Antioxidant Grain Passivation for Air-Stable Tin-Based Perovskite Solar Cells.

Tin-based perovskites with excellent optoelectronic properties and suitable band gaps are promising candidates for the preparation of efficient lead-free perovskite solar cells (PSCs). However, it is challenging to prepare highly stable and efficient tin-based PSCs because Sn2+ in perovskites can be easily oxidized to Sn4+ upon air exposure. Here we report the fabrication of air-stable FASnI3 solar cells by introducing hydroxybenzene sulfonic acid or its salt as an antioxidant additive into the perovskite precursor solution along with excess SnCl2 . The interaction between the sulfonate group and the Sn2+ ion enables the in situ encapsulation of the perovskite grains with a SnCl2 -additive complex layer, which results in greatly enhanced oxidation stability of the perovskite film. The corresponding PSCs are able to maintain 80 % of the efficiency over 500 h upon air exposure without encapsulation, which is over ten times longer than the best result reported previously. Our results suggest a possible strategy for the future design of efficient and stable tin-based PSCs.

Influence of membrane fatty acid composition and fluidity on airborne survival of Escherichia coli.

Finding ways to predict and control the survival of bacterial aerosols can contribute to the development of ways to alleviate a number of crucial microbiological problems. Significant damage in the membrane integrity of Escherichia coli during aerosolization and airborne suspension has been revealed which has prompted the question of how the membrane fatty acid composition and fluidity influence the survival of airborne bacteria. Two approaches of using isogenic mutants and different growth temperatures were selected to manipulate the membrane fatty acid composition of E. coli before challenging the bacteria with different relative humidity (RH) levels in an aerosol chamber. Among the mutants (fabR - , cfa. fadA - ), fabR - had the lowest membrane fluidity index (FI) and generally showed a higher survival than the parental strain. Surprisingly, its resistance to airborne stress was so strong that its viability was fully maintained even after airborne suspension at 40% RH, a harsh RH level to bacterial survival. Moreover, E. coli cultured at 20 °C with a higher FI than that at 30 and 37 °C generally had a lower survival after aerosolization and airborne suspension. Unlike FI, individual fatty acid and cyclopropane fatty acid composition did not relate to the bacterial survival. Lipid peroxidation of the membrane was undetected in all the bacteria. Membrane fluidity plays a stronger role in determining the bacteria survival during airborne suspension than during aerosolization. Certain relationships between FI and bacteria survival were identified, which could help predict the transmission of bacteria under different conditions.

Differential gene expression in Escherichia coli during aerosolization from liquid suspension.

Comparative transcriptome analysis was used to determine the differentially expressed genes in Escherichia coli during aerosolization from liquid suspension. Isogenic mutant studies were then used to examine the potential part played by some of these genes in bacterial survival in the air. Bioaerosols were sampled after 3 min of nebulization, which aerosolized the bacteria from the liquid suspension to an aerosol chamber (A0), and after further 30 min of airborne suspension in the chamber (A30). Bacteria at A0 showed 65 differentially expressed genes (30 downregulated and 35 upregulated) as compared to the original bacteria in the nebulizer. Droplet evaporation models predicted a drop in temperature in the bioaerosols, which coincides with the change in the expression of cold shock protein genes-cspB and cspG in the bacteria. The most notable group of differentially expressed genes was sorbitol transport and metabolism genes (srlABDEMR). Other genes associated with osmotic stress, nutrient limitation, DNA damage, and other stresses were differentially expressed in the bacteria at A0. After further airborne suspension, one gene (ypfM, which encodes a hypothetical protein with unknown function) was downregulated in the bacteria at A30 as compared to those at A0. Finally, isogenic mutants with either the dps or srlA gene deleted (both genes were upregulated at A0) had lower survival than the parental strain, which is a sign of their potential ability to protect the bacteria in the air.

Mesoporous Nanosheet Networked Hybrids of Cobalt Oxide and Cobalt Phosphate for Efficient Electrochemical and Photoelectrochemical Oxygen Evolution.

A novel mesoporous nanosheet networked hybrid comprising Co3 O4 and Co3 (PO4 )2 is successfully synthesized using a facile and scalable method through calcinating the carbon, cobalt hydroxy carbonate, and cobalt phosphate composite precursor. Electron transfer from Co3 O4 to Co3 (PO4 )2 , together with the special networked structure and the porous nature of the nanosheets enable the Co3 (PO4 )2 -Co3 O4 hybrid to have a high oxygen evolution reaction (OER) activity and outstanding stability in alkaline electrolyte, e.g., an overpotential of 270 mV at current density of 10 mA cm-2 , and a Tafel slope of 39 mV dec-1 , which are superior to most non-noble metal-based OER electrocatalysts reported thus far and as well the commercial RuO2 electrocatalyst. Furthermore, Co3 (PO4 )2 -Co3 O4 hybrid is demonstrated to be used as an efficient cocatalyst to enhance the photoelectrochemical OER performance of BiVO4 photoanode. A significantly increased photocurrent density of 3.0 mA cm-2 at 1.23 V (vs reversible hydrogen electrode, RHE), and a potential reduction of 530 mV with respect to that of bare BiVO4 at the photocurrent density of 0.5 mA cm-2 are achieved. The electron transfer-induced enhancement of OER by a hybrid structure may pave the new routes for the design and synthesis of low-cost catalysts for electrochemical and photoelectrochemical oxygen evolution.

Dual Roles of Capsular Extracellular Polymeric Substances in Photocatalytic Inactivation of Escherichia coli: Comparison of E. coli BW25113 and Isogenic Mutants.

The dual roles of capsular extracellular polymeric substances (EPS) in the photocatalytic inactivation of bacteria were demonstrated in a TiO2-UVA system, by comparing wild-type Escherichia coli strain BW25113 and isogenic mutants with upregulated and downregulated production of capsular EPS. In a partition system in which direct contact between bacterial cells and TiO2 particles was inhibited, an increase in the amount of EPS was associated with increased bacterial resistance to photocatalytic inactivation. In contrast, when bacterial cells were in direct contact with TiO2 particles, an increase in the amount of capsular EPS decreased cell viability during photocatalytic treatment. Taken together, these results suggest that although capsular EPS can protect bacterial cells by consuming photogenerated reactive species, it also facilitates photocatalytic inactivation of bacteria by promoting the adhesion of TiO2 particles to the cell surface. Fluorescence microscopy and scanning electron microscopy analyses further confirmed that high capsular EPS density led to more TiO2 particles attaching to cells and forming bacterium-TiO2 aggregates. Calculations of interaction energy, represented by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) potential, suggested that the presence of capsular EPS enhances the attachment of TiO2 particles to bacterial cells via acid-base interactions. Consideration of these mechanisms is critical for understanding bacterium-nanoparticle interactions and the photocatalytic inactivation of bacteria.

A recyclable mineral catalyst for visible-light-driven photocatalytic inactivation of bacteria: natural magnetic sphalerite.

Motivated by recent studies that well-documented mineral photocatalyst for bacterial inactivation, a novel natural magnetic sphalerite (NMS) in lead-zinc deposit was first discovered and evaluated for its visible-light-driven (VLD) photocatalytic bactericidal properties. Superior to the reference natural sphalerite (NS), vibrating sampling magnetometeric (VSM) analysis revealed the ferromagnetic property of NMS, indicating its potential for easy separation after use. Under the irradiation of fluorescence tubes, NMS could inactivate 7 log10 Gram-negative Escherichia coli K-12 without any regrowth and metal ions leached out from NMS show no toxicity to cells. The cell destruction process starting from cell wall to intracellular components was verified by TEM. Some products from damaged cells such as aldehydes, ketones and carboxylic acids were identified by FTIR with a decrease of cell wall functional groups. The relative amounts of potassium ion leakage from damaged cells gradually increased from initial 0 to approximately constant concentration of 1000 ppb with increasing reaction time. Superoxide radical (•O2(-)) rather than hydroxyl radical (•OH) was proposed to be the primary reactive oxidative species (ROSs) responsible for E. coli inactivation by use of probes and electron spin resonance (ESR). H2O2 determined by fluorescence method is greatly involved in bacterial inactivation in both nonpartition and partition system. Multiple cycle runs revealed excellent stability of recycled NMS without any significant loss of activity. This study provides a promising natural magnetic photocatalyst for large-scale bacterial inactivation, as NMS is abundant, easily recycled and possessed an excellent VLD bacterial inactivation ability.

Anti-inflammatory, antipyretic efficacy and safety of inhaled Houttuynia cordata thunb. essential oil formulation.

ETHNOPHARMACOLOGICAL RELEVANCE: Houttuynia cordata Thunb. (H. cordata) is a well-known folk traditional Chinese medicine that is renowned for its use in the management of inflammatory respiratory diseases and pneumonia. Its essential oils have demonstrated their anti-inflammatory efficacy in vitro, however, their in vivo biological effects via inhalation have not been elucidated. AIM OF THE STUDY: This study aims to evaluate the anti-inflammation and toxicology of H. cordata essential oil-containing formulation, H16 aerosol in vivo. MATERIALS AND METHODS: A laser diffraction particle size analyser and a Next Generation Impactor were used to measure the mass median aerodynamic diameter (MMAD) of the H16 aerosol. The anti-inflammatory and antipyretic effects of the H16 aerosol were evaluated in the xylene-evoked ear oedema and Brewer's yeast-induced fever models, respectively. The biological safety of the H16 aerosol was evaluated by acute toxicity and local toxicity tests in animal models. RESULTS: Our data showed that the MMAD of the bioactive aerosol was 3-5 µm, which implied tracheal and pharyngeal deposits. Significant anti-inflammatory and antipyretic effects were also observed in the animal models treated with H16 aerosol. The maximum tolerable dose of H16 in rats was >2.5 mL/kg. Irritation was not found on respiratory tract mucosa in the local toxicity test. CONCLUSIONS: Taken together, the present study suggested that H16 could be delivered in the form of aerosol and possessed its antipyretic and anti-inflammatory effects. This study provides a new perspective for the development of a new herbal aerosol therapy and herbal modernization.

2D materials for conducting holes from grain boundaries in perovskite solar cells.

Grain boundaries in organic-inorganic halide perovskite solar cells (PSCs) have been found to be detrimental to the photovoltaic performance of devices. Here, we develop a unique approach to overcome this problem by modifying the edges of perovskite grain boundaries with flakes of high-mobility two-dimensional (2D) materials via a convenient solution process. A synergistic effect between the 2D flakes and perovskite grain boundaries is observed for the first time, which can significantly enhance the performance of PSCs. We find that the 2D flakes can conduct holes from the grain boundaries to the hole transport layers in PSCs, thereby making hole channels in the grain boundaries of the devices. Hence, 2D flakes with high carrier mobilities and short distances to grain boundaries can induce a more pronounced performance enhancement of the devices. This work presents a cost-effective strategy for improving the performance of PSCs by using high-mobility 2D materials.

Plant-derived isoquinoline alkaloids that target ergosterol biosynthesis discovered by using a novel antifungal screening tool.

The ergosterol pathway is a prime antifungal target as it is required for fungal survival, yet is not involved in human homeostasis. Methods to study the ergosterol pathway, however, are often time-consuming. The minimum inhibitory concentration (MIC) assay is a simple research tool that determines the lowest concentration at which a novel antimicrobial is active in vitro with limited scope to determine the mechanism of action for a drug. In this study, we show that by adding hydrogen peroxide, an oxidative stressor, or glutathione (GSH), an antioxidant, to modify a commonly performed MIC assay allowed us to screen selectively for new antifungal drugs that target ergosterol biosynthesis in fungi. A human pathogen and dermatophyte, Microsporum gypseum, was used as a test organism. When exposed to ergosterol targeting drugs, the hydrogen peroxide treatment significantly decreased fungal survival by reducing ergosterol in the cell wall, whereas GSH increased survival of M. gypseum. Further, by performing a series of experiments with M. gypseum and Trichophyton rubrum, it was determined that the oxidative stress from hydrogen peroxide causes cell death at different developmental stages based on fungal species. These findings allow us to describe a simple, high-throughput method for simultaneously screening new antifungal drugs for activity and effects on the ergosterol pathway. By using this tool, two isoquinoline alkaloids were discovered to be potent inhibitors of ergosterol biosynthesis in vitro by reducing the amount of ergosterol without affecting the expression of 1,3-ß-glucan. Both compounds also significantly reduced the severity of acanthosis, hyperkeratosis, spongiosis and dermal edema in vivo.

Charge Energetics and Electronic Level Changes At the Copper(II) Phthalocyanine/Fullerene Junction Upon Photoexcitation.

Energy offset at the donor (D)/acceptor (A) interface plays an important role in charge separation in organic photovoltaics. Its magnitude determines the charge separation process under illumination. Extensive studies have been carried out for elucidating the charge transfer (CT) process at different D/A junctions. These works lead to two different views: upon photoexcitation, energies would be (1) consumed in molecular polarization and orientation such that those opposite charges would overcome mutual Coulombic attractive potential at the interface and (2) spent on promoting charges to high-lying delocalized energy states (i.e., hot states), which is necessarily important prior to charge separation. Under these two scheme of studies, the electronic structures and the charge behaviors at the D/A interface should be different under photoexcitation, yet there is so far no direct experimental approach for probing the changes in electronics structures (i.e., Fermi level, vacuum level, frontier molecular orbitals, etc.) upon photoexcitation. Herein, a modified photoelectron spectroscopy (PES) system with an additional solar simulator is used to study the charge distributions and electronic interactions for a standard D/A heterojunction (i.e., copper phthalocyanine (CuPc)/ fullerene (C60)) under photoexcitation. CT states formed as a result of photon energy transfer at the CuPc/C60 junction. Subsequent superpositions of charge transfer and electron polarization effects increase the D/A energy level offsets from 0.75 (ground state measured in the dark) to 1.07 eV (high-lying state measured upon illumination). We showed that there is excess energy consumed for a subtle change in the energy level alignment of the CuPc/C60 junction under illumination, suggesting a new insight for the energy loss mechanism during the photocharge generation processes.

Organic-Inorganic Charge Transfer Complex with Charge Modulation after Electrical Pre-biasing.

Several breakthroughs in organic optoelectronic devices with new applications and performance improvement have been made recently by exploiting novel properties of charge transfer complexes (CTCs). In this work, a CTC film formed by coevaporating molybdenum(VI) oxide and pentacene (MoO3:pentacene) shows a strong dipole of 2.4 eV with direction controllability via pre-biasing with an external voltage. While CTCs are most widely known for their much red-shifted energy gaps, there is so far no report on their controllable dipoles. By controlling this dipole with an electrical pre-bias in a MoO3:pentacene CTC based device, current changes over 2 orders of magnitude can be achieved. Kelvin probe force microscopy further confirms that surface potential of the MoO3:pentacene film can be modulated by an external electric field. It is shown for the first time that a dipole of controllable direction can be set up inside a CTC layer by pre-biasing. This concept is further tested by incorporating the CTC layer in organic photovoltaic (OPV) devices. It was demonstrated that by pre-biasing the OPV devices in different directions, their open circuit voltages (Voc) can be significantly tuned via the built-in potentials.

Formation of assimilable organic carbon (AOC) during drinking water disinfection: A microbiological prospect of disinfection byproducts.

Disinfection processes might alter the chemical structure of biological recalcitrant natural organic matter (NOM) in source water to form assimilable organic carbon (AOC), which can be readily utilized by microbes for growth. However, AOC has not been classified as disinfection byproducts (DBPs) before and little is known about the chemical and structural nature of AOC. This study, for the first time, considers the disinfection-induced AOC as DBPs from a microbiological perspective. The AOC formation by three types of disinfection processes, i.e., chlorination, UVC irradiation (254 nm) and photocatalysis represented by TiO2-UVA in drinking water containing two reference NOM materials of Suwannee River and Nordic Reservoir (SRNOM and NRNOM, respectively) were comparatively benchmarked using Pseudomonas aeruginosa as inoculum. Results showed that chlorination caused a substantial increase in AOC content, whereas TiO2-UVA led to a moderate increase in AOC content and UVC rendered the AOC content unchanged, independent of the types of NOM. Molecular weight indicated by spectral slope ratio and fluorescence fingerprint were found to not provide critical information about the AOC formation potential. FTIR and FT-ICR-MS results indicated that the AOC formation by chlorination was attributed to the oxidation and chlorine substitution on aromatic molecules to form molecules with carboxylic- and alcohol- functionalities, as well as chlorinated aromatics. These molecules could be metabolized and assimilated by Pseudomonas species by a catechol pathway. The results obtained in this study can provide valuable insight regarding the selection of proper technologies for disinfection to prevent microbial growth/regrowth in the distributing system and is intended to encourage more thinking and research on AOC as a new prospect of DBPs during disinfection of drinking water.

Airborne Survival of Escherichia coli under Different Culture Conditions in Synthetic Wastewater.

Bioaerosol generated in wastewater treatment plants has potential to harm human health. Survival of bacteria in bioaerosol during suspension is one of the major factors that affect its biological risk. It is hypothesized that bacteria grown in different wastewater have different physiology and lead to variation in airborne survival. This study investigated the relationship between the cultured conditions and the bioaerosol survival. Synthetic wastewater was used as the culture medium to simulate the water quality of wastewater. Escherichia coli BW25113 were cultured in different conditions, including growth salinity, growth temperature, growth pH, and presence of pesticide. The fatty acid composition and the reduction in airborne survival of the E. coli cultured under these conditions were determined and compared. Results showed that increasing growth salinity and temperature led to a lower reduction in airborne survival of E. coli.E. coli cultured at pH 6 had a higher reduction in airborne survival than those cultured at pH 7 and 8. Moreover, a correlation was observed between the membrane fluidity (fluidity index) and the reduction airborne survival for both aerosolization and airborne suspension. A link between culture conditions, bacterial membrane fluidity, and airborne survival was established. Culture conditions (wastewater quality) that lead to a low membrane fluidity of bacteria increase the airborne survival of bioaerosol, and vice versa. This provides a new aspect to evaluate bioaerosol survival and improve assessment on biological risk of bioaerosols.

In-Cabin Air Quality during Driving and Engine Idling in Air-Conditioned Private Vehicles in Hong Kong.

Many people spend lengthy periods each day in enclosed vehicles in Hong Kong. However, comparably limited data is available about in-cabin air quality in air-conditioned private vehicles, and the car usage that may affect the air quality. Fifty-one vehicles were tested for particulate matter (PM0.3 and PM2.5), total volatile organic compounds (TVOCs), carbon monoxide (CO), carbon dioxide (CO2), airborne bacteria, and fungi levels during their routine travel journey. Ten of these vehicles were further examined for PM0.3, PM2.5, TVOCs, CO, and CO2 during engine idling. In general, during driving PM2.5 levels in-cabin reduced overtime, but not PM0.3. For TVOCs, 24% vehicles exceeded the recommended Indoor Air Quality (IAQ) level in offices and public places set by the Hong Kong Environmental Protection Department. The total volatile organic compounds (TVOC) concentration positively correlated with the age of the vehicle. Carbon monoxide (CO) levels in all of the vehicles were lower than the IAQ recommendation, while 96% vehicles exceeded the recommended CO2 level of 1000 ppmv; 16% vehicles >5000 ppmv. Microbial counts were relatively low. TVOCs levels at idle engine were higher than that during driving. Although the time we spend in vehicles is short, the potential exposure to high levels of pollutants should not be overlooked.

Environmental Sustainability and Mold Hygiene in Buildings.

Environmental sustainability is one of the key issues in building management. In Hong Kong, one of the initiatives is to reduce the operation hours of air-conditioning in buildings to cut down energy consumption. In this study, we reported a mold contamination case in a newly refurbished laboratory, in which the air-conditioner was switched from 24- to 18-h mode after refurbishment. In order to prevent mold recurrence, the air-conditioner was switched back to 24-h mode in the laboratory. During the mold investigation, visible mold patches in the laboratory were searched and then cultured, counted and identified. Building and environmental conditions were recorded, and used to deduce different causes of mold contamination. Eight contaminated sites including a wall, a bench, some metal and plastic surfaces and seven types of molds including two Cladosporium spp., two Aspergillus spp., one Rhizopus sp., one Trichoderma sp., and one Tritirachium sp. were identified. Cladosporium spp. were the most abundant and frequently found molds in the laboratory. The contaminated areas could have one to five different species on them. Based on the mold and environmental conditions, several scenarios causing the mold contamination were deduced, and different mold control measures were discussed to compare them with the current solution of using 24-h air-conditioning to control mold growth. This study highlights the importance of mold hygiene in sustainable building management.

2D Perovskites with Short Interlayer Distance for High-Performance Solar Cell Application.

2D perovskites have emerged as one of the most promising photovoltaic materials owing to their excellent stability compared with their 3D counterparts. However, in typical 2D perovskites, the highly conductive inorganic layers are isolated by large organic cations leading to quantum confinement and thus inferior electrical conductivity across layers. To address this issue, the large organic cations are replaced with small propane-1,3-diammonium (PDA) cations to reduce distance between the inorganic perovskite layers. As shown by optical characterizations, quantum confinement is no longer dominating in the PDA-based 2D perovskites. This leads to considerable enhancement of charge transport as confirmed with electrochemical impedance spectroscopy, time-resolved photoluminescence, and mobility measurements. The improved electric properties of the interlayer-engineered 2D perovskites yield a power conversion efficiency of 13.0%. Furthermore, environmental stabilities of the PDA-based 2D perovskites are improved. PDA-based 2D perovskite solar cells (PSCs) with encapsulation can retain over 90% of their efficiency upon storage for over 1000 h, and PSCs without encapsulation can maintain their initial efficiency at 70 °C for over 100 h, which exhibit promising stabilities. These results reveal excellent optoelectronic properties and intrinsic stabilities of the layered perovskites with reduced interlayer distance.

Heat Treatment for Regenerating Degraded Low-Dimensional Perovskite Solar Cells.

Organolead halide perovskite devices are reported to be susceptible to thermal degradation, which results from heat-induced fast ion diffusion and structural decomposition. In this work, it is found that the performances of degraded low-dimensional perovskite solar cells can be considerably improved (e.g., power conversion efficiency shows ∼10% increase over the fresh device) by a short-time heat treatment (85 °C, 3 min). Capacitance-frequency, X-ray diffraction, and ionic diffusion calculation results suggest that heat treatment can enhance the crystallinity of the degraded low-dimensional perovskite and minimize the detrimental effects caused by water molecules, leading to improved performances. Our results indicate that the heat treatment does not necessarily lead to the accelerated degradation but can also regenerate the degraded low-dimensional perovskite.

Unconventional Nickel Nitride Enriched with Nitrogen Vacancies as a High-Efficiency Electrocatalyst for Hydrogen Evolution.

Development of high-performance and cost-effective non-noble metal electrocatalysts is pivotal for the eco-friendly production of hydrogen through electrolysis and hydrogen energy applications. Herein, the synthesis of an unconventional nickel nitride nanostructure enriched with nitrogen vacancies (Ni3N1-x ) through plasma-enhanced nitridation of commercial Ni foam (NF) is reported. The self-supported Ni3N1-x /NF electrode can deliver a hydrogen evolution reaction (HER) activity competitive to commercial Pt/C catalyst in alkaline condition (i.e., an overpotential of 55 mV at 10 mA cm-2 and a Tafel slope of 54 mV dec-1), which is much superior to the stoichiometric Ni3N, and is the best among all nitride-based HER electrocatalysts in alkaline media reported thus far. Based on theoretical calculations, it is further verified that the presence of nitrogen vacancies effectively enhances the adsorption of water molecules and ameliorates the adsorption-desorption behavior of intermediately adsorbed hydrogen, which leads to an advanced HER activity of Ni3N1-x /NF.

Importance of stress-response genes to the survival of airborne Escherichia coli under different levels of relative humidity.

Other than the needs for infection control to investigate the survival and inactivation of airborne bacterial pathogens, there has been a growing interest in exploring bacterial communities in the air and the effect of environmental variables on them. However, the innate biological mechanism influencing the bacterial viability is still unclear. In this study, a mutant-based approach, using Escherichia coli as a model, was used to prove the concept that common stress-response genes are important for airborne survival of bacteria. Mutants with a single gene knockout that are known to respond to general stress (rpoS) and oxidative stress (oxyR, soxR) were selected in the study. Low relative humidity (RH), 30-40% was more detrimental to the bacteria than high RH, >90%. The log reduction of ∆rpoS was always higher than that of the parental strain at all RH levels but the ∆oxyR had a higher log reduction than the parental strain at intermediate RH only. ∆soxR had the same viability compared to the parental strain at all RH levels. The results hint that although different types and levels of stress are produced under different RH conditions, stress-response genes always play a role in the bacterial viability. This study is the first reporting the association between stress-response genes and viability of airborne bacteria.