Upcycling Waste Plastics into Fuel and Carbon Nanomaterials

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Amphiphilic carbon nanotubes for catalytic wet peroxide oxidation of 4-nitrophenol

Publication . Roman, Fernanda; Sanches, Flávia Kim; Díaz de Tuesta, Jose Luis; Marin, Pricila; Machado, Bruno; Serp, Philippe; Silva, Adrián; Faria, Joaquim; Gomes, Helder

Carbon nanotubes (CNTs) were synthesized via chemical vapor deposition (CVD) over an AlCoFeO4 catalyst by a sequential feed of ethylene (E, as carbon source) and acetonitrile (A, as nitrogen source). The resulting samples were noted E20 (hydrophobic), E10A10 (amphiphilic), and A20 (hydrophilic), the number referring to the feed time (minutes) of each precursor, as reported elsewhere1. These materials were tested in the catalytic wet peroxide oxidation (CWPO) of 4-nitrophenol (4-NP). The reaction was monitored by HPLC (to determine the concentration of 4-NP and respective intermediates), TOC analyzer, and UV-vis spectrophotometry (to quantify H2O2) (Figure 1). After 8 h of reaction, A20 led to the highest consumption of H2O2 (90%), followed by E10A10 (61%) and E20 (52%). On the other hand, the highest degradation of 4-NP was observed with the amphiphilic E10A10 material (98%) followed by E20 (95%), whereas A20 only led to a removal of 69%. Similar behavior was found when analyzing the formation of reaction intermediates (data not shown), i.e., while A20 resulted in the accumulation of 4-nitrocatechol (4-NTC) and hydroquinone (HQ) E10A10 and E20 led to the total conversion of formed 4-NTC and HQ. This resulted in a lower TOC removal for A20 (37%) than to E10A10 and E20 (53%). Therefore, the amphiphilic E10A10 material is a promising catalyst for the CWPO of 4-NP.

2021Conference object

Open access

Carbon nanofibers from plastic solid waste

Publication . Lopes, Jéssica Paula Marim; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Lenzi, Giane G.; Faria, Joaquim; Silva, Adrián; Gomes, Helder

Production of plastics reached 360 million tonnes in 2018, the EU production corresponding to 62 million tonnes (i.e. 17%), from which only 9.2 million tonnes were collected for recycling. Low- and high-density polyethylene (PE) and polypropylene (PP), commonly used for packaging purposes, represent 40% of EU production [1]. In 2018, landfilling of plastic solid waste still represented 18.5% of the collected material [1], so there is still a great fraction of plastic waste being sent to landfill, representing a strong concern, as this plastic waste does not easily decompose. On the other hand, plastic polymers are mostly composed by carbon, as both PE and PP have a carbon content of 85.6% [2]. In this context, those plastics containing PE or PP represent a good source to produce carbon-based materials. In this work, low-density PE was used as precursor for the synthesis of carbon nanofibers (CNFs) by Chemical Vapour Deposition (CVD) (800 °C, 1 h, under N2 flow), with the aim to evaluate the influence of different CVD catalysts based on Fe, Ni and Al, synthesized using coprecipitation or wet impregnation methods, on the valorisation of PE-containing plastic waste. Fig 1 displays the scanning electron micrographs (SEM) of the carbonaceous materials obtained using two different catalysts. As can be observed, filamentous carbons were obtained in both cases, attributed to the growth of CNFs. The CNFs were obtained with similar yields of carbonaceous material (37.6% with Ni+Fe@Al2O3-coprecipitation and 36.2% with Ni+Fe@Al2O3-wet impregnation). Catalyst Ni+Fe@Al2O3-coprecipitation (Fig 1(a)) led to the formation of entangled CNFs, with high density and diameters in the range 12 – 28 nm, with the catalysts metals visible at the tip of the fiber (brighter spots on the SEM image). On the other hand, the catalyst Ni+Fe@Al2O3- wet impregnation (Fig 1(b)) resulted in the growth of CNFs with higher apparent diameters, which indicates that the catalyst obtained via coprecipitation is more suitable for growing carbon nanostructures.

2020Conference object

Open access

Selective biphasic oxidation of nitrogenated contaminants with H2O2 using polyolefin-derived carbon nanotubes

Publication . Roman, Fernanda; Piccinin, Larissa; Silva, Adriano S.; Díaz de Tuesta, Jose Luis; Vieira, Admilson L.; Silva, Adrián; Faria, Joaquim; Gomes, Helder

Liquid/liquid biphasic oxidations are extensively employed in the chemical industry to manufacture a variety of chemicals and for environmental issues, such as the oxidative denitrogenated (ODN) and desulfurization of fuels. The ubiquitous presence of nitrogenated and sulfonated compounds in petroleum-derived fuels is associated with environmental and health issues, driving legislation to become stricter regarding the content or related emissions of those impurities. However, catalysts with high performance, low cost and high activity towards selective oxidation of targeted contaminants should be developed. This work deals with the oxidative denitrogenation of quinoline and pyridine, used as model nitrogenated compounds, using carbon nanotubes as catalysts, which were derived from polyolefins (low-density polyethylene, high-density polyethylene and propylene) representative of plastic solid waste (PSWs) mixtures found in municipal solid wastes. The carbon precursor used offers not only a solution to reduce PSWs accumulation in waste management systems but also a cheap feedstock for preparing CNTs. All PSWs-derived CNTs allowed to remove quinoline completely, pyridine, and both of them in a mixture under the same conditions (1 h, 80 ◦C, ccat = 2.5 g L^-1, [H2O2]0 = 247 g L^-1, O/W volume ratio = 80:20, [N]0 = 108 mg L^-1). These results were maintained for up to 5 additional reuse cycles for the catalyst prepared with mixed polyolefins.

2025Journal article

Open access

Magnetic carbon nanotubes obtained from plastic as catalysts for wet peroxide oxidation of paracetamol

Publication . Sanches, Lucas Fenato; Silva, Adriano S.; Roman, Fernanda; Díaz de Tuesta, Jose Luis; Silva, Fernando Alves; Silva, Adrián; Gomes, Helder

Magnetic carbon nanotubes (MCNTs) were prepared by catalytic chemical vapour deposition (CCVD) and tested as catalysts for catalytic wet peroxide oxidation (CWPO) of paracetamol (PCM). For the synthesis of the MCNTs, low-density polypropylene (LDPE) and high-density polypropylene (HDPE) were used as model carbon precursors present in urban plastic solid waste (Aboul-Enein, 2018). The catalyst employed in CCVD was magnetite supported on alumina prepared by a sol-gel process. The CWPO runs were conducted with the stoichiometric concentration of H2O2 needed for the full mineralization of 100 ppm of PCM, at 80 °C and initial pH 3.5, following experimental methods described elsewhere (Silva, 2019). The catalyst prepared from LDPE, LDPE_MCNTW, was able to completely degrade the pollutant within 6 h of reaction, while HDPE_MCNTW took 8 h to achieve the same removal. Iron measurement in the final reaction solutions showed the absence of possible additional pollution coming from iron leaching of the catalysts.

2021Conference object

Open access

Magnetic carbon nanotubes prepared from LDPE, HDPE and PP

Publication . Sanches, Lucas Fenato; Silva, Adriano S.; Roman, Fernanda; Silva, Ana P. F.; Díaz de Tuesta, Jose Luis; Silva, Fernando Alves; Silva, Adrián; Faria, Joaquim; Gomes, Helder

Plastics are among the most generated solid wastes, predominantly composed by polymers, as low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP).1 This work deals with the preparation of magnetic carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CCVD) at 850 ºC, considering LDPE, HDPE and PP as carbon precursors representative of urban plastic solid waste in a perspective of circular economy.1 Magnetite supported in alumina nanoparticles previously synthesized by sol-gel were used as catalysts in the CCVD process. Afterward, each synthesized CNT was washed with 50% H2SO4 at 140 °C during 3 h to remove the remaining magnetite, following methods previously described.2 The successful removal of the magnetite particles was assessed measuring the ashes content of the CNTs, removals higher than 83% being achieved (ashes content of final CNT products ranging from 4.2 to 7.9%). The remaining catalyst was located inside the CNTs, conferring magnetic properties to the materials even after washing (Figure 1). BET specific surface areas of 94, 75, and 66 m2 g-1 were found for CNT_LDPE, CNT_HDPE and CNT_PP, respectively, and a slight increase of 1-5 m2 g-1 was observed after washing the materials with acid.

2022Conference object

Open access