Insight into the Properties of Plasmonic Au/TiO2 Activated by O2/Ar Plasma

The performance of CO oxidation over plasmonic Au/TiO2 photocatalysts is largely determined by the electric discharge characteristics and physicochemical properties of discharge gas. To explore the activation mechanism of Au/TiO2, an O2 and Ar mixture gas as a discharge gas was employed to activate Au/TiO2. The photocatalytic activity in CO oxidation over activated Au/TiO2 was obtained, and the electric discharge characteristics, Au nanoparticle size, surface chemical state, optical property and CO chemisorption were thoroughly characterized. As the O2 content increases from 10% to 50%, the amplitude of the current pulses increases, but the number of pulses and the discharge power decrease. The photocatalytic activity of Au/TiO2 rises rapidly at first and then remains constant at 75% when the O2 content is above 50%. Compared with the discharge gas of 10% and 30% O2/Ar, the sample activated by 50% O2/Ar plasma possesses less metallic Au and more surface oxygen species and carbonate species by X-ray photoelectron spectroscopy, which is consistent with UV-vis diffuse reflectance spectra and CO chemisorption. The CO chemisorption capacities of the activated samples are the same at a long exposure time due to the approximate Au nanoparticle size observed by transmission electron microscopy. An increase in carbonate species generated from the oxygen species on the surface of TiO2 is discovered.

Extension of the AIOMFAC model by iodine and carbonate species: applications for aerosol acidity and cloud droplet activation

Iodine and carbonate species are important components in marine and dust aerosols, respectively. The non-ideal interactions between these species and other inorganic and organic compounds within aqueous particle phases affect hygroscopicity, acidity, and gas–particle partitioning of semi-volatile components. In this work, we present an extended version of the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model by incorporating the ions I−, IO3−, HCO3−, CO32−, OH−, and CO2(aq) as new species. First, AIOMFAC ion interaction parameters for aqueous solutions were determined based on available thermodynamic data, such as water activity, mean molal activity coefficients, solubility, and vapor–liquid equilibrium measurements. Second, the interaction parameters for the new ions and various organic functional groups were optimized based on experimental data or, where data are scarce, alternative estimation methods such as multiple linear regression or a simple substitution by analogy approach. Additional bulk water activity and electrodynamic balance measurements were carried out to augment the database for the AIOMFAC parameter fit. While not optimal, we show that the use of alternative parameter estimation methods enables physically sound predictions and offers the benefit of a more broadly applicable model. Our implementation of the aqueous carbonate/bicarbonate/CO2(aq) system accounts for the associated temperature-dependent dissociation equilibria explicitly and enables closed- or open-system computations with respect to carbon dioxide equilibration with the gas phase. We discuss different numerical approaches for solving the coupled equilibrium conditions and highlight critical considerations when extremely acidic or basic mixtures are encountered. The fitted AIOMFAC model performance for inorganic aqueous systems is considered excellent over the whole range of mixture compositions where reference data are available. Moreover, the model provides physically meaningful predictions of water activity under highly concentrated conditions. For organic–inorganic mixtures involving new species, the model–measurement agreement is found to be good in most cases, especially at equilibrium relative humidities above ~70 %; reasons for deviations are discussed. Several applications of the extended model are shown and discussed, including: the effects of ignoring the auto-dissociation of water in carbonate systems, the effects of mixing bisulfate and bicarbonate compounds in closed- or open-system scenarios on pH and solution speciation, and the prediction of critical cloud condensation nucleus activation of NaI or Na2CO3 particles mixed with suberic acid.

Probing the Interaction of Plasma with Nano-Catalysts for CO2 Conversion Using In-Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy

The effect of γ-Al2O3 and Ce/Al2O3 nano-catalysts under plasma on CO2 conversion was investigated via In-Situ DRIFTS. The adsorption of CO2 on the nanoparticle of γ-Al2O3 surface caused to produce the carbonate species, of which the amount was dependent on temperature. In addition, we confirmed that the formation of carbonate could be more activated by plasma. The Ce nano-catalyst played a role to inhibit the production of carbonate on the surface of Al2O3 under the plasma. Indeed, when the Ce/Al2O3 catalyst was exposed to plasma-excited CO2, the carbonate was almost eliminated at over 300 °C, resulting in the improved CO2 conversion. Notably, the Ce-promoted catalyst was able to enhance the formation of intermediate formate species by the plasma-excited CO2. Consequently, the formed intermediate species facilitated the generation of CO by the reaction of formate and bicarbonate.

Unexpected Link between the Template Purification Solvent and the Structure of Titanium Dioxide Hollow Spheres

Carbon spheres were applied as templates to synthesize titanium dioxide hollow spheres. The templates were purified with either ethanol or acetone, and the effects of this treatment on the properties of the resulting titania were investigated. The photocatalytic activity of the catalysts was measured via the decomposition of phenol model pollutant under visible light irradiation. It was found that the solvent used for the purification of the carbon spheres had a surprisingly large impact on the crystal phase composition, morphology, and photocatalytic activity. Using ethanol resulted in a predominantly rutile phase titanium dioxide with regular morphology and higher photocatalytic activity (r0,phenol = 3.9 × 10−9 M∙s−1) than that containing mainly anatase phase prepared using acetone (r0,phenol = 1.2 × 10−9 M∙s−1), surpassing the photocatalytic activity of all investigated references. Based on infrared spectroscopy measurements, it was found that the carbon sphere templates had different surface properties that could result in the appearance of carbonate species in the titania lattice. The presence or absence of these species was found to be the determining factor in the development of the titania’s properties.

Simulating the binding of organic functional groups to aqueous calcium carbonate species

The interaction of organic molecules with mineral systems is relevant to a wide variety of scientific problems both in the environment and minerals processing. In this study, the coordination of...

Formation and Evolution of Carbonate Species in CO Oxidation over Mono-dispersed Fe on Graphene

Fe is not only the most abundant metal on the planet, but also the key component of many enzymes in organisms that are capable to catalyze many chemical conversions. Mono-dispersed...

CO2 Absorption Mechanism by the Nonaqueous Solvent Consisting of Hindered Amine 2-[(1,1-dimethylethyl)amino]ethanol and Ethylene Glycol

In this work, we studied the CO2 absorption mechanism by nonaqueous solvent comprising hindered amine 2-[(1,1-dimethylethyl)amino]ethanol (TBAE) and ethylene glycol (EG). The NMR and FTIR results indicated that CO2 reacted with an -OH group of EG rather than the -OH of TBAE by producing hydroxyethyl carbonate species. A possible reaction pathway was suggested, which involves two steps. In the first step, the acid–base reaction between TBAE and EG generated the anion HO-CH2-CH2-O-; in the second step, the O− of HO-CH2-CH2-O− attacked the C atom of CO2, forming carbonate species.