## 3 Results and Discussion
### Adsorption Kinetics  
To understand how 4-MBC interacts with biochar from corn, hemp, and straw, it was necessary to study the adsorption kinetics and determine the time required to reach adsorption equilibrium. The kinetics of 4-MBC adsorption on biochar were monitored over 96 h to assess the adsorption capacity of the selected adsorbents. The results, depicted in Figure 2, show that the adsorption equilibrium of 4-MBC on all biochars (BC1, BC2, and BC3) was achieved after 48 h. Additionally, the efficiency of 4-MBC removal by the carbon adsorbents was calculated, showing no significant difference in removal efficiency among the adsorbents. The removal efficiency of 4-MBC ranged from 22% to 75% over time. These findings suggest that all three biochars have the potential as effective adsorbents for 4-MBC. The adsorption kinetics of 4-MBC on various types of microplastics (MPs) were also investigated (Figure 3). Comparing biochar with microplastics in the context of adsorption reveals interesting contrasts. While biochar is predominantly an adsorbent with high surface area and functional group diversity, microplastics tend to act more as passive carriers of pollutants due to their hydrophobic surfaces and lower surface reactivity. A rapid adsorption was observed within the first 6 h for PEg, PP, and PLA, after which the adsorption rate plateaued until equilibrium was reached. In contrast, PET showed slower kinetics, with equilibrium achieved after 24 h. The adsorption affinities differed across MPs, with PET showing the highest affinity (qt = 11.5 \(\upmu\)g/g), followed by PEg and PP (qt = 8.5 \(\upmu\)g/g) [8,43,49]. PLA, a biodegradable microplastic, exhibited the lowest adsorption affinity (qt = 3.52 \(\upmu\)g/g), likely due to the presence of oxygen-containing functional groups [50,51]. These groups, particularly carbonyl, facilitate hydrogen bonding with water molecules, leading to water cluster formation on the surface, which in turn reduces the availability of 4-MBC for adsorption. The results are consistent with the study conducted by [PERSON] and [PERSON] [52,53], which highlights the influence of MPs type on the adsorption rate of organic pollutants. Kinetic modeling was applied to better understand the adsorption mechanisms. The data were analyzed using four kinetic models: pseudo-first-order (PFC), pseudo-second-order (PSO), Elovich, and Weber-Morris (W-M) (Figure 4, Table 2). Among the models, the PSO model showed the highest correlation coefficients (\(R^{2}\) = 0.831-0.968) for PEg, PET, and PP, indicating that chemisorption may dominate the adsorption process for these MPs. The Elovich model also provided a good fit, suggesting the occurrence of multilayer adsorption on PLA. These findings indicate the occurrence of multilayer adsorption between a chosen UV filter and the PLA surface [54]. To investigate the contribution of intraparticle diffusion to the overall adsorption process of 4-MBC on PEg, PET, PP, and PLA, the W-M model was applied (Figure 4d). The plots of the W-M model indicate whether intraparticle diffusion is the rate-limiting factor in adsorption. The obtained results showed that the initial and rapid adsorption took place within a few hours, followed by a slower second step during the equilibrium stage [55]. Figure 2: Kinetics of 4-MBC adsorption on biochar from corn (BC1), hemp (BC2), and straw (BC3) (Ce denotes the equilibrium concentration, Co denotes the initial concentration). Figure 4: Plots illustrating the adsorption kinetics of 4-MBC on PEg, PET, PP, and PLA particles in synthetic water matrix using different models: (**a**) pseudo-first-order model, (**b**) pseudo-second-order model, (**c**) Elovich, and (**d**) Weber–Morris model. Figure 3: Adsorption kinetics of 4-MBC on PEg, PET, PP, and PLA. In conclusion, while both biochar and MPs exhibit sorption potential for 4-MBC, biochar shows more consistent and efficient performance.