Multiscale evolution mechanism of sandstone under wet-dry cycles of deionized water:From molecular scale to macroscopic scale

Water is the most abundant molecule found on the earth’s surface and is a key factor in multiscale rock destruction.However,given the fine-grained nature of rock and the complexity of its internal structure,the microstructural evolution of rock under the action of water has not yet been elucidated in detail,and little is understood about the relationship between the rock structure and solideliquid unit.A variety of techniques were used in this study to track the mechanical properties,pore and crack characteristics,and mineral structure degradation characteristics of sandstone at different stages under the action of deionized water,and the evolution mechanisms of the microstructure were analyzed at the molecular scale.The results showed that during the watererock interaction process,water was adsorbed onto the surface of dolomite minerals and the hydrophilic surface of clay minerals,forming a high-density hydrogen bond network.However,different mineral surface structures had different water adsorption structures,resulting in the strain of the dense clay mineral aggregates under expansion action.Stress concentrated at crack tips under the capillary force of dolomite minerals(very weak dolomite dissolution).These effects resulted in a substantial increase in the number of small pores and enhancements in poreecrack connectivity,and the rock strength exhibited varying degrees of decline at different stages of wet-dry cycles.In general,the results of this paper will help to further elucidate the internal connections between molecular-scale and macroscale processes in rock science.

DFT study for combined influence of C-doping and external electric field on electronic structure and optical properties of TiO_(2)(001)surface

The electron structure and optical properties of C-TiO_(2)(001)surface under external electric field were studied by DFT method.After carbon doping,a new impurity level is introduced in the bandgap region of TiO_(2)(001)surface,and leads to the decrease of band gap,contributing to the shift of optical absorption to the visible region.When external electric field is applied across the C-TiO_(2)(001)surface,the band gap is further reduced with the increase of the electric field intensity from 0.1 eV to 0.5 eV.The electric field over 0.5 eV induces the electronic polarization.The spin-up bands show a gap,while spin-down electrons correspond to a metallic state.The energy gap of spin-up band decreases with increasing the electric field from 0.7 eV to 1.0 eV.The optical absorption of C-TiO_(2)(001)shifts to long wavelength compared with pure TiO_(2)(001).The electric filed make the optical absorption red-shift further,and the shift increases with an increase of the electric field,especially in the range of 0.7 eV-1.0 eV.The results show that the combined effect of carbon doping and electric field can enhance the photocatalytic activity of TiO_(2)(001)surface in visible region.