N.S. Das

Enhanced Adsorption of Hexavalent Chromium onto Magnetic Calcium Ferrite Nanoparticles: Kinetic, Isotherm, and Neural Network Modeling

Calcium ferrite nanoparticles with super-paramagnetic behavior were synthesized via simple chemical precipitation method for effective removal of hexavalent chromium from aqueous media. The properties of synthesized nanoparticles were studied by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), and vibrating sample magnetometer (VSM) measurements. The ferrite nanoparticles have shown polycrystalline nature and high BET specific surface area (229.83 m2/g) with active functional groups on the surface. The adsorption process follows second-order kinetics with the involvement of intra-particle diffusion and adsorption capacity as much as 124.11 mg/g was determined from the Langmuir isotherm. The thermodynamic analysis revealed that the adsorption process was feasible, spontaneous, and exothermic in nature. A three-layer feed-forward back-propagation artificial neural network (ANN) model was employed to predict the removal (%) of Cr(VI) ions as output. Optimal ANN network (4:8:1) shows the minimum mean squared error (MSE) of 0.00161 and maximum coefficient of determination (R2) of 0.984. The adsorption process is mostly influenced by solution pH and followed by adsorbent dosage, initial Cr(VI) concentration, and contact time as illustrated by sensitivity analysis. With small size and high surface area, biocompatibility, ecofriendly nature, easy magnetic separation, and enhanced adsorption capacity towards Cr(VI), calcium ferrite nanoparticles will find its potential application in wastewater remediation. GRAPHICAL ABSTRACT

Edge effect enhanced electron field emission in top assembled reduced graphene oxide assisted by amorphous CNT-coated carbon cloth substrate

In this work a hybrid structure assembly of amorphous carbon nanotubes (a-CNTs) -reduced graphene oxide (RGO) has been fabricated on carbon cloth/PET substrates for enhanced edge effect assisted flexible field emission device application. The carbon nanostructures prepared by chemical processes were finally deposited one over the other by a simple electrophoretic deposition (EPD) method on carbon cloth (CC) fabric. The thin films were then characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscope (HRTEM). Field assisted electron emission measurement was performed on this hybrid structure. It was observed that the hybrid carbon nanostructure showed exceptional field emission properties with outstanding low turn-on and threshold field (Eto∼ 0.26 Vμm−1, Eth ∼ 0.55 Vμm1). These observed results are far better compared to standalone and plasma etched edge enhanced RGO systems due to the bottom layer a-CNTs bed which assisted in significant enhancement of edge effect in RGO sheets.

Simple Chemical Route Synthesis of Fe2O3 Nanoparticles and its Application for Adsorptive Removal of Congo Red from Aqueous Media: Artificial Neural Network Modeling

Nanocrystalline Fe2O3 powder was synthesized by a simple chemical route involving FeCl3 and NaOH. The Fe2O3 powder thus prepared was characterized using x-ray diffraction study, scanning electron microscopy, and Fourier transform infrared spectroscopy. The adsorption properties of crystalline Fe2O3 powder have been investigated with an aim to explore a possible low cost and efficient way to remove Congo red (CR) from waste water. Fe2O3 powder was found as an excellent adsorbent for CR from aqueous medium. Adsorption capacity as much as 203.66 mg g−1 is reported at room temperature. Effect of different experimental parameters such as reaction pH, initial CR dye concentration, adsorbent dose, and reaction temperature were studied on adsorption capacity of Fe2O3 powder and modeled by artificial neural network (ANN). Optimal ANN structure (4–5–1) shows minimum mean squared error (MSE) of 0.00235 and determination coefficient (R2) of 0.991 with Levenberg–Marquardt algorithm. Isotherm analysis of experimental data exhibited better fit to the Langmuir isotherm. The adsorption process was found to follow second-order kinetics as depicted by the analysis of experimental results. Thermodynamic study shows that the adsorption process is endothermic, spontaneous, and thermodynamically favorable in the temperature range of 27°C to 60°C. GRAPHICAL ABSTRACT

rGO-Wrapped flowerlike Bi2Se3 nanocomposite: synthesis, experimental and simulation-based investigation on cold cathode applications

Bi2Se3 nanoflowers (NFs) and reduced graphene oxide (rGO) nanocomposite (BG) have been synthesized by a cost-effective, ecofriendly and easy hydrothermal route for the first time. Thorough characterizations confirm the phase, chemical composition and morphology of the samples. Room temperature transport measurement showed that the composite samples exhibit enhanced electrical conductivity compared to the pure Bi2Se3 nanoflowers (NFs). The possibility of using this composite in applications such as low macroscopic field emitters for cold cathode application has been investigated. For this, theoretical simulations are performed for pure and composite samples with graphene wrapping of different degrees and to evaluate the relation between the degree of rGO wrapping and the enhancement of FE properties, and the same was verified experimentally. It is observed that the enhancement factor for cold cathode emission of Bi2Se3–rGO (BG) composite is almost 5 times higher than that of pristine GO, 2.6 times that of rGO and nearly 1.5 times higher than that of pure Bi2Se3 NFs. The enhancement of the cold emission properties is attributed to suitable wrapping of rGO sheets over Bi2Se3 NFs. This produces more curvature at the nanoflakes edges and the electron affinities between the materials are favorable for the enhancement of cold cathode emission. The sample exhibiting the best FE properties also showed photoresponse properties under visible light excitation.

Experimental and theoretical investigation of enhanced cold cathode emission by plasma-etched 3d array of nanotips derived from CuPc nanotube

In the present work, we report fabrication and field emission responses of 3D copper phthalocyanine (CuPc) nanotip arrays synthesized over nanotube walls by facile plasma treatment. Significant field emission enhancement is confirmed for a nanotip–nanotube hybrid system (turn-on field 4.2 V μm−1@10 μA cm−2) as compared to pristine CuPc nanotubes (turn-on field 6.8 V μm−1@10 μA cm−2). Root of the observed enhanced cold cathode emission performances is further probed by a finite element method based simulation protocol that computed local electric field distribution for a single tube without and with plasma etching in a manner parallel to the experimental setup. Our obtained results strongly suggest that CuPc nanotip–nanotube hybrid nanostructures are a major potential candidate as field emitters for vacuum nanoelectronics and cold cathode based emission display applications.

Co3O4 Nanowires on Flexible Carbon Fabric as a Binder-Free Electrode for All Solid-State Symmetric Supercapacitor

Developing portable, lightweight, and flexible energy storage systems has become a necessity with the advent of wearable electronic devices in our modern society. This work focuses on the fabrication of Co3O4 nanowires on a flexible carbon fabric (CoNW/CF) substrate by a simple cost-effective hydrothermal route. The merits of the high surface area of the prepared Co3O4 nanostructures result in an exceptionally high specific capacitance of 3290 F/g at a scan rate of 5 mV/s, which is close to their theoretical specific capacitance. Furthermore, a solid-state symmetric supercapacitor (SSC) based on CoNW/CF (CoNW/CF//CoNW/CF) was fabricated successfully. The device attains high energy and power densities of 6.7 Wh/kg and 5000 W/kg. It also demonstrates excellent rate capability and retains 95.3% of its initial capacitance after 5000 cycles. Further, the SSC holds its excellent performance at severe bending conditions. When a series assembly of four such devices is charged, it can store sufficient energy to power a series combination of five light-emitting diodes. Thus, this SSC device based on a three-dimensional coaxial architecture opens up new strategies for the design of next-generation flexible supercapacitors.

Topological Insulator Bi2Se3/Si-Nanowire-Based p–n Junction Diode for High-Performance Near-Infrared Photodetector

Chemically derived topological insulator Bi2Se3 nanoflake/Si nanowire (SiNWs) heterojunctions were fabricated employing all eco-friendly cost-effective chemical route for the first time. X-ray diffraction studies confirmed proper phase formation of Bi2Se3 nanoflakes. The morphological features of the individual components and time-evolved hybrid structures were studied using field emission scanning electron microscope. High resolution transmission electron microscopic studies were performed to investigate the actual nature of junction whereas elemental distributions at junction, along with overall stoichiometry of the samples were analyzed using energy dispersive X-ray studies. Temperature dependent current-voltage characteristics and variation of barrier height and ideality factor was studied between 50 and 300 K. An increase in barrier height and decrease in the ideality factor were observed with increasing temperature for the sample. The rectification ratio (I+/I-) for SiNWs substrate over pristine Si substrate under dark and near-infrared (NIR) irradiation of 890 nm was found to be 3.63 and 10.44, respectively. Furthermore, opto-electrical characterizations were performed for different light power intensities and highest photo responsivity and detectivity were determined to be 934.1 A/W and 2.30 × 1013 Jones, respectively. Those values are appreciably higher than previous reports for topological insulator based devices. Thus, this work establishes a hybrid system based on topological insulator Bi2Se3 nanoflake and Si nanowire as the newest efficient candidate for advanced optoelectronic materials.

Novel Quaternary Chalcogenide/Reduced Graphene Oxide-Based Asymmetric Supercapacitor with High Energy Density

In this work we have synthesized quaternary chalcogenide Cu2NiSnS4 (QC) nanoparticles grown in situ on 2D reduced graphene oxide (rGO) for application as anode material of solid-state asymmetric supercapacitors (ASCs). Thorough characterization of the synthesized composite validates the proper phase, stoichiometry, and morphology. Detailed electrochemical study of the electrode materials and ASCs has been performed. The as-fabricated device delivers an exceptionally high areal capacitance (655.1 mF cm-2), which is much superior to that of commercial micro-supercapacitors. Furthermore, a remarkable volumetric capacitance of 16.38 F cm-3 is obtained at a current density of 5 mA cm-2 combined with a very high energy density of 5.68 mW h cm-3, which is comparable to that of commercially available lithium thin film batteries. The device retains 89.2% of the initial capacitance after running for 2000 cycles, suggesting its long-term capability. Consequently, the enhanced areal and volumetric capacitances combined with decent cycle stability and impressive energy density endow the uniquely decorated QC/rGO composite material as a promising candidate in the arena of energy storage devices. Moreover, Cu2NiSnS4 being a narrow band gap photovoltaic material, this work offers a novel protocol for the development of self-charging supercapacitors in the days to come.

NiO nanosteps on Ni: wide band gap p-type nanostructure for efficient cold cathode and magnetically separable photocatalyst

Pure nickel micro particles were chemically treated with various concentrations of NaOH and were subsequently annealed in 800 °C. The dimensions of the resulting nanosteps were tuned by simply varying the annealing time durations. Formation of Ni-NiO composite phase was confirmed by x-ray diffraction studies. The morphology of the as-prepared samples was investigated by field emission scanning electron microscope whereas the transmission electron microscope revealed the Ni core NiO shell structure of the samples. The NiO nanosteps showed much improved field emission properties compared to pure Ni micro particles and pure NiO powder synthesized by simply annealing the Ni particles. Finite element based simulation studies revealed strong enhancement of the electric field in the NiO nanostep samples and the simulated results were compared with the experimental outcome. The photocatalytic activities of the as-prepared samples were also investigated, which showed that Ni-NiO nanosteps is a magnetically separable photocatalyst.

CuBO2: a new highly transparent p-type wide band gap electron field emitter

Nanocrystalline copper boron oxide, the latest addition to the p-type transparent conductive oxide family, was synthesized via the cost effective sol–gel technique and here we report the first-time observation of its excellent electron field emission property. Proper phase formation of the as-prepared samples was confirmed from x-ray diffraction studies whereas energy dispersive x-ray analysis showed the composition of the samples to be near stoichiometric. High resolution transmission electron microscopic studies were carried out to obtain morphological information and the exact particle size. The information regarding the work function was theoretically obtained using density functional theory. The optical transmittance and band gaps of the samples were obtained from ultraviolet-visible spectroscopic studies. The electron field emission property of the sample was studied with a standard field emission measurement set-up and the samples exhibited very good field emission performance compared to other Cu-delafossites, resulting in a turn-on field as low as 2.2 V μm−1 with the maximum emission current density up to 872 μA cm2, which gradually decreased with increasing particle size.