The results indicated that oxidative damage of MWCNT was not closely related to acid strength, and that the MWCNT was more sensitive to the oxidizing nature of the acid. The oxidation of highly oriented pyrolytic graphite (HOPG) by chemical oxidants in air was investigated. Consequently, the MWCNT treated with the strongest acid, trifluoromethanesulfonic acid (pKa = -15.9), only reached oxygen content of 1.8%, while nitric acid (pKa = -1.5)/sulfuric acid (pKa = -3.0) treated MWCNT showed. oxygen content as high as 19% after 24 hours of treatment.
The remaining acidic media did not appreciably increase the oxygen content of the MWCNT until treatment for up to 24 hours. The results are supported by a gradual increase in D-band intensity in Raman spectra with time. a) X-ray diffraction pattern; (b) Raman spectrum;. (c) SEM image. (a) TGA thermograms obtained at a rate of increase of 10 °C/min in air; (b) FT-IR spectra (KBr pellet);
A white arrow indicates a trapped metal particle. a) TGA thermograms obtained with a ramping rate of 10 °C/min in air; (b) FT-IR spectra (KBr pellets); White arrows indicate the carbon coating covering the 24 h H2SO4 treated MWCNT. a) X-ray diffraction patterns of HNO3/H2SO4-treated MWCNTs versus treatment time; (b) two theta changes as a function of treatment time. a) TGA thermograms obtained with increasing speed. a) microraman spectrum; (b) XPS spectrum;
List of schemes
Nomenclature
- Materials
- Instrumentations
- Acid treatments of MWCNT in CF 3 SO 3 H, H 2 SO 4, HNO 3 /H 2 SO 4, PPA, PPA/ P 2 O 5
- Acid treatments of HOPG in HNO3/H2SO4
- MWCNT in Acids
- Acid treatments of MWCNT
For some potential applications of graphite, exfoliation and inertness are major challenges when it comes to materials preparation. The presence of oxygen-containing functionalities facilitates the exfoliation of graphite into graphene and increases the dispersibility of polar solvents 46. As a result, the unique mechanical and electrical properties of graphene can be transferred to hybrid materials 49.
Second study is that the effects of commonly used acids oxidation and surface morphology are 45 studies, but not in a systematic way. In the present report we carry out a systematic study of the chemical oxidation of the upper surface of highly oriented pyrolytic graphite (HOPG) formed in polyethylene treated by sulfuric acid and nitric acid mixture at 100 ºC for different durations. TEM was used to show the depth of the damage with different time durations at constant temperature.
In order to correlate MWCNT stability and acid strength, pKa values of the acids are summarized in Table 1. The ratio of the Raman D and G band intensities (ID/IG) is 1.13, indicating the presence of some defects.
Multi-walled carbon nanotubes (MWCNT) were treated in commonly used acids
- Trifluoromethanesulfonic acid (CF 3 SO 3 H) treatment of MWCNT
- Nitric acid (HNO 3 )/sulfuric acid (H 2 SO 4 ) mixture treatment of MWCNT
- Polyphosphoric acid (PPA)/phosphorous pentoxide (P 2 O 5 ) mixture treatment of MWCNT
- Acid treatments of HOPG
Furthermore, the XPS spectra confirmed that oxygenated defects were introduced, as indicated by the noticeable intensity of the O 1s peak for the 24 h-treated sample (Fig. 2d). The SEM image obtained from the 24h CF3SO3H-treated sample shows similar morphology to that of the pristine MWCNT (Figure 3a), implying that CF3SO3H treatment does not seriously damage the MWCNT framework. TGA thermograms show that all H2SO4-treated samples have very similar thermooxidative stabilities, showing no noticeable weight loss up to 600 °C in air (Figure 4a).
Based on the EA (Table 2) and TGA (Figure 4a) results of the 24 h H2SO4 treated sample, the total CHNO content approaches 100% and the char yield at 800 °C approaches 0%, respectively. The ID/IG ratios of all H2SO4-treated samples remain constant at 0.83 (Figure 4c) and are lower than that of pristine MWCNT (see Figure 1b). Furthermore, from the XPS results, no noticeable O 1s peak is detected for any of the H2SO4 treated samples, ruling out the possibility of sulfonation (Figure 4d).
Similar to the case of the 24 h CF3SO3H treated MWCNT (see Figure 3), the SEM image obtained for the 24 h H2SO4 treated MWCNT shows a clean and smooth surface morphology (Fig. Unlike the results of other acidic treatments show TGA thermograms obtained from HNO3/H2SO4 treated samples clearly show significant weight losses at much lower temperatures than pristine MWCNT (Figure 6a). The surface of the MWCNT appears to be severely damaged even after 1 hour of treatment (Figure 7a). , with a swollen surface and a relatively much shorter tube length.
Finally, more than 90% of the graphitic MWCNT walls are transformed into an amorphous carbonaceous layer after 24 h treatment (Figure 7f). Because PPA is a mild and non-destructive acid, it does not damage the CNT framework; TGA thermograms obtained from PPA-treated MWCNT samples show that the thermooxidative stability is similar to that of pristine MWNCTs (Figure 9a). The SEM image taken from the 24 h PPA-treated sample shows a morphology similar to that of pristine MWCNT (Figure 1c), indicating that PPA treatment does not critically damage MWCNT.
Furthermore, a trapped metal particle can be clearly observed in the HR-TEM image (Figure 10b, white arrow). The thermooxidative stabilities of the PPA/P2O5 treated samples were almost identical to that of pristine MWCNTs (Figure 11a). Similar to the PPA-treated samples, the FT-IR spectra of the PPA/P2O5-treated samples clearly show that no additional peak(s) appeared after 24 h treatment (Figure 11b).
The SEM image taken from the sample treated for 24 hours with PPA/P2O5 reveals a morphology similar to that of pristine MWCNT (see Figure.. 1c) and PPA-treated MWCNT (Figure.. 10a), respectively, indicating that the PPA/P2O5 treatment does not seriously damage the MWCNT framework for 24 h under the given conditions. The overall tube length and surface smoothness were not significantly changed compared to those of pristine MWCNTs (Figure 1c).
The molding process in polyethylene and reaction with sulfuric acid and nitric acid
- Oxidizing properties. Nitric acid is a strong oxidizing agent as shown by its large positive reduction potential (E 0 r )
The increase in the amount of oxygen can be clearly observed by comparing the observation spectra of different samples (Figure 14a, Table 4). Spent points of O1 show the increase in the amount of oxygen in different samples with respect to time. This process creates vacancies in the conjugated network and limits some of the properties of graphene.
In pristine HOPG there is no D band (ID/IG =0.01) and a very sharp G band, but after treatment with acid mixtures, the D band starts to appear. 16b) is the most important feature in the Raman spectrum of graphite, related to the number of layers and crystallinity. The intensity of the 2D band decreases with increasing treatment time, indicating a decrease in the crystallinity of the upper layers.
In the first study, five acidic media, commonly used for the purification and functionality of MWCNT, were evaluated in terms of their acid strength and oxidative nature. Other acids such as H2SO4, PPA and PPA/P2O5 are safe enough for the purification and functionality of MWCNT in the media for 24 hours under the tested conditions. To confirm the functionality and number of damaged layers in the acid mixture, various characterization techniques were used.
Raman spectroscopy was used to verify the crystallinity of the acid-treated HOPG, which clearly shows the damage formed on the top surface with a gradual increase in depth with increasing treatment time. Changes in chiral distribution induced by sonication: a complication in using single-walled carbon nanotube fluorescence to determine species distributions. The role of carboxylated carbon fragments in the functionalization and spectroscopy of single-walled carbon nanotube material.
Stability of Multiwalled Carbon Nanotubes in Different Acids” Polymer Society of Korea Daegu, October 7-8). Synthesis of Multiwalled Polyaniline-Sulfonated Multibranched Multiwalled Carbon Nanotube In Situ Interfacial Static Polymerization” Polymer Society of Korea Daejeon, April 7-8). Stability of Multiwalled Carbon Nanotubes in Different Acidic Media” Recent Progress in Graphene Research 2011, (Suwon, Oct 3-6).
황산과 질산에 의해 생성된 고배향열분해흑연(HOPG)의 손상 조사 및 분석", 대한고분자학회 광주, 10월 6~7일). 앞으로도 실망시키지 않도록 열심히 노력하겠습니다.
