Search

A facile post-synthetic strategy was developed to functionalize the preformed hollow mesoporous silica spheres by encapsulating the molybdenum dioxide (MoO2) nanoparticles inside the interior cavity. Hollow mesoporous silica spheres were prepared and employed as carriers, and the encapsulation of MoO2 nanoparticles was achieved through a one-pot hydrothermal protocol. After characterization, the encapsulated MoO2 nanoparticles were certified to be ultrafine and highly dispersed, which greatly promoted the catalytic activity. The as-prepared catalysts were utilized in epoxidation of alkenes and exhibited as a promising catalyst in this reaction. After reacting for 10 h, the optimal catalyst MoO2@SiO2-1 achieved a conversion above 95% and selectivity above 95%, respectively. Moreover, the catalysts also exhibited good reusability, conversion of 78% and selectivity of 89% (reaction time 4 h) were still obtained after recycling for 5 times. Meanwhile, the employed facial and efficient hydrothermal approach could be expanded to other molybdenum modified heterogeneous catalysts in various applications. Keywords: Post-synthesis, Ultrafine, Molybdenum dioxide, Alkene, Epoxidation

Functionalization of vegetable oils (VOs) including edible, non-edible, and waste cooking oil (WCOs) to epoxides (EVOs) is receiving great attention by many researchers from academia and industry because they are renewable, versatile, sustainable, non-toxic, and eco-friendly, and they can partially or totally replace harmful phthalate plasticizers. The epoxidation of VOs on an industrial scale has already been developed by the homogeneous catalytic system using peracids. Due to the drawbacks of this method, other systems including acidic ion exchange resins, polyoxometalates, and enzymes are becoming alternative catalysts for the epoxidation reaction. We have reviewed all these catalytic systems including their benefits and drawbacks, reaction mechanisms, intensification of each system in different ways as well as the physicochemical properties of VOs and EVOs and new findings in recent years. Finally, the current methods including titrimetric methods as well as ATR-FTIR and 1H NMR for determination of conversion, epoxidation, and selectivity of epoxidized vegetable oils (EVOs) are also briefly described.

Polymeric carbon nitride (C3N4) is currently the most potential nonmetallic photocatalyst, but it suffers from low catalytic activity due to rapid electron–hole recombination behavior and low specific surface area. The morphology control of C3N4 is one of the effective methods used to achieve higher photocatalytic performance. Here, bulk, lamellar and coralloid C3N4 were synthesized using different chemical methods. The as-prepared coralloid C3N4 has a higher specific surface area (123.7 m2 · g−1) than bulk (5.4 m2 · g−1) and lamellar C3N4 (2.8 m2 · g−1), thus exhibiting a 3.15- and 2.59-fold higher photocatalytic efficiency for the selective oxidation of benzyl alcohol than bulk and lamellar C3N4, respectively. Optical characterizations of the photocatalysts suggest that coralloid C3N4 can effectively capture electrons and accelerate carrier separation, which is caused by the presence of more nitrogen vacancies. Furthermore, it is demonstrated that superoxide radicals (·O2 −) and holes (h+) play major roles in the photocatalytic selective oxidation of benzyl alcohol using C3N4 as a photocatalyst.

Nowadays, environmental problems such as petroleum resources exhaustion, pollution and global warming are in ceaseless aggravation. Consequently, vegetable oil becomes one of the most important resources due to its cheapness, easily availability and environmental regeneration. In this study, a series of sustainable polyurethanes based on epoxy soybean oil modified by different contents of 3,13-dimethyhydroxysilyl double-decker phenylsilsesquioxane [DDSQ(Me)OH] have been prepared. Polyol prepared with epoxy soybean oil has effectively replaced the petroleum-based polyol and the DDSQ(Me)OH performed as chain extender together with 1,4-butanediol (BDO). The structure of DDSQ(Me)OH was verified by 1H NMR and MALDI–TOF–MS. The structure and properties of sustainable polyurethanes were characterized by FTIR, DSC, TGA, SEM, tensile test and static contact angle. TGA demonstrated that hybrid polyurethanes were thermally stable due to the covalent incorporation of DDSQ(Me)OH in polymer main chain, the 5% weight loss temperatures (Td5) of hybrid polyurethane can be 21 °C higher than pure PU. DSC revealed the improved glass transition temperature (Tg) of polyurethanes, and the Tg can be 12.4 °C improved compared with pure polyurethane. SEM showed that the aggregation of DDSQ(Me)OH has dispersed homogeneously in the hybrid polyurethanes matrix. The results of the static contact angle revealed that with the increase of DDSQ(Me)OH content, the surface hydrophobicity has been enhanced significantly, and the static contact angle of water for hybrid polyurethanes can be up to about 110.2°.

A general thermal decomposition strategy is reported to fabricate MoO3@SiO2 nanoreactors, with a mesoporous silica shell and embedded MoO3 nanoparticles. The novel preparation procedure involves mixing certain mass ratio of (NH4)6Mo7O24·4H2O (AMM) and hollow mesoporous silica spheres (HMSS) by grinding, fusion and thermal decomposition of (NH4)6Mo7O24·4H2O under calcination and removing the residual via filtration. The as-prepared MoO3@SiO2 nanoreactors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), N2 adsorption/desorption and X-ray photoelectron spectra (XPS). The nanoreactors were utilized in epoxidation of alkenes and displayed high catalytic activity and stability. The mass ratio of AMM and HMSS greatly affected the properties and catalytic performance of the nanoreactors. The optimal mass ratio of AMM: HMSS has been confirmed as 1/2. After reacting for 12 h with H2O2 (50 wt%) as oxidant, conversion and selectivity of optimal MoO3@SiO2-400-1/2 almost reached up to 98% and 99%, respectively. Furthermore, the catalyst still had high conversion (78%) and selectivity (95%) at 4 h epoxidation of cyclooctene after recycling for 6 runs. Kinetics study was also carried out and demonstrated the epoxidation of alkenes follows the first order model.

Nowadays, the most commonly used cold-resistant plasticizer, bis(2-ethylhexyl)adipate (DOA), not only has the poor migration resistance so that it can only be used as auxiliary plasticizer, but also causes huge pollution to the environment, especially water. Here, using renewable and green oleic acid as raw material, we had synthesized a series of oleate plasticizers. By means of capability tests, we detected that the Ti (initial degradation temperature) of PVC films plasticized with oleate plasticizers was 40 °C higher than that of DOA/PVC and 20 °C higher than that of DOTP/PVC. More importantly, in addition to illustrious migration resistance, they could maintain remarkable flexibility in cold environments as well. The low-temperature efficiency value of these oleate plasticizers exceeded 70 °C, which was much higher than DOTP and DOA. These results demonstrated that they possessed the potential to replace toxic DOP and poorly stable DOA, which provided an effective and green approach to solve the harm of plastic products to human health and the threat to the environment. In addition, these plasticizers broadened the application of PVC in cold environments, which was a boon for the application of PVC industry in the cold-resistant field, and contributed to sustainability of the hackneyed and oft-maligned PVC industry.

The efficient catalysts were designed to allow the entry and release of reactants and products into the mesoporous SBA-15 in which the active sites, peroxophosphotungstate, were entrapped by silylation with three different silylating agents (C3, C5, and C8 arm). The as-prepared catalysts were characterized by elemental analysis, ICP analysis, TGA, XRD, N2 adsorption/desorption, SEM, TEM, and FT-IR spectra. Their catalytic performances were tested for the epoxidation of soybean oil using different parameters such as temperature, H2O2 to unsaturation molar ratio, catalyst loading and stirring speed. The resulting epoxidized soybean oil was analyzed qualitatively and quantitatively by FT-IR and 1HNMR. The results confirmed that the catalyst silylated with C8 arm is promising for the synthesis of epoxides of long-chain carbon and reusable at least three times without obvious decrease in activity. Moreover, use of H2O2 oxidant and free of solvent in the epoxidation reaction are the main advantages of these catalysts.

Epoxides are important industrial intermediates applied in a variety of industrial processes. During the production of epoxides, catalysts have played an irreplaceable and unique role. In this review, the historic progress of molybdenum-based catalysts in alkene epoxidation are covered and an outlook on future challenge discussed. Efficient catalysts are demonstrated including soluble molybdenum complexes, polyoxometalates catalysts, molybdenum-containing metal organic frameworks, silica supported molybdenum-based catalysts, polymer supported molybdenum-based catalysts, magnetic molybdenum-based catalysts, hierarchical molybdenum-based catalysts, graphene-based molybdenum containing catalysts, photocatalyzed epoxidation catalysts, and some other systems. The effects of different solvents and oxidants are discussed and the mechanisms of epoxidation are summarized. The challenges and perspectives to further enhance the catalytic performances in alkenes epoxidation are presented.