Showing papers by "Thalappil Pradeep published in 2018"

Polymorphism of Ag29(BDT)12(TPP)43− cluster: interactions of secondary ligands and their effect on solid state luminescence

Abstract: We present the first example of polymorphism (cubic & trigonal) in single crystals of an atomically precise monolayer protected cluster, Ag29(BDT)12(TPP)43-. We demonstrate that C-Hπ interactions of the secondary ligands (TPP) are dominant in a cubic lattice compared to a trigonal lattice, resulting in a greater rigidity of the structure, which in turn, results in a higher luminescence efficiency in it.

Synthesis of Silicon Nanoparticles from Rice Husk and their Use as Sustainable Fluorophores for White Light Emission

Abstract: Silicon nanoparticles (Si NPs) exhibiting observable luminescence have many electronic, optical, and biological applications. Owing to reduced toxicity, they can be used as cheap and environmentally friendly alternatives for cadmium containing quantum dots, organic dyes, and rare earth-based expensive phosphors. Here, we report an inexpensive silicon precursor, namely rice husk, which has been employed for the synthesis of Si NPs by rapid microwave heating. The Si NPs of ∼4.9 nm diameter exhibit observable green luminescence with a quantum yield of ∼60%. They show robust storage stability and photostability and have constant luminescence during long-term UV irradiation extending over 48 h, in contrast to other luminescent materials such as quantum dots and organic dyes which quenched their emission over this time window. Green luminescent Si NPs upon mixing with synthesized red and blue luminescent Si NP species are shown to be useful for energy-efficient white light production. The resulting white light ...

A thirty-fold photoluminescence enhancement induced by secondary ligands in monolayer protected silver clusters

Abstract: In this paper, we demonstrate that systematic replacement of the secondary ligand PPh3 leads to an enhancement in the near-infrared (NIR) photoluminescence (PL) of [Ag29(BDT)12(PPh3)4]3-. While the replacement of PPh3 with other monophosphines enhances luminescence slightly, the replacement with diphosphines of increasing chain length leads to a drastic PL enhancement, as high as 30 times compared to the parent cluster, [Ag29(BDT)12(PPh3)4]3-. Computational modeling suggests that the emission is a ligand to metal charge transfer (LMCT) which is affected by the nature of the secondary ligand. Control experiments with systematic replacement of the secondary ligand confirm its influence on the emission. The excited state dynamics shows this emission to be phosphorescent in nature which arises from the triplet excited state. This enhanced luminescence has been used to develop a prototypical O2 sensor. Moreover, a similar enhancement was also found for [Ag51(BDT)19(PPh3)3]3-. The work presents an easy approach to the PL enhancement of Ag clusters for various applications.

Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods.

Abstract: The self-assembled structures of atomically precise, ligand-protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding-directed self-assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p-mercaptobenzoic acid (pMBA)-protected atomically precise silver nanocluster, Na4 [Ag44 (pMBA)30 ], and pMBA-functionalized GNRs were used. High-resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver nanoclusters via H-bonding, leading to octahedral symmetry. The use of water-dispersible gold nanoclusters, Au≈250 (pMBA)n and Au102 (pMBA)44 , also formed layered shells encapsulating GNRs. Such cluster assemblies on colloidal particles are a new category of precision hybrids with diverse possibilities.

Fullerene-Functionalized Monolayer-Protected Silver Clusters: [Ag29(BDT)12(C60)n]3– (n = 1–9)

Abstract: We report the formation of supramolecular adducts between monolayer-protected noble metal nanoclusters and fullerenes, specifically focusing on a well-known silver cluster, [Ag29(BDT)12]3–, where BDT is 1,3-benzenedithiol We demonstrate that C60 molecules link with the cluster at specific locations and protect the fragile cluster core, enhancing the stability of the cluster A combination of studies including UV–vis, high-resolution electrospray ionization mass spectrometry, collision-induced dissociation, and nuclear magnetic resonance spectroscopy revealed structural details of the fullerene-functionalized clusters, [Ag29(BDT)12(C60)n]3– (n = 1–9) Density functional theory (DFT) calculations and molecular docking simulations affirm compatibility between the cluster and C60, resulting in its attachment at specific positions on the surface of the cluster, stabilized mainly by π–π and van der Waals interactions The structures have also been confirmed from ion mobility mass spectrometry by comparing the

Isomerism in Supramolecular Adducts of Atomically Precise Nanoparticles

Abstract: We present isomerism in a few supramolecular adducts of atomically precise nanoparticles, [Ag29(BDT)12∩(CD)n]3– (n = 1–6), abbreviated as I where BDT and CD are 1,3-benzenedithiol and cyclodextrins (α, β and γ), respectively; ∩ symbolizes an inclusion complex. The different host–guest complexes of I were characterized in the solution state as well as in the gas phase. The CDs (α, β and γ) encapsulate a pair of BDT ligands protecting the Ag29 core. This unique geometry of the supramolecular adducts makes the system similar to octahedral complexes of transition metals, which manifest various isomers. These isomers of I (n = 2–4) were separated by ion mobility mass spectrometry (IM MS). We proposed structures of all the inclusion complexes with the help of IM MS measurements and molecular docking, density functional theory (DFT), and collision cross section (CCS) calculations.

Poly(ether sulfone) Nanofibers Impregnated with β-Cyclodextrin for Increased Micropollutant Removal from Water

Abstract: Cyclodextrin–polymer composite electrospun nanofibers were developed for micropollutant (MP) removal from water. The fibers were fabricated by electrospinning of mixed poly(ether sulfone) (PES) and β-cyclodextrin (CD) solutions under optimal conditions. The composite fibers were compared with bare PES nanofibers prepared by the same method. Scanning electron microscopy revealed that CD did not alter the fiber morphology, while the fiber capacity for MP uptake was enhanced by CD through the formation of inclusion complexes. The availability of CD on the fibers was confirmed by the emergence of visible luminescence due to the inclusion of a quantum cluster, Au25SBB18 (SBB = 4-(tert-butyl)benzylmercaptan in thiolate form), in the cavities of CD exposed on fiber surfaces. The steroid hormone estradiol (E2) (100 ng/L) and pesticide chlorpyrifos (CP) (5 mg/L) were used as model pollutants in batch experiments designed to measure uptake potential. The nanofibers interact strongly with the model pollutants becaus...

Species-Specific Uptake of Arsenic on Confined Metastable 2-Line Ferrihydrite: A Combined Raman-X-Ray Photoelectron Spectroscopy Investigation of the Adsorption Mechanism

Abstract: The present study is targeted toward understanding the interaction between important and technologically relevant polymorphs of iron oxides/oxyhydroxides with arsenic species at neutral pH. The existence of various arsenic (As) species in solution was verified by Raman measurements. Their species-dependent adsorption on the affordable arsenic removal media, confined metastable 2-line ferrihydrite (CM2LF) was investigated. The results were compared with common adsorption media, hematite (α-Fe2O3) and magnetite (Fe3O4). X-ray photoelectron spectroscopy was used to investigate the changes in the core levels of Fe 2p and As 3d resulting from the uptake of arsenic species. Binding of various As species with CM2LF was confirmed by FTIR studies. Raman adsorption data were found to fit a pseudo-second-order model. Results of this study show the synthesized nanocomposite of CM2LF to be very effective for the removal of As(III) and As(V) species in comparison to various materials at neutral pH. A model for the adso...

Chapter 7 - Capacitive Deionization (CDI): An Alternative Cost-Efficient Desalination Technique

Abstract: Capacitive deionization (CDI) is an emerging and promising new technology for removal of ionic as well as polarizable species from water. It is an alternative to membrane-based technologies, having low operational cost, enhanced energy efficiency, and less water rejection. The technology works on the principle of electroadsorption of ions at the surface of electrically charged electrodes, generally made of porous carbon materials. The concept of CDI date back to the 1960s but the community of CDI has grown exponentially in last two decade. The chapter deals with the history of CDI, different patents which revolutionized the technology and the theory of electroadsorption. Different advancements in the technology such as introduction of different cell architectures, parameters responsible for efficient CDI cells, development of different novel electrode materials such as carbon aerogel (CA), carbon cloth, carbon nanotubes (CNTs), graphene and its composites, carbon fibers, and mexenes, and commercialization of CDI products have been discussed in detail. The chapter also gives a brief outlook on the current status and future development of this technology.

Holey MoS2 Nanosheets with Photocatalytic Metal Rich Edges by Ambient Electrospray Deposition for Solar Water Disinfection.

Abstract: A new method for creating nanopores in single-layer molybdenum disulfide (MoS2) nanosheets (NSs) by the electrospray deposition of silver ions on a water suspension of the former is introduced Electrospray-deposited silver ions react with the MoS2 NSs at the liquid-air interface, resulting in Ag2S nanoparticles which enter the solution, leaving the NSs with holes of 3-5 nm diameter Specific reaction with the S of MoS2 NSs leads to Mo-rich edges Such Mo-rich defects are highly efficient for the generation of active oxygen species such as H2O2 under visible light which causes efficient disinfection of water 105 times higher efficiency in disinfection for the holey MoS2 NSs in comparison to normal MoS2 NSs is shown Experiments are performed with multiple bacterial strains and a virus strain, demonstrating the utility of the method for practical applications A conceptual prototype is also presented

Understanding proton capture and cation-induced dimerization of [Ag29(BDT)12]3- clusters by ion mobility mass spectrometry.

Abstract: Proton transfer reactions have been a topic of fundamental interest in several areas of chemistry and biology. However, such reactivity has not been explored in detail for nanoscale materials. In this article, we present a unique reaction of an atomically precise monolayer-protected silver nanocluster, [Ag29(BDT)12]3−, with a proton (H+). Under controlled conditions, the strong proton affinity facilitated a complete conversion of the cluster to its protonated form, [Ag29(BDT)12H]2−. Moreover, binding of alkali metal ions (Li+, Na+, K+, Rb+ and Cs+) induced specific structural changes and also favored dimerization of the cluster. In this case, the cations acted as a bridge between the two clusters and the degree of dimerization was specific to the size of the cations. The conformational changes and separation of the alkali–metal ion bound dimers from their respective monomers have been investigated by ion mobility mass spectrometry (IM MS) and tandem mass spectrometric studies. Density functional theory (DFT) calculations have been used to determine the possible structures of the monomers and the dimers. Similar reactivity of the cluster can also be extended to other metal ions. While the present study helps to expand the ion-chemistry of atomically precise clusters, gas-phase basicity of the molecule can be explored in further detail and this can find applications in the areas of sensing and materials in general.

Detection of Hydrocarbons by Laser Assisted Paper Spray Ionization Mass Spectrometry (LAPSI MS)

Abstract: Here we introduce a new ambient ionization technique named laser assisted paper spray ionization mass spectrometry (LAPSI MS). In it, a 532 ± 10 nm, ≤10 mW laser pointer was shone on a triangularly cut paper along with high voltage, to effect ionization. The analyte solution was continuously pushed through a fused silica capillary, using a syringe pump, at a preferred infusion rate. LAPSI MS promises enhanced ionization with high signal intensity of polycyclic aromatic hydrocarbons (PAHs), which are normally not ionizable with similar ionization methods involving solvent sprays. LAPSI MS works both in positive and negative modes of ionization. A clear enhancement of signal intensity was visualized in the total ion chronogram for most analytes in the presence of the laser. We speculate that the mechanism of ionization is field assisted photoionization. The field-induced distortion of the potential well can be large in paper spray as the fibers comprising the paper are separated at tens of nanometers apart,...

Metals in urine in relation to the prevalence of pre-diabetes, diabetes and atherosclerosis in rural India.

Abstract: Objective Diabetes and cardiovascular diseases are growing burdens in rural communities worldwide. We have observed a high prevalence of diabetes among rural farming communities in India and sought to evaluate the association of non-traditional risk factors, such as metals, with diabetes and other cardiometabolic risk factors in this community. Methods Anthropometric measurements, chemistries and carotid intima-media thickness were determined in 865 participants of the Kovai Medical Center and Hospital-Nallampatti Non-Communicable Disease Study-I (KMCH-NNCD-I, 2015), a cross-sectional study conducted in a farming village in South India. Urinary metal levels were determined by inductively couped plasma-mass spectrometry analysis and corrected to urinary creatinine level. Statistical analyses were performed to study the association between urinary metal levels and clinical parameters. Results 82.5% of the study population were involved in farming and high levels of toxic metals were detected in the synthetic fertilisers used in the study village. The prevalence of pre-diabetes, diabetes and atherosclerosis was 43.4%, 16.2% and 10.3%, respectively. On logistic regression analysis, no association of traditional risk factors such as body mass index, blood pressure and total cholesterol with disease conditions was observed, but urinary levels of metals such as arsenic, chromium, aluminium and zinc showed an association with diabetes, while arsenic and zinc showed an association with pre-diabetes and atherosclerosis. Conclusions Our data suggest a probable role of metals in the aetiology of diabetes and cardiovascular diseases in rural communities. Identifying and eliminating the causes of increased levels of these environmental chemicals could have a beneficial impact on the burden of non-communicable diseases in rural population.

Fabrication of a Waterborne Durable Superhydrophobic Material Functioning in Air and under Oil

Abstract: A fundamental challenge in artificially structured or chemically modified superhydrophobic surfaces is their poor chemical, mechanical and structural robustness towards different mechanical abrasions. This limits their application potential in different fields of science and technology. Herein, a stable waterborne superhydrophobic material composed of clay particles is developed through a one-pot chemical modification in ambient conditions, forming durable micro-nano dual-structured coatings at room temperature over a range of substrates, without adhesive. This chemical modification inverts the inherent hydrophilic nature of clay particles and provides an excellent superhydrophobic surface having a water contact angle>170°(±2°) and contact angle hysteresis<5°(±2°). The coating shows excellent durability against various induced damages (mechano-chemicalenvironmental) and works efficiently both in air and within oils. The observed property is due to the controlled surface energy obtained by the incorporated chemical functionalities and enhanced surface roughness facilitated by the hydrophobic-effect during slow evaporation of 2 water from the coating material. Being a stable water-dispersion, it enables large area coatings, thereby minimising safety and environmental concerns. Use of this material to develop rugged waterproof-paper for various paper-based technologies is also demonstrated. As clay is commercially available and economical, we believe, this scalable organic-solvent-free superhydrophobic material will have a positive impact on various industries.

Interconversions of Structural Isomers of [PdAu8(PPh3)8]2+ and [Au9(PPh3)8]3+ Revealed by Ion Mobility Mass Spectrometry

Abstract: Collision cross sections (CCSs) of ligand-protected metal clusters were evaluated using ion mobility mass spectrometry The targets used in this study were phosphine-protected clusters [PdAu8(PPh3)8]2+ and [Au9(PPh3)8]3+, for which the total structures have been resolved by single-crystal X-ray analysis The arrival time distributions of [PdAu8(PPh3)8]2+ as a function of the He flow rate in a cell located just in front of a traveling wave ion mobility cell filled with N2 buffer gas demonstrated that it got converted to another structural isomer having a smaller CCS, with the increase in the nominal collision energy A similar phenomenon was observed for [Au9(PPh3)8]3+ These results were explained by the collisional excitation and cooling with the buffer gas inducing the conversion of the packing arrangement of the ligands rather than the atomic structure of the metallic core: the ligand layer was converted from disordered to the closely packed arrangement found in a single crystal during this process Th

Patterned Nanobrush Nature Mimics with Unprecedented Water‐Harvesting Efficiency

Abstract: DOI: 10.1002/admi.201800667 This is due to the fact that at any given moment, the earth’s atmosphere contains an astounding 37.5 million billion gallons of water as vapor,[2] and an efficient device to capture a fraction of this water vapor, in a cost-effective way would help solve the water crisis. Over the period of human existence, it has become apparent that biomimicking is the most efficient way to tackle such problems. When we look into nature, there are organisms, which in the course of evolution have acquired physical traits that enabled them to capture atmospheric water, even in the most arid corners of our planet. One such example is the Stenocara beetle of Namib Desert which capture water on its hardened forewings.[3] Electron microscopic images of these have revealed unique array of hydrophilic regions distributed on a superhydrophobic background,[4] creating a surface energy gradient, which facilitates efficient condensation and transportation of atmospheric water. Another such example is spider silk, which shows unique periodic spindle-knot structure when wetted and efficiently collects water from atmosphere through the combination of surface energy gradient and Laplace pressure difference. Other inspirations from nature are some cactaceae species which live in arid environments and are extremely drought-tolerant.[5] These species are shown to have structures with spines and trichomes which enable them to condense humidity efficiently from the atmosphere. Grasslands are also examples of natural atmospheric water harvesters. Hence, micro/nanostructuring of the water-collecting surface plays a critical role in determining the efficiency of water capture. With the advancement of nanotechnology, significant efforts have been directed toward fabricating surfaces with similar morphological features and chemical patterning to enable efficient water capture.[6,7] However, these natural and nature-mimicked surfaces collect atmospheric water in the form of dew/fog and require the temperature to drop below the dew point to cause condensation. For building a practical and round-the-clock operating atmospheric water generator, it is important to cool the condensing surfaces and the surrounding air efficiently, with minimum energy input. Heat transfer efficiency of the condensing surface material is as important as the water transfer efficiency for creating a viable radiative condenser. Although many biomimetic, patterned surfaces have been made for fog collection, inspired by active condensing Water scarcity is one of the most alarming problems of the planet. An ambient ion based method is developed to make hydrophilic-hydrophobic patterned silver nanowires (NWs) as humidity harvesters of unprecedented efficiency. Such water harvesters are developed by two-step surface modification of the as-synthesized NWs (known from a report earlier) using electrospray. These patterned NWs of ≈20 μm length and ≈200 nm width grown over a relatively large area (2 × 2 cm2) exhibit atmospheric water capture (AWC) efficiency of 56.6 L m−2 d−1, the highest reported so far. The whole fabrication process of the surface is performed under ambient conditions with a home-built nanoelectrospray ion source, without the help of any sophisticated instrumentation. The synthesized material combines and mimics two exciting examples of AWC in nature, which are cactae and Namib Desert beetles, which utilize AWC for their living. It is believed that the combination of the special features of the above two natural species helps to achieve the highest water capture efficiency reported till date. A working prototype using this surface for AWC is also fabricated.

Detection of [Au25(PET)18(O2)n]− (n = 1, 2, 3) Species by Mass Spectrometry

Abstract: [Au25(SR)18]− nanoclusters have been tested as a model catalyst in multiple oxidation reactions involving CO, alkenes, cyclohexane, and alcohols. Oxygen is used as an oxidizing agent in most of the...

Early Detection of Biofouling on Water Purification Membranes by Ambient Ionization Mass Spectrometry Imaging.

Abstract: By direct analysis of water purification membranes using ambient ionization mass spectrometry, an attempt has been made to understand the molecular signatures of bacterial fouling. Membrane based purification methods are used extensively in water treatment, and a major challenge for them is biofouling. The buildup of microbes and their extracellular polymeric matrix clog the purification membranes and reduce their efficiency. To understand the early stages of bacterial fouling on water purification membranes, we have used desorption electrospray ionization mass spectrometry (DESI MS), where ion formation occurs in ambient conditions and the ionization event is surface sensitive. Biosurfactants at the air–water interface generated by microorganisms as a result of quorum sensing, influence the water–membrane interface and are important for the bacterial attachment. We show that these biosurfactants produced by bacteria can be indicator molecular species signifying initiation of biofilms on membrane surfaces...

Rapid reaction of MoS2 nanosheets with Pb2+ and Pb4+ ions in solution

Abstract: Understanding the chemical changes happening to nanostructures during a process is vital in selecting them for applications. Here, we investigated the difference in the reactivity of the bulk and nanoscale forms of molybdenum disulfide (MoS2) in solution with lead ions (Pb2+ and Pb4+) as probes, at room temperature. While the bulk form did not show any reactivity in the experimental timescale, the two-dimensional (2D) nanoscale form showed not only reactivity but also quite rapid kinetics that resulted in the formation of distinct products, principally PbMoO4 with anion substitution, in a few seconds. Depending on the charge state of the cation, and the pH of the reaction mixture, two different kinds of morphologies of the same reaction product were formed. Furthermore, we demonstrate that this unusual reactivity of the MoS2 nanosheets (NSs) was retained in its supported form and hence, such supported materials can be effective for the abstraction of toxic lead from water, with fast kinetics.

Electrohydrodynamic Assembly of Ambient Ion-Derived Nanoparticles to Nanosheets at Liquid Surfaces

Abstract: We describe an ambient ion-based method to create free-standing metal nanosheets, which in turn are composed of nanoparticles of the corresponding metal. These nanoparticle-nanosheets (NP-NSs) were formed by the electrospray deposition (ESD) of metal ions on a liquid–air interface leading to nanoparticles that self-organize under the influence of electrohydrodynamic flows, driven by the electric field induced by the applied potential. Such a two-dimensional organization of noble metals is similar to the assembly of molecules at liquid–air interface and has the possibility of creating a category of new materials useful for diverse applications. Enhanced catalytic activity of the formed NP-NSs for Suzuki–Miyaura coupling reaction was demonstrated, which was attributed to their large surface-to-volume ratios.

Bent Keto Form of Curcumin, Preferential Stabilization of Enol by Piperine, and Isomers of Curcumin∩Cyclodextrin Complexes: Insights from Ion Mobility Mass Spectrometry.

Abstract: A detailed examination of collision cross sections (CCSs) coupled with computational methods has revealed new insights into some of the key questions centered around curcumin, one of the most intensively studied natural therapeutic agents. In this study, we have distinguished the structures and conformers of the well-known enol and the far more elusive keto form of curcumin by using ion mobility mass spectrometry (IM MS). The values of the theoretically predicted isomers were compared with the experimental CCS values to confirm their structures. We have identified a bent structure for the keto form and the degree of bending was estimated. Using IM MS, we have also shown that ESI MS reflects the solution phase structures and their relative populations, in this case. Piperine, a naturally occurring heterocyclic compound, is known to increase the bioavailability of curcumin. However, it is still not clearly understood which tautomeric form of curcumin is better stabilized by it. We have identified preferenti...

Preparation of gas phase naked silver cluster cations outside a mass spectrometer from ligand protected clusters in solution.

Abstract: Gas phase clusters of noble metals prepared by laser desorption from the bulk have been investigated extensively in a vacuum using mass spectrometry. However, such clusters have not been known to exist under ambient conditions to date. In our previous work, we have shown that in-source fragmentation of ligands can be achieved starting from hydride and phosphine co-protected silver clusters leading to naked silver clusters inside a mass spectrometer. In a recent series of experiments, we have found that systematic desorption of ligands of the monolayer protected atomically precise silver cluster can also occur in the atmospheric gas phase. Here, we present the results, wherein the [Ag18H16(TPP)10]2+ (TPP = triphenylphosphine) cluster results in the formation of the naked cluster, Ag17+ along with Ag18H+ without mass selection, outside the mass spectrometer, in air. These cationic naked metal clusters are prepared by passing electrosprayed ligand protected clusters through a heated tube, in the gas phase. Reactions with oxygen suggest Ag17+ to be more reactive than Ag18H+, in agreement with their electronic structures. The more common thiolate protected clusters produce fragments of metal thiolates under identical processing conditions and no naked clusters were observed.

Propane and propane-water interactions: a study at cryogenic temperatures

Abstract: The phase transition of solid propane and a propane–water mixture under ultrahigh vacuum has been investigated using reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption mass spectrometry (TPD-MS). Here, the investigation is divided into two sections: the phase transition of pure propane and the interaction of propane with water. RAIR spectra of pure propane reveal an unknown crystalline phase at 50 K (phase I), which gradually converts to a known crystalline phase (phase II) at higher temperature. This conversion is associated with certain kinetics. Co-deposition of water and propane restricts the amorphous to crystalline phase transition, while sequential deposition (H2O@C3H8; propane over predeposited water) does not hinder it. For an alternative sequential deposition (C3H8@H2O; water over predeposited propane), the phase transition is hindered due to diffusional mixing within the given experimental time, which is attributed to the reason behind the restricted phase transition.

Self-propagated combustion synthesis of few-layered graphene: an optical properties perspective.

Abstract: This paper describes a labour efficient and cost-effective strategy to prepare few-layered of reduced graphene oxide like (RGOL) sheets from graphite. The self-propagated combustion route enables the bulk production of RGOL sheets. Microscopic and spectroscopic analyses confirmed the formation of few-layer graphene sheets of an average thickness of ∼3 nm and the presence of some oxygen functional groups with a C/O ratio of 8.74. A possible mechanistic pathway for the formation of RGOL sheets is proposed. The optical properties of the RGOL sample were studied in detail by means of Spectroscopic Ellipsometry (SE). The experimental abilities of SE in relating the optical properties with the number of oxygen functionalities present in the samples are explored. The data were analysed by a double-layered optical model along with the Drude–Lorentz oscillatory dispersion relation. The refractive index (n = 2.24), extinction coefficient (k = 2.03), and dielectric functions are obtained using point-by-point analysis and are also checked for Kramers–Kronig (KK) consistency.

Towards atomically precise luminescent Ag2S clusters separable by thin layer chromatography

Abstract: Here, we report the synthesis of monolayer protected, luminescent and atomically precise silver sulfide (Ag2S) clusters. Cluster formation was studied by varying the conditions of the reaction. Matrix assisted laser desorption ionization mass spectrometry (MALDI MS) was used to monitor the growth of clusters to nanoparticles (NPs). Clusters of different nuclearity were obtained at a lower temperature, and were efficiently separated by thin layer chromatography (TLC). One of the clusters was assigned as Ag158S79(SBB)32, where SBB is 4-tert-butylbenzyl mercaptan.

Probing the Mechanical Response of Luminescent Dithiol-Protected Ag29(BDT)12(TPP)4 Cluster Crystals

Abstract: Atomically precise clusters of noble metals are considered to be an important class of advanced materials. Crystals of these clusters composed of inorganic cores and organic ligands are fascinating owing to their tunable and unique properties. Understanding their mechanical properties can give more insight into the design of nanocluster-based devices. Here, we probe the mechanical response of single crystals of Ag29(BDT)12(TPP)4 cluster (BDT = 1,3 benzenedithiol, TPP = triphenylphosphine) under both quasi-static and dynamic loading conditions. Surprisingly, the measured reduced Young’s modulus (Er) and hardness (H) were 4.48 and 0.285 GPa, respectively, similar to those of polymers and much smaller than the values for bulk silver. These observations indicate a significant role of capping ligands on the physical properties of such materials. The observed storage modulus, loss modulus and loss factor were also found to be similar to those of polymers. The magnitude of loss factor suggested the ability of nanocrystals to absorb energy under dynamic loading. These studies of mechanical properties of cluster materials could be useful in developing their applica-

Atomically precise cluster-based white light emitters $$^{\S }$$ §

Abstract: Materials emitting white luminescence are receiving increasing attention due to their potential applications in electroluminescent devices, information displays and fluorescent sensors. To produce white light, one must have either three primary colors, blue, green and red or two colors, blue and orange. In this paper, we have used thiol/phosphine protected red luminescent silver nanoclusters (Ag NCs), $$[\hbox {Ag}_{29}(\hbox {BDT})_{12}(\hbox {PPh}_{3})_{4} ]^{3\hbox {-}}\, (\hbox {BDT}=1,\!3\hbox {-benzenedithiol})$$ , $$[\hbox {Au}_{\mathrm{x}}\hbox {Ag}_{29\hbox {-}\mathrm{x}}(\hbox {BDT})_{12} (\hbox {PPh}_{3})_{4}]^{3\hbox {-}}$$ and $$\hbox {Ag}_{29}(\hbox {LA})_{12}$$ ( $$\hbox {LA}= \hbox {lipoic acid}$$ ) as one of the fluorophores for white light emission. These clusters are mixed with blue luminescent silicon nanoparticles (Si NPs) and green luminescent fluorescein isothiocyanate (FITC). The mixtures show white luminescence with CIE coordinates of (0.31, 0.34), (0.33, 0.35) and (0.29, 0.31) which are in good agreement with pure white light (0.33, 0.33). The other clusters with yellow, blue, orange, etc., luminescence can also be used to make white light. This work provides a prospective pathway for white light emission based on atomically precise noble metal NCs. Synopsis Monolayer protected noble metal nanoclusters such as $$[\hbox {Ag}_{29}(\hbox {BDT})_{12}(\hbox {PPh}_{3})_{4}]^{3\hbox {-}}\, (\hbox {BDT}=1,3\hbox {-benzenedithiol})$$ , $$[\hbox {Au}_{\mathrm{x}}\hbox {Ag}_{29\hbox {-}\mathrm{x}}(\hbox {BDT})_{12} (\hbox {PPh}_{3})_{4}]^{3\hbox {-}}$$ and $$\hbox {Ag}_{29}(\hbox {LA})_{12}$$ ( $$\hbox {LA}= \hbox {lipoic acid}$$ ) are used as red luminophores which can produce white light emission when mixed with blue luminescent silicon nanoparticles (Si NPs) and green luminescent fluorescein isothiocyanate (FITC). The mixtures produce white luminescence with CIE (Commission Internationale d’Eclair) coordinates of (0.31, 0.34), (0.33, 0.35) and (0.29, 0.31), respectively. All-cluster-based white light emission is indeed possible.

Phase Transfer Induced Enhanced Stability of Monolayer Protected Silver Quantum Clusters

Abstract: Mercaptosuccinic acid (MSA) protected silver clusters (Ag@MSA) were synthesized and their stability was monitored both in an aqueous and in a toluene phase. In the former, the pH of the cluster solution was tuned between 3 and 10 using ammonium acetate buffer, and the cluster stability was tested. The clusters were unstable at all measured pH values, whereas in the toluene phase, by using sterically hindered counter ion (tertraoctylammonium, TOA), the stability of the clusters was improved significantly. The phase transferred clusters in the toluene phase showed very high stability over months at room temperature. Transmission electron microscopy images show an average cluster size of ~ 2.05 nm. Size exclusion chromatography and Electrospray Ionisation Mass Spectrometry (ESI–MS) measurements were employed to analyse the phase transferred clusters. Importantly, Ag4MSA4 − type stable fragments were observed in ESI–MS measurements. The [Ag8(MSA)8(TOA)5]2− was the largest cluster identified by ESI–MS.