Metal Precursor Concentration Research Articles

Batch production of centimeter-scale monolayer MoS2 with low nucleation by face-to-face metal precursor supply

Transition-metal dichalcogenides (TMDs) show great potential for next-generation semiconductor due to its atomic level thickness, tunable band gap and high carrier mobility. However, high-quality monolayer MoS2 (ML-MoS2) films require stringent growth conditions during preparation. Here, we report a face-to-face metal precursor supply approach during chemical vapor deposition (CVD) to batch production of uniform ML-MoS2 films. Mo foils provide a stable concentration of metal precursors leading to uniform film generation with low nucleation. Comprehensive characterization techniques, including spectroscopic, surface topography and atomic scale analysis confirm the centimeter-scale homogeneity and high crystallographic quality of the monolayer films. Back-gate field effect transistors (FET) fabricated by ML-MoS2 exhibit excellent electrical performance. This methodology provides a pathway for the growth of TMDs, which should promote their applications in high-performance electronics or other fields.

3D-Continuous Nanoporous Covalent Framework Membrane Nanoreactors with Quantitatively Loaded Ultrafine Pd Nanocatalysts.

The confinement effect of catalytic nanoreactors containing metal catalysts within nanometer-sized volumes has attracted significant attention for their potential to enhance reaction rate and selectivity. Nevertheless, unregulated catalyst loading, aggregation, leaching, and limited reusability remain obstacles to achieving an efficient nanoreactor. A robust and durable catalytic membrane nanoreactor prepared by incorporating palladium nanocatalysts within a 3D-continuous nanoporous covalent framework membrane is presented. The reduction of palladium precursor occurs on the pore surface within 3D nanochannels, producing ultrafine palladium nanoparticles (Pd NPs) with their number density adjustable by varying metal precursor concentrations. The precise catalyst loading enables controlling the catalytic activity of the reactor while preventing excess metal usage. The facile preparation of Pd NP-loaded free-standing membrane materials allows hydrodechlorination in both batch and continuous flow modes. In batch mode, the catalytic activity is proportional to the loaded Pd amount and membrane area, while the membrane retains its activity upon repeated use. In continuous mode, the conversion remains above 95% for over 100h, with the reactant solution passing through a single 50µm-thick Pd-loaded membrane. The efficient nanoporous film-type catalytic nanoreactor may find applications in catalytic reactions for small chemical devices as well as in conventional chemistry and processes.

Plasmon assisted synthesis of TiN-supported single-atom nickel catalysts

We report the deposition of single atom nickel catalyst on refractory plasmonic titanium nitride (TiN) nanomaterials supports using the wet synthesis method under visible light irradiation. TiN nanoparticles efficiently absorb visible light to generate photoexcited electrons and holes. Photoexcited electrons reduce nickel precursor to deposit Ni atoms on TiN nanoparticles’ surface. The generated hot holes are scavenged by the methanol. We studied the Ni deposition on TiN nanoparticles by varying light intensity, light exposure time, and metal precursor concentration. These studies confirmed the photodeposition method is driven by hot electrons and helped us to find optimum synthesis conditions for single atoms deposition. We characterized the nanocatalysts using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We used density functional theory (DFT) calculations to predict favorable deposition sites and aggregation energy of Ni atoms on TiN. Surface defect sites of TiN are most favorable for single nickel atoms depositions. Interestingly, the oxygen sites on native surface oxide layer of TiN also exhibit strong binding with the single Ni atoms. Plasmon enhanced synthesis method can facilitate photodeposition of single atom catalysts on a wide class of metallic supports with plasmonic properties.

Fabrication of Ultra-Fine Ag NPs on TiO2 Thin Films by Alcohol-Assisted Photodeposition Process for Photocatalysis-Related Applications.

Noble metal/semiconductor nanocomposites have been synthesized using various methods, including precipitation and hydrothermal and electrochemical processes. Among these, the photodeposition method stands out for its simplicity, without the need for high temperatures, redox agents, or complex steps. This method facilitates the control over noble metal nanoparticle size by adjusting parameters such as metal precursor concentration, irradiation time, and power. However, understanding the interaction between solid and liquid interfaces, particularly the role of solution viscosity in the growth process, remains a challenge. This knowledge is crucial for precise control over nanoparticle size and distribution. Our study highlights the influence of viscosity, manipulated through different alcohols, on the formation of Ag nanostructures on TiO2 thin films via photodeposition, offering insights into optimizing nanocomposite synthesis.

Tailoring local structures of atomically dispersed copper sites for highly selective CO2 electroreduction

AbstractAtomically‐dispersed copper sites coordinated with nitrogen‐doped carbon (Cu–N–C) can provide novel possibilities to enable highly selective and active electrochemical CO2 reduction reactions. However, the construction of optimal local electronic structures for nitrogen‐coordinated Cu sites (Cu–N4) on carbon remains challenging. Here, we synthesized the Cu–N–C catalysts with atomically‐dispersed edge‐hosted Cu–N4 sites (Cu–N4C8) located in a micropore between two graphitic sheets via a facile method to control the concentration of metal precursor. Edge‐hosted Cu–N4C8 catalysts outperformed the previously reported M–N–C catalysts for CO2‐to‐CO conversion, achieving a maximum CO Faradaic efficiency (FECO) of 96%, a CO current density of –8.97 mA cm–2 at –0.8 V versus reversible hydrogen electrode (RHE), and over FECO of 90% from –0.6 to –1.0 V versus RHE. Computational studies revealed that the micropore of the graphitic layer in edge‐hosted Cu–N4C8 sites causes the d‐orbital energy level of the Cu atom to shift upward, which in return decreases the occupancy of antibonding states in the *COOH binding. This research suggests new insights into tailoring the locally coordinated structure of the electrocatalyst at the atomic scale to achieve highly selective electrocatalytic reactions.

Electrodeposition of defect-rich high entropy ZIF and its application in water oxidation

High-entropy materials has achieved much attention in the recent decade years. However, there is few reports on high-entropy MOFs due to the large difference of coordination ability for different metal ions. In this work, high-entropy ZIFs are successfully electrodeposited on the nickel foam substrate under high overpotential, and the effects of potential, electrodeposition time and metal precursor concentration on the morphologies and catalytic activity of deposits are examined. The results indicate that the prepared HE-ZIF is made of nanoparticles with a low crystalline structure, and it shows a high electrocatalytic activities for oxygen evolution reaction (OER) as it possesses an abundance of defects such as vacancy defects, lattice distortions and amorphous structure. The overpotential at the current density of 100 mA cm−2 is 290 mV with good durability in 100 h continuous test for OER in 1 mol L−1 KOH.

Electrochemical sensing platform with gold nanoparticles capped by PDDA for benzyl alcohol determination

An electrochemical sensor has been developed, by modifying screen-printed carbon devices (SPCE) with photochemically synthesized gold nanoparticles (AuNP), to determine benzyl alcohol, a preservative widely used in the cosmetic industry. To obtain the AuNP with the best properties for electrochemical sensing applications, the photochemical synthesis was optimized using chemometric tools. A response surface methodology based on central composite design was used to optimize the synthesis conditions, as irradiation time, and the concentrations of metal precursor and the capping/reducing agent (poly(diallyldimethylammonium) chloride, PDDA). The anodic current of benzyl alcohol on SPCE modified with the AuNP was used as response of the system. The best electrochemical responses were obtained using the AuNP generated by irradiating for 18 min a 7.20 times 10−4 mol L−1 AuCl4−-1.7% PDDA solution. The AuNP were characterized by transmission electron microscopy, cyclic voltammetry and dynamic light scattering. The nanocomposite-based sensor formed by the optimal AuNP (AuNP@PDDA/SPCE) was used to determine benzyl alcohol by linear sweep voltammetry in 0.10 mol L−1 KOH. The anodic current at + 0.017 ± 0.003 V (vs. AgCl) was used as analytical signal. Detection limit obtained under these conditions was 2.8 µg mL−1. The AuNP@PDDA/SPCE was applied to determine benzyl alcohol in cosmetic samples.Graphical

Copper oxide nanoparticles: Synthesis via chemical reduction, characterization, antibacterial activity, and possible mechanism involved

Copper oxide nanoparticles (CuO NPs) were synthesized via chemical reduction method using oxalic acid (OA), sodium borohydride (SBH), and tri-sodium citrate (TSC) as both reducing and stabilizing agents. The CuO NPs were synthesized at different concentrations (0.02 M, 0.04 M, 0.06 M, 0.08 M, 0.10 M, and 1.00 M) of metal precursor and reducing agent. The as-synthesized CuO NPs (18 samples) showed maximum absorbance in the range of 200 nm to 450 nm wavelength. X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the synthesis of CuO NPs. Among the CuO NPs, S-CuO NPs, showed good particle size (15.8 to 44 nm) and surface charge (42.1 to 23 mV). S-CuO NPs showed highest anti-bacterial activity (ZOI) against Bacillus subtilis (19 mm), Escherichia coli (15 mm), Lactococcus lactis (20 mm), Micrococcus luteus (14 mm), and Pseudomonas putida (21 mm) at 100 mg/L test concentration in comparison with OA and TSC synthesized CuO NPs. Therefore, as-synthesized CuO NPs has great potential to employ as effective anti-bacterial agents in medical applications as the synthesis process is faster, economical, and more importantly reliable and reproducible.

Seed Engineering toward Layer‐Regulated Growth of Magnetic Semiconductor VS2

AbstractThe discovery of layered magnetic semiconductor materials has stimulated a search for the magnetic order of atomically thin‐layered materials. However, layer‐controlled growth is difficult because of the high nucleation barrier of the material surface during the few‐layer formation of 2D materials. Herein, a seeding solution method is demonstrated that changes the nucleation mode of seed crystals on the substrate surface by precisely controlling the concentration of metal precursors and promoting the formation of cluster seed nuclei to ensure a sufficient source of metal for subsequent reactions. It is studied that the kinetic and thermodynamic synergy through temperature control is readily to grow VS2 with a tunable layer number. Monolayer VS2 exhibits strong ferromagnetic ordering with a saturation magnetization strength (Ms) of 37 emu per cc and a coercivity (Hc) of 135 Oe at 300 K. Notably, the ferromagnetism of VS2 has layer‐dependent performance of the saturation magnetization and coercivity decreases with increasing number of layers. Monolayer VS2 exhibits typical semiconductor properties in Hall devices. This study broadens the chemical pathway for the tunable synthesis of 2D layered magnetic materials and provides the possibility for the construction of novel spintronic and magnetoelectronic devices.

Size-Dependent Electrochemical Metal Growth Kinetics

This work explores the electrochemical deposition (ECD) of Au onto chemically preformed Au nanoparticles (NPs) as a function of Au NP size. The growth potential and current depend strongly on the size of the preformed Au NPs (seeds) due to different Au NP size-dependent kinetics of the growth process. Electrochemical reversibility depends on the Au NP size, scan rate, metal precursor concentration ([AuCl4–]), and Au NP coverage. The Au NPs need to reach a critical total surface area to have enough active area to cause the ECD over the entire electrode to be electrochemically reversible and operate under linear diffusion mass transfer-limited conditions. The smaller Au NPs require less total surface area to reach this condition because they have higher activity per surface area, which is not fully understood but could be due to a greater percentage of defects on their surface, such as edge and corner atom sites.

Multifunctional Heterogeneous Ion-Exchange Membranes for Ion and Microbe Removal in Low-Salinity Water.

Here, multifunctional heterogeneous ion-exchange metal nanocomposite membranes were prepared for surface water desalination and bacterial inactivation under low-pressure (0.05 MPa) filtration conditions. Ultrafiltration (UF) heterogeneous ion exchange membranes (IEMs) were modified with different concentrations of AgNO3 and CuSO4 solutions using the intermatrix synthesis (IMS) technique to produce metal nanocomposite membranes. Scanning electron microscopy (SEM) images revealed that the metal nanoparticles (MNPs) (Ag and Cu) were uniformly distributed on the surface and the interior of the nanocomposite membranes. With increasing metal precursor solution concentration (0.01 to 0.05 mol·L-1), the metal content of Ag and Cu nanocomposite membranes increased from 0.020 to 0.084 mg·cm-2 and from 0.031 to 0.218 m·cm-2 respectively. Results showed that the hydrodynamic diameter diameters of Ag and Cu nanoparticles (NPs) increased from 62.42 to 121.10 nm and from 54.2 to 125.7 nm respectively, as the metal precursor concentration loaded increased. The leaching of metals from metal nanocomposite membranes was measured in a dead-end filtration system, and the highest leaching concentration levels were 8.72 ppb and 5.32 ppb for Ag and Cu, respectively. The salt rejection studies indicated that ionic selectivity was improved with increasing metal content. Bacterial filtration showed higher antibacterial activity for metal nanocomposite membranes, reaching 3.6 log bacterial inactivation.

Kinetics and Mechanism of Electroless Silver Deposition on a Polyurethane Substrate at Moderate to High Concentration of Metal Precursor and Reductant

Kinetics and Mechanism of Electroless Silver Deposition on a Polyurethane Substrate at Moderate to High Concentration of Metal Precursor and Reductant

Facile Biological-Based Synthesis of Size-Controlled Palladium Nanoclusters Anchored on the Surface of Geobacter sulfurreducens and Their Application in Electrocatalysis

Metal nanoclusters can be synthesized following the top-down or bottom-up approaches involving multiple chemical and/or physical steps where strong ligands, toxic chemicals, and high temperature and pressure are normally applied. In contrast, biological methods eliminate the use and generation of hazardous substances and do not require the application of high temperature and pressure during the synthesis process. Biological methods based on the extracellular electron transfer (EET) capability of electroactive bacteria (EAB) are considered a promising sustainable route for the synthesis of metal nanoparticles; however, a fine control of the size of the nanoparticles has not been achieved yet. Herein, we report a facile biological-based synthesis method of size-controlled palladium (Pd) nanoclusters using the EET capability of Geobacter sulfurreducens. By controlling the metal precursor concentrations and dosing and incubation times, we synthesized size-controlled Pd nanoclusters (1.0 ± 0.6 to 4.8 ± 1.4 nm) anchored on the surface of G. sulfurreducens. The as-synthesized Pd nanoclusters anchored on the surface of G. sulfurreducens cells (Pd/GS) were tested for their performance as bifunctional electrocatalysts for the overall alkaline water splitting reaction. Despite a very low mass loading of 0.002 mg Pd cm–2, the hybrid material (i.e., Pd/GS) showed exceptionally higher activity for hydrogen evolution reaction (HER) when compared to benchmark 10 wt % Pt/C and Pd/C. Similarly, Pd/GS showed higher activity for oxygen evolution reaction (OER) when compared to Pd/C and comparable OER activity when compared to benchmark IrO2. The findings in this study provide a promising sustainable route for designing size-controlled metal nanoclusters anchored on the surface of EAB as efficient and low-cost electrocatalysts for various applications.

Droplet‐Based Microfluidics Platform for the Synthesis of Single‐Atom Heterogeneous Catalysts

Wet chemical approaches are among the most versatile and scalable strategies for preparing single‐atom heterogeneous catalysts (SACs). However, despite their broad application, the synthesis of SACs via these routes remains largely ad hoc, with limited attention to the effect of different synthetic parameters on the stabilization of metal species. As a proof of concept, herein, a microfluidic platform is demonstrated for short‐timescale (<10 s), systematic syntheses of SACs via wet impregnation using a range of metal precursor–carrier combinations. The microfluidic environment within rapidly mixed, nanoliter droplets ensures precise control of the concentrations and residence times of the support particles in the metal precursor solutions. This enables the rapid assessment of the influence of the metal precursor concentration on the uptake and dispersion of the adsorbed metal species, as demonstrated for the synthesis of palladium and platinum SACs based on a high‐surface form of graphitic carbon nitride (C3N4). Extension to SACs based on other metals (Ni) and relevant carriers (N‐doped carbon, γ‐alumina) confirms the generality of the synthesis method. The microfluidic approach opens possibilities for high‐throughput parameter screening and mechanistic studies in the design of heterogeneous single‐atom catalysts.

Sodium borohydride mediated synthesis of nano-sized silver particles: Their characterization, anti-microbial and cytotoxicity studies

This work reports the one-step, fast, easy, simple and economical process for the synthesis of nano-sized and stable silver particles. AgNPs were synthesized at six (0.02 M, 0.04 M, 0.06 M, 0.08 M, 0.10 M and 1.00 M) different concentrations of metal precursor and reducing agent. Sodium borohydride was used as both reducing and stabilizing agent. Characterization studies revealed that all the silver nanoparticles (AgNPs) synthesized were in the range of 10 nm–50 nm, spherical shaped, crystalline nature and with high negative surface charge (−30 mV to −47 mV). Among the AgNPs evaluated for their anti-microbial activity through well diffusion method against Escherichia coli (Gram negative bacteria), Bacillus subtilis (Gram positive bacteria) and Candida albicans (fungi), AgNPs-1.00 showed maximum zone of inhibition with 11.5 mm, 18.5 mm and 10 mm at highest test concentration (100 mg/L), respectively. Cytotoxicity of the AgNPs was determined against MCF-7, PVA1 and Caco-2 cancer cell lines through standard MTT assay. AgNPs-0.08 showed highest mortality% with 90% and 80% against MCF-7 and PVA1 at maximum test concentration (100 mg/L), respectively. However, none of the AgNPs showed toxicity towards Caco-2 cancer cell line. Therefore, AgNPs can be used as anti-microbial agents in the biomedical applications.

Electrochemically-Assisted Synthesis of Platinum Nanoparticles Using Gas-Diffusion Electrocrystallization (GDEx) and Their Electrocatalytic Activity for Methanol Oxidation

In recent years, interest in using unsupported catalysts, especially Pt-based nanomaterials, has resurged in direct methanol fuel cells (DMFC). Unsupported catalysts eliminate the problems related to the corrosion of carbon catalyst supports, thus improving the long-term stability of DMFC. In addition, the design of catalyst synthesis protocols to tailor nanostructured materials with high surface area and catalytic activity improves catalyst performance.1 Consequently, we recently reported a method for the synthesis of platinum group metal (PGM, i.e., Pt, Pd, Rh) nanoparticles (NPs), using a process called Gas Diffusion Electrocrystallization (GDEx) (Fig. 1a).2 The simultaneous electrochemical reduction of CO2 and water occurs at the triple-phase boundary of uncatalyzed gas-diffusion electrodes, producing H2 and CO. Both gases, but especially H2, are reducing agents for water-soluble noble metal ions leading to the formation of small metal nanoclusters. CO can also act as a capping agent. Furthermore, the presence of CO2 stabilizes the pH, avoiding the formation of metal (hydr)oxides.In this work, we used the GDEx process to synthesize unsupported Pt NPs using polyvinyl pyrrolidone (PVP, 55000 Mw) as a stabilizer and evaluated their electrocatalytic activity for methanol oxidation. The synthesis was performed at -30 mA cm-2, using 3.0 mM Pt4+ (as H2PtCl4) as metal precursor and different concentrations of PVP (i.e., 0.0, 0.01, 0.1 and 1.0 g L-1). We chose low concentrations of stabilizer to facilitate its removal after synthesis, as clean surface catalysts are required for electrocatalytic applications. The size distribution of the Pt NPs, measured using Scanning Electron Microscopy (SEM), was 64 ± 22, 60 ± 22, 42 ± 18, and 38 ± 12 nm for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0, respectively. For comparison, the reduction of 3.0 mM Pt4+ using 1.0 g L-1 PVP with only H2 (either electrogenerated or bubbled) produced bigger and much more polydisperse particles (100 nm–1000 nm), highlighting the importance of the GDEx process and the presence of CO to synthesize small NPs using low concentrations of stabilizer. Furthermore, Transmission Electron Microscopy (TEM) images (Fig. 1b) revealed that the NPs are nanoclusters of single crystals of 2 nm–4 nm in diameter.The synthesized Pt NPs were cleaned using NaOH,3 and their electrocatalytic activity was evaluated in acidic media. The CV curves of Pt NPs in 0.5 M H2SO4 are shown in Fig. 1c. All catalysts showed hydrogen adsorption-desorption peaks from -0.2 to 0.1 VAg/AgCl. The calculated electrochemical surface area (ECSA), obtained by integrating the charge in the hydrogen adsorption-desorption region, was 7.6 ± 0.7, 14.1 ± 1.2, 33.6 ± 1.2, and 30.3 ± 1.0 m2 g-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1 and PVP 1.0 respectively. The MeOH electro-oxidation experiments were performed in 0.5 M H2SO4 containing 1.0 M MeOH, and the CV curves are shown in Fig. 1d. The forward anodic peak (If) at about 0.7 VAg/AgCl corresponds to MeOH oxidation, while the backward anodic peak (Ib) at about 0.5 VAg/AgCl corresponds to the oxidation of the incompletely oxidized carbonaceous species formed in the forward sweep. The mass activity (MA), defined by the forward peak current density per unit of catalyst loading, was 71 ± 2, 136 ± 7, 463 ± 28, and 341 ± 25 mA mg-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0 g L-1, respectively. Hence, the MA scale with the ECSA . Besides, ECSA (and hence MA) increases when the PVP concentration during synthesis increases. However, this trend is not followed for a PVP concentration of 1.0 g L-1. Even though all catalysts were cleaned using the same protocol, residual PVP might still be left on the surface of Pt NPs synthesized using 1.0 g L-1 PVP, lowering their electrocatalytic activity.Overall, the GDEx process was a useful tool for synthesizing unsupported Pt NPs using low concentrations of stabilizer and with high electrocatalytic activity. This project has received funding from the European Union's Horizon 2020 Research and Innovation program under Grant Agreements n° 730224 (PLATIRUS) and n° 958302 (PEACOC) 1. E. Antolini, J. Perez, J. Mat. Sci, 2011, 46, 4435–4457.2. X. Dominguez-Benetton, O. Martinez-Mora, J. Fransaer, EP21165681, 2021.3. A. Zalineeva, S. Baranton, C. Coutanceau, G. Jerkiewicz, Langmuir, 2015, 31, 1605–1609. Figure 1

A membrane-less Glucose/O2 non-enzymatic fuel cell based on bimetallic Pd–Au nanostructure anode and air-breathing cathode: Towards micro-power applications at neutral pH

Herein, the authors propose a miniaturized glucose/O2 n-EFC based on a new direct electron transfer. The anode is a screen-printed carbon electrode (SPCE) modified with functionalized carbon nanotubes (f-CNTs) and cauliflower-like PdAu nanostructures (PdAuNS). The PdAuNS/f-CNT biomimetic nanocatalyst was prepared using a cost-effective and straightforward method, which consisted of drop-casting well-dispersed f-CNTs over the SPCE surface before PdAuNS electrodeposition. This enzyme-free interface was used for glucose electrooxidation at neutral medium (pH 7.4). The electrochemical behaviour of the PdAuNS/f-CNT/SPCE was investigated using cyclic voltammetry, linear sweep voltammetry, and amperometry. Several parameters were optimized and discussed, including the metal precursor concentration (HAuCl4, PdCl2) and the electrodeposition conditions. The cathode for oxygen electroreduction is an air-cathode which is composed of Pt-coated carbon cloth. The electrochemical performances of the anode and the cathode were evaluated separately for glucose oxidation and oxygen reduction, respectively. Both electrodes were then assembled in a membrane-less single chamber n-EFC with an innovative architecture. Electrical characterization of the n-EFC supplied with a neutral buffered solution containing 20 mM glucose showed a maximal power output of 129 ± 11 μW cm−2, a current density of 600 ± 39 μA cm−2 with a cell voltage of 0.35 V, and an open circuit potential of 0.56 V. The proposed electrocatalyst possesses several advantages such as fast response, low cost, reusability, poison-free characteristics, and good stability. Hence, glucose/O2 n-EFC could be of great interest in direct glucose fuel cell applications (e.g., powering mountable/implantable biomedical micro-devices running at low electrical power supply) or in self-powered biosensing.

Microwave-Assisted Solution Synthesis of Metastable Intergrowth of AgInS2 Polymorphs.

The intergrowth of stable and metastable AgInS2 polymorphs was synthesized using a microwave-assisted synthesis. The samples were synthesized in water and in a deep eutectic solvent (DES) consisting of choline chloride and thiourea. An increase in the metal precursor concentration improved the crystallinity of the synthesized samples and affected the particle size. AgInS2 cannot be synthesized from crystalline binary Ag2S or In2S3 via this route. The solution synthesis reported here results in the intergrowth of the thermodynamically stable polymorph (space group I2d, chalcopyrite structure) and the high-temperature polymorph (space group Pna21, wurtzite-like structure) that is metastable at room temperature. A scanning transmission microscopy (STEM) study revealed the intergrowth of tetragonal and orthorhombic polymorphs in a single particle and unambiguously established that the long-thought hexagonal wurtzite polymorph has pseudo-hexagonal symmetry and is best described with the orthorhombic unit cell. The solution-synthesized AgInS2 polymorphs intergrowth has slightly lower bandgap values in the range of 1.73 eV–1.91 eV compared to the previously reported values for tetragonal I2d (1.86 eV) and orthorhombic Pna21 (1.98 eV) polymorphs.

Asymmetric seed passivation for regioselective overgrowth and formation of plasmonic nanobowls.

Plasmonic nanoparticles (NPs) have garnered excitement over the past several decades stemming from their unique optoelectronic properties, leading to their use in various sensing applications and theranostics. Symmetry dictates the properties of many nanomaterials, and nanostructures with low, but still defined symmetries, often display markedly different properties compared to their higher symmetry counterparts. While numerous methods are available to manipulate symmetry, surface protecting groups such as polymers are finding use due to their ability to achieve regioselective modification of NP seeds, which can be removed after overgrowth as shown here. Specifically, poly(styrene-b-polyacrylic acid) (PSPAA) is used to asymmetrically passivate cubic Au seeds through competition with hexadecyltrimethylammonium bromide (CTAB) ligands. The asymmetric passivation via collapsed PSPAA causes only select vertices and faces of the Au cubes to be available for deposition of new material (i.e., Au, Au-Ag alloy, and Au-Pd alloy) during seeded overgrowth. At low metal precursor concentrations, deposition follows observations from unpassivated seeds but with new material growing from only the exposed seed portions. At high metal precursor concentrations, nanobowl-like structures form from interaction between the depositing phase and the passivating PSPAA. Through experiment and simulation, the optoelectronic properties of these nanobowls were probed, finding that the interiors and exteriors of the nanobowls can be functionalized selectively as revealed by surface enhanced Raman spectroscopy (SERS).

Studies on Surface Plasmon Resonance of Murdannia loriformis Silver Nanoparticles

In this work, surface plasmon resonance (SPR) was investigated over the effect of concentration of metal precursor, concentration of reducing agent, reaction time and pH on formation of silver nanoparticles (AgNPs) using biological method. In this method, Murdannia loriformis extract (MLE) was used as reducing agent and silver nitrate as metal precursor. SPR of Murdania loriformis silver nanoparticles (MLE-AgNPs) was measured through UV-vis spectrophotometer over a range of 380 – 800 nm wavelength. It was found that, as the concentration of MLE, pH and reaction time increases, the SPR peak of MLE-AgNPs at 430 - 490 nm also increases. However, for effect of concentration of metal precursor, the result showed that SPR peak of MLE-AgNPs increases when 1 to 5 mM of silver nitrate was used but decreases for 10 and 15 mM. Significant of this study is to identify the optimum conditions for synthesis of MLE-AgNPs.