Subramaniam Neelamani

Bio: Subramaniam Neelamani is an academic researcher from Kuwait Institute for Scientific Research. The author has contributed to research in topics: Wave height & Reflection (physics). The author has an hindex of 21, co-authored 84 publications receiving 1051 citations. Previous affiliations of Subramaniam Neelamani include Indian Institute of Technology Madras & Braunschweig University of Technology.

Assessment of the levels of coastal marine pollution of Chennai city, Southern India

Abstract: The levels of hydrological pollution of Chennai coastal zone in the southeastern part of India have been increased in the recent years by an uncontrolled disposal of wastewater and pollutants due to human activities. This study gave a special emphasis on the determination of the levels of pollution, the identification of vulnerable zones and providing some probable remedial measures for severely impacted coastal zone of Chennai city. During the period from September to November 2002, sampling was carried out along the shore in two traverses running in the seaside (surf zone) and landside (coastal aquifer). When sampling efforts took place the middle of the above period experienced a monsoonal storm over Chennai coast that significantly influenced large variations in the pollution level at both traverses in seaside and landside. Analysis of physical, chemical and biological parameter determinations indicated that the concentrations of dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), nutrients (nitrate, nitrite and phosphate), turbidity, maximum probable number (MPN) and chlorophyll a (Chl a) reached notably high levels at all sample locations before monsoonal storm prevailed over these areas during October 2002, which resulted in large fresh water input to the coastal system reducing the levels of pollution to some extent. Analysis of water samples collected during November apparently indicated that the concentrations of above parameters attained abnormal level and often exceeded the permissible limit of international standards. The concentrations of trace/toxic metals such as manganese, copper, nickel, lead, cadmium and cobalt also reached very high levels as a result of their sub-aqueous disposal to these areas, leading to further habitat and ecological destruction. On the other hand, analysis of groundwater samples collected from coastal aquifer for determination of certain chemical parameters such as Ca2+/Mg2+, Cl−/(CO2−3+HCO3-) and the ratio of total alkalinity (TA) and total hardness (TH) revealed that coastal groundwater appeared to be severely contaminated by saltwater intrusion as a result of overexploitation and enormous pressure imposed by monsoonal storm of October. Higher concentrations of toxic elements, for example, lead, nickel, cobalt and cadmium from the influence of industrial wastes and contaminated coastal waters, were also found to deteriorate the quality of coastal aquifer system. Based on detailed examination, four sites including Cuvum estuary, Adyar estuary, Kannikoil and Bharathiyar nagar are identified as highly venerable zones because of receiving a large quantity of municipal and industrial wastes. To reduce severe pollution levels in these areas it is therefore necessary to design and construct the submarine pipeline system to transport and disperse such a large quantity of waste materials to the deep open ocean areas.

Well-Aligned Graphene Oxide Nanosheets Decorated with Zinc Oxide Nanocrystals for High Performance Photocatalytic Application

Abstract: Graphene oxide (GO) nanosheets modified with zinc oxide nanocrystals were achieved by a green wet-chemical approach. As-obtained products were characterized by XRD, Raman spectra, XPS, HR-TEM, EDS, PL and Photocatalytic studies. XRD studies indicate that the GO nanosheet have the same crystal structure found in hexagonal form of ZnO. The enhanced Raman spectrum of 2D bands confirmed formation of single layer graphene oxides. The gradual photocatalytic reduction of the GO nanosheet in the GO:ZnO suspension of ethanol was studied by using X-ray photoelectron (XPS) spectroscopy. The nanoscale structures were observed and confirmed using high resolution transmission electron microscopy (HR-TEM). The evolution of the elemental composition, especially the various numbers of layers were determined from energy dispersive X-ray spectra (EDS). PL properties of GO:ZnO nanosheet were found to be dependent on the growth condition and the resultant morphology revealed that GO nanosheet were highly transparent in the visible region. The photocatalytic performance of GO:ZnO nanocomposites was performed under UV irradiation. Therefore, the ZnO nanocrystals in the GO:ZnO composite could be applied in gradual chemical reduction and consequently tuning the electrical conductivity of the graphene oxide nanosheet.

On the efficiency of wave energy caissons in array

Abstract: A detailed experimental investigation on the efficiency of the power absorption of Multi-resonant Oscillating Water Column (MOWC) wave energy caissons in an array is reported. Regular wave measurements were conducted on an 1:50 scale model of an array of Multiresonant Oscillating Water Column (MOWC) type free standing wave energy caissons using the images method. A range of hydrodynamic parameters, with a different damping of Oscillating Water Column (OWC) chamber and various centre to centre spacings (S) between the caissons in an array for a constant OWC width (b), were used, i.e., experiments were conducted for different S b ratios. It is found that, hydrodynamic efficiency of MOWC for power absorption increases with increased S b value up to 3, beyond which it reduces. About 60% efficiency can be achieved with a S b ratio of 3 which is considered as optimum spacing. The efficiency decreases with increase in wave steepness ( H L ), due to a greater blow up period for higher H L values than for lower H L values during which the pressure becomes atmospheric. The percentage energy reflection decreases with increasing relative water depth. The average energy reflection is found to be 30%. Further investigation is recommended in order to enhance the efficiency considering the structure geometry as well as the damping of the air chamber.

Wave interaction with T-type breakwaters

Abstract: The wave transmission, reflection and energy dissipation characteristics of partially submerged `T'-type breakwaters ( Fig 1 Download : Download high-res image (120KB) Download : Download full-size image Fig 1 Schematic view of the T-type breakwater ) were studied using physical models Regular and random waves, with wide ranges of wave heights and periods and a constant water depth were used Five different depths of immersions of the `T'-type breakwater were selected The coefficient of transmission, Kt, coefficient reflection, Kr, were obtained from the measurements and the coefficient of energy loss, Kl is calculated using the law of conservation of energy It is found that the coefficient of transmission generally reduces with increased wave steepness and increased relative water depth, d/L This breakwater is found to be effective closer to deep-water conditions Kt values less than 035 is obtained for both normal and high input wave energy levels, when the horizontal barrier of the T type breakwater is immersed to about 7% of the water depth This breakwater is also found to be very efficient in dissipating the incident wave energy to an extent of about 65% (ie Kl>08), especially for high input wave energy levels The wave climate in front of the breakwater is also measured and studied

Wave interaction with twin plate wave barrier

Abstract: The wave transmission and reflection characteristics and wave induced pressures on single surface plate and twin plate barriers were investigated experimentally for a wide range of wave heights and periods in regular and random waves. Seven different spacing between the plates were tested. It is found in general, hydrodynamically the twin plate is better than the single surface plate to reduce the wave transmission and increase the wave reflection. It is found that the transmission coefficient of twin plate reduced from 0.8 to 0.3 when the relative plate width is increased from 0.18 to 0.84. Transmission coefficient of twin plate barrier shows oscillating behavior, when relative plate width is increased due to blocking and pumping effect. The reflection coefficient increased from 0.25 to 0.65, when the relative width of the plate is increased from 0.18 to 0.84. The increase in spacing between the plates was also found to increase the reflection coefficient. The transmission coefficient, K t for 98% probability of non-exceedence was found to be minimum and is about 0.60 when the relative spacing between the plate is about 0.12, compared to K t =0.76 for single surface plate. The reflection coefficient for 98% probability of non-exceedence was found to exceed 0.66 for single surface plate, whereas it is 0.73 for twin plate with relative spacing of about 0.40. From the investigation with wide range of input parameters, it is found that the twin plate barrier needs to be designed for highest 98% pressure ratio of 2.0, which is equal to the static pressure induced by the design incident wave height.

Climate Change 2007: Impacts, Adaptation and Vulnerability.

Abstract: Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

Green synthesis of NiO nanoparticles using Aegle marmelos leaf extract for the evaluation of in-vitro cytotoxicity, antibacterial and photocatalytic properties.

Abstract: In the present study, we report the green synthesis of NiO nanoparticles using Aegle marmelos as a fuel and this method is ecofriendly and cost effective. The plant Aegle marmelos is used in the field of pharmaceuticals to cure diseases like chronic diarrhea, peptic ulcers and dysentery in India for nearly 5 centuries. The as-prepared nanoparticles were confirmed as pure face centered cubic phase and single crystalline in nature by XRD. The formation of agglomerated spherical nanoparticles was shown by HR-SEM and HR-TEM images. The particle size calculated from HR-SEM was in the range 8-10 nm and it matches with the average crystallite size calculated from the XRD pattern. NiO shows intense emission peaks at 363 and 412 nm in its PL spectra. The band gap of 3.5 eV is observed from DRS studies and the formation of pure NiO is confirmed by FT-IR spectra. The as-prepared NiO nanoparticles show super paramagnetic behavior, when magnetization studies are carried out. It is then evaluated for cytotoxic activity towards A549 cell culture, antibacterial activity and photocatalytic degradation (PCD) of 4‑chlorophenol (4‑CP), which is known as the endocrine disrupting chemical (EDC). From the results, it is found that the cell viability of A549 cells was effectively reduced and it showed better antibacterial activity towards gram positive bacterial strains. It is also proved to be an efficient and stable photocatalyst towards the degradation of 4‑CP.

Evaluation on the heterostructured CeO2/Y2O3 binary metal oxide nanocomposites for UV/Vis light induced photocatalytic degradation of Rhodamine - B dye for textile engineering application

Abstract: In the present study, we describe an effective synthetic strategy of pure and heterostructured CeO2/Y2O3 binary metal oxide nanostructures in distinct molar ratios (1:1; 1:2 & 2:1) in which sodium hydroxide act as a reducing agent under chemical precipitation assisted hydrothermal method (CPHM). Controlled shape and size of CeO2/Y2O3 hierarchical nanostructures was achieved by using cerium nitrate and yttrium nitrate as a precursor. Synthesized nanostructure was fully analyzed by various techniques to detect its crystalline nature such as size, morphology; purity & optical activity is followed by the evaluation of its photocatalytic activity in the degradation of RhB dye. The crystalline structure was examined by X-ray diffraction (XRD), shows the cubic phase for both metal oxides in synthesized systems and found to be an efficient catalyst to generate reactive oxygen species (ROS) in presence of UV/Visible light, which tends to degrade various polyaromatic organic dyes into small fractions. Among all the heterostructured CeO2/Y2O3 binary metal oxide nanostructures the Ce2/Y1 sample shows the formation of hierarchical nanorods with particle diameter in the range of 8–50 nm. Due to their hierarchical one-dimensional nanostructures and increased surface areas, the CeO2/Y2O3 hierarchical nanorods exhibit substantially higher photocatalytic performance than the pure CeO2 and other mixed nanostructures in the degradation of RhB synthetic dye.

Elucidation of photocatalysis, photoluminescence and antibacterial studies of ZnO thin films by spin coating method.

Abstract: The ZnO thin films have been prepared by spin coating followed by annealing at different temperatures like 300 °C, 350 °C, 400 °C, 450 °C, 500 °C & 550 °C and ZnO nanoparticles have been used for photocatalytic and antibacterial applications. The morphological investigation and phase analysis of synthesized thin films well characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Photoluminescence (PL), Transmission Electron Microscopy (TEM) and Raman studies. The luminescence peaks detected in the noticeable region between 350 nm to 550 nm for all synthesized nanosamples are associated to the existence of defects of oxygen sites. The luminescence emission bands are observed at 487 nm (blue emission), and 530 nm (green emission) at the RT. It is observed that there are no modification positions of PL peaks in all ZnO nanoparticles. In the current attempt, the synthesized ZnO particles have been used photocatalytic and antibacterial applications. The antibacterial activity of characterized samples was regulated using different concentrations of synthesized ZnO particles (100 μg/ml, 200 μg/ml, 300 μg/ml, 400 μg/ml, 500 μg/ml and 600 μg/ml) against gram positive and gram negative bacteria (S. pnemoniae, S. aureus, E. coli and E. hermannii) using agar well diffusion assay. The increase in concentration, decrease in zone of inhibition. The prepared ZnO morphologies showed photocatalytic activity under the sunlight enhancing the degradation rate of Rhodamine-B (RhB), which is one of the common water pollutant released by textile and paper industries.

Synthesis and characterization studies of NiO nanorods for enhancing solar cell efficiency using photon upconversion materials

Abstract: We report the effect of calcination on the structural and optical properties of nanocrystalline NiO nanoparticles were successfully synthesized by virtue of a single source precursor method at mild reaction conditions between nickel nitrate and sodium hydroxide. Composition, structure and morphology of the products were analyzed and characterized by X-ray powder diffraction (XRD). The ultra-violet visible (UV–vis) absorption peaks of NiO exhibited a large blue shift and the luminescent spectra had a strong and broad emission band centered at 328 nm. The intense band gap was also observed, with some spectral tuning, to give a range of absorption energies from 2.60 to 3.41 eV. The various functional groups present in the NiO nanorods were identified by FTIR analysis. High resolution transmission electron microscopy (HRTEM) and the chemical composition of the samples the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS) in detail. The electrochemical response of NiO proved that the nano-nickel has a high level of functionality due to its small size and higher electrochemical activity without any modifications. The above studies demonstrate the potential for the utilization of NiO nanoparticles as a promising material for opto-electronics applications.