Development and Functionalization of Visible-Light-Driven Water-Splitting Photocatalysts

Visible-Light Harvesting SrTiO3 Solid Solutions for Photocatalytic Hydrogen Evolution from Water

The fabrication of solid solutions represents a compelling approach to modulating the physicochemical properties of materials. In this study, we achieved the successful synthesis of solid solutions comprising SrTiO3 and SrTaO2N (denoted as (SrTiO3)1-x-(SrTaO2N)x, 0≤x≤1) using the magnesium powder-assisted nitridation method. The absorption edge of (SrTiO3)1-x-(SrTaO2N)x is tunable from 500 to 600 nm. The conduction band minimum (CBM) of (SrTiO3)1-x-(SrTaO2N)x comprises the Ti 3d orbitals and the Ta 5d orbitals, while the valence band maximum (VBM) consists of the O 2p and N 2p orbitals. The microstructure of the (SrTiO3)1-x-(SrTaO2N)x consists of small nanoparticles, exhibiting a larger specific surface area than the parent compounds of SrTiO3 and SrTaO2N. In the photocatalytic hydrogen evolution reaction (HER) with sacrificial reagents, the activity of solid solutions is notably superior to that of nitrogen-doped SrTiO3 and SrTaO2N. This superiority is mainly attributed to its broad light absorption range and high charge separation efficiency, which indicates its potential as a promising photocatalytic material. Moreover, the magnesium powder-assisted nitridation method exhibits obvious advantages for the synthesis of oxynitrides and bears instructional significance for the synthesis of other nitrogen-containing compounds and even sulfur-containing compounds.

How to Survive at Point Nemo? Fischer-Tropsch, Artificial Photosynthesis, and Plasma Catalysis for Sustainable Energy at Isolated Habitats

Inhospitable, inaccessible, and extremely remote alike the famed pole of inaccessibility, aka Point Nemo, the isolated locations in deserts, at sea, or in outer space are difficult for humans to settle, let alone to thrive in. Yet, they present a unique set of opportunities for science, economy, and geopolitics that are difficult to ignore. One of the critical challenges for settlers is the stable supply of energy both to sustain a reasonable quality of life, as well as to take advantage of the local opportunities presented by the remote environment, e.g., abundance of a particular resource. The possible solutions to this challenge are heavily constrained by the difficulty and prohibitive cost of transportation to and from such a habitat (e.g., a lunar or Martian base). In this essay, the advantages and possible challenges of integrating Fischer-Tropsch, artificial photosynthesis, and plasma catalysis into a robust, scalable, and efficient self-contained system for energy harvesting, storage, and utilization are explored.

Electrostatic Self-Assembled Synthesis of Amorphous/Crystalline g-C3N4 Homo-Junction for Efficient Photocatalytic H2 Production with Simultaneous Antibiotic Degradation

g-C3N4 has been regarded as a promising photocatalyst for photo-reforming antibiotics for H2 production but still suffers from its high charge recombination, which has been proven to be solvable by constructing a g-C3N4 homo-junction. However, those reported methods based on uncontrollable calcination for preparing a g-C3N4 homo-junction are difficult to reproduce. Herein, an amorphous/crystalline g-C3N4 homo-junction (ACN/CCN) was successfully synthesized via the electrostatic self-assembly attachment of negatively charged crystalline g-C3N4 nanorods (CCN) on positively charged amorphous g-C3N4 sheets (ACN). All the ACN/CCN samples displayed much higher photo-reforming of antibiotics for H2 production ability than that of pristine ACN and CCN. In particular, ACN/CCN-2 with the optimal ratio exhibited the best photocatalytic performance, with a H2 evolution rate of 162.5 μmol·g-1·h-1 and simultaneous consecutive ciprofloxacin (CIP) degradation under light irradiation for 4 h. The UV-vis diffuse reflectance spectra (DRS), photoluminescence (PL), and electrochemical results revealed that a homo-junction is formed in ACN/CCN due to the difference in the band arrangement of ACN and CCN, which effectively suppressed the charge recombination and then led to those above significantly enhanced photocatalytic activity. Moreover, H2 was generated from the water reduction reaction with a photogenerated electron (e-), and CIP was degraded via a photogenerated hole (h+). ACN/CCN exhibited adequate photostability and reusability for photocatalytic H2 production with simultaneous CIP degradation. This work provides a new idea for rationally designing and preparing homo-junction photocatalysts to achieve the dual purpose of chemical energy production and environmental treatment.

Regulating excitonic effects in non-oxide based XPSe3 (X = Cd, Zn) monolayers towards enhanced photocatalysis for overall water splitting

The non-oxide 2D materials have garnered considerable interest due to their potential utilization as photocatalysts, which offer a superior substitute to metal-oxide-based photocatalysts. This study investigates the impact of the dielectric environment on the size and binding energy of excitons in atomically thin, experimentally synthesized semiconducting monolayers [XPSe₃, X = (Cd, Zn)] to address the critical problem of electron-hole recombination, which significantly hinders the efficiency of most photocatalysts. We employ a precise non-hydrogenic model surpassing the hydrogenic-based Mott-Wannier model. Our findings are among the first few demonstrations of an increase in exciton size (and decrease in exciton binding energy) as environmental screening increases. These findings have implications for photocatalytic water splitting and are not limited to metal phosphorus trichalcogenides, but can be applied to other classes of 2D materials as well. This work also compares metal-oxide photocatalysts, which have been the focus of much research over the past five decades, to non-oxide-based metal phosphorus trichalcogenide photocatalysts, which offer a superior alternative due to their ability to address issues such as light-harvesting inability in the visible spectrum and unwanted charge recombination centres. Furthermore, the implications of this study extend beyond photocatalysts and are significant for the design and development of next-generation optoelectronic devices that incorporate excitonic processes, such as solar cells, photodetectors, LEDs, etc.

Promoting Photocatalytic Carbon Dioxide Reduction by Tuning the Properties of Cocatalysts

Suppressing the amount of carbon dioxide in the atmosphere is an essential measure toward addressing global warming. Specifically, the photocatalytic CO2 reduction reaction (CRR) is an effective strategy because it affords the conversion of CO2 into useful carbon feedstocks by using sunlight and water. However, the practical application of photocatalyst-promoting CRR (CRR photocatalysts) requires significant improvement of their conversion efficiency. Accordingly, extensive research is being conducted toward improving semiconductor photocatalysts, as well as cocatalysts that are loaded as active sites on the photocatalysts. In this review, we summarize recent research and development trends in the improvement of cocatalysts, which have a significant impact on the catalytic activity and selectivity of photocatalytic CRR. We expect that the advanced knowledge provided on the improvement of cocatalysts for CRR in this review will serve as a general guideline to accelerate the development of highly efficient CRR photocatalysts.

Platinum@Hexaniobate Nanopeapods: A Directed Photocatalytic Architecture for Dye-Sensitized Semiconductor H2 Production under Visible Light Irradiation

Platinum@hexaniobate nanopeapods (Pt@HNB NPPs) are a nanocomposite photocatalyst that was selectively engineered to increase the efficiency of hydrogen production from visible light photolysis. Pt@HNB NPPs consist of linear arrays of high surface area Pt nanocubes encapsulated within scrolled sheets of the semiconductor H _x K_4-x Nb₆O₁₇ and were synthesized in high yield via a facile one-pot microwave heating method that is fast, reproducible, and more easily scalable than multi-step approaches required by many other state-of-the-art catalysts. The Pt@HNB NPPs' unique 3D architecture enables physical separation of the Pt catalysts from competing surface reactions, promoting electron efficient delivery to the isolated reduction environment along directed charge transport pathways that kinetically prohibit recombination reactions. Pt@HNB NPPs' catalytic activity was assessed in direct comparison to representative state-of-the-art Pt/semiconductor nanocomposites (extPt-HNB NScs) and unsupported Pt nanocubes. Photolysis under similar conditions exhibited superior H₂ production by the Pt@HNB NPPs, which exceeded other catalyst H₂ yields (μmol) by a factor of 10. Turnover number and apparent quantum yield values showed similar dramatic increases over the other catalysts. Overall, the results clearly demonstrate that Pt@HNB NPPs represent a unique, intricate nanoarchitecture among state-of-the-art heterogeneous catalysts, offering obvious benefits as a new architectural pathway toward efficient, versatile, and scalable hydrogen energy production. Potential factors behind the Pt@HNB NPPs' superior performance are discussed below, as are the impacts of systematic variation of photolysis parameters and the use of a non-aqueous reductive quenching photosystem.

Efficient Removal of Methylene Blue and Ciprofloxacin from Aqueous Solution Using Flower-like, Nanostructured ZnO Coating under UV Irradiation

Flower-like ZnO architectures assembled with many nanorods were successfully synthesized through Thermionic Vacuum Arc, operated both in direct current (DC-TVA) and a pulsed mode (PTVA), and coupled with annealing in an oxygen atmosphere. The prepared coatings were analysed by scanning-electron microscopy with energy-dispersive X-ray-spectroscopy (SEM-EDX), X-ray-diffraction (XRD), and photoluminescence (PL) measurements. By simply modifying the TVA operation mode, the morphology and uniformity of ZnO nanorods can be tuned. The photocatalytic performance of synthesized nanostructured ZnO coatings was measured by the degradation of methylene-blue (MB) dye and ciprofloxacin (Cipro) antibiotic. The ZnO (PTVA) showed enhancing results regarding the photodegradation of target contaminants. About 96% of MB molecules were removed within 60 min of UV irradiation, with a rate constant of 0.058 min−1, which is almost nine times higher than the value of ZnO (DC-TVA). As well, ZnO (PTVA) presented superior photocatalytic activity towards the decomposition of Cipro, after 240 min of irradiation, yielding 96% degradation efficiency. Moreover, the agar-well diffusion assay performance against both Gram-positive and Gram-negative bacteria confirms the degradation of antibiotic molecules by the UV/ZnO (PTVA) approach, without the formation of secondary hazardous products during the photocatalysis process. Repeated cyclic usage of coatings revealed excellent reusability and operational stability.

Metal-nanocluster Science and Technology: My Personal History and Outlook

Metal nanoclusters (NCs) are among the leading targets in research of nanoscale materials, and elucidation of their properties (science) and development of control techniques (technology) have been continuously studied for...