Converting Polyethylene Waste into Large Scale One-Dimensional

Article pubs.acs.org/IECR

Converting Polyethylene Waste into Large Scale One-Dimensional Fe3O4@C Composites by a Facile One-Pot Process Junhao Zhang,*,† Bo Yan,† Sheng Wan,† and Qinghong Kong*,‡ †

School of Biological and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu, 212018, People’s Republic of China ‡ Jiangsu University Branch Center of State Key Lab of Urban Water Resource and Environment, Jiangsu University, Zhenjiang, Jiangsu, 212013, People’s Republic of China ABSTRACT: Polyethylene-based waste plastics need hundreds of years to degrade in atmospheric conditions, so innovative upcycling processes are necessary in addition to traditional recycling services. This study presents an environmentally benign and solvent-free autogenic process, in which waste plastics such as waste polyethylene (PE) were converted into Fe3O4@C core− shell structures with about 800 nm in diameter and tens of micrometers in length with the presence of catalysts while oxygen was absent. The composition and morphology of the as-obtained Fe3O4@C core−shell structures were characterized by advanced structural, spectroscopic, and imaging techniques. The magnetic measurement at room temperature indicates that the values of saturation magnetization (22.5 emu/g) and coercivity (152.9 Oe) of the one-dimensional Fe3O4@C core−shell structures are different from those of Fe3O4 nanoparticles and bulk Fe3O4 due to the different carbon content, dipolar interaction, size, and morphology of the products. The results indicate that the one-dimensional Fe3O4@C core/shell structures possess well acid resistance.

1. INTRODUCTION The enormous and escalating volume of waste from the ubiquitous polyolefin-based plastics might cause severe negative environmental impact on human life if left unchecked.1 Hence, the disposal of waste plastics has been an important concern for the society. Since plastics are not biodegradable,2 it is not an effective solution to store them in landfills. The most usual alternative in many countries for the treatment of waste plastics is incineration accompanied by energy recovery.3 This option is often socially rejected because of the risk of toxic compound emission, such as dioxins and furans. Nowadays, extensive collection, transportation, separation, and recycling facilities are available for processing waste thermoplastic products. Unfortunately, by chemically mixing different waste plastics, homogeneous materials might not be obtained being suitable for making quality products. The problem of mixed plastics has been partially solved by separation technologies such as flotation,4 plasma gasification technology,5 and so on. However, these multistep recycling processes are not cost-effective. Consequently, the great efforts should be directed to the exploration of mature technologies that can eliminate and process polyolefin waste with the lowest environmental impact and the highest possible profitability. At present, one proposed strategy is gasification of waste plastic to yield synthesis gas, but it requires the construction of large plants to be profitable.6 In this regard, catalytic cracking technologies toward fuels and chemicals are more flexible and receive increased attention.7 Among the several methods, pyrolysis is a promising approach with various potential applications. For example, thermal cracking of polymers may produce materials with low molecular weight.8−11 However, it is limited by some drawbacks, such as the broad range of products, and the high temperature which is more than 600 °C and even up to 900 °C.12−14 © 2013 American Chemical Society

To address the environmental issues associated with waste plastics, some new techniques were developed to systematically degrade waste plastics.15,16 For example, Kartel et al.17 prepared activated carbon with a BET surface area of 1030 m2/g and an effective pore size of 1.8 nm using polyethylene terephthalate as carbon source. However, the yield of solid carbon was only 22%. Recently, a simple one-step process without solvents was used to convert PE and other waste plastics (such as polyethylene terephthalate, polypropylene, and polystyrene) into carbon spheres and carbon nanotubes.18−24 This approach is efficient and scalable, but it needs high reaction temperature. From the viewpoint of economically applicable process in industry, it is necessary to improve the production yield of solid carbon under mild conditions. Additionally, it should be noted that only a few documents report the synthesis of Fe3O4@C core/shell structures through catalytic pyrolysis of polymers.25,26 As a result, the fabrication of the Fe3O4@C core/shell still remains a great challenge by the method. In this study, a simple and economical process was designed to synthesize Fe3O4@C core/ shell structures in situ in high yield from waste PE as carbon source without solvents at lower temperature (500 °C). This reproducible process presents an opportunity to use waste plastics as feedstock to produce carbon materials or Fe3O4@C composites, industrially significant value-added products. It is expected to be practical in the disposal of waste plastics, and be also possible to use the magnetic Fe3O4@C composites to realize magnetic targeting drug delivery, recycling of nanocatalysts, Received: Revised: Accepted: Published: 5708

February 6, 2013 March 15, 2013 March 27, 2013 March 28, 2013 dx.doi.org/10.1021/ie4004392 | Ind. Eng. Chem. Res. 2013, 52, 5708−5712

Industrial & Engineering Chemistry Research

Article

spectroscopy (XPS) spectra of Fe3O4@C core/shell structures were supplied, as shown in Figure 2. It can be found that the peaks in the full pattern are mainly attributed to C1s (284.7 eV), O1s (533.2 eV), and their corresponding Auger peaks, shown in Figure 2(a). Figure 2(b) and 2(c) describe the high-resolution XPS spectra of C 1s and O 1s region, respectively. From the XPS spectrum of Fe 2p region in Figure 2(d), the characteristic peaks of Fe 2p1/2 and Fe 2p3/2 are very weak, which indicates that all Fe3O4 cores in the composites are confined within carbon shell. So it can be believed that Fe3O4 nanoparticles are completely encapsulated in thicker carbon layers. Iron oxides encapsulated in carbon based systems have intrigued great scientific interest due to their featured electric and magnetic properties and a wide range of potential technological application. In recent years, there have been a number of studies of iron oxides and carbon composites. Among them, nanoparticles, nanowires, nanoplates, and hexapod-like microstructures have been synthesized. Another type of Fe3O4 and carbon composites is presented in high morphological yield in Figure 3. A typical FESEM image (Figure 3(a)) of the assynthesized products shows extremely abundant one-dimensional structures by converting waste PE, which shows the onedimensional structures with several micrometers to tens of micrometers in length. Moreover, these one-dimensional structures almost attach together. Here, it should be noteworthy to point out that the FESEM images are obtained from the assynthesized carbon materials without purification, which indicate that a large quantity of one-dimensional structures have been produced by catalytic decomposition of waste PE at 500 °C. Figure 3(b) shows a high magnification FESEM image of the one-dimensional structures, which displays the detailed structure. It can be clearly seen that the one-dimensional structures are worm-shape with the diameter of about 800 nm. TEM studies give further information about the morphology and structure of the one-dimensional structures. Figure 3(c) is a TEM image before acid treatment, which indicates that the products are made of two parts: the outer shell (carbon) and the inner core (Fe3O4). Careful observation shows that the diameter of Fe3O4 nanoparticles inside the carbon shell is in the range of 80−200 nm, and the Fe3O4 nanoparticles are self-assembled into one-dimensional necklace-shaped structures. The thickness of carbon shells is about 300 nm. The diameter and length of onedimensional structures coincide with the results of FESEM images. It is noteworthy mentioning that the Fe3O4 nanoparticles are still in the carbon shells after acid treatment, shown in Figure 3(d), which indicates that the Fe3O4@C core/shell structures possess well acid resistance. From TEM and XRD analysis, it is clear that the products are composed of Fe3O4 core and carbon shell, which were prepared at 500 °C for 12 h in the presence of 2 g of NH4HCO3. As it is known that ferrocene (Fe-(Cp)2, Cp = C5H5) is a sandwich organo-metallic compound in which the Fe-Cp bond is formed through the d-electrons of the metal Fe atom and the π-electrons of the Cp group, and this bond is generally less stable than the bonds in the Cp ring itself. With the increase of temperature, Fe atoms were released by decomposition of ferrocene (subliming point: 100 °C, decomposition temperature: 400 °C),27 which acted as an effective and necessary dehydrogenation catalysts in the experiment. To elucidate clearly the catalyzing carbonization mechanism of PE to form the one-dimensional Fe3O4@C core/shell structures, an illustrative scheme is presented in Figure 4. At first, NH4HCO3 decomposes to produce NH3, H2O, and CO2 at

selective capture of target objects, and magnetically controllable on−off reactions.

2. EXPERIMENTAL SECTION In a typical procedure, waste PE (2.0 g), ferrocene (0.5 g), and ammonium acid carbonate (2.0 g) were loaded into a 20 mL stainless steel autoclave. The autoclave was tightly sealed and heated in an electronic furnace. The temperature of furnace increased to 500 °C in 50 min and maintained at 500 °C for 12 h. Then, the autoclave was cooled to room temperature naturally. It was found that the final products in the autoclave were black precipitates and residual gases. The black precipitates were collected and divided into two parts: one part was washed with distilled water and ethanol for several times, and the other part was heated in HCl solution of about 3 mol·L−1 at 80 °C for 6 h and washed with distilled water and ethanol for several times. After that, the products were dried in a vacuum box at 50 °C for 4 h and collected for characterization. The X-ray powder diffraction (XRD) pattern of the products without acid treatment was recorded on a Rigaku (Japan) D/ max-γA X-ray diffractometer equipped with graphite-monochromatized Cu Kα radiation (λ = 1.54178 Å). The X-ray photoelectron spectroscopy (XPS) of the products was performed using a VGESCALABMK X-ray photoelectron spectrometer and nonmonochromated Mg Kα radiation as the excitation source. The field-emission scanning electron microscopy (FESEM) images of the products were examined by a fieldemission scanning electron microscope (JEOL-6300F). The transmission electron microscope (TEM) images were taken on a JEOL 2010 high-resolution transmission electron microscope at an acceleration voltage of 200 kV. The magnetic properties (M-H curve) were measured at room temperature on an MPMS XL magnetometer made in Quantum Design Corporation. 3. RESULTS AND DISCUSSION Figure 1 shows the powder XRD pattern of the resulting Fe3O4@ C core/shell structures without acid treatment. The sharp

Figure 1. A typical XRD pattern of the Fe3O4@C core/shell structures.

diffraction peaks with relative high peak intensity can be well indexed as crystalline face-centered cubic (fcc) Fe3O4, in agreement with the literature values (Joint Committee on Powder diffraction Standards (JCPDS), Card No. 85-1436). Meanwhile, the broad peak located at about 25.1° can be assigned as amorphous graphite. No other impurity peaks were detected, revealing the high purity of the synthesized products. In order to identify the surface elemental compositions and chemical state of the particle surface, X-ray photoelectron 5709

dx.doi.org/10.1021/ie4004392 | Ind. Eng. Chem. Res. 2013, 52, 5708−5712

Industrial & Engineering Chemistry Research

Article

Figure 2. X-ray photoelectron spectra of Fe3O4@C core/shell structures: (a) a wide scan spectrum; (b) high-resolution XPS spectrum of the C 1s region; (c) high-resolution XPS spectrum of the O 1s region; (d) high-resolution XPS spectrum of the Fe 2p region.

Figure 3. (a) Low magnification FESEM image of Fe3O4@C core/shell structures; (b) high magnification FESEM image of Fe3O4@C core/shell structures; (c) TEM image of Fe3O4@C core/shell structures before acid treatment; (d) TEM image of Fe3O4@C core/shell structures after acid treatment.

low temperature, shown in process (1).28 With increasing temperature, PE chains undergo endothermic chain scission to release pyrolyzed products that mainly consist of ethylene,

ethane, propylene, propane, and other fragments in the absence of oxygen, most of which are gases at 500 °C, shown in process (2). Fe atoms were released by decomposition of ferrocene at 5710

dx.doi.org/10.1021/ie4004392 | Ind. Eng. Chem. Res. 2013, 52, 5708−5712

Industrial & Engineering Chemistry Research

Article

Figure 4. Mechanism for converting waste PE into Fe3O4@C core/shell structures through catalytic pyrolysis.

Figure 5. Magnetic hysteresis curves measured at room temperature for the Fe3O4@C core/shell structures: (a) before acid treatment; (b) after acid treatment.

400 °C, shown in process (3). Meanwhile, these small molecules carbonyl compounds were catalytically decomposed to form carbon atoms under Fe nanoparticles as catalysts, shown in process (4). Then, as-formed Fe nanoparticles gradually reacted with H2O and CO2 to form Fe3O4 nanoparticles, shown in process (5), and further grew into bigger particles with the size ranging from 80 to 200 nm. Under the drive of magnetic dipole interaction, the as-formed Fe3O4 particles were self-assembled to chain-like structures. These Fe3O4 particles chains were speedy wrapped by a small number of carbon atoms (forming a thin carbon lamella) to reduce their surface energy and form Fe3O4 particles encapsulated in thin carbon capsules. These thin carbon lamella confined the continued growth of Fe3O4 particles. As carbon atoms are enough in these experiments, the continued addition (or diffusion) of carbon atoms finally leads to the formation of one-dimensional Fe3O4@C core/shell structures. On the whole, the degradation PE wastes were catalyzed to form carbon shells by a dissociation-diffusion-precipitation process. In many reported Fe3O4 nanostructures, a significant enhancement in ferromagnetic character has been observed. The increased coercivity (Hc) of materials has been attributed to the enhanced structural anisotropy and one-dimensional structures. Herein, the typical magnetic hysteresis loop measured at room temperature is depicted with an applied field from −10000 to 10000 Oe. Figure 5(a) and 5(b) show magnetic properties of the Fe3O4@C core/shell structures before acid treatment and after acid treatment, respectively. The magnetic hysteresis loop of the Fe3O4@C core/shell structures before acid treatment shows ferromagnetic behavior with saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) values of ca. 22.5 emu/g, 4.2 emu/g, and 152.9 Oe. From these results of magnetic properties, the saturation magnetization value of the products is lower than that of bulk Fe3O4 (92 eum/g).29 The decrease in the value of Ms found in this work might be most likely attributed to the wide existence of carbon layers on the surface of Fe3O4 particles, which results in the formation of many Fe3O4 particles encapsulated in carbon shell with relative order arrangement. These carbon layers restrict the optional movement and interactions of the Fe3O4 particles. Its role is similar to that of the surfactant existing on the Fe3O4 nanopartcles, which leads to decrease Ms value.30 The high shape anisotropy of the Fe3O4 chains and the presence of a detrimental surface/crystalstructure are also related to the demagnetization effects. However, the coercivity value is higher than that of bulk Fe3O4

and Fe3O4 nanoparticles,31 but it is lower than those of previously reported Fe3O4−C nanowires (244.5) and Fe3O4− C coaxial nanofibers (324.5 Oe).32,33 The reason may be that the higher shape anisotropy, together with reduced size,34 may be responsible for the increase in Hc value compared with bulk Fe3O4 and Fe3O4 nanoparticles. The high shape anisotropy of the chains prevents them from magnetizing in other directions. With chains randomly oriented, the projection of magnetization vectoring along the field direction will be lower than that of nanoparticles. Compared with Fe3O4−C nanowires and coaxial nanofibers with single crystalline Fe3O4 cores, the chain-like Fe3O4@C composites have lower shape anisotropy, resulting in the decrease of the Hc value. Although the exact reasons are not very clear, it is broadly accepted that the size, structure, and morphology are main factors that determine the magnetic properties of the products. Figure 5(b) shows that the results after acid treatment are similar to those before acid treatment, so it is confirmed that the Fe3O4@C core/shell structures possess well acid resistance. The Fe3O4@C composites may be used in acidic medium, such as adsorbing pollutant in acidic wastewater. The composites not only have adsorption performance but also can be easily separated from water by applying a relatively low magnetic field.

4. CONCLUSIONS In summary, the uniform self-assembly Fe3O4@C core−shell structures have been prepared through catalytic decomposition of waste PE. The reaction mechanism for growth of Fe3O4@C core−shell structures was postulated on the basis of the experiments. Magnetic hysteresis loop measurement shows that the Fe3O4@C core−shell structures display ferromagnetic properties at room temperature, and the coercivity (Hc) value (152.9 Oe) is higher than those of Fe3O4 nanoparticles and bulk Fe3O4. The Fe3O4 nanoparticles were not dissolved in HCl solution of about 3 mol·L−1 at 80 °C for 6 h, which indicate that the Fe3O4@C core−shell structures possess well acid resistance. This reproducible process presents an opportunity to use waste plastics as feedstock for the production of carbon materials or Fe3O4@C composites, industrially significant value-added products. Among the known methods for the fabrication of Fe3O4@C core−shell structures, the present controlled dis5711

dx.doi.org/10.1021/ie4004392 | Ind. Eng. Chem. Res. 2013, 52, 5708−5712

Industrial & Engineering Chemistry Research

Article

rich synthesis gas and high quality carbon nanotubes. RSC Adv. 2012, 2, 4045−4047. (16) Bazargan, A.; McKay, G. A review-synthesis of carbon nanotubes from plastic waste. Chem. Eng. J. 2012, 195−196, 377−391. (17) Kartel, M. T.; Sych, N. V.; Tsyba, M. M.; Strelko, V. V. Preparation of porous carbons by chemical activation of polyethyleneterephthalate. Carbon 2006, 44, 1019−1022. (18) Pol, S. V.; Pol, V. G.; Sherman, D.; Gedanken, A. A solvent free process for the generation of strong, conducting carbonspheres by the thermal degradation of waste polyethylene terephthalate. Green Chem. 2009, 11, 448−451. (19) Pol, V. G.; Thiyagarajan, P. Measurement of autogenouspressureand dissociated species during the thermolysis of mesitylene for the synthesis of monodispersed, pure, paramagnetic carbon partcles. Ind. Eng. Chem. Res. 2009, 48, 1484−1489. (20) Pol, V. G.; Thiyagarajan, P. Remediating plastic waste into carbon nanotubes. J. Environ. Monit. 2010, 12, 455−459. (21) Pol, V. G. Upcycling: converting waste plastics into paramagnetic, conducting, solid, pure carbon microspheres. Environ. Sci. Technol. 2010, 44, 4753−4759. (22) Zhang, J. H.; Li, J.; Cao, J.; Qian, Y. T. Synthesis and characterization of larger diameter carbon nanotubes from catalytic pyrolysis of polyprolene. Mater. Lett. 2008, 62, 1839−1842. (23) Kong, Q. H.; Zhang, J. H. Synthesis of straight and helical carbon nanotubes from catalytic pyrolysis of polyethylene. Polym. Degrad. Stab. 2007, 92, 2005−2010. (24) Zhang, J. H.; Du, J.; Qian, Y. T.; Xiong, S. L. Synthesis, characterization and properties of carbon nanotubes microspheres from pyrolysis of polypropylene and maleated polypropylene. Mater. Res. Bull. 2010, 45, 15−20. (25) Zhang, J. H.; Du, J.; Qian, Y. T.; Yin, Q. H.; Zhang, D. J. Shapecontrolled synthesis and their magnetic properties of hexapod-like, flake-like and chain-like carbon-encapsulated Fe3O4 core/shell composites. Mater. Sci. Eng., B 2010, 170, 51−57. (26) Zhang, J. H.; Yan, B.; Zhang, F. Synthesis of carbon-coated Fe3O4 composites with pine-tree-leaf structures from catalytic pyrolysis of polyethylene. CrystEngComm 2012, 14, 3451−3455. (27) Bernhauer, M.; Braun, M.; Hüttinger, K. J. Kinetics of mesophase formation in a stirred tank reactor and properties of the products-V Catalysis by ferrocene. Carbon 1994, 32, 1073−1085. (28) Liu, B. Y.; Jia, D. C.; Meng, Q. C.; Rao, J. C.; Shao, Y. F. Synthesis of hollow six-armed carbon particles by a self-assembly template method. Carbon 2008, 46, 717−720. (29) Chen, X. Y.; Zhang, Z. J.; Li, X. X.; Shi, C. W. Hollow magnetite spheres: synthesis, characterization, and magnetic properties. Chem. Phys. Lett. 2006, 422, 294−298. (30) Ghosh, S.; Jiang, W.; Mcclements, J. D.; Xing, B. S. Colloidal stability of magnetic iron oxide nanoparticles: influence of natural organic matter and synthetic polyelectrolytes. Langmuir 2011, 27, 8036−8043. (31) Fang, Q. L.; Xuan, S. H.; Jiang, W. Q.; Gong, X. L. Yolk-like micro/nanoparticles with superparamagnetic iron oxide cores and hierarchical nickel silicate shells. Adv. Funct. Mater. 2011, 21, 1902− 1909. (32) Xu, L. Q.; Zhang, W. Q.; Ding, Y. W.; Peng, Y. Y.; Zhang, S. Y.; Yu, W. C.; Qian, Y. T. Formation, characterization, and magnetic properties of Fe3O4 nanowires encapsulated in carbon microtubes. J. Phys. Chem. B 2004, 108, 10859−10862. (33) Cao, F. Y.; Chen, C. L.; Wang, Q.; Chen, Q. W. Synthesis of carbon-Fe3O4 coaxial nanofibres by pyrolysis of ferrocene in supercritical carbon dioxide. Carbon 2007, 45, 727−731. (34) Beal, J. H. L.; Prabakar, S.; Gaston, N.; Teh, G. B.; Etchegoig, P. G.; Williams, G.; Tilley, R. D. Synthesis and comparison of the magnetic properties of iron sulfide spinel and iron oxide spinel nanocrystals. Chem. Mater. 2011, 23, 2514−2517.

sociation of plastics waste is one of the inexpensive and straightforward methods.

■

AUTHOR INFORMATION

Corresponding Author

*Phone: +86-511-84401181. Fax: +86-511-84407381. E-mail: [email protected] (J.Z.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

■

REFERENCES

The work was financially supported by the research fund of Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province, the Foundation of State Key Laboratory of Fire Science (No HZ2010-KF03), Natural Science Fund of University in Jiangsu (No. 09KJD620001), and the Open Project Program of Key Kaboratory of ECO-Textiles (Jiangnan University), Ministry of Education, China (No. KLET 1103).

(1) Salmiaton, A.; Garforth, A. Waste catalysts for waste polymer. Waste Manage. 2007, 27, 1891−1896. (2) Ross, S.; Evans, D. The environmental effect of reusing and recycling a plastic-based packaging system. J. Cleaner Prod. 2003, 11, 561−571. (3) Wager, P. A.; Schluep, M.; Muller, E.; Gloor, R. RoHS regulated substances in mixed plastics from waste electrical and electronic equipment. Environ. Sci. Technol. 2012, 46, 628−635. (4) Fraunholcz, N. Separation of waste plastics by froth flotations-a review. Miner. Eng. 2004, 17, 261−268. (5) Park, H. S.; Kim, C. G.; Kim, S. J. Characteristics of PE gasification by steam plasma. J. Ind. Eng. Chem. 2006, 12, 216−223. (6) Vispute, T. P.; Zhang, H.; Sauna, A.; Xiao, R.; Huber, G. W. Renewable chemical commodity feedstocks from integrated catalytic processing of pyrolysis oils. Science 2010, 330, 1222−1227. (7) Serrano, D. P.; Aguado, J.; Escola, J. M. Developing advanced catalysts for the conversion of polyolefinic waste plastics into fuels and chemicals. ACS Catal. 2012, 2, 1924−1941. (8) Kang, B. S.; Kim, S. G.; Kim, J. S. Thermal degradation of poly(methyl methacrylate) polymers: kinetics and recovery of monomers using a fluidized bed reactor. J. Anal. Appl. Pyrolysis 2008, 81, 7−13. (9) Al-Salem, S. M.; Lettieri, P.; Baeyens, J. R. Recycling and recovery routes of plastic solid waste (PSW): A review. Waste Manage. 2009, 29, 2625−2643. (10) Insura, N.; Onwudili, J. A.; Williams, P. T. Catalytic pyrolysis of low-density polyethylene over alumina-supported noble metal catalysts. Energy Fuels 2010, 24, 4231−4240. (11) Mullen, C. A.; Boateng, A. A.; Mihalcik, D. J.; Goldberg, N. M. Catalytic fast pyrolysis of white oak wood in a bubbling fluidized bed reactor. Energy Fuels 2011, 25, 5444−5451. (12) Ouiminga, S. K.; Rogaume, T.; Sougoti, M.; Commandre, J. M.; Koulidiati, J. Experimental characterization of gaseous species emitted by the fast pyrolysis of biomass and polyethylene. J. Anal. Appl. Pyrolysis 2009, 86, 260−268. (13) Jung, S. H.; Cho, M. H.; Kang, B. S.; Kim, J. S. Pyrolysis of a fraction of waste polypropylene and polyethylene for the recovery of BTX aromatics using a fluidized bed reactor. Fuel Process. Technol. 2010, 91, 277−284. (14) Lu, A. H.; Li, W. C.; Salabas, E. L.; Spliethoff, B.; Schuth, F. Low temperature catalytic pyrolysis for the synthesis of high surface area, nanostructured graphitic carbon. Chem. Mater. 2006, 18, 2086−2094. (15) Wu, C. F.; Wang, Z. C.; Wang, L. Z.; Williams, P. T.; Huang, J. Sustainable processing of waste plastics to produce high yield hydrogen5712

dx.doi.org/10.1021/ie4004392 | Ind. Eng. Chem. Res. 2013, 52, 5708−5712