An in Situ ATR-FTIR Investigation of Sulfate Bonding Mechanisms on Goethite

Journal of Environmental Sciences

Sun

et al. 2016

The effect of phosphate on adsorption and oxidation of catechol, 1,2-dihydroxybenzene, in a heterogeneous Fenton system was investigated. In situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) was used to monitor the surface speciation at the nano-Fe 3 O 4 catalyst surface. The presence of phosphate decreased the removal rate of catechol and the abatement of dissolved organic compounds, as well as the decomposition of H 2 O 2 . This effect of phosphate was mainly due to its strong reaction with surface sites on the iron oxide catalyst. At neutral and acid pH, phosphate could displace the adsorbed catechol from the surface of catalyst and also could compete for surface sites with H 2 O 2 . In situ IR spectra indicated the formation of iron phosphate precipitation at the catalyst surface. The iron phosphate surface species may affect the amount of iron atoms taking part in the catalytic decomposition of H 2 O 2 and formation of hydroxyl radicals, and inhibit the catalytic ability of Fe 3 O 4 catalyst. Therefore, phosphate ions worked as stabilizer and inhibitor in a heterogeneous Fenton reaction at the same time, in effect leading to an increase in oxidation efficiency in this study. However, before use of phosphate as pH buffer or H 2 O 2 stabilizer in a heterogeneous Fenton system, the possible inhibitory effect of phosphate on the actual removal of organic pollutants should be fully considered.

Section: Atr-ftir Measurementsmentioning

confidence: 99%

Effect of phosphate on heterogeneous Fenton oxidation of catechol by nano-Fe 3 O 4 : Inhibitor or stabilizer?

Journal of Environmental Sciences

Sun

et al. 2016

“…In situ ATR infrared measurements were performed using the flow cell technique described elsewhere [23,24,26]. The pH of the reaction solutions were monitored by a combined pH electrode and adjusted when needed.…”

Section: Spectra Of Sodium Silicate In Solution and On Magnetitementioning

confidence: 99%

“…Their results indicated the formation of two types of monodentate surface complexes, ≡FeH 3 SiO 4 and ≡FeH 2 SiO − 4 . Attenuated total reflection Fourier transformed infrared (ATR-FTIR) spectroscopy has been proven to be a powerful in situ technique to study solid-liquid interface reactions, where various inorganic anions (such as arsenate, sulfate, phosphate) and organic compounds interacts with metal oxides and minerals [23][24][25][26]. Although there are some IR, XPS and EXAFS studies on the interaction of silicate with iron oxides or polymers [27,28], no in situ spectroscopy study monitoring the sorption of silicate from dilute solutions, viz.…”

Section: Introductionmentioning

confidence: 99%

A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy

Journal of Colloid and Interface Science

Roonasi

Holmgren

2008

163

105

The sorption of sodium silicate by synthetic magnetite (Fe 3 O 4 ) at different pH conditions (pH 7-11) and initial silicate concentrations (1 × 10 −3 and 10 × 10 −3 mol L −1 ) was studied using in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The analysis of infrared spectra of sodium silicate in solution as well as adsorbed on magnetite nano-particles clearly showed the evolution of different silicate species depending on pH and silica concentration. The silicate concentration studied (10 × 10 −3 mol L −1 ) contained polymeric or condensed silicate species at lower pH as well as monomers at high pH, as evident from infrared spectra. Condensation of monomers resulted in an increased intensity of absorptions in the high frequency part (>1050 cm −1 ) of the spectral region, which contains information about both silicate in solution and sorbed silicate viz. 1300 cm −1 -850 cm −1 . In the pH range studied, infrared spectra of sorbed silicate and sorbed silicate during desorption both indicated the presence of different types of surface complexes at the magnetite surface. The sorption mechanism proposed is in accordance with a ligand exchange reaction where both monodentate and bidentate complexes could exist at low surface loading level, the relative proportion of the complexes being due to both pH and concentration in solution. Oligomerization occurred on the magnetite surface at higher surface loading.

“…In situ ATR infrared measurements were performed using the flow-cell technique described by Peak and others [16,17]. The small amount of iron oxide used (<1 mg) assures that the depth of penetration is much larger than the thickness of the evenly distributed oxide layer.…”

Section: Atr-ftir Spectra Of Sorbed Silicatementioning

confidence: 99%

Kinetics of silicate sorption on magnetite and maghemite: An in situ ATR-FTIR study

Colloids and Surfaces A: Physicochemical and Engineering Aspect

Roonasi

Jolsterå

et al. 2009

a b s t r a c tAttenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to monitor the in situ sorption of sodium metasilicate from aqueous solution onto synthesized magnetite and maghemite particles in the pH range of 10.8-7.0 using silicate concentrations between 0.1 mM and 5 mM. The spectral data showed that both pH and silicate concentration had great influence on the interfacial reaction between soluble silicate and the iron oxide surfaces, regarding the amount adsorbed per unit mass of iron oxide and the surface species formed. A pH dependent sorption of silicate on iron oxides was observed, implying that a maximum sorption took place in the pH range of 9.5-7.0. All experiments showed a fast initial increase in the absorption intensity followed by a slower sorption stage which was strongly dependent on the concentration of silicate in solution and the pH value. The amount of sorption onto magnetite was 3-5 times larger than onto maghemite, but there was no significant difference in the line shape of corresponding absorption bands. At pH 8.5 and low concentration (≤0.1 mM), the silicate monomers dominate in solution and on the iron oxide surface also monomeric species were dominating as evident from the infrared band at 950 cm −1 . However, at higher concentration (0.4-5.0 mM), the dominating absorption band at about 1000 cm −1 shifted to higher frequency during the sorption indicating that oligomeric surface silicate species were formed on the iron oxide surface. Desorption of silicate from the surface of the iron oxides was easier to accomplish at low silicate concentration, whilst the highest concentration showed a comparatively low relative amount of desorbed silicate, suggesting that polymerized species had a stronger affinity for the iron oxide surface as compared to monomeric species.