The point of zero charge of manganese dioxides

Gray, Malcolm J.; Malati, Mounir A.; Rophael, M.W.

doi:10.1016/s0022-0728(78)80038-2

Cited by 44 publications

(9 citation statements)

References 8 publications

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“…This means that the surface of the particles is positively charged for pH lower than 4 (blue square) and negatively charged at higher pH values. This result is consistent with the values found in the literature, which show a pH pzc between 3.3 and 4 for δ and β-MnO 2 nanoparticles [20,21].…”

Section: Film Characterizationsupporting

confidence: 93%

Facile Elaboration of Wet Cellulose Film as Catalyst Support of MnOx Nanoparticles for the Catalytic Oxidation of Dyes in Absence of Light

et al. 2021

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In the present work a remarkably simple procedure for the elaboration of wet cellulose film containing manganese oxide nanoparticles was developed. The films were produced using a mold made by 3D printing using cellulose dissolved in an ionic liquid, which allows the production of thin and homogeneous films of different shapes, types and designs which cannot be made using conventional techniques. Thanks to this possibility, the final catalytic object can be implemented in specific reactors. Manganese oxide nanoparticles were prepared as a colloidal solution by a redox/sol-gel procedure and then deposited on the cellulose films by wet impregnation. The catalytic film obtained was tested in the decomposition of a dye, indigo carmine (IC), in the absence of light. The influence of the pH of the solution on the decomposition rate was investigated. IC total decomposition was measured after 1-h reaction at pH below 3. At pH = 2, no deactivation of the catalyst was observed even after four decomposition cycles. This work provides a new strategy to design cellulose-based catalysts for dye removal from wastewater.

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Section: Film Characterizationsupporting

confidence: 93%

Facile Elaboration of Wet Cellulose Film as Catalyst Support of MnOx Nanoparticles for the Catalytic Oxidation of Dyes in Absence of Light

et al. 2021

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“…The point of zero charges (PZC) of MnO2 is ~ 4.7. 26,44,45 Below this pH the surface is positively charged, and hence its oxidizing ability will be relatively higher. IC is a dianionic dye in aqueous solution, and this configuration is maintained in the pH range 3-11.…”

Section: Figure 7 Effect Of Ph On the Photocatalytic Degradation Of mentioning

confidence: 99%

“…IC is a dianionic dye in aqueous solution, and this configuration is maintained in the pH range 3-11. 24,45 Below the PZC of MnO2, the electrostatic interaction between the positive catalyst surface and the dianions can lead to strong interaction between them and subsequent degradation of the dye. At higher pH when the surface is negatively charged, the adsorption is less due to the electrostatic repulsion between the negatively charged surface and the dye.…”

Section: Figure 7 Effect Of Ph On the Photocatalytic Degradation Of mentioning

confidence: 99%

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MnO2 AND MnO2/TiO2 MEDIATED, PERSULPHATE ENHANCED PHOTOCATALYSIS FOR THE REMOVAL OF INDIGO CARMINE DYE POLLUTANT FROM WATER

Lekshmi¹,

Yesodharan²,

Yesodharan³

2017

ECB

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Heterogeneous photocatalysis using UV/VIS light or natural solar radiation as the energy source is one of the most efficient advanced oxidation processes (AOP) for the removal of chemical and bacterial pollutants from water. One of the least investigated oxides in this context, i.e. MnO2 and its combination MnO2/TiO2 are examined as potential photocatalysts for the removal of Indigo carmine (IC) dye pollutant from the water. The catalysts are characterized by XRD, FTIR, SEM, TEM, adsorption and surface area measurements. While MnO2 is very efficient for the decolorization of the dye, it is not effective enough for mineralization. MnO2 /TiO2 as the photocatalyst at the optimized ratio of 9:1 combines the advantages of both the oxides, i.e., rapid decolorization and efficient mineralization. Persulphate (S2O8 2-) enhances the degradation while H2O2 inhibits the same. The degradation is dependent on pH with higher degradation under extremely acidic conditions. The influence of dissolved salts/anions in the water on the degradation varies from 'moderate inhibition' to 'no effect' or even 'enhancement' depending on the chemistry of the anion and reaction conditions. Effect of various parameters such as reaction time, substrate concentration, catalyst dosage, the presence of O2, recycling of the catalyst, etc. on the efficiency of degradation is investigated. The results are critically analyzed, and a tentative mechanism is proposed.

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“…9 The particles are therefore negatively charged at higher pH values. 9 The particles are therefore negatively charged at higher pH values.…”

Section: Characterisation Resultsmentioning

confidence: 99%

Adsorption from aqueous solution by δ‐manganese dioxide I. Adsorption of the alkaline‐earth cations

Gray

Malati

1979

J. Chem. Technol. Biotechnol.

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The adsorption isotherms of M2+ ions (M = Mg, Ca, Sr or Ba) were determined at pH 7.0 and at different temperatures. The adsorbent, δ‐MnO2, was converted to the K+ form prior to adsorption and about 1.5 mol K+ ions were released per mol of M2+ ions adsorbed. The adsorption capacity at a given temperature increased in the series: Mg2+ < Ca2+ ≦ Sr2+ < Ba2+. This was explained by an ion exchange mechanism between hydrated ions: K+ ions in the outer Helmholtz layer and M2+ ions in the bulk of the solution. The radii of the hydrated ions decreased in the series: Mg2+ > Ca2+ > Sr2+ > Ba2+. The adsorption of M2+ ions at pH values below the point of zero charge (pH 3.3) was significant for Mg2+ ions only. Although adsorption was not strictly reversible, the results fitted the Langmuir isotherm and ‘apparent heats of adsorption’, Q, were calculated. The endothermic heats (Q = 20,18, 11 and 5 kJ mol−1 for Mg2+, Ca2+, Sr2+ and Ba2+ adsorption respectively) indicated positive entropy contributions which are expected for the adsorption mechanism suggested. The decrease in Q down the alkaline‐earth group was correlated to the entropy effects and to the hydration numbers of the cations.

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The point of zero charge of manganese dioxides

Cited by 44 publications

References 8 publications

Facile Elaboration of Wet Cellulose Film as Catalyst Support of MnOx Nanoparticles for the Catalytic Oxidation of Dyes in Absence of Light

Facile Elaboration of Wet Cellulose Film as Catalyst Support of MnOx Nanoparticles for the Catalytic Oxidation of Dyes in Absence of Light

MnO2 AND MnO2/TiO2 MEDIATED, PERSULPHATE ENHANCED PHOTOCATALYSIS FOR THE REMOVAL OF INDIGO CARMINE DYE POLLUTANT FROM WATER

Adsorption from aqueous solution by δ‐manganese dioxide I. Adsorption of the alkaline‐earth cations

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