Neena John - Academia.edu (original) (raw)

Papers by Neena John

Research paper thumbnail of Waste to wealth: spent catalyst as an efficient and stable bifunctional oxygen electrocatalyst for zinc–air batteries

Sustainable Energy & Fuels, 2021

The spent catalysts obtained from catalytic decomposition of methane are often considered as wast... more The spent catalysts obtained from catalytic decomposition of methane are often considered as waste and typically subjected to energy intensive processes such as high-temperature combustion for recycling or chemical treatment for metal reclamation.

Research paper thumbnail of Hydrogen and Hydrocarbons as Fuel

Research paper thumbnail of Metal phthalocyanines and their composites with carbon nanostructures for applications in energy generation and storage

Design, Fabrication, and Characterization of Multifunctional Nanomaterials, 2022

Research paper thumbnail of Molecularly Imprinted Scaffold Based on poly (3-aminobenzoic acid) for Electrochemical Sensing of Vitamin B6

Journal of The Electrochemical Society, 2021

Research paper thumbnail of Role of Metal Ion Sites in Bivalent Cobalt Phosphorus Oxygen Systems toward Efficient Oxygen Evolution Reaction

The Journal of Physical Chemistry C, 2021

Research paper thumbnail of Low cost, catalyst free, high performance supercapacitors based on porous nano carbon derived from agriculture waste

Journal of Energy Storage, 2020

The present work exhibits experimental results obtained from the analysis of porous nano carbon s... more The present work exhibits experimental results obtained from the analysis of porous nano carbon synthesized from agriculture waste for the evaluation of high-performance supercapacitors. The material has been prepared by pyrolysis at different temperatures. All the synthesized materials were characterized using EDS, FE-SEM, TEM, FTIR, XPS, and Raman spectroscopy. Porous nature was determined from N 2 sorption experiments. The electrochemical studies were done in three and two electrode setups. The maximum specific capacitance obtained was 174 F/g at 0.1 A/g in 4.0 M KOH electrolyte. The symmetric supercapacitor exhibited a specific capacitance of 119.2 F/g at 0.1 A/g and a specific energy of 32.6 Wh/kg. The device exhibited impeccable stability for 25,000 charge-discharge cycles, with 97.8% coulombic efficiency. Capacitance retention of 93% was observed even at the end of 10000th cycles, suggesting the huge capacity of biomass-derived non-activated carbon nanomaterials for efficient, stable high-performance electrodes in electrochemical energy storage applications.

Research paper thumbnail of Insight into the Multistate Emissive N, P‐doped Carbon Nano‐Onions: Emerging Visible‐Light Absorption for Photocatalysis

Chemistry – An Asian Journal, 2021

Carbon Dots (CDs) have become one of the most emerging materials as an alternative solar light-in... more Carbon Dots (CDs) have become one of the most emerging materials as an alternative solar light-induced photocatalyst in contrast to the traditional metal-based systems. However, one of the major challenges is the lack of visible light absorption. Herein, we have fabricated a unique N, P- co-doped CDs with self-assembled onion-like layered structure by bottom-up facile synthesis technique from chitosan gel and phosphoric acid as molecular precursors. This typical layered structure, of N, P-co-doped carbon nano onions (N, P-CNOs) with an average size of 25-50 nm, displays an enhanced visible light absorption. Detailed structural and elemental characterizations confirm the extensive aromatic domain with P containing surface functionalities, while electrochemical study clarifies the lowering of band gaps as well as the creation of new electronic states in comparison to the pristine N-CDs. Furthermore, the intrinsic structural features are correlated with the underpinning photophysical processes by steady-state and time-resolved fluorescence spectroscopy. In addition, steady-state polarized emission and thermo-responsive PL properties have been carried to unveil further the structure-property correlation of N, P-CNOs, and their comparative study with pristine N-CDs at the different excitation wavelengths. Finally, N, P-CNOs exhibit efficient visible-light-induced photocatalysis, and the detailed mechanistic study is carried out by trapping the photogenerated species in an aqueous medium. The prepared N, P-CNOs displayed an excellent visible-light photocatalytic performance over the MB dye with a degradation efficiency of 75.8 % within 120 min along with a degradation rate constant of ~0.0109 min -1 . It is concluded that the prepared N, P-CNOs with unique morphology, easy to synthesize, and low-cost has great potential application for visible-light photocatalysis.

Research paper thumbnail of Molecular, Aromatic, and Amorphous Domains of N-Carbon Dots: Leading toward the Competitive Photoluminescence and Photocatalytic Properties

The Journal of Physical Chemistry C, 2021

Carbon dots (CDs) have become one of most promising fluorescent materials in recent days, because... more Carbon dots (CDs) have become one of most promising fluorescent materials in recent days, because of their promising photoluminescence and photocatalytic properties. However, the practical applicab...

Research paper thumbnail of Femtomolar detection of thiram via SERS using silver nanocubes as an efficient substrate

Environmental Science: Nano, 2020

Silver nanocubes are demonstrated to be an efficient substrate for the detection of the fungicide... more Silver nanocubes are demonstrated to be an efficient substrate for the detection of the fungicide thiram, at ultra-low concentrations.

Research paper thumbnail of Templating effect of single-layer graphene supported by an insulating substrate on the molecular orientation of lead phthalocyanine

Beilstein Journal of Nanotechnology, 2020

The influence of single-layer graphene on top of a SiO2/Si surface on the orientation of nonplana... more The influence of single-layer graphene on top of a SiO2/Si surface on the orientation of nonplanar lead phthalocyanine (PbPc) molecules is studied using two-dimensional grazing incidence X-ray diffraction. The studies indicate the formation of a mixture of polymorphs, i.e., monoclinic and triclinic forms of PbPc with face-on (lying down) and edge-on (standing up) PbPc orientations, respectively. The formation of monoclinic fractions is attributed to the presence of the graphene layer directing the π interactions between the highly delocalized macrocycles. The competing interfacial van der Waals forces and molecule–molecule interactions lead to the formation of a small fraction of triclinic moieties. The nanoscale electrical characterization of the thin PbPc layer on graphene by means of conducting atomic force microscopy shows enhanced vertical conductance with interconnected conducting domains consisting of ordered monoclinic crystallites through which the charge transfer occurs vi...

Research paper thumbnail of Competing Effect of Co3+ Reducibility and Oxygen-Deficient Defects Toward High Oxygen Evolution Activity in Co3O4 Systems in Alkaline Medium

ACS Applied Energy Materials, 2020

In Co 3 O 4 systems, the oxygen vacancy is reported to improve the oxygen evolution reaction (OER... more In Co 3 O 4 systems, the oxygen vacancy is reported to improve the oxygen evolution reaction (OER) activity due to higher Co 2+ /Co 3+ surface ratio. In-situ studies have revealed Co 3+-site reducibility as the key factor for OER activity of cobalt oxide based systems. In this context, we have synthesized and analyzed OER activity of two Co 3 O 4 systems; c-Co 3 O 4 with higher oxygen defects or Co 2+ /Co 3+ ratio and n-Co 3 O 4 with relatively less Co 2+ /Co 3+ ratio but more Co 3+-reducibility. The systems, n-& c-Co 3 O 4 show over potential of 380 mV and 440 mV at 10 mA/cm 2 and Tafel slope of 153 mV/dec and 53 mV/dec, respectively, for OER. Electrochemical characterization reveals that the lowering of OER onset potential is influenced by Co 3+-reducibility rather than defects in Co 3 O 4 systems while adsorption capacitance arising from surface irregularities, pores and its geometry and Co 3+-Oh sites cause increase in Tafel slope values or lower OER kinetics. The correlation of the key factors such as Co 3+-reducibility and oxygen defects of two different Co 3 O 4 systems towards OER activity can aid the designing of highly efficient cobalt oxide based OER catalysts.

Research paper thumbnail of A general route to free-standing films of nanocrystalline molybdenum chalcogenides at a liquid/liquid interface under hydrothermal conditions

Applied Surface Science, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of Origin of Luminescence‐Based Detection of Metal Ions by Mn–Doped ZnS Quantum Dots

Research paper thumbnail of Current Mapping of Lead Phthalocyanine Thin Films in the Presence of Gaseous Dopants

Physical Chemistry Chemical Physics, 2019

The structural organization and its effect on conducting pathways in lead phthalocyanine (PbPc) t... more The structural organization and its effect on conducting pathways in lead phthalocyanine (PbPc) thin films, a nonplanar phthalocyanine, deposited on Si and highly oriented pyrolytic graphite (HOPG) substrates in the...

Research paper thumbnail of Effect of Graphene and MoS2 Flakes in Industrial Oils to Enhance Lubrication

ACS Omega, 2019

Tribological studies of the 2D nanoadditives such as MoS 2 and graphene are mostly performed in b... more Tribological studies of the 2D nanoadditives such as MoS 2 and graphene are mostly performed in base oils such as SN500, SN150, or paraffin. We have focused on their effect in lubrication properties of industrial oils (e.g., axle, transmission, and compressor oils) along with SN500 oil employing a four-ball tester. Two types of graphene powders (GpowA with fewer defects than GpowC), MoS 2 powder, and their physical mixtures are chosen as nanoadditives. The tribology performance for 0.05 wt% of additives in various industrial oils is evaluated by monitoring the coefficient of friction (COF) during rubbing and wear scar diameter (WSD) of the steel balls after rubbing. Elemental analysis and electron microscopy have been performed on the wear surfaces for evidence of any tribofilm formation. GpowA favors antifriction for axle and transmission oils with 40% reduction in axle oil, whereas it improved antiwear properties in most of the oils. GpowC shows a COF decrement by 12% only for compressor oil, but contribute to wear reduction in all oils. The observed COF reduction is attributed to the compatibility of nonfunctionalized GpowA with nonpolar axle oil and functionalized GpowC with polar compressor oil. MoS 2 shows a decrease in the COF and WSD in most industrial oils; the best being 60% COF and 7% WSD reduction in axle oil. For additives in oils that favor antiwear, flakes or particles are observed on the wear surface supported by the higher elemental contribution of the constituents from the wear region. The mixtures of GpowA or C with MoS 2 , however, does not seem to favor improvement in the COF or WSD in industrial oils. With assistance from oleylamine surfactants, the lubrication properties of most additives are improved, particularly for the mixtures with 12−15% COF reduction and 4−7% WSD reduction in compressor oil. The study indicates that a large sheet size of high-quality graphene aids antifriction and addition of surfactant molecules facilitates a cooperative effect between MoS 2 and graphene for improved tribology.

Research paper thumbnail of Reduced Graphene oxide / Nanoparticle hybrid structures: A new generation smart materials for optical sensors

Materials Today: Proceedings, 2018

Graphene oxide/reduced Graphene oxide hybrid nanomaterials have been widely used as substrates fo... more Graphene oxide/reduced Graphene oxide hybrid nanomaterials have been widely used as substrates for surface enhanced Raman spectroscopy. This is mainly due to that they have unique structures and inherent properties including highest specific surface area, chemical and electrochemical inertness and easy surface modification etc. It is the parent of all graphite form and is an interesting topic of research in the last three to four years. It can be stacked to form 3D graphite, rolled to form ID nanotubes and wrapped to form 0D fullerenes. The long-range π-conjugation in graphene shows extraordinary thermal, mechanical and electrical properties. The carbon nanomaterial-based spectroscopy detection of chemical and biological molecules has gained much attention with its extensive applications to genomic, proteomic and environmental analysis as well as for clinical diagnosis.Surface enhanced Raman (SERS) spectroscopy has proven to be an effective technique for analyzing the innovative nanomaterials, graphene. This technique has also helped in identifying some unique properties of graphene as a Raman substrate for the suppression of fluorescence. The requirement for a substrate that is biocompatible, chemically inert, and capable of Raman enhancement is a major technological objective and graphene serves as a suitable material.

Research paper thumbnail of Graphene-Augmented Polymer Stabilization: Drastically Reduced and Temperature-Independent Threshold and Improved Contrast Liquid Crystal Device

ACS Omega, 2019

Polymers reinforced with nanofillers, especially graphene in recent times, have continued to attr... more Polymers reinforced with nanofillers, especially graphene in recent times, have continued to attract attention to realize novel materials that are cheap and also have better properties. At a different level, encapsulating liquid crystals (LCs) in polymer networks not only adds mechanical strength, but could also result in devicebased refractive index mismatch. Here, we describe a novel strategy combining the best of both these concepts to create graphene-incorporated polymer-stabilized LC (PSLC) devices. The presence of graphene associated with the virtual surface of the polymer network besides introducing distinct morphological changes to the polymer architecture as seen by electron microscopy brings out several advantages for the PSLC characteristics, which include 7-fold lowered critical voltage, its temperature invariance, and enhanced contrast ratio between field-off scattering/field-on transparent states. The results bring to fore the importance of working at verydilute-concentration limits of the filler nanoparticles in augmenting the desired properties. These observations open up a new vista for polymer−graphene composites in the area of device engineering, including substrate-free smart windows.

Research paper thumbnail of Supercapacitor application of nickel phthalocyanine nanofibres and its composite with reduced graphene oxide

Applied Surface Science, 2018

The combination of double layer capacitor and pseudocapacitor materials are the next generation c... more The combination of double layer capacitor and pseudocapacitor materials are the next generation composites for energy storage. Nitrogen enriched species like metal phthalocyanines with metal redox centres may be combined with electrical double layer capacitive carbon materials for improved charge storage. We have explored electrochemical capacitance applications of nickel phthalocyanine (NiPc) nanofibres and its composite with reduced graphene oxide (rGO) synthesized through simple chemical routes. The composite material exhibits a superior specific capacitance, 223.28 Fg −1 at 1 Ag −1 , four fold higher than the individual components and also good stability over continuous cycling for 1000 cycles. The synergistic effect of NiPc and rGO with excellent physical interface offers less charge transfer resistance and better charge storage capacity.

Research paper thumbnail of Influence of Iodine Doping on the Structure, Morphology, and Physical Properties of Manganese Phthalocyanine Thin Films

The Journal of Physical Chemistry C, 2018

Doping with halide ions is a popular method to alter the properties of metal phthalocyanines (MPc... more Doping with halide ions is a popular method to alter the properties of metal phthalocyanines (MPcs), particularly magnetic and electrical nature of organic semiconductors for applications in spintronic or electronic devices. Doping can cause a structural rearrangement in MPc packing and the physical properties may be correlated with molecular packing. Films of a planar and magnetic MPc, manganese(II)phthalocyanine (MnPc) is chosen for iodine doping study. The optical, magnetic and the electrical properties of pristine and iodine doped MnPc thin films are investigated and can be directly associated with their molecular structure. 2D grazing incidence Synchrotron X-ray diffraction reveals structural disorder in MnPc films upon iodine infusion induced by the reorientation of ordered, edge-on molecular configuration to tilted and face-on configurations in a random fashion. The film morphology changes accordingly, where in the uniform crystallites reorganize in a disordered manner. The ferromagnetic nature of the pristine film gets weakened due to iodine species and favors antiferromagnetic coupling. The study of electrical properties at room temperature by conducting atomic force microscopy reveals that the conductance is enhanced independently of the film thickness due to disorder induced by iodine inclusion.

Research paper thumbnail of Architecturing Metallic MoO2 nanostructures on Rigid Substrates for Electrochemical Water Activation

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 5, 2018

In-situ growth of metallic MoO2 films on fluorine doped tin oxide (FTO) and MoO2 powder in soluti... more In-situ growth of metallic MoO2 films on fluorine doped tin oxide (FTO) and MoO2 powder in solution has been achieved simultaneously by a simple hydrothermal process employing citric acid as the surfactant. The growth mechanism of MoO2 nanostructures at the heterogeneous interface and in a homogeneous medium proceeds in a different manner wherein seeds grow in a preferred orientation on FTO while they propagate in all directions in the solution. The high lattice matching of FTO and MoO2 favours the film growth and could not be obtained on other conventional substrates. The disc morphology of MoO2 nanostructures could be varied to other diverse morphology by varying the synthesis conditions; particularly by the addition of nitric acid. A competitive effect of nitric acid and citric acid in structure direction gives rise to various shapes. The electrochemical water activation studies show that hydrogen annealed MoO2 is an excellent hydrogen evolution reaction (HER) catalyst with good ...

Research paper thumbnail of Waste to wealth: spent catalyst as an efficient and stable bifunctional oxygen electrocatalyst for zinc–air batteries

Sustainable Energy & Fuels, 2021

The spent catalysts obtained from catalytic decomposition of methane are often considered as wast... more The spent catalysts obtained from catalytic decomposition of methane are often considered as waste and typically subjected to energy intensive processes such as high-temperature combustion for recycling or chemical treatment for metal reclamation.

Research paper thumbnail of Hydrogen and Hydrocarbons as Fuel

Research paper thumbnail of Metal phthalocyanines and their composites with carbon nanostructures for applications in energy generation and storage

Design, Fabrication, and Characterization of Multifunctional Nanomaterials, 2022

Research paper thumbnail of Molecularly Imprinted Scaffold Based on poly (3-aminobenzoic acid) for Electrochemical Sensing of Vitamin B6

Journal of The Electrochemical Society, 2021

Research paper thumbnail of Role of Metal Ion Sites in Bivalent Cobalt Phosphorus Oxygen Systems toward Efficient Oxygen Evolution Reaction

The Journal of Physical Chemistry C, 2021

Research paper thumbnail of Low cost, catalyst free, high performance supercapacitors based on porous nano carbon derived from agriculture waste

Journal of Energy Storage, 2020

The present work exhibits experimental results obtained from the analysis of porous nano carbon s... more The present work exhibits experimental results obtained from the analysis of porous nano carbon synthesized from agriculture waste for the evaluation of high-performance supercapacitors. The material has been prepared by pyrolysis at different temperatures. All the synthesized materials were characterized using EDS, FE-SEM, TEM, FTIR, XPS, and Raman spectroscopy. Porous nature was determined from N 2 sorption experiments. The electrochemical studies were done in three and two electrode setups. The maximum specific capacitance obtained was 174 F/g at 0.1 A/g in 4.0 M KOH electrolyte. The symmetric supercapacitor exhibited a specific capacitance of 119.2 F/g at 0.1 A/g and a specific energy of 32.6 Wh/kg. The device exhibited impeccable stability for 25,000 charge-discharge cycles, with 97.8% coulombic efficiency. Capacitance retention of 93% was observed even at the end of 10000th cycles, suggesting the huge capacity of biomass-derived non-activated carbon nanomaterials for efficient, stable high-performance electrodes in electrochemical energy storage applications.

Research paper thumbnail of Insight into the Multistate Emissive N, P‐doped Carbon Nano‐Onions: Emerging Visible‐Light Absorption for Photocatalysis

Chemistry – An Asian Journal, 2021

Carbon Dots (CDs) have become one of the most emerging materials as an alternative solar light-in... more Carbon Dots (CDs) have become one of the most emerging materials as an alternative solar light-induced photocatalyst in contrast to the traditional metal-based systems. However, one of the major challenges is the lack of visible light absorption. Herein, we have fabricated a unique N, P- co-doped CDs with self-assembled onion-like layered structure by bottom-up facile synthesis technique from chitosan gel and phosphoric acid as molecular precursors. This typical layered structure, of N, P-co-doped carbon nano onions (N, P-CNOs) with an average size of 25-50 nm, displays an enhanced visible light absorption. Detailed structural and elemental characterizations confirm the extensive aromatic domain with P containing surface functionalities, while electrochemical study clarifies the lowering of band gaps as well as the creation of new electronic states in comparison to the pristine N-CDs. Furthermore, the intrinsic structural features are correlated with the underpinning photophysical processes by steady-state and time-resolved fluorescence spectroscopy. In addition, steady-state polarized emission and thermo-responsive PL properties have been carried to unveil further the structure-property correlation of N, P-CNOs, and their comparative study with pristine N-CDs at the different excitation wavelengths. Finally, N, P-CNOs exhibit efficient visible-light-induced photocatalysis, and the detailed mechanistic study is carried out by trapping the photogenerated species in an aqueous medium. The prepared N, P-CNOs displayed an excellent visible-light photocatalytic performance over the MB dye with a degradation efficiency of 75.8 % within 120 min along with a degradation rate constant of ~0.0109 min -1 . It is concluded that the prepared N, P-CNOs with unique morphology, easy to synthesize, and low-cost has great potential application for visible-light photocatalysis.

Research paper thumbnail of Molecular, Aromatic, and Amorphous Domains of N-Carbon Dots: Leading toward the Competitive Photoluminescence and Photocatalytic Properties

The Journal of Physical Chemistry C, 2021

Carbon dots (CDs) have become one of most promising fluorescent materials in recent days, because... more Carbon dots (CDs) have become one of most promising fluorescent materials in recent days, because of their promising photoluminescence and photocatalytic properties. However, the practical applicab...

Research paper thumbnail of Femtomolar detection of thiram via SERS using silver nanocubes as an efficient substrate

Environmental Science: Nano, 2020

Silver nanocubes are demonstrated to be an efficient substrate for the detection of the fungicide... more Silver nanocubes are demonstrated to be an efficient substrate for the detection of the fungicide thiram, at ultra-low concentrations.

Research paper thumbnail of Templating effect of single-layer graphene supported by an insulating substrate on the molecular orientation of lead phthalocyanine

Beilstein Journal of Nanotechnology, 2020

The influence of single-layer graphene on top of a SiO2/Si surface on the orientation of nonplana... more The influence of single-layer graphene on top of a SiO2/Si surface on the orientation of nonplanar lead phthalocyanine (PbPc) molecules is studied using two-dimensional grazing incidence X-ray diffraction. The studies indicate the formation of a mixture of polymorphs, i.e., monoclinic and triclinic forms of PbPc with face-on (lying down) and edge-on (standing up) PbPc orientations, respectively. The formation of monoclinic fractions is attributed to the presence of the graphene layer directing the π interactions between the highly delocalized macrocycles. The competing interfacial van der Waals forces and molecule–molecule interactions lead to the formation of a small fraction of triclinic moieties. The nanoscale electrical characterization of the thin PbPc layer on graphene by means of conducting atomic force microscopy shows enhanced vertical conductance with interconnected conducting domains consisting of ordered monoclinic crystallites through which the charge transfer occurs vi...

Research paper thumbnail of Competing Effect of Co3+ Reducibility and Oxygen-Deficient Defects Toward High Oxygen Evolution Activity in Co3O4 Systems in Alkaline Medium

ACS Applied Energy Materials, 2020

In Co 3 O 4 systems, the oxygen vacancy is reported to improve the oxygen evolution reaction (OER... more In Co 3 O 4 systems, the oxygen vacancy is reported to improve the oxygen evolution reaction (OER) activity due to higher Co 2+ /Co 3+ surface ratio. In-situ studies have revealed Co 3+-site reducibility as the key factor for OER activity of cobalt oxide based systems. In this context, we have synthesized and analyzed OER activity of two Co 3 O 4 systems; c-Co 3 O 4 with higher oxygen defects or Co 2+ /Co 3+ ratio and n-Co 3 O 4 with relatively less Co 2+ /Co 3+ ratio but more Co 3+-reducibility. The systems, n-& c-Co 3 O 4 show over potential of 380 mV and 440 mV at 10 mA/cm 2 and Tafel slope of 153 mV/dec and 53 mV/dec, respectively, for OER. Electrochemical characterization reveals that the lowering of OER onset potential is influenced by Co 3+-reducibility rather than defects in Co 3 O 4 systems while adsorption capacitance arising from surface irregularities, pores and its geometry and Co 3+-Oh sites cause increase in Tafel slope values or lower OER kinetics. The correlation of the key factors such as Co 3+-reducibility and oxygen defects of two different Co 3 O 4 systems towards OER activity can aid the designing of highly efficient cobalt oxide based OER catalysts.

Research paper thumbnail of A general route to free-standing films of nanocrystalline molybdenum chalcogenides at a liquid/liquid interface under hydrothermal conditions

Applied Surface Science, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of Origin of Luminescence‐Based Detection of Metal Ions by Mn–Doped ZnS Quantum Dots

Research paper thumbnail of Current Mapping of Lead Phthalocyanine Thin Films in the Presence of Gaseous Dopants

Physical Chemistry Chemical Physics, 2019

The structural organization and its effect on conducting pathways in lead phthalocyanine (PbPc) t... more The structural organization and its effect on conducting pathways in lead phthalocyanine (PbPc) thin films, a nonplanar phthalocyanine, deposited on Si and highly oriented pyrolytic graphite (HOPG) substrates in the...

Research paper thumbnail of Effect of Graphene and MoS2 Flakes in Industrial Oils to Enhance Lubrication

ACS Omega, 2019

Tribological studies of the 2D nanoadditives such as MoS 2 and graphene are mostly performed in b... more Tribological studies of the 2D nanoadditives such as MoS 2 and graphene are mostly performed in base oils such as SN500, SN150, or paraffin. We have focused on their effect in lubrication properties of industrial oils (e.g., axle, transmission, and compressor oils) along with SN500 oil employing a four-ball tester. Two types of graphene powders (GpowA with fewer defects than GpowC), MoS 2 powder, and their physical mixtures are chosen as nanoadditives. The tribology performance for 0.05 wt% of additives in various industrial oils is evaluated by monitoring the coefficient of friction (COF) during rubbing and wear scar diameter (WSD) of the steel balls after rubbing. Elemental analysis and electron microscopy have been performed on the wear surfaces for evidence of any tribofilm formation. GpowA favors antifriction for axle and transmission oils with 40% reduction in axle oil, whereas it improved antiwear properties in most of the oils. GpowC shows a COF decrement by 12% only for compressor oil, but contribute to wear reduction in all oils. The observed COF reduction is attributed to the compatibility of nonfunctionalized GpowA with nonpolar axle oil and functionalized GpowC with polar compressor oil. MoS 2 shows a decrease in the COF and WSD in most industrial oils; the best being 60% COF and 7% WSD reduction in axle oil. For additives in oils that favor antiwear, flakes or particles are observed on the wear surface supported by the higher elemental contribution of the constituents from the wear region. The mixtures of GpowA or C with MoS 2 , however, does not seem to favor improvement in the COF or WSD in industrial oils. With assistance from oleylamine surfactants, the lubrication properties of most additives are improved, particularly for the mixtures with 12−15% COF reduction and 4−7% WSD reduction in compressor oil. The study indicates that a large sheet size of high-quality graphene aids antifriction and addition of surfactant molecules facilitates a cooperative effect between MoS 2 and graphene for improved tribology.

Research paper thumbnail of Reduced Graphene oxide / Nanoparticle hybrid structures: A new generation smart materials for optical sensors

Materials Today: Proceedings, 2018

Graphene oxide/reduced Graphene oxide hybrid nanomaterials have been widely used as substrates fo... more Graphene oxide/reduced Graphene oxide hybrid nanomaterials have been widely used as substrates for surface enhanced Raman spectroscopy. This is mainly due to that they have unique structures and inherent properties including highest specific surface area, chemical and electrochemical inertness and easy surface modification etc. It is the parent of all graphite form and is an interesting topic of research in the last three to four years. It can be stacked to form 3D graphite, rolled to form ID nanotubes and wrapped to form 0D fullerenes. The long-range π-conjugation in graphene shows extraordinary thermal, mechanical and electrical properties. The carbon nanomaterial-based spectroscopy detection of chemical and biological molecules has gained much attention with its extensive applications to genomic, proteomic and environmental analysis as well as for clinical diagnosis.Surface enhanced Raman (SERS) spectroscopy has proven to be an effective technique for analyzing the innovative nanomaterials, graphene. This technique has also helped in identifying some unique properties of graphene as a Raman substrate for the suppression of fluorescence. The requirement for a substrate that is biocompatible, chemically inert, and capable of Raman enhancement is a major technological objective and graphene serves as a suitable material.

Research paper thumbnail of Graphene-Augmented Polymer Stabilization: Drastically Reduced and Temperature-Independent Threshold and Improved Contrast Liquid Crystal Device

ACS Omega, 2019

Polymers reinforced with nanofillers, especially graphene in recent times, have continued to attr... more Polymers reinforced with nanofillers, especially graphene in recent times, have continued to attract attention to realize novel materials that are cheap and also have better properties. At a different level, encapsulating liquid crystals (LCs) in polymer networks not only adds mechanical strength, but could also result in devicebased refractive index mismatch. Here, we describe a novel strategy combining the best of both these concepts to create graphene-incorporated polymer-stabilized LC (PSLC) devices. The presence of graphene associated with the virtual surface of the polymer network besides introducing distinct morphological changes to the polymer architecture as seen by electron microscopy brings out several advantages for the PSLC characteristics, which include 7-fold lowered critical voltage, its temperature invariance, and enhanced contrast ratio between field-off scattering/field-on transparent states. The results bring to fore the importance of working at verydilute-concentration limits of the filler nanoparticles in augmenting the desired properties. These observations open up a new vista for polymer−graphene composites in the area of device engineering, including substrate-free smart windows.

Research paper thumbnail of Supercapacitor application of nickel phthalocyanine nanofibres and its composite with reduced graphene oxide

Applied Surface Science, 2018

The combination of double layer capacitor and pseudocapacitor materials are the next generation c... more The combination of double layer capacitor and pseudocapacitor materials are the next generation composites for energy storage. Nitrogen enriched species like metal phthalocyanines with metal redox centres may be combined with electrical double layer capacitive carbon materials for improved charge storage. We have explored electrochemical capacitance applications of nickel phthalocyanine (NiPc) nanofibres and its composite with reduced graphene oxide (rGO) synthesized through simple chemical routes. The composite material exhibits a superior specific capacitance, 223.28 Fg −1 at 1 Ag −1 , four fold higher than the individual components and also good stability over continuous cycling for 1000 cycles. The synergistic effect of NiPc and rGO with excellent physical interface offers less charge transfer resistance and better charge storage capacity.

Research paper thumbnail of Influence of Iodine Doping on the Structure, Morphology, and Physical Properties of Manganese Phthalocyanine Thin Films

The Journal of Physical Chemistry C, 2018

Doping with halide ions is a popular method to alter the properties of metal phthalocyanines (MPc... more Doping with halide ions is a popular method to alter the properties of metal phthalocyanines (MPcs), particularly magnetic and electrical nature of organic semiconductors for applications in spintronic or electronic devices. Doping can cause a structural rearrangement in MPc packing and the physical properties may be correlated with molecular packing. Films of a planar and magnetic MPc, manganese(II)phthalocyanine (MnPc) is chosen for iodine doping study. The optical, magnetic and the electrical properties of pristine and iodine doped MnPc thin films are investigated and can be directly associated with their molecular structure. 2D grazing incidence Synchrotron X-ray diffraction reveals structural disorder in MnPc films upon iodine infusion induced by the reorientation of ordered, edge-on molecular configuration to tilted and face-on configurations in a random fashion. The film morphology changes accordingly, where in the uniform crystallites reorganize in a disordered manner. The ferromagnetic nature of the pristine film gets weakened due to iodine species and favors antiferromagnetic coupling. The study of electrical properties at room temperature by conducting atomic force microscopy reveals that the conductance is enhanced independently of the film thickness due to disorder induced by iodine inclusion.

Research paper thumbnail of Architecturing Metallic MoO2 nanostructures on Rigid Substrates for Electrochemical Water Activation

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 5, 2018

In-situ growth of metallic MoO2 films on fluorine doped tin oxide (FTO) and MoO2 powder in soluti... more In-situ growth of metallic MoO2 films on fluorine doped tin oxide (FTO) and MoO2 powder in solution has been achieved simultaneously by a simple hydrothermal process employing citric acid as the surfactant. The growth mechanism of MoO2 nanostructures at the heterogeneous interface and in a homogeneous medium proceeds in a different manner wherein seeds grow in a preferred orientation on FTO while they propagate in all directions in the solution. The high lattice matching of FTO and MoO2 favours the film growth and could not be obtained on other conventional substrates. The disc morphology of MoO2 nanostructures could be varied to other diverse morphology by varying the synthesis conditions; particularly by the addition of nitric acid. A competitive effect of nitric acid and citric acid in structure direction gives rise to various shapes. The electrochemical water activation studies show that hydrogen annealed MoO2 is an excellent hydrogen evolution reaction (HER) catalyst with good ...