Low Metal Leaching Research Articles

Accelerating peroxymonosulfate-based Fenton-like reaction via Mott-Schottky heterojunction

A Mott-Schottky heterojunction is reported to boost the peroxymonosulfate (PMS) activation in Fenton-like reaction through a non-radical path. The heterojunction with Co nanoparticles encapsulated by nitrogen-doped graphitized carbon (N-GC) shell was synthesized via pyrolysis of ZIF67 @ZIF8 and subsequent acidic treatment. Benefiting from Mott-Schottky effect, the electrons were transferred from Co nanoparticles to the N-GC shell, leading to the rearranged electron density on N-GC surface and improvement of the PMS activation. The PMS activation efficiency of heterojunction (86.0%) was much higher than the reference catalyst without Mott-Schottky effect (35.3%), and even comparable to Co2+ (86.2%). 85.0% of tetracycline (TC) removal efficiency was realized after only 10.0 s. Moreover, the intrinsic advantages of non-radical path were well inherited by Mott-Schottky heterojunction, including high anti-interfere property toward various anions, cations and organics, high catalytic activity in a wide pH range, low metal leaching, and high magnetic recyclability.

A biochar-based catalyst prepared by potassium ferrate oxidation coupled high-temperature pyrolysis and its application for the activation of peroxymonosulfate towards the degradation of norfloxacin: Performance and mechanism insight

Developing an efficient catalyst for persulfate activation is critical to the high-efficiency degradation of organic pollutants in an aqueous solution using a persulfate-based advanced oxidation method. A biochar-based catalyst, 800Fe2BC2, was prepared using a novel technology of potassium ferrate oxidation coupled with high-temperature pyrolysis based on the biomass raw material of waste branches pruned from apple trees in an orchard. Batch tests were conducted to degrade norfloxacin using 800Fe2BC2 to activate peroxymonosulfate (PMS). Norfloxacin was almost completely degraded within 10 min. The reactive oxygen species (ROS), for instance, •OH, SO4•−, O2•−and 1O2, were generated in the 800Fe2BC2/PMS system. The iron oxides, defective structures, and CO groups in 800Fe2BC2 served as catalytic sites for generating free radicals. However, the recombination of superoxide radicals, the interaction of CO groups on the catalyst surface with PMS, and the self-decomposition of PMS contributed to generating 1O2. The quenching test showed that the degree of the contribution of •OH, SO4•−, O2•−and 1O2 to NOR degradation was approximately 1O2 > O2•− > SO4•− > •OH, respectively. We proposed three potential NOR degradation pathways: piperazine ring opening (P), quinolone ring oxidation (Q), and benzene ring defluorination (F). Then part of these intermediates was completely mineralized into inorganics like CO2, H2O, NO3− and F−. The acute and chronic toxicity of the degradation products were estimated, and the evolution of toxicity in the present catalytic system could not be ignored and should be overcome by deeper mineralization. The prepared 800Fe2BC2 demonstrated a good application prospect with good stability, recyclability, low metal leaching, and versatility to various refractory pollutants. Therefore, this study offered a new way of producing biochar-based catalysts for activating PMS using biomass wastes.

Efficient emerging contaminants (EM) decomposition via peroxymonosulfate (PMS) activation by Co3O4/carbonized polyaniline (CPANI) composite: Characterization of tetracycline (TC) degradation property and application for the remediation of EM-polluted water body

Earth abundant transition metal-based materials are widely served as peroxymonosulfate (PMS) activators for degradation of emerging contaminants. However, the agglomeration of catalyst particles and metal ion leaching hinder their practical applications for pollutant decomposition. In this study, a Co3O4-carbonized polyaniline composite (Co3O4/CPANI) was implemented for PMS activation. The Co3O4/CPANI + PMS system exhibited high catalytic performance toward tetracycline (TC) degradation (degradation efficiency of 92.11%, initial TC level of 20 mg/L). Moreover, the practical application potential of Co3O4/CPANI + PMS system was well verified with three antibiotics (i.e., TC, doxycycline (DOX), and ciprofloxacin (CIP)) at highest actual aquatic environmental levels (1.0 and 0.5 mg/L). In the established Co3O4/CPANI + PMS system, both radicals (•O2−, •OH and SO4•-) and non-radical (1O2) contributed to TC degradation, and 1O2 was the dominant reactive oxygen species (ROS). CO groups, oxygen vacancies (OVS), redox pairs of Co2+/Co3+ species, and graphitic N all served as active sites in the PMS activation process, especially, OVS were crucial for the generation of 1O2. This study provides an efficient method for the synthesis of metal-based nanocatalysts with low nanoparticle aggregation and metal leaching which could act as a sustainable PMS activator for the remediation of TC-polluted water environment.

Role of Ion-Exchange Resins in Hydrogenation Reactions

The role of ion-exchange resins (IERs) as catalysts or catalysts supports, in hydrogenation reactions is revised and their potential application is presented. Both gel-type and macroreticular, basic or acid, IERs have been used for manifold metal-catalyzed hydrogenation processes in gas and liquid phase, including hydrogenation of alkenes, alkynes, carbonyls, arenes, nitroaromatics, and more. When available, qualitative relationships between the morphology and structure of resins and their performance as solid supports for metal catalysts are observed. Noble metals, such as Pt, Au, and Pd, and non-noble metals, such as Fe and Cu, have been introduced into IERs polymeric backbones by simple ion-exchange of a metal salt precursor with the resin, or by a combination of ion-exchange and other protocols, to obtain mono- and bimetallic catalysts supported on IERs. High yields towards target product, as well as the recyclability of metal-doped IERs, have been reported in the literature, with low metal leaching, which makes them highly interesting solid catalysts for a wide array of industrial applications. Multistep reaction processes, involving hydrogenation and hydration/cyclization/aldol condensation/etc., constitute promising applications due to the one-pot synthesis approach and relatively low temperatures required, which adds environmental interest in terms of process integration and optimization.

Copper Foam-Supported CuxO@Fe2O3 Core–Shell Nanotubes: An Efficient Ozonation Catalyst for Degradation of Organic Pollutants

Copper foam (CF)-supported CuxO@Fe2O3 core–shell nanotubes (CF/CuxO@Fe2O3 NTs) were synthesized as a hybrid catalyst for heterogeneous catalytic ozonation (HCO). The hybrid catalyst exhibits high activity and excellent stability for the HCO of organic pollutants. The total organic carbon removal rates of methyl orange, ibuprofen, and nitrobenzene via HCO were 89, 82, and 88%, respectively, which are over 2 times higher than the corresponding values obtained without the catalyst. The hybrid catalyst also displays wide pH operation range, low metal leaching, easy separation from treated water, and excellent recyclability. We prove that large amounts of Lewis acid sites with medium acidity are created at the CuxO/Fe2O3 interface due to the synergic effect of CuxO and Fe2O3. These medium acid sites are the main active centers for the production of free hydroxyl radicals (•OH) and superoxide radicals (O2•– or HO2•) in neutral solution. Moreover, the 3D porous framework of the catalyst enables easy dispersion in and separation from water. This work develops a new strategy to design HCO catalysts by combining strong and weak Lewis acid oxides and also opens a new avenue for developing HCO catalysts on a 3D porous framework.

Efficient degradation of sulfamethoxazole in various waters with peroxymonosulfate activated by magnetic-modified sludge biochar: Surface-bound radical mechanism

First time, this study synthesized a magnetic-modified sludge biochar (MSBC) as an activator of peroxymonosulfate (PMS) to eliminate sulfamethoxazole (SMX). The removal efficiency of SMX reached 96.1% at t = 60 min by PMS/MSBC system. The larger surface area and magnetic Fe3O4 of MSBC surface enhanced its activation performance for PMS. The PMS decomposition, premixing and reactive oxygen species (ROS) identification experiments combined with Raman spectra analysis demonstrated that the degradation process was dominated by surface-bound radicals. The transformed products (TPs) of SMX and the main degradation pathways were identified and proposed. The ecotoxicity of all TPs was lower than that of SMX. The magnetic performance was beneficial for its reuse and the removal efficiency of SMX was 83.3% even after five reuse cycles. Solution pH, HCO3− and CO32− were the critical environmental factors affecting the degradation process. MSBC exhibited environmental safety for its low heavy metal leaching. PMS/MSBC system also performed excellent removal performance for SMX in real waters including drinking water (88.1%), lake water (84.3%), Yangtze River water (83.0%) and sewage effluent (70.2%). This study developed an efficient PMS activator for SMX degradation in various waters and provided a workable way to reuse and recycle municipal sludge.

Utilizing scrap printed circuit boards to fabricate efficient Fenton-like catalysts for the removal of pharmaceutical diclofenac and ibuprofen from water

Pharmaceutical concentrations in waterways have now gradually increased to alarming levels, posing a threat to the environment and human health. The heterogeneous Fenton-based advanced oxidation process is a promising treatment process for cleaning water from organic pollutants. Utilizing waste-to-resource technologies, electronic waste can be transformed into practical weapons for environmental remediation. In this work, scrap printed circuit boards (PCBs) were used to prepare green, simple, and scalable heterogeneous H2O2 activators namely, non-carbonized catalyst (NC-PCB) under air combustion and carbonized catalyst (C-PCB) under nitrogen pyrolysis. Diclofenac (DCF) and ibuprofen (IBP) were used as model pharmaceutical pollutants to investigate the efficacy of the synthesized catalysts in Fenton-like oxidation. The morphology, composition, and photocatalytic activities of both catalysts were characterized by various analytical techniques. The effect of experimental factors such as catalyst/H2O2 dosages, solution pH, and initial concentrations on the removal rate was studied and optimized. Under optimum conditions, the degradation efficiencies for DCF and IBP using the NC-PCB catalyst were 86% and 66%, respectively, and 61% and 65.7% using C-CPB within 30 min. The TOC removal for DCF and IBP after 60 min was 61% and 50% using NC-CPB and 45% and 43% using C-CPB, respectively. Copper oxides in the catalysts plays the primary role in the degradation process. For five cycles, the catalysts have good reusability and low metal leaching. The degradation kinetics were followed, by a pseudo-first-order model. The present study is expected to provide a new approach for promoting Fenton-like wastewater treatment systems to practical application.

Catalytic oxidation of methylene blue by using Ni-Fe bimetallic catalyst/NaClO system: Performance, kinetics, mechanism, and DFT calculations

Nickel-iron bimetallic catalysts (Ni-Fe/Al2O3) with activated alumina as the carrier were prepared by impregnation pyrolysis, and the structure and morphology of the catalysts were analyzed by characterization via X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, programmed temperature rise reduction, and X-ray photoelectron spectroscopy. The prepared Ni-Fe/Al2O3 was used to catalyze sodium hypochlorite (NaClO) for oxidative degradation of methylene blue (MB). The effects of the dosage of iron nitrate in the preparation process and the catalyst dosage, effective chlorine concentration, pH, temperature, initial MB concentration, and coexisting ions on the MB removal effect in the oxidative degradation experiment were investigated. Then, the oxidative degradation mechanism and practical application prospects of the system were examined. Results showed that the Ni and Fe nitrate mass ratio of 5:1 was favorable for the dispersion of Ni elements in the catalyst preparation process. When the temperature was 45 °C, the initial concentration of MB was 50 mg/L, the dosage of Ni-Fe/Al2O3 was 20 g/L, the initial effective chlorine concentration was 1.76%, and the initial pH was 4.0. The removal rate of MB could reach 98.98% within 40 min, and the degradation process was in accordance with quasi primary kinetics, with reaction rate constant of 0.0873 min−1. The experimental result of free radical quenching and electron paramagnetic resonance indicated that the addition of Ni-Fe/Al2O3 induced the decomposition of NaClO to produce a large amount of singlet oxygen (1O2), 1O2 and HOCl worked together to oxidatively degrade MB. Ni3+/Ni2+ redox cycles play an important role in activating HOCl to produce active species. The common inorganic anions (Cl−, NO3−, and SO42−) did not inhibit the removal of MB significantly, whereas humic acid showed a more significant inhibitory effect only at concentrations greater than 20 mg/L. In the five recycling experiments, the catalysts showed low metal leaching rate and high MB removal rate. Ni-Fe/Al2O3 was reusable, and it showed excellent application potential.

Ferrate modified carbon felt as excellent heterogeneous electro-Fenton cathode for chloramphenicol degradation

In this study, a novel and efficient heterogeneous electro-Fenton (EF) process with a potassium ferrate (K2FeO4) modified carbon felt (Fe-CF) cathode was developed for chloramphenicol (CAP) removal. The catalytic activity was assessed by the comparison of different systems and the effects of multiple operating parameters (K2FeO4 dosage, initial solution pH, applied current) and co-existing constituents. Results indicated that the Fe-CF cathode exhibited excellent performance for CAP degradation (almost 100% removal efficiency within 60 min) over a wide range of pH (pH 3–9) during heterogeneous EF ascribed to the synergistic effect of embedded iron species and porous graphitic carbon structure and effective utilization of the in-situ generated H2O2. Moreover, the Fe-CF cathode possessed good recyclability with low metal leaching (98.2% CAP removal efficiency after reused for 5 times) and outstanding real water application performance. The ∙OH and O2∙− were responsible for CAP degradation, while ∙OH played a main role. Moreover, the toxicity evaluation by E. coli growth experiments demonstrated an efficient toxicity reduction in this system. Overall, a novel heterogeneous EF functional cathode with superior performance was fabricated via a green, low-cost one-step method, which shows promising application potential for actual wastewater treatment.

A novel multi-components hierarchical porous composite prepared from solid wastes for benzohydroxamic acid degradation

In this study, a novel carbon-wrapped-iron hierarchical porous catalyst (Fe/C-Mn800) was prepared from electrolytic manganese residue (EMR) and sewage sludge (SS), which showed outstanding degradation ability toward benzohydroxamic acid (BHA, nearly 90 % was removed within 60 min) with low metal leaching rate. Mechanism exploration found transition metal ions (Fe and Mn) can serve as electron acceptors and facilitate the generation of persistent free radicals (PFRs). These transition metal ions and PFRs mainly participated in the single-electron pathway via activating PMS to generate a large amount of reactive oxygen species (ROS). While the electron negative graphitic N and CO groups not only improve the electronegatively of catalyst, but also acted as the electron sacrificers to favor the electron transfer and directly oxidized the absorbed BHA through the ternary activated outer-sphere complexes. Eley–Rideal (E-R) and Langmuir–Hinshelwood (L-H) analysis further demonstrated the crucial role of pre-adsorption during the degradation process. This work provided a deep insight into the degradation mechanism of metal/carbon composite and promising opportunity widened the horizon of the high-value utilization of EMR and SS.

Peroxymonosulfate activation by Fe-N-S co-doped tremella-like carbocatalyst for degradation of bisphenol A: Synergistic effect of pyridine N, Fe-Nx, thiophene S

Bisphenol A (BPA) has received increasing attention due to its long-term industrial application and persistence in environmental pollution. Iron-based carbon catalyst activation of peroxymonosulfate (PMS) shows a good prospect for effective elimination of recalcitrant contaminants in water. Herein, considering the problem about the leaching of iron ions and the optimization of heteroatoms doping, the iron, nitrogen and sulfur co-doped tremella-like carbon catalyst (Fe-NS@C) was rationally designed using very little iron, S-C3N4 and low-cost chitosan (CS) via the impregnation-calcination method. The as-prepared Fe-NS@C exhibited excellent performance for complete removal of BPA (20 mg/L) by activating PMS with the high kinetic constant (1.492 min−1) in 15 min. Besides, the Fe-NS@C/PMS system not only possessed wide pH adaptation and high resistance to environmental interference, but also maintained an excellent degradation efficiency on different pollutants. Impressively, increased S-C3N4 doping amount modulated the contents of different N species in Fe-NS@C, and the catalytic activity of Fe-NS@C-1-x was visibly enhanced with increasing S-C3N4 contents, verifying pyridine N and Fe-Nx as main active sites in the system. Meanwhile, thiophene sulfur (C-S-C) as active sites played an auxiliary role. Furthermore, quenching experiment, EPR analysis and electrochemical test proved that surface-bound radicals (·OH and SO4⋅−) and non-radical pathways worked in the BPA degradation (the former played a dominant role). Finally, possible BPA degradation route were proposed. This work provided a promising way to synthesize the novel Fe, N and S co-doping carbon catalyst for degrading organic pollutants with low metal leaching and high catalytic ability.

Removal of bisphenol A (BPA) by fermented sludge-derived granular biochar from template-like method: From batch experiment to continuous operation

Endocrine disruptors have biological toxicity and can interfere with the endocrine system of organisms. They widely exist in natural water bodies. Here, the granular biochar was prepared from fermented sludge for the first time by using cationic polyacrylamide as template agent via a template-like method. The as prepared biochar was investigated for the removal of BPA in aqueous media by batch experiment and continuous flow experiment. The pyrolysis temperature and template concentration had a great influence on the properties of residual biochar and BPA capture. The static adsorption results show that when the template concentration was 1% with the pyrolysis temperature of 800 °C, the optimal biochar P-1%− 800 achieved the BPA adsorption value up to 84.78 mg/g. Its adsorption behavior, influencing factors, and recycling capability on BPA reduction were evaluated. Kinetics, isotherms and characterization analysis suggested that the adsorption mechanism involved pore filling, electrostatic attraction, π-π interactions and hydrogen bonding. Good regeneration performance, low concentration heavy metal leaching and lasting continuous flow stability in fixed-bed device under different water quality background demonstrated that fermented sludge-derived granular biochar P-1%− 800 is a desirable adsorbent for reducing BPA in complex water environment.

Production of water-permeable ceramic bricks derived from fly ash via a simple pellet method: Mechanism of mechanical strength and permeability

• Water-permeable ceramic bricks were prepared from fly ash via a simple pellet method. • The consumption of fly ash in the ceramic brick was up to 80 wt%. • Average pore size of water-permeable ceramic bricks reached 123.9 μm. • Anorthite phases generated at high temperature contributed to strength of bricks. • The water-permeable ceramic bricks had a low heavy metal leaching toxicity. Rising with the sponge city construction, water-permeable bricks as emerging materials, are receiving more and more attentions. It is a beneficial way to produce water-permeable bricks using industrial solid wastes as raw materials, which could not only eliminate the adverse effect of solid wastes, but also produce sustainable products. Herein, water-permeable ceramic bricks were produced by recycling fly ash as the main material with consumption up to 80 wt% via a simple pellet method. Fly ash was firstly mixed evenly with tailings at a mass ratio of 4:1 to adjust plasticity to prepare pellets. Pellets were then pressed under low forming pressure to obtain raw bricks, which were dried and sintered at high temperature to prepare water-permeable ceramic bricks. Effects of size and water content of pellets, forming pressure, and sintering temperature on the performance of water-permeable ceramic bricks were investigated. Under optimized conditions, ceramic bricks with compressive strength of 48.6 MPa, bending strength of 6.1 MPa and water permeability of 2.83 × 10 -2 cm/s were produced. Average pore size of optimized bricks reached 123.9 μm, which guaranteed excellent water permeability. The generated anorthite phases at high temperature contributed to the high mechanical strength of water-permeable bricks. The evaluation of heavy metal leaching toxicity indicated that the prepared bricks were environmentally-friendly. This study provides a strategy to produce water-permeable ceramic bricks derived from industrial solid wastes.

Efficient degradation of sulfacetamide by CoFe PBAs and PBA@PVDF composite membrane activating peroxymonosulfate

More and more antibiotics that are difficult to biodegrade have been detected in water environments threatening ecosystems and human health. Therefore, it is urgent to develop efficient water treatment methods to degrade antibiotics. In this work, Co-Fe Prussian blue analogues (PBAs) with different molar ratios were synthesized for peroxymonosulfate (PMS) activation to degrade sulfacetamide (SAM, 10 mg/L). By increasing Co molar ratio, the PMS activation capability and electrochemical properties of PBAs were enhanced. Due to its excellent reactivity (degradation efficiency of 84.2% and mineralization efficiency of 52.79%), cost benefit (electrical energy per order, 0.01019 kWh/L) and lower metal leaching ([Co] = 0.259 mg/L, [Fe] = 0.128 mg/L), PBA-1, the as-prepared catalyst with a molar ratio of cobalt to iron of 1:1, was selected for further study. The radical scavenging experiments and an electron paramagnetic resonance (EPR) trapping experiments were performed and revealed that PBA-1 addition was required to produced •OH and SO4•− from PMS activation. Accordingly, we proposed a PMS activation mechanism and SAM decomposition pathways for PBA-1/PMS reaction system. Besides, a PBA-1@polyvinylidene fluoride (PVDF) catalytic membrane was further prepared to expand the application potential of PBA nanoparticles. The PBA-1@PVDF catalytic membrane was highly effective and exhibited a great reusability; thus, it could be considered for applications in actual water treatment processes.

Fe-Cu@γ-Al2O3 microspheres as a heterogeneous Fenton-like catalyst for degrading polyvinyl alcohol, Rhodamine-B, and Reactive Red X-3B

In this study, to prepare a copper-iron bimetallic Fenton catalyst with low metal leaching and good recyclability, a heterogeneous Fenton-like catalyst, Fe-Cu@γ-Al2O3 microspheres-modified γ-Al2O3, was fabricated by a spray drying-calcination method. At a calcination temperature of 450 °C, a molar ratio of γ-Al2O3: Cu(NO3)2·3H2O: Fe3O4 of 0.98: 6.2: 8.6, pH 7, a catalyst dosage of 2.2 g/L, a reaction temperature of 70 °C, and a H2O2 dosage of 10.5 g/L, the Fe-Cu@γ-Al2O3 microspheres degraded 99.61 %, 99.91 %, and 99.94 % polyvinyl alcohol (PVA, 2.5 g/L), Rhodamine-B (200 μg/mL), and Reactive Red X-3B (200 μg/mL) within 210 s, respectively. The experimental results showed that an interactive effect between Cu and Fe atoms was responsible for the high catalytic activity. Furthermore, the Fe-Cu@γ-Al2O3 microspheres showed good reusability and stability after ten degradation cycles. This study demonstrates the potential of using Fe-Cu@γ-Al2O3 microspheres for the Fenton-like degradation of industrial wastewater.

Interface mechanism of peroxymonosulfate activation by cobalt-copper-ferrite nanoparticles mediated by palygorskite for bisphenol S degradation: A dual-path activation mechanism

Peroxymonosulfate (PMS)-based advanced oxidation processes are perceived as a novel strategy for water purification. However, designing an efficient catalyst with a low metal leaching rate remains challenging. Here, under palygorskite (PAL) mediation, 16%-CoCu0.4Fe1.6O4@PAL (16%-CCFO@PAL) was constructed, exhibiting ample oxygen vacancies (VO) and low metal leakage. The VO was confirmed by systematic characterizations and theoretical calculations. The catalyst showed the efficient catalytic capacity for PMS by dual-path (i.e., metal sites and VO) activation. Large amounts of SO4•-, •OH, and 1O2 were produced, greatly destroying bisphenol S (BPS). BPS removal was greater than 99% within 25 min in the 16%-CCFO@PAL/PMS system. At the metal sites, PMS was activated under the synergistic effects of Co(II)/Co(III), Fe(II)/Fe(III), and Cu(I)/Cu(II) pairs and electron transfer. In addition to metal sites, the VO was also an activation center for PMS, which mainly captured the OI atom in [H-OI-OII-SO3]-, donating an electron to OI and promoting SO4•- generation. The interfacial reaction mechanism was explored by in situ tests, and a dual-path activation mechanism was proposed. This work provides a new perspective for VO-assisted PMS activation for water treatment.

Enhanced photodegradation of tetracycline hydrochloride by hexameric AgBr/Zn-Al MMO S-scheme heterojunction photocatalysts: Low metal leaching, degradation mechanism and intermediates

A novel hexagonal AgBr/Zn-Al MMO S-scheme photocatalyst was prepared by adopting a simplified hydrothermal and co-precipitation method. The prepared photocatalytic system exhibited excellent photocatalytic performance in degradation of tetracycline hydrochloride (TC). In particular, the ABMO0.2/Vis system generated the best TC removal rate (95%) within 60 min of visible light irradiation. Moreover, no significant decrease of the photocatalytic performance had been observed after four cycles, while the leaching of silver ions was effectively controlled. The excellent photocatalytic performance can be attributed to the synergistic effect occurring between the unique morphological structure and the S-scheme heterojunction charge transfer mechanism, since that that synergistic effect enhanced light absorption capacity and separation efficiency of the photogenerated carriers and the redox ability. In addition, liquid chromatography-mass spectrometry (LC-MS) analysis clarified the mineralization behavior and detailed decomposition pathways of TC. This work opens a new pathway for the design of efficient S-scheme heterojunctions and provides new insights into the photocatalytic degradation mechanism of antibiotics.

Controlling oxygen vacancies of CoMn2O4 by loading on planar and tubular clay minerals and its application for boosted PMS activation

A representative transition metal oxide (TMO), CoMn2O4 (CMO), is recognized as an effective peroxymonosulfate (PMS) activator with disadvantages like limited reactive sites and metal leakage. Herein, novel catalysts were synthesized by anchoring CMO on kaolinite (Kln) and halloysite (Hal) matrixes, two natural clay minerals with lamellar and tubular structures, for PMS activation in pharmaceutical degradation. Hal and Kln helped to control the crystallinity of CMO spontaneously with induce oxygen vacancies (OVs), which significantly enhanced the working efficiency. The reaction rate constants of Hal/CMO and Kln/CMO towards OFX degradation were nearly triple and twice that of bare CMO, respectively, with a 60% decrease in metal usage. The formation of OVs provided additional active sites for the reaction and accelerated the electron transfer. CMO/Hal and CMO/Kln exhibited better stability and durability than CMO, while CMO/Kln showed higher structural stability with lower metal leaching after 3 rounds of reaction. The higher crystallinity of CMO/Kln resulted in less OVs, but higher structural stability. The universal applicability of CMO/Hal and CMO/Kln were verified by using three other pharmaceuticals as probes. This work shed light on the modification of TMO catalysts by introducing clay mineral substrates for the efficient and ecofriendly remediation of pharmaceuticals in wastewater.

Synergistic degradation of Methylene Blue by novel Fe-Co bimetallic catalyst supported on waste silica in photo-Fenton-like system

In this present study, a novel method to fabricate bimetallic Fe-Co catalyst supported on waste silica was investigated for the photo-Fenton-like (PFL) degradation of Methylene Blue (MB) dye. The uniqueness of this work is on the preparation of the catalyst via fluidized-bed crystallization (FBC) process. Under the optimum conditions of initial pH of 3.0, 3.0 mM of H2O2, and 1.0 g L-1 of FBC-derived Fe-Co/SiO2 catalyst (fFCS), the maximum response for the decoloration and mineralization efficiencies of 20 mg L-1 of MB in 60 min were 100 and 65%, respectively. Compared to the impregnated Fe-Co/SiO2 catalyst, the fFCS catalyst exhibited comparable decoloration and mineralization efficiencies, and relatively lower metal leaching for both iron and cobalt. Superoxide radical was unveiled to be the dominant reactive oxygen species in the PFL system over the fFCS catalyst. The catalysts were characterized by Fourier Transform Infrared spectroscopy, Energy Dispersive X-ray spectroscopy and Scanning Electron Microscopy. The results show the successful incorporation of iron and cobalt on the surface of the SiO2 support material.

Synthesis of Co-doped CeO2 nanoflower: Enhanced adsorption and degradation performance toward tetracycline in Fenton-like reaction

In Fenton-like reaction, adsorption and degradation are inseparable processes. The pollutants were enriched on the surface of catalyst by adsorption leading to the increase of the local concentration, and this was beneficial for acceleration of the degradation rate. Therefore, a catalyst with high adsorption capacity, low metal leaching and rapid activation rate toward peroxymonosulfate (PMS) was highly desirable. In this paper, Co-doped CeO2 (Co-CeO2) nanoflower was prepared via a solvothermal-calcination process. The nanoflower with a hierarchical porous structure was made up of dozens of nanosheets. Compared to CeO2, more Ce(Ⅲ) sites and defects were generated on Co-CeO2 surface, and the maximum adsorption capacity was increased by 1.92 times. Benefiting from the high activity of Co toward the activation of PMS, the degradation rate was enhanced 6.7 times. The major radicals were determined and the corresponding degradation mechanism was revealed. Additionally, Co-CeO2 nanoflower was demonstrated to be high efficient in many persistent organic pollutant degradation and also exhibited outstanding reusability after several cycles. Moreover, the leaching of toxic Co ions was 12 times lower than the referenced Co3O4. This work provides a promising approach on rational design a catalyst with high adsorption property and degradation efficiency in Fenton-like reaction for environmental remediation.