Activated carbons have been prepared from rice straw by considering the material forms of rice straw, the chemical activation agent and the preparation method. The study seeks optimal conditions for giving better mico- and nano- properties, and to support the corresponding molecular structure. All the obtained results are referred to those of a commercial sample. Fourier transform infrared absorption, X-ray photoelectron spectroscopy, and dispersive X-ray spectroscopy are combined to determine functional groups. Moreover, a quantum chemical calculation has been done using density functional theory to argue the proposed molecular structure. Principally, the vibrational properties are compared to experimental results, and the corresponding electronic structure is calculated. Thermal stability and eventual reactions are evidenced by both differential and gravimetric thermal analysis. The surface topography of the resulting activated carbon is checked by scanning electron microscope and correlated with their chemical and textual characteristics carried out from Brunauer, Emmett and Teller analysis. Results illustrate that the resulting product is a mixture of carbon graphic structure and acidic/basic entities and exhibit a global acidic pH. The use of KOH as oxidant agent and the ground raw material form leads to obtain good properties such as higher surface area and higher porosity. Based on the size compatibility making it possible to introduce low-radius single-walled carbon nanotubes, the electronic structures of the prepared activated carbon and that of chiral (5,5) SWCNTs and their corresponding frontier molecular orbitals have been carried out at the DFT/6-31-G(d) level. These calculations are carried out to evidence the charge transfer between both components in the bulk hetero-nano-junctions as interpenetrating network.