Kugalur Shanmugam Ranjith

Facile construction of vertically aligned ZnO nanorod/PEDOT:PSS hybrid heterojunction-based ultraviolet light sensors: efficient performance and mechanism

UNLABELLED We demonstrate a simple, planar manufacturing process-compatible fabrication of highly efficient UV sensors based on a hybrid heterojunction of an array of vertically aligned ZnO nanorods (NRs) and PEDOT PSS. The ZnO NR array was grown by the solution growth process and the aspect ratio (length 1 to 4 μm, diameter ∼80 nm) of the rods was controlled by varying the growth time. UV sensors based on (i) naked ZnO NRs and (ii) ZnO NR/PEDOT:PSS heterojunctions were fabricated and tested. The UV sensitivity of bare ZnO NRs was found to increase with increasing aspect ratio of the NRs due to the increase in the photogenerated charge carriers as the fraction of material interacting with the light increases. Under 5 V bias, naked ZnO NR arrays showed a photocurrent of 8.84 × 10(-5) A, a responsivity of 0.538 A W(-1) and a sensitivity of 4.80 under UV (λ = 256 nm, 130 μW) illumination. ZnO NR/PEDOT:PSS hybrid heterojunctions showed diode-like behavior with a leakage current less than 2.54 × 10(-8) A at -5 V and forward turn-on voltage of 1.1 V. ZnO NR/polymer-based hybrid heterojunctions show a photocurrent of 6.74 × 10(-4) A, responsivity of 5.046 A W(-1) and excellent sensitivity of 37.65 under UV (λ = 256 nm, 130 μW) illumination. Compared with bare ZnO NR arrays, the ZnO NR/polymer heterojunction device shows responsivity enhanced by a factor of 10, sensitivity enhanced by a factor of 8 and faster rise and decay time. The enhanced performance may be due to effective charge separation guided by the built-in potential formed at the interface between ZnO NRs and PEDOT PSS.

Photocatalytic degradation of endocrine disruptor Bisphenol-A in the presence of prepared CexZn1-xO nanocomposites under irradiation of sunlight.

Photocatalytic degradation of Bisphenol A (BPA), a representative endocrine disruptor chemical, was carried out under irradiation of sunlight in the presence of CexZn1-xO nanophotocatalyst. Cerium (Ce) ions were successfully incorporated into the bulk lattice of ZnO by simple co-precipitation process. The CexZn1-xO composite nanostructures exhibited higher photocatalytic efficiency than pure ZnO in the degradation of BPA under sunlight irradiation and nearly complete mineralization of BPA was achieved. The degradation rate was strongly dependent on factors such as the size and structure of catalyst, doping material concentration, BPA concentration, catalyst load, irradiation time and pH levels. This work suggested that the CexZn1-xO assisted photocatalytic degradation is a versatile, economic, environmentally benign and efficient method for BPA removal in the aqueous environment.

Recent Progress on the Synthesis and Applications of Carbon Based Nanostructures

This article reviews the latest developments in the synthesis of Graphene, Carbon nanotubes and graphene/CNT based devices based on patents, patent applications and articles published in the last two years. A brief introduction about CNT and Graphene is presented, followed by the latest techniques and advanced processing for the large scale synthesis of Graphene and CNTs. Furthermore, a brief account of emerging devices based on applications of CNTs and graphene not limited to sensors, high speed electronics, energy harvesting and storage applications are presented.

Regeneration of an efficient, solar active hierarchical ZnO flower photocatalyst for repeatable usage: controlled desorption of poisoned species from active catalytic sites

To date, reusable properties of nano photocatalysts (PCs) have been investigated for five to ten consecutive cycles with a mild decrease in photocatalytic performance. Systematic investigation on the decrease in photocatalytic performance and regeneration of the nanocatalyst after repeatable usage have rarely been reported. Hierarchical forms of self-assembled zinc oxide (ZnO) with a flower-like structure have been successfully synthesized by an aqueous solution based precipitation and show visible photocatalytic degradation efficiency of 98% against methylene blue (MB) dye in 120 min under natural solar irradiation and visible irradiation. Reusable catalytic properties were studied for 50 consecutive cycles and the degradation efficiencies obtained were around 85.9, 61.4, 47.3, 31.6 and 21.3% in 120 min of photo irradiation for 10, 20, 30, 40 and 50 consecutive repeatable cycles, respectively. On increasing the number of cycles, the photocatalytic efficiency of the ZnO flowers decreased due to adsorption of hydrocarbon molecules on the active sites of the catalyst, a phenomenon termed as catalytic poisoning. Furthermore, we show that the photocatalytic performance of ZnO hierarchical flowers could be completely reverted by a simple chemical treatment for further repeatable usage by removing the hydrocarbon groups on the active sites of the surface of the nanocatalysts. Our results provide insights into the effective visible photocatalytic nature and controlled process which removes the poisoning effect and regenerates the catalytic properties.

Synthesis and Antibacterial Studies of Nano Structured Ag Thin Films

Silver thin film of 5 nm thicknesses was evaporated on glass and stainless steel substrates and annealed at 300°C for one hour. Then these samples were characterized by using X-ray diffraction method (XRD), Scanning Electron Microscopy (SEM), UV-VIS spectroscopy, and subjected to anti-microbial resistance test. XRD analysis showed as deposited silver thin film coated on glass substrate and stainless steel substrates have amorphous nature. The annealed Ag thin film coated on glass and stainless steel substrates showed crystallinity with silver phase and their crystalline size were in the range of 30-40 nm and 17 nm respectively. SEM image indicates that formation of silver nanoparticles with spherical morphology after annealing on the glass substrate. But there is no nanoparticles formation was observed on annealed steel substrates. The anti microbial resistance test was done against E.Coli and that microbial growth was observed after 24 and 48 hrs. The results displayed a microbial resistance after 24 hrs for annealed Ag thin film coated on glass substrate due the formation of silver nanoparticles.

Optimisation on the Growth and Alignment of ZnO Nanorods

Synthesis of aligned ZnO nanorods (NRs) is important for electronic and optoelectronic devices. In this work we demonstrate the growth of ZnO nanorods by co-precipitation method using zinc nitrate and hexamine precursors. The samples were characterized by X-ray diffraction analysis, Scanning electron microscopy and Raman spectroscopy. On introducing the seeded substrate into the growth solution, the seeds offer nucleation sites for one-dimensional growth of ZnO nanorods. ZnO nanorod arrays grown on the successive ionic layer adsorption and reaction (SILAR) seed layer found to be irregular and non-uniform due to the etching of the seed substrate by growth solution. However, dip-coated seed substrate yielded uniform growth of ZnO nanostructures. ZnO nanostructures with flower-like morphology were obtained for pH of 9. On reducing the pH of the growth solution the flower morphology transformed into rod-like morphology with rod diameter of 200nm. On reducing the pH to 3 the diameter of the nanorods is decreased to 20 to 25nm. On reducing the precursor concentration the faceted morphology of the nanorods changed into needle-like shape (with sharp tips) along with reduction in diameter (about 20nm). The growth of uniform and vertically aligned ZnO nanorods is observed in dip-coated seed substrate with 5 pH. The results indicate that the diameter of ZnO nanorod array could be controlled by varying the precursor concentration.

Morphology Dependent Photocatalytic Properties of ZnO Nanostructures

ZnO nanostructures of different morphology (Rods, spindles, stars, buds) were successfully synthesized by co‐precipitation method. The prepared ZnO nanostructures were systematically characterized by X‐ray diffraction, Scanning electron microscopy (SEM). XRD results show the prepared nanostructures were in the hexagonal wurtzite structure. The photocatalytic degradation of methylene blue (MB) in aqueous solution under UV‐irradiation was investigated with different ZnO nanostructures. The photocatalytic experiments reveal that spindle like nanostructures showed fast photocatalytic activity compared to the other rods, stars and buds like nanostructures.

Effect of samarium doping on structural, optical and magnetic properties of vertically aligned ZnO nanorod arrays

Abstract Samarium doped vertically aligned one dimensional ZnO nanorod (NR) arrays were grown by vapor phase transport (VPT) method through vapor solid (VS) growth process. Influence of different concentrations (0% to 8%) of Sm (all Sm contents in the paper are in mass fraction) on the ZnO NR arrays were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), Raman spectroscopy and vibrating sample magnetometry (VSM) techniques, respectively. X-ray diffraction studies revealed that the ZnO NR arrays were perfectly oriented along (002) crystallographic orientation with wurtzite crystal structure. Photoluminescence results showed an increase in oxygen vacancies due to increase in Sm doping. M-H curves revealed enhanced ferromagnetic behavior, and the magnetic moment values were 0.45, 0.363, 1.694, 3.613 and 2.197 emu/cm 3 for (0–8%) Sm doped ZnO NR arrays respectively. The curve revealed that paramagnetic behavior was observed for undoped ZnO NR arrays and on increasing the Sm dopant to 4%, paramagnetic switched to ferromagnetic behavior.

Facile construction of vertically aligned EuS-ZnO hybrid core shell nanorod arrays for visible light driven photocatalytic properties

We demonstrated the development of coupled semiconductor in the form of hybrid heterostructures for significant advancement in catalytic functional materials. In this article, we report the preparation of vertically aligned core shell ZnO-EuS nanorod photocatalyst arrays by a simple chemical solution process followed by sulfudation process. The XRD pattern confirmed formation of the hexagonal wurtzite structure of ZnO and cubic nature of the EuS. Cross sectional FESEM images show vertical rod array structure, and the size of the nanorods ranges from 80 to 120 nm. UV-Vis DRS spectra showed that the optical absorption of ZnO was significantly enhanced to the visible region by modification with EuS surfaces. TEM study confirmed that the surface of ZnO was drastically improved by the modification with EuS nanoparticle. The catalytic activity of EuS−ZnO core shell nanorod arrays were evaluated by the photodegradation of Methylene Blue (MB) dye under visible irradiation. The results revealed that the photocatalytic activity of EuS−ZnO was much higher than that of ZnO under natural sunlight. EuS−ZnO was found to be stable and reusable without appreciable loss of catalytic activity up to four consecutive cycles.

UV light sensing properties of Sm doped vertically aligned ZnO nanorod arrays

Samarium doped ZnO nanorods were grown on silicon substrate by using vapor phase transport method (VPT) with the growth temperature of 950°C. The synthesized nanorods were characterized by XRD, field emission scanning electron microscopy, Raman spectra, and photocurrent measurements. The XRD result revealed that Sm was successfully doped into lattice plane of hexagonal ZnO nanorods. The FESEM result confirms the pure ZnO has nanorod like morphology with an average diameter and length of 130nm and 10µm respectively. The above observation is supported by the Micro-Raman spectroscopy result. The photocurrent in the visible region has been significantly enhanced due to deposition of Sm on the surface of the ZnO nanorods. Sm acts as a visible sensitizer because of its lower band gap compared to ZnO.