Ferric (hydr)oxide/mesoporous carbon composites as Fenton-like catalysts for degradation of phenol

Fe/sponge structure peanut shell carbon composite preparation for efficient Fenton oxidation crystal violet

In order to obtain super synergy effect between adsorption and Fenton oxidation for crystal violet (CV) removement from water, in this study, Fe modified on a sponge structure peanut shell carbon (Fe/SPSC) nanocomposite was successfully synthesized by a wet impregnation method. In the Fe/SPSC sample, the prepared peanut shell carbon had a sponge-like structure, (002) crystal plane of graphite crystallite, and Fe/SPSC composite coexisted Fe2O3 and Fe3O4 crystalline, which could adsorb and enrich crystal violet molecule, decrease the concentration of CV solution rapidly. And also SPSC could do better for electrons transfer and further promote CV oxidation degradation. The removal efficiency results showed that the 7% Fe/SPSC (500 °C, 2 h) had the best CV removal activity. The composite prepared under the optimum conditions is 2.0 g/L, 0.1 mL 30% H2O2, pH = 7.0, 300 mg/L crystal violet water solution, and the CV degradation rate can reach 95.5%, and the CV degradation amount for Fe/SPSC was 143.25 mg/g. It was confirmed that hydroxyl radicals (•OH) is the active center of Fenton oxidation degradation reaction. XPS results showed that Fe, O, and C elements coexist in the 7% Fe/SPSC composite, and N element content increases after the reaction. Remarkable synergies between adsorption and Fenton oxidation, which could make Fe/SPSC, have quick CV abatement ability. The possible systematic effect mechanism of adsorption and Fenton-oxidation CV was also supplied. The present system has advantages on high CV dye degradation performance, no other Fe sludge formation, short reaction time, and better catalyst reusability.

The construction of a palladium–hydrogen accelerated catalytic Fenton system enhanced by UiO-66(Zr)

The introduction of H2 and Pd/UiO-66(Zr) accelerated the FeII/FeIII cycle and led to higher contaminant degradation using only a trace level of FeII in several reaction cycles.

Abatement of 1,2,4-Trichlorobencene by Wet Peroxide Oxidation Catalysed by Goethite and Enhanced by Visible LED Light at Neutral pH

There is significant environmental concern about chlorinated organic compounds (COCs) in wastewater, surface water, and groundwater due to their low biodegradability and high persistence. In this work, 1,2,4-trichlorobenzene (124-TCB) was selected as a model compound to study its abatement using wet peroxide oxidation at neutral pH with goethite as a heterogeneous catalyst, which was enhanced with visible monochromatic light-emitting diode (LED) light (470 nm). A systematic study of the main operating variables (oxidant and catalyst concentration and irradiance) was accomplished to investigate their influence in the abatement of 124-TCB in water. The reaction was carried out in a well-mixed reactor of glass irradiated by a visible LED light. The hydrogen peroxide concentration was tested from 0 to 18 mM, the goethite concentration within the range 0.1–1.0 g·L−1 and the irradiance from 0.10 to 0.24 W·cm−2 at neutral pH. It was found that this oxidation method is a very efficient technique to abate 124-TCB, reaching a pollutant conversion of 0.9 when using 0.1 g·L−1 of goethite, 18 mM of H2O2, and 0.24 of W·cm−2. Moreover, the system performance was evaluated using the photonic efficiency (ratio of the moles of 124-TCB abated and the moles of photons arriving at the reactor window). The maximum photonic efficiencies were obtained using the lowest lamp powers and moderate to high catalyst loads.

Iron nanoparticles encapsulated within nitrogen and sulfur co-doped magnetic porous carbon as an efficient peroxymonosulfate activator to degrade 1-naphthol

A novel iron nanoparticles encapsulated within nitrogen and sulfur co-doped magnetic porous carbon (Fe-N-S-MPC) was proposed by one-pot pyrolysis strategy to activate peroxymonosulfate (PMS) to degrade 1-naphthol using low-cost lignin as precursors. The Fe-N-S-MPC was characterized for structure and properties by different characterizations. The obtained materials had the morphology of iron nanoparticles encapsulated within nitrogen and sulfur co-doped magnetic porous carbon with rich functional groups and large specific surface area, which made the materials have a good catalytic property. It was proved that the doping of nitrogen and sulfur is pivotal for improving the catalytic performance. The radical quenching experiment confirmed that sulfate radical (SO₄^-) and hydroxyl radical (OH) are two major reactive oxygen groups. The reaction had phenomenon of the free radicals upsurge in the early stage and the shortage in the later stage. Therefore, a mathematical model was put forward to represent the two-stage reaction kinetics. By adding oxidants in batches, the degradation effect could reach nearly 100% within 30 min. The Fe-N-S-MPC were applied to the degradation of 1-naphthol in soil and showed high degradation performance. This work provided a new type of catalytic material by the high-value utilization of waste for the degradation of organic pollutants.

Effective degradation of phenol via catalytic wet peroxide oxidation over N, S, and Fe-tridoped activated carbon

The N, S, and Fe-tridoped carbon catalysts (NSFe-Cs), Fe/ACNS1 and Fe/ACNS2, were synthesized by wet impregnation with different concentration of ammonium ferrous sulfate solution. The prepared catalysts have a similar textural structure. The N species, S species, Fe^II and Fe^III were simultaneously introduced onto the surface of catalysts. Comparison with the only Fe doped catalyst, NSFe-Cs showed greater stability and higher phenol removal in catalytic wet peroxide oxidation at different reaction condition. The main intermediates including p-hydroxybenzoic acid, formic acid, and maleic acid were determined in the treated wastewater. The high catalytic activity for NSFe-C was related to the ability of H₂O₂ decomposition. NSFe-Cs have more amount of Fe^II partially due to the formation of FeS₂, which promoted the decomposition of H₂O₂ on Fe/ACNS1 and Fe/ACNS2 surface. The generation of ·OH and ·HO₂/·O₂^- radicals in the bulk solution was crucial to phenol degradation, and the decomposition of H₂O₂ complied with the pseudo-first-order kinetics. The highly linear relationship between decomposition kinetic constant for H₂O₂ and the amount of surface groups suggested, including Fe^II species, pyridinic N/Fe-bonded N, pyrrolic N as well as graphitic N were responsible to the high activity of NSFe-Cs.

Comparison of real wastewater oxidation with Fenton/Fenton-like and persulfate activated by NaOH and Fe(II)

Treatment of polluted wastewaters from industrial activities has become a source of major concern for the environment. In this work, real wastewater from a physico-chemical (WWFQ) treatment was tested through different oxidation technologies: Fenton and Fenton-like reagent and persulfate activated by NaOH and Fe(II). Oxidation reactions with Fenton's reagent were carried out in a 0.25 L batch reactor at 25 °C by adding either Fe(II) or Fe(III) and H₂O₂ to an aqueous solution of wastewater, whose pH was previously adjusted to 2 or 3. Iron concentration ranging from 25 to 100 mg/L and peroxide concentration from 2500 to 10000 mg/L were used. The total organic carbon slightly decreased when WWFQ was treated. Moreover, better results were obtained when Fe(II) was used than Fe(III). Both iron concentration and oxidant dosage had a positive influence on the chemical oxygen demand (COD) removal, until an asymptotic value of 30% was obtained. Oxidation of pollutants contained in WWFQ was studied with persulfate (18.4-294 mM) activated with NaOH and Fe(II) (36.8-588 mM). Again, a positive influence of both persulfate and NaOH was observed, although a similar asymptotic COD value was observed. This parallelism between both technologies confirms recalcitrant compounds were obtained.

Singlet Oxygen Triggered by Superoxide Radicals in a Molybdenum Cocatalytic Fenton Reaction with Enhanced REDOX Activity in the Environment

As an important reactive oxygen species (ROS) with selective oxidation, singlet oxygen (¹O₂) has wide application prospects in biology and the environment. However, the mechanism of ¹O₂ formation, especially the conversion of superoxide radicals (·O₂^-) to ¹O₂, has been a great controversy. This process is often disturbed by hydroxyl radicals (·OH). Here, we develop a molybdenum cocatalytic Fenton system, which can realize the transformation from ·O₂^- to ¹O₂ on the premise of minimizing ·OH. The Mo⁰ exposed on the surface of molybdenum powder can significantly improve the Fe³⁺/Fe²⁺ cycling efficiency and weaken the production of ·OH, leading to the generation of ·O₂^-. Meanwhile, the exposed Mo⁶⁺ can realize the transformation of ·O₂^- to ¹O₂. The molybdenum cocatalytic effect makes the conventional Fenton reaction have high oxidation activity for the remediation of organic pollutants and prompts the inactivation of Staphylococcus aureus, as well as the adsorption and reduction of heavy metal ions (Cu²⁺, Ni²⁺, and Cr⁶⁺). Compared with iron powder, molybdenum powder is more likely to promote the conversion from Fe³⁺ to Fe²⁺ during the Fenton reaction, resulting in a higher Fe²⁺/Fe³⁺ ratio and better activity regarding the remediation of organics. Our findings clarify the transformation mechanism from ·O₂^- to ¹O₂ during the Fenton-like reaction and provide a promising REDOX Fenton-like system for water treatment.

Wet Peroxide Oxidation of Chlorobenzenes Catalyzed by Goethite and Promoted by Hydroxylamine

In this work, the abatement of several chlorobenzenes commonly found as pollutants in the aqueous phase has been carried out by catalytic wet peroxide oxidation using goethite as the catalyst and hydroxylamine as the promotor. Spiked water with monochlorobenzene and different positional isomers of dichlorobenzene, trichlorobenzene, and tetrachlorobenzene, at concentrations ranging from 0.4 to 16.9 mg L−1 was treated. Runs were carried out batch-way, at room conditions, without headspace. The heterogeneous catalyst was commercial goethite, with a specific surface area (SBET) of 10.24 m2 g−1 and a total iron content of 57.3 wt%. Iron acts as a catalyst of hydrogen peroxide decomposition to hydroxyl radicals. Hydroxylamine (in a range from 0 to 4.9 mM) was added to enhance the iron redox cycle from Fe (III) to Fe (II), remarkably increasing the radical production rate and therefore, the conversion of chlorobenzenes. Iron was stable (not leached to the aqueous phase) even at the lowest pH tested (pH = 1). The effect of pH (from 2 to 7), hydrogen peroxide (from 1 to 10 times the stoichiometric dosage), hydroxylamine, and catalyst concentration (from 0.25 to 1 g/L) was studied. Pollutant removal increased with hydroxylamine and hydrogen peroxide concentration. An operating conditions study demonstrated that the higher the hydroxylamine and hydrogen peroxide concentrations, the higher the removal of pollutants. The optimal pH value and catalyst concentration was 3 and 0.5 g L−1, respectively. Operating with 2.4 mM of hydroxylamine and 10 times the stoichiometric H2O2 amount, a chlorobenzenes conversion of 90% was achieved in 2.5 h. Additionally, no toxic byproducts were obtained.

Morphology-tunable WMoO nanowire catalysts for the extremely efficient elimination of tetracycline: kinetics, mechanisms and intermediates

The presence of antibiotics in aquatic environments has attracted global concern. The Fenton system is one of the most popular methods for eliminating antibiotics in aquatic environments, but the existing Fenton system is limited due to the potential for secondary pollution, and the narrow pH range (∼3-5). In this study, we report that the bottlenecks for high-strength tetracycline (TC) wastewater treatment under neutral conditions can be tackled well by a class of mixed-valence W/Mo containing oxides (WMoO-x) with tunable morphologies. Triethanolamine was selected as a structure-directing agent to control the morphologies of the catalysts going from ultrathin nanowires (UTNWs) to wire-tangled nanoballs (WTNBs). As a proof of concept, the most efficient catalyst in the batch samples, WMoO-1 ultrathin nanowires, was employed as a model material for TC degradation, in which the coordinatively unsaturated metal atoms with oxygen defects serve as the sites for TC chemisorption and electron transfer. As a result, 91.75% of TC was degraded in 60 min for the initial TC concentration of 400 μM. Furthermore, LC-MS analysis confirmed that the TC could be degraded to nontoxic by-products without benzene rings, and finally mineralized to CO2 and H2O. ICP-MS and cycle experiments showed the good stability and reusability of WMoO-1 UTNWs in the Fenton-like system. The findings of this work provide fresh insights into the design of nanoscale catalyst morphology and reaffirm the versatility of doping in tuning catalyst activity, extending the range of the optimal pH values to neutral conditions. This is significant for the expansion of the heterogeneous Fenton-like family and its application in the field of water treatment.