Solar reduced graphene oxide decorated with manganese dioxide nanostructures for brackish water desalination using asymmetric capacitive deionization.

Capacitive deionization (CDI) has emerged as a low-cost, reagent-free technique for the desalination of water. This technique is based on the immobilization of dissolved ions on the electrically charged electrodes, by the electrosorption phenomenon. The electrosorption of dissolved ions by using CDI is limited for feed water having a low concentration of salts. To address this problem, we employ an asymmetric capacitive deionization (Asy-CDI) architecture having solar reduced graphene oxide decorated with manganese dioxide nanostructures (SRGO-MnO2 composite). The Asy-CDI possesses an SRGO-MnO2 composite as the cathode and SRGO as the anode with an anion exchange membrane. The cathode formed from the SRGO-MnO2 composite serves the purpose of immobilization of cations, whereas the anode formed from SRGO is responsible for anion removal. The crystal structure, chemical composition and morphology of the as-synthesized SRGO-MnO2 composite electrode materials are characterized by several techniques, confirming that the surface of SRGO is successfully loaded with α-MnO2 nanostructures. The electrochemical characterization reveals a high specific capacitance of the as-synthesized SRGO-MnO2 composite (419.9 F g-1) at 100 mV s-1. The Asy-CDI provides a higher salt adsorption capacity (40.2 mg g-1) compared to Sy-CDI (28.3 mg g-1) with feed water containing a salt concentration of 2000 mg L-1. These results indicate that the Asy-CDI may be employed as an efficient technique for the desalination of high concentration salt water.

Overlapping large polaron tunnelling in lanthanum silicate oxyapatite.

Amongst the various fast ion conductors, lanthanum excess lanthanum silicate oxyapatite (La10-α(SiO4)6O2+δ) has shown higher oxide ion conductivity with lower activation energy. On the other hand, the activation energy increases with La vacancies (La at 4f site). In the present work, La site is altered with Ca to form (La1-xCax)9.67(SiO4)6O2+δ(x=0.0,0.05,0.10and 0.15) with minimum oxygen non-stoichiometry and studied the hopping/tunnelling mechanism with the Ca substitution. The elemental content obtained from Rietveld refinement of the x-ray diffractograms suggests La deficiency with minimum oxygen deficiency. Further, XPS and TGA studies confirm the formation of La deficient samples. Temperature and frequency dependent ac conductivity in the temperature range (548-973 K) suggests that the conduction takes place via overlapping large polaron tunnelling. Further, the tunnelling distance and polaron radii as a function of temperature and frequency are observed to be altered with Ca and affecting the ion conducting channel through the elongation of La(6 h) triangles. Our study suggests the phononic contribution play a pivotal role in ionic transport.

Recent progress in materials and architectures for capacitive deionization: A comprehensive review.

Capacitive deionization is an emerging and rapidly developing electrochemical technique for water desalination across the globe with exponential growth in publications. There are various architectures and materials being explored to obtain utmost electrosorption performance. The symmetric architectures consist of the same material on both electrodes, while asymmetric architectures have electrodes loaded with different materials. Asymmetric architectures possess higher electrosorption performance as compared with that of symmetric architectures owing to the inclusion of either faradaic materials, redox-active electrolytes, or ion specific pre-intercalation material. With the materials perspective, faradaic materials have higher electrosorption performance than carbon-based materials owing to the occurrence of faradaic reactions for electrosorption. Moreover, the architecture and material may be tailored in order to obtain desired selectivity of the target component and heavy metal present in feed water. In this review, we describe recent developments in architectures and materials for capacitive deionization and summarize the characteristics and salt removal performances. Further, we discuss recently reported architectures and materials for the removal of heavy metals and radioactive materials. The factors that affect the electrosorption performance including the synthesis procedure for electrode materials, incorporation of additives, operational modes, and organic foulants are further illustrated. This review concludes with several perspectives to provide directions for further development in the subject of capacitive deionization. PRACTITIONER POINTS: Capacitive deionization (CDI) is a rapidly developing electrochemical water desalination technique with exponential growth in publications. Faradaic materials have higher salt removal capacity (SAC) because of reversible redox reactions or ion-intercalation processes. Combination of CDI with other techniques exhibits improved selectivity and removal of heavy metals. Operational parameters and materials properties affect SAC. In future, comprehensive experimentation is needed to have better understanding of the performance of CDI architectures and materials.

Valorization of mutant Bacillus licheniformis M09 supernatant for green synthesis of silver nanoparticles: photocatalytic dye degradation, antibacterial activity, and cytotoxicity.

The present study reports the optimization of a green method for the synthesis of silver nanoparticles (AgNPs) via reduction of Ag+ ions using cell-free supernatant of mutant Bacillus licheniformis M09. UV-Visible spectroscopy showing an absorption peak at ~ 430 nm confirmed the synthesis of AgNPs. Transmission electron microscope (TEM) analysis exhibited spherical AgNPs within the size range of 10-30 nm. Fourier transform infrared (FTIR) measurements assured the presence of effective functional molecules which could be responsible for stabilizing the AgNPs. X-ray diffraction (XRD) pattern verified the crystalline nature of AgNPs. Furthermore, the synthesized AgNPs showed an excellent photocatalytic degradation of methylene blue dye in less than 3 h under visible light proving their potential as a catalytic agent for bioremediation for next-generation dye degradation in effluent treatment. The AgNPs demonstrated antimicrobial activity against Gram-positive and Gram-negative foodborne pathogens which endorsed its suitability as agents to extend shelf-life in food packaging and food safety applications. The results also revealed a strong concentration-dependent cytotoxicity of AgNPs against human breast adenocarcinoma cells (MCF-7), while 15.07 µg/mL of IC50 was attained. The outcome suggests the possible application of these AgNPs in nanomedicine formulations. Thus, these findings propose promising ways for the valorization of the waste fermentation supernatant left after cell harvesting and desired metabolite extraction.

Functionalized single-walled carbon nanotube-based fuel cell benchmarked against US DOE 2017 technical targets.

Chemically modified single-walled carbon nanotubes (SWNTs) with varying degrees of functionalization were utilized for the fabrication of SWNT thin film catalyst support layers (CSLs) in polymer electrolyte membrane fuel cells (PEMFCs), which were suitable for benchmarking against the US DOE 2017 targets. Use of the optimum level of SWNT -COOH functionality allowed the construction of a prototype SWNT-based PEMFC with total Pt loading of 0.06 mg(Pt)/cm²--well below the value of 0.125 mg(Pt)/cm² set as the US DOE 2017 technical target for total Pt group metals (PGM) loading. This prototype PEMFC also approaches the technical target for the total Pt content per kW of power (<0.125 g(PGM)/kW) at cell potential 0.65 V: a value of 0.15 g(Pt)/kW was achieved at 80°C/22 psig testing conditions, which was further reduced to 0.12 g(Pt)/kW at 35 psig back pressure.

Development of Au nanoparticles dispersed carbon nanotube-based biosensor for the detection of paraoxon.

A disposable and sensitive biosensor has been fabricated for the detection of the organophosphorous (OP) compound paraoxon using an amperometric technique. For the measurements, gold nanoparticles dispersed on the outer surface of multiwalled carbon nanotubes (Au-MWNTs) has been used as the electrode material, as it possesses high electron transfer rates and provides large immobilization sites for the bioenzymes, which combines with the high electrocatalytic activity of MWNTs for thiocholine oxidation at low potential. Au-MWNTs have been synthesized by chemically reducing Au salt over functionalized MWNTs, and the same has been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution transmission electron microscopic (HRTEM) techniques. The ability of the Au-MWNTs nanocomposite-based biosensor has been demonstrated to reliably measure the concentration of paraoxon in the nanomolar range.

Carbon nanotube-polymer based nanocomposite as electrode material for the detection of paraoxon.

Biosensor based on the inhibition of enzymes has been used for the detection of organophosphorous compounds wherein amperometic method has been employed. Carbon nanotubes (CNT) has been grown over YNi3 alloy hydrides and purified for further use. The high surface area and the acidic sites created during the purification of CNT with oxidizing acids have been exploited for the adsorption and entrapment of the enzyme acetylcholine esterase. In the present work, conducting polymer polypyrrole has been uniformly coated over the CNT surface using chemical oxidative technique. The nanocomposite was characterized by scanning electron microscopy (SEM) and High resolution transmission electron microscopy (HRTEM). In the present report high catalytic activity of CNT towards the electroxidation of thiocholine has been utilized for the detection of organophosphorous compound paraoxon. Developed biosensor uses the principal of acetylcholinesterase inhibition by nerve agent and hence reduction in oxidation current of thiocholine for the detection of paraoxon. Synthesized PPY-MWNT nanocomposite has been used for the electrode preparation over GC electrode. Due to high porosity of polymer and high electrical conductivity of CNT, a detection level of 3 nM paraoxon could be achieved. The details of fabrication of the sensor and the dependence of the sensitivity have been discussed.

Development of MWNT based disposable biosensor on glassy carbon electrode for the detection of organophosphorus nerve agents.

The development of a disposable Acetylcholinesterase (AChE) based biosensor is described. Synthesis, purification and further functionalization with oxygen containing hydrophilic functional groups of Carbon nanotubes (CNTs) have been detailed. Biosensing activity of functionalized multi walled carbon nanotubes (MWNTs) towards the detection of Organo phosphorus (OP) compound, paraoxon, has been tested using Amperometric method. Functional groups on the surface of MWNTs creates favorable surface for enzyme immobilization and enhances the enzyme electrode interaction by increasing the electron transfer rate due to high electrical conductivity of the MWNTs. Inhibition of AChE by paraoxon is determined by the decrease in catalytic activity of AChE. This results in less production of enzymatic product thiocholine, which leads to reduction in the electroxidation current. The ability of MWNTs based sensor to reliably measure concentration in the range 7 to 0.5 nM has been demonstrated. The detection limit of biosensor has been found to be as low as 0.5 nM.