• International Journal of Technology (IJTech)
  • Vol 15, No 4 (2024)

Physical, Chemical and Electrical Conductivity Properties of Bismuth Oxide/ Rice Husk-Based Activated Carbon/Graphite Composite Prepared by the Hydrothermal Method

Physical, Chemical and Electrical Conductivity Properties of Bismuth Oxide/ Rice Husk-Based Activated Carbon/Graphite Composite Prepared by the Hydrothermal Method

Title: Physical, Chemical and Electrical Conductivity Properties of Bismuth Oxide/ Rice Husk-Based Activated Carbon/Graphite Composite Prepared by the Hydrothermal Method
Yayuk Astuti, Lifiany Annisa, Didik Setiyo Widodo, Adi Darmawan

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Astuti, Y., Annisa, L., Widodo, D.S., Darmawan, A., 2024. Physical, Chemical and Electrical Conductivity Properties of Bismuth Oxide/ Rice Husk-Based Activated Carbon/Graphite Composite Prepared by the Hydrothermal Method. International Journal of Technology. Volume 15(4), pp. 987-998

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Yayuk Astuti Department of Chemistry, Faculty of Natural Sciences and Mathematics, Universitas Diponegoro, Jl. Prof. Jacob Rais, Tembalang, Semarang, Central Java 50275, Indonesia
Lifiany Annisa Department of Chemistry, Faculty of Natural Sciences and Mathematics, Universitas Diponegoro, Jl. Prof. Jacob Rais, Tembalang, Semarang, Central Java 50275, Indonesia
Didik Setiyo Widodo Department of Chemistry, Faculty of Natural Sciences and Mathematics, Universitas Diponegoro, Jl. Prof. Jacob Rais, Tembalang, Semarang, Central Java 50275, Indonesia
Adi Darmawan Department of Chemistry, Faculty of Natural Sciences and Mathematics, Universitas Diponegoro, Jl. Prof. Jacob Rais, Tembalang, Semarang, Central Java 50275, Indonesia
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Abstract
Physical, Chemical and Electrical Conductivity Properties of Bismuth Oxide/ Rice Husk-Based Activated Carbon/Graphite Composite Prepared by the Hydrothermal Method

The synthesis of Bismuth Oxide/Rice Husk-based Activated Carbon/Graphite (BO/RH-AC/G) composites using the hydrothermal method with varying concentrations of bismuth nitrate pentahydrate has been conducted. The composites are synthesized from bismuth nitrate pentahydrate, sodium sulfate, and sodium hydroxide precursors added with activated carbon from rice husks and graphite using the hydrothermal method at 110oC for 5 hours. The characterization results show that the concentration of the added bismuth nitrate pentahydrate precursor affects the physical, chemical, and electrical properties of the resulting composites such as crystallinity, presence of functional groups, pore and surface properties, morphology, element distribution, thermal stability, and electrical conductivity. In the use of smaller bismuth nitrate pentahydrate, composite has the highest crystallinity containing mostly Bi2O3 having monoclinic crystal structure, small pore size and high surface area. Each composite showed different pattern of thermal decomposition. Moreover, most products have the same rod-like morphology even though the highest precursor used resulted in lumpy surface shape. The electrical conductivity of composites is higher than that of pure bismuth oxide and rice husk-activated carbon.

Bismuth Oxide (BO); Composite; Graphite (G); Hydrothermal; Rice Husk-activated Carbon (RH-AC)

Introduction

The battery is a source of energy supply that works by converting the chemical energy contained in the active ingredients of the battery components into electrical energy through electrochemical reactions of reduction and oxidation (Reddy, 2011). Batteries have important components that enable generate chemical reactions to create electricity. These components include electrodes, electrolytes, and separators.

The electrode is the conductor in which the redox reaction takes place. The battery electrode is divided into cathode and anode, which are the positive and negative electrodes, respectively. The anode is a negative electrode, with reference to the half-cell oxidation reaction, that releases electrons into the external circuit (Subhan, 2011). Materials that are able to be used as anodes must have properties that include good charge/ion conductivity (>103 Sm-1), large energy capacity (Li metal: 3850 mAh.g-1 (Goriparti et al., 2014), and long life cycle, and they also need to be easy to process, safe in use (non-toxic) and low in price.

Metal oxides (Li et al., 2021; Kim et al., 2019) have been studied intensively as somethe most promising candidates for battery anodes due to their high theoretical capacities and low costs. One of the metal oxides that have the potential to be used as an electrode is bismuth oxide (Xu et al., 2022; Nandi and Das, 2020). Expediently, bismuth oxide has high theoretical capacity value (690 mAh.g-1), volumetric capacity value of 3765 mAh.cm-1, a potential difference of 2.8 V, is non-toxic, abundant, and relatively cheap (Fang et al., 2017; Li et al., 2013). However, the problem with using bismuth oxide as a battery anode is that it possesses low conductivity value which has a tendency to give a result of the slow charge/ion conductivity of the battery anode. This low conductivity value, however, is able to overcome by adding other materials that have the ability to increase the conductivity value, namely activated carbon and graphite.

Activated carbon is an amorphous carbon consisting of a flat plate with carbon atoms arranged and covalently bonded in a hexagonal lattice (Gilles and Loehr, 1994). Activated carbon has a conductivity value of 6.04 S.m-1 and a large surface area between 300 m2.g-1 to 3500 m2.g-1 (Kim et al., 2016). A large surface area is one of the advantageous factors that comprise an electrode material (Ariyanto, Prasetyo, and Rochmadi, 2012), whereby the larger the surface area, the greater the capacitance value (Ciszewski et al., 2015). In addition to the surface area, the volumetric capacity of 1770 mAh.cm-1 and a potential difference of 0.2 V (Kim et al., 2016) of activated carbon are highly sought-after in an electrode-making material (Bijesh, Selvaraj, and Andal, 2022). Graphite is one of the carbon core materials that act as an electrical conductor and able to be used as an electrode material (Sari, 2015). Graphite has the characteristics of being soft, light, and capable of conducting electricity, though graphite has a low theoretical capacity (372 mAh.g-1) (Fang et al., 2017).

Research on bismuth oxide and carbon as electrodes has been done before. Astutim, Aprialdi, and Haryanto (2019) reported the synthesis of Bi2O3/rice husk-based activated carbon composite with mass ratios of bismuth nitrate pentahydrate to activated carbon (Bi:AC) of 1:1; 1:2 and 2:1, giving electrical conductivity values of 1.24×10-5 S.m-1; 0.59×10-5 S.m-1 and 0.51×10-5 S.m-1, respectively. The resulting electrical conductivities were still quite low. In addition, the X-ray Diffraction (XRD) data showed that Bi2O3 had not been formed which might have also been the cause of the small electrical conductivity values.
On those accounts, bismuth oxide needs combined or added with activated carbon and dopped with graphite so that it may have high conductivity value. The composites are able to be made using the hydrothermal method. The hydrothermal method has several advantages, namely the use of relatively low temperatures, a safe reaction process (Gupta, Aberg, and Carrizosa, 2016), and larger and purer single crystal generation (Byrappa, and Yoshimura, 2000). The composite products derived from bismuth oxide, rice husk-based activated carbon, and graphite are expected to have increased electrical conductivity values.

Experimental Methods

2.1. Materials

      The materials used in this study are Bi(NO3)3.5H2O (sigma aldrich), H3PO4 (Merck), Na2SO4 (Merck), NaOH (Merck) bought from Darmstadt-Germany, rice husks, and distilled water.       

2.2. Research Procedure

2.2.1. Rice Husk-Based Activated Carbon Production

The production of rice husk-based activated carbon followed the procedure reported by Arnelli, Santoso, and Astuti (2021). Clean rice husks were charred by pyrolysis at 300oC for 10 minutes. A total of 5 grams of the carbon produced were activated by the addition of 125 mL 60% H3PO4 and processing in the microwave with a power of 400 W for 5 minutes. The activated carbon was then washed with distilled water until the pH was constant. The activated carbon that had been washed was then dried using an oven at 105oC for 5 minutes. The resulting activated carbon was destructed and sieved to a size of 100 mesh.

2.2.2. Synthesis of Bismuth Oxide/Rice Husk-Activated Carbon/Graphite Composite

       The synthesis of BO/RH-AC/G composites was carried out using the hydrothermal method with variations in Bi(NO3)3.5H2O of 8, 24, and 32 mmol. For the 8 mmol BO/RH-AC/G variation, initially 8 mmol of bismuth nitrate pentahydrate was added with 12 mmol of Na2SO4. They were dissolved in 40 mL of distilled water and then stirred using a magnetic stirrer for 45 minutes. Later, 40 mL of 72 mmol of NaOH was added to the solution mixture followed by 0.5 grams of rice husk-activated carbon and 0.1 grams of graphite and the mixture was stirred. The mixture was then poured into a stainless-steel tube and into a hydrothermal reactor, heated at 110oC for 5 hours. At the final stage, the product was filtered and dried using an oven at a temperature of 110oC for 1 hour, then sieved to a size of 100 mesh. The same procedure was used to synthesize the 24 mmol and 32 mmol BO/RH-AC/G composites. The three composite products were labeled[BO/RH-AC/G]1, [BO/RH-AC/G]2 and [BO/RH-AC/G]3 for the composites that were synthesized with variations of 8 mmol, 24 mmol, and 32 mmol, respectively.

2.2.3. Characterization of the Bismuth Composite Material

       The characterizations of the three composites were carried out using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Thermo Gravimetric Analyzer-Derivative Thermogravimetri (TGA-DTG), Inductance, Capacitance, and Resistance (LCR), and Gas Sorption Analyzer (GSA) instruments. The characterization of the composite products by FTIR (Shimadzu IRAffinity-1) was carried out in the wave number range of 400 cm-1 - 4000 cm-1 to determine the presence of functional groups in the resulting composite products. Analysis of composite products using XRD (Shimadzu 7000) was done with 2theta ()= 0 to 90, to identify the crystal structure of bismuth oxide in the synthesized composites. Furthermore, the Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX) instrument (Jeol JED 6510LA) was used to identify the surface morphology of the sample and the compositions of the composites. A mapping test was also carried out to determine the distribution of the elements that make up the composite materials. The characterization of the composite products using TGA (Mettler Toledo TGA/DSC 3+) was used to determine the thermal stability of the composites. Meanwhile, the electrical conductivities of the composite products were determined using an LCR meter (HIOKI 3532-50). Composite characterization with GSA (Tristar II 3020) was carried out with N2 gas adsorbate to determine the surface area, pore volume, and pore size of the composites.

Results and Discussion

3.1 BO/RH-AC/G Composite

       The synthesis of BO/RH-AC/G composites was initiated by reacting the precursor materials consisting of Bi(NO3)3.5H2O, Na2SO4, and NaOH according to the procedure reported by Wu et al. (2011). Subsequently, the solution was added with rice husk-activated carbon and graphite, homogenized, and heated in a hydrothermal reactor.

       The bulk appearance of the three composite products is presented in Figure 1a, b and c. Figures 1.a and 1.b show powders of distinct gray colors, whereas in Figure 1c the composite produced has an agglomerated appearance. The colors of the composites were obtained from the combination of the yellow color of bismuth oxide (Astuti et al., 2016), as well as activated carbon and graphite which are black, generating a complementary color in the form of blackish gray of different shades.

Figure 1 Synthesized (a) [BO/RH-AC/G]1 (b) [BO/RH-AC/G]2 and (c) [BO/RH-AC/G]3 composites

3.2   BO/RH-AC/G Composite Material Characteristics

3.2.1. Composites Functional Groups Structures

        Figure 2 shows that the FTIR spectra of the three composites were almost the same. The FTIR spectra (see Figure 2) show the absorption of the Bi-O-Bi group at the wave numbers of 878.7 cm-1; 904.78 cm-1; and 824.97 cm-1 for [BO/RH-AC/G]1, [BO/RH-AC/G]1, and [BO/RH-AC/G]3, respectively. In addition, the absorption for the Bi-O group is also observed in each of the samples at 1383.93 cm-1, 1383.87 cm-1, and 1381.91 cm-1, respectively.

Figure 2 FTIR spectra of composite products, graphite, activated carbon, bismuth oxide pentahydrate

        The absorptions of Bi-O-Bi and Bi-O groups in the composite products shown in the results were in accordance with research on products containing Bi2O3 which displayed absorptions of the Bi-O-Bi group at the wave numbers 809 cm-1 (Bartonickova Cihlar, and Castkova, 2007) and the Bi-O stretching vibration at 1358 cm-1 (Bandyopadhyay and Dutta, 2017). Based on the two groups’ absorption regions, it is argued that the bismuth oxide has been successfully synthesized (Astuti et al., 2020a).
Table 1 Functional groups identification from the FTIR analysis

The composite products also contain activated carbon, indicated by the presence of the absorption of the C-O group at the wave numbers of 1118 cm-1, 1103.10 cm-1, and 1112.16 cm-1 for the [BO/RH-AC/G]1, [BO/RH-AC/G]2, and [BO/RH-AC/G]3 products, respectively. The absorption of the C=C group which indicates the presence of activated carbon and graphite was also observed in the three composites at wave numbers of 1631 cm-1, 1634.94 cm-1, and 1645.85 cm-1. The existence of the two absorption areas is consistent with a conducted by (Sastrohamidjojo, 2018), stating that activated carbon is characterized by a sharp absorption at wave number 1626.64 cm-1 indicating the presence of the C=C group and absorption at wave number 1039.87 cm-1 that denotes the C-O group. The absorption of the C=C group at the wave number 1630 cm-1 also indicates the presence of graphite (Huang et al., 2017). The identifications of the functional groups in the composite samples, pure Bi2O3, rice husk-activated carbon, and graphite are summarized in Table 1.

3.2.2. Crystal Structures

        The XRD characterization results of the composites are depicted in Figure 3. Composite [BO/RH-AC/G]3 has sharp peaks at 2 theta () 21.720o; 28.896o; and 33.211o. The peaks have similarities with the peaks in the pure Bi(NO3)3.5H2O diffractogram, namely at 21.943o; 28.7854o, and 32.783o. Meanwhile, the composite [BO/RH-AC/G]2 possesses no sharp and specific peaks, meaning it is possible that the amounts of -Bi2O3 crystals formed in this composite was small making the sample amorphous.

        Figure 3 also displays peaks at 2 theta () 27.418o; 33.286o; 46.337o; 52.403o, and 54.792o in the [BO/RH-AC/G]1 composite product. The peaks of the diffractogram indicate the presence of -Bi2O3 crystals with a monoclinic crystal system.

Figure 3 Diffractograms of the [BO/RH-AC/G]1, [BO/RH-AC/G]2, and [BO/RH-AC/G]3 composites, rice husk-activated carbon, graphite, and bismuth nitrate pentahydrate (BNP)

3.2.3. Morphology and Elemental Distribution

       Composite analysis results using SEM presented in Figure 4a and b and shows that the composite products [BO/RH-AC/G]1 and [BO/RH-AC/G]2 at magnifications of 1000x and 5000x have almost the same rod-like morphology. The [BO/RH-AC/G]1 composite has rod-like particles with a length of 2.72–20.9  and a width of 2.72–8.28 , while the [BO/RH-AC/G]2 is 3.63–18.18  long and 0.9–3.36  wide. The shape of the particle is distinct from the shape of the Bi2O3 particles as reported by Yakout (2020). Meanwhile, in Figure 4c, the composite [BO/RH-AC/G]3 has an irregular and a lumpy surface shape. Bismuth oxide synthesized using the hydrothermal method generates rod-like shape particles (Astuti et al., 2022b) meanwhile other methods result in irregular shapes (Astuti et al., 2021; Astuti et al., 2020a; 2020b). This morphology affects the value of the electrical conductivity of bismuth oxide (Astuti et al., 2022b). The particle shapes in one dimension including wires, rods, or tubes are the most magnificent shape for developing the electrochemical behavior due to the large surface areas and the shortened ion diffusion paths (Yousif et al., 2022).

Figure 5 shows the Bi element marked in red, the C element in green, the O element in neutral, and the Si element in blue. In the composite [BO/RH-AC/G]1, the elements C and Bi are evenly distributed in the composite and appear to dominate (Figure 5a). Whereas in [BO/RH-AC/G]2 (Figure 5b), and [BO/RH-AC/G]3 (Figure 5c), the Bi elements seem to dominate and spread evenly in the composite because the precursor concentrations used were quite high compared to [BO/RH-AC/G]1. Meanwhile, the C, O, and Si elements contained in the two composites are less prominent and are evenly distributed.
Figure 4 SEM images of (a) [BO/RH-AC/G]1, (b) [BO/RH-AC/G]2, (c) [BO/RH-AC/G]3 at 1000x and 5000x magnifications

Figure 5 Mapping of (a) [BO/RH-AC/G]1; (b) [BO/RH-AC/G]2; (c) [BO/RH-AC/G]3

3.2.4. Composite Thermal Stability

The TGA-DTG curves of the [BO/RH-AC/G]1 composite (Figure 6a) shows five stages weight loss. The first and second stages occurred at the temperatures between 200–380oC in which around 0.2% and 13% of mass are lost and are attributed to the removal of NaOH, NaNO3, and SO42- residues as well as the mass lost from the transformation of the precursors into Bi2O3 (Zhang et al., 2011). In stage three, there was a further Bi2O3 formation process which occurred at temperatures between 400 – 450oC with mass loss of around 2% (Ma et al., 2010; Christensen et al., 2003). In stage four, about 0.2% weight reduction was observed 0.2% at 500oC, denoting the phase transition from -Bi2O3 to -Bi2O3 (Shen et al., 2012). The fifth stage at 640oC indicated by a weight loss of about 0.2% is identified as the phase transition from -Bi2O3 to -Bi2O3 (Klinkova et al., 2007).

There are four stages of mass loss that occurred in [BO/RH-AC/G]2 as shown in Figure 6.b. The first stage was able to be observed at temperatures between 200–380oC where there was a weight loss of about 9% which was able to be attributed to the removal of residues such as NaOH, NaNO3, and SO42- and the mass loss from the transformation from the precursors to Bi2O3 (Zhang et al., 2011). In the second stage, there was a reduction in weight at temperatures between 400–450oC as much as 1.5%, representing the process of further formation of Bi2O3 (Ma et al., 2010; Christensen et al., 2003). In the third stage, there was a reduction in weight of 0.5% at the temperatures around 500oC denoting the phase transition from -Bi2O3 to -Bi2O3 (Shen et al., 2012). In the last stage, at 640oC, mass loss of about 2% occurred, which is the phase transition from -Bi2O3 to -Bi2O3 (Klinkova et al., 2007).

Figure 6 TGA and DTG curves of (a) [BO/RH-AC/G]1; (b) [BO/RH-AC/G]2; (c) [BO/RH-AC/G]3 composites

The [BO/RH-AC/G]3 composites underwent three stages of mass loss as shown in Figure 6.c. In the first stage, there was a weight loss of 8% at temperatures between 200-275oC which may be derived from the removal of functional groups (-COO-, -CO-, -OH-, and hydrate) from graphite (Deng et al., 2017). The second stage was accentuated by a mass reduction of 10% at the temperature of about 400oC which was assigned to the transformation of the precursors to form Bi2O3 (Ma et al., 2010). In the third stage, a mass loss of 0.2% occurred at the temperature of about 500oC which was attributed to the phase transition from  (Shen et al., 2012).

3.2.5 Composite Electrical Conductivity

        The ionic and electrical conductivity of a material is determined by its crystal structure. The electrical conductivity values of the three composite products, pure bismuth oxide (Bi2O3), activated carbon and graphite are presented in Table 2.

Table 2 LCR meter conductivity measurement

         Table 2 shows that the electrical conductivity value of pure Bi2O3 is very low. So is the case of the rice husk-based activated carbon with its electrical conductivity value. Meanwhile graphite as the dopant has a high conductivity value. The three composites that have been formed have higher electrical conductivity values than pure Bi2O3 and activated carbon from rice husks. The rice husk-activated carbon added into the composite functions as a matrix so that the distribution of bismuth oxide particles is more even, which would make it easier for the electrons to flow, thus allowing good electrical conductivity.

        The [BO/RH-AC/G]3 composite product has the highest electrical conductivity value compared to the [BO/RH-AC/G]1 and [BO/RH-AC/G]2 composites. This is because there are more initial precursors contained, in which bismuth nitrate pentahydrate has a high electrical conductivity value, causing the electrical conductivity of the [BO/RH-AC/G]3 composites to be high.

        The [BO/RH-AC/G]2 composite has the smallest electrical conductivity value. The value of the electrical conductivity is influenced by the crystallinity of a material. The more crystalline a material is, the higher its electrical conductivity it becomes (Kim, Lee, and Jang, 2014). The XRD data presented that the [BO/RH-AC/G]3 and [BO/RH-AC/G]1 are crystalline, while [BO/RH-AC/G]2 is amorphous. Therefore, the electrical conductivity value [BO/RH-AC/G]2 is low.

        The [BO/RH-AC/G]1 has an electrical conductivity value in between the [BO/RH-AC/G]3 and [BO/RH-AC/G]2. This is attributed to the successfully formed Bi2O3 confirmed through the XRD and FTIR data. The XRD data showed that the composite [BO/RH-AC/G]1 contained Bi2O3 crystals and the FTIR spectra confirmed the presence of the Bi-O group with the highest intensity.

3.3.6 Pore and Surface Properties

        The nitrogen adsorption-desorption isotherms for all samples are shown in Figure 7a, b and c. The greatest loop hysteresis is observed in the [BO/RH-AC/G]1 composite (see Figure 7a). This is because the [BO/RH-AC/G]1 composite has a small pore size but a large pore volume and a large number of pores, resulting in a large surface area, causing more adsorbate (N2) to be left in the pores. Accordingly, the hysteresis loop observed is large. The [BO/RH-AC/G]3 (Figure 7c) composite has a large pore size with a small pore volume and small number of pores. This means that the surface area is small, and the amount of the adsorbate (N