Iron Leaching Research Articles

In Situ-Formed PdFe Nanoalloy and Carbon Defects in Cathode for Synergic Reduction–Oxidation of Chlorinated Pollutants in Electro-Fenton Process

Complete dechlorination and mineralization of chlorophenols via the reduction-oxidation-mediated electro-Fenton process with a composite bulk cathode is first proposed. The in situ formation of a PdFe nanoalloy and carbon defects as key active sites is mutually induced during the formation of a carbon aerogel-based electrode. Specifically, the PdFe nanoalloy promotes the generation of [H]ads as reduction sites and improves the electron transfer via an electrical circuit, while the carbon defects selectively favor the 2e- oxygen reduction pathway. Notably, this work implies a novel electrocatalytic model for the formation of ·OH via (2 + 1)e- oxygen reduction by a consecutive reaction with carbon defects and a PdFe nanoalloy. Complete total organic carbon removal and dechlorination of 3-chlorophenol were performed after 6 h. The kinetic rate constant for removing haloacetamides (HAMs) in drinking water was 0.21-0.41 h-1, and the degradation efficiency was self-enhanced after electrolysis for 2 h because of the increased concentration of [H+]. The specific energy consumption was ∼0.55 W·h·g-1 at 100% removal of some HAMs, corresponding to a power consumption of 0.6-1.1 kW·h for complete dehalogenation per ton of drinking water in waterworks. Moreover, the PdFe alloy/CA exhibited extreme mechanical and electrochemical stability with limited iron (∼0.07 ppm) and palladium (0.02 ppm) leaching during the actual application.

A comparative study of RO membrane scale inhibitors in wastewater reclamation: Antiscalants versus pH adjustment

Scaling is the most common challenge that reverse osmosis (RO) membranes encounter in potable reuse applications due to the high product recovery. Usage of antiscalants or pH adjustment can suppress scale formation on membranes without sacrificing overall recovery. A series of experiments was conducted to evaluate the effectiveness of two different antiscalants (phosphonate-based and acrylic acid-based) and pH adjustment for the inhibition of scaling on polyamide RO membranes during the separation of microfiltration (MF) treated secondary effluent wastewater. Product recovery was targeted at 50%, increasing the residual concentration of scale forming ions by a factor of 2 in the feed. Substantial scale formation, dominated by calcium carbonate, was observed during the separation of the feed. In the presence of antiscalants, calcium carbonate scaling was successfully abated, while iron based scalants did not significantly decrease. Phosphonate-based antiscalants were found to be more effective in inhibiting calcium carbonate scaling as compared to acrylic acid-based antiscalants. As such, RO membranes treated with phosphonate-based antiscalants demonstrated lower permeate flux decline and less calcium scale deposition on membrane surfaces under the tested conditions. The addition of a strong acid to control scaling is a less expensive alternative to antiscalant addition. pH adjustment using sulfuric acid was effective for the inhibition of calcium carbonate scaling. However, acid addition resulted in corrosion of piping leading to considerable leaching of iron and copper into the feed. The presence of iron and copper adversely increased the scaling potential of the membranes.

Fe(III) adsorption on graphene oxide: A low-cost and simple modification method for persulfate activation

We report that simple adsorption of iron ions to graphene oxide (GO) can enhance a persulfate (PS) activation to degrade organic pollutants. The GO-Fe(II) and GO-Fe(III) were synthesized by directly adsorbing iron salts (Fe(II) and Fe(III), respectively) to GO. It is the first report to improve the PS activation by GO with simple Fe(III) addition without using toxic chemicals or high temperature/pressure conditions. Compared to GO and GO-Fe(II), the GO-Fe(III) exhibited highest phenol degradation (97.3%, 600 min) by activating PS, which was an encouraging result considering a competitive price of Fe(III). A comprehensive study utilizing particle characterization and iron leaching test revealed that PS reacted with the generated Fe(II) ions and oxygen-containing functional groups on the surface of GO-Fe(III). For the first time, the generation of 1O2 accompanied by radicals (OH, SO4− and O2−) was discovered in the PS activation by iron heteroatom doping on GO. Lastly, the PS/GO-Fe(III) was applied to remediate a phenol spiked groundwater, river water and wastewater for possible practical applications. The findings can be used for the cost-efficient and scalable synthesis of GO catalysts for various heterogeneous catalytic processes.

Magnetic MIL(Fe)-type MOF-derived N-doped nano-ZVI@C rods as heterogeneous catalyst for the electro-Fenton degradation of gemfibrozil in a complex aqueous matrix

The application of metal-organic frameworks (MOFs) as suspended heterogeneous catalysts in electro-Fenton (EF) process for water treatment is almost inexistent. Fe-MOFs synthesized from phthalic acid-based linkers were spindle-shaped MIL(Fe)-88B and NH2-MIL(Fe)-88B crystals, whereas their calcination yielded nano-ZVI@C and nano-ZVI@C-N. The lipid regulator gemfibrozil was spiked into 0.050 M Na2SO4 solutions or urban wastewater and treated in electrolytic cells with an air-diffusion cathode to generate H2O2. The nano-ZVI@C-N catalyst obtained at 800 °C showed the highest activity, with high stability as deduced from the low iron leaching and high recyclability. Almost total drug removal and significant mineralization was feasible in both matrices at near-neutral pH. The presence of core-shell nano-ZVI and Fe3O4 nanoparticles encapsulated in N-doped fusiform porous carbon rods was revealed, ensuring the Fe(III) conversion to Fe(II). Carbon doping with N contributed to the enhanced catalytic activity, and the strong magnetism facilitated the post-treatment catalyst recovery.

Selective leaching of lead from lead smelter residues using EDTA.

Ethylenediaminetetraacetic acid (EDTA) has been widely used as an effective reagent for removal of lead from soil because of its high lead extraction efficiency caused by the high thermodynamic stability of the Pb(ii)–EDTA complex. In this study, EDTA was used as a lixiviant for recovery of lead from residues (matte and slag) of secondary lead smelter plants. The residues were composed mainly of iron (34–66 wt%) and lead (7–11 wt%). Leaching parameters (EDTA concentration, pH, temperature, liquid-to-solid ratio and leaching time) were optimized. The optimum leaching efficiency was achieved when leached for 1 h at room temperature using 0.05 mol L−1 EDTA at a liquid-to-solid ratio of 5 mL g−1. At such conditions, 72 to 80% of lead and less than 1% of iron were leached from both matte and slag. The high selectivity towards lead with minimal co-dissolution of iron is a major advantage since it reduces the chemical consumption and simplifies the downstream processes. Although the stability constants of the complexes Fe(iii)–EDTA, Fe(ii)–EDTA and Pb–EDTA are all large (log KS 25.1, 14.33 and 18.04, respectively), the leaching of iron was most likely limited by its presence in insoluble phases such as iron oxides, sulfides and silicates in the residues. 100% leaching of lead was achieved by a multi-step leaching process where the leaching residues were contacted three times by a fresh EDTA solution. To recover EDTA, first iron was precipitated as iron hydroxide by raising the pH of pregnant leach solution (PLS) above 12.6 using sodium hydroxide, followed by precipitation of lead as lead sulfide by adding ammonium sulfide. The recovered EDTA was successfully reused two times for leaching without significant changes in leaching yields.

Ultra-efficient and stable heterogeneous iron-based Fenton nanocatalysts for degrading organic dyes at neutral pH via a chelating effect under nanoconfinement.

An ultra-efficient and stable heterogeneous iron-based Fenton nanocatalyst has been developed for degrading organic dyes at neutral pH via a chelating effect under nanoconfinement. The catalyst demonstrates an exceptionally high degradation capacity of 2600 mg g-1 for methylene blue and rapid degradation efficiencies at neutral and basic conditions. Moreover, MPOPs are highly stable and recyclable without any obvious performance loss and iron leaching under different pH conditions.

Degradation of reactive dye using heterogeneous photo-Fenton catalysts: ZnFe2O4 and GO-ZnFe2O4 composite

Dyes, being potential pollutants, need alarming attention for their degradation from wastewater. Advanced oxidation processes (AOPs) are among the most effective methodology for the degradation of pollutants. In the present study, the heterogeneous photo-Fenton catalysts (ZnFe2O4 and graphene oxide based ZnFe2O4 composite) were prepared and used to study the degradation of synzol red reactive dye. The prepared catalysts were well characterized by using SEM, FTIR and XRD analysis. The effect of various parameters like pH, catalysts dosage, H2O2 dosage, effect of dye concentration and irradiation time during heterogeneous photo-Fenton processes was studied. The results showed 57% and 94% degradation of dye under optimized conditions (e.g. pH = 3, Catalysts dose = 75 mg l−1 for ZnFe2O4 and 50 mg l−1 for GO- ZnFe2O4, H2O2 dose = 27 mM and irradiation time of 60 min) was observed for ZnFe2O4 and GO-ZnFe2O4, respectively. A comparison of degradation potential of catalysts using various light sources like UV-254 nm, ambient solar light and white LED, was studied. The current findings support the application of solar and LED light for the degradation of organic pollutants in wastewater. The stability and reusability of these catalysts for the degradation of the dye were also studied. The GO- ZnFe2O4 composite showed negligible iron leaching and no considerable reduction in degradation efficiency upto six consecutive cycles of reusability. It has been found that the composite (GO–ZnFe2O4) showed enhanced degradation of dye as compared to ZnFe2O4.

Highly efficient removal of Pb(II) from aqueous systems using a new nanocomposite: Adsorption, isotherm, kinetic and mechanism studies

In this research, amino-guanidinopentanoic acid (AGPA) functionalized benzene dicarboxylic coated magnetic nanoparticles (Fe3O4@BDC) was synthesized (Fe3O4@BDC@AGPA) by in situ co-precipitation process for removal of toxic Pb(II) ions from aqueous environment. The Fe3O4@BDC@AGPA nanocomposite was characterized by various instrumental technique viz., Fourier-transform infrared spectroscopy, X-ray diffraction, zeta potential, thermogravimetric analysis, energy-dispersive, and transmission electron microscopy, The effect of various parameters such as contact time, adsorbent dose, pH solution, initial Pb(II) concentration and temperature on the adsorption capacity of Pb(II) by the Fe3O4@BDC@AGPA nanocomposite was achieved. The results reveal that the adsorption process conforms to Langmuir adsorption isotherm models and the pseudo-second-order kinetic. The maximum Pb(II) adsorption capacity of Fe3O4@BDC@AGPA was 157 mg/g at condition factors min (Co– 300 mg/L; pH– 5.6; adsorbent dosage- 20 mg; temperature– 25 °C). After Pb(II) ions removal, Fe3O4@BDC@AGPA were separated using external magnetic field from aqueous medium and efficiently regenerated using 0.01 M HCl eluting. The percentage of leaching of iron in both adsorbents Fe3O4 and Fe3O4@BDC@AGPA in 0.01 M HCl for 24 h were 6.32% and 0.01%, respectively which indicating the good stability under acidic condition. The Fe3O4@BDC@AGPA possessed excellent regenerative performance after five cycles.

Iron-loaded carbon nanotube-microfibrous composite for catalytic wet peroxide oxidation of m-cresol in a fixed bed reactor.

A kind of novel iron-loaded carbon nanotube-microfibrous composite (Fe2O3-CNT-MF) catalyst is prepared and tested for fixed bed m-cresol catalytic wet peroxide oxidation (CWPO) reaction. Results show that the Fe2O3-CNT-MF can significantly decline the pressure drop of the fixed bed. Higher temperature, lower feed flow rate, higher catalyst bed height, and higher H2O2 dosage are beneficial to m-cresol degradation. Lower pH can also improve m-cresol degradation, but it will cause severe iron leaching. The highest m-cresol removal (over 99.5%) and total organic carbon (TOC) removal (53.6%) can be observed under condition of 2cm bed height, flow rate of 2mL/min, reaction temperature of 70°C, 6g/L H2O2, and initial pH = 1. Meanwhile, the Fe2O3-CNT-MF catalyst shows good stability with less than 10% decrease in m-cresol conversion and 7% decrease in TOC conversion after 24-h reaction and less than 2mg/L iron leaching is observed in all conditions except for strong acid condition. Two probable pathways of m-cresol degradation process are presented. Under most conditions, m-cresol will first be turned into methylhydroquinone, followed by oxidation to p-toluquinone. In basic condition, some m-cresol will first be changed into 4-methylpyrocatechol. These aromatic intermediates will then be oxidized into some small molecular acids and finally be mineralized to CO2 and H2O.

Degradation of the β-blocker propranolol by sulfite activation using FeS

A new advanced oxidation process, FeS-activated sulfite system, was firstly established to degrade β-blockers in water at near neutral pH. By choosing propranolol (PRO) as a model compound, the experimental conditions including FeS and sulfite doses, initial pH, dissolved oxygen, and co-existed components were investigated. Up to 95% of PRO was eliminated after 20 min reaction with FeS and sulfite doses being 20 mg/L and 1 mM, respectively, at initial pH 6.0. The PRO removal was pH-dependent with an optimal pH of 6.0, and the dissolved oxygen was essential. The presence of Cl−, HCO3− and humic acid could inhibit the FeS/sulfite process to different degrees. Radical scavenging experiment and electron spin resonance technology indicate that SO4− played a predominant role in PRO removal. The possible degradation pathway was subsequently inferred in terms of the detected products. The leached iron from FeS actually induced the activation of sulfite, rather than the structural Fe(II/III). Five other organic contaminants including metoprolol, fluoxetine, estriol, aniline, and p-chlorobenzoic acid could also be effectively degraded. In contrast with persulfate and peroxymonosulfate, the introducing of sulfite to FeS achieved much higher removal performance of PRO. Our study suggests a novel promising process of FeS/sulfite for water treatment.

Oxidative Degradation of Methylene Blue via PDS-Based Advanced Oxidation Process Using Natural Pyrite.

H2O2- and PDS-based reactions are two typical advanced oxidation processes (AOPs). In this paper, a comparative study of H2O2/PDS-based AOPs employing natural pyrite as a catalyst to degrade methylene blue (MB) was reported. The adaptive pH range in pyrite/PDS extended from 3 to 11, in contrast to the narrow effective pH range of 3–7 in pyrite/H2O2. As a result of the iron leaching, a synergistic effect of both homogeneous and heterogeneous catalysis was observed in pyrite/PDS, whereas heterogeneous catalytic oxidation dominated pyrite/H2O2. Furthermore, the batch results showed that the MB removal by pyrite/PDS was highly dependent on chemical conditions (e.g., pH, pyrite and PDS concentration, temperature). Powerful SO4•− was generated by pyrite rapidly under acidic or weakly acidic conditions, while SO4•− and PDS were assumed by OH− under alkaline condition. The lower pyrite loading (from 0.1 to 0.5 g/L) was affected the removal efficiency obviously, while the scavenging of SO4•− did not seem to be remarkable with the excessive amounts of pyrite (>0.5 g/L). Excessive amounts of PDS (>2 mmol/L) might negatively affect the pyrite/PDS system. The reaction temperature that increased from 20 to 40 °C had a positive effect on the degradation of MB. SEM and XRD showed that the passivation of catalyst did not occur due to the strong acid-production ability of pyrite/PDS, inhibiting the formation of Fe-oxide covering the pyrite surface.

Iron oxide nanoparticles wrapped in graphene aerogel composite: Fabrication and application in electro-fenton at a Wide pH

A novel composite material of α-Fe2O3 nanoparticles wrapped in grape aerogel (α-Fe2O3/GA) was successfully fabricated and proposed for the electro-Fenton (EF) system. The α-Fe2O3/GA, which prepared by the natural drying method, presented characteristics of a porous structure of graphene sheets with α-Fe2O3nanoparticles uniformly dispersed. Efficient electro-catalytic performance was exhibited when applied to degrade Rhodamine B (RhB). The results showed that the degradation rate reached 99% after 30 min, which was about 1.1 times higher than that of graphene aerogel (GA). Meanwhile, the chemical oxygen demand (COD) elimination rates up to 82% in the reaction, and the corresponding energy consumption is 90% of that with GA. Furthermore, it's worth noting that the α-Fe2O3/GA presented low iron leaching (<,2.3 mg/l) even in an acidic medium, without significant decrease in catalytic activity after six cycles. Besides, α-Fe2O3/GA retained an efficient degradation efficiency at a wide pH range. Therefore, α-Fe2O3/GA was used as a candidate cathode material for treatment of organic wastewater by EF system.

Effects and mechanisms of lincomycin degradation by six promoters in the mZVI/H2O2 systems

In this paper, the effects of lincomycin (LCM) degradation by six typical promoters such as tea polyphenols (TP), oxalic acid (OA), ethylenediaminetetraacetic acid disodium (EDTA), hydroxylamine hydrochloride (HA), sodium tripolyphosphate (TPP) and ascorbic acid (AA) on the Fe0/H2O2 system based on microscale zero valent iron (mZVI) were compared through batches of experiments. The degradation effects of promoters on the Fe0/H2O2 system in 90 min showed significant promotion (OA, AA and HA), moderate promotion (TP) and inhibition (EDTA, TPP), respectively. Moreover, this result was very consistent with the results of •OH and ORP. First, by studying the effects of each promoter on the pH value and the iron leaching of the Fe0/H2O2 system, it was preliminarily proved that the main reason for the enhancement of Fenton-like degradation of OA, HA and AA is to lower the pH and thus promote iron leaching. Then, through comparative experiments of reducing and chelating abilities of six promoters, it was proved that TP promoted the Fenton-like degradation mainly by reduction and chelation without significantly changing the pH of the system. Although EDTA and TPP have strong chelating ability and ability to promote iron leaching, respectively, they caused the pH to be too high, which inhibited the reaction. The results show that lowering the pH of system, promoting iron leaching, reducing ferric iron and chelating iron ions to avoid the formation of iron sludge are the main mechanisms of the current Fenton-like promoters. Moreover, the combination of multiple promotion methods can better adapt to different reaction conditions.

Characterisation and utilization of steel industry waste sludge as heterogeneous catalyst for the abatement of chlorinated organics by advanced oxidation processes.

Catalytic advanced oxidation processes (AOPs) utilising UV irradiation have been reported to be highly efficient for the degradation of recalcitrant compounds. The focus of present study was to evaluate the potential of steel industry waste as an alternative to homogenous iron salts often used in AOPs. Iron rich sludge from effluent treatment plant (ETP) of a steel industry was subjected to acid washing and acid washing followed by calcination before using as catalyst for the oxidative removal of chlorinated organics present in synthetic and simulated bleaching effluents. The maximum total organic carbon removals of 64% and 25% from 4-chlorophenol solution and simulated pulp bleaching effluent, respectively were observed during photo-catalytic oxidation with acid washed steel sludge at stoichiometric H2O2 dose after 2 h reaction (catalyst dose = 1 g/L, and pH = 4.4). Low iron leaching (<2%) was observed from the catalyst even in acidic conditions and it could be reused twice without significant loss of catalytic activity.

Heterogeneous Catalytic Performance and Stability of Iron-Loaded ZSM-5, Zeolite-A, and Silica for Phenol Degradation: A Microscopic and Spectroscopic Approach

In this study, we compared the performances of three iron-containing crystalline and amorphous catalysts, that is, Fe-Zeo-A, Fe-ZSM-5, and Fe-silica, respectively, for the degradation of phenol in an aqueous solution. Catalytic activity for the degradation of phenol was assessed by heterogeneous photolysis, Fenton, and photo-Fenton oxidation. All catalysts exhibited higher activity in the photo-Fenton process. In addition, the catalyst stability was evaluated by the estimation of the iron loss and structural variations after the oxidation processes. Results revealed that Fe-silica and Fe-ZSM-5 exhibit higher catalytic activity (~100% phenol removal), while only 64% of phenol removal over Fe-Zeo-A was observed. Moreover, among all catalysts, Fe-ZSM-5 exhibited higher stability with low iron leaching, attributed to the uniform distribution of bonded Fe in the crystalline framework and narrow channels. On the contrary, amorphous Fe-silica exhibited higher iron leaching due to the presence of isolated iron species in the structure, leading to the partial involvement of a homogeneous reaction during the degradation of phenol. The structural stability of Fe-based catalysts was examined using microscopic and spectroscopic techniques.

Magnetic graphene TiO2-based photocatalyst for the removal of pollutants of emerging concern in water by simulated sunlight aided photocatalytic ozonation

Magnetite and titania have been supported onto graphene for the photocatalytic ozonation of aqueous micropollutants. Titania and magnetite were successfully attached to graphene nanoparticles keeping with a reasonable separation and photocatalytic activity. Although the presence of graphene did not enhance the photoactivity of bare titania, graphene acted as a good support of magnetite nanoparticles and removed the leaching of iron, a problem observed with the graphene free composite. The synthesized photocatalysts were characterized by diverse techniques. The efficiency of the processes involving ozone was assessed by different tools such as HO exposure vs time, RCT and RHO,O3 ratios. Photocatalytic ozonation was the most efficient for the removal of the target compound and mineralization. No loss of activity was registered after reusing or appreciable iron leaching. Finally, the catalyst was also tested in a real secondary effluent from a wastewater treatment plant containing ten micropollutants of emerging concern.

Degradation mechanisms of ofloxacin and cefazolin using peroxymonosulfate activated by reduced graphene oxide-CoFe2O4 composites

In this work, reduced graphene oxide (rGO) sheets were integrated with CoFe2O4 to construct distinctive composites that were evaluated as heterogeneous catalysts activating peroxymonosulfate (PMS) for the oxidative degradation of ofloxacin (OFX) and cefazolin (CFZ), two widely used pharmaceuticals belonging to the fluoroquinolone and β-lactam antibiotic families, respectively. The results showed that of all of the catalysts tested, the composite with an CoFe2O4 to rGO weight ratio of 20:2 (CFGO202) had the best reactivity, and achieved superior stability with negligible leaching of cobalt and iron under mild acidic conditions. Radical quenching experiments showed that the degradation of OFX was a radical-based oxidation process, while the decomposition and transformation of CFZ were largely due to PMS-induced direct oxidation via direct two-electron transfer. The near-complete degradation of OFX and CFZ could be attained under optimal conditions: pH 6.0, 0.1 g L−1 CFGO202 and 1 mM (for OFX) or 100 μM PMS (for CFZ). In comparison with OFX, the degradation of CFZ suffered less interference from the water matrix. An underlying mechanism was proposed based on the detection of radicals and X-ray photoelectron spectroscopy spectral data. Degradation intermediates were identified and the possible degradation pathways were proposed with the aid of density functional theory (DFT) calculations.

MIL-100(Fe) metal–organic framework catalyzed oxidation of phenol revisited: dark-Fenton activity of the catalyst

This work presents the Fenton-type aqueous-phase oxidation of phenol with two MIL-100(Fe) catalysts prepared by hydrothermal and reflux methods. The catalysts were systematically characterized by infrared spectroscopy, X-ray powder diffraction, thermogravimetry, scanning electron microscopy, and surface analysis techniques. The influence of various experimental parameters on the course of the oxidation process conducted at room temperature was examined. The catalysts showed significant stability when phenol/H2O2 = 1:1 molar ratio was applied. In this case, 93% conversion was obtained with minimal iron leaching (ca. 0.2%). The hydrothermally prepared MIL-100(Fe) catalyst displayed higher catalytic activity due to its larger surface area. The results were also discussed to evaluate the “dark-Fenton” contribution of the system in “photo-Fenton” reactions previously reported with similar catalysts for phenol oxidation. This study has demonstrated that dark-Fenton reaction with MIL-100(Fe) catalysts has an important contribution to the mineralization of phenol without requiring irradiation or ZnO assistance. A schematic illustration of the fabrication processes of MIL-100(Fe) catalysts and their use in Fenton-type phenol oxidation reaction.

Phenol photocatalytic degradation over Fe-TiO2 materials synthesized by different methods

The photocatalytic activity and stability of 3% Fe-TiO2 materials synthesized by incipient wet impregnation (% Fe-TiO2-DP25) and sol-gel (3% Fe-TiO2-sol-gel) were studied using the phenol degradation as test reaction. The effects of various operation parameters including photocatalyst concentration, solution pH and initial H2O2 concentration on phenol degradation were also investigated. The higher phenol degradation was achieved using 26 mg of photocatalyst, H2O2 initial concentration of 600 mg/l and initial pH of 3.0 with both materials. It was found that 3% Fe-TiO2-DP25 enhanced activity, achieving a 99% phenol degradation, in comparison with 70% phenol degradation with the 3% Fe-TiO2-sol-gel. Notwithstanding, the material prepared by incipient wet impregnation method, evidenced leaching of iron ions from the material surface. Therefore, this catalyst is not suitable for the phenol degradation for environmental and economic reasons. The catalyst prepared by the sol-gel method did not show iron leaching during the reaction and maintain its catalytic activity after several reuses.

Heteroatom-doped graphene aerogels and carbon-magnetite catalysts for the heterogeneous electro-Fenton degradation of acetaminophen in aqueous solution

Nitrogen (N) and nitrogen/sulphur (N/S) co-doped graphene aerogels were synthesized by hydrothermal method using graphene oxide and urea or thiourea as precursors following a freezing-drying process. The determination of the number of the electrons involved in the mechanism of electro-reduction of oxygen (ORR) in alkaline medium was assessed. The mechanism of 4e− was obtained with N/S-doped graphene aerogels showing good electrocatalytic behavior and larger kinetic current densities. The 2e− ORR process (involving in situ H2O2 generation) was mainly obtained using N-doped graphene aerogels and it was related to the content of N functionalities as well as to the porous texture of the samples. Carbon-magnetic catalyst was synthesized to promote the decomposition of H2O2 to HO for the degradation of acetaminophen (ACE) in heterogeneous electro-Fenton (EF) process. The highest pollutant removal (71.0%) and mineralization (51.6%) were obtained with N-doped materials and carbon-Fe3O4 catalyst, showing good stability and low iron leaching (0.33 mg L−1).