Electrochemical-sensor, antimicrobial and environmental assessments of Bi³⁺:Mg_(1−x)Zr_xO₄ NPs synthesised by bio-mediated combustion method

Abstract

The reported research elucidates on a facile Phyllanthus acidus green-assisted solution combustion process developed for the synthesis of Bi³⁺:Mg_(1−x)Zr_xO₄ nanoparticles (BMZ-NPs) and evaluation of their multifunctional applications. PXRD investigation shows the structural evidences and average-particle size (∼30-44) nm of prepared BMZ NPs. SEM-EDAX characterises the surface-morphology and chemical constituents of BMZ-NPs. The band gap energy (Eg) values of undoped and Bi doped MgZrO₄ NPs (0.01-0.05 mol%) were noted between 3.86 to 2.8 eV, investigated by UV-Visible spectral techniques. The electrochemical analysis of prepared samples revealed a good sensor activity towards paracetamol drug chemical detection under both acidic and basic electrolytic media. An excellent photo-degradation activity was noted for BMZ-NPs on AO-7 as model dye and shows 91.4% at 90 min under irradiation of UV Visible-light. Additionally, the antibacterial activity of BMZ NPs against gram + ve and gram -ve bacteria was examined in well diffusion agar technique. The obtained diameter of zone inhibition illustrates BMZ NPs hinders the growth of S. aureus bacteria (5.2 mm against antibiotic streptomycin of 2 mm) much more effectively than E. coli (5.2 mm against ampicillin of 7.7 mm). These results are confirms that the BMZ NPs is an potential candidate for catalytic, sensor and optoelectronic device applications.

Keywords:

• Bi³⁺:Mg₍₁₋x)ZrxO₄
• Phyllanthus acidus
• electrochemical sensor
• photocatalysis
• anti-bacterial activity

1. Introduction

Nanotechnology has most prominent field towards synthesis, design and multiple-applications of various nano-structured materials. Nowadays, the nanomaterials are getting more attention due to its unique physico-chemical characteristics such as optical, catalytic, thermal, electrical, magnetic, etc. (Chen et al. 2011; Perry Murray, Tsai, and Barnett 1999; Kang and Wang 2003; Malleshappa et al. 2015). Accordingly, the literature review shows that various nanomaterials viz; CuO, ZrO₂, MgO, TiO₂, CuFe₂O₄ and other metal-oxides, have been projected as excellent materials for specific applications due to their physico-chemical characteristics (Thirumalai et al. 2019; Subash et al. 2013; Li et al. 2015; Wang et al. 2004). However, the quick population growth and industrialisation activities are adversely affects ecological system by releasing various toxic effluents into natural water sector, which creates a challenging task for researcher to implement the prevention of water pollution from such issues. Among the various nanoparticles, BMZ-NPs has gained great attention towards such kind of pollution treatment activity because of its enhancement in the properties. The nanomaterials having higher photochemical stability and lesser thermal conductivity leads to creates an optimised luminescent material. The phosphor nanomaterials for Solid State Lighting practices are traditionally prepared using the solid-state technique (Pompapathi et al. 2023; Hegde et al. 2020). Thus, ZrO₂ and doped-ZrO₂ NPs have been used in wider applications such as catalyst for preparation of carbon nanotubes (Reddy et al. 2012), photocatalyst for dye degradation (Thakur, Kaur, and Singh 2019) activity, thermal barrier application in IC engines (Surendra et al. 2020) and other industries.

The various synthetic approaches are employed for preparation of ZrO₂ and doped-ZrO₂ NPs. Among that, the combustion method is potential tool due to low cost, greater surface area and purity with high yield of sample (Mahadeva Swamy et al. 2021; Meenakshi et al. 2023). Nowadays, the photo-degradation studies are gaining great attention for removal of industrial effluents containing various azo-derivatives of organic compounds and other industrial organic dyes (Madanakumara et al. 2022; Baran et al. 2021; Fu et al. 2012; Shu, He, and Chen 2008; Guo et al. 2010). Various semiconductors have been used in photo-degradation investigation for polluted water containing hazardous dyes. Doped-ZrO₂ has been used as a photocatalyst, specifically as heterogeneous photocatalysis, for several years among semiconductors. Over the last two decades, ecological contamination affected through hazardous organisms and contaminants has increased the health risks to human and animal life (Al-Ghouti et al. 2003; Borse et al. 2008; Hayati et al. 2021; Zabihpour et al. 2020). As a result, heterogeneous photocatalysis with metal oxides demonstrated remarkable photo decolouration effectiveness against a wide range of harmful dye pollutants, which were transformed into harmless by-products. To overcome these challenges, nano metal oxides were developed, and they quickly gained popularity since they are inexpensive, have better photocatalytic properties, and can be used in a wide range of biological and industrial applications. Therefore, these properties distinguish a metal oxide as a potent photocatalysts for the discolouration of industrial pollutants (Hasanzadeh et al. 2021; Hegde et al. 2022; Saeed and Khan 2017; Shahab et al. n.d.; Ebrahimi and Beitollahi 2021; Surendra 2018). The present reported research on prepared nanoparticle achieved first time by green fuel assisted combustion route encloses a qualitative measurement of glucose and paracetamol medicinal chemical by sensor sensitivity studies using electrochemical analysis under both acidic and basic electrolytic media in 0.1 M KCl at 0.01-0.05 V/s scan rate. Further, photo-degradation activity of prepared nanomaterial was examined for maximum photo-decolouration of AO-7 textile dyes under irradiation of UV-Visible light.

2. Experimental procedure

2.1 Synthesis of BMZ NPs

The experimental route of synthesised BMZ nanomaterials consisting an stoichiometric amount of initial reactants such as Mg(NO₃)₂.3H₂O, ZrO(NO₃)₂.H₂O, Bi(NO₃)₃.5H₂O (analytical grade) in the presence of green fuel (Phyllanthus acidus leaves). These reactants and optimised volume (3.5 mL) of green fuel are transferred into the silica crucible and subject them to continuous stirring by magnetic stirrer about 15 min at 650 rpm. The achieved homogeneous mixture was placed into muffle furnace for combustion under maintained temperature at 600 ± 10 °C. Finally, the white nano-powder of undoped and BMZ samples were collected and used for structural confirmation by spectral characterisations. The schematic representation of synthesised nanoparticles as shown in the Figure 1.

Figure 1. Schematic representation of bio-mediated synthesis of nanoparticles.

3. Results and discussion

3.1 X-Ray diffraction (XRD) investigation of BMZ NPs

Powder XRD patterns of prepared BMZ NPs shows the structural properties of phase formation and crystallite nature, which is recorded and displayed in Figure 2. The appeared all diffractions peaks observed from XRD analysis has been well indexed tetragonal phase structure confirmed by JCPDS no. 88-1007 (Savaloni and Savari 2018) with situated peaks of 2θ values at (200), (101), (112) and (131) peaks. The observed diffractions peaks at (011), (101), (111), (200), (021), (022), (112), (221), (131) and (311) of pure ZrO₂ NPs was well related to monoclinic structure through standard JCPDS data (Surendra et al. 2023; Gurushantha et al. 2022). The average crystallite size of prepared undoped and doped samples were recorded to be ∼ 30 - 44 nm by Scherrer’s expression (Eq. (1)(1) $$d=\frac{k\lambda }{\beta \mathrm{ }\cos \theta }$$(1) ) (Kariyanna et al. 2023). The other structural parameters; dislocation density (δ), stacking fault were determined using Eqs. (1)–(3) and estimated parameters were provided in Table 1. (1) $$d=\frac{k\lambda }{\beta \mathrm{ }\cos \theta }$$(1) (2) $$\delta =\frac{1}{D^2}$$(2) (3) $$SF=\left[\frac{2{\pi }^2}{45{(3\hspace{0.17em}\tan \hspace{0.17em}\theta )}^{1/2}}\right]$$(3)

Figure 2. PXRD Spectra of host ZrO₂, MgZrO₄ and BMZ (0.01-0.05 mol%) NPs.

Table 1. Estimated crystallite size, strain, dislocation density and surface factor of BMZ NPs.

Sl. No	Samples	Crystallite size (nm)	Stress (ε) × 10^-3	Stacking fault (S. F)	Dislocation density
1	MgZrO4	43.82	51.29	0.3145	5.207 × 10^14
2	BiMgZrO4 (0.01 mol%)	36.08	50.63	0.3957	5.505 × 10^14
3	BiMgZrO4 (0.03 mol%)	37.68	55.38	0.3953	7.043 × 10^14
4	BiMgZrO4 (0.05 mol%)	30.3	69.32	0.3943	10.892 × 10^14

The variations in structural properties of zirconia were ascertained due to the impact of increasing Bi³⁺ ion concentrations from 0.01 to 0.05 mol%. This will influences the small shifting of reflections planes of BMZ samples towards lower angle side than those of undoped MZ material. As a result, the doping of Bi³⁺ ions shows expansion in volume of crystal lattice cell, leads to alter tensile stress and micro strain properties due to its higher ionic radius of Bi³⁺ (1.03 Å), Mg²⁺ (0.72 Å) than those of Zr⁴⁺ (0.80 Å). Thus, the XRD examination showed that the prepared samples having smaller crystallite size with larger surface area supported to higher catalytic and redox reaction analysis.

3.2 Scanning electron microscopy (SEM) analysis

The structural surface morphology of synthesised BMZ (0.01-0.05 mol%) NPs were examined by SEM analysis as depicted in Figure 3. The SEM images of undoped-MgZrO₄ (UMZ) NPs shows no major morphology modifications were observed. The structural changes with spherical shaped particles was observed for BMZ NPs may be by the impact of Bi³⁺ ions present in UMZ NPs Figure 3(a–c). The percentage composition of chemicals present in prepared nanomaterials were evaluated by Energy Dispersive X-ray Analysis (EDAX) techniques as presented in the Figure 3(d–f). The obtained outcomes confirm the presence of Bi, Zr, Mg and O compositions by observing the peaks in EDAX pictures. This result represents the purity of achieved nanoparticles without any additional impurities in the prepared materials.

Figure 3. SEM images (a, b and c) of BMZ (0.01-0.05 mol percentage) NPs and the corresponding EDAX spectra (d, e and f).

3.3 Diffused reflectance spectral (DRS) analysis

The DRS analysis shows energy-band gap of prepared BMZ nanomaterials carried out at 200–800 nm wavelength range as shown in Figure 4b. Kubelka-Munk method is used to determine the relationship between the diffuse reflectance of synthesised BMZ NPs (R), the absorption coefficient (K), and the scattering coefficient (S) (Kubelka and Munk 1931). The value of ‘n’ determines whether a direct (n = 1/2) or indirect (n = 2) transition is permitted. (4) $$F\left(R\right)=\frac{{(1-R)}^2}{2R}$$(4)

Figure 4. (a) Absorbance Spectras; b) reflectance spectra; and c) DRS of undoped MgZrO₄ and BMZ (0.01-0.05 mol%) NPs.

Band-gap-Energy (Eg) of prepared BMZ nanomaterials are determined through Tauc equation, is given by (5) $$\left[F\right(R\left)h\nu \right]=A\left[h\nu -Eg\right]n$$(5)

From the [F(R)hν]² versus hν plot, the value of Eg was obtained by extrapolating the linearly fitted regions to [F(R)hν]²=0 and the band gap energy of synthesised host MgZrO₄ and BMZ NPs with different concentrations of 0.01, 0.03, and 0.05 mol percentage were recorded to be 2.8, 3.56, 3.71, and 3.86 eV respectively (Figure 4c). The rectification of Eg values of prepared BMZ nanomaterials by altering dopant-concentrations, resulted Eg values are directly consistent to higher photocatalytic dye degradation studies.

3.4 Fourier transform infra-red (FT-IR) spectral studies

Figure 5 shows molecular stretching and bending vibrations and bonding behaviours of synthesised undoped MgZrO₄ and BMZ NPs were investigated under FT-IR spectral analysis measured at 4000–400 cm⁻¹. The presence of strong peaks at 3522 and 2340 cm⁻¹ are representing existence of hydroxyl-group and C-H stretching vibration in synthesised host and doped samples respectively (Sinha et al. 2021). The observed bands at 1652 and 1375 cm⁻¹ corresponding to bending-vibrations of carbon-hydrogen assembly. The peaks recorded at 510 cm⁻¹ and 1110 cm⁻¹ are indicating molecular bending vibrations of host MgZrO₄ material containing metal-oxygen bonding like Mg-O, and Zr-O linkages respectively. Similarly, the reported bands at 1164, 1110, 836 and 510 cm⁻¹ of BMZ NPs are corresponding to Bi-Mg-Zr, Bi-O, Zr-O, and Mg-O linkages respectively (Dhar et al. 2018).

Figure 5. FTIR spectra of undoped MgZrO₄ and BMZ (0.05 mol%) NPs.

3.5 Thermal stability examination

Thermogravimetric measurement of prepared BMZ (0.05 mol %) NPs illustrates the heat-stability with chemical arrangement by observing weight loss through the impact of temperature ranging from 20 to 900 °C. Normally, higher rate of weight loss can be observed for BMZ NPs by the effect of temperature may be the decomposition and dehydration of water molecules (Thakur, Kaur, and Singh 2019). Figure 6(a,b) shows the thermal stability examinations of synthesised BMZ (0.05 mol %) NPs which was achieved by impact of oxygen with varying temperature of 10 °C - 900 °C with a rate of heating at 20 °C min⁻¹. The obtained results shows that BMZ NPs has higher thermal-stability and resist up to 580 °C without any weight loss leading to the development of crystallised monoclinic phase. Additionally, the decreasing heat-stability of synthesised nanomaterials were noted beyond 580 °C and observed two main stages at temperature of maximum disintegration of prepared material in 580-620 and 625-800 °C as shown in Figure 6a. Therefore, BMZ NPs was sintered at 600 °C for 4 hr in a temperature monitoring combustion furnace.

Figure 6. (a) TGA plot and b) DSC of BMZ (0.05 mol percentage) NPs.

4. Potential measurements and sensor activities of prepared graphite-nano electrodes

The electrochemical studies of undoped MgZrO₄ and BMZ (0.05 mol%) nanomaterials were carried out in 0.1 M HCl with various scan rate of 1 to 5 mV/s using cyclic-voltammetric and electrochemical-impedance spectroscopic methods as depicted in Figure 7. The cyclic-voltammetric (CV) analysis revealed that an enhanced supercapacitor in nature by measuring capacitance and potential activity by the impact of redox reaction of modified graphite-nano (GN) working electrodes in presence of counter (Pt) and reference (calomel) electrodes. The smaller potential differential of undoped GN-electrode was found by CV curve in the potential range of 0.5 to – 0.34 V at scan rate of 0.03 V/s was depicted in the Figure 7a. Similarly, higher potential differential of BMZ-GN-electrode was found by CV curve in the potential range of 0.5 to – 0.27 V at same scan rate of 0.03 V/s Figure 7b. The electrochemical-impedance spectral plot of BMZ-GN-electrode shows an smaller semicircle arc than those of undoped GN-electrode liable towards X-axis, which is due to the impact of Bi ion in MgZrO₄ nanoparticles. The obtained results corresponds to higher capacitance and its line more liable towards Y-axis, signifying higher capacitance as shown in the Figure 7c. The electrical capacitance values of achieved undoped MgZrO₄ and BMZ NPs were found to be 272 and 193 Ω respectively recorded by EIS-Nyquist plot (Figure 7c), which is confirming that BMZ NPs having larger in electrical conductivity with lesser resistance (Uma et al. 2022; Santos et al. 2007). The EIS plot can be explained by an equivalent Randles circuit that comprises solution resistance (Rs), double layer capacitance (Cdl), charge transfer resistance (Rct), and Warburg impedance. The equivalent circuits for prepared host MgZrO₄ and Bi³⁺:MgZrO₄ NPs were reported (in inset Figure 7c) showed 0.26 and 0.08% error respectively confirms the higher capacitance acquire a semicircle at low frequency region in Nyquist plot (Surendra et al. 2021; Lakshmi Ranganatha et al. 2020). The electrochemical analysis of other reported studies as given in Table 2.

Figure 7. (a) Cyclic voltammetric plot of undoped MgZrO₄; (b) cyclic voltammetric of BMZ (0.05%) NPs. (CV) and c) Electrochemical impedance spectroscopy of undoped MgZrO₄ and BMZ (0.05 mol%) NPs.

Table 2. Comparison of electrochemical studies of different nanomaterials for various sensors.

Sample	Electrochemical studies (Sensor detections)	Reference
Mercury drop electrode	Voltammeric behaviour of Rimsulfuron herbicide sensing properties	Ersin and İnam 2014
Glassy carbon electrode	Square wave voltammetric determination of pencycuron fungicide	Acer, Demir, and İnam 2020
Poly(maleic acid) modified carbon electrode	Detection of dopamine in the presence of uric acid	Manjunatha et al. 2011
Polymethionine modified carbon sensor	Sensor for sensitive and selective determination of L-tryptophan	Prinith and Manjunatha 2020
Poly(Glutamic Acid) carbon nanotube paste electrode	Electrochemical analysis of Indigo Carmine in Food and Water Samples	Edwin et al. 2021
Graphene paste electrode	Electrochemical sensor for the sensitive and simultaneous determination of catechol and resorcinol	Manjunatha 2020
BMZ-GN-electrode	on bio-molecule (glucose) and industrial drug chemical (Paracetamol)	Present Work

Further, the sensor investigation of BMZ-GN-electrode on bio-molecule (glucose) and industrial drug chemical (Paracetamol) were explored by CV spectral analysis under different electrolytic conditions (1 M KCl and NaOH). These CV studies revealed that the obtained results confirms that the BMZ-GN-electrode has outstanding sensor sensitivity towards paracetamol medicinal chemical was found under both electrolytic media (Figure 8a,b) than those of glucose sensing analysis at scan rate of 0.03 V/s as shown in Figure 9(a,b). However, the recorded data reveals that the best sensitivity action of BMZ-GN-electrode was found for paracetamol chemical in 1 M NaOH electrolytic medium than those of 1 M KCl electrolyte. Thus, the stronger variations of redox peak-potential positions CV plots of BMZ GN-electrodes confirms their chemical sensor activities in alkaline medium with 1–5 mM in 1 M NaOH electrolyte (Manjunatha 2018).

Figure 8. (a and b) Paracetamol sensor studies of BMZ (0.05 mol%) NPs under 1 M KCl and 1 M NaOH electrolytes respectively.

Figure 9. (a and b) Glucose sensor studies of BMZ (0.05 mol%) NPs under 1 M KCl and 1 M NaOH electrolytes respectively.

5. Photocatalytic dye degradation studies

The photocatalytic investigation of synthesised samples over industrial dye effluents containing various azo-derivatives of organic compounds are gaining great attention around the globe. Thus, the BMZ semiconductor material is used successfully for heterogeneous photocatalysis against a wide range of harmful dye pollutants and transformed into harmless by-products. This kind of semiconductors are most significant and widely used as an heterogeneous photocatalysts due to their intrinsic physical and chemical properties that distinguish them from metals and prevent the electron hole recombination caused by photo-activation. The photocatalytic performance of synthesised BMZ-photocatalyst was measured over AO-7 model dye under irradiation of UV-Visible light by monitoring its absorbance wavelength at 484 nm.

The photocatalytic measurements were performed by using mixture of 40 ppm stock AO-7 dye solution and 50 mg of BMZ-photocatalyst under UV-Visible light. During these photocatalytic measurements, the small volume (4 mL) of dye solution was collected for every 15 min of time interval and measured its absorbance having reduction in AO-7 dye concentration due to the impact of undoped and BMZ NPs photocatalysts using UV-Visible spectrometer as shown in the Figure 10a,b, respectively. Thus, the experimental photocatalytic measurements of undoped MgZrO₄ and BMZ NPs on AO-7 dye displayed an excellent photodegradation performance with increasing irradiation light time and recorded to be 82.3 and 91.4% at 90 min as depicted in Figure 10c. The photodegradation activities of AO-7 dye shows first-order kinetic theory and its kinetics values are calculated by ln (C/C0) = −kt. Where k is reaction rate constant, C0 is the initial concentration of AO-7 dye, and C is the concentration of AO-7 dye at the reaction time t. Figure 10d shows first-order kinetic graphs for photo-degradation of AO-7 dye in presence of BMZ NPs under irradiation of UV-Visible light. The reaction rate constants were calculated as given in Table 3.

Figure 10. (a and b) Absorbance spectra of AO-7 dye BMZ (0.05 mol percentage) NPs and BMZ (0.05 mol percentage) NPs photocatalyst (c and d) % degradation and C/C₀ V/s Time plot respectively.

Table 3. Kinetic studies under UV on BMZ (0.05 mol percentage) photocatalysts.

Sl. No	Photocatalysts	% of degradation	K × 10^-3 (min^-1)
1	BiZrO4	82.3	19.89
2	Mg0.01Bi0.99ZrO4	84.0	21.32
3	Mg0.03Bi0.97ZrO4	86.2	22.82
4	Mg0.05Bi0.95ZrO4	91.4	28.11

Figure 11 representing the general mechanism for photocatalytic AO-7 dye degradation using BMZ photocatalyst under UV-Visible light. The dye gets photosensitised by the impact of applied UV-Visible light on the surface of photocatalyst (Eq. (6)(6) $$5\mathrm{ }\mathit{mol}\mathrm{ }\mathrm{\%}-\mathit{BMZ}\mathrm{ }\mathit{NPs}+\left(UV\mathrm{ }\mathit{energy}\right)----\to \mathit{BMZ}\mathrm{ }\mathit{NPs}\star \left(\mathit{Energy}\right)$$(6) ). These process leads generate number of excitons consisting equal number of electrons (e^-) and holes due to their movement from the valence band in to conduction band (Eq. (7)(7) $$\mathit{BMZ}\mathrm{ }\mathit{NPs}\star \left(\mathit{Energy}\right)--------\to \mathit{BMZ}\mathrm{ }\left(h^{+}+e^{-}\right)$$(7) ). These produced charges (e^-) get moves into the BMZ-photocatalyst surfaces and initiates to form superoxide radicals (${\mathrm{O}}_2^{•-}$) by reacting with O₂ (Eq. (8)(8) $$\mathit{BMZ}\mathrm{ }\left(5\mathrm{ }\mathit{mol}\mathrm{ }\mathrm{\%}\right)\left(e^{-}\right)+O_2----\to O^{2\mathrm{⦁}-}\left(\mathit{Superoxide}\mathrm{ }\mathit{radical}\right)$$(8) ). Correspondingly, the positive charges in valence band are directly involved in production of hydroxyl radicals ${(OH}^{•-})$ (Eq. (9)(9) $$O^{2\mathrm{⦁}-}+H_{2}O--------------\to {OH}^{\mathrm{⦁}}+{OH}^{-}$$(9) ) by their interaction towards water molecules. The mechanistic aspect of photocatalysis can be explained based on activation of BMZ photocatalyst under UV-light irradiation, which leads to produces an free active radicals such as OH^•, O₂^•- and H₂O^• that are recognised as major contributors to the photodegradation method in industrial dyes (Uma et al. 2023; Basavaraju et al. 2021; Shanbhag et al. 2021; Surendra et al. 2022; Dinamani et al. 2023; Mahmoodi et al. 2019; Mahmoodi, Bashiri, and Moeen 2012). (6) $$5\mathrm{ }\mathit{mol}\mathrm{ }\mathrm{\%}-\mathit{BMZ}\mathrm{ }\mathit{NPs}+\left(UV\mathrm{ }\mathit{energy}\right)----\to \mathit{BMZ}\mathrm{ }\mathit{NPs}\star \left(\mathit{Energy}\right)$$(6) (7) $$\mathit{BMZ}\mathrm{ }\mathit{NPs}\star \left(\mathit{Energy}\right)--------\to \mathit{BMZ}\mathrm{ }\left(h^{+}+e^{-}\right)$$(7) (8) $$\mathit{BMZ}\mathrm{ }\left(5\mathrm{ }\mathit{mol}\mathrm{ }\mathrm{\%}\right)\left(e^{-}\right)+O_2----\to O^{2\mathrm{⦁}-}\left(\mathit{Superoxide}\mathrm{ }\mathit{radical}\right)$$(8) (9) $$O^{2\mathrm{⦁}-}+H_{2}O--------------\to {OH}^{\mathrm{⦁}}+{OH}^{-}$$(9)

Figure 11. The photo-degradation mechanism of AO-7 dye.

6. Antimicrobial studies

The antibacterial activity of BMZ NPs against Gram-positive and Gram-negative bacteria were evaluated using the agar well diffusion method as shown in Figure 12. In Nutrient broth, cultures of the test organism were grown to the late logarithmic phase. Aliquots of 100 μL from the cultures were spread on solidified nutrient agar plates. The wells were created on solidified agar plates and loaded with 50 µL/well of 50 mg concentration of nanoparticle dispersed in distil water. The plates were incubated at 37 °C for 24-48 hr and observed for zone of inhibition (Hayati, Mahmoodi, and Maleki 2015).

Figure 12. Antibacterial activity of BMZ (0.05 mol percentage) NPs (c = represent positive control streptomycin and ampicillin for S. areus E.coli respectively, followed by 50 µL/well of 50 mg BMZ NPs).

The inhibition zone was recorded for test culture for 24 h of incubation due to the presence of BMZ NPs. However, the inhibition zone measured was found to be less for strain E. coli and more for S. aureus against positive control. The antibiotic ampicillin showed 7.7 mm against E. coli of 5.2 mm and antibiotic streptomycin showed 2 mm against S. aureus of 5.2 mm of zone of inhibition radii (Figure 13). The obtained zone of inhibition diameter representing BMZ NPs blocking development of S. aureus bacteria efficiently than those of E. coli. The difference in zone of inhibition was due to difference in cell membrane E. coli and it was reported in several literatures (Asefi, Mahmoodi, and Arami 2010; Mohammad Mahmoodi 2013; Xu et al. 2011; Yan, Li, and Zou 2010; Rai et al. 2021). Additionally, the biological investigations as explained from Karthik Kannan et al., supports the above mentioned parameters with increased cellular internalisation of BMZ NPs. The addition of dopant (Bi atoms) in to host material modifies Eg values, which is directly responsible for generation of reactive superoxide (RSO) anions (O²·⁻) corresponding to the modification in cellular redox potential (Khan et al. 2020; Kannan et al. 2020) and cell responses thereby promoting cell apoptosis as displayed in Figure 14.

Figure 13. Zone inhibition of antibacterial activity of BMZ (0.05 mol percentage) NPs.

Figure 14. Probable mechanism for enhanced antibacterial activity of BMZ (0.05 mol percentage) NPs.

7. Conclusion

The nanocrystalline host and Bi³⁺ doped MgZrO₄ nanoparticles have been successfully prepared by bio-fuel mediated combustion method. P-XRD analysis confirms that the prepared material having crystalline nature with monoclinic phase and its average-crystallite sizes were calculated around ∼30-44 nm. The band-gap energy of synthesised BMZ nanoparticles of different concentrations of NPs were observed to be 2.8, 3.56, 3.71, and 3.86 eV using DRS spectral analysis. These variations of band gap value from of 2.8-3.86 eV due to the increasing addition of Bi³⁺ into host material. The qualitative electrochemical measurements of host and BMZ NPs was studied for its potential role as supercapacitor electrode by performing CV and EIS techniques using three-electrode system in 0.1 M HCl electrolyte. The sensor study revealed that the less sensing activity towards glucose and excellent sensor sensitivity for paracetamol. The antibacterial activity of BMZ NPs against gram-positive and gram-negative bacteria were discussed in details using the agar well diffusion method. The obtained diameter of zone inhibition reveals that the BMZ NPs hinders the growth of the S. aureus bacteria (5.2 mm against antibiotic streptomycin of 2 mm) much more effectively than E. coli (5.2 mm against ampicillin of 7.7 mm). The photocatalytic dye removal efficiency of achieved BMZ nanoparticles on AO-7 dye exhibited very good dye decomposition activity (91.4%) at 90 min under irradiation of UV-light. Thus, the reported research provides an new insight for developing specific nanomaterials towards higher the photocatalytic activity, electrochemical sensor studies under different electrolytic conditions and multiple applications.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability

The data used to support the findings of this study are included within the article.