Low-temperature Solution Route Research Articles

Solution epitaxy of polarization-gradient ferroelectric oxide films with colossal photovoltaic current

Solution growth of single-crystal ferroelectric oxide films has long been pursued for the low-cost development of high-performance electronic and optoelectronic devices. However, the established principles of vapor-phase epitaxy cannot be directly applied to solution epitaxy, as the interactions between the substrates and the grown materials in solution are quite different. Here, we report the successful epitaxy of single-domain ferroelectric oxide films on Nb-doped SrTiO3 single-crystal substrates by solution reaction at a low temperature of ~200 oC. The epitaxy is mainly driven by an electronic polarization screening effect at the interface between the substrates and the as-grown ferroelectric oxide films, which is realized by the electrons from the doped substrates. Atomic-level characterization reveals a nontrivial polarization gradient throughout the films in a long range up to ~500 nm because of a possible structural transition from the monoclinic phase to the tetragonal phase. This polarization gradient generates an extremely high photovoltaic short-circuit current density of ~2.153 mA/cm2 and open-circuit voltage of ~1.15 V under 375 nm light illumination with power intensity of 500 mW/cm2, corresponding to the highest photoresponsivity of ~4.306×10−3 A/W among all known ferroelectrics. Our results establish a general low-temperature solution route to produce single-crystal gradient films of ferroelectric oxides and thus open the avenue for their broad applications in self-powered photo-detectors, photovoltaic and optoelectronic devices.

Superparamagnetic Iron Oxide Nanoparticles (SPIONs) and Reduced Graphene Oxide (RGO) Based Nanocomposites Prepared by Low-Temperature Route and Their Anticancer Properties

In this work, a facile low temperature solution route was reported for the preparation of monodisperse Fe3O4 nanoparticles and their reduced graphene oxide (RGO) based nanocomposites and used as anticancer agents. X-ray diffraction spectroscopy XRD and Raman studies revealed the high crystalline nature of the Fe3O4 nanoparticles and the presence of characteristic peaks of RGO in Fe3O4/RGO nanocomposites. Transmission electron microscopy (TEM) micrographs showed the morphology of the RGO nanosheets decorated by Fe3O4 nanoparticles with sizes ranging from 10–15 nm. High resolution (HR)-TEM study revealed the formation of Fe3O4/RGO nanocomposites with the interplanar spacing corresponding to the (311) plane of Fe3O4. The anti-cancer properties of Fe3O4/RGO nanocomposites against A549 cells were investigated using MTT, NRU assay, morphology of cells, and ROS generation analyses and compared with the pure Fe3O4 nanoparticles. In comparison between both the pure Fe3O4 and Fe3O4/RGO nanocomposites, more damage to the A549 cells resulted from the nanocomposites at a similar concentration of 100 μg/ml. The cell viability test showed that 36% cell viability was observed at a concentration of 100 μg/ml for Fe3O4/RGO nanocomposites. Additionally, the percentage of ROS generation for Fe3O4/RGO nanocomposites was higher than that of Fe3O4 at a concentration of 100 μg/ml. These results suggested that the as-synthesized nanocomposites might be a potential candidate for future anticancer agents.

Control synthesis of low aspect ratio Zn1-xAgxO nanorods using low temperature solution route: Evidence of Ag concentration dependent shape transition

Understanding the effect of doping concentration on the various properties of metal-doped ZnO nanoparticles (NPs) near the shape transition point (sphere to the rod) is essentially required for their possible applications. Given these, we have successfully synthesized spherical to rod-shaped Zn1-xAgxO employing a simple chemical route considering Ag doping with concentrations of 1, 2, and 3 mol percentage (%). Although, the shape transition from spherical to rod has been triggered at doping concentration of 2 mol%, the shape transition has been found to be completed for 3 mol% generating nanorods with an aspect ratio of ∼1.33. Structural, optical, and antimicrobial properties of Zn1-xAgxO NPs show significant changes at the transition concentration of Ag. The shape transition occurs mainly due to the process of synthesis and change in the surface states of the NPs in presence of excess Ag+ ions in the local environment of the nucleation sites of ZnO.

Low-Temperature Solution-Processed Synthesis of Hollow SnO2@TiO2 Core–Shell Hierarchical Structure for Self-Powered Ultraviolet Photodetectors

The interest in investigating hollow core–shell nanostructures was stimulated by their intrinsic advantage in light absorption and photocarrier separation for promising applications in photoelectrochemical devices. Here, SnO2@TiO2 core–shell hierarchical tubular structure was designed and prepared via a low-temperature solution route using carbon nanofibers as templates. The heterostructure consists of SnO2 nanotubes and TiO2 nanocones, which facilities photocarrier separation and transport by built-in electric field at their interface, and direct transport path served by SnO2 nanotubes. The large specific surface area was also believed to contribute to improve performance by providing more active sites for chemical reactions. After assembling into a photoelectrochemical-type ultraviolet photodetector, the detector exhibits a high short-circuit photocurrent density of 870 μA cm–2 under ultraviolet illumination (λ = 365 nm) of 35 mW cm–2 without bias voltage. The photosensitivity can reach up to 3781, and the feature response time was in microseconds, 33 ms for rise process and 13 ms for decay process. It is believed that this structure with combined advantageous features is extendable to other photoelectrochemical cases, such as dye-sensitized solar cells and artificial photosynthesis.

Structural characterization and gas sensing applications of ultrafine ZrO2 nanospheres using low temperature solution route

Monophasic ZrO2 nanoparticles were successfully prepared by using low temperature solution route. As-prepared nanoparticles were characterized by different techniques like XRD, SEM, TEM, BET and UV–Visible studies. X-ray diffraction analysis revealed the crystalline tetragonal phase of ZrO2. Transmission electron microscopic studies show the formation of 15 nm sized spherical particles of zirconia. The surface morphological studies were established by Scanning Electron Microscopy. UV–Visible diffused reflectance spectroscopy studies give the optical band gap of 4.9 eV for the synthesized nanoparticles. BET surface area studies revealed the high surface area of 128 m2/g. Enhanced gas sensing property was revealed by the ZrO2 nanoparticles over carbon monoxide at 50 ppm concentration and at a minimal operating temperature of 240 °C. The good sensing properties can indeed be ascribed to the large oxygen surface vacancies available and the high surface area possessed by the ZrO2 nanoparticles which are favorable for both the transport of gas molecules and sensing reactions to occur as was deduced from the sensing mechanism.

A facile low-cost preparation of high-k ZrO2 dielectric films for superior thin-film transistors

Herein, we report a facile low-cost approach to high-k ZrO2 dielectric films and integrated devices by using lightwave (LW) irradiation induced chloride-based low-temperature solution route. The as-prepared devices have exhibited comparable performances to the traditional thermally-annealed devices, which are prepared at high temperatures. The as-prepared high-k ZrO2 films exhibit the smooth surface, amorphous phase and large band gap. LW-irradiated ZrO2 films, processed at ~230 °C for 40 min, rendered excellent performance, including a great capacitance of 270 nF/cm2 and a low leakage current of 10−8 A/cm2, superior to those of ZrO2 films obtained through thermal annealing (430 °C for 60 min). The present LW irradiation effectively promoted M-O framework and, simultaneously, facilitated the elimination of oxygen defects from the precursor film. Furthermore, the LW irradiation of metal chlorides can be extended to fabricate other oxides. For instance, we have used LW irradiation to prepare In2O3 and InZnO semiconductor films from chloride precursors. Moreover, LW irradiated In2O3-based TFTs, with ZrO2 dielectric films, exhibited a large mobility of 19.4 cm2/V as well as a desirable on/off ratio of 106. In addition, LW irradiated In2O3-based TFTs exhibited negligible hysteresis and high bias stability, which are highly desirable in practical applications. The results reveal that LW irradiation of chlorides holds promise for the facile low-cost production of high-performance dielectric films for diverse applications.

High-Mobility IGZO TFTs by Infrared Radiation Activated Low-Temperature Solution Process

This letter presents high-mobility thin-film transistors (TFTs) based on InGaZnO by a novel infrared (IR) radiation activated low-temperature solution process. A high mobility of over 60 cm2V−1s−1, an ${I}_{\mathrm{\scriptscriptstyle ON}}/{I}_{\mathrm{\scriptscriptstyle OFF}}$ ratio of 106, and a decreased operating voltage of 4 V were achieved at 230 °C. This mobility was four times higher than that of a device by high-temperature (450 °C) annealing, and was comparable to those of oxide TFTs previously produced via vacuum or high-temperature processes. The synergistic IR radiation and thermal energy mechanism resulted in more effective removal of precursor impurities, a more extensive metal-oxygen lattice, and more oxygen vacancies to serve as charge carriers, which contributed to the much higher performance achieved with IR radiation. Moreover, the IR-processed devices exhibited excellent operational stability with a small ${V}_{\textsf {th}}$ shift under bias stress. Our results may provide new low-temperature solution routes to high-performance TFTs.

Low Temperature Synthesis of Superparamagnetic Iron Oxide (Fe3O4) Nanoparticles and Their ROS Mediated Inhibition of Biofilm Formed by Food-Associated Bacteria.

In the present study, a facile environmentally friendly approach was described to prepare monodisperse iron oxide (Fe3O4) nanoparticles (IONPs) by low temperature solution route. The synthesized nanoparticles were characterized using x-ray diffraction spectroscopy (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) measurements, Fourier-Transform Infrared Spectroscopy (FTIR), and Thermogravimetric analysis (TGA) analyses. XRD patterns revealed high crystalline quality of the nanoparticles. SEM micrographs showed the monodispersed IONPs with size ranging from 6 to 9 nm. Synthesized nanoparticles demonstrated MICs of 32, 64, and 128 μg/ml against Gram negative bacteria i.e., Serratia marcescens, Escherichia coli, and Pseudomonas aeruginosa, respectively, and 32 μg/ml against Gram positive bacteria Listeria monocytogenes. IOPNs at its respective sub-MICs demonstrated significant reduction of alginate and exopolysaccharide production and subsequently demonstrated broad-spectrum inhibition of biofilm ranging from 16 to 88% in the test bacteria. Biofilm reduction was also examined using SEM and Confocal Laser Scanning Microscopy (CLSM). Interaction of IONPs with bacterial cells generated ROS contributing to reduced biofilm formation. The present study for the first time report that these IONPs were effective in obliterating pre-formed biofilms. Thus, it is envisaged that these nanoparticles with broad-spectrum biofilm inhibitory property could be exploited in the food industry as well as in medical settings to curtail biofilm based infections and losses.

Scalable Room-Temperature Synthesis of Multi-shelled Na3(VOPO4)2F Microsphere Cathodes

Summary The large-scale application of rechargeable batteries in electric vehicles and energy-storage systems is still hindered by their high cost, particularly from the active materials. Here we proposed a concept of integration of extraction-separation and materials-preparation to further reduce the materials' cost. The power of this concept was demonstrated by the large-scale room-temperature synthesis (150 g per batch) of multi-shelled Na3(VOPO4)2F microspheres based on in situ generated bubbles as soft templates. The as-prepared Na3(VOPO4)2F shows superior rate capability with discharge capacity of 81 mAh g−1 at 15 C current rate and capacity retention of 70% after 3,000 cycles. Ex situ UV-vis was first employed to characterize the variation of oxidation state for vanadium during the charging and discharging process. This is the first report of a rapid and facile large-scale room-temperature controllable synthesis of Na3(VOPO4)2F microspheres, and this approach could be extended to synthesize other similar compounds.

Mesoporous Cu2O–CeO2 composite nanospheres with enhanced catalytic activity for 4-nitrophenol reduction

In this paper, mesoporous Cu2O–CeO2 nanospheres were fabricated via a facile, low-temperature solution route in the presence of poly(2-vinylpyridine)-b-poly(ethylene Oxide) (P2VP-b-PEO) block copolymers. The prepared mesoporous Cu2O–CeO2 nanospheres were characterized systematically by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption/desorption. The formation mechanism of mesoporous Cu2O–CeO2 nanospheres was discussed. The results show that the molar ratios of Ce3+/Cu2+ and the reaction time have an important influence on the nanostructure of Cu2O–CeO2 composite spheres. The resultant Cu2O–CeO2 nanospheres exhibit superior catalytic activities in the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. The activity factor (K = k/m) for the Cu2O–CeO2 nanospheres prepared with the molar ratio of Ce3+/Cu2+ of 5/1 is 3006.6 s−1 g−1, which is much higher than reported values. This paper demonstrates a highly controllable approach to the production of mesoporous Cu2O–CeO2 nanospheres, which have potential applications in the areas of catalysis, adsorption, sensors and so on.

Ag nanoparticles decorated ZnO nanoarrays with enhanced surface-enhanced Raman scattering and field emission property

A simple, low-temperature solution route was reported for the coating of ZnO nanoarrays with Ag nanoparticles. Ag nanoparticles were decorated on the surface of ZnO nanoarrays, which was demonstrated by field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Additionally, the ZnO/Ag composite nanoarrays manifested high surface-enhanced Raman scattering (SERS) sensitivity of 10−6 M rhodamine 6G with a maximum enhancement factor of 1.24 × 105. Moreover, the field emission property of the ZnO/Ag composite nanoarrays was studied in details. The turn-on field of the ZnO/Ag composite nanoarrays was 6.3 V/µm, and the threshold field was 11.4 V/µm. The field enhancement factor of the ZnO/Ag composite nanoarrays was about 1927. These superior properties indicated that the ZnO/Ag composite nanoarrays could be a good cathodes candidate for SERS detection and field emission.

Solution Process Synthesis of High Aspect Ratio ZnO Nanorods on Electrode Surface for Sensitive Electrochemical Detection of Uric Acid

This study demonstrates a highly stable, selective and sensitive uric acid (UA) biosensor based on high aspect ratio zinc oxide nanorods (ZNRs) vertical grown on electrode surface via a simple one-step low temperature solution route. Uricase enzyme was immobilized on the ZNRs followed by Nafion covering to fabricate UA sensing electrodes (Nafion/Uricase-ZNRs/Ag). The fabricated electrodes showed enhanced performance with attractive analytical response, such as a high sensitivity of 239.67 μA cm−2 mM−1 in wide-linear range (0.01–4.56 mM), rapid response time (~3 s), low detection limit (5 nM), and low value of apparent Michaelis-Menten constant (Kmapp, 0.025 mM). In addition, selectivity, reproducibility and long-term storage stability of biosensor was also demonstrated. These results can be attributed to the high aspect ratio of vertically grown ZNRs which provides high surface area leading to enhanced enzyme immobilization, high electrocatalytic activity, and direct electron transfer during electrochemical detection of UA. We expect that this biosensor platform will be advantageous to fabricate ultrasensitive, robust, low-cost sensing device for numerous analyte detection.

Development of highly-stable binder-free chemical sensor electrodes for p-nitroaniline detection

Herein, pre-seeded fluorine doped tin oxide (FTO) glass substrates were used as an electrode for zinc oxide nanorods (ZnO NRs) growth by a low-temperature solution route in order to fabricate binder-free high-sensitive chemical sensor. The vertically-grown ZnO NRs exhibited a more favorable active morphology and improved sensing properties for p-nitroaniline (pNA) detection. On investigation with different concentrations of pNA, the ZnO NRs/FTO electrode showed an excellent sensitivity (10.18μAμM−1cm−2) and low detection limit (0.5μM) with good selectivity, outstanding long-term stability, and high reproducibility. Collectively, the present work emphasizes the potency of ZnO NRs/FTO electrodes for fabrication of an efficient and reliable chemical sensing device with improved performances.

Highly stable hydrazine chemical sensor based on vertically-aligned ZnO nanorods grown on electrode

Herein, we report a binder-free, stable, and high-performance hydrazine chemical sensor based on vertically aligned zinc oxide nanorods (ZnO NRs), grown on silver (Ag) electrode via low-temperature solution route. The morphological characterizations showed that the NRs were grown vertically in high density and possess good crystallinity. The as-fabricated hydrazine chemical sensors showed an excellent sensitivity of 105.5 μAμM−1cm−2, a linear range up to 98.6μM, and low detection limit of 0.005μM. It also showed better long-term stability, good reproducibility and selectivity. Furthermore, the fabricated electrodes were evaluated for hydrazine detection in water samples. We found the approach of directly growing nanostructures as a key factor for enhanced sensing performance of our electrodes, which effectively transfers electron from ZnO NRs to conductive Ag electrode. Thus it holds future prospective applications as binder-free, cost-effective, and stable sensing devices fabrication.

Cu particles induced distinct enhancements for reduced graphene oxide-based flexible supercapacitors

Novel Cu/reduced graphene oxide (Cu/RGO) supercapacitors with excellent performance were prepared via a proposed low-temperature, binder-free, and low-cost solution route. Transmission electron microscopy analysis shows the as-synthesized Cu nanoparticles (NPs) are highly crystalline, and the associated redox reactions during charging/discharging cycles take place partially only in the exterior, leaving behind the central part as highly crystalline Cu with high conductivity. The cyclic voltammetry measurements show the Cu/RGO composites with different Cu NP sizes demonstrate distinct enhancements for energy and power densities at low and high scan rates compared with RGO. The galvanostatic charging/discharging measurements show that the capacitor with the smallest Cu NPs has a high specific capacitance of 335 F/g, energy density of 47 Wh/kg, and power density of 804 W/kg at a current density of 1 A/g. Cyclic life tests show the capacitance is increased to 125% of the initial value after 3400 cycles, and then demonstrates excellent cyclic stability to 8000 cycles without decay at a high current density of 5 A/g. The employment of metal NPs as pseudocapacitance materials in RGO-based supercapacitors opens up the opportunity to fabricate excellent flexible supercapacitors.

A new low-temperature solution route to Aurivillius-type layered oxyfluoride perovskites Bi2MO5F (M = Nb, Ta) as photocatalysts

Aurivillius oxyfluoride perovskites exhibit great potential in photocatalysis, which are generally prepared by high-temperature solid-state reactions and some impurity phases are always unavoidable. Herein, a new low-temperature solution method has been successfully developed for the synthesis of Bi2NbO5F and Bi2TaO5F pure phases. The electron microscopy results reveal that the products were composed of the hierarchical hollow spheres with porous surface. The formation and growth mechanisms of the products were proposed based on the time-dependent evolution. The experimental band gaps of Bi2NbO5F (2.86eV) and Bi2TaO5F (2.95eV) were also first obtained. The photodegradation tests demonstrated that the products could be effectively served as catalysts for degradation of Rhodamine B and methyl orange under UV-light irradiation via the photocatalytic reaction, and also could be used in visible-light degradation of Rhodamine B via the photosensitization process. This low-temperature solution preparation of Aurivillius oxyfluorides opens a new facile route to tackle the versatile chemistry of various oxyfluoride perovskites.

Rapid methyl orange degradation using porous ZnO spheres photocatalyst

Porous zinc oxide (ZnO) spheres were synthesized by facile low temperature solution route. The as-synthesized porous ZnO spheres were characterized in detail in terms of their morphological, structural, optical and photocatalytic properties using field-emission scanning electron microscopy (FESEM, equipped with energy dispersive spectroscopy (EDS)), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffractometer (XRD), UV–visible spectroscopy and Raman-scattering measurements. Nitrogen adsorption-desorption analysis was performed to determine pore size distribution from the adsorption isotherm curves using the Barrett-Joyner-Halenda (BJH) method. Morphological and structural characterizations showed porous nature of ZnO spheres with high surface area, good crystallinity, wurtzite hexagonal phase and good optical features. Next, ZnO spheres were studied as photocatalyst for photodegradation of harmful dye, methyl orange (MO). Under ultraviolet light irradiation, the decrease in MO dye concentration was monitored by UV–visible spectroscopy at different time intervals until the dye was completely degraded to colorless end product. Rapid MO dye decomposition was observed with a degradation rate of ~96.3% within the initial 120min, which is attributed to the porous nature, large specific surface area (114.6m2g−1), narrow pore size distribution (~2.5 to 25nm) evaluated from N2 adsorption-desorption isotherms analysis and excellent electron accepting features of the engineered porous ZnO spheres.

Improving performance of inverted organic solar cells using ZTO nanoparticles as cathode buffer layer

In this study, a low-temperature solution-processed zinc tin oxide (ZTO) films are successfully utilized as the cathode buffer layer in the inverted organic P3HT:PCBM bulk heterojunction solar cells. ZTO film cathode buffer layer with an appropriate Sn-doping concentration outperforms the zinc oxide (ZnO) film with an improved power conversion efficiency (1.96% (ZTO film) vs. 1.56% (ZnO film)). Furthermore, ZTO nanoparticles (NPs) are also synthesized via low-temperature solution route and the device with ZTO NPs buffer layer exhibits a significant improvement in device performance to reach a PCE of 2.60%. The crystallinity of the cathode buffer layer plays an influential factor in the performance. From impedance spectroscopy analysis, a correlation between short circuit current (Jsc), carrier life time (τavg) and, thus, PCE is observed. The interplay between composition and crystallinity of the cathode buffer layers is discussed to find their influences on the solar cell performance.

Degradation of Lindane using two nanosized BiOXs and their heterojunction under visible light

In this paper, bismuth oxybromide (BiOBr), bismuth oxyiodide (BiOI), and heterojunction (BiOI0.5Br0.5) were prepared via facile co-precipitation method, a low-temperature solution route, and facile chemical etching method, respectively. They were prepared by Bi(NO3)3·5H2O as the Bi source. The resulting BiOBr, BiOI, and BiOI0.5Br0.5 photocatalysts were fully characterized using X-ray diffraction, energy-dispersive X-ray spectroscopic, scanning electron microscopy, high-resolution transmission electron microscopy, SAED, Brunauer–Emmett–Teller surface area, and UV–vis diffuse reflectance spectra techniques. The prepared photocatalysts were of pure tetragonal phase, and homogeneous particles. Their surface area are 6.19, 296.6, and 186.6 m2/g, and their band gaps were about 2.9, 1.9, and 2.1 eV for BiOBr, BiOI, and BiOI0.5 Br0.5, respectively. Their photocatalytic property was investigated by the degradation of Lindane in aqueous solution under commercial visible metal halide lamp. The optimum amounts of BiOBr, BiOI, and BiOI0.5Br0.5 powders were 1.0 g/L at pH 8 that degraded 60, 80, and 95% of Lindane, respectively, after 2 h of irradiation. Moreover, BiOI0.5Br0.5 heterojunction exhibited much higher photocatalytic activity for the degradation of Lindane under visible light (λ > 420 nm) than pure BiOBr and BiOI, Since, the reaction kinetic constants for degradation of Lindane by BiOBr, BiOI, and BiOI0.5Br0.5 heterojunction were 0.0073, 0.0126, and 0.0194 min−1, respectively. It is a prospective strategy for constructing highly efficient bismuth halide-based heterojunction to eliminate organic pollutants in water.

Facile Approach to Synthesize Au@ZnO Core-Shell Nanoparticles and Their Application for Highly Sensitive and Selective Gas Sensors.

We successfully prepared Au@ZnO core-shell nanoparticles (CSNPs) by a facile low-temperature solution route and studied its gas-sensing properties. The obtained Au@ZnO CSNPs were carefully characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, and UV-visible spectroscopy. Mostly spherical-shaped Au@ZnO CSNPs were formed by 10-15 nm Au NPs in the center and by 40-45 nm smooth ZnO shell outside. After the heat-treatment process at 500 °C, the crystallinity of ZnO shell was increased without any significant change in morphology of Au@ZnO CSNPs. The gas-sensing test of Au@ZnO CSNPs was examined at 300 °C for various gases including H2 and compared with pure ZnO NPs. The sensor Au@ZnO CSNPs showed the high sensitivity and selectivity to H2 at 300 °C. The response values of Au@ZnO CSNPs and pure ZnO NPs sensors to 100 ppm of H2 at 300 °C were 103.9 and 12.7, respectively. The improved response of Au@ZnO CSNPs was related to the electronic sensitization of Au NPs due to Schottky barrier formation. The high selectivity of Au@ZnO CSNPs sensor toward H2 gas might be due to the chemical as well as catalytic effect of Au NPs.