Study On Catalytic Antibacterial Properties Of G-C₃N₄-Based Nanomaterials

Bacterial infections afflict millions of people each year and remain a public health problem worldwide,especially in economically disadvantaged areas.antibiotics were first discovered and used in the 1940s,but with over-reliance on them,more and more bacteria are now resistant to them.If the misuse of antibiotics is not curbed,bacterial infections could pose a more serious global threat than cancer.There is therefore an urgent need for research into new methods of sterilisation.As we all know,with the rise of nanotechnology in recent years,nano materials have a larger specific surface area,which is conducive to improve the reaction efficiency.At the same time,they also have more surface defects,which can improve the carrier separation efficiency.Nano sized catalysts show a greater application prospect than bulk materials.Therefore,people pay attention to the new antibacterial technologies promoted by nanotechnology,namely nano material photocatalytic antibacterial and enzyme catalyzed antibacterial technologies.Photocatalytic antimicrobial activity is based on the production of photo-induced reactive oxygen species（ROS）by photocatalysts under light irradiation,including singlet oxygen（¹O₂）,hydroxyl radicals（·OH）and superoxide（·-O₂）leading to the peroxidation of polyunsaturated phospholipids in bacterial lipid membranes,resulting in the interruption of cellular respiration and thus killing bacteria.Enzyme-catalyzed bactericides mainly use the enzyme-like activity of the material to catalyse the production of highly toxic free radicals from low concentrations of hydrogen peroxide（H₂O₂）or oxygen（O₂）.These free radicals strongly bind proteins,lipids and polysaccharides at the mildly acidic site of infection and attack them,subsequently breaking down the bacterial membrane and causing perforation of the bacterial membrane and subsequent cell death.Nanomaterials can also physically damage bacterial membranes when their size is small enough.In addition,the ability of nanomaterials to trap bacteria is enhanced due to the designable nature of their morphology,which greatly contributes to the bactericidal efficiency of nanomaterials.Carbon nitride（g-C₃N₄）is an emerging class of metal-free semiconductors with a band gap of about 2.4 e V,easy to prepare,stable properties,safe and non-toxic,and has received widespread attention in the field of catalytic antimicrobial because of its unique optical and electronic properties.In this paper,g-C₃N₄based nano materials are taken as the research object.Through the design and regulation of the morphology of g-c3n4 based nano materials and the composition of composite materials,nano catalysts with high antibacterial activity are synthesized and explored in the application of catalytic sterilization.The main research contents are as follows:Firstly,high specific surface area is one of the keys to improve catalytic efficiency.In order to construct low-cost pure photocatalysts,porous few-layer g-C₃N₄nanophotocatalysts were synthesized by a two-step hydrothermal method.The specific surface area of the designed porous few-layer g-C₃N₄is approximately six times higher than that of the unmodified bulk C₃N₄,therefore,the porous few-layer g-C₃N₄nanophotocatalyst exhibits higher photocatalytic bactericidal performance.Also,the layered and porous structure is more favourable for the catalyst to bind to bacteria when considered from a kinetic perspective.The production of singlet oxygen（¹O₂）,hydroxyl radicals（·OH）and superoxide（·-O₂）was detected by electron paramagnetic resonance（ESR）,demonstrating that porous few-layer g-C₃N₄can produce ROS under visible light irradiation.In addition the antibacterial photocatalytic activity of porous few-layer g-C₃N₄was also confirmed by photocatalytic inactivation tests on Staphylococcus aureus The photocatalytic activity of porous layer less g-C₃N₄was significantly enhanced.This study has potential applications in water purification and antimicrobial photocatalytic therapy.Secondly,as people’s awareness of health and environmental protection increases and under the influence of the epidemic,there is an increasing demand for antibacterial materials,and the single catalytic mechanism limits the antibacterial efficiency of g-C₃N₄,so based on the two catalytic effects of nanomaterials,experimental photocatalysis and enzyme catalysis synergistic antibacterial,so that it has excellent bactericidal properties in both darkness and light,to achieve"white".In addition,the two effects are complementary and mutually reinforcing,achieving a"1+1>2"therapeutic effect.Based on the fact that the active centres of biological enzymes are mostly complexes of sulphur,nitrogen and other elements,S-doped g-C₃N₄was designed and synthesised for photocatalytic and enzyme-catalyzed antibacterial therapy.Experiments have demonstrated that g-SCN can produce ROS in a dark environment,while light promotes enhanced ROS production.In vitro antibacterial experiments have demonstrated that g-SCN exhibits excellent antibacterial ability against Gram-negative Escherichia coli and Gram-positive methicillin-resistant Staphylococcus aureus,it is able to kill all bacteria within 40 minutes,and scanning electron micrographs of the material and bacteria can see significant lysis and deformation.