Electrochemically-Obtained Polysulfonic-Acids Doped Polyaniline Films-A Comparative Study by Electrochemical, Microgravimetric and XPS Methods

La-Ca/Fe-LDH-coupled electrochemical enhancement of organophosphorus removal in water: Organophosphorus oxidation improves removal efficiency

Metal ions or metal (hydrogen) oxides are widely used as active sites in the construction of phosphate-adsorbing materials in water, but the removal of soluble organophosphorus from water remains technically difficult. Herein, synchronous organophosphorus oxidation and adsorption removal were achieved using electrochemically coupled metal-hydroxide nanomaterials. La-Ca/Fe-layered double hydroxide (LDH) composites prepared using the impregnation method removed both phytic acid (inositol hexaphosphate, IHP) and hydroxy ethylidene diphosphonic acid (HEDP) acid under an applied electric field. The solution properties and electrical parameters were optimized under the following conditions: organophosphorus solution pH = 7.0, organophosphorus concentration = 100 mg L-1, material dosage = 0.1 g, voltage = 15 V, and plate spacing = 0.3 cm. The electrochemically coupled LDH accelerates the removal of organophosphorus. The IHP and HEDP removal rates were 74.9% and 47%, respectively in only 20 min, 50% and 30% higher, respectively, than that of La-Ca/Fe-LDH alone. The removal rate in actual wastewater reached 98% in only 5 min. Meanwhile, the good magnetic properties of electrochemically coupled LDH allow easy separation. The LDH adsorbent was characterized using scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. It exhibits a stable structure under electric field conditions, and its adsorption mechanism mainly includes ion exchange, electrostatic attraction, and ligand exchange. This new approach for enhancing the adsorption capacity of LDH has broad application prospects in organophosphorus removal from water.

Ratiometric Sensing for Ultratrace Tetracycline Using Electrochemically Active Metal-Organic Frameworks as Response Signals

A novel ratiometric sensor using an electrochemically active metal-organic framework of Mo@MOF-808 and NH₂-UiO-66 as response signals was developed to detect tetracycline (TET) in ultratrace quantities. To achieve the dual-response strategy, Mo@MOF-808, with a reduction peak at -1.06 V, and NH₂-UiO-66, with an oxidation peak at 0.724 V, were used as signal probes directly. Concretely, Mo@MOF-808, single-stranded DNA (ssDNA), and complex system (Apt@NH₂-UiO-66) of aptamer (Apt) and NH₂-UiO-66 were sequentially immobilized on the electrode. With the addition of TET, Apt was hybridized with TET and Apt@NH₂-UiO-66 was detached from the electrode, resulting in an increase in the current at -1.06 V and a decrease in the current at 0.724 V. Through this strategy, the sensor achieved a wide linear range (0.1-10000 nM) and a low limit of detection (0.009792 nM) for TET. Moreover, the ratiometric sensor exhibited better sensitivity, reproducibility, and stability than a single-signal sensor. Furthermore, the constructed sensor was successfully applied to detect TET in milk samples, suggesting excellent application prospects.

Spectroelectrochemistry of Electroactive Polymer Composite Materials

In this review, we have summarized the main advantages of the method of spectroelectrochemistry as applied to recent studies on electrosynthesis and redox processes of electroactive polymer composite materials, which have found wide application in designing organic optoelectronic devices, batteries and sensors. These polymer composites include electroactive polymer complexes with large unmovable dopant anions such as polymer electrolytes, organic dyes, cyclodextrins, poly(β-hydroxyethers), as well as polymer-inorganic nanocomposites. The spectroelectrochemical methods reviewed include in situ electron absorption, Raman, infrared and electron spin resonance spectroscopies.

Enhanced Chemical and Electrochemical Stability of Polyaniline-Based Layer-by-Layer Films

Polyaniline (PANI) has been widely used as an electroactive material in various applications including sensors, electrochromic devices, solar cells, electroluminescence, and electrochemical energy storage, owing to PANI’s unique redox properties. However, the chemical and electrochemical stability of PANI-based materials is not sufficiently high to maintain the performance of devices under many practical applications. Herein, we report a route to enhancing the chemical and electrochemical stability of PANI through layer-by-layer (LbL) assembly. PANI was assembled with different types of polyelectrolytes, and a comparative study between three different PANI-based layer-by-layer (LbL) films is presented here. Polyacids of different acidity and molecular structure, i.e., poly(acrylic acid) (PAA), polystyrene sulfonate (PSS), and tannic acid (TA), were used. The effect of polyacids’ acidity on film growth, conductivity, and chemical and electrochemical stability of PANI was investigated. The results showed that the film growth of the LbL system depended on the acidic strength of the polyacids. All LbL films exhibited improved chemical and electrochemical stability compared to PANI films. The doping level of PANI was strongly affected by the type of dopants, resulting in different chemical and electrochemical properties; the strongest polyacid (PSS) can provide the highest conductivity and chemical stability of conductive PANI. However, the electrochemical stability of PANI/PAA was found to be better than all the other films.

Electrochemically Obtained Polysulfonates Doped Poly(3,4-ethylenedioxythiophene) Films-Effects of the Dopant's Chain Flexibility and Molecular Weight Studied by Electrochemical, Microgravimetric and XPS Methods

Electrochemically synthesized poly(3,4,-ethylenedioxythiophene) (PEDOT) films obtained in the presence of eight different polysulfonate dopants are comparatively studied by means of electrochemical quartz crystal microbalance (EQCM) and X-ray Photoelectron Spectroscopy (XPS). Differences with respect to oxidation and doping levels (OL and DL), polymerization efficiency and redox behavior are revealed based on the interplay of three factors: the type of the dopant (acid or salt form), flexibility of the polysulfonate chains and molecular weight of the polysulfonate species. For the rigid- and semi-rigid-chain dopants, use of the salt form results in higher OL and DL values and substantial involvement of solvent molecules in the course of polymerization and redox transitions whereas in the presence of their acid form compact PEDOT films with minor ionic-solvent fluxes upon redox transitions are formed. In contrast, use of the salt form of the flexible chain polysulfonates results in PEDOT with lower OL and DL in comparison to the corresponding acid form. Significant effects are observed when comparing flexible chain dopants with different molecular weights. From a practical point of view the present investigations demonstrate the large scope of possibilities to influence some basic properties of PEDOT (Ol and DL, intensity and type of the ionic and solvent fluxes upon redox transition) depending on the used polysulfonate dopants.