Enhanced leaching of manganese from low-grade pyrolusite using ball milling and electric field.

In this study, electric field and ball milling were used to leach Mn2+ from low-grade pyrolusite (LGP). The effects of current density, reaction time, reaction temperature, ball-to-powder weight ratio, and ball milling time on the leaching efficiency of Mn2+ from LGP as well as the leaching mechanism were systematically studied. The results showed that the combined use of electric field and ball milling enhanced the leaching of Mn2+ from LGP. The leaching efficiency of Mn2+ reached 97.79% under the optimum conditions of LGP-to-pyrite mass ratio of 1:0.18, current density of 30 mA/cm2, LGP-to-H2SO4 mass ratio of 1:0.4, liquid-to-solid ratio of 5:1, ball-to-powder weight ratio of 1:1, ball milling time of 2 h, temperature of 80 °C, and leaching duration of 120 min. This value was 25.95% higher than that attained without ball milling and 41.45% higher than that attained when neither ball milling nor electric field was employed. Pyrite was fully oxidized to generate additional SO42- and Fe3+, and was further hydrolyzed to form jarosite (KFe3(SO4)2(OH)6) and hydronium jarosite (Fe3(SO4)2(OH)5·2H2O) via ball milling and electric field application. Moreover, the electric field changed the surface charge distribution of the mineral particles and promoted collisions between them as well as the collapse of the crystal lattice, further improving the leaching efficiency of Mn2+ from LGP. This study provided a new method for leaching Mn from LGP.

Tunable CO2-to-syngas conversion via strong electronic coupling in S-scheme ZnGa2O4/g-C3N4 photocatalysts.

The conversion of CO2 into syngas, a mixture of CO and H2, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa2O4 nanodots (∼7 nm) rooted g-C3N4 nanosheets (denoted as ZnGa2O4/C3N4) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO2-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C3N4 and highly distributed ZnGa2O4 nanodots synergistically contribute to a strong interaction between metal oxide and C3N4 support. Furthermore, the desirable S-scheme heterojunction in ZnGa2O4/C3N4 efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa2O4/C3N4 exhibited remarkable activity and selectivity in photochemical conversion of CO2 into syngas, with a syngas production rate of up to 103.3 µ mol g-1 h-1, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H2 ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO2-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.

Electrolytic manganese residue disposal based on basic burning raw material: Heavy metals solidification/stabilization and long-term stability.

Solidification/stabilization (S/S) is an option for the treatment of electrolytic manganese residue (EMR). Basic burning raw material (BRM) could successfully solidify/stabilize EMR, though heavy metals S/S mechanism and long-term stability remain unclear. Herein, Mn2+ and NH4+ S/S behavior, hydrated BRM and S/S EMR characterization, Mn2+ long-term leaching behavior, phase and morphology changes for long-term leaching were discussed in detail to clarify these mechanisms. Mn2+ and NH4+ leaching concentrations as well as pH value in S/S EMR were respectively 0.02 mg/L, 0.68 mg/L and 8.75, meeting the regulations of Chinese standard GB 8978-1996. Long-term stability of EMR was significantly enhanced after S/S. Mn2+ leaching concentration, Mn2+ migration, Mn2+ cumulative release, Mn2+ apparent diffusion coefficient and conductivity of EMR reduced to 0.05 mg/L, 5.5 × 10-6 mg/(m2·s), ~ 9 mg/m2, 6.30 × 10-15 m2/s and 435 µs/cm. Mechanism studies showed that the hydration of BRM forms OH-, calcium silicate hydrate gels (C-S-H) and ettringite. Therefore, during S/S process, NH4+ was escaped as NH3, Mn2+ was solidified/stabilized as tephroite (Mn2SiO4), johannsenite (CaMnSi2O6) and davreuxite (MnAl6Si4O17(OH)2), and Pb2+, Cu2+, Ni2+, Zn2+ were solidified/stabilized by C-S-H and ettringite via substitution and encapsulation. This study provides a good choice for EMR long-term stable storage.

Aggregation-based phase transition tailored heterophase junctions of AgInS2 for boosting photocatalytic H2 evolution.

Due to high defect tolerance and multiphase allowance, AgInS2 (AIS) quantum dots (QDs) provide chances for designing new type junctions via tailoring defects, size, or phase structure. These new type junctions potentially enhance photoelectric performance, such as photocatalytic H2 evolution (PHE). Here, ultra-small AIS QDs (∼1 nm) with well-defined exciton absorption were prepared aqueously via a reverse hot-injection procedure for the first time. A coalescence or fast aggregation-based growth was observed for coarsening at 95 or 135 ℃, respectively. XRD and TEM investigations revealed that the tetragonal-orthorhombic (t-o) phase transition occurred via aggregation-based growth. The studies on phase transition kinetics resulted in fine-tailoring on AIS polymorphs, favoring t-o AIS junctions. UV-vis absorption spectra confirm the double absorption edge of the t-o heterophase junction with enhanced visible absorption. Steady and transient PL spectra suggest improvements in carriers' separation/transfer in this t-o junction. As a result, the optimized t-o AIS shows superior photocatalytic H2 evolution rates of 1022 µmol. g-1. h-1, 51.1 times that of t-AIS or 3.8 times that of o-AIS. This work is expected to provide new insight for designing ternary alloyed QDs with strongly coupled interfaces for effective H2 generations.

Efficient exfoliation of UV-curable, high-quality graphene from graphite in common low-boiling-point organic solvents with a designer hyperbranched polyethylene copolymer and their applications in electrothermal heaters.

The use of stabilizer with designer structures can effectively promote graphite exfoliation in common solvents to render functionalized graphene desirable for their various applications. Herein, a hyperbranched polyethylene copolymer, HBPE@Py@Acryl, simultaneously bearing multiple pyrene terminal groups and pendant acryloyl moieties has been successfully synthesized from ethylene with a Pd-diimine catalyst based on unique chain walking mechanism. The unique structural design of the HBPE@Py@Acryl makes it capable of effectively promote graphite exfoliation in a series of common, low-boiling-point organic solvents, e.g. CHCl3, to render stable graphene dispersions with concentrations effectively adjustable by changing feed concentrations of graphite and polymer or sonication time. Meanwhile, it can be irreversibly adsorbed on the exfoliated graphene surface based on the π-π interactions between them to concurrently render acryloyl-functionalized graphene free of structural defects, with majority (92.7%) of them having a thickness of 2-3 layers. This allows us to obtain graphene electrothermal films simply by filtration and UV irradiation, which exhibit outstanding stability in use. The action mechanism of the HBPE@Py@Acryl as stabilizer for promoting graphite exfoliation and the role of UV irradiation on improving the stability in use of resulting graphene films have been elucidated.

Heavy Metals Removing from Municipal Solid Waste Incineration Fly Ashes by Electric Field-Enhanced Washing.

Municipal solid waste incineration (MSWI) fly ash contains chlorides, heavy metals, and organic pollutants, which requires appropriate disposal to eliminate this risk. In this study, the effects of agents on heavy metals removal from MSWI fly ash by electric field-enhanced washing were systematically studied. The results show that when these fly ashes were washed at a current density of 35 mA/cm2, polarity switching frequency of 40 Hz, Ethylenediaminetetraacetic acid (EDTA) dosage of 0.5 mol/L, and a pH of 2 for 4 h, almost all of the Cd and Ni could be were removed, with a removal efficiency of 100.00% and 99.59%, respectively. Meanwhile, it also shows a significant effect on Cu and Zn, with a removal efficiency higher than 85%. After washing, the results of the sequential extraction procedure showed that the residual forms of Pb, Cu, Zn, Cd, Ni, and As increased obviously. According to GB5085.3-2007, the toxicity of the treated MSWI fly ash were below their thresholds of 5 and 1 mg/L for Pb and Cd, respectively. Thus, a novel technology for heavy metals removal from MSWI fly ash is proposed.

Sol-gel hydrothermal synthesis of nano crystalline silicotitanate and its strontium and cesium adsorption.

Crystalline silicotitanate (CST) was synthesized via a sol-gel hydrothermal method using Na2Si2O3·9H2O and TiCl4 as silicon and titanium sources. The effects of pH, silicon concentration, hydrothermal temperature, and time on the CST synthesis were studied at a fixed molar ratio of silicon:titanium (0.98:1). Pure nano-CST crystals were synthesized at pH = 12.5, silicon concentration of 5 g L-1, 170 °C for 7 days. The average CST particle size was < 100 nm, with a Sr2+/Cs+ distribution coefficient up to 1.9 × 106 mL g-1/9.4 × 103 mL g-1 under the optimum conditions. In addition, nano-CST absorbed Sr2+/Cs+ over a wide pH range. The nano-CST also displayed a much faster equilibrium time, 4 h, as compared with previous studies. Furthermore, nano-CST adsorption of Sr2+/Cs+ followed a Langmuir adsorption model and was consistent with pseudo-second-order kinetics.