Purabi Kar

Bio: Purabi Kar is an academic researcher from National Institute of Technology, Rourkela. The author has contributed to research in topics: Montmorillonite & Catalysis. The author has an hindex of 6, co-authored 9 publications receiving 100 citations.

Silicotungstic acid nanoparticles dispersed in the micropores of Cr-pillared clay as efficient heterogeneous catalyst for the solvent free synthesis of 1,4-dihydropyridines

Abstract: Chromium pillared clay (Cr-P) is prepared by intercalating chromium oligomeric clusters into the interlayer of the montmorillonite clay. The Cr-oligomeric clusters are prepared by the partial base hydrolysis of chromium nitrate solution. Cr-P clay served as efficient support for dispersion of silicotungstic acid (STA). The STA particles are dispersed in the micropores of Cr-P clay by wet impregnation method. The synthesized materials are characterized by XRD, FTIR, UV–Vis, sorptometric, TGA, SEM and TEM techniques. XRD study indicates an expansion in the interlayer space as a result of Cr-polycations pillaring. The interlayer spacing is found to be retained after incorporation of STA particles. IR and UV–Vis study illustrates the structural integrity of the STA particles in the micropores of the pillared clay. N2 adsorption/desorption shows that the synthesized materials are microporous in nature exhibiting Type I sorption isotherm. The catalytic activity of the STA/Cr-P materials is evaluated for the synthesis of 1,4-dihydropyridines (DHPs) by multicomponent reaction of aldehydes/chalcones, ethylacetoacetate and ammonium acetate. Structurally diverse DHPs are prepared by using different aryl aldehydes and chalcones as starting materials. The STA/Cr-P materials are found to be highly efficient for the multicomponent reaction generating a variety of DHPs with high yield and purity under microwave irradiation and solvent free conditions.

Sulfate Grafted Iron Stabilized Zirconia Nanoparticles as Efficient Heterogenous Catalysts for Solvent-Free Synthesis of Xanthenediones under Microwave Irradiation

Abstract: Sulfate grafted iron stabilized zirconia nanoparticles (SO42–/xFe–Zr–O) are prepared by a coprecipitation method followed by sulfate ion grafting. The SO42–/xFe–Zr–O materials have been characterized using XRD, UV–vis, FTIR, Raman, SEM, and TEM techniques. XRD study indicated incorporation of iron ions (up to 20 mol %) into the zirconia lattice, resulting in the formation of a substitutional solid solution. The vibrational features corresponding to the S═O and S–O stretching of anchored sulfate species are observed in the FTIR study. The Raman study indicated the presence of nanosize hematite and tetragonal zirconia phase in the composite oxide. The presence of iron oxide in the zirconia lattice improves the sulfate retention capacity of the host zirconia. The SO42–/xFe–Zr–O materials are found to be efficient catalysts for the synthesis of structurally diverse xanthenediones by one-pot condensation of dimedone with aryl aldehydes under solvent-free conditions and microwave irradiation.

Polyphosphoric acid–zirconia pillared clay composite catalytic system for efficient multicomponent one pot synthesis of tetrahydropyridines under environmentally benign conditions

Abstract: A series of zirconia pillared clay–polyphosphoric acid (PPA) composites are synthesized by adopting different preparative strategies. Initially, PPA is intercalated to the clay matrix with and without the use of structure expanding agent (CTAB). Subsequently, the PPA–clay composite is pillared with Zr-polycation to form the composite materials. In an alternate approach, Zr-pillared clay is synthesized by insertion of Zr-polycation, which is then used for dispersion of PPA moiety in the pillared clay matrix. The synthesized composites are characterized by XRD, FTIR, UV–vis, TGA, EDX, FE-SEM and sorptometric techniques. XRD study indicated an expansion in the clay structure after intercalation of PPA as well as the Zr-polycations. The FTIR spectra exhibit characteristic vibrational features of the clay sheet as well as PPA moiety indicating the structural stability of the composite materials. The phosphorous content in the composite samples is analyzed using EDX study. FE-SEM study indicated morphological changes upon intercalation of PPA and Zr-polycations to the clay matrix. The catalytic activity of the composite catalysts has been examined for the synthesis of tetrahydropyridines under environmental benign conditions by one pot multicomponent condensation of β-dicarbonyl compounds, substituted anilines and substituted benzaldehydes. The PPA intercalated clay pillared with Zr polycations (PPA–ZrP) is found to be highly efficient for the synthesis of structurally diverse substituted tetrahydropyridines under mild conditions.

Preparation and catalytic application of sulfonated PVA-Zr-pillared clay nanocomposite materials towards one pot synthesis of hexahydropyrimidines

Abstract: A series of sulfonated polyvinyl alcohol-Zr-pillared clay nanocomposites were synthesized. A low molecular weight polyvinyl alcohol (PVA) was sulfonated using chlorosulfonic acid. The sulfonated PVA was intercalated inside the parent clay and Zr-pillared clay (Zr-P) matrix. In an alternative approach, the polyvinyl alcohol was initially intercalated into the clay and Zr-P structure followed by in-situ sulfonation inside the clay matrix. The composite materials were characterized using XRD, FTIR, Raman, UV–vis and FE-SEM analytical techniques. Expansion in clay interlayer due to insertion of the polymeric species and the Zr-pillars was observed from XRD study. FTIR and UV–vis study revealed presence of hydrated sulfonic acid clusters in the composite materials. The clay sheets were largely present in an exfoliated state in the clay-polymer composite materials. Insertion of the Zr-pillar imparts structural rigidity and consequent changes in the morphological features. The catalytic activity of the Zr-pillared clay-sulfonated polyvinyl alcohol composite materials has been investigated for synthesis of hexahydropyrimidines by multicomponent condensation of substituted aniline, formaldehyde and β-dicarbonyl compounds. The composite materials were found to be highly active for synthesis of structurally diverse hexahydropyrimidines in high yield and purity.

Potential application of Pd-Ni bimetallic nanoparticles dispersed in Al-pillared clay matrix as catalyst for hydrodechlorination of chloroanilines from aqueous sources

Abstract: The Al-pillared clay (Al-P) was prepared by insertion of [AlO 4 Al 12 (OH) 24 (H 2 O) 12 ] 7+ clusters into the interlayer of montmorillonite clay and subsequent thermal activation. Al-pillared clay was used as an efficient inorganic matrix for dispersion of Pd-Ni bimetallic nanoparticles. The bimetallic nanoparticles were synthesized using chemical reduction method. The supported bimetallic catalysts were characterized using XRD, IR, UV–vis, TGA, sorptometric, FE-SEM-EDX and TEM techniques. The expansion of the interlayer space of the parent clay as a result of pillaring and its subsequent retention in the Pd-Ni/Al-P system was noted from XRD study. The structural integrity as well as electronic environment of the pillars and supported metal particles has been inferred from the FTIR and UV–vis study. FE-SEM study implies changes in morphological feature of the clay materials upon pillaring and dispersion of the bimetallic nanoparticles. The TEM study of the supported bimetallic system indicated well dispersion of the metal species with particle size in the range of 10–25 nm. The Pd-Ni/Al-P system was used as an efficient heterogeneous catalyst for hydrodechlorination of chloroanilines under hydrogen transfer condition using hydrazine hydrate as hydrogen donating agent. The catalytic studies indicated that the bimetallic Pd-Ni system supported over Al-P is highly active for the reaction. The effect of various reaction parameters such as molar ratio of metallic components, temperature, and time, type of hydrogen transfer agents and functionality of substrate was studied in details.

Conversion of Carbon Dots from Fluorescence to Ultralong Room-Temperature Phosphorescence by Heating for Security Applications

Abstract: Stimuli-responsive optical materials have received tremendous interest in the last several decades due to their numerous promising applications. Here, fluorescence emissive polymer carbon dots (F-CDs), prepared with a simple heating treatment from ethylenediamine and phosphoric acid, are found to produce unexpected ultralong room-temperature phosphorescence (URTP), which lasts for about 10 s with a lifetime of 1.39 s. This is the first example to achieve the conversion of a fluorescence material to URTP by means of an external heating stimulus. Further investigations reveal that the doping of N and P elements and self-immobilization of the excited triplet species are likely mainly responsible for the observed URTP after the heating treatment, due to the facilitation of the intersystem crossing and formation of more compact cores for effective intraparticle hydrogen bonds, respectively. Importantly, this study also demonstrates the potential for aqueous dispersion of the F-CDs as an advanced security ink for information encryption and anticounterfeiting; this is a feature that has not been reported before. This study is believed to open possibilities to extend stimuli-responsive optical materials to rarely exploited phosphorescence-relevant systems and applications, and also to provide a novel strategy to easily prepare URTP materials.

Synthesis of waste cooking oil-based biodiesel via effectual recyclable bi-functional Fe2O3MnOSO42−/ZrO2 nanoparticle solid catalyst

Abstract: The ferric–manganese doped sulfated zirconia nanoparticle solid acid catalyst was prepared through the impregnation reaction followed by calcination at 600 °C for 3 h. The characterization was performed using X-ray diffraction (XRD), Temperature programed desorption of NH 3 (TPD-NH 3 /CO 2 ), Thermal gravimetric analysis (TGA), Fourier Transform Infrared spectrometer (FT-IR), Brunner–Emmett–Teller (BET) surface area measurement, Energy dispersive X-ray spectroscopy (EDS), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). In addition, the dependence of the biodiesel yield on the reaction variables, such as reaction temperatures, catalyst loading, as well as the molar ratio of methanol/oil and reusability, were also investigated. The catalyst was reused six times without loss in its activity with the maximum yield of 96.5 ± 0.02% achieved under the optimized conditions of the reaction temperature of 180 °C; stirring speed of 600 rpm, 1:20 M ratio of oil to alcohol and 3 wt/wt% catalyst loading. Additionally, the fuel properties of producing biodiesel from waste cooking oil were investigated and compared with those of the American and European standards.

Recent advances in electrocatalysts for halogenated organic pollutant degradation

Abstract: Electrocatalysis has recently been extensively employed for the degradation of halogenated organic pollutants (HOPs) that normally act as persistent, toxic, and bioaccumulative substances in the environment and pose threats to aquatic species as well as human beings. This review article broadly gives the up-to-date status on promising electrocatalysts for the degradation of HOPs, with particular emphasis on the strategies for promoting the activities of catalysts. Firstly, the catalysts for the oxidative mineralization process including metallic oxide- and carbon-based anodes, as well as the oxidative dehalogenation mechanism of these catalysts, are comprehensively presented. Secondly, the catalysts for the reductive degradation process, which involves metal- and metal complex-based cathodes, together with their applications and organic transformation pathways, are fully analyzed. Thirdly, recent advances in the integrated techniques are introduced, and the integration of membrane techniques, biological methods, Fenton processes, and photocatalysis with electrocatalysis is discussed. Finally, several key directions for further research are exploited, which include catalyst design, experimental optimization, scientific exploration, and effective coupling techniques.

Complete hydrodechlorination of chlorobenzene and its derivatives over supported nickel catalysts under liquid phase conditions (vol 60, pg 131, 2005)

Abstract: Abstract Liquid phase hydrodechlorination of chlorobenzene was studied over Ni/active carbon (Ni/AC), Ni/γ-Al 2 O 3 , Ni/SiO 2 and Raney Ni. The complete hydrodechlorination of chlorobenzene was realized at 333–343 K on Ni/AC under hydrogen atmosphere of 1.0 MPa in the presence of alkaline hydroxide. Aryl halides, three chlorotoluenes ( o -, m - and p -), three chloroanilines, three chlorobenzotrifluorides, three dichlorobenzenes and two trichlorobenzenes (1,2,3- and 1,2,4-) were also completely hydrodechlorinated under the similar conditions. Chlorobenzene derivatives having either an electron-donating group or an electron-withdrawing group decreased their reactivities with respect to the unsubstituted chlorobenzene. The reactivities of polychlorinated benzenes slightly decreased with the increasing chlorine atom number in a molecule. The steric effect of trichlorobenzene gave a large influence on the product distribution. The reaction rate did not depend on chlorobenzene concentration and increased with increasing hydrogen pressure. The reaction did not proceed in the absence of alkaline hydroxide. The active catalysts were characterized by hydrogen chemisorption and transmission electron microscopy techniques. The apparent activity strongly depends on the active surface area of nickel on catalyst surface. Based on the above results, the reaction route was discussed. The deactivation of Ni catalyst was observed in the dechlorinating process. An accumulation of NaCl on the catalyst surface is probably one of the reasons for the deactivation. The deactivated catalysts can be partially recovered by washing with distillated water and reactivating.