Impact of annealing temperature on the photocatalytic performance of α-Zn ₂ V ₂ O ₇ nanoparticles: A potent catalyst for the degradation of methylene blue dye and its antibacterial properties

Zinc vanadate (α-Zn
2
V
2
O
7
) nanoparticles were prepared using a hydrothermal-assisted co-precipitation method and annealed at three different temperatures, viz, 400°C, 500°C, and 600°C. The influence of annealing temperatures on their photocatalytic activities has been studied, and the superior photocatalytic action was identified for 600°C annealed samples. The annealed nanoparticles at different temperatures are subjected to X-ray diffraction (XRD) analysis, which confirms the monoclinic structure of the synthesized α-Zn
2
V
2
O
7
nanoparticles. The average crystallite size calculated using Scherrer's formula is found to increase with the increase in annealing temperature. The morphological properties of the nanoparticles were analyzed using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) was used to confirm the presence of Zn, V, and O in the prepared nanoparticle. The XPS survey of the prepared sample revealed the presence of Zn, O, and V without any impurities except a small amount of absorbed carbon, and the spectra also confirmed that the sample had a pure phase of Zn
2
V
2
O
7
. A UV-visible spectrophotometer investigation confirmed reduction of band gap values with the annealing temperature. The broad peak of photoluminescence (PL) emission spectra in the green wavelength region implied the creation of deep energy levels inside the band gap of the nanoparticles. The photocatalytic activity of the synthesized sample in the degradation of methylene blue (MB) dye under sunlight was studied using a UV-visible spectrometer. The degradation efficiency increased with the annealing temperature and the efficiency attained the maximum for the sample annealed at 600°C. The values escalated from 94.3 for 400°C α-Zn
2
V
2
O
7
to 95.1 for 400°C α-Zn
2
V
2
O
7
. The antibacterial activity of the synthesized chemical compounds with varying concentrations ranging from 250–1000 μg (25–1 mg) against
Escherichia coli
resulted in the formation of inhibition zones. The zones of bacterial inhibition in α-Zn
2
V
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O
7
exhibited an increase from 100 μL - 22 mm at 400°C α-Zn
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V
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O
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to at 100 μL - 33 mm 6 wt% 600°C α-Zn
2
V
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O
7
. The nanoparticles with 600°C annealing α-Zn
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V
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O
7
nanoparticle exhibited enhanced antibacterial activity, which can be ascribed to their considerably more significant surface area, improving their effectiveness.