Drop-coating Method Research Articles

A functional material based photodiode for solar tracking systems

To prepare phosphotungstic acid (PTA) thin film was used drop-coating method. The film was dropped on p-Si having ohmic contact. The electrical and photovoltaic properties the fabricated Al/p-Si/phospotungstic acid(PTA)/Al photodiode were investigated. The current-voltage (I-V) measurements were carried out under dark and various illumination intensities. Under illumination, the photocurrent of the photodiode was found to be higher than the dark current. The prepared photodiode exhibited photovoltaic behavior. Also, the transient photocurrent measurement confirms that the photocurrent is sensitive to the illumination intensities. In addition, the capacitance/conductance-voltage (C/G-V) measurements were studied in the frequency range of 10kHz to 1MHz. The capacitance decreases with increasing frequency, suggesting a continuous distribution of interface states. As result, the prepared photodiode can be used in optoelectronic device applications.

Effect of the Fabrication Parameters of the Nanosphere Lithography Method on the Properties of the Deposited Au-Ag Nanoparticle Arrays.

The nanosphere lithography (NSL) method can be developed to deposit the Au-Ag triangle hexagonal nanoparticle arrays for the generation of localized surface plasmon resonance. Previously, we have found that the parameters used to form the NSL masks and the physical methods required to deposit the Au-Ag thin films had large effects on the geometry properties of the nanoparticle arrays. Considering this, the different parameters used to grow the Au-Ag triangle hexagonal nanoparticle arrays were investigated. A single-layer NSL mask was formed by using self-assembly nano-scale polystyrene (PS) nanospheres with an average radius of 265 nm. At first, the concentration of the nano-scale PS nanospheres in the solution was set at 6 wt %. Two coating methods, drop-coating and spin-coating, were used to coat the nano-scale PS nanospheres as a single-layer NSL mask. From the observations of scanning electronic microscopy (SEM), we found that the matrixes of the PS nanosphere masks fabricated by using the drop-coating method were more uniform and exhibited a smaller gap than those fabricated by the spin-coating method. Next, the drop-coating method was used to form the single-layer NSL mask and the concentration of nano-scale PS nanospheres in a solution that was changed from 4 to 10 wt %, for further study. The SEM images showed that when the concentrations of PS nanospheres in the solution were 6 and 8 wt %, the matrixes of the PS nanosphere masks were more uniform than those of 4 and 10 wt %. The effects of the one-side lifting angle of substrates and the vaporization temperature for the solvent of one-layer self-assembly PS nanosphere thin films, were also investigated. Finally, the concentration of the nano-scale PS nanospheres in the solution was set at 8 wt % to form the PS nanosphere masks by the drop-coating method. Three different physical deposition methods, including thermal evaporation, radio-frequency magnetron sputtering, and e-gun deposition, were used to deposit the Au-Ag triangle hexagonal periodic nanoparticle arrays. The SEM images showed that as the single-layer PS nanosphere mask was well controlled, the thermal evaporation could deposit the Au-Ag triangle hexagonal nanoparticle arrays with a higher quality than the other two methods.

A Facile Approach to Preparing Molecularly Imprinted Chitosan for Detecting 2,4,6-Tribromophenol with a Widely Linear Range

The environmental pollution of 2,4,6-tribromophenol (TBP) has attracted attention. Based on an urgent need for the better provision of clean water, in situ determination of TBP is of great importance. Here, a facile and effective approach for detecting TBP is developed, based on coupling molecular imprinting technique with electrodeposition of chitosan (CS) on the gold electrode. The TBP imprinting CS film was fabricated by using CS as functional material and TBP as template molecule. The experiments show that the morphologies and electrochemical properties of the imprinted film sensor was different from non-imprinted film electrode. The current of the imprinted film was linearly proportional to the TBP concentration, with a wide linear range of 1.0 × 10−7 mol•L−1 to 1.0 × 10−3 mol•L−1. By selecting drop-coating method as a reference for controlled trials with the same functional material, the results illustrated that the electrodeposition enjoyed a widely linear range advantage.

MoS2 Nanosheets Functionalized Composite Mixed Matrix Membrane for Enhanced CO2 Capture via Surface Drop-Coating Method.

Molybdenum disulfide (MoS2) is a graphene-like two-dimensional inorganic material, which has been used for the first time as an inorganic nanofiller to prepare a composite mixed matrix membrane to separate CO2 and N2. Polysulfone (PSf) was used as a support substrate and poly(dimethylsiloxane) (PDMS) was used as the gutter layer. The selective layer was prepared by mixing a CO2-philic copolymer Pebax 1657 with MoS2 nanosheets to enhance CO2 permeance. In addition, a simple drop-coating and evaporation method was developed to prepare the selective layer. Both permeability and selectivity of the MoS2-Pebax membrane have exceeded the pristine Pebax membrane. The permeability and selectivity reached to the maximum values of 64 Barrer and 93, respectively, at 0.15 wt % MoS2 nanosheets loadings. This result has been on the Robeson's upper bound line. The membrane also showed higher stability. The separation mechanism of the membrane is based on the well-known solution-diffusion mechanism. In addition, the stronger adsorption energy of MoS2 nanosheets to CO2 than N2 also provides the enhancement of gas selectivity.

Synthesis and Characteristics of FePt Nanoparticle Films Under In Situ-Applied Magnetic Field

In situ external magnetic field was applied during the synthesis of FePt nanoparticles via a chemical solution method. FePt nanoparticle films were prepared on Si by a drop-coating method with and without a magnetic field. Annealing at 700 °C in reductive atmosphere was explored to obtain ferromagnetic FePt L10 phase. The effect of in situ-applied magnetic field on the structure, morphology, and magnetic properties of FePt nanoparticle films was characterized. It is found that the applied magnetic field during the chemical synthesis of FePt nanoparticles plays a key role in the crystallinity and magnetic property of FePt nanoparticle films. As-synthesized FePt nanoparticles under the magnetic field are monodispersed and can be self-assembled over a larger area by a dropping method. The applied magnetic field during the synthesis of FePt nanoparticles not only significantly improves the nanoparticles’ c-axis preferred orientation but also benefits the phase transition of FePt nanoparticles from face-centered cubic to face-centered tetragonal structure during the annealing process. The FePt nanoparticle films derived under magnetic field also show some magnetic anisotropy.

Superhydrophobic and self-cleaning surfaces prepared from a commercial silane using a single-step drop-coating method

Abstract A simple and time-saving approach for preparing superhydrophobic and self-cleaning surfaces from a commercial silane, Octadecyltrichlorosilane (ODTS) is reported in this study. A solution of the silane was prepared by dissolving in hexane. Prior to film deposition, the substrates were treated with oxygen plasma etching to remove organic contaminants from the surface followed by immediate immersion in deionized (DI) water to form hydroxyl groups. A few drops of the prepared silane solution were then placed on the treated surface and allowed to dry under ambient conditions. The modified surfaces exhibited superhydrophobic behavior with advancing water contact angles (WCA) in the range 160–170° and the contact angle hysteresis (CAH) less than 10°. Surface characterization with scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed the presence of dual-scale roughness. Dust particles readily adhered to and were washed away with the rolling water droplets placed on the deposited film. Furthermore, the resulting surface was able to maintain these characteristics under the impact of a water jet. It should be mentioned that the demonstrated efficiency of this method makes it very feasible candidate for preparing self-cleaning surfaces for a variety of industrial applications.

MoSe2 nanosheet/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) composite film as a Pt-free counter electrode for dye-sensitized solar cells

A composite film of molybdenum diselenide nanosheets and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (MoSe2 NS/PEDOT:PSS) was prepared for the counter electrode (CE) of a dye-sensitized solar cell (DSSC), via a low-cost drop-coating method. The two-dimensional (2D) nanosheets of MoSe2 (MoSe2 NS) were aimed to provide the composite film not only a large amount of electrocatalytic active sites but also orientational pathways for electron transfer, from the conducting substrate of the CE to the interface at the CE electrolyte. The PEDOT:PSS acts as the conductive matrix for the composite film, and also enables multiple interfacial electron transfer pathways between the MoSe2 NS and the substrate. Owing to the combination of the advantages of both MoSe2 NS and PEDOT:PSS, the DSSC with the composite film of MoSe2 NS/PEDOT:PSS on its CE exhibited a power conversion efficiency (η) of 7.58±0.05%, which is comparable to that of the cell with a Pt CE (7.81±0.03%). The counter electrode films were characterized by scanning electron microscopy. Various electrochemical analyses, including those with cyclic voltammetry, rotating disk electrode, Tafel polarization curves, and electrochemical impedance spectroscopy, were performed intending to quantify the electrocatalytic ability of the counter electrode films; these techniques were able to precisely distinguish the functions of MoSe2 NS and PEDOT:PSS in the composite films; the former worked as an electrocatalyst and the latter as a conductive binder. Incident photon-to-current conversion efficiency (IPCE) was used to substantiate the photovoltaic parameters. When the MoSe2 NS/PEDOT:PSS composite film was coated on a flexible titanium (Ti) foil, the pertinent DSSC showed even a higher η of 8.51±0.05%, as compared to a lower η of 8.21±0.02% using the Pt-coated Ti foil CE. The results indicate the promising potential of MoSe2 NS/PEDOT:PSS composite film to replace the expensive Pt.

Nitrogen-doped graphene/molybdenum disulfide composite as the electrocatalytic film for dye-sensitized solar cells

A composite thin film of nitrogen-doped graphene and molybdenum disulfide (NGr/MoS2) was prepared via a simple drop-coating method, and used as an electrocatalytic film for the counter electrode (CE) of a dye-sensitized solar cell (DSSC). The NGr was intended for increasing the conductivity and serving as the skeleton of the composite film, while the MoS2 with remarkable electrocatalytic ability increased the effective electrocatalytic sites in the composite film. The NGr acts as the architecture framework for MoS2 sheet, which could expose the active sites on its edge, as demonstrated in scanning electron microscopy (SEM). The weight percent (wt %) of the NGr in the composite film was optimized for obtaining the best performance to the pertinent DSSC. The NGr/MoS2 composite film shows much higher electrocatalytic ability for the reduction of I−/I3−, compared to the films of bare NGr and bare MoS2. Electrocatalytic abilities of the films were estimated by cyclic voltammetry (CV), rotating disc electrode (RDE), Tafel polarization plot, and electrochemical impedance spectroscopy (EIS) analyses. The DSSC with the NGr/MoS2 CE exhibits a solar-to-electricity power conversion efficiency of 7.82%, close to 8.25% of the DSSC with a platinum CE film. The low-cost NGr/MoS2 composite film is a potential alternative to replace the expensive platinum film for use as the catalytic film on the counter electrode of a DSSC.

Fabrication of smart coatings based on wood substrates with photoresponsive behavior and hydrophobic performance

Abstract A smart coating based on wood substrate with photochromic behavior and hydrophobic performance was successfully fabricated by depositing modified organic photochromic material (PM) on wood surface using a simple drop-coating method. The prepared samples were characterized by the scanning electron microscopy (SEM) and attenuated total reflectance–Fourier transformation infrared (ATR–FTIR) techniques. The colorimetric parameters L *, a *, b *, and Δ E * of the samples under ultraviolet (UV) irradiation and visible (VIS) irradiation were measured, respectively. The response time of samples was calculated and the water contact angles (CAs) were also measured. The ATR–FTIR spectra and the SEM analysis demonstrate that PM modified by polyvinyl alcohol and the dextrin deposited on the wood surface, and the resulted coating was firmly adhered to wood by adhesion test results. With the PM concentrations increasing from 0 to 3.0%, the Δ E * values of samples remarkably increased from 3.7 to 58.2. Furthermore, the coloration time and fading time in the cross section were longer than the radial and tangential sections. Through the octadecyltrichlorosilane (OTS) treatment, the sample surface exhibited hydrophobic property with a contact angle of 134°, broadening the applications of the photoresponsive coatings in a harsh environment such as prolonged exposure under UV light or rain.

Three-Dimensional Porous NiO Nanosheets Vertically Grown on Graphite Disks for Enhanced Performance Non-enzymatic Glucose Sensor

Vertically aligned 3D porous NiO nanosheets (s-NiO) were directly grown on graphite disks (GD) by chemical bath deposition via a surfactant template under mild reaction conditions. Such porous s-NiO as active electrode materials for non-enzymatic glucose sensors manifested a much better electrocatalytic performance than most of the existing electrodes of non-enzymatic glucose sensors, including a fast response time (<1s), a high sensitivity (36.13μAmM−1mm−2), a wide linear range (up to 10.0mM) and a low detection limit (0.9μM at signal/noise ratio (S/N=3) at a potential of 0.50V (vs. Ag/AgCl). Significantly, in comparison with the porous NiO nanofilms (f-NiO) fabricated by the traditional drop-coating method, the as-prepared porous s-NiO showed better stability towards the oxidation of glucose. The high electrocatalytic performance and stability were possibly attributed to the unique 3D porous structure of s-NiO. The 3D porous s-NiO vertically grown on GD (s-NiO/GD) could be a desirable electrocatalyst for enhanced performance non-enzymatic glucose sensor.

A non-enzymatic hydrogen peroxide sensor based on vertical NiO nanosheets supported on the graphite sheet

In this study, a non-enzymatic hydrogen peroxide sensor was fabricated by directly growing vertically aligned NiO nanosheets on the graphite sheet through a simple, effective process, i.e. the surfactant-templated method. Compared with most of the reported hydrogen peroxide sensor through drop-coating method, our sensor exhibits a higher sensitivity and a good stability, resulting from the vertically aligned NiO nanosheets and method features. The as-prepared sensor exhibited a detection limit of 0.4μM (at signal/noise=3), a good reproducibility (relative standard deviation (RSD) of 3.36%), a wide linear range (up to 4.0mM) with a sensitivity of 1077μAmM−1cm−2 under the optimal conditions. Furthermore, the as-prepared sensor also showed excellent selectivity and stability for hydrogen peroxide detection. This study provides a promising electrochemical electrode for hydrogen peroxide detection by a facile method.

Determination of Lead (Pb2+) by Anodic Stripping Voltammetry Based on [Ru(NH3)6]3+/Nafion Modified Electrodes

Chemically modified [Ru(NH3)6]3+ doped Nafion® thin film was fabricated on indium tin oxide (ITO) coated glass electrodes by using the drop-coating method to detect heavy metal ions of Pb(II) in de-ionized water analyte solution via anodic stripping voltammetry (ASV). This study also determined the effect of varying the concentration of the mediator ([Ru(NH3)6]3+) on the detection of the said heavy metals. The redox mediator Ru(NH3)6]3+ used in the study was effectively incorporated and immobilized within the Nafion modified electrodes. Lead concentration in the electrolyte solution and the concentration of the redox mediator was varied to control the properties of the fabricated electrodes which utilized for heavy metal detection through ASV. The conducting properties of ITO electrodes were enhanced with the deposition of Nafion® attaining minimal interference. The stripping current peaks increased with the concentration of the heavy metal present in the solution as well as with the mediator concentration.

Chitosan-stabilized silver nanoparticles for voltammetric detection of nitrocompounds

A material comprised of chitosan-stabilized silver nanoparticles (nAg-chitosan) was prepared and characterized by UV–vis and TEM. The average diameter of the nAg obtained was 3.4nm and the particles were well dispersed in the chitosan matrix. The liquid suspension of nAg-chitosan was deposited by the drop-coating method onto a glassy carbon electrode (GCE) surface to build a voltammetric sensor (nAg-chitosan/GCE sensor). The voltammetric sensor was successfully used for the detection of nitrocompounds. Under optimized experimental conditions, a reduction peak current was observed which increased with increasing concentrations of 4-nitrophenol (4-NP) in the range of 0.07 to 2.0μmolL−1 (R2=0.994). The visual detection limit was 70nmolL−1. At this level of concentration, the sensor was not sensitive to other nitrophenols. For concentrations higher than 0.05mmolL−1 the sensor was sensitive to the three isomers, namely 2-NP, 3-NP and 4-NP. These findings indicate that the material comprised of chitosan-stabilized silver nanoparticles is a very promising candidate to assemble voltammetric sensors for practical applications in the field of analytical chemistry.

Methane reforming and water splitting using zirconia-supported cerium oxide in a volumetric receiver–reactor with different types of foam devices

Abstracts Syngas and hydrogen production from CeO 2 /ZrO 2 -coated foam devices was investigated under simulated solar radiation. Three different types of foam devices were employed in order to find the effect of the physical properties of foam material on the cyclic reaction of methane reforming and water splitting. CeO 2 /ZrO 2 -coated SiC, Ni, and Cu foam were prepared using drop-coating method. The methane reforming was performed at 900 °C for 15–25 min, and the water splitting was performed at the same temperature for 45 min. In addition, the methane reforming and water splitting were repeated ten cycles to compare the CO and H 2 yields in the methane reforming, and the H 2 yield in the water splitting. Metallic foam such as Ni and Cu showed better production yield than SiC foam and ten cycles average conversion of CeO 2 on the SiC, Ni and Cu foam were 54%, 74% and 65%, respectively. It is believed that the increased production yield of metallic foam was due to higher thermal conductivity of metallic foam and the partial reduction and re-oxidation of Ni and Cu foam.

Bipolar resistive switching characteristics in LaTiO3 nanosheets

In this work, we reported a facile approach to fabricate LaTiO3 (LTO) nanosheets for resistive switching memory applications. Different from other lanthanum titanates synthesized via solvothermal approaches, herein the unique composition ratio of La : Ti : O = 1 : 1 : 3 has been found. The drop-coating method was utilized to deposit LTO films followed by gold top electrode deposition to complete device fabrication. The pristine device was found to exhibit excellent bipolar resistance switching characteristics with resistance ON/OFF ratio of ∼100, high uniformity in switching parameters and stability at elevated temperatures as well. The origin of switching behaviour in these devices on the basis of formation and annihilation of conducting filaments was addressed.

One-step synthesis of unique silica particles for the fabrication of bionic and stably superhydrophobic coatings on wood surface

The silica particles with unique morphology and hydrophobicity have been synthesized via a drop-coating method. After this one-step sol–gel process, silica particles as well as polystyrene were employed in the bionic and stably superhydrophobic coatings on wood surface (with water contact angle of 153±1° and sliding angle less than 5±0.5°). Scanning electron microscopic (SEM) studies revealed that the composite coatings possess two dimensional hierarchical structures comprising of micron scale papilla and submicron scale granules. The synergistic effect of micron/submicron binary structure and low surface energy layer was responsible for the superhydrophobicity of wood surface. Moreover, the chemical and mechanical stabilities of treated wood have been investigated as well, and the results show that the product possesses superhydrophobic property in a wide extent, such as pure water, corrosive water under both acidic and basic conditions, and some common organic solvents. More importantly, it will offer an opportunity to extend the range of practical applications for wood resources.

Deposition of CIGS films by hydrazine-free solution method

In this paper, copper indium gallium diselenide (CIGS) thin films were deposited by a hydrazine-free solutions method. In the proposed method, acetylacetonate salts and Se powder were simply dissolved in triethylenetetramine under ambient conditions, respectively. These two solutions were mixed in a certain percentage to form the final CIGS precursor solution. CIGS films were obtained by a drop-coating method and subsequently annealed in nitrogen atmosphere. The facile formation of the precursor solution without the need to prefabricate nanoparticles enables a rapid and easy processing. The high stability of the solution in air further ensures the precursor preparation and the film deposition in ambient conditions without a glove box. The crystal structure, morphology, composition, electronic state, optical, and electrical qualities of CIGS films were characterized by XRD, SEM, EDS, XPS, UV–vis, and I–V. The easy preparation and low-cost nature of the proposed strategy make it quite attractive. The proposed synthesis strategy developed in this work may be used as a general process for low-cost deposition of CIGS film and may have bright application prospects in high-efficiency, yet low-cost, photovoltaic areas in the future.

Fabrication of superhydrophobic cotton textiles for water–oil separation based on drop-coating route

In the present study, we are so excited to report a simple drop-coating method for fabricating the superhydrophobic cotton textiles which can remove the water in oil (or the oil in water). It is confirmed that the superhydrophobic composite thin film containing modified-ZnO nanoparticles and polystyren (PS) has been successfully fabricated on the cotton textiles surface by a single-step procedure, and the superhydrophobic cotton textiles displays an excellent property in water–oil separation which is rarely put forward and studied. The static water contact angle on the superhydrophobic cotton sample surface arranges from 153° to 155°, and stays almost the same after exposure to ambient air or immersion in the corrosive liquids and oil, indicating the considerable range of potential applications for the superhydrophobic cotton textiles fabricated by this simple method.

Electrochemical behavior of dihydroxybenzene isomers at MWCNTs modified electrode and simultaneous determination in neutral condition

Simultaneous determination of dihydroxybenzene isomers in neutral condition was successfully realized by a simple and easy prepared modified electrode without previous chemical or physical separations. The multi-walled carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE), which was prepared by the drop-coating method, was characterized by FE-SEM and TEM. Then, the electrochemical behavior of dihydroxybenzene isomers at MWCNTs/GCE was systematically studied at different temperature and pH conditions. The oxidation peak potentials were separated in neutral condition with 105 mV to hydroquinone (HQ) and catechol (CC) and 390 mV to CC and resorcinol (RS). And in neutral condition, the amperometric current were found to be linear with concentration of HQ, CC, and RS (20–140 μM) with the presence of 100 μM other isomers. Furthermore, excellent anti-interference, stability, and reproducibility were also presented by this modified electrode.

A novel amperometric biosensor for hydrogen peroxide and glucose based on cuprous sulfide nanoplates.

A facile, greener and template free route has been developed to produce cuprous sulfide (Cu2S) nanoplates (NPs) with average diameters of 70-150 nm, via one step solvothermal decomposition of a single-source precursor (SSP) Cu(ACDC)2 [ACDC = 2-aminocyclopentene-1-dithiocarboxylate] in the presence of ethylenediamine (EN) and triethylenetetramine (TETA) as structure orienting agents. The precursor complex and nanomaterials were thoroughly characterized by several common techniques and measurements, which give the composition and characteristics of the materials. Amperometric biosensors for hydrogen peroxide (H2O2) and glucose have been constructed by immobilizing the synthesized Cu2S NPs in glutaraldehyde on a glassy carbon (GC) electrode using a direct drop-coating method. The proposed sensor has displayed faster response, high and reproducible sensitivity (64.27 μA mM-1) with linear range of 10 μM to 3.75 mM, towards the electrochemical biosensing of H2O2 at -0.35 V (vs. Ag/AgCl). The sensor also showed high and reproducible sensitivity (61.67 μA mM-1) towards glucose determination with linear range of 10 μM to 3.1 mM. The anti-inference ability of electroactive molecules and favorable stability are some of the advantages of the proposed sensor. Finally, using the sensor we have determined the glucose concentration in a human blood serum sample. The results strongly demonstrate the usefulness of Cu2S NPs for biosensor design and other biological applications.