Parameters Optimization and Physicochemical Properties Characterization of Nanobiochar Prepared from Apple Branches by Ball Milling.

Nanobiochar exhibits promising applications across a spectrum of fields due to its exceptional physicochemical properties. Ball milling, a prominent nanobiochar synthesis method, is influenced by process factors and biochar pretreatments, yet dominant controls still remain uncertain. In this study, the apple branch bulk biochar (pyrolyzed under 350 ∘ C) was ball milled under different milling speeds, ball-to-powder mass ratios, and milling durations to investigate the optimal process parameter combinations for ball milling method. Then, we evaluated the impact of pyrolysis temperature and pretreatment temperature of bulk biochar on ball milling effect using optimized parameter combinations. Subsequently, the physicochemical properties of the bulk biochar and nanobiochar were measured. The results showed that high speed with low ball-to-powder mass ratio, low speed with high ball-to-powder mass ratio, and high pyrolysis temperature could significantly decrease the particle sizes of nanobiochar. Ball milling duration and pretreatment temperature had no significant effect on the particle sizes of biochar. The optimal combination of the rotational speed, ball-to-powder mass ratio and milling duration was 400 RPM, 100:1, 2 h and 700 RPM, 20:1, 2 h. The bulk biochar pyrolyzed at 550 ∘ C could be milled into biochar nanoparticles with an average particle size smaller than 100 nm via above parameters. Nanobiochar shows improved properties such as specific surface area, cation exchange capacity, and surface functional groups over bulk biochar. This study provides a scientific basis for the widespread application of ball milling in the field of preparing nanobiochar. We successfully synthesized biochar nanoparticles from apple branches by optimizing key parameters in the ball milling process, including biochar pyrolysis temperature, milling speed, duration, and ball-to-powder ratio. The resulting biochar nanoparticles exhibited significantly enhanced physicochemical properties, such as increased specific surface area, cation exchange capacity, and surface functional groups, in comparison to the native biochar. This study provides a scientific basis for the widespread application of ball milling in the field of preparing nano-biochar. [ABSTRACT FROM AUTHOR]