Colloidal metal nanocatalysts to advance orange II hydrogenolysis tracked by a microplate reader

The thermal reduction method was applied to synthesize metal nanoparticles using poly(1-vinyl-2-pyrrolidone) as an organic stabilizer to control metal nanoparticle agglomeration. Colloidal metal nanoparticles, gold, palladium, and gold–palladium nanoparticles were synthesized, and UV–visible spectrophotometry and high-resolution transmission electron microscopy analyses were conducted to characterize them. The metal nanoparticle micrographs showed well-dispersed particles with an average size of 9.6 nm (Au), 15.4 nm (Pd), and 10.6 nm (AuPd). All the colloidal metal nanoparticles served as nanocatalysts to advance a reductive degradation of orange II in presence of borohydride ions. For a prompt screening of catalytic activity, the microplate reader system was considered at a fixed maximum absorbance wavelength of λ 489 nm respected by orange II. Excess borohydride ions were used to construct pseudo-first kinetic conditions. The Langmuir–Hinshelwood model allowed the finding of kinetic activity on the surface of metal nanoparticles. AuPd nanocatalyst interface exhibited low activation energy (5.38 kJ mol−1) compared to the one on Au (8.19 kJ mol−1) and Pd (7.23 kJ mol−1).

Graphical Abstract

Green synthesized cobalt oxide nanoparticles with photocatalytic activity towards dye removal

The present study aimed at the synthesis of cobalt oxide nanoparticles (CONPs) mediated by leaf extract of Muntingia calabura using a rapid and simple method and evaluation of its photocatalytic activity against methylene blue (MB) dye. UV-vis absorption spectrum showed multiple peaks with an optical band gap of 2.05 eV, which was concordant with the literature. FESEM image signified the irregular-shaped, clusters of CONPs, and EDX confirmed the existence of the Co and O elements. The sharp peaks of XRD spectrum corroborated the crystalline nature with a mean crystallite size of 27.59 nm. Raman spectrum substantiated the purity and structural defects. XPS signified the presence of Co in different oxidation states. FTIR image revealed the presence of various phytochemicals present on the surface and the bands at 515 and 630 cm^-1 designated the characteristic Co-O bonds. VSM studies confirmed the antiferromagnetic property with negligible hysteresis. The high BET specific surface area (10.31 m²/g) and the mesoporous nature of the pores of CONPs signified the presence of a large number of active sites, thus, indicating their suitability as photocatalysts. The CONPs degraded 88% of 10 mg/L MB dye within 300 min of exposure to sunlight. The degradation of MB dye occurred due to the formation of hydroxyl free radicals on exposure to sunlight, which followed first-order kinetics with rate constant of 0.0065 min^-1. Hence, the CONPs synthesized herein could be applied to degrade other xenobiotics and the treatment of industrial wastewater and environmentally polluted samples.

Enhanced reactivity of the CuO-Fe2O3 intimate heterojunction for the oxidation of quinoline yellow dye (E104)

This research work describes the degradation of quinoline yellow (QY) in aqueous solutions by the heterogeneous Fenton and photo-Fenton processes in the presence of CuO/Fe₂O₃ photocatalyst. CuO/Fe₂O₃ derived from LDH structure was synthesized by the co-precipitation method. The physiochemical characteristics of CuO/Fe₂O₃ were described by XRD, TEM/SEM, BET surface area, and FTIR techniques. The effects of pH, H₂O₂ concentration, dye concentration, catalyst dose, reaction temperature, and reusability of catalyst on the QY decolorization efficiency were studied. The results indicated that a complete removal of QY was achieved within 150 min, when the H₂O₂ and QY concentrations were 27.6 mM and 100 mg/L, respectively. The rate constants for QY removal by the heterogeneous Fenton system were calculated, and the experimental data were found to fit the pseudo-first order model. Under optimal conditions, the rate constants were, respectively, 0.02032 and 0.01715 min^-1 for the photo-Fenton and Fenton systems; this means that the addition of light has not a noticeable effect.

5-Hydroxymethylfurfural Oxidation to 2,5-Furandicarboxylic Acid on Noble Metal-Free Nanocrystalline Mixed Oxide Catalysts

Noble metal-free catalysts based on earth-abundant and inexpensive mixed oxides are active catalysts of all steps of the reaction cascade leading from 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) using tert-butyl hydroperoxide (TBHP) as oxidation agent. Catalysts covering the whole range of composition in the Cu-Mn and Co-Fe series have been prepared and characterised. The nature and composition of the catalyst strongly affect conversion and selectivity. The distribution of products indicates that radical-type oxygen species, deriving from the activation of TBHP, play a determining role in the reaction. The early steps of reaction mainly follow the pattern expected for heterogeneous Fenton catalysts. Mixed oxide catalysts are the most effective in further oxidation steps, leading to the formation of FDCA, both in the Cu-Mn and Co-Fe systems. This behaviour can be related to the distribution of charge in the mixed oxides, suggesting a possible implication of the lattice oxygen in the last reaction steps. The results provide indications on how to optimize the reaction and minimize the formation of byproducts (humins and oligomers).

A comprehensive study on the adsorption-photocatalytic processes using CoFe2O4/SiO2/MnO2 magnetic nanocomposite as a novel photo-catalyst for removal of Cr (VI) under simulated sunlight: Isotherm, kinetic and thermodynamic studies

PURPOSE

The present study aimed to investigate the efficiency of CoFe₂O₄/SiO₂/flower-like MnO₂ nanoparticles as a catalyst for Cr (VI) adsorption-photocatalytic processes.

METHODS

The magnetic nanocomposite used was first synthesized and then characterized using TEM, SEM, EDX, XRD, FTIR, XRF and BET advanced techniques. The removal of the Cr (VI) was performed through a batch adsorption approach and the effects of sample pH (A; 2-6), initial chromate concentration (B; 50-100 ppm) and adsorbent weight to sample volume ratio (C; 1-3 mg ml^-1), hole scavenger (0.1 -0.3%w/v) and time (E; 30-60 min), to evaluate the individual and interactive effects under ultraviolet light conditions, were also studied by the central composite design in the photocatalytic process of adsorption.

RESULTS

The adsorption-photocatalytic performance of the CoFe₂O₄/SiO₂/MnO₂ composite was high in which 98.1% of Cr(VI) after 30 min of photocatalytic treatment in optimum conditions (i.e. pH = 3, catalyst concentration = 2 mg L^-1, Cr(VI) concentration = 200 mg L^-1, and hole scavenger concentration = 0.4% (w/ v), At laboratory temperature, speed = 400 rpm, under UV radiation).Under optimum conditions, Cr(VI) reductive followed pseudo-second-order kinetics and followed the Langmuir and Temkin isotherms, also, positive value of ΔH° indicates endothermic nature.

CONCLUSIONS

The results showed that the synthesized CoFe₂O₄/SiO₂/MnO₂ magnetic nanocomposite holds a great potential for use as a photocatalyst to remove Cr (VI) in adsorption reactions. It can be used as an effective catalyst in the eradication of Cr (VI) wastewater.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00763-1.

In-situ catalytic degradation of sulfamethoxazole with efficient CuCo-O@CNTs/NF cathode in a neutral electro-Fenton-like system

In this paper, a CuCo-O@CNTs/NF electrode was successfully prepared and used for in-situ degradation of sulfamethoxazole (SMX) in an electro-Fenton-like system. Carbon nanotubes (CNTs) and coral-like copper-cobalt oxides were successively loaded on nickel foam (NF). CNTs contributed to improving the dispersibility and stability of copper-cobalt oxides, and the coral-like copper-cobalt oxide catalyst was anchored on CNTs without any adhesive. In the electro-Fenton-like system, dissolved oxygen can be reduced to superoxide anions in a one-electron step, which could be further transformed into hydrogen peroxide and then reacted with the active components on the electrode to generate reactive oxygen species (ROS) to participate in the degradation of SMX. Almost 100% SMX removal was obtained within 60 min in a wide near-neutral pH range (5.6-9.0), and the electrode could still achieve a 90.4% removal rate after ten recycle runs. Radical-quenching results showed that superoxide anions were the main species in the degradation of SMX. In addition, a possible degradation pathway of SMX was proposed. According to the result of toxicological simulations, the toxicity of the pollutant solution during the degradation process exhibited a decreasing trend. This study provides new insights for in-situ catalysis of electrodes with bimetallic active components to generate ROS for high-efficiency degradation of refractory organic pollutants.

Oxygen reduction reaction electrocatalysis inducing Fenton-like processes with enhanced electrocatalytic performance based on mesoporous ZnO/CuO cathodes: Treatment of organic wastewater and catalytic principle

To treat typical organic wastewater efficiently, a novel Fenton-like processes based on ZnO/CuO composite cathode induced by oxygen reduction reaction (ORR) electrocatalysis with enhanced electrocatalytic performance was established successfully. Electrochemical testing investigation indicated that the ZnO/CuO cathode possessed conspicuous redox peak and better conductivity than uncompounded electrodes. Additionally, the removal efficiency of methylene blue and its chemical oxygen demand (COD) reached 96.4% and 70.8% after 120 min, respectively. Next, the feasibility of the material in practical application was also discussed. Subsequently, electrocatalytic principle based on valence state changes of metal elements on the electrode surface were also studied by x-ray photoelectron spectroscopy (XPS). Redox reactions between the active species H₂O₂ and the species Cu⁺ promoting Fenton-like processes were deduced. Namely, the conversion of Cu(I) and Cu(II) on the electrode surface was accompanied by OH generation. The combination of ZnO and CuO improved the surface morphology, increasing the active site of ORR and the yield of H₂O₂, thus greatly enhanced the Fenton-like activity. Finally, the main intermediates were identified by Gas chromatography-mass spectrometer (GC-MS), and possible pathways for dye degradation were proposed. In short, the research of ZnO/CuO cathode provided great significance for heterogeneous Fenton-like degradation and also showed its application potential in water treatment and remediation.

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.

Synergistic Catalysis of Co(OH)2/CuO for the Degradation of Organic Pollutant Under Visible Light Irradiation

The exploration of advanced water treatment technologies e.g. heterogeneous photocatalysis is the most promising way to address organic pollution issues. Semiconductors based bimetallic photocatalysis with wide bandgap, have displayed splendid degradation performance in the UV light region, but their extension to the visible light/near infra-red region is still a matter of great concern. CuO, Co(OH)₂, CoO and Co(OH)₂/CuO nanocomposites were synthesized via simple co-precipitation method and further practiced for Rhodamine B (RhB) decomposition by introducing per-sulfate (PS) as a sacrificial agent. Results revealed that Co(OH)₂/CuO catalyst had shown robust catalytic activity for RhB photodegradation (degradation time 8 min, k = 0.864 min⁻¹) under light illumination, significantly less (12–60 times) than the other reported bimetallic catalysts. Catalyst also have verified excellent performance for a broader pH range (5–9) with excellent stability. Main reactive species responsible for the photocatalytic reaction were sulfate (SO₄^•−) and superoxide (O₂^•) radicals, duly verified by ESR and by using radical scavengers. With outstanding recycling abilities, this is probably the fewer successful attempt for RhB decolorization and can be highly favorable for effluent treatment by using the synergic effect of absorption and photodegradation.

Decomplexation removal of Ni(II)-citrate complexes through heterogeneous Fenton-like process using novel CuO-CeO2-CoOx composite nanocatalyst

A novel CuO-CeO₂-CoO_x nanocatalyst was prepared for heterogeneous Fenton-like reaction to break the Ni²⁺-chelate into free Ni²⁺ in electroless nickel plating wastewater, followed by separation of Ni²⁺ in an insoluble form. The composite nanocatalysts prepared by co-precipitation method were characterized by XRD, TEM, and XPS, et al. Its catalytic activity as Fenton-like reagent was evaluated by the removal efficiency of Ni(II)-citrate after decomplexation and postprecipitation treatment. Subsequently, the effects of operating parameters on the decomplexation efficiency of the nanocatalysts were investigated including calcination temperature of catalysts, H₂O₂ concentration, catalyst dosage, initial pH and reaction temperature. Under optimized condition, the Ni(II)-citrate complexes (C₀ = 1.0 mM) achieved the complete decomplexation (>99.9%) within 60-min reaction using 0.3 g/L of CuO-CeO₂-CoO_x calcined at 450 °C and 75 mM of H₂O₂ at pH 3.0 under 50 °C of reaction. Then, Ni²⁺ after decomplexation could be completely removed by the subsequent precipitation at pH 11.0. In addition, the life test of CuO-CeO₂-CoO_x catalyst indicated that, after recycled 10 times, its activity for decomplexation of Ni(II)-citrate decreased no more than 8%. As a result, this new heterogeneous Fenton-like process is promising for decomplexation and purification of electroless nickel plating wastewater as a sludge reduction technology.

Environmental remediation processes by zero valence copper: reaction mechanisms

Recent studies have shown Cu(0) as a promising material for the removal of organic and inorganic pollutants. However, there is no review addressing the studies performed. This fact may be related to the toxicity of the particles and the copper released in solution that has not motivated researchers, which entails in a reduced number of publications. However, studies point out how to solve the problem of Cu deposition in support materials. In this work, a detailed review of Cu(0) applications was performed. The specific focus was the reaction mechanisms related to adsorption, oxidation, and reduction processes. Initially, the resources that allow the understanding of the reaction mechanism, such as characterization techniques and the experimental conditions for investigation of the species involved in the process, were presented. The studies were evaluated separately, showing the mechanisms involved only with the application of Cu(0) in pure and isolated form and in association with oxidizing or reductive agents, combined with irradiation sources and ultrasonic waves and in the form supported in polymer matrices. It was verified that by the proposed reaction mechanisms, the exclusive participation of Cu(0), being the removal process, explained only by the redox behavior of copper. Therefore, the review showed the need for future research regarding the redox behavior of the contaminants.

Enhanced Fenton-like catalytic performance of N-doped graphene quantum dot incorporated CuCo2O4

In the present study, a novel nanocomposite based on CuCo₂O₄ and N-doped graphene quantum dots (N-GQDs) as an iron-free heterogeneous Fenton-like catalyst was prepared by a two-step solvothermal method.

Co–Fe hydrotalcites for efficient removal of dye pollutants via synergistic adsorption and degradation

Layered double hydroxides (LDHs) with hydrotalcite-like structures containing Co(ii) and Fe(iii) were prepared and used for the removal of direct red 23 (DR23) from water solution.

Influence of CuO morphology on the enhanced catalytic degradation of methylene blue and methyl orange

The sheet-like CuO shows enhanced catalytic activity, compared to polycrystalline CuO for the catalytic degradation of methylene blue and methyl orange.

Treatment of textile effluent containing recalcitrant dyes using MOF derived Fe-ZSM-5 heterogeneous catalyst

Fe-ZSM-5 is synthesized through a newly established 2-step process. 82% yield of Fe-ZSM-5 catalyst is possible at low temperature and pressure. 100% degradation of dyes is achieved with lesser amounts of catalyst and H₂O₂.

Heterogeneous Fenton-like degradation of methyl blue using MCM-41-Fe/Al supported Mn oxides

We prepared uniform and spherical M-Fe/Al at room temperature. Furthermore, this material was supported with Mn oxides by an impregnation method to accelerate the degradation process of methyl blue.