Showing papers by "Asim Bhaumik published in 2021"

Metformin-Templated Nanoporous ZnO and Covalent Organic Framework Heterojunction Photoanode for Photoelectrochemical Water Oxidation

Abstract: Photoelectrochemical water-splitting offers unique opportunity in the utilization of abundant solar light energy and water resources to produce hydrogen (renewable energy) and oxygen (clean environment) in the presence of a semiconductor photoanode. Zinc oxide (ZnO), a wide bandgap semiconductor is found to crystallize predominantly in the hexagonal wurtzite phase. Herein, we first report a new crystalline triclinic phase of ZnO by using N-rich antidiabetic drug metformin as a template via hydrothermal synthesis with self-assembled nanorod-like particle morphology. We have fabricated a heterojunction nanocomposite charge carrier photoanode by coupling this porous ZnO with a covalent organic framework, which displayed highly enhanced photocurrent density of 0.62 mA/cm2 at 0.2 V vs. RHE in photoelectrochemical water oxidation and excellent photon-to-current conversion efficiency at near-neutral pH vis-a-vis bulk ZnO. This enhancement of the photocurrent for the porous ZnO/COF nanocomposite material over the corresponding bulk ZnO could be attributed to the visible light energy absorption by COF and subsequent efficient charge-carrier mobility via porous ZnO surface.

Metal-Free Triazine-Based 2D Covalent Organic Framework for Efficient H2 Evolution by Electrochemical Water Splitting.

Abstract: Hydrogen evolution reaction (HER) by electrochemical water splitting is one of the most active areas of energy research, yet the benchmark electrocatalysts used for this reaction are based on expensive noble metals. This is a major bottleneck for their large-scale operation. Thus, development of efficient metal-free electrocatalysts is of paramount importance for sustainable and economical production of the renewable fuel hydrogen by water splitting. Covalent organic frameworks (COFs) show much promise for this application by virtue of their architectural stability, nanoporosity, abundant active sites located periodically throughout the framework, and high electronic conductivity due to extended π-delocalization. This study concerns a new COF material, C6 -TRZ-TFP, which is synthesized by solvothermal polycondensation of 2-hydroxybenzene-1,3,5-tricarbaldehyde (TFP) and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tris[(1,1'-biphenyl)-4-amine]. C6 -TRZ-TFP displayed excellent HER activity in electrochemical water splitting, with a very low overpotential of 200 mV and specific activity of 0.2831 mA cm-2 together with high retention of catalytic activity after a long duration of electrocatalysis in 0.5 m aqueous H2 SO4 . Density functional theory calculations suggest that the electron-deficient carbon sites near the π electron-donating nitrogen atoms are more active towards HER than those near the electron-withdrawing nitrogen and oxygen atoms.

Novel Nanoporous Ti-Phosphonate Metal–Organic Framework for Selective Sensing of 2,4,6-Trinitrophenol and a Promising Electrode in an Energy Storage Device

Abstract: Designing a multifunctional metal–organic framework (MOF) based on a novel ligand architecture for fluorescence sensing of explosives and energy storage applications is very challenging from the pe...

Mesoporous Porphyrin-Silica Nanocomposite as Solid Acid Catalyst for High Yield Synthesis of HMF in Water.

Abstract: Solid acid catalysts occupy a special class in heterogeneous catalysis for their efficiency in eco-friendly conversion of biomass into demanding chemicals. We synthesized porphyrin containing porous organic polymers (PorPOPs) using colloidal silica as a support. Post-modification with chlorosulfonic acid enabled sulfonic acid functionalization, and the resulting material (PorPOPS) showed excellent activity and durability for the conversion of fructose to 5-hydroxymethyl furfural (HMF) in green solvent water. PorPOPS composite was characterized by N2 sorption, FTIR, TGA, CHNS, FESEM, TEM and XPS techniques, justifying the successful synthesis of organic networks and the grafting of sulfonic acid sites (5 wt%). Furthermore, a high surface area (260 m2/g) and the presence of distinct mesopores of ~15 nm were distinctly different from the porphyrin containing sulfonated porous organic polymer (FePOP-1S). Surprisingly the hybrid PorPOPS showed an excellent yield of HMF (85%) and high selectivity (>90%) in water as compared to microporous pristine-FePOP-1S (yield of HMF = 35%). This research demonstrates the requirement of organic modification on silica surfaces to tailor the activity and selectivity of the catalysts. We foresee that this research may inspire further applications of biomass conversion in water in future environmental research.

Nickel Nanoparticles Immobilized over Mesoporous SBA-15 for Efficient Carbonylative Coupling Reactions Utilizing CO2: A Spotlight.

Abstract: Ecofriendly routes for the synthesis of carbamates and carbonylative coupling products such as benzyl formate derivatives are very demanding for both academia and industries. Foreseeing a sustainable green future, we systematically analyzed the synthesis history of both these chemicals, mentioning their pros and cons. As a step towards green chemistry, here we have optimized the reaction conditions for the synthesis of various benzyl formates from corresponding benzyl halides and carbamates from substituted anilines and alkyl halides catalyzed by Ni(0) nanoparticles (NPs) immobilized over amine-functionalized ordered mesoporous SBA-15 material in the presence of CO2 as C1 source. This spotlight on applications is aimed to provide a clear outlook to date regarding the gradual progress in the synthesis of both these aforementioned chemicals and finally addresses further efforts for overcoming the current challenges.

A Tetradentate Phosphonate Ligand-based Ni-MOF as a Support for Designing High-performance Proton-conducting Materials.

Abstract: Developing a robust metal-organic framework (MOF) which facilitates proton hopping along the pore channels is very demanding in the context of fabricating an efficient proton-conducting membrane for fuel cells. Herein, we report the synthesis of a novel tetradentate aromatic phosphonate ligand H8 L (L=tetraphenylethylene tetraphosphonic acid) based Ni-MOF, whose crystal structure has been solved from single-crystal X-ray diffraction. Ni-MOF [Ni2 (H4 L)(H2 O)9 (C2 H7 SO)(C2 H7 NCO)] displays a monoclinic crystal structure with a space group of P 21 /c, a=11.887 A, b=34.148 A, c=11.131 A, α=γ=90°, β=103.374°, where a nickel-hexahydrate moiety located inside the void space of the framework through several H-bonding interactions. Upon treatment of the Ni-MOF in different pH media as well as solvents, the framework remained unaltered, suggesting the presence of strong H-bonding interactions in the framework. High framework stability of Ni-MOF bearing H-bonding interactions motivated us to explore this metal-organic framework material as proton-conducting medium after external proton doping. Due to the presence of a large number of H-bonding interactions and the presence of water molecules in the framework we have carried out the doping of organic p-toluenesulfonic acid (PTSA) and inorganic sulphuric acid (SA) in this Ni-MOF and observed high proton conductivity of 5.28×10-2 S cm-1 at 90 °C and 98% relative humidity for the SA-doped material. Enhancement of proton conductivity by proton doping under humid conditions suggested a very promising feature of this Ni-MOF.

Novel Tetradentate Phosphonate Ligand Based Bioinspired Co-Metal–Organic Frameworks: Robust Electrocatalyst for the Hydrogen Evolution Reaction in Different Mediums

Abstract: The limited stock of classical nonrenewable energy sources has motivated researchers to explore efficient strategies for sustainable and renewable energy production. Hydrogen production via electro...

A new 2D lanthanum based microporous MOF for efficient synthesis of cyclic carbonates through CO2 fixation

Abstract: Metal–organic frameworks (MOFs) containing multiple carboxylate and sulfonate linkers together with positively charged rare earth metals can offer new opportunities in heterogeneous catalysis. The high efficiency of the CO2 fixation reaction at low temperature and pressure over MOF-based catalysts is very challenging as it involves the renewable feedstock CO2 as a C1 source for the synthesis of value-added fine chemicals. Here we develop a new microporous La(III) based MOF through the solvothermal reaction using 5-sulfoisophthalic acid as the ligand, and the resulting La-5-SIP-MOF showed a high catalytic activity for the synthesis of cyclic carbonates from epoxides through the CO2 fixation reaction at room temperature and moderate (3–5 MPa) pressure. The optimum product yield was obtained in only 1 h reaction with the desired yield up to 98%. The La-5-SIP-MOF was characterized by using different analytical techniques such as single crystal X-ray diffraction, FTIR, PXRD, N2 adsorption/desorption study, UHR-TEM, solid UV-vis spectroscopy and TGA. The recycling efficiency and the structural stability of this MOF catalyst is also very high, suggesting a sustainable future of this La-MOF in heterogeneous catalysis.

Sulfur-containing nitrogen-rich robust hierarchically porous organic polymer for adsorptive removal of mercury: experimental and theoretical insights

Abstract: The development of an efficient and robust material for adsorptive removal of highly toxic metals like mercury from water resources is very challenging from the perspectives of hygiene and sustainable environment. Heteroatoms such as sulfur and nitrogen in this high surface area porous organic polymer is very promising for mercury remediation because it offers strong interactions between Hg(II) ions and S/N bound at the pore surface of the adsorbent. Thus, herein we developed a new secondary amine-linked, sulfur-containing and N-rich porous organic polymer, TTP-1, via polycondensation of a tetrapodal amine and thiophene-2-carbaldehyde. TTP-1 displayed a high BET surface area of 1034 m2 g−1 with hierarchical porosity and exceptionally high uptakes of 3106 and 691 mg g−1 for inorganic Hg2+ and organic methylmercury (CH3Hg+), respectively. The high adsorption efficiency for mercury capture is also supported from the strong noncovalent interaction of the ligand S and N lone pairs with Hg2+, as revealed from the ab initio quantum chemical calculation and AIM analysis. Cost-effective, eco-friendly and scaleable synthesis of porous organic polymer with hierarchical porosity reported herein may contribute to the design of a benchmark adsorbent for the remediation of mercury (Hg(II)/CH3Hg+) and may significantly aid in industrial and environmental cleanup.

The design and synthesis of heterogeneous catalysts for environmental applications

Abstract: With the rapid advancements in synthetic strategies, the field of heterogeneous catalysis has expanded enormously over the last few decades, and today it is one of the foremost areas in energy and environmental research. Various templating and non-templating routes for designing porous nanomaterial-based catalysts starting from precursor building blocks are highlighted here. CO2 and biomass are two major abundant resources that can be utilized as feedstocks for various heterogeneous catalytic processes. These are described in brief, together with environmental clean-up applications and future perspectives for addressing environmental issues.

A novel crystalline nanoporous iron phosphonate based metal–organic framework as an efficient anode material for lithium ion batteries

Abstract: A new Fe-MOF prepared by using a tetraphosphonic acid as a ligand is reported and it showed high specific capacity and excellent recycling efficiency in lithium-ion batteries.

Lithium embedded hierarchically porous aluminium phosphonate as anode material for lithium-polymer battery

Abstract: Crystalline porous nanomaterials having large surface area and exchangeable cation sites are very useful for high mobility of Li-ions, which is the key for developing an efficient energy storage material. Herein, we have reported a novel organic–inorganic hybrid hierarchically porous aluminium phosphonate (AlPIm) material through the polycondensation of Al(III) with an organophosphorus precursor iminodi(methylphosphonic acid) under hydrothermal reaction conditions without using any structure-directing agent. Lithium immobilization over aluminium phosphonate yields LiAlPIm, which showed excellent electrochemical property of a freestanding anode for the lithium polymer battery. AlPIm and LiAlPIm materials were characterized through several instrumental tools i.e. PXRD, N2-sorption, FE-SEM, TEM, XPS, FT-IR spectroscopy and thermogravimetric analysis. Due to high BET surface area and nanoscale porosity, Li-ion transportation was facilitated and thus LiAlPIm anode material displayed high specific discharge capacity of 238 mA h g−1 together with an outstanding retention stability in the lithium-polymer battery.

Transformation of Wurtzite ZnO to a New Triclinic Nanoporous ZnO Phase via Hydrothermal Treatment with Metformin for Designing Proton Conducting Material.

Abstract: Zinc oxide is one of the most widely studied semiconductor metal oxides, which predominantly crystallizes as hexagonal wurtzite and often cubic zinc-blende phases. Here we report the transformation of the highly stable wurtzite ZnO to a new triclinic phase NZO-2 by using metformin as a template during post-synthesis hydrothermal treatment. This crystalline phase of the material NZO-2 has been identified through the refinement of the powder XRD data. NZO-2 possesses porous rod like particle morphology consisting of the self-assembly of 3-7 nm size spherical nanoparticles and interparticle nanoscopic voids spaces. NZO-2 has been surface phosphorylated and the resulting material displayed good proton conductivity. Further, NZO-2 displayed ultra-low band gap of 1.74 eV, thereby responsible for red emission under high energy laser excitation and this may open new opportunities in optoelectronic application of ZnO.

Solvent-free benzylic oxidation of aromatics over Cu(II)-containing propylsalicylaldimine anchored on the surface of mesoporous silica catalysts.

Abstract: A sustainable method was used to produce aromatic ketones by the solvent-free benzylic oxidation of aromatics over mesoporous Cu(II)-containing propylsalicylaldimine anchored on the surface of Santa Barbara Amorphous type material-15 (CPSA-SBA-15) catalysts. For comparison, mesoporous Cu(II)-containing propylsalicylaldimine anchored with Mobil Composition of Matter-41 (CPSA-MCM-41) was assessed for these reactions under similar reaction conditions. The washed CPSA-SBA-15(0.2) (W-CPSA-SBA-15(0.2)) catalyst was prepared using an easy chemical method for the complete removal of non-framework CuO nanoparticle species on the surface of pristine CPSA-SBA-15(0.2) (p-CPSA-SBA-15(0.2) prepared with 0.2 wt% of Cu, and its catalytic activity was evaluated with different reaction parameters, oxidants and solvents. In order to confirm the catalytic stability, the recyclability was assessed, and the performance of hot-filtration experiments was also evaluated. All the catalysts used for these catalytic reactions were characterized using many instrumental techniques to pinpoint the mesoporous nature and active sites of the catalysts. The proposed reaction mechanism has been well documented on the basis of catalytic results obtained for solvent-free oxidation of aromatics. Based on the catalytic results, we found that W-CPSA-SBA-15(0.2) is a very ecofriendly catalyst with exceptional catalytic activity.