Ajayan Mano

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.

Synthesis of superacid-functionalized mesoporous nanocages with tunable pore diameters and their application in the synthesis of coumarins.

Here we demonstrate for the first time the preparation of a triflic acid (TFA)-functionalized mesoporous nanocage with tunable pore diameters by the wet impregnation method. The obtained materials have been unambiguously characterized by XRD, N(2) adsorption, FTIR spectroscopy, and NH(3) temperature-programmed desorption (TPD). From the characterization results, it has been found that the TFA molecules are firmly anchored on the surface of the mesoporous supports without affecting their acidity. We also demonstrate the effect of the pore and cage diameter of the KIT-5 supports on the loading of TFA molecules inside the pore channels. It has been found that the total acidity of the materials increases with an increase in the TFA loading on the support, whereas the acidity of the materials decreases with an increase in the pore diameter of the support. The acidity of the TFA-functionalized mesoporous nanocages is much higher than that of the zeolites and metal-substituted mesoporous acidic catalysts. The TFA-functionalized materials have also been employed as the catalysts for the synthesis of 7-hydroxy-4-methylcoumarin by means of the Pechmann reaction under solvent-free conditions. It has been found that the catalytic activity of the TFA-functionalized KIT-5 is much higher than that of zeolites and metal-substituted mesoporous catalytic materials in the synthesis of coumarin derivatives. The stability of the catalyst is extremely good and can be reused several times without much loss of activity in the above reaction.

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.

Functionalization of Mesoporous Carbon with Superbasic MgO Nanoparticles for the Efficient Synthesis of Sulfinamides

Highly basic MgO nanoparticles with different sizes have been successfully immobilized over mesoporous carbon with different pore diameters by a simple wet-impregnation method. The prepared catalysts have been characterized by various sophisticated techniques, such as XRD, nitrogen adsorption, electron energy loss spectroscopy, high-resolution TEM, X-ray photoelectron spectroscopy, and the temperature-programmed desorption of CO(2). XRD results reveal that the mesostructure of the support is retained even after the huge loading of MgO nanoparticles inside the mesochannels of the support. It is also demonstrated that the particle size and dispersion of the MgO nanoparticles on the support can be finely controlled by the simple adjustment of the textural parameters of the supports. Among the support materials studied, mesoporous carbon with the largest pore diameter and large pore volume offered highly crystalline small-size cubic-phase MgO nanoparticles with a high dispersion. The basicity of the MgO-supported mesoporous carbons can also be controlled by simply changing the loading of the MgO and the pore diameter of the support. These materials have been employed as heterogeneous catalysts for the first time in the selective synthesis of sulfinamides. Among the catalysts investigated, the support with the large pore diameter and high loading of MgO showed the highest activity with an excellent yield of sulfinamides. The catalyst also showed much higher activity than the pristine MgO nanoparticles. The effects of the reaction parameters, including the solvents and reaction temperature, and textural parameters of the supports in the activity of the catalyst have also been demonstrated. Most importantly, the catalyst was found to be highly stable, showing excellent activity even after the third cycle of reaction.

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.

Cobalt oxide functionalized nanoporous carbon electrodes and their excellent supercapacitive performance

Nanoporous carbon (CMK-3-150) functionalized with different amounts of cobalt oxide (CoO) nanoparticles was synthesized by an incipient wetness impregnation technique for supercapacitor application. The characterization results reveal that the specific surface area and pore volume of the CoO functionalized CMK-3-150 marginally decrease upon increasing the amount of the CoO whereas the pore diameter and the structure of the CMK-3-150 were not affected even after the functionalization. The electrochemical measurements show that the specific capacitance of the electrodes was enhanced after the functionalization with CoO. Among the electrodes studied, CMK-3-150 functionalized with 15 wt% CoO shows an excellent cycling stability and specific capacitance of 331 F g−1, which is ca. two times higher than that of the pure nanoporous carbon. This enhanced performance is due to the combined contribution of electrical double layer capacitance and pseudocapacitance. A symmetric supercapacitor device based on the CMK-3-150–15Co electrode gives the maximum energy density of 29.67 W h kg−1 at a power density of 0.07 kW kg−1.

High temperature microwave-assisted synthesis and the physico-chemical characterisation of mesoporous crystalline titania

Mesoporous TiO2 with nanocrystalline architecture has been synthesised by using microwave-assisted high temperature method using polymeric surfactant. The polymeric template was removed by stepwise carbonisation process. The structural order, band structure and the textural parameters of the calcined mesoporous titania were investigated by using numerous sophisticated techniques such as XRD, nitrogen adsorption, HRSEM, UV-Vis DRS and HRTEM. The obtained mesoporous TiO2 material have mesoscopic order, high surface area, crystalline walls and narrow pore size distribution as evident from the XRD and nitrogen adsorption results. Wide-angle X-ray diffraction pattern obtained for calcined mesoporous TiO2 shows that the pore wall of the sample is composed of highly crystalline Ti-O-Ti framework with an anatase phase. The photoluminescence properties of the mesoporous TiO2 was also analysed and the results were discussed in detail.

Highly Selective Synthesis of Ortho‐Prenylated Phenols and Chromans by using a New Bimetallic CuAl‐KIT‐5 with a 3D‐Cage‐type Mesoporous Structure

A nice piece of KIT: The first synthesis of a new bimetallic 3D-cage-type mesoporous catalyst CuAl-KIT-5 and its remarkable performance for the highly selective synthesis of ortho-prenylated phenols and chromans is reported.

Room-temperature direct bonding of graphene films by means of vacuum ultraviolet (VUV) / vapor-assisted method

A room temperature direct bonding between graphene thin films was realized by using vacuum ultraviolet (VUV) / vapor-assisted surface modification method at atmospheric pressure. In this paper, we examined the bonding between graphene mono layers and multi layers. X-ray photoelectron spectroscopy (XPS) showed that, in the ambient air, the graphene surfaces were easy to be oxidized, which resulted in the formation of CO2 (C-O 286.6eV) and organic hydrocarbons. Additionally, chlorine from the graphene production process was found on the outmost surface. For such oxidized and adsorbed surfaces, the vacuum ultraviolet (VUV) treatment was found highly effective to modify the chemical binding condition. The VUV irradiation eliminated the oxide and contaminations, and changed the binding condition of carbon. For the monolayer graphene surface, the oxidized site was almost completely removed and C-C bond, which has the binding energy of 284.4 eV, became dominant. For the multilayer surface, although C-O bonds remained, the atomic weight percentage of carbon increased. Raman spectroscopy study results showed that the intensity of defect, which was indicated by D-band, decreased both on the monolayer and multilayer. Moreover, the intensity of 2D band, which was attributable to graphene formation, became stronger; the VUV irradiation turned out effective to modify the crystalline structure to create graphene outmost surface layer. After the VUV irradiation, the surfaces were exposed to the water vapor to make the surface hydrophilic, because molecular water can adsorbe on the hydrophilic carbon surfaces, create hydrogen bond between on the moment of contact, and make good adhesion between the surfaces. XPS observations indicated that the bridging layers including molecular layers, which were assigned as CHO (286.2eV) and/or COOH (288.2eV), were created by water exposure. Raman observations confirmed that the intensity ratio of D band and G band (ID/IG) decreased and the ratio of 2D band and G band (I2D/IG) increased apparently on the monolayer and multilayer, respectively. This inferred that the defect decreased and the disordered graphene layer was reduced on the outmost surface, and the quantitative quality of graphene was improved due to the water exposure. Similarly, the peak shifts showed that, both on the monolayer and multilayer, the crosslink between carbon and hydrogen became closer. Without using chemical process, the simple VUV irradiation combined with the water exposure turned out highly effective to make tight bond between graphene surfaces without degrading the quantitative quality.

UV/vapor-assisted hybrid bonding technology as a tool for future nanopackaging

Hybrid bonding of electrode metal, glass insulator, and organic substrate, by using a single UV/vapor-assisted method at low temperature and atmospheric pressure, is highly feasible and will be of practical use in three-dimensional hetero-integration of nanosystems onto flex substrates where the surfaces of electrode and insulation layer appear on the same plane. Given Cu, SiO2, polyimide, and polydimethylsiloxane as the typical materials for a hybrid integration, the vapor and UV-assisted surface modification method was used to create a compatible bridging layer to diverse materials in a single process. Bridging layers, which are based on Cu hydroxide hydrate, silanol and hydroxyl groups from SiO2, polyimide and polydimethylsiloxane, respectively, could be prepared by introducing water molecules onto the clean surfaces created with Ar atom beam irradiation. The growth speed of the bridging layers on Cu, SiO2, and polyimide was tunable via the absolute humidity only. Based on the diffusion distance of Cu, an exposure of 8 g/m3 was chosen as an optimum condition. Heating at 150 °C after exposure to humidity caused tight adhesion between the mating surfaces for all combinations of Cu, SiO2, and polyimide. At the metal interface, a resistivity of around 4 × 10-8Ω·m was obtained. Furthermore, the UV treatment in nitrogen gas, which was carried out to the initial surfaces of polydimethylsiloxane and Cu (with native oxide) films at atmospheric pressure, was found feasible in enhancing the generation of water adsorption sites without using vacuum processes.