Synergistic utilization of industrial solid wastes: Extraction of valuable metals from tungsten leaching residue by photovoltaic sawing waste.

Solid waste challenges in both the tungsten and photovoltaic industries present significant barriers to achieving carbon neutrality. This study introduces an innovative strategy for the efficient extraction of valuable metals from hazardous tungsten leaching residue (W-residue) by leveraging photovoltaic silicon kerf waste (SKW) as a silicothermic reducing agent. W-residue contains 26.2% valuable metal oxides (WO3, CoO, Nb2O5, and Ta2O5) and other refractory oxides (SiO2, TiO2, etc.), while micron-sized SKW contains 91.9% Si with a surface oxide layer. The impact of SKW addition on the silicothermic reduction process for valuable metal oxides in W-residue was investigated. Incorporating SKW and Na2CO3 flux enables valuable metal oxides from W-residue to be effectively reduced and enriched as a valuable alloy phase, with unreduced refractory oxides forming a harmless slag phase during the Na2O-SiO2-TiO2 slag refining process. This process achieved an overall recovery yield of valuable metals of 91.7%, with individual recovery yields of W, Co, and Nb exceeding 90% with the addition of 8 wt.% SKW. This innovative approach not only achieves high-value recovery from W-residue and utilization of SKW but also minimizes environmental impact through an efficient and eco-friendly recycling pathway. The strategy contributes significantly to the establishment of a resource-efficient circular economy, wherein the recovered high-value alloy phase return to the tungsten supply chain, and the harmless slag phase become raw materials for microcrystalline glass production.

Three-Dimensional Porous Si@SiOx/Ag/CN Anode Derived from Deposition Silicon Waste toward High-Performance Li-Ion Batteries.

The application of photovoltaic (PV) solid waste to the field of lithium-ion batteries is deemed to be an effective solution for waste disposal, which can not only solve the problem of environmental pollution but also avoid the loss of secondary resources. Herein, based on the volatile deposited waste produced by electron beam refining polysilicon, a simple and environmentally friendly method was designed to synthesize P-Si@SiOx/Ag/CN as an anode material for lithium-ion batteries. Remarkably, the presence of silver and the formation of a carbon-nitrogen network can enhance the electrical conductivity of the composite and boost the transport efficiency of lithium ions. Furthermore, the porous Si@SiOx structure is generated by silver-assisted chemical etching (Ag-ACE), and the carbon-nitrogen grid architecture is formed after lyophilization with NaCl as a template, which can jointly provide sufficient buffer space for the volume change of silicon during lithiation/delithiation. Benefitting from these advantages, the P-Si@SiOx/Ag/CN anode exhibits outstanding cycling performance with 759 mA h g-1 over 300 cycles at 0.5 A g-1. Meanwhile, the lithium-ion batteries employing the P-Si@SiOx/Ag/CN anodes present a superior rate capability of 950 mA h g-1 at 2 A g-1 and retain a high reversible specific capacity of 956 mA h g-1 at 1 A g-1 after 50 cycles. This work opens up a new economic strategy for the fabrication of high-performance silicon anodes and affords a promising avenue for the recycling of PV silicon waste.

Recycling of silicon from waste PV diamond wire sawing silicon powders: A strategy of Na2CO3-assisted pressure-less sintering and acid leaching.

Recycling diamond wire sawing silicon powders (DWSSP) from photovoltaic (PV) silicon wafers production has become an urgent problem. The challenge of recovery is the surface oxidation and contamination of the ultra-fine powder with impurities during the sawing and collection process. In this study, a clean recovery strategy of Na2CO3-assisted sintering and acid leaching was proposed. Due to the Al contamination from the perlite filter aid, the introduced Na2CO3 sintering aid can react with the SiO2 shell of DWSSP to form a slag phase with accumulated impurity Al during the pressure-less sintering process. Meanwhile, the evaporation of CO2 contributed to the formation of ring-like pores surrounded by a slag phase, which can be easily removed by acid leaching. When 15 % Na2CO3 was added, the content of impurity Al in DWSSP could be reduced to 0.07 ppm with a removal rate of 99.9 % after acid leaching. The mechanism suggested that the addition of Na2CO3 can trigger the liquid phase sintering (LPS) process of the powders, and the cohesive force and liquid pressures difference generated during the process facilitated the transportation of impurity Al from the SiO2 shell of DWSSP to the formed liquid slag phase. The efficient silicon recovery and impurity removal of this strategy demonstrated its potential for solid waste resource utilization in the PV industry.

Preparation of Al-Si alloy from silicon cutting waste: Enabling oxide surface removing and silicon utilization improving via vacuum sintering.

Environmentally harmful silicon cutting waste (SCW) generated during the production of silicon solar cells possesses a high reuse value. However, the presence of oxide surface and impurities restrict the Si-cores reuse. Herein, inspired by the structure and composition of SCW, designed a combined process consisting of vacuum sintering and alloying to reuse SCW into Al-Si alloy at a low cost. Vacuum sintering promotes the reduction of the oxide surface by Si-core. Oxygen content was decreased by 92.54 %, demonstrating the successful removal of the oxide surface. The discharge of reduction products contributes to the densification, and the Si-core has converged into dense Vac-ceramic (Si block), rendering a relative density of 96.17 %. More importantly, during the alloying process, the formation of Vac-ceramic dredges the mass transfer pathway from Si-core to Al melt. As a result, the Si utilization rate increased about seven times compared with the direct reuse of pristine SCW. Compared with commercial Al-Si alloys, the Al-Si alloys prepared by reusing silicon cutting waste in this work have satisfactory mechanical properties. The method has the prominent advantages of being protective-atmosphere-free, additive-free, and scalability, and may be a promising candidate for the silicon cutting waste purifying and reusing field.

Construction of porous Si/Ag@C anode for lithium-ion battery by recycling volatile deposition waste derived from refining silicon.

Owing to the rapid advancement of the photovoltaic industry, a lot of photovoltaic (PV) silicon waste will be generated. Thus, the recycling and reuse of waste silicon have become particularly important, both for environmental remediation and economic benefits. In this work, a special structure of porous Si nanoparticles embedded nano-Ag and coated carbon layer (P-SiNPs/Ag@C) was produced by silver-assisted chemical etching (Ag-ACE) the deposited silicon waste. The special porous structure and carbon layer coating can effectively address the volume expansion issues during charge/discharge. The intercalated Ag nanoparticles greatly reduced the transfer impedance and enhanced the electrical conductivity of the anode material. As a result, the novel-designed P-SiNPs/Ag@C anode can maintain a prominent reversible capacity (1521 mAh·g-1 at 0.2 A g-1 after 50 cycles) and outstanding rate performance (1099 mAh·g-1 at 2 A g-1). When the current density at 1 A g-1, the specific capacity still maintains at 706 mAh·g-1 over 300 cycles. The superiority of the prepared P-SiNPs/Ag@C structures was further confirmed by Comsol Multiphysics software. Impressively, the synthesis route provides a novel avenue for value-added utilization of residual silicon waste resources from EB refining silicon and the preparation of high-performance lithium battery silicon-based anode.

Retraction: In situ Raman investigation of the phase transition of NaVO2F2 under variable temperature conditions.

[This retracts the article DOI: 10.1039/D1RA02827H.].

Recycling silicon kerf waste: Use cryolite to digest the surface oxide layer and intensify the removal of impurity boron.

The surface oxide layer (SiO2 layer) is still one of the main limitations of the recovery and purification of silicon kerf waste (SKW). Herein, to recycle SKW as the low-boron silicon ingot, an effective combination strategy that digests the surface oxide layer by pretreatment and then removes impurity boron by slag treatment is proposed. In the pretreatment part, the surface oxide layer of SKW was successfully digested into a liquid phase after mixing 10.5 wt% cryolite and sintering at 1400 °C, and the obtained SKW-ceramic has a dense structure. Moreover, when holding at 1400 °C for 2 h, the boron concentration in SKW-ceramic was decreased to 5.75 ppmw, and the removal rate reaches 14.18%. In the slag treatment part, CaO and SiO2 are selected as slag agents. The CaO/SiO2 mass ratio and reaction temperature were determined to be 2 and 1600 °C based on thermodynamic simulation. Besides, Na2O formed due to the dissociation of cryolite, which can enhance the oxygen ion activity and boron-absorbing capacity of the slag. The experimental result exhibited that the boron removal efficiency reached 86.56%. The simplicity and scalability of this strategy provide a better alternative for the recovery of SKW.

Structural design of cobalt phosphate on nickel foam for electrocatalytic oxygen evolution.

The elaborate design and synthesis of low-cost, efficient and stable electrocatalysts for the oxygen evolution reaction (OER), which may alleviate the current energy shortage and environment pollution, is still a great challenge. Herein, metal phosphonate precursors with controllable morphologies were synthesizedin situon the surface of nickel foam with different solvents, and could be easily converted into carbon- and nitrogen-doped cobalt phosphate through a calcination method. The OER catalytic performance of the final products was studied in detail. The results showed that the nanowire shaped samples of CoPiNF-800 synthesized with deionized water under hydrothermal conditions had the strongest electrochemical performance. They exhibited extraordinary catalytic activity with a very low overpotential of 222 mV at 100 mA cm-2, the smallest impedance and excellent electrochemical stability. These results not only demonstrate the possibility of preparing low-cost OER catalysts based on transition metal phosphate, but also aid our understanding of the controllable synthesis process of different morphologies.

In situ Raman investigation of the phase transition of NaVO2F2 under variable temperature conditions.

In this study, the phase transition of NaVO2F2 was measured at different temperatures via in situ Raman spectroscopy. The NaVO2F2 compounds were synthesized by a hydrothermal method and were identified to be monoclinic with the P21/c space group at room temperature by XRD. Accordingly, the variations of Raman shifts and intensities of the characteristic peaks for NaVO2F2 associated with temperature were obtained and investigated. It was confirmed that NaVO2F2 had three types of phase transitions, which occurred in the temperature region from 78 K to 573 K. Further, the results indicate that transition from a low-temperature phase (I) to another low-temperature phase (II), low-temperature phase (II) to P21/c phase and P21/c phase to P21/m phase occurred near the three temperature points of 93 K, 233 K, and 453 K, respectively, during the heating process. Therefore, a novel characterization method was provided for further research on the phase transition theory and performance of vanadate compounds.

Enhancing Delithiation Reversibility of Li15Si4 Alloy of Silicon Nanoparticles-Carbon/Graphite Anode Materials for Stable-Cycling Lithium Ion Batteries by Restricting the Silicon Particle Size.

Silicon nanoparticles (SiNPs) with a median size of 51 nm are prepared by the sand mill from waste silicon, and then carbon-interweaved SiNPs/graphite anode materials are designed. Because of the size of SiNPs is restricted below a critical fracture size of 150 nm as well as the rational decoration of carbon and graphite, fracture of SiNPs, and volume deformation of active materials are highly alleviated, leading to low impedance, enhanced electrochemical reaction kinetics, and good electronic connection between active materials and current collector. Furthermore, delithiation reversibility of the formed crystalline Li15Si4 alloy is enhanced. As a result, the anode with 10.5 wt % content of Si (including SiOx) delivers a properly high initial reversible capacity of 505 mA h g-1, high cycling stability with capacity retentions of 86.3%, and 91.5% at 0.1 and 1 A g-1 after 500 cycles, respectively. After cycling at a series of higher current densities, the reversible capacity recovers to the original level completely (100% recovery) when the current density is set back to the original value, exhibiting outstanding rate performance. The results indicate that the silicon-carbon anode can achieve high cycling performances with enhanced delithiation reversibility of the formed crystalline Li15Si4 alloy by restricting size of SiNPs and decoration of carbon materials, which are discussed systematically. The SiNPs are recycled from waste Si, and synthetic strategy of anode materials is very facile, cost-effective, and nontoxic, which has potential for industrial production.

Recycling of carbonized rice husk for producing high purity silicon by the combination of electric arc smelting and slag refining.

In this study, the combination of electric arc smelting and slag refining was employed to produce high purity silicon from Carbonized rice husk (CRH) and silica sand. CaO-SiO2-CaF2 were selected as the slagging agents. Firstly, the CRH was mixed with silica sand and slagging agents. Secondly, the mixed raw materials were pelletized and then melted in an experimental electric arc furnace. Thirdly, the cooling graphite crucible was dissected and divided into four parts, i.e., the loose granular zone, skull zone, cavity zone and product zone. Samples were taken from these four parts and analyzed to study the silicon producing mechanism. It was found that the silicon was produced mainly in the skull zone, and silicon with a purity of 96.97% was obtained at the product zone. By adding slagging agents during the smelting process, the impurities in silicon, i.e., Fe, Al and P were reduced thoroughly from 2.06%, 1.33%, 0.09% to 1.04%, 0.08%, and 0.04%, respectively. The results indicate that adding slagging agents CaO-SiO2-CaF2 can remove the impurities effectively from silicon. After acid leaching, the purity of the silicon can reach up to 99.9%.

Preparation of Si-SiOx nanoparticles from volatile residue produced by refining of silicon.

Residual Si was produced on a furnace wall when upgraded metallurgical grade Si was refined by electron beam melting. It was then recycled to prepare Si-SiOx nanoparticles with an average size of 100 nm by planetary ball milling. The obtained Si-SiOx nanoparticles mainly consist of amorphous Si, crystalline Si and amorphous SiOx, which was confirmed by XRD, FTIR, XPS and TEM. SiOx is mainly composed of SiO2 and SiO1.35. Distilled water used as a grinding aid not only enhances milling efficiency, but also plays a key role in obtaining SiOx. During refining of upgraded metallurgical grade Si, the deposition pattern of residual Si on furnace wall agrees with model of three-dimension growth. Growth of Si-SiOx nanoparticles is the mutual effect of distilled water and ball milling. Si-SiOx nanoparticles were doped into phenolic resin pyrolysis carbon as anode materials for lithium ion batteries, and 10% doping was observed to improve the specific capacity. After 500 cycles, specific capacity of delithiation remained around 550 mA h/g. It suggests the residual Si is a value-added by-product, and it can be recycled as anode materials for lithium ion batteries.

Novel Co3O4 Nanoparticles/Nitrogen-Doped Carbon Composites with Extraordinary Catalytic Activity for Oxygen Evolution Reaction (OER).

Herein, Co3O4 nanoparticles/nitrogen-doped carbon (Co3O4/NPC) composites with different structures were prepared via a facile method. Structure control was achieved by the rational morphology design of ZIF-67 precursors, which were then pyrolyzed in air to obtain Co3O4/NPC composites. When applied as catalysts for the oxygen evolution reaction (OER), the M-Co3O4/NPC composites derived from the flower-like ZIF-67 showed superior catalytic activities than those derived from the rhombic dodecahedron and hollow spherical ZIF-67. The former M-Co3O4/NPC composite displayed a small over-potential of 0.3 V, low onset potential of 1.41 V, small Tafel slope of 83 mV dec-1, and a desirable stability. (94.7% OER activity was retained after 10 h.) The excellent performance of the flower-like M-Co3O4/NPC composite in the OER was attributed to its favorable structure.

Development of dual-drug-loaded stealth nanocarriers for targeted and synergistic anti-lung cancer efficacy.

Combination chemotherapy is widely exploited for suppressing drug resistance and achieving synergistic anticancer efficacy in the clinic. In this paper, the nanostructured targeting methotrexate (MTX) plus pemetrexed (PMX) chitosan nanoparticles (CNPs) were developed by modifying methoxy polye (thylene glycol) (mPEG), in which PEGylation CNPs was used as stealth nanocarriers (PCNPs) and MTX was employed as a targeting ligand and chemotherapeutic agent as well. Studies were undertaken on human lung adenocarcinoma epithelial (A549) and Lewis lung carcinoma (LLC) cell lines, revealing the anti-tumor efficacy of nanoparticle drug delivery system. The co-delivery nanoparticles (MTX-PMX-PCNPs) had well-dispersed with sustained release behavior. Cell counting kit-8 (CCK8) has been used to measure A549 cell viability and the research showed that MTX-PMX-PCNPs were much more effective than free drugs when it came to the inhibition of growth and proliferation. Cell cycle assay by flow cytometry manifested that the MTX-PMX-PCNPs exhibited stronger intracellular taken up ability than free drugs at the same concentration. In vivo anticancer effect results indicated that MTX-PMX-PCNPs exhibited a significantly prolong blood circulation, more tumoral location accumulation, and resulted in a robust synergistic anticancer efficacy in lung cancer in mice. The results clearly demonstrated that such unique synergistic anticancer efficacy of co-delivery of MTX and PMX via stealth nanocarriers, providing a prospective strategy for lung cancer treatment.

ZIF-8 derived Ag-doped ZnO photocatalyst with enhanced photocatalytic activity.

Recently, zeolitic imidazolate framework-8 (ZIF-8) has been widely studied and used as a catalyst in various fields, due to its high specific surface area, tunable channels and thermal and chemical stability. In this paper, ZIF-8 was used as a precursor to fabricate a Ag/ZnO photocatalyst, and the influence of Ag on the photocatalytic activity of ZnO has been explored. All samples were characterised using XRD, SEM, TEM, and UV-vis diffuse reflectance spectra. The photocatalytic activity of all samples was evaluated by the degradation of a rhodamine B solution under UV light. The results show that ZIF-8 was completely transformed into ZnO when it was calcined at 550 °C for 6 h, and Ag was well loaded onto ZnO. The photocatalytic efficiency of ZnO is 92.32%. When ZnO was doped with Ag, its photocatalytic efficiency was highly improved (99.64%). Furthermore, Ag/ZnO exhibited high photocatalytic stability. After five repeated cycles, the photocatalytic activity of Ag/ZnO was highly retained at 97.48%.

Novel Ag@Nitrogen-doped Porous Carbon Composite with High Electrochemical Performance as Anode Materials for Lithium-ion Batteries.

A novel Ag@nitrogen-doped porous carbon (Ag-NPC) composite was synthesized via a facile hydrothermal method and applied as an anode material in lithium-ion batteries (LIBs). Using this method, Ag nanoparticles (Ag NPs) were embedded in NPC through thermal decomposition of AgNO3 in the pores of NPC. The reversible capacity of Ag-NPC remained at 852 mAh g-1 after 200 cycles at a current density of 0.1 A g-1, showing its remarkable cycling stability. The enhancement of the electrochemical properties such as cycling performance, reversible capacity and rate performance of Ag-NPC compared to the NPC contributed to the synergistic effects between Ag NPs and NPC.

Sonocrystallization of ZIF-8 on Electrostatic Spinning TiO2 Nanofibers Surface with Enhanced Photocatalysis Property through Synergistic Effect.

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.

Methotrexate-loaded PEGylated chitosan nanoparticles: synthesis, characterization, and in vitro and in vivo antitumoral activity.

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.