# A Thermogravimetric Analysis of Biomass Conversion to Biochar: Experimental and Kinetic Modeling
## 3 Results and Discussion
### Effect of Temperature on Biomass Waste Surface Structure
#### 3.3.2 SEM Analysis Results
Surrounding nodes like \"adsorption\", \"removal\", \"pyrolysis\", \"biomass\", and \"waste\" exhibit moderate density, suggesting these are also significant topics within biochar research but not central. In contrast, terms like \"potato peel\", \"waste\", and \"kinetics\" appear with lower density, indicating limited research in these specific areas. This visualization emphasizes research gaps, particularly in the study of biochar derived from specific agro-wastes like apple and potato peels. Therefore, there is a noticeable gap in the literature regarding biochar derived from specific agro-wastes like apple and potato peels, especially in relation to pollutant removal. In this context, the apple and potato peel biochar obtained at 250 \({}^{\circ}\)C and 800 \({}^{\circ}\)C were tested for NO\({}_{3}\)- adsorption [87]. The used experimental conditions were the optimal parameters evaluated by our team in previous studies [32; 87], where different types of biomass were used to obtain adsorbents. The comparison of the nitrate sorption efficiency of various biochar data are presented in Table 6.  
Figure 11: Bibliometric map generated based on density visualization. As can be seen compared with previous studies the apple and potato peel pyrolyzed at 250 \({}^{\circ}\)C have lower nitrate efficiency with difference values between 10.71 and 15.15%. The same behavior was observed also for the samples pyrolyzed at 800 \({}^{\circ}\)C, which exhibited a nitrate efficiency removal of 52.78% for apple peel and 45.46% for potato peel, respectively. These results can be explained by the fact that the optimal parameters for each individual sample have not been determined, they depend on the physico-chemical characteristics of each sample. According to [PERSON], et al. [88], the feedstock and temperature during pyrolysis can influence molecular structure and pores size distribution of biochar, and thus affect biochar sorption characteristics. [PERSON], et al. [89] reported that different feedstocks developed biochars with varying values of surface area, porosity, and functional groups; factors that have an impact on the sorption properties of the biochars. According to [PERSON], et al. [90], even though two types of biochar were produced at the same temperature (400 \({}^{\circ}\)C), the biochar made from poultry litter had a higher specific surface area and porosity than the biochar made from wheat straw. It should also be mentioned that, in order to reduce the residual washing water, the 4 adsorbents prepared in this study, were tested without being subjected to other treatments, as was conducted for the magnetic adsorbent and black tea waste which were washed with deionized water for several times. There are other studies which indicates that the washing of biochar with water and acid leads to the removal of ash from the pores, thus creating new additional adsorption centers facilitating the retention of the nitrate anion [88; 91; 92]. Therefore, in the future studies, the optimal parameters for each obtained biochar will be determined and how the washing step influences the efficiency of nitrate retention.