Disinfection Mechanism Research Articles

Quantitative evaluation of the antibacterial factors of ZnO nanorod arrays under dark conditions: Physical and chemical effects on Escherichia coli inactivation

Although zinc oxide nanorod (ZnO NR) arrays are a nanomaterial that offers efficient bactericidal activity, they have not been systematically evaluated to quantitatively investigate their disinfection mechanism under dark conditions. In this study, ZnO NR arrays of different lengths (0.5–4 μm) were uniformly grown via hydrothermal synthesis. The longer arrays exhibited higher Escherichia coli (E. coli) inactivation efficiency up to 94.2% even under darkness for 30 min. When the NR arrays were coated via Al2O3 atomic layer deposition, the inactivation efficiency was decreased to 56.4% because the generation of reactive oxygen species (ROS) and the leaching of Zn2+ ions were both hindered by the surficial coverage of defect sites. The morphological effect, i.e., the mechanical rupture of E. coli on the surface, contributed 56.4% of the bactericidal efficiency; chemical effects, i.e., ROS formation and zinc ion release, contributed the remaining 37.8% under dark conditions. The bactericidal effect of fabricated ZnO NR arrays was further validated in bottled and pond water spiked with E. coli, exhibiting 87.5% and 80.4% inactivation efficiencies, respectively, within 30 min. Understanding these antibacterial mechanisms is not only of significance for research in this and related fields but also beneficial for potential application in various fields, e.g., biomedical and antifouling areas.

The inactivation mechanism of chemical disinfection against SARS-CoV-2: from MD and DFT perspectives.

Exploring effective disinfection methods and understanding their mechanisms on the new coronavirus is becoming more active due to the outbreak of novel coronavirus pneumonia (COVID-19) caused by severe acute respiratory coronavirus 2 (SARS-CoV-2). By combining molecular dynamics and first-principles calculations, we investigate the interaction mechanism of chemical agents with 3CL hydrolase of SARS-CoV-2. The radial distribution functions indicate that the biocidal ingredients are sensitive to the unsaturated oxygen atoms of 3CL hydrolase and their interactions remarkably depend on the concentration of the biocidal ingredients. Besides, we find that the adsorption performance of the active ingredients for the unsaturated oxygen atoms is superior to other styles of atoms. These computational results not only decipher the inactivation mechanism of chemical agents against SARS-CoV-2 from the molecule-level perspective, but also provide a theoretical basis for the development and application of new chemical methods with a high disinfection efficiency.

Electrocoagulation Process in the Context of Disinfection Mechanism

During the last three decades, the electrocoagulation (EC) process has known an exemplary renaissance in the field of water and wastewater treatment. Sev-eral researchers focused on applying this electrochemical technology in re-moving diverse pollutants such as pathogens. During EC method, the coagulant is furnished via solubilizing sacrificial electrodes upon an applied electric field. The easiness of the technology and the side phenomena involving the generation of gas bubbles are the major advantages. This work discusses briefly the main achievements and mechanisms in employing EC in disinfecting water. In the EC process, the microbes may be demobilized thanks to the direct adsorption on the surface of the anode pursued by electron transfer, and physical elimination through floating pathogens with formed hydrogen gas and/or precipitating with the produced flocs. Integrating EC with free radical assisted processes (e.g., electrooxidation), magnetic field and/or ultrasonic field remains an encouraging method to promote its implantation at full scale. Membrane processes should be considered as safe barriers towards disinfection by-products and hydroxyl radicals.

Metagenomic Analysis of Infectious F-Specific RNA Bacteriophage Strains in Wastewater Treatment and Disinfection Processes.

F-specific RNA bacteriophages (FRNAPHs) can be used to indicate water contamination and the fate of viruses in wastewater treatment plants (WWTPs). However, the occurrence of FRNAPH strains in WWTPs is relatively unknown, whereas FRNAPH genotypes (GI–GIV) are well documented. This study investigated the diversity of infectious FRNAPH strains in wastewater treatment and disinfection processes using cell culture combined with next-generation sequencing (integrated culture–NGS (IC–NGS)). A total of 32 infectious strains belonging to FRNAPH GI (nine strains), GI-JS (two strains), GII (nine strains), GIII (seven strains), and GIV (five strains) were detected in wastewater samples. The strains of FRNAPH GI and GII exhibited greater resistance to wastewater treatment than those of GIII. The IC–NGS results in the disinfected samples successfully reflected the infectivity of FRNAPHs by evaluating the relationship between IC–NGS results and the integrated culture–reverse-transcription polymerase chain reaction combined with the most probable number assay, which can detect infectious FRNAPH genotypes. The diversity of infectious FRNAPH strains in the disinfected samples indicates that certain strains are more resistant to chlorine (DL52, GI-JS; T72, GII) and ultraviolet (T72, GII) disinfection. It is possible that investigating these disinfectant-resistant strains could reveal effective mechanisms of viral disinfection.

Effectiveness of reactive oxygen species generated from rGO/CdS QD heterostructure for photodegradation and disinfection of pollutants in waste water.

The present study investigates the role of reactive oxygen species (ROS) generated on surface of nanophotocatalyst in wastewater treatment discharged from exponentially growing industries. A facile synthetic route is presented to produce reduced graphene oxide/CdS quantum dot (rGO/CdS QD) heterostructure by monowave-assisted solvothermal method where room temperature ionic liquid 1-ethyl-3-methylimidazolium thiocyanate serves as a "green" precursor. The prepared photocatalyst was tested for: (1) photodegradation performance against various cationic dyes, anionic dyes, and antibiotics as model organic water pollutants; and (2) disinfection performance against gram-positive S. aureus and gram-negative E. coli bacterial strains as pathogenic water pollutants. The negative surface charge of rGO/CdS QD precisely attracted the cationic dye molecules to its surface and degraded the dyes at a higher rate. Moreover, excellent antibacterial activity of rGO/CdS QD were observed against S. aureus and E. coli with a minimum inhibitory concentration of 16 μg ml-1 and 32 μg ml-1, respectively. A plausible mechanism of the photocatalytic activity suggested that ROS with strong oxidizing ability reacts with the organic pollutants to mineralize them into CO2, H2O or some other small molecules, and reacts with pathogens to damage the macromolecules like proteins, lipids, DNA, etc in the bacterial cells. Among all the surface generated ROS, hydroxyl radicals was found to be the main contributor in the photodegradation and disinfection mechanism.

Defective engineering in graphitic carbon nitride nanosheet for efficient photocatalytic pathogenic bacteria disinfection

In this work, porous defective g-C3N4 ultrathin nanosheets were prepared through thermal condensation of freeze-dried precursor. First-principles density functional theory (DFT) calculations well predicted the role of VN in modulating energy levels and photocatalytic properties. The optimally defective g-C3N4 manifested the better photocatalytic disinfection performance towards E. coli and S. aureus than pristine g-C3N4, respectively. The gradual damaged cell membrane for E. coli and the intimate mechanical constraint for S. aureus was imaged to further decipher the antibacterial behavior. The synergistic effect of enhanced visible light absorption ability, more exposed active sites and improved photogenerated charge separation was responsible for excellent photocatalytic disinfection activity. The photocatalytic disinfection mechanism towards E. coli was explored by electron spinning resonance (EPR), radical scavenger and spectral quantification technology, confirming the major role of h+ and O2−. This study provides alternative strategy for rational design of effective g-C3N4-based photocatalysts by defective engineering for environmental remediation.

Free Chlorine Disinfection Mechanisms of Rotaviruses and Human Norovirus Surrogate Tulane Virus Attached to Fresh Produce Surfaces.

To fill the knowledge gap on how effective free chlorine is against viral-contaminated produce, we inoculated the surfaces of outdoor- or greenhouse-grown kale and mustard with Rotavirus (RV) or a human norovirus surrogate (Tulane virus, TV) and then disinfected the leaves with free chlorine. Disinfection efficacies for RV strain OSU and Wa were approximately 1-log10 higher when attached to mustard than to kale. Similar disinfection efficacies were observed for TV attached to mustard or kale. When examining TV and RV OSU in suspension (not attached to leaf surfaces), TV was more resistant to free chlorine than RV OSU. Inactivation efficacies were higher for these viruses in suspension versus viruses attached to produce the surface. We also found that free chlorine damaged viral capsids, allowing free chlorine access to viral RNA to damage viral genomes. Exposure to free chlorine at 1.7 ppm over 1 min caused VP8* of RV OSU to lose its ability to bind to its host receptors. TV lost its ability to bind to its receptor only after exposure to free chlorine at 29 ppm over 1 min. Thus, to reduce foodborne viral infections, it is important to consider the differences in virus' reactivity and inactivation mechanisms with free chlorine.

Visible light driven CuBi2O4/Bi2MoO6 p-n heterojunction with enhanced photocatalytic inactivation of E. coli and mechanism insight

Here, a novel CuBi2O4/Bi2MoO6 (CBO/BMO) p-n heterojunction was fabricated and exhibited markedly improved photocatalytic inactivation capacity of E. coli cells under visible light excitation (λ > 420 nm) compared with pure CuBi2O4 and Bi2MoO6. The CBO/BMO-0.5 hybrid displayed the highest photoinactivation ability which could completely inactivate the E. coli cellswithin 4 h. The mechanism of photocatalytic disinfection towards E. coli of CBO/BMO heterojunctions was attributed to the disruption of cell-membrane, leakage and damage of cellular content including total protein and DNA as verified with SEM, fluorescence-base dead/live stain, sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) and agarose gel electrophoresis (AGE). Additionally, the scavenge experiments showed that the reactive species h+, e− and •O2−play the predominant role in the photocatalytic system of CBO/BMO hybrids. The improved photocatalytic activity of CBO/BMO composites was mainly attributed to the promotion of spatial separation and migration rate of photoproduced electron-hole pairs, enhancement of visible light absorption and more generation of reactive species (•O2−) on the interface of catalyst and water which was demonstrated by nitroblue tetrazolium (NBT) and EPR. Our work indicated that construction of CuBi2O4/Bi2MoO6 p-n heterostructure photocatalyst is a promising environmental friendly alternative method to deal with the biohazards of pathogenic microorganisms.

Disinfection mechanism of E. coli by CNT-TiO2 composites: Photocatalytic inactivation vs. physical separation

Magnetic carbon nanotube (MCNT) composites with titanium dioxide (TiO2) have an enhanced photocatalytic disinfection efficiency (i.e. higher disinfection rate) and better applicability (i.e. solar light applicability and catalyst separation using its magnetic property) than bare TiO2 and/or MCNT. However, the role and mechanism of MCNT in the disinfection process are still unclear. Therefore, this study aimed at investigating the disinfection mechanism of Escherichia coli using MCNT-TiO2 nanocomposites under various conditions (i.e. the presence and absence of light and reactive oxygen species scavengers, and different MCNT-TiO2 ratio) and photocatalytic disinfection models. The results showed that (i) MCNT and its nanocomposites with TiO2 had much higher disinfection efficiencies than bare TiO2, (ii) the physical bacterial capture was the dominant disinfection mechanism, (iii) the higher disinfection rate was found at an optimum MCNT:TiO2 ratio of 5:1 under the tested experimental conditions, (iv) hydroxyl radical (OH) was the influencing reactive oxygen species on the photocatalytic disinfection using MCNT-TiO2, and (v) good correlation between experimental parameters (i.e. carbon contents, surface area and concentration of MCNT-TiO2) and the contribution rate of physical and photocatalysis reactions. The finding from this study and the methods proposed herein are essential for understanding the photocatalytic disinfection processes using TiO2 and its carbonaceous nanocomposites, which can promote the application of photocatalytic disinfection process.

Enhanced photocatalytic disinfection of Escherichia coli K-12 by porous g-C3N4 nanosheets: Combined effect of photo-generated and intracellular ROSs

The porous graphitic carbon nitride nanosheets (PCNSs) with high yields were synthesized by using one–step chemical exfoliation method. PCNSs accelerated separation efficiency of photo-generated electron−hole pairs in comparison to bulk graphitic carbon nitride. The PCNS5 (exfoliation for 5 h) exhibited optimal photocatalytic disinfection capability towards Escherichia coli K-12 under simulated solar light irradiation with complete disinfection of 6.5 log10 cfu/mL of E. coil K-12 within 2 h. The enhanced photocatalytic activity of PCNS5 originated from mesoporous nanosheet structure. The possible mechanism of photocatalytic disinfection has proposed that intracellular reactive oxygen species levels and the activities of antioxidant enzymes (e.g., catalase and superoxide dismutase) were enhanced. Transmission electron microscope images observed during photocatalytic disinfection process suggested that the cell membrane was regarded as the first target for oxidation, resulting in a faster leakage of cytoplasmic content and finally degradation of DNA leading to bacterial death. Furthermore, the trapping experiment showed that superoxide radical (•O2−) and holes (h+) were responsible for E. coli K-12 disinfection by PCNS5.

Differences in Viral Disinfection Mechanisms as Revealed by Quantitative Transfection of Echovirus 11 Genomes.

Virus inactivation mechanisms can be elucidated by methods that measure the loss of specific virus functionality (e.g., host attachment, genome internalization, and genome replication). Genome functionality is frequently assessed by PCR-based methods, which are indirect and potentially inaccurate; genome damage that affects detection by high-fidelity PCR enzymes may not adversely affect the ability of actual cellular enzymes to produce functional virus. Therefore, we developed here a transfection-based assay to quantitatively determine viral genome functionality by inserting viral RNA into host cells directly to measure their ability to produce new functional viruses from damaged viral genomes. Echovirus 11 was treated with ozone, free chlorine (FC), UV light at 254 nm (UV254), or heat, and then the reductions in genome functionality and infectivity were compared. Ozone reduced genome functionality proportionally to infectivity, indicating that genome damage is the main mechanism of virus inactivation. In contrast, FC caused little or no loss of genome functionality compared to infectivity, indicating a larger role for protein damage. For UV254, genome functionality loss accounted for approximately 60% of virus inactivation, with the remainder presumably due to protein damage. Heat treatment resulted in no reduction in genome functionality, in agreement with the understanding that heat inactivation results from capsid damage. Our results indicate that there is a fundamental difference between genome integrity reductions measured by PCR enzymes in previous studies and actual genome functionality (whether the genome can produce virus) after disinfection. Compared to PCR, quantitative transfection assays provide a more realistic picture of actual viral genome functionality and overall inactivation mechanisms during disinfection.IMPORTANCE This study provides a new tool for assessing virus inactivation mechanisms by directly measuring a viral genome's ability to produce new viruses after disinfection. In addition, we identify a potential pitfall of PCR for determining virus genome damage, which does not reflect whether a genome is truly functional. The results presented here using quantitative transfection corroborate previously suggested virus inactivation mechanisms for some virus inactivation methods (heat) while bringing additional insights for others (ozone, FC, and UV254). The developed transfection method provides a more mechanistic approach for the assessment of actual virus inactivation by common water disinfectants.

Visible-Light-Mediated Photodynamic Water Disinfection @ Bimetallic-Doped Hybrid Clay Nanocomposites.

This study reports a new class of photocatalytic hybrid clay nanocomposites prepared from low-cost sources (kaolinite clay and Carica papaya seeds) doped with Zn and Cu salts via a solvothermal process. X-ray diffraction analysis suggests that Cu-doping and Cu/Zn-doping introduce new phases into the crystalline structure of Kaolinite clay, which is linked to the reduced band gap of kaolinite from typically between 4.9 and 8.2 eV to 2.69 eV for Cu-doped and 1.5 eV for Cu/Zn hybrid clay nanocomposites (Nisar, J.; Århammar, C.; Jämstorp, E.; Ahuja, R. Phys. Rev. B 2011, 84, 075120). In the presence of solar light irradiation, Cu- and Cu/Zn-doped nanocomposites facilitate the electron-hole pair separation. This promotes the generation of singlet oxygen which in turn improves the water disinfection efficiencies of these novel nanocomposite materials. The nanocomposite materials were further characterized using high-resolution scanning electron microscopy, fluorimetry, thermogravimetric analysis, and Raman spectroscopy. The breakthrough times of the nanocomposites for a fixed bed mode of disinfection of water contaminated with 2.32 × 107 cfu/mL E. coli ATCC 25922 under solar light irradiation are 25 h for Zn-doped, 30 h for Cu-doped, and 35 h for Cu/Zn-doped nanocomposites. In the presence of multidrug and multimetal resistant strains of E. coli, the breakthrough time decreases significantly. Zn-only doped nanocomposites are not photocatalytically active. In the absence of light, the nanocomposites are still effective in decontaminating water, although less efficient than under solar light irradiation. Electrostatic interaction, metal toxicity, and release of singlet oxygen (only in the Cu-doped and Cu/Zn-doped nanocomposites) are the three disinfection mechanisms by which these nanocomposites disinfect water. A regrowth study indicates the absence of any living E. coli cells in treated water even after 4 days. These data and the long hydraulic times (under gravity) exhibited by these nanocomposites during photodisinfection of water indicate an unusually high potential of these nanocomposites as efficient, affordable, and sustainable point-of-use systems for the disinfection of water in developing countries.

Visible-light-driven photocatalytic disinfection mechanism of Pb-BiFeO3/rGO photocatalyst

While the visible-light-driven photocatalytic disinfection techniques for drinking water have recently attracted tremendous attentions, it is necessary to further improve the solar energy utilization efficiency. In this study, we synthesized Pb-BiFeO3 photocatalysts doped with different amounts of reduced graphene oxide (Pb-BiFeO3/rGO). The photocatalytic disinfection efficiencies toward gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) were evaluated under visible-light irradiation (λ ≥ 400 nm). The results indicated that Pb-BiFeO3 with 0.5 wt% rGO (Pb-BiFeO3/0.5% rGO) exhibited the highest disinfection efficiency. Complete inactivation was reached within 30 min and 90 min for E. coli and S. aureus, respectively. The transcriptomic analysis results indicated that Pb-BiFeO3/0.5% rGO deregulates the genes in E. coli cells that are involved in the cell membrane damage and oxidative stress responses. This was validated by the cell leakage of nucleic acids or proteins, transmission electron microscopy images of the bacteria, and the disinfection efficiency decrease caused by the introduction of scavenger of hydroxyl radical (HO•). Metal ions (Pb2+, Bi2+, and Fe3+) released from the photocatalysts did not contribute to the disinfection process. For the first time, our results elucidated that the photocatalytic disinfection mechanism of Pb-BiFeO3/rGO toward E. coli was mainly associated with oxidative stress due to HO• generation and the loss of membrane integrity from direct contact with the photocatalyst. After four consecutive cycles, the Pb-BiFeO3/0.5% rGO photocatalyst exhibited a strong antibacterial efficiency. The excellent disinfection efficiency and stability of Pb-BiFeO3/0.5% rGO suggests that this photocatalyst shows great potential for drinking water disinfection.

Integrating a new adaptive PV system for ozone production process

Available data from 2013 suggest that 17% of the global population does not have access to electricity, 95% of those live in sub-Saharan Africa and developing Asia, with sub-Saharan Africa leading with 80%. This lack of electrical power accessibility reduces the number of water sanitation facilities; so the population faces a constant life-threatening risk when it comes to drinkable water because water sources are often highly polluted with germs and bacteria. The main purpose of this study is the design and implementation of a water treatment system based on the ozone disinfection mechanism and powered by solar renewable energy. The particularity of this system is its low cost versus high efficiency, and the heart of the system is a half-bridge inverter built around 16F628A microcontroller connecting the PV panel to the ozone generator. An experimental study was conducted using polluted water to test the effectiveness of the filtering system.

Photocatalytic disinfection efficiency of 2D structure graphitic carbon nitride-based nanocomposites: a review

Nanostructured carbon-based photocatalysts have gained attention in photocatalytic disinfection of microbial species. With distinctive features of possessing appropriate electronic band gap structure and high chemical and thermal stability, metal-free polymeric 2D stacked structure graphitic carbon nitride (g-C3N4) is an important photocatalytic material for environmental and energy applications. Besides, it has the potential for inactivation of harmful pathogens. Disinfection of microbial species is mainly ascribed to the formation of reactive oxidative species. Further, surface modification of g-C3N4 can remarkably improves photocatalytic disinfection efficiency. In this review, we have discussed the recent advances in photocatalytic disinfection using g-C3N4-based nanocomposites. An overview of metal-free nanostructure g-C3N4, metal (anions) and nonmetal (cations)-doped g-C3N4 and g-C3N4 hybridized with low band gap semiconductor is also presented. Moreover, we have emphasized on the photocatalytic disinfection mechanism associated with g-C3N4-modified composites. Nitrogen-rich g-C3N4 polymeric material can serve as an alternative to metal oxide (TiO2 and ZnO) photocatalysts for photocatalytic disinfection technology. Other applications such as CO2 photoreduction, H2 generation, organic pollutant degradation, and sensing using g-C3N4-based nanocomposites are also summarized.

Metal-organic frameworks with photocatalytic bactericidal activity for integrated air cleaning

Air filtration has become an essential need for passive pollution control. However, most of the commercial air purifiers rely on dense fibrous filters, which have good particulate matter (PM) removal capability but poor biocidal effect. Here we present the photocatalytic bactericidal properties of a series of metal-organic frameworks (MOFs) and their potentials in air pollution control and personal protection. Specifically, a zinc-imidazolate MOF (ZIF-8) exhibits almost complete inactivation of Escherichia coli (E. coli) (>99.9999% inactivation efficiency) in saline within 2 h of simulated solar irradiation. Mechanistic studies indicate that photoelectrons trapped at Zn+ centers within ZIF-8 via ligand to metal charge transfer (LMCT) are responsible for oxygen-reduction related reactive oxygen species (ROS) production, which is the dominant disinfection mechanism. Air filters fabricated from ZIF-8 show remarkable performance for integrated pollution control, with >99.99% photocatalytic killing efficiency against airborne bacteria in 30 min and 97% PM removal. This work may shed light on designing new porous solids with photocatalytic antibiotic capability for public health protection.

Hydrodynamic cavitation using vortex diode: An efficient approach for elimination of pathogenic bacteria from water

The present study successfully demonstrates greener methodology of hydrodynamic cavitation using rotational flows for disinfection of water. Disinfection of two model microbial strains-gram- negative (Escherichia coli) and gram-positive (Staphylococcus aureus) using vortex diode was evaluated. The removal efficacy was quantified for two different cavitation reactors. Practically complete elimination of E. coli was achieved (99%) after 1 h of cavitation at a pressure drop of only 0.5 bar. However, elimination of S. aureus using vortex diode was observed to be lower in comparison to the removal of E. coli and only 60% disinfection could be achieved under similar conditions, which can be subsequently enhanced up to 98% by increasing pressure drop. The results were compared with another cavitating device that employs linear flow for cavitation, orifice. The reactor geometry has significant impact on the disinfection process and orifice was found to require significantly higher pressure drop (10 bar) conditions for disinfection and for eliminating gram-positive bacteria with high efficiency. A plausible mechanism for disinfection was proposed to elucidate the role of cavitation in cell destruction leading to death of cells through the rupture of cell wall, oxidative damage and possible DNA denaturation. Also, a cavitation model using per pass disinfection was developed that can provide meaningful physical description of the disinfection process as against the conventional first order reaction rate model. This study would provide meaningful insight into cavitation process based on hydrodynamic cavitation for the destruction of both gram-negative and gram-positive bacteria from various water sources, including industrial wastewaters.

Nanowire-Based Energy Conversion Devices and Technologies for Waste Heat Scavenging and Water Disinfection

Over the last two decades, nanowires have been demonstrated to be useful in a host of energy conversion devices and applications, including solar cells, thermoelectrics, and photocatalysis. Enhanced charge transfer resulting from the single-crystalline nature of nanowires, coupled with the ability to control their electrical, thermal and electronic properties through diameter variations, has allowed for accomplishing this task. In a series of papers, our group has also demonstrated the following: (a) Ultrathin nanowires of compound semiconductors could be obtained using thermal decomposition (1), and this process could subsequently be employed for engineering the bandgaps of compound semiconductors; and (b) large-scale assembly of nanowires could be made to exhibit thermal and electrical transport properties different from their bulk crystal counterparts, similar to those reportedly observed in individual nanowires (2-4). In accomplishing these tasks, we have developed strategies for the mass production of nanowires, their surface functionalization/decoration using organic/inorganic molecules, and their assembly in an interface-engineered manner into bulk devices (1-7). These all-dry routes for mass producing and assembling nanowires have been employed to precisely control the chemical compositions and ultimately the thermal, electrical and chemical properties of large-scale nanowire assemblies (2-7). Encouraged by these successes, our group has recently started studying the use of nanowires and their assemblies as photocatalysts for disinfecting water off harmful bacteria, such as E.coli. In this talk, strategies developed for the mass production of nanowires that involve the direct reaction of component elements in a chemical vapor deposition (CVD) chamber will be discussed (5). Extension of these strategies for mass producing nanowires in a byproduct-free manner (i.e., without the associated production of nanoparticles or other bulk crystal byproducts) will be presented and discussed (8). The latter strategy aids in fabricating energy conversion devices with precisely controlled performances, by eliminating the need to purify nanowires before they are incorporated into devices. Vapor phase in-situ methods useful in the decoration of nanowire surfaces with inorganic/organic molecules immediately after their synthesis for imparting them resistance against moisture- and acid-assisted degradation will also be discussed (5-6). Use of all-dry hot uniaxial pressing for assembling the mass produced nanowires into bulk devices will also be discussed, with a specific emphasis on interface-engineered assembly of nanowires (2-4, 7). Finally, the performances of these bulk nanowire assemblies as thermoelectric devices (2-4) and as photocatalysts for disinfecting water will be discussed in detail. In the latter case, specific discussion on visible light-assisted photocatalysis for the removal of harmful bacteria from water will be discussed. The kinetics of the disinfection process, the possible disinfection mechanisms along with the photocatalyst lifetimes will be discussed in this talk. The efficacy of this disinfection process relative to those accomplished using current state-of-the-art approaches, such as UV-assisted water disinfection, will be discussed. Finally, the possibility of deploying photocatalysis-based disinfection technologies on a large-scale will be explored and discussed.

Corn-silk-templated synthesis of TiO2 nanotube arrays with Ag3PO4 nanoparticles for efficient oxidation of organic pollutants and pathogenic bacteria under solar light

A novel highly ordered TiO2 nanotube arrays (TiO2 NTAs) have been successfully prepared via a simple, cost-effective and environmentally friendly corn-silk-templated strategy, and Ag3PO4 nanoparticles were deposited onto the TiO2 surface by a facile in-situ growth method. The crystal structure, morphology and optical properties of the as-prepared samples were characterized via a series of characterized techniques. Systematic studies demonstrated that Ag3PO4/TiO2 heterojunction photocatalyst displayed enhanced photocatalytic activity for rhodamine B (RhB) and ciprofloxacin (CIP) degradation compared to pristine TiO2 NTAs and Ag3PO4. In addition, Ag3PO4/TiO2 heterojunction exhibited significantly superior antibacterial activity than single component. By UV–vis diffuse reflectance (DRS) and photoluminescence (PL) spectra, the Ag3PO4/TiO2 heterojunction showed enhanced adsorption of visible light and reduced recombination of photo-generated electrons (e–) and holes (h+). The photocurrent and electrochemical impedance spectroscopy (EIS) demonstrated that Ag3PO4/TiO2 heterojunction possessed a faster photocurrent, lower charge migration resistance compared to pristine TiO2 NTAs and Ag3PO4. The possible enhanced photocatalytic degradation and disinfection mechanism were studied by employing the active species trapping and electron spin resonance (ESR) experiments, indicating that h+ and superoxide radicals (•O2–) played significant roles during the photocatalytic process. This work provided an attractive avenue to design highly ordered TiO2 nanotube arrays based composite photocatalysts from corn silks for pathogenic bacteria and organic pollutants wastewater purification and will be useful for design of other highly ordered nanotube arrays photocatalysts.

Different mechanisms for E. coli disinfection and BPA degradation by CeO2-AgI under visible light irradiation

CeO2-AgI, synthesized via depositing AgI nanoparticles onto CeO2 nanorods, was utilized for bacterial disinfection and organic contaminant degradation. Escherichia coli (E. coli) and Bisphenol A (BPA) were used as the model bacteria and emerging organic contaminant to test the photocatalytic activity of CeO2-AgI, respectively. Results showed that CeO2-AgI with the optimal AgI content exhibited superior photocatalytic activity over pure CeO2 or AgI for both inactivation of E. coli cells and BPA removal. However, the photocatalytic mechanisms for E. coli inactivation and BPA degradation were different. Specifically, the photo-generated holes (h+), photo-generated electrons (e−) and superoxide radicals (O2−) were the dominated active species for E. coli inactivation, whereas, BPA degradation relied on the generation of O2− and e−. Cell membrane disruption was found to be the main disinfection mechanism. The decomposition of BPA was clarified by detecting the degradation intermediates by LC–MS and DFT calculation. The facile synthesized CeO2-AgI exhibited good photocatalytic stability in four reused cycles and thus could be potentially applied to purify water.