Mixed-node A-Cu-BTC and porous carbon based oxides derived from A-Cu-BTC as low temperature NO–CO catalyst

Theoretical investigation of the carbonyl-ene reaction between encapsulated formaldehyde and propylene over M-Cu-BTC paddlewheels (M= Be, Mg, and Ca): A DFT study

Formaldehyde is a VOC gas that plays a key role in air pollution. To limit emissions into the environment, the utilization of this waste as a raw material is a promising way. In this work, the M06-L functional calculation was used to investigate the structure, electronic properties, and catalytic activity of group IIA metals (Be, Mg, and Ca) partial substitution on Cu-BTC paddlewheels for formaldehyde encapsulation and carbonyl-ene reaction with propylene. Formaldehyde is absorbed by the metal center of the paddlewheel via its oxygen atom. The adsorption of formaldehyde on the substituted metal sites increased as compared to the parent Cu-BTC which can facilitate formaldehyde to react with propylene. The adsorption free energies are predicted to be -15.1 (Be-Cu-BTC), -14.7 (Mg-Cu-BTC), and -14.5 (Ca-Cu-BTC) kcal mol-1, respectively. The substituted metal has a slight effect on the Lewis acidity of the Cu ion in the paddlewheel. The adsorption free energy of formaldehyde, similar to that found in the pristine Cu-BTC, is observed. For the carbonyl-ene reaction, the reaction is proposed via a single step involving the C-C bond formation between two reactants and one hydrogen of propylene methyl group moves to formaldehyde oxygen, simultaneously. It was found that the substituted metals do not affect the catalytic performance of the Cu center for this reaction. The activation energies for the reaction at the Cu center are in the range of 22.0-23.4 kcal mol-1, which are slightly different from Cu-BTC (21.5 kcal mol-1). Interestingly, the catalytic activity of this reaction on the substituted metal is greater than that on the Cu center. The catalytic activities are in the order Be-Cu-BTC (13.3 kcal mol-1) > Mg-Cu-BTC (15.9 kcal mol-1) > Ca-Cu-BTC (17.8 kcal mol-1). Among them, the Be site of the bimetallic Be-Cu-BTC paddlewheel is predicted as a promising candidate catalyst.

Structural modification of aluminum oxides for removing fluoride in water: crystal forms and metal ion doping

In this paper, the effect of different crystal forms of Al₂O₃ on fluoride removal was studied. All crystal forms of Al₂O₃ were based on the same boehmite precursor and were obtained using a hydrothermal and calcination method. γ-Al₂O₃ had higher fluoride removal performance (52.15 mg/g) compared with θ-Al₂O₃ and α-Al₂O₃. Density functional theory (DFT) calculations confirmed that fluoride removal was greatest for γ-Al₂O₃, followed by θ-Al₂O₃ and α-Al₂O₃, and γ-Al₂O₃ possessed the strongest fluoride binding energy (-3.93 eV). The typical adsorption behaviour was consistent with the Langmuir model and pseudo-second-order model, indicating chemical and monolayer adsorption. Different metal ions were used to modify γ-Al₂O₃, and lanthanum had the best effect. Lanthanum oxide was shown to play an important role in fluoride removal. The best La/Al doping ratio was 20 At%. The adsorption process of the composite was also consistent with chemical and monolayer adsorption. When the La/Al doping rate was 20%, the adsorption capacity reached 94.64 mg/g. Compared with γ-Al₂O₃ (1.39 × 10^-7 m/s), the adsorption rate of 20La-Al₂O₃ was 3.93 × 10^-7 m/s according to the mass transfer model. Furthermore, DFT was used to provide insight into the adsorption mechanism, which was mainly driven by electrostatic attraction and ion exchange.

Heterostructured TiO2@HKUST-1 for the enhanced removal of methylene blue by integrated adsorption and photocatalytic degradation

Aiming at exploring an effective photocatalytic adsorbent for organic dye removal, a series of heterostructured TiO₂@HKUST-1 photocatalysts, by incorporating HKUST-1 with different TiO₂ nanoparticles loading, were prepared by single-step hydrothermal method. The morphology and surface characteristics of the as-prepared TiO₂@HKUST-1were analyzed using SEM, HRTEM, XRD, FTIR, UV-vis DRS, and Photoluminescence techniques. The adsorption-photocatalytic degradation of the model dye methylene blue (MB) on the catalysts was investigated. It was indicated that the introduction of a certain amount of TiO₂ on the surface of HKUST-1 could improve the transfer and separation of the photogenerated charge carriers, resulting in the enhanced photocatalytic activity. The optimal 0.02TiO₂@HKUST-1 exhibited the highest MB removal rate with about 4.4 and 19.3 times as high MB removal efficiency as that of HKUST-1 and TiO₂, respectively. Heterostructured TiO₂@HKUST-1 materials for the removal of MB involved the integrated adsorption and visible light photocatalysis. Meanwhile, the composite exhibited good reusability in the process of cyclic experiments. Therefore, this work provides a potential MOF-based photocatalytic adsorbent for organic dye removal.

Rare-Earth-Based Metal-Organic Frameworks as Multifunctional Platforms for Catalytic Conversion

The development of catalytic conversion is very important for human society. In the catalytic process, metal-organic frameworks (MOFs) can be utilized to obtain effective catalysts for their porous structures and adjustable properties. In addition, the introduction of rare-earth (RE) elements with unique properties for catalysts can realize good catalytic performances. Thus, the RE-MOF related catalysts for catalytic conversion are summarized. Due to the cooperation of RE elements and porous MOF structures, the RE-based MOFs can be used as promising catalysts or precursors/supports for other catalysts in the areas of energy conversion, environmental governance, and organic synthesis. These aggregated studies highlight the RE-MOFs as promising candidates for catalytic conversion.

Experimental and modeling studies for adsorbing different species of fluoride using lanthanum-aluminum perovskite

We investigated the adsorption mechanisms for removing fluoride based on experimental and modeling studies. Lanthanum-aluminum perovskite was designed for treating wastewater contaminated by fluoride. A fluorine-species model was developed to calculate the concentrations of different species of fluorine: F^-, HF, HF₂^-. Multiple kinetic models were examined and the pseudo-second order model was found the best to fit the experimental data, implying fast-chemisorption. The thermodynamic data were fitted by the Langmuir model and Freundlich model at different temperatures, indicating heterogeneous adsorption at low temperature and homogeneous adsorption at high temperature. The La₂Al₄O₉ material had less influence from negative ions when adsorbing fluoride. The adsorption mechanisms were further studied using experiments and Density Functional Theory calculations. The adsorption experiments could be attributed to the lattice plane (1 2 1) and La, O, Al sites. More Al sites were required than La sites for the increase of fluoride concentration. By contrast, more La sites than Al sites were needed for increased pH.

Structures and mechanisms of CO2 cycloaddition with styrene oxide on bimetallic M–Cu–BTC MOFs (M = Mg, Ca, Al, and Ga): a DFT study

The Al–Cu–BTC catalyst having the strongest interaction with the SO molecule is the most promising catalyst for the conversion of CO₂ to cyclic carbonate.

Adsorption mechanism for removing different species of fluoride by designing of core-shell boehmite

Many kinds of adsorbents have been developed for removing fluoride from water. However, the unclear actual mechanism of fluoride adsorption greatly restricts the structural design and application of novel adsorbents. Based on the understanding of the interaction between hydroxyl and fluoride, a novel core-shell nanostructure of boehmite was synthesized via an in-situ-induced assembly for removing fluoride. The formed polycrystalline boehmite (γ-AlOOH) nanostructure significantly enhances adsorption performance. The transformation of fluoride forms (including F^-, HF, HF₂^-) is closely related to the solution property. The acidic solution is more favorable, mainly because of the conversion of HF (pyrazine) and HF₂^- (the bifluoride ion) with a strong hydrogen bond effect from fluoride (F^-) with pH < 3.18. The lattice plane of (0 0 2) belongs to the dominant face for removing fluoride in this structure. According to the experimental and theoretical calculation, strong bonding of Al, O and H sites with fluoride species (F^-, HF, HF₂^-) in acidic solution are demonstrated, but not in alkaline solution due to OH^- interference. The possible mechanism of fluoride adsorption on boehmite (AlOOH) structures is proposed. Our findings show a new potential prospect of structural designing for novel fluoride adsorbent.

Removal of fluoride from wastewater solution using Ce-AlOOH with oxalic acid as modification

In this paper, Ce-AlOOH were investigated to develop as an adsorbent for removing fluoride. Oxalic acid was selected as an effectively modified reagent to improve the performance of adsorption. Cerium existed in the form of CeO₂ and kept good stability during the adsorption process through XRD, TEM, BET, Raman, and Infrared spectra. The adsorption capacity could be improved with the addition of cerium (62.8 mg/g). Specially, the oxalic acid modification significantly promoted the adsorption capacity to 90 mg/g. There adsorption isotherm and kinetics were estimated independently. These adsorption behaviors were in accordance with the Freundlich model and pseudo-second-order model, indicating that chemisorption was the rate-determining step. the obtained adsorbents all exhibited good recycling performance using oxalic acid as the regeneration reagent. The species of tetravalent cerium was the important adsorption sites. The mechanism was carefully explored by XPS analysis. The fluoride adsorption process can be ascribed to the combined effect of the electrostatic action, surface coordination, and ion exchange between M-OH and F^-. Furthermore, modification of oxalic acid exhibited a new easier way to quickly increase M-OH content, which contributed to the dominated adsorption sites.

A Critical Review of Recent Progress and Perspective in Practical Denitration Application

Nitrogen oxides (NOx) represent one of the main sources of haze and pollution of the atmosphere as well as the causes of photochemical smog and acid rain. Furthermore, it poses a serious threat to human health. With the increasing emission of NOx, it is urgent to control NOx. According to the different mechanisms of NOx removal methods, this paper elaborated on the adsorption method represented by activated carbon adsorption, analyzed the oxidation method represented by Fenton oxidation, discussed the reduction method represented by selective catalytic reduction, and summarized the plasma method represented by plasma-modified catalyst to remove NOx. At the same time, the current research status and existing problems of different NOx removal technologies were revealed and the future development prospects were forecasted.

Combining the Photocatalysis and Absorption Properties of Core-Shell Cu-BTC@TiO₂ Microspheres: Highly Efficient Desulfurization of Thiophenic Compounds from Fuel

A core-shell Cu-benzene-1,3,5-tricarboxylic acid (Cu-BTC)@TiO₂ was successfully synthesized for photocatalysis-assisted adsorptive desulfurization to improve adsorptive desulfurization (ADS) performance. Under ultraviolet (UV) light irradiation, the TiO₂ shell on the surface of Cu-BTC achieved photocatalytic oxidation of thiophenic S-compounds, and the Cu-BTC core adsorbed the oxidation products (sulfoxides and sulfones). The photocatalyst and adsorbent were combined using a distinct core-shell structure. The morphology and structure of the fabricated Cu-BTC@TiO₂ microspheres were verified by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, X-ray powder diffraction, nitrogen adsorption-desorption and X-ray photoelectron spectroscopy analyses. A potential formation mechanism of Cu-BTC@TiO₂ is proposed based on complementary experiments. The sulfur removal efficiency of the microspheres was evaluated by selective adsorption of benzothiophene (BT) and dibenzothiophene (DBT) from a model fuel with a sulfur concentration of 1000 ppmw. Within a reaction time of 20 min, the BT and DBT conversion reached 86% and 95%, respectively, and achieved ADS capacities of 63.76 and 59.39 mg/g, respectively. The BT conversion and DBT conversion obtained using Cu-BTC@TiO₂ was 6.5 and 4.6 times higher, respectively, than that obtained using Cu-BTC. A desulfurization mechanism was proposed, the interaction between thiophenic sulfur compounds and Cu-BTC@TiO₂ microspheres was discussed, and the kinetic behavior was analyzed.

Metal organic framework-derived Co3O4 microcubes and their catalytic applications in CO oxidation

Porous Co₃O₄ catalysts were successfully synthesized via a one-step pyrolysis of Co-based metal-formate frameworks, which exhibit excellent catalytic activity for CO oxidation.