Academic literature on the topic 'Photocatalytic driven antibacterial effect'

Pure titanium dioxide TiO2 photocatalytic substrates exhibit antibacterial activity only when they are irradiated with ultraviolet light, which comprises high-energy wavelengths that damage all life. Impurity doping of TiO2-related materials enables visible light to stimulate photocatalytic activity, which enhances opportunities for TiO2 to be used as a disinfectant in living environments. Boron-doped TiO2 displays visible-light-responsive bactericidal properties. However, because boron-derived compounds also exert notable antibacterial effects, most reports did not clearly demonstrate the extent to which the bactericidal property of boron-doped TiO2 is contributed by visible-light-stimulated photocatalysis. In addition, TiO2 thin films have considerable potential for applications in equipment that requires sterilization; however, the antibacterial properties of boron-doped TiO2 thin films have been examined by only a few studies. We found that boron-doped TiO2 thin films displayed visible-light-driven antibacterial properties. Moreover, because boron compounds may have intrinsic antibacterial properties, using control groups maintained in the dark, we clearly demonstrated that visible light stimulated the photocatalysis of boron-doped TiO2 thin films but not the residue boron compounds display antibacterial property. The bactericidal effects induced by visible light are equally potent for the elimination of the model organism Escherichia coli and human pathogens, such as Acinetobacter baumannii, Staphylococcus aureus, and Streptococcus pyogenes. The antibacterial applications of boron-doped TiO2 thin films are described, and relevant perspectives discussed.

Catalysts for visible-light-driven oxidative cleaning processes and antibacterial applications (also in the dark) were developed. In order to extend the photoactivity of titanium dioxide into the visible region, nitrogen-doped TiO2 catalysts with hollow and non-hollow structures were synthesized by co-precipitation (NT-A) and sol–gel (NT-U) methods, respectively. To increase their photocatalytic and antibacterial efficiencies, various amounts of silver were successfully loaded on the surfaces of these catalysts by using a facile photo-deposition technique. Their physical and chemical properties were evaluated by using scanning electron microscopy (SEM), transmission electron microscopy–energy dispersive X-ray spectroscopy (TEM–EDS), Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), and diffuse reflectance spectra (DRS). The photocatalytic performances of the synthesized catalysts were examined in coumarin and 1,4-hydroquinone solutions. The results showed that the hollow structure of NT-A played an important role in obtaining high specific surface area and appreciable photoactivity. In addition, Ag-loading on the surface of non-hollow structured NT-U could double the photocatalytic performance with an optimum Ag concentration of 10−6 mol g−1, while a slight but monotonous decrease was caused in this respect for the hollow surface of NTA upon increasing Ag concentration. Comparing the catalysts with different structures regarding the photocatalytic performance, silverized non-hollow NT-U proved competitive with the hollow NT-A catalyst without Ag-loading for efficient visible-light-driven photocatalytic oxidative degradations. The former one, due to the silver nanoparticles on the catalyst surface, displayed an appreciable antibacterial activity, which was comparable to that of a reference material practically applied for disinfection in polymer coatings.

Titanium and its alloys have been widely used for orthopedic and dental implants. However, implant failures often occur due to the implant-related bacterial infections. Herein, titanium oxide nanotubes (TNTs) with an average diameter of 75 nm were formed by anodizing on the surface of titanium, and subsequently gold (Au) nanoparticles were deposited on TNTs by magnetron sputtering (Au@TNTs). The antibacterial study shows that TNTs surface decorated with Au nanoparticles exhibits the preferable effect in restricting the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) even under dark conditions, and the antibacterial rates reached 84% and 75%, respectively. In addition, the constructed film showed no cytotoxicity. Such a selective bactericidal effect of Au@TNTs samples might be attributed to the photocatalytic memory effect, which provides a new insight in the designing of antibacterial surfaces for biomedical application.

Conductive polymers have been widely investigated in various applications. Several conductive polymers, such as polyaniline (PANI), polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT)), and polythiophene (PTh) have been loaded with various semiconductor nanomaterials to prepare the composite photocatalysts. However, a critical review of conductive polymer-based composite photocatalysts has not been available yet. Therefore, in this review, we summarized the applications of conductive polymers in the preparation of composite photocatalysts for photocatalytic degradation of hazardous chemicals, antibacterial, and photocatalytic hydrogen production. Various materials were systematically surveyed to illustrate their preparation methods, morphologies, and photocatalytic performances. The synergic effect between conductive polymers and semiconductor nanomaterials were observed for a lot of composite photocatalysts. The band structures of the composite photocatalysts can be analyzed to explain the mechanism of their enhanced photocatalytic activity. The incorporation of conductive polymers can result in significantly improved visible-light driven photocatalytic activity by enhancing the separation of photoexcited charge carriers, extending the light absorption range, increasing the adsorption of reactants, inhibiting photo-corrosion, and reducing the formation of large aggregates. This review provides a systematic concept about how conductive polymers can improve the performance of composite photocatalysts.

This research is a continuing study on F9-filter development via Ag-TiO2 coating to promote volatile organic compounds (VOCs) removal and antibacterial activity. Problems of poor adhesion and uniform distribution of coating material on the filter surface were observed, so the addition of a polymeric surfactant (PS), which behaves as both a binder and a surfactant, was applied in this study in order to solve such problems. Dip coated F9-filter samples with a selection of Ag-TiO2 suspension were characterized and tested. Environmental scanning electron microscope was used to characterize uniform coating distribution on an air filter. Self-cleaning test was performed in accordance with ISO 27448. The results showed that Ag-TiO2 with PS dip coating on air filters provide good adhesion and high uniformity. It is also found that self-cleaning capability of Ag-TiO2 with PS coated filter is increasing with increasing of Ag-TiO2 and PS concentrations. Within a scope of this work, only visible light can drive Ag-TiO2 to undertake photocatalytic activity. Hence, improvement of Ag-TiO2 coating on F9- filter is confirmed when PS is applied.

In this study, a photocatalytic antibacterial composite of polydopamine-reduced graphene oxide (PDA-rGO)/BiVO4 is prepared by a hydrothermal self-polymerization reduction method. Its morphology and physicochemical properties are characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared (FT-IR), and X-ray diffraction (XRD). The results indicate that BiVO4 particles are evenly distributed on the rGO surface. Escherichia coli (E. coli) MG1655 is selected as the model bacteria, and its antibacterial performance is tested by flat colony counting and the MTT method under light irradiation. PDA-rGO/BiVO4 inhibits the growth of E. coli under both light and dark conditions, and light significantly enhances the bacteriostasis of PDA-rGO/BiVO4. A combination of BiVO4 with PDA-rGO is confirmed by the above characterization methods as improving the photothermal performance under visible light irradiation. The composite possesses enhanced photocatalytic antibacterial activity. Additionally, the photocatalytic antibacterial mechanism is investigated via the morphology changes in the SEM images of MG1655 bacteria, 2′,7′-dichlorofluorescein diacetate (DCFH-DA), the fluorescence detection of the reactive oxygen species (ROS), and gene expression. These results show that PDA-rGO/BiVO4 can produce more ROS and lead to bacterial death. Subsequently, the q-PCR results show that the transmembrane transport of bacteria is blocked and the respiratory chain is inhibited. This study may provide an important strategy for expanding the application of BiVO4 in biomedicine and studying the photocatalytic antibacterial mechanism.

Ag/ZnO/cellulose nanocomposites were synthesised through in-situ solution casting method, which offers a good adhesion and dispersity of nanostructured materials. SEM analysis revealed formation of nanodiscs-like structures for ZnO while nanospheres and hierarchical nanosheets were observed for Ag and cellulose, respectively. XRD analysis pointed to the monoclinic type-1 phase of cellulose. Peaks corresponding to typical hexagonal wurtzite structure of ZnO and face-centredcubic Ag structure were also identified. Photodecomposition of aqueous methylene blue (MB) under direct sunlight irradiation was monitored to study the photocatalytic activity of the nanocomposite. About 92% of MB dye was photodegraded in the presence of Ag/ZnO/cellulose nanocomposite. The influence of Ag+ ions on the photocatalytic efficiency of ZnO is discussed. The antibacterial efficiency of the synthesised samples was investigated against two Gram positive pathogenic bacteria species: Staphylococcus aureus and a spore forming Bacillus subtilis as well as a Gram-negative Escherichia coli. The prepared nanocomposite exhibited strong activity against the growth of all the bacterial species though in different quantified measures.

The spread of disease-causing microorganisms through high-touch surfaces and their increased tolerance against antimicrobials and the host immune system is responsible for several fatal diseases. By the year 2050, Antimicrobial resistance (AMR) is expected to cause 10 million deaths annually and a loss of US$100 trillion. Today, some bacterial species (e.g., Carbapenem-resistant Enterobacteriaceae group of bacteria) are immune to all major classes of available antibiotics. This has encouraged the scientific community to develop alternatives to antibiotics to fight the AMR. Primary sources of spread and resistance acquisition among bacteria include cross-contamination of surfaces in hospitals, catheters, stethoscopes, and surgical tools. Any such abiotic surface is vulnerable to bacterial colonization that begins with a few primary colonizers attaching themselves to the surface to condition it for further attachment of arriving bacteria. After initial attachment, bacteria start to proliferate and develop into surface-bound colonies. It then forms a robust protective layer of biofilm that brings advantages to bacterial survival against environmental odds. Hence, the initial stage of attachment is a weak link in the bacterial journey to forming a protective biofilm. Exploiting this weak link, nanostructured surfaces hinder initial attachment by physically rupturing the cell without the involvement of any chemical or biocides, hence are consistently called “promising” in controlling bacterial proliferation. Although various theories over the past few years have tried to explain the behavior of bacteria on these nanostructures, there is a lack of consensus on the precise mechanism that leads to bacterial death. To efficiently restrain bacterial colonization, it is of profound importance to understand the fundamental cause of bacterial death on these nanopillars. Only such fundamental understanding can guide us to the answer to the question: What precise nanopillars feature participate in bacterial cell-rupture and how? In this doctoral dissertation, we investigated the mechano-response of E. Coli cells as it attaches itself to a regular array of precise dimension-controlled nanopillars. Overcoming the fabrication limitations, two sets of ordered arrays of nanopillars by varying one dimension at a time makes it possible to study the involvement of individual dimensions on the response of single bacterial cell, which is crucial in understanding the rupture mechanism. The bacterial cell extends out via thread-like projections in the direction of neighboring pillars to establish contact with them. At a particular interpillar spacing (pitch) of straight pillars, the attached nanopillars appear to bend towards the cell due to the application of force. This displacement of pillars and hence the force increases with interpillar spacing. Bactericidal efficacy was proportional to the applied force, and hence interpillar spacing. The method of calculating force applied by bacteria on nanopillars adds direct experimental evidence towards the proposed mechanism of bacterial interaction with nanopillars at the single-cell level. We have focussed on one bacterial strain E. Coli; however, this method of studying bacterial-nanopillar interaction can pinpoint the governing parameter for cell rupture for different bacterial strains. After establishing the fundamentals of mechano-bactericidal mechanism, the subsequent work progresses to dual action antibacterial surfaces that aim towards studying alternatives to biocide coatings aiding from mechanical rupture of cells. A common non-selective way to kill bacteria without using antibiotic chemicals, and hence following the risk of developing antibacterial resistance, is to use photocatalytic materials. They produce reactive oxygen species (ROS) in the presence of light and water that cause bacterial death on the surface. The dual action surfaces benefit from nanostructures and photocatalytic antibacterial coatings over it. We establish the design principles of such “dual-action” surfaces, and answer several open questions, for example: which material should the nanostructures be made of? What is the optimum photocatalyst thickness? What geometries are most effective? In this work, TiO2 is used as the photocatalytic coating on nanostructures made of Si and SiO2. It is demonstrated that TiO2-coated “black-silica" (nanostructured SiO2), is more effective in producing the bactericidal effect. The bacterial kill rate is improved by 73% on replacing the underlying Si nanopillars with SiO2 nanopillars. To understand the dynamics of light absorption and subsequent ROS diffusion in such systems, FDTD and FEM simulations were used for modeling. FDTD simulations show that parasitic absorption in the underlying base pillar of high extinction coefficient leads to significant loss of incident optical energy. Hence, the “total absorption” of a system can be a misleading proxy for photocatalytic activity. Only absorption in the photocatalyst (TiO2) matters, which can be enhanced by fabricating nanopillars with a more transparent material like SiO2 or PDMS, having a low extinction coefficient. Further, FDTD coupled with FEM simulations shows that taller nanopillars don’t always lead to higher bulk ROS concentration, despite more absorption. Beyond 5 µm height, ROS are unable to diffuse out of the nanopillar forest. After articulating the design rules, the next step is to come up with a scalable process that can be deployed as practical antibacterial surfaces. In this work, we further extend the effectiveness of the TiO2-coated B-Si. By substituting TiO2 with TiO2 nanoparticles, the effective surface area for the production of ROS increases significantly. The extraction of photocarriers also improves because bulk of TiO2 is always within a few nm of a surface. The films are fabricated with three different techniques, all of which are scalable to large-areas. We establish the impact of the different techniques on the film’s topology and ability to kill bacteria. Antibacterial photocatalytic coatings are a promising alternative; however, the band gaps of most metal oxides are too wide, requiring UV/blue illumination. To deal with this, we discovered a new antibacterial photocatalyst, Mn2V2O7 (MVO), that works in ambient light or low-intensity solar radiation. The β-phase has a bandgap of 1.7 eV, so MVO absorbs visible light up to 600 nm.7 Under visible light, MVO reduces bacterial load by four orders of magnitude. MVO can be coated into films by drop-casting, which kills 76% of bacteria. In conclusion, work done in this thesis address the problem of spread of antimicrobial resistant bacteria via surfaces. We establish the mechanism of interaction of bacteria with nano-pillars also called as mechano-bactericidal mechanism. This formulates the understanding behind contact-kill mechanism of nanostructures. We extended efficiency of nanopillars by coating it with photocatalytic material that non-selectively degrades any organic material including bacterial cells, hence adds as a second line of defense again bacterial colonization. Using FEM and FDTD simulations, we articulated the design rules of such coated nanostructures. We developed technique to coat mesoporous photocatalyst on these nanostructures allowing larrge area deployment. At last, we overcame the UV-activated limitation of photocatalysts by enabling a visible light-activated antibacterial material suitable for large area coatings.
MHRD, DST

Abstract This study investigates the effect of composition on the antibacterial and antiviral properties of hydroxyapatite/titania composite coatings deposited by suspension plasma spraying. Hydroxyapatite is a bioceramic material used as a plasma-sprayed coating to promote osseointegration of femoral stems. TiO2 has promising photocatalytic activity and good efficiency in destroying bacteria, viral species, and parasites. Prior to coating, substrates were grit blasted, ultrasonically cleaned, and heated to enhance adhesion strength. The microstructure of the resulting coatings was then characterized using XRD and Raman spectroscopy. Test results indicated that SPS transformed Ti2O3 into TiO2 with mixed phases. Ti4O7 and Ti3O5 phases were also identified, which show photocatalytic activity due to oxygen vacancies. Antibacterial and antiviral tests were conducted as well.

Abstract Titanium dioxide in anatase phase structure has high antibacterial activity. For this study, titanium dioxide coatings on stainless steel were produced by cold spraying. The bactericidal effect of the coatings was tested with Pseudomonas aeruginosa bacteria at a high concentration of more than 107 CFU (colony-forming units) per milliliter. The bacteria were applied on the surface and exposed to UV light with a peak intensity of 360 nm. A kill rate of 99,99% was already achieved after 5 minutes, while the raw stainless steel reference did not show any significant reduction even after 60 min. The results show that cold-sprayed titanium dioxide coatings can serve as self-disinfecting surfaces.

Ag-TiO2 and Ag-TiO2/reduced graphene oxide nanopowders were deposited onto 100% cotton fabrics via electrostatic spraying method. The surface of cotton fabrics was pre-treated by plasma at atmospheric pressure using argon and nitrogen mixture. The as-prepared cotton fabrics were characterized in terms of structural and optical properties by X-ray diffraction (XRD) and optical reflectance measurements. The photocatalytic self-cleaning ability of Ag-TiO2 and Ag-TiO2/reduced graphene oxide coated cotton fabrics was evaluated by the photo-discoloration of methylene blue and berries juice stains, under 6 h simulated visible light irradiation. The combined functionalized coating on cotton fabrics demonstrated an improved photocatalytic effect compared with untreated cotton fabrics. The antimicrobial activity of Ag-TiO2 and Ag-TiO2/reduced graphene oxide coated cotton fabrics was tested against the Staphylococcus aureus and Candida albicans test strains as model microorganism of skin bacteria and fungi, respectively. An antimicrobial effect against the Staphylococcus aureus is observed even if the inhibition zone is not present. Untreated fabrics showed no antibacterial activity. No inhibitory effect on fungi colony growth was observed.

Abstract The ever-mounting drilling operations of the petroleum industry has been accompanied by tremendous wasted drilling fluid, Polycyclic Aromatic Hydrocarbons (PAHs) in which pose a huge threat to the health of human and ecosystem. Varying approaches have been proposed to remediate the damage caused by wasted drilling fluid, among which photocatalysis has been one of the most promising approaches for organic contaminants removal. The latest investigation shows that Bi2WO6 decorated on hydrophobic CNT can remove up to 80 % organic contaminant within a short time, exhibiting a preferable photocatalytic performance. Moreover, this hydrophobic CNT can play a vital role in stabilizing the wellbore due to its excellent water repellent. The objective of the study was to find out the effect of Bi2WO6 modified hydrophobic CNT on the PAHs photodegradation and wellbore stability in the process of drilling. Bi2WO6 as a near-infrared driven photocatalyst has attracted worldwide attention due to its preferable oxygen vacancy and quantum efficiency. However, the application of Bi2WO6 was impeded by the low migration efficiency of photo-generated carriers. The combination of Bi2WO6 and composite with good conductivity has been an effective method to resolve this problem. The instability of wellbore caused by shale hydration during oil and gas drilling operations also brings a huge challenge. In this study, a photocatalyst with wellbore stabilization capacity is achieved by hydrophobic CNT modified via Bi2WO6 sheet with nano-size. The fluid loss and wettability property were measured to evaluate the wellbore stabilization capacity of this novel agent. Meanwhile, photodegradation experiments and pathway analysis were conducted to evaluate the effect of photodegradation by Bi2WO6/CNT on the organic contaminants. Data of photodegradation indicated that the PAHs can be degraded up to 80% after treated by Bi2WO6/CNT, the migration efficiency of photogenerated carriers improved significantly. A slight decrease in fluid loss and distinctive increase in viscosity can be observed after treated with 0.3% Bi2WO6/CNT solution. The results of the rheology test verified that the photocatalyst has little effect on the rheological properties of drilling fluid. The result of SEM indicated that this novel Bi2WO6/CNT composite with a bombax structure can absorb preferentially organic contaminants, which is good at in-situ photodegradation and prevention of water invasion. To sum up, PAHs in wasted drilling fluids can be photodegraded by the novel Bi2WO6 nano-sheet modified CNT, and the stability of wellbore can also be significantly enhanced due to wettability alteration.