Morphological Control of Biochar with Emerging Functionalities by Thermodynamic and Kinetic Approaches

ConspectusFunctional materials with controllable morphology and structural compositions starting from natural precursors using environmentally friendly processes are an appealing topic in materials chemistry today. Encompassing environmental and economic issues, much attention has recently been focused on the use of biomass to produce functional carbonaceous materials. The conversion of biomass to highly valuable "green" carbonaceous materials by a process of low-temperature hydrothermal carbonization (HTC) other than traditional high-temperature HTC or pyrolysis is crucial because it allows fine control of the morphology and structural compositions in order to meet the desired applications.Low-temperature HTC was generally performed with renewable resources (e.g., glucose and fructose) in an aqueous medium in the temperature range of 160–250 °C under self-generated pressure. However, traditional HTC materials prepared by this straightforward method are commonly irregular and bulky. The relatively high temperature, weak assembly ability of carbohydrate-derived carbon domains, and complicated tandem reactions severely limited the development of HTC. The ability to control the assembly during the HTC process to shape the microstructure of carbonaceous materials remains a key synthetic objective. Moreover, it is anticipated that the synthetic protocols developed to solve this challenge ought to reasonably remain simple, nontoxic, and cost-effective. To address these issues, we have developed several methods in terms of precise control of the microstructure (i.e., morphology, pore size and structure, and hybrid nanostructure) through manipulating the thermodynamic and kinetic behavior, enabling access to a wide range of compositions and applications.The focus of this Account revolves around new methodologies to access carbonaceous materials with special morphology and nanoarchitecture that could not be easily prepared previously, as developed by our group. We first started with a kinetically controlled soft-templating strategy to enable the preparation of a series of carbonaceous materials or hybrid materials with ordered porous and various morphological structures. Next, the improvement of HTC occurred through -polymer-/polyelectrolyte-assisted structure formation and facile yet efficient processes to prepare monodisperse primary nanoparticles or secondary superstructures. In subsequent sections, we present how to control the packing parameter or utilize template properties during the assembly process for asymmetric construction and anisotropic growth. The benefits for applications raised from the special control of HTC carbonaceous materials are also discussed. Finally, a brief summary of challenges and opportunities in this field is presented.