Effect of carbon black particle size in chitin sponges on microplastics adsorption

Microplastics (MPs) pollution is becoming a serious challenge, but the adsorption efficiency of adsorbents cannot meet the high requirements of environmental protection, and the adsorption mechanism of MPs is not clear at present. To improve the MPs adsorption efficiency of chitin sponges, this work introduced carbon black (CB) with different particle sizes into chitin matrix to prepare Chitin-CB sponge (ChCB) and explored the relationship between embedded adsorbent particle size and its adsorption effects on MPs. With the decrease of CB particle size from 180 to 40 μm, the removal efficiency of MPs increased from 83.9% to 90.2%. The primary driving force of MPs adsorption was proved to be π-π interaction. Smaller CB provided higher surface energy, enhanced the π-π interactions to MPs and thus showed higher removal efficiency. The results of adsorption kinetics indicated that the MPs adsorption on ChCB fitted with the pseudo-second-order model, indicating that the adsorption process is chemisorption. The results of isotherm at different temperatures and the thermodynamic parameter calculation showed that MPs adsorption conformed to the Freundlich isotherm model, and the adsorption process of MPs is multi-layer spontaneous adsorption. The adsorption intensity value was in the range of 0 ∼ 1, suggesting that ChCB was strong adsorbent material. Moreover, the high porous ChCB shows high water adsorption and excellent physical properties, which facilitated to its application on MPs adsorption. These findings provided valuable experience for the study of the adsorption mechanism of MPs and could guide the design of MPs adsorption materials.