Low-cost Fe/SiO 2 catalysts for continuous Fenton processes

Preparation of ceramsite using solid residue from anaerobic digestion of waste activated sludge and its enhancing effect on catalytic ozonation

Anaerobic digestion is an environmentally friendly method for reclaiming waste activated sludge. However, it cannot be overlooked that the solid residue generated from this process can still pose environmental risks and impose economic pressure on society. To mitigate and recycle the solid residue, this study utilized it as a primary raw material for manufacturing ceramsite with potential applications in wastewater treatment. The optimal ratio of solid residue to fly ash was demonstrated to be 6:4 with an additional 15% of clay supplementing the raw ceramsite materials. Furthermore, the optimal sintering process was established as preheating at 300 °C for 25 min followed by sintering at 1085 °C for 10 min, as determined through an L16 (44) Orthogonal test. The prepared ceramsite demonstrated advantageous performance parameters that exceeded the standards outlined in the Chinese industry standard CJ/T 299-2008 for water treatment artificial ceramsite. When utilized in an ozonation system, the ceramsite exhibited remarkable catalytic activity for phenol degradation by promoting the decomposition of molecular O3 into hydroxyl radicals. Additionally, it displayed minimal leaching of heavy metals and lower application costs. These findings emphasize its attractiveness in water and wastewater treatment processes and present a practical strategy for reclaiming this solid residue.

Clay, Zeolite and Oxide Minerals: Natural Catalytic Materials for the Ozonation of Organic Pollutants

Ozone has been successfully employed in water treatment due to its ability to oxidize a wide variety of refractory compounds. In order to increase the process efficiency and optimize its economy, the implementation of heterogeneous catalysts has been encouraged. In this context, the use of cheap and widely available natural materials is a promising option that would promote the utilization of ozone in a cost-effective water treatment process. This review describes the use of natural clays, zeolites and oxides as supports or active catalysts in the ozonation process, with emphasis on the structural characteristics and modifications performed in the raw natural materials; the catalytic oxidation mechanism; effect of the operating parameters and degradation efficiency outcomes. According to the information compiled, more research in realistic scenarios is needed (i.e., real wastewater matrix or continuous operation in pilot scale) in order to transfer this technology to the treatment of real wastewater streams.

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.

Preparation of novel catalyst-free Fe3C nanocrystals encapsulated NCNT structured catalyst for continuous catalytic wet peroxide oxidation of phenol

Novel nitrogen-doped carbon nanotubes encapsulating Fe₃C nanocrystals coated paper-like sintered stainless steel fibers (PSSF) structured catalyst (Fe₃C@NCNT/PSSF) was designed for continuous catalytic wet peroxide oxidation of phenol. Firstly, Fe₃C@NCNT/PSSF was fabricated by directly growing the Fe₃C encapsulated NCNTs onto the three-dimensional PSSF substrate through CVD method using melamine as precursor, the monolithic PSSF substrate served as a self-catalyzing agent for catalyst preparation. Secondly, the surface morphology and structure of Fe₃C@NCNT/PSSF were investigated to optimize the synthesis condition. Then Fe₃C@NCNT/PSSF was employed as a structured catalyst for continuous CWPO of phenol, effect of operating conditions was studied. Catalytic results showed that the encapsulated Fe₃C nanoparticles significantly enhanced the degradation efficiency of phenol, and catalytic performance was improved with the increase of temperature. However, catalytic performance appeared unusual when residence time was considered, due to the effect of strongly polar surface of NCNTs on the contact efficiency between pollutants and hydroxyl radicals. Reusability experiments showed that catalytic performance of catalyst was improved with the increase of reusability cycles although the iron leaching concentration decreased, attributing to enhanced reaction within internal channel of Fe₃C@NCNT. The fourth reaction run achieved a stable phenol conversion of 90%, TOC conversion around 41% under optimized conditions.

Al-Doped magnetite encapsulated in mesoporous carbon: a long-lasting Fenton catalyst for CWPO of phenol in a fixed-bed reactor under mild conditions

Al substituted magnetite was identified as a promising heterogeneous Fenton catalyst for CWPO of 200 ppm phenol in a continuous system under mild conditions (pH 5, 40 °C, 0.1 ml min−1, 1.2S H2O2) for 500 h with 80% TOC conversion, 1 ppm Fe leaching.

Efficient removal of several estrogens in water by Fe-hydrochar composite and related interactive effect mechanism of H2O2 and iron with persistent free radicals from hydrochar of pinewood

Recently, hydrochar (HC) with existed persistent free radicals (PFRs) has attracted researches' attention for the potential application in heterogeneous Fenton-like reactions, but studies on the interactive effects of H₂O₂, iron, and HC in removal of organic pollutants are still limited. In this paper, magnetic iron (hydr)oxides immobilized hydrochar composite (Fe/HC) derived from hydrothermal carbon (HTC) of pinewood were synthesized and characterized. The interactive effects of H₂O₂, iron, and HC in the removal of several estrogens were systematically investigated to understand the removal performance and related mechanism, especially at a pH range close to natural water environment. Batch experiments results showed that estrogens could be efficiently removed over Fe/HC material under a wide pH range of 4-9. Based on the analysis of electron spin resonance, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and electrochemical impedance spectroscopy, mechanism study indicated that the carbon-centered PFRs on the surface of hydrochar can act as electron donors, and transfer the electrons on adsorbed O₂ to generate O₂^- rapidly, while the addition of H₂O₂ enhanced the transmission ability of electron to produce OH_(ads) on the material surface. The iron and hydrochar components contributed to the desirable removal of estrogens via the synergistic effect between catalysis and adsorption. This study provides a promising application for the use of Fe/HC materials on remediation of pollution with trace estrogens in water environment.

A Study of Catalytic Oxidation of a Library of C₂ to C₄ Alcohols in the Presence of Nanogold

The classical stoichiometric oxidation of alcohols is an important tool in contemporary organic chemistry. However, it still requires huge modifications in order to comply with the principles of green chemistry. The use of toxic chemicals, hazardous organic solvents, and the large amounts of toxic wastes that result from the reactions are a few examples of the problems that must be solved. Nanogold alone or conjugated with palladium were supported on different carriers (SiO₂, C) and investigated in order to evaluate their catalytic potential for environmentally friendly alcohol oxidation under solvent-free and base-free conditions in the presence H₂O₂ as a clean oxidant. We tested different levels of Au loading (0.1⁻1.2% wt.) and different active catalytic site forms (monometallic Au or bimetallic Au⁻Pd sites). This provided new insights on how the structure of the Au-dispersions affected their catalytic performance. Importantly, the examination of the catalytic performance of the resulting catalysts was oriented toward a broad scope of alcohols, including those that are the most resistant to oxidation-the primary aliphatic alcohols. Surprisingly, the studies proved that Au/SiO₂ at a level of Au loading as low as 0.1% wt. appeared to be efficient and prospective catalytic system for the green oxidation of alcohol. Most importantly, the results revealed that 0.1% Au/SiO₂ might be the catalyst of choice with a wide scope of utility in the green oxidation of various structurally different alcohols as well as the non-activated aliphatic ones.

Fe3O4 nanoparticle-encapsulated mesoporous carbon composite: An efficient heterogeneous Fenton catalyst for phenol degradation

Magnetite (Fe₃O₄) nanoparticle-encapsulated mesoporous carbon nanocomposite was fabricated from Fe-based metal-organic framework (MOF) (MIL-102) through carbonization. It was found that Fe-based MOF (MIL-102) is a potential precursor for the fabrication of hexagonal mesoporous carbon nanodisk functionalized with Fe₃O₄ nanoparticles. The obtained nanocomposite was characterized by XRD, FT-IR, N₂ adsorption and desorption, FE-SEM and HRTEM techniques. As a Fenton-like solid catalyst for phenol degradation, Fe₃O₄ nanoparticle-encapsulated mesoporous carbon showed greater catalytic activity for the production of hydroxyl radical from the decomposition of H₂O₂ and it accomplished 100% phenol and 82% total organic carbon (TOC) conversion, within 120 min of reaction. This enhanced catalytic performance was due to confined access for the pollutant to the iron oxide nanoparticles provided by mesopores in carbon shell. Bare Fe₃O₄ nanodisk shows poor catalytic performance in the degradation of phenol, and it obviously reveals the significance of the mesoporous carbon support for iron oxide nanoparticles.

Influence of precursor pH on the structure and photo-Fenton performance of Fe/hydrochar

Fe/hydrochar exhibited high visible light photo-Fenton activity because hydrochar accelerated the Fe³⁺/Fe²⁺ cycle at the catalyst/water interface.