A green synthesis of polyvinylpyrrolidone stabilized platinum nanoparticles (PtNPs) has been done by microwave irradiation in the presence of glucose. The formation process of the PtNPs is pursued by UV-visible spectroscopy. The morphology of the PtNPs was characterized by transmission electron microscopy and X-ray diffraction techniques. Catalytic activity of the above PtNPs has been substantiated through photodecolorization of aqueous methyl violet solution.

In this work, the removal of methyl orange (MO) dye by adsorption on silver nanoparticles (AgNPs) coated activated carbon (AC) has been studied. The effect of various process parameters has been investigated by the column adsorption technique. Equilibrium adsorption data of MO were carried out at room temperature. Using AgNPs-coated AC, 72.5 % of MO was removed, whereas only 50.0 % when using AC after reacting for 16 h with an initial MO concentration of 2 mg/L (pH = 7). The equilibrium time is independent of the initial dye concentration and the percentage removal of MO increased with increase in contact time. The adsorption data were analyzed using adsorption isotherm. The characteristic parameters for isotherm and related correlation coefficients were determined from graphs of their linear equations. Kinetic studies showed that the adsorption of MO followed pseudosecond-order kinetics. AgNPs-coated AC is found to be suitable adsorbent for the adsorption of MO. Desorption studies were made to elucidate recovery of the adsorbate and adsorbent for the economic competitiveness of the removal system. The AgNPs-coated AC was successfully recycled for 10 successive adsorption-desorption cycles indicating its high reusability.

Benzo-18-crown-6 is employed to work as both reducing and stabilizing reagent in the reaction for synthesis of silver nanoparticles. Silver nanoparticles are analyzed using transmission electron microscope and UV-visible spectroscopic technique. The silver nanoparticles prepared in this way are uniform and stable, which can be stored at refrigerator for 5 months. Appearance of surface plasmon band at 420 nm indicated the formation of silver nanoparticles. Highly monodispersed stable silver nanoparticles were obtained within 3 min of microwave irradiation. Through transmission electron microscopy, silver nanoparticles were observed to be spherical.

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The removal of phenolic compounds, i.e., o-cresol, m-cresol, and p-cresol from aqueous solution have been evaluated employing activated carbon (AC) coated with polymer supported iron nanoparticles (FeNPs). The synthesized FeNPs were characterized by scanning electron microscope and X-ray diffraction analysis. High correlation coefficient values indicated that the adsorption of phenolic compounds onto AC coated with polyvinylpyrrolidon (PVP) supported FeNPs obey Freundlich and Langmuir adsorption isotherms. Higher Freundlich and Langmuir constant values for AC coated with PVP supported FeNPs indicated its greater efficiency than AC. The adsorption data are well represented by both the Freundlich and Langmuir isotherms, indicating favourable adsorption of cresols by the adsorbents. Cresols were effectively removed (90 %) by adsorption process from aqueous solution using AC coated with FeNPs. The percentage removal of above phenolic compounds was studied under varying experimental conditions such as pH, temperature, adsorbent dosage, and contact time. The adsorption of phenolic compounds is quite sensitive to pH of the suspension and optimum uptake value was found at pH 7.0. Temperature also has a favorable effect on adsorption when varied from 20 to 50°C. On the contrary, beyond 30°C, a decrease in the adsorption was noticed.