A kind of 2D-layered material, Ti3C2 MXenes, was successfully used as a new and efficient co-catalyst to improve the photocatalytic NH3 synthesis performance of P25, due to its large surface area/2D-layered structure, large electric capacity, excellent electrical conductivity and effective chemisorption/activation of N2 molecules. The generation yield of NH3 was improved by 5 times on the optimized sample of 6% Ti3C2 MXenes-P25 compared with pure P25 under full spectrum light irradiation, consistent with the measured both photocurrent densities and charge lifetime. The further mechanistic study showed that Ti3C2 MXenes played an important role in the separation of photogenerated electron-hole pairs by accumulating the excited electrons from the excited P25. Most importantly, Ti3C2 MXenes could dramatically improve chemisorption and activation of N2 as demonstrated by ESR spectra and DFT calculations. In addition, Ti3C2 MXenes loading on P25 could introduce oxygen vacancies in P25, also beneficial for photocatalytic NH3 synthesis. Thus this study provides an efficient and promising co-catalyst for the photocatalytic NH3 synthesis process from N2 in air

In order to reveal the origin of enhanced photocatalytic activity of N-doped La2Ti2O7 in both the visible light and ultraviolet light regions, its electronic structure has been studied using spin-polarized conventional density functional theory (DFT) and the Heyd-Scuseria-Ernzerhof (HSE06) hybrid approach. The results show that the deep localized states are formed in the forbidden band when nitrogen solely substitutes for oxygen. Introducing the interstitial Ti atom into the N-doped La2Ti2O7 photocatalyst still causes the formation of a localized energy state. Two nitrogen substitutions co-exist stably with one oxygen vacancy, creating a continuum energy band just above the valence band maximum. The formation of a continuum band instead of mid-gap states can extend the light absorption to the visible light region without increasing the charge recombination, explaining the enhanced visible light performance without deteriorating the ultraviolet light photocatalytic activity.

The correlation of the electronic band structure with the photocatalytic activity of AgTaO3 has been studied by simulation and experiments. Doping wide band gap oxide semiconductors usually introduces discrete mid-gap states, which extends the light absorption but has limited benefit for photocatalytic activity. Density functional theory (DFT) calculations show that compensated co-doping in AgTaO3 can overcome this problem by increasing the light absorption and simultaneously improving the charge carrier mobility. N/H and N/F co-doping can delocalize the discrete mid-gap states created by sole N doping in AgTaO3, which increases the band curvature and the electron-to-hole effective mass ratio. In particular, N/F co-doping creates a continuum of states that extend the valence band of AgTaO3. N/F co-doping thus improves the light absorption without creating the mid-gap states, maintaining the necessary redox potentials for water splitting and preventing from charge carrier trapping. The experimental results have confirmed that the N/F-codoped AgTaO3 exhibits a red-shift of the absorption edge in comparison with the undoped AgTaO3, leading to remarkable enhancement of photocatalytic activity toward hydrogen generation from water.

This work proposed the mechanism of luminescence chromism switching and band structure modulation for enhancing the photocarriers' separation of PhC2Cu, a new kind of metal–organic coordination polymer semiconductor.