Drop-coating Method Research Articles

In situ synthesis of [Cu(BODN)·5H2O]n@nano-Al composite energetic films with tunable properties in pyro-MEMS.

Integrating energetic materials with microelectromechanical systems (MEMS) to achieve miniaturized integrated smart energetic microchips has broad application prospects in miniaturized aerospace systems and civil explosive systems. In this work, MEMS compatible [Cu(BODN)·5H2O]n arrays and [Cu(BODN)·5H2O]n@nano-Al composite energetic films were successfully fabricated on copper substrates by the in situ reaction method and drop-coating method. Single crystal X-ray diffraction, powder X-ray diffraction, scanning electron microscopy, infrared spectroscopy, differential thermal analyses, and pulsed laser ignition were employed to characterize the prepared samples. The results show that [Cu(BODN)·5H2O]n arrays formed by the coordination reaction between the Cu(OH)2 template and the BODN ligand exhibit a porous supramolecular structure with excellent thermal and energy properties. Their morphology and composition on a copper substrate can be effectively regulated by adjusting the reaction time and solution concentration. In addition, adjustable energetic properties of [Cu(BODN)·5H2O]n@nano-Al composite films can be achieved after the encapsulation of nano-Al. Their heat release, flame height and ignition duration can reach as much as 1987.5 J g-1, 13.2 mm, and 5900 μs, respectively, indicating that [Cu(BODN)·5H2O]n@nano-Al can be used as an excellent pyrotechnic agent in MEMS ignition chips. Overall, this work provides a reference for the integration and application of energetic materials in MEMS systems.

Self-driven near infrared photoelectric detector based on C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub>/Au Schottky junction

Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>, as one of new two-dimensional materials MXene, has abundant surface functional groups (—OH, —F, and —O, etc.) and can exhibit semiconductor properties through further surface functionalization. In addition, it has excellent absorption capabilities for both infrared and visible light. Currently, there is limited research on applying the semiconductor properties of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> to infrared photodetectors. In this study, a self-driven near-infrared photodetector based on a C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub>/Au Schottky junction is developed. The modified C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub> two-dimensional semiconductor is prepared by a simple solution method, in which the phosphonic acid group reacts with the hydroxyl group on the Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> surface. The C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub>/Au photodetector is constructed by using a drop-coating method at room temperature. The observation of an S-shaped curve in the <i>I</i>-<i>V</i> characteristics indicates the formation of a Schottky junction between C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub> nanosheets and the Au electrode. The device exhibits good detection performance in the near-infrared band (808–1342 nm), with a maximum responsivity of 0.28 A/W, a detectivity of 4.3×10<sup>7</sup> Jones and an external quantum efficiency (EQE) of 32.75% under 1064 nm infrared light illumination. The <i>I</i><sub>on</sub>/<i>I</i><sub>off</sub> ratio is 10.4, which is about 7.3 times higher than that under 1342 nm light. The response time and the recovery time of the device are 0.9 s and 0.5 s, respectively. After 10 cycles of <i>I</i>-<i>t</i>, the photocurrent does not show any significant decay, indicating excellent repeatability and cycle stability of the device. Owing to the built-in electric field formed by the Schottky junction, photo-generated electrons and holes can quickly separate and produce photocurrent in the external circuit without the need for external voltage driving. In addition, the C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub> film obtained by drop-casting on Au is composed of several layers of nanosheets that are randomly stacked, which can effectively relax the plasma momentum limitation, promote the generation of hot electrons, and contribute to the photocurrent. As the C<sub>14</sub>H<sub>31</sub>O<sub>3</sub>P-Ti<sub>3</sub>C<sub>2</sub>/Au Schottky junction photodetector possesses self-driven characteristics and simple fabrication process, it exhibits great potential applications in detecting weak light signals, such as in the fields of astronomy and biomedical science. The successful fabrication of this photodetector provides a new approach for designing and developing MXene-based near-infrared detectors, thus promoting further advancements in this field.

Surface enhanced fluorescence potential of ZnO nanoparticles and gold decorated ZnO nanostructures embedded in a polyvinyl alcohol matrix

In this paper we report on the development of ZnO nanostructures based platforms for surface enhanced fluorescence emission. ZnO nanoparticles were prepared using a simple, low-cost chemical precipitation method and were decorated with Au nanoparticles following a controlled chemical synthesis. Nanostructures suspended in water and incorporated in a polyvinyl alcohol (PVA) matrix were used to design Rhodamine 6G-containing films by a simple drop-coating method. The PVA environment hindered the aggregation of the nanostructures yielding improved film formation capability. Surface enhanced fluorescence emission of Rhodamine 6G was obtained in the presence of ZnO nanoparticles embedded in the PVA matrix. The enhancement depended on the concentration of both the fluorophore and the ZnO nanoparticles. No fluorescence enhancement was observed in the case of Au decorated ZnO nanocomposites and both types of nanostructures exhibited fluorescence quenching of the dye outside of the PVA environment. Time-resolved fluorescence investigations revealed that in the presence of PVA neither the ZnO NPs nor the Au decorated ZnO nanocomposites modified the dye’s lifetime. In the absence of the PVA matrix, however, an additional decay pathway emerged, leading to modified fluorescence lifetime.

A simple approach for coffee-ring suppression yielding homogeneous drying patterns of ZnO and TiO2 nanoparticles

Evaporation-induced self-assembly in colloidal droplets is a method for organising nanoparticles on substrates, with various resulting patterns. The coffee-ring pattern is among the most common ones, but its non-uniformity limits its applicability, which led to efforts for developing coffee-ring suppression strategies. Considering the wide applicability of ZnO and TiO2 nanoparticles, there is a high demand for practical means to deposit them as uniform films. Here, we present a simple approach for obtaining highly uniform thin films of ZnO and TiO2 nanoparticles by drop-coating in ambient conditions, without using surfactants or other surface chemistry modifications. Disc-like films were obtained via a restricted evaporation achieved by covering the droplets with a lid during drying, seconded by the relatively high sedimentation rate of these nanoparticles. To better understand the assembly mechanism, the influence of suspension concentration, type and temperature of the substrate, droplet volume, colloid type, and evaporation rate were studied. The method allows preparing disc-like nanoparticle films with a good control over their diameter and thickness, onto different kinds of substrates (glass, Si, polyethylene terephthalate, polystyrene). By fabricating both two-dimensional lattices and custom disc patterns we highlight the versatility of this drop-coating method and its potential for, e.g., automatized serial production processes.

Preparation of hydrophobic stearic acid-modified Fe3O4/graphite oxide/melamine sponge for oil-water separation

A fluorine-free strategy was developed for the hydrophobic modification of the melamine (MA) sponge, in which both the stearic acid-modified Fe3O4 nanoparticles (SA-Fe3O4) and the graphite oxide were immobilized on the MA sponge with the use of 3-aminopropyltriethoxysilane by a drop-coating method to prepare the SA-Fe3O4/GO/MA sponge for oil-water separation. The structure of the SA-Fe3O4/GO/MA sponge was investigated by FITR, WAXD, SEM, two-dimensional EDS mapping, TGA, and VSM. The contact angles of the SA-Fe3O4/GO/MA sponge prepared with different amounts of SA-Fe3O4 and GO were in the range of 140.2° − 145.0°, which confirmed the successful hydrophobic surface modification for the MA sponge. The demonstrations exhibited that the SA-Fe3O4/GO/MA sponge could separate the oil from the oil-water mixture by both direct absorption and gravity-driven filtration. Additionally, the SA-Fe3O4/GO/MA sponge possessed not only high absorption capacities for peanut oil, n-hexane, soybean oil, and diesel oil, but also good abilities of being able to recollect magnetically and reuse. The proposed preparation strategy and overall performance of SA-Fe3O4/GO/MA sponge were promising for the oil-water separation in the future.

Construction of porous and free-standing film electrodes composed of MXene, carbon nanocoils and PEDOT:PSS for high-performance flexible supercapacitors

The development of high-performance and flexible supercapacitors is of urgent demand but still challenging. MXene, a novel two-dimensional material, has metallic conductivity, good hydrophilicity, and high redox activity. Significantly, its good electrochemical and mechanical properties suggest its great potential in flexible supercapacitors. However, the poor interlayer conductivity and self-stacking of MXene flakes hinder the charge transfer and ion transport. Herein, a three-dimensional porous structure composed of MXene, carbon nanocoils (CNCs) and Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) (denoted as MXene/CNC/PP) has been successfully prepared by a facile drop-coating method for flexible film electrode. The CNCs, having unique 3D helical structures and excellent dispersity, insert into the MXene flakes to prevent their over stack and provide spaces and channels for electrolyte storage and ion transport inside the composite structure. Meanwhile, the CNCs also act as highly conductive bridges to connect the MXene flakes, enhancing the charge transfer. To increase the stability of the composite structure, the conducting polymer PEDOT:PSS was selected as an conductive binder to prepare self-supported MXene/CNC/PP film electrodes without additional additives. The MXene/CNC/PP electrode exhibits an areal capacitance of 232 mF cm−2 at 10 mV s−1 with superior rate capability, excellent cycling stability and flexibility. This paper provides a new strategy for construction of wearable high-performance flexible electrodes and supercapacitors.

Wearable Conductive Polymer Matrix Composites for Breath Monitoring with Ammonia Detection

Conductive polymers, such as polyaniline (PANI), Polythiophene (PTh), polypyrrole (PPy), etc., are widely used for gas sensors due to their excellent electrical conductivity and low cost to manufacture [1]. In particular, PANI has attracted more attention due to its ease of synthesis, high environmental stability, and high reactivity with ammonia gas. In addition, the selection of acid-base dopant during the preparation process of polyaniline can adjust carrier concentrations for the change in electrical conduction or resistance to improve sensing properties. There have been many reports on the fabrication of flexible gas sensors using PANI [2-4]. Bandgar et al. [5] synthesized a low-temperature flexible polyaniline gas sensor by in-situ chemical oxidation polymerization of aniline on a polyethylene terephthalate (PET) substrate, showing 99% reproducibility, rapid response and recovery. Still, the response value was only 26% in 100 ppm ammonia atmosphere. Qi et al. [6] prepared a gas sensor by in-situ polymerization of aniline on non-woven fabric. The high air permeability of the fabric effectively improved the performance of the polyaniline-based gas sensor. Due to the outbreak of the COVID-19 pandemic, the use of face masks in public has become essential to reduce the spread of the virus. Some reports claim that the increased carbon dioxide in the mask over time may cause medical issues related to the respiratory system. Therefore, monitoring breathing air quality can help detect the wearer's vital conditions.In this study, we used a disposable mask as a flexible substrate to prepare polypropylene/carbon nanotube/polyaniline composite film through a layer-by-layer method. The polypropylene/carbon nanotube composite films were prepared by applying the carbon nanotube aqueous solution with surfactants evenly on the surface of a mask filter layer by a drop-coating method. Then, the in-situ polyaniline polymerization was performed on the surface of the polypropylene/carbon nanotube composite film through ammonium sulfate. The polypropylene/carbon nanotube /polyaniline composite film exhibits high sensitivity, fast sensing response/recovery time, room temperature operation, reliable flexibility, and cycle stability. The synthesized and wearable masks have demonstrated real-time detection respiratory rate and other breathing conditions such as CO2 and humidity. The ammonia gas sensing can also be used as a potential biomarker for health screening. The design and integration of multiple gas sensing materials in masks will help wearers better understand their own body conditions.

Self-healing artificial solid electrolyte interphase enhanced by quadruple hydrogen bonding for stable lithium metal anode

Lithium metal is considered as the ultimate anode material for lithium batteries due to its high theoretical specific capacity and lowest redox potential. However, the growth of lithium dendrites and strong side reactions seriously hinder the commercialization of Li metal anode. Here, we modify the Li metal anode with a self-healing artificial solid electrolyte interphase (SEI), where PVA-Upy with quadruple hydrogen bonds is formed on Li metal by a simple drop-coating method. This polymer artificial SEI possesses self-healing hydrogen bonds and abundant lithiophilic bonds, which can simultaneously suppress the generation of microcracks in the SEI and enable uniform deposition of Li metal. Hence, the PVA-Upy@Li symmetric cell can stably cycle for more than 2000 h (1 mA cm−2, 1 mAh cm−2) with only about 10 mV of voltage polarization. This artificial SEI provides new insight into the subsequent modification strategies of Li metal anode and can be extended to the protection of other alkali metal anodes.

Nickel-vanadium layered double hydroxide for a mid-infrared 2 µm Tm:YAG ceramic ultrafast laser.

In this study, a nickel-vanadium layered double hydroxide (NiV-LDH) nanosheet was prepared as a saturable absorber (SA) by liquid phase exfoliation and a drop-coating method. The microstructure and optical transmission properties of the obtained NiV-LDH nanosheet were then systematically studied. An "X"-type fold cavity was designed to evaluate the ultrafast laser modulation performance of the NiV-LDH nanosheet with a Tm:YAG ceramic gain medium. A stable passively Q-switched mode-locked (QML) pulse centered at 2011.6 nm has successfully been realized, with a repetition frequency of 145 MHz and a pulse duration of 320 ps. To the best of our knowledge, this is the first time that the LDH has been used as an SA in a mid-infrared range ultrafast laser.

Interface modification of Ru-CeO2 co-infiltrated SFM electrode and construction of SDC/YSZ bilayer electrolyte for direct CO2 electrolysis

A novel electrolysis cell with SDC/YSZ bilayer electrolyte structure and Ru-CeO2 co-infiltrated SFM-SDC electrode has been fabricated by facile drop-coating method and vacuum infiltration process. The drop-coated YSZ thin film facilitates SDC electrolyte to be employed in direct CO2 electrolysis. The results of TPD analysis and AC impedance spectroscopy measurement indicate that the infiltration of Ru and CeO2 nanocatalysts of SFM-SDC electrode significantly enhance the chemical adsorption of CO2 and electrochemical performance of the electrode. With LSM-SDC as the anode, LSM-SDC/YSZ-SDC/Ru-CeO2-SFM-SDC single cell exhibits good coking-resistant and stability for CO2 reduction electrolysis, reaching a peak current density of 1.82 A·cm−2 under an applied voltage of 1.5 V. The combined strategy offers a promising approach to cell structure construction and interface modification for solid oxide electrolysis cells.

Highly sensitive determination of paracetamol, uric acid, dopamine, and catechol based on flexible plastic electrochemical sensors.

Flexible sensing is an alternative to traditional sensing and possesses good flexibility and wearability. Intrinsically conductive polymers, particularly poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), have received significant attention due to their high mechanical flexibility and good biocompatibility. Here, we report the design of highly conductive and electrochemically active PEDOT:PSS-coated plastic substrate electrodes by combining N-doped graphene (NG) or S-doped graphene (SG) with methanesulfonic acid-treated PEDOT:PSS (denoted as NG-f-MSA-PEDOT:PSS/PET and SG-f-MSA-PEDOT:PSS/PET) by a simple drop-coating method. At room temperature, the NG-f-MSA-PEDOT:PSS/PET electrode demonstrated the lowest detection limits of 17.09, 33.84, 28.30, and 44.96 nM for paracetamol, uric acid, dopamine, and catechol (S/N = 3), respectively. The NG-f-MSA-PEDOT:PSS/PET electrode had good anti-interference ability and reproducibility without employing expensive noble metals and requiring much effort to polish the surface of traditional glass carbon electrodes. Most importantly, this film electrode could maintain a stable electrochemical response under different bending and crease states and had excellent mechanical stability and flexibility.

A Facile Centrifuge Coating Method for High-Performance CsPbBr3 Compact and Crack-Free Nanocrystal Thin Film Photodetector

All-inorganic perovskite quantum dots (QDs), a promising semiconductor material, is suitable for new generation optoelectronic application. While there are many kinds of coating procedures for producing perovskite QDs peorovskite film, those methods require post-treatments and an additional dispersion support agent while still retaining pinholes and cracks. In this work, we report a facile method to produce CsPbBr3 film on a pre-patterned Pt electrode using a centrifuge coating method for photodetector (PD) application. Compact and crack-free films with ~500 nm thick from various particle sizes of 8 nm, 12 nm, and >30 nm were achieved with a suitable ratio of toluene/ethyl acetate solvent for visible light photodetector application. The optimized device has an on/off ratio of 103, detectivity of 3 × 1012 Jones, and responsivity of 6 A/W. In comparison, the on/off ratio of the device fabricated by the centrifuge coating method was 102 times higher than by the drop-coating method. The PD performance exhibited considerable moisture stability at mild high ambient temperature with no encapsulation for more than two weeks. The results suggest that this is a potential method for fabricating all inorganic perovskite nano-semiconductor films for further optoelectronic application in photodetectors, LEDs, and solar cells.

Biomimetic superhydrophobic films drop-coated with zinc oxide modified molecular sieves

Superhydrophobic films have a wide range of applications in industry due to their hydrophobic and self-cleaning properties. A simple and economical method is proposed in this paper to prepare a superhydrophobic surface by creatively using microstructures consisting of zinc oxide particles on molecular sieves. The combination of zinc oxide particles and molecular sieves are embedded into polydimethylsiloxane films to form stable biomimetic superhydrophobic surfaces. In this way, a superhydrophobic surface with a water contact angle of up to 162.3° and a water rolling angle of about 3.2° have been prepared. The surface has excellent self-cleaning ability, thermal stability, water impact resistance, UV stability and environmental friendliness. The film could be prepared using a drop-coating method, which greatly broaden the range of applications for the superhydrophobic film.

Electrical and magnetic network design for improving electromagnetic interference shielding performance of waterborne polyurethane fabrics

Waterborne polyurethane (WPU) fabrics containing multiwalled carbon nanotubes (CNTs) and Ni coated multiwalled carbon nanotubes (Ni@CNTs) were successfully fabricated through emulsion mixing and drop-coating method. Carbon-based nanofillers were distributed in the conformal WPU matrix and fabric substrate, and intertwined with each other to form electric/magnetic network. The electromagnetic interference shielding effectiveness (EMI SE) of PU/10Ni@CNTs/10CNTs fabric reaches 77.2 dB, batter than that PU/20CNTs fabrics due to the synergistic effect of electrical, dielectric, and magnetic loss.

Factors affecting fabrication of silicon nanopillars using silica nanoparticle lithography and metal-assisted chemical etching

Different technologies have been explored for fabricating silicon nanopillars (SiNPs). One of the emerging technologies is the combined fabrication process based on silica nanoparticle lithography and metal-assisted chemical etching (MACE). However, the process flow to fabricate successfully SiNPs depends on various technology factors. We report investigations on factors affecting the fabrication technology, from the assembly of close-packed silica nanoparticle monolayers using drop-coating method, formation of nonclose packed silica nanoparticle monolayers using HF vapor etching, to creation of SiNPs using MACE. Etching mechanisms are suggested to explain observed experiment results.

Drop-coated C2N electrode for Hydrogen Evolution Reaction

In this work, a novel catalyst based on holey nitrogenated graphene (C2N) was developed for hydrogen evolution reaction (HER). C2N nanosheets were deposited on Fluorine doped Tin Oxide substrate by using a facile drop-coating method. Electrochemical tests indicated that C2N based work electrode exhibited excellent stability in acidic environment. To improve its catalytic performance, various noble-metal nanoparticles were deposited on the surface of C2N using physical vapor deposition, including Au, Cu, Co, Ni and Pt. The size most particles was observed to be 3–5 nm, which was beneficial for catalyst reaction. Among those samples with different metal particles, Pt coated C2N multi-catalysts exhibited an overpotential of 33 mV and Tafel slope of 53 mV/dec, which outperformed other metal particles, and also pure Pt particles or C2N nanosheets without metallic particles, demonstrating its great potential of multi-catalyst Pt/C2N for HER application.

Reversibly photochromic wood constructed by depositing microencapsulated/polydimethylsiloxane composite coating

Photochromic wood was fabricated by coating microencapsulated photochromic material (MP)/polydimethylsiloxane composites onto wood using a simple drop-coating method. Urea-melamine–formaldehyde resin was used to microencapsulate the photochromic material (PM) via in situ polymerization. The concentration of the MP affected the photochromic property of the wood surface. The total color change (ΔE*) reached 82.2 when the concentration of the composite coating is 8%. Adhesion tests confirmed that the composite coating adhered firmly to the wood. This method is potentially useful for the production of functional wooden products, such as anti-counterfeiting materials and aesthetic wood.

Surfactant‐free synthesis of self-assembled CuO spheres composited with MnO2 nanorods for non-enzymatic glucose detection

Cupric oxide (CuO) spheres and manganese dioxide (MnO 2 ) nanorods by hydrothermal synthesis are investigated for non-enzymatic glucose sensors. Self-assembled CuO spheres were first synthesized on ITO/glass substrate without surfactant. MnO 2 nanorods were then composited on the exterior of CuO spheres by using a drop-coating method. The MnO 2 nanorods/CuO sphere/ITO working electrode was used to analyze the catalytic ability to glucose. Large surface-to-volume ratio of the material enhances the glucose sensing performances. MnO 2 improves the sensitivity and the linearity of the glucose detection. The working electrode has high sensitivity of 2360.81 μA mM −1 cm −2 to glucose. Good linear range between 0.5 and 2.5 mM glucose concentration can also be found. It also has great anti-interference ability. Excellent performances of the MnO 2 nanorods/CuO sphere to glucose can help more accurately and quickly detecting the blood sugar concentration. • Cupric oxide sphere and manganese dioxide nanorods were synthesized by low-temperature hydrothermal method. • Cupric oxide can self-assembled into a spherical structure without surfactant. • Manganese dioxide nanorods/cupric oxide sphere has high sensitivity of 2360.81 μA mM −1 cm −2 to glucose.

Self-spreading produces highly efficient perovskite solar cells

A facile two-step drop-coating method was used to make FA0.88MA0.12PbIxBr3−x (0 ≤x ≤ 3) perovskite films for the first time. The films formed via a self-spreading process, without the assistance of coating apparatuses, gas blowing, vacuum, or antisolvent. High-quality perovskite films with different bandgaps were made and the photovoltaic performance was investigated. The cells with FA0.88MA0.12PbI2.85Br0.15 offered a champion PCE of 21.08%, which is higher than the PCEs for perovskite solar cells made by other two-step non-spin-coating methods. The FA0.88MA0.12PbBr3 cells gave a champion PCE of 10.86%, which is the highest PCE for FAxMA1−xPbBr3 cells. The drop-coating method enables making perovskite solar cells without complex equipment. “Fully handmade” perovskite solar cells with drop-coated SnO2, drop-coated perovskite, and painted carbon electrode were made in air, giving a PCE of 14.04%.

Efficient MAPbI3 solar cells made via drop-coating at room temperature

Here we demonstrate a room-temperature drop-coating method for MAPbI3 films. By using low-boiling-point solvent, high-quality MAPbI3 films were made by simply casting a drop of solution onto the substrate at room temperature. This approach took advantage of the synergistic effect of good wettability and volatility of the solvent, enabling high nuclei density and compact film at room temperature. The crystal growth in different solvents was in-situ observed by using optical microscope, which helped us to understand the mechanism for the formation of different film morphology. Perovskite solar cells gave a PCE of 18.21%.