Fabrication of cost-effective green assisted synthesis of MoO₃ NPs: its photocatalytic activity and electrochemical sensing actions on lead, mercury, and paracetamol molecules

Abstract

The synthesis of transition molybdenum metal oxide (MoO₃ nanoparticle) was achieved by bio-mediated (Aegle marmelos leaves) combustion process. The characteristics of prepared nanoparticle were well analysed by Powder-X-ray diffraction (PXRD), Scanning electron microscopy-Energy dispersive X-ray (SEM-EDAX), Fourier transform infra-red (FT-IR) spectroscopy, and UV–Visible absorption spectroscopy. The formation of orthorhombic phase structure and average crystallite size (23.6 nm) of MoO₃ nanoparticle was confirmed by PXRD studies. The energy-band gap of achieved sample was found to be 3.1 eV recorded by UV–Visible absorption spectroscopy. This electron transition property directly influences the prepared sample as an excellent photo-catalyst for textile industrial Bromophenol Blue (BPB) dye under irradiation of UV light. The excellent photocatalytic performance on BPB dye was observed with 89.7% at 105 min, which is supported by its lower kinetic constants 17.42 × 10⁻³min⁻¹. The electrochemical measurements for investigating capacitance and resistance of modified graphite-MoO₃ nanoparticle electrode under three-electrode system using 0.1 M HCl in the different scan rates 0.01–0.05 V/s by cyclic-voltammetry (CV) and electrochemical impedance spectroscopic (EIS) analysis. This investigation confirms the good sensing actions towards Lead, mercury, and Paracetamol molecules by impact of alteration in redox peak potentials.

Keywords:

• MoO₃ nanoparticle
• Aegle marmelos green fuel
• electrochemical sensor analysis
• photocatalytic activity

1. Introduction

The nanotechnology has gaining increased attention due to tailoring the physico-chemical properties, such as surface area, size, and composition of samples on nano-scale for efficient actions on necessary multiple applications. The enhanced properties of nanomaterial like chemical stability, conductivity, catalytic and gas adsorption properties were achieved based on its larger surface area to volume ratio of nanoparticles (Jeevanandam et al. 2018; Malleshappa et al. 2015). Nowadays, the various benign of metal oxides, metal composites, and hybrid heterogeneous nanomaterials have drawn the attention of young researcher for its new multiple-application in almost all the areas (Ijaz et al. 2020; Malleshappa et al. 2015). The nanomaterials have played a significant role in novel multiple applications, such as drug transport, bio-therapeutics, pharmaceuticals, electronics, cosmetics, biotechnology, nano-fertilizers, ointments, lotions, water treatment, and electrochemical sensing applications (Baliga et al. 2020; Gudikandula and Charya Maringanti 2016; Iqbal et al. 2021). Generally, the nanoparticles are majorly prepared by physical, chemical, and biological methods as primarily utilised procedures. However, the bio-synthesis is the most cost-effective, simple, and eco-friendly process for providing an notable platform for the preparation of environmentally benign nanoparticle (Mahadevaswamy et al. 2022; Taghavi Fardood et al. 2023). Thus, the presented study focused on green mediated preparation of MoO₃ nanomaterial using solution combustion process.

In the last few decades, transition metal oxides have attracted the research community in great deal due to their diversified applications. According to the survey, the great consideration of nanomaterials has been paid to the fabrication of various kinds of nanometal oxides like TiO₂, ZnO, ZrO₂, CuO, MgO, etc., semiconductors from the last few decades (Gurushantha et al. 2022; Mylarappa et al. 2022; Surendra et al. 2022; Taghavi Fardood et al. 2018; Uma et al. 2022). However, these metal oxides exhibit poor photocatalytic efficiency in the presence of visible light because of their wider energy band gap (Bhuvan Raj et al. 2021; Foroughi et al. 2014; Garkani Nejad et al. 2021; Tajik et al. 2020, 2021). Among these metal oxide, MoO₃ nanomaterial finds the most fascinating materials due to its low-cost, higher the chemical stability, distinct, unique structural, optical, electrical, and mechanical properties. Thus, this kind of material was applied successfully in multiple applications of various fields, such as photocatalysis, light emitting diodes, therapies, gas sensing, and in many medical protocols (Barzinjy et al. 2020; Mazloum-Ardakani et al. 2012; Sneha et al. 2011). Photocatalysis process plays a vital role towards industrial waste water treatment in the presence of suitable photocatalyst having low band gap energy under light irradiation. The achieved nanomaterial having smaller crystallite size and larger surface is directly corresponding to higher the recombination rate of photo-generated electron-hole (e^- -h) pairs and influences its larger photocatalytic efficiency (Chen et al. 2021; Gour and Jain 2019; Umadevi, Bindhu, and Sathe 2013).

Currently, the nanoparticles have drawn great interest towards sensors activities due to their physico-chemical properties ideal for different kinds of applications in electroanalytical devices (Rao et al. 2021; Sowmyashree et al. 2021). The prepared nanoparticle is a class of special anticipated due to their specific structural and optical properties. Thus, the MoO₃ nanoparticles are cost-effective, conductive nature, and employed as an excellent nanosensor for electroanalytical sensing actions. The present study focused on medicinal plant leaf extracts assisted synthesis of MoO₃ nanoparticle via combustion process and successfully applied in electrochemical sensing actions on Paracetamol, lead, and mercury heavy metals detection in 0.1 M HCl. Additionally, the photocatalytic performance of MoO₃ nanoparticle on dye degradation studies and antibacterial properties were discussed in detail.

2. Materials and methods

2.1. Materials

The reagent used for the experimental synthesis of MoO₃ NPs is ammonium molybdate tetrahydrate ((NH₄)₆Mo₇O₂₄.5H₂O) as a starting material purchased from SD fine-chem Ltd. and were used as received without further purification.

2.2. Synthesis of MoO₃ NPs

Stoichiometric ratios of 3.089 g of ammonium molybdate tetrahydrate as a starting material and 4 ml of Aegle marmelos extract were taken in a silica crucible and heated on a hot plate with continuous stirring for solidification (to form gel like consistency). The obtained homogeneous mixture was placed in muffle furnace for the combustion process maintained temperature of 495 ± 5 °C. The final product obtained by combustion reaction in the presence of green fuel preheated under muffle furnace for about 3–5 min was subjected to calcination at temperature of 500 ± 5 °C for about 3 h to attain high purity of sample (Figure 1). Further, the yielded fine, grey green MoO₃ sample was confirmed by several spectral characterisations.

Figure 1. Schematic representation of bio-assisted preparation of MoO₃ nanoparticles.

2.3. Characterisation

The prepared MoO₃ NP was done by the following characterisation techniques to confirm the material size, shape, surface properties, and morphology. X-ray diffraction studies confirm the specific shape and structure of prepared compound under ambient atmosphere at 30 °C by the X’pert Pro diffractometer (Cu-Kα radiation, λCu = 1.5148 Å). The MoO₃ NPs were degassed under vacuity at 300 °C for 3 h before the measurement. The effective absorption study was estimated by UV–vis spectrophotometer (Agilent Cary 60 UV–visible spectrophotometer).

3. Results and discussions

3.1. P-XRD analysis

PXRD studies are a characteristic technique for measuring the crystallite size, nature of crystallinity, and purity with specific phase formation of prepared nanomaterial. The existence of sharp diffraction peaks in XRD pattern of MoO₃ nanoparticle confirms its fine crystal-like particles as depicted in Figure 2. The obtained diffraction planes at different angles (2θ) values of 12.68, 23.29, 25.68, 27.52, 29.78, 33.88, 38.82, 39.81, 45.51, 46.32, 50.14, 52.96, 57.62, 58.76, 62.76, 164.98, and 12.68° were corresponds to (020), (110), (040), (021), (130), (111), (060), (150), (141), (210), (161), (211), (171), (081), (251), and (190) peaks, respectively with orthorhombic structure with higher the purity due to its lack of impurity peaks associated MoO₃ phases were noticed. The reported diffraction peaks of MoO₃ nanoparticle are well-matched with JCPDS Card No.-05-0508 (Chen et al. 2009; Krishnamoorthy et al. 2014). However, the extreme intensity of the deflection points was witnessed in the plane (040) and its familiar crystalline dimension of the MoO₃ nanoparticle was found to be 23.6 nm calculated with Scherrer’s formula (Equation 1(1) $$D=\frac{k\lambda }{\beta \mathrm{\text{cos}}\theta }$$(1) ) (Nagabhushana, Samrat, and Chandrappa 2014; Surendra et al. 2021; Swamy et al. 2021). (1) $$D=\frac{k\lambda }{\beta \mathrm{\text{cos}}\theta }$$(1)

Figure 2. XRD pattern of synthesised MoO₃ nanoparticle from green assisted combustion method.

Where β is full width half maxima of the peak, D is crystal size, λ is X-ray wavelength. Lesser the constituent dimension of MoO₃ NPs illustrate the greater the micro straining and lesser displacement compactness in place of fine crystalline particles.

3.2. Scanning electron microscopy (SEM) examination

SEM analysis shows the effectiveness of internal surface morphology of MoO₃ nanoparticle prepared bio mediated solution combustion technique at different magnifications as depicted in Figures 3(a,c), respectively. These SEM micrographs confirm the existence of rod shaped structures and flake like with agglomeration morphology of MoO₃ nanoparticle. According to the PXRD patterns, there are no impurities present in prepared nanomaterial and further, it was confirmed by determination of elemental composition using Energy dispersive X-ray (EDX) spectroscopy technique as shown in Figure 3(b). This EDX spectral report revealed that the synthesised MoO₃ nanoparticle incorporated by only Mo and O elements without any impurities. The atomic and weight percentage of these existed elements in synthesised MoO₃ nanoparticle was presented in the table (inset Figure 3(b)).

Figure 3. (a,b) SEM micrographs and (c) EDAX analysis of synthesised MoO₃ nanoparticle.

EDX technique is based on the emission of a specimen characteristic of X-rays by the impact of beam of high energy charged particles (electrons or protons) on examining material. An electron from a higher binding energy electron level falls into the core hole and an X-ray with the energy of the difference of the electron level binding energies is emitted. EDX analysis gives a spectrum that displays the peaks correlated to the elemental composition of the investigated sample. In addition, the elemental mapping of a sample can be created with this characterisation method to confirm the synthesised MoO₃ nanoparticle consisting of only Mo and O elements as shown in Figure 4.

Figure 4. The elemental mapping of synthesised MoO₃ nanoparticle.

3.3. Diffused reflectance spectroscopy (DRS) study

The optical examination of synthesised MoO₃ NPs was achieved by measuring its energy band gap using DRS analysis carried out at wavelength ranges of 200–800 nm as shown in Figure 5(a). The energy-band gap and relation between the reflectance of achieved nanomaterials (R), the absorption coefficient (K), and scattering coefficient (S) were calculated according to the reflectance spectral data by Kubelka-Munk function (Equation 2(2) $$F\left(R\right)=\frac{{(1-R)}^n}{2R}=\frac{K}{S}$$(2) ). (2) $$F\left(R\right)=\frac{{(1-R)}^n}{2R}=\frac{K}{S}$$(2)

Figure 5. (a) The reflectance spectral plot and (b) DRS plot of MoO₃ nanoparticle.

Tauc relation for the band gap-energy and the linear absorption coefficient (α) of synthesised MoO₃ NPs are given by (3) $$\mathrm{⍺}=\frac{{C_1(h\nu -E_g)}^{\frac{1}{2}}}{h\nu }$$(3) (4) $${\left[F\right(R\left)h\nu \right]}^2=C_2\left[h\nu -E_g\right]$$(4)

From the graphical plot of [F(R)hν]² on y-axis versus incident photon energy (hγ) on x-axis, the energy-band gap (E_g) values of achieved MoO₃ NPs were found to be 3.1 eV by the extrapolations of linearly dotted line as shown in Figure 5(b). The lower band gap value shows higher photocatalytic action due to the quantum confinement effect and oxygen vacancies (Dinamani et al. 2023; Meenakshi et al. 2023).

3.4. Functional group analysis by FT-IR spectroscopy

The symmetric and asymmetric vibrations of functional groups present in synthesised MoO₃ NPs were recorded by FT-IR spectral technique. The FT-IR spectrum of prepared MoO₃ NPs from green (A. marmelos leaves) mediated combustion process was observed in between 400 and 4000 cm⁻¹ as depicted in Figure 6. The absence of broad peak around 3400–3600 cm⁻¹ indicating the absence of water content in the crystal lattice of material and confirms its higher purity by the absence of additional peaks. The bands appeared in low frequency region representing the bending vibrations of metal-oxygen (M-O) linkages observed in the range between 1000 and 500 cm⁻¹. The ascertained band at 987 and 867 cm⁻¹ in finger-print area corresponding to the bending vibrations of co-ordination linkage of Mo-O-Mo group and the band at 641 cm⁻¹ for Mo-O linkage (Sanchez et al. 2018; Xia et al. 2006).

Figure 6. FT-IR analysis of synthesised MoO₃ nanoparticle.

3.5. Raman spectroscopy

The existence of functional groups and stretching modes of achieved MoO₃ nanomaterial was examined by Raman spectral technique. The Raman peaks of synthesised MoO₃ nanoparticle were recorded in the region of 500–4000 cm⁻¹ as displayed in Figure 7. The Raman peaks appeared at 995, 820, 666, 287, 157, and 126 cm⁻¹ corresponding to octahedral stretching modes of synthesised MoO₃ NPs. The existence of very sharp and high intense Raman band at 820 cm⁻¹ is well-matched to the octahedral stretching modes of synthesised MoO₃ nanoparticle recorded in the spanning region of 1000–600 cm⁻¹. These major Raman bands at 995 and 820 cm⁻¹ confirms the symmetric stretching vibrations of M=O and Mo–O–Mo linkages, respectively in synthesised MoO₃ nanoparticle. Similarly, the octahedral bending vibrations and lattice modes of achieved MoO₃ nanomaterial were observed in the region from 400 to 200 cm⁻¹ and lower modes <200 cm⁻¹.

Figure 7. Raman spectral analysis of synthesised MoO₃ nanoparticle.

4. Photocatalytic dye degradation activity

The current scenario of management of waste water discharged into surrounding water-bodies causing serious problems all over the world. Hence, the presented research work focused on photo-dye degradation activity using the prepared photo-catalyst under UV-Light irradiation. The photo-catalytic process is a significant cost-effective tool and has attracted greater attention towards degradation of various dye-contaminated water released from different sections (Gurushantha et al. 2023; Hegde et al. 2022; Moradnia et al. 2020; Pompapathi et al. 2023; Shanbhag et al. 2021). This process has covered a wide variety of chemical reactions, such as pollutant degradation, high catalytic reaction due to its larger surface area, hydrogen transfer by dehydrogenation process, and photo-oxidation routes. Thus, the MoO₃ nanoparticle synthesised from green mediated combustion method has extensive semiconductor that is widely exploited as heterogeneous photocatalyst due to its intrinsic physio-chemical properties that distinguish them from metals and prevent the electron hole recombination caused by photo-activation.

The synthesised MoO₃ nanoparticle has played a vital role in photocatalytic dye-degradation action on BB dye carried out under UV-Light irradiation with 20 ppm stock solution and 20 mg of photocatalyst. The photocatalytic dye degradation efficiency of achieved MoO₃ nanoparticle on BB dye was examined by measuring the absorbance of light treated dye-samples (15 min) using UV-Visible spectroscopy as shown in Figure 8(a). The photo-dye-degradation action of prepared MoO₃ nanoparticle on dye under UV-Light irradiation was recorded to be 89.7% at 105 min as shown in Figure 8(b). Additionally, the photo-dye-degradation stability actions of synthesised MoO₃ nanoparticle were recorded by carried out with five cycles under above constant conditions. Figure 5(c) shows the photocatalytic action measurement of MoO₃ photocatalyst towards recycle-ability performance on dye degradation activity. This obtained data reveals that MoO₃ photocatalyst has excellent stability on photocatalytic action up to five cycles. Further, the half-time photo-dye degradation studies of MoO₃ photocatalyst were examined by plotting (C/C0) v/s time under UV-light irradiation as shown in Figure 8(d). The photo-dye degradation studies revealed that BPB dye degradation takes place 89.7% at 105 min and its half-time photo-dye degradation occurs at 42.6 min under UV-light irradiation (Figure 8(d)). The standard error bar plot of BPB dye degradation spectral studies is carried out under UV-light irradiation as shown in Table 1. The chemical kinetic studies for photo-dye degradation activity using MoO₃ photocatalyst were studied as shown in Figure 8(e). The comparative investigation of various nanomaterials in photocatalytic studies was discussed and its report has been mentioned in Table 2 (Raghavendra et al. 2021; Surendra et al. 2018, 2020).

Figure 8. (a) Spectral absorbance of MoO₃ nanoparticle with the variation of irradiation time under UV-light irradiation on BPB dye; (b) percentage decomposition of and (c) stability performance; (d) half-time dye-decolouration study; and (e) kinetics studies of MoO₃ nanoparticle.

Table 1. The standard error of spectral absorbance plots for BPB dye.

Time (min)	Value	Standard error
0	0.16326	4.33E-05
	−2.80E-04	0.02291
15	0.14976	3.97E-05
	−2.57E-04	0.02104
30	1.5222	8.44E-05
	−0.00245	0.04464
45	4.19514	2.33E-04
	−0.00675	0.12302
60	1.00402	5.66E-05
	−0.00161	0.02998
75	2.47055	1.39E-04
	−0.00396	0.07377
90	2.7492	1.54E-04
	−0.00443	0.08156
105	2.35645	1.32E-04
	−0.0038	0.0699

Table 2. Comparative study of photocatalytic performance of various nanomaterials.

Sl. No.	Photocatalyst	Dye/ compound	Time (min)	% Of degradation	References
1	MoO3 NPs	BPB	105	89.7%	Current study
2	ZnO	MB	98%	120 min	Moradi and Taghavi Fardood 2019
3	ZnFe2O4 NPs		98%		Surendra et al. 2018
4	ZnFe2O4:Cu NPs	Rh-B	94%	90 min	Swamy et al. 2021
5	ZrO2 and ZrO2:Mg^2+	Acid green (AG)	74.46 and 88%, respectively	105 min	Surendra et al. 2020
6	CuFe2O4 NPs	MG	87.5%	140 min	Raghavendra et al. 2021
7	Clay/MgO nanocomposite	Rh-B	90%	100 min	Shanbhag et al. 2021

4.1. Photocatalytic dye degradation mechanism

The possible photocatalytic dye degradation mechanism of MoO₃ photocatalyst on BB dye under UV-light irradiation is displayed in Figure 9. The influences of light energy on synthesised photocatalyst surface show a photo-sensitization of BB dye under irradiated UV-light (Equation 5(5) $$\mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{ }\mathit{\text{NPs}}+\left(\mathit{\text{Light energy}}\right)----\to \mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{*}\left(\mathit{\text{Energy}}\right)$$(5) ). This process comprises equal numbers of electrons ($e^{-}$) and holes ($h^{+}$) by moving from valence band to the conduction band (Equation 6(6) $$\mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{*}\left(\mathit{\text{Energy}}\right)----\to \mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{ }\left(h^{+}+e^{-}\right)$$(6) ). In the photocatalytic dye decolouration reaction, the water and oxygen molecules are directly influencing the formation of superoxide radicals (${\mathrm{O}}_2^{•-}$) by the presence of $e^{-}$ in conduction band (Equation 7(7) $$\mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{ }\left(e^{-}\right)+O_2---\to O^{2\mathrm{⦁}-}\left(\mathit{\text{Superoxide radical}}\right)$$(7) ) and hydroxyl radicals ${(\mathit{\text{OH}}}^{•-})$ (Equation 8(8) $$O^{2\mathrm{⦁}-}+H_{2}O---------\to {\mathit{\text{OH}}}^{\mathrm{⦁}}+{\mathit{\text{OH}}}^{-}$$(8) ) by the presence of holes in valence band, respectively. The generated radicals are played a vital role in the photocatalytic dye decolouration activities by breaking of complex dye structures into eco-friendly by-products (Raghavendra et al. 2021; Surendra et al. 2018, 2020, 2023). (5) $$\mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{ }\mathit{\text{NPs}}+\left(\mathit{\text{Light energy}}\right)----\to \mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{*}\left(\mathit{\text{Energy}}\right)$$(5) (6) $$\mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{*}\left(\mathit{\text{Energy}}\right)----\to \mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{ }\left(h^{+}+e^{-}\right)$$(6) (7) $$\mathrm{\text{Mo}}{\mathrm{O}}_3\mathrm{ }\left(e^{-}\right)+O_2---\to O^{2\mathrm{⦁}-}\left(\mathit{\text{Superoxide radical}}\right)$$(7) (8) $$O^{2\mathrm{⦁}-}+H_{2}O---------\to {\mathit{\text{OH}}}^{\mathrm{⦁}}+{\mathit{\text{OH}}}^{-}$$(8)

Figure 9. Photocatalytic mechanism of MoO₃ photocatalyst on BB dye under UV-light irradiation.

5. Electrochemical investigations of MoO₃ NPs

The qualitative potential analysis of achieved MoO₃ nanomaterial was examined by electrochemical studies using CV and EIS techniques in three electrode systems under 0.1 M HCl media as depicted in Figure 10. The CV investigation of MoO₃ NPs displays an effective action towards investigation of thermodynamics of reduction and oxidation reactions and specific-capacitance of achieved MoO₃ nanomaterial was carried out by using prepared working electrode in scan rate of 0.01–0.05 V/s. The cycling potential of achieved MoO₃ nanomaterial with graphite paste electrode was recorded by CV plot across a potential range of +1.0 to –1.3 V with a scan rate of 0.01–0.05 V/s as represented in Figure 10(a).

Figure 10. (a) CV graph and (b) EIS-Nyquist plot of MoO₃ NPs electrodes at the scan rate of 0.01–0.05 V/s in 0.1 M HCl.

The specific capacitance of achieved MoO₃ nanomaterial was determined by influence of encircled area received from CV plots using the following formula (Equation 9(9) $$C_{\mathit{\text{SP}}}=\frac{\int \mathit{\text{IdV}}}{v*m*\Delta V}$$(9) ). (9) $$C_{\mathit{\text{SP}}}=\frac{\int \mathit{\text{IdV}}}{v*m*\Delta V}$$(9)

Where; C_SP is denotes the specific-capacitance (F/g), m is the mass of sample (g), I is current (A), v is scan rate (mV/s) and ΔV corresponds to potential windows (V). The measured lower specific-capacitance value from above mentioned formula for MoO₃-Graphite paste electrode has been found to be 44.8 F/g. EIS-Nyquist plot of MoO₃-Graphite paste working electrode revealed the nature of resistance and capacitance of synthesised MoO₃ nanoparticle due to the impact of semicircle arc liable towards X-axis and straight line towards Y-axis. The EIS-Nyquist plot shows lower capacitance value found to be 58 Ω and its line more liable towards X-axis, indicating the higher capacitance synthesised MoO₃ nanoparticle as shown in Figure 10(b) (Hareesha et al. 2021; Jamballi Manjunatha 2020; Jamballi Manjunatha 2013; Manjunatha 2018, 2020; Manjunatha et al. 2011; Prinith and Manjunatha 2023). The electrochemical examination of synthesised MoO₃ nanoparticle is compared with other reported studies as shown in Table 3.

Table 3. Comparison of electrochemical analysis of different nanomaterials.

Sample	Electrochemical studies (sensor detections)	Scan rates	References
ZnO NPs	Paracetamol sensing properties	0.03 V/s	Moradi and Taghavi Fardood 2019
ZnFe2O4 NPs	Mifepristone and misoprostol (1–5 mM) chemical	0.03 V/s	Surendra et al. 2018
ZnFe2O4:Cu NPs	Mifepristone-misoprostol (1–6 mM) chemical	0.03 V/s	Swamy et al. 2021
Clay/MgO nanocomposite	Stannous chloride sensor, dextrose, and eye drop chemicals	0.03 V/s	Shanbhag et al. 2021
Nano ferrite bentonite clay	Dextrose biomolecule	0.03 V/s	Manjunatha et al. 2011
ZrO2:Mg^2+	Paracetamol sensor and eye drops	0.03 V/s	Surendra et al. 2020
CuFe2O4 NPs	Specific capacitance	1–5 mV/s	Raghavendra et al. 2021
MoO3	Paracetamol and lead sensor	0.03 V/s	Present work

5.1. Cyclic voltammetry sensor actions of MoO₃ NPs

Cyclic voltammetric curves of graphite-MoO₃ NPs electrode show characteristic sensing activities towards Lead, mercury, and Paracetamol molecules under 0.1 M HCl at a specific scan rate of 0.03 V/s as shown in Figures 11(a–c). Figure 11(a) shows the CV plot of prepared graphite-MoO₃ NPs electrode for sensing action on Lead detection with different concentrations of 1–5 mM in 0.1 M HCl medium. Therefore, this analysis confirms that the good sensing performance of graphite-MoO₃ NPs electrode on Lead ions due to its current density for oxidation potential peak appears at 0.9 V and reduction potential peaks at 0.6 V (Figure 11(a)). Similarly, the sensing analysis of prepared graphite-MoO₃ NPs electrode on mercury and paracetamol molecules was recorded and its changing current density and redox potential peaks are observed at 0.9 and 0.6 V as shown in Figures 11(b,c).

Figure 11. (a) CV sensing graph for lead, (b) mercury, and (c) paracetamol using MoO₃ NPs electrode in 0.1 M HCl.

6. Conclusion

The present reported work revealed the preparation of MoO₃ nanoparticle by bio-mediated (A. marmelos leaves) combustion process. The structural examinations of achieved sample were well studied by specific spectral techniques. The structural orthorhombic phase formation and purity of MoO₃ nanoparticle was confirmed by PXRD spectra studies. The crystalline dimensions of MoO₃ nanoparticle were found to be 23.6 nm calculated by Scherer’s method based on the existence of extreme intensity of the deflection points witnessed in the plane (040). Its energy-band gap was found to be 3.1 eV measured by UV–Visible absorption spectroscopy. This electron transition property has directly influenced the prepared sample act as an excellent photo-catalyst for textile industrial Bromophenol Blue (BPB) dye degradation with 89.7% at 105 min under irradiation of UV light, which is supported by its lower kinetic constants 17.42 × 10⁻³min⁻¹. The electrochemical measurements for investigating capacitance and resistance of modified graphite-MoO₃ nanoparticle electrode under three-electrode system using 0.1 M HCl in the different scan rates of 0.01–0.05 V/s by CV and EIS analysis. This investigation confirms the good sensing action on characteristic sensing activities towards Lead, mercury, and Paracetamol molecules under 0.1 M HCl at specific scan rate of 0.03 V/s by its alteration of redox peak potentials. This study provides a cost-effective, eco-friendly, and potential new insight into multiple practical applications.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data is available on request from the authors.