Radhakrishna Prabhu

CARMINE AND FAST GREEN AS CORROSION INHIBITORS FOR MILD STEEL IN HYDROCHLORIC ACID SOLUTION

The inhibition action of carmine and fast green dyes on corrosion of mild steel in 0.5 M HCl was investigated using mass loss, polarization and electrochemical impedance (EIS) methods at 300 K. The inhibition efficiency was found to increase with increasing concentration of the inhibitors. The inhibition efficiency of fast green (%η - 98) is higher than that of carmine (%η - 92) and found to be maximum in 1 × 10-3 M solution. The inhibitors act as mixed type with predominant cathodic effect. The inhibitors were adsorbed on the mild steel surface according to the Temkin adsorption isotherm. The surface morphology of the mild steel specimens was evaluated using SEM images.

Highly textured and transparent RF sputtered Eu2O3 doped ZnO films

Background Zinc oxide (ZnO) is a wide, direct band gap II-VI oxide semiconductor. ZnO has large exciton binding energy at room temperature, and it is a good host material for obtaining visible and infrared emission of various rare-earth ions. Methods Europium oxide (Eu2O3) doped ZnO films are prepared on quartz substrate using radio frequency (RF) magnetron sputtering with doping concentrations 0, 0.5, 1, 3 and 5 wt%. The films are annealed in air at a temperature of 773 K for 2 hours. The annealed films are characterized using X-ray diffraction (XRD), micro-Raman spectroscopy, atomic force microscopy, ultraviolet (UV)-visible spectroscopy and photoluminescence (PL) spectroscopy. Results XRD patterns show that the films are highly c-axis oriented exhibiting hexagonalwurtzite structure of ZnO. Particle size calculations using Debye-Scherrer formula show that average crystalline size is in the range 15–22 nm showing the nanostructured nature of the films. The observation of low- and high-frequency E2 modes in the Raman spectra supports the hexagonal wurtzite structure of ZnO in the films. The surface morphology of the Eu2O3 doped films presents dense distribution of grains. The films show good transparency in the visible region. The band gaps of the films are evaluated using Tauc plot model. Optical constants such as refractive index, dielectric constant, loss factor, and so on are calculated using the transmittance data. The PL spectra show both UV and visible emissions. Conclusion Highly textured, transparent, luminescent Eu2O3 doped ZnO films have been synthesized using RF magnetron sputtering. The good optical and structural properties and intense luminescence in the ultraviolet and visible regions from the films suggest their suitability for optoelectronic applications.

Photocatalytic degradation of eleven microcystin variants and nodularin by TiO2 coated glass microspheres.

Microcystins and nodularin are toxic cyanobacterial secondary metabolites produced by cyanobacteria that pose a threat to human health in drinking water. Conventional water treatment methods often fail to remove these toxins. Advanced oxidation processes such as TiO2 photocatalysis have been shown to effectively degrade these compounds. A particular issue that has limited the widespread application of TiO2 photocatalysis for water treatment has been the separation of the nanoparticulate powder from the treated water. A novel catalyst format, TiO2 coated hollow glass spheres (Photospheres™), is far more easily separated from treated water due to its buoyancy. This paper reports the photocatalytic degradation of eleven microcystin variants and nodularin in water using Photospheres™. It was found that the Photospheres™ successfully decomposed all compounds in 5 min or less. This was found to be comparable to the rate of degradation observed using a Degussa P25 material, which has been previously reported to be the most efficient TiO2 for photocatalytic degradation of microcystins in water. Furthermore, it was observed that the degree of initial catalyst adsorption of the cyanotoxins depended on the amino acid in the variable positions of the microcystin molecule. The fastest degradation (2 min) was observed for the hydrophobic variants (microcystin-LY, -LW, -LF). Suitability of UV-LEDs as an alternative low energy light source was also evaluated.

UV LED sources for heterogeneous photocatalysis

This review article presents an overview of the application of ultraviolet light-emitting diode (UV LED) sources in heterogeneous photocatalysis within the context of artificial UV sources. The feasibility of UV LEDs as a source of UV irradiation in heterogeneous photocatalysis was first demonstrated almost a decade ago; however, for the most part, photocatalytic experimental set-ups utilise artificial light sources in the form of conventional UV lamps to initiate the desired photocatalytic transformations. A look at all sources of UV irradiation used in heterogeneous photocatalysis is taken with a focus on the growing importance of solid-state lighting devices such as UV LEDs. UV LEDs have higher external quantum efficiency and a lifetime of over 100,000 h; they are small in size and produce directional UV light which can be of the desired wavelength. In recent times, these UV LED sources have become widely applied in heterogeneous photocatalysis studies in the research literature and are fast becoming a viable alternative to conventional UV lamps.

Investigation of positioning of FBG sensors for smart monitoring of oil and gas subsea structures

Condition monitoring of offshore structures is an indispensable task in the oil and gas industry. Fibre Bragg Grating (FBG) is the key technology used down-hole in order to sense different physical parameters such as strain, vibration, etc. This paper investigates the effect of FBG sensor positions on its reflected signal, in order to optimise the sensor positioning plan in structural health monitoring of subsea structures. Theoretical and experimental study was carried out on FBG sensors, to evaluate its strain sensitivities with varying positions. In addition, micro-displacement based strain analysis of FBG was carried out using a cantilever setup, in order to identify the effects of tensile and compressive strain under various load conditions. Furthermore, the effect of different grating parameters on FBG sensing signal were also analyzed. Theoretical modeling and simulation of FBG was conducted in MATLAB using the coupled mode theory.

Rare Elements Electrochemistry: The Development of a Novel Electrochemical Sensor for the Rapid Detection of Europium in Environmental Samples Using Gold Electrode Modified with 2-pyridinol-1-oxide.

This work presents for the first time the electrochemical determination of europium using cyclic voltammetry at gold electrodes modified with 2-pyridinol-1-oxide. A well-defined oxidation peak was observed in cyclic voltammetry as a result of the oxidation of the europium at ∼1100 mV in phosphate buffer at pH 7.0. The peak current increased linearly with the increase of concentration of the europium over the range from 1 to 80 μM and detection limit (based on 3-sigma) and quantification were found to be 0.3 and 0.549 μM, respectively. The analytical utility of the developed protocol was evaluated by performing the detection of the europium in river water. Europium is also linear over the concentration range 10 to 150 μM. (I(p)/μA = 0.7239x + 108.19, R(2) = 0.9981 and n = 9) with a detection limit of 6.5 μM (based on 3-sigma). This simple and effective protocol exhibited good sensitivity, precision and reliability towards the detected analyte.

Development of dithizone based fibre optic evanescent wave sensor for heavy metal ion detection in aqueous environments

Detection of highly toxic heavy metal ions requires rapid, simple, sensitive and selective detection methods in the environment. Optical fibre based sensing facilitates the remote, continuous and in-situ detection approaches in the environment. Herein, we report the development of a dithizone based fibre optic sensor with a simple procedure to detect heavy metal ions in the aqueous environment using an evanescent wave sensing approach. The chromogenic ligand dithizone and its spectral specificity with metal ions has been elaborated in this work.

Design of optical fibre based highly sensitive acoustic sensor for underwater applications

Fibre optic sensing is a key technology for a variety of underwater sensing and monitoring applications. Fibre optic acoustic sensors are mainly based on interferometric detection approach where the acoustic pressure-induced phase shift of light has been used as sensing principle. Recently, fibre optic acoustic sensors based on speciality fibres like Photonic Crystal Fibre (PCF) were reported. However, interferometry based detection approaches amongst all these fibre optics sensors are intensity based and therefore susceptible to light power fluctuations and require a complex instrumentation related to signal detection. Besides, wavelength based detection approach using FBG (Fibre Bragg Grating) offers significant advantages over the conventional approach. FBG sensors were reported to have higher performance for underwater acoustic sensing applications. This paper reports a novel design of an underwater acoustic pressure sensor using a combination of PCF and FBG to provide high sensitivity. Theoretical investigations were carried out on the PCF-FBG sensor to study the effect of applied pressure and induced strain on the FBG inscribed in the core of PCF. Effect of light confinement in PCF was studied for different geometrical parameters and 4-ring PCF structure was reported. Further, sensitivity enhancement was proposed utilizing air hole structure of the PCF to enhance the impact of acoustic pressure on the induced strain in FBG.

Holographic interferometry for security and forensic applications

Security holograms having unique 3D images are one of the tools for enhancing the security for product and personnel authentication and anti-counterfeiting. Apart from the high technology that is required, the uniqueness of a 3D object presents a significant additional threshold for the counterfeiting of such security holograms. But, due to the development of 3D printing technology, the hurdles are disabled and allow the chances of counterfeiting. In order to overcome this, holographic interferometry is effectively utilized and the object is recorded twice before and after the state of random object change. At the time of reconstruction, two signal waves generated simultaneously interfere each other, resulting in a fringe modulation. This fringe modulation in 3D image hologram with respect to the random object change is exploited to generate a rigid and unique anticounterfeit feature. Though holographic interferometry techniques are being widely used for the non-destructive evaluation, the applicability of this technology for the security and forensic activity is less exploited. This paper describes our efforts to introduce holographic interferometry in 3D image holograms for security and forensic applications.

Pharmaceutical electrochemistry: The electrochemical detection of aspirin utilising screen printed graphene electrodes as sensors platforms

A sensitive electrochemical sensor was designed for acetyl salicylic acid detection using graphene modified Screen Printed Electrodes. The electrochemical response of the sensor with graphene was improved compared to Screen Printed Electrodes without graphene and displayed an excellent analytical performance for the detection of acetyl salicylic acid. The high acetyl salicylic acid loading capacity on the electrode surface and the outstanding electric conductivity of graphene were also discussed in this manuscript. When a range of different concentrations of acetyl salicylic acid from 0.1 to 100 μM into a pH 4 buffer solution (N defined as the sample size N = 9) were plotted against the oxidation peak a linear response was observed. The detection limit was found to be 0.09 μM based on (3-σ/slope). Screen Printed Graphene electrodes sensors methodology is shown to be useful for quantifying low levels of acetyl salicylic acid in a buffer solution as well as in biological matrixes such as human oral fluid. A linear response was obtained over a range of concentrations from 10 to 150 μM into a human oral fluid solution (N = 10) giving a detection limit of 8.7 μM.