Bibhutibhushan Show

Mesoporous CuO–ZnO p–n heterojunction based nanocomposites with high specific surface area for enhanced photocatalysis and electrochemical sensing

We report the synthesis and characterization of p-CuO/n-ZnO heterojunction nanocomposites and their application as a broad spectrum photocatalyst. The different systems were also found to serve significantly as an electrode material for electrochemical (amperometric) sensing of H2O2 and NH3 (in μM or ppm level). To investigate their photochemical activities, three dyes, viz. Alizarin Red S, Methylene Blue and Rose Bengal, were chosen. The 60 hour milled composite gave better photocatalytic activity than the unmilled and 30 hour milled systems due to homogeneous mixing, formation of appropriate p–n junction, significant lowering of particle size and enhanced specific surface area. The defect level of ZnO, which also increases with increasing milling duration, again helps in better catalytic performance by trapping the photogenerated electrons and holes and also by raising the valance band edge and thus narrowing the band gap. The 60 hour milled sample took 55, 60 and 70 minutes to degrade the ARS, MB and RB dyes, respectively, which are better than many previous reports. The degradation rate was 0.01931, 0.04663 and 0.02318 min−1 for the ARS, MB and RB dyes, respectively.

Electrochemically synthesized microcrystalline tin sulphide thin films: high dielectric stability with lower relaxation time and efficient photochemical and photoelectrochemical properties

A detailed study has been carried out on the structural, dielectric and impedance properties of polycrystalline p-type SnS thin films grown on transparent conducting oxide (TCO) coated glass substrates from an aqueous solution of tartaric acid, SnSO4 and Na2S2O3 by a modified electrochemical technique. The as-deposited films were found to be smooth, almost pinhole free and well adherent to the bottom substrate. X-ray diffraction studies revealed the formation of polycrystalline SnS films with an orthorhombic phase. Field emission scanning electron microscopy and atomic force microscopy revealed a moderately compact surface morphology with evenly distributed almost spherical grains. Optical measurements showed direct band gap energy of 1.5 eV. Detailed electrical (dc and ac) analyses showed the p-type nature of the deposited films with unique dielectric behavior. The band-gap energy, resistivity, dielectric constant and relaxation time make this material and ideal absorber layer, which is also reflected in the efficient photochemical and photoelectrochemical behavior.

α-Fe2O3 nanospheres: facile synthesis and highly efficient photo-degradation of organic dyes and surface activation by nano-Pt for enhanced methanol sensing

We report a simplified electrochemical route to synthesize thin films of nanosphere α-Fe2O3 from a suitable electrolytic solution. X-ray diffraction studies revealed the formation of pure hematite phase (hexagonal structure) α-Fe2O3 films. Field emission scanning electron microscopy revealed a highly compact surface morphology with evenly distributed almost spherical grains. Raman, electron paramagnetic resonance and Fourier transform infrared spectroscopic analyses confirmed the presence of α phase Fe2O3 (hematite). Optical analysis revealed a band gap energy of 2.15 eV; this is most suitable for visible light driven photocatalysis towards the degradation of Indigo Carmine (IC) and Rhodamine B (Rh B) dyes, which are widely used in the textile industry and were taken as model organic compounds. About 90% photodegradation was achieved at rates of 0.0188 min−1 for IC and 0.0133 min−1 for Rh B. The synthesized films were used as modified electrodes, and their catalytic activity towards methanol oxidation was investigated. A comparison was also made between Pt modified FTO/Fe2O3 and unmodified FTO/Fe2O3 electrodes towards dye degradation and methanol oxidation, and it was found that the Pt modified FTO/Fe2O3 electrode yielded superior results.

Synthesis and characterisation of cerium(IV)-incorporated hydrous iron(III) oxide as an adsorbent for fluoride removal from water

Surface-altered hydrous iron(III) oxide incorporating cerium(IV) (CIHFO) was prepared and characterised via modern analytical tools for applications in fluoride removal from groundwater. The material with a Fe : Ce ratio of 1.0 : 0.5 (mol : mol) calcined at 473 K shows 24.8 ± 0.5 mg F− g−1 adsorption capacity at pH 5.0–7.0 from a solution with a concentration of 15.0 mg L−1; the material was established to be microcrystalline (∼5 nm) with a 140.711 m2 g−1 surface area, irregular surface morphology and porous structure. The time-dependent fluoride adsorption capacities of CIHFO at 293, 303 and 313 K are well described by the pseudo-first order, pseudo-second order and Weber–Morris kinetic models, respectively. The adsorption reaction occurs via a film/boundary layer diffusion process. The very low Arrhenius activation energy (Ea = 0.026 kJ mol−1) indicates the high feasibility of fluoride adsorption over CIHFO. The equilibrium data fit better with the Freundlich and Redlich–Peterson (g < 1.0) isotherms than with the Langmuir isotherm, which suggests multilayer adsorption. The values of the Freundlich parameters, n = 3.10, 4.47 and 7.57 and KF = 8.58, 10.88 and 11.25 at 293, 303 and 313 K, respectively, indicate high affinity for fluoride. Thermodynamic analysis of the reaction equilibrium shows that the reaction is highly exothermic (ΔH0 = −25.924 and −36.279 kJ mol−1 for Ci = 25.0 and 35.0 mg L−1), whereas the negative ΔG0 values indicate the spontaneous nature of the reaction. The fluoride adsorption over CIHFO occurs via ion-exchange that progresses to chemisorption. The presence of sulphate shows an adverse influence on fluoride adsorption by CIHFO, and the fluoride level of 2.4 g per L groundwater (9.05 mg F L−1) can be reduced below the permissible value.

Reusable iron sulfide nanospheres towards promoted photocatalytic and electrocatalytic activities

We report a facile electrochemical route for the synthesis of FeS nanospheres on fluorine doped tin oxide (FTO, SnO2:F) coated glass substrates. X-ray diffraction revealed the formation of the troilite phase of FeS, whereas field emission scanning electron microscopy and atomic force microscopy revealed highly compact surface morphology with evenly distributed almost spherical grains. Optical measurements showed a direct band gap energy of ∼1.95 eV, characteristic of FeS. The prepared FeS films showed significant photocatalytic degradation towards some widely used hazardous chemicals like Alizarin Red S, Methylene Blue, Rose Bengal and phenol. FeS modified FTO electrodes also showed excellent electrochemical properties towards hydrogen peroxide reduction and hence could be used as an efficient H2O2 sensor. The proposed sensor exhibited a good linear response in the range 10–700 μM with a detection limit of 2.699 μM with sensitivity 0.38717 μA μM−1 under optimal conditions.

Tuned synthesis and characterizational insight into β-cyclodextrin amended hydrous iron-zirconium hybrid oxide: a promising scavenger of fluoride in aqueous solution

The consumption of water contaminated with fluoride (>1.5 mg L−1) causes serious problems to public health and ultimately leads to skeletal fluorosis. Thus, the development of more efficient fluoride scavenging materials for designing water filters is an immediate task for researchers. β-Cyclodextrin (β-CD) amended hydrous iron–zirconium hybrid oxide (CHIZO), which is a new type of surface modified highly selective composite in organic–inorganic frameworks, is synthesized and characterized using various state of the art analytical tools, and its efficacy on fluoride removal from an aqueous solution is explored. The agglomerated micro structured composite material has no significant fingerprint such as surface appearance in TEM images and is inclined to possess very poor crystallinity. The BET analysis of CHIZO reveals a surface area of 0.2070 m2 g−1 and pore volume of 0.0476 cm3 g−1. The highly pH dependent fluoride adsorption by CHIZO decreases with an increase in pH, and pseudo-second order kinetics control the reaction. The Langmuir isotherm was recognized to be the best fit model to describe the adsorption equilibrium with a significantly higher monolayer adsorption capacity of fluoride (31.35 mg g−1) than the host hydrous Fe–Zr oxide (8.21 mg g−1) at pH ∼7.0 and 303 K. The thermodynamically spontaneous nature of CHIZO is due to the exothermic nature of the reaction. In addition, phosphate and sulphate show an adverse effect on fluoride adsorption. β-CD forms inclusion complexes by taking up fluoride ions from water into its central cavity and the driving forces associated with the complex formation include the release of enthalpy-rich water molecules from its cavity, electrostatic interactions, hydrogen bonding and release of conformational strain. The poor regeneration of the spent adsorbent even in 1.0 M NaOH (below 20%) is probably a consequence of entrapping fluoride inside the cavity of β-CD with hydrogen bonding. It has been found that only 0.9 g of CHIZO is able to reduce the fluoride level to below 1.0 mg L−1 in one-litre of fluoride spiked (5.0 mg L−1) natural water sample. The present study thus reveals that CHIZO could be an efficient adsorbent for fluoride because of its high adsorption capacity and economical viability.

A regular rippled pattern formed by the molecular self-organization of polyvinylpyrrolidone encapsulated Ag nanoparticles: a high transmissive coating for efficiency enhancement of c-Si solar cells

The formation, characterization and application of polyvinylpyrrolidone (PVP) encapsulated silver nanoparticles with a regular rippled pattern is reported. The metal precursor was reduced by an in situ reduction technique, where glucose was used as an organic and mild reducing agent to control the process. In order to create the rippled structured of the film by molecular self organization of the encapsulated Ag nanoparticles, the concentrations of the reactants were optimized. The structural properties of the deposited films were established by X-ray diffraction, transmission electron microscopy, atomic force microscopy and dynamic light scattering techniques. Atomic force microscopy (AFM) revealed a highly ordered ripple structure of the film, which originated due to the self organization of the Ag nanoparticles in the PVP matrix, whereas, transmission electron microscopy (TEM) revealed the core–shell structure of the Ag/PVP unit. UV-vis spectrophotometric analysis resulted in a broad absorption peak between 350 to 500 nm (centered at 418 nm), which is characteristic of Ag nanoparticles. A notable reduction in reflectance and an increase in transmittance, leading to an enhancement in the overall efficiency, were observed when the rippled pattern was spin-coated on a c-Si solar cell.

A turn-on fluorogenic chemosensor for Fe3+ and a Schottky barrier diode with frequency-switching device applications

A novel highly sensitive and selective fluorescent chemosensor L has been synthesized and characterized by various physicochemical techniques. In 3 : 7 water : MeCN (v/v) at pH 7.2 (10 mM HEPES buffer, μ = 0.05 M LiCl), it selectively recognizes Fe3+ through 1 : 1 complexation resulting in a 106-fold fluorescence enhancement and a binding constant of 8.10 × 104 M-1. The otherwise non-fluorescent spirolactam form of the probe results a dual-channel (absorbance and fluorescence) recognition of Fe3+via CHEF (chelation enhanced fluorescence) through the opening of the spirolactam ring. We have also carried out fluorescence titration and anisotropy (r) studies in pure water in the presence of SDS (sodium dodecyl sulphate). Based on the dependence of FI (fluorescence intensity) and r on [SDS] it was proposed that the probe is trapped between two SDS monolayers which again interact among themselves by ππ stacking. As a result, there is an increase in FI up to [SDS] ∼ 7 mM - a phenomenon reminiscent of aggregation-induced enhancement of emission (AIEE). Beyond this concentration of SDS (7 mM), micelle formation takes place and the ππ stacked polymer now becomes a monomer and is trapped inside the micellar cavity. As a result, there is a decrease in FI at [SDS] > 7 mM. But for anisotropy, it increases with [SDS] beyond 7 mM. Ligand, metal, and SDS interactions are well established through different optical and morphological studies. [L-Fe(NO3)]2+ thin films on FTO (Fluorine-doped Tin Oxide) glass substrates have been designed with the help of the spin-coating deposition technique. The deposited film of thickness 1.6 × 10-5 cm is well characterized by optical band gap calculation with a direct band gap, εg ∼ 1.6 eV. FESEM was also performed for the [L-Fe(NO3)]2+/FTO film. The current-voltage characteristics were measured by the two-probe technique. Light-dependent exciton generation was carried out by taking the top and bottom contacts with graphite paste on FTO and on the [L-Fe(NO3)]2+ films for the measurement of switching behavior. The response ratio curve for the light-induced frequency-switching phenomena has been obtained. The frequency taped here is the oscillation frequency of the photo-generated electron and the hole in an exiton. Thus, the light-induced frequency-switching behavior and Schottky barrier diode characteristics of the material were established.

Design of a Pyrene Scaffold Multifunctional Material: Real-Time Turn-On Chemosensor for Nitric Oxide, AIEE Behavior, and Detection of TNP Explosive

A dual-emission pyrene-based new fluorescent probe (N-(4-nitro-phenyl)-N′-pyren-1-ylmethyl-ene-ethane-1,2-diamine (PyDA-NP)) displays green fluorescence for nitric oxide (NO) sensing, whereas it exhibits blue emission in the aggregated state. The mechanism of nitric oxide (NO/NO+) sensing is based on N-nitrosation of aromatic secondary amine, which was not interfered by reactive oxygen species and reactive nitrogen species. The aggregation-induced enhancement of emission (AIEE) behaviors of the PyDA-NP could be attributed to the restriction of intramolecular rotation and vibration, resulting in rigidity enhancement of the molecules. The AIEE behavior of the probe was well established from fluorescence, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, optical fluorescence microscopy, and time-resolved photoluminescence studies. In a H2O/CH3CN binary mixture (8:2 v/v), the probe showed maximum aggregation with extensive (833-fold) increases in fluorescence intensity and high quantum yield (0.79). The aggregated state of the probe was further applied for the detection of nitroexplosives. It displayed efficient sensing of 2,4,6-trinitrophenol (TNP), corroborating mainly the charge-transfer process from pyrene to a highly electron-deficient TNP moiety. Furthermore, for the on-site practical application of the proposed analytical system, a contact-mode analysis was performed.