Advances in photocatalytic disinfection of bacteria: Development of photocatalysts and mechanisms

Enhanced virucidal activity of facet-engineered Cu-doped TiO2 nanorods under visible light illumination

Crystal facet engineering has emerged as a promising approach to enhance photocatalytic activity of semiconductors by preferentially accumulating charge carriers (electrons and holes) on specific facets. This facilitates efficient electron and hole transfer across the semiconductor/cocatalyst interface, enabling their transport to the cocatalyst surface for redox reactions. In this study, three Cu-doped TiO2 nanorods with small, medium, and large ratios of reductive {110} to oxidative {111} facets were synthesized (namely Cu-TiO2-SR, Cu-TiO2-MR, and Cu-TiO2-LR, respectively). These materials were comparatively evaluated for the inactivation of phiX174 bacteriophage under visible light illumination. Notably, Cu-TiO2-LR demonstrated an outstanding inactivation rate of phiX174 (0.42 log inactivation/min), approximately 11.8 times higher than that of Cu-TiO2-SR. Photo- and electrochemical analyses revealed that Cu-TiO2-LR exhibited superior electron/hole separation efficiency, leading to enhanced Cu redox reactions. Various experiments, encompassing viral inactivation tests with different additives, protein oxidation assays, and DNA damage assessments, indicated that Cu(III) is the major virucidal species responsible for the phiX174 inactivation by illuminated Cu-TiO2-LR. Under visible light illumination, Cu-TiO2-LR also showed excellent reusability and minimal activity loss in the presence of humic acid and inorganic anions, as well as general microbicidal effects on other viral and bacterial species.

Advanced photocatalysis as a viable and sustainable wastewater treatment process: A comprehensive review

In our era, water pollution not only poses a serious threat to human, animal, and biotic life but also causes serious damage to infrastructure and the ecosystem. A set of physical, chemical, and biological technologies have been exploited to decontaminate and/or disinfect water pollutants, toxins, microbes, and contaminants, but none of these could be ranked as sustainable and scalable wastewater technology. The photocatalytic process can harmonize the sunlight to degrade certain toxins, chemicals, microbes, and antibiotics, present in water. For example, transition metal oxides (ZnO, SnO2, TiO2, etc.), when integrated into an organic framework of graphene or nitrides, can bring about more than 90% removal of dyes, microbial load, pesticides, and antibiotics. Similarly, a modified network of graphitic carbon nitride can completely decontaminate petrochemicals. The present review will primarily highlight the mechanistic aspects for the removal and/or degradation of highly concerned contaminants, factors affecting photocatalysis, engineering designs of photoreactors, and pros and cons of various wastewater treatment technologies already in practice. The photocatalytic reactor can be a more viable and sustainable wastewater treatment opportunity. We hope the researcher will find a handful of information regarding the advanced oxidation process accomplished via photocatalysis and the benefits associated with the photocatalytic-type degradation of water pollutants and contaminants.

Chemical multiscale robotics for bacterial biofilm treatment

A biofilm constitutes a bacterial community encased in a sticky matrix of extracellular polymeric substances. These intricate microbial communities adhere to various host surfaces such as hard and soft tissues as well as indwelling medical devices. These microbial aggregates form a robust matrix of extracellular polymeric substances (EPSs), leading to the majority of human infections. Such infections tend to exhibit high resistance to treatment, often progressing into chronic states. The matrix of EPS protects bacteria from a hostile environment and prevents the penetration of antibacterial agents. Modern robots at nano, micro, and millimeter scales are highly attractive candidates for biomedical applications due to their diverse functionalities, such as navigating in confined spaces and targeted multitasking. In this tutorial review, we describe key milestones in the strategies developed for the removal and eradication of biofilms using robots of different sizes and shapes. It can be seen that robots at different scales are useful and effective tools for treating bacterial biofilms, thus preventing persistent infections, the loss of costly implanted medical devices, and additional costs associated with hospitalization and therapies.

Copper-doped bismuth oxychloride nanosheets assembled into sphere-like morphology for improved photocatalytic inactivation of drug-resistant bacteria

The devastating microbiological contamination as well as emerging drug-resistant bacteria has posed severe threats to the ecosystem and public health, which propels the continuous exploitation of safe yet efficient disinfection products and technology. Here, copper doping engineered bismuth oxychloride (Cu-BiOCl) nanocomposite with a hierarchical spherical structure was successfully prepared. It was found that due to the exposure of abundant active sites for the adsorption of both bacteria cells and molecular oxygen in the structure, the obtained Cu-BiOCl with nanosheets assembled into sphere-like morphology exhibited remarkable photocatalytic antibacterial effects. In particular, compared to the pure BiOCl, composite Cu-BiOCl possessed improved antibacterial effects against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Methicillin-resistant Staphylococcus aureus (MRSA). The combination of physicochemical characterizations and theoretical calculations has revealed that copper doping significantly promoted the light absorbance, inhibited the recombination of electron-hole pairs, and enhanced molecular oxygen adsorption, which resulted in more generation of active species including reactive oxygen species (ROS) and h+ to achieve superior photocatalytic bacterial inactivation. Finally, transcriptome analysis on MRSA pinpointed photocatalytic inactivation induced by Cu-BiOCl may retard largely the development of drug-resistance. Therefore, the built spherical Cu-BiOCl nanocomposite has provided an ecofriendly, economical and robust strategy for the efficient removal of drug-resistant bacteria with promising potentials for environmental and healthcare utilizations.

High-throughput experimentation for photocatalytic water purification in practical environments

High-throughput screening instrument was developed for photocatalytic water purification, enabling the simultaneous testing of 132 photocatalytic reactions under uniform visible light irradiation, temperature control, and stirring. The instrument was used to investigate the effects of different catalysts (TiO2, ZnO, α-Fe2O3) and environmental waters (seawater, urban wastewater, and industrial wastewater) on dye degradation. It was observed environmental ions, particularly carbonate and phosphate ions, significantly reduced catalyst activity by inhibiting the adsorption of dye molecules. To develop effective catalysts for dye degradation in industrial wastewater, 15 types of noble metal nanoparticles (NPs) were supported on photocatalysts. The study found that noble metal NPs with high work functions and oxidation resistance, such as Au and Pt, exhibited higher activity even in the industrial wastewater, likely converting environmental ions into active species. These findings, based on 432 test results, demonstrate the effectiveness of the developed high-throughput screening instrument for optimizing photocatalytic water purification.

Advances in reparative materials for infectious bone defects and their applications in maxillofacial regions

Infectious bone defects are characterized by the partial loss or destruction of bone tissue resulting from bacterial contaminations subsequent to diseases or external injuries. Traditional bone transplantation and clinical methods are insufficient in meeting the treatment demands for such diseases. As a result, researchers have increasingly focused on the development of more sophisticated biomaterials for improved therapeutic outcomes in recent years. This review endeavors to investigate specific reparative materials utilized for the treatment of infectious bone defects, particularly those present in the maxillofacial region, with a focus on biomaterials capable of releasing therapeutic substances, functional contact biomaterials, and novel physical therapy materials. These biomaterials operate via heightened antibacterial or osteogenic properties in order to eliminate bacteria and/or stimulate bone cells regeneration in the defect, ultimately fostering the reconstitution of maxillofacial bone tissue. Based upon some successful applications of new concept materials in bone repair of other parts, we also explore their future prospects and potential uses in maxillofacial bone repair later in this review. We highlight that the exploration of advanced biomaterials holds promise in establishing a solid foundation for the development of more biocompatible, effective, and personalized treatments for reconstructing infectious maxillofacial defects.

Research status and prospects of organic photocatalysts in algal inhibition and sterilization: a review

An increasing amount of sewage has been discharged into water bodies in the progression of industrialization and urbanization, causing serious water pollution. Meanwhile, the increase of nutrients in the water induces water eutrophication and rapid growth of algae. Photocatalysis is a common technique for algal inhibition and sterilization. To improve the utilization of visible light and the conversion efficiency of solar energy, more organic photocatalytic materials have been gradually developed. In addition to ultraviolet light, partial infrared light and visible light could also be used by organic photocatalysts compared with inorganic photocatalysts. Simultaneously, organic photocatalysts also exhibit favorable stability. Most organic photocatalysts can maintain a high degradation rate for algae and bacteria after several cycles. There are various organic semiconductors, mainly including small organic molecules, such as perylene diimide (PDI), porphyrin (TCPP), and new carbon materials (fullerene (C60), graphene (GO), and carbon nanotubes (CNT)), and large organic polymers, such as graphite phase carbon nitride (g-C3N4), polypyrrole (PPy), polythiophene (PTH), polyaniline (PANI), and polyimide (PI). In this review, the classification and synthesis methods of organic photocatalytic materials were elucidated. It was demonstrated that the full visible spectral response (400-750 nm) could be stimulated by modifying organic photocatalysts. Moreover, some problems were summarized based on the research status related to algae and bacteria, and corresponding suggestions were also provided for the development of organic photocatalytic materials.

Effluent toxicity study using biomarkers for ciprofloxacin photoelectrocatalytic degradation by bismuth-doped titanium dioxide nanotubes

Ciprofloxacin hydrochloride (CIP) is a broad-spectrum synthetic antibiotic often found in domestic sewage and industrial waste due to the inefficiency of conventional treatments. Given the potential risk of drug accumulation, this study presents coatings of titanium dioxide nanotubes (TiO2) doped with different bismuth (Bi) concentrations to degrade CIP through photocatalytic and photoelectrochemical processes. Characterization studies revealed that bismuth (Bi) doping affected the morphology of the materials, with concentrations of 0.01 and 0.05 mol L-1, resulting in collapsed materials with a smaller active surface area. Photocatalysis tests for all the materials exhibited a similar degree of efficiency to photolysis, approximately 33%. Ecotoxicity tests using the biomarkers Lactuca sativa L., Lemna minor, and Artemia salina indicated that, although they were similar to photolysis in terms of efficiency, the effluents generated when employing the doped catalysts showed lower levels of toxicity, with the best results achieved for the material doped with 0.005 mol L-1 of Bi, with a toxicity level approximately 40% lower. Photoelectrocatalysis proved to be the most efficient CIP degradation technique. The highest degradation rate was observed for materials doped with 0.005 mol L-1 of Bi, with an efficiency of 46%, which is 1.4 times more efficient than photolysis. These results demonstrate that materials doped with low amounts of Bi can be effectively used as photoanodes for drug degradation, as their performance is superior, and the final product generated exhibits low toxicity to living organisms.

Sulphated TiO2 Reduced by Ammonia and Hydrogen as an Excellent Photocatalyst for Bacteria Inactivation

This study presents a relatively low-cost method for modifying TiO2-based materials for photocatalytic bacterial inactivation. The photocatalytic inactivation of Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus epidermidis) bacteria using modified sulphated TiO2 was studied. The modification focused on the reduction of TiO2 by ammonia agents and hydrogen at 400-450 °C. The results showed a high impact of sulphate species on the inactivation of E. coli. The presence of these species generated acid sites on TiO2, which shifted the pH of the reacted titania slurry solution to lower values, around 4.6. At such a low pH, TiO2 was positively charged. The ammonia solution caused the removal of sulphate species from TiO2. On the other hand, hydrogen and ammonia molecules accelerated the removal of sulphur species from TiO2, as did heating it to 450 °C. Total inactivation of E. coli was obtained within 30 min of simulated solar light irradiation on TiO2 heat-treated at 400 °C in an atmosphere of Ar or NH3. The S. epidermidis strain was more resistant to photocatalytic oxidation. The contact of these bacteria with the active titania surface is important, but a higher oxidation force is necessary to destroy their cell membrane walls because of their thicker cell wall than E. coli. Therefore, the ability of a photocatalyst to produce ROS (reactive oxidative species) will determine its ability to inactivate S. epidermidis. An additional advantage of the studies presented is the inactivation of bacteria after a relatively short irradiation time (30 min), which does not often happen with photocatalysts not modified with noble metals. The modification methods presented represent a robust and inexpensive alternative to photocatalytic inactivation of bacteria.

Research Progress on Inactivation of Bacteriophages by Visible-Light Photocatalytic Composite Materials: A Mini Review

Infectious diseases caused by waterborne viruses have attracted researchers' great attention. To ensure a safe water environment, it is important to advance water treatment and disinfection technology. Photocatalytic technology offers an efficient and practical approach for achieving this goal. This paper reviews the latest studies on visible-light composite catalysts for bacteriophage inactivation, with a main focus on three distinct categories: modified UV materials, direct visible-light materials and carbon-based materials. This review gives an insight into the progress in photocatalytic material development and offers a promising solution for bacteriophage inactivation.

Photocatalytic Antimicrobials: Principles, Design Strategies, and Applications

Nowadays, the increasing emergence of antibiotic-resistant pathogenic microorganisms requires the search for alternative methods that do not cause drug resistance. Phototherapy strategies (PTs) based on the photoresponsive materials have become a new trend in the inactivation of pathogenic microorganisms due to their spatiotemporal controllability and negligible side effects. Among those phototherapy strategies, photocatalytic antimicrobial therapy (PCAT) has emerged as an effective and promising antimicrobial strategy in recent years. In the process of photocatalytic treatment, photocatalytic materials are excited by different wavelengths of lights to produce reactive oxygen species (ROS) or other toxic species for the killing of various pathogenic microbes, such as bacteria, viruses, fungi, parasites, and algae. Therefore, this review timely summarizes the latest progress in the PCAT field, with emphasis on the development of various photocatalytic antimicrobials (PCAMs), the underlying antimicrobial mechanisms, the design strategies, and the multiple practical antimicrobial applications in local infections therapy, personal protective equipment, water purification, antimicrobial coatings, wound dressings, food safety, antibacterial textiles, and air purification. Meanwhile, we also present the challenges and perspectives of widespread practical implementation of PCAT as antimicrobial therapeutics. We hope that as a result of this review, PCAT will flourish and become an effective weapon against pathogenic microorganisms and antibiotic resistance.

Photocatalytic microbial disinfection under indoor conditions: Prospects and challenges of near IR-photoactive materials

The accumulation of microbes especially in the air and in water bodies is causing the major disease outbreaks. Indoor environment remediation methods are necessary today to clean up these microbes. Among the remediation methods available, in situ generation of highly reactive and oxidizing radical species by advanced oxidation processes (AOPs) inactivate most of the microbes unselectively. Of these AOPs, photocatalytic microbial disinfection especially under indoor conditions is of great interest to maintain microbe-free indoor environment. For efficient microbes' inactivation under indoor conditions, the near IR and IR response of the photocatalysts must be improved. Though the photocatalytic disinfection of microbes using semiconductor-based photocatalysts has been extensively investigated, most of the photocatalysts that have been investigated are either weekly responsive or totally not irresponsive to IR photons due to inappropriate bandgap energies. Several strategies have been investigated to enhance the light harvesting properties of semiconductor based photocatalysts under indoor conditions and make them active to near IR and IR radiations. This review summarizes the recent progress in the field of materials for photocatalysts employed for microbial removal in indoor environments over the past decade as well as outlines key perspectives to enlighten future researches. The paper details the fundamentals of photocatalysis and basic properties of photocatalytic materials in the disinfection of common microbes under indoor conditions. The applications of photocatalytic materials in the disinfection of microbes in indoor environmental conditions are discussed and reviewed. Finally, the remaining challenges and future strategies/prospects in the design and synthesis of IR (and near IR) responsive photocatalysts are discussed.

Composite Nanocoatings of Biomedical Magnesium Alloy Implants: Advantages, Mechanisms, and Design Strategies

The rapid degradation of magnesium (Mg) alloy implants erodes mechanical performance and interfacial bioactivity, thereby limiting their clinical utility. Surface modification is among the solutions to improve corrosion resistance and bioefficacy of Mg alloys. Novel composite coatings that incorporate nanostructures create new opportunities for their expanded use. Particle size dominance and impermeability may increase corrosion resistance and thereby prolong implant service time. Nanoparticles with specific biological effects may be released into the peri-implant microenvironment during the degradation of coatings to promote healing. Composite nanocoatings provide nanoscale surfaces to promote cell adhesion and proliferation. Nanoparticles may activate cellular signaling pathways, while those with porous or core-shell structures may carry antibacterial or immunomodulatory drugs. Composite nanocoatings may promote vascular reendothelialization and osteogenesis, attenuate inflammation, and inhibit bacterial growth, thus increasing their applicability in complex clinical microenvironments such as those of atherosclerosis and open fractures. This review combines the physicochemical properties and biological efficiency of Mg-based alloy biomedical implants to summarize the advantages of composite nanocoatings, analyzes their mechanisms of action, and proposes design and construction strategies, with the purpose of providing a reference for promoting the clinical application of Mg alloy implants and to further the design of nanocoatings.

Potential of novel dual Z-scheme carbon quantum dots decorated MnIn2S4/CdS/Bi2S3 heterojunction for environmental applications

In this work, CQDs decorated MnIn₂S₄/CdS/Bi₂S₃ heterojunction was prepared successfully by hydrothermal technique for photocatalytic disinfection of Escherichia coli (E. coli) and mineralization of methyl orange (MO) dye. The charge transferal route and mineralization process in CQDs-MnIn₂S₄/CdS/Bi₂S₃ heterojunction were comprehensively investigated by advanced spectroscopic techniques. The improved visible-light activity and enhanced photo-generated charge transferal efficacy caused dual Z-scheme CQDs-MnIn₂S₄/CdS/Bi₂S₃ heterojunction to achieve boosted photodegradation ability. The catalytic degradation trend was followed as CQDs-MnIn₂S₄/CdS/Bi₂S₃ > MnIn₂S₄ > CdS > Bi₂S₃. The dye was mineralized within 180 min under visible light irradiation. The effect of reaction parameters, pH effect, catalyst dosage, and H₂O₂ addition on MO degradation was also investigated. The degradation rate was maximal at pH 4 with a pseudo-first-order rate constant, 0.0438 min^-1. The assessment of antibacterial properties revealed that CQDs-MnIn₂S₄/CdS/Bi₂S₃ composite effectively inactivated E. coli under visible light. Scavenging experiments, transient photocurrent response, and electron spin resonance spectroscopy suggested that ^•[Formula: see text] and holes were the dominant reactive species. The Z-scheme heterojunction is recyclable up to ten photocatalytic cycles according to recycling experiments. This research indicates the importance of dual Z-scheme CQDs decorated MnIn₂S₄/CdS/Bi₂S₃ heterojunction in wastewater remediation.

Applications of BiOX in the Photocatalytic Reactions

BiOX (X = Cl, Br, I) families are a kind of new type of photocatalysts, which have attracted the attention of more and more researchers. The suitable band gaps and their convenient tunability via the change of X elements enable BiOX to adapt to many photocatalytic reactions. In addition, because of their characteristics of the unique layered structure and indirect bandgap semiconductor, BiOX exhibits excellent separation efficiency of photogenerated electrons and holes. Therefore, BiOX could usually demonstrate fine activity in many photocatalytic reactions. In this review, we will present the various applications and modification strategies of BiOX in photocatalytic reactions. Finally, based on a good understanding of the above issues, we will propose the future directions and feasibilities of the reasonable design of modification strategies of BiOX to obtain better photocatalytic activity toward various photocatalytic applications.

Deciphering the photoactive species-directed antibacterial mechanism of bismuth oxychloride with modulated nanoscale thickness

As an environmentally benign disinfection strategy, photocatalytic bacterial inactivation using nanoparticles involves photogenerated reactive species that cause cellular oxidative stress. Rationalising the structural performance of photocatalysts for the practical uses such as wastewater treatment has attracted significant attention; however, the contribution of reactive species to their photocatalytic antibacterial activities at the molecular and transcriptomic levels remains unclear. In this study, nontoxic bismuth oxychloride (BiOCl) photocatalysts with different nanoscale thicknesses, including nanosheets (Ns, ∼5.4 nm), nanoplates (Np, ∼1.8 nm), and ultra-nanosheets (Uns, ∼1.1 nm), were synthesised under hydrothermal conditions. Among the three samples, BiOCl Uns exhibited the most effective photocatalytic degradation efficiency with the calculated apparent rate constant of 0.0294 min^-1, ∼4 times faster than that of Ns, whereas BiOCl Ns possessed the most pronounced bactericidal effect (5.4 log inactivation). Such findings indicate the distinct role of the photoactive species responsible for photocatalytic bacterial inactivation. Moreover, transcriptome analysis of Escherichia coli after photocatalytic treatment revealed that the underlying photocatalytic antibacterial mechanism at the genetic expression level involves cellular component biosynthesis, energy metabolism, and material transportation. Notably, the differences between BiOCl Ns and BiOCl Uns were significantly enriched in purine metabolism. Therefore, the cost-effective preparation of BiOCl nanosheets with nanoscale thickness-modulated photocatalytic antibacterial activity has remarkable potential for sustainable environmental and biomedical applications.

Effect of Doping TiO2 NPs with Lanthanides (La, Ce and Eu) on the Adsorption and Photodegradation of Cyanide-A Comparative Study

Free cyanide is a highly dangerous compound for health and the environment, so treatment of cyanide-contaminated water is extremely important. In the present study, TiO₂, La/TiO₂, Ce/TiO₂, and Eu/TiO₂ nanoparticles were synthesized to assess their ability to remove free cyanide from aqueous solutions. Nanoparticles synthesized through the sol-gel method were characterized by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transformed infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), and specific surface area (SSA). Langmuir and Freundlich isotherm models were utilized to fit the adsorption equilibrium experimental data, and pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to fit the adsorption kinetics experimental data. Cyanide photodegradation and the effect of reactive oxygen species (ROS) on the photocatalytic process were investigated under simulated solar light. Finally, reuse of the nanoparticles in five consecutive treatment cycles was determined. The results showed that La/TiO₂ has the highest percentage of cyanide removal (98%), followed by Ce/TiO₂ (92%), Eu/TiO₂ (90%), and TiO₂ (88%). From these results, it is suggested that La, Ce, and Eu dopants can improve the properties of TiO₂ as well as its ability to remove cyanide species from aqueous solutions.

Photocatalytic Applications of ReS2-Based Heterostructures

ReS2-based heterostructures, which involve the coupling of a narrow band-gap semiconductor ReS2 with other wide band-gap semiconductors, have shown promising performance in energy conversion and environmental pollution protection in recent years. This review focuses on the preparation methods, encompassing hydrothermal, chemical vapor deposition, and exfoliation techniques, as well as achievements in correlated applications of ReS2-based heterostructures, including type-I, type-II heterostructures, and Z-scheme heterostructures for hydrogen evolution, reduction of CO2, and degradation of pollutants. We believe that this review provides an overview of the most recent advances to guide further research and development of ReS2-based heterostructures for photocatalysis.

How to Tackle Bacteriophages: The Review of Approaches with Mechanistic Insight

Bacteriophage-based applications have a renaissance today, increasingly marking their use in industry, medicine, food processing, biotechnology, and more. However, phages are considered resistant to various harsh environmental conditions; besides, they are characterized by high intra-group variability. Phage-related contaminations may therefore pose new challenges in the future due to the wider use of phages in industry and health care. Therefore, in this review, we summarize the current knowledge of bacteriophage disinfection methods, as well as highlight new technologies and approaches. We discuss the need for systematic solutions to improve bacteriophage control, taking into account their structural and environmental diversity.

Advanced photocatalytic sterilization for recalcitrant Enterococcus sp. contaminated water by newly developed Z-scheme Bi2WO6 based composites under solar light

Pathogenic contamination is one of the major causes of clean water shortage, which poses great risk to human health. Herein, g-C₃N₄ (CN) was firstly introduced to Ag/Ag₂O/BiPO₄/Bi₂WO₆ (Ag/P/BWO) to construct a novel Z-scheme composite CN-Ag/P/BWO for disinfecting Enterococcus sp. contaminated water. CN-Ag/P/BWO showed excellent disinfection performance toward recalcitrant Enterococcus sp. under simulated solar light irradiation, achieving complete inactivation of 1.5 × 10⁷ cfu mL^-1 of bacterial cells only within 60 min, which was mainly attributed to the improved light absorption ability, charge carries separation/transfer efficiency and surface wettability. Additionally, the disinfection mechanism of CN-Ag/P/BWO toward Enterococcus sp. was systematically investigated. Photogenerated active species h⁺, ·OH and ·O₂^- worked together and played crucial roles in photocatalytic inactivation. The antioxidant system enabled Enterococcus sp. self-protection ability at the beginning of disinfection through secreting more antioxidant enzymes. However, with accumulation of active species, bacterial cell membrane and energy system were damaged, which further led to leakage of intracellular components and decomposition of bacteria. Besides, CN-Ag/P/BWO exhibited high practicability for different environmental factors and also performed well for real lake water disinfection. The high stability further confirmed its practicability for water disinfection. This work not only systematically revealed the disinfection mechanism toward Enterococcus sp., but also provided an efficient method for water disinfection.

Construction of a domestic wastewater disinfection filter from biosynthesized and commercial nanosilver: a comparative study

Purpose

Biosynthesis of nanoparticles is an eco-friendly process and considered one of the most significant aspects of nanotechnology. Silver nanoparticles (Ag NPs) have a better bactericidal activity due to its high surface area to volume ratio. In this paper, Streptomyces sp. U13 (KP109813) was used to biosynthesize silver nanoparticles (Ag NPs) to construct wastewater disinfection filter.

Methods

The biosynthesized nanosilver and a commercially available ink nanosilver were characterized, and their wastewater disinfection efficiency was compared. The nanometrological characteristics of both nanosilver such as structure, shape, and size were investigated using the X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), high-resolution transmission electron microscope (HR-TEM), and UV-visible spectroscopy.

Result

The results revealed that the biosynthesized and ink Ag NPs were well dispersed and had a spherical shape, with sizes ranged from 5 to 37 nm and from 2 to 26 nm, respectively. To examine the disinfection capabilities, Ag NPs were loaded on two substrates, foam and limestone gravel, and packed into a glass column receiving domestic wastewater. Results showed that Ag NPs attached to limestone gravel eliminate 100% of the coliform bacteria better than foam. Comparing to control columns (without silver), only 50 and 10% reduction of the total coliform in gravel and foam column were achieved, respectively.

Conclusion

This work concluded that the type of substrate controls the amount of Ag NPs loaded on it and thus controls the disinfection process. No significant difference between biosynthesized and ink nanosilver in wastewater disinfection was observed. Using limestone gravel filter loaded with 200 mg/l Ag NPs with contact time of 150 min achieves a complete eradication of coliform bacteria.

Research Progress on Graphitic Carbon Nitride/Metal Oxide Composites: Synthesis and Photocatalytic Applications

Although graphitic carbon nitride (g-C3N4) has been reported for several decades, it is still an active material at the present time owing to its amazing properties exhibited in many applications, including photocatalysis. With the rapid development of characterization techniques, in-depth exploration has been conducted to reveal and utilize the natural properties of g-C3N4 through modifications. Among these, the assembly of g-C3N4 with metal oxides is an effective strategy which can not only improve electron-hole separation efficiency by forming a polymer-inorganic heterojunction, but also compensate for the redox capabilities of g-C3N4 owing to the varied oxidation states of metal ions, enhancing its photocatalytic performance. Herein, we summarized the research progress on the synthesis of g-C3N4 and its coupling with single- or multiple-metal oxides, and its photocatalytic applications in energy production and environmental protection, including the splitting of water to hydrogen, the reduction of CO2 to valuable fuels, the degradation of organic pollutants and the disinfection of bacteria. At the end, challenges and prospects in the synthesis and photocatalytic application of g-C3N4-based composites are proposed and an outlook is given.

Inhibition of biofouling on reverse osmosis membrane surfaces by germicidal ultraviolet light side-emitting optical fibers

Biofouling of membrane surfaces poses significant operational challenges and costs for desalination and wastewater reuse applications. Ultraviolet (UV) light can control biofilms while reducing chemical usage and disinfection by-products, but light deliveries to membrane surfaces in spiral wound geometries has been a daunting challenge. Thin and flexible nano-enabled side-emitting optical fibers (SEOFs) are novel light delivery devices that enable disinfection or photocatalytic oxidation by radiating UV light from light-emitting diodes (LEDs). We envision SEOFs as an active membrane spacer to mitigate biofilm formation on reverse osmosis (RO) membranes. A lab-scale RO membrane apparatus equipped with SEOFs allowed comparison of UV-A (photocatalysis-enabled) versus UV-C (direct photolysis disinfection). Compared against systems without any light exposure, systems with UV-C light formed thinner-but denser-biofilms, prevented permeate flux declines due to biofouling, and maintained the highest salt rejection. Results were corroborated by in-situ optical coherence tomography and ex-situ measurements of biofilm growth on the membranes. Transcriptomic analysis showed that UV-C SEOFs down-regulated quorum sensing and surface attachment genes. In contrast, UV-A SEOFs upregulated quorum sensing, surface attachment, and oxidative stress genes, resulting in higher extracellular polymeric substances (EPS) accumulation on membrane surfaces. Overall, SEOFs that deliver a low fluence of UV-C light onto membrane surfaces are a promising non-chemical approach for mitigating biofouling formation on RO membranes.

Photocatalytic Inactivation of Viruses and Prions: Multilevel Approach with Other Disinfectants

Ag, Cu, Zn, Ti, and Au nanoparticles show enhanced photocatalytic properties. Efficient indoor disinfection strategies are imperative to manage the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Virucidal agents, such as ethanol, sodium hypochlorite, 222-nm UV light, and electrolyzed water inactivate SARS-CoV-2 in indoor environments. Tungsten trioxide (WO3) photocatalyst and visible light disinfect abiotic surfaces against SARS-CoV-2. The titanium dioxide (TiO2)/UV system inactivates SARS-CoV-2 in aerosols and on deliberately contaminated TiO2-coated glass slide surfaces in photocatalytic chambers, wherein 405-nm UV light treatment for 20 min sterilizes the environment and generates reactive oxygen species (ROS) that inactivate the virus by targeting S and envelope proteins and viral RNA. Mesoscopic calcium bicarbonate solution (CAC-717) inactivates pathogens, such as prions, influenza virus, SARS-CoV-2, and noroviruses, in fluids; it presumably acts similarly on human and animal skin. The molecular complexity of cementitious materials promotes the photocatalysis of microorganisms. In combination, the two methods can reduce the pathogen load in the environment. As photocatalysts and CAC-717 are potent disinfectants for prions, disinfectants against prionoids could be developed by combining photocatalysis, gas plasma methodology, and CAC-717 treatment, especially for surgical devices and instruments.

Visible-light-responsive photocatalytic inactivation of ofloxacin-resistant bacteria by rGO modified g-C3N4

The visible light responsive graphitic nitride (g-C₃N₄) mediated photocatalysis has drawn extensive attention in water treatment field. Carbon doping could improve the photocatalytic activity of g-C₃N₄ in promoting charge separation efficiency, visible-light utilization, etc. In this paper, the g-C₃N₄ (as MC) was modified by barbituric acid (as MCB_0.07) and further treated by reduced graphene oxide (rGO) (as n%GCN) and then applied to inactivate ofloxacin-resistant bacteria (OFLA) under light irradiation at UVA-visible wavelength. The results showed that the n%GCN presented strong photocatalytic activity when the GO mass ratio was 7.5% (as 7.5%GCN). The inactivation efficiencies of OFLA by MC, MCB_0.07, and 7.5%GCN were 5.77 log, 8.48 log, and 8.25 log, respectively, under UVA-visible wavelength (λ > 305 nm), compared to 4.83 log, 5.56 log, and 6.08 log, respectively, within 16 h under visible wavelength (λ > 400 nm). The rGO-doping obviously improved the inactivation efficiency of MCB_0.07 on OFLA under visible wavelength. Furthermore, the photoreactivation and dark repair phenomena of OFLA were examined after MC, MCB_0.07, and 7.5%GCN treatment, respectively, and it was found that all approaches led to permanent damage to OFLA of which the regrowth was not observed after 24-48 h. Based on the quenching test, reactive oxygen species of O₂^-• and hole (h⁺) exhibited dominant roles in the photocatalytic inactivation of OFLA, which may result in oxidative stress and damage to the cell membrane. This study could shed light on the inactivation of OFLA under visible light radiation by rGO modified g-C₃N₄.

Photocatalytic disinfection for point-of-use water treatment using Ti3+ self-doping TiO2 nanoparticle decorated ceramic disk filter

The challenge from pathogenic infections still threatens the health and life of people in developing areas. An efficient, low-cost, and abundant-resource disinfection method is desired for supplying safe drinking water. This study aims to develop a novel Ti³⁺ doping TiO₂ nanoparticle decorated ceramic disk filter (Ti³⁺/TiO₂@CDF) for point-of-use (POU) disinfection of drinking water. The production of Ti³⁺/TiO₂@CDF was optimized to maximize disinfection efficiency and flow rate. Under optimal conditions, the log reduction value (LRV) could reach up to 7.18 and the flaw rate was 108 mL/h. The influences of environmental factors were also investigated. Natural or slightly alkaline conditions, low turbidity, and low concentration of humic acid were favorable for the disinfection of Ti³⁺/TiO₂@CDF, while co-existing HCO₃^- ions and diatomic cations (Ca²⁺ and Mg²⁺) exhibited the opposite effect. Furthermore, the practicability and stability of Ti³⁺/TiO₂@CDF was demonstrated. Ti³⁺/TiO₂@CDF showed high disinfection efficiency for E. coli and S. aureus under a range of concentrations. Long-term experiment indicated that Ti³⁺/TiO₂@CDF was stable. The underlying disinfection mechanisms were investigated and concluded as the combination of retention, adsorption, and photocatalytic disinfection. The developed Ti³⁺/TiO₂@CDF can provide an effective and reliable disinfection tool for POU water treatment in remote area.

Enhanced disinfection of E. faecalis and levofloxacin antibiotic degradation using tridoped B-Ce-Ag TiO2 photocatalysts synthesized by ecofriendly citrate EDTA complexing method

Since its use for photochemical water splitting reported first in 1972, TiO₂ is one of the most extensively studied photocatalysts for a diverse range of applications. Monodoping or codoping of the catalyst is a proven strategy to enhance the functionality of TiO₂ under solar or visible light. However, the use of three or more dopants in the development of more efficient and visible light active photocatalysts has not been investigated widely, especially for microbial disinfection. Boron/cerium/silver tridoped TiO₂ photocatalysts with curated amounts of the dopants (B = 1, 2 at.%, Ce = 0.1 at.%, Ag = 0.06 at.%), synthesized by the ecofriendly EDTA-citrate method, were evaluated for the disinfection of water using Enterococcus faecalis under UV-A irradiation and degradation of levofloxacin antibiotic under solar light. The catalyst characterization revealed that the spherical nanoparticles had a crystallite size of ~ 13 nm and bandgap energy values of 2.8-2.9 eV. 2B-0.1Ce-0.06Ag-TiO₂ is the best catalyst for microbial disinfection with a log reduction and kinetic rate constant ~ 30 and ~ 4.5 times higher than those values determined for the other codoped or monodoped catalysts, confirming an enhanced performance. Regarding levofloxacin degradation, the best performing catalyst is 1B-0.1Ce-0.06Ag-TiO₂ with degradation of 99% and 83% COD reduction in 100 min. The tridoped photocatalysts are very effective in the inactivation of Enterococcus faecalis, thus solving the problem of antimicrobial resistance in waters containing antibiotic residues.

Photocatalytic disinfection of Coliforms and degradation of natural organic matters in river water using titanate nanotubes

In this study, we synthesized and modified titanate nanotubes (TNTs) under different conditions of acid rinsing and calcination. The produced materials were then characterized by transmission electron microscopy, X-ray diffraction, ultraviolet-visible spectroscopy, temperature programmed desorption, inductively coupled plasma atomic emission spectroscopy, and Brunauer-Emmett-Teller analysis. The activity of material was evaluated via its application for disinfection of Coliforms and removal of natural organic matters (NOMs) in river water. Results showed that TNTs rinsed at pH 1.6 and calcined at 500°C had the highest removal efficiency for the treatment of Coliforms and NOMs in Sai Gon river water, possibly due to its high surface area, crystallinity, and surface acidity. The application of this TNTs material for the treatment of waters from Dong Nai River and Mekong River also show high removal efficiency, which could meet the quality standard for supply water, suggesting the potential of TNTs for practical drinking water treatment.

The practicality and prospects for disinfection control by photocatalysis during and post-pandemic: A critical review

The prevalence of global health implications from the COVID-19 pandemic necessitates the innovation and large-scale application of disinfection technologies for contaminated surfaces, air, and wastewater as the significant transmission media of disease. To date, primarily recommended disinfection practices are energy exhausting, chemical driven, and cause severe impact on the environment. The research on advanced oxidation processes has been recognized as promising strategies for disinfection purposes. In particular, semiconductor-based photocatalysis is an effective renewable solar-driven technology that relies on the reactive oxidative species, mainly hydroxyl (•OH) and superoxide (•O2-) radicals, for rupturing the capsid shell of the virus and loss of pathogenicity. However, the limited understanding of critical aspects such as viral photo-inactivation mechanism, rapid virus mutagenicity, and virus viability for a prolonged time restricts the large-scale application of photocatalytic disinfection technology. In this work, fundamentals of photocatalysis disinfection phenomena are addressed with a reviewed remark on the reported literature of semiconductor photocatalysts efficacies against SARS-CoV-2. Furthermore, to validate the photocatalysis process on an industrial scale, we provide updated data on available commercial modalities for an effective virus photo-inactivation process. An elaborative discussion on the long-term challenges and sustainable solutions is suggested to fill in the existing knowledge gaps. We anticipate this review will ignite interest among researchers to pave the way to the photocatalysis process for disinfecting virus-contaminated environments and surfaces for current and future pandemics.

Nanoparticle Engineered Photocatalytic Paints: A Roadmap to Self-Sterilizing against the Spread of Communicable Diseases

Applications of visible-light photocatalytic engineered nanomaterials in the preparation of smart paints are of recent origin. The authors have revealed a great potential of these new paints for self-sterilizing of the surfaces in hospitals and public places simply with visible light exposure and this is reported for the first time in this review. A recent example of a communicable disease such as COVID-19 is considered. With all precautions and preventions taken as suggested by the World Health Organization (WHO), COVID-19 has remained present for a longer time compared to other diseases. It has affected millions of people worldwide and the significant challenge remains of preventing infections due to SARS-CoV-2. The present review is focused on revealing the cause of this widespread disease and suggests a roadmap to control the spread of disease. It is understood that the transmission of SARS-CoV-2 virus takes place through contact surfaces such as doorknobs, packaging and handrails, which may be responsible for many preventable and nosocomial infections. In addition, due to the potent transmissibility of SARS-CoV-2, its ability to survive for longer periods on common touch surfaces is also an important reason for the spread of COVID-19. The existing antimicrobial cleaning technologies used in hospitals are not suitable, viable or economical to keep public places free from such infections. Hence, in this review, an innovative approach of coating surfaces in public places with visible-light photocatalytic nanocomposite paints has been suggested as a roadmap to self-sterilizing against the spread of communicable diseases. The formulations of different nanoparticle engineered photocatalytic paints with their ability to destroy pathogens using visible light, alongwith the field trials are also summarized and reported in this review. The potential suggestions for controlling the spread of communicable diseases are also listed at the end of the review.

Mechanism investigation for ultra-efficient photocatalytic water disinfection based on rational design of indirect Z-scheme heterojunction black phosphorus QDs/Cu2O nanoparticles

Photocatalysis has been regarded as a promising inactivation technology targeting to reduce drug-resistant bacteria contamination, but developing efficient photocatalysts with broad visible light harvesting capability is still a challenge. Here we report a MOFs-derived BPQDs/Cu₂O/N-doped hollow porous carbon (BP/CNC) with indirect Z-scheme heterojunctions (BPQDs/Cu₂O), which can inactivate 99.99999% Methicillin-resistant Staphylococcus aureus (MRSA) at a concentration of only 10 mg/L. Combining photoelectrochemical techniques and electrochemical measurements, the efficient inactivation process was attributed to the synergistic effect of enhanced light utilization and effective suppression of photogenerated carrier recombination. The mechanism of gradually damaged cell membrane for MRSA was studied by employing scanning electron microscopy (SEM), fluorescence staining and coagulase titer test to further decipher the changes in bacterial cells. We propose that reactive oxygen species (ROS) destroys the cell wall membrane and causes the leakage of cell contents, eventually leading to death. In addition, a series of in vitro and in vivo toxicity tests were conducted to evaluate the biocompatibility of the antibacterial system and its potential use in practice. This strategy of BPQDs/Cu₂O indirect heterojunction fabrication can spatially inhibit the recombination of photogenerated carriers, expands the light absorption range, providing a feasible method for disinfecting microbial contaminated water.

Recent progress of silver-containing photocatalysts for water disinfection under visible light irradiation: A review

Photocatalysis has emerged as an environmentally friendly approach for microbial disinfection. The development of visible-light-driven (VLD) photocatalysts for water pollution remediation is imperative, considering that visible light constitutes a substantial fraction of the solar spectrum. The modification of photocatalysts by Ag/AgX (X = Cl, Br, I) deposition can be used to improve photocatalytic efficiencies. This is achieved by preventing photogenerated electron-hole pairs recombination through electron trapping mechanisms. With the introduction of silver NPs, visible light absorption can also be increased through its SPR enhancement. Silver also possesses excellent antimicrobial properties. Consequently, a novel class of Ag/AgX-containing hybrid materials has recently emerged as a promising candidate for water disinfection. This review summarizes the latest advances in the synthesis of Ag/AgX-containing photocatalysts using various synthetic methods. The microbial disinfection efficiencies of the as-prepared materials, the main reactive oxygen species and disinfection mechanisms are also reviewed in detail. Finally, some areas that need to be improved are discussed along with new insights as perspectives for future developments in this field.

Facemask Global Challenges: The Case of Effective Synthesis, Utilization, and Environmental Sustainability

Coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused a rapidly spreading pandemic and is severely threatening public health globally. The human-to-human transmission route of SARS-CoV-2 is now well established. The reported clinical observations and symptoms of this infection in humans appear in the range between being asymptomatic and severe pneumonia. The virus can be transmitted through aerosols and droplets that are released into the air by a carrier, especially when the person coughs, sneezes, or talks forcefully in a closed environment. As the disease progresses, the use and handling of contaminated personal protective equipment and facemasks have become major issues with significant environmental risks. Therefore, providing an effective method for treating used/contaminated facemasks is crucial. In this paper, we review the environmental challenges and risks associated with the surge in facemask production. We also discuss facemasks and their materials as sources of microplastics and how disposal procedures can potentially lead to the contamination of water resources. We herein review the potential of developing nanomaterial-based antiviral and self-cleaning facemasks. This review discusses these challenges and concludes that the use of sustainable and alternative facemask materials is a promising and viable solution. In this context, it has become essential to address the emerging challenges by developing a new class of facemasks that are effective against the virus, while being biodegradable and sustainable. This paper represents the potentials of natural and/or biodegradable polymers for manufacturing facemasks, such as wood-based polymers, chitosan, and other biodegradable synthetic polymers for achieving sustainability goals during and after pandemics.

Red Phosphorus: An Up-and-Coming Photocatalyst on the Horizon for Sustainable Energy Development and Environmental Remediation

Photocatalysis is a perennial solution that promises to resolve deep-rooted challenges related to environmental pollution and energy deficit through harvesting the inexhaustible and renewable solar energy. To date, a cornucopia of photocatalytic materials has been investigated with the research wave presently steered by the development of novel, affordable, and effective metal-free semiconductors with fascinating physicochemical and semiconducting characteristics. Coincidentally, the recently emerged red phosphorus (RP) semiconductor finds itself fitting perfectly into this category ascribed to its earth abundant, low-cost, and metal-free nature. More notably, the renowned red allotrope of the phosphorus family is spectacularly bestowed with strengthened optical absorption features, propitious electronic band configuration, and ease of functionalization and modification as well as high stability. Comprehensively detailing RP's roles and implications in photocatalysis, this review article will first include information on different RP allotropes and their chemical structures, followed by the meticulous scrutiny of their physicochemical and semiconducting properties such as electronic band structure, optical absorption features, and charge carrier dynamics. Besides that, state-of-the-art synthesis strategies for developing various RP allotropes and RP-based photocatalytic systems will also be outlined. In addition, modification or functionalization of RP with other semiconductors for promoting effective photocatalytic applications will be discussed to assess its versatility and feasibility as a high-performing photocatalytic system. Lastly, the challenges facing RP photocatalysts and future research directions will be included to propel the feasible development of RP-based systems with considerably augmented photocatalytic efficiency. This review article aspires to facilitate the rational development of multifunctional RP-based photocatalytic systems by widening the cognizance of rational engineering as well as to fine-tune the electronic, optical, and charge carrier properties of RP.

Application of β-Cyclodextrin metal-organic framework/titanium dioxide hybrid nanocomposite as dispersive solid-phase extraction adsorbent to organochlorine pesticide residues in honey samples

A simple and efficient dispersive solid-phase extraction (D-SPE) method combined with gas chromatography tandem mass spectrometry (GC-MS/MS) was developed to determine organochlorine pesticides (OCP) in honey. Firstly, a type of hybrid nanocomposite (CD-MOF/TiO₂) was prepared by grafting a metal-organic framework material synthesized with cyclodextrin as an organic ligand onto titanium dioxide. Then, the CD-MOF/TiO₂ was used as a D-SPE adsorbent to extract the OCP, and the effects of the amount of adsorbent, ultrasonic time, vortex time, pH, and salinity on the extraction were investigated using Plackett-Burman design and Box-Behnken Design. Under the optimized adsorption and desorption conditions, an analysis method that combined D-SPE with GC-MS/MS was established. The linear ranges of 14 OCP are 1-500 μg kg^-1 and the correlation coefficients are between 0.9991 and 1.000. The limits of detection and quantification vary from 0.01 to 0.04 μg kg^-1 and 0.04 to 0.12 μg kg^-1, respectively. The intra-day and inter-day precision of this method are suitable (RSDs% less than 11.3%). The established CD-MOF/TiO₂ / D-SPE method was used for the extraction of OCP in honey samples with recovery in the range of 76.4 to 114.3%. The results demonstrate that the CD-MOF/TiO₂ has a good selective enrichment ability for OCP and is suitable for the D-SPE pretreat of honey sample analysis.

Synthesis and application of g-C3N4/Fe3O4/Ag nanocomposite for the efficient photocatalytic inactivation of Escherichia coli and Bacillus subtilis bacteria in aqueous solutions

Contamination of water with bacteria is one of the main causes of waterborne diseases. The photocatalytic method on the basis of bacterial inactivation seems to be a suitable disinfectant due to the lack of by-products formation. Herein, g-C3N4/Fe3O4/Ag nanocomposite combined with UV-light irradiation was applied for the inactivation two well-known bacteria namely, E. coli and B. subtilis. The nanocomposite was prepared by a hydrothermal method, and subsequently it was characterized by XRD, FT-IR, SEM, EDX and PL analyses. The optimum conditions established for the inactivation of both bacteria were as follows: nanocomposite dosage 3 g/L and bacterial density of 103 CFU/mL. In the meantime, the efficient inactivation of E. coli and B. subtilis took 30 and 150 min, respectively. The results also revealed that inactivation rate dropped with an increase in the bacterial density. It is also pointed out that OH˚ was found out to be the main radical species involved in the inactivation process. Finally, the kinetic results indicated that the inactivation of E. coli and B. subtilis followed the Weibull model. It is concluded that C3N4/Fe3O4/Ag nanocomposite along with UV-light irradiation is highly effective in inactivating E. coli and B. subtilis bacteria in the aqueous solutions.

Floating Carbon-Doped TiO2 Photocatalyst with Metallic Underlayers Investigation for Polluted Water Treatment under Visible-Light Irradiation

In the current study, we analysed the influence of metallic underlayers on carbon-doped TiO2 films for RhB decomposition and Salmonella typhimurium inactivation under visible-light irradiation. All the experiments were divided into two parts. First, layered M/C-doped-TiO2 film structures (M = Ni, Nb, Cu) were prepared by magnetron sputtering technique on borosilicate glass substrates in the two-step deposition process. The influence of metal underlayer on the formation of the carbon-doped TiO2 films was characterised by X-ray diffractometer, scanning electron microscope, and atomic force microscope. The comparison between the visible-light assisted photocatalytic activity of M/C-doped TiO2 structures was performed by the photocatalytic bleaching tests of Rhodamine B dye aqueous solution. The best photocatalytic performance was observed for Ni/C-doped-TiO2 film combination. During the second part of the study, the Ni/C-doped-TiO2 film combination was deposited on high-density polyethylene beads which were selected as a floating substrate. The morphology and surface chemical analyses of the floating photocatalyst were performed. The viability and membrane permeability of Salmonella typhimurium were tested in cycling experiments under UV-B and visible-light irradiation. Three consecutive photocatalytic treatments of fresh bacteria suspensions with the same set of floating photocatalyst showed promising results, as after the third 1 h-long treatment bacteria viability was still reduced by 90% and 50% for UV-B and visible-light irradiation, respectively. The membrane permeability and ethidium fluorescence results suggest that Ni underlayer might have direct and indirect effect on the bacteria inactivation process. Additionally, relatively low loss of the photocatalyst efficiency suggests that floating C-doped TiO2 photocatalyst with the Ni underlayer might be seen as the possible solution for the used photocatalyst recovery issue.

Recent advances in photocatalytic removal of airborne pathogens in air

The abatement of airborne pathogens such as bacteria, viruses, and fungi has become an important goal of air-quality management. Efficient and effective treatment techniques such as photocatalysis are essential for disinfection of airborne microorganisms. This review focuses on recent advances in the formulation and development of photocatalytic disinfection, design of efficient photocatalysts, choice of photocatalytic reactor, removal and/or disinfection mechanisms, and the role of reactive ion species. Data from recent studies are analyzed to accurately assess the efficacy of such disinfection approaches. This review also highlights the application of innovative materials in individual and combined abatement systems against airborne bacterial, viral, and fungal pathogens. We discuss the efficiency and benefits presented by such systems, address the challenges, and provide a perspective for future research.

Use of the catalytic complex TiO2/red cabbage anthocyanins to reduce the biofilm formation by planktonic bacteria

The bacterial cells dwelling within the biofilm usually develop resistance against common disinfectants. In this current study, to improve the effectiveness of photocatalytic treatment, a natural sensitizer in combination with unsupported titanium dioxide nanoparticles (TiO₂-NPs) was used to optimize the absorbance of NPs in the visible region and, to enhance the catalytic activity of the semiconductor. Different kinetic parameters were determined according to the first-order and the biphasic models to evaluate the ability of tested bacteria to form biofilm under different photocatalytic treatment conditions. As a result, the addition of red cabbage anthocyanins (RCA) as photosensitizer allows the enhancement of biocide activity of TiO₂-NPs and the reduction of biofilm formation by tested bacteria.

Solar disinfection (SODIS) technologies as alternative for large-scale public drinking water supply: Advances and challenges

Gastrointestinal waterborne diseases, continue to stand out among the most lethal diseases in developing countries, because of consuming contaminated water taken from unsafe sources. Advances made in recent decades in methods of solar water disinfection (SODIS) have shown that SODIS is an effective and inexpensive method of providing drinking water, capable of substantially reducing the prevalence and mortality of waterborne diseases. The increased impact of SODIS in communities lacking drinking water services depends on a successful upgrade from conventional SODIS (based on PET bottle reactors) in high flow continuous flow systems for solar water disinfection (CFSSWD). This review aimed to identify the main limitations of conventional SODIS that hinder its application as a large-scale drinking water supply strategy, and to propose ways to overcome these limitations (without making it economically inaccessible) based on the current frontier of advances technological. It was found that the successful development of the CFSSWD depends on overcoming the current limitations of conventional SODIS and the development of systems whose configurations allow combining the properties of solar pasteurization (SOPAS) and SODIS. Different improvements need to be made to the main components of the CFSSWD, such as increasing the performance of solar radiation collectors, photo and thermal reactors and heat exchangers. The integration of disinfection technologies based on photocatalytic and photothermal nanomaterials also needs to be achieved. The performance evaluation of the CFSSWD should be made considering resistant microorganisms, such as the environmental resistance structures of bacteria or protozoa (spores or (oo)cysts) as targets of disinfection approaches.

Enhancement of optoelectronic properties of layered MgIn 2 Se 4 compound under uniaxial strain, an ab initio study

We argue that tuning the structure of a semiconductor offers abundant scope for use in a number of applications. In this work, by means of comprehensive density functional theory computations, we demonstrated that layered MgIn 2 Se 4 could be a promising candidate for future electronic and optoelectronic technologies. To do this task, we have applied a uniaxial strain in the z-direction. The results show that MgIn 2 Se 4 can support only a - 2.5 % of deformation without losing its dynamical stability. However, we showed that the effect of strain strongly affects the bonding pattern, which tends to increase the bandgap value. Both the charge density and noncovalent interactions were analyzed to understand this behavior. In addition, we saw that the application of non-hydrostatic pressure also enhanced the photocatalytic/optoelectronic performance of the investigated material, offering useful insights into layered MgIn 2 Se 4 for future development in this area.

Controlling morphology evolution of titanium oxide-gold nanourchin for photocatalytic degradation of dyes and photoinactivation of bacteria in the infected wound

We report a one-pot, room-temperature, morphology-controlled synthesis of titanium oxide (TiO_x)-gold nanocomposites (TiO_x-Au NCs) using HAuCl₄ and TiCl₃ as precursors, and catechin as reducing agent. TiO_x-Au NCs have a range of morphologies from star-like to urchin-like shape depending on the concentration of TiCl₃ in the reaction mixture. The urchin-shaped TiO_x-Au NCs exhibited excellent photocatalytic activity toward dye degradation due to strong light absorption, plasmon-induced excitation, high conductivity of the gold, and reduced hole-electron pair recombination. TiO_x-Au NCs have the advantage of a wide range of light absorption and surface plasmon absorption-mediated excitation due to their abundant gold spikes, which enabled the degradation of dyes over 97% in 60 min, using a xenon lamp as a light source. In addition, TiO_x-Au NCs are highly efficient for the photoinactivation of Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA), and Candida albicans through the photodynamic generation of reactive oxygen species (ROS) and damage to the bacterial membrane. The catechin derivatives on the NCs effectively promoted curing MRSA infected wounds in rats through inducing collagen synthesis, migration of keratinocytes, and neovascularization.

State-of-the-art and prospects of Zn-containing layered double hydroxides (Zn-LDH)-based materials for photocatalytic water remediation

With the rapid worldwide development of industry and human activities, increasing amounts of multifarious contaminants have significantly threatened environmental ecosystems and human health. Solar photocatalytic decontamination, as an environmentally friendly technology, has been regarded as a good approach to eliminate water pollutants. To date, various photocatalysts have been developed for the purpose of water remediation. Zn-containing layered double hydroxides (Zn-LDHs) and their derivatives are promising candidates due to their suitable band edge positions (oxidation-reduction potentials) for high photocatalytic performances, flexible properties derived from adjustable components and tailorable electronic structures, chemical stabilities, and low toxicities. This review focuses on the fabrication and modification of Zn-LDHs and their photocatalytic applications for the elimination of contaminants in water, including the degradation of toxic organic pollutants, transfer of hazardous heavy metals to lower toxicity heavy metals, and bacterial inactivation. The mechanisms involved in the photocatalytic processes are also thoroughly reviewed. Finally, the emerging scientific and engineering opportunities and challenges in environmental photocatalysis are presented. This review provides basic insights into the construction of Zn-LDH-based materials with high photocatalytic activities and new perspectives on their applications for the photocatalytic elimination of contaminants, which is helpful for the development of photocatalysis for environmental remediation from the lab to industry.

The Antimicrobial Properties of Nanotitania Extract and Its Role in Inhibiting the Growth of Klebsiella pneumonia and Haemophilus influenza

Titanium dioxide (TiO2) is an antimicrobial agent which is considered of potential value in inhibiting the growth of multiple bacteria. Klebsiella pneumonia and Haemophilus influenza are two of the most common respiratory infection pathogens, and are the most. Klebsiella pneumonia causes fatal meningitis, while Haemophilus influenza causes mortality even in younger patients. Both are associated with bacteremia and mortality. The purpose of this study was to test a new antibacterial material, namely nanotitania extract combined with 0.03% silver that was developed at Universiti Malaysia Sabah (UMS) and tested against K. pneumonia and H. influenza. The nanoparticles were synthesized through a modified hydrothermal process, combined with molten salt and proven to have excellent crystallinity, with the band-gap energy falling in the visible light spectrum. The nanoparticle extract was tested using a macro-dilutional method, which involved combining it with 0.03% silver solution during the process of nanoparticle synthesis and then introducing it to the bacteria. A positive control containing the bacteria minus the nanoparticles extract was also prepared. 25 mg/mL, 12.5 mg/mL, and 6.25 mg/mL concentrations of the samples were produced using the macro dilution method. After adding the bacteria to multiple concentrations of nanoparticle extract, the suspensions were incubated for 24 h at a temperature of 37 °C. The suspensions were then spread on Mueller-Hinton agar (K. pneumonia) and chocolate blood agar (H. influenza), where the growth of bacteria was observed after 24 h. Nanoparticle extract in combination with silver at 0.03% was proven to have potential as an antimicrobial agent as it was able to inhibit H. influenza at all concentrations. Furthermore, it was also shown to be capable of inhibiting K. pneumonia at concentrations of 25 mg/mL and 50 mg/mL. In conclusion, the nanoparticle extract, when tested using a macro-dilutional method, displayed antimicrobial properties which were proven effective against the growth of both K. pneumonia and H. influenza.