查看更多>>摘要：Radioactive iodine as a harmful fission product can be released in the environment and bring unpredictable risks to humans even at trace. Porous organic materials with flexible units and high porosity are potential adsorbents for iodine removal. Herein, four molecule-guided conjugated microporous polymers (ImCMPs) with imidazole derivative units were synthesized by Sonogashira-Hagihara coupling reactions and used for the capture of iodine in vapour and solution. With the permanent nanopores, conjugated networks and N-rich units, ImCMPs all show higher uptakes of volatile iodine than the corresponding monomers which have strong adhesion ability to iodine. Remarkably, the vapour iodine uptake of ImCMP-1 up to 2.36 g g~(-1) at 80 °C, and ImCMP-1 with privileged imidazolyl unit and highest specific surface area possesses the exceptional potential for encasing iodine. This result provides a persuasive approach for design synthesis of excellent adsorbents.
查看更多>>摘要：MXenes are the emerging class of 2D materials with numerous applications such as in energy storage, biomedical, catalysis, gas sensing, etc. Among these, the gas sensing application of MXene materials is gaining attention due to their higher sensitivity towards various gases but is least explored. Herein we report the fabrication of highly sensitive CO2 gas sensors using a porous silicon/Mo2CT_x hybrid system. The structure of the Mo-In-C non-MAX phase and formation of Mo2CT_x MXene were studied using X-ray diffraction. The elemental characterization through XPS and EDS confirms the presence of the functional groups and the deposition of the Mo2CT_x MXene films. The uniform deposition of the layered sheet-like 2D Mo2CT_x on the substrates was identified using the FESEM images. The sensor is found functional from room temperature to high-temperature conditions (30-250 °C). On the normal humid condition of 30% RH, the gas sensing response of the fabricated sensor is almost double in comparison with the crystalline silicon/Mo2CT_x sensor at 250 °C. The introduction of humidity leads to further enhancement of the sensing response from 25% to 32%. Moreover, the fabricated sensor presents a good sensing response at room temperature (30 °C) for a CO2 concentration of 50 ppm along with a fast response and recovery times of 32 and 45 s with a high degree of stability.
Katherine GingrichKarthikeyan BaskaranMuhammad Ali
15页
查看更多>>摘要：With the continuous growth in global population, energy demands are summoning the development of novel materials with high specific surface areas (SSA) for energy and environmental applications. High-SSA silica-based materials, such as aerogels, are highly popular as they are easy to form and tune. They also provide thermal stability and easy functionalization, which leads to their application in batteries, heavy metal adsorption, and gas capture. However, owing to large pore volumes, high-SSA silica exhibits weak mechanical behavior, requiring enhancement or modification to improve the mechanical properties and make them viable for these applications. The creation of macropores in these mesoporous solids is also desirable for applications utilizing membranes. To facilitate research in these critical areas, this review describes the research into sol-gel formation of silica, as well as polymer-based tailoring carried out in the last decade. Additionally, this review summarizes applications of polymer-tailored high-SSA silica materials in the energy and environmental fields and discusses the challenges associated with implementing and scaling of these materials for these applications.
查看更多>>摘要：Low valence bismuth cationic centers were introduced into hydrogen forms of ZSM-5 and mordenite zeolites via impregnation of zeolites in aqueous solution of bismuth salts and subsequent reductive solid state ion exchange (SSIE). It has been found that Near IR photoluminescent bismuth monocations Bi~+ and cluster ions are formed in the exchange positions and their optical properties in ZSM-5 and mordenite depend mainly on a zeolite Si/Al ratio and, to a lesser extent, on the amount of loaded bismuth. The photoluminescence emission and excitation spectra of bismuth cationic species (monocations or clusters) are markedly different in ZSM-5 and mordenite. This difference can be explained, taking into the account, that extraframework (exchanged) cations in mordenite zeolite, unlike ZSM-5, can occupy only several distinct positions relative to the mordenite framework structure.
查看更多>>摘要：As the only use of 95% of industrial lignin is as a low-value fuel, it is urgent to explore novel approaches to transform lignin into useful materials. Herein, we report the first transformation of lignin into value-added and inexpensive sulfur-doped carbon photocatalysts by one-step carbonization of sodium lignosulfonates in the presence/absence of Na2S·9H2O. The sulfur-doped carbon photocatalysts were thoroughly characterized by various physicochemical techniques, including N2 adsorption, X-ray photoelectron spectroscopy (XPS), scanning transmission microscopy (SEM), photocurrent response, photoluminescence (PL) spectroscopy, and electrochemical impedance spectroscopy (EIS). The IR and XPS spectra show that the dominant sulfur species in the prepared carbon materials are thiophene and SO_x groups, such as sulfone groups and sulfonic acid groups. Photocatalytic degradation of tetracycline was employed as a model reaction to evaluate the photocatalytic activities of the sulfur-doped carbons. The incorporation of sulfur-containing groups was found to efficiently decrease the band gaps of these carbon materials and enhance photogenerated charge carrier separation and transfer, thus boosting the tetracycline degradation efficiency. The active sulfur species potentially responsible for the photocatalytic degradation of tetracycline and the degradation mechanism of tetracycline were determined. An innovative strategy for the valorization of lignin to produce valuable carbon photocatalysts was developed in this study.
查看更多>>摘要：A bulky composite material, CaCO3@TS-1, was synthesized in a tetrapropylammonium bromide hydrothermal system by adding nanosized CaCO3 particles of 60-80 nm to a titanium silicalite-1 (TS-1) synthesis gel. The macroporous TS-1 free of extraframework Ti was then obtained by the posttreatment of the CaCO3@TS-1 in HCl solution to remove CaCO3 and extraframework Ti simultaneously. This study demonstrates that this new synthesis route, the acidity posttreatment, can produce a bulky TS-1 with volume-controllable intracrystal macropores. The crystallization mechanism of the macroporous TS-1 was studied systematically. The addition of CaCO3 accelerates the crystallization of silicon source, and leads to the similar crystallization rates of silicon and titanium sources. Therefore, the formation of extraframework Ti was inhibited, and more Ti ions were inserted into the TS-1 framework. The catalytic performance of macroporous TS-1 was evaluated in the hydroxylation of phenol. An outstanding catalytic activity was obtained due to their enhanced diffusion property and reduced extraframework Ti.
查看更多>>摘要：Ti-MWW zeolite has attracted much attention because of its excellent catalytic oxidation performance. As one of the essential components in zeolites, phosphorus (P) has been widely used for modification to enhance the hydrothermal stability and catalytic performance of aluminosilicate zeolite. Herein, a series of P-modified Ti-MWW zeolite samples were prepared with a simple way by directly adding various amounts of phosphoric acid into the acid-treated system. The effect of P modification on both structure and catalytic performance of Ti-MWW zeolite was systematically investigated. We demonstrated that some highly active framework TiO_4~* species with Ti-O-P structure are formed after modification with moderate P, leading to the remarkable improvement of catalytic activity in 1-hexene epoxidation. While introducing excess amounts of phosphoric acid would result in the formation of much inactive titanium phosphate species, which block the channels and finally decrease the catalytic performance significantly. Density functional theory calculations confirmed that the new formed Ti-H2PO4 site is more active than the Ti-OH site in Ti-MWW zeolite for model propene epoxidation, revealing the promotional effect of P modification. This work would deepen our understanding of P modification at the atomic level and benefit to improve the catalytic performance of titanosilicate zeolite.
Shubhashish ShubhashishSarah J. KarasikLuisa F. Posada
13页
查看更多>>摘要：Herein, we report a general and straightforward synthesis method for gold supported on mesoporous and microporous metal oxides. Supported materials, in general, show higher crystallinity compare to unsupported systems as verified through powder X-ray diffraction (XRD). Also, through XRD, most of the metal is observed to be in its oxide form, whereas the gold support was found to be in its metallic state, which has been further confirmed from TEM. In terms of surface area, the catalyst was not found to follow any trend. Morphology wise, there are no changes observed after doping except in few cases. Combined results from XRD, X-ray fluorescence spectroscopy, Auger, and X-ray photoelectron spectroscopy suggest that gold is mainly in the bull; and very little (0.04% in case of gold doped calcium oxide) or non (in case of gold doped mixed manganese-cerium oxide) on the surface. The presence of Au (0) 4f peaks in XPS further confirms the metallic state of the gold. Oxides of indium, magnesium and calcium have been studied for the organic transformation reactions. An enhancement in activity and product selectivity was observed in the case of the gold supported catalysts. Indium serves as a great catalyst for C-C coupling and electrophilic aromatic substitution reactions and gives >99% conversion. Interestingly, 88% selectivity for C-C coupling and >99% selectivity for aromatic substitution have been achieved at 100 °C and room temperature respectively. Magnesium and calcium give Knoevenagel condensation products. At room temperature with very low catalyst loading, >99% conversion and selectivity were observed for the Knoevenagel reaction with as high as 35.30 TOF. A mechanism for the C-C coupling reaction has been proposed based on these results.
查看更多>>摘要：Azonia-spiro compounds have been reported as organic templates for synthesizing many extra-large pore high silica zeolites, often isomorphically substituted by germanium. However, these templates are usually obtained in the presence of sodium hydroxide, leading to persisting sodium ions in the final products. Sodium cations may compete with azonia-spiro organics as templates during zeolite synthesis. Therefore, effect of any residual sodium cations on the synthesis results needs to be investigated. This work documents the effect of sodium ions on zeolite formation using four structurally similar azonia-spiro compounds as templates. Different silicogermanate zeolites (UTL, an unknown zeolitic phase, etc.) were formed in the absence of sodium cations. Notably, the syntheses of silicogermanate UTL and siliceous MTW zeolites using azonia-spiro [4,6] and [6,6] are reported for the first time. Controlled amounts of sodium chloride were added to zeolite crystallization mixtures without residual sodium hydroxide. In the presence of 0.005-0.1 mol/L Na~+, silicogermanate zeolites were the dominant phases. Further increasing the Na~+ concentration to 0.152 and 0.317 mol/L, formation of UTL and an unknown silicogermanate phase were inhibited in favor of a dense sodiumgermanate (Na4Ge9O_(20)). Moreover, sodium ions next to azonia-spiro organic templates also influence the morphologies of the MTW zeolites. The observed high sensitivity of zeolite formation in the presence of even traces of sodium therefore has impact on synthesis protocols of large pore silicogermanate zeolites. This work highlights how small, often overlooked, factors in inorganic material synthesis can drastically change the outcome.
查看更多>>摘要：Formaldehyde (HCHO) is a common organic pollutant, and it is necessary to prepare an efficient catalyst to degrade it. Metal oxides, especially TiO2, have received widespread attention in the field of HCHO degradation. In this paper, a Zr based MOF UiO-66 was added in the process of Zr doping TiO2 to enhance the ultraviolet light absorption capacity of the catalyst. Then the supported Ag by photoreduction was used to further improve the dispersibility and visible light absorption capacity of the catalyst. When 1000 mg UiO-66 is added, Ag@Zr-TiO2-1000U6 shows the best degradation rate of 83.4%, and has good stability. Through a series of characterizations, it was found that the ZrO2 nanoparticles derived from UiO-66 were uniformly distributed on the flake TiO2, and the visible light absorption capacity of the catalyst was significantly improved. This work provides a certain reference value for the application of MOF and its derivatives in the field of HCHO degradation.
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