Chun-Nien Liu

Kinetics of phosphate adsorption on iron oxides formed under the influence of citrate.

The influence of organic acids on the formation of Fe oxyhydroxides and oxides has been intensively studied. However, scant attention has been paid to the subsequent effect on surface chemistry of the Fe oxides formed. The kinetics and mechanisms of phosphate adsorption by the Fe oxides formed in the presence of citrate ligands at initial citrate/Fe(II) molar ratios (MR) of 0, 0.001, 0.01, and 0.1 were investigated using the conventional batch method. The adsorption studies were conducted at the initial phosphate concentration of 0.5 mM and pH 4.0 during the reaction period from 2 min to 56 h at 278, 288, 298, and 313 K. The results show that the phosphate adsorption followed multiple second-order kinetics and had two distinct rates in each reaction system. The amount, rate coefficient, activation energy and pre-exponential factor of phosphate adsorption by the Fe oxides formed greatly varied with their structural and surface properties. These properties, which included crystal structure, specific surface...

Sorption of cadmium on humic acid: Mechanistic and kinetic studies with atomic force microscopy and X-ray absorption fine structure spectroscopy

Humic acids (HA) constitute a major fraction of the organic matter in soils and sediments. Little is known about the kinetics and mechanisms of Cd sorption by HAs, especially those pertaining to the surface features and structure of the Cd-humate complexes. We investigated Cd sorption by HA using the conventional batch method, N2-BET method, atomic force microscopy (AFM), and extended X-ray absorption fine structure (EXAFS) spectroscopy to gain a better understanding of the kinetics and mechanisms. Cadmium sorption by HA can be described by the parabolic diffusion equation. The increase in the apparent diffusion coefficient with an increase in the initial Cd concentration was less pronounced at higher initial Cd concentrations, apparently due to an enhancement in aggregation of the Cd-humate complexes. The HA before and after Cd sorption at Cd concentrations ≤ 10–6 M in different reaction times was spheroidal in shape. The Cd-humate complexes formed at 10–4 and 10–3 M Cd gradually changed to resemble the ...

Fabrication and Characteristics of Ce-Doped Fiber for High-Resolution OCT Source

The fabrication of Ce-doped fibers (CeDFs) is demonstrated by drawing-tower method employing rod-in-tube technique. The fluorescence spectrum of CeDFs with a 16-μm core exhibited a 160-nm broadband emission with 1.45-μm axial resolution. This CeDF may be functioned as a high-resolution light source for optical coherence tomography applications.

Fluorescence enhancement in broadband Cr-doped fibers fabricated by drawing tower

The fluorescence enhancement in broadband Cr-doped fibers (CDFs) fabricated by a drawing tower with a redrawn powder-in-tube preform is proposed and demonstrated. The CDFs after heat treatment exhibited Cr⁴⁺ emission enhancement with spectral density of 200 pW/nm, verified by the formation of α-Mg₂SiO₄ nanocrystalline structures in the core of CDFs. The high fluorescence achievement in the CDFs is essential to develop a broadband CDF amplifier for next-generation optical communication systems.

Sesquioxidic components of selected Taiwan soils

Abstract Twenty two surface soils, representing six parent materials and four soil groups, were sampled in Taiwan for the present study. Except in the soil derived from volcanic ash, the sesquioxidic components and relatively easily extractable Si were present only in small amounts in the NaOAc and H2O2- NaOAc extractable fractions. In addition to Fe, both Si and Al were present in the dithionite-citrate-bicarbonate extracts in considerable amounts, indicating that Si and Al were either present separately or in association with Fe in the sesquioxidic fractions of the soils. The amounts of Si, Al and Fe extracted by the dithionite-citrate-bicarbonate and boiling KOH treatments differed from sample to sample, indicating that they are important variables in the nature of the soils studied. The amounts of the ammonium oxalate-extractable Al and Fe, representing the noncrystalline sesquioxidic products of relatively recent weathering, also differed with parent materials and pedogenic processes. The statistical data indicate that the ammonium oxalate-extractable Al and Fe are related to the contents of organic matter but not to acidity and the contents of clay. The percentage distribution of the extractable Al in the > 2 μm fractions of the selected soil samples ranged from 22.0 to 52.5% and that of the extractable Fe from 11.1 to 38.1%, indicating that the active non-crystalline Al and Fe components in the non-clay fractions deserve close attention in the study of pedogenesis and other soil physicochemical reactions in relation to soil fertility and environmental protection.

A New Scheme of Oriented Hyperboloid Microlens for Passive Alignment Lasers to Polarization Maintaining Fibers

A new scheme of oriented-hyperboloid microlens (OHM) with passive alignment to achieve high polarized extinction ratio (PER) is proposed and demonstrated high efficiency coupling of high-power 980 nm pump lasers to polarization maintaining fibers (PMFs). Using an automatic grinding machine and a charge-coupled-device to precisely control and attain the required minor radius of curvature 4-4.8 μm, offset within 0.7 μm, and axis orientation accuracy ±1°, the OHM exhibited a high-average PER of 31.7 dB, and a high-average coupling efficiency of 83.4%. For a 30 dB PER, the angular misalignment tolerance of the OHM was measured to be ±2°. The unique advantage of the proposed OHM is passive alignment to achieve high PER by only aligning the OHM endface of the fast axis parallel to the axis of laser polarization. This newly developed OHM with unique passive alignment to achieve high polarization is beneficial for the applications of laser/PMF modules where mode polarization and high coupling efficiency are required for use in high precision fiber optic gyroscopes as well as many low-cost and high-performance lightwave interconnection applications.

Kinetics of 2,4-dichlorophenoxyacetic acid (2,4-D) adsorption by metal oxides, metal oxide-humic complexes, and humic acid

Metal oxides and humic substances have a large and physicochemically active surface area and thus provide a major sink for the retention of pesticides. Although organic and inorganic components are closely associated in soil, the kinetics of 2,4-D adsorption by metal oxide–humic complexes in comparison with metal oxides and humic acid (HA) remains obscure. In the present study, the kinetics of 14C-labeled 2,4-D adsorption by Al, Fe, and Mn oxides, the metal oxide–humic complexes that were formed in metal oxide–catechol systems, and the standard soil HA from the International Humic Substances Society were investigated. The results show that the amounts and rate of 2,4-D adsorption greatly varied with the type and the surface properties of the metal oxides. The 2,4-D adsorption by the metal oxides, metal oxide–humic complexes, and HA can be described by multiple 1st-order kinetic models (the fast and slow reactions) and the rate-limiting step of 2,4-D adsorption was a diffusion process as indicated by their activation energy values, which ranged from 16.6 to 25.9 kJ mol−1. The complexation of humic macromolecules with the metal oxides substantially reduced the amount and the rate of 2,4-D adsorption as the result of the resultant alteration of the surface properties. The specific surface of the Al oxide–, Fe oxide–, and Mn oxide–humic complexes, respectively, decreased by 49, 92, and 66%, compared with the metal oxides. The rate coefficients of the fast reaction of 2,4-D adsorption by metal oxides were 2.2 to 3.1 times higher than the respective metal oxide–humic complexes. Humic acid had a much lower reactivity than the metal oxides and a similar reactivity with the metal oxide-humic complexes to 2,4-D. The findings of this study are significant in understanding the ability of soil components to bind the pesticide such as 2,4-D, as influenced by catechol polymerization and the impact on the transformations and degradation of the pesticide in soil environments.

New scheme of a highly-reliable glass-based color wheel for next-generation laser light engine

A new scheme of a highly-reliable glass-based color wheel applied to a laser light engine (LLE) for a high-power laser operation is demonstrated for the first time. The glass-based color wheel showed better thermal stability than the silicone-based color wheel, about 13.6 times less lumen loss and 3 times less chromaticity shift after being operated under a 30 Wopt laser for 2000 hours, respectively. The excellent thermal stability can be attributed to the high glass transition temperature up to 570 °C exhibited by the glass-based color wheel. The easy fabrication and the good reliability on optical performance under thermal stress benefit the novel glass-based color wheels as promising candidates to replace the silicone-based color wheels in the LLE modules for the next-generation laser projector.

Few-mode Cr-doped crystalline core fiber cladded by high-index glass

A few-mode Cr-doped crystalline core fiber (FMCDCCF) cladded by high-index glass is demonstrated. The FMCDCCF exhibited a V-value below four at 1400nm to provide five few-mode characteristics for possibility use in broadband fiber amplifiers.

Kinetics of cadmium desorption from iron oxides formed under the influence of citrate

ABSTRACT Research on cadmium (Cd) dynamics in the environment has received increasing attention. However, little is known about desorption kinetics of Cd from short-range-ordered mineral colloids formed under the influence of various ionic environments. The present study examines the desorption kinetics of Cd following its adsorption on iron oxides formed under the influence of citric acid which is common in soil and water. Iron oxides were formed at pH 6.00 ± 0.05 and 25°C at an initial Fe(II) concentration of 10 −2 M in the presence of citrate ligand at initial citrate/Fe(II) molar ratios (MRs) of 0, 0.001, 0.01 and 0.1. The kinetics of Cd desorption by 0.01 M KNO 3 , KCl, K-acetate, and K-citrate (adjusted to pH 5.0) from the iron oxides, following 1-day Cd adsorption at the initial Cd concentration of 50 μM, was investigated at 20°C from 5 min to 7 days. The fast (5 min to 2 h) and slow (2–24 h) processes of Cd desorption from the iron oxides can be satisfactorily described by the overall parabolic diffusion equation. The amount of Cd released and the reaction rate varied greatly with surface properties of the iron oxides formed under the influence of citrate. The amount of Cd released by all the extractants from the iron oxides was in the sequence of the initial citrate/Fe(II) MR of 0.1 > 0.01 > 0 > 0.001, which is in accord with the specific surface, microporosity, citrate content in the precipitates, degree of disorder of iron oxides, and amount of Cd adsorbed. The rate of Cd release by different extractants for the fast reaction was in the order chloride > citrate > acetate > nitrate, which was generally consistent with the sequence of the stability constants of Cd-extractant ligand complexes. The rate of Cd release by different extractants for the slow reaction was in the order citrate > acetate ≥ chloride > nitrate, indicating that a longer induction period was required for an extractant with a larger molecule to desorb the Cd adsorbed on the micropore surface. The research findings are of fundamental significance in understanding the role of the nature and properties of iron oxides formed under the influence of organic acids such as citric acid in influencing Cd dynamics in soil and related environments.