Carbothermal Treatment Research Articles

Pt/C and PtRu/C Catalysts Prepared by Modified Sulfite Complex Routes for Fuel Cell Applications

In-house 30 wt.% Pt and 50 wt.% Pt1Ru1 catalysts supported on high-surface area carbon (Ketjenblack, abbreviated as KB) were synthesized by the sulfite complex route. Two different procedures involving either a direct mixing of Pt-sulfite and Ru-sulfite complexes or Pt-sulfite preparation and subsequent impregnation of Ru precursor were adopted for the bimetallic species. In both cases, an impregnation of the formed metal oxides onto KB was adopted to increase the electronic conductivity of the samples. Finally, a carbothermal treatment at 600°C in He atmosphere was carried out for the reduction of the metal oxides to metallic PtRu/C compounds. The Pt1Ru1 ratio was calculated and revealed by X-ray fluorescence (XRF) analysis whereas the carbon percentage was calculated by weight loss. 50 mg of sample was treated in air at 550°C for 2 h and, after cooling, the weight corresponded to 25 mg, confirming a carbonaceous matrix percentage of 50 wt.%. In a similar way, the 30 wt.% Pt/C was determined. X-ray diffraction (XRD) revealed that the samples showed face centered cubic (fcc) structure for Pt nanoparticles. It appears that two distinct crystallographic phases of Pt and Ru nanoparticles were encountered after the synthesis conducted by Ru impregnation. In contrast, only a single fcc phase is visible when the Pt and Ru sulfite precursors were mixed, confirming the formation of an alloy. Furthermore, Scanning Transmission Electron Microscopy-Energy dispersive X-ray spectroscopy (S/TEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the differences in morphology and surface characteristics of the catalysts.For the electrochemical measurements, rotating disc electrode (RDE) technique under acid and alkaline conditions was employed to investigate the half cell reactions. The catalysts were also deposited at the anode and cathode of fuel cells to evaluate the activity, performance, and short-term durability. Acknowledgement “This research was funded by the European Union – EIT Raw Materials in the framework of the following project: LYDIA- Recycling Critical Metals from Fuel Cells (G.A. 22019)”

A comparative adsorption study of activated carbon and Fe-modified activated carbon for trinitrotoluene removal

BackgroundActivated carbon (AC) is commonly used to remove many pollutants from water due to its appealing adsorption properties. However, the pristine surface properties of AC limit its ability to effectively remove 2,4,6-trinitrotoluene (TNT, a widely used explosive water contaminant). Modifying AC with Fe nanoparticles (NPs) can significantly improve the surface properties of the Fe/AC composite, thereby enhancing its adsorption capabilities. MethodCommercial charcoal-based AC was modified with Fe NPs via wet impregnation followed by a one-step carbothermal synthesis (labeled Fe-AC-800). A detailed characterization of Fe-AC-800 and its counterparts, pristine AC and thermally modified AC (AC-800, without Fe NPs doping) was performed using XRD, Raman Spectroscopy, SEM, EDS, BET, XPS, and FTIR. Then, the adsorption characteristics and performances of Fe-AC-800 were analyzed to determine its effectiveness in removing TNT and compared to AC and AC-800, considering the impact of in-situ Fe-modification and carbothermal treatment. Significant findingsFe-AC-800 displayed a higher adsorption capacity for TNT (387.74 mg/g) than the pristine AC (265.52 mg/g) but only slightly higher than AC-800 (339.64 mg/g). This was ascribed to the combined effect of the carbothermal treatment and Fe NPs doping, which constructed a richer porous structure that improved the Fe-AC-800 surface features and favored TNT removal. The optimal adsorption capacity of Fe-AC-800 was 464.13 mg/g under ambient conditions. TNT adsorption onto Fe-AC-800 and AC-800 conformed to only the Langmuir isotherm model, indicating uniform monolayer adsorption, whereas on the pristine AC, it satisfied both Langmuir and Freundlich isotherm models, respectively. The primary mechanism of TNT adsorption onto Fe-AC-800 was physical adsorption through pore filling, hydrogen bonding, and π-π EDA interactions, respectively.

In situ carbothermal synthesis of carbonized bacterial cellulose embedded with nano zero-valent iron for removal of Cr(VI)

Carbonized bacterial cellulose embedded with highly dispersed nano zero-valent iron (nZVI), denoted as nZVI@CBC, was prepared through one-step in situ carbothermal treatment of bacterial cellulose adsorbing iron(III) nitrate. The structure characteristics of nZVI@CBC and its performance in removing hexavalent chromium Cr(VI) were investigated. Results showed the formation of nZVI@CBC with a surface area of 409.61 m2/g at 800 °C, with nZVI particles of mean size 28.2 nm well distributed within the fibrous network of CBC. The stability of nZVI was enhanced by its carbon coating, despite some inevitable oxidation of exposed nZVI. Batch experiments demonstrated that nZVI@CBC exhibited superior removal efficiency compared to bare nZVI and CBC. Under optimal conditions, nZVI@CBC exhibited a high Cr(VI) adsorption capacity of up to 372.42 mg/g. Therefore, nZVI@CBC shows promise as an effective adsorbent for remediating Cr(VI) pollution in water.

Carbothermal treatment of municipal solid waste incineration fly ash: Purification and valuable elements extraction

Thermal separation of heavy metals from municipal solid waste incineration fly ash (MSWI FA) is a promising approach for both fly ash purification and heavy metal recovery. However, its commercial viability is hindered by excessive energy consumption. In this study, we introduce carbothermal reduction for MSWI FA treatment as an innovative strategy to enhance heavy metal volatilization and reduce the required heating temperature. By incorporating carbon (FA/Carbon = 1:0.2), the volatilization fractions of Pb, Cd and Zn reached 96.5 %, 100 %, and 63.9 %, respectively, when subjected to 900 °C for 2 h. Remarkably, these volatilization amount surpassed the volatilization fractions attained when raw fly ash (RFA) was independently calcined at 1000 °C for 2 h: Pb (90.2 %), Cd (92.9 %) and Zn (30.2 %). Conversely, Cu volatilization was impeded by carbon inclusion. Comparable trends were shown in washing fly ash (WFA). Notably, concentrated carbothermal reduction led to substantial concentrations of Pb (2.5–7.1 %) and Zn (4.9–20.7 %), rendering them amenable for recycling through metallurgical routes. Intriguingly, higher carbon content (FA/Carbon = 1:0.3) hindered rather than enhanced heavy metal volatilization from RFA. We found that condensation of NaCl and KCl occurred in carbon pores, causing the formation of molten eutectic which trapped the heavy metals at high temperatures. Therefore, more carbon showed more enhancement of heavy metal volatilization from WFA which was free of NaCl and KCl. Ultimately, two comprehensive pathways for the resourceful utilization of fly ash based on carbon thermal reduction were proposed and compared. This study demonstrates carbothermal reduction as an effective approach for simultaneous purification and metal recovery of MSWI FA, exhibiting promising potential for industrial application.

Synthesis and Structure of Carbon‐doped TiO2 by Carbothermal Treatment

AbstractCarbon modified titanium dioxide (TiO2) is a promising candidate for catalytic applications or fuel cells, where the modified oxide could replace currently used catalyst support materials. Carbothermally treated TiO2 was successfully prepared by annealing under acetylene/nitrogen gas flow in a rotary tube furnace. The carbon content in the TiO2 samples ranged from 5 to 14.5 wt.‐% as determined by thermogravimetric measurements. The powders showed suppression of the phase transition from anatase to rutile up to a treatment temperature of 825°C. Above 600°C rutile is the thermodynamically stable phase, therefore the suppression must be attributed to either carbon in the lattice or the reducing atmosphere in the furnace. Raman spectra revealed the characteristic G and D bands, indicating the formation of carbonaceous species in the samples. In addition, a shift of the anatase Eg(1) band was observed indicating a lattice disorder pointing toward carbon incorporation into the lattice. Diffuse reflectance spectra show sub band gap absorption together with a shift of the absorption edge. Depending on the extraction method of band gaps from spectra, the band gap values show a decrease or increase with increasing carbon content. Details of the evaluation and interpretation of the spectra are discussed.

Performance enhancement of Hf-Ta-O nanofiber based energy storage materials using oxygen-vacancy and its application for supercapacitor

Nowadays, materials that possess high activity and natural oxygen vacancy have garnered significant attention as potential electrode materials for supercapacitors. In this study, we successfully prepared the Hf6Ta2O17 (HTO) nanofibres (NFs) with an orthorhombic superlattice structure using the electrospinning technique and sintering process. The characterization results indicate that the HTO NFs synthesized at 750 °C show good micro nanostructures and outstanding electrochemical properties. To enhance its energy storage performance, additional oxygen vacancies (OVs) were introduced through a carbothermal treatment under an Ar atmosphere. Although longer reduction reaction times can produce more OVs, the integration of grain boundaries and the growth of grain size caused by large annealing times may limit its electrochemical performance. Therefore, the HTO NFs treated for 1 h (HTO/C-1) exhibited the maximum Cs of 925 F·g−1 at 1 A·g−1 with a larger voltage window of 2.1 V. Furthermore, a symmetric supercapacitor fabricated by two reduced HTO NFs electrodes and 1 M Na2SO4 solution, recorded as r-HTO NFs//r-HTO NFs. The device demonstrated excellent energy density of 73.3 Wh·kg−1 (at power density of 1050 W·kg−1) and a long cycling life (81.8% retained after 5000 cycles). These results suggest that the optimized reduction process can provide appropriate oxygen vacancies in HTO NFs, thereby effectively enhancing its performance.

Renewable, Organic and Related Carbon Aerogel Monoliths from the Polycondensation of Tannin with 5-(Hydroxymethyl)furfural

AbstractAs a result of the global demand for sustainable products, a suitable alternative to the resorcinol-formaldehyde aerogels, which are frequently used as precursors for carbon aerogels, is searched for. In this study, the replacement of petroleum-derived formaldehyde with a natural, biobased crosslinker, namely 5-(hydroxymethyl)furfural (5-HMF) is shown, and the synthesis of renewable, monolithic tannin aerogels is demonstrated. Compared to well-known tannin-formaldehyde aerogels, this green alternative shows lower reactivity of the crosslinker associated with lower gelation times as well as lower specific surface areas at the organic stage. Nonetheless, the morphologies and synthesis-structure relationships follow similar trends for both tannin-based aerogels, e.g., the pore size is influenced by the initial pH in the same manner. The turnover to carbon aerogels by a carbothermal treatment results in enhanced high-specific surface areas of the tannin-5-HMF-based carbon aerogels, which are similar and even slightly outperform those obtained from tannin-formaldehyde aerogels. This suggests that they are a convenient alternative for carbon aerogel applications. Graphical Abstract

A low-temperature operated in situ synthesis of TiC-modified carbon nanotubes with enhanced thermal stability and electrochemical properties.

Carbon nanotubes (CNTs) with superior thermal and electrochemical properties are desirable for a large variety of applications. Herein, an in situ synthesis carried out at 1050 °C is proposed for the realization of titanium carbide (TiC) modified CNTs (TiC@CNTs) via a carbothermal treatment of the TiO2-coated CNTs deposited by a TALD technology, preserving the structural morphologies of CNT samples. Crystalline and amorphous TiC layers/nanoparticles are observed around the walls of CNTs, serving as a thermal insulation layer to enhance the thermal stability of CNTs. The TiC@CNT sample exhibits a minimal mass loss of 3.1%, which is 20.9% and 82.3% for the TiO2@CNT and pristine-CNT samples, respectively. In addition, the TiC@CNT electrode shows good energy storage performances, with a specific capacitance of 2.83 mF cm−2 at 20 μA cm−2, which is about 3.5 times higher than that of the pristine-CNT electrode, showing the potential of TiC@CNTs as next-generation electrode materials.

Carbothermal synthesis of micron‐sized, uniform, spherical silicon carbide (SiC) particles

AbstractSilicon carbide (SiC) particles are exciting structures because of their hardness, chemical inertness, and dielectric properties. In particular, their absorption/emission properties in the mid‐infrared range render them suitable structures for ambient temperature thermal emitters. However, the synthesis of uniform, spherical structures is still challenging. Here, we present a robust synthesis procedure based on carbothermal reduction of silica precursor particles. With an isotropic shrinkage of ∼30 %, the spherical particle shape and uniformity are retained. Furthermore, we outline the influence of the gas atmosphere during the carbothermal treatment and demonstrate the successful conversion to SiC by electron microscopy, X‐ray diffraction, thermal and optical analysis.

Mechanochemical Processing and Characterisation Studies of Si-Based Refractory Compounds Derived from Sugarcane Bagasse

ABSTRACT The present study reports on the mechanochemical processing and characterisation studies of Si-based refractory compounds derived from sugarcane bagasse (SCB). SCB was preliminarily washed and sun-dried for 48 hr. 1 M HCl acid was used for the leaching of the SCB, before which carbothermal treatment was carried out in an enclosed, improvised crucible using a temperature sequence of 600–1000°C at a heating rate of 10°C/min. Fourier transmission infrared spectrometer (FTIR), scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to characterise the reaction products. From the results obtained, the major functional groups indicated in the IR spectra are O-H, N-O, O-Si-O and Si-C. The carbothermal treatment showed the viability of producing an Si-based refractory compound (SBRC). There is a high population of SiC in the XRD pattern at 900°C, indicating that 700°C was not sufficient for the full transformation of the SiC phases. The results indicate the presence of unreacted carbon phase precipitates in the reaction product.

Multidimensional carbon template preparation of 3D multilayered TiC nanoflakes for high performance symmetric supercapacitor

Titanium carbide (TiC)-based electrodes are attractive in supercapacitor due to their ultra-high density and pseudocapacitive charge storage mechanism. However, TiC films with horizontal alignment of flakes or random nanostructures limit the high rate of charge transfer and hinder the migration of ions to redox active sites. In this work, the TiC nanotubes and three-dimensional interconnected nanoflakes are synthesized by electrodeposition and carbothermal treatment of carbon nanotube (CNT) film and graphite, respectively. To study the capacitance mechanism of TiC nanotube-interconnected branch (NTIB) films, the in-situ Raman spectrums of the TiC-NTIB negative electrode during the charge/discharge processes in H2SO4 show that hydronium is bonded to the terminal O during discharge, and debonding occurs during charging. The integrated TiC NTIB electrode is capable of operating at rates faster than that of carbon, conductive polymers or transition metal oxides, but still delivers a specific capacitance of 273 F g−1 at 10 A g−1 after repeating 2000 cycles at current densities of 1, 3, 5 and 10 A g−1. The symmetric supercapacitor composed of the TiC NTIB electrodes delivers an energy density of 64.4 Wh kg−1 (at 892.3 W kg−1) and a power density of 9.5 kW kg−1 (at 55.6 Wh kg−1), and a good cycle stability (≈86.7% retention after 15,000 cycles).

Nanoarchitectured porous carbons derived from ZIFs toward highly sensitive and selective QCM sensor for hazardous aromatic vapors

Metal-organic frameworks (MOFs) are a versatile source of carbon nanoarchitectures in gas sensing applications (Torad et al., 2019). Herein, several types of nanoporous carbons (NPCs) have been prepared by in-situ carbothermal treatment of zeolitic imidazolate frameworks (ZIFs) under different inert atmospheres to achieve a highly sensitive discrimination of vaporized aromatic compounds. In this study, we demonstrate how different carbonization conditions under the flow of N2 or H2 gases affect the surface area and the degree of graphitization of the resulting NPCs polyhedrons, and their consequent effect on the sensing performance in terms of sensitivity and selectivity toward toxic volatile hydrocarbons. A growth of carbon nanotubes (CNTs) is observed on the surface of polyhedral NPCs after careful carbonization of ZIF crystals under H2 atmosphere. The fabricated quartz crystal microbalance (QCM) sensor with CNT-containing NPCs demonstrates increased sensitivity and selectivity towards toxic volatile aromatic hydrocarbons over the aliphatic analogues, suggesting the rich growth of hairy graphitic-like CNTs on the surface of carbon framework act as highly selective sensing antennae for vapor molecular discrimination of toxic aromatic hydrocarbons. Despite of increased selectivity towards volatile aromatic compounds, however, the surface area of CNT-rich NPCs derived from hybrid ZIFs and ZIF-67 is greatly sacrificed as compared to CNT-free NPCs from ZIF-8 polyhedron. In the case of Co-containing ZIF-67, the rich growth of hair-like CNTs, which is induced by the presence of Co, is observed during carbothermal reduction under a flow of H2 gas, thus allowing ultra-selective detection of aromatic hydrocarbons in the vapor phase, such as benzene (C6H6) and toluene (C6H5CH3) over their aliphatic analogue, c-hexane (c-C6H12) of same molecular mass, size and vapor pressure.

Beyond CO2 Reduction: Vistas on Electrochemical Reduction of Heavy Non-metal Oxides with Very Strong E-O Bonds (E = Si, P, S).

The carbon dioxide reduction reaction (CO2RR), in particular electrochemically, to produce carbonaceous fuels is considered as a viable approach to store energy and to enable a CO2-neutral carbon management. Besides CO2RR, there is an additional strong demand for benign electrochemical reduction of other important heavy non-metal oxo species (e.g., SiO2, phosphine oxides, SO2) with thermodynamically stable E-O bonds, which accrue in large quantities in industry. In this respect, the energy-intense deoxygenation of oxo compounds of silicon, phosphorus, and sulfur is of particular technological importance because they represent some of the main feedstocks to produce important molecules and functional materials. For example, the release of elemental silicon, phosphorus (P4), and sulfur (S8) from naturally occurring minerals (e.g., silicate, phosphate, sulfate) follows energy-intensive chemical routes. Thus, the established chemical reduction routes to deoxygenate such oxo precursors produce tons of reagent waste or, in the case of carbothermal treatment of minerals, afford a lot of CO2. On the contrary, electrochemical strategies developed for the selective deoxygenation of E-O compounds remain as a feasible alternative powered by renewable electricity instead of fossil energy. Moderate reaction conditions, a large scope in experiment design for selective reactions, easy product isolation, and zero reagent waste by applying electrochemical methods offer a promising solution to overcome the drawbacks of chemical reduction routes. This Perspective summarizes the emergence of electrochemical strategies developed for the reduction of selected examples of E-O/E═O compounds with E = silicon, phosphorus, and sulfur in the past few decades and highlights opportunities and future challenges.

Molybdenum carbide clusters for thermal conversion of CO2 to CO via reverse water-gas shift reaction

Abstract Molybdenum carbides are highly active for CO2 conversion to CO via the reverse water-gas shift (RWGS) reaction, however the large grain size up to micrometers renders its relatively lower active sites utilization efficiency while generating CH4 as a by-product. In this work, a homogeneously dispersed molybdenum carbide hybrid catalyst with sub-nanosized cluster (the average size as small as 0.5 nm) is prepared via a facile carbothermal treatment for highly selective CO2–CO reduction. The partially disordered Mo2C clusters are characterized by synchrotron high-resolution XRD and atomic resolution HAADF-STEM analysis, for which the source cause of the disorder is pinpointed by XAFS analysis to be the nitrogen intercalants from the carbonaceous precursor. The partially disordered Mo2C clusters show a RWGS rate as high as 184.4 μ mol g M o 2 C − 1 s − 1 at 400 °C with a superior selectivity toward CO (> 99.5%). This work highlights a facile strategy for fabricating highly dispersed and partially disordered Mo2C clusters at a sub-nano size with beneficial N-doping for delivering high catalytic activity and operational stability.

Effect of washing conditions on adsorptive properties of mesoporous silica carbon composites by in-situ carbothermal treatment.

Mesoporous silicon carbon (MSC) composites were prepared by in-situ carbothermal treatment of cetyl trimethyl ammonium bromide derived from mesoporous silica. MSC composites were used as adsorbent for methylene blue (MB) removal. Research was focused on investigating effect of washing conditions (deionized water or alkali) on surface properties and adsorption capacity of MSC composites. Results showed that best adsorption performance was given by the MSC composite washed by alkali at optimum pH 13.0. Adsorption mechanism for MB removal was systematically investigated by X-ray photoelectron spectrometer analysis, adsorption isotherms, adsorption kinetics and adsorption thermodynamics. MB adsorption by the MSC composites was found to be driven by three possible schemes: physical exothermic reaction, hydrogen bonds and π-interaction. The maximum adsorption capacity was 156.56 mg/g for MSCa13. The negative values of ΔG0, ΔH0 and ΔS0 indicated that the adsorption process was a spontaneous exothermic reaction. The adsorbent can be regenerated for reuse.

Synthesis of Si-Based Refractory Compounds from Coconut Shell by Carbothermal Method

The synthesis of Si-based refractory compounds from coconut shells (CS) by carbothermal treatment was investigated. Coconut shells, an agro-waste was utilised in the processing of the Si-based refractory compounds in a single stage carbothermal processing route. The treatment scheduled was carried out in a conventional heat treatment furnace at a temperature window of (900-1900 °C) at 10 °C/min heating rate in a controlled atmosphere. X-ray Diffractometer (XRD) was used to analyzed and quantify the crystalline and amorphous phases in the reaction products. The results from Fourier transform infrared spectroscopy (FTIR) revealed that, the dominant functional groups present after the carbothermal treatment were mainly Si-O-Si and Si-C groups. Also, the XRD results showed that the polytypes are mainly of α-SiC type precipitating as hexagonal symmetry of 6H-SiC and 4H-SiC type. The silica polytypes amount to about 8-14 wt.% of the silica polytypes as observed for different processing temperatures adopted. However, the total yield of SiC-made up between 11 to 40 wt.% of the crystalline phases as identified by XRD from the process. It is evident that the adoption of this processing route is a viable option for the synthesis of coconut shells as potential reinforcement for composites design.

Processing and structural characterization of Si-based carbothermal derivatives of bamboo leaf

Sustainable use of agro-wastes has attracted interest from researchers owing to their rich silica content; which makes them potential materials in the production of silicon carbide (SiC). Conventional processing methods such as Acheson, plasma, microwave plasma discharge and chemical vapor deposition are quite energy demanding and expensive to sustain by most third world economies (thus limiting the capacity for local production of SiC in these nations). In the present study, the viability of producing SiC and other Si-based compounds using bamboo leaves and carbothermal treatment processing schedule was investigated. Bamboo leaves (BL) was used as starting material in a single stage processing route to produce Si-based refractory compounds via carbothermal treatment. The processing was carried out in a modified conventional muffle furnace at temperatures windows (900-1900 oC) at 10 oC/min heating rate in a controlled atmosphere. The functional groups of the Si-based refractory compounds was analyzed using Fourier transform infrared spectroscopy (FTIR). The crystalline and amorphous phases were identified by X-ray Diffractometer (XRD) while the morphological features of the Si-based refractory compounds was examined by scanning electron microscopy (SEM). It was observed that the major functional groups present after carbothermal treatment of the bamboo leaves are Si-O-Si and Si-C groups. The yield of SiC polytypes was observed to be between 5-10 wt.% while other phases in the reaction products are mainly polytypes of silica. The carbothermal treatment explored showed evidence of viability for production of Si-based refractory compounds which can serve as reinforcement in the development of metal matrix composites.

Structural Characterization of Silica based Carbothermal Derivatives of Rice Husk

The economy of using agro-wastes in the design of novel ceramic materials is a good option to environmental waste management. A good number of these agro-wastes have been adjudged to be rich in silica, thus making them potentially useful materials for the development of silica-based refractory compounds. The present study was motivated by this prospect and the investigation focused on the structural characteristics of silica-based carbothermal derivatives of rice husk (ash). Rice husk ash (RHA), an agro-waste was used as starting material in a double stage processing route to produce silica-based refractory compounds via carbothermal treatment. The processing was carried out at different temperatures windows (900-1350 oC) at 10 oC/min heating rate in a controlled atmosphere using a conventional heat treatment furnace. The functional groups of the silica-based refractory compounds were analyzed through Fourier transform infrared spectroscopy (FTIR) while the crystalline and amorphous phases were identified by X-ray Diffractometry (XRD). It was observed that the major functional groups present after carbothermal treatment of the RHA are –OH, Si-O-Si and Si-O groups. The optimum yield of silica polytypes amounting to 74.2% was observed in sample designated A, while sample designated C showed the least value of silica polytypes of 53.04%. It was observed that no yield of SiC phases was observed in the carbothermal sequence. The carbothermal treatment explored showed evidence of viability for production of silica-based refractory compounds.

Influence of crystal growth conditions and carbothermal treatment on activator charge state in Ti:sapphire

Influence of crystal growth conditions and carbothermal treatment on activator charge state in Ti:sapphire

Immobilization, enrichment and recycling of Cr(VI) from wastewater using a red mud/carbon material to produce the valuable chromite (FeCr2O4)

It is a long-term goal to develop an inexpensive, eco-friendly, and effective approach for the purification of wastewater containing heavy metal elements such as Cr(VI). In this study, a red mud (RM)/carbon material with dispersed nano zero-valent iron (nZVI) is fabricated to collect, immobilize, enrich, and recycle Cr(VI) from wastewater by repeatedly using the spent sample after carbothermal regeneration. The regenerated RM/carbon sample maintains an excellent removal efficiency of Cr(VI), and the collected Cr species can be firmly immobilized and gradually accumulated through forming highly stable chromite (FeCr2O4) with the assistance of carbothermal treatment. A detailed study of structure–function relationships reveals that Cr(VI) in wastewater is first reduced to Cr(III) by nZVI, and is then collected on RM/carbon in the form of Cr-Fe hydroxide species, which is converted to a stable FeCr2O4 phase immobilized on the regenerated RM/carbon by carbothermal treatment. Moreover, the repeated use/regeneration process facilitates the gradual growth, separation, and exposure of nZVI particles on the external surface of the RM/carbon, which improves its reaction activity with H+ and Cr(VI). The elevated activity of nZVI as well as the high stability of the accumulated FeCr2O4 account for the excellent cycle efficiency of Cr(VI) removal. Nearly all of the nZVI (97.8%) in RM/carbon can be utilized to produce FeCr2O4 with more than 45 wt% Cr2O3 content in the final calcined ash, which can be recycled as a valuable substitute for natural chromite ore in the steel industry with no secondary pollution. The demonstrated superiority of the material and process offer promising technological, economic and environmental benefits for the simultaneous utilization of chromium wastewater and RM solid wastes.