Papers by Keyword: Absorbance

Abstract: This study relates to the development of geopolymer concrete (GPC) and empirical models which can be used to predict strength and durability under different curing temperatures. The binders and alkaline activators used for the GPC production were characterized to determine their physical and chemical properties. The partial and pure geopolymer concrete samples were produced. The partial replacement of Geopolymer concrete (GPC) samples was done with cement at varying percentages of 0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5 and 20% to determine the optimum cement stabilization. Fourier transform infrared spectroscopy (FTIR) results show key absorbance level at the zone between 950.1 and 3250.12 cm⁻¹. It means that enhancement of the laboratory-produced (bespoke) superplasticizer enhanced the performance of GPC by reducing the viscosity and enriching the flow behaviour of the concrete. The optimal geopolymer product showed substantial strength and durability enhancements at 70°C followed by declining values at temperatures above 70°C, indicating material deterioration. A positive correlation between hot-state temperature, strength and durability properties was also established. Furthermore, scrutiny of the model shows that overall dataset points for training and test sets are clustered close to the diagonal line, signifying that the model provides precise estimation of the strength and durability features. .

Abstract: Dye-sensitizer is heart of dye-sensitized solar cell which is an electron donor when receiving irradiation on the surface. Dye can be classified as synthesized dye or natural dye. Natural dye can be obtained colourfully from various plants such as tomato, carrot, grapes, chili, and so on. In this work, three selected plants which are locally available were chosen for three different colours. Green colour was extracted from leaves of Tiliacora triandra (Ya-nang). Red colour was from flower of Hibiscus sabdariffa (Rosella), and purple colour was from fruits of Morus alba (Mulberry). They were dried and ground into powder and their colour was extracted using 95%-ethanol. The concentrations of solution were 5, 10, and 20 g of powder per 200 ml for solvent extraction of each colour. These three colours were tested for absorbance index indicating ability of light absorption. The absorbance index curves showed that Ya-nang in green colour gave the best absorbance index having several peaks at 458 and 675 nm wavelengths for the 20 g/200 ml solution. While Rosella in red colour showed the peak at 534 nm wavelength and Mulberry in purple colour gave peak at 666 nm wavelength. The characteristics from the absorbance index curves also revealed the type of colour pigment in the dye. It was found that Ya-nang in green dye, Rosella in red dye and Mulberry in purple dye contained “Chlorophyll”, “Anthocyanin” and “Betacyanin” pigments respectively. Moreover, the area under the curves obviously indicated that the area of the green colour from Ya-nang was higher than those of Rosella and Mulberry. This implied that Ya-nang had higher potential to be dye-sensitizer and would give better dye sensitized solar performance compared with Rosella and Mulberry.

Abstract: In this paper, near unity broadband absorption of Van der Waals semiconductors on a metallic substrate, and their photovoltaic performances in the visible spectrum are simulated. Ultrathin layered semiconductors such as Molybdenum disulfide (MoS₂), Tungsten disulfide (WS₂), Molybdenum di-selenide (MoSe₂), Tungsten di-selenide (WSe₂), Molybdenum ditelluride (MoTe₂), and Tungsten ditelluride (WTe₂) can create strong interference by damping optical mode in their multilayer form and increase light absorption at their heterojunctions with noble metals. From our simulation, it is observed that this absorbance can reach up to 94% when the semiconductors are placed on a gold substrate. The optimum thickness of these semiconductors in their heterostructures with gold is analyzed to create resonant absorption to generate the maximum amount of current density. The power conversion efficiency of the designed Schottky junction solar cells is calculated from their current density vs bias voltage characteristics that ranges from 1.57% to 6.80%. Moreover, the absorption coefficient, dark current characteristic, electric field intensity distribution in the device, and carrier generation rate during light illumination are presented with a view to characterizing and comparing among the parameters of TMDC based nanoscale solar cell.

Abstract: Separate and combined effects of sodium hex metaphosphate (SHMP) and polycarboxylate superplasticizer (PCS) of different dosages (0.5%, 1%, 1.5%, and 2%) on the dispersion stability of nanoSiO₂ (NS) were studied. The effect of the dispersant was characterized by the change of absorbance. When SHMP and PCS were used separately and in combination, the stability of nanoSiO₂ dispersions was compared and the optimal amount of dispersant for different dosage of nanoSiO₂ dispersions were summarized. Finally, the mechanism of dispersant compounding was discussed. The results show that with the increase of the concentration, the optimal amount of SHMP increases significantly while the optimal amount of PCS dispersant is lower and better than SHMP. A clear linear relationship between the optimal dosage of SHMP and the concentration of NS could be found. If SHMP is used combined with PCS, the stability of the dispersed NS will increase and the dosages of both dispersants will be reduced.

Abstract: Several studies have been made on cell growth by the ultrasound irradiation. It is important to change the output, irradiation time and duty cycle for cell growth. The duty cycle determined the proportion of the time that the ultrasound was “on”. We can control cell growth by changing these three terms. The purpose of this study is to find the optimum conditions for cell growth and examine a new factor to influence cell growth. Cell concentration was determined by measuring the absorbance with a spectrophotometer. In this study, the absorbance became highest on 10min ultrasound irradiation and the duty cycle of 67% in experimental conditions. However, when 30 min ultrasound irradiation and the duty cycles of 86%, the absorbance became close to the highest value too. The results suggested that, in addition to the duty cycle, the off time of ultrasound might also affect the cell growth.

Abstract: TiO₂ has become a widely investigated photocatalyst because of its low cost, low toxicity and high photocatalytic activity under UV irradiation that causes photocatalytic decomposition of organic compounds. Impurities dopant and metal are often used to acquire impurities doped or metal doped TiO₂ powder by a sol-gel method. In this paper, we made nitrogen doped TiO₂ by a simple process. TiO₂ (P25) thin films with 80 % of anatase and 20 % of rutile were fabricated on FTO glass by electrophoretic deposition (EPD). These were then doped with nitrogen by using urea and sintered in electric furnace at 500 and 600 degrees Celsius. EPD was superior for film formation at dispersibility. We calculated absorbance spectra of nitrogen doped TiO₂ thin film fabricated on FTO glass. As the result, 600 degrees Celsius is superior sintering temperature at absorbance under visible light than 500 degrees Celsius. Moreover, when the samples sintered at 600 degrees Celsius, each additive amount had different increment of absorbance in specific visible light range. This result indicates the improvement in visible-light response on TiO₂ by the simple process. To further research, it is essential to make nitrogen doped TiO₂ under pressure and measure the photodegradation reaction.

Abstract: It was shown, that using of sodium metasilicate (Na₂SiO₃) as stabilizing agent for CdS quantum dots or Ag nanoparticles in water leads to the formation of stable colloids of CdS/SiO₃^2- and Ag/SiO₃^2- particles. These colloids are active in the visible range of the spectrum. According to TEM and UV-visible spectroscopy data, an average size of the particles in colloids was ∼ 5 nm for CdS and 2-10 nm for Ag. Ag/SiO₃^2- water colloids showed an absorption band with a maximum at 380-410 nm. This band belonged to surface plasmon resonance. CdS/SiO₃^2- water dispersions were characterized by luminescence at the region of 500-800 nm. The luminescence intensity increased after addition of Ag⁺ into the colloids of CdS/SiO₃^2-.

Abstract: The emerging of bacteria/cell culturing in biological/biomedical research and industry is in demand for low cost, fast, non-invasive, and reliable alternative/approach for evaluation and measurement. Microfluidic approach is one of the promising alternatives for replacing the expensive commercial cuvvete for bacteria/cell culture and suspension for optical measurement. This study demonstrates the integration of absorbance measurement with microfluidic platform for Escherichia coli (E. coli) bacteria suspension analysis. The E. coli was cultured and prepared for suspension medium which then transferred inside the PDMS-glass based microfluidic. Then, the absorbance measurement is carried out using UV-Visible spectrophotometer. We demonstrate this method by measuring absorption of light transmitted through microfluidic chambers within the visible light range (350nm - 750nm). From the result, it had indicates that the graph pattern and growth behavior of E. coli suspension in microfluidic platform are reliable and comparable to commercial cuvvete reading. This finding

Abstract: Dye-sensitized solar cell (DSSC) consists of TiO₂ nanoporous coating which acts as a photo electrode, a sensitizer of dye molecules soaked in the TiO₂ film, liquid electrolyte and a counter electrode. This paper focuses on the usage of a sensitizer from the Pitaya fruit. Pitaya or commonly known as dragon fruit (Hylocereus polyrhizus) was extracted and used as a sensitizer to fabricate the dye sensitized solar cell (DSSC). The photoelectrochemical performance of Pitaya based solar cell shows an open circuit voltage (V_OC) of 237 mV, short circuit current (I_SC) of 4.98 mA, fill factor (FF) of 0.51, solar cell efficiency (η) of 0.70 % and has a peak absorbance rate of 2.7 at 550 nm. The photoelectrochemical and UV-Visible light absorbance performance of Pitaya-DSSC shows good potential in future solar cell fabrication.

Abstract: Carbon Dots (C-Dots) was successfully prepared by simple heating method. The effect of additional elemental sulfur on the luminiscent performance of C-Dots was investigated. The preparation, chemical composition and optical properties such as absorbance and band gap energy are studied. The C-Dots were prepared with various mass sulfur 0.5-3.0 g and citric acid-urea was constant, i.e. 1.0 g and 4.0 g, respectively. This study used sulfur from natural deposit in Indonesia. The raw materials were prepared by mixing in pure water. The homogeneous solutions were heated at 225°C for 15 minutes under atmospheric pressure. The color emission of C-Dots is found in the visible light spectrum. The addition of sulfur in C-Dots phosphor caused the shifting of absorbance wavelength, i.e. 350-429 nm. By increasing mass of sulfur, the band gap energy of C-Dots decreased from 2.4 eV to 1.8 eV.