Modulated Binary–Ternary Dual Semiconductor Heterostructures

A generic modular synthetic strategy for the fabrication of a series of binary‐ternary group II‐VI and group I‐III‐VI coupled semiconductor nano‐heterostructures is reported. Using Ag₂Se nanocrystals first as a catalyst and then as sacrificial seeds, four dual semiconductor heterostructures were designed with similar shapes: CdSe‐AgInSe₂, CdSe‐AgGaSe₂, ZnSe‐AgInSe₂, and ZnSe‐AgGaSe₂. Among these, dispersive type‐II heterostructures are further explored for photocatalytic hydrogen evolution from water and these are observed to be superior catalysts than the binary or ternary semi‐conductors. Details of the chemistry of this modular synthesis have been studied and the photophysical processes involved in catalysis are investigated.     

Biomimetic Synthesis of Ag2Se Quantum Dots with Enhanced Photothermal Properties and as “Gatekeepers” to Cap Mesoporous Silica Nanoparticles for Chemo–Photothermal Therapy

Ag₂Se quantum dots (QDs) with near‐infrared (NIR) fluorescence have been widely utilized in NIR fluorescence imaging in vivo because of their narrow bulk band gap and excellent biocompatibility. However, most of synthesis methods for Ag₂Se QDs are expensive and the reactants are toxic. Herein, a new protein‐templated biomimetic synthesis approach is proposed for the preparation of Ag₂Se QDs by employing bovine serum albumin (BSA) as a template and dispersant. The BSA‐templated Ag₂Se QDs (Ag₂Se@BSA QDs) showed NIR fluorescence with high fluorescence quantum yield (≈21.2 %), excellent biocompatibility and good dispersibility in different media. Moreover, the obtained Ag₂Se@BSA QDs exhibited remarkable photothermal conversion (≈27.8 %), which could be used in photothermal therapy. As a model application in biomedicine, the Ag₂Se@BSA QDs were used as “gatekeepers” to cap mesoporous silica nanoparticles (MSNs) by means of electrostatic interaction. By taking the advantages of NIR fluorescence and photothermal property of Ag₂Se@BSA QDs, the obtained MSN‐DOX‐Ag₂Se nanoparticles (MDA NPs) were employed as a nanoplatform for combined chemo‐photothermal therapy. Compared with free DOX and MDA NPs without NIR laser, the laser‐treated MDA NPs exhibited lower cell viability in vitro, implying that Ag₂Se@BSA QDs are highly promising photothermal agents and the MDA NPs are potential carriers for chemo–photothermal therapy.     

A Novel One‐Pot Synthesis of UV‐Blue ZnSe Nanocrystals in Aqueous Solution

Described herein is a novel one‐pot aqueous synthesis of ZnSe nanocrystals has featuring the utilization of Na₂SeO₃ and Zn(AC)₂×2H₂O as Se and Zn source, glutathione (GSH) as stabilizing agent and reducing agent. By this approach, the UV‐blue ZnSe QDs with quantum yield (QYs) up to 19% have been synthesized with a molar ratio of Se/Zn/GSH at 1:4:8.5 under aqueous conditions at 110 °C. XRD and TEM show the ZnSe QDs are zinc cubic structure particles with an average diameter of 3–5 nm.     

Environmentally Benign and Efficient Ag2S‐ZnO Nanowires as Photoanodes for Solar Cells: Comparison with CdS‐ZnO Nanowires

In this work, we develop a low‐temperature, facile solution reaction route for the fabrication of quantum‐dot‐sensitized solar cells (QDSSCs) containing Ag₂S‐ZnO nanowires (NWs), simultaneously ensuring low manufacturing costs and environmental safety. For comparison, a CdS‐ZnO NW photoanode was also prepared using the layer‐by‐layer growth method. Ultraviolet photoelectron spectroscopy analysis revealed type‐II band alignments for the band structures of both photoanodes which facilitate electron transfer/collection. Compared to CdS‐ZnO QDSSCs, Ag₂S‐ZnO QDSSCs exhibit a considerably higher short‐circuit current density (J_sc) and a strongly enhanced light‐harvesting efficiency, but lower open‐circuit voltages (V_oc), resulting in almost the same power‐conversion efficiency of 1.2 %. Through this work, we demonstrate Ag₂S as an efficient quantum‐dot‐sensitizing material that has the potential to replace Cd‐based sensitizers for eco‐friendly applications.     

Preparation of ZnSe Nanoparticles via Low‐Temperature Solid Phase Process

ZnSe nanoparticles were prepared from ZnCl₂, Se and KBH₄ in the presence of cetyltrimethyl ammonium bromide (CTAB) through a room temperature solid phase process. The products were characterized with x‐ray diffraction (XRD), transmission electron microscope (TEM), and energy dispersive analysis of x‐ray (EDAX). The results show that the cubic zincblende phase ZnSe nanoparticles can be obtained using this simple method. The size of nanoparticles was evaluated to be from 8 to 30 nm.     

Formation of Metal Selenide and Metal–Selenium Nanoparticles using Distinct Reactivity between Selenium and Noble Metals

Small Se nanoparticles with a diameter of ≈20 nm were generated by the reduction of selenium chloride with NaBH₄ at ?10 °C. The reaction with Ag at 60 °C yielded stable Ag₂Se nanoparticles, which subsequently were transformed into M–Se nanoparticles (M=Cd, Zn, Pb) through cation exchange reactions with corresponding ions. The reaction with Pt formed Pt layers that were evenly coated on the surface of the Se nanoparticles, and the dissolution of the Se cores with hydrazine generated uniform Pt hollow nanoparticles. The reaction with Au generated tiny Au clusters on the Se surface, and eventually formed acorn‐shaped Au–Se nanoparticles through heat treatment. These results indicate that small Se nanoparticles with diameters of ≈20 nm can be used as a versatile platform for the synthesis of metal selenide and metal–selenium hybrid nanoparticles with complex structures.     

Thiolate‐Mediated Photoinduced Synthesis of Ultrafine Ag2S Quantum Dots from Silver Nanoparticles

Photoinduced syntheses offer significant advantages over conventional thermal strategies, including improved control over reaction kinetics and low synthesis temperatures, affording nanoparticles with nontrivial and thermodynamically unstable structures. However, the photoinduced syntheses of non‐metallic nanocrystalline products (such as metal sulfides) have not yet been reported. Herein, we demonstrate the first photoinduced synthesis of ultrafine (sub‐2 nm) Ag₂S quantum dots (QDs) from Ag nanoparticles at 10 °C. By thorough investigation of the mechanism for the transformation, a fundamental link was established between the intrinsic structures of the molecular intermediates and the final Ag₂S products. Our results confirm the viability of low‐temperature photochemical approaches in metal sulfide synthesis, and demonstrate a new rule which could be followed in it.     

Bioinspired Unidirectional Silk Fibroin–Silver Compound Nanowire Composite Scaffold via Interface‐Mediated In Situ Synthesis

Bioinspired unidirectional porous materials have emerged as a unique class of scaffolds for the fabrication of macroscopic nanomaterial assemblies. However, these scaffolds usually serve simply as mechanical carriers to support various building blocks. Here, we report that the unidirectional silk fibroin scaffold can not only act as a carrier, but also serve as a controllable multiscale reactor to achieve the in situ synthesis of a Ag₃PO₄ nanowire network anchored to ordered channels. Both the silk fibroin matrix and the interface play important roles in the nucleation and growth of the Ag₃PO₄ nanowires. This unidirectional composite scaffold can be used for efficient water disinfection. Furthermore, the facile chemical transformation of Ag₃PO₄ in the composite scaffold into Ag₂S provided an analogous unidirectional composite silk scaffold that displays both efficient solar water evaporation effect and antibacterial activity. It is expected that this method can be extended to fabricate a series of silk‐based unidirectional composite scaffolds with varying functionalities.     

Surface modified silver selinide nanoparticles as extracting probes to improve peptide/protein detection via nanoparticles-based liquid phase microextraction coupled with MALDI mass spectrometry

We report the first use of functionalized Ag₂Se nanoparticles (NPs) as effective extracting probes for NPs-based liquid-phase microextraction (NPs-LPME) to analyze hydrophobic peptides and proteins from biological samples (urine and plasma) and soybean in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Surface modified functional groups such as octadecanethiol (ODT) and 11-mercaptoundecanoic acid (MUA) on Ag₂Se NPs were found to play an important role for efficient extraction of peptides and proteins from test samples through hydrophobic interactions. The peptides can be efficiently extracted using functionalized Ag₂Se NPs as extracting probes in the presence of high concentration of matrix interferences such as 4 M urea, 0.5% Triton X-100 and 3% NaCl. Ag₂Se@ODT NPs have shown better extraction efficiency and detection sensitivity for peptides than Ag₂Se@MUA NPs, bare Ag₂Se NPs and conventional MALDI-MS. The LODs are 20-68 nM for valinomycin and 100-180 nM for gramicidin D using Ag₂Se@ODT NPs-LPME in the MALDI-MS. The current approach is highly sensitive and the target analytes can be effectively isolated without sample loss and efficiently analyzed in MALDI-MS.     

氧化银纳米线在官能化二氧化硅颗粒表面的自组装合成

在碱性水醇溶液中, 硝酸银与用3-(2-氨乙基氨丙基)三甲氧基硅烷[N-(2-aminoethyl)-3-aminopropyl-trimethoxy- silane, AMPTS]表面修饰后的二氧化硅胶体颗粒相互作用, 发现所生成的氧化银纳米颗粒可以在二氧化硅颗粒表面自组装为氧化银纳米线. 通过调变反应物中Ag/Si摩尔比, 可对氧化银纳米线的形貌进行调控. 在较小的Ag/Si摩尔比下, 可以得到结构均匀、直径约为50 nm、长度几十微米的氧化银纳米线. 随Ag/Si摩尔比增大, 得到的氧化银纳米线逐渐变短变粗, 且结构变得不均匀. 高分辨透射电镜(HRTEM)显示, 所有的氧化银纳米线均由直径10～20 nm的氧化银颗粒定向堆积而得. 利用透射电镜(TEM)对氧化银纳米线的形成过程进行了观察, 并对氧化银颗粒形成及组装机理进行了探讨.     

Tumor Microenvironment‐Activated NIR‐II Nanotheranostic System for Precise Diagnosis and Treatment of Peritoneal Metastasis

Activatable theranostic systems show potential for improved tumor diagnosis and therapy owing to high detection specificities, effective ablation, and minimal side‐effects. Herein, a tumor microenvironment (TME)‐activated NIR‐II nanotheranostic system (FEAD1) for precise diagnosis and treatment of peritoneal metastases is presented. FEAD1 was fabricated by self‐assembling the peptide Fmoc‐His, mercaptopropionic‐functionalized Ag₂S quantum dots (MPA‐Ag₂S QDs), the chemodrug doxorubicin (DOX), and NIR absorber A1094 into nanoparticles. We show that in healthy tissue, FEAD1 exists in an NIR‐II fluorescence “off” state, because of Ag₂S QDs‐A1094 interactions, while DOX remains in stealth mode. Upon delivery of FEAD1 to the tumor, the acidic TME triggers its disassembly through breakage of the Fmoc‐His metal coordination and DOX hydrophobic interactions. Release of A1094 switches on Ag₂S fluorescence, illuminating the tumor, accompanied by burst release of DOX within the tumor tissue, thereby achieving precise tumor theranostics. This TME‐activated theranostic strategy holds great promise for future clinical applications.     

Photoelectrochemical properties of TiO2 films obtained by electrical explosion

The electrical explosion of wires was used to prepare titanium dioxide nanopowders alloyed with silver nanoparticles. The photoelectrochemical properties and electronic structure of these materials were studied. The quantum yield for the photoelectrochemical current η and the flat band potential E _fb for TiO₂/Ag films were found to be proportional to the content of the Ag⁰ phase on the electrode surface.     

Converting Ag2SCdS and Ag2SZnS into AgCdS and AgZnS Nanoheterostructures by Selective Extraction of Sulfur

A mild three‐step solution strategy is developed to prepare Ag? MS (M=Zn, Cd) nanoheterostructures composed of MS nanorods with silver tips. First, Ag₂S? MS heterostructures are synthesized by following a solution–liquid–solid mechanism with Ag₂S nanoparticles as catalysts, then the Ag₂S sections of the heterostructures are converted into silver nanoparticles by selective extraction of sulfur. Notably, for the prepared Ag? CdS heterostructures, the localized surface plasmon resonance of silver remarkably intensifies the photoluminescence of CdS by enhancing the excitation light absorption, which is beneficial for potential applications of CdS nanoparticles in the fields of biolabeling, light‐emitting diodes, and so forth. The strategy reported herein would be useful for designing and fabricating other metal–semiconductor hybrid nanostructures with desirable performances.     

Synthesis of protein‐assisted aqueous Ag2S quantum dots in the bovine serum albumin solution

A one‐step method was developed for preparing Ag₂S quantum dots (QDs) using a common protein [bovine serum albumin (BSA)] to entrap QDs precursors (BSA–Ag⁺). Fluorescence (FL) and ultraviolet spectra showed that the molar ratio of Ag⁺/BSA, temperature, and pH are the crucial factors for the quality of QDs. The QDs absorption wavelength and emission wavelength were about 340 and 450 nm. The average QDs particle size was estimated to be less than 5 nm, determined by transmission electron microscopy. The X‐ray power diffraction and XPS results showed that the synthesized product was indeed monoclinic Ag₂S. With Fourier transform infrared spectra and thermogravimetry analysis, there might be conjugated bonds between Ag₂S QDs and –OH, –NH, and –SH groups in BSA. In addition, FL spectra suggest that the designed QDs can produce static quenching with BSA and the Stern–Volmer quenching constant (K_sv) was calculated as 2.145 × 10⁴. Copyright © 2014 John Wiley & Sons, Ltd.     

AgSbS2 semiconductor-sensitized solar cells

We present a ternary semiconductor nanoparticle sensitizer – AgSbS₂ – for solar cells. AgSbS₂ nanoparticles were grown using a two-stage successive ionic layer adsorption and reaction process. First, Ag₂S nanoparticles were grown on the surface of a nanoporous TiO₂ electrode. Secondly, a Sb–S film was coated on top of the Ag₂S. The double-layered structure was transformed into AgSbS₂ nanoparticles ~ 40 nm in diameter, after post-deposition heating at 350 °C. The AgSbS₂-sensitized TiO₂ electrodes were fabricated into liquid-junction solar cells. The best cell yielded a power conversion efficiency of 0.34% at 1 sun and 0.42% at 0.1 sun. The external quantum efficiency (EQE) spectrum covered the range of 380–680 nm with a maximal EQE of 10.5% at λ = 470 nm. The method can be applied to grow other systems of ternary semiconductor nanoparticles for solar absorbers.     

Atom‐Precise Polyoxometalate–Ag2S Core–Shell Nanoparticles

Atomically precise polyoxometalate–Ag₂S core–shell nanoparticles were generated in a top‐down approach under solvothermal conditions and structurally confirmed by X‐ray single‐crystal diffraction as an interesting core–shell structure comprising an in situ generated Mo₆O₂₂^8? polyoxometalate core and a mango‐like Ag₅₈S₃₈ shell. This result demonstrates the possibility to integrate polyoxometalate and Ag₂S nanoparticles into a core–shell heteronanostructure with precisely controlled atomical compositions of both core and shell.     

Structural Phase Transitions in Ag2Se (Naumannite)

Ag₂Se (naumannite) was investigated by means of temperature dependent synchrotron powder diffraction and DTA. Upon heating in air the known 1^st order phase transition from orthorhombic low‐temperature Ag₂Se (P2₁2₁2₁, Z = 4) to cubic ion conducting high‐temperature Ag₂Se (Im3m, Z = 2) was observed at approx. 140 °C. Upon cooling a small hysteresis was detected (T_PU = 120 °C). It was found that when heated in air Ag₂Se segregates elemental selenium. After cooling to ambient temperature the resulting low‐temperature Ag₂Se can no longer be described in the known structural model with harmonic terms, the use of anharmonic terms is probably necessary. The phase transition and the segregation of selenium are accompanied by an increased crystallinity of the sample, as the halfwidths of the reflections become significantly smaller. Approaching the phase transition the lattice parameters of orthorhombic Ag₂Se show a distinct anisotropic behaviour: b and c show a positive and a a negative thermal expansion. When heated in argon the segregation of selenium is not observed.     

Catalysis of the Reduction of Silver Ions by Ag2S Nanoparticles

Silver sulfide nanoparticles were found to catalyze the reduction of Ag⁺ ions by sodium sulfite and hydroquinone. The change in the absorption spectrum of the reaction mixtures was studied. New bands were found to arise at 403, 415, and 426 nm depending on the reaction conditions. These bands were identified as plasmon bands of metallic silver nanoparticles. The kinetics of this process was determined under various conditions and Ag₂S nanoparticles were found to be a highly active catalyst.     

Hydrothermal synthesis of nanocrystalline ZnSe: An in situ synchrotron radiation X-ray powder diffraction study

The hydrothermal synthesis of nanocrystalline ZnSe has been studied by in situ X-ray powder diffraction using synchrotron radiation. The formation of ZnSe was studied using the following starting mixtures: Zn+Se+H₂O (route A) and ZnCl₂+Se+H₂O+Na₂SO₃ (route B). The route A experiment showed that Zn powder starts reacting with water at 134 °C giving ZnO and H₂ followed by the formation of ZnSe which takes place in temperature range from 167 to 195 °C. The route B experiment shows a considerably more complex reaction path with several intermediate phases and in this case the formation of ZnSe starts at 141 °C and ZnSe and Se were the only crystalline phases observed at the end of the experiment where the temperature was 195 °C. The sizes of the nanocrystalline particles were determined to 18 and 9 nm in the route A and B experiments, respectively. Nanocrystalline ZnSe was also synthesized ex situ using the route A and B methods and characterized by conventional X-ray powder diffraction and transmission electron microscopy. An average crystalline domain size of ca. 8 nm was determined by X-ray powder diffraction in fair agreement with TEM images, which showed larger aggregates of nanoparticles having approximate diameters of 10 nm. Furthermore, a method for purification of the ZnSe nanoparticles was developed and the prepared particles showed signs of anisotropic size broadening of the diffraction peaks.     

Synthesis and Characterization of Silver Sulfide Nanoparticles Containing Sol-Gel Derived HPC-Silica Film for Ion-Selective Electrode Application

Silver sulfide nanoparticles dispersed in sol-gel derived hydroxypropyl cellulose (HPC)-silica films have been successfully synthesized using H₂S gas diffusion method. This is the first attempt to produce silver sulfide nanoparticles using this technique. Ag₂S nanoparticles are generated through reaction of H₂S gas with AgNO₃ precursor dissolved in the HPC-silica matrix. Transmission electron microscope (TEM) and atomic force microscope (AFM) analysis reveal nanoparticles size distribution from 2.5 nm to 56 nm for H₂S gas exposed sample. The surface chemistry of Ag₂S nanoparticles and sol-gel derived HPC-silica matrix is confirmed by X-ray photoelectron spectroscopy (XPS). The negative shifts in the core-level XPS Ag (3d) binding energy of Ag₂S nanoparticles are attributed to Ag : S surface atomic ratio exhibited by these nanoparticles with varying processing conditions. Following processing and characterization, suitability of the present method to produce silver sulfide ion-selective electrode is demonstrated by depositing Ag₂S nanoparticles on a graphite rod. The high reponse function of the electrode is due to the presence of nanoparticles.