Chat Pholnak

Effects of precursor concentration and reaction time on sonochemically synthesized ZnO nanoparticles

The sonochemical reaction between Zn(NO 3 ) 2 and hexamethylenetetramine (HMT) resulted in different products depending on amounts of Zn(II) cations in the aqueous solution. Crystalline phase pure ZnO nanoparticles were obtained by using 0.05 M Zn(NO 3 ) 2 -HMT. This single phase was formed by low power sonication for 20 min in an ultrasonic bath at ambient conditions and its morphology did not change for the next 60 min. Higher concentrations of precursors (0.1 and 0.5 M) led to a mixture of zinc compounds including plate-like Zn 5 (OH) 8 (NO 3 ) 2 (H 2 O). In contrast, a mixed phase ZnO/Zn 5 (OH) 6 (CO 3 ) 2 and a single phase Zn 5 (OH) 6 (CO 3 ) 2 were formed when the precursor concentrations were decreased to 0.01 and 0.005 M, respectively. The resulting infrared absorption and ultraviolet/visible emission were dependent on the phases and defects in these zinc compounds.

Sonochemical Synthesis of Zinc Oxide Nanoparticles Using an Ultrasonic Homogenizer

Zinc oxide nanoparticles were synthesized using a commercial ultrasonic homogenizer in a sonochemical reaction between 0.05 M zinc nitrate and hexamethylenetetramine. The solutions in glass vessels of varying shapes i.e. cube, cylinder and sphere were sonicated with a 45 W 20 kHz ultrasonic pulse for 60 min under ambient conditions. The crystalline ZnO phase was confirmed by powder X-ray diffraction and scanning electron microscopy with average particle diameters around 70 nm from the three different vessels. These ZnO particles were smaller than those previously synthesized in ultrasonic baths and sonoreactors.

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.