Sudarsan Neogi

Effective bacterial inactivation using low temperature radio frequency plasma

Staphylococcus aureus is one of the most common pathogens responsible for hospital-acquired infections. In this study, S. aureus was exposed to 13.56MHz radiofrequency (RF) plasma generated by two different gases namely nitrogen and nitrogen-oxygen mixture and their sterilization efficacies were compared. Nitrogen plasma had a significant effect on sterilization due to generation of ultraviolet (UV) radiation. However, the addition of 2% oxygen showed enhanced effect on the sterilization of bacteria through nitric oxide (NO) emission and various reactive species. The presence of these reactive species was confirmed by optical emission spectroscopy (OES). Scanning electron microscopy (SEM) analysis was carried out to study the morphological changes of bacteria after plasma treatment. From the SEM results, it was observed that the bacterial cells treated by N(2)-O(2) mixture plasma were severely damaged. As a result, a log(10) reduction factor of 6 was achieved using N(2)-O(2) plasma after 5min treatment with 100W RF power.

A model for multiphase (gas-water-oil) stratified flow in horizontal pipelines

A mechanistic model for gas-liquid-liquid systems has been developed. Given the superficial velocities of the constituent phases and their physical properties, and the pipe diameter the corresponding oil and water film thicknesses in three phase stratified flow can be predicted. Experimental data has been obtained for gas velocities up to 7 m/s. The model predictions agree well with the experimental data.

Inactivation Characteristics of Bacteria in Capacitively Coupled Argon Plasma

Plasma technology is being focused on the medical, food, and pharmaceutical fields for sterilization applications. The sterilizing effect of the 13.56-MHz radio-frequency (RF) plasma generated by using argon gas was studied using Staphylococcus aureus, one of the most common pathogens liable to hospital-acquired infections. The major focus of this paper was to perform a parametric study by varying the external-process parameters such as plasma treatment time, RF power, gas-flow rate, and pressure on the inactivation of S. aureus. The results were supported by optical emission spectroscopy and scanning electron microscopy studies.

Enhanced Cell Adhesion to Helium Plasma-Treated Polypropylene

Materials used for biomedical applications are required to have suitable surface properties since they depend more on the surface properties than on the bulk properties. Surface properties greatly influence the cell adhesion and its behavior either directly by guiding cell spreading or indirectly by controlling proteins adsorption and their structural rearrangement on the material. Modulation of physical and chemical properties of polymers by various treatments can render the substrates adhesive for cells in a culture. In the present study, polypropylene surface was modified using helium plasma to enhance cell adhesion to its surface. The experiments were run according to the central composite design of response surface methodology to optimize the process conditions. The effects of the process variables, namely, RF power, pressure, flowrate and treatment time on surface energy and percentage weight loss were studied through central composite design (CCD). A statistical model relating the process variables and the responses was developed. The improved hydrophilicity of polypropylene through helium plasma treatment was observed from its surface energy data. Changes in surface chemistry and surface morphology were studied by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Enhanced cell adhesion to polypropylene treated with helium plasma at the optimum conditions, obtained from the statistical design, was observed from cell adhesion test and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay with L929 mouse fibroblast cells.

Electrochemical performance of nitrogen and oxygen radio-frequency plasma induced functional groups on tri-layered reduced graphene oxide

Tri-layered reduced graphene oxide with better graphitization was synthesized and functioned using radio frequency N2 and O2 plasma. The layer numbers of reduced graphene oxide were determined by atomic force microscopy (AFM) and x-ray diffraction (XRD). The effect of plasma treatment on crystal structure, surface morphology and chemical composition were studied from XRD, transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), Fourier transforms infrared spectroscopy (FTIR) and Raman spectroscopy. The chemical species present in N2/O2 plasma during functionalization of tri-layered reduced graphene oxide was analyzed by optical emission spectroscopy. Tri-layered reduced graphene oxide and functioned tri-layered reduced graphene oxide exhibits higher electrochemical performance towards ferrocyanide redox reaction than glassy carbon and platinum electrode with much decrease in overpotential. This indicates that tri-layered reduced graphene oxide and N2/O2 functionalized tri-layered reduced graphene oxide are promising working electrodes in the application of electrochemical based biosensor.

Investigation on Argon–Oxygen Plasma Induced Blood Compatibility of Polycarbonate and Polypropylene

Surface properties of polycarbonate and polypropylene were modified using low pressure radiofrequency argon–oxygen mixture plasma in order to increase their wettability and make them useful for biomedical applications. The effects of process variables on wettability and weight loss were studied statistically using response surface methodology. Increased surface energies were observed for both argon–oxygen plasma treated polycarbonate and polypropylene. Formation of aldehyde and hydroxyl groups on polycarbonate and hydroxyl group on polypropylene were the surface chemistry changes observed by means of Fourier transform infrared spectroscopy. Qualitative analysis of surface morphology was performed through scanning electron microscopy. A statistical model was developed relating the process variables with the responses: surface energy and percentage weight loss. The obtained statistical models were optimized to maximize the surface energy and minimize the percentage weight loss. Blood compatibility of the polymers was tested for control sample and polymers treated with argon–oxygen plasma at optimized conditions by measuring the partial thromboplastin time. Increased partial thromboplastin time (PTT) was observed for both polycarbonate (144 s) and polypropylene (149 s) after plasma treatment compared to both control samples (128 s).

Studies on the Treatment of Rice Mill Effluent by Electrocoagulation

Rice mill effluent contains high concentration of organic and inorganic substances leading to significant source of pollution. The effluent has high Biological oxygen demand (BOD), Chemical oxygen demand (COD), and Total Dissolved solid (TDS). The major advantage of electrocoagulation is that it avoids the usage of any chemicals and so there is no need for neutralizing agents. The effective performance of this technique in the treatment of rice mill wastewater has been investigated using a combination of aluminum and iron electrodes. After the treatment, BOD, COD, and dissolved solids were sufficiently reduced. In addition, it was found that an increase in the current density enhanced the speed of the treatment significantly and the Fe-Fe electrode combination gave the highest removal efficiency.

Helium Plasma Treatment to Improve Biocompatibility and Blood Compatibility of Polycarbonate

Radiofrequency discharge of helium gas at low pressure was employed to modify surface properties of polycarbonate. The effects of process parameters on wettability and plasma etching were determined by monitoring surface energy and weight loss, respectively. Quadratic equations for surface energy and weight loss, in terms of process variables, namely power, pressure, flowrate and treatment time were developed. Multiple response optimization was performed using central composite design (CCD) of response surface methodology (RSM) to maximize the surface energy and minimize the weight loss. Helium plasma treated polycarbonate resulted in increased hydrophilicity. From optical emission spectroscopic studies helium was identified as excited and metastable atom and ions which caused surface chemistry and morphology changes. Enhanced biocompatibility in terms of increased cell adhesion and proliferation was observed for all plasma treatment conditions. Confluent cell growth was observed with helium plasma treated polycarbonate. Both reduced platelet adhesion and increased partial thromboplastin time (increased to 204 s from 128 s corresponding to untreated polycarbonate) confirm the improved blood compatibility of plasma treated polycarbonate.

Synthesis of potential biosorbent from used stevia leaves and its application for malachite green removal from aqueous solution: kinetics, isotherm and regeneration studies

To develop a highly efficient, low-cost adsorbent from waste materials, powdered activated carbon (AC) was synthesized from used stevia leaves post the extraction of the glycosides used for producing a natural sweetener. The modification of the chemical characteristics of the biosorbent surface was achieved by impregnating it with sodium hydroxide (NaOH) at two different weight ratios. The AC biosorbent was applied for the removal of hazardous dye malachite green from an aqueous solution and the effects of the key operating parameters, such as initial dye concentration, agitation time, adsorbent dosage, solution pH, and the presence of electrolyte on the dye removal efficiency, were analyzed. The adsorption data were fitted to different isotherm and kinetic models to predict the adsorption mechanism. The Freundlich isotherm model showed the best fit to the adsorption equilibrium data and the adsorption kinetics followed a pseudo-second order model. A thermodynamic study was carried out and the data showed the endothermic and non-spontaneous nature of the process in the studied temperature range. The high adsorption efficiency shown after the regeneration studies indicated the high potential for the adsorbent to be used as a highly efficient, low-cost biosorbent.

Enhancement of Microwave Absorption Properties of Epoxy by Sol–Gel-Synthesised ZnO Nanoparticles

Abstract The microwave absorption property of epoxy resins is generally poor, which can be improved by introducing fillers such as carbon nanotubes and metal oxide nanoparticles (NPs) having good microwave absorption characteristics. In this paper, the microwave absorption properties of epoxy-ZnO nanocomposites have been studied. The ZnO NPs were synthesised using the sol–gel technique and characterised for size, shape and composition. It was observed that the NPs had a polycrystalline structure and an average particle size of 27.5 nm. The synthesised NPs were incorporated into the epoxy resin at 1% and 2% loading using a closed mould technique. The flexural strength of the composites was examined using Universal Testing Machine and the glass transition temperature was measured using differential scanning calorimetry. It was seen that the flexural modulus increased by around 6% and 11% for 1% and 2% ZnO loading. The microwave absorbance of pure and ZnO-filled epoxy was tested using a Network Analyzer and it was found that the microwave absorbance is dependent on the frequency and nanoparticle loading and it increased with the increase in ZnO loading.