## 3 Results and Discussion
### Comparative Sorption Behavior of 4-MBC on Biochar and Microplastics  
The sorption of 4-MBC, an organic UV filter, onto biochar and microplastics shows distinct differences due to the varying physical and chemical properties of these materials. Biochar, derived from agricultural biomass, and microplastics, both commercial and biodegradable types, have been extensively studied for their ability to remove contaminants from water. In the case of biochar, the sorption of 4-MBC is well described by the Freundlich isotherm model. This model suggests that the sorption process on biochar is nonlinear and involves multiple mechanisms, such as surface adsorption, pore filling, and interactions with functional groups. The study revealed high correlation coefficients for all types of biochar, indicating that these materials have strong adsorption potential for 4-MBC. Biochar produced from different biomass sources, such as corn, hemp, and straw, exhibited variations in adsorption capacity, with those having a larger specific surface area (SSA) showing a higher efficiency in 4-MBC removal. The larger surface area of biochar allows for greater interaction between the adsorbent and the contaminant, enhancing the material's ability to remove pollutants from water. In contrast, the sorption of 4-MBC onto microplastics like polyethylene granules (PEg), polyethylene terephthalate (PET), polypropylene (PP), and polylactic acid (PLA) follows a slightly different pattern. For PEg, PET, and PP, the Langmuir isotherm model provided the best fit, indicating that adsorption occurs at specific sites on the microplastic surface, with no further adsorption once these sites are saturated. PET demonstrated the highest adsorption capacity among the microplastics studied, which could be due to its functional terephthalate groups that increase its affinity for 4-MBC. On the other hand, the biodegradable microplastic PLA had the lowest adsorption capacity, which is attributed to its oxygen-containing functional groups. These groups interact with water molecules, forming water clusters on the PLA surface, which in turn reduce the availability of sites for 4-MBC adsorption. Overall, biochar and microplastics both show potential for 4-MBC removal from water, but their adsorption mechanisms differ significantly. Biochar's high surface area and porous structure make it an efficient sorbent, while microplastics, particularly PET, also demonstrate notable adsorption capabilities, though the process is influenced more by the material's functional groups and surface chemistry. Understanding these differences is crucial for optimizing their use in water treatment applications, where material selection can be tailored to the specific contaminant and environmental conditions. In terms of practical application, biochar has several advantages over microplastics. Biochar is a renewable, biodegradable, and environmentally friendly material that can be produced from a wide variety of agricultural and organic waste. Its ability to adsorb a wide range of contaminants, including UV filters like 4-MBC, heavy metals, and organic pollutants, makes it a versatile material for environmental remediation. Additionally, biocharcan be modified to enhance its adsorption capacity, for example, by introducing functional groups or increasing porosity through chemical treatments. In contrast, microplastics, while effective at adsorbing certain contaminants, pose significant environmental risks due to their persistence in the environment, the potential for fragmentation, and their role as vectors for pollutant transfer in aquatic and terrestrial ecosystems. Overall, these findings highlight the need for further comparative studies between biochar and microplastics, especially in terms of long-term adsorption performance, environmental sustainability, and potential risks.