Bibekananda De

A green and facile approach for the synthesis of water soluble fluorescent carbon dots from banana juice

Green luminescent water soluble oxygenous carbon dots with an average size of 3 nm were synthesized by simply heating banana (Musa acuminata) juice at 150 °C for 4 h without using any surface passivating and oxidizing agent or inorganic salt. The literature was used to propose a possible mechanism for the formation of carbon dots by this approach. The resulting carbon dots exhibited concentration, excitation wavelength and pH dependent luminescent behavior in the visible range. The quantum yield was 8.95 on excitation at a wavelength of 360 nm, using quinine sulfate as the reference. The presence of large amounts of oxygenous functionality was confirmed by FTIR and EDX studies. XRD and TEM illustrated the poor crystalline nature and narrow distribution of these spherical carbon dots. Thus bio-based fluorescent carbon dots with a high yield were reported for the first time through a simple and effective route without using any special apparatus or reagents.

Novel high performance tough hyperbranched epoxy by an A2 + B3 polycondensation reaction

High performance tough epoxy thermoset with excellent adhesive strength is one of the most in demand materials for advanced engineering applications. In the present investigation three hyperbranched epoxy resins with varying compositions were synthesized by a single step controlled polycondensation reaction using an A2 + B3 approach for the first time. The physical properties like epoxy equivalent, hydroxyl value, viscosity, etc. of the synthesized epoxy resins were determined by different analytical techniques. The hyperbranched structure of the resins was characterized by spectroscopic techniques. The degrees of branching were found to be 0.60, 0.79 and 0.51 for the resins with 10, 20 and 30 wt% of the B3 moiety respectively, as obtained from the 13C NMR study. The poly(amidoamine) cured hyperbranched epoxy thermosets exhibited high thermostability (up to 293, 298 and 296 °C), tensile strength (38, 47 and 26 MPa), elongation at break (43, 21 and 52%), strain energy or toughness (1277, 758 and 1056 MPa), exceptionally high adhesive strength (1987, 2662, 1638 MPa), impact resistance (>100 cm) and scratch hardness (8.5, 9.0, 8.0 kg). The results showed the prominent role of the amount of the B3 moiety in the performance of the thermosets. The study, therefore, revealed that the unison of the aliphatic–aromatic moiety in the hyperbranched structure can offer a high performance tough epoxy thermoset without any processing difficulty.

Transparent luminescent hyperbranched epoxy/carbon oxide dot nanocomposites with outstanding toughness and ductility.

A luminescent transparent hyperbranched epoxy nanocomposite with previously unachieved outstanding toughness and elasticity has been created by incorporation of a very small amount of carbon oxide nanodots. The nanocomposites of the hyperbranched epoxy with carbon oxide dots at different dose levels (0.1, 0.5, and 1.0 wt %) have been prepared by an ex situ solution technique followed by curing with poly(amido-amine) at 100 °C. Different characterizations and evaluations of mechanical and optical properties of the nanocomposites have been performed. The toughness (area under the stress-strain curve) of the pristine system has been improved dramatically by 750% with only 0.5 wt % carbon oxide dots. The tensile strength has been enhanced from 38 to 46 MPa, whereas the elongation at break improved noticeably from 15 to 45%. Excellent adhesive strength combined with transparency and photoluminescent behavior renders these materials highly interesting as functional films in optical devices like light-emitting diodes and UV light detection systems as well as in anticounterfeiting applications.

Carbon dot reduced Cu2O nanohybrid/hyperbranched epoxy nanocomposite: mechanical, thermal and photocatalytic activity

In the present study a highly tough thermostable hyperbranched epoxy nanocomposite was fabricated by the incorporation of carbon dot reduced Cu2O nanohybrid, which exhibited efficient reusable photocatalytic activity towards the degradation of pesticide under solar light (light intensity: 800–1000 lux). The catalytic efficacy of the above nanohybrid was compared with that of the parent carbon dot. Carbon dot reduced Cu2O nanohybrid particles were prepared by the reduction of cupric acetate solution with carbon dots at 70 °C for 6 h. The formation of nanohybrid (size: 3–4 nm), as well as its nanocomposites with hyperbranched epoxy, was confirmed by FTIR, XRD, Raman and TEM analyses. The significant improvement in the performance in terms of tensile strength (20%), elongation at break (2.5 fold), toughness (3.5 fold) and thermal stability (23 °C) of the pristine epoxy thermoset was observed by the formation of nanocomposite with 1.5 wt% of nanohybrid. The degradation of ethyl paraoxon pesticide was studied under ambient conditions using normal solar light and the changes of concentration with respect to initial were monitored by UV study. Thus, the high performance nanocomposite with photocatalytic attributes has strong potential to be used as a functional thin film material, as well as thermostable reusable photocatalyst.

Recent progress in carbon dot–metal based nanohybrids for photochemical and electrochemical applications

Carbon dot (CD) is the youngest member of the carbon based nanomaterials family but it has emerged as the brightest in recent times, as now it is one of the most intensive research topics in the domain of materials science. The popularity is due to its excellent aqueous dispersibility, functionality, biocompatibility and ease of preparation from different carbon based resources. All such favorable attributes help CDs to find applications in the fields of optoelectronic, energy conversion, bio-imaging, drug delivery, sensors, catalysis, etc. Most recently, CD–metal based nanohybrids have been extensively employed for several photochemical and electrochemical applications due to their unique and interesting up-conversion photoluminescence and photo-induced electron/charge transfer properties. Therefore, the recent progress of CD–metal based nanohybrids in such applications needs to be compiled in the form of a review for highlighting their benefits to researchers in this field. In the present review, hence, fabrication methods, structural characterizations, properties and applications of CD–metal based nanohybrids are highlighted in a concise but systematic way to cover the desired information. Different photochemical and electrochemical applications like photocatalysis, solar cell or photovoltaic, energy storage, and photochemical and electrochemical sensors of the CD–metal based nanohybrids are focused in this article. This review thus tries to provide a decent and updated coverage on the topic.

Enhanced Electrochemical and Photocatalytic Performance of Core–Shell CuS@Carbon Quantum Dots@Carbon Hollow Nanospheres

A controlled structural morphology, high specific surface area, large void space, and excellent biocompatibility are typical favorable properties in electrochemical energy storage and photocatalytic studies; however, a complete understanding about this essential topic still remains a great challenge. Herein, we have developed a new type of functionalized carbon hollow-structured nanospheres based on core-shell copper sulfide@carbon quantum dots (CQDs)@carbon hollow nanosphere (CHNS) architecture. This CuS@CQDs@C HNS is accomplished by a simple, scalable, in situ single-step hydrothermal method to produce the material that can be employed as an electrode for electrochemical energy storage and photocatalytic applications. Impressively, the CuS@CQDs@C HNS nanostructure delivers exceptional electrochemical energy storage characteristics with high specific capacitance (618 F g-1 at a current density of 1 A g-1) and an excellent rate capability with an extraordinary capacitance (462 F g-1 at current density of 20 A g-1) and long cycle life (95% capacitance retention after 4000 cycles). Further, the proposed photocatalyst exhibited superior photocatalytic activity under solar light due to the efficient electron transfer, which was revealed by photoluminescence studies. Such superior electrochemical and photocatalytic performance can be ascribed to the mutual contribution of CuS, CQDs, and CHNS and unique core-shell architecture. These results exhibit that the core-shell CuS@CQDs@C HNS nanostructure is one of the potential candidates for supercapacitors and photocatalytic applications.

Ultralow dielectric, high performing hyperbranched epoxy thermosets: synthesis, characterization and property evaluation

In the present report, low viscosity hyperbranched epoxy resins are synthesized using a simple A2 + B4 polycondensation reaction between pentaerythritol and the in situ prepared diglycidyl ether of bisphenol-A, with variation of the reaction time and amount of B4 reactant. The structural features and degree of branching (DB) of the hyperbranched epoxy resins are determined by spectroscopic analyses, such as FTIR, 1H NMR and 13C NMR studies. The highest DB (0.78) with the lowest epoxy equivalent (394 g eq−1), viscosity (2.99 Pa s) and specific gravity (1.03) values is found for the resin formed after a reaction time of 4 h with 10 wt% pentaerythritol. The thermoset of the same resin also exhibits the highest tensile strength (51 MPa), elongation at break (37.5%), toughness (1432 MPa), adhesive strength (3429 MPa) and thermal stability (∼300 °C), as well as the lowest dielectric constant (1.8), dielectric loss (0.009) and moisture absorption (0.09%). The results are also compared with a linear diglycidyl ether of bisphenol-A based epoxy (without the addition of pentaerythritol) prepared under the same conditions. The study also shows that the hyperbranched epoxy is superior in terms of physical properties as well as performance (especially, the toughness value is 800% higher) compared to the linear analog. Thus the synthesized hyperbranched epoxy thermoset can solve the genuine problem of the brittleness character of the conventional epoxy. This epoxy thermoset can also be used efficiently as a low dielectric adhesive material in the field of electronics.

Biocide immobilized OMMT-carbon dot reduced Cu2O nanohybrid/hyperbranched epoxy nanocomposites: Mechanical, thermal, antimicrobial and optical properties.

The present work demonstrated a transparent thermosetting nanocomposite with antimicrobial and photoluminescence attributes. The nanocomposites are fabricated by incorporation of different wt.% (1, 2 and 3) of a biocide immobilized OMMT-carbon dot reduced Cu2O nanohybrid (MITH-NH) in the hyperbranched epoxy matrix. MITH-NH is obtained by immobilization of 2-methyl-4-isothiazolin-3-one hydrochloride (MITH) at room temperature using sonication on OMMT-carbon dot reduced Cu2O nanohybid. The nanohybrid is prepared by reduction of cupric acetate using carbon dot as the reducing agent in the presence of OMMT at 70°C. The significant improvements in tensile strength (~2 fold), elongation at break (3 fold), toughness (4 fold) and initial thermal degradation temperature (30°C) of the pristine hyperbranched epoxy system are achieved by incorporation of 3wt.% of MITH-NH in it. The nanocomposites exhibit strong antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae and Pseudomonas aeruginosa bacteria and Candida albicans, a fungus. The nanocomposite also shows significant activity against biofilm formation compared to the pristine thermoset. Further, the nanocomposite films emit different colors on exposure of different wavelengths of UV light. The properties of these nanocomposites are also compared with the same nanohybrid without OMMT.

A room temperature cured low dielectric hyperbranched epoxy adhesive with high mechanical strength

Abstract.A low dielectric constant hyperbranched epoxy thermoset with excellent adhesive and mechanical strength is the demand for advanced electronics and engineering applications. The present investigation provided a room temperature, curable hyperbranched epoxy, obtained by an A2 + B3 polycondensation reaction. The synthesized hyperbranched epoxy was cured by a combined hardener system consisting of a commercial poly(amido-amine) and a first generation aliphatic poly(amido-amine) dendrimer (PAD) prepared by Michael addition reaction of methyl acrylate and aliphatic amines. The thermoset exhibited high mechanical strength, excellent adhesive strength, low dielectric constant, good thermal stability and excellent weather resistance along with very good moisture resistance. The results showed the influence of the amount of PAD on the performance of the thermoset. Thus, the study revealed that the combined poly(amido-amine) cured hyperbranched epoxy has high potential in advanced electrical packaging and microelectronic devices. ᅟThe present study describes a combined hardener system consisting of dendritic and linear poly(amido-amine) for curing of hyperbranched epoxy at room temperature. This thermoset exhibits high mechanical strength, excellent adhesive strength and low dielectric constant. Thus it has high potential to be used as a low dielectric adhesive.

An in situ prepared photo-luminescent transparent biocompatible hyperbranched epoxy/carbon dot nanocomposite

A photo-luminescent transparent biocompatible hyperbranched epoxy/carbon dot nanocomposite was prepared by incorporation of carbon dots during formation of hyperbranched epoxy resin. The prepared nanocomposite was characterized by FTIR, NMR and TEM analyses. The poly(amido-amine) cured nanocomposite exhibited high tensile strength (62.5 MPa), high elongation at break (45%), good thermal stability (291 °C), high transparency and excellent wavelength dependent photoluminescence behavior along with biocompatibility with skin cells. The performance of this nanocomposite was also compared with the pristine hyperbranched epoxy as well as hyperbranched epoxy/carbon dot nanocomposite obtained through an ex situ solution technique. The study revealed that the in situ prepared nanocomposite possessed superior mechanical, optical and biocompatible properties compared to pristine epoxy as well as the ex situ prepared nanocomposite. Thus, the study will significantly contribute to the field of high performance transparent fluorescent polymeric materials used in optoelectronics. Good viability, spreading and proliferation of skin fibroblasts and keratinocyte cells on the nanocomposite suggest it is also a highly potential material for bio-sealant application.