Search Results (11)

The transition to renewable energy makes energy storage crucial. Aqueous organic redox flow batteries (AORFBs) show great potential in large-scale energy storage due to their outstanding safety compared to conventional systems. Derivatives of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) show significant promise as catholyte materials in AORFBs. In this work, a bipyridine-ester dual-modified TEMPO derivative, (2,2,6,6-tetramethyl-1-piperidinyloxy)carbonyl-ethyl-(4-(pyridin-4-yl)benzyl) ammonium bromide (TEMP-BPy) was successfully synthesized via a two-step functionalization. The synthesized compound was experimentally confirmed to possess excellent electrochemical stability. The electron-withdrawing effect of the 4,4′-bipyridine moiety elevates the redox potential by 60 mV. When implemented as a catholyte paired with methyl viologen (MV) as the anolyte in AORFB, the TEMP-BPy/MV system demonstrates excellent performance: achieving a cell voltage of 1.28 V and an energy density of 14.5 Wh L⁻¹ at a 0.6 M (16.08 Ah L⁻¹) concentration with 71.3% material utilization. Notably, it demonstrates exceptional cycling stability with an average capacity retention of 99.86% per cycle over 200 cycles, and it exhibits particularly impressive initial stability, with an average capacity retention of 99.997% per cycle during the first 100 cycles. Full article

New 3D printing aerogel materials are environmentally friendly and could be used in environmental protection and biomedical fields. There is significant research interest in 3D printing cellulose-based aerogels since cellulose materials are biocompatible and are abundant in nature. The gel-like nature of the cellulose water suspension is suitable for 3D printing; however, the complexity and resolution of the geometry of aerogels are quite limited, mainly due to the inks’ low viscosity that fails to maintain the integrity of the shape after printing. To address this limitation, a carefully optimized formulation incorporating three key ingredients, i.e., nanofibrils (TEMPO-CNFs), 2,2,6,6-tetramethyl-1-piperidinyloxy modified cellulose nanocrystals (TEMPO-CNC), and sodium carboxymethyl cellulose (CMC), is utilized to enhance the viscosity and structural stability of the ink. This combination of cellulose derivatives utilizes the electrostatic repulsive forces between the negatively charged components to form a stable and uniformly distributed suspension of cellulose materials. Our ink formulations improve printability and shape retention during 3D printing and are optimal for DIW printing. We print by employing an all cellulose-based composite ink using a modified direct ink writing (DIW) 3D printing method, plus an in situ freezing stage to form a layer-by-layer structure, and then follow a freeze-drying process to obtain the well-aligned aerogels. We have investigated the rheological properties of the ink formulation by varying the concentration of these three cellulose materials. The obtained aerogels exhibit highly ordered microstructures in which the micropores are well-aligned along the freezing direction. This study demonstrates a strategy for overcoming the challenges of 3D printing cellulose-based aerogels by formulating a stable composite ink, optimizing its rheological properties, and employing a modified DIW printing process with in situ freezing, resulting in highly ordered, structurally robust aerogels with aligned microporous architectures. Full article

We report on the synthesis and characterization of Mn(III) chloride (Mn^IIICl₃) complexes coordinated with N-oxide ylide ligands, namely trimethyl-N-oxide (Me₃NO) and pyridine-N-oxide (PyNO). The compounds are reactive and, while isolable in the solid-state at room temperature, readily decompose into Mn(II). For example, “[Mn^IIICl₃(ONMe₃)_n]” decomposes into the 2D polymeric network compound complex salt [Mn^II(µ-Cl)₃Mn^II(µ-ONMe₃)]_n[Mn^II(µ-Cl)₃]_n·(Me₃NO·HCl)_3n (4). The reaction of Mn^IIICl₃ with PyNO forms varied Mn(III) compounds with PyNO coordination and these react with hexamethylbenzene (HMB) to form the chlorinated organic product 1-cloromethyl-2,3,4,5,6-pentamethylbenzene (8). In contrast to N-oxide coordination to Mn(III), the reaction between [Mn^IIICl₃(OPPh₃)₂] and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) resulted in electron transfer-forming d⁵ manganate of the [TEMPO] cation instead of TEMPO–Mn(III) adducts. The reactivity affected by N-oxide coordination is discussed through comparisons with other L–Mn^IIICl₃ complexes within the context of reduction potential. Full article

The spectral and dynamic properties of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in a series of 1-alkanols ranging from methanol to 1-decanol over a temperature range 100–300 K were investigated by electron spin resonance (ESR). The main characteristic ESR temperatures connected with slow to fast motion regime transition; T_50G ‘s and T_X1^fast ‘s are situated above the corresponding glass temperatures, T_g, and for the shorter members, the T_50G ‘s lie above or close to melting point, T_m, while the longer ones the T_50G < T_m relationship indicates that the TEMPO molecules are in the local disordered regions of the crystalline media. The T_50G ‘s and especially T_X1^fast ‘s are compared with the dynamic crossover temperatures, T_X^VISC = 8.72M^0.66, as obtained by fitting the viscosity data in the liquid n-alkanols with the empirical power law. In particular, for N_C > 6, the T_X1^fast ‘s lie rather close to the T_X^VISC resembling apolar n-alkanes [PCCP 2018,20,11145-11151], while for N_C < 6, they are situated in the vicinity of T_m. The absence of a coincidence for lower1-alkanols indicates that the T_50G is significantly influenced by the mutual interaction between the polar TEMPO and the protic polar medium due to the increased polarity and proticity destroyed by the larger-scale melting transition. Full article

Fiber-shaped dye-sensitized solar cells (FDSSCs) with flexibility, weavablity, and wearability have attracted intense scientific interest and development in recent years due to their low cost, simple fabrication, and environmentally friendly operation. Since the Grätzel group used the organic radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as the redox system in dye-sensitized solar cells (DSSCs) in 2008, TEMPO has been utilized as an electrolyte to further improve power conversion efficiency (PCE) of solar cells. Hence, the TEMPO with high catalyst oxidant characteristics was developed as a hybrid solid-state electrolyte having high conductivity and stability structure by being integrated with a lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) film for FDSSCs. The optimized 4-Oxo TEMPO (OX) based solid-state FDSSC (SS-FDSSC) showed the PCE of up to 6%, which was improved by 34.2% compared to that of the reference device with 4.47%. The OX-enhanced SS-FDSSCs reduced a series resistance (R_s) resulting in effective electron extraction with improved short-circuit current density (J_SC), while increasing a shunt resistance (R_sh) to prevent the recombination of photo-excited electrons. The result is an improvement in a fill factor (FF) and consequently a higher value for the PCE. Full article

Hydrogels have reached momentum due to their potential application in a variety of fields including their ability to deliver active molecules upon application of a specific chemical or physical stimulus and to act as easily recyclable catalysts in a green chemistry approach. In this paper, we demonstrate that the same redox-responsive hydrogels based on polymer networks containing 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) stable nitroxide radicals and oligoethylene glycol methyl ether methacrylate (OEGMA) can be successfully used either for the electrochemically triggered release of aspirin or as catalysts for the oxidation of primary alcohols into aldehydes. For the first application, we take the opportunity of the positive charges present on the oxoammonium groups of oxidized TEMPO to encapsulate negatively charged aspirin molecules. The further electrochemical reduction of oxoammonium groups into nitroxide radicals triggers the release of aspirin molecules. For the second application, our hydrogels are swelled with benzylic alcohol and tert-butyl nitrite as co-catalyst and the temperature is raised to 50 °C to start the oxidation reaction. Interestingly enough, benzaldehyde is not miscible with our hydrogels and phase-separate on top of them allowing the easy recovery of the reaction product and the recyclability of the hydrogel catalyst. Full article

To afford an intact double network (sample abbr.: DN) hydrogel, two-step crosslinking reactions of poly(2-acrylamido-2-methylpropanesulfonic acid) (i.e., PAMPS first network) and then poly(acrylic acid) (i.e., PAA second network) were conducted both in the presence of crosslinker (N,N′-methylenebisacrylamide (MBAA)). Similar to the two-step processes, different contents of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) oxidized cellulose nanofibers (TOCN: 1, 2, and 3 wt.%) were initially dispersed in the first network solutions and then crosslinked. The TOCN-containing PAMPS first networks subsequently soaked in AA and crosslinker and conducted the second network crosslinking reactions (TOCN was then abbreviated as T for DN samples). As the third step, various (T–)DN hydrogels were then treated with different concentrations of FeCl_3(aq) solutions (5, 50, 100, and 200 mM). Through incorporations of ferric ions into (T–)DN hydrogels, notably, three purposes are targeted: (i) strengthen the (T–)DN hydrogels through ionic bonding, (ii) significantly render ionic conductivity of hydrogels, and (iii) serve as a catalyst for the forth step to proceed with in situ chemical oxidative polymerizations of pyrroles to afford polypyrrole-containing (sample abbr.: Py) hydrogels [i.e., (T–)Py–DN samples]. The characteristic functional groups of PAMPS, PAA, and Py were confirmed by FT–IR. Uniform microstructures were observed by cryo scanning electron microscopy (cryo-SEM). These results indicated that homogeneous composites of T–Py–DN hydrogels were obtained through the four-step process. All dry samples showed similar thermal degradation behaviors from the thermogravimetric analysis (TGA). The T₂–Py₅–DN sample (i.e., containing 2 wt.% TOCN with 5 mM FeCl_3(aq) treatment) showed the best tensile strength and strain at breaking properties (i.e., σ_Tb = 450 kPa and ε_Tb = 106%). With the same compositions, a high conductivity of 3.34 × 10⁻³ S/cm was acquired. The tough T₂–Py₅–DN hydrogel displayed good conductive reversibility during several “stretching-and-releasing” cycles of 50–100–0%, demonstrating a promising candidate for bioelectronic or biomaterial applications. Full article

The recycled paper and board industry needs to improve the quality of their products to meet customer demands. The refining process and strength additives are commonly used to increase mechanical properties. Interfiber bonding can also be improved using cellulose nanofibers (CNF). A circular economy approach in the industrial implementation of CNF can be addressed through the in situ production of CNF using side cellulose streams of the process as raw material, avoiding transportation costs and reducing industrial wastes. Furthermore, CNF fit for use can be produced for specific industrial applications.This study evaluates the feasibility of using two types of recycled fibers, simulating the broke streams of two paper machines producing newsprint and liner for cartonboard, to produce in situ CNF for direct application on the original pulps, old newsprint (ONP), and old corrugated container (OCC), and to reinforce the final products. The CNF were obtained by 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-mediated oxidation and homogenization at 600 bar. Handsheets were prepared with disintegrated recycled pulp and different amounts of CNF using a conventional three-component retention system. Results show that 3 wt.% of CNF produced with 10 mmol of NaClO per gram of dry pulp improve tensile index of ONP ~30%. For OCC, the same treatment and CNF dose increase tensile index above 60%. In both cases, CNF cause a deterioration of drainage, but this effect is effectively counteracted by optimising the retention system. Full article

Cell viability studies for benzo[1,2,4]triazin-7-ones and 1,2,4-benzotriazinyl (Blatter-type) radical precursors are described with comparisons made with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). All of the stable free radicals were several orders of magnitude less cytotoxic than the benzo[1,2,4]triazin-7-ones. The synthesis and evaluation of two new pyrid-2-yl benzo[1,2,4]triazin-7-ones are described, where altering the 1,3-substitution from phenyl to pyrid-2-yl increased cytotoxicity against most cancer cell lines, as indicated using National Cancer Institute (NCI) one-dose testing. COMPARE analysis of five-dose testing data from the NCI showed very strong correlations to the naturally occurring anti-cancer compound pleurotin. COMPARE is program, which analyzes similarities in cytotoxicity data of compounds, and enables quantitative expression as Pearson correlation coefficients. Compounds were also evaluated using the independent MTT assay, which was compared with SRB assay data generated at the NCI. Full article

A novel and efficient oxidation of salicyl alcohols to the corresponding salicylaldehydes catalyzed by lipase is reported for the first time. Under the optimal reaction conditions, the method exhibited high yields (81–95%) and selectivities for salicylaldehydes. Moreover, this study expands the application of enzyme catalytic promiscuity in organic synthesis. Full article

Large quantities (>3 g) of a new series of alkyl uronates were synthesized in two steps from commercial methyl hexopyranosides. Firstly, several tens of grams of free methyl α-d-glucopyranoside were selectively and quantitatively oxidized into corresponding sodium uronate using 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO)-catalyzed oxidation. Hydrophobic chains of different length were then introduced by acid-mediated esterification with fatty alcohols (ethyl to lauryl alcohol) leading to the desired alkyl glucuronates with moderate to good yields (49%–72%). The methodology was successfully applied to methyl α-d-mannopyranoside and methyl β-d-galactopyranoside. Physicochemical properties, such as critical micelle concentration (CMC), equilibrium surface tension at CMC (γ_cmc), solubility, and Krafft temperature were measured, and the effect of structural modifications on surface active properties and micelle formation was discussed. Full article