Nano-Photoelectrochemical Cell Arrays with Spatially Isolated Oxidation and Reduction Channels

Interfacial Charge Transport in 1D TiO2 Based Photoelectrodes for Photoelectrochemical Water Splitting

1D nanostructured photoelectrodes are promising for application as photoelectrochemical (PEC) devices for solar energy conversion into hydrogen (H₂ ) owing to the optical, structural, and electronic advantages. Titanium dioxide (TiO₂ ) is the most investigated candidate as a photoelectrode due to its good photostability, low production cost, and eco-friendliness. The obstacle for TiO₂ 's practical application is the inherent wide bandgap (UV-lights response), poor conductivity, and limited hole diffusion length. Here, a comprehensive review of the current research efforts toward the development of 1D TiO₂ based photoelectrodes for heterogeneous PEC water splitting is provided along with a discussion of nanoarchitectures and energy band engineering influences on interfacial charge transfer and separation of 1D TiO₂ composited with different dimensional photoactive materials. The key focus of this review is to understand the charge transfer processes at interfaces and the relationship between photogenerated charge separation and photoelectrochemical performance. It is anticipated that this review will afford enriched information on the rational designs of nanoarchitectures, doping, and heterojunction interfaces for 1D TiO₂ based photoelectrodes to achieve highly efficient solar energy conversion.

Study on Simultaneous Removal of Dye and Heavy Metal Ions by NiAl-Layered Double Hydroxide Films

Herein, nickel-aluminum-layered double hydroxide (NiAl-LDH) films were prepared by the hydrothermal method. Based on the photoinduced reduction ability and degradation of LDHs on heavy metal ions and organic compounds, NiAl-LDH films displayed favorable simultaneous removal performance. Benefiting from the electron traps of heavy metals reduced from solution, the coexisting metal ions improved the photocatalytic activity of NiAl-LDH films on methyl orange. The higher the Fermi level of coexisting metal ion was, the higher the photocatalytic degradation rate of methyl orange obtained. Meanwhile, the removal rates of heavy metal ions (Ag⁺, Pb²⁺, and Cu²⁺) from wastewater were both enhanced and could reach 95%. NiAl-LDH films showed affinity toward Ag⁺. Furthermore, NiAl-LDH films are tightly coupled with the substrate, providing active sites and a simple method for the catalyst recovery. This study provides new insights into the simultaneous removal of heavy metal ions and organic pollutants using LDH films.

Ta-Doped porous TiO2 nanorod arrays by substrate-assisted synthesis: efficient photoelectrocatalysts for water oxidation

Owing to its excellent chemical stability and low cost, titanium dioxide (TiO₂) has been widely studied as a photoanode for photoelectrochemical (PEC) water splitting. However, TiO₂'s practical applications in solar energy-to-synthetic fuel conversion processes have been constrained by its inherently poor ability to transport photogenerated electrons and holes. In this paper, we report Ta-doped porous TiO₂ nanorod arrays on Ta foil (Ta-PTNA) that do not possess this issue and that can thus efficiently photoelectrocatalyze water oxidation, helping the production of H₂ (a clean fuel) from water at the expense of solar light. The materials are synthesized by a new, facile synthetic approach involving the hydrothermal treatment of a TiO₂ precursor with Ta foil, without seeds and templates, and followed by calcination of the product. Besides serving as a source of Ta dopant atoms, Ta foil is found to play a vital role in the formation of nanopores in the materials. The material obtained with hydrothermal treatment at 180 °C for 10 h (Ta-PTNA-10), in particular, affords very large photocurrent density and very high photoconversion efficiency (0.32% at 0.79 V vs. RHE, which is better than those of many previously reported photocatalysts and ∼4 times larger than that of undoped TiO₂ nanorod arrays). Ta-PTNAs' remarkable PEC catalytic performance is found to be due to their nanoporous structure and high electronic conductivity.

Fabrication of Core-Shell Nanotube Array for Artificial Photosynthesis Featuring an Ultrathin Composite Separation Membrane

Macroscale arrays of cobalt oxide-silica core-shell nanotubes with high aspect ratio and ultrathin walls of less than 20 nm have been fabricated. The silica shells feature embedded oligo-para(phenylenevinylene) molecules for charge transport across the insulating silica layer, which is tightly controlled by their electronic properties. The assembly is based on the use of a sacrificial Si nanorod array template combined with atomic layer deposition, covalent anchoring of organic wire molecules, and dry cryo-etching. High-resolution TEM imaging of samples prepared by microtome affords structural details of single core-shell nanotubes. The integrity of silica-embedded organic wire molecules exposed to atomic layer deposition, thermal treatment, and harsh etching procedures is demonstrated by grazing angle ATR FT-IR, FT-Raman, and XPS spectroscopy. The inorganic oxide-based core-shell nanotubes with ultrathin gas-impermeable, proton-conducting silica shells functionalized by molecular wires enable complete nanoscale photosynthetic units for CO₂ reduction by H₂O under membrane separation. Arrays of massive numbers of such core-shell nanotube units afford a design that extends the separation of the incompatible H₂O oxidation and CO₂ reduction catalysis environments across the continuum of length scales from nanometers to centimeters.

Photocatalytic Active Mesoporous Carbon/ZnO Hybrid Materials from Block Copolymer Tethered ZnO Nanocrystals

Severe water pollution issues present an important contemporary challenge that drives the development and advancement of efficient and environmentally benign photocatalysts that enable the degradation of pollutants upon visible light irradiation. One example is zinc oxide/carbon (ZnO/C) hybrid materials that have been shown to be effective photocatalysts. To maximize the effectiveness of ZnO/C hybrids, materials with high accessible surface area of ZnO are required. Here, a novel strategy is presented to enable the synthesis of fine dispersions of ZnO nanoparticles within a porous carbon matrix. The synthesis entails the grafting of ZnO nanparticles with polystyrene-b-poly(styrene-co-acrylonitrile) (PS-b-PSAN) block copolymer and subsequent pyrolysis of the material under inert gas (N₂) atmosphere. During the pyrolysis process, the PS block effectively prevents agglomeration of ZnO particles, thus resulting in a fine dispersion of ZnO nanocrystals within a prorous C matrix. Materials are found to exhibit a dye adsorption capacity of 125 mg g^-1 (from a methylene blue aqueous solution with a concentration of 305 mg L^-1) and dye degradation rate constant of 0.021 min^-1. The significant increase of effective surface area and degradation efficacy (as compared to ZnO/C synthesized by the pyrolysis of binary PSAN/ZnO blends) is rationalized as a consequence of the increased porosity that promotes dye adsorption and transport within the hybrid material.