Advanced Materials Research Vol. 506

Abstract: The recovery of gold from chloride solutions using bioadsorbent synthesized from waste rambutan peel was studied. The initial gold concentration 25-900 mg/L, solution pH 1-4, temperature 25-60 °C and the amount of adsorbent 1-25 mg were found to affect the efficiency for gold recovery as well as loading capacity. The 99.8 % gold recovery was accomplished in 1 h with loading capacity of 100 mg Au/g adsorbent at the following conditions: adsorbent 25 mg, initial gold concentration 100 mg/L, pH 2 and temperature 60 °C. The decrease of adsorbent from 25 to 1 mg resulted in the highest loading capacity of 2530 mg Au/g adsorbent and 100 % gold recovery within 100 h. The adsorption isotherm as well as mechanism were also elucidated. The Langmuir isotherm and the pseudo second-order kinetic model were fitted well with the experimental results. The activation energy of reaction was calculated to be 31.07 kJ/mol. The mechanism of adsorption is clarified to be the oxidation of hydroxyl groups and reduction of trivalent gold ions to metallic gold on the adsorbent surface which were supported by FT-IR, XRF and SEM.

Abstract: In this research, the films which were prepared from inclusion complexes (ICs) of acetyl-beta-cyclodextrin (Acetyl-β-CD) with chitosan were characterized and the membrane properties were investigated. Acetyl-β-CD either improved the solubility of chitosan or increased the salt rejection of the membrane. The crystalline ICs, were formed and found on the membrane surface. There were isolated and characterized by scanning electron microscopy (SEM), X-ray diffraction and atomic force microscopy (AFM). The stability and conformation of the inclusion complexes in solvent and limited number of acetyl-β-CD threaded on chitosan molecules were studied and compared the results on a molecular level of the pseudopolyrotaxane.

Abstract: The removal of arsenic from synthetic arsenic contaminated water sample by precipitating arsenic (in the form of arsenate oxyanion) with calcium phosphate hydroxyapatite, HAp, was studied under conditions that induce arsenate incorporated calcium phosphate hydroxyapatite, Ca (P/As)HAp, to form. Arsenate is able to substitute for a fraction of the phosphate in HAp host material as it forms. Consequently, arsenic is successfully removed from the contaminated water achieving up to 99% arsenic removal from 25 ppm initial arsenic concentration. The Ca:(P+As) and P:As mole ratios were found to play an important role in arsenic removal efficiency. Higher Ca:(P+As) and P:As mole ratios give higher arsenic removal efficiency. Surprisingly, the pH of the initial anion solution, a key parameter in arsenic speciation, was found to not have a significant effect on arsenic removal by this process. The advantage of this process is that the precipitation can occur rapidly at relatively low levels of arsenic contamination, implying an easy and inexpensive process for arsenic removal can be developed based on this approach.

Abstract: Carboxymethyl chitosan (CMCH) from different sources (shrimp, crab and squid) and molecular sizes (polymer and oligomer) was synthesized via carboxymethylation with monochloroacetic acid (MCA) in isopropyl alcohol (IPA) under alkaline condition. Next, chitosan and CMCH films were prepared and their properties were studied. Crystallinity, mechanical properties [tensile strength (TS) and percent elongation at break (EB)], water vapor transmission rate (WVTR), and color change were investigated. The crystallinity and TS value of each CMCH film was less than that of chitosan. The highest TS (28.6 MPa) was provided by chitosan film from crab oligomer (CO). The CMCH films from various types displayed the higher EB value comparing with those of chitosan films. The CMCH film from shrimp polymer (SP) exhibited the highest EB value (44%). The WVTR of each CMCH films were interestingly lower than that of chitosan, and the lowest value was obtained by the CMCH film from crab oligomer (CO) (15 g/m²day¹). The CMCH films showed higher color L* and a* value but lower b* value comparing with those of chitosan films from the same type.

Abstract: The aim of research was to elucidate effect of annealing temperature and shellac (SHL) content on properties of shellac-based matrix tablets. Theophylline was selected as a model drug. The tablets were prepared by direct compression process and then annealed at various temperatures for 24 hours. The tablet properties, including hardness and disintegration time were comparatively. The result demonstrated that annealing temperature directly affected the hardness and disintegration time of tablets. At 60oC or more, the hardness was increased more than 1.5 times as compared to that of un-annealed tablet. The disintegration time was also increased and well correlated with the increased hardness. In addition, the more pronounced effect was observed as increasing SHL content. The more amount of SHL should provide more condensed network that improved cohesiveness and delayed disintegration time of tablets. The results from this research could provide the basic knowledge for development of drug containing shellac-based matrix tablet.

Abstract: Natural diatomite was modified by manganese chloride via the low temperature hydrothermal route. The chemical properties and adsorption efficiency of the natural and the modified diatomite were characterized. The chemical compositions of the natural and the modified diatomite were determined by X-ray fluorescence spectroscopy (XRF) and energy dispersive X-ray spectrometry (EDXS). Morphology of the natural and the modified diatomite was investigated by scanning electron microscopy (SEM). The adsorptions of Cd (II) and Pb (II) ions onto the natural and the modified diatomite were determined by atomic absorption spectroscopy (AAS).

Abstract: The objective of this study was to investigate the effect of coconut oil and different surfactants on stability of nanoemulsions that were prepared by simple homogenization (13,500 rpm, 10 minutes). Coconut oil, sunflower oil and castor oil at the concentration of 20-40% w/w were used as the oil phase. Polysorbate 20, polysorbate 80 and Cremophore RH40 were used as surfactant whereas sorbitan monooleate and polyethylene glycol 400 were used as co-surfactants. The formulations containing coconut oil in the range of 20-40% w/w and the ratio of polysorbate 80 to sorbitan monooleate of 2:1 and 3:1 provided nanosized emulsions (100-500 nm). The zeta potential values ranged from-41.51 to-16.97 mV. The prepared nanoemulsions were stable for at least 7 days at 8 °C. The temperature cycling test (storage at 4 °C for 24 hours and at 45 °C for 24 hours) was performed. It was found that the formulation containing 30% w/w of coconut oil, 22.5% w/w of polysorbate 80 and 7.5% w/w of sorbitan monooleate was stable for 1 cycle. The results indicated that a decrease in the concentration of surfactant and an increase in the concentration of oil affected the stability of nanoemulsions.

Abstract: Cyclodextrin complexation and pH adjustments have been reported as useful tools to increase the solubility of drug. The aim of this study was to investigate the influence of both cyclodextrin and pH on the overall solubility of ketoprofen. β-cyclodextrin (β-CD) and hydroxypropyl β-cyclodextrin (HP-β-CD) were used for the preparation of inclusion complex by shaking method in aqueous solution at pH 2, 5, 7 and 10. It was found that the solubility of ketoprofen significantly increased with increasing pH and cyclodextrin concentration, showing A_L type phase solubility diagram. However, the apparent stability constant of complex (K_C) was found to decrease with increasing pH due to the decreased affinity of ionized drug to cyclodextrin cavity. The ionization of ketoprofen increased when the pH was raised, corresponding with its higher zeta potential. The result indicated that the solubility of ketoprofen could be improved by using a combined approach of pH adjustments and complexation with cyclodextrin. Moreover, the unionized drug that was formed by pH adjustments interacted with cyclodextrin more strongly than the ionized drug.

Abstract: In this study, polystyrene nanofiber ion exchangers (PSNIE) were successfully prepared by a new method comprising of electrospinning and the subsequent crosslinking with formaldehyde and sulfonation in sulfuric acid to create the cation exchange functionality on the fibers surfaces. The PS solution at 15% w/v in dimethylacetamide (DMAc) produced the smallest PS nanofibers (399±38 nm) with good performance. The degree of crosslink and ion exchange capacity (IEC) of PSNIE depended upon the crosslinking time. The longer crosslinking time caused the greater crosslinked PS fibers. At the longest crosslinking time of 75 min, the remaining crosslinked PS fibers in dichloromethane were 94.12%; whereas, the starting fibers completely dissolved. This crosslinking agent (e.g. formaldehyde) might introduce methylene bridges in addition to sulfone bridges into the fibers. However, IEC decreased as crosslinking time increased, probably due to the difficulty of sulfonic functional groups to react with crosslinked PS fibers. The PSNIE crosslinked for 10 min showed the maximum IEC of 2.86 meq/g-dry-PSNIE, and the diameter of the PSNIE after sulfonation increased to 450-460 nm. Since cationic drug could be loaded onto this novel PSNIE, this nanofiber ion exchanger may be applied for controlled release delivery.

Abstract: The aim of this study was to prepare microemulsion for transdermal drug delivery of ketoprofen (KP). The physicochemical and chemical properties of microemulsion were evaluated. The microemulsion were composed of isopropyl myristate (IPM) as oil phase, water, PEG40-hydrogenated castor oil (Cremophor^® RH40) as surfactant and PEG400 as co-surfactant, and the surfactant: co-surfactant ratio used was 1:1. The viscosity, droplet size, pH, conductivity of microemulsion and skin permeation of KP through shed snake skin were evaluated. The particle size, viscosity and conductivity of microemulsions were in the range of 172-468 nm, 234.82-1067.35 cP and 6.80-20.87µS/cm, respectively. The ratio of IPM and surfactant mixture played an important role on KP loading capacity of microemulsions formulation and skin permeation of KP. While amount of surfactant increased, the loading capacity of KP increased, but the skin permeation of KP decreased. The results suggested that the novel microemulsion system composed of IPM, water, Cremophor^® RH40:PEG400 (ratio 1:1) can be applied for using as a transdermal drug delivery carrier.