Effect of pH and (Y, Ag) co-doping on the antibacterial and toxicity properties of ZrO₂ nanoparticles

Nowadays, the effective bacterial inhibition and minimal toxicity properties of ZrO₂ nanoparticles are creating opportunities in various applications, including biomedical, dental, antimicrobial coatings, packaging, anticancer and pesticide applications. Therefore, researchers are employing various approaches to enhance the antibacterial activity and reduce the toxicity of ZrO₂ nanoparticles. In this study, undoped or pure ZrO₂ nanoparticles were synthesized at different pH levels (1, 3, 7, and 11) and Y and Ag were codoped in different doping concentrations (1%, 2%, and 3%). A sucrose-assisted sol-gel method was used to synthesis both undoped and codoped ZrO₂ nanoparticles. The main objective of this research was to analyze the effect of pH and codoping on the antibacterial and toxicity properties of ZrO₂ nanoparticles. The synthesized particles were extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) spectroscopy. XRD analysis confirmed the existence of ZrO₂ nanoparticles with a tetragonal structure at low pH (1 and 3), a monoclinic structure at higher pH (7 and 11) and a multiphase structure after codoping. The crystallite size of undoped ZrO₂ particles increased with pH, from 8 nm at pH 1 to 20 nm at pH 11, indicating enhanced crystallinity at higher pH levels. Also, the crystallite size was 12.05, 14.81, and 11.95 nm at 1%, 2%, and 3% doping concentrations, respectively. SEM analysis revealed that the average particle size increased with increasing pH from 31.956 nm to 63.653 nm. The particle size was 34.90 nm, 48.66 nm, and 40.23 nm for 1%, 2% and 3% doped samples, respectively. The shape of the particles was irregular and mostly spherical, rod-like, and platelet-like with agglomeration. The EDX data determined the elemental composition of the particles, which indicated the successful doping with Y and Ag. The FTIR data revealed the existence of O-H, Zr-O, and other metal-oxygen vibrations in the synthesized materials. The antibacterial activity of undoped and codoped ZrO₂ nanoparticles was evaluated against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) using the disk diffusion method. The result showed that a superior antibacterial activity was observed at pH 11 for undoped particles and 3% Y-Ag codoped particles. The toxicity of the undoped and codoped ZrO₂ nanoparticles was inspected using the brine shrimp lethality assay, which showed that the material was less cytotoxic at lower pH (1 and 3), and the toxicity increased with increasing doping concentration. Increasing pH and doping concentration both enhanced the antibacterial and cytotoxic activities, making the material suitable for antimicrobial coatings, packaging, and textiles, with potential for pesticide or anticancer applications pending further evaluation.