Metal Nanoclusters Research Articles

Tandem Nitrate-to-Ammonia Conversion on Atomically Precise Silver Nanocluster/MXene Electrocatalyst.

Electrocatalytic reduction of nitrate (NO3 RR) to synthesize ammonia (NH3 ) provides a competitive manner for carbon neutrality and decentralized NH3 synthesis. Atomically precise nanoclusters, as an advantageous platform for investigating the NO3 RR mechanisms and actual active sites, remain largely underexplored due to the poor stability. Herein, we report a (NH4 )9 [Ag9 (mba)9 ] nanoclusters (Ag9 NCs) loaded on Ti3 C2 MXene (Ag9 /MXene) for highly efficient NO3 RR performance towards ambient NH3 synthesis with improved stability in neutral medium. The composite structure of MXene and Ag9 NCs enables a tandem catalysis process for nitrate reduction, significantly increasing the selectivity and FE of NH3 . Besides, compared with individual Ag9 NCs, Ag9 /MXene has better stability with the current density performed no decay after 108 hours of reaction. This work provides a strategy for improving the catalytic activity and stability of atomically precise metal NCs, expanding the mechanism research and application of metal NCs.

Tandem Nitrate‐to‐Ammonia Conversion on Atomically Precise Silver Nanocluster/MXene Electrocatalyst

AbstractElectrocatalytic reduction of nitrate (NO3RR) to synthesize ammonia (NH3) provides a competitive manner for carbon neutrality and decentralized NH3 synthesis. Atomically precise nanoclusters, as an advantageous platform for investigating the NO3RR mechanisms and actual active sites, remain largely underexplored due to the poor stability. Herein, we report a (NH4)9[Ag9(mba)9] nanoclusters (Ag9 NCs) loaded on Ti3C2 MXene (Ag9/MXene) for highly efficient NO3RR performance towards ambient NH3 synthesis with improved stability in neutral medium. The composite structure of MXene and Ag9 NCs enables a tandem catalysis process for nitrate reduction, significantly increasing the selectivity and FE of NH3. Besides, compared with individual Ag9 NCs, Ag9/MXene has better stability with the current density performed no decay after 108 hours of reaction. This work provides a strategy for improving the catalytic activity and stability of atomically precise metal NCs, expanding the mechanism research and application of metal NCs.

Hydride-Containing Pt-doped Cu-rich Nanoclusters: Synthesis, Structure, and Electrocatalytic Hydrogen Evolution.

A structurally precise hydride-containing Pt-doped Cu-rich nanocluster [PtH2 Cu14 {S2 P(Oi Pr)2 }6 (CCPh)6 ] (1) has been synthesized. It consists of a bicapped icosahedral Cu14 cage that encapsulates a linear PtH2 unit. Upon the addition of two equivalents of CF3 COOH to 1, two hydrido clusters are isolated. These clusters are [PtHCu11 {S2 P(Oi Pr)2 }6 (CCPh)4 ] (2), which is a vertex-missing Cu11 cuboctahedron encaging a PtH moiety, and [PtH2 Cu11 {S2 P(Oi Pr)2 }6 (CCPh)3 ] (3), a distorted 3,3,4,4,4-pentacapped trigonal prismatic Cu11 cage enclosing a PtH2 unit. The electronic structure of 2, analyzed by Density Functional Theory, is a 2e superatom. The electrocatalytic activities of 1-3 for hydrogen evolution reaction (HER) were compared. Notably, Cluster 2 exhibited an exceptionally excellent HER activity within metal nanoclusters, with an onset potential of -0.03 V (at 10 mA cm-2 ), a Tafel slope of 39 mV dec-1 , and consistent HER activity throughout 3000 cycles in 0.5 M H2 SO4 . Our study suggests that the accessible central Pt site plays a crucial role in the remarkable HER activity and may provide valuable insights for establishing correlations between catalyst structure and HER activity.

Electrostatic-Driven Self-Assembly of Janus-like Monolayer-Protected Metal Nanoclusters.

The generation of controlled microstructures of functionalized nanoparticles has been a crucial challenge in nanoscience and nanotechnology. Efforts have been made to tune ligand charge states that can affect the aggregation propensity and modulate the self-assembled structures. In this work, we modeled zwitterionic Janus-like monolayer ligand-protected metal nanoclusters (J-MPCs) and studied their self-assembly using atomistic molecular dynamics and on-the-fly probability-based enhanced sampling simulations. The oppositely charged ligand functionalization on two hemispheres of a J-MPC elicits asymmetric solvation, primarily driven by distinctive hydrogen bonding patterns in the ligand-solvent interactions. Electrostatic interactions between the oppositely charged residues in J-MPCs guide the formation of one-dimensional and ring-like self-assembled superstructures with molecular dipoles oriented in specific patterns. The pertinent atomistic insights into the intermolecular interactions governing the self-assembled structures of zwitterionic J-MPCs obtained from this work can be used to design a general strategy to create tunable microstructures of charged MPCs.

Crafting Insulating Polymer Mediated and Atomically Precise Metal Nanoclusters Photosensitized Photosystems Towards Solar Water Oxidization.

Atomically precise metal nanoclusters (NCs) have been deemed as a new generation of metal nanomaterials because of their characteristic atomic stacking fashion, quantum confinement effect, and multitude of active sites. The discrete molecular-like energy band structure of metal NCs endows them with photosensitization capability for light harvesting and conversion. However, applications of metal NCs in photoelectrocatalysis are limited by the ultrafast charge recombination and unfavorable stability, impeding the construction of metal NC-based photosystems. In this work, we elaborately crafted multilayered metal oxide (MO)/(metal NCs/insulating polymer)n photoanodes by a facile layer-by-layer (LbL) assembly technique. In these well-defined heterostructured photoanodes, glutathione (GSH)-wrapped metal NCs (Agx@GSH, Ag9@GSH6, Ag16@GSH9, and Ag31@GSH19) and an insulating poly(allylamine hydrochloride) (PAH) layer are alternately deposited on the MO substrate in a highly ordered integration mode. We found that photoelectrons of metal NCs can be tunneled into the MO substrate via the intermediate ultrathin insulating polymer layer by stimulating the tandem charge transfer route, thus facilitating charge separation and boosting photoelectrochemical water oxidation performances. Our work would open a new frontier for judiciously regulating directional charge transport over atomically precise metal NCs for solar-to-hydrogen conversion.

Thermally activated delayed fluorescence Au‐Ag‐oxo nanoclusters: From photoluminescence to radioluminescence

AbstractThermally activated delayed fluorescence (TADF) materials have numerous applications in energy conversion and luminescent imaging. However, they are typically achieved as metal‐organic complexes or pure organic molecules. Herein, we report the largest Au‐Ag‐oxo nanoclusters to date, Au18Ag26(R1COO)12(R2C≡C)24(μ4‐O)2(μ3‐O)2 (Au18Ag26, where R1 = CH3‐, Ph‐, CHOPh‐ or CF3Ph‐; R2 = Ph‐ or FPh‐). These nanoclusters exhibit exceptional TADF properties, including a small S1‐T1 energy gap of 55.5 meV, a high absolute photoluminescence quantum yield of 86.7%, and a microseconds TADF decay time of 1.6 μs at ambient temperature. Meanwhile, Au18Ag26 shows outstanding stability against oxygen quenching and ambient conditions. Atomic level analysis reveals the strong π⋯π and C‐H⋯π interactions from the aromatic alkynyl ligands and the enhancement of metal‐oxygen‐metal interactions by centrally coordinated O2−. Modeling of the electronic structure shows spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital, which promote charge transfer from the ligand shell, predominantly carboxylate ligands, to O2−‐embedded metal core. Furthermore, TADF Au‐Ag‐oxo nanoclusters exhibit promising radioluminescence properties, which we demonstrate for X‐ray imaging. Our work paves the way for the design of TADF materials based on large metal nanoclusters for light‐emission and radioluminescence applications.

Multimodal Golden DNA Superstructures (GDSs) for Highly Efficient Photothermal Immunotherapy.

DNA-templated metallization has emerged as an efficient strategy for creating nanoscale-metal DNA hybrid structures with a desirable conformation and function. Despite the potential of DNA-metal hybrids, their use as combinatory therapeutic agents has rarely been examined. Herein, we present a simple approach for fabricating a multipurpose DNA superstructure that serves as an efficient photoimmunotherapy agent. Specifically, we adsorb and locally concentrate Au ions onto DNA superstructures through induced local reduction, resulting in the formation of Au nanoclusters. The mechanical and optical properties of these metallic nanoclusters can be rationally controlled by their conformations and metal ions. The resulting golden DNA superstructures (GDSs) exhibit significant photothermal effects that induce cancer cell apoptosis. When sequence-specific immunostimulatory effects of DNA are combined, GDSs provide a synergistic effect to eradicate cancer and inhibit metastasis, demonstrating potential as a combinatory therapeutic agent for tumor treatment. Altogether, the DNA superstructure-templated metal casting system offers promising materials for future biomedical applications.

Parasitism in Metal Nanoclusters: A Case Study of (AuAg)25·(AuAg)27.

Studying the interactions of atomically precise metal nanoclusters in their assembly systems is of great significance in the nanomaterial research field, which has attracted increasing interest in the last few decades. Herein, we report the cocrystallization of two oppositely charged atomically precise metal nanoclusters in one unit cell: [Au1Ag24(SR)18]- ((AuAg)25 for short) and [AuxAg27-x(Dppf)4(SR)9]2+ (x = 10-12; (AuAg)27 for short) with a 1:1 ratio. (AuAg)27 could maintain its structure in the presence of (AuAg)25, whether in the crystalline and the solution state, while the metastable (AuAg)27 component underwent a spontaneous transformation to (AuAg)16(Dppf)2(SR)8 after dissociating the (AuAg)25 component from this cocrystal, demonstrating the "parasitism" relationship of the (AuAg)27 component over (AuAg)25 in this dual-cluster system. This work enriches the family of cluster-based assemblies and elucidates the delicate relationship between nanoparticles of cocrystals.

Metal Clusters Confined in Chiral Zeolitic Imidazolate Framework for Circularly Polarized-Luminescence Inks.

Chiroptical activities arising in nanoclusters (NCs) are emerging as one of the most dynamic areas of modern science. However, devising an overarching strategy that is capable of concurrently enhancing the photoluminescence (PL) and circularly polarized luminescence (CPL) of metal NCs remains a formidable challenge. Herein, gold and silver nanoclusters (AuNCs, AgNCs) are endowed with CPL, for the first time, through a universal host-guest approach─centered around perturbing a chiral microenvironment within chiral hosts, simultaneously enhancing emissions. Remarkably, the photoluminescence quantum yield (PLQY) of AuNCs has undergone an increase of over 200 times upon confinement, escalating from 0.05% to 12%, and demonstrates a CPL response. Moreover, a three-dimensional (3D) model termed "NCs@CMOF" featuring CPL activity is created using metal cluster-based assembly inks through the process of 3D printing. This work introduces a potentially straightforward and versatile approach for achieving both PL enhancement and CPL activities in metal clusters.

Enzyme-mimic catalytic activities and biomedical applications of noble metal nanoclusters.

Noble metal (e.g., Au and Ag) nanoclusters (NCs), which exhibit structural complexity and hierarchy comparable to those of natural proteins, have been increasingly pursued in artificial enzyme research. The protein-like structure of metal NCs not only ensures enzyme-mimic catalytic activity, including peroxidase-, catalase-, and superoxide dismutase-mimic activities, but also affords an unprecedented opportunity to correlate the catalytic performance with the cluster structure at the molecular or atomic levels. In this review, we aim to summarize the recent progress in programming and demystify the enzyme-mimic catalytic activity of metal NCs, presenting the state-of-the-art understandings of the structure-property relationship of metal NC-based artificial enzymes. By leveraging on a concise anatomy of the hierarchical structure of noble metal NCs, we manage to unravel the structural origin of the catalytic performance of metal NCs. Noteworthily, it has been proven that the surface ligands and metal-ligand interface of metal NCs are instrumental in influencing enzyme-mimic catalytic activities. In addition to the structure-property correlation, we also discuss the synthetic methodologies feasible to tailoring the cluster structure at the atomic level. Prior to the closure of this review with our perspectives in noble metal NC-based artificial enzymes, we also exemplify the biomedical applications based on the enzyme-mimic catalysis of metal NCs with the theranostics of kidney injury, brain inflammation, and tumors. The fundamental and methodological advancements delineated in this review would be conducive to further development of metal NCs as an alternative family of artificial enzymes.

Applications of metal nanoclusters supported on the two-dimensional material graphene in electrocatalytic carbon dioxide reduction.

Metal nanoclusters (MNCs) have been demonstrated to exhibit superior catalytic performance compared to single nanoparticles. This is attributed to their quantized electronic structure, unique geometrical stacking and abundant active sites. While the exposed metal atoms can markedly enhance the efficiency of catalysis, unfortunately, MNCs are susceptible to agglomeration, which impairs their catalytic activity and stability. Graphene is a two-dimensional material consisting of a single atomic layer formed by the hybridization of the s and p orbitals of carbon atoms. It exhibits stable physical and chemical properties and has an easily controllable structure, making it an ideal carrier for MNCs. When metal nanoclusters (MNCs) are loaded on a graphene substrate, the MNCs can form a stable binding site on the graphene substrate. Furthermore, the construction of a defective structure on the graphene substrate enables the formation of robust interactions between the metal atoms of the MNCs and the substrate, facilitating the rapid establishment of electron conduction pathways and markedly enhancing the electrocatalytic performance. This paper presents a review of the applications of metal nanoclusters supported on graphene skeletons in the field of the electrocatalytic CO2 reduction reaction (CO2RR). Firstly, we briefly introduce the reaction mechanism of the CO2RR, then we systematically discuss the synthesis strategies, properties and applications of metal nanoclusters in electrocatalytic carbon dioxide reduction from both experimental and theoretical perspectives, and lastly, we discuss the opportunities and challenges of metal nanocluster catalysts supported on carbon materials.

Design of Ultra-High Density Archival Storage Memory with Nanoprobe and Patterned Oxygenated Amorphous Carbon with Metal Nanoclusters

Recent prosperity of artificial intelligence is undoubtedly making global data increase at a phenomenal rate. This obviously poses more stringent requirements on current storage devices. Unfortunately, considerable effort is only devoted to the development of on-chip storage device, while off-chip storage technology, particularly for archival storage device, remains slowly progressed. To further innovate the archival storage device, and thus revive its market, we here proposed a novel concept of an archival storage device based on scanning nanoprobe and oxygenated amorphous carbon having metal nanoclusters. A comprehensive numerical model was developed to mimic the write and readout performances of such archival storage device. It was found that the introduction of metal nanoclusters induced much stronger electric field inside the amorphous carbon layer than the case without metal nanoclusters. This beneficially facilitated the growth of conductive filament along metal nanoclusters, and the feasibility of using the proposed device to achieve an areal density of terabit per-square-inch area density, a write energy of picojoule energy per bit, and a switching speed of tens of nanoseconds, was demonstrated.

Atomically precise metal nanoclusters combine with MXene towards solar CO2 conversion.

Atomically precise metal nanoclusters (NCs) have been deemed a new generation of photosensitizers for light harvesting on account of their quantum confinement effect, peculiar atom-stacking mode, and enriched catalytic active sites. Nonetheless, to date, precise charge modulation over metal NCs has still been challenging considering their ultra-short carrier lifetime and poor stability. In this work, we conceptually demonstrate the integration of metal NCs with MXene in transition metal chalcogenide (TMC) photosystems via a progressive, exquisite, and elegant interface design to trigger tunable, precise and high-efficiency charge motion over metal NCs, stimulating a directional carrier transport pathway. In this customized ternary heterostructured photosystem, metal NCs function as light-harvesting antennas, MXene serves as a terminal electron reservoir, and the TMC substrate provides suitable energy level alignment for retracting photocarriers of metal NCs, giving rise to a spatial cascade charge transport route and markedly boosting charge separation efficiency. The interface configuration and energy level alignment engineering synergistically contribute to the considerably enhanced visible-light-driven photocatalytic CO2-to-CO reduction performance of the metal NCs/TMCs/MXene heterostructure. The intermediate active species during the photocatalytic CO2 reduction are unambiguously determined, based on which the photocatalytic mechanism is elucidated. Our work will provide an inspiring idea to bridge the gap between atomically precise metal NCs and MXene in terms of controllable charge migration for solar-to-fuel conversion.

Fluorescent metal nanoclusters: prospects for photoinduced electron transfer and energy harvesting.

Research on noble metal nanoclusters (MNCs) (elements with filled electron d-bands) is progressing forward because of the extensive and extraordinary chemical, optical, and physical properties of these materials. Because of the ultrasmall size of the MNCs (typically within 1-3 nm), they can be applied in areas of nearly all possible scientific domains. The greatest advantage of MNCs is the tunability that can be imposed, not only on their structures, but also on their chemical, physical, and biological properties. Nowadays, MNCs are very effectively used as energy donors and acceptors under suitable conditions and hence act as energy harvesters in solar cells, semiconductors, and biomarkers. In addition, ultrafast photoinduced electron transfer (PET) can be practised using MNCs under various circumstances. Herein, we have focused on the energy harvesting phenomena of Au-, Ag-, and Cu-based MNCs and elaborated on different ways to apply them.

Exceptional stability of ultrasmall cubic copper metal nanoclusters - a molecular dynamics study.

The fabrication of shape-selective coinage metal nanoclusters (MNCs) has promising applications due to their exceptional physical and chemical molecule-like properties. However, the stability of the specific geometry of the nanoclusters, such as their cubic shapes, is unclear and has been unraveled by assessing the nanoclusters' interactions with different environments. In this work, we investigate the morphological stability of cubic structured, coinage metal nanoclusters of varying sizes ranging from 14 to 1099 atoms. The impact of solvent environments like water and the presence of ionic liquids (IL) on the stabilization of the MNCs were assessed using molecular dynamics (MD) simulations. In general, smaller MNCs composed of less than 256 atoms encountered structural distortion easily compared to the larger ones, which preserved their cubic morphology with minimal surface aberrations in water. However, in the presence of 4M 1-butyl-1,1,1-trimethyl ammonium methane sulfonate [N1114][C1SO3] IL solution, the overall cubic shape of the MNCs was successfully preserved. Strikingly, it is observed that in contrast to the noble MNCs like Au and Ag, the cubic morphology for Cu MNCs with sizes less than 256 atoms exhibited significant stability even in the absence of IL.

DNA-templated fluorescent metal nanoclusters and their illuminating applications.

After the discovery of DNA during the mid-20th century, a multitude of novel methodologies have surfaced which exploit DNA for its various properties. One such recently developed application of DNA is as a template in metal nanocluster formation. In the early years of the new millennium, a group of researchers found that DNA can be adopted as a template for the binding of metal nanoparticles that ultimately form nanoclusters. Three metal nanoclusters have been studied so far, including silver, gold, and copper, which have a plethora of biological applications. This review focuses on the synthesis, mechanisms, and novel applications of DNA-templated metal nanoclusters, including the therapies that have employed them for their wide range of fluorescent properties, and the future perspectives related to their development by exploiting machine learning algorithms and molecular dynamics simulation studies.

Recent progress in atomically precise metal nanoclusters for photocatalytic application.

Photocatalysis is a widely recognized green and sustainable technology that can harness inexhaustible solar energy to carry out chemical reactions, offering the opportunity to mitigate environmental issues and the energy crisis. Photocatalysts with wide spectral response and rapid charge transfer capability are crucial for highly efficient photocatalytic activity. Atomically precise metal nanoclusters (NCs), an emerging atomic-level material, have attracted great interests owing to their ultrasmall size, unique atomic stacking, abundant surface active sites, and quantum confinement effect. In particular, the molecule-like discrete electronic energy level endows them with small-band-gap semiconductor behavior, which allows for photoexcitation in order to generate electrons and holes to participate in the photoredox reaction. In addition, metal NCs exhibit strong light-harvesting ability in the wide spectral UV-near IR region, and the diversity of optical absorption properties can be precisely regulated by the composition and structure. These merits make metal NCs ideal candidates for photocatalysis. In this review, the recent advances in atomically-precise metal NCs for photocatalytic application are summarized, including photocatalytic water splitting, CO2 reduction, organic transformation, photoelectrocatalytic reactions, N2 fixation and H2O2 production. In addition, the strategy for promoting photostability, charge transfer and separation efficiency of metal NCs is highlighted. Finally, a perspective on the challenges and opportunities for NCs-based photocatalysts is provided.

Role of transition metals in coinage metal nanoclusters for the remediation of toxic dyes in aqueous systems.

A difficult issue in chemistry and materials science is to create metal compounds with well-defined components. Metal nanoclusters, particularly those of coinage groups (Cu, Ag, and Au), have received considerable research interest in recent years owing to the availability of atomic-level precision via joint experimental and theoretical methods, thus revealing the mechanisms in diverse nano-catalysts and functional materials. The textile sector significantly contributes to wastewater containing pollutants such as dyes and chemical substances. Textile and fabric manufacturing account for about 7 × 105 tons of wastewater annually. Approximately one thousand tons of dyes used in textile processing and finishing has been recorded as being discharged into natural streams and water bodies. Owing to the widespread environmental concerns, research has been conducted to develop absorbents that are capable of removing contaminants and heavy metals from water bodies using low-cost technology. Considering this idea, we reviewed coinage metal nanoclusters for azo and cationic dye degradation. Fluorometric and colorimetric techniques are used for dye degradation using coinage metal nanoclusters. Few reports are available on dye degradation using silver nanoclusters; and some of them are discussed in detailed herein to demonstrate the synergistic effect of gold and silver in dye degradation. Mostly, the Rhodamine B dye is degraded using coinage metals. Silver nanoclusters take less time for degradation than gold and copper nanoclusters. Mostly, H2O2 is used for degradation in gold nanoclusters. Still, all coinage metal nanoclusters have been used for the degradation due to suitable HOMO-LUMO gap, and the adsorption of a dye onto the surface of the catalyst results in the exchange of electrons and holes, which leads to the oxidation and reduction of the adsorbed dye molecule. Compared to other coinage metal nanoclusters, Ag/g-C3N4 nanoclusters displayed an excellent degradation rate constant with the dye Rhodamine B (0.0332 min-1). The behavior of doping transition metals in coinage metal nanoclusters is also reviewed herein. In addition, we discuss the mechanistic grounds for degradation, the fate of metal nanoclusters, anti-bacterial activity of nanoclusters, toxicity of dyes, and sensing of dyes.

N-Heterocyclic carbene-functionalized metal nanoparticles and nanoclusters for nanocatalysis.

N-Heterocyclic carbenes (NHCs) have recently emerged as a popular ligand for the functionalization of metal nanoparticles and atomically precise metal clusters. The strong electron-donating properties of NHCs and robust NHC-metal covalent bonding endow metal nanostructures with improved stability and enhanced catalytic performances. In this review, we focus on NHC-coordinated metal nanoparticles and nanoclusters for the electrochemical CO2 reduction reaction (eCO2RR), selective hydrogenation of unsaturated compounds, and asymmetrical catalytic reactions. We discuss the underlying factors that may be at play in determining the improved activity of NHC-functionalized metals and address a few promising perspectives of NHC functionalization for new and better catalytic metal nanostructures.

Extrinsically conducting MOFs: guest-promoted enhancement of electrical conductivity, thin film fabrication and applications.

Conductive metal-organic frameworks are of current interest in chemical science because of their applications in chemiresistive sensing, electrochemical energy storage, electrocatalysis, etc. Different strategies have been employed to design conductive frameworks. In this review, we discuss the influence of different types of guest species incorporated within the pores or channels of metal-organic frameworks (MOFs) and porous coordination polymers (PCPs) to generate charge transfer pathways and modulate their electrical conductivity. We have classified dopants or guest species into three different categories: (i) metal-based dopants, (ii) molecule and molecular entities and (iii) organic conducting polymers. Different types of metal ions, metal nano-clusters and metal oxides have been used to enhance electrical conductivity in MOFs. Metal ions and metal nano-clusters depend on the hopping process for efficient charge transfer whereas metal-oxides show charge transport through the metal-oxygen pathway. Several types of molecules or molecular entities ranging from neutral TCNQ, I2, and fullerene to ionic methyl viologen, organometallic like nickelcarborane, etc. have been used. In these cases, the charge transfer process varies with the guest species. When organic conducting polymers are the guest, the charge transport occurs through the polymer chains, mostly based on extended π-conjugation. Here we provide a comprehensive and critical review of these strategies to add electrical conductivity to the, in most cases, otherwise insulating MOFs and PCPs. We point out the guest encapsulation process, the geometry and structure of the resulting host-guest complex, the host-guest interactions and the charge transport mechanism for each case. We also present the methods for thin film fabrication of conducting MOFs (both, liquid-phase and gas-phase based methods) and their most relevant applications like electrocatalysis, sensing, charge storage, photoconductivity, photocatalysis,… We end this review with the main obstacles and challenges to be faced and the appealing perspectives of these 21st century materials.