Introduction

Graphene (Gr), a single layer of sp 2-hybridized carbon atoms in a closely packed honeycomb two-dimensional lattice, has attracted enormous attention since its discovery in 2004 [1]. Graphene, a new two-dimensional carbon nanomaterial and a fundamental building block for graphitic materials, has been the hotspot in multidisciplinary field owing to its high surface area (surface/mass), excellent electrical behavior, and thermal properties [2–6].

One of the most commonly used derivatives of graphene is graphene oxide (GO). One of the important structural elements of graphite is GO that is conjunct together by van der Waals forces. GO has attracted a lot of attention because of its capability of being used in energy, electronics, water treatment membranes, etc. [7].

Glycine with the formula NH2CH2COOH (abbreviated as Gly or G) [8] is one of the organic compounds. Glycine is the smallest among amino acids usually found in proteins. With considering a hydrogen substituent assist side-chain [8]. Glycine is used as a biocompatible compound for the synthesis of many molecules [9] and for treating schizophrenia, benign prostatic hyperplasia (BPH), and some rare inherited metabolic disorders. It is also employed in memory enhancement and cancer prevention, and protects kidneys from the harmful side effects of certain drugs used after organ transplantation as well as the liver from the harmful effects of alcohol [10, 11].

Nanocomposite is a multiphase solid material in which one of the phases has one, two, or three dimensions of lower than 100 nm [11], or structures having nanoscale repeat distances between the different phases that make up the material [11]. Graphene oxide–glycine (GO–G) nanocomposites can be used in adsorption process and other applications.

In this study, we have synthesized GO–G nanocomposites. To produce this nanocomposite of GO sheets, glycine with known concentration was added to GO suspension in ethanol solvent. Nanocomposites provided were characterized by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FT-IR), respectively. Thermogravimetric analysis (TGA) was employed to investigate the thermal stability of these nanocomposites.

Materials and methods

Materials

Graphene oxide

GO used in this work was provided by “nanocs” company –graphene (USA) with a purity of over 90 %. The GO used was a dry powder with the following characteristics: color: brown, composition: carbon (79 %), oxygen (20 %), flake size: 0.5–5 microns, thickness: 1 atomic layer—at least 80 % (Fig. 1).

Fig. 1
figure 1

Scanning electron microscope (SEM) for graphene oxide (GO)

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Glycine

Glycine used in this work was provided by Sigma-Aldrich Company with a purity of more than 99 %. The glycine used possessed the following characteristics: CAS number: 56-40-6, impurities: ≤0.01 % insoluble matter, pKa (25 °C): 2.35 and m.p.: 240 °C (dec.) (lit.).

Preparation of graphene oxide–glycine nanocomposites

GO–G nanocomposites were prepared according to the following method: 45 mg of dry powder of GO and 80 mg of glycine were dissolved in ethanol and shaken well until the solution becomes even. Then 50 mg of 1-ethyl(3,3-die-amino-propel acetate) Carobo amide 99 % (EDC) was added to initiate the reaction between GO and glycine (with purity ≥99 % provided by Aldrich Company). Then 25 mg of N-hydroxyl 99.9 % (Aldrich Company) was added to the above mixture and refluxed for 36 h at 70 °C. After 2 days, GO–G nanocomposites were prepared, and using a vacuum pump and micro-cellulose paper with a pore size 22/0 micrometer, these nanocomposites were separated from other materials and the deposit was washed with ethanol and water mixture in equal proportions until the pH of the water coming out of the filter paper becomes neutral. After GO–G nanocomposites were formed, they were placed in vacuum oven for 1 day at 45 °C to dry completely.

Results and discussion

Characterization of GO–G nanocomposites

FT-IR spectroscopies of the GO and GO–G nanocomposites are shown in Figs. 2 and 3.

Fig. 2
figure 2

FT-IR of graphene oxide surface

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Fig. 3
figure 3

FT-IR of graphene oxide–glycine nanocomposites

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As shown in Fig. 3 for GO, the peak at 1084 cm−1 is attributed to the (C–O) stretching, peak at 1387 cm−1 is attributed to the (C–O) bending, band at 1627 cm−1 is assigned to vibrations of the carbon–carbon double bond, small band at 1726 cm−1 is assigned to the ketone double bond vibrations (C=O), peak at 2362 cm−1 is attributed to the carboxylic group, peaks at 2849 cm−1 and 2921  cm−1 are attributed to the (C–H) bending vibrations and O–H) peak is also seen at 3434 cm−1 position [11–13].

As observed in Fig. 3, the intensity of the peak of carboxylic group was reduced, because of its reaction with glycine. Also the peak formed at 1555 cm−1 confirms the presence of an imide functional group in the nanocomposite.

Thermal gravity analysis for the stability of graphene oxide–glycine nanocomposites (TGA studies)

The decomposition behaviors of GO and GO–G nanocomposites have been investigated by thermal gravity analysis. Figure 4 shows the thermal stability of the GO, which is relatively good, but at a temperature of about 200 °C, the thermal stability of GO was found to decrease. due to the decomposition of carboxylic and release of CO2 gas.

Fig. 4
figure 4

Thermogravimetric analysis (TGA) of graphene oxide

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But as seen in Fig. 5, the GO–G nanocomposites have less thermal stability than GO. Because nanocomposite GO–G, in addition to the withdrawal of CO2 gas from the molecular structure, structure of nanocomposite with increasing temperature decomposed and nitrogen gas, carbon dioxide gas, etc., will be withdrawal from the molecule of nanocomposite GO–G [13–15].

Fig. 5
figure 5

Thermogravimetric analysis (TGA) of graphene oxide–glycine nanocomposites

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Conclusions

In this study, we investigated the stability of GO–G nanocomposites by thermal gravity analysis. In order to study the thermal stability, we synthesized nanocomposite by performing reaction between dry powder of GO and glycine. Results of characterization by SEM and FT-IR showed that nanocomposite was created by the reaction between GO and glycine. Then, we used TGA and found that the thermal stability of GO is more than that of the GO–G nanocomposites.