Silver vanadate nanoparticles: Green synthesis, enhanced photocatalytic and antibacterial activity Open Access

The expeditious growth of urbanization and industrialization has unfavorably contaminated our precious nature and natural resources, leading to health problems in living organisms, mainly in human beings. Primarily, water pollution due to waste effluents from the textile industry and pathogenic bacteria and other microbes results from the mixing of fecal materials, industrial and domestic sewage, pasture, and agricultural runoff with drinking water. Due to these, several infectious diseases, such as typhoid, cholera, and dysentery, affect human beings. Due to their toxic nature, organic dyes are considered one of the main poisons in industrial wastewater among chemical contaminants. Some of these dyes are extremely poisonous and pose serious harm to the ecosystem in the area.¹ Thus, we need technology that can monitor, detect, and, if possible, clean the pollutants from the water. Research into the science and technology of diverse nanostructures has greatly increased as a result of the current circumstances, and this technology is rapidly evolving and will have a big impact on the future of materialization.² Conventional wastewater treatment technologies have a number of major drawbacks, including cost, energy use, maintenance and operation costs, transportation and storage issues, time requirements, equipment handling, etc.

Nanotechnology has been incorporated into cleaner industrial processes and the creation of environmentally friendly products because it plays a priceless role in the purification of the environment through the detection, prevention, and removal of hazardous pollutants. For wastewater treatment, such as photocatalyst degradation of a variety of organic pollutants in wastewater, such as detergents, dyes, pesticides, etc., nano-catalysts and catalytic membranes, nano-adsorbents, nano-membranes, bioactive nanoparticles, and biomimetic membranes are used.³ 

The synthesis of nanomaterials using green nanotechnology is an evolving research trend in current days because this technique is eco-friendly, non-toxic or less-toxic, and economical as compared to other current methods (physico-chemical). Various living entities, such as plants, fungi, bacteria, and algae, benefit from this nanoparticle production.⁴ However, researchers from all over the biosphere are now concentrating more on plant-based nanoparticle synthesis. Due to their great efficiency and biocompatibility, nanoparticles are now used in a number of characterization approaches for water and wastewater treatment. When wastewater is purified for reuse and recycled via green nanoparticle synthesis, heavy metals from waste water can be recovered and eliminated, as well as a range of organic pollutants. This helps address numerous global problems with water quality.⁵ These days, research has concentrated on the creation and evaluation of nanoparticles such as ZnO,⁶ Zr₃(PO₄)₄,⁷ NiO,⁸ CuO,⁹ Cr₂O₃,¹⁰ Ag₂O,¹¹ BiOCl,¹² etc., for their physicochemical and biological properties.

In this situation, nanotechnology offers a bright spot and a glimmer of hope for resolving these problems and preserving our ecosystem. In current years, green synthesis of silver vanadate nanoparticles by plants such as Tagetes erecta,^13, Selaginella bryopteris,^14, Tabernaemontana divaricata,^15, Phoenix dactylifera,^16, Alchornea laxiflora,^17, Trigonella foenum-graecum seed extract,¹⁸ capsicum Chinese plant,^19, Conocarpus lancifolius plant extract,^20, Lantana camara leaf extract,²¹  Aegle marmelos,⁷ and several others has been reported to have photodegradation and antimicrobial properties.

Green synthesis of iron,²² Ag@Au,²³ Ag,²⁴ ZnO,²⁵ Bi₂O₃,²⁶ and other nanoparticles has been performed using jackfruit extract. Among these, AgVO₃ received more attention for its specific properties, such as photocatalysis,²⁷ gas sensing,²⁸ use in lithium-ion batteries,²⁹ and antimicrobial³⁰ and optoelectronic properties.³¹ 

To the best of our knowledge and after a thorough literature review, no effort has been made so far to prepare silver vanadate nanoparticles using jackfruit extract by the precipitation method. The obtained silver vanadate nanoparticles were characterized by scanning electron microscopy (SEM), x-ray diffraction analysis (XRD), the Brunauer–Emmett–Teller (BET) method, a Fourier transmission infrared spectrometer (FTIR), energy dispersive spectra (EDS), and Raman spectra. Following production, AgVO₃ nanoparticles were treated to evaluate their photodegradation capacity of the methylene blue dye by varying the different parameters, such as dye concentration, catalyst concentration, pH, and detection of ·OH radicals. Antimicrobial studies of gram-negative and gram-positive bacteria were also carried out. A comparison table of nanoparticles from green synthesis and their photodegradation efficiency with applications is shown in Table I.

All chemicals were pure and of analytical reagent grade. NH₄VO₃, AgNO₃, and NaOH were purchased from S.D. Fine Chemicals Ltd., and jackfruit extract was used to synthesize the AgVO₃ nanoparticles by the precipitation method. Double-distilled water was used throughout the experiment.

Healthy, unripe, and unharmed jackfruits were identified and procured in Bengaluru from the Indian Institute of Horticultural Research (IIHR). After that, the fruit pulp was dried for 15 days in the shade. To obtain jackfruit powder, the resulting dried fruit pulp underwent additional processing by being homogenized in a blender. A Soxhlet apparatus was then used to extract from the 5 g of powder over the course of 15 cycles.

To make AgVO₃ nanoparticles by precipitation, ammonium metavanadate (0.1M), a silver source, and aqueous jackfruit extract were used. The synthesis was started by adding 5 ml of jackfruit extract to 20 ml of NH₄VO₃ solution (0.1M) in a beaker. At a temperature of 50 °C, the mixture was gently stirred for 30 min. The beaker was then filled with 20 ml of silver nitrate solution (0.1M). NaOH was cautiously applied in order to maintain a pH level of 6. The resulting precipitate was extensively washed with distilled water to remove any impurities. The AgVO₃ precipitate was then dried at 100 °C for ∼5 h. The resulting AgVO₃ nanoparticles were subsequently used for further characterization and other applications. pH was controlled and the acidic condition was maintained to prevent the reduction of Ag⁺ to Ag. The synthesis pathway was adopted to get silver vanadate by controlling the pH, metal concentration, aging time, and drying temperature. Therefore, the methodology detailed here describes the optimum conditions to get the coveted metalate, limiting the polymerization of vanadium ions and the precipitation of silver oxides. The secondary phase of these potential implications does not affect the photocatalytic and antimicrobial applications of synthesized AgVO₃.

The crystallinity and structure of the AgVO₃ nanoparticles were assessed using an x-ray diffractometer (Rigaku SmartLab) furnished with monochromatic high-intensity Cu-Kα radiation, where λ (lambda) equals 1.5418 Å. Using a TESCAN Vega 3LMV instrument, SEM was carried out to study the material’s surface morphology. Through energy-dispersive x-ray diffraction analysis coupled with SEM, the purity and elemental composition were ascertained. In addition, an Agilent Cary 60 UV–Visible spectrophotometer was used to record the UV–Visible spectra of the degraded solution. Using nitrogen adsorption at −196 °C, the BET-specific surface area of the Ag vanadate was determined using Quanta Chrome Instruments Version 10.01. Using an Ar⁺ ion laser (514.5 nm laser line) with a power-varying laser density, measurements of Raman spectroscopy were performed. To assess the scattered light, a Jobin Yvon T64000 spectrometer with a cooled charge-coupled device (CCD) detector was utilized.

The photocatalytic activity of AgVO₃ as a catalyst for degrading the organic dye methylene blue in water was investigated using visible light. A HEBER scientific photo-reactor was used to increase the degradation’s effectiveness. This reactor has fans to dissipate the heat produced by the light source and a water jacket to block out visible light, which may affect how quickly the methylene blue dye degrades. 100 ml of a 5 ppm methylene blue solution was placed in a 9-in. quartz tube, along with 50 mg of photocatalyst, for the degradation process. The mixture was given 30 min to equilibrate in the dark in order to reach adsorption–desorption equilibrium. A water-cooled condenser surrounds a high-pressure mercury lamp (250 W, 365 nm) that is installed inside a quartz chamber and, at about 12 cm, separates the solution from the light source. After a 20-min interval, samples were removed from the reactor and centrifuged to separate the photocatalyst and the solution. After each time interval, the amount of absorption was measured with a UV–Visible spectrophotometer to determine the level of degradation. It is important to note that a number of factors, including catalyst load, pH variations, and varying dye concentrations, affect the degradation efficiency. In order to achieve high degradation efficiency, all of these restrictions were methodically investigated and improved in this study.

The effectiveness of antimicrobial screening against gram-negative (Klebsiella pneumonia and Pseudomonas aeruginosa) and gram-positive (Staphylococcus aureus and Bacillus subtilis) bacterial strains has been investigated using three different dosages of AgVO₃ nanoparticles.

Figure 2 shows how the functional groups in the AgVO₃ nanoparticles were detected using the Fourier transform infrared (FTIR) approach. The study was performed between 4000 and 500 cm⁻¹. Notably, the appearance of three separate peaks at 960, 750, and 600 cm⁻¹ indicates the presence of (V–O–V) bonds, in which two vanadium atoms are connected to the central oxygen atom. Asymmetric stretching modes are linked to these peaks. In addition, new peaks were found at 2100 and 2300 cm⁻¹, which indicate the presence of C–C double bonds, and at 1400 cm⁻¹, which indicate the presence of a C–C single bond. These results help characterize the molecular structure of the AgVO₃ nanoparticles by offering important insights into the chemical composition and bonding inside them.

Scanning electron microscopy (SEM) was used to examine the morphology of the synthetic AgVO₃ nanoparticles. The SEM analysis yielded nanographs of the AgVO₃ nanoparticles, all of which consistently revealed a distinctive feature: rod-shaped structures. Through SEM analysis, we were able to determine that the Ag vanadate nanoparticles exhibited a heterogeneous morphology composed of Ag vanadate rods 100 nm in width. These SEM images of AgVO₃ nanoparticles are presented in Fig. 3(a), providing clear visual evidence of their characteristic morphology.

The EDS spectra presented in Figs. 3(b) and 3(c) confirms the existence of signals corresponding to silver, vanadium, and oxygen. This observation indicates the purity of the prepared AgVO₃ sample. Moreover, the quantitative analysis reveals a stoichiometric ratio for AgVO₃ of 11.72:12.03:76.25, which closely aligns with the theoretical value.

An important analysis method for measuring a material’s specific surface area is based on the Brunauer–Emmett–Teller (BET) hypothesis, which attempts to explain the physical adsorption of gas molecules on a solid surface.³³ Surface parameters such as pore size, volume, and area have a significant impact on nanomaterial qualities. The BET technique is very important in elucidating the surface parameters of the nanoparticles. The BET surface area was evaluated by adsorption or physisorption of N₂, utilizing a surface analysis device (Beishide, 3H–2000PSI, China). Figures 4(a)−4(c) depict the N₂ adsorption/desorption isotherm, pore size distribution of AgVO₃ nanomaterials, and BET surface area plot of AgVO₃ nanoparticles. This figure also shows the type IV Langmuir hysteresis curve, depending on the form of the pore in the manufactured sample, which has a surface area of 25.8 m² g⁻¹.

Raman scattering is utilized to analyze the crystalline state of nanoparticles as well as to discover defects in the manufactured AgVO₃ nanomaterials. Figure 5 depicts the Raman scattering spectrum of AgVO₃ nanoparticles produced with jackfruit extract as fuel. The large peaks at 336 and 442 cm¹ correspond to the hexagonal structure of AgVO₃. The high signal at 884 cm¹ indicates monoclinic AgVO₃ nanomaterials with a mixed phase. The Raman bands at 383 and 334 cm¹ are ascribed to the asymmetric deformation modes of the VO43-tetrahedron.^34–36 

The photocatalytic activity involves four steps: first, electrons and holes are generated by the light irradiation; second, charge carriers cause separation and migration of the semiconductor to the surface; third, the involvement of the generated electrons and holes in the oxidation and reduction reactions to intermediate products; finally, the recombination of charge carriers on the photocatalytic surface. The photocatalytic activity depends on many factors, such as crystallite size, surface area, and mainly the bandgap. One of the promising options for improving photocatalytic ability is silver vanadate, primarily because optical absorption can be extended to the visible light region and effectively reduce the recombination of the photogenerated electrons and holes. This allows for the development of an efficient way to fully utilize solar light at higher photocatalytic activity.^38,39 This happens as a result of effective absorption centers in the vanadate groups, VO₃⁻, where electronic transitions from oxygen (2p orbital) to V⁵⁺ (3d orbital) ions can be easily generated.⁴⁰ 

The synthesized AgVO₃ nanoparticles were tested for the degradation of other pollutants such as rhodamine-B (Rh–B), methylene blue (MB), methyl orange (MO), and rose bengal (RB). The below-mentioned graph shows the degradation efficiency of synthesized AgVO₃ nanoparticles. The degradation study has been performed for 3 h with an interval of 30 min (Fig. 7). The degradation efficiency of synthesized AgVO₃ nanoparticles after 180 min for Rh–B, MB, MO, and RB was found to be 75.89%, 98.15%, 68.14%, and 68.36%, respectively. Therefore, methylene dye has been selected for further photocatalytic study.

AgVO₃ nanoparticles were tested in a series of doses (10, 20, 30, and 40 mg), and the results are shown in Fig. 8. Notably, the elimination efficiency increased to an astonishing 98% at a dosage of 20 mg. However, the elimination efficiency showed a modest decline to 40% as the dosage was increased to 30 and 40 mg. This behavior is explained by the extraordinary ability of AgVO₃ nanoparticles to absorb light, which promotes the formation of photogenerated electrons and holes. These charge carriers create superoxide and hydroxyl radicals when they interact with water and dissolved oxygen. However, as the dosage increases, light transmittance decreases, decreasing how well light is used and, as a result, lowering photodegradation efficiency. Furthermore, large dosages may cause nanoparticles to aggregate, further reducing their effectiveness.

Figure 9 shows the effect of dye concentration on the percentage of dye degradation under visible light. Different concentrations of MB dye, such as 5, 10, 15, and 20 ppm for 100 ml of the reaction mixture, were tested by maintaining the AgVO₃ nanoparticles constant at 20 mg. Figure 9 shows that photodegradation activity gradually decreases, with efficiency decreasing from 98% at 5 ppm to 50% at 20 ppm. Notably, the most efficient amount of effective degradation was attained at 5 ppm with a 98% efficiency. This finding shows that the effectiveness of dye degradation decreases as dye molecule concentrations increase because they tend to adsorb more thickly on the catalyst’s surface. The increase in methylene blue dye concentration also leads to reduced light penetration, which is a likely contributing factor to the decreased degradation of methylene blue.⁴¹ 

The pH of a reaction mixture is responsible for the production of reactive species, which are the reason for the degradation of the organic dye. Hence, we explored by varying the pH of a reaction mixture at 3, 5, 7, 9, and 11, while the catalyst is 20 mg and the concentration of dye is 5 ppm. At a pH of 11, synthesized AgVO₃ shows maximum degradation at its peak, as shown in Fig. 10.

A radical scavenging activity experiment was carried out to better understand the contributions provided by reactive oxygen species in the photodegradation activity of AgVO₃ nanomaterials during the breakdown of methylene blue organic dye. Figure 14 shows the outcomes of this experiment, which used the scavengers EDTA, TBA, and K₂Cr₂O₇.

The degrading efficiency of AgVO₃ nanoparticles can be significantly affected by the pH of the solution during the photocatalytic process. It can improve the methylene blue dye’s surface adsorption onto the photocatalyst. In addition, both H⁺ and OH⁻ play a role in the production of reactive oxygen species, which is directly influenced by the pH levels in the solution. Therefore, a thorough examination of the pH effect was conducted over the pH range of 3–11, and the outcomes are shown in Fig. 10.

In order to investigate the reactive species that are accountable for the degradation of methylene blue organic dye by the AgVO₃ nanoparticles, to check the role of the generated active species in the degradation of MB, various scavengers were employed. These scavengers serve to capture and reduce the production of reactive species, such as holes (h⁺), hydroxyl radicals (·OH), and superoxide anion radicals (O₂). As shown in Fig. 12, in our experiment, we used the scavengers tert-butyl alcohol (TBA, 1 mM), potassium dichromate (1 mM), and ethylenediaminetetraacetic acid disodium (EDTA-2Na) to target holes (h⁺), superoxides (O₂⁻), and hydroxyl radicals (·OH), respectively. The results conveyed that the percentage of degradation decreases in the presence of TBA. Hence, this indicates that hydroxyl radicals play a major role in the degradation of organic dye. Figure 13 shows the EPR spectra for the detection of oxygen radicals. This technique was used to identify the reactive species during the reaction. There was no O₂ found when the reaction mixture was kept under dark conditions. Then, under visible light for 10 min, the intensities were detected, which suggests agreement with the results of the radical trapping test.⁴³ 

The photodegradation of organic dye primarily arises from the presence of reactive oxygen species, particularly hydroxyl radicals. Using coumarin as a probe molecule and the PL (photoluminescence) method, it is possible to measure how many of these hydroxyl radicals are produced. This reaction produces 7-hydroxycoumarin, which exhibits a strong fluorescence at 452 nm wavelength, by combining coumarin and hydroxyl radicals. Initially, 50 mg of the photocatalyst was dissolved in a 100-ml solution of 1 mM coumarin to start the reaction. An equilibrium adsorption–desorption process was established by letting the mixture rest for 30 min. After that, the solution was exposed to visible light. 2 ml aliquots of the reaction mixture were taken out and examined with a photoluminescent spectrophotometer at intervals of 10 min. Figure 14 shows how the concentration of hydroxyl radicals goes along with the strength of the peak seen in the spectrum. This experimental process underscores the critical role played by reactive oxygen species, particularly hydroxyl radicals, in the degradation of methylene blue organic dye. Figure 15 shows the EPR spectra for the confirmation of hydroxyl radicals.

The stability of a photocatalyst primarily hinges on its recycling and reproducibility, maintaining consistent efficiency.⁴⁴ In our study, we conducted a series of repeated experiments comprising five cycles, employing 50 mg of AgVO₃ under UV light. The nano-catalyst was thoroughly washed and dried at 110 °C for 2 h following each cycle. Remarkably, the efficiency of photodegradation remained nearly constant throughout these cycles. This underscores the exceptional stability and reproducibility of AgVO₃ nanoparticles in the context of photochemical reactions, as demonstrated in Fig. 16.

In this research, we examined the potential of AgVO₃ nanoparticles as effective antimicrobial agents. Utilizing three different doses of AgVO₃ nanoparticles, our antimicrobial screening examined their efficiency against both gram-positive and gram-negative bacterial species. AgVO₃ nanoparticles at a concentration of 25 g/well in a solution have demonstrated strong antibacterial activity at all dosages tested. It established distinct 20- and 25-mm-wide inhibitory zones for the gram-positive micro-organisms S. aureus and B. subtilis. Significant zones of inhibition were also discovered, with the K. pneumonia zone measuring 22 mm and the P. aeruginosa zone measuring 26 mm (Table II). These nanoparticles work because of their small size and large surface area, which promote electrostatic interaction between the negatively charged bacterial strains and the positively charged nanoparticles. The electrostatic attraction between the two opposing charges is primarily responsible for the antibacterial activity. In addition, as indicated in Table III, our research found that all of the compounds under consideration were effective at preventing spore germination in the fungus under consideration. In this case, the results of our tests for the minimum bactericidal concentration (MBC), minimum fungicidal concentration (MFC), and minimum inhibitory concentration (MIC) are shown in Table IV.

In this study, we employed jackfruit extract as a green fuel and as a reducing agent to produce AgVO₃ nanoparticles by a simple, inexpensive, easy, and environmentally friendly precipitation procedure. AgVO₃ nanoparticles were further evaluated for environmentally friendly uses, such as photocatalytic reactions with methylene blue organic dye, by varying the concentration of the catalyst, pH, dye, scavenging activity, and OH radical detection. Based on the findings, we can say that the synthesized AgVO₃ can effectively remove organic waste from water, works well as a photocatalyst to remove pollutants, and degrades 98% of the organic waste in 180 min. Ultimately, the synthesized nanoparticles improved the photocatalytic activity against the organic dye methylene blue, which is verified by their bandgap of 2.54 eV. This work shows how easily and affordably greener extracts may be used as fuel for the synthesis of AgVO₃ photocatalyst. Another application of AgVO₃ is that it acts as a good antimicrobial agent.

The authors extend their appreciation to BET^®, JSS College, Ooty Road, Mysuru, and RIE, Bhubaneswar, for providing the necessary facilities to carry out research work.

The authors would also like to acknowledge the support provided by Researchers Supporting (Project No. RSP2024R297), King Saud University, Riyadh, Saudi Arabia.

The authors have no conflicts to disclose.

R. Prakruthi: Conceptualization (equal); Data curation (equal). H. N. Deepakumari: Conceptualization (equal); Data curation (equal). H. D. Revanasiddappa: Conceptualization (equal); Formal analysis (equal). Faisal M. Alfaisal: Conceptualization (equal); Formal analysis (equal). Shamshad Alam: Conceptualization (equal); Data curation (equal). Hasan Sh. Majdi: Data curation (equal); Formal analysis (equal). Mohammad Amir khan: Conceptualization (equal); Data curation (equal). Shareefraza J. Ukkund: Conceptualization (equal); Data curation (equal).

All the data studied during this work are included in this article.