Aged TiO2-based nanocomposite used in sunscreens produces singlet oxygen under long-wave UV and sensitizes Escherichia coli to cadmium

Seasonal variations and the prevalence of phenolic profiles in ambient fine particulate matter and their impact on oxidative potential

Exposure to fine particulate matter (PM2.5) poses numerous health risks, with oxidative potential (OP) serving as a critical marker of its toxicity. Synthetic phenolic antioxidants (SPAs) and bisphenols (BPs) influence reactive oxygen species (ROS) levels in PM2.5, and exposure to these compounds induces oxidative stress in organisms, thereby potentially affecting the OP of PM2.5. We detected 26 phenols (including 12 SPAs, 5 transformation products (TPs), and 9 BPs) in PM2.5 sample collected from October 2018 to September 2021 in Wuhan, China. Among them, 19 substances were detected at a detection frequency greater than 50 % in PM2.5 sample. AO 2246 and BHT were the main components of SPAs, and BHT-Q and BPA had the highest concentrations in TPs and BPs, respectively. PM2.5 mass concentrations and phenolic levels were higher in winter and autumn. Substances within groups were strongly correlated, suggesting the same or similar source of exposure. This finding aid in more precise pollution source identification and is crucial for comprehensively evaluating their combined health effects. Furthermore, we determined the OP of PM2.5 and found that BPs were related to increased OP and ROS. This suggests that the toxicity of PM2.5 is influenced not only by its concentration but also by its chemical composition, with BPs potentially enhancing its toxic effects. These factors should be fully considered when assessing the health impacts of PM2.5.

Were Persulfate-Based Advanced Oxidation Processes Really Understood? Basic Concepts, Cognitive Biases, and Experimental Details

Persulfate (PS)-based advanced oxidation processes (AOPs) for pollutant removal have attracted extensive interest, but some controversies about the identification of reactive species were usually observed. This critical review aims to comprehensively introduce basic concepts and rectify cognitive biases and appeals to pay more attention to experimental details in PS-AOPs, so as to accurately explore reaction mechanisms. The review scientifically summarizes the character, generation, and identification of different reactive species. It then highlights the complexities about the analysis of electron paramagnetic resonance, the uncertainties about the use of probes and scavengers, and the necessities about the determination of scavenger concentration. The importance of the choice of buffer solution, operating mode, terminator, and filter membrane is also emphasized. Finally, we discuss current challenges and future perspectives to alleviate the misinterpretations toward reactive species and reaction mechanisms in PS-AOPs.

New Barrier Role of Iron Plaque: Producing Interfacial Hydroxyl Radicals to Degrade Rhizosphere Pollutants

Iron plaque, as a natural barrier between rice and soil, can reduce the accumulation of pollutants in rice by adsorption, contributing to the safe production of rice in contaminated soil. In this study, we unveiled a new role of iron plaque, i.e., producing hydroxyl radicals (·OH) by activating root-secreted oxygen to degrade pollutants. The ·OH was produced on the iron plaque surface and then diffused to the interfacial layer between the surface and the rhizosphere environment. The iron plaque activated oxygen via a successive three-electron transfer to produce ·OH, involving superoxide and hydrogen peroxide as the intermediates. The structural Fe(II) in iron plaque played a dominant role in activating oxygen rather than the adsorbed Fe(II), since the structural Fe(II) was thermodynamically more favorable for oxygen activation. The oxygen vacancies accompanied by the structural Fe(II) played an important role in oxygen activation to produce ·OH. The interfacial ·OH selectively degraded rhizosphere pollutants that could be adsorbed onto the iron plaque and was less affected by the rhizosphere environments than the free ·OH. This study uncovered the oxidative role of iron plaque mediated by its produced ·OH, reshaping our understanding of the role of iron plaque as a barrier for rice.

Finding Nano: Challenges Involved in Monitoring the Presence and Fate of Engineered Titanium Dioxide Nanoparticles in Aquatic Environments

In recent years, titanium dioxide (TiO2) has increasingly been used as an inorganic ultraviolet (UV) filter for sun protection. However, nano-TiO2 may also pose risks to the health of humans and the environment. Thus, to adequately assess its potential adverse effects, a comprehensive understanding of the behaviour and fate of TiO2 in different environments is crucial. Advances in analytical and modelling methods continue to improve researchers’ ability to quantify and determine the state of nano-TiO2 in various environments. However, due to the complexity of environmental and nanoparticle factors and their interplay, this remains a challenging and poorly resolved feat. This paper aims to provide a focused summary of key particle and environmental characteristics that influence the behaviour and fate of sunscreen-derived TiO2 in swimming pool water and natural aquatic environments and to review the current state-of-the-art of single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) approaches to detect and characterise TiO2 nanoparticles in aqueous media. Furthermore, it critically analyses the capability of existing fate and transport models to predict environmental TiO2 levels. Four particle and environmental key factors that govern the fate and behaviour of TiO2 in aqueous environments are identified. A comparison of SP-ICP-MS studies reveals that it remains challenging to detect and characterise engineered TiO2 nanoparticles in various matrices and highlights the need for the development of new SP-ICP-MS pre-treatment and analysis approaches. This review shows that modelling studies are an essential addition to experimental studies, but they still lack in spatial and temporal resolution and mostly exclude surface transformation processes. Finally, this study identifies the use of Bayesian Network-based models as an underexplored but promising modelling tool to overcome data uncertainties and incorporates interconnected variables.

The Adverse Effects of TiO2 Photocatalycity on Paraloid B72 Hybrid Stone Relics Protective Coating Aging Behaviors under UV Irradiation

The incorporation of photocatalytic nanomaterials into polymer coatings is used to protect stone relics from weathering. However, the photocatalytic nanomaterials might generate excess free radicals to degrade the polymer matrix. In this work, a certain amount of TiO₂ nanoparticles were dispersed into Paraloid B72 and applied onto sandstone relics to explore the adverse effects of TiO₂ nanoparticles on Paraloid B72 under ultraviolet (UV) irradiation. To fulfill this goal, the effects of TiO₂ on pore formation and the structure of Paraloid B72 was studied by scanning electron microscopy (SEM). Moreover, the surface chemical composition, pore structure, surface roughness and surface wettability were explored via Fourier transform infrared (FTIR) spectroscopy, SEM, optical profilometer and water contact angle measurement under UV irradiation. Results showed that the incorporation of TiO₂ nanoparticles prohibited the generation of pores in Paraloid B72 and there were no pores formed when the content of TiO₂ exceeded 0.8 wt%. The water contact angle of origin Paraloid B72 and TiO₂/Paraloid B72 decreased with the prolonging UV irradiation. Moreover, TiO₂ nanoparticles were extracted from the matrix and the pores cannot be detected with the prolonging UV irradiation time under a higher content of TiO₂. These research findings might promote the understanding of using photocatalytic nanomaterials in developing stone relics' protective coating.

Status Quo in Data Availability and Predictive Models of Nano-Mixture Toxicity

Co-exposure of nanomaterials and chemicals can cause mixture toxicity effects to living organisms. Predictive models might help to reduce the intensive laboratory experiments required for determining the toxicity of the mixtures. Previously, concentration addition (CA), independent action (IA), and quantitative structure–activity relationship (QSAR)-based models were successfully applied to mixtures of organic chemicals. However, there were few studies concerning predictive models for toxicity of nano-mixtures before June 2020. Previous reviews provided comprehensive knowledge of computational models and mechanisms for chemical mixture toxicity. There is a gap in the reviewing of datasets and predictive models, which might cause obstacles in the toxicity assessment of nano-mixtures by using in silico approach. In this review, we collected 183 studies of nano-mixture toxicity and curated data to investigate the current data and model availability and gap and to derive research challenges to facilitate further experimental studies for data gap filling and the development of predictive models.

Au-Cu@PANI Alloy Core Shells for Aerobic Fibrin Degradation under Visible Light Exposure

Fibrin plays a critical role in wound healing and hemostasis, yet it is also the main case of cardiovascular diseases and thrombosis. Here, we show the unique design of Au-Cu@PANI alloy core-shell rods for fibrin clot degradation. Microscopic (transmission electron microscopy (TEM), scanning transmission electron microscopy-energy-dispersive X-ray (STEM-EDX)) and structural characterizations (powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS)) of the Au-Cu@PANI hybrid material reveal the formation of Au-Cu heterogeneous alloy core rods (aspect ratio = 3.7) with thin Cu₂O and PANI shells that create a positive surface charge (ζ-potential = +22 mV). This architecture is supported by the survey XPS spectrum showing the presence of Cu 2p, N 1s, and C 1s features with binding energies of 934.8, 399.7, and 284.8 eV, respectively. Upon photolysis (λ ≥ 495 or 590 nm), these hybrid composite nanorods provide sufficient excited-state redox potential to generate reactive oxygen species (ROS) for degradation of model fibrin clots within 5-7 h. Detailed scanning electron microscopy (SEM) analysis of the fibrin network shows significant morphology modification including formation of large voids and strand termini, indicating degradation of fibrin protofibril by Au-Cu@PANI. The dye 1,3-diphenylisobenzofuran (DPBF) used to detect the presence of ¹O₂ shows a 27% bleaching of the absorption at λ = 418 nm within 75 min of irradiation of an aqueous Au-Cu@PANI solution in air. Moreover, electron paramagnetic resonance (EPR) spin-trapping experiments reveal a hyperfine-coupled triplet signature at room temperature with intensities 1:1:1: and g-value = 2.0057, characteristic of the reaction between the spin probe 4-Oxo-TEMP and ¹O₂ during irradiation. Controlled ¹O₂ scavenging experiments by NaN₃ show 82% reduction in the spin-trapped EPR signal area. Both DPBF bleaching and EPR spin trapping indicate that in situ generated ¹O₂ is responsible for fibrin strand scission. This unique nanomaterial function via use of ubiquitous oxygen as a reagent could open creative avenues for future in vivo biomedical applications to treat fibrin clot diseases.

Constructing magnetic and high-efficiency AgI/CuFe2O4 photocatalysts for inactivation of Escherichia coli and Staphylococcus aureus under visible light: Inactivation performance and mechanism analysis

Magnetic materials usually exhibit advanced performance in many areas for their easy separating and recycle ability. In this study, silver iodide/copper ferrite (AgI/CuFe₂O₄) catalysts with excellent magnetic property were successfully synthesized and characterized by a series of techniques. Two typical bacteria Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were applied to estimate the photocatalytic inactivation performance of obtained AgI/CuFe₂O₄ catalysts. Results revealed that the AgI/CuFe₂O₄ (12.5% AgI) composite could absolutely inactivate 3 × 10⁹ CFU/mL E. coli and 2.7 × 10⁸ CFU/mL S. aureus cells severally in 50 min and 40 min under visible light irradiation, which showed a much higher photo-disinfection activity than monomers. Transmission electron microscopy was used to study the biocidal action of this nanocatalyst, the results confirmed that the treated E. coli cells were damaged, the nanocatalyst permeated into cells and resulting in death of cells. Besides, it was found that the destruction of bacterial membrane together with substantial leaked potassium ion (K⁺) which caused by the photo-generated reactive species superoxide radical (O₂^-) and holes (h⁺) could be the direct disinfection principles. For a deep insight into practical applications, the influences of different catalyst concentrations and reaction pH were also taken into discussion in details. The overall results indicated the novel photocatalyst with strong redox capacity and outstanding reusability can be widely employed in bacteria elimination.

Superior disinfection effect of Escherichia coli by hydrothermal synthesized TiO2-based composite photocatalyst under LED irradiation: Influence of environmental factors and disinfection mechanism

The photocatalytic inactivation of Escherichia coli (E. coli) under light-emitting diode (LED) light irradiation was performed with P/Ag/Ag₂O/Ag₃PO₄/TiO₂ photocatalyst to investigate the photocatalytic bactericidal activity. Our work showed that this composite photocatalyst possessed remarkable bacterial disinfection ability and could completely inactivate 10⁸ cfu/mL of E. coli within just 40 min under the optimum catalyst loading of 0.5 g/L. The effects of different environmental factors, including light wavelength, light intensity, temperature, solution pH and inorganic ions, on the inactivation efficiency were evaluated. The results showed that bacteria inactivation by P/Ag/Ag₂O/Ag₃PO₄/TiO₂ was more favorable with blue colored LED irradiation, light intensity at 750 W/m², temperature in the range of 30-37 °C and pH values at natural or slightly alkaline condition. The existence of different inorganic ions under normal environmental level had no significant impact on the bactericidal performance. In addition, during the inactivation process, the morphology changes of E. coli cells were directly observed by scanning electron microscope (SEM) and further proved by the measurement of K⁺ leakage from the inactivated E. coli. The results demonstrated that the photocatalytic inactivation caused drastic damage on bacterial cells membrane. Furthermore, the mechanisms of photocatalytic bacterial inactivation were also systemically studied and the results confirmed that the excellent disinfection activity of P/Ag/Ag₂O/Ag₃PO₄/TiO₂ resulted from the major reactive species: h⁺ and ·O₂^- from photocatalytic process instead of the leakage of Ag⁺ (≤0.085 ± 0.005 mg/L) from photocatalyst. These results indicate that P/Ag/Ag₂O/Ag₃PO₄/TiO₂ photocatalyst has promising potential for real water sterilization application.

Chronic Exposure to an Environmentally Relevant Triclosan Concentration Induces Persistent Triclosan Resistance but Reversible Antibiotic Tolerance in Escherichia coli

The major concern regarding the biocide triclosan (TCS) stems from its potential coselection for antibiotic resistance. However, environmental impacts are often investigated using high concentrations and acute exposure, while predicted releases are typified by chronic low concentrations. Moreover, little information is available regarding the reversibility of TCS and derived antibiotic resistance with diminishing TCS usage. Here, the model Gram-negative bacterium Escherichia coli was exposed to 0.01 mg/L TCS continuously for more than 100 generations. The adapted cells gained considerable resistance to TCS as indicated by a significant increase in the minimal inhibitory concentration (MIC₅₀) from 0.034 to 0.581 mg/L. This adaptive evolution was attributed to overexpression and mutation of target genes (i.e., fabI) as evidenced by transcriptomic and genomic analyses. However, only mild tolerance to various antibiotics was observed, possibly due to reduced membrane permeability and biofilm formation. After TCS exposure ceased, the adapted cells showed persistent resistance to TCS due to inheritable genetic mutations, whereas their antibiotic tolerance declined over time. Our results suggest that extensive use of TCS may promote the evolution and persistence of TCS-resistant bacterial pathogens. A quantitative definition of the conditions under which TCS selects for multidrug resistance in the environment is crucially needed.

Environmental mixtures of nanomaterials and chemicals: The Trojan-horse phenomenon and its relevance for ecotoxicity

The usage of engineered nanomaterials (NM) offers many novel products and applications with advanced features, but at the same time raises concerns with regard to potential adverse biological effects. Upon release and emission, NM may interact with chemicals in the environment, potentially leading to a co-exposure of organisms and the occurrence of mixture effects. A prominent idea is that NM may act as carriers of chemicals, facilitating and enhancing the entry of substances into cells or organisms, subsequently leading to an increased toxicity. In the literature, the term 'Trojan-horse effect' describes this hypothesis. The relevance of this mechanism for organisms is, however, unclear as yet. Here, a review has been performed to provide a more systematic picture on existing evidence. It includes 151 experimental studies investigating the exposure of various NM and chemical mixtures in ecotoxicological in vitro and in vivo model systems. The papers retrieved comprised studies investigating (i) uptake, (ii) toxicity and (iii) investigations considering both, changes in substance uptake and toxicity upon joint exposure of a chemical with an NM. A closer inspection of the studies demonstrated that the existing evidence for interference of NM-chemical mixture exposure with uptake and toxicity points into different directions compared to the original Trojan-horse hypothesis. We could discriminate at least 7 different categories to capture the evidence ranging from no changes in uptake and toxicity to an increase in uptake and toxicity upon mixture exposure. Concluding recommendations for the consideration of relevant processes are given, including a proposal for a nomenclature to describe NM-chemical mixture interactions in consistent terms.

Time-gated luminescence imaging of singlet oxygen photoinduced by fluoroquinolones and functionalized graphenes in Daphnia magna

Singlet oxygen (¹O₂) can be photogenerated by photoactive xenobiotics and is capable of causing adverse effects due to its electrophilicity and its high reactivity with biological molecules. Detection of the production and distribution of ¹O₂ in living organisms is therefore of great importance. In this study, a luminescent probe ATTA-Eu³⁺ combined with time-gated luminescence imaging was adopted to detect the distribution and temporal variation of ¹O₂ photoinduced by fluoroquinolone antibiotics and carboxylated/aminated graphenes in Daphnia magna. Results show that the xenobiotics generate ¹O₂ in living daphnids under simulated sunlight irradiation (SSR). The photogeneration of ¹O₂ by carboxylated/aminated graphenes was also confirmed by electron paramagnetic resonance spectroscopy. The strongest luminescence signals of ¹O₂ were observed in the hindgut of daphnids, and the signals in different areas of the daphnids (gut, thoracic legs and post-abdominal claw) displayed a similar trend of enhancement over irradiation time. Mean ¹O₂ concentrations at different regions of daphnids within one hour of SSR irradiation were estimated to be in the range of 0.5∼4.8μM. This study presented an efficient method for visualizing and quantifying the temporal and spatial distribution of ¹O₂ photogenerated by xenobiotics in living organisms, which can be employed for phototoxicity evaluation of xenobiotics.

In Situ Hydrothermally Grown TiO2@C Core-Shell Nanowire Coating for Highly Sensitive Solid Phase Microextraction of Polycyclic Aromatic Hydrocarbons

Nanostructured materials have great potential for solid phase microextraction (SPME) on account of their tiny size, distinct architectures and superior physical and chemical properties. Herein, a core-shell TiO₂@C fiber for SPME was successfully fabricated by the simple hydrothermal reaction of a titanium wire and subsequent amorphous carbon coating. The readily hydrothermal procedure afforded in situ synthesis of TiO₂ nanowires on a titanium wire and provided a desirable substrate for further coating of amorphous carbon. Benefiting from the much larger surface area of subsequent TiO₂ and good adsorption property of the amorphous carbon coating, the core-shell TiO₂@C fiber was utilized for the SPME device for the first time and proved to have better performance in extraction of polycyclic aromatic hydrocarbons. In comparison to the polydimethylsiloxane (PDMS) and PDMS/divinylbenzene (DVB) fiber for commercial use, the TiO₂@C fiber obtained gas chromatography responses 3-8 times higher than those obtained by the commercial 100 μm PDMS and 1-9 times higher than those obtained by the 65 μm PDMS/DVB fiber. Under the optimized extraction conditions, the low detection limits were obtained in the range of 0.4-7.1 ng L^-1 with wider linearity in the range of 10-2000 ng L^-1. Moreover, the fiber was successfully used for the determination of polycyclic aromatic hydrocarbons in Pearl River water, which demonstrated the applicability of the core-shell TiO₂@C fiber.

Nano-TiO2 affects Cu speciation, extracellular enzyme activity, and bacterial communities in sediments

In aquatic ecosystems, titanium dioxide nanoparticles (nano-TiO₂) coexist with heavy metals and influence the existing forms and toxicities of the metal in water. However, limited information is available regarding the ecological risk of this coexistence in sediments. In this study, the effect of nano-TiO₂ on Cu speciation in sediments was investigated using sequential extraction. The microcosm approach was also employed to analyze the effects of the coexistence of nano-TiO₂ and Cu on extracellular enzyme activity and bacterial communities in sediments. Results showed that nano-TiO₂ decreased the organic matter-bound fraction of Cu and increased the corresponding residual fraction Cu. As a result, speciation of exogenous Cu in sediments changed. During the course of the 30-day experiment, the presence of nano-TiO₂ did not affect Cu-induced changes in bacterial community structure. However, the coexistence of nano-TiO₂ and Cu restrained the activity of bacterial extracellular enzymes, such as alkaline phosphatase and β-glucosidase. The degree of inhibition also varied because of the different properties of extracellular enzymes. This research highlighted the importance of understanding and predicting the effects of the coexistence of nanomaterials and other pollutants in sediments.

Toxicity of ZnO and TiO2 to Escherichia coli cells

We performed a comprehensive investigation of the toxicity of ZnO and TiO2 nanoparticles using Escherichia coli as a model organism. Both materials are wide band gap n-type semiconductors and they can interact with lipopolysaccharide molecules present in the outer membrane of E. coli, as well as produce reactive oxygen species (ROS) under UV illumination. Despite the similarities in their properties, the response of the bacteria to the two nanomaterials was fundamentally different. When the ROS generation is observed, the toxicity of nanomaterial is commonly attributed to oxidative stress and cell membrane damage caused by lipid peroxidation. However, we found that significant toxicity does not necessarily correlate with up-regulation of ROS-related proteins. TiO2 exhibited significant antibacterial activity, but the protein expression profile of bacteria exposed to TiO2 was different compared to H2O2 and the ROS-related proteins were not strongly expressed. On the other hand, ZnO exhibited lower antibacterial activity compared to TiO2, and the bacterial response involved up-regulating ROS-related proteins similar to the bacterial response to the exposure to H2O2. Reasons for the observed differences in toxicity and bacterial response to the two metal oxides are discussed.

Effect of preparation and processing conditions on UV absorbing properties of hydroxyapatite-Fe2O3 sunscreen

The development of innovative, safe and non-photocatalytic sunscreens is urgently needed, as it is essential to have sunscreen filters offering appropriate UV protection without damaging the environment and/or generating free radicals when in contact with the skin. Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) when substituted with iron has UV protection properties and is not photocatalytic; HAp was used to make a sunscreen filter by treating cod fish bones in an iron-containing solution, and then calcining them at 700°C. Here we present a systematic and advanced study on this material, to obtain a sunscreen with improved UV absorbing properties. Bones were treated with three different iron salts - Fe(II) chloride, Fe(II) lactate and Fe(III) nitrate - under various pH conditions. Results showed that Fe(II) chloride in basic pH led to the most effective iron inclusion. High energy ball milling or ultrasound were investigated to increase surface area and corresponding UV absorption; high energy ball milling treatment led to the best optical properties. The optimum powders were used to formulate UV protection creams, which showed Sun Protection Factor (SPF) values significantly superior to the control cream (up to 4.1). Moreover the critical wavelength (λ_crit) was >370nm (388-389nm) and UVA/UVB ratios were very close to 1. With these properties these sunscreens can be classified as broad UV protectors. Results also showed that combining these powders with other sunscreens (i.e. titanium dioxide), a synergic effect between the different components was also observed. This investigation showed that HAp-based sunscreens of marine origin are a valid alternative to commercial products, safe for the health of the customers and, being non-photocatalytic, do not pose a threat to the environment.

Photo-enhanced oxidizability of tetrazolium salts and its impact on superoxide assaying

Herein, we report for the first time the enhanced oxidation properties of tetrazolium salts induced by UV-irradiation, and demonstrate that there is real deviation in the photo-induced superoxide anion radical assay based on tetrazolium salts.

Development of preservative-free nanoparticles-based emulsions: Effects of NP surface properties and sterilization process

Model emulsions were developed with or without commercial titanium dioxide nanoparticles (NP) carrying various surface treatments in order to get close physicochemical properties whatever the NP surface polarity (hydrophilic and hydrophobic). Rheology and texturometry highlighted that the macroscopic properties of the three formulated emulsions were similar. However, characterizations by optical microscopy, static light scattering and zetametry showed that their microstructures reflected the diversity of the incorporated NP surface properties. In order to use these model emulsions as tools for biological evaluations of the NP in use, they had to show the lowest initial microbiological charge and, specifically for the NP-free emulsion, the lowest bactericidal effect. Hence, formulae were developed preservative-free and a thermal sterilization step was conducted. Efficiency of the sterilization and its impact on the emulsion integrity were monitored. Results highlighted the effect of the NP surface properties: only the control emulsion and the emulsion containing hydrophilic NP fulfilled both requirements. To ensure the usability of these model emulsions as tools to evaluate the 'NP effect' on representative bacteria of the skin microflora (S. aureus and P. fluorescens), impact on the bacterial growth was measured on voluntary inoculated formulae.

Photocatalytic reduction of triclosan on Au-Cu2O nanowire arrays as plasmonic photocatalysts under visible light irradiation

Triclosan (TCS) is a potential threat to the environment and human health. Photocatalysis can be used to degrade TCS, but the photocatalytic efficiency is usually limited by the photoabsorptivity and photostability of the photocatalyst. In addition, some toxic by-products might also be generated during photocatalytic processes. In this study, we prepared Au-coated Cu2O nanowire arrays (Au-Cu2O NWAs) by beam sputtering Au onto Cu2O nanowires grown from a Cu foil. We found that photocatalytic degradation of TCS under visible light (420 nm < λ < 780 nm) irradiation and Au-Cu2O NWAs had several advantages. Au-Cu2O NWAs had good photoabsorptivity, high photostability (negligible activity loss after 16 runs), excellent photocatalytic activity (47.6 times faster than that of Cu2O), and low yield of dichlorodibenzo-dioxins/dichlorohydroxydibenzofurans. The degradation intermediates were identified as chlorophenoxyphenol, phenoxyphenol, chlorophenol, catechol, phenol, benzoquinone, and lower volatile acids. We developed the degradation pathway of TCS which follows electron reduction and then oxidation by reactive oxygen species. The mechanism was developed and strengthened using the radical trapping and other measurements. The unusual mechanism and photostability of Au-Cu2O NWAs were attributed to the Au/Cu2O/Cu "sandwich"-like structure. This structure yields a sustained and steady internal electric field, raises the conduction band of Cu2O, reinforces the reductive activity of the photo-generated electrons, and eliminates the photo-generated holes that are responsible for the photo-etching of Cu2O.

Preparation of rutile TiO2@avobenzone composites for the further enhancement of sunscreen performance

It is well known that organic avobenzone and inorganic TiO₂ are applied to shield UVA and UVB, respectively.

Enhanced visible-light-driven photocatalytic inactivation of Escherichia coli using g-C3N4/TiO2 hybrid photocatalyst synthesized using a hydrothermal-calcination approach

Biohazards are widely present in wastewater, and contaminated water can arouse various waterborne diseases. Therefore, effectively removing biohazards from water is a worldwide need. In this study, a novel visible-light-driven (VLD) graphitic carbon nitride (g-C3N4)/TiO2 hybrid photocatalyst with high photocatalytic bacterial inactivation activity was successfully synthesized using a facile hydrothermal-calcination approach. The optimum synthesized hybrid photocatalyst is composed of micron-sized TiO2 spheres (average diameter: ca. 2 μm) and wrapped with lamellar g-C3N4 (thickness: ca. 2 nm), with narrowing bandgap (ca. 2.48 eV), leading to a significant improvement of visible light (VL) absorption and effective separation of photo-generated electron-hole pairs. This greatly enhances VL photocatalytic inactivation activity towards bacteria in water. Using this hybrid photocatalyst, 10(7) cfu mL(-1) of Escherichia coli K-12 could be completely inactivated within 180 min under VL irradiation. SEM images indicate that bacterial cells were greatly damaged, leading to a severe leakage of intracellular components during photocatalytic inactivation processes. The study concludes that bacterial cell destruction and water disinfection can be achieved using this newly fabricated VLD hybrid photocatalyst.

Effect of 10 different TiO2 and ZrO2 (nano)materials on the soil invertebrate Enchytraeus crypticus

Nearly 80% of all the nano-powders produced worldwide are metal oxides, and among these materials titanium dioxide (TiO2 ) is one of the most produced. Titanium dioxide's toxicity is estimated as low to soil organisms, but some studies have shown that TiO2 nanoparticles can cause oxidative stress. Additionally, it is known that TiO2 is activated by ultraviolet (UV) radiation, which can promote photocatalytic generation of reactive oxygen species, which is seldom taken into account in toxicity testing. In the present study, the authors investigated the effects of different TiO2 and zirconium materials on the soil oligochaete Enchytraeus crypticus, using exposure via soil, water, and soil:water extracts, and studied the effects combined with UV radiation. The results showed that zirconium dioxide (bulk and nano) was not toxic, whereas zirconium tetrachloride reduced enchytraeid reproduction in soil (50% effect concentration = 502 mg/kg). The TiO2 materials were also not toxic via soil exposure or under UV radiation. However, pre-exposure to TiO2 and UV radiation via aqueous media caused a lower reproductive output post-exposure in clean soil (20-50% less but only observed at the lowest concentration tested, 1 mg/L); that is, the effect of TiO2 in water was potentiated by the UV radiation and measurable as a decrease in reproduction in soil media.

Evidence for TiO2 nanoparticle transfer in a hard-rock aquifer

Water flow and TiO2 nanoparticle (NP) transfer in a fractured hard-rock aquifer were studied in a tracer test experiment at a pilot site in Brittany, France. Results from the Br tracer test show that the schist aquifer can be represented by a two-layer medium comprising i) fractures with low longitudinal dispersivity in which water and solute transport is relatively fast, and ii) a network of small fissures with high longitudinal dispersivity in which transport is slower. Although a large amount of NPs was retained within the aquifer, a significant TiO2 concentration was measured in a well 15m downstream of the NP injection well, clearly confirming the potential for TiO2 NPs to be transported in groundwater. The Ti concentration profile in the downstream well was modelled using a two-layer medium approach. The delay used for the TiO2 NPs simulation compared to the Br concentration profiles in the downstream well indicate that the aggregated TiO2 NPs interacted with the rock. Unlike Br, NPs do not penetrate the entire pore network during transfer because of electrostatic interactions between NP aggregates and the rock and also to the aggregate size and the hydrodynamic conditions, especially where the porosity is very low; NPs with a weak negative charge can be attached onto the rock surface, and more particularly onto the positively charged iron oxyhydroxides coating the main pathways due to natural denitrification. Nevertheless, TiO2 NPs are mobile and transfer within fracture and fissure media. Any modification of the aquifer's chemical conditions is likely to impact the groundwater pH and, the nitrate content and the denitrification process, and thus affect NP aggregation and attachment.