Degradation Of O-xylene Research Articles

Insight into the degradation mechanism of mixed VOCs oxidation over Pd/UiO-66(Ce) catalysts: Combination of operando spectroscopy and theoretical calculation

Herein, Pd/UiO-66(Ce) catalysts were successfully synthesized by N2H4, H2, and NaBH4 reduction methods with UiO-66(Ce) as support. The best catalyst was selected via utilizing o-xylene as the probe molecule, and its degradation performance of mixed VOCs was further investigated. It was found that the reduction methods greatly influenced the size of Pd nanoparticles, the state of surface Pd, and the support structure in the catalysts, which in turn affected their catalytic performance. Among them, Pd/UiO-66(Ce)-Na exhibited the best o-xylene degradation activity (T90 = 192 °C) due to its smaller average Pd particle size (Pd Average = 2.93 nm) and higher surface Pd0 content (Pd0/Pdtotal = 0.79). The performance and interaction of Pd/UiO-66(Ce)-Na catalyst for degradation of mixed VOCs (o-xylene and toluene/benzene) were investigated by DFT adsorption energy calculation, in situ DRIFTS and GC–MS. Results suggested that the single adsorption energy of o-xylene was −1.20 eV, while in the system with toluene/benzene, the adsorption energy decreased to −0.78 and −0.6 eV, respectively. This showed the competitive adsorption effect between benzene and o-xylene was stronger than that between benzene and o-xylene. Finally, combined with in situ DRIFTS and GC–MS, the degradation path of mixed components was analyzed and studied systematically, and the mechanism of intermolecular interaction of benzene in the degradation process of mixed components was further revealed.

Effect of NH2-functionalization of MIL-125 on photocatalytic degradation of o-xylene and acetaldehyde

Ligand functionalization of metal organic framework (MOF) is a great important strategy to enhance the various properties of pristine materials. In this study, MIL-125 with different extents of NH2-functionalization were synthesized by solvothermal method. The photocatalytic degradation efficiency of the optimal sample for o-xylene and acetaldehyde were 88 % and 49 %, respectively, which were much improved compared to pristine MIL-125 (56 % for o-xylene and 3 % for acetaldehyde). Compared to pristine MIL-125, NH2-functionlized MIL-125 were more easily photoexcited to form photogenerated carriers, which facilitated the formation of more OH and O2− radicals under visible light irradiation. In addition, NH2 groups as the adsorption site interacted with o-xylene and acetaldehyde by the H-bonding and the Lewis acid-base effect, respectively. The above results contribute to a deep understanding of the influence of ligand functionalization of MOF on the photocatalytic degradation of VOCs.

Catalytic performance of mesoporous Mn-Co-Ti for o-xylene degradation: Mechanistic study under practical conditions

Catalytic combustion of volatile organic compounds from industrial flue gases at low temperatures remains a challenge. Herein, we developed a mesoporous Mn-Co-Ti catalyst for o-xylene degradation by a solvothermal strategy. The optimized Mn0.1Co-TiO2 catalyst possessed a nanoflower structures with a surface area of 83.1 m2/g and mesoporous volume of 0.1191 cm3/g. Mn-doping modulated the electronic interactions between Mn and Co, which promoted the formation of MnCo2O4.5 phase and increased Co3+ and Mn4+ content of the catalyst. The Mn0.1Co-TiO2 catalyst had an improved reduction capacity from 170 to 644 °C, with a maximum H2 consumption of 4.56 mmol/g. The Mn0.1Co-TiO2 catalyst achieved 50% o-xylene conversion at 193 °C at a GHSV of 60,000 h−1, whereas the equivalent catalyst prepared by impregnation required 315 °C for 50% o-xylene conversion. In the presence of NO, the generated NO2 accelerated o-xylene conversion because it promoted the generation of more Mn4+-O-Co3+ active sites and accumulation of intermediates such as maleate and acetate species. NH3 and H2O had slight inhibitory effects on o-xylene conversion, which were attenuated by abundant mesopores and redox ability of catalyst. SO2 gas caused inactive sulfates and chemical deactivation on catalyst surface, thus leading to excessive formation of benzoquinone products.

Room-temperature degradation of o-xylene in simulated air using an online-regenerable plasma-catalysis reactor with low amounts of nanosized noble metals on Co3O4

The plasma catalytic degradation of o-xylene in simulated air was improved by loading low amounts of Pt, Pd, or Au onto Co3O4. At room temperature, o-xylene conversion and CO x selectivity using a 0.1 wt% Pt/Co3O4 catalyst reached 98.9% and 80%, and the energy efficiency was at the top level in comparison with values in the literature. A stable o-xylene degradation performance could be obtained by online regenerating the heat-insulated reactor with a high energy density. After characterization, it was found that the loading of nanosized Pt not only increased the Co3+/Co2+ ratio, where the Co3+ benefitted the formation of reactive oxygen species, but also conduced Pt0 to oxygen activation, resulting in effective promotion of complete o-xylene oxidation. Operando plasma diffuse reflectance infrared Fourier transform spectroscopy demonstrated the complete o-xylene oxidation and proved that Pt played a key role in the complete oxidation of o-xylene.

Multiple interfaces from nano-sized Pt on bimetal oxides of CeO2 and MnO2 promote complete degradation of o-xylene in a room-temperature operated plasma-catalytic reactor

Pt/CeO2/β-MnO2 catalyst with multiple interfaces (Pt and CeO2, Pt and MnO2, CeO2 and MnO2, and Pt sandwiched by CeO2 and MnO2) was developed by supporting nano-sized Pt on CeO2-loaded MnO2 for o-xylene degradation in a room-temperature operated plasma catalytic reactor. It was found that 100 % o-xylene conversion and 88 % CO2 selectivity can be achieved using Pt/CeO2/β-MnO2 catalyst. Characterization results revealed that the best performance of Pt/CeO2/β-MnO2 is due to the highest ratios of Ce3+/Cetotal, Pt0/Pttotal, and Oads/Ototal, while the lowest ratio of Mn3+/Mntotal. Pt and CeO2 on β-MnO2 have synergistic effect on the formation of Ce3+ and Pt0, which can promote the generation of oxygen vacancies and surface reactive oxygen species. The relationship between structure factors and reaction activities has been correlated, the Ce3+/Cetotal ratio can be used as the descriptor to reveal the plasma catalytic activity.

Ti3C2 MXene assembled with TiO2 for efficient photocatalytic mineralization of gaseous o-xylene

In the research of photocatalytic removal of VOCs, the mineralization rate of organic pollutants has been ignored. High mineralization rate means the reduction of intermediates, which is more conducive to environmental protection and photocatalysts stability. In this work, we successfully compounded conductive Ti3C2 with TiO2 for photocatalytic degradation of o-xylene. The production of CO2 by 1 % Ti3C2-TiO2 composite was about twice than that of pure TiO2. The results of PL and photocurrent response showed that 1 % Ti3C2-TiO2 composite had less carrier recombination and higher photocurrent response, which endows its stronger photocatalytic oxidation ability than TiO2. The in-situ infrared spectroscopy revealed that more aromatic anhydride species deposited on the TiO2 surface and led to the less mineralization degree for TiO2 sample. The four-cycle tests further confirmed the better stability of 1 % Ti3C2-TiO2 sample. This work disclosed the role of Ti3C2 in enhancing the mineralization of VOCs, which may provide a new perspective for the design of high-efficiency photocatalysts.

Pulling needles out of a haystack: Subtractive Community Metatranscriptomics retrieves anaerobic o-xylene degradation pathway genes out of a mixed microbial culture

For many contaminants, biomarker genes are unknown or assays are unavailable, and most biomarker assays target the first pathway step. Herein, we obtained sequences for all of the genes in a previously hypothesized o-xylene degradation pathway based on similarities to analogous genes in a known toluene degradation pathway. Comparative metatranscriptomics resulted in sequences for genes annotated as bssA, bbsEF, bbsCD, and bbsB, while genes for bbsG and bbsH were notably missing. Prokaryotic Suppressive Subtractive Hybridization PCR cDNA Subtraction (Prokaryotic SSH-PCR cDNA Subtraction) was applied for the first time to a mixed-species microbiome to enrich abundances of genes up-regulated during o-xylene degradation prior to metatranscriptomic sequencing. The subtracted metatranscriptome was sequenced using the MinION; this approach was highly effective at retrieving sequences for biodegradation genes including the previously missing bbsG and bbsH. Reverse transcription quantitative PCR (RT-qPCR) analysis confirmed up-regulation. Thus, data reported herein lend credence to the previously hypothesized anaerobic o-xylene degradation pathway, and new biomarker assays are presented. A novel biomarker development tool for mixed species systems, Subtractive Community Metatranscriptomics (SCM), is demonstrated.

Mass transfer and reaction simultaneously enhanced airlift microbial electrolytic cell system with high gaseous o-xylene removal capacity

To overcome the limitation of mass transfer and reaction rate involved in the biodegradation of gaseous o-xylene, the airlift reactor and microbial electrolysis cell were integrated to construct an airlift microbial electrolysis cell (AL-MEC) system for the first time, in which the bioanode was modified by polypyrrole to further improve biofilm attachment. The developed AL-MEC system achieved 95.4% o-xylene removal efficiency at optimized conditions, and maintained around 75% removal efficiency even while the inlet o-xylene load was as high as 684 g m−3 h−1. The existence of O2 exhibited a competition in electrons with the bioanode but a positive effect on ring-opening process in the o-xylene oxidation. The limitation of mass transfer had been overcome as the empty bed resistance time in the range of 20–80 s did not influence the system performance significantly. The microbial community analysis confirmed the o-xylene degradation microbes and electroactive bacteria were the dominant, which could be further enriched at 0.3 V against standard hydrogen electrode. This work revealed the feasibility of the AL-MEC system for the degradation of o-xylene and similar compounds, and provided insights into bioelectrochemical system design with high gaseous pollution removal capacity.

Photocatalytic oxidation mechanism of Gas-Phase VOCs: Unveiling the role of holes, •OH and •O2−

To identify the distinctive role of reactive oxygen species (ROS) and trace the intermediates not only help to decompose the pollutants in high efficiency but also for avoiding more harmful intermediates formed. Here, we developed a new method to generate different ROSs by controlling the atmosphere to distinguish their role in the degradation of flowing gas-phase VOCs, including o-xylene, styrene, and acetaldehyde. This method is in good agreement with the traditional sacrificial agent capture experiment. The results show that •OH radicals play a dominant role in the degradation of o-xylene and styrene, while •O2− radicals primarily take part in the acetaldehyde degradation. Additionally, we distinguish the role of holes, •OH and •O2− played during the VOCs photo-oxidation through the radical trapping, in situ DRIFTS, and GC-MS analysis. Under the attack of •O2− radicals, aromatic VOCs were photo-oxidized to intermediates containing benzene rings and ketones (i.e., toluene and butanone), while carbon chain compounds (i.e., 3-methylfuran and ethanol) tend to form under the action of •OH and holes. This can be associated with the different reaction paths initiated by ROS. For acetaldehyde removal, •O2− species facilitate the formation of acids (i.e., acetic acid) while the •OH species and holes lead to the production of ketones (i.e., acetone). This work provides deep understanding on the role of various ROS in the photocatalytic oxidation of VOCs, which can guide the design of efficient photocatalysts, selective formation of intermediates to be easily decomposed or as raw materials for further application.

Rare-earth single atoms decorated 2D-TiO2 nanosheets for the photodegradation of gaseous O-xylene

In this work, rare-earth single atoms (La, Er) were decorated on the surface of 2D-TiO2 nanosheets by an impregnation-calcination strategy. The formation of rare-earth single atoms was certified by AC HAADF-STEM and XAS. TiO2 decorated with rare-earth single atoms (La1-TiO2 and Er1-TiO2) exhibited outstanding photocatalytic activity than pure 2D-TiO2 nanosheets (2D-TiO2) towards gas-phase degradation of O-xylene. Compared with 2D-TiO2, the rare-earth single atoms greatly improved the adsorption capacity of O-xylene without increasing their specific surface area. This is because rare-earth single atoms provide additional adsorption sites and reduce the adsorption energy of O-xylene. In addition, the hybrid orbital formed by the combination of rare-earth single atom and oxygen atom is beneficial to the rapid transmission and separation of photo-induced electrons, thereby improving the performance of photocatalytic degradation. In addition, in-situ DRIFTS and GC–MS were used to reveal the photocatalytic oxidation mechanism. Interestingly, the results showed that the La1-TiO2 and Er1-TiO2 samples can reduce the types of intermediates and simplify the reaction route, implying that the single atoms play an important role in the modulation and thorough mineralization of intermediate products. This work shows that the rare-earth single atom decorated 2D-TiO2 nanosheets have great potential in photocatalytic air pollution control.

Transcriptomic Analysis of Rhodococcus opacus R7 Grown on o-Xylene by RNA-Seq.

Xylenes are considered one of the most common hazardous sources of environmental contamination. The biodegradation of these compounds has been often reported, rarer the ability to oxidize the ortho-isomer. Among few o-xylene-degrading bacteria, Rhodococcus opacus R7 is well known for its capability to degrade diverse aromatic hydrocarbons and toxic compounds, including o-xylene as only carbon and energy source. This work shows for the first time the RNA-seq approach to elucidate the genetic determinants involved in the o-xylene degradation pathway in R. opacus R7. Transcriptomic data showed 542 differentially expressed genes that are associated with the oxidation of aromatic hydrocarbons and stress response, osmotic regulation and central metabolism. Gene ontology (GO) enrichment and KEGG pathway analysis confirmed significant changes in aromatic compound catabolic processes, fatty acid metabolism, beta-oxidation, TCA cycle enzymes, and biosynthesis of metabolites when cells are cultured in the presence of o-xylene. Interestingly, the most up-regulated genes belong to the akb gene cluster encoding for the ethylbenzene (Akb) dioxygenase system. Moreover, the transcriptomic approach allowed identifying candidate enzymes involved in R7 o-xylene degradation for their likely participation in the formation of the metabolites that have been previously identified. Overall, this approach supports the identification of several oxidative systems likely involved in o-xylene metabolism confirming that R. opacus R7 possesses a redundancy of sequences that converge in o-xylene degradation through R7 peculiar degradation pathway. This work advances our understanding of o-xylene metabolism in bacteria belonging to Rhodococcus genus and provides a framework of useful enzymes (molecular tools) that can be fruitfully targeted for optimized o-xylene consumption.

Unveiling the unconventional roles of methyl number on the ring-opening barrier in photocatalytic decomposition of benzene, toluene and o-xylene

The ring-opening reaction is the rate-determining step for photocatalytic decomposition of aromatic VOCs with different methyl number. However, as a key challenge, the intrinsic relationship between the methyl number and ring-opening reaction efficiency has not been revealed. In order to clarify the ring-opening barriers and enhance the photocatalytic efficiency, the photocatalytic degradation pathway was systematically investigated aiming to elucidate the pivotal roles of methyl number on ring-opening mechanisms. The SnO2 is chosen as a photocatalyst to achieve highly efficient and stable photocatalytic degradation of benzene, toluene, and o-xylene respectively. It is unexpected to discover that the photocatalytic degradation performance and quantum efficiency are significantly elevated along with the increase of methyl number, reaching the highest efficiency for o-xylene with two methyl groups. The photocatalytic degradation efficiency of o-xylene on SnO2 is as high as 78.2 %, much higher than that of toluene (63.4 %) and benzene (55.9 %). The introduction of methyl groups could exert great influence on the distribution of electrons on the phenyl ring, enhance the adsorption and activation of benzene rings, and finally reduce the energy barrier of ring-opening reaction. The methyl number in the benzene ring is dominantly responsible for the elevated decomposition efficiency. This work proposes a new concept in mechanistic understanding of VOCs decomposition and propels the application of photocatalytic technology for efficient degradation of aromatic VOCs.

Determining the impacts of environmental parameters on model microbial community dynamics isolated from Rustumihia WWTP/Iraq

The composition of Rustumihia microbial community and their diversity with o-xylene-contaminants were investigated by applying molecular techniques, Polymerase chain reaction and denaturing gradient gel electrophoresis (PCR and DGGE) via investigating 16S rRNA gene fragments and understand the interrelationships between microbial community composition and structure for established microbial model community isolated from Rustumihia WWTP. To this end, that the established consortium could be used to assess the microbial response as defined by diversity and richness shifts, which are linked to changes in growth conditions. In this research paper a synthetic consortium was created by isolating indigenous microbial community members from the Rustumihia WWTP and subjecting consortium to different pH of (6.5, 7.0 and 7.5) and o-xylene concentrations of (0.5, 5 and 50 Mm) and temperatures (25°C, 35°C, 45°C and 55°C).The results of this study indicated that the high o-xylene concentration of 50 mM was tolerated and degraded effectively at 35°C and 55°C, and pH 6.5 (P < 0.001). Bacterial richness and diversity were recorded according to the Hill parameters of 0 D, 1 D and 2 D under each of the growth conditions, and then linked to the o-xylene degradation efficiency. At 35°C and pH 6.5, the consortium achieved high degradation percentage for each of 0.5, 5 and 50 mM of o-xylene with values 73.1%, 94.8% and 63.08%, respectively. The current study is the first of its kind in Iraq. It investigates the enrichment, isolation, and identification of a microbial community from the Rustumihia WWTP and determines the efficiency of the isolates to tolerate and degrade o-xylene, highlighting their sole source of hydrocarbon. This research underscores the usefulness of molecular techniques for both diversity and richness to understand the ecological impact of o-xylene as a contaminant and to identify potential molecular techniques for detection of gene that is responsible for o-xylene degradation.

Characterisation of indigenous microbial community isolated from wastewater treatment phases Baghdad/Iraq

Biodegradation processes could be efficient for such organic contaminants like o-xylene within sewage. Since the biodegradation processes is mainly controlled by microbial communities therefore, this research paper intended that the bioaugmentation process application might speed up or improve biodegradation process in Rustumihia plant. It delivers an initial knowledge of the effects of one of the most complicated organic contaminants at Rustumihia plant. In addition to that, it suggested the using of indigenous microbial communities that is isolated from the treatment plant within the application of bioaugmentation. It reveals findings on the ecology of o-xylene degradation via using bacterial communities that were already enriched and isolated from the four important treatment phases of Iraq’s Rustumihia plant

Ultrasound-assisted heterogeneous activation of persulfate and peroxymonosulfate by asphaltenes for the degradation of BTEX in water

This study investigated – for the first time – the simultaneous degradation of benzene, toluene, ethylbenzene and o-xylene (BTEX) by persulfate (PS) and peroxymonosulfate (PMS) activated by asphaltenes (Asph) under ultrasound (US) irradiation. Advantageous properties such as high thermal stability, low production cost and extensive availability make asphaltenes as an appealing carbonaceous material for heterogeneous catalysis. The application of asphaltenes in PS/US increased the degradation of BTEXs from 31%, 34%, 35%, 32%–78%, 94%, 98% and 98%, while the removal of these compounds in PMS/US system was improved from 26%, 27%, 24%, 20%–76%, 91%, 97%, 97%, respectively. PS and PMS activation followed a typical sulfate-radical based advanced oxidation processes. In terms of activation of PS and PMS, the particles of asphaltenes intensified formation of reactive radicals by creating additional centers of cavitational events. Moreover, owing to π–π stacking interaction between asphaltenes and sp2-hybridized systems of BTEX, the contaminants undergo adsorption on the surface of asphaltenes and subsequent oxidation by formed radicals. The radical route of BTEX degradation in both PS/US/Asph and PMS/US/Asph systems was mainly contributed by sulfate (SO4•−) and hydroxyl radicals (HO•) and coexisting superoxide radical anions (O2•−) played a minor role.

Band bending of TiO2 induced by O-xylene and acetaldehyde adsorption and its effect on the generation of active radicals

Most studies on the photodegradation of volatile organic compounds (VOCs) have focused on the synthesis of efficient photocatalysts. However, little attention has been paid to the band bending change of semiconductive photocatalysts after the adsorption of VOCs. Herein, we first disclose how the adsorption of two typical VOCs influences the band bending of P-type rutile TiO2 and consequently changes the amount of reactive radicals. This provides a new way to understand the experimental phenomenon of heterogeneous reactions. Theoretical computations of the adsorption model and zeta potential tests both verified that o-xylene is an acceptor molecule when it adsorbs on the TiO2 surface, and it tends to attract electrons from TiO2. In contrast, acetaldehyde is a donor molecule. A distinct electron transfer direction between TiO2 and adsorbed molecules (o-xylene and acetaldehyde) induces a different band bending degree. O-xylene adsorption alleviates the downward band bending of TiO2 itself, whereas acetaldehyde adsorption strengthens the downward band bending. The probability of electrons and holes reaching the TiO2 surface is influenced by this change, which has a considerable influence on the generation of active radicals. Consequently, o-xylene adsorption leads to more hydroxyl radical generation, and acetaldehyde adsorption results in less hydroxyl radical generation. As a result, hydroxyl radicals play the predominant role in the degradation of o-xylene, whereas the photocatalysis of acetaldehyde is dominant for superoxide radicals. In addition, the band bending of a semiconductor induced by gaseous molecule adsorption has the potential for application in gas sensors to improve sensitivity.

Enhancement of gaseous o-xylene degradation in a microbial fuel cell by adding Shewanella oneidensis MR-1

An exoelectrogens, Shewanella oneidensis MR-1 (S. oneidensis MR-1), was supplied to a microbial fuel cell (MFC) to enhance the degradation of a recalcitrant organic compound, o-xylene. The experimental results revealed that, with the addition of the S. oneidensis MR-1, the o-xylene removal efficiency increased by 35–76% compared with the original MFC. The presence of the S. oneidensis MR-1 not only improved the activity of the biofilm in the bioanode but also developed the connections between the bacteria by nanowires. Therefore, the maximum power density increased from 52.1 to 92.5 mW/m3 after the addition of the S. oneidensis MR-1. The microbial community analysis showed that adding the S. oneidensis MR-1 increased the biodiversity in bioanode. The dominant exoelectrogens shifted from Zoogloea sp., Delftia sp., Achromobacter sp., Acinetobacter sp., Chryseobacterium sp., and Stenotrophomonas sp. to Zoogloea sp., Delftia sp., Shewanella sp., Achromobacter sp., Hydrogenophaga sp., Sedimentibacter sp. and Chryseobacterium sp.. Furthermore, the cyclic voltammetry analysis showed that the outer membrane bound protein complex of OmcA–MtrCAB was involved as direct electron transfer pathway in the S. oneidensis MR-1 containing bioanode. We believed that this work is promising to provide optional strategy for efficient VOCs degradation by adjusting the microbial community in the bioanode.

Surface adsorption configurations of H3PO4 modified TiO2 and its influence on the photodegradation intermediates of gaseous o-xylene

Abstract For the oxide-based photocatalysts, polyoxylic acid modification can affect their adsorption/desorption properties and further regulate photocatalytic reaction pathway, which is crucial for enhancing photocatalytic activity and selectivity. Herein, phosphoric acid modified TiO2 was synthesized by a facile impregnation-calcination method for photocatalytic degradation of gaseous o-xylene. According to FTIR, XPS, and EDS analysis, phosphoric acid was anchored on the surface of TiO2 successfully. The surface P atomic percentages for PT1 was 2.45%. The as-prepared phosphoric acid modified TiO2 (PTx) had a photocatalytic performance superior to that of commercial TiO2 and unmodified TiO2 (PT0), with increasing by 2.2 times at most. Interestingly, the phosphoric acid molecules strongly adsorbed on anatase TiO2 surface by forming H–O2C and =O–Ti5C chemical bonds according to the first principle calculations, which changed TiO2 surface properties (specific surface area and surface negative electrostatic field) and further improved adsorption and charge carrier separation and transfer, thus improving the photocatalytic activity. Additionally, according to the intermediates results, the relative abundance of intermediates shows obvious difference. Acetone was detected as the most abundant intermediates during o-xylene degradation for PT0, whereas that was o-methyl benzaldehyde for PT1, which could be ascribed to the difference of surface adsorption configuration of o-xylene. According to the temperature-programmed desorption (TPD) results, the surface modified by phosphoric acid could change the o-xylene adsorption configuration to favor its methyl oxidation (standing configuration), whereas the unmodified surface could be more favorable to the benzene ring-open reaction (lying configuration). This work will deepen the understanding of the relevance of surface modification and surface photocatalytic reaction, which also provides a feasible strategy to improve photocatalytic selectivity.

Degradation of gas-phase o-xylene via combined non-thermal plasma and Fe doped LaMnO3 catalysts: Byproduct control

A series of Fe doped LaMnO3 catalysts were prepared to control the production of byproducts such as O3, N2O, and CO, during the degradation of volatile organic compounds with a non-thermal plasma. Eliminating these potentially toxic byproducts will make non-thermal plasma technologies applicable for a wider range of commercial applications. The modified LaMnO3 catalysts are combined in NTP-catalysis reactor with optimal configuration. Experimental results show that doping Fe on LaMnO3 catalysts can not only enhance the oxidation of o-xylene, but also lower the emission levels of byproducts. LaMn0.9Fe0.1O3 catalyst shows the best catalytic activity among the formulations tested herein. In addition to the strong mineralization of 88.1 %, the catalyst has the highest performance for o-xylene conversion (91.3 %), O3 inhibition efficiency (84.9 %), and N2O inhibition efficiency (61.2 %) due to the strong concentration of active oxygen species on the surface of the catalyst. Moreover, the high reducibility of Fe3+ demonstrated with H2-TPR (hydrogen temperature-programed reduction) further enhances the removal of O3 by oxygen species exchange between Mn3+/Mn4+ and Fe2+/Fe3+.

Sonochemical Synthesis of Ce-doped TiO2 Nanostructure: A Visible-Light-Driven Photocatalyst for Degradation of Toluene and O-Xylene.

Ce-doped TiO2 nanostructures (CeT) with different amounts of Ce (0.5, 0.75, 1.0, 1.5, and 2.0 wt. %) were synthesized using a sonochemical processing method. The physicochemical properties of the prepared samples were explored using UV-visible diffuse reflectance spectroscopy (UV-vis DRS), field-emission TEM (FE-TEM), XRD, X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), and surface area and pore size analyzers. The photocatalytic performance of the prepared CeT was assessed by monitoring their degradation efficiencies for gaseous toluene and o-xylene—widely known as significant indoor air pollutants—under daylight irradiation. The prepared CeT exhibited significantly improved photocatalytic performance towards the degradation of toluene and o-xylene, which was much higher than that observed for pure TiO2 and commercial P25 TiO2. Particularly, photocatalytic degradation efficiencies by the prepared CeT catalysts increased remarkably in the case of o-xylene (up to 99.4%) compared to toluene (up to 49.1%). The degradation efficiency by the CeT was greatest for the CeT-0.75 sample, followed by, in order, CeT-1.0, CeT-0.5, CeT-1.5, and CeT-2.0 samples in agreement with the order of the surface area and the particle size of the catalysts. According to the change of light source, the average decomposition efficiencies for toluene and o-xylene by CeT-0.75 were shown in the order of conventional daylight lamp > violet light emitting diodes (LEDs) > white LEDs. The decomposition efficiencies normalized to supplied electric power, however, were estimated to be in the following order of violet LEDs > white LEDs > conventional daylight lamp, indicating that the LEDs could be a much more energy efficient light source for the photodecomposition of target toluene and o-xylene using the CeT-0.75 photocatalyst.