Heterogeneous sono-Fenton-like process using magnetic cobalt ferrite-reduced graphene oxide (CoFe2O4-rGO) nanocomposite for the removal of organic dyes from aqueous solution

Recent trends in magnetic spinel ferrites and their composites as heterogeneous Fenton-like catalysts: A review

In recent years, there has been a growing interest in utilizing spinel ferrite and their nanocomposites as Fenton-like catalysts. The use of these materials offers numerous advantages, including ability to efficiently degrade pollutants and potential for long-term and repeated use facilitated by their magnetic properties that make them easily recoverable. The remarkable catalytic properties, stability, and reusability of these materials make them highly attractive for researchers. This paper encompasses a comprehensive review of various aspects related to the Fenton process and the utilization of spinel ferrite and their composites in catalytic applications. Firstly, it provides an overview of the background, principles, mechanisms, and key parameters governing the Fenton reaction, along with the role of physical field assistance in enhancing the process. Secondly, it delves into the advantages and mechanisms of H2O2 activation induced by different spinel ferrite and their composites for the removal of organic pollutants, shedding light on their efficacy in environmental remediation. Thirdly, the paper explores the application of these materials in various Fenton-like processes, including Fenon-like, photo-Fenton-like, sono-Fenton-like, and electro-Fenton-like, for the effective removal of different types of contaminants. Furthermore, it addresses important considerations such as the toxicity, recovery, and reuse of these materials. Finally, the paper presents the challenges associated with H2O2 activation by these materials, along with proposed directions for future improvements.

Metronidazole degradation mechanism by sono-photo-Fenton processes using a spinel ferrite cobalt on activated carbon catalyst

A heterogeneous catalyst was prepared by anchoring spinel cobalt ferrite nanoparticles on porous activated carbon (SCF@AC). The catalyst was tested to activate hydrogen peroxide (HP) in the Fenton degradation of metronidazole (MTZ). SCF nanoparticles were produced through the co-precipitation of iron and cobalt metal salts in an alkaline condition. Elemental mapping, physico-chemical, morphological, structural, and magnetic properties of the as-fabricated catalyst were analyzed utilizing EDX mapping, FESEM-EDS, TEM, BET, XRD, and VSM techniques. The porous structure of AC enhanced the catalytic activity of SCF by a significant decrease in the agglomeration of SCF nanoparticles. The effectiveness of SCF@AC in Fenton degradation improved substantially when UV light and ultrasound (US) irradiations were induced, most likely due to the strong synergistic effect between the catalyst and these irradiation sources. The photo-Fenton system was more efficient than the Fenton, sono-, and sono-photo-Fenton processes eliminating both MTZ and TOC. It was found that AC not only dispersed SCF nanoparticles and improved the stability of the catalyst, but also provided a high adsorption capacity of MTZ, resulting in a faster degradation. After 60 min of the photo-Fenton reaction, the elimination efficiencies of MTZ (30 mg L-1) and TOC were 97 and 42.1% under optimum operational conditions (pH = 3.0, HP = 4.0 mM, SCF@AC = 0.3 g L-1, and UV = 6 W). SCF@AC showed excellent stability with low leaching of metal ions during the reaction. Radical and non-radical (O2•-, HO•, and 1O2 species), alongside adsorption and photocatalysis mechanisms, were responsible for MTZ decontamination over the SCF@AC/HP/UV system. A comprehensive study on the HP activation mechanism and MTZ degradation pathway was obtained through scavenging tests. The findings demonstrate that SCF@AC is an effective, reusable, and environmentally sustainable catalyst for advanced oxidation processes that can effectively remove organic pollutants from wastewater. This study offers valuable insights into the feasibility of employing SCF@AC catalysts in Fenton-based processes for the degradation of MTZ.

One-pot hydrothermal synthesis of FeNbO4 microspheres for effective sonocatalysis

FeNbO4 sonocatalysts were successfully synthesized by a simple hydrothermal route at pH values of 3, 5, 7, 9 and 11. The catalysts were characterized by XRD, XPS, TEM, SEM, N2 adsorption and DRS to analyse the effect of pH parameters on the physicochemical properties of the materials during hydrothermal synthesis. The sonocatalytic activity of FeNbO4 microspheres was evaluated by using acid orange 7 (AO7) as the simulated contaminant. The experimental results showed that the best sonocatalytic degradation ratio (97.45%) of organic dyes could be obtained under the conditions of an initial AO7 concentration of 10 mg L-1, an ultrasonic power of 200 W, a catalyst dosage of 1.0 g L-1, and a pH of 3. Moreover, the sonocatalysts demonstrated consistent durability and stability across multiple test cycles. After active species capture experiments and calculation of the energy band, a possible mechanism was proposed based on the special Fenton-like mechanism and the dissociation of H2O2. This research shows that FeNbO4 microspheres can be used as sonocatalysts for the purification of organic wastewater, which has a promising application prospect.

Enhanced degradation of Direct Red 80 dye via Fenton-like process mediated by cobalt ferrite: generated superoxide radicals and singlet oxygen

Azo dyes, widely used in the textile industry, contribute to effluents with significant organic content. Therefore, the aim of this work was to synthesize cobalt ferrite (CoFe2O4) using the combustion method and assess its efficacy in degrading the azo dye Direct Red 80 (DR80). TEM showed a spherical structure with an average size of 33 ± 12 nm. Selected area electron diffraction and XRD confirmed the presence of characteristic crystalline planes specific to CoFe2O4. The amount of Co and Fe metals were determined by ICP-OES, indicating an n(Fe)/n(Co) ratio of 2.02. FTIR exhibited distinct bands corresponding to Co-O (455 cm-1) and Fe-O (523 cm-1) bonds. Raman spectroscopy detected peaks associated with octahedral and tetrahedral sites. For the first time, the material was applied to degrade DR80 in an aqueous system, with the addition of persulfate. Consistently, within 60 min, these trials achieved nearly 100% removal of DR80, even after the material had undergone five cycles of reuse. The pseudo-second-order model was found to be the most fitting model for the experimental data (k2 = 0.07007 L mg-1 min-1). The results strongly suggest that degradation primarily occurred via superoxide radicals and singlet oxygen. Furthermore, the presence of UV light considerably accelerated the degradation process (k2 = 1.54093 L mg-1 min-1). The material was applied in a synthetic effluent containing various ions, and its performance consistently approached 100% in the photo-Fenton system. Finally, two degradation byproducts were identified through HPLC-MS/MS analysis.

Progress in layered double hydroxides (LDHs): Synthesis and application in adsorption, catalysis and photoreduction

Layered double hydroxides (LDHs), also known as anionic clays, have attracted significant attention in energy and environmental applications due to their exceptional physicochemical properties. These materials possess a unique structure with surface hydroxyl groups, tunable properties, and high stability, making them highly desirable. In this review, the synthesis and functionalization of LDHs have been explored including co-precipitation and hydrothermal methods. Furthermore, extensive research on LDH application in toxic pollutant removal has shown that modifying or functionalizing LDHs using materials such as activated carbon, polymers, and inorganics is crucial for achieving efficient pollutant adsorption, improved cyclic performance, as well as effective catalytic oxidation of organics and photoreduction. This study offers a comprehensive overview of the progress made in the field of LDHs and LDH-based composites for water and wastewater treatment. It critically discusses and explains both direct and indirect synthesis and modification techniques, highlighting their advantages and disadvantages. Additionally, this review critically discusses and explains the potential of LDH-based composites as absorbents. Importantly, it focuses on the capability of LDH and LDH-based composites in heterogeneous catalysis, including the Fenton reaction, Fenton-like reactions, photocatalysis, and photoreduction, for the removal of organic dyes, organic micropollutants, and heavy metals. The mechanisms involved in pollutant removal, such as adsorption, electrostatic interaction, complexation, and degradation, are thoroughly explained. Finally, this study outlines future research directions in the field.

Evaluation of synergistic approach of spinel cadmium-copper nanoferrites as magnetic catalysts for promoting wastewater decontamination: Impact of Ag ions doping

Metal substitution is an efficient strategy to improve the catalytic activity of ferrite-based catalysts. In this study, Cd0.5Cu0.5-xAgxFe2O4 (where 0 ≤ x ≤ 0.5) ferrites were fabricated via a simple co-precipitation method. The influence of the silver ions on the structural, magnetic, and catalytic characteristics of the spinel nanoparticles, as well as on their morphology, was examined. X-ray diffractograms revealed a crystalline cubic spinel structure with crystallite sizes in the nanoregime (7-15 nm). The saturation magnetization reduced from 29.8 to 2.80 emu as the Ag+ doping increased. Two prominent absorption bands were visible in Fourier-transform infrared spectra at 600 cm-1 and 400 cm-1, respectively, and they belonged to the tetrahedral (A) and octahedral (B) sites. The samples were then used as catalysts for the oxidative breakdown of the typical organic contaminant indigo carmine dye (IC). The catalytic process followed the first-order kinetic model, and the rate constant increased from 0.007 to 0.023 min-1 with increasing of Ag+ doping. Cd0.5Cu0.5-xAgxFe2O4 exhibited excellent catalytic performance in the pH range of 2-11, which means that they are promising efficient and stable materials for Fenton-based alkaline wastewater treatment. Finally, the pathway includes, HO•, HO2-•, and O2-• as oxidants resulted from the synergistic effects of Fe3+, Cu2+, and Ag+, with H2O2 and surface hydroxyl groups have been proposed.

Nanocomposites from spent coffee grounds and iron/zinc oxide: green synthesis, characterization, and application in textile wastewater treatment

This study reports on a novel composite of bimetallic FeO/ZnO nanoparticles supported by spent coffee grounds (SCGs). The leaves of eucalyptus (Eucalyptus globulus Labill) and trumpet (Cuphea aequipetala Cav), with their high antioxidant content, serve as bio-reductant agents for the green synthesis of nanoparticles. It was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Stable nanoparticles were produced with different diameters of 5-30 nm, and they were applied as catalysts in Fenton-like processes. Box-Behnken experimental design (BBD) was used to determine the optimal removal efficiency with three factors and was used in the degradation of textile dyes from wastewater. The nanocomposite displayed a high decolorization ratio (88%) of indigo carmine in the presence of H2O2 combined. This resulted in a reduction in chemical oxygen demand (COD) of 56% at 120 min of contact time at an initial pH of 3.0 and a 0.5 g/L of catalyst dose, a H2O2 concentration of 8.8 mM/L, an initial dye concentration of 100 mg/L, and a temperature of 25 °C.

Heterogeneous Sono-Fenton like catalytic degradation of metronidazole by Fe3O4@HZSM-5 magnetite nanocomposite

In this research, Fe₃O₄@HZSM-5 magnetic nanocomposite was synthesized via a coprecipitation method for metronidazole (MNZ) degradation from aqueous solutions under ultrasonic irradiation which showed superb sonocatalytic activity. The synthesized magnetite nanocomposite was characterized by using field-emission scanning electron microscope-energy dispersive X-ray Spectroscopy, (FESEM-EDS), Line Scan, Dot Mapping, X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET). To investigate the sonocatalytic activity of the Fe₃O₄@HZSM-5 magnetite nanocomposite, the sonocatalytic removal conditions were optimized by evaluating the influences of operating parameters like the dosage of catalyst, reaction time, pH, the concentration of H₂O₂, MNZ concentration, and pH on the MNZ removal. The MNZ maximum removal efficiency and TOC at reaction time 40 min, catalyst dose 0.4 g/L, H₂O₂ concentration 1 mM, MNZ initial concentration 25 mg/L, and pH 7 were achieved at 98% and 81%, respectively. Additionally, the MNZ removal efficiency in the real wastewater sample under optimal conditions was obtained at 83%. The achieved results showed that using Langmuir-Hinshelwood kinetic model K_L-H = 0.40 L mg^-1, K_C = 1.38 mg/L min) can describe the kinetic removal of the process. The radical scavenger tests indicated that the major reactive oxygen species were formed by hydroxyl radicals in the Sono-Fenton-like process. Evaluation of the nanocomposite reusability showed an 85% reduction in the MNZ removal efficiency after seven cycles. Based on the results, it can be concluded that Fe₃O₄@HZSM-5 were synthesized as magnetic heterogeneous nano-catalysts to effectively degrade MNZ, and the observed stability and recyclability demonstrated that Fe₃O₄@HZSM-5 was promising for the treatment of wastewater contaminated with antibiotics.

Direct Z-Scheme CoFe2O4-Loaded g-C3N4 Photocatalyst with High Degradation Efficiency of Methylene Blue under Visible-Light Irradiation

Magnetically recyclable direct Z-scheme CoFe2O4-loaded g-C3N4 photocatalyst material was fabricated using a facile hydrothermal technique and subsequently characterized by XRD, VSM, PL, FT-IR, EDX, DRS, SEM, and BET techniques. The characterization results confirmed that nanoparticles of CoFe2O4 are loaded on the surface of g-C3N4 sheets. The optical band gap of g-C3N4 has been decreased from 2.65 eV to 1.30 eV by means of the loading of CoFe2O4 nanoparticles onto the nanosheets of g-C3N4. This has enhanced the separation process of electron-hole. Under visible light irradiation, the photocatalytic activity of the developed direct Z-scheme CoFe2O4-loaded g-C3N4 photocatalyst was evaluated for the photodegradation of methylene blue (MB); during this process the MB decomposed by up to 98.86% in 140 min. Meanwhile, under the same irradiation and time conditions, the g-C3N4 and CoFe2O4 themselves degraded MB up to 74.92% and 51.53%, respectively. The direct Z-scheme CoFe2O4-loaded g-C3N4 material was recovered from the solution after the photocatalytic activity using an external magnet and studied to determine its stability. It was shown that the photoactivity did not change significantly after five consecutive cycles.

Advanced oxidation process: a sustainable technology for treating refractory organic compounds present in industrial wastewater

The world faces tremendous challenges and environmental crises due to the rising strength of wastewater. The conventional technologies fail to achieve the quality water that can be reused after treatment means "zero effluent" discharge of the industrial effluent. Therefore, now the key challenge is to develop improved technologies which will have no contribution to secondary pollution and at the same time more efficient for the socio-economic growth of the environment. Sustainable technologies are needed for wastewater treatment, reducing footprint by recycling, reusing, and recovering resources. Advanced oxidation process (AOP) is one of the sustainable emerging technologies for treating refractory organic contaminants present in different industrial wastewaters like textile, paper and pulp, pharmaceuticals, petrochemicals, and refineries. This critical review emerges details of advanced oxidation processes (AOPs), mentioning all possible permutations and combinations of components like ozone, UV, the catalyst used in the process. Non-conventional AOP systems, microwave, ultrasound, and plasma pulse assisted are the future of the oxidation process. This review aims to enlighten the role of AOPs for the mineralization of refractory organic contaminants (ROC) to readily biodegradable organics that cannot be either possible by conventional treatment. The integrated AOPs can improve the biodegradability of recalcitrant organic compounds and reduce the toxicity of wastewater, making them suitable for further biological treatment.

Peroxydisulfate-assisted sonocatalytic degradation of metribuzin by La-doped ZnFe layered double hydroxide

Metribuzin is an herbicide that easily contaminates ground and surface water. Herein, La-doped ZnFe layered double hydroxide (LDH) was synthesized for the first time and used for the degradation of metribuzin via ultrasonic (US) assisted peroxydisulfate (PDS) activation. The synthesized LDH had a lamellar structure, an average thickness of 26 nm, and showed mesoporous characteristics, including specific surface area 110.93 m2 g-1, pore volume 0.27 cm3 g-1, and pore diameter 9.67 nm. The degradation efficiency of the US/La-doped ZnFe LDH/PDS process (79.1 %) was much greater than those of the sole processes, and the synergy factor was calculated as 3.73. The impact of the reactive species on the sonocatalytic process was evaluated using different scavengers. After four consecutive cycles, 10.8 % loss occurred in the sonocatalytic activity of the La-doped LDH. Moreover, the efficiency of the US/La-doped LDH/PDS process was studied with respect to the degradation of metribuzin in a wastewater matrix. According to GC-MS analysis, six by-products were detected during the degradation of metribuzin. Our results indicate that the US/La-doped ZnFe LDH/PDS process has great potential for efficient degradation of metribuzin-contaminated water and wastewater.

Sustainable replacement of EDTA-Biojarosite for commercial iron in the Fenton's and UV-Fenton's degradation of Rhowedamine B - a process optimization using Box-Behnken method

Biojarosite as a replacement for commercial iron catalyst in the oxidative degradation of the dye Rhodamine B was confirmed and established. Investigations on the oxidative degradation by Fenton's oxidation and UV-Fenton's oxidation with EDTA at neutral pH were conducted and degradation of target compound was evaluated. UV-Fenton's oxidation was shown to be efficient over Fenton's oxidation in the degradation of Rhodamine B with removal efficiency of 90.0%. Design of Experiments was performed with Box-Behnken design. Investigation was conducted for the predicted values separately for both Fenton's oxidation and UV-Fenton's oxidation and the Rhodamine B removal was taken as response. Variable parameters biojarosite, H₂O₂ dosage and EDTA were optimized in the range of 0.1-1 g/L, 2.94-29.4 mM and 10-100 mM, respectively. A quadratic regression model is fitted for both Fenton's and UV-Fenton's oxidation. Analysis of variance (ANOVA) is performed and model fit is discussed.

Preparation of Ag3PO4/CoWO4 S-scheme heterojunction and study on sonocatalytic degradation of tetracycline

In this study, 0.6Ag3PO4/CoWO4 composites were synthesized by hydrothermal method. The prepared materials were systematically characterized by techniques of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption/desorption, and UV-vis diffuse reflectance spectrum (DRS). Furthermore, the sonocatalytic degradation performance of 0.6Ag3PO4/CoWO4 composites towards tetracycline (TC) was investigated under ultrasonic radiation. The results showed that, combined with potassium persulfate (K2S2O8), the 0.6Ag3PO4/CoWO4 composites achieved a high sonocatalytic degradation efficiency of 97.89 % within 10 min, which was much better than bare Ag3PO4 or CoWO4. By measuring the electrochemical properties, it was proposed that the degradation mechanism of 0.6Ag3PO4/CoWO4 is the formation of S-scheme heterojunction, which increases the separation efficiency of electron-hole pairs (e--h+) and generates more electrons and holes, thereby enhancing the degradation activity. The scavenger experiments confirmed that hole (h+) was the primary active substance in degrading TC, and free radicals (OH) and superoxide anion radical (O2-) were auxiliary active substances. The results indicated that 0.6Ag3PO4/CoWO4 nanocomposites could be used as an efficient and reliable sonocatalyst for wastewater treatment.

Sonocatalytic degradation of ciprofloxacin using hydrogel beads of TiO2 incorporated biochar and chitosan

Pharmaceuticals are necessary to be removed from environment. Herein TiO₂ incorporated biochar made from pyrolysis of agricultural wastes was encapsulated into chitosan to obtain a novel hydrogel beads. This hydrogel beads executed a dual role as both adsorbent and sonocatalyst, which proved to be suitable for the removal of antibiotic ciprofloxacin (CIP) from water. The results showed that adsorption of CIP followed pseudo first order kinetics model and Langmuir adsorption isotherm model, having maximum adsorption at pH 9. Whereas the degradation was more efficient at pH 6 due to greater standard potential for ^•OH/H₂O in acidic media. The degradation was maximum at 150 W of ultrasonic power, then decreased in presence of dissimilar electrolytes and even reduced to 0 in presence of Na₃PO₄. Different quenchers such as benzoquinone (BQ), Triethanolamine (TEA) and isopropyl alcohol (IPA) reduced degradation efficiency (DE) and mineralization efficiency (ME). The DE was decreased from 85.23% to 81.50% (BQ), 74.27% (TEA), and 61.77% (IPA) within 25 min. The prepared sonocatalyst was capable of regeneration with DE, remaining sufficiently high (62%) even after four regeneration steps. These results indicate that titanium-biochar/chitosan hydrogel beads (TBCB) are durable and effective for long-term CIP removal.

Oxalate regulate the redox cycle of iron in heterogeneous UV-Fenton system with Fe3O4 nanoparticles as catalyst: Critical role of homogeneous reaction

The redox cycle of iron is a well-known rate-determining step for hydroxyl radical generation in photo-Fenton system. In this study, oxalate was employed as regulator to enhance the degradation of Orange II in Fe₃O₄ magnetic nanoparticles (NPs)-catalyzed heterogeneous UV-Fenton system. Results showed that the oxalate could interact with the surface ≡Fe^III species of catalyst, which weakened the bond of ≡Fe^III-O and promoted the leaching of iron ions. Then the redox cycle of iron and generation of HO· would be accelerated via the homogeneous UV-Fenton reaction. The degradation rate constant of Orange II reached 0.220 min^-1 when additional oxalate concentration was 0.4 mM, which was 2.5 times as high as that without oxalate in heterogeneous UV-Fenton system. In this case, the removal efficiencies of color and TOC were 99.3% and 92.0% after 30 and 120 min treatment, respectively. In addition, based on the results of XRD and XPS characterization, it could be deduced that the crystal structure and elemental configuration of Fe₃O₄ magnetic nanoparticles could be maintained after reaction. Besides, the results of FTIR and magnetization characterization indicated that the C₂O₄^2- on surface of catalyst could be degraded and the catalyst could be easily separated from aqueous by applying an external magnetic field. The Fe₃O₄ magnetic nanoparticles showed high catalytic stability and reusability under the regulation of oxalate due to the fact that the leached iron ions could be re-adsorbed on the catalyst after treatment.

Effective mitigation of single-component and mixed textile dyes from aqueous media using recyclable graphene-based nanocomposite

The present study reported the synthesis and utilization of a graphene-based hybrid nanocomposite (MnFe₂O₄/G) to mitigate several synthetic dyes, including methylene blue, malachite green, crystal violet, and Rhodamine B. This adsorbent was structurally analyzed by several physicochemical techniques such as X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, N₂ adsorption-desorption isotherm measurement, point of zero charge, and Boehm titrations. BET surface area of MnFe₂O₄/G was measured at 382.98 m²/g, which was substantially higher than that of MnFe₂O₄. MnFe₂O₄/G possessed diverse surface chemistry properties with the presence of many functional groups such as carboxylic acid, phenolic, lactone, and basic groups. MnFe₂O₄/G was used to remove synthetic dyes in the aqueous media. The effect of many factors, e.g., concentration (5-50 mg/L), pH (4-10), dose (5-20 mg), and temperature (25-45 °C) on adsorption performance of MnFe₂O₄/G was conducted. Kinetic, isotherm, intraparticle, and thermodynamic models were adopted for investigating adsorption phenomenon of dyes on MnFe₂O₄/G. The maximum adsorption capacity of dyes over MnFe₂O₄/G was found as Rhodamine B (67.8 mg/g) < crystal violet (81.3 mg/g) < methylene blue (137.7 mg/g) < malachite green (394.5 mg/g). Some tests were performed to remove mixed dyes, and mixed dyes in the presence of antibiotics with total efficiencies of 65.8-87.9% after 120 min. Moreover, the major role of π-π stacking interaction was clarified to gain insight into the adsorption mechanism. MnFe₂O₄/G could recycle up to 4 cycles, which may be beneficial for further practical water treatment.

Coal fly ash supported CoFe2O4 nanocomposites: Synergetic Fenton-like and photocatalytic degradation of methylene blue

Rapid industrialization is causing a serious threat for the environment. Therefore, this research was aimed in developing ceramic cobalt ferrite (CoFe₂O₄) nanocomposite photocatalyst coated with coal fly ash (CFA-CoFe₂O₄) using facile hydrothermal synthesis route and their applications against methylene blue. The pristine cobalt ferrite photocatalyst was also prepared, characterized, and applied for efficiency comparison. Prepared photocatalyst were characterized by X-ray diffraction (XRD), fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). Optical response of catalysts was check using photoluminescence spectroscopy (PL). pH drift method was used for the surface charge characteristics of the material under acidic and basic conditions of solution pH. The photocatalytic degradation potential of all the materials were determined under ultra-violet irradiations. The influencing reaction parameters like pH, catalyst dose, oxidant dose, dye concentration, and irradiation time, were sequentially optimized to obtain best suited conditions. The 99% degradation of 10 ppm methylene blue was achieved within 60 min of reaction time under pH = 5 and 7, catalyst dose = 10 and 12 mg/100 mL, oxidant = 12 mM and 5 mM for cobalt ferrite and CFA-CoFe₂O₄ photocatalysts, respectively. Afterwards, the radical scavenging experiments were conducted to find out the effective radical scavengers (˙OH, h⁺, and e^-) in photocatalytic degradation process. The kinetic study of the process was done by applying 1st order, 2nd order, and BMG models. Statistical assessment of interaction effect among experimental variables was achieved using response surface methodology (RSM).

Recent progress on ultrasound-assisted electrochemical processes: A review on mechanism, reactor strategies, and applications for wastewater treatment

The electrochemical advanced oxidation processes (EAOPs) have received significant attention among the many other water and wastewater treatment technologies. However, achieving a desirable removal effect with a single technique is frequently difficult. Therefore, the integration of ultrasound technique with other processes such as electrocoagulation, electro-Fenton, and electrooxidation is a critical way to achieve effective organic pollutants decomposition from wastewater. This review paper is focused on ultrasound-assisted electrochemical (US/electrochemical) processes, so-called sonoelectrochemical processes of various organic pollutants. Emphasis was given to recently published articles for discussing the results and trends in this research area. The use of ultrasound and integration with electrochemical processes has a synergistic impact owing to the physical and chemical consequences of cavitation, resulting in enhancing the mineralization of organic pollutants. Various types of sonoelectrochemical reactors (batch and continuous) employed in the US/electrochemical processes were reviewed. In addition, the strategies to avoid passivation, enhanced generation of reactive oxygen species, and mixing effect are reviewed. Finally, concluding remarks and future perspectives on this research topic are also explored and recommended.

Zinc-chromium layered double hydroxides anchored on carbon nanotube and biochar for ultrasound-assisted photocatalysis of rifampicin

In this study, ZnCr layered double hydroxide (LDH), ZnCr LDH/carbon nanotube (CNT), and ZnCr LDH/Biochar (BC) were synthesized and characterized by various analyses. The successful synthesis and the great crystallinity of the samples were consented by XRD analysis. SEM and TEM were applied to study the morphology of the synthesized samples. The simultaneous presence of C, Zn, and Cr elements was well confirmed by EDX and dot mapping analyses demonstrating the successful preparation of nanocomposites. According to the BET analysis, ZnCr LDH nanocomposites with BC and CNT had more specific surface area compared to ZnCr LDH alone. The catalytic performances of the samples were determined for the degradation of rifampicin (RF). The degradation efficiency of the sonophotocatalytic process in the presence of 0.6 g L^-1 of ZnCr LDH/BC toward 15 mg L^-1 of RF under 150 W ultrasound and visible light irradiation was found to be about 100% within 40 min. The influence of the reactive species on the sonophotocatalytic process was assessed via the addition of different scavengers (para-benzoquinone (p-BQ), formic acid (FA), isopropyl alcohol (IPA)), and enhancers (hydrogen peroxide and potassium persulfate). The GC-MS analysis was carried out and eleven by-products during the RF decomposition were detected.

Magnetically recoverable nickel-palladium alloy nanocatalysts for direct C-H arylation reactions

Novel magnetically recoverable nanocatalyst comprising nickel-palladium (NiPd) alloy nanoparticles (NPs) supported on reduced graphene oxide (rGO) modified with cobalt ferrite (CoFe₂O₄) NPs was fabricated for the direct C-H arylation of imidazopyridine, imidazole, indolizine and furan with aryl halides. To prepare the presented catalyst, rGO nanosheets were first modified with as-synthesized CoFe₂O₄ NPs and then the obtained CoFe₂O₄-rGO nanocomposites served as a support material for the synthesis of bimetallic NiPd alloy NPs at various compositions. The obtained CoFe₂O₄-rGO/NiPd nanocatalysts were characterized by many advanced analytical techniques including TEM, STEM-EDS, XRD, XPS, and ICP-MS. Next, to optimize the reaction conditions, CoFe₂O₄-rGO/NiPd nanocatalysts with different alloy compositions and their monometallic counterparts (CoFe₂O₄-rGO/Ni and CoFe₂O₄-rGO/Pd) were initially tested in the direct C-H arylation of imidazopyridine with bromobenzene. Among all tested nanocatalysts under the optimum reaction conditions, CoFe₂O₄-rGO/Ni₂₀Pd₈₀ showed the best catalytic activity in terms of the isolated product yields. The C-H arylation reactions were studied over a broad substrate scope (35 examples from 36 substrates) and gave the related biaryl products in good to excellent yields. Besides a broad substrate scope, the late-stage C-H arylation of zolimidine, a gastroprotective drug, was realized under the optimized reaction conditions. Moreover, the CoFe₂O₄-rGO/Ni₂₀Pd₈₀ nanocatalysts were recovered from the reaction medium using a simple magnet and reused in the C-H arylation reactions up to five consecutive runs without a significant drop in the product yield. This study shows that magnetically recoverable Pd nanoalloys are promising heterogeneous catalysts to be used in sustainable C-H functionalization reactions.

Silver/silver halide supported on mesoporous ceria particles and photo-CWPO degradation under visible light for organic compounds in acrylonitrile wastewater

Silver/silver halide supported on ordered mesoporous ceria particles (Ag/AgCl/CeO2) were rapidly prepared by microwave-assisted soft template method, deposition precipitation method and photoreduction method, using cerium nitrate and silver nitrate as raw materials and block copolymer F127 as a template. The morphology, structure and chemical composition of the catalyst were characterized by XRD, SEM, EDS, TEM, N2 adsorption-desorption and UV-Vis Drs. Catalytic wet peroxide system assisted with visible light photocatalysis (photo-CWPO) was conducted to investigate the performance of organics degradation by Ag/AgCl/CeO2 as a catalyst in acrylonitrile wastewater. The results showed that the Ag/AgCl/CeO2 prepared has an ordered mesoporous structure, Ag and AgCl are formed on the surface of CeO2, with a specific surface area of 302.6-336.2 m2 g-1 and the average pore size is 8.04-8.90 nm. There is a strong absorption in the visible region and a band gap of 2.9 eV. The Ag/AgCl/CeO2 catalyst has higher catalytic performance in the photo-CWPO system than in the CWPO system alone. Ag loading, catalyst and H2O2 dosage, and pH value can affect the COD removal. When the concentration of COD in acrylonitrile wastewater was 500 mg L-1, the amount of catalyst was 200 mg, the amount of H2O2 (30%) was 8 mL, and the reaction time was 60 min, the COD removal reached 90%.

Sonochemical activation-assisted biosynthesis of Au/Fe3O4 nanoparticles and sonocatalytic degradation of methyl orange

In this research, a sonochemical activation-assisted biosynthesis of Au/Fe₃O₄ nanoparticles is proposed. The proposed synthesis methodology incorporates the use of Piper auritum (an endemic plant) as reducing agent and in a complementary way, an ultrasonication process to promote the synthesis of the plasmonic/magnetic nanoparticles (Au/Fe₃O₄). The synergic effect of the green and sonochemical synthesis favors the well-dispersion of precursor salts and the subsequent growth of the Au/Fe₃O₄ nanoparticles. The hybrid green/sonochemical process generates an economical, ecological and simplified alternative to synthesizing Au/Fe₃O₄ nanoparticles whit enhanced catalytic activity, pronounced magnetic properties. The morphological, chemical and structural characterization was carried out by high- resolution Scanning electron microscopy (HR-SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray diffraction (XRD), respectively. Ultraviolet-visible (UV-vis) and X-ray photoelectron (XPS) spectroscopy confirm the Au/Fe₃O₄ nanoparticles obtention. The magnetic properties were evaluated by a vibrating sample magnetometer (VSM). Superparamagnetic behavior, of the Au/ Fe₃O₄ nanoparticles was observed (M_s = 51 emu/g and H_c = 30 Oe at 300 K). Finally, the catalytic activity was evaluated by sonocatalytic degradation of methyl orange (MO). In this stage, it was possible to achieve a removal percentage of 91.2% at 15 min of the sonocatalytic process (160 W/42 kHz). The initial concentration of the MO was 20 mg L^-1, and the Fe3O4-Au dosage was 0.075 gL^-1. The MO degradation process was described mathematically by four kinetic adsorption models: Pseudo-first order model, Pseudo-second order model, Elovich and intraparticle diffusion model.

Bimetal CuFe Nanoparticles—Synthesis, Properties, and Applications

Bimetal CuFe (copper-iron) nanoparticles, which are based on the earth-abundant and inexpensive metals, have generated a great deal of interest in recent years. The possible modification of the chemical and physical properties of these nanoparticles by changing their size, structure, and composition has contributed to the development of material science. At the same time, the strong tendency of these elements to oxidize under atmospheric conditions makes the synthesis of pure bimetallic CuFe nanoparticles still a great challenge. This review reports on different synthetic approaches to bimetallic CuFe nanoparticles and bimetallic CuFe nanoparticles supported on various materials (active carbide, carbide nanotubes, silica, graphite, cellulose, mesoporous carbide), their structure, physical, and chemical properties, as well as their utility as catalysts, including electrocatalysis and photocatalysis.

A High-Efficient Carbon-Coated Iron-Based Fenton-Like Catalyst with Enhanced Cycle Stability and Regenerative Performance

Carbon coated iron-based Fenton-like catalysts are now widely studied in wastewater treatment. However, their poor stability is still a big challenge and the related regenerative performance is seldom investigated. Herein, a carbon-coated Fe3O4 on carbon cloth (cc/Fe3O4@C) was prepared with glucose as carbon source via electrodeposition and ethanol solvothermal methods. An amorphous carbon layer with polar C-groups covers the surface of Fe3O4, which presents a flaky cross-linked network structure on the carbon cloth (cc). The cc/Fe3O4@C exhibits an improved catalytic activity with nearly 84% phenol was removed within 35 min with polar C-groups. What’s more, around 80% phenol can still be degraded in 120 min after 14 degradation cycles. After the regeneration treatment, the degradation performance was restored to the level of the fresh in the first two regenerations. The enhanced cycle stability and regeneration performance of the catalyst are as follows: Firstly, the catalyst’s composition and structure were recovered; Secondly, the reduction effect of the amorphous carbon layer ensuring timely supplement of Fe2+ from Fe3+. Also, the carbon layer reduces Fe leaching during the Fenton-like process.

Degradation of Acid Red 73 by Activated Persulfate in a Heat/Fe3O4@AC System with Ultrasound Intensification

This work aimed to investigate the degradation efficiency of waste water with an azo dye, Acid Red 73 (AR73), by persulfate/heat/Fe₃O₄@AC/ultrasound (US). The introduction of ultrasound into the persulfate/heat/Fe₃O₄@AC system greatly enhanced the reaction rate because of the physical and chemical effects induced by cavitation. Various parameters such as temperature, initial pH, sodium persulfate dosage, catalyst dosage, initial concentration of AR73, ultrasonic frequency and power, and free-radical quenching agents were investigated. The optimal conditions were determined to be AR73 50 mg/L, PS 7.5 mmol/L, catalyst dosage 2 g/L, ultrasound frequency 80 kHz, acoustic density 5.4 W/L, temperature 50 °C, and pH not adjusted. Nearly, 100% decolorization was achieved within 10 min under optimal conditions. Different from some other similar research studies, the reaction did not follow a radical-dominating way but rather had ¹O₂ as the main reactive species. The recycling and reusability test confirmed the superiority of the prepared Fe₃O₄@AC catalyst. The research achieved a rapid decolorization method not only using waste heat of textile water as a persulfate activator but also applicable to a complex environment where common radical scavengers such as ethanol exist.

Use mechanochemical activation to enhance interfacial contaminant removal: A review of recent developments and mainstream techniques

Interfacial processes, including adsorption and catalysis, play crucial roles in environmental contaminant removal. Mechanochemical activation (MCA) emerges as a competitive method to improve the performance of adsorbents and catalysts. The development and application of MCA in the last decades are thereby systematically reviewed, particularly highlighting its contribution to interfacial process modulation. Two typical apparatuses for MCA are ball milling (BaM) and bead milling (BeM). Compared to BaM, BeM is able to yield a much higher MCA intensity, because it could pulverize bulk solid particles to nearly 100 nm. Since MCA intensity on the adsorbents and catalysts is directly responsible for the contaminant removal afterwards, quantitative and qualitative determination methods for valid MCA intensity are introduced. MCA benefits both the adsorption kinetics and capacity of powdered activated carbon by increasing the specific surface area. Carbon oxidation should be given an additional attention, but potentially favors the adsorption of heavy metals. MCA favors the catalyst performance by providing abundant surface functional group and increasing the free energy in the near-surface region. Finally, the future research needs are identified.

Ultrasonically Induced Sulfur-Doped Carbon Nitride/Cobalt Ferrite Nanocomposite for Efficient Sonocatalytic Removal of Organic Dyes

The sulfur-doped carbon nitride/cobalt ferrite nanocomposite (SCN/CoFe2O4) was prepared via ultrasonication and studied for the sonocatalytic degradation of wastewater organic dye pollutants including methylene blue, rhodamine B, and Congo red. The X-ray photoelectron spectroscopy confirmed the presence and atomic ratios of S, C, N, Co, Fe, and O elements and their corresponding bonds with Co2+ and Fe3+ cations. The nanocomposite was found to have aggregated nanoparticles on a sheet-like structure. The bandgap energy was estimated to be 1.85 eV. For the sonocatalytic degradation of 25-ppm methylene blue at 20 kHz, 1 W and 50% amplitude, the best operating condition was determined to be 1 g/L of catalyst dosage and 4 vol % of hydrogen peroxide loading. Under this condition, the sonocatalytic removal efficiency was the highest at 96% within a reaction period of 20 min. SCN/CoFe2O4 outperformed SCN and CoFe2O4 by 2.2 and 6.8 times, respectively. The SCN/CoFe2O4 nanocomposite was also found to have good reusability with a drop of only 7% after the fifth cycle. However, the degradation efficiencies were low when tested with rhodamine B and Congo red due to difference in dye sizes, structural compositions, and electric charges.

Facile hydrothermal synthesis of novel Fe-Cu layered double hydroxide/biochar nanocomposite with enhanced sonocatalytic activity for degradation of cefazolin sodium

This study reports the successful synthesis of Fe-Cu layered double hydroxide (Fe-Cu-LDH) /biochar (BC) nanocomposite by a hydrothermal method. The sonocatalytic performance of Fe-Cu-LDH/BC nanocomposite was investigated for the degradation of cefazolin sodium (CFZ), as a model emerging contaminant, from the solution. The physico-chemical properties of the synthesized samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), and UV-Vis diffuse reflectance spectroscopy (DRS) analyses. The best sonocatalytic efficiency of 97.6% was achieved by using 1.0 g/L sonocatalyst, 0.1 mM CFZ, and an ultrasonic power of 300 W at pH = 6.5 (natural) within 80 min. Additionally, the effects of the addition of various oxidants, dissolved gases, and organic and inorganic scavengers on the degradation of CFZ were studied. Moreover, the possible sonocatalytic mechanism of the sonochemical degradation of CFZ in the presence of Fe-Cu-LDH/BC sonocatalyst was proposed based on the results of GC-MS analysis. The mineralization of CFZ solution was evaluated using COD and IC analyses. Finally, the reusability test of Fe-Cu-LDH/BC nanocomposite in the CFZ degradation revealed that almost 9% drop occurred after five successive cycles.

A High-Efficiency CuO/CeO2 Catalyst for Diclofenac Degradation in Fenton-Like System

An efficient Fenton-like catalyst CuO/CeO₂ was synthesized using ultrasonic impregnation and used to remove diclofenac from water. The catalyst was characterized by N₂ adsorption-desorption, SEM-EDS, XRD, HRTEM, Raman, and XPS analyses. Results showed that CuO/CeO₂ possessed large surface area, high porosity, and fine elements dispersion. Cu was loaded in CeO₂, which increased the oxygen vacancies. The exposed crystal face of CeO₂ (200) was beneficial to the catalytic activity. The diclofenac removal experiment showed that there was a synergistic effect between CuO and CeO₂, which might be caused by more oxygen vacancies generation and electronic interactions between Cu and Ce species. The experimental conditions were optimized, including pH, catalyst and H₂O₂ dosages, and 86.62% diclofenac removal was achieved. Diclofenac oxidation by ·OH and adsorbed oxygen species was the main mechanism for its removal in this Fenton-like system.

Stone cutting industry waste-supported zinc oxide nanostructures for ultrasonic assisted decomposition of an anti-inflammatory non-steroidal pharmaceutical compound

Powdered stone waste (PSW) obtained from a stone cutting industrial unit was applied as support for the immobilization of nano-sized ZnO to be utilized as an effective catalyst for the catalytic conversion of acetaminophen (ACE) under ultrasonication. The incorporation of ZnO nanostructures into PSW structure enhanced the specific surface area and pore volume of the as-prepared nanocompound. The change in the value of zero point of charge (pH_zpc) of the PSW after being covered also demonstrated the good immobilization and distribution of ZnO nanostructures on the surface of PSW. The sonocatalysis of ACE over ZnO/PSW followed pseudo-first order kinetic (reaction rate of 2.27 × 10^-2 1/min). The highest degradation efficiency of 98.1% was attained when the ZnO/PSW-contained sono-reactor was irradiated by UVC light. The presence of t-butanol led to the lowest degradation efficiency (57.7%), indicating that the sonocatalytic conversion of ACE was hydroxyl radical (OH)-dependent. Although the mineralization efficiency of ACE by the process was not excellent, bio-toxicity assessment on the effluent revealed decreasing the inhibition percent from 50.8 to 16.7% within reaction time of 240 min.

Heterogeneous sonocatalytic degradation of an anionic dye in aqueous solution using a magnetic lanthanum dioxide carbonate-doped zinc ferrite-reduced graphene oxide nanostructure

We report herein the sonochemical synthesis of a lanthanum dioxide carbonate (La₂O₂CO₃) and zinc ferrite (ZnFe₂O₄)-loaded reduced graphene oxide (LZF-rGO) nanoheterostructure for ultrasound (US)-assisted degradation of methyl orange (MO) from water. The MO was chosen as a model organic dye due to its toxicological and biodegradable-resistant properties. The LZF-rGO catalyst was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results of characterizations confirmed successful synthesis of sonocatalyst. Among different removal systems, US/LZF-rGO displayed outstanding sonodegradation performance for degradation of MO. The maximum removal efficiency of 75.9% was achieved using 0.2 g/L sonocatalyst, 20 mg/L MO, and 0.71 W/cm² US power intensity for 65 min. MO can be partially adsorbed on LZF-rGO but mostly sonodegraded by reactive radical species. The reaction conditions were optimized by investigating the effect of key operating parameters, including the sonocatalyst dosage, initial MO concentration, US power intensity, presence of inorganic salts, and use of an enhancer, on the decolorization of MO. The degradation intermediates produced from MO during the sonocatalytic process were identified by UPLC^®/MS-MS, and possible mechanism and pathway for the degradation of MO in the US/LZF-rGO system were also proposed. Reusability experiments with this sonocatalyst revealed a less than 10% drop in the degradation efficiency after four adsorption-desorption cycles.

Biosynthesized silver nanoparticles using Bacillus amyloliquefaciens; Application for cytotoxicity effect on A549 cell line and photocatalytic degradation of p-nitrophenol

The present study reports the biosynthesis of silver nanoparticles (AgNPs) using Bacillus amyloliquefaciens MSR5. The cellfree supernatant of B. amyloliquefaciens acted as a stabilizing agent for the synthesis of AgNPs. The synthesized AgNPs were characterized using UV-vis spectrophotometer, PXRD, FTIR, SEM-EDX, DLS, and TEM. TEM image showed the spherical shape of the biosynthesized AgNPs and it was found to be 20-40 nm in range. In this study, the AgNPs were prepared by ultrasonic irradiation. The stability of the AgNPs was found to be -33.4 mV using zeta potential. The catalytic 4-nitrophenol (4-NP) degradation by AgNPs was examined under solar irradiation and furthermore, the effects of several degradation parameters were studied. The biosynthesized AgNPs exhibited a strong chemocatalytic action with a comprehensive degradation (98%) of 4-NP to 4-aminophenol (4-AP) using NaBH₄ within 15 min. In addition, MTT assay was performed to evaluate the cytotoxicity of the biosynthesized AgNPs (10 - 200 μg). The results have shown that the AgNPs exhibited significant activity on A549 cells, which was dosedependent. The study elucidates the AgNPs synthesized using cellfree culture supernatant can be used for the elimination of hazardous pollutants from wastewater.

Modeling azo dye removal by sono-fenton processes using response surface methodology and artificial neural network approaches

Textile industry wastewaters, which cause serious problems in the environment and human health, include synthetic dyes, complex organic pollutants, surfactants, and other toxic chemicals and therefore must be removed by advanced treatment methods. Determination of appropriate treatment conditions for efficient use of advanced treatment methods is an important and necessary step. In the last thirty years, the Artificial Neural Network-Genetic Algorithm (ANN-GA) and Response Surface Methodology (RSM) have emerged as the most effective empirical modeling and optimization methods especially for nonlinear systems. Reactive Red 195 azo dyestuff was chosen as the target pollutant. The color removal efficiency was modeled and optimized as a function of Sono-Fenton conditions such as H₂O₂ dosage, Fe²⁺ dosage, initial pH value, ultrasound power, and ultrasound frequency, using ANN-GA and RSM. The generalization and predictive ability of these methods were compared using the results of the 46 experimental sets generated by the Box-Behnken design. The mean square errors for these models are 3.01612 and 0.00295, and the regression coefficients showing the superiority of ANN in determining nonlinear behavior are 0.9856 and 0.9164, respectively. In optimal conditions, the prediction errors with hybrid ANN-GA and RSM models are 0.002% and 3.225%, respectively.

Hazardous waste treatment technologies

This is a review of the literature published in 2018 on topics related to hazardous waste management in water, soils, sediments, and air. The review covers treatment technologies applying physical, chemical, and biological principles for contaminated water, soils, sediments, and air. PRACTITIONER POINTS: The management of waters, wastewaters, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) was reviewed according to the technology applied, namely, physical, chemical and biological methods. Physical methods for the management of hazardous wastes including adsorption, coagulation (conventional and electrochemical), sand filtration, electrosorption (or CDI), electrodialysis, electrokinetics, membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, persulfate-based, Fenton and Fenton-like, and potassium permanganate processes for the management of hazardous were reviewed. Biological methods such as aerobic, anaerobic, bioreactor, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed.

Ultrasound-assisted heterogeneous Fenton-like process for bisphenol A removal at neutral pH using hierarchically structured manganese dioxide/biochar nanocomposites as catalysts

Bisphenol A (BPA) is an important emerging contaminant with endocrine-disrupting potential that has frequently been detected in aquatic environments. In this study, two types of hierarchically structured manganese dioxide/biochar nanocomposites (MnO₂/BCs) were prepared for the first time via facile hydrothermal synthesis. The hydrothermal reaction was maintained at 100 °C for 6 h or 12 h, after which an ultrasound-assisted heterogeneous Fenton-like process was used to catalyze the removal of BPA under neutral pH condition. The characterization results indicated that MnO₂ nanoparticles were successfully formed on the nanocomposite surfaces and had flower-like (δ-MnO₂, 6 h) and urchin-like (α-MnO₂, 12 h) morphology. This enabled a significant improvement in the catalytic activity of BPA removal by the reversible redox reaction. A series of experiments confirmed that the crystalline properties of the nanocomposites affected their catalytic activity. In particular, the α-MnO₂/BCs exhibited catalytic activity in the ultrasound-assisted heterogeneous Fenton-like process and completely removed BPA within 20 min under the following conditions: [BPA]₀ = 100 μM; [H₂O₂]₀ = 10 mM; [catalyst]₀ = 0.5 g/L; ultrasound = 20 kHz (130 W) at 40% amplitude; pH = 7.0 ± 0.1; and temperature = 25 ± 1 °C. This efficiency may have been due to the synergistic effect of ultrasound and α-MnO₂/BCs, which simultaneously induce the effective generation of reactive free radicals and increase the mass transfer rate at the solid-liquid interface. Overall, these results demonstrated that hierarchical urchin-like α-MnO₂/BCs have significant potential as an efficient and low-cost catalyst in ultrasound-assisted heterogeneous Fenton-like systems.

Ultrasound assisted zero valent iron corrosion for peroxymonosulfate activation for Rhodamine-B degradation

In this work, ultrasound (US) irradiation assisted powder zero valent iron (ZVI) corrosion was conducted for peroxymonosulfate (PMS) activation. PMS activation activity was evaluated by Rhodamine-B (Rh B) degradation efficiency. The other US/PMS, ZVI/PMS, Fe²⁺/PMS and US/PMS/Fe²⁺ systems were performed to investigate the synergistic effects of US and ZVI on PMS activation activity. US/PMS/ZVI system performed the highest activity of Rh B degradation. 99.76% of Rh B was removed within 12 min under the optimum condition (pH = 4.5, ZVI dosage = 1 g/L, PMS = 1 mM, US power = 50 W). A comparison of US/PMS/ZVI system with PMS/ZVI and homogeneous US/PMS/Fe²⁺ systems for Rh B degradation was conducted, indicating that ultrasound irradiation contributed to acceleration of ZVI corrosion and removal of passive films. Besides, the electrons transformation from Fe⁰ to PMS made main contribution to the generation of sulfate radical, which resulted in the ability of degradation of Rh B. ZVI could be reused for five cycles with efficient activity of PMS activation. Exhaustion of ZVI led to the decrease in PMS activation at the sixth recycle. Thus, this work presents important information on understanding reuse of iron fillings for PMS/PS activation in practical application of pollution remediation.