A new 3D conceptual structure modeling of biochars by molecular mechanic and molecular dynamic simulation

The combination of analytical chemistry and simulation methods provides more complete information about biochars. The biochars prepared by pyrolysis of the crop straw at 300 and 500 A degrees C were investigated by elemental analysis, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and solid-state C-13 nuclear magnetic resonance (NMR) spectrometry to build the 2D structural models of biochars. The most stable and balanced 3D conformations were gained by optimizing in the optimized potential for liquid simulation (OPLS) force field of molecular mechanic and molecular dynamic simulation of HyperChemA (R) software. There were few O-containing and N-containing compounds in biochars. According to the results of Py-GC-MS, 41 and 28 pyrolysis products were identified for the building of the conceptual models of 300 and 500 A degrees C biochars. Solid-state C-13 NMR data also demonstrated that there were very high values of unsaturated C in biochars. The agreement between elemental concentration and chemical functional groups of two simulated models and experimental biochars was successfully achieved. Quantitative structure activity relationship (QSAR) properties were calculated and indicated the correlation of molecular structures with properties such as surface area, volume, polarizability, refractivity, and hydration energy. The conceptual structural models of corn straw biochars produced at 300 and 500 A degrees C were C78H68N2O25 and C59H29NO10, respectively. The simulation results showed that the 3D structure of the 300 A degrees C biochar with -4 charges and the nonprotonated 3D structure of the 500 A degrees C biochar were the most stable. Deprotonation reaction is an endothermic process.