Abatement of Volatile Organic Compounds Emission as a Target for Various Human Activities Including Energy Production

Eu3+ doped ethylenediamine functionalized UiO-66 probe for fluorescence sensing of formaldehyde

The development of probes with selectivity and prompt detection of aldehydes molecules is of great importance for protecting human health and public security. Herein, a system based on ethylenediamine (EDA) functionalized and Eu3+-doped UiO-66, namely EDA-Eu3+@UiO-66, was designed to detect formaldehyde molecules. Based on the "antenna effect" of lanthanide elements, UiO-66 transfers the absorbed energy to Eu3+ ions and emits characteristic fluorescence belonging to Eu3+. By using the fluorescence peaks of UiO-66 and Eu3+ respectively, a ratiometric fluorescence sensing probe can be constructed. Formaldehyde molecules react with the -NH2 on the surface of EDA-Eu3+@UiO-66 through an aldehyde-amine condensation reaction and connect to the functionalized surface of UiO-66. Due to the absorption of excitation light energy by formaldehyde molecules, the energy transfer efficiency from UiO-66 to Eu3+ ions is reduced, resulting in the fluorescence quenching of EDA-Eu3+@UiO-66, thus achieving selective detection of formaldehyde. The fabricated sensing platform successfully detected residual formaldehyde in frozen shrimp tail samples. The system was also used to respond to formaldehyde vapor, and a significant fluorescence quenching effect was observed. This strategy provides a sensitive, selective, and reliable method for the visual sensing of formaldehyde.

Screening of xylene degrading bacteria and optimization of their degradation characteristics in heavily polluted areas

Aiming at the problems of high xylene concentration and difficult removal in heavily polluted areas, high-efficient degrading bacteria of volatile organic compounds (VOCs) xylene in heavily polluted areas were selected and screened from sewage sludge, and their degradation characteristics were studied. The response surface methodology (RSM) optimized the optimal degradation conditions. The results showed that the screened degrading strain was identified as Klebsiella by the 16SrDNA technology and named H-16. During the start-up phase of the reactor, the removal rate of xylene by strain H-16 fluctuated, and it was stable above 71.3% for 150 min. At 40°C, the degradation rate is the highest, reaching 63.25%. With an increasing inoculum amount of strain H-16, the degradation rate of xylene gradually increased, and the degradation rate could reach 86.1% when the inoculation amount was 25%. A neutral environment was more conducive to the degradation and removal of xylene. Through the analysis of the model and RSM, the optimal conditions for the degradation of xylene by H-16 were obtained: 38.89°C, pH 6.94 and 18.07%. GC-MS results showed that the possible degradation pathway of xylene began with demethylation, formation of pentene diacid by benzene ring cleavage, and finally oxidation to generate CO2 and H2O.

Adsorption Behavior of Multi-Component BTEX on the Synthesized Green Adsorbents Derived from Abelmoschus esculentus L. Waste Residue

Benzene, toluene, ethylbenzene, and xylene (BTEX) removal is one of the most common difficulties in air pollution control. They are emitted from several processes, prejudicial to the environment and humans. BTEX leads to various environmental risks, and there is a significant need for a creating process for the complete removal of BTEX from air streams. This study's objective is the multi-component adsorption of BTEX pollutants from an air stream, by synthesizing activated carbons (ACs) under several operations. A lignocellulosic waste biomass, Abelmoschus esculentus L. (AE), was utilized as the precursor for synthesizing activated carbons (AE-ACs), and their surface chemical characteristics were investigated. Optimization processes were examined, and the change in the surface area of AE-ACs was investigated as change of some variables results like activation agent, impregnation ratio, temperature, and activation time. The maximum surface area of 968 m2/g and total pore volume of 0.51 cm3/g were attained at 1:2 impregnation ratio, activation time of 110 min, and activation temperature of 800 °C, under N2 atmosphere. A mixture of BTEX pollutants was employed to consider the effect of humidity (0.5, 1, 1.5, and 2 wt%) and initial concentrations (from 5 to 300 mg/m3), using a contact time of 120 min at the temperature of 25 °C. Under the studied conditions, the multi-component and single-component BTEX adsorption capacities by HCl-activated carbon, AE-ACH, were specifically achieved to 6.86-51.36 mg/g and 22-93.62 mg/g, respectively. Overall, Abelmoschus esculentus L. was exploited for the synthesis of AE-ACH which was successfully utilized for efficient BTEX capture from a polluted air stream.

Engineering of oxygen vacancy defect in CeO2 through Mn doping for toluene catalytic oxidation at low temperature

Catalytic oxidation is considered a highly effective method for the elimination of volatile organic compounds. Oxygen vacancy defect engineering in a catalyst is considered an effective approach for high-performance catalysts. Herein, a series of doped Mn_xCe_1-xO₂ catalysts (x = 0.05-0.2) with oxygen vacancy defects were synthesized by doping low-valent Mn in a CeO₂ lattice. Different characterization techniques were utilized to inspect the effect of doping on oxygen vacancy defect generation. The characterization results revealed that the Mn_0.15Ce_0.85O₂ catalyst has the maximum oxygen vacancy concentration, leading to increased active oxygen species and enhanced oxygen mobility. Thus, Mn_0.15Ce_0.85O₂ catalyst showed an excellent toluene oxidation activity with 90% toluene conversion temperature (T₉₀) of 197 °C at a weight hourly space velocity of 40,000 mL g^-1 h^-1 as compared to undoped CeO₂ (T₉₀ = 225 °C) and Ce based oxides in previous reports. In addition, the Mn_0.15Ce_0.85O₂ catalyst displayed strong recyclability, water resistant ability and long-time stability. The in situ DRIFT results showed that the Mn_0.15Ce_0.85O₂ catalyst has a robust oxidation capability as toluene is quickly adsorbed and actuated as compared to CeO₂. Thus, the present work lays the foundation for designing a highly active catalyst for toluene elimination from the environment.

The Synthesis of Cu–Mn–Al Mixed-Oxide Combustion Catalysts by Co-Precipitation in the Presence of Starch: A Comparison of NaOH with Organic Precipitants

Cu–Mn mixed oxides are well known as active combustion catalysts. The common method for their synthesis is based on co-precipitation, with NaOH as a precipitant, and is burdened with the possibility of introducing undesired Na contamination. This work describes the use of two organic bases, tetrabutylammonium hydroxide and choline hydroxide, as precipitating agents in a novel alkali-free route for Cu–Mn–Al catalyst synthesis. To obtain fine crystalline precursors, which are considered advantageous for the preparation of active catalysts, co-precipitation was carried out in the presence of starch gel. Reference materials prepared with NaOH in the absence of starch were also obtained. Mixed oxides were produced by calcination at 450 °C. The precursors contained MnCO3 doped with Cu and Al, and an admixture of amorphous phases. Those prepared in the presence of starch were less crystalline and retained biopolymer residues. The combustion of these residues during calcination enhanced the formation of larger amounts of the Cu1.5Mn1.5O4 spinel phase, with better crystallinity in comparison to catalysts prepared from conventionally synthesized precursors. Tests of toluene combustion demonstrated that the catalysts prepared with starch performed better than those obtained in starch-free syntheses, and that the mixed oxides obtained by the alkali-free route were more active than catalysts prepared with NaOH. Catalytic data are discussed in terms of property–performance relationships.

Discovering the key role of MnO2 and CeO2 particles in the Fe2O3 catalysts for enhancing the catalytic oxidation of VOC: Synergistic effect of the lattice oxygen species and surface-adsorbed oxygen

Highly active mesoporous Fe-Mn-Ce catalysts with high specific surface area (S_BET) were synthesized by a modified precipitation process for catalyzing toluene oxidation. The Fe_0.85Mn_0.1Ce_0.05 catalyst presents richer surface oxygen species (OS), a higher proportion of Mn⁴⁺ and Ce⁴⁺, a higher concentration of lattice defects and oxygen vacancies, the highest O_ads/O_latt ratio, and a superior low-temperature redox property compared with the Fe-Mn binary oxide and Fe₂O₃ and MnO₂ catalysts. The properties contribute to a high catalytic activity to achieve T₉₀% of toluene conversion at 264 °C and 185 °C with a gas hourly space velocity (GHSV) at 180,000 and 20,000 mL/(g∙h), respectively. The introduction of a slight quantity of Ce and Mn onto the Fe₂O₃ catalyst is the key to enhancing the synergistic effect of the lattice OS and surface-adsorbed oxygen, contributing to the activation oxidation procedure of toluene. In-situ DRIFTS analysis reveals that the rich oxygen vacancy concentration of catalysts accelerates the key steps for the generation and activation of oxidized products. These catalysts with rich oxygen vacancies can efficiently diminish the accumulation of a small number of the intermediary species (phenolate, C₆H₅-OH) produced during the catalytic oxidation of toluene.

Supramolecular self-assembly of a nitro-incorporating quinoxaline framework: insights into the origin of fluorescence turn-on response towards the benzene group of VOCs

Hazardous volatile organic compounds (VOCs) can significantly impact human health and the environment. Hence, the detection of VOCs is of foremost importance. A quinoxaline-based fluorimetric probe (1) unveils a notable "turn-on" fluorescence response towards mesitylene in the presence of other VOCs and common interfering ions in aqueous media. The sensing phenomenon involves specific 1 : 1 stoichiometric binding of the probe with mesitylene with a ∼2.66 ppm detection limit. Furthermore, the probe experiences morphological transformations from a fibril-network to a stone-shaped hetero-structure upon treatment with mesitylene, indicating mesitylene induced self-assembly. The detection induced self-assembly of the probe was further corroborated by dynamic-light-scattering (DLS) and fluorescence microscopy study. Importantly, this proposed approach is applicable to detect mesitylene in natural water sources and in the vapor phase using portable, low-cost filter paper strips.

Design of Co3O4@SiO2 Nanorattles for Catalytic Toluene Combustion Based on Bottom-Up Strategy Involving Spherical Poly(styrene-co-acrylic Acid) Template

Bearing in mind the need to develop optimal transition metal oxide-based catalysts for the combustion of volatile organic compounds (VOCs), yolk-shell materials were proposed. The constructed composites contained catalytically active Co3O4 nanoparticles, protected against aggregation and highly dispersed in a shell made of porous SiO2, forming a specific type of nanoreactor. The bottom-up synthesis started with obtaining spherical poly(styrene-co-acrylic acid) copolymer (PS30) cores, which were then covered with the SiO2 layer. The Co3O4 active phase was deposited by impregnation using the PS30@SiO2 composite as well as hollow SiO2 spheres with the removed copolymer core. Structure (XRD), morphology (SEM), chemical composition (XRF), state of the active phase (UV-Vis-DR and XPS) and reducibility (H2-TPR) of the obtained catalysts were studied. It was proven that the introduction of Co3O4 nanoparticles into the empty SiO2 spheres resulted in their loose distribution, which facilitated the access of reagents to active sites and, on the other hand, promoted the involvement of lattice oxygen in the catalytic process. As a result, the catalysts obtained in this way showed a very high activity in the combustion of toluene, which significantly exceeded that achieved over a standard silica gel supported Co3O4 catalyst.

In Search of Factors Determining Activity of Co3O4 Nanoparticles Dispersed in Partially Exfoliated Montmorillonite Structure

The paper discusses a formation of Mt–PAA composite containing a natural montmorillonite structure partially exfoliated by poly(acrylic acid) introduced through intercalation polymerization of acrylic acid. Mt–PAA was subsequently modified by controlled adsorption of Co²⁺ ions. The presence of aluminosilicate packets (clay) and carboxyl groups (hydrogel) led to the deposition of significant amounts of Co²⁺ ions, which after calcination formed the Co₃O₄ spinel particles. The conditions of the Co²⁺ ions’ deposition (pH, volume and concentration of Co(NO₃)₂ solution, as well as a type of pH-controlling agent) were widely varied. Physicochemical characterization of the prepared materials (including X-ray fluorescence (XRF), X-ray powder diffraction (XRD), low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (H₂-TPR)) revealed that the modification conditions strongly influenced the content as well as the distribution of the Co₃O₄ active phase, tuning its reducibility. The latter parameter was, in turn, very important from the point of view of catalytic activity in the combustion of aromatic volatile organic compounds (VOCs) following the Mars–van Krevelen mechanism.

Highly Active Transition Metal-Promoted CuCeMgAlO Mixed Oxide Catalysts Obtained from Multicationic LDH Precursors for the Total Oxidation of Methane

To improve the catalytic performance of an active layered double hydroxide (LDH)-derived CuCeMgAlO mixed oxide catalyst in the total oxidation of methane, it was promoted with different transition-metal cations. Thus, two series of multicationic mixed oxides were prepared by the thermal decomposition at 750 °C of their corresponding LDH precursors synthesized by coprecipitation at constant pH of 10 under ambient atmosphere. The first series of catalysts consisted of four M(3)CuCeMgAlO mixed oxides containing 3 at.% M (M = Mn, Fe, Co, Ni), 15 at.% Cu, 10 at.% Ce (at.% with respect to cations), and with Mg/Al atomic ratio fixed to 3. The second series consisted of four Co(x)CuCeMgAlO mixed oxides with x = 1, 3, 6, and 9 at.% Co, while keeping constant the Cu and Ce contents and the Mg/Al atomic ratio. All the mixed oxides were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with X-ray energy dispersion analysis (EDX), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption at −196 °C, temperature-programmed reduction under hydrogen (H2-TPR), and diffuse reflectance UV-VIS spectroscopy (DR UV-VIS), while thermogravimetric and differential thermal analyses (TG-DTG-DTA) together with XRD were used for the LDH precursors. The catalysts were evaluated in the total oxidation of methane, a test reaction for volatile organic compounds (VOC) abatement. Their catalytic performance was explained in correlation with their physicochemical properties and was compared with that of a reference Pd/Al2O3 catalyst. Among the mixed oxides studied, Co(3)CuCeMgAlO was found to be the most active catalyst, with a temperature corresponding to 50% methane conversion (T50) of 438 °C, which was only 19 °C higher than that of a reference Pd/Al2O3 catalyst. On the other hand, this T50 value was ca. 25 °C lower than that observed for the unpromoted CuCeMgAlO system, accounting for the improved performance of the Co-promoted catalyst, which also showed a good stability on stream.