Selective Sorption Research Articles

New Sorbents Based on Polyacrylonitrile Fiber and Transition Metal Ferrocyanides for 137Cs Recovery from Various Composition Solutions

For the first time, new sorbents based on polyacrylonitrile (PAN) fiber and transition metal ferrocyanides were obtained. The main difference between the obtained sorbents and the existing ones is the stage of preliminary preparation of the initial support by converting it into the forms PAN-Fe(OH)3 or PAN-MnO2, due to which additional ion exchange groups (carboxyl, carbonyl, etc.) are formed, which increases the amount of ferrocyanide fixed to the support. The best components and conditions for the synthesis of new sorbents were determined (concentration (0.1–0.2 mol/L), as well as pH (1 for sorbents based on PAN-Fe(OH)3, and 1–5—PAN-MnO2) of potassium ferrocyanide solution, concentration of transition metal salts (0.02 mol/L), temperature conditions). The influence of the studied solution composition (pH, concentration of Na+, K+, NH4+ ions) on the cesium distribution coefficients during its recovery by the obtained sorbents was assessed. The possibility of cesium recovery from solutions with pH 1–9 containing macro quantities of cations was demonstrated. The sorbents derived were characterized by modern structural methods such as infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy with EDS analysis. A study of the trace amount sorption of 137Cs was carried out in comparison with commercially available highly efficient sorbents (FNS-10 and Termoksid-35), and it was shown that the resulting sorbents are not inferior to industrial ferrocyanide sorbents and can be used for 137Cs selective sorption from technological solutions and natural waters.

Engineered species-selective ion-exchange in tuneable dual-phase zeolite composites.

Controllable sorption selectivity in zeolites is crucial for their application in catalysis, gas separation and ion-exchange. Whilst existing approaches to achieving sorption selectivity with natural zeolites typically rely on screening for specific geological deposits, here we develop partial interzeolite transformation as a straightforward and highly tuneable method to achieve sorption selectivity via forming dual-phase composites with simultaneous control of both phase-ratio and morphology. The dual-cation (strontium and caesium) exchange properties of a series of granular mordenite/zeolite P composites formed from a parent natural mordenite material are demonstrated in complex, industrially relevant multi-ion environments pertinent to nuclear waste management. The relative uptake of caesium and strontium is controlled via the extent of transformation: composites exhibit significantly increased ion-exchange affinity for strontium compared to both the parent mordenite and physical mixtures of mordenite/zeolite P phases with similar phase ratios. The composite with a 40 : 60 mordenite : zeolite P ratio composite achieves higher uptake rates than the natural clinoptilolite material currently used to decontaminate nuclear waste streams at the Sellafield site, UK. In situ X-ray image-guided diffraction experiments during caesium exchange demonstrate that the mordenite core retains rapid caesium uptake likely responsible for the unique ion-exchange chemistry achievable through the partial inter-zeolite transformation. These results offer a straightforward and controllable route to optimised zeolite functionality and a strategy to engineer composites from low-grade natural sources at low cost and with formulation advantages for industrial deployment.

Perilla frutescens: A new strategy for uranium decorporation

Radionuclide uranium is a great threat to human health, due to its high chemical toxicity and radioactivity. Finding suitable uranium decorporation to reduce damage caused by uranium internal contamination is an important aspect of nuclear emergency response. However, the poor selectivity and/or high toxicity of the only excretory promoter approved by Food and Drug Administration (FDA) is an obvious disadvantage. Herein, we choose an edible natural product, the traditional Chinese medicine called Perilla frutescens (PF), which has wide sources and can be used as an excellent and effective uranyl decorporation. In vivo uranium decorporation assays illustrate the removal efficiency of uranium in kidney were 68.87% and 43.26%, in femur were 56.66% and 54.53%, by the test of prophylactic and immediate administration, respectively. Cell level experiments confirmed that it had better biocompatibility than CaNa3-DTPA (CaNa3-diethylenetriamine pentaacetate, a commercial actinide excretion agent). In vitro static adsorption experiments exhibited that its excellent selectivity sorption for uranyl. All those results findings would provide new research insights about natural product for uranyl decorporation.

Directly measured pyrolysis temperature dependence of sorption selectivity for carbon dioxide/methane in Matrimid® polyimide-derived carbon molecular sieve membranes

In this study, we augment our analysis of pyrolysis temperature dependence of carbon molecular sieve (CMS) membranes derived from a polyimide, Matrimid® useful for advanced CMS membranes. Our direct sorption results prove that the strong pyrolysis temperature dependence of permselectivity for the CO2/CH4 gas pair is promoted by an unusual trend in sorption selectivity reported here. This trend complements conventional diffusion selectivity trends for this pair with increasing pyrolysis temperatures. Our results show that the elimination of pyridinic and pyrrolic groups over the same pyrolysis temperature range occurs. Elimination of such CO2-philic pyridinic and pyrrolic groups typically would be expected to cause a trend opposite to that actually measured directly for CO2/CH4 selectivity. The resulting trend for pyrolysis temperatures between 550 °C and 900 °C, however, can be explained in terms of microporous and ultramicroporous properties of the CMS for increasing pyrolysis temperatures. Specifically, apparent thermodynamic exclusion selectivity of the 0.5 Å larger CH4 vs. the slim 3.3 Å CO2 provides a consistent explanation of the trends. This discovery provides additional options to tune permselectivity of CMS membranes to complement molecular sieving based on diffusion contributions.

Determination of iron in water by flame atomic absorption spectrometry with sorption preconcentration

Determination and monitoring of pollutants in the natural environment is an urgent task because of their impact on living organisms as a result of numerous anthropogenic impacts. For this reason, a large number of publications are devoted to the development, modification or optimization of analytical methods that can solve these problems. When determining trace elements present in various samples, such as natural and waste water, biological samples and alloy samples, direct determination by various instrumental methods is often impossible due to the matrix effect and rather low concentration of metal ions in the sample. The atomic absorption method is one of the methods widely used for the determination of iron ions, which has such advantages as simplified sample preparation, low probability of contamination and loss of elements, increased analytical productivity, the detection limit of components in the analyzed mixture reduced by several orders of magnitude, and the ability to determine trace amounts of elements in small samples. The aim of the study was to develop a technique for the preliminary concentration of Fe (III) ions in waters of various origins using a sorbent immobilized with sulfosalicylic acid and their further determination by flame atomic absorption spectrometry. Sorbents obtained on the basis of polyacrylonitrile modified with polyethylene polyamine (PPF-1 and PPA-1) with sulfosalicylic acid immobilized on their surface were used for selective sorption of Fe (III) ions. Optimal conditions for the immobilization of sulfosalicylic acid on sorbents and the formation of complexes with Fe (III) ions were studied. The developed sorption-atomic absorption technique provided determination of low concentrations of Fe (III) ions in various waters. The use of PPF-1 as a sorbent with immobilized sulfosalicylic acid for pre-concentration of iron has a number of advantages compared to traditional atomic absorption procedure, i.e., the simplicity, high degree of iron extraction, high sensitivity and selectivity of iron determination, as well as a low cost. The detection limit of iron ions is 0.01 μg/L, Sr does not exceed 0.033.

SORPTION EXTRACTION OF RHENIUM BY DIFFERENT IONITES FROM URANIUM SORPTION COLUMNS

This text discusses the importance of rhenium in modern science and technology, particularly its significance in various production spheres due to its properties. The purpose of this work is extracting rhenium is the mother liquors of uranium production.However, due to its low concentration in raw materials, research into more advanced extraction methods is necessary. One such method is sorption extraction of rhenium.Currently, extensive research is being conducted to obtain highly effective sorbents for rhenium. Among the most promising are ion-exchange resins such as Purolite A660/4759, Puromet MTS9300, SQD 201U, and Biolite 200U. Conditions for rhenium sorption using these resins from standard, model, and mother solutions under various acidity levels have been studied, along with conditions for desorption of this metal from the sorbents.The latter two, SQD 201U and Biolite 200U, demonstrated high efficiency. Conclusion.They exhibited high rhenium sorption results from acidic solutions, showing high selectivity in both sorption and desorption concerning rhenium. Their sorption capacity for rhenium in strongly acidic solutions exceeded 21 mg/g. When sorbing from model and mother solutions, these sorbents showed a rhenium sorption degree exceeding 60%. During desorption, the rhenium desorption degree from these sorbents using a mixture of acids reached values higher than 85%.Therefore, ion-exchange resins SQD 201U and Biolite 200U perform well in industrial solution conditions, allowing their use in extracting rhenium from uranium mother liquors.

Selective Sorption of Heavy Metals by Renewable Polysaccharides.

Renewable and biodegradable polysaccharides have attracted interest for their wide applicability, among them their use as sorbents for heavy metal ions. Their high sorption capacity is due mainly to the acidic groups that populate the polysaccharide backbone, for example, carboxylic groups in alginate and sulfate ester groups in the iota and lambda carrageenans. In this study, these three polysaccharides were employed, alone or in different mixtures, to recover different heavy metal ions from aqueous solutions. All three polysaccharides were capable of adsorbing Eu3+, Sm3+, Er3+, or UO22+ and their mixtures, findings that were also confirmed using XPS, TGA, and FTIR analyses. In addition, the highest sorption yields of all the metal ions were obtained using alginate, alone or in mixtures. While the alginate with carboxylic and hydroxyl groups adsorbed different ions with the same selectivity, carrageenans with sulfate ester and hydroxyl groups exhibited higher adsorption selectivity for lanthanides than for uranyl, indicating that the activity of the sulfate ester groups toward trivalent and smaller ions was higher.

Fabrication of a novel chitosan/polyaspartic acid composite: A pH-tunable sorbent for efficient adsorption of heavy metal ions and dyes from water

Heavy metal ions and dyes pollutants have caused significant environmental pollution, posing a threat to human life and ecosystems. Herein, a novel pH-tunable composite adsorbent CS-PA integrated chitosan (CS) with polyaspartic acid (PA) was fabricated. The morphology and structure of CS-PA were characterized. The results indicated that PA was successfully introduced into CS, and the particle size of CS-PA was irregular and porous with a pore diameter of 10–100 μm. Adsorption experiments demonstrated that CS-PA was efficient in removing various charge properties of heavy metal ions and dyes: cationic [Cu(II) and methylene blue (MB)], anionic [Cr(VI) and congo red (CR)] species. Also, the sorption process in the experimental conditions fitted pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity of Cu(II), MB, Cr(VI), and CR were 133.33, 172.41, 138.89, and 178.57 mg/g, respectively, based on the Langmuir isotherm study. CS-PA has strong selective sorption ability for MB over Cu(II) under the acidic condition and CR over Cr(VI) at a weakly alkaline solution in their binary systems. Multiple attractions occurred in adsorbing Cu(II), MB, Cr(VI), and CR because of their diverse charge properties and structural characteristics. Finally, regeneration studies further demonstrate that <5 % in sorption efficiency on CS-PA after 5 cycles. Thus, this composite adsorbent is tunable, versatile and potentially applicable to wastewater treatment.

Enhanced removal of short- and long-chain per- and poly-fluoroalkyl substances from aqueous phase using crushed grafted chitosan beads: Performance and mechanisms

The widespread use of per- and poly-fluoroalkyl substances (PFASs), environmentally persistent halogenated hydrocarbons, in various industrial and commercial applications has caused significant concerns owing to their contamination of soil and groundwater. Chitosan is a biopolymer substance with abundant amine and hydroxyl functional groups, making it a good candidate for adsorption of PFASs. This study aimed to increase chitosan's adsorption capacity by grafting additional amine functional groups on its surface for the removal of long- and short-chain PFASs from an aqueous phase. Two types of chitosan-based sorbents were developed: crushed chitosan beads (CBs) and polyethyleneimine-grafted CBs (GCBs). Batch adsorption tests assessed the adsorption capacities of the sorbents in terms of the sorption kinetics, isotherms, selectivity, and reusability. Based on the results, the GCBs had significant potential for adsorbing PFASs. These capacities were significantly higher than those demonstrated by the CBs. The sorption kinetics data revealed that the GCBs had a fast sorption rate. Furthermore, the GCBs demonstrated a high adsorption affinity, with log Kd values ranging from 1.5 to 2.5 for PFASs at environmentally relevant concentrations (1000 ng L−1). They also demonstrated excellent selectivity sorption for these compounds, even in the presence of other organic and inorganic pollutants.

A NEW QUANTITATIVE METHOD OF EXPRESS ANALYSIS OF NATURAL RUBBER DIRECTLY IN THE ROOT OF THE RUBBER PLANT BY THE SPIN PROBE EPR METHOD

In this work, the phenomenon of selective sorption of a stable nitroxyl radical TEMPO on rubber particles in the powder of dried and dispersed root of kok-sagyz was discovered. This feature of the rubber-bearing root material contributed to the development of a new, highly sensitive method of quantitative analysis of rubber by the integral intensity of the EPR TEMPO signal. The main advantages of the proposed method are the speed and the ability to determine the content of rubber directly in the roots of the plant in microquantities (5–30 mg).

Fabrication of electrospun cellulose/ball-milled bone char membranes for fast, efficient and selective sorption of aquatic U(VI)

Powdered sorbents in aqueous solutions suffer from the deficiency in the solid/liquid separation even the sorption capacities were higher than their bulk or less-dispersed forms. The combination of powdered sorbents with membranes would be highly desired to balance the contradiction between high separation efficiency and sorption capability. In this study, cellulose/ball-milled bone char (CL/MB) membranes with sub-micrometer diameter (276.0–281.7 nm) and developed porosity (21.5–98.6 m2/g) were fabricated by electrospinning technique. Bone chars originated from the pyrolysis of bone residuals at 350 °C, 500 °C and 650 °C could well dispersed in the electrospinning solvent. CL/MB membranes could adsorb U(VI) with fast kinetics (180.0 min), efficient capacity (309.8 mg/g at pH 5.00 and T 298 K) and excellent selectivity against the interference of coexisting ions in simulated waters. With spectroscopic analysis, the formation of (Ca(UO2)2(PO4)2(H2O)3 precipitation was dominant for the selectivity. The surface complexation of O-/reductive N-groups with U(VI), the electrostatic attraction of deprotonated O- with positively charged U(VI) species, the cation exchange of U(VI) with Ca2+ components, and the cation-π coordination of U(VI) should also be considered. This study pave the way for the feasible utilization of electrospun CL/MB membranes as a promising sorbent to capture aquatic U(VI).

Selectivity of β-Cyclodextrin Polymer toward Aquatic Contaminants: Insights from Ultrahigh-Resolution Mass Spectrometry of Dissolved Organic Matter.

Selectivity in solid-phase extraction (SPE) materials has become increasingly important for analyte enrichment in sensitive analytical workflows to alleviate detrimental matrix effects. Molecular-level investigation of matrix constituents, which are preferentially extracted or excluded, can provide the analytical chemist with valuable information to learn about their control on sorbent selectivity. In this work, we employ nontargeted Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) to elucidate the molecular chemodiversity of freshwater-derived dissolved organic matter (DOM) extracted by the selective model sorbent β-cyclodextrin polymer (β-CDP) in comparison to conventional, universal SPE sorbents (i.e., Oasis HLB, Supel-Select HLB, and LiChrolut EN). Statistical analysis of MS data corroborated the highly selective nature of β-CDP by revealing the extracted DOM spectra that are most dissimilar to original compositions. We found that its selectivity was characterized by pronounced discrimination against highly oxygenated and unsaturated DOM compounds, which were associated with the classes of lignin-like, tannin-like, and carboxylic-rich alicyclic molecules. In contrast, conventional sorbents excluded less highly oxygenated compounds and showed a more universal extraction behavior for a wide range of DOM compositional space. We lay these findings in a larger context that aids the analyst in obtaining an a priori estimate of sorbent selectivity toward any target analyte of interest serving thereby an optimization of sample preparation. This study highlights the great value of nontargeted ultrahigh-resolution MS for better understanding of targeted analytics and provides new insights into the selective sorption behavior of novel sorbents.

Impact of Dye Encapsulation in ZIF-8 on CO2, Water, and Wet CO2 Sorption.

The fast adsorption kinetics of zeolitic imidazolate frameworks (ZIFs) enable a wide range of sorption applications. The most commonly used framework, ZIF-8, is relatively non-polar. Increasing the polarity of ZIF-8 through the encapsulation of different polar species shows promise for enhancing the sorption performance for pure CO2. Recently, the outlook has re-focused on gas mixtures, mostly in the context of post-combustion CO2 capture from wet flue gasses. While water is known to sometimes have a synergistic effect on CO2 sorption, we still face the potential problem of preferential water vapor adsorption. Herein, we report the preparation of three ZIF-8/organic dye (OD) composites using Congo red, Xylenol orange, and Bromothymol blue, and their impact on the sorption properties for CO2, water, and a model wet CO2 system at 50% RH. The results show that the preparation of OD composites can be a promising way to optimize adsorbents for single gasses, but further work is needed to find superior ZIF@OD for the selective sorption of CO2 from wet gas mixtures.

Thermal Stability and Resistance to Biodegradation of Humic Acid Adsorbed on Clay Minerals

This article studies sorption regularities and evaluates thermal stability and resistance to microbial degradation of humic acid during three sorption cycles on bentonite clay, kaolinite, and muscovite using TGA/DSC, XRD, hydrophobic chromatography, light and electron microscopy, etc. The experiment revealed that kaolinite sorbed more humic acids (HAs) in terms of unit surface area (1.03 × 10−3 C, g/m2) compared to bentonite (0.35 × 10−3 C, g/m 10−3 g/m2). Sorption at pH 4.5 showed HA fractionation in amphiphilicity and chemical composition. HA was sorbed on the surface of all sorbents, mainly via hydrophobic components. No intercalation of HA into the interlayer spaces of montmorillonite was observed during sorption. Sorption via hydrophilic interactions was mostly performed on muscovite and bentonite rather than on kaolinite. Sorption of HA resulted in changes in its chemical composition and decreased C/N compared to free HA, which demonstrated selective sorption of nitrogen-containing compounds more typical of muscovite. All minerals adsorbed only a relatively thermolabile HA fraction, while its thermal stability increased compared to that before the experiment. The thermal stability and ratio of the Exo2/Exo1 peak areas on the DSC curves of sorbed HA increased with each subsequent sorption cycle. We revealed the following relationship between thermal stability and resistance to microbial oxidation of the sorbed HA: The higher the thermal stability, the less available the sorbed HA becomes for utilization by microorganisms.

Current Density Dependence of Transport Selectivity of Metal Ions in the Electrodriven Process across the Cation Exchange Membrane.

Understanding the mechanisms leading to the selective transport of cations in an electrodriven process across a cation exchange membrane is important to design and control the potential gradient-based separation process. In this study, a comprehensive description of the current density (I, over a broad current regime) dependence of transport selectivity (Si) between cations of the same/different valence is presented. The role of conventional transport mechanisms such as diffusion, electromigration, and electroconvection in controlling the Si was identified theoretically as well as by multiple experimental approaches. These parameters were found to be dependent on the limiting current density (Ilim). In general, irrespective of the cations involved, Si (over Na+) decreased gradually with increasing I and then increased slowly (and saturated) after Ilim. This extent of variation of Si was heavily dependent on the charge and hydration state of the cations. At I < Ilim, both diffusion and electromigration processes contributed and, notably, the sorption selectivity outweighed the migration selectivity. At I → Ilim, diffusion was the solitary mechanism responsible for cation transport and migration selectivity was the major contributor in Si. At I > Ilim, as also validated by the Peclet numbers, the overall transport was dictated by electroconvection.

Fabrication of electrospun cellulose/chitosan/ball-milled bone char membranes for efficient and selective sorption of Pb(II) from aqueous solutions.

Separation materials have received increasing attention given their broad applications in the management of environmental pollution. It is desired to balance the contradiction between high separation efficiency and selectivity of separation materials. The integration of ball-milled bone chars with electrospun membranes might achieve this balance. In this study, electrospun cellulose/chitosan/ball-milled bone char (CL/CS/MB) membranes were by well-dispersing ball-milled bone chars with nanoscale size (98.9-167.5 nm) and developed porosity (40.2-373.1 m2/g) in the electrospinning solvent. The synergistic integration of distributed MBs (5.4-31.5 wt.% of loading hydroxyapatite on the membrane matrix) allowed the efficient sorption of Pb(II) with fast kinetics (20.0 min), excellent capacity (219.9 mg/g at pH 5.0, T 298 K), and favorable selectivity coefficients (2.76-6.79). The formation of minerals was dominant for the selective sorption of Pb(II) by combining the spectral analysis and quantitative determination. The surface complexation with O-/reductive N-species, the cation exchange with inorganic Ca2+, the electrostatic attraction with deprotonated O-, and the cation-π coordination with the aromatic carbon via the π-electrons should be not ignored for the capture of Pb(II). This work demonstrated the feasibility of electrospun CL/CS/MB membranes as a promising candidate for the remediation of aquatic pollutants.

Nanofiltration Purification of Liquid Radioactive Waste

The paper presents the results of testing the purification of real liquid radioactive waste from radionuclides, bottom residues of the Kola and Beloyarsk nuclear power plants (NPP), as well as low-level wastewater from the radiochemical building of the Institute of Physical Chemistry and Electrochemistry RAS (IPCE RAS) using the method of nanofiltration (NF) using a polymer membrane manufactured by the Russian company “RM Nanotech.” It has been shown that in the case of single-stage NF purification of bottoms of the Kola NPP, the coefficient of purification from 60Co is 2.8, while no purification from 137Cs practically occurs. When cleaning the bottom residues of the Beloyarsk NPP from 60Co using a five-stage scheme, a coefficient of purification from 60Co equal to 388 was obtained. The combination of nanofiltration purification and selective sorption of cesium on the ferrocyanide sorbent Temoksid-35 makes it possible to obtain a dry salt residue that is not related to radioactive waste. When using the method of nanofiltration for the treatment of low-level wastewater of the Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences, the degree of purification was, %: 137Сs ~ 75; 90Sr ~ 91; 241Am ~ 99.5; 152Eu ~ 91; 239Pu ~ 99.5.

Thiourea resole polymers for recovery of noble element

The recovery of noble elements from secondary source, industrial effluent, which are classified as high concentrated noble elements solution are very essential. Liquid-solid extraction systems are an attractive process used for the separation and purification of noble elements. For this purpose, a solid-phase extraction system was investigated for the recovery of noble metals (Au(III), Pd(II), and Rh(III)). Chelating resins were synthesized by a polycondensation reaction between phenolic thiourea monomers and formaldehyde under alkaline conditions. The resulting polymers were characterized and evaluated for their chelating properties with regard to noble metal sorption. Also, the selectivity of sorption of noble elements was studied in the presence of competitive elements that can be present in effluent waste, such as Zn, Cu, Ni, Fe, and Al. Here, we present a promising materials based on formo-phenolic thiourea resins as a potential candidate for high-capacity (> 350 mg/g for Au; > 50 mg/g for Pd; > 30 mg/g for Rh) and high-selectivity solid-liquid sorption of noble elements, particularly for Au.

Chitosan functionalized with pyrazolinone derivative for water treatment: Application to Hg(II) removal

Due to its high toxicity, the removal of mercury from groundwater in contaminated industrial areas is of critical importance to avoid health problems for living beings. The functionalization of chitosan with pyrazolinone derivative, allows designing a sorbent (CH-PYZ) with high efficiency and selectivity for mercury sorption at acidic pH values (1.40 mmol Hg g−1, at pH 3). The sorbent is characterized by elemental analysis, thermogravimetric and textural analyses (increase in specific surface area and decrease in pore size), Fourier transform infrared spectroscopy, and shift of the pH point of zero charge toward higher value. The sorption was mainly performed through carbonyl, thiocarbonyl, hydroxyl, and amine groups. Under selected experimental conditions, sorption equilibrium is reached in 40 min (faster than crosslinked chitosan, CH) and the kinetic profile is fitted by the pseudo-first order rate equation. The Langmuir equation finely fits sorption isotherms: the functionalization improves both the maximum sorption capacity and the affinity coefficient (by four to six folds). The benefit of the functionalization is also demonstrated by the improved stability of the sorbent at recycling (loss at the fifth cycle does not exceed 2 % for CH-PYZ, against 8 % for CH). The grafting of pyrazolinone derivative brings another advantage in terms of selectivity against other mono-, di- and tri- valent metal ions. The sorbent also preferentially sorbs mercury from groundwater collected in a contaminated area. Under selected experimental conditions, the sorbent allows decontaminating the collected sample for livestock feeding, but the treated water cannot reach the levels for human drinking water.

Discriminative Behavior of Cyclodextrin Polymers against Dissolved Organic Matter: Role of Cavity Size and Sorbate Properties.

Cyclodextrin polymers (CDPs) are promising next-generation adsorbents in water purification technologies. The selectivity of the polymer derivate cross-linked with tetrafluoroterephthalonitrile (TFN-CDP) for nonionic and cationic micropollutants (MPs) over dissolved organic matter (DOM) renders the adsorbent also attractive for many analytical applications. The molecular drivers of the observed selectivity are, nonetheless, not yet fully understood. To provide new insights into the sorption mechanism, we (i) synthesized TFN-CDPs with different cavity sizes (α-, β-, γ-CDP); (ii) assessed their extraction efficiencies for selected nonionic MPs in competition with different DOM size fractions (<1, 1-3, 3-10, >10 kDa) to test for size-selectivity; and (iii) performed nontargeted, ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry analysis on CDP-extracted DOM compounds (<1 kDa) to probe for molecular sorbate properties governing their selective sorption. First, no evidence of size-selectivity was obtained through either the different CD cavity sizes (i) or the two independent approaches (ii) and (iii). Second, we found a dominant impact of sorbate oxygenation and polarity on the extraction of DOM and MPs, respectively, with relatively oxygen-poor/nonpolar molecules favorably retained on all α-, β-, and γ-CDP. Third, our data indicates exclusion of an anionic matrix, such as carboxylic acids, but preferential sorption of cationic nitrogen-bearing DOM, pointing at repulsive and attractive forces with the negatively charged cross-linker as a likely reason. Therefore, we ascribe TFN-CDP's selectivity to nonpolar and electrostatic interactions between MPs/DOM and the polymer building blocks. These molecular insights can further aid in the optimization of efficient and selective sorbent design for environmental and analytical applications.