NO2 Adsorption on Biochar Derived from Wood Shaving Litter: Understanding Surface Chemistry and Adsorption Mechanisms

Abstract

This study investigates the production of biochar from fresh wood shavings (B-WSF) and used wood shavings (B-WSU–animal litter) biomass through pyrolysis at 450 °C and explores its potential for NO2 adsorption at different temperatures from 22 °C to 250 °C. The biochars’ thermal stability, elemental composition, mineral content, textural properties, and surface chemistry were comprehensively analyzed using various techniques, including thermogravimetric analysis (TGA), ultimate analysis, proximate analysis, mineral composition analysis, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and NO2 adsorption experiments. The results indicate that biochars derived from WSF and WSU biomass possess high stability and exhibit significant changes in their elemental composition, surface functional groups, and textural properties compared to the raw biomass. The biochars demonstrated substantial NO2 adsorption capacities and reduction, with B-WSU biochar exhibiting higher adsorption capacity attributed to its higher specific surface area, mineral content, and functional groups. In addition, the results reveal distinct patterns in NO2 adsorption and NO release, with temperature playing a pivotal role in the process. At lower temperatures, NO2 adsorption on both biochars exhibits gradual increases, while higher temperatures facilitate immediate adsorption and subsequent reduction to NO. The adsorption of NO2 increased with increasing adsorption temperature, with B-WSU biochar achieving a maximum adsorption capacity of 43.54 mg/g at 250 °C, compared to 9.62 mg/g for B-WSF biochar. Moreover, XPS analysis revealed alterations in surface functional groups upon NO2 exposure, indicating enhanced surface oxidation and formation of nitrogen-containing species. In addition, differences in surface heterogeneity and mineral content influence NO2 adsorption behavior between the biochar samples. These findings highlight the potential of WSF biomass-derived biochar as an effective adsorbent for NO2 removal, offering insights into its application in air pollution mitigation strategies. The mechanism of NO2 adsorption involves chemisorption on oxygen-containing functional groups and physical adsorption, facilitated by the high specific surface area and pore volume of the biochar. Furthermore, the rich mineral content in B-WSU biochar explains its high adsorption capacity, demonstrating the potential for valorization of waste materials in the circular economy.