Electrosynthesis and efficient electrocatalytic performance of poly(neutral red)/ordered mesoporous carbon composite

A novel composite film which contains ordered mesoporous carbon (OMC) along with the incorporation of poly(neutral red) (PNR) has been synthesized on glassy carbon electrode by potentiostatic method. This composite film was characterized by scanning electron microscope (SEM) and cyclic voltammetry (CV). Two pairs of the redox peaks appear at formal potential E^0′ = +0.045 V (peak I) and E^0′ = −0.49 V (peak II) at the PNR/OMC/GC electrode. And it is found that only the redox waves (peak I) exhibits good electrocatalytic activity towards nicotinamide adenine dinucleotide (NADH) and 2-mercaptoethanol (2-ME). Under a lower operation potential of +0.07 V, amperometry method was used to determine the concentration of NADH and 2-ME, respectively. In pH 7.0, sensors for two molecules under their corresponding optimized conditions were developed with acceptable sensitivity and low detection limits in large determination ranges. In addition, these sensors have good reproducibility and stability.     

Oxygen reduction at Fe-N-modified multi-walled carbon nanotubes in acidic electrolyte

Multi-walled carbon nanotubes (MWCNTs) modified with iron tetramethoyxphenyl-porphyrin chloride (FeTMPP-Cl) and heat treated are active towards electrocatalytic oxygen reduction in acidic media. The activity slightly depends on the heat treatment temperature (850 < 550 °C) and the amount of porphyrin deposited onto the nanotubes before the heat treatment step. In comparison with as-received MWCNTs no increase in activity has been found with iron phenanthroline or iron acetate impregnated and heat treated MWCNTs. When MWCNTs are pretreated in an oxidation step using HNO₃, there is only a slight increase in activity after FeTMPP-Cl modification and heat treatment compared to the not pretreated MWCNTs. The HNO₃ treatment itself, however, leads to an increase in activity of the unmodified MWCNTs. TEM-measurements revealed an amorphous layer surrounding the MWCNTs after HNO₃ treatment, while XPS showed an increased amount of oxygen functional groups. It is suggested that there are different kinds of active sites at the catalyst surface, the first ones consisting of oxygen functionalities or other entities introduced by the HNO₃ treatment, and the second ones containing nitrogen (and probably iron) introduced via the porphyrin. Pyridine-type nitrogen has been found by XPS after heat treatment at both temperatures, indicating that the active sites are already formed at 550 °C.     

Comparative study on the electrocatalytic activities of ordered mesoporous carbons and graphene

In this work, a comparative study on the electrocatalytic activities of ordered mesoporous carbons (OMCs) and graphene (GR) is presented. Using voltammetry and amperometry as detection methods, four DNA bases, double-stranded DNA (dsDNA), six important electroactive compounds and various biomolecules were employed to investigate their electrochemical responses on OMC and GR modified glassy carbon electrodes (OMC/GCE and GR/GCE). The results show that OMC/GCE enhances the electron transfer kinetics of these compounds compared to GR/GCE. The discrepancy in electrochemical activities can be attributed to the different microstructures of OMC and GR, which were examined by transmission electron microscopy, X-ray photoelectron spectra, X-ray diffraction, Raman spectra and nitrogen adsorption–desorption.     

Superior electric double layer capacitors using ordered mesoporous carbons

This paper reports for the first time superior electric double layer capacitive properties of ordered mesoporous carbon (OMCs) with varying ordered pore symmetries and mesopore structure. Compared to commercially used activated carbon electrode, Maxsorb, these OMC carbons have superior capacitive behavior, power output and high-frequency performance in EDLCs due to the unique structure of their mesopore network, which is more favorable for fast ionic transport than the pore networks in disordered microporous carbons. As evidenced by N₂ sorption, cyclic voltammetry and frequency response measurements, OMC carbons with large mesopores, and especially with 2-D pore symmetry, show superior capacitive behaviors (exhibiting a high capacitance of over 180 F/g even at very high sweep rate of 50 mV/s, as compared to much reduced capacitance of 73 F/g for Maxsorb at the same sweep rate). OMC carbons can provide much higher power density while still maintaining good energy density. OMC carbons demonstrate excellent high-frequency performances due to its higher surface area in pores larger than 3 nm. Such ordered mesoporous carbons (OMCs) offer a great potential in EDLC capacitors, particularly for applications where high power output and good high-frequency capacitive performances are required.     

Monolayer covalent modification of 5-hydroxytryptophan on glassy carbon electrodes for simultaneous determination of uric acid and ascorbic acid

5-Hydroxytryptophan (5-HTP) was covalently grafted on the surface of glassy carbon electrodes (GCEs) using cyclic voltammetric method in a phosphate buffer solution. The prepared electrode, denoded as 5-HTP/GCE, was characterized by X-ray photoelectron spectroscopy, cyclic voltammetry and differential pulse voltammetry (DPV). Tryptophan grafted GCE (TRP/GCE) and 5-hydroxytryptamine grafted GCE (5-HTP/GCE) were also prepared by the same method for comparison. It was found that the electrocatalytic activities toward the oxidation of uric acid (UA) and ascorbic acid (AA) was in the order of 5-HT/GCE > 5-HTP/GCE > TRP/GCE for UA oxidation and 5-HT/GCE = 5-HTP/GCE > TRP/GCE for AA oxidation. However, the CV current sensitivity was estimated as 4:2:1 for 5-HTP/GCE:5-HT/GCE:TRP/GCE. The DPV peaks for UA and AA oxidation appeared at 0.07 V and 0.34 V versus SCE, respectively, allowing simultaneous determination in mixtures. A linearly response in the range of: 5.0 × 10⁻⁷ to 1.1 × 10⁻⁵ M with the detection limit (s/n = 3) of 2.8 × 10⁻⁷ M for UA determination, and a linear response in the range of: 5.0 × 10⁻⁶ to 1.0 × 10⁻⁴ M with the detection limit of 4.2 × 10⁻⁶ M for AA determination were obtained. This electrode was used for UA and AA determinations in human urine samples satisfactorily.     

Effects of oxidative modification of carbon surface on the adsorption of sulfur compounds in diesel fuel

This work examines the effects of modification of activated carbons (ACs) by HNO₃ oxidation and gas-phase O₂ oxidation, respectively, on the liquid-phase adsorption of sulfur compounds in diesel fuel. The adsorption characteristics of the oxidized and the original AC samples were evaluated in a fixed-bed flow system by using a model diesel fuel containing 400 parts per million by weight (ppmw) of sulfur as thiophenic compounds and 10 wt% of aromatics in a paraffinic solvent. The pore structure and surface properties of the AC samples were characterized by N₂ adsorption, SEM, FTIR, XPS and surface pH measurements. The adsorptive selectivity factor of the AC samples increases in the order of benzothiophene (BT) ≈ naphthalene (Nap) < 2-methyl naphthalene (2-MNap) < dibenzothiophene (DBT) < 4-methyldibenzothiophene (4-MDBT) < 4,6-dimethyldibenzothiophene (4,6-DMDBT). It was found that the HNO₃ oxidation was an efficient method in improvement of the adsorption performance of the AC for sulfur compounds. The improved adsorption performance upon the HNO₃ oxidation can be attributed mainly to an increase in the acidic oxygen-containing functional groups. However, the improved adsorption capacity upon oxidation is unlikely due to an increase in mesoporous or microporous surface/volume, although such attribution might have been inferred from the literature. An excellent correlation between the concentration of the surface oxygen-containing functional groups and the adsorption capacity per unit area as well as a good relationship between the adsorption capacity and the surface pH value were observed in this work, which suggest that the adsorption of the sulfur compounds over AC from the liquid hydrocarbon fuel may involve an interaction of the acidic oxygen-containing groups on AC with the sulfur compounds.     

Modified activated carbon with an enhanced nitrobenzene adsorption capacity

To enhance nitrobenzene removal from aqueous solution, commercial activated carbon (AC) was modified by oxidation with HNO₃ followed by heat treatment in a nitrogen atmosphere. The modification process introduced oxygen-containing functional groups and changed the charge properties of the AC surface. The effects of surface chemical properties and pore structure on the adsorption of nitrobenzene by the AC were investigated through kinetics and equilibrium isotherms. HNO₃ oxidation modified the surface chemical properties and increased the number of acidic oxygen-containing surface groups, but had an almost negligible effect on the pore structure. Subsequent heat treatment caused decomposition of oxygen-containing functional groups on the AC surface, increased the pH point of zero charge (pH_PZC) and increased the number of mesopores. The maximum adsorption capacity achieved by the modified AC was 1,443.53 mg g^?1, 3.33 times of that unmodified AC. HNO₃ oxidation combined with heat treatment was an effective method for the preparation of AC with high nitrobenzene adsorption capacity and fast adsorption kinetics. An appropriate pH_PZC, amount of surface oxygen groups and the presence of well-developed mesopores together with micropores were the main reasons for the high nitrobenzene adsorption capacity of the modified AC.     

Ordered mesoporous carbons synthesized by a modified sol-gel process for electrosorptive removal of sodium chloride

Capacitive deionization (CDI) represents an alternative process to remove the ions from the brackish water. In this study two series of ordered mesoporous carbons (OMCs) that demonstrated the potential use for capacitive desalination have been synthesized by a modified sol-gel process involving nickel salts. It was shown that the preferred formation of crown-ether type complexes between nickel ions and triblock copolymers resulted in higher BET surface area and smaller mesopores. As the electrode materials for CDI, OMC obtained by the addition of NiSO₄ · 6H₂O exhibited best electrochemical performance compared with other OMCs and a commercial activated carbon either in 0.1 M NaCl solution or in 0.0008 M NaCl solution, plus the amount of adsorbed ions measured by a flow through apparatus reached 15.9 μmol g⁻¹ and the ions could be fully released into the solution. The excellent electrosorption desalination performance of OMC obtained by the addition of NiSO₄ · 6H₂O was ascribed to its high BET surface area of 1491 m² g⁻¹ and ordered mesopores of 3.7 nm. Based on these results, it is deduced that the modified sol-gel process might be a potential method of obtaining the excellent electrode materials for CDI.     

Glassy carbon electrode modified with Nafion-Au colloids for clenbuterol electroanalysis

Stable Nafion-Au colloids were immobilized on a glassy carbon electrode (GCE) for detection of β-agonist clenbuterol by electroanalysis. The Au colloids were prepared by a one-step electrodeposition onto GCE, with obvious electrocatalytic activity present. The negatively charged Nafion film was an efficient barrier to negatively charged interfering compounds, resulting in accumulation of positively charged clenbuterol at the Nafion film. The electrochemical characters of the electrode during various modified steps in a redox probe system of K₄[Fe(CN)₆]/K₃[Fe(CN)₆] were confirmed by cyclic voltammetry (CV) and AC-impedance. In Britton-Robinson (B-R) buffer solution (pH = 2.0) and the potential range of −0.2 to 1.2 V, the Nafion-Au colloid modified electrode, compared to a bare GCE, exhibits obvious electrocatalytic activity towards the redox of clenbuterol by greatly enhancing the peak current with a linear calibration curve from 8.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol/L and a detection limit of (1.0 × 10⁻⁷ mol/L) (R = 0.996). The modified electrode shows high sensitivity, selectivity and reproducibility. The recovery for detecting clenbuterol (∼10⁻⁶ mol/L) in human serum is up to 98.19%.     

Electrocatalytic oxidation of hydrazine on platinum electrodes in alkaline solutions

The mechanism and structure sensitivity of the electrocatalytic oxidation of hydrazine on platinum in alkaline solutions were investigated using cyclic voltammetry, steady-state current measurements, and on-line electrochemical mass spectrometry. The voltammetry of hydrazine oxidation on platinum in alkaline media is characterized by a single diffusion-controlled wave. The on-line electrochemical mass spectrometry measurements of hydrazine oxidation on Pt(1 1 1), Pt(1 0 0), and Pt(1 1 0) surfaces indicated the formation of molecular nitrogen. No oxygen-containing nitrogen compounds were detected under the given experimental conditions. A comparative analysis of voltammetric data for hydrazine oxidation in alkaline solutions on the three surfaces at low overpotentials points to a structure sensitivity of the reaction. The electrocatalytic activity of basal planes increases in the order Pt(1 1 0) > Pt(1 0 0) > Pt(1 1 1), as deduced from the onset of the oxidation wave. The structure of the electrocatalyst surface affects the mechanism of the reaction, although without affecting the selectivity. At low overpotentials the hydrazine oxidation on the Pt(1 1 0) and Pt(1 1 1) surfaces is limited by the rate of electrochemical steps, whereas on Pt(1 0 0) a chemical step that probably involves N₂H₂ adsorbed intermediate is the rate-determining step. Platinum is more active in hydrazine oxidation in alkaline solution than in acidic solutions. In contrast to hydrazine oxidation on platinum in acidic media, the stabilization of chemisorbed hydrazine does not occur to a significant extent in alkaline media.     

Electrochemical study on cobalt film modified glassy carbon electrode and its application

A novel electroactive material for ascorbic acid (AA) determination was successfully prepared by plating/potential cycling method. The cobalt film was first deposited on the surface of glassy carbon electrode (GCE) in CoSO₄ solution by potential cycling, and then a cobalt film on the surface of GCE was activated by potential cycling in 0.1 mol L⁻¹ NaOH. The electrochemical performance of the resulted film (Co/GCE) and factors affecting its electrochemical activity were investigated by cyclic voltammetry and amperometry. This film electrode exhibited good electrocatalytic activity to the oxidation of AA. This biosensor had a fast response of AA less than 3 s and excellent linear relationships were obtained in the concentration range of 3 × 10⁻⁷ to 1 × 10⁻⁴ mol L⁻¹ with a detection limit of 2 × 10⁻⁷ mol L⁻¹ (S/N = 3) under the optimum conditions. Moreover, the selectivity, stability and reproducibility of this biosensor were evaluated with satisfactory results.     

Varying carbon structures templated from KIT-6 for optimum electrochemical capacitance

Bicontinuous ordered mesoporous carbons (OMCs), fabricated from a KIT-6 template using aluminosilicate as catalyst and furfuryl alcohol as carbon source, were successfully prepared and studied as electrodes in supercapacitors. Their structures were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction (SAXD) and N₂ cryosorption methods. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the capacitive performance of the OMCs was found to be strongly dependent on the mesostructure. Specific capacitance value greater than 130 F g⁻¹ at 20 mV s⁻¹ were obtained from an OMC that featured high surface area with the existence of additional large pores to enhance the specific capacitance at high discharge rate. For the OMC with the best performance, we found that a power density as high as 4.5 kW kg⁻¹ at an energy density of 6.1 Wh kg⁻¹ can be delivered when the discharge current density is 20 A g⁻¹ and can also be continuously charged and discharged with little variation in capacitance after 2500 cycles. These results indicate that this OMC with optimized structure has potential to be used as a power component in electric vehicles.     

Oxidation of activated carbon by dry and wet methods: Surface chemistry and textural modifications

The effects of dry and wet oxidation treatments of activated carbon (AC) on the surface chemistry and porous structure are studied. Using cherry stones (CS), AC was first prepared by carbonization at 900 °C for 2 h in N₂ and activation at 850 °C for 2 h in CO₂. Then, the resulting AC was oxidized in O₂(air) or O₃ atmosphere and with HNO₃ and H₂O₂ solutions. The acidic-basic surface sites were analyzed by FT-IR spectroscopy, Boehm method, and pH of the point of zero charge (pH_pzc) and the porous structure by N₂ adsorption and mercury porosimetry. It has been found that the oxidizing agent, under specific reaction conditions, rather than whether it was a gas or a solute in aqueous solution, is the main factor that controls the changes produced in the surface chemistry and porous structure of AC. O₃ and HNO₃ are the most effective oxidants to form acidic oxygen surface groups. However, the content of basic groups decreases for the four oxidants, the effect being much stronger for HNO₃. A microporosity reduction is also observed, which is more important for O₂(air) and especially for HNO₃ than for O₃ and H₂O₂. The percentage of microporosity loss is as high as 43.3 for HNO₃. Mesoporosity significantly develops, whereas macroporosity usually remains practically unchanged. Dry oxidation of AC at 100 °C in O₃ has proved to be the most promising method to increase the content of acidic oxygen surface groups in the material without greatly decreasing the content of basic sites and microporosity and with a significant mesoporosity development.     

The influence of oxidation on the texture and the number of oxygen-containing surface groups of carbon nanofibers

The effect of liquid-phase oxidation on the texture and surface properties of carbon nanofibers has been studied using XRD, TEM, SEM, N₂-physisorption, TGA-MS, XPS and acid-base titrations. Oxidation was performed by refluxing the nanofibers in HNO₃ and mixtures of HNO₃/H₂SO₄ for different times. The graphite-like structure of the treated fibers remained intact, however, the specific surface area and the pore volume increased with the severity of oxidation treatment. For the first time it is shown that the most predominant effect that gives rise to these textural modifications is the opening of the inner tubes of the fibers. Moreover, it is demonstrated that both the total oxygen content (O/C=0.02-0.07 at/at) as well as the number of acidic groups (1-3 nm⁻²) are a function of the type of oxidizing agent used and the treatment time. The total oxygen content of the oxidized samples turns out to be substantially higher than can be accommodated in the form of oxygen-containing groups at the exterior surface.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

Bimodal, templated mesoporous carbons for capacitor applications

Several high capacitance ordered mesoporous carbon (OMC) materials, containing a bimodal pore distribution, were synthesized directly using hexagonal mesoporous silicas (HMS) as the template material. The HMS templates were formed using amine surfactants (C_nH_2n+1NH₂) with hydrophobic chain lengths containing 8-16 carbons (n = 8-16). These HMS structures were found to have an interconnected wormhole structure, high textural mesoporosity, a surface area ranging from 910 to 1370 m²/g, and a total pore volume of 1.09-1.83 cm³/g. Also, evidence for a change in structure from hexagonally ordered to layered (for surfactants of chain length with n > 12) was found. The resulting OMCs, formed using sucrose as the carbon precursor, contain bimodal pores 1.6-1.8 and 3.3-3.9 nm in diameter and have a very high surface area (980-1650 m²/g). The OMCs were evaluated as electrode materials for electrochemical capacitors using cyclic voltammetry in 0.5 M H₂SO₄ solution, giving a tunable gravimetric capacitance that increased linearly with BET area (and surfactant chain length), up to 260 F/g, among the highest yet reported for ordered carbon formed from an HMS templated precursor. All OMCs studied in this work displayed a specific capacitance of ∼0.15 F/m².     

Ordered mesoporous carbons (OMC) as supports of electrocatalysts for direct methanol fuel cells (DMFC): Effect of carbon precursors of OMC on DMFC performances

This paper presents the effect of graphitic character of ordered mesoporous carbons (OMCs) on the performances of OMC supported catalysts for direct methanol fuel cells (DMFC). Two OMC samples with hexagonal mesostructure were prepared from phenanthrene and sucrose by nano-replication method using mesoporous silica as a template. Structural characterizations revealed that both OMCs exhibited large BET surface area and uniform mesopores, while the OMC synthesized from phenanthrene exhibited lower sheet resistance than the OMC derived from sucrose. The Pt nanoparticles were supported on both OMCs with very high dispersion, as the particle size was estimated under 3 nm despite high metal loading of 60 wt.%. In DMFC single cell test, the OMC supported Pt catalysts exhibited much higher performance than the commercial catalyst, which may be attributed to the high surface area and uniform mesopore networks of OMC. In particular, it was found that the performance of OMC supported catalysts can be significantly enhanced by lowering the resistance of OMC.     

Electrodeposited MnO2/Au composite film with improved electrocatalytic activity for oxidation of glucose and hydrogen peroxide

The major drawback of currently used MnO₂ film sensor is the loss of electrical conductivity due to the formation of a poorly conductive MnO₂ layer. To overcome this problem, a coating in which the Au is alloyed with MnO₂ has been developed. The fabrication of the codeposited film electrode of Au and MnO₂ by using a cyclic voltammetric (CV) method was described, and systematic physical and electrochemical characterization was performed. This MnO₂/Au film electrode enhanced MnO₂ electrocatalytic activity. The oxidation process of glucose at the codeposited MnO₂/Au shows a well-defined peak at 0.27 V in alkaline aqueous solution. In contrast, the glucose oxidation at Au modified glassy carbon electrode (GCE) just shows a shoulder wave at 0.42 V. The experimental results indicate that the modification of MnO₂ on the surface of GCE significantly improved the electrocatalytic activity towards the oxidation of glucose. Further study shows that the MnO₂/Au could also effectively catalyze the oxidation of hydrogen peroxide in pH 7.0 phosphate buffer solution (PBS).     

Effect of potential cycling on structure and activity of Pt nanoparticles dispersed on different carbon supports

Platinum particles synthesized via the Bönnemann methods were dispersed on two different Vulcan XC72 carbon supports. One was used after thermal treatment at 400 °C under nitrogen atmosphere, the other after oxidation of its surface by acid leaching using diluted HNO₃ in water (1/3). Characterization of the carbon support indicated that HNO₃ treatment leads to the decrease of the BET surface and to the increase of the surface acidity of the carbon support. After dispersion of the platinum catalyst, TEM results indicated that the mean particle size was a little higher on the non-oxidized support (Pt/XC72) than that on the functionalized one (Pt/XC72_HNO3), being 2.5 and 2.0 nm, respectively. However, potential cycles from 0.05 to 1.25 V vs. RHE led to a higher increase of the particle size when catalyst is dispersed on the functionalized support, reaching after 400 potential cycles 5.5 nm against 4.0 nm with the non-functionalized one. The effect of the upper limit (1.0 and 1.25 V vs. RHE) of the potential cycles on the active surface area and on the activity towards the oxygen reduction reaction (orr) was determined for both catalysts. Results indicated that the particle growth was not the main degradation process over the whole duration of the electrochemical experiments, but that dissolution/redeposition (Otswald ripening) was also involved. The predominant role of each degradation process depends on the number of cycles, on the upper potential limit and on the carbon surface state, and could be temporally separated. However, the lower activity towards orr was recorded for the (Pt/XC72_HNO3) cycled up to 1.0 V vs. RHE.     

The efficiency of the oxidation of carbon nanofibers with various oxidizing agents

The oxidation of carbon nanofibers (CNFs) with various oxidizing agents; 6 M HNO₃, KMnO₄, RuO₄, and a mixture of concentrated H₂SO₄/HNO₃ is studied to determine the reaction conditions that optimizes yield and chemical functionalization. The oxidized nanofibers were examined by scanning electron microscopy, and Raman spectroscopy to characterize the defects caused by oxidation. The amount of acidic sites generated during oxidative treatment was quantified by reacting them with amine terminated octadecane and the subsequent quantification of the products of this grafting process by Fourier transform infrared spectroscopy. The concentrated H₂SO₄/HNO₃ mixture created the maximum number of carboxylic acid groups and the highest amount of defect sites, but had very low yield (∼12%). Six molar of HNO₃ generated fewer defect sites and a lower number of -COOH groups, but did exhibit a 70% yield. RuO₄ and KMnO₄ resulted in similar amounts of overall defect sites, however the yield and amount of -COOH groups for KMnO₄ treated CNF were significantly lower than the RuO₄ treatment. Overall, oxidation of these CNF with RuO₄ provides the best balance of yield and carboxylation.