# Investigation of Biochars in Terms of Vitamin E Adsorption Capacity
A comparison of the adsorption capacity of activated carbon and two mesoporous carbon molecular sieves prepared from silica templates indicated that the activated carbon adsorbed less vitamin E than the mesoporous molecular sieves. The reason could be the high quantity of micropores in the activated carbon, which were not filled during the adsorption process [34]. The use of biochar as a carrier for vitamin E is particularly interesting, due to its synergistic effects: biochar can be filled with the vitamin [34], transport it into the animal, and, after desorption, remove unwanted substances to improve animal health [35; 36], while the vitamin E can be absorbed. After absorption, vitamin E can contribute to improving udder health through its positive effects on metabolism [11; 12], e.g., by reducing clinical mastitis [37; 38]. Moreover, biochar can function as an adsorbent of pathogens, improving gut fermentation, which results in an overall improvement in the animals' immune system [39]. This is why biochar can also function as an alternative to antibiotics [16; 40]. A carrier in this field needs to have the following characteristics: (1) it should have a high adsorption capacity for the substance to be adsorbed (vitamin E); (2) the biological activity of the adsorptive (vitamin E) should be kept after adsorption; and (3) the connection between the adsorbent (biochar) and the adsorbate (vitamin E) needs to loosen over time to let the adsorbate desorb [29]. Based on previous studies using carbon-based adsorbents to adsorb vitamin E [25; 34], and based on the statement that adsorbed \(\alpha\)-tocopherol acetate retains biological activity [29], we assumed that biochars can adsorb and carry vitamin E, especially \(\alpha\)-tocopherol acetate. As micropores are not accessible during digestion [35], the adsorption of \(\alpha\)-tocopherol acetate in the mesopores is relevant for the use of biochar as a carrier. Thus, ten biochars, authorised as feed additives [41; 42; 43], were analysed in terms of their theoretical and experimental capacity to adsorb vitamin E. Using authorised biochars emphasises the application-oriented approach of this study, since the results can directly be transferred to an industrial application. Our results should support the evaluation of a biochar for application as a carrier for \(\alpha\)-tocopherol acetate for transport to the small intestine of dairy cows. The use of biochar as a carrier should prevent the metabolization of vitamin E before reaching the small intestine. To our knowledge, this is the first study comparing the theoretically necessary pore diameter for the adsorption of \(\alpha\)-tocopherol acetate. Additionally, this is the first time that the theoretical adsorption capacity has been used with the aim to predict a suitable biochar for feeding trials. The hypothesis of this study is that commercially available biochars obtain different adsorption capacities caused by the pyrolysis of varying woody biomasses and production parameters. We hypothesise that biochars with a larger surface area in the range of the molecular size of \(\alpha\)-tocopherol acetate adsorb more. In addition, we hypothesise that the theoretical calculation of the adsorption capacity of \(\alpha\)-tocopherol acetate, using the surface area and theoretical molecular size of \(\alpha\)-tocopherol acetate, is a suitable approach to select a compatible biochar. To prove this, we compare the theoretical with the experimental adsorption capacity.