Nanomaterials have broad application potential in biomedical and environmental science. Engineered nanomaterials are required to explore such potential. Among them carbon-based fluorescent nanoparticles offer promising alternative of conventionally used semiconductor nanocrystals, as they do not have heavy metals and associated toxicity issues. We are developing synthetic methods for high quality fluorescent carbon nanoparticle, suitable for biological staining and diagnostics. Here we focus on synthesis of fluorescent carbon nanoparticle from biomolecules, exploiting the conventionally used nucleation-growth conditions for synthesis of high quality nanocrystals such as quantum dot and metal oxides. We have shown that high quality fluorescent carbon nanoparticle can be synthesized from folic acid, riboflavin and lactose and they can be used as non-toxic bio-imaging probe.

Synthesis of functional noble metal nanoparticles (AuNPs, AgNPs, and PdNPs) and its multi-metallic analogues have received greater attentions for selective applications. The selective applications of the these nanoparticles essentially requires the processability of as synthesized nanoparticles in the medium of desired polarity index that manifest the potential exploration of nanomaterial based design in targeted area. The use of conventional reducing and stabilizing agents during routine synthesis of such nanoparticles are not suitable with the system of practical significance and require additional reagents that limit the optimum activity of nanomaterial in targeted design. According there is a challenging issue in the synthesis of noble metal nanoparticles that allow the controlled synthesis of such nanoparticles involving same starting material with option to control the processability of as generated nanomaterial in the system of desired polarity index. The present report is focused on such challenging issues. We have found that 3-aminopropyltrimethoxysilane (3-APTMS) capped noble metal cations can be precisely converted into respective monometallic, bimetallic and trimetallic analogues and can be made processable in water at one end having controlled option to reversed the processability of the same in the toluene as a function of small organic reducing agents. The organic reducing agents not only convert 3-APTMS-capped noble cations into respective nanoparticles but also control the processability of the as generated nanoparticles in the systems of desired polarity index. The similar process also allows the synthesis of function bimetallic and tri-metallic nanoparticles. The role of cyclohexanone, formaldehyde and acetone in the presence of 3-APTMS is reported.

In the past few years, our group worked on the area of transformation from the two-dimensional (2-D) nanocrystalline films to one-dimensional (1-D) nanomaterials by using thermal oxidation. In this paper, we overview the research work on the controllable growth processes, transformation phenomena, growth mechanisms and applications. In general, the preparation process includes the following steps: 1) prepare a pure metal nanocrystalline film via a pulse electro – deposition; 2) grow variant 1-D nanomaterials, such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and 1-D metal oxide nanoneedles involving ZnO, CuO and Fe3O4, etc. by using this film as catalyst. This process exhibits the following features: 1) the 1-D nanomaterials grow according to “base growth” model and no residual catalyst exists at the tip of the products; 2) the diameter of the 1-D nanomaterials can be controlled by controlling grain sizes of the 2-D films through adjusting pulse electro-deposition parameters; 3) it is more easily to get the 1-D nanomaterials with large area, uniform, vertical alignment and good shape on the substrates. We propose a “solid state based-up diffusion growth mechanism” for growth of the 1-D metal oxide nanoneedles, and “base growth model” for the 1-D carbon nanomaterials. The physical properties, such as Field emission and magnetics, of the 1-D metal oxide nanoneedles were studied, which showed desired values. In addition, we couple the ZnO nanoneedles with NiO, TiO2, graphene, Au nanoparticles, etc. for enhancing photocatalytic properties in the areas of environmental purification.

Graphene quantum dots (GQDs) are zero-dimensional material with characteristics derived from functionalized graphene precursors are graphene sheets a few nanometers in the lateral dimension having a several-layer thickness. Combining the structure of graphene with the quantum confinement and edge effects, GQDs possess unique chemical behavior and physical properties. Intense research activity in GQDs is attributed to their novel phenomena of charge transport and light absorption and photoluminescence excitation. The optical transitions are known to be available up to 6 eV in GQDs, applicable for ultraviolet photonics and optoelectronics devices, biomedical imaging capabilities and technologies. We present facile hydrothermal and solvothermal methods for synthesizing homogenous dispersed and uniform sized GQDs with a strong greenish and violet blue emission peaks at ∼10-14% yield. This approach enabled a large-scale production of aqueous GQD dispersions without the need for chemical stabilizers. The structure and emission mechanism of the GQDs have been studied by combining extensive characterization techniques and rigorous control experiments. We further demonstrate the distinctive advantages of such GQDs as high-performance photodetectors (PDs). Here we also report high-efficient photocurrent (PC) behaviors consisting of multilayer GQDs sandwiched between monolayer graphene sheets. It is conceivable that the observed unique PD characteristics proved to be dominated by tunneling of charge carriers which occurs through the multiple energy states within the bandgap of GQDs, based on bias-dependent variation of the band profiles. This results in novel dark current and PC behaviors. The external quantum efficiency (η) is predicted to be 47% at applied potential 2 V. These findings highlight rich photophysics and comparable performance of graphene/graphene oxide hybrids opening up potential applications as optoelectronic devices.

The graphene quantum dots (GQD) are unique for several different applications especially in the area of sensors as they provide a platform for large surface area on which sensing material can be attached. We wish to report here a new analytical method for sensing ciprofloxacin (CPFX) antibiotic using GQD electrode in differential pulse voltammetry (DPV) which is based on the ferric ion interaction with CPFX. Ferric ion undergoes a well defined one electron reduction at GQD electrode in DPV at Ep=0.310 V vs saturated calomel electrode (SCE) with a peak width of 0.100 V. When nanomolar to micromolar concentrations of CPFX is present in the electrolytic bath, the ferric ion reduction peak decreases with the appearance of three new peaks at EpI=0.200 V, EpII=0.050 V and EpIII= -0.085V. The three peaks are attributed to the three stages of binding of CPFX with three positive charges of ferric ion. The decrease of the ferric ion peak at 0.31 V is proportional to the concentration of CPFX. Due to large surface area of GQD, the CPFX bound ferric ion shows enhanced currents in comparison to glassy carbon electrode. The sensor is fabricated by depositing GQD containing known concentration of ferric ion. The sensor response to different concentrations of CPFX is measured for an analytical purpose.

Graphene quantum dots (GQDs) - zero-dimensional materials - are sheets of a few nanometers in lateral dimension and exhibit quantum confinement and edge site effects where sp2-bonded carbon nanocore surrounded with edged plane functional moieties is promising as advanced electroactive sensing platforms. In this work, GQDs are synthesized by solvothermal and hydrothermal techniques, with optimal size of 5 nm. Their potential in fundamental (direct electron transfer) and applied (enzymatic glucose biosensor) electrochemistry are demonstrated. Glucose oxidase (GOx) immobilized on glassy carbon (GC) electrodes modified with GQDs are investigated by means of cyclic voltammetry, differential pulse voltammetry, and amperometry. Well-defined quasi-reversible redox peaks observed under various electrochemical parameters helped to determine diffusion coefficient (D) and first-order electron transfer rate (kET). The cyclic voltammetry curves showed homogeneous ion transport for GQD with D ranging between 8.45 × 10−9 m2 s−1 and 3 × 10−8 m2 s−1 following GO < rGO < GQD < GQD (with FcMeOH as redox probe) < GOx/rGO < GOx/GO < HRP/GQDs < GOx/GQDs. The developed GOx-GQDs biosensor responds efficiently and linearly to the presence of glucose over concentrations ranging 10 μM and 3 mM with limit of detection 1.35 μM and sensitivity 0.00769 μA μM−1·cm−2 as compared with rGO (0.025 μA μM−1 cm−2, 4.16 μM) and GO (0.064 μA μM−1 cm−2, 4.82 μM) nanosheets. The high performance and stability of GQDs is attributed to sufficiently large surface-to-volume ratio, excellent biocompatibility, abundant hydrophilic edge site density, and partially hydrophobic planar sites that favors GOx adsorption on the electrode surface and versatile architectures to ensure rapid charge transfer and electron/ion conduction (<10 ms). We also carried out similar studies with other enzymatic protein biomolecules on electrode surfaces prepared from GQD precursors for electrochemical comparison, thus opening up potential sensing applications in medicine as well as bio-nanotechnology.

In recent years, the graphene/metal nanoparticles (NPs) hybrids have sparked burgeoning interest in varied application fields due to its unique physicochemical properties. In this paper, we present an overview of preparation methods of the graphene/metal NPs hybrids, which includes some common routes as well as other particular strategies. In addition, we introduce a novel physical route to decorate metal NPs upon graphene sheets. Our expectation is that this review will provide references for the exploitation of emerging preparation technologies, and expand application fields for graphene/metal NPs hybrids in the future.

Compact-size kilohertz (kHz) AC-supercapacitors are being pursued for ripple current filtering and pulsed energy storage. However, their development is limited by a small areal capacitance density due to very thin electrode used for meeting frequency requirement. In our work, crosslinked carbon nanofiber aerogel (CCNFA) was investigated as freestanding electrode for kHz AC-supercapacitors with an areal capacitance density as large as 4.5 mF cm-2 at 120 Hz, 5-10 times larger than most reports. The CCNFA was obtained in a rapid plasma carbonization process of bacterial cellulose. The fabrication route adopted here is simple and straightforward, and the produced CCNFA electrode was found to be very suitable for high-frequency AC-supercapacitors. The operating voltage range of CCNFA based AC-supercapacitors can be expanded to 3 V by utilizing an organic electrolyte. In addition to AC-Supercapacitor performance, the morphology and material properties of bacterial cellulose aerogel and CCNFA were also reported.

Metallic silver nanoparticles were synthesized using a hydrothermal route for use in high throughput biosensing applications. Particle shape was engineered by varying polyvinyl pyrollidone (PVP) concentration in the precursor mixture, resulting in the emergence of flat triangular shaped nanoparticles with increasing PVP content. The hydrothermal method was found to yield particles with better particle size distribution and longer shelf life relative to polyol synthesis particles.

In this paper, we report a method of increasing fracture toughness (KIC) and strain energy release rate (GIC) of vinyl ester matrix by adopting a dual reinforcement strategy. Reinforcements were carbon nanotubes (CNT) and graphene nanoplatelets (GNP). Both categories of nanoparticles were functionalized with COOH. The idea was to enhance crack bridging and interface sliding with CNT inclusions, given their high aspect ratio. In addition, promote crack-tip blunting and cross-linking density with GNP inclusions, due to their platelet structures. Both KIC and GIC were measured using ASTM D5045-14. An exhaustive experimental study revealed an optimum loading of both nanoparticles to be 0.25 wt% CNT and 0.5 wt% GNP, based on the highest combination of KIC and GIC values. We observed that stress intensity factor, KIC, of neat vinyl ester increased by 43% from 1.14 to 1.62 MPa*(m½). Meanwhile, the improvement in GIC was even greater with an increase of 65%, i.e., from 370 to 610 J/(m2). Differential scanning calorimetry (DSC) studies showed a discernible shift in glass transition temperature (Tg) from 123 to 128°C. The slight temperature increase was similar in thermogravimetric analysis (TGA). We observed the maximum thermal decomposition temperature (Tp) increase from 410 to 414°C, as was evident in the derivative TGA (DTG) curves.