Development of Multifunctional Magnetic Core Nanoparticles

Multifunctional magnetic materials have a great importance in various fields of application, e.g., material science, chemistry, physics, environmental chemistry and biomedicine. Although a large number of scientific papers already describe the synthesis of multifunctional materials by various methods and technologies, a simple, fast and economically feasible synthesis procedure to combine all the materials in one system is still of interest.  This thesis contributes to the development of multifunctional magnetic-core materials scientifically in three parts. Firstly, the synthesis of magnetic core, i.e., magnetite nanoparticles, was attempted using only ferrous ions (Fe2+) of various concentrations as a magnetite precursor under ambient atmosphere. It was found that the synthesized magnetite was in a non-stoichiometric state, i.e., oxidation occurs. The introduction of Stöber silica (SiO2) layer in the form of a coreshell structure prevented the oxidation of the synthesized particles, as suggested by the low temperature magnetic measurement and Mössbauer study. Secondly, this thesis introduces a simple, room temperature synthesis method for further functionalization of the magnetite-silica coreshell powders with silver (Ag) and silver/silver chloride (Ag/AgCl) nanoparticles. Based on the proposed approaches, the Ag deposition on the silica shells can take place by three possible mechanisms: a) absorption of Ag+ on the silica surface by ionic bonding between the silver ions and hydroxyl groups (OH) of silica followed by the reduction of Ag+ by polyvinylpyrrolidone (PVP), b) hydrogen bonding between the PVP-coated Ag and the SiO2 shells, and c) electrostatic attraction between PVP-coated Ag and SiO2 shells. The silver chloride particles are formed when a certain amount of hydrochloric acid (HCl) is introduced. The particle morphology is controlled by the concentration of HCl. Thirdly, the thesis makes a scientific contribution by introducing novel properties by compacting the magnetite-silica coreshell powders into bulk material by pulsed electric current sintering (PECS). By adjusting the amount of magnetite-core inside the silica structure, it is possible to produce a transparent magnetic compact. In addition, the effects of the sintering atmosphere and temperature on the final properties of the compacts were also studied.

Electrical performance of curcuma longa extract dye using SnO2- based photoanode dye-sensitized solar cell

Due to their low output costs, straightforward manufacturing, and high effectiveness, dye-sensitized solar cell (DSSC) has a large following interest in the solar energy industry. Furthermore, due to its outstanding properties, tin oxide (SnO2) is an appealing semiconducting material suitable as a photoanode in DSSCs. In this research, the photoelectrodes of DSSC were fabricated using commercial SnO2 nanoparticles and sensitized with inorganic and organic dyes, N719 and Curcuma longa (turmeric) extract dye. On top of that, a platinum (Pt) counter electrode, iodide electrolyte and fluorine-doped tin oxide (FTO) coated glass substrate were used to fabricate the DSSC. The crystallographic structure and surface morphology of the SnO2 nanopowder were identified using X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations respectively. In addition, UV-Visible and current density-voltage curves were used to analyze the optical properties of the photoanodes and the cell’s electrical performance. As a result, it was found that the DSSC fabricated with N719 dye exhibited higher efficiency in contrast with the turmeric extract dye with SnO2 photoanodes

The effect of Spinacia oleracea dye absorption time on ZnO-based dye-sensitized solar cells’ electrical performance

Dye-sensitized solar cells (DSSC) have attracted much attention over the past 20 years due to their significance in energy conversion. However, the dye soaking time may significantly impact the efficacy of the photoanode semiconductor to carry the electronic charge to which the dye molecules adhere. An optimized dye soaking time may prevent the recombination of photo-excited electrons that are injected into the semiconductor of the DSSC. This study scrutinized the dependence of the zinc oxide (ZnO) photoanode soaking time of Spinacia oleracea (spinach) dye on the photocurrent-voltage characteristics. The ZnO film layer (photoanode) was prepared with commercial ZnO nanopowder and applied onto a fluorine-doped tin oxide (FTO) glass substrate using the doctor blade method. The prepared DSSCs’ were subjected to a variety of characterizations, including current density-voltage (J-V) characterization, UV-visible characterization, scanning electron microscope (SEM), and X-ray diffraction (XRD). Comparing four variations of dye soaking time, ZnO-based DSSC photoanode soaked in the dye for an hour achieved an optimum efficiency of 0.03 %. This study proved that the efficiency of a DSSC can be improved by optimizing the dye soaking time

Properties of a new insulation material glass bubble in geopolymer concrete

This paper details analytical research results into a novel geopolymer concrete embedded with glass bubble as its thermal insulating material, fly ash as its precursor material, and a combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as its alkaline activator to form a geopolymer system. The workability, density, compressive strength (per curing days), and water absorption of the sample loaded at 10% glass bubble (loading level determined to satisfy the minimum strength requirement of a load-bearing structure) were 70 mm, 2165 kg/m3, 52.58 MPa (28 days), 54.92 MPa (60 days), and 65.25 MPa (90 days), and 3.73 %, respectively. The thermal conductivity for geopolymer concrete decreased from 1.47 to 1.19 W/mK, while the thermal diffusivity decreased from 1.88 to 1.02 mm2/s due to increased specific heat from 0.96 to 1.73 MJ/m3K. The improved physicomechanical and thermal (insulating) properties resulting from embedding a glass bubble as an insulating material into geopolymer concrete resulted in a viable composite for use in the construction industry

Review on Thermal Insulation Performance in Various Type of Concrete

Thermal insulation concrete building plays an important role in environment sustainability especially energy saving buildings. Buildings are one of the largest consumers of energy worldwide. Therefore, significant energy saving can be realized by buildings with proper materials, design and operation. Thermal insulation systems are nowadays mostly applied for such building envelopes where the materials of load bearing structure such as concrete do not have a substantial thermal insulation capability. Thermal insulation in concrete are materials or combinations of materials that are used to provide resistance to heat flow, should have low conductivity for building application in order to represence of a temperature gradient, has an important effect on the heat exchange between the building interior and the ambiance. The aim of this paper is to review the thermal properties include thermal conductivity and specific heat on various types of concrete

Recent improvements on TiO2 and ZnO nanostructure photoanode for dye sensitized solar cells: A brief review

Dye sensitized solar cell (DSSC) is a promising candidate for a low cost solar harvesting technology as it promised a low manufacturing cost, ease of fabrication and reasonable conversion efficiency. Basic structure of DSSC consists of photoanode, dye, electrolyte and counter electrode. Photoanode plays an important role for a DSSC as it supports the dye molecules and helps in the electron transfer that will determine the energy conversion efficiency. This paper emphasizes the various improvements that had been done on the TiO2 and ZnO photoanode nanostructures synthesized through thermal method. For overall comparisons, ZnO nanoflowers photoanode had achieved the highest energy conversion efficiency of 4.7% due to its ability of internal light scattering that had increased the electron transportation rate. This has made ZnO as a potential candidate to replace TiO2 as a photoanode material in DSSC

Recent improvements on TiO

Dye sensitized solar cell (DSSC) is a promising candidate for a low cost solar harvesting technology as it promised a low manufacturing cost, ease of fabrication and reasonable conversion efficiency. Basic structure of DSSC consists of photoanode, dye, electrolyte and counter electrode. Photoanode plays an important role for a DSSC as it supports the dye molecules and helps in the electron transfer that will determine the energy conversion efficiency. This paper emphasizes the various improvements that had been done on the TiO2 and ZnO photoanode nanostructures synthesized through thermal method. For overall comparisons, ZnO nanoflowers photoanode had achieved the highest energy conversion efficiency of 4.7% due to its ability of internal light scattering that had increased the electron transportation rate. This has made ZnO as a potential candidate to replace TiO2 as a photoanode material in DSSC

The influence of density, compressive strength and thermal conductivity under variety percentage of glass bubble in geopolymer concrete

In this study of various percentage addition of glass bubble as thermal insulated material (2.5, 5.0, 7.5 and 10 %) has influenced the concrete performance such as density, compressive strength and thermal conductivity. The compressive strength of geopolymer concretes achieved the maximum strength with 10 % glass bubble at 65.25 MPa for 90 days with the lowest density achieved at 2165 kg/m³. The thermal conductivity of geopolymer concrete with the present addition of glass bubble as thermal insulated materials showing better thermal insulation properties with decrease of density to 1.20 W/mK. Results highlight the thermal conductivity showing better result with reducing density of the geopolymer concrete due to the addition of glass bubble in the geopolymer concrete. The unique of spherically shape and light hollow sphere of glass bubble in the geopolymer concrete contributed better performance towards thermal insulation application with low density and thermal conductivity within applicable strength