Graphene Oxide and Graphene Oxide-TiO2 Nanocomposites: Synthesis, Characterization, and Rhodamine B Photodegradation Investigation.

In this study, graphene oxide (GO) sheets were successfully synthesized using two routes: conventional Hummers' (HGO) and modified Hummers' (or Marcano's) (MGO) methods. GO sheets were then assembled with TiO2 nanoparticles to form nanocomposites (i.e., HGO-TO and MGO-TO). The properties of HGO and MGO and their nanocomposites with TiO2 were evaluated by Fouriertransform infrared (FTIR), Raman, ultraviolet-visible (UV-Vis) adsorption, and diffuse reflectance (DRS) spectroscopies, X-ray diffraction (XRD), and thermal gravimetric analysis (TGA). The specific surface area, pore volume, and pore size of MGO, determined by Brunauer-Emmett-Teller (BET) equation, were 565 m²g-1, 376 cm³ g-1, and 30 nm, respectively; all of these parameters decreased after MGO was combined with TiO2. In addition, compared with HGO, MGO possessed higher oxidation level and more stable bonding with TiO2 nanoparticles. The morphology of HGO and MGO, which were characterized by scanning electron (SEM) and transmission electron microscopies (TEM), together with energy-dispersive X-ray (EDX) spectroscopy and elemental mapping technique, was determined to consist of TiO2 nanoparticle-assembled GO sheets. All GO-TiO2 nanocomposite samples exhibited a very high activity (˜100%) toward rhodamine B (RhB) dye photodegradation under natural sunlight exposure within 60 min. The obtained results for the GO-TiO2 nanocomposite showed the potential of its application in wastewater purification and other environmental aspects.

Numerical modeling of nanoparticle deposition in realistic monkey airway and human airway models: a comparative study.

BACKGROUND: One of the most promising approaches to understand inhalation toxicology and to assess the potential risks of inhaled particles is to examine the disposition of the hazardous airborne particles in the monkey airway. This study presents a comparative, numerical investigation of nanoparticle deposition in the monkey and human airway models. MATERIALS AND METHODS: Computational fluid dynamics (CFD) method was applied to analyze the steady flow rates under light and moderate metabolic conditions. The nanoparticles, ranging from 5 to 100 nm in diameter, were used to predict the total and regional deposition fraction in both the models. RESULTS: The Brownian and turbulent motion significantly impacted the transportation and deposition of nanoparticles as evidenced by the large fluctuations of particle acceleration. A higher deposition efficiency was observed in the monkey model at the particle size of 25 nm or less. Nonetheless, on applying the geometric factors for combined diffusion term parameters, the total deposition fraction of both models converged into a single curve. The site-specific deposition of the particles of size 5 nm in the vestibule, valve, and nasal turbinate regions of the monkey model was observed to be greater compared to the human model. A study of the deposition curves of the particle diameter ranging from 2 nm to 10 µm showed that the highest deposition rates were associated with particles of size 2 nm and 10 µm. CONCLUSIONS: The results of this study can contribute to the research involving extrapolation of inhalation toxicology studies, from monkeys to humans.

Particle and inhalation exposure in human and monkey computational airway models.

Regional deposition of inhaled aerosols is essential for assessing health risks from toxic exposure. Upper airway physiology plays a significant role in respiratory defense by filtering micrometer particles, whose deposition mechanism is predominantly inertial impaction and is mainly controlled by airflow characteristics. The monkey is commonly used in tests that study inhalation toxicity as well as in preclinical tests as human surrogates due to their anatomical similarities to humans. Therefore, accurate predictions and an understanding of the inhaled particles and their distribution in monkeys are essential for extrapolating laboratory animal data to humans. The study goals were as follows: (1) to predict the particle deposition based on aerodynamic diameters (1-10 µm) and various steady inspiratory flow rates in computational models of monkey and human upper airways; and (2) to investigate potential differences in inhalation flow and particle deposition between humans and monkeys by comparing numerical simulation results with similar in-vitro and in-vivo measurements from recent literature. The deposition fractions of the monkey's numerical airway model agreed well with in-vitro and human model data when equivalent Stokes numbers were compared, based on the minimum cross-sectional area as representative of length scale. Vestibule removal efficiencies were predicted to be higher in the monkey model compared with the human model. Our results revealed that the particle transportations were sensitive to the anatomical structure, airway geometry, airflow rates, inflow boundary conditions and particle size.