Applications of nanotechnology in water and wastewater treatment

Mistakes and inconsistencies regarding adsorption of contaminants from aqueous solutions: A critical review.

Developments in nanotechnology are leading to a rapid proliferation of new materials that are likely to become a source of engineered nanoparticles (ENPs) to the environment, where their possible ecotoxicological impacts remain unknown. The surface properties of ENPs are of essential importance for their aggregation behavior, and thus for their mobility in aquatic and terrestrial systems and for their interactions with algae, plants and, fungi. Interactions of ENPs with natural organic matter have to be considered as well, as those will alter the ENPs aggregation behavior in surface waters or in soils. Cells of plants, algae, and fungi possess cell walls that constitute a primary site for interaction and a barrier for the entrance of ENPs. Mechanisms allowing ENPs to pass through cell walls and membranes are as yet poorly understood. Inside cells, ENPs might directly provoke alterations of membranes and other cell structures and molecules, as well as protective mechanisms. Indirect effects of ENPs depend on their chemical and physical properties and may include physical restraints (clogging effects), solubilization of toxic ENP compounds, or production of reactive oxygen species. Many questions regarding the bioavailability of ENPs, their uptake by algae, plants, and fungi and the toxicity mechanisms remain to be elucidated.

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Environmental behavior and ecotoxicity of engineered nanoparticles to algae, plants, and fungi

https://www.dora.lib4ri.ch/eawag/islandora/object/eawag%3A7182/datastream/PDF2/Michael-2013-Urban_wastewater_treatment_plants_as-%28accepted_version%29.pdf

Urban wastewater treatment plants as hotspots for the release of antibiotics in the environment: a review

The unique and tunable properties of carbon-based nanomaterials enable new technologies for identifying and addressing environmental challenges. This review critically assesses the contributions of carbon-based nanomaterials to a broad range of environmental applications: sorbents, high-flux membranes, depth filters, antimicrobial agents, environmental sensors, renewable energy technologies, and pollution prevention strategies. In linking technological advance back to the physical, chemical, and electronic properties of carbonaceous nanomaterials, this article also outlines future opportunities for nanomaterial application in environmental systems.

Environmental applications of carbon-based nanomaterials.

Understanding adsorptive interactions between organic contaminants and carbon nanotubes is critical to both the environmental application of carbon nanotubes as special adsorbents and the assessment of the potential impact of carbon nanotubes on the fate and transport of organic contaminants in the environment. The adsorption of organic compounds with varied physical−chemical properties (hydrophobicity, polarity, electron polarizability, and size) to one single-walled carbon nanotube (SWNT) and two multiwalled carbon nanotubes (MWNTs) was evaluated. For a given carbon nanotube, the adsorption affinity correlated poorly with hydrophobicity but increased in the order of nonpolar aliphatic < nonpolar aromatics < nitroaromatics, and within the group of nitroaromatics, the adsorption affinity increased with the number of nitro-functional groups. We propose that the strong adsorptive interaction between carbon nanotubes and nitroaromatics was due to the π−π electron-donor–acceptor (EDA) interaction between nitr...

Adsorption of polar and nonpolar organic chemicals to carbon nanotubes.

Significant concerns have been raised over the presence of antibiotics including tetracyclines in aquatic environments. We herein studied single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes (MWNT) as potential effective adsorbents for removal of tetracycline from aqueous solution. In comparison, a nonpolar adsorbate, naphthalene, and two other carbonaceous adsorbents, pulverized activated carbon (AC) and nonporous graphite, were used. The observed adsorbent-to-solution distribution coefficient (Kd, L/kg) of tetracycline was in the order of 10(4)-10(6) L/kg for SWNT, 10(3)-10(4) L/kg for MWNT, 10(3)-10(4) L/kg for AC, and 10(3)-10(5) L/kg for graphite. Upon normalization for adsorbent surface area, the adsorption affinity of tetracycline decreased in the order of graphite/ SWNT > MWNT >> AC. The weaker adsorption of tetracycline to AC indicates that for bulky adsorbates adsorption affinity is greatly affected by the accessibility of available adsorption sites. The remarkably strong adsorption of tetracycline to the carbon nanotubes and to graphite can be attributed to the strong adsorptive interactions (van der Waals forces, pi-pi electron-donor-acceptor interactions, cation-pi bonding) with the graphene surface. Complexation between tetracycline and model graphene compounds (naphthalene, phenanthrene, pyrene) in solution phase was verified by ring current-induced 1H NMR upfield chemical shifts of tetracycline moieties.

Mechanisms for strong adsorption of tetracycline to carbon nanotubes: a comparative study using activated carbon and graphite as adsorbents.

The combined effects of hydroxyl/amino functional groups of aromatics and surface O-containing groups of carbon nanotubes on adsorption were evaluated. When normalized for hydrophobicity, 2,4-dichlorophenol and 2-naphthol exhibited a greater adsorptive affinity to carbon nanotubes and graphite (a model adsorbent without the surface O functionality) than structurally similar 1,3-dichlorobenzene and naphthalene, respectively, and 1-naphthylamine exhibited a much greater adsorptive affinity than all other compounds. Results of the pH-dependency experiments further indicated that the hydroxyl/amino functional groups of the adsorbates and the surface properties of the adsorbents played a combinational role in determining the significance of the nonhydrophobic adsorptive interactions. We propose that the strong adsorptive interaction between hydroxyl-substituted aromatics and carbon nanotubes/graphite was mainly due to the electron-donating effect of the hydroxyl group, which caused a strong electron-donor−acce...

Adsorption of hydroxyl- and amino-substituted aromatics to carbon nanotubes.

Adsorption of single-ringed N- and S-heterocyclic aromatics on carbon nanotubes

The environmental transport and fate of nanomaterials are largely dependent on their colloidal stability. To date, the stability of reduced graphene oxide (RGO) materials is not well understood. We examined the electrokinetic properties and aggregation kinetics of three RGOs synthesized by reducing graphene oxide (GO) with N2H4, NaBH4, and L-ascorbic acid. In NaCl solution, the critical coagulation concentrations of the materials correlated reasonably with their C/O ratios. However, the increased aggregation tendency of RGOs was caused mainly by their increased hydrophobicity rather than decreased surface charge negativity. For both monovalent and divalent cations, less densely hydrated cations were more effective in causing aggregation than more densely hydrated cations (e.g., K+vs. Na+, and Ca2+vs. Mg2+) owing to the greater efficiency of the former in neutralizing surface charges and the bridging effect in the case of Ca2+. The RGOs exhibited high stability in artificial surface water, whereas different degrees of aggregation were observed in artificial groundwater. Strikingly, in artificial groundwater the aggregation tendency of the materials correlated poorly with the degree of reduction but strongly with the types and concentrations of surface O functionalities, which determined the nature and strength of interactions between RGO and cations in solution. The findings further underline that the stability of nanomaterials is controlled by the complex interplay between nanomaterial surface properties and solution chemistry factors.

Lin Duan

Papers

Adsorption of polar and nonpolar organic chemicals to carbon nanotubes.

Mechanisms for strong adsorption of tetracycline to carbon nanotubes: a comparative study using activated carbon and graphite as adsorbents.

Adsorption of hydroxyl- and amino-substituted aromatics to carbon nanotubes.

Adsorption of single-ringed N- and S-heterocyclic aromatics on carbon nanotubes

Colloidal stability of reduced graphene oxide materials prepared using different reducing agents