The Combination of Hydrogen and Methanol Production through Artificial Photosynthesis-Are We Ready Yet?

Robust Heterogeneous Photocatalyst for Visible-Light-Driven Hydrogen Evolution Promotion: Immobilization of a Fluorescein Dye-Encapsulated Metal-Organic Cage on TiO2

The design of artificial photocatalytic devices that simulates the ingenious and efficient photosynthetic systems in nature is promising. Herein, a metal-organic cage [Pd₆(NPyCzPF)₁₂]¹²⁺ (MOC-PC6) integrating 12 organic ligands NPyCzBP and 6 Pd²⁺ catalytic centers is designed, which is well defined to include organic dye fluorescein (FL) for constructing a supramolecular photochemical molecular device (SPMD) FL@MOC-PC6. Photoinduced electron transfer (PET) between MOC-PC6 and the encapsulated FL has been observed by steady-state and time-resolved emission spectroscopy. FL@MOC-PC6 is successfully heterogenized with TiO₂ by a facile sol-gel method to achieve a robust heterogeneous FL@MOC-PC6-TiO₂. The close proximity between the Pd²⁺ catalytic site and FL included in the cage enables PET from the photoexcited FL to Pd²⁺ sites through a powerful intramolecular pathway. The photocatalytic hydrogen production assessments of the optimized 4 wt % FL@MOC-PC6-TiO₂ demonstrate an initial H₂ production rate of 2402 μmol g^-1 h^-1 and a turnover number of 4356 within 40 h, enhanced by 15-fold over that of a homogeneous FL@MOC-PC6. The effect of the MOC content on photocatalytic H₂ evolution (PHE) is investigated and the inefficient comparison systems, such as MOC-PC6, MOC-PC6-TiO₂, FL-sensitized MOC-PC6/FL-TiO₂, and analogue FL/MOC-PC6-TiO₂ with free FL, are evaluated. This study provides a creative and distinctive approach for the design and preparation of novel heterogeneous SPMD catalysts based on MOCs.

Nanostructured Photocatalysts for the Production of Methanol from Methane and Water

The direct photocatalytic conversion of methane into methanol with water at room temperature and pressure has attracted particular attention in recent decades. Valuable insight has been obtained into the reaction mechanisms and the key descriptors that control photoactivity and selectivity. This Minireview highlights the different efforts that have been undergone on the design of nanostructured photocatalytic systems to enhance the selectivity to methanol. The effect of structural and electronic aspects, such as surface area, morphologies, crystal facets, redox properties, metal doping, and heterojunctions, on photocatalytic performance, are discussed. The roles of free hydroxyl radicals and/or hydroxy groups for methane activation on the photocatalyst surface are also presented. This Minireview aims to provide an insight into the optimal properties and configurations of the nanostructured photocatalytic materials for tuning their reactivity on the selective oxidation of CH₄ to methanol with water. The remaining challenges and promising directions for bringing this technology a step closer to real-world application are also highlighted.