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1. Introduction
The development of technological devices, especially in the industrial sector, is increasingly advanced where one of the applications is the use of data on industrial waste products (Vijay et al., 2016). Most of the biowaste residual from oil palm mill plantations is burned or disposed of in dumping ponds. This phenomenon causes global climate change by emitting carbon dioxide and methane gas (Awalludin et al., 2015; Sembiring et. al., 2019; Utama et al., 2018). Palm oil mill effluent contains 60-83 million tons of waste, the amount of which increased by 85-110 million tons in 2020 (Onoja et al., 2019). Palm oil mill effluent has been successfully used by with natural ingredients graphene for textile Teow et al. (2019) color cleaning applications, bio-lubricant (Syaima et al, 2015) and environmental hygiene in the industrial sector (Iskandar et al., 2018).
The increasing awareness about pollution has led to the development of solutions to environmental problems by maximizing the utilization of abundant biomass for the manufacture of nanocarbons. Biomass, especially from agricultural by-products, is a rich source of cellulosic material. Biomass contains an average composition of 40%-50% cellulose, 20%-30% hemicellulose, 20%-25% lignin and 1%-5% ash and exhibits excellent water solubility, making it an attractive source of nanocarbons (Rafatullah et al., 2013). Various raw materials from biomass, including grass (Kang et al., 2005), rice husks (Muramatsu et al., 2014), coconut shells and husks (Chunduri et al., 2016), coffee beans (Jiang et al., 2014), banana leaves or peels (De & Karak, 2013), lemon peels and watermelon peels Zhou et al. (2012) have been used as carbon sources. In addition, fruit extract can be used as a carbon source and can be applied in bioimaging, as a fluorescent probe to detect Fe3+ ions and fluorescence ink (Zhang et al., 2018). However, the utilization of biomass from POME waste is very attractive due to the environmental friendliness of lignocellulosic material (Tanikkul et al., 2019) and its main advantages, including its abundant availability and low cost, make this biomass a suitable precursor for nanocarbon manufacture.
Nanocarbon is a semiconductor nanocrystalline material that has a diameter smaller than 10 nanometers which has good photostability, high water solubility, and its chemical properties are easy to modify. Then, the hydrothermal method is an effective method for making carbonization and can make materials in nanosize (Abbas et al., 2018). The manufacture of nanocarbons has been widely carried out using the hydrothermal method from rice husks (Sun & Lei, 2017), then fluorescent nanocarbon using the hydrothermal method from fruit extracts for catalyst applications (Arul et al., 2017).
We performed the research on the synthesis of the nanocarbon particle from palm oil mill effluent using a hydrothermal method. The characterization of the structure and particle size distribution using XRD and PSA is presented.
2. Materials and methods
Palm oil mill effluent solution was collected from palm oil in Sumatera Utara, Indonesia. Palm oil mill effluent solution as precursor of 100 g was added to 1000 ml of distilled water and centrifuged for 60 seconds at 3000 rpm for 3 times. Furthermore, the precursor was centrifuged and stirred on a hotplate for 30 minutes at room temperature. The solution was poured into a Teflon tube and put in an oven heated at 200oC for 6 hours. After cooling, the nanocarbon solution was centrifuged at 3000 rpm for 60 seconds and the supernatant solution was filtered using a dialysis membrane (0.45 µm nylon) dipped in distilled water for 24 hours. To evaluate the properties of the sample developed in this study, structural and particle size characterizations were performed by X-ray diffraction analysis (XRD), particle size analyzer (PSA), Fourier Transform Infrared (FT-IR) spectroscopy and UV-Vis spectroscopy.
3. Results and discussion
The X-ray diffraction (XRD) analysis of the nanocarbon particle from palm oil mill effluent is shown in Figure 1. For the evaluation of degree in the nanocarbon particle from palm oil mill effluent, also called crystallized structured in PF nanocomposites, the XRD profile of sample was used as a reference. According to the XRD results, the absence of a peak in the XRD pattern indicated that the nanocarbon particle from palm oil mill effluent was a crystalline structure with the variations of carbon.
Figure 1 shows structural of nanocarbon from palm oil mill effluent. In Figure 1, the peak of nanocarbon can be seen in (hkl) of (114), (002), (102), (210), (211), (202), (100), (102), (004), (103), (110). XRD pattern in Figure 1 confirmed carbon structures in all peaks. The results are the same as those reported by Howe et al. (2003) that carbon structures observed in 002 and 102, among others. The parameters of the crystal sample nanocarbon from palm oil mill effluent in all crystal planes can be seen in Table 1.
Table 1 Parameters of the crystal sample nanocarbon from palm oil mill effluent in all crystal planes.
| Peak | 2θ (deg.) |
hkl | FWHM (deg.) |
D (nm) |
|---|---|---|---|---|
| 1 | 20.74 | 114 | 0.31 | 26.91 |
| 2 | 25.01 | 002 | 0.24 | 34.76 |
| 3 | 25.97 | 102 | 0.22 | 37.93 |
| 4 | 28.33 | 210 | 0.41 | 20.35 |
| 5 | 29.87 | 211 | 0.29 | 28.77 |
| 6 | 31.07 | 202 | 0.19 | 43.91 |
| 7 | 40.54 | 100 | 0.24 | 34.76 |
| 8 | 50.51 | 102 | 0.25 | 33.37 |
| 9 | 58.82 | 004 | 0.22 | 37.92 |
| 10 | 66.40 | 103 | 0.53 | 15.74 |
| 11 | 73.28 | 110 | 0.38 | 21.95 |
In Table 1, the peaks list increases with FWHM but it decreases with crystal size (D). This research shows that the XRD pattern can be provide information about impurty of nanocarbon from palm oil mill effluent synthesized using the hydrothermal method. As seen in Figure 1, some peaks confirmed the other carbon unsure. Generally, the palm oil mill effluent has amorphous structures. The results of the amorphous structure from nanocarbon is also confirmed from previous results with a precursor of citric acid (Hu et al., 2017; Bhaisare et al., 2015; Takayanagi et al., 2020). However, in this research, making palm oil mill effluent by using the hydrothermal method could confirm that carbon unsure from Figure 1.
Figure 2 shows the particle size distribution of nanocarbon from palm oil mill effluent using a particle size analyzer (PSA) with a hydrothermal method. The average particle size of nanocarbon from palm oil mill effluent in Figure 2 was 1.153 nm.; whereas the average crystal size sown in Table 1 was 30.58 nm. These results showed that synthesized carbon particle from palm oil mill effluent using the hydrothermal method was successfully in nanosize. The particle size of nanocarbon increases because of the measurement of the hydrodynamic diameter of a nanocarbon containing a hydrophilic functional group on the surface of nanocarbon (Wu et al., 2017; Yang et al., 2011).
The FTIR results from nanocarbon synthesized through a hydrothermal process are shown in Figure 3.
In Figure 3, the wave numbers of 3332 cm-1 confirmed for O-H and N-H groups, while the wave number of 2838 and 2949 cm-1 confirmed for C-H vibrational groups (Gong et al., 2019). Correspondingly, at wave number of 1645 cm-1 is the bending vibrational group of N-H, where at wave number of 1014 and 1409 cm-1 can be considered as stretching asymmetry and symmetry of the C-O-C group which is a functional group of nanocarbon (Bu et al., 2019). The results of the nanocarbon FTIR obtained are also similar to the results of the nanocarbon FTIR obtained from coal as reported by Purwandari et al. (2020). The above functional groups indicate that nanocarbons have been found in POME samples with luminescence generated from the surface state.
The absorption of nanoscale carbon from a wavelength of 280 - 400 nm with the absorption peak at the peak of 300 nm. The results of the UV-Vis spectrum show that the POME solution has been successfully converted into nanocarbon in the presence of blue fluorescence under UV light and has light absorption in the UV region at a peak of ~300 nm. This peak indicates the transition peak of the aromatic bond by C=C of nanocarbon (Ansi et al., 2021). The results of this absorption spectrum are also similar to previous studies for the conversion of food waste to carbon dot with an absorption spectrum at a peak of around 300 nm (Gan et al., 2020; Zhou et al., 2018).
4. Conclusions
Based on the XRD analysis crystals of carbon structures in all peaks and an average crystal size of 30.58 nm were found. The PSA analysis showed that the average particle sizes of nanocarbons from palm oil mill effluent was 1.153 nm. The FTIR spectrum confirmed that the functional groups indicate that nanocarbon have been found in POME samples with luminescence generated from the surface state. The POME solution was successfully converted into nanocarbon in the presence of blue fluorescence under UV light and has a light absorption in the UV region at a peak of ~300 nm based on the UV-Vis results.
Conflict of interest
The author(s) does/do not have any type of conflict of interest to declare.
Financing
The authors did not receive any sponsorship to carry out the research reported in the present manuscript.
