Biogenic Synthesis of Carboxymethyl Cashew Gum Modified Gold Nanoparticles and its Sensitive and Selective Calorimetric Detection of Hg2+ Ions and Catalytic Reduction of Methyl Red.

In the present study, we have successfully synthesized and characterized carboxy methyl cashew gum modified gold nanoparticles (CMCG-AuNPs) via a microwave-assisted method and used as a calorimetric probe for selective detection of Hg2+ ions as well as catalytic reduction of methyl red in an aqueous medium. The effect of different parameters including concentration and irradiation time on the formation of CMCG-AuNPs was also investigated. The presence of strong surface plasmon resonance (SPR) peak in the visible region indicated the formation of AuNPs. The characterization techniques were identified the interaction between the CMCG and AuNPs with estimation of size and morphology. The face centred cubic (FCC) crystal structure was identified by using XRD and supporting with SAED pattern. TEM images of CMCG-AuNPs were exhibited as polydispersed with spherical in shape and the average particle size was 12 ± 3 nm. The synthesized CMCG-AuNPs were utilized to sensing Hg2+ ions in an aqueous medium, the presence of Hg2+ ions selectively among other metal ions, the CMCG-AuNPs were aggregated by changing the color from wine red to purple blue accompanied by change in the position of SPR peak and intensity. It was observed as a strong linear relationship based on the change in intensity, the limit of detection was determined to be 0.277 nM. The catalytic activity was also examined for the reduction of methyl red (MR) in the presence of CMCG-AuNPs was completed within 12 min and followed pseudo-first order kinetics with a rate constant of 0.261 min-1. From the obtained results, the synthesized CMCG-AuNPs were useful for detection of heavy metal ions as well as toxic pollutants degradation via a green method, and utilized sensing, environmental, and biomedical application in future.

Microwave-assisted fabrication of g-C3N4 nanosheets sustained Bi2S3 heterojunction composites for the catalytic reduction of 4-nitrophenol.

In this work, we report a stable g-C3N4, Bi2S3, and g-C3N4/Bi2S3 composite catalysts were prepared via a facile one-pot microwave-assisted method and characterized. The orthorhombic phase and nearly spherical shape of the particles with an average diameter of 5-25 nm of g-C3N4/Bi2S3 composite were obtained from XRD and TEM. The composite also exhibits a high surface area (32.15 m2/g), which may provide convenient transportation and diffusion for substrate molecule. The optical studies were displayed the g-C3N4/Bi2S3 composite has a sharp absorption band in the visible region, higher charge separation, and reduced recombination rate. These results show that the Bi2S3 NPs have good crystallinity and are uniformly deposited on the surface of the g-C3N4 sheet. The catalytic performance of the g-C3N4/Bi2S3 composite for the reduction of 4-NP to 4-AP was exhibited approximately 100%, which is 1.48 and 2.34 times higher than the Bi2S3 and g-C3N4 catalysts, respectively. The pseudo-first-order rate constant was estimated as 1.648 × 10 -2 min-1 for the reduction of 4-NP using g-C3N4/Bi2S3 composite in 1 h reaction time. The effect of catalyst dosage (0-30 mg) was also investigated for the reduction of 4-NP using g-C3N4/Bi2S3 composite catalyst. Moreover, the reusability of the g-C3N4/Bi2S3 composite was exhibited a better reduction of the 4-NP even after 5 cycles and it was found that 8% reduction in the initial reduction rate. The obtained results from this study show that g-C3N4/Bi2S3 composite has the potential efficiency and stability to make it an ideal catalyst for the reduction of toxic effluents and wastewater treatment.

Ternary semiconductor ZnxAg1-xS nanocomposites for efficient photocatalytic degradation of organophosphorus pesticides.

The construction of ternary semiconductor nanostructures has attracted much attention in photocatalysis by virtue of their tunable elemental composition and band structure. Here, ternary semiconductor ZnxAg1-xS (0 ≤ x ≤ 1) composites were successfully prepared by a simple and low-cost hydrothermal method without using any surfactant. Combined analyses using XRD, N2 sorption, SEM, TEM and UV-vis DRS revealed that the ternary composite semiconductor materials exhibited well-developed crystalline frameworks, large surface areas of 15-70 m2 g-1, sizes of 10-30 nm, and outstanding UV light absorption properties. Data from XRD and TEM indicate that photocatalysis might contribute to the formation of the strong interfacial interaction between ZnS and Ag2S nanoparticles. The photocatalytic activities were investigated via the degradation of organophosphorus pesticides, including malathion (MLT), monocrotophos (MCP) and chlorpyrifos (CPS), using the ZnxAg1-xS composites under UV light irradiation. The toxicity of MLT, MCP, and CPS was reduced by photocatalysis and photolysis; however, photocatalysis had a greater impact. Superior photocatalytic performance was exhibited by the Zn0.5Ag0.5S catalyst owing to its large surface area and the presence of Ag0 with improved charge transfer in comparison with that of bare ZnS and Ag2S. Assays of stability and reusability indicated that the Zn0.5Ag0.5S composite retained more than 85% of its activity after five cycles of use. On the basis of the results, a possible photocatalytic mechanism of the prepared samples was proposed. This study indicates a potential application of the ternary semiconductor materials in the efficient UV light-driven photocatalytic degradation of other pollutants that may cause environmental pollution.

Green Synthesis, Optical, Structural, Photocatalytic, Fluorescence Quenching and Degradation Studies of ZnS Nanoparticles.

The study describes a simple hydrothermal method for the synthesis of zinc sulfide nanoparticles (ZnS NPs) using bovine serum albumin (BSA). The synthesized NPs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), fluorescence, UV-visible diffuse reflectance spectra (DRS) and zeta potential techniques. The morphologies and sizes were characterized by SEM and TEM. The size of ZnS NPs was observed with an effective diameter size of 20 nm. The photocatalytic activity of ZnS NPs was evaluated by the degradation of rhodamine B (RB) dye under sunlight irradiation. The degradation reaction follows the pseudo-first order kinetics. In addition, the fluorescence quenching and binding of ZnS NPs with crystal violet (CV) molecules have been studied. The binding constant (Ka) between ZnS NPs and CV is calculated using modified Stern-Volmer equation. The photocatalytic degradation and kinetics of CV dye by ZnS NPs in the presence of UV light has been investigated using spectrofluorometer.

Green synthesis, characterization, photocatalytic, fluorescence and antimicrobial activities of Cochlospermum gossypium capped Ag2S nanoparticles.

The study describes a simple and green method for the synthesis of silver sulfide nanoparticles (Ag2S NPs) using gum kondagogu (Cochlospermum gossypium) (GK). The synthesized NPs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), fluorescence, UV-vis absorption, zeta potential and thermogravimetric analysis (TGA) techniques. The optical properties and quantum confinement effect of the products were confirmed by means of spectroscopic measurements. The morphologies and sizes were characterized by SEM and TEM. The Ag2S NPs were spherical in shape with an effective diameter size of 25 nm. The photocatalytic property of Ag2S NPs was evaluated by the degradation of fluorescein (FL) dye under solar light. The effect of Ag2SNPs on the photocatalytic degradation of FL dye and influence of other parameters such as Ag2S loading, H2O2, temperature and under solar light irradiation was also evaluated. The degradation reaction follows the pseudo-first order kinetics. The apparent reaction rate was used to calculate the apparent activation energy (Ea=13.95 kJ/mol) of the degradation process. The activation thermodynamic parameters (ΔG*, ΔH* and ΔS*) were obtained from variable temperature kinetic studies. The interaction between Ag2S NPs and bovine serum albumin (BSA) was studied by using fluorescence spectroscopic measurements. The synthesized Ag2S NPs were showing good antimicrobial activity.

Efficient pH dependent drug delivery to target cancer cells by gold nanoparticles capped with carboxymethyl chitosan.

Doxorubicin (DOX) was immobilized on gold nanoparticles (AuNPs) capped with carboxymethyl chitosan (CMC) for effective delivery to cancer cells. The carboxylic group of carboxymethyl chitosan interacts with the amino group of the doxorubicin (DOX) forming stable, non-covalent interactions on the surface of AuNPs. The carboxylic group ionizes at acidic pH, thereby releasing the drug effectively at acidic pH suitable to target cancer cells. The DOX loaded gold nanoparticles were effectively absorbed by cervical cancer cells compared to free DOX and their uptake was further increased at acidic conditions induced by nigericin, an ionophore that causes intracellular acidification. These results suggest that DOX loaded AuNPs with pH-triggered drug releasing properties is a novel nanotheraputic approach to overcome drug resistance in cancer.