Structure-led manifestation of photocatalytic activity in magnetically recoverable spinel CuFe2O4nanoparticles and its application in degradation of industrial effluent dyes under solar light.

An efficient removal of the photocatalysts used in the decontamination of water is crucial after its application beside its expected visible light sensitive activities. This study presents the synthesis of magnetically separable CuFe2O4nanoparticles (CFNPs) with enhanced photoactivity under AM 1.5 G sunlight. A simple two-step process involving co-precipitation and hydrothermal treatment is employed, with subsequent annealing at temperatures from 200 °C to 1000 °C to synthesize the CFNPs. The characteristic features of the highest photoactive tetragonal phase of CFNP are confirmed by powder XRD studies with Rietveld refinement. This scheme strategically controls the growth of a highly photoactive tetragonal phase with predominant (224) facets over other less active facets in cubic CuFe2O4. Mott-Schottky analysis confirms thep-type semiconducting nature of CFNPs. A favourable direct optical band gap of 1.73 eV, as well as photoluminescence emission quenching for visible photons, show that the (224) oriented CFNPs are good photocatalysts in the visible spectrum with demonstrated organic dye degradations, including methylene blue and others. A density functional theory-based approach validates that the adsorption of such dye is thermodynamically more favourable on (224) facets of CuFe2O4to facilitate the redox action by the excitons.

Thermal crowning mechanism in gold-silica nanocomposites: plasmonic-photonic pairing in archetypal two-dimensional structures.

A close-packed monolayer of a two-dimensional periodic array of Silica nanospheres (SNs) with gold (Au) crowning, forming a long-ranged archetypal plasmonic-photonic nanocomposite, has been achieved. We investigate the thermal crowning mechanism in such a nanocomposite using electron microscopy and X-ray diffraction techniques. Pre- and post-annealing morphological features reveal gold crowning on top of SNs, at different annealing temperatures for various thicknesses of the sputter-deposited gold. In situ grazing incidence X-ray diffraction was employed to structurally characterize the reconstruction in the Au-layer as a function of the annealing temperature. Finite element methods were used to simulate the interaction between the paired nanocomposites and the incident electromagnetic radiations to elucidate the crowning and nanodrop formation mechanism. This study provides an insight into real-time morphological and structural changes of a dewetting plasmonic film over a photonic basis and explores a robust, reliable, and scalable route to fabricate coupled nanocomposites. Such nanocomposites allow prospective applications in optoelectronics, sensing, catalysis, and surface-enhanced Raman spectroscopy by exploiting the plasmonic-photonic pairing in archetypal two-dimensional structures.

Role of nanowire length on the performance of a self-driven NIR photodetector based on mono/bi-layer graphene (camphor)/Si-nanowire Schottky junction.

In this article, we have demonstrated a solid carbon source such as camphor as a natural precursor to synthesize a large area mono/bi-layer graphene (MLG) sheet to fabricate a nanowire junction-based near infrared photodetectors (NIRPDs). In order to increase the surface-to-volume ratio, we have developed Si-nanowire arrays (SiNWAs) of varying lengths by etching planar Si. Then, the camphor-based MLG/Si and MLG/SiNWAs Schottky junction photodetectors have been fabricated to achieve an efficient response with self-driven properties in the near infrared (NIR) regime. Due to a balance between light absorption capability and surface recombination centers, devices having SiNWAs obtained by etching for 30 min shows a better photoresponse, sensitivity and detectivity. Fabricated NIRPDs can also be functioned as self-driven devices which are highly responsive and very stable at low optical power signals up to 2 V with a fast rise and decay time of 34/13 ms. A tremendous enhancement has been witnessed from 36 µA W-1 to 22 mA W-1 in the responsivity at 0 V for MLG/30 min SiNWAs than planar MLG/Si PDs indicating an important development of self-driven NIRPDs based on camphor-based MLG for future optoelectronic devices.

Effective light polarization insensitive and omnidirectional properties of Si nanowire arrays developed on different crystallographic planes.

In this paper, fabrication of vertical Si nanowire arrays (SiNWAs) by a facile metal assisted chemical etching approach on different crystallographic planes of Si has been reported. A very low specular reflectance (R spec ) of 0.04% and 0.03% has been achieved in the whole visible range for SiNWAs grown on Si(100) and Si(111) oriented substrates, respectively. High broadband enhancement has been detected for vertical SiNWAs due to multiple scattering paths inside the nanowire arrays. On the other hand, inclined nanowires showed a fascinating behavior at the longer wavelength regime, where light gets the longer path to reflect back-forth and ease to reflect back outward at normal incidence. Moreover, for [100] SiNWAs, transverse electric field component demonstrates the strong polarization insensitive properties at the expense of transverse magnetic field component with a minimum reflectance of <2% up to 1200 nm. The [100] SiNWAs demonstrates extraordinary omnidirectional properties at θ B ≥ 58°. Theoretical validation of COMSOL with an effective medium approach reveal the effective dipole coupling and the presence of strong absorption modes for vertical SiNWs at a typical wavelength regime. The highly bound states of the particle tunneling through classical forbidden region shows a strong dependence on the gradient in the refractive index (mi ) from 1 to 3.4. The high order scattering effect is observed at ∼520 cm-1 in a disordered optical medium. This novel finding of light localization properties for SiNWAs with different orientation gives a new route to support various photonic applications.

Electrodeposition of Si from an Ionic Liquid Bath at Room Temperature in the Presence of Water.

The electrochemical deposition of Si has been carried out in an ionic liquid medium in the presence of water in a limited dry nitrogen environment on highly oriented pyrolytic graphite (HOPG) at room temperature. It has been found that the presence of water in ionic liquids does not affect the available effective potential window to a large extent. Silicon has been successfully deposited electrochemically in the overpotential regime in two different ionic liquids, namely, BMImTf2N and BMImPF6, in the presence of water. Although a Si thin film has been obtained from BMImTf2N; only distinguished Si crystals protected in ionic liquid droplets have been observed from BMImPF6. The most important observation of the present investigation is that the Si precursor, SiCl4, instead of undergoing hydrolysis, even in the presence of water, coexisted with ionic liquids, and elemental Si has been successfully electrodeposited.

Impedance analysis of inherently redox-active ionic-liquid-based photoelectrochemical cells: charge-transfer mechanism in the presence of an additional redox couple.

An intensive electrochemical impedance study was carried out to understand the charge-transfer processes in photoelectrochemical (PEC) cells based on ionic liquid (IL) electrolytes. Three different electrolytes were utilized to understand the role of redox species as well as the medium on the charge-transfer mechanism. The negligible diffusion resistance, despite the presence of two different redox species in the case of Fe(CN)(6) (-4/-3) in IL, was explained on the basis of charge transfer between species of two different redox couples. Accordingly, the redox species are not required to travel through the bulk of the electrolyte for the removal of accumulated charges, as short-range charge transfer between the IL and the Fe(CN)(6) (-4/-3) species facilitates the removal of accumulated charges. It is also shown that PEC cells utilizing dual redox couples are highly stable with larger photoelectrochmeical windows, >3 V.

Elucidating the effect of copper as a redox additive and dopant on the performance of a PANI based supercapacitor.

In this article, the effect of copper (Cu) as a redox additive and dopant on the performance of a polyaniline (PANI) based supercapacitor was thoroughly investigated. The electrochemical properties of PANI in H2SO4 and in H2SO4 + CuSO4 and Cu doped PANI in H2SO4 were studied using cyclic voltammetry (CV) and impedance spectroscopy (IS). The CV result indicates that the capacity of PANI in H2SO4 was significantly improved with the introduction of Cu(2+) ions into the electrolyte, but it appeared unstable because of underpotential deposition of copper over the PANI surface and the relatively irreversible nature of the redox reaction. However, a stable and improved performance was obtained for Cu doped PANI due to the combined effect of an increase in conductivity and the surface modification of the PANI film. For Cu doped PANI, nearly ∼2.4 and ∼1.5 fold improved interfacial capacitance was achieved compared to that of PANI (H2SO4) and PANI (H2SO4 + CuSO4) respectively. The obtained Nyquist spectra for all the configurations were analysed using an equivalent circuit to understand the fundamentals of capacitive and resistive response of the supercapacitor. The IS measurements lead to direct determination of parameters like series resistance, rate capability of electrodes, ion diffusion phenomena and interfacial capacitance. The experimental results and their analysis will have significant impact on understanding the effect of dopants and redox additives on the performance of PANI based supercapacitors and also lay the basis for designing a supercapacitor with an appropriate electrode and electrolyte material for numerous industrial and consumer applications.

Unraveling the photoelectrochemical properties of ionic liquids: cognizance of partially reversible redox activity.

Ionic liquid based electrolytes are gaining great interest in the field of photoenergy conversion. We have found that the ionic liquids namely BMIm Cl, BMIm PF6 and BMIm Tf2N inherently offer redox activity. The device performance of the photoelectrochemical (PEC) cells of the configuration PbOx (0.25 cm(2))|blank ionic liquids|platinum (2 cm(2)) was analyzed in detail to get insights into the working principle of such systems. It was found that partially reversible redox ion pairs diminish the performance of such cells as power generating devices. The partial redox activity of the ionic liquids was confirmed by a number of observations derived from the PEC spectra. The important parameter, Vredox, which determines the performance of any PEC cell was also calculated for all the ionic liquids. The difficulties that arise in high frequency C-V measurements for ionic liquid systems were overcome by choosing the appropriate probing frequency. The evaluated Vredox of BMIm Cl, BMIm PF6 and BMIm Tf2N ionic liquids was found to be -0.30, -0.20 and -0.78 V (vs. NHE), respectively. This study will be beneficial to understand the role of ionic liquids as redox active electrolyte media in several applications.

Revealing the charge transport mechanism of a photoelectrochemical cell: analysis using A.C. voltage perturbation.

In this paper, we have carefully investigated the operation of a photoelectrochemical (PEC) cell configured of PbOx|Fe(CN)6(-4/-3)|Pt in the accumulation, flat band, depletion, inversion and deep-depletion regions using impedance measurements. The increases in the photocurrent for the different regions differ in their nature: a logarithmic increase in the depletion region, a linear increase in the inversion region along with a linear increase in the dark current and an exponential increase in the photo- and dark current in the deep-depletion region. All these variations are studied in detail to correlate these observations to the charge transfer mechanisms. The characteristics of the impedance spectrum itself can be assigned to the mentioned regions. We have found that the maximum photocurrent of the PEC cell, in the present investigation, can be extracted when the cell is working in the inversion region, while the maximum rate of the increase in photocurrent is found when the junction behaves as an ideal Schottky diode with a single RC element. Systematic experiments are suggested to establish a correlation between the observations obtained from the photocurrent, impedance, conductance, low frequency and high frequency capacitance measurements. It was found that light induced trap states in the semiconductor limit the photocurrent which has a linear dependency on the irradiance. A detailed investigation with A.C. conductivity measurements showed that the trap states actively participate in the current mechanism via a hopping phenomenon with small activation energies of 0.2 and 0.8 meV. The hopping rate increased exponentially with the applied bias under dark and illumination conditions. We also show a new way of finding the potential at which the maximum photocurrent will be extracted from the PEC cell, wherein the hopping via trap states is a dominating charge transfer mechanism. This study will help in pin pointing the key affecting parameters which limit the charge transfer process in the cell.

Plasmon enhanced light trapping to improve efficiency of dye-sensitized solar cell.

Photoelectric conversion efficiency of a dye-sensitized solar cell was improved by trapping more light into the absorbing region using Ag nanoparticle. Improved light transmission is observed experimentally in silver nanoparticle coated FTO glass. The size of Ag nanoparticle is estimated as 110 nm by comparing theoretical results with experimental data. The transmission data is used to explore the effect on electrical parameters of dye-sensitized solar cell using theoretical model. Plasmon enhanced DSSC showed increased efficiency of 11.76% under AM1.5 solar spectrum compared with 10.86% for a DSSC without Ag nanoparticles.

Transparent conductive multiwall carbon nanotubes-polymer composite for electrode applications.

Disperse Multiwall carbon nanotubes (MWCNTs) are incorporated aqueous N-hydroxy methyl acrylamide, which is subjected to crosslinking to develop a transparent conductive composite free standing film. The effects of the concentration of MWCNTs and temperature on optical and electrical properties of nano-composites are investigated. Interestingly, only 0.06 mg/ml of MWCNTs is sufficient to reach the percolation threshold (Phi) for transition in electrical conductivity up to 10(-4) S/cm, with a visible transmittance over 85%, which is well above the reported for such a low level of MWCNTs loading. The electrical conductivity of the composite was measured at 120 degrees C. It has been observed that electrical conductivity increases significantly with the increase in temperature, signifying the semiconducting nature of nano-composites. Finally, current-voltage (I-V) characteristics show liner behaviour, confirms Ohmic nature of nano-composites and metal contact.

Fabrication of bi-layer graphene and theoretical simulation for its possible application in thin film solar cell.

High quality graphene film is fabricated using mechanical exfoliation of highly-oriented pyrolytic graphite. The graphene films on glass substrates are characterized using field-emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy, UV-vis spectroscopy and Fourier transform infrared spectroscopy. A very high intensity ratio of 2D to G-band (to approximately 1.67) and narrow 2D-band full-width at half maximum (to approximately 40 cm(-1)) correspond to the bi-layer graphene formation. The bi-layer graphene/p-GaN/n-InGaN/n-GaN/GaN/sAl2O3 system is studied theoretically using TCAD Silvaco software, in which the properties of exfoliated bi-layer graphene are used as transparent and conductive film, and the device exhibits an efficiency of 15.24% compared to 13.63% for ITO/p-GaN/n-InGaN/n-GaN/GaN/Al2O3 system.

Exploring the Possibility of Machine Learning for Predicting Ionic Conductivity of Solid-State Electrolytes.

Unlike conventional liquid electrolytes, solid-state electrolytes (SSEs) have gained increased attention in the domain of all-solid-state lithium-ion batteries (ASSBs) due to their safety features, higher energy/power density, better electrochemical stability, and a broader electrochemical window. SSEs, however, face several difficulties, such as poorer ionic conductivity, complicated interfaces, and unstable physical characteristics. Vast research is still needed to find compatible and appropriate SSEs with improved properties for ASSBs. Traditional trial-and-error procedures to find novel and sophisticated SSEs require vast resources and time. Machine learning (ML), which has emerged as an effective and trustworthy tool for screening new functional materials, was recently used to forecast new SSEs for ASSBs. In this study, we developed an ML-based architecture to predict ionic conductivity by utilizing the characteristics of activation energy, operating temperature, lattice parameters, and unit cell volume of various SSEs. Additionally, the feature set can identify distinct patterns in the data set that can be verified using a correlation map. Because they are more reliable, the ensemble-based predictor models can more precisely forecast ionic conductivity. The prediction can be strengthened even further, and the overfitting issue can be resolved by stacking numerous ensemble models. The data set was split into 70:30 ratios to train and test with eight predictor models. The maximum mean-squared error and mean absolute error in training and testing for the random forest regressor (RFR) model were obtained as 0.001 and 0.003, respectively.

Controlled growth of polyaniline fractals on HOPG through potentiodynamic electropolymerization.

Polyaniline (PANI) in fractal dimension has been electrodeposited reproducibly on highly oriented pyrolytic graphite (HOPG) from 0.2 M aniline in 1 M aqueous HCl solution by potentiodynamic sweeping in the range of -0.2 to 0.76 V vs Ag/AgCl at room temperature. Fractal growth of PANI dendrimers is affected by diffusion limited polymerization (DLP) at a sweep rate of 15 mV s(-1) for 43 min. This type of PANI dendrimer is prepared for the first time on such large area HOPG substrate by electrochemical technique using rather simple cell setup. The fractal dimension has been determined by chronoamperometry (CA) and box counting technique and is found to vary from 1.4 to 1.9 with the duration of electropolymerization. The sweep rate, terminal oxidation potential, and the diverse surface anisotropy of the HOPG surface are found to be crucial factors in controlling the growth of such PANI fractals.

The effects of some components on the electrodeposition process used for solar cell applications.

The study has described through the extrapolation method the roles of those precursors' ions as main substances accompanying the progress of electroplating processes that have been used mainly in the deposition of semiconductor thin film and in the fabrication of solar cells. The role of some materials as primary salts have been compared to each other according to their structures, and through the extrapolation method the atomic structures of the metals included in those salts have been reviewed in 3D forms, investigated and compared. The nuances, on the other hand, cannot be denied. However, the study has reached a plausible point of comparison to substantiate the pieces of evidence of these ions' role in the aqueous solitons. Definitely, the aim is to build up the ultimate steps to finally disclose the essential role of some inorganic or organic compounds in the deposition solution, claiming a step ahead for particular purposes about some elements in the periodic table. Basically, the study cannot rebuke that the available data play an innate part in this study and the next investigating steps in the future. This attempt has somehow illustrated the role of sulfate, nitrate and chloride as accompanying ions in the major salts that have been used to get the desired results in solar cells fabrications. Also, the study has confirmed the basics of mechanisms in which those ions could be compared to each other. For instance, sulfate, nitrate and chloride ions can compare the final results of some metals electrodeposition according to the positions of those metals in the periodic table when fabricating the solar cells. The thickness or the atomic composition of Cu and Zn deposits can be increased at considerably higher voltages starting from IB to IIB columns, whilst for Ga and In deposits, they can be increased starting from the top to the bottom of IIIA column.

Controlled Island Formation of Large-Area Graphene Sheets by Atmospheric Chemical Vapor Deposition: Role of Natural Camphor.

Camphor-based mono-/bilayer graphene (MLG) sheets have been synthesized by very facile atmospheric chemical vapor deposition processes on Si/SiO2, soda lime glass, and flexible polyethylene terephthalate films. The effect of camphor concentration with respect to distance between camphor and the Cu foil (D) has been varied to investigate the controlled formation of a homogeneous graphene sheet over a large area on Cu foil. Raman studies show a remarkable effect of camphor at a typical distance (D) to form a monolayer to multilayer graphene (MULG) sheet. The signature of MLG to MULG sheets appears due to increase in the number of nucleation sites, even over the subsequent domains that contribute stacks of graphene over each other as observed by high-resolution transmission electron microscopy images. Moreover, the increase in camphor concentration at a particular distance generates more defect states in graphene as denoted by D band at 1360 cm-1. Uniform distribution of large-area MLG demonstrates an intense 2D/G ratio of ∼2.3. Electrical and optical measurements show a sheet resistance of ∼1 kΩ/sq with a maximum transmittance of ∼88% at 550 nm for low camphor concentration. An improvement in the rectification and photodiode behavior is observed from the diodes fabricated on n-Si/MULG as compared to n-Si/MLG in dark and light conditions.

Development of highly sensitive H2O2 redox sensor from electrodeposited tellurium nanoparticles using ionic liquid.

A new, non-enzymatic, low-cost sensor based on tellurium nanoparticles (TeNPs) for the analytical determination of H2O2 has been proposed. An economically viable electrochemical technique was employed for the synthesis of TeNPs based non-enzymatic H2O2 sensor. Thin films of TeNPs were successfully electrodeposited on fluorine-doped tin oxide (FTO) substrate using [BMIM][Ac] ionic liquid at 90 °C. The effect of deposition potential on the morphology, phase formation, and electrochemical characterisation of nanostructured Te films has been studied. Field emission scanning electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy were employed to characterize the nanostructured Te films on FTO surface. The electro-catalytic performance of the proposed TeNPs/FTO sensor has been studied by cyclic voltammetry (CV) and chronoamperometry (CA) in phosphate buffer (Argon saturated) in the absence and presence of H2O2. TeNPs/FTO fabricated at applied potential of -1.40 V showed an excellent electro-catalytic activity towards H2O2 reduction. The proposed TeNPs/FTO sensor shows an excellent sensitivity of 757 µA mM-1 cm-2. The sensor possess good selectivity and stability with an excellent amperometric response time of about 5 s. The present study also demonstrates that TeNPs/FTO is a promising sensing material suitable for determination of H2O2 in practical samples.

Nanostructured SnS with inherent anisotropic optical properties for high photoactivity.

In view of the worldwide energy challenge in the 21(st) century, the technology of semiconductor-based photoelectrochemical (PEC) water splitting has received considerable attention as an alternative approach for solar energy harvesting and storage. Two-dimensional (2D) structures such as nanosheets have the potential to tap the solar energy by unlocking the functional properties at the nanoscale. Tin(ii) sulfide is a fascinating solar energy material due to its anisotropic material properties. In this manuscript, we report on exploiting the 2D structure modulated optical properties of nanocrystalline SnS thin film synthesized by chemical spray pyrolysis using ambient transport in the harvesting of solar energy. We obtained the nanostructured SnS with well-preserved dimensions and morphologies with one step processing. The work demonstrates that the intrinsically ordered SnS nanostructure on FTO coated glass can tap the incident radiation in an efficient manner. The structure-property relationship to explain the photo-response in nanocrystalline-SnS is verified experimentally and theoretically. The novel design scheme for antireflection coating along with the anisotropic properties of SnS is conceived for realizing a PEC cell. The developed PEC cell consists of a SnS photoanode which shows considerably high photocurrent density of 7 mA cm(-2) with aqueous media under AM 1.5G, 100 mW cm(-2) exposure with notably stable operation. Electrochemical impedance spectroscopy revealed that a non-ideal capacitive behavior as well as drift assisted transport across the solid-state interface is responsible for such a high photo-current density in the nanocrystalline-SnS photoanode.

Electrical Characteristics of Horizontally and Vertically Oriented Few-Layer Graphene on Si-Based Dielectrics.

Horizontally and vertically oriented few-layer graphenes have been synthesized directly on SiO2 coated Si substrates via thermal and hot-filament chemical vapor deposition, respectively. The effect of the direction of mass flow on the fabrication of graphene film is analysed and a plausible mechanism is proposed. The graphene/p-Si heterojunction is fabricated and tested for its potential in optoelectronic devices. Rectification behaviour is observed at the interface of graphene/p-Si under dark conditions. A dark current of 1.1 mA with an ideality factor of 1.5, in addition of a high rectification ratio of 15.99 at ± 0.5 V is found for the vertically oriented graphene/p-Si heterojunction.

Elucidating different mass flow direction induced polyaniline-ionic liquid interface properties: insight gained from DC voltammetry and impedance spectroscopy.

This work describes the use of direct current (DC) cyclic voltammetry (CV) and alternating current (AC) electrochemical impedance spectroscopy (EIS) as a means to monitor an electrochemical interface of different mass flow direction induced polyaniline (PANI) film in IL (BmimPF6). Observed by SEM, vertical mass flow (VMF) and horizontal mass flow (HMF) induce porous nanorod and compact granular morphology of PANI, respectively. The present work explores in detail analysis of double layer capacitance, polarization resistance, diffusion mechanism, as well as other electrochemical features associated with the PANI-IL interface. A comparatively higher value of capacitance obtained for VMF PANI film from CV measurement confirms the higher electroactivity at the VMF electrode than the HMF film. Impedance spectroscopy, using a small amplitude perturbation, confirms the CV result. Impedance measurement gives a value of capacitance larger than that from CV where the amplitude of the perturbation is much larger. The implications of these results for its potential application in energy storage devices are discussed.