The photocurrent-voltage characteristic of a photoelectrochemical cell for solar hydrogen production via water splitting, using undoped-hematite as photoanode, was obtained. Photoelectrochemical ...characteristics of the cell were also investigated by electrochemical impedance spectroscopy. Both techniques were carried out in the dark and under illumination. The analysis of the frequency spectra for the real and imaginary parts of the complex impedance allowed obtaining equivalent electrical analogs for the PEC cell operating in the dark and under 1 sun simulated illumination. Additionally, different electrode configurations were used (two and three-electrode arrangements). The two-electrode configuration allowed the study of the overall charge transfer phenomena occurring at the semiconductor, within the electrolyte and at the counter-electrode side of the cell, whereas the three-electrode configuration gave more detailed information concerning the double charged layer at the semiconductor/electrolyte interface.
A phenomenological model is proposed for a better understanding of the basic mechanisms of photoelectrochemical (PEC) cells. The main assumptions of the one-dimensional transient phenomenological ...model are: i) bulk recombination of the conduction band electrons with holes in the valence band; ii) the mobile charge transport takes place via diffusion, which arises from the concentration profiles, and migration, caused by a macroscopic electric field; iii) negligible effects of microscopic electric fields in the cell and screening effects, as well as negligible Helmholtz and diffuse layers. For modeling purposes, the photoanode was assumed to be a homogeneous nanocrystalline hematite structure, with thickness
L, porosity
ɛ
p
and tortuosity
τ. The TCO/semiconductor interface was modeled as an ideal ohmic contact, while the electrolyte/platinized TCO interface was described by a Butler–Volmer approach. An alkaline electrolyte solution was used, allowing the transport of the ionic species from the counter-electrode to the photoanode. The continuity and transport governing equations are defined for the mobile species involved: electrons in the conduction band of the semiconductor, holes in the valence band and hydroxyl ions in the electrolyte. Simulated
I–
V characteristics were computed and the corresponding results compared with the experimental values. The simulated results were in straight agreement with the experimental data.
The present work reports the photoelectrochemical characterization of a dye-sensitized solar cell (DSC) to assist water split in a photoelectrochemical (PEC) cell. Performance parameters were ...extracted from standard current–voltage characteristic (
I–V) and the charge transfer phenomena occurring at different interfaces of the DSC were evaluated by electrochemical impedance spectroscopy (EIS). The DSC comprised the N719 dye and a robust electrolyte (1-propyl-3-methylimidazolium iodide in guanidinium thiocyanate additive). At 1 sun illumination the DSC yielded a short-circuit photocurrent density of 14.9 mA cm
−2, an open-circuit voltage of 0.797 V, a fill factor of 0.712 and an overall efficiency of 8.5%. Different PEC systems based on silicon-doped and undoped hematite photoelectrodes were considered. The required additional anodic bias necessary for actual water cleavage was supplied by two DSCs in series operating just under open-circuit voltage (1.56 V), allowing a conversion efficiency of about 1.12% for the silicon-doped hematite deposited by APCVD, 0.51% for the silicon-doped prepared by USP and 0.12% for the undoped hematite sample.
UV-stabilizers are a class of additives that provide extended polymer resistance to UV-degradation, but have also been suggested to have antimicrobial activity, potentially preventing the spread of ...pathogens, and inhibiting microbial-induced biodegradation. In this work, we incorporated different UV-stabilizers, a hindered amine light stabilizer (HALS), Tinuvin 770 DF and Tinuvin PA 123, or a hybrid HALS/UV-absorber, Tinuvin 5151, in polyurethane formulations to produce lacquer-films, and tested their antimicrobial activity against Staphylococcus aureus (methicillin-resistant and -sensitive strains), Escherichia coli and Candida albicans . Lacquer-films incorporated with Tinuvin 770 DF showed strong antimicrobial performance against bacteria and fungi, while maintaining cytocompatibility. The mechanism of action revealed a positive relationship between Tinuvin 770 DF concentration, microbial death, and reactive nitrogen species (RNS), suggesting that RNS produced during autoxidation of Tinuvin 770 DF is responsible for the antimicrobial properties of this UV-stabilizer. Conversely, lacquer-films incorporated with Tinuvin 5151 or Tinuvin PA 123 exhibited no antimicrobial properties. Collectively, these results highlight the commercial potential of Tinuvin 770 DF to prevent photo- and biodegradation of polymers, while also inhibiting the spread of potentially harmful pathogens. Furthermore, we provide a better understanding of the mechanism underlying the biocidal activity of HALS associated to autooxidation of the amine group.
Microorganisms can be found in almost all environments with high-touch surfaces being an important fomite for microbial growth. Considering the health issues associated to acquired infection from ...inanimate surfaces, as well as the raising hygienic concerns, the incorporation of antimicrobial compounds in high-touch surfaces emerges as an effective solution for biomedical and common daily applications.
In this work, we incorporated different antimicrobial agents (phenolic-, ionic- and copper-based compounds) into polyurethane commercial formulations to produce antimicrobial lacquer-films and evaluated not only their physical/chemical properties, but also their antimicrobial activity against bacteria (Staphylococcus aureus, Escherichia coli), fungi (Candida albicans), and virus (SARS-CoV-2).
The incorporation of antimicrobial agents did not affect the performance of lacquer-films and the main properties were maintained, specifically the visual aspect, gloss values, optical properties and chemical stability.
Among the different compounds tested, copper-based lacquer-films exhibited the strongest antibacterial and antifungal activity, with a >4 log reduction, but not against virus. Importantly, copper-based lacquer-films maintained their cytocompatibility, even at high concentrations. Regarding the ionic lacquer-films, the highest tested concentration also showed a strong antimicrobial action (5 log reduction) against fungi and gram-positive bacteria, but not against gram-negative bacteria and virus. However, at this concentration, the ionic-containing lacquer-films presented cytotoxic potential. The phenolic-based compounds were not associated with antimicrobial activity, regardless the concentrations tested.
Collectively, these results highlight the potential of incorporating antimicrobial agents in polyurethane surface coatings as a promising strategy to avoid the microbial colonization on inanimate surfaces and, ultimately, prevent the spreading of potentially harmful pathogens among humans.
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Cystic fibrosis (CF) patients with
Burkholderia cepacia
complex
(Bcc) pulmonary infections have high morbidity and mortality. The aim of this study
was to compare different methods for identification ...of Bcc species isolated from
paediatric CF patients. Oropharyngeal swabs from children with CF were used to obtain
isolates of Bcc samples to evaluate six different tests for strain identification.
Conventional (CPT) and automatised (APT) phenotypic tests, polymerase chain reaction
(PCR)-
recA
, restriction fragment length
polymorphism-
recA
,
recA
sequencing, and
matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) were applied.
Bacterial isolates were also tested for antimicrobial susceptibility.
PCR-
recA
analysis showed that 36 out of the 54 isolates were Bcc.
Kappa index data indicated almost perfect agreement between CPT and APT, CPT and
PCR-
recA
, and APT and PCR-
recA
to identify Bcc,
and MALDI-TOF and
recA
sequencing to identify Bcc species. The
recA
sequencing data and the MALDI-TOF data agreed in 97.2% of the
isolates. Based on
recA
sequencing, the most common species
identified were
Burkholderia cenocepacia
IIIA
(33.4%),
Burkholderia vietnamiensis
(30.6%),
B.
cenocepacia
IIIB (27.8%),
Burkholderia multivorans
(5.5%), and
B. cepacia
(2.7%). MALDI-TOF proved to be a useful tool
for identification of Bcc species obtained from CF patients, although it was not able
to identify
B. cenocepacia
subtypes.
A phenomenological model is proposed for a better understanding of the basic working mechanisms of dye-sensitized solar cells (DSCs). A steady-state approach allows the construction of the
I–
V ...characteristics, giving important informations about the main factors that influence DSCs’ performance. On the other hand, the transient approach model is an important tool to relate the phenomenological behavior with certain dynamic techniques, such as Electrochemical Impedance Spectroscopy (EIS). Bearing in mind the uncertainty arising from fitting the experimental Nyquist diagrams to general electrical analogues, this transient model contributes for a deeper understanding of the DSCs and for obtaining the relevant kinetic parameters with higher accuracy. The one-dimensional transient phenomenological model presented here assumes that the injected conduction-band electrons may recombine only with the electrolyte redox species. Due to the small dimension of the titania particles, no significant electrical potential gradient is considered, resulting only in a diffusive electron transport across the semiconductor. For modeling purposes, the mesoscopic porous structure, consisting of TiO
2 nanoparticles covered with light-absorbing dye molecules and interpenetrated by the
I
-
/
I
3
-
redox mediator (electrolyte), is considered as a homogeneous nanocrystalline structure of thickness
L. The continuity and transport governing equations are defined for the mobile species involved: electrons in the TiO
2 conduction band and
I
-
/
I
3
-
ions in the electrolyte. The simulated results are in straight agreement with the experimental data.
The predisposition of patients with cystic fibrosis (CF) for recurrent pulmonary infections can result in poor prognosis of the disease. Although the clinical significance in CF of micro-organisms, ...such as Staphylococcus aureus, Haemophilus influenzae and Pseudomonas aeruginosa, is well established, the implication of uncommon glucose non-fermenting Gram-negative bacilli (UGNF-GNB) in respiratory samples from CF patients is still unclear. Because of limitations of traditional methods used in most clinical laboratories, the accurate identification of these microbes is a challenge. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) is an alternative tool for efficient identification of bacteria. This was a retrospective study to evaluate different identification methods in a collection of UGNF-GNB isolated from children with CF during a period of three years. The performance of MALDI-TOF was compared to that of 16S rDNA gene sequencing and to a conventional and automated phenotypic identification. The discriminatory power of MALDI-TOF (75.0 % agreement) was superior to automated techniques (67.1 % agreement) and to conventional phenotypical identification (50.0 % agreement). MALDI-TOF also demonstrated high accuracy in identifying Stenotrophomonas maltophilia, Achromobacter xylosoxidans and Chryseobacterium indologenes, but had limited utility in identifying Pandoraea spp. and some species of Acinetobacter and Chryseobacterium (other than C. indologenes). Although MALDI-TOF identified only 75 % of the isolates in comparison with 16S rDNA gene sequencing, the prompt identification and high discriminatory power exhibited by MALDI-TOF make it a useful tool for the characterization of micro-organisms that are difficult to identify using routine methods.
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