Publications by authors named "Degao Wang"

52 Publications

International snapshot of new psychoactive substance use: Case study of eight countries over the 2019/2020 new year period.

Water Res 2021 Apr 3;193:116891. Epub 2021 Feb 3.

Health and Biomedical Innovation, UniSA: Clinical and Health Sciences, University of South Australia, Adelaide 5001, South Australia, Australia. Electronic address:

There is considerable concern around the use of new psychoactive substances (NPS), but still little is known about how much they are really consumed. Analysis by forensics laboratories of seized drugs and post-mortem samples as well as hospital emergency rooms are the first line of identifying both 'new' NPS and those that are most dangerous to the community. However, NPS are not necessarily all seized by law enforcement agencies and only substances that contribute to fatalities or serious afflictions are recorded in post-mortem and emergency room samples. To gain a better insight into which NPS are most prevalent within a community, complementary data sources are required. In this work, influent wastewater was analysed from 14 sites in eight countries for a variety of NPS. All samples were collected over the 2019/2020 New Year period, a time which is characterized by celebrations and parties and therefore a time when more NPS may be consumed. Samples were extracted in the country of origin following a validated protocol and shipped to Australia for final analysis using two different mass spectrometric strategies. In total, more than 200 were monitored of which 16 substances were found, with geographical differences seen. This case study is the most comprehensive wastewater analysis study ever carried out for the identification of NPS and provides a starting point for future, ongoing monitoring of these substances.
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http://dx.doi.org/10.1016/j.watres.2021.116891DOI Listing
April 2021

Combined Toxicity of TiO Nanospherical Particles and TiO Nanotubes to Two Microalgae with Different Morphology.

Nanomaterials (Basel) 2020 Dec 20;10(12). Epub 2020 Dec 20.

School of Environmental Science and Technology, Dalian Maritime University, Dalian 116023, China.

The joint activity of multiple engineered nanoparticles (ENPs) has attracted much attention in recent years. Many previous studies have focused on the combined toxicity of different ENPs with nanostructures of the same dimension. However, the mixture toxicity of multiple ENPs with different dimensions is much less understood. Herein, we investigated the toxicity of the binary mixture of TiO nanospherical particles (NPs) and TiO nanotubes (NTs) to two freshwater algae with different morphology, namely, and . The physicochemical properties, dispersion stability, and the generation of reactive oxygen species (ROS) were determined in the single and binary systems. Classical approaches to assessing mixture toxicity were applied to evaluate and predict the toxicity of the binary mixtures. The results show that the combined toxicity of TiO NPs and NTs to was between the single toxicity of TiO NTs and NPs, while the combined toxicity to was higher than their single toxicity. Moreover, the toxicity of the binary mixtures to was higher than that to A toxic unit assessment showed that the effects of TiO NPs and NTs were additive to the algae. The combined toxicity to and can be effectively predicted by the concentration addition model and the independent action model, respectively. The mechanism of the toxicity caused by the binary mixtures of TiO NPs and NTs may be associated with the dispersion stability of the nanoparticles in aquatic media and the ROS-induced oxidative stress effects. Our results may offer a new insight into evaluating and predicting the combined toxicological effects of ENPs with different dimensions and of probing the mechanisms involved in their joint toxicity.
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http://dx.doi.org/10.3390/nano10122559DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7766607PMC
December 2020

Stabilization of a molecular water oxidation catalyst on a dye-sensitized photoanode by a pyridyl anchor.

Nat Commun 2020 Sep 14;11(1):4610. Epub 2020 Sep 14.

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.

Understanding and controlling the properties of water-splitting assemblies in dye-sensitized photoelectrosynthesis cells is a key to the exploitation of their properties. We demonstrate here that, following surface loading of a [Ru(bpy)] (bpy = 2,2'-bipyridine) chromophore on nanoparticle electrodes, addition of the molecular catalysts, Ru(bda)(L) (bda  =  2,2'-bipyridine-6,6'-dicarboxylate) with phosphonate or pyridyl sites for water oxidation, gives surfaces with a 5:1 chromophore to catalyst ratio. Addition of the surface-bound phosphonate derivatives with L = 4-pyridyl phosphonic acid or diethyl 3-(pyridin-4-yloxy)decyl-phosphonic acid, leads to well-defined surfaces but, following oxidation to Ru(III), they undergo facile, on-surface dimerization to give surface-bound, oxo-bridged dimers. The dimers have a diminished reactivity toward water oxidation compared to related monomers in solution. By contrast, immobilization of the Ru-bda catalyst on TiO with the 4,4'-dipyridyl anchoring ligand can maintain the monomeric structure of catalyst and gives relatively stable photoanodes with photocurrents that reach to 1.7 mA cm with an optimized, applied bias photon-to-current efficiency of 1.5%.
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http://dx.doi.org/10.1038/s41467-020-18417-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7490713PMC
September 2020

Chemical approaches to artificial photosynthesis: A molecular, dye-sensitized photoanode for O production prepared by layer-by-layer self-assembly.

J Chem Phys 2020 Jun;152(24):244706

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA.

We describe here the preparation of a family of photoanodes for water oxidation that incorporate an electron acceptor-chromophore-catalyst in single molecular assemblies on nano-indium tin oxide (nanoITO) electrodes on fluorine-doped tin oxide (FTO). The assemblies were prepared by using a layer-by-layer, Atomic Layer Deposition (ALD), self-assembly approach. In the procedure, addition of an electron acceptor viologen derivative followed by a Ru(bpy) chromophore and a pyridyl derivative of the water oxidation catalyst [Ru(bda) (L)] (bda = 2,2'-bipyridine-6,6'-dicarboxylate), were linked by ALD by addition of the bridge precursors TiO, ZrO, and AlO as the bridging groups giving the assemblies, FTO|nanoITO|-MV-ALD MO-RuP-ALD M'O-WOC. In a series of devices, the most efficient gave water oxidation with an incident photon to current efficiency of 2.2% at 440 nm. Transient nanosecond absorption measurements on the assemblies demonstrated that the slow step in the intra-assembly electron transfer is the electron transfer from the chromophore through the viologen bridge to the nanoITO electrode.
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http://dx.doi.org/10.1063/5.0007383DOI Listing
June 2020

A molecular tandem cell for efficient solar water splitting.

Proc Natl Acad Sci U S A 2020 06 1;117(24):13256-13260. Epub 2020 Jun 1.

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599;

Artificial photosynthesis provides a way to store solar energy in chemical bonds. Achieving water splitting without an applied external potential bias provides the key to artificial photosynthetic devices. We describe here a tandem photoelectrochemical cell design that combines a dye-sensitized photoelectrosynthesis cell (DSPEC) and an organic solar cell (OSC) in a photoanode for water oxidation. When combined with a Pt electrode for H evolution, the electrode becomes part of a combined electrochemical cell for water splitting, 2HO → O + 2H, by increasing the voltage of the photoanode sufficiently to drive bias-free reduction of H to H The combined electrode gave a 1.5% solar conversion efficiency for water splitting with no external applied bias, providing a mimic for the tandem cell configuration of PSII in natural photosynthesis. The electrode provided sustained water splitting in the molecular photoelectrode with sustained photocurrent densities of 1.24 mA/cm for 1 h under 1-sun illumination with no applied bias.
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http://dx.doi.org/10.1073/pnas.2001753117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7306789PMC
June 2020

Using wastewater-based epidemiology to estimate consumption of alcohol and nicotine in major cities of China in 2014 and 2016.

Environ Int 2020 03 27;136:105492. Epub 2020 Jan 27.

Queensland Alliance for Environmental Health Sciences (QAEHS), The University of Queensland, 20 Cornwall Street, Woolloongabba, QLD 4102, Australia.

Monitoring the use of alcohol and tobacco in the population is important for public health planning and evaluating the efficacy of intervention strategies. The aim of this study was to use wastewater-based epidemiology (WBE) to estimate alcohol and tobacco consumption in a number of major cities across China and compare WBE estimates with other data sources. Daily composite influent wastewater samples were collected from wastewater treatment plants (WWTPs) across China in 2014 (n = 53) and 2016 (n = 45). The population-normalized daily consumption estimated by WBE were compared with other data sources where available. The average consumption of alcohol was 8.1 ± 7.0 mL ethanol/person aged 15+/day (EPD) in the investigated cities of 2016 while those involved in 2014 had an average consumption of 4.7 ± 3.0 EPD. The average tobacco consumption was estimated to be 3.7 ± 2.2 cigarettes/person aged 15+/day (CPD) in 2016 and 3.1 ± 1.9 CPD in 2014. The changes in the average consumption in those cities from 2014 to 2016 were supported by the results from a limited number of WWTPs where samples were collected in both years. Consumption of alcohol and tobacco in urban China is at a medium level compared with other countries on a per capita basis. WBE estimates of tobacco consumption were relatively comparable with results of traditional surveys and sales statistics. WBE estimates of alcohol consumption were lower than WHO survey results, probably due to EtS degradation and uncertainty in the EtS excretion factor.
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http://dx.doi.org/10.1016/j.envint.2020.105492DOI Listing
March 2020

A stable dye-sensitized photoelectrosynthesis cell mediated by a NiO overlayer for water oxidation.

Proc Natl Acad Sci U S A 2020 06 5;117(23):12564-12571. Epub 2019 Sep 5.

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599;

In the development of photoelectrochemical cells for water splitting or CO reduction, a major challenge is O evolution at photoelectrodes that, in behavior, mimic photosystem II. At an appropriate semiconductor electrode, a water oxidation catalyst must be integrated with a visible light absorber in a stable half-cell configuration. Here, we describe an electrode consisting of a light absorber, an intermediate electron donor layer, and a water oxidation catalyst for sustained light driven water oxidation catalysis. In assembling the electrode on nanoparticle SnO/TiO electrodes, a Ru(II) polypyridyl complex was used as the light absorber, NiO was deposited as an overlayer, and a Ru(II) 2,2'-bipyridine-6,6'-dicarboxylate complex as the water oxidation catalyst. In the final electrode, addition of the NiO overlayer enhanced performance toward water oxidation with the final electrode operating with a 1.1 mA/cm photocurrent density for 2 h without decomposition under one sun illumination in a pH 4.65 solution. We attribute the enhanced performance to the role of NiO as an electron transfer mediator between the light absorber and the catalyst.
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http://dx.doi.org/10.1073/pnas.1821687116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293597PMC
June 2020

A strategy for stabilizing the catalyst CoO in a metal-organic framework.

Proc Natl Acad Sci U S A 2019 07 20;116(28):13719-13720. Epub 2019 Jun 20.

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599

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http://dx.doi.org/10.1073/pnas.1909543116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6628654PMC
July 2019

A donor-chromophore-catalyst assembly for solar CO reduction.

Chem Sci 2019 Apr 14;10(16):4436-4444. Epub 2019 Mar 14.

Department of Chemistry , University of North Carolina Chapel Hill , Chapel Hill , North Carolina 27599 , USA . Email:

We describe here the preparation and characterization of a photocathode assembly for CO reduction to CO in 0.1 M LiClO acetonitrile. The assembly was formed on 1.0 μm thick mesoporous films of NiO using a layer-by-layer procedure based on Zr(iv)-phosphonate bridging units. The structure of the Zr(iv) bridged assembly, abbreviated as NiO|-DA-RuCP-Re(i), where DA is the dianiline-based electron donor (,,','-((CH)POH)-4,4'-dianiline), RuCP is the light absorber [Ru((4,4'-(POHCH)-2,2'-bipyridine)(2,2'-bipyridine))], and Re(i) is the CO reduction catalyst, Re((4,4'-POHCH)-2,2'-bipyridine)(CO)Cl. Visible light excitation of the assembly in CO saturated solution resulted in CO reduction to CO. A steady-state photocurrent density of 65 μA cm was achieved under one sun illumination and an IPCE value of 1.9% was obtained with 450 nm illumination. The importance of the DA aniline donor in the assembly as an initial site for reduction of the RuCP excited state was demonstrated by an 8 times higher photocurrent generated with DA present in the surface film compared to a control without DA. Nanosecond transient absorption measurements showed that the expected reduced one-electron intermediate, RuCP, was formed on a sub-nanosecond time scale with back electron transfer to the electrode on the microsecond timescale which competes with forward electron transfer to the Re(i) catalyst at = 2.6 μs ( = 2.7 × 10 s).
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http://dx.doi.org/10.1039/c8sc03316aDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6482438PMC
April 2019

Aquatic behavior and toxicity of polystyrene nanoplastic particles with different functional groups: Complex roles of pH, dissolved organic carbon and divalent cations.

Chemosphere 2019 Aug 17;228:195-203. Epub 2019 Apr 17.

College of Environmental Science and Engineering, Dalian Maritime University, Dalian, 116026, China.

Herein we systematically examined the roles of water chemistry (pH, dissolved organic carbon (DOC), and divalent cations) and particle surface functionality that control the aqueous stability, aggregation, and toxicity of engineered nanoplastic particles in simulated natural environmental conditions. Model polystyrene latex nanoparticles (PLNPs) with three different functional groups, namely unmodified (uPLNPs), amine-modified (aPLNPs), and carboxyl-modified (cPLNPs), were investigated. Results indicate that the presence of only DOC increased the surface charge and exhibited negligible effects on the size distribution of the PLNPs in aqueous suspensions. The presence of the divalent cations (Ca and Mg) was observed to decrease the surface charge and increase the size of the PLNPs. The coexistence of DOC and the divalent cations enhanced the extent of aggregation of the PLNPs in the water columns. The surface modification and pH were sensitive factors influencing the stability of PLNPs during long-term suspension when DOC and the divalent cations coexisted. Direct visual further testified the conclusions on the combined effects of solution and surface chemistry parameters. Furthermore, in situ transmission electron microscope observations revealed that the enhancement of PLNP aggregation in the presence of DOC and the divalent cation was caused by bridge formation. Toxicity test indicated the PLNPs exhibited acute toxicity and physical damage to Daphnia magna. The more complex the solution conditions, the more toxicity the aPLNPs and cPLNPs. Analysis of mode of toxic action implied that the PLNPs mainly caused the accumulation of oxidative damage to the gut of D. magna.
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http://dx.doi.org/10.1016/j.chemosphere.2019.04.115DOI Listing
August 2019

Molecular Photoelectrode for Water Oxidation Inspired by Photosystem II.

J Am Chem Soc 2019 05 3;141(19):7926-7933. Epub 2019 May 3.

Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States.

In artificial photosynthesis, the sun drives water splitting into H and O or converts CO into a useful form of carbon. In most schemes, water oxidation is typically the limiting half-reaction. Here, we introduce a molecular approach to the design of a photoanode that incorporates an electron acceptor, a sensitizer, an electron donor, and a water oxidation catalyst in a single molecular assembly. The strategy mimics the key elements in Photosystem II by initiating light-driven water oxidation with integration of a light absorber, an electron acceptor, an electron donor, and a catalyst in a controlled molecular environment on the surface of a conducting oxide electrode. Visible excitation of the assembly results in the appearance of reductive equivalents at the electrode and oxidative equivalents at a catalyst that persist for seconds in aqueous solutions. Steady-state illumination of the assembly with 440 nm light with an applied bias results in photoelectrochemical water oxidation with a per-photon absorbed efficiency of 2.3%. The results are notable in demonstrating that light-driven water oxidation can be carried out at a conductive electrode in a structure with the functional elements of Photosystem II including charge separation and water oxidation.
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http://dx.doi.org/10.1021/jacs.9b02548DOI Listing
May 2019

Ecotoxicological effects on Scenedesmus obliquus and Danio rerio Co-exposed to polystyrene nano-plastic particles and natural acidic organic polymer.

Environ Toxicol Pharmacol 2019 Apr 22;67:21-28. Epub 2019 Jan 22.

College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, PR China.

The importance of attention to unravel the interaction of nano-plastic particles (NPs) with natural acidic organic polymer (NAOP) in freshwater environment should not be neglected. However, toxicological data available for the interaction between NPs and NAOP remain limited. Here, we investigate the toxicological effects of three model polystyrene (PS) NPs with different functional groups (unmodified, amino- and carboxyl-modified PS NPs) on two freshwater organisms of different trophic levels (Scenedesmus obliquus and Danio rerio) in the absence and presence of two classes of NAOP, namely fulvic acid and humic acid. The NAOP interaction with the NPs is shown to alter oxidative stress and disturb membrane function in S. obliquus cells to a certain extent. Combined oxidative stress responses to the NPs and NAOP in D. rerio as a function of their mixture levels showed inhibition, alleviation, and reinforce. Changes in cellular oxidative stress and membrane function depended on the concentration and types of both NPs and NAOP. Furthermore, the characterization parameters of the NPs were important for the explanation of the ecotoxicological mechanism of the NPs in the presence of NAOP. Our findings emphasized the critical role of NAOP in the fate and toxicity of plastic particles in freshwater environment.
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http://dx.doi.org/10.1016/j.etap.2019.01.007DOI Listing
April 2019

Light-driven water oxidation by a dye-sensitized photoanode with a chromophore/catalyst assembly on a mesoporous double-shell electrode.

J Chem Phys 2019 Jan;150(4):041727

Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.

A mesoporous atomic layer deposition (ALD) double-shell electrode, AlO (insulating core)//ALD ZnO|ALD TiO, on a fluorine-doped tin oxide (FTO) conducting substrate was explored for a photoanode assembly, FTO//AlO (insulating core)//ALD ZnO|ALD TiO|-chromophore-catalyst, for light-driven water oxidation. Photocurrent densities at photoanodes based on mesoporous ALD double-shell (ALD ZnO|ALD TiO|) and ALD single-shell (ALD ZnO|, ALD TiO|) electrodes were investigated for O evaluation by a generator-collector dual working electrode configuration. The high photocurrent densities obtained based on the mesoporous ALD ZnO|ALD TiO photoanode for O evolution arise from a significant barrier to back electron transfer (BET) by the optimized tunneling barrier in the structure with the built-in electric field at the ALD ZnO|ALD TiO interface. The charge recombination is thus largely decreased. In the films, BET following injection has been investigated through kinetic nanosecond transient absorption spectra, and the results of energy band analysis are used to derive insight into the internal electronic structure of the electrodes.
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http://dx.doi.org/10.1063/1.5048780DOI Listing
January 2019

Stabilized photoanodes for water oxidation by integration of organic dyes, water oxidation catalysts, and electron-transfer mediators.

Proc Natl Acad Sci U S A 2018 08 6;115(34):8523-8528. Epub 2018 Aug 6.

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599;

Stabilized photoanodes for light-driven water oxidation have been prepared on nanoparticle core/shell electrodes with surface-stabilized donor-acceptor chromophores, a water oxidation catalyst, and an electron-transfer mediator. For the electrode, fluorine-doped tin oxide FTO|SnO/TiO|-Org1-|1.1 nm AlO|-RuP-WOC (water oxidation catalyst) with Org1 (1-cyano-2-(4-(diphenylamino)phenyl)vinyl)phosphonic acid), the mediator RuP ([Ru(4,4-(POH)-2,2-bipyridine)(2,2-bipyridine)]), and the WOC, Ru(bda)(py(CH)P(OH)) (bda is 2,2-bipyridine-6,6-dicarboxylate with x = 3 or 10), solar excitation resulted in photocurrents of ∼500 µA/cm and quantitative O evolution at pH 4.65. Related results were obtained for other Ru(II) polypyridyl mediators. For the organic dye PP (5-(4-(dihydroxyphosphoryl)phenyl)-10,15,20-Tris(mesityl)porphyrin), solar water oxidation occurred with a driving force near 0 V.
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http://dx.doi.org/10.1073/pnas.1802903115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6112685PMC
August 2018

Aqueous multivariate phototransformation kinetics of dissociated tetracycline: implications for the photochemical fate in surface waters.

Environ Sci Pollut Res Int 2018 Jun 25;25(16):15726-15732. Epub 2018 Mar 25.

Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian, 116023, China.

Antibiotics are ubiquitous pollutants in aquatic systems and can exist as different dissociated species depending on the water pH. New knowledge of their multivariate photochemical behavior (i.e., the photobehavior of different ionized forms) is needed to improve our understanding on the fate and possible remediation of these pharmaceuticals in surface and waste waters. In this study, the photochemical degradation of aqueous tetracycline (TC) and its dissociated forms (TCH, TCH, and TC) was investigated. Simulated sunlight experiments and matrix calculations indicated that the three dissociated species had dissimilar photolytic kinetics and photooxidation reactivities. TC photodegraded the fastest due to apparent photolysis with a kinetic constant of 0.938 ± 0.021 min, followed by TCH (0.020 ± 0.005 min) and TCH (0.012 ± 0.001 min), whereas TCH was found to be the most highly reactive toward •OH (105.78 ± 3.40 M s), and TC reacted the fastest with O (344.96 ± 45.07 M s). Water with relatively high pH (e.g., ~ 8-9) favors the dissociated forms of TCH and TC which are most susceptible to photochemical loss processes compared to neutral TC. The calculated corresponding environmental half-lives (t) in sunlit surface waters ranged from 0.05 h for pH = 9 in midsummer to 3.68 h for pH = 6 in midwinter at 45° N latitude. The process was dominated by apparent photolysis (especially in summer, 62-91%), followed by O and •OH oxidation. Adjusting the pH to slightly alkaline conditions prior to UV or solar UV light treatment may be an effective way of enhancing the photochemical removal of TC from contaminated water. Graphical abstract Aqueous multiple photochemical behavior of dissociated tetracycline (TCH, TCH, and TC) is first comprehensively reported on revealing the phototransformation kinetics and implications for the fate in surface waters.
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http://dx.doi.org/10.1007/s11356-018-1765-0DOI Listing
June 2018

Dissolved organic matter and aluminum oxide nanoparticles synergistically cause cellular responses in freshwater microalgae.

J Environ Sci Health A Tox Hazard Subst Environ Eng 2018 Jun 22;53(7):651-658. Epub 2018 Feb 22.

b School of Environmental Science and Technology, Dalian Maritime University , Dalian , PR China.

This study investigated the impact of dissolved organic matters (DOM) on the ecological toxicity of aluminum oxide nanoparticles (AlONPs) at a relatively low exposure concentration (1 mg L). The unicellular green alga Scenedesmus obliquus was exposed to AlONP suspensions in the presence of DOM (fulvic acid) at various concentrations (1, 10, and 40 mg L). The results show that the presence of DOM elevated the growth inhibition toxicity of AlONPs towards S. obliquus in a dose-dependent manner. Moreover, the combination of DOM at 40 mg L and AlONPs resulted in a synergistic effect. The relative contribution of Al-ions released from AlONPs to toxicity was lower than 5%, indicating that the presence of the particles instead of the dissolved ions in the suspensions was the major toxicity sources, regardless of the presence of DOM. Furthermore, DOM at 10 and 40 mg L and AlONPs synergistically induced the upregulation of intercellular reactive oxygen species levels and superoxide dismutase activities. Analysis of the plasma malondialdehyde concentrations and the observation of superficial structures of S. obliquus indicated that the mixtures of DOM and AlONPs showed no significant effect on membrane lipid peroxidation damage. In addition, the presence of both DOM and AlONPs contributed to an enhancement in both the mitochondrial membrane potential and the cell membrane permeability (CMP) in S. obliquus. In particular, AlONPs in the presence of 10 and 40 mg L DOM caused a greater increase in CMP compared to AlONPs and DOM alone treatments. In conclusion, these findings suggest that DOM at high concentrations and AlONPs synergistically interrupted cell membrane functions and triggered subsequent growth inhibition toxicity.
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http://dx.doi.org/10.1080/10934529.2018.1438814DOI Listing
June 2018

TiO₂, SiO₂ and ZrO₂ Nanoparticles Synergistically Provoke Cellular Oxidative Damage in Freshwater Microalgae.

Nanomaterials (Basel) 2018 Feb 8;8(2). Epub 2018 Feb 8.

School of Environmental Science and Technology, Dalian Maritime University, Dalian 116023, China.

Metal-based nanoparticles (NPs) are the most widely used engineered nanomaterials. The individual toxicities of metal-based NPs have been plentifully studied. However, the mixture toxicity of multiple NP systems ( ≥ 3) remains much less understood. Herein, the toxicity of titanium dioxide (TiO₂) nanoparticles (NPs), silicon dioxide (SiO₂) NPs and zirconium dioxide (ZrO₂) NPs to unicellular freshwater algae was investigated individually and in binary and ternary combination. Results show that the ternary combination systems of TiO₂, SiO₂ and ZrO₂ NPs at a mixture concentration of 1 mg/L significantly enhanced mitochondrial membrane potential and intracellular reactive oxygen species level in the algae. Moreover, the ternary NP systems remarkably increased the activity of the antioxidant defense enzymes superoxide dismutase and catalase, together with an increase in lipid peroxidation products and small molecule metabolites. Furthermore, the observation of superficial structures of revealed obvious oxidative damage induced by the ternary mixtures. Taken together, the ternary NP systems exerted more severe oxidative stress in the algae than the individual and the binary NP systems. Thus, our findings highlight the importance of the assessment of the synergistic toxicity of multi-nanomaterial systems.
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http://dx.doi.org/10.3390/nano8020095DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5853726PMC
February 2018

Aqueous aggregation and stability of graphene nanoplatelets, graphene oxide, and reduced graphene oxide in simulated natural environmental conditions: complex roles of surface and solution chemistry.

Environ Sci Pollut Res Int 2018 Apr 4;25(11):10956-10965. Epub 2018 Feb 4.

School of Environmental Science and Technology, Dalian Maritime University, Dalian, 116023, People's Republic of China.

Graphene-family nanomaterials (GFNs) exhibit universal applications and consequently will inevitably enter aquatic systems. However, both the fate and behavior of GFNs in aquatic environments have not been completely explored at field relevant conditions. Herein, we have systematically investigated the aqueous aggregation and stability of graphene nanoplatelets (GNPs), graphene oxide (GO), and reduced graphene oxide (RGO) under varied solution chemistry parameters (pH, divalent cations, and dissolved organic carbon (DOC)) during 21 days of incubation in simulated natural environmental conditions. Results indicate that pH values from 6 to 9 had a notable impact on the aqueous behaviors of the three GFNs. Divalent cations (Ca and Mg) at the concentrations of 2.5 and 10 mM remarkably increased the extent of aggregation of the three GFNs and resulted in severe sedimentation, independently of surface chemical functionalization. The presence of only DOC ranging from 0.5 to 2 mg C/L significantly elevated the dispersion stability of GNPs and RGO in a dose-dependent manner, whereas no effects were observed on GO. Furthermore, DOC at the studied concentrations and surface functionality were insufficient to counterbalance the impact of the divalent cations. Direct visual and in situ observations further supported the conclusions on the effects of divalent cations or/and DOC. These findings further underline that the environmental behaviors of GFNs are controlled by the complex interplay between water chemistry parameters and GFN surface properties.
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http://dx.doi.org/10.1007/s11356-018-1326-6DOI Listing
April 2018

Light-Driven Water Splitting Mediated by Photogenerated Bromine.

Angew Chem Int Ed Engl 2018 03 1;57(13):3449-3453. Epub 2018 Mar 1.

Department of Chemistry, University of North Carolina at Chapel Hill, Campus Box 3290, Chapel Hill, NC, 27599-3290, USA.

Light-driven water splitting was achieved using a dye-sensitized mesoporous oxide film and the oxidation of bromide (Br ) to bromine (Br ) or tribromide (Br ). The chemical oxidant (Br or Br ) is formed during illumination at the photoanode and used as a sacrificial oxidant to drive a water oxidation catalyst (WOC), here demonstrated using [Ru(bda)(pic) ], (1; pic=picoline, bda=2,2'-bipyridine-6,6'-dicarboxylate). The photochemical oxidation of bromide produces a chemical oxidant with a potential of 1.09 V vs. NHE for the Br /Br couple or 1.05 V vs. NHE for the Br /Br couple, which is sufficient to drive water oxidation at 1 (Ru ≈1.0 V vs. NHE at pH 5.6). At pH 5.6, using a 0.2 m acetate buffer containing 40 mm LiBr and the [Ru(4,4'-PO H -bpy)(bpy) ] (RuP , bpy=2,2'-bipyridine) chromophore dye on a SnO /TiO core-shell electrode resulted in a photocurrent density of around 1.2 mA cm under approximately 1 Sun illumination and a Faradaic efficiency upon addition of 1 of 77 % for oxygen evolution.
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http://dx.doi.org/10.1002/anie.201708879DOI Listing
March 2018

CO reduction to acetate in mixtures of ultrasmall (Cu) ,(Ag) bimetallic nanoparticles.

Proc Natl Acad Sci U S A 2018 01 26;115(2):278-283. Epub 2017 Dec 26.

Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599;

Monodispersed mixtures of 6-nm Cu and Ag nanoparticles were prepared by electrochemical reduction on electrochemically polymerized -Fe(vbpy)(PF) film electrodes on glassy carbon. Conversion of the complex to -Fe(vbpy)(CN) followed by surface binding of salts of the cations and electrochemical reduction gave a mixture of chemically distinct clusters on the surface, (Cu) ,(Ag) |polymer|glassy carbon electrode (GCE), as shown by X-ray photoelectron spectroscopy (XPS) measurements. A (Cu),(Ag)|(80-monolayer--Fe(vbpy)|GCE electrode at -1.33 V vs. reversible hydrogen electrode (RHE) in 0.5 M KHCO, with 8 ppm added benzotriazole (BTA) at 0 °C, gave acetate with a faradaic efficiency of 21.2%.
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http://dx.doi.org/10.1073/pnas.1713962115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5777049PMC
January 2018

Interfacial Deposition of Ru(II) Bipyridine-Dicarboxylate Complexes by Ligand Substitution for Applications in Water Oxidation Catalysis.

J Am Chem Soc 2018 01 2;140(2):719-726. Epub 2018 Jan 2.

Department of Chemistry, University of North Carolina Chapel Hill , Chapel Hill, North Carolina 27599, United States.

Water oxidation is a critical step in artificial photosynthesis and provides the protons and electrons used in reduction reactions to make solar fuels. Significant advances have been made in the area of molecular water oxidation catalysts with a notable breakthrough in the development of Ru(II) complexes that use a planar "bda" ligand (bda is 2,2'-bipyridine-6,6'-dicarboxylate). These Ru(II)(bda) complexes show lower overpotentials for driving water oxidation making them ideal for light-driven applications with a suitable chromophore. Nevertheless, synthesis of heterogeneous Ru(II)(bda) complexes remains challenging. We discuss here a new "bottom-up" synthetic method for immobilizing these catalysts at the surface of a photoanode for use in a dye-sensitized photoelectrosynthesis cell (DSPEC). The procedure provides a basis for rapidly screening the role of ligand variations at the catalyst in order to understand the impact on device performance. The best results of a water-oxidation DSPEC photoanode based on this procedure reached 1.4 mA/cm at pH 7 in 0.1 M [POH]/[POH]solution with minimal loss in catalytic behavior over 30 min, and produced an incident photon to current efficiency (IPCE) of 24.8% at 440 nm.
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http://dx.doi.org/10.1021/jacs.7b10809DOI Listing
January 2018

Dye-Sensitized Hydrobromic Acid Splitting for Hydrogen Solar Fuel Production.

J Am Chem Soc 2017 11 30;139(44):15612-15615. Epub 2017 Oct 30.

Department of Chemistry, University of North Carolina Chapel Hill , Chapel Hill, North Carolina 27599, United States.

Hydrobromic acid (HBr) has significant potential as an inexpensive feedstock for hydrogen gas (H) solar fuel production through HBr splitting. Mesoporous thin films of anatase TiO or SnO/TiO core-shell nanoparticles were sensitized to visible light with a new Ru polypyridyl complex that served as a photocatalyst for bromide oxidation. These thin films were tested as photoelectrodes in dye-sensitized photoelectrosynthesis cells. In 1 N HBr (aq), the photocatalyst undergoes excited-state electron injection and light-driven Br oxidation. The injected electrons induce proton reduction at a Pt electrode. Under 100 mW cm white-light illumination, sustained photocurrents of 1.5 mA cm were measured under an applied bias. Faradaic efficiencies of 71 ± 5% for Br oxidation and 94 ± 2% for H production were measured. A 12 μmol h sustained rate of H production was maintained during illumination. The results demonstrate a molecular approach to HBr splitting with a visible light absorbing complex capable of aqueous Br oxidation and excited-state electron injection.
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http://dx.doi.org/10.1021/jacs.7b09367DOI Listing
November 2017

Water Photo-oxidation Initiated by Surface-Bound Organic Chromophores.

J Am Chem Soc 2017 11 31;139(45):16248-16255. Epub 2017 Oct 31.

Department of Chemistry, University of North Carolina at Chapel Hill , CB 3290, Chapel Hill, North Carolina 27599, United States.

Organic chromophores can be synthesized by established methods and offer an opportunity to expand overall solar spectrum utilization for dye-sensitized photoelectrosynthesis cells. However, there are complications in the use of organic chromophores arising from the instability of their oxidized forms, the inability of their oxidized forms to activate a water oxidation catalyst, or the absence of a sufficiently reducing excited state for electron injection into appropriate semiconductors. Three new triarylamine donor-acceptor organic dyes have been investigated here for visible-light-driven water oxidation. They offer highly oxidizing potentials (>1 V vs NHE in aqueous solution) that are sufficient to drive a water oxidation catalyst and excited-state potentials (∼-1.2 V vs NHE) sufficient to inject into TiO. The oxidized form of one of the chromophores is sufficiently stable to exhibit reversible electrochemistry in aqueous solution. The chromophores also have favorable photophysics. Visible-light-driven oxygen production by an organic chromophore for up to 1 h of operation has been demonstrated with reasonable faradaic efficiencies for measured O production. The properties of organic chromophores necessary for successfully driving water oxidation in a light-driven system are explored along with strategies for improving device performance.
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http://dx.doi.org/10.1021/jacs.7b08317DOI Listing
November 2017

Plasmon-enhanced light-driven water oxidation by a dye-sensitized photoanode.

Proc Natl Acad Sci U S A 2017 09 28;114(37):9809-9813. Epub 2017 Aug 28.

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599;

Dye-sensitized photoelectrosynthesis cells (DSPECs) provide a flexible approach for solar water splitting based on the integration of molecular light absorption and catalysis on oxide electrodes. Recent advances in this area, including the use of core/shell oxide interfacial structures and surface stabilization by atomic layer deposition, have led to improved charge-separation lifetimes and the ability to obtain substantially improved photocurrent densities. Here, we investigate the introduction of Ag nanoparticles into the core/shell structure and report that they greatly enhance light-driven water oxidation at a DSPEC photoanode. Under 1-sun illumination, Ag nanoparticle electrodes achieved high photocurrent densities, surpassing 2 mA cm with an incident photon-to-current efficiency of 31.8% under 450-nm illumination.
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http://dx.doi.org/10.1073/pnas.1708336114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5604030PMC
September 2017

Layer-by-Layer Molecular Assemblies for Dye-Sensitized Photoelectrosynthesis Cells Prepared by Atomic Layer Deposition.

J Am Chem Soc 2017 10 30;139(41):14518-14525. Epub 2017 Aug 30.

Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.

In a dye sensitized photoelectrosynthesis cell (DSPEC), the relative orientation of the catalyst and chromophore plays an important role in determining the device efficiency. Here we introduce a new, robust atomic layer deposition (ALD) procedure for the preparation of molecular chromophore-catalyst assemblies on wide bandgap semiconductors. In this procedure, solution deposited, phosphonate derivatized metal complexes on metal oxide surfaces are treated with reactive metal reagents in the gas phase by ALD to form an outer metal ion bridging group, which can bind a second phosphonate containing species from solution to establish a R-PO-O-M-O-PO-R type surface assembly. With the ALD procedure, assemblies bridged by Al(III), Sn(IV), Ti(IV), or Zr(IV) metal oxide units have been prepared. To evaluate the performance of this new type of surface assembly, intra-assembly electron transfer was investigated by transient absorption spectroscopy, and light-driven water splitting experiments under steady-state illumination were conducted. A SnO bridged assembly on SnO/TiO core/shell electrodes undergoes light-driven water oxidation with an incident photon to current efficiency (IPCE) of 17.1% at 440 nm. Light-driven water reduction with a ruthenium trisbipyridine chromophore and molecular Ni(II) catalyst on NiO films was also used to produce H. Compared to conventional solution-based procedures, the ALD approach offers significant advantages in scope and flexibility for the preparation of stable surface structures.
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http://dx.doi.org/10.1021/jacs.7b07216DOI Listing
October 2017

Oxidation of alkyl benzenes by a flavin photooxidation catalyst on nanostructured metal-oxide films.

Proc Natl Acad Sci U S A 2017 08 11;114(35):9279-9283. Epub 2017 Aug 11.

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599

We describe here a surface-bound, oxide-based procedure for the photooxidation of a family of aromatic hydrocarbons by a phosphate-bearing flavin mononucleotide (FMN) photocatalyst on high surface area metal-oxide films.
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http://dx.doi.org/10.1073/pnas.1707318114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5584444PMC
August 2017

Co-exposure of Freshwater Microalgae to Tetrabromobisphenol A and Sulfadiazine: Oxidative Stress Biomarker Responses and Joint Toxicity Prediction.

Bull Environ Contam Toxicol 2017 Oct 9;99(4):438-444. Epub 2017 Aug 9.

School of Environmental Science and Technology, Dalian Maritime University, Dalian, 116023, China.

Combined toxicity and oxidative stress biomarker responses were determined for tetrabromobisphenol A (TBBPA) and sulfadiazine (SDZ) to the unicellular green alga Scenedesmus obliquus. Concentration-response analyses were performed for single toxicants and for mixtures containing TBBPA and SDZ with two different mixture ratios. The effect concentrations and the observed effects of the mixtures were compared to the predictions of the joint toxicity by the concentration addition (CA) model and independent action (IA) model. Results showed that the observed joint toxicity was within the scope of the highest (TBBPA) and lowest (SDZ) toxicity observed for the individual components. Furthermore, co-exposure of S. obliquus to TBBPA and SDZ provided preliminary evidence that the mixtures induced oxidative stress leading to cell damage. The CA and IA models proved to be valid for the prediction of the joint toxicity of TBBPA and SDZ. This study highlights a combined environmental risk assessment for two emerging pollutants.
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http://dx.doi.org/10.1007/s00128-017-2153-zDOI Listing
October 2017

Fluoropolymer-Stabilized Chromophore-Catalyst Assemblies in Aqueous Buffer Solutions for Water-Oxidation Catalysis.

ChemSusChem 2017 06 23;10(11):2380-2384. Epub 2017 May 23.

Department of Chemistry, University of North Carolina at Chapel Hill, CB 3290, Chapel Hill, North Carolina, 27599, USA.

Here, the application of the fluorinated polymer [Dupont AF, a copolymer of 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole and tetrafluoroethylene] is described in stabilizing phosphonate-derivatized molecular assemblies on oxide electrodes. In the procedure, the polymer was dip-coated onto the surfaces of oxide electrodes with pre-bound, phosphonate-derivatized chromophores and assemblies, including assemblies for water oxidation. The results of the experiments showed a high degree of stabilization by the added polymer and a demonstration of its use in stabilizing surface-bound assemblies for water-oxidation catalysis.
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http://dx.doi.org/10.1002/cssc.201700630DOI Listing
June 2017

Inner Layer Control of Performance in a Dye-Sensitized Photoelectrosynthesis Cell.

ACS Appl Mater Interfaces 2017 Oct 2;9(39):33533-33538. Epub 2017 Mar 2.

Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.

Interfacial charge transfer and core-shell structures play important roles in dye-sensitized photoelectrosynthesis cells (DSPEC) for water splitting into H and O. An important element in the design of the photoanode in these devices is a core/shell structure which controls local electron transfer dynamics. Here, we introduce a new element, an internal layer of AlO lying between the Sb:SnO/TiO layers in a core/shell electrode which can improve photocurrents by up to 300%. In these structures, the results of photocurrent, transient absorption, and linear scan voltammetry measurements point to an important role for the AlO layer in controlling internal electron transfer within the core/shell structure.
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http://dx.doi.org/10.1021/acsami.7b00225DOI Listing
October 2017

All-in-One Derivatized Tandem pn-Silicon-SnO/TiO Water Splitting Photoelectrochemical Cell.

Nano Lett 2017 04 3;17(4):2440-2446. Epub 2017 Mar 3.

Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.

Mesoporous metal oxide film electrodes consisting of derivatized 5.5 μm thick SnO films with an outer 4.3 nm shell of TiO added by atomic layer deposition (ALD) have been investigated to explore unbiased water splitting on p, n, and pn type silicon substrates. Modified electrodes were derivatized by addition of the water oxidation catalyst, [Ru(bda)(4-O(CH)POH)-pyr)], 1, (pyr = pyridine; bda = 2,2'-bipyridine-6,6'-dicarboxylate), and chromophore, [Ru(4,4'-POH-bpy) (bpy)], RuP, (bpy = 2,2'-bipyridine), which form 2:1 RuP/1 assemblies on the surface. At pH 5.7 in 0.1 M acetate buffer, these electrodes with a fluorine-doped tin oxide (FTO) back contact under ∼1 sun illumination (100 mW/cm; white light source) perform efficient water oxidation with a photocurrent of 1.5 mA/cm with an 88% Faradaic efficiency (FE) for O production at an applied bias of 600 mV versus RHE ( ACS Energy Lett. , 2016 , 1 , 231 - 236 ). The SnO/TiO-chromophore-catalyst assembly was integrated with the Si electrodes by a thin layer of titanium followed by an amorphous TiO (Ti/a-TiO) coating as an interconnect. In the integrated electrode, pn-Si-Ti/a-TiO-SnO/TiO|-2RuP/1, the pn-Si junction provided about 350 mV in added potential to the half cell. In photolysis experiments at pH 5.7 in 0.1 M acetate buffer, bias-free photocurrents approaching 100 μA/cm were obtained for water splitting, 2HO → 2H + O. The FE for water oxidation was 79% with a hydrogen efficiency of ∼100% at the Pt cathode.
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http://dx.doi.org/10.1021/acs.nanolett.7b00105DOI Listing
April 2017