Effect of pH and Irradiation Power in the Synthesis of Gold Nanoparticles by using Binahong (Anredera cordifolia) Leaves Extract

Au nano particles have been successfully synthesized using extract of binahong (Anredera cordifolia) leaves at various pH, irradiation power and irradiation time. The synthesis was conducted using microwave oven for some minutes, at certain adjusted experimental condition. pH of solution was varied from 2 – 10, irradiation power was adjusted in the range of 30% - 100% of total power of 800W, and iiradiation time was studied in the range of 30 – 120 second. The experimental results showed at low pH, the nonspherical particle was more commonly formed. The stabilization of particles took place more effectively at the higher pH. At low pH, the nano particles were below 50 nm in size and were in form of triangle, rod, rhombic, cubic, or truncated form of these shapes. UV-Vis spectra also indicated that both microwave irradiation power and time significantly affect the morphology of particles. These research provide clear explanation about the effect of the pH and irradiation time over the AuNP synthesis by using greener method, which can be further studied in optimizing experimental parameters for conducting industrial scale synthesis.

Approximate T matrix and optical properties of spheroidal particles to third order with respect to size parameter

© 2019 American Physical Society. In electromagnetic scattering, the so-called T matrix encompasses the optical response of a scatterer for any incident excitation and is most commonly defined using the basis of multipolar fields. It can therefore be viewed as a generalization of the concept of polarizability of the scatterer. We calculate here the series expansion of the T matrix for a spheroidal particle in the small-size, long-wavelength limit, up to third lowest order with respect to the size parameter, X, which we will define rigorously for a nonspherical particle. T is calculated from the standard extended boundary condition method with a linear system involving two infinite matrices P and Q, whose matrix elements are integrals on the particle surface. We show that the limiting form of the P and Q matrices, which is different in the special case of spheroid, ensures that this Taylor expansion can be obtained by considering only multipoles of order 3 or less (i.e., dipoles, quadrupoles, and octupoles). This allows us to obtain self-contained expressions for the Taylor expansion of T(X). The lowest order is O(X3) and equivalent to the quasistatic limit or Rayleigh approximation. Expressions to order O(X5) are obtained by Taylor expansion of the integrals in P and Q followed by matrix inversion. We then apply a radiative correction scheme, which makes the resulting expressions valid up to order O(X6). Orientation-averaged extinction, scattering, and absorption cross sections are then derived. All results are compared to the exact T-matrix predictions to confirm the validity of our expressions and assess their range of applicability. For a wavelength of 400 nm, the new approximation remains valid (within 1% error) up to particle dimensions of the order of 100-200 nm depending on the exact parameters (aspect ratio and material). These results provide a relatively simple and computationally friendly alternative to the standard T-matrix method for spheroidal particles smaller than the wavelength, in a size range much larger than for the commonly used Rayleigh approximation.

Approximate T matrix and optical properties of spheroidal particles to third order with respect to size parameter

© 2019 American Physical Society. In electromagnetic scattering, the so-called T matrix encompasses the optical response of a scatterer for any incident excitation and is most commonly defined using the basis of multipolar fields. It can therefore be viewed as a generalization of the concept of polarizability of the scatterer. We calculate here the series expansion of the T matrix for a spheroidal particle in the small-size, long-wavelength limit, up to third lowest order with respect to the size parameter, X, which we will define rigorously for a nonspherical particle. T is calculated from the standard extended boundary condition method with a linear system involving two infinite matrices P and Q, whose matrix elements are integrals on the particle surface. We show that the limiting form of the P and Q matrices, which is different in the special case of spheroid, ensures that this Taylor expansion can be obtained by considering only multipoles of order 3 or less (i.e., dipoles, quadrupoles, and octupoles). This allows us to obtain self-contained expressions for the Taylor expansion of T(X). The lowest order is O(X3) and equivalent to the quasistatic limit or Rayleigh approximation. Expressions to order O(X5) are obtained by Taylor expansion of the integrals in P and Q followed by matrix inversion. We then apply a radiative correction scheme, which makes the resulting expressions valid up to order O(X6). Orientation-averaged extinction, scattering, and absorption cross sections are then derived. All results are compared to the exact T-matrix predictions to confirm the validity of our expressions and assess their range of applicability. For a wavelength of 400 nm, the new approximation remains valid (within 1% error) up to particle dimensions of the order of 100-200 nm depending on the exact parameters (aspect ratio and material). These results provide a relatively simple and computationally friendly alternative to the standard T-matrix method for spheroidal particles smaller than the wavelength, in a size range much larger than for the commonly used Rayleigh approximation.

Approximate T matrix and optical properties of spheroidal particles to third order with respect to size parameter

© 2019 American Physical Society. In electromagnetic scattering, the so-called T matrix encompasses the optical response of a scatterer for any incident excitation and is most commonly defined using the basis of multipolar fields. It can therefore be viewed as a generalization of the concept of polarizability of the scatterer. We calculate here the series expansion of the T matrix for a spheroidal particle in the small-size, long-wavelength limit, up to third lowest order with respect to the size parameter, X, which we will define rigorously for a nonspherical particle. T is calculated from the standard extended boundary condition method with a linear system involving two infinite matrices P and Q, whose matrix elements are integrals on the particle surface. We show that the limiting form of the P and Q matrices, which is different in the special case of spheroid, ensures that this Taylor expansion can be obtained by considering only multipoles of order 3 or less (i.e., dipoles, quadrupoles, and octupoles). This allows us to obtain self-contained expressions for the Taylor expansion of T(X). The lowest order is O(X3) and equivalent to the quasistatic limit or Rayleigh approximation. Expressions to order O(X5) are obtained by Taylor expansion of the integrals in P and Q followed by matrix inversion. We then apply a radiative correction scheme, which makes the resulting expressions valid up to order O(X6). Orientation-averaged extinction, scattering, and absorption cross sections are then derived. All results are compared to the exact T-matrix predictions to confirm the validity of our expressions and assess their range of applicability. For a wavelength of 400 nm, the new approximation remains valid (within 1% error) up to particle dimensions of the order of 100-200 nm depending on the exact parameters (aspect ratio and material). These results provide a relatively simple and computationally friendly alternative to the standard T-matrix method for spheroidal particles smaller than the wavelength, in a size range much larger than for the commonly used Rayleigh approximation.

Parameterization of The Single-Scattering Properties of Dust Aerosols in Radiative Flux Calculations

In this study, we present parameterization schemes of dust single-scattering properties (SSPs) in order to establish a fast and accurate way to obtain the SSPs for dust shortwave radiative flux calculation. Based on the assumption that dust particles are spheroids, we represent a single nonspherical particle with a collection of monodisperse spheres that contain the same total surface area and volume as the original particle to convert the spheroid to a sphere. The SSPs of dust particles were parameterized in terms of the effective radius ( R e ) and imaginary part of the refractive index ( M i ). The averaged relative errors of the parameterized to the “exact” single-scattering properties, which refer to the results from the Mie theory program, are below 1.5%. To further quantify the impact of parametrization on the radiative flux simulation, we computed the radiative fluxes at both the top of the atmosphere (TOA) and the surface by using SSPs from the parameterization and the “exact”, respectively. The maximum relative errors were below 1% at both the TOA and the surface, proving that the SSPs of dust calculated by our parameterization schemes are well suited for radiative flux calculations. This parameterization differs from previous works by being formulated not only with R e but also with M i . We also investigated the sensitivity of dust-aerosol forcing to R e , M i , optical depth (τ), and solar zenith angle (SZA). The results show that the value of shortwave (SW) radiative forcing (RF) at the TOA changes from negative to positive as the M i is increasing, which means that, as the absorption of dust particles becomes stronger, more energy is kept in the atmosphere to heat the earth–atmosphere system. The SW RF gradually becomes less negative at the TOA and more negative at the surface with increasing R e , due to the decreases of reflection and transmission along with the single-scattering albedo decreasing. As the optical depth increases, the values of the SW RF decrease because of the strong attenuation for heavy loading. When SZA increases, the SW RF becomes more negative at both the TOA and the surface due to the long optical path at a large SZA. The errors induced from the parameterized SSPs of dust in the SW RF calculation are very small, which are less than 2.1%, demonstrating the accuracy of the parameterization and its reliability for climate model applications.