Hybrid approach to obtain high-quality BaMO3 perovskite nanocrystals

A novel hybrid solvothermal approach for perovskite nanocrystal formation via accurate control of the hydrolytic process is reported. This new synthetic methodology sets a whole general route to successfully tune the sizes of high-quality BaMO₃ (M = Ti⁴⁺, Zr⁴⁺, and Hf⁴⁺) perovskite nanocrystals. Purely cubic-phase nanocrystals (stable in alcohol media) were obtained using controlled water amounts, combining the well-known aqueous sol–gel process with the classic solvothermal method. Exhaustive optimizations revealed feasibility of a fast (1 hour) and reproducible synthesis with small variations in the crystal size or agglomeration parameters. The study also reveals water content as the pivotal factor to achieve this wide range of sizes through a controlled hydrolytic step. Finally, the study of the hydrolytic process made it possible to shed some light on mechanistic insights of this synthetic route.

A novel hybrid solvothermal approach for perovskite nanocrystal formation via accurate control of the hydrolytic process is reported.     

Facile anion-exchange reaction in mixed-cation lead bromide perovskite nanocrystals

The present paper reports a facile and fast anion exchange reaction approach for perovskite nanocrystals (NCs). The reaction has been applied to a mixed-cation sample, namely FA_0.8Cs_0.2PbBr_3, and just employs lead halide precursors to achieve a significant shift in the nanocrystals emission. Within 30 minutes reaction time and a molar ratio between the NCs and the halide precursors of 1 : 1, it was possible to cover more than 120 nm in the visible region. The exchanged NCs maintain their cubic-shaped morphology and narrow emission peak width for the whole compositional range explored. The present approach also allows a reduction in solvent use since it does not require any halide precursor synthesis nor complex post-synthesis treatments.

The present paper reports a facile and fast anion exchange reaction approach for perovskite nanocrystals (NCs).     

RAFT-mediated Pickering emulsion polymerization with cellulose nanocrystals grafted with random copolymer as stabilizer

The synthesis of a RAFT-mediated Pickering emulsion was firstly achieved by using cellulose nanocrystals (CNCs) grafted with a random copolymer as the stabilizer. Firstly, poly(acrylonitrile-r-butyl acrylate) (poly(AN-r-nBA)) was synthesized by Cu(0)-mediated CRP, which was further modified via a click chemistry strategy to obtain poly(ethylene tetrazole-r-butyl acrylate) (poly(VT-r-nBA)). Then, poly(VT-r-nBA) was grafted onto the CNCs through a Mitsunobu reaction to obtain poly(VT-r-nBA)-g-CNCs. Stabilized by poly(VT-r-nBA)-g-CNCs, an O/W RAFT-mediated Pickering emulsion was formed for the preparation of well-controlled poly(methyl methacrylate) (PMMA) particles with water-soluble potassium persulfate (KPS) as an initiator and oil-soluble 4-cyanopentanoic acid dithiobenzoate (CPADB) as a chain transfer agent. Rheological analysis suggested that the prepared Pickering emulsion possessed good stability under the influences of changes in strain, time, frequency and temperature. Furthermore, the recycling and further utilization of the poly(VT-r-nBA)-g-CNCs could be simply realized through centrifugal separation.

A RAFT-mediated Pickering emulsion with cellulose nanocrystals grafted with a random copolymer was used for the preparation of poly(methyl methacrylate) particles..     

Broadband emission from zero-dimensional Cs4PbI6 perovskite nanocrystals

To overcome the drawbacks in three-dimensional (3D) perovskites, such as instability, surface hydration, and ion migration, recently researchers have focused on comparatively stable lower-dimensional perovskite derivatives. All-inorganic zero-dimensional (0D) perovskites (e.g., Cs₄PbX₆; X = Cl⁻, Br⁻, I⁻) can be evolved as a high performing material due to their larger exciton binding energy and better structural stability. The clear understanding of carrier recombination process in 0D perovskites is very important for better exploitation in light-emitting devices. In this work, we comprehensively studied the light emission process in 0D Cs₄PbI₆ nanocrystals (NCs) and interestingly we observe intense white light emission at low temperatures. According to our experimental observations, we conclude that the white light emission contains an intrinsic exciton emission at 2.95 eV along with a broadband emission covering from 1.77 eV to 2.6 eV. We also confirm that the broadband emission is related to the carrier recombination of both self-trapped excitons (STE) and defect state trapped excitons. Our investigations reveal the carrier recombination processes in Cs₄PbI₆ NCs and provide experimental guidelines for the potential application of white light generation.

The broadband white light emission is realized in zero dimensional (OD) Cs₄PbI₆ nanocrystals at low temperatures. The white light emission originates from recombination of both self-trapped excitons and defect state trapped excitons.     

Amphiphilic diblock copolymer of hydrophilic-functionalized lactone and lactide via switchable organocatalytic polymerization

Main-chain degradable amphiphilic diblock copolymers composed of a hydrophilic-functionalized polyester and PLA were facilely prepared by one-pot ring-opening polymerization (ROP) via actively manipulating the catalytic states of an acid–base catalytic system. The resultant block copolymers showed low critical micelle concentration (CMC) in water and were capable of forming stable micelles with optimal hydrodynamic particle size (average diameter 83 nm) and narrow particle distribution.

Main-chain degradable amphiphilic diblock copolymers prepared by one-pot ring-opening polymerization via actively manipulating catalytic states of an acid–base catalytic system were capable of forming stable micelle with optimal particle size.

Amphiphilic block copolymers have many important applications in the life sciences, especially in drug delivery. They are able to self-assemble into micelles or polymersomes which are extensively exploited as vehicles for encapsulation and delivery of bioactive reagents. Hydrophobic blocks provided lipophilic compartments or cores for encapsulation of highly hydrophobic therapeutics. Polyesters, especially polylactide (PLA), are widely used as the hydrophobic segments of the copolymers for drug delivery due to their good biodegradability, biocompatibility and renewability.¹ Hydrophilic blocks form a fully hydrated outer shell for dispersion and reducing bio-molecule attachment. So far, water soluble poly(ethylene glycol) (PEG) is probably the mostly used hydrophilic segment in constructing copolymers for medical applications,² due to its good water solubility and resistance to the adsorption of bio-molecules in plasma. Many PEG-b-polyester amphiphilic block copolymers have been synthesized and extensively studied as delivery platforms.³ However the inherent non-biodegradable issue of PEGs has caused increasing concerns.^4,5 Though, high molecular weight PEGs (over 40 kDa) are considered to be metabolically inert, their excretion rates are significantly reduced with increase of molecular weight.⁶ Evidences have emerged showing that high molecular weight PEGs can accumulate and cause vacuolation in the liver, kidney, spleen and tissues after administration.^7,8 Growing concerns on bioaccumulation and cytoplasmic vacuolization issues of PEG prompted efforts of searching alternatives of PEG. We have recently reported facile preparation of well-defined functional poly(δ-valerolactone) (PFVL) with oligo(ethylene glycol) methyl ether (OEGME) pendant groups and demonstrated that this functional PVL was highly hydrophilic and fully comparable with PEGs in terms of bio-compatibility and capabilities of resistance to non-specific protein adsorption, which made it a promising biomaterial as fully degradable version of PEG for applications in life science.⁹ The excellent protein resistant properties of this hydrophilic polyester led to our further investigation into the feasibility of using PFVL as an alternative of PEG to construct polymeric nano-carriers for drug delivery. As proof of concept, we set out to synthesize well defined amphiphilic diblock copolymers, PFVL-b-PLA, with our functional PFVL as the hydrophilic segments and PLA as the hydrophobic blocks, and investigate the self-assembly behaviors of these diblock copolymers.Conventionally, PEG/polyester copolymers are prepared in a multi-step process which involves isolation and purification of one block before other blocks are installed to the end(s) of the first block by polymerization or by covalent conjugation. This multi-step process is time consuming and more importantly often results in loss of polymer yield and broad polydispersity.¹⁰ On the other hand, one-pot polymerization methods such as sequential monomer feeding are more efficient and can provide better control over the polymerization processes, which is highly desirable in preparation of copolymers. Though many organometallic catalysts have been successfully used to prepare copolymers by ROP of lactones and lactide,^11,12 metal-free organocatalysts are generally preferred in preparation of copolymers intended for biomedical applications due to concerns of the possible residual metallic catalyst in polymer product though not all organocatalysts are fully biocompatible.^13,14 In our previous study, it was found that diphenyl phosphate (DPP) was the most efficient catalyst among other organocatalysts screened for polymerization of δ-valerolactone with oligo(ethylene glycol) functional group under ambient conditions.⁹ Traditional one-pot synthesis of copolymers usually requires a common catalyst that works with high efficiency for all monomers of individual blocks. Unfortunately, in our case, DPP, a weak organic Brønsted acid, works efficient for our functional lactone monomers by electrophilic activation but are almost inactive for lactide which requires basic or nucleophilic activation.^15,16 Then, we noticed that Hedrick group recently reported a rather surprising discovery that a equimolar mixture of 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) and benzoic acid (BA) which was usually used in excess to quench activity of DBU at the end of ROP of lactide turned out to be a better catalyst than DBU itself in terms of promoting well controlled ROP of lactide under mild condition.¹⁷ It was proposed that an ion pair catalyst system was formed from the mixture of BA and DBU (1 : 1, molar ratio) and a dual-activation mechanism might be involved.^18,19 Specifically, the protonated DBU cation was believed to be able to activate the initiating/propagating hydroxyl groups and benzoate anion concurrently activate the monomer carbonyl in ROP of LA.¹⁷ More intriguingly, it was found that the addition of 2 or more equivalents of BA could lead to complete deactivation of this BA/DBU ion pair catalyst system.¹⁷ Inspired by this discovery, we envisioned that the equimolar BA/DBU ion pair catalyst could be employed to efficiently prepare well defined PLA as the first block then, subsequently, two equivalents of DPP could be added to the reaction mixture to deactivated the BA/DBU ion pair and switch catalytic mode of the catalyst from being “lactide-active” to “lactide-inactive” and “lactone-active”. Thus, the newly added DPP would play double roles: (1) 1 equivalent of DPP would fully deactivate the BA/DBU ion pair (pK_a of benzoic acid, 4.204, is similar to pK_a of DPP, 3.88); (2) the other equivalent of DPP would function as catalyst for ROP of functional δ-valerolactones. Herein, we report one-pot preparation of amphiphilic PFVL-b-PLA diblock copolymers via active switch of activating states of a ROP catalyst complex. The self-assembly of the resultant amphiphilic copolymers in water was then investigated and found them readily form stable micelle structures with ideal particle size in water.As depicted in Scheme 1, PLA, the hydrophobic segment of the amphiphilic copolymers, can be facilely prepared by well controlled ROP of lactide with BA/DBU (1 : 1) as a bi-functional catalyst. And switching of catalyst states from being lactide active to lactone active is realized by introducing DPP into the reaction mixture. The performance of the catalyst complex in different active states was evaluated by homo-polymerization before employing this catalytic switching strategy in block copolymer preparation. As summarized in Scheme 1. Briefly, the ROP of lactide was carried out with benzyl alcohol as initiator and BA/DBU (1 : 1) complex as catalyst and with a [BnOH]₀/[catalyst]₀ ratio of 100 : 1 at 36 °C. While lactide conversion reaching 90%, DPP (3 equivalents with regard to BnOH) was introduced to the reaction solution to “turn-off” lactide-active mode of the catalyst complex and switch to lactone-active mode for the ROP of the incoming function lactone monomers. When the conversion of the functional lactone reached 85%, the reaction was quenched by addition of an excess amount of triethyl amine. Following this protocol, block copolymers with various block length were successfully obtained (entry 5–8) with M_n values close to theoretical ones and fairly narrow molecular weight distribution (PDI, 1.1–1.3, Fig. S2^†), which proved that this sequential addition protocol based on facile catalytic mode switching was an efficient strategy for one-pot preparation of block copolymer of lactide and the functional lactone.Open in a separate windowScheme 1One-pot synthesis of functional lactone-b-PLA diblock copolymer through catalytic activity switching.Experimental conditions and characterization of the homopolymers and copolymers^a

High intensity focused ultrasound-responsive release behavior of PLA-b-PEG copolymer micelles

Poly(lactic acid) (PLA) was synthesized by solution polycondensation of L-lactic acid and further reacted with dihydroxyl poly(ethylene glycol) (PEG) to obtain the amphiphilic block copolymer PLA-b-PEG. The biodegradable PLA-b-PEG copolymer can self-assemble into spherical micelles in aqueous solution. Nile Red, as a payload model, was used to examine the release behavior of the micelles. The hydrophobic Nile Red can be adsolubilized into the hydrophobic inner core of PLA-b-PEG micelles. With the introduction of Nile Red, the size of micelles increased. Moreover, high intensity focused ultrasound (HIFU), as a non-contact and remote control approach, was introduced to control the release behavior of PLA-b-PEG micelles containing Nile Red. The release behavior of Nile Red was monitored by fluorescence emission spectra. The results showed that HIFU can trigger the release of the encapsulated Nile Red from PLA-b-PEG micelles. By adjusting the HIFU time, intensity and location, the release behavior of Nile Red from micelles can be tuned. Base on the results, an irreversible release mechanism under HIFU was proposed. The irreversible release of Nile Red from the PLA-b-PEG micelle was attributed to a chemically breaking process of micelle structure due to the degradation of the PLA-b-PEG chain that resulted from the transient cavitation in the HIFU focal spot.     

Solvothermal synthesis of Mn-doped CsPbCl3 perovskite nanocrystals with tunable morphology and their size-dependent optical properties

Doping metal ions in inorganic halide perovskite (CsPbX₃, X = Cl, Br, I) nanocrystals (NCs) endows the NCs with unique optical characteristics, and has thus attracted immense attention. However, controllable synthesis of high-quality doped perovskite NCs with tunable morphology still remains challenging. Here, we report a facile, effective and unified strategy for the controllable synthesis of Mn-doped CsPbCl₃ quantum dots (QDs) and nanoplatelets (NPLs) via a single-step solvothermal method. The incorporation of Mn²⁺ into CsPbCl₃ NCs introduces new broad photoluminescence (PL) emission from Mn²⁺ while maintaining the structure of host CsPbCl₃ NCs nearly intact. The PL intensity, emission peak position and size of the NCs can be accurately adjusted by altering the experimental parameters such as Mn-to-Pb feed ratio and reaction time. Especially, by changing the amount of ligands, Mn-doped CsPbCl₃ QDs, NPLs or their mixtures can be obtained. Both of the Mn-doped QDs and NPLs exhibit a size-dependent quantum confinement effect, which is confirmed by the relationship between the size of NCs and the exciton emission peaks. The solvothermal reaction condition plays an important role for the precise control of the structure, morphology and PL properties of the Mn-doped NCs. The as-prepared Mn-doped CsPbCl₃ NPLs with thickness down to ∼2 nm exhibit a PL quantum yield (PLQY) of more than 22%. This work introduces a new strategy for the controllable synthesis of Mn-doped perovskite NCs, which provides ideas for the in-depth study of the dope-and-grow process and can be extended to approaches of doping other metal ions.

A facile solvothermal reaction strategy was developed to obtain Mn-doped CsPbCl₃ nanocrystals with tunable morphology and optical properties.     

Biodegradable polymeric micelles composed of doxorubicin conjugated PLGA-PEG block copolymer.

Biodegradable polymeric micelles containing doxorubicin in the core region were prepared from a di-block copolymer composed of doxorubicin-conjugated poly(DL-lactic-co-glycolic acid) (PLGA) and polyethyleneglycol (PEG). The di-block copolymer of PLGA-PEG was first synthesized and the primary amino group of doxorubicin was then conjugated to the terminal hydroxyl group of PLGA, which had been pre-activated using p-nitrophenyl chloroformate. The resulting polymeric micelles in aqueous solution were characterized by measurement of size, drug loading, and critical micelle concentration. The micelles containing chemically-conjugated doxorubicin exhibited a more sustained release profile than PEG-PLGA micelles containing physically-entrapped doxorubicin. The cytotoxic activity of the micelles against HepG2 cells was greater than free doxorubicin, suggesting that the micelles containing conjugated doxorubicin were more effectively taken up cellularly, by an endocytosis mechanism rather than by passive diffusion. Confocal microscopic observation and flow cytometry analysis supported the enhanced cellular uptake of the micelles.     

A facile method for preparing Yb3+-doped perovskite nanocrystals with ultra-stable near-infrared light emission

Colloidal all-inorganic cesium lead halide (CsPbX₃, X = Cl, Br, I) nanocrystals (NCs) are very important optoelectronic materials and have been successfully utilized as bright light sources and high efficiency photovoltaics due to their facile solution processability. Recently, rare-earth dopants have opened a new pathway for lead halide perovskite NCs for applications in near-infrared wave bands. However, these materials still suffer from serious environmental instability. In this study, we have successfully developed a facile method for fabricating all-inorganic SiO₂-encapsulated Yb³⁺-doped CsPbBr₃ NCs by slowly hydrolyzing the organosilicon precursor in situ. Experimental results showed that the Yb³⁺ ions were uniformly distributed in the NCs, and the whole NCs were completely encapsulated by a dense SiO₂ layer. The as-prepared SiO₂-encapsulated NCs can emit a strong near-infrared (985 nm) photoluminescence, which originates from the intrinsic luminescence of Yb³⁺ in the NCs, pumped by the perovskite host NCs. Meanwhile, the SiO₂-encapsulated NCs possessed excellent high PLQYs, narrow FWHM, and excellent environmental stability under a room atmosphere for over 15 days. We anticipate that this work will be helpful for promoting the optical properties and environmental stability of perovskite NCs and expanding their practical applications to near infrared photodetectors and other optoelectronic devices.

A facile method for fabricating CsPbBr₃:Yb³⁺@SiO₂ NCs which guarantees high PLQY and excellent stability at the same time.     

Stability of bovine serum albumin complexed with PEG-poly(L-histidine) diblock copolymer in PLGA microspheres.

The aim of this study was to examine the stability of bovine serum albumin (BSA) in poly(DL-lactic acid-co-glycolic acid) (PLGA) microspheres upon addition of a new excipient, poly(ethylene glycol)-poly(L-histidine) diblock copolymer (PEG-PH). Poly(L-histidine) component can form an ionic complex with BSA under acidic conditions within a narrow pH range. To optimize the ionic complexation conditions for BSA with PEG-PH, the resulting complex sizes were monitored using the Zetasizer. PLGA microspheres containing BSA as a model protein were prepared by w/o/w double emulsion method. BSA stability in aqueous solutions and after release from PLGA microspheres was determined using circular dichroism (CD) spectroscopy for secondary structure analyses and fluorescence measurements for tertiary structure analyses. The release profile of BSA from the microspheres was monitored using UV spectrophotometry. The rate of PLGA degradation was monitored by gel permeation chromatography. The pH profile within microspheres was further evaluated by confocal microscopy using a pH-sensitive dye. Approximately 19 PEG-PH molecules and one BSA molecule coalesced to form an ionic complex around a pH range of 5.0-6.0. Plain BSA/PLGA and BSA/PEG-PH/PLGA microspheres had a mean size of 27-35 microm. PLGA microspheres with a BSA loading efficiency >80% were prepared using the double emulsion method. PEG-PH significantly improved the stability of BSA both in aqueous solutions and in PLGA microspheres. The release profiles of BSA from different formulations of PLGA microspheres were significantly different. PEG-PH effectively buffered the local acidity inside the microspheres and improved BSA release kinetics by reducing initial burst release and extending continuous release over a period of time, when encapsulated as an ionic complex. PLGA degradation rate was found to be delayed by PEG-PH. There was clear evidence that PEG-PH played multiple roles when complexed with BSA and incorporated into PLGA microspheres. PEG-PH is an effective excipient for preserving the structural stability of BSA in aqueous solution and BSA/PLGA microspheres formulation.     

Heating-up synthesis of cesium bismuth bromide perovskite nanocrystals with tailored composition,morphology, and optical properties

This study represents the heating-up synthesis of lead-free cesium bismuth bromide perovskite nanocrystals (NCs). CsBr and BiBr₃ precursors are used to synthesize uniform and phase-pure cesium bismuth bromide NCs, and the reaction is performed via an injection-free, heating-up method in the presence of a solvent mixture with a high boiling point. The size and composition of cesium bismuth bromide NCs are readily controlled by changing the reaction time, temperature, and amount of surfactant added to the reaction mixture. Upon heating, sequential phase evolution occurs, resulting in the formation of kinetically stable BiOBr in the early reaction stages, which transformed into the thermodynamically stable Cs₃BiBr₆ and Cs₃Bi₂Br₉ with an increase in either the reaction time or the reaction temperature. Furthermore, the absorption and photoluminescence properties of Cs₃BiBr₆ and Cs₃Bi₂Br₉ NCs are characterized to investigate their composition-dependent optical properties. This work provides the potential to synthesize various types of lead-free perovskite NCs by tailoring the size and compositions.

Lead-free cesium bismuth bromide perovskite nanocrystals are synthesized via the heating-up method with tailored morphology and optical properties.     

Influence of formulation variables on the biodistribution of multifunctional block copolymer micelles

The physico-chemical characteristics and composition of block copolymer micelles (BCMs) may influence the pharmacokinetics and consequently, the desired delivery characteristics. In this study the influence of formulation variables such as size, density of targeting ligand [i.e. epidermal growth factor (hEGF)] and the bifunctional chelator (BFC) used for labelling the BCMs with (111)In, on the pharmacokinetics and biodistribution in mice were evaluated. BCMs were prepared from Me-PEG(x)-b-PCL(y) (x=2.5 k, y=1.2 k for 15 nm BCMs and x=5 k, y=5 k for 60 nm BCMs) with (targeted, 1 or 5 mol% hEGF) or without (non-targeted) hEGF-PEG(x)-b-PCL(y). To investigate the effect of the BFC on the pharmacokinetics, the BCMs were labelled with (111)In using p-SCN-Bn-DOTA (Bn-DOTA-PEG(x)-b-PCL(y)), H(2)N-DOTA (DOTA-PEG(x)-b-PCL(y)), DTPA anhydride (DTPA-PEG(x)-b-PCL(y)) or p-SCN-Bn-DTPA (Bn-DTPA-PEG(x)-b-PCL(y)). The resulting 15 nm or 60 nm non-targeted or targeted (1 or 5 mol% hEGF) were injected via a tail vein to mice bearing MDA-MB-468 human breast cancer xenograft that overexpress EGFR, followed by pharmacokinetics and biodistribution studies. Pharmacokinetic parameters were determined by fitting the blood concentration vs time data using a two compartment model with i.v. bolus input. Pharmacokinetic parameters were found to depend on BCM size, the BFC used as well as the density of hEGF on the surface of the BCMs. BCMs labelled with p-SCN-Bn-DTPA ((111)In-Bn-BCMs) showed improved pharmacokinetics (i.e. extended circulation lifetime) and tumor uptake compared to those labelled with DOTA-PEG(x)-b-PCL(y), p-SCN-Bn-DOTA or DTPA dianhydride. Formulations with a high density of hEGF (5 mol% hEGF) had short circulation half-lives. BCMs labelled with (111)In via p-SCN-Bn-DTPA showed highest accumulation in the liver and spleen and slower whole body elimination. Smaller sized BCMs were rapidly cleared from the circulation. Increasing the density of hEGF on the surface did not improve tumor uptake due to faster clearance from the circulation. To achieve improved pharmacokinetics and in turn effective exploitation of the EPR effect, p-SCN-Bn-DTPA emerged as the optimal BFC for radiolabelling BCMs while a lower density of hEGF gave more favourable organ distribution.     

Highly bright perovskite light-emitting diodes based on quasi-2D perovskite film through synergetic solvent engineering

Recently, quasi-two dimensional (2D) perovskites have attracted great interest as they can be facilely fabricated and yield high photoluminescence quantum yield. However, the luminance and the efficiency of perovskite light-emitting diodes (PeLEDs) based on quasi-2D perovskites are limited by the carrier transport and the crystallization properties of the quasi-2D perovskite films. Herein, a synergetic solvent engineering approach is proposed to improve the crystallinity and the carrier transport by optimizing the film morphology of the quasi-2D perovskite films. Consequently, the maximum luminance of green PeLEDs based on quasi-2D PEA₂ (MAPbBr₃)₂PbBr₄ perovskite is dramatically enhanced from 4000 cd m⁻² to 18 000 cd m⁻² and the current efficiency increases from 3.40 cd A⁻¹ to 8.74 cd A⁻¹. This work provides a promising way to control the morphology and the crystallinity properties of quasi-2D perovskite films for high-performance optoelectronic devices.

A synergetic solvent engineering approach to improve crystallinity and carrier transport, by optimizing film morphology of the quasi-2D perovskite films.     

Synthesis and characterization of Mn-doped CsPb(Cl/Br)3 perovskite nanocrystals with controllable dual-color emission

Metal-halide perovskite nanocrystals (NCs) are considered to be promising types of optoelectronic and photonic materials. The emission colors of the cesium lead halide perovskite (CsPbX₃, X = Cl, Br, I) NCs depend on the joint influence of the emission peaks of the host and its dopant ions. Herein, we report a phosphine-free strategy to synthesize Mn-doped CsPb(Cl/Br)₃ NCs to tune their optical properties in a wide color gamut. Colloidal Mn-doped CsPb(Cl/Br)₃ NCs were synthesized by injecting Cs-oleate solution into the MnCl₂ and PbBr₂ precursor solution. The as-prepared Mn-doped CsPb(Cl/Br)₃ NCs are highly crystalline and uniform sized nanocubes with two emission peaks, including the host emission around 450 nm and the Mn²⁺ dopant emission around 600 nm, which are sensitive to the MnCl₂-to-PbBr₂ molar feed ratio and the reaction temperature. By varying the MnCl₂-to-PbBr₂ molar feed ratio or the reaction temperature, the relative PL intensities of dual color emission can be manipulated, showing their ability in tunable color output.

Colloidal Mn-doped CsPb(Cl/Br)₃ NCs were synthesized at different MnCl₂-to-PbBr₂ molar feed ratios or reaction temperatures to tune their color emission.     

Block copolymer micelles: preparation, characterization and application in drug delivery.

Block copolymer micelles are generally formed by the self-assembly of either amphiphilic or oppositely charged copolymers in aqueous medium. The hydrophilic and hydrophobic blocks form the corona and the core of the micelles, respectively. The presence of a nonionic water-soluble shell as well as the scale (10-100 nm) of polymeric micelles are expected to restrict their uptake by the mononuclear phagocyte system and allow for passive targeting of cancerous or inflamed tissues through the enhanced permeation and retention effect. Research in the field has been increasingly focused on achieving enhanced stability of the micellar assembly, prolonged circulation times and controlled release of the drug for optimal targeting. With that in mind, our group has developed a range of block copolymers for various applications, including amphiphilic micelles for passive targeting of chemotherapeutic agents and environment-sensitive micelles for the oral delivery of poorly bioavailable compounds. Here, we propose to review the innovations in block copolymer synthesis, polymeric micelle preparation and characterization, as well as the relevance of these developments to the field of biomedical research.     

Electrochemical preparation system for unique mesoporous hemisphere gold nanoparticles using block copolymer micelles

Gold nanoparticles (AuNPs) are widely used in various applications, such as biological delivery, catalysis, and others. In this report, we present a novel synthetic method to prepare mesoporous hemisphere gold nanoparticles (MHAuNPs) via electrochemical reduction reaction with the aid of polymeric micelle assembly as a pore-directing agent.

Mesoporous hemisphere Au nanoparticles using self-assembled micelles, for the first time, are demonstrated by using electrochemical reduction on a Ti substrate.

Gold (Au) is one of the most stable and versatile elements utilized in various fields, including catalysis, optics, and industrial purposes. Consequently, various shapes and sizes of AuNPs have been intensively studied to improve the performance of Au in different applications.^1–6 Previously, nanoporous or dendritic metal nanostructures, including Au nanostructures, have been synthesized by employing different reagents and conditions such as SH-terminated amphiphilic surfactant,⁷ pH controlling,⁸ and hard-templates.^9,10 The reported porous and dendritic Au nanostructures possess high surface areas and rich active sites, which in turn lead to highly enhanced catalytic activities.Recently, a soft-template method using self-assembled micelles or lyotropic liquid crystals as pore-directing agents has allowed the successful synthesis of mesoporous nanoparticles^11–13 and films^14–17 with different metal compositions. The metals with mesoporous structures demonstrate superior catalytic activity per weight or surface area over their nonporous bulk forms. Previously, our group reported a several-fold increase in the catalytic activity of mesoporous metals in reactions such as the methanol oxidation reaction (MOR),^14,15 ethanol oxidation reaction (EOR),^13,15–17 and nitric oxide reduction¹² as compared to their bulk nanoparticles and films. Such improvement in the catalytic activity of mesoporous structures is mainly attributed to their significantly larger surface areas, more exposed catalytically active sites, and increased durability against aggregation.Interestingly, nanoporous or mesoporous Au structures had been successfully synthesized by using a dealloying method¹⁸ and a hard templating method.⁹ Such methods, however, are a little complicated, and pore-directing templates often remain within the pores, thus leading to severe contamination. Using a thiol group is an alternative way to synthesize mesoporous Au nanospheres.⁷ A significant drawback of using a thiol group, however, is its strong chemical bonding with Au, thus becoming unable to be removed. The synthesis of mesoporous structures using self-assembled polymeric micelles as soft-templates, on the other hand, is a more facile method with fewer synthetic steps, and it is also known to be free of contaminations within the pores. Although a soft-templating method using polymeric micelles has been utilized for the preparation of mesoporous Au and Au-based alloy films towards surface-enhanced Raman scattering (SERS) signals,¹⁹ glucose sensing,^20,21 and MOR,²² the obtained morphologies have been limited to only films.Despite such apparent benefits arising from mesoporous structures and their synthesis using soft-templates, the synthesis of mesoporous AuNPs using soft-templates has not been achieved yet. It is mainly due to the physical and chemical properties of Au which make it extremely hard to form mesoporous structures. Herein, we adopt an electrochemical approach and the soft-template method to synthesize MHAuNPs successfully. As discussed above, we expect MHAuNPs to be highly efficient in various applications in medical diagnosis,²³ optical sensing,²⁴etc.In this report, MHAuNPs with different shapes and sizes are for the first time reported by changing various electrochemical deposition conditions such as applied potentials between electrodes and deposition times. Scheme 1 shows the schematic illustrations of the entire process of precursor preparation (Scheme 1a) and the MHAuNPs fabrication process (Scheme 1b), including the deposition and the detachment of the nanoparticles. The characterization methods implemented in this paper are mentioned in ESI.^†Open in a separate windowScheme 1(a) The process of Au precursor solution preparation and (b) fabricating MHAuNPs by electrochemical reduction.In a typical experiment, a p-doped silicon (Si) wafer was cleaned by using acetone, isopropyl alcohol, and deionized water (DIW) with sonication for 5 minutes, followed by nitrogen (N₂) gas blowing to dry the Si wafer. After the wet cleaning process, the Si surface was treated by oxygen (O₂) plasma for 5 minutes (Oxford Instruments PlasmaPro 80 Reactive Ion Etcher) to remove residual organic impurities. Then, 10 nm of titanium (Ti) layer and 100 nm of Au layer were deposited sequentially by electron beam evaporation (Temescal FC-2000 e-beam evaporator) at 10⁻⁶ torr. Commercially available Au etchant (Sigma-Aldrich) was used to etch the Au film to expose the Ti area (the left image in Scheme 1b). During etching, about 20 percent of Au area was left to be connected to the electrochemical work station, as drawn in Scheme 1b. In preparation of the Au precursor solution, 5 mg of poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO, the number of average molecular weight (M_w) for each block is 18 000 for PS and 7500 for PEO, respectively) was mixed in 1.5 ml of tetrahydrofuran (THF) followed by stirring at 300 rpm for 8 hours. Then, 0.75 ml of ethanol, 0.5 ml of HAuCl₄ aqueous solution (40 mM), and 1.25 ml of DIW were added sequentially. The solution was stirred for another 30 minutes at 200 rpm. The existing block copolymer micelles can be confirmed by TEM observation, and the average diameter is 25 nm, as shown in Fig. S1.^† For the electrochemical deposition, an electrochemical workstation (CH Instruments Inc. 660e) with three electrode system was used to deposit MHAuNPs on the Ti/Si substrate. After the deposition, the particles were carefully washed by chloroform, followed by a rinse using DIW to remove the residual micelles completely. To detach and collect MHAuNPs from the Ti/Si substrate, the substrate was soaked in ethanol and strongly sonicated for a few minutes (Scheme 1b).Fig. S2^† shows the details of the growth mechanism of MHAuNPs by different deposition times. At the initial stage (Fig. S2a^†), small nanoparticles are generated by reducing Au ions in the precursor solution throughout the substrate. Then, the seed starts growing and forming MHAuNPs as the deposition time increases (Fig. S2b–e^†). This similar growth mechanism is the same as the previous report.¹⁹ The high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) image (Fig. S2f^†) shows the mesopores inside the MHAuNPs are homogeneously generated. As-obtained MHAuNPs consist of a pure Au element without any impurities, as shown in Fig. S3.^† Fig. 1 and S4^† show scanning electron microscope (SEM) images of MHAuNPs deposited at different voltages from −0.2 V to −0.9 V vs. Ag/AgCl at high magnification and low magnification, respectively. Different deposition voltages lead to significant changes in the particle sizes but slight differences in the particle shapes. The size distributions of MHAuNPs and the plots of the average diameters of MHAuNPs by different deposition voltages are described in Fig. 2. The distribution graphs show the large sizes of particles, such as more than 1 μm in diameter, when the high voltage (−0.2 V vs. Ag/AgCl) is applied (Fig. 2a). The distribution becomes narrower upon the lower applied voltage. The average diameter-applied voltage plots in Fig. 2b show that the average particle size decreases from around 1.1 μm at −0.2 V to about 300 nm at −0.9 V. Thus when the lower deposition voltages are applied (i.e., the deposition rate is higher) (Fig. 1g–h), the smaller particles with a higher degree of size uniformity are obtained. The opposite trend is observed at higher deposition voltages (i.e., the deposition rate is lower) (Fig. 1a and b), at which the particles become larger and their size uniformity decreases. This trend is because the higher voltage allows only a limited number of seed particles to be deposited on the Ti/Si substrate, and each seed individually grows with no additional seed formation. Whereas the lower voltage can allow a higher number of seeds, leading to a uniform supply of electrons from the working Ti/Si electrode (Fig. S5^†). In addition, the lower deposition voltages make the particle shape more hemispherical in Fig. 1f–h.Open in a separate windowFig. 1The SEM images of MHAuNPs electrochemically deposited at (a) −0.2 V, (b) −0.3 V, (c) −0.4 V, (d) −0.5 V, (e) −0.6 V, (f) −0.7 V, (g) −0.8 V, and (h) −0.9 V for 500 s. The scale bars indicate 200 nm.Open in a separate windowFig. 2(a) Size distributions of MHAuNPs generated by different voltages and (b) the average diameter–the applied voltage plots. Fig. 3 shows the SEM images of MHAuNPs deposited at −0.2 V and for different deposition times from 250 s to 1000 s. Although longer deposition time does not change the number of MHAuNPs, it leads to the growth of MHAuNPs in lateral and vertical directions. Although the MHAuNPs grow more than about two or three times larger at long deposition time, the mesoporous formation does not seem to be changed, as shown in insets in Fig. 3. This point indicates that the deposition time is not the main factor affecting the formation of mesoporous structures as well as the number of particles (seeds), but it affects the sizes of particles.Open in a separate windowFig. 3The SEM images of MHAuNPs deposited at −0.2 V (vs. Ag/AgCl) for (a) 250 s, (b) 500 s, and (c) 1000 s. The scale bars indicate 10 μm. The insets in each figure are magnified SEM images of each condition (The scale bars in insets indicate 500 nm).In this report, 10 nm Ti layer on Si wafer plays an important key role in the formation of MHAuNPs, as previously mentioned in the experimental procedure. The use of the Ti substrate with low conductivity (ca. 2.38 × 10⁶ S m⁻¹), which is about only 5.8% in comparison with that of Au (ca. 4.10 × 10⁷ S m⁻¹), is not common in the electrochemical plating research field.^25–30 Most of the papers on mesoporous metal structures synthesized by electrochemical deposition have utilized Au or Pt substrates due to its chemical stability and high electrical conductivity.^14–17 Fig. S6^† shows the amperometry (i–t) curves during the deposition of MHAuNPs (black dots) on a Ti/Si substrate and mesoporous gold films (red dots) on an Au substrate at the same deposition condition. As shown in Fig. S6,^† around 1/7 times less current flows on the Ti/Si substrate throughout the deposition time. This low current density on the Ti/Si substrate is one of the factors for fabricating MHAuNPs. Low current density causes the formation of a few particles (i.e., seeds) at the initial stage of the deposition and leads to seed growth in a few places, as explained in Fig. S2.^† Furthermore, the use of Ti/Si substrates affects the bottom parts of MHAuNPs to become an arch shape. Only edges of MHAuNPs attach onto the Ti/Si substrates, as shown in Fig. 4. This attachment is because the interaction between the deposited MHAuNPs and the Ti substrate surface (probably, the Ti surface can be partially oxidized, forming TiO_x) is very weak. Therefore, the deposited MHAuNPs can be easily detached from the Ti/Si substrates by sonicating the substrates in solvents (Scheme 1b). The collected MHAuNPs in a solvent are obtained as colloidal particles as shown in Fig. S7.^† Such interesting hemispherical mesoporous nanoparticles have advantages to electrocatalytic activities in comparison to spherical mesoporous metals.³¹ The method using a Ti/Si substrate as a working electrode can be repeatedly implemented with one substrate and without change of the precursor solution, thus it can be effective for mass production in the future.Open in a separate windowFig. 4The SEM image of MHAuNPs deposited at −0.6 V. The arrow shows that the bottom of the MHAuNPs is an arch.Finally, surface-enhanced Raman scattering (SERS) effects on MHAuNPs were investigated by using an adsorbate called rhodamine 6G (R6G), as shown in Fig. S8.^† The resulting MHAuNPs at all conditions (−0.3 V, −0.6 V, and −0.9 V) show substantially strong SERS intensity (Fig. S8a^†), while Ti/Si and Si substrates without MHAuNPs show noise level of intensity. To further investigate enhancement factor (EF) and limit of detection (LoD), various concentrations of R6G with MHAuNPs fabricated at −0.9 V were used for the SERS studies (Fig. S8b^†). The main peak of SERS is 1363 cm⁻¹, and it disappears from less than 10⁻⁶ M concentration, while the 1183 cm⁻¹ peak still exists at 10⁻⁸ M (Fig. S8c^†). The maximum EFs at 1363 cm⁻¹ (10⁻⁶ M) and 1183 cm⁻¹ (10⁻⁸ M) are 1.5 × 10⁴ and 3.1 × 10⁶, respectively (Fig. S8d^†). Transmission electron microscope (TEM) images in Fig. S9^† show the detailed particle structures and the electron diffraction (ED) pattern confirmed the crystal structure is the face-center cubic (FCC) structure. The sharp surface structures and the pores on MHAuNPs provide abundant hot spots that have been reported as the origin that enhances SERS intensity owing to the plasmon resonances.^19,32 Besides, the high density of small-sized MHAuNPs (Fig. S5 and S10^†) boosted higher SERS intensity.In conclusion, we have synthesized MHAuNPs by using 10 nm Ti-coated Si substrates as a working electrode on a Si wafer and electrochemical deposition using self-assembled polymeric micelles as pore-directing agents. The low current generates Au seeds at only a few places, and it acts as the points that MHAuNPs start growing. The particle shapes and sizes can be controlled by changed applied voltages and deposition times. The lower voltages make small particles and the great hemispherical AuNPs with mesoporous architecture. The long-time deposition does not affect any mesoporous formation, but the particle shape and size. Besides, the low affinity between Au and Ti (probably, oxidized layer) results in the arch on the bottom of MHAuNPs, which helps the particles detached from the substrates easily. These results indicate that different thicknesses and compositions of working electrodes can provide different metal deposition phenomena, which can bring out unique shaped particles with mesoporous architectures in the future.     

Development of moisture-proof polydimethylsiloxane/aluminum oxide film and stability improvement of perovskite solar cells using the film

A method for enhancing the moisture barrier property of polydimethylsiloxane (PDMS) polymer films is proposed. This is achieved by filling the PDMS free volume with aluminum oxide (AlO_x). To deposit AlO_x inside PDMS, thermal atomic layer deposition (ALD) is employed. The PDMS/AlO_x film thus produced has a 30 nm AlO_x layer on the surface. Its water vapor transmission rate (WVTR) is 5.1 × 10⁻³ g m⁻² d⁻¹ at 45 °C and 65% relative humidity (RH). The activation energy of permeability with the PDMS/AlO_x film for moisture permeation is determined to be 35.5 kJ mol⁻¹. To investigate the moisture barrier capability of the PDMS/AlO_x layer, (FAPbI₃)_0.85(MAPbBr₃)_0.15/spiro-OMeTAD/Au perovskite solar cells are fabricated, and encapsulated by the PDMS/AlO_x film. To minimize the thermal damage to solar cells during ALD, AlO_x deposition is performed at 95 °C. The solar cells exposed to 45 °C-65% RH for 300 h demonstrate less than a 5% drop in the power-conversion efficiency.

A method for enhancing the moisture barrier property of polydimethylsiloxane (PDMS) polymer films is proposed. This is achieved by filling the PDMS free volume with aluminum oxide (AlO_x).     

Rapid synthesis of cesium lead halide perovskite nanocrystals by l-lysine assisted solid-phase reaction at room temperature

Nowadays, there are many ways to obtain cesium lead halide perovskite nanocrystals. In addition to the synthesis methods carried out in solution, the solid-phase synthesis was reported involving grinding and milling. In this paper, we synthesized luminescent CsPbBr₃/Cs₄PbBr₆ perovskite nanocrystals (PNCs) by three solid-phase synthesis methods (grinding, knocking, stirring) using l-lysine as a ligand. This is the first attempt to use an amino acid for assisting the solid phase synthesis of perovskite and to study the difference in the products obtained by the three solid phase synthesis methods. The results show that the productivity of the solid-phase synthesis methods can be greatly improved by adding l-lysine and the perovskites obtained by the methods are more resistant to water due to the addition of l-lysine. The simplicity of the synthesis process expanded the use of solid-phase synthesis to obtain more perovskites and provided potential applications of perovskite in analytical detection and sensing in aqueous solution.

By comparing three different solid-phase reactions of perovskite powder synthesized using lysine, the reaction process and properties were studied.