Colloidal Synthesis Techniques Research Articles

ZIF‐8 decorated FeMo nanoparticles: H2 Production from the catalytic hydrolysis of ammonia‐borane

AbstractAmmonia‐Borane (AB) is considered a promising solid hydrogen storage material due to its high hydrogen content (19.6 wt%) and its use for safe hydrogen transport. The most effective way to produce H2 from AB is to perform the hydrolysis reaction in the presence of a suitable catalyst. In this study, Fe0.2Mo0.8/ZIF‐8 nanocatalyst was synthesized in two steps: (i) synthesis by following the colloidal synthesis technique by thermal decomposition of Mo(CO)6 and Fe(acac)3 in the presence of OM and ODE at high temperatures, and (ii) the resulting colloidal Fe0.2Mo0.8 NPs were decorated into ZIF‐8. The as‐prepared Fe0.2Mo0.8/ZIF‐8 catalyst was identified using advanced characterization techniques such as ICP‐OES, P‐XRD, SEM, SEM–EDX, TEM, TEM‐EDX, XPS, and BET. The catalytic activities of the Fe0.2Mo0.8/ZIF‐8 catalyst in the hydrolysis of AB were investigated in different parameters (temperature, catalyst [Fe0.2Mo0.8] and substrate [H3NBH3] concentration, and recyclability). The results show that high crystallinity Fe0.2Mo0.8 NPs with a uniform 1.31 ± 0.13 nm distribution were formed on the ZIF‐8 surface. Fe0.2Mo0.8/ZIF‐8 catalyst provides a maximum H2 generation rate of 184.2 mLH2 (g catalyst)−1 (min)−1 at 343 K. This uniquely cost‐effective, active and durable Fe0.2Mo0.8/ZIF‐8 catalyst has strong potential for H2‐based fuel cell (PEM: Proton Exchange Membrane) applications where AB is a suitable H2 carrier.Highlights FeMo NPs were synthesized by a colloidal synthesis method and decorated into ZIF‐8. FeMo/ZIF‐8 catalyst is an active catalyst in the hydrolysis of AB. FeMo/ZIF‐8 catalyst showed an initial TOF value of 449.85 mol(H2)·molFe0.2Mo0.8−1·h−1 in the AB hydrolysis at 338 K.

Synthesis of Nickel-Based Nanoparticles by Pulsed Laser Ablation in Liquids: Correlations between Laser Beam Power, Size Distribution and Cavitation Bubble Lifetime

Pulsed laser ablation in liquids (PLAL) is a colloidal synthesis technique attracting significant interest from the scientific community due to the quality of the nanoparticles being produced. In this type of synthesis protocol, the cavitation bubble plays a vital role during the synthesis of nanoparticles. This work studied the effect of the laser beam power on cavitation bubble lifetime. Three different laser beam power values (5.8 W, 7.5 W and 10.5 W) were used to irradiate a pure nickel target in de-ionized (DI) water to synthesize nickel-based nanoparticles. The optimal repetition rate maximizing the production of nanoparticles was determined by atomic emission spectroscopy for each laser beam power. It was determined that the optimal repetition rate increased exponentially with laser beam power, while the cavitation bubble lifetime decreased logarithmically with the laser beam power. Moreover, the effect of the laser beam power on the cavitation bubble lifetime also had an effect on the size distribution of the nanoparticles being produced; the smallest size distribution was obtained at the highest laser beam power.

Size-tunable silicon nanoparticles synthesized in solution via a redox reaction.

A current challenge in silicon chemistry is to perform liquid-phase synthesis of silicon nanoparticles, which would permit the use of colloidal synthesis techniques to control size and shape. Herein we show how silicon nanoparticles were synthesized at ambient temperature and pressure in organic solvents through a redox reaction. Specifically, a hexacoordinated silicon complex, bis(N,N'-diisopropylbutylamidinato)dichlorosilane, was reduced by a silicon Zintl phase, sodium silicide (Na4Si4). The resulting silicon nanoparticles were crystalline with sizes tuned from a median particle diameter of 15 nm to 45 nm depending on the solvent. Photoluminescence measurements performed on colloidal suspensions of the 45 nm diameter silicon nanoparticles indicated a blue emission signal, attributed to the partial oxidation of the Si nanocrystals or to the presence of nitrogen impurities.

Amine as a bottom-line functionality on DDS surface for efficient endosomal escape and further subcellular targets

Subcellular targeting of drug delivery system (DDS) and hence delivery of drugs to individual organelles enhance efficacy, efficiency and effectiveness of drug treatment, and subsequently trim adverse cytotoxic effects. But efficient subcellular targeting is often limited due to their endosomal trapping and lysosomal degradation. Here we report a pilot study using quantum dot (QD) based smart nanoparticle as model DDS of small hydrodynamic diameter that can escape endosome efficiently due to surface amine functionalities having weak basic properties on its surface and target to the cell nucleus. We have synthesized high quality QD using colloidal synthesis technique and introduced optimum ratio of primary, secondary and tertiary amines on their surface using surface decoration strategies, having high cellular uptake and efficient endosomal escape property and trafficked to cell nucleus after functionalization with TAT peptide. Our developed polymeric coating chemistry has been exploited for the extensive variation and finer adjustment of different amine functionalities on the DDS surface. Developed amine functionalization method is simple, versatile, adjustable for further functional variations and extendable to different DDS.

Understanding Selectivity in CO2 Hydrogenation to Methanol for MoP Nanoparticle Catalysts Using In Situ Techniques

Molybdenum phosphide (MoP) catalyzes the hydrogenation of CO, CO2, and their mixtures to methanol, and it is investigated as a high-activity catalyst that overcomes deactivation issues (e.g., formate poisoning) faced by conventional transition metal catalysts. MoP as a new catalyst for hydrogenating CO2 to methanol is particularly appealing for the use of CO2 as chemical feedstock. Herein, we use a colloidal synthesis technique that connects the presence of MoP to the formation of methanol from CO2, regardless of the support being used. By conducting a systematic support study, we see that zirconia (ZrO2) has the striking ability to shift the selectivity towards methanol by increasing the rate of methanol conversion by two orders of magnitude compared to other supports, at a CO2 conversion of 1.4% and methanol selectivity of 55.4%. In situ X-ray Absorption Spectroscopy (XAS) and in situ X-ray Diffraction (XRD) indicate that under reaction conditions the catalyst is pure MoP in a partially crystalline phase. Results from Diffuse Reflectance Infrared Fourier Transform Spectroscopy coupled with Temperature Programmed Surface Reaction (DRIFTS-TPSR) point towards a highly reactive monodentate formate intermediate stabilized by the strong interaction of MoP and ZrO2. This study definitively shows that the presence of a MoP phase leads to methanol formation from CO2, regardless of support and that the formate intermediate on MoP governs methanol formation rate.

Enhanced catalytic activity of ultrasmall NiMoW trimetallic nanocatalyst for hydrodesulfurization of fuels

As the need of the hour, it is imperative to develop highly active HDS catalyst capable of desulfurizing refractory organic sulfur compounds (DBT; 4, 6 DMDBT etc.). In comparison to well established bimetallic catalysts (e.g. NiMo/NiW), trimetallic catalysts exhibit synergistic effect between active metal species which promotes both direct desulfurization (DDS) and hydrogenation pathway (HYD) and hence display higher catalytic activity. The synergistic effect is determined by the catalytically active amorphous phase formed due to partial substitution of Mo by W during synthesis of trimetallic nanocatalysts. This can be achieved by synthesizing the catalyst as ultrasmall size nanocatalysts. To this end, in the present study we report NiMoW trimetallic nanocatalysts preparation procedure using colloidal synthesis technique. For the sake of better comparison, Ni/(Ni + Mo + W) molar ratio for all the investigated catalysts (bimetallic and trimetallic) was kept the same (~0.28 ± 0.03). For the hydrodesulfurization of dibenzothiophene (DBT), because of improved synergistic effect, trimetallic NiMoW/γ-Al2O3 showed ~ 36% higher conversion in comparison to NiMo/ γ-Al2O3 and ~ 21% higher DBT conversion in comparison to NiW/ γ-Al2O3 catalyst. The catalytic activity of synthesized nanocatalysts was compared with catalyst prepared using well established metal impregnation method. Improved catalytic activity in case of synthesized NiMoW nanoclusters is attributed to the controlled partial substitution of Mo by W during the colloidal synthesis which enhances the synergistic effect.

Colloidal Synthesis of Ternary Copper Halide Nanocrystals for High-Efficiency Deep-Blue Light-Emitting Diodes with a Half-Lifetime above 100 h.

Currently, the blue perovskite light-emitting diodes (PeLEDs) suffer from a compromise in lead toxicity and poor operation stability, and most previous studies have struggled to meet the crucial blue NTSC standard. In this study, electrically driven deep-blue LEDs (∼445 nm) based on zero-dimensional (0D) Cs3Cu2I5 nanocrystals (NCs) were demonstrated with the color coordinates of (0.16, 0.07) and a high external quantum efficiency of ∼1.12%, comparable with the best-performing blue LEDs based on lead-halide perovskites. Encouraged by the remarkable stability of Cs3Cu2I5 NCs against heat and environmental oxygen/moisture, the proposed device was operated in a continuous current mode for 170 h, producing a record half-lifetime of ∼108 h. The device stability was further verified by an aggressive thermal cycling test (300-360-300 K) and a 35-day storage test. Together with the eco-friendly features and facile colloidal synthesis technique, the 0D Cs3Cu2I5 NCs can be therefore regarded as a promising candidate for deep-blue LEDs applications.

Highly Stable White-Light-Emitting Carbon Dot Synthesis Using a Non-coordinating Solvent.

In this article, synthesis of white-light-emitting, highly stable carbon dots (CDs) using a colloidal synthesis technique is reported. It has been observed that the use of a non-coordinating solvent plays a vital role in the successful fabrication of highly stable CDs. Dilution-independent emissive behavior in CDs is achieved. Excitation-energy-dependent emissive behavior is observed in CDs. However, by surface passivating the CD core by using hexadecylamine (HDA), excitation wavelength dependence of emission is successfully minimized. Surface-functionalized CDs (SFCDs) show blue to green light tunable emission with the change in synthesis conditions. HDA also plays an important role in achieving dilution-independent emission in SFCDs. Furthermore, the carbon dots synthesized are highly inert, and their emission spectra are unaffected on exposure to an open atmosphere for as long as 9 days. A new class of highly crystalline carbon dots called “carbon onion rings” is reported.

An exploration into the quantum confinement of CTS/natural dye core- shell quantum dots

In this work, we have presented a simple way of changing the confinement energies of Copper Tin Sulphide (CTS) quantum dots using natural dyes as shell material. Tetragonal CTS quantum dots in the size range of 1.7 nm–2.2 nm, of bandgaps of 2.48eV and 5.0 eV were prepared by means of a green colloidal synthesis technique. These quantum dots were treated with natural dyes such as onion and beetroot skin dyes. Pelargonidin and Betanin (pigments of onion and beetroot skin dye respectively) formed hydrogen bonding with the capping agent, thus forming a shell around the CTS quantum dots. The change in confinement due to the effect of dye as shell was studied from absorption, photoluminescence and infrared spectroscopic techniques. The transitions occurring were analysed using a theoretical approach. CTS quantum dots, with its high transmittance in a wide range of wavelengths find promising applications in the buffer layer of solar cells.

Near-Infrared Active Lead Chalcogenide Quantum Dots: Preparation, Post-Synthesis Ligand Exchange, and Applications in Solar Cells.

Quantum dots (QDs) of lead chalcogenides (e.g. PbS, PbSe, and PbTe) are attractive near-infrared (NIR) active materials that show great potential in a wide range of applications, such as, photovoltaics (PV), optoelectronics, sensors, and bio-electronics. The surface ligand plays an essential role in the production of QDs, post-synthesis modification, and their integration to practical applications. Therefore, it is critically important that the influence of surface ligands on the synthesis and properties of QDs is well understood for their applications in various devices. In this Review we elaborate the application of colloidal synthesis techniques for the preparation of lead chalcogenide based QDs. We specifically focus on the influence of surface ligands on the synthesis of QDs and their solution-phase ligand exchange. Given the importance of lead chalcogenide QDs as potential light harvesters, we also pay particular attention to the current progress of these QDs in photovoltaic applications.

Fluorine-assisted structural engineering of colloidal anatase TiO2 hierarchical nanocrystals for enhanced photocatalytic hydrogen production.

Anatase TiO2 materials are well-known for their photocatalytic properties and their structure-performance relationship has been intensively studied over the past few decades. In this study, we report a versatile strategy to control the geometric and electronic structure of hierarchical anatase TiO2 nanocrystals via a colloidal synthesis technique in order to optimize their photocatalytic performances. The synthesis is modified from a classical nonaqueous sol-gel approach in which titanium alkoxides and long carbon chain carboxylic acids are used as titanium sources and hydrolysis/capping agents, respectively. By introducing fluoride ions into the reaction as competitive capping agents and controlling other parameters, the geometric structure of TiO2 nanocrystals can be regulated from nanorods and nanobipyramids to their hierarchical assembly structures with controlled dimension and crystallinity. Meanwhile, it is confirmed that the fluoride capping agents also affect the surface structure of TiO2 by fluorine doping, which exerts an additional impact on the electronic structure of TiO2 nanocrystals apart from morphology variation. Further investigation of photocatalytic hydrogen production performances of TiO2 nanocrystals with different structures indicates that the catalytic efficiency is highly dependent on structural factors including hierarchical shape, surface area and doping status. Obvious improvement of photocatalytic performance is observed in the optimized hierarchical TiO2 nanocrystals (2033.6 μmol g-1 h-1) compared to that in commonly prepared TiO2 nanobipyramids (1135.5 μmol g-1 h-1) and other hierarchical TiO2 nanocrystals (1331.9 μmol g-1 h-1 or lower), which demonstrates the effectiveness of material optimization by the strategy developed in this study.

Synthesis and Characterization of Nanostructured Nickel Diselenide NiSe2 from the Decomposition of Nickel Acetate, (CH3CO2)2Ni

Solution processed NiSe2 nanorods were synthesized by a modified colloidal synthesis technique, by chemical reaction of TOPSe and nickel acetate at 150°C. The rods exist as an oleic acid ligand stabilized solution, with oleic acid acting as a capping group. Structural characterization by X‐ray diffraction and transmission electron microscopy indicates that the particles are rod‐like shaped crystals with a high and relatively constant aspect ratio (30 : 1). TEM shows that the width and the length of the nanorods are in the range 10–20 nm and 300–350 nm, respectively. XRD indicates that the nanorods are pure and well crystallized. The size of nanorods based on the Debye‐Scherrer effect, was 150 nm, the average value of length and width. They display thermal stability over prolonged heating times (<100 hours) at 150°C, for which the average particle size is roughly constant. After about 100 hours of heating time there is an onset and growth of micron sized cubes and concurrent decomposition of NiSe2 to Ni and NiSe at 150°C.

Design of semiconductor ternary quantum dots with optimal optoelectronic function

The function of nanometer‐size quantum dots (QDs) of ternary compound semiconductors, such as InxGa1−xAs and ZnSe1−xTex, used in the fabrication of optoelectronic and photovoltaic devices can be optimized by precise tuning of their electronic band gap through control of the QD composition (x) and diameter. Results on compositional distributions in ternary QDs and how they affect the QDs' electronic band gap are reported. A hierarchical modeling approach is followed that combines first‐principles density functional theory calculations and classical Monte Carlo simulations with a continuum model of species transport in spherical nanocrystals. In certain cases, the model predicts the formation of core/shell‐like structures with shell regions rich in the surface segregating species. A systematic parametric analysis generates a database of transport properties, which can be used to design post‐growth thermal annealing processes that enable the development of thermodynamically stable QDs with optimal electronic properties grown through simple one‐step colloidal synthesis techniques. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3223–3236, 2013

Spectroscopic Analysis and Synthesis of Wide Band Gap CdS Quantum Dots Using Colloidal Synthesis Technique at Low Temperature

A broad range of II-VI materials has been investigated in order to produce light in the full visible range for optoelectronic applications. The present investigation was carried out for the spectroscopic analysis and synthesis of wide band gap cadmium sulfide nanoparticles. Large-band gap semiconductors have the added advantage in that; they can support higher electric field before breaking down, which means that they can be used for high-power electronic devices.Synthesis has been carried out using colloidal synthesis technique at low temperature. The size, stabilization and optical properties were studied using UV-vis Spectrophotometer and Spectroflourometer. Further, the structural studies of synthesized powder were carried out using X-ray diffraction technique; which also confirms the formation of desired product. The capping ligand and the impurities present in the sample were characterized by Fourier transform infra red spectroscopy. Synthesized CdS powder dispersed in aqueous media gave the value of 193 nm for the onset wavelength using UV-vis spectrophotometer, which is significantly blue-shifted compared to bulk CdS and shows the quantum confinement effect. From the onset wavelength the radius of CdS quantum dot calculated using the Brus equation was found to be ca. 0.7 nm.