The interactions between O–H groups in kaolinite and re-adsorption water is an important aspect that should be considered in the hydraulic fracturing method for the production of shale gas, because the external water adsorbed by kaolinite in shale would significantly affect the desorption of methane. In this study, the interactions were investigated via changing the amount of O–H groups and re-adsorption water in kaolinite by heating treatment and water re-adsorption. To overcome the overlap of IR vibration bands of the O–H functional groups in H2O and those in parent kaolinite, kaolinite samples with D2O re-adsorption were prepared by drying the H2O from raw kaolinite and soaking the dried kaolinite in D2O. The interactions between O–H groups in kaolinite and D2O molecules were investigated by in situ DRIFT and TG-MS. The results demonstrated that the vibration at 3670 ± 4 cm−1 in the DRIFT spectra could be due to the outer O–H groups of the octahedral sheet on the upper surface of the kaolinite microcrystal structure, rather than a type of inner-surface O–H group. All types of O–H groups, including the inner O–H groups in kaolinite, could be transformed into O–D groups after D2O re-adsorption at room temperature. The inner-surface O–H groups in kaolinite are the most preferred sites for D2O re-adsorption; thus, they would be the key factor for studying the effect of re-adsorption water on methane desorption. When the temperature increased from 100 °C to 300 °C, two layers of kaolinite slipped away from each other, resulting in the transformation of inner-surface O–H groups into outer O–H groups. Thus, the temperature range of 100 to 300 °C was suggested for the heat treatment of kaolinite to decrease the content of inner-surface O–H groups; thereby, the amount of re-adsorption water was reduced. However, to thoroughly remove the re-adsorption water, a temperature higher than 650 °C should be used.
Hanxiao Liao,Xiaodong Zhang,Shuwen Niu,Pengfei Tan,Kejun Chen,Yong Liu,Gongming Wang,Min Liu,Jun Pan
Transition metal-based pre-catalysts undergo drastic reconstruction to form the active catalysts during the alkaline oxygen evolution reaction (OER). However, the effect of escaped inactive ion from pre-catalysts themselves is usually ignored during reconstruction processes. Here, we investigate the effect of inactive MoO 4 2- escaped from a pre-catalyst of Fe incorporated nickel-molybdenum oxyhydroxide (NiMo-Fe) on OER performance. The results of in-situ Raman and X-ray photoelectron spectroscopy reveal that MoO 4 2- can be easily dissolved into KOH electrolyte and re-adsorbed on surface of catalyst during OER processes, which delivers a promoting effect on OER performance. The dissolution of MoO 4 2- is beneficial for increasing the reconstruction degree of NiMo-Fe to form the active phase of NiFeOOH. Theoretical calculations demonstrate that the re-adsorbed MoO 4 2- is favorable for the adsorption of the OOH* intermediate, thus boosts the OER activity. As expected, the NiMo-Fe shows a superior electrocatalytic performance for OER, outperforming the pre-catalyst without Mo species. This finding enriches the knowledge of inactive-ion effect on alkaline OER performance and offers a path for developing efficient electrocatalysts.
Addressing the significant technical hurdle of efficiently capturing mixed-component volatile organic compounds (VOCs) in real-world environments is indispensable. An innovative synthesis strategy for three-dimensional high positive potential (3D-HPP) has been proposed to develop MOF composites (U66N-FT/COF) for the synergistic adsorption of toluene and formaldehyde (FA). Structural and density functional theory (DFT) simulation analyses revealed that the thiophene, amide, and amino sites in U66N-FT/COF synergistically captured FA and toluene. This phenomenon of VOCs capture occurred through π-π conjugation and electrostatic interactions, significantly reducing the competitive adsorption effect among VOCs molecules. Interestingly, the preferential adsorption of FA molecules created secondary adsorption sites for toluene molecules, thereby augmenting the adsorption capacity of toluene by 47.2 % through the dynamic and synergistic mechanism of “Adsorption-Induced-Resorption”. Furthermore, the COF unit in U66N-FT/COF acted as a hydrophobic barrier, significantly impeding the diffusion of H 2 O molecules in the pores and thus effectively weakening the competitive adsorption of H 2 O to VOCs. The experimental findings implied that the U66N-FT/COF composites possessed a remarkable synergistic adsorption activity with a total adsorption capacity of 2.15 mmol/g and a synergistic adsorption coefficient α of 1.11 for the mixed-component VOCs. This study provides an important technical approach and theoretical guidance for addressing the synergistic treatment of multicomponent VOCs in practical scenarios.
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