Ruangsri Watanesk

Cost Effective Natural Adsorbent for Fluoride Removal

In this study, the uptake of fluoride by raw diatomite and diatomite activated by heat treatment was investigated. Influential parameters such as contact time, pH and adsorption isotherm were also studied. The results showed that the diatomite heated to 500 oC performed better than other heat treatment products and the equilibration time needed for fluoride removal by the adsorbents was reached at 60 min. Results revealed that the capacity of the adsorbents for removing fluoride is independent of the pH when the pH is higher than 4. The adsorption isotherm of the 500 oC treated diatomite showed its Langmuir behavior. The maximum adsorption capacity of raw diatomite and 500 oC calcinated diatomite are 2.253 and 4.162 mg/g, respectively. Based on the results it can be concluded that the diatomite appears to be an economical and environmentally friendly material for defluoridation of water.

Role of Chitosan on Some Physical Properties and the Urea Controlled Release of the Silk Fibroin/Gelatin Hydrogel

Natural polymers are widely used as biodegradable matrices for the controlled release technology because they can improve the performance of the materials and make them environmentally friendly. In this work, the silk fibroin (SF)/gelatin hydrogel with chitosan (CS) was prepared by solvent casting aiming to reduce the rate of urea release from the hydrogels. Results from the Fourier transform infrared confirmed that no intermolecular interactions had taken place after the addition of CS into the SF/gelatin. Furthermore, the increase of CS content in the SF/gelatin blended hydrogels caused the decrease in their porosity that affected the increase in their crystallinity, degree of swelling, water solubility, and surface hydrophobicity. The rate of urea release from the hydrogels also depended on the content of CS of which its value of diffusion exponent characteristics (n) determined from the Korsmeyer-Peppas model for SF/gelatin/CS hydrogels were greater than 1.0. This indicated that the urea release from the SF/gelatin hydrogels with CS was a super case II transport type. Moreover, the urea release rate (k) of the SF/gelatin/CS hydrogels was lower than that of the SF/gelatin hydrogel itself indicating an extension of the urea release from the SF/gelatin hydrogels by CS which could be utilized for controlled release applications.

Effect of Gelatin on Secondary Structure, Crystallinity and Swelling Behavior of Silk Fibroin - Gelatin Hydrogels and its Application in Controlled Release of Nitrogen

Utilization of natural polymer as biodegradable matrix for the controlled releasing fertilizer can improve the performance of the materials and make them environmentally friendly. In this work, the effect of gelatin on the properties of hydrogels was investigated. The silk fibroin (SF)-gelatin hydrogels were prepared by solvent casting and β-crystallization of SF was promoted via methanol treatment. The secondary structure and the crystallinity of the blended hydrogels were investigated using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction analysis (XRD), respectively. Moreover, the swelling ratio of the hydrogels and also their kinetics of nitrogen (N) release were also studied. Results from the FT-IR confirmed that no intermolecular interactions had taken place between SF and gelatin. Furthermore, the increase of gelatin content in the blended hydrogels caused the decrease of the SF crystallinity detected by XRD which corresponded to the swelling behavior of the hydrogel. The release rate of nitrogen (N) depends on the composition of SF and gelatin of which its value of diffusion exponent characteristics (n) determined from the Korsmeyer-Peppas model for all of the hydrogels are smaller than 0.5. This indicates that the release of N from the hydrogels is a quasi-Fickian diffusion. Moreover, the release rate (k) and diffusion coefficient (D) of the SF-gelatin hydrogels are lower than those of the SF itself indicating a potential to use the SF-gelatin hydrogel for nitrogen controlled release application.

Fabrication of Ascorbic Acid Biosensor Based on Coupling Polyethylene Glycol Modified Silk Fibroin Membrane onto Glassy Carbon Electrode

Nowadays biosensors have been extensively used in a wide variety of applications especially in clinical works and food industry. In this work, a specific ascorbic acid (AA) biosensor was developed by immobilizing ascorbate oxidase (ASOD) on a polyethylene glycol (PEG) modified silk fibroin (SF) membrane then coupling to the glassy carbon electrode (GCE). The SF-PEG-ASOD membrane provided the highest enzyme activity in phosphate buffer at pH 5. As being the electrode, the SF-PEG-ASOD modified GCE displayed the highest response when it is operated under the condition of 0.40 mg/L of ASOD in phosphate buffer at pH 5. This biosensor provided both good linearity (r2 = 0.999 in the range of 1.0-10.0 mM) and sensitivity with short response time (26s). It also exhibited good anti-interference ability with the storage time of 5 days without changing its initial response.

Crosslinking Density of Silk Fibroin – Rice Starch Hydrogels Modified with Trisodium Trimetaphosphate

Silk fibroin (SF) and rice starch (RS) are both biopolymers being non-toxic, biocompatible and biodegradable which can be utilized as hydrogels. The aim of this study was to prepare the SF–RS hydrogels modified with trisodium trimetaphosphate (STMP) and determine its crosslinking density for providing a guideline for preparing better quality absorbable hydrogels. The SF–RS hydrogels modified with various percentages of STMP were prepared by solution casting at pH 12 then neutralized to pH 7. The functional groups and molecular linkages of the hydrogels were investigated by Fourier transform infrared spectrometry (FTIR) and proton nuclear magnetic resonance (1H NMR) spectrometry, respectively. Finally, the crosslinking density of the hydrogels was determined by UV/Vis spectrophotometry via the measurement of the relative amount of methylene blue (RMB) bound to the hydrogels. Results from the FTIR and 1H NMR spectra revealed that linkages within the hydrogels occurred mainly between the O–H groups of RS and the triphosphate groups of STMP. From the MB adsorption study, the crosslinking density of the SF–RS hydrogel with 1.0 %w/w STMP at the 60 min saturation time was approximately 63 %.

Hydrophobicity Enhancement of the Polyvinyl Alcohol/Rice Starch/Silk Fibroin Films by Glycerol

Eco-friendly films have been prepared using various biopolymers and their properties have been improved in order to meet the requirements for appropriate applications. However, the frequently encountered weakness of the properties of most biopolymer film is its water solubility. In this study, the polyvinyl alcohol/rice starch/silk fibroin (PVA/RS/SF) films were modified by the addition of glycerol aiming to increase the hydrophobicity of the films. Some properties of the modified films including water contact angle, degree of swelling and water solubility were compared with the unmodified PVA/RS/SF film. Results from the contact angle measurement showed that the films with glycerol could be transformed to be hydrophobic after soaking in ethanol medium. The increase in soaking time tends to increase the hydrophobicity of the films. However, at about 60 min soaking, the water contact angles on the films were quite constant with the values of about 107.9±5.2º comparing with 65.3±2.4º of the ethanol-untreated PVA/RS/SF films. In addition, the ethanol-treated glycerol-modified films also show higher degree of swelling with constant solubility and better mechanical properties.

Comparison of Porosity Improvement of Silk Fibroin Membrane Using Polyethylene Glycol and Glutaraldehyde for Increasing Oxygen Permeability

Biomaterial is one of the good candidates for porous membrane preparation according to its environmental friendliness. In this work, the porous membranes of silk fibroin (SF) were prepared by solution casting with the addition of polyethylene glycol (PEG) and glutaraldehyde (GTA) aiming to improve the porosity and oxygen permeability of SF membrane. The conformation of SF was changed from random coil to β sheet form after treatment with MeOH. The interaction existing between SF chains and both PEG and GTA were characterized using Fourier Transform Infrared spectroscopy (FT-IR). The addition of PEG could produce more porosity in the membrane than GTA confirmed by their morphology observed from scanning electron microscopy (SEM). Moreover, the swelling behavior of the SF-PEG and SF-GTA membranes depended on the porous structure of the membrane which directly correlated to their oxygen permeability. The porosity of the SF membranes increased with the increase of PEG and GTA contents up to 40% and 3%w/w, respectively. After that, their porosity decreased as seen through the SEM and water swelling results. In addition, the SF-PEG membrane turned out to have higher degrees of both porosity and oxygen permeability than the SF-GTA membrane which related to its water swelling behavior.

Application of the PEGDE Modified Silk Fibroin Membrane to an Amperometric Glucose Biosensor

Stable silk fibroin (SF) membranes were prepared by modifying SF with polyethylene glycol diglycidyl ether (PEGDE) for use as enzyme immobilizing matrix. Morphology, structure, and water solubility of the modified silk fibroin (MSF) membrane were investigated. SEM images revealed greater porosity in the MSF membranes. IR spectra confirmed the predominant β-sheet conformation when the PEGDE was greater than 4%. In addition, the MSF membranes were highly insoluble within the pH range 4 10. An amperometric glucose biosensor was initially constructed using glucose oxidase (GOx) immobilized on the MSF membrane, coupled to a Prussian Blue (PB) deposited Au electrode. The response characteristics of the biosensors based on the GOx immobilized onto the 4% and 8% PEGDE modified SF membranes (4P-MSF and 8P-MSF) and the methanol treated SF membrane (MT-SF) were investigated. Amperometric measurements at the applied potential of 0.0 V demonstrated that the glucose biosensor based on the GOx immobilized onto the 4P-MSF membrane exhibited high sensitivity to glucose with a short response time, less than 3 s. Moreover, the stability of the biosensors based on the 4P-MSF membranes was better than those based on the MT-SF membrane after 2 weeks of storage in a phosphate buffer of pH 7.0 at 4 °C. These fundamental electroanalytical features of the sensor are therefore expected to be useful in biosensor application