Rational design of liquid metal organic frameworks for the enhanced CO2 absorption and their photocatalytic reduction

Metal organic frameworks (MOFs) has been widely investigated as co-catalysts for photocatalysis owing to their unique property for controlling the reaction kinetics. They are generally presented in a solid state. Recent studies have presented MOF in the liquid phase, meanwhile preserving the framework structure. Acting as a co-catalyst, significantly improved efficiency has been realized for photocatalytic CO2 reduction. This concept article focuses on the chemical principle of liquid MOF (LMOF). Their applications in CO2 adsorption and the photocatalytic CO2 reduction have been discussed with showing key examples. In addition, the other relevant applications of LMOF have been presented. </p

Driving NiTiO3 photocatalyst for oxygen evolution reaction with near-infrared light

A nickel titanate (NTO) photocatalyst has been developed for the oxygen evolution reaction (OER) with an exceptionally broad light wavelength excitation ranging from visible to infrared. Specifically, by loading CoOxas the co-catalyst, the apparent quantum yields for the OER were ca. 2.2%, 1.0%, and 0.8% at wavelengths of 470, 760, and 850 nm, respectively. The achievements reveal that the NTO photocatalyst is highly efficient even under illumination with near-infrared (NIR) light, which confers the potential for highly efficient solar-driven oxidation reactions.</p

Tailoring Metal-Ion-Doped Carbon Nitrides for Photocatalytic Oxygen Evolution Reaction

Poly(heptazine imides) (PHIs) have emerged as prominent layered carbon nitride-based materials with potential oxygen evolution reaction (OER) catalytic activity owing to their strong VIS light absorption, long excited-state lifetimes, high surface-to-volume ratios, and the possibility of tuning their properties via hosting different metal ions in their pores. A series of metal-ion-doped PHI-M (M = K+, Rb+, Mg2+, Zn2+, Mn2+, and Co2+) were first systematically explored using density functional theory calculations. These simulations led an in-depth understanding of the microscopic OER mechanism in these systems and identified PHI-Co2+ as the best OER catalyst of this family of PHIs, whereas PHI-Mn2+ can be an alternative promising OER catalyst. This level of performance was attributed to a thermodynamically favorable formation of the reaction intermediates as well as its red-shifted absorption in the VIS region involving the population of long-lived states, as revealed by time-dependent density functional theory calculations. We further demonstrated that the electronic properties of the *OH intermediates (Bader population, crystal orbital Hamilton population analysis, and adsorption energies) are reliable descriptors to anticipate the OER activity of this family of PHIs. This rational analysis paved the way toward the prediction of the OER performance of another PHI-M derivative, i.e., PHI-Fe2+. The computationally explored PHI-Fe2+, PHI-Mn2+, and PHI-Co2+ systems were then synthesized alongside PHI-K+, and their photocatalytic OER activities were assessed. These experimental findings confirmed the best photocatalytic OER performance for PHI-Co2+ with an oxygen production of 31.2 μmol·h–1 that is 60 times higher than the pristine g-C3N4 (0.5 μmol·h–1), whereas PHI-Fe2+ and PHI-Mn2+ are seen as alternative OER catalysts with attractive oxygen production of 11.20 and 4.69 μmol·h–1, respectively. Decisively, this joint experimental–computational study reveals PHI-Co2+ to be among the best of the OER catalysts so far reported in the literature including some perovskites

Hydroxyl-Bonded Ru on Metallic TiN Surface Catalyzing CO₂ Reduction with H₂O by Infrared Light

Synchronized conversion of CO2 and H2O into hydrocarbons and oxygen via infrared-ignited photocatalysis remains a challenge. Herein, the hydroxyl-coordinated single-site Ru is anchored precisely on the metallic TiN surface by a NaBH4/NaOH reforming method to construct an infrared-responsive HO-Ru/TiN photocatalyst. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (ac-HAADF-STEM) and X-ray absorption spectroscopy (XAS) confirm the atomic distribution of the Ru species. XAS and density functional theory (DFT) calculations unveil the formation of surface HO-RuN5–Ti Lewis pair sites, which achieves efficient CO2 polarization/activation via dual coordination with the C and O atoms of CO2 on HO-Ru/TiN. Also, implanting the Ru species on the TiN surface powerfully boosts the separation and transfer of photoinduced charges. Under infrared irradiation, the HO-Ru/TiN catalyst shows a superior CO2-to-CO transformation activity coupled with H2O oxidation to release O2, and the CO2 reduction rate can further be promoted by about 3-fold under simulated sunlight. With the key reaction intermediates determined by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and predicted by DFT simulations, a possible photoredox mechanism of the CO2 reduction system is proposed

Light trapping by porous TiO2 hollow hemispheres for high efficiency photoelectrochemical water splitting

Photocatalytic water splitting has recently received increasing attention as a green fuel source. The controlled nano-geometry of the photocatalytic material can improve light harvesting. In this study, as a proof of concept, hollow hemisphere (HHS)-based films of TiO2 material were created by a conventional electrospray method and subsequently applied for photoelectrochemical (PEC) water splitting. To preserve the morphology of the HHS structure, a hydrolysis precipitation phase separation method (HPPS) was developed. As a result, the TiO2 HHS-based thin films presented a maximum PEC water splitting efficiency of ca. 0.31%, almost two times that of the photoanode formed by TiO2 nanoparticle-based films (P25). The unique morphology and porous structure of the TiO2 HHSs with reduced charge recombination and improved light absorption are responsible for the enhanced PEC performance. Light scattering by the HHS was demonstrated with total reflection internal fluorescence microscopy (TRIFM), revealing the unique light trapping phenomenon within the HHS cavity. This work paves the way for the rational design of nanostructures for photocatalysis in fields including energy, environment, and organosynthesis