Synthesis and characterization of fluorescent poly(α-cyclodextrin)/carbon quantum dots composite for efficient removal and detection of toluene and xylene from aqueous media.

This study reports the synthesis and characterization of a supramolecular composite comprised of carbon dots (CDots) embedded within net-poly[(α-cyclodextrin)-ν-(citric acid)] (α-CD/CA/CDots) for the removal and detection of toluene and xylene from aqueous media. The remarkable stability of CDots within the composite enables the preservation of photoluminescence properties for prolonged storage and extended UV-light irradiation. As demonstrated, following the adsorption of both organic compounds, the composite detected them in the aqueous medium due to a fluorescence quenching mechanism. Spectroscopic analyses reveal that the accessible Stern-Volmer quenching constants for toluene and xylene are KSVa = 15.4 M-1 and KSVa = 10.3 M-1, respectively. As a result, the α-CD/CA/CDots composite were sensitive to the tested volatile organic compounds (LODtoluene = 3.7 mg/L and LODxylene = 4.9 mg/L). Optimal conditions for toluene and xylene adsorption were found, allowing to achieve noticeable adsorption capabilities (qe(toluene) = 68.9 and qe(xylene) = 48.2 mg/g) and removal efficiencies exceeding 70%. Different characterization techniques confirmed the successful synthesis of the composite and elucidated the interaction mechanisms between the adsorbent and the tested compounds. In summary, the multifunctionality demonstrated by the α-CD/CA/CDots composite ranks it as an efficient and promising adsorbent and detection probe for this class of water contaminants.

Chitosan-Silica Composite Aerogel for the Adsorption of Cupric Ions.

A chitosan-silica hybrid aerogel was synthesized and presented as a potential adsorbent for the purification of cupric ion-contaminated media. The combination of the organic polymer (chitosan), which can be obtained from fishery wastes, with silica produced a mostly macroporous material with an average pore diameter of 33 µm. The obtained aerogel was extremely light (56 kg m-3), porous (96% porosity, 17 cm3 g-1 pore volume), and presented a Brunauer-Emmett-Teller surface area (SBET) of 2.05 m2 g-1. The effects of solution pH, aerogel and Cu(II) concentration, contact time, and counterion on cupric removal with the aerogel were studied. Results showed that the initial pH of the cation-containing aqueous solution had very little influence on the removal performance of this aerogel. According to Langmuir isotherm, this material can remove a maximum amount of ca. 40 mg of cupric ions per gram and the kinetic data showed that the surface reaction was the rate-limiting step and equilibrium was quickly reached (in less than one hour). Thus, the approach developed in this study enabled the recovery of waste for the preparation of a novel material, which can be efficiently reused in a new application, namely water remediation.

Chitosan-Based Beads Incorporating Inorganic-Organic Composites for Copper Ion Retention in Aqueous Solutions.

In recent years, there has been a challenging interest in developing low-cost biopolymeric materials for wastewater treatment. In the present work, new adsorbents, based on different types of chitosan (commercial, commercial chitin-derived chitosan and chitosan synthesized from shrimp shell waste) and inorganic-organic composites have been evaluated for copper ions removal. The efficacy of the synthesis of chitosan-based composite beads has been determined by studying various characteristics using several techniques, including FTIR spectroscopy, X-ray diffraction, porosimetry (N2 adsorption), and scanning electron microscopy (SEM). Adsorption kinetics was performed using different adsorption models to determine the adsorption behavior of the materials in the aqueous media. For all composite beads, regardless of the type of chitosan used, good capacity to remove copper ions from simulated waters was observed (up to 17 mg/g), which proves that the new materials hold potential for heavy metal retention. However, the adsorption efficiency was influenced by the type of chitosan used. Thus, for the series where commercial chitosan (CC) was used, the removal efficiency was approximately 29%; for the series with chitosan obtained from commercial chitin (SC), the removal efficiency was approximately 34%; for the series with chitosan enriched with CaCO3 (SH), the removal efficiency was approximately 52%.

State-of-the-Art Macromolecules in Portugal.

This Special Issue presents five contributions covering various topics, as it would be expected for an area as comprehensive and multidisciplinary as Macromolecules [...].

Click nanosponge - A novel amine-rich ß-cyclodextrin-based crosslinked polymer for heterogeneous catalysis.

Cyclodextrin-based nanosponges are promising materials for heterogeneous catalysis due to their inherent synthetic versatility, tunable porosity and nontoxicity. In this work, a primary amine-rich ß-cyclodextrin nanosponge was synthesized via click imine condensation reaction between 1,6-hexamethylamine-functionalized ß-cyclodextrin (CDAM) and glutaraldehyde (GLT) to afford CDGLAM, in mild conditions. The crosslinked polymer exhibited a BET surface area of 36.39 m2 g-1, an average pore diameter of 3.09 nm (as assessed by the BJH method), and thermal stability up to 253 °C. CDGLAM was tested as heterogeneous catalyst for the metal-free Henry and Knoevenagel reactions, between aromatic aldehydes and nitromethane or ethyl cyanoacetate, respectively, affording the products in moderate to very high yields. These results show the ease of preparation of ß-CD-based nanosponges from a green chemistry perspective, as well as their potential for future use in catalytic systems.

Crafting and Analyzing Multi-Structured Aramid Materials and Their Pyrolytic Transformations: A Comprehensive Exploration.

Gradient porous materials, particularly carbon-based materials, hold immense potential in the fields of batteries, energy storage, electrocatalysis, and sensing, among others, by synergistically combining the attributes associated with each pore size within a unified structural framework. In this study, we developed a gradient porous aramid (GP-Aramid) by incorporating cellulose acetate as a porosity promoter in the polymer casting solution in different proportions. These GP-Aramids were subsequently transformed into their pyrolyzed counterparts (GP-Pyramids), retaining their original structures while displaying diverse cellular or dense microstructures inherited from the parent aramid, as confirmed via scanning electron microscopy. X-ray diffraction spectra provided evidence of the conversion of aramids into carbonaceous materials. The materials showed structural defects observed through the intensity ratio of the G and D bands (ID/IG = 1.05) in the Raman spectra, while X-ray photoelectron spectra (XPS) revealed that the carbonization process yielded pyrolyzed carbon materials unusually rich in nitrogen (6%), oxygen (20%), and carbon (72%), which is especially relevant for catalysis applications. The pyrolyzed materials showed bulk resistivities from 5.3 ± 0.3 to 34.2 ± 0.6 depending on the meta- or para-orientation of the aramid and the porous structure. This work contributes to understanding these gradient porous aromatic polyamides' broader significance and potential applications in various fields.

Luminescent Papers with Asymmetric Complexes of Eu(III) and Tb(III) in Polymeric Matrices and Suggested Combinations for Color Tuning.

Complexes of lanthanide ions, such as Eu(III) (red light emission) and Tb(III) (green light emission), with proper ligands can be highly luminescent and color-tunable, also attaining yellow and orange emission under UV radiation. The ligands employed in this work were poly(sodium acrylate), working as polymeric matrix, and 1,10-phenanthroline, taking advantage of its antenna effect. Possibilities of color display were further enhanced by incorporating a cationic polyfluorene with blue emission. This strategy allowed for obtaining cyan and magenta, besides the aforementioned colors. Uncoated cellulose paper was impregnated with the resulting luminescent inks, observing a strong hypsochromic shift in excitation wavelength upon drying. Hence, while a cheap UV-A lamp sufficed to reveal the polyfluorene's blue emission, shorter wavelengths were necessary to visualize the emission due to lanthanide ions as well. The capacity to reveal, with UV-C radiation, a full-color image that remains invisible under natural light is undoubtedly useful for anti-counterfeiting applications. Furthermore, both lanthanide ion complexes and polyfluorenes were shown to have their luminescence quenched by Cu(II) ions and nitroarenes, respectively.

Engineering novel phenolic foams with lignin extracted from pine wood residues via a new levulinic-acid assisted process.

Phenolic foams are typically produced from phenolic resins, using phenol and formaldehyde precursors. Therefore, common phenolic foams are non-sustainable, comprising growing environmental, health, and economic concerns. In this work, lignin extracted from pine wood residues using a "green" levulinic acid-based solvent, was used to partially substitute non-sustainable phenol. The novel engineered foams were systematically compared to foams composed of different types of commercially available technical lignins. Different features were analyzed, such as foam density, microstructure (electron microscopy), surface hydrophilicity (contact angle), chemical grafting (infrared spectroscopy) and mechanical and thermal features. Overall, it was observed that up to 30 wt% of phenol can be substituted by the new type of lignin, without compromising the foam properties. This work provides a new insights on the development of novel lignin-based foams as a very promising sustainable and renewable alternative to petrol-based counterparts.

Levulinic Acid-Based "Green" Solvents for Lignocellulose Fractionation: On the Superior Extraction Yield and Selectivity toward Lignin.

The high potential use of lignin in novel biomaterials and chemicals represents an important opportunity for the valorization of the most abundant natural resource of aromatic molecules. From an environmental perspective, it is highly desirable replacing the hazardous methods currently used to extract lignin from lignocellulosic biomass and develop more sustainable and environmentally friendly approaches. Therefore, in this work, levulinic acid (a "green" solvent obtained from biomass) was successfully used, for the first time, to selectively extract high-quality lignin from pine wood sawdust residues at 200 °C for 6 h (at atmospheric pressure). Moreover, the addition of catalytic concentrations of inorganic acids (i.e., H2SO4 or HCl) was found to substantially reduce the temperature and reaction times needed (i.e., 140 °C, 2 h) for complete lignin extraction without compromising its purity. NMR data suggests that condensed OH structures and acidic groups are present in the lignin following extraction. Levulinic acid can be easily recycled and efficiently reused several times without affecting its performance. Furthermore, excellent solvent reusability and performance of extraction of other wood residues has been successfully demonstrated, thus making the developed levulinic acid-based procedure highly appealing and promising to replace the traditional less sustainable methodologies.

Reduced Chitosan as a Strategy for Removing Copper Ions from Water.

Toxic heavy metals are priority pollutants in wastewater, commonly present in dangerous concentrations in many places across the globe. Although in trace quantities copper is a heavy metal essential to human life, in excess it causes various diseases, whereby its removal from wastewater is a necessity. Among several reported materials, chitosan is a highly abundant, non-toxic, low-cost, biodegradable polymer, comprising free hydroxyl and amino groups, that has been directly applied as an adsorbent or chemically modified to increase its performance. Taking this into account, reduced chitosan derivatives (RCDs 1-4) were synthesised by chitosan modification with salicylaldehyde, followed by imine reduction, characterised by RMN, FTIR-ATR, TGA and SEM, and used to adsorb Cu(II) from water. A reduced chitosan (RCD3), with a moderate modification percentage (43%) and a high imine reduction percentage (98%), proved to be more efficient than the remainder RCDs and even chitosan, especially at low concentrations under the best adsorption conditions (pH 4, RS/L = 2.5 mg mL-1). RCD3 adsorption data were better described by the Langmuir-Freundlich isotherm and the pseudo-second-order kinetic models. The interaction mechanism was assessed by molecular dynamics simulations, showing that RCDs favour Cu(II) capture from water compared to chitosan, due to a greater Cu(II) interaction with the oxygen of the glucosamine ring and the neighbouring hydroxyl groups.

Triazine-Based Porous Organic Polymers: Synthesis and Application in Dye Adsorption and Catalysis.

The scientific community has been developing promising materials to increase the sustainability and efficiency of production processes and pollutant environmental remediation strategies. Porous organic polymers (POPs) are of special interest, as they are insoluble custom-built materials at the molecular level, endowed with low densities and high stability, surface areas, and porosity. This paper describes the synthesis, characterization, and performance of three triazine-based POPs (T-POPs) in dye adsorption and Henry reaction catalysis. T-POPs were prepared by a polycondensation reaction between melamine and a dialdehyde (terephthalaldehyde (T-POP1) or isophthalaldehyde derivatives with a hydroxyl group (T-POP2) or both a hydroxyl and a carboxyl group (T-POP3)). The crosslinked and mesoporous polyaminal structures, with surface areas between 139.2 and 287.4 m2 g-1, positive charge, and high thermal stability, proved to be excellent methyl orange adsorbents, removing the anionic dye with an efficiency >99% in just 15-20 min. The POPs were also effective for methylene blue cationic dye removal from water, reaching efficiencies up to ca. 99.4%, possibly due to favorable interactions via deprotonation of T-POP3 carboxyl groups. The modification of the most basic polymers, T-POP1 and T-POP2, with copper(II) allowed the best efficiencies in Henry reactions catalysis, leading to excellent conversions (97%) and selectivities (99.9%).

Interactions of Sodium Salicylate with ß-Cyclodextrin and an Anionic Resorcin[4]arene: Mutual Diffusion Coefficients and Computational Study.

The interaction between sodium salicylate (NaSal) and the two macrocycles 5,11,17,23-tetrakissulfonatomethylene-2,8,14,20-tetra(ethyl)resorcinarene (Na4EtRA) and ß-cyclodextrin (ß-CD) has been studied by the determination of ternary mutual diffusion coefficients, and spectroscopic and computational techniques. The results obtained by the Job method suggest that the complex formation is given in a 1:1 ratio for all systems. The mutual diffusion coefficients and the computational experiments have shown that the ß-CD-NaSal system presents an inclusion process, whereas the Na4EtRA-NaSal system forms an outer-side complex. This fact is also in line with the results obtained from the computational experiments, where the calculated solvation free energy has been found to be more negative for the Na4EtRA-NaSal complex because of the partial entry of the drug inside the Na4EtRA cavity.

Interactions between Sodium Hyaluronate and ß-Cyclodextrin as Seen by Transport Properties.

Knowledge of mass transport parameters, diffusion, and viscosity of hyaluronic acid (HA) in the presence of cyclodextrins is of considerable importance for areas such as food packaging and drug delivery, among others. Despite a number of studies investigating the functionalization of HA or the corresponding sodium salt by cyclodextrins, only a few studies have reported the effect of cyclodextrins on the mass transport of HA in the presence of these oligosaccharides. Here, we report the tracer binary and ternary interdiffusion coefficients of sodium hyaluronate (NaHy) in water and aqueous ß-cyclodextrin solutions. The diffusion behavior of sodium hyaluronate was dependent on the reduced viscosity of NaHy, which, in turn, presented a concave dependence on concentration, with a minimum at approximately 2.5 g dm-3. The significant decrease in the limiting diffusion coefficient of NaHy (at most 45%) at NaHy concentrations below 1 g dm-3 in the presence of ß-cyclodextrin, taking water as the reference, allowed us to conclude that NaHy strongly interacted with the cyclodextrin.

Straightforward purification method for the determination of the activity of glucose oxidase and catalase in honey by extracting polyphenols with a film-shaped polymer.

Glucose oxidase (GOX) and catalase (CAT) regulate the amount of H2O2 in honey, by generating or consuming it, so they are related to the antibacterial and antioxidant activity of honey. However, their activities are hardly analysed, since the process requires a previous dialysis that is non-selective, very time-consuming (>24 h), eco-unfriendly (>6L of buffer) and expensive. This research shows the design and performance of a material that selectively removes the actual interferents. The film-shaped-polymer is immersed for 90́ within a honey solution (12.5 mL of buffer), where it interacts exclusively with 1,2-dihydroxybenzenes, which we proved to be the real interferents (the material contains motifs derived from phenylboronic acid to interact with 1,2-diols). Polymeric chains favour condensation to occur exclusively with 1,2-dihydroxybenzenes, excluding monosaccharides. The interferents' removal using our designed polymer is selective, low cost (1.42€ per test), rapid and eco-friendly (saves 6L of buffer and 20.5 h of experimental workout per sample).

Nanostructuring with Surfactants: The Self-Assembly of a New Poly(thiophene-phenylene) Conjugated Polymer Bearing Azacrown Ether Pendant Groups.

We report the synthesis of a new conjugated polymer bearing crown ether moieties, poly[(N(1-aza-[18]crown-6)carbamido)thiophene-2,5-diyl-alt-1,4-phenylene] (BG2). In water, BG2 forms a dispersion with a slightly cloudy appearance. We have studied the effect of adding surfactants, with different polar head groups, on these polymer-polymer aggregates. Special attention is given to the system with the anionic surfactant, sodium dodecyl sulfate (SDS). The combination of photophysical techniques with electrical conductivity, NMR (1H, 13C, and 27Na), DFT calculations, molecular dynamics simulations, and small-angle neutron scattering (SANS) provides a detailed picture on the behavior of the SDS/BG2 system in aqueous solution and in thin films. NMR, electric conductivity, and DFT results suggest that hydrophilic interactions occur between the polar headgroup of the surfactant (OSO3- Na+) and the aza-[18]-crown-6 moiety. DFT calculations confirmed the capability of BG2 to form stable complexes with the Na+ cations, where the cation can be either inside the azacrown cavity or sandwiched between the cavity and the polymer chain, which seem to determine the position of the surfactant hydrocarbon chain and, therefore, be responsible for the disruption of the BG2 aggregates and subsequent increase in the photoluminescence quantum yields. SANS measurements, made with hydrogenated and deuterated SDS in D2O, clearly show how micron-sized aggregates of BG2 are broken down by SDS and then how BG2 becomes preferentially incorporated within joint colloidal particles of BG2 and SDS with increasing [SDS]/[BG2] molar ratio.

Synthesis of ß-cyclodextrin-based nanosponges for remediation of 2,4-D polluted waters.

Two cyclodextrin-based nanosponges (CD-NSs) were synthesized using diamines with 6 and 12 methylene groups, CDHD6 and CDHD12, respectively, and used as adsorbents to remove 2,4-D from aqueous solutions. The physico-chemical characterization of the CD‒NSs demonstrated that, when using the linker with the longest chain length, the nanosponges show a more compact structure and higher thermal stability, probably due to hydrophobic interactions. SEM micrographs showed significant differences between the two nanosponges used. The adsorption of 2,4-D was assessed in terms of different parameters, including solid/liquid ratio, pH, kinetics and isotherms. Adsorption occurred preferentially at lower pH values and for short-chain crosslinked nanosponges; while the former is explained by the balance of acid-base characteristics of the adsorbent and adsorbate, the latter can be justified by the increase in the crosslinker-crosslinker interactions, predominantly hydrophobic, rather than adsorbent-adsorbate interactions. The maximum adsorption capacity at the equilibrium (qe) was 20,903 mmol/kg, obtained using CDHD12 with an initial 2,4-D concentration of 2 mmol/L. An environmentally friendly strategy, based on alkali desorption, was developed to recycle and reuse the adsorbents. On the basis of the results obtained, cyclodextrin-based nanosponges appear promising materials for an economically feasible removal of phenoxy herbicides, to be used as potential adsorbents for the sustainable management of agricultural wastewaters.

ß-Ketoenamine Covalent Organic Frameworks-Effects of Functionalization on Pollutant Adsorption.

Water pollution due to global economic activity is one of the greatest environmental concerns, and many efforts are currently being made toward developing materials capable of selectively and efficiently removing pollutants and contaminants. A series of ß-ketoenamine covalent organic frameworks (COFs) have been synthesized, by reacting 1,3,5-triformylphloroglucinol (TFP) with different C2-functionalized and nonfunctionalized diamines, in order to evaluate the influence of wall functionalization and pore size on the adsorption capacity toward dye and heavy metal pollutants. The obtained COFs were characterized by different techniques. The adsorption of methylene blue (MB), which was used as a model for the adsorption of pharmaceuticals and dyes, was initially evaluated. Adsorption studies showed that -NO2 and -SO3H functional groups were favorable for MB adsorption, with TpBd(SO3H)2-COF [100%], prepared between TFP and 4,4'-diamine- [1,1'-biphenyl]-2,2'-disulfonic acid, achieving the highest adsorption capacity (166 ± 13 mg g-1). The adsorption of anionic pollutants was less effective and decreased, in general, with the increase in -SO3H and -NO2 group content. The effect of ionic interactions on the COF performance was further assessed by carrying out adsorption experiments involving metal ions. Isotherms showed that nonfunctionalized and functionalized COFs were better described by the Langmuir and Freundlich sorption models, respectively, confirming the influence of functionalization on surface heterogeneity. Sorption kinetics experiments were better adjusted according to a second-order rate equation, confirming the existence of surface chemical interactions in the adsorption process. These results confirm the influence of selective COF functionalization on adsorption processes and the role of functional groups on the adsorption selectivity, thus clearly demonstrating the potential of this new class of materials in the efficient and selective capture and removal of pollutants in aqueous solutions.

Micro-/Nanofibrillated Cellulose-Based Coating Formulations: A Solution for Improving Paper Printing Quality.

The use of micro-/nanofibrillated celluloses (M/NFCs) is often considered for the enhancement of paper properties, while it is still challenging to use them in lower weight gain coatings. This work explores how they might be used on the paper surface to improve the printing quality. In this regard, M/NFCs were produced using different pre-treatment methods, including mechanical (m-MFC), enzymatic (e-MFC), TEMPO-mediated oxidation (t-NFC) and cationization (c-NFC), and uniform coating formulations were developed through the cooking of starch and M/NFCs simultaneously. The formulations, at 6-8% of total solid concentration, were applied to the paper surface by roll coating, resulting in a dry coating weight of 1.5 to 3 g/m2. Besides M/NFCs, other components such as starch betainate (a cationic starch ester; SB), Pluronics® (a triblock co-polymer), precipitated calcium carbonate (PCC) and betaine hydrochloride (BetHCl) were also used in the M/NFC-based coating formulations to observe their combined influence on the printing quality. The presence of M/NFCs improved the paper printing quality, which was further enhanced by the increase in cationic charge density due to the presence of BetHCl/SB, and also by Pluronics®. The cationic charge of c-NFC was also found to be effective for improving the gamut area and optical density of coated papers, whereas whiteness was often reduced due to the quenching of the brightening agent. BetHCl, on the other hand, improved the printing quality of the coated papers, even though it was more effective when combined with M/NFCs, PCC and Pluronics®, and also helped to retain paper whiteness.

Diffusion of Vanadium Ions in Artificial Saliva and Its Elimination from the Oral Cavity by Pharmacological Compounds Present in Mouthwashes.

In this study, diffusion coefficients of ammonium vanadate at tracer concentrations in artificial saliva with and without sodium fluoride, at different pH values, were measured using an experimental model based on the Taylor dispersion technique. Ternary mutual diffusion coefficients (D11, D22, D12, and D21) for four aqueous systems {NH4VO3 (component 1) + ß-cyclodextrin (ß-CD) (component 2),} {NH4VO3 (component 1) + ß-cyclodextrin (HP-ß-CD) (component 2)}, {NH4VO3 (component 1) + sodium dodecyl sulphate (SDS) (component 2)} and {NH4VO3 (component 1) + sodium hyaluronate (NaHy) (component 2)} at 25.00 °C were also measured by using the same technique. These data showed that diffusion of ammonium vanadate was strongly affected in all aqueous media studied. Furthermore, a significant coupled diffusion of this salt and ß-CD was observed through the non-zero values of the cross-diffusion coefficients, D12, allowing us to conclude that there is a strong interaction between these two components. This finding is very promising considering the removal, from the oral cavity, of vanadium resulting from tribocorrosion of Ti-6Al-4V prosthetic devices.