Assembly Of Quantum Dots Research Articles

Boosting Photocatalytic CO2 Methanation through Interface Fusion over CdS Quantum Dot Aerogels.

In the field of photocatalytic CO2 reduction, quantum dot (QD) assemblies have emerged as promising candidate photocatalysts due to their superior light absorption and better substrate adsorption. However, the poor contacts within QD assemblies lead to low interfacial charge transfer efficiency, making QD assemblies suffer from unsatisfactory photocatalytic performance. Herein, a novel approach is presented involving the construction of strongly interfacial fused CdS QD assemblies (CdS QD gel) for CO2 reduction. The novel CdS QD gel demonstrates outstanding photocatalytic performance for CO2 methanation, achieving a CH4 generation rate of ≈296 µmol g-1 h-1, with a selectivity surpassing 76% and an apparent quantum yield (AQY) of 1.4%. Further investigations reveal that the robust interfacial fusion in these CdS QDs not only boosts their ability to absorb visible light but also significantly promotes charge separation. The present work paves the way for utilizing QD gel photocatalysts in realizing efficient CO2 reduction and highlights the critical role of interfacial engineering in photocatalysts.

Carbon quantum dots assemblies integrated with spatial confined Co nanoparticles for antibiotic degradation via peroxymonosulfate activation

Heterogeneous Co-based materials are well-known for their exceptional catalytic properties in activating peroxymonosulfate (PMS) for the degradation of antibiotic pollutants. However, the potential applications of these materials are often hindered by significant Co nanoparticle aggregation and ion leaching. In this study, a carbon quantum dot-mediated self-assembly strategy was used to fabricate three-dimensional porous sponge-like Co@CDs-x (x represents the calcination tempeatures) catalysts with spatially confined Co nanoparticles. Among the samples, Co@CDs-900 exhibited a remarkable 97.8 % removal efficiency of TC in 11 minutes, with an apparent rate constant of 0.313 min−1. The exceptional performance of Co@CDs-900/PMS can be attributed to its large specific surface area, unique porosity, and abundant catalytically active sites, which generate ample reactive oxygen species for TC degradation. The catalyst demonstrated good degradation capabilities across a wide pH range of 3–11 and various organic pollutants such as tetranitrophenol, oxytetracycline, ciprofloxacin, methyl orange, and rhodamine B. Moreover, Co@CDs-900 maintained high activity even after the 5th cycle due to its magnetic property and spatial confinement effect, preventing catalyst loss and ion leaching during recycling tests. The degradation mechanism involved both free-radical and non-free radical pathways, with SO4•− and 1O2 identified as the primary reactive oxygen species. The degradation intermediates of TC were identified and a plausible degradation pathway was proposed. Toxicity assessment revealed that the Co@CDs-900/PMS system effectively reduced the toxicity of TC post-degradation. This study presents an effective approach for developing sponge-like CDs assemblies with spatially confined metal nanoparticles for activating PMS in antibiotic degradation.

Coffee-Ring Mediated Thinning and Thickness-Dependent Dewetting Modes in Printed Polymer Droplets Coupled with Assembly of Quantum Dots for Anti-Counterfeiting.

Molecular transport processes in printed polymer droplets hold enormous importance for understanding wetting phenomena and designing systems in applications such as encoding, electronics, photonics, and sensing. This paper studies thickness-dependent dewetting modes that are activated by thermal annealing and driven by interfacial interactions within microscopically confined polymeric features. The printing of poly(2-vinylpyridine) is performed in a regime where coffee-ring effects lead to strong thinning of the central region of the deposit. Thermal annealing leads to two different modes of dewetting that depend on the thickness of the central region. Mode I refers to the formation of randomly positioned small features surrounded by large hemispherical ones located along the periphery of the printed features and occurs when the central regions are thin. Observed at large central thicknesses, Mode II mediates significant molecular transport from edges toward the center of the printed droplet with thermal annealing and forms a hemispherical feature from the initial ring-like deposit. The selective adsorption of red, green, and blue emitting quantum dots over the poly(2-vinylpyridine) results in photoluminescent patterns. The selective assembly of photoluminescent quantum dots over patterned surfaces leads to deterministic and stochastic features beneficial to creating security labels for anti-counterfeiting applications.

Fabrication and Efficient Interfacial Assembly of Bright Red-Emitting Carbon Quantum Dots for Security-Warning Textiles.

Carbon quantum dots (CQDs) have attracted more attentions due to their multiple performances. However, the fabrication of long-wavelength emitting CQDs with aliphatic precursors still remains a challenge, mainly because it is difficult to generate large sp2 domains to reduce energy gap, which is not conducive to a redshift of the luminescence peak. Hereon, by regulating the pH of citric acid and thiourea mixture, a N, S co-doped CQD emitting bright red fluorescence at 635nm is successfully fabricated through the solvothermal reaction under acidic condition, achieving a high quantum yield of 32.66%. Solvatochromic effects of the CQDs are discussed through theoretical equations and models, which confirm that the hydrogen-bonding interaction dominates the fluorescence emission behavior of CQDs in polar solvents. Besides, a feasible strategy is proposed to prepare an anti-counterfeiting textile via the deposition of red-emitting CQDs onto cotton fibers, through rapidly evaporating the preferred organic solvent. As expected, the CQD-decorated textiles exhibit encouraging anti-counterfeiting and security-warning functions, along with underwater and long-distance detectability, washability, and sun resistance. It is worth noting that the present work is innovative in realizing the application of red-light-emitting CQDs in the fields of security-warning textiles.

Optoelectronic Properties of Nitrogen-Doped Hexagonal Graphene Quantum Dots: A First-Principles Study.

Graphene quantum dots have been widely studied owing to their unique optical, electrical, and optoelectrical properties for various applications in solar devices. Here, we investigate the optoelectronic properties of hexagonal and nitrogen-doped graphene quantum dots using the first-principles method. We find that doping nitrogen atoms to hexagonal graphene quantum dots results in a significant red shift toward the visible light range as compared to that of the pristine graphene quantum dots, and the doped nitrogen atoms also induce a clear signature of anisotropy of the frontier orbitals induced by the electron correlation between the doped nitrogen atoms and their adjacent carbon atoms. Moreover, time-dependent density functional theory calculations with the M06-2X functional and 6-311++G(d,p) basis set reproduce well the experimental absorption spectra reported recently. These results provide us with a novel approach for more systematic investigations on next-generation solar devices with assembled quantum dots to improve their light selectivity as well as efficiency.

Ligand Mediated Assembly of CdS Colloids in 3D Porous Metal–Organic Framework Derived Scaffold with Multi‐Sites Heterojunctions for Efficient CO2 Photoreduction

AbstractThe inclusion of colloidal particles into 3D porous constructs to realize heterostructure ensembles enhances surface interactions and energy transfer that can transform the catalytic properties of conventional catalysts. However, assembling hydrophobic colloidal nanoparticles within hydrophilic 3D porous matrices to create tailored heterostructures and catalytic properties is particularly challenging. Here, a modified ligand grafting method is presented to spontaneously assemble CdS inorganic colloidal quantum dots within a metal‐organic framework (MOF) derived porous framework for efficient photocatalytic CO2 reduction. The grafted long chain molecular ligands effectively suppress phase separation and endow a molecular‐recognition effect to form ordered assembly microstructures. The proof‐of‐concept assembly of CdS and Prussian blue analogues (PBA) derived Co3O4 facilitates a high density of heterojunctions formation, improving charge transfer and extended lifetimes of photo‐induced electrons. Consequently, CdS/Co3O4 assembly exhibits exceptionally active and stable photocatalytic CO2 reduction activity, with a CO production rate of 73.9 µmol g−1 h−1 and CO selectivity of 98.9%. Importantly, the ligand grafting method can be generalized to achieve spontaneous assembly of quantum dots within various metal organic framework derived porous scaffolds. This work provides a rational strategy for precise self‐assembly of colloidal nanoparticles within porous microstructures, allowing tailored heterointerfaces for functional materials and applications.

Certification Grade Quantum Dot Luminescent Solar Concentrator Glazing with Optical Wireless Communication Capability for Connected Sustainable Architecture

AbstractEnergy sustainability and interconnectivity are the two main pillars on which cutting‐edge architecture is based and require the realization of energy and intelligent devices that can be fully integrated into buildings, capable of meeting stringent regulatory requirements and operating in real‐world conditions. Luminescent solar concentrators, particularly those based on near‐infrared emitting reabsorption‐free quantum dots, are considered good candidates for the realization of semi‐transparent photovoltaic glazing, but despite important advances in optical property engineering strategies, studies of finished devices suitable for real‐world operation are still lacking. In this paper, the first example of a fully assembled quantum dot luminescent solar concentrator‐based photovoltaic glazing is demonstrated that meets all international standards for photovoltaic and building elements. It is also shown that these devices are capable of functioning as efficient Visible Light Communication (VLC) receivers even under full sunlight, thus combining energy and wireless connectivity functions in a realistic solution for smart, sustainable buildings.

Effect of Connectivity on the Carrier Transport and Recombination Dynamics of Perovskite Quantum-Dot Networks.

Quantum-dot (QD) solids are being widely exploited as a solution-processable technology to develop photovoltaic, light-emission, and photodetection devices. Charge transport in these materials is the result of a compromise between confinement at the individual QD level and electronic coupling among the different nanocrystals in the ensemble. While this is commonly achieved by ligand engineering in colloidal-based systems, ligand-free QD assemblies have recently emerged as an exciting alternative where nanostructures can be directly grown into porous matrices with optical quality as well as control over their connectivity and, hence, charge transport properties. In this context, we present a complete photophysical study comprising fluence- and temperature-dependent time-resolved spectroscopy to study carrier dynamics in ligand-free QD networks with gradually varying degrees of interconnectivity, which we achieve by changing the average distance between the QDs. Analysis of the photoluminescence and absorption properties of the QD assemblies, involving both static and time-resolved measurements, allows us to identify the weight of the different recombination mechanisms, both radiative and nonradiative, as a function of QD connectivity. We propose a picture where carrier diffusion, which is needed for any optoelectronic application and implies interparticle transport, gives rise to the exposure of carriers to a larger defect landscape than in the case of isolated QDs. The use of a broad range of fluences permits extracting valuable information for applications demanding either low- or high-carrier-injection levels and highlighting the relevance of a judicious design to balance recombination and diffusion.

Assembled Quantum Dot Porous Clusters for Enhanced Photocatalytic Reduction of Quinone to Hydroquinone

Assembled Quantum Dot Porous Clusters for Enhanced Photocatalytic Reduction of Quinone to Hydroquinone

Spatial-Arrangement-Assisted Emission Energy Fine Tuning of CdSe Quantum Dots (QDs) in QD–Block Copolymer Complexes

Quantum dots (QDs) exhibit size-dependent optical properties, where both the absorption and fluorescence energy levels vary with QD size. However, this dependence results in a discontinuity of intrinsically accessible energy levels for the bandgap, posing challenges in achieving precise energy tuning within a specific range. Herein, we demonstrate emission energy control of QDs with identical absorption energy levels by manipulating the spatial arrangement of QDs within QD–polymer complexes through hydrophobic interactions. The phase behavior of the QD–polymer complexes was modulated by adjusting the mass fraction of hydrophilic and hydrophobic blocks in the block copolymer, utilizing two types of amphiphilic block copolymers and varying temperatures. The QDs were spontaneously trapped within the hydrophobic region of the polymer template in water, resulting in spherical, cylindrical, and vesicle structures of QD–polymer complexes, corresponding to spherical, cylindrical, and layered assemblies of QDs, respectively. Depending on the QDs’ location within the QD–polymer complex, the surface area in contact with water varied, leading to different degrees of oxidation and, consequently, a change in the fluorescence energy level of QDs. This study introduces a novel method to fine tune the emission energy (<15 eV) of QDs by adjusting the polymer form factor without complicated procedures.

Bio-catalytic nanoparticle shaping for preparing mesoscopic assemblies of semiconductor quantum dots and organic molecules.

We report a unique bio-catalytic nanoparticle shaping (BNS) method for preparing a variety of mesoscopic particles by a facile process. For example, the BNS method affords mesoscopic QD assembly dispersions. Large-size sedimentations (>1 μm) of QDs are first formed using oligo-L-lysine linkers. These then undergo controlled enzymatic cleavage of the linkers using trypsin, which surprisingly leads to mesoscopic particles about 84 nm in size with a narrow size distribution. A detailed mechanism of the BNS method is investigated using tetrakis(4-carboxyphenyl)porphyrin (TCPP), instead of QDs, as a probe molecule. Interestingly, the BNS method can also be applied to other combinations of enzymes and enzymatically degradable linkers, such as hyaluronidase with hyaluronan. As a potential application, the mesoscopic particles of QDs and oligo-lysine exhibit their ability to act as a drug delivery carrier originating from the features of both QDs and oligo-lysine. The BNS method demonstrates the universality and versatility of preparing mesoscopic particles and opens new doors for studying QD assemblies and molecular-based mesoscopic particles.

Improving the efficiency of quantum dot-sensitized solar cells by increasing the QD loading amount.

In quantum dot-sensitized solar cells (QDSCs), optimized quantum dot (QD) loading mode and high QD loading amount are prerequisites for great device performance. Capping ligand-induced self-assembly (CLIS) mode represents the mainstream QD loading strategy in the fabrication of high-efficiency QDSCs. However, there remain limitations in CLIS that constrain further enhancement of QD loading levels. This review illustrates the development of various QD loading methods in QDSCs, with an emphasis on the outstanding merits and bottlenecks of CLIS. Subsequently, thermodynamic and kinetic factors dominating QD loading behaviors in CLIS are analyzed theoretically. Upon understanding driving forces, resistances, and energy effects in a QD assembly process, various novel strategies for improving the QD loading amount in CLIS are summarized, and the related functional mechanism is established. Finally, the article concludes and outlooks some remaining academic issues to be solved, so that higher QD loading amount and efficiencies of QDSCs can be anticipated in the future.

Portable fluorescent lateral flow assay for ultrasensitive point-of-care analysis of acute myocardial infarction related microRNA

Point-of-care quantitative analysis of tracing microRNA disease-biomarkers remains a great challenge in the clinical diagnosis. In this paper, we developed a portable fluorescent lateral flow assay for ultrasensitive quantified detection of acute myocardial infarction related microRNAs in bio-samples. SiO2@DQD (bilayer quantum dots assembly with SiO2 core) based fluorescent lateral flow strip was fabricated as the analysis tool. In order to quantify the tracing microRNA in biosamples, a catalytic hairpin assembly and CRISPR/Cas12a cascade amplification method was performed and combined with the fabricated SiO2@DQD lateral flow strip. Thus, our platform gathered double advantages of portability and ultrasensitive quantification. Based on our strips, target myocardial biomarker microRNA-133a can be detected with a detection limit of 0.32 fM, which was almost 1000-fold sensitive compared with previous reported microRNAs-lateral flow strips. Significantly, this portable fluorescent strip can directly detect microRNAs in serum without any pretreatment and PCR amplification steps. When spiked in serum samples, a recovery of 99.65 %-102.38 % can be obtained. Therefore, our method offers a potential tool for ultrasensitive quantification of diseases related microRNA in the point-of-care diseases diagnosis field.

Designed Polymer Ligands for Perovskite Quantum Dots and Their Block Copolymer Nanocomposites

AbstractPerovskite quantum dots (QDs) have efficient optical absorption and emission in the visible range, and show a strong quantum confinement effect and high external quantum efficiency. They have been at the forefront of next‐generation photovoltaics and optoelectronics applications. However, two major challenges associated with perovskites and their nanomaterials are poor stability (such as against moisture and polar solvents), as well as the lack of efficient nanopatterning methods. In this work, a promising approach is provided to address both of those major challenges by molecular engineering and integration of QDs with block copolymers (BCP). The BCP thermoplastic elastomers not only substantially improve the stability of perovskite QDs by encapsulating them in a highly stable and soft matrix, but also enable molecular‐level control of the alignment and assembly of perovskite QDs in the microphase‐separated BCP matrix. It is demonstrated that designing and synthesis of compatible polymer ligands for perovskite QDs is key to enabling their selective and strong interaction with the BCP matrix. The structure and molecular weight of the BCP also play an important role in the interfacial structure and optical properties of the QDs‐BCP nanocomposites. Such soft and flexible optical nanocomposites have potential applications in flexible optoelectronics, optical storage, and displays.

Copper‐Free Click Chemistry‐Mediated Assembly of Single Quantum Dot Nanosensor for Accurately Monitoring Locus‐Specific m6A in Cancer Cells†

Comprehensive SummaryN6‐methyladenosine (m6A) plays an important role in embryogenesis, nuclear export, transcription splicing, and protein translation control. Herein, we demonstrate a copper‐free click chemistry‐mediated assembly of single quantum dot (QD) nanosensor for accurately monitoring locus‐specific m6A in cancer cells. The m6A‐sensitive endoribonuclease MazF can digest the unmethylated A‐RNA, and the intact m6A‐RNA then hybridizes with DNA probes a and b to produce a sandwich hybrid, initiating the click chemistry to generate probe a–b ligation product via first tandem ligation detection reaction (LDR) cycle. Subsequently, DNA probes c and d can hybridize with the probe a–b ligation product to generate the probe c–d ligation product via second LDR cycle. Both LDR cycles can be repeated through denaturation and annealing reaction to generate abundant biotin‐/fluorophore‐modified probe c–d ligation products that can easily assemble on the QD surface to induce distinct fluorescence resonance energy transfer (FRET) between QD and Cy5. This assay can be homogenously performed without the involvement of copper catalyst, m6A‐specific antibody, radioactive labeling, ligase enzyme, enzymatic reverse transcription, and next‐generation sequencing. Moreover, it can discriminate even 0.01% m6A level in complex samples and accurately measure cellular m6A‐RNA expression, providing a promising avenue for clinical diagnostics and biomedical research.

Supra-Quantum Dot Assemblies to Maximize Color-Based Multiplexed Fluorescence Detection with a Smartphone Camera.

Photoluminescence (PL) imaging and bioanalysis with smartphone-based devices are of growing interest for point-of-care/point-of-need diagnostics. Strategies for maximizing sensitivity have been explored in this context, but color multiplexing has been very limited, with its maximum level unexplored. Here, we evaluated color multiplexing with smartphone-based PL imaging by using supra-nanoparticle assemblies of quantum dots (supra-QDs). These materials were prepared as composite colors that were tailored to the red-green-blue (RGB) color space of smartphone cameras by coassembling different ratios of R-, G-, and B-emitting QDs on a silica nanoparticle scaffold. The supra-QDs were characterized and used to label cell-sized objects that were measured under flow with a smartphone-based device. Each color followed an approximately linear trajectory in the RGB space, and training of support vector machine models enabled color classification with overall accuracies ≥87% for 10-color multiplexing and better accuracies for fewer colors. Most misclassification occurred at low signal levels, such that establishing a nonclassifiable zone near the origin of RGB color space improved the overall 10-color classification accuracy to ≥94%. Similar improvements in accuracy with greater retention of data were possible with a probabilistic rather than a radial threshold. Simulations that were parameterized by experimental data suggested that ≥14-color multiplexing with accuracies ≥90% should be possible with an optimized supra-QD color set. This study is an important foundation for advancing RGB color-based multiplexing for imaging and analyses with smartphone cameras and related charge-coupled device and CMOS color image sensor technologies.

PH Tunable Patterning of Quantum Dots.

Patterning of quantum dots (QDs) is essential for many, especially high-tech, applications. Here, pH tunable assembly of QDs over functional patterns prepared by electrohydrodynamic jet printing of poly(2-vinylpyridine) is presented. The selective adsorption of QDs from water dispersions is mediated by the electrostatic interaction between the ligand composed of 3-mercaptopropionic acid and patterned poly(2-vinylpyridine). The pH of the dispersion provides tunability at two levels. First, the adsorption density of QDs and fluorescence from the patterns can be modulated for pH > ≈4. Second, patterned features show unique type of disintegration resulting in randomly positioned features within areas defined by the printing for pH ≤ ≈4. The first capability is useful for deterministic patterning of QDs, whereas the second one enables hierarchically structured encoding of information by generating stochastic features of QDs within areas defined by the printing. This second capability is exploited for generating addressable security labels based on unclonable features. Through image analysis and feature matching algorithms, it is demonstrated that such patterns are unclonable in nature and provide a suitable platform for anti-counterfeiting applications. Collectively, the presented approach not only enables effective patterning of QDs, but also establishes key guidelines for addressable assembly of colloidal nanomaterials.

Modeling electronic conduction in quantum dot constituted assemblies coupled to metallic electrodes

It is shown that the electrical transport in quantum dot (QD) constituted films, synthesized through electrochemical doping, could be described through a two-step model considering (i) the tunneling transport of electrons from an electron source, and subsequent (ii) Ohmic transport through the film governed by a temperature (T) dependent mobility (μ), varying as T−α. A transfer matrix algorithm based approach for electrical field induced tunneling and α ∼ 1, was used. The indicated modeling principles could be deployed to predict the current–voltage characteristics of QD films and assemblies coupled to metallic electrodes.

Al doping promoted photocatalytic degradation of tetracycline hydrochloride on CuInS2 QDs assembly

Doping plays key roles in tailoring morphologies or electronic structure of ternary alloyed CuInS2 (CIS) nanocrystals, aiming toward efficient photocatalytic performance. Here, aluminum ions (Al3+) were used as dopants to prepare aluminum ion-doped CIS (Al-CIS) quantum dots (QDs) via a hydrothermal route. By controlling the doping amount of aluminum and growth kinetics, sheet-like Al-CIS were prepared. TEM, HRTEM, and EDX results confirm the 2D meso-crystal structure of the Al-CIS, which was built by Al-CIS QDs via the same crystal orientation. The 2D meso-crystal combines the enlarged bandgaps of QDs with the high conductivity of single crystals, exhibiting higher photocurrent response and lower resistance than CIS QDs or Al-CIS QDs. As result, the 2D meso-crystals exhibit tetracycline (TC) degradation rates 2.5 times higher than that of coarsened CIS QDs, with excellent TC removal ratio of 96.2%. Kinetic investigations on TC degradation indicate that superoxide radicals (·O2-) dominate the process of TC oxidation. Mott-Schottky and band analysis suggest that the formation of 2D meso-crystal of Al-CIS increases carriers’ concentration in the conduction band, and lowers the position of the conduction band, favoring electron transfers toward reactants for boosting TC degradation.

First-Principles Modeling of Bottom-Up Synthesis of Carbon Quantum Dots

In this work, we report the results of various scenarios related to the initial stages in the assembly of carbon quantum dots (CQDs) from citric acid (CA) or o-phenylenediamine (OPD). The results of the step-by-step simulations of the synthesis demonstrate that all possible scenarios of CQD assembly are different from those previously proposed. For example, in synthesizing CQDs from citric acid, each addition of a new carbon ring to the growing nanographene leads to the appearance of the carbonyl (C=O) groups on the edges and carboxyl (–COOH) groups in the interior parts of the nanographenes. Even the initial steps of CQD assembly from CA are accompanied by the formation of bushy structures from carboxyl and –CH2–COOH groups on the edges. On the other hand, in manufacturing CQDs from OPD, the formation of flat nanographenes is extremely energetically favorable. This result is in qualitative agreement with a very high yield of synthesized CQDs from OPD. However, the discussed process of nanographene formation proceeds simultaneously with the oxidation of newly formed nanographenes in a medium of superheated water accompanied by the appearance of C–OH bonds in the internal parts of newly formed sp2- carbon species or even in their etching. For both cases, the scenario of eliminating excessive carboxyl or hydroxyl groups by forming interlayer C–C bonds between two adjacent nanographenes is estimated as possible.