Synthesis of Three-Layer Perovskite Oxynitride K2Ca2Ta3O9N·2H2O and Photocatalytic Activity for H2 Evolution under Visible Light

In situ growth of Cu0-modified oxynitride for optimized photocatalytic nitric oxide oxidation

Photocatalysis technology provides a promising and green strategy for the abatement of low-concentration NO pollutants in the ambient air. An earthworm-like oxynitride decorated with in situ grown Cu nanoparticles is synthesized through the ammonolysis of the CuO-doped ZnGa2O4 spinel. The optimized morphology promoted the exposure of active sites and expanded the reaction interface for efficient NO adsorption and photocatalytic conversion. The decoration of Cu0 and N3- doping enhanced the light absorption and imparted a tunable energy band structure. The strong interactions between Cu0 and the Ga1-xZnxN1-yOy interface maximize the utilizing photo-induced charge by facilitating the transfer and inhibiting the recombination of the charge carrier. The strong adsorption of H2O and NO on Cu0 and internal electric field of Cu0-Ga1-xZnxN1-yOy junction contribute to the high selectivity of NO. This study provides a new perspective on the design of visible-light-driven photocatalysts with Schottky junction for environmental remediation.

Layered Anion-Mixed Oxycompounds: Synthesis, Properties, and Applications

Layered anion-mixed oxycompounds have emerged as pivotal materials across diverse technological domains encompassing electronics, optics, sensing, catalysis, and energy applications. Capitalizing on the unique properties imparted by the additional anion, these compounds exhibit exceptional characteristics including ultra-large charge carrier mobility, giant second-harmonic generation, visible-light-driven photocatalysis, and outstanding thermoelectricity. This article aims to provide a comprehensive summary of layered anion-mixed oxychalcogenides, oxyhalides, oxynitrides, and oxypnictides. Organized by chemical composition and crystal structures, the classification of these oxycompounds precedes an in-depth exploration of various synthesis methodologies. Subsequently, their properties are elucidated in electronics, optics, magnetics, and ferroelectrics, contextualizing their utility in electronic, optical, and catalytic applications. The review culminates in a critical assessment of extant challenges and opportunities within this realm. Furthermore, insights are proffered into the future trajectory of research, underpinning the significance of advancing novel 2D multi-anion oxygenated compounds and their attendant applications.

Recent progress in doping engineering of perovskite oxides for photocatalytic green hydrogen production via water splitting

Given the immense potential for addressing energy and environmental issues, the utilization of solar energy for hydrogen production by water splitting (WS) has garnered widespread attention in the scientific community. Perovskite oxides (POs), with their compositional flexibility and structural stability, hold significant promise in the photocatalytic hydrogen evolution reaction (HER). Rational doping of POs is the key to enhancing the rate of the photocatalytic HER. In this review, with the aim of providing guidance for the enhancement of photocatalytic efficiency, the recent advancements in ion-doping engineering of PO-based photocatalysts are summarized. The principles of photocatalytic WS, the preparation methods of ion-doped POs, the types of dopants, and the effects of doping on the photocatalytic performance of the HER are systematically reviewed and discussed. Background and advances in practical applications are further elaborated. Ultimately, prospects and challenges of the doped POs for the photocatalytic HER are proposed. This review provides a good reference for making informed decisions regarding the selection of doped ions and a valuable suggestion for establishing high-stability photocatalytic systems toward large-scale applications.

Designed functions of oxide/hydroxide nanosheets via elemental replacement/doping

Partial replacement of one structural element in a solid with another of a similar size was conducted to impart functionality to the solids and modify their properties. This phenomenon is found in nature in coloured gemstones and clay minerals and is used in materials chemistry and physics, endowing materials with useful properties that can be controlled by incorporated heteroelements and their amounts. Depending on the area of research (or expected functions), the replacement is referred to as "isomorphous substitution", "doping", etc. Herein, elemental replacement in two-dimensional (2D) oxides and hydroxides (nanosheets or layered materials) is summarised with emphasis on the uniqueness of their preparation, characterisation and application compared with those of the corresponding bulk materials. Among the 2D materials (graphene, metallenes, transition metal chalcogenides, metal phosphate/phosphonates, MXenes, etc.), 2D oxides and hydroxides are characterised by their presence in nature, facile synthesis and storage under ambient conditions, and possible structural variation from atomic-level nanosheets to thicker nanosheets composed of multilayered structures. The heteroelements to be doped were selected depending on the target application objectively; however, there are structural and synthetic limitations in the doping of heteroelements. In the case of layered double hydroxides (single layer) and layered alkali silicates (from single layer to multiple layers), including layered clay minerals (2 : 1 layer), the replacement (commonly called isomorphous substitution) is discussed to understand/design characteristics such as catalytic, adsorptive (including ion exchange), and swelling properties. Due to the variation in their main components, the design of layered transition metal oxide/hydroxide materials via isomorphous substitution is more versatile; in this case, tuning their band structure, doping both holes and electrons, and creating impurity levels are examined by the elemental replacement of the main components. As typical examples, material design for the photocatalytic function of an ion-exchangeable layered titanate (lepidocrocite-type titanate) and a perovskite niobate (KCa2Nb3O10) is discussed, where elemental replacement is effective in designing their multiple functions.

Defect engineering of two-dimensional Nb-based oxynitrides for visible-light-driven water splitting to produce H2 and O2

Two-dimensional (2D) Nb-based oxynitrides are promising visible-light-responsive photocatalysts for the water splitting reaction, but their photocatalytic activity is degraded by the formation of reduced Nb⁵⁺ species and O^2- vacancies. To understand the influence of nitridation on the formation of crystal defects, this study synthesized a series of Nb-based oxynitrides through the nitridation of LaKNaNb_1-xTa_xO₅ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). During nitridation, K and Na species volatilized, which helped transform the exterior of LaKNaNb_1-xTa_xO₅ into a lattice-matched oxynitride shell. Ta inhibited defect formation, yielding Nb-based oxynitrides with a tunable bandgap between 1.77 and 2.12 eV, straddling the H₂ and O₂ evolution potentials. After loading with Rh and CoO_x cocatalysts, these oxynitrides exhibited good photocatalytic activity for H₂ and O₂ evolution in visible light (650-750 nm). The nitrided LaKNaTaO₅ and LaKNaNb_0.8Ta_0.2O₅ delivered the maximum H₂ (19.37 μmol h^-1) and O₂ (22.81 μmol h^-1) evolution rates, respectively. This work provides a strategy for preparing oxynitrides with low defect densities and demonstrates the promising performance of Nb-based oxynitrides for water splitting.

Cost-effective preparation of layered tantalum oxynitrides for visible light-driven photocatalysis

Layered oxynitrides are promising materials for visible light photocatalysis. However, the conventional method for the synthesis of oxynitrides using ammonia as a nitrogen source is dangerous. In this work, we successfully synthesized two layered tantalum oxynitrides, K_1.35LaTa₂O_6.65N_0.35 and K_1.4Ca₂Ta₃O_9.6N_0.4, via a topochemical nitridation process using urea as a solid nitrogen source. Employing different characterization methods, we determined the structure and composition of layered oxynitrides. Furthermore, using Pt as a co-catalyst, these two layered oxynitrides showed excellent photocatalytic performances under visible light irradiation. In contrast to ammonia, urea process provides easy access for the synthesis of layered oxynitrides and sheds new light on the design of effective visible light-driven photocatalysts.

Bandgap Tunable Oxynitride LaNb2 O7-x Nx Nanosheets

Bandgap tunable lanthanum niobium oxynitride [LaNb₂ O_7-x N_x ]^(1+x)- nanosheet is prepared by the delamination of a Ruddlesden-Popper phase perovskite oxynitride via ion-exchange and two-step intercalation processes. The lanthanum niobium oxynitride nanosheets have a homogeneous thickness of 1.6 nm and exhibit a variety of chromatic colors depending on the nitridation temperature of the parent-layered oxynitride. The bandgap energy of the nanosheets is determined by ultraviolet photoemission spectroscopy, Mott-Schottky, and photoelectrochemical measurements and is found to be tunable in the range of 2.03-2.63 eV. Furthermore, the oxide/oxynitride superlattice structures are fabricated by face-to-face stacking of 2D crystals using oxynitride [LaNb₂ O_7-x N_x ]^(1+x)- and oxide [Ca₂ Nb₃ O₁₀ ]^- nanosheets as building blocks. Moreover, the superlattices-like restacked oxynitride/oxide nanosheets hybrid exhibits unique proton conductivity and dielectric properties strongly influenced by the oxynitride nanosheets and enhanced photocatalytic activity under visible light irradiation.

Improvement of Visible‐Light H 2 Evolution Activity of Pb 2 Ti 2 O 5.4 F 1.2 Photocatalyst by Coloading of Rh and Pd Cocatalysts

Pb₂Ti₂O_5.4F_1.2 modified with various metal cocatalysts was studied as a photocatalyst for visible‐light H₂ evolution. Although unmodified Pb₂Ti₂O_5.4F_1.2 showed negligible activity, modification of its surface with Rh led to the best observed promotional effect among the Pb₂Ti₂O_5.4F_1.2 samples modified with a single metal cocatalyst. The H₂ evolution activity was further enhanced by coloading with Pd; the Rh−Pd/Pb₂Ti₂O_5.4F_1.2 photocatalyst showed 3.2 times greater activity than the previously reported Pt/Pb₂Ti₂O_5.4F_1.2. X‐ray absorption fine‐structure spectroscopy, photoelectrochemical, and transient absorption spectroscopy measurements indicated that the coloaded Rh and Pd species, which were partially alloyed on the Pb₂Ti₂O_5.4F_1.2 surface, improved the electron‐capturing ability, thereby explaining the high activity of the coloaded Rh−Pd/Pb₂Ti₂O_5.4F_1.2 catalyst toward H₂ evolution.

Effect of layers on the photocatalytic hydrogen evolution in Dion-Jacobson layered-tantalum perovskites

Tantalum-based layered perovskites have always been an interesting topic in photocatalysis, but limited information has been reported in terms of their layer factor. In this work, we have synthesized Dion-Jacobson layered perovskites (A'[A_n-1Ta_nO_3n+1]) of LaTaO₄, KLaTa₂O₇, and KCa₂Ta₃O₁₀ with n = 1, 2, and 3, respectively. With the modification of 1 wt% Pt co-catalysts, the photocatalytic analysis showed that the performance order of these layered perovskites with different layers is KLaTa₂O₇ (n = 2) > KCa₂Ta₃O₁₀ (n = 3) ≫ LaTaO₄ (n = 1) with both methanol and NaI as the sacrificial agents. This suggested the importance of interlayer K⁺ for high photocatalytic performance. We further analyzed the layered perovskites in detail by BET, photoelectrochemical analysis, Mott-Schottky, and VB-XPS test. The combined results indicated that the positions of the conduction band are the dominant factors for the photocatalytic performance of tantalum-based Dion-Jacobson layered perovskites with n = 2 and 3. This work sheds new light on the field of layered perovskites as efficient photocatalysts.