Graphite Intercalation Compounds Derived by Green Chemistry as Oxygen Reduction Reaction Catalysts

Application of iron-intercalated graphite for modification of nickel foam cathode in heterogeneous electro-Fenton system: Bisphenol A removal from water at neutral pH

The presence of bisphenol A (BPA) in natural waters can be highly harmful due to its high persistence and adverse effects, raising concerns to remove this hazardous compound. Herein, an electro-Fenton system is proposed to eliminate BPA, wherein the iron source in the Fenton reaction is provided by its intercalation into the carbon layers of graphite. The produced heterogeneous catalyst was then coated onto the nickel foam serving as a cathode. The magnetic graphite intercalated compound (mGIC) and the modified cathode (before and after experiments) were characterized by FE-SEM, EDX, XPS, and XRD analyses. Some effective parameters, namely pH (3-9), current density (0-20 mA cm-2), and BPA concentration (0.5-20 mg L-1) were studied. At pH 3, the removal of BPA was 95.52%, and under neutral circumstances, the BPA and TOC removals were 85.70 and 58.12%, respectively at the initial BPA concentration of 10 mg L-1. The proposed system was also applied to several water sources spiked with BPA at the concentration of 5 mg L-1 under neutral pH, which exhibited considerable removal of 99.74%, 99.72%, and 92.70% for groundwater, municipal effluent wastewater, and tap water, respectively. The proposed system was applied for 15 consecutive cycles without showing significant changes in BPA removal, indicating its excellent stability and reusability. Furthermore, based on the analysis of intermediates, a possible decomposition pathway was proposed, indicating a reduction in overall toxicity. By using the proposed heterogeneous electro-Fenton system, iron waste is avoided, and operational costs of treatment can be reduced due to the absence of iron sludge production and catalyst loss.

Bisphenol A removal in treated wastewater matrix at neutral pH using magnetic graphite intercalation compounds as persulfate activators

Effluents of municipal wastewater treatment plants (WWTPs) are major sources for releasing contaminants of emerging concern (CECs) into the aquatic environment, which can result in negative effects on aquatic ecosystems and, as a consequence, on humans. Herein, the graphite intercalation concept was used to synthesize heterogeneous catalysts to degrade bisphenol A (BPA) as a model CEC in municipal WWTP effluents at neutral pH. The catalyst was synthesized using the simple molten salt method and showed several benefits, such as iron leaching prevention and stability in environmental matrices. Different methods were applied to describe the catalyst's structural characteristics. The proposed system removed 99.3% of BPA in 75 min using 2 g/L of the synthesized catalyst and 1.19 g/L (5 mM) persulfate at neutral pH. Quenching experiments showed that catalytic activities and BPA removals were significantly aided by both radical and non-radical pathways through the generation of free radicals and singlet oxygen (¹ O₂ ). Furthermore, the reuse of recycled synthesized catalyst was investigated on treated urban wastewater, and the results showed that the catalyst could degrade BPA from the wastewater in consecutive cycles, demonstrating its applicability under real conditions. PRACTITIONER POINTS: BPA was effectively removed from the effluents of municipal WWTPs at neutral pH. A new catalyst (magnetic GIC) was fabricated for heterogeneous catalytic systems. The catalyst activates persulfate to generate free radicals and ¹ O₂ , indicating that radical and non-radical pathways contribute to BPA degradation. The catalyst showed the ability to remove BPA even in the sixth cycle of use, demonstrating its stability and reusability.

Effect of Process Parameters on the Graphite Expansion Produced by a Green Modification of the Hummers Method

Adsorption stand out among other standard techniques used for water treatment because of its remarkable simplicity, easy operation, and high removal capability. Expanded graphite has been selected as a promising agent for oil spill adsorption, but its production involves the generation of corrosive remnants and massive amounts of contaminated washing waters. Although the advantageous use of the H2O2–H2SO4 mixture was described in 1978, reported works using this method are scarce. This work deals with the urgent necessity for the development of alternative chemical routes decreasing their environmental impact (based on green chemistry concepts), presenting a process for expanded graphite production using only two intercalation chemicals, reducing the consumption of sulfuric acid to only 10% and avoiding the use of strong oxidant salts (both environmentally detrimental). Three process parameters were evaluated: milling effect, peroxide concentration, and microwave expansion. Some remarkable results were obtained following this route: high specific volumes elevated oil adsorption rate exhibiting a high oil–water selectivity and rapid adsorption. Furthermore, the recycling capability was checked using up to six adsorption cycles. Results showed that milling time reduces the specimen’s expansion rate and oil adsorption capacity due to poor intercalant insertion and generation of small particle sizes.

Mechanism for the Intercalation of Aniline Cations into the Interlayers of Graphite

The dynamic behaviors of aniline cation (ANI⁺) intercalating into graphite interlayers are systematically studied by experimental studies and multiscale simulations. The in situ intercalation polymerization designed by response surface methods implies the importance of ultrasonication for achieving the intercalation of ANI⁺. Molecular dynamics and quantum chemical simulations prove the adsorption of ANI⁺ onto graphite surfaces by cation–π electrostatic interactions, weakening the π–π interactions between graphene layers. The ultrasonication that follows breaks the hydrated ANI⁺ clusters into individual ANI⁺. Thus, the released positive charges of these dissociative cations and reduced steric hindrance significantly improve their intercalation ability. With the initial kinetic energy provided by ultrasonic field, the activated ANI⁺ are able to intercalate into the interlayer of graphite. This work demonstrates the intercalation behaviors of ANI⁺, which provides an opportunity for investigations regarding organic-molecule-intercalated graphite compounds.

Evidence of carbon-supported porphyrins pyrolyzed for the oxygen reduction reaction keeping integrity

Fe(III) 5,10,15,20-(tetraphenyl)porphyrin chloride (FeTPP) and Co(III) 5,10,15,20-(tetraphenyl)porphyrin chloride (CoTPP) were adsorbed on carbon Vulcan and studied as electrocatalysts for the oxygen reduction reaction (ORR) before and after pyrolysis. The pyrolysis process was also simulated through ab initio molecular dynamic simulations and the minimum energy path for the O₂ dissociation after the interaction with the metal center of the FeTPP and CoTPP were calculated. After the pyrolysis the FeTPP showed the best performances reducing O₂ completely to H₂O with increased limiting current and lower overpotential. Tafel slops for the various catalysts did not change after the pyrolytic process suggesting that the mechanism for the ORR is not affected by the heat treatment. TEM images, X-ray diffraction, XPS spectroscopy, ⁵⁷Fe Mössbauer, and DFT simulations, suggest that there is no breakdown of the macrocyclic complex at elevated temperatures, and that the macro cyclic geometry is preserved. Small variations in the Metal-O₂ (M-O₂) binding energies and the M–N bond length were observed which is attributed to the dispersive interaction between the macrocycles and the irregular surface of the Vulcan substrate induced by the heat treatment and causing better interaction with the O₂ molecule. The theoretical strategy herein applied well simulate and explain the nature of the M–N–C active sites and the performances towards the ORR.

Manipulating the Electronic Structure of Graphite Intercalation Compounds for Boosting the Bifunctional Oxygen Catalytic Performance

Developing highly efficient bifunctional catalysts for the oxygen reduction and oxygen evolution reaction (ORR/OER) can open possibilities for future zinc air batteries (ZABs). Herein, cost-effective and highly conductive few-layer ferric and nickel chloride co-intercalated graphite intercalation compounds (FeCl₃ -NiCl₂ -GIC) are designed as bifunctional oxygen catalysts for ZAB. The optimized few-layer FeCl₃ -NiCl₂ -GIC catalyst exhibits a small overpotential of 276 mV at 10 mA cm^-2 for the OER and achieves a high onset potential of 0.89 V for the ORR. The theoretical analysis demonstrates the electron-rich state on the carbon layers of FeCl₃ -NiCl₂ -GIC during the catalytic process favors the kinetics of electron transfer and lowers the absorption energy barriers for intermediates. Impressively, the ZAB assembled with few-layer FeCl₃ -NiCl₂ -GIC catalyst displays a 160 h cycling stability and a high energy efficiency of 72.6%. This work also suggests the possibility of utilizing layer electronic structure regulation on graphite intercalation compounds as effective bifunctional catalysts for ZABs.

Synergistic Modulation of Carbon-Based, Precious-Metal-Free Electrocatalysts for Oxygen Reduction Reaction

Developing alternatives to noble-metal-based catalysts toward the oxygen reduction reaction (ORR) process plays a key role in the application of low-temperature fuel cells. Carbon-based, precious-metal-free electrocatalysts are of great interest due to their low cost, abundant sources, active catalytic performance, and long-term stability. They are also supposed to feature intrinsically high activity and highly dense catalytic sites along with their sufficient exposure, high conductivity, and high chemical stability, as well as effective mass transfer pathways. In this Review, we focus on carbon-based, precious-metal-free nanocatalysts with synergistic modulation of active-site species and their exposure, mass transfer, and charge transport during the electrochemical process. With this knowledge, perspectives on synergistic modulation strategies are proposed to push forward the development of Pt-free ORR catalysts and the wide application of fuel cells.