学术文献库

The general topic of energy is regarded to be one of the most important areas for any research and development activities at the start of the twentyfirst century. Therefore, large research efforts are already based on or will be targeted on the development of clean fuels to replace fossil fuels, the improvement of the existing resources and the discovery of new sustainable energy resources, the establishment of new efficient ways to store sustainable energy, and the replacement of the existing high energy consuming technologies with the more energy efficient ones. The latter concept has resulted in considerable efforts recently to renovate the conventional synthetic chemical industry by introducing new green chemistry concepts, where the energy requirements for chemical processing or synthesis would be drastically reduced. In this context, a vast amount of novel chemical synthesis techniques have been developed during the last decades. Such innovative techniques include combustion, sol gel and coprecipitation methods, sonochemistry, hydrothermal synthesis, and microwave-assisted techniques. Significant qualitative drawbacks in materials synthesized by such novel ways in terms of crystal quality and physical properties are usually not encountered. In some cases, even quantitative improvements, novel crystal arrangements, and interesting particle shapes can be achieved. The concept of combining several of the recently developed nonconventional and innovative synthesis techniques is an interesting concept to even further reduce the energy requirements and particle sizes as compared to one technique alone. Microwave assisted combustion and sol gel synthesis are now employed frequently, as well as the combination of hydrothermal and microwave assisted synthesis, where the latter technique is the topic of this review.