Abstract
Biochar has attracted increasing research attention. Various modification methods have been proposed to enhance a certain biochar function. However, these modifications may also result in an unstable structure, additional energy consumption, secondary pollution, and/or extra cost. Balanced consideration of different aspects will ensure the sustainable development of biochar technology. This review first summarizes the most commonly used methods for biochar modification. These methods are categorized according to the purposes of modification, such as surface area enlargement, persistent free radical manipulation, magnetism introduction, and redox potential enhancement. More importantly, a systematic analysis and discussion are provided regarding the balanced consideration of biochar designs, such as the balance between effectiveness and stability, functions and risks, as well as effectiveness and cost. Then, perspectives regarding biochar modification are presented. This review calls for attention that biochar modifications should not be evaluated for their functions only. A balanced design of biochars will ensure both the practicability and the effectiveness of this technology.