ZnO Heterostructures Research Articles

Synthesis, physicochemical characterization of ZnO and α-MoO3/ZnO heterostructures and their photocatalytic activity for the methylene blue (MB) dye degradation

This research fabricated a hybrid of α-MoO3/ZnO heterostructures via ultrasonic-assisted hydrothermal synthesis and evaluated its photocatalytic activity by degradation of Methylene Blue dye (MB) under visible light irradiations. The physicochemical properties of the heterostructure were characterized using several solid-state characterization techniques. Which indicated that with the addition of α-MoO3, there is a change in morphology from ZnO hexagonal to anorthic nanorods, then gradual to a rod like shape. The α-MoO3/ZnO in the ratio of 2:1 (MZ-21) exhibited a faster MB degradation rate of 0.411 min−1, which is three times faster than that of the ZnO nanoparticle. Various parameters, such as catalyst dosage, initial MB concentration, and pH, were varied to determine the optimum condition for the MB degradation. The photodegradation percentage for α-MoO3/ZnO (MZ21) of 99% is higher than that of ZnO (53%), suggesting that the addition of MoO3 to the hybrids enhanced the degradation efficiency. The photodegradation process follows pseudo-first-order kinetics. The radical scavenger's influence on MB degradation provides insights into the MB degradation mechanism. The dominant species that contributed the highest effect toward MB degradation were the OH radical, followed by .O2− radical species, signifying that they are the species largely responsible for the attack of MB dye molecules. The reusability studies revealed that the hybrid photocatalyst could be repeatedly used up to four times without severe deactivation, indicating the excellent reliability of the hybrid.

Synthesis, characterization, and 5-fluorouracil release behavior of superparamagnetic γ-Fe2O3/ZnO hetero-nanostructures for biomedical applications

In this study, superparamagnetic maghemite (γ-Fe2O3) nanosystems in the form of nanoparticles were fabricated through the co-precipitation method at different processing conditions. Additionally, novel γ-Fe2O3/ZnO heterostructures were fabricated using zinc acetate as the zinc source and polyvinyl pyrrolidone (PVP), and ethylenediaminetetraacetic acid (EDTA) as the capping agents. The results revealed that the size of the crystallites of the prepared maghemite nanopowders was between 6 nm and 7.8 nm depending on the synthesis temperature. The saturation magnetization value of maghemite nanopowders synthesized at 90 °C was measured to be 51.58 emu/g without hysteresis with negligible coercivity. FTIR analysis results proved the presence of ZnO in the maghemite core-based nanosystem. The formation of a ZnO coating using zinc acetate in the presence of PVP and EDTA as a capping agent caused a decrease in magnetization value to 12 emu/g. A ZnO coating provided better dispersion of maghemite nanoparticles and it also affected the drug (5-FU) delivery behavior. ZnO-coated nanoparticles showed prolonged and sustained drug release additionally, they continue to release the drug after 410 h. The 5-FU release kinetics of the prepared heterogeneous nanostructures fitted well with the Korsmeyer-Peppas model.

Development of Bi2WO6 and Bi2O3 - ZnO heterostructure for enhanced photocatalytic mineralization of Bisphenol A.

Present study proposed the synthesis of mixed p-type and n-type nanocomposite heterostructures by co-precipitation method. The as-synthesized heterostructures were characterized through different characterization techniques. The as-synthesized Bi2WO6 and Bi2O3-ZnO heterostructures were tested as photocatalysts during the photodegradation of Bisphenol A (BPA). The Bi2O3-ZnO heterostructure nanocomposite was found to be a more effective photocatalyst than Bi2WO6. The effect of operating parameters including catalytic dose (0.02-0.15 gL-1), initial BPA concentration (5-20 mgL-1), temperature change (5-20 °C) and solution pH changes (4, 5, 7, and 8) were evaluated with Bi2O3-ZnO under UV-light irradiation by selecting a 300 W Xe lamp. More than 90% BPA was degraded with 0.15 gL-1 Bi2O3-ZnO, keeping 1.0 mM H2O2concentration fixed in 250 mL of reaction suspension. The HPLC and GC-MS were used to detect the reaction intermediates and final products. A plausible degradation pathway was proposed on the basis of the identification of reaction intermediates. Repeatability test analysis confirmed that the as-synthesized catalyst showed superb catalytic performance on its removal trend. The kinetics of degradation of BPA were well fitted by the power laws model. With the order of reaction being 0.6, 0.9, 1.2, and 1.3 for different operating parameters, i.e., catalyst dose, initial pH, temperature, and initial BPA concentration.

Prospects of non-linear optical behaviour of PZT/ZnO heterostructures

PZT and ZnO heterostructures were fabricated by using the sol-gel spin-coating method on two different substrates, viz., ITO-coated glass and Corning glass. UV–Vis spectroscopy of these heterostructures showed 80% transparency in the visible region of the electromagnetic spectrum, which is desirable for optical device applications. Tauc's relation was used to calculate the energy bandgap, which was found to be blue shifted to 3.96 eV in the case of the heterostructure on ITO-coated glass and 3.9 eV for that on Corning glass, indicating a difference of ΔE = 0.06 eV due to the change in substrate. The refractive index (n), extinction coefficient (k), and the real and imaginary parts of the dielectric constant (ε1 and ε2) of the heterostructures were estimated. The second order non-linear refractive index (n2) and the third order non-linear optical susceptibility (χ(3)) were determined by generalized Miller's rule in the photon energy range of 0.5–6.5 eV by using the UV–Vis spectroscopic data. The respective values of χ(1) and χ(3) values were found to be in the range 0.10–0.45 and 3.88 × 10−13–6.0 × 10−12. The optical and structural studies established that the nanocrystalline PZT-ZnO heterostructure on ITO-coated glass was more optically transparent and had better non-linear properties as compared to that on the corning glass substrate. These properties are advantageous for optoelectronic device applications.

Copper sulfide and zinc oxide hybrid nanocomposite for wastewater decontamination of pharmaceuticals and pesticides

In this work, hybrid nanocomposites of CuS QDs @ ZnO photocatalysts are fabricated through a facile microwave-assisted (MW) hydrothermal method as a green preparation process. The prepared photocatalysts (PCs) are employed under simulated sunlight (SL) for the degradation of ciprofloxacin, ceftriaxone, ibuprofen pharmaceuticals, methylene blue dye, and 2,4,5-trichlorophenoxyacetic acid (2,4-D) pesticide. The prepared photocatalysts are characterized in detail using several compositional, optical, and morphological techniques. The influence of the CuS (QDs) wt. % on morphological, structural, as well as photocatalytic degradation efficiency have been investigated. The small displacement between the (107) plane of CuS and the (102) plane of ZnO can confirmed the existence of lattice interaction, implying the formation of p-n heterojunctions. TEM and XRD results demonstrated that the CuS QDs are established and uniformly decorated on the surface of ZnO NRs, confirming the forming of an efficient CuS QDs @ ZnO heterojunction nanostructures. The CuS QDs @ ZnO hybrid nanocomposites showed enhancement in crystallinity, light absorption, surface area, separation of e–h pair and inhibition in their recombination at an interfacial heterojunction. In addition it is found that, 3 wt% CuS QDs @ ZnO has the foremost influence. The results showed improvement of photocatalytic activity of the 3% CuS QDs @ ZnO hybrid nanocomposite as compared to the bare ZnO nanorods. The impressive photocatalytic performance of CuS @ ZnO heterostructure nanorods may be attributed to efficient charge transfer. The prepared CuS QDs @ ZnO hybrid nanocomposites exhibited 100% removal for MB dye, after 45 min, and after 60 min for ibuprofen, ciprofloxacin pharmaceuticals, and 2.4.5 trichloro phenoxy acetic acid pesticide with the catalyst amount of 0.2 g/L. Although 100% removal of ceftriaxone pharmaceutical acheived after 90 min. In addition CuS QDs @ ZnO hybrid nanocomposites exhibited complete removal of COD for ibuprofen, ceftriaxone pharmaceuticals and 2.4.5 trichloro phenoxy acetic acid pesticide after 2 h with no selectivity. Briefly, 3% CuS QDs@ZnO hybrid nanocomposites can be considered as promising photoactive materials under simulated sunlight for wastewater decontamination.

Recent developments in ZnO-based heterostructures as photoelectrocatalysts for wastewater treatment: A review

The industry's global expansion has resulted in a significant increase in the production and accumulation of harmful pollutants in the environment. Many researchers were interested in employing ZnO semiconductor material as a photocatalyst due to its environmentally friendly nature, biocompatible, availability and durability qualities for eliminating harmful pollutants. This review critically examines the findings and highlights new research based on ZnO heterostructures as a photoelectrocatalyst (PEC) for the remediation of organically polluted wastewater. It also discusses significant advancements to overcome the challenges associated with bare ZnO. Numerous efforts have taken on the hybridization of ZnO along with a narrow bandgap material, metal/non-metal doping and the construction of heterojunction that extends the absorption region of ZnO from UV to the visible region and reduces the photo-corrosion process up to a certain extent. Furthermore, the load separation/transfer mechanism, enhancement of photocatalytic activity strategies and improved light-harvesting capabilities of ZnO have been elaborated in detail. This review contains intriguing information for future research and highlights the use of ZnO-based heterostructures, which can be used as photoelectrocatalysts for wastewater purification. In the near future, attention must be paid to developing a low-cost photocatalyst immobilization technology for solid-liquid separation and catalyst reuse. In order to assure environmental safety and cost-effectiveness, the use of abundant and non-toxic components is desirable. Furthermore, due to the vast availability of solar energy, future research works must focus on employing natural sunlight as an illumination source, compared to commercially simulated solar light. Finally, this paper elaborates on potential enhancements and intriguing future directions for the use of modified ZnO as a photoelectrocatalysts.

NH2-MIL-125(Ti) nanoparticles decorated over ZnO microrods: An efficient bifunctional material for degradation of levofloxacin and detection of Cu(II)

The evolution of MOF/metal oxide composites has recently been recognized as excellent photocatalysts and sensors establishing the door for research into the treatment and detection of toxic contaminants from an aqueous phase. The decoration of MOF nanoparticles onto the surface of ZnO microrods with substantial benefits was significantly studied in the current study. Herein, we have developed NH2-MIL-125(Ti)/ZnO heterostructure as a dual functional platform for the degradation of levofloxacin (LVX) as well as detection of Cu(II) ions. The heterostructure was fabricated by a simple ultrasonic-assisted hydrothermal method followed by numerous characterizations. NH2-MIL-125(Ti)/ZnO-(II) showed an average crystallite size of 47.64 nm, surface area of 39.508 m2/g, and band gap of 2.98 eV. The morphological studies revealed the deposition of NH2-MIL-125(Ti) nanoparticles on ZnO microrods in high density. Under solar irradiation, 90% degradation of LVX was attained in 240 min at optimum conditions (pH–7, catalyst dose–0.25 g/L, and LVX concentration–10 mg/L). The improved photocatalytic ability of composite in contrast to MOF and ZnO could be usually ascribed to the interface created between them, assisting the charge transfer. Additionally, the current system exhibited good recyclability over five runs. Further, to realize the application of NH2-MIL-125(Ti)/ZnO-(II) as a sensor, the material was exposed to the solution of Cu(II) ions and significant quenching was observed demonstrating high selectivity of the current system. Moreover, the detection limit in the linear range of 0–25 μM was calculated to be 1.135 μM which indicated a good sensitivity of the prepared material towards Cu(II) ions, sufficiently low to detect micromolar concentrations of Cu(II). All in all, this study provided a simple and propitious approach for fabricating solar light active photocatalysts for the degradation of organic pollutants and their dual role as fluorescent (FL) sensor towards the determination of Cu(II) ions from aqueous phase.

Efficient Reduction Photocatalyst of 4-Nitrophenol Based on Ag-Nanoparticles-Doped Porous ZnO Heterostructure.

Oxide-supported Ag nanoparticles have been widely reported as a good approach to improve the stability and reduce the cost of photocatalysts. In this work, a Ag-nanoparticles-doped porous ZnO photocatalyst was prepared by using metal–organic frameworks as a sacrificial precursor and the catalytic activity over 4-nitrophenol was determined. The Ag-nanoparticles-doped porous ZnO heterostructure was evaluated by UV, XRD, and FETEM, and the catalytic rate constant was calculated by the change in absorbance value at 400 nm of 4-nitrophenol. The photocatalyst with a heterogeneous structure is visible, light-responsive, and beneficial to accelerating the catalytic rate. Under visible light irradiation, the heterostructure showed excellent catalytic activity over 4-nitrophenol due to the hot electrons induced by the localized surface plasmon resonance of Ag nanoparticles. Additionally, the catalytic rates of 4 nm/30 nm Ag nanoparticles and porous/nonporous ZnO were compared. We found that the as-prepared Ag-nanoparticles-doped porous ZnO heterostructure catalyst showed enhanced catalytic performance due to the synergetic effect of Ag nanoparticles and porous ZnO. This study provides a novel heterostructure photocatalyst with potential applications in solar energy and pollutant disposal.

Ag nanowires assisted CH3NH3PbBr3–ZnO heterostructure with fast negative photoconductive response

Due to its attractive interaction with light, negative photoconductivity (NPC) has received widespread attention and has been used in optoelectronic logic devices with excellent performance. However, long negative response time triggered by photogenerated carriers trapping mechanism became a bottleneck in further application. Therefore, an enhanced strategy that can speed up negative response is urgently needed. Herein, we prepared a zinc oxide microwire (ZnO MW)–silver nanowires (Ag NWs)–methylammonium lead halide perovskite (CH3NH3PbBr3) heterostructure with enhanced negative response than the previous NPC device. The Ag NWs with high mobility at the interface of ZnO and CH3NH3PbBr3 accelerate the photoresponse time from 50 to 5.4 s and improve the dark current recovery time by two orders of magnitude. This work provides a strategy to improve the negative response speed with simple operation, which represents a step toward applications in the field of fast NPC optoelectronics.

Interfacial charge transfers and ultrafast nonlinear optical response via constructing electronic structure-induced MoS2/ZnO heterostructure

The molybdenum disulfide (MoS 2 ) and ZnO composite system have reported as micro-nano photonic crystals in integrated optics. Based on interface engineering, their tunable nonlinear absorption (NLA) and photoelectric characteristics offer a flexible design strategies for saturation absorber and optical limiters. Nevertheless, the mechanism leading to the tunable NLA behavior has not been clearly elucidated, which were attribute to complex charge transfers and carrier regulation characteristics. In this article, MoS 2 /ZnO heterostructures with excellent nonlinear properties composed of ZnO nanorods (NRs) wrapped with MoS 2 nanosheets were prepared by magnetron sputtering (MS) synthesis of MoS 2 on highly stacked ZnO NRs. The MoS 2 /ZnO heterostructures exhibit an interesting brush-like morphology with abundant heterointerfaces base on optimizing sputtering time and temperature, which was beneficial to provide efficient charge transfer pathways. Due to the uneven distribution of the lowest nucleation free energy, MoS 2 nanosheets possess a hybrid mode of parallel (C // ) and perpendicular orientations (C ┴ ) on surface of ZnO NRs, which tends to form the bending and vertical growth of layered MoS 2 nanosheets. From electron-photon coupling effect, MoS 2 nanosheets, ZnO NRs and MoS 2 /ZnO heterostructures possess favorable saturation absorption (SA), reverse saturation absorption (RSA) and coexisting absorption behavior, respectively. In addition, a changeover from RSA to SA could be realized in MoS 2 /ZnO heterostructures by increasing the sputtering time. The NLA coefficient of MoS 2 /ZnO heterostructures are in the order of 10 −10 cm/W, which are about 2 times larger than those of the ZnO NRs. Thus, the MoS 2 /ZnO heterostructures with excellent NLA properties will be promising candidates in optoelectronic devices. • The interfacial charge transfers and carrier regulation characteristics of MoS 2 /ZnO composite have been studied. • The ultrafast nonlinear optical properties of MoS 2 /ZnO composite were analyzed. • The mechanism of growth and nonlinear absorption for MoS 2 /ZnO composite is analyzed.

A novel self-cleaning functional composite coating with extraordinary anti-corrosion performance in high pressure CO2 conditions

This study demonstrates an alternative method for fabricating a novel integrated anticorrosion self-cleaning functional coating using the GO nanosheets with the TiO2–ZnO heterostructure to effectively induce charge separation and to accomplish photoinduced hydrophilic conversion. Through ultraviolet light (UV) irradiation, the PFDTMS-modified filler transformed from hydrophobic to hydrophilic, while the fluorine groups on the surface of the filler still existed. Research of EIS shows that the impedance at 0.01 Hz of 20% F/T-Z-G Polyurea coating was about 1 × 103 times higher than polyurea coatings, after 24 h of immersion in 2.8 MPa, 110 °C pure CO2 and NaCl solution. The results demonstrate that F/T-Z improves the dispersion of GO and make the polyurea matrix denser, inhibiting the diffusion of corrosive medium. Additionally, the GO and fluorine groups strengthen the shielding performance of the coating. Moreover, the TiO2–ZnO heterojunction traps H2O molecules to form hydroxyl radicals (OH•). Simultaneously, Fe2+ and Fe3+ combine with OH• to form Fe3O4, and the passivation film was formed on the surface of steel. It is believed that this hydrophilic-hydrophobic integrated functional coating will be an excellent candidate for technological applications, such as anticorrosion, self-cleaning materials and composite coatings.

Formation of CdO/CdS/textured-ZnO/ZnO heterostructures by chemical deposition

CdO/CdS/textured-ZnO/ZnO heterostructure was synthesized using a combination of electrochemical etching and chemical deposition methods. Electrochemical etching was used to form a textured ZnO layer. Chemical deposition of a solution containing CdCl2 was performed to prepare a CdS film with CdO nanoparticles on the surface. The obtained nanocomposite was characterized using SEM, EDX and Raman methods for structural, morphological and component studies. SEM images and Raman scattering showed the existence of cubic phase of CdO nanocrystals. The SEM study revealed the dispersion of 50-200 nm agglomerated nanostructures on the surface of CdS film.

A review on chemiresistive ZnO gas sensors

Chemiresistive gas sensors have been widely applied to monitor analytes of environmental, food and health importance. Among the plethora of materials that can be used for designing chemiresistive sensors, ZnO is one of the most explored for gas sensing, as this material has a low-cost, is non-toxic and can be easily obtained through standard chemical synthesis. Adding to this, ZnO can form heterostructures capable to improve sensor performance regarding sensitivity, selectivity and stability. Moreover, ZnO heterostructures also contribute to lower operating temperature of gas sensors, since the synergistic effects contribute to amplify the sensor signal. In this review, we survey recent advances on different types of chemiresistive ZnO-based gas sensors, focusing on how the morphology and structure of these materials influence on the sensor response. Challenges and future perspectives for ZnO chemiresistive sensors are also discussed.

Bidirectional Photoresponse in Perovskite‐ZnO Heterostructure for Fully Optical‐Controlled Artificial Synapse

AbstractCompared with electrical synapses, optoelectronic synapses exhibit great potential for ultrafast computing and wireless communication in neuromorphic hardware with advantages of low crosstalk, high bandwidth, and low power consumption. However, due to the unidirectional photoresponse in most of optoelectronic synapses, the related researches still focus on the electrical stimulation of inhibitory behaviors. Herein, a synaptic device based on perovskite−ZnO heterostructure is prepared with the characteristic of bidirectional photoresponse and can realize both the potentiation and depression by ultraviolet (UV) and green light stimuli, respectively. Consecutive UV and green light stimuli for potentiation and depression reveal the reliability and repeatability of the fully optical‐controlled artificial synapse. A series of logic functions including “OR,” “AND,” “NOR,” and “NAND” has also been demonstrated in a fully‐optical pathway. This work not only offers an innovative architecture based on the perovskite single crystal and ZnO for fully optical‐controlled artificial synapse, but also represents a step toward optical wireless neuromorphic systems.

A dual-functional flexible sensor based on defects-free Co-doped ZnO nanorods decorated with CoO clusters towards pH and glucose monitoring of fruit juices and human fluids

Herein, ZnO nanorods were doped with Co and decorated with CoO clusters through an in situ technique to create a CoO/Co-doped ZnO (CO/CZO) heterostructure at low temperatures (150 °C) on a flexible PET substrate. In the CO/CZO heterostructure, the Co dopant has a low energy barrier to substitute Zn atoms and adsorb over oxygen atoms and their vacancies. Therefore, it decreased the charge density (ND = 2.64 × 1019 cm−3) on non-active sites of ZnO and lowered the charge transfer resistance (317 Ω) at Co-doped-ZnO/electrolyte interface by suppressing the native defects and reducing the Schottky barrier height (− 0.35 eV), respectively. Furthermore, CoO clusters induced a p-n heterostructure with Co-doped ZnO, prevented corrosion, increased the active sites for analyte absorption, and increased the ultimate tensile strength (4.85 N m−2). These characteristics enabled the CO/CZO heterostructure to work as a highly sensitive, chemically stable, and flexible pH and glucose oxidation electrode. Therefore, CO/CZO heterostructure was explored for pH monitoring in human fluids and fruit juices, demonstrating a near-Nernst-limit pH sensitivity (52 mV/pH) and fast response time (19 s) in each human fluid and fruit juice. Also, it demonstrated high sensitivity (4656 µM mM−1 cm−2), low limit of detection (0.15 µM), a broad linear range (0.04 mM to 8.85 mM) and good anti-interference capacity towards glucose-sensing. Moreover, it demonstrated excellent flexibility performances, retained 53% and 69% sensitivity of the initial value for pH and glucose sensors, respectively, after 500 bending, stretching, and warping cycles.Graphical

Precisely engineered type II ZnO-CuS based heterostructure: A visible light driven photocatalyst for efficient mineralization of organic dyes

Herein, type-II band alignment of magnetic ZnO/CuS has been achieved by assembling p-type CuS nanoparticles on n-type ZnO heterostructures to accomplish the photocatalytic degradation of two colored cationic dyes, namely, methylene blue (MB) and toluidine blue (TB). The material exhibited excellent photocatalytic efficiency towards MB and TB with 93% and 87.5% degradation in just 16 and 18 min respectively. The efficacy of doped photocatalyst (FSZCS) was found to be 6 times higher than the undoped material (Fe3O4@SiO2@ZnO; FSZ) whereas pristine CuS degraded only 50% of the dye sample under identical conditions. Therefore, the dramatic enhancement of the photocatalytic degradation performance could be attributed to the synergetic effect created by doping CuS over magnetic ZnO nanocomposites which extended the photoresponse of ZnO by driving the entire degradation process under visible light irradiation and also reducing the charge recombination rate. The plausible mechanistic pathway and identification of degradation products was discussed in detail on the basis of scavenger studies as well as GC–MS analysis. Furthermore, the designed catalyst could be recycled and reused up to 5 runs without any significant decrease in its photocatalytic activity. The reported procedure exhibited multiple advances as it proceeded by utilizing renewable household LEDs as power source at room temperature without the use of any additional oxidant under neutral pH conditions thus, paving a strong path towards sustainable, green and responsible chemistry.

Pine‐Branch‐Like SnO2/ZnO Heterostructure with Suppressed Dark Current and Enhanced On/Off Ratio for Visible‐Blind UV Imaging

AbstractIn general, wide bandgap semiconductors (Eg > 3.0 eV) are sensitive to visible‐blind ultraviolet (UV) radiation. However, a large dark current makes it difficult to implement efficient visible‐blind sensing, which impedes their application in visible‐blind UV image. In this work, pine‐branch‐like photodetectors (PDs) based on SnO2/ZnO heterostructure are successfully fabricated. Compared with the high dark current (1.5 × 10‐8 A) and low on/off ratio (42) of SnO2 PD, the designed SnO2/ZnO/4 (S/Z/4) PD shows a significantly reduced dark current (1.3 × 10‐12 A), ultrahigh on/off ratio (16 405) under 300 nm UV illumination at 1 V bias. In addition, the UV/visible rejection ratio (R310/R400) of S/Z/4 PD is 1193, which is almost 48‐times of that of SnO2 PD (25). This shows great promise for application in visible‐blind image sensors. The enhancement in performance is attributed to the formation of the type‐II energy band structure, the low conductivity of ZnO layer, and the light trapping effect of pine‐branch‐like structure. Moreover, the SnO2/ZnO/4 PD also exhibits fast response speed with a rising time of 0.48 ms and decay time of 2.07 ms, which exceeds most of the metal oxide‐based PDs. The fabrication approach of pine‐branch‐like heterojunction can be extended to other one‐dimensional materials for high‐performance optoelectronic devices.

Morphology of ZnO nanorods and Au–ZnO heterostructures on different seed layers and their influence on the optical behavior

Zinc oxide nanorods were synthesized by low cost and low temperature chemical synthesis path by taking both ZnO and metal as the seed layer on the silicon substrate. The morphological study depicts seed layer as one of the key parameter in the growth process. ZnO NR/Au nanoparticles heterostructures were also fabricated. The enhancement of the visible emissions of the ZnO nanostructures is seen after the incorporation of gold nanoparticles at the surface. The visible (defect) emission corresponds to the yellow emission caused by oxygen interstitials. Luminescence vary considerably with position on the nanorod. The optical band gap obtained for Au–ZnO heterostructure to be 2.63 eV, which is lower than that of ZnO NRs. This changing trend of optical band gap for prepared Au/ZnO sample originated from the variety of defects. Tuning of the band gap energy of such wide band gap semiconductor is highly important for room temperature optical devices.

Development of Bi2O3-ZnO heterostructure for enhanced photodegradation of rhodamine B and reactive yellow dyes

Semiconductor based photocatalysis is one of the effective techniques of AOPs for environmental remediation. In present work, the development of an efficient photocatalyst formed by coupling of p-type Bi2O3 and n-type ZnO is reported. The Bi2O3-ZnO heterostructures with 5, 10 and 15% Bi2O3 were synthesized by co-precipitation method. The prepared heterostructures were characterized by various advanced techniques including XRD, XPS, UV-Visible spectroscopy, FTIR, SEM and surface area measurement. The prepared ZnO and Bi2O3-ZnO heterostructures were tested as photocatalysts for photodegradation of dyes using mixed solution of rhodamine B and reactive yellow dyes. The 5% Bi2O3-ZnO heterostructure was found as most efficient photocatalyst with 93 and 91% photodegradation of rhodamine B and reactive yellow dyes, respectively. It was found that incorporation of 5% Bi2O3 with ZnO enhanced the photocatalytic activity about 15 times towards photodegradation of dyes.

Synergistic Effect of Au Interband Transition on Graphene Oxide/ZnO Heterostructure: Experimental Analysis with FDTD Simulation.

We furnish a comprehensive study on light-induced carrier generation due to the synergistic contribution of Au interband transition and graphene oxide (GO)/ZnO heterostructure. Plasmonic gold nanoparticles (Au_nps) are incorporated as a substructure sandwiched between GO and ZnO, assisting in additional photo-induced charge carrier generation. GO is prepared by a single-step plasma-enhanced chemical vapor deposition process. The GO/ZnO heterostructure having an active working area of 0.25 cm2 is created to unleash the pyroelectric property of ZnO, and subsequently, Au_np is introduced at the interface of GO/ZnO. Here, the interband transition of Au_np and its capability for charge carrier generation combined with the excitonic charge carrier generation of the highly crystalline non-centrosymmetric hexagonal wurtzite ZnO enhances the photoresponse. Furthermore, the interaction of Au_np with ZnO and its spatial electric field intensity distribution is demonstrated by finite difference time domain simulation which indicate toward an efficient carrier generation at the interface of Au_np and ZnO. The fabricated heterostructure has an active working wavelength in the UV-A region with the highest responsivity at 375 nm of the electromagnetic spectrum. The ultrafast response time (∼29 μs) of the device is due to the pyro-phototronic effect of the GO/ZnO heterostructure enhanced by the interband transition of Au. In the comparative study of the Au_np-enriched GO/ZnO heterostructure device with a GO/ZnO device, the former shows better performance. Both the devices work in the self-powered mode as well as the photoconductive mode, but with a higher on–off current ratio in the photoconductive mode. Hence, this work helps in properly understanding photo-induced charge generation in a Au interband transition enriched GO/ZnO heterostructure.