BORON DOPED GRAPHENE OXIDE: SYNTHESIS AND APPLICATION TO GLUCOSE

In this present research, we have synthesized graphene oxide (GO) by modified Hummer’s method using graphite flake as starting material. Boron atoms were succ framework with an atomic percentage of 1.64 as a precursor. The presence of B analyses. Shifting of XRD peak from 10 incorporation of boron atoms. The crystalline defect was further confirmed by the Raman spectroscopy. Finally, the C=C, C environments were preci reduced graphene oxide (B significant glucose adsorption reactivity of 65 towards oxygen atoms of the glucose molecules.

Numerous researches have been conducted on graphene oxide (GO) since its first invention by Brodie (Brodie 1859). The hybridized carbon domain and different oxygen functionalities oxyl, and carbonyl groups showed distinctive mechanical, electrical and opto-electronical properties (Geim 2007 andMcAllister 2007). The outstanding physical properties of GO makes it an attractive material for fabrication of various nanocomposites, polymer materials, high performances microelectronic devices, energy storage materials, and for biomedical applications (Lightcap 2014, Huang 2012and Zhu 2010. Moreover, due to the hydrophilicity character of GO, it could be easily dispersed in gen functionalities in GO caused a severe decline in electrical properties, thermo mechanical stability and based materials (Dreyer et al., 2010). To minimize these problems, incorporation of nonitrogen, sulfur fluorine, and phosphorous into the GO layer have been developed to improve the electrochemical properties (Stephan 1994, Ekimov doped GO by chemical vapor deposition, thermal annealing, plasma irradiation methods have been reported for the application of electrical, enhancement of surface energy, increment of n polarization energy (Czerw 2001, Xia 2004, Wei 2009, Wang 2013, Li 2009and Kumar 2013. incomplete purification and excessive amount of by products were remaining in the resulting GO materials and post treatment requires high temperature (800 cause structural degradation and morphological defects (Wei al. 2015). Boron and boron-nitrogen co thermal anneling and microwave assisted method have been reported for the application of supercapacitor, high performance anode material in Li ion battery, electromagnetic radiation in Ku-band etc. (Li 2016(Li , 2015. In this research, we report a novel approach for synthesizing boron doped reduced graphene oxide (B through treating a mixture of graphene oxide (GO) and boric acid solution by simple hydrothermal condition in vessel reaction chamber. The B different techniques, and its application to glucose adsorption reactivity was evaluated. The B other applications such as sensor and/or energy storage devices.
In this present research, we have synthesized graphene oxide (GO) by modified Hummer's method using graphite flake as starting material. Boron atoms were successfully doped into the GO 1.89 at. % by hydrothermal reduction using boric acid O bonds was predicted from the FT-IR spectral presumably indicated the reduction of GO by the incorporation of boron atoms. The crystalline defect was further confirmed by the Raman COO -, B 2 O 3 , and C-OH chemical sely predicted by the XPS peak fitting analyses. The boron functionalized rGO) was subjected to the glucose adsorption reaction that showed 70% due to the high adsorption affinity of boron ribution License, which permits unrestricted reported for the application of electrical, enhancement of surface energy, increment of n-type carrier concentration and polarization energy (Czerw 2001, Xia 2004, Wei 2009, Wang 2013, Li 2009and Kumar 2013. However, drawbacks like incomplete purification and excessive amount of by products were remaining in the resulting GO materials and post treatment requires high temperature (8001200C) which may cause structural degradation and morphological defects (Wei et nitrogen co-doped GO by simple thermal anneling and microwave assisted method have been reported for the application of supercapacitor, high performance anode material in Li ion battery, electromagnetic tc. (Li 2016, Yeom 2015and Umrao 2015. In this research, we report a novel approach for synthesizing boron doped reduced graphene oxide (B-rGO) through treating a mixture of graphene oxide (GO) and boric acid solution by simple hydrothermal condition in a closed vessel reaction chamber. The B-rGO was characterized using different techniques, and its application to glucose adsorption reactivity was evaluated. The B-rGO could be investigated for other applications such as sensor and/or energy storage

Synthesis of B-rGO:
Graphene oxide (GO) was synthesized by modified Hummerʼs method in which graphite flake was used as the starting material (Allahbakhsh 2014). In a 1L beaker, 4.0 g of NaNO 3 weigh out and concentrated H 2 SO 4 (148 mL) were added and stirred for 30 minutes in an ice bath. Thereafter, KMnO 4 (20.0 g) was added slowly to the solution and stirred for 40 minutes at 35C. Then, distilled water (184 mL) was added while mixing for 15 minutes at 95C. All the steps are done in an oil bath. Further, 400 mL of H 2 O and about 25 mL of hydrogen peroxide (H 2 O 2 ) were added and stirred at 4000 rpm for 10 minutes. Subsequently, the mixture was washed with 5% HCl and centrifuged at 4000 rpm for 30 minutes. The next step was exfoliation by sonication for 46 hrs. After that centrifuged the mixture at 10,000 rpm for 30 minutes and the resulting supernatant was GO. Finally, it was dried for 3 to 4 days in an oven at 60C. The obtained GO was functionalized by simple hydrothermal reaction method in which the reactor was equipped with an 8.8 mL inconel batch. A schematic of the synthesis and functionalization process of GO with inconel batch reactor is shown in Fig.1. Typical 0.25g of GO and 5.0 mL aqueous solution of boric acid with different concentrations were loaded into the reactor. Thereafter, desired reaction conditions such as temperature, pressure and time were set in the reaction period and are shown in Table-1. The resulting samples were referred as functionalized reduced graphene oxide (B-rGO),which were collected, washed, filtered and dried overnight in an oven at 60C. Finally, the samples were characterized by using different instrumental techniques such as FT-IR, XRD, Raman, XPS, UV-vis, HPLC etc.

Characterization of B-rGO:
Fourier transform infrared spectroscopy (JASCO, FTIR-4100) was used to determine different functional groups present in GO and functionalized B-rGO. The measurements were carried out in the wavelength range of 4000 to 400 cm -1 . X-ray photoelectron spectroscopy (Perkin Elmer Phi 1600 ESCA) was used to determine the elemental compositions. The XPS was performed at Kumamoto University Instrumental Centre, Japan in which the AlK α was used as the X-ray source for irradiation of the sample surface. Solid state crystallographic structure was determined by X-ray diffractometer (Rigaku, MiniFlex600) using CuK α radiation source. Diffraction data were taken at 2= 5 to 90 with step energy 0.02 eV. Raman spectroscopy was used to evaluate the microstructure using JASCO NRS-3100 Laser Raman spectrophotometer. The Raman shift was recorded at 500-4000 cm -1 wavelength region.

Determination of glucose adsorption capacity of B-rGO:
Glucose adsorption capacity of B-rGO was determined by HPLC and UV-vis spectroscopic methods. In this experiment, a typical reagent DNS (3,5-dinitrosalicylic acid) was used. It reacts with reducing sugar, forming 3-amino-5-nitrosalicylic acid, which strongly absorbs light at 540 nm wavelength region (Miller 1959). About 1.5 g DNS and 45.0 g sodium potassium tartrate were dissolved in 75.0 mL of distilled water and 30.0 mL of 2M NaOH, respectively. Then the sodium potassium tartrate and DNS solutions were mixed together and the volume was made up to 150 mL with distilled water and named it as DNS reagent. 50.0 mg glucose was taken into 45.0 mL centrifuge tube and 12.0 mL deionized water was added then the tube was vortexed vigorously. Thereafter, 100.0 mg of the B-rGO was loaded into different five test tubes and the contents were mixed well. All the test tubes were kept at room temperature and vortexed (MIXER UZUSIO, VTX-3000L) for 2 minutes after every 5 minutes. One test tube was taken after 20 minutes and centrifuged (speed and time). In this way, all the five test tubes were centrifuged at each of the following reaction times: 20, 30, 40, 60 and 120 minutes. 1.0 mL of the supernatant, 2.0 mL distilled water and 3.0 mL of the freshly prepared DNS solution were mixed together. Light yellow colored solution of the reaction mixture was put into boiling water bath for the period of about 5 minutes and then it was cooled by flowing cool tap water. The absorbance was taken by UV-vis spectrophotometer (JASCO, V-660 spectrophotometer) at 540 nm. A standard curve of D(+) glucose was made with five different concentrations such as 1, 2, 3, 4, and 5 ppm. Unknown concentration was determined from the standard curve. Concentration of the unknown sample solution was also determined via high performance liquid chromatography (JASCO, UV-970). In this case, a standard curve was also plotted and the glucose adsorption capacity was calculated by using the following equation. The following equation (1) was used in both the UV-vis and HPLC measurements: Where, I Initial and I Final are the initial and final concentration of the glucose in solution.

RESULTS AND DISCUSSION
FT-IR analyses: Different functional groups present in the synthesized GO and B-rGO were assessed by FT-IR spectroscopic measurement. The FT-IR spectra of GO and B-rGO are shown in Fig. 2 (a-b). It is observed that at least five distinctive peaks characteristics of GO are seen in the spectrum (Fig. 2a). The peaks at 3300 cm -1 , 1736, 1620, 1232, and 1060 cm -1 , are assigned for GO by the stretching vibration of hydroxyl (-OH), carbonyl (C-O), aromatic (C=C), epoxy (C-O-C) and alkoxy (C-O) bonds, respectively, (Song 2014 and. In the spectra of the B-rGO (Fig. 2b), the hydroxyl peak became sharp and observed at around 3250 cm -1 due to incorporation of boron atoms and consequently the reduction of GO. There are three new peaks observed additionally at 1450 cm -1 , 1200 and 1120 cm -1 , respectively. These new peaks could be assigned for the stretching vibration of B-O, B-C and C-O bonds (Ram 1989, Jacox 2000and Gago 2000. From the spectral analyses, therefore, we can suggest that the B-O and B-C bonds have been created in the GO network after boron functionalities. XRD analyses: Crystalline structures of GO and B-rGO were investigated by XRD analyses. XRD patterns for the samples were shown in Fig. 3. A strong and intense peak at around 2=10 (d=0.44 nm) has been observed which is assigned for the non-functionalized graphene oxide (Eda 2008 andChen 2010). This characteristics peak in the XRD pattern of GO is completely disappeared in those of B-rGO, indicating that the oxygen containing groups of GO were efficiently removed at a certain percentage. Meanwhile, a new peak at around 2=24.5 (d=0.170.19 nm) has been found after hydrothermal functionalization with boric acid. This broad peak (2=24.5) suggests the exfoliation and reduction of GO with boron functionalities (Panchakarla et. al. 2009). A significant decrease in the interlayer spacing distance from d=0.44 to d=0.170.19 nm also support incorporation of boron atom into the GO layer. The absence of the peaks associated with oxygen functionalities in the FT-IR spectra (Fig. 2a) agrees well with XRD results. This findings has also been coincided with the XPS analyses, since, the atomic concentration of boron was found to be 1.641.89 at % (Table-1) expressed in the following section.
XPS analyses: X-ray photoelectron spectroscopy (XPS) measurements were carried out in order to further investigate the chemical composition and chemical environment around carbon, oxygen and boron atoms for B-rGO samples. The XPS survey scan spectra showed the evidence of C, O, and B elements and are shown in Fig. 4a. The elemental compositions (at. %) were calculated from the XPS peak intensities and are shown in Table 1.  As synthesized GO It is seen that boron incorporation is increased up to 1.89 at.% with the increase of reaction temperature and the concentration of boric acid. High resolution core shell XPS spectra of C1s, O1s and B1s are carried out in order to explain the chemical environment around the C, O and B atoms of the B-rGO after boron doping. The deconvoluted C1s, B1s and O1s spectra are shown in Fig. 4 (b-d). The C1s spectra could be deconvoluted into three peaks. The main peak located at the binding energy 284.2 eV is due to the sp 2 -C=C chemical environment and the peak located at the binding energy region of 284.9 eV could be suggested for the C-C/C=C bonds. The shoulder peak at 285.8 eV is due to the carbonyl C-O chemical environments (Sahoo 2015, Duan 20015 andLi 2015). The B1s could be deconvoluted into three component peaks Fig. 4c. The peaks at 191.8,192.6 and 193.2 eV are assigned for the -BC 3 , -BC 2 O and -BCO 2 chemical environment, respectively, since the results are very good agreement with the reported value (Sahoo 2015 andFang 2014). From the deconvolution of O1s spectrum, correspondingly, four components peaks at 530.7 532.0, 533.2 and 534.2 eV were found which could be suggested for the carbonyl C-O, carboxylic -COO -, -B 2 O 3 and hydroxyl -C-OH chemical environments, respectively (Sahoo 2015). These results are in good agreement with the FT-IR analyses (Fig. 2b).
Raman analyses: Raman spectroscopy was used for indentifying the crystalline structure and quality of the asreceived GO as well as B-rGO. C1s 198 196 194 192 190 188 186 184 Intensity (arb.unit)

(c) (d)
The measurements have been done in the spectral region of 1000-2000 cm -1 using same laser power (632 nm laser excitation) for all the samples. The Raman spectra of the samples are shown in Fig. 5. It is seen that the D band intensity is increased while the G band intensity is decreased for the assynthesized GO and the B-rGO in comparison to that of the pristine graphite flake. The increase in intensity and broadening of both the D and G band confirmed the assimilation of oxygen containing functional groups as well as the assimilation of boron elements in the GO framework. This functionality caused the loss of crystalline structure of both the GO and B-rGO. Forward shifting of the G band position from 1595 to 1600 cm -1 B-rGO suggesting the inclusion of boron atoms in the GO lattice leading to increase the disordered structure (Hishiyama 2001). The increment in the I D /I G ratio clearly demonstrates the formation of defects in the graphene sheets by boron doping that might leads to considerable changes in the structural properties, electrical and other physicochemical properties.  Fig. 6. It was found that the adsorption reactivity of graphite and GO were found to be almost comparable. The highest adsorption was observed (6570%) for B-rGO in the reaction period of 40 minutes and then the reactivity was declined with reaction time. The adsorption mechanism could be initially presumed that the boron atoms of B-rGO could bind to the C-1/C-2 diol and C-4/C-6 diol of glucose in its hexopyranose form (Ferrier 1965). Another possibility is that the binding between the boron atoms of B-rGO and the oxygen atoms of the furanoside form of free hexoses (Eggert 1999). The plausible mechanism of the binding site is shown in Fig. 7. From the results, it could be acclaimed that the B-rGO could be used as the blood glucose biosensing receptors. However, more researches have to be done to confirm the bio-sensing reactivity of the B-rGO.

Conclusions
We have synthesized GO by modified Hummer's method using graphite flake as the starting material and boron doping was successfully achieved by hydrothermal reaction using boric acid as precursor. FT-IR confirmed the presence of different functional groups in the GO and B-C and B-O bonds in B-rGO. The crystalline defect structural was confirmed by XRD and Raman spectroscopic analyses. This method gives about 1.641.89 at.% of boron doping onto the GO lattice which was confirmed by XPS. The B-rGO exhibited significant glucose responsive reactivity with the adsorption percentage of 6570%. The B-rGO could be used as glucose adsorption bio-sensing applications.