Acidic and basic properties of hydroxylated metal oxide surfaces

Boehm, H. P.

doi:10.1039/df9715200264

Cited by 591 publications

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“…This is because the bridged OH groups have greater thermodynamic stability than terminal OH groups. 29 Since the bridging hydroxyl is acidic (pKa 2.9), whereas the terminal hydroxyl is basic (pKa 12.7), 30,31 generation of more bridging hydroxyls at pH 5.40 would contribute more negative charges and reduce the overall positive charge on TiO 2 as observed in EPM measurement. This is consistent with the above DLVO calculations.…”

Section: ■ Introductionmentioning

confidence: 99%

UV Irradiation Induced Transformation of TiO₂ Nanoparticles in Water: Aggregation and Photoreactivity

Sun

Guo

Zhang

et al. 2014

Environ. Sci. Technol.

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Transformation of nanomaterials in aqueous environment has significant impact on their behavior in engineered application and natural system. In this paper, UV irradiation induced transformation of TiO 2 nanoparticles in aqueous solutions was demonstrated, and its effect on the aggregation and photocatalytic reactivity of TiO 2 was investigated. UV irradiation of a TiO 2 nanoparticle suspension accelerated nanoparticle aggregation that was dependent on the irradiation duration. The aggregation rate increased from <0.001 nm/s before irradiation to 0.027 nm/s after 50 h irradiation, resulting in aggregates with a hydrodynamic diameter of 623 nm. The isoelectric point of the suspension was lowered from 7.0 to 6.4 after irradiation, indicating less positive charges on the surface. ATR-FTIR spectra displayed successive growth of surface hydroxyl groups with UV irradiation which might be responsible for the change of surface charge and aggregation rate. UV irradiation also changed the photocatalytic degradation rate of Rhodamine B by TiO 2 , which initially increased with irradiation time, then decreased. Based on the photoluminescence decay and photocurrent collection data, the change was attributed to the variation in interparticle charge transfer kinetics. These results highlight the importance of light irradiation on the transformation and reactivity of TiO 2 nanomaterials. ■ INTRODUCTIONSemiconductor nanomaterials have attracted intensive interest due to their ability to drive photochemical reactions under solar light irradiation. 1−4 In particular, TiO 2 nanoparticles are widely used in photocatalytic devices to achieve environmental remediation and water splitting because of their low-cost, low toxicity and robust performance. 5,6 Modeling studies predicted the annual production of nano-TiO 2 would exceed 2.5 million tons by 2025. 7 With the high reactivity and the rising demand of nano-TiO 2 , it is essential to elucidate both their stability in the practical devices during the life cycle of these products and their transformation process after discharge into the natural environment.Typical transformation processes of nanomaterials include aggregation, dissolution, redox reaction, photochemical reaction, and biocatalyzed degradation. 8−10 A nanomaterial may participate in one or more processes, depending not only on its inherent properties but also on the surrounding environmental factors. Indeed, once introduced to the practical applications, nano-TiO 2 encounters the environmental factors (e.g., natural organic matter, ionic species and sunlight) and then nano-TiO 2 will inevitably undergo physical and chemical transformations due to their high surface reactivity and large specific surface area. These transformation pathways will in turn govern their photoreactivity and environmental fate. Because of its high chemical stability, studies on the nano-TiO 2 behavior are mainly related to aggregation process. 11−13 Typically, The hydroxyl groups covered on nano-TiO 2 surface would interact with differe...

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Section: ■ Introductionmentioning

confidence: 99%

UV Irradiation Induced Transformation of TiO₂ Nanoparticles in Water: Aggregation and Photoreactivity

Sun

Guo

Zhang

et al. 2014

Environ. Sci. Technol.

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“…Active surface hydroxyl groups dissociates in aqueous solutions and forms electric charges as shown in Fig. 5.4b [15][16][17][18]. Positive or negative charge due to the dissociation is governed by pH of the surrounding aqueous solution: positive and negative charges are balanced and apparent charge is zero at a certain pH.…”

Section: Mechanism Of Osseointegration In Titaniummentioning

confidence: 99%

Biofunctionalization of Metallic Materials: Creation of Biosis–Abiosis Intelligent Interface

Hanawa

2015

Interface Oral Health Science 2014

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Osseointegration, the first concept of biosis-abiosis intelligent interface, is primarily explained, and researches on the elucidation of osseointegration mechanism and titanium-tissue interface observation are reviewed to understand a concept to create biosis-abiosis intelligent interface. In addition, current status of surface treatment of metallic materials is reviewed. In particular, a gap between research level progress and commercialization in surface treatments is focused. Mechanical property, durability, and manufacturing process of surface layer formed on titanium by surface treatment, are significant to commercialize the treatment, while most of researches focuses only evaluation of biocompatibility and biofunction. IntroductionExcellent biocompatibility and biofunction of ceramics and polymers are expected to show excellent properties as biomaterials; in fact many devices consisting of metals have been substituted by those consisting of ceramics and polymers. In spite of this event, over 70 % of implant devices in medical field including dentistry, especially over 95 % in orthopedics, still consist of metals, and this share is currently maintained, because of their high strength, toughness, and durability.On the contrary, a disadvantage of using metals as biomaterials is that they are typically artificial materials and have no biofunction. Therefore, metal surface naturally forms a clear interface against living tissue that works as a barrier to conduct biofunctions. To add biocompatibility and biofunction to metals, in other words, to create biosis-abiosis intelligent interface, surface treatment is essential,

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“…Vor einigen Jahren berichteten wir im Zuge unserer Untersuchungen über die Chemie der Oberfläche des Titandioxids [1][2][3][4][5], daß die Ti02-0berfläche unter normalen Bedingungen hydroxyliert ist und daß die Hydroxylgruppen oder Hydroxidionen zur Hälfte sauren [2], zur Hälfte basischen Charakter besitzen [3]. Das in erster Linie untersuchte AnatasPräparat P 25 (I) besaß nach Entfernung des molekular absorbierten Wassers etwa 440 //mol/g Hydroxylgruppen [1].…”

Section: Introductionunclassified

“…Die Neutralisations-Adsorptionsisothermen mit Alkali-oder Erdalkalihydroxiden gaben bereits bei kleinen Gleichgewichtsaktivitäten unter IO -2 mol/1 Absättigung von 220 //mol/g sauren Zentren. Bei höheren Konzentrationen stiegen die Isothermen viel langsamer an, die NaOHIsotherme hatte bei einer Konzentration von 0,2 mol/1 noch nicht den Endwert erreicht, der bei etwa 440 /miol/g zu liegen scheint [2,5]. Aus dem Verlauf der Adsorptionsisotherme bei niedrigen Konzentrationen ließ sich unter Vernachlässigung der Effekte der Oberflächenladung der Teilchen abschätzen, daß die sauren OH-Gruppen auf der Ti02-Oberfläche mittelstarke Säuren mit einem pKs von etwa 3 sind [2].…”

Section: Introductionunclassified

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Über die Chemie der Oberfläche des Titandioxids, V Die Oberflächenacidität von Titandioxid und von mit Phosphationen belegtem Titandioxid /On the Chemistry of the Surface of Titaniumoxide, V Surface Acidity of Titanium Dioxide and of Titanium Dioxide Covered with Adsorbed Phosphate Ions

Cornejo

Steinle

Boehm

1978

Zeitschrift Für Naturforschung B

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Abstract The acidity of surface OH groups on TiO2 (anatase and rutile) was determined using the Benesi titration technique. The most acidic groups have acidity constants (Ho) between 3 and 5. On treatment with solutions of phosphoric acid or phosphates, H2PO4 -ions are adsorbed by ion exchange for basic OH -ions of the surface. The chemisorbed H2PO4 -ions react strongly acidic with an acidity constant Ho between -5.6 and -3.3. Possible reasons for this extreme increase in acidity are briefly discussed.

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Acidic and basic properties of hydroxylated metal oxide surfaces

Cited by 591 publications

References 0 publications

UV Irradiation Induced Transformation of TiO₂ Nanoparticles in Water: Aggregation and Photoreactivity

UV Irradiation Induced Transformation of TiO₂ Nanoparticles in Water: Aggregation and Photoreactivity

Biofunctionalization of Metallic Materials: Creation of Biosis–Abiosis Intelligent Interface

Über die Chemie der Oberfläche des Titandioxids, V Die Oberflächenacidität von Titandioxid und von mit Phosphationen belegtem Titandioxid /On the Chemistry of the Surface of Titaniumoxide, V Surface Acidity of Titanium Dioxide and of Titanium Dioxide Covered with Adsorbed Phosphate Ions

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Acidic and basic properties of hydroxylated metal oxide surfaces

Cited by 591 publications

References 0 publications

UV Irradiation Induced Transformation of TiO2 Nanoparticles in Water: Aggregation and Photoreactivity

UV Irradiation Induced Transformation of TiO2 Nanoparticles in Water: Aggregation and Photoreactivity

Biofunctionalization of Metallic Materials: Creation of Biosis–Abiosis Intelligent Interface

Über die Chemie der Oberfläche des Titandioxids, V Die Oberflächenacidität von Titandioxid und von mit Phosphationen belegtem Titandioxid /On the Chemistry of the Surface of Titaniumoxide, V Surface Acidity of Titanium Dioxide and of Titanium Dioxide Covered with Adsorbed Phosphate Ions

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UV Irradiation Induced Transformation of TiO₂ Nanoparticles in Water: Aggregation and Photoreactivity

UV Irradiation Induced Transformation of TiO₂ Nanoparticles in Water: Aggregation and Photoreactivity