Specific Recognition and Adsorption of Volatile Organic Compounds by Using MIL-125-Based Porous Fluorescence Probe Material

The severity of the volatile organic compounds (VOCs) issue calls for effective detection and management of VOC materials. Metal-organic frameworks (MOFs) are organic-inorganic hybrid crystals with promising prospects in luminescent sensing for VOC detection and identification. However, MOFs have limitations, including weak response signals and poor sensitivity towards VOCs, limiting their application to specific types of VOC gases. To address the issue of limited recognition and single luminosity for specific VOCs, we have introduced fluorescent guest molecules into MOFs as reference emission centers to enhance sensitivity. This composite material combines the gas adsorption ability of MOFs to effectively adsorb VOCs. We utilized (MIL-125/NH2-MIL-125) as the parent material for adsorbing fluorescent molecules and selected suitable solid fluorescent probes (FGFL-B1) through fluorescence enhancement using thioflavin T and MIL-125. FGFL-B1 exhibited a heightened fluorescence response to various VOCs through charge transfer between fluorescent guest molecules and ligands. The fluorescence enhancement effect of FGFL-B1 on tetrahydrofuran (THF) was particularly pronounced, accompanied by a color change from yellow to yellowish green in the presence of CCl4. FGFL-B1 demonstrated excellent adsorption properties for THF and CCl4, with saturated adsorption capacities of 655.4 mg g-1 and 811.2 mg g-1, respectively. Furthermore, FGFL-B1 displayed strong luminescence stability and reusability, making it an excellent sensing candidate. This study addresses the limitations of MOFs in VOC detection, opening avenues for industrial and environmental applications.

Emissions and light absorption of PM2.5-bound nitrated aromatic compounds from on-road vehicle fleets

Vehicle emissions are an important source of nitrated aromatic compounds (NACs) in particulate size smaller 2.5 μm (PM_2.5), which adversely affect human health and biodiversity, especially in urban areas. In this study, filter-based PM_2.5 samples were collected during October 14-19, 2019, in a busy urban tunnel (approximately 35,000 vehicles per day) in south China to identify PM_2.5-bound NACs. Among them, 2,8-dinitrodibenzothiophene, 3-nitrodibenzofuran and 2-nitrodibenzothiophene were the most abundant nitrated polycyclic aromatic hydrocarbons (NPAHs), while 2-methyl-4-nitrophenol, 2,4-dinitrophenol, 3-methyl-4-nitrophenol and 4-nitrophenol were the most abundant nitrophenols (NPs). The observed mean fleet emission factors (EFs) of NPAHs and NPs were 2.2 ± 2.1 and 7.7 ± 4.1 μg km^-1, and were 2.9 ± 2.7 and 10.2 ± 5.4 μg km^-1 if excluding electric and liquefied petroleum gas vehicles, respectively. Regression analysis revealed that diesel vehicles (DVs) had NPAH-EFs (55.3 ± 5.3 μg km^-1) approximately 180 times higher than gasoline vehicles (GVs) (0.3 ± 0.2 μg km^-1), and NP-EFs (120.6 ± 25.8 μg km^-1) approximately 30 times higher than GVs (4.1 ± 0.2 μg km^-1), and thus 89% NPAH emissions and 56% NP emissions from the onroad fleets were contributed by DVs although DVs only accounted for 3.3% in the fleets. Methanol solution-based light absorption measurements demonstrated that the mean incremental light absorption for methanol-soluble brown carbon at 365 nm was 6.8 ± 2.2 Mm^-1, of which the 44 detected NACs only contributed about 1%. The mean EF of the 7 toxic NACs was approximately 3% that of the 16 priority PAHs; However, their benzo(a)pyrene toxic equivalence quotients (TEQ_BaP) could reach over 25% that of the PAHs. Moreover, 6-nitrochrysene mainly from DVs contributed 93% of the total TEQ_BaP of the NACs. This study demonstrated that enhancing DV emission control in urban areas could benefit the reduction of exposure to air toxins such as 6-nitrochrysene.

Oxidative desulfurization of model and real fuel samples with natural zeolite-based catalysts: experimental design and optimization by Box–Behnken method

In this study, oxidative desulfurization was performed on simulated oil fraction consist of 1000 ppm dibenzothiophene. Cobalt supported on natural zeolite of Kaolin has been used as heterogeneous catalysts. 10% Co/metaKaolin with hydrogen peroxide as oxidant and acetonitrile as extraction solvent have shown excellent performance on desulfurization. Response surface methodology in experimental design and its subset Box–Benken was used to evaluate the performance of the selected catalyst in different operating conditions such as temperature, oxidant to sulfur molar ratio, time and catalyst amount. Also, optimum conditions was obtained are equal to 60 °C, O/S molar ratio (10.8 mol/mol), time (46 min) and catalyst amount 0.04 g with 97.1% sulfur removal. Oxidative desulfurization of model oil containing 1000 ppm of each sulfur component benzothiophene and thiophene was also tested at the optimum conditions, Oxidative desulfurization yield was ordered as DBT > BT > Th. In addition, after four steps consecutive recycle under optimum conditions oxidative desulfurization capacity of 10% Co/metaKaolin catalyst decreased from 97% to 92%, which is still high desulfurization capability. Finally, the performance of 10% Co/metaKaolin catalyst in oxidative desulfurization was evaluated for real oil fractions, gasoline and gasoil that was provided from regional oil refinery with sulfur content of 286 ppm and 7900 ppm, respectively. At the optimum conditions of operating variables desulfurization yield was 58% and 79% of total sulfur removal for gasoline and gasoil respectively with no significant changes in fuels properties.

Scale-up reactivation of spent S-Zorb adsorbents for gasoline desulfurization

Reactivating and recycling spent S-Zorb adsorbents reduce fresh adsorbents consumption and hazardous wastes emissions. Though the spent adsorbents have been successfully reactivated in the laboratory, a pilot-scale practice is indispensable before the industrial production. Herein, the reactivation of spent adsorbents was performed at laboratory (1.0 L), middle (10 L) and pilot (3000 L) scale, respectively. The inert Zn₂SiO₄ and ZnS over the spent adsorbents are recovered to active ZnO, and the NiS is transformed into NiO. There is almost no amplification effect in pore structure and acidity of the reactivated adsorbents, while NiO particle size reduces slightly with the reactivation scales. The computational fluid dynamic simulation indicates that enhanced contact between spent adsorbents and acid/alkaline reagents at larger scale account for the smaller NiO particle. It provides more hydrogenolysis centers for CS bonds breakage after reduction, increasing initial desulfurization activity. More importantly, the adsorbent reactivated at pilot scale exhibits comparable activity to the fresh one in gasoline desulfurization. The sulfur content in the outlet decreases to less than 10 μg g^-1 from 1 h of reaction. Thus, the reactivation of spent S-Zorb adsorbents is successfully scaled up to the pilot scale, accelerating industrial practice in recycling the spent adsorbents.

Efficient hydrodesulfurization of dibenzothiophene over core–shell Ni/Al2O3@SOD and Mo/Al2O3 composite catalysts

A DBT HDS reaction scheme based on different composite catalysts (Ni/Al2O3@SOD–Mo/Al2O3 and Ni/Al2O3–Mo/Al2O3) is proposed.

Mild Oxidation of Organosulfur Compounds with H2O2 over Metal-Containing Microporous and Mesoporous Catalysts

Mild catalytic oxidation of thioethers and thiophenes is an important reaction for the synthesis of molecules with pharmaceutical interest, as well as for the development of efficient processes able to remove sulfur-containing pollutants from fuels and wastewater. With respect to the green chemistry principles, hydrogen peroxide (H2O2) is the ideal oxidant and the Me-containing porous materials (Me = Ti, V, Mo, W, Zr) are among the best heterogeneous catalysts for these applications. The main classes of catalysts, including Me-microporous and mesoporous silicates, Me-layered double hydroxides, Me-metal–organic frameworks, are described in this review. The catalytic active species generated in the presence of H2O2, as well as the probable oxidation mechanisms, are also addressed. The reactivity of molecules in the sulfoxidation process and the role played by the solvents are explored.

Improving the hydrodesulfurization performance of the sulfur-resistant intermetallic Ni2Si based on a MOF-derived route

Carbon-supported intermetallic nickel silicide (Ni₂Si/C) derived from Ni-MOF-74 as a non-sulfide catalyst presents high activity and sulphur-resistance in the hydrodesulfurization (HDS) of dibenzothiophene (DBT).

A new simple protocol for the synthesis of nanohybrid catalyst for oxidative desulfurization of dibenzothiophene

This study offers an investigation of the catalytic activity of TiO₂/SiO₂ during oxidative desulfurization (ODS) of a model fuel that includes dibenzothiophene (DBT), using hydrogen peroxide (H₂O₂) as a green oxidant in the absence of UV irradiation. For the first time, though a novel and simple protocol, TiO₂/SiO₂ nanohybrid was synthesized using ascorbic acid and glycerol as green complexing and polymerizing agents, respectively. The TiO₂/SiO₂ catalyst was thoroughly characterized by XRD, FT-IR, nitrogen adsorption-desorption measurements, TEM, FESEM, and TGA. Results revealed a high catalytic oxidative activity for the catalyst in the removal of DBT regarding sulfur removal up to 99.4% within 20 min under optimum reaction conditions. The main factors affecting the ODS process, including catalyst dosage, temperature, O/S molar ratio, and different oxidizing agents, were evaluated to identify optimum conditions. The desulfurization efficiency of the recoverable catalysts showed no loss in activity after four times. The present article suggests a new and green method for the synthesis and characterization of an efficient catalyst (TiO₂/SiO₂) in deep oxidative desulfurization at 25 °C and removal of refractory organosulfur compounds that yield ultra-low sulfur fuels. Also, it proved to have a much higher catalytic oxidation capacity when compared to pure TiO₂.

New VIVO-complexes for oxidative desulfurization of refractory sulfur compounds in fuel: synthesis, structure, reactivity trend and mechanistic studies

A series of 5-coordinate oxidovanadium(iv) complexes based on 2-(2'-hydroxyphenyl)imidazole (HPIMH), with substituent groups of different electronegativities on the phenolic para position (HPIMX; X = -H, -Br, -OMe and -NO2), were synthesized and characterized. Three of these complexes were characterized by single crystal X-ray diffraction, [VIVO(PIMH)2], [VIVO(PIMBr)2] and [VIVO(PIMNO2)2], as well as a dioxidovanadium(v) compound ([VVO2(PIMH)(PIMH2)]). The complexes were tested for their catalytic activities in the oxidation of dibenzothiophene (DBT), the major refractory organosulfur compound found in fuel. The nitro substituted compound [VIVO(PIMNO2)2] had the highest catalytic oxidation activity followed by: [VIVO(PIMH)2] > [VIVO(PIMBr)2] > [VIVO(PIMMeO)2]. The decrease in activity is attributed to the different electronegativities of the substituent groups, which influence the electron density on the metal center, the V[double bond, length as m-dash]O bond distances and infrared stretching bands. Geometry index (τ) values calculated from single crystal X-ray diffraction (SC-XRD) data and DFT studies provided further insights on the trend in activity observed. SC-XRD, EPR, 51V NMR and UV-Vis spectroscopies, and DFT studies were instrumental in studying the mechanism of the catalyzed reaction and proposal of intermediate species. Both radical and non-radical pathways are plausible for the catalytic oxidation and participation of reactive oxygen species in both pathways is also postulated.

An overview of conventional and alternative technologies for the production of ultra-low-sulfur fuels

Environmental concerns have given a great deal of attention for the production of ultra-low-sulfur fuels. The conventional hydrodesulfurization (HDS) process has high operating cost and also encounters difficulty in removing sulfur compound with steric hindrance. Consequently, various research efforts have been made to overcome the limitation of conventional HDS process and exploring the alternative technologies for deep desulfurization. The alternative processes being explored for the production of ultra-low-sulfur content fuel are adsorptive desulfurization (ADS), biodesulfurization (BDS), oxidative desulfurization (ODS), and extractive desulfurization (EDS). The present article provided the comprehensive information on the basic principle, reaction mechanism, workability, advantages, and disadvantages of conventional and alternative technologies. This review article aims to provide valuable insight into the recent advances made in conventional HDS process and alternative techniques. For deep desulfurization of liquid fuels, integration of conventional HDS with an alternative technique is also proposed.

Fast and deep oxidative desulfurization of dibenzothiophene with catalysts of MoO3–TiO2@MCM-22 featuring adjustable Lewis and Brønsted acid sites

The synthesis of high-performance and recyclable catalysts for oxidative desulfurization (ODS) from fuels has been a significant challenge.

Enhanced catalytic activity of monodispersed porous Al2O3 colloidal spheres with NiMo for simultaneous hydrodesulfurization and hydrogenation

Fabrication of monodispersed porous Al₂O₃ spheres with controlled morphologies.

A new approach to construct a hydrodesulfurization catalyst from a crystalline precursor: ligand-induced self-assembly, sulfidation and hydrodesulfurization

This paper proposes a new approach for investigating the mechanism of the formation of the active phase of a hydrodesulfurization (HDS) catalyst via crystalline polyoxometalate (POM) precursors.

Adsorptive denitrogenation of fuel over molecularly imprinted poly-2-(1H-imidazol-2-yl)-4-phenol microspheres

Molecularly imprinted poly 2-(1H-imidazol-2-yl)-4-phenol prepared by suspension polymerization of 2-(1H-imidazol-2-yl)-4-vinylphenol in the presence of selected nitrogen containing compounds showed adsorption selectivity for target nitrogen-containing compounds in fuel oil.

TiO2-Containing Carbon Derived from a Metal-Organic Framework Composite: A Highly Active Catalyst for Oxidative Desulfurization

A new metal-organic framework (MOF) composite consisting of Ti- and Zn-based MOFs (ZIF-8(x)@H₂N-MIL-125; in brief, ZIF(x)@MOF) was designed and synthesized. The pristine MOF [H₂N-MIL-125 (MOF)]- and an MOF-composite [ZIF(30)@MOF]-derived mesoporous carbons consisting of TiO₂ nanoparticles were prepared by pyrolysis (named MDC-P and MDC-C, respectively). MDC-C showed a higher surface area, larger pore sizes, and larger mesopore volumes than MDC-P. In addition, the TiO₂ nanoparticles on MDC-C have more uniform shapes and sizes and are smaller than those of MDC-P. The obtained MDC-C and MDC-P [together with MOF, ZIF(30)@MOF, pure/nanocrystalline TiO₂, and activated carbon] were applied in the oxidative desulfurization reaction of dibenzothiophene in a model fuel. The MDC-C, even with a lower TiO₂ content than that of MDC-P, showed an outstanding catalytic performance, especially with a very low catalyst dose (i.e., a very high quantity of dibenzothiophene was converted per unit weight of the catalyst), fast kinetics (∼3 times faster than that for MDC-P), and a low activation energy (lower than that for any reported catalyst) for the oxidation of dibenzothiophene. The large mesopores of MDC-C and the well-dispersed/small TiO₂ might be the dominant factors for the superior catalytic conversions. The oxidative desulfurization of other sulfur-containing organic compounds with various electron densities was also studied with MDC-C to understand the mechanism of catalysis. Moreover, the MDC-C catalyst can be reused many times in the oxidative desulfurization reaction after a simple washing with acetone. Finally, composing MOFs and subsequent pyrolysis is suggested as an effective way to prepare a catalyst with well-dispersed active sites, large pores, and high mesoporosity.

Protonated MIL-125-NH2: Remarkable Adsorbent for the Removal of Quinoline and Indole from Liquid Fuel

The removal of nitrogen-containing compounds (NCCs) from fossil fuels prior to combustion is currently of particular importance, and so we investigated an adsorptive method using metal-organic frameworks (MOFs) for the removal of indole (IND) and quinoline (QUI), which are two of the main NCCs present in fossil fuels. We herein employed an amino (-NH₂)-functionalized MIL-125 (MIL-125-NH₂) MOF, which was further modified by protonation (P-MIL-125-NH₂). These modified MOFs exhibited extraordinary performance in the adsorption of both IND (as representative neutral NCC) and QUI (as representative basic NCC). These MOFs were one of the most efficient adsorbents for the removal of NCCs. For example, P-MIL-125-NH₂ showed the highest adsorption capacity for QUI among ever reported adsorbent. The improved adsorption of IND was explained by H-bonding and cation-π interactions for MIL-125-NH₂ and P-MIL-125-NH₂, respectively, while the mechanisms for QUI were H-bonding and acid-base interactions, respectively. This is a rare phenomenon for a single material (especially not with very high porosity) to exhibit such remarkable performances in the adsorption of both basic QUI and neutral IND. The adsorption results obtained using regenerated MIL-125-NH₂ and P-MIL-125-NH₂ also showed that these materials can be used several times without any severe degradation.

Mechanisms of direct hydrogen peroxide synthesis on silicon and phosphorus dual-doped graphene: a DFT-D study

Hydrogen peroxide (H₂O₂) is an important chemical commodity, with demand growing significantly in chemical synthesis due to its green characteristics.

Adsorptive desulfurization and denitrogenation using metal-organic frameworks

With the increasing worldwide demand for energy, utilization of fossil fuels is increasing proportionally. Additionally, new and unconventional energy sources are also being utilized at an increasing rate day-by-day. These sources, along with some industrial processes, result in the exposal of several sulfur- and nitrogen-containing compounds (SCCs and NCCs, respectively) to the environment, and the exposure is one of the greatest environmental threats in the recent years. Although, several methods were established for the removal of these pollutants during the last few decades, recent advancements in adsorptive desulfurization and denitrogenation (ADS and ADN, respectively) with metal-organic frameworks (MOFs) make this the most promising and remarkable method. Therefore, many research groups are currently involved with ADS and ADN with MOFs, and the results are improving gradually by modifying the MOF adsorbents according to several specific adsorption mechanisms. In this review, ADS and ADN studies are thoroughly discussed for both liquid-phase and gas-phase adsorption. The MOF modification procedures, which are important for improved adsorption, are also described. To improve the knowledge among the scientific community, it is very important to understand the detailed chemistry and mechanism involved in a chemical process, which also creates the possibility and pathway for further developments in research and applications. Therefore, the mechanisms related to the adsorption procedures are also discussed in detail. From this review, it can be expected that the scientific community will obtain an understanding of the current state of ADS and ADN, their importance, and some encouragement and insight to take the research knowledge base to a higher level.

Enhancement of dibenzothiophene biodesulfurization by weakening the feedback inhibition effects based on a systematic understanding of the biodesulfurization mechanism by Gordonia sp. through the potential “4S” pathway

Gordonia sp. JDZX13 (source: industrial petroleum soil) shows good potential for dibenzothiophene (DBT) biodesulfurization.

A review on research progress in the direct synthesis of hydrogen peroxide from hydrogen and oxygen: noble-metal catalytic method, fuel-cell method and plasma method

The direct synthesis of H₂O₂ from H₂ and O₂ using Pd catalyst, fuel cell and plasma methods have been reviewed systematically.