Investigation of electrical transport properties in solution-processed Bi2Se3-AgMnOOH nanocomposite

In this paper, we report the fundamental electrical transport properties measured in Bi₂Se₃-AgMnOOH nanocomposite disc, which is prepared for the first time by convenient low temperature solution-phase chemistry in conjunction with redox-mediated methodology. The comparative structural and morphological analyses for the nanocomposite with pristine Bi₂Se₃ are comprehensively investigated by different material characterization techniques. The results demonstrate the successful in situ composite fabrication between the Bi₂Se₃, Ag and γ-MnOOH components. Besides, the present work introduces a systematic approach for the examination of electrical transport properties in Ohmic and non-Ohmic regimes over a wide temperature range. The results from the room temperature transport measurement exhibited that the nanocomposite demonstrated non-linearity after a certain current I₀ (onset current), whereas Bi₂Se₃ was linear in the entire measured current range. An enhancement of the conductance was observed for Bi₂Se₃-AgMnOOH compared to the pure Bi₂Se₃ material, which is credited to the composite effect. The onset exponents x_T (DC conductance) and x_f (AC conductance) with phase-sensitive character demonstrate different values below and above 180 K separating two different phases with different conduction mechanisms. Also, flicker noise analysis established the correlation between the DC conductance in terms of Ohmic to non-Ohmic transition after the onset voltage V₀. This transition phenomenon from Ohmic to non-Ohmic behaviour is explained from the structural point of view of the nanocomposite. The present investigation highlights the importance of using the bottom-up solution-phase strategy for the synthesis of high quality Bi₂Se₃-based nanocomposites for transport studies and their possible future applications.

Cobalt-Doped Manganese Dioxide Hierarchical Nanostructures for Enhancing Pseudocapacitive Properties

Herein, overall improvement in the electrochemical performance of manganese dioxide is achieved through fine-tuning the microstructure of partially Co-doped manganese dioxide nanomaterial using facile hydrothermal method with precise control of preparative parameters. The structural investigation exhibits formation of a multiphase compound accompanied by controlled reflections of α-MnO₂ as well as γ-MnO₂ crystalline phases. The morphological examination manifests the presence of MnO₂ nanowires having a width of 70-80 nm and a length of several microns. The Co-doped manganese dioxide electrode displayed a particular capacitive behavior along with a rising order of capacitance concerning with increased cobalt ion concentration suitable for certain limits. The value of specific capacitance achieved by a 5% Co-doped manganese dioxide sample was 1050 F g^-1 at 0.5 A g^-1, which was nearly threefold greater than that achieved by a bare manganese dioxide electrode. Furthermore, Co-doped manganese dioxide nanocomposite electrode exhibits exceptional capacitance retention (92.7%) till 10,000 cycles. It shows the good cyclability as well as stability of the material. Furthermore, we have demonstrated the solid-state supercapacitor with good energy and power density.

Turning carbon-ZnMn2O4 powder in primary battery waste to be an effective active material for long cycling life supercapacitors: In situ gas analysis

A simple and chemical-free recycled carbon-ZnMn₂O₄ powder (composite) from the spent Zn-carbon batteries is proposed as an effective active material for the supercapacitor. This approach may amplify the economic and environmental benefits of the recycling process. We also synthesized the spherical MnO_x nanoparticles by the calcination followed by the chemical treatment. Recycled composite and the MnO_x nanoparticles were comprehensively characterized. Symmetrical supercapacitors with the composite and the MnO_x nanoparticles show specific capacitances of 118 F g^-1 and 88 F g^-1 at 0.1 A g^-1, respectively. Also, the supercapacitor with the composite offers a specific energy of 8.0Whkg^-1 at 0.1A g^-1 while 4.3Whkg^-1 is obtained for MnO_x nanoparticles. The stable cell potential limits of 1.4 V and 1.2 V were established for the supercapacitors of the composite and MnO_x nanoparticles with the capacitance retention of 83% and 96%, respectively at the end of 100,000 cycles at 2.5Ag^-1. Also, the excellent energy efficiencies of 80% and 72% with the coulombic efficiency of 100% are estimated for the supercapacitors of the composite and the MnO_x nanoparticles, respectively. Finally, in situ gas analysis of the symmetrical supercapacitors are carried out using the differential electrochemical mass spectrometry. The proposed approach may be more economical and the environmentally benign recycling of spent Zn-carbon battery for circular economy and sustainability.

Structural-Phase Catalytic Redox Reactions in Energy and Environmental Applications

The structure-property engineering of phase-based materials for redox-reactive energy conversion and environmental decontamination nanosystems, which are crucial for achieving feasible and sustainable energy and environment treatment technology, is discussed. An exhaustive overview of redox reaction processes, including electrocatalysis, photocatalysis, and photoelectrocatalysis, is given. Through examples of applications of these redox reactions, how structural phase engineering (SPE) strategies can influence the catalytic activity, selectivity, and stability is constructively reviewed and discussed. As observed, to date, much progress has been made in SPE to improve catalytic redox reactions. However, a number of highly intriguing, unresolved issues remain to be discussed, including solar photon-to-exciton conversion efficiency, exciton dissociation into active reductive/oxidative electrons/holes, dual- and multiphase junctions, selective adsorption/desorption, performance stability, sustainability, etc. To conclude, key challenges and prospects with SPE-assisted redox reaction systems are highlighted, where further development for the advanced engineering of phase-based materials will accelerate the sustainable (active, reliable, and scalable) production of valuable chemicals and energy, as well as facilitate environmental treatment.

Employment of ultrasonic irradiation for production of poly(vinyl pyrrolidone)/modified alpha manganese dioxide nanocomposites: Morphology, thermal and optical characterization

This work explains the production, morphology, and features of novel nanocomposite (NC) established on poly(vinyl pyrrolidone) (PVP) as polymer background and modified alpha manganese dioxide (α-MnO₂) nanorod (NR) asan efficient filler. At first, one-dimensional α-MnO₂ nanorods (NRs) were produced by a hydrothermal technique and then they were amended with stearic acid (SA) by a solvothermal process. In following, the NCs were made by adding different volumes of α-MnO₂-SA NR (1, 3 and 5wt%) in the PVP matrix through ultrasonic irradiation as a green, low-cost, fast, and useful technique. Structural and morphological descriptions confirm crystallinity of α-MnO₂-SA NRs and showed that NRs have been separately dispersed in PVP matrix with rod-like morphology and diameter of about 40-60nm. The use of modifier and ultrasonic waves is accountable for good homogeneities of NRs. Thermogravimetric analysis revealed that thermal permanency of the obtained NCs has grown with increasing the α-MnO₂-SA content. Also, the UV-vis absorption of NCs was enhanced with the incorporation of the modified α-MnO₂ NR in PVP matrix. The substantial perfections in NCs properties are associated to compatible intermolecular relations between the surface modifying groups of the α-MnO₂-SA and PVP chain.

Pseudocapacitive Coating for Effective Capacitive Deionization

Capacitive deionization (CDI) features a low-cost and energy-efficient desalination approach based on electrosorption of saline ions. To enhance the salt electrosorption capacity of CDI electrodes, we coat ion-selective pseudocapacitive layers (MnO₂ and Ag) onto porous carbon electrodes (activated carbon cloth) with only minimal use of a conductive additive and a polymer binder (<1 wt % in total). Optimized pseudocapacitive electrodes result in excellent single-electrode specific capacitance (>300 F/g) and great cell stability (70% retention after 500 cycles). A CDI cell out of these pseudocapacitive electrodes yields as high charge efficiency as 83% and a remarkable salt adsorption capacity up to 17.8 mg/g. Our finding of outstanding CDI performance of the pseudocapacitive electrodes with no use of costly ion-exchange membranes highlights the significant role of a pseudocapacitive layer in the electrosorption process.

Capturing Cd2+ ions from wastewater using PVA/α-MnO2–oleic acid nanocomposites

A poly(vinyl alcohol) nanocomposite containing α-MnO₂–oleic acid has been fabricated as an efficient adsorbent for capturing Cd²⁺ ions from aqueous solution.

Enhanced plasmon-driven photoelectrocatalytic methanol oxidation on Au decorated α-Fe2O3 nanotube arrays

Highly ordered, porous α-Fe₂O₃/Au nanotube arrays (NTAs) were successfully synthesized through a facile approach.

3,4-Diaminotoluene sensor development based on hydrothermally prepared MnCoxOy nanoparticles

A facile hydrothermal process was used to prepare MnCo_xO_y nanoparticles (NPs) in alkaline medium (pH~10.5) at room temperature. The NPs were characterized by Fourier-transform infrared spectroscopy (FTIR), ultraviolet visible spectroscopy (UV/vis), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and powder X-ray diffraction (XRD). A thin layer of NPs film as a chemical sensor was fabricated on a glassy carbon electrode (GCE) with the help of a conducting binder. The sensor was implemented successfully for the detection 3,4-DAT with reliable I-V approach at low potential. The sensor-features include good sensitivity (0.37 mAµmolL^-1cm^-2), low detection limit (LOD=0.26±0.01 pmolL^-1 at a signal to noise ratio of 3), low limit of quantification (LOQ=7.80±0.01 pmolL^-1), good reliability, good reproducibility, ease of integration, and long-term stability were investigated. The sensor response towards 3,4-DAT is linear in logarithmic scale over a large concentration range (1.0 pmolL^-1 to 1.0 µmolL^-1). This work is introduced a route for future sensitive sensor development based on MnCo_xO_y NPs by reliable I-V method for the detection of hazardous and carcinogenic toxins in environmental and health care fields.