Yen Hua Chen

Kinetic study on removal of copper(II) using goethite and hematite nano-photocatalysts

Goethite and hematite nanomaterials (nano-goethite and nano-hematite) can be synthesized using a coprecipitation method. Nano-hematite is synthesized via the reaction of HCl and FeCl(3) solution at 100 degrees C for 2 days, while nano-goethite is prepared by adding Fe(2)(SO(4))(3) into the 2.5 M NaOH solution for 4h, and then heated at 40 degrees C for 2 days. Afterward the photocatalytic decomposition of methylene blue solution is performed by UV-light irradiation, and the adsorption procedure is carried out by batch experiments. It is observed that both nano-hematite and nano-goethite exhibit some photocatalytic activity and possess a high adsorption capacity for copper ions. The maximum Cu(II) adsorption capacity is 149.25 and 84.46 mg/g for nano-goethite and nano-hematite, respectively. Further, the experimental data are well fitted to the pseudo-second-order equation. It also suggests that the Langmuir isotherm is more adequate than the Freundlich isotherm in simulating the adsorption isotherm of Cu(2+), and the Cu(2+) adsorption onto nanomaterials is a spontaneous process. Therefore, these findings indicate that nano-goethite and nano-hematite are effective materials for Cu(2+) removal and, together with its photocatalytic activity, may be applied in the removal of heavy metal ions from aqueous streams.

Kinetics and mechanism of arsenate removal by nanosized iron oxide-coated perlite

This study discussed the adsorption kinetics of As(V) onto nanosized iron oxide-coated perlite. The effects of pH, initial concentration of As(V) and common anions on the adsorption efficiency were also investigated. It was observed that a 100% As(V) adsorption was achieved at pH value of 4-8 from the initial concentration containing 1.0 mg-As(V)L(-1) and the adsorption percentage depended on the initial concentration; the phosphate and silicate ions would not interfere with the adsorption efficiency. Furthermore, nanosized iron oxide-coated perlite (IOCP) has been shown to be an effective adsorbent for the removal of arsenate from water. The adsorption kinetics were studied using pseudo-first- and pseudo-second-order models, and the experimental data fitted well with the pseudo-second-order model. Moreover, it suggests that the Langmuir isotherm is more adequate than the Freundlich isotherm in simulating the adsorption isotherm of As(V). The adsorption rate constant is 44.84 L mg(-1) and the maximum adsorption capacity is 0.39 mg g(-1). These findings indicate that the adsorption property of IOCP gives the compound a great potential for applications in environmental remediation.

Kinetic study of Cu(II) adsorption on nanosized BaTiO3 and SrTiO3 photocatalysts

In this study, nanoparticles with perovskite structure (nano-SrTiO(3) and nano-BaTiO(3)) were synthesized via a co-precipitation method, and their photocatalytic and adsorption characteristics were investigated. Both of them exhibited some photocatalytic activity and possessed a high adsorption capacity for copper ions. Further, the pseudo-first-order model was found to be more suitable to fit the experimental data. Moreover, it suggested that the Langmuir model was more adequate in simulating the adsorption isotherm. The maximum adsorption capacity was 370.4 mg/g and 200.0mg/g for nano-SrTiO(3) and nano-BaTiO(3), respectively. The negative apparent free energy confirmed that the Cu(2+) adsorption onto the nano-photocatalysts was a spontaneous process. The underlying mechanism of adsorption of Cu(II) onto nano-perovskites could be due to the ion exchange and surface complexation. From the results, SrTiO(3) and BaTiO(3) nanoparticles may be an effective material for Cu(2+) removal and, together with its photocatalytic activity, may be suitable for environmental remediation applications.

Amine modification on kaolinites to enhance CO2 adsorption

The objective of our study was to prepare an effective and low-cost adsorbent for CO2 capture and to provide detailed analyses of adsorption-related properties. For this purpose, we treat the naturally abundant kaolinite with amines using the wet impregnation method. The thermogravimetric analysis indicates that the CO2 adsorption capacity of kaolinite (3.3 mg/g) can be enhanced through amine modification and increases with an increase in amine loading. In terms of amine-modified parameters, it is observed that kaolinite modified with 4MEA+1EDA with 50 wt% has the best CO2 adsorption capacity (149.0 mg/g). We also speculate, based on X-ray diffraction and Fourier transformation infrared spectroscopy results, that CO2 adsorption onto amine-modified kaolinite occurs through chemical adsorption. This further substantiates the conclusion that the inexpensive and commonly available kaolinite is a potential solid carrier and is also a good adsorbent for CO2 capture with amine modification.

Adsorption and desorption properties of arsenate onto nano-sized iron-oxide-coated quartz

This study was conducted to investigate the adsorption and desorption properties of arsenate [As(V)] on nano-sized iron-oxide-coated quartz (IOCQ) through batch experiments. The coating of nano-sized iron oxide on the quartz surface was performed using the heat treatment process which aimed to utilize the adsorption properties of the nano-sized iron oxide and the filtration properties of the quartz. Environmental SEM-EDAX and BET techniques were used to analyze the surface morphology, elemental composition, surface area and the porosity of the adsorbent. SEM-EDAX analyses confirmed that arsenate was adsorbed on the IOCQ surface. BET results showed that the IOCQ adsorbent had higher pore volumes and high specific surface areas compared with the pure quartz. The study revealed that the adsorption rate of As(V) ion was very rapid and reached the equilibrium within 5 min. This study also revealed that almost 100% of As(V) removal was achieved within 5 minutes of adsorption reaction from the initial solution containing 1,000 microg-As(V)/L. The Langmuir adsorption isotherm model suitably explained the sorption characteristics of As(V) onto IOCQ. This desorption study showed that the adsorbent could be reused after reacting with mild HCl solution but the concentration of acid eluant or pH has a great impact on the coated adsorbent surface. The results indicate that the nano-sized iron oxide-coated adsorbent is potentially suitable for removal of arsenate from drinking water.

The Taiwan crisis: a showcase of the global arsenic problem

In the 1950s, the residents of the southwestern coastal areas of Taiwan suffered greatly from Blackfoot disease (BFD) due to the consumption of arsenic-contaminated groundwater. Groundwater with high levels of arsenic in southwestern and northeastern Taiwan received much attention. After arsenic-safe tap water was utilized for drinking instead of groundwater in the 1970s, BFD cases decreased greatly. After 1990, no new BFD cases were reported, and as a consequence, BFD problems disregarded. However, arsenic is still present in the groundwater. This book will improve the knowledge and understanding of the occurrence and genesis of arsenic-rich groundwaters in Taiwan. It deals with constraints on the mobility of arsenic in groundwater, its uptake from soil and water by plants, arsenic-propagation through the food chain, human health impacts, and arsenic-removal technologies. Taiwan case experiences are described in this book and can be applied worldwide.

Thickness Dependent on Photocatalytic Activity of Hematite Thin Films

Hematite (Fe2O3) thin films with different thicknesses are fabricated by the rf magnetron sputtering deposition. The effects of film thicknesses on the photocatalytic activity of hematite films have been investigated. Hematite films possess a polycrystalline hexagonal structure, and the band gap decreases with an increase of film thickness. Moreover, all hematite films exhibit good photocatalytic ability under visible-light irradiation; the photocatalytic activity of hematite films increases with the increasing film thickness. This is because the hematite film with a thicker thickness has a rougher surface, providing more reaction sites for photocatalysis. Another reason is a lower band gap of a hematite film would generate more electron-hole pairs under visible-light illumination to enhance photocatalytic efficiency. Experimental data are well fitted with Langmuir-Hinshelwood kinetic model. The photocatalytic rate constant of hematite films ranges from 0.052 to 0.068 min-1. This suggests that the hematite film is a superior photocatalyst under visible-light irradiation.

Strain Effects on the Ferromagnetic and Electronic Properties in ( La0.91 , Sr0.09 ) MnO3 Thin Films

La 1-x Sr x MnO 3 (LSMO) thin films with a polycrystalline structure of variable thickness were deposited by a radio-frequency magnetron sputtering system on SiO 2 (200 nm)/Si(100) substrate. The ferromagnetic property and electrical transport increased with increasing film thickness. This can be considered as the result of small deformation of the Mn-O bond length/bond angle due to the relaxation of tensile strain, which enhances the ferromagnetotransport properties. Additionally, there is an oxide layer found at the interface between the film and substrate from the transmission electron microscopy observation. It is also exhibited by conductive atomic force microscopy measurement that the metallic and insulative regions are coexisted in all of the films.

Preferred-Orientation Effects on the Ferromagnetic Properties of La1 − x Sr x MnO3 Films Deposited on Si Substrates

La 1-x Sr x MnO 3 (LSMO) films of x ∼0.1 with and without (100)-preferred orientation were fabricated on SiO 2 /Si substrates. A slight oxygen deficiency and high tensile stress were found in LSMO films. All the films exhibit a ferromagnetic transition at temperature (T c ) around 250 K and a metal-insulator transition at temperature (T M-1 ) much lower. However, a significant increase of saturated magnetization and a decrease of resistivity along with a significant raise of T M-1 are observed in the film without (100)-preferred orientation. The change of ferromagnetic property is attributed to the alleviation of Jahn-Teller distortion induced by the thermal stress in films having different preferred orientations.

Thickness dependent transport properties and percolative phase separation in polycrystalline manganite thin films

The effects of film thicknesses on the electronic transport and percolative metal-insulator (M-I) transition of La1−xSrxMnO3 (LSMO) films have been investigated. The conductivity increases with the layer thickness; this is regarded as the relaxation of tensile strains and reduction in grain boundaries (fewer scattering centers) as well as shorter hopping distances, which suppresses the Jahn–Teller distortion or enhances the double exchange. It is also observed by conductive atomic force microscopy (CAFM) that metallic and insulating regions coexist in LSMO films. The domains undergo a percolative M-I transition, and TM-I observed by CAFM is consistent with the result of four-point probe measurements.