ZnO nanopowders and their excellent solar light/UV photocatalytic activity on degradation of dye in wastewater

Low-cost and scalable preparation,high photocatalytic activity,and convenient recycle of Zn O nanopowders(NPs)would determine their practical application in purifying wastewater.In this contribution,ZnO NPs were scalably synthesized via the simple reaction of Zn powder with H_2O vapor in autoclave.The structural,morphological and optical properties of the samples were systematically characterized by X-ray diffraction,scanning electron microscopy,Fourier transform infrared spectra,transmission electron microscopy,Micro-Raman,photoluminescence,and ultraviolet-visible spectroscopy.The as-prepared Zn O NPs are composed of nanoparticles with 100–150 nm in diameter,and have a small Brunauer-Emmett-Teller surface area of 6.85 m~2/g.The formation of Zn O nanoparticles is relative to the peeling of H_2 release.Furthermore,the product has big strain-stress leading to the red-shift in the band gap of product,and shows a strong green emission centered at 515 nm revealing enough atomic defects in Zn O NPs.As a comparison with P25,the obtained dust gray Zn O NPs have a strong absorbance in the region of 200–700 nm,suggesting the wide wave-band utilization in sunlight.Based on the traits above,the Zn O NPs show excellent photocatalytic activity on the degradation of rhodamine B(Rh-B)under solar light irradiation,close to that under UV irradiation.Importantly,the Zn O NPs could be well recycled in water due to the quick sedimentation in themselves in solution.The low-cost and scalable preparation,high photocatalytic activity,and convenient recycle of Zn O NPs endow themselves with promising application in purifying wastewater.     

Nanoflower-like composites of ZnO/SiO2 synthesized using bamboo leaves ash as reusable photocatalyst

In this study, the synthesis of ZnO/SiO₂ nanocomposites using bamboo leaf ash (BLA) and tested their photocatalytic activity for rhodamine B decolorization have been conducted. The nanocomposites were prepared by the sol–gel reaction of zinc acetate dihydrate, which was used as a zinc oxide precursor, with silica gel obtained from the caustic extraction of BLA. The effect of the Zn content (5, 10, and 20 wt%) on the physicochemical characteristics and photocatalytic activity of the nanocomposites was investigated. The results of X-ray diffraction, scanning electron microscopy, gas sorption, and transmission electron microscopy characterization confirmed the mesoporous structure of the composites containing nanoflower-like ZnO (wurtzite) nanoparticles of 10–30 nm in size dispersed on the silica support. Further, the nanocomposites were confirmed to be composed of ZnO/SiO₂ by X-ray photoelectron spectroscopy analysis. Meanwhile, diffuse-reflectance UV–visible spectrophotometry analysis of the nanocomposites revealed band gap energies of 3.38–3.39 eV. Of the tested nanocomposites, that containing 10 wt% Zn exhibited the highest decolorization efficiency (99%) and fastest decolorization rate. In addition, the degradation efficiencies were not reduced significantly after five repeated runs, demonstrating the reusability of the nanocomposite catalysts. Therefore, the ZnO/SiO₂ nanocomposite obtained from BLA is a promising reusable photocatalyst for the degradation of dye-polluted water.     

Influence of different precursors and Mn doping concentrations on the structural,optical properties and photocatalytic activity of single-crystal manganese-doped ZnO

Mn-doped ZnO single-crystal micronuts were synthesized via hydrothermal method in an hexamethylenetetramine aqueous solution. These micronuts are of wurtzite crystal structure. The effects of Mn doping amount and precursor concentration on the structural, optical properties and photocatalytic activity have been investigated. The synthesized Mn-doped ZnO was characterized by X-ray powder diffraction, field emission scanning electron microscopy (FESEM), UV–Vis absorption and photoluminescence spectroscopy. The structural analyses based on X-ray diffraction revealed the absence of Mn-related secondary phases. According to FESEM results, the length of ZnO micronuts was in the range of 5–8 μm. The band gap energy increased on increasing Mn doping concentration. The photocatalytic activity was studied by degradation of methyl orange aqueous solution, which showed that the Mn-doped ZnO micronuts prepared in precursor concentration of 0.1 M and 4% Mn doping had the highest photocatalytic activity. The effects of crystal defect and band gap energy on photocatalytic activity of Mn-doped ZnO samples were studied in different precursors and Mn doping amounts.     

Synthesis,Characterization and Photocatalytic Activity of Mg‐Impregnated ZnO–SnO2 Coupled Nanoparticles

ZnO–SnO₂ nanoparticles were prepared by coprecipitation method; then Mg, with different molar ratios and calcination temperatures, was loaded on the coupled nanoparticles by impregnation method. The synthesized nanoparticles were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDX), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), and Brunauer–Emmett–Teller (BET) techniques. Based on XRD results, the ZnO–SnO₂ and Mg/ZnO–SnO₂ nanoparticles were made of ZnO and SnO₂ nanocrystallites. According to DRS spectra, the band gap energy value of 3.13 and 3.18 eV were obtained for ZnO–SnO₂ and Mg/ZnO–SnO₂ nanoparticles, respectively. BET analysis revealed a Type III isotherm with a microporous structure and surface area of 32.051 and 49.065 m² g^?1 for ZnO–SnO₂ and Mg/ZnO–SnO₂, respectively. Also, the spherical shape of nanocrystallites was deduced from TEM and FESEM images. The photocatalytic performance of pure ZnO–SnO₂ and Mg/ZnO–SnO₂ was analyzed in the photocatalytic removal of methyl orange (MO). The results indicated that Mg/ZnO–SnO₂ exhibited superior photocatalytic activity to bare ZnO–SnO₂ photocatalyst due to high surface area, increased MO adsorption and larger band gap energy. Maximum photocatalytic activity of Mg/ZnO–SnO₂ nanoparticles was obtained with 0.8 mol% Mg and calcination temperature of 350°C.     

Biosynthesized Zinc Oxide Nanoparticles as Efficient Photocatalytic and Antimicrobial Agent

This work reports an innovative, effortless and inexpensive method for the preparation of ZnO nanoparticles by green approach using leaf extract of Piper betleas a reducing-stabilizing negotiator. The prepared ZnO NPs were characterized through XRD, FTIR, UV–Visible spectroscopy, and EDX etc. The band gap energy of the sample was estimated as 3.41 eV which is larger than the bulk ZnO (E_g?=?3.37 eV). The observed blue shift is attributed to the quantum confinement of excitons. FTIR analysis showed the presence of alkaloids, flavonoids, polyphenols, and terpenoid. TEM analysis showed that each nanoparticle comprised of 1 to 2 nano-crystallites. Photocatalytic activity results revealed that ZnO-NPs prepared through green synthesis route were found to be efficient in the degradation of toxic reactive red dye with degradation efficiency of 96.4% having high photodegradation rate-constant of 1.6?×?10^–2 min^?1. As an antimicrobial agent, the ZnO NPs are effective against both gram-positive (Bacillus subtilis) and negative bacteria (Escherichia coli), with the zones of clearance as 16.4 and 14.3 mm, respectively. Therefore, present research signifies an effective approach to utilize as-prepared ZnO NPs as efficient photocatalysts as well as antimicrobial agent.

     

Preparation and photocatalytic activity of TiO2-coated granular activated carbon composites by a molecular adsorption-deposition method

TiO₂ nanoparticle-coated granular activated carbon (GAC) composite photocatalysts (CPs) were successfully prepared by a molecular adsorption-deposition (MAD) method. The CPs were detected by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), BET surface area and UV-Vis adsorption spectroscopy, and their photoactivity was evaluated by methyl orange (MO) photodegradation. The results show that small-sized TiO₂ nanoparticles were dispersed well, deposited on the surface of GAC, and showed slight blue shift in comparison with pure TiO₂. With the increase in TiO₂ content, the CPs showed band gaps in lower energy, smaller surface areas and the higher content of Ti³⁺ ions. Compared with pure TiO₂ and others CPs samples, CPs-382 sample showed the highest photoactivity due to the optimum TiO₂ content and surface area besides the synergic effect of photocatalytic degradation of TiO₂ and adsorptive property of GAC. In addition, the CPs could be very easily reclaimed, recycled and reused for methyl orange removal while high photoactivity is preserved.     

CdS‐Encapsulated TiO2 Nanotube Arrays Lidded with ZnO Nanorod Layers and Their Photoelectrocatalytic Applications

A novel TiO₂ nanotube array/CdS nanoparticle/ZnO nanorod (TiO₂ NT/CdS/ZnO NR) photocatalyst was constructed which exhibited a wide‐absorption (200–535 nm) response in the UV/Vis region and was applied for the photoelectrocatalytic (PEC) degradation of dye wastewater. This was achieved by chemically assembling CdS into the TiO₂ NTs and then constructing a ZnO NR layer on the TiO₂ NT/CdS surface. Scanning electron microscopy (SEM) results showed that a new structure had been obtained. The TiO₂ NTs looked like many “empty bottles” and the ZnO NR layer served as a big lid. Meanwhile the CdS NPs were encapsulated between them with good protection. After being sensitized by the CdS NPs, the absorption‐band edge of the obtained photocatalyst was obviously red‐shifted to the visible region, and the band gap was reduced from its original 3.20 eV to 2.32 eV. Photoelectric‐property tests indicated that the TiO₂ NT/CdS/ZnO NR material maintained a very high PEC activity in both the ultraviolet (UV) and the visible region. The maximum photoelectric conversion efficiencies of TiO₂ NT/CdS/ZnO NR were 31.8 and 5.98 % under UV light (365 nm) and visible light (420–800 nm), respectively. In the PEC oxidation, TiO₂ NT/CdS/ZnO NR exhibited a higher removal ability for methyl orange (MO) and a high stability. The kinetic constants were 1.77×10^?4 s^?1 under UV light, which was almost 5.9 and 2.6 times of those on pure TiO₂ NTs and TiO₂ NT/ZnO NR, and 2.5×10^?4 s^?1 under visible light, 2.4 times those on TiO₂ NT/CdS.     

Calcination temperature-dependent morphology of photocatalytic ZnO nanoparticles prepared by an electrochemical–thermal method

ZnO nanoparticles (NPs) with tunable morphologies were synthesized by a hybrid electrochemical–thermal method at different calcination temperatures without the use of any surfactant or template. The NPs were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, dynamic light scattering, thermogravimetry–differential thermal analysis, scanning electron microscope and N₂ gas adsorption–desorption studies. The FT-IR spectra of ZnO NPs showed a band at 450 cm^?1, a characteristic of ZnO, which remained fairly unchanged at calcination temperatures even above 300 °C, indicating complete conversion of the precursor to ZnO. The products were thermally stable above 300 °C. The ZnO NPs were present in a hexagonal wurtzite phase and the crystallinity of ZnO increased with an increasing calcination temperature. The ZnO NPs calcined at lower temperature were mesoporous in nature. The surface areas of ZnO NPs calcined at 300 and 400 °C were 51.10 and 40.60 m² g^?1, respectively, which are significantly larger than commercial ZnO nanopowder. Surface diffusion has been found to be the key mechanism of sintering during heating from 300 to 700 °C with the activation energy of sintering as 8.33 kJ mol^?1. The photocatalytic activity of ZnO NPs calcined at different temperatures evaluated by photocatalytic degradation of methylene blue under sunlight showed strong dependence on the surface area of ZnO NPs. The ZnO NPs with high surface area showed enhanced photocatalytic activity.     

Fabrication of zinc/silver binary nanoparticles,their enhanced microbial and adsorbing properties

Monometallic ZnO nanoparticles were prepared by hydrolysis of zinc acetate with ammonium hydroxide solution. Bimetallic zinc-silver nanoparticles (ZnO-AgNPs) were prepared using metal displacement galvanic cell reaction in presence of cetyltrimethylammonium bromide (CTAB). The optical and photo-physical properties of both NPs were determined. Surface plasmon resonance (SPR) intensity of ZnO-AgNPs depends on the ratio of metal salt precursors and other experimental conditions. The optical band gap (2.98 eV), agglomeration number (26819.92), and molar concentration (1.14 × 10⁻⁴ mol/liter) of ZnO-AgNPs were determined. Langmuir adsorption monolayer, Freundlich, intraparticles diffusion and multilayer adsorption isotherms used for the determination of maximum adsorption efficiency and adsorption isotherm parameters to the removal of safranin dye from an aqueous solution. The kinetics of safranin removal has also been discussed with pseudo-first order, pseudo-second order, intraparticle diffusion and multilayer kinetic models. The antibacterial and antifungal activities of ZnO, Ag and ZnO-AgNPs were determined against human pathogens using growth kinetic and disk diffusion methods. The concentrations of ZnO-AgNPs have significant effect on the bacterial growth kinetics. The death rate constants increase with increasing the NPs concentrations. It has been found that the ZnO-AgNPs hold higher microbial activities than that of monometallic counterpart, ZnO and AgNPs. Mechanism of bacterial growth and death was discussed.     

Preparation and photocatalytic activity of TiO2-coated granular activated carbon composites by a molecular adsorption-deposition method

TiO₂ nanoparticle-coated granular activated carbon (GAC) composite photocatalysts (CPs) were successfully prepared by a molecular adsorption-deposition (MAD) method. The CPs were detected by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), BET surface area and UV-Vis adsorption spectroscopy, and their photoactivity was evaluated by methyl orange (MO) photodegradation. The results show that small-sized TiO₂ nanoparticles were dispersed well, deposited on the surface of GAC, and showed slight blue shift in comparison with pure TiO₂. With the increase in TiO₂ content, the CPs showed band gaps in lower energy, smaller surface areas and the higher content of Ti³⁺ ions. Compared with pure TiO₂ and others CPs samples, CPs-382 sample showed the highest photoactivity due to the optimum TiO₂ content and surface area besides the synergic effect of photocatalytic degradation of TiO₂ and adsorptive property of GAC. In addition, the CPs could be very easily reclaimed, recycled and reused for methyl orange removal while high photoactivity is preserved. Supported by the Natural Science Foundation of Hunan Province (Grant No. 06JJ50150), the Scientific Research Fund of Science and Technology Department of Hunan Province (Grant No. 2007GK3060) and Jishou University (Grant No. JSDXKYZZ200648)     

Effect of precursor sol pH on microstructural, optical and photocatalytic properties of vacuum annealed zinc tin oxide thin films on glass

Dip coated vacuum annealed zinc tin oxide thin films on soda lime silica glass have been deposited from the precursor sols containing zinc acetate dihydrate and tin (IV) chloride pentahydrate (Zn:Sn = 67:33, atomic ratio in percentage) in 2-methoxy ethanol by varying sol pH (0.85–5.5). Crystallinity, morphology, optical and photocatalytic properties of the films strongly depend on sol pH. Measurement of grazing incidence X-ray diffraction confirms the presence of hexagonal nano ZnO in the films derived from the sols of pH < 5.5. Film crystallinity deteriorates on increasing sol pH and the film deposited from the sol of pH 5.5 shows XRD amorphous but the selected area diffraction pattern and HRTEM image evidence the presence of nano Zn₂SnO₄ (size, 5–6 nm). Direct band gap energy of films increases on increasing sol pH. To visualize the film surface microstructure, FESEM study has been done and a rod-like surface feature is revealed in the film deposited from the sol of pH 2.85. A dependence of precursor sol pH on the photocatalytic activity of films towards degradation of Rhodamine 6G dye under UV (254 nm) irradiation is found and the highest decomposition rate constant, ‘k’ value is obtained from the film prepared from the sol of pH 5.5. The presence of zinc deficient nano Zn₂SnO₄ in the film may consider for generating the highest ‘k’ value. We also measure gelling time, viscosity of sols as well as UV and FTIR studies on the films and propose chemical reactions.     

RF magnetron sputtering of ZnO and Al-doped ZnO films from ceramic and nanopowder targets: a comparative study

Undoped zinc oxide (ZnO) and aluminium-doped zinc oxide (ZAO) thin films have been prepared on glass substrates by RF magnetron sputtering from ceramic and nanopowder targets at room temperature (RT). The effects of target nature on the properties of the films have been studied. The X-ray diffraction (XRD) patterns show that ZnO and Al-doped ZnO thin films are highly textured along the c-axis perpendicular to the surface of the substrate from either nanopowder or ceramic targets. From the SEM images, it appears that the surface morphologies of ZAO films exhibit difference from that of undoped ZnO films. All films exhibit a transmittance higher than 80% in the visible region. The optical band gap (E_g) of ZnO and ZAO films obtained from nanopowder target is higher than those prepared using ceramic target. In two cases, Al-doping leads to a larger optical band gap (E_g) of the films.     

合成ZnO纳米阵列及刺突状CuO/ZnO异质结

采用低温水热法在掺氟SnO₂ (FTO)导电玻璃表面制备ZnO纳米阵列, 研究了前驱体溶液浓度摩尔配比对ZnO纳米阵列形貌、光学性能及其生长机理的影响. 研究发现, 随着前驱体溶液浓度摩尔配比的增加, ZnO纳米阵列形貌及光学性能也随之变化. ZnO纳米阵列高度逐渐降低, ZnO纳米阵列直径和光学带隙值大体上出现先增大后降低的趋势. 而当前驱体溶液(Zn(NO₃)₂:环六亚甲基四胺(HMT, C₆H₁₂N₄))浓度摩尔配比为5:5时, 其光学禁带值(3.2 eV)接近于理论值. 结果显示制备ZnO纳米阵列的最优浓度摩尔配比为5:5. 随后选用最优浓度摩尔配比下制备的ZnO纳米阵列为基底, 通过一种两步溶液法成功在其表面制备刺突状CuO/ZnO异质结.从场发射扫描电镜(FE-SEM)结果中可以清楚看见, 大量的CuO纳米粒子沉积在ZnO纳米阵列表面形成刺突状异质结结构.研究发现该CuO/ZnO纳米异质结相对于纯ZnO纳米阵列在紫外光下光催化性能明显增加. 最后, 讨论了CuO/ZnO纳米异质结光催化机理.     

Enzymes and phytochemicals from neem extract robustly tuned the photocatalytic activity of ZnO for the degradation of malachite green (MG) in aqueous media

The malachite green (MG) is very difficult to degrade in water; thus, it needs an efficient photocatalyst. In this study, neem extract was used to tune the surface and crystal properties of ZnO nanostructures for the photodegradation of MG. The biosynthesized ZnO samples were prepared by hydrothermal method in the presence of 5, 10 and 15 mL of neem extract. The structural characterization has shown nanoparticle like morphology of ZnO as revealed by scanning electron microscopy (SEM) and hexagonal phase was confirmed by powder X-ray diffraction (XRD) technique. The XRD analysis has shown a shift in the 2 theta towards lower angle for ZnO with increasing amount of neem extract. Also, the crystallite particle size of ZnO was decreased with increasing neem extract. The UV–visible spectroscopy has shown the decrease in the optical band gap of ZnO, and the lowest band gap is possessed by ZnO sample produced with 15 mL of neem extract. The ZnO sample obtained with 15 mL of neem extract has shown approximately 99% degradation efficiency for MG for 70 min in aqueous solution. The superior photocatalytic activity of ZnO sample with 15 mL of neem extract could be attributed from the decrease in charge recombination rate due to the decreased optical band gap and particle size.

     

Tuning the aspect ratio of hydrothermally grown ZnO by choice of precursor

Variable aspect ratio (length/diameter), one dimensional ZnO nanostructures are synthesized by reacting Zn²⁺ precursor derived from Zn·Ac₂, Zn·Cl₂ and Zn·(NO₃)₂ under hydrothermal treatment. The growth mechanism illustrating the formation of self-assembling from individual ZnO nanoparticles to rod-like form is explained briefly. XRD reveals that the ZnO obtained from various zinc salts are pure, wurtzite structure, with crystalline hexagonal phase. The qualitative analysis of ZnO formation and morphology of ZnO nanoparticles are estimated from FESEM and TEM micrographs. Strong UV absorption corresponding to the recombination of electron-hole pair is observed and the blue shift absorption obeys the size confinement effect. The extent of absorption relatively varies when the morphology is changed from nano-bundles to individual rod-like ZnO. When electrons are excited at wavelength of 240 nm, a strong near band edge (NBE) emission and surface defects emission are observed in the PL spectra. The broader emission situated in the blue-green region of the visible spectrum, originating from surface oxygen defects, is not observed in ZnO derived from Zn·Ac₂.     

Mixed hemimicelles solid-phase extraction of chlorophenols in environmental water samples with 1-hexadecyl-3-methylimidazolium bromide-coated Fe3O4 magnetic nanoparticles with high-performance liquid chromatographic analysis

In this paper, 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr)-coated Fe₃O₄ magnetic nanoparticles (NPs) as an adsorbent of mixed hemimicelles solid-phase extraction was investigated for the preconcentration of two chlorophenols (CPs) in environmental water samples prior to HPLC with UV detection at 285 nm. The high surface area and excellent adsorption capacity of the Fe₃O₄ NPs after modification with C₁₆mimBr were utilized adequately in the SPE process. By the rapid isolation of Fe₃O₄ NPs through placing a strong magnet on the bottom of beaker, the time-consuming preconcentration process of loading large volume sample in conventional SPE method with a column can be avoided. A comprehensive study of the adsorption conditions such as the zeta-potential of Fe₃O₄ NPs, added amounts of C₁₆mimBr, pH value, standing time and maximal extraction volume were also presented. Under optimized conditions, two analytes of 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) were quantitatively determined. The method was then used to determine the two CPs in real environmental water samples. The accuracy of method was evaluated by recovery measurements on spiked samples. Good recovery results (74–90%) were achieved. It is important to note that satisfactory preconcentration factors and extraction recoveries for the two CPs were obtained with only a small amount of Fe₃O₄ NPs (40 mg) and C₁₆mimBr (24 mg).     

Effect of post-annealing on the band gap of sol–gel prepared nano-crystalline Mg x Zn1−x O (0.0 ≤ x ≤ 0.3) thin films

Polycrystalline Mg _x Zn_1?x O (MZO) thin films on glass substrates were prepared by sol–gel method. All the films retained the hexagonal wurtzite structure of ZnO. The band gap values determined from transmission spectra were found to be smaller than the values obtained from Vegard’s law for the as-deposited MZO films. For the films with x = 0.1, 0.2 and 0.3, the band gap blue-shifted initially and then red-shifted with increase in the annealing temperature. The reason for this anomalous shift in the band gap is attributed to the proper substitution of Mg atoms into the Zn lattice sites after a certain critical annealing temperature.     

Investigation of molar concentration effect on structural,optical, electrical,and photovoltaic properties of spray‐coated Cu2O thin films

High quality copper oxide thin films were prepared by nebulizer spray pyrolysis technique using different concentrations of copper precursor solution. Concentration‐dependent structural, morphological, optical, and electrical properties of the prepared films are discussed. X‐ray diffraction studies done for the samples confirmed that the deposited films are in Cu₂O phase with polycrystalline cubic structure. Atomic force microscopy analysis revealed that all the films are composed of nano sheet shaped grains covering the substrate surface. Optical studies done on the samples showed band gap values 2.42, 2.31, and 2.02 eV for the solution concentration 0.01, 0.05, and 0.1 M, respectively. Photoluminescence spectral analysis showed the emission band at 620 nm confirming the formation of cuprous oxide. Electrical analysis of the films showed p‐type conductivity with a low resistivity 2.19 × 10² Ω.cm and high carrier concentration 16.76 × 10 ¹⁵ cm⁻³ for the molar concentration 0.1 M. In this work, Cu₂O/ZnO heterojunctions were also prepared, and solar cell properties were studied; they were found to show increased open circuit voltage and short circuit current for higher copper concentration.     

The synthesis of nano-sized undoped,Bi doped and Bi,Cu co-doped SrTiO3 using two sol–gel methods to enhance the photocatalytic performance for the degradation of dibutyl phthalate under visible light

Two sol–gel methods (the citric acid gel and the Pechini methods) were used for the preparation of nano-sized undoped, Bi-doped and Bi, Cu co-doped SrTiO₃ samples to optimize their properties for the photocatalytic degradation of dibutyl phthalate. The perovskite-like phase was detected for the samples prepared by the citric acid gel method after calcination at 800 °C for 3 h, while in the case of the Pechini method; it was detected after calcination at 800 °C for 9 h. The particle size of the samples prepared by the citric acid gel method is greater than that of the samples prepared by the Pechini method. Cu doping in both methods increased the particle size. Cu doping, Bi doping and Bi, Cu co-doping in both methods shifted the absorption edge to the visible light range as well. The band gap of Bi, Cu co-doped SrTiO₃ is smaller than that of Bi doped SrTiO₃, which in turn is smaller than that of undoped SrTiO₃. The highest removal of the total organic carbon (TOC) of DBP was obtained using a Bi, Cu co-doped SrTiO₃ sample prepared by the citric acid gel method. TOC removal of DBP followed pseudo-first order kinetics.     

Structures and optical properties of Zn1?x Ni x O nanoparticles by coprecipitation method

Nanocrystals of undoped and nickel-doped zinc oxide (Zn_1?x Ni _x O, where x?=?0.00?C0.05) were synthesized by the coprecipitation method. Crystalline size, morphology, and optical absorption of prepared samples were determined by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and UV?Cvisible spectrometer. XRD and SEM studies revealed that Ni-doped ZnO crystallized in hexagonal wurtzite structure. Doping of ZnO with Ni²⁺ was intended to enhance the surface defects of ZnO. The incorporation of Ni²⁺ in place of Zn²⁺ provoked an increase in the size of nanocrystals as compared to undoped ZnO. Crystalline size of nanocrystals varied from 10 to 40?nm as the calcination temperature increased. Enhancement in the optical absorption of Ni-doped ZnO indicated that it can be used as an efficient photocatalyst under visible light irradiation. Optical absorption measurements indicated a red shift in the absorption band edge upon Ni doping. The band gap value of prepared undoped and Ni-doped ZnO nanoparticles decreased as annealing temperature was increased up to 800?°C.