Fabricating an adsorbent and micro-nano bubble catalyst through confining maghemite in the β cage of NaY zeolite

This work reports the ion exchange fabrication of maghemite (γ-Fe2O3) modified NaY zeolite (Fe2O3@Y) with bifunction of adsorption and catalysis. The Fe3+ successfully replaced the Na+ in the β cage of zeolite in the ion exchange process and coordinated with framework oxygens to form magnetic γ-Fe2O3. Therefore, most of the γ-Fe2O3 particles were confined in the β cages, which resulted in the high dispersal and stability of the catalyst. The Fe2O3@Y could remove methylene blue (MB) model pollutants up to 59.02 and 61.47% through the adsorption and catalysis process, respectively. The hydrogen bond between the OH- ions around the Fe2O3@Y surface and the N and O presented in the MB molecules enabled the chemical adsorption to MB, which accorded with the pseudo-second-order kinetic model. Further, the H+ existed in the solution and the β cage of zeolite promoted the collapse of micro-nano bubbles (MNBs). Then, the γ-Fe2O3 catalyst would be activated by high temperature and oxidated OH- to produce hydroxyl radicals for pollutant degradation. Thus, pollutant removal was attributed to the combined effects of adsorption and catalysis in the Fe2O3@Y + MNB system. In this work, the Fe2O3@Y was demonstrated as a potentially magnetic adsorbent or MNB catalyst for wastewater treatment.

Cyclohexane oxidation using advanced oxidation processes with metals and metal oxides as catalysts: a review

Selective oxidation of cyclohexane has gained substantial interest in the field of research due to the prominence of its products in industrial processes. Particularly, advanced oxidation processes (AOPs) constitute a positive technology for the oxidation of cyclohexane owing to their high oxidation potentials and environmental benign properties. This review entails to address the progress made in advanced oxidation of cyclohexane over nanostructured metals and metal oxides catalysts. The main focus is directed toward the photocatalysis, Fenton oxidation and ozonation as advanced oxidation processes. Mainly, the fundamental principles, prime factors of the AOPs in conjunction with metal and metal oxide catalysts and the mechanistic insight toward the oxidation of cyclohexane are highlighted. The affirmative effects of the metals and metal oxide catalysts mainly focusing on particle size, structure and elemental composition is stressed. Lastly, the advantages and disadvantages of the AOPs and the strategic approaches to counter the disadvantages are also clearly elucidated.

Effectiveness of a novel polyaniline@Fe-ZSM-5 hybrid composite for Orange G dye removal from aqueous media: Experimental study and advanced statistical physics insights

A polyaniline@Fe-ZSM-5 composite was synthesized via an in situ interfacial polymerization procedure. The morphology, crystallinity, and structural features of the as-developed PANI@Fe-ZSM-5 composite were assessed using scanning electron microscopy - energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The composite was efficiently employed for the first time as an adsorbent Orange G (OG) dyestuff from water. The OG dye adsorption performance was investigated as a function of several operating conditions. The kinetic study demonstrated that a pseudo-second-order model was appropriate to anticipate the OG adsorption process. The maximum adsorption capacity was found to be 217 mg/g. The adsorption equilibrium data at different temperatures were calculated via advanced statistical physics formalism. The entropy function indicated that the disorder of OG molecules improved at low concentrations and lessened at high concentrations. The free enthalpy and internal energy functions suggested that the OG adsorption was a spontaneous process and physisorption in nature. Regeneration investigation showed that the PANI@Fe-ZSM-5 could be effectively reused up to five cycles. The main results of this work provided a deep insight on the experimental study supported by advanced statistical physics prediction for the adsorption of Orange G dye onto the novel polyaniline@Fe-ZSM-5 hybrid composite. Additionally, the experimental and advanced statistical physics findings stated in this study may arouse research interest in the field of wastewater treatment.

Zeolites and Related Materials as Catalyst Supports for Hydrocarbon Oxidation Reactions

Catalytic oxidation is a key technology for the conversion of petroleum-based feedstocks into useful chemicals (e.g., adipic acid, caprolactam, glycols, acrylates, and vinyl acetate) since this chemical transformation is always involved in synthesis processes. Millions of tons of these compounds are annually produced worldwide and find applications in all areas of chemical industries, ranging from pharmaceutical to large-scale commodities. The traditional industrial methods to produce large amounts of those compounds involve over-stoichiometric quantities of toxic inorganic reactants and homogeneous catalysts that operate at high temperature, originating large amounts of effluents, often leading to expensive downstream processes, along with nonrecovery of valuable catalysts that are loss within the reactant effluent. Due to the increasingly stringent environmental legislation nowadays, there is considerable pressure to replace these antiquate technologies, focusing on heterogeneous catalysts that can operate under mild reactions conditions, easily recovered, and reused. Parallelly, recent advances in the synthesis and characterization of metal complexes and metal clusters on support surfaces have brought new insights to catalysis and highlight ways to systematic catalysts design. This review aims to provide a comprehensive bibliographic examination over the last 10 years on the development of heterogeneous catalysts, i.e., organometallic complexes or metal clusters immobilized in distinct inorganic supports such as zeolites, hierarchical zeolites, silicas, and clays. The methodologies used to prepare and/or modify the supports are critically reviewed, as well as the methods used for the immobilization of the active species. The applications of the heterogenized catalysts are presented, and some case-studies are discussed in detail.

Sustainability in Catalytic Cyclohexane Oxidation: The Contribution of Porous Support Materials

The development of green and sustainable protocols for synthetic routes is a growing area of research in chemistry worldwide. The development of sustainable processes and products through innovative catalytic materials and technologies, that allow a better use of resources, is undoubtedly a very important issue facing research chemists today. Environmentally and economically advanced catalytic processes for selective alkane oxidations reactions, as is the case of cyclohexane oxidation, are now focused on catalysts’ stability and their reuse, intending to overcome the drawbacks posed by current homogeneous systems. The aim of this short review is to highlight recent contributions in heterogeneous catalysis regarding porous support materials to be applied to cyclohexane oxidation reaction. Different classes of porous materials are covered, from carbon nanomaterials to zeolites, mesoporous silicas, and metal organic frameworks. The role performed by the materials to be used as supports towards an enhancement of the activity/selectivity of the catalytic materials and the ability of recycling and reuse in consecutive catalytic cycles is highlighted.