Sumetha Suwanboon

Photocatalytic degradation of dye by Ag/ZnO prepared by reduction of Tollen’s reagent and the ecotoxicity of degraded products

A heterostructure of Ag/ZnO powder was prepared by a reduction of Ag(NH3)2+ ions in a basic solution or Tollen’s reagent. From this method, the existence of a metallic Ag coating on the ZnO surface was confirmed by transmission electron microscope and x-ray photoelectron spectroscopy. The photocatalytic activity of the Ag/ZnO powders was investigated by analyzing the degradation of an aqueous methylene blue solution under a blacklight irradiation. Furthermore, the parameters, including Ag content, catalyst loading, initial dye concentration and pH, were also studied. After the methylene blue solution was irradiated for 30min under a blacklight illumination, total mineralization was not observed as the presence of some carbon compound species was indicated in a mass spectrum. Furthermore, the toxicity of the treated methylene blue solution produced by the Ag/ZnO powders was also investigated by a test for the inhibition of the growth of Chlorella vulgaris.

Photocatalytic degradation of dyes by AgBr/Ag3PO4 and the ecotoxicities of their degraded products

Ag3PO4 powders were prepared through a precipitation reaction between AgNO3 and precipitating agent solutions that were prepared by adjusting the amount of H3PO4 in the Na3PO4 solutions. The Ag3PO4 powders prepared from the precipitation solution with a pH of 6 showed the highest photocatalytic activity for decolorizing the methylene blue and rhodamine B dyes. These Ag3PO4 powders were further modified by the addition of KBr solutions to obtain AgBr/Ag3PO4 powders and these photocatalysts can decolorize the anionic dyes as reactive orange and methyl orange. The reactive species involved in the photocatalytic degradation process were evaluated for their inhibitory activity using the appropriate scavengers. After photocatalysis, mass spectrometry confirmed that the dyes were degraded to smaller molecules. The ecotoxicities of the dye solutions before and after treatment were evaluated by studying their ability to inhibit the growth of the bioindicator Chlorella vulgaris.

Photocatalytic degradation of methylene blue by C3N4/ZnO: the effect of the melamine/ZnO ratios

The C3N4/ZnO composite photocatalysts were synthesized by mechanical milling combined with a calcination process. Various ratios of melamine and ZnO powders were milled by a planetary ball mill for 10 h. After heating at 540∘C for 3 h in air, melamine was converted to C3N4 but the formation of C3N4 depended on the ratios of the melamine and ZnO (M/Z) powders. From the experimental results, the conversion of melamine to C3N4 could be inhibited by ZnO particles; as there was no detectable C3N4 in the sample at low M/Z values or high ZnO contents. The photocatalytic activities of prepared samples were investigated under the illumination of blacklight and fluorescent lamps as the low wattage light source. The C3N4/ZnO showed a better photocatalytic activity than ZnO to degrade a methylene blue (MB) dye solution using blacklight lamps, but there is no significant difference in photocatalytic activities between ZnO and prepared C3N4/ZnO under visible light by the fluorescent lamps. However, the prepared C3N4/ZnO can well function under illumination by Xe lamp as the high power light source. Ecotoxicities of MB solutions before and after photocatalytic process were also studied through growth inhibition of the alga Chlorella vulgaris.

Antibacterial and physical properties of ZnO with pH-sensitive morphology

ABSTRACT The variation in morphology of zinc oxide (ZnO) with the pH of 0.05 M Zn(NO3)2 and 1.00 M NaOH aqueous solutions is demonstrated. Microstructured ZnO ranges from cuboid to spindle as the pH is reduced from 12 to 9. The ratio of visible-to-UV peak from photoluminescence spectra is also decreased, whereas the energy gap calculated from UV-Vis spectra remains comparable. Furthermore, nanospheroids and microellipsoid are, respectively, obtained when the molar concentration of NaOH is reduced to 0.20 and 0.10 M for the synthesis with the pH of 7. Due to their large surface-to-volume ratio, these ZnO nanospheroids exhibit a higher antibacterial activity than that of commercial ZnO in the disc diffusion method. According to this method as well as the minimal inhibitory concentration measurement, the effectiveness is substantial in the case of Staphylococcus aureus and Escherichia coli. By contrast, the inhibitions of Klebsiella pneumoniae, Salmonella typhimurium and Pseudomonas aeruginasa are barely observed.

Synthesis of superhydrophobic core–shell mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNPs) have been used in variety of applications due to their morphology and porous structure. This work reports the one-pot synthesis of ultrahydrophobic MSNPs using N-cetyl-n,n,n trimethyl ammonium bromide as a cationic surfactant template and ethanol (EtOH) as a cosolvent to form mesopores in the MSNPs. The effects of EtOH on the size and the pore structure of the MSNPs were studied by scanning electron microscopy and transmission electron microscopy. The results show that an addition of EtOH led to an enlargement of the MSNPs and a change in pore structure from a lamellar structure to a radially oriented structure. Co-condensation with two different types of fluoroalkyl silanes; trimethyl(fluoromethyl)silane, and trichloro(1H,1H,2H,2H-perfluorooctyl)silane provided low surface energy MSNPs with a core–shell structure. An assembly on the surface of these F-MSNPs generated nanostructure surface roughness rendering an improvement in surface wettability with water contact angle of 158.6°, which is a characteristic of oleophobic and ultrahydrophobic material.

Influence of Ni Doping on Structural, Morphological and Optical Properties of Sol-Gel ZnO Thin Films

Ni-doped ZnO thin films were prepared on glass slide substrates by a sol-gel dip coating method with different Ni doping concentrations (0-33 mol%). The effect of Ni doping concentration on structural, surface morphology and optical properties of the thin films was characterized by XRD, FESEM and UV-Vis spectrophotometer. The XRD results indicated that pure ZnO thin film exhibited a hexagonal wurtzite structure. Ni (OH)2 phase were observed at a high Ni doping concentration. The FESEM images showed that the surface morphology and surface roughness were sensitive to the Ni doping concentration. The optical transmission measurements were observed that the transmittance decreased with increasing the Ni doping concentration.

Synthesis, Characterization and Optical Properties of La-Doped ZnO Nanoparticles Prepared by Precipitation Method

ZnO and La-doped ZnO nanoparticles were synthesized by precipitation method by using Zn (CH3COO)22H2O, (CH2)6N4, (PEO)128-(PPO)54-(PEO)128 and LaCl3H2O as zinc source, precipitating agent, capping agent and dopant, respectively. The calcined samples exhibited a hexagonal wurtzite structure. The smallest particle size of pure ZnO nanoparticles of about 88 nm was obtained when 0.7 mmol (PEO)128-(PPO)54-(PEO)128 was used. The particle size of La-doped ZnO nanoparticles increased when La concentrations increased. The La-doped ZnO nanoparticles showed the energy band gap between 3.159-3.222 eV.

Effect of Annealing Temperature on NiO/ZnO Heterojunction Thin Films Prepared by Sol-Gel Method

In this research, NiO/ZnO heterojunction thin films were fabricated on a ITO substrate by a sol–gel technique. The as-prepared thin films were annealed at various temperatures. The effect of annealing temperature on structural, surface morphology and electrical properties of thin films was investigated by XRD, FESEM and I-V characteristic measurement. The XRD results revealed that NiO/ZnO thin film was polycrystalline and exhibited better crystallization when annealing temperature was increased. The current-voltage curve of all sample exhibited the diode behaviour.

Morphological, Photocatalytic and Bactericidal Properties of ZnO Powders Prepared by a Precipitation Method

Structural, optical and photocatalytic properties of ZnO powders prepared by a precipitation method were systematically investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), UV-Vis diffuse reflectance measurement and UV-Vis absorbance measurement. The antibacterial activity was tested by a broth microdilution method. All calcined ZnO powders exhibited a hexagonal wurtzite structure. The ZnO powders formed various shapes depending upon the concentration of n-propylamine used. The Eg value of ZnO powders depended upon defect concentration. The photocatalytic property of ZnO powders depended on the particle shape and defect concentration. The best photocatalytic efficiency of 100% was observed from the ZnO powders prepared at R = 2 after irradiating by the blacklight for 90 min. All ZnO powders can damage only S. aureus and the agglomerated sheet-like ZnO powders prepared at R = 2 showed the best antibacterial property with a MIC value of 1.5625 mg/mL.

Dye Degradation Using Ag/ZnO Illuminated by Fluorescent Lamps

Heterostructure of Ag/ZnO was synthesized by a reduction of Tollen’s reagent on ZnO powders. The photocatalytic activity of Ag/ZnO was investigated through the degradation of three different dye solutions (methylene blue, rhodamine B and reactive orange 16) under visible light using the fluorescent lamps with a 420 nm longpass filter. The efficiencies of dye degradations for all three dyes by Ag/ZnO are better than that of pure ZnO. Furthermore, the parameters including photocatalyst loadings and initial pHs of dye solutions were also studied. The photocatalytic degradations for all three dyes were increased with the increasing of catalyst loadings. The effect of pHs on photocatalytic activity of Ag/ZnO can be explained by the interaction between the charge on the surface of photocatalyst and the charge of dye ions.