Soon-Il Yun

Formation of ZnO Micro-Flowers Prepared via Solution Process and their Antibacterial Activity.

This paper presents the fabrication and characterization of zinc oxide micro-flowers and their antibacterial activity. The micro-flowers of zinc oxide composed of hexagonal nanorods have been prepared via solution process using precursor zinc acetate di-hydrate and sodium hydroxide in 3 h of refluxing time at ~90°C. The antibacterial activities of grown micro-flowers were investigated against four pathogenic bacteria namely S. aureus, E. coli, S. typhimurium and K. pneumoniae by taking five different concentrations (5–45 μg/ml) of ZnO micro-flowers (ZnO-MFs). Our investigation reveals that at lowest concentration of ZnO-MFs solution inhibiting the growth of microbial strain which was found to be 5 μg/ml for all the tested pathogens. Additionally, on the basis of morphological and chemical observations, a chemical reaction mechanism of ZnO-MFs composed of hexagonal nanorods was also proposed.

Sequestration of Reactive Blue 4 by free and immobilized Bacillus subtilis cells and its extracellular polysaccharides

Bacillus subtilis a gram positive bacteria and its extracellular polysaccharide were used in free form as well as immobilized form as biosorbent for sequestration of an anionic dye, Reactive Blue 4 (RB) in aqueous phase. The dye uptake enhanced with decrease in pH. Extracellular polymeric substances (EPS) and free cells were found to be better adsorbents when compared to alginate immobilized cells (IC) and EPS (IEPS). The presence of functional groups in free cells and EPS was confirmed by FT-IR analysis. Immobilization resulted in poor adsorption performance due to increase in mass transfer resistance by the polymeric matrix. High Q(max) and b values were noted in the case of free cells and free EPS in contrast to IC and IEPS. From the kinetic experiments, the adsorption system was found to be a pseudo-first-order reaction at low dye concentration. Desorption of RB was found to be 100% in 1N NaOH. However, the alginate beads were found to be unstable under high alkaline conditions of NaOH.

Solar-photocatalytic disinfection of Vibrio cholerae by using Ag@ZnO core-shell structure nanocomposites.

Disinfection of Gram-negative bacterium Vibrio cholerae 569B in aqueous matrix by solar-photocatalysis mediated by Ag@ZnO core-shell structure nanocomposite particles was investigated. Silver nanoparticles are synthesized by the reduction of silver perchlorate followed by precipitation of zinc oxide shell and are employed in the photocatalytic disinfection of the model pathogen. Effect of photocatalyst loading and reaction temperature on the disinfection kinetics was studied. Disinfection efficiency in laboratory as well as real water samples was compared with that of pure-ZnO and TiO2 (Degussa P25). Nanocomposite system has shown optimum disinfection (≈98%) at 40-60min of sun-light exposure with a catalyst loading of 0.5mg/L of the reaction solution. The reduction of aquatic bacterial densities by photocatalytically active Ag@ZnO core-shell nanocomposite in presence of natural sun-light may have potential ex situ application in water decontamination at ambient conditions.

In Vivo toxicological assessment of biologically synthesized silver nanoparticles in adult Zebrafish (Danio rerio)

The present study examines the deleterious effect of biologically synthesized silver nanoparticles in adult zebrafish. Silver nanoparticles (AgNPs) used in the study were synthesized by treating AgNO3 with aqueous leaves extract of Malva crispa Linn., a medicinal herb as source of reductants. LC50 concentration of AgNPs at 96 h was observed as 142.2 μg/l. In order to explore the underlying toxicity mechanisms of AgNPs, half of the LC50 concentration (71.1 μg/l) was exposed to adult zebrafish for 14 days. Cytological changes and intrahepatic localization of AgNPs were observed in gills and liver tissues respectively, and the results concluded a possible sign for oxidative stress. In addition to oxidative stress the genotoxic effect was observed in peripheral blood cells like presence of micronuclei, nuclear abnormalities and also loss in cell contact with irregular shape was observed in liver parenchyma cells. Hence to confirm the oxidative stress and genotoxic effects the mRNA expression of stress related (MTF-1, HSP70) and immune response related (TLR4, NFKB, IL1B, CEBP, TRF, TLR22) genes were analyzed in liver tissues and the results clearly concluded that the plant extract mediated synthesis of AgNPs leads to oxidative stress and immunotoxicity in adult zebrafish.

Porogen effect on characteristics of banana pith carbon and the sorption of dichlorophenols

Banana pith was used as precursor material to prepare carbon with and without porogens. Characterization of the carbons showed higher BET surface area (1285 m2/g) for ZnCl2-treated carbon, comparatively. Adsorption experiments were conducted to study the removal of 2,4-dichlorophenol (DCP) from aqueous solutions using the carbons under varying experimental conditions. Decrease in pH increased the percentage removal. All the carbons studied showed greater percentage of DCP removal with decrease in the initial concentration of DCP. Kinetic studies showed that the adsorption of DCP on the carbons was a rapid process. Nonlinear forms of pseudo-first-order and pseudo-second-order models were used to fit the experimental data. Among these the pseudo-first-order model described the data with high correlation coefficients and low percentage error values. Four nonlinear isotherm models including the Langmuir, Freundlich, Toth, and Sips were used to analyze the experimental DCP isotherms under different pH (2-4) conditions. Adsorption capacities (Qmax) from the Langmuir model were found to be 129.4, 67.7, and 49.9 mg/g for ZnCl2-treated, KOH-treated, and porogen-free carbon, respectively, at pH 2. From desorption studies it seemed that chemisorption played a major role in the adsorption process. The results indicated that ZnCl2-treated carbon could effectively remove phenols from wastewater.

Role of bicontinuous microemulsion in the rapid enzymatic hydrolysis of (R,S)-ketoprofen ethyl ester in a micro-reactor.

Bicontinuous microemulsion was employed as the medium for enzymatic hydrolysis of (R,S)-ketoprofen ethyl ester in the presence of esterase for the first time. In addition, a methodology for the separation of optically pure ketoprofen from the microemulsion system for analysis by gas chromatography was developed. Various factors influencing the enzymatic hydrolysis of (R,S)-ketoprofen ethyl ester such as temperature, enzyme concentration and reaction time were optimized experimentally. The enzymatic hydrolysis in a bicontinuous microemulsion system showed a final conversion of 84.6% after 50 h of reaction, while hydrolysis in Tris-HCl buffer solution resulted in only 26.9% conversion after 150 h without completing the reaction. A comparison of the rate of the enzymatic hydrolysis reaction with rates of reaction in other biphasic media revealed that the bicontinuous microemulsion system was faster and more advantageous. The extremely large interfacial area of the latter fluid likely facilitated the contact between the catalyst and the substrate. Because the enzyme applied was not selective, formation of (R)-ketoprofen was also observed. Therefore, application of an enzyme with higher selectivity would provide better results.

Organic micro-pollutant removal in liquid-phase using carbonized silk cotton hull.

Phenolic compounds constitute one of the major pollutants in the modern world. Although many physical and chemical treatment technologies for their removal exist, most of them are economically not feasible. The present study was aimed at using silk cotton hull, a potent agricultural waste as an adsobent for removal of 2,4-dichlorophenol (2,4-DCP), which was used as a model phenolic compound. The process parameters were investigated and optimized conditions were determined. The equilibrium time was found to be 60 and 80 min for 10 and 20 mg/L and 100 min for 30 and 40 mg/L 2,4-DCP concentrations, respectively. Among the kinetic models applied, pseudo-second order model fitted well. The maximum adsorption capacity was 16.0 mg/g by Langmuir isotherm. Acidic pH was found favorable for the adsorption of 2,4-DCP. Studies on pH effect and desorption seemed to show that chemisorption played a major role in the adsorption process. In thermodynamic study, the change in entropy (DeltaS0) and heat of adsorption (DeltaH0) of silk cotton hull carbon (SCHC) was estimated as 14.01 J/(mol x K) and 3.04 kJ/mol, respectively. SCHC as adsorbent for removal of 2,4-DCP from aqueous solution, is effective, inexpensive, indigenous, reusable, has low treatment time and is easily available in large quantities as waste there by significantly lowers the cost of wastewater treatment.

Anticancer activity of biologically synthesized silver and gold nanoparticles on mouse myoblast cancer cells and their toxicity against embryonic zebrafish

The aim of this study was to evaluate the anticancer activity of bioinspired silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) against mouse myoblast cancer cells (C2C12). Both AgNPs and AuNPs were biologically synthesized using Spinacia oleracea Linn., aqueous leaves extract. UV-Vis. spectrophotometer, high resolution-transmission electron microscopy (HR-TEM), field emission-scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) studies supported the successful synthesis of AgNPs and AuNPs. Both these NPs have shown cytotoxicity against C2C12 cells even at very low concentration (5μg/mL). Acridine orange/Ethidium bromide (AO/EB) dual staining confirmed the apoptotic morphological features. The levels of caspase enzymes (caspase-3 and caspase-7) were significantly up-regulated in NPs treated myoblast cells than the plant extract. Furthermore, in zebrafish embryo toxicity study, AgNPs showed 100% mortality at 3μg/mL concentration while AuNPs exhibited the same at much higher concentration (300mg/mL). Taken together, these results provide a preliminary guidance for the development of biomaterials based drugs to fight against the fatal diseases for example cancer.

Understanding the Antifungal Mechanism of Ag@ZnO Core-shell Nanocomposites against Candida krusei

In the present paper, facile synthesis of Ag@ZnO core-shell nanocomposites is reported where zinc oxide is coated on biogenic silver nanoparticles synthesized using Andrographis paniculata and Aloe vera leaf extract. Structural features of as synthesized nanocomposites are characterized by UV-visible spectroscopy, XRD, and FTIR. Morphology of the above core-shell nanocomposites is investigated by electron microscopy. As synthesized nanocomposite material has shown antimicrobial activity against Candida krusei, which is an opportunistic pathogen known to cause candidemia. The possible mode of activity of the above material has been studied by in-vitro molecular techniques. Our investigations have shown that surface coating of biogenic silver nanoparticles by zinc oxide has increased its antimicrobial efficiency against Candida krusei, while decreasing its toxicity towards A431 human epidermoid carcinoma cell lines.

Carbaryl Sorption by Porogen-treated Banana Pith Carbon

This paper reports the adsorption ability of banana pith activated carbon, with ZnCl2 as the porogen, towards carbaryl (1-naphthyl-N-methylcarbamate) from aqueous solution. The pH-edge experiments revealed that carbaryl adsorption onto ZnCl2-treated banana pith activated carbon (ZTC) was a pH-dependent process with maximum adsorption occurring at pH 11. The adsorption isotherm obtained at pH 11 revealed that ZTC possessed a maximum adsorption capacity of 45.9 mg/g. The adsorption isotherms were well described by the Langmuir and Freundlich models. The kinetic data obtained at different initial carbaryl concentrations were modelled using pseudo-first- and -second-order models. Acetone successfully desorbed carbaryl with a 99.8% elution efficiency.