Aqueous Chemical Growth Technique Research Articles

Enhanced photocatalytic activity of graphene oxide incorporated ZnO nanorods doped with post-transition metals

Photocatalytic activity of graphene oxide incorporated pure and selected post-transition metal doped zinc oxide nanorods were investigated for the degradation of methylene blue dye. Thin film seed layers were deposited on microscopic glass slides using an automated spray pyrolysis technique at a substrate temperature of 425 °C. Aluminium, gallium, and indium were the metals used for doping. Graphene oxide content in the precursor solution was fixed at 0.00375 g/L. Nanorods of the aforesaid transparent conducting oxide materials were grown by aqueous chemical growth technique, vertically over the respective as-deposited seed layers. Structural and optical properties of the nanorods were studied. Growth of the vertical nanorods was confirmed by scanning electron microscopy. All the nanorod samples were utilized as catalysts for repeated cycles of photocatalysis and the graphene oxide incorporated indium doped zinc oxide nanorod was found to be an efficient and stable photocatalyst by degrading 96.1 % of methylene blue dye in 180 min under simulated solar irradiation.

Obtaining Nanostructured ZnO onto Si Coatings for Optoelectronic Applications via Eco-Friendly Chemical Preparation Routes.

Although the research on zinc oxide (ZnO) has a very long history and its applications are almost countless as the publications on this subject are extensive, this semiconductor is still full of resources and continues to offer very interesting results worth publishing or warrants further investigation. The recent years are marked by the development of novel green chemical synthesis routes for semiconductor fabrication in order to reduce the environmental impacts associated with synthesis on one hand and to inhibit/suppress the toxicity and hazards at the end of their lifecycle on the other hand. In this context, this study focused on the development of various kinds of nanostructured ZnO onto Si substrates via chemical route synthesis using both classic solvents and some usual non-toxic beverages to substitute the expensive high purity reagents acquired from specialized providers. To our knowledge, this represents the first systematic study involving common beverages as reagents in order to obtain ZnO coatings onto Si for optoelectronic applications by the Aqueous Chemical Growth (ACG) technique. Moreover, the present study offers comparative information on obtaining nanostructured ZnO coatings with a large variety of bulk and surface morphologies consisting of crystalline nanostructures. It was revealed from X-ray diffraction analysis via Williamson–Hall plots that the resulting wurtzite ZnO has a large crystallite size and small lattice strain. These morphological features resulted in good optical properties, as proved by photoluminescence (PL) measurements even at room temperature (295 K). Good optical properties could be ascribed to complex surface structuring and large surface-to-volume ratios.

Enhanced luminescence property of 1 D nanorods realised by aqueous chemical growth on indium doped zinc oxide thin films

The current piece of research aims at the depiction of the adaptability of the 1 D nanorods on Zinc Oxide (ZnO) for Light Emitting Diode applications. Undoped and Indium doped ZnO films are deposited on glass substrates by Spray Pyrolysis at 425 °C. The indium doping level is varied from 1 to 4 at. % and the variation of structural, morphological and opto - electronic properties with indium doping are studied. The films with 2.5 at. % of indium doping showed better transmittance (~90%) and low electrical resistivity (1.77 × 10−2 Ωcm). 1 D nanorods have been deposited on In:ZnO thin films with better luminescence properties by Aqueous Chemical Growth (ACG) technique at various time durations. It is found that the morphology of the seed layer is the major factor determining the alignment of the nanorods. The In:ZnO 1 D nanorods deposited at 10 hours of ACG process is seen to have better electrical conductivity due to the effective networking of the nanorods. The X-Ray Diffraction analysis and X-Ray Photoelectron Spectroscopy analysis confirms the effective indium incorporation in the nanorods. The photoluminescence emission is found to depend strongly on the duration of ACG process and various defects are assigned for the emission in the visible region.

Chitosan blend iron oxide nanostructure-based biosensor for healthy & malignant tissue glucose/urea detection

A urease trapped chitosan-Fe3O4 based nano-composite biosensor of controlled morphology is successfully fabricated by applying the aqueous chemical growth technique. Final product of nanodevice was characterized by applying various techniques. Log of the concentration of various solutions (1 to 80 mM) ranged between 0.0 to 2.5 mM for urea and glucose sample and an output signal of ∼ 42 mV per decade was detected at room temperature. It disclosed the presence of chitosan composite with Fe3O4 results enhanced active surface area of sensing along with up to the mark precession, as compared to traditional biosensor for immobilization of enzymes. The current developed form of chitosan-Fe3O4 nano-composite biosensor illustrated a significant stable potentiometric response in the minimal time period. Besides, nafion/polypyrrole addition to the top surface of CH-Fe3O4 nanocomposite not only protected it from degradation but also upgraded the characteristic of sensor regarding rapid electron transfer enhancement and higher shelf life of this hybrid form of nanomaterial. The advanced form of this voltammetry implied that Ur-GLDH/CH-Fe3O4 bioelectrode is found to be very sensitive in the range of 4-120 mg/dl urea/glucose concentration and can detect as low amount as 0.4mg/dl.

Improvement in photo voltaic performance of rutile-phased TiO2 nanorod/nanoflower-based dye-sensitized solar cell

An improved dye-sensitized solar cell (DSC) of rutile-phased titanium dioxide (TiO2) electrode with increased power conversion efficiency was successfully fabricated. Rutile-phased TiO2 nanorods and nanoflowers were grown directly on fluorine-doped SnO2 (FTO) by simple aqueous chemical growth technique using one-step hydrothermal process. The solution was prepared by mixing hydrochloric acid, deionized water, and titanium butoxide used as precursor. In the preparation of DSC, both TiO2 nanorods and nanoflowers, platinum (Pt), ruthenium dye N719, and DPMII electrolyte were used as photoelectrode, counter electrode, dye solution, and liquid electrolyte, respectively. The prepared rutile-phased TiO2 nanorods and nanoflowers samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The DSCs were fabricated based on the rutile-phased titanium dioxide nanorod and nanoflower photoelectrodes. For their energy conversion efficiency, I-V characteristics and electrochemical impedance spectroscopy were studied. We also investigated the effect of cetyltrimethylammonium bromide (CTAB) reaction times 2, 5, and 10 h in the preparation of rutile-phased TiO2 nanoflowers for DSC. CTAB is one of the capping agents that cover the refine surface of nanoparticles and prevent them from coagulation or aggregation. In our final result, the combination of rutile-phased TiO2 nanorod- and nanoflower-based DSCs showed best efficiency at approximately 3.11% due to its good electron transport of TiO2 nanorods and increased surface area by the TiO2 nanoflowers that had increased dye absorption.

Inactivation of bacterial biofilms using visible-light-activated unmodified ZnO nanorods

Various zinc oxide (ZnO) nanostructures are widely used for photocatalytic antibacterial applications. Since ZnO possesses a wide bandgap, it is believed that only UV light may efficiently assist bacterial inactivation, and diverse crystal lattice modifications should be applied in order to narrow the bandgap for efficient visible-light absorption. In this work we show that even unmodified ZnO nanorods grown by an aqueous chemical growth technique are found to possess intrinsic defects that can be activated by visible light (λ = 405 nm) and successfully applied for total inactivation of various highly resistant bacterial biofilms rather than more sensitive planktonic bacteria. Time-resolved fluorescence analysis has revealed that visible-light excitation creates long-lived charge carriers (τ > 1 μs), which might be crucial for destructive biochemical reactions achieving significant bacterial biofilm inactivation. ZnO nanorods covered with bacterial biofilms of Enterococcus faecalis MSCL 302 after illumination by visible light (λ = 405 nm) were inactivated by 2 log, and Listeria monocytogenes ATCL3C 7644 and Escherichia coli O157:H7 biofilms by 4 log. Heterogenic waste-water microbial biofilms, consisting of a mixed population of mesophilic bacteria after illumination with visible light were also completely destroyed.

NiO nanoarrays of a few atoms thickness on 3D nickel network for enhanced pseudocapacitive electrode applications

The present work focuses on the development of template-free mesoporous NiO nanoarrays with large surface area grown on 3D nickel foam networks by a seed mediated aqueous chemical growth technique and subsequent annealing process. The resultant binder-free, well-aligned and vertically grown NiO nanoarrays exhibits a micron-sized planar structure as well as an ultrathin thickness (∼7 nm). The unique surface and electronic structure facilitates surface-dependent electrochemical reaction processes with no dead volume. They deliver a high capacitance of 2065 F g−1 at a current density of 16 A g−1 as a three electrode system. A specific capacitance of 1247 F g−1 is maintained at a higher current rate of 70 A g−1 with 88.9% retention after 5000 cycles. Finally, in a solid-state asymmetric supercapacitor configuration using NiO//activated carbon, the device delivers an enhanced supercapacitive performance, with an energy density of 43.5 Wh kg−1 and power density of 2.1 kW kg−1. Thus, the current research paves the way for the use of NiO nanoarrays as an electrode material for practical supercapacitor devices with higher cycling retention and rate capacity.

Interface state density distribution in Au/n-ZnO nanorods Schottky diodes

Interface states density (NSS) distribution is extracted in Au/ ZnO Schottky diodes. Nanorods of ZnO are grown on silver (Ag) using aqueous chemical growth (ACG) technique. Well aligned hexagonal–shaped vertical nanorods of a mean diameter of 300 - 450 nm and 1.3 -1.9 μm high are revealed in SEM. Gold (Au) Schottky contacts of thickness 60 nm and 1.5mm diameter were evaporated. For electrical characterization of Schottky diodes current-voltage (I-V) and capacitance-Voltage (C-V) measurements are performed. The diodes exhibited a typical non-linear rectifying behavior with a barrier height of 0.62eV and ideality factor of 4.3. Possible reasons for low barrier height and high ideality factor have been addressed. Series resistance (RS) has been calculated from forward I-V characteristics using Chueng's function. The density of interfacial states (NSS) below the conduction band (EC-ESS) is extracted using I-V and C-V measured values. A decrease in interface states density (NSS) is observed from 3.74 × 1011 − 7.98 × 1010 eV−1 cm−2 from 0.30eV - 0.61eV below the conduction band edge.

Enhanced light to electricity conversion efficiency of CdS–ZnO composite nanorod based electrochemical solar cell

Cadmium sulfide–zinc oxide composite nanorods having at least 100nm diameters were synthesized by a two-step chemical deposition technique. Polycrystalline nanorods of ZnO were grown on indium tin oxide coated quartz substrate by aqueous chemical growth technique. Cadmium sulfide was deposited on the surface of the ZnO nanorod thin film by chemical bath deposition. The X-ray diffraction results revealed the co-existence of polycrystalline CdS and ZnO, both having hexagonal structures. Neither any phase mixing nor any surface diffusion induced alloying was observed. Micro-Raman study detected a pair of optical phonons at 301cm−1 and 438cm−1 corresponding to hexagonal CdS and ZnO, respectively. An enhanced light to electricity conversion efficiency of 2.52% was recorded from CdS–ZnO photoanode based electrochemical solar cell under 0.5 sun illumination condition (50mWcm−2). We observed a significant enhancement of short circuit current of the electrochemical solar cells due to addition of ionic salt solution to the electrolyte.

Effect of Annealing on the Ultraviolet Sensing Properties of the Chemically Synthesized n-Type Nanodots of ZnO

Isolated nanodots of ZnO of at least 100 nm in size were deposited on transparent conducting substrate (Indium Tin Oxide coated quartz) by aqueous chemical growth technique. The nanodots have polycrystalline character and their crystallinity improves due to annealing in vacuum and oxygen atmosphere. The ultraviolet sensing property of the ZnO nanodot was investigated by current-voltage measurement. Under ultraviolet irradiation, the photo current was observed to be higher for the nanodots having higher volume density of point defects. Keywords: Nanodots, Atomic Force Microscope, Photocurrent, oxygen Vacancies, semiconductors, ZnO, GaAs PMT detector

GROWTH, PROPERTIES AND SENSOR APPLICATIONS OF LOW TEMPERATURE GROWN ZnO NANORODS

ZnO nanorods with the average diameter of about 60–300 nm have been grown by the low temperature aqueous chemical growth technique. The impact of growth time and reactant concentration on the morphology on ZnO structures was tested by scanning electron microscopy and photoluminescence spectroscopy. High optical quality of obtained ZnO nanorod films was evidenced by dominating free exciton transitions. The reduction of surface to volume ratio by increasing the diameter of ZnO nanorods resulted in a linear increase of excitonic luminescence intensity with respect to the defect related emission. Excellent photoluminescence properties and high surface area of ZnO nanorods can be used for the detection of organic contaminants dissolved in water. The quenching of both excitonic and defect luminescence was observed upon exposure of ZnO nanorod films to various organic contaminants.

Annealing Effects on Electrical and Optical Properties of N-ZnO/P-Si Heterojunction Diodes

The effects of post fabrication annealing on the electrical characteristics of n-ZnO/p-Si heterostructure are studied. The nanorods of ZnO are grown by aqueous chemical growth (ACG) technique on p-Si substrate and ohmic contacts of Al/Pt and Al are made on ZnO and Si. The devices are annealed at 400 and 600 °C in air, oxygen and nitrogen ambient. The characteristics are studied by photoluminescence (PL), current–voltage (I-V) and capacitance - voltage (C-V) measurements. PL spectra indicated higher ultraviolet (UV) to visible emission ratio with a strong peak of near band edge emission (NBE) centered from 375-380 nm and very weak broad deep-level emissions (DLE) centered from 510-580 nm. All diodes show typical non linear rectifying behavior as characterized by I-V measurements. The results indicated that annealing in air and oxygen resulted in better electrical characteristics with a decrease in the reverse current.

Synthesis, characterization, and growth mechanism of α-Cr 2O 3 monodispersed particles

Monodispersed spherical particles of chromium (III) oxide, α-Cr 2O 3, were successfully synthesized from a diluted solution of KCr(SO 4) 2·12H 2O using the Aqueous Chemical Growth (ACG) technique. The spherical α-Cr 2O 3 particles obtained were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy for structural, surface morphological, chemical, and physical properties, as a function of deposition time. The XRD and Raman spectroscopy showed that aging had no apparent effect on the structure of the obtained uniform fine (in the range of micron–nano-level)-spherical particles of α-Cr 2O 3. The use of SEM demonstrated that aging had a clear influence on the size and the particles size distribution. Accordingly, the time dependence of the average diameter of α-Cr 2O 3 spherical particles follows the d 3 law as required for diffusion-limited Ostwald ripening.

The origin of the red emission in n-ZnO nanotubes/p-GaN white light emitting diodes

In this article, the electroluminescence (EL) spectra of zinc oxide (ZnO) nanotubes/p-GaN light emitting diodes (LEDs) annealed in different ambients (argon, air, oxygen, and nitrogen) have been investigated. The ZnO nanotubes by aqueous chemical growth (ACG) technique on p-GaN substrates were obtained. The as-grown ZnO nanotubes were annealed in different ambients at 600°C for 30 min. The EL investigations showed that air, oxygen, and nitrogen annealing ambients have strongly affected the deep level emission bands in ZnO. It was concluded from the EL investigation that more than one deep level defect is involved in the red emission appearing between 620 and 750 nm and that the red emission in ZnO can be attributed to oxygen interstitials (Oi) appearing in the range from 620 nm (1.99 eV) to 690 nm (1.79 eV), and to oxygen vacancies (Vo) appearing in the range from 690 nm (1.79 eV) to 750 nm (1.65 eV). The annealing ambients, especially the nitrogen ambient, were also found to greatly influence the color-rendering properties and increase the CRI of the as - grown LEDs from 87 to 96.

Surface Modification of α-Fe2O3 Nanorod Array Photoanodes for Improved Light-Induced Water Splitting

ABSTRACTα-Fe2O3 nanorod arrays were fabricated by a low-temperature aqueous chemical growth (ACG) technique and followed by an annealing process. For the surface doping of α-Fe2O3 nanorods, β-FeOOH nanorods obtained via ACG were coated with a thin layer of Cr3+ precursor solution by spin coating, and then underwent the annealing treatment in air. Conducting polymer polypyrrole (PPy) decorated α-Fe2O3 nanorods were prepared by electrodeposition method using malic acid contained pyrrole aqueous solution. Primary results showed that the photocurrents of α-Fe2O3 nanorod array photoanodes were greatly enhanced by surface doping of Cr3+, as well as PPy decoration. This might be due to the retarded charge recombination and promoted surface reaction rate of photogenerated holes with water. Further investigation on surface modification of α-Fe2O3 nanorod array photoanodes is currently conducted in our group.

Growth, properties and sensor applications of low temperature grown ZnO nanorods

ZnO nanorods with the average diameter of about 60–300 nm have been grown by the low temperature aqueous chemical growth technique. The impact of growth time and reactant concentration on the morphology on ZnO structures was tested by scanning electron microscopy and photoluminescence spectroscopy. High optical quality of obtained ZnO nanorod films was evidenced by dominating free exciton transitions. The reduction of surface to volume ratio by increasing the diameter of ZnO nanorods resulted in a linear increase of excitonic luminescence intensity with respect to the defect related emission. Excellent photoluminescence properties and high surface area of ZnO nanorods can be used for the detection of organic contaminants dissolved in water. The quenching of both excitonic and defect luminescence was observed upon exposure of ZnO nanorod films to various organic contaminants.

Growth and Structure of ZnO Nanorods on a Sub-Micrometer Glass Pipette and Their Application as Intracellular Potentiometric Selective Ion Sensors.

This paper presents the growth and structure of ZnO nanorods on a sub-micrometer glass pipette and their application as an intracellular selective ion sensor. Highly oriented, vertical and aligned ZnO nanorods were grown on the tip of a borosilicate glass capillary (0.7 µm in diameter) by the low temperature aqueous chemical growth (ACG) technique. The relatively large surface-to-volume ratio of ZnO nanorods makes them attractive for electrochemical sensing. Transmission electron microscopy studies show that ZnO nanorods are single crystals and grow along the crystal’s c-axis. The ZnO nanorods were functionalized with a polymeric membrane for selective intracellular measurements of Na+. The membrane-coated ZnO nanorods exhibited a Na+-dependent electrochemical potential difference versus an Ag/AgCl reference micro-electrode within a wide concentration range from 0.5 mM to 100 mM. The fabrication of functionalized ZnO nanorods paves the way to sense a wide range of biochemical species at the intracellular level.

Intracellular ZnO Nanorods Conjugated with Protoporphyrin for Local Mediated Photochemistry and Efficient Treatment of Single Cancer Cell.

ZnO nanorods (NRs) with high surface area to volume ratio and biocompatibility is used as an efficient photosensitizer carrier system and at the same time providing intrinsic white light needed to achieve cancer cell necrosis. In this letter, ZnO nanorods used for the treatment of breast cancer cell (T47D) are presented. To adjust the sample for intracellular experiments, we have grown the ZnO nanorods on the tip of borosilicate glass capillaries (0.5 μm diameter) by aqueous chemical growth technique. The grown ZnO nanorods were conjugated using protoporphyrin dimethyl ester (PPDME), which absorbs the light emitted by the ZnO nanorods. Mechanism of cytotoxicity appears to involve the generation of singlet oxygen inside the cell. The novel findings of cell-localized toxicity indicate a potential application of PPDME-conjugated ZnO NRs in the necrosis of breast cancer cell within few minutes.

Observation of catalytic properties of CdS–ZnO composite nanorods synthesized by aqueous chemical growth technique

We have synthesized the nanorods of CdS–ZnO composite by chemical method and have investigated their structure, optical and electrical properties by suitable techniques. The X-rays diffraction results prove the co-existence of CdS and ZnO in usual hexagonal structure and no peak corresponding to any intermediate phase has been identified. The above observation has been confirmed by micro-Raman study. The photo-current action spectra of CdS–ZnO nanorods show a significant enhancement of the photo-current due to visible sensitization by surface CdS layer. In an attempt to explore the catalytic activity of CdS–ZnO, the photodegradation of 3,4-dihydroxy benzoic acid has been investigated under visible irradiation from a halogen lamp. The concentration of aqueous solution of 3,4-dihydroxy benzoic acid decreases with increase in the irradiation time which is attributed to photodegradation of the benzoic acid. A possible mechanism for the redox reactions responsible for degradation of the benzoic acid has been suggested.

Fabrication and characterization of high-brightness light emitting diodes based on n-ZnO nanorods grown by a low-temperature chemical method on p-4H-SiC and p-GaN

Light emitting diodes (LEDs) based on n-ZnO nanorods (NRs)/p-4H-SiC and n-ZnO (NRs)/p-GaN were fabricated and characterized. For the two LEDs the ZnO NRs were grown using a low temperature (<100 °C) aqueous chemical growth (ACG) technique. Both LEDs showed very bright nearly white light electroluminescence (EL) emission. The observed luminescence was a result of the combination of three emission lines composed of violet-blue, green and orange-red peaks observed from the two LEDs. Room temperature photoluminescence (PL) was also measured and consistency with EL was observed. It was found that the green and violet-blue peaks are red-shifted while the orange peak is blue-shifted in the EL measurement. It was also found that due to the effect of the GaN substrate the violet-blue peak in the EL measurement is more red-shifted in n-ZnO (NRs)/p-GaN LEDs as compared to n-ZnO (NRs)/p-4H-SiC LEDs.