Soft Solution Processing Research Articles

Continuous Production of Functionalized Graphene Inks by Soft Solution Processing.

The continuous production of high-quality, few-layer graphene nanosheets (GNSs) functionalized with nitrogen-containing groups was achieved via a two-stage reaction method. The initial stage produces few-layer GNSs by utilizing our recently developed glycine-bisulfate ionic complex-assisted electrochemical exfoliation of graphite. The second stage, developed here, uses a radical initiator and nitrogen precursor (azobisisobutyronitrile) under microwave conditions in an aqueous solution for the efficient nitrogen functionalization of the initially formed GNSs. These nitrile radical reactions have great advantages in green chemistry and soft processing. Raman spectra confirm the insertion of nitrogen functional groups into nitrogen-functionalized graphene (N-FG), whose disorder is higher than that of GNSs. X-ray photoelectron spectra confirm the insertion of edge/surface nitrogen functional groups. The insertion of nitrogen functional groups is further confirmed by the enhanced dispersibility of N-FG in dimethyl formamide, ethylene glycol, acetonitrile, and water. Indeed, after the synthesis of N-FG in solution, it is possible to disperse N-FG in these liquid dispersants just by a simple washing-centrifugation separation-dispersion sequence. Therefore, without any drying, milling, and redispersion into liquid again, we can produce N-FG ink with only solution processing. Thus, the present work demonstrates the 'continuous solution processing' of N-FG inks without complicated post-processing conditions. Furthermore, the formation mechanism of N-FG is presented.

Diamond-like Carbon Patterning by the Submerged Discharge Plasma Technique via Soft Solution Processing.

Submerged plasma-assisted discharge direct patterning of diamond-like carbon (DLC) onto the silicon substrate in ambient conditions has succeeded as a new and novel soft solution process. In this environmentally benign technique, a copious amount of pure ethanol (ca. 4 mL) was locally activated with a maximum of ca. 0.23 mkWh by an as-electrochemically synthesized ultrasharp tungsten tip. With the assisted submerged plasma, the decomposed ethanol molecules are anodically patterned directly onto the silicon substrate in ambient conditions. The physical nature of DLC patterns was accessed by profilometry, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy analysis. Furthermore, Fourier-transform infrared, Raman, and X-ray photoelectron spectra were analyzed for chemical compositions and structures, such as surface functionalization, carbon-carbon bonding, and sp2-sp3 ratio, respectively. From a Berkovich-configured nanoindentation analysis, Young's modulus and hardness have shown increasing trend with increasing sp3-sp2 ratio in DLC patterns of 68.5 and 2.8 GPa, respectively. From the electrochemical cyclovoltammetry analysis, a maximum areal specific capacitance of 205.5 μF/cm2 has been achieved at a scan rate of 5 mV/s. The one-step, green, and environmentally sustainable approach of rapid formation of DLC patterns is thus a promising technique for various carbon-based electrode fabrication processes.

Why is Soft (Green) Processing (= Low-Energy Production) of Advanced Nano-Materials Difficult but Necessary for Sustainable Society?

Modern our society has been developed with various advanced nano-materials. Most of the advanced materials, Metallurgical materials, Semiconductors, Ceramic materials, and Plastics have been used in a wide area of applications like structural, mechanical, chemical, electrical, electronic, optical, photonic, biological, medical, etc. Most of them, except for bio-polymers & bio-minerals, have never been produced via biological systems. Thus they have generally been fabricated artificially and/or industrially by so-called high-technology, where harsh conditions & high energy species like high temperature, high pressure, vacuum, molecule, atom, ion, plasma, etc. have been used for their fabrications, thus consumed a huge amount of resources and energies then exhausted huge amounts of wastes: materials, heats, and entropy. To save this tragedy, we must consider “Cascade use of Heats” and “Low energy Production of advanced nano-materials via water-based processings.” Bio-inspired process, which means that “Learn from Bio-systems then Exceed them”. We have challenged to fabricate those advanced inorganic materials with the desired shape/size/location, etc. directly in low energetic routes using aqueous solutions since 1989 when we found a method to fabricate BaTiO3 film on Ti substrate in a Ba(OH)2 solution by Hydrothermal Electrochemical[HEC] method at low temperatures of 60-200 C. We proposed in 1995 an innovative concept and technology, “Soft Processing” or “Soft Solution Processing,” which aims low energetic (=environmentally friendly) fabrication of shaped, sized, located, and oriented inorganic materials in/from solutions1,2). It can be regarded as green processing or eco-processing. When we have activated/stimulated interfacial reactions locally and/or moved the reaction point dynamically, we can get patterned ceramic films directly in solution without any firing, masking, nor etching—direct Patterning of CdS, PbS, and CaWO4 on papers by Ink-Jet Reaction method. Furthermore, we have succeeded in fabricating BaTiO3 patterns on Ti by a laser beam scanning3) and carbon patterns on Si by plasma using a needle electrode scanning directly in solutions. Successes in TiO2 and CeO2 patterns by Ink-Jet Deposition, where nano-particles are nucleated and grown successively on the surface of the substrate, thus become dense even below 300 oC will be presented. Nano-structured films will also be talked. .A recent novel subject, Soft Processing for various nano-carbons including graphene and functionalized graphene will be introduced. Where we have succeeded to prepare functionalized Graphene Ink via successive processes under ambient temperature and pressure conditions.

High-performance p-channel transistors with transparent Zn doped-CuI

‘Ideal’ transparent p-type semiconductors are required for the integration of high-performance thin-film transistors (TFTs) and circuits. Although CuI has recently attracted attention owing to its excellent opto-electrical properties, solution processability, and low-temperature synthesis, the uncontrolled copper vacancy generation and subsequent excessive hole doping hinder its use as a semiconductor material in TFT devices. In this study, we propose a doping approach through soft chemical solution process and transparent p-type Zn-doped CuI semiconductor for high-performance TFTs and circuits. The optimised TFTs annealed at 80 °C exhibit a high hole mobility of over 5 cm2 V−1 s−1 and high on/off current ratio of ~107 with good operational stability and reproducibility. The CuI:Zn semiconductors show intrinsic advantages for next-generation TFT applications and wider applications in optoelectronics and energy conversion/storage devices. This study paves the way for the realisation of transparent, flexible, and large-area integrated circuits combined with n-type metal-oxide semiconductor.

Optical properties of silver nanoparticles deposited onto silicon substrates by different soft-solution processing techniques

Silver nanoparticles have been grown onto crystalline silicon substrates. Three soft-solution one-step processing techniques have been assayed: electroless metal deposition (EMD), electrodeposition (ED) and spray pyrolysis (SP). The shapes exhibited by the silver nanoparticles prepared by EMD and ED are hemispherical, while the shapes of those prepared by SP (for long processing times) are similar to disks of aspect ratio 0.5 approximately. Integrated total reflectance spectra and integrated diffuse reflectance spectra shows distinctive features due to the electronic structure of silicon. Specular reflectance spectra of samples (except those grown by SP with long processing times) show a dip, corresponding to a surface plasmon resonance. Simulations, considering granular composite media were made. The simulated spectra confirm the presence of the spectral dip. Surface plasmon resonance show shifts with the angle of incidence. For samples prepared by ED, the tendency is the same as the one of the model, indicating that there is not much coupling between nanoparticles.

Optoelectronic gas sensor sensitized by hierarchically structured ZnO nanorods/Ag nanofibers via on-chip fabrication

Hierarchically structured ZnO nanorods/Ag nanofibers fabricated on chip using soft solution and polyol process was utilized for optoelectronic gas sensors. Since a built-in electric field forms between the two materials, an enhanced gas sensitivity in NO2, ethanol, CO and CH4 gas environments with assisted of UV illumination at room temperature in comparison with the pristine hierarchically structured ZnO nanorods.

A smart bottom-up strategy for the fabrication of porous carbon nanosheets containing rGO for high-rate supercapacitors in organic electrolyte

Exploration of various porous carbon materials with enhanced electrochemical performance is critical for the development of long-term sustainable energy storage and production systems. Herein, we have designed a smart bottom-up strategy to transformation of pitch into porous carbon nanosheets containing rGO (reduced graphene oxides) (PCSG) through a soft solution process coupling with KOH activation. This efficient solution process without involving hard templates or harmful solvents, which is clearly different from all the previously reported process, opening a new route towards porous carbons for energy storage applications. Notably, the as-obtained PCSG-60 sample (synthesized from 60mg of GO) presents an optimum integration of a large specific surface area of 2217m2/g, uniform micropore size (∼1.5nm), and sheet-like morphologies. When evaluated as electrode materials for supercapacitor in 1M TEABF4/AN electrolyte, the PCSG-60 exhibits excellent capacitive performance including large specific capacitances of 221F/g (at 1A/g), considerable rate capability (71.9% capacitance retention from 1A/g to 50A/g), smaller IR drop (0.637V at 50A/g), good cycling stability (91.8% of the initial capacitance after 3000 cycles at 10A/g) and an energy density up to 38.2 Wh/kg even at an ultrahigh power density of 40500W/kg, which puts the PCSG-60 among the best electrochemical performance in the reported pitch-derived carbon electrodes for supercapacitors. The outstanding capacitive electrochemical performance combined with the low-cost and readily accessible precursors enable the PCSG-60 is a promising electrode material for supercapacitor and other electrochemical energy storage system applications.

Limitations and Opportunities for Optical Metafluids To Achieve an Unnatural Refractive Index

Optical metafluids have held a special position among the platforms of metamaterials, because other than the lithography-based hard approaches, the soft fluidity-based solution process not only enables their immediate practical utility but also allows for reconfigurable and adaptable nanophotonic systems. However, the fundamental limits of the available effective parameters of optical metafluids are not yet clearly defined. Of particular interest is the accessible range of the refractive index under a practically available volume fraction ϕ and the structural motifs of building blocks. In addition, previously reported theoretical works are based on an effective medium theory that excludes dipolar coupling between building blocks. Using these initial approaches, the interaction between the building blocks at a relatively higher ϕ was not accurately rationalized. In this work, we advance an effective medium theory by using the 3D dressed polarizability. Then, we successfully rationalize the dipolar coupling...

Facial development of high performance room temperature NO2 gas sensors based on ZnO nanowalls decorated rGO nanosheets

A highly sensitive NO2 gas sensor based on ZnO nanowalls decorated rGO nanosheets was fabricated using a thermal reduction and soft solution process. The highly developed interconnected microporous networks of ZnO nanowalls were anchored homogeneously on the surface of reduced graphene oxide (rGO). Sensors fabricated with heterojunction structures achieved a higher response (S=9.61) and shorter response-recovery (25s, 15s) behavior at room temperature to 50ppm level NO2 effectively in contrast to those sensors based on net ZnO nanowalls or rGO layers. The stability and selectivity of ZnO/rGO heterojunction were carried out. Meanwhile, the effects of humidity on ZnO/rGO heterojunction gas sensor were investigated. The more preferable sensing performance of ZnO/rGO heterojunction to NO2 was discussed. It can be surmised that this NO2 gas sensor has potential for use as a portable room temperature gas sensor.

液相析出法(Liquid Phase Deposition;LPD法)による水溶液からの機能性酸化物の調製と形状規制( 材料物性から見たフッ化物・酸化物単結晶の育成技術)

液相析出法(Liquid Phase Deposition;LPD法)による水溶液からの機能性酸化物の調製と形状規制( 材料物性から見たフッ化物・酸化物単結晶の育成技術)

Cobalt-iron Oxide, Alloy and Nitride: Synthesis, Characterization and Application in Catalytic Peroxymonosulfate Activation for Orange II Degradation

In meeting the need for environmental remediation in wastewater treatment and the development of popular sulfate-radical-based advanced oxidation processes (SR-AOPs), a series of Co/Fe-based catalysts with confirmed phase structure were prepared through extended soft chemical solution processes followed by atmosphere-dependent calcination. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and 57Fe Mössbauer spectroscopy were employed to characterize the composition, morphology, crystal structure and chemical state of the prepared catalysts. It was shown that calcination in air, nitrogen and ammonia atmospheres generated Co-Fe catalysts with cobalt ferrite (CoFe2O4), Co-Fe alloy and Co-Fe nitride as dominant phases, respectively. The prepared Co/Fe-based catalysts were demonstrated to be highly efficient in activating peroxymonosulfate (PMS) for organic Orange II degradation. The activation efficiency of the different catalysts was found to increase in the order CoFe2O4 < Co-Fe nitride < Co-Fe alloy. Sulfate radical was found to be the primary active intermediate species contributing to the dye degradation for all the participating catalysts. Furthermore, a possible reaction mechanism was proposed for each of the studied catalysts. This study achieves progress in efficient cobalt-iron catalysts using in the field of SR-AOPs, with potential applications in environment remediation.

Fabrication, Characterization, and Growth Mechanism of Cobalt Oxide Nanodots to Nanospheres Via Soft Chemical Solution Process

In this study, the authors report a facile synthesis for the formation of nanoscale CoO dots to nanospheres via solution technique at low temperature and characterized in terms of their morphological, structural, compositional, and thermal properties. The morphological characterizations of as-synthesized and annealed CoO structures were done by scanning electron microscopy (SEM) and transmission electron microscopy, which confirmed that synthesized products are very small in size and bears small dots to spheres such as structures. The surface of nanodots is smooth and clean throughout the whole morphology. The crystalline property was analyzed with X-ray diffraction pattern and it reveals that the formed structures exhibit small size and clearly consistent with SEM observation. The compositional and thermal properties of as-synthesized and annealed CoO structures were observed via Fourier transform infrared spectroscopy and Thermogravimetric analysis, which confirmed that synthesized structures are pure CoO and showed good thermal stability. Finally, plausible mechanisms for the formation of CoO nanodots to nanospheres are also discussed.

Solution-Grown Silver Nanowire Ordered Arrays as Transparent Electrodes.

A transparent conducting film composed of regular networks of silver nanowires is obtained by combining a soft solution process (Tollens' reaction) and nanoimprint lithography. The solution-grown nanowire networks show a threefold higher conductivity than grids obtained by metal evaporation. This is due to the larger grain size in the solution-grown nanowires, which results in a strong reduction of electron scattering by grain boundaries.

광촉매 활성이 우수한 판상형 ZnO 결정의 대용량 합성

결정핵-매개 소프트-용액 방법을 이용하여 판상형 ZnO 나노입자를 합성하였다. 합성된 판상형 ZnO 나노입자는 많은 결함이 존재하는 (0001)면이 발달하여 상업적인 ZnO 나노입자 보다 광촉매 특성이 우수하였다. 또한, 판상형 ZnO 나노입자의 세포독성이 실리카 코팅을 통해 감소함을 확인하였다. 마지막으로 판상형 ZnO를 합성하는데 필요한 성장용액의 다양한 시약 조건들을 변화시키면서 상업적인 적용이 가능한 수백 그램 스케일로 대량합성 하는데 처음으로 성공하였다. ZnO nanoplates were prepared by seed-mediated soft-solution process. Photocatalytic property of ZnO nanoplates was superior to that of conventional ZnO nanoparticles owing to the enhanced (0001) plane with large defect sites. In addition, we found that silica coating method could provide to reduce cytotoxicity of ZnO nanoplates. Finally, we have successfully synthesized for the first time large-scale synthesis of plate-type ZnO as few hundreds gram scale for industrial applications through controlling various reagents of growth solution.

Correlation investigation on the visible-light-driven photocatalytic activity and coordination structure of rutile Sn-Fe-TiO2 nanocrystallites for methylene blue degradation

Rutile Sn-Fe-TiO2 photocatalysts with high visible-light-driven activity were synthesized by an improved soft chemical solution process for investigating the potential correlation between their photocatalytic performance and coordination structure. The prepared photocatalysts were systematically characterized by XRD, BET, Raman, TEM, UV–vis, XPS, XAFS and Mössbauer techniques. Their photocatalytic performances were evaluated by degrading the model pollutant of methylene blue aqueous solution under visible light irradiation (λ≥400nm). The results indicated that tin and iron ions could substitute Ti4+ in the rutile TiO2 lattice, and specially, iron ions were located at tetrahedrally coordinated titanium sites. Their visible-light-driven photocatalytic activities were found to culminate at a very low level of iron doping (Fe/Ti=∼0.1at.%, Sn/Ti=2.0at.%), this was 5-fold of P25 and 2-fold of undoped rutile TiO2. It was confirmed that besides the high surface area, fine crystallinity, enhanced visible light absorption and optimized oxygen vacancy concentration, the mole ratio of tetrahedrally coordinated iron and titanium was also essential to modify their visible-light-driven photocatalytic properties.

Utilization of photocatalytic ZnO nanoparticles for deactivation of safranine dye and their applications for statistical analysis

A soft chemical solution process was used in synthesis of photocatalytic zinc oxide nanoparticles (ZnO-PNPs) at low temperature. The synthesized PNPs were characterized in terms of their crystallinity, morphological, catalytic, spectroscopic and statistical analysis techniques. X-ray powder diffraction patterns (XRD) were used to know the crystalline property of the prepared materials whereas field emission electronic microscopy (FESEM) was employed to observe the morphology of grown NPs. UV–visible spectroscopy was employed to analyze the absorbance of degraded safranine (SA) dye in presence of NPs at desired time interval. Parameters of statistical analysis give necessary information for established analytical procedures to ensure quality and purity of results. With the help of this analytical method, outcomes were calculated in terms of absorbance such as standard deviation (SD), relative standard deviation (RSD), etc. at 95% confidence level. The photocatalytic deactivation/degradation process significantly enhanced the activity of ZnO-PNPs under UV–visible light in presence of SA dye. The effective concentration of used PNPs was optimized and validated via standard analytical procedure, which exhibited greater significance on deactivation process. The absorption spectra of photocatalyzed solution and activity of ZnO-PNPs were compared with those of pure ZnO, obtained by UV–visible spectroscopy.

Reactive oxygen species mediated bacterial biofilm inhibition via zinc oxide nanoparticles and their statistical determination.

The formation of bacterial biofilm is a major challenge in clinical applications. The main aim of this study is to describe the synthesis, characterization and biocidal potential of zinc oxide nanoparticles (NPs) against bacterial strain Pseudomonas aeruginosa. These nanoparticles were synthesized via soft chemical solution process in a very short time and their structural properties have been investigated in detail by using X-ray diffraction and transmission electron microscopy measurements. In this work, the potential of synthesized ZnO-NPs (∼10–15 nm) has been assessed in-vitro inhibition of bacteria and the formation of their biofilms was observed using the tissue culture plate assays. The crystal violet staining on biofilm formation and its optical density revealed the effect on biofilm inhibition. The NPs at a concentration of 100 µg/mL significantly inhibited the growth of bacteria and biofilm formation. The biofilm inhibition by ZnO-NPs was also confirmed via bio-transmission electron microscopy (Bio-TEM). The Bio-TEM analysis of ZnO-NPs treated bacteria confirmed the deformation and damage of cells. The bacterial growth in presence of NPs concluded the bactericidal ability of NPs in a concentration dependent manner. It has been speculated that the antibacterial activity of NPs as a surface coating material, could be a feasible approach for controlling the pathogens. Additionally, the obtained bacterial solution data is also in agreement with the results from statistical analytical methods.

Zinc oxide quantum dots: a potential candidate to detain liver cancer cells.

The term cancer is used for diseases in which abnormal cells proliferate without control and are able to attack with other tissues. Over various types of cancers, liver cancer is the most hurtful disease, which affects the whole body system. The aim of the present study was to investigate the efficiency against cancer cells of HepG2 cells, with quantum dots of ZnO. The cytotoxic effects were analyzed with MTT assays in range of 1-100 μg/ml. The cells were exposed to ZnO-QDs and it exhibit significant reduction, which starts from concentration 5 μg/ml (4 %; p < 0.05). The assay was justified with quantitative RT-PCR and it demonstrates, exposure of ZnO-QDs on HepG2 cells. The level of mRNA expressions was significantly up-regulated (Bax, P53, and Caspase-3), whereas the anti-apoptotic gene (Bcl-2) was down-regulated. The QDs (5 ± 2 nm) were prepared via soft chemical solution process and analyzed using FESEM, TEM and HR-TEM.

Modulation of physical and photocatalytic properties of (Cr, N) codoped TiO2 nanorods using soft solution processing

Facile polymerized complex reactions together with a hydrothermal reaction were implemented to make single crystalline TiO2 nanorods for the first time. Chromium (Cr) and nitrogen (N2) co-doping was performed to tailor the physical properties. Transmission electron microscopy and x-ray diffraction study illustrated that highly reactive facets of (101), (111), and (001) dominated rutile TiO2 nanorods. A growth model, based on formation of complex species, was proposed to elucidate effectiveness of the soft solution processing in making TiO2 nanorods. X-ray photoelectron spectroscopy analysis and consideration of fundamentals of charge neutrality showed N2 doping could inhibit formation of Cr6+ and oxygen vacancies (VO2+). An investigation of the photocatalytic properties exhibited high efficiency of photodegradation of methylene blue in 15 min under pH = 10, using a nanocomposite of (7% Cr, 0.0021% N) codoped and 3% Cr doped TiO2 nanorods.

Metal Oxide Coated Porous Silicon electrode fabricated By Anodized Liquid Phase Deposition

We fabricated titanium oxide/PSi nanocomposite by anodic liquid phase deposition (LPD) method. This method is soft-solution process for preparation of metal oxide thin film via hydrolysis of metal fluoro-complex with assist of F- scavenger (e.g. H3BO3, SiO2 and Al). Titanium oxide is superhydrophilic material and changes little volume during Li insertion and extraction, therefore this composite is expected to be high efficiency anode material. PSi was formed by etching of silicon wafer(p-type, 3-4 mΩ•cm) with 60 mA/cm2 in HF(47 %):EtOH (1:1, in vol) for 10 min[3] and immersed in (NH4)2TiF6-H3BO3 solution (LPD-H3BO3), thermaloxidized and immersed in (NH4)2TiF6 solution (LPD-SiO2) or anodized in H2TiF6-EtOH solution (LPD-anodized Si). Each sample was characterized by SEM-EDX, XPS, N2-isotherm and electrochemical measurement. The deposition amount of titanium was quantified by ICP-AES.The diameter of PSi was ca.7.4 nm and titanium oxide was deposited on all samples. However, the fine structure of LPD-H3BO3 was removed by covering of titanium oxide. After depositon of Ti oxide, the Ti2P binding energy decreased during the LPD reaction measured by XPS. This result suggests titanium oxide deposition derived from removal of fluorine from metal fluoro-complex via hydrolysis with H3BO3, SiO2 or anodized Si. Anodic electrodepostion of titanium oxide on PSi was performed at 0.3 V vs Ag/AgCl, and the deposition amount; ca. 3x10-6 mol m-2 as shown in Fig.1.