Research on Three-Dimensional Porous Composite Nano-Assembled α-MnO₂/Reduced Graphene Oxides and Their Super-Capacitive Performance

A series of three-dimensional porous composite α-MnO2/reduced graphene oxides (α-MnO2/RGO) were prepared by nano-assembly in a hydrothermal environment at pH 9.0–13.0 using graphene oxide as the precursor, KMnO4 and MnCl2 as the manganese sources and F− as the control agent of the α-MnO2 crystal form. The α-MnO2/RGO composites prepared at different hydrothermal pH levels presented porous network structures but there were significant differences in these structures. The special pore structure promoted the migration of ions in the electrolyte in the electrode material, and the larger specific surface area promoted the contact between the electrode material and the electrolyte ions. The introduction of graphene solved the problem of poor conductivity of MnO2, facilitated the rapid transfer of electrons, and significantly improved the electrochemical performance of materials. When the pH was 12.0, the specific surface area of the 3D porous composite material αMGs-12.0 was 264 m2·g−1, and it displayed the best super-capacitive performance; in Na2SO4 solution with 1.0 mol·L−1 electrolyte, the specific capacitance was 504 F·g−1 when the current density was 0.5 A·g−1 and the specific capacitance retention rate after 5000 cycles was 88.27%, showing that the composite had excellent electrochemical performance

Structural Regulation and Electroconductivity Change of Nitrogen-Doping Reduced Graphene Oxide Prepared Using p-Phenylene Diamine as Modifier

Using p-phenylene diamine (PPD) as a modifier and nitrogen resource, nitrogen-doping reduced graphene oxide was prepared by one-step refluxing method. The influence of PPD-GO (graphene oxide) mass ratio X on surface functional groups, layer structure, and electroconductivity of nitrogen-doping reduced grapheme oxide (NRGO-X) was investigated by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-vis absorption spectrum, and electrical measurement. The results showed that GO can be simultaneously reduced and nitrogen-doped by PPD. When PPD-GO mass ratio X ≤ 6, there existed three types of N configurations in NRGO-X, including pyridinic N, pyrrolic N, and graphitic N. However, when X > 6, the pyridinic N disappeared in a six-membered ring. Further, the reduction process of NRGO as well as the nitrogen doping level and type can be regulated by changing the mass ratio X. With the increase of X, the d-spacing of NRGO-X layers increased first and then decreased, while the electrical conductivity increased gradually

Effect of SiO2/Al2O3 ratio on sintering behavior, crystallization behavior and properties of diopside-anorthite glass-ceramics

ABSTRACTDiopside-anorthite glass-ceramics were prepared by direct sintering with extracted titanium slag (ETS), coal fly ash (CFA) and quartz sand (SA), the effect of sintering temperature (1120–1180°C) and the SiO2/Al2O3 ratio (1.85–2.63) on the phase transitions, physical characteristics and microstructure was examined by adding CFA (28.5–40%) and SA (0–12.5%) to ETS (60%). The results revealed that the sintering temperature and the ratio of SiO2/Al2O3 have a substantial impact on the sintering and processing properties of glass-ceramics. When the sintering temperature is lower than 1160°C, the sample sintering is incomplete, and when the sintering temperature is higher than 1170°C, the sample is prone to over-sintering and foaming. With the increase of SiO2/Al2O3 ratio, anorthite content increases, while diopside content decreases. When SiO2/Al2O3 ratio is 2.13, 1160°C sintering 1 h, the better performance of diopside-anorthite-based glass-ceramics was prepared. The linear shrinkage, bulk density, water absorption and bending strength of the obtained glass-ceramics are 9.96%, 2.52 g/cm3, 0.943%, and 96.1 MPa, respectively. The results show that the prepared glass-ceramics are industrially applicable

One-Step Synthesis of Hydroxysodalite Using Natural Bentonite at Moderate Temperatures

Ca-bentonite was used as the feedstock material for the synthesis of hydroxysodalite due to its high Al, Si content, good chemical reactivity, and natural abundance. A one-step method is proposed here to fabricate hydroxysodalite in a water bath at moderate temperature. The effects of the Na/Si molar ratio, Si/Al molar ratio, reaction time, and reaction temperature on the synthesis of hydroxysodalite have been systematically investigated here. The crystallizing phases and morphology of the synthetic products were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results showed that the Na/Si molar ratio and reaction temperature both played important roles in controlling the degree of crystallinity of the synthetic hydroxysodalite. The Si/Al molar ratio and reaction time both affect the purity of the synthetic hydroxysodalite. Optimum conditions for synthesizing hydroxysodalite using a one-step water-bath method at moderate temperature are as follows: a Na/Si molar ratio of 12, a Si/Al molar ratio of 1.0, a reaction temperature of 90 °C, and a reaction time of 12 h

Synthesis and characterization of calcium carbonate whisker from yellow phosphorus slag

In this study, a procedure for producing calcium carbonate whisker through yellow phosphorus slag carbonation without adding any crystal control agents was proposed. The influence of process parameters on the crystal phase and morphology of the product was discussed. The content of aragonite in the product was more than 90% under optimal conditions. The whiteness of the product was 97.6%. The diameter of a single particle was about 1.5–3 μm, and the length of a single particle was about 8–40 μm. Various polymorphs and morphologies of CaCO3 could be formed by adjusting the production conditions. The by-products produced during the whole preparation process could also be reused. The whole preparation process of fibrous aragonite from yellow phosphorus slag without using any chemical additives was also proposed. These indicated that the production strategy had a good application prospect

Structural alteration of montmorillonite by acid activation and its effect on the decolorization of rapeseed oil

Low-temperature atmospheric calcination is a new technology for solving the current environmental issues associated with activated clay production. In this study, the structural alteration of montmorillonite during the production of activated clay was investigated by this new technology. The results revealed that the increase in temperature aggravates the destruction of montmorillonite layers, which mainly constituted octahedral sheets due to the continuous dissolution of cations in the sheets, with relatively stable tetrahedral sheets. Activated montmorillonite layers became curled and stacked in disorder, which was different from that in the original. The maximum acidity of 230 mmol/kg was achieved at an optimum temperature of 200°C. Under this condition, the specific surface area and total pore volume increased from 78.4 m2/g to 226 m2/g and from 0.107 cm3/g to 0.318 cm3/g, respectively. With the improvement in the decolorization ability of the clay, the absorbance of the rapeseed oil decreased to 0.867 from 4.070

The Leaching Kinetics of Iron from Titanium Gypsum in a Citric Acid Medium and Obtain Materials by Leaching Liquid

In this study, the effect of citric acid on iron leaching from titanium gypsum (TiG) was systematically investigated. The conditions for the leaching of valuable metals were optimized while varying such parameters as the leaching time, citric acid mass fraction, leaching temperature, and the liquid–solid ratio. It was found that under the conditions of a citric acid mass fraction of 10%, at a 80 °C leaching temperature, a leaching duration of 80–90 min and a liquid–solid ratio of 8, the whiteness of titanium gypsum (TiG) increased from 8.1 to 36.5, and the leaching efficiencies of iron reached 84.37%. The kinetic analysis indicated that the leaching process of iron from TiG was controlled by the reaction product layer from 0–20 min, while the leaching process of iron from TiG was controlled by internal diffusion from 20–90 min. The apparent activation energy of the leaching reactions was 33.91 kJ/mol and 16.59 kJ/mol, respectively. High-value-added calcium oxalate and ferrous oxalate were prepared from the calcium and iron in the filtrate of the oxalic acid extraction. The leaching liquid could be recycled, which will provide a new way to utilize titanium gypsum

Influencing Mechanism of Titanium-Extracted Tailing Slag on the Strength of CaO Steel Slag Hardened Paste

Hardened pastes with different mass percentages of steel slag (SS)/titanium-extracted tailing slag (TETS) were prepared under fixed CaO content to determine the influencing mechanism of TETS on the strength of CaO SS hardened paste. Furthermore, the effects and laws of curing time and SS/TETS ratios on the strength of hardened pastes were also investigated in this study. Importantly, hydration products, microstructures and the micro-area compositions of hardened pastes were analysed using X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy–energy dispersive spectrometer, respectively, to reveal the influencing mechanism of TETS on the CaO SS hardened pastes. The results demonstrated that the early strength of hardened pastes increases considerably following the inclusion of TETS. Specifically, the strength of the sample with an SS/TETS ratio of 22.5:67.5 at 1 d can be increased by more than 14 times. Notably, its strength at 90 days reached 19.36 MPa. Moreover, the diffraction peaks of calcite and C-S-H in the samples were also strengthened. Meanwhile, a diffraction peak of hydrocalumite appeared, and the calcites in the samples were curled up. When the SS/TETS ratio was equal to or more than 45:45, a diffraction peak of Ca(OH)2 appeared in the sample. Only a diffraction peak of Ca(OH)2 and weak diffraction peaks of calcite and C-S-H were observed in the samples without TETS, but there was no diffraction peak of hydrocalumite. The strength at 90 days was only 4.92 MPa. The increased strength of the hardened paste is closely related to the production of new phases after adding TETS. Solid particles in the hardened paste are cemented into a whole because of the hydration of C-S-H. Calcite forms the skeleton of the hardened pastes, whereas hydrocalumite fills in the pores among particles in hardened pastes, thus making them more compacted. As a result, there is increased

Recovery of Residual Carbon from Ti-Extraction Blast Furnace Slag by Flotation with Simultaneous Dechlorination

Ti-extraction blast furnace slag (EBFS) is a secondary slag produced by titanium extraction of titanium-bearing blast furnace slag (TBBFS), which is challenging to be used directly because of its residual carbon and chlorine. This study was performed to recover the residual carbon and remove chlorine from EBFS by froth flotation. The finely ground EBFS (FEBFS) contained graphitized carbon and khamrabaevite and had a 10.19% loss on ignition (LOI) and 5.52% Cl. The graphitized carbon was mainly recovered by flotation rather than khamrabaevite. Graphitized carbon appeared as flakes embedded in or stacked on the surface of the concentrate grains. The irregular-shaped particles were amorphous aluminosilicate glasses, whose presence adversely affected the quality and performance of the flotation concentrate. The Cl contents of the flotation concentrate and tailings obtained under the optimized flotation conditions were significantly reduced to 1.17% and 0.4%, respectively. The dechlorination efficiency reached 71.56%. Meanwhile, the LOI of flotation tailing was reduced to 1.32% and the carbon recovery was 84.79%. Froth flotation could recover residual carbon and remove chlorine from EBFS simultaneously, a novel way to deal with EBFS as a resource and harmless process

Study on the Overall Reaction Pathways and Structural Transformations during Decomposition of Coal Fly Ash in the Process of Alkali-Calcination

In this research, phase transformation and the role of NaOH on the structure of coal fly ash (CFA) during an alkali-calcination process were identified by a combination of X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and deconvolution analysis. The variation in the different functional groups and structural parameters of the raw and post-alkali calcinated CFA were analysed by deconvolution of the FTIR results, conducted with a Gaussian approach. The results, firstly, provide a deep insight into the functional groups in CFA. In CFA systems, the vibration signals of Q0, Q1, Q2 and Q3 were detected and the dominant structural units associated with Si tetrahedron groups were isolated to Q3 and Q2. Deconvolution analysis of the band from 400 to 1400 cm−1 showed that the added NaOH resulted in an increase in Q1 at the cost of Q3 and Q2 and the degree of reaction of the CFA was, therefore, decreased. Concurrently, it was established that the changes in the Gaussian peak component were related to the calcination temperature and time that allowed us to tailor the model of the structural decomposition of CFA