves. To bridge the adsorption data and adsorption process, it is important to first develop a simple model or method to describe these isotherms of various complex adsorption systems. In this work, assuming that the effect of the diffusion rate can be neglected under the static condition and the adsorption process is discontinuous, the number of adsorption isotherm inflection points can be used to represent the changed number of adsorption interactions. With the introduction of the polynomial structure, a series of empirical or semi-empirical polynomial adsorption models were developed. The N-site polynomial Langmuir-Freundlich equation could accurately fit common type I, II, III, IV, and V adsorption isotherms and complex stepwise adsorption isotherms covering various adsorbates, such as volatile organic compounds (VOCs), toxic industrial chemicals (TICs), water vapor, and carbon dioxide, as well as different adsorbents, such as metal/covalent organic frameworks (MOFs/COFs), zeolites, and porous carbons. Similarly, the introduction of a polynomial structure, such as the N-site polynomial Yoon-Nelson equation, was also successful in the description of interesting stepwise breakthrough curves. This work provides a more accurate adsorption equilibrium model to characterize all types of isotherms. As a foundation model, it is expected to be used to simulate the gas-solid adsorption process inside the fixed and fluidized beds packed with porous adsorbents.

Properties and Evaluation of Functionalized Mixed Membrane Adsorbents for the Adsorption of Vanillic Acid from Palm Oil Waste

Identifying factors that can improve the ability of mixed matrix membrane (MMM) adsorbents to isolate phenolic chemicals from palm oil waste is a major challenge. This study prepared a mixed matrix membrane with improved efficiency using a quaternary doping solution and a hydroxyapatite (HAp) filler and denoted as modified mixed matrix membrane (MMMHAp). Prior to use, HAp powder obtained from eggshells calcined at different temperatures was evaluated as an absorbent for the desired phenolic compounds. All the prepared HAp and MMMHAp powders were evaluated for their properties by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and X-ray diffraction (XRD). For this study, vanillic acid was selected as a phenolic chemical because it is widely used in the pharmaceutical, biomedical and food industries. The optimal adsorption and vanillic acid isolation from crude palm oil samples by MMMHAp occurred using an acetate buffer solution with a pH of 8. The data from the equilibrium adsorption study were also in agreement with the Freundlich isotherm, as the R2 value was 0.9900 suggesting heterogeneous adsorption of vanillic acid on the surface of MMMHAp. The kinetic adsorption study clearly shows a pseudo-second-order fit (R2=0.9992), suggesting that chemisorption occurs between the adsorbed substance and the adsorbent. The modified membrane (MMMHAp) has characteristics of its finger-like structures is more elongated and connected to the porous layer, indicating that the incorporation of hydroxyapatite nanoparticles into the membrane enhances the adsorption of vanillic acid from real sample and has the highest adsorption capacity of 170.8 mg/g. These results show that this improved MMMHAp can be developed and used for waste utilization to obtain useful materials.

Effectiveness of a novel composite filler to enhance phosphorus removal in constructed wetlands.

Improving the adsorption performance of wetland fillers is of great significance for enhancing pollutant removal in constructed wetlands. Currently, limited by complex preparation processes and high costs, large numbers of high adsorption fillers studied in lab are difficult to be applied in practical engineering. In this study, a newly low-cost and efficient phosphorus removal composite wetland filler (CFB) is prepared by using industrial and agriculture waste (steel slag and oyster shells) and natural ore (volcanic rock) as raw materials. The results show that phosphorus removal efficiency was largely enhanced by synergistic effects of steel slag, oyster shells, and volcanic rock, and it was mainly influenced by the proportion of each component of CFB. Based on the fitting of the classical isothermal equation, the adsorption capacity of CFB is 18.339 mg/g. The adsorption of phosphorus by CFB is endothermic and spontaneous, and there are heterogeneous surfaces and multi-layer adsorption processes, as well as pH value and temperature, are free from the influence on CFB phosphorus removal. During the practical wastewater application experiments, the phosphorus removal rate of the CFB-filled constructed wetland apparatus (CW-A) can reach 94.89% and is free from the influence on the removal of other pollutants (COD, TN, and NH3-N) by the system. Overall, the prepared CFB is of excellent decontamination effect, an extremely simple preparation process, low cost, and sound practical engineering application potential, providing new ideas and approaches for enhancing the phosphorus removal capacity and waste resource utilization of constructed wetland systems.

Removal of pesticides by layered double hydroxide modified different clay minerals and site energy analysis

Layered double hydroxides (LDHs) modified montmorillonite, mica, illite, and chlorite to from composites adsorbents of LDH@Mt, LDH@Mi, LDH@Ill, and LDH@Chl were prepared for removal of atrazine (ATZ) and 4-chloro-2-methylphenoxyacetic acid (MCP), and characterized through XRD, FT-IR, BET, and SEM analyses. In kinetics study, four composite adsorbents well fitted pseudo-second-order kinetics and intraparticle diffusion. Generalized Langmuir model described adsorption process better than Langmuir model in isothermal study, indicating there were heterogeneous adsorption sites for ATZ/MCP on adsorbents. LDH@Mt possessed better adsorption performance for ATZ/MCP, and the adsorption capacities are 8.19 mg/g and 90.9 mg/g, respectively. Theory of site energy distribution analyzed the number of adsorption sites qualitatively, and showed that the accessible adsorption sites on LDH@Mt were more than that of other adsorbents. Thermodynamic analysis revealed that the removal processes were endothermic and spontaneous. The removal of ATZ/MCP by LDHs modified clays offers an effective approach for pesticides removal.

Recycled plastic powder for oil spill clean-up

This work investigated an eco-friendly, low-cost approach for oil spill remediation using recycled plastic powder (RPP). SEM, TEM and BET analysis, characterized the plastic sorbents. Batch adsorption experiments demonstrated RPP's effectiveness in oil removal under various conditions. Pseudo-second-order kinetics provided a good description of adsorption kinetics, indicating chemisorption as the main mechanism. Optimal oil removal of 96.1 % was achieved at pH 7, 25 °C temperature, 90 min contact time, 50 mg L−1 starting oil content, and 20 mg RPP dose. Adsorption equilibrium followed the Sips isotherm model, suggesting complex heterogeneous adsorption with highest capability of 53.4 mg g−1. Thermodynamic studies verified the endothermic and spontaneous nature of adsorption. RPP also showed excellent regeneration capability, recovering 95.2 % of the initial adsorption capacity after 5 reuse cycles. Generally, recycled plastic may be more cost-effective than producing new plastic from raw materials, as it reduces the need for virgin materials and can save energy.

Efficiently simultaneous sorption and oxidation of antimonite on nitroso grafting-manganese loading binary-modified biochar from aqueous solution

Modification of the biochar platform with organic reagents could enrich active functional groups, and incorporation of magnetic mineral on it could facilitate separation from the aqueous solution after practical application. The present research took advantage of both by performing –NO2 grafting and MnOx loading binary modification on biochar derived from bagasse. The results demonstrated that the binary modification dramatically enhanced the antimonite (Sb(III)) adsorption ability of the sole-modified biochar. The Sb(III) sorption experiment revealed the optimal binary modified parameters were 300 °C pyrolysis temperature and the reagent doses of 2.0 g urea, 1.0 g NaOH, 1.5 mL CCl4, 2.0 g NaNO2, and 0.1 g KMnO4. Binary-modified biochar synthesized under the optimal condition (MNBC300) could efficiently remove Sb(III) in the aqueous solution with an adsorption amount of 142.86 mg/g, which was much higher than that of the sole (27.70 and 13.43 mg/g). At a fast rate, the Sb(III) sorption behavior was governed by multilayer heterogeneous chemisorption adsorption via the complexation between –NO2/Mn-O bond and Sb(III). Fitting peaks on X-ray photoelectron spectra (XPS) demonstrated the oxidizability of MNBC300 due to the electron transfer from Sb(Ⅲ) to Mn3+, which was thereby oxidizing Sb(Ⅲ) to less toxic Sb(V). Overall, the present study showed a novel biochar modification technique to eliminate the ecological and human health hazards of Sb-containing wastewater.

Preparation and Application of Si@Al Adsorbents for Different Pollutants Removal from Aqueous Solution

This study tried to use electroflocculating precipitated waste to prepare a Si@Al adsorbent by simply mixing sodium silicate at a mass ratio of 4:1 and calcining at 200 °C for 2 h. The adsorbent was low cost, high efficiency, and could remove a variety of contaminants (organic pollutants, antibiotics, and metal ions) from water. In this study, adsorbent characterization and pollutant adsorption experiments were carried out. The results showed that: Si@Al adsorbent had uniform particles, distinct layers, a loose porous appearance, and the internal structure was scattered without a crystal structure. The optimal adsorption conditions for tetracycline were as follows: dosage of adsorbent 2.0 g/L, reaction time 10 min, pH = 4.5, and tetracycline removal rate of 97.13%. The optimal adsorption conditions for MB (MB stands for methylene blue) were an adsorption dosage of 4.0 g/L, a reaction time of 15 min, pH = 4.5–8.5, and a removal rate of 96.39%. The optimal adsorption conditions for Cu were a 2.0 g/L dosage of adsorbent, a reaction time of 30 min, a pH of 8.5, and a highest removal rate of 97.47%. It was worth noting that the effect of temperature on TC, MB and Cu was not significant. At the same time, the kinetic fitting results showed that the adsorption of MB was more consistent with the quasi-second-order kinetic model, with R2 ranging from 0.9788 to 1.0000. The adsorption of TC and Cu was more consistent with the quasi-first-order kinetic model, with R2 ranging from 0.9598 to 0.9999 and 0.9844 to 0.9988, respectively. According to the results of thermodynamics, kinetics and zero potential point, the adsorption of tetracycline and methylene blue was mainly a physical adsorption, multilayer heterogeneous or single-layer homogeneous adsorption process. The adsorption of Cu was categorized as multi-layer heterogeneous chemical adsorption. The co-existing substances had little effect on the properties of the adsorbent, and the adsorbent could be recycled 5 times. Compared with other adsorbents, the results showed that the adsorbents had obvious advantages in terms of the raw material source, preparation method, time cost and removal effect. This study provided a “waste into treasure, green and efficient” multi-pollutant adsorption method.

Comprehensive assessment of carbon-, biomaterial- and inorganic-based adsorbents for the removal of the most hazardous heavy metal ions from wastewater.

Owing to the high cost of recycling waste, underdeveloped countries discharge industrial, agricultural, and anthropogenic effluents without pretreatment. As a result, pollutant-loaded waste enters water bodies. Among the diverse toxic contaminants, heavy metal ions are the most detrimental because of their chronic toxicity, non-degradability, prevalence, and bioaccumulation. The growing shortage of water resources demands the removal of heavy metal ions from wastewater. Three SDGs of the sustainability agenda of the United Nations appeal for clean water to protect life beneath water and on land depending on the water sources. Therefore, efficient environmentally friendly approaches for wastewater treatment are urgently required. In this regard, several methods have been developed for the removal of heavy metal ions from wastewater, including adsorption as the most widely used method owing to its eco-friendly, cost-effective, and sustainable nature. The present review discusses the progress in the preparation and application of various adsorbents based on carbon, micro-organisms, agricultural waste and inorganic materials for the extraction of toxic metal ions such as Pb2+, Cr6+, As3+, As5+, Hg2+ and Cd2+. Herein, we provide information on the role of the homogeneity and heterogeneity of adsorbents, kinetics of the adsorption of an adsorbate on the surface of an adsorbent, insights into adsorption reaction pathways, the mechanism of the sorption process, and the uptake of solutes from solution. The present review will be useful for researchers working on environmental protection and clean environment.

A Prussian blue analog-based copper-aluminum layered double hydroxide for cesium removal from water: fabrication, density functional theory-based molecular modeling, and the adsorption mechanism.

A new type of adsorbent, a Prussian blue analog-based copper-aluminum layered double hydroxide (PBA@CuAl-LDH), was successfully synthesized using a one-step method for the removal of radioactive Cs+ from wastewater. The adsorption performance, characteristics and the underlying adsorption mechanism of PBA@CuAl-LDH were systematically examined. The results showed that PBA@CuAl-LDH exhibited excellent adsorption performance, with a maximum adsorption capacity of 109.2 mg g-1. Over 85% of PBA@CuAl-LDH can be recycled, and the material exhibited only a 6.6% loss in adsorption performance. The adsorption process was well-fitted using the pseudo-second-order kinetic model and the Freundlich isotherm model, revealing the surface heterogeneity of the composite adsorbent. A molecular model of PBA@CuAl-LDH was constructed by combining density functional theory and multiple instrumental characterization techniques. Our results indicate that PBA crystals can be generated between layers and on the surface. Ion exchange was revealed as the main adsorption mechanism of Cs+ by PBA@CuAl-LDH. Specifically, the interstitial spaces of the PBA crystals generated between the layers and on the surface played an important role in ion exchange. These findings provide concrete theoretical support for radioactive pollution control and have significant value in directing the fabrication of cesium removal materials and their future engineering application.

Enhanced Performance of the Composite of FeMgAl‐Layered Double Hydroxide and Rice Husk Biochar to Adsorb Heavy Metal Ions of Lead and Cadmium in Aqueous Solutions

The layered double hydroxide (LDH) of FeMgAl and its composite with the rice husk biochar (FeMgAl/RHB) was tried for the first time for removing heavy metal ions of lead (Pb2+) and cadmium (Cd2+) in batch tests. Scanning electron microscopy and Fourier transform infrared spectroscopy demonstrated that FeMgAl/LDH was successfully synthesized and integrated into RHB. Furthermore, the presence of Cd2+ and Pb2+ was confirmed by energy‐dispersive X‐ray spectroscopy, exhibiting an effective adsorption process. The equilibrium contact time was estimated at 15 and 60 min, for Pb2+ and Cd2+, respectively, with high removal efficiencies and adsorption capacities upon immediate contact. Within the observed range (0–100 mg·L−1) of initial metal concentrations, the removal efficiencies decreased constantly using both adsorbents, while 50 or 60 mg·L−1 of Pb2+ and Cd2+, respectively, was estimated as the optimum values due to a steady increase in the adsorption capacities with composite adsorbent presenting a better efficiency, twice of the metal uptake capacity compared with FeMgAl/LDH. The lowest used amount of each adsorbent (0.05 g) exhibited highest adsorption capacity which decreased with increasing amount of adsorbent (up to 0.8 g), whereas the removal efficiencies increased for both heavy metal ions. A solution of pH value 0.7–0.8 was estimated as an optimum value with a uniform increasing pattern of adsorption capacities and percentage removal of both heavy metal ions using the FeMgAl/LDH as well as the composite adsorbent. A perfect fitting of the adsorption data was seen using the pseudo‐second‐order kinetic model, suggesting the chemical sorption to be the control mechanism of adsorption. The fitting of the Langmuir and Temkin isotherm models proposed a monolayer as well as heterogeneous adsorption system. The same was further confirmed based on the reasonable fit of both (Sips and Redlich–Peterson) three‐parameter isotherms in addition to a physical adsorption system, as suggested by the Dubinin–Radushkevich isotherm model.

Preparation of low-cost acidic modified-adsorbent from agricultural waste palm leaf to remove methylene blue from aqueous solutions

Disposing wastewater from textile industries and dyes into water bodies has aesthetic effects on the nature of water, it can also cause serious adverse environmental impacts on the water ecosystem by reducing sunlight penetration and photosynthetic reactions. Adsorption is one of the most common methods for removal of toxic pollutants due to its easy and cheap operation. Using agricultural waste to prepare cheap and simple adsorbents is an alternative method for commercial carbons. In this research, a cost-effective adsorbent was fabricated from palm leaf agricultural waste during two stages of carbonization and modification with acid. XRD and FTIR analyses were used to characterize the carbon-based adsorbent. The funding indicated that the removal performance of methylene blue at an initial concentration of 25 mg/L is about 99.6 % after 60 min of reaction at solution pH 7. However, the highest adsorption capacity of 175.6 mg/g was achieved at the adsorbent dose of 25 mg. The adsorption isotherm and kinetics evaluation indicated that the adsorption of methylene blue on the adsorbent prepared from palm leaf waste is chemical heterogeneous adsorption. The findings of the present research promise the development of a cost-effective adsorbent from agricultural waste to remove dye compounds from industrial wastewater at near-neutral conditions.

Bio-adsorption of heavy metals from aqueous solution using the ZnO-modified date pits

The bio-adsorption of heavy metals (including Cu2+, Ni2+, and Zn2+) in aqueous solution and also in an industry wastewater using the ZnO-modified date pits (MDP) as the bio-adsorbent are investigated. The fresh and used bio-adsorbents were characterized by FT-IR, SEM, BET, and XRD. The bio-adsorption parameters (including the pH of solution, the particle size of MDP, the shaking speed, the initial concentration of heavy metals, the dosing of MDP, the adsorption time, and the adsorption temperature) were screened and the data were used to optimize the bio-adsorption process and to study the bio-adsorption isotherms, kinetics, and thermodynamics. Two adsorption models (Langmuir isotherm model and Freundlich isotherm model) and three kinetic models (pseudo-first-order model, pseudo-second-order model, and intra-particle diffusion model) were applied to model the experimental data. Results show that the maximum adsorption amount of Cu2+, Ni2+, and Zn2+ on a complete monolayer of MDP are 82.4, 71.9, and 66.3 mg g−1, which are over 4 times of those of date pits-based bio-adsorbents reported in literature. The bio-adsorption of heavy metals on MDP is spontaneous and exothermic, and is regulated by chemical adsorption on the homogeneous and heterogeneous adsorption sites of MDP surface. This work demonstrates an effective modification protocol for improved bio-adsorption performance of the date pits-based bio-adsorbent, which is cheap and originally from a waste.

Preparation and adsorption kinetics and thermodynamics of sodium humate‐modified diatomite

AbstractDiatomaceous earth has been used as a nonorganic carrier to prepare a sodium humate modified diatomaceous space using the sol‐gel method. X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscope, the Brunauer–Emmett–Teller (BET) method, and other methods were used to characterize its physio‐chemical properties. The effects of sodium humate/diatomite on the pH of tetracycline in water, the dosage of adsorbent, and pollutant temperature on the adsorption effect were studied. The results show that after alkali modification, the porous structure of diatomite remains undamaged, and the specific surface area of the modified sample is increased to 12.712 m2/g, and the average pore diameter is reduced to 146.19 nm. Adding 20‐mg sodium humate/diatomite into 100‐mL tetracycline wastewater with an initial concentration of 20 mg/L, and pH of 5 at a temperature of 55°C, the adsorption capacity reaches 75.1 mg/L, and the removal rate reaches 78.3%. The quasi‐second‐order kinetic model was fitted by regression and found to have R2 > 0.99, indicating that the adsorption process was one of surface adsorption. It is a process that involves initially rapid adsorption and then slowly reaching equilibrium. As an adsorption thermodynamics model, the Temkin, Redlich‐Peterson and Koble‐Corrigan models can explain humic acid sodium/diatomite behavior in the adsorption of tetracycline in water (each with R2 ≥ 0.99), and the effects of surface behavior in multilayer adsorption and electrostatic attraction on uneven heterogeneous adsorption.

Investigation of Emulsified Oil Adsorption onto Functionalized Magnetic Nanoparticles—Kinetic and Isotherm Models

Recently, considerable attention has been given to using magnetic nanoparticles (MNPs) for capturing oil from oil-in-water (O/W) emulsions, despite MNPs’ inherent instability and agglomeration. Their stabilization through changing surface chemistry is required to increase dispersivity. In this research, we use cetyltrimethylammonium bromide (CTAB) as a cationic surfactant to increase the positive surface charge of the particles, resulting in a better stability in the aqueous solution because of increased repulsive forces. The functionalized MNPs are characterized using transmission electron microscopy (TEM), zeta potential, and contact angle (CA) measurements. The aim of this study is to investigate the oil separation efficiency (SE) and equilibrium oil adsorption capacity of the synthesized particles, which are determined using gas chromatography analysis. We also study the adsorption behavior using isotherm and kinetic models. The SE values indicate the superior performance of MNP@CTAB for oil adsorption from dodecane-in-water nanoemulsion (SE = 99.80%) compared to the bare MNPs with SE of approximately 57.46%. These findings are attributed to the stronger electrostatic attraction between the MNP@CTAB having high positive charge and negatively charged oil droplets. The adsorption isotherm results using both linear and non-linear regression methods show that the Freundlich isotherm is the best fit to the experimental equilibrium data (with calculated R2 > 0.97), verifying a multilayer heterogeneous adsorption. Moreover, the pseudo-first-order kinetic model describes the experimental equilibrium data in a greater congruence (R2 = 0.99), suggesting physical adsorption of oil onto MNPs through van der Waals and physical bonding, which is also confirmed through zeta potential measurements.

Synthesis of Zr-based metal-organic framework/MWCNTs composite for adsorption of enrofloxacin from aqueous solution

Enrofloxacin, as one of the specialized fluoroquinolone antibiotics, has become a typical “emerging” pollutant in aqueous environment because of its great stability and resistance to degradation. Therefore, it is important to find an effective method to remove it from aqueous solution. In order to check the presence of synergies between UiO-66 and MWCNTs on removal of enrofloxacin from aqueous solution, a composite material, known as UiO-66/MWCNTs, was synthesized by using hydrothermal method. The physical and chemical properties of the synthesized composite were characterized by using methods such as XRD, N2 adsorption–desorption, FT-IR, SEM and XPS. The results revealed that UiO-66/MWCNTs has large specific surface area (837.56 m2/g) and high porosity, as well as rich functional groups (C = C, –OH, –COOH). Factors such as contact time, initial concentration, temperature, pH, and ionic strength were considered to test the adsorption performance of pristine MWCNTs, pristine UiO-66 and UiO-66/MWCNTs composite for enrofloxacin. The results showed that the UiO-66/MWCNTs composite has a higher adsorption capacity at basic condition and the maximum adsorption capacities of enrofloxacin on composite was improved from 67.8 mg/g for MWCNTs and 92.8 mg/g for UiO-66 to 134.2 mg/g due to its higher adsorption active sites. The adsorption kinetics studies implied that the adsorption of enrofloxacin onto the studied sorbents involves in physio-chemical interactions and is an intra-particle diffusion controlling process. The isothermal experimental data were compatible with both Langmuir and Freundlich models, suggesting heterogeneous adsorption was the dominant during the course of adsorption. Additionally, the thermodynamic parameters indicated that the adsorption of enrofloxacin on UiO-66/MWCNTs was spontaneous and endothermic in nature. Finally, in combination with XPS analysis, the adsorption mechanism of enrofloxacin on UiO-66/MWCNTs was clarified to be the synergetic effect of chemical adsorption, hydrogen bond and π-π interaction. This work provides a new strategy for the removal of drugs from aqueous environment.

Adsorption of sulfadiazine on novel bilayer porous resin: Synergism of micropore filling and anion exchange

A novel bilayer porous resin with micropore filling and anion exchange (PsCH2BP) was synthesized. The aim was to investigate the adsorption of sulfadiazine on PsCH2BP. The micropore area of PsCH2BP was reduced by 73.91 % after the adsorption of sulfadiazine. PsCH2BP exhibited the synergism of micropore filling and anion exchange in the adsorption of sulfadiazine. Within the pH range of 7.29–13.31, the adsorption capacity trend of sulfadiazine on PsCH2BP was consistent with its ionization curve of pka 6.48. The adsorption of sulfadiazine on PsCH2BP was endothermic, spontaneous, entropy increase and heterogeneous multilayer adsorption, reflecting the bilayer pore structure of PsCH2BP. 100 % C2H5OH and 4 % NaCl could desorb 75.13 % and 65.06 % of sulfadiazine adsorbed on PsCH2BP, respectively, reflecting the synergism of the micropore filling and anion exchange in the adsorption of sulfadiazine on PsCH2BP. 100 % of desorption ratio of sulfadiazine adsorbed by PsCH2BP was achieved with 4 mol/LNaOH.

Rapid oxidation and deep As(III) purification from water using gelatin-supported iron-based metal-organic framework aerogel coupled with H2O2: Preparation, performance and mechanism

Metal-organic frameworks (MOFs) are considered a reliable adsorbent for controlling arsenic contamination. However, developing rapid and efficient MOF adsorbents with the capability of easy recovery is still challenging. Herein, we prepared a three-dimensional porous MIL-88A-Fe/gelatin aerogel (PMGA) with macroscopic size and coupled it with H2O2 to fabricate a heterogeneous catalytic oxidation adsorption system to remove As(III) in water. The green synthesis strategy of this catalyst by foaming and low-temperature carbonization not only avoided the use of toxic chemical crosslinkers but also endowed PMGA with a rich hierarchical porous structure and exposed more active sites. Thus, the PMGA/H2O2 system was able to reduce the concentration of As(III) from 1106 to below 10 µg/L and simultaneously realize the complete oxidation of As(III) to As(V) in only 120 min. Meanwhile, the system exhibited an excellent saturation adsorption capacity (24.863 mg/g) for As(III), superior to most similar bio-based or iron-based materials. Quenching experiments, EPR and DFT calculations showed that the active species (surface •OOH and surface •OH) generated by the Fenton-like interaction between the exposed (100) facet of MIL-88A-Fe in PMGA and H2O2 played an essential role in promoting the oxidative removal of As(III). Moreover, the reaction system could work efficiently for As(III) in a wide pH range and was hardly affected by other substances such as chlorides, sulfates, carbonates, silicates, and humic acids. Simultaneously, the fixed bed column filled with PMGA could stably and continuously treat As(III) in groundwater. Therefore, this study not only broadens the horizon for the development and design of 3D functional materials but also provides a new strategy in water purification to eliminate arsenic pollutants using Fe-MOF aerogels.

On adsorption azeotropy and a classification based on the dual site Langmuir isotherm

Adsorption azeotropy is a phenomenon that has been known for nearly a century, yet few properties have been formally proven. Here four general properties of adsorption azeotropy in porous materials are discussed and shown to apply irrespective of the isotherm, including the fact that there is always a lower bound on the pressure at which an azeotrope may be present. As molecules of different size will favour the occurrence of an azeotrope, this study considers in detail the thermodynamically consistent dual site Langmuir model, where azeotropy is solely the result of the adsorbent heterogeneity. Six categories of adsorption azeotropes, which can be grouped into three pairs of mirror cases, are formally identified for this model. Dimensionless ratios allow to determine formally each category and the analysis also includes a discussion of the crossing of the pure component isotherms. The heterogeneity of the adsorbent is shown to lead to azeotropes that can include an upper bound on pressure; that can occur even if the pure component isotherms do not cross; and can be present below the pressure at which the pure component isotherms cross. Finally, the analysis allows to identify also the ranges of parameters for which the pure component isotherms cross but an azeotrope is not present.

MXene/AgNW composite material for selective and efficient removal of radioactive cesium and iodine from water

Toxic fission products, such as cesium (137Cs) and iodine (129I) are of great concern because of their long half-lives and high solubility in water. The simultaneous removal of Cs and I using a single adsorbent is an area of increasing interest. In this study, MXene/silver nanowire (AgNW) composite was synthesized through physical mixing and employed for simultaneous removal of iodide (I−) and cesium (Cs+) ions from contaminated water. The MXene/AgNW composite demonstrated excellent adsorption capacities of 84.70 and 26.22 mg/g for I− and Cs+, respectively. The experimental data supported the hypothesis of multilayer adsorption of Cs+ owing to the inter-lamellar structures and the presence of heterogeneous adsorption sites in MXene. The interaction between I− and the AgNW involved chemisorption followed by monolayer adsorption. MXene/AgNW composite material exhibited promising results in the presence of competitive ions under extreme pH conditions. Thus, synthesized composite materials holds promising potential as an adsorbent for the remediation of radioactive liquid waste.

Adsorption behavior of shale oil and water in the kerogen-kaolinite pore by molecular simulations

It is very meaningful to study the adsorption behavior of oil and water in shale nanopores in the context of enhanced oil recovery. Whereas, the investigation of shale and water adsorption in organic–inorganic pores is scarce. In this work, molecular dynamics (MD) simulations were used to study the adsorption behavior of multi-component shale oil and water in the novel kerogen-kaolinite pores. The adsorption characteristics of shale oil were studied through fluid density distribution, and the interaction energies between the fluid and the walls were calculated to describe the adsorption strength. The results show that different roughness, wettability, and polarity of the organic and inorganic walls caused the adsorption characteristics and strengths of shale oil and water to be asymmetrical. In the kerogen-gibbsite pore, water can form a film and adsorb near the hydrophilic gibbsite surface, while the shale oil exhibits heterogeneous adsorption on the other side of the pore. The presence of water will shield the influence of hydrophilic surfaces on the adsorption behavior of shale oil. Moreover, the active components of shale oil will form hydrogen bonds with water and regularly arrange near the water film, which makes it easy to capture the asphaltene clusters and block the pores. In the kerogen-siloxane pore, the adsorption peak of shale oil near the hydrophobic siloxane wall is much higher than that near the kerogen wall, while the adsorption strength is lower than that of the kerogen wall. Furthermore, we investigated the effects of water content, saline, and deprotonation (protonation) of active components on fluid adsorption behavior. Our study provides an in-depth understanding of shale oil and water adsorption in complex nanopores, especially the influence of wall wettability on the adsorption behavior.