# Investigation of Biochars in Terms of Vitamin E Adsorption Capacity
## 3 Results and Discussions
### Adsorption Capacity of \(\upalpha\)-Tocpheryl Acetate  
To compare the theoretical calculation of pore filling, the biochars were analysed for their adsorption capacity of \(\upalpha\)-tocopherol acetate. The theoretical adsorption capacity was higher for all biochars than the experimental adsorption capacity, with the extent varying greatly (Figure 4). The order of highest to fifth highest adsorption capacity remained the same for both the theoretical and experimental adsorption capacities (E > D > F > A > J). Interestingly, biochars D and E had a high moisture content, but adsorbed the highest amount of the fat-soluble \(\upalpha\)-tocopherol acetate. This shows that the distribution of the pores and the surface area and pore volume is more important than the initial moisture content of the biochar. The difference between the experimental and theoretical adsorption capacity might have been due to the short adsorption time of 10 min. This is supported by [PERSON] et al.'s [25] finding that a longer adsorption time increased the adsorption capacity. [PERSON] et al. [25] found an adsorption capacity of 96.2 mg\({}_{\alpha\text{-tocopherol}}\)/g\({}_{\text{activated carbon}}\) after incubation at 25 \({}^{\circ}\)C for 24 h for an activated carbon with a total pore volume of 0.56 cm\({}^{3}\)/g. Biochars D and E resulted in experimental adsorption capacities of 7.3 and 7.6 mg\({}_{\text{dil-}\alpha\text{-tocopherol}}\)/g\({}_{\text{Biochar DM}}\), with a mesopore volume of 0.08 and 0.09 cm\({}^{3}\)/g, after incubation for 10 min at 20 \({}^{\circ}\)C, respectively (Figure 2B). The difference in the adsorption between biochars D and E and the activated carbon might have been due to the difference in pore volume, as well as the adsorption time. [PERSON] et al. [17] found a maximum achieved experimental equilibrium sorption capacity after 48 h incubation at 19 \({}^{\circ}\)C of 9.9 mg\({}_{\text{dil-}\alpha\text{-tocopherol}}\)/g\({}_{\text{Zeolite DM}}\) for zeolite with a pore volume of 0.11 cm\({}^{3}\)/g. This indicates that in our study, firstly, the short adsorption time was enough for sufficient adsorption; and secondly, the use of biochar as a carrier for \(\alpha\)-tocopherol might be more feasible than zeolite.  
We assume that, despite the differences between the experimental and the theoretical adsorption capacity, the feasibility of this approach is meaningful. These results indicate that using Equation (1) to determine the theoretical, monomolecular, and maximal adsorption capacity of \(\alpha\)-tocopherol acetate, under the experimental conditions applied, was correct. Using an increased adsorption time, monomolecular multilayer adsorption might occur instead, resulting in the necessity to calculate the theoretical adsorption capacity with mathematical models other than [PERSON]'s [17]. Irrespective of this, considering the experimental adsorption capacity for the respective biochar will provide the necessary information to determine the necessary load, e.g., when biochar is used as a carrier for vitamin E in dairy cows. In addition, free pores of biochars can be useful for these animals, e.g., for the adsorption of unwanted substances, such as pathogens or mycotoxins [16; 39].  
Figure 3: Theoretical filling into the six mesopore classes, ranging from 2.58 to 20.01 nm, of biochars A to J (\(n=2\)). Different small letters (abcde) indicate significant differences between biochars for each mesopore class, and different capital letters (ABCDEF) indicate significant differences between mesopore classes for each biochar, determined by One-Way ANOVA and [PERSON]’s post hoc test (\(p<0.05\)), even if the normality test and/or the equal variance test failed (\(p>0.05\)).