Efficient photocatalytic removal of orange II by a Mn3O4-FeS2/Fe2O3 heterogeneous catalyst

Applying bottom ash as an alternative Fenton catalyst for effective removal of phenol from aqueous environment

In this study, coal bottom ash from a thermoelectric plant was tested as an alternative Fenton catalyst for phenol degradation in water. The effect of operating parameters such as initial pH, catalyst dosage and H2O2 concentration were evaluated. The characterization results indicated that the material has a mesoporous structure, with active species (Fe) well distributed on its surface. Under the optimal reaction conditions (6 mM H2O2, 1 g L-1 of catalyst and pH = 3), 98.7% phenol degradation efficiency was achieved in 60 min, as well as 71.6% TOC removal after 150 min. Hydroxyl radical was identified as the main oxidizing agent involved on the cleavage of the phenol molecule. After four consecutive reuse cycles, phenol degradation efficiency was around 80%, indicating good reusability and stability of the catalyst. Therefore, the obtained results demonstrated that the bottom ash presents remarkable activity for application in the Fenton reaction towards phenol degradation.

Efficient degradation of the refractory organic pollutant by underwater bubbling pulsed discharge plasma: performance, degradation pathway, and toxicity prediction

It is essential to develop an efficient technology for the elimination of refractory contaminants due to their high toxicity. In this study, a novel underwater bubbling pulsed discharge plasma (UBPDP) system was proposed for the degradation of Orange II (OII). The degradation performance experiments showed that by enhancing the peak voltage and pulse frequency, the degradation efficiency of OII increased gradually. The removal efficiencies under different air flow rates were close. Reducing OII concentration and solution conductivity could promote the elimination of OII. Compared with neutral and alkaline conditions, acidic condition was more beneficial to OII degradation. The active species including ·OH, ·O2-, 1O2, and hydrated electrons were all involved in OII degradation. The concentrations of O3 and H2O2 in OII solution were lower than those in deionized water. During discharge, the solution pH increased while conductivity decreased. The variation of UV-vis spectra with treatment time indicated the effective decomposition of OII. Possible degradation pathways were speculated based on LC-MS. The toxicity of intermediate products was predicted by the Toxicity Estimation Software Tool. Coexisting constituents including Cl-, SO42-, HCO3-, and humic acid had a negative effect on OII removal. Finally, the comparison with other technology depicted the advantage of the UBPDP system.

Synthesis of β-FeOOH/polyaniline heterogeneous catalyst for efficient photo-Fenton degradation of AOII dye

Discharge of the untreated dye-containing wastewaters will induce water source pollution and further harm aquatic organisms. In this study, the akaganéite/polyaniline catalyst (β-FeOOH/PANI, about 1.0 μm) could be successfully composed by polyaniline (PANI, (C₆H₇N)_n, 200-300 nm) and akaganéite (β-FeOOH, FeO(OH)_1-xCl_x, less than 200 nm), according to the identification and characterization results of XRD, Ramon, FTIR, XPS, SEAD, EDS, and FESEM (or HRTEM). Due to PANI providing more photogenerated electrons, the β-FeOOH/PANI composite (compared with β-FeOOH) in photo-Fenton system had the more highly catalytic degradation capacity to Acid Orange II (AOII) under an optimal condition (7.5 mmol/L of H₂O₂ oxidant, 40 mg/L of AOII, 0.2 g/L of catalyst dosage, and pH 4.0). The AOII degradation kinetics could be well fitted by pseudo-first-order model. In photo-Fenton catalytic process of AOII dye, the ∙OH and h⁺ were the main reaction substances. The AOII in solutions could be gradually mineralized into non-toxic inorganic H₂O molecule and CO₂. The β-FeOOH/PANI catalyst also had a good reusable ability of about 91.4% AOII degradation after 4 runs. These results can provide a reference for synthesis of catalyst used in photo-Fenton system and the applications in degradation removal of organic dye from wastewaters.

Construction of ternary (1D/2D/3D) Fe2O3-supported micro pillared Cu-based MOF on chitosan with improved photocatalytic behavior on removal of paraquat

A hetero-structured metal organic framework of Cu-BTC and Fe₂O₃ nano-photocatalyst were tethered over chitosan using the hydrothermal method and fabricated a hybrid porous nanocomposite (CS-Fe@Cu-BTC). X-ray diffractometer results exposed the existence of Fe₂O₃ peaks. Surface area measurements using BET showed a mesoporous structure and the formation of type IV adsorption isotherm for nanocomposite. XPS and SEM-EDAX confirmed the existence of Fe₂O₃ nanoparticles in the hybrid porous structure. The UV-vis diffuse reflectance absorption shape emphasized the role of Fe₂O₃ in enhancing the band gap of CS-Fe@Cu-BTC nanohybrid. The lower intensity photoluminescence spectra of the CS-Fe@Cu-BTC shows a competent charge partition and delayed the recombination of electron-hole pairs. The photo-mineralization efficiency of Cu-BTC and CS-Fe@Cu-BTC was evaluated in terms of electronic interactions using paraquat (PQT) as the probe molecule, which shows a mineralization of 91% at the pH range of ~ 5. The contribution of •OH in the degradation of PQT over CS-Fe@Cu-BTC nanocomposites revealed using the trapping test and the degradation mechanism follows the Langmuir-Hinshelwood model and pseudo-first-order kinetics. The durability of the CS-Fe@Cu-BTC nanocomposite was also established after four cycling processes.

Stoichiometric Control Synthesis of Pyrite and Greigite Particles Used for Photo-Fenton Degradation Catalysis

Two types of iron sulfide, i.e., highly crystalline pyrite (FeS2) and greigite (Fe3S4) were synthesized via hot-injection method only by changing the precursor ratios of iron to sulfur (Fe:S) from...

Study on the efficient removal of azo dyes by heterogeneous photo-Fenton process with 3D flower-like layered double hydroxide

As organic dyes are the main pollutants in water pollution, seeking effective removal solutions is urgent for humans and the environment. A novel environmentally friendly three-dimensional CoFe-LDHs (3D CoFe-LDHs) catalyst was synthesized by one-step hydrothermal method. Scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectra, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller technique as well as UV-Vis diffuse reflectance spectra were used to characterize the prepared samples. The experimental results revealed that 3D CoFe-LDHs exhibited a rapid decolorization of methyl orange and Rhodamine B by heterogeneous photo-Fenton process after reaching the adsorption equilibrium, and the final decolorization efficiency reached 91.18% and 93.56%, respectively. On the contrary, the decolorizing effect of 3D CoFe-LDHs on neutral blue was relatively weak. The initial concentrations of azo dyes, pH and H₂O₂ concentration affected the decolorization of dyes and the catalyst maintained excellent reusability and stability after reuse over five cycles. The quenching experiments found that •OH, •O₂ ^- and h⁺ were the main active substances and reaction mechanisms were further proposed. The study suggests that the synergistic effect of photocatalysis and Fenton oxidation process significantly improved the removal of azo dyes and the synthesized catalyst had potentially promising applications for difficult-to-biodegrade organic pollutants in wastewater.

Insight into the enhanced catalytic activity of a red mud based Fe2O3/Zn–Al layered double hydroxide in the photo-Fenton reaction

In this work, the enhanced catalytic activity of red mud based Fe₂O₃/Zn–Al layered double hydroxide in the photo-Fenton reaction has been studied in detail.