Removal of High-Concentration C.I. Acid Orange 7 from Aqueous Solution by Zerovalent Iron/Copper (Fe/Cu) Bimetallic Particles

Recycling of waste aluminum scraps to fabricate sulfidated zero-valent iron-aluminum particles for enhanced chromate removal

Massive waste aluminum scraps produced from the spent aluminum products have high electron capacity and can be recycled as an attractive alternative to materials based on zero-valent iron (Fe0) for the removal of oxidative contaminants from wastewater. This study thus proposed an approach to fabricate micron-sized sulfidated zero-valent iron-aluminum particles (S-Al0@Fe0) with high reactivity, electron selectivity and capacity using recycled waste aluminum scraps. S-Al0@Fe0 with a three-layer structure contained zero-valent aluminum (Al0) core, Fe0 middle layer and iron sulfide (FeS) shell. The rates of chromate (Cr(VI)) removal by S-Al0@Fe0 at pH 5.0‒9.0 were 1.6‒5.9 times greater than that by sulfidated zero-valent iron (S-Fe0). The Cr(VI) removal capacity of S-Al0@Fe0 was 8.2-, 11.3- and 46.9-fold greater than those of S-Fe0, zero-valent iron-aluminum (Al0-Fe0) and Fe0, respectively. The chemical cost of S-Al0@Fe0 for the equivalent Cr(VI) removal was 78.5% lower than that of S-Fe0. Negligible release of soluble aluminum during the Cr(VI) removal was observed. The significant enhancement in the reactivity and capacity of S-Al0@Fe0 was partially ascribed to the higher reactivity and electron density of the Al0 core than Fe0. More importantly, S-Al0@Fe0 served as an electric cell to harness the persistent and selective electron transfer from the Al0-Fe0 core to Cr(VI) at the surface via coupling Fe0-Fe2+-Fe3+ redox cycles, resulting in a higher electron utilization efficiency. Therefore, S-Al0@Fe0 fabricated using recycled waste aluminum scraps can be a cost-effective and environmentally-friendly alternative to S-Fe0 for the enhanced removal of oxidative contaminants in industrial wastewater.

Nanoscale zerovalent copper (nZVC) catalyzed environmental remediation of organic and inorganic contaminants: A review

Over the past decade, the nano zerovalent copper has emerged as an effective nano-catalyst for the environment remediation processes due to its ease of synthesis, low cost, controllable particle size and high reactivity despite its release during the remediation process and related concentration dependent toxicities. However, the improvised techniques involving the use of supports or immobilizer for the synthesis of Cu⁰ has significantly increased its stability and motivated the researchers to explore the applicability of Cu⁰ for the environment remediation processes, which is evident from access to numerous reports on nano zerovalent copper mediated remediation of contaminants. Initially, this review allows the understanding of the various resources used to synthesize zerovalent copper nanomaterial and the structure of Cu⁰ nanoparticles, followed by focus on the reaction mechanism and the species involved in the contaminant remediation process. The studies comprehensively presented the application of nano zerovalent copper for remediation of organic/inorganic contaminants in combination with various oxidizing and reducing agents under oxic and anoxic conditions. Further, it was evaluated that the immobilizers or support combined with various irradiation sources originates a synergistic effect and have a significant effect on the stability and the redox properties of nZVC in the remediation process. Therefore, the review proposed that the future scope of research should include rigorous focus on deriving an exact mechanism for synergistic effect for the removal of contaminants by supported nZVC.

Rapid debromination of tetrabromobisphenol A by Cu/Fe bimetallic nanoparticles in water, its mechanisms, and genotoxicity after treatments

Tetrabromobisphenol A (TBBPA), a widely used brominated flame retardants, has been detected in various environmental matrices and is known to cause various adverse effects on human bodies. This study examined the feasibility and effectiveness of remediating TBBPA using Cu/Fe bimetallic nanoparticles (Cu/Fe BNPs) at various environmental and operational conditions. In general, TBBPA removal rate and debromination efficiency increased with higher Cu doping, higher Cu/Fe BNPs loading, higher temperature, and lower pH. At optimal conditions, TBBPA was completed removed at a rate constant > 0.2 min^-1 where over 90% TBBPA was transformed to BPA within 30 min. The activation energy was found to be 35.6 kJ/mol, indicating that TBBPA was predominantly removed via surface-controlled reactions. Under pH 3-7 and ≥ 25 °C, debromination was the dominant removal mechanism compared to adsorption. The complete debromination pathway and the time-evolution of intermediates byproducts at different pHs were also presented. Cu/Fe BNPs can be reused for more than 6 times with performance constancy. Genotoxic tests showed that the treated solution did not find a significant hazardous potential. The byproducts can be further degraded by additional H₂O₂ through Fenton reaction. These results demonstrated the efficacy of Cu/Fe BNPs for treating TBBPA and its potential for degrading other halogenated organic compounds.

Nanoscale Fe0/Cu0 bimetallic catalysts for Fenton-like oxidation of the mixture of nuclear-grade cationic and anionic exchange resins

Spent resins generated from the nuclear industrial processes are still difficult to be treated and disposed. Fenton-like processes have great application potential in the treatment of spent resins, but the Fenton reaction mechanisms and resin degradation pathways remain challenging. In this study, nanoscale Fe⁰/Cu⁰ bimetallic catalysts were prepared and characterized for the Fenton-like degradation of the mixture of cationic and anionic resins. High catalytic property of Fe⁰/Cu⁰ bimetallic nanoparticles activated by H₂O₂ was evaluated, according to the effects of various nanoparticles, temperature, catalyst amount, H₂O₂ concentration and the mixing ratio of cationic and anionic resins. Combined the shape and color changes of mixed resins with the experimental and calculated characterization results, different degradation difficulty of cationic and anionic resins and their degradation mechanisms were studied. According to the density functional theory calculations of the optimized resin molecules with the Fe⁰/Cu⁰ catalyst, the mechanisms of Fenton-like reactions and the degradation of mixed resins through the synergistic effect of Fe and Cu species were proposed. The comprehensive Fenton-like reactions and degradation mechanisms provide new insights to advance the treatment of spent resins and organic polymers by Fenton-like processes.

Synthesis and catalytic utilization of bimetallic systems for wastewater remediation: A review

The environment is affected by agricultural, domestic, and industrial activities that lead to drastic problems such as global warming and wastewater generation. Wastewater pollution is of public concern, making the treatment of persistent pollutants in water and wastewater highly imperative. Several conventional treatment technologies (physicochemical processes, biological degradation, and oxidative processes) have been applied to water and wastewater remediation, but each has numerous limitations. To address this issue, treatment using bimetallic systems has been extensively studied. This study reviews existing research on various synthesis methods for the preparation of bimetallic catalysts and their catalytic application to the treatment of organic (dyes, phenol and its derivatives, and chlorinated organic compounds) and inorganic pollutants (nitrate and hexavalent chromium) from water and wastewater. The reaction mechanisms, removal efficiencies, operating conditions, and research progress are also presented. The results reveal that Fe-based bimetallic catalysts are one of the most efficient heterogeneous catalysts for the treatment of organic and inorganic contamination. Furthermore, the roles and performances of bimetallic catalysts in the removal of these environmental contaminants are different.

MOFs derived Co/Cu bimetallic nanoparticles embedded in graphitized carbon nanocubes as efficient Fenton catalysts

In this work, Cu-Co bimetallic nanoparticles embedded carbon nanocubes (Cu_xCo_10-x/CNC) are synthesized by direct carbonization of Cu-Co bimetal ZIF. The ratio of Cu and Co nanoparticles in Cu_xCo_10-x/CNC as well as morphology, pore structure and graphitization degree of carbon substrates can be tuned by adjusting the molar ratio of Cu/Co (0:10, 1:9, 2:8, 3:7, 4:6 and 5:5) in ZIF precursors. The Fenton catalytic performances of Cu_xCo_10-x/CNC are further studied by degrading a typical azo dye, Acid Orange II (AOII). The results show the Cu_xCo_10-x/CNC with a Cu/Co ratio of 4/6 display the highest catalytic activity with faster dye degradation rate than other catalysts, which may be ascribed to the synergetic effects of optimized ratio of Cu/Co bimetals, high surface area and graphitized carbon framework. The stability and reusability of the catalyst has been investigated, showing a good performance after five consecutive runs. The catalysts prepared in this study can be used as an attractive alternative in heterogeneous Fenton chemistry and wastewater treatment.

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.

Synthesis and applications of various bimetallic nanomaterials in water and wastewater treatment

Bimetallic nanoparticles are the complex combination of two different metal constituents in nanoscale. Water and wastewater treatment utilizing bimetallic particles is an emerging research area. When two metals are combined, it can show not only the properties of its constituents but also new and enhanced properties derived by the synergy of the combination. These properties of bimetallic nanoparticles inevitably depend on the size, structure, and morphology of the particles. Thus the adopting synthesis strategy is very crucial to achieve desired results. Here in this review, the various bimetallic synthesis strategies are compared. The bimetallic nanoparticles decontaminate water through adsorption and/or catalysis mechanism. The various degradation pathways, specifically, adsorption, reduction, oxidation, and advanced oxidation processes are discussed in detail in this review.

Enhanced heterogeneous Fenton-like systems based on highly dispersed Fe0-Fe2O3 nanoparticles embedded ordered mesoporous carbon composite catalyst

Acceleration of Fe³⁺/Fe²⁺ cycle and simultaneous reduction of particle size with enhanced stability is extremely important for iron-based heterogeneous Fenton catalysts. In this work, Fe⁰-Fe₂O₃ composite nanoparticles embedded ordered mesoporous carbon hybrid materials (Fe⁰-Fe₂O₃/OMC) were rationally designed as efficient heterogeneous Fenton catalysts. Because of the confinement and reduction of OMC, highly dispersed Fe⁰-Fe₂O₃ active species with diameter of ∼8 nm were generated by an optimized carbothermic reduction process. In addition, Fe⁰-Fe₂O₃/OMC possesses ordered mesoporous structure with uniform mesopore, high surface area and pore volume. For comparison, two other catalysts, including solely Fe⁰ nanoparticles supported on ordered mesoporous carbon (Fe⁰/OMC) and solely Fe₂O₃ nanoparticles supported on ordered mesoporous carbon (Fe₂O₃/OMC) were also prepared. The Fenton catalytic performance of synthesized catalysts was evaluated by using H₂O₂ as oxidizing agent to degrade Acid Orange II (AOII). The results show that almost 98.1% of 100 mg L^-1 AOII was removed by Fe⁰-Fe₂O₃/OMC in condition of neutral pH and nearly room temperature, which is much higher than those of compared catalysts. The enhanced catalytic activity of Fe⁰-Fe₂O₃/OMC for AOII removal is due to the efficient electron transfer between the Fe⁰ and iron oxide and the accelerated Fe³⁺/Fe²⁺ cycle. The stability and reusability of the catalyst was also investigated, which showed a good performance even after five consecutive runs. The as-synthesized catalyst is proved to be an attractive candidate in heterogeneous Fenton chemistry and practical application.

Comparative study of the direct black removal by Fe, Cu, and Fe/Cu nanoparticles

In this study, direct black dye removal was investigated using iron nanoparticles (Fe NPs), copper (Cu NPs), and Fe/Cu (Fe/Cu NPs). NPs were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Using a dose of 0.25 g L^-1 of Fe, Cu, and Fe/Cu NPs, a degradation efficiency of 13, 26, and 43% respectively was obtained. For the 1.00 g L^-1 dose, the efficiency increased to 100, 43, and 100%, respectively. Studies in anoxic and oxic conditions presented degradation rates, respectively, of 100 and 30% for Fe NPs, 90 and 50% for Fe/Cu NPs, and 40% in both reactions for Cu NPs, indicating that the mechanism of dye degradation by NPs is predominantly reducing under the conditions studied. The addition of EDTA decreased the dye removal rate for Fe, Cu, and Fe/Cu NPs at 27, 10, and 35%, respectively. In addition to the degradation, the adsorption phenomena of the by-products formed during the reaction were confirmed by the Fourier transform infrared (FTIR) analysis and verified by the desorption tests. Fe and Fe/Cu NPs showed the highest efficiency in direct black dye reductive degradation and adsorption of by-products, removing 100% of the dye at a dose of 1 g L^-1 within 10 min of reaction. Graphical abstracts ᅟ.

Preparation of magnetic carbon/Fe3O4 supported zero-valent iron composites and their application in Pb(II) removal from aqueous solutions

Nanoscale zero-valent iron (NZVI) was first assembled on magnetic carbon/Fe₃O₄ (CM) with a combination of hydrothermal and liquid phase reduction methods. The novel NZVI@CM magnetic nanocomposites have the merits of large surface area, unique magnetic property, low cost and environmental friendliness. They can be used for Pb(II) removal in aqueous solution. The materials were characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) adsorption. The various parameters, such as reaction time, dosage of catalyst, solution pH and acid ions concentrations were studied. The removal efficiency of Pb(II) can be obviously increased by the combination of appropriate CM and NZVI. The removal efficiency of Pb(II) is 99.7% by using 60 mg of NZVI@CM at pH 7. The kinetics study indicates that the Pb(II) removal accords to pseudo-second-order kinetics model.

Degradation of azo dye with activated peroxygens: when zero-valent iron meets chloride

Selection of the most appropriate Fe-based peroxygen oxidation technology depends on the dye wastewater constituents and pH.

Coagulation-flocculation as pre-treatment for micro-scale Fe/Cu/O3 process (CF-mFe/Cu/O3) treatment of the coating wastewater from automobile manufacturing

A coagulation-flocculation as pre-treatment combined with mFe/Cu/O₃ (CF-mFe/Cu/O₃) process was developed to degrade the pollutants in automobile coating wastewater (ACW). In coagulation-flocculation (CF) process, high turbidity removal efficiency (97.1%) and low COD removal efficiency (10.5%) were obtained under the optimal conditions using Al₂(SO₄)₃·18H₂O and CaO. The effluent of CF process (ECF) was further disposed by mFe/Cu/O₃ process, and its key operating parameters were optimized by batch experiments. Optimally, COD removal efficiency of ECF obtained by the mFe/Cu/O₃ process (i.e., 87.6% after 30 min treatment) was much higher than those of mFe/Cu alone (8.3%), ozone alone (46.6%), and mFe/Cu/air (6.1%), which confirms the superiority of the mFe/Cu/O₃ process. In addition, the analysis results of UV-vis, excitation-emission matrix (EEM) fluorescence spectra and GC/MS further confirm that the phenol pollutants of ECF had been effectively decomposed or transformed after CF-mFe/Cu/O₃ process treatment. Meanwhile, B/C ratio of ACW increased from 0.19 to 0.56, which suggests the biodegradability was improved significantly. Finally, the operating cost of CF-mFe/Cu/O₃ process was about 1.83 USD t^-1 for ACW treatment. Therefore, the combined process is a promising treatment technology for the coating wastewater from automobile manufacturing.

Studies on competitive adsorption of dyes onto carbon (XC-72) and regeneration of adsorbent

Carbon as an adsorbent has been widely studied for wastewater treatment, but the regeneration of adsorbent has been scarcely reported. In this paper, an economical and environmental method was applied to regenerate carbon (XC-72). Results showed that both anhydrous ethanol and deionized water did not obtain optimal effect for the desorption of Acid Orange 7, Ponceau 2R and Rhodamine B, but the desorption effect was dramatically improved when anhydrous ethanol and deionized water were mixed in a certain volume ratio. In addition, the adsorption kinetics of the three dyes were investigated, which showed that the process of adsorption could be well represented by the pseudo-second-order model. For the study of competitive adsorption, this indicated that the interaction between adsorbent and adsorbate had something to do with electrostatic attraction.

Continuous Bulk FeCuC Aerogel with Ultradispersed Metal Nanoparticles: An Efficient 3D Heterogeneous Electro-Fenton Cathode over a Wide Range of pH 3-9

Novel iron-copper-carbon (FeCuC) aerogel was fabricated through a one-step process from metal-resin precursors and then activated with CO2 and N2 in environmentally friendly way. The activated FeCuC aerogel was applied in a heterogeneous electro-Fenton (EF) process and exhibited higher mineralization efficiency than homogeneous EF technology. High total organic carbon (TOC) removal of organic pollutants with activated FeCuC aerogel was achieved at a wide range of pH values (3-9). The chemical oxygen demand (COD) of real dyeing wastewater was below China's discharge standard after 30 min of treatment, and the specific energy consumption was low (9.2 kW·h·kg(-1)COD(-1)), corresponding to a power consumption of only ∼0.34 kW·h per ton of wastewater. The enhanced mineralization efficiency of FeCuC aerogel was mostly attributable to ultradispersed metallic Fe-Cu nanoparticles embedded in 3D carbon matrix and the CO2-N2 treatment. The CO2 activation enhanced the accessibility of the aerogel's pores, and the secondary N2 activation enlarged the porosity and regenerated the ultradispersed zerovalent iron (Fe(0)) with reductive carbon. Cu(0) acted as a reduction promoter for interfacial electron transfer. Moreover, activated FeCuC aerogel presented low iron leaching (<0.1 ppm) in acidic solution and can be molded into different sizes with high flexibility. Thus, this material could be used as a low-cost cathode and efficient heterogeneous EF technology for actual wastewater treatment.

Activation of peroxymonosulfate by base: Implications for the degradation of organic pollutants

Increasing attention has been paid to environmentally friendly activation methods of peroxymonosulfate (PMS) in advanced oxidation processes (AOPs) for organic pollutant elimination. This work demonstrates that Base can be applied as a novel activator for PMS. The Base/PMS system, at ambient temperature, was able to degrade a variety of organic pollutants, including acid orange 7 (AO7), phenol and bisphenol A. In subsequent experiments with AO7, the decolorization rates for AO7 followed pseudo-first-order kinetics, with rate constant values ranging from 0.0006 to 0.1749 min(-1) depending on the operating parameters (initial PMS, Base, AO7 concentrations and reaction temperature). Furthermore, the mechanism for PMS activation by the Base was elucidated by radical scavenger (tert-butyl alcohol, methanol, sodium azide and p-benzoquinone) and electron spin resonance trapping studies. The results revealed that superoxide anion radical and singlet oxygen other than sulfate radical were the primary reactive oxygen species in the Base/PMS system. The findings of this study present a new pathway for PMS activation and provide useful information for the treatment of wastewater.

Treatment of wastewater derived from dinitrodiazophenol (DDNP) manufacturing by the Fe/Cu/O3 process

In this paper, the Fe/Cu bimetallic particles and ozone were combined to decompose or transform the toxic and refractory pollutants in dinitrodiazophenol (DDNP) wastewater.

Iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres: the effect of Fe/Cu ratio on heterogeneous Fenton degradation of a dye

A series of iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres with different Fe/Cu ratios were prepared using a simple post-impregnation and sodium borohydride reduction strategy.

Property of Cu2O-CuO/ZSM-5 nanocomposite and degradation process of azo dye AO7 without sacrificial agent (H2O2)

In this study, Cu2O-CuO/ZSM-5 nanocomposite was synthesized by the impregnation method, and its catalytic performance for the destruction of AO7 in aqueous solutions was investigated. The morphology, structure and surface element valence state of Cu2O-CuO/ZSM-5 were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The operating conditions on the degradation of AO7 by Cu2O-CuO/ZSM-5, such as initial pH values, concentration of AO7 and catalyst dosage were investigated and optimized. The results showed that the sample had good catalytic activity for destruction of AO7 in the absence of a sacrificial agent (e.g. H2O2): it could degrade 91% AO7 in 140 min at 25 °C and was not restricted by the initial pH of the AO7 aqueous solutions. Cu2O-CuO/ZSM-5 exhibited stable catalytic activity with little loss after three successive runs. The total organic carbon and chemical oxygen demand removal efficiencies increased rapidly to 69.36% and 67.3% after 120 min of treatment by Cu2O-CuO/ZSM-5, respectively.

Study on the preparation and photocatalytic oxidation properties of TiO2/nano-Fe0 photocatalysts

TiO₂/nano-Fe⁰ composite photocatalysts were prepared via a liquid phase reduction deposition method using anatase nano-TiO₂ as a deposition substrate.

Iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres: an effective heterogeneous Fenton catalyst for orange II degradation

Iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres as a composite catalyst (FeCu/HMS) was synthesized.