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 (NiCo₂O₄ ) 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 NiCo₂O₄ 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 NiCo₂O₄ 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 TiO₂ (E171) from foodstuffs and pharmaceutical products and separating the nano- and submicron-sized fractions.

<p>Schematic guide for isolating TiO₂ (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 (TiO₂) 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 TiO₂ (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 TiO₂ 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 (TiO₂) 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 TiO₂ that is nanoscale, or the physical and chemical properties of TiO₂ that influence its human and environmental fate or toxicity. Instead of analyzing TiO₂ properties in complex food or environmental samples, we procured samples of food-grade TiO₂ 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-TiO₂ that is generally sold for catalytic applications (P25) and widely used in toxicity studies, was analyzed for comparison. Food-grade and P25 TiO₂ 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 TiO₂ 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 TiO₂ 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 TiO₂. 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 TiO₂ suspension in deionized water ranged from −10 to −45 mV around pH 7, and the iso-electric point for food-grade TiO₂ (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 TiO₂. X-ray diffraction analysis confirmed the presence of anatase and/or rutile in the food-grade materials, and although the presence of amorphous TiO₂ could not be ruled out, it is unlikely on the basis of Raman analysis. The food-grade TiO₂ was solar photoactive. Cationic dyes adsorbed more readily to food-grade TiO₂ than P25, indicating very different potentials for interaction with organics in the environment. This research shows that food-grade TiO₂ contains engineered nanomaterials with properties quite different from those of P25, which has previously been used in many ecotoxicity studies, and because food-grade TiO₂ 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 TiO₂