Modified ZnO Nanorods Research Articles

Coffee grounds carbon quantum dots modified ZnO nanorods for Near-UV photodetectors

Near-ultraviolet photodetectors (NUV PDs) are widely used in various applications such as autonomous driving, UV radiation monitoring, and medical diagnostics. ZnO is a low-cost, high-performance semiconductor material for UV light detection. However, solution-processed ZnO thin films exhibit poor conductivity, high density of defects and insufficient light absorption, which limits the development and application of ZnO-based NUV PDs. Herein, we have developed a novel, eco-friendly, and efficient method for extracting carbon quantum dots (CQDs) from discarded coffee grounds, named as CCQDs, and successfully integrated them into ZnO nanorods (NRs) for the first time to improve NUV PDs. The CCQDs modified ZnO NRs show a boosting light scattering with an increased haze by 120.0 % in 300–420 nm, and enhanced conductivity enable a lowered dark current and a higher photo current. The resulting NUV PDs exhibits a significant improvement in the ratio of Iphoto/Idark by 3467.3 % and a relatively sizeable normalized detection (D*: 9.81 × 1010 Jones), high linear dynamic range (LDR: 65.32 dB), and low equivalent noise power (NEP: 2.88 × 10−12 W) compared to the intrinsic ZnO NRs device. The outstanding performance can be attributed to the increased light absorption, reduced defects of ZnO NRs after the modification of CCQDs, and the faster electron transfer on the ZnO NRs/CCQDs thin films. This work provides a simple method for developing low-cost, high-performance ZnO-based PDs.

Fabrication of Vertically Aligned ZnO Nanorods Modified with Dense Silver Nanoparticles as Effective SERS Substrates

Surface-enhanced Raman scattering (SERS) spectroscopy has attracted increasing attention due to its high spectral reproducibility and unique selectivity to target molecules. Here, a facile approach is proposed to prepare Ag nanoparticles modified ZnO nanorod arrays (Ag/ZnO NR arrays). Ag nanoparticles were densely decorated on the surface of ZnO nanorods through silver mirror reaction and subsequent seed-assisted electrodeposition. The prepared Ag/ZnO NR arrays can be used as a sensitive, uniform, and repeatable SERS substrate for the rapid detection of organic dye molecules and biomolecules with concentrations higher than the corresponding limits of detection (LODs). The LODs for rhodamine 6G (R6G), 4-aminothiophenol (PATP) and adenine are calculated to be 1.0 × 10−13 M, 1.6 × 10−12 M and 3 × 10−11 M, respectively. The enhancement factor (EF) of the SERS substrate is estimated to be as high as ~2.7 × 108 when detecting 10−10 M R6G. Particularly, the as-synthesized substrate exhibits high selectivity to multiple components. In addition, the fabricated Ag/ZnO NR arrays can be recycled due to their superior self-cleaning ability and can realize photocatalytic degradation of R6G in water within 1 h driven by UV light, showing that the three-dimensional recyclable SERS substrates have wide applications in environmental pollution monitoring and biomedical analysis.

Novel Au Nanoparticle-Modified ZnO Nanorod Arrays for Enhanced Photoluminescence-Based Optical Sensing of Oxygen.

Novel optical gas-sensing materials for Au nanoparticle (NP)-modified ZnO nanorod (NR) arrays were fabricated using hydrothermal synthesis and magnetron sputtering on Si substrates. The optical performance of ZnO NR can be strongly modulated by the annealing temperature and Au sputtering time. With exposure to trace quantities of oxygen, the ultraviolet (UV) emission of the photoluminescence (PL) spectra of Au/ZnO samples at ~390 nm showed a large variation in intensity. Based on this mechanism, ZnO NR based oxygen gas sensing via PL spectra variation demonstrated a wide linear detection range of 10-100%, a high response value, and a 1% oxygen content sensitivity detection limit at 225 °C. This outstanding optical oxygen-sensing performance can be attributed to the large surface area to volume ratio, high crystal quality, and high UV emission efficiency of the Au NP-modified ZnO NR arrays. Density functional theory (DFT) simulation results confirmed that after the Au NPs modified the surface of the ZnO NR, the charge at the interface changed, and the structure of Au/ZnO had the lowest adsorption energy for oxygen molecules. These results suggest that Au NP-modified ZnO NR are promising for high-performance optical gas-sensing applications.

Highly Selective Colorimetric Detection of Cu2+ Using EDTA-Complexed Chlorophyll-Copper/ZnO Nanorods with Cavities Specific to Cu2+ as a Light-Activated Nanozyme.

In this study, chlorophyll-copper (ChlCu)-modified ZnO nanorods (ChlCu/ZnO) were prepared, and then sodium ethylenediamine tetraacetate (EDTA) was used to remove part of Cu2+ in ChlCu, leaving cavities with specific adsorption activity for Cu2+ in E-ChlCu/ZnO. Appropriate EDTA treatment improved the photoactivity of ChlCu/ZnO and the adsorption selectivity to Cu2+. However, excessive EDTA treatment might lead to the collapse of the ChlCu structure, resulting in a decrease in photoactivity. The E-ChlCu/ZnO sample with 8 h of ChlCu treatment and 2 h of EDTA treatment showed optimal photoactivity. The as-prepared E-ChlCu/ZnO exhibited activity as a light-activated nanozyme, which could oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to blue under illumination, but when Cu2+ was present in the solution, this colorimetric reaction was inhibited; therefore, E-ChlCu/ZnO could be used for colorimetric detection of Cu2+. Because of the existence of specific cavities, E-ChlCu/ZnO showed excellent detection selectivity, a wide linear detection range (0-1 and 1-15 μM), and a low detection limit (0.024 μM) in the colorimetric detection of Cu2+.

Brazilein modified zinc oxide nanorods with enhanced visible light-responsive photocatalytic efficiency

Photocatalytic efficiency of ZnO nanorods has been investigated with respect to the concentration of brazilein. Brazilein modified ZnO nanorods were prepared by an impregnation process with 1.0%w/v, 2.5%w/v, and 5.0%w/v of brazilein solution. In order to correlate the variation in concentration distributions and photocatalytic performance, the phase composition, optical properties, and photo-catalytic activities of brazilein modified ZnO nanorods prepared with different brazilein concentrations have been investigated and compared to an unmodified ZnO nanorods. The photocatalytic properties were measured in terms of indigo carmine degradation under visible light irradiation. It was found that ZnO nanorods with the highest visible light-responsive photocatalytic efficiency were achieved by the modification of 5.0%w/v of brazilein resulting in indigo carmine degraded faster than the case of unmodified ZnO nanorod about 60% within 5 h.

Cu(I) complexes sensitized ZnO nanorods for photocatalytic water splitting

The earth-abundant Cu(I) is one of the promising dye-sensitized photoelectrochemical cells (DS-PECs) for sustainable energy production. We report that the heteroleptic Cu (I) complex's catalysis consisting of diphenylphosphinoaminoacetic acid and bipyridine derivatives have investigated with DS-PECs on water splitting application. HOMO-LUMO energy levels of 2,2′bipyridine Cu(I) diphenylphosphinoaminoacetic acid (Cu(L1)) 4,4′dimethyl-2,2′bipyridineCu(I)diphenyl phosphinoaminoacetic acid (Cu(L2)) are calculated with cyclic voltammetry and Uv-vis spectrometer. Both optic band gap and electrochemical band gap energy levels of Cu(I) complex indicates that Cu(L1) has a narrower band gap (2.74 eV and 2.75 eV) compared with Cu(L2) (2.86 eV and 2.79 eV). The photocatalytic hydrogen production of Cu(L1) and Cu(L2) complexes on ZnO nanorods are monitored with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in 0.5 M Na2SO4 under 100 mW cm−2 solar light irradiation. Cu(L1) modified ZnO nanorod photoelectrode indicates an utmost photocatalytic response (0.452 mA cm−2), the lowest charge transfers resistance (Rct) against to bare the ZnO and Cu(L2)/ZnO electrodes, and Cu(I) complex decreases injected electron lifetime leading to the enhanced photocatalytic response under solar light irradiation.

Ethanolamine Modified ZnO Nanorods-Based Disposable Gate-AlGaN/GaN High Electron Mobility Transistor for pH Sensing

In this paper, a pH sensor based on disposable gate-AlGaN/GaN high electron mobility transistor was proposed, where ethanolamine modified ZnO nanorods was functionalized as sensing membrane. Different from those reported before that molecular modifications were utilized as sensing probes, disposable gate with functionalized ZnO nanorods possesses higher sensitivity and better stability. Moreover, ethanolamine modified on ZnO nanorods could provide highly reproducible homogeneous and dense monolayer-coating with amines, which not only protect ZnO from being dissolved in acidic and alkaline solutions and enables the sensor conduct pH detection in a wider range, but also promotes the sensitivity of the pH sensor. The physical and pH sensing characteristics has been investigated. These results demonstrate the new proposed disposable gate-AlGaN/GaN HEMT pH sensor a promising pH sensor for practical application.

Synthesis of modified ZnO nanorods and investigation of its application for removal of phthalate from landfill leachate: A case study in Aradkouh landfill site.

In this study, zinc oxide nanorods, co-doped with iron and silver, were synthesized in a co-precipitation method. Its properties were determined using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Field Emission Scanning Electron Microscopy (FE-SEM), Brunauer-Emmett-Teller (BET), Dynamic light scattering (DLS) and X-ray photoelectron spectroscopy (XPS) analysis. The results of FE-SEM and TEM showed that zinc oxide nanoparticles synthesized and co-doped with iron and silver were formed as separate nanorods. Also, the average values of DBP and DEHP amount of phthalates in the leachate from the landfill site of Aradkouh were obtained 52.5 and 94.69mg/L, respectively. The highest removal efficiency in real samples for phthalates was found to be 52%. The highest removal efficiency of TOC were was 61%. The synthesized nanostructure could have proper efficiency in removal of phthalates from water sources under the visible light of LED lamp.

Pd Nanoparticle Adsorption ZnO Nanorods for Enhancing Photodetector UV-Sensing Performance

Ultraviolet (UV) detection is an important index, as UV rays can cause skin diseases in humans. To enhance the performance of UV photodetectors, we fabricated palladium nanoparticles(Pd NPs) modified ZnO nanorods. The surface morphology is observed by using transmission electron microscopy and transmission electron microscopy. The crystal structure is analysed by using X-ray diffraction. The optical property is investigated by using photoluminescence spectra. The I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dark</sub> of the ZnO and Pd/ZnO samples was 5.05 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> and 2.24 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> A when a 1 V bias was applied. On the other hand, the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">photo</sub> of the ZnO and Pd/ZnO samples was 2.56 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> and 4.38 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> A when the sample is illuminated UV light (365 nm). The current ratio of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">photo</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dark</sub> for the ZnO and Pd/ZnO samples was 50.8 and 1960, respectively. The enhanced performance of the Pd NPs can produce a strong electric field after light is absorbed via the localised surface plasmon resonance effect.

Experimental and Theoretical Comparable Study of Pure and Zinc Porphyrin Surface Modified ZnO Nanorod Arrays for Hybrid Solar Cell Applications

Experimental and Theoretical Comparable Study of Pure and Zinc Porphyrin Surface Modified ZnO Nanorod Arrays for Hybrid Solar Cell Applications

Experimental and Theoretical Comparable Study of Pure and Zinc Porphyrin Surface Modified ZnO Nanorod Arrays for Hybrid Solar Cell Applications

Experimental and theoretical study Porphyrin-grafted ZnO nanowire arrays were investigated for organic/inorganic hybrid solar cell applications. Two types of porphyrin – Tetra (4-carboxyphenyle) TCPP and meso-Tetraphenylporphine (Zinc-TPP)were used to modify the nanowire surfaces. The vertically aligned nanowires with porphyrin modifications were embedded in graphene-enriched poly (3-hexylthiophene) [G-P3HT] for p-n junction nanowire solar cells. Surface grafting of ZnO nanowires was found to improve the solar cell efficiency. There are different effect for the two types of porphyrin as results of Zn existing. Annealing effects on the solar cell performance were investigated by heating the devices up to 225 °C in air. It was found that the cell performance was significantly degraded after annealing. The degradation was attributed to the polymer structural change at high temperature as evidenced by electrochemical impedance spectroscopy measurements.

UV-assisted chemiresistors made with gold-modified ZnO nanorods to detect ozone gas at room temperature.

Two kinds of flexible ozone (O3) sensors were obtained by placing pristine ZnO nanorods and gold-modified ZnO nanorods (NRs) on a bi-axially oriented poly(ethylene terephthalate) substrate. The chemiresistive sensor is operated at typically 1V at room temperature under the UV-light illumination. The ZnO nanorods were prepared via a hydrothermal route and have a highly crystalline wurtzite structure, with diameters ranging between 70 and 300nm and a length varying from 1 to 3μm. The ZnO NRs were then coated with a ca. 10nm gold layer whose presence was confirmed with microscopy analysis. This sensor is found to be superior to detect ozone at a room temperature. Typical figures of merit include (a) a sensor response of 108 at 30ppb ozone for gold-modified ZnO NRs, and (b) a linear range that extends from 30 to 570ppb. The sensor is stable, reproducible and selective for O3 compared to other oxidizing and reducing gases. The enhanced performance induced by the modification of ZnO nanorods with thin layer of gold is attributed to the increased reaction kinetics compared to pristine ZnO NRs. The sensing mechanism is assumed to be based on the formation of a nano-Schottky type barrier junction at the interface between gold and ZnO. Graphical abstract Room temperature, flexible UV-enhanced gold modified ZnO nanorods can detect ppb levels of ozone.

Post-treatment with ZnFe2O4 nanoparticles to improve photo-electrochemical performance of ZnO nanorods based photoelectrodes

The ZnFe2O4 nanoparticles (ZNF NPs) modified ZnO nanorods (NRs) have proven to be an effective strategy to enhance photoelectrochemical water splitting applications. Hierarchical ZNF/ZnO NRs with ZnO NRs and ZNF NPs were successfully prepared by a facile sol-gel spin coating and hydrothermal method. Noticeably, the wettability of ZNF/ZnO nanostructures can be modified by changing the immersion time in ZNF NPs solution. The bare ZnO NRs showed a photocurrent density of 0.10 mA/cm2 for potential value of 0.5V vs. Ag/AgCl. In contrast, ZNF/ZnO nanostructured samples showed an enhanced linear increase of the photocurrent density of 1.15 mA/cm2 with an applied potential of 0.5V. An optimum amount of ZNF NPs on the ZnO NRs enhanced the photocurrent density more than 10 times and the photo-conversion efficiency more than 10 times compared to those of the bare ZnO NRs. This optimized sample has a lower charge recombination rate due to increase in transition decay time by 2 times compared to bare ZnO NRs samples. The photocurrent enhancement was induced by increase of photo-generated electron–hole separation and improved charge transfer of photo-generated carriers, which reduces recombination and hence can be applied for photo-electrochemical water splitting application.

Bismuth oxysulfide modified ZnO nanorod arrays as an efficient electron transport layer for inverted polymer solar cells

Vertically aligned zinc oxide nanorod arrays (ZnO NRAs) are expected to provide a direct and stable electron transport pathway in polymer solar cells (PSCs) so as to enhance charge carrier collection and transport.

The Effect of CTAB addition in ZnO Nanorods Optical Properties

ZnO nanorods have been successfully synthesized using precursor of zinc nitrate tetrahydrate and cetyltrimethylammonium bromide (CTAB) as the surfactant. The composition adopted is specified by the ratio of Zn(NO3)2·4H2O:CTAB = 1:0, 1:1, 1:2, and 1:3 (w/w) using hydrothermal method at temperature of 180 °C for 24 hours. The resulted ZnO nanorods were characterized by X-Ray Diffraction (XRD), Transmission electron microscopy (TEM) and UVVis Spectrophotometer. The presence of CTAB addition was found to increase the crystal size. The TEM characterization results showed the formation of homogeneous rods in nano scale. Modified ZnO nanorods improved optical properties, attaining a band gap energy of ∼2.9 eV. The transmittance increases and the reflectance decreases with increasing CTAB.

Nonenzymatic flexible field-effect transistor based glucose sensor fabricated using NiO quantum dots modified ZnO nanorods

Herein, we fabricated nonenzymatic flexible field-effect transistor (f-FET) based glucose sensor using nickel oxide quantum dots (NiO QDs) modified zinc oxide nanorods (ZnO NRs). The ZnO NRs surfaces were coated with NiO QDs using radio frequency (RF) magnetron sputtering to enhance the electrocatalytic feature and the surface area of ZnO NRs. Under physiological conditions (pH 7.4), the nonenzymatic f-FET glucose sensor shows two linear ranges of 0.001–10mM and 10–50mM with the high sensitivity of 13.14μAcm−2mM−1 and 7.31μAcm−2mM−1, respectively, along with good selectivity, stability and repeatability during glucose detection. The examination of human whole blood and serum samples reveal that the nonenzymatic f-FET based glucose sensor is capable of measuring glucose concentration efficiently in the presence of interfering species and thus can be offered as a promising device for further applications in clinical and non-clinical fields.

Fabrication of NiO quantum dot-modified ZnO nanorod arrays for efficient photoelectrochemical water splitting

NiO quantum dot (QD)-modified ZnO nanorod arrays with enhanced photoelectrochemical activity under simulated sunlight were prepared via hydrothermal and drop-drying methods. The results show an obviously decreases in the PL emission intensity and UV-to-Visible emission ratio in NiO QD-modified ZnO, indicating that the recombination of the photogenerated charge carrier is greatly inhibited in the heterojunction. Photocurrent density of the QD-modified nanorod photoanode reaches four times higher than its dark current density; the difference between the photo and dark current densities of QD-modified nanorod electrode is nearly two times higher than that of nanorod electrode. NiO QD-modified ZnO nanorods exhibit excellent photoelectrocatalytic activity owing to their large specific surface area and high separation efficiency of photogenerated electron–hole pairs. This study provides a promising strategy for fabricating highly efficient photoanodes for water splitting by configuring a QD-composed p–n junction.

Performance improvement of dual processed perovskite solar cell-acid-modified ZnO nanorods with Cl-doped light harvesting layer

Effect of ZnO nanorod surface on fabricating the perovskite solar cell and its performance were studied. Varied thickness of ZnO nanorod arrays with rough surface condition were achieved through the control of hydrothermal growth time and acid treatment. Samples based on modified ZnO nanorod arrays exhibit an impressive increase on the open-circuit voltage (Voc) and fill factor (FF) compared with the untreated ones. Further research onto the surface topography and electrochemical impedance spectroscopy test indicates that the improvement should be attributed to the suppression of the charge recombination rate at the ZnO nanorod/CH3NH3PbI3 interface. In order to enhance the short-circuit current density (Jsc) performance one step further, Cl-doped perovskite crystal was introduced into the cell. Because of its longer electron diffusion length, an impressive Jsc is received. The final combination of the two methods with the optimized thickness of the ZnO nanorod brought a total power conversion efficiency of 13.3% together with Voc~0.92 V, Jsc~23.1 mA/cm2, and FF~63%. This work highlights the importance of the surface morphology of the electron transport layer and its interface contact with the light absorbing layer in a solar cell structure. Copyright © 2017 John Wiley & Sons, Ltd.

Copper-doped modified ZnO nanorods to tailor its light assisted charge transfer reactions exploited for photo-electrochemical and photo-catalytic application in environmental remediation

The amount of dopant concentration, alongwith the choice of dopant, is one of the most conducive factor for the favourable outcome for light driven activities of a material. The present paper reports on the synthesis of zinc oxide nanorods doped with different concentrations of copper (Cu–ZnO) by simple, low-cost mechanical assisted thermal decomposition process. The as synthesized samples were tested for visible light driven photo-electrochemical (PEC) and photocatalytic activities on various hazardous dyes using methylene blue (MB), methyl orange and mixed green dye (methyl thymol blue + methylene blue). The study helped us to reveal that highest degradation efficiency was achieved for Cu concentration of 5% in ZnO on MB (91.1% degradation in 40 min). Compared to pure ZnO, the photoactivity of 5% Cu–ZnO composites shows higher photodegradation of dyes. Moreover, the photocatalytic results were found consistent with PEC studies which showed maximum current generation of +9.4 mA for 5% Cu–ZnO (carried out under dark and illumination condition). The mechanism for this enhanced photoactivity has been proposed based on the relationship established between oxygen vacancies and defects generation in the material due to different doping concentrations that directly influence its photocatalytic efficiency.

Cellular-membrane inspired surface modification of well aligned ZnO nanorods for chemosensing of epinephrine

Modified ZnO nanorods array to form a chemical sensor for neurotransmitters. The interspaces between the nanorods offer highly efficient immobilization of the lipid membrane containing the calixarene, which act as receptor molecule.