Assessment of Antimicrobial Activity in TiO2@SiO2-Modified Graphitic Carbon Nitride Nanomaterials

Estefanny Sonia, Ngalih (2026) Assessment of Antimicrobial Activity in TiO2@SiO2-Modified Graphitic Carbon Nitride Nanomaterials. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

This study investigated the synthesis, characterisation, and antimicrobial efficacy of TiO2@SiO2/g-C3N4 nanocomposite against microbial contamination. The increasing challenges posed by microbial pathogens highlight the need for sustainable and efficient disinfection strategies. The nanocomposite integrates three components–titanium dioxide (TiO2), silicon dioxide (SiO2), and graphitic carbon nitride (g-C3N4)–each contributing unique and complementary properties. TiO2 provides robust photocatalytic activity under ultraviolet (UV) light, generating reactive oxygen species (ROS). SiO2 enhances charge separation, stabilises TiO2, and prevents nanoparticle aggregation. Meanwhile, g-C3N4 extends the photocatalytic activity into the visible light spectrum, improving the nanocomposite’s utility under ambient conditions. These synergistic interactions result in a high-performing material with superior photocatalytic and antimicrobial properties. The synthesis and characterisation of the nanocomposite were confirmed using techniques such as Field-Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray (EDX) analyses, which revealed a nanostructure with high surface area and heterogeneous morphology. This structure enhances ROS production and facilitates physical interactions with microbial cells, amplifying antimicrobial efficacy. Antimicrobial activity was evaluated against bacterial (Escherichia coli and Staphylococcus aureus) and fungal (Clavispora lusitaniae and Saccharomyces cerevisiae) strains using agar well diffusion, disk diffusion, and broth macrodilution (minimum inhibitory concentration, MIC) assays. While no visible zones of inhibition (ZOI) were observed in agar-based assays–likely due to the low solubility and particulate nature of the nanocomposite–broth macrodilution revealed differential susceptibility among microbial strains. Lower MIC values were observed for E. coli and C. lusitaniae (2500 µg/mL), indicating higher susceptibility, whereas S. aureus demonstrated greater resistance with a higher MIC value (10000 µg/mL). These variations correlate with cell wall composition and structural differences, with Gram-positive bacteria and robust fungal cell walls demonstrating stronger resistance to oxidative stress. SEM analysis confirmed significant morphological damage to all tested microorganisms, supporting the nanocomposite's antimicrobial effects. The primary antimicrobial mechanism involves photocatalytic ROS generation, including hydroxyl radicals (•OH) and superoxide anions (•O2−), which disrupt microbial DNA, proteins, and lipids through oxidative stress. Additionally, the nanocomposite’s irregular shape and rough surface enhance physical interactions with microbial cells, exerting mechanical stress that complements its chemical activity. Compared to conventional antimicrobial agents such as azoles, β-lactams, and aminoglycosides, the nanocomposite offers a multi-modal mechanism of action, thus reducing the likelihood of resistance development. Therefore, it can be inferred that TiO2@SiO2/g-C3N4 nanocomposite exhibits antimicrobial properties and holds promise as a cost-efficient, sustainable, and advanced material for microbial control applications.

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