Single-Atom Iron Can Steer Atomic Hydrogen toward Selective Reductive Dechlorination: Implications for Remediation of Chlorinated Solvents-Impacted Groundwater.

Atomic hydrogen (H*) is a powerful and versatile reductant and has tremendous potential in the degradation of oxidized pollutants (e.g., chlorinated solvents). However, its application for groundwater remediation is hindered by the scavenging side reaction of H2 evolution. Herein, we report that a composite material (Fe0@Fe-N4-C), consisting of zerovalent iron (Fe0) nanoparticles and nitrogen-coordinated single-atom Fe (Fe-N4), can effectively steer H* toward reductive dechlorination of trichloroethylene (TCE), a common groundwater contaminant and primary risk driver at many hazardous waste sites. The Fe-N4 structure strengthens the bond between surface Fe atoms and H*, inhibiting H2 evolution. Nonetheless, H* is available for dechlorination, as the adsorption of TCE weakens this bond. Interestingly, H* also enhances electron delocalization and transfer between adsorbed TCE and surface Fe atoms, increasing the reactivity of adsorbed TCE with H*. Consequently, Fe0@Fe-N4-C exhibits high electron selectivity (up to 86%) toward dechlorination, as well as a high TCE degradation kinetic constant. This material is resilient against water matrix interferences, achieving long-lasting performance for effective TCE removal. These findings shed light on the utilization of H* for the in situ remediation of groundwater contaminated with chlorinated solvents, by rational design of earth-abundant metal-based single-atom catalysts.

Citrate-promoted dissolution of nanostructured manganese oxides: Implications for nano-enabled sustainable agriculture.

Nanostructured manganese oxides (nano-MnOx) have shown great promises as versatile agrochemicals in nano-enabled sustainable agriculture, owing to the coupled benefits of controlled release of dissolved Mn2+, an essential nutrient needed by plants, and oxidative destruction of environmental organic pollutants. Here, we show that three δ-MnO2 nanomaterials consisting of nanosheet-assembled flower-like nanospheres not only exhibit greater kinetics in citrate-promoted dissolution, but also are less prone to passivation, compared with three α-MnO2 nanowire materials. The better performance of the δ-MnO2 nanomaterials can be attributed to their higher abundance of surface unsaturated Mn atoms-particularly Mn(III)-that is originated from their specific exposed facets and higher abundance of surface defects sites. Our results underline the great potential of modulating nanomaterial surface atomic configuration to improve their performance in sustainable agricultural applications.

Current Methods and Prospects for Analysis and Characterization of Nanomaterials in the Environment.

Analysis and characterization of naturally occurring and engineered nanomaterials in the environment are critical for understanding their environmental behaviors and defining real exposure scenarios for environmental risk assessment. However, this is challenging primarily due to the low concentration, structural heterogeneity, and dynamic transformation of nanomaterials in complex environmental matrices. In this critical review, we first summarize sample pretreatment methods developed for separation and preconcentration of nanomaterials from environmental samples, including natural waters, wastewater, soils, sediments, and biological media. Then, we review the state-of-the-art microscopic, spectroscopic, mass spectrometric, electrochemical, and size-fractionation methods for determination of mass and number abundance, as well as the morphological, compositional, and structural properties of nanomaterials, with discussion on their advantages and limitations. Despite recent advances in detecting and characterizing nanomaterials in the environment, challenges remain to improve the analytical sensitivity and resolution and to expand the method applications. It is important to develop methods for simultaneous determination of multifaceted nanomaterial properties for in situ analysis and characterization of nanomaterials under dynamic environmental conditions and for detection of nanoscale contaminants of emerging concern (e.g., nanoplastics and biological nanoparticles), which will greatly facilitate the standardization of nanomaterial analysis and characterization methods for environmental samples.

In Vivo Effects of Silver Nanoparticles on Development, Behavior, and Mitochondrial Function are Altered by Genetic Defects in Mitochondrial Dynamics.

Silver nanoparticles (AgNPs) are extensively used in consumer products and biomedical applications, thus guaranteeing both environmental and human exposures. Despite extensive research addressing AgNP safety, there are still major knowledge gaps regarding AgNP toxicity mechanisms, particularly in whole organisms. Mitochondrial dysfunction is frequently described as an important cytotoxicity mechanism for AgNPs; however, it is still unclear if mitochondria are the direct targets of AgNPs. To test this, we exposed the nematodeCaenorhabditis elegans to sublethal concentrations of AgNPs and assessed specific mitochondrial parameters as well as organismal-level endpoints that are highly reliant on mitochondrial function, such as development and chemotaxis behavior. All AgNPs tested significantly delayed nematode development, disrupted mitochondrial bioenergetics, and blocked chemotaxis. However, silver was not preferentially accumulated in mitochondria, indicating that these effects are likely not due to direct mitochondria-AgNP interactions. Mutant nematodes with deficiencies in mitochondrial dynamics displayed both greater and decreased susceptibility to AgNPs compared to wild-type nematodes, which was dependent on the assay and AgNP type. Our study suggests that AgNPs indirectly promote mitochondrial dysfunction, leading to adverse outcomes at the organismal level, and reveals a role of gene-environment interactions in the susceptibility to AgNPs. Finally, we propose a novel hypothetical adverse outcome pathway for AgNP effects to guide future research.

Enhanced Hydrolysis of p-Nitrophenyl Phosphate by Iron (Hydr)oxide Nanoparticles: Roles of Exposed Facets.

Iron (hydr)oxide nanoparticles are one of the most abundant classes of naturally occurring nanoparticles and are widely used engineered nanomaterials. In the environment these nanoparticles may significantly affect contaminant fate. Using two goethite materials with different contents of exposed {021} facet and two hematite materials with predominantly exposed {001} and {100} facets, respectively, we show that exposed facets, one of the most intrinsic properties of nanocrystals, significantly affect the efficiency of iron (hydr)oxide nanoparticles in catalyzing acid-promoted hydrolysis of 4-nitrophenyl phosphate (pNPP, selected as a model organophosphorus pollutant). Attenuated total reflectance Fourier-transform infrared spectroscopy analysis and density functional theory calculations indicate that the pNPP hydrolysis reaction on the iron (hydr)oxide surface involves the inner-sphere complexation between the phosphonate moiety of pNPP and the surface ferric iron (Fe(III)), through ligand exchange with primarily the singly coordinated surface hydroxyl groups of iron (hydr)oxides. Both the abundance and affinity of these adsorption sites are facet-dependent. Exposed facets also determine the reaction kinetics of surface-bound pNPP mainly by regulating the Lewis acidity of the surface Fe(III) atoms. These findings underline the important roles of facets in determining the reactivity of naturally occurring metal-based nanoparticles toward environmental contaminants and may shed light on the development of nanomaterial-based remediation strategies.

A Facile Synthesis of Ternary Nickel Iron Sulfide Nanospheres as Counter Electrode in Dye-Sensitized Solar Cells.

The incorporation of a foreign metal into a material may adjust the surface electronic structure and promote charge transfer, which then ultimately improves electrical conductivity and electrocatalytic performance because of the possible charge delocalization between the metal cations. As a result, for the first time, ternary nickel iron sulfide nanospheres have been successfully fabricated through a two-step solvothermal approach with the help of glucose (Ni0.5 Fe0.5 S2 /C). Subsequently, the electrochemical performance and electrocatalytic activity of Ni0.5 Fe0.5 S2 /C were evaluated by electrochemical impedance spectroscopy, Tafel polarization and cyclic voltammetry, indicating high electrical conductivity and great electrocatalytic activity. Ni0.5 Fe0.5 S2 /C was employed as a counter electrode for dye-sensitized solar cells, and exhibited higher power conversion efficiency (6.79 %) than the device with Pt CE (6.31 %) under full sunlight illumination (100 mW cm-2 , AM 1.5G).

FcγRIIB receptor-mediated apoptosis in macrophages through interplay of cadmium sulfide nanomaterials and protein corona.

Humans are likely exposed to cadmium sulfide nanomaterials (CdS NMs) due to the increasing environmental release and in vivo application of these materials, which tend to accumulate and cause toxic effects in human lungs, particularly by interrupting the physiological functions of macrophage cells. Here, we showed that protein corona played an essential role in determining cellular uptake and cytotoxicity of CdS NMs in macrophages. Protein-coated CdS NMs enhanced the expression of FcγRIIB receptors on the cell surface, and the interaction between this receptors and proteins inhibited cellular uptake of CdS NMs while triggering cell apoptosis via the AKT/Caspase 3 signaling pathway. Cytotoxicity of CdS NMs was greatly alleviated by coating the nanomaterials with polyethylene glycol (PEG), because PEG decreased the adsorption of proteins that interact with the FcγRIIB receptors on cell surface. Overall, our research demonstrated that surface modification, particularly protein association, significantly affected cellular response to CdS NMs, and cellular uptake may not be an appropriate parameter for predicting the toxic effects of these nanomaterials in human lungs.

Hierarchical Porous O-Doped g-C3 N4 with Enhanced Photocatalytic CO2 Reduction Activity.

Artificial photosynthesis of hydrocarbon fuels by utilizing solar energy and CO2 is considered as a potential route for solving ever-increasing energy crisis and greenhouse effect. Herein, hierarchical porous O-doped graphitic carbon nitride (g-C3 N4 ) nanotubes (OCN-Tube) are prepared via successive thermal oxidation exfoliation and curling-condensation of bulk g-C3 N4 . The as-prepared OCN-Tube exhibits hierarchically porous structures, which consist of interconnected multiwalled nanotubes with uniform diameters of 20-30 nm. The hierarchical OCN-Tube shows excellent photocatalytic CO2 reduction performance under visible light, with methanol evolution rate of 0.88 µmol g-1 h-1 , which is five times higher than bulk g-C3 N4 (0.17 µmol g-1 h-1 ). The enhanced photocatalytic activity of OCN-Tube is ascribed to the hierarchical nanotube structure and O-doping effect. The hierarchical nanotube structure endows OCN-Tube with higher specific surface area, greater light utilization efficiency, and improved molecular diffusion kinetics, due to the more exposed active edges and multiple light reflection/scattering channels. The O-doping optimizes the band structure of g-C3 N4 , resulting in narrower bandgap, greater CO2 affinity, and uptake capacity as well as higher separation efficiency of photogenerated charge carriers. This work provides a novel strategy to design hierarchical g-C3 N4 nanostructures, which can be used as promising photocatalyst for solar energy conversion.

Relative Contributions of Copper Oxide Nanoparticles and Dissolved Copper to Cu Uptake Kinetics of Gulf Killifish (Fundulus grandis) Embryos.

The toxicity of soluble metal-based nanomaterials may be due to the uptake of metals in both dissolved and nanoparticulate forms, but the relative contributions of these different forms to overall metal uptake rates under environmental conditions are not quantitatively defined. Here, we investigated the linkage between the dissolution rates of copper(II) oxide (CuO) nanoparticles (NPs) and their bioavailability to Gulf killifish (Fundulus grandis) embryos, with the aim of quantitatively delineating the relative contributions of nanoparticulate and dissolved species for Cu uptake. Gulf killifish embryos were exposed to dissolved Cu and CuO NP mixtures comprising a range of pH values (6.3-7.5) and three types of natural organic matter (NOM) isolates at various concentrations (0.1-10 mg-C L-1), resulting in a wide range of CuO NP dissolution rates that subsequently influenced Cu uptake. First-order dissolution rate constants of CuO NPs increased with increasing NOM concentration and for NOM isolates with higher aromaticity, as indicated by specific ultraviolet absorbance (SUVA), while Cu uptake rate constants of both dissolved Cu and CuO NP decreased with NOM concentration and aromaticity. As a result, the relative contribution of dissolved Cu and nanoparticulate CuO species for the overall Cu uptake rate was insensitive to NOM type or concentration but largely determined by the percentage of CuO that dissolved. These findings highlight SUVA and aromaticity as key NOM properties affecting the dissolution kinetics and bioavailability of soluble metal-based nanomaterials in organic-rich waters. These properties could be used in the incorporation of dissolution kinetics into predictive models for environmental risks of nanomaterials.

Catalytic decomposition and mechanism of formaldehyde over Pt-Al2O3 molecular sieves at room temperature.

To overcome the drawbacks of powder-like catalysts in practical application, an Al2O3 molecular sieve supported Pt (Pt-Al2O3) catalyst was prepared by the impregnation method combined with dilute hydrochloric acid solution pretreatment. The role of the pretreatment solution in catalyst preparation and formaldehyde (HCHO) decomposition over Pt-Al2O3 catalysts was investigated. The acid solution with pH = 1 was optimal for Pt dispersion on the Al2O3 surface. The Pt-Al2O3 catalyst was capable of achieving complete and stable HCHO oxidation at ambient temperature. In addition, the excellent activity for HCHO removal was promoted by the mesoporous structure, large specific surface area and high adsorption ability of Al2O3 molecular sieves, as determined by N2-sorption studies. Dioxymethylene (DOM) and formate species were identified as major intermediates by in situ DRIFTS studies. These intermediates were subsequently oxidized into CO2 and H2O at ambient temperature. Moreover, a possible reaction mechanism of HCHO removal and a regeneration pathway of surface hydroxyls were proposed. This study provides new insights into the preparation of practical, low-cost catalysts for indoor air purification.

Photochemical decomposition of 1H,1H,2H,2H-perfluorooctane sulfonate (6:2FTS) induced by ferric ions.

Perfluorooctane sulfonate (PFOS) had wide applications, such as in the electroplating industry, but its use was restricted in 2009 by the Stockholm Convention, due to its environmental persistence and potential hazards. As the most common PFOS alternative, 1H,1H,2H,2H-perfluorooctane sulfonic acid (6:2FTS) and its salts have been increasingly used. However, little is known about its photochemical decomposition. This paper reports the ferric ion-induced efficient decomposition and defluorination of 6:2FTS under 254nm ultraviolet (UV) irradiation; the underlying mechanisms were also investigated. In the presence of 100µmol/L ferric ion and at pH3.0, the first-order decomposition rate constant of 6:2FTS (10mg/L) was 1.59/hr, which was 6 times higher than for direct UV photolysis. The effects of the ferric ion concentration and the solution pH on the 6:2FTS photodecomposition were investigated and the optimal reaction conditions were determined. In addition to fluoride and sulfate ions, shorter-chain PFCAs (C2-C7) were detected as major intermediates. The addition of hydrogen peroxide or oxalic acid accelerated the decomposition of 6:2FTS under UV irradiation, but not its defluorination, indicating that hydroxyl radicals can directly react with 6:2FTS but not with the shorter-chain PFCAs. Accordingly, a mechanism for 6:2FTS photochemical decomposition in the presence of ferric ion was proposed, which comprises two reaction pathways. First, hydroxyl radicals can directly attack 6:2FTS, leading to CC bond cleavage. Alternatively, 6:2FTS coordinates with ferric ion to form Fe(III)-6:2FTS complexes, which can undergo ligand-to-metal charge transfer under UV irradiation, causing CS bond cleavage.

Effects of Natural Organic Matter Properties on the Dissolution Kinetics of Zinc Oxide Nanoparticles.

The dissolution of zinc oxide (ZnO) nanoparticles (NPs) is a key step of controlling their environmental fate, bioavailability, and toxicity. Rates of dissolution often depend upon factors such as interactions of NPs with natural organic matter (NOM). We examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution using anodic stripping voltammetry to directly measure dissolved zinc concentrations. The observed dissolution rate constants (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg C L(-1)) for Suwannee River humic and fulvic acids and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, kobs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. The findings of this study facilitate a better understanding of the fate of ZnO NPs in organic-rich aquatic environments and highlight SUVA as a facile and useful indicator of NOM interactions with metal-based nanoparticles.

Room-Temperature Oxidation of Formaldehyde by Layered Manganese Oxide: Effect of Water.

Layered manganese oxide, i.e., birnessite was prepared via the reaction of potassium permanganate with ammonium oxalate. The water content in the birnessite was adjusted by drying/calcining the samples at various temperatures (30 °C, 100 °C, 200 °C, 300 °C, and 500 °C). Thermogravimetry-mass spectroscopy showed three types of water released from birnessite, which can be ascribed to physically adsorbed H2O, interlayer H2O and hydroxyl, respectively. The activity of birnessite for formaldehyde oxidation was positively associated with its water content, i.e., the higher the water content, the better activity it has. In-situ DRIFTS and step scanning XRD analysis indicate that adsorbed formaldehyde, which is promoted by bonded water via hydrogen bonding, is transformed into formate and carbonate with the consumption of hydroxyl and bonded water. Both bonded water and water in air can compensate the consumed hydroxyl groups to sustain the mineralization of formaldehyde at room temperature. In addition, water in air stimulates the desorption of carbonate via water competitive adsorption, and accordingly the birnessite recovers its activity. This investigation elucidated the role of water in oxidizing formaldehyde by layered manganese oxides at room temperature, which may be helpful for the development of more efficient materials.

Silver nanoparticle behavior, uptake, and toxicity in Caenorhabditis elegans: effects of natural organic matter.

Significant progress has been made in understanding the toxicity of silver nanoparticles (Ag NPs) under carefully controlled laboratory conditions. Natural organic matter (NOM) is omnipresent in complex environmental systems, where it may alter the behavior of nanoparticles in these systems. We exposed the nematode Caenorhabditis elegans to Ag NP suspensions with or without one of two kinds of NOM, Suwannee River and Pony Lake fulvic acids (SRFA and PLFA, respectively). PLFA rescued toxicity more effectively than SRFA. Measurement of total tissue silver content indicated that PLFA reduced total organismal (including digestive tract) uptake of ionic silver, but not of citrate-coated Ag NPs (CIT-Ag NPs). The majority of the CIT-Ag NP uptake was in the digestive tract. Limited tissue uptake was detected by hyperspectral microscopy but not by transmission electron microscopy. Co-exposure to PLFA resulted in the formation of NOM-Ag NP composites (both in medium and in nematodes) and rescued AgNO3- and CIT-Ag NP-induced cellular damage, potentially by decreasing intracellular uptake of CIT-Ag NPs.

Preferential association of polycyclic aromatic hydrocarbons (PAHs) with soil colloids at an e-waste recycling site: Implications for risk of PAH migration to subsurface environment.

Polycyclic aromatic hydrocarbon (PAH) contamination at e-waste recycling sites poses high ecological and human-health risks. Of note, PAHs in surface soils can be mobilized through colloid-facilitated transport, and may migrate into the subsurface and pollute groundwater. Here, we show that the colloids released from the soil samples at an e-waste recycling site in Tianjin, China contain high concentrations of PAHs, with total concentrations of 16 PAHs as high as 1520 ng/g dw. Preferential association of the PAHs with the colloids is observed, with the distribution coefficients of PAHs between colloids and bulk soil often above 10. Source diagnostic ratios show that soot-like particles are the main source of PAHs at the site, due to the incomplete combustion of fossil fuels, biomass, and electronic wastes during the e-waste dismantling practices. Due to their small sizes, a large fraction of these soot-like particles can be remobilized as colloids, and this explains the preferential association of PAHs with colloids. Moreover, the colloids-soil distribution coefficients are higher for the low-molecular-weight PAHs than for the high-molecular-weight ones, possibly attributable to the different binding routes/modes of these two groups of PAHs to the particles during combustion. Notably, the preferential association of PAHs with colloids is even more pronounced for the subsurface soils, corroborating that the presence of PAHs in the deeper soils is primarily the results of downward migration of PAH-bearing colloids. The findings highlight the important role of colloids as a vector for the subsurface transport of PAHs at e-waste recycling sites, and call for further understanding of colloid-facilitated transport of PAHs at e-waste recycling sites.

Recent advances in stimuli-response mechanisms of nano-enabled controlled-release fertilizers and pesticides.

Nanotechnology-enabled fertilizers and pesticides, especially those capable of releasing plant nutrients or pesticide active ingredients (AIs) in a controlled manner, can effectively enhance crop nutrition and protection while minimizing the environmental impacts of agricultural activities. Herein, we review the fundamentals and recent advances in nanofertilizers and nanopesticides with controlled-release properties, enabled by nanocarriers responsive to environmental and biological stimuli, including pH change, temperature, light, redox conditions, and the presence of enzymes. For pH-responsive nanocarriers, pH change can induce structural changes or degradation of the nanocarriers or cleave the bonding between nutrients/pesticide AIs and the nanocarriers. Similarly, temperature response typically involves structural changes in nanocarriers, and higher temperatures can accelerate the release by diffusion promoting or bond breaking. Photothermal materials enable responses to infrared light, and photolabile moieties (e.g., o-nitrobenzyl and azobenzene) are required for achieving ultraviolet light responses. Redox-responsive nanocarriers contain disulfide bonds or ferric iron, whereas enzyme-responsive nanocarriers typically contain the enzyme's substrate as a building block. For fabricating nanofertilizers, pH-responsive nanocarriers have been well explored, but only a few studies have reported temperature- and enzyme-responsive nanocarriers. In comparison, there have been more reports on nanopesticides, which are responsive to a range of stimuli, including many with dual- or triple-responsiveness. Nano-enabled controlled-release fertilizers and pesticides show tremendous potential for enhancing the utilization efficiency of nutrients and pesticide AIs. However, to expand their practical applications, future research should focus on optimizing their performance under realistic conditions, lowering costs, and addressing regulatory and public concerns over environmental and safety risks.

Recyclable Carbon Cloth-Supported ZnO@Ag3PO4 Core-Shell Structure for Photocatalytic Degradation of Organic Dye.

The extensive use of organic dyes in industry has caused serious environmental problems, and photocatalysis is a potential solution to water pollution by organic dyes. The practical application of powdery photocatalysts is usually limited by the rapid recombination of charge carriers and difficulty in recycling. In this study, recyclable carbon cloth-supported ZnO@Ag3PO4 composite with a core-shell structure was successfully prepared by solvothermal treatment and subsequent impregnation-deposition. The as-prepared carbon cloth-supported ZnO@Ag3PO4 composite showed an improved photocatalytic activity and stability for the degradation of rhodamine B (RhB), a model organic dye, under visible light irradiation. The decomposition ratio of RhB reached 87.1% after exposure to visible light for 100 min, corresponding to a reaction rate constant that was 4.8 and 15.9 times that of carbon cloth-supported Ag3PO4 or ZnO alone. The enhanced performance of the composite can be attributed to the effectively inhibited recombination of photoinduced electron-hole pairs by the S-scheme heterojunction. The carbon fibers further promoted the transfer of charges. Moreover, the carbon cloth-supported ZnO@Ag3PO4 can be easily separated from the solution and repeatedly used, demonstrating a fair recyclability and potential in practical applications.

Key factors controlling colloids-bulk soil distribution of polybrominated diphenyl ethers (PBDEs) at an e-waste recycling site: Implications for PBDE mobility in subsurface environment.

Accumulation of polybrominated diphenyl ethers (PBDEs) in surface soils at elevated concentrations is common at e-waste recycling sites. Even though highly insoluble, migration of PBDEs into the vadose zone and groundwater is possible, due to their association with soil colloids. Here, we show that upon equilibration with artificial rainwater surface and subsurface soil samples collected at an e-waste recycling site release significant quantities of colloids, with the total concentrations of 14 PBDE congeners as high as 990 ng/g dw. The concentrations of different congeners vary markedly in the colloids, and that of BDE-209 is the highest in all the samples. Notably, even the colloids released from the soil collected at a depth of 95-105 cm contain high concentrations of PBDEs. Preferential binding of PBDEs to soil colloids is observed, with the colloids-soil distribution coefficients above 10 in certain cases. The extent of preferential binding displays no apparent correlation with the relative hydrophobicity of the PBDEs, nor can it be explained simply by considering the higher specific surface area, pore volume, and clay content of the soil colloids than the respective bulk soil. Principal component analysis shows that multiple soil properties are collectively responsible for the preferential distribution of PBDEs. Specifically, the differences in pore volume, soil organic carbon content, and pore size between colloids and soils are likely the major factors affecting the distribution of high-concentration PBDEs, whereas the differences in clay content, pore volume and specific surface area are the key factors affecting the distribution of low-concentration PBDEs. The findings clearly show that colloids are an important medium with which PBDEs are associated at contaminated sites, and underline the need of understanding colloid-facilitated transport of PBDEs at e-waste sites.

Substoichiometric titanium oxide Ti2O3 exhibits greater efficiency in enhancing hydrolysis of 1,1,2,2-tetrachloroethane than TiO2 nanomaterials.

Oxygen-deficient substoichiometric titanium oxides, or "titanium suboxides," are produced incidentally from coal combustion and are environmentally abundant. Additionally, titanium suboxide nanomaterials are promising new materials with likely future environmental release. How these materials may affect contaminant fate differently than stoichiometric TiO2 (nano)materials is largely unknown. Here, we show that Ti2O3 (selected as a model titanium suboxide) exhibits significantly greater efficiency in enhancing the hydrolysis of 1,1,2,2-tetrachloroethane (TeCA), a common groundwater contaminant, than the stoichiometric anatase and rutile TiO2. At environmentally relevant pH (6.5-7.5), the surface area-normalized pseudo-first-order hydrolysis rate constant in the presence of Ti2O3 is approximately an order of magnitude higher than those associated with TiO2. The superior catalytic efficiency of Ti2O3 can be attributed to both its higher surface hydrophobicity, which renders higher adsorption affinity for TeCA, and its higher concentration of Lewis acid sites (mainly the Ti3+ and the five-coordinated Ti4+). Particularly, the deprotonated hydroxyl groups attached to Ti3+ (a weaker Lewis acid than Ti4+) exhibit higher basicity and thus, are more effective in catalyzing the base-promoted hydrolysis reaction. The findings call for further understanding of the environmental implications of titanium suboxide (nano)materials, which may not be readily predictable based on the knowledge acquired for TiO2.

Enhanced hydrolysis of 1,1,2,2-tetrachloroethane by multi-walled carbon nanotube/TiO2 nanocomposites: The synergistic effect.

Once released into the environment, engineered nanomaterials can significantly influence the transformation and fate of organic contaminants. To date, the abilities of composite nanomaterials to catalyze environmentally relevant abiotic transformation reactions of organic contaminants are largely unknown. Herein, we investigated the effects of two nanocomposites - consisting of anatase titanium dioxide (TiO2) with different predominantly exposed crystal facets (i.e., {101} or {001} facets) anchored to hydroxylated multi-walled carbon nanotubes (OH-MWCNT) - on the hydrolysis of 1,1,2,2-tetrachloroethane (TeCA), a common groundwater contaminant, at ambient pH (6, 7 and 8). Both OH-MWCNT/TiO2 nanocomposites were more effective in catalyzing the dehydrochlorination of TeCA than the respective component materials (i.e., bare OH-MWCNT and bare TiO2). Moreover, the synergistic effect of the two components was evident, in that the incorporation of OH-MWCNT increased the TeCA adsorption capacity of the nanocomposites, significantly enhancing the catalytic effect of the deprotonated hydroxyl and carboxyl groups on nanocomposite surfaces, which served as the main catalytic sites for TeCA hydrolysis. The findings may have important implications for the understanding of the environmental implications of composite nanomaterials and may shed light on the design of high-performance nanocomposites for enhanced contaminant removal.