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• Dependence of crystallite size and morphology of nanocrystalline ZnO on synthesis temperature. • Defect dominated photoluminescence spectra and its assignment. • Dependence of photocurrent response on crystallite size and its wavelength dependence. • Dependence of photocatalytic activity and reuse on crystallite size. Nanocrystalline zinc oxide (ZnO) samples are synthesized through a facile hydrothermal route at different temperatures. Sample synthesized at 80 °C (sample code HT80) has average crystallite size of 32 ± 2 nm and the morphology is not unform with the presence of rods, wires and discs. Sample prepared at 160 °C (sample code HT160) has rod-like morphology with an average crystallite size of 130 ± 5 nm. X-ray photoelectron spectra reveal the presence of hydroxyl groups bonded to Zn2+, oxygen vacancies and adsorbed oxygen species in both the samples. Atomic percentage of the bonded/adsorbed hydroxides and oxygen containing species is higher in HT80. Band gaps values are lower in comparison with bulk ZnO due to band bending. Photoluminescence spectra has a UV peak at ∼381 nm (3.25 eV) and a broad emission band in the visible region centred at ∼550 nm (2.25 eV) respectively corresponding to the band edge emission and defect mediated emission. The emission profile of both samples is similar indicating the presence of similar type of native point defects viz., Zn vacancies, Zn interstitials and oxygen vacancies in different charge states. Sample HT160 has more intense emission due to the better photonic absorption. The photocurrent response under wide light irradiation is also larger for HT160 with a sensitivity of 37 due to the better photonic absorption and larger crystallite size. Wavelength dependent photocurrent response for this sample shows highest sensitivity at 380 nm with a sensitivity of 152 corresponding to the band-to-band excitation. A weak photoresponse for visible light irradiation (∼600 nm) due to the desorption of adsorbed O 2 or hydroxide species caused by the direct photoexcitation of the captured electron to the conduction band is also noted. Photocatalytic efficiency of both the samples are comparable with rate constants 3.1 × 10−2 min−1 and 3.7 × 10−2 min−1 respectively for HT80 and HT160. The reusability is much better for sample HT160 which is attribute to larger average crystallite size and uniform morphology. [ABSTRACT FROM AUTHOR]

Different crystal planes of nanocrystalline often displayed diverse physical and chemical properties. In this paper, the effects of nano-ZnO with two kinds of crystal planes on crystallization, thermal stability and mechanical properties of PLLA were investigated. The results show that the (1010) planes with no-polar and low surface energy increased the chain mobility of PLLA chain, showed a plasticizing effect; the glass transition temperature, melt and cold crystallization temperature decreased by 12 °C, 10 °C and 12 °C, respectively. The size of spherulites increased and the number of spherulites decreased, the crystal form changed from mixed crystal form α, α′ to unique α crystal form. However, the (0002) planes with polar and high surface energy has highly nucleating effective for PLLA, the crystallization temperature increased to 106.41 °C, the cold crystallization peak disappear. The size of spherulites decreased and the number of spherulites increased. Moreover, the (0002) planes increases the elongation at break of PLLA to 20.34% but the (1010) planes reduces to 7.49%. Their thermo-gravimetric analysis results showed the similar trend. Our results indicate that the interface wettability and compatibility between crystal planes and PLLA, which was caused by the polarity and surface energy of (1010) or (0002) planes played key role in improving the performance of polymers.

Well-crystallized and hexagonal wurtzite ZnO was synthesized with nanocellulose using a facile hydrothermal method. Many highly active (001) facets were retained in the obtained ZnO nanocrystals, presumably due to interaction between the polar facet of ZnO and the nanocellulose. Given its effective surface area, the synthesized ZnO exhibited good photocatalytic activity of degrading methylene blue. Its degradation efficiency reached 94.4% within 30 min (UV irradiation power of 6 W), which was 34% higher than that of Degussa TiO2 P25. The ZnO photocatalyst also exhibited excellent reusability, confirmed by no obvious abatement after its being re-used for 8 cycles. These ZnO nanomaterials were synthesized using renewable nanocellulose derived from cotton. This environmentally friendly and cost-effective approach is anticipated to be applied in the future synthesis of small-sized ZnO photocatalysts.

We experimentally investigated the effect of post-growth annealing on the morphological, structural, and electrophysical parameters of nanocrystalline ZnO films fabricated by pulsed laser deposition. The influence of post-growth annealing modes on the electroforming voltage and the resistive switching effect in ZnO nanocrystalline films is investigated. We demonstrated that nanocrystalline zinc oxide films, fabricated at certain regimes, show the electroforming-free resistive switching. It was shown, that the forming-free nanocrystalline ZnO film demonstrated a resistive switching effect and switched at a voltage 1.9 ± 0.2 V from 62.42 ± 6.47 (RHRS) to 0.83 ± 0.06 kΩ (RLRS). The influence of ZnO surface morphology on the resistive switching effect is experimentally investigated. It was shown, that the ZnO nanocrystalline film exhibits a stable resistive switching effect, which is weakly dependent on its nanoscale structure. The influence of technological parameters on the resistive switching effect in a forming-free ZnO nanocrystalline film is investigated. The results can be used for fabrication of new-generation micro- and nanoelectronics elements, including random resistive memory (ReRAM) elements for neuromorphic structures based on forming-free ZnO nanocrystalline films.

We have synthesized nanocrystalline ZnO by a simple precipitation method. The prepared ZnO was found to be highly phase pure and nanocrystalline hexagonal wurtzite structure. UV-Visible-DRS spectroscopy showed the material to have bandgap energy of 3.22eV. HR-SEM image revealed the material to be made up of distinct hexagonal particles with a highly porous surface. AFM analysis was employed to confirm the high surface roughness and porosity of the material. The photocatalytic activity of the prepared ZnO was evaluated by the degradation of benzene-1,4-diol (hydroquinone), under visible light irradiation. Preliminary experiments showed the catalyst to be effective at neutral pH with an optimum catalyst dosage of 4g/L. Kinetic studies showed the degradation reaction to follow pseudo-first-order kinetics. In the presence of commonly used industrial electrolytes, the catalyst exhibited a decrease in efficiency. Reusability studies showed the catalytic efficiency of ZnO to diminish marginally after the third cycle of reuse. [ABSTRACT FROM AUTHOR]

In the present study, ZnO nanostructures were ultrasonically synthesized and immobilized on the surface of diatomite and used for visible light photocatalysis of Acid Red 88 (AR88) in the aqueous phase. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were employed for characterization of the samples. The process was optimized via response surface methodology (RSM) on the basis of central composite design (CCD). Based on numerical optimization, for the maximized color removal of 96% the initial dye concentration, the catalyst dosage, the reaction time, and the initial pH were 13 mg/L, 1.5 g/L, 85 min, and 4, respectively. The initial pH produced the largest effect, while the adsorbent dosage represented the lowest individual effect on the photocatalysis of AR88. The reusability test showed a 20% reduction in decolorization efficiency (%) within four consecutive experimental runs. Overall, ZnOdiatomite nanocomposite can be applied as an efficient photocatalyst for the visible light photocatalysis of target organic dyes. [ABSTRACT FROM AUTHOR]

Ultrasound assisted wet-chemical method has been carried out to incorporate different metal and non-metal ions such as; Li, S and Ag into ZnO. Characteristic studies on the structural and optical properties of the samples especially; the ultra-violet (UV) light absorption have been carried out. X-ray diffraction (XRD) analysis shows the formation of hexagonal crystal structure of ZnO along with changes in crystallinity and micro-strain with impurity doping. The morphology of the doped samples changes from particle like structure to flower and rod like structures showing the influence of dopant ions on nano ZnO growth. Infra-red (IR) transmittance spectra give information about the presence of metal–oxygen bond along with other stretching and bending modes. UV–visible absorption studies show the narrowing and sharpening of UV absorption band along with a blue shift for the doped samples. This shows the intensification in the excitonic absorption in ZnO after doping specific elements which will find application in UV blocking agents. Photoluminescence (PL) measurement shows the presence of excitonic emission and emissions due to intrinsic defects and external impurities in UV and visible regions respectively. These emission bands show a change in their position and intensity which has been explained on the basis of the existence of impurity levels in the band gap of ZnO. [ABSTRACT FROM AUTHOR]

Mn substituted zinc oxide (ZnO) nanoparticles with general formula Zn 1− x Mn x O ( x =0.0, 0.03, 0.05 and 0.10) were synthesized through a sol–gel route. The result of x-ray diffraction (XRD) analysis confirms the presence of wurtzite crystal structure for all samples suggested that doped Mn ions are occupying regular Zn sites. Transmission electron microscopy (TEM) images exhibit the growth of particle size in the range of 30–50 nm. The results of dielectric measurement indicate that the parameters ε ′, ε ″, tan δ and σ ac are decreasing with the increase in frequency; whereas these parameters increase with the increase in temperature. Dielectric parameters are also found to increase with the increase in Mn concentration up to 5%, beyond this value the parameters become lower. The dielectric properties have been explained on the basis of space charge polarization according to Maxwell and Wagner’s two-layer model and the hopping between adjacent Mn 2+ and Mn 3+ ions. The analysis of temperature dependant magnetization data gives the idea about ferromagnetic (FM) exchange interaction. [ABSTRACT FROM AUTHOR]

A series of Hf-doped ZnO nanocatalysts were synthesized by sol–gel method with a doping content up to 6 mol%. The structure, morphologies, and optical properties of the synthesized catalysts were characterized by XRD, TEM, FTIR and UV–Vis absorption spectrometer. The photocatalytic activity was evaluated by the Methylene Blue degradation in aqueous solution under sun light irradiation. Irradiation time and doping content had important effects on the photocatalytic activity of Hf-doped ZnO. Hafnium content had an optimum value of 2 mol% for achieving high photocatalytic activity. The experiments demonstrated that MB was effectively degraded up to 85% within 120 minutes. It was confirmed that the presence of Hafnium in ZnO catalysts could enhance the photocatalytic oxidation. [ABSTRACT FROM AUTHOR]