In this paper, we have employed DFT and HSE06 methods to study the doping effects on the NaTaO3 photocatalyst. N, S, C, and P monodoping and N–N, C–S, P–P, and N–P codoping have been studied. The ...redopants’ formation energies have been calculated, and we find S monodoping is energetically more favorable than any other elemental doping. The mechanism of anion doping on the electronic properties of NaTaO3 is discussed. We find the band gap reduces significantly if we dope with anionic elements whose p orbital energy is higher than the O 2p orbitals. N and S can shift the valence band edge upward without losing the ability to split water into H2 and O2. Double-hole-mediated codoping can decrease the band gap significantly. On the basis of our calculations, codoping with N–N, C–S, and P–P could absorb visible light. However, they can only decompose water into H2 when the valence band edge is above the water oxidation level.
A solid solution photocatalyst, Na1–x La x Fe1–x Ta x O3 (x up to 0.06), was prepared by the conventional solid-state method. The photophysical properties of the samples were studied by various ...experimental techniques and the electronic structures were investigated by using screened hybrid density functional (HSE06) calculations. The solid solution photocatalyst showed absorption of visible light extending up to 450 nm. Upon loading of platinum nanoparticles cocatalyst, the photocatalytic hydrogen evolution of 0.81 μ·mol·h–1·g–1 was obtained for 2% doping of LaFeO3 in NaTaO3, under visible radiation (λ > 390 nm; 20% methanol solution). The photocatalytic properties of the solid solution were found to be better than Fe doped NaTaO3 compounds on account of the suitable band structure. The electronic structure analysis revealed that, in the case of Fe doping at the Ta site, unoccupied electronic states in between the band gap appear that are responsible for the visible-light absorption. However, in the case of La and Fe codoping (passivated doping) the mid-gap electronic states are completely filled, which makes the band structure suitable for the visible-light photocatalysis. The present solid solution of perovskites (LaFeO3 and NaTaO3) sheds light on the interesting photophysical properties and photocatalytic activities which could be beneficial for the photocatalysts derived from these compounds.
ZnO/NiO nanocomposite electrodes have successfully been developed using a cost-effective method, and for the first time used in LT-SOFCs at 300–600
°C. They exhibit high conductivity and a dual ...catalytic functionality in both the cathode and the anode for the electrochemical reduction of O
2 and oxidation of H
2, respectively. An excellent fuel cell performance, e.g. a maximum power density of 1107
W
cm
−
2
, has been shown for a symmetrical fuel cell that contained ZnO/NiO nanocomposite electrodes at 500
°C. To our knowledge, to date this is by far the highest power density achieved at this temperature.
► A novel nanostructure anode showed excellent performance, 1257
mW/cm
2. ► It exhibits high conductivity and a dual catalytic functionality in both the cathode and the anode for the electrochemical reduction of O
2 and oxidation of H
2. ► It might be useful for avoiding carbon deposition during the internal reforming and fuel cell reactions. It could prevent catalyst deactivation in SOFC anodes when using the hydrocarbon fuels.
Nanosized BiTaO4 and BiNbO4 were prepared by the citrate method. The electronic and optical properties of BiTaO4 and BiNbO4 have been investigated by means of photo‐acoustic spectroscopy (PAS), X‐ray ...photo‐electron spectroscopy (XPS), and first‐principles calculations based on density functional theory. The measured valence band (from XPS) of both materials agreed well with the theoretical findings. It was also found that the calculated optical properties such as dynamical dielectric function and optical absorption spectra are in good agreement with the experimental findings. According to the absorption spectra, the absorption edges of BiNbO4 and BiTaO4 are located at 370 and 330 nm, respectively. Both phases have the ability to harvest UV light and relatively high surface area to volume ratio and can be used as UV/visible light‐driven photocatalysts.
Fixation of SO2 molecules on anatase TiO2 surfaces with defects have been investigated by first-principles density functional theory (DFT) calculations and in situ Fourier transform infrared (FTIR) ...surface spectroscopy on porous TiO2 films. Intrinsic oxygen-vacancy defects, which are formed on TiO2(001) and TiO2(101) surfaces by ultraviolet (UV) light irradiation and at elevated temperatures, are found to be most effective in anchoring the SO2 gas molecules to the TiO2 surfaces. Both TiO2(101) and TiO2(001) surfaces with oxygen vacancies are found to exhibit higher SO2 adsorption energies in the DFT calculations. The adsorption mechanism of SO2 is explained on the basis of electronic structure, charge transfer between the molecule and the surface, and the oxidation state of the adsorbed molecule. The theoretical findings are corroborated by FTIR experiments. Moreover, the (001) surface with oxygen vacancies is found to bind SO2 gas molecules more strongly, as compared to the (101) surface. Higher concentration of oxygen vacancies on the TiO2 surfaces is found to significantly increase the adsorption energy. The results shed new insight into the sensing properties of TiO2-based gas sensors.
Density functional theory (DFT) calculations have been employed to explore the gas-sensing mechanisms of NiO (100) surface on the basis of energetic and electronic properties. We have calculated the ...adsorption energies of NO2, H2S, and NH3 molecules on NiO (100) surface using GGA+U method. The calculated results suggest that the interaction of NO2 molecule with NiO surface becomes stronger and contributes more extra peaks within the band gap as the coverage increases. The band gap of H2S-adsorbed systems decrease with the increase in coverage up to 0.5 ML and the band gap does not change at 1 ML because H2S molecules are repelled from the surface. In case of NH3 molecular adsorption, the adsorption energy has been increased with the increase in coverage and the band gap is directly related to the adsorption energy. Charge transfer mechanism between the gas molecule and the NiO surface has been illustrated by the Bader analysis and plotting isosurface charge distribution. It is also found that that work function of the surfaces shows different behavior with different adsorbed gases and their coverage. The work function of NO2 gas adsorption has a hill-shaped behavior, whereas H2S adsorption has a valley-shaped behavior. The work function of NH3 adsorption decreases with the increase in coverage. On the basis of our calculations, we can have a better understanding of the gas-sensing mechanism of NiO (100) surface toward NO2, H2S, and NH3 gases.
Site levels of VBM and CBM for OH:O=1 and OH:O=2 graphene oxide with different coverage rate: (a), (b), (c), (d), and (e) represented C36O8H4, C24O8H4, and C24O12H6 with OH:O=1, C20O6H4 and C16O6H4 ...with OH:O=2, respectively. The dot lines are standard water redox potentials. The reference potential is the vacuum level.
Our results not only explain the recent experimental observations that graphene oxide is a promising two-dimensional material for visible-light photocatalysis but can be very helpful in designing the optimal composition for higher performance. Display omitted
► Show GO is a promising material for visible-light-driven photocatalyst. ► Explain recent observations. ► Helpful in designing GO.
To elucidate the usage of graphene oxide (GO) as a photocatalysis material, we have studied the effect of epoxy and hydroxyl functionalization on the electronic structure, work function, CBM/VBM position, and optical absorption spectra of GO using density functional theory calculations. By varying the coverage and relative ratio of the surface epoxy (O) and hydroxyl (OH) groups, both band gap and work function of the GO materials can be tuned to meet the requirement of photocatalyst. Interestingly, the electronic structures of GO materials with 40–50% (33–67%) coverage and OH:O ratio of 2:1 (1:1) are suitable for both reduction and oxidation reactions for water splitting. Among of these systems, the GO composition with 50% coverage and OH:O (1:1) ratio can be very promising materials for visible-light-driven photocatalyst. Our results not only explain the recent experimental observations about 2-D graphene oxide as promising visible-light-driven photocatalyst materials but can also be very helpful in designing the optimal composition for higher performance.
Hybrid Density Functional calculations have been performed on the electronic structure of anionic mono- (S, N, P, and C) and co-doped (N–N, N–P, N–S, P–P) SrTiO3 to improve their visible light ...photocatalytic activity. The electronic band position of doped system has been aligned with respect to the water oxidation/reduction potential. The electronic band position and optical absorption study shows that the mono- (S) and co-doped (N–N, N–P and P–P) SrTiO3 systems are promising materials for the visible-light photocatalysis. The calculated binding energies show that the co-doped systems are more stable than their respective mono-doped systems.
► Hybrid Density Functional Study for efficient photocatalyst. ► Mono- and co- anion doped SrTiO3 for hydrogen production. ► Redox potential alignment with respect to Band edges. ► Optical absorption for mono or co-doped SrTiO3.
The layered perovskite Sr2Ta2O7 has been investigated for efficient visible light photocatalysis using the first principles study. The electronic structure of Sr2Ta2O7 is tuned by the anionic ...(N)/cationic (Mo, W) mono- and co-doping. Such doping creates impurity states in the band gap and therefore reduces the band gap significantly. The absolute band edge position of the doped Sr2Ta2O7 with respect to the water oxidation/reduction potential depends a lot on the p/d-orbital’s energies of anionic/cationic dopants, respectively. The stability of the co-doped system is governed by the Coulomb interactions and charge compensation effects.
Hybrid Density Functional calculations have been performed on the electronic structure of anionic mono- (S, N, P, and C) and co-doped (N-N, N-P, N-S, P-P) SrTiO 3 to improve their visible light ...photocatalytic activity. The electronic band position of doped system has been aligned with respect to the water oxidation/reduction potential. The electronic band position and optical absorption study shows that the mono- (S) and co-doped (N-N, N-P and P-P) SrTiO 3 systems are promising materials for the visible-light photocatalysis. The calculated binding energies show that the co-doped systems are more stable than their respective mono-doped systems.
