Carbothermal reduction synthesis of zero-valent iron and its application as a persulfate activator for ciprofloxacin degradation

Self-Fenton Cu-Mn catalysts for efficient ciprofloxacin removal: in-situ H2O2 generation and activation

The Fenton oxidation system is a widely employed advanced oxidation processes (AOPs) in wastewater treatment. However, the traditional Fenton oxidation system suffers from low oxidant utilization efficiency, leading to significant resource wastage. This study presents a novel self-Fenton Cu-Mn bimetallic catalyst (with a Cu:Mn ratio of 10:1), which is capable of simultaneously activating O2 to generate H2O2 in situ and further catalyzing the decomposition of H2O2 to produce reactive oxygen species (ROS). Notably, this self-Fenton system demonstrate high removal efficiency for ciprofloxacin (CIP) across a broad pH range (2-9), achieving up to 92.55 % removal in water. Quenching experiments, electron paramagnetic resonance (EPR) analysis, steady-state concentration measurements, and Galvanic oxidation reactor (GOR) experiments collectively confirmed the generation of multiple ROS species (·OH, ·O2-, and 1O2) and indicated that electron transfer plays a significant role in pollutant degradation. X-ray photoelectron spectroscopy (XPS) analysis revealed that Cu0 exhibited high catalytic activity, enabling simultaneous generation and activation of H2O2. Liquid chromatography-mass spectrometry (LC-MS) and toxicity assessments demonstrated a significant reduction in the toxicity of CIP degradation products. This work elucidates a novel Cu-Mn synergistic mechanism wherein Mn facilitates the generation of H2O2, while Cu effectively activates it into ROS. This synergism effect enables the removal of pollutants through both radical and non-radical pathways, thereby offering an innovative strategy for environmental remediation and AOPs.

One material, two functions: A dual-mechanistic approach for the removal of persistent and mobile organic micropollutants from drinking water

Organic micropollutants (OMP), especially those that are more persistent and mobile due to their physico-chemical properties, are resistant to common water treatment techniques and might reach drinking water. Considering the wide range and different physico-chemical properties of persistent and mobile (PM) substances, the strategic integration of synergistic processes appears as a promising solution for the removal of persistent and mobile substances. In this study, the development of a dual-functional material is explored for synergistic adsorption and catalysis, presenting a dual-mechanistic approach for removing potentially persistent and mobile substances from drinking water. The material was fabricated using waste materials (coffee and aluminum wastes) and tested for removing 23 selected OMP. The results demonstrate that the dual-functional material can both adsorb some target OMP and activate persulfate to oxidize OMP by generating reactive oxygen species (ROS). Recycling of the material in repeated cycles revealed removal of several OMP even in 5th cycle, using 0.5 g/L of the synthesized material, 0.5 mM persulfate and 1 h contact time. Quenching experiments indicated that singlet oxygen (1O2) is the dominant ROS in the proposed system, implying that it is a non-radical advanced oxidation process.

Performance of nano zero-valent iron activated peroxydisulfates prepared by carbothermal reduction using various bagasse components

Biomass has been utilized in the carbothermal reduction method to reduce iron cations, thereby synthesizing nano zero-valent iron (nZVI). The effect of the biomass components on the regulation of the performance of prepared nZVI is not clear and the mechanism of action remains to be explored. Biomass components such as cellulose, hemicellulose, lignin, and amylum were used to prepare carbon-loaded nano zero-valent iron. It was demonstrated that increasing the cellulose content of the mixture led to higher Fe0 content by 2-6 times and a greater activation efficiency of peroxydisulfate (PDS) by 2-5 times. nZVI prepared by carbothermal reduction using bagasse (Fe0/CB) removed 99.8 % of metronidazole in 60 min. The bagasse's cellulose content was found to be 59.5 % and the results demonstrated that the composites prepared with the cellulose content exceeded 60 % had unusual properties. The pyrolysis process of the mixtures showed that cellulose promotes the production of nZVI by generating more reducing gases (e.g. CO, CH4). Furthermore, the efficiency of activated PDS in removing metronidazole was confirmed, with cellulose-prepared nZVI (c-Fe0/C) proving to be the most effective activator. Its removal rate was 1.3 times higher than that of Fe0/CB. Physical characterization and mechanistic investigations demonstrated that c-Fe0/C has the same active sites as Fe0/CB and produces the same type and amount of reactive oxygen species. These demonstrates that cellulose is a critical component in the preparation of nZVI during carbothermal reduction. This study provides guidelines for preparing carbothermal reduced nZVI and establishes a theoretical basis for its engineering application.

The morphology and structure of zero-valent iron nanosheets promote the activation of persulfate for degradation of ciprofloxacin

Herein, a biochar-supported zero-valent iron (ZVI) nanosheet catalyst (Fe@BC2-2) for the activation of persulfate to degrade ciprofloxacin (CIP) was prepared using industrial kraft lignin and Fenton sludge as carbon and iron sources, respectively. Fe@BC2-2 showed considerably better CIP degradation efficiency (96.9% at 20 mg L-1) than traditional catalysts. Furthermore, Fe@BC2-2 exhibited CIP degradation efficiency above 96% in a wide pH range (3-11) and high resistance to interference from various inorganic anions and humic acid even under real water body conditions. The Fe@BC2-2 catalyst showed good magnetic separation performance and maintained high CIP degradation efficiency (87.0%) after five degradation-regeneration cycles. CIP degradation was facilitated by ZVI nanosheets along with functional groups and defects on the surface of the biochar. As determined through radical-quenching experiments, both radical and non-radical pathways contributed to the degradation of CIP, with the non-radical pathway being dominant, especially with singlet oxygen (1O2) as the active species. The degradation pathway of CIP was inferred through the analysis of intermediate products, which showed lower toxicity than CIP. This work not only proposes a strategy for the utilization of traditional kraft pulping lignin and Fenton sludge but also presents an innovative catalyst for the degradation of antibiotics.

Removal of Di (2-ethylhexyl) phthalate from groundwater by sodium persulfate activated by hollow micron zero-valent iron: Reaction mechanism and degradation path

In this study, hollow micron zero-valent iron (H-mZVI) was prepared using the ethylenediamine liquid phase reduction method. The microstructures were characterized by SEM, XRD, BET and FTIR. The results showed that H-mZVI possessed a spherical hollow structure with a particle size of approximately 1 μm. The density of H-mZVI was notably lower compared to solid micron zero-valent iron (S-mZVI). Furthermore, with an increase in ethylenediamine addition, the density initially decreased before stabilizing. Results demonstrated that the degradation efficiency of H-mZVI/PS for DEHP was 2.96 times higher than that of S-mZVI/PS. The charge density of H-mZVI/PS degradation DEHP system was higher than that of S-mZVI/PS system, and H-mZVI exhibited a fast electron migration rate and strong electron transport ability between the solution and the interface material. The degradation of DEHP by H-mZVI/PS system was carried out jointly by the surface reaction on the surface of H-mZVI particles and the homolytic reaction led by Fe2+ ions in the solution. Additionally, the contribution rate of free radicals in the degradation process of DEHP was in the order SO4-· > ·OH > 1O2. There were three degradation pathways of DEHP in H-mZVI/PS system, and the toxicity of DEHP degradation products was significantly lower than that of the parent.

Potential of metallurgical iron-containing solid waste-based catalysts as activator of persulfate for organic pollutants degradation

The production of solid wastes in the metallurgical industry has significant implications for land resources and environmental pollution. To address this issue, it is crucial to explore the potential of recycling these solid wastes to reduce land occupation while protecting the environment and promoting resource utilization. Steel slag, red mud, copper slag and steel picking waste liquor are examples of solid wastes generated during the metallurgical process that possess high iron content and Fe species, making them excellent catalysts for persulfate-based advanced oxidation processes (PS-AOPs). This review elucidates the catalytic mechanisms and pathways of Fe2+ and Fe0 in the activation PS. Additionally, it underscores the potential of metallurgical iron-containing solid waste (MISW) as a catalyst for PS activation, offering a viable strategy for its high-value utilization. Lastly, the article provides an outlook towards future challenges and prospects for MISW in PS activation for the degradation of organic pollutants.

Simultaneous immobilization of V and Cr availability, speciation in contaminated soil and accumulation in ryegrass by using Fe-modified pyrolysis char

In this study, municipal waste pyrolytic char (PEWC) was prepared by pyrolysis from municipal solid waste extracted in landfills, and Fe-based modified pyrolytic char (Fe-PEWC) was prepared by modification. Focusing on the evaluation of the stabilization capacity of Fe-PEWC for vanadium (V) and chromium (Cr) in soils, the effects of PEWC addition on soil properties, bioavailability and morphological distribution of V and Cr, ryegrass growth, and V and Cr accumulation were thoroughly investigated. The results of pot experiment showed that the application of PEWC and Fe-PEWC significantly (P < 0.05) improved soil properties (such as pH, EC, total nitrogen, available phosphorus, available potassium, and organic matter). After 42 days of cultivation, Fe-PEWC has a better fixation effect on heavy metals, and the bioavailable V and Cr of 3% Fe-PEWC decreased by 14.96% and 19.48%, respectively. The exchangeable state and reducible state decreased, while the oxidizable state and residual state increased to varying degrees. The Fe-PEWC can effectively reduce the accumulation of V and Cr in ryegrass by 71.25% and 76.43%, respectively, thereby reducing their toxicity to plants. In summary, modified pyrolytic char can effectively solidify heavy metals in soil, improve soil ecology and reduce the toxicity to plants. The use of excavated waste as a raw material for the preparation of soil heavy metal curing agent has the significance of resource recycling, low price, and practical application.

Integration of metal organic framework nanoparticles into sodium alginate biopolymer-based three-dimensional membrane capsules for the efficient removal of toxic metal cations from water and real sewage

Sodium alginate (SA) biopolymer has been recognized as an efficient adsorbent material owing to their unique characteristics, including biodegradability, non-toxic nature, and presence of abundant hydrophilic functional groups. Accordingly, in the current research work, UiO-66-OH and UiO-66-(OH)2 metal organic framework (MOF) nanoparticles (NPs) have been integrated into SA biopolymer-based three-dimensional (3-D) membrane capsules (MCs) via a simple and facile approach to remove toxic metal cations (Cu2+ and Cd2+) from water and real sewage. The newly configured capsules were characterized by FTIR, SEM, XRD, EDX and XPS analyses techniques. Exceptional sorption properties of the as-developed capsules were ensured by evaluation of the pertinent operational parameters, i.e., contents of MOF-NPs (1-100 wt%), adsorbent dosage (0.001-0.05 g), content time (0-360 h), pH (1-8), initial concentration of metal cations (5-1000 mg/L) and reaction temperature (298.15-333.15 K) on the eradication of Cu2+ and Cd2+ metal cations. It was found that hydrophilic functional groups (-OH and -COOH) have performed an imperative role in the smooth loading of MOF-NPs into 3-D membrane capsules via intra/inter-molecular hydrogen bonding and van der waals potencies. The maximum monolayer uptake capacities (as calculated by the Langmuir isotherm model) of Cd2+ and Cu2+ by 3-D SGMMCs-OH were 940 and 1150 mg/g, respectively, and by 3-D SGMMCs-(OH)2 were 1375 and 1575 mg/g, respectively, under optimum conditions. The as-developed capsules have demonstrated superior selectivity against targeted metal cations under designated pH and maintained >80 % removal efficiency up to six consecutive treatment cycles. Removal mechanisms of metal cations by the 3-D SGMMCs-OH/(OH)2 was proposed, and electrostatic interaction, ion-exchange, inner-sphere coordination bonds/interactions, and aromatic ligands exchange were observed to be the key removal mechanisms. Notably, FTIR and XPS analysis indicated that hydroxyl groups of Zr-OH and BDC-OH/(OH)2 aromatic linkers played vital roles in Cu2+ and Cd2+ adsorption by participating in inner-sphere coordination interactions and aromatic ligands exchange mechanisms. The as-prepared capsules indicated >70 % removal efficiency of Cu2+ from real electroplating wastewater in the manifestation of other competitive metal ions and pollutants under selected experimental conditions. Thus, it was observed that newly configured 3-D SGMMCs-OH/(OH)2 have offered a valuable discernment into the development of MOFs-based water decontamination 3-D capsules for industrial applications.

Synergistic oxidation induced by underwater bubbling plasma and diatomite-CoFe2O4 activated peroxymonosulfate for the degradation of ciprofloxacin hydrochloride

Underwater bubbling plasma (UBP) coupled with diatomite-CoFe2O4 (Dt-CFO) activated peroxymonosulfate (PMS) was proposed for the degradation of ciprofloxacin hydrochloride (CIP) in this work. The catalyst sample of Dt-CFO with large specific surface area, rich active sites and excellent magnetic property was prepared by the hydrothermal method and systematically characterized to investigate its material properties. The combination of UBP and Dt-CFO activated PMS (UBP/Dt-CFO/PMS) showed excellent synergy with the synergistic factor of 1.98, and reached the CIP degradation percentage of 94.7%, which corresponded to the kinetic constant of 0.097 min-1. Dt-CFO with the diatomite content of 30 wt% achieved the best catalytic activity in the reaction system. Higher catalyst and PMS dose, peak voltage, pulse frequency and lower initial CIP concentration were beneficial for CIP removal. The addition of Cl-, HCO3-, SO42- and humic acid suppressed CIP degradation, while NO3- had no effect on CIP removal. The Dt-CFO composite exhibited excellent reusability and low leaching metal amount, demonstrating its good stability. SO4-·, ·OH, ·O2-, 1O2, eaq, O3 and H2O2 were the active species confirmed to be involved in CIP degradation. The redox circles of ≡ Co(Ⅱ)/≡Co(Ⅲ) and ≡ Fe(Ⅱ)/≡Fe(Ⅲ) on Dt-CFO surface and the plasma-induced physicochemical effects dominated PMS activation. The decomposition process of CIP was explored through fluorescence spectra. Three degradation pathways were inferred, and the toxicity analysis showed the toxicity of CIP solution weakened after discharge treatment.

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.

Synthesis of CuO/GO-DE Catalyst and Its Catalytic Properties and Mechanism on Ciprofloxacin Degradation

A new catalyst, copper oxide/graphene oxide-diatomaceous earth (CuO/GO-DE), was prepared by the ultrasonic impregnation method. The optimal conditions for catalyst preparation were explored, and its structure and morphology were characterized by BET, XRD, SEM, TEM, FTIR, Raman and XPS. By taking ciprofloxacin as the target pollutant, the performance and reusability of CuO/GO-DE to degrade antibiotic wastewater was evaluated, and the optimal operating conditions were obtained. The main oxidizing substances in the catalytic system under different pH conditions were analyzed, as well as the synergistic catalytic oxidation mechanism. The intermediate products of ciprofloxacin degradation were identified by LC-MS, and the possible degradation process of ciprofloxacin was proposed.

Spherical ZVI/Mn-C Bimetallic Catalysts for Efficient Fenton-Like Reaction under Mild Conditions

The heterogeneous Fenton-like reaction has been receiving increasing attention for its inexpensiveness and high efficiency in water treatment. In this study, a novel strategy was proposed for preparing spherical ZVI/Mn-C bimetallic catalysts with a high activity for a Fenton-like reaction by using the ammonium alginate assisted sol–gel method coupled with a carbothermic reduction. The results showed that the obtained ZVI/Mn-C spheres had a uniform size, smooth surface and good sphericity, and the particle size of ZVI was limited to about 30 nm by the carbon layer. Among all catalysts, the ZVI/Mn-C-31 catalyst exhibited the highest phenol degradation efficiency in the Fenton-like process, and almost 100% phenol degradation efficiency was achieved under neutral pH at room temperature within 5 min. Moreover, the ZVI/Mn-C-31/H2O2 system showed a 100% degradation efficiency for removing a wide range of aromatic pollutants, including catechol, resorcinol and o-nitrophenol. Moreover, the radicals-scavenging experiment illustrated that the ·OH played a key factor in mineralizing the organic matters, and the ·O2− generated from the MnO-H2O2 system accelerated the conversion rate of ferric iron to ferrous iron. Due to the synergistic effects between ZVI and MnO, the ZVI/Mn-C-31 catalyst performed excellently in the Fenton-like reaction at an extended pH range.