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Recycling of materials containing inorganic and carbonaceous nanomaterials

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Abstract

As to inorganic and carbonaceous nanomaterials considerable scope exists for a variety of recycling called resource cascading. Resource cascading aims at the maximum exploitation of quality and service time of natural resources. Extension of product use, product reuse, remanufacturing, and the reuse of materials are important elements in resource cascades. Options for resource cascading are available regarding nanomaterials applied in reactors, used as recoverable analyte, and for nanomaterials embedded in, or bound to the surface of, large-sized materials. Important research issues for nanomaterials applied in reactors are: recovery of nanomaterials in commercial processes, preventing aggregation of nanomaterials, kinetics of catalysts and adsorbents and preventing and reversing poisoning of catalysts and adsorbents. Options facilitating extended use and reuse of nanocomposites with large-sized materials include: preventing loss of nanomaterials, preventing poisoning of nanomaterials, preventing degradation of polymers and introducing self-healing properties. For the recycling of nanomaterials and nanocomposite materials a wide range of technologies has been investigated. Performance of thermoplastic polymeric nanocomposites often deteriorates on reprocessing. There is also scope for recycling of nanomaterials and sacrificed nanomaterials present in wastes. There can be good reasons for resource cascading of nanomaterials and recycling of wastes linked to functionality, resource savings and hazard minimization. Much work is still needed to extend our knowledge about options for resource cascading and the minimization of the environmental burden thereof, and to make resource cascading of nanomaterials fully operational.

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Article
Fly ash from municipal solid waste incineration contains a large potential for recyclable metals such as Zn, Pb, Cu and Cd. The Swiss Waste Ordinance prescribes the treatment of fly ash and recovery of metals to be implemented by 2021. More than 60% of the fly ash in Switzerland is acid leached according to the FLUWA process, which provides the basis for metal recovery. The investigation and optimization of the FLUWA process is of increasing interest and an industrial solution for direct metal recovery within Switzerland is in development. With this work, a detailed laboratory study on different filter cakes from fly ash leaching using HCl 5% (represents the FLUWA process) and concentrated sodium chloride solution (300 g/L) is described. This two-step leaching of fly ash is an efficient combination for the mobilization of a high percentage of heavy metals from fly ash (Pb, Cd ! 90% and Cu, Zn 70-80%). The depletion of these metals is mainly due to a combination of redox reaction and metal-chloride-complex formation. The results indicate a way forward for an improved metal depletion and recovery from fly ash that has potential for application at industrial scale.
Article
Surface functionalized multiwall carbon nanotube (MWCNT) reinforced teflon fibrils (MWCNT@Teflon) were successfully tested as an - oil - absorbent that can be used as a potential oil recovery material at the time of oil spill accidents in water. We found that oleic acid functionalization of MWCNTs was important for their adhesion onto teflon fibrils and at the same time prevented the MWCNT leaching into oil/water interface. The fibrils had displayed superior mechanical and thermal stability and provided a new insight to oil spill clean-up applications with easy recovery of absorbed oil by simple squeezing. Recycling of exhausted MWCNT@Teflon fibrils after oil recovery applications was conducted by pyrolysis under inert atmosphere in presence of magnetic clay. The magnetic clay absorbed the pyrolysis products, resulting in a heterostructured magnetic clay carbon composite (MCC) which was found super paramagnetic and chemically stable in all pH. The MCC was found capable of adsorbing textile dye from water ultra-fast with in a maximum contact time of 2 min and magnetically separable after adsorption experiments.
Article
Al–4.5 wt.% Cu-based nanocomposites, reinforced with various weight percentages of ZrO2, have been synthesized via mechanical alloying method. The mixture powders were cold pressed and sintered at various firing temperatures up to 500 °C for 1 h in argon atmosphere. X-ray diffraction technique is utilized to investigate structural phases and elemental diffusion of milled powders. Transmission and scanning electron microscopies coupled with energy dispersive spectroscopy were employed to examine the morphology of milled powders and the microstructure of sintered specimens, respectively. Physical, mechanical and electrical properties of sintered samples were measured. Moreover, the sintered samples followed by heat treatments at 460 °C for 3 h, quenched and then, artificial aging was performed. The results revealed that Al2Cu precipitate phase was clearly observed after milling reflecting the formation of supersaturated solution of Cu in Al. Increase of ZrO2 contents caused weakness of Al2Cu phase, decrease in the crystal and particle sizes. Furthermore, successive increase of ZrO2 contents led to, in contrast to relative density and electrical conductivity, remarkable enhancement of mechanical properties of the nanocomposites. The results pointed out that microhardness, compressive strength and conductivity, for specific ZrO2 content, obviously increased at the early stage of aging and then, decreased.
Article
To better understand the effect of rectorite and carbon black (CB) on the aging performance of styrene-butadiene rubber (SBR), SBR/CB, SBR/CB/rectorite and SBR/rectorite nanocomposites with the same total filler loading were prepared. The microstructure of the three SBR nanocomposites was characterized by XRD, TEM and SEM. After thermal aging, oxygen-containing molecules were found to be formed in the SBR nanocomposites, as verified by FTIR analysis. The SBR/rectorite nanocomposite showed the highest aging coefficient and the lowest change rate of tensile strength and stress at 100% strain among the three SBR nanocomposites, indicating that the introduction of nano-dispersed rectorite layers can enhance the thermal aging resistance of the nanocomposites. For the SBR/CB/rectorite nanocomposite, the addition of CB helped to improve the interfacial compatibility between the filler and matrix, resulting in the best crack resistance as the aged SBR/CB/rectorite nanocomposite always demonstrated the least cracks on the surface during either stretching or bending experiments.
Article
Sustainable manufacturing processes are becoming more important in industrial practice. A critical part of the manufacturing process is understanding the recycling behavior of nanocomposite materials, particularly as more recycled plastic nanocomposites are entering the market for a variety of different applications. A common method to recycle thermoplastic composites is by melting and remolding, which often leads to decreased mechanical properties. This work was conducted to investigate the effect of nanofillers on the recycling behavior and structure–property relationships of carbon nanotube (CNT)-filled polycarbonate (PC). Materials were recycled by repeated injection molding and granulating up to twenty cycles. The effect of recycling on chemical, rheological, and mechanical properties was investigated. The results indicated a general decrease in melt viscosity and mechanical properties (with the exception of Young's Modulus). The CNT-filled PC shows less resistance to recycling compared to neat PC. POLYM. ENG. SCI., 2017.
Article
This study provides a comparison between environmental impacts of the recovery of platinum group metals (PGMs) from the end-of-life catalytic converters by hydrometallurgical and pyrometallurgical methods. A gate to grave life cycle assessment of a typical three-way catalytic converter manufactured for an Australian passenger car was carried out using GaBi professional environmental package. Recovery rates, as well as qualities, quantities, losses, and fugitive emissions for all materials and elements used in both methods were calculated based on the developed flowsheets. A life cycle impact assessment was then made by carrying out a mass balance calculation. Inventory data show that the hydrometallurgical route for recycling of the platinum group metals out of catalytic converter scrap has lower impacts on the environment compared with the pyrometallurgical method. In terms of emission effects, the hydrometallurgical process was found to be highly advantageous since it causes insignificant emissions to air, sea water, and fresh water. It is also found that the hydrometallurgical route performs comparatively superior in terms of acidification, eutrophication, fossil depletion, and human toxicity. The obtained results are applicable only to the Australian setting.
Article
The present era is dominated by nano-materials. Researchers are keen to explore the potential of nano-particles (NPs) in composites because of their intensive interaction with the matrix and surfaces due to very large surface area. Potassium titanate (KT) is used as a filler in a good quality non-asbestos organic (NAO) friction materials (FMs). Based on a little information available in the literature, it is claimed to reduce friction-fluctuations, fade and wear. However, exact role of KT in FMs is not so clear due to contradictory findings. Interestingly, no paper is available on exploration of NPs of KT in FMs. Keeping this in view, two realistic multi-ingredient NAO FMs in the form of brake-pads with identical compositions but differing in size of a theme ingredient, KT were developed. One composite was without KT (K0), while two composites containing 3% micro and 3% nano-KT particles were designated as KM and KN. These were characterized for physical, mechanical and tribological performance. Initial tribo-evaluation of composites was done on a reduced scale prototype (RSP) under various operating conditions. Final tribo-performance was evaluated on a full scale brake dynamometer following JASO C 406 Schedule using gray cast iron disc. Various performance parameters such as performance µ, fade µ, recovery µ; fade ratio, recovery ratio, wear resistance etc. were used to evaluate the performance of FMs. Both testing data (prototype and realistic machine) showed that almost all performance parameters were significantly and beneficially affected due to NPs of KT. Nano-KT particles proved to improve performance µ and wear resistance significantly compared to its micro-partner. Worn surface analysis of pads and discs was done to understand wear mechanism by SEM and EDAX technique. It was finally concluded that Nano-KT particles have a potential to enhance performance of FMs significantly.
Article
We introduce the synthesis and in-depth characterization of platinum(II)-crosslinked single-chain nanoparticles (Pt(II) -SCNPs) to demonstrate their application as a recyclable homogeneous catalyst. Specifically, a linear precursor copolymer of styrene and 4-(diphenylphosphino)styrene was synthesized via nitroxide-mediated polymerization. The triarylphosphine ligand moieties along the backbone allowed for the intramolecular crosslinking of single chains via the addition of [Pt(1,5-cyclooctadiene)Cl2 ] in dilute solution. The successful formation of well-defined Pt(II) -SCNPs was evidenced by size exclusion chromatography, dynamic light scattering, nuclear magnetic resonance ((1) H, (31) P{(1) H}, (195) Pt), and diffusion-ordered spectroscopy. Finally, the activity of the Pt(II) -SCNPs as homogeneous, yet recyclable catalyst was successfully demonstrated using the example of the amination of allyl alcohol.
Article
In this paper, polypropylene (PP) filled with different levels of multi-walled carbon nanotubes (MWCNTs) manufactured by injection molding was closed-loop recycled in order to investigate the effect of recycling and reprocessing on its rheological, electrical and mechanical properties. It was found that the PP/MWCNT composites keep the flow performance after mechanical recycling. Moreover, the stress and strain at break increase after one reprocessing cycle (mechanical recycling and injection molding) whereas no statistically significant changes in electrical conductivity, Young modulus and tensile strength of the PP/MWCNT composites filled with 1, 3 and 5 wt.% were observed.
Article
Surface-enhanced Raman scattering (SERS) has proven to be an effective technique for identifying and providing fingerprint structural information of various analytes in low concentration. However, this analytical technique has been plagued by the ubiquitous presence of organic contaminants on roughened SERS substrate surfaces, which not only often result in poorer detection sensitivity but also significantly affect the reproducibility and accuracy of SERS analysis. Herein, we developed a clean, stable, and recyclable three dimensional (3D) chestnut-like Ag/WO3-x (0<x<0.28) SERS substrate by simple hydrothermal reaction and subsequent green in-situ decoration of silver nanoparticles. None of the organic additives was used in synthesis which ensures the substrate surfaces are completely clean and free of interferences from impurities. The innovative design combines the SERS enhancement effect and self-cleaning property, making it a multifunctional and reusable SERS platform for highly sensitive SERS detection. Using malachite green as a model target, the as-prepared SERS substrates exhibited good reproducibility (relative standard deviation of 7.5%) and pushed the detection limit down to 0.29 pM. The enhancement factor was found to be as high as 1.4 × 107 based on the analysis of 4-aminothiophenol. The excellent regeneration performance indicated that the 3D biomimetic SERS substrates can be reused many times. In addition, the fabricated substrate was successfully employed for detecting thiram in water with a detection limit of 0.32 nM, and a good linear relationship was obtained between the logarithmic intensities and the logarithmic concentrations of thiram ranging from 1 nM to 1 μM. More importantly, the resultant SERS-active colloid can be used for accurate and reliable determination of thiram in real fruits peels. These results predict that the proposed SERS system have great potential toward rapid, reliable, and on-site analysis, especially for food safety and environmental supervision.
Article
In this work, a green and template-recyclable method was designed to obtain Fe3O4/petroleum asphalt based carbons (Fe3O4/PC) with different Fe3O4 contents as anode material for Li-ion batteries. 73-Fe3O4/PC with 73% Fe3O4 can deliver a high reversible capacity of 785 mAh g⁻¹ at 200 mA g⁻¹ with excellent stability. The superior electrochemical performance of as-made Fe3O4/PC is attributed to the good electrical conductivity of carbon framework from asphalt and its dimensional confinement on Fe3O4 nanoparticles. This study not only demonstrates a green and economical route for high-value utilization of petroleum asphalt in energy storage, but also paves a new way for the preparation of porous carbon via recyclable template, which is indispensable for green chemistry.
Article
A very simple synthesis of bimetallic Pd–Pt–Fe3O4 nanoflake-shaped alloy nanoparticles (NPs) for cascade catalytic reactions such as dehydrogenation of ammonia borane (AB) followed by the reduction of nitro compounds (R-NO2) to anilines or alkylamines (R-NH2) in methanol at ambient temperature is described. The Pd–Pt–Fe3O4 NPs were easily prepared via a solution phase hydrothermal method involving the simple one-pot co-reduction of potassium tetrachloroplatinate (II) and palladium chloride (II) in polyvinylpyrrolidone with subsequent deposition on commercially available Fe3O4 NPs. The bimetallic Pd–Pt alloy Nps decorated on Fe3O4 NPs provide unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. Various nitroarene derivatives were reduced to anilines with very specific chemoselectivity in the presence of other reducible functional group. The bimetallic Pd–Pt–Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. The nitro reduction proceeded in 5 min with nearly quantitative conversions and yields. Furthermore, the magnetically recyclable nanocatalysts were readily separated using an external magnet and reused up to 250 times without any loss of catalytic activity. A larger scale (10 mmol) reaction was also successfully performed with >99% yield. This efficient, recyclable Pd–Pt–Fe3O4 NPs system can therefore be repetitively utilized for the reduction of various nitro-containing compounds.