Publications by authors named "Mohannad Mayyas"

16 Publications

  • Page 1 of 1

Doping Process of 2D Materials Based on the Selective Migration of Dopants to the Interface of Liquid Metals.

Adv Mater 2021 Sep 12:e2104793. Epub 2021 Sep 12.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, New South Wales, 2052, Australia.

The introduction of trace impurities within the doping processes of semiconductors is still a technological challenge for the electronics industries. By taking advantage of the selective enrichment of liquid metal interfaces, and harvesting the doped metal oxide semiconductor layers, the complexity of the process can be mitigated and a high degree of control over the outcomes can be achieved. Here, a mechanism of natural filtering for the preparation of doped 2D semiconducting sheets based on the different migration tendencies of metallic elements in the bulk competing for enriching the interfaces is proposed. As a model, liquid metal alloys with different weight ratios of Sn and Bi in the bulk are employed for harvesting Bi O -doped SnO nanosheets. In this model, Sn shows a much stronger tendency than Bi to occupy surface sites of the Bi-Sn alloys, even at the very high concentrations of Bi in the bulk. This provides the opportunity for creating SnO 2D sheets with tightly controlled Bi O dopants. By way of example, it is demonstrated how such nanosheets could be made selective to both reducing and oxidizing environmental gases. The process demonstrated here offers significant opportunities for future synthesis and fabrication processes in the electronics industries.
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http://dx.doi.org/10.1002/adma.202104793DOI Listing
September 2021

Nanotip Formation from Liquid Metals for Soft Electronic Junctions.

ACS Appl Mater Interfaces 2021 Sep 30;13(36):43247-43257. Epub 2021 Aug 30.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, NSW 2052, Australia.

Liquid metals and alloys with high-aspect-ratio nanodimensional features are highly sought-after for emerging electronic applications. However, high surface tension, water-like fluidity, and the existence of self-limiting oxides confer specific peculiarities to their characteristics. Here, we introduce a high accuracy nanometric three-dimensional pulling and stretching method to fabricate liquid-metal-based nanotips from room- or near-room-temperature gallium-based alloys. The pulling rate and step size were controlled with a resolution of up to 10 nm and yielded different nanotip morphologies and lengths as a function of the base liquid metal alloy composition and the pulling parameters. The obtained nanotips presented high aspect ratios over lengths of a few microns and apexes between 10 and 100 nm. The liquid metal alloys were found confined within nanotips with about 10 nm apexes when vertically pulled at 100 nm/s. An amorphous gallium oxide skin was shown to cover the surface of the nanotips, while the liquid core was composed of the initial liquid metal alloys. The electrical contact established at the nanotips was characterized under dynamic conditions. The liquid metal nanotips showed an Ohmic resistance when a continuous liquid metal channel was formed, and a controllable semiconductor state corresponding to a heterojunction formed at the junction between the liquid metal phase and the gallium oxide semiconductor skin. The variable threshold voltages of the heterojunction were controlled via stretching of the nanotips with a 10 nm step resolution. The liquid metal nanotips were also used for establishing soft electronic junctions. This novel method of liquid metal nanotip fabrication with Ohmic and semiconducting behaviors will lead to exciting avenues for developing electronic and sensing devices.
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http://dx.doi.org/10.1021/acsami.1c11213DOI Listing
September 2021

Liquid Crystal-Mediated 3D Printing Process to Fabricate Nano-Ordered Layered Structures.

ACS Appl Mater Interfaces 2021 Jun 10;13(24):28627-28638. Epub 2021 Jun 10.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney 2052, New South Wales, Australia.

The emergence of three-dimensional (3D) printing promises a disruption in the design and on-demand fabrication of smart structures in applications ranging from functional devices to human organs. However, the scale at which 3D printing excels is within macro- and microlevels and principally lacks the spatial ordering of building blocks at nanolevels, which is vital for most multifunctional devices. Herein, we employ liquid crystal (LC) inks to bridge the gap between the nano- and microscales in a single-step 3D printing. The LC ink is prepared from mixtures of LCs of nanocellulose whiskers and large sheets of graphene oxide, which offers a highly ordered laminar organization not inherently present in the source materials. LC-mediated 3D printing imparts the fine-tuning required for the design freedom of architecturally layered systems at the nanoscale with intricate patterns within the 3D-printed constructs. This approach empowered the development of a high-performance humidity sensor composed of self-assembled lamellar organization of NC whiskers. We observed that the NC whiskers that are flat and parallel to each other in the laminar organization allow facile mass transport through the structure, demonstrating a significant improvement in the sensor performance. This work exemplifies how LC ink, implemented in a 3D printing process, can unlock the potential of individual constituents to allow macroscopic printing architectures with nanoscopic arrangements.
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http://dx.doi.org/10.1021/acsami.1c05025DOI Listing
June 2021

Near-Field Excited Archimedean-like Tiling Patterns in Phonon-Polaritonic Crystals.

ACS Nano 2021 May 30;15(5):9134-9142. Epub 2021 Apr 30.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, NSW 2052, Australia.

Phonon-polaritons (PhPs) arise from the strong coupling of photons to optical phonons. They offer light confinement and harnessing below the diffraction limit for applications including sensing, imaging, superlensing, and photonics-based communications. However, structures consisting of both suspended and supported hyperbolic materials on periodic dielectric substrates are yet to be explored. Here we investigate phonon-polaritonic crystals (PPCs) that incorporate hyperbolic hexagonal boron nitride (hBN) to a silicon-based photonic crystal. By using the near-field excitation in scattering-type scanning near-field optical microscopy (s-SNOM), we resolved two types of repetitive local field distribution patterns resembling the Archimedean-like tiling on hBN-based PPCs, , dipolar-like field distributions and highly dispersive PhP interference patterns. We demonstrate the tunability of PPC band structures by varying the thickness of hyperbolic materials, supported by numerical simulations. Lastly, we conducted scattering-type nanoIR spectroscopy to confirm the interaction of hBN with photonic crystals. The introduced PPCs will provide the base for fabricating essential subdiffraction components of advanced optical systems in the mid-IR range.
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http://dx.doi.org/10.1021/acsnano.1c02507DOI Listing
May 2021

Unique surface patterns emerging during solidification of liquid metal alloys.

Nat Nanotechnol 2021 Apr 18;16(4):431-439. Epub 2021 Jan 18.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, New South Wales, Australia.

It is well-understood that during the liquid-to-solid phase transition of alloys, elements segregate in the bulk phase with the formation of microstructures. In contrast, we show here that in a Bi-Ga alloy system, highly ordered nanopatterns emerge preferentially at the alloy surfaces during solidification. We observed a variety of transition, hybrid and crystal-defect-like patterns, in addition to lamellar and rod-like structures. Combining experiments and molecular dynamics simulations, we investigated the influence of the superficial Bi and GaO layers during surface solidification and elucidated the pattern-formation mechanisms, which involve surface-catalysed heterogeneous nucleation. We further demonstrated the dynamic nature and robustness of the phenomenon under different solidification conditions and for various alloy systems. The surface patterns we observed enable high-spatial-resolution nanoscale-infrared and surface-enhanced Raman mapping, which reveal promising potential for surface- and nanoscale-based applications.
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http://dx.doi.org/10.1038/s41565-020-00835-7DOI Listing
April 2021

Pulsing Liquid Alloys for Nanomaterials Synthesis.

ACS Nano 2020 Oct 21;14(10):14070-14079. Epub 2020 Sep 21.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, New South Wales 2052, Australia.

Although it remains unexplored, the direct synthesis and expulsion of metals from alloys can offer many opportunities. Here, such a phenomenon is realized electrochemically by applying a polarizing voltage signal to liquid alloys. The signal induces an abrupt interfacial perturbation at the Ga-based liquid alloy surface and results in an unrestrained discharge of minority elements, such as Sn, In, and Zn, from the liquid alloy. We show that this can occur by either changing the surface tension or inducing a reversible redox reaction at the alloys' interface. The expelled metals exhibit nanosized and porous morphologies, and depending on the cell electrochemistry, these metals can be passivated with oxide layers or fully oxidized into distinct nanostructures. The proposed concept of metal expulsion from liquid alloys can be extended to a wide variety of molten metals for producing metallic and metallic compound nanostructures for advanced applications.
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http://dx.doi.org/10.1021/acsnano.0c06724DOI Listing
October 2020

Concentrative isolation of uranium traces in aqueous solutions via resurfaced-magnetic carbon nanotube suspension.

J Environ Manage 2020 Oct 30;271:110970. Epub 2020 Jun 30.

University of New South Wales, School of Chemical Engineering, Sydney, 2052, Australia.

The concentrative isolation of metal traces from aqueous solutions is of vital importance for environmental and industrial processes. Developing reliable systems of nanoscale that can be fine-tuned to effectively isolate these metals remains an intriguing aim which can potentially beget economic benefits and mitigate major environmental concerns. Here we demonstrate a conceptual metal extraction system where magnetic multi-wall carbon nanotubes (M-MWCNTs) are surface-equipped with a molecular network of polyethylenimine (PEI) to serve as a reusable nano-ionic exchanger, referred to as "M-MWCNTs-PEI". The designed nano-ionic exchanger forms readily stable suspensions with the metal-bearing aqueous solutions eliminating the need for vigorous agitation. Besides, it can be magnetically manipulated and separated in/from the solution. To exemplify its potential for the isolation of metal traces, the M-MWCNTs-PEI was tested with the uranium trace ions in aqueous media. The M-MWCNTs-PEI featured distinct sorption capacity of ~488 mg/g at pH 6, with moderate, but stable, binding affinity toward uranium ions. As such, excellent isolation performance is demonstrated while bound uranium ions are effectively concentrated and recovered from the interfacial PEI molecular network. This was efficiently achieved by exposing the loaded M-MWCNTs-PEI to solutions of small volumes and specific chemistry. Such combined qualities of large capacity and reusability have not been observed with the previously reported ion exchange systems. Altogether, our observations here demonstrate how functional systems of nanoscale can be adapted for industrial applications while this concept can be extended to address other important resources such as rare-earth and lanthanide elements.
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http://dx.doi.org/10.1016/j.jenvman.2020.110970DOI Listing
October 2020

Liquid-Metal-Templated Synthesis of 2D Graphitic Materials at Room Temperature.

Adv Mater 2020 Jul 8;32(29):e2001997. Epub 2020 Jun 8.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, 2052, Australia.

Room-temperature synthesis of 2D graphitic materials (2D-GMs) remains an elusive aim, especially with electrochemical means. Here, it is shown that liquid metals render this possible as they offer catalytic activity and an ultrasmooth templating interface that promotes Frank-van der Merwe regime growth, while allowing facile exfoliation due to the absence of interfacial forces as a nonpolar liquid. The 2D-GMs are formed at low onset potential and can be in situ doped depending on the choice of organic precursors and the electrochemical set-up. The materials are tuned to exhibit porous or pinhole-free morphologies and are engineered for their degree of oxidation and number of layers. The proposed liquid-metal-based room-temperature electrochemical route can be expanded to many other 2D materials.
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http://dx.doi.org/10.1002/adma.202001997DOI Listing
July 2020

Bi-Sn Catalytic Foam Governed by Nanometallurgy of Liquid Metals.

Nano Lett 2020 Jun 7;20(6):4403-4409. Epub 2020 May 7.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, New South Wales 2052, Australia.

Metallic foams, with intrinsic catalytic properties, are critical for heterogeneous catalysis reactions and reactor designs. Market ready catalytic foams are costly and made of multimaterial coatings with large sub-millimeter open cells providing insufficient active surface area. Here we use the principle of nanometallurgy within liquid metals to prepare nanostructured catalytic metal foams using a low-cost alloy of bismuth and tin with sub-micrometer open cells. The eutectic bismuth and tin liquid metal alloy was processed into nanoparticles and blown into a tin and bismuth nanophase separated heterostructure in aqueous media at room temperature and using an indium brazing agent. The CO electroconversion efficiency of the catalytic foam is presented with an impressive 82% conversion efficiency toward formates at high current density of -25 mA cm (-1.2 V vs RHE). Nanometallurgical process applied to liquid metals will lead to exciting possibilities for expanding industrial and research accessibility of catalytic foams.
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http://dx.doi.org/10.1021/acs.nanolett.0c01170DOI Listing
June 2020

Magnetic and Conductive Liquid Metal Gels.

ACS Appl Mater Interfaces 2020 Apr 15;12(17):20119-20128. Epub 2020 Apr 15.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, New South Wales 2052, Australia.

Liquid metals are fast becoming a new class of universal and frictionless additives for the development of multifunctional soft and flexible materials. Herein, nanodroplets of eutectic gallium-indium alloy, which is liquid at room temperature, were used as a platform for the formulation of electrically conductive and magnetically responsive gels with the incorporation of FeO nanoparticles. The nanoadditives were prepared within a water-based solution of polyvinyl alcohol. A borax cross-linking reaction was then performed to yield multifunctional flexible and self-healing gels. The physicochemical properties and changes in the nanoadditives at each step of the gel preparation method were characterized. Oxidation and complexation reactions between the liquid metal and iron oxide nanoadditives were observed. A mixture of nanosized functional magnetic FeO/FeO and In-Fe oxide complexes was found to enable the magnetic susceptibility of the gels. The mechanical and self-healing properties of the gels were assessed, and finally, this flexible and multifunctional material was used as an electronic switch via remote magnetic actuation. The developed conductive and magnetic gels demonstrate great potential for the design of soft electronic systems.
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http://dx.doi.org/10.1021/acsami.0c03166DOI Listing
April 2020

Boundary-Induced Auxiliary Features in Scattering-Type Near-Field Fourier Transform Infrared Spectroscopy.

ACS Nano 2020 Jan 23;14(1):1123-1132. Epub 2019 Dec 23.

School of Chemical Engineering , University of New South Wales (UNSW) , Sydney Campus, NSW 2052 Australia.

Phonon-polaritons (PhPs) in layered crystals, including hexagonal boron nitride (hBN), have been investigated by combined scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared (FTIR) spectroscopy. Nevertheless, many of such s-SNOM-based FTIR spectra features remain unexplored, especially those originated from the impact of boundaries. Here we observe real-space PhP propagations in thin-layer hBN sheets either supported or suspended by s-SNOM imaging. Then with a high-power broadband IR laser source, we identify two major peaks and multiple auxiliary peaks in the near-field amplitude spectra, obtained using scattering-type near-field FTIR spectroscopy, from both supported and suspended hBN. The major PhP propagation interference peak moves toward the major in-plane phonon peak when the IR illumination moves away from the hBN edge. Specific differences between the auxiliary peaks in the near-field amplitude spectra from supported and suspended hBN sheets are investigated regarding different boundary conditions, associated with edges and substrate interfaces. The outcomes may be explored in heterostructures for advanced nanophotonic applications.
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http://dx.doi.org/10.1021/acsnano.9b08895DOI Listing
January 2020

Liquid Metal Droplet and Graphene Co-Fillers for Electrically Conductive Flexible Composites.

Small 2020 Mar 29;16(12):e1903753. Epub 2019 Sep 29.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney, NSW, 2052, Australia.

Colloidal liquid metal alloys of gallium, with melting points below room temperature, are potential candidates for creating electrically conductive and flexible composites. However, inclusion of liquid metal micro- and nanodroplets into soft polymeric matrices requires a harsh auxiliary mechanical pressing to rupture the droplets to establish continuous pathways for high electrical conductivity. However, such a destructive strategy reduces the integrity of the composites. Here, this problem is solved by incorporating small loading of nonfunctionalized graphene flakes into the composites. The flakes introduce cavities that are filled with liquid metal after only relatively mild press-rolling (<0.1 MPa) to form electrically conductive continuous pathways within the polymeric matrix, while maintaining the integrity and flexibility of the composites. The composites are characterized to show that even very low graphene loadings (≈0.6 wt%) can achieve high electrical conductivity. The electrical conductance remains nearly constant, with changes less than 0.5%, even under a relatively high applied pressure of >30 kPa. The composites are used for forming flexible electrically-conductive tracks in electronic circuits with a self-healing property. The demonstrated application of co-fillers, together with liquid metal droplets, can be used for establishing electrically-conductive printable-composite tracks for future large-area flexible electronics.
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http://dx.doi.org/10.1002/smll.201903753DOI Listing
March 2020

Application of High-Resolution NMR and GC-MS to Study Hydrocarbon Oils Derived from Noncatalytic Thermal Transformation of e-Waste Plastics.

ACS Omega 2018 Aug 16;3(8):9282-9289. Epub 2018 Aug 16.

Centre for Sustainable Materials Research and Technology ([email protected]), School of Materials Science and Engineering, UNSW Sydney, Sydney, New South Wales 2052, Australia.

The increases in the volumes of electronic waste have become an aggravating environmental, economic, and social health issue in recent times. This study investigates the conversion of e-waste plastics into hydrocarbon oils via noncatalytic thermal transformation followed by an in-depth characterization of these oils using diverse analytical techniques such as gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. In particular, NMR spectroscopy is a key analytical tool utilized in this study to gain a comprehensive insight into the chemical nature of the resultant oils along with a semiquantitative investigation of the changes in their composition over a temperature range of 800-1200 °C. The one-dimensional (1D) H and two-dimensional (2D) heteronuclear single-quantum correlation spectra were acquired for the oils, wherein the 2D NMR spectrum provided improved resolution of peaks to address the overlaps encountered in the 1D spectrum. The experimental results obtained from GC-MS, FTIR spectroscopy, and NMR spectroscopy were found to align well with each other. The oils produced in this study have a high calorific value of 38.27 MJ/kg and thus may find use in several applications. A detailed mechanism for the thermal degradation of styrene acrylonitrile plastics and the formation of major products is elucidated in this study.
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http://dx.doi.org/10.1021/acsomega.8b01284DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6645135PMC
August 2018

Nano-carbons from waste tyre rubber: An insight into structure and morphology.

Waste Manag 2017 Nov 14;69:110-116. Epub 2017 Aug 14.

Centre for Sustainable Materials Research and Technology (SMaRT), School of Materials Science and Engineering, University of New South Wales, Sydney 2052, Australia.

This study reports on the novel and sustainable synthesis of high value carbon nanoparticles (CNPs) from waste tyre rubber (WTR), using an innovative high temperature approach. As waste tyres are composed, primarily, of carbon - accounting for some 81.2wt% - they represent a promising source of carbon for many potential applications. However, cost-effective options for their processing are limited and, consequently, billions of waste tyres have accumulated in landfills and stockpiles, posing a serious global environmental threat. The rapid, high temperature transformation of low value WTR to produce valuable CNPs, reported here, addresses this challenge. In this study, the transformation of WTRs was carried out at 1550°C over different reaction times (5s to 20min). The structure and morphology of the resulting CNPs were investigated using X-ray diffraction (XRD), Raman spectroscopy, X-ray photon spectroscopy (XPS), N isothermal adsorption method and scanning electron microscopy (SEM). The formation of CNPs with diameters of 30 and 40nm was confirmed by Field Emission Electron Microscopy (FE-SEM). Longer heating times also resulted in CNPs with regular and uniform spherical shapes and a specific surface area of up to 117.7m/g, after 20min. A mechanism that describes the formation of CNPs through mesophase nuclei intermediate is suggested.
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http://dx.doi.org/10.1016/j.wasman.2017.08.020DOI Listing
November 2017

Waste conversion into high-value ceramics: Carbothermal nitridation synthesis of titanium nitride nanoparticles using automotive shredder waste.

J Environ Manage 2017 Mar 4;188:32-42. Epub 2016 Dec 4.

Centre for Sustainable Materials Research and Technology (SMaRT), School of Materials Science and Engineering, University of New South Wales, Sydney 2052, Australia.

Environmental concern about automotive shredder residue (ASR) has increased in recent years due to its harmful content of heavy metals. Although several approaches of ASR management have been suggested, these approaches remain commercially unproven. This study presents an alternative approach for ASR management where advanced materials can be generated as a by-product. In this approach, titanium nitride (TiN) has been thermally synthesized by nitriding pressed mixture of automotive shredder residue (ASR) and titanium oxide (TiO). Interactions between TiO and ASR at non-isothermal conditions were primarily investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry. Results indicated that TiO influences and catalyses degradation reactions of ASR, and the temperature, at which reduction starts, was determined around 980 °C. The interaction between TiO and ASR at isothermal conditions in the temperature range between 1200 and 1550 °C was also studied. The pressed mixture of both materials resulted in titanium nitride (TiN) ceramic at all given temperatures. Formation kinetics were extracted using several models for product layer diffusion-controlled solid-solid and solid-fluid reactions. The effect of reactants ratio and temperature on the degree of conversion and morphology was investigated. The effect of reactants ratio was found to have considerable effect on the morphology of the resulting material, while temperature had a lesser impact. Several unique structures of TiN (porous nanostructured, polycrystalline, micro-spherical and nano-sized structures) were obtained by simply tuning the ratio of TiO to ASR, and a product with appreciable TiN content of around 85% was achieved after only one hour nitridation at 1550 °C.
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http://dx.doi.org/10.1016/j.jenvman.2016.11.079DOI Listing
March 2017

Preliminary investigation on the thermal conversion of automotive shredder residue into value-added products: Graphitic carbon and nano-ceramics.

Waste Manag 2016 Apr 11;50:173-83. Epub 2016 Feb 11.

Centre for Sustainable Materials Research and Technology (SMaRT), School of Materials Science and Engineering, UNSW Australia, Sydney, NSW 2052, Australia.

Large increasing production volumes of automotive shredder residue (ASR) and its hazardous content have raised concerns worldwide. ASR has a desirable calorific value, making its pyrolysis a possible, environmentally friendly and economically viable solution. The present work focuses on the pyrolysis of ASR at temperatures between 950 and 1550°C. Despite the high temperatures, the energy consumption can be minimized as the decomposition of ASR can be completed within a short time. In this study, the composition of ASR was investigated. ASR was found to contain about 3% Ti and plastics of high calorific value such as polypropylene, polyethylene, polycarbonate and polyurethane. Based on thermogravimetric analysis (TGA) of ASR, the non-isothermal degradation kinetic parameters were determined using Coats-Redfern's and Freeman and Carroll methods. The evolved gas analysis indicated that the CH4 was consumed by the reduction of some oxides in ASR. The reduction reactions and the presence of Ti, silicates, C and N in ASR at 1550°C favor the formation of specific ceramics such as TiN and SiC. The presence of nano-ceramics along with a highly-crystalline graphitic carbon in the pyrolysis residues obtained at 1550°C was confirmed by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Raman imaging microscope (RIM) analyses.
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http://dx.doi.org/10.1016/j.wasman.2016.02.003DOI Listing
April 2016
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