Photocatalytic degradation of nitrobenzene in wastewater by persulfate integrated with Ag/Pb3O4 semiconductor under visible light irradiation

Pb/Pb3O4 Metal-Semiconductor Nanocomposite Obtained on 4A Zeolite-Optical and Structural Properties

This work describes a controlled and low-cost synthesis method to obtain Pb/Pb3O4 nanocomposites using synthetic zeolite 4A. The nanostructures obtained have a core-shell configuration with 5-25 nm diameters. High-resolution transmission electron microscopy (HRTEM), BF, high-angle annular dark-field annular scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible (UV-vis) characterization techniques were used. Crystallographic planes (111), (200), and (220) for the core and planes (110) and (211) for the shell, corresponding to FCC and tetragonal structures for Pb and Pb3O4, respectively, were determined using HRTEM. The HAADF-STEM images allowed the analysis of intensity contrast images proportional to the number of atoms. XPS spectral analysis showed a 4.8 eV difference in binding energy between Pb 4f7/2 and Pb 4f5/2 for lead and lead oxide. EDS elemental mapping, XPS, and UV-vis spectroscopy analyses revealed the simultaneous presence of lead and lead oxide in the same structure. The band gap obtained for the shell was determined to be 4.50 eV. Consequently, Pb/Pb3O4 nanocomposites show a higher response to high-energy photons, making them suitable for UV photocatalysis applications.

Evaluation of the hydrogenation reaction on the electrocatalytic nitrobenzene degradation over (FeCoNiCuZn)xOy high entropy oxides (HEOs)

Environmental pollution is one of the main challenges currently faced by mankind; especially industrial waste-waters treatment and remediation using energy-efficient methodologies. This research focused on the electrochemical degradation of the hazardous nitrobenzene (NB) in aqueous solutions, using novel high-entropy oxide (HEO) electrodes to elucidate the influence of the electrochemical reduction step on the degradation process. The effect of solution pH, dissolved oxygen concentration, anodic applied potential, and cell configurations on NB hydrogenation reaction were evaluated. A synergistic effect between the hydrogenation of nitrobenzene and the degradation was found to drastically enhance the conversion rates. The presence of dissolved oxygen promoted the oxidation reactions, reaching more than 90% nitrobenzene removal at 1.7 V and pH 14. The degradation of the organic by-products was attributed to the formation of the superoxide radical (O2*-) as the main oxidant species. A degradation mechanism was proposed based on the detected intermediates and the decoupling of electrochemical surface reactions observed by EIS at different solution pH.

Ultrasound-Assisted Mineralization of 2,4-Dinitrotoluene in Industrial Wastewater Using Persulfate Coupled with Semiconductors

Oxidative degradation of 2,4-dinitrotoluenes in aqueous solution was executed using persulfate combined with semiconductors motivated by ultrasound (probe type, 20 kHz). Batch-mode experiments were performed to elucidate the effects of diverse operation variables on the sono-catalytic performance, including the ultrasonic power intensity, dosage of persulfate anions, and semiconductors. Owing to pronounced scavenging behaviors caused by benzene, ethanol, and methanol, the chief oxidants were presumed to be sulfate radicals which originated from persulfate anions, motivated via either the ultrasound or sono-catalysis of semiconductors. With regard to semiconductors, the increment of 2,4-dinitrotoluene removal efficiency was inversely proportional to the band gap energy of semiconductors. Based on the outcomes indicated in a gas chromatograph-mass spectrometer, it was sensibly postulated that the preliminary step for 2,4-dinitrotoluene removal was denitrated into o-mononitrotoluene or p-mononitrotoluene, followed by decarboxylation to nitrobenzene. Subsequently, nitrobenzene was decomposed to hydroxycyclohexadienyl radicals and converted into 2-nitrophenol, 3-nitrophenol, and 4-nitrophenol individually. Nitrophenol compounds with the cleavage of nitro groups synthesized phenol, which was sequentially transformed into hydroquinone and p-benzoquinone.

A critical review of textile industry wastewater: green technologies for the removal of indigo dyes

The denim textile industry represents an important productive sector. It generates wastewater with low biodegradability due to the presence of persistent pollutants, which can produce toxic and carcinogenic compounds; therefore, wastewater treatment reduces risks to aquatic life and public health. This paper presents a review of 172 papers regarding textile industry wastewater treatment for the removal of contaminants, especially indigo dyes used in the denim industry, in the context of green technologies. The physicochemical characteristics of textile wastewater, its environmental and health impacts, and the permissible limit regulations in different countries were reviewed. Biological, physicochemical and advanced oxidation processes for the removal of indigo dyes were reviewed. The goal of this study was to analyze the characteristics of green technologies; however, the research does not clearly demonstrate an effect on energy consumption savings, carbon footprint decreases, and/or waste generation. Advanced oxidation processes showed the highest color removal efficiency (95 and 97% in synthetic or real wastewater, respectively). Photocatalysis and Fenton reactions were the most efficient processes. None of the revised works presented results regarding upscaling for industrial application, and the results should be discussed in terms of the guidelines and maximum permissible limits established by international legislation. New technologies need to be developed and evaluated in a sustainable context with real wastewater.

Remediation of environmentally persistent organic pollutants (POPs) by persulfates oxidation system (PS): A review

Over the past few years, persistent organic pollutants (POPs) exhibiting high ecotoxicity have been widely detected in the environment. Persulfate-oxidation hybrid system is one of the most widely used novel advanced oxidation techniques and is based on the persulfate generation of SO₄^-∙ and ∙OH from persulfate to degrade POPs. The overarching aim of this work is to provide a critical review of the variety of methods of peroxide activation (e.g., light activated persulfate, heat-activated persulfate, ultrasound-activated persulfate, electrochemically-activated persulfate, base-activated persulfate, transition metal activated persulfate, as well as Carbon based material activated persulfate). Specifically, through this article we make an attempt to provide the important characteristics and uses of main activated PS methods, as well as the prevailing mechanisms of activated PS to degrade organic pollutants in water. Finally, the advantages and disadvantages of each activation method are analyzed. This work clearly illustrates the benefits of different persulfate activation technologies, and explores persulfate activation in terms of Sustainable Development Goals, technical feasibility, toxicity assessment, and economics to facilitate the large-scale application of persulfate technologies. It also discusses how to choose the most suitable activation method to degrade different types of POPs, filling the research gap in this area and providing better guidance for future research and engineering applications of persulfates.

A comprehensive review on persulfate activation treatment of wastewater

With increasingly serious environmental pollution and the production of various wastewater, water pollutants have posed a serious threat to human health and the ecological environment. The advanced oxidation process (AOP), represented by the persulfate (PS) oxidation process, has attracted increasing attention because of its economic, practical, safety and stability characteristics, opening up new ideas in the fields of wastewater treatment and environmental protection. However, PS does not easily react with organic pollutants and usually needs to be activated to produce oxidizing active substances such as sulfate radicals (SO₄^-) and hydroxyl radicals (OH) to degrade them. This paper summarizes the research progress of PS activation methods in the field of wastewater treatment, such as physical activation (e.g., thermal, ultrasonic, hydrodynamic cavitation, electromagnetic radiation activation and discharge plasma), chemical activation (e.g., alkaline, electrochemistry and catalyst) and the combination of the different methods, putting forward the advantages, disadvantages and influencing factors of various activation methods, discussing the possible activation mechanisms, and pointing out future development directions.