112 research outputs found
Electrogenerated hydrophilic carbon nanomaterials with tailored electrocatalytic activity
This work investigates the influence of the type of buffer electrolyte used in the generation of Electrochemical Hydrophilic Carbon (EHC) on their physical-chemical properties and electrocatalytic activity. The EHC nanomaterials were prepared in three different biological buffers, phosphate, glycine and citrate buffers (EHC@phosphate, EHC@glycine, EHC@citrate) and their surface properties were fully characterized by AFM, XPS and Raman. The EHC nanomaterials drop cast onto a glassy carbon electrode were electrochemically characterized in [Fe(CN)6]3-/4- and [Ru(NH3)6]3+/2+ redox probes solutions, and their electrocatalytic activity was investigated towards hydrogen peroxide and oxygen reduction reactions (ORR) in a phosphate buffer solution. It was found that the nature of buffer electrolyte strongly influences the surface chemical state of the EHC materials, disorder degree in the hexagonal sp2 carbon network and oxygen functional groups, affecting both the EHC electrocatalytic activity towards the ORR and H2O2 reduction reaction. The most catalytic material for the ORR was EHC@citrate, whereas EHC@glycine showed the highest oxygen conversion (n ≅ 2.7 to 3). Moreover, it was shown that the content of oxygen singly bonded to carbon correlates strongly with the number of electrons transferred.
A very singular behaviour in the electrochemical reduction of hydrogen peroxide was observed on EHC@glycine, qualitatively interpreted as an autocatalytic reaction. In contrast, a blocking-like effect was depicted on EHC@phosphate. These results must have an important impact in the development of materials with peroxidase-like activity and in the design of O2 sensors with non-sensitivity to H2O2.publishe
Determinants of workplace exposure and release of ultrafine particles during atmospheric plasma spraying in the ceramic industry
Atmospheric plasma spraying (APS) is a frequently used technique to produce
enhanced-property coatings for different materials in the ceramic industry. This work
aimed to characterise and quantify the impact of APS on workplace exposure to
airborne particles, with a focus on ultrafine particles (UFPs, <100 nm) and
nanoparticles (<50 nm). Particle number, mass concentrations, alveolar lung deposited
surface area concentration, and size distributions, in the range 10 nm – 20 μm were
simultaneously monitored at the emission source, in the worker breathing zone, and in
outdoor air. Different input materials (known as feedstock) were tested: (a) micro-sized
powders, and (b) suspensions containing submicron- or nano-sized particles. Results
evidenced significant UFP emissions (up to 3.3x106/cm3) inside the projection
chamber, which impacted exposure in the breathing zone outside the projection
chamber (up to 8.3x105/cm3). Environmental release of UFPs was also detected and
quantified (3.9x105/cm330 ). Engineered nanoparticle (ENP) release to workplace air was
also evidenced by TEM microscopy. UFP emissions were detected during the
application of both micro-sized powder and suspensions containing submicron- or
nano-sized particles, thus suggesting that emissions were process- (and not material-)
dependent. An effective risk prevention protocol was implemented, which resulted in a
reduction of worker UFP exposure in the breathing zone. These findings evidence the
potential risk of occupational exposure to UFPs during atmospheric plasma spraying,
and raise the need for further research on UFP formation mechanisms in high-energy
industrial processes
Ultrafine and nanoparticle formation and emission mechanisms during laser processing of ceramic materials
The use of laser technology in the ceramic industry is undergoing an increasing trend, as it improves surface properties. The present work aimed to assess ultrafine and nanoparticle emissions from two different types of laser treatments (tile sintering and ablation) applied to two types of tiles. New particle formation mechanisms were identified, as well as primary nanoparticle emissions, with concentrations reaching up to 6.7 x 10(6) particles Cm-3 and a mean diameter of 18 nm. Nanoparticle emission patterns were strongly dependent on temperature and raw tile chemical composition. Nucleation events were detected during the thermal treatment independently of the laser application. TOM images evidenced spherical ultrafine particles, originating from the tile melting processes. When transported across the indoor environment, particles increased in size (up to 38 nm) with concentrations remaining high (2.3 x 10(6) particles cm(-3)), Concentrations of metals such as Zn, Pb, Cu, Cr, As and al were found in particles < 250 nm
Health risk assessment from exposure to particles during packing in working environments
Packing of raw materials in work environments is a known source of potential health
impacts (respiratory, cardiovascular) due to exposure to airborne particles. This activity
was selected to test different exposure and risk assessment tools, aiming to
understand the effectiveness of source enclosure as a strategy to mitigate particle
release. Worker exposure to particle mass and number concentrations was monitored
during packing of 7 ceramic materials in 3 packing lines in different settings, with low
(L), medium (M) and high (H) degrees of source enclosure. Results showed that
packing lines L and M significantly increased exposure concentrations (119-609 μg m-3
respirable, 1150-4705 μg m-3 inhalable, 24755-51645 cm-3 particle number), while nonsignificant
increases were detected in line H. These results evidence the effectiveness
of source enclosure as a mitigation strategy, in the case of packing of ceramic
materials. Total deposited particle surface area during packing ranged between 5.4-11.8x105 μm2 min-1, with particles depositing mainly in the alveoli (51-64%) followed by
head airways (27-41%) and trachea bronchi (7-10%). The comparison between the
results from different risk assessment tools (Stoffenmanager, ART, NanoSafer) and the
actual measured exposure concentrations evidenced that all of the tools overestimated
exposure concentrations, by factors of 1.5-8. Further research is necessary to bridge
the current gap between measured and modelled health risk assessments
The Role of Rosmarinic Acid on the Bioproduction of Gold Nanoparticles as Part of a Photothermal Approach for Breast Cancer Treatment.
Breast cancer is a high-burden malignancy for society, whose impact boosts a continuous search for novel diagnostic and therapeutic tools. Among the recent therapeutic approaches, photothermal therapy (PTT), which causes tumor cell death by hyperthermia after being irradiated with a light source, represents a high-potential strategy. Furthermore, the effectiveness of PTT can be improved by combining near infrared (NIR) irradiation with gold nanoparticles (AuNPs) as photothermal enhancers. Herein, an alternative synthetic method using rosmarinic acid (RA) for synthesizing AuNPs is reported. The RA concentration was varied and its impact on the AuNPs physicochemical and optical features was assessed. Results showed that RA concentration plays an active role on AuNPs features, allowing the optimization of mean size and maximum absorbance peak. Moreover, the synthetic method explored here allowed us to obtain negatively charged AuNPs with sizes favoring the local particle accumulation at tumor site and maximum absorbance peaks within the NIR region. In addition, AuNPs were safe both in vitro and in vivo. In conclusion, the synthesized AuNPs present favorable properties to be applied as part of a PTT system combining AuNPs with a NIR laser for the treatment of breast cancer
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