Sonochemical and sono-assisted reduction of carbon dioxide: A critical review

In the last decades, great interest has been focused on developing innovative, efficient and eco-friendly methods for the reduction of carbon dioxide (CO2). The use of ultrasound (sonochemistry) has appeared as one of these techniques, thanks to its operational simplicity (working at ambient conditions), safety and being environmentally benign (in general, no need for chemical additives). To date, several works have been dedicated to the sonochemical and sono-assisted carbon dioxide reduction, where various operating conditions were analyzed. The present review aims at analyzing the multiple works focusing on the sonochemical and sono-assisted reduction of carbon dioxide. Through these works, the mechanism of CO2 sono-reduction, its limitations and probable solutions are discussed. Additionally, the combination of sonolysis with other technological techniques (absorption, adsorption, photocatalysis, photolysis, electrochemistry, etc.) has been analyzed with a demonstration of the promising solutions of each of these methods. In addition, theoretical works focusing upon sonodecomposition of CO2 inside the acoustic bubble are also discussed. Finally, future directions and perspectives have been proposed for more improvement of the available techniques or for the creation of plausible hybrid methods. To the best of our knowledge, this is the first literature review addressing the CO2 reduction by ultrasound.