The 2,2,6,6-tetramethylpiperidine-1-oxyl Research Articles

Morphological engineering of PTAm@CNTs cathode for high-rate potassium dual-ion battery

Redox-active polymers are regarded as one of the most promising electroactive materials for non-lithium electrochemical energy storage devices due to the inherent molecular flexibility that can tolerate the structure change during the charge/discharge process. Their diverse functional groups provide abundant active sites to accommodate large-sized electrolyte ions. In this work, for the first time, the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical group, equipped at poly(TEMPO-acrylamide) (PTAm), is employed as an active cathode for potassium dual-ion batteries (KDIBs). Carbon nanotubes (CNTs) assist morphological engineering of the PTAm to create a conductive nanostructured composite, namely PTAm@CNTs. Systematic material characterizations and electrochemical evaluation suggest that the PTAm@CNTs nanocomposite possesses significant surface area and nanopores, enabling enhanced electronic and ionic conductivity. The PTAm@CNTs cathode reversibly stores hexafluorophosphate (PF6−) anions in KDIBs, delivering high energy density, rate capability, and robust cycling stability. The fast reaction kinetics of nitroxide radicals (N–O.), the redox-active groups on the PTAm, and their association with the PF6− anions contribute to the dual-ion storage. As a result, the PTAm@CNTs cathode delivers a high specific capacity of 108 mAh g−1 at 2 A g−1 (16.8C) over 300 cycles. The work suggests a promising pathway to design and synthesize functional organic electrode materials for potassium dual-ion batteries.

Electrocatalytic Poly(3,4-ethylenedioxythiophene) for Electrochemical Conversion of 5-Hydroxymethylfurfural.

This study investigates the utilization of the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) as a catalytic material for the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). PEDOT films doped with different counterions were electrodeposited on graphite foil. In particular, the mobile anion perchlorate and the polymeric ionomers polystyrenesulfonate, Nafion, and Aquivion were used. The electrocatalytic properties of PEDOT films were evaluated toward the TEMPO redox mediator in the absence and the presence of HMF as a substrate for oxidation reactions. The electrocatalytic HMF oxidation was confirmed to occur at PEDOT electrodes, and it was also found that the chemical nature of PEDOT counterions controls the electrocatalytic conversion of HMF by modulating the kinetics of the electrochemical generation of the oxoammonium cation TEMPO(+). Potentiostatic electrolysis experiments showed that both the reference graphite electrode and PEDOT substrates were able to convert HMF to FDCA with an 80% faradaic efficiency (FE) and a >90% yield (FDCA), but, compared to graphite, the complete conversion of HMF to FDCA required a ca. 30% shorter time when using PEDOT electrodes doped with perchlorate or Aquivion, thanks to their ability to sustain a higher current density in the initial phase of the electrolysis. In addition, while all PEDOT films were chemically stable under the electrochemical conditions herein described, only PEDOT films doped with Aquivion were also mechanically robust and stable against delamination. Thus, the new PEDOT/Aquivion composite may represent the best choice for the implementation of PEDOT-based electrodes in TEMPO-mediated electrocatalytic applications.

Preparation of Silver Nanoparticles Deposited on TEMPO-Oxidized Cellulose Nanofibers

Silver nanoparticles (AgNPs) were synthesized by a chemical method in which cellulose nanofibers (CNFs) extracted from pineapple leaves served as a stabilizing and reducing agent. In this study, pineapple leaves were oxidized by the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation with sodium hypochlorite (NaClO) to obtain CNFs. After the oxidation, the transformation from hydroxyl groups to carboxylate groups of cellulose was confirmed by Fourier-transform infrared spectroscopy (FTIR), and TEMPO-oxidized CNFs with a higher carboxylate content were obtained. Then, TEMPO-oxidized CNFs with a carboxylate content of 2.49 mmol/g and non-oxidized CNFs with a carboxylate content of 0.68 mmol/g were used as a reducing agent to synthesize AgNPs. The formation of AgNPs was confirmed by color changes of the Ag solutions from white to yellow. Furthermore, AgNPs with an average diameter of 76.5 ± 22.15 nm were obtained when TEMPO-oxidized CNFs were used as a reducing agent, while non-oxidized CNFs generated AgNPs with a larger particle size of 181.2 ± 66.16 nm. This suggested that the TEMPO-oxidized CNFs could be used as a stabilizing and reducing agent for the synthesis of AgNPs with smaller diameters.

Nitrogen and sulfur doped carbon dots coupled cellulose nanofibers: A surface functionalized nanocellulose membranes for air filtration

BackgroundThe current study demonstrates a process to produce a hybrid bio-organic cellulose nanofiber (CNF) membrane with high filtration performance and mechanical strength. This was accomplished by 1) tailoring the functional groups of CNFs, notably using the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical oxidation and 2) coupling them with carbon dots (CDs). MethodsThe surface chemistry of CNF was modified through TEMPO oxidation. Subsequently, a coupling reaction was conducted with CDs synthesized hydrothermally, as well as synthesized N/S-CDs derived from palm bunch. The impact of these modifications on the formation of air filters was investigated. Modification and coupling of surface modified CNF were evaluated by advanced analytical techniques. The toxicity of pristine and N/S-CDs coupled cellulose nanofibers was studied by cytotoxicity assay. Vacuum filtration and sequential compression molding techniques were applied to fabricate CNF filters, and the particle filtration efficiency of different filters was determined. Significant findingsThe coupling of N/S-CDs to CNF significantly enhanced the tensile strength of the membranes. Coupling of N/S-CDs to TEMPOCNF membrane showed the highest tensile strength (9.3 ± 1.9 MPa), while N/S-CDs coupling to CNF membrane exhibited slightly lower tensile strength (9.0 ± 1.3 MPa). The average pore diameter of the filters was slightly reduced after the CNF surface modification, which led to higher differential pressure across the filters. Both the pristine and TEMPO-modified CNF filters displayed high filtration efficiency for 0.3 μm-aerosol particles (∼70–81 %) and 0.1 μm-aerosol model particles (∼50–68 %), which was in a range of bacteria and viruses. This study provided detailed information about the fabrication of modified CNF filters with high air filtration efficiency for micro/nano-sized particles using cost-effective biodegradable raw materials.

Preparation and Characterization of Carrot Nanocellulose and Ethylene/Vinyl Acetate Copolymer-Based Green Composites

This study aims to investigate the effect of nanocellulose on the properties and physical foaming of ethylene/vinyl acetate (EVA) copolymer. The nanocellulose is prepared from waste carrot residue using the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation method (CT) and is further modified through suspension polymerization of methyl methacrylate (MMA) monomer (CM). The obtained nanocellulose samples (CT or CM) are added to EVA to create a series of nanocomposites. Moreover, the EVA and CM/EVA composite were further foamed using supercritical carbon dioxide physical foaming. TEM results show that the average diameters of CT and CM are 24.35 ± 3.15 nm and 30.45 ± 1.86 nm, respectively. The analysis of mechanical properties demonstrated that the tensile strength of pure EVA increased from 10.02 MPa to 13.01 MPa with the addition of only 0.2 wt% of CM. Furthermore, the addition of CM to EVA enhanced the melt strength of the polymer, leading to improvements in the physical foaming properties of the material. The results demonstrate that the pore size of the CM/EVA foam material is smaller than that of pure EVA foam. Additionally, the cell density of the CM/EVA foam material can reach 3.23 × 1011 cells/cm3.

Highly Soluble TEMPO‐Viologen Bipolar Molecule for Ultra‐Stable Aqueous Redox Flow Batteries

AbstractBipolar redox‐active organic molecule (BROM) is a feasible strategy to address the cross‐contamination issue of the electrolyte and, thus, improve the stability of the flow battery. Herein, a highly‐soluble BROM is developed by combining the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) and viologen moieties, and extensive characterizations are performed to evaluate its applicability in flow battery. Salient findings are as follows. First, the compound, viz. 1‐(1‐oxyl‐2,2,6,6‐tetramethylpiperidin‐4‐yl)‐1′‐(3‐(trimethylammonio)propyl)‐4,4′‐bipyridinium trichloride ((TPABPy)Cl3), features highly hydrophilic groups and yields a high aqueous solubility of 1.76 m. Second, the electrochemical result reveals that the (TPABPy)Cl3 displays two pairs of highly reversible peaks at −0.56 and 0.76 V, which respectively correspond to the viologen and TEMPO moieties. The electronic structure during the redox reactions is identified by both the density functional theory calculation and the electron paramagnetic resonance. Third, the flow battery fed with the 1.0 m (TPABPy)Cl3 solution delivers a high capacity of 25 Ah L−1 and a superior stability over the non‐bipolar counterparts. More to the point, the capacity decay can be effectively recovered by applying the polarity‐inversion rebalance strategy on the BROM. In summary, this work provides a molecular engineering way to rationally design a BROM to improve the capacity and stability of aqueous organic redox flow batteries.

Electrochemical Properties and Local Structure of the TEMPO/TEMPO+ Redox Pair in Ionic Liquids.

Redox-active organic species play an important role in catalysis, energy storage, and biotechnology. One of the representatives is the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical, used as a mediator in organic synthesis and considered a safe alternative to heavy metals. In order to develop a TEMPO-based system with well-controlled electrochemical and catalytic properties, a reaction medium should be carefully chosen. Being highly conductive, stable, and low flammability fluids, ionic liquids (ILs) seem to be promising solvents with easily adjustable physical and solvation properties. In this work, we give an insight into the local structure of ILs around TEMPO and its oxidized form, TEMPO+, underlining striking differences in the solvation of these two species. The analysis is coupled with a study of thermodynamics and kinetics of oxidation in the frame of Marcus theory. Our systematic investigation includes imidazolium, pyrrolydinium, and phosphonium families combined with anions of different size, polarity, and flexibility, opting to provide a clear and comprehensive picture of the impact of the nature of IL ions on the behavior of radical/cation redox pairs. The obtained results will help to explain experimentally observed effects and to rationalize the design of TEMPO/IL systems.

Isolation and Characterization of Cellulose Nanofibers from Wheat Straw and Their Application for the Supercapacitor

As a by-product of wheat planting, wheat straw is an abundant agricultural residue with the highest cellulose content of all agricultural fibers. Its resourceful utilization contributes to alleviating the environmental problems it caused. In this study, cellulose from wheat straw (WS) is used as a dispersing agent to prepare a novel multi-walled carbon nanotube-modified nickel foam (NF) electrode. The new electrode is investigated for electrochemical properties relevant to supercapacitors. The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation is chosen to produce cellulose nanofibers (CNF) from wheat straw. The prepared CNF is used to facilitate the uniform dispersion of multi-walled carbon nanotubes (MWCNT) and favor the formation of a stable CNF-CNTs membrane on the nickel foam skeleton. The influence of dispersing materials and content of CNF on the electrochemical performance of electrodes is investigated. It is revealed that the incorporation of CNF can improve the electrochemical stability of electrodes. Moreover, it also exhibits optimum capabilities (70.2% capacitance retention from 1 to 40 mA cm−2) when CNF:MWCNT = 1:0.7. The areal capacity of the CNF-MWCNT/NF electrode for a scanning rate of 5 mV s−1 is twice that of the MWCNT/NF electrode and 30 times that of the NF electrode, indicating it is a promising candidate to ensure the synchronization of a green environment and energy development.

Comparison of pre-treatments mediated by endoglucanase and TEMPO oxidation for eco-friendly low-cost energy production of cellulose nanofibrils.

Specific kinds of enzymes have been used as an eco-friendly pre-treatment for mechanical extraction of cellulose nanofibrils (CNFs) from vegetal pulps. Another well-established pre-treatment is the 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-mediated oxidation, which has gained considerable attention. Pre-treatments assist in fiber swelling, facilitating mechanical fibrillation, and reducing energy consumption; however, some of these methods are extremely expensive. This work aimed to evaluate the influence of enzymatic pre-treatment with endoglucanase on the energy consumption during mechanical fibrillation of cellulose pulps. Bleached pulps from Eucalyptus sp. and Pinus sp. were pre-treated with endoglucanase enzyme compared to TEMPO-meditated oxidation. Average diameters of CNFs pre-treated with enzymes were close to that found for TEMPO-oxidized nanofibrils (TOCNFs). Results showed that enzymatic pre-treatment did not significantly modify the pulp chemical and morphological characteristics with efficient stabilization of the CNFs suspension at higher supernatant turbidity. Energy consumption of pulps treated with endoglucanase enzymes was lower than that shown by pulps treated with TEMPO, reaching up to 58% of energy savings. The enzyme studied in the pulp treatment showed high efficiency in reducing energy consumption during mechanical fibrillation and production of films with high mechanical quality, being an eco-friendly option for pulp treatment.

Highly efficient and low pollution catalytic oxidation of ramie degumming by NHPI

A new ramie degumming method, N-Hydroxyphthalimide (NHPI) catalytic oxidation degumming method (NCODM), was proposed to solve the environmental pollution problems as well as the energy consumption problems of the traditional alkaline degumming method (TADM) and the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation degumming method (TODM). In this paper, the effect of parameters on the properties of ramie fibers degummed by NCODM was investigated. Then, the degumming process was optimized by comparing with the different degumming methods using central composite design method. The results showed that the H2O2 concentration and reaction time were significant factors that determined the properties of ramie fibers. The optimum H2O2 concentration was 16.70 g/L and the optimum reaction time was 19.38 min. The time required for NCODM was only 79.38 min, which was 26.46% and 62.19% of that of TADM (300 min) and TODM (127.64 min), respectively. Moreover, the chemical oxygen demand (COD) value of the wastewater from NCODM was 31% and 3% lower than that of TADM and TODM, respectively. Therefore, NCODM has great potential to replace the TADM and TODM for ramie degumming.

The location of TEMPO moiety of TEMPO-PC is membrane phase-dependent

TEMPO-PC is a nitroxide spin-labeled lipid in which the 2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPO) group is covalently attached to the choline head group of phosphatidylcholine (PC). TEMPO-PC has been utilized to interpret the dynamics of water molecules near membrane surfaces in electron resonance spectroscopy as well as to assess the penetration depth of water molecules through the membranes. Because of an amphiphilic character of TEMPO moiety, and the flexibility of lipid molecules, the depth distribution of TEMPO moiety is potentially affected by the lipid type and the phase of bilayer membranes.

Facile Single-step Preparation of Cellulose Nanofibers by TEMPO-mediated Oxidation and Their Nanocomposites

ABSTRACT Water hyacinth (Eichhornia crassipes) with a lignin concentration of 4.15% was directly oxidized by the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation without any pre-treatments (alkaline and bleaching). After oxidation, TEMPO-oxidized cellulose nanofibers (CNFs) with widths between 5 and 10 nm were successfully disintegrated. The improvement in crystallinity associated with the decrease in thermal properties was observed for TEMPO-oxidized CNFs in comparison with those features of the untreated fibers. Most lignin was eliminated after the oxidation while the remaining of hemicellulose was observed in the treated nanofibers. The transformation from hydroxyl groups to sodium carboxylic groups was confirmed by Fourier-transform infrared spectroscopy. The application of the prepared TEMPO-oxidized CNFs in ethylene vinyl acetate copolymer (EVA) nanocomposites was studied, and results showed that no degradation in the light transmittance and thermal properties was observed with the introduction of TEMPO-oxidized CNFs. The improvement of ~30% for tensile modulus was noticeable with the incorporation of 1 wt% TEMPO-oxidized CNFs while the tensile strain of the nanocomposites was close to that of the neat EVA films. CNFs from lignin-poor water hyacinth using the direct TEMPO-oxidation process would be a candidate to replace wood-derived CNFs for specific applications such as composites, coatings, packaging and electronic devices.

Facile preparation of cellulose nanofibers prepared by TEMPO-mediated oxidation

Cellulose nanofibers (CNFs) with width of 20 nm and lengths of up to several µm were fully disintegrated from water hyacinth (Eichhornia crassipes) with aids of the 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation and mild-mechanical treatment. TEMPO-oxidized CNFs were characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). FTIR reveals the conversion of C-6 hydroxyl groups to sodium carboxylate groups, and lower thermal degradation was obtained from the TEMPO-oxidized CNFs in comparison to untreated cellulose fibers. The as-prepared TEMPO-oxidized CNFs might be possibly used in packaging and composite applications.

Developing chitin nanocrystals for flexible packaging coatings

This study assessed the applicability of chitin nanocrystals employed in combination with an existing coating material intended for flexible packaging. The 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) oxidized chitin nanocrystals (TOCNs) were applied 1) as an additive in a water-based acrylic resin (WBAR) that was then coated onto the surface of a biaxially oriented polypropylene (BOPP) film, and 2) as a neat layer in multilayered BOPP laminates bonded by a WBAR adhesive layer. The results indicated that the flow behavior and shear viscosity of the TOCN/WBAR system were dependent on TOCN contents. The TOCNs as a dispersed phase in the acrylic resin matrix did not improve the oxygen barrier property of the resulting coated BOPP. By contrast, the neat continuous TOCN coating layer improved the oxygen barrier property of the laminates of BOPP and TOCNs bonded by the acrylic resin, a 44% oxygen transmission rate reduction for a laminate with a 8.33-μm TOCN layer compared to the laminate without a TOCN layer. The inclusion of the TOCNs maintained the optical transparency of the resulting films.

Nanocellulose-Reinforced Polyurethane for Waterborne Wood Coating.

With the enhancement of people’s environmental awareness, waterborne polyurethane (PU) paint—with its advantages of low release of volatile organic compounds (VOCs), low temperature flexibility, acid and alkali resistance, excellent solvent resistance and superior weather resistance—has made its application for wood furniture favored by the industry. However, due to its lower solid content and weak intermolecular force, the mechanical properties of waterborne PU paint are normally less than those of the traditional solvent-based polyurethane paint, which has become the key bottleneck restricting its wide applications. To this end, this study explores nanocellulose derived from biomass resources by the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation method to reinforce and thus improve the mechanical properties of waterborne PU paint. Two methods of adding nanocellulose to waterborne PU—chemical addition and physical blending—are explored. Results show that, compared to the physical blending method, the chemical grafting method at 0.1 wt% nanocellulose addition results in the maximum improvement of the comprehensive properties of the PU coating. With this method, the tensile strength, elongation at break, hardness and abrasion resistance of the waterborne PU paint increase by up to 58.7%, ~55%, 6.9% and 3.45%, respectively, compared to the control PU; while the glossiness and surface drying time were hardly affected. Such exploration provides an effective way for wide applications of water PU in the wood industry and nanocellulose in waterborne wood coating.

4-Acetamido-TEMPO-Mediated Oxidation of Wood Chips and Thermomechanical Pulp in Large Scale

The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation was mainly studied in laboratory scale and needs to be scaled-up for any future industrial implantation. With this objective, the...

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells.

Novel caged nitroxides (nitroxide donors) with near-infrared two-photon (TP) responsive character, 2,2,6,6-tetramethyl-1-(1-(2-(4-nitrophenyl)benzofuran-6-yl)ethoxy)piperidine (2a) and its regioisomer 2b, were designed and synthesized. The one-photon (OP) (365 ± 10 nm) and TP (710–760 nm) triggered release (i.e., uncaging) of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical under air atmosphere were discovered. The quantum yields for the release of the TEMPO radical were 2.5% (2a) and 0.8% (2b) in benzene at ≈1% conversion of 2, and 13.1% (2a) and 12.8% (2b) in DMSO at ≈1% conversion of 2. The TP uncaging efficiencies were determined to be 1.1 GM at 740 nm for 2a and 0.22 GM at 730 nm for 2b in benzene. The cytocidal effect of compound 2a on lung cancer cells under photolysis conditions was also assessed to test the efficacy as anticancer agents. In a medium containing 100 μg mL−1 of 2a exposed to light, the number of living cells decreased significantly compared to the unexposed counterparts (65.8% vs 85.5%).

Synthesis of a protected ribonucleoside phosphoramidite-linked spin label via an alkynyl chain at the 5′ position of uridine

New, spin-labeled nucleosides, and an efficient synthetic route for a modified uridine amidite, were developed. The spin-labeled part was the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) group, which was linked via an alkynyl chain at the 5 position of uridine. Three typical protecting groups, the t-butyldimethylsilyl (TBDMS) group at 2′, the dimethoxytrityl (DMTr) group at 5′, and the phosphoramidite group at 3′, were introduced to produce an automated nucleic acid synthesizer. The TEMPO group at the 5 position in the uridine structure affected introduction of bulky protecting groups, such as the DMTr group at the 5′ position and the TBDMS group at the 2′ position. The electron paramagnetic resonance (EPR) data revealed a nitroxyl radical in the structure of synthetic nucleoside compounds; however, RNA produced by automated synthesis using a TEMPO-linked uridine phosphoramidite building block was EPR silent.

Inhibition effects of flavonoids on 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline and 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline formation and alkoxy radical scavenging capabilities of flavonoids in a model system.

Heterocyclic aromatic amines (HAAs) have been considered as carcinogenic and mutagenic chemicals generated during thermal processing of protein-rich foods that can be inhibited by some flavonoids. Free radical scavenging is a major characteristic of flavonoids. The half-maximal inhibitory concentration (IC50 ) values of nine flavonoids were determined by evaluating their capacity to inhibit 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline (7,8-DiMeIQx) formation in a model system. The results of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) test validated that MeIQx and 7,8-DiMeIQx formed via a free radical pathway. Electron spin resonance (ESR) spectroscopic analysis with spin trapping (α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN) spin adduct, aN = 15.2 G and aH = 2.7 G) revealed that an alkoxy radical was the generated intermediate. The scavenging capacities of the nine flavonoids on alkoxy radicals were then evaluated based on the ESR spectra of the POBN spin adducts. The weak correlation between the alkoxy radical scavenging capacities and IC50 of the flavonoids suggested that their inhibitory activity against MeIQx and 7,8-DiMeIQx formation operates by a more complex mechanism than simply scavenging alkoxy radicals. © 2017 Society of Chemical Industry.

Cellulose Nanofibers Prepared Using the TEMPO/Laccase/O2 System.

The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)/laccase/O2 system was used to prepare cellulose nanofibers from wood cellulose without requiring any chlorine-containing oxidant. Laccase was degraded by oxidized TEMPO (TEMPO+) formed by laccase-mediated oxidation with O2, which competed with the oxidation of wood cellulose. Thus, large amounts of laccase and TEMPO and a long reaction time were needed to introduce ∼0.6 mmol g-1 of C6-carboxylate groups onto wood cellulose. The TEMPO/laccase/O2 system underwent one-way reaction from TEMPO to reduced TEMPO through TEMPO+. When the oxidation was applied again to the oxidized wood cellulose following isolation and purification, the C6-carboxylate groups increased to ∼1.1 mmol g-1, which was sufficient to convert the sample to cellulose nanofibers by sonication in water. However, the higher the carboxylate content of the oxidized celluloses, the lower their degree of polymerization.