Chokkalingam Anand

Synthesis of Nitrogen‐Rich Mesoporous Carbon Nitride with Tunable Pores, Band Gaps and Nitrogen Content from a Single Aminoguanidine Precursor

Highly ordered mesoporous carbon nitride (CN) with an extremely high nitrogen content and tunable pore diameters was synthesized by using a new precursor with a high nitrogen content, aminoguanidine hydrochloride and mesoporous silica SBA-15 with different pore diameters as hard templates. Surprisingly, the N/C ratio of the prepared mesoporous CN (MCN-4: 1.80) was considerably higher than that of the theoretically predicted C(3)N(4) nanostructures (1.33). This is mainly due to the fact that the CN precursor easily undergoes polymerization at high temperature and affords a highly stable polymer composed of a diamino-s-tetrazine moiety with a six-membered aromatic ring containing six nitrogen atoms that are linked trigonally with the nitrogen atoms. The obtained materials were thoroughly characterized by means of XRD, nitrogen adsorption, high resolution TEM, electron energy loss spectra, high resolution SEM, X-ray photoelectron spectroscopy, FTIR, and C, N, O, and S analysis. The results show that the MCN-4 materials possess a well-ordered mesoporous structure similar to SBA-15 with a high specific surface area and tunable band gap in the range of 2.25-2.49 eV. Interestingly, the pore diameter of the materials can be finely tuned from 3.1-5.8 nm by increasing the pore diameter of the hard-template SBA-15. The reaction temperature plays a critical role for the formation of MCN, and we found that 400 °C is the best condition to obtain MCN-4 with a high nitrogen content. We have further investigated the catalytic application of the MCN-4 materials towards Friedel-Crafts hexanoylation of benzene and compared the results with the mesoporous CN with less nitrogen content (MCN-1) and nonporous CN. Among the materials studied, MCN-4 showed the highest activity, affording a high yield of hexanophenone within a few hours, which is mainly due to the presence of free amine groups on the wall structure of MCN-4.

Unusual Magnetic Properties of Size‐Controlled Iron Oxide Nanoparticles Grown in a Nanoporous Matrix with Tunable Pores

Magnetic iron oxide nanoparticles have been much investigated because of their promising applications in data storage, electronic and biomedical devices, and magnetic carriers for drug delivery. 2] However, many of these applications require Fe2O3 nanoparticles with controllable sizes, as they exhibit interesting magnetic properties. The fabrication of such nanoparticles is always a challenging task. Consequently, several synthetic approaches, including heating, hot injection, sonochemistry, and thermal decomposition of organometallic compounds, have been employed for the fabrication of Fe2O3 nanoparticles with uniform size and shape. However, most of the synthetic approaches generate agglomerated Fe2O3 nanoparticles with large sizes and irregular shapes. These nanoparticles have drawbacks such as low magnetic moments. An interesting way to finely control the particle size and shape is to encapsulate magnetic particles inside a porous inorganic template matrix with defined pore size and shape. Herein, we demonstrate the first nanosieve approach for the fabrication of magnetic Fe2O3 nanoparticles with controllable sizes inside a nanoporous confined matrix of hexagonally ordered silica materials with tunable pore diameters. The preparation of this matrix using a high-temperature hydrothermal approach was recently reported by us. We further demonstrate that the sizes and the magnetic properties of the nanoparticles can easily be controlled by simply tuning the pore size of the nanoporous silica matrix. The loading of a metal source in the nanoporous matrix also plays a critical role in controlling the particle size in the confined nanoporous matrix and significantly affects the magnetic properties of the particles. Mesoporous SBA-15 supports with various pore diameters were prepared by a hydrothermal technique following our previous reported procedure (see Tables 1S and 2S in the Supporting Information for the textural parameters and the conditions for synthesis of the samples). The Fe2O3 nanoparticles in the supports were prepared by the wet impregnation method (see the Experimental Section). The samples were denoted as XF-SBA-15-Z where X and Z are the weight% of the Fe and the temperature used for the synthesis of SBA-15, respectively, and F denotes Fe2O3 . The representative HRTEM image and the related HRTEM histogram of 30F-SBA-15-130 are shown in Figure 1a and 1b, respectively. The image clearly shows that the Fe2O3 nanoparticles have uniform size and shape. It is also clear that the nanoparticles are encapsulated inside the linear array of SBA-15-130 pores, which are arranged in regular intervals, thus confirming that the ordered pores indeed control the size and shape of the Fe2O3 nanoparticles (Figure 1a inset). It is interesting to note that the diameter of the Fe2O3 particles grown inside the SBA-15 nanochannels is between 6.5 and 9.0 nm, which is quite similar to the pore size of the SBA-15 supports and significantly smaller than that of the particles made without SBA-15 matrix (Tables 1S, 2S and Figures 1S, 2S in the Supporting Information). Interestingly, the size of the Fe2O3 nanoparticles increases with the pore size of SBA-15. The powder XRD diffraction patterns of 30F-SBA-15-130 and parent SBA-15-100 are compared in Figure 1b. Both samples show a sharp peak at lower angles, and several higher-order peaks, which can be indexed to the (100), (110), and (200) reflections of the hexagonal space group p6 mm, and are indicative of hexagonally ordered pore structure. However, the intensity of the peaks at lower angles decreases significantly as the loading of Fe2O3 nanoparticles inside the mesochannels of SBA-15 is increased (Figure 3S in the Supporting Information). It is unlikely that the large difference in the intensity of the (100) peak before and after the Fe2O3 immobilization arises from damage to the structure, but rather from a larger contrast in density between the silica walls and the open pores relative to that between the silica walls and iron oxide inside the porous channels. The wideangle XRD pattern of 30F-SBA-15-130 shows several higherangle peaks, which are quite similar to those of pure Fe2O3 nanoparticles. The structure of the parent silica remains intact even after loading higher amounts of Fe2O3 (see Figure 3S in the Supporting Information. A complete discussion about [*] Dr. S. Alam, C. Anand, Dr. K. Ariga, Dr. A. Vinu International Center for Materials Nanoarchitectonics World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science 1-1 Namiki, Tsukuba 305-0044, Ibaraki (Japan) Fax: (+ 81)29-860-4706 E-mail: vinu.ajayan@nims.go.jp Homepage: http://www.nims.go.jp/super/HP/vinu/websitevinu/ V-top.htm

Highly ordered macro-mesoporous carbon nitride film for selective detection of acidic/basic molecules

Well-ordered meso-macroporous carbon nitride film fabricated via a simple and flexible template replication method by using the P123 block copolymer and polystyrene spheres as dual templates shows selective sensing performance for acetic acid but after treating the surface of the film with UV light and oxygen, the selectivity of sensing can be tuned for basic molecules.

Enhanced Supercapacitor Performance of N‐Doped Mesoporous Carbons Prepared from a Gelatin Biomolecule

Nitrogen-containing mesoporous carbon electrodes with tunable pore diameters for supercapacitor applications are synthesized by the nanocasting technique using a naturally abundant gelatin polymer as the single precursor for nitrogen and carbon.

Inclusion of size controlled gallium oxide nanoparticles into highly ordered 3D mesoporous silica with tunable pore diameters and their unusual catalytic performance

Here we demonstrate for the first time a novel nanosieve approach for tuning the size, shape, dispersion and the quantity of the gallium oxide nanoparticles inside a mesoporous silica support with a three dimensional porous structure, high surface area, and large pore volume (KIT-6). It was found that the size and shape of the gallium oxide nanoparticles in the pore channels of the KIT-6 can be controlled by simply tuning the pore diameter of the support. The obtained gallium oxide/KIT-6 nanocomposites with different gallium oxide contents have been characterized by several characterization techniques such as powder XRD, SAXS, nitrogen adsorption, UV-Vis, FT-IR, HRSEM and HRTEM. XRD, HRTEM and nitrogen adsorption results reveal that the mesostructural order of the KIT-6 materials was not affected even after the encapsulation of ca. 30 wt% gallium oxide nanoparticles. UV-Vis results reveal that bandgap of the materials can be controlled by simply changing the concentration of the gallium oxide or varying the pore diameter of the support. The above catalytic materials have been also successfully employed for the benzylation of benzene and other aromatic compounds. The role of the pore diameter of the support, the loading of the metal oxide nanoparticles and other reaction parameters affecting the activity of the catalysts has been clearly demonstrated. It has been found that gallium oxide supported KIT-6 materials are highly stable and active, and show superior performance over other metal substituted mesoporous and zeolite materials with a high substrate conversion and a high product selectivity in the alkylation of benzene under the optimized reaction conditions.

A facile photo-induced synthesis of COOH functionalized meso-macroporous carbon films and their excellent sensing capability for aromatic amines

A simple photo-induced approach is developed for the preparation of COOH functionalized meso-macroporous carbon films with tunable pores without using any inorganic mesoporous silica templates, which show excellent sensing selectivity for aniline and the selectivity can be enhanced upon increasing COOH functional groups.

Catalytic Polymerization of Anthracene in a Recyclable SBA‐15 Reactor with High Iron Content by a Friedel–Crafts Alkylation

Ironing it out: A FeSBA-15 catalyst with a high iron content as well as a large pore diameter has been synthesized and used for the production of soluble poly(methylene anthracene) (PMAn, see scheme). The catalyst is stable, active, reusable, and affords a high yield of high-molecular-weight PMAn. The properties of the PMAns obtained can be controlled by tuning the specific surface area, pore diameter, pore volume, and Fe content of the catalysts.

Bifunctional Mesoporous Carbon Nitride: Highly Efficient Enzyme-like Catalyst for One-pot Deacetalization-Knoevenagel Reaction

Recently, mesoporous carbon nitride (MCN) has aroused extensive interest for its potential applications in organocatalysis, photo- and electrochemistry and CO2 capture. However, further surface functionalization of MCN for advanced nanomaterials and catalysis still remains very challenging. Here we show that acidic carboxyl groups can be smoothly introduced onto the surface of well-ordered MCN without annihilation between the introduced acid groups and MCN’s inherent basic groups through a facile UV light oxidation method. The functionalization generates a novel bifunctional nanocatalyst which offers an enzyme-like catalytic performance in the one-pot deacetalization-Knoevenagel reaction of benzaldehyde dimethylacetal and malononitrile with 100% conversion and more than 99% selectivity due to the cooperative catalysis between the acid and base groups separated on the surface of the catalyst. The results provide a general method to create multifunctional nanomaterials and open new opportunities for the development of high efficient catalyst for green organic synthesis.

A Single-Step Synthesis of Electroactive Mesoporous ProDOT-Silica Structures

The single-step preparation of highly ordered mesoporous silica hybrid nanocomposites with conjugated polymers was explored using a novel cationic 3,4-propylenedioxythiophene (ProDOT) surfactant (PrS). The method does not require high-temperature calcination or a washing procedure. The combination of self-assembly of the silica surfactant and in situ polymerization of the ProDOT tail is responsible for creation of the mesoporosity with ultralarge pores, large pore volume, and electroactivity. As this novel material exhibits excellent textural parameters together with electrical conductivity, we believe that this could find potential applications in various fields. This novel concept of creating mesoporosity without a calcination process is a significant breakthrough in the field of mesoporous materials and the method can be further generalized as a rational preparation of various mesoporous hybrid materials having different structures and pore diameters.

Continuous flow synthesis of ZSM-5 zeolite on the order of seconds.

Significance Zeolites have greatly contributed to modern industries. Consumption of zeolites is expected to increase with the emergence of newly commercialized applications. Typical synthesis of zeolites relies on batchwise hydrothermal synthesis, which usually takes tens of hours or even several days to complete. People have thus long believed that the crystallization of zeolites is very slow in nature. We herein demonstrate the continuous flow synthesis of ZSM-5, an industrially important zeolite, on the order of seconds. Crystallization from amorphous state to full crystallinity could be completed in tens of or even several seconds. The synthesis on the order of seconds provides a great potential to facilitate the mass production as well as to deepen the fundamental understanding of zeolite crystallization. The hydrothermal synthesis of zeolites carried out in batch reactors takes a time so long (typically, on the order of days) that the crystallization of zeolites has long been believed to be very slow in nature. We herein present a synthetic process for ZSM-5, an industrially important zeolite, on the order of seconds in a continuous flow reactor using pressurized hot water as a heating medium. Direct mixing of a well-tuned precursor (90 °C) with the pressurized water preheated to extremely high temperature (370 °C) in the millimeter-sized continuous flow reactor resulted in immediate heating to high temperatures (240–300 °C); consequently, the crystallization of ZSM-5 in a seed-free system proceeded to completion within tens of or even several seconds. These results indicate that the crystallization of zeolites can complete in a period on the order of seconds. The subtle design combining a continuous flow reactor with pressurized hot water can greatly facilitate the mass production of zeolites in the future.