The effect of CaO–SiO2–CaF2 slag treatment on acid leaching of metallurgical-grade silicon was investigated in this study. Based on the analysis of the acid sensitivity of silicide precipitated phases, it was found that HCl + HF mixed acid was a better solvent to remove Si–Fe system intermetallics from metallurgical-grade silicon, and HCl was an effective leaching agent for eliminating Si–Ca system intermetallics from slag treated metallurgical-grade silicon. Acid leaching experimental results revealed that slag treatment enhanced the extraction of impurities Fe, Al, Mn, and Ti from metallurgical-grade silicon compared with results in the absence of slag treatment. Moreover, a remarkable decrease in the concentration of impurities B and P was attributed to the oxidation reaction in the slag refining process.

Metal doped ZnO supported on porous materials have unique and highly attractive properties and have drawn worldwide attention. Herein, we explored the synthesis of Co/ZIF-8@silicalite-1 catalysts containing different amounts of Co by using metal organic frameworks as precursors and silicalite-1 as support. Then Co/ZIF-8@silicalite-1 catalysts were calcined at 550 °C to prepare the Co/ZnO@silicalite-1 photocatalysts. All samples were characterized by XRD, SEM, FT-IR and UV-vis diffuse reflectance spectra. The results show that the doping Co can increase the particle size of Co/ZIF-8 and decrease the content of Zn in Co/ZIF-8@silicalite-1. When ZnO@silicalite-1 is doped with Co from 0% to 20%, its band gap absorption is extended from 380 to 480 nm and a new band gap absorption at about 720 nm appears. The photocatalystic properties were investigated by degradation of rhodamine B (RhB) aqueous solution under UV light. In the series of Co/ZnO@silicalite-1 photocatalysts, 5Co/ZnO@silicalite-1 shows the highest photocatalytic efficiency.

In order to explore the synthesis of silicate-1 membrane on kaolin clay ceramic and the effect of Na+ ion substitution on the dielectric properties of ceramic, silicate-1@kaolin clay ceramics containing different content of Na+ were successfully synthesized by combining sintering, sol-gel, and ion exchange method. Samples were analyzed by chemical composition (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), digital hardness tester, and microwave dielectric measurement system. SEM images exhibited that a layer of silicate-1 was successfully grown on the surface of the kaolin clay ceramic. The energy dispersive spectrometer (EDS) revealed that the content of Na+ in silicate-1 decreased with increase of ion exchange time. The content of Na+ in silicate-1@kaolin clay ceramic decreased from 1.46 to 0.29% when the silicate-1@kaolin clay ceramic was treated by the unsaturated solution of NH3 from zero to two times. In this process, the dielectric constant of the silicate-1@kaolin clay ceramic almost kept the same. But the dielectric loss of silicate-1@kaolin clay ceramic decreased from 0.474 to 0.131. Silicate-1@kaolin clay ceramic is expected to be used as sensor to detect some metal ions.

SiO2@silicalite-1, using silica sol (pH = 9.47, SiO2 ≈ 30 wt%) as the silica source, was directly synthesized in a eutectic mixture where silicalite-1 grains were formed in the three-dimensional net structure of silica gel, grown in situ by transforming amorphous SiO2 into an MFI-type structure and coated with amorphous SiO2. The alkalinity, template agent, and crystallization time strongly affect the physicochemical properties of SiO2@silicalite-1. The physicochemical properties of these samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra and nitrogen adsorption. The results show that the SiO2@silicalite-1 is synthesized in a eutectic mixture and its physicochemical properties can be tuned by controlling the content of sodium hydroxide and tetrapropyl ammonium bromide (TPABr). A time-dependent study reveals that the formation process obeys an in situ epitaxial growth and phase transformation mechanism. Finally, SiO2@silicalite-1 was used as the support to prepare TiO2-loaded SiO2@silicalite-1 (TiO2@SiO2@silicalite-1). After five loading procedures, it could load 0.44% TiO2 nanoparticles, which is higher than the TiO2 nanoparticle loading in traditional silicalite-1 (0.13%). When the catalysts were used as a catalyst for the degradation of rhodamine B (RhB) aqueous solution under UV light, the photocatalytic efficiency of TiO2@SiO2@silicalite-1 (89.2%) is higher than TiO2@silicalite-1 (only 34.6%). The rate of degradation using TiO2@SiO2@silicalite-1 is 4.3 times faster than that using TiO2@silicalite-1. Furthermore, SiO2@TiO2@silicalite-1 exhibits high stability of photocatalytic performance. After five repeated cycles, the photocatalytic efficiency of TiO2@SiO2@silicalite-1 is 88.09%, which reduces only by 1.1%.

The effect of adding hydrogen peroxide (H2O2) as an oxidizing agent on purifying metallurgical grade silicon (MG-Si) by leaching with hydrofluoric acid (HF) was studied as a function of leaching temperature, particle size, leaching duration, and concentration of leaching agents. It was found that the extraction capacity for metallic impurities could be significantly enhanced with introduction of H2O2 into HF lixiviant with little dependence on HF concentration. Upon leaching with 1 mol·L–1 HF and 2 mol·L–1 H2O2 for only 0.25 h at 55 °C, the MG-Si purity could be upgraded from 99.74% to 99.96%, to 99.99% with further prolonging of leaching duration. The sensitivity sequences of precipitates to each etchant were obtained through revealing the microstructural evolution of MG-Si before and after etching. With the help of Raman spectrometry and transmission electron microscopy, the chemical etching mechanism is discussed.

•Corrosion would bring smooth oxide coating and looser structure to Al layer.•Corrosion would bring discoloration and oxide coating to rear electrode.•Corrosion region will expand from the edge to the center of soldered joints.•Degradation rate of traditional modules was low before 2000 h, and then increased.Corrosion behavior of crystalline silicon (C-Si) solar cells was investigated. For this purpose, three groups of cells were conducted with three kinds of aging test which cells setting in indoor environment (25 °C, 45% RH, 0– 2 months), cells immersing in moisture atmosphere (25 °C, 85% RH, 0– 240 h) and cells immersing in acetic acid atmosphere (25 °C, 85% RH, 0– 240 h). Subsequently the microstructure characteristic of the alumina paste layer (APL), rear electrode and soldered connection of cells and the corrosion production during aging test were analyzed and compared. The results show that the smooth oxide coating and looser structure were found in the APL of cell after aging test. In addition the discoloration and elements diffusion were found on the rear electrode. And the corrosion region expanded gradually from the edge to the center of soldered connection along the interface between Ag electrode and Sn37Pb alloy. Thereafter, a model was put forward to try to explain the degradation mechanism of traditional photovoltaic (PV) modules during damp-heat (DH) test based on corrosion behavior of C-Si cells in this experiment.

•The intermittent addition of CaCl2 will promote the boron removal by maintain the CaCl2 weight ratio in optimal range.•The increase of CaCl2 in slag could not decrease the final boron amount in silicon.•Mechanism of intermittent addition of CaCl2 is discussed according to the thermodynamics and kinetics.•This method can reduce to total slag amount, showing potential in simplifying industrial manufacturing of solar grade silicon.CaO-SiO2-CaCl2 slag refining with intermittent CaCl2 addition has been performed to eliminate boron from metallurgical-grade silicon (MG-Si). The boron-removal efficiency was measured at different refining times, refining temperatures, and amounts of added CaCl2; boron amounting to 90% was removed from the MG-Si. The experimental results show that intermittent CaCl2 addition promotes the elimination of boron from the silicon. The impurity distributions and micro-morphologies of the slag and silicon are examined. The mass transfer coefficient of boron from silicon to the slag is calculated as 3.64 × 10−4–10−6 cm/s (r (droplet radii) = 50–5000 μm at 1873 K (1600 °C)) and 4.41 × 10−4–10−6 cm/s (r = 50–5000 μm at 1973 K (1700 °C)). The reaction mechanism of boron removal is discussed as well. This method shows potential for simplifying the industrial manufacturing of solar-grade silicon.

For exploring the using of silicate-1 zeolite in dielectric ceramic, SiO2@silicate-1 ceramics were fabricated by combining oxidation-bonding, sol–gel directional infiltration and sintering methods. The resulting samples were analyzed by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, digital hardness tester and microwave dielectric measurement system. It can be found that silicate-1 particles are well bond by silica sol. And the pores of perform are partially filled with silica. The sintering temperature has great effect on microstructure and properties of SiO2@silicate-1 ceramics. When the ceramic is sintered at 400 and 600 °C, it keeps the MFI-type structure and almost has the same low-dielectric-constant (5.71 and 5.62, respectively). When the ceramic is sintered at 800 and 1000 °C, its MFI-type structure is broken down and its dielectric constant is 7.38 and 6.75, respectively.

Semiconductor–metal-organic framework (MOF) hybrid photocatalysts have attracted increasing attention because of their enhanced photocatalytic activity. However, the effect of the interface reaction between semiconductor and MOFs is rarely studied. In this work, we studied the synthesis and photocatalytic activity of zeolitic imidazolate framework-8 (ZIF-8) decorated electrostatic spinning TiO2 nanofibers (TiO2 ESNFs). TiO2/ZIF-8 hybrid photocatalysts were prepared via a facile sonochemical route. It was crucial that the ZIF-8 was assembled homogeneously on the surface of TiO2 ESNFs and formed a N–Ti–O bond under sonochemical treatment, which may result in reducing recombination of the electron–hole pairs. The chemically bonded TiO2/ZIF-8 nanocomposites displayed excellent performance of thermal stability, controllable crystallinity, and great enhancement of photocatalytic activity in Rhodamine B (Rh B) photodegradation. Furthermore, the UV–vis light adsorption spectra of TiO2/ZIF-8 nanocomposites showed that the ZIF-8 photosensitizer extended the spectral response of TiO2 to the visible region. The new strategy reported here can enrich the method for designing new semiconductor–MOF hybrid photocatalysts.Keywords: electrostatic spinning TiO2 nanofibers; hybrid photocatalysts; photodegradation; TiO2/ZIF-8 nanocomposites; ZIF-8

•Synthesis two new metal phosphonates with 5-phosphononicotinic acid.•Using multifunctional phosphonate ligand in synthesis of phosphonate based MOFs.•Directing the MOF structures with organic amines.Two metal phosphonates, namely [Co3(OOCC5H3NPO3)2(H2O)6]·2(H2O) (1) and [Ni5(OOCC5H3NPO3H)2(OOCC5H3NPO3)2(H2O)8]·2(H2O) (2) were hydrothermally synthesized by reacting 5-phosphononicotinic acid with corresponding metal sulfate in the presence of organic amines as templates. In compound 1, bicobaltic clusters are corner-shared with {CPO3} tetrahedrons and subsequently connected by phosphonyl and pyridyl groups into layered structures. These layers are further linked with {Co3O6} octahedrons through carboxyl groups forming a three dimensional pillared layered frameworks. In compound 2, {NiO6} and two {NiO5N} octahedrons are linked by μ-OH2 bridge of water forming a trimeric cluster of Ni3. Subsequently, Ni3 clusters are corner-shared with {CPO3} tetrahedron and link to {Ni3O5N} octahedron forming a double-chain structure. These double-chains are further connected to a three dimensional structure by three functional groups of ligands. Magnetic property of compound 2 was investigated.DABCO directed in a pillared layered structure of compound 1 while monoamine tetrapropylammonium bromide leads to porous structure of compound 2.

Redistribution of iron during directional solidification of metallurgical-grade silicon (MG-Si) was conducted at low growth rate. Concentrations of iron were examined by ICP-MS and figured in solid and liquid phases, at grain boundary and in growth direction. Concentrations are significantly different between solid and liquid phases. The thickness of the solute boundary layer is about 4 mm verified by mass balance law, and the effective distribution coefficient is 2.98×10−4. Iron element easily segregates at grain boundary at low growth rate. In growth direction, concentrations are almost constant until 86% ingot height, and they do not meet the Scheil equation completely, which is caused by the low growth rate. The effect of convection on the redistribution of iron was discussed in detail. Especially, the “dead zone” of convection plays an important role in the iron redistribution.

•Segregation ratio of Fe in MG-Si during SiCu alloy solvent refining was analyzed.•Effect of back diffusion on the segregation of Fe was studied.•Phase transformation of Fe during the solidification process was observed.Impurity removal from metallurgical grade silicon (MG-Si) is an important issue for solar-grade silicon production, and solvent refining is used as an effective method to purify silicon. To evaluate the purification ability of solvent refining with SiCu melt at 1343–1603 K, the effective segregation ratio of the main impurity element Fe between solid Si and SiCu melt was experimentally and theoretically determined. The results demonstrated that the effective segregation ratio of Fe increased with the increasing temperature at the range of 1343–1603 K. The corresponding removal mechanism of Fe was investigated in detail. It was found that the effective segregation ratio of Fe calculated by Scheil equation presented the same tendency with experimental results, and the theoretical calculation was more consistent with experimental results when back diffusion was considered. Moreover, Fe was found to form SiFeMn and FeMnTi phases into SiCu alloy phase from MG-Si with the presence of Cu. It can be concluded that removal mechanism of Fe was not only a segregation process, but also a recombining process of impurity phase transformation.

Boron removal from metallurgical-grade silicon by Li2O-SiO2 slag refining under an air atmosphere was experimentally investigated to explore the potential of this method for achieving high boron removal. The boron concentration in the refined silicon was studied under different conditions of holding time, slag composition, and mass ratio of slag to silicon. The boron concentration in metallurgical-grade silicon was successfully reduced from 8.6 ppmw to 0.4 ppmw after slag refining for 0.5 h at 1973 K when the mass ratio of the 60 wt.% Li2O-40 wt.% SiO2 slag to metallurgical-grade silicon was 3. It was proposed that the addition of CaF2 decreased the activity of silica, which brings about a negative effect on the boron removal capacity of Li2O-SiO2 slags. Moreover, the reaction mechanism and kinetics of boron removal were further studied. Analysis of the boron concentration in the resulting slag after refining revealed that the primary boron removal approach was that a large amount of boron was oxidized and then volatilized to the atmosphere in the form of gaseous borates. Based on the two-film theory, the total mass transfer coefficient of boron was determined to be 2.3 × 10−2 μm/s.

•Growth rate can be designed through the evaluation of heat flux.•Process of Si purification can be optimized by designing heater temperature and pulling down rate.•Growth rate decreases linearly with increase of heater temperature and exponentially with decrease of pulling down rate.A numerical model is proposed to investigate influences of process parameters, including crucible pulling down rates and heater temperature, on crystal growth rates for silicon purification by vacuum directional solidification. The crystal growth rates of a silicon ingot are analyzed based on the interface energy balance equation combining with the temperature field calculated by software of ProCAST, and the segregation behavior of impurities is investigated with the Scheil's equation. The results show that the crystal growth rates decrease linearly with the increase of heater temperature at a fixed value of the crucible pulling down rate, and increase exponentially with the increase of the crucible pulling down rates at a fixed value of the heater temperature. The numerical model is verified by removal of iron impurity from 300 ppmw to 1 ppmw and by the temperature of melt silicon which is recorded by a thermocouple. The results show that numerical results agree well with experimental results. This research is used for adjusting process parameters to control crystal growth during silicon purification by directional solidification.

•Distribution of insoluble inclusions under different vacuum conditions is obtained.•Effect of impurity on redistribution of insoluble inclusions is studied.•The redistribution mechanism of impurities under different conditions is studied.•Different vacuum conditions provide guidance for removal of impurities.The distribution of insoluble inclusions in multi-crystalline (m-c) silicon was investigated by directional solidification under different vacuum conditions using recycled scraps. We found an abnormal peak (weight ratio of 1.19%) of SiC and Si3N4 with an average size of 100 μm located at the bottom of the silicon ingot obtained under low-vacuum conditions. At the top of the ingot, the impurity phase featured a weight ratio exceeding 10.62% and a size of 20 μm. Results showed that large particles sank to the bottom of the ingots whereas small particles floated upward. Further investigation suggested that the dominant factor influencing inclusion distribution is related to the presence of metallic impurities (e.g., Ca, Al, and Na) and their corresponding microstructure. A mechanism of migration was proposed to reveal that bonding of metallic impurities and insoluble inclusions contribute to the abnormal distribution of impurities. The results provide guidance for controlling the distribution of insoluble inclusions in recycled m-c silicon.

Cancer nanotherapeutics are rapidly progressing and being implemented to solve several limitations of conventional drug delivery systems. In this paper, we report a novel strategy of preparing methotrexate (MTX) nanoparticles based on chitosan (CS) and methoxypoly(ethylene glycol) (mPEG) used as nanocarriers to enhance their targeting and prolong blood circulation. MTX and mPEG-conjugated CS nanoparticles (NPs) were prepared and evaluated for their targeting efficiency and toxicity in vitro and in vivo. The MTX–mPEG–CS NP size determined by dynamic light scattering was 213 ± 2.0 nm with a narrow particle size distribution, and its loading content (LC %) and encapsulation efficiency (EE) were 44.19 ± 0.64% and 87.65 ± 0.79%, respectively. In vitro release behavior of MTX was investigated. In vivo optical imaging in mice proved that MTX was released from particles subsequently and targeted to tumor tissue, showing significantly prolonged retention and specific selectivity. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay obviously indicated that the higher inhibition efficiency of MTX–mPEG–CS NPs meant that much more MTX was transferred into the tumor cells. A significant right-shift in the flow cytometry (FCM) assay demonstrated that MTX-loaded nanoparticles were far superior to a pure drug in the inhibition of growth and proliferation of Hela cells. These results suggest that MTX–mPEG–CS NPs could be a promising targeting anticancer chemotherapeutic agent, especially for cervical carcinoma.Keywords: cellular uptake; chitosan; methotrexate; mPEG; targeted delivery;

The removal of boron from metallurgical-grade silicon by Na2O-SiO2 slag refining was investigated. The final content of boron in refined silicon was examined under different conditions of temperature, slag composition, holding time, mass ratio of slag to silicon, and slag refining times. The content of boron in silicon decreased from 10.6 to 0.65 ppmw by slag treatment in one time, and increasing slag refining times was beneficial for removing boron at the conditions of the small mass ratio of slag to silicon and short holding time. Moreover, the removal mechanism of boron was also discussed. The primary removal mechanism of boron was that a large amount of boron was oxidized and then volatilized to the atmosphere in the form of boron oxides. The mass transfer coefficient of boron from silicon to slag was connected with the radius of silicon droplet in the slag refining process.

Phosphorus can be expected to evaporate preferentially from silicon melt by induction vacuum refining (IVR). In the present study, on the assumption of phosphorus evaporating from silicon melt as gas species P and P2, a numerical model of phosphorus removal from silicon by IVR was developed. The factors affecting phosphorus removal in decreasing order are temperature, chamber pressure, geometry of silicon melt, holding time, and original phosphorus concentration. Calculated phosphorus removal shows good agreement with the present experimental data.

An experimental investigation into the mass transfer of phosphorus in molten silicon under vacuum induction refining has been carried out. In a pilot-scale experiment, in the temperature range 1773 K (1500 °C) to 1873 K (1600 °C) and a vacuum of 0.1 to 0.035 Pa smelting for 7200 seconds (2 hours), phosphorus is decreased from 15 ppmw to 0.08 ppmw, which achieved the target for solar-grade silicon of less than 0.1 ppmw. Lab-scale experiments are used to determine the effects of vacuum, refining time, and temperature on the rate of mass transfer of phosphorus during vacuum refining. Hardly any phosphorus was removed when the vacuum pressure is greater than 100 Pa. Mass-transfer coefficients are nearly independent of pressure at 1783 K (1510 °C) when pressures are below 0.1 Pa and are highly correlated with vacuum pressures above 0.1 Pa. A model of vacuum refining of inductively stirred silicon melts is discussed to explain the transfer path of phosphorus out of the melt.

•Compared with other impurities, content of calcium is variable and discontinuous.•The variable removal is caused by the existence of insoluble calcium-oxide.•Calcium-oxide exists as foreign insoluble material in the feedstock.•The mechanism of envelopment of particle is discussed by thermodynamics.Directional solidification is often used to remove metallic impurity in the photovoltaic industry for the low equilibrium distribution coefficient between solid and melt. However, in our present experiments, compared with other impurities, the removal of calcium is variable at the low height of ingot, which is caused by the existence of insoluble CaO particle. CaO exists as insoluble particle in the feedstock. During directional solidification stage, CaO motions with the melt convection, and it is likely to envelop in solid. Consequently, the content of calcium is relatively high if many CaO particles are just contained, which is verified by the analysis of SEM-EDS. In a word, the removal efficiency depends upon the chemical state of calcium. The reason why CaO exists is studied, and the envelopment of the particle is mainly discussed by means of thermodynamics, especially on gravitational force, repulsive force, and drag force.

•The redistribution of P and metallic impurities were studied in Si–Al–Sn alloy.•β-Al5SiFe compound was found accompanying with βSn phase.•The Si–Al–Sn alloy with Sn addition had a higher impurity removal ratio than Al.Metallurgical grade silicon was purified through solvent refining method by adding tin to the Si–Al alloy. The distribution of phosphorus and metallic impurities in the resulting Si–Al–Sn melts was investigated. Compared with the primary Si and the eutectic αAl+Si, the phosphorus and metallic impurities were more distinctly distributed in the βSn phase, which was always accompanied by needle-like intermetallic β-Al5SiFe compounds. To improve the phosphorus and metallic impurity removal ratios, Si–Al–Sn ternary alloys with different composition were investigated. The phosphorus removal ratio increased with the aluminum and tin content in the Si–Al–Sn ternary alloy. Compared to increasing the Al content and keeping the Si/Sn ratio fixed, the impurity removal ratios were higher when the Sn content was increased to the same mass percentage and the Si/Al ratio was kept fixed in the Si–Al–Sn melt.

•Shadows are caused by SiC and Si3N4.•Sedimentation is discussed according to the thermodynamics and kinetics.•Melt convection results in particles in center more than the nearby.•The particles have no significant influences on the minority carrier lifetime.Upgraded metallurgical-grade silicon is used to cast an ingot by directional solidification. Black shadows are randomly distributed in the ingot, and the shadows are caused by natural sedimentation of insoluble particles. The insoluble particles mainly consist of SiC and Si3N4. SiC and Si3N4 exist as foreign particles and mainly sedimentate at the bottom of the ingot, not generating during directional solidification. Melt convection performs an important role in the sedimentation, resulting in the insoluble particles in the ingot center more than the nearby. Interestingly, since SiC and Si3N4 will not be the recombination center of the minority carrier, the insoluble particles do not have a significant influence on the minority carrier lifetime. In particular, the sedimentation is discussed according to the thermodynamics and kinetics in detail.