16 research outputs found
Effect of Urine Compounds on the Electrochemical Oxidation of Urea Using a Nickel Cobaltite Catalyst: An Electroanalytical and Spectroscopic Investigation
Cyclic
voltammetry (CV) and in situ attenuated total reflectance
Fourier transform infrared (ATR-FTIR) spectroscopy were used to investigate
the effect of major urine compounds on the electro-oxidation activity
of urea using a nickel cobaltite (NiCo<sub>2</sub>O<sub>4</sub> )
catalyst. As a substrate, carbon paper exhibited better benchmark
potential and current values compared with stainless steel and fluorine-doped
tin oxide glass, which was attributed to its greater active surface
area per electrode geometric area. CV analysis of synthetic urine
showed that phosphate, creatinine, and gelatin (i.e., proteins) had
the greatest negative effect on the electro-oxidation activity of
urea, with decreases in peak current up to 80% compared to that of
a urea-only solution. Further investigation of the binding mechanisms
of the deleterious compounds using in situ ATR-FTIR spectroscopy revealed
that urea and phosphate weakly bind to NiCo<sub>2</sub>O<sub>4</sub> through hydrogen bonding or long-range forces, whereas creatinine
interacts strongly, forming deactivating inner-sphere complexes. Phosphate
is presumed to disrupt the interaction between urea and NiCo<sub>2</sub>O<sub>4</sub> by serving as a hydrogen-bond acceptor in place of
catalyst sites. The weak binding of urea supports the hypothesis that
it is oxidized through an indirect electron transfer. Outcomes of
this study contribute to the development of electrolytic systems for
treating source-separated urine
Single-Particle Analysis of the Photodegradation of Submicron Polystyrene Particles Using Infrared Photothermal Heterodyne Imaging
Sunlight irradiation is the predominant
process for degrading
plastics
in the environment, but our current understanding of the degradation
of smaller, submicron (<1000 nm) particles is limited due to prior
analytical constraints. We used infrared photothermal heterodyne imaging
(IR-PHI) to simultaneously analyze the chemical and morphological
changes of single polystyrene (PS) particles (∼1000 nm) when
exposed to ultraviolet (UV) irradiation (λ = 250–400
nm). Within 6 h of irradiation, infrared bands associated with the
backbone of PS decreased, accompanied by a reduction in the particle
size. Concurrently, the formation of several spectral features due
to photooxidation was attributed to ketones, carboxylic acids, aldehydes,
esters, and lactones. Spectral outcomes were used to present an updated
reaction scheme for the photodegradation of PS. After 36 h, the average
particle size was reduced to 478 ± 158 nm. The rates of size
decrease and carbonyl band area increase were −24 ± 3.0
nm h–1 and 2.1 ± 0.6 cm–1 h–1, respectively. Using the size-related rate,
we estimated that under peak terrestrial sunlight conditions, it would
take less than 500 h for a 1000 nm PS particle to degrade to 1 nm
SEM micrographs of human intestine <i>in vitro</i> cell models exposed to gum-E171 nano- or submicron-enriched fractions.
<p>(a) Epithelia exposed to 1 μg/mL of submicron-enriched fraction in the upright configuration resulted in a large number of particles (white arrows) decorating the surface of the epithelium after 7 minutes of exposure. (b) However, exposing replicate samples to the nano-enriched fraction with 1 μg/mL for 7 minutes in the upright configuration resulted in few particles adhered to the epithelial surface. (c) Inverting the epithelium and subsequently exposing the cells with 1 μg/mL of the submicron-enriched fraction for 7 minutes resulted in few particles adhered to the epithelial surface. (d) However, exposing replicate samples in the inverted configuration to 1 μg/mL of the nano-enriched fraction for 7 minutes resulted in relatively more particles adhered to the epithelial surface. All images are shown at identical magnification. Scale bar is 5 μm.</p
Primary particle analysis via TEM reveals a difference in size between nano- and submicron-enriched fractions after the sucrose step-gradient centrifugation procedure.
<p>(a) Submicron-enriched commercial-grade E171 appear large compared to (b) the nano-enriched fraction. (c) Utilizing the same procedure on gum-E171 revealed a large, submicron-enriched fraction and (d) a small, nano-enriched fraction. All images are shown at identical magnification. The scale bar in the lower right corner of each micrograph is 100 nm.</p
Primary particle analysis using TEM for commercial-grade E171 and gum-E171 nano- and submicron-enriched fractions.
<p>Primary particle analysis using TEM for commercial-grade E171 and gum-E171 nano- and submicron-enriched fractions.</p
Cumulative size distribution for TEM primary particle analysis of commercial-grade E171 and gum-E171 nano- and submicron-enriched fractions.
<p>Solid vertical line indicates nanoparticle size cutoff using the 100 nm definition.</p
Schematic guide for isolating TiO<sub>2</sub> (E171) from foodstuffs and pharmaceutical products and separating the nano- and submicron-sized fractions.
<p>Schematic guide for isolating TiO<sub>2</sub> (E171) from foodstuffs and pharmaceutical products and separating the nano- and submicron-sized fractions.</p
A Facile Method for Separating and Enriching Nano and Submicron Particles from Titanium Dioxide Found in Food and Pharmaceutical Products
<div><p>Recent studies indicate the presence of nano-scale titanium dioxide (TiO<sub>2</sub>) as an additive in human foodstuffs, but a practical protocol to isolate and separate nano-fractions from soluble foodstuffs as a source of material remains elusive. As such, we developed a method for separating the nano and submicron fractions found in commercial-grade TiO<sub>2</sub> (E171) and E171 extracted from soluble foodstuffs and pharmaceutical products (<i>e</i>.<i>g</i>., chewing gum, pain reliever, and allergy medicine). Primary particle analysis of commercial-grade E171 indicated that 54% of particles were nano-sized (<i>i</i>.<i>e</i>., < 100 nm). Isolation and primary particle analysis of five consumer goods intended to be ingested revealed differences in the percent of nano-sized particles from 32%‒58%. Separation and enrichment of nano- and submicron-sized particles from commercial-grade E171 and E171 isolated from foodstuffs and pharmaceuticals was accomplished using rate-zonal centrifugation. Commercial-grade E171 was separated into nano- and submicron-enriched fractions consisting of a nano:submicron fraction of approximately 0.45:1 and 3.2:1, respectively. E171 extracted from gum had nano:submicron fractions of 1.4:1 and 0.19:1 for nano- and submicron-enriched, respectively. We show a difference in particle adhesion to the cell surface, which was found to be dependent on particle size and epithelial orientation. Finally, we provide evidence that E171 particles are not immediately cytotoxic to the Caco-2 human intestinal epithelium model. These data suggest that this separation method is appropriate for studies interested in isolating the nano-sized particle fraction taken directly from consumer products, in order to study separately the effects of nano and submicron particles.</p></div
TEM primary particle analysis for TiO<sub>2</sub> found in selected foodstuffs and pharmaceuticals.
<p>(a) commercial-grade E171 (b) chewing gum (c) name-brand allergy medicine, (d) generic allergy medicine, (e) name-brand pain reliever, and (f) generic pain reliever medicine. All images are shown at identical magnification. Scale bar in the lower right corner of each micrograph is 100 nm.</p
Characterization of Food-Grade Titanium Dioxide: The Presence of Nanosized Particles
Titanium
dioxide (TiO<sub>2</sub>) is widely used in food products,
which will eventually enter wastewater treatment plants and terrestrial
or aquatic environments, yet little is known about the fraction of
this TiO<sub>2</sub> that is nanoscale, or the physical and chemical
properties of TiO<sub>2</sub> that
influence its human and environmental fate or toxicity. Instead of
analyzing TiO<sub>2</sub> properties in complex food or environmental
samples, we procured samples of food-grade TiO<sub>2</sub> obtained
from global food suppliers and then, using spectroscopic and other
analytical techniques, quantified several parameters (elemental composition,
crystal structure, size, and surface composition) that are reported
to influence environmental fate and toxicity. Another sample of nano-TiO<sub>2</sub> that is generally sold for catalytic applications (P25) and
widely used in toxicity studies, was analyzed for comparison. Food-grade
and P25 TiO<sub>2</sub> are engineered products, frequently synthesized
from purified titanium precursors, and not milled from bulk scale
minerals. Nanosized materials were present in all of the food-grade
TiO<sub>2</sub> samples,
and transmission electron microscopy showed that samples 1–5
contained 35, 23, 21, 17, and 19% of nanosized primary particles (<100
nm in diameter) by number, respectively
(all primary P25 particles were <100 nm in diameter). Both types
of TiO<sub>2</sub> aggregated in water with an average hydrodynamic
diameter of >100 nm. Food-grade samples contained phosphorus (P),
with concentrations ranging from 0.5 to 1.8 mg of P/g of TiO<sub>2</sub>. The phosphorus content of P25 was below inductively coupled plasma
mass spectrometry
detection limits. Presumably because of a P-based coating detected
by X-ray photoelectron spectroscopy, the ζ potential of the
food-grade TiO<sub>2</sub> suspension in deionized water ranged from
−10
to −45 mV around pH 7, and the iso-electric point for food-grade
TiO<sub>2</sub> (2 (Si content of 0.026–0.062%
and Al content of 0.0006–0.810%) was also different from the
case for P25 and would influence the
environmental fate of TiO<sub>2</sub>. X-ray diffraction analysis
confirmed the presence of anatase and/or rutile in the food-grade
materials, and although the presence of amorphous TiO<sub>2</sub> could
not be ruled out, it is unlikely on the basis of Raman analysis. The
food-grade TiO<sub>2</sub> was solar photoactive. Cationic dyes adsorbed
more readily to food-grade TiO<sub>2</sub> than P25, indicating very
different potentials for interaction with
organics in the environment. This research shows that food-grade TiO<sub>2</sub> contains engineered nanomaterials with properties quite different
from those of P25, which has previously been used in many ecotoxicity
studies, and because food-grade TiO<sub>2</sub> is more likely than
P25 to enter the environment (i.e., potentially higher exposure levels),
there is a need to design environmental (and human) fate and toxicity
studies comparing food-grade to catalytic TiO<sub>2</sub>