Ultrasound-Assisted Catalytic Degradation of Methyl Orange with Fe3O4/Polyaniline in Near Neutral Solution

Enhancing acid orange II degradation in ozonation processes with CaFe2O4 nanoparticles as a heterogeneous catalyst

This study used CaFe2O4 nanoparticles as a catalyst for ozonation processes to degrade Acid Orange II (AOII) in aqueous solution. The study compared heterogeneous catalytic ozonation (CaFe2O4/O3) with ozone treatment alone (O3) at different pH values (3-11), catalyst dosages (0.25-2.0 g L-1), and initial AOII concentrations (100-500 mg L-1). The O3 alone and CaFe2O4/O3 systems nearly completely removed AOII's color. In the first 5 min, O3 alone had a color removal efficiency of 75.66%, rising to 92% in 10 min, whereas the CaFe2O4/O3 system had 81.49%, 94%, and 98% after 5, 10, and 20 min, respectively. The O3 and CaFe2O4/O3 systems degrade TOC most efficiently at pH 9 and better with 1.0 g per L CaFe2O4. TOC removal effectiveness reduced from 85% to 62% when the initial AOII concentration increased from 100 to 500 mg L-1. The study of degradation kinetics reveals a pseudo-first-order reaction mechanism significantly as the solution pH increased from 3 to 9. Compared to the O3 alone system, the CaFe2O4/O3 system has higher k values. At pH 9, the k value for the CaFe2O4/O3 system is 1.83 times higher than that of the O3 alone system. Moreover, increasing AOII concentration from 100 mg L-1 to 500 mg L-1 subsequently caused a decline in the k values. The experimental data match pseudo-first-order kinetics, as shown by R2 values of 0.95-0.99. AOII degradation involves absorption, ozone activation, and reactive species production based on the existence of CaO and FeO in the CaFe2O4 nanocatalyst. This catalyst can be effectively recycled multiple times.

Plant-Mediated Green Synthesis of Ag NPs and Their Possible Applications: A Critical Review

The potential applications of Ag NPs are exciting and beneficial in a variety of fields; however, there is less awareness of the new risks posed by inappropriate disposal of Ag NPs. The Ag NPs have medicinal, plasmonic, and catalytic properties. The Ag NPs can be prepared via physical, chemical, or biological routes, and the selection of any specific route depends largely on the end-use. The downside of a physical and chemical approach is that it requires a wide space, high temperature, high temperature for a longer time to preserve the thermal stability of synthesized Ag NPs, and the use of toxic chemicals. Although these methods produce nanoparticles with high purity and well-defined morphology, it is critical to develop cost-effective, energy-efficient, and facile route, such as green synthesis; it suggests the desirable use of renewable resources by avoiding the use of additional solvents and toxic reagents in order to achieve the ultimate goal. However, each method has its pros and cons. The synthesized Ag NPs obtained using the green approach have larger biocompatibility and are less toxic towards the biotic systems. However, identifying the phytoconstituents that are responsible for nanoparticle synthesis is difficult and has been reported as a suitable candidate for biological application. The concentration of the effective bioreducing phytoconstituents plays a crucial role in deciding the morphology of the nanoparticle. Besides these reaction times, temperature, pH, and concentration of silver salt are some of the key factors that determine the morphology. Hence, careful optimization in the methodology is required as different morphologies have different properties and usage. It is due to which the development of methods to prepare nanoparticles effectively using various plant extracts is gaining rapid momentum in recent days. To make sense of what involves in the bioreduction of silver salt and to isolate the secondary metabolites from plants are yet challenging. This review focuses on the contribution of plant-mediated Ag NPs in different applications and their toxicity in the aquatic system.

Fe/N-doped carbon magnetic nanocubes toward highly efficient selective decolorization of organic dyes under ultrasonic irradiation

Fe/N-doped carbon magnetic nanocubes (Fe/N-C MNCs) were feasibly fabricated through in situ thermal transformations of Prussian blue nanocubes (PB NCs) in an inert atmosphere, and the resultant composite employed as the heterogeneous noble-metal-free catalyst possessed satisfactory catalytic performance in hydrogen peroxide activation. By examining the properties of Fe/N-C MNCs, we demonstrate for the first time that the catalyst could act in synergy with ultrasonic irradiation and accelerate the selectivity of the degradation reaction of dyes. The degradation efficiency of the organic positively charged dye (methylene blue) is significantly increased after ultrasonic irradiation addition, probably owing to charge matching between a positively charged dye and the Fe/N-C MNCs. Interestingly, organic pollution degradation mainly follows a non-radical pathway. Furthermore, singlet oxygen (¹O₂) is predominantly produced by Fe/N-C MNCs on H₂O₂ activation, and it is the contributor to catalytic degradation instead of hydroxyl and/or superoxide anion radicals. Moreover, the Fe/N-C MNCs exhibit excellent stability and reusability. These findings offer interesting insights into the potential application of functional noble-metal-free materials in catalysis and wastewater remediation under ultrasonic radiation.

A strategy of heterogeneous polyurethane-based sponge for water purification: Combination of superhydrophobicity and photocatalysis to conduct oil/water separation and dyes degradation

The diffusion of stubborn oils and organic pigments has become a severe environmental pollution problem. Promisingly, the combination of superhydrophobicity and photocatalysis is expected to provide an efficient, economical and simple solution. In this paper, a kind of superhydrophobic and super-lipophilicity polyurethane (PU)-based sponge was reported by a strategy of undergoing ferric tetroxide loading (Fe₃O₄@PU), polydopamine fixation (PDA-Fe₃O₄@PU), octadecylamine grafting (ODA-Fe₃O₄@PU) and molybdenum disulfide loading (MoS₂-ODA-Fe₃O₄@PU) successively. The results show that the MoS₂-ODA-Fe₃O₄@PU sponge exhibits outstanding superhydrophobicity (with maximum water contact angle of 161.64°), excellent oil absorption capacity (60-109 wt/wt), robust stability in extreme environments and great oil/water separation ability. In addition, the MoS₂-loaded sponge demonstrates desirable outcomes in decomposing methyl orange and methylene blue under light source, and a dual-functional purification system with a heterogeneous polyurethane-based sponge (the upper part is MoS₂-ODA-Fe₃O₄@PU and the bottom part is MoS₂@PU) endowed with superhydrophobicity and photocatalysis can purify water by separating oils and decomposing methylene blue simultaneously.

Harvesting the vibration energy of α-MnO2 nanostructures for complete catalytic oxidation of carcinogenic airborne formaldehyde at ambient temperature

Vibration is one of the most prevalent energy sources in natural environment, which can also be harvested and utilized to drive chemical reaction. Herein, mechanical vibration is used for enhancing the catalytic decomposition of formaldehyde at ambient temperature with the assistance of four well-defined morphologies α-MnO₂ (nanowire, nanotube, nanorod and nanoflower). In particular, α-MnO₂ nanowire exhibits the best catalytic activity, which can completely mineralize formaldehyde into carbon dioxide at ambient temperature by harvesting the vibration energy. To the best of our knowledge, this may be the first report that α-MnO₂, as a non-noble metal catalyst, can completely decompose formaldehyde to carbon dioxide at ambient temperature. The characterization results show that α-MnO₂ nanowire has a much higher oxygen vacancy concentration than other three catalysts. In addition, thermal effect generated from friction between nanoparticles induced by ultrasonic vibration may enhance its catalytic activity. More importantly, it is the vibration that effectively promotes the activation of O₂ adsorbed on the surface oxygen vacancy to produce more , thus increasing the catalytic decomposition performance. The strategy presented herein demonstrates a new approach for efficient use of mechanical vibration to improve catalytic activity of traditional catalysts.

Fast and Efficient Piezo/Photocatalytic Removal of Methyl Orange Using SbSI Nanowires

Piezocatalysis is a novel method that can be applied for degradation of organic pollutants in wastewater. In this paper, ferroelectric nanowires of antimony sulfoiodide (SbSI) have been fabricated using a sonochemical method. Methyl orange (MO) was chosen as a typical pollutant, as it is widely used as a dye in industry. An aqueous solution of MO at a concentration of 30 mg/L containing SbSI nanowires (6 g/L) was subjected to ultrasonic vibration. High degradation efficiency of 99.5% was achieved after an extremely short period of ultrasonic irradiation (40 s). The large reaction rate constant of 0.126(8) s^-1 was determined for piezocatalytic MO decomposition. This rate constant is two orders of magnitude larger than values of reaction rate constants reported in the literature for the most efficient piezocatalysts. These promising experimental results have proved a great potential of SbSI nanowires for their application in environmental purification and renewable energy conversion.

Heterogeneous Fenton-like degradation of EDTA in an aqueous solution with enhanced COD removal under neutral pH

By providing the key carbon and nitrogen elements needed for eutrophication, the potential toxicity of ethylenediaminetetraacetic acid (EDTA) prompts the exploration of effective treatment methods to minimize the amount of EDTA released into the environment. In this study, Fe₃O₄ magnetic nanoparticles (MNPs) were prepared and used as catalysts to study the mineralization of EDTA in Fenton-like reactions under neutral pH. Fe₃O₄ MNPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET). The effects of pH, ferric ion leaching, and H₂O₂ concentration on chemical oxygen demand (COD) removal of EDTA were investigated. The morphological characterization of the nanoparticles suggests a quasi-spherical structure with small particle size and a surface area of 49.9 m²/g. The results show that Fe₃O₄ MNPs had good catalytic activity for the mineralization of EDTA under pH 5.0-9.0. The optimum conditions for the COD removal of 45% at pH 7.0 were: 40 mM H₂O₂, 10 mM Fe₃O₄, and 1 g/L EDTANa₂·2H₂O at 303 K. Fe₃O₄ MNPs maintained high catalytic activity after five cycles of continuous degradation of EDTA. According to reactive oxidizing species measurements obtained by electron spin resonance (ESR), it was confirmed that HO· free radicals, presented in the H₂O₂/Fe₃O₄ MNPs heterogeneous Fenton-like reaction, were the primary active group in the removal of EDTA. These features can be considered beneficial to the application of Fe₃O₄ MNPs towards industrial wastewater treatment.

MIL-101(Cr)–cobalt ferrite magnetic nanocomposite: synthesis, characterization and applications for the sonocatalytic degradation of organic dye pollutants

In this study, for the first time, a novel magnetically recyclable MIL-101(Cr)/CoFe₂O₄ nanocomposite was prepared via a facile solvothermal method. The morphology, structural, magnetic and optical properties of the nanocomposite were characterized via field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), UV-visible spectroscopy (UV-visible) and BET surface area analysis. Furthermore, the sonocatalytic activity of the MIL-101(Cr)-based magnetic nanocomposite was explored for the degradation of organic dye pollutants such as Rhodamine B (RhB) and methyl orange (MO) under ultrasound irradiation in the presence of H₂O₂. Under optimized conditions, the degradation efficiency reached 96% for RhB and 88% for MO. The sonocatalytic activity of MIL-101(Cr)/CoFe₂O₄ was almost 12 and 4 times higher than that of the raw MIL-101(Cr) and pure CoFe₂O₄, respectively. The improved sonocatalytic performance of the as-prepared binary nanocomposite can be attributed to the relatively high specific surface area of MIL-101(Cr) and magnetic property of CoFe₂O₄, as well as the fast generation and separation of charge carriers (electrons and holes) in MIL-101(Cr) and CoFe₂O₄. In addition, the trapping tests demonstrated that ·OH radicals are the main active species in the dye degradation process. Moreover, the most influencing factors on the sonocatalytic activity such as the H₂O₂ amount, initial dye concentration and catalyst dosage were investigated. Finally, the nanocomposite was magnetically separated and reused without any observable change in its structure and performance even after four consecutive runs.

A magnetically separable MIL-101(Cr)/CoFe₂O₄ binary nanocomposite was prepared via a hydrothermal route and applied as a sonocatalyst for the efficient degradation of organic dyes.

A facile SERS strategy for quantitative analysis of trace glucose coupling glucose oxidase and nanosilver catalytic oxidation of tetramethylbenzidine

Highly stable, SERS active and catalytic nanosilver sol (AgNP) was synthesized under the exposure of light wave, using AgNO₃ as precursor and sodium citrate as reducer. Under the conditions of pH 7.0 NaH₂PO₄-Na₂HPO₄ buffer solution (PBS), the glucose can be catalyzed by glucose oxidase to produce H₂O₂ specifically. Based on the nanocatalyst and SERS substrate of AgNP, H₂O₂ can oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) quickly to form a blue oxidation product (TMB_ox) that induced the AgNPs aggregation, which exhibited a strong SERS signal at 1606 cm^-1. As the concentration of glucose increases, the TMB_ox molecular probes and AgNPs aggregation increase, and the intensity of SERS peak at 1606 cm^-1 increase linearly. Thus, a new SERS strategy for quantitative analysis of 0.33-6.67 μmol/L glucose was developed, with a detection limit of 0.035 μmol/L, coupled the catalysis of nanosilver with glucose oxidase, and label-free molecular probe of TMB_ox.

A magnetically recyclable photocatalyst with commendable dye degradation activity at ambient conditions

An efficient, economical, environment-friendly and easy separable catalyst to treat environmental contaminants is an enduring attention in recent years due to their great potential for environmental protection and remediation. Here we have reported the excellent performance of polyaniline activated heterojunctured Ni_0.5Zn_0.5Fe₂O₄ catalyst to degrade azo dye in an aqueous solution at ambient condition. The catalyst was prepared via a simple facile polymerization procedure. The physicochemical properties and structure of the synthesized catalyst was confirmed by TGA, PXRD, FTIR, SEM, HRTEM, XPS, EDX, and DRS techniques. The developed catalyst has shown an accelerated degradation ability of an organic pollutant Orange ll Sodium salt azo dye about 100% for the dye concentration of 50 ppm within five minutes at ambient conditions with 1 g/l loading of catalyst. Simple facile synthesis, easy separation by an external magnet, good reusability and high degradation capability of the catalyst may promote the practical applications of the heterostructured catalyst at ambient condition for water remediation. The present study also explored possible credible charge transfer directions and mechanism of photocatalysis supported by trapping experiments and electrochemical impedance spectroscopy (EIS) measurement for the effective improvement of photocatalytic activity and enhancement of the visible light adsorption.

A Novel Cyclodextrin-Functionalized Hybrid Silicon Wastewater Nano-Adsorbent Material and Its Adsorption Properties

A novel cyclodextrin-functionalized hybrid silicon nano-adsorbent material (6-EA-β-CD-Si) was synthesized via the nucleophilic substitution method. The structure was detected by Fourier transform infrared (FT-IR), X-ray, thermogravimetric analysis, and Brunauer-Emmett-Teller (BET) analysis. Results reveal that the BET surface area of 6-EA-β-CD-Si is 240 m²/g and the average pore size is 4.16 nm. The adsorption properties of 6-EA-β-CD-Si onto methylene blue (MB) were studied and fitted with adsorption kinetic models. Both the Freundlich adsorption isotherm model and pseudo-second-order model were fitted with well shows that the multi-layer adsorption with chemisorption and physisorption co-existing in the system. The maximum adsorption capacities are 39.37, 39.21, 36.90, and 36.36 mg/g at temperatures 303, 313, 323, and 333 K, respectively. The maximum removal rate of MB could reach 99.5%, indicating the potential application value of 6-EA-β-CD-Si in wastewater treatment. The adsorption mechanisms of 6-EA-β-CD-Si showed that the hydrophobic cave of β-CD plays an important role on the adsorption of MB.

Highly Efficient, Low-Cost, and Magnetically Recoverable FePt⁻Ag Nanocatalysts: Towards Green Reduction of Organic Dyes

Nowadays, synthetic organic dyes and pigments discharged from numerous industries are causing unprecedentedly severe water environmental pollution, and conventional water treatment processes are hindered due to the corresponding sophisticated aromatic structures, hydrophilic nature, and high stability against light, temperature, etc. Herein, we report an efficient fabrication strategy to develop a new type of highly efficient, low-cost, and magnetically recoverable nanocatalyst, i.e., FePt⁻Ag nanocomposites, for the reduction of methyl orange (MO) and rhodamine B (RhB), by a facile seed deposition process. X-ray diffraction results elaborate that the as-synthesized FePt⁻Ag nanocomposites are pure disordered face-centered cubic phase. Transmission electron microscopy studies demonstrate that the amount of Ag seeds deposited onto the surfaces of FePt nanocrystals increases when increasing the additive amount of silver colloids. The linear correlation of the MO and RhB concentration versus reaction time catalyzed by FePt⁻Ag nanocatalysts is in line with pseudo-first-order kinetics. The reduction rate constants of MO and RhB increase with the increase of the amount of Ag seeds. FePt⁻Ag nanocomposites show good separation ability and reusability, and could be repeatedly applied for nearly complete reduction of MO and RhB for at least six successive cycles. Such cost-effective and recyclable nanocatalysts provide a new material family for use in environmental protection applications.

Iron Based Catalysts Used in Water Treatment Assisted by Ultrasound: A Mini Review

The characteristics and performances of catalyst are the key in catalytic ultrasonic treatment of wastewater, and iron based catalysts are known for low cost, high accessibility and safety. This paper reviewed the current research status of iron-based catalysts in water treatment assisted by ultrasound. Zero valent iron, Fe₃O₄ and iron composited with other metals were analyzed, their behaviors in catalytic sonochemistry were summarized, and the potential catalytic mechanisms were discussed in details. Finally, the future development in this field was proposed.

Diclofenac degradation in water by FeCeOx catalyzed H2O2: Influencing factors, mechanism and pathways

The degradation of diclofenac in a like Fenton system, FeCeO_x-H₂O₂, was studied in details. The influencing factors, reaction kinetics, reaction mechanism and degradation pathways of diclofenac were investigated. The optimum conditions were at a solution pH of 5.0, H₂O₂ concentration of 3.0mmol/L, diclofenac initial concentration of 0.07mmol/L, FeCeO_x dosage of 0.5g/L, and 84% degradation of diclofenac was achieved within 40min. The kinetics of FeCeO_x catalyzed H₂O₂ process involved adsorption-dominating and degradation-dominating stages and fitted pseudo-second order model and pseudo-first order model, respectively. Singlet oxygen ¹O₂ was the primary intermediate oxidative species in the degradation process; superoxide radical anion O₂^- also participated in the reaction. The surface cerium and iron sites and the oxygen vacancies in the FeCeO_x catalyst were proposed to play an important role in H₂O₂ decomposition and active species generation. The detected intermediates were identified as hydroxylated derivatives (m/z of 310, 326 and 298), quinone imine compounds (m/z of 308, 278 and 264) and hydroxyl phenylamine (m/z of 178). The majority intermediates were hydroxylated derivatives and the minority was hydroxyl phenylamine. The degradation pathways were proposed to involve hydroxylation, decarboxylation, dehydrogenation and CN bond cleavage.

Sonocatalytic rapid degradation of Congo red dye from aqueous solution using magnetic Fe0/polyaniline nanofibers

Nano-sized magnetic Fe⁰/polyaniline (Fe⁰/PANI) nanofibers were used as an effective material for sonocatalytic degradation of organic anionic Congo red (CR) dye. Fe⁰/PANI_, was synthesized via reductive deposition of nano-Fe⁰ onto the PANI nanofibers at room temperature. Prepared catalyst was characterized using HR-TEM, FE-SEM, XRD, FTIR instruments. The efficacy of catalyst in removing CR was assessed colorimetrically using UV-visible spectroscopy under different experimental conditions such as % of Fe⁰ loading into the composite material, solution pH, initial concentration of dye, catalyst dosage, temperature and ultrasonic power. The optimum conditions for sonocatalytic degradation of CR were obtained at catalyst concentrations=500mg.L^-1, concentration of CR=200ppm, solution pH=neutral (7.0), temperature=30°C, % of Fe⁰ loading=30% and 500W ultrasonic power. The experimental results showed that ultrasonic process could remove 98% of Congo red within 30min with higher Q_max value (Q_max=446.4 at 25°C). The rate of degradation of CR dye was much faster in this ultrasonic technique rather than conventional adsorption process. The degradation efficiency declined with the addition of common inorganic salts (NaCl, Na₂CO₃, Na₂SO₄ and Na₃PO₄). The rate of degradation suppressed more with increasing salt concentration. Kinetic and isotherm studies indicated that the degradation of CR provides pseudo-second order rate kinetic and Langmuir isotherm model compared to all other models tested. The excellent high degradation capacity of Fe⁰/PANI under ultrasonic irradiation can be explained on the basis of the formation of active hydroxyl radicals (OH) and subsequently a series of free radical reactions.

Ultrasound-assisted degradation of organic dyes over magnetic CoFe2O4@ZnS core-shell nanocomposite

Magnetic CoFe₂O₄@ZnS core-shell nanocomposite was successfully synthesized via one-step hydrothermal decomposition of zinc(II) diethanoldithiocarbamate complex over CoFe₂O₄ nanoparticles at low temperature of 200°C. The obtained nanocomposite was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, UV-Vis spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, magnetic measurements, and Brunauere-Emmette-Teller. The results confirmed the formation of CoFe₂O₄@ZnS nanocomposite with the average crystallite size of 18nm. The band gap of 3.4eV was obtained using UV-vis absorption of CoFe₂O₄@ZnS nanocomposite, which made it a suitable candidate for sono-/photo catalytic processes. This nanocomposite was applied as a novel sonocatalyst for the degradation of organic pollutants under ultrasound irradiation. The results showed complete degradation of methylene blue (MB) (25mg/L) within 70min in the presence of CoFe₂O₄@ZnS nanocomposite and H₂O₂ (4mM). The trapping experiments indicated that OH radicals are the main active species in dye degradation. In addition, sonocatalytic activity of the CoFe₂O₄@ZnS nanocomposite was higher than those of pure ZnS and CoFe₂O₄, showing that the combining ZnS with magnetic CoFe₂O₄ could be an excellent choice to improve its sonocatalytic activity. The nanocomposite could be magnetically separated and reused without any observable change in its structure and performance even after five consecutive runs.

Fe-based metal organic framework/graphene oxide composite as an efficient catalyst for Fenton-like degradation of methyl orange

A MIL-100(Fe)/graphene oxide (GO) composite was prepared by a one-step hydrothermal method and utilized as a heterogeneous Fenton-like catalyst for methyl orange (MO) degradation.

Effective removal of cationic dyes using carboxylate-functionalized cellulose nanocrystals

A novel carboxylate-functionalized adsorbent (CNM) based on cellulose nanocrystals (CNCs) was prepared and adsorptive removal of multiple cationic dyes (crystal violet, methylene blue, malachite green and basic fuchsin) were investigated. The maximum cationic dyes uptakes ranged from 30.0 to 348.9mgg(-1) following the order of: CNM>CNCs>raw cellulose. Furthermore, the removal of crystal violet by CNM was investigated representatively where kinetics, thermodynamics and isotherm analysis were employed to explain in-depth information associated with the adsorption process. The adsorption kinetics fitted well to the pseudo-second-order model and thermodynamic analysis revealed that the adsorption process was spontaneous and exothermic. Meanwhile, isothermal study demonstrated a monolayer adsorption behavior following the Langmuir model with a calculated maximum absorption capacity of 243.9mgg(-1), which is higher than those of many other reported adsorbents. These findings prefigure the promising potentials of CNM as a versatile adsorbent for the efficient removal of cationic dyes from wastewater.