Production of biomass-based carbon materials in hydrothermal media: A review of process parameters, activation treatments and practical applications

The depletion of fossil fuels heralds the rise of renewable energy resources. Biomass is the most widespread renewable energy resource that can be used not only as an energy resource, but also to produce functional carbon-based materials with excellent properties using various processes. Hydrothermal carbonization (HTC) is an effective way to convert biomass in a low-cost and green way. The resulting hydrochar materials have potential applications in many fields. The current review describes the effect of various reaction parameters on the HTC process and the resulting products through the reaction mechanism. The work summarizes the nonlinear relationship between the influencing parameters and the properties of products. Moreover, the work focuses on the effect of different treatment methods on hydrochar, reviews the recent studies on the improvement of the targeting of hydrochar in specific fields by modulating its surface properties, and makes an outlook on the subsequent development of HTC. The work also suggests a few possible bottlenecks that the process may encounter in the future.