Longjun Xu

Preparation and characterization of composite magnetic photocatalyst MnxZn1−xFe2O4/β-Bi2O3

Composite magnetic photocatalyst MnxZn1−xFe2O4/β-Bi2O3 was synthesized by a dip-calcination method using manganese zinc ferrite as a magnetic substrate. The effects of composite mass ratio, reaction time and calcination temperature on the degradation of Rhodamine B (RhB) under the simulated sunlight were observed with various investigations. The as-prepared MnxZn1−xFe2O4/β-Bi2O3 was characterized by XRD, FTIR, VSM, UV-vis DRS and SEM. The photodegradation rate of RhB in MnxZn1−xFe2O4/β-Bi2O3 was higher (99.1%) than that (83.6%) in pure β-Bi2O3 within 2.5 h. XRD spectra revealed that the composites presented a tetragonal type, which was similar to that of β-Bi2O3. FTIR spectra exhibit peaks for the absorption of both Bi–O bonds and MnxZn1−xFe2O4. The saturation magnetization (Ms) and coercivity (Hc) of the composite photocatalyst were 7.01 A m2 kg−1 and 25.38 A m−1, respectively. DRS analysis revealed that the optical band gap of this composite was 2.31 eV, which was lower than that of β-Bi2O3 (2.45 eV). Moreover, the photocatalytic activity was still maintained at 82.7% after five cycles. The magnetic property with an appropriate amount of manganese zinc ferrite inhibited the recombination of photo-produced electrons (e−) and holes (h+), and enhanced the photocatalytic property of β-Bi2O3.

Fractal-like kinetic characteristics of rock salt dissolution in water

Abstract Fractal-like kinetic characteristics of rock salt dissolution in water have been studied by using fractal geometry theory. The results show that the dissolution kinetics of rock salt in static and dynamic state is fractal-like. The kinetic parameters k o and h in static state increase while temperature is increased, and those in dynamic state decrease with the increase of flow.

Leaching process and kinetics of manganese in low-grade manganese ore

Manganese was extracted from leaching low-grade manganese ore in sulfuric acid medium. The effects of granule diameter, leaching time, liquid/solid ratio (V/W) and the concentration of sulfuric acid were investigated through orthogonal and single factor experiments. The experimental results showed that the optimal leaching conditions are, size of 0.054 mm, 120 minutes of reaction time, 3 (V/W) of liquid/solid ratio and 30% of the concentration of sulfuric acid (g/g). Under those conditions, the leaching efficiency is 96.73%. The kinetics of the leaching process is in accordance with the characteristics of fractal reaction.

Dielectric and magnetic response of Sr–Zn ferrite composite

Sr–Zn ferrite composites were synthesized by chemical coprecipitation with different sintering process. The composites were characterized by XRD, XPS, IR, VSM, and N2-adsorption. The results revealed that the composites were composed of S-type ZnFe2O4 and M-type SrFe12O19. Zn2+ ions inserted and occupied the 12k or 2a sites for Fe3+ ions in M-type SrFe12O19. The Zn2+ ions were therefore not on the external surface of the composites. The microwave absorption properties at a frequency range of 0–18 GHz were estimated using the electromagnetic parameters obtained through the agency of microwave vector network analyzer. The microwave absorbing properties of composites were excellently superior to that of the pure SrFe12O19 or ZnFe2O4 due mainly to the exchange coupling between the hard- and soft-magnetic phases. The synthesis process was found to facilitate mass production for various composite materials, especially the two phases or multiphase composite materials.

Compressibility of coal matter and coal pore

Abstract In the light of definition of compressibility of matter and fractal description of coal pore volume, a calculating formula on pore compressibility of coal (βP) has been obtained, and that βP and βS (compressibility of coal matter) decrease with the increase of experimental pressure, and they are relative to sampling sites of coals.

Improved C2H2 sensing properties of Ni doped ZnO nanorods

Abstract Pure and Ni doped ZnO nanorods were successfully synthesised via a simple hydrothermal synthesis method and characterised by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM respectively. Sensing properties were systematically measured towards acetylene gas (C2H2). The Ni doped ZnO gas sensor exhibits excellent gas sensing performances, such as lower working temperature, higher gas response, rapid response and recovery time, than those of pure ZnO gas sensors. All results demonstrate the potential of Ni dopant for improving the gas sensing properties of ZnO gas sensors to C2H2 gas.

Calcified roasting-acid leaching process of vanadium from low-grade vanadium-containing stone coal

The low-grade vanadium-containing stone coal used in this experiment was collected from Wuxi Country, Chongqing City, China. The experiment focused on the vanadium recovery from roasted residue through optimizing the process conditions of an effective and environmentally-friendly technology, named calcified roasting-sulfuric acid leaching technology. By single-factor experiments and orthogonal experiments, the effects of roasting temperature, roasting time, sulfuric acid concentration and leaching time on the leaching ratio of vanadium were analyzed. The results showed that the leaching ratio of vanadium reached 85.5% under the proper technological conditions of roasting temperature=950°C, roasting time=4 h, 40% concentration of sulfuric acid and leaching time=6 h.

Preparation of strontium ferrite from strontium residue

Strontium ferrite was prepared from Strontium Waste Residue (SWR) as a material. Strontium chloride was obtained by leaching SWR with ammonia chloride, and then SrCl2 was converted to SrCO3. Strontium ferrite (SrFe12O19) was formed by roasting the mixture of SrCO3 and FeCl3 in a proper proportion. The structure and magnetic susceptibility of strontium ferrite were investigated. The results showed that strontium conversion ratio increased with decreasing SWR grain diameter. The largest ratio was presented when n(NH4Cl/Sr) was 3.6. What is more, the conversion process coincided with the kinetic characteristics of fractal reaction. The magnetic susceptibility of strontium ferrite decreased with increasing Fe3+/Sr2+ mole ratio and pH. SrFe12O19 exhibited face-centered and cubic closely-packed hexagonal structures. There were the strong diffraction peaks of Fe2O3 in the X-ray diffractogram of strontium ferrite. Strontium recovery ratio was 87.0%.

Preparation of chemical manganese dioxide from low-grade rhodochrosite ore

The preparation of chemical manganese dioxide (CMD) from low-grade rhodochrosite ore (LGRO) in Xiushan, Chongqing, was studied and improved, including leaching with sulfuric acid, purifying, crystallizing and decomposing of MnCO3, and refining of primary MnO2. The product was characterized by X-ray diffraction. The results showed that the extraction ratio, the manganese recovery ratio of purifying, crystallization and refining reached 96.8%, 93.9%, 97.7% and 85.4%, respectively. The optimum conditions of refining were described as follows: liquid (H2SO4)/solid (primary MnO2) ratio was 3 L/g, the concentrations of NaClO exceeded 20%, and reaction time was 3 hours. Under the above conditions, the contents of MnO2 and Mn in the obtained manganese dioxide were respectively 85.1% and 53.9%. The refined MnO2 can be used as the super grade manganese dioxide mine powder in chemical industry. The XRD indicated that the structure of the product was γ-MnO2.

Kinetics analysis of the enzymatic hydrolysis of cellulose from straw stalk

The effects of several parameters on the simultaneous saccharification and fermentation of straw stalk for ethanol fuel production were investigated on the basis of orthogonal experiments. The parameters include temperature and time of fermentation, quantity and proportion of yeast inoculation, as well as cellulase dosage. An ethanol yield of 0.183 g/g was obtained from the straw stalk pretreated with diluted acid under determined optimum conditions. These conditions were: fermentation temperature: 38°C; fermentation time: 72 h; yeast inoculation quantity: 15%; yeast inoculation proportion: 2:1; and cellulose enzyme dosage: 20 U/g. The relationship between ethanol concentration c and fermentation time t is presented as follows, c=abt/(1+bt). The rate constant k of straw stalk hydrolysis by the cellulose enzyme depends on hydrolysis time, as described by k=k1t−h. Therefore, straw stalk hydrolysis reaction by the cellulose enzyme is fractal-like.