A review of recent advances in catalytic combustion of VOCs on perovskite-type catalysts

Along with the rapid development of industry, VOCs gradually move into the spotlight, and now become a kind of harmful environmental pollutants that cannot be overlooked. This paper introduces the hazards of VOCs and the common catalytic combustion catalysts, noble metal catalysts and non-noble metal catalysts, for the elimination of VOCs. Perovskite catalysts, as one of the non-noble catalysts, play an important role in the field of catalytic combustion in recent years. According to the classification of elements doping in perovskites, the research achievements in the past five years were analyzed and reviewed. In addition, this paper also analyzes and elaborates the reaction kinetics and QSAR/QSPR models for the introduction of structural properties and reaction mechanisms.     

Molybdenum (VI)‐functionalized UiO‐66 provides an efficient heterogeneous nanocatalyst in oxidation reactions

A novel heterogeneous nanocatalyst was established by supporting molybdenum (VI) on Zr₆ nodes in the structure of the well‐known UiO‐66 metal–organic framework (MOF). The structure of the UiO‐66 before and after Mo (VI) immobilization was confirmed with XRD, DR‐FTIR and UV–vis spectroscopy, and the presence and amount of Mo (VI) was identified by X‐ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy. TEM imaging confirmed the absence of Mo clusters on the MOF surface, while SEM confirmed that the appearance of the MOF has not changed upon immobilizing the Mo (VI) catalyst. BET adsorption measurements were used to confirm the porosity of the catalyst. The catalytic activity of this heterogeneous catalyst was investigated in oxidation of sulfides with H₂O₂ in acetonitrile and oxidative desulfurization of dibenzothiophene. Easy work up, convenient and steady reuse and high activity and selectivity are prominent properties of this new hybrid material.     

Efficient Gating of Ion Transport in Three‐Dimensional Metal–Organic Framework Sub‐Nanochannels with Confined Light‐Responsive Azobenzene Molecules

1D nanochannels modified with responsive molecules are fabricated to replicate gating functionalities of biological ion channels, but gating effects are usually weak because small molecular gates cannot efficiently block the large channels in the closed states. Now, 3D metal–organic framework (MOF) sub‐nanochannels (SNCs) confined with azobenzene (AZO) molecules achieve efficient light‐gating functionalities. The 3D MOFSNCs consisting of a MOF UiO66 with ca. 9–12 Å cavities connected by ca. 6 Å triangular windows work as angstrom‐scale ion channels, while confined AZO within the MOF cavities function as light‐driven molecular gates to efficiently regulate the ion flux. The AZO‐MOFSNCs show good cyclic gating performance and high on–off ratios up to 17.8, an order of magnitude higher than ratios observed in conventional 1D AZO‐modified nanochannels (1.3–1.5). This work provides a strategy to develop highly efficient switchable ion channels based on 3D porous MOFs and small responsive molecules.     

Renormalized solutions of elliptic equations with Robin boundary conditions

In the present paper, we consider elliptic equations with nonlinear and nonhomogeneous Robin boundary conditions of the type{-div(B(x, u)▽u) = f in ?,u = 0 on Γ_0,B(x, u)▽u·n→+γ(x)h(u) =g on Γ_1,where f and g are the element of L~1(?) and L~1(Γ_1), respectively. We define a notion of renormalized solution and we prove the existence of a solution. Under additional assumptions on the matrix field B we show that the renormalized solution is unique.     

Metal Nodes of Metal-Organic Frameworks can Activate Molecular Hydrogen

Hydrogenation of multiple bonds are among the most general and important organic reactions. Typical heterogeneous catalysts are based on transition metal nanoparticles, including noble metals. Data are presented here showing that metal nodes of MIL-101(Cr) and UiO-66 in the absence of occluded metal nanoparticles can promote hydrogenation of polarized X=Y double bonds of nitro and carbonyl groups. The catalytic activity is a function of the composition of the metal node and the organic linker. It is proposed that the reaction mechanism is based on the operation of frustrated Lewis acid/base pairs.     

Post Synthetic Modification of NH2-(Zr-MOF) via Rapid Microwave-promoted Synthesis for Effective Adsorption of Pb(II) and Cd(II)

Excessive heavy metals in the water constitute a health hazard to humans, yet it may be efficiently purified using adsorbents. Herein, for the first time, UiO-66-NH₂ was modified by Glycidyl methacrylate (GMA) via microwave heating method to investigate its potential for adsorption of Pb(II) and Cd(II) metal ions. Synthesized MOF was characterized by TGA, XRD, BET, FE-SEM-EDX, and FTIR. The MOF has a huge surface area of 1144 m²/g, a mean pore diameter of 2.84 nm, and a total pore volume of 0.37 cm³/g. The effect of UiO-66-GMA performance was evaluated by investigating the impact of pH (1–9), contact time (0–200 min), initial metal ions concentration (20–1000 mg/L), temperature (25–55 °C), adsorbent dosage (0.5–3 g/L), and co existences of other metals was investigated on Pb(II) and Cd(II) percentage removal. Following an analysis of the adsorption isotherms, kinetics, and thermodynamics, the Temkin isothermal model showed an excellent fit with the adsorption data (R² = 0.99). The adsorption process was a spontaneous endothermic reaction and kinetically followed the pseudo-second-order kinetics model. Microwave heating method produced highly crystalline small Zr-MOF nanoparticles with a short reaction time. It promoted the simple yet highly efficient synthesis of Zr-based MOFs, as shown by the reaction mass space-time yield. The adsorption capability of Pb to the presence of several polar functional groups, including as primary and secondary amines, ester, alkene, and hydroxyl groups. This adsorbent is a potential candidate for wastewater treatment due to its outstanding structural stability in acidic and basic solutions, high removal efficiency, and recyclability.     

Synthesis of UiO-66 with addition of HKUST-1 for enhanced adsorption of RBBR dye

Toxic dye removal, one of the most serious and common industrial pollutants released into natural water, is a critical issue for modern civilization. In this study, a series of UiO-66 composites was synthesized with addition of HKUST-1 using solvothermal method, which was used to remove RBBR dye. The structure, morphology and surface area of the composites were studied by several analyses. HK(5)/UiO-66 possessed a specific surface area of 557.63 m²/g and showed an adsorption capacity of 400 mg/g, higher than that of UiO-66 (261.92 mg/g) with a contact time of 50 min. Several adsorption parameters that influenced RBBR removal efficiency were investigated, such as pH, initial dye concentrations, and temperature. All the composites followed pseudo-first order kinetics and Langmuir isotherm adsorption. Moreover, the adsorption process occurred exothermically and spontaneously, indicating that the adsorption process was advantageous in terms of energy. The possible adsorption mechanism and cost analysis of the adsorbent were also studied in detail.     

Zr-MOF空心纳米球固载离子液体对CO2环加成反应的催化性能

通过后合成修饰方法(PSM)构筑了空心纳米球(Void@UiO-66-Ⅰ)和实心块(UiO-66-Ⅰ) 2种形貌的季铵盐功能化UiO-66-NH₂(Zr), 得到兼具酸碱活性位点和氢键给体的新型功能化金属-有机框架材料. 通过一系列表征证明2种催化剂的成功合成, 并将它们用于催化转化CO₂和氧化苯乙烯的环加成反应. 由于Void@UiO-66-Ⅰ催化剂的季铵盐部分含有大量的羟基和卤素阴离子, 可以通过氢键和亲核攻击与环氧化合物连接, 诱导环氧化合物开环, 促使反应顺利进行, 且催化剂的中空结构有利于物质进出催化剂, 起到加快反应速率的作用, 使得该催化剂在CO₂与氧化苯乙烯环加成反应中表现出比实心块UiO-66-Ⅰ催化剂更好的催化性能. Void@UiO-66-Ⅰ催化剂在120 ℃, CO₂压力为1.2 MPa, 反应时间为6 h, 无溶剂和助催化剂的反应条件下, 碳酸苯乙烯酯的收率和选择性分别为85.5%和95%.     

离子对UIO-66-2OH光催化性能的影响

实际废水中存在的离子会对有机污染物的光催化降解产生影响。以ZrCl₄和2,5-二羟基对苯二甲酸为原料,通过水热合成法成功制备了金属有机骨架材料UIO-66-2OH。通过红外（IR）、X射线粉末衍射（XRD）、X射线光电子能谱（XPS）和扫描电子显微镜（SEM）对UIO-66-2OH的结构进行表征。利用水中常见的金属阳离子和无机阴离子,探索UIO-66-2OH的光催化性能。研究发现,金属阳离子Fe³⁺和无机阴离子HCO₃^-、CO₃^2-可以加快光催化降解的速度。然而,金属离子Na⁺、K⁺、Ca²⁺、Mg²⁺、Cu²⁺和无机阴离子Cl^-、SO₄^2-、PO₄^3-会抑制光催化性能,且离子价态越高,抑制效果越明显。     

UiO-66 and hcp UiO-66 Catalysts Synthesized from Ionic Liquids as Linker Precursors

Using ionic liquids (ILs) as linker precursors, the well-known metal-organic framework (MOF) UiO-66 (Universitetet i Oslo) and the recently reported MOF hcp UiO-66 (hexagonal closed packed) have been successfully synthesized and characterized. The advantage of the applied novel synthesis approach is an economically and environmentally benign work-up procedure, due to the better solubility of the IL. Additionally, the reactivity of the terephthalate anions is increased compared to terephthalic acid, resulting in faster MOF formation with an increased amount of defects in the MOF structure. In order to explore to the influence of defects on the catalytic performance, the cyclisation of citronellal to isopulegol was employed as test reaction. The activity of hcp UiO-66 and fcc UiO-66 (face centered cubic) is improved compared to other MOF or zeolite based catalysts, while the selectivity is similar.