The loading of Fe ions on N-doped carbon nanosheets to boost photocatalytic cascade for water disinfection.

The pervasive presence of pathogenic bacteria in water environment poses a serious threat to public health. Here, a photocatalytic cascade was developed to reveal great water disinfection. Firstly, N-doped carbon nanosheets (N-CNSs) about 30-50 nm in size were synthesized by a hydrothermal strategy. It revealed wide-spectrum photocatalysis for H2O2 generation via a typical two-step single-electron process. A Fenton agent (Fe ion) was loaded, N-CNSs-Fe can in-situ convert photocatalytic H2O2 into ·OH with high oxidation potential. Moreover, its Fenton active is three times greater than pure Fe2+ owing to electron enrichment from N-CNSs to Fe for Fe3+/Fe2+ cycle. Further investigation displayed that Fe loading also could decrease bad gap and promote charge separation to boost photocatalysis. In addition, N-CNSs-Fe possesses positive surface potential to exhibit strong interaction with negative bacteria, facilitating the capture. Therefore, the nanocomposite can effectively inactivate E. coli with a lethality rate of 99.7 % under stimulated sunlight irradiation. In addition, it also was employed to treat a complex lake water sample, revealing great antibacterial (95.1 %) and dye-decolored (92.3 %) efficiency at the same time. With novel biocompatibility and antibacterial ability, N-CNSs-Fe possessed great potential for water disinfection.

Enhancing disinfection and microcontaminant removal by coupling LED driven UVC and UVA/photo-Fenton processes in continuous flow reactors.

For the first time, the sequential combination of UVC-LED (276 nm) and photo-Fenton/UVA-LED (376 nm) process has been assessed in continuous flow mode for wastewater reclamation according to the new European Regulation for reuse in agricultural irrigation (EU 2020/741). The results show that it is possible to obtain water quality class B (Escherichia coli ≤ 100 CFU/100 mL) by UVC-LED irradiation alone, operating the system with a hydraulic residence time (HRT) of 6.5 min and liquid depth of 5 cm in the case of secondary effluents with low Escherichia coli load (8.102-3.1.103 CFU/100 mL). As for high bacteria concentrations (1.2-4.2.104 CFU/100 mL), HRTs longer than 30 min are required. The bacterial load has not influenced decontamination, removing 18 ± 4 % of microcontaminants. Coupling the UVC (30-min HRT and 5.0 cm liquid depth) and the UVA/photo-Fenton (60-min and 15-cm liquid depth) systems allows 58 ± 4 % of real organic microcontaminants to be removed, in addition to achieving water quality class B.

Construction of a g-C3N4/Bi(OH)3 Heterojunction for the Enhancement of Visible Light Photocatalytic Antibacterial Activity.

Photocatalytic technology has been recently conducted to remove microbial contamination due to its unique features of nontoxic by-products, low cost, negligible microbial resistance and broad-spectrum elimination capacity. Herein, a novel two dimensional (2D) g-C3N4/Bi(OH)3 (CNB) heterojunction was fabricated byincorporating Bi(OH)3 (BOH) nanoparticles with g-C3N4 (CN) nanosheets. This CNB heterojunction exhibited high photocatalytic antibacterial efficiency (99.3%) against Escherichia coli (E. coli) under visible light irradiation, which was 4.3 and 3.4 times that of BOH (23.0%) and CN (28.0%), respectively. The increase in specific surface area, ultra-thin layered structure, construction of a heterojunction and enhancement of visible light absorption were conducive to facilitating the separation and transfer of photoinduced charge carriers. Live/dead cell staining, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) assays and scanning electron microscopy (SEM) have been implemented to investigate the damage to the cell membrane and the leakage of the intracellular protein in the photocatalytic antibacterial process. The e-, h+ and O2•- were the active species involved in this process. This study proposed an appropriate photocatalyst for efficient treatment of bacterial contamination.

Germicidal efficacy of continuous and pulsed ultraviolet-C radiation on pathogen models and SARS-CoV-2.

Ultraviolet radiation's germicidal efficacy depends on several parameters, including wavelength, radiant exposure, microbial physiology, biological matrices, and surfaces. In this work, several ultraviolet radiation sources (a low-pressure mercury lamp, a KrCl excimer, and four UV LEDs) emitting continuous or pulsed irradiation were compared. The greatest log reductions in E. coli cells and B. subtilis endospores were 4.1 ± 0.2 (18 mJ cm-2) and 4.5 ± 0.1 (42 mJ cm-2) with continuous 222 nm, respectively. The highest MS2 log reduction observed was 2.7 ± 0.1 (277 nm at 3809 mJ cm-2). Log reductions of SARS-CoV-2 with continuous 222 nm and 277 nm were ≥ 3.4 ± 0.7, with 13.3 mJ cm-2 and 60 mJ cm-2, respectively. There was no statistical difference between continuous and pulsed irradiation (0.83-16.7% [222 nm and 277 nm] or 0.83-20% [280 nm] duty rates) on E. coli inactivation. Pulsed 260 nm radiation (0.5% duty rate) at 260 nm yielded significantly greater log reduction for both bacteria than continuous 260 nm radiation. There was no statistical difference in SARS-CoV-2 inactivation between continuous and pulsed 222 nm UV-C radiation and pulsed 277 nm radiation demonstrated greater germicidal efficacy than continuous 277 nm radiation. Greater radiant exposure for all radiation sources was required to inactivate MS2 bacteriophage. Findings demonstrate that pulsed irradiation could be more useful than continuous UV radiation in human-occupied spaces, but threshold limit values should be respected. Pathogen-specific sensitivities, experimental setup, and quantification methods for determining germicidal efficacy remain important factors when optimizing ultraviolet radiation for surface decontamination or other applications.

Towards molecular understanding of surface and interface catalytic engineering in TiO2/TiOF2 nanosheets photocatalytic antibacterial under visible light irradiation.

TiO2/TiOF2 Z-scheme nanosheets have been successfully synthesized for photocatalytic antibacterial. The antibacterial efficiency of TiO2/TiOF2 against E. coli and S. aureus were 99.90 % and 81.89 % at low material concentration (110 µg/mL), respectively, which are higher than those of pure TiO2, TiOF2, and Degussa P25. In situ molecular spectroscopy results demonstrate that the microstructure of the synthesized material can be reconstructed and optimized to enhance the exposure of the active sites·H2O and O2 are effectively adsorbed on the catalyst surface and activated to form OH…Ti and O…Ti surface active species. Furthermore, the dense interface formed in TiO2/TiOF2 acts as an efficient transport path for photoexcited electrons from TiO2 to TiOF2, and thus accelerates the formation of reactive oxygen species. Finally, the mechanism of bacterial inactivation is systematically discussed considering the main active substances, cell morphological changes, and activity of antioxidant enzymes.

Synergistic effect of UV-A and UV-C light is traced to UV-induced damage of the transfer RNA.

UV light emitting diodes (LEDs) are considered the new frontier of UV water disinfection. As UV technologies continue to evolve, so does the need to understand disinfection mechanisms to ensure that UV treatment continues to adequately protect public health. In this research, two Escherichia coli (E. coli) strains (the wild type K12 MG1655 and K12 SP11 (ThiI E342K)) were irradiated with UV-C at 268 nm both independently and after exposure to UV-A (365 nm). A synergistic effect was found on the viability of the wild type E. coli K12 strain when UV-A irradiation was applied prior to UV-C. Sublethal UV-A doses, which had a negligible effect on cell viability alone, enhanced UV-C inactivation by several orders of magnitude. This indicated a specific cellular response mechanism to UV-A irradiation, which was traced to direct photolysis of the transfer RNA (tRNA), which are critical links in the translation of messenger RNA to proteins. The wild type K12 strain MG1655, containing tRNAs with a thiolated uridine, directly absorbs the UV-A light, which leads to a reduction in protein synthesis, making them more susceptible to UV-C induced damage. However, the K12 strain SP11 (ThiI E342K), with a point mutation in the thiI gene that prevents a post-transcriptional modification of tRNA, experienced less inactivation upon subsequent irradiation by UV-C. The growth rate of cells, which was inhibited by sublethal UV-A doses, was not inhibited in this mutant strain with the modified tRNA. Time-lapse microscopy with microfluidics showed that sub-lethal UV-A caused a transient, reversible, growth arrest in E. coli. However, once the growth resumed, the cell division time resembled that of unirradiated cells. Damage induced by UV-A impaired the recovery of damage induced by UV-C. Depending on the UV-A dose applied, the synergistic effect remained even when there was a time delay of several hours between UV-A and UV-C exposures. The effect of sublethal UV-A was reversible over time; therefore, the synergistic effect was strongest when UV-C was applied immediately after UV-A. Combining UV-A and UV-C irradiation may serve as a practical tool to increase UV disinfection efficacy, which could potentially reduce costs while still adequately protecting public health.

Application of coliphage as biocontrol agent in combination with gamma irradiation to eliminate multi-drug-resistant E. coli in minimally processed vegetables.

Biofilm formation is a rising concern in the food industry. Escherichia coli (E. coli) is one of the most important food-borne pathogens that can survive in food and food-related environments and eventually produce biofilms. This study suggested that both coliphages used were successful in preventing the creation of new biofilms as well as removing existing ones. Confocal laser scanning microscopy verified these findings. According to the findings, neither coliphage survived at 37 °C, but both remained stable at 4 °C and - 20 °C for extended periods of time. The study revealed that both coliphages demonstrated a greater degree of gamma irradiation resistance when compared to E. coli. The study's results indicate that the implementation of a dual method, which incorporates gamma irradiation (1.5 kGy) and coliphage treatment, on various kinds of vegetables that were infected with E. coli, resulted in a significant reduction in bacterial count (surpassing 99.99%) following a 24-h incubation period. Combining gamma irradiation and the coliphage approach was significantly effective at lowering polysaccharide concentrations and proteins in the biofilm matrix. The results revealed that the pairing of gamma irradiation and coliphages acted in conjunction to cause disruptions in the matrix of biofilm, thereby promoting cell removal compared with either of the individual treatments. Ca+ ions strengthen the weak virion interaction with the relevant bacterial host cell receptors during the adsorption process. In conclusion, use of coliphage in combination with gamma irradiation treatment can be applied to improve fresh produce's microbial safety and enhance its storability in supermarkets.

Monomer and Oligomer Transition of Zinc Phthalocyanine Is Key for Photobleaching in Photodynamic Therapy.

Photodynamic therapy (PDT) is recognized as a powerful method to inactivate cells. However, the photosensitizer (PS), a key component of PDT, has suffered from undesired photobleaching. Photobleaching reduces reactive oxygen species (ROS) yields, leading to the compromise of and even the loss of the photodynamic effect of the PS. Therefore, much effort has been devoted to minimizing photobleaching in order to ensure that there is no loss of photodynamic efficacy. Here, we report that a type of PS aggregate showed neither photobleaching nor photodynamic action. Upon direct contact with bacteria, the PS aggregate was found to fall apart into PS monomers and thus possessed photodynamic inactivation against bacteria. Interestingly, the disassembly of the bound PS aggregate in the presence of bacteria was intensified by illumination, generating more PS monomers and leading to an enhanced antibacterial photodynamic effect. This demonstrated that on a bacterial surface, the PS aggregate photo-inactivated bacteria via PS monomer during irradiation, where the photodynamic efficiency was retained without photobleaching. Further mechanistic studies showed that PS monomers disrupted bacterial membranes and affected the expression of genes related to cell wall synthesis, bacterial membrane integrity, and oxidative stress. The results obtained here are applicable to other types of PSs in PDT.

Avoidance of the use of tryptophan in buried chromosomal proteins as a mechanism for reducing photo/oxidative damage to genomes.

In cells that are exposed to terrestrial sunlight, the indole moiety in the side chain of tryptophan (Trp) can suffer photo/oxidative damage (POD) by reactive oxygen species (ROS) and/or ultraviolet light (UV-B). Trp is oxidized to produce N-formylkynurenine (NFK), a UV-A-responsive photosensitizer that further degenerates into photosensitizers capable of generating ROS through exposure to visible light. Thus, Trp-containing proteins function as both victims, and perpetrators, of POD if they are not rapidly replaced through protein turnover. The literature indicates that protein turnover and DNA repair occur poorly in chromosomal interiors. We contend, therefore, that basic chromosomal proteins (BCPs) that are enveloped by DNA should have evolved to lack Trp residues in their amino acid sequences, since these could otherwise function as 'Trojan horse-type' DNA-damaging agents. Our global analyses of protein sequences demonstrates that BCPs consistently lack Trp residues, although DNA-binding proteins in general do not display such a lack. We employ HU-B (a wild-type, Trp-lacking bacterial BCP) and HU-B F47W (a mutant, Trp-containing form of the same bacterial BCP) to demonstrate that the possession of Trp is deleterious to BCPs and associated chromosomal DNA. Basically, we show that UV-B and UV-A (a) cause no POD in HU-B, but cause extensive POD in HU-B F47W (in vitro), as well as (b) only nominal DNA damage in bacteria expressing HU-B, but extensive DNA damage in bacteria expressing F47W HU-B (in vivo). Our results suggest that Trp-lacking BCPs could have evolved to reduce scope for protein-facilitated, sunlight-mediated damage of DNA by UV-A and visible light, within chromosomal interiors that are poorly serviced by protein turnover and DNA repair machinery.

Nitrate Protects Microorganisms and Promotes Formation of Toxic Nitrogenous Byproducts during Water Disinfection by Far-UVC Radiation.

Far-UVC radiation is an emerging tool for combating pathogenic microorganisms in water, but its vulnerability to water matrix components remains unclear. We herein report the critical impacts of nitrate during Far-UVC disinfection of water. Nitrate at environmentally relevant concentrations (0.5-10.0 mg-N L-1) significantly inhibits Escherichia coli inactivation by Far-UVC radiation at 222 nm, via prolonging the "lag phase" of inactivation and reducing the inactivation rate constants by 1.08-2.74 times, while it shows negligible impact on E. coli inactivation by UVC radiation at 254 nm. The inhibitory impact of nitrate on Far-UVC disinfection is attributed to its strong light-shielding effect. Although hydroxyl radicals and reactive nitrogen species are generated from Far-UVC photolysis of nitrate at high concentrations of 10-13 and ∼10-7 M, respectively, those radicals are unable to compensate for the light-shielding effect of nitrate on E. coli inactivation. Moreover, reactive nitrogen species lead to the formation of nitrogenous byproducts, which increase the genotoxicity of the water. The findings advance the fundamental photochemistry and radical chemistry of nitrate at 222 nm and provide useful insights to guide the operation of Far-UVC in treating nitrate-containing water.

Construction of S-Scheme CuS/Bi5O7I Heterojunction for Boosted Photocatalytic Disinfection with Visible Light Exposure.

In this paper, a novel S-scheme CuS/Bi5O7I heterojunction was successfully constructed using a two-step approach comprising the alkaline hydrothermal method and the adsorption-deposition method, and it consisted of Bi5O7I microrods with CuS particles covering the surface. The photocatalytic antibacterial effects on Escherichia coli (E. coli) were systematically examined with visible light exposure. The results suggested that the 3%-CuS/Bi5O7I composite showed the optimal antibacterial activity, completely inactivating E. coli (5 × 108 cfu/mL) in 180 min of irradiation. Moreover, the bacterial inactivation process was scientifically described. •O2- and h+ were the major active species for the inactivation of the bacteria. In the early stages, SOD and CAT initiated the protection system to avoid the oxidative destruction of the active species. Unfortunately, the antioxidant protection system was overwhelmed thereafter, which led to the destruction of the cell membrane, as evidenced by the microstructure changes in E. coli cells. Subsequently, the leakage of intracellular components including K+, proteins, and DNA resulted in the unavoidable death of E. coli. Due to the construction of the S-scheme heterojunction, the CuS/Bi5O7I composite displayed the boosted visible light harvesting, the high-efficiency separation of photogenerated electrons and holes, and a great redox capacity, contributing to an outstanding photocatalytic disinfection performance. This work offers a new opportunity for S-scheme Bi5O7I-based heterojunctions with potential application in water disinfection.

Superiority of UV222 radiation by in situ aquatic electrode KrCl excimer in disinfecting waterborne pathogens: Mechanism and efficacy.

Microbial safety in water has always been the focus of attention, especially during the COVID-19 pandemic. Development of green, efficient and safe disinfection technology is the key to control the spread of pathogenic microorganisms. Here, an in situ aquatic electrode KrCl excimer radiation with main emission wavelength 222 nm (UV222) was designed and used to disinfect model waterborne virus and bacteria, i.e. phage MS2, E. coli and S. aureus. High inactivation efficacy and diversity of inactivation mechanisms of UV222 were proved by comparision with those of commercial UV254. UV222 could totally inactivate MS2, E. coli and S. aureus with initial concentrations of ∼107 PFU or CFU mL-1 within 20, 15, and 36 mJ/cm2, respectively. The UV dose required by UV254 to inactivate the same logarithmic pathogenic microorganism is at least twice that of UV222. The protein, genomic and cell membrane irreparable damage contributed to the microbial inactivation by UV222, but UV254 only act on nucleic acid of the target microorganisms. We found that UV222 damage nucleic acid with almost the same or even higher efficacy with UV254. In addition, free base damage of UV222 in similar ways with UV254(dimer and hydrate). But due to the quantum yield of free base degradation of UV222 was greater than UV254, the photolysis rates of UV222 to A, G, C and U four bases were 11.5, 1.2, 3.2 and 1 times as those of UV254, respectively. Excellent disinfection performance in UV222 irradiation was also achieved in real water matrices (WWTP and Lake). In addition, it was proved that coexisting HCO3- or HPO42 - in real and synthetic water matrices can produce • OH to promote UV222 disinfection. This study provided novel insight into the UV222 disinfection process and demonstrated its possibility to take place of the conventional ultraviolet mercury lamp in water purification.

Photocatalytic Inactivation of Co-Culture of E. coli and S. epidermidis Using APTES-Modified TiO2.

The presented work shows the antibacterial activity of TiO2 photocatalysts modified by 3-aminopropyltriethoxysilane (APTES). The APTES-functionalized TiO2 samples were obtained by the solvothermal process followed by calcination. The antibacterial activity of APTES/TiO2 samples was evaluated with two species of bacteria, Escherichia coli and Staphylococcus epidermidis, under artificial solar light (ASL) irradiation. The used bacteria are model organisms characterized by negative zeta potential (approx. -44.2 mV for E. coli and -42.3 mV for S. epidermidis). For the first time, the antibacterial properties of APTES-functionalized TiO2 were evaluated against mono- and co-cultured bacteria. The high antibacterial properties characterized the obtained APTES-modified nanomaterials. The best antibacterial properties were presented in the TiO2-4 h-120 °C-300 mM-Ar-300 °C sample (modified with 300 mM of APTES and calcined at 300 °C). The improvement of the antibacterial properties was attributed to a positive value of zeta potential, high surface area, and porous volume.

Natural photosensitizer-loaded in micellar copolymer to prevent bovine mastitis: A new post-dipping protocol on milking.

Good management practices such as post-dipping applications (post-milking immersion bath) contribute to the dairy cattle health during lactation and minimize the appearance of mastitis (an infection in the mammary gland). The post-dipping procedure is performed conventionally using iodine-based solutions. The search for therapeutic modalities that are not invasive and do not cause resistance to the microorganisms that cause bovine mastitis instigates the interest of the scientific community. In this regard, antimicrobial Photodynamic Therapy (aPDT) is highlighted. The aPDT is based on combining a photosensitizer (PS) compound, light of adequate wavelength, and molecular oxygen (3O2), which triggers a series of photophysical processes and photochemical reactions that generate reactive oxygen species (ROS) responsible for the inactivation of microorganisms. The present investigation explored the photodynamic efficiency of two natural PS: Chlorophyll-rich spinach extract (CHL) and Curcumin (CUR), both incorporated into the Pluronic® F127 micellar copolymer. They were applied in post-dipping procedures in two different experiments. The photoactivity of formulations mediated through aPDT was conducted against Staphylococcus aureus, and obtained a minimum inhibitory concentration (MIC) of 6.8 mg mL-1 for CHL-F127 and 0.25 mg mL-1 for CUR-F127. Only CUR-F127 inhibited Escherichia coli growth with MIC 0.50 mg mL-1. Concerning the count of microorganisms during the days of the application, a significant difference was observed between the treatments and control (Iodine) when the teat surface of cows was evaluated. For CHL-F127 there was a difference for Coliform and Staphylococcus (p < 0.05). For CUR-F127 there was a difference for aerobic mesophilic and Staphylococcus (p < 0.05). Such application decreased bacterial load and maintained the milk quality, being evaluated via total microorganism count, physical-chemical composition, and somatic cell count (SCC).

An excimer lamp to provide far-ultraviolet C irradiation for dining-table disinfection.

Dining tables may present a risk to diners by transmitting bacteria and/or viruses. Currently, there is a lack of an environmental-friendly and convenient means to protect diners when they are sitting together. This investigation constructed far-UVC excimer lamps to disinfect dining-table surfaces. The lamps were mounted at different heights and orientations, and the irradiance on table surfaces was measured. The irradiation doses to obtain different inactivation efficiencies for Escherichia coli (E. coli) were provided. In addition, numerical modeling was conducted for irradiance and the resulting inactivation efficiency. The surface-to-surface (S2S) model was validated with the measured irradiance. The germicidal performance of far-UVC irradiation, the far-UVC doses to which diners were exposed, and the risk of exposure to the generated ozone were evaluated. The results revealed that an irradiation dose of 12.8 mJ/cm2 can disinfect 99.9% of E. coli on surfaces. By varying the lamp irradiance output, the number and positions of the lamps, the far-UVC irradiation can achieve a 3-log reduction for a dining duration of 5 min. Besides, the far-UVC lamp has a low damage risk to diners when achieving an effective inactivation rate. Moreover, there is virtually no ozone exposure risk in a mechanically ventilated dining hall.

Photocatalytic activity of P-doped TiO2 photocatalyst.

In this study, P-doped TiO2 photocatalysts with different molar percentages (in the range 0.071-1.25 mol %) of the non-metallic element were prepared and their photocatalytic activity under visible light irradiation was tested. All achieved samples were characterized by XRD, Raman, UV-Vis DRS and SEM-EDX techniques. XRD and Raman analysis showed that all doped photocatalysts were in anatase phase and evidenced that P ions were successfully incorporated into the TiO2 crystal lattice, affecting also the crystallinity degree of the P-doped TiO2 photocatalysts. Noticeably, the UV-Vis DRS spectra evidenced that the highest redshift in absorption edge was observed for the photocatalyst with the lowest P content (0.071PT), which showed also the lowest bandgap (2.9 eV). The photocatalytic performances of all P-doped TiO2 samples were compared with that of commercial TiO2 by evaluating the decolorization of methylene blue (MB) dye under visible light irradiation. Results showed that phosphorus doping strongly promoted photocatalytic activity in the presence of visible light. Furthermore, the most active photocatalyst in visible light tests (0.071PT) also showed better photocatalytic activity than commercial TiO2 in the decolorization of MB under simulated sunlight irradiation. Finally, 0.071PT photocatalyst was preliminarily tested against Escherichia coli (E. coli) under simulated solar light, showing an inactivation efficiency of 90% after 2 h of treatment time.

Investigation of diode laser effect on the inactivation of selected Gram-negative bacteria, Gram-positive bacteria and yeast and its disinfection on wastewater and natural milk.

Disinfection can be accomplished by adding external chemical agents to kill harmful microorganisms or by removing them using membranes. However, most chemicals are toxic for humans and animals if it is consumed above a certain concentration. Likewise, membranes have fouling problems. The aim of this study is to investigate the effect of diode laser, which is an environmentally friendly application, on pathogenic microorganisms such as Escherichia coli (ATCC 10536), Staphylococcus aureus (ATCC 6538) and Candida albicans. To reveal the effect of diode laser on aforementioned, various parameters have been studied on how diode laser type, laser irradiation time, laser power density, laser penetration efficiency and biofilm inhibition affect microorganisms. As a result of the study, it was observed that the blue laser was more effective than red and green lasers, and the inhibition rates for 15 min at 0.36 W/cm2 laser power density were 65.9% > 34.52% > 43.63% for S. aureus, E. coli and C. albicans, respectively. After 30 min of blue laser irradiation, the microbial growth inhibitions were found as 85.39%, 41.18% and 54.55% for S. aureus, E. coli and C. albicans, respectively. The highest biofilm inhibition was 94.61% when S. aureus cells were exposed to blue laser irradiation for 60 min. The microbial growth kinetics on three microorganisms were tested by using at 0.54 W/cm2 laser power density for 28 h, and there were not observed any microbial development in microbial cultures. Moreover, blue laser irradiation was successfully disinfected wastewater and natural milk at 0.54 W/cm2 laser power density.

Methylene Blue/Carbon Dots Composite with Photothermal and Photodynamic Properties: Synthesis, Characterization, and Antibacterial Application.

Photodynamic therapy and photothermal therapy provide new ways to combat antibiotic resistance. In this research, methylene blue (MB) as an effective photosensitizer was conjugated with carbon quantum dots (CQDs), the composite product not only possessed good antibacterial properties against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) due to excellent singlet oxygen (1 O2 ) production rate and light heat transfer performance, but also showed good biocompatibility. Combined with 808 nm and 660 nm laser irradiation, the minimum bactericidal concentration of CQDs-MB towards S. aureus and E. coli was 5 µm. Therefore, this study provides a potential candidate material based on CQDs for clinical applications.

Evaluation of disinfection efficacy of single UV-C, and UV-A followed by UV-C LED irradiation on Escherichia coli, B. spizizenii and MS2 bacteriophage, in water.

Ultraviolet light-emitting diodes (UV LEDs) have shown ability to inactivate microorganisms and viruses in water. The unique characteristic of the UV-LEDs' diversity in wavelengths ranging from UV-C, UV-B, and UV-A, allows for wavelengths to be combined in different manners for polychromatic irradiation. Previous studies reported no synergy from simultaneous or sequential UV-C and UV-B as well as UV-C or UV-B followed by UV-A irradiation. However, synergy was reported for UV-A followed by UV-C or UV-B irradiation on various microorganisms. Nevertheless, no clear ground has been reached on whether to adopt single UV-C wavelengths or UV-A followed by UV-C LED, irradiation on inactivation of microorganisms and viruses in water. Therefore, this work evaluates the disinfection efficacy of single UV-C as well as UV-A followed by UV-C LED irradiation on Escherichia coli, Bacillus spizizenii spores and MS2 bacteriophage in water. The UV-C wavelengths were represented by 267 and 278 nm UV LEDs, and UV-A by 368 nm UV LEDs. In this study, E. coli was highly susceptible to UV radiation followed by B. spizizenii spores, and lastly MS2. Repair following UV inactivation was only observed in E. coli. The synergistic effect found in both E. coli, and B. spizizenii spores was attributed to the different inactivation mechanisms of the UV-C and UV-A wavelengths. In both single UV-C, and UV-A followed by UV-C LED irradiations, single 267 nm UV-C LED showed higher inactivation efficacy. Meanwhile, single 278 nm UV-C LED showed higher efficacy in terms of suppression of repair, and electrical energy consumption. Using single UV-C LEDs in a water disinfection system cuts down on related extra costs by avoiding combined wavelengths while still attaining better levels of microorganism inactivation, repair suppression and electrical energy consumption. These findings are applicable for the design and implementation of UV LED water disinfection systems.

Construction of a novel double S-scheme structure WO3/g-C3N4/BiOI: Enhanced photocatalytic performance for antibacterial activity.

In recent years, the threat to human health from bacteria in wastewater has attracted attention, and photocatalytic technology has emerged as a promising strategy for inactivating bacteria in water. Therefore, it is of great research value to develop a novel high-efficiency photocatalytic system with the visible light response. We successfully designed a double S-scheme heterojunction composite WO3/g-C3N4/BiOI (WCB) in this paper. The preparation of WCB composites was demonstrated by a series of characterizations, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The antibacterial effects of photocatalysts against representative Gram-negative strain Escherichia coli (E. coli) and Gram-positive strain Staphylococcus aureus (S. aureus) were tested under LED light irradiation. The novel photocatalyst presented excellent antibacterial properties, inactivating E. coli in 12 min and S. aureus in 20 min. The bacterial cell inactivation process was studied by scanning electron microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). Active species capture experiments show that the active species present in the WCB composites in the process of inactivating bacteria are h+, e-, OH and O2-. In conclusion, the synthesized double S-scheme WCB photocatalyst exhibits remarkable photocatalytic antibacterial activity under LED light and has broad prospects for practical application in water antibacterial treatment.