Solution Phase Growth and Ion Exchange in Microassemblies of Lead Chalcogenide Nanoparticles

We demonstrate the synthesis of micron-sized assemblies of lead chalcogenide nanoparticles with controlled morphology, crystallinity, and composition through a facile room-temperature solution phase reaction. The amine-thiol solvent system enables this synthesis with a unique oriented attachment growth mechanism of nanoparticles occurring on the time scale of the reaction itself, forming single-crystalline microcubes of PbS, PbSe, and PbTe materials. Increasing the rate of reaction by changing reaction parameters further allows disturbing the oriented attachment mechanism, which results in polycrystalline microassemblies with uniform spherical morphologies. Along with polycrystallinity, due to the differences in reactivities of each chalcogen in the solution, a different extent of hollow-core nature is observed in these microparticles. Similar to morphologies, the composition of such microparticles can be altered through very simplistic room-temperature solution phase coprecipitation, as well as ion-exchange reactions. While coprecipitation reactions are successful in synthesizing core-shell microstructures of PbSe-PbTe materials, the use of solution phase ion-exchange reaction allows for the exchange of not only Te with Se but also Ag with Pb inside the core of the PbTe microparticles. Despite exchanging one Pb with two Ag cations, the hollow-core nature of particles aids in the retention of the original uniform microparticle morphology.

Reducing the Photodegradation of Perovskite Quantum Dots to Enhance Photocatalysis in CO2 Reduction

Solution-processed perovskite quantum dots (QDs) have been intensively researched as next-generation photocatalysts owing to their outstanding optical properties. Even though the intrinsic physical properties of perovskite QDs have been significantly improved, the chemical stability of these materials remains questionable. Their low long-term chemical stability limits their commercial applicability in photocatalysis. In this study, we investigated the photodegradation mechanisms of perovskite QDs and their hybrids via photoluminescence (PL) by varying the excitation power and the ultraviolet (UV) exposure power. Defects in perovskite QDs and the interface between the perovskite QD and the co-catalyst influence the photo-stability of perovskite QDs. Consequently, we designed a stable perovskite QD film via an in-situ cross-linking reaction with amine-based silane materials. The surface ligand comprising 2,6-bis(N-pyrazolyl)pyridine nickel(II) bromide (Ni(ppy)) and 5-hexynoic acid improved the interface between the Ni co-catalyst and the perovskite QD. Then, ultrathin SiO2 was fabricated using 3-aminopropyltriethoxy silane (APTES) to harness the strong surface binding energy of the amine functional group of APTES with the perovskite QDs. The Ni co-catalyst content was further increased through Ni doping during purification using a short surface ligand (3-butynoic acid). As a result, stable perovskite QDs with rapid charge separation were successfully fabricated. Time-correlated single photon counting (TCSPC) PL study demonstrated that the modified perovskite QD film exhibited slow photodegradation owing to defect passivation and the enhanced interface between the Ni co-catalyst and the perovskite QD. This interface impeded the generation of hot carriers, which are a critical factor in photodegradation. Finally, a stable red perovskite QD was synthesized by applying the same strategy and the mixture between red and green QD/Ni(ppy)/SiO2 displayed an CO2 reduction capacity for CO (0.56 µmol/(g∙h)).

PbS Quantum Dots Decorating TiO2 Nanocrystals: Synthesis, Topology, and Optical Properties of the Colloidal Hybrid Architecture

Fabrication of heterostructures by merging two or more materials in a single object. The domains at the nanoscale represent a viable strategy to purposely address materials’ properties for applications in several fields such as catalysis, biomedicine, and energy conversion. In this case, solution-phase seeded growth and the hot-injection method are ingeniously combined to fabricate TiO₂/PbS heterostructures. The interest in such hybrid nanostructures arises from their absorption properties that make them advantageous candidates as solar cell materials for more efficient solar light harvesting and improved light conversion. Due to the strong lattice mismatch between TiO₂ and PbS, the yield of the hybrid structure and the control over its properties are challenging. In this study, a systematic investigation of the heterostructure synthesis as a function of the experimental conditions (such as seeds’ surface chemistry, reaction temperature, and precursor concentration), its topology, structural properties, and optical properties are carried out. The morphological and chemical characterizations confirm the formation of small dots of PbS by decorating the oleylamine surface capped TiO₂ nanocrystals under temperature control. Remarkably, structural characterization points out that the formation of heterostructures is accompanied by modification of the crystallinity of the TiO₂ domain, which is mainly ascribed to lattice distortion. This result is also confirmed by photoluminescence spectroscopy, which shows intense emission in the visible range. This originated from self-trapped excitons, defects, and trap emissive states.

An in vitro and in vivo bio-interaction responses and biosafety evaluation of novel Au-ZnTe core-shell nanoparticles

Novel gold-zinc telluride (Au-ZnTe) core-shell nanoparticles were synthesized to support surface modifications for enhanced drug delivery in cancer therapeutics. Knowledge of the biosafety and biocompatibility properties of these materials within biological systems is very limited and needs to be evaluated before their potential bio-applications may be demonstrated. We report the in vitro and in vivo bio-interactions of the Au-ZnTe nanoparticles, which were exposed to various human cancer and healthy cells, an in vitro immune simulation using peripheral blood mononuclear cells, followed by the analysis of cytokine expression. Acute in vivo exposure studies using low (50 μg ml-1), intermediate (500 μg ml-1) and high (1500 μg ml-1) concentrations of the Au-ZnTe particles were used to investigate histopathological effects in rats. Normal human mammary epithelial and colon cells in addition to human breast, prostate and colon cancer cells displayed cell viability between 86.4 ± 7.4% and 99.0 ± 3.6% when co-cultured with core-shell nanoparticles for 48 hours. Acute exposure studies using rat models displayed no significant changes in full blood counts, liver and kidney enzyme regulation and histopathology. These findings confirmed that Au-ZnTe core-shell nanoparticles display biosafety and biocompatibility features which can be exploited in future bio-applications.

Metal Semiconductor Heterostructures for Photocatalytic Conversion of Light Energy

For fast separation of the photogenerated charge carriers, metal semiconductor heterostructures have emerged as one of the leading materials in recent years. Among these, metal Au coupled with low bandgap semiconductors remain as ideal materials where both can absorb the solar light in the visible region. It is also established that on excitation, the plasmonic state of gold interacts with excited state of semiconductor and helps for the delocalization of the photogenerated electrons. Focusing these materials where electron transfer preferably occurs from semiconductor to metal Au on excitation, in this Perspective, we report the latest developments in the synthetic chemistry in designing such nano heterostructures and discuss their photocatalytic activities in organic dye degradation/reduction and/or photocatalytic water splitting for generation of hydrogen. Among these, materials such as Au-CZTS, Au-SnS, Au-Bi2S3, Au-ZnSe, and so forth are emphasized, and their formation chemistry as well as their photocatalytic activities are discussed in this Perspective.

Synthesis of biocompatible Au-ZnTe core-shell nanoparticles

A novel, solution-based route to biocompatible, cysteine-capped gold-zinc telluride (Au-ZnTe) core-shell nanoparticles with potential in biomedical applications is described. The optical properties of the core-shell nanoparticles show combined beneficial features of the individual parent components. The tunable emission properties of the semiconductor shell render the system useful for imaging and biological labeling applications. Powder X-ray diffraction analysis reveals the particles contain crystalline Au and ZnTe. Transmission electron microscope (TEM) imaging of the particles indicates they are largely spherical with sizes in the order of 2-10 nm. Elemental mapping using X-ray energy dispersive spectroscopy (XEDS) in the scanning transmission electron microscope (STEM) mode supports a core-shell morphology. The biocompatibility and cytotoxicity of the core-shells was investigated on a human pancreas adenocarcinoma (PL45) cell line using the WST-1 cell viability assay. The results showed that the core-shells had no adverse effects on the PL45 cellular proliferation or morphology. TEM imaging of PL45 cell cross sections confirmed the cellular uptake and isolation of the core-shell nanoparticles within the cytoplasm via membrane interactions. The fluorescence properties of the Au-ZnTe core-shell structures within the PL45 cell lines results confirmed their bio-imaging potential. The importance and novelty of this research lies in the combination of gold and zinc telluride used to produce a water soluble, biocompatible nanomaterial which may be exploited for drug delivery applications within the domain of oncology.

Nanostructure formation via post growth of particles

Post growth of nanoparticles enables new nanostructure formation and blurs the boundary between crystals and molecules.

Multifunctional Sn- and Fe-Codoped In2O3 Colloidal Nanocrystals: Plasmonics and Magnetism

We prepared Fe- and Sn-codoped colloidal In2O3 nanocrystals (∼6 nm). Sn doping provides free electrons in the conduction band, originating localized surface plasmon resonance (LSPR) and electrical conductivity. The LSPR band can be tuned between 2000 and >3000 nm, depending on the extent and kind of dopant ions. Fe doping, on the other hand, provides unpaired electrons, resulting in weak ferromagnetism at room temperature. Fe doping shifts the LSPR band of 10% Sn-doped In2O3 nanocrystals to a longer wavelength along with a reduction in intensity, suggesting trapping of charge carriers around the dopant centers, whereas Sn doping increases the magnetization of 10% Fe-doped In2O3 nanocrystals, probably because of the free electron mediated interactions between distant magnetic ions. The combination of plasmonics and magnetism, in addition to electronic conductivity and visible-light transparency, is a unique feature of our colloidal codoped nanocrystals.