Green Synthesis of CdS and CdS/rGO Nanocomposites: Evaluation of Electrochemical, Antimicrobial, and Photocatalytic Properties.

The green approach has been employed for the synthesis of various types of nanomaterials including metal nanoparticles, metal oxides, and carbon-based nanomaterials. These processes involve natural sources that contain bioactive compounds that act as reducing, stabilizing, and capping agents for the formation and stabilization of nanomaterials. This study reports the green synthesis of CdS and CdS/rGO nanocomposites using Lactobacillus bacteria. The UV-visible spectrophotometer, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy spectra confirm the synthesis of the nanocomposite. The electrochemical characterization using cyclic voltammetry, differential pulse voltammetry, and EIS revealed that the CdS/rGO nanocomposites showed a higher electron transfer rate compared with CdS nanoparticles, indicating the potential of the nanocomposites for biosensing applications. The zone of inhibition revealed significant antimicrobial activity against Escherichia coli and Staphylococcus aureus for both CdS nanoparticles and CdS/rGO nanocomposites. Additionally, CdS/rGO nanoparticles exhibited high photocatalytic activity for the degradation of methylene blue dye. Overall, this study demonstrates that the synthesized CdS and CdS/rGO nanocomposites have good electrochemical properties, photocatalytic, and antimicrobial activity and, therefore, can be employed for various applications such as biosensing, photocatalysis, and antimicrobial activity.

Ternary nanocomposite-based smart sensor: Reduced graphene oxide/polydopamine/alanine nanocomposite for simultaneous electrochemical detection of Cd2+, Pb2+, Fe2+, and Cu2+ ions.

Heavy metal ion (HMI) sensors are the most sought commercial devices for environmental monitoring and food analysis research due to serious health concerns associated with HMI overdosage. Herein, we developed an effective electrochemical sensor for simultaneous detection of four HMI (Cd2+, Pb2+, Fe2+, and Cu2+) using a ternary nanocomposite of reduced graphene oxide functionalized with polydopamine and alanine (ALA/pDA/rGO). Comprehensive spectroscopic and microscopic characterizations were performed to ensure the formation of the ternary nanocomposite. The developed nanocomposite on glassy carbon electrode (GCE) yields >2-fold higher current than GO/GCE electrode with excellent electrochemical stability and charge transfer rate. Using DPV, various chemical and electrochemical parameters, such as supporting electrolyte, buffer pH, metal deposition time, and potential, were optimized to achieve highly sensitive detection of targeted HMI. For Cd2+, Pb2+, Fe2+, and Cu2+ sensing devised sensor exhibited detection limits of 1.46, 2.86, 50.23, and 17.95 ppb and sensitivity of 0.0929, 0.0744, 0.0051, and 0.0394 µA/ppb, respectively, with <6% interference. The sensor worked similarly well for real water samples with HMI. This study demonstrates a novel strategy for concurrently detecting and quantifying multiple HMI in water and soil using a smart ternary nanocomposite-based electrochemical sensor, which can also detect HMI in food samples.

Investigation of Li-rich manganese oxide spinel structures for electrochemical water oxidation catalysis.

The rapid development of efficient and cost-effective catalysts is essential for the oxygen evolution reaction. Herein, nanostructured spinels LiMn2O4, delithiated λ-MnO2, and Li4Mn5O12 have been synthesized at low temperatures and are investigated as electrocatalysts for alkaline water oxidation reactions. Among the nanostructured spinels, LiMn2O4, delithiated λ-MnO2, and Li4Mn5O12, the former spinel which is classical LiMn2O4 with 1/6th of the Mn replaced by Li outperforms for the OER that shows a current density of 5 mA cm-2 at a lowest overpotential of 430 mV and Tafel slope of 74 mV per decade. Electrochemical impedance studies revealed the least value of charge transfer resistance of the Li4Mn5O12 spinel and suggest fast reaction kinetics for the oxygen evolution reaction as compared to other spinels. The XPS and TEM of Li4Mn5O12, recorded after a 12-hour stability test for oxygen evolution activity, confirm that the oxidation state of Mn and the morphology of Li4Mn5O12 remain intact even after the electrocatalytic reaction, however, it undergoes amorphization. The higher activity of Li4Mn5O12 synthesized in the present work is attributed to the low temperature synthesis resulting in the formation of a nanostructured Li rich spinel with a high surface area, along with an increased percentage of ionic bonding and the presence of 3D Li diffusion channels. The role of Li was further supported by XPS studies that revealed a shift in Li 1s binding energy as well as quantitative reduction relative to Mn for Li4Mn5O12 after a long term test.