Microwave-assisted Chemical Process Research Articles

PH dependent morphology and texture evolution of ZnO nanoparticles fabricated by microwave-assisted chemical synthesis and their photocatalytic dye degradation activities

ZnO nanostructures are well-known photocatalysts for the degradation of toxic organic dyes and their morphology, size, and other physicochemical properties play important roles in their photocatalytic performance. To study the effect of size, morphology, and synthesis conditions in photocatalytic performance, we synthesized ZnO nanoparticles of different morphologies through a simple microwave-assisted chemical process at different pH values of the reaction mixture. Different pH values of the reaction mixture produced ZnO nanoparticles of different morphologies and sizes. The nature of the pH controlling agent and final pH of the reaction mixture were seen to have considerable effects on the lattice parameters and microstrain of the ZnO nanocrystals, along with their photocatalytic performance. We observed that while the ZnO nanostructures synthesized at very high pH values of the reaction mixture have a high specific surface area, their photocatalytic activity is higher when they are synthesized at acidic pH or pH near the isoelectric point of ZnO. The results demonstrate that the photocatalytic activity of ZnO nanostructures not only depends on their size or specific surface area but also strongly depends on the concentration of catalytic sites at their surface.

Microwave-Assisted Synthesis of Potential Bioactive Benzo-, Pyrido- or Pyrazino-thieno[3,2-d]pyrimidin-4-amine Analogs of MPC-6827.

Efficient microwave-assisted chemical processes were applied to the synthesis of an array of novel N-(4-methoxyphenylamino)-2-methyl benzo-, pyrido- or pyrazino-thieno[3,2-d]pyrimidin-4-amine derivatives. These heteroaromatic systems were envisioned as potent bioisosteric analogues of MPC-6827, an anticancer agent previously developed until phase II clinical studies. A brief evaluation and comparison of their antiproliferative activity on HT-29 and Caco-2, two human colorectal cancer cell lines, were also reported. At the tested concentrations (5 and 10 µM), thieno[3,2-d]pyrimidin-4-amines 4a and 4c exhibited an inhibitory effect similar to MPC-6827 on human colorectal cancer cell proliferation.

Fe-Based Sorbent for Hot Coal Gas under Microwave Irradiation: Desulfurization Performance and Microwave Effects

The microwave-assisted chemical process is environmentally friendly and energy-saving. In this study, microwave irradiation was applied to enhance the hot coal gas desulfurization process with modified semi-coke-supported Fe2O3 as the sorbent. The results indicate that the sorbent with 20% Fe2O3 shows the greatest breakthrough sulfur capacity (9.0%) at 500 °C in the simulated coal gas. Besides Fe1–xS, sulfur was also produced during the desulfurization process. The deactivation model could be used to simulate the adsorption behavior of the sorbents for H2S. The activation energies of the sulfidation reaction by microwave and conventional techniques are 26.9 and 27.8 kJ mol–1, respectively. The sorbents adsorbing H2S under microwave irradiation show much larger initial rate constants (308–2071 m3 min–1 kg–1) for the sulfidation reaction. In comparison to the conventional technique, microwave desulfurization generally results in much better performance of H2S removal and leads to less negative effects on th...

A Microwave-Based Chemical Factory in the Lab: From Milligram to Multigram Preparations

Microwave technology is changing the way we design and optimize synthetic protocols and their scaling up to multigram production levels. The latest generation of dedicated microwave reactors enables operators to quickly screen reaction conditions by means of parallel tests and select the best catalyst, solvent, and conditions. Pilot scale synthetic procedures require flow-through conditions in microwave flow reactors which can be obtained by adapting classic batch protocols. Microwave-assisted chemical processes play a pivotal role in the design of sustainable multigram preparations which address the double requirement of process intensification and competitive production costs. Although most researchers are likely to be acquainted with the great potential of dielectric heating, the advantages and disadvantages of a particular device or the conditions needed to maximize efficiency and functionality are often overlooked. The double aims of the present review are to provide a panoramic snapshot of commercially available lab microwave reactors and their features as well as highlighting a few selected applications of microwave chemistry of particular relevance.

An Efficient Empirical Model for Microwave-Induced Average Temperature of Liquid Cylindrical Reactants

Microwave-assisted chemical reactions have become very popular in preparative chemistry due to many advantages such as accelerated reaction rate, higher chemical yield and lower energy use. In dedicated equipment, however, the microwave units operate as “black boxes” keeping the role of the thermal effects in microwave-assisted chemical processes somewhat obscure. To address this issue, in this paper, we propose a simple mathematical model for computing microwave-induced temperature in a three-media cylindrical structure representing a core element of a typical microwave reactor with the reactant assumed to be stirred by convection flows. The model determines the average temperature of the reactant for the known absorbed microwave power and heating time. To illustrate its functionality, the model is used to compute time-temperature characteristics of water, ethanol, and methanol heated in the batch reactor MiniFlow 200SS. The curve calculated for water appears to be in an excellent agreement with an experiment. This confirms the hypothesis on temperature homogenization in liquid reactants in batch reactors due to convection and suggests that modeling can be helpful in clarifying and quantifying the details of microwave-assisted chemical processes.

Fluid interactions with metafilms/metasurfaces for tuning, sensing, and microwave-assisted chemical processes

In this paper we demonstrate tunability of a metasurface, which is the two-dimensional equivalent of a metamaterial, also referred to as a metafilm, by changing the permittivity in a continuous flow channel that interacts with the metasurface. Numerical simulations and experimental results are presented for a metasurface consisting of metallic electric-field coupled resonators operating in $S$ band near 3.6 GHz. The localization and enhancement of the electric field in the metasurface that interacts with the fluid channels is explored as a means for implementing and aiding microwave assisted chemical processes. Applications of such continuous flow tunable metasurfaces are discussed.