Document Type : Research Paper
Authors
Department of physics, College of Science for Women, University of Babylon, Hilla, Iraq
Abstract
Keywords
INTRODUCTION
Graphene is known as an atomic layer of graphite, which is also the essential unit for fullerenes and CNTs. It is a two dimensional (2D) crystal that is stable under ambient conditions [1, 2]. Graphene has exceptional in-plane structural, mechanical, thermal and electrical properties. These properties make it attractive for application in many research fields [3, 4]. Optoelectronic devices based on graphene have garnered significant interest and show potential for use in solar cells, touch screens, and photodetectors [5-10]. The exceptional optical characteristics of graphene, such as linear optical absorption [11, 12], tunable band-gap [13], and intrinsic photocurrent have been established [14-17]. These qualities can be combined with other unique mechanical and electrical characteristics of graphene to provide novel functions. The weakness of pristine graphene’s absorption, which can reach 2.3%, severely restricts its use in photodetection.
As a result, other strategies have been used to improve the interaction between graphene and photons, such as plasmonic effects [18, 19], photothermoelectric effects [20], sensitization by quantum dots [10, 21, 22], or bulk semiconductors [23]. In this work, we employ chlorophyll as a light-absorbing material for graphene phototransistors and examine the hybrid graphene-chlorophyll devices’ optoelectronic performance. As an organic semiconductor, chlorophyll absorbs light very well. Furthermore, chlorophyll is an exceptionally stable and abundant biomaterial [24]. Studies on chlorophyll photosensitization could be useful for organic photovoltaics [25, 26], optical sensors [27], and artificial photosynthesis [28], since chlorophyll is essential to the process of photosynthesis. Furthermore, because chlorophyll-related molecules come in a variety of forms, it is possible to tailor the energy level alignment in hybrid graphene-organic molecule systems to maximize charge separation and transfer. There are two types of chlorophyll—types A and B—found in green algae and terrestrial plants. The presence of methyl in chlorophyll a, which is substituted by a formyl group in chlorophyll b, is what distinguishes these two types of chlorophylls. In higher plants, the ratio of chlorophyll a to chlorophyll b is roughly 3:1. The visible spectrum’s red (650–700 nm) and blue–violet (400–500 nm) bands are the primary wavelengths that chlorophyll absorbs [29].
MATERIALS AND METHODS
Pulse laser ablation
Graphene powders can be obtained by using Q-Switched Nd: YAG pulsed laser in liquids as showed in Fig. 1.
Preparation of chlorophyll (collection of plants and chlorophyll extraction)
The spinach leaves from the plant is collected. Ten milliliters of 80% acetone were used to grind five grams of freshly chopped leaves. Then, for five minutes, it was centrifuged at 5000–10000 rpm. Once the supernatant was moved, the process was repeated until the residue lost all of its color [29].
RESULTS AND DISCUSSION
XRD pattern
A significant peak at 2θ = 26° can be seen in the XRD pattern of graphene, as illustrated in Fig. 2. It’s a unique peak that appear to be quite broad with lesser intensity when compared to bulk graphite’s patterns, which is consistent with the previous report [30].
Morphological study
Using FESEM, the surface morphology was examined. The graphene nanoparticles have a spherical shape and different sizes and have an almost homogeneous distribution as showed in Fig. 3. The Image J program was used to calculate the average particle size and it was about 40 nm, which is close to what the researcher reported in the reference [31].
Optical properties
UV-visible spectrum
The UV-visible spectrum of graphene is displayed in Fig. 4. According to earlier research, graphene has an absorption peak at 285.4nm [32]. The electrical arrangement of graphene during the reduction of graphene oxide is the cause of this peak. The n-π* transition of C–O bonds, which are now embedded on the graphene due to exfoliation and intercalation, is responsible for this absorption peak.
Fig. 5 illustrates the UV-Vis spectrum of chlorophyll extract dissolved in acetone absorption. The highest absorption was seen at 433.3 and 664.2 nm [33].
Fig. 6 shows the UV-Vis spectrum of graphene/chlorophyll sample. The absorption peaks for the chlorophyll/graphene are located at 340.8 and 666.2 nm.
Photoluminescence
The researchers [34] affirmed that the emission peak of carbon is usually wide with large stocks shift as compared with that of organic dyes and it may result from the wide distributions of dierently sized particles and surface chemistry, different emissive traps (salvation effect), or a mechanism currently unresolved [35]. The emission of the graphene typically shows wide optical emission in the visible region (Fig. 7).
Also, the additional PL data of graphene/chlorophyll sample is shown in Fig. 8. In this sample, there is a clear quenching of PL. The PL quenching suggests that charge transfer occurs between the chlorophyll film and graphene, which reduces radiative recombination since electron–hole pairs are produced in the chlorophyll molecules under illumination [36].
CONCLUSION
The pulsed laser, with a wavelength of 1064 nm, energy of 80 mJ, a frequency of 6 Hz, and a number of pulses of 400 pulses, has the ability to generate nanoparticles having a spherical shape and homogeneous distribution with absorption peak at 285.4nm. The pulsed laser has the ability to exfoliate graphite layers through the appearance of a single peak of low intensity as compared to graphite. Through the PL results, we notice that mixing chlorophyll with graphene nanoparticles enhanced the emission spectrum at 400.7 nm, and this indicates the removal of a small portion of impurities during the mixing process and showed quenching of graphene as a result of charge transfer from chlorophyll, which caused a reduction in radiative recombination.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.
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