S BET vs. S DFT. Supporting Information

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1 Supporting Information Naturally Nitrogen and Calcium-doped Nanoporous Carbon Derived from Pine Cone with Superior CO 2 Capture Capacities Bingjun Zhu, Congxiao Shang and Zhengxiao Guo S BET vs. S DFT Table S1: Comparison between specific surface area calculated by BET equation and NLDFT methods. Sample PC1-700 PC2-700 PC2-700H PC3-700 PC2-600 PC2-800 S BET S DFT The specific surface area calculated by the BET equation is slightly different from that calculated by the DFT method, due to the limitation of the BET equation (assumption of homogeneous surface). Specific CO 2 uptakes (CO 2 uptake/porosity) in Figure S1 are calculated by using specific BET surface area (S BET ), in order to be consistent with experimental data from literature. S1

2 Specific CO 2 uptake vs. Porosities Figure S1: CO 2 uptake versus porosity parameters (a) BET surface area, (c) total pore volume and (e) ultramicropore volume; (b), (d) and (f) are their corresponding specific CO 2 uptake (CO 2 uptake /porosity) versus porosity parameter. This is an update to the author s analysis on London Plane leaf-derived carbon. 1 S2

3 Micropore pore size distribution Figure S2: Micropore size distribution of pine cone derived carbon, determined by the 0 C CO 2 adsorption isotherms. S3

4 Further analysis on heat of adsorption (a) (b) (c) Figure S3: (a) 3 rd order Polynomial fitted heat of adsorption (HoA) curves of pine cone derived carbon and its corresponding (b) 1 st order derivative and (c) integrated plots. S4

5 Figure S3a is the 3 rd order polynomial fitted HoA curve. The fitting process extends the lower and upper limits of CO 2 uptake to 0.1 and 8 wt%, respectively. Therefore, the extended data can be used to further analyse the heat of adsorption at both low and high CO 2 molecule coverage. Figure S3b is the 1 st order derivative of heat of adsorption derived from Figure S3a. The plot indicates how fast the heat of adsorption changes with the increasing CO 2 uptake. While PC1-700 shows the highest heat of adsorption in Figure S3a, Figure S3b shows the sample PC3-700 has the steepest curve and lowest value at 0.1wt%, which indicates the HoA of PC3-700 drops faster than the other samples. The initial high HoA can be attributed to the start of CO 2 monolayer formation on carbon surface and stronger interaction between CO 2 and active sites (such as metal and nitrogen dopants). The faster drop rate can be attributed to the cover of active sites by the first CO 2 layer and thus the reduced strength of interaction between CO 2 multilayer and carbon surface. Because PC3-700 and PC1-700 have almost the same nitrogen and calcium contents, this difference in drop rate may be attributed to the difference in porosity, considering PC3-700 has both larger specific surface area and ultramicropore volume than those of PC Part of the heat of adsorption may be contributed by the interaction between CO 2 and walls of ultramicropores during the gas filling process. When all the ultramicropores are covered by the CO 2 monolayer, the contribution from the ultramicropores to the average HoA is reduced, and thus it results in a slower HoA drop rate at the later stage of adsorption. In addition, Figure S3c is the integrated HoA plot within the selected CO 2 uptake range (0.1 8wt%). It shows the HoA of all samples almost change linearly with the increasing CO 2 uptake. The figure is consistent with Figure S3a, where PC1-700 occupies the highest place. It indicates CO 2 remains stronger interaction with the surface of this sample at different level of CO 2 uptake (i.e., CO 2 coverage), compared with the other samples. It suggests the influence of dopants may not limit at the first layer of CO 2 coverage. S5

6 CO 2 adsorption isotherm at 50 C Figure S4: CO 2 adsorption isotherms of pine cone-derived carbon at 50 C. Figure S4 shows CO 2 uptakes of pine cone-derived carbon at 50 C. Comparing this figure with Figure 4a and 4b in the main manuscript, it can clearly be observed that the CO 2 uptake decrease with the increasing temperature from 0 to 50 C, which is a typical characteristic of such physical adsorbents. S6

7 CHN analysis Table S2: Elemental composition of pine cone-derived carbon by CHN analysis (unit: at%). Sample C H N Other Elements Pine Cone PC PC PC PC PC PC Similar to the case of leaf-derived carbon, a CHN analysis was also applied to pine conederived carbon to obtain the elemental composition of the whole sample. The corresponding results are summarised in Table S2. A small proportion of nitrogen (0.3 at%) was detected in the pine cone by the CHN analyser, while none was detected by XPS, due to the detection limit of XPS. It can also be noted that nitrogen content in pine cone is much less than that in London Plane leaf, because the main function of pine cone shell is protection rather than photosynthesis. Moreover, the activated sample PC2-600 shows an even higher nitrogen content than those of the original pine cone and carbonised pine cone PC This may be attributed to the loss of other elements caused carbonisation/activation and the non-uniform distribution of chemical elements within biomass. In conclusion, the result of CHN analysis further confirms that nitrogen dopants in pine cone-derived carbon is inherited from the biomass precursor. Furthermore, both XPS and CHN analyses show the level of nitrogen content is low in all S7

8 pine cone-derived carbon. Therefore, the influence of nitrogen dopant on CO 2 capture can be expected limited. S8

9 Yield Table S3: Carbon yield after carbonisation of pine cone and activation of carbonised pine cone (unit: wt%). Carbonisation Pine cone to PC Activation PC0-600 to PC PC0-600 to PC PC0-600 to PC PC0-600 to PC PC0-600 to PC S9

10 Reference (1) Zhu, B.; Qiu, K.; Shang, C.; Guo, Z. Naturally derived porous carbon with selective metal-and/or nitrogen-doping for efficient CO 2 capture and oxygen reduction. J. Mater. Chem. A 2015, 3, S10