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Article

Synthesis, Optical, Electrical, and Thermoelectric Characterization of SbSI/Graphite Nanocomposite

by
Bartłomiej Nowacki
1,2,
Krystian Mistewicz
3,*,
Jakub Jała
2,3,
Mateusz Kozioł
4 and
Albert Smalcerz
1
1
Department of Industrial Informatics, Faculty of Materials Engineering and Industrial Digitalization, Silesian University of Technology, Krasinskiego 8, 40-019 Katowice, Poland
2
Joint Doctoral School, Silesian University of Technology, Akademicka 2A, 44-100 Gliwice, Poland
3
Institute of Physics—Centre for Science and Education, Silesian University of Technology, Krasińskiego 8, 40-019 Katowice, Poland
4
Department of Materials Technologies, Faculty of Materials Engineering and Industrial Digitalization, Silesian University of Technology, Krasińskiego 8, 40-019 Katowice, Poland
*
Author to whom correspondence should be addressed.
Energies 2026, 19(1), 9; https://doi.org/10.3390/en19010009
Submission received: 13 October 2025 / Revised: 10 December 2025 / Accepted: 15 December 2025 / Published: 19 December 2025
(This article belongs to the Special Issue Advances in Nanomaterial-Based Sustainable Energy Harvesting Technologies)
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Abstract

Carbon nanocomposites have gained interest due to the rapid development of nanotechnology. The graphite-based composites have been demonstrated to possess unique mechanical, electrical, and thermal properties. This paper presents a facile one-step sonochemical synthesis of antimony sulfoiodide (SbSI)/graphite nanocomposite. The weight concentrations of graphite in the prepared material varied from 0% to 33.3%. The morphology and chemical composition of the SbSI/graphite nanocomposites are studied with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. SEM examination shows that SbSI/graphite nanocomposite consists of one-dimensional SbSI nanostructures and graphite microparticles. The influence of graphite concentration on the energy band gap of SbSI/graphite nanocomposite is investigated using diffuse reflectance spectroscopy (DRS). The prepared materials are cold-pressed to obtain the bulk samples. They are characterized by direct current (DC) electrical measurements and thermoelectric examination. The increase in the graphite concentration in the SbSI/graphite nanocomposite resulted in a significant reduction in the electrical resistivity of the material. The Seebeck coefficients of the pristine SbSI nanowires and SbSI/graphite nanocomposite are determined for the first time. The investigations of the thermoelectric effect reveal that these nanomaterials exhibited p-type electrical conductivity. The thermoelectric power factor of the SbSI/graphite nanocomposite is examined as a function of the graphite concentration. The presented work demonstrates the comprehensive optical, electrical, and thermoelectric characterization of novel hybrid SbSI/graphite nanocomposites, which has not been studied before.

1. Introduction

Chalcohalides are inorganic materials that consist of chalcogen and halogen atoms. Pnictogen chalcohalides [1,2] also contain chemical elements from group 15 of the Periodic Table. They are usually denoted as A5B6C7 [3] or AVBVICVII [4] compounds. Chalcohalides have been reported to have remarkable photosensitive [5,6], photovoltaic [7,8], photocatalytic [9,10], piezoelectric [11], and gas sensing [12] properties. Among pnictogen chalcohalide materials, the antimony sulfoiodide (SbSI) is one of the most examined compounds. The existence of ferroelectricity [13], pyroelectricity [14], piezoelectricity [15], and photoconductivity [16] in this material makes it attractive for use in optoelectronics [17], photovoltaics [18], photocatalysis [19], and energy harvesting [16,20]. Rao and Mansingh [21,22] investigated the thermoelectric properties of SbSI thin films. They identified holes as the majority charge carriers and measured a large Seebeck coefficient of 8 mV/K at 320 K for 1 µm thick SbSI layer [21]. First-principles calculations of the thermoelectric properties of SbSI were presented in refs. [23,24]. It should be noted that the electrical conductivity of SbSI is low. Furthermore, the SbSI nanowires, as one-dimensional nanostructures, are even more resistive than the bulk crystals of this material. This drawback limits the potential thermoelectric applications of SbSI nanowires. Therefore, a new method of this material preparation must be proposed to enhance the electrical transport properties of SbSI nanowires. This aim can be achieved by the preparation of a hybrid composite that exhibits both low electrical resistivity and strong thermoelectric properties.
Graphite composites possess a large potential for industrial applications since their fabrication is simple and low-cost in comparison to the preparation of composites based on other carbon materials, such as graphene [25,26,27] and carbon nanotubes [28,29]. Graphite composites were demonstrated to be suitable for use in electromagnetic shielding materials [30], lithium-ion batteries [31], supercapacitors [32], electrically conductive concrete [33], heating elements for de-icing applications [34], and thermoelectric generators [35,36,37]. Anjum et al. [38] reported improved mechanical strength and thermoelectric properties of Bi2S3/graphite composite. Hu and co-workers [39] presented that the introduction of graphite into graphite/Bi0.5Sb1.5Te3 composite decreased material thermal conductivity, slightly increased electrical properties, and gained thermoelectric figure of merit (ZT). Similarly, determination of an optimum concentration of graphite enabled a reduction in the thermal conductivity of both polyaniline/graphite/Bi2Te3 [40] and Sb2Te3/graphite [41] composites. Different carbon materials were used to fabricate nanocomposites of chalcohalide compounds with desired functional properties, such as BiOBr/nitrogen-doped carbon dots [42], BiOBr/AgBr/carbon nanofibers [43], BiOI/BiOIO3/carbon spheres [44], BiOI/activated carbon [45], and BiSI/amorphous carbon [46]. The majority of aforementioned chalcohalide-based carbon nanocomposites were investigated as photocatalysts suitable for the removal of harmful organic dyes from aqueous solutions [42,43,45] and gaseous inorganic contaminants from the air [44]. However, a description of the electrical and thermoelectric properties of the chalcohalide-based carbon nanocomposites is missing in the scientific literature and needs detailed examination.
In this paper, a facile and low-temperature ultrasonic method is used to synthesize SbSI/graphite nanocomposite with various weight concentrations of graphite ranging from 0% to 33.3%. This method is undertaken to obtain hybrid materials with improved electrical conductivity in comparison to the highly resistive pristine SbSI nanowires. The SbSI/graphite nanocomposite is characterized through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), direct current (DC) electrical examination, and thermoelectric measurements. The electrical conductivity type of the prepared materials is determined. The influence of the graphite weight concentration on the electrical conductivity, Seebeck coefficient, and thermoelectric power factor of the SbSI/graphite nanocomposite is investigated. It allowed us to find the most optimal graphite weight concentration for which the best thermoelectric performance is observed. This study clearly confirmed that a sonochemical synthesis can be applied to prepare hybrid nanomaterials with the desired electrical properties.

2. Materials and Methods

2.1. Sonochemical Synthesis of SbSI/Graphite Nanocomposite

The material was synthesized using a sonochemical method similar to the one described in ref. [47]. The synthesis process was carried out in a 20 mL closed polypropylene/polyethylene vessel. Antimony (Sigma–Aldrich, St. Louis, MO, USA), sulfur (Avantor Performance Materials Poland S.A., Gliwice, Poland), and iodine (Avantor Performance Materials Poland S.A., Gliwice, Poland) were put into the vessel in stoichiometric amounts (Figure 1a). Five different amounts of graphite were weighed and added to the separate vessels to fabricate composites with different graphite (B&K, Bytom, Poland, technical purity, 60 μm) content (0, 4.8, 11.1, 20, and 33.3 wt.%). Then, the cylinders were immersed in an ultrasonic cleaner 509 (Ultron, Dywity, Poland) for 2.5 h (Figure 1b). When the synthesis was completed, the materials were washed six times with deionized water and four times with pure ethanol to remove the remaining residuals. After each washing process, the composites were separated from the ethanol by centrifuging at 3000 rpm (Figure 1c). Finally, the prepared materials were dried for 24 h at 323 K (Figure 1d).
The acoustic pressure inside the liquid, subjected to the action of ultrasounds, changes periodically with time (Figure 1e). It leads to an acoustic cavitation effect [48,49], which involves the nucleation of gas bubbles in the irradiated liquid, their growth, and collapse when their radii achieve critical values. The extraordinary conditions (large pressure and temperature) are generated locally during the bubble implosion [50,51]. It favors the creation of radicals in the solvent, which promote chemical reactions [52]. Three sites for various chemical reactions are available in sonochemical synthesis, i.e., bubble interior, the interface region at around the bubble surface, and the liquid volume outside the interface region [48]. Therefore, a sonochemical method is a versatile approach that allows us to prepare low-dimensional nanomaterials [49,53]. SbSI exhibits a tendency to grow into the double one-dimensional [54,55,56] chains connected with others with weak van der Waals forces (Figure 1f). The action of ultrasonic waves may lead to the fragmentation and exfoliation [57] of graphite flakes. Moreover, the ultrasounds are expected to drive particle collisions (Figure 1f), affecting the formation of carbon-SbSI heterostructures. This results in the formation of a mixed-dimensional composite consisting of 1D nanowires and 2D carbon sheets (Figure 1g). The possibility of the creation of such carbon-based nanohybrids using an ultrasonication-assisted method was also demonstrated in the case of another chalcohalide compound, i.e., BiOBr [42].

2.2. Characterization of SbSI/Graphite Nanocomposite Morphology, Chemical Composition, and Optical Properties

The morphology and chemical composition of the prepared material were examined using a Phenom Pro X (Thermo Fisher Scientific, Waltham, MA, USA) SEM microscope equipped with an EDS detector. The SEM microscope was operated at an acceleration voltage of 5, 10, or 15 kV. The EDS spectrum was quantified using ProSuite Element Identification software (Thermo Fisher Scientific).
The DRS spectrum of the nanocomposite was recorded at room temperature using a PC-2000 spectrophotometer (Ocean Optics Inc., Duiven, The Netherlands) connected to the ISP-REF integrating sphere (Ocean Optics Inc.). A small amount of materials was suspended in isopropanol using ultrasonic mixing for 15 min. The measurements were made on 10 mL of suspension.

2.3. Examination of SbSI/Graphite Nanocomposite Electrical and Thermoelectric Properties

The prepared powders of nanocomposites were pressed into bulk pellets at room temperature using the 4469 testing machine (Instron, Norwood, MA, USA). The nanocomposite mass of 0.2 g was evenly inserted into a metal cylinder mold with an inner diameter of 1 cm. Then, a force of 30 kN was applied to the mold and held for 2 min. A density of 2.23 g/cm3 of compressed SbSI/graphite nanocomposite was calculated using information on sample thickness, diameter, and mass loaded into the mold. In order to prepare electrodes required for electrical measurements, the top and bottom sides of the samples were covered with 0.4 mm-thick electric paint (Bare Conductive, London, UK).
The pellets of SbSI/graphite nanocomposite were placed inside the SH-242 (Espec, Osaka, Japan) environmental chamber to investigate their electrical properties. The measurements were carried out at a relative humidity (RH) of 50% and within the temperature range from 283 K to 343 K. The 6517B bench multimeter (Keithley, Solon, OH, USA) was connected to the sample. The automatic measurement acquisition was undertaken using LabView software. Current-voltage (I-U) characteristics were registered in the voltage range from –0.2 V to 0.2 V at temperatures of 283 K and 293 K. Resistance-temperature measurements were conducted at a DC voltage of 0.2 V in the temperature range from 283 K to 343 K with a temperature change rate of 0.3 K/min.
The thermoelectric properties of SbSI/graphite nanocomposites were examined using a self-built experimental setup. It consisted of two thermostats: Haake AC200 (Thermo Fisher Scientific) and Haake DC30 (Thermo Fisher Scientific). The thermoelectric voltage was measured using a precise 2182 A nanovoltmeter (Keithley). The temperatures at the hot and cold sides of the sample were measured using Pt100 sensors connected to the 2410-C source meter (Keithley) and 196 multimeter (Keithley). The time dependence of the hot side temperature was controlled via a program written in the Python 3.10 programming language. The measurement data were collected using the LabView program.

3. Results and Discussion

3.1. SEM, EDS, and DRS Investigations

The SEM studies revealed that crystalline nanowires of SbSI (Figure 2a) and the SbSI/graphite (Figure 2b,c) nanocomposite were obtained as the products of sonochemical synthesis without and in the presence of graphite, respectively. The SbSI nanowires grown in a graphite vicinity showed an increased tendency toward agglomeration, as presented in Figure 2b,c. The SbSI nanowires seem to adhere to the surfaces of larger graphite flakes, suggesting a good connection between these two phases.
The sizes of the SbSI nanowires and graphite flakes were examined in detail. The distribution histograms and average values of the particle sizes are presented in Figure 3 and Table 1, respectively. A determined mean width of the pristine SbSI nanowires (56 nm) is equal within measurement uncertainty (18 nm) to the average diameter of 69 nm reported in ref. [8]. A remarkable decrease in the SbSI nanowires widths and lengths was observed with an increase in graphite concentration in the SbSI/graphite nanocomposite. Therefore, the presence of graphite can be recognized as a key factor responsible for the inhibition of SbSI nanowires growth.
Figure 4 shows the exemplary result of the EDS analysis performed for the SbSI/graphite nanocomposite containing 11.1 wt.% graphite. An almost uniform distribution of detected elements was obtained. A significant contribution to the EDS signal originated from silicon, since the examined SbSI/graphite nanocomposite was deposited on a Si wafer. No other chemical elements than Si, C, Sb, S, and I were identified. It confirmed the high purity of the prepared material. The exact concentrations of all the detected chemical elements are provided in Table 2. A slight deviation of graphite weight concentration (8.5%) from this expected (11.1%) probably resulted from the fact that the graphite flakes could not be evenly distributed on the small surface sample. Thus, a higher area of the sample was needed to obtain a more accurate average value of graphite concentration. The atomic ratio of 38.9:26.5:34.6 was determined for antimony, sulfur, and iodine when carbon contribution to the SbSI/graphite nanocomposite was neglected. This result is close to the expected theoretical atomic composition of SbSI and confirms the formation of this compound. The excess amount of antimony, revealed by the EDS analysis, is a typical feature of SbSI prepared using different methods, including physical vapor deposition [58], hydrothermal growth [59], and sonochemical synthesis [8]. Average atomic and weight concentrations of chemical elements for all the investigated materials are given in Tables S1–S5 in the Supplementary Materials. The comparison of nominal and experimentally determined weight concentrations of graphite, antimony, sulfur, and iodine in SbSI/graphite nanocomposite is presented in Tables S6–S9, respectively. The maximum and average graphite concentration errors attained the small values of 2.3% and 1.1%, respectively.
The diffuse reflectance spectra of pristine SbSI nanowires and SbSI/graphite nanocomposite are presented in Figure 5a. The Kubelka–Munk function (Figure 5b) was calculated using the following formula [60]:
F K − M = 1 − R d 2 2 R d ,
where Rd is a dimensionless diffuse reflectance coefficient in the range from 0 to 1. The Kubelka–Munk function is proportional to the absorption coefficient (α). The Tauc formula [61,62] is used to determine the energy band gaps (Eg) for all the prepared materials, which is given as follows:
F K − M h v 1 / n = A h v − E g ,
where h denotes the Planck constant expressed in units of J∙s, υ is the frequency of the electromagnetic wave given in Hz units, hν is an incident photon energy expressed in eV, and A and n are dimensionless constants. SbSI is a semiconductor with an indirect energy band gap [54,63,64]. Thus, the n coefficient was set at 2. It was observed that all the studied materials exhibited considerable light absorption for photon energies lower than the energy corresponding to the absorption edge (Figure 5b). This is probably due to the existence of intraband gap states, which were introduced by a modification of the SbSI surface with graphite flakes. In such a case, a simple application of the Tauc formula (Equation (2)) may result in an improper determination of an energy band gap. Therefore, a special strategy, known as the “baseline approach” [65], was used to calculate a more accurate value of Eg. According to this method, the energy band gap is determined by finding an intersection of the absorption edge and the baseline in the sub-band gap region of the Tauc plot. The calculated Eg values are given in Table 3. They are slightly higher than the energy band gaps usually reported for nanowires [64] or nanorods [66] of SbSI. Furthermore, a slight shift of Eg toward higher energies was observed with an increase in graphite concentration. This can be explained by electron confinement at the nanoscale, known as a quantum size effect [67]. A rise in graphite concentration for the SbSI/graphite nanocomposite led to an evident drop in the widths and lengths of the SbSI nanowires, as shown in Figure 3 and Table 1. This corresponded to an increase in the energy band gap, which is in agreement with the quantum size effect theory.

3.2. Electrical and Thermoelectric Examination

Figure 6a–c present the current-voltage (I-U) dependence of the prepared materials cold-pressed into the bulk samples. Hysteresis was observed in the I-U characteristics of bare SbSI nanowires (Figure 6a) and SbSI/graphite nanocomposite with a small concentration of graphite (Figure 6b). It suggests the existence of polarization effects in these materials, probably originating from the ferroelectric properties of SbSI [13,69]. The measurements were performed at a ferroelectric phase, i.e., below a phase transition temperature of SbSI, which was determined by different researchers as 294 K [70], 295 K [13], or 300 K [69]. Hysteresis vanished when the graphite concentration in the nanocomposite reached 20% (Figure 6c). A vast increase in the electric current by over three orders of magnitude was noted for the SbSI/graphite nanocomposite (Figure 6b,c) in comparison to pristine SbSI nanowires (Figure 6a). This clearly proves that the graphite sheets were responsible for the improvement of the electrical transport. The geometrical dimensions of the samples were used to calculate electrical conductivity, as follows:
σ = d R · A    S m ,
where R is the electrical resistance of a sample [Ω], d is the sample thickness [cm], and A is the area of the electrodes [cm2]. Arrhenius plots of electrical conductance (Figure 6d) confirmed the typical semiconductor behavior of pristine SbSI nanowires and SbSI/graphite nanocomposite with small graphite concentration (4.8 wt.%). The increase in temperature led to a logarithmic rise in σ due to the mechanism of thermal generation of carriers in a semiconductor. This effect was not so evident in the case of SbSI/graphite nanocomposite containing a high amount of graphite (20 wt.%).
Figure 7a presents an experimental setup used to measure the Seebeck coefficient (S) of the examined materials in the steady-state condition. The sample was mounted between two heating and cooling parts, combined with two thermostats with high thermal capacity. One side of the sample was maintained at room temperature (T1), whereas the second one was heated up to T2 temperature. The spatial temperature gradient led to the generation of an open-circuit thermoelectric voltage (Uth) between the two sides of the investigated sample. In order to avoid an undesirable interference between temperature and thermoelectric voltage monitoring, the measurements were performed using two independent circuits.
A large difference in the magnitude of open-circuit thermoelectric voltage was observed between samples of pristine SbSI nanowires (Figure 7b) and SbSI/graphite nanocomposite (Figure 7c). The Seebeck coefficient (also called the thermopower) can be calculated using a well-known relation [71,72,73], i.e.,
S = U t h ∆ T    V K ,
where Uth is the thermoelectric voltage (also known as a thermoelectromotive force) [µV] and ∆T is the temperature difference [K]. It is commonly agreed [71,74,75] that the Seebeck coefficient can be negative or positive for n-type and p-type semiconductors, respectively. The Seebeck coefficients of examined materials (Figure 8a) were determined as slopes of linear dependences that best fit the experimental data, as presented in Figure 7b,c. A high-valued thermopower of 106.2(8) µV/K was obtained for pristine SbSI nanowires. However, this value is lower than a large Seebeck coefficient of 8 mV/K measured by Rao and Mansingh for the SbSI film at a temperature of 320 K [21]. The presence of graphite in the SbSI/graphite nanocomposite led to a reduction in the Seebeck coefficient by over one order of magnitude (Figure 8a). A similar effect of a thermopower decrease with an increase in graphite concentration was reported for polythiophene (PTh)/graphite composite [76]. In this case, a significant drop in the Seebeck coefficient of PTh/graphite composite occurred above the graphite concentration threshold of 50%. There are discrepancies in research on the Seebeck coefficient of pure graphite published in different scientific papers. The negative values of this parameter of −8 µV/K [77], −13.6 µV/K [78], and −2.6 µV/K [79] were measured for graphite samples confirming the n-type electrical conductivity of this material. In contrast to these results, Mulla and co-workers reported a positive Seebeck coefficient of 16.1 µV/K for p-type graphite at room temperature. Piao et al. [37] fabricated the composite of expanded graphite (ExG), polyvinyl alcohol (PVA), and polyethyleneimine (PEI). They measured the Seebeck coefficients as −25.3 µV/K and 10.4 µV/K for n-type ExG/PVA/PEI composite thin film and p-type ExG foil, respectively. Culebras and co-workers [80] investigated thermoelectric properties of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/ExG composites with different concentrations of expanded graphite. Almost no influence of the expanded graphite content on the Seebeck coefficient was observed. This parameter was approximately equal to 15 µV/K [80]. The positive values of the Seebeck coefficients indicated a p-type conduction of PEDOT:PSS/ExG composites.
As presented in Figure 8b, the incorporation of graphite into the SbSI/graphite nanocomposite resulted in a vast increase in the electrical conductivity by over three orders of magnitude in comparison to the bare SbSI nanowires. This is in agreement with other papers on graphite composites [76,80,81,82], which describe the rise in electrical conductivity with graphite content increase.
The thermoelectric power factor (Figure 8c) was calculated using the following equation [36,82,83]:
P F = S 2 σ    W K 2 m
The highest thermoelectric power coefficient was obtained for 11.1% graphite concentration. This corresponded to a Seebeck coefficient of 2.48(9) µV/K and electrical conductivity of 2.58(7)∙10−2 S/m. A comprehensive summary of the electrical and thermoelectric parameters of all the examined materials is provided in Table 4.
It should be noted that the method used for sample preparation significantly affected their electrical and thermoelectric properties. A high-pressure compression of SbSI/graphite nanocomposite at room temperature allowed us to avoid the need for material heating. Therefore, it eliminated any undesired change in the chemical composition of the processed material. This technology provides a simple and convenient way to transform the xerogel of one-dimensional chalcohalide nanostructures with a low packing factor of 4.7% [47] into the denser samples. However, chalcohalide nanowires still do not constitute more than 50% of the total volume of the sample [84]. In the present study, the fill factor ranged from approximately 42% to 52% depending on the graphite weight concentration from 0% to 33.3%, respectively. Furthermore, the presence of the nano/micro voids between the separate nanowires and nanowire bundles was confirmed as a characteristic property of the samples fabricated through compression of the chalcohalide nanowires at room temperature [84]. This feature significantly limited electrical conductivity, as well as affected the thermoelectric performance by reducing the Seebeck coefficient and the power factor. Further progress in sample preparation technology by the application of pressure-assisted sintering may lead to an improvement of the connections between individual SbSI nanowires and graphite flakes. This should result in improved thermoelectric performance of the material.
The sign of the thermoelectric voltage was analyzed to determine the electrical conductivity type of the investigated materials. In the case of all the samples of SbSI/graphite nanocomposites and pristine SbSI nanowires, a negative electric potential appeared at the heated sample side, demonstrating holes as the majority charge carriers (Figure 8d). It should be underlined that this observation is in agreement with the scientific literature on SbSI. A p-type electrical conductivity of bare SbSI was confirmed in different experimental methods, such as thermoelectric examination [21,22], investigation of electrical response to adsorption of oxidizing or reducing gases [85], X-ray photoelectron spectroscopy (XPS) [86], and ultraviolet photoelectron spectroscopy (UPS) combined with UV–vis absorption spectroscopy [87].
The electrical conductivity of cold-pressed SbSI/graphite nanocomposite is relatively low in comparison to good thermoelectric materials, such as commonly used Bi2Te3. Therefore, the possible applications of it can be devoted to temperature measurement, rather than thermal energy harvesting. Since SbSI possesses excellent pyroelectric properties [14], the SbSI/graphite nanocomposite can be considered for use in novel hybrid pyroelectric/thermoelectric devices for the sensitive detection of temperature variations.

4. Conclusions

A facile and low-temperature sonochemical synthesis was developed to prepare SbSI/graphite nanocomposite with various graphite concentrations. The application of an ultrasonic method allowed us to turn highly resistive SbSI nanowires into a hybrid material with improved electrical conductivity. The thermoelectric properties of bare SbSI nanowires and SbSI/graphite nanocomposites were studied experimentally for the first time.
The SEM investigations revealed the formation of a mixed-dimensional composite consisting of 1D nanowires and 2D carbon flakes. The EDS analysis indicated high purity of the obtained materials and confirmed the growth of stoichiometric SbSI inside the SbSI/graphite nanocomposite. The indirect energy band gaps of pristine SbSI nanowires and SbSI/graphite nanocomposite were derived from the DRS examination. A slight shift in the energy band gap toward higher values was observed with an increase in graphite concentration. The temperature dependences of electrical conductivity showed that the semiconductor properties were preserved up to a 20% graphite weight concentration in SbSI/graphite nanocomposite. A vast increase in the electrical conductivity of over three orders of magnitude was observed for SbSI/graphite nanocomposite compared with pristine SbSI nanowires. This clearly proved that the graphite flakes played a key role in the improvement of electrical transport. The influence of graphite concentration on the Seebeck coefficient and thermoelectric power factor of SbSI/graphite nanocomposite was examined. The best thermoelectric performance was achieved with an 11.1% graphite concentration. A p-type electrical conductivity of pristine SbSI nanowires and SbSI/graphite nanocomposite was concluded from the results of the thermoelectric experiments.
A sonochemical synthesis, as described in this paper, is a convenient and promising way for preparing hybrid nanomaterials with desired electrical properties. It is expected that, in the near future, it will be used to fabricate mixed-dimensional nanocomposites of SbSI and a second phase other than graphite.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/en19010009/s1, Table S1. Atomic (at.) and weight (wt.) concentrations of the chemical elements averaged for SbSI nanowires deposited on Si wafer. Table S2. Atomic (at.) and weight (wt.) concentrations of the chemical elements averaged for SbSI/graphite nanocomposite (4.8 wt.% graphite) deposited on Si wafer. Table S3. Atomic (at.) and weight (wt.) concentrations of the chemical elements averaged for SbSI/graphite nanocomposite (11.1 wt.% graphite) deposited on Si wafer. Table S4. Atomic (at.) and weight (wt.) concentrations of the chemical elements averaged for SbSI/graphite nanocomposite (20 wt.% graphite) deposited on Si wafer. Table S5. Atomic (at.) and weight (wt.) concentrations of the chemical elements averaged for SbSI/graphite nanocomposite (33.3 wt.% graphite) deposited on Si wafer. Table S6. A comparison of nominal and experimentally determined weight concentrations of graph-ite in SbSI/graphite nanocomposite. Table S7. A comparison of nominal and experimentally determined weight concentrations of anti-mony in SbSI/graphite nanocomposite. Table S8. A comparison of nominal and experimentally determined weight concentrations of sulfur in SbSI/graphite nanocomposite. Table S9. A comparison of nominal and experimentally determined weight concentrations of iodine in SbSI/graphite nanocomposite.

Author Contributions

Conceptualization, B.N. and K.M.; methodology, B.N., K.M. and J.J.; software, K.M.; validation, B.N., K.M., and J.J.; investigation, B.N., K.M., and M.K.; resources, A.S.; data curation, B.N.; writing—original draft preparation, K.M.; writing—review and editing, K.M., B.N., J.J., M.K., and A.S.; visualization, B.N. and K.M.; supervision, K.M. and A.S.; project administration, K.M. and A.S.; funding acquisition, B.N., K.M., M.K., and A.S. All authors have read and agreed to the published version of the manuscript.

Funding

This paper was partially supported by Silesian University of Technology (Gliwice, Poland) through the statutory research projects for young scientists BKM-748/RM4/2024 (11/040/BKM24/0038), BKM-554/RM4/2025 (11/040/BKM25/0042), the pro-quality Rector’s grant no. 14/010/RGJ25/0018, and within the frame of the statutory research grants no. BK-208/RIF1/2025, 11/030/BK_25/1221, 11/040/BK_25/0040, EU funds FSD—10.25 Development of higher education focused on the needs of the green economy. European Funds for Silesia 2021–2027: The modern methods of the monitoring of the level and isotopic composition of atmospheric CO2 (project no. FESL.10.25-IZ.01-06C9/23-00, PM: Barbara Sensuła).

Data Availability Statement

The data is contained within the article.

Conflicts of Interest

The authors declare no competing interests.

Abbreviations

The following abbreviations are used in this manuscript:
CNTscarbon nanotubes
DRSdiffuse reflectance spectroscopy
EDSenergy-dispersive X-ray spectroscopy
NCnanocomposite
NRsnanorods
NWsnanowires
PANpolyacrylonitrile
PEDOTpoly(3,4-ethylenedioxythiophene)
PSSpoly(styrenesulfonate)
RHrelative humidity
SbSIantimony sulfoiodide
SEMscanning electron microscopy
UPSultraviolet photoelectron spectroscopy

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Figure 1. Key steps for the sonochemical preparation of SbSI/graphite nanocomposite: (a) inserting stoichiometric amounts of reagents into the vessel, (b) synthesis under ultrasonic treatment, (c) washing and centrifugation, and (d) drying of material. A diagram showing a mechanism of material synthesis: (e) cavitation phenomenon, (f) growth of 1D SbSI nanostructures and their collisions with graphite particles, driven by ultrasound, leading to (g) formation of the final product.
Figure 1. Key steps for the sonochemical preparation of SbSI/graphite nanocomposite: (a) inserting stoichiometric amounts of reagents into the vessel, (b) synthesis under ultrasonic treatment, (c) washing and centrifugation, and (d) drying of material. A diagram showing a mechanism of material synthesis: (e) cavitation phenomenon, (f) growth of 1D SbSI nanostructures and their collisions with graphite particles, driven by ultrasound, leading to (g) formation of the final product.
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Figure 2. SEM images of prepared materials: (a) pristine SbSI nanowires and SbSI/graphite nanocomposite with graphite weight concentrations of (b) 4.8% and (c) 20%.
Figure 2. SEM images of prepared materials: (a) pristine SbSI nanowires and SbSI/graphite nanocomposite with graphite weight concentrations of (b) 4.8% and (c) 20%.
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Figure 3. A distribution of particles sizes of pristine SbSI and SbSI/graphite nanocomposite: (a) widths, (b) lengths of SbSI nanowires, and (c) graphite dimensions.
Figure 3. A distribution of particles sizes of pristine SbSI and SbSI/graphite nanocomposite: (a) widths, (b) lengths of SbSI nanowires, and (c) graphite dimensions.
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Figure 4. Combined elemental maps of (a) SbSI/graphite nanocomposite (11.1 wt.% graphite) deposited on Si substrate, (b) corresponding SEM image of selected sample area, and distributions of (c) silicon, (d) carbon, (e) antimony, (f) sulfur, and (g) iodine. The chemical composition of the examined material is provided in Table 2.
Figure 4. Combined elemental maps of (a) SbSI/graphite nanocomposite (11.1 wt.% graphite) deposited on Si substrate, (b) corresponding SEM image of selected sample area, and distributions of (c) silicon, (d) carbon, (e) antimony, (f) sulfur, and (g) iodine. The chemical composition of the examined material is provided in Table 2.
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Figure 5. (a) Diffuse reflectance spectra and (b) corresponding Tauc plots measured for pristine SbSI nanowires and SbSI/graphite nanocomposite. The determined energy band gap values of the examined materials are provided in Table 3. The solid lines in (b) represent the best fit dependence described by Equation (2). The baselines in the sub-band gap region of the Tauc plot are represented by dashed lines. A detailed description is provided in the text.
Figure 5. (a) Diffuse reflectance spectra and (b) corresponding Tauc plots measured for pristine SbSI nanowires and SbSI/graphite nanocomposite. The determined energy band gap values of the examined materials are provided in Table 3. The solid lines in (b) represent the best fit dependence described by Equation (2). The baselines in the sub-band gap region of the Tauc plot are represented by dashed lines. A detailed description is provided in the text.
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Figure 6. Current-voltage characteristics of (a) pristine SbSI nanowires and SbSI/graphite nanocomposite with graphite weight concentrations of (b) 4.8% and (c) 20%, measured at the two temperatures of 283 K and 293 K. (d) Arrhenius plot of electrical conductance for the investigated materials.
Figure 6. Current-voltage characteristics of (a) pristine SbSI nanowires and SbSI/graphite nanocomposite with graphite weight concentrations of (b) 4.8% and (c) 20%, measured at the two temperatures of 283 K and 293 K. (d) Arrhenius plot of electrical conductance for the investigated materials.
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Figure 7. (a) A schematic representation of the experimental setup used for the determination of the Seebeck coefficients of the examined materials. The open-circuit thermoelectric voltage as a function of temperature difference measured for (b) pristine SbSI nanowires and (c) SbSI/graphite nanocomposite with various graphite weight concentrations.
Figure 7. (a) A schematic representation of the experimental setup used for the determination of the Seebeck coefficients of the examined materials. The open-circuit thermoelectric voltage as a function of temperature difference measured for (b) pristine SbSI nanowires and (c) SbSI/graphite nanocomposite with various graphite weight concentrations.
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Figure 8. Influence of the graphite weight concentration on (a) Seebeck coefficient, (b) electrical conductance, and (c) thermoelectric power factor of SbSI/graphite nanocomposite. (d) A scheme describing thermoelectric voltage generation in p-type SbSI/graphite nanocomposite subjected to the spatial temperature difference.
Figure 8. Influence of the graphite weight concentration on (a) Seebeck coefficient, (b) electrical conductance, and (c) thermoelectric power factor of SbSI/graphite nanocomposite. (d) A scheme describing thermoelectric voltage generation in p-type SbSI/graphite nanocomposite subjected to the spatial temperature difference.
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Table 1. Average sizes of the particles in the examined materials 1. The values in the brackets represent two significant digits of standard deviations of particle size measurements.
Table 1. Average sizes of the particles in the examined materials 1. The values in the brackets represent two significant digits of standard deviations of particle size measurements.
MaterialAverage Size of Particles
SbSI NanowiresGraphite Flakes
Width, nmLength, µmSize, µm
SbSI NWs56(18)2.01(50)–
SbSI/graphite NC (4.8 wt.% graphite)28(10)0.56(23)13.3(58)
SbSI/graphite NC (20 wt.% graphite)20(12)0.38(19)6.9(32)
1 Used abbreviations: NC—nanocomposite, NWs—nanowires.
Table 2. Atomic (at.) and weight (wt.) concentrations of the chemical elements of the sample, which are presented in Figure 2 (SbSI/graphite nanocomposite deposited on Si wafer).
Table 2. Atomic (at.) and weight (wt.) concentrations of the chemical elements of the sample, which are presented in Figure 2 (SbSI/graphite nanocomposite deposited on Si wafer).
ElementConcentration of Elements
All Detected ElementsComponents Without Si
at., %wt., %at., %wt., %
silicon63.644.4––
carbon15.84.743.58.5
antimony8.024.122.043.4
sulfur5.54.415.07.8
iodine7.122.419.540.3
Table 3. Literature data on the energy band gaps of the SbSI-based nanomaterials compared with Eg values determined for pristine SbSI nanowires and SbSI/graphite nanocomposite 1. The uncertainties of energy band gaps are given in round brackets. These values were calculated using Equation (S2) presented in the Supplementary Materials.
Table 3. Literature data on the energy band gaps of the SbSI-based nanomaterials compared with Eg values determined for pristine SbSI nanowires and SbSI/graphite nanocomposite 1. The uncertainties of energy band gaps are given in round brackets. These values were calculated using Equation (S2) presented in the Supplementary Materials.
MaterialSynthesis MethodEg, eVEnergy TypeReference
SbSI/PAN NCsonochemical1.81indirect[8]
SbSI NRshydrothermal1.877direct[66]
SbSI/g-C3N4 NC (5 wt.% SbSI)hydrothermal2.755direct[66]
SbSI/g-C3N4 NC (15 wt.% SbSI)hydrothermal2.718direct[66]
SbSI/g-C3N4 NC (25 wt.% SbSI)hydrothermal2.652direct[66]
SbSI encapsulated in CNTssonochemical1.86indirect[68]
SbSI NWssonochemical1.862indirect[63]
SbSI NWssonochemical1.91indirect[64]
SbSI NWssonochemical1.94(2)indirectthis work
SbSI/graphite NC (4.8 wt.% graphite)sonochemical2.00(2)indirect
SbSI/graphite NC (20 wt.% graphite)sonochemical2.03(3)indirect
1 Used abbreviations: CNTs—carbon nanotubes, NRs—nanorods, NC—nanocomposite, NWs—nanowires, PAN—polyacrylonitrile.
Table 4. Influence of the graphite concentration on the Seebeck coefficient, electrical conductivity, and power factor of SbSI/graphite nanocomposites. The values in the brackets represent measurement uncertainties. Detailed information on the uncertainty calculation is provided in the Supplementary Materials.
Table 4. Influence of the graphite concentration on the Seebeck coefficient, electrical conductivity, and power factor of SbSI/graphite nanocomposites. The values in the brackets represent measurement uncertainties. Detailed information on the uncertainty calculation is provided in the Supplementary Materials.
Graphite Concentration, wt.%S, µV/Kσ, mS/mPF, pW/(K2∙m)
0106.2(8)5.9(3)∙10−40.0067(1)
4.81.84(1)3.2(2)0.0108(1)
11.12.48(9)25.8(7)0.16(1)
20.02.41(2)7.4(2)0.0428(7)
33.30.70(1)49.9(4)0.0242(6)
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Nowacki, B.; Mistewicz, K.; Jała, J.; Kozioł, M.; Smalcerz, A. Synthesis, Optical, Electrical, and Thermoelectric Characterization of SbSI/Graphite Nanocomposite. Energies 2026, 19, 9. https://doi.org/10.3390/en19010009

AMA Style

Nowacki B, Mistewicz K, Jała J, Kozioł M, Smalcerz A. Synthesis, Optical, Electrical, and Thermoelectric Characterization of SbSI/Graphite Nanocomposite. Energies. 2026; 19(1):9. https://doi.org/10.3390/en19010009

Chicago/Turabian Style

Nowacki, Bartłomiej, Krystian Mistewicz, Jakub Jała, Mateusz Kozioł, and Albert Smalcerz. 2026. "Synthesis, Optical, Electrical, and Thermoelectric Characterization of SbSI/Graphite Nanocomposite" Energies 19, no. 1: 9. https://doi.org/10.3390/en19010009

APA Style

Nowacki, B., Mistewicz, K., Jała, J., Kozioł, M., & Smalcerz, A. (2026). Synthesis, Optical, Electrical, and Thermoelectric Characterization of SbSI/Graphite Nanocomposite. Energies, 19(1), 9. https://doi.org/10.3390/en19010009

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