Comparison of the photocatalytic degradation of trypan blue by undoped and silver-doped zinc oxide nanoparticles

Zinc oxide (ZnO) and silver doped zinc oxide (ZnO:Ag) nanoparticles were prepared using nitrates of zinc and silver as oxidizers and ethylene diaminetetraacetic acid (EDTA) as a fuel via low-temperature combustion synthesis (LCS) at 500 °C. X-ray diffraction (XRD) pattern indicates the presence of silver in the hexagonal wurtzite structure of ZnO. Fourier transform infrared (FTIR) spectrum indicates the presence of Ag–Zn–O stretching vibration at 510 cm⁻¹. Transmission electron microscopy (TEM) images shows that the average particle size of ZnO and ZnO:Ag nanoparticles were found to be 58 nm and 52 nm, respectively. X-ray photoelectron spectroscopy (XPS) data clearly indicates the presence of Ag in ZnO crystal lattice. The above characterization techniques indicate that the incorporation of silver affects the structural and optical properties of ZnO nanoparticles. ZnO:Ag nanoparticles exhibited 3% higher photocatalytic efficiency than pure ZnO nanoparticles. ZnO:Ag nanoparticles show better photocatalytic activity for the degradation of trypan blue (TrB) compared to undoped ZnO nanoparticles.     

Preparation,characterization and photocatalytic activity of porous zinc oxide superstructure

A porous ZnO “timber-like” superstructures comprising nanoparticles was synthesized through the thermal decomposition of zinc oxalate precursor, prepared from zinc sulfate and oxalic acid, without additive(s) in water. The resulting ZnO superstructure was systematically characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence measurement. Using methyl orange as model, photocatalytic activity of ZnO superstructure was investigated. The heat treatment temperature and time was proved to have important influence for photocatalytic activity of ZnO superstructure. Longer heat treatment time at fixed heat treatment temperature and lower heat treatment temperature at fixed heat treatment time were favorable for the enhancement of photocatalytic activity. The optimum preparation condition for ZnO superstructure with higher photocatalytic activity was at 450 °C for 6 h.     

Structure,luminescence and photocatalytic activity of Mg-doped ZnO nanoparticles prepared by auto combustion method

A series of Zn_1−xMg_xO nanoparticles with x=0 to 0.15 were prepared by auto combustion method using citric acid as the fuel and chelating agent. Structure, luminescence and photocatalytic properties were systematically investigated by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectra, ultraviolet–visible absorbance measurement and photochemical reactions etc. The samples retained hexagonal wurtzite structure of ZnO and single phase below x=0.13, and the sizes of the nanoparticles were 60–70 nm. The photoluminescence spectroscopy demonstrated blue shift of ultraviolet emission with increasing Mg doping concentration. Both optical measurements of the as grown and Mg doped ZnO nanoparticles showed that the optical band gap could be modified from ~3.28 eV to 3.56 eV as the Mg content x increased from 0 to 0.13. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange, and the results showed that the doping of Mg into ZnO nanoparticles could enhance photocatalytic activity compared to the undoped ZnO nanoparticles, which was attributed to increased band gap and superior textural properties. In addition, according to the PL and photocatalytic studies, the critical doping content of effective Mg in ZnO is up to 0.09.     

Electrical switching and conduction mechanisms of nonvolatile write-once-read-many-times memory devices with ZnO nanoparticles embedded in polyvinylpyrrolidone

We reported on the influence of zinc oxide nanoparticles (ZnO NPs) on the electrical bistable behavior of nonvolatile write-once-read-many-times (WORM) memory devices based on an indium-tin oxide/polyvinylpyrrolidone (PVP):ZnO NPs/aluminum (ITO/PVP:ZnO/Al) structure. The maximum ON/OFF current ratio of the nonvolatile WORM memory devices was approximately 3 × 10³ and the devices remained in the ON state even after the applied voltage was turned off. In addition, reliability studies for response time and once write/continuous read operations of the optimal ZnO NPs concentration are presented. The response times of both rise-time and fall-time were about 3 and 6 μs respectively. The conduction mechanisms of all voltage regions of the device were analyzed by theoretical models and electron trapping in the ZnO NPs of the electron tunneling among a PVP matrix was discussed.     

Biosynthesis of zinc oxide nanoparticles from Azadirachta indica for antibacterial and photocatalytic applications

Green synthesis of nanoparticles is gaining importance and has been suggested as possible alternatives to chemical and physical methods. The present work reports low-cost, green synthesis of zinc oxide (ZnO) nanoparticles using 25% (w/v) of Azadirachta indica (Neem) leaf extract. The biosynthesized nanoparticles were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), UV–visible spectroscopy (UV–vis), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR). The synthesized ZnO nanoparticles were pure, predominantly spherical in shape with size ranging from 9.6 to 25.5 nm. In the present work, the biosynthesized ZnO nanoparticles have been used for antibacterial and photocatalytic applications. The antibacterial activity of characterized samples was determined using different concentrations of biosynthesized ZnO nanoparticles (20 µg/mL, 40 µg/mL, 60 µg/mL, 80 µg/mL and 100 µg/mL) against Gram-positive and Gram-negative bacteria: Staphylococcus aureus, Streptococcus pyogenes and Escherichia coli using shake flask method. The obtained results revealed that the bacterial growth decreases with increase in concentration of biosynthesized ZnO nanoparticles. In Addition, Gram-positive bacteria seemed to be more sensitive to ZnO nanoparticles than Gram-negative bacteria. The biosynthesized ZnO nanoparticles showed photocatalytic activity under the UV light enhancing the degradation rate of methylene blue (MB), which is one of the main water-pollutant released by textile industries.     

Enhanced photocatalytic activity of zinc oxide synthesized by calcination of zinc sulfide precursor

ZnO nanoparticles were synthesized by calcination of ZnS precursor in an air atmosphere, in which ZnS had been firstly synthesized through precipitation with sodium sulfide (Na₂S) as the precipitator. Detailed structure and morphology of the samples were characterized by X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, and transmission electronic microscopy. Optical properties were examined by UV–vis absorption spectroscopy. Photocatalytic activities of the samples were evaluated by degradation of Reactive Blue 14 (KGL). The results indicate that ZnS precursor converted into pure ZnO stepwise via calcination at a temperature range of 400–800 °C, and pure ZnO can be achieved above 700 °C. ZnO obtained by calcination at 700 °C had an average crystalline size around 45 nm and exhibited the highest photocatalytic activity, degrading KGL by almost 97.1% after 60 min under ultraviolet irradiation, which was superior to that of the directly synthesized and commercial ZnO. The inherent correlation between different samples and their photocatalytic activities was discussed. The phase, crystalline size, specific surface area and oxygen vacancy defects of the samples were proposed to affect their photocatalytic activity.     

Bio-fabrication of zinc oxide nanoparticles using leaf extract of curry leaf (Murraya koenigii) and its antimicrobial activities

The present study focused on the development of zinc oxide nanoparticles (ZnO NPs) from the leaf extract of Murraya koenigii where zinc nitrate acts as the precursor. The X-ray diffraction (XRD) analysis showed the crystalline structure, and atomic force microscopy (AFM) showed the morphology of the ZnO NPs to be spherical with an average size of 12 nm. Functional groups of the sample were identified by using Fourier transmission infrared (FT-IR) spectroscopy. Their shape, structure and composition were assessed by Field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The results depicted that synthesized ZnO NPs were moderately stable and hexagonal shape, spherical shape with maximum particle size less than 100 nm. The green-synthesized ZnO NPs had prominent activities against Staphylococcus aureus (14.0±0.50 mm) and followed by Bacillus subtilis (13.8±0.76 mm) at the concentration of 200 µg/mL.     

ZnO nanonails: Organometallic synthesis,self-assembly and enhanced hydrogen gas production

We report the rational synthesis and characterizations of defect-rich zinc oxide (ZnO) nanonails that were prepared by organometallic approach and their implementation as an efficient photocatalyst for hydrogen (H₂) generation. The ZnO nanonails were prepared from zinc stearate in n-octadecene that serves as non-coordinating solvent without the presence of any capping agent. Transmission electron microscopy (TEM) studies reveal that the individual triangular prismatic nanonail has an average edge length of 50–70 nm and it appears to have preferred growth orientation along [0001] crystal axis. Intriguingly, this nanonails show oriented-attachment along the flat-basal edge and self-assembled into twinned structure. Such structure is interconnected via a narrow-gap to form symmetrical twinned-like nanonails with truncated tips at both ends. In comparison to ZnO commercial nanopowder, ZnO nanonails show significant enhancement in photocatalytic H₂ gas generation rate of 53.33% under UV light for 5 h. These results demonstrate ZnO nanonails to be a substantial potential photocatalyst for efficient photocatalytic applications.     

Organic photovoltaics with V2O5 anode and ZnO nanoparticles cathode buffer layers

We report the hybrid inorganic–organic photovoltaics incorporating vanadium pentoxide (V₂O₅) as hole and zinc oxide (ZnO) nanoparticles (NPs) as electron extraction layers. This device demonstrates high open circuit voltage of about 0.89 V with considerably high short-circuit current density of 10.13 mA/cm² along with fill factor of about 61.03%. Combining all these parameters, the power conversion efficiency is 5.53% which is higher compared to that (3.6%) of the cell without ZnO NPs.     

Carrier transport mechanisms of multilevel nonvolatile memory devices with a floating gate consisting of hybrid organic/inorganic nanocomposites

Nonvolatile memory devices based on a poly(4-vinylphenol) (PVP) layer containing Cu₂ZnSnS₄ (CZTS) nanoparticles were fabricated by using a simple spin-coating method. An energy dispersive spectrum revealed that the CZTS nanoparticles were Cu poor and Zn rich. Transmission electron microscopy images showed that the CZTS nanoparticles were randomly distributed in the PVP layer. Capacitance–voltage (C–V) curves for Al/CZTS nanoparticles embedded in PVP layer/p-Si devices at 1 MHz showed a hysteresis with flat-band voltage (V_fb) shifts, which resulted from the existence of CZTS nanoparticles acting as trap sites in the memory devices. The magnitudes of the V_fb corresponding to the memory window shifts between 1.0 and 2.5 V, as determined from the C–V data at 1 MHz, were dependent on the voltages applied to the memory device, indicative of multilevel characteristics for the memory effect. The operating mechanisms of the writing and the erasing processes for Al/CZTS nanoparticles embedded in PVP layer/p-Si devices are described on the basis of the C–V results and the energy-band diagrams.     

Preparation of highly photocatalytically active rutile titania nanorods decorated with anatase nanoparticles produced by a titanyl-oxalato complex solution

Rutile phase titania (TiO₂) nanorods and anatase nanoparticles were successfully synthesized from a titanyl-oxalato complex solution prepared using titanium (IV) sulfate and oxalic acid by a hydrothermal process. The impact of various hydrothermal conditions on the formation, morphology, phase, and grain size of the TiO₂ nanocrystals was investigated using fourier transformation infrared spectroscopy, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and nitrogen adsorption. The photocatalytic activities have been evaluated for the photo-decomposition of phenol under ultraviolet visible illumination. The results revealed that the TiO₂ rutile nanorods decorated with anatase nanoparticles (with ~22% anatase) prepared at 160 °C for 72 h exhibit a higher photocatalytic activity than those pure anatase nanoparticles. This behavior was closely related to the better charge carrier separation in the cases of rutile–anatase mixtures. In addition, the possible growth mechanism and phase development of the rutile nanorods and anatase nanoparticles were illustrated.     

Optical properties of ZnS nanoparticles prepared by high energy ball milling

In this work, we synthesized zinc sulfide (ZnS) nanoparticles by the mechanochemical route using zinc acetate and sodium sulfide as source materials in a high energy planetary ball mill at rotation speed of 300 rpm with ball to powder ratio 5:1 for 30–120 min. Powder samples were collected at duration of 30 min for different analyses. The milled powders were washed with methanol to remove impurity and dried at 50 °C for 2 h. ZnS nanoparticles are characterized by X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, UV–vis–NIR spectrophotometry and fluorescence spectrophotometry. The crystallite size of synthesized ZnS nanoparticles is found to be approximately 2 nm. The optical band gap of the ZnS nanoparticles is found to be in the range of 4.71–5.17 eV. Room temperature photoluminescence (PL) spectra of the samples exhibit blue-light emission using UV excitation wavelength of 280 nm.     

Post-annealing modification in structural properties of ZnO thin films on p-type Si substrate deposited by evaporation

Zinc oxide (ZnO) films of thickness ∼380 nm were deposited on p-type Si (1 1 1) substrate maintained at 300 °C under 3×10⁻⁶ Torr by a radio frequency (RF) heating source. Transmission Fourier transform infrared (FTIR) spectrum exhibited a clear Zn–O bond excitation frequency of ∼408 cm⁻¹. X-ray diffraction spectrum demonstrated four peaks (P₁–P₄) at 2θ (deg) ∼36±0.06, 40±0.09, 82±0.17 and 86±0.2, which originated from (1 0 0), (0 0 2), (2 0 1) and (0 0 4) hexagonal planes, respectively. P₂ being the highest intensity peak indicated that the growth of ZnO predominantly occurred along the c-axis i.e. (0 0 2) plane. Micrographs of the samples obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) identically displayed scattered nanocrystallites, which grew bigger with the increase of sample annealing temperature (°C) in the range of 400–1000. AFM pictures, in particular, exposed the hexagonal structure of the deposited films along with voids. However, ZnO composition ∼6:1 (Zn:O) as calculated from the energy dispersive spectrum (EDS) revealed that the formation of ZnO was not stoichiometric, rather of Zincsuboxide structure ZnO_x (x<1). Arrhenius plot of the resistivity data yielded a donor level (zinc interstitial and/or Zn–on–O site) with ionization energy E_c–1.26 eV, thereby it supports our measured results, in general.     

Optical studies of nano-structured La-doped ZnO prepared by combustion method

Coral-shaped nano-structured zinc oxide (ZnO) was successfully synthesized and La-doped via a facile combustion process using glycine as a fuel. The auto-ignition (at ∼185 °C) of viscous reactants zinc nitrate and glycine resulted in ZnO powders. Hexagonal wurtzite structure of pure and doped ZnO powder was confirmed by X-ray powder diffraction analysis. The transmission electron micrograph shows that the nano-structured ZnO is coral-shaped and possess maximal pore (∼10–50 nm pore size) density in it and the grain size is approximately about 15 nm. Addition of dopants subsequently alters the structural and optical properties which were confirmed by UV–VIS studies.     

Effects of silver substrates on the visible light photocatalytic activities of copper-doped titanium dioxide thin films

Novel copper-doped titanium dioxide (Cu-doped TiO₂) thin films on silver (Ag) substrates with different thicknesses were prepared by sol–gel and magnetron sputtering methods. The influences of the Ag substrate thickness on the morphology and performance of the films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, UV–visible spectroscopy, and photocatalytic degradation testing with methylene blue aqueous solution under visible light irradiation. The results indicated that Ag substrates with an optimal thickness of 30 nm not only maintained the tiny nanocrystals but also greatly improved dispersion of the nanoparticles on the surface of the nanofilms. Furthermore, during the calcination process, part of the Ag atoms diffused from the substrates into the Cu–TiO₂ films and substituted for the Cu ions to form Ag–TiO₂. A proper Ag substrate thickness (30 nm) greatly improved the photocatalytic properties of TiO₂ with photocatalytic efficiency, reaching approximately 86% in 300 minutes under visible light irradiation. However, an excess of Ag substrate not only led to the Cu ion separating out in the form of CuO but also resulted in the agglomeration of TiO₂ particles on the surface, which were detrimental to photocatalytic activities.     

Cobalt-doped cerium oxide nanoparticles: Enhanced photocatalytic activity under UV and visible light irradiation

CeO₂ nanoparticles (NPs) were synthesized by coprecipitation using cerium(III) nitrate hexahydrate as the precursor and ethanol as the solvent. Different concentration of cobalt-doped cerium oxide NPs (3mol % and 6 mol %) were prepared by adding various concentrations of cobalt chloride to cerium nitrate. The as-synthesized NPs were characterized through X-ray diffraction (XRD) measurements, ultraviolet (UV)–visible spectroscopy, Photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). XRD results reveal that the as-prepared CeO₂ NPs had a face-centered cubic structure with crystallite size in the range of 5–8 nm. TEM analyses showed that the CeO₂ NPs and Co-doped CeO₂ NPs had a homogenous size distribution (sizes were within 5–12 nm). Band-edge absorption of CeO₂ NPs redshifted upon increasing the Co concentration as compared to undoped CeO₂ NPs. PL spectra reveal a peak shift of CeO₂ emission upon cobalt doping, which were due to an increase in oxygen defects localized between the Ce4f and O2p energy levels (i.e., via formation of Ce³⁺ states). Photocatalytic degradation of methylene blue in aqueous solution under UV and visible (sunlight) irradiation in the presence of pure CeO₂ NPs and of Co-doped CeO₂ NPs was investigated. The efficiency of photocatalytic degradation of CeO₂ NPs increased with the Co concentration both under UV irradiation and under visible light. Co-doped CeO₂ NPs (6 mol%) showed degradation efficiencies of 98% and 89% at 420 min of exposure to UV irradiation and to visible light, respectively.     

Preparation,characterization and photocatalytic properties of polythiophene-sensitized zinc oxide hybrid nanocomposites

The composites of polythiophene (PT)/zinc oxide (ZnO) nanoparticles with different PT wt%, (2%, 4%, 6%, 10% and 20%), were synthesized by an in situ chemical oxidative polymerization method. Zinc oxide nanoparticles, prepared by polymer pyrolysis method, with average particle size of 30 nm were used as inorganic phase of these composites. The particle size of ZnO powder was measured by transmission electron microscopy (TEM). FTIR measurements and X-ray diffraction analyses showed that PT/ZnO composites were successfully synthesized. Optical properties of the prepared composites were investigated by diffuse reflectance spectroscopy (DRS) that showed a broad peak in the visible region. The morphologies of the obtained composites were studied by scanning electron microscopy (SEM). Also Barrett–Emmett–Teller (BET) technique was used to measure the specific surface area of the samples. The photocatalytic activities of the composites were evaluated by degradation of methyl orange (MO) aqueous solution under visible light (9 W LED lamp) and sunlight irradiation.     

Preparation and photocatalytic activity of Ag/bamboo-type TiO2 nanotube composite electrodes for methylene blue degradation

Photocatalysis phenomena in TiO₂ have been intensively investigated for its potential application in environmental remediation. The present work reports improved photocatalytic degradation of methylene blue dye in aqueous solution by using bamboo-type TiO₂ nanotubes deposited with Ag nanoparticles via electrochemical deposition. The photocatalytic processes are performed on Ag-modified TiO₂ bamboo-type nanotube arrays, Ag-modified smooth-walled nanotube arrays, and bare smooth-walled nanotube arrays. Both Ag-modified bamboo-type and smooth-walled nanotube arrays show improved photocatalytic degradation efficiencies (64.4% and 52.6%) compared to smooth-walled TiO₂ nanotubes of the same length (44.4%), due to the enhanced electron–hole seperation and more surface area provided by bamboo ridges. The photocatalytic activity and kinetic behavior of Ag-modified bamboo-type nanotube arrays are also optmized by tuning pulse deposition time of Ag nanoparticles. Bamboo-type nanotubes deposited with Ag nanoparticles via pulse deposition time of 0.5 s/1.5 s shows the highest methylene blue degradation efficiency of 78.5%, which represents 21.9% and 76.8% enhancement of efficiency compared to those of bare bamboo-type and smooth-walled nanotubes, respectively, indicating that a proper amount of Ag nanoparticles on TiO₂ can maximize the photocatalytic processes. In addition, overly long pulse deposition time will not further increase photocatalytic activity due to agglomeration of Ag paticles. For example, when the pulse deposition time is increased to 2 s/6 s, Ag-modified bamboo-type nanotube array exhibits a lower photocatalytic degradation efficiency of 62.9%.     

Structural,optical and photocatalytic properties of ZnO nanoparticles modified with Cu

ZnO and ZnO modified with Cu nanoparticles have been prepared by a simple forced hydrolysis method. The concentration of Cu incorporated in ZnO ranged from 1% to 5% by atomic weight, and the influence of Cu concentration on the physical properties of ZnO and the relation to the photocatalytic performance has been investigated. The prepared ZnO and ZnO:Cu samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and UV–vis transmittance spectroscopy. The results show that the ZnO nanomaterial was crystalline with the hexagonal wurtzite structure, with the preferential orientation of the grains along the (101) plane. The average grain size for samples with 1–5% Cu was in the range of 11–29 nm. The ZnO nanoparticles annealed at 420 °C showed an increased photocatalytic activity for the decomposition of methylene blue.     

Effect of oxygen vacancy in tungsten oxide on the photocatalytic activity for decomposition of organic materials in the gas phase

The relationship between the oxygen vacancy of tungsten oxide and its ability to decompose organic materials under visible-light irradiation was investigated experimentally. In the field of rechargeable batteries, the highest charge-discharge rate is obtained when tungsten oxide is used as a negative electrode with an O/W ratio of 2.72. This result suggested that the number of oxygen vacancies in tungsten oxide affects the photocatalytic decomposition behavior of organic materials. Therefore, with the aim of increasing the photocatalytic activity of tungsten oxide to decompose organic materials, we attempted to clarify the role of the oxygen vacancy. WO_3 − x nanoparticles, including WO_2.83 and WO_2.72 nanoparticles, were fabricated by changing the annealing temperature in a 10% H₂, 90% N₂ atmosphere to generate different densities of oxygen vacancies. Tungsten oxide with O/W ratios of 2.83 and 2.72 exhibited no photocatalytic activity for the photodecomposition of organic materials. The maximum decomposition rate was obtained for stoichiometric WO₃ (O/W = 3). The reason for the decrease or disappearance of the photodecomposition ability should originate in the increase in the number of electrons generated by the oxygen vacancies. These excess electrons promote the recombination reaction between electrons and holes in WO_3 − x, and hence reduce the lifetime of electron-hole pairs.