Microwave-assisted synthesis of ultrafine Au nanoparticles immobilized on MOF-199 in high loading as efficient catalysts for a three-component coupling reaction

Controlled integration of ultrafine metal nanoparticles (MNPs) and metalorganic frameworks (MOFs) has drawn much attention due to their unique physical and chemical properties.However,the development of a one-step strategy for preparing ultrafine MNPs within MOFs still remains a great challenge.Herein,a facile synthetic approach toward the abovementioned composites was developed.In contrast to the conventional approach,these hybrids were prepared by the direct mixing of metal and MOF precursors in the reaction solution assisted by microwave irradiation.Impressively,the Au/MOF-199 composite with uniformly distributed ultrafine Au nanoparticles could be fabricated in only two minutes,and the Au loading could be increased up to a level of 5.13％.The multifunctional Au/MOF-199 catalysts exhibited high turnover numbers (TONs)and turnover frequencies (TOFs) in the three-component coupling reaction of formaldehyde,phenylacetylene,and piperidine (A3-coupling).Owing to the confinement effect of MOF-199,the 5.13％Au/MOF-199 catalyst could be recycled for five runs without serious loss of activity,with no obvious aggregation of Au NPs detected.     

金属-有机骨架材料MOF-199对甲醛气体吸附行为的研究

初步探讨了金属-有机骨架材料MOF-199对甲醛气体的吸附性能.采用分光光度法测定MOF-199对甲醛气体的吸附量,研究了吸附量与吸附温度及吸附时间的关系,并探讨了MOF-199对甲醛的吸附机理,提出了一种测定MOF-199对甲醛吸附量的方法.结果表明,在50℃、6h的吸附条件下,MOF-199对甲醛气体的吸附量最大,达到83.84mg/g;MOF-199对甲醛气体具有较好的吸附效果.     

Application of accelerated electron beam and microwave irradiation to biological waste treatment

The comparative results obtained by applying separate electron beam (EB) irradiation, separate microwave (MW) heating and combined (successive and simultaneous) electron beam irradiation and microwave heating to reduction of viable cells of Escherichia coli, Salmonella typhi, Staphylococcus intermedius, Pseudomonas aeruginosa, and Trichinella spiralis are presented. The results of studies concerning the disinfection by separate and combined EB and MW irradiation of sewage sludge performed from a food industry wastewater treatment station (vegetable oil plant) are also presented. The research results demonstrated that the simultaneous EB and MW irradiation produces the biggest reduction of microorganisms.     

Degradation of 4-chlorophenol by a microwave assisted photocatalysis method

In this work, the degradation of 4-chlorophenol (4CP) under simultaneous microwave assisted UV (electrodeless discharge lamp) photocatalysis technique (MW/UV/TiO2) was investigated. Several factors affecting the degradation of 4CP by MW/UV/TiO2 method, such as the dosage of photocatalysts, the initial pH value of the solutions, gas bubbling, light intensity and addition of H2O2 oxidant, were studied in detail. The synergistic effects between microwave irradiation and TiO2 photocatalysis were also studied. The major intermediates were found to be chlorobenzene, phenol, hydroquinone, benzoquinone and 4-chlorocatechol. Based on the results, a general reaction pathway for the degradation of 4CP was proposed.     

Combined Electron Beam and Microwave Treatment for Flue Gas Purification

The results of a research program concerning the application of the electron beam EB) irradiation, microwave MW) irradiation and simultaneous electron beam and microwave EB + MW) irradiation for removing nitrogen oxides NOX) and sulfur dioxide SO₂) in simulated Due gases are presented. Several microwave applicators and reaction chambers used for NO_X and SO₂ removal tests are also presented. The additional use of MW energy and EB energy or the use of MW energy only proved to be a promising method for removal of pollutants in view of the reduction of power consumption and flue gas treatment process cost. Experiments performed at lower temperature 65-70°C) of the gaseous mixture air, Argon up to 7%, H₂O up to 25%, CO₂ up to 10%, SO₂ up to 2000 ppm, NO_X up to 1000 ppm, NH₃ added in stoichiometric amounts) demonstrated a higher SO₂ removal efficiency with lower absorbed dose. Promising results are obtained especially for SO₂ removal efficiency: up to 80% for MW, 85% for EB irradiation and up to 90% for EB + MW irradiation. A considerable amount of SO₂ can be separated even without MW, EB or EB + MW irradiation due the spontaneous reaction with ammonia at gaseous mixture temperature below 70°C. The most important conclusion concerning MW irradiation is that efficiency of removal of pollutants strongly depends on microwave applicator structure type, residence time and MW power level.     

Diverse effects of microwave heating on anatase crystallization in ionothermal synthesis of nanostructured TiO<Subscript>2</Subscript>

This article examines anatase crystallization in the ionothermal synthesis [sol gel method in the presence of ionic liquid (IL)] of nanostructured TiO₂ under microwave (MW) irradiation. MW heating can lead to rapid temperature increase of chemical reactions. In this study, we found that rapid temperature increasing effects on anatase crystallization were diverse and dependent on initial water concentration, MW irradiation time, and IL concentration. The results indicated that higher anatase crystallinity was obtained at high water amount irrespective of IL concentration. However, at lower water amounts, higher anatase crystallinity occurred only when MW heating was applied after the mixtures reacted for certain duration, especially at lower initial temperature and at a specific IL concentration. Different MW heating effects on the hydrolysis–condensation reaction and the post-treatment stage under MW/IL conditions can explain this diversity. Heating characteristics of IL/water mixtures under MW irradiation were also discussed.     

Boron removal and recovery from concentrated wastewater using a microwave hydrothermal method

Boron compounds are widely-used raw materials in industries. However, elevated boron concentrations in aqueous systems may be harmful to human and plants. In this study, calcium hydroxide (Ca(OH)(2)) alone and Ca(OH)(2) with phosphoric acid (H(3)PO(4)) addition (P-addition) were used to remove and recover boron from wastewater using hydrothermal methods. A microwave (MW) hydrothermal method was used and compared with the conventional heating (CH) method in batch experiments. Physicochemical properties of the precipitates obtained from both methods were analysed by XRD, SEM with EDX and BET. For the case of Ca(OH)(2) alone and the MW method, experimental results showed that boron recovery efficiency reached 90% within 10 min, and crystals of Ca(2)B(2)O(5)·H(2)O were found in the precipitates as indicated by the XRD analysis. For the case of P-addition and the MW method, boron recovery efficiency reached 99% within 10 min, and calcium phosphate species (CaHPO(4)·H(2)O, CaHPO(4) and Ca(10)(PO(4))(6)(OH)(2)) were formed. The experimental results of this study indicate that the required reaction time of the MW method was much less than that of the CH method, and the MW method is an effective and efficient method for boron removal and recovery from concentrated wastewater.     

Controlled growth and composition of multivariate metal-organic frameworks-199 via a reaction-diffusion process

In this paper,we exploit our prior successful synthesis of MOF-199 single crystals using the reaction-diffusion framework(RDF),to synthesize multivariate metal-organic frameworks(MTV-MOFs)version with enhanced properties.The MTV-MOFs are synthesized by creating defects within the MOF-199 crystal structure by integrating organic linkers entailing different functional groups.Accordingly,5-aminoisophthalic acid(NH₂-BDC)and 5-hydroxyisophthalic acid(OH-BDC)are separately mixed with 1,3,5-benzenetricarboxylic acid(BTC)in three different starting ratios of X-BDC:BTC(1:3,1:1)and(3:1).The effects of this linker on the morphology of the synthesized MTV-MOFs,their thermal stability,and their surface area are investigated.The extent of the incorporation of the linkers in the framework is elucidated via¹H-NMR spectroscopy and it is shown that the incorporation varies as a function of the location along the tubular reactor,a characteristic of RDF.The enhanced properties of the synthesized MTV-MOFs are further demonstrated by measuring its adsorptive capability for methylene blue(MB)and rhodamine B(Rh B)in aqueous solution,and compared with that of the as-synthesized MOF-199.The kinetic and thermodynamic studies reveal that MTV-MOFs with the ratio of X-BDC:BTC(1:1)exhibit the best uptakes of MB(263 mg/g)for X=OH and Rh B(156 mg/g)for X=NH₂.The adsorbents are also easily regenerated for three consecutive cycles without losing their efficiency.We finally demonstrate that MTV-MOFs can be designed to tune the dye removal selectivity and enhance the removal capacity of both MB and RhB in a binary aqueous solution of these dyes.     

Microwave assisted Friedel–Crafts acylation reactions of Amberlite XAD-4™ resin

This article reports the convenient synthesis of benzoyl resins which were produced by the acylation of a poly(styrene-co-divinylbenzene) commercial resin (Amberlite XAD-4™). Conventional and microwave (MW) assisted acylation reactions on the resin were compared. Acylation in nitrobenzene and solvent-free reactions have been developed under MW irradiation or employing a conventional heating, both in the presence of Lewis acid (AlCl₃). The MW radiation effects and the time of exposure on the acylation extent were studied. The unmodified commercial and modified resins were characterized by apparent density, swelling degree, elemental analysis, infrared spectrometry (FTIR), optical microscopy (OM) and scanning electron microscopy (SEM). The use of MW led to a great reduction in the reaction time and high benzoyl incorporations were reached.     

Ce改性金属有机骨架材料对氟的吸附

利用水热合成法，将金属Ce与合成金属有机骨架材料(MOFs)所需的反应前体混合，通过“一锅法”和“两步法”分别合成性能不同的Ce/MOF-5材料。采用SEM、XRD、BET等对合成材料进行表征。结果表明:不同的方法合成的Ce/MOF-5形貌有较大差异，对氟吸附性能也不同。并测定了初始浓度、pH值、吸附时间对F?吸附效果的影响。实验表明，通过“一锅法”合成的Ce/MOF-5材料对F?的吸附在pH=7、吸附时间为60 min左右即可达到吸附平衡，吸附量为109.6 mg·g?1，符合准二级动力学模型和Freundlich等温吸附模型。      

Indirect detection of mercury-199 nuclear magnetic resonance spectra of methylmercury complexes.

Measurement of 199Hg NMR spectra of methylmercury species by the heteronuclear multiple quantum coherence (HMQC) indirect proton detection method and its application to the study of the solution chemistry of CH3HgII-thiol ligand complexes are described. A sensitivity enhancement factor of 16 is obtained for measurement of the 199Hg NMR spectrum of a 4 mM solution of the CH3HgII-glutathione complex by the indirect detection method, as compared to a theoretical enhancement of 74. The less-than-theoretical enhancement is attributed to loss of signal by relaxation during the HMQC pulse sequence. Longitudinal relaxation of the 199Hg in CH3HgII-thiolate complexes is fast at the field strength used in this research (11.7 T) due to efficient relaxation by the chemical shift anisotropy mechanism. This in turn causes the transverse relaxation rate for the 199Hg spin-coupled methyl protons to be fast due to efficient relaxation by another mechanism, scalar relaxation of the second kind. Depending on the rate of exchange of CH3HgII among its complexed forms, the 199Hg line width can also include a large contribution from exchange broadening. In such cases, it is shown that extremely broad 199Hg resonances, which would be difficult to detect by direction observation, can be observed by the indirect detection method. For example, 199Hg resonances with exchange-broadened line widths up to 8000 Hz are observed by the indirect detection method for CH3HgII in mixtures of CH3HgOD and the CH3HgII-mercaptoethanol or CH3HgII-glutathione complex. The chemical shift of 199Hg in CH3HgII-thiolate ligand complexes is found to be extremely sensitive to the nature of the thiolate ligand.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functionalization of silicon nanowire surfaces with metal-organic frameworks

Metal-organic frameworks (MOFs) and silicon nanowires (SiNWs) have been extensively studied due to their unique properties; MOFs have high porosity and specific surface area with well-defined nanoporous structure, while SiNWs have valuable one-dimensional electronic properties. Integration of the two materials into one composite could synergistically combine the advantages of both materials and lead to new applications. We report the first example of a MOF synthesized on surface-modified SiNWs. The synthesis of polycrystalline MOF-199 (also known as HKUST-1) on SiNWs was performed at room temperature using a step-by-step (SBS) approach, and X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy elemental mapping were used to characterize the material. Matching of the SiNW surface functional groups with the MOF organic linker coordinating groups was found to be critical for the growth. Additionally, the MOF morphology can by tuned by changing the soaking time, synthesis temperature and precursor solution concentration. This SiNW/MOF hybrid structure opens new avenues for rational design of materials with novel functionalities.      

溶剂尺度对MOF-808结构及性能影响

以不同溶剂尺度的酰胺类溶剂与甲酸混合溶液为溶剂模板,利用溶剂热法制备MOF-808。利用傅里叶变换红外光谱仪、扫描电镜、X-射线衍射仪和比表面积分析仪对样品进行性能表征。结果表明,溶剂尺度越小,MOF-808孔径越小,比表面积越大,N_2吸附性能越强。当甲酰胺/甲酸混合溶液作为溶剂模板时,MOF-808孔径最小,为1.19nm;比表面积最大,达到1625m²/g。     

Study of the degradation behaviour of dimethoate under microwave irradiation

In this work, the degradation of dimethoate under microwave irradiation assisted advanced oxidation processes (MW/oxidants) were studied. The efficiencies of the degradation of dimethoate in dilute aqueous solutions for a variety of oxidants with or without MW irradiation were compared. The results showed that the synergistic effects between MW and K(2)S(2)O(8) had high degradation efficiency for dimethoate. Simultaneously, UV/TiO(2)/K(2)S(2)O(8) photocatalytic oxidation degradation of dimethoate was investigated. The experimental results indicated that the method of microwave degradation of organic pollutants in the presence of oxidant could reduce reaction time and improve product yield. Microwave irradiation was an advisable choice for treating organic wastewaters and has a widely application perspective for non- or low-transparent and fuscous dye wastewaters.     

Gold seed-assisted synthesis of silver nanomaterials under microwave heating

We report a low-temperature process for preparing templateless and polymerless silver nanomaterials in the presence of gold seeds under microwave (MW) heating. In addition to spherical nanoparticles, silver nanorods are also produced. Key aspect for the production of nanorods is the addition of adequate volume of gold seeds. This finding demonstrates that the combination of MW heating synthesis method in the presence of gold seeds is a good approach to prepare templateless and polymerless silver nanorods.     

Structure distortion of Zn4O13C24H12 framework (MOF-5)

Zn₄O₁₃C₂₄H₁₂ framework (MOF-5) can occupy either cubic or tetragonal structure. It was recognized that the tetragonal MOF-5 was a distorted cubic MOF-5 caused by filling effect of ZnO or solvent. However, herein, it was found that the ZnO and solvent inside the pores of the framework did not cause the distortion of cubic MOF-5. Furthermore, the distortion is strongly dependent on the solvent vacuumed to dry the framework. If the vacuumed solvent was dimethylformamide (DMF), the crystal structure of MOF-5 was tetragonal. In contrast, if DMF was displaced by CH₂Cl₂ before the vacuum, the obtained MOF-5 occupied a perfect cubic structure. The thermal decomposition of cubic and tetragonal MOF-5s produced the same products: CO₂, benzene, amorphous carbon, and crystal ZnO. However, the thermal decomposition of cubic MOF-5 requires a higher temperature than the tetragonal one, indicating that cubic MOF-5 is more stable than the tetragonal one.     

Assessment of radiofrequency/microwave radiation emitted by the antennas of rooftop-mounted mobile phone base stations

Radiofrequency (RF) and microwave (MW) radiation exposures from the antennas of rooftop-mounted mobile telephone base stations have become a serious issue in recent years due to the rapidly evolving technologies in wireless telecommunication systems. In Malaysia, thousands of mobile telephone base stations have been erected all over the country, most of which are mounted on the rooftops. In view of public concerns, measurements of the RF/MW levels emitted by the base stations were carried out in this study. The values were compared with the exposure limits set by several organisations and countries. Measurements were performed at 200 sites around 47 mobile phone base stations. It was found that the RF/MW radiation from these base stations were well below the maximum exposure limits set by various agencies.     

Using speciated isotope dilution with GC-inductively coupled plasma MS to determine and unravel the artificial formation of monomethylmercury in certified reference sediments

Speciated isotope-dilution mass spectrometry (SID-MS) is claimed to be an absolute method; however, it has been found to be affected by artifact monomethylmercury (MMHg) formation in sediments. The determination of MMHg in sediments was carried out by SID-MS after open-focused microwave extraction. The extracted mercury species were then ethylated and separated by capillary gas chromatography (CGC). Isotope ratios (peak area ratios at different masses) were measured by on-line ICP-MS detection of the CGC-separated compounds. Reproducibility of 202Hg/201Hg isotope ratio measurements were 0.60% for MeEtHg and 0.69% for Et2Hg; for 202Hg/199Hg, 0.43 and 0.46%, respectively, were determined. The absolute detection limits for CGC-ICPMS measurements were better than 26 fg for 202Hg, 20 fg for 201Hg, and 24 fg for 199Hg. For the direct determination of MMHg in sediment reference materials (CRM 580, IAEA 356, and IAEA 405), higher values than the certified were always found. Systematic experiments were carried out to localize the sources of the unintentional abiotic methylmercury formation during analysis. Different spiking and derivatization procedures (either ethylation, propylation, or derivatization by Grignard reagents) were tested. In addition, isotopically enriched inorganic mercury was spiked. The amount of inorganic mercury initially present in the sample was found to be the critical factor that should be known and carefully controlled. A simple solvent extraction technique involving no critical cleanup steps was applied in order to reduce high Hg2+ amounts. The method was applied to the determination of MMHg in sediment reference material IAEA-405 with satisfactory results after organic solvent extraction. The limitations of applicability of the proposed method are evaluated as related to inorganic mercury, organic carbon, and sulfur contents. The results obtained confirmed that available sediment reference materials are adequate to achieve traceable mercury speciation analysis and to detect potential sources of MMHg artifact formation.     

Robust magnetic and electromagnetic wave absorption performance of reduced graphene oxide loaded magnetic metal nanoparticle composites

With the increasing demand for microwave absorbing materials, to develop a microwave absorber with a simple synthesis process is of great significance to the field of protection. Herein we have successfully loaded iron-cobalt-nickel oxide (FeCoNiO_x) onto the as-prepared polydopamine-reduced graphene oxide (PDA-rGO) through a two-step process. The preparation method has mild reaction conditions without high temperature and pressure compared with the traditional method, which is conducive to large-scale production. Based on effectively combining dielectric loss and magnetic loss mechanism, the obtained material possesses excellent electromagnetic waves absorbing performance with the minimum RL value of ?36.28 dB. The results proved that the composites can be endowed with various microwave absorption effects by the adjustion of different component ratios. In addition, the microwave absorption mechanism was dicussed in detail, and we believe that the results of our research have certain guiding significance for preparation of efficient microwave absorbers.     

Microwave-mediated synthesis for improved morphology and pseudocapacitance performance of nickel oxide

Synthetic methods greatly control the structural and functional characteristics of the materials. In this article, porous NiO samples were prepared in conventional-reflux and microwave assisted heating method under homogeneous precipitation conditions. The NiO samples synthesized in conventional reflux method showed flakelike morphology, whereas the sample synthesized in microwave methods showed hierarchical porous ball like surface morphology with uniform ripple-shaped pores. The NiO samples characterized using BET method were found to bear characteristic meso- and macroporosity due to differently crystallized Ni(OH)(2) precursors under various heating conditions. Thermogravimety analysis showed morphology dependent decomposition of Ni(OH)(2) precursors. The microwave synthesized porous NiO sample with unique morphology and pore size distribution showed significantly improved charge storage and electrochemical stability than the flaky NiO sample synthesized by employing conventional reflux method. The cyclic voltammetry measurements on microwave synthesized NiO sample showed considerably high capacitance and better electrochemical reversibility. The charge-discharge measurements made at a discharge current of 2 A/g showed higher rate specific capacitance (370 F/g) for the NiO sample synthesized by microwave method than the sample synthesized by reflux method (101 F/g). The impedance study illustrates lower electronic and ionic resistance of rippled-shaped porous NiO due to its superior surface properties for enhanced electrode-electrolyte contact during the Faradaic redox reactions. It has been further established from the Ragone plot that the microwave synthesized NiO sample shows higher energy and power densities than the reflux synthesized NiO sample. Broadly, this study reveals that microwave-mediated synthesis approach is significantly a better strategy for the synthesis of porous NiO suitable to electrochemical supercapacitor applications.