Manglai Gao

Comparison between the removal of phenol and catechol by modified montmorillonite with two novel hydroxyl-containing Gemini surfactants.

Na-montmorillonites were modified with two novel hydroxyl-containing Gemini surfactants, 1,3-bis(hexadecyldimethylammonio)-2-hydroxypropane dichloride (BHHP) and 1,3-bis(octyldimethylammonio)-2-hydroxypropane dichloride (BOHP), via ion-exchange reaction in this study. The modified samples were characterized by X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy. Phenol and catechol were removed from aqueous solution by these two kinds of organo-montmorillonites in a batch system. Important parameters have been investigated, which affect the adsorption efficiency, such as the amount of modifier, temperature, pH and contact time. The adsorption kinetics of phenol and catechol were discussed using pseudo-first-order, pseudo-second-order and intra-particle diffusion model. It indicated that the experimental data fitted very well with the pseudo-second-order kinetic model, and the equilibrium adsorption data was proved in good agreement with the Langmuir isotherm. The result also showed the adsorption capacity of catechol was higher than that of phenol in the same conditions, which might result from the extra hydroxyl in the structure of catechol. Thermodynamic quantities such as Gibbs free energy (ΔG°), the enthalpy (ΔH°), and the entropy change of sorption (ΔS°) were also determined. These parameters suggested the adsorption of phenol was a spontaneous and exothermic process, while the sorption of catechol was endothermic.

Facet-dependent photocatalytic decomposition of N2O on the anatase TiO2: a DFT study

The photocatalytic N2O dissociation on anatase TiO2 is an attractive reaction and the mechanism of the photocalytic process, the role of excited electrons, and the favorable facet for higher activity need a more detailed study at the molecular level. Using DFT + U calculations, we investigate the dissociation process of N2O into N2 with and without photoexcited electrons on anatase TiO2 (001) and (101) facets to unravel such puzzles. The optical absorption properties of TiO2 (001) and (101) facets are compared in combination with electronic analysis. The localization of excited electrons on the two surfaces with the existence of oxygen vacancies is explored. When there is no photo-excitation, on a perfect TiO2 surface, N2O decomposition is difficult due to the inhibitive high reaction energy. In contrast, the reaction energy decreases dramatically in the presence of photoexcited or excess electrons on the TiO2 surface. The reaction energy is related to the electronic state of dissociated O. The more negative charges make O more stable, and accordingly lead to higher exothermic reaction energy. Based on this point, the influence of surface morphology and excited states can be understood. This is the first theoretical study of the photocatalytic process of N2O elimination, which will guide further experimental study and improve its activity.

Unraveling the structure–sensitivity of the photocatalytic decomposition of N2O on CeO2: a DFT+U study

The photocatalytic activity of N2O dissociation on CeO2 strongly depends on the exposed surface termination, with the (110) surface being much more reactive than the (111) surface. However, the physical nature requires a more detailed molecular level study. Using the DFT+U method, in the present study, we intend to explore the influence of surface termination from the following three aspects: the optical absorption, transfer kinetics of electron polaron, and the photo-chemical reaction process based on comparative studies of CeO2 (111) and (110) model surfaces. Due to the large band gap value, both CeO2 surfaces show negligible optical absorption difference. For both surfaces, the electron polaron is preferably localized on the surface rather than in the bulk. The Ce3+ ion close to the oxygen vacancy repels the excited electron due to Coulomb interactions. The migration barrier of the electron polaron from the bulk to the surface on the (110) surface is slightly lower than that on the (111) surface, suggesting a higher transfer rate of the electron polaron. The dissociation process of N2O into N2 with and without the photoexcited electron on CeO2 (110) and (111) surfaces is explored. On the stoichiometric CeO2 surface, N2O decomposition is difficult due to the inhibitive high reaction energy. In contrast, the reaction energy dramatically decreases in the presence of photoexcited or excess electrons on the CeO2 surface. The reaction energy is related to the electronic state of dissociated O. More negative charges make O more stable and accordingly lead to higher exothermic reaction energy.