The influence of the catalyst on the CO formation during catalytic wet peroxide oxidation process

Advancements in MAX phase materials: structure, properties, and novel applications

The MAX phase represents a diverse class of nanolaminate materials with intriguing properties that have received incredible global research attention because they bridge the divide separating metals and ceramics. Despite the numerous potential applications of MAX phases, their complex structure leads to a scarcity of readily accessible pure MAX phases. As a result, in-depth research on synthesis methods, characteristics, and structure is frequently needed for appropriate application. This review provides a comprehensive understanding of the recent advancements and growth in MAX phases, focusing on their complex crystal structures, unique mechanical, thermal, electrical, crack healing, corrosion-resistant properties, as well as their synthesis methods and applications. The structure of MAX phases including single metal MAX, i-MAX and o-MAX was discussed. Moreover, recent advancements in understanding MAX phase behaviour under extreme conditions and their potential novel applications across various fields, including high-temperature coatings, energy storage, and electrical and thermal conductors, biomedical, nanocomposites, etc. were discussed. Moreover, the synthesis techniques, ranging from bottom-up to top-down methods are scrutinized for their efficacy in tailoring MAX phase properties. Furthermore, the review explores the challenges and opportunities associated with optimizing MAX phase materials for specific applications, such as enhancing their oxidation resistance, tuning their mechanical properties, and exploring their functionality in emerging technologies. Overall, this review aims to provide researchers and engineers with a comprehensive understanding of MAX phase materials and inspire further exploration into their versatile applications in materials science and engineering.

Catalytic wet peroxide oxidation of phenol through mesoporous silica-pillared clays supported iron and/or titanium incorporated catalysts

Catalytic performances of Silica Pillared Clay (SPC) supports synthesized in different silica amounts both from standard SWy-2 clay mineral and Hançılı region bentonite rock (HWB), and iron (Fe) and/or titanium (Ti) incorporated SPCs in different combinations were evaluated in various advanced Catalytic Wet Peroxide Oxidation (CWPO) of phenol. Host clay mineral type led to different oxidation performances and metal loading created significant increases in the catalytic performance. CWPO performance of Fe-loaded SPCs was better than Ti-loaded ones, so oxidation parameters for Fe-SPCs were studied in detail. Catalyst amount and rise in temperature increased phenol conversion values significantly, and catalysts were more effective in lower pH reaction medium. Aromatic intermediates such as catechol, hydroquinone and benzoquinone formed at the beginning of oxidation were oxidized to carboxylic acids with an advancing oxidation time. The presence of carboxylic acids such as oxalic and formic acid resulted in relatively low total organic carbon (TOC) conversion values. The highest catalytic activity was obtained with high silica content Fe-SPCs synthesized with both host clays. Complete conversion was nearly achieved within 60 min with an experimental condition of T = 30 °C, pH = 3.7 and catalyst/solution ratio = 2 g/L for SWy-2 based catalyst by applying either CWPO or PCWPO (Photo Catalytic Wet Peroxide Oxidation) techniques. SCWPO (Sono Catalytic Wet Peroxide Oxidation) technique also yielded this value at the same oxidation conditions for HWB based catalyst. TOC conversion values at 240 min oxidation time were determined as 33% and 48% for SWy-2 based catalyst with CWPO and PCWPO techniques, respectively, and 37% for HWB based catalyst with SCWPO technique. SWy-2 based catalyst still retained its performance after 3 cycles.

Green Synthesis of Magnetite-Based Catalysts for Solar-Assisted Catalytic Wet Peroxide Oxidation

A novel synthesis method under green philosophy for the preparation of some magnetite-based catalysts (MBCs) is presented. The synthesis was carried out in aqueous media (i.e., absence of organic solvents) at room temperature with recovery of excess reactants. Terephthalic acid (H2BDC) was used to drive the synthesis route towards magnetite. Accordingly, bare magnetite (Fe3O4) and some hybrid magnetite-carbon composites were prepared (Fe3O4-G, Fe3O4-GO, and Fe3O4-AC). Graphene (G), graphene oxide (GO), and activated carbon (AC) were used as starting carbon materials. The recovered H2BDC and the as-synthetized MBCs were fully characterized by XRD, FTIR, Raman spectroscopy, XPS, SQUID magnetometry, TGA-DTA-MS, elemental analysis, and N2-adsorption-desorption isotherms. The recovered H2BDC was of purity high enough to be reused in the synthesis of MBCs. All the catalysts obtained presented the typical crystalline phase of magnetite nanoparticles, moderate surface area (63–337 m2 g−1), and magnetic properties that allowed their easy separation from aqueous media by an external magnet (magnetization saturation = 25–80 emu g−1). The MBCs were tested in catalytic wet peroxide oxidation (CWPO) of an aqueous solution of metoprolol tartrate (MTP) under simulated solar radiation. The Fe3O4-AC materials showed the best catalytic performance among the prepared MBCs, with MTP and total organic carbon (TOC) removals higher than 90% and 20%, respectively, after 3 h of treatment. This catalyst was fairly successfully reused in nine consecutive runs, though minor loss of activity was observed, likely due to the accumulation of organic compounds on the porous structure of the activated carbon and/or partial oxidation of surface Fe2+ sites.

Performance of Iron-Functionalized Activated Carbon Catalysts (Fe/AC-f) on CWPO Wastewater Treatment

Two commercial activated carbon were functionalized with nitric acid, sulfuric acid, and ethylenediamine to induce the modification of their surface functional groups and facilitate the stability of corresponding AC-supported iron catalysts (Fe/AC-f). Synthetized Fe/AC-f catalysts were characterized to determine bulk and surface composition (elemental analysis, emission spectroscopy, XPS), textural (N2 isotherms), and structural characteristics (XRD). All the Fe/AC-f catalysts were evaluated in the degradation of phenol in ultrapure water matrix by catalytic wet peroxide oxidation (CWPO). Complete pollutant removal at short reaction times (30–60 min) and high TOC reduction (XTOC = 80 % at ≤ 120 min) were always achieved at the conditions tested (500 mg·L−1 catalyst loading, 100 mg·L−1 phenol concentration, stoichiometric H2O2 dose, pH 3, 50 °C and 200 rpm), improving the results found with bare activated carbon supports. The lability of the interactions of iron with functionalized carbon support jeopardizes the stability of some catalysts. This fact could be associated to modifications of the induced surface chemistry after functionalization as a consequence of the iron immobilization procedure. The reusability was demonstrated by four consecutive CWPO cycles where the activity decreased from 1st to 3rd, to become recovered in the 4th run. Fe/AC-f catalysts were applied to treat two real water matrices: the effluent of a wastewater treatment plant with a membrane biological reactor (WWTP-MBR) and a landfill leachate, opening the opportunity to extend the use of these Fe/AC-f catalysts for complex wastewater matrices remediation. The degradation of phenol spiked WWTP-MBR effluent by CWPO using Fe/AC-f catalysts revealed pH of the reaction medium as a critical parameter to obtain complete elimination of the pollutant, only reached at pH 3. On the contrary, significant TOC removal, naturally found in complex landfill leachate, was obtained at natural pH 9 and half stoichiometric H2O2 dose. This highlights the importance of the water matrix in the optimization of the CWPO operating conditions.