A facile method for the synthesis of quaternary Ag-In-Zn-S alloyed nanorods

Indium(II) Chloride as a Precursor in the Synthesis of Ternary (Ag-In-S) and Quaternary (Ag-In-Zn-S) Nanocrystals

A new indium precursor, namely, indium(II) chloride, was tested as a precursor in the synthesis of ternary Ag-In-S and quaternary Ag-In-Zn-S nanocrystals. This new precursor, being in fact a dimer of Cl2In-InCl2 chemical structure, is significantly more reactive than InCl3, typically used in the preparation of these types of nanocrystals. This was evidenced by carrying out comparative syntheses under the same reaction conditions using these two indium precursors in combination with the same silver (AgNO3) and zinc (zinc stearate) precursors. In particular, the use of indium(II) chloride in combination with low concentrations of the zinc precursor yielded spherical-shaped (D = 3.7-6.2 nm) Ag-In-Zn-S nanocrystals, whereas for higher concentrations of this precursor, rodlike nanoparticles (L = 9-10 nm) were obtained. In all cases, the resulting nanocrystals were enriched in indium (In/Ag = 1.5-10.3). Enhanced indium precursor conversion and formation of anisotropic, longitudinal nanoparticles were closely related to the presence of thiocarboxylic acid type of ligands in the reaction mixture. These ligands were generated in situ and subsequently bound to surfacial In(III) cations in the growing nanocrystals. The use of the new precursor of enhanced reactivity facilitated precise tuning of the photoluminescence color of the resulting nanocrystals in the spectral range from ca. 730 to 530 nm with photoluminescence quantum yield (PLQY) varying from 20 to 40%. The fabricated Ag-In-S and Ag-In-Zn-S nanocrystals exhibited the longest, reported to date, photoluminescence lifetimes of ∼9.4 and ∼1.4 μs, respectively. It was also demonstrated for the first time that ternary (Ag-In-S) and quaternary (Ag-In-Zn-S) nanocrystals could be applied as efficient photocatalysts, active under visible light (green) illumination, in the reaction of aldehydes reduction to alcohols.

A fluorometric assay for α-glucosidase activity based on quaternary AgInZnS QDs

A sensitive fluorescence strategy was constructed for the detection of α-glucosidase activity based on AgInZnS QDs. The AIZS QDs which were synthesized by hydrothermal method have a fluorescence emission wavelength of 554 nm. Ce⁴⁺ was able to oxidize p-phenylenediamine (PPD) to generate oxPPD, which can quench the fluorescence of AIZS QDs through dynamic quenching. When α-glucosidase was introduced into the system, L-ascorbic acid-2-O-α-D-glucopyranosyl (AAG) could be hydrolyzed to form ascorbic acid (AA), which can reduce Ce⁴⁺ and prevent the oxidation of PPD. Thus, the dynamic quenching process was blocked accompanying with the fluorescence recovery of AIZS QDs. The developed detection system for α-glucosidase displayed a good linear relationship between 0.01 and 0.16 U·mL^-1 with a detection limit of 0.0073 U·mL^-1. The sensing platform with high feasibility and anti-interference is a competitive alternative applied to α-glucosidase-related diagnostics.

Flexible translucent chitosan-glycerin/QD nanocomposite glue for anti-counterfeiting films with strong adhesion and stability

With the rapid development of commodity circulation, more attention has been paid to the anticounterfeiting technology of commodities, including stability, universality and ease of distinguishing. The authors report the use of gelatin-chitosan-glycerin/QD nanocomposite-functionalized glue for luminescent anti-counterfeiting labels. As the blend and plasticizer, the addition of chitosan and glycerin effectively improved the flexibility and formability of the gelatin-chitosan-glycerin/QD composite films, which show excellent mechanical properties, including high transparency, luminescence and flexibility, and they are easy to prepare on a large scale, providing certain reference values for new anticounterfeiting technology applying a variety of morphologies.

AgInS2-ZnS Quantum Dots: Excited State Interactions with TiO2 and Photovoltaic Performance

Multinary quantum dots such as AgInS₂ and alloyed AgInS₂-ZnS are an emerging class of semiconductor materials for applications in photovoltaic and display devices. The nanocrystals of (AgInS₂)_x-(ZnS)_1-x (for x = 0.67) exhibit a broad emission with a maximum at 623 nm and interact strongly with TiO₂ nanostructures by injecting electrons from the excited state. The electron transfer rate constant as determined from transient absorption spectroscopy was 1.8 × 10¹⁰ s^-1. The photovoltaic performance was evaluated over a period of a few weeks to demonstrate the stability of AgInS₂-ZnS when utilized as sensitizers in solar cells. We report a power conversion efficiency of 2.25% of our champion cell 1 month after its fabrication. The limitations of AgInS₂-ZnS nanocrystals in achieving greater solar cell efficiency are discussed.

Controlling Shape Anisotropy of ZnS-AgInS2 Solid Solution Nanoparticles for Improving Photocatalytic Activity

Independently controlling the shape anisotropy and chemical composition of multinary semiconductor particles is important for preparing highly efficient photocatalysts. In this study, we prepared ZnS-AgInS₂ solid solution ((AgIn)_xZn_2(1-x)S₂, ZAIS) nanoparticles with well-controlled anisotropic shapes, rod and rice shapes, by reacting corresponding metal acetates with a mixture of sulfur compounds with different reactivities, elemental sulfur, and 1,3-dibutylthiourea, via a two-step heating-up process. The chemical composition predominantly determined the energy gap of ZAIS particles: the fraction of Zn²⁺ in rod-shaped particles was tuned by the ratio of metal precursors used in the nanocrystal formation, while postpreparative Zn²⁺ doping was necessary to increase the Zn²⁺ fraction in the rice-shaped particles. The photocatalytic H₂ evolution rate with irradiation to ZAIS particles dispersed in an aqueous solution was significantly dependent on the chemical composition in the case of using photocatalyst particles with a constant morphology. In contrast, photocatalytic activity at the optimum ZAIS composition, x of 0.35-0.45, increased with particle morphology in the order of rice (size: ca. 9 × ca. 16 nm) < sphere (diameter: ca. 5.5 nm) < rod (size: 4.6 × 27 nm). The highest apparent quantum yield for photocatalytic H₂ evolution was 5.9% for rod-shaped ZAIS particles, being about two times larger than that obtained with spherical particles.

CuGaS2-ZnS p-n nanoheterostructures: a promising visible light photo-catalyst for water-splitting hydrogen production

In this work, novel CuGaS₂-ZnS p-n type semiconductor nanoheterostructures were synthesized by a solution route, and demonstrated experimentally to be a very promising visible light active photo-catalyst for water-splitting hydrogen production. The construction of CuGaS₂-ZnS heterostructures follows a multi-step strategy, employing Cu_1.94S nanocrystals first as catalytic assistants for the hetero-growth of ZnS on their surfaces, and then as sacrificial seeds for the formation of CuGaS₂. Excitingly, attributed to the efficient charge separation introduced by the p-n heterojunctions, the hydrogen production ability of the CuGaS₂-ZnS nanoheterostructures under visible light irradiation is 15 times higher than that of the CuGaS₂ component, and comparable to that of the CdS nanophase which is currently regarded as one of the most active visible photo-catalysts for hydrogen generation.