Annealing temperature dependent catalytic water oxidation activity of iron oxyhydroxide thin films

Nanostructured iron oxyhydroxide(Fe OOH) thin films have been synthesized using an electrodeposition method on a nickel foam(NF) substrate and effect of air annealing temperature on the catalytic performance is studied. The as-deposited and annealed thin films were characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS), field emission scanning electron microscopy(FE-SEM) and linear sweep voltammetry(LSV) to determine their structural, morphological, compositional and electrochemical properties, respectively. The as-deposited nanostructured amorphous Fe OOH thin film is converted into a polycrystalline Fe_2O_3 with hematite crystal structure at a high temperature. The Fe OOH thin film acts as an efficient electrocatalyst for the oxygen evolution reaction(OER) in an alkaline 1 M KOH electrolyte. The film annealed at 200 °C shows high catalytic activity with an onset overpotential of 240 m V with a smaller Tafel slope of 48 m V/dec. Additionally, it needs an overpotential of 290 mV to the drive the current density of 10 m A/cm~2 and shows good stability in the 1 M KOH electrolyte solution.     

Influence of particle size on the photoactivity of Ti/TiO2 thin film electrodes,and enhanced photoelectrocatalytic degradation of indigo carmine dye

Photoanodes based on Ti/TiO₂ thin films were prepared by the sol–gel method, using either tetraisopropoxide (Ti(OPri)₄) or modified tetraisopropoxide, producing electrodes with different sized nanoparticle coatings, termed nanoporous (20 nm) or nanoparticulated (10 nm) electrodes. The anatase form dominated the composition of the nanoparticulated electrode, which presented a higher surface area, a flat band potential shift of ?160 mV and a 50% improvement in photoactivity, compared to the nanoporous electrode. 100% color removal, and 75% mineralization, of indigo carmine dye were achieved after 15 min of photoelectrocatalytic treatment using a nanoparticulated Ti/TiO₂ electrode operated at a current density of 0.4 mA cm^?2. Our findings indicate that the use of nanoparticulated electrodes, under UV irradiation and with controlled current density, is an efficient alternative for the removal of food dye contaminants during wastewater treatment.     

Applied bias photon-to-current conversion efficiency of ZnO enhanced by hybridization with reduced graphene oxide

The role of reduced graphene oxide(rGO) in the enhancement of photo-conversion efficiency of ZnO films for photoelectrochemical(PEC) water-splitting applications was analyzed. ZnO and rGO-hybridized ZnO(rGO/ZnO) films were prepared via a two-step electrochemical deposition method followed by annealing at 300 °C under argon gas flow. The physical, optical and electrochemical properties of the films were characterized to identify the effect of rGO-hybridization on the applied bias photon-to-current efficiency(ABPE) of ZnO. Scanning electron microscopy and X-ray diffraction indicated the formation of verticallyaligned, wurtzite-phase ZnO nanorods. Diffuse-reflectance UV–visible spectroscopy indicated that rGO-hybridization was able to increase the light absorption range of the rGO/ZnO film. UPS analysis showed that hybridization with rGO increased the band gap of ZnO(3.56 eV) to 3.63 eV for rGO/ZnO sample,which may be attributed to the Burstein–Moss effect. Photoluminescence(PL) spectra disclosed that rGOhybridization suppressed electron-hole recombination due to crystal defects. Linear sweep voltammetry of the prepared thin films showed photocurrent density of 1.0 and 1.8 m A/cm~2 for ZnO and rGO/ZnO at+0.7 V, which corresponded to an ABPE of 0.55% and 0.95%, respectively. Thus, this report highlighted the multi-faceted role of rGO-hybridization in the enhancement of ZnO photo-conversion efficiency.     

Synthesis of nickel selenide thin films for high performance all-solid-state asymmetric supercapacitors

As a significant semiconductor, nickel selenide shows enormous potential and extensive application prospects in the field of sensor, photocatalysis and supercapacitor. In this paper, nickel selenide (Ni₃Se₂, NiSe) thin films were successfully fabricated on stainless-steel sheet using a facile, effective electrodeposition technique. The morphologies, microstructures and chemical compositions of the thin films are characterized systematically. Electrochemical tests exhibit that the Ni₃Se₂ and NiSe possess high specific capacitance of 581.1 F/g and 1644.7 F/g, respectively. A flexible, all-solid-state asymmetric supercapacitor is assembled by utilizing NiSe film as positive electrode and activated carbon as negative electrode. The solid device delivers a high areal capacitance of 27.0 mF/cm² at the current density of 0.7 mA/cm². The maximum volumetric energy density and power density of the NiSe//AC asymmetric SCs can achieve 0.26 mWh/cm³ and 33.35 mW/cm³, respectively. The device shows robust cycling stability with 84.6% capacitance retention after 10,000 cycles, outstanding flexibility and satisfactory mechanical stability. Moreover, two devices in series can light up a red light-emitting diode, which displayed great potential applications for energy storage.     

Amperometric glucose sensor based on glucose oxidase immobilized on gelatin-multiwalled carbon nanotube modified glassy carbon electrode

We investigated the direct electrochemistry of glucose oxidase (GOx) at gelatin-multiwalled carbon nanotube (GCNT) modified glassy carbon electrode (GCE). GOx was covalently immobilized onto GCNT modified GCE through the well known glutaraldehyde (GAD) chemistry. The immobilized GOx showed a pair of well-defined reversible redox peaks with a formal potential (E⁰′) of ? 0.40 V and a peak to peak separation (ΔE_p) of 47 mV. The surface coverage concentration (Г) of GOx in GCNT/GOx/GAD composite film modified GCE was 3.88 × 10^? 9 mol cm^? 2 which indicates the high enzyme loading. The electron transfer rate constant (k_s) of GOx immobilized onto GCNT was 1.08 s^? 1 which validates a rapid electron transfer processes. The composite film shows linear response towards 6.30 to 20.09 mM glucose. We observed a good sensitivity of 2.47 μA mM^?1 cm^? 2 for glucose at the composite film. The fabricated biosensor displayed two weeks stability. Moreover, it shows no response to 0.5 mM of ascorbic acid (AA), uric acid (UA), acetaminophen (AP), pyruvate (PA) and lactate (LA) which shows its potential application in the determination of glucose from human serum samples. The composite film exhibits excellent recovery for glucose in human serum at physiological pH with good practical applicability.     

Synthesis and properties of polyfluorene copolymers bearing thiophene and porphyrin

To search for more wider absorption and higher charge carriers mobilities materials of polymer solar cell, a series of soluble alternating polyfluorene copolymers were synthesized by palladium-catalyzed Suzuki coupling reaction. Their structures were determined by 1H NMR, IR and UV-vis. And their UV-vis absorption spectra indicated that they had strong absorption over 600 nm spectral range and nearly cover 400-700 nm visible region. The band gaps of copolymers calculated according to cyclic voltammetry （CV） were between 1.96 and 2.03 eV. Polymer：TiO2 bulk-heterojunction films were made from mixtures of polymer and titanium isopropoxide, a precursor for TiO2, via hydrolysis in air overnight. The photoluminescence at 380-800 nm of the blend film of PT-TPP20 （5 mg/mL）：Ti（OC3H7）4 （80 μL/mL） （20% volume fraction） was significantly quenched in the 50% Ti（OC3H7）4 blend film, indicating that rapid and efficient separation of photoinduced electron-hole pairs.     

Gas permeation properties of poly(lactic acid)

The need for the development of polymeric materials based on renewable resources has led to the development of poly(lactic acid) (PLA) which is being produced from a feedstock of corn rather than petroleum. The present study examines the permeation of nitrogen, oxygen, carbon dioxide, and methane in amorphous films of PLA cast from solution. The properties of PLA are compared to other commodity plastics and it is shown that PLA permeation closely resembles that of polystyrene. At 30°C, N₂ permeation in PLA is 1.3 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and the activation energy is 11.2 kJ/mol. For oxygen the corresponding values are 3.3 (10⁻¹⁰ cm³(STP) cm/cm² s cm Hg) and 11.1 kJ/mol. The values for carbon dioxide permeation are 1.2 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and 6.1 kJ/mol. For methane values of 1.0 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and an activation energy of 13.0 kJ/mol are found. Studies with pure gases show that polymer chain branching and small changes in l:d stereochemical content have no effect on permeation properties. Crystallinity is found to dominate permeation properties in a biaxially oriented film. The separation factor for a CO₂/CH₄ mixed gas system is measured between 0 and 50°C and does not deviate significantly from the calculated ideal separation factor; at 0°C the separation factor is 16, a value that suggests continued studies of PLA as a separation medium are warranted.     

Optical,structural and electrochromic studies of molybdenum oxide thin films with nanorod structure

The MoO₃ thin films were prepared via sol–gel dip coating method on glass and FTO glass substrate. The optical and other properties of multilayered MoO₃ films with 2–10 layers were investigated. The MoO₃ films were studied using UV–Visible transmission, XRD, SEM, FTIR and Cyclic Voltammetry (CV) measurements. The band gap value for MoO₃ films was evaluated and in the range of 3.2 eV–3.72 eV. The XRD spectrum reveals that the crystallinity increases along the (020) and (040) planes with the increase in thickness. The SEM images showed the formation of nanorods upto six layers. The FTIR spectrum confirms the formation of MoO₃. The 6 layered films show the maximum anodic (spike)/cathodic (peak) diffusion coefficient of 18.84/1.701 × 10^?11 cm²/s. The same film exhibits the change in optical transmission of 49% with the bleached/coloured state transmission of 62/13%.     

Nanoporous WO3 from anodized RF sputtered tungsten thin films

We report the first electrochemical anodization of RF (radio-frequency) sputtered tungsten (W) thin films. High pressure sputtering was utilized to produce W films of low intrinsic stress with a high degree of adhesion to the transparent substrates. Structurally and uniformly porous tungsten trioxide (WO₃) films were obtained under optimised anodization conditions in fluoride ion-containing electrolyte. Crystalline WO₃ was obtained after annealing the films at 450 °C. SEM and XRD characterisation techniques were used to determine the surface morphology and crystal structure of the non-anodized and anodized films.     

Low-temperature growth of vertically aligned In2O3 nanoblades with improved lithium storage properties

Vertically aligned Indium oxide (In₂O₃) nanoblades are successfully obtained through plasma enhanced chemical vapor deposition (PECVD) approach. By using plasma, the reaction between InCl₃ and O₂ was able to take place, yielding vertically aligned blade like nanostructure. The novel In₂O₃ nanostructures exhibit improved electrochemical properties when used as anode materials for lithium-ion batteries. The In₂O₃ electrode reveals reversible capacity of 580 mAh g^?1 after 100 cycles, much higher than that of the In₂O₃ thin films. The result suggests that proper structural modification of In₂O₃ thin film may contribute to the improvement of electrochemical properties. The In₂O₃ electrodes with large reversible capacity and stable cycling performance may provide new insight of anode materials applied in thin film lithium-ion batteries.     

Investigation of structural,optical and luminescent properties of sprayed N-doped zinc oxide thin films

N-doped ZnO (NZO) thin films are synthesized via spray pyrolysis technique in aqueous medium treating zinc acetate and N,N-dimethylformamide as precursors. Influence of N doping on structural, optical and luminescence properties have been investigated. Films are nanocrystalline having hexagonal crystal structure. Raman analysis depicts an existence of NZnO structure in NZO thin film. XPS spectrum of N 1s shows the 400 eV peak terminally bonded, well screened molecular nitrogen (γ-N₂). Lowest direct band gap of 3.17 eV has been observed for 10 at% NZO thin film. The UV, blue, and green deep-level emissions in photoluminescence of NZO films are due to Zn interstitials and O vacancies.     

Rationally designed/constructed MnOx/WO3 anode for photoelectrochemical water oxidation

The activity of WO₃ photoanode could be improved efficiently after loading MnO_x by photodeposition. The maximum photocurrent density of composite photoanode is achieved with a deposition time of 3 min, which is higher than that of pristine WO₃ photoanode around 40%.     

Chromophoric thin film based on cellulose triacetate blends for sensing metal ions

Chromophoric sensors were made based on 8-hydroxyquinoline immobilized onto a thin film of a polymer blend matrix. The thin films were made by the solution casting method using cellulose triacetate and polyethylene glycol (PEG 600) as plasticizer and pore-forming agent. Different contents of PEG 600 additive were investigated. The prepared films were characterized by FTIR and thermal analysis. The absorption and fluorescence spectra of different films were dependent on the content of PEG 600 with clear quenching of the fluorescence of the film that contains PEG 600 compared to that with zero content. This behavior was attributed to the collective effect of hydrogen bonding (intra- and intermolecular hydrogen bonding) that enhances the process of excited-state proton transfer. This result is favorable to a responsive sensor that shows fluorescence off in the absence of metal ions and fluorescence on upon metal ion chelation. The detection of 5 × 10⁻⁵ M of Al³⁺, Zn²⁺ and thallium (I) in aqueous solution has been observed with the fluorescence method. The result obtained is consistent with the enhancing effect of PEG 600 in the detectability of metal ions. Compared with the detection of Al³⁺ and Zn²⁺, the sensor shows better detection of thallium (I), with clear fluorescence spectra.     

Structural and electrochemical properties of a porous nanostructured SnO2 film electrode for lithium-ion batteries

A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the electrodeposition and the hydrothermal treatment, and its structure and electrochemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and galvanostatic charge–discharge tests. It was found that the as-prepared modified SnO₂ film shows a porous network structure with large specific surface area and high crystallinity. The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^?1 at the fourth cycle, close to the theoretical capacity of SnO₂ (790 mAh g^?1); and it still delivers a reversible Li storage capacity of 524 mAh g^?1 after 50 cycles. The reasons that the modified SnO₂ film electrode shows excellent electrochemical properties were also discussed.     

Fe-doped SnO2 transparent semi-conducting thin films deposited by spray pyrolysis technique: Thermoelectric and p-type conductivity properties

In this paper, we report structural, electrical, optical, and especially thermoelectrical characterization of iron (Fe) doped tin oxide films, which have been deposited by spray pyrolysis technique. The doping level has changed from 0 to 10 wt% in solution ([Fe]/[Sn] = 0–40 at% in solution). The thermoelectric response versus temperature difference has exhibited a nonlinear behavior, and the Seebeck coefficient has been calculated from its slope in temperature range of 300–500 K. The Hall effect and thermoelectric measurements have shown p-type conductivity in SnO₂:Fe films with [Fe]/[Sn] ≥ 7.8 at%. In doping levels lower than 7.8 at%, SnO₂:Fe films have been n-type with a negative thermoelectric coefficient. The Seebeck coefficient for SnO₂:Fe films with 7.8 at% doping level has been obtained to be as high as +1850 μV/K. The analysis of as-deposited samples with thicknesses ～350 nm by X-ray diffraction (XRD) and scanning electron microscopy (SEM) has shown polycrystalline structure with clear characteristic peak of SnO₂ cassiterite phase in all films. The optical transparency (T%) of SnO₂:Fe films in visible spectra decreases from 90% to 75% and electrical resistivity (ρ) increases from 1.2 × 10^?2 to 3 × 10³ Ω cm for Fe-doping in the range 0–40 at%.     

Spontaneous formation of an electroactive co-polymeric film derived from nordihydroguaiaretic acid and 4,4′-diaminobibenzyl

Binary solution of nordihydroguaiaretic acid (NDGA) and 4,4′-diaminobibenzyl (DABB) undergoes rapid oxidation by ambient oxygen to form a thin film of poly-NDGA-co-DABB on the surface of the reaction chamber and on immersed substrates. Electrochemistry of thus formed films was studied in 0.1 M sulfuric acid and in phosphate buffer (pH 7.4). Electrochemical behavior of the co-polymeric film is characterized by two redox couples, the predominant one being observed at more negative potentials comparing to parent NDGA i.e. 0.28 vs. 0.49 V (vs. Ag/AgCl) in 0.5 M H₂SO₄. The peak potentials were shifted toward lower values with solution pH at the rate of 59 mV/pH unit indicating a 2e/2H⁺ transition as expected for quinone-containing films. The poly-NDGA-co-DABB film exhibits catalytic activity toward electroreduction of nitrite to nitric oxide in acidic electrolytes. This reaction can be used to quantify nitrite in a broad concentration range with low detection limit (0.3 μM, S/N = 3).     

Electrochemical supercapacitor application of pervoskite thin films

We have explored electrochemically deposited pervoskite nanocrystalline porous bismuth iron oxide (BiFeO₃) thin film electrode from alkaline bath for electrochemical supercapacitors. The pervoskite BiFeO₃ nanocrystalline thin film electrode showed comparable specific capacitance of 81 F g⁻¹ and electrochemical supercapacitive performance and stability in an aqueous NaOH electrolyte to that of commonly used ruthenium based pervoskites.     

Conformational and stereoelectronic investigation of chloromethyl methyl sulfide and its sulfinyl and sulfonyl analogs

Three compounds based on polyoxometalate building blocks, [Cu(en)₂]{[Cu(en)₂]₂[Mo^VI₅Mo^V₃V^IV₈O₄₀(PO₄)]} · 4H₂O (1), [Co(en)₂]{[Co(en)₂]₂[HMo^VI₄Mo^V₄V^IV₈O₄₀(PO₄)]} · 5H₂O (2) and [Ni(en)₂]{[Ni(en)₂]₂[Mo^VI₅Mo^V₃V^IV₈O₄₀(VO₄)]} · 2H₂O (3) (en = ethylenediamine), have been synthesized and characterized by elemental analysis, IR, XPS, XRD, TGA and single-crystal X-ray diffraction analysis. The result of structure determination shows that isomorphic compounds 1, 2 and 3 feature a one-dimensional chain built from the reduced tetra-capped pseudo-Keggin polyoxoanion, which is further interconnected by [M(en)₂]²⁺ (M = Cu, Co and Ni) groups via the terminal oxygen atoms of polyoxoanions. The crystal data for these compounds are the following: 1, monoclinic, space group C2/c, a = 26.702(3) Å, b = 13.4539(14) Å, c = 19.5987(19) Å, β = 108.650(2)°, V = 6671.0(12) Å³, Z = 4; 2, monoclinic, space group C2/c, a = 26.244(3) Å, b = 13.5070(17) Å, c = 19.581(3) Å, β = 106.881(2)°, V = 6641.8(15) Å³, Z = 4; 3, monoclinic, space group C2/c, a = 26.2789(15) Å, b = 13.5408(6) Å, c = 19.6312(9) Å, β = 106.2590(10)°, V = 6706.1(6) Å³, Z = 4. Variable-temperature magnetic susceptibility measurements of compounds 1 and 3 reveal the feature of antiferromagnetic exchange in these compounds.     

Synthesis and characterization of WO3 nanoparticles prepared by the precipitation method: Evaluation of photocatalytic activity under vis-irradiation

WO₃ nanoparticles were synthesized by the precipitation method varying the time employed in the formation of their precursor in aqueous media and the calcination temperature. The WO₃ crystallization process and morphology of the synthesized samples were followed by the XRD, TEM and SEM techniques. The effects of the calcination temperature on the surface area and optical properties of the WO₃ nanoparticles were also investigated. Nanoparticles with morphologies such as square and rectangular plates and ovoid forms were observed for the different experimental conditions. WO₃ nanoparticles with different morphologies were tested for the photocatalytic degradation of organic dyes. In general, the photocatalysts showed a capacity to bleach the dye solution in the following sequence: indigo carmine (IC) > rhodamine B (rhB) > congo red (CR). The extent of mineralization was determined by means of total organic carbon (TOC) measurements, which showed a satisfactory TOC reduction (93%, within 75 h) only for IC. This value was even better than the one concerning the P-25 Degussa reference.     

Towards sustainable materials for solar energy conversion: Preparation and photoelectrochemical characterization of Cu2ZnSnS4

The feasibility of a new fabrication route for films of the attractive solar absorber Cu₂ZnSnS₄ (CZTS) has been studied, consisting of electrodeposition of metallic precursors followed by annealing in sulfur vapour. Photoelectrochemical measurements using a Eu³⁺ contact have been used to establish that the polycrystalline CZTS films are p-type with doping densities in the range (0.5–5) × 10¹⁶ cm⁻³ and band gaps of 1.49 ± 0.01 eV, making them suitable for terrestrial solar energy conversion. It has been shown that a somewhat Cu-poor composition favours good optoelectronic properties.