Enhanced heterogeneous Fenton oxidation of organic pollutant via Fe-containing mesoporous silica composites: A review

Engineering yolk-double-shell Au@CN@ZnIn2S4 architecture with enhanced photocatalytic properties

The efficient utilization of light and the prolonged lifetime of photo-induced charge carriers are essential elements that contribute to superior photocatalytic activity. Yolk-shell nanostructures with porous shells and mobile cores offer significant structural advantages in achieving these goals. However, designing yolk-shell multicomponent nanocomposites with diverse architectures remains a persistent challenge. The present study involves the utilization of zinc indium sulfide (ZnIn2S4) flakes, which are uniformly incorporated into the yolk-shell Au@CN structure. The inclusion of ZnIn2S4 flakes in carbon nitride (CN) significantly enhances the performance of the overall system, allowing for efficient and rapid charge transfer. The uniform distribution of ZnIn2S4 flakes throughout the yolk-shell matrix ensures the catalytic activity is maximized, resulting in superior performance compared to conventional systems. The designed photocatalyst has a hollow interior which strengthens light absorption, a thin shell that shortens the electron migration distance, tight adhesion between shells, which makes it easier to separate and transfer carriers, and a movable Au core with localized surface plasmon resonance (LSPR) which can facilitate additional charge carrier generation for CN and ZnIn2S4. The yolk-shell microsphere composite of Au@CN@ZnIn2S4 shows a TC photodegradation rate of 72% within 2 h, which is more than double the photodegradation rate of hollow CN and ZnIn2S4. The present study's experimental demonstrations valuable insights into the rational design of sophisticated metal-semiconductors double yolk-shell nanocrystals, particularly those composed of metal sulfides cocatalyst, for superior photocatalytic applications.

Enhanced Heterogeneous Fenton Degradation of Organic Dyes by Bimetallic Zirconia-Based Catalysts

The qualitative impact of pollutants on water quality is mainly related to their nature and their concentration, but in any case, they determine a strong impact on the involved ecosystems. In particular, refractory organic compounds represent a critical challenge, and several degradation processes have been studied and developed for their removal. Among them, heterogeneous Fenton treatment is a promising technology for wastewater and liquid waste remediation. Here, we have developed mono- and bimetallic formulations based on Co, Cu, Fe, and Mn, which were investigated for the degradation of three model organic dyes (methylene blue, rhodamine B, and malachite green). The treated samples were then analyzed by means of UV-vis spectrophotometry techniques. Bimetallic iron-based materials achieved almost complete degradation of all three model molecules in very short time. The Mn-Fe catalyst resulted in the best formulation with an almost complete degradation of methylene blue and malachite green at pH 5 in 5 min and of rhodamine B at pH 3 in 30 min. The results suggest that these formulations can be applied for the treatment of a broad range of liquid wastes comprising complex and variable organic pollutants. The investigated catalysts are extremely promising when compared to other systems reported in the literature.

Prism-like integrated Bi2WO6 with Ag-CuBi2O4 on carbon nanotubes (CNTs) as an efficient and robust S-scheme interfacial charge transfer photocatalyst for the removal of organic pollutants from wastewater

Photocatalytic hybrid carbon nanotubes (CNTs)-mediated Ag-CuBi2O4/Bi2WO6 photocatalyst was fabricated using a hydrothermal technique to effectively eliminate organic pollutants from wastewater. The as-prepared samples were characterized via Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction patterns (XRD), high-resolution transmission electron microscope (HR-TEM), UV-vis Diffuse Reflectance spectrum (UV-Vis DRS), and photoluminescence (PL) studies. The photocatalytic performance of fabricated pristine and hybrid composites was examined by photo-degradation of toxic dye viz. Rhodamine B (RhB) under visible light. Photo-degradation results revealed that the fabricated Ag-CuBi2O4/CNTs/Bi2WO6 semiconductor photocatalyst followed pseudo-first-order kinetics and displayed a higher photocatalytic rate, which was found to be approximately 3.33 and 2.35 times higher than the pristine CuBi2O4 and Bi2WO6 semiconductor photocatalyst, respectively. Re-cyclic results demonstrated that the formed composite owns excellent stability, even after five consecutive cycles. As per the matched Fermi level of CNTs in between Ag-CuBi2O4 and Bi2WO6, carbon nanotubes severed as electron transfer-bridge, Ag doping on CuBi2O4 surface successfully increased photon absorption all across CuBi2O4 surface. Also, it hindered the assimilation of photoinduced electron-hole pairs. The increased photocatalytic efficiency is contributed to the uniform dispersion of photo-generated electron-hole pairs via the construction of an S-scheme system. ROS trapping and ESR experiments suggested that (∙OH) and (O2-∙) were the main radical species for enhanced photo-degradation of RhB dye. The current investigation, from our perspective, highlights the new insights for the fabrication of practical CNTs-mediated S-scheme-based semiconductor photocatalyst for the resolution of environmental issues based on practical considerations.

Visible-light-driven iron-based heterogeneous photo-Fenton catalysts for wastewater decontamination: A review of recent advances

Visible-light-driven heterogeneous photo-Fenton process has emerged as the most promising Fenton-derived technology for wastewater decontamination, owing to its prominent superiorities including the potential utilization of clean energy (solar light), and acceleration of ≡Fe(II)/≡Fe(III) dynamic cycle. As the core constituent, catalysts play a pivotal role in the photocatalytic activation of H₂O₂ to yield reactive oxidative species (ROS). To date, all types of iron-based heterogeneous photo-Fenton catalysts (Fe-HPFCs) have been extensively reported by the scientific community, and exhibited satisfactory catalytic performance towards pollutants decomposition, sometimes even exceeding the homogeneous counterparts (Fe(II)/H₂O₂). However, the relevant reviews on Fe-HPFCs, especially from the viewpoint of catalyst-self design are extremely limited. Therefore, this state-of-the-art review focuses on the available Fe-HPFCs in literatures, and gives their classification based on their self-characteristics and modification strategies for the first time. Two classes of representative Fe-HPFCs, conventional inorganic semiconductors of Fe-containing minerals and newly emerging Fe-based metal-organic frameworks (Fe-MOFs) are comprehensively summarized. Moreover, three universal strategies including (i) transition metal (TMs) doping, (ii) construction of heterojunctions with other semiconductors or plasmonic materials, and (iii) combination with supporters were proposed to tackle their inherent defects, viz., inferior light-harvesting capacity, fast recombination of photogenerated carriers, slow mass transfer and low exposure and uneven dispersion of active sites. Lastly, a critical emphasis was also made on the challenges and prospects of Fe-HPFCs in wastewater treatment, providing valuable guidance to researchers for the reasonable construction of high-performance Fe-HPFCs.

Efficient preparation of graphene oxide-immobilized copper complex and its catalytic performance in the synthesis of imidazoles

This paper focused on the synthesis of phenylthiocarbamide-grafted graphene oxide (GO)-supported Cu complex (Cu-PTC@GO) as a highly efficient and recyclable catalyst synthesis by various analytical techniques such as TG, FT-IR, XRD, BET, N₂ adsorption-desorption isotherms, SEM, EDX, and elemental mapping analysis. Cu-PTC@GO showed outstanding results in preparing various imidazoles with higher yields, reduced reaction time, ease of product separation, and a simple procedure. In addition, the catalyst demonstrated appreciable recyclability up to five successive runs, and there was no substantial loss in catalytic performance. The result indicated that the heterogeneous base GO catalyst performed high activity and excellent recyclability in synthesizing various imidazoles and their derivatives, owing to the unique state of the GO-supported copper complex.

One-Step Synthesized Iron-Carbon Core-Shell Nanoparticles to Activate Persulfate for Effective Degradation of Tetrabromobisphenol A: Performance and Activation Mechanism

Tetrabromobisphenol A (TBBPA), as an emerging endocrine disrupter, has been considered one of the persistent organic contaminants in water. It is urgently necessary to develop an efficient technique for the effective removal of TBBPA from water. Herein, a one-step hydrothermal synthesis route was employed to prepare a novel iron-carbon core-shell nanoparticle (Fe@MC) for effectively activating persulfate (PS) to degrade TBBPA. Morphological and structural characterization indicated that the prepared Fe@MC had a typical core-shell structure composed of a 5 nm thick graphene-like carbon shell and a multi-valence iron core. It can be seen that 94.9% of TBBPA (10 mg/L) could be degraded within 30 min at pH = 7. This excellent catalytic activity was attributed to the synergistic effect of the porous carbon shell and a multi-valence iron core. The porous carbon shell could effectively prevent the leaching of metal ions and facilitate PS activation due to its electron transfer capability. Furthermore, numerous micro-reaction zones could be formed on the surface of Fe@MC during the rapid TBBPA removal process. Radical quenching experiments and electron paramagnetic resonance (EPR) technology indicated that reactive oxygen species (ROS), including OH, SO₄^-, O₂^-, and ¹O₂, were involved in the TBBPA degradation process. Based on density functional theory (DFT) calculation, the carbon atoms linked by phenolic hydroxyl groups would be more vulnerable to attack by electron-rich groups; the central carbon was cracked and hydroxylated to generate short-chain aliphatic acids. The toxicity evaluation provides clear evidence for the promising application potential of our prepared material for the efficient removal of TBBPA from water.

Design of Polymer-Embedded Heterogeneous Fenton Catalysts for the Conversion of Organic Trace Compounds

Advanced oxidation processes are the main way to remove persistent organic trace compounds from water. For these processes, heterogeneous Fenton catalysts with low iron leaching and high catalytic activity are required. Here, the preparation of such catalysts consisting of silica-supported iron oxide (Fe2O3/SiOx) embedded in thermoplastic polymers is presented. The iron oxide catalysts are prepared by a facile sol–gel procedure followed by thermal annealing (calcination). These materials are mixed in a melt compounding process with modified polypropylenes to stabilize the Fe2O3 catalytic centers and to further reduce the iron leaching. The catalytic activity of the composites is analyzed by means of the Reactive Black 5 (RB5) assay, as well as by the conversion of phenol which is used as an example of an organic trace compound. It is demonstrated that embedding of silica-supported iron oxide in modified polypropylene turns the reaction order from pseudo-first order (found for Fe2O3/SiOx catalysts), which represents a mainly homogeneous Fenton reaction, to pseudo-zeroth order in the polymer composites, indicating a mainly heterogeneous, surface-diffusion-controlled process.

Novel Magnetic Fe3O4/α-FeOOH Nanocomposites and Their Enhanced Mechanism for Tetracycline Hydrochloride Removal in the Visible Photo-Fenton Process

Magnetic Fe₃O₄/α-FeOOH heterojunction nanocomposites (denoted as Fe-NCs) have been synthesized by a fast one-pot hydrothermal method. The obtained Fe-NCs contain rich micropores with a high surface area of 135.15 m²/g. The different phases in the composites can efficiently enhance the visible-light absorption, improving the separation and transfer of photogenerated electron-hole pairs during the photocatalytic reaction. Thus, they show excellent degradation and mineralization of tetracycline (TC) over a wide pH range (5-9) in the visible photo-Fenton reaction. Especially, the catalyst exhibits the highest adsorption capacity toward TC at a neutral pH, which facilitates the surface reactions of TC with active species. Experiments evidence that the high production of photogenerated holes and superoxide radicals (O₂ ^•-) in Fe-NCs are favorable to the high catalytic efficiency. Combined with liquid chromatography-mass spectrometry, the possible pathway toward TC degradation was proposed.