Shell thickness-induced thermal dependence: highly sensitive core-shell CdSe/ZnS/POSS-based temperature probes.

Fluorescence nanothermometry based on quantum dots is a current research hotspot for novel non-contact temperature monitoring, and is of vital significance for the modulation and design of the sensing properties of sensors. Herein, a design strategy to modulate the temperature-sensing characteristics of quantum dots based on the thickness of a shell is proposed. In this study, CdSe/ZnS quantum dot/POSS-based temperature probe films with varying fluorescence characteristics were developed, and the influence of the ZnS shell on temperature sensing was examined by varying the thickness of the ZnS shell. The temperature dependency, linearity, range of applications, and reversibility of quantum dot thin film probes were all considerably regulated by the ZnS shell, according to research on quantum dot/POSS-based films coated with various shell thicknesses. The CdSe/ZnS temperature probe with 4 monolayers (MLs) stood out among the rest due to its strong thermal stability (at least 5 cycles), large usable temperature range (20-80 °C), and excellent temperature sensitivity (R2 > 0.994). The results demonstrated that the temperature sensing performance of quantum dots was the consequence of the combined effect of multiple temperature response properties induced by the thickness of the shell, and the shell control of quantum dots to optimize the temperature sensing performance was an essential approach for the design of temperature probes. This work demonstrates the great potential of the shell in tuning the temperature sensing performance of quantum dots and provides a viable approach for the design of quantum dot temperature probes.

Luminescent Perovskite-Cross-Linked Polymer with Low Shrinkage and Excellent Stability.

When organic cross-linked polymers are combined with metal halide perovskite nanocrystals (PNCs) for realizing luminescent perovskite-polymer display materials, the stability of PNCs is enhanced and their shrinkage is suppressed. This work presents a feasible strategy for preparing CsPbBr3 nanocrystals (NCs) within a polydicyclopentadiene (PDCPD) thermosetting cross-linked resin matrix simultaneously via a one-step reaction. The obtained PDCPD@PNCs composite exhibits narrow peak half-widths (15-20 nm), high light transmittance (80%), low curing volume shrinkage (1.4%), tunable tensile properties, excellent stability, and a photoluminescence quantum yield (PLQY) of 44.3%. The composite material exhibits long-term stability in water, acid, and base solutions for over 90 days, with the PL intensity being maintained at over 90%. Furthermore, the composite is highly resistant to polar organic solvents owing to the insolubility imparted by cross-linking. White LEDs (WLED) fabricated using the as-prepared composite demonstrate excellent potential as light sources in optical devices.

Controllable fabrication of well-shaped PMBA@CsPbBr3 nanoparticles for highly sensitive detection of HCl and HBr.

We report a facile two-step strategy to construct well-shaped PMBA@CsPbBr3 nanoparticles, with this strategy involving combining in situ adsorption and controlled polymerization. The morphological evolution process and mechanism of formation of the nanoparticles were demonstrated, and the nanoparticles showed high sensitivity to corrosive acid gas. This work has provided an effective approach for fabricating well-structured perovskite-based nanocomposites.

Fabricating a type II heterojunction by growing lead-free perovskite Cs2AgBiBr6in situ on graphite-like g-C3N4 nanosheets for enhanced photocatalytic CO2 reduction.

Perovskite-based photocatalysts have received significant attention for converting CO2 into fuels, such as CO, CH4 or long alkyl chains. However, the use of these catalysts is plagued by several limitations, such as poor stability, lead toxicity, and inadequate conversion efficiency due to the rapid recombination of carriers. Herein, a g-C3N4@Cs2AgBiBr6 (CABB) type II heterojunction photocatalyst has been prepared by growing lead-free CABB nanocrystals (10-14 nm) on the graphite-like carbon nitride (g-C3N4) nanosheet using the in situ crystallization method. The resulting nanocomposite, g-C3N4@CABB, demonstrated an efficient charge transfer pathway via a typical type II heterojunction. With formation rates of 10.30 µmol g-1 h-1 for CO and 0.88 µmol g-1 h-1 for CH4 under visible light irradiation, the nanocomposite exhibited enhanced photocatalytic efficiency in CO2 reduction compared to CABB and g-C3N4. The improved photocatalytic performance of the g-C3N4@CABB nanocomposite was attributed to the fabricated type II heterojunction, which boosted the interfacial charge transfer from g-C3N4 to CABB. This work will inspire the design of heterojunction-based photocatalysts and increase the fundamental understanding of perovskite-based catalysts in the CO2 photoreduction process.

Well-shaped poly(dimethylsiloxane)-based copolymer nanowires from spherical micelles via kinetic shape evolution.

The formation of self-assembled arrays or superstructures from copolymers has attracted intense research interest. Herein, we propose a kinetic approach to form self-assembled nanowires using a PDMS-based block copolymer consisting of poly(dimethylsiloxane)-b-poly[2-(cinnamoyloxy)ethyl methacrylate] (PDMS-b-PCEMA). The copolymer was synthesized by using the macroinitiator PDMS-Br to initiate 2-(trimethylsiloxy)ethyl methacrylate (HEMA-TMS) via ATRP, followed by hydrolysis of the TMS group and gradual esterification with cinnamoyl chloride. PDMS-b-PCEMA presented core-shell spherical micelles in tetrahydrofuran, which transformed into nanowires within 5 days self-assembly via a typical kinetic shape evolution. The diameter of the assembled nanowires with a PCEMA inner core and PDMS shell was about 25-35 nm. The formation of these nanowires reflected a balance between the PDMS and PCEMA components: the PDMS segment was soluble enough to form a corona block, which was beneficial for the transformation of the micellar shape. Meanwhile, the PCEMA segment was able to control the diameter of the nanowire micelles but had no decisive effect on their formation. The effect of solvents on the self-assembled micelles indicated that nanowires were formed in tetrahydrofuran and dichloromethane, while core-shell micelles were formed in acetone. This was due to the different permittivities of these solvents. The nanowires were fixed by cross-linking the PCEMA group under UV irradiation, which enhanced their stability. We believe that this work provides a new strategy for the formation of nanowires and offers a guide for the diversified self-assembly of nanostructures from copolymers.

CsPbBr3 perovskite quantum dots grown within Fe-doped zeolite X with improved stability for sensitive NH3 detection.

All-inorganic cesium lead halide (CsPbX3, X = Cl, Br and I) perovskite quantum dots (QDs) have received enormous research interest because of their exceptional optoelectronic properties, but their low chemical stability under ambient conditions from inevitable defects restricts their practical applications. In an effort to enhance the stability of QDs, in this study, novel functional nanocomposites were fabricated by encapsulating perovskite QDs with zeolite X doped with iron ions. Focusing on the as-obtained nanocomposites labeled with QDs@Fe/X-n, doping a reasonable amount of Fe3+ ions can tremendously improve the order of perovskite lattices and reduce the halide vacancies. The results of stability improvement in nanocomposites with an optimal Fe3+ load (QDs@Fe/X-3) are presented. After storage in air for 100 days, the emission-peak position of the composites can remain almost unchanged, and the photoluminescence (PL) intensity can reach ∼98% of the original intensity. Additionally, the PL intensity of QDs@Fe/X-3 can decrease immediately when exposing it to a NH3 atmosphere at room temperature. The PL intensity can be linearly varied with a change in the NH3 concentration. The original value of the PL can be rapidly recovered by separating the sample from the NH3 environment. This work enables the QDs@Fe/X composite to be an ideal active material for ammonia sensing.

Insight into a Bentonite-Based Hydrogel for the Conservation of Sandstone-Based Cultural Heritage: In Situ Formation, Reinforcement Mechanism, and High-Durability Evaluation.

Conservation of sandstone-based cultural heritage has attracted a great deal of interest. We propose herein a novel protecting strategy, via in situ fabrication of bentonite-based hydrogels (B-H) inside sandstones, where the bentonite-based hydrogels serve as the underlying cement. To create bentonite-based hydrogels with controllable structure, possessing good mechanical and anti-swelling properties, we have optimized forming time, appearance, and viscosity. The hydrogel precursor penetrated into the pores of the sandstone; the hydrogel would then form within 3-5 h. As found by employing a fluorescent tracer, the precursor remained controllably in place without any apparent change in the sandstone morphology. The bentonite-based hydrogels that formed inside the sandstones presented strong hydrogen bonding, coordination, and ionic bonding, as well as strong mechanical interlocking to the sandstone matrix. As a result, the sandstones possessed enhanced mechanical compressive strength and excellent resistance to acid, salt, and freeze-thaw cycles. Our approach provides for a non-destructive, eco-friendly, easy-to-use, and long-term strategy for cultural preservation, one with excellent protection effects.

CsPbBr3 Perovskite Nanocrystal Grown on MXene Nanosheets for Enhanced Photoelectric Detection and Photocatalytic CO2 Reduction.

All-inorganic CsPbX3 (X = Cl, Br or I) perovskite nanocrystals have attracted extensive interest recently due to their exceptional optoelectronic properties. In an effort to improve the charge separation and transfer following efficient exciton generation in such nanocrystals, novel functional nanocomposites were synthesized by the in situ growth of CsPbBr3 perovskite nanocrystals on two-dimensional MXene nanosheets. Efficient excited state charge transfer occurs between CsPbBr3 NCs and MXene nanosheets, as indicated by significant photoluminescence (PL) quenching and much shorter PL decay lifetimes compared with pure CsPbBr3 NCs. The as-obtained CsPbBr3/MXene nanocomposites demonstrated increased photocurrent generation in response to visible light and X-ray illumination, attesting to the potential application of these heterostructure nanocomposites for photoelectric detection. The efficient charge transfer also renders the CsPbBr3/MXene nanocomposite an active photocatalyst for the reduction of CO2 to CO and CH4. This work provides a guide for exploration of perovskite materials in next-generation optoelectronics, such as photoelectric detectors or photocatalyst.

Unusual Stability and Temperature-Dependent Properties of Highly Emissive CsPbBr3 Perovskite Nanocrystals Obtained from in Situ Crystallization in Poly(vinylidene difluoride).

All-inorganic cesium lead halide perovskite nanocrystals (CsPbX3, X = Cl, Br, or I) present broad applications in the field of optoelectronics due to their excellent photoluminescence (PL), narrow spectral bandwidth, and wide spectral tunability. However, their poor stability limits their practical application. In this work, we successfully use an in situ crystallization strategy for growing and cladding CsPbBr3 perovskite nanocrystals in poly(vinylidene difluoride) (PVDF). The CsPbBr3 nanocrystals in the as-fabricated CsPbBr3@PVDF composites have an average diameter of 16-18 nm and a strong PL emission (537 nm), with a photoluminescence quantum yield exceeding 30%. In addition, the fabricated CsPbBr3@PVDF composites present improved resistance to heat and water preserving with remarkable optical performance, owing to the effective protection of PVDF. Moreover, the CsPbBr3 nanocrystals generated in PVDF can withstand temperatures up to 170 °C and can be completely immersed in water for 60 days while still retaining high PL intensity, which facilitate the practical application of CsPbBr3 perovskite nanocrystals. These CsPbBr3@PVDF composite films with remarkable optical performances and superior anti-interference ability have broad application prospects in optoelectronics as well as good potential as temperature sensors in mechanical engineering.

Stable Luminous Nanocomposites of Confined Mn2+-Doped Lead Halide Perovskite Nanocrystals in Mesoporous Silica Nanospheres as Orange Fluorophores.

Creating highly stable inorganic perovskite nanocrystals (CsPbX3, where X = Cl, Br, and I) with excellent optical performance is challenging because their optical properties depend on their ionic structure and its inherent defects. Here, we present a facile and effective synthesis using a nanoconfinement strategy to grow Mn2+-doped CsPbCl3 nanocrystals embedded in dendritic mesoporous silica nanospheres (MSNs). The resulting nanocomposite is abbreviated as Cs(Pb x/Mn1- x)Cl3@MSNs and can serve as the orange emitter for white light-emitting diodes (WLEDs). The MSN matrix was prepared via a templated sol-gel technique as monodispersed center-radial dendritic porous particles, with a diamater of ∼105 nm and an inner pore size of ∼13 nm. The MSN was then utilized as the matrix to initiate the growth of Mn-doped perovskite nanocrystals (NCs). The NCs in the resulting composite have an average diameter of 8 nm and a photoluminescence quantum yield of >30%. In addition, the optical properties of the Cs(Pb x/Mn1- x)Cl3@MSNs can be tuned by varying the Mn2+ doping level. The resulting composites presented a significantly improved resistance to ultraviolet (UV) light, temperature, and moisture compared to that of bare Cs(Pb0.72/Mn0.28)Cl3. Finally, we fabricated down-converting WLEDs by using Cs(Pb x/Mn1- x)Cl3@MSNs as the orange-emitting phosphor deposited onto UV-emitting chips, demonstrating their promising applications in solid-state lighting. This work provides a valuable approach to fabricating stable orange luminophores as replacements for traditional emitters in light-emitting diode devices.

White-Light-Emitting Melamine-Formaldehyde Microspheres through Polymer-Mediated Aggregation and Encapsulation of Graphene Quantum Dots.

Graphene quantum dot (GQD) encapsulated melamine-formaldehyde (MF) polymer microspheres with uniform particle size and tunable high-quality white-light emissions are prepared via a polymer-mediated GQD assembly and encapsulation strategy. In solution, GQDs are first aggregated with MF prepolymer through electrostatic interaction and further encapsulated inside the microspheres formed by polymerization of MF prepolymer under acid catalysis and heating. During this process, the aggregated GQDs are fixed in the MF polymer matrix with their emission extended from blue to full visible range, presenting bright white luminescence under ultraviolet excitation. The prepared white-light-emitting GQD-MF microspheres exhibit uniform morphology with an average particle size of 2.0 ± 0.08 µm and their luminescence properties are effectively regulated by the doping concentration of GQDs in the MF polymer matrix. A series of white-light-emitting GQD-MF microspheres with quantum yields from 0.83 to 0.43, Commission Internationale de L'Eclairage coordinates from (0.28, 0.28) to (0.33, 0.32), and color rendering index from 0.75 to 0.88 are obtained with excellent photostability and thermal stability. By dispersing the GQD-MF microspheres in cross-linked polydimethylsiloxane matrix, flexible film with dual functions of high-quality white-light-emitting and light diffusion is obtained and successfully applied for white light-emitting diode fabrication.

Design Rules for Self-Assembly of 2D Nanocrystal/Metal-Organic Framework Superstructures.

We demonstrate the guiding principles behind simple two dimensional self-assembly of MOF nanoparticles (NPs) and oleic acid capped iron oxide (Fe3 O4 ) NCs into a uniform two-dimensional bi-layered superstructure. This self-assembly process can be controlled by the energy of ligand-ligand interactions between surface ligands on Fe3 O4 NCs and Zr6 O4 (OH)4 (fumarate)6 MOF NPs. Scanning transmission electron microscopy (TEM)/energy-dispersive X-ray spectroscopy and TEM tomography confirm the hierarchical co-assembly of Fe3 O4 NCs with MOF NPs as ligand energies are manipulated to promote facile diffusion of the smaller NCs. First-principles calculations and event-driven molecular dynamics simulations indicate that the observed patterns are dictated by combination of ligand-surface and ligand-ligand interactions. This study opens a new avenue for design and self-assembly of MOFs and NCs into high surface area assemblies, mimicking the structure of supported catalyst architectures, and provides a thorough fundamental understanding of the self-assembly process, which could be a guide for designing functional materials with desired structure.

Templated self-assembly of one-dimensional CsPbX3 perovskite nanocrystal superlattices.

Ordered self-assembled arrays or superstructures of nanocrystals (NCs) have attracted intense research interest due to their ability to translate valuable nanoscale properties to larger length scales. Numerous techniques have been explored to induce self-assembly into various superstructures. Here we investigated a simple kinetic approach to form self-assembled one-dimensional perovskite CsPbX3 (X: halides) nanocrystal arrays templated inside a pod shaped inert lead sulfate (PbSO4) scaffold. Both the solvent effects, and the self-assembly process and mechanism, are systematically studied based on a uniform procedure developed to generate CsPbX3 nanocrystal superlattices with different sizes and compositions. The formation of one-dimensional (1D) chains of NCs within a half-cylindrical pod of PbSO4 reflects a balance between solvophobicity and solvophilicity of the components. By reducing the size of NCs, we successfully realized 2D superlattices with two or three rows of close-packed CsPbBr3 NCs, in addition to single string-of-pearl type 1D assemblies. The superlattices can be assembled both inside and outside of the half-cylindrical shells by regulating the reaction conditions. The self-assembly behavior is reminiscent of the host-guest systems of organic molecular species where supramolecular recognition rules apply to give well-defined complexes. The current study opens a door for controlling self-assembled nanostructures of CsPbX3 NCs, and provides an attainable platform for future optoelectronic devices.

Nanorod Suprastructures from a Ternary Graphene Oxide-Polymer-CsPbX3 Perovskite Nanocrystal Composite That Display High Environmental Stability.

Despite the exceptional optoelectronic characteristics of the emergent perovskite nanocrystals, the ionic nature greatly limits their stability, and thus restricts their potential applications. Here we have adapted a self-assembly strategy to access a rarely reported nanorod suprastructure that provide excellent encapsulation of perovskite nanocrystals by polymer-grafted graphene oxide layers. Polyacrylic acid-grafted graphene oxide (GO-g-PAA) was used as a surface ligand during the synthesis of the CsPbX3 perovskite nanocrystals (NCs), yielding particles (5-12 nm) with tunable halide compositions that were homogeneously embedded in the GO-g-PAA matrix. The resulting NC-GO-g-PAA exhibits a higher photoluminescence quantum yield than previously reported encapsulated NCs while maintaining an easily tunable bandgap, allowing for emission spanning the visible spectrum. The NC-GO-g-PAA hybrid further self-assembles into well-defined nanorods upon solvent treatment. The resulting nanorod morphology imparts extraordinary chemical stability toward protic solvents such as methanol and water and much enhanced thermal stability. The introduction of barrier layers by embedding the perovskite NCs in the GO-g-PAA matrix, together with its unique assembly into nanorods, provides a novel strategy to afford robust perovskite emissive materials with environmental stability that may meet or exceed the requirement for optoelectronic applications.

Insight into the Ligand-Mediated Synthesis of Colloidal CsPbBr3 Perovskite Nanocrystals: The Role of Organic Acid, Base, and Cesium Precursors.

While convenient solution-based procedures have been realized for the synthesis of colloidal perovskite nanocrystals, the impact of surfactant ligands on the shape, size, and surface properties still remains poorly understood, which calls for a more detailed structure-morphology study. Herein we have systematically varied the hydrocarbon chain composition of carboxylic acids and amines to investigate the surface chemistry and the independent impact of acid and amine on the size and shape of perovskite nanocrystals. Solution phase studies on purified nanocrystal samples by (1)H NMR and IR spectroscopies have confirmed the presence of both carboxylate and alkylammonium ligands on surfaces, with the alkylammonium ligand being much more mobile and susceptible to detachment from the nanocrystal surfaces during polar solvent washes. Moreover, the chain length variation of carboxylic acids and amines, ranging from 18 carbons down to two carbons, has shown independent correlation to the size and shape of nanocrystals in addition to the temperature effect. We have additionally demonstrated that employing a more soluble cesium acetate precursor in place of the universally used Cs2CO3 results in enhanced processability without sacrificing optical properties, thus offering a more versatile recipe for perovskite nanocrystal synthesis that allows the use of organic acids and amines bearing chains shorter than eight carbon atoms. Overall our studies have shed light on the influence of ligand chemistry on crystal growth and stabilization of the nanocrystals, which opens the door to functionalizable perovskite nanocrsytals through surface ligand manipulation.

Fabrication pentablock copolymer/silica hybrids as self-assembly coatings.

Novel organic/inorganic hybrid for coating material is prepared by the pentablock copolymer PDMS-b-(PMMA-b-PMPS)2 (PMMDMM) and SiO2 nanoparticles. PMMDMM is obtained via atom transfer radical polymerization (ATRP) by using polydimethylsiloxane (PDMS) as bifunctional macroinitiator. Poly 3-(trimethoxysilyl)propyl methacrylate (PMPS) is designed as the end block for facilitating the chemical bond of triethoxysilane (Si(OCH3)3) groups with SiO2 nanoparticles produced by tetraethyl orthosilicate (TEOS), and poly (methyl methacrylate) (PMMA) is designed as the middle block for improving the solubility and the film-forming ability of copolymer. The homogeneous dispersion of SiO2 nanoparticles in the pentablock copolymer matrix enables PMMDMM/SiO2 to self-assemble into 210 nm SiO2 core/PMMDMM shell elliptic or spherical micelles in tetrahydrofuran (THF) solution. This self-assembled aggregate could provide the film surface with uniform distribution of SiO2 nanoparticles, obvious hydrophobicity (101-102° water contact angles), lower surface free energy (22.3-21.8 nN/m) and lower viscoelasticity. SiO2 involved into the copolymer matrix could increase the nanostructures roughness. When TEOS is controlled as 20 wt.%, the hybrid performs higher glass transition temperature (Tg = 113 °C) and excellent thermostability (520 °C) than PMMDMM (Tg = 87 °C, 295 °C) due to the introduction of SiO2 nanoparticles. These excellent properties promise PMMDMM/SiO2 hybrid as the candidate for coating material.

Well-defined inorganic/organic nanocomposite by nano silica core-poly(methyl methacrylate/butylacrylate/trifluoroethyl methacrylate) shell.

The novel inorganic/organic core-shell SiO2/P(MMA/BA/3FMA) nanocomposite for coating application is synthesized in this paper by seed emulsion polymerization, in which the inorganic phase is composed of nano-SiO2 modified by vinyl-trimethoxysilane (VMS) or γ-methacryloxy propyl trimethoxylsilane (MPMS), and the organic phase is made of terpolymer by 2,2,2-trifluoroethyl methacrylate (3FMA), methyl methacrylate (MMA), and n-butyl acrylate (BA). The chemical structure of SiO2/P(MMA/BA/3FMA) is characterized by FTIR. The effect of surfactant polyvinylpyrrolidone (PVP), sodium dodecyl sulfate (SDS)/octyl phenyl polyoxyethylene ether (TX-10), sodium dodecyl benzene sulfonate (SDBS)/TX-10 and sodium hexametaphosphate (SHMP) on the grafting ratio (GR) of VMS and MPMS, the dispersion of nano-SiO2 particles and the film properties of SiO2/P(MMA/BA/3FMA) are investigated by TGA, DLS, TEM, SEM, and XPS. The morphology variation and the particle size distributions of SiO2/P(MMA/BA/3FMA) with the content of surfactant and P(MMA/BA/3FMA) are characterized. It is found that MPMS is more effective than VMS in improving GR and the dispersion of nano-SiO2 particles. The surfactants are favor of gaining the higher GR in the multilayer grafted nano-SiO2, especially SDS/TX-10 for 17.6% GR. The morphology of SiO2/P(MMA/BA/3FMA) is controlled by the amount of SDS/TX-10 and P(MMA/BA/3FMA) as the core-shell particles, the stacked pomegranate seed with multicore and the multicore-single shell structure when w(MMA)/w(BA)/w(3FMA)=1.3/1/1. Among the different surfactants, SDBS/TX-10 and PVP could give the monodispersing nano-SiO2 in the terpolymer matrix of the films, but SDS/TX-10 and SDBS/TX-10 could perform the fluorine-rich surface.