Single-crystalline ZnO Nanosheets Research Articles

High selectivity and sensitivity gas sensors to n-butanol based on Ni-doped ultra-thin porous single-crystalline ZnO nanosheets

Ni doped porous single-crystalline (PSC) ZnO nanosheets were successfully synthesized through a facile wet-chemical method. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrum (EDS). It can be found that the Ni doped PSC ZnO nanosheets with a few micrometers in length and 8–10 nm in thickness. The gas sensing properties of the Ni doped PSC ZnO nanosheets were systematically investigated. And the results reveal that the 2 at% Ni doped PSC ZnO nanosheets shows dramatically high sensitivity and selectivity for the detection of n-butanol compared to the performance of pure ZnO nanosheets. The as-prepared products combined the advantages of porous structure, single-crystalline, and ultra-thin thickness, and Ni doping, which definitely resulted in high sensing performance and selectivity property in n-butanol detection. Therefore, the doping of Ni into PSC ZnO nanosheets may be a promising method to develop advanced nanomaterials for the practical application of n-butanol detection in complex gas atmosphere.

Controllable growth of single-crystalline zinc oxide nanosheets under ambient condition toward ammonia sensing with ultrahigh selectivity and sensitivity

To date, the synthesis of crystalline ZnO nanostructures was often performed under high temperatures and/or high pressures with tiny output, which limits their commercial applications. Herein, we report the progress on synthesizing single-crystalline ZnO nanosheets under ambient conditions (i.e., room temperature (RT) and atmospheric pressure) based on a sonochemistry strategy. Furthermore, their controllable growth is accomplished by adjusting the pH values of solutions, enabling the tailored crystal growth habits on the polar-charged faces of ZnO along c-axis. As a proof of concept for their potential applications, the ZnO nanosheets exhibit highly efficient performance for sensing ammonia at RT, with ultrahigh sensitivity (S = 610 at 100 ppm), excellent selectivity, rapid detection (response time/recover time = 70 s/4 s), and outstanding detection limit down to 0.5 ppm, superior to those of all pure ZnO nanostructures and most ZnO-based composite counterparts ever reported. The present work might open a door for controllable production of ZnO nanostructures under mild conditions, and facilitate the exploration of modern gas sensors for detecting gaseous molecules at RT, which underscores their potential toward practical applications in opto-electronic nanodevices.

Memristive Behavior Enabled by Amorphous-Crystalline 2D Oxide Heterostructure.

The emergence of memristive behavior in amorphous-crystalline 2D oxide heterostructures, which are synthesized by atomic layer deposition (ALD) of a few-nanometer amorphous Al2 O3 layers onto atomically thin single-crystalline ZnO nanosheets, is demonstrated. The conduction mechanism is identified based on classic oxygen vacancy conductive channels. ZnO nanosheets provide a 2D host for oxygen vacancies, while the amorphous Al2 O3 facilitates the generation and stabilization of the oxygen vacancies. The conduction mechanism in the high-resistance state follows Poole-Frenkel emission, and in the the low-resistance state is fitted by the Mott-Gurney law. From the slope of the fitting curve, the mobility in the low-resistance state is estimated to be ≈2400 cm2 V-1 s-1 , which is the highest value reported in semiconductor oxides. When annealed at high temperature to eliminate oxygen vacancies, Al is doped into the ZnO nanosheet, and the memristive behavior disappears, further confirming the oxygen vacancies as being responsible for the memristive behavior. The 2D heterointerface offers opportunities for new design of high-performance memristor devices.

Unit Cell Level Thickness Control of Single-Crystalline Zinc Oxide Nanosheets Enabled by Electrical Double-Layer Confinement.

Ionic layer epitaxy (ILE) has recently been developed as an effective strategy to synthesize nanometer thick 2D materials with a nonlayered crystal structure, such as ZnO. The packing density of the amphiphilic monolayer is believed to be a key parameter that controls the nanosheet nucleation and growth. In this work, we systematically investigated the growth behavior of single-crystalline ZnO nanosheets templated at the water-air interface by an anionic oleylsulfate monolayer with different packing densities. The thicknesses of ZnO nanosheets were tuned from one unit cell to four unit cells and exhibited good correlation with the width of Zn2+ ion concentration zone (the Stern layer) underneath the ionized surfactant monolayer. Further analysis of the nanosheet sizes and density revealed that the nanosheet growth was dominated by the steric hindrance from the surfactant monolayer at lower surface pressure, while the nucleation density became the dominating factor at higher surface pressure. The ZnO nanosheets exhibited a decreasing work function as the thickness reduced to a few unit cells. This research validated a critical hypothesis that the nanosheet growth is self-limited by the formation of a double layer of ionic precursors. This work will open up a new way toward controlled synthesis of novel 2D nanosheets from nonlayered materials with a thickness down to one unit cell.

Trimethylamine Sensors Based on Au-Modified Hierarchical Porous Single-Crystalline ZnO Nanosheets.

It is of great significance for dynamic monitoring of foods in storage or during the transportation process through on-line detecting trimethylamine (TMA). Here, TMA were sensitively detected by Au-modified hierarchical porous single-crystalline ZnO nanosheets (HPSCZNs)-based sensors. The HPSCZNs were synthesized through a one-pot wet-chemical method followed by an annealing treatment. Polyethyleneimine (PEI) was used to modify the surface of the HPSCZNs, and then the PEI-modified samples were mixed with Au nanoparticles (NPs) sol solution. Electrostatic interactions drive Au nanoparticles loading onto the surface of the HPSCZNs. The Au-modified HPSCZNs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrum (EDS), respectively. The results show that Au-modified HPSCZNs-based sensors exhibit a high response to TMA. The linear range is from 10 to 300 ppb; while the detection limit is 10 ppb, which is the lowest value to our knowledge.

Chlorobenzene sensor based on Pt-decorated porous single-crystalline ZnO nanosheets

Detection of chlorobenzene is a challenge for metal oxide gas sensors because of its stable molecule structure. In this work, Pt-decorated porous single-crystalline ZnO nanosheets (PSC ZnO NSs) were successfully synthesized via a one-pot hydrothermal method followed by a liquid phase reduction process. The morphology and structure of the as-prepared sample were well characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectrum (EDS) and ICP-MS analysis. From gas-sensing test, it can be found that the decoration of Pt nanoparticles largely enhanced the sensing performance of the PSC ZnO NSs. The Pt-decorated PSC ZnO NSs showed good response to low concentrations of chlorobenzene from 10 to 500ppb. In contrast, the Au and Ag-decorated PSC ZnO NSs had still no response to 500ppb of chlorobenzene. The enhancement sensing mechanism of Pt nanoparticle decoration has also been discussed in detail.

Novel volatile organic compound (VOC) sensor based on Ag-decorated porous single-crystalline ZnO nanosheets

Novel volatile organic compound (VOC) sensor based on Ag-decorated porous single-crystalline ZnO nanosheets

New Strategy for Rapid Detection of the Simulants of Persistent Organic Pollutants Using Gas Sensor Based on 3-D Porous Single-Crystalline ZnO Nanosheets

It is significant to detect the persistent organic pollutants (POPs) in an environment for both human health and environmental risk assessment. However, most of the current analytical techniques require complicated and tedious processes and are time consuming. Semiconducting metal-oxide sensors are predominant solid-state gas detecting devices for domestic, commercial, and industrial application. Here, combing both the advantages of instrument analytical methods and the metal-oxide sensors, a gas chromatography column was placed in front of a metal-oxide sensor to separate POP simulants from a mixture. The metal-oxide sensor was used to detect the separated sample. To improve the sensitivity, 3D porous single-crystalline ZnO nanosheets (PSCZNs) were synthesized by a one-pot hydrothermal method followed by an annealing treatment. Then, the as-prepared 3D PSCZN-based sensors were exploited to couple with gas chromatography column. The simulants of POPs were used to assess the as-prepared sensor and chromatography column coupled measurement method. The experiment results showed a promise for rapid detection of POPs by metal-oxide sensors.

Sub-ppb detection of acetone using Au-modified flower-like hierarchical ZnO structures

Flower-like hierarchical ZnO structures assembled by porous single-crystalline nanosheets were firstly synthesized by a one-pot wet-chemical method followed by an annealing treatment. Then, polyethylenimine (PEI) was used to modify the flower-like hierarchical ZnO structures followed by anchoring Au nanoparticles (NPs) on their surface through electrostatic interactions. The Au-modified flower-like hierarchical ZnO structures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectrum (EDS). It can be found that Au NPs with a mean diameter of 12nm was uniformly modified on the surface of the porous single-crystalline ZnO nanosheets. The as-prepared products exhibited a good response to acetone with a linear range of 0.5–100ppb under the optimized operating temperature of 300°C. The lowest detection concentration was 0.5ppb, which is the lowest detection limit to our knowledge.

Ag-decorated ultra-thin porous single-crystalline ZnO nanosheets prepared by sunlight induced solvent reduction and their highly sensitive detection of ethanol

Using a solvent reduction method, Ag nanoparticles were successfully decorated onto ultra-thin porous single-crystalline (UTPSC) ZnO nanosheets which were synthesized through a one-pot wet-chemical method followed by an annealing treatment. The as-prepared products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrum (EDS), X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS) and photoluminescence (PL) measurements. It can be found that the UTPSC ZnO nanosheets with a few micrometers in length and 8–10nm in thickness were uniformly coated with Ag nanoparticles. The as-prepared products combined the advantages of porous structure, single-crystalline, ultra-thin thickness and Ag decoration, which definitely resulted in a dramatically sensing performance in ethanol detection. The lowest detection concentration was 1ppb, which is the lowest detection limit to our knowledge. It is expected that the Ag-decorated UTPSC ZnO nanosheets may provide a new pathway to develop advanced nanomaterials for the application of trace gas detection.

Flower-like hierarchical structures consisting of porous single-crystalline ZnO nanosheets and their gas sensing properties to volatile organic compounds (VOCs)

Flower-like hierarchical structures consisting of porous single-crystalline ZnO nanosheets (FHPSCZNs) were synthesized by a one-pot wet-chemical method followed by an annealing treatment, which combined the advantages between flower-like hierarchical structure and porous single-crystalline structure. XRD, SEM and HRTEM were used to characterize the synthesized FHPSCZN samples. The sensing properties of the FHPSCZN sensor were also investigated by comparing with ZnO powder sensor, which exhibited higher response and shorter response and recovery times. The sensing mechanism of the FHPSCZN sensor has been further analyzed from the aspects of electronic transport and gas diffusion.

A facile one-step method for synthesising a parallelogram-shaped single-crystalline ZnO nanosheet

a b s t r a c t ZnO nanosheets are found to be useful in many fields such as sensors and electronics. Non-uniformshaped ZnO nanosheets are synthesised using several methods; moreover, uniformly shaped ones are less studied. Here, we report on a simple one-step method to synthesise parallelogram-shaped singlecrystalline ZnO nanosheets. By controlling the reaction of Zn(NO3)2 and hexamethylenetetramine (HMT) in ethanol, average 30 nm-thick nanosheets with a high aspect ratio of 1:100 were obtained. The parallelogram angles were between 97 ◦ and 99 ◦ . Transmission electron microscopy (TEM) diffraction and X-ray diffraction (XRD) showed that the nanosheets were wurtzite-structured single-crystalline ZnO. Moreover, a growth mechanism of these parallelogram nanosheets is suggested based on the experimental results. These results suggest a new simple solution process to synthesise uniformly shaped ZnO nanosheets allowing large-scale production to be employed.

Highly Enhanced Acetone Sensing Performances of Porous and Single Crystalline ZnO Nanosheets: High Percentage of Exposed (100) Facets Working Together with Surface Modification with Pd Nanoparticles

Porous and single crystalline ZnO nanosheets, which were synthesized by annealing hydrozincite Zn(5)(CO(3))(2)(OH)(6) nanoplates produced with a water/ethylene glycol solvothermal method, are used as building blocks to construct functional Pd-ZnO nanoarchitectures together with Pd nanoparticles based on a self-assembly approach. Chemical sensing performances of the ZnO nanosheets were investigated carefully before and after their surface modification with Pd nanoparticles. It was found that the chemical sensors made with porous ZnO nanosheets exhibit high selectivity and quick response for detecting acetone, because of the 2D ZnO nanocrystals exposed in (100) facets at high percentage. The performances of the acetone sensors can be further improved dramatically, after the surfaces of ZnO nanosheets are modified with Pd nanoparticles. Novel acetone sensors with enhanced response, selectivity and stability have been fabricated successfully by using nanoarchitectures consisting of ZnO nanosheets and Pd nanoparticles.

Synthesis of ZnO Nanosheets by Microwave Thermal Vapor Method

Two-dimensional single-crystalline ZnO nanosheets have been successfully synthesized in high yield from a mixture of ZnO and graphite powders via a microwave thermal vapor process. Morphological analysis indicates that the widths and thickness of the nanosheets are in the range of several to tens of microm and 20-80 nm, respectively. ZnO nanosheets grew along the [0001] and [2110] directions, and the width-to-thickness ratio of the nanosheets could reach up to 1,000. The room temperature photoluminescence revealed that the ZnO nanosheets exhibited a weak ultraviolet (UV) emission at approximately 378 nm and a strong green emission at approximately 505 nm.

Novel porous single-crystalline ZnO nanosheets fabricated by annealingZnS(en)0.5 (en = ethylenediamine) precursor. Application in a gas sensor for indoor air contaminant detection

Novel single-crystalline ZnO nanosheets with porous structure have been fabricated by annealingZnS(en)0.5 (en = ethylenediamine) complex precursor. The morphology and structure observations performed by fieldemission scanning electronic microscopy (FESEM) and high-resolution transmissionelectron microscopy (HRTEM) indicate that numerous mesopores with a diameter of about26.1 nm distribute all through each nanosheet with a high density. The transformation ofstructure and composition of samples obtained during thermal treatment processes wereinvestigated by x-ray diffraction (XRD), x-ray photoelectron spectrometry (XPS),thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) absorptionspectroscopy. The formation mechanism of the porous structure is proposed. For indoor aircontaminant detection in which formaldehyde and ammonia are employed as targetgases, the as-prepared ZnO nanosheets were applied for the fabrication of gassensors. It was found that the as-fabricated sensors not only exhibit highly sensitiveperformance, e.g., high gas-sensing responses, short response and recovery time, but alsopossess significant long-term stability. It is indicated that these ZnO nanostructurescould promisingly be applied in electronic devices for environmental evaluation.

Composition fluctuation induced growth of Al:ZnO rectangular nanorod arrays

Arrays of single-crystalline Al doped ZnO rectangular nanorods were synthesizedand nucleated from single-crystalline ZnO nanosheets by thermal chemical vapordeposition. The rectangular nanorods were grown from the periodic thicker regionsof the nanosheets, associated with Al concentration fluctuation and evidencedfrom electron energy loss spectroscopy. High-resolution transmission electronmicroscopy also shows variations in the lattice constant and dislocations at theinterface due to lattice strain. The composition modulation induced by dopingmay serve as a driving force for creating interesting nanostructures with tunableproperties.