Makwena J. Moloto

The Effect of Solvents, Acetone, Water, and Ethanol, on the Morphological and Optical Properties of ZnO Nanoparticles Prepared by Microwave

HDA-capped ZnO nanoparticles were prepared by solvothermal method using solvents of different polarities. A number of parameters were kept constant such as temperature, pressure, time, and pH while solvents were varied, that is, water, ethanol, and acetone. The TEM was used for the structural properties and morphologies such as spheres, mixture of rods, and spheres and stars were obtained in ethanol, acetone, and water, respectively, in a given reaction time of 15 minutes. Both ethanol and acetone gave rods with high aspect ratio primarily because of the lengths of the rods. Water and ethanol have the hydroxyl groups which interact with nanoparticles from nucleation, growth, and termination giving rise to nonspherical shapes. The hydroxyl group promotes growth in a nonuniform way resulting in stars and rods. The optical features were typical of ZnO nanoparticles with excitonic peaks in the range 368 to 374 nm from their absorption spectra. The XRD patterns of the particles gave the most stable form of ZnO which is the hexagonal phase, with high degree of crystallinity and with the 101 plane predominant in all solvents.

Structural modification and band-gap crossover in indium selenide nanosheets

Herein, we report on the synthesis of InSe nanosheets. We further report on the interdependency of concentration and time on the evolution of the nanosheets as well as the role of the capping agents on the crystal phase and morphology of the resultant particles. Our results show that hexagonal-like InSe nanosheets were synthesized at different optimum times depending on the amount of indium precursor. Regardless of the amount of indium precursor used, the product remained unchanged, i.e. InSe. This was attributed to the nature of the oleylamine capping agent. Oleylamine is known to be a reducing agent and in this case resulted in the reduction of In3+ to In2− and elemental selenium to Se2−, thus always resulting in the formation of rhombohedral InSe nanosheets. A non-reducing 1-dodecanthiol co-surfactant was thus used. Dodecanthiol was thought to stabilize the In3+ ions by coordinating and forming a complex, thus preserving the 3+ oxidation state of indium, resulting in the formation of the final product of In2Se3 nanocrystals. The morphology of In2Se3 changed depending on the amount of oleylamine used. The optical properties of the InSe were further evidence that nanosheets had been synthesized due to the band gap crossover.

Green synthetic approach for starch capped silver nanoparticles and their antibacterial activity

Abstract In this work silver nanoparticles (AgNPs) have been prepared from silver nitrate (AgNO3) precursor using a green synthesis method at room temperature. Starch with its abundance of hydroxyl groups and its biocompatibility was used as a capping and reducing agent. The formation of AgNPs was confirmed by absorption spectroscopy with the surface plasmon resonance peak at 400 nm. The sharp reflection at (111), (200), (220) and (311) was observed by powder X-ray diffraction (XRD), which indicated the presence of cubic phase AgNPs. Transmission electron microscopy (TEM) revealed that the average size of AgNPs were between 0.5 and 4 nm with a spherical shape under optimum conditions. The nanoparticles showed a decrease in size with an increase in precursor concentration as well as the increase in capping agent concentration. The nanoparticles also showed to be bactericidal towards the tested Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria.

Colloidal synthesis of pure CuInTe2 crystallites based on the HSAB theory

The colloidal method has extensively been used to synthesize ternary and quaternary copper sulfides and selenides. The formation pathway and the crystallization mechanism of these nanostructures have also been investigated. Although tellurides form part of the chalcogenides, little has been reported on them particularly the crystallization mechanism of these nanostructures. Herein, we report on the colloidal synthesis of CuInTe2. Typically reaction temperatures play a vital role in the formation of colloidal nanostructures. At temperatures below 250 °C, no formation of CuInTe2 was seen. At 250 °C formation of CuInTe2 could be observed with formation of binary impurities. A change in the sequence in which precursors were added at 250 °C yielded pure CuInTe2. Therefore starting with InCl3 and elemental Te dissolved in OLA and TOP, respectively, then adding CuCl dissolved in OLA yielded a pure CuInTe2 phase with agglomerated cubic structures. The pure CuInTe2 crystallites had an optical band gap of 1.22 eV in comparison to 0.93 eV of the impure CuInTe2 phase.

The Effect of Structural Properties of Cu2Se/Polyvinylcarbazole Nanocomposites on the Performance of Hybrid Solar Cells

It has been said that substitution of fullerenes with semiconductor nanocrystals in bulk heterojunction solar cells can potentially increase the power conversion efficiencies PCE of these devices far beyond the 10% mark. However new semiconductor nanocrystals other than the potentially toxic CdSe and PbS are necessary. Herein we report on the synthesis of Cu2Se nanocrystals and their incorporation into polyvinylcarbazole PVK to form polymer nanocomposites for use as active layers in hybrid solar cells. Nearly monodispersed 4 nm Cu2Se nanocrystals were synthesized using the conventional colloidal synthesis. Varying weight % of these nanocrystals was added to PVK to form polymer nanocomposites. The 10% polymer nanocomposite showed retention of the properties of the pure polymer whilst the 50% resulted in a complete breakdown of the polymeric structure as evident from the FTIR, TGA, and SEM. The lack of transport channels in the 50% polymer nanocomposite solar cell resulted in a device with no photoresponse whilst the 10% polymer nanocomposite resulted in a device with an open circuit voltage of 0.50 V, a short circuit current of 7.34 mA/cm2, and a fill factor of 22.28% resulting in a PCE of 1.02%.

Synthesis and characterization of Cu3N nanoparticles using pyrrole-2-carbaldpropyliminato Cu(II) complex and Cu(NO3)2 as single-source precursors: the search for an ideal precursor

Herein, we report the synthesis and characterization of Cu3N nanocrystals using two single-source precursors, bis(pyrrole-2-carbalpropyliminato) Cu(II) (PPC) and Cu(NO3)2·3H2O. The optical and structural properties were investigated and the suitability of the two precursors was studied in terms of producing good quality Cu3N nanocrystals without the detection of Cu or oxidation to CuO. Both precursors resulted in crystalline Cu3N with an anti-ReO3 cubic structure with no presence of copper impurities, however, peaks due to excess capping agent were detected by XRD and confirmed with XPS. The PPC complex resulted in spherical nanocrystals whilst the copper nitrate resulted in nanocubes. The band gaps were in the visible region with the copper nitrate nanocrystals slightly red shifted from the PPC derived particles due to larger crystal sizes. The emission spectra were blue-shifted from the absorption band edges hence indicating an up-conversion process.

Antimicrobial Activity of Amino Acid-Capped Zinc and Copper Sulphide Nanoparticles

The synthesis of polydispersed zinc sulphide and copper sulphide nanocrystals capped with polar L-alanine (Aln) and l-aspartic acid (Asp) molecules is reported. The resulting nanocrystals were characterized by UV-visible spectroscopy (UV-Vis), photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). UV-Vis absorption spectra of all samples were blue-shifted from the bulk band edges due to quantum confinement effects. PL emission spectrum of the nanoparticles showed peaks at 453 and 433 nm for Aln-capped ZnS and CuS nanoparticles, respectively, while peaks for Asp-capped ZnS and CuS nanoparticles were observed at 455 and 367 nm, respectively. The average particle sizes for Aln-capped ZnS and Asp-capped ZnS nanoparticles synthesized at 35°C were measured to be 2.88 nm and 1.23 nm, respectively. The antibacterial properties were tested using different strains of both positive and negative bacteria and fungi. It was found that capped-copper sulphide nanoparticles were more effective against the bacteria than capped-zinc sulphide nanoparticles. Staphylococcus aureus (ATCC 25923) was the most susceptible one with an MIC of 0.05 mg/mL for uncapped-CuS nanoparticles while Pseudomonas aeruginosa (ATCC 15442) and Cryptococcus neoformans (ATCC 14116) were the least ones with the MIC of 3.125 mg/mL for both uncapped-CuS and Aln-capped CuS.

Effect of diphenylphosphinic acid on cesium lead iodide perovskite stability

Cesium lead iodide nanocrystals (NCs) are one of the best perovskites to date. The quality of CsPbI3 tends to degrade with time and many researchers have embarked on studies for the improvement of CsPbI3 stability. Herein, CsPbI3 nanoparticles were synthesized via a colloidal approach by varying the capping agent and the coordinating solvent. The effect of a phosphinic ligand on the synthesis of CsPbI3 was assessed with the aim of getting new properties and/or improving its existing properties. The stability of the synthesized CsPbI3 perovskites was evaluated through photoluminescence emission over time. A nearly cubic phase of CsPbI3 was obtained through synthesis with diphenylphosphinic acid (DPPA) in benzyl ether (BE). Smaller nanocubes with an average size of 14 nm were prepared using DPPA in BE. The emission intensity lasted beyond 6 days with only 40% emission lost compared to that of materials prepared using a mixture of solvents and the conventional method. In order to illustrate possible applications, the NCs were used in a simple solar cell device with the configuration substrate-FTO-TiO2-CsPbI3/NiO-Au. A power conversion efficiency and a fill factor of 2.0% and 38%, respectively, were obtained from a 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-MeOTAD)-free solar device which was made of the more stable synthesized CsPbI3.

Effect of Concentration on Synthesis of Organic Passivated Cu2-xS Nanoparticles from N-Pyrrolidine Dithiocarbamate Molecular Precursor

Dithiocarbamate (DTC) compounds have gained lot of attention due to their strong coordinating capacity with various metal ions [1]. This has resulted in the wide usage of dithiocarbamate compounds in several areas such as in industry, agriculture, medicine and in analytical chemistry [2]. Dithiocarbamate ligands are normally prepared by the reaction of an amine (either primary or secondary) with carbon disulfide (CS2) in the presence of a strong base [3-5]. In the past years, the thermolysis of the dithiocarbamate based metal complexes has proved to be the most interesting route in the synthesis of metal chalcogenide nanoparticles [6]. Their versatility in the molecular structure (high spin-low spin crossover phenomena) makes them the subjected of interest in the synthesis of metal sulfide nanoparticles [7]. Several researchers have explored the thermolysis of dithiocarbamate compounds as precursors for metal sulfide nanoparticles. Ajibade and Osuntokun thermolyzed heteroleptic complexes in hexadecylamine [8] to obtain ZnS, CdS and HgS quantum dots. ZnS dots were obtained, while spherical and agglomerated shapes were obtained for CdS and HgS, respectively. Nirmal and co-workers used a complex of Cd with pyrrolidine dithiocarbamate Cd(pdtc)2 to obtain CdS Effect of Concentration on Synthesis of Organic Passivated Cu2-xS Nanoparticles from N-Pyrrolidine Dithiocarbamate Molecular Precursor

The Influence of Temperature on the Formation of Cubic Structured CdO Nanoparticles and Their Thin Films from Bis(2-hydroxy-1-naphthaldehydato)cadmium(II) Complex via Thermal Decomposition Technique

Recently, researchers have developed a great interest in the synthesis of metal oxide nanoparticles due to their potential applications in various fields of science and industry, especially in catalysis, due to their high activity. Bis(2-hydroxy-1-naphthaldehydato)cadmium(II) complexes were prepared and used as precursors for the synthesis of cadmium oxide nanoparticles via thermal decomposition method using HDA as a stabilizing agent. The prepared complexes were also used as single source precursors to prepare CdO thin films onto the glass substrates by spin coating and were annealed at 250, 300, and 350°C, respectively. The precursors were characterized by Fourier transform infrared (FTIR) spectroscopy, elemental analysis, nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). The synthesized CdO nanoparticles and CdO thin films were characterized by ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM).