微波辐射对TiO2制备及其光催化氧化乙醛性能的影响

采用微波辐射与常规加热法由TiO₂溶胶制备出TiO₂催化剂，采用高频低功率微波-光催化装置考察了微波对两种催化剂上CH₃CHO光催化氧化转化率和产物分布的影响。结果表明，微波干燥制备的TiO₂晶体比普通加热制备的TiO₂晶体对乙醛有更高的光催化活性和更强的氧化能力，且它们对乙醛光催化氧化的途径不同，前者的初始中间体为甲醛和甲酸，后者的初始中间体却为乙酸。还发现，微波辐射对两种样品上乙醛的光催化转化率有不同的影响，对微波辐射法所制样品的影响比对常规加热法所制样品的影响显著。微波辐射通过场效应可加速光催化初始中间体的转化，但它不改变光催化反应的途径，反应途径取决于光催化剂的特性。     

Microwave processing of TiO2 blocking layers for dye-sensitized solar cells

The microwave heat treatment of blocking layers for dye-sensitized solar cells has been investigated. It has been found that the solar cell efficiencies achieved with microwave heating were considerably higher than those achieved with conventional heating at low temperatures (100°C). This was attributed to microwave heating providing better sintering of the blocking layer and better interfacial contact between the substrate and the TiO₂ layers. These results are promising with regard to the application of microwave heating to the production of dye-sensitized solar cells on flexible polymer substrates.     

Microwave-assisted synthesis and antitumor activity of the supramolecular complexes of betulin diacetate with arabinogalactan

In this work, a water-soluble supramolecular complex was synthesized in an aqueous suspension of betulin diacetate (BDA) and arabinogalactan (AG) upon microwave heating. Microwave heating allows reducing the time required for the complex formation, compared with conventional heating in a water bath. The specific effect of microwave irradiation on the initial reagents and preparation of a supramolecular complex was studied. In contrast to conventional heating, under microwave heating AG macromolecules may break into roughly equal fragments when the temperature increases up to 100 °C. A change in the surface morphology of BDA crystals under microwave heating of the suspension suggests that microwave irradiation facilitates the dissolution of BDA in water. It has been shown that the use of dimethylsulfoxide as a reaction medium for microwave heating led to a decrease in BDA content in the product due to the inclusion of DMSO into AG macromolecules. The BDA–AG complex was isolated from the microwave-heated aqueous solution, after water evaporation, as a thin amorphous film, which exhibited antitumor activity against Ehrlich ascites carcinoma cells and can be a promising material for pharmacological applications.     

Single‐Mode Microwave Heating‐Induced Concurrent Out‐of‐Plane Twin Growth Suppression and In‐Plane Epitaxial Growth Promotion of b‐Oriented MFI Film under Mild Reaction Conditions

In this study, single‐mode microwave heating was applied in epitaxial growth of b‐oriented MFI seed monolayer prepared by facile manual assembly, resulting in the formation of well‐intergrown and highly b‐oriented MFI film with few twins. It exhibited a precise molecular sieving property at a reaction temperature no higher than 100 °C within 2 hours, therefore making it possible for easy operation in an open environment. The capability for concurrent suppression of undesired out‐of‐plane twin growth and promotion of in‐plane epitaxial growth rate under mild reaction conditions was attributed to the obvious superiority of single‐mode microwave heating in comparison with conventional multi‐mode microwave heating in aspects of microwave field uniformity and intensity. Our research indicated that the single‐mode microwave heating technique could potentially be a useful tool for improving the microstructure and therefore the performance of diverse zeolite films.     

Dehydration of sodium carbonate monohydrate with indirect microwave heating

In this study, dehydration of sodium carbonate monohydrate (Na₂CO₃·H₂O) (SCM) in microwave (MW) field with silicon carbide (SiC) as an indirect heating medium was investigated. SCM samples containing up to 3% free moisture were placed in the microwave oven. The heating experiments showed that SCM is a poor microwave energy absorber for up to 6 min of irradiation at an 800 W of microwave power. The heat for SCM calcination is provided by SiC which absorbs microwave. The monohydrate is then converted to anhydrous sodium carbonate on the SiC plate by calcining, i.e. by removing the crystal water through heating of the monohydrate temperatures of over 120 °C. The calcination results in a solid phase recrystallization of the monohydrate into anhydrate. In the microwave irradiation process, dehydration of SCM in terms of indirect heating can be accelerated by increasing the microwave field power.     

Kinetics study on the dissolution of UO<Subscript>2</Subscript> particles by microwave and conventional heating in 4 mol/L nitric acid

The dissolution of UO₂ particles in 4 mol·L⁻¹ nitric acid medium at temperatures of 90–110°C by microwave heating and conventional heating has been investigated, respectively. It is found that the dissolution ratios of UO₂ particles by microwave heating were 10%–40% higher than that by conventional heating. Kinetics research shows that the dissolution of UO₂ particles in 4 mol·L⁻¹ nitric acid is controlled by the diffusion control model for microwave heating and by the surface reaction control model for conventional heating. The diffusion control model for the dissolution of UO₂ particles by microwave heating could be explained by the diffuseness on the surface of UO₂ particles.     

Studying the effect of microwave heating on the digestion process and identification of proteins

The impact of microwave irradiation on the in‐solution digestion processes and the detection limit of proteins are systematically studied. Kinetic processes of many peptides produced through the trypsin digestion of various proteins under microwave heating at 50°C were investigated with MALDI‐MS. This study also examines the detection limits and digestion completeness of individual proteins under microwave heating at 50°C and at different time intervals (1, 5 and 30 min) using LC‐MS. We conclude that if the peptides without missed cleavage dictate the detection limit, conventional digestion will lead to a better detection limit. The detection limit may not differ between the microwave and conventional heating if the peptides with missed cleavage sites and strong intensity are formed at the very early stage (i.e., less than 1 min) and are not further digested throughout the entire digestion process. The digestion of Escherichia coli lysate was compared under conventional and short time (microwave) conditions. The number of proteins identified under conventional heating exceeded that obtained from microwave heating over heating periods less than 5 min. The overall results show that the microwave‐assisted digestion is not complete. Although the sequence coverage might be better, the detection limit might be worse than that under conventional heating.     

不同条件对硫酸钙结晶影响的实验研究

近年来由于微波化学的快速发展使人们认识到微波作为一种手段对化学反应的过程有着深刻的影响,在材料领域更是得到了日益广泛的应用,因此把微波应用于结晶过程也成为人们关注的热点。早在1966年磁场就被应用于晶体的生长。近年来,已有很多文献报道电场、磁场对晶体生长的影响。     

Polymeric flocculants processing by accelerated electron beams and microwave heating

Results obtained by accelerated electron beam, microwave and simultaneous microwave and electron beam application in the chemistry of acrylamide and acrylic acid copolymers (polymeric flocculants used for wastewater treatment) are presented. Comparative results concerning the molecular weight and Huggins’ constant for the acrylamide and acrylic acid copolymers obtained by classical heating, microwave heating, electron beam irradiation and simultaneous microwave and electron beam treatment are reported. Microwave heating produces high water solubility of the polymeric flocculants but median molecular weight values. Electron beam irradiation gives high molecular weight values but associated with a cross-linked structure (poor water solubility) while microwave energy addition to electron beam energy gives simultaneously high molecular weight values and high water solubility.     

In situ SAXS/WAXS of zeolite microwave synthesis: NaY, NaA, and beta zeolites.

A custom waveguide apparatus is constructed to study the microwave synthesis of zeolites by in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The WR-284 waveguide is used to heat precursor solutions using microwaves at a frequency of 2.45 GHz. The reaction vessels are designed to include sections of thin-walled glass, which permit X-rays to pass through the precursor solutions with minimal attenuation. Slots were machined into the waveguide to provide windows for X-ray energy to enter and scatter from solutions during microwave heating. The synthesis of zeolites with conventional heating is also studied using X-ray scattering in the same reactor. SAXS studies show that the crystallization of beta zeolite and NaY zeolite is preceded by a reorganization of nanosized particles in their precursor solutions or gels. The evolution of these particles during the nucleation and crystallization stages of zeolite formation depends on the properties of the precursor solution. The synthesis of NaA and NaX zeolites and sodalite from a single zeolite precursor is studied by microwave and conventional heating. Microwave heating shifts the selectivity of this synthesis in favor of NaA and NaX over sodalite; conventional heating leads to the formation of sodalite for synthesis from the same precursor. The use of microwave heating also led to a more rapid onset of NaA zeolite product crystallization compared to conventional heating. Pulsed and continuous microwave heating are compared for zeolite synthesis. The resulting rates of formation of the zeolite products, and the relative amounts of the products determined from the WAXS spectra, are similar when either pulsed or continuous microwave heating is applied in the reactor while maintaining the same synthesis temperature. The consequences of these results in terms of zeolite synthesis are discussed.