Band Gap Of ZnO Research Articles

ZnO/CuO heterojunction prepared by sol-gel: characterization and photocatalytic evaluation

ZnO, CuO and the ZnO/CuO heterojunction were prepared using zin acetate and copper acetate by sol-gel method. The materials were characterized by: TGA, XRD, XPS, SEM, TEM, EDS and UV-Vis. The heterostructure showed a synergistic effect compared to pure materials. The XPS results confirm the existence of a heterostructure. The morphology is a combination of characteristic morphologies of ZnO and CuO. The bandgap of ZnO decreases with the incorporation of CuO. The photocatalytic efficiency of the heterostructure increases; the degradation percentages were better for the heterostructures in both radiations: Ultraviolet and Visible.

Synthesis of zinc oxide semiconductor nanoparticles using natural extract: a systematic evaluation of cationic dye photodegradation influenced by extract concentration, catalyst dose, and pH.

This work obtained zinc oxide nanoparticles (ZnO NPs) using organic components extracted from Waltheria americana at different concentrations. ZnO materials were subsequently applied in the photodegradation of two cationic dyes, Rhodamine B (RB) and methylene blue (MB), at different doses of catalyst and pH. The crystallinity and hexagonal Wurtzite structure of ZnO were established through XRD analysis. The Zn-O bond in the ZnO NPs was confirmed in the FTIR, with the characteristic signals observed in the fingerprint region at ~ 400cm-1. SEM and TEM revealed the formation of quasi-spherical particles with an average size ranging from 2 to 12nm, depending on extract concentrations during synthesis. UV-Vis studies indicated the optical bandgap of ZnO, with values below 3eV, also dependent on extract concentration. PL analysis revealed the recombination of free excitons and defects in ZnO. Photocatalytic studies of ZnO materials demonstrated excellent degradation efficiency of RB and MB dyes, which was influenced by the extract concentration of NPs, while the degradation of MB was enhanced with a 1:1 dye-to-catalyst ratio under acidic conditions. In contrast, due to RB more complex structure, an increased ratio of 1:1 to 1:3 and acidic pH conditions improved its degradation. Green-synthesized ZnO NPs using photocatalysis techniques exhibit significant potential as eco-friendly alternatives for removing contaminants from water.

Cerium-Modulated Zinc Oxide for enhanced Photoelectrochemical Non-Enzymatic biosensing of Cholesterol: An experimental and First Principle Analysis

Herein, we synthesized CexZn1-xO (x = 0.00, 0.01, 0.02, and 0.03) using the wet chemical method. The investigation explores photoelectrochemical (PEC) biosensors for enzyme-free detection of cholesterol, employing Ce0.03Zn0.97O (CZO3)/Nickel Foam (NF) as the active material. The investigation revealed notable enhancements in sensitivity for cholesterol detection, with a recorded activity of 2.812 mA.mM−1.cm−2, marking a twofold increase in comparison to dark mode (1.37 mA.mM−1.cm−2). The Limit of Detection (LOD) was determined to be 17 µM (light) and 28 µM (dark), while the Limit of Quantification (LOQ) was measured at 54 µM (light) and 98 µM (dark) in 0.1 M KOH solution. These findings demonstrate a linear detection range spanning from 80 µM to 2 mM. Ab-initio calculations based on Density Functional Theory (DFT) were carried out on 101 surfaces of both pristine ZnO and CZO3 to understand how the doping affected the pristine ZnO band gap. The findings indicate that CZO3 exhibits superior activity compared to pristine ZnO, underscoring its enhanced performance and potential for sensing application. The CZO3/NF photoelectrochemical (PEC) biosensor displayed notable cyclic stability, retaining 97 % of its performance over a 60-day period. This underscores its potential for reliable and enduring operation in biosensing applications. Additionally, CZO3/NF exhibited robust sensing capabilities when utilized with human serum samples, showcasing consistent performance in both dark and illuminated conditions.

Co-doped ZnO nanofibers fabricated via electrospinning for rapid and ppb-level detection of listeria biomarker 3-hydroxy-2-butanone

Listeria monocytogenes, a food-borne pathogen capable of releasing biomarker 3-hydroxy-2-butanone (3H-2B), generally causes a serious threat to human health. Developing 3H-2B gas sensor with excellent performance is of great significance in the diagnosis and prevention of Listeria. Here, we have successfully fabricated Co-doped ZnO nanofibers gas sensor via an electrospinning method, which can be well used for real-time monitoring of Listeria. The results show that the Co-doped ZnO nanofibers have a wurtzite crystal structure and a nanofiber-like morphology with a diameter of 62 nm. The band gap (3.15 eV) of the Co-doped ZnO is significantly narrower than that of the pure ZnO (3.25 eV). The response (168) of the 0.5%Co-doped ZnO based sensor to 100 ppm 3H-2B at 305 °C is 5.37 times greater than that of the pure ZnO (31.3), with a high selectivity, a lower detection limit (100 ppb) and a short response time of 1 s. The enhanced gas sensing mechanism is ascribed to the depletion layer on the ZnO surface, a superposition effect of interface barrier, and the narrowed band gap of the ZnO.

50 MeV Li- and 80 MeV Ni- ions induced modification in ZnO cauliflower like structure: Structural, optical and electrical studies

In this work, ZnO has been synthesized by co-precipitation method and mixed with 0.5 % of polyvinyl alcohol for the preparation of thin film. These ZnO thin films have been irradiated with lithium (Li) and nickel (Ni) beams of energy 50 MeV and 80 MeV respectively, at different fluence. XRD pattern reveals that the crystallite size varies from 41 nm to 21 nm for Li-irradiated ZnO and to 16 nm for Ni irradiated ZnO compared to pure ZnO. From UV–Visible spectroscopy, the bandgap of Li-irradiated ZnO to a fluence of 5 × 1012 ions/cm2 is found to be 3.20 eV However, for Ni-irradiated ZnO bandgap varies from 3.11 to 3.08 eV Upon investigation of PL spectra, it has been observed that broadening in the defect region is observed on increasing the Li fluence. However, Ni-ions lead to enhancement of defects with increase in fluence. Electrical properties reveal the enhancement of current in order of three for both the ions irradiated ZnO. Li irradiation leads to reduction in resistivity whereas Ni irradiation leads to the enhancement in ZnO resistivity. This suggests that the ion beam induced modification in ZnO lattice could be useful for tuning the optoelectronic properties & can be used for organic light emitting diodes.

High sensitivity of nitrobenzene on the ZnO monolayer and the role of strain engineering

Volatile organic compounds (VOCs) emissions have been a recurring problem that has challenged research centers to find new ways to monitor them. From this perspective, this work investigates nitrobenzene sensing through computational simulations, a well-known toxic compound, using the strained and strain-free two-dimensional (2D) ZnO monolayer, a traditional metal oxide semiconductor (MOS). The results indicate that nitrobenzene is adsorbed via strong physisorption on the 2D ZnO and maintains interaction with the sensor under thermal stimulus (500 K), as demonstrated via ab initio molecular dynamics (AIMD) simulations. The nitrobenzene also changes the ZnO band gap energy from 4.59 to 1.85 eV and shifts 0.35 eV the work function value. Under biaxial strain, the nitrobenzene becomes chemisorbed on the ZnO monolayer. Also, remarkable conductivity changes are observed with the nitrobenzene adsorption on the strained ZnO. Excellent values of sensitivity are found, 2.29 × 1023, 8.11 × 1022 and 2.80 × 1016 for strain-free ZnO and the maximum compressed and stretched ZnO monolayer, respectively. Short recovery times of 1.16 × 10−4 s (T = 300 K) and 6.89 × 10−8 s (T = 500 K) are also found for strain-free ZnO monolayer, indicating a great reusability for nitrobenzene. Consequently, the ZnO monolayer can be used to detect nitrobenzene.

Optimization of the thermoelectric performance of aluminum-doped zinc oxide-graphene heterojunctions under high temperature and high pressure

High-pressure effects can be used to effectively optimize the thermoelectric performance of wide-bandgap oxides. We build upon this finding to show that the synergistic effects of doping with aluminum and graphene composite give excellent thermoelectric performance under high pressure. By employing the parabolic band model, the Pisarenko curves are derived at different pressures, coupled with the band structure of Al-doped ZnO. An analysis indicates that pressure-induced narrowing of the bandgap in Al-doped ZnO reduces the electron excitation energy, thereby optimizing the electrical properties of the samples. The Debye Callaway model is also used to fit the lattice thermal conductivity of the samples, thus enabling an in-depth analysis of the phonon scattering mechanisms. Our analysis suggests that graphene composites significantly enhance point defect scattering and Umklapp scattering, thus increasing the phonon relaxation time and effectively reducing the lattice thermal conductivity of the samples. The improvement in the figure of merit (zT) of ZnO is attributed to the simultaneous enhancement of its electrical properties under high pressure and the synergistic optimization of reducing the lattice thermal conductivity through doping and composites. In this work, we consider a fixed doping ratio of Al and a constant proportion of graphene composite, and analyze the microstructure and thermoelectric properties of 0.1C–ZnAl0.04O (C–ZnAlO) samples synthesized under pressures ranging from 1 to 5 GPa, with the aim of elucidating the influence of pressure and graphene composite on the electro-acoustic transport properties of ZnO. We find that the zT value for a sample synthesized at 5 GPa is increased to 0.27 at 973 K.

Enhancement of photodetector performance of aluminum-doped zinc oxide thin films fabricated via SILAR method: Structural, optical, and electrical analysis

This study presents a comprehensive analysis of the structural, optical, electrical, and photosensing characteristics of aluminum-doped zinc oxide (Al:ZnO) thin films, fabricated via successive ionic layer adsorption and reaction (SILAR) techniques. The Raman and X-ray diffraction (XRD) analyses validated the hexagonal wurtzite structure and revealed that Al doping enhances crystallinity and crystal growth of ZnO. The average crystallite size increased from 21.6 nm in undoped sample to 23.8 nm in 5.0 wt% Al-doped sample, while strain effects decreased from 4.67 × 10-3 to 4.36 × 10-3. Scanning electron microscopy (SEM) images revealed improved film morphology and more defined geometries with increased Al doping, while energy-dispersive X-ray analysis (EDAX) confirmed successful Al integration into the ZnO lattice. Optical analyses indicate a narrowing of the ZnO bandgap to 2.81 eV in 5.0 wt% Al:ZnO from 3.02 eV in the undoped variant, while photoluminescence (PL) peak positions remains unchanged. Time-resolved fluorescence (TRF) indicated a reduction in electron lifetime with higher Al doping. Furthermore, Hall effect assessments reveal a decrease in carrier mobility and electrical resistivity, alongside a rise in carrier concentration with higher Al content. The photodetection efficacy was substantially improved with Al doping, particularly at 2.5 wt% Al, achieving a responsivity of 42.5 × 10-2 A/W, external quantum efficiency of 99.3 %, and detectivity of 1.8 × 1011 Jones. These findings exhibit that Al-doping substantially enhances the photodetection properties of ZnO thin films.

Aqueous synthesis of bare and Ag incorporated ZnO, CuO and ZnO–CuO nanomaterials with enhanced catalytic potential

The present work demonstrates a low-cost, single-step route for synthesizing ZnO, CuO, and ZnO–CuO nanomaterials using oxalic acid as a precipitating agent, avoiding using other surfactants. The current research also demonstrates the chemical reduction method for incorporating Ag nanoparticles onto the surface of the synthesized metal oxide nanostructures using sodium borohydride as the reductant. X-ray diffraction studies reveal the phase purity and crystallinity of the nanoparticles, while X-ray Photoelectron Spectroscopy characterizes the chemical states of surface elements. UV–vis spectra of the samples disclose the modifications shaped by Ag nanoparticles in the absorption characteristics and energy band gap of ZnO, CuO, and ZnO–CuO nanomaterials. The catalytic potentials of the synthesized materials are tested by monitoring degradation reactions of hazardous organic pollutants, including methylene blue and methyl orange, within a few minutes. The significant finding of the present study emphasizes the incorporation of Ag nanoparticles to ZnO–CuO nanocomposite and the use of sodium borohydride in photocatalysis effectively to enhance the rates of degradation of pollutant dyes without the use of intense radiation or unique lamps by initiating a three-stage electron transfer mechanism.

Effective sunlight photodegradation of methylene blue dye using zinc oxide doped with mono- and bi-metals of Ag and Ce

Nanosized spherical particles of pure ZnO and their doped ZnO photocatalysts with mono- or bi- Ag and Ce-metal oxides at different weight portions (i.e., 2 and 4 wt%) through the sol-gel route followed by a calcination at 500 °C for 2 h were employed for exploring the photodegradation of methylene blue (MB) dye under direct sunlight. The produced photocatalysts were characterized by X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET) surface area, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), fourier transform infrared (FTIR), and UV-Vis diffuse reflectance spectroscopy (DRS). XRD patterns confirmed the formation of hexagonal wurtzite polycrystalline structure of ZnO with good crystallinity. Bi-doped ZnO photocatalysts with smaller particle sizes showed efficient improving in the photocatalytic activity of ZnO under direct sunlight irradiation. The enhanced photodegradation performance of doped samples could be attributed to the reduction in the crystallite size and band gap, as well as the presence of excess oxygen vacancies and Zn interstitial sites in the nanoparticles obtained. The calculated band gap of pure ZnO decreased from 3.07 to 2.79 eV for 2 %Ag-4 %Ce/ZnO. This doped sample degraded the MB dye completely at 60 min, whereas pure ZnO exhibited 100 % degradation of MB at 180 min. Moreover, 2 % Ag-4 %Ce/ZnO photocatalyst has the highest kinetic rate of photodegradation as compared to other samples over two initial concentrations of MB dye (0.09667 min−1 at Co= 10 mg/L and 0.04433 min−1 at Co= 20 mg/L). Hence, the obtained 2 % Ag-4 % Ce doped ZnO showcased the superb breakdown of MB dye under sunlight irradiation for positioning it as a promising material for water remediation.

Study of the electronic transport performance of ZnO-SiO2 film: the construction of grain boundary barrier

PurposeThe purpose of this study is to adjust the electronic transport performance of zinc oxide–silicon dioxide (ZnO-SiO2) film by the construction of a grain boundary barrier.Design/methodology/approachZnO-SiO2 thin films were prepared on glass substrates by a simple sol-gel method. The crystal structure of ZnO and ZnO-SiO2 powders were tested by X-ray diffraction with copper (Cu) Kα radiation. The absorption spectra of ZnO and ZnO-SiO2 films were recorded by a ultraviolet-visible spectrophotometer. The micro electrical transport performance of ZnO-SiO2 thin films were investigated by conductive atomic force microscope and electrostatic force microscope.FindingsThe results show that the current of ZnO-SiO2 film decrease, indicating that the mobility of ZnO-SiO2 film is greatly decreased, owing to the formation of the grain boundary barrier between ZnO and SiO2. The phase variation of ZnO-SiO2 film increases due to the electron accumulation at grain boundaries.Originality/valueZnO and ZnO-5SiO2 thin films prepared on glass substrates by a simple sol-gel method were first studied by CAFM and EFM. The band gaps of ZnO and ZnO-5SiO2 is ∼3.05 eV and 3.15 eV, respectively. The barrier height of ZnO-5SiO2 film increased by ∼0.015 eV after introducing SiO2. The phase variation intensity increased to a certain extent after doping SiO2, due to the increased GB barrier. ZnO-5SiO2 film will be a promising ETL candidate in the application of QLEDs field.

Vibrational, optical, and photocatalytic properties of ZnO/layered carbon nanocomposite synthesized by ball milling

ZnO/layered carbon nanocomposites with varied sizes of ZnO nanoparticles (NPs) were synthesized by mechanical milling of mixture of ZnO NPs and carbon NPs. The NP size of ZnO was controlled with average particle sizes about 19.33, 21.87, 24.21, and 27.89 nm by varying the concentrations of carbon NPs viz 0, 2, 5, and 10 weight percent, respectively, in the mixture. Presence of carbon with ZnO in the form of composite also resulted in the enhanced shift of the band gap of ZnO due to the optical transitions in the impurity states or presence of carbon as compared to the ZnO size change alone. Additionally, the enhancement of absorbance in the visible region with an increase in carbon content was observed. Such an increase in absorbance can enhance the photocatalytic activity of ZnO NPs. Raman bands for ZnO NPs also were found to shift faster in the presence of layered carbon. The quenching of visible photoluminescence emission of ZnO NPs with an increase in concentration of carbon NPs in the composite indicated the phenomenon associated with transfer of electrons from ZnO to layered carbon helping the separation of photo-generated electrons and holes in ZnO and can lead to enhancement of the photocatalytic activity of ZnO NPs. In the photocatalytic studies, it was observed that the degradation of methylene blue (MB) dye was significantly enhanced by the increase of content of layered carbon in the nanocomposite. The sample containing 10% carbon showed the highest adsorption in dark conditions which was up to 60% of the starting strength and this was further enhanced to 88% in the presence of UV radiation. Enhanced adsorption of MB dye and the effective separation of electron–hole pairs due to charge transfer were believed to be the main causes behind such kind of improvement in the photocatalytic effects.

Visible-light response ZnO/CuCo2O4 nanocomposite: Vibrational, optical, structural, morphological, photocatalytic, and kinetic analyses

Compatible nanoparticle properties in photocatalytic applications are crucial. Within the scope of this investigation, we constructed a nanocomposite of ZnO and CuCo2O4 (ZnO/CuCo2O4) to boost the photocatalytic properties of ZnO by constructing ZnO/CuCo2O4 nanocomposite using Artocarpus altilis leaves extracts (AALE). Essential secondary metabolites contribute to the origin of weak bases and capping agents to form the spherical shape of ZnO/CuCo2O4. X-ray diffractometry (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX) are some of the techniques that are utilized for the validation of nanocomposite properties, such as vibrational, crystallinity, band gap, morphology, particle size, and elemental composition. The formation of ZnO/CuCo2O4 decreased the bandgap energy and enhanced the photocatalytic performance by 93.01 % under visible light irradiation for 2 h. ZnO/CuCo2O4 followed pseudo-second-order kinetic in the photodegradation of malachite green (MG). It is noted that the increase in photocatalytic characteristics can be brought about by the narrower band gap of ZnO and increased kinetic rate toward dye degradation. Radical species analysis was of utmost importance in acknowledging that holes (h+) were the most crucial species that were indispensable to MG degradation. The photodegradation efficiency of the recycled catalyst only declines by approximately 12 % after five cycles of consumption. This study demonstrates a compelling method using plant extracts to prepare visible-light response ZnO-based nanocomposites for better photocatalytic activity and stability.

Rapid photocatalytic dye degradation, enhanced antibacterial and antifungal activities of silver stacked zinc oxide garnished on carbon nanotubes

A composite of Zinc oxide loaded with 5-weight % silver decorated on carbon nanotubes (Ag-loaded ZnO: CNT) was synthesized using a simple refluxed chemical method. The influence of deviation in the weight % of carbon nanotube loading on photocatalytic dye degradation (methylene blue and rose bengal) and antibiotic (antimicrobial and antifungal) performance was investigated in this study. The light capture ability of Ag-loaded ZnO:CNT in the visible region was higher in photocatalytic activity than that of Ag-loaded ZnO and ZnO:CNT. The bandgap of the Ag-loaded ZnO: CNT was tuned owing to the surface plasmon resonance effect. The photocatalytic degradation investigations were optimized by varying the wt% in CNTs, pH of dye solution, concentration of the dye solution, and amount of catalytic dose. Around 100% photocatalytic efficiency in 2 min against MB dye was observed for Ag doped ZnO with 10 wt% CNT composite at pH 9, at a rate constant 1.48 min−1. Bipolaris sorokiniana fungus was first time tested against a composite material, which demonstrated optimum fungal inhibition efficiency of 48%. They were also tested against the bacterial strains Staphylococcus aureus, Bacillus cerius, Proteus vulgaris, and Salmonella typhimurium, which showed promising antibacterial activity compared to commercially available drugs. The composite of Ag doped ZnO with 5 wt% CNT has shown competitive zone inhibition efficacy of 21.66 ± 0.57, 15.66 ± 0.57, 13.66 ± 0.57 against bacterial strains Bacillus cerius, Proteus vulgaris, and Salmonella typhimurium which were tested for the first time against Ag-loaded ZnO:CNT.

Improving photocatalytic efficiency of ZnO nanoflowers through gold incorporation for Rhodamine B photodegradation

In this study, we reported the synthesis and characterization of Au-doped ZnO hybrid nanostructures via a wet chemical approach and assessed their photocatalytic efficiency for the removal of Rhodamine (Rh–B). X-ray powder diffraction (XRD) has been done to verify the crystal structure, i.e. phase identification, crystallite size, texture, stress, and strain. The XRD patterns demonstrate that the wurtzite structure has been retained and that Au nanoparticles were effectively ingested into the ZnO nanoflowers lattice. This demonstrates that Au nanoparticles are effectively absorbed into the ZnO nanoflowers lattice, considering that peaks shifted in the direction of smaller Bragg's angles. As a result, the size of the crystallites increases from (20.7–25.3) nm, and their microstrain decreases from (0.92–0.72) x 10−3 A0 for pure-ZnO to Au-doped ZnO heterostructures, respectively. Scanning Electron Microscopy (SEM) investigation reveals flower-like structures of pure ZnO while a further closed look indicates that these flowers are made up of a variety of oriented, thorn-like branched NWs with diameters ranging from (50–90) nm and lengths ranging from a few microns. The corresponding EDS evaluation of pure ZnO nanoflowers and Au-doped ZnO heterostructures clearly shows that the noble metal Au NPs are deposited, and enormously safeguard the surface of ZnO nanoflowers. Reducing the Au-doped ZnO band gap which generated a red shift in light absorption, was confirmed by the PL spectra which in turn increased the photocatalytic efficiency and reduced the dye degradation time of Rh–B. The photocatalytic ability of Au-doped ZnO heterostructures considerably increased the photodegradation efficiency of Rh–B molecules from 28 min for pure ZnO to 10 min for Au-doped ZnO heterostructures. Due to their wide surface area and distinct morphology as compared to pure ZnO nanoflowers.

Effect of particle size on optical and electrical properties of thin films – a simulation approach

This paper presents a simulated investigation of the relationship between surface roughness and particle size as well as the resulting impact of the both on the thin film’s physical and optical properties. Non-porous thin films are created through computer simulation for a range of particle sizes following the random deposition with a surface relaxation approach. For the deposited thin films different fundamental parameters like transmittance, reflectance, absorption coefficients, frequency dependent dielectric constants, loss angle, refractive indices, optical band gap have all been calculated and in this process of calculation the fundamental values of two different materials; zinc oxide (ZnO and cadmium selenide (CdSe) are taken. It has been seen that when the particle sizes are comparable the calculated values of optical band gap of both ZnO and CdSe matches well with the experimental values of the same reported by others. This is probably the first effort to develop a direct relation between the particle size with different fundamental optical properties of different materials through simple simulation which agrees well with the experimental result. This would definitely help the experimental researchers in the field of material science to design their experiments as per the desired requirements.

Plasma-deposited reactive species assisted synthesis of colloidal zinc-oxide nanostructures

A surface-wave microwave discharge is applied to deposit reactive oxygen and nitrogen species (RONS) into the liquid subsequently used as a medium for laser ablation of a Zn metallic target. It is shown that during laser ablation in plasma-treated liquids the H2O2 concentration decreases, while in deionized water (DIW) significant H2O2 is produced. Meanwhile, the pH—initially adjusted by applying reductive metals—increases in the acidic liquids and decreases in the alkaline ones. During months of storage the pH of colloids stabilize around pH 6, which insures the long-term stability of RONS. It is demonstrated that in DIW metallic Zn NPs are created, which gradually oxidize during storage, while in the plasma-treated liquids ZnO NPs are produced with the mean size of 18 nm. In the alkaline plasma-treated liquid the NPs form large aggregates, which slows the dissolution of NPs. In the acidic and neutral solutions besides NPs nanosheets are also formed, which during storage evolve into nanosheet networks as a result of the dissolution of NPs. The band gap of the colloidal ZnO is found to decrease with the formation of aggregates and nanosheet networks. The ZnO NPs ablated in plasma-treated liquids exhibit a high-intensity visible emission covering the green-to-red spectral region. The photoluminescence spectra is dominated by the orange-red emission—previously not detected in the case of laser-ablated ZnO NPs and attributed to the interstitial Zn and oxygen sites—and the yellow emission, which can be attributed to the OH groups on the surface. It is shown that during months of storage, due to the dissolution of NPs and formation of nanosheets, the intensity of the visible emission decreases and shifts to the blue-green spectral region.

Modulating oxygen vacancy of ZnO for visible-light driven photocatalytic H2 evolution via facile gas treatment approach

Photocatalytic hydrogen production through water splitting is one of the most promising approaches for sustainable and renewable energy source. In recent years, research on defect rich metal oxide semiconductors has increased tremendously. N-type semiconductor ZnO exhibits a wide direct band gap of 3.3eV, limiting the optical absorption at UV range, hindering the photocatalytic performance of pristine ZnO. Furthermore, short charge carriers life time can also decrease the efficiency for hydrogen evolution. In this report, crystal defect engineering via oxygen vacancy tailoring was conducted, narrowing the bandgap of ZnO, while creating interstitial defects that reduces the recombination rate of electrons and holes. ZnO was synthesized via hydrothermal method using zinc acetate dihydrate and sodium hydroxide as precursors before subjecting for conditional annealing for 30, 60, 90 and 120 min for 200 °C, 300 °C, 400 °C and 500 °C. A series of characterization techniques were used to authenticate the effects of oxygen vacancy in ZnO. Experimental studies revealed that ZnO annealed at 400 °C for 120 min exhibit the highest amount of hydrogen produced through photochemical reactions. Therefore, the degree of oxygen vacancies in ZnO semiconductor can be regulated through diligent control of annealing parameters. Specifically, finding the optimum annealing temperature and duration were the focus in this study that relates to its photocatalytic hydrogen evolution rate.

Investigating mechanism of photo refractivity in Mg substituted ZnO thin films using pump and probe technique

In the current investigation magnesium (Mg) has been incorporated in the ZnO matrix to induce photo refractivity thereby adding an extra dimension to its already present multi-functionality. Undoped and MgxZn1-xO (x = 0.25, 0.30, 0.35, 0.40, 0.45) thin films have been grown using Chemical Solution Deposition (CSD) technique. Obtained X-Ray Diffraction (XRD) spectra exhibits a slight shift in the peak value along (002) plane whereas UV–visible spectra indicates corresponding widening of ZnO band gap values (3.24–3.64 eV) with increase in Mg content. Mg substituted ZnO films were then investigated for their ferroelectric properties using a P-E hysteresis loop tracer. It was noted that ZnO film with 35 % Mg content (x = 0.35) exhibited the high values for saturation (Ps = 1.8 μC/cm2) and remnant (Pr = 0.7 μC/cm2) polarization. Hence the ZnO with same Mg concentration was investigated for nonlinear optical properties (two wave mixing phenomenon) using pump and probe technique. In order to enhance the beam amplification gain and impart stability Au micro-dots were thermally evaporated onto MgxZn1-xO (x = 0.35) films. The maximum beam amplification gain was noted to shoot up to 2.7 post patterning of MgxZn1-xO (x = 0.35) film surface by Au micro-dots.

Characterization of GO Added ZnO Crystal Growth Using Electric Current Heating Method

ZnO has attractive and great properties especially in the fields of photonics, electronics and optics and it is widely used in the manufacturing industry of photodetectors, laser diodes and gas detectors. Therefore, various methods have been carried out to produce ZnO crystals and one of them is the Electric Current Heating method. Electric Current Heating (ECH) method is a fabrication technique applied in researches to grow ZnO crystal on a ceramic bar. This method is preferred because of it is easy to operate in laboratory, low growth temperature and also low cost. In this research, by using powder metallurgy process, Graphene Oxide/GO (in various weight percentage) added into ZnO was pelletized in a compaction die with dimension of 14.95 mm x 30 mm x 40 mm and pressure of 4 bar. The pellet green body was then sintered at 1100 °C with rate 10.0 °C/min for 3 hours. The sintered GO added ZnO ceramic was cut into ceramic bar with dimensio of 13mm x 2mm x 2mm. ECH with current 3 A and applied voltage of 30 V was used to heat the ceramic bar to produce crystals. Under scanning electron observation, it was found different crystal-like structures for each percentage GO addition. UV-Vis measurement has shown that each crystal-like structure of a GO added ZnO has own degree of energy absorbsion because of different band gap. Addition GO into ZnO would increase band gap of pure ZnO.