We use a soft-approach for synthesis of quasi-spherical, ultra-small, digestively-ripened, stable copper oxide QDs (radius < 3 nm). Common copper precursors (acetate, sulphite, nitrate and chloride) are explored. Triethanolamine (TEA) capping results in substantial increase of zetapotential (25 ± 5 meV); this is invariant with respect to Cu-precursor used. Relevant spectral analysis indicates that solvent and the surfactant are the most critical parameters. Hard-hard-acid-base-interaction (between CuO and TEA) based (i) mass-transfer (for pre-DR QDs) and (ii) passivation (for DR-QDs) seems to be the mechanism behind observed ceramic-DR; interestingly this is consistent with the metallic-DR-model proposed by Prasad et al. (Chem. Phys. Lett., 2012). © 2017 Elsevier B.V.

Tiju Thomas

Department of Metallurgical and Materials Engineering

Bhusankar Talluri

Copper

Copper oxides

Spectrum Analysis

ACID BASE INTERACTION

COPPER PRECURSORS

DIGESTIVE RIPENING

HARD-SOFT ACID-BASE

TRIETHANOLAMINES

Ultra-small

Semiconductor quantum dots

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IIT Madras

Chemical Physics Letters

Recently a nanorod-to-nanodot reversible transformation was reported by Niya et al. in case of nano-ZnO colloidal dispersion. The reversibility of this transformation, coupled with the need for a specific surfactant and solvent, indicates thermo-chemical origins of the phenomenon. Results indicate that surfactants play a critical role in the process. However, an explanation for this phenomena has not been reported yet. In this work, we derive and develop the chemical potential expressions that capture the roles played by surface-interactions, in driving this reversible transformation. Equations associated with both the dot (spherical) and rod (cylindrical) morphologies are reported. Using agent based modelling, and realistic parameters, we indeed observe a temperature induced morphology transformation that is consistent with experiment. The transition temperature is shown to vary slowly for a wide range of surfactant-surface chemistries and surface charges, which are parametrically captured. We indicate that such rod-to-dot transitions in colloids can be expected across other compositions as well. © 2019 Elsevier B.V.

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Modelling thermochemical reversible dot-to-rod transformation in colloidal nanomaterials

The physico-chemical mechanisms associated with surfactant-free depletant stabilized water-in-oil microemulsion based shell encapsulation processes merit detailed investigation owing to the possibility of a direct correlation between encapsulation and the stable water-in-oil microemulsion system. The presence of core nanoparticles is expected to influence the formation of stable water-in-oil microemulsion system wherein polyethylene glycol (PEG) is used as depletant material. The depletant is expected to play a dual role: on one hand, it reduces the surface tension of de-ionized water during the synthesis of core while on the other hand, it helps to form stable water-in-oil microemulsion system (surfactant free) and the subsequent organization of silica coating over magnetite and systematic measurements have implications on nano encapsulation. The water-in-oil microemulsion system stabilized by depletant material is formulated with the presence of core-nanoparticles. The stability of the water-in-oil microemulsion is quantified by measuring the average hydrodynamic diameter. The presence of silica coating on core nanoparticles is robustly demonstrated using (a) small angle X-ray scattering data and Guinier plot analysis, (b) isoelectric point measurement, (c) high-resolution transmission electron microscopy, and (d) infrared spectroscopy. When the concentration of PEG and water-particles mixture (WP mixture) increases, the average hydrodynamic diameter of water-in-oil microemulsion decreases. Multiple magnetite nanoparticles are accommodated within each water droplet, without the occurrence of instability/agglomeration event. This ensures a higher yield via this process. Breakdown of stable water-in-oil microemulsion hinders the shell coating process and this is a first attempt to form the surfactant-free depletant stabilized water-in-oil microemulsion systems. The effects observed in this work have important implications for the development of new approaches to the formation of water-in-oil microemulsion systems and subsequent encapsulation processes. © 2019 Elsevier B.V.

Do depletant stabilized water-in-oil microemulsions have implications for nanoencapsulation?

Ultra-small (r &lt; 2 nm), semiconductor quantum dots (QDs) based composites are underexplored in electrochemical energy-storage devices. This is due to practical challenges associated with synthesis of QDs such as (i) stabilization, (ii) scalability, and (iii) achieving monodispersed population. In this context, ultra-small, highly monodispersed copper oxide QDs (∼2.5 ± 0.4 nm) have been synthesized by using soft-chemical and scalable approach based on digestive ripening. Composites of digestively ripened (DRd) copper oxide QDs deposited on graphene oxide are tested electrochemically for battery-like supercapacitor. The composites are grown in-situ on a Ni-foam to make binder-free battery-like supercapacitor electrode by hydrothermal process. Results indicates that battery-like behavior of the composites. Among the composites, 50%QDs-GO provides maximum specific capacity of 191 mA h g−1 at 2 mV s−1 which is maintained up to 63 mA h g−1 even at a high scan rate of 200 mV s−1. The specific capacity increases ∼4 times for the 50%QDs-GO composite, compared to the graphene oxide. The maximum energy density provided by the system is 57.2 Wh kg−1 at 2 mV s−1. Specific capacity and charge-discharge stability of the composites are found to be improved with increasing concentration of QDs. This is the first report on deployment of DRd copper oxide QDs in battery-like supercapacitors and it opens up possibilities for further exploration of other DRd QDs. © 2019 Elsevier Ltd

Electrochimica Acta

Nanocomposites of digestively ripened copper oxide quantum dots and graphene oxide as a binder free battery-like supercapacitor electrode material

Ultra-small and uniform sized ZnO quantum dots (QDs)have been synthesized by using a chimie-douce, scalable and eco-friendly method. The physicochemical properties of digestively ripened ZnO QDs have been explored. Uniform sized colloidal QDs are achieved by employing a size control approach called digestive ripening (DR). In DR, monodispersed colloidal nanoparticles are obtained from polydispersed colloidal nanoparticles through the addition of substantial amount of a suitably chosen surfactant (having a suitable ligand). This is performed in the presence of a suitable solvent. Capping with the surfactant (triethanolamine)results in a change in the zeta potential of QDs (increased from 7 ± 3 mV to +22 ± 3 mV)which is responsible for the observed DR and a decrease in particle size from ˜3.5 ± 2 nm to ˜2.8 ± 0.5 nm also noticed. Hard-Soft-Acid-Base surface chemical interactions taking place between ZnO QDs and the surfactant (triethanolamine)are responsible for the formation of digestively ripened ZnO QDs. The as formed ZnO QDs are highly monodispersed in nature and the optical absorption studies indicate that band gap of ZnO QDs found to be Eg˜3.6 eV, indicating strong confinement. The photoluminescence (PL)studies clearly indicates that the major contribution to the photoluminescence is defects present of ZnO QDs-surface and the existence of oxygen vacancy defects on the ZnO QDs-surface are confirmed with PL studies. Time-resolved photoluminescence studies indicate that lifetimes of photo-generated carriers in digestively ripened (DRd)QDs is ˜12 ns and coating with digestive ripening agent reduces the surface-related emission and improves the radiative transitions in DRd ZnO QDs. Spectroscopic studies indicate that formation of highly pure ZnO QDs. These highly monodisperse, stable and ZnO QDs are prospectively useful in contemporary applications such as nanoscale electronic devices and photocatalysis. © 2019

Physicochemical properties of chimie douce derived, digestively ripened, ultra-small (r&lt;2 nm)ZnO QDs

Through digestive ripening (DR), a polydispersed colloid can be processed to obtain a monodispersed system. Recent advances in DR have rendered the process prospectively scalable, soft-chemical and green. This in turn makes it relevant for industrial-scale manufacturing of nanoparticles (NPs) and quantum dots (QDs); a crucial step forward from a technological standpoint. However predictive models and associated results that offer chemical insights for experimental design for DR are largely missing. Currently two attempts to explain DR are notable: (i) Lee's theory (essentially accounts for surface electrostatic enthalpy), and (ii) Clark's model (flow-flux modelling across interfaces around the NP). Given recent experimental results, hard-soft-acid-base interactions associated with surfactant-surface interface seem essential. In this work, an expression is written to account for hard-soft-acid-base-interactions on particle surface, and dynamics of particle size evolution is simulated using an agent based approach. Parametric studies indicate following trends for the convergent radius: (a) considerable variance with surface charge, (b) considerable variance with surface energy, (c) dependence on absolute temperature which is almost entirely due to the thermal dependence of the solubility product term, and (d) a linear relationship to the negative logarithm of product of solubility and bulk diffusion constant. The solubility term, in light of recent reports, needs to be interpreted also in terms of solute solubility in the interfacial surfactant phase. The solvation-precipitation approach provided here offer preliminary but experimentally-relevant and computationally-grounded physico-chemical insights for design of DR experiments. © 2018

Applied Surface Science

Surface enthalpy driven size focussing trends: Predictive modelling for digestive ripening of spherical particles

LaTiO2N photocatalysts were prepared by thermal ammonolysis of flux-synthesized La2Ti2O7 and La2TiO5, and were investigated for water oxidation. Though LaTiO2N derived from La2TiO5 appears defect-free by UV/Vis/near-IR and electron paramagnetic resonance (EPR) spectroscopy, its performance is much lower than that of conventional La2Ti2O7-derived LaTiO2N with defects. It is shown by Mott–Schottky analysis that La2TiO5-derived LaTiO2N has significantly lower donor density; this can result in insufficient built-in electric field for the separation of photogenerated electrons and holes. The lower donor density is also consistent with the smaller difference between the Fermi level and the valence-band maximum, which accounts for a lower oxidative power of the holes. In light of this discovery, the donor density was increased substantially by introducing anion vacancies through annealing in Ar. This resulted in improved performance. The CoOx-assisted La2TiO5-derived LaTiO2N annealed at 713 °C has a higher quantum efficiency (25 %) at 450 nm than high-performance conventional CoOx/LaTiO2N (21 %). © 2017 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim

ChemSusChem

Crucial Role of Donor Density in the Performance of Oxynitride Perovskite LaTiO2N for Photocatalytic Water Oxidation

Oxford Dictionary of National Biography

Clayton, Thomas (fl 1706)

RSC Advances

Quantum dot-assembled mesoporous CuO nanospheres based on laser ablation in water

Synthesis of monodisperse copper nanoparticles using a modified digestive ripening technique and formation of superlattices

Solid State Sciences

Hydrothermal synthesis and photocatalytic property of porous CuO hollow microspheres via PS latex as templates

Indications of hard-soft-acid-base interactions governing formation of ultra-small (r &lt; 3 nm) digestively ripened copper oxide quantum-dots

Journal	Data powered by TypesetChemical Physics Letters
Publisher	Data powered by TypesetElsevier B.V.
Open Access	No