Synthesis and characterization of Fe0/TiO2 nano-composites for ultrasound assisted enhanced catalytic degradation of reactive black 5 in aqueous solutions

Reductive dechlorination of 2,4-dichlorophenol by using MWCNTs-Pd/Fe nanocomposites prepared in the presence of ultrasonic irradiation

The research on developing a purification technology for 2,4-dichlorophenol (2,4-DCP) polluted water with high efficiency and the low energy consumption is crucial for achieving several Sustainable Development Goals (SDGs). In order to achieve these goals, MWCNTs-Pd/Fe nanocomposites were prepared by Fe nanoparticles modified with multi-walled carbon nanotubes (MWCNTs) and palladium (Pd) in the presence of ultrasonic irradiation. The MWCNTs-Pd/Fe nanocomposites were characterized by using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and X-Ray Diffraction (XRD), and others. Characterization results confirmed that the MWCNTs-Pd/Fe was successfully prepared, with the particle size of 80 nm and the specific surface area of 89.5 m2/g confirmed. We studied the reductive dechlorination of 2,4-Dichlorophenol (2,4-DCP) by MWCNTs-Pd/Fe nanocomposites under different conditions, and the optimized experimental results were found when the Pd loading was 0.4 %, the pH was 3, and the temperature was 30 °C. The phenol yield increased from 76.5 % (without ultrasonic irradiation) to 92.3 % (with ultrasonic irradiation) in 300 min and the 2,4-DCP removal rate reached 98.7 % under the optimal conditions. Therefore, ultrasonic irradiation enhanced the performance of MWCNTs-Pd/Fe nanocomposites for 2,4-DCP removal. We also established the degradation mechanism of chlorophenol by analyzing the intermediates, and proposed the degradation kinetics model. The degradation of 2,4-DCP followed the pseudo-first-order kinetics with the rate constant of 0.05988 min-1. Also, this study demonstrated the potential of using ultrasonic irradiation to improve the properties and recovery of MWCNTs-Pd/Fe nanocomposites, contributing to achievement of the Sustainable Development Goals (SDGs), including SDG-3, SDG-6.

Hexavalent chromium ion removal from wastewater using novel nanocomposite based on the impregnation of zero-valent iron nanoparticles into polyurethane foam

In this study, we developed a novel nanocomposite, polyurethane foam impregnated with zero-valent iron nanoparticles (PU@nZVI), for the effective removal of chromium(VI) from various water sources. The characterization of nanocomposite (PU@nZVI) was performed by XRD, SEM-EDS, TEM and FT-IR techniques. Using the response surface methodology, we optimized the removal conditions, achieving an optimal pH of 2 and a dose of 0.5 g/L. The PU@nZVI demonstrated an excellent maximum adsorption capacity of 600.0 mg/g for Cr6+. The adsorption kinetics and isotherms were best described by the pseudo-second-order model and the Freundlich isotherm, respectively. Significantly, the nanocomposite removed 99.98% of Cr6+ from tap water, 96.81% from industrial effluent, and 94.57% from treated sewage wastewater. Furthermore, the PU@nZVI maintained its efficiency over five adsorption-desorption cycles, highlighting its reusability. These results suggest that the PU@nZVI nanocomposite is a highly efficient and sustainable option for chromium(VI) removal in water treatment applications.

Degradation of formaldehyde by photo-Fenton process over n-ZVI/TiO2 catalyst

The degradation of formaldehyde in a photo-Fenton reaction was studied using n-ZVI/TiO2 as the catalyst. The effects of %n-ZVI loading, catalyst dosage, H2O2, and pH on formaldehyde degradation were studied. The n-ZVI/TiO2 catalysts were prepared by impregnation with chemical reduction, and their catalytic activity was evaluated in a batch reactor under UVC light. Transmission electron microscopy (TEM) was used to determine that the n-ZVI nanoparticle size was 39.41 nm. X-ray photoelectron spectroscopy (XPS) was used to study the oxidation states of 2%n‑ZVI/TiO2, and the Fe 2p spectrum of 2%n-ZVI/TiO2 indicated the presence of Fe0. The optimal conditions for the complete removal of formaldehyde within 30 min were an n-ZVI loading of 2 wt.%, a catalyst dosage of 0.5 g/L, 30 mM H2O2, and an initial pH of 3. After the reaction, the C-H functional group of formaldehyde was not observed due to the •OH radicals generated by Fe0 and H2O2 attacking the formaldehyde molecule. Moreover, no Fe leaching was observed, presenting an advantage compared with homogeneous Fe catalysts. Therefore, 2%n‑ZVI/TiO2 shows excellent potential as a photo-Fenton catalyst for the environmentally friendly degradation of formaldehyde.

Secondary bond interface assembly of polyethyleneimine on zein microparticles for rapid adsorption of Reactive Black 5

Textile dye wastewater has the characteristics of high concentration, complex composition and changeable color degree and pH, which is difficult to be effectively and completely treated, and easy to cause environmental pollution. Here, a strategy of secondary bond interface assembly of polyethyleneimine on zein microparticles (PEI) (PEI@zein) was constructed to achieve rapid and efficient removal of Reactive Black 5 (RB5), which is one of the most widely used reactive dyes in the textile industry. Structural analysis indicated that the as-prepared PEI layer immobilized on zein microparticles was constructed based on the interface assembly dominated by hydrophobic interactions and electrostatic attraction between PEI molecules and zein chains. The novel interface showed excellent absorption performance for RB5 with an absorption capacity of 631.0 mg·g^-1, rapid adsorption in 2 min, wide pH range of 4-10. Mechanism analysis suggested the effective adsorption of RB5 by PEI@zein microparticles was mainly attributed to secondary bond interface such as electrostatic interaction and hydrogen bond between RB5 and PEI immobilized on the surface of zein microparticles. Moreover, due to the presence of secondary bond interface, RB5 adsorbed on microparticles can be easily desorbed by using 0.01 M NaOH. Therefore, the strategy of secondary bond interface assembly with polyethyleneimine on zein microparticles has high potential for practical application in the treatment of dye-containing wastewater.

Synthesis of mesoporous Fe/Al/La trimetallic oxide for photodegradation of various water-soluble dyes: Kinetic, mechanistic, and pH studies

Phase pure, trigonal, mesoporous Fe/Al/La trimetallic nano-oxide (abbreviated as FAL) was synthesized using energy efficient chemical route with bandgap 1.97 eV and S_BET = 50.02 m²/g and an average pore size of 8.95 nm for photodegradation of azo (di and tri) and thiazine class of dyes successfully. The valence band and conduction band potentials were calculated using the Mott-Schottky plot. The highest photodegradation efficiency was 93.85 ± 2% for reactive black 5 (RB5) at pH 7 under solar irradiation. The phase formation of FAL was confirmed by PXRD, TEM, and HRTEM analyses. The other characterizations include FESEM, Raman, EPR, UV, HPLC, LC-MS, etc. The presence of the metal centers and their corresponding oxidation states were confirmed by the SAEDS, elemental mapping, and XPS analyses respectively. FAL was also able to photodegrade direct blue 71 (DB71) and methylene blue (MB) under the same condition at different pH efficiently (pH 2-11). The photodegradation obeyed the pseudo-1st-order kinetics and was reusable up to 5 successive cycles. This study may be an efficient tool to meet UNs' SDG:6.

Development of zerovalent iron and titania (Fe0/TiO2) composite for oxidative degradation of dichlorophene in aqueous solution: synergistic role of peroxymonosulfate (HSO5-)

Binary composite of zerovalent iron and titanium dioxide (Fe⁰/TiO₂) was synthesized for the catalytic removal of dichlorophene (DCP) in the presence of peroxymonosulfate (PMS). The as-prepared composite (Fe⁰/TiO₂) exhibits synergistic effect and enhanced properties like improved catalytic activity of catalyst and greater magnetic property for facile recycling of catalyst. The results showed that without addition of PMS at reaction time of 50 min, the percent degradation of DCP by TiO₂, Fe⁰, and Fe⁰/TiO₂ was just 5%, 11%, and 12%, respectively. However, with the addition of 0.8 mM PMS, at 10 min of reaction time, the catalytic degradation performance of Fe⁰, TiO₂, and Fe⁰/TiO₂ was significantly improved to 82%, 18%, and 88%, respectively. The as-prepared catalyst was fully characterized to evaluate its structure, chemical states, and morphology. Scanning electron microscopy results showed that in composite TiO₂ causes dispersion of agglomerated iron particles which enhances porosity and surface area of the composites and X-ray diffraction (XRD), energy dispersive X-ray (EDX), and Fourier-transform infrared (FTIR) results revealed successful incorporation of Fe⁰, and oxides of Fe and TiO₂ in the composite. The adsorption-desorption analysis verifies that the surface area of Fe⁰/TiO₂ is significantly larger than bare Fe⁰ and TiO_2. Moreover, the surface area, particle size, and crystal size of Fe⁰/TiO₂ was surface area = 85 m² g^-1, particle size = 0.35 μm, and crystal size = 0.16 nm as compared to TiO₂ alone (surface area = 22 m² g^-1, particle size = 4.25 μm, and crystal size = 25.4 nm) and Fe⁰ alone (surface area = 65 m² g^-1, particle size = 0.9 μm, and crystal size = 7.87 nm). The as-synthesized material showed excellent degradation performance in synthesized wastewater as well. The degradation products and their toxicities were evaluated and the resulted degradation mechanism was proposed accordingly. The toxicity values decreased in order of DP1 > DP5 > DP2 > DP3 > DP4 and the LC₅₀ values toward fish for 96-h duration decreased from 0.531 to 67.2. This suggests that the proposed technology is an excellent option for the treatment of antibiotic containing wastewater.

Ultrasound-assisted electrodeposition synthesis of nZVI-Pd/AC toward reductive degradation of methylene blue

A novel composite (nZVI/Pd-AC) was prepared by loading nanoscale zero-valent iron (nZVI) and Pd on activated carbon (AC) electrode under electrodeposition with ultrasound, which was used to reductive degradation of methylene blue (MB). The loading contents of Fe and Pd in composite materials were 15.84% and 2.06%, respectively. XPS results further confirmed that the as-prepared material contained Fe0 and Pd0. Without external conditions, MB could be degraded in the presence of nZVI/Pd-AC and reached equilibrium within 180 min. To investigate the reusability, the re-electrodeposition strategy was effective to refresh the active sites of nZVI/Pd-AC, and the removal efficiency only reduced by 4.51% in five circles indicating the good reusability of nZVI/Pd-AC composites. GC-MS was used to identify possible degradation pathways of MB; the results showed that the degradation products were mainly N, N-dimethylaniline and 2-amino-5-dimethylamino-benzenesulfonic acid. And the S-C, C-N bonds are the sites easier to be attacked.

Co-metabolic degradation of refractory dye: A metagenomic and metaproteomic study

Fructose was utilized as an additional co-substrate to systematically investigate the molecular mechanism of its boosting effect for the degradation of refractory dye reactive black 5 (RB5) by a natural bacterial flora DDMZ1. A decolorizing rate of 98% was measured for sample YE + FRU(200) (with 3 g/L fructose additionally to yeast extract medium, 10% (v/v) inoculation size of flora DDMZ1, 200 mg/L RB5) after 48 h. This result was 21% and 77%, respectively, higher than those of samples with only yeast extract or only fructose. Fructose was found to significantly stimulated both intracellular and extracellular azoreductase secretion causing enhanced activity. Metagenomic sequencing technology was used to analyze the functional potential of genes. A label-free quantitative proteomic approach further confirmed the encoding of functional proteins by the candidate genes. Subsequently, the molecular mechanism of RB5 degradation by candidate genes and functional proteins of the dominant species were proposed. This study provides important perspectives to the molecular mechanism of co-metabolic degradation of refractory pollutants by a natural bacterial flora.

Sugar sources as Co-substrates promoting the degradation of refractory dye: A comparative study

Four sugar sources were used as co-substrates to promote the degradation of a selected refractory dye reactive black 5 (RB5) by the natural bacterial flora DDMZ1. The boosting performance of the four sugar sources on RB5 decolorization ranked as: fructose > sucrose > glucose > glucose + fructose. Kinetic results of these four co-metabolism systems agreed well with a first-order kinetic model. Four sugar sources stimulated the extracellular azoreductase secretion causing enhanced enzyme activity. An increased formation of low molecular weight intermediates was caused by the addition of sugar sources. The toxicity of RB5 degradation products was significantly reduced in the presence of sugar sources. The bacterial community structure differed remarkably as a result of sugar sources addition. For a fructose addition, a considerably enriched population of the functional species Burkholderia-Paraburkholderia and Klebsiella was noted. The results enlarge our knowledge of the microkinetic and microbiological mechanisms of co-metabolic degradation of refractory pollutants.

Electrochemical treatment of pharmaceutical wastewater through electrosynthesis of iron hydroxides for practical removal of metronidazole

Antibiotics as the severe contaminants of aqueous environments were received growing attention during the last decades. The current work is the first report on investigating the potency and efficiency of electrocoagulation process in the successful removal of metronidazole (MNZ) from pharmaceutical wastewater using response surface methodology based on central composite design. The applied method by optimizing the independent and combined effects of significant variables which affecting the EC process enhanced the removal efficiency of MNZ. Analysis of variance was applied to verify the significance of independent variables solely and their interactions. The best removal efficiency of 100% found under the optimal operating condition of initial MNZ concentration 21.6 mg L^-1, pH 8.2, current density 6.0 mA cm^-2, inter-electrode distance 3 cm, and reaction time of 14.6 min. Isotherm investigations revealed that the Langmuir model with the R² of 0.994 best fitted to the obtained experimental equilibrium results. The fast adsorption of MNZ on the surface of Fe(OH)₃ and [Fe(OH)₂]⁺ with the equilibrium time of 15 min confirmed that the kinetics of the electrocoagulation process follow the pseudo-second-order model (R² = 0.962). The electrocoagulation process under the optimal operating condition revealed that the electrical energy consumption per each m³ of treated pharmaceutical wastewater, per each g of MNZ, removed, and per each kg of Fe electrode consumed, were found to be 0.516 kWh m^-3, 0.0234 kWh g^-1, and 0.0436 kWh kg^-1, respectively.

Facile approach for synthesis of stable, efficient, and recyclable ZnO through pulsed sonication and its application for degradation of recalcitrant azo dyes in wastewater

In the present study, the ultrasound in pulsed mode was used as a part of an advanced oxidation method. The influence of the pulsed ultrasound mode for the preparation of the zinc oxide (ZnO) wurtzite nanoparticle was investigated. The catalysts synthesized were analysed using SEM, TEM, EDAX, BET surface area, XRD, and DRS to study their morphological and structural characterizations. The ZnO nanoparticles exhibited a highly hexagonal structure from pulsed sonication synthesis route. The efficiency of the decolourization of the reactive red 4 (RR4) dye was studied under different operation parameters such as dye concentration, initial solution pH, oxidant (e.g., H2O2) concentration, and catalyst loading. The hybrid combined process of pulsed sonolysis, pH (4.0), H2O2 (17.64 mmol), and catalyst (0.35 g/L) achieved 97% degradation and 87.5% chemical oxygen demand removal in about 20 min of reaction time. The cyclic degradation studies of RR4 removal with 0.35 g/L of ZnO showed the reusability of catalyst up to the fifth removal cycle with negligible loss in the catalytic performance. GC–MS study, used for the detection of the RR4 intermediates, revealed the oxidation–reduction reaction by the reactive radicals proceeded via the reductive cleavage of the azo bonds. The studied process, based on the pulsed ultrasound, is found to be effective for the degradation of RR4 dye.

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.