Behavior of TiO₂ Released from Nano-TiO₂‑Containing Paint and Comparison to Pristine Nano-TiO₂

In the assessment of the fate and effects of engineered nanomaterials (ENM), the current focus is on studying the pristine, unaltered materials. However, ENM are incorporated into products and are released over the whole product life cycle, though mainly during the use and disposal phases. So far, released ENMs have only been characterized to a limited extent and almost nothing is known about the behavior of these materials under natural conditions. In this work we obtained material that was released from aged paint containing nano-TiO₂, characterized the particulate materials, and studied their colloidal stability in media with different pH and ionic composition. A stable suspension was obtained from aged paint powder by gentle shaking in water, producing a dilute suspension of 580 μg/L TiO₂ with an average particle size of 200–300 nm. Most particles in this suspension were small pieces of paint matrix that also contained nano-TiO₂. Some free nano-TiO₂ particles were observed by electron microscopy, but the majority was enclosed by the organic paint binder. The pristine nano-TiO₂ showed the expected colloidal behavior with increasing stability with increasing pH and strong agglomeration above the isoelectric point and settling in the presence of Ca. The released TiO₂ showed very small variations in particle size, ζ potential, and colloidal stability, even in the presence of 3 mM Ca. The results show that the behavior of released ENM may not necessarily be predicted by studying the pristine materials. Additionally, effect studies need to focus more on the particles that are actually released as we can expect that the toxic effect will also be markedly different between pristine and product released materials

Effects of a Combined Diesel Particle Filter-DeNOx System (DPN) on Reactive Nitrogen Compounds Emissions: A Parameter Study

The impact of a combined diesel particle filter-deNO_<i>x</i> system (DPN) on emissions of reactive nitrogen compounds (RNCs) was studied varying the urea feed factor (α), temperature, and residence time, which are key parameters of the deNO_<i>x</i> process. The DPN consisted of a platinum-coated cordierite filter and a vanadia-based deNO_<i>x</i> catalyst supporting selective catalytic reduction (SCR) chemistry. Ammonia (NH₃) is produced in situ from thermolysis of urea and hydrolysis of isocyanic acid (HNCO). HNCO and NH₃ are both toxic and highly reactive intermediates. The deNO_<i>x</i> system was only part-time active in the ISO8178/4 C1cycle. Urea injection was stopped and restarted twice. Mean NO and NO₂ conversion efficiencies were 80%, 95%, 97% and 43%, 87%, 99%, respectively, for α = 0.8, 1.0, and 1.2. HNCO emissions increased from 0.028 g/h engine-out to 0.18, 0.25, and 0.26 g/h at α = 0.8, 1.0, and 1.2, whereas NH₃ emissions increased from <0.045 to 0.12, 1.82, and 12.8 g/h with maxima at highest temperatures and shortest residence times. Most HNCO is released at intermediate residence times (0.2–0.3 s) and temperatures (300–400 °C). Total RNC efficiencies are highest at α = 1.0, when comparable amounts of reduced and oxidized compounds are released. The DPN represents the most advanced system studied so far under the VERT protocol achieving high conversion efficiencies for particles, NO, NO₂, CO, and hydrocarbons. However, we observed a trade-off between deNO_<i>x</i> efficiency and secondary emissions. Therefore, it is important to adopt such DPN technology to specific application conditions to take advantage of reduced NO_<i>x</i> and particle emissions while avoiding NH₃ and HNCO slip

PCDD/F Formation in an Iron/Potassium-Catalyzed Diesel Particle Filter

Catalytic diesel particle filters (DPFs) have evolved to a powerful environmental technology. Several metal-based, fuel soluble catalysts, so-called fuel-borne catalysts (FBCs), were developed to catalyze soot combustion and support filter regeneration. Mainly iron- and cerium-based FBCs have been commercialized for passenger cars and heavy-duty vehicle applications. We investigated a new iron/potassium-based FBC used in combination with an uncoated silicon carbide filter and report effects on emissions of polychlorinated dibenzodioxins/furans (PCDD/Fs). The PCDD/F formation potential was assessed under best and worst case conditions, as required for filter approval under the VERT protocol. TEQ-weighted PCDD/F emissions remained low when using the Fe/K catalyst (37/7.5 μg/g) with the filter and commercial, low-sulfur fuel. The addition of chlorine (10 μg/g) immediately led to an intense PCDD/F formation in the Fe/K-DPF. TEQ-based emissions increased 51-fold from engine-out levels of 95 to 4800 pg I-TEQ/L after the DPF. Emissions of 2,3,7,8-TCDD, the most toxic congener (TEF = 1.0), increased 320-fold, those of 2,3,7,8-TCDF (TEF = 0.1) even 540-fold. Remarkable pattern changes were noticed, indicating a preferential formation of tetrachlorinated dibenzofurans. It has been shown that potassium acts as a structural promoter inducing the formation of magnetite (Fe₃O₄) rather than hematite (Fe₂O₃). This may alter the catalytic properties of iron. But the chemical nature of this new catalyst is yet unknown, and we are far from an established mechanism for this new pathway to PCDD/Fs. In conclusion, the iron/potassium-catalyzed DPF has a high PCDD/F formation potential, similar to the ones of copper-catalyzed filters, the latter are prohibited by Swiss legislation