Photocatalytic Activity Of ZnO Research Articles

ZnO Materials as Effective Anodes for the Photoelectrochemical Regeneration of Enzymatically Active NAD.

This work reports the study of ZnO-based anodes for the photoelectrochemical regeneration of the oxidized form of nicotinamide adenine dinucleotide (NAD+). The latter is the most important coenzyme for dehydrogenases. However, the high costs of NAD+ limit the use of such enzymes at the industrial level. The influence of the ZnO morphologies (flower-like, porous film, and nanowires), showing different surface area and crystallinity, was studied. The detection of diluted solutions (0.1 mM) of the reduced form of the coenzyme (NADH) was accomplished by the flower-like and the porous films, whereas concentrations greater than 20 mM were needed for the detection of NADH with nanowire-shaped ZnO-based electrodes. The photocatalytic activity of ZnO was reduced at increasing concentrations of NAD+ because part of the ultraviolet irradiation was absorbed by the coenzyme, reducing the photons available for the ZnO material. The higher electrochemical surface area of the flower-like film makes it suitable for the regeneration reaction. The illumination of the electrodes led to a significant increase on the NAD+ regeneration with respect to both the electrochemical oxidation in dark and the only photochemical reaction. The tests with formate dehydrogenase demonstrated that 94% of the regenerated NAD+ was enzymatically active.

Synergistic effect of pH solution and photocorrosion of ZnO particles on the photocatalytic degradation of Rhodamine B

This research aims to study the synergistic effect of pH solution and photocorrosion of ZnO particles on the photodegradation of Rhodamine B (RhB) dye. The stability of ZnO particles was investigated by zeta potential measurement. The structure, morphology and photocatalytic activity of ZnO were analysed by X-ray diffraction, scanning electron microscope and ultraviolet–visible spectrophotometer, respectively. The ZnO particles were highly crystalline with a bandgap energy of 3.23 eV. The surface charges of particles were found to be pH-sensitive, where they were more negative under alkaline condition, i.e., −11.1, −5.3 and −38.2 mV at pH 3, 7 and 11, respectively. ZnO particles that dissolved in pH 3 solution produce Zn2+ ions, while precipitation of Zn(OH) 4 2− was observed in pH 11 solution, resulting in morphology change of ZnO from rod shape to lamellar shape . The synergistic effect of photocorrosion and dissolution of ZnO particles in acidic solution reduced RhB dye removal efficiency from ~90% at pH 7 to ~70% at pH 3. In alkaline solution, ZnO particles displayed remarkable reusability as it still recorded a 94.8% degradation efficiency after five successive cycles.

Antibacterial and photocatalytic activity of ZnO, SnO2 and Zn2SnO4 nanoparticles prepared by Microwave assisted method

ABSTRACT A simple microwave assisted method was employed to synthesiseZnO, SnO2 and Zn2SnO4 nanoparticles (NPs). XRD studies revealed the crystalline formation of ZnO with wurtzite, SnO2 with rutile and Zn2SnO4 with cubic respectively. FESEM showed that the ZnO, SnO2 and Zn2SnO4 NP’s morphology constituted of spindle, spherical and polygonal grains respectively. EDAX, FT-IR, Raman and PL studies have established the composition, the functional groups, phonon modes and the emission behaviour of NP’s respectively. The higher antibacterial activity of Zn2SnO4 NPs than the ZnO and SnO2 is attributed to the effect of composite ions that create oxygen defects to damage the microbe synthesis activity leading to the cell losing their ability of cell division, which may lead to the cell death of the bacteria. Further, Zn2SnO4 NPs exhibit appreciable photocatalytic activity and the photocatalytic degradation of methylene blue was increased up to 90.9 % with respective time duration of 120 minutes.

Band gap in photocatalytic ZnO–TiO2

Zinc oxide and titanium dioxide composite thin films were prepared on Corning 7059 glass substrates by co-sputtering. The reactive gas-surroundings used was ultrahigh purity oxygen. To analyze the structural, optical and photocatalytic properties of the ZnO–TiO2 samples, X-ray diffraction (XRD), atomic force microscopy (AFM), optical absorption, Raman spectroscopy and methylene blue bleaching were carried out at room temperature. XRD pat- terns indicate the presence of TiO2 (anatase and rutile phases), ZnO, ZnTiO3, and Zn2 TiO4 crystalline structures. AFM images allow the observation of non-homogeneous surface in the ZnO–TiO2 system, suggesting the separation of different crystalline phases in the composite. Raman studies exhibit different spectra in the films depending on the area analyzed, which can be interpreted as a result of the existence of well separated crystalline regions as seen in AFM images. The photocatalytic activity (PA) of TiO –ZnO–ZnTiO3–Zn2 TiO4 composite, as expected for adequate coupling semiconductors, is larger than PA of ZnO and TiO2 oxides, used as references. A simple proposal about the probable alignment of the conduction band, the valence band, and the Fermi level is included.

Synthesis, Characterization and Comparative Study of TiO2 and ZnO Nanoparticles and their Application as a Photocatalysts for a Trichromatic Dye

Background:The textile industrial effluents cause profound imbalances in ecosystems, when released into nature; dyes are oxidized by micro-organisms, resulting in a decrease in the dissolved oxygen, which is necessary for the aquatic life. For this reason, it is important to implement economic, efficient, and green methods ensuring both the discoloration and detoxification of water.Objective:TiO2and ZnO nanoparticles were synthesized by sol-gel and precipitation methods, respectively. These two nanoparticles were used to compare photocatalytic degradation under UV and solar irradiation for three reactive azoic dyes (trichromatic): Reactive Bezactive Yellow (RBY), Reactive Bezactive Red (RBR), and Reactive Bezactive Blue (RBB).Methods:The structural, i.e., morphological surface properties of the synthesized photocatalysts were characterized by Fourier Transform Infrared, X-ray diffraction, UV-Visible diffuse reflectance spectroscopy, and Scanning Electron Microscopy.X-ray diffraction shows that TiO2has a tetragonal structure with an anatase form. The effects of some operational parameters, such as the amount of TiO2 and ZnO, initial dye concentration, dye mixtures, and pH, were examined. The progress of photodegradation reaction was monitored by UV-Visible spectroscopy for decolorization and by High-Performance Liquid Chromatography for degradation, and the efficiency of degradation was confirmed by Chemical Oxygen Demand measurement.Results:The dye degradation was found to be better in the presence of solar irradiation than under UV irradiation. The photocatalytic activity of ZnO was higher than TiO2 when used in its optimal conditions.Conclusion:The percentage of degradation of each dye is different, and the order of degradation of the three reactive dyes is as follows: RBY> RBR> RBB.

Experimental Study on the Link between Optical Emission, Crystal Defects and Photocatalytic Activity of Artist Pigments Based on Zinc Oxide

The historical knowledge inherited from house paint documents and the experimental research on synthetic pigments show that production methods have an important role in the performance of paint. In this regard, this work investigates the links existing between the optical emission, crystal defects and photocatalytic activity of zinc white pigment from different contemporary factories, with the aim of elucidating the effects of these characteristics onto the tendency of the pigment to induce paint failures. The analysed samples display highly similar crystallite structure, domain size, and specific surface area, whilst white pigments differ from pure ZnO in regards to the presence of zinc carbonate hydrate that is found as a foreign compound. In contrast, the photoluminescence measurements categorize the analysed samples into two groups, which display different trap-assisted emissions ascribed to point crystal defects introduced during the synthesis process, and associated to Zn or O displacement. The photocatalytic degradation tests infer that the emerged defective structure and specific surface area of ZnO-based samples influence their tendency to oxidize organic molecules under light irradiation. In particular, the results indicate that the zinc interstitial defects may be able to promote the photogenerated electron-hole couples separation with a consequent increase of the overall ZnO photocatalytic activity, negatively affecting the binding medium stability. This groundwork paves the way for further studies on the link between the photoluminescence emission of the zinc white pigment and its tendency to decompose organic components contained in the binding medium.

Producing multifunctional wool fabrics using nano zinc oxide in presence of natural dye henna

Colored wool fabric with special functions, including self-cleaning, anti-bacterial, and ultraviolet (UV) blocking, has been prepared by applying nano ZnO as a photocatalyst and henna as both a natural dye for coloration and an agent capable of modifying the ZnO nanoparticles. Natural dye henna has been used as photo sensitizer to fabricate zinc oxide nanoparticles. Coloration of wool fabrics and surface modification of fabric are performed by adding modified zinc oxide nanoparticles in exhaustion bath. The self-cleaning property of treated wool fabrics is evaluated through discoloring methylene blue dye under sunlight irradiation. The antibacterial activities of the samples against two common pathogenic bacteria, namely Escherichia coli and Staphylococcus aureus have also been assessed. The results indicate that adding natural dye henna to zinc oxide leads to better self-cleaning properties, even the photocatalytic activity of ZnO has no negative effect on fabric color. Moreover, this process imparts proper antibacterial properties and UV-blocking activity to wool fabrics.

Copper-Doped ZnO Visible Light Photocatalyst for Degradation of Methylene Blue.

Water pollution due to uncontrolled liberation of industrial toxic chemicals, materials, drugs and dyes is one of the major causes of environmental contamination. Solar energy is one of the natural energy sources that can degrade toxic dyes in the presence of suitable active catalysts. Despite of having several advanced semiconductor-based photocatalysts, there is an open domain for the preparation of economical, cheap and high effective photocatalysts for the degradation of toxic dyes. In this study, we have prepared nanosized Cu-doped ZnO photocatalysts containing different amounts of Cu (0.1, 0.2, and 0.3 wt%) by a hydrothermal process followed by calcination at 500 °C for methylene blue (MB) degradation. The incorporation of Cu into the ZnO lattice and the crystal structure stability of the prepared catalysts are confirmed by X-ray photoelectron spectroscopy and powder X-ray diffraction. Our study shows that the photocatalytic activity of ZnO toward MB degradation under visible light can be effectively enhanced by doping it with Cu.

Incorporation of Zinc Oxide Nanoparticles in RHA-MTW Zeolite and its Application for Degradation of Dye

White rice husk ash (RHA), an agricultural waste, was used as a silica source forMTW zeolite synthesis. The RHA-MTW zeolite derived from RHA was preparedby hydrothermal method at 150 °C in the presence of tetraethylammoniumhydroxide. ZnO nanoparticles (NPs) were grown in zeolite substrates using asolid state reaction. The synthesized nanocomposite (NC) was characterized byXRD, SEM, DRS and TEM and tested as photocatalytic degradation of methyleneblue (MB) dye from aqueous solution under ultraviolet (UV) light. The BET resultsindicated that pore volume and surface area of ZnO/RHA-MTW NC was smallerthan RHA-MTW zeolite. On the basis of the obtained experimental results, it wasfound that zinc oxide NPs were encapsulated into the channels of RHA-MTWzeolite. The SEM and TEM images of ZnO/RHA-MTW NC confirmed the formationof RHA-MTW particles with size diameter of 2.5 μm and locating of zinc oxideNPs in channels of zeolite with an average size of between 35 nm. The resultsshowed MB degradation had reached 85 % under UV light. The MB indicatedmaximum adsorption at pH=9. The photocatalytic activity of ZnO was enhancedin the presence of zeolite due to reduction of recombination rate of the electrohole in ZnO semiconductor.ARTICLE INF O

Hybridisation of ZnO with Ti 3 C 2 as a co‐catalyst for enhanced photocatalytic activity

In this study, a typical MXene material, Ti3C2, was selected as a co-catalyst and then integrated with ZnO via a facile hydrothermal strategy. The phase composition, morphology, and photophysical properties of as-prepared samples were investigated by XRD, field emission SEM, ultraviolet–visible spectrophotometer, and fluorescence spectrophotometer, respectively. In addition, the results of the photocatalysis experiment showed that the photocatalytic activity of ZnO can be improved significantly through the hybridisation with Ti3C2, which arises from the inhibition of the photogenerated carriers recombination. Furthermore, the theoretical analysis indicated that the high-quantum efficiency arises from the appropriate Fermi level position of Ti3C2. This work demonstrated that Ti3C2 will show great potential for constructing novel and efficient photocatalysts.

Silver-doped ZnO for photocatalytic degradation of methylene blue

Removal of organic dyes from wastewater has become an important issue because of their carcinogenic and mutagenic effects. In this study, we prepared Ag-doped ZnO (Ag_ZnO) photocatalysts containing various amounts of Ag (0.05-0.5mol%) by a hydrothermal process followed by calcination at 500 °C and evaluated the photocatalytic degradation of methylene blue (MB) under sunlight irradiation. The incorporation of Ag into the ZnO lattice and the hexagonal wurtzite structure of the prepared catalysts could be confirmed by X-ray photoelectron spectroscopy and powder Xray diffraction analysis. BET analysis shows that the pore volume and pore size was increased with doping Ag into ZnO. The photocatalytic degradation of methylene blue followed a pseudo-first-order kinetics and the rate constant for dye degradation with 0.1% mol Ag was almost three-times bigger than that with bare ZnO. Our study shows that the photocatalytic activity of ZnO toward MB degradation under sunlight can be effectively enhanced by doping with Ag.

Improved Adsorption Capacity and Photoactivity of ZnO-ZIF-8 Nanocomposites

ZnO-ZIF-8 300 °C nanocomposite is synthesized by combining of ZnO with ZIF-8via facile route. The structural properties of ZnO-ZIF-8 300 °C are compared with the bare ZnO, ZIF-8 and ZIF-8 300 °C using various analytical methods. XRD analysis and FTIR spectroscopy confirm the successful growth of ZnO in the nanocomposite. ZnO-ZIF-8 300 °C shows a mesoporous structure. SEM (EDX) and XPS verify formation of ZnO on the surface of ZnO-ZIF-8 300 °C. The characteristic ZnO edge is noticed in the UV-Vis DRS spectrum of ZnO-ZIF-8 300 °C. The adsorption capacities and photocatalytic activities of ZnO, ZIF-8, ZIF-8 300 °C and ZnO-ZIF-8 300 °C are examined in the presence of methyl orange (MO) and methylene blue (MB).The enhanced adsorption ability and photoactivity of ZnO-ZIF-8 300 °Care mainly attributed to high surface area and porous structure inherited from ZIF-8. The activity of ZnO-ZIF-8 300 °C is also investigated under 40%, 67% and 84% relative humidity (RH) conditions. The highest performance is obtained in the presence of ZnO-ZIF-8 300 °C (84% RH) owing to formation of more hydroxyl radicals.ZnO-ZIF-8 300 °C and ZnO-ZIF-8 300 °C (84% RH) show also good stability, hence they can be proposed as potential photocatalysts for environmental applications.

A Comparative Study on Photocatalytic Activity of ZnO, ZnS and ZnO-ZnS Composite

A Comparative Study on Photocatalytic Activity of ZnO, ZnS and ZnO-ZnS Composite

Synthesis, characterization, photocatalytic effect of thiourea and thioglycolic acid on ZnO/CuS nanocomposites for degradation of Mordant black 11 dye

ZnO/CuS nanocomposite was synthesized by hydrothermal technique using two different sulfur source such as TU = thiourea and TA = thioglycolic acid. Pure ZnO and CuS (TU and TA) nanoparticles were synthesized, and a comparative analysis was performed. X-ray diffraction discloses the average crystalline size of the ZnO/CuS (TU and TA) to be 18 nm and 12 nm, respectively. HR-TEM exhibits a particle size of 27.50 nm and 30.50 nm for ZnO/CuS (TU) and ZnO/CuS (TA). Brunauer–Emmett–Teller analysis confirms the surface area of ZnO/CuS (TU) to be 1.246 m2/g and ZnO/CuS (TA) to be 11.086 m2/g. The band gaps were estimated to be 3.1 eV for ZnO/CuS (TU) and 1.6 eV and 2.64 eV for ZnO/CuS (TA). The photocatalytic activity of ZnO, ZnO/CuS (TU) and ZnO/CuS (TA) nanocomposites was investigated by the solar irradiation of mordant black 11 dye in an aqueous medium.

Photocatalytic Properties and Preparation of Nano-ZnO by Thermal Decomposition Based on ZIF-8

Using Zn(NO3)2·2H2O, 2-methylimidazole and CH3COONa·3H2O as main raw materials and methanol as solvent, ZIF-8 samples were prepared by hydrothermal reaction at 120 °C. And ZnO was obtained by calcination ZIF-8 in muffle furnace at 600 °C. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS) and thermos gravimetry-differential scanning calorimetry (TG-DSC). The photocatalytic activity of ZnO was investigated by methyl orange which was used as simulated sewage. The results show that the prepared ZnO is irregular, average grain size is about 80 nm, and the band gap width is 3.12 eV. Under UV-light, the degradation rate of 10 mg/L methyl orange is more than 70% in the presence of ZnO, while the degradation rate of methyl orange by commercial P25 is only 40%. The photocatalytic experiments show that the as-prepared ZnO has much higher photocatalytic activity than the commercial P25 photocatalyst. The ZnO is a kind of green photocatalyst which has a wide application prospect in the field of photocatalysis.

Investigating Methylene Blue Adsorption and Photocatalytic Activity of ZnO/CNC Nanohybrids

Nanohybrids of zinc oxide/cellulose nanocrystals (ZnO/CNCs) were successfully prepared by using a low cost and green method for adsorption and photocatalytic degradation of methylene blue (MB). CNCs have been derived through the hydrolysis reaction by citric/hydrochloric acid from the pure cellulose isolated from Vietnamese Nypa fruticans trunk. The influence of the Zn2+ ion concentration on the morphology, microstructure, and thermal properties as well as the photocatalytic activity of the ZnO/CNC nanohybrids was investigated in detail. Analyses of FTIR spectra, XRD, and SEM indicated that the ZnO nanocrystals with the size of 50 nm formed and loaded on the surface of CNC. Based on the DRS spectra and the nitrogen adsorption–desorption isotherms (BET) analysis, the absorption of ultraviolet light with a strong absorption band around 400 nm was found for all the ZnO/CNC nanohybrids, and the values of specific surface areas (SBET) of materials can be controlled by changing the concentration ratio of Zn2+ ion and CNC. The TGA analysis demonstrated that the ZnO loading samples (ZnO/CNC) had the thermal degradation onset temperature higher than that of neat CNC. The effect of MB removal showed the results which were contributed not only by the adsorption ability of CNC but also by the photocatalytic activity of ZnO. The photocatalytic efficiency significantly depended on the content of ZnO loading. The maximum degradation of MB was about 95% in 150 min for the ZnO/CNC-1.0 sample in which the concentration ratio of zinc-precursor Zn(NO3)2·6H2O and CNC was 1.0.

Photocatalytic activity of ZnO + CuO thin films deposited by dip coating: coupling effect between oxides

ZnO + CuO thin films were obtained by the dip-coating method on glass substrates. The precursor solution was obtained from the mixture of ZnO and CuO independent precursor solutions prepared at room temperature (RT). The atomic percentage of Cu in solution (X at.%), in steps of 10 at.%, was varied in the full range. The number of coatings was fixed to obtain thicknesses of ~250 nm for all films, which were sintered in an open atmosphere at 450 °C for 1 h. A detriment of crystalline quality was observed for ZnO as the X value was increased up to 50, decreasing its crystallite size (CS) from 20 to 12 nm. For CuO, CS remained almost constant (~10 nm). No presence of other compounds was observed in X-ray diffraction measurements. EDS measurements showed that Cu and Zn contents in the films (Y) are in accordance with the nominal concentration set in solution, being both uniformly distributed in the films. SEM images showed dependence of the texture on the X value: (i) a homogeneous distribution of spherical particles of higher size for X = 0 (ZnO) and X = 50 (CuO + ZnO), and (ii) particles of irregular shape–size for other X values. The direct band gap for ZnO (3.28 eV) and, indirect band gap for CuO (1.2 eV) were calculated from transmission spectra. A shift of edge absorption to higher wavelengths was observed as the Cu content increased. The photocatalytic activity was quantified by the photobleaching of methylene blue. ZnO films showed the highest photocatalytic activity, but also another maximum was obtained for the ZnO + CuO films with X = 50 at.%. This result has been attributed to the coupling effect among both oxides and a higher packing density of the crystallites.

Impacts of copper-containing precursors on the photocatalytic activity of Cu-modified ZnO nanoparticles

Cu-modified ZnO photocatalysts were prepared using a thermal shock method with different copper-containing precursors (Cu(NO3)2, Cu(CH3COO)2, CuSO4) in order to study the impacts of the thermal shock method on the photocatalytic activity of ZnO under both UVA light and visible light irradiation. The influences of copper-containing precursors on the crystal structure, morphology, surface structure and surface composition were investigated by X-ray diffraction, transmission electron microscopy, infrared spectroscopy and X-ray photoelectron spectroscopy. The UVA-light and visible-light-induced photocatalytic activities were evaluated through the degradation of methylene blue. According to the experimental results, ZnO catalysts modified with Cu(NO3)2 and Cu(CH3COO)2 exhibited higher performance than unmodified ZnO, which may be explained by the formation of oxygen vacancies and Cu(I) species on the surface of modified oxides. However, when ZnO was modified by CuSO4, the absence of oxygen vacancies and the presence of large sulphate ions on the ZnO surface were supposed to be the factors decreasing its photocatalytic activity.

Solar Photocatalytic Activity of Nanocrystalline ZnO Obtained from Different Precursors

In present study, ZnO photocatalysts were successfully synthesized by thermal decomposition of different precursors. Thermal decomposition temperatures of precursors were obtained by thermogravimetric analysis. The synthesized ZnO photocatalysts were characterized for their crystalline phase, surface morphology and band gap, respectively by powder X-ray diffraction, scanning electron microscopy and diffuse reflectance spectroscopic methods. Chemical analysis of synthesized ZnO photocatalysts was performed for Zn(II) content. Photocatalytic activity of ZnO photocatalysts was evaluated under the solar irradiation on crystal violet dye in aqueous solution. The results of experiments showed that ZnO synthesized from zinc carbonate consists of higher photocatalytic activity than ZnO synthesized from other precursors, which is even higher than bench mark Degussa P-25 TiO2 photocatalyst. ZnO synthesized from zinc carbonate is further used for mineralization of dyes from three different effluents.

The performance of daylight photocatalytic activity towards degradation of MB by the flower-like and approximate flower-like complexes of graphene with ZnO and Cerium doped ZnO

Semiconductor photocatalysts have played an important role in degrading water pollution in recent years. In this paper, the effects of graphene on the structure, morphology, optical properties and photocatalytic activity of ZnO and Ce-doped ZnO were studied. The photocatalysts of ZnO, Ce doped ZnO (ZnCeO), ZnO-Graphene (ZG), Ce doped ZnO-Graphene (ZGCeO) were synthesized via one-step hydrothermal method and were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), ultraviolet visible absorption (UV–vis). The results of XRD show the synthesized samples were all ZnO phases without impurity peaks. The prepared ZnO was hexagonal wurtzite crystal structure. A flower-like ZG and an approximate flower-like ZGCeO were characterized via SEM. The UV–vis spectra shows that the absorption edges have red-shifts and the absorption band broaden in all doped or composite samples, meanwhile, the band gap energy decreased from 3.26 eV to 3.06 eV. In addition, compared with pure ZnO, the photocatalytic activity of ZnCeO, ZG and ZGCeO are improved. Among them, ZGCeO shows superior photocatalytic activity: the degradation rate of organic dye MB was 99.17 % in 90 min under simulated solar irradiation.