Browsing by Author "Raj Laxmi"

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A palladium nanoparticle implanted polymer membrane for reusable dip-catalysis of diverse C-C and C-heteroatom (O/S/N) coupling reactions
(Royal Society of Chemistry, 2023) Raj Laxmi; Ravi Prakash Behere; Arunava Manna; Biplab Kumar Kuila
The criteria for the development of a successful catalyst are simple yet cheap fabrication, high efficiency, stability, flexibility, straightforward recovery, reusability, and ease of scale-up. There are reports of palladium nanoparticle (PdNP)-based catalysts for performing carbon-carbon cross-coupling reactions, but the aforesaid criteria are rarely met in a single system. Moreover, a single catalyst system performing different types of C-C and C-heteroatom cross-coupling reactions is very rare. Herein, we achieved the above-mentioned criteria by using a reusable polymer-embedded Pd nanoparticle dip-catalyst membrane without any other ligands or additives under milder reaction conditions. The composite membrane was fabricated by simply depositing poly(4-vinyl pyridine) anchored PdNPs (average size 9.9 nm) onto a nylon-6 membrane followed by UV cross-linking. C-C bond formation reactions using diverse reagents (Suzuki-Miyaura, Heck, Sonogashira, Stille, Hiyama reactions) were achieved to give the desired products in high to excellent isolated yields, while C-X (X = N/O/S) bond formations were accomplished in moderate to good isolated yields. The turnover number (TON) and frequency (TOF) for the Suzuki-Miyaura cross-coupling reaction are calculated as ≥×104 and 3.11 s−1, respectively. The P4VP-PdNP dip-catalyst system was stable under the reaction conditions without significant leaching of Pd into the solution. The dip-catalyst membrane can be reused at least 10 times without losing any significant activity. The substrate scope for most of the cross-coupling reactions was tested, which indicates functional group tolerance and that the coupling reaction can take place with moieties having electron donating or withdrawing groups. © 2023 The Royal Society of Chemistry
Donor-acceptor organic nanostructure based on conjugated polymer for improving visible-light-driven photocatalytic activity towards degradation of dye in aqueous medium
(Royal Society of Chemistry, 2022) Ravi Prakash Behere; Raj Laxmi; Neelam Gupta; Uttam Sharma; Santanu Das; Biplab Kumar Kuila
Conjugated-polymer-based donor-acceptor hybrid nanostructures have been the subject of great interest, mainly due to their potential applications in photovoltaic and other electronic and optoelectronic devices. Here, we have demonstrated a different aspect of these hybrid nanostructures toward efficient photocatalysis in an aqueous medium. The hybrid donor-acceptor nanostructures were prepared by assembling a carboxylic acid-functionalized fullerene molecule (phenyl C-61 butyric acid) (PCBA) on the surface of an amine-functionalized regioregular P3HT nanostructure through acid-base interaction. The efficient photoinduced charge separation and charge transfer in the hybrid material were investigated by steady-state and time-resolved photoluminescence and photocurrent measurements. The photocatalytic activity of the hybrid nanostructure in water under visible light irradiation (using a 20 W white LED bulb) was investigated, and it was found to show 82.5% dye degradation efficiency. To facilitate the reusability of the photocatalyst, a membrane-based dip-photocatalyst was developed from this material, and it shows 87.5% dye degradation efficiency and can be reused multiple times without a significant change in degradation efficiency. © 2022 The Royal Society of Chemistry.
Fluorene and Triazine-Based Conjugated Polymer Networks with Tuned Frontier Orbital Energy Levels for Improving Organic Photocatalysis
(American Chemical Society, 2024) Raj Laxmi; Anshuman; Neelam Gupta; None Anamika; Arpita Maurya; Ravi Prakash Behere; Rahul Sharma; Biswajit Maiti; Biplab K. Kuila
Here, we describe a method for fine-tuning the frontier orbital energy levels or redox potential of a conjugated polymer network (CPN) consisting of triazine and fluorene by systematically introducing electron-withdrawing groups at the fluorene moiety through simple structural modification. The band gap of CPN decreases with an increase in the strength of the electron-withdrawing group, and the relative position of the frontier orbital energy becomes more favorable for reactions like photocatalytic aerobic oxidation, which has been further confirmed by theoretical and experimental studies. The CPN with a CN group at the 9 position of fluorene (CPN3) shows the maximum photocatalytic activity (32% higher) compared to CPN1 (hydrogen at the 9 position) in white light. The best-performing catalyst CPN3 was further employed for photocatalytic reactions under white light, like the oxidation of alcohols to carbonyl and boronic acid to the corresponding alcohol, which show noteworthy characteristics like low catalyst loading, high yield, and selectivity with broad substrate scope (aliphatic, aromatic, biphenyl, and heterocyclic). CPN3 exhibited turnover frequencies of 13.33 and 10.9 mmol g-1 h-1 in 3 W blue and white LED lights, respectively, which are much higher than those of state-of-art photocatalysts. The recyclability of the catalyst was tested for up to 5 cycles without much change in the catalytic activity. The practical usefulness of the suggested method was further demonstrated by the CPN3-photocatalyzed gram-scale synthesis of high-value chemicals such as acetophenone from 1-phenylethanol and phenol from phenylboronic acid. © 2024 American Chemical Society.
In situ palladium-doped conjugated polymer network for visible light and natural sunlight-driven Suzuki type cross-coupling reaction at room temperature
(Royal Society of Chemistry, 2024) Raj Laxmi; None Anshuman; None Anamika; Neelam Gupta; Biplab K. Kuila
Here, we describe the direct exploitation of visible light energy by using a conjugated polymer network (CPN) that is susceptible to an in situ loading of Pd metal for photocatalytic Suzuki-type C-C cross-coupling reaction. The requisite products were quantitatively achieved (yield >90%), under photo-illumination using an environment-friendly solvent. Under normal solar light, similar catalytic activity was maintained using the same experimental conditions. To comprehend the function of every variable and reactive species involved in the reaction's path, in-depth mechanistic studies were carried out. It is further underlined that the CPN has greater catalytic efficiency based on its exceptional resistance to 50 substrates of varying functionality, for 5 consecutive catalyst recycling cycles as well as bulk-scale reactions and a turnover frequency value of up to 1840 h−1 at a low catalyst dose of Pd (0.0125 mol%), while maintaining its catalytic efficacy. Its catalytic competence in terms of scope, scalability, environmental friendliness, and sustainability supports its proficiency. © 2024 The Royal Society of Chemistry.
Ni-Pd bimetallic nanoparticle stabilized polymer membrane as an efficient dip-catalyst for oxidative coupling of aromatic amines to access symmetrical and unsymmetrical azo compounds
(Royal Society of Chemistry, 2025) None Anshuman; Raj Laxmi; Padmini Gupta; Renu Mishra; Neelam Gupta; Biplab Kumar Kuila
The azo linkage is an important chemical motif with wide applications in the pharmaceutical, agrochemical, textile, paint, and food industries. The development of effective dip-catalysts that would convert aromatic amines to symmetric or asymmetric azobenzenes in the presence of aerobic molecular oxygen under mild conditions is really challenging. Here, we have developed a dip-catalyst by immobilizing poly(vinylpyrrolidone)(PVP) stabilized Ni-Pd bimetallic nanoparticles on a nylon-6 membrane through UV-crosslinking for performing such reactions. The catalyst was highly efficient for the oxidative coupling of aromatic amines to the corresponding aromatic azo compounds under aerobic conditions without employing hazardous substances or ecologically harmful nitrites. Notable reaction features include a broad substrate range (aromatic, heterocyclic, and polyaromatic amines), a high yield (∼98%), low catalyst loading, and a simple work-up method. The dip-catalyst exhibits exceptional reusability for multiple catalytic cycles while retaining its high performance and structural characteristics. The gram-scale synthesis of high-value compounds like azobenzene provided additional evidence of the practical utility of the proposed catalyst. © 2025 The Royal Society of Chemistry.
UV Cross-Linked Polymer Stabilized Gold Nanoparticles as a Reusable Dip-Catalyst for Aerobic Oxidation of Alcohols and Cross-Aldol Reactions
(American Chemical Society, 2023) Raj Laxmi; None Anshuman; Ravi Prakash Behere; Arunava Manna; Biplab K. Kuila
In this work, a gold nanoparticle (AuNP)-embedded composite polymer membrane for dip-catalysis is developed. Primarily, a polyvinylpyrrolidone-stabilized AuNP (PVP-AuNP) with an average size of 6.50 nm was synthesized by the reduction of a composite solution of Au salt and PVP. Next, the composite membrane was fabricated by simply depositing the PVP-AuNP on the Nylon membrane followed by UV cross-linking. The composite membrane having the cross-linked PVP-AuNP was utilized as a dip-catalyst for the aerobic oxidation of alcohols to carbonyl compounds under oxygen and clean reaction conditions. The catalyst was further tested for performing cross-aldol reactions. The PVP-AuNP-catalyzed oxidation reaction also has other noteworthy characteristics, such as a low catalyst loading (Au, 1.2 mol %), high yield, and selectivity with a broad substrate scope (aliphatic, aromatic, biphenyl, and heterocyclic alcohols). The turnover number (TON) and turnover frequency (TOF) for the oxidation reaction of the alcohol are calculated to be 74.5 and 12.41 h-1, respectively. The P4VP-AuNP dip-catalysts are highly stable under the reaction conditions without significant leaching of Au into the solution. The dip-catalyst demonstrates outstanding reusability up to 10 catalytic cycles while maintaining high catalytic performance and structural features. It can be easily recovered by simply pulling it out from the reaction mixture once the reaction is complete, followed by washing and drying. The practical usefulness of the suggested method was further demonstrated by the PVP-AuNP-catalyzed gram-scale synthesis of high-value chemicals like acetophenone. Although the AuNPs are already used for different reactions, their integration into dip-catalysts for oxidation of alcohols and cross-aldol reactions with a wide substrate scope is rare. Overall, these findings demonstrate that developing composite dip-catalyst systems is a realistic strategy for creating high-value chemicals in a sustainable and environmentally friendly way. © 2023 American Chemical Society
Visible light driven C-N cross-coupling reactions catalysed by a conjugated polymer network
(Royal Society of Chemistry, 2025) Anshuman; Raj Laxmi; Renu Mishra; Biplab Kumar Kuila
This work describes the use of a fluorine and triazine containing conjugated polymer network (CPN) susceptible to in situ Pd doping during its preparation for photocatalytic C-N cross-coupling reactions between aryl halides and amines under visible light irradiation at room temperature. Comprehensive mechanistic investigations were conducted in order to understand the role of each variable and reactive species involved in the reaction pathway. The broad substrate range (aliphatic, aromatic, and heterocyclic) with good functional group tolerance, recyclability, low catalyst loading (5.0 wt%), use of low intensity white LED light (0.05 W cm−2), high yields (95-82%), and high turnover frequency values of up to 1515.46 h−1 are some of the primary advantages of the described method. The CPN photocatalyzed gram-scale synthesis of high-value compounds like 4-(4-nitrophenyl)morpholine, 4-phenylmorpholone, and N-benzylpyridine-2-amine further illustrated the practical utility of the proposed approach. © 2025 The Royal Society of Chemistry.