Highly efficient visible light-induced O₂ generation by self-assembled nanohybrids of inorganic nanosheets and polyoxometalate nanoclusters

Tailoring functional two-dimensional nanohybrids: A comprehensive approach for enhancing photocatalytic remediation

Photocatalysis is gaining prominence as a viable alternative to conventional biohazard treatment technologies. Two-dimensional (2D) nanomaterials have become crucial for fabricating novel photocatalysts due to their nanosheet architectures, large surface areas, and remarkable physicochemical properties. Furthermore, a variety of applications are possible with 2D nanomaterials, either in combination with other functional nanoparticles or by utilizing their inherent properties. Henceforth, the review commences its exploration into the synthesis of these materials, delving into their inherent properties and assessing their biocompatibility. Subsequently, an overview of mechanisms involved in the photocatalytic degradation of pollutants and the processes related to antimicrobial action is presented. As an integral part of our review, we conduct a systematic analysis of existing challenges and various types of 2D nanohybrid materials tailored for applications in the photocatalytic degradation of contaminants and the inactivation of pathogens through photocatalysis. This investigation will aid to contribute to the formulation of decision-making criteria and design principles for the next generation of 2D nanohybrid materials. Additionally, it is crucial to emphasize that further research is imperative for advancing our understanding of 2D nanohybrid materials.

Synthesis of polyoxometalate-pillared Zn-Cr layered double hydroxides for photocatalytic CO2 reduction and H2O oxidation

Polyoxometalate (POM)-pillared Zn-Cr layered double hydroxides (LDHs) exhibited high photocatalytic activities in CO2 reduction and H2O oxidation reactions. For CO2 reduction in pure water, the CO production was 1.17 μmol g-1 after a 24 h reaction. For O2 evolution in NaIO3 solution, the O2 production reached 148.1 μmol g-1 after a 6 hour reaction. A mechanism study indicated that the electron transfer from Zn-Cr LDHs to POMs (SiW12O404-) promoted photocatalytic activities.

2D-2D lattice engineering route for intimately coupled nanohybrids of layered double hydroxide and potassium hexaniobate: Chemiresistive SO2 sensor

2D-2D lattice engineering route is used to synthesize intimately coupled nanohybrids of layered double hydroxide (LDH) and potassium hexaniobate. The 2D-2D lattice engineering route is based on the electrostatically derived self-assembly of delaminated zinc-chromium-layered double hydroxide (ZC-LDH) nanosheets and potassium hexaniobate (HNb) nanosheets (ZCNb nanohybrids). The 2D-2D lattice-engineered ZCNb nanohybrids display expanded surface area, mesoporous anchored nanosheets network morphology, and intimate coupling between nanosheets. The 2D-2D lattice engineered ZCNb nanohybrids are used for the low temperature operated gas sensor. The ZCNb nanohybrids display outstanding selectivity for the SO₂, with the high response of 61.5% compared to pristine ZC-LDH (28.08%) and potassium niobate (8%) at 150 °C. Moreover, ZCNb sensors demonstrate superior response and recovery periods of 6 and 167 s at 150 °C, respectively. This result underscores the exceptional functionality of the ZCNb nanohybrids as efficient SO₂ sensors. Moreover, these findings vividly demonstrate that the 2D-2D lattice-engineered ZCNb nanohybrids are quite effective not only in improving the gas sensor activity but also in developing of new type of intimately coupled mesoporous LDH-metal-oxide based hybrid materials.

Effect of cobalt doping on photocatalytic water splitting activity of NiTi-layered double hydroxide

Cobalt-doping a NiTi layered double hydroxide affords CoNiTi-LDH with smaller plate sizes and a higher degree of order, which allows the band gap to shrink from 2.7 eV to 2.4 eV. CoNiTi-LDH is active for both water oxidation and reduction.

Transition metal-based layered double hydroxides for photo(electro)chemical water splitting: a mini review

The conversion of solar energy into usable chemical fuels, such as hydrogen gas, via photo(electro)chemical water splitting is a promising approach for creating a carbon neutral energy ecosystem. The deployment of this technology industrially and at scale requires photoelectrodes that are highly active, cost-effective, and stable. To create these new photoelectrodes, transition metal-based electrocatalysts have been proposed as potential cocatalysts for improving the performance of water splitting catalysts. Layered double hydroxides (LDHs) are a class of clays with brucite like layers and intercalated anions. Transition metal-based LDHs are increasingly popular in the field of photo(electro)chemical water splitting due to their unique physicochemical properties. This article aims to review recent advances in transition metal-based LDHs for photo(electro)chemical water splitting. This article provides a brief overview of the research in a format approachable for the general scientific audience. Specifically, this review examines the following areas: (i) routes for synthesis of transition metal-based LDHs, (ii) recent developments in transition metal-based LDHs for photo(electro)chemical water splitting, and (iii) an overview of the structure-property relationships therein.

Precious Metal-Free Photocatalytic Water Oxidation by a Layered Double Hydroxide-Prussian Blue Analogue Hybrid Assembly

The development of earth-abundant photocatalytic assemblies has been one of the bottlenecks for the advancement of scalable water splitting cells. In this study, a ZnCr layered double hydroxide and a CoFe Prussian blue analogue are combined to afford an earth-abundant photocatalytic assembly involving a visible light-absorbing semiconductor (SC) and a water oxidation catalyst (WOC). Compared to bare ZnCr-LDH, the SC-WOC hybrid assembly exhibits a threefold enhancement in photocatalytic activity, which is maintained for 6 h under photocatalytic conditions at pH 7. The band energy diagram was extracted from optical and electrochemical studies to elucidate the origin of the enhanced photocatalytic performance. This study marks a straightforward pathway to develop low-cost and precious metal-free assemblies for visible light-driven water oxidation.

Solvothermal synthesis and structural characterization of three polyoxotitanium-organic acid clusters

Three new titanium oxo-clusters Ti₄O₂(OⁱPr)₁₀(OOCPhMe)₂ (I), Ti₆O₄(OEt)₈(OOCPhMe)₈ (II) and Ti₆O₆(OEt)₆(OOCCHPh₂)₆ (III) were obtained by easy one-step solvothermal reactions of titanium(iv) isopropoxide, alcohols and carboxylic acids. The three compounds were characterized by single-crystal and powder X-ray diffraction, TGA/DSC, optical and electron microscopy, and FTIR and NMR spectroscopy. X-ray powder diffraction and spectroscopy confirmed the purity of the compounds. Structural analysis indicates that in all compounds the titanium(iv) ions are six-coordinated (distorted octahedra). (I) is a tetranuclear complex containing a Ti₄(μ₄-O)(μ₂-O) core, which is linked by two (μ₂-OOCPhMe), four (μ₂-OⁱPr) and six OⁱPr ligands. (II) and (III) are hexanuclear complexes with different cores, respectively Ti₆(μ₃-O)₂(μ₂-O)₂ and Ti₆(μ₃-O)₆. The coordination sphere of the Ti atoms is filled by eight (μ₂-OOCPhMe), two (μ₂-OEt) and six OEt in (II) and six (μ₂-OOCHPh₂) and six OEt in (III). Different steric hindrance of substituents attached to the carboxyl group or different concentrations lead to three main different cluster geometries with two ligands. The tetranuclear and the hexanuclear clusters were obtained with the OOCPhMe ligand, while the hexagonal prism cluster was obtained with the OOCCHPh₂ ligand. Hirshfeld surface calculations indicated that the packing is driven by C–O⋯H–C weak hydrogen bonds. The clusters can be used as molecular models of organic molecules bonded to titania surface, used in organic photovoltaic (dye sensitized solar cells) or other optoelectronic applications.

Crystal structures of three novel titanium oxo-clusters with different cores and ligands obtained by an easy and convenient solvothermal method.

Cr3+ substituted Zn-Al layered double hydroxides as UV-Vis light photocatalysts for NO gas removal from the urban environment

The ZnAl-CO₃, ZnAlCr-CO₃ and ZnCr-CO₃ LDH samples were studied as De-NOx photocatalysts in this work. Samples without Cr and increasing the presence of Cr³⁺ in the LDH framework in the 0.06, 0.15 and 0.3 Cr/Zn ratio were prepared by co-precipitation method, all of them constituted by pure LDH phase. The increase of chromium content in the LDH framework leads to lower crystallinity and higher specific surface area in the samples. Moreover, the CrO₆ octahedron centres expand the photo-activity from UV to Visible light and assist to decrease the recombination rate of the electrons and holes. The favourable textural, optical and electronic properties of Cr-containing LDH samples explain the good NO removal efficiency (55%) and outstanding selectivity (90%) found for the analysed De-NOx process.

Free-Standing CoO-POM Janus-like Ultrathin Nanosheets

A single-step solution-based strategy is used to obtain 2D Janus-like free-standing ultrathin nanosheets build from two structurally unrelated species, that is, polyoxomolybdate (POM) and CoO. A controlled 2D-to-1D morphological transition was achieved by judiciously adjusting the solvent choice. These POM-CoO heterostructures can behave as an ideal catalyst for the epoxidation of styrene. Benefiting from their amphiphilic nature, these 2D POM-CoO nanosheets have also been used as surfactant to emulsify immiscible solvents. It is anticipated that structurally diverse polyoxometalates will offer promise as design elements for variety of structurally and compositionally tunable van der Waals integrated heteromaterials having a broad range applications.

2D Oxide Nanomaterials to Address the Energy Transition and Catalysis

2D oxide nanomaterials constitute a broad range of materials, with a wide array of current and potential applications, particularly in the fields of energy storage and catalysis for sustainable energy production. Despite the many similarities in structure, composition, and synthetic methods and uses, the current literature on layered oxides is diverse and disconnected. A number of reviews can be found in the literature, but they are mostly focused on one of the particular subclasses of 2D oxides. This review attempts to bridge the knowledge gap between individual layered oxide types by summarizing recent developments in all important 2D oxide systems including supported ultrathin oxide films, layered clays and double hydroxides, layered perovskites, and novel 2D-zeolite-based materials. Particular attention is paid to the underlying similarities and differences between the various materials, and the subsequent challenges faced by each research community. The potential of layered oxides toward future applications is critically evaluated, especially in the areas of electrocatalysis and photocatalysis, biomass conversion, and fine chemical synthesis. Attention is also paid to corresponding novel 3D materials that can be obtained via sophisticated engineering of 2D oxides.

Two-Dimensional Layered Hydroxide Nanoporous Nanohybrids Pillared with Zero-Dimensional Polyoxovanadate Nanoclusters for Enhanced Water Oxidation Catalysis

The oxygen-evolution reaction (OER) is critical in electrochemical water splitting and requires an efficient, sustainable, and cheap catalyst for successful practical applications. A common development strategy for OER catalysts is to search for facile routes for the synthesis of new catalytic materials with optimized chemical compositions and structures. Here, nickel hydroxide Ni(OH)₂ 2D nanosheets pillared with 0D polyoxovanadate (POV) nanoclusters as an OER catalyst that can operate in alkaline media are reported. The intercalation of POV nanoclusters into Ni(OH)₂ induces the formation of a nanoporous layer-by-layer stacking architecture of 2D Ni(OH)₂ nanosheets and 0D POV with a tunable chemical composition. The nanohybrid catalysts remarkably enhance the OER activity of pristine Ni(OH)₂ . The present findings demonstrate that the intercalation of 0D POV nanoclusters into Ni(OH)₂ is effective for improving water oxidation catalysis and represents a potential method to synthesize novel, porous hydroxide-based nanohybrid materials with superior electrochemical activities.

Fabrication of a Co(OH)2/ZnCr LDH "p-n" Heterojunction Photocatalyst with Enhanced Separation of Charge Carriers for Efficient Visible-Light-Driven H2 and O2 Evolution

Photocatalytic generation of H₂ and O₂ by water splitting remains a great challenge for clean and sustainable energy. Taking into the consideration promising heterojunction photocatalysts, analogous energy issues have been mitigated to a meaningful extent. Herein, we have architectured a highly efficient bifunctional heterojunction material, i.e., p-type Co(OH)₂ platelets with an n-type ZnCr layered double hydroxide (LDH) by an ultrasonication method. Primarily, the Mott-Schottky measurements confirmed the n- and p-type semiconductive properties of LDH and CH material, respectively, with the construction of a p-n heterojunction. The high resolution transmission electron microscopy results suggest that surface modification of ZnCr LDH by Co(OH)₂ hexagonal platelets could form a fabulous p-n interfacial region that significantly decreases the energy barrier for O₂ and H₂ production by effectively separating and transporting photoinduced charge carriers, leading to enhanced photoreactivity. A deep investigation into the mechanism shows that a 30 wt % Co(OH)₂-modified ZnCr LDH sample liberates maximum H₂ and O₂ production in 2 h, i.e., 1115 and 560 μmol, with apparent conversion efficiencies of H₂ and O₂ evolution of 13.12% and 6.25%, respectively. Remarkable photocatalytic activity with energetic charge pair transfer capability was illustrated by electrochemical impedance spectroscopy, linear sweep voltammetry, and photoluminescence spectra. The present study clearly suggests that low-cost Co(OH)₂ platelets are the most crucial semiconductors to provide a new p-n heterojunction photocatalyst for photocatalytic H₂ and O₂ production on the platform of ZnCr LDH.

Intercalative hybridization of layered double hydroxide nanocrystals with mesoporous g-C3N4 for enhancing visible light-induced H2 production efficiency

Highly efficient visible-light-active hybrid photocatalysts with enhanced electronic coupling are synthesized via the intercalative hybridization of Zn–Cr-LDH nanocrystals with mesoporous g-C₃N₄.

Synergistic effects of plasmon induced Ag@Ag3VO4/ZnCr LDH ternary heterostructures towards visible light responsive O2 evolution and phenol oxidation reactions

The SPR effect of monodisperse Ag nanoparticles in Ag@Ag₃VO₄/ZnCr LDH heterostructures exhibits high photocatalytic activity towards evolution of O₂ and oxidation of phenol.

High-Throughput Preparation of New Photoactive Nanocomposites

New low-cost photoactive hybrid materials based on organic luminescent molecules inserted into hydrotalcite (layered double hydroxides; LDH) were produced, which exploit the high-throughput liquid-assisted grinding (LAG) method. These materials are conceived for applications in dye-sensitized solar cells (DSSCs) as a co-absorbers and in silicon photovoltaic (PV) panels to improve their efficiency as they are able to emit where PV modules show the maximum efficiency. A molecule that shows a large Stokes' shift was designed, synthesized, and intercalated into LDH. Two dyes already used in DSSCs were also intercalated to produce two new nanocomposites. LDH intercalation allows the stability of organic dyes to be improved and their direct use in polymer melt blending. The prepared nanocomposites absorb sunlight from UV to visible and emit from blue to near-IR and thus can be exploited for light-energy management. Finally one nanocomposite was dispersed by melt blending into a poly(methyl methacrylate)-block-poly(n-butyl acrylate) copolymer to obtain a photoactive film.

Highly Stable Nanocontainer of APTES-Anchored Layered Titanate Nanosheet for Reliable Protection/Recovery of Nucleic Acid

A universal technology for the encapsulative protection of unstable anionic species by highly stable layered metal oxide has been developed via the surface modification of a metal oxide nanosheet. The surface anchoring of (3-aminopropyl)triethoxysilane (APTES) on exfoliated titanate nanosheet yields a novel cationic metal oxide nanosheet, which can be universally used for the hybridization with various biological and inorganic anions. The encapsulation of deoxyribonucleic acid (DNA) in the cationic APTES-anchored titanate lattice makes possible the reliable long-term protection of DNA against enzymatic, chemical, and UV-vis light corrosions. The encapsulated DNA can be easily released from the titanate lattice via sonication, underscoring the functionality of the cationic APTES-anchored titanate nanosheet as a stable nanocontainer for DNA. The APTES-anchored titanate nanosheet can be also used as an efficient CO2 adsorbent and a versatile host material for various inorganic anions like polyoxometalates, leading to the synthesis of novel intercalative nanohybrids with unexplored properties and useful functionalities.

An Effective Way to Optimize the Functionality of Graphene-Based Nanocomposite: Use of the Colloidal Mixture of Graphene and Inorganic Nanosheets

The best electrode performance of metal oxide-graphene nanocomposite material for lithium secondary batteries can be achieved by using the colloidal mixture of layered CoO2 and graphene nanosheets as a precursor. The intervention of layered CoO2 nanosheets in-between graphene nanosheets is fairly effective in optimizing the pore and composite structures of the Co3O4-graphene nanocomposite and also in enhancing its electrochemical activity via the depression of interaction between graphene nanosheets. The resulting CoO2 nanosheet-incorporated nanocomposites show much greater discharge capacity of ~1750 mAhg(-1) with better cyclability and rate characteristics than does CoO2-free Co3O4-graphene nanocomposite (~1100 mAhg(-1)). The huge discharge capacity of the present nanocomposite is the largest one among the reported data of cobalt oxide-graphene nanocomposite. Such a remarkable enhancement of electrode performance upon the addition of inorganic nanosheet is also observed for Mn3O4-graphene nanocomposite. The improvement of electrode performance upon the incorporation of inorganic nanosheet is attributable to an improved Li(+) ion diffusion, an enhanced mixing between metal oxide and graphene, and the prevention of electrode agglomeration. The present experimental findings underscore an efficient and universal role of the colloidal mixture of graphene and redoxable metal oxide nanosheets as a precursor for improving the electrode functionality of graphene-based nanocomposites.

Highly efficient photocatalytic hydrogen generation by incorporating CdS into ZnCr-layered double hydroxide interlayer

Incorporating CdS nanoparticles into the interlayer of ZnCr–LDH nanosheets led to the formation of CdS-pillared ZnCr–LDH nanohybrid, which exhibited superior photocatalytic hydrogen-generation performance from water splitting.

An unprecedented (3,4,24)-connected heteropolyoxozincate organic framework as heterogeneous crystalline Lewis acid catalyst for biodiesel production

A novel 3D hexadecanuclear heteropolyoxozincate organic framework, IFMC-200, has been successfully synthesized based on a late transition metal-oxygen cluster. IFMC-200 not only represents the first example of (3,4,24)-connected framework but also contains the first 24-connected single metal cluster in a crystal structure. It exhibits superior thermal stability, good water-stability, and even insensitivity to the existence of acid and base within a certain range of pH values. Furthermore, it performs as a heterogeneous crystalline Lewis acid catalyst with good activity for the conversion of long-chain fatty acids rather than short-chain ones, and high recycling efficiency for esterification reaction of fatty acids with alcohols to produce biodiesel.