Green Synthesis of Thin Shell Carbon-Encapsulated Iron Nanoparticles via Hydrothermal Carbonization

Abstract

Nanoscale zerovalent iron (nZVI) has proven to be a promising solution for contaminant remediation, but its application is limited due to its high cost of synthesis and instability. Encapsulating the nZVI in carbon spheres generates more stable particles with improved properties due to the adsorption capacity provided by the carbon. The aim of this work was to synthesize thin shell carbon-encapsulated iron nanoparticles (CE-nFe) through hydrothermal carbonization (HTC) using olive mill wastewater as a carbonaceous source, which is a cheaper and more sustainable method of synthesis than the current practice. With this method, a high quality nanomaterial was obtained, which displayed surface areas up to 220 m 2 /g and was composed of ∼4 nm iron nanoparticles spheres surrounded by a thin layer of carbon (<1 nm). The effect of HTC conditions on the nanoparticle structure and morphology was evaluated. Post-treatment of the samples under nitrogen flow at high temperatures (600−800 °C) was used to increase the ZVI content of the samples. Finally, the synthesized CE-nFe were tested for the removal of heavy metals from water. Thanks to the carbon layer, CE-nFe proved to avoid the delivery of heavy metal ions back to water, a behavior previously observed with nZVI due to its aging after long time periods.

Heterogeneous Fenton Degradation of Patulin in Apple Juice Using Carbon-Encapsulated Nano Zero-Valent Iron (CE-nZVI)

“…The OMW was clarified by centrifugation at 5000 rpm for 30 min using a 4K10 centrifuge (Sigma Aldrich, Madrid, Spain), followed by filtration with an 8 µm fiberglass filter based on work done by Calderon et al (2018). In this experiment, the iron salt Fe(NO 3 ) 3 •9H 2 O was reduced through a hydrothermal reaction.…”

“…These particles presented had a higher surface area and greater incorporation of iron into the material. This is reported to be due to the different carbon sources used compared to the traditional refined carbon sources which are regularly used [23]. In CE-nZVI synthesis, there existed a diverse variety of polyphenols, organic acids, alcohols, and lipids in the hydrolysis and condensation reactions that formed the nanoparticles.…”

“…Methods that are not commonly in use but have the potential of being developed to be used due to their advantages are: precision milling, carbothermal reduction, ultrasound-assisted production, electrochemical generation, and green synthesis [22]. In this study, a green synthesis approach applying carbothermal reduction using olive-oil mill waste (OMW) as a carbon source, to produce encapsulated nano-zero valent iron (CE-nZVI) particles, was considered [23]. The selection of these particles is motivated by their potential ability to release fewer dissolved iron ions into the juice.…”

Salt-template hydrothermal carbonization for Pd NP-loaded porous carbonaceous material

“…2b), which implied that the addition of porogen LiCl had some influence on the Pd loading of the lignin porous carbonaceous material. One interpretation was that some of the obtained ultrafine Pd NPs were encapsulated in the constructed micropores during the HTC process and concealed within the carbonaceous structure (Calderon et al 2018), but not all homogeneously dispersed on the carbon surface (Tran et al 2015), which made them undetectable in the XRD analysis and resulted in a slight decrease in the characteristic peaks.…”

Spheroidization of Nickel Powder and Coating with Carbon Layer through Laser Heating

“…However, when exposed to high temperature and/or humid environment, they are known to show poor oxidation resistance [ 1 , 2 , 3 , 4 ]. Extensive investigations have been made to improve the resistance of such nanopowders without compromising their functionalities, the most efficient strategies found being the introduction of additives (e.g., Ag [ 1 , 2 ], Cu [ 3 ], and ZrO 2 [ 4 ]) or the formation of a protective carbon layer [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. So far, many techniques have been developed to coat a carbon layer over metal nanoparticles, such as arc discharge [ 5 , 6 ], magnetron sputtering [ 7 ], hydrothermal carbonization [ 8 ], detonation [ 9 ], chemical vapor deposition [ 10 , 11 ], spray pyrolysis [ 12 ], and pyrolysis of organometallic compounds [ 13 , 14 ].…”