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Catalyst-free p-n homojunction ZnO nanowire (NW) arrays in which the phosphorus (P) and zinc (Zn) served as p- and n-type dopants, respectively, have been synthesized for the first time by a controlled in situ doping process for fabricating efficient ultraviolet light-emitting devices. The doping transition region defined as the width for P atoms gradually occupying Zn sites along the growth direction can be narrowed down to sub-50 nm. The cathodoluminescence emission peak at 340 nm emitted from n-type ZnO:Zn NW arrays is likely due to the Burstein-Moss effect in the high electron carrier concentration regime. Further, the electroluminescence spectra from the p-n ZnO NW arrays distinctively exhibit the short-wavelength emission at 342 nm and the blue shift from 342 to 325 nm is observed as the operating voltage further increasing. The ZnO NW p-n homojunctions comprising p-type segment with high electron concentration are promising building blocks for short-wavelength lighting device and photoelectronics.

Vertically aligned ZnO: Ga nanotowers can be directly synthesized on a glass substrate with a ZnO seed film via the chemical bath method. A novel heterostructure of ZnO: Ga@ITO@Ag nanotowers was subsequently deposited in the ITO layer and Ag nanoparticles via the facile two-step ion-sputtering processes on the ZnO: Ga nanotowers. The appropriate ion-sputtering times of the ITO layer and Ag nanoparticles can benefit the fabrication of ZnO: Ga@ITO@Ag nanotowers with higher surface-enhanced Raman scattering (SERS) enhancement in detecting rhodamine 6G (R6G) molecules. Compared with ZnO: Ga@Ag nanotowers, ZnO: Ga@ITO@Ag nanotowers exhibited a high SERS enhancement factor of 2.25 × 108 and a lower detection limit (10−14 M) for detecting R6G molecules. In addition, the ITO layer used as an intermediate layer between ZnO: Ga nanotowers and Ag nanoparticles can improve SERS enhancement, sensitivity, uniformity, reusability, detection limit, and stability for detecting amoxicillin molecules. This phenomenon shall be ascribed to the ITO layer exhibiting a synergistic Raman enhancement effect through interfacial charge transfer for enhancing SERS activity. As a result, ZnO: Ga@ITO@Ag nanotowers can construct a three-dimensional SERS substrate for potential applications in environmentally friendly and cost-effective chemical or drug detection. [ABSTRACT FROM AUTHOR]

ZnO nanowires and nanowalls can be fabricated on the glass substrate with a ZnO seed film and low-cost aluminum (Al) foil by the aqueous solution method (ASM), respectively. The different concentrations of ZnO precursors can use to control the densities of ZnO nanowalls. In addition, FESEM, FETEM, EDS, XRD, XPS, and CL were used to evaluate the characteristics of ZnO nanowalls. The ZnO nanowalls exhibited higher photocatalytic efficiency (99.4%) than that of ZnO nanowires (53.3%) for methylene blue (MB) degradation under UVC light irradiation at the ZnO precursors of 50 mM. This result is attributed to ZnO nanowalls with Al-doped, which can improve the separation of photogenerated electron-hole pairs for enhanced photocatalytic activity. In addition, ZnO nanowalls can also reveal higher photocatalytic activity for the degradation of tetracycline capsules (TC) rather than commercial ZnO nanopowder under UVC light irradiation. The superoxide and hydroxyl radicals play essential roles in the degradation of MB and TC solutions by the radical-trapping experiment. Furthermore, the ZnO nanowalls exhibit excellent recycling and reuse capacity for up to four cycles for the degradation of MB and TC. This study highlights the potential use of ZnO nanowalls directly grown on commercial and low-cost Al foil as noble metal-free photocatalysis. [ABSTRACT FROM AUTHOR]

This study used a rapid and simple microwave-assisted synthesis method to grow ZnO nanoneedle arrays on the silicon substrate with the ZnO seed layer. The effects of reaction temperature and time on the lengths of ZnO nanoneedle arrays were investigated. The appropriate temperature programming step can grow the longer ZnO nanoneedle arrays at the same reaction time (25 min), which is 2.08 times higher than without the temperature programming step. The geometry of the ZnO nanoneedle arrays features a gradual decrease from the Si substrate to the surface, which provides an excellent progressive refractive index between Si and air, resulting in excellent antireflection properties over an extensive wavelength range. In addition, the ZnO nanoneedle arrays exhibit a suitable structure for uniform deposition of Ag nanoparticles, which can provide three-dimensional hot spots and surface active sites, resulting in higher surface-enhanced Raman scattering (SERS) enhancement, high uniformity, high reusability, and low detection limit for R6G molecule. The ZnO/Ag nanoneedle arrays can also reveal a superior SERS-active substrate detecting amoxicillin (10−8 M). These results are promising for applying the SERS technique for rapid low-concentration determination in different fields. [ABSTRACT FROM AUTHOR]

The novel ZnIn 2 S 4 /ZnO heterostructures can prepare by combining a facile hydrothermal and wet chemical methods. Various microscale and nanoscale characterization techniques analyzed the surface topography, structural and optical properties of the ZnIn 2 S 4 /ZnO heterostructures. The addition amount of ZnIn 2 S 4 nanosheets plays an essential role in controlling the optical properties of ZnIn 2 S 4 /ZnO heterostructures. ZnIn 2 S 4 /ZnO heterostructures can improve charge carriers separation and specific surface area for enhancing the photocatalytic decomposition of the 4-aminobenzoic acid solution and hydrogen evolution under blue LED irradiation. Furthermore, ZnIn 2 S 4 /ZnO heterostructures also revealed high photocatalytic stability and reusability for long-term reaction processes. Therefore, ZnIn 2 S 4 /ZnO heterostructures can be used as efficient visible-light-induced photocatalysts for the practical applications in water splitting and wastewater treatment. Image 1 • ZnO modified ZnIn 2 S 4 nanosheets were prepared by a wet chemical approach. • The heterostructures can greatly enhance visible-light hydrogen evolution activity. • The photodecomposition mechanism of PABA was mainly via h+ and ·OH radicals. • ZnIn 2 S 4 /ZnO heterostructures revealed excellent photocatalytic reusability and stability. [ABSTRACT FROM AUTHOR]

In this study, zinc oxide nanostructures integrated with reduced graphene oxide (RGO) were fabricated on foldable indium tin oxide substrates. To study the influence of RGO on the material, antibacterial, and piezoelectric properties on the nanostructures, multiple material, antibacterial, and electrical measurements were performed. Results indicate that inserting a RGO layer on the foldable substrate could form nanocylinder ZnO structures, which induced hydrophobicity and better antibacterial properties. Moreover, addition of appropriate RGO into ZnO seed layer may cause the growth of finer ZnO nanorods (NRs) and enhance piezoelectric effects. With stable electrical pulse generative piezoelectric effects and antibacterial properties, ZnO nanostructures with addition of RGO on foldable substrates have potential for future flexible biomedical and electronics applications. [ABSTRACT FROM AUTHOR]

• CuO/ZnO heterostructured nanomaces have directly grown on the copper gauze. • CuO/ZnO heterostructures exhibit high photocatalytic efficiency and reusability. • CuO/Ag/ZnO/Ag heterostructured nanomaces exhibited higher photocatalytic activity. • Ag nanoparticles play a critical role to enhance the photocatalytic efficiency. • This study provides a new strategy to construct the quaternary heterostructured arrays. The CuO/ZnO heterostructured nanomaces can be directly grown on the copper gauze substrates with CuO nanowires by a wet chemical approach at the lower reaction temperature. The concentration of ZnO precursor can easily control the sizes of ZnO branched nanowires. CuO/ZnO heterostructured nanomaces presented superior photocatalytic activity toward rhodamine 6 G removal compared with commercial ZnO or TiO 2 nanoparticles under low-powered UV-light irradiation. Further investigation has revealed that CuO/ZnO heterostructured nanomaces significantly improved activity as a recyclable photocatalyst for the degradation of rhodamine 6 G. Also, the uniform sizes of Ag nanoparticles can decorate onto the interface and surface of CuO/ZnO heterostructured nanomaces via a sample ion-beam sputtering method. The quaternary CuO/Ag/ZnO/Ag heterostructured nanomaces can provide the adequate separation of photoinduced electron-hole pairs and more surface active sites, which exhibited a higher photocatalytic efficiency rather than CuO/ZnO heterostructured nanomaces. [ABSTRACT FROM AUTHOR]

Cu-doped ZnO nanoneedles have been successfully fabricated on glass, stainless steel mesh, and carbon cloth substrates with pre-coated ZnO seed film by a facile aqueous chemical growth method at the low reaction temperature. The copper chloride and 1,3 diaminopropane play critical roles to control grow the uniform and vertical-aligned Cu-doped ZnO nanoneedles on the glass substrate. In addition, the different reaction conditions (such as reaction time, copper precursors, zinc precursors, and reaction temperature) were also exploited to control the morphologies of Cu-doped ZnO nanostructures. The PL spectrum results have demonstrated that Cu-doped ZnO nanoneedles could reduce the photogenerated electrons from band gap, thus leading to effective separation of electrons and holes. Cu-doped ZnO nanoneedles grown on the carbon cloth substrate can provide a more surface active sites and separation efficiency of photogenerated electron-hole pairs, which exhibit excellent photocatalytic activity and stability for the photodegradation of methylene blue under 10 W UV light irradiation. [ABSTRACT FROM AUTHOR]

Single-crystalline Cu-doped ZnO nanowires have been directly grown on the flexible brass mesh substrates in a large-scale by using a one-step annealing process under ambient condition. Cu-doped ZnO nanowires on the dense brass mesh substrates can provide a higher surface-to-volume ratio and better stability against aggregation, which exhibit excellent photocatalytic activity rather than the different amounts of commercial TiO 2 nanopowders under a 10 W UV light irradiation. In addition, Cu-doped ZnO nanowires are also revealed a good dynamic photocatalytic efficiency, which shall be beneficial in industrial wastewater treatment. [ABSTRACT FROM AUTHOR]

Different layered ZnO nanotower arrays can be successfully grown on ZnO nanorod films by in situ replenishing of the reaction precursors. The volume and timing of replenishment of the reaction precursors plays an important role in controlling the morphology of ZnO nanostructures. Two-layered ZnO nanotower arrays can provide a higher surface-to-volume ratio and more exposed polar surface, resulting in higher photocatalytic activity under 10 W UV light irradiation. [ABSTRACT FROM AUTHOR]

In the present work, Cu-doped ZnO nanowires have been fabricated by direct heating method on brass foils under ambient condition. The reaction temperature was not only controlling the morphology of Cu-doped ZnO nanostructures, but also influencing the Cu doping concentration. Cu-doped ZnO nanowires have good geometric structures, appropriate substrates, and doping states for field emission, which led to very low turn-on and threshold fields. In addition, the Cu-doped ZnO nanowires exhibit strong green emission attributed to oxygen vacancies and small UV emission from band gap. The Cu-doped ZnO nanowires revealed much higher photodegradation efficiency than commercial TiO 2 nanopowders. This result is attributed to increase the separation of photogenerated electron-hole pairs by Cu ions substitute in ZnO lattices and the higher surface-to-volume ratio to enhance the photocatalytic activity. Furthermore, the reusability test can demonstrated that the Cu-doped ZnO nanowires on the brass foils still maintained high photocatalytic activity for the degradation of three kinds of organic pollutants even after five cycles without any obvious decline. The results demonstrate that Cu-doped ZnO nanowires on the brass foils shall be also promising in many related areas, such as solar energy conversion, water splitting, and energy storage. [ABSTRACT FROM AUTHOR]

The ZnO nanorods have been grown on the cotton threads with ZnO seed layer by an aqueous chemical growth method at the low reaction temperature. The ZnO nanorods can provide a good geometric structure to deposit Pt nanoparticles with uniform size by a facile ion sputtering method. The photocatalytic activity of the different lengths of cotton threads with ZnO nanorods were evaluated in the photocatalytic degradation of rhodamine 6G by a 10 W UV light irradiation. The ZnO/Pt core-shell nanorods revealed much higher photodegradation efficiency than ZnO nanorods or commercial TiO 2 nanopowders, which improved the separation of photogenerated electrons and holes. Furthermore, the reusability test can demonstrated that the ZnO/Pt core-shell nanorods on the cotton threads still maintained high photocatalytic activity over five cycles. The ZnO/Pt core-shell nanorods provide a facile, low cost, high surface-to-volume ratio, high photocatalytic efficiency, and high reusability, which shall be also promising in the decomposition of environment pollutants and reusing of wastewater treatment. [ABSTRACT FROM AUTHOR]

The complex ZnO/ZnS nanocable and nanotube arrays have been grown on the silicon or glass substrates with ZnO nanowire arrays by an aqueous chemical growth method at the low reaction temperature. The concentration of ZnS precursor and reaction time can be used to control the different sizes and shell thicknesses of complex ZnO/ZnS nanocable and nanotube arrays. The complex ZnO/ZnS nanocable and nanotube arrays exhibit very prominent blue emission and week UV emission from ZnS defect and ZnO band gap in the cathodoluminescence spectrum, respectively. The photocatalytic activity of the different complex ZnO/ZnS nanocable and nanotube arrays were evaluated in the photocatalytic degradation of methylene blue under 10 W UV light irradiation. The complex ZnO/ZnS nanocable and nanotube arrays revealed much higher photodegradation efficiency than ZnO nanowire arrays. This result is attributed to increase the separation of photogenerated electron–hole pairs on the surface of ZnO/ZnS nanocable and the surface-to-volume ratio on the ZnS nanotube. The photocatalytic mechanism under UV light irradiation was proposed. Furthermore, the reusability test can demonstrated that the complex ZnO/ZnS nanocable and nanotube arrays still maintained high photocatalytic activity over ten cycles. The complex ZnO/ZnS nanocable and nanotube arrays provide a facile, low cost, high surface-to-volume ratio, high photocatalytic efficiency, and high reusability, which shall be also promising in many related areas, such as solar energy conversion, water splitting, and energy storage. [ABSTRACT FROM AUTHOR]

Large-scale ZnO nanoneedle arrays have been grown on four-inch silicon wafers with ZnO seed film by an aqueous chemical growth method at a low growth temperature and short reaction time. The volumes of 1,3 diaminopropane play an important role in controlling the dimension and optical emission properties of ZnO nanoneedle arrays, which exhibit a very prominent green emission and weak UV emission from defect and band gaps in the cathodoluminescence spectrum, respectively. The ZnO nanoneedle arrays with large alignment variations display broadband and omnidirectional antireflection properties from the gradual index profile, and can provide a higher surface-to-volume ratio and stronger defect emission, which results in a peak photocatalytic performance at a light irradiation of 10 W UV. The appropriate Ag sputtering durations on the ZnO nanoneedle arrays have been optimized to yield the greatest surface-enhanced Raman scattering effect in the rhodamine 6G molecule. The ZnO/Ag composite arrays provide a facile, high enhancement, low detection limit and low cost fabrication, which shall be of significant value for practical applications of other SERS sensing systems. [ABSTRACT FROM AUTHOR]

The ultra-sharp ZnO nanopagoda arrays have been grown on the silicon substrate with ZnO nanorod arrays by appropriate volumes of reaction precursor in conjunction with aqueous chemical growth method and downward growth process. Cathodoluminescence properties of ultra-sharp ZnO nanopagoda arrays exhibited very high performance ultraviolet emission in the temperature range of 10–300 K. [ABSTRACT FROM AUTHOR]

Aligned ZnO nanowire arrays have been grown on the silicon substrates with ZnO seed layer by an aqueous chemical growth process at low reaction temperature. The volumes of ammonium hydroxide solution are not only controlled by the dimension and density of ZnO nanowires, but are also influenced by their optical emission property. The ZnO nanowire arrays exhibit very strong and broad green emission from defect in the cathodoluminescence spectrum. In addition, the ZnO nanowires grown on the silicon substrates can serve as effective and convenient recyclable photocatalysts. Only a very slight decrease in the photodecomposition rate was observed after ten cycles of the photocatalysis experiment. [ABSTRACT FROM AUTHOR]

In this study, we fabricated Er-doped ZnO/CuS/Au core-shell nanowires using two-step wet chemical methods and an ion-sputtering method on a glass substrate as a bifunctional photocatalytic and surface-enhanced Raman scattering (SERS) substrate. The characteristic properties of as-prepared photocatalysts were confirmed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, DR/UV-Vis spectroscopy, and photoluminescence spectroscopy. Compared with Er-doped ZnO nanowires and Er-doped ZnO/CuS core-shell nanowires, Er-doped ZnO/CuS/Au core-shell nanowires exhibited remarkably photocatalytic activity to degrade acid orange 7 solutions under blue LED light. These results ascribed to the Er-doped ZnO/CuS/Au core-shell nanowires can enhance the visible-light absorbance and the separation efficiency of photogenerated electron-hole pairs, inducing their higher photocatalytic activity under blue LED light. In addition, Er-doped ZnO/CuS/Au core-shell nanowires exhibit high sensitivity, a low detection limit (10−6 M), uniformity, recyclability, and stability of SERS performance for detected acid orange 7. [ABSTRACT FROM AUTHOR]

This present study used a simple aqueous chemical growth method to synthesize Al-doped ZnO (ZnO: Al) nanoneedles on ZnO seeds/glass substrates. The surface morphology and length of ZnO: Al nanostructures can suitably control by the concentration of aluminum sulfate. The surface-enhanced Raman scattering (SERS) effect of Ag sputtering durations on the ZnO: Al nanoneedles and the concentration of aluminum sulfate on the ZnO: Al/Ag heterostructures systematically investigated. The ZnO: Al/Ag heterostructures (2 mM aluminum sulfate and 60 s sputtering time) exhibited a more substantial enhancement, a lower detection limit (10−10 M), excellent uniformity, high reusability and stability for the SERS detection of rhodamine 6G molecule. The ZnO: Al/Ag heterostructures can also use to detect the lower concentration of melamine (10−9 M) and 5-fluorouracil (10−7 M). ZnO: Al/Ag heterostructures can provide a low-cost and straightforward manufacturing method with high enhancement, low detection limit, excellent uniformity, and reusability for the SERS applications in areas of chemical and medicine. Image 1 • A facile aqueous chemical growth method can use to grow ZnO: Al nanostructures on the ZnO seeds/glass substrates. • The morphology and length of ZnO: Al nanostructures can suitably control by the concentration of aluminum sulfate. • ZnO: Al/Ag heterostructures exhibited excellent SERS performance in the detection of rhodamine 6G molecule. • ZnO: Al/Ag heterostructures can use to detect the lower concentration of melamine (10−9 M) and 5-fluorouracil (10−7 M). [ABSTRACT FROM AUTHOR]

ZnO nanostructures were grown on the stainless steel mesh substrates using an aqueous chemical growth method. The different additives (such as 1,3-diaminopropane and polyethyleneimine) can be used to control the morphology of ZnO nanostructures. ZnO nanowires exhibit very prominent green emission and week UV emission from defect and band gap in the cathodoluminescence spectrum, respectively. The different morphology of ZnO nanostructures on the stainless steel mesh substrates can be used to irradiate UV light for the photocatalytic degradation of four kinds of organic pollutants, such as methylene blue, rhodamine 6G, methyl orange, and 4-nitrophenol. The ZnO nanowires can provide a higher surface-to-volume ratio and stronger defect emission, resulting in their highest photocatalytic performance in 10 W UV light irradiation. The ZnO nanowire arrays on the stainless steel mesh substrates provide a large-scale, facile, low-cost, high surface area, and high photocatalytic efficiency, which shall be of significant value for practical applications of the decomposition of environment pollutants and reusing of wastewater treatment. [ABSTRACT FROM AUTHOR]

• Ag nanoparticles-Ga-doped ZnO nanoneedles-pyramidal silicon hybrids were prepared as SERS substrates. • The hybrids exhibited excellent SERS performance with good uniformity and stability. • SERS signal enhancement of up to 6.52 × 108 was observed in the detection of R6G. • Ag/Ga-doped ZnO/pyramidal silicon substrate can be facilely self-cleaned using UV light. • Ag/Ga-doped ZnO/pyramidal silicon substrate can use to detect different types of drugs with low detection limits. [Display omitted] High-performance surface-enhanced Raman scattering (SERS)-active substrate can be fabricated by deposited silver (Ag) nanoparticles on the pyramidal silicon with Ga-doped zinc oxide (ZnO) nanoneedles. Properly manufacturing a ZnO seed layer on pyramidal silicon may be beneficial to grow vertically aligned Ga-doped ZnO nanoneedles to deposit silver nanoparticles uniformly. Suitable silver sputtering duration on the Ga-doped ZnO nanoneedles has been upgraded to produce the most remarkable SERS effect in rhodamine 6G (R6G) molecules. SERS results show that Ag/Ga doped ZnO/pyramidal silicon is better than Ag/pyramidal silicon and Ag/silicon substrates. This phenomenon is attributed to Ag/Ga-doped ZnO/pyramidal silicon geometry, providing more hot spots and surface-active sites to exhibit high SERS enhancement, good reproducibility, and long-term stability. Ag/Ga doped ZnO/pyramidal silicon can also provide excellent SERS active substrates for detecting different types of drugs with low detection limits, such as amoxicillin (10−10 M) and irinotecan (10−7 M). [ABSTRACT FROM AUTHOR]

In this study, ZnO nanotubes, ZnO/ZnS core-shell nanorods, and ZnO/ZnS nanotubes were fabricated. To fabricate different types of ZnO-based nanocomposites, the central area of the ZnO nanorods was etched by a KCl solution and the outward shell was sulfurized to form ZnS/ZnO shell structures. Surface morphologies and material properties of the various nanostructures were examined by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Transmission X-ray Microscopy (TXM). Multiple material characterizations including X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), and Photoluminescence (PL) were performed. Results indicate that larger surface areas and higher defect concentrations can be obtained by the etching of ZnO nanorods. ZnO/ZnS nanotubes formed by sulfurization roughen the shell surface and mitigate defects. Results indicate that ZnO and ZnO/ZnS nanotubes show promise for future sensing device applications. [ABSTRACT FROM AUTHOR]

In this study, ZnO nanorods (NRs) were grown using solgel/hydrothermal methods on SiO 2 , carbon nanotube (CNT)/SiO 2 , and graphene/SiO 2 substrates to form hydrogen gas sensing chips. Results indicate that ZnO NRs/CNT/SiO 2 structures exhibited better H 2 sensing performance than the other two types of ZnO NRs-based structures. Furthermore, multiple electrical and material characterizations show that ZnO NRs/CNT/SiO 2 structures had a stronger (002) crystalline phase, with nanorod fusion near the bottom, and more oxygen-related defects. Owing to their small size, simple fabrication, and low cost, the ZnO NRs/CNT/SiO 2 based H 2 gas sensors are promising for future industrial H 2 sensing applications. [ABSTRACT FROM AUTHOR]