Overall Photocatalytic CO2 Reduction over Heterogeneous Semiconductor Photocatalysts.

The overall photocatalytic CO2 reduction reaction (PCRR), which uses solar energy to convert CO2 and H2 O into chemical feedstocks or fuels without sacrificial reagents, plays a momentous role in CO2 utilization and solar energy conversion. However, significant challenges remain in achieving efficient conversion. Researchers have explored various strategies to realize the overall PCRR efficiently. In this Review, we first explain the criteria for evaluating the overall PCRR and then summarize the following strategies developed over the past decade to promote it: self-driving material development, Z-scheme heterojunction construction, cocatalyst loading, heteroatom doping, surface vacancy creation, and carrier-material matching. Finally, we discuss essential future research directions in the field. Through this comprehensive Review, we aim to provide strategic guidance for the development of efficient overall PCRR systems.

Enabling High Loading in Single-Atom Catalysts on Bare Substrate with Chemical Scissors by Saturating the Anchoring Sites.

Atomically dispersed metal catalysts often exhibit high catalytic performances, but the metal loading density must be kept low to avoid the formation of metal nanoparticles, making it difficult to improve the overall activity. Diverse strategies based on creating more anchoring sites (ASs) have been adopted to elevate the loading density. One problem of such traditional methods is that the single atoms always gather together before the saturation of all ASs. Here, a chemical scissors strategy is developed by selectively removing unwanted metallic materials after excessive loading. Different from traditional ways, the chemical scissors strategy places more emphasis on the accurate matching between the strength of etching agent and the bond energies of metal-metal/metal-substrate, thus enabling a higher loading up to 2.02 wt% even on bare substrate without any pre-treatment (the bare substrate without any pre-treatment generally only has a few ASs for single atom loading). It can be inferred that by combining with other traditional methods which can create more ASs, the loading could be further increased by saturating ASs. When used for CH3 OH generation via photocatalytic CO2 reduction, the as-made single-atom catalyst exhibits impressive catalytic activity of 597.8 ± 144.6 µmol h-1 g-1 and selectivity of 81.3 ± 3.8%.

Three-Phase Photocatalysis for the Enhanced Selectivity and Activity of CO2 Reduction on a Hydrophobic Surface.

The photocatalytic CO2 reduction reaction (CRR) represents a promising route for the clean utilization of stranded renewable resources, but poor selectivity resulting from the competing hydrogen evolution reaction (HER) in aqueous solution limits its practical applicability. In the present contribution a photocatalyst with hydrophobic surfaces was fabricated. It facilitates an efficient three-phase contact of CO2 (gas), H2 O (liquid), and catalyst (solid). Thus, concentrated CO2 molecules in the gas phase contact the catalyst surface directly, and can overcome the mass-transfer limitations of CO2 , inhibit the HER because of lowering proton contacts, and overall enhance the CRR. Even when loaded with platinum nanoparticles, one of the most efficient HER promotion cocatalysts, the three-phase photocatalyst maintains a selectivity of 87.9 %. Overall, three-phase photocatalysis provides a general and reliable method to enhance the competitiveness of the CRR.

Solar-driven CO2-to-ethanol conversion enabled by continuous CO2 transport via a superhydrophobic Cu2O nano fence.

The overall photocatalytic CO2 reduction reaction presents an eco-friendly approach for generating high-value products, specifically ethanol. However, ethanol production still faces efficiency issues (typically formation rates <605 µmol g-1 h-1). One significant challenge arises from the difficulty of continuously transporting CO2 to the catalyst surface, leading to inadequate gas reactant concentration at reactive sites. Here, we develop a mesoporous superhydrophobic Cu2O hollow structure (O-CHS) for efficient gas transport. O-CHS is designed to float on an aqueous solution and act as a nano fence, effectively impeding water infiltration into its inner space and enabling CO2 accumulation within. As CO2 is consumed at reactive sites, O-CHS serves as a gas transport channel and diffuser, continuously and promptly conveying CO2 from the gas phase to the reactive sites. This ensures a stable high CO2 concentration at reactive sites. Consequently, O-CHS achieves the highest recorded ethanol formation rate (996.18 µmol g-1 h-1) to the best of our knowledge. This strategy combines surface engineering with geometric modulation, providing a promising pathway for multi-carbon production.

Double-shelled Cu2O/MnOx mesoporous hollow structure for CO2 photoreduction with enhanced stability and activity.

Photocatalytic CO2 reduction reaction (CRR) represents a prospective route for the clean utilization of greenhouse gas CO2 and solar energy, and cuprous oxide (Cu2O) is a favourable material for the CRR to avoid excess generation of hydrogen through the competitive hydrogen evolution reaction (HER). However, the application of Cu2O-based photocatalysts is limited by their poor stability and low activity, which result from the self-corrosion by photogenerated holes. Here we construct a double-shelled Cu2O/MnOx mesoporous hollow structure (D-CMH) to enhance the stability and activity of Cu2O-based photocatalysts. Because of the thin shells, which can shorten the diffusion distance of charge carriers, and the oxidation cocatalyst MnOx, which can efficiently attract holes, the photogenerated holes can be immediately removed from Cu2O and react with reactants. Additionally, the D-CMH can also provide enhanced efficiency of charge separation, prolonged path of light scattering and reflection and enlarged surface area for active sites, which result in the initial activity enhanced by 7.1 times and stability enhanced by 11.2 times compared with benchmark Cu2O nanoparticles.

Plasmid DNA isolation using amino-silica coated magnetic nanoparticles (ASMNPs).

A simple and efficient approach for the rapid isolation of plasmid DNA from crude cell lysates has been described. The approach took advantage of the amino-modified silica coated magnetic nanoparticles (ASMNPs) with positive zeta potential at neutral pH and superparamagnetism under the external magnetic fields. As a demonstration, the pEGFP-N3 plasmid has been concentrated and isolated from the E. coli DH5alpha transformed with pEGFP-N3 plasmid through electrostatic binding between the positive charge of the amino group of ASMNPs and the negative charge of the phosphate groups of the plasmid DNA. Then the pEGFP-N3 plasmid has been released easily and quickly from the pEGFP-N3 plasmid-ASMNPs complexes with 3M NaCl. The entire procedure could be carried out by the aid of external magnetic fields in 15min and eliminate the need of phenol, cesium chloride gradients or other noxious reagents and complexes operation. Moreover, the pEGFP-N3 plasmid obtained by this approach retains biological activity that can be suitable for restriction enzyme digestion and cells transfection with expression of green fluorescence protein.