A Novel Strategy for Sustainable Synthesis of Soluble‐Graphene by a Herb Delphinium denudatum Root Extract for Use as Light‐Weight Supercapacitors

Abstract

Synthesis of high‐quality graphene nanosheets under eco‐friendly strategies is of enormous interest today hence graphene‐based materials offer unique advantages in a wide range of applications including light‐weight supercapacitors. The reduction of graphene oxide (GO) by chemical reagents frequently involves hazardous reductants that are also dangerous to humans. In view of sustainability, we develop a facile and green procedure to synthesize soluble‐graphene by reducing the GO in delphinium root extraction for the first time. The reducing property of organic compounds that exist in the aqueous delphinium root extract may be accountable for the reduction of exfoliated GO to D‐graphene under reflux condition. The efficient elimination of oxygen functionalities from GO was verified by powder X‐ray diffraction (PXRD), UV‐Visible spectroscopy (UV‐Vis), Fourier transform infrared (FT‐IR), and X‐ray photoelectron spectroscopy (XPS) studies. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) studies indicate the successful development of few‐layer graphene. The electrochemical activities are delivered by cyclic voltammetry (CV) and galvanic charge‐discharge (GCD) studies. This uniquely‐synthesized D‐graphene electrode offers superior electrochemical performance at 2 A g−1 with an utmost specific capacitance (Cs) of 158 F g−1 and high energy density (E) of 22 Wh Kg−1. Taking the above remarkable results, the characteristics of eco‐friendly, easy synthesis and cheap endow this green approach as a promising avenue for the exploitation of graphene‐based materials in numerous applications, particularly for graphene‐based light‐weight supercapacitors.

Synthesis and Functionalization of Graphene Materials for Biomedical Applications: Recent Advances, Challenges, and Perspectives

“…[ 31 ] Although there are thousands of substances, there are almost no two substances whose diffraction spectra are the same, so a qualitative analysis of the phase of the substance can be carried out. [ 50 ] The XRD spectra of GO and rGO showed in Figure 2i are a good instance; there is an increase of d nkl in GO due to the oxygen moieties between graphene layers. Thus, the peak at 12.2° of GOs shifts to 26.64° of the rGO, which brings an obvious difference in the XRD spectra between the two samples.…”

“…Applying chemical reductants that do not react with water is traditional. [ 1,45 ] For example, hydrazine monohydrate, [ 14 ] hydrazine hydrate, [ 46 ] a large excess of NaBH 4 , [ 47 ] phenylhydrazine, [ 40 ] hydroxylamine, [ 41 ] glucose, [ 23b ] ascorbic acid, [ 45,48 ] proteins, [ 49 ] and novel green‐reductant like delphinium root extract [ 50 ] were utilized as reductants. Electrochemical reduction is another reducing method, where rGO was demonstrated to precipitate on the graphite electrode with a voltage change from −0.8 to −1.5 V. [ 51 ] This method is relatively clean and is based on the reaction of GO + H + + e − = rGO + H 2 O.…”

“…The functional groups in the samples can be ensured to identify further the type of graphene materials (Figure 2h). [ 50 ] For example, GO, and rGO can be distinguished based on XPS, where the intensity of sp 2 carbons in aromatic rings (CC, 284.5 eV) exhibits no change. By contrast, the intensity of carbonyl (CO, 287.7 eV) peaks significantly decreases in the case of rGO.…”

“…By contrast, the intensity of carbonyl (CO, 287.7 eV) peaks significantly decreases in the case of rGO. [ 41,50 ]…”

“…[31] Some corresponding standard relationships exist between wavelengths in the FT-IR spectrum and bond types. [35,50] For instance, 1620 nm is attributed to the aromatic C=C bond, 1060 nm corresponds to the C-O stretching vibration mode in the alkoxy group, 1170 nm originates from the epoxy C-O stretching peak, 1400 nm arises from the C-OH carboxyl group, 1740 nm is attributed to the C=O stretching mode in the carboxyl group, 2930 nm is assigned to C-H, and 3420 nm is for the O-H groups (Figure 2f). [23b] As shown in Figure 2f, the absorbance signals of bond types in p-G, GO, and rGO are different; for example, rGO exhibits the highest absorbance signal of all bond types, from which the types of graphene materials can be identified.…”