To improve photoelectrochemical (PEC) activity of hematite, the modification of energy band by doping 3d transition metal ions Cu and Ti into α-Fe2O3 were studied via the first-principles calculations with density function theory (DFT)+U method. The results show that the band gap of hematite is ∼2.1 eV and n-type dopant Ti improves the electric conductivity, confirmed by recent experiments. The p-type dopant Cu enhances the utilization ratio of solar energy, shifts both valance, and conduction band edges to a higher energy level, satisfying hydrogen production in the visible light driven PEC water splitting without voltage bias.

To investigate the influence of the Morin transition on the photoelectrochemical (PEC) activity of hematite, electronic properties in different magnetic phases were studied on the basis of the first-principles calculations within the GGA+U approximation. The results show that the effective electron mass in the (0001) plane changes remarkably due to the spin−flop transition, while the effective electron masses in other Miller planes are not sensitive to the spin orientation around irons. The electronic structure calculations of Sn-doped hematite predict that the improved PEC activities of Sn-doped hematite are proved to arise from a shrinking of the band gap, decreasing of the effective electron mass, and thus enhanced electronic conductivity. More interestingly, the heavier doping of Sn (≥16.7 atom %) in hematite would induce a new level between the valence band maximum (VBM) and Fermi level E F , which facilitates its PEC activity of visible light water splitting.

It has been reported that phase structure and surface polarity largely affect the photocatalytic efficiency of semiconductor nanostructures. To understand the chemical activity of ZnS at the electronic level, we investigate electron structures and carrier transportation ability for bulk intrinsic zinc blende (ZB) and wurtzite (WZ) ZnS, as well as the reaction pathway of hydrogen generation from water splitting on Zn-and S-terminated polar surfaces. The electron structure calculations prove that the WZ phase possesses a higher reducing ability than the ZB phase. The conductivity of the bulk ZB phase surpasses that of the WZ phase at or above room temperature. As the temperature increases, the asymptotic conductivity ratio of WZ/ZB is close to the Golden Ratio, 0.62. Reaction kinetics studies indicate that Zn-terminated polar surfaces are more chemically active than S-terminated polar surfaces in the reaction of hydrogen generation from water splitting. The calculation results suggest that the first H splitting from water on Zn-terminated polar surfaces can occur with ground state electronic structures, while photoassistance is necessary for the first H splitting on the S-terminated surfaces. Electronic triplet states calculations further show that Zn-terminated surfaces are more photosensitive than S-terminated surfaces.

No abstract

Poly(o-toluidine) (POT) and p-toluenesulfonic acid doped poly(o-toluidine) (TSA-POT) were synthesized via chemical oxidation and emulsion polymerization, respectively. The rheological measurements of the dedoped POT and TSA-POT silicone oil suspensions showed that both of the suspensions exhibited electrorheological (ER) effect under electric field. The analyses of the rheological curves of suspension indicated that POT and TSA-POT suspensions presented different flow behaviors. POT suspensions presented fast polarization under external electric field with the existence of critical shear rates (γ crit ), and POT suspensions behaved well with Bingham model above γ crit TSA-POT suspension behaved very well with Cho-Choi-Jhon model in all shear rate regions. Both of static and dynamic yield stresses for POT and TSA-POT suspensions in electric field were proportional to the square of electric field strength. The different ER performances between POT and TSA-POT suspensions were explained based on the conductivity and dielectric constant of the particles. The modification of conductivity and dielectric constant by doping POT with TSA improved the ER performance of TSA-POT suspension.