Download PDF
Perspective  |  Open Access  |  25 Apr 2023

Emerging microporous materials as novel templates for quantum dots

Views: 723 |  Downloads: 611 |  Cited:  0
Microstructures 2023;3:2023021.
10.20517/microstructures.2023.08 |  © The Author(s) 2023.
Author Information
Article Notes
Cite This Article

Abstract

Microporous structures have attracted significant attention in recent years. In particular, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have received considerable attention due to their tailorable structures that offer a wide range of choices in terms of molecular building blocks. Due to their high tunability, these materials are considered as ideal host matrices for templating and encapsulating guest materials, particularly quantum dots (QDs). QDs are investigated heavily for various applications such as light-emitting diodes (LED), biosensors, catalysts, and solar cells due to their unique properties from the quantum confinement effect. However, one of the drawbacks of QDs is their tendency to aggregate and exhibit low stability due to their small size and kinetic trapping in nanoparticle form. This perspective highlights promising approaches to enhance the performance and stability of QDs by using microporous materials as an encapsulation layer. Additionally, potential mitigating strategies are discussed to overcome current challenges and improve the practicality of QDs embedded in microporous nanocomposites.

Keywords

Metal-organic frameworks, covalent organic frameworks, zeolites, microstructures, QD encapsulation

INTRODUCTION

Quantum dots (QDs) are nanocrystals that behave similarly to an atom as a result of quantum physics. When the size of nanomaterials reaches a level comparable to or even smaller than the Bohr radius, the materials will experience the quantum confinement effect. This phenomenon relates to the exciton and electronic energy level, which is continuous in bulk but becomes discrete in nanocrystals as the electron movement is confined to a specific energy level. An exciton is a bound state between an electron hole in valence band (VB) and an electron through Coulomb interaction. When a photon interacts with a semiconductor material and the energy of the photon exceeds or equals the bandgap (Eg), an electron in the VB is excited to the conduction band (CB), resulting in the formation of a positively charged hole referred to as an electron hole. As the excited electron and electron hole are confined within a limited space, more energy is required to excite them, which results in size-dependent band gaps and light emission. When a material is confined in one dimension, it forms a quantum well structure. Similarly, two-dimensional confinement results in a quantum wire, while three-dimensional confinement leads to a quantum dot, which is a material that is confined in all three dimensions[1-8]. This energy state results in unique characteristics, including long fluorescence lifetime, narrow and symmetrical photoluminescence emission, wide absorption, and high photoluminescence quantum yield (PLQY). Furthermore, the photoluminescence emission band gap can be tuned by varying the size of QDs. Traditionally, combinations of 0D core-shell structure materials and group 12-16 elements have been investigated as promising quantum dot materials, such as ZnSe, ZnO, InP, InAs, and CdSe[9-11]. Recently, organic-inorganic metal halide perovskites have been noticed as promising QD materials due to the recent successful development of photovoltaic (PV) cells, LEDs, and sensors based on perovskite QDs[12-17]. However, in light of increasing concerns about the potential toxicity of some materials, there is growing interest in developing alternatives that are more biocompatible and environmentally friendly. For instance, carbon quantum dots (CQDs) and graphene quantum dots (GQDs) are emerging as promising candidates[18-20]. Graphene Quantum Dots (GQDs) exhibit remarkable size-dependent luminescence properties that are attributed to their quantum confinement and edge effects. These properties make GQDs highly attractive for optoelectronic and photodetector applications, including LEDs and electroluminescent devices. However, GQDs often suffer from reduced fluorescence, which hampers their ability to function as optoelectronic devices due to phase separation and agglomeration in organic or inorganic solvents. Furthermore, the non-stoichiometric nature of GQDs makes it particularly challenging to achieve precise control over their chemical structure, size, shape, and structural defects, which are directly related to their optoelectronic properties. Therefore, there have been numerous attempts to incorporate GQDs into matrices such as polymer films or mesoporous solids in order to control the size of the nanoparticles and stabilise them. However, since many of the current fabrication methods are complicated and difficult to control, there is a need to investigate more reproducible and simpler methods to fully utilise the great fluorescence properties of GQDs[21-25].

Despite the promising potential of quantum dots (QDs) in various applications and the significant progress achieved in material sciences, several challenges continue to hinder their widespread implementation. These challenges include issues such as agglomeration, precise size control, and operational stability, which demand further research and development to mitigate effectively. Generally, QDs show a strong tendency to aggregate into larger particles due to their high surface energy, which leads to the loss of their unique characteristics. Several recent studies have tried to mitigate the limitations of QDs through solvent engineering, surface passivation using semiconducting film, encapsulation with polymers, or embedment of QDs within porous nanomaterials[26-29]. However, most of these strategies require complex fabrication processes, and it remains difficult to control the outcomes, which may reduce the efficacy of these methods.

Traditional nanomaterials with microporosity, such as mesoporous silica, zeolites, and porous carbon, have been investigated for various applications, including drug delivery, biosensing, separation, and catalysts[30,31]. Despite their great advantages, i.e., high surface area, tunable porosity, and biocompatibility, they tend to have limited chemical tunability. This limitation inspired scientists to develop microporous functional materials that can be readily tailored. In recent years, covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) have received tremendous attention from the materials science community as they can form tailored microstructures with metal-organic linker coordination bonds or covalent bonds[32-34]. In addition, the material itself can be chemically active and biocompatible, as some types of COFs are studied for cancer diagnosis and therapy[35-37]. Thanks to their high surface area, tunable structure, biocompatibility and diverse topology, these materials have been recognised as a promising functioning host matrix to mitigate some of the issues that quantum dots had. In view of this prosperous research area, we have outlined the quantum dots encapsulation in these emerging microporous materials and their potential applications. We believe that this Perspective will guide the potential future research directions in emerging QDs embedment in functional porous materials. The purpose of this Perspective is not to provide a comprehensive review and summary of these composite materials, but instead to give a brief history of the field, a summary of current progress, and, more importantly, highlight and discuss unsolved questions that are worth further investigation.

A HISTORICAL OVERVIEW OF QUANTUM DOTS WITHIN MICROPOROUS STRUCTURE

Quantum dots (QDs) are nanocrystals that exhibit quantum confinement effects due to their small size, leading to unique optical and electronic properties. These properties arise from the confinement of electrons and holes in a three-dimensional space, resulting in a behaviour similar to an atom because of quantum physics. It is generally agreed that the first QDs were discovered by Russian physicist Alexei Ekimov in the early 1980s. He synthesised copper chloride (CuCl2) and cadmium selenide (CdSe) nanocrystals embedded in a glass matrix and observed a gradient of colours in the fluorescence emission spectra, which was dependent on the size of the nanocrystals[38]. Ever since their discovery, much of the research on QDs has focused on improving size control to reduce size variation, producing high-quality nanocrystals, and achieving tunable fluorescence colours. Recently, significant improvements have been made in the quality and tunability of QDs, as well as in their photovoltaic applications such as in solar cells. However, QDs have a tendency to aggregate into larger particles due to their high surface energy, which can lead to the loss of their unique characteristics and efficiency. To mitigate this drawback, there have been attempts to fabricate QDs within microporous matrices in order to not only control the size of the QDs but also provide a protective layer that prevents their aggregation and loss of unique characteristics.

Mesoporous silica, zeolites, and porous carbon have conventionally been studied as templates for the growth of QDs. Among these, zeolites have received extensive attention due to their unique tunable characteristics and excellent stability. Zeolites are crystalline aluminosilicate polymers with an inorganic framework consisting of SiO4 and AlO4 tetrahedra. They possess a three-dimensional nanometre-sized structure with uniform windows, channels, and cavities, and have been extensively studied. While this family of materials may not be considered as “emerging” compared to other types of microporous materials, they can still offer valuable insights into regulating the structure, interface, and chemistry between the microporous template and guest QDs. Therefore, this Perspective will first provide a brief summary of early studies on using zeolite templates for encapsulating QDs. The unique properties of zeolites that combine features of both ionic and covalent crystals arise from the covalent network structures formed by sharing oxygen atoms between SiO4 and AlO4 tetrahedra, which depends on the Si/Al ratio[39,40]. Materials exhibiting a ratio greater than 3 are categorised as high silica zeolites or zeolite Y. These high silica zeolites have good physical and chemical stability as well as hydrophobicity[41]. When the ratio is less than 3, it is called zeolite X or low-silica zeolites. These zeolites display high ion exchange capacity, which makes them good candidates as ion exchange agents[42]. Furthermore, pore size can also be tuned by changing the ratio and number of oxygen atoms connections to tetrahedra structure, or more directly through different synthetic conditions such as the use of surfactants. Their three-dimensional porous structure, along with their tunability and uniformity, make these materials good candidates as host scaffolds for QDs.

An interesting topic in the field of synthesizing QDs in zeolites is the use of cadmium sulphide (CdS) QDs in zeolite Y. While this concept was established and researched in the 1980s, it continues to provide new insights for the next generation of researchers. CdS quantum dots are one of the most studied II-IV binary semiconductor materials due to their narrow band gap of 2.42 eV[43]. However, the performance of the material highly depends on its size and three-dimensional structure. Thus, much research effort has been dedicated to avoiding aggregation, size control and stabilisation of QD structure. Herron et al. introduced the idea of cadmium sulphide quantum dots (CdS QDs) in zeolite Y to improve their stability and optoelectronic properties[44]. In this work, CdS semiconductor clusters were synthesized using an aqueous solution process which involves cadmium ion exchange followed by hydrogen sulphide (H2S) gas flowing to create CdS cluster within the zeolite pores. It was reported that during synthesis, QDs are formed in sodalite cages (5 Å) instead of supercage pores (13 Å) of zeolite Y structure through a percolative process [Figure 1A][45]. However, a recent study showed that CdS QDs exist in supercages rather than sodalite cages. The author found that the migrated Cd2+ ions in sodalite cage during drying process diffused back to supercage in later reaction process with H2S to form QDs, showing the highly dynamic nature of the QD even in their condensed phase. The isolated CdS nanoclusters form interconnection through supercage window in [CdS]4 unit, as shown in Figure 1B[46]. This example demonstrates the templated growth methodology to form QDs within the micropores, and it also clearly shows that the QDs in the template are still preserving their dynamic properties.

Emerging microporous materials as novel templates for quantum dots

Figure 1. (A) Illustration of the zeolite-Y incorporating one (CdS)4 unit in each sodalite cage and (B) the zeolite-Y incorporating a larger CdS QD in each supercage. Reprinted with permission[46]. Copyright © 2007 American Chemical Society.

Another important guest material is lead sulphide (PbS) QD which has a narrow band gap and size-dependent optical properties due to its large exciton Bohr radius which makes it a good candidate for third-order nonlinear optical (3NLO) applications[47-49]. High 3NLO responses are enabled by smaller-size QDs and increased material density in the same matrix volume. However, the increased population of QDs in a small volume introduces aggregations and reduces the efficacy of the composite. Kim et al. demonstrated a significant increase in the third-order nonlinear optical (3NLO) activity of PbS quantum dots (QDs) by embedding them within the nanopores of zeolite Y[50]. This work also highlighted the interplay between the host and guest materials. By replacing of H+ cation in the zeolite Y matrix with cations of different sizes, such as NH4+, Li+, Na+, K+ and Rb+, the stability and 3NLO activity of the composite were noticeably enhanced[50]. Considering it is difficult to tailor the chemical functionality or structure properties of zeolites based on guest materials, like other evolving porous materials, metal-organic frameworks (MOFs) or covalent organic frameworks (COFs), systematic replacement of zeolite’s counter cations to guest material is one of the viable options to control pore volume, framework donor strength, cation acceptor strength, and electric field strength. This work shows a promising new approach to improve 3NLO activity within the zeolite matrix and the potential guest QDs.

In recent years, CsPbX3 (X = Cl, Br, or I) perovskites QDs are receiving great attention as PVs or LEDs as they have a narrow emission band and high PLQY[51,52]. They can be easily processed in liquid form, making them particularly suitable for templated growth within zeolites[53]. Kim et al. used zeolite X as a host matrix for Na4Cs6PbBr4 QDs, benefiting from its hydrophilic nature and relatively high aluminium content, which resulted in an increased number of extra framework cations (Na+) that effectively enhanced the stability of the quantum dots when compared to zeolite Y[54]. This work was initially designed to create CsPbBr3 QDs within zeolite X based on the previous research that encapsulates CsPbX3 QDs within zeolite Y matrix. However, the author found out that the Cs+ cations interact with counter cations (Na+), forming new types of QDs, Na4Cs6PbBr4. Those QDs are placed within the supercage of zeolite structure and interconnected through the window, as shown in Figure 2. The composite showed a much narrower light emission band and improved stability in water compared with unprotected CsPbBr3 QDs, due to uniform distribution and interconnection of QDs within supercage of zeolite X structure[54]. This work suggests that counter cations of zeolite structures are important to improve stability and sensitivity while also forming more direct interaction with guest material to create new types of QDs. The discovery of this interaction opens a whole set of new research directions for the selection of QDs and cations of zeolite structure.

Emerging microporous materials as novel templates for quantum dots

Figure 2. (A) Schematics of the framework structure of zeolite X. Near the center of each line segment is an oxygen atom. The nonequivalent oxygen atoms are indicated by the numbers 1-4. The common extraframework cation positions are labeled with Roman numerals. One of the four entrances to the supercage is highlighted in red. (B) The [Na4Cs6PbBr4]8+ quantum dot (QD) in a supercage of zeolite X. (C) Stereoview of the [Na4Cs6PbBr4]8+ QD. (D) Stereoview of the [Na4Cs6PbBr4]8+ QD in a Pb, Br, H, Cs, Na-X supercage. This structure may be viewed as a series of concentric spheres of alternating charge (48 O2- ions of the zeolite framework, 10 Cs+ and Na+ ions, and 4 Br- ions) with a Pb2+ ion at its center. The two water molecules (at O5 that bond to each Cs+ ion at Cs31 are not shown. Reprinted with permission[54] © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

QUANTUM DOTS IN COVALENT ORGANIC FRAMEWORKS

Compared to zeolites, COFs are porous materials formed through chemical bonds between organic-organic moieties. These building blocks consist of organic molecules that are covalently linked to form a porous crystalline structure. The resulting chemical bonds between organic building blocks create a flexible and tunable framework structure that enables precise control over the size, shape, and chemical properties of the pores and channels within the material. This flexibility and tunability make COFs highly versatile and suitable for a wide range of applications, such as gas storage, separation, catalysis, and sensing. Additionally, zeolites are composed of rigid inorganic frameworks, which limits their flexibility and tunability, though they are still widely used in applications such as catalysis and adsorption.

Considering the dynamic interaction observed between zeolites and QDs, it is anticipated that COFs, in addition to their inherent structure, can provide further tunability to improve the performance of the resulting composites. The dynamic nature of COFs presents both opportunities and challenges for the generation of QDs within their pores. Obtaining a well-ordered three-dimensional crystalline COF structure and preserving its integrity during QD synthesis are among the most critical challenges that need to be overcome in the development of QD-COF composites. COFs can form two- or three-dimensional structures through covalent bonds between organic monomers composed of light elements such as C, H, N, B, and O[55,56]. In natural systems, covalent and noncovalent interactions play crucial roles in the formation of pre-designed protein structures. For example, DNA and RNA utilise covalent bonds to regulate the sequence of their primary-order chain structure, while noncovalent interactions control their high-order morphology. Although biological polymer systems already use covalent interactions to form high-order structures, synthesising precise microporous organic coordination polymer structures was once considered particularly challenging until Yaghi’s team reported the first COFs in 2005[55]. To obtain well-ordered crystalline three-dimensional organic structures held together by strong covalent bonds between each block, it is crucial to carefully design the covalent and noncovalent interaction sites in the primary structure. In the absence of a proper guiding system, the organic chains may grow randomly on a two-dimensional plane, resulting in either an amorphous structure or a packed one-dimensional (linear) crystalline structure[57]. To address this issue, researchers have been studying different types of linkers, organic blocks, and fabrication conditions to tailor the COFs with diverse structures, as depicted in Figure 3[58]. These explorations opened new opportunities for COFs to be considered as porous host materials due to their high specific surface area, tailorable pores and structure, and low density.

Emerging microporous materials as novel templates for quantum dots

Figure 3. Dependency of pore size and column π-density of 2D COFs on topologies. Reprinted with permission[58]. Copyright © 2020 American Chemical Society.

Mn-ZnS QDs are considered as one of the promising materials for chemical contamination fluorescent detectors as ZnS has low toxicity and a wide band gap of 3.7 eV[59]. Furthermore, it has been broadly studied for metal ions, small molecules, and biopolymers detections. However, pure Mn-ZnS QDs have the limitation of low stability in a complex medium as the selectivity and sensitivity of the material reduce significantly over time[60]. To overcome these issues, molecularly imprinted polymers (MIPs) methods have been investigated. MIP is a procedure to generate specifically tailored cavities in polymers that works like antibody-antigen systems in our bodies to select precisely aimed molecules in the matrix[61]. This hybrid material showed great selectivity from shaped polymer and high sensitivity from QD material. However, achieving a uniform distribution and increasing the active material volume density remain challenging issues to address. Zhang et al. reported a new hybrid composite consisting of Mn-ZnS QDs embedded in TpPa-1 COFs with molecularly imprinted polymer (MIP) to improve the detection limit and stability of the composite in water[62]. This technique was further developed to fabricate fluorescent probes for ferulic acid with high selectivity and sensitivity, as demonstrated in Figure 4[63]. The fabricated composite demonstrated improved stability at room temperature, as well as a high photoluminescence quantum yield (PLQY) of 37%. In these applications, the COF serves not only as a passive protective framework but also as a platform for achieving even distribution and minimising aggregation of QDs.

Emerging microporous materials as novel templates for quantum dots

Figure 4. A schematic representation of the synthesis of molecularly imprinted polymers (MIPs) based on quantum dot-grafted covalent organic frameworks (QD-grafted COFs) for optosensing of ferulic acid (FA). Tetraethyl orthosilicate (TEOS) and (3-aminopropyl) triethoxysilane (APTES) are used as cross-linker and functional monomer, respectively, in MIP fabrication process. Reprinted with permission[63].

Carbon quantum dots (CQDs) have been studied widely as a new type of fluorescent nanomaterials primarily due to their favourable characteristics such as environmental friendliness, functionalisability, excellent stability, biocompatibility, solubility, and low toxicity. These properties have rendered CQDs an ideal candidate for various applications such as sensing cellular copper, glucose, nucleic acids, and cancer detection and treatment. As a result, the investigation and exploration of CQDs continue to grow significantly[64,65]. Despite significant advantages, the limited size control, uniformity, and low quantum yield of carbon quantum dots present major challenges. To address these issues, researchers have attempted to improve synthesis methods using various techniques such as solvent engineering, electrochemical fabrication, and laser ablation, as well as fabricating hybrid composites that include encapsulating CQDs with polymers and embedding them within porous matrices. Recent progress in encapsulating carbon quantum dots (CQDs) involves surface functionalization by coating them with amphiphilic monomers or polymers. Amphiphilic molecules contain both hydrophilic and hydrophobic components, which allows them to interact with both water and the CQDs surface. This method can provide a protective layer around CQDs which can improve their stability, reduce aggregation, and provide other desirable properties such as solubility in different solvents[66-68]. Encapsulating CQDs within micro to mesoporous matrices such as mesoporous silica is a common approach to improve their stability and efficacy. Mesoporous silica, in particular, has attracted significant interest due to its large specific surface area, low toxicity, and good biocompatibility.

Recently, covalent organic frameworks have emerged as a promising alternative for encapsulating CQDs in microporous structures, offering advantages such as high stability, excellent control over pore size and shape, and the ability to tune the chemical and physical properties of the framework for specific applications. The presence of a large number of conjugated structures for both CQDs and COFs enables a unique opportunity to engineer their interfacial properties. Generally, CQDs have a size between 3 and 5 nm, which can be considered as a big molecular block within a typical COFs structure. Chen et al. formed, for the first time, two COFs consisting of carbon quantum dots which were generated through the Schiff base reactions with CQDs and phenylenediamine (pPDA) and BODIPY with two amino groups, as shown in Figure 5[69]. In this study, solvothermal methods were utilised to synthesise spherical CQDs with a size of ca. 5 nm. The synthesised CQDs were then dispersed in ethyl alcohol along with pPDA (p-phenylenediamine), and in a mixed solvent of ethyl alcohol and acetic acid with BODIPY, to form novel types of carbon dot-based covalent organic frameworks (CCOFs).

Emerging microporous materials as novel templates for quantum dots

Figure 5. Schematic illustration of the synthesis of CCOF-1@PEG and CCOF-2@PEG and the application of CCOF-2@PEG for photodynamic therapy as reactive oxygen species (ROS) Carbon dots (CDs) and phenylenediamine (pPDA) and BODIPY are forming CCOF1 and CCOF2 respectively. Reprinted with permission[69] © 2020 Wiley-VCH GmbH

These newly synthesised CCOFs exhibit a bulk, spherical nanoparticle morphology, ranging in size from 200 to 500 nanometres. These structures are composed of carbon quantum dots, which are covalently bonded to organic ligands. Subsequently, the surfaces of these CCOFs are modified with polyethylene glycol (PEG) to further enhance their stability and dispersibility in aqueous environments. Following modification, the composite demonstrates no signs of aggregation for up to 24 h when exposed to a 10% fetal bovine serum (FBS) solution in water. By contrast, unmodified CCOFs exhibit aggregation under the same conditions. In addition, blood compatibility was evaluated by administering a dose of 10 mg/kg of modified CCOFs to mice, demonstrating no adverse effects on biosafety at that concentration. Furthermore, under green LED laser irradiation, the composite exhibited marked inhibition of tumour growth and size reduction. This carbon quantum dot-based covalent organic framework exhibits highly desirable characteristics, including excellent physiological stability, biocompatibility, and remarkable reactivity in oxygen generation, positioning them as a promising contender for cancer treatment[69].

QUANTUM DOTS IN METAL-ORGANIC FRAMEWORKS

Compared to zeolites and COFs, MOFs are a highly versatile family of microporous materials with a hybrid organic-inorganic continuous porous structure. They are formed by the coordination of metal ions with organic ligands, creating a three-dimensional network of pores and channels with high surface area and tunable properties. This material was introduced by Tomic in 1965 as a porous coordination framework. More than 80,000 types of MOFs have been reported so far, due to the wide selection of metal ions and organic ligands used to form a structure [Figure 6][70-73]. The presence of inorganic and organic coordination is a distinguishing factor of MOFs compared to covalent organic COFs, which are composed solely of light organic elements such as carbon, nitrogen, hydrogen, boron, and oxygen. High surface area, uniform structure, flexible choice of metal and organic ligands, structure tunability, and chemical functionality make this material unique and ideal for various applications such as separation, catalysis, sensing, and as a protective host matrix. One of the most extensively studied topics in the field of MOFs is hybrid nanocomposite materials. Due to the strong coordination between metal nodes and organic ligands, MOFs exhibit good chemical resistance to a wide range of solvents, including polar, nonpolar, and apolar solvents. Furthermore, porous structures can be tailored to a given requirement. These advantageous characteristics make this material a strong candidate as the protective host matrix for hybrid nanocomposites[74-77].

Emerging microporous materials as novel templates for quantum dots

Figure 6. Representations of MOF structures and the corresponding node and linker constituents. Reprinted with permission[73,74]. Copyright © 2016 American Chemical Society.

Organic-inorganic metal halide perovskites have been a trending subject in material science as a semiconducting light-harvesting material for various applications due to their outstanding properties, such as high light absorption coefficient, high defect tolerances and long charge carrier diffusion distances[78,79]. However, relatively low stability to moisture, heat and most common polar solvents limits the applicable devices and shortens the life expectancy of the application[80-82]. There have been various attempts to mitigate this major drawback of perovskite materials, such as compositional and interfacial engineering, surface passivation, and encapsulation[83]. Especially in the encapsulation process, the efficacy of the active material can often be reduced. Therefore, using a porous structure is crucial to minimise the unwanted sacrifices. In this sense, MOFs are strong candidates as a protective layer since they can provide a hydrophobic surface and a uniformly tailored porous structure. A cesium lead bromide (CsPbBr3), an inorganic halide perovskite, has garnered interest as a viable photocatalyst for CO2 reduction. However, it shares similar limitations with other perovskites. Recently, researchers have made significant progress by employing zeolitic imidazolate frameworks (ZIFs), a subfamily of MOFs, as a host matrix for CsPbBr3 quantum dots. Figure 7 illustrates the successful coating of CsPbBr3 QDs with ZIFs through a “building a bottle around a ship” approach. The mild synthesis conditions of MOFs enable the fabrication of QD-MOF composites in this manner, providing reliable protection. The coated composite exhibits an improved CO2 reduction efficiency due to its superior capturing ability and charge separation efficiency, as well as enhanced stability against moisture, compared to naked CsPbBr3. However, this method may pose challenges in controlling QD particle size as the size is no longer restricted by the inherent pore structure of the template. Moreover, the synthesis solvent may cause partial dissolution/decomposition of QDs, which can adversely affect the overall efficiency. Thus, it is crucial to exercise caution in regulating the final solvent removal and nucleation process[84].

Emerging microporous materials as novel templates for quantum dots

Figure 7. (A) Schematic illustration of the fabrication process and CO2 photoreduction process of CsPbBr3/ZIFs. (B and C) Low- and high-magnification TEM images of CsPbBr3@ZIF-8. The inset of (C) is the high-resolution image of a single CsPbBr3 QD marked with a red circle. (D) High-angle annular dark-field STEM image and elemental mapping of CsPbBr3@ZIF-8. Scale bar: 50 nm. (E) TEM image of CsPbBr3@ZIF-67. Reprinted with permission[84]. Copyright © 2018 American Chemical Society.

Typically, the pores in MOFs are considered too small to accommodate QDs, as most reported MOFs have microporous structures with pore diameters less than 2 nm. While this size range is suitable for the adsorption and separation of small molecules, such as gases, it is not ideal for QDs which are typically between 2 and 10 nm in size[85,86]. Synthesising QDs within the MOF cavity offers significant advantages in controlling QD crystal size through MOF pores and limiting aggregation during fabrication. However, the primary challenge lies in fabricating large-pore MOFs, as they can result in pore interpenetration and blockage. A meticulous design of the pore structure is also crucial, with an ideal cavity having a narrow entry to suppress the dissolution or dissociation of the encapsulated QDs[87]. To address this limitation, various efforts have been made to modify the pore sizes of MOFs to accommodate larger molecules such as QDs. One such approach involves introducing larger functional groups into the organic ligands or metal nodes, thereby expanding the pore size. Another approach is to employ post-synthesis modification techniques, including solvent or ligand exchange, to adjust the pore size of the MOF. These strategies have demonstrated promising outcomes in enlarging the pore size of MOFs, facilitating the integration of larger guest molecules like QDs[88-90].

In a recent advance, Qiao et al. reported the successful fabrication of CsPbBr3 quantum dots within the PCN-33 MOF pores through a sequential deposition method[91]. PCN-333(Fe) possesses an extraordinary hierarchically porous structure with mesoporous cages ranging from ca. 4 to 5 nm and microporous cages with a diameter of around 1 nm, as well as excellent chemical stability. Its large mesoporous cages enable the accommodation of perovskite nanoparticles, while its microporous cages facilitate the diffusion of reactants for catalysis. In this study, PbBr2 was positioned within the PCN-333(Fe) cavity, followed by the diffusion of CsBr into the pores to form CsPbBr3 QDs within the mesoporous cage[91]. This composite showed green fluorescence under ultraviolet (UV) light, which confirms the formation of CsPbBr3 QDs. Also, the resultant shows excellent stability, oxygen reduction, and evolving catalytic reaction in an aprotic medium. As these photoelectrochemical characteristics are desired for photocathodes in lithium-oxygen batteries, the material was tested as a cathode without any carbon support. The round-trip efficiency of the battery under illumination was 92.7%, which was comparably higher than that of pure CsPbBr3 (82.8%) or PCN-333(Fe) (85.2%). Furthermore, it improved stability noticeably compared with pure CsPbBr3 as the MOF provides the protective aspect. This work shows the potential compatibility of perovskite QDs and MOFs and also offers new promising directions and insights for photo-rechargeable batteries [Figure 8][91].

Emerging microporous materials as novel templates for quantum dots

Figure 8. Schematic illustration of the Preparation of PCN-333(Fe) and CsPbBr3@PCN-333(Fe) Composite CsPbBr3@PCN-333(Fe) can be used as a photoelectric cathode material for light-assisted Li-O2 batteries. Reprinted with permission[91]. Copyright © 2021 American Chemical Society

So far, most research works on MOFs have focused on crystalline forms. However, limited processability and deprived interfacial bonding between host and guest materials have motivated the synthesis of non-crystalline structures. Recent studies showed that some of the MOFs, especially some of ZIFs, can form amorphous structures via temperature-induced amorphisation through melting upon heating followed by a fast cooling (quenching) process at ambient pressure[92,93]. These ZIF glasses form a continuous random network similar to the amorphous structure of silica glass. Also, these emerging new types of glasses show structural diversity and unique properties compared to inorganic, organic and metallic glasses[94]. Recently, our group further developed this idea and successfully fabricated embedded perovskites within the ZIF glass matrix. This nanocomposite not only showed significantly improved photoluminescence under UV light in ambient conditions, but the stability also improved noticeably in most solvents. Figure 9 shows how CsPbI3 perovskite is encapsulated within the ZIF-62 glass matrix after the sintering process and the phase distribution based on ADF and SED-STEM spectroscopy[95].

Emerging microporous materials as novel templates for quantum dots

Figure 9. Phase distribution for the (CsPbI3)0.25(agZIF-62)0.75 composite fabricated with 300 °C sintering. (A) ADF-STEM image, (B) SED-STEM mapping, and (C) CsPbI3 crystal phase classification results for (CsPbI3)0.25(agZIF-62)0.75 composite. (D) Volume rendering of tomographic reconstruction of (CsPbI3)0.25(agZIF-62)0.75 and a single cross-sectional plane extracted from the volume. Color-coded arrows indicate the regions where electron diffraction data were collected. Scale bars, (A-D) 250 nm. Reprinted with permission[95]. Copyright © 2021 American Chemical Society

SUMMARY AND OUTLOOK

In conclusion, the embedment of various quantum dots into microporous materials has shown enormous potential for applications due to its ability to enhance long-term stability, reduce aggregation, improve efficiency, increase active material density, provide protective layers, and achieve uniform distribution. However, some of the methods are complicated and challenging to control during the fabrication process, which makes upscaling difficult. Although most of the studies are still in their early stages, especially QDs in COFs and MOFs, they have proved significant functionalities and potential. Based on above mentioned strategies, we hope this Perspective has highlighted the promising future research directions related to QDs in microporous structure.

(1) Biocompatible nanocomposite of QDs within microporous frameworks: The demand for biocompatible quantum dots and microporous templates is rapidly increasing for a wide range of applications, including disease detection, drug delivery, molecule detection, and cancer treatment. Currently, most of the research on biocompatible QDs is focused on surface engineering, including surface organic ligand exchange, polymer encapsulation and conjugation of biomolecules on the surface of QDs. However, those approaches still experience several issues such as size uniformity, aggregation, and stability in the biological environment. Furthermore, although there are numerous ongoing explorations for biocompatible and biodegradable MOFs and COFs for biomedicine applications, there have been limited investigations to combine biocompatible framework matrixes and QDs. Thus, by intermarriage of two biocompatible materials, QDs and specifically tailored flameworks matrix, can improve the selectivity of QDs and enable biological targeting of small molecules and antigens, as well as providing uniformity and stability to the composite.

(2) MOF glasses: one of the most recent and significant progress in porous materials is the development of MOF glasses. MOF glasses are new types of glasses that have unique characteristics compared with traditional glass materials. As these emerging materials have only been studied for less than 10 years, there are still many research gaps to investigate. We demonstrated a MOF glass with perovskite QD nanocomposites that greatly improved interfacial connectivity, which MOF crystals have not been able to achieve[95]. Furthermore, MOF glasses can be obtained through mechanical vitrification or direct synthesis as glass[96]. Thus, researching various types of MOFs and QDs hybrid materials as well as alternative fabrication routes of MOFs glass could open more new possibilities for QDs and MOF glasses nanocomposite.

(3) Fundamental study of QDs within microporous structure: Although great efforts have been made to fabricate QDs in microporous structures and improve their efficacy, there are remaining questions for a deeper understanding of the nanocomposite due to its set of rich physiochemical properties and dynamic interaction between two materials. In particular, x-ray-based techniques such as small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) could show the micro to atomic scale structures and interactions of the composite materials. Recently, our group revealed the nanoparticle size, homogeneity, and internal structure behaviour during the liquid phase sintering process of pure MOF to MOF-glass and hybrid nanocomposite with perovskite, and MOF-glass using WAXS and SAXS analysis[92,94]. Furthermore, pair distribution functions (PDFs) from the X-ray diffusion pattern could explain the atomic structure formation, especially for composites with an amorphous matrix, as it can reveal information that X-ray diffraction is unable to obtain.

Terahertz/far-infrared (THz/far-IR) spectroscopy is another powerful technique that should be considered for investigating the dynamic properties of localised features within the composite. When paired with in-situ investigation capabilities, THz/far-IR spectroscopy can effectively identify the dynamic structural behaviour and emerging new chemical bonding between the guest and host materials. Hou et al. successfully integrated this technique to identify halogenation reactions during the melting process of MOF glass[95]. Combined with thermal behaviour analysis and X-ray-based techniques, this spectroscopy can reveal additional dynamic properties of QDs embedded in the microporous matrix and how they interface internally.

Overall, despite the significant and rapid progress in quantum dots (QDs) and tailorable microporous structures, they remain relatively immature technologies that have not yet been fully integrated into real-life applications, leaving significant space for exploration. A deeper and more fundamental understanding of complicated properties, such as interfacial bonding, conductivity, and structural and functional diversity, is expected to unlock new opportunities in the areas of light emission, biomedicine, catalysts, and energy storage.

DECLARATIONS

Authors’ contributions

Conceptual design and manuscript draft: Lee J

Manuscript Revision and Project supervision: Wang L, Hou JW

Availability of data and materials

Not applicable.

Financial support and sponsorship

This research was partially financially supported by the Australian Research Council (ARC) through Future Fellowship, Laureate Fellowship programs (FT210100589 and FL190100139) and an Australian Government Research Training Program (RTP) Scholarship.

Ethical approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Conflicts of interest

All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Copyright

© The Author(s) 2023.

REFERENCES

1. Fujii M, Fujii R, Takada M, Sugimoto H. Silicon quantum dot supraparticles for fluorescence bioimaging. ACS Appl Nano Mater 2020;3:6099-107.

2. Kwon J, Jun SW, Choi SI, et al. FeSe quantum dots for in vivo multiphoton biomedical imaging. Sci Adv 2019;5:eaay0044.

3. Shaik SA, Sengupta S, Varma RS, Gawande MB, Goswami A. Syntheses of N-doped carbon quantum dots (NCQDs) from bioderived precursors: a timely update. ACS Sustain Chem Eng 2021;9:3-49.

4. Sun Y, Zheng S, Liu L, et al. The cost-effective preparation of green fluorescent carbon dots for bioimaging and enhanced intracellular drug delivery. Nanoscale Res Lett 2020;15:55.

5. Cho Y, Soufiani AM, Yun JS, et al. Mixed 3D-2D passivation treatment for mixed-cation lead mixed-halide perovskite solar cells for higher efficiency and better stability. Adv Energy Mater 2018;8:1703392.

6. Cordero F, Craciun F, Trequattrini F, et al. Stability of cubic FAPbI3 from X-ray diffraction, anelastic, and dielectric measurements. J Phys Chem Lett 2019;10:2463-9.

7. Rambabu D, Bhattacharyya S, Singh T, Maji TK. Stabilization of MAPbBr3 perovskite quantum dots on perovskite MOFs by a one-step mechanochemical synthesis. Inorg Chem 2020;59:1436-43.

8. Zhang Y, Zhou Z, Ji F, et al. Trash into treasure: δ-FAPbI3 polymorph stabilized MAPbI3 Perovskite with power conversion efficiency beyond 21. Adv Mater 2018;30:e1707143.

9. Iravani S, Varma RS. Green synthesis, biomedical and biotechnological applications of carbon and graphene quantum dots: a review. Environ Chem Lett 2020;18:703-27.

10. Jouyandeh M, Mousavi Khadem SS, Habibzadeh S, et al. Quantum dots for photocatalysis: synthesis and environmental applications. Green Chem 2021;23:4931-54.

11. Ye B, Jiang R, Yu Z, et al. Pt(111) quantum dot engineered Fe-MOF nanosheet arrays with porous core-shell as an electrocatalyst for efficient overall water splitting. J Catal 2019;380:307-17.

12. Alsalloum AY, Turedi B, Zheng X, et al. Low-temperature crystallization enables 21.9% efficient single-crystal MAPbI3 inverted perovskite solar cells. ACS Energy Lett 2020;5:657-62.

13. Chen Z, Chen Z, Li H, Zhao X, Zhu M, Wang M. Investigation on charge carrier recombination of hybrid organic-inorganic perovskites doped with aggregation-induced emission luminogen under high photon flux excitation. Adv Opt Mater 2018;6:1800221.

14. Masi S, Gualdrón-reyes AF, Mora-seró I. Stabilization of black perovskite phase in FAPbI3 and CsPbI3. ACS Energy Lett 2020;5:1974-85.

15. Wang D, Wright M, Elumalai NK, Uddin A. Stability of perovskite solar cells. Solar Energy Mater Solar Cells 2016;147:255-75.

16. Hou J, Wang Z, Chen P, Chen V, Cheetham AK, Wang L. Intermarriage of halide perovskites and metal-organic framework crystals. Angew Chem Int Ed 2020;59:19434-49.

17. Hao M, Bai Y, Zeiske S, et al. Ligand-assisted cation-exchange engineering for high-efficiency colloidal Cs1-xFAxPbI3 quantum dot solar cells with reduced phase segregation. Nat Energy 2020;5:79-88.

18. Nagaraj G, Mohammed MKA, Shekargoftar M, et al. High-performance perovskite solar cells using the graphene quantum dot-modified SnO2/ZnO photoelectrode. Mater Today Energy 2021;22:100853.

19. Zhao H, Yu X, Li C, et al. Carbon quantum dots modified TiO2 composites for hydrogen production and selective glucose photoreforming. J Energy Chem 2022;64:201-8.

20. Yoo D, Park Y, Cheon B, Park MH. Carbon dots as an effective fluorescent sensing platform for metal ion detection. Nanoscale Res Lett 2019;14:272.

21. Abbas A, Tabish TA, Bull SJ, Lim TM, Phan AN. High yield synthesis of graphene quantum dots from biomass waste as a highly selective probe for Fe3+ sensing. Sci Rep 2020;10:21262.

22. Ganganboina AB, Dega NK, Tran HL, Darmonto W, Doong RA. Application of sulfur-doped graphene quantum dots@gold-carbon nanosphere for electrical pulse-induced impedimetric detection of glioma cells. Biosens Bioelectron 2021;181:113151.

23. Shi Y, Wang Z, Meng T, et al. Red phosphorescent carbon quantum dot organic framework-based electroluminescent light-emitting diodes exceeding 5% external quantum efficiency. J Am Chem Soc 2021;143:18941-51.

24. Wang S, Kang G, Cui F, Zhang Y. Dual-color graphene quantum dots and carbon nanoparticles biosensing platform combined with Exonuclease III-assisted signal amplification for simultaneous detection of multiple DNA targets. Anal Chim Acta 2021;1154:338346.

25. Biswal BP, Shinde DB, Pillai VK, Banerjee R. Stabilization of graphene quantum dots (GQDs) by encapsulation inside zeolitic imidazolate framework nanocrystals for photoluminescence tuning. Nanoscale 2013;5:10556-61.

26. Swarnkar A, Marshall AR, Sanehira EM, et al. Quantum dot-induced phase stabilization of α-CsPbI3 perovskite for high-efficiency photovoltaics. Science 2016;354:92-5.

27. Kar MR, Ray S, Patra BK, Bhaumik S. State of the art and prospects of metal halide perovskite core@shell nanocrystals and nanocomposites. Mater Today Chem 2021;20:100424.

28. Yee PY, Brittman S, Mahadik NA, et al. Cu2-x S/PbS core/shell nanocrystals with improved chemical stability. Chem Mater 2021;33:6685-91.

29. Zhao Y, Xie C, Zhang X, Yang P. CsPbX3 quantum dots embedded in zeolitic imidazolate framework-8 microparticles for bright white light-emitting devices. ACS Appl Nano Mater 2021;4:5478-85.

30. Pham T, Lee B, Kim J, Lee C. Enhancement of CO2 capture by using synthesized nano-zeolite. J Taiwan Inst Chem Eng 2016;64:220-6.

31. Zahmakiran M. Preparation and characterization of LTA-type zeolite framework dispersed ruthenium nanoparticles and their catalytic application in the hydrolytic dehydrogenation of ammonia-borane for efficient hydrogen generation. Mater Sci Eng B 2012;177:606-13.

32. Frentzel-beyme L, Kloß M, Pallach R, et al. Porous purple glass - a cobalt imidazolate glass with accessible porosity from a meltable cobalt imidazolate framework. J Mater Chem A 2019;7:985-90.

33. Hou J, Ríos Gómez ML, Krajnc A, et al. Halogenated metal-organic framework glasses and liquids. J Am Chem Soc 2020;142:3880-90.

34. Fang Q, Gu S, Zheng J, Zhuang Z, Qiu S, Yan Y. 3D microporous base-functionalized covalent organic frameworks for size-selective catalysis. Angew Chem Int Ed 2014;53:2878-82.

35. Bhunia S, Deo KA, Gaharwar AK. 2D covalent organic frameworks for biomedical applications. Adv Funct Mater 2020;30:2002046.

36. Chedid G, Yassin A. Recent trends in covalent and metal organic frameworks for biomedical applications. Nanomaterials 2018;8:916.

37. Feng L, Qian C, Zhao Y. Recent advances in covalent organic framework-based nanosystems for bioimaging and therapeutic applications. ACS Mater Lett 2020;2:1074-92.

38. Ekimov A, Efros A, Onushchenko A. Quantum size effect in semiconductor microcrystals. Solid State Commun 1985;56:921-4.

39. Davis ME. Ordered porous materials for emerging applications. Nature 2002;417:813-21.

40. Kianfar E. Synthesis and characterization of AlPO4/ZSM-5 catalyst for methanol conversion to dimethyl ether. Russ J Appl Chem 2018;91:1711-20.

41. Yin T, Meng X, Jin L, Yang C, Liu N, Shi L. Prepared hydrophobic Y zeolite for adsorbing toluene in humid environment. Microporous Mesoporous Mater 2020;305:110327.

42. Campanile A, Liguori B, Ferone C, Caputo D, Aprea P. Zeolite-based monoliths for water softening by ion exchange/precipitation process. Sci Rep 2022;12:3686.

43. Wang S, Yu J, Zhao P, Guo S, Han S. One-step synthesis of water-soluble CdS quantum dots for silver-ion detection. ACS Omega 2021;6:7139-46.

44. Herron N, Wang Y, Eddy MM, et al. Structure and optical properties of cadmium sulfide superclusters in zeolite hosts. J Am Chem Soc 1989;111:530-40.

45. Moller K, Bein T, Herron N, Mahler W, Wang Y. Encapsulation of lead sulfide molecular clusters into solid matrixes. Structural analysis with X-ray absorption spectroscopy. Inorg Chem 1989;28:2914-9.

46. Jeong NC, Kim HS, Yoon KB. New insights into CdS quantum dots in zeolite-Y. J Phys Chem C 2007;111:10298-312.

47. Yin X, Zhang C, Guo Y, Yang Y, Xing Y, Que W. PbS QD-based photodetectors: future-oriented near-infrared detection technology. J Mater Chem C 2021;9:417-38.

48. Zheng S, Chen J, Johansson EMJ, Zhang X. PbS colloidal quantum dot inks for infrared solar cells. iScience 2020;23:101753.

49. Kim HS, Lee MH, Jeong NC, Lee SM, Rhee BK, Yoon KB. Very high third-order nonlinear optical activities of intrazeolite PbS quantum dots. J Am Chem Soc 2006;128:15070-1.

50. Kim HS, Yoon KB. Increase of third-order nonlinear optical activity of PbS quantum dots in zeolite Y by increasing cation size. J Am Chem Soc 2012;134:2539-42.

51. Liu Y, Li Y, Hu X, et al. Ligands for CsPbBr3 perovskite quantum dots: the stronger the better? Chem Eng J 2023;453:139904.

52. Sun J, Rabouw FT, Yang X, et al. Facile two-step synthesis of all-inorganic perovskite CsPbX3 (X = Cl, Br, and I) Zeolite-Y composite phosphors for potential backlight display application. Adv Funct Mater 2017;27:1704371.

53. Wang HC, Lin SY, Tang AC, et al. Mesoporous silica particles integrated with all-inorganic CsPbBr3 perovskite quantum-dot nanocomposites (MP-PQDs) with high stability and wide color gamut used for backlight display. Angew Chem Int Ed 2016;55:7924-9.

54. Kim JY, Shim KI, Han JW, Joo J, Heo NH, Seff K. Quantum dots of [Na4Cs6PbBr4]8+, water stable in Zeolite X, luminesce sharply in the green. Adv Mater 2020;32:e2001868.

55. Côté AP, Benin AI, Ockwig NW, O’Keeffe M, Matzger AJ, Yaghi OM. Porous, crystalline, covalent organic frameworks. Science 2005;310:1166-70.

56. Ding SY, Wang W. Covalent organic frameworks (COFs): from design to applications. Chem Soc Rev 2013;42:548-68.

57. Wang H, Yang Y, Yuan X, et al. Structure-performance correlation guided applications of covalent organic frameworks. Mater Today 2022;53:106-33.

58. Geng K, He T, Liu R, et al. Covalent organic frameworks: design, synthesis, and functions. Chem Rev 2020;120:8814-933.

59. Binu PJ, Ganesh RC, Muthukumaran S. Crystal structure, energy gap and photoluminescence investigation of Mn2+/Cr3+-doped ZnS nanostructures by precipitation method. J Mater Sci Mater Electron 2021;32:23174-88.

60. Liu Z, Hou J, He Q, Luo X, Huo D, Hou C. New application of Mn-doped ZnS quantum dots: phosphorescent sensor for the rapid screening of chloramphenicol and tetracycline residues. Anal Methods 2020;12:3513-22.

61. Li F, Gao J, Wu H, Li Y, He X, Chen L. A highly selective and sensitive fluorescent sensor based on molecularly imprinted polymer-functionalized Mn-doped ZnS quantum dots for detection of roxarsone in feeds. Nanomaterials 2022;12:2997.

62. Zhang Y, Yuan X, Jiang W, Liu H. Determination of nereistoxin-related insecticide via quantum-dots-doped covalent organic frameworks in a molecularly imprinted network. Mikrochim Acta 2020;187:464.

63. Wang Y, Wang Y, Liu H. A novel fluorescence and SPE adsorption nanomaterials of molecularly imprinted polymers based on quantum dot-grafted covalent organic frameworks for the high selectivity and sensitivity detection of ferulic acid. Nanomaterials 2019;9:305.

64. Jana J, Lee HJ, Chung JS, Kim MH, Hur SH. Blue emitting nitrogen-doped carbon dots as a fluorescent probe for nitrite ion sensing and cell-imaging. Anal Chim Acta 2019;1079:212-9.

65. Wang J, Sheng Li R, Zhi Zhang H, Wang N, Zhang Z, Huang CZ. Highly fluorescent carbon dots as selective and visual probes for sensing copper ions in living cells via an electron transfer process. Biosens Bioelectron 2017;97:157-63.

66. Fowley C, McCaughan B, Devlin A, Yildiz I, Raymo FM, Callan JF. Highly luminescent biocompatible carbon quantum dots by encapsulation with an amphiphilic polymer. Chem Commun 2012;48:9361-3.

67. Sharma A, Das J. Small molecules derived carbon dots: synthesis and applications in sensing, catalysis, imaging, and biomedicine. J Nanobiotechnol 2019;17:92.

68. Wang F, Pang S, Wang L, Li Q, Kreiter M, Liu C. One-step synthesis of highly luminescent carbon dots in noncoordinating solvents. Chem Mater 2010;22:4528-30.

69. Chen S, Sun T, Zheng M, Xie Z. Carbon dots based nanoscale covalent organic frameworks for photodynamic therapy. Adv Funct Mater 2020;30:2004680.

70. Fonseca J, Gong T, Jiao L, Jiang H. Metal-organic frameworks (MOFs) beyond crystallinity: amorphous MOFs, MOF liquids and MOF glasses. J Mater Chem A 2021;9:10562-611.

71. Hou J, Sutrisna PD, Wang T, et al. Unraveling the interfacial structure-performance correlation of flexible metal-organic framework membranes on polymeric substrates. ACS Appl Mater Interfaces 2019;11:5570-7.

72. Baumann AE, Burns DA, Liu B, Thoi VS. Metal-organic framework functionalization and design strategies for advanced electrochemical energy storage devices. Commun Chem 2019:2.

73. Howarth AJ, Peters AW, Vermeulen NA, Wang TC, Hupp JT, Farha OK. Best practices for the synthesis, activation, and characterization of metal-organic frameworks. Chem Mater 2017;29:26-39.

74. Hong DH, Shim HS, Ha J, Moon HR. MOF-on-MOF architectures: applications in separation, catalysis, and sensing. Bull Korean Chem Soc 2021;42:956-69.

75. Kalaj M, Bentz KC, Ayala S Jr, et al. MOF-polymer hybrid materials: from simple composites to tailored architectures. Chem Rev 2020;120:8267-302.

76. Kwon O, Kim JY, Park S, et al. Computer-aided discovery of connected metal-organic frameworks. Nat Commun 2019;10:3620.

77. Tripathy SP, Subudhi S, Parida K. Inter-MOF hybrid (IMOFH): a concise analysis on emerging core-shell based hierarchical and multifunctional nanoporous materials. Coord Chem Rev 2021;434:213786.

78. Chen P, Bai Y, Wang S, Lyu M, Yun J, Wang L. Perovskite solar cells: in situ growth of 2D perovskite capping layer for stable and efficient perovskite solar cells. Adv Funct Mater 2018;28:1870113.

79. Peng J, Kremer F, Walter D, et al. Centimetre-scale perovskite solar cells with fill factors of more than 86 per cent. Nature 2022;601:573-8.

80. Shi L, Wang J, Zhou L, Chen Y, Yan J, Dai C. Facile in-situ preparation of MAPbBr3@UiO-66 composites for information encryption and decryption. J Solid State Chem 2020;282:121062.

81. Zhang Y, Lyu M, Qiu T, et al. Halide perovskite single crystals: optoelectronic applications and strategical approaches. Energies 2020;13:4250.

82. He R, Ren S, Chen C, et al. Wide-bandgap organic-inorganic hybrid and all-inorganic perovskite solar cells and their application in all-perovskite tandem solar cells. Energy Environ Sci 2021;14:5723-59.

83. Lu H, Krishna A, Zakeeruddin SM, Grätzel M, Hagfeldt A. Compositional and interface engineering of organic-inorganic lead halide perovskite solar cells. iScience 2020;23:101359.

84. Kong Z, Liao J, Dong Y, et al. Core@Shell CsPbBr3@Zeolitic imidazolate framework nanocomposite for efficient photocatalytic CO2 reduction. ACS Energy Lett 2018;3:2656-62.

85. Yuan S, Zou L, Qin JS, et al. Construction of hierarchically porous metal-organic frameworks through linker labilization. Nat Commun 2017;8:15356.

86. Aubert T, Golovatenko AA, Samoli M, et al. General expression for the size-dependent optical properties of quantum dots. Nano Lett 2022;22:1778-85.

87. Wang T, Gao L, Hou J, et al. Rational approach to guest confinement inside MOF cavities for low-temperature catalysis. Nat Commun 2019;10:1340.

88. Jiang Z, Xue W, Huang H, Zhu H, Sun Y, Zhong C. Mechanochemistry-assisted linker exchange of metal-organic framework for efficient kinetic separation of propene and propane. Chem Eng J 2023;454:140093.

89. Qi SC, Qian XY, He QX, et al. Generation of hierarchical porosity in metal-organic frameworks by the modulation of cation valence. Angew Chem Int Ed 2019;58:10104-9.

90. Yang P, Mao F, Li Y, Zhuang Q, Gu J. Hierarchical porous Zr-based MOFs synthesized by a facile monocarboxylic acid etching strategy. Chemistry 2018;24:2962-70.

91. Qiao GY, Guan D, Yuan S, et al. Perovskite quantum dots encapsulated in a mesoporous metal-organic framework as synergistic photocathode materials. J Am Chem Soc 2021;143:14253-60.

92. Hou J, Sapnik AF, Bennett TD. Metal-organic framework gels and monoliths. Chem Sci 2020;11:310-23.

93. Tuffnell JM, Ashling CW, Hou J, et al. Novel metal-organic framework materials: blends, liquids, glasses and crystal-glass composites. Chem Commun 2019;55:8705-15.

94. Hou J, Ashling CW, Collins SM, et al. Metal-organic framework crystal-glass composites. Nat Commun 2019;10:2580.

95. Hou J, Chen P, Shukla A, et al. Liquid-phase sintering of lead halide perovskites and metal-organic framework glasses. Science 2021;374:621-5.

96. Keen DA, Bennett TD. Structural investigations of amorphous metal-organic frameworks formed via different routes. Phys Chem Chem Phys 2018;20:7857-61.

Cite This Article

Perspective
Open Access
Emerging microporous materials as novel templates for quantum dots
Jaeho Lee, ... Jingwei HouJingwei  Hou

How to Cite

Lee, J.; Wang, L.; Hou, J. Emerging microporous materials as novel templates for quantum dots. Microstructures. 2023, 3, 2023021. http://dx.doi.org/10.20517/microstructures.2023.08

Download Citation

If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click on download.

Export Citation File:

Type of Import

Tips on Downloading Citation

This feature enables you to download the bibliographic information (also called citation data, header data, or metadata) for the articles on our site.

Citation Manager File Format

Use the radio buttons to choose how to format the bibliographic data you're harvesting. Several citation manager formats are available, including EndNote and BibTex.

Type of Import

If you have citation management software installed on your computer your Web browser should be able to import metadata directly into your reference database.

Direct Import: When the Direct Import option is selected (the default state), a dialogue box will give you the option to Save or Open the downloaded citation data. Choosing Open will either launch your citation manager or give you a choice of applications with which to use the metadata. The Save option saves the file locally for later use.

Indirect Import: When the Indirect Import option is selected, the metadata is displayed and may be copied and pasted as needed.

About This Article

© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, sharing, adaptation, distribution and reproduction in any medium or format, for any purpose, even commercially, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Related

Open Access | Perspective | 29 May 2024
Views: 355 | Downloads: 124
Download PDF 0 4
Open Access | Review | 9 Oct 2023
Views: 921 | Downloads: 269
Download PDF 0 1
Open Access | Review | 9 Aug 2023
Views: 1251 | Downloads: 392
Download PDF 0 4
Open Access | Research Article | 13 Feb 2023
Views: 1107 | Downloads: 770
Download PDF 0 2
Open Access | Perspective | 15 Jun 2022
Views: 2427 | Downloads: 1359
Download PDF 0 33
Open Access | Review | 16 Jan 2022
Views: 2888 | Downloads: 1547
Download PDF 0 29
Open Access | Research Article | 12 Jan 2022
Views: 2300 | Downloads: 951
Download PDF 0 0
Open Access | Research Article | 22 Sep 2021
Views: 1899 | Downloads: 937
Download PDF 0 14
Open Access | Review | 23 Oct 2024
Views: 348 | Downloads: 155
Download PDF 0 0
Open Access | Research Article | 16 Oct 2024
Views: 383 | Downloads: 101
Download PDF 0 0

Data & Comments

Data

Views
723
Downloads
611
Citations
0
Comments
0
3

Comments

Comments must be written in English. Spam, offensive content, impersonation, and private information will not be permitted. If any comment is reported and identified as inappropriate content by OAE staff, the comment will be removed without notice. If you have any queries or need any help, please contact us at support@oaepublish.com.

0
Download PDF
Share This Article
Scan the QR code for reading!
See Updates
Contents
Figures
Related
Microstructures
ISSN 2770-2995 (Online)

Portico

All published articles are preserved here permanently:

https://www.portico.org/publishers/oae/

Portico

All published articles are preserved here permanently:

https://www.portico.org/publishers/oae/