A resource-utilization way of the waste printed circuit boards to prepare silicon carbide nanoparticles and their photocatalytic application

In situ high-valued transformation of nonmetals in waste printed circuit boards into supercapacitor electrodes with excellent performance

Nonmetals in waste printed circuit boards after metal separation containing brominated resin and fiberglass are considered hazardous and low-recoveryvalue e-waste. However, if these nonmetals are not treated or are improperly treated, they can cause serious environmental pollution. Therefore, there is an urgent and significant need to develop an efficient recycling process for these nonmetals. Based on the concept of high-valued recycling of waste, this study in situ utilized such nonmetals to prepare a porous supercapacitor electrode through a facile carbonization, activation, and carbon thermal reduction process. The results indicated that the activation was a key role in constructing a porous structure. The optimal parameters for activation were a temperature of 800 °C, mass ratio of KOH to pyrolytic residues of 2, and an activation time of 1 h. The electrode materials exhibited a surface area of 589 m2 g-1 and hierarchical porous structures. In addition, the supercapacitors exhibited a capacitance of 77.14 mF cm-2 (62.5 mF cm-2) at 0.5 mA cm-2 (100 mV s-1). Moreover, the supercapacitors had excellent temperature resistance and adaptability. The capacitance retention was 89.36% and 90% at -50 °C and 100 °C after 10 000 cycles, respectively. This study provides a high-valued recycling strategy to utilize the nonmetals in e-waste as energy materials.

Investigation of pyrolysis for the recovery of metallic values from ball grid arrays

The massive generation of electronic waste has led to a significant interest in sustainable metal recovery and recycling. Ball grid arrays, mounted on printed circuit boards, are identified as a potentially valuable source of metals (Cu, Ni, Au, Ag, Pb, and Sn). In this study, pyrolysis is found as a promising treatment for the degradation of the epoxy resin of ball grid arrays. As a consequence, the liberation of metallic values and glass fibers is attained. The thermal analysis revealed that the major degradation occurs in the temperature range of 300-650 °C, with overall activation energy estimated as ~ 243 kJ/mol. The concentration of CO gas reaches a maximum value at a comparatively lower residence time with an increase in pyrolysis temperature. The metal enrichment was significantly influenced by the variation in pyrolysis temperatures with an optimal condition chosen as 600 °C. The metallic fractions (Cu, Ni, Ag, and Au) were separated from the glass fibers by water-based density separation and enriched in the sink product by three-fold. The recovery of Cu, Ni, Ag, and Au is achieved at 97%, 88%, 95%, and 96%, respectively. The metal fraction can be either used as a feedstock for the Cu smelting process or can be subjected to selective hydrometallurgical treatment. The glass fiber fraction comprises of Si, Al, and Ca oxides with potential application in laminate fabrication. High-quality gaseous products can be reutilized as fuel for other metallurgical processes. It can be concluded that 100 g of BGA yielded Cu ~ 23.7 g, Ni ~ 0.57 g, Ag ~ 23.4 mg, and Au ~ 73 mg after pyrolysis and density separation, which is equivalent to 1.35 kg, of primary Cu ore, 0.042 kg Ni ore, 4.68 kg Ag ore, and 14.6 kg Au ore.

Glass waste derived silicon carbide synthesis via direct current atmospheric arc plasma

The paper presents the results of the experimental studies addressing the production of silicon carbide from glass waste by electric arc plasma processing. A feature of the method is the possibility of its implementation without the use of vacuum equipment. It is possible due to the effect of self-shielding of the reaction volume from atmospheric oxygen. This approach significantly simplifies the design of the electric arc reactor and its performance. After plasma processing of various types of glass waste (such as bottle glass, window glass, medical glass, quartz glass, parts of worn-out scientific and industrial equipment), silicon carbide based material was produced. Silicon carbide was obtained from a mixture of various glass waste at a current 200 A, where blend was first purified from unbound carbon and then was consolidated by spark plasma sintering at 1800 °C and 60 MPa pressure for 10 min. As a result, a ceramic bulk sample was fabricated from a mixture of glass waste of various origin. Such sample was characterized with hardness of 14.8 GPa, and attained density of 92.5 %. Despite a possible increase in the density due to impurities and inhomogeneities, the hardness of the fabricated sample is comparable to that of other silicon carbide based materials, including commercial ones. Since the hardness of the produced silicon carbide based material is comparable to that of commercial materials, the use of glass waste of various origin could be feasible for synthesis of silicon carbide based powders.

Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

There is an obvious gap between efforts dedicated to the control of chemicophysical and morphological properties of catalyst active phases and the attention paid to the search of new materials to be employed as functional carriers in the upgrading of heterogeneous catalysts. Economic constraints and common habits in preparing heterogeneous catalysts have narrowed the selection of active-phase carriers to a handful of materials: oxide-based ceramics (e.g. Al₂O₃, SiO₂, TiO₂, and aluminosilicates-zeolites) and carbon. However, these carriers occasionally face chemicophysical constraints that limit their application in catalysis. For instance, oxides are easily corroded by acids or bases, and carbon is not resistant to oxidation. Therefore, these carriers cannot be recycled. Moreover, the poor thermal conductivity of metal oxide carriers often translates into permanent alterations of the catalyst active sites (i.e. metal active-phase sintering) that compromise the catalyst performance and its lifetime on run. Therefore, the development of new carriers for the design and synthesis of advanced functional catalytic materials and processes is an urgent priority for the heterogeneous catalysis of the future. Silicon carbide (SiC) is a non-oxide semiconductor with unique chemicophysical properties that make it highly attractive in several branches of catalysis. Accordingly, the past decade has witnessed a large increase of reports dedicated to the design of SiC-based catalysts, also in light of a steadily growing portfolio of porous SiC materials covering a wide range of well-controlled pore structure and surface properties. This review article provides a comprehensive overview on the synthesis and use of macro/mesoporous SiC materials in catalysis, stressing their unique features for the design of efficient, cost-effective, and easy to scale-up heterogeneous catalysts, outlining their success where other and more classical oxide-based supports failed. All applications of SiC in catalysis will be reviewed from the perspective of a given chemical reaction, highlighting all improvements rising from the use of SiC in terms of activity, selectivity, and process sustainability. We feel that the experienced viewpoint of SiC-based catalyst producers and end users (these authors) and their critical presentation of a comprehensive overview on the applications of SiC in catalysis will help the readership to create its own opinion on the central role of SiC for the future of heterogeneous catalysis.

High temperature silicon-carbide-based flexible electronics for monitoring hazardous environments

With its unprecedented properties over conventional rigid platforms, flexible electronics have been a significant research topic in the last decade, offering a broad range of applications from bendable display, flexible solar-energy systems, to soft implantable-devices for health monitoring. Flexible electronics for harsh and hazardous environments have also been extensively investigated. In particular, devices with stretchability and bend-ability as well as tolerance to extreme and toxic operating conditions are imperative. This work presents silicon carbide grown on silicon and then transferred onto polyimide substrate as a new platform for flexible sensors for hostile environments. Combining the excellent electrical properties of SiC and high temperature tolerance of polyimide, we demonstrated for the first time a flexible SiC sensors that can work above 400 °C. This new sensing platform opens exciting opportunities toward flexible sensing applications in hazardous environments.

Catalytic performance and debromination of Fe-Ni bimetallic MCM-41 catalyst for the two-stage pyrolysis of waste computer casing plastic

A computer casing plastic waste containing brominated flame retardants (BFRs) was pyrolyzed in a two-stage vertical quartz tube reactor using iron and nickel metals modified MCM-41 catalysts. Various catalysts with different ratios of Fe and Ni were prepared and utilized to study their catalytic performance. At the presence of 20%Ni/MCM-41 catalyst, the pyrolytic yield of oil and gas reached maximum values of 49.9 wt% and 13.8 wt% respectively. The co-existence of Fe and Ni showed synergistic effect on oil composition by promoting the formation of valuable single ring hydrocarbons. With regard to the 15%Fe-5%Ni/MCM-41, 10%Fe-10%Ni/MCM-41 and 5%Fe-15%Ni/MCM-41 catalysts, the production of single ring hydrocarbons were 64.58%, 65.93% and 64.74% respectively. The bimetallic catalysts also exhibited remarkable effect on eliminating bromine from pyrolytic oil. At the presence of Fe-Ni/MCM-41, the bromine in pyrolytic oil was reduced to below 4 wt% compared with 10 wt% without catalyst. Higher amounts of Fe in the catalyst is beneficial for the debromination efficiency. The debromination process by the Fe-Ni/MCM-41 may be realized by these different mechanisms: catalytic cracking of organobromines, reaction of loaded metal oxides with HBr/SbBr₃, and deposition of organobromines on the surface of catalyst.

Bioleaching of copper from large printed circuit boards for synthesis of organic-inorganic hybrid

The present study described a process for copper (Cu) bioleaching from waste printed circuit boards (PCBs). The 45 (± 0.18) mg/g Cu was found in waste PCBs. Acidiphilium acidophilum (NCIM 5344) (A. acidophilum) and hydrogen peroxide (H₂O₂) were used for two-step Cu bioleaching. A. acidophilum showed growth in 9K medium containing glucose and sulfur. During the growth the bacteria decreased medium pH from 3.5 (± 0.01) to 1.0 (± 0.02) in 10 days. The results showed that it required 2.5 h to leach all of the Cu from single PCB piece using 60 mL culture supernatant + 15 mL H₂O₂ at 60 °C temperature and static condition. The leached Cu was further used to synthesize the organic-inorganic hybrid (OIH). For this study, egg white was used as a polyphenol oxidase (PPO) enzyme source. The morphological, elemental, and structural analysis was carried out using scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Further the PPO enzyme activity was tested in OIH and crude enzyme (egg white). The egg white showed 0.00014 (± 0.00001) U/mg/min PPO activity while OIH showed 0.005 (± 0.00016) U/mg/min PPO activity. The pH 7 and 30 °C temperature were found to be optimum for PPO enzyme activity. The OIH was applied for phenol degradation. It degraded 95 (± 0.49)% of phenol (5 mM). The efficiency of phenol degradation decreased with an increase in phenol concentration.