Rapid and simple electrochemical detection of morphine on graphene-palladium-hybrid-modified glassy carbon electrode.

A hybrid of reduced graphene oxide-palladium (RGO-Pd) nano- to submicron-scale particles was simultaneously chemically prepared using microwave irradiation. The electrochemical investigation of the resulting hybrid was achieved using cyclic voltammetry and differential pulse voltammetry. RGO-Pd had a higher current response than unmodified RGO toward the oxidation of morphine. Several factors that can affect the electrochemical response were studied, including accumulation time and potential, Pd loading, scan rate, and pH of electrolyte. At the optimum conditions, the concentration of morphine was determined using differential pulse voltammetry in a linear range from 0.34 to 12 µmol L(-1) and from 14 to 100 µmol L(-1), with detection limits of 12.95 nmol L(-1) for the first range. The electrode had high sensitivity toward morphine oxidation in the presence of dopamine (DA) and of the interference compounds ascorbic acid (AA) and uric acid (UA). Electrochemical determination of morphine in a spiked urine sample was performed, and a low detection limit was obtained. Validation conditions including reproducibility, sensitivity, and recovery were evaluated successfully in the determination of morphine in diluted human urine.

Effect of Guest Solvents on the Ionic Conductivity and Electrochemical Performance of Metal-Organic Framework-Based Magnesium Semi-Solid Electrolytes.

Developing suitable electrolytes is crucial for the advancement of rechargeable magnesium batteries. Recently, metal-organic frameworks (MOFs) have shown a great interest in the field of solid electrolytes for metal ion batteries. However, the ionic conductivity as well as the electrolyte stability in the presence of Mg electrodes are shown to be strongly dependent on the guest solvent used to solvate Mg salts in MOFsSEs. Our measurements showed that full evacuation of the MOF structure before semi-solid electrolytes (sSEs) preparation is crucial for achieving relatively low Mg overpotentials regardless of the ionic conductivity values. Moreover, the behavior of the anode/MOFsSEs interfaces (MOF: α-Mg3 [HCOO]6 ; Mg salt : MgCl2 -Mg[TFSI]2 (1 : 1 wt %); guest solvent: acetone, DMF, DEG, DME and tetraglyme) was investigated by EIS, CV and galvanostatic measurements. The current comparative study of the electrochemical deposition processes of magnesium from MOFsSEs revealed that magnesium deposition/dissolution reactions vary depending on the MOF structure, the guest anion species as well as the nature of the guest solvents.

Influence of Residual Water Traces on the Electrochemical Performance of Hydrophobic Ionic Liquids for Magnesium-Containing Electrolytes.

A trace amount of water is typically unavoidable as an impurity in ionic liquids, which is a huge challenge for their application in Mg-ion batteries. Here, we employed molecular sieves of different pore diameters (3, 4, and 5 Å), to effectively remove the trace amounts of water from 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPip-TFSI) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI). Notably, after sieving (water content <1 mg ⋅ L-1 ), new anodic peaks arise that are attributed to the formation of different anion-cation structures induced by minimizing the influence of hydrogen bonds. Furthermore, electrochemical impedance spectroscopy (EIS) reveals that the electrolyte resistance decreases by ∼10 % for MPPip-TFSI and by ∼28 % for BMP-TFSI after sieving. The electrochemical Mg deposition/dissolution is investigated in MPPip-TFSI/tetraglyme (1 : 1)+100 mM Mg(TFSI)2 +10 mM Mg(BH4 )2 using Ag/AgCl and Mg reference electrodes. The presence of a trace amount of water leads to a considerable shift of 0.9 V vs. Mg2+/ Mg in the overpotential of Mg deposition. In contrast, drying of MPPip-TFSI enhances the reversibility of Mg deposition/dissolution and suppresses the passivation of the Mg electrode.

Energy and cost-efficient nano-Ru-based perovskites/RGO composites for application in high performance supercapacitors.

Nano-Ru-based perovskites RGO are prepared simultaneously in presence of various A-metal salts (A = Sr, Ba or Ca salts) using two different methods for reaction initiation. No further calcination step is needed for the formation of well-defined perovskite structure. Graphene oxide (GO) is used as a fuel to prepare various Ru-based perovskites for the first time. The resulted low-Ru content nanocomposites are used as supercapacitor electrodes in a neutral electrolyte (1.0 M NaNO3). The results show that the specific capacitance of the resulted nanocomposites strongly depends on the method of their preparation as well as the type of A-site of the nanocomposites. Ru-based perovskites RGO nanocomposites that are prepared by combustion method show higher specific capacitance than those prepared by microwave irradiation. The maximum specific capacitance of Sr-, Ba- and Ca-RG-C composites at scan rate 2 mV s-1 are 564 (598 mF cm-2), 460 (487 mF cm-2) and 316 (336 mF cm-2) F g-1, respectively. This value is higher than our previous work using a physical mixture between the individually prepared RGO and SrRuO3. Lowest values for specific capacitance are obtained when using CaRuO3/RGO prepared using microwave-assisted method (Ca-RG-M). The resulted A-RG-nanocomposites show very high cycling stability and good specific capacitance compared to other Ru-based structures previously reported in the literature. A correlation is defined between the structure and specific capacitance of the nanocomposites. It is confirmed that the nanocomposite size, morphology and distribution over the RGO matrix influence the supercapacitor characteristics.

Synthesis, structural and morphological characterizations of nano-Ru-based perovskites/RGO composites.

Highly-dispersed Ru-based perovskites supported on reduced graphene oxide (A-RG) nanocomposites are prepared using different A-metal salts (Sr(NO3)2, Ba(NO3)2 and Ca(NO3)2). The procedure is based on a redox reaction between the metal precursors and graphene oxide (GO) using two different routes of reaction initiation: through thermal heating or by microwave-assisted heating. The resulting nanocomposites do not require further calcination, making this method less energy-demanding. In addition, no additional chemical reagents are required for either the GO reduction or the metal precursor oxidation, leading to an overall simple and direct synthesis method. The structure and morphology of the as-prepared A-RG (non-calcined) nanocomposites are characterized using various structural analyses including XRD, XPS, SEM/EDX and HR-TEM. Changing metal A in the perovskite as well as the "activation method" resulted in significant structural and morphological changes of the formed composites. SrRuO3 and BaRuO3 in combination with RuO2 are obtained using a conventional combustion method, while SrRuO3 (~1 nm size) in combination with Ru nanoparticles are successfully prepared using microwave irradiation. For the first time, a microwave-assisted synthesis method (without calcination) was used to form crystalline nano-CaRuO3.