Na2SO4 Aqueous Solution Research Articles

Electrodeposition of Sb2S3 light absorbers on TiO2 nanorod array as photocatalyst for water oxidation

Artificial photosynthesis provides a direct approach toward addressing energy and environmental issues by producing chemical fuels such as hydrogen for fuel cells. A photoanode composed of the composite of titanium dioxide (TiO2) nanorod and antimony sulfide (Sb2S3) nanoparticles was proposed in this work. The TiO2 nanorod array is made on a fluorine-doped tin oxide glass by using the hydrothermal reaction, and the Sb2S3 nanoparticles were deposited on the TiO2 nanorod array by using the electrodeposition method with different depositing currents. The electrodeposition method is more time-saving as compared with the commonly used chemical bath reaction method. The Sb2S3 was selected as the coating material due to its broader light absorption range and suitable band-edge positions relating to those of TiO2 for forming a type II heterojunction, aiming to improve the poor visible light absorption and low quantum efficiency of TiO2. A higher photocurrent density of 0.33 mA cm−2 (measured at 1.23 V vs. reversible hydrogen electrode) is obtained for the TiO2/Sb2S3 photoanode in a 0.5 M Na2SO4 aqueous solution under the air mass 1.5 global illumination, comparing to that of 0.017 mA cm−2 for the TiO2 electrode measured under the same conditions. This successful combination of two n-type semiconductors as the photocatalyst for achieving efficient water oxidation provides a conceptual blueprint for designing the composite with complementary optical and electrical properties.

Self-organized TiO2 nanotubes grown on Ti substrates with different crystallographic preferential orientations: Local structure of TiO2 nanotubes vs. photo-electrochemical response

Here we report on structural properties and the photo-electrochemical response of annealed TiO2 nanotube layers, grown on four different Ti substrates by an identical anodization process. TiO2 nanotube layers were grown on Ti substrates by anodization in glycerol containing NH4F and water. The layers were then annealed at 400 °C for 1 h in air. Photocurrent densities of annealed nanotubes were recorded upon irradiation with ultraviolet (UV) light at a constant potential of 0.4 V, in a 0.1 M Na2SO4 aqueous solution. Approximately, a 280% difference in the photocurrent densities was recorded from TiO2 nanotubes fabricated from different Ti substrates. To elucidate the origin of this difference, the nanotube layers were scrutinized by Mott-Schottky measurements, X-ray diffraction (XRD) and Electron Energy Loss Spectroscopy (EELS). Inspection of the XRD patterns revealed preferential crystallographic orientations in various Ti substrates from which TiO2 nanotube layers were produced. Subsequent EELS analyses of the annealed nanotube layers disclosed significant differences in the Ti:O stoichiometry, in accordance with XRD evaluation of preferential orientation differences among used Ti substrates.

Tetra-heteroatom self-doped carbon nanosheets derived from silkworm excrement for high-performance supercapacitors

Carbon materials are deemed to be competitive candidate electrode materials for energy storage systems. It is still a great challenge to explore advanced carbon-based electrode materials for high-performance supercapacitors by a facile, economical and efficient method. In this work, N-, P-, S-, O-self-doped carbon nanosheets with high surface area and well-developed porosity are successfully prepared by pyrolysis carbonization and post KOH activation from silkworm excrement, a novel abundant, low-cost and eco-friendly agricultural waste. Thanks to their unique multi-heteroatom doping and porous structure, the obtained carbon materials exhibit high charge storage capacity with a specific capacitance of 401 F g−1 at a current density of 0.5 A g−1 in 6 M KOH and good cycling stability with a capacitance retention of 93.8% over 10000 cycles. A symmetric supercapacitor device using 1 M Na2SO4 aqueous solution as the electrolyte can deliver a specific capacitance of 41.7 F g−1 at a current density of 0.5 A g−1, and a high energy density of 23.17 Wh kg−1 at a power density of 500 W kg−1 with a wide voltage window of 2.0 V. This work develops a new strategy to produce favorable carbon-based electrode materials for supercapacitors with high electrochemical performances.

MnO2 and biomass-derived 3D porous carbon composites electrodes for high performance supercapacitor applications

MnO2/biomass-derived porous carbon (BPC) composites have been prepared by a hydrothermal method, in which the BPC 3D porous carbon structure was based on a banana peel. The banana peel, after freeze drying, can maintain its hierarchical natural porous structure, which provides enough growth space for MnO2 and reduces the agglomeration of MnO2 particles. The MnO2/BPC composites were characterized by XRD, FT-IR, XPS, TGA, SEM, TEM, BET. The electrochemical performance of the composites was tested in three-electrode supercapacitors using 1 M Na2SO4 aqueous solution as an electrolyte. Due to the large amounts of hierarchical pores and large pore volume, the as-prepared composites exhibited good electrochemical performance. Electrochemical measurements indicated that the MnO2/BPC composites applied in supercapacitors had a specific capacitance of 139.6 F g−1 at 300 mA g−1, and exhibited a good cycling stability with a capacitance retention ratio of 92.3% after 1000 cycles (at 1 A g−1). The MnO2/BPC composites with 3D porous structure are promising materials in the application of supercapacitors.

The corrosion mechanism of the sintered (Ce, Nd)-Fe-B magnets prepared by double main phase and single main phase approaches

The sintered (Ce, Nd)-Fe-B magnets were produced widely by Double Main Phase (DMP) method in China as the magnetic properties of the DMP magnets are superior to those of single main phase (SMP) magnets with the same nominal composition. In this work, the microstructure and corrosion mechanism of the sintered (Ce0.2Nd0.8)30FebalB (wt.%) magnets prepared by DMP and SMP method were studied in detail. Compared to SMP magnets, the DMP magnets have more positive corrosion potential, lower corrosion current density, larger electron transfer resistance, and lower mass loss of the free corrosion experiment in 0.5mol/l Na2SO4 aqueous solution. All of the results show that the DMP magnets have better corrosion resistance than SMP magnets. The back scattered electron images show that the crystalline grains of the DMP magnets are sphericity with a smooth surface while the SMP ones have plenty of edges and corners. Besides, the distribution of Ce/Nd is much more uneven in both magnetic phase and rare earth (Re)-rich phase of the DMP magnets than those of SMP magnets. After corrosion, DMP magnets show eroded magnetic phase and intact Re-rich phase, which indicate that galvanic corrosion of the Re-rich phase acting as the cathode appears.

Fabrication of Molybdenum Trioxide Nanobelts as High Performance Supercapacitor

Electrochemical supercapacitors based on transition metal oxides nanostructures have aroused much attention for energy storage and conversion owing to their ability to intercalate ions in a wide range of sites. In this work, we have reported electrochemical properties of molybdenum trioxide (MoO3) nanobelts synthesized via facile low temperature hydrothermal method and used it as an electrode material for the supercapacitor applications. The morphology and crystal structure of the MoO3 nanobelts have been characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscope (HRTEM) and X-ray powder diffraction (XRD) respectively. The BET surface area was found to be 59.285 m2 g-1. The supercapacitor performances of the nanobelts electrodes have been investigated by cyclic voltammetry (CV). The MoO3 based supercapacitor shows a specific capacitance as high as 256.83 F g-1 at a scan rate of 5 mV s-1 in 0.5 M Na2SO4 aqueous electrolyte solution. Moreover, the low series resistance (1.20 Ω) and charge transfer resistance (3.85 Ω) values at high frequency range obtained from MoO3 electrode indicate that it is a promising supercapacitor electrode material and suitable for other electrochemical applications. In addition, MoO3 supercapacitor electrode shows high electrochemical stability and can withstand over 200 cycles with no obvious change in the CV curves.

Improved photocatalytic and photoelectrochemical performance of monoclinic bismuth vanadate by surface defect states (Bi1-xVO4)

Due to visible light absorption and photochemical stability, Bismuth vanadate (BiVO4), recognized to be a promising photoanodes for designing high efficiency semiconductor photoelectrochemical (PEC) devices. To improve the photocatalytic and PEC performance of BiVO4, the porous monoclinic BiVO4 with surface bismuth vacancy (Bi1-xVO4 (s-m)) was obtained after the calcination of tetrahedron bismuth vanadate (BiVO4 (s-t)). The photocatalytic experiments showed that despite the relatively lower adsorption capacity of Bi1-xVO4 (s-m) as compared with BiVO4 (s-t), its photocatalytic activity for the photodegradation of tetracyclines (TCs) was 15-fold greater. A four-layer thin films of BiVO4 were deposited by spin coating with intermediate annealing treatment between layers and final calcination at 450 °C in air to shed light on carrier transport in Bi1-x VO4 (s-m). The PEC results indicated that BiVO4 (s-t) showed poor charge carrier mobility, while the Bi1-x VO4 (s-m) showed great improvement by transformation of the tetrahedron BiVO4 (s-t) into monoclinic phase, creation of new surface defect states and formation of a porous structure in Bi1-xVO4 (s-m). Furthermore, Bi1-xVO4 (s-m) showed enhanced and stable photocurrent density of 1.2 mA/cm2 at 1.0 V vs. Ag/AgCl which was achieved under visible light illumination using 0.1 M Na2SO4 aqueous solution. The porous Bi1-xVO4 (s-m) showed the band gap narrowing of 0.08 eV, valence band up-shifting of 0.150 eV and 100 mV cathodic shift in onset potential relative to BiVO4 (s-t). This enhancement is assigned to the longer electron lifetime of Bi1-xVO4 (s-m), 10-fold compared to that of BiVO4 (s-t), resulting in a minimized electron-hole pairs recombination.

Fabrication of hierarchical MoO3–PPy core–shell nanobelts and “worm-like” MWNTs–MnO2 core–shell materials for high-performance asymmetric supercapacitor

Asymmetric supercapacitors (ASCs) are successfully developed with configuration of negative electrode using hierarchical MoO3–PPy core–shell nanobelts (MoO3–PPy) and positive electrode with “worm-like” MWNTs–MnO2 core–shell materials (CNTs–MnO2) in Na2SO4 aqueous electrolyte. The MoO3 nanobelts are prepared by a facile hydrothermal method and get significant improvement in specific capacitance with modification of PPy layer from 124 to 285 F/g. Furthermore, the optimized ASCs based on the MoO3–PPy//CNTs–MnO2 can achieve 1.8 V high voltage even in Na2SO4 aqueous solution and possess a high energy density of 21.03 Wh/kg at the power density of 0.22 kW/kg. Additionally, the ASCs exhibit excellent cycle stability, with 76% retention of its original value even after 10000 cycles. The ASCs are further demonstrated to light up a red light-emitting diode in series. These encouraging results indicate a promising application in the energy-storage devices with high power density and energy density.

Electrochemical behavior of phthaloyl peroxide in aqueous media

The electrochemical behavior of phthaloyl peroxide C8H4O4 on an Au disk electrode in a 0.05 M aqueous solution of Na2SO4 was studied by cyclic voltammetry (CVA). It demonstrated a high activity in cathodic reduction with the formation of an irreversible peak on the CVA curve at E =–0.81 V. Additionally, during the anodic oxidation of C8H4O4, the surface of the Au electrode became passivated by compounds which prevented its oxidation during the registration of repeated cycles. Apparently, these compounds are surface complexes of phthaloyl peroxide with a gold cation.

Investigation of Na2SO4 removal from a supercritical aqueous solution in a dip-tube salt separator

Solar-driven hydrothermal gasification is an efficient process to exploit the energetic potential of biomass containing high amounts of water. This process requires effective removal of the type-2 salts from the feedstock as their precipitates can plug the equipment and poison the gasification catalyst. This work investigates the effect of the axial temperature profile on type-2 salt deposition in a dip-tube salt separator operated with an aqueous Na2SO4 solution as model feed and presents a method for online detection and monitoring of the growth of the deposits. Our results suggest that preventing the salt deposition at the wall of the separator by controlling the axial temperature profile is not possible. The online monitoring of the salt deposition is thus indispensable for scheduling the timely removal of the salt deposits.

Facile preparation of CuWO4 porous films and their photoelectrochemical properties

In this study, the structure and photoelectrochemical properties of CuWO4 porous films synthesized by a co-precipitation method followed by a hydrothermal treatment were investigated. The film was deposited on fluorine-doped tin oxide (FTO)-conducting glass, from a suspension containing polyethylene glycol, and heat-treated at 500°C for 30min. X-ray diffraction patterns, the Rietveld refinement data, and the micro-Raman spectrum showed that the CuWO4 film has a triclinic structure. The optical band gap energy of the film was estimated to be 2.45eV by the Tauc plot. Field emission scanning electron microcopy images of the films indicated that they are about 4.0±0.5μm thick. The photoelectrochemical properties of the film were investigated in a Na2SO4 aqueous solution, in the absence of light and under polychromatic irradiation. The CuWO4 film exhibited photoelectrochemical behavior of a n-type semiconductor, with a negative photopotential and an anodic photocurrent density of 68μAcm−2 at 0.73V vs. Ag/AgCl (1.23V vs. RHE). The n-type photoelectrochemical behavior was confirmed by a chronoamperometry measurement biased condition at+0.7V, at different pH values. From these studies, it was noted that when the pH values increased from 3 to 11, the photocurrent density increased about 9 times. Also, the flat band potential (Efb) of the semiconductor was estimated by the Butler-Gärtner model at+0.34V, which was utilized to calculate the conduction band edge. The studies presented here reveal that the CuWO4 porous film is a promising candidate to be applied as a photoanode in photocatalytic processes under irradiation by visible light.

A facile synthesis of azoviolet@Mn3O4 nanoparticles for supercapacitor

The azoviolet@Mn3O4 nanoparticles have been successfully synthesized using the azoviolet as a stable absorbed reagent for the supercapacitor. The prepared nanoparticles have been characterized by X-ray diffractometry, scanning electron microscopy, energy dispersive spectrometry, infrared spectrometry, surface area and pore size analysis. The cyclic voltammetry and galvanostatic charge/discharge measurements were performed in 1 M Na2SO4 aqueous solutions in a fixed voltage window of ~(0–1.00) V vs. Ag/AgCl. The specific capacitance at 1 A/g is 112.0 F/g. The azoviolets can improve the reaction areas of Mn3O4 nanoparticles in Na2SO4 aqueous solution for the supercapacitor.

Surface and Interfacial Tension Behavior of Salt Water Containing Dissolved Amphiphilic Compounds of Crude Oil: The Role of Single-Salt Ionic Composition

A detailed investigation into the effect of dissolved amphiphilic compounds of crude oil in salt water on its surface tension/interfacial tension (ST/IFT) behavior has been conducted in this paper. To simulate water–oil contact during water injection into oil reservoirs, 16 single-salt aqueous solutions of NaCl, CaCl2, and Na2SO4 having ionic strengths of up to 2.0 M were mixed with a natural acidic–basic crude oil. The mixing was performed by a rocking mechanism in a visual pressure–volume–temperature cell at an elevated temperature. After the mixing process, two phases were completely separated from each other using a high-temperature centrifuge. Finally, in addition to pH measurements, the air–water ST and decane–water IFT of salt water were measured using the pendant-drop method. The results reveal that the dissolution of crude oil amphiphilic compounds, especially the acidic or basic compounds, in salt water can considerably decrease its ST/IFT. It seems that there is the same optimal ionic strength ...

Electrodeposition preparation of Ce-doped Ti/SnO2-Sb electrodes by using selected addition agents for efficient electrocatalytic oxidation of methylene blue in water

Abstract This paper describes assembling Ce-doped Ti/SnO2-Sb (CTSS) electrodes via electrodeposition by using glucose, citric acid, tartaric acid, oxalic acid and nothing (for comparison) as addition agent, respectively, for highly efficient organic wastewater treatment. The physicochemical properties of five CTSS electrodes were characterized by using the scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscope and electrochemical measurements. The measurement using SEM exhibited the highly porous coralline-like surface morphology of CTSS(glucose) electrode. It is attributed to fewer carboxylic groups in glucose than in other four addition agents. LSV curves showed that the oxygen evolution overpotentials were 2.36 V, 2.29 V, 2.35 V, 2.25 V, and 2.14 V for CTSS(glucose), CTSS(citric acid), CTSS(tartaric acid), CTSS(oxalic acid) and CTSS(nothing), respectively, indicating that using glucose as addition agent is conductive to electrode preparation for efficient electrocatalytic oxidation of organic wastewaters. The electrocatalytic oxidation removal of methylene blue (MB) was investigated in a 0.5 M H2SO4 and 0.1 M Na2SO4 aqueous solution. The color removal efficiencies after one-hour electrolysis treatment with CTSS(glucose) electrode in this aqueous medium at the current densities of 20, 40, 60 mA cm−2 were all more than 99%. It was found that the CTSS(glucose) electrode has more sufficient active catalytic sites and a service life of 23 h in an accelerated life test, which is longer than the other CTSS ones. Adding glucose into the electroplate liquid to assemble CTSS electrode did achieve more obvious decolorization.

Strontium doped lanthanum manganite (LSM) effects on electrochemical performance of LSM/MnO2 composites for supercapacitor

Sr-doped LaMnO3 (LSM)/MnO2 composites show different electrochemical performance and thus indicate that LSM has a positive effect on the capacitance of MnO2 electrode. A typical LSM(10 wt%)/MnO2 electrode presents a higher capacitance of 287.8 F g−1 in 1.0 M Na2SO4 aqueous solution, comparing to the pristine MnO2 electrode, 251.7 F g−1. More interesting, LSM can evidently improve the capacitance of MnO2 electrode under the high rate discharging condition. Compared with the pristine MnO2, LSM(10 wt%)/MnO2 shows excellent capacitance improvement of 11% at low scan rate of 2 mV s−1, 33% at intermediate scan rate of 50 mV s−1 and 47.1% at a high scan rate of 200 mV s−1, respectively. The higher the discharge rate is, the better capacitance improvement can be obtained. Moreover, LSM/MnO2 composite electrode also exhibits excellent cycle performance even after 1000 cycles. These characteristics suggest that LSM/MnO2 composites are promising electrode materials for supercapacitor with high performance.

Coprinus Comatus-Based Nitrogen-Doped Active Carbon for High Performance Supercapacitor

Coprinus comatus-based nitrogen-doped activated carbon (N-ACC) is prepared by chemical activation and nitrogen-doped methods. The N-ACC possesses large specific surface areas (976.96[Formula: see text]m2[Formula: see text]g[Formula: see text]), high nitrogen contents (11.53[Formula: see text]wt.%), and super hydrophilicity. As electrode material for supercapacitors, the N-ACC shows remarkable electrochemical performance, such as 346[Formula: see text]F[Formula: see text]g[Formula: see text] maximum specific capacitance at a current density of 1[Formula: see text]A[Formula: see text]g[Formula: see text], which retains 260[Formula: see text]F[Formula: see text]g[Formula: see text] even at a high current density of 10[Formula: see text]A[Formula: see text]g[Formula: see text] (about 75% capacitance retention) in 2[Formula: see text]M KOH aqueous electrolyte. The assembled N-ACC//N-ACC symmetric supercapacitor exhibits energy density of 14.63[Formula: see text]Wh[Formula: see text]kg[Formula: see text] at power density of 810[Formula: see text]W kg[Formula: see text], and excellent cycling stability with 92% specific capacitance retention after 10000 cycles in the voltage range 0–1.8[Formula: see text]V in 0.5[Formula: see text]M Na2SO4aqueous solution. These results indicate that the N-ACC as electrode materials can be used for high performance supercapacitors.

Biomolecule-assisted hydrothermal synthesis of ZnxCd1−xS nanocrystals and their outstanding photocatalytic performance for hydrogen production

To achieve scalable applications in solar hydrogen production, it is necessary to develop visible-light-responsive photocatalysts that are highly efficient, cost-effective, stable and environmentally-benign. Here narrow bandgap Zn–Cd–S solid solution photocatalysts (Eg = 2.11–2.53 eV) were prepared via a facile and green hydrothermal strategy under mild conditions. Amazingly, over the naked Zn0.5Cd0.5S photocatalyst, an extraordinarily high H2 production activity in Na2S–Na2SO3 aqueous solution is achieved up to 18.3 mmol h−1 g−1 with an apparent quantum efficiency of 73.8% per 50 mg under 420 nm light irradiation, which, to our knowledge, outperforms cocatalyst-free metal sulfide photocatalysts previously reported to date. Such super high performance arises from the enhanced visible-light-absorption capacity, suitable conduction and valence band potential together with the facilitated charge transport in Zn–Cd–S solid solutions. This work may open an avenue for the green preparation of inexpensive photocatalysts for solar H2 production.

PHOTOELECTROCHEMICAL ANALYSIS OF TITANIUM DIOXIDE BY USING OXALIC ACID AS A SACRIFICIAL DONOR

Photoelectrochemical (PEC) water splitting is a very promising green method to produce solar fuel. Titanium dioxide (TiO2) has been widely used as photocatalyst for this type of reaction. Improving the performance of TiO2 for PEC water splitting has been ongoing and addition of sacrificial donor especially from waste is an attractive option to achieve this. Oxalic acid is one component in organic waste stream that can be used as sacrificial donor. The TiO2 thin films has been fabricated by coating TiO2 paste on Fluorine Tin oxide (FTO) glass surface. The morphology of the TiO2 thin films were porous and rough with uniform particles size with crystallite size of about 20 nm and dominant anatase peak. The TiO2 photoelectrode undergo PEC testing to measure its photolectroactivity by using oxalic acid as a sacrificial donor in two different type of electrolytes which are distilled water and sodium sulfate (NA2SO4) aqueous solution. The photocurrent produced without addition of oxalic acid is much lower than with the acid. The saturation photocurrent for aqueous NA2SO4 solution and water electrolyte is 0.1 mA/cm2 and negligible respectively. While the photocurrent for addition of oxalic acid in NA2SO4 aqueous solution is 0.5 mA/cm2 and the photocurrent for oxalic acid in water only is 0.9 mA/cm2, which is almost double compared to in NA2SO4 and tenfold in water only. The highest photocurrent produced by TiO2 photoelectrode is by addition of oxalic acid in aqueous (H2O) electrolyte.

Interpretation of the microwave effect on induction time during CaSO4 primary nucleation by a cluster coagulation model

The effects of microwave on the induction time of CaSO4 are studied experimentally and theoretically. In the experiments, calcium sulfate is precipitated by mixing aqueous CaCl2 solution and Na2SO4 solution. The induction time is measured by recording the change of turbidity in solution. Various energy inputs are used to investigate the effect of energy input on nucleation. The results show that the induction time decreases with increasing supersaturation and increasing energy input. Employing the classical nucleation theory, the interfacial tension is estimated. In addition, the microwave effects on nucleation order (n) and nucleation coefficient (kN) are also investigated, and the corresponding values of homogeneous nucleation are compared with the values of heterogeneous nucleation in the microwave field.A cluster coagulation model, which brings together the classic nucleation models and the theories describing the behavior of colloidal suspension, was applied to estimate the induction time under various energy inputs. It is found that when nucleation is prominently homogeneous, the microwave energy input does not change the number of monomers in dominating clusters. And when nucleation is prominently heterogeneous, although the dominating cluster size increases with supersaturation increasing, at the same supersaturation level, the dominating cluster size remains constant in the microwave field.

An improved model for CO2 solubility in aqueous electrolyte solution containing Na+, K+, Mg2 +, Ca2 +, Cl− and SO42 − under conditions of CO2 capture and sequestration

Based on the Pitzer electrolyte theory for activity coefficient and an accurate equation of state for vapor fugacity, an improved activity-fugacity model is developed to calculate CO2 solubility in aqueous KCl, MgCl2, CaCl2, Na2SO4, K2SO4 and MgSO4 solutions, respectively. The valid range of temperature, pressure and ion strength is up to 450K, 500bar and 5molkg−1. Average absolute deviation of CO2 solubility is about 5% compared to a large number of experimental data available, within or close to experimental uncertainties. By combining the interaction parameters of CO2 and ions developed here with those of CO2 and Na+ and Cl− from an earlier study of Mao et al. (2013), this model can be used to accurately predict CO2 solubility in aqueous mixed-salt solution containing Na+, K+, Mg2+, Ca2+, Cl− and SO2–4under conditions of CO2 capture and sequestration (generally less than 423K and 500bar). Computer code of the application program can be obtained from the corresponding author (maoshide@163.com).