C1s X-ray Photoelectron Spectroscopy Research Articles

Synthesis and characterization of chemical vapour deposited pyrolytic graphite

Pyrolytic graphite (PyG) is the candidate process crucibles material (containers/liners) in pyro reprocessing applications of spent metallic nuclear fuels. In the present work, the chemical vapor deposition (pyrolysis) temperature effects on the density, texture, degree of preferred orientation, defects, graphitization and growth kinetics of PyG were investigated. The sink and float technique, polarized light microscopy, X-ray diffraction, laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), and electron microscopy techniques were used. The near theoretical density (>2.2 g/cm3) was achieved at pyrolysis above 2100 °C. The preferred orientation by extinction angle and orientation density measurement reveals an increasing degree of texture and anisotropy with increasing pyrolysis temperature. The residual strain and defects concentration inferred from the blue shift of the G band position and integrated ratio ID/IG in LRS analysis shows that intermediate temperature pyrolysis at 1800 °C is more defective. The degree of graphitization defined by sp2:defect ratio in the peak fit analysis of C1s XPS peak show 2400 °C processed PyG is highly graphitized while at 1800 °C show higher fractions for sp3, CO content. The crystallite domain sizes parallel and perpendicular to the c-axis show an increasing ordering with pyrolysis temperature. The activation energy calculated for the surface pyrolysis reaction is ∼60 kJ/mol for the surface kinetics controlled regime between 1400 and 2200 °C, producing a conformal, smooth, and uniform PyG growth as evident by the Volmer-Weber 3D island growth model.

Unveiling bonding states and roles of edges in nitrogen-doped graphene nanoribbon by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) is among the most utilized analytical methods for nitrogen-doped carbon materials. Clarifying the assignments of nitrogen-doped carbon materials with different degrees of carbonization, which relates to conjugated systems, is essential to correlate structures with the performance of various applications, but such precise assignments were challenging. In this work, precise analyses were conducted to overcome the difficulty to assign the peaks of carbon materials with different degrees of carbonization, different edges, and various nitrogen-containing functional groups in graphene nanoribbons (GNRs), such as nitrile, pyridinic, primary with/without charges, secondary with/without charge, tertiary without charges (graphitic nitrogen), and quaternary nitrogen. Electrons donated from hydrogen and Madelung potentials showed a higher correlation to the peak shift of C1s and N1s XPS spectra than Mulliken charges on nitrogen. Zigzag edges showed a greater influence on the peak shift of tertiary amine (graphitic nitrogen) than armchair edges on XPS spectra. Besides, as the degree of carbonization is increased from aromatic compound-like structures to GNRs, the peak positions of C–N in C1s and N1s XPS spectra shifted to higher binding energies. This research proved that XPS could be applied to the precise structural analyses of nitrogen-containing carbon materials.

Thermal Degradation, Kinetic Analysis and Char Formation in the Pyrolysis of Poly(melamine-co-phenolic resin) Copolymer

Understanding the mechanism of thermal degradation of a material may suggest a promising way for further improving its thermal properties. poly(melamine-co-phenolic resin) (P(M-co-PR)) has been widely used in flame resistant and fire-proof materials. Our characterization of the thermal degradation of P(M-co-PR) is described in this work. Fourier-transform infrared (FTIR) and X-ray photo-electron spectroscopy (XPS) analyses were used to investigate the structural evolution during the thermal degradation of the copolymer. The evolutions of C = N and C-N bonding in heteroaromatic rings were monitored during the degradation process by C1s and N1s XPS spectra. The degradation processes of P(M-co-PR) is divided into three stages. The degradation kinetics of P(M-co-PR) was researched by using the Ozawa and Kissinger activation energy equation methods. The conclusion is that the Kissinger equation applied to the first stage, and the Ozawa equation applied to the second and third stages.

Carbon materials with high pentagon density

Pentagons in carbon materials have attracted attentions because of the potential high chemical reactivity, band gap control, and electrochemical activity. However, it is challenging to prepare a carbon film with high pentagon density because of the curvature and the high reactivity caused by the presence of pentagons, and it is also challenging to estimate the percentage of pentagons in carbon materials because of the limitation of current analytical techniques. In this work, the percentage of pentagons in carbon materials was experimentally estimated for the first time using experimental and calculated C1s X-ray photoelectron spectroscopy and elemental analysis. Carbon films with 7% of pentagons (40% of pentagons compared to the raw material) with electrical resistivity of 1.1 × 104 Ω meter were prepared by heat treatment of corannulene at 873 K. On the other hand, fluoranthene and fullerene remained as non-film solid and powder without forming films at 873 K. Experimental and calculated Raman and IR spectra revealed the peaks of different types of pentagons. Decrement of pentagons in corannulene and fluoranthene heated at high temperatures can be explained mainly by the scission of C=C bond in pentagons, as suggested by the results of reactive molecular dynamics simulation (ReaxFF).

Effect of VUV Radiation on Surface Modification of Polystyrene Exposed to Atmospheric Pressure Plasma Jet.

Precise tailoring of surface properties by gaseous plasma treatments remains a key scientific challenge, especially when adequate surface wettability should be laterally distributed, and sharp interfaces between hydrophobic and hydrophilic areas are desirable. The evolution of surface wettability and functional groups on polystyrene (PS) upon treatment with argon plasma jet was monitored by water contact angles and X-ray photoelectron spectroscopy (XPS). An array of water droplets was deposited on PS samples treated either directly by the plasma jet or only VUV radiation arising from the plasma. Rather sharp interfaces between the activated and not-affected regions were observed in both cases. The functionalization with highly-oxidized carbon functional groups, as determined by high-resolution C1s XPS spectra, was by far more efficient using the VUV radiation only. In contrast, the optimal wettability was achieved using direct plasma treatment. The results were explained by different mechanisms involved in the interaction of radiation and reactive plasma species with the polymer surface.

Study of graphene layer growth on dielectric substrate in microwave plasma torch at atmospheric pressure

The initial stage of graphene layer deposition on silicon oxide substrate by ethanol decomposition in dual-channel microwave plasma torch at atmospheric pressure was studied in dependence on precursor flow rate and delivered microwave power. Depending on ethanol flow rate and substrate temperature, horizontally or vertically aligned graphene nanosheets with various density could be prepared directly on dielectric substrate. In the regime with high microwave power, above 400 W, mixture of amorphous carbon particles and graphene sheets was deposited on the substrate. Prepared layers were analyzed by scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The microwave plasma diagnostics was carried out using optical emission spectroscopy (OES). The sample analysis showed increasing density of horizontally aligned carbon nanosheets with increasing ethanol flow rate and their delamination and transition into vertically aligned graphene sheets with increasing substrate temperature. The Raman spectroscopy analysis of layers showed presence of D (1345 cm−1), G (1585 cm−1) and 2D (2685 cm−1) peaks with 2D/G ratio of 1.59 and full width at half maximum (FWHM) of 2D peak was 42 cm−1, corresponding to few layer graphene structure. In case of amorphous nanoparticles deposition, the D* peak at 1210 cm−1 and D** at 1500 sccm−1 was observed in Raman spectra with D/G ratio of 1.19 and C1s XPS spectra of carbon contained 20.4 at.% of sp3 carbon phase in comparison to 8.3 at.% in case of graphene nanosheets layer. High D/G ratio, up to 3.5, and low intensity 2D band was characteristic for vertically aligned graphene nanosheets layers. The possibility to influence density and size of graphene nanosheets on substrate represents promising alternative for future deposition of graphene on arbitrary substrate.

Graphene oxide as a radiation sensitive material for XPS dosimetry

The suitability of graphene oxide (GO) foils as radiation sensitive materials for soft X-ray irradiation is investigated by means of X-ray photoelectron spectroscopy (XPS). In particular GO micrometric foils have been irradiated by soft X-rays at a 1486.6 eV energy at high flux (>1012 photons/cm2s) in ultra-high vacuum. The XPS analysis of the carbon-carbon (CC) and the carbon-oxygen links (CO) characterizes the composition of the first layers of the GO foils. The CC/CO ratio of the high-resolution C1s XPS spectrum is used as dosimetric index. The incident X-ray photons, proportionally to their fluence, partially reduce GO foils decreasing the amount of oxygen groups chemically bonded to carbon network. This decrease causes an increase on the CC/CO ratio that is correlated to the irradiation time, i.e. to the dose absorbed by the GO foil, showing a linear increment with the dose. Our preliminary investigations indicate that GO can be employed to realize a thin foil dosimeter giving a linear response to the absorbed dose in the (275.76 kGy ÷ 8.02 MGy) range. The absorbed dose can be also evaluated by measuring the C/O ratio from the C1s and O1s XPS spectra analysis or with different techniques, as discussed in the paper.

Function of Tetra (4-Aminophenyl) Porphyrin in Altering the Electronic Performances of Reduced Graphene Oxide-Based Field Effect Transistor.

Porphyrin functionalized reduced graphene oxide (rGO) is attractive for multi-disciplinary research studies, and its improvements for an rGO-based field effect transistor (rGO-FET) were exploited to realize ultrasensitive biochemical and clinical assay. Although it was believed that the hybrids of porphyrin and rGO can make positive impacts on the rGO-FET’s electronic performances, the understandings of its functions are still piecemeal. Herein, the reduced mixtures of tetra (4-aminophenyl) porphyrin (TAP), GO (TAP-rGO), and the FET channeled by them are examined to throw a light on the possible approaches through which TAP affects rGO’s quality and its carrier mobilities. A TAP-caused game relationship is established by deliberating about the results of the intentionally altered experimental conditions, including TAP contents and the overmixing pretreatment. The p-type doping deduction for the right-shifted ambipolar transfer characteristic curves is evidenced by X-ray photoelectron spectroscopy (XPS). The problems posed by the TAP-induced FET features’ improvement, regression, and deterioration are clarified by the integrated proofs from Raman fingerprints, the amide and carboxyl groups’ changing trajectory found by C1s XPS core spectra, and the enlarged few-layer graphene morphology from atomic force microscope and transmission electron microscope. We hope that this effort will provide some constructive recommendations for producing low-cost graphene derivatives and promoting their applications in FET-like electronic components.

Electronic structures and spectral characteristics of the six C32 fullerene isomers.

In this paper, the six C32 isomers which were of crucial importance in the manufacture of new electronic components were identified by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). For the discernment, geometry optimizations of the six isomers have been carried out, and the C1s XPS and NEXAFS spectra have been simulated in the frame of density functional theory (DFT). XPS spectra, as accurately reflection of different chemical environments where a particular element was located, provided an effective way to identify the six isomers of C32. The NEXAFS spectra, which were commonly used in the electronic structure detection, captured information of unoccupied orbital and showed many recognizable characteristics. To further investigate the source of spectral features, the spectral components calculated from different types of carbon atoms in each C32 isomer also have been well explored and discussed.

Composition and origin of PM2.5 in Mediterranean Countryside

In this work PM2.5 was collected during winter and summer in a Sardinian village (Gonnostramatza, Italy) highly affected by biomass burning emissions. A multi-technique approach was adopted for the complete PM chemical characterization. The bulk characterization was performed by IC (Ion Chromatography), HPAEC (High-Performance Anion-Exchange Chromatography), TOT (Thermal Optical Transmittance) and ED-XRF (Energy-Dispersive X-Ray Fluorescence) while XPS (X-ray Photoelectron Spectroscopy) was used for the surface characterization. Using levoglucosan as specific tracer of biomass burning emissions, the assessment of the impact of this source was carried out and it represent the major PM source at the investigate site during winter. In winter the average levoglucosan concentration is 2096 ± 324 ng/m3 while during summer its concentration is negligible (18 ± 7 ng/m3). Levoglucosan content in PM2.5 during winter is on average 13.7%; it is estimated that 65% of PM2.5 is due to wood burning. XPS has been exploited in this work aiming at highlighting possible differences between surface and bulk composition of PM2.5. The surface of the particulate matter resulted enriched in carbon compared to the bulk. Among the components of XPS C1s signals recorded on the samples collected during winter, it was found that the signal at 286.5 eV, which is due to the presence of COH, reflects the bulk composition of levoglucosan.

Distinguishing the six stable C36 fullerene isomers by means of soft X-ray spectroscopies at DFT level

ABSTRACTThe six most stable isomers of C36 fullerene (8Cs-C36, 9C2v-C36, 11C2-C36, 12C2-C36, 14D2d-C36, 15D6h-C36) have been distinguished in theory by analysing their C1s X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra, which are both simulated by the combination of density functional theory and full-core-hole potential approximation. The NEXAFS spectra exhibit stronger sensitivity to the structures of studied C36 molecules than the XPS; it can be regarded as an effective technology to distinguish the isomers of C36 fullerene. In addition, the decomposed spectra describing the influence of Carbon atoms with different local environments to the total spectra have also been discussed in detail. The results show that the spectral differences are mainly due to the distinct combinations of the Carbon atoms.

Tuned magnetic properties of Co-doped ZnO/B-doped graphene PN junction

Co-doped ZnO(Zn1−xCoxO)/B-doped graphene(BG) PN junction with quasi-core-shell nanostructure is designed and fabricated by a facile chemical process. The interplay between the Zn1−xCoxO core and the BG shell is discussed. X-ray Photoelectron Spectroscopy (XPS) and photoluminescence (PL) spectra confirm that B and Co2+ ions are doped successfully. The C1s XPS spectra suggest the formation of the Zn(Co)OCO bonds, which can efficiently transfer the holes from BG to Zn1−xCoxO. X-ray diffraction (XRD) displays that Co doping hardly changes the wurtzite structure of ZnO. It can be clearly seen that edge of the BG covers Zn1−xCoxO to form the quasi-core-shell structure by High-resolution transmission electron microscopy (HRTEM). The position of the G band in Raman spectrum indicates that BG is P-type. The interaction between the Zn1−xCoxO and BG can be found by the red-shifts of E2H band of Zn1−xCoxO and broader 2D of BG as well. Magnetization measurement demonstrates that the increasing of the ferromagnetic phases in Zn1−xCoxO/BG nanoparticles with the increasing temperature. The observed ferromagnetic phases can be due to the exchange of the electron/hole at interface in the Zn1−xCoxO/BG PN junction.

Defects of clean graphene and sputtered graphite surfaces characterized by time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy

Clean surface of graphene was obtained at 500 °C and characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In the XPS C1s spectrum of graphene, besides an asymmetric sp2 carbon peak and a π-π∗ shake-up peak appeared, an additional sp3 carbon peak representing sp3 defects was also present. In the ToF-SIMS positive ion spectrum of graphene, a series of CxH2+ ions originated from the defects of graphene was found. To determine the origin of the CxH2+ ions, defects were created on the surface of nearly defect-free highly oriented pyrolytic graphite (HOPG) by bombarding it with a Cs+ ion beam at various sputtering doses. A detailed examination of the positive ion spectra of ion-bombarded HOPG surfaces reveals the presence of the CxH2+ ions, confirming that these CxH2+ ions, which came from the defects created on the sputtered HOPG surfaces, are similar to the defects present on graphene surface. A sp3 carbon peak at 285.3 eV, representing sp3 defects appeared in the XPS spectra of sputtered HOPG samples, confirms that the surface of the sputtered HOPG is similar to that of graphene. Fragmentation mechanisms of selected ions in the ToF-SIMS spectra of graphene and HOPG were proposed.

Thermally induced modification of the graphene oxide film on the tantalum surface

The interface chemical reactions, the deoxygenation and the overall thermal stability of the ex situ deposited graphene oxide (GO) thick film on the polycrystalline tantalum surface were studied by means of x-ray photoelectron spectroscopy (XPS) at room temperature and after annealing up to 600°С. The evolution of the Ta4f, C1s and O1s XPS core level spectra from the Ta/GO structure under study upon the increase of the annealing temperature was investigated with the reference to the uncovered Ta substrate surface. In the Ta/GO structure the Ta relative atomic concentration was about 1% at room temperature due to the low porosity of the GO layer while the thermal desorption of the overlayer at the elevated temperatures was accompanied by an increase of the Ta concentration up to 47% at 500°С. The C atoms relative concentration started decreasing after the annealing at 250°С accompanying the thermal desorption of the GO overlayer. The formation of the TaC compound starting from the 250°С annealing temperatures was determined. The relative oxygen concentration in the GO thick film was decreased upon increasing the annealing temperature accompanying both the thermal desorption of the GO material and the thermal reduction of the GO film.

Ionically Crosslinked Chitosan-Tripolyphosphate Binder for Silicon Anode in Lithium Ion Batteries

Lithium-ion batteries have become the choice for portable electronics and EVs because of their high energy density and reasonable cost. To meet today’s demand of high capacity lithium-ion batteries one has to look beyond the commonly used graphite-based anodes. Silicon is capable of electrochemically alloying with Li to have high charge capacity but its high volumetric expansion on lithiation often results in low rate capability and limited cycle life. Binders play an important role in the cycling stability of the batteries. They keep active materials in electrical contact, and are critical to assembling high-quality electrodes, regardless of the particle size. An ideal binder should provide best elasticity to the anode composite and should accommodate the expansion of the active material during the lithiation/delithiation process. It has been found that using different biopolymers like cellulose, carboxymethyl cellulose, sodium alginate, etc. as binders can give a better cycling stability than polyvinylidene fluoride, a commonly used binder. This research focuses on using Chitosan, the second most abundant biopolymer found in nature, and its derivative Chitosan-tripolyphosphate (TPP), as binders for Silicon (Si) anode. Specifically, 2% Chitosan solution was prepared in 1% acetic acid solution. The ionically cross-linked hybrid gel polymer was prepared by adding 14 ml of 4 mg/ml solution of Sodium tripolyphosphate (TPP) solution dropwise into 35 ml of 2% Chitosan gel under mechanical stirring at 300 rpm for 5 hours. Anode slurries were prepared by mixing active material Si nanoparticles with conductive agents super P and carbon nanofibers (CNF), and binder gel solutions in a ball mill (Zheng Xian QM-3SP04, Nanjing University) at 400 rpm for 6 hours. The mass ratio for Si:C:Binder (Chitosan or Chitosan-TPP) was 4:4:2. For Si:C:CNF:Chitosan-TPP, it was 6:1.5:0.5:2. The anode slurries were then coated on copper foil and vacuum dried for coin cells preparation. Pure lithium metal was employed as the counter electrode, Celgard 2325 film as separator and 1M LiPF6 in EC: DMC (1:1) as electrolyte. The cells were charged and discharged at constant rate of 0.1C (1C = 4200 mA/g) between 0.01 and 1 V. Figure 1 shows the cycling performance of Si anodes using different binders. The initial discharge capacities for anodes using Chitosan and Chitosan-TPP binders were around 1400 mAh/g and the discharge capacity retention was around 55% and 70% respectively, after 500 cycles. Initial discharge capacity for anode using CNF as conducting agent with higher amount of Si was around 2100 mAh/g and the discharge capacity retention was around 82% after 500 cycles. The large drop in discharge capacity in the initial cycles is caused by the incomplete delithiation during the initial delithiation cycles, during which the particle size is decreased and the electrode resistance, predominantly contact and SEI resistance increases and inhibits Li extraction. Upon subsequent cycling, a stable SEI layer is formed and the Li alloys with the partially delithiated Si, thus producing a stable discharge capacity in the later cycles. The improved cycling performance of the Si anode is attributed to the formation of the chemical bonds and interactions between the Si active material and binder molecules. X-Ray photoelectron spectroscopy (XPS) was employed to determine the spectral shifts in the Carbon and Nitrogen present in the binder molecules. As shown in Figure 2, the C1s XPS spectrum of the Chitosan-TPP shows three obvious characteristic peaks corresponding to C-C and C-H bonds (283.8 eV), C-O bond (285.7 eV) and C=O bond (283.0 eV). The N1s XPS spectrum also showed the strong N-H bond (399 eV) in Chitosan-TPP. As expected, pristine Si powder does not show any signs of C and N atoms on the surface. Comparing with Chitosan-TPP, the binding energy of C-H and C-O of the Si-C-Chitosan-TPP mixture increased from 283.8 to 284.2 eV and 285.7 to 287 eV, respectively, while the N1s signal shifted from 399 to 400.8 eV. In spite of careful purification by washing with water for four times, the Si-C-Chitosan-TPP still shows strong C1s and N1s signals in XPS spectra, indicating that a large amount of Chitosan still remains on the surface of Si nanoparticles. This implies that the -OH, -CH2OH and -NH2 groups of C-chitosan were bound to the hydroxylated Si surface through formation of abundant number of hydrogen bonds between the hydroxylated Si surface and Chitosan. The above results show us that Chitosan and its ionically crosslinked derivative can be ideal binders for Si to be used as an active material for anode in Li-ion batteries. Figure 1

Spectral change of simulated X-ray photoelectron spectroscopy from graphene to fullerene

C1s X-ray photoelectron spectroscopy (XPS) spectra of graphene with two to eight pentagons and fullerene pentagons were simulated using density functional theory calculation. Peak shifts and full width at half maximum (FWHM) of calculated C1s spectra were compared with those of actual C1s spectra. Introduction of up to four isolated pentagons had no influence on shifts of the calculated peak maxima of graphene (284.0 eV), whereas the introduction of six or more pentagons shifted the calculated peak maximum toward low binding energies because the number of connected pentagons increased. The presence of pentagons also influenced FWHMs. Introduction of six pentagons increased the calculated FWHMs from 1.25 to 1.45 eV, whereas introduction of eight or more pentagons decreased the FWHMs. The FWHM reached at 1.15 eV by introducing twelve pentagons (fullerene). These calculated shifts and FWHMs were close to the actual shifts of graphite (284.0 eV) and fullerene (282.9 eV) and FWHMs of graphite (1.25 eV) and fullerene (1.15 eV). Based on the calculated and the actual results, we proposed peak shifts and FWHMs of graphene with the different number of pentagons, which can be utilized for analyzing actual XPS spectra. Proposed FWHMs can be adjusted by measuring actual FWHMs using each device.

XPS STUDY ON THE EFFECT OF LOW-ENERGY ELECTRON IRRADIATION ON DNA DAMAGE BY Fe3+ION

We have employed X-ray photoelectron spectroscopy (XPS) technique to examine the combined effects of low-energy electron (LEE) irradiation and ion on DNA damage. pBR322 plasmid DNA extracted from E. coli ER2420 was used for preparing DNA- sample. The C1s XPS spectra were scanned for LEE-irradiated and LEE-unirradiated samples and then curve-fitted. For the samples with LEE irradiation only or with Fe ion only, no significant changes from pure DNA samples were observed - a single effect of either ion or LEE irradiation did not cause a significant damage. However, when these two components were combined, the DNA damage was increased quite significantly, compared to the sum of DNA damages caused by ion and by LEE irradiation independently. This observation is consistent with our previous results [Radiat. Res. 177, 775 (2012)] which was done using gel-electrophoresis technique. Partial interpretation of the observed spectrum peaks was also attempted.

Deposition of Water-Stable Coatings Containing Carboxylic Acid Groups by Atmospheric Pressure Cold Plasma Jet

Thin films containing carboxylic acid groups are deposited from mixtures of helium, acrylic acid, and ethylene using an atmospheric pressure cold plasma jet in dielectric barrier discharge (DBD) configuration. The influence of the feed gas composition on the properties of the deposits is investigated. As assessed by X-ray photoelectron spectroscopy (XPS), the oxygen atomic concentration of the coatings as well as the percentage of the XPS C1s component ascribed to carboxylic groups (i.e., COOH and COOR moieties) increase with the acrylic acid concentration in the feed gas. On the other hand, ethylene addition enhances the deposition rate, reduces the carboxylic groups content of the coatings, and significantly improves their chemical and morphological stability upon immersion in water for 72 h. The surface concentration of COOH groups before and after immersion in water is determined by chemical derivatization in conjunction with XPS.

Functionalization of multiwall carbon nanotubes with nitrogen containing polyelectrolyte by a simple method

Commercially available multiwall carbon nanotubes (MWCNTs) have been functionalized with poly(diallyl dimethylammonium) chloride (PDDA), a nitrogen containing polyelectrolyte by a simple on-off ultrasonication method. The results obtained from Raman and X-ray photoelectron spectroscopy (XPS) studies confirm the functionalization of MWCNTs with PDDA. An up- shift in the positions of C1s XPS peak and a down-shift in the positions of the N1s XPS peak, has been observed along with an up-shift in the G-peak position in the Raman spectra, which suggest the occurrence of inter-molecular charge transfer from carbon atoms in MWCNTs to N+ centres in PDDA. The preliminary linear sweep voltammetry (LSV) results show good electrocatalytic activity of MWCNTs functionalized with nitrogen containing polyelectrolyte, which is comparable to the results with platinum based electrodes. Thus, MWCNTs non-covalently functionalized with a nitrogen containing polyelectrolyte (PDDA) by a simple on-off ultrasonication method could be advantageous for developing efficient metal-free electrocatalysts for the oxygen reduction reaction (ORR).

Study on the Electrochemical Characteristics of Multiwalled CNTs Decorated By Various Oxygen Functional Groups (Non-Aqueous and Aqueous based Electrolytes)

Functionalized nano carbon have been reported as promising cathode materials for Li ion battery (LIB).[1-2] Unlike the conventional Li intercalation into host material, the Li storage mechanism on this materials was thought to be the Faradaic reaction between surface functional groups and Li, C=O + Li+ + e- = C-O-Li.[1-2] Introducing functional groups on few walled carbon nanotubes (CNTs) by acid treatment resulted in Li storage capacity up to 120 mAh/g.[2] However, the origin of which functional groups is responsible for such reaction still elusive. A better understanding on the electrochemical characteristics of functionalized nano carbon is not only important for LIB storage but also aqueous based electrochemical systems. It is known that there are two major dominant surface groups present on functionalized CNTs; they are carboxyl and carbonyls.[3] To be able to study the electrochemical characteristics of different oxygen functional groups, controlling the type of surface groups on CNTs is obligatory. Here, different kind of functional groups are introduced onto multiwalled CNTs (VGCFX) by varying different oxidizing agent, such as reflux under inorganic acid solution or reacting with organic acid (i.e. citric acid). Furthermore, by annealing at certain temperatures, we also could selectively attain the functional groups present on the surface of CNTs. The electrochemical studies of oxygen functional groups are carried out in non-aqueous (organic) and aqueous based electrolytes, to obtain comprehensive knowledge on the functional groups reactivity. On the other hand, X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) are extensively used to examine the type and amount of surface groups. Fig. 1 shows the C1s XPS spectra of two of different samples, they are acid treated CNTs (HA) and citric acid treated HA (HA-CA). Briefly, acid treated CNTs was derived from refluxing pristine CNTs in the mixture of H2SO4/HNO3, while citric acid treatment was conducted by mixing the HA with citric acid, followed by annealing in air at 300 oC. It can be seen from XPS scan, that HA-CA has an appeared peak relating to the carboxyl group (288.9 eV) than HA. This suggests that citric acid treatment is plausible to introduce carboxyl groups on the surface of multiwalled CNTs. The roles of the oxygen functional groups play in the electrochemical characteristics will be discussed in the presentation.