Kripal S. Lakhi

Highly Ordered Nitrogen-Rich Mesoporous Carbon Nitrides and Their Superior Performance for Sensing and Photocatalytic Hydrogen Generation

Mesoporous carbon nitrides (MCN) are fascinating materials with unique semiconducting and basic properties that are useful in many applications including photocatalysis and sensing. Most syntheses of MCN focus on creating theoretically predicted C3 N4 stoichiometry with a band gap of 2.7 eV using a nano-hard templating approach with triazine-based precursors. However, the performance of the MCN in semiconducting applications is limited to the MCN framework with a small band gap, which would be linked with the addition of more N in the CN framework, but this remains a huge challenge. Here, we report a precursor with high nitrogen content, 3-amino-1,2,4-triazole, that enables the formation of new and well-ordered 3D MCN with C3 N5 stoichiometry (MCN-8), which has not been predicted so far, and a low-band-gap energy (2.2 eV). This novel class of material without addition of any dopants shows not only a superior photocatalytic water-splitting performance with a total of 801 μmol of H2 under visible-light irradiation for 3 h but also excellent sensing properties for toxic acids.

Energy efficient synthesis of highly ordered mesoporous carbon nitrides with uniform rods and their superior CO2 adsorption capacity

An energy efficient route for the synthesis of mesoporous carbon nitride (MCN) materials with highly ordered mesopores and a rod shaped morphology from uncalcined mesoporous SBA-15 (SEW-SBA-15) templates with a controlled morphology through a nanocasting technique using ethylenediamine and carbon tetrachloride as carbon and nitrogen sources is introduced. Porosity in the SBA-15 templates is created by washing with ethanol whereas the controlled rod shaped morphology in the nanotemplates is obtained by modifying the synthesis conditions from stirring to static conditions. The prepared MCN from the SEW-SBA-15 templates retains the morphological and structural order of the template. By tuning the pore diameter of SEW-SBA-15, it is possible to prepare MCN with tuneable pore diameters, which exhibits a specific BET surface area of 596–655 m2 g−1, pore diameter of 2.8–5.7 nm, and specific pore volume of 0.49–0.89 cm3 g−1. These values are similar to those of MCN-1 prepared from the calcined SBA-15 template with an irregular morphology. The SEW-MCN-1-T samples are used as CO2 adsorbents at 0, 10 and 25 °C and pressures from 1 up to 30 bar. Among the samples, the SEW-MCN-1-130 sample with the highest specific surface area, uniform particle size and morphology, and the largest pore volume exhibits the highest CO2 uptake capacity of 15.4 mmol g−1 at 0 °C and 30 bar, which is similar to the sample prepared by the calcination route but higher than that of activated carbon and multiwalled carbon nanotubes. This is the first report of the MCN prepared from uncalcined SBA-15 which helps to avoid the required energy intensive calcination step of the template and offers a promising system for CO2 capture.

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.

Diaminotetrazine based mesoporous C3N6 with a well-ordered 3D cubic structure and its excellent photocatalytic performance for hydrogen evolution

Novel nitrogen enriched diamino-s-tetrazine based highly ordered 3D mesoporous carbon nitride (MCN-9) hybrid materials with a body centered cubic Ia3d structure having high specific surface areas, large pore volumes, and tunable pore diameters were prepared by employing 3D body centered cubic KIT-6 mesoporous silica having a gyroidal porous structure and various pore diameters as the sacrificial hard template through a simple self-condensation followed by polymerization reaction of aminoguanidine hydrochloride inside the nanochannels of the KIT-6 template. Characterization results reveal that the prepared materials exhibit a 3D porous structure with well-defined mesopores and possess excellent physical parameters including high surface areas (157–346 m2 g−1), large pore volumes (0.36–0.63 cm3 g−1), different pore diameters (5.5–6.0 nm) and a high N/C ratio of 1.87, which is much higher than that of ideal C3N4 (1.33). The deep yellow colored MCN-9 with a 3D porous structure also shows good absorption properties with a tunable narrow bandgap of 2.25–2.5 eV, which is again much lower than that of C3N4 (2.7 eV) and helps to achieve much higher photocatalytic water splitting activity than non-porous C3N4 and other carbon nitrides under visible light irradiation.

Highly Efficient Method for the Synthesis of Activated Mesoporous Biocarbons with Extremely High Surface Area for High-Pressure CO2 Adsorption

A simple and efficient way to synthesize activated mesoporous biocarbons (AMBs) with extremely high BET surface area and large pore volume has been achieved for the first time through a simple solid state activation of freely available biomass, Arundo donax, with zinc chloride. The textural parameters of the AMB can easily be controlled by varying the activation temperature. It is demonstrated that the mesoporosity of AMB can be finely tuned with a simple adjustment of the amount of activating agent. AMB with almost 100% mesoporosity can be achieved using the activating agent and the biomass ratio of 5 and carbonization at 500 °C. Under the optimized conditions, AMB with a BET surface area of 3298 m2 g-1 and a pore volume of 1.9 cm3 g-1 can be prepared. While being used as an adsorbent for CO2 capture, AMB registers an impressively high pressure CO2 adsorption capacity of 30.2 mmol g-1 at 30 bar which is much higher than that of activated carbon (AC), multiwalled carbon nanotubes (MWCNTs), highly ordered mesoporous carbons, and mesoporous carbon nitrides. AMB also shows high stability with excellent regeneration properties under vacuum and temperatures of up to 250 °C. These impressive textural parameters and high CO2 adsorption capacity of AMB clearly reveal its potential as a promising adsorbent for high-pressure CO2 capture and storage application. Also, the simple one-step synthesis strategy outlined in this work would provide a pathway to generate a series of novel mesoporous activated biocarbons from different biomasses.

Preparation of Highly Active Triflic Acid Functionalized SBA-15 Catalysts for the Synthesis of Coumarin under Solvent-Free Conditions

Highly acidic SBA‐15 with different pore diameters has been prepared by functionalizing the mesoporous walls with different amounts of triflic acid (TFA). The structure of the SBA‐15 before and after the functionalization with TFA was investigated by powder X‐ray diffraction and nitrogen adsorption isotherms. The interaction of TFA with the surface silanol groups of SBA‐15 and the acidity of the materials have been investigated by FTIR spectroscopy and temperature‐programmed desorption of ammonia, respectively. The characterization results reveal that the mesoporous structure of the SBA‐15 is retained even after the loading of TFA in the mesochannels and that the TFA molecules are bonded with the surface silanol groups of the SBA‐15 supports. The acidity of the materials increases with increasing amount of TFA from 5 to 20 wt %. These functionalized, highly acidic materials are found to be highly active in the synthesis of coumarin and the catalytic efficiency was found to correlate with the total acidity or the amount of TFA in the porous channels of the SBA‐15 catalysts. It has also been found that the activity of the TFA‐functionalized SBA‐15 in the synthesis of coumarin is much higher than that of different zeolites, pure mesoporous silica SBA‐15, and other mesoporous catalysts used in this study.

Heteroatom functionalized activated porous biocarbons and their excellent performance for CO2 capture at high pressure

Activated biocarbons with a porous structure and nitrogen functionalities are synthesized from the prolific waste biomass, Arundo donax, and an organic material, chitosan, by a simple one step chemical activation with ZnCl2. The nitrogen functional groups in the porous activated biocarbons are significantly increased by the addition of chitosan in the synthesis mixture. The textural properties and N content can easily be tuned by varying the amount of activating agent and the carbonization temperature. The optimized biocarbon sample was obtained at a fairly low carbonization temperature of 500 °C by employing an impregnation mass ratio of ZnCl2 to Arundo donax/chitosan of 3. This optimized material exhibits the best specific surface area of 1863 m2 g−1, pore volume of 1.0 cm3 g−1 and nitrogen content of 5.4 wt%. The presence of nitrogen functionalities on the materials provides a negatively charged surface which is critical for the adsorption of CO2 molecules which are acidic in nature. The sample shows remarkable adsorption capacities of 18.2 mmol g−1 at 0 °C/30 bar and 13.1 mmol g−1 at 25 °C/30 bar under the conditions corresponding to pre-combustion CO2 capture from flue gas streams. High CO2 adsorption values of 3.6 mmol g−1 at 0 °C/1 bar and 2.1 mmol g−1 at 25 °C/1 bar are also observed under post-combustion CO2 capture conditions of the material. The N-doped activated biocarbon shows an exceptionally high value of isoelectric heat of adsorption (32.2 kJ mol−1), indicating that the surface polarity generated by N dopant plays a crucial role in enhancing interactions between CO2 and porous N-doped activated biocarbons.

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.

Mesoporous BN and BCN nanocages with high surface area and spherical morphology

Novel mesoporous BN and BCN materials with cage type porous structure and spherical morphology have been synthesized using carbon nanocages with 3D porous structure as a template via an elemental substitution method at a low synthesis temperature. The obtained materials exhibit a large specific pore volume with uniform pore size distribution and the specific surface area ranging from 945 to 1023 m(2) g(-1).

A Nanoporous Cytochrome c Film with Highly Ordered Porous Structure for Sensing of Toxic Vapors

Creating well-ordered nanoporosity in biomolecules promises stability and activity, offering access to an even wider range of application possibilities. Here, the preparation of nanoporous protein films containing cytochrome c protein molecules is reported through a soft-templating strategy using polystyrene (PS) spheres of different sizes as templates. The stability of the cytochrome c film is demonstrated through electrochemistry studies to show a reusable nature of these films over a long period of time. The size of the PS spheres is varied to tune the pore diameter and the thickness of the cytochrome c films, which are quite stable and highly selective for sensing toxic acidic vapors. The fusion of the templating strategy and the self-assembly of biomolecules may offer various possibilities by generating a new series of porous biomolecules including enzymes with different molecular weights and diameters, peptides, antibodies, and DNA with interesting catalytic, adsorption, sensing, and electronic properties.