In this work, we have developed a novel aqueous two-phase system (ATPS) composed of 1,4-bis(2-hydroxypropyl)-piperazine (HPP), Na2SO4, and H2O, which can determine the liquid–liquid equilibrium and phase diagrams at the temperatures of 303.15–323.15 K. Simultaneously, the physical properties such as density, viscosity, refractive index, and surface tension have been determined for the top phases and bottom ones of the ATPS. The results indicate that temperature has no significant effect upon the biphasic region, implying a small enthalpy contribution during phase separation. However, the changes in temperature result in a decrease of tie line slope, because H2O molecules are transferred from the bottom phase to the top phase. In determining the physical properties of the system, viscosity and refraction index increase with the system components increasing, during the phase of both HPP and Na2SO4, while density and surface tension fall with the increase of system components in the top phase and decrease in the bottom one. ATPS would be a new method for removing the heat-stable salts (HSS) containing sulfuric acid root of absorbent for flue gas desulfurization, which is as HPP.

Nanoporous carbon material with large specific surface area (2208 m2 g–1) and high pore volume (4.15 cm3 g–1) has been synthesized by the template carbonization method, using a glucose–zinc nitrate complex as the precursor. Moreover, adding redox-mediated ferrous ammonium sulfate (FAS) to an H2SO4 electrolyte and regulating the potential windows in a two-electrode system can result in an ultrahigh specific capacitance of 1499 F g–1 at 10 A g–1 and a high energy density of 58.70 Wh kg–1, which are higher than those of the pristine one without any FAS. These remarkable improvements are attributed to Faradaic pseudocapacitances by the reversible Faradaic reactions of FAS as well as the edge active carbons showing excellent electrosorption toward Fe2+/3+, NH4+, and H+. Furthermore, regulating the potential windows also exerts crucial roles in the capacitive performances. It is revealed that the potential of the −0.5–0.5 V window can lead to optimum capacitance and energy efficiency.

High performance porous carbons for supercapacitors have been successfully prepared through a template carbonization process with the help of magnesium acetate, using a zinc salicylate complex as a carbon source. The carbon–Zn–Mg-900 sample has amorphous features and a developed porous structure. Note that it has a high BET surface area of 2008 m2 g−1, a large pore volume of 3.44 cm3 g−1 and a rationally hierarchical pore size distribution. In a three-electrode system using 6 mol L−1 KOH as the electrolyte, it displays a high specific capacitance of 288.3 F g−1 at 1 A g−1, as well as a good rate capability and long term cycling durability (the retention is 96.6% after cycling 10000 times). Furthermore, in a two-electrode system using [EMIm]BF4/AN as a mixed electrolyte, it reveals that operation temperatures of 25, 50, and 80 °C can greatly influence the electrochemical behavior. Higher operation temperatures can usually result in a better electrochemical performance. The measurements in a two-electrode system especially at different operation temperatures can, to a large extent, amplify the application scope of practical supercapacitors.

Porous carbons have been synthesized by a direct carbonization of potassium biphthalate without an activation process. The experimental results demonstrate that the carbonization temperature plays a crucial role in determining the surface area and pore structure as well as the correlative capacitive performance. The carbon-700/800/900 samples display surface areas of 672, 1,023, and 1,380 m2 g−1 and total pore volumes of 0.38, 0.56, and 0.78 cm3 g−1, respectively. The specific capacitances of the carbon-700/800/900 samples are 300.4, 272.3, and 243.4 F g−1, respectively, at a current density of 0.5 A g−1. More importantly, the carbon-900 sample possesses the highest capacitance retention (~98.4 %) even undergoing charge–discharge 10,000 times. The potassium biphthalate used as a carbon source is inexpensive and commercially available, making it promising for the large-scale production of porous carbons as an excellent electrode material for supercapacitors.

•A direct carbonization method was developed for nitrogen-doped porous carbon.•Tartrazine can serve as not only carbon source but also as nitrogen source.•High surface areas and pore volumes are achieved with Ca(OAc)2·H2O.•The carbon samples exhibit excellent capacitive behaviors.Nitrogen-doped porous carbons possessing high surface areas and large pore volumes have been prepared by directly heating the mixture of tartrazine and Ca(OAc)2·H2O at 800 °C especially without further physical or chemical activation, where Ca(OAc)2·H2O serves as the hard template to regulate the surface area and pore structures. It reveals that the addition of Ca(OAc)2·H2O can remarkably improve the surface area and total pore volume. The T-Ca-800-3:1 sample displays the highest BET surface area as 1669 m2 g−1 and largest total pore volume 0.85 cm3 g−1, which is much larger than those without adding Ca(OAc)2·H2O. Furthermore, it exhibits excellent capacitive performances, including high specific capacitance (ca. 224.3 F g−1 at 0.5 A g−1), good rate capability (the retention of 42.6% at 60 A g−1) and good cycling stability (the retention of 92.3% within 5000 cycles).High-performance nitrogen-doped porous carbons have been prepared by directly heating the mixture of tartrazine and Ca(OAc)2·H2O at 800 °C, and the Ca(OAc)2·H2O serves as the hard template.

High-performance porous carbons as supercapacitor electrode materials have been prepared by a simple but efficient template carbonization process, in which commercially available terephthalic acid–zinc complex is used as a carbon source. It reveals that the carbonization temperature plays a crucial role in determining the structure and capacitive performance of carbons. The carbon-1000 sample has high surface area of 1138 m2 g–1 and large pore volume of 1.44 cm3 g–1 as well as rationally hierarchical pore size distribution. In a three-electrode system, the carbon-1000 sample possesses high specific capacitances of 266.0 F g–1 at 0.5 A g–1 and good cycling stability. In a two-electrode system, the operation temperature (25/50/80 °C) can greatly influence the electrochemical performance of the carbon-1000 sample, especially with an extended voltage window (∼ 3 V). The temperature-dependent operation makes it possible for the application of supercapacitors under extreme conditions.

The density, viscosity, and surface tension of aqueous solution of 1,4-bis-(2-hydroxypropyl)-piperazine (HPP) sulfate, corresponding to a molar ratio of HPP to sulfuric acid of 2:1, were measured at different temperatures, up to 333.15 K. The HPP sulfate mass fraction ranged from (0.062 to 0.372). The density and viscosity experimental data have been correlated with different equations. Results showed that the density, viscosity, and surface tension of the aqueous solution of HPP sulfate decreased as the temperature increases. The density and viscosity increased with mass fraction of HPP sulfate, whereas surface tension decreased linearly with temperatures from (303.15 to 333.15) K. The density and viscosity correlated values are in good agreement with the experimental ones. The surface tension of the aqueous solution of HPP sulfate decreased with HPP sulfate mass fraction quickly in HPP sulfate mass range of (0.062 to 0.248); however, when HPP sulfate mass fraction was from (0.248 to 0.372), the decrease rate obviously reduced, suggesting that molecular association in HPP sulfate solution played an important role on surface tension.

WO3 nanorods @ graphene (WO3@GE) nanocomposites were successfully synthesized via a photoreduction method. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Raman spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy (DRS) techniques. The functional groups present in graphene oxide (GO) such as carboxyl (C=O) were mostly reduced in the WO3@GE nanocomposites. The photocatalytic activity of the samples was evaluated by the degradation of methyl orange (MO). The results showed that the WO3@GE nanocomposites exhibited higher photocatalytic activity compared to bare WO3 nanorods.Highlights►WO3@GE nanocomposites were successfully synthesized via a photoreduction method. ►The GE @ WO3 nanocomposites exhibited higher photocatalytic activity compared to bare WO3 nanorods. ►This work highlighted the potential application of graphene-based materials in the field of photocatalysis.