Orientation of reduced graphene oxide in composite coatings.

Composite coatings containing reduced graphene oxide (rGO) and 3-(aminopropyl)triethoxysilane functionalised rGO (APTES-rGO) were prepared by sol-gel technology and deposited on Al 2024 T-3. Covalent functionalisation of GO by APTES occurred by formation of amide bonds, accompanied by GO reduction. The thin sheets were retained. The hydrophilicity of the coating increased when APTES-rGO was added. The opposite was observed when GO was added. A key finding is that the rGO flakes agglomerate and lie in a random orientation in the coating, whereas the APTES-rGO flakes are more evenly distributed in the matrix and appear to lie along the plane of the substrate.

Ecotoxicological Effects of Transformed Silver and Titanium Dioxide Nanoparticles in the Effluent from a Lab-Scale Wastewater Treatment System.

In this study, a lab-scale wastewater treatment plant (WWTP), simulating biological treatment, received 10 µg/L Ag and 100 µg/L TiO2 nanoparticles (NPs) for 5 weeks. NP partitioning was evaluated by size fractionation (>0.7 µm, 0.1-0.7 µm, 3 kDa-0.1 µm, < 3 kDa) using inductively coupled plasma mass spectrometry (ICP-MS), single particle ICP-MS and transmission electron microscopy. The ecotoxicological effects of the transformed NPs in the effluent were assessed using a battery of marine and freshwater bioassays (algae and crustaceans) and an in vitro gill cell line model (RTgill-W1). TiO2 aggregates were detected in the effluent, whereas Ag NPs (0.1-0.22 µg/L) were associated with S, Cu, Zn. Fractionation showed that >80% of Ag and Ti were associated with the effluent solids. Increased toxicity was observed during weeks 2-3 and the effects were species-dependent; with marine epibenthic copepods and algae being the most sensitive. Increased reactive oxygen species formation was observed in vitro followed by an increase in epithelial permeability. The effluent affected the gill epithelium integrity in vitro and impacted defense pathways (upregulation of multixenobiotic resistance genes). To our knowledge, this is the first study to combine a lab-scale activated sludge WWTP with extensive characterization techniques and ecotoxicological assays to study the effects of transformed NPs in the effluent.

Occurrence, characterisation and fate of (nano)particulate Ti and Ag in two Norwegian wastewater treatment plants.

Due to their widespread application in consumer products, elemental titanium (e.g., titanium dioxide, TiO2) and silver (Ag), also in nanoparticulate form, are increasingly released from households and industrial facilities to urban wastewater treatment plants (WWTPs). A seven-day sampling campaign was conducted in two full-scale WWTPs in Trondheim (Norway) employing only primary treatment. We assessed the occurrence and elimination of Ti and Ag, and conducted size-based fractionation using sequential filtration of influent samples to separate particulate, colloidal and dissolved fractions. Eight-hour composite influent samples were collected to assess diurnal variations in total Ti and Ag influx. Measured influent Ti concentrations (up to 290 µg L-1) were significantly higher than Ag (<0.15-2.1 µg L-1), being mostly associated with suspended solids (>0.7 µm). Removal efficiencies ≥70% were observed for both elements, requiring for one WWTP to account for the high Ti content (∼2 g L-1) in the flocculant. Nano- and micron-sized Ti particles were observed with scanning transmission electron microscopy (STEM) in influent, effluent and biosolids, while Ag nanoparticles were detected in biosolids only. Diurnal profiles of influent Ti were correlated to flow and pollutant concentration patterns (especially total suspended solids), with peaks during the morning and/or evening and minima at night, indicating household discharges as predominant source. Irregular profiles were exhibited by influent Ag, with periodic concentration spikes suggesting short-term discharges from one or few point sources (e.g., industry). Influent Ti and Ag dynamics were reproduced using a disturbance scenario generator model, and we estimated per capita loads of Ti (42-45 mg cap-1 d-1) and Ag (0.11 mg cap-1 d-1) from households as well as additional Ag load (14-22 g d-1) from point discharge. This is the first study to experimentally and mathematically describe short-term release dynamics and dry-weather sources of emissions of Ti and Ag in municipal WWTPs and receiving environments.