Potential antibacterial, antibiofilm, and photocatalytic performance of gamma-irradiated novel nanocomposite for enhanced disinfection applications with an investigated reaction mechanism

Abstract

Background: Water scarcity is now a global challenge due to the population growth and the limited amount of available potable water. In addition, modern industrialization, and microbial pathogenesis is resulting in water pollution on a large scale.

Methods: In the present study, reusable Co_0.5Ni_0.5Fe₂O₄/SiO₂/TiO₂ composite matrix was incorporated with CdS NPs to develop an efficient photocatalyst, and antimicrobial agents for wastewater treatment, and disinfection purpose. The antibacterial performance of the gamma-irradiated samples was evaluated against various types of Gram-positive bacteria using ZOI, MIC, antibiofilm, and effect of UV-exposure. Antibacterial reaction mechanism was assessed by bacterial membrane leakage assay, and SEM imaging. In addition, their photocatalytic efficiency was tested against MB cationic dye as a typical water organic pollutant.

Results: Our results showed that, the formed CdS NPs were uniformly distributed onto the surface of the nanocomposite matrix. While, the resulted CdS-based nanocomposite possessed an average particle size of nearly 90.6 nm. The antibacterial performance of the prepared nanocomposite was significantly increased after activation with gamma and UV irradiations. The improved antibacterial performance was mainly due to the synergistic effect of both TiO₂ and CdS NPs; whereas, the highest photocatalytic efficiency of MB removal was exhibited in alkaline media due to the electrostatic attraction between the cationic MB and the negatively-charged samples. In addition, the constructed heterojunction enabled better charge separation and increased the lifetime of the photogenerated charge carriers.

Conclusion: Our results can pave the way towards the development of efficient photocatalysts for wastewater treatment and promising antibacterial agents for disinfection applications.

Keywords: Antibacterial activity; Bacterial membrane leakage; CdS NPs; Disinfection; Methylene blue; Photocatalysis.

Fig. 1

Surface morphology, particle size, and shapes of the synthesized CdS NPs, and CdS-loaded nanocomposite, where a SEM of CdS NPs, b SEM of CdS-loaded nanocomposite, c HRTEM of CdS NPs, and d HRTEM of CdS-loaded nanocomposite

Fig. 2

Elemental analysis of the synthesized CdS NPs, and CdS-loaded nanocomposite, where (a) EDX of CdS NPs, and (b) EDX of CdS-loaded nanocomposite

Fig. 3

Antibacterial activity of bare CdS NPs and CdS-Co_xNi_1-xFe₂O₄/SiO₂/TiO₂ NPs, at different concentrations (20, and 10 μg/mL (PPM)) against some pathogenic bacteria as ZOI (mm)

Fig. 4

Antimicrobial activities as ZOI (mm), of CdS-Co_xNi_1-xFe₂O₄/SiO₂/TiO₂ NPs, irradiated at different gamma-irradiation doses (25, 50 and 100 kGy) against a Staphylococcus aureus, and b Staphylococcus lentus

Fig. 5

Antibiofilm potential of gamma irradiated-CdS nanocomposite against some pathogenic bacteria inhibition %

Fig. 6

Antimicrobial effect of gamma irradiated-CdS nanocomposite in liquid media under UV-irradiation effect against different pathogenic microbes, where a S. aureus, b S. lentus, c S. vilulinus, d E. columbae, e A. viridians, and f S. sciuri

Fig. 7

The effect of non-irradiated, irradiated-CdS nanocomposite on the growth curve of S. aureus

Fig. 8

The effect of non-irradiated, and irradiated-CdS nanocomposite on the protein leakage from S. aureus cell membranes

Fig. 9

SEM of S. aureus where a Normal bacterial cells without gamma irradiated-CdS nanocomposite treatment, and b Depressed and deformed bacterial cell after gamma irradiated-CdS nanocomposite treatment

Fig. 10

Schematic representation regarding the four prominent ways of antimicrobial potential of CdS-Co_xNi_1-xFe₂O₄/SiO₂/TiO₂ nanocomposites, where (1) CdS-Co_xNi_1-xFe₂O₄/SiO₂/TiO₂ nanocomposites adhere to and wrapped the microbial cell surface and results in CdS NPs release which causing membrane damage and altered transport activity, (2) CdS-Co_xNi_1-xFe₂O₄/SiO₂/TiO₂ nanocomposites block the ions transport from and to the microbial cell, (3) CdS-Co_xNi_1-xFe₂O₄/SiO₂/TiO₂ nanocomposites increase the ROS (due to the activation after gamma irradiation) leading to cell damage, and (4) CdS-Co_xNi_1-xFe₂O₄/SiO₂/TiO₂ nanocomposites penetrate inside the microbial cells and interact with cellular organelles and biomolecules, and thereby affect respective cellular machinery. CdS NPs may serve as a vehicle to effectively-deliver Cd²⁺, and S²⁺ ions to the microbial cytoplasm and membrane, where proton motive force would decrease the pH to be less than 3.0 and therefore improve the release of Cd²⁺, and S²⁺ ions. "Created with BioRender.com''

Fig. 11

MB photocatalytic degradation by a composite matrix, b CdS NPs, and c CdS-loaded nanocomposite

Fig. 12

MB photocatalytic degradation reaction mechanism "created with BioRender.com''

Fig. 13

Reaction kinetics and apparent rate constant for MB photocatalytic removal by a) composite matrix NPs, b CdS NPs, and c CdS-loaded nanocomposite