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Liu B, Ai L, Lei M, Lin H. Efficient fluoride removal using nano MgO: mechanisms and performance evaluation. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2024; 31:28428-28442. [PMID: 38538999 DOI: 10.1007/s11356-024-33083-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 03/21/2024] [Indexed: 04/30/2024]
Abstract
In this study, highly efficient fluoride removal of nano MgO was successfully synthesized using a simple hydrothermal precipitation method. Hexadecyl trimethyl ammonium bromide (CTMAB) was utilized as a surfactant. Its long-chain structure tightly wrapped around the precursor crystal of basic magnesium chloride, inhibiting the growth of precursor crystals, reducing their size, and improving crystal dispersion. This process enhanced the adsorption capacity of nano MgO for fluoride. The adsorption performance of nano MgO on fluoride was investigated. The results indicate that pseudo-second-order kinetics and the Langmuir isotherm model can describe the adsorption behavior for fluoride, with a maximum adsorption capacity of 122.47 mg/g. Methods such as XRD, SEM, XPS, and FTIR were employed to study the adsorption mechanisms of the adsorbent. Additionally, factors potentially affecting adsorption performance in practical applications, such as pH and competing ions, were examined. This study enhances our profound understanding of the defluorination effectiveness and mechanisms of nano MgO.
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Affiliation(s)
- BoWen Liu
- Key Laboratory of Chemistry and Engineering of Forest Products, State Ethnic Affairs Commission, Guangxi Key Laboratory of Chemistry and Engineering of Forest Products/Guangxi Collaborative Innovation Center for Chemistry and Engineering of Forest Products, Guangxi Minzu University, Nanning, 530006, China
| | - Li Ai
- Key Laboratory of Chemistry and Engineering of Forest Products, State Ethnic Affairs Commission, Guangxi Key Laboratory of Chemistry and Engineering of Forest Products/Guangxi Collaborative Innovation Center for Chemistry and Engineering of Forest Products, Guangxi Minzu University, Nanning, 530006, China
| | - Ming Lei
- Key Laboratory of Chemistry and Engineering of Forest Products, State Ethnic Affairs Commission, Guangxi Key Laboratory of Chemistry and Engineering of Forest Products/Guangxi Collaborative Innovation Center for Chemistry and Engineering of Forest Products, Guangxi Minzu University, Nanning, 530006, China.
| | - Hongfei Lin
- Guangxi Bossco Environmental Protection Technology Co., Ltd, Nanning, 530007, China
- Guangxi Key Laboratory of Environmental Pollution Control and Ecological Restoration Technology, Nanning, 530007, China
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Niedermaier M, Schwab T, Kube P, Zickler GA, Trunschke A, Diwald O. Catalytic activity, water formation, and sintering: Methane activation over Co- and Fe-doped MgO nanocrystals. J Chem Phys 2020; 152:074713. [PMID: 32087664 DOI: 10.1063/1.5138894] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Microstructure, structure, and compositional homogeneity of metal oxide nanoparticles can change dramatically during catalysis. Considering the different stabilities of cobalt and iron ions in the MgO host lattice [M. Niedermaier et al., J. Phys. Chem. C 123, 25991 (2019)], we employed MgO nanocube powders with or without transition metal admixtures for the oxidative coupling of methane (OCM) reaction to analyze characteristic differences in catalytic activity and sintering behavior. Undoped MgO nanocrystals exhibit the highest C2 selectivity and retain the nanocrystallinity of the starting material after 24 h time on stream. For the Co-Mg-O nanoparticle powder, which exhibits the highest activity and COx selectivity and where OCM-induced coarsening is strongest, we found that the Co2+ ions remain homogeneously distributed over the MgO lattice. Trivalent Fe ions migrate to the surface of Fe-Mg-O nanoparticles where they form a magnesioferrite phase (MgFe2O4) with a characteristic impact on catalytic performance: Fe-Mg-O is initially less selective than MgO despite its lower activity. An increase in C2 selectivity and a decrease in the CO2/CO ratio with time on stream are attributed to the increasing fraction of coarsened particles that become depleted in redox active Fe. Surface water is a by-product of the OCM reaction, favors mass transport across the particle surfaces, and serves as a sintering aid during catalysis. The characteristic changes in size and morphology of MgO, Co-doped, and Fe-doped MgO particles can be consistently explained by activity and C2 selectivity trends. The original morphology of the nanocubes as a starting material for the OCM reaction does not impact the catalytic activity.
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Affiliation(s)
- Matthias Niedermaier
- Department of Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Strasse 2a, A-5020 Salzburg, Austria
| | - Thomas Schwab
- Department of Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Strasse 2a, A-5020 Salzburg, Austria
| | - Pierre Kube
- Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Gregor A Zickler
- Department of Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Strasse 2a, A-5020 Salzburg, Austria
| | - Annette Trunschke
- Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Oliver Diwald
- Department of Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Strasse 2a, A-5020 Salzburg, Austria
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Kocsis K, Niedermaier M, Kasparek V, Bernardi J, Redhammer G, Bockstedte M, Berger T, Diwald O. From Anhydrous Zinc Oxide Nanoparticle Powders to Aqueous Colloids: Impact of Water Condensation and Organic Salt Adsorption on Free Exciton Emission. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:8741-8747. [PMID: 31244249 PMCID: PMC7116045 DOI: 10.1021/acs.langmuir.9b00656] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Variations in the composition and structure of ZnO nanoparticle interfaces have a key influence on the materials' optoelectronic properties and are responsible for high number of discrepant results reported for ZnO-based nanomaterials. Here, we conduct a systematic study of the room-temperature photoluminescence of anhydrous ZnO nanocrystals, as synthesized in the gas phase and processed in water-free atmosphere, and of their colloidal derivatives in aqueous dispersions with varying amounts of organic salt admixtures. A free exciton band at hν = 3.3 eV is essentially absent in the anhydrous ZnO nanocrystal powders measured in vacuum or in oxygen atmosphere. Surface hydration of the nanoparticles during colloid formation leads to the emergence of the free exciton band at hν = 3.3 eV and induces a small but significant release in lattice strain as detected by X-ray diffraction. Most importantly, admixture of acetate or citrate ions to the aqueous colloidal dispersions not only allows for the control of the ζ-potential but also affects the intensity of the free exciton emission in a correlated manner. The buildup of negative charge at the solid-liquid interface, as produced by citrate adsorption, increases the free exciton emission. This effect is attributed to the suppression of electron trapping in the near-surface region, which counteracts nonradiative exciton recombination. Using well-defined ZnO nanoparticles as model systems for interface chemistry studies, our findings highlight water-induced key effects that depend on the composition of the aqueous solution shell around the semiconducting metal oxide nanoparticles.
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Affiliation(s)
- Krisztina Kocsis
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Matthias Niedermaier
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Vít Kasparek
- Central European Institute of Technology, Brno University of
Technology, Purkynova 123, 612 00 Brno, Czech Republic
| | - Johannes Bernardi
- University Service Centre for Transmission Electron
Microscopy, Technische Universität Wien, 1040 Vienna, Austria
| | - Günther Redhammer
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Michel Bockstedte
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Thomas Berger
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
| | - Oliver Diwald
- Department of Chemistry and Physics of Materials, University
of Salzburg, Jakob-Haringer-Strasse 2a, 5020 Salzburg, Austria
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Niedermaier M, Taniteerawong C, Schwab T, Zickler G, Bernardi J, Diwald O. Impurity Segregation and Nanoparticle Reorganization of Indium Doped MgO Cubes. CHEMNANOMAT : CHEMISTRY OF NANOMATERIALS FOR ENERGY, BIOLOGY AND MORE 2019; 5:634-641. [PMID: 31231606 PMCID: PMC6563704 DOI: 10.1002/cnma.201900077] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/02/2019] [Accepted: 02/26/2019] [Indexed: 06/09/2023]
Abstract
Metal oxide nanocomposites are non-equilibrium solids and promising precursors for functional materials. Annealing of such materials can provide control over impurity segregation and, depending on the level of consolidation, represents a versatile approach to engineer free surfaces, particle-particle interfaces and grain boundaries. Starting with indium-magnesium-oxide nanoparticle powders obtained via injection of an indium organic precursor into the magnesium combustion flame and subsequent particle quenching in argon, we investigated the stability of the trivalent In3+ ions in the host lattice of MgO nanoparticles by determining grain growth, morphology evolution and impurity segregation. The latter process is initiated by vacuum annealing at 873 K and can be tracked at 1173 K on a time scale of minutes. In the first instance the surface segregated indium wets the nanoparticle interfaces. After prolonged annealing indium evaporates and leaves the powder via the gas phase. Resulting MgO nanocubes are devoid of residual indium, regain their high morphological definition and show spectroscopic fingerprints (UV Diffuse Reflectance and Photoluminescence emission) that are characteristic of electronically unperturbed MgO cube corner and edge features. The results of this combined XRD, TEM, and spectroscopy study reveal the parameter window within which control over indium segregation is used to introduce a semiconducting metal oxide component into the intergranular region between insulating MgO nanograins.
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Affiliation(s)
- Matthias Niedermaier
- Department of Chemistry and Physics of MaterialsUniversity of SalzburgJakob-Haringer-Strasse 2a5020SalzburgAustria
| | - Chatpawee Taniteerawong
- Department of Chemistry and Physics of MaterialsUniversity of SalzburgJakob-Haringer-Strasse 2a5020SalzburgAustria
| | - Thomas Schwab
- Department of Chemistry and Physics of MaterialsUniversity of SalzburgJakob-Haringer-Strasse 2a5020SalzburgAustria
| | - Gregor Zickler
- Department of Chemistry and Physics of MaterialsUniversity of SalzburgJakob-Haringer-Strasse 2a5020SalzburgAustria
| | - Johannes Bernardi
- University Service Centre for Transmission Electron MicroscopyTechnische Universität Wien1040ViennaAustria
| | - Oliver Diwald
- Department of Chemistry and Physics of MaterialsUniversity of SalzburgJakob-Haringer-Strasse 2a5020SalzburgAustria
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Exploring multiple effects of Zn 0.15Mg 0.85O nanoparticles on Bacillus subtilis and macrophages. Sci Rep 2018; 8:12276. [PMID: 30115985 PMCID: PMC6095908 DOI: 10.1038/s41598-018-30719-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 07/23/2018] [Indexed: 12/15/2022] Open
Abstract
The increasing number of multidrug resistant bacteria raises a serious public-health concern, which is exacerbated by the lack of new antibiotics. Metal oxide nanoparticles are already applied as an antibacterial additive in various products used in everyday life but their modes of action have remained unclear. Moreover, their potential negative effects to human health are still under evaluation. We explored effects of mixed metal oxide Zn0.15Mg0.85O on Bacillus subtilis, as a model bacterial organism, and on murine macrophages. Zn0.15Mg0.85O killed planktonic bacterial cells and prevented biofilm formation by causing membrane damages, oxidative stress and metal ions release. When exposed to a sub-inhibitory amount of Zn0.15Mg0.85O, B. subtilis up-regulates proteins involved in metal ions export, oxidative stress response and maintain of redox homeostasis. Moreover, expression profiles of proteins associated with information processing, metabolism, cell envelope and cell division were prominently changed. Multimode of action of Zn0.15Mg0.85O suggests that no single strategy may provide bacterial resistance. Macrophages tolerated Zn0.15Mg0.85O to some extend by both the primary phagocytosis of nanoparticles and the secondary phagocytosis of damaged cells. Bacterial co-treatment with ciprofloxacin and non-toxic amount of Zn0.15Mg0.85O increased antibiotic activity towards B. subtilis and E. coli.
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Dai D, Ma Q, Pei Y, Zheng Z, Yuan L. Template-free synthesis of nanoparticle-built MgO and Zn-doped MgO hollow microspheres with superior performance for Congo red adsorption from water. Dalton Trans 2018; 47:17421-17431. [DOI: 10.1039/c8dt03803a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A template-free route was developed to synthesize MgO and Zn-doped MgO hollow microspheres with ultrahigh adsorption performances and excellent reusability.
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Affiliation(s)
- Dan Dai
- College of Chemistry and Molecular Sciences
- Wuhan University
- Wuhan
- China
| | - Qian Ma
- College of Chemistry and Molecular Sciences
- Wuhan University
- Wuhan
- China
| | - Yanyan Pei
- College of Chemistry and Molecular Sciences
- Wuhan University
- Wuhan
- China
| | - Zhong Zheng
- College of Chemistry and Molecular Sciences
- Wuhan University
- Wuhan
- China
| | - Liangjie Yuan
- College of Chemistry and Molecular Sciences
- Wuhan University
- Wuhan
- China
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Stankic S, Suman S, Haque F, Vidic J. Pure and multi metal oxide nanoparticles: synthesis, antibacterial and cytotoxic properties. J Nanobiotechnology 2016; 14:73. [PMID: 27776555 PMCID: PMC5075760 DOI: 10.1186/s12951-016-0225-6] [Citation(s) in RCA: 249] [Impact Index Per Article: 31.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 10/12/2016] [Indexed: 12/16/2022] Open
Abstract
Th antibacterial activity of metal oxide nanoparticles has received marked global attention as they can be specifically synthesized to exhibit significant toxicity to bacteria. The importance of their application as antibacterial agents is evident keeping in mind the limited range and effectiveness of antibiotics, on one hand, and the plethora of metal oxides, on the other, along with the propensity of nanoparticles to induce resistance being much lower than that of antibiotics. Effective inhibition against a wide range of bacteria is well known for several nano oxides consisting of one metal (Fe3O4, TiO2, CuO, ZnO), whereas, research in the field of multi-metal oxides still demands extensive exploration. This is understandable given that the relationship between physicochemical properties and biological activity seems to be complex and difficult to generalize even for metal oxide nanoparticles consisting of only one metal component. Also, despite the broad scope that metal oxide nanoparticles have as antibacterial agents, there arise problems in practical applications taking into account the cytotoxic effects. In this respect, the consideration of polymetallic oxides for biological applications becomes even greater since these can provide synergetic effects and unify the best physicochemical properties of their components. For instance, strong antibacterial efficiency specific of one metal oxide can be complemented by non-cytotoxicity of another. This review presents the main methods and technological advances in fabrication of nanostructured metal oxides with a particular emphasis to multi-metal oxide nanoparticles, their antibacterial effects and cytotoxicity.
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Affiliation(s)
- Slavica Stankic
- CNRS, Institut des Nanosciences de Paris (INSP), UMR 7588, 4 Place Jussieu, 75252, Paris Cedex 05, France. .,UPMC-Université Paris 06, INSP, UMR 7588, Paris, France.
| | - Sneha Suman
- Birla Institute of Technology & Science, Pilani Campus, Vidya Vihar, Pilani, Rajasthan, India
| | - Francia Haque
- CNRS, Institut des Nanosciences de Paris (INSP), UMR 7588, 4 Place Jussieu, 75252, Paris Cedex 05, France.,UPMC-Université Paris 06, INSP, UMR 7588, Paris, France
| | - Jasmina Vidic
- Virologie et Immunologie Moléculaires, UR892, INRA, Paris Saclay University, Jouy en Josas, France. .,School of Material Science and Engineering, Nanyang Technological University, 50 Nanyang Ave, Singapore, 639798, Singapore. .,NTU-HJU-BGU CREATE Programme, 1 Create Way, Research Wing # 02-06 to 08, Singapore, 138602, Singapore.
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Kocsis K, Niedermaier M, Bernardi J, Berger T, Diwald O. Changing interfaces: Photoluminescent ZnO nanoparticle powders in different aqueous environments. SURFACE SCIENCE 2016; 652:253-260. [PMID: 32903287 PMCID: PMC7116034 DOI: 10.1016/j.susc.2016.02.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We transformed vapor phase grown ZnO nanoparticle powders into aqueous ZnO nanoparticle dispersions and studied the impact of associated microstructure and interface property changes on their spectroscopic properties. With photoluminescence (PL) spectroscopy, we probed oxygen interstitials O i 2 - in the near surface region and tracked their specific PL emission response at hvEM = 2.1 eV during the controlled conversion of the solid-vacuum into the solid-liquid interface. While oxygen adsorption via the gas phase does affect the intensity of the PL emission bands, the O2 contact with ZnO nanoparticles across the solid-liquid interface does not. Moreover, we found that the near band edge emission feature at hvEM = 3.2 eV gains relative intensity with regard to the PL emission features in the visible light region. Searching for potential PL indicators that are specific to early stages of particle dissolution, we addressed for aqueous ZnO nanoparticle dispersions the effect of formic acid adsorption. In the absence of related spectroscopic features, we were able to consistently track ZnO nanoparticle dissolution and the concomitant formation of sol- vated Zinc formate species by means of PL and FT-IR spectroscopy, dynamic light scattering, and zeta potential measurements. For a more consistent and robust assessment of nanoparticle properties in different continuous phases, we discuss characterization challenges and potential pitfalls that arise upon replacing the solid-gas with the solid-liquid interface.
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Affiliation(s)
- Krisztina Kocsis
- Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Hellbrunnerstrasse 34/III, A - 5020, Salzburg, Austria
| | - Matthias Niedermaier
- Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Hellbrunnerstrasse 34/III, A - 5020, Salzburg, Austria
| | - Johannes Bernardi
- University Service Center for Transmission Electron Microscopy (USTEM), TU Wien, Wiedner Hauptstrasse 8-10, A-1040 Vienna, Austria
| | - Thomas Berger
- Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Hellbrunnerstrasse 34/III, A - 5020, Salzburg, Austria
| | - Oliver Diwald
- Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Hellbrunnerstrasse 34/III, A - 5020, Salzburg, Austria
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In vitro and ex vivo antimicrobial efficacy of nano-MgO in the elimination of endodontic pathogens. Clin Oral Investig 2014; 19:349-56. [PMID: 24859291 DOI: 10.1007/s00784-014-1253-y] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Accepted: 05/04/2014] [Indexed: 11/27/2022]
Abstract
OBJECTIVES The use of metal oxide nanoparticles has attracted lots of attention, mostly because of their promising antimicrobial activity along with their biocompatibility with mammalian cells. This study aims to investigate the in vitro and ex vivo antimicrobial efficiency of nano-magnesium oxide (MgO) aqueous solution against endodontic pathogens. MATERIALS AND METHODS The cytotoxicity of different concentrations of nano-MgO was assessed using lactate dehydrogenase cytotoxicity assay (LDH assay). A comparison of the antimicrobial efficiency of several concentrations of nano-MgO solution, sodium hypochlorite (NaOCl), and chlorhexidine (CHX) gluconate against Staphylococcus aureus, Enterococcus faecalis, and Candida albicans was made using the direct contact method. An ex vivo model of decoronated and experimentally infected human teeth was employed to compare the efficiency of nano-MgO (5 mg/L) solution with NaOCl (5.25 %) in the elimination of E. faecalis. RESULTS There was no statistically significant difference between nano-MgO solutions (10 and 5 mg/L), 5.25 % NaOCl, and 2 % CHX gluconate in terms of the required time to inhibit the growth of the tested pathogens (p > 0.05). The LDH assay showed no cytotoxicity of different concentrations of nano-MgO used in this study (p < 0.001). In the ex vivo model of infected human teeth, 6 h post-irrigation, there was no statistically significant difference between colony-forming units (CFU) per milliliter of nano-MgO (5 mg/L) and NaOCl (5.25 %)-treated teeth (5-6 log scale reduction). However, the nano-MgO group showed a significant decrease in colony-forming units per milliliter (7 log scale), 24 h post-irrigation (p < 0.05). At other tested time points-24, 48, 72, and 168 h-the levels of CFU per milliliter were significantly less in the nano-MgO group (2-3 log scale difference) compared to the NaOCl group, indicating long-term antibacterial activity of nano-MgO (p < 0.05). At 72 and 168 h post-irrigation, no detectable bacterial growth was observed in the nano-MgO group. The detection limit was 10 CFU/mL. CONCLUSIONS Nano-MgO aqueous solutions represent promising antimicrobial activities, both in vitro and ex vivo with minimal toxicity. CLINICAL RELEVANCE Compared to NaOCl (5.25 %), nano-MgO (5 mg/L) exhibits statistically significant long-term efficiency in the elimination of E. faecalis in the root canal system. After further investigations, nano-MgO could be considered as a new root canal irrigant.
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Wobbe MCC, Kerridge A, Zwijnenburg MA. Optical excitation of MgO nanoparticles; a computational perspective. Phys Chem Chem Phys 2014; 16:22052-61. [DOI: 10.1039/c4cp03442b] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The optical absorption spectra of magnesium oxide nanoparticles, along with the atomic centres responsible for the absorption, are studied using time-dependent density functional theory.
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Affiliation(s)
| | - Andrew Kerridge
- Department of Chemistry
- University College London
- London WC1H 0AJ, UK
- Department of Chemistry
- Lancaster University
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Sternig A, Stankic S, Müller M, Siedl N, Diwald O. Surface exciton separation in photoexcited MgO nanocube powders. NANOSCALE 2012; 4:7494-7500. [PMID: 23100068 DOI: 10.1039/c2nr31844j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In MgO nanocube powders surface excitons can separate and the resulting charge carriers provide reactive adsorption sites at well-defined surface elements. We employed photoluminescence (PL) emission bands originating from the photoexcitation of nanocube corners and edges as quantitative probes to explore their chemical reactivity towards molecular hydrogen. Surface excitons which form at corners and edges exhibit similar cross-sections for separation in vacuum. The separation of edge excitons, however, is significantly enhanced in hydrogen atmosphere when hydrogen adsorption occurs as a simultaneous surface process. The electronic structure of MgO nanocube edges which split hydrogen heterolytically upon generation of surface hydroxyls and hydrides is unaffected by the photoexcitation of corners. Respective edges, however, are efficient absorption sites for UV photons. Transfer of exciton energy to oxygen ions in corners is followed by exciton separation which transforms corner ions into surface radicals leading to a well-defined starting point for the site selective functionalization of metal oxide nanostructures.
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Affiliation(s)
- Andreas Sternig
- Cluster of Excellence - Engineering of Advanced Materials (EAM), Friedrich-Alexander University Erlangen-Nuremberg, Cauerstrasse 4, 91058 Erlangen, Germany
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Zhang H, Gheisi AR, Sternig A, Müller K, Schowalter M, Rosenauer A, Diwald O, Mädler L. Bulk and surface excitons in alloyed and phase-separated ZnO-MgO particulate systems. ACS APPLIED MATERIALS & INTERFACES 2012; 4:2490-2497. [PMID: 22530613 DOI: 10.1021/am300184b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The rational design of composite nanoparticles with desired optical and electronic properties requires the detailed analysis of surface and bulk contributions to the respective overall function. We use flame spray pyrolysis (FSP) to generate nanoparticles of the ternary Zn-Mg-O system the compositions of which range from solid solutions of Zn(2+) ions in periclase MgO to phase separated particle mixtures which consist of periclase (cubic) MgO and wurtzite (hexagonal) ZnO phases. The structure and composition of the composite Zn(x)Mg(1-x)O (0 ≤ x ≤ 0.3) particles are investigated using X-ray diffraction and high-resolution transmission electron microscopy, whereas UV diffuse reflectance and photoluminescence (PL) spectroscopy are used for the investigation of their optical properties. Vacuum annealing has been carried out to track the effects of stepwise elimination of surface adsorbates on the photoexcitation and PL emission properties. We demonstrate that for Zn(0.1)Mg(0.9)O particles, the admixed ZnO suppresses the MgO specific surface excitons and produces a PL emission band at 470 nm. Although gaseous oxygen partially reduces the emission intensity of hydroxylated particles, it leads to entire quenching in completely dehydroxylated samples after vacuum annealing at 1173 K. Consequently, surface hydroxyls at the solid-gas interface play a significant role as protecting groups against the PL-quenching effects of O(2). The obtained results are relevant for the characterization of ZnO-based devices as well as for other metal oxide materials where the impact of the surface composition on the photoelectronic properties is usually neglected.
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Affiliation(s)
- Huanjun Zhang
- Foundation Institute of Materials Science (IWT), Department of Production Engineering, University of Bremen, Badgasteinerstrasse 3, 28359 Bremen, Germany
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