Highly diverse structures and pore sizes make metal–organic frameworks (MOFs) good candidates for the fabrication of gas separation membranes. The synthesis of continuous MOF membranes still remains ...a challenge. In this work, an integrated Cu-BTC membrane was successfully prepared on the novel potassium hexatitanate support for the first time by in situ solvothermal growth. This kind of support was found to be more suitable for the growth of Cu2+-containing MOF membranes than other traditional supports, such as a porous alumina support. The permeation results of Cu-BTC membranes obtained in this work show moderate separation selectivities of helium over other small gas molecules, including CO2, N2, and CH4. Compared to other MOF membranes, the Cu-BTC membrane exhibits higher ideal selectivity for helium under the condition of similar helium permeance, while it has higher helium permeance with similar ideal selectivity.
In the absence of any doping and modification, the anatase-to-rutile phase transformation was inhibited at high temperatures giving rise to highly thermal stable and highly crystalline anatase TiO2 ...fibers. The initial formation of the TiO2(B) phase is found to be key in inhibiting this transformation. The intermediate structure of the TiO2 fiber comprises an inner anatase core with an outer TiO2(B) shell, which has a specific crystallographic orientation with respect to the anatase structure. During the calcination process from 300 to 800 °C, both the TiO2(B) shell and the bulk anatase crystal structure was preserved. At temperatures of 800−900 °C the TiO2(B)-to-anatase transformation was finished and a near-pure and thermally stable anatase fiber was obtained. This final product shows the same activity as a standard commercial photocatalyst Degussa P-25 when measured against unit mass, and 5 times the activity when measured with respect to the unit surface area. The anatase TiO2 fibers presented here have considerable interest as practical photocatalysts for water purification, as they can be easily recycled without a decrease in their photocatalytic activity and can be prepared at large scale and at low cost.
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Ca2+/Na+ separation is a common problem in industrial applications, biological and medical fields. However, Ca2+ and Na+ have similar ionic radii and hydration radii, thus Ca2+/Na+ ...separation is challenging. Inspired by biological channels, group modification is one of the effective methods to improve the separation performance. In this work, molecular dynamics simulations were performed to investigate the effects of different functional groups (COO−, NH3+) on the separation performance of Ca2+ and Na+ through graphene nanopores under an electric field. The pristine graphene nanopore was used for comparison. Results showed that three types of nanopores preferred Ca2+ to Na+, and Ca2+/Na+ selectivity followed the order of GE-COO− (4.06) > GE (1.85) > GE-NH3+ (1.63). Detailed analysis of ionic hydration microstructure shows that different nanopores result in different hydration factors for the second hydration layer of Ca2+ and the first layer of Na+. Such different hydration factors corresponding to the dehydration ability can effectively evaluate the separation performance. In addition, the breaking of hydrogen bonds between water molecules due to electrostatic effects can directly affect the dehydration ability. Therefore, the electrostatic effect generated by group modification will affect the ionic hydration microstructure, thus reflecting the differences in dehydration ability. This in turn affects the permeable and separation performance of cations. The results of this work provide perceptive guidelines for the application of graphene-based membranes in ion separation.
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► Static mixer is used to intensify heterogeneous photocatalysis. ► The intensification effects of five different systems are investigated. ► This method allows for easier engineering ...applications. ► A deep insight into the mechanism of heterogeneous photocatalytic process. ► Therefore, we hope our manuscript could hit the general interest of readers of Catalysis Today.
The process intensification (PI) of heterogeneous photocatalysis using the Kenics static mixer was investigated and its mechanism was proposed. Three model compounds (phenol, Cr(VI), and acid orange 7 (AO7)) with different photocatalytic reaction mechanisms were selected. The use of the Kenics static mixer increased the degradation rate of phenol from 20% to 150%, but appeared to have no effect on the photodegradation of Cr(VI) and AO7. However, with the addition of formic acid and NaF to the Cr(VI) and AO7 systems, respectively, the reaction mechanism shifted from a surface-mediated reaction to a radical-mediated reaction, and the photoreduction of Cr(VI) and photo-oxidation of AO7 using the Kenics static mixer exhibited higher reaction rates. In addition, the results of experiments with the terephthalic acid (TA) fluorescence probe indicated that the Kenics static mixer increased the yield of hydroxyl radicals. Based on the reaction mechanisms, we propose that the Kenics static mixer played a role in heterogeneous photocatalysis by creating intense mixing and increasing the interfacial mass transfer, which resulted in the enhanced mobility of reactive radicals from the catalyst surface or boundary layer to the solution. This approach intensified the heterogeneous photocatalysis process by enhancing the mass transfer of the reactive species rather than the reactant substrate, provided an alternative to the PI of heterogeneous photocatalysis, and allowed for easier engineering applications.
Mesoporous TiO2 containing different potassium content was prepared from potassium titanate by mediating the pH value of the ion exchange, which was used as catalytic support to load NiMo for ...hydrodesulfurization of dibenzothiophene. The as-prepared samples were characterized by X-ray diffraction, N2 physical adsorption/desorption, temperature-programmed reduction, scanning electron microscope/energy dispersive X-ray mapping analysis, high resolution transmission electron microscopy, and pyridine-adsorbed Fourier transform infrared spectroscopy. The characterization results showed that NiO and MoO3 were well dispersed on mesoporous TiO2 with varying potassium content. A crystal NiMoO4 phase was formed on the TiO2 with relatively high potassium content, which could decrease the reduction temperature of oxidized active species. The evaluation results from the hydrodesulfurization displayed that as the potassium content of the catalyst increased, the dibenzothiophene conversion firstly increased and then slightly decreased when potassium content exceeded 6.41 wt %. By contrast, the direct desulfurization selectivity could continuously increase along with the potassium content of catalyst. Furthermore, the change in direct desulfurization selectivity of a TiO2-supported NiMo catalyst was independent of the reaction condition. The mesoporous TiO2-supported NiMo catalyst incorporated with potassium could have near both 100% of dibenzothiophene and 100% of direct desulfurization selectivity. According to the structure–performance relationship discussion, the incorporation of potassium species could benefit the formation of more sulfided active species on mesoporous TiO2. Moreover, excessive free potassium species may poison the active sites of the hydrogenation pathway. Both factors determined the characteristics of complete hydrodesulfurization of dibenzothiophene via a direct desulfurization pathway for potassium-incorporated mesoporous TiO2 supported NiMo catalysts.
By means of density functional theory (DFT) calculations, we study the water adsorption behavior on two common surfaces, (001) and (100) TiO(2)-B, which maintains the monoclinic structure as high as ...approximately 550 degrees C or higher in ambient conditions. The two surfaces show totally different activity for water dissociation. The dissociative chemisorption of water on TiO(2)-B (100) is identified at both submonolayer and monolayer coverages, which indicates considerable reactivity. In contrast, the non-dissociative molecular adsorption of water is the most stable state on TiO(2)-B (001) which suggests no special activity. Furthermore, we compare the structural features of different surfaces with diverse crystal structures, such as rutile, anatase, brookite, TiO(2)-B etc. Keeping a close eye on the exposed atoms on the surface, we conclude a more general criterion for a quick evaluation of reactivities of different TiO(2) surfaces merely based on local surface structure features.
•Waste–heat recovery integration possibly reduced costs for biogas upgrading by 6.2%.•Aqueous ionic liquid with low viscosity reduced costs by 24.7% over that of water.•New index combined with ...various properties reflected a linear impact on the cost.
Biogas plays a vital role in many renewable and sustainable energy strategies, where CO2 removal is required to produce biomethane (i.e., biogas upgrading). New ideas and technologies have been proposed to improve the process efficiency of biogas upgrading with liquid absorbents, and ionic liquids have been identified as promising candidates. Meanwhile, there is an urgent need to effectively utilize low-quality waste heat in industry. In this study, two strategies (i.e., waste heat integration and desorption unit modification) were proposed and compared with the original high-pressure water scrubbing; in addition, the effects of the temperatures of the heat source and solvents on the energy usage and cost were further investigated. The results showed that the total cost of the process integrated with waste heat recovery decreased by 6.2% compared with the original high-pressure water scrubbing, and the higher temperature of the waste heat source corresponded to a lower cost. The comparison of different solvents further confirmed that ionic liquid-based solvents were promising, with a potential cost reduction of 24.7%; the properties of the solvent, such as the CO2 absorption capacity, selectivity, and viscosity had significant influences on the total cost, and a new and single index “comparative absorption factor” was proposed to reflect the overall impact of these properties on the cost.
A mesoporous MoO
3
/TiO
2
composite was prepared from titanate derivative by consecutive self-supporting and ammonia method. All samples were characterized by X-ray Diffraction, N
2
...adsorption–desorption, Raman Spectra and Field-Emission Scanning Electron Microscopy. The results showed that mesoporous MoO
3
/TiO
2
composite had a higher surface area (173 m
2
/g) and a better MoO
3
dispersion than that prepared by traditional impregnation (90 m
2
/g). As for hydrodesulfurization tests, mesoporous MoO
3
/TiO
2
composite in this case presented a better catalytic performance, attributed to its high surface area and good dispersion of MoO
3
. It can be found that self-supporting played a key role in preparing mesoporous MoO
3
/TiO
2
composite with high surface area. Additionally, aqueous ammonia could effectively dissolve excess MoO
3
, which helped to obtain mesoporous MoO
3
/TiO
2
composite with better dispersion of MoO
3
.
Graphical Abstract
•The RETM model is proposed based on the zwitterion mechanism in aqueous solution.•Both chemical and physical solubility of CO2 are quantified separately.•The enthalpy of physical dissolution and ...chemical reaction are calculated.•The main species concentrations in aqueous solution are determined.•Aqueous ChoAAs solutions are thermodynamically potential for CO2 capture.
Five choline-based amino acid ionic liquids (ChoAAs) are prepared by neutralization between choline hydroxide and amino acids with different molecular weight and alkalinity. Solubility of CO2 in 30 wt% aqueous solutions of these five ChoAAs has been measured at temperatures from 303.15 to 333.15 K and pressures up to 7 bar. Based on the zwitterion mechanism, the solubility of CO2 in aqueous ChoAAs solutions is correlated with a reaction equilibrium thermodynamic model (RETM). The corresponding thermodynamic parameters, such as Henry’s law constants, reaction equilibrium constants, and enthalpy of physical dissolution and chemical reaction are all calculated and compared to evaluate the CO2 absorption performance in aqueous solutions of five ChoAAs. Meanwhile, the recyclability of the aqueous solution with 30 wt% ChoLys has been also investigated.
A scale-up model for photoreactors based on a comparative study of the photocatalytic efficiency of suspended and immobilized systems was developed. The model is independent of reactor size and ...configurations, and it assumes that photocatalytic efficiency is the same when normalized per unit of illuminated catalyst area in both systems. In all cases, phenol/TiO2 (Degussa P25) was selected as the photodegradation system. First, a kinetic model was built in an immobilized system based on the corresponding experimental data, and then predicted rates of phenol degradation in the suspended system were calculated using the above kinetic model combined with a simplified radiation model, which was expressed as an apparent form of the Lambert law. Second, to obtain experimental rates, experiments conducted in the suspended system were carried out under the same conditions used in the immobilized system. Ratios between experimental rates and predicted rates were obtained, revealing the differences in efficiency between the suspended and immobilized systems. The typical value of the ratio was 2.5−9.2, suggesting that the efficiency of the suspended system was 2.5−9.2 times higher than that of the immobilized system. The ratio decreased with increasing concentrations of both phenol and catalyst. When the catalyst concentration and initial concentration of phenol were set, the ratio became constant within the range of the light intensity of 1.71−3.60 mW cm−2. Finally, for photoreactor scale-up, the proposed model was validated in a larger photoreactor operated in the suspended system, and good agreements were obtained with errors less than 5%. This methodology provides an alternative to the scale-up of photoreactors, which allows for easier engineering applications.
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