Bactericidal Activity of TiO2 Nanotube Thin Films on Si by Photocatalytic Generation of Active Oxygen Species

Titanium dioxide-supported mercury photocatalysts for oxidative removal of hydrogen sulfide from the air using a portable air purification unit

Photocatalytic removal of gaseous hydrogen sulfide (H2S) has been studied through the control of key process variables using a prototype air purifier (AP) fabricated with titanium dioxide (TiO2)-supported mercury. The performance of Hg/TiO2 systems, prepared with different Hg mass proportions over TiO2 (such as 0.1%, 1%, 2%, and 5%), is measured against 5 ppm H2S at 160 L min-1 under UV irradiation. Accordingly, their removal efficiency (RE) values after 360 s are 40.3%, 74.8%, 99.3%, and 99.9%, respectively (relative to 33.5% of AP (TiO2)). An AP with a 2% Hg/TiO2 unit achieves a clean air delivery rate of 32 L min-1 with kinetic reaction rate (r (at 10% RE)) of 0.774 mmol h-1 g-1, quantum yield of 2.19E-02 molecules photon-1, and space-time yield of 1.46E-04 molecules photon-1 mg-1. The superior photocatalytic performance of Hg/TiO2 is supported by superoxide anion and hydroxyl radicals formed in dry air and humid nitrogen (N2) environments, respectively. A density functional theory simulation suggests that the presence of oxygen vacancies should promote the disparities in the electronic structure to subsequently affect the reaction pathways and energetics. The presence of moisture enhances the robust formation of a mercury-OH bond to favorably yield β-mercury sulfide from H2S.

Synthesis of the Ag2S/PANI@PES Composite Membrane and Its Antipollution Properties

Membrane separation technology offers a sustainable and efficient solution to wastewater management; however, membrane fouling significantly impedes its application. Photocatalytic membranes, integrating photocatalytic and membrane separation technologies, enhance membrane separation efficacy while effectively mitigating organic and biological contaminations. In this work, Ag2S/PANI@PES composite membranes were prepared via a facile in situ polymerization and successive layer adsorption technique. The modified poly(ether sulfone) (PES) membrane demonstrated improved hydrophilicity and separation performance, and its heterostructure between polyaniline (PANI), Ag0, and Ag2S effectively addressed organic fouling issues. Moreover, Ag2S/PANI@PES exhibited outstanding antimicrobial properties, as well as chemical and mechanical stability.

Progress of disinfection catalysts in advanced oxidation processes, mechanisms and synergistic antibiotic degradation

Human diseases caused by pathogenic microorganisms make people pay more attention to disinfection. Meanwhile, antibiotics can cause microbial resistance and increase the difficulty of disease treatment, resulting in risk of triggering a vicious circle. Advanced oxidation process (AOPs) has been widely studied in the field of synergistic treatment of the two contaminates. This paper reviews the application of catalytic materials and their modification strategies in the context of AOPs for disinfection and antibiotic degradation. It also delves into the mechanisms of disinfection such as the pathways for microbial inactivation and the related influencing factors, which are essential for understanding the pivotal role of catalytic materials in disinfection principles by AOPs. More importantly, the exploratory research on the combined use of AOPs for disinfection and antibiotic degradation is discussed, and the potential and prospects in this field is highlighted. Finally, the limitations and challenges associated with the application of AOPs in disinfection and antibiotic degradation are summarized. It aims to provide a starting point for future research efforts to facilitate the widespread use of advanced oxidation processes in the field of public health.

Radical generation and bactericidal activity of nanobubbles produced by ultrasonic irradiation of carbonated water

Our previous study showed that nanobubbles (NBs) encapsulating CO2 gas have bactericidal activity due to reactive oxygen species (ROS) (Yamaguchi et al., 2020). Here, we report that bulk NBs encapsulating CO2 can be efficiently generated by ultrasonically irradiating carbonated water using a piezoelectric transducer with a frequency of 1.7 MHz. The generated NBs were less than 100 nm in size and had a lifetime of 500 h. Furthermore, generation of ROS in the NB suspension was investigated using electron spin resonance spectroscopy and fluorescence spectrometry. The main ROS was found to be the hydroxyl radical, which is consistent with our previous observations. The bactericidal activity lasted for at least one week. Furthermore, a mist generated by atomizing the NB suspension with ultrasonic waves was confirmed to have the same bactericidal activity as the suspension itself. We believe that the strong, persistent bactericidal activity and radical generation phenomenon are unique to NBs produced by ultrasonic irradiation of carbonated water. We propose that entrapped CO2 molecules strongly interact with water at the NB interface to weaken the interface, and high-pressure CO2 gas erupts from this weakened interface to generate ROS with bactericidal activity.

Evaluation of chitosan-Ag/TiO2 nanocomposite for the enhancement of shelf life of chili and banana fruits

Post-harvest losses of fruits and vegetables account for a large share of food waste in the world due to improper handling and packaging. By using the sol-gel method, Ag/TiO2 nanocomposite was prepared in this study from micro-sized commercial TiO2 powder and incorporated in a chitosan-cellulose matrix for the purpose of promising food packaging. The particle size and distribution of Ag nanoparticles (9.2437 nm size) confirmed their successful inclusion in the TiO2 surface. The morphology of the package assured the successful and uniform disbursement of Ag/TiO2 nanocomposite into the chitosan-cellulose matrix, which led to enhanced water resistance and photocatalytic activity. The developed package is proficient in hindering the growth of fecal coliform bacteria (Esche (Escherichia coli) by 9 mm in the agar plate. Moreover, the efficient application of chitosan-Ag/TiO2 nanocomposite in food coating and packaging was examined in extending shelf life, minimizing water loss, and preventing microbial infection during the storage of chili (up to 7 days at 37 °C) and banana, respectively. It can be concluded from the results that chitosan-Ag/TiO2 nanocomposite-based food coating and packaging have competent potential for enhancing the shelf life of moist foods.

Strategy for Patterning Titania Dendrites by Gas-Solution Interaction at Droplet Surfaces

Interaction of the solution droplet surface with gaseous components of the environment can lead to the formation of highly ordered patterns, such as dendrites. Here, we show that these structures can be spontaneously created during the open-air interaction of aqueous solution drop of titanium(III) salt with gaseous NH3 at the contact boundary thereof. The conditions have been identified under which radially ordered dendritic patterns can form on the surface of the TiCl3 solution droplet. The formation of these self-organized dendrite patterns can be attributed to the surface instability manifesting in Marangoni thermal flows in a droplet occurring during open-air fabrication. The composition of as-synthesized structures corresponds to coprecipitated crystalline NH4Cl and amorphous TiO2nH2O. After thermal treatment at 450 °C, TiO2 with the anatase crystal lattice is formed; meanwhile, the ordered dendrite patterns are preserved.

Plasmon-Sensitized Silica-Titanium Aerogels as Potential Photocatalysts for Organic Pollutants and Bacterial Strains

Photocatalysis reactions are of great interest as an effective tool against the profusely increasing population of antibiotic-resistant bacteria species. In particular, the promising evidence on plasmon-sensitized titanium dioxide (TiO2) photocatalysis inspired us to investigate their antibacterial activity stemming from the photogenerated reactive oxygen species (ROS). Herein, TiO2 nanostructures were grown in situ within a silica (SiO2) aerogel matrix with high surface area and porosity, and their ROS-related phototoxic effects against Escherichia coli bacteria were investigated under solar- and visible-light irradiations. Photodegradation profiles obtained from Rhodamine B (RhB) organic dye used as a chemical probe proved that the types of ROS produced by SiO2/TiO2 aerogels varied depending on the electromagnetic spectrum portion that was used during material irradiation. Further, the SiO2/TiO2 aerogel matrix was decorated with silver-gold nanostars (Ag@Au NSs) to enhance its photocatalytic efficiency under visible light irradiations. Our design showed that plasmon-enriched composite aerogels efficiently boosted ROS production under visible light exposures and that the structures containing Ag@Au NSs showed a much more effective antibacterial effect compared to their counterparts.

Photocatalytic degradation effect and mechanism of Karenia mikimotoi by non-noble metal modified TiO2 loading onto copper metal organic framework (SNP-TiO2@Cu-MOF) under visible light

In this study, the SNP-TiO₂@Cu-MOF composite was prepared successfully by loading non-noble metal modified TiO₂ (SNP-TiO₂) on the surface of copper metal organic skeleton (Cu-MOF), and compared the inactivation efficiency of different photocatalysts to Karenia mikimotoi (K. mikimotoi) under visible light. The obtained photocatalyst had the characteristic crystal faces of Cu-MOF and SNP- TiO₂, and contained functional groups such as Cu-O, -COOH, N-O, P-O, etc., which indicated the structural stability of the photocatalyst. The band gap of SNP-TiO₂@Cu-MOF composite was 2.82 eV, and it had great light absorption ability in visible light region. It was proved to be a mesoporous adsorption material, which had a huge specific surface area (245 m²/g). Compared with other photocatalysts, SNP-TiO₂@Cu-MOF composite showed the strongest photocatalytic activity. When the concentration of composite material was set to 100 mg/L and the exposure time was 6 h, the visible light photocatalytic inactivation efficiency of K. mikimotoi was 93.75 %. By measuring various metabolic indexes of K. mikimotoi under the action of different photocatalysts for 1 h, it was confirmed that cell inactivation was due to the increased membrane permeability and degradation of photosynthetic pigments and main life proteins. This research showed that SNP-TiO₂@Cu-MOF composite material was full of great potential and application prospect in controlling the outbreak of eutrophication.

Current Knowledge on the Oxidative-Stress-Mediated Antimicrobial Properties of Metal-Based Nanoparticles

The emergence of multidrug-resistant (MDR) bacteria in recent years has been alarming and represents a major public health problem. The development of effective antimicrobial agents remains a key challenge. Nanotechnologies have provided opportunities for the use of nanomaterials as components in the development of antibacterial agents. Indeed, metal-based nanoparticles (NPs) show an effective role in targeting and killing bacteria via different mechanisms, such as attraction to the bacterial surface, destabilization of the bacterial cell wall and membrane, and the induction of a toxic mechanism mediated by a burst of oxidative stress (e.g., the production of reactive oxygen species (ROS)). Considering the lack of new antimicrobial drugs with novel mechanisms of action, the induction of oxidative stress represents a valuable and powerful antimicrobial strategy to fight MDR bacteria. Consequently, it is of particular interest to determine and precisely characterize whether NPs are able to induce oxidative stress in such bacteria. This highlights the particular interest that NPs represent for the development of future antibacterial drugs. Therefore, this review aims to provide an update on the latest advances in research focusing on the study and characterization of the induction of oxidative-stress-mediated antimicrobial mechanisms by metal-based NPs.

The Photocatalysis-Enhanced TiO2@HPAN Membrane with High TiO2 Surface Content for Highly Effective Removal of Cationic Dyes

The elimination of dye pollutants from wastewater is a significant concern that has prompted extensive research into the development of highly efficient photocatalytic membranes. A novel method was proposed to prepare photocatalysis-enhanced poly(acrylonitrile-methyl acrylate) (PAN-based) membranes in this study. In detail, the blended membrane containing SiO₂@TiO₂ nanoparticles with a shell-core structure was first prepared via thermal-induced phase separation. The SiO₂ nanoshells were dissolved, and the released TiO₂ nanoparticles migrated to the membrane surface during a simple hydrolysis process, which prevents the TiO₂ nanoparticles from directly contacting or interacting with the polymer matrix. The hydrogen bonds bind the exposed TiO₂ with the PAN membrane surface, resulting in the formation of the TiO₂@HPAN hybrid membrane. The photocatalytic efficiency of the TiO₂@HPAN membrane doubled compared with that of nonhydrolyzed membranes. In the presence of UV light, the hybrid membrane can degrade 99.8% of methylene blue solution in less than 2 h, compared to only 86.1% for the blended membranes. Further, the TiO₂@HPAN membrane showed excellent photocatalytic activity for cationic dyes due to electrostatic attraction. Moreover, the high-flux recovery rate and recycling stability of the TiO₂@HPAN membrane lead to an excellent antifouling property. The facile preparation method proposed in this work shows extraordinary potential for the development of highly efficient selective photocatalytic materials for cationic dyes to be used in wastewater treatment applications.

Bactericidal Activity of Bulk Nanobubbles through Active Oxygen Species Generation

We investigated the bactericidal activity of bulk nanobubbles (NBs) using E. coli, a model bacterium. Bulk NBs were produced by forcing gas through a porous alumina membrane with an ordered arrangement of nanoscale straight holes in contact with water. NBs with different gas contents, including CO2, O2, and N2, were generated and evaluated for their bactericidal effects. The survival rate of E. coli was significantly reduced in a suspension of CO2-containing NB (CO2-NB water). The N2-NB water demonstrated a small amount of bactericidal behavior, but its impact was not as significant as that of CO2-NB water. When E. coli was retained in O2-NB water, the survival rate was even higher than that in pure water (PW). We investigated the generation of reactive oxygen species (ROS) in NB suspensions by electron spin resonance spectroscopy. The main ROS generated in the NB water were hydroxyl radicals and OH·, and the production of ROS was the strongest in CO2-NB water, which was consistent with the results of the bactericidal effect measurements. We assumed that NB mediated by ROS would exhibit bactericidal behavior and proposed a kinetic model to explain the retention time variation of the survival rate. The results calculated based on the proposed model matched closely with the experimental results.