Priyakshree Borthakur

Sunlight assisted degradation of dye molecules and reduction of toxic Cr(VI) in aqueous medium using magnetically recoverable Fe3O4/reduced graphene oxide nanocomposite

In view of the significant impact of magnetically recoverable catalysts in photocatalytic applications, Fe3O4/reduced graphene oxide (rGO) nanocomposite photocatalyst was synthesized by adopting an eco-friendly solution chemistry approach and has been characterized by high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL) spectroscopy. Fe3O4/rGO nanocomposite is efficiently utilized towards photocatalytic degradation of carcinogenic and mutagenic cationic as well as anionic dye molecules namely methyl green (MG), methyl blue (MB) and rhodamine B (RhB) under direct sunlight irradiation. The Fe3O4/rGO nanocomposite also demonstrated excellent photocatalytic reduction of aqueous Cr(VI) solution to nontoxic aqueous Cr(III) solution of more than 96% within 25 min under sunlight irradiation. Moreover, reusability of the magnetically recovered photocatalyst was studied efficiently up to 10 cycles in the degradation process. The catalyst was also characterized after the degradation of the dye molecule and the particle size of the Fe3O4 nanoparticles on the rGO sheets remained unchanged. The present investigation focuses on the importance of the use of Fe3O4/rGO nanocomposite towards photocatalytic degradation of waste water containing organic dye pollutants and toxic Cr(VI), as an easily recoverable and reusable photocatalyst with potential for many environmental remediation applications.

Hydrothermal assisted decoration of NiS 2 and CoS nanoparticles on the reduced graphene oxide nanosheets for sunlight driven photocatalytic degradation of azo dye: Effect of background electrolyte and surface charge

The semiconductor NiS2 nanoparticles with an average size of 10 ± 0.317 nm were successfully deposited on the reduced graphene oxide (rGO) sheets by simple hydrothermal method. The synthesized nanocomposite was characterized by various instrumental techniques like XRD, FTIR, FESEM, EDX, HRTEM, fluorescence spectrophotometer analysis. In this study we mainly focus on the determination of the surface potential values of NiS2-rGO and CoS-rGO nanocomposite under different experimental conditions and evaluated the photodegradation efficiency towards azo dye Congo Red (CR) molecule under natural sunlight irradiation. We found that the surface charge (zeta potential) of the both nanocomposite materials in presence of different inorganic ions salt solutions like NaCl, NaNO3, Na2SO4, MgCl2, CaCl2 etc. is varied based on the polarizability of the ions as well as pH of the suspension. Different inorganic ions present in the catalyst suspension can alter the surface charge of the catalyst by forming a double layer around the molecule and thus change the electrostatic interaction between the dye molecule and the catalyst surface which change the degradation efficiency of the photocatalyst towards CR molecule. The photocatalytic efficiency of NiS2-rGO and CoS-rGO nanocomposite towards CR degradation was found to be 97.03% and 88.03% in 40 min, respectively under same experimental condition whereas NiS2 and CoS nanoparticles without support exhibited photodegradation efficiency 57.89% and 50.52%, respectively. The observed improved photocatalytic activity of the metal sulfide-rGO nanocomposite results the presence of synergistic effect between the metal sulfide nanoparticles and the rGO sheets of the photocatalysts which inhibits the recombination rate of photogenerated electrons and holes. The mechanism of the degradation process was investigated by photoluminescence study in presence of terephthalic acid and also quenching experiment in presence of isopropanol and benzoquinone. The photocatalyst was characterized after degradation process and found that the crystallinity and the morphology of the nanocomposite remained unchanged. The ion-chromatography experiment confirms the formation of non-toxic products after degradation. The present study focuses on the importance of the use of metal sulphide-rGO nanocomposite towards environment remediation process and study of the influence of inorganic salts on the surface charge of the photocatalyst as well as on the degradation process.

Nanoemulsion: preparation and its application in food industry

Nanoemulsions with droplet size less than 100 nm are finding numerous applications in the field of pharmaceuticals, cosmetics, and food industries. Owing to their small droplet size they are transparent and kinetically stable systems. Specifically in food industries nanoemulsions are used in food encapsulation, food processing, protection, storage, and as a delivery system of bioactive lipophilic components. Nanoemulsions display enhanced activity in contrast to other conventional emulsions. They are prepared by high-energy methods and low-energy methods and then characterized by dynamic light scattering (DLS), zeta potential, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), small angle X-ray scattering (SAXS), transmission electron microscope (TEM), scanning electron microscope (SEM), small-angle neutron scattering (SANS), nuclear magnetic resonance (NMR), conductivity, viscosity, atomic force microscopy (AFM) techniques, and so on. In this chapter, we focus on the synthesis, characterization, and applications of nanoemulsion in food industries.

Metal free MoS2 2D sheets as a peroxidase enzyme and visible-light-induced photocatalyst towards detection and reduction of Cr(VI) ions

Two-dimensional molybdenum disulphide (MoS2) sheets were prepared by using simple thermal decomposition method. The synthesized sheets were characterized by different analytical tools including FTIR, XRD, XPS, Raman spectroscopy, HRTEM and FESEM analyses. The synthesized sheets exhibited outstanding peroxidase mimicking activity towards the peroxidase oxidation of chromogenic probe molecule 3,3′,5,5′-tetramethyl benzidine (TMB), producing a blue coloured solution of 3,3′,5,5′-tetramethylbenzidine diimine (TMBDI) in an acidic medium (pH 4). Based on this peroxidase mimicking activity it was utilized for colorimetric determination of toxic Cr(VI) ions present in aqueous medium. The MoS2 sheets showed excellent sensitivity towards Cr(VI) detection with a lower detection limit of 40.09 nM. Moreover, these 2D sheets also acted as an excellent photocatalyst because of their direct band gap of 1.90 eV, and were used for the reduction of inorganic toxic pollutant Cr(VI) ions to environmentally benign Cr(III) ions under the irradiation of visible light. MoS2 sheets showed 98% photo reduction efficiency towards Cr(VI) ions within 20 min. Furthermore, the synthesized MoS2 sheets were successfully recycled up to five times without significant decrease of their photocatalytic reduction efficiency towards Cr(VI) ions. The present study demonstrates that metal free MoS2 sheets prepared by a simple solid state synthesis approach provide a simple, cost-effective and easy method for determination and removal of toxic Cr(VI) ions in aqueous medium.