Reduction of Nitrate By Fe<sup>2+</sup> in Clay Minerals

Ernstsen, Vibeke

doi:10.1346/ccmn.1996.0440503

Cited by 71 publications

(51 citation statements)

References 13 publications

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“…Embedding TiO 2 nanoparticles in clay matrices is expected to improve the photocatalytic performance by enhancing VOC retention through adsorption in clay pores. In addition, clays can also act as electron acceptors or donors (32) and have the ability to catalyze diverse chemical processes such as polymerization, reduction, decomposition or acid-base reactions (32)(33)(34)(35).…”

Section: Introductionmentioning

confidence: 99%

Efficiency of Clay−TiO₂ Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

Kibanova

Cervini-Silva

Destaillats

2009

Environ. Sci. Technol.

113

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Clay-supported TiO 2 photocatalysts can potentially improve the performance of air treatment technologies via enhanced adsorption and reactivity of target volatile organic compounds (VOCs). In this study, a bench-top photocatalytic flow reactor was used to evaluate the efficiency of hectorite-TiO 2 and kaolinite-TiO 2 , two novel composite materials synthesized in our laboratory. Toluene, a model hydrophobic VOC and a common indoor air pollutant, was introduced in the air stream at realistic concentrations, and reacted under UVA (λ max = 365 nm) or UVC (λ max = 254 nm) irradiation. The UVC lamp generated secondary emission at 185 nm, leading to the formation of ozone and other short-lived reactive species. Performance of clay-TiO 2 composites was compared with that of pure TiO 2 (Degussa P25), and with UV irradiation in the absence of photocatalyst under identical conditions. Films of clay-TiO 2 composites and of P25 were prepared by a dip-coating method on the surface of Raschig rings, which were placed inside the flow reactor. An upstream toluene concentration of ~170 ppbv was generated by diluting a constant flow of toluene vapor from a diffusion source with dry air, or with humid air at 10, 33 and 66 % relative humidity (RH). be partially attributed to the contribution of gas phase reactions by short-lived radical species. When the reaction rate was normalized to the light irradiance, T r /I λ , the UV/TiO 2 reaction under UVA irradiation was more efficient for samples with a higher content of TiO 2 (P25 and Hecto-TiO 2 ), but not for Kao-TiO 2 . In all cases, reaction rates

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Section: Introductionmentioning

confidence: 99%

Efficiency of Clay−TiO₂ Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

Kibanova

Cervini-Silva

Destaillats

2009

Environ. Sci. Technol.

113

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“…The potential for modification of smectite properties for industrial, engineering, and environmental applications by controlling the oxidation state of Fe is great (Chen et al, 1987;Low et al, 1983). The knowledge of the reduction mechanism of Fe 3+ to Fe 2 § is, therefore, essential for understanding a number of natural weathering processes as well as for purposely modifying specific properties of smectite (Ernstsen, 1998). This subject has been extensively studied in the past two decades, and also largely reviewed in the literature (Heller-Kallai, 1997; Rozenson and Heller-Kallai, 1976;Russell et al, 1979;Stucki, 1988;Stucki et al, , 1996Stucki andRoth, 1976, 1977).…”

Section: Introductionmentioning

confidence: 99%

A Model for the Mechanism of Fe³⁺ to Fe²⁺ Reduction in Dioctahedral Smectites

Drits

Manceau

2000

Clays and clay miner.

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A model to compensate the 2:1 layer having excess negative charge owing to the reduction of Fe 3+ to Fe 2+ by sodium dithionite buffered with citrate-bicarbonate in nontronite, beidellite, and montmorillonite is proposed. This model is based on reassessing published experimental data for Fe-containing smectites and on a recently published structural model for reduced Garfield nontronite. In the reduced state, Fe 2+ cations remain six-fold coordinated, and increases of negative charge in the 2:1 layer are compensated by the sorption of Na + and H + from solution. Some of the incorporated protons react with structural OH groups to cause dehydroxylation. Also, some protons bond with undersaturated oxygen atoms of the octahedral sheet. The amount of Na + (p) and H + (n~) cations incorporated in the structure as a function of the amount of Fe reduction can be described quantitatively by two equations: p = m/(1 + K0mrel) and rt i = KornmrJ(1 + K0rnrel); with K 0 = CEC (9.32 -1.06mto t + 0.02mt2ot), where into t is the total Fe content in the smectite, m is the Fe 2+ content, mr,~ is the reduction level (m/mtot) , CEC is the cation-exchange capacity, and K 0 is a constant specific to the smectite. The model can predict, from the chemical composition of a smectite, the modifications of its properties as a function of reduction level. Based on this model, the structural mechanism of Fe 3 § reduction in montmorillonite differs from that determined in nontronite and beidellite owing to differences in the distribution of cations over trans-and cis-octahedral sites.

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“…Embedding TiO 2 nanoparticles in clay matrices is expected to improve the photocatalytic efficiency by enhancing VOC retention through adsorption in clay pores. In addition, clays can also act as electron acceptors or donors (Solomon, 1968), and have the ability to catalyze diverse chemical processes such as polymerization, reduction, decomposition, or acid-base reactions (Ernstsen, 1996).…”

Section: Introductionmentioning

confidence: 99%

Application of ultraviolet light-emitting diode photocatalysis to remove volatile organic compounds from indoor air

Sharmin

Ray

2012

Journal of the Air & Waste Management Association

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Photocatalytic oxidation (PCO) is a promising technology for indoor air purification due to low operating cost, potentially long service life, and low maintenance. Ultraviolet light-emitting diode (UVLED) is a new concept in the field of PCO, which has several advantages over conventional UV light sources. Limited research has been conducted using UVLED PCO for air treatment. This study demonstrated the potential application of UVLED for the removal of volatile organic compounds (VOCs; toluene and xylene) from indoor air under different operating conditions including flow rate (25-117 cubic feet per minute [cfm]), types of catalysts (Degussa P25, sol-gel TiO 2 , nitrogen-doped TiO 2 , clay TiO 2 , and Bi 2 O 3 ), LED intensity, and humidity in a continuous reactor. About 7-32% VOC removal occurred depending on the experimental conditions. The results show that UVLED can activate different types of photocatalysts effectively.Implications: This study demonstrates the effectiveness of UVLED in photocatalytic oxidation applied for indoor air cleaning. Several TiO 2 catalysts (Degussa P25, sol-gel TiO 2 , nitrogen-doped TiO 2 , clay TiO 2 , and Bi 2 O 3 ) were used in the reactor to characterize the removal performance of indoor air pollutants, for example, VOCs. This is one of the very few studies that have, to date, examined toluene and xylene removal from indoor air using these catalysts with UVLED in a continuous reactor. The intent is to develop an energy-efficient continuous reaction system to remove VOCs from indoor air. The performance of the system was characterized with respect to air flow rate, humidity, types of catalysts, and light intensity.

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Reduction of Nitrate By Fe²⁺ in Clay Minerals

Cited by 71 publications

References 13 publications

Efficiency of Clay−TiO₂ Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

Efficiency of Clay−TiO₂ Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

A Model for the Mechanism of Fe³⁺ to Fe²⁺ Reduction in Dioctahedral Smectites

Application of ultraviolet light-emitting diode photocatalysis to remove volatile organic compounds from indoor air

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Reduction of Nitrate By Fe2+ in Clay Minerals

Cited by 71 publications

References 13 publications

Efficiency of Clay−TiO2 Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

Efficiency of Clay−TiO2 Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

A Model for the Mechanism of Fe3+ to Fe2+ Reduction in Dioctahedral Smectites

Application of ultraviolet light-emitting diode photocatalysis to remove volatile organic compounds from indoor air

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Reduction of Nitrate By Fe²⁺ in Clay Minerals

Efficiency of Clay−TiO₂ Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

Efficiency of Clay−TiO₂ Nanocomposites on the Photocatalytic Elimination of a Model Hydrophobic Air Pollutant

A Model for the Mechanism of Fe³⁺ to Fe²⁺ Reduction in Dioctahedral Smectites