pH-responsive dispersed reduced graphene oxide using poly(3-aminophenylboronic acid) via in situ polymerization method

Content Provider	Semantic Scholar
Author	Feng, Huixia Yones, Hamza Abdalla
Copyright Year	2015
Abstract	Homogeneous aqueous suspensions of graphene have been prepared by chemical reduction of graphene oxide in the presence of poly(3-aminophenylboronic acid) (PABA) in alkale solution. The graphene sheets in thus prepared suspensions can stable several months and can be switch to aggregated state with low-er pH values. Introduction Reduced graphene oxide (RGO), a single layer of sp2-bonded carbon atoms, has attracted enormous attention owing to its unique structure and its exceptional electronic, mechanical, and thermal properties [A. K. Geim. 2007]. These properties make graphene a highly promising material for many potential applications such as logic devices, transparent electrodes and sensors [Y. -M. Lin, 2010]. Unfortunately, as-produced graphene generally shows limited solubility in conventional solvents, which has severely hindered its practical application. Noncovalent functionalization has provided a simple but effective route to solve this problem. Up to now, various polymers and surfactants such as chitosan [Jiyang Liu. 2012], lysozyme [Fan Yang. 2010], poly(ethyleneimine) [Angus Griffith. 2011], have been used to facilitate the dispersion of graphene. However, little attention has been paid to the possibility of controlling the dispersion/aggregation of graphene in solutions using Polyaniline (PANI) and PANI derivatives due to the poor solubility of PANI. poly(3-aminophenylboronic acid) (PABA) is self-doped PANI derivatives, which is a stimulusresponsive polymer with a solubility that can be reversibly alerted by pH changes [Bhavana A. Deore. 2003]. Using PABA as a mediating agent for graphene dispersing may bring about an interesting system that is possible integrated with both the merits of graphene and PABA. Here, we demonstrate the fabrication of such graphene/PABA system and discuss the pH-responsiveness of the system. Homogeneous aqueous suspension of graphene has been prepared by chemical reduction of graphene oxide (GO) in the presence of PABA in basic condition, and the graphene in the asprepared suspension can be switched irreversibly to a more aggregated state with reducing pH value as a stimulus due to the strong van der Waals interactions between them. This perhaps provides a new way to preparation of unique graphene composite. Experimental section Materials Graphite powder, 3-aminophenylboronic acid hemisulfate salt (ABA), potassium fluoride, fructose, were purchased from Aldrich. Other reagents were analytical grade and used as received. All of the solutions were prepared using deionized water (18.2 MΩ). General Methods GO nanosheets were prepared from natural graphite powders by a modified Hummer’s method1. In the first step, preoxidized graphite powder was synthesized through reaction of natural graphite (1 g), sulfuric acid (4 mL), K2S2O8 (0.8 g), and P2O5 (0.8 g), the reaction mixture was maintained at 80 oC for 5h and was terminated by adding 170mL deionized water. This preoxidized graphite powder (600 mg) was further oxidized by sulfuric acid (24 mL), KMnO4 (3 g), the reaction mixture International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) © 2015. The authors Published by Atlantis Press 1167 was stirred at 35 oC for 2h. In the end, the reaction mixture was maintained at 98 oC for 0.5h and was terminated by adding 50 mL deionized water. It was then further treated with H2O2 (30 wt %, 6 mL). The resulting GO solution was filtered and washed with deionized water several times, and complete remove of metal ions by dialysis membrane for a week, and vacuum dried overnight at 40 oC. In a typical synthesis, GO was dispersed in deionized water to create 0.1 mg/mL dispersion with the aid of ultrasonication. After dissolving g PABA in pH=12 NaOH solution, homogeneous GO/PABA solution was prepared by simply mixing 6 mL PABA and 2mL GO suspension under stirring (the amount of PABA should be at least 50 times larger than that of GO). g Hydrazine monohydrate (0.1 mL, 98%) was then added, and the suspension was heated at 80 oC for 24h. Finally, black RGO dispersion was obtained and be stabled more than half a year. Results and analysis Characterization To identify the crystalline phase and the extent of surface functionalization of GO and RGO, Xray diffraction (XRD) patterns and Elemental analyses data were collected using a Rigaku D/MAX 2400 diffractometer and an elementar analysensysteme GmbH varioEL cube analyzer, respectively. The conductivities of GO and RGO were also explored by the four-point probe system (ST2253, Suzhou Jingge Electronic Co., China). Figure 1 shows the XRD patterns of pristine graphite powder, GO and RGO. Graphite powder shows a sharp (002) peak at 26.4o with a typical d-spacing of 3.37 Å. GO exhibits a diffraction peak (002) at 2theta of 11.37o corresponding to a d-spacing of 7.82 Å, which suggests that graphite has been successfully oxidized by Hummers’ method. It is also seen that the corresponding peak disappears after reduction, indicating the successful formation of RGO. Fig. 1 XRD patterns of pristine graphite powder, GO and RGO Likewise, elemental analyses revealed deoxygenation of GO to form RGO. An increase in the C/O atomic ratio of RGO was found to be 2.66 compared to 1.08 in as-prepared GO (Table. 1). C (wt%) N (wt%) H (wt%) O (wt%) C/O GO 43.40 0.24 3.06 53.39 1.08 RGO 62.58 4.03 1.99 31.4 2.66 Table 1 Elemental analysis results of GO and RGO It is well-known that, during reductions, GO gradually loses its oxygen-containing groups and becomes hydrophobic, so that direct reduction of GO in water without proper mediating agents generally causes irreversible aggregations. PABA is a weak polyelectrolyte and its molecular conformation and solubility can be reversibly altered by pH changes (Figure 2). Therefore, noncovalent
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DOI	10.2991/ipemec-15.2015.216
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