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

Deciphering the virucidal potential of hydroxyl radical during ozonation: Implications for waterborne virus inactivation

The heightened public health risks associated with viral contamination in water have led to a strong emphasis on effective disinfection strategies. Ozone is a potent disinfectant widely employed for the inactivation of pathogens, yet comprehensive reports detailing the virucidal efficacy of hydroxyl radical (•OH) generated during ozonation are limited. The present research meticulously deciphered the role and influencing factors of •OH during ozone disinfection processes, elucidating how •OH enhanced ozone-mediated virus inactivation from both kinetic and molecular biological perspectives. The inactivation rate constants of ozone-derived •OH for Phi6 (9.67 × 1010 M-1 s-1) and PhiX174 (3.85 × 1010 M-1 s-1) were 4-5 orders of magnitude higher than those of ozone molecules. At 20 °C and pH 7.0, the contribution of •OH to the reduction of viral infectivity has been quantified as ranging from 11.3 % to 52.7 %. The yield of •OH increased notably as pH rose from 6.0 to 8.0, which was the principal cause for the accelerated apparent virus inactivation rates by ozone. An elevation in temperature (10-30 °C) had a negligible impact on •OH yield but facilitated virus removal by enhancing the reactivity of oxidants with viral particles. The damage inflicted on the viral genome by •OH vastly surpassed that caused by ozone, with the log reduction in gene copies in the presence of •OH being 297-343 % higher than the effect observed with ozone alone. The potential interaction sites of ozone and •OH with viral genetic material were predicted using Density Functional Theory static calculations and further compared. The present research offers comprehensive insights into the inactivation capabilities and underlying mechanisms of •OH for the effective control of waterborne viruses, establishing a theoretical foundation for employing the advanced oxidation properties of ozone-derived •OH in developing innovative water disinfection strategies.

Degradation of ciprofloxacin using CoFe2O4@three-dimensional TiO2@graphene aerogels composite: kinetic, reusability, mineralization, degradation pathway, and toxicity assessment

An investigation into the degradation of ciprofloxacin (CIP) under visible light was carried out using an efficient photocatalyst, i.e., CoFe2O4@3D-TiO2@GA, synthesized by doping CoFe2O4@three-dimensional-TiO2 into a hierarchical porous graphene aerogel. Optimal conditions for achieving complete removal of CIP involved a reaction time of 60 min, a catalyst dose of 0.6 g/L, an initial CIP concentration of 25 mg/L, and a solution pH range of 3-5. The reusability of CoFe2O4@3D-TiO2@GA was observed to remain high even after four consecutive cycles, as the CIP degradation only slightly decreased from 94.3 to 87.1%. Following a 2-h photocatalytic degradation process, the intermediate products within the CIP solution no longer posed a threat to E. coli. The TOC analysis confirmed that CIP achieved 86% total mineralization. In the raw sewage, the BOD5/COD and BOD5/TOC ratios were 0.774 and 0.232, respectively. However, after a 120-min photocatalytic reaction, these ratios increased to 1.38 and 0.754, respectively. These findings suggest that non-biological sewage can be successfully transformed into biodegradable effluent through photocatalytic degradation. The photocatalytic process has a reaction rate coefficient that is 8.7 to 20.7 times higher than the adsorption process, depending on the concentration. The half-life constant is 117.4 min for the optimal concentration of 10 mg/L for the adsorption process, while for the photocatalytic process, it is 6.24 min. The research has highlighted the importance of integrating adsorption and photocatalysis, whereby primary reactive oxidative species, including superoxide and hydroxyl radicals, were identified. The study presents a pioneering approach for producing CoFe2O4@3D-TiO2@GA, which has promising potential for environmental applications utilizing visible light.

Perspectives for Photocatalytic Decomposition of Environmental Pollutants on Photoactive Particles of Soil Minerals

The literature shows that both in laboratory and in industrial conditions, the photocatalytic oxidation method copes quite well with degradation of most environmental toxins and pathogenic microorganisms. However, the effective utilization of photocatalytic processes for environmental decontamination and disinfection requires significant technological advancement in both the area of semiconductor material synthesis and its application. Here, we focused on the presence and "photocatalytic capability" of photocatalysts among soil minerals and their potential contributions to the environmental decontamination in vitro and in vivo. Reactions caused by sunlight on the soil surface are involved in its normal redox activity, taking part also in the soil decontamination. However, their importance for decontamination in vivo cannot be overstated, due to the diversity of soils on the Earth, which is caused by the environmental conditions, such as climate, parent material, relief, vegetation, etc. The sunlight-induced reactions are just a part of complicated soil chemistry processes dependent on a plethora of environmental determinates. The multiplicity of affecting factors, which we tried to sketch from the perspective of chemists and environmental scientists, makes us rather skeptical about the effectiveness of the photocatalytic decontamination in vivo. On the other hand, there is a huge potential of the soils as the alternative and probably cheaper source of useful photocatalytic materials of unique properties. In our opinion, establishing collaboration between experts from different disciplines is the most crucial opportunity, as well as a challenge, for the advancement of photocatalysis.

Recent advances and new insights on the construction of photocatalytic systems for environmental disinfection

Photocatalysis, as a sustainable and environmentally friendly green technology, has garnered widespread recognition and application across various fields. Especially its potential in environmental disinfection has been highly valued by researchers. This study commences with foundational research on photocatalytic disinfection technology and provides a comprehensive overview of its current developmental status. It elucidates the complexity of the interface reaction mechanism between photocatalysts and microorganisms, providing valuable insights from the perspectives of materials and microorganisms. This study reviews the latest design and modification strategies (Build heterojunction, defect engineering, and heteroatom doping) for photocatalysts in environmental disinfection. Moreover, this study investigates the research focuses and links in constructing photocatalytic disinfection systems, including photochemical reactors, light sources, and material immobilization technologies. It studies the complex challenges and influencing factors generated by different environmental media during the disinfection process. Simultaneously, a comprehensive review extensively covers the research status of photocatalytic disinfection concerning bacteria, fungi, and viruses. It reveals the observable efficiency differences caused by the microstructure of microorganisms during photocatalytic reactions. Based on these influencing factors, the economy and effectiveness of photocatalytic disinfection systems are analyzed and discussed. Finally, this study summarizes the current application status of photocatalytic disinfection products. The challenges faced by the synthesis and application of future photocatalysts are proposed, and the future development in this field is discussed. The potential for research and innovation has been further emphasized, with the core on improving efficiency, reducing costs, and strengthening the practical application of photocatalysis in environmental disinfection.

Experimental study on the microwave radiation disinfection of E. coli on SiC composite filter

Filter is an important component in the air-conditioning system. The airborne microorganisms can be intercepted and further multiply on the filter, which might cause a secondary pollution. The present work proposed a SiC composite filter (SCF), namely combining the filter with the absorbing material SiC. The disinfection efficiency (η) and mechanism of the microwave radiation method (MRM) on E. coli and S. aureus attached to the SCF were experimentally explored. The impacts of the microwave power (P) and disinfection time (t) on η were investigated. The results show that the SCF can be heated well by the microwave, but the normal filter (NF) cannot. The MRM can effectively and rapidly disinfect bacteria on the SCF at a sufficiently high P and an appropriate t. Generally, η increases with P and t. Under a specific P, η can be only increased with t at a certain range and a peak η might be reached. When this peak is achieved, η will not be further increased with t. The disinfection by the MRM is attributed to the thermal and non-thermal effects. Specially, at P = 600 W and t = 10 min, the non-thermal effect contributes about 89.6% to the disinfection of the E. coli and about 43.1% to the S. aureus. A universal relationship between η and temperature is given for E. coli and S. aureus to predict η at various P and t. Finally, the effective temperatures required by the MRM to satisfactorily disinfect bacteria on the SCF are identified, i.e., about 41 °C for E. coli and 71 °C for S. aureus.

Analysis of a UV photocatalytic oxidation-based disinfection system for hydroxyl radicals, negative air ions generation and their impact on inactivation of pathogenic micro-organisms

This work presents a large-scale surface disinfection system, which has a unique lantern arrangement of ultraviolet-C (UV-C) light (254 nm) in conjunction with nanotechnology in a protective biosafety environment. Shadow regions are best dealt in this system by the generation of hydroxyl radicals (•OH) and negative air ions at sites where UV light cannot penetrate. More than 35 000 negative air ions/cm3 along with •OH were produced continuously in the disinfection chamber through the advanced photocatalytic oxidation process [UV-C + titanium dioxide (TiO2)]. The arrangement has been made to provide an optimized UV irradiation (∼2 mW/cm2) throughout the disinfection system. In order to distinguish between effects arising from (i) the action of UV dose alone and (ii) the action of UV dose along with •OH and negative air ions, E. coli and P. aeruginosa were chosen for bacterial testing and two interventions were made. The first intervention involved placing only UV lamps in the disinfection chamber to see the effect of only UV dose on bacterial inactivation efficiency. The second intervention involved placing the TiO2 nanoparticle coated aluminum plates along with UV lamps; this allows for the generation of negative air ions and •OH inside the disinfection chamber and enhanced bacterial inactivation efficiency. More than 95% bacterial inactivation efficiency has been reported in the case of UV-C + TiO2 compared to only 77% in UV only at the same time interval (90 s).

Modeling the Interaction of Coronavirus Membrane Phospholipids with Photocatalitically Active Titanium Dioxide

The outbreak of viral infectious diseases urges airborne droplet and surface disinfection strategies, which may rely on photocatalytic semiconductors. A lipid bilayer membrane generally encloses coronaviruses and promotes the anchoring on the semiconductor surface, where, upon photon absorption, electron-hole pairs are produced, which can react with adsorbed oxygen-containing species and lead to the formation of reactive oxygen species (ROSs). The photogenerated ROSs may support the disruptive oxidation of the lipidic membrane and pathogen death. Density functional theory calculations are employed to investigate adsorption modes, energetics, and electronic structure of a reference phospholipid on anatase TiO2 nanoparticles. The phospholipid covalently bound on TiO2, engaging a stronger adsorption on the (101) than on the (001) surface. The energetically most stable structure involves the formation of four covalent bonds through phosphate and carbonyl oxygen atoms. The adsorbates show a reduction of the band gap compared with standalone TiO2, suggesting a significant interfacial coupling.

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.

The environment, epidemics, and human health

In this editorial piece, the Editors of the Virtual Special Issue (VSI) "The environment, epidemics, and human health" comment on the papers accepted for publication, which were selected after peer-reviewing among all those manuscripts submitted to the Special Issue. In view of the title of the VSI, it is clear that its aim goes beyond the COVID-19 pandemic, trying to explore relations among environmental aspects, any kind of epidemics, and human health. However, COVID-19 is still hitting as a global and current main issue, causing that manuscripts dealing with this disease and the SARS-CoV-2 virus are of high relevance in the whole set of research papers published.

Bifunctional 2D/2D g-C3N4/BiO2-x nanosheets heterojunction for bacterial disinfection mechanisms under visible and near-infrared light irradiation

The efficient deployment of visible and near-infrared (NIR) light for photocatalytic disinfection is of great concern a matter. Herein, we report a specific bifunctional 2D/2D g-C₃N₄/BiO_2-x nanosheets heterojunction, prepared through a self-assembly approach. Delightfully, the obtained 2D/2D heterojunctions exhibited satisfactory photocatalytic disinfection performance towards Escherichia coli K-12 (E. coli K-12) under visible light irradiation, which was credited to the Z-scheme interfacial heterojunction facilitating the migration of photogenerated carries. The photoactivity enhancement driven by NIR light illumination was ascribed to the cooperative synergy effect of photothermal effect and "hot electrons", engineering efficient charge transfer. Intriguingly, the carboxyl groups emerged on g-C₃N₄ nanosheets contributed a vital role in establishing the enhanced photocatalytic reaction. Moreover, the disinfection mechanism was systematically described. The cell membrane was destroyed, evidenced by the generation of lipid peroxidation reaction and loss of energy metabolism. Subsequently, the damage of defense enzymes and release of intracellular constituents announced the irreversible death of E. coli K-12. Interestingly enough, considerable microbial community shifts of surface water were observed after visible and NIR light exposure, highlighting the critical feature of disinfection process in shaping microbial communities. The authors believe that this work gives a fresh light on the feasibility of heterostructures-enabled disinfection processes.

Boron doped Fluorescent Carbon Nano Dots for reduction of ionic dyes and as Encryption and decryption QR code labels

This work discusses the synthesis of fluorescent undoped and boron-doped carbon nanodots (BDCNDs) by a simple hydrothermal approach using Tribulus terretris as carbon precursor and boric acid as boron source....