Funktionelle Gruppen an Festkörper‐Oberflächen

Boehm, H. P.

doi:10.1002/ange.19660781202

Cited by 201 publications

(48 citation statements)

References 120 publications

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“…Also, the data of Unger [112,146] derived from the reaction of OH groups with CH 3 Li and the heavy water HTO accord well with our results. There is a qualitative agreement between our results and the data as reported by Papee [24], Gokcek and Boehm [80,81] and several other authors. The b-cristobalite models of dehydroxylation process as developed by Branda et al [265], Sindorf and Maciel [159,160] and Chuang and Maciel [285] support the evidence of a two-stage temperature dependence of the silanol number h OH .…”

Section: Dehydroxylation and Rehydroxylation Of The Silica Surface Dsupporting

confidence: 93%

The surface chemistry of amorphous silica. Zhuravlev model

Zhuravlev

2000

Colloids and Surfaces A: Physicochemical and Engineering Aspect

2,027

142

1,967

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A review article is presented of the research results obtained by the author on the properties of amorphous silica surface. It has been shown that in any description of the surface silica the hydroxylation of the surface is of critical importance. An analysis was made of the processes of dehydration (the removal of physically adsorbed water), dehydroxylation (the removal of silanol groups from the silica surface), and rehydroxylation (the restoration of the hydroxyl covering). For each of these processes a probable mechanism is suggested. The results of experimental and theoretical studies permitted to construct the original model (Zhuravlev model-1 and model-2) for describing the surface chemistry of amorphous silica. The main advantage of this physico-chemical model lies in the possibility to determine the concentration and the distribution of different types of silanol and siloxane groups and to characterize the energetic heterogeneity of the silica surface as a function of the pretreatment temperature of SiO 2 samples. The model makes it possible to determine the kind of the chemisorption of water (rapid, weakly activated or slow, strongly activated) under the restoration of the hydroxyl covering and also to assess of OH groups inside the SiO 2 skeleton. The magnitude of the silanol number, that is, the number of OH groups per unit surface area, h OH , when the surface is hydroxylated to the maximum degree, is considered to be a physico-chemical constant. This constant has a numerical value: h OH,AVER =4.6 (least-squares method) and h OH,AVER = 4.9 OH nm − 2 (arithmetical mean) and is known in literature as the Kiselev-Zhuravlev constant. It has been established that adsorption and other surface properties per unit surface area of silica are identical (except for very fine pores). On the basis of data published in the literature, this model has been found to be useful in solving various applied and theoretical problems in the field of adsorption, catalysis, chromatography, chemical modification, etc. It has been shown that the Brunauer -EmmettTeller (BET) method is the correct method and gives the opportunity to measure the real physical magnitude of the specific surface area, S Kr (by using low temperature adsorption of krypton), for silicas and other oxide dispersed solids.

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Section: Dehydroxylation and Rehydroxylation Of The Silica Surface Dsupporting

confidence: 93%

The surface chemistry of amorphous silica. Zhuravlev model

Zhuravlev

2000

Colloids and Surfaces A: Physicochemical and Engineering Aspect

2,027

142

1,967

View full text Add to dashboard Cite

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“…sample was measured using a Flowsorb II 2300 (Micromeritics, Japan), the number of surface hydroxyl groups was measured by fluoride ion adsorption, 16) and the pH of each solution was measured using a digital pH meter (Mettler-Toledo International Inc., Japan).…”

Section: Methodsmentioning

confidence: 99%

Characteristics of Granular Boehmite and Its Ability to Adsorb Phosphate from Aqueous Solution

et al. 2012

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In this study, we investigated the surface properties of granulated boehmite with vinyl acetate (G-BE20) and measured the amount of phosphate it adsorbed and the effect of contact time and solution pH on the adsorption process. The specific surface area (144.9 m 2 /g) and the number of surface hydroxyl groups (0.88 mmol/g) of G-BE20 were smaller than those of virgin boehmite (BE), which gave a specific surface area and number of surface hydroxyl groups of 297.0 m 2 /g and 1.08 mmol/g, respectively. The amount of phosphate adsorbed increased with the temperature. The isotherm model of Langmuir was used to fit experimental adsorption equilibrium data for phosphate adsorption onto G-BE20. The calculated thermodynamic parameters show the spontaneous and endothermic nature of the adsorption process. The equilibrium adsorption onto G-BE20 was reached within 16 h and the amount of phosphate adsorbed was 8.4 mg/g. The kinetic mechanism of phosphate uptake was evaluated with two different models: the Largergren pseudo first-and pseudo second-order models. The data obtained showed a better fit to the pseudo second-order model (0.991) than to the pseudo first-order model (0.967), as indicated by the r values. The rate constants for the adsorption of phosphate onto G-BE20 were calculated as 0.481 1/h and 0.029 g/mg h. The adsorption of phosphate onto G-BE20 was the maximum in the pH range 3.0-4.0. Key words phosphate; adsorption; boehmitePhosphorus is an important nutrient involved in several biochemical reactions, and it cannot be substituted by other elements. It is widely used in agriculture and industry.1) The presence of trace amounts of phosphorus, exceeding about 1 mg/L, in treated wastewater can stimulate algal growth (eutrophication); phosphorus is usually considered a rate-limiting factor for algal growth.2) Algal blooms lead to short-and longterm environmental and aesthetic problems in lakes, coastal areas, and other confined water bodies.3) Moreover, phosphate is an exhaustible resource, and Japan depends solely on imports owing to a lack of native rock phosphate. As a consequence, phosphate removal and recovery from wastewater has been considered an important factor related to environmental sustainability. 4)Several physicochemical and biological processes have been investigated for the removal of dissolved nutrients in water and wastewaters. 5-9) They include adsorption methods, physical processes (settling and filtration), chemical precipitation (with aluminum, iron, and calcium salts), and biological processes that rely on biomass growth (bacteria, algae, and plants) or intracellular bacterial polyphosphate accumulation.10) Adsorption is one of the most attractive approaches in water treatment, and it has the advantage of having high removal efficiency without producing harmful by-products. 11)It is also well known that phosphates have a strong affinity for mineral surfaces.12) Its affinity for hydroxide surfaces depends not only on the anion's complexing capacity, which allows phosphates to bind to surface ...

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“…The adhesive functional metal primers bond powerfully to pure metals and alloys, because of their affinity to metal oxides that exist on the metal surface [22,23]. The zirconium surface is easily covered with a passive oxide film (ZrO 2 ), similar to the titanium surface (TiO 2 ) [24]. Thus, chemical characteristics of zirconia ceramic surface are similar to those of metal surface.…”

Section: Introductionmentioning

confidence: 99%