## 5 Conclusions  
This work shows that graphene oxide can be modified with different heteroatoms based on a simple reaction with triethoxysilanes. Apart from O and Si functionalities, the various chemical compounds can offer other heteroatoms such as S from TMOS, N, and O from TMON, S, and N from TMOSN. This work showed that the different chemical compounds form monolithic structures due to different self-assembly, which led to various properties and porosity. Porosity showed that almost all modified samples increased the pore volume and the specific surface, whereas microporosity imaging showed mixed results. A combination of parameters with the different elements for each monolith led to various adsorption capacities for CO\({}_{2}\). Adsorption of gas was measured in two different temperatures (25 \({}^{\circ}\)C and 60 \({}^{\circ}\)C), and we observed that high specific areas or voluminous pores also result in high adsorptions. It is believed that to achieve high adsorption, a combination of parameters must be in accordance. Microporosity at a high percentage and different functionalities from heteroatoms are the significant parameters that affect adsorption.  
Nevertheless, the high SV ratio (a relationship between specific area and pore volume) is also essential. We showed that the monolith has area and volume for hosting the gas molecules. Another important aspect for high CO\({}_{2}\) adsorption is the average pore diameter. Finally, the macropores percentage showed ambiguous results and should be studied in more detail.  
Ideally, a sample that complies the next values could possibly show high adsorptions: (i) oxygen functionality of more than 23.0%, with a medium of 26.7%; (ii) ratio C/heteroatoms in a range of 1.28-2.07, with a medium of 1.76; (iii) micropores percentage more than 3.7%, with a medium of 5.5%; (iv) macropores percentage more than 48.0%, with a medium of 52.5%; (v) SV ratio of more than 0.345 nm\({}^{-1}\) and a medium of 0.374 nm\({}^{-1}\); (vi) average pore diameter 13.2-14.4 nm with a medium of 13.8 nm.  
The following are available online at [[https://www.mdpi.com/article/10](https://www.mdpi.com/article/10)]([https://www.mdpi.com/article/10](https://www.mdpi.com/article/10))  
3390/app11209631/s1, Figure S1: FTIR spectra for blank sample rGO60_2, Figure S2: Blank samples: (a1) rGO60_0.5; (b1) rGO60_2; (c1) rGO90_0.5; (d1) rGO90_2. Modified ones: (a2) S60_0.5; (b2) S60_2; (c2) S90_0.5; (d2) S90_2; (a3) N60_0.5; (b3) N60_2; (c3) N90_0.5; (d3) N90_2; (a4) SN60_0.5; (b4) SN60_2; (c4) SN90_0.5; (d4) SN90_2 at magnification x500, Figure S3: Cumulative pore volume in a micro to macro range pores (Samples 60_0.5 and 60_2), Figure S4: Cumulative pore volume in a micro to macro range pores (Samples 90_0.5 and 90_2), Figure S5: Adsorption of CO\({}_{2}\) of all samples (blank and modified ones) at two different temperatures  
Conceptualization, N.P.; methodology, N.P.; formal analysis, N.P., T.C.-L. and R.T.; investigation, N.P. and T.C.-L.; resources, R.T.; data curation, N.P. and T.C.-L.; writing--original draft preparation, N.P.; writing--review and editing, N.P., R.T. and T.C.-L.; project administration, N.P. and R.T.; funding acquisition, R.T. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Basque Government, grant number GV IT999-16.  
Not applicable.  
Data Availability Statement: Data are contained within the article or supplementary material.  
The authors declare no conflict of interest.