Degradation of p-Nitrophenol using magnetic Fe0/Fe3O4/Coke composite as a heterogeneous Fenton-like catalyst

Transformational fixation of Cr(VI) during microwave-enhanced reduction of soil iron minerals by tea polyphenols

Hexavalent chromium [Cr(VI)] presents substantial environmental and health hazards due to its pronounced toxicity and mobility in soils. Traditional chemical reduction methods for Cr(VI) are often inadequate for treating chromium-contaminated soils, as they may fail to fully reduce Cr(VI), leading to incomplete remediation. Consequently, there is a critical need to develop more efficient and environmentally sustainable methods for the treatment of hexavalent chromium. This study explores an innovative approach using microwave-enhanced reduction of soil iron minerals facilitated by tea polyphenols to achieve transformational fixation of Cr(VI). The microwave-assisted treatment (0.5 wt% TP combined with MW at 700 W for 10 min) significantly reduced Cr(VI) concentrations in iron-rich soil from 363.4 mg kg-1 to 0.3 mg kg-1, achieving a removal rate of 99.9%, compared to TP treatment alone (0.5 wt%). Transmission electron microscopy (TEM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses revealed that the enhanced removal efficiency of Cr(VI) by microwave-assisted tea polyphenols is attributable to the accelerated reduction of soil iron minerals by the polyphenols. Furthermore, microwave enhancement facilitated the transformation of Cr into more stable forms, such as Cr2O3 and FeCr2O4. Additionally, the Cr(VI) content in the treated soil remained below 3 mg kg-1 after 360 days of atmospheric exposure, indicating sustained immobilization. This study demonstrates that the integration of tea polyphenols with microwave irradiation constitutes a promising strategy for the remediation of Cr(VI)-contaminated soils.

Columnar cobalt molybdate spinel rooted on three-dimensional nickel foam as robust catalyst for 4-nitrophenol degradation through peroxymonosulfate activation

Metal oxides-catalyzed peroxymonosulfate (PMS) activation systems show promise in decomposing organic pollutants, whereas the critical challenges such as catalyst aggregation and metal ion leaching significantly impact the stability and reusability of catalysts and thus limit widespread application. To address these issues, an effective self-supported three-dimensional PMS activator consisted of spinel cobalt molybdate (CoMoO4) and nickel foam (NF) (CoMoO4/NF) is fabricated through hydrothermal and annealing processes. The cooperative redox interaction between Co and Mo metal sites in CoMoO4/NF play a crucial role in efficiently activating PMS to degrade 4-nitrophenol (4-NP). Specifically, the CoMoO4/NF/PMS system achieves a 95% degradation rate for 4-NP within 35 min. Attributing to the unique columnar structure and strong connection between CoMoO4 and NF, the catalyst/PMS system maintains high efficiency after five cycles. Furthermore, the system demonstrates broad applicability for degrading various organic pollutants and resistance to interference from different pH levels, inorganic anions, and humic acid. This study proposes radical/non-radical degradation pathways by identifying active species and investigates the degradation mechanism and toxicity of intermediate products for 4-NP. These findings offer valuable insights for designing and synthesizing self-supported catalysts to eliminate pollutants through PMS activation.

Magnetized bentonite modified rice straw biochar: Qualitative and quantitative analysis of Cd(II) adsorption mechanism

Industrialization has caused a significant global issue with cadmium (Cd) pollution. In this study, Biochar (Bc), generated through initial pyrolysis of rice straw, underwent thorough mixing with magnetized bentonite clay, followed by activation with KOH and subsequent pyrolysis. Consequently, a magnetized bentonite modified rice straw biochar (Fe3O4@B-Bc) was successfully synthesized for effective treatment and remediation of this problem. Fe3O4@B-Bc not only overcomes the challenges associated with the difficult separation of individual bentonite or biochar from water, but also exhibited a maximum adsorption capacity of Cd(II) up to 241.52 mg g-1. The characterization of Fe3O4@B-Bc revealed that its surface was rich in C, O and Fe functional groups, which enable efficient adsorption. The quantitative calculation of the contribution to the adsorption mechanism indicates that cation exchange and physical adsorption accounted for 65.87% of the total adsorption capacity. In conclusion, Fe3O4@B-Bc can be considered a low-cost and recyclable green adsorbent, with broad potential for treating cadmium-polluted water.

Review in application of blast furnace dust in wastewater treatment: material preparation, integrated process, and mechanism

Blast furnace dust (BFD) is the solid powder and particulate matter produced by dust removal process in ironmaking industry. The element composition of BFD is complex, and a direct return to sintering will lead to heavy metal enrichment and blast furnace lining corrosion. In recent years, the application of BFD in wastewater treatment has attracted widespread attention. Based on the mechanisms of action of BFD in wastewater, this paper discusses in detail the application of BFD in iron-carbon micro-electrolysis, biological enhancement, adsorption, flocculation, and Fenton/Fenton-like reactions. Iron oxides and carbon in BFD are key substances. Thus, BFD has great potential as a raw material in wastewater treatment, and the waste utilization of BFD can be realized. However, the difference in elements and composition of BFD limits its large-scale application. We can classify BFD according to different proportions of elements. In the future, it is necessary to focus on the service life of BFD in water and whether it shall bring secondary pollution to water.

Effective degradation of tetracycline via recyclable cellulose nanofibrils/polyvinyl alcohol/Fe3O4 hybrid hydrogel as a photo-Fenton catalyst

In this work, the method of in-situ co-precipitation was used to prepare PVA/CNF/Fe₃O₄ hybrid hydrogel, and the relationship between its structure and performance was explored. The Fe₃O₄NPs prepared by this method were dispersed on the carrier PVA/CNF hydrogel and were easy to recover. The catalytic degradation of tetracycline was investigated using PVA/CNF/Fe₃O₄ hybrid hydrogel as photo-Fenton catalysts. The results showed that light and hydrogel carriers were pivotal factors in promoting Fe²⁺ and Fe³⁺ cycling and that the PVA/CNF/Fe₃O₄ hybrid hydrogel as catalysts were able to activate H₂O₂ to generate a large amount of oxygen radical •OH, resulting in efficient removal of tetracycline. The tetracycline degradation followed a proposed first-order kinetic model and achieved a removal rate of about 98% in 120 min at an optimum pH of 3, H₂O₂ 100 mM, catalyst 0.3 g/L, and a temperature of 25 °C.

Pyrene contaminated soil remediation using microwave/magnetite activated persulfate oxidation

Polycyclic aromatic hydrocarbons (PAHs) are important mutagen prevalent in the contaminated sites, bringing potential risks to human health. Iron oxides are important natural components in soils. Pyrene removal in soil using persulfate (PS) oxidation activated by microwave (MW) and magnetite (Fe₃O₄) was investigated. Fe₃O₄ significantly promoted pyrene removal in the soil; 91.7 % of pyrene was degraded within 45 min treatment. Pyrene removal rate in the Fe₃O₄/MW/PS system was 5.18 and 3.00 times higher than that in the Fe₃O₄/PS and MW/PS systems. Increasing in Fe₃O₄ dosage, PS concentration, MW temperature, and soil moisture content in the selected range were conducive for pyrene degradation. SO₄^•-, ^•OH, O₂^•-, and ¹O₂ were responsible for pyrene degradation, and the conversion of Fe (Ⅱ) in the Fe₃O₄ to Fe (Ⅲ) contributed to the formation of O₂^•- and ¹O₂. Characteristic bands of pyrene were more obviously destroyed by the Fe₃O₄/MW/PS oxidation, in comparison with MW/PS oxidation. Ring hydroxylation and ring-opening reactions were the main degradation pathways of pyrene. The toxicities of the formed byproducts were significantly reduced after treatment. This study provided a promising option for pyrene contaminated soil remediation.

Core-Shell Structured Magnetic Carboxymethyl Cellulose-Based Hydrogel Nanosorbents for Effective Adsorption of Methylene Blue from Aqueous Solution

This article reports effective removal of methylene blue (MB) dyes from aqueous solutions using a novel magnetic polymer nanocomposite. The core-shell structured nanosorbents was fabricated via coating Fe₃O₄ nanoparticles with a layer of hydrogel material, that synthesized by carboxymethyl cellulose cross-linked with poly(acrylic acid-co-acrylamide). Some physico-chemical properties of the nanosorbents were characterized by various testing methods. The nanosorbent could be easily separated from aqueous solutions by an external magnetic field and the mass fraction of outer hydrogel shell was 20.3 wt%. The adsorption performance was investigated as the effects of solution pH, adsorbent content, initial dye concentration, and contact time. The maximum adsorption capacity was obtained at neutral pH of 7 with a sorbent dose of 1.5 g L⁻¹. The experimental data of MB adsorption were fit to Langmuir isotherm model and Pseudo-second-order kinetic model with maximum adsorption of 34.3 mg g⁻¹. XPS technique was applied to study the mechanism of adsorption, electrostatic attraction and physically adsorption may control the adsorption behavior of the composite nanosorbents. In addition, a good reusability of 83.5% MB recovering with adsorption capacity decreasing by 16.5% over five cycles of sorption/desorption was observed.

N-compounds speciation analysis in environmental samples using ultrasound-assisted solid-liquid extraction and non-chromatographic techniques

A fast, efficient, and non-chromatographic method was presented in this study for nitrite, nitrate, and p-nitrophenol (N-compounds) extraction and speciation analysis of environmental samples. By applying ultrasound-assisted solid-liquid extraction (USLE), analytes were efficiently extracted from water, soil, or sediment collected in areas of environmental disaster. These analytes were selectively converted to NO_(g) through UV photolysis (NO₃^-), H₂O₂/UV photocatalysis (PNP), and direct conversion (NO₂^-). Following conversion, NO_(g) was separated from the liquid phase and determined by high-resolution continuum source molecular absorption spectrometry (HR-CS MAS). The LODs obtained were 0.097 ± 0.004 mg L^-1 for nitrite, 0.119 ± 0.004 mg L^-1 for nitrate, and 0.090 ± 0.006 mg L^-1 for p-nitrophenol. On applying this speciation method to environmental samples, concentrations were found to be up to 0.99 ± 0.03 mg L^-1 (NO₂^-), 49.80 ± 2.5 mg L^-1 (NO₃^-), and 0.10 ± 0.02 mg L^-1 (PNP). Finally, addition/recovery study of real water, soil, and sediment samples showed 101 ± 2% recovery for NO₂^-, 100 ± 1% for NO₃^-, and 96 ± 5% for PNP.

In-situ self-assembly of robust Fe (III)-carboxyl functionalized polyacrylonitrile polymeric bead catalyst for efficient photo-Fenton oxidation of p-nitrophenol

From the view of channel confinement and functional site capture, we develop an in-situ self-assembly strategy to fabricate the carboxyl functionalized Fe-HPAN bead catalyst with highly stable and uniformly dispersed metallic sites for efficient photo-Fenton oxidation of p-nitrophenol (p-NP). BET and FTIR analysis reveal that numerous carboxyl groups and mesopores exist in Fe-HPAN beads, which acts to capture and immobilize iron ions. Catalytic results show that the degradation rate and TOC removal for p-NP were up to 99.78 and 91.68% under the optimal condition. Even at near neutral pH, the degradation rate almost keep the same and the TOC removal can still reach 73.05%. Due to the autocatalytic cycle of Fe^III/Fe^II, the apparent rate constant of Fe-HPAN (0.2247 min^-1) was 5.4 times as high as unmodified Fe-PAN (0.0415 min^-1) in the presence of H₂O₂ and visible light irradiation, which was 2-3 orders of magnitude larger than that of other reaction systems. More importantly, Fe-HPAN bead catalyst exhibited little loss of activity even after 20 cycles of re-utilization. The possible degradation pathway of p-NP was also proposed based on GC/MS analysis. The present work may provide a new perspective for the use of synthetic polymer to prepare low-cost, efficient and robust photo-Fenton oxidation catalysts.

Ozonation process intensification of p-nitrophenol by in situ separation of hydroxyl radical scavengers and microbubbles

The ozonation efficiency for removal of recalcitrant organic pollutants in alkaline wastewater is always low because of the presence of some hydroxyl radical scavengers. To solve this problem, the O₃/Ca(OH)₂ system was put forward, and p-nitrophenol (PNP) was chosen to explore the mechanism of this system. The effects of key operational parameters were studied respectively; the Ca(OH)₂ dosage 3 g/L, ozone inlet flow rate 3.5 L/min, ozone concentration 65 mg/L, reactor pressure 0.25 MPa, and temperature 25 °C were obtained as the optimal operating conditions. After 60 min treatment, the organic matter mineralized completely, which was higher than the sum of the ozonation-alone process (55.63%) and the Ca(OH)₂ process (3.53%). It suggests that the calcium hydroxide in the O₃/Ca(OH)₂ process possessed a paramount role in the removal of PNP. The liquid samples and the precipitated substances were analyzed by gas chromatography mass spectrometry, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy; it was demonstrated that Ca(OH)₂ could accelerate the generation of hydroxyl radical and simultaneously in situ separate partial intermediate products and CO₃ ^2- ions through some precipitation reactions.

Heterogeneous Fenton-Like Degradation of p-Nitrophenol over Tailored Carbon-Based Materials

Activated carbon (AC), carbon xerogel (XG), and carbon nanotubes (CNT), with and without N-functionalities, were prepared. Catalysts were obtained after impregnation of these materials with 2 wt.% of iron. The materials were characterized in terms of N2 adsorption at −196 °C, elemental analysis (EA), and the pH at the point of zero charge (pHPZC). The p-nitrophenol (PNP) degradation and mineralization (assessed in terms of total organic carbon–TOC–removal) were evaluated during adsorption, catalytic wet peroxidation (CWPO), and Fenton process. The textural and chemical properties of the carbon-based materials play an important role in such processes, as it was found that the support with the highest surface area -AC- presents the best performance in adsorption, whereas the materials with the highest mesopore surface area -XG or Fe/XG- lead to best removals by oxidation processes (for XG it was achieved 39.7 and 35.0% and for Fe/XG 45.4 and 41.7% for PNP and TOC, respectively). The presence of N-functionalities increases such removals. The materials were reused in consecutive cycles: the carbon-based materials were deactivated by hydrogen peroxide, while the catalysts showed high stability and no Fe leaching. For the support with superior performances -XG-, the effect of nitrogen content was also evaluated. The removals increase with the increase of the nitrogen content, the maximum removals (81% and 65% for PNP and TOC, respectively) being reached when iron supported on a carbon xerogel doped with melamine was used as catalyst.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Catalytic micro-ozonation by Fe3O4 nanoparticles @ cow-dung ash for advanced treatment of biologically pre-treated leachate

In this work, the biologically pre-treated leachate was subjected to catalytic micro-ozonation using cow-dung ash composites loaded with Fe₃O₄ nanoparticles (nano-Fe₃O₄@CDA) as the catalyst. The optimal conditions used were nano-Fe₃O₄@CDA dosage of 0.8 g/L, input ozone of 3.0 g/L, and reaction time of 120 min. This environment yielded the following results: The COD and color number (CN) removal reached 53% and 89%, respectively, and the BOD₅/COD increased from 0.05 to 0.32. The catalytic micro-ozonation partially degraded the refractory substances into intermediates with lower molecular weight. The percentage of phenolic compounds decreased sharply from 28.08% to 8.56%, largely due to the opening of the ring as well as to the formation of organic intermediates with a low molecular weight. Based on the results culled from the electron paramagnetic resonance (EPR), it is evident that the nano-Fe₃O₄@CDA catalyst can accelerate in order to generate OH. This was the main mechanism involved in its excellent ability to degrade refractory pollutants. These results demonstrated the potential use of nano-Fe₃O₄@CDA as a catalyst in the catalytic micro-ozonation process.

Treatment of stabilized landfill leachate by Fenton-like process using Fe3O4 particles decorated Zr-pillared bentonite

Fe₃O₄ particles decorated Zr pillared bentonite (Fe₃O₄/Zr-B) were successfully synthesized, which were used to treat stabilized landfill leachate by Fenton-like process. The organics removal and biodegradability were both significantly improved owing to good catalytic stability of the magnetically recoverable catalyst. With the catalyst dosage of 1.0 mg L^-1, initial pH of 2 and peroxide concentration of 0.1 mmol L^-1, the COD removal efficiency increased to 68% and BOD₅/COD of 0.27 was achieved. According to the results of the GC-MS, Fenton-like reaction with Fe₃O₄/Zr-B had an excellent removal performance for almost all the heterocyclic compounds. The 3D-EEM fluorescence spectra indicated that the fluorescence intensity was dramatically reduced and the UV humic-like and fulvic-like substances were removed effectively during the catalytic degradation. It seemed advisable to implement this process as a pre-treatment to facilitate the further biological treatment.

Enhanced heterogeneous Fenton-like degradation of methylene blue by reduced CuFe2O4

To facilitate rapid dye removal in oxidation processes, copper ferrite (CuFe2O4) was isothermally reduced in a H2 flow and used as a magnetically separable catalyst for activation of hydrogen peroxide (H2O2). The physicochemical properties of the reduced CuFe2O4 were characterized with several techniques, including transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and magnetometry. In the catalytic experiments, reduced CuFe2O4 showed superior catalytic activity compared to raw CuFe2O4 for the removal of methylene blue (MB) due to its relatively high surface area and loading Fe0/Cu0 bimetallic particles. A limited amount of metal ions leached from the reduced CuFe2O4 and these leached ions could act as homogeneous Fenton catalysts in MB degradation. The effects of experimental parameters such as pH, catalyst dosage and H2O2 concentration were investigated. Free radical inhibition experiments and electron spin resonance (ESR) spectroscopy revealed that the main reactive species was hydroxyl radical (˙OH). Moreover, reduced CuFe2O4 could be easily separated by using an external magnet after the reaction and remained good activity after being recycled five times, demonstrating its promising long-term application in the treatment of dye wastewater.

Influence of precursor pH on the structure and photo-Fenton performance of Fe/hydrochar

Fe/hydrochar exhibited high visible light photo-Fenton activity because hydrochar accelerated the Fe³⁺/Fe²⁺ cycle at the catalyst/water interface.

Catalytic oxidation of organic pollutants in wastewater via a Fenton-like process under the catalysis of HNO3-modified coal fly ash

Organic wastewater can be treated effectively via a heterogeneous Fenton-like process under the catalysis of HNO₃-modified coal fly ash.