Porous graphitic carbon nitride with high concentration of oxygen promotes photocatalytic H2 evolution.

Porous structure design and the content regulation of heteroelements have been proved to be effective strategies to boost photocatalytic H2 generation activity of graphitic carbon nitride (g-C3N4) based photocatalyst. Herein, a series of porous graphitic carbon nitride with high concentration of oxygen (g-C3N4-O) photocatalysts were synthesized via in situ polymerization process using colloidal SiO2 as oxygen source. The content of oxygen within the g-C3N4-O photocatalysts could be tuned by adjusting the amount of added colloidal SiO2 during the preparation procedure. The introduced oxygen replaced two-coordinated nitrogen atom, influencing band edge position and localized electron distribution, thereby enhancing visible light harvesting and photoelectric conversion. As a result, the g-C3N4-O photocatalyst with an optimal oxygen content (8.39 wt%) showed 10.5 fold enhancement in H2 evolution rate compared to that of bulk g-C3N4, attributed to the porous structure and high concentration of incorporated oxygen.

Effects of Osteocyte Shape on Fluid Flow and Fluid Shear Stress of the Loaded Bone.

This study was conducted to better understand the specific behavior of the intraosseous fluid flow. We calculated the number and distribution of bone canaliculi around the osteocytes based on the varying shapes of osteocytes. We then used these calculated parameters and other bone microstructure data to estimate the anisotropy permeability of the lacunar-canalicular network. Poroelastic finite element models of the osteon were established, and the influence of the osteocyte shape on the fluid flow properties of osteons under an axial displacement load was analyzed. Two types of boundary conditions (BC) that might occur in physiological environments were considered on the cement line of the osteon. BC1 allows free fluid passage from the outer elastic restraint boundary, and BC2 is impermeable and allows no free fluid passage from outer displacement constrained boundary. They both have the same inner boundary conditions that allow fluid to pass through. Changes in the osteocyte shape altered the maximum value of pressure gradient (PG), pore pressure (PP), fluid velocity (FV), and fluid shear stress (FSS) relative to the reference model (spherical osteocytes). The maximum PG, PP, FV, and FSS in BC2 were nearly 100% larger than those in BC1, respectively. It is found that the BC1 was closer to the real physiological environment. The fluid flow along different directions in the elongated osteocyte model was more evident than that in other models, which may have been due to the large difference in permeability along different directions. Changes in osteocyte shape significantly affect the degrees of anisotropy of fluid flow and porous media of the osteon. The model presented in this study can accurately quantify fluid flow in the lacunar-canalicular network.