Double-shelling AgInS2nanocrystals with GaSx/ZnS to make them emit bright and stable excitonic luminescence.

This paper presents the successful synthesis of AgInS2nanocrystals (NCs) double-shelled with GaSxand ZnS for emitting bright and narrow excitonic luminescence from AgInS2core NCs. Additionally, the AgInS2/GaSx/ZnS NCs with a core/double-shell structure have demonstrated high chemical and photochemical stability. The AgInS2/GaSx/ZnS NCs were prepared via three steps: (i) synthesis of AgInS2core NCs by solvothermal method at 200 °C for 30 min, (ii) shelling GaSxon AgInS2core NCs at 280 °C for 60 min to produce the AgInS2/GaSxcore/shell structure, and (iii) the outermost ZnS shelling at 140 °C for 10 min. The synthesized NCs were characterized in detail by using appropriate techniques such as x-ray diffraction, transmission electron microscopy, and optical spectroscopies. The luminescence evolution of the synthesized NCs is as follows: from the broad spectrum (peaking at 756 nm) of the AgInS2core NCs to become the narrow excitonic emission (at 575 nm) prominent beside the broad one after shelling with GaSx, then only the bright excitonic luminescence (at 575 nm) without broad emission after double-shelling with GaSx/ZnS. The double-shell has made the AgInS2/GaSx/ZnS NCs not only remarkably enhance their luminescence quantum yield (QY) up to ∼60% but also maintain the narrow excitonic emission stably for a long-term storage over 12 months. The outermost ZnS shell is believed to play a key role in enhancing QY and protecting AgInS2and AgInS2/GaSxfrom certain damage.

Systematic synthesis of different-sized AgInS2/GaSxnanocrystals for emitting the strong and narrow excitonic luminescence.

This paper presents for the first time the systematic synthesis of AgInS2(AIS) nanocrystals (NCs) with different sizes of 2.6-6.8 nm just by controlling only the reaction temperature. The synthesis of AIS core NCs was carried out in 2 steps: (i) synthesis of Ag2S NCs and then (ii) partial exchange of Ag+with In3+in the template Ag2S NCs. For step (i), Ag2S NCs of different sizes were synthesized by reaction of the Ag and S precursors at different temperatures of 30 °C to 130 °C, for the same reaction time of 30 min. For step (ii), AIS NCs were created by the exchange of Ag+with In3+at 120 °C for 60 min. Finally, GaSxwas shelled on AIS core NCs to produce the AgInS2/GaSxcore/shell structures. The synthesized AIS/GaSxNCs demonstrate the clear excitonic absorptions and strong, narrow excitonic luminescence peaking at 530-606 nm depending on the size of AIS core NCs.

Assembly of Mid-Nanometer-Sized Gold Particles Capped with Mixed Alkanethiolate SAMs into High-Coverage Colloidal Films.

We investigated the influence of the mixed n-alkanethiolate self-assembled monolayer (SAM) formed on gold nanoparticles (AuNPs: 50.0 ± 3.2 nm in diameter) on their assembly into colloidal films. Dodecanethiol and octadecanethiol were selected as the short- and long-chain alkanethiols, respectively. The mixed SAMs were formed by immersing AuNPs in a mixed alkanethiol solution at different molar ratios. Au colloidal films were fabricated on indium tin oxide substrates by our previously reported hybrid method. The composition of the two alkanethiolates in the SAM was deduced from the intensity ratio of two Raman bands at 1080 and 1105 cm(-1). The surface coverage of the colloidal films increased by forming equimolar or dodecanethiolate-dominant mixed SAMs on AuNPs instead of a pure dodecanethiolate or octadecanethiolate SAM. The highest coverage exceeded 80%. This improvement is attributed to the high dispersion stability of AuNPs covered with equimolar or dodecanethiolate-dominant mixed SAMs.

Cu and Zn promoted Al-fumarate metal organic frameworks for electrocatalytic CO2 reduction.

Metal organic frameworks (MOFs) are attractive materials to generate multifunctional catalysts for the electrocatalytic reduction of CO2 to hydrocarbons. Here we report the synthesis of Cu and Zn modified Al-fumarate (Al-fum) MOFs, in which Zn promotes the selective reduction of CO2 to CO and Cu promotes CO reduction to oxygenates and hydrocarbons in an electrocatalytic cascade. Cu and Zn nanoparticles (NPs) were introduced to the Al-fum MOF by a double solvent method to promote in-pore metal deposition, and the resulting reduced Cu-Zn@Al-fum drop-cast on a hydrophobic gas diffusion electrode for electrochemical study. Cu-Zn@Al-fum is active for CO2 electroreduction, with the Cu and Zn loading influencing the product yields. The highest faradaic efficiency (FE) of 62% is achieved at -1.0 V vs. RHE for the conversion of CO2 into CO, HCOOH, CH4, C2H4 and C2H5OH, with a FE of 28% to CH4, C2H4 and C2H5OH at pH 6.8. Al-fum MOF is a chemically robust matrix to disperse Cu and Zn NPs, improving electrocatalyst lifetime during CO2 reduction by minimizing transition metal aggregation during electrode operation.

Enhanced Photocatalytic Activity of {110}-Faceted TiO2 Rutile Nanorods in the Photodegradation of Hazardous Pharmaceuticals.

Rutile TiO2 with highly active facets has attracted much attention owing to its enhanced activity during the photocatalytic degradation of pollutants such as pharmaceuticals in wastewater. However, it is difficult to obtain by controlling the synthetic conditions. This paper reports a simple hydrothermal synthesis of rutile TiO2 nanorods with highly exposed {110} facets. The obtained rutile was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. The main contribution to the photocatalytic activity comes from rutile nanorods with highly dominant active {110} facets, which were studied in the photodegradation of reactive cinnamic acid and more recalcitrant ibuprofen. The contribution of active species was also investigated. The present work further confirmed the hydrothermal synthesis route for controlling the preparation of highly crystalline and active rutile nanocrystals.

Novel Amorphous Molybdenum Selenide as an Efficient Catalyst for Hydrogen Evolution Reaction.

Amorphous molybdenum selenide nanopowder, obtained by refluxing Mo(CO)6 and Se precursors in dichlorobenzene, shows several structural and electrochemical similarities to the amorphous molybdenum sulfide analogue. The molybdenum selenide displays attractive catalytic properties for the hydrogen evolution reaction in water over a wide range of pH. In a pH 0 solution, it operates with a small onset overpotential of 125 mV and requires an overpotential of 270 mV for generating a catalytic current of 10 mA/cm2. Compared with molybdenum sulfide, the selenide analogue is more robust in a basic electrolyte. Therefore, molybdenum selenide is a potential candidate for incorporating within an electrolyzer or a photoelectrochemical cell for water electrolysis in acidic, neutral, or alkaline medium.

Europium doped In(Zn)P/ZnS colloidal quantum dots.

Chemically synthesised In(Zn)P alloy nanocrystals are doped with Eu(3+) ions using europium oleate as a molecular precursor and are subsequently covered with a ZnS shell. The presence of zinc in the synthesis of the InP core nanocrystals leads to the formation of an In(Zn)P alloy structure, making it possible to obtain stable fluorescence emission at 485 nm. We demonstrate by means of steady state and time resolved photoluminescence measurements that resonant energy transfer takes place from the In(Zn)P/ZnS host to the Eu(3+) dopant ions. It results in the characteristic phosphorescence lines of Eu(3+) originating from the transitions between the lowest-lying excited state (5)D0 to the (7)F(J) (J = 1, 2, 3, 4) ground states. The maximum phosphorescence efficiency is obtained for an initially applied Eu(3+) : In(3+) molar ratio of 0.3 : 1, resulting in a final doping level of approximately 4%.