Electrochemically controlled transport of anions across polypyrrole-based membranes

Chlorpromazine-Polypyrrole Drug Delivery System Tailored for Neurological Application

Nowadays, drug delivery systems (DDSs) are gaining more and more attention. Conducting polymers (CPs) are efficiently used for DDS construction as such systems can be used in therapy. In this research, a well-known CP, polypyrrole (PPy), was synthesized in the presence of the polysaccharide heparin (HEP) and chlorpromazine (CPZ) using sodium dodecyl sulfate (SDS) as electrolyte on a steel substrate. The obtained results demonstrate the successful incorporation of CPZ and HEP into the polymer matrix, with the deposited films maintaining stable electrochemical parameters across multiple doping/dedoping cycles. Surface roughness, estimated via AFM analysis, revealed a correlation with layer thickness-decreasing for thinner layers and increasing for thicker ones. Moreover, SEM images revealed a change in the morphology of PPy films when PPy is electropolymerized in the presence of CPZ and HEP, while FTIR confirmed the presence of CPZ and HEP within PPy. Due to its lower molecular mass compared to HEP, CPZ was readily integrated into the thin polymer matrix during deposition, with diffusion being unimpeded, as opposed to films with greater thickness. Finally, the resulting system exhibited the ability to release CPZ, enabling a dosing range of 10 mg to 20 mg per day, effectively covering the therapeutic concentration range.

A controllably fabricated polypyrrole nanorods network by doping a tetra-β-carboxylate cobalt phthalocyanine tetrasodium salt for enhanced ammonia sensing at room temperature

The morphology adjustment and functional doping optimization of polypyrrole (PPy) are of great significance in improving its gas sensing performance. Here, the PPy-0.5TcCoPc nanorods with a uniform dispersed 3-D network were prepared using one-step in situ polymerization using the electrostatic interaction between dopant counterion substituents in tetra-β-carboxylate cobalt phthalocyanine tetrasodium salt (TcCoPcTs) with larger space structure and pyrrole (Py) molecules, in which TcCoPcTs is not only used as a dopant molecule crosslinking PPy chains to obtain a 3-D network, thus improving the conductivity, but also as a sensor accelerator to improve the gas-sensing performance. The resulting PPy-TcCoPc hybrid exhibits superior NH3-sensing properties than PPy and tetra-β-carboxylate cobalt phthalocyanine (TcCoPc) under the same test conditions, especially the PPy-0.5TcCoPc sensor shows ultrafast response/recovery time to 50 ppm NH3 (8.1 s/370.8 s), low detection limit of 8.1 ppb and excellent gas selectivity at room temperature (20 °C). Besides, the PPy-0.5TcCoPc sensor also maintains superior response (49.3% to 50 ppm NH3), humidity resistance and conspicuous stability over 45 days. The excellent NH3-sensing performance of the PPy-0.5TcCoPc hybrid arises from the excellent gas selectivity of TcCoPc, the remarkable response mechanism between PPy and NH3, the high electrical conductivity, abundant active sites and good electron transport ability of the unique 3-D network with large specific surface area. The morphology regulation and functional doping optimization strategy of TcCoPcTs doped PPy broaden the research direction of ideal gas sensor materials.

Selective separation of monovalent anions by PPy/pTS membrane electrodes in redox transistor electrodialysis

Selective separation of nitrate over chloride is crucial for eutrophication mitigation and nitrogen resource recovery but remains a challenge due to their similar ionic radius and the same valence. Herein, a polypyrrole membrane electrode (PME) was fabricated by polymerization of pyrrole (Py) and p-toluenesulfonate (pTS), which was used as a working electrode in redox transistor electrodialysis. The anions in the source solution were first incorporated into the PME at reduction potentials and then released to receiving solution at oxidation potentials. Pulse widths and potentials were optimized to maximize the ion separation performance of PME, resulting in the improvement of NO₃^-/Cl^- separation factor up to 6.93. The ion distributions in various depths of PME indicated that both NO₃^- and Cl^- were incorporated into PME at negative potentials. Then, NO₃^- was preferentially released from PME at positive potentials, but most Cl^- was retained. This was ascribed to the high binding energy between Cl^- and PPy/pTS structure, which was 51.4% higher than that between NO₃^- and PPy/pTS structure. Therefore, the higher transport rate of NO₃^- in comparison with Cl^- was achieved, leading to a high NO₃^- selectivity over Cl^-. This work provides a promising avenue for the selective separation of nitrate over chloride, which may contribute to nitrogen resource recycling and reuse.

Facile fabrication of a conductive polypyrrole membrane for anti-fouling enhancement by electrical repulsion and in situ oxidation

Conductive membranes provide a promising method to alleviate membrane fouling, but their cost-effective fabrication, which is urgently needed, is still a challenge. This paper describes the facile fabrication of an ultrafiltration conductive polypyrrole (PPy)-modified membrane (PMM) by in situ chemical polymerization of FeCl₃ and monomer pyrrole vapor on a commercial membrane surface. The resulting membrane had a high electrical conductivity and an outstanding water flux of 2766.55 L m^-2 h^-1 bar^-1. The preparation cost of the PPy deposition was $2.22/m², which was ∼8% of the commercial ultrafiltration membrane cost. Once the PMM was charged at -1 V as a membrane electrode, the normalized water flux was maintained at 92.48 ± 1.14% after fouling by bovine serum albumin (BSA) solutions, which was 18.82% higher than that when the PMM was not charged. The reduced membrane fouling was ascribed to the electrical repulsion between the negatively charged BSA and the PMM cathode. In addition, hydroxyl and sulfate radicals were generated by peroxymonosulfate (PMS) activation on the PMM surface through electron transfer by PPy, which facilitated foulant oxidation. The PPy on the PMM surface was oxidized after catalysis and electrochemically reduced when the PMM was charged as a cathode, exhibiting continuous catalytic ability for PMS activation. These findings provide an alternative method for the facile fabrication of cost-effective conductive membranes to mitigate membrane fouling.

Graphene oxide-induced formation of a boron-doped iron oxide shell on the surface of NZVI for enhancing nitrate removal

The surface products have a significant influence on the reactivity of zero-valent iron-based materials. Although the enhancing effect of graphene on the reactivity of nanoscale zero-valent iron (NZVI)/graphene composites have been confirmed, the effect of graphene on the formation of surface products of NZVI is not well understood. In order to assess the effect of graphene on the structural of the outer iron oxide layers of NZVI, the NZVI was pre-oxidized by graphene oxide (ONZVI-GO). Compared with the NZVI oxidized by O₂ (ONZVI-O₂), ONZVI-GO was shown to be effective at NO₃^- removal with a high efficiency over a wide range of initial pH values. The results from characterization showed that GO could induce the formation of a tight iron oxide shell with dense spinel structures. The boron introduced during the preparation of NZVI was doped into iron oxides on the surface of ONZVI-GO. The B-O in adsorbed borate was transformed to B-B/B-Fe in the lattice structure of iron oxides, causing the formation of highly electron-deficient Lewis acid sites on the surface of ONZVI-GO, which could effectively gather NO₃^- and OH^-, leading to the higher efficiency removal of NO₃^- than ONZVI-O₂ over a wide range of initial pH values. This study provides new insight into the interaction between graphene and the surface species of NZVI.

Efficient removal of Cr(VI) from water by the uniform fiber ball loaded with polypyrrole: Static adsorption, dynamic adsorption and mechanism studies

A novel adsorbent, the uniform fiber ball (UFB) loaded with polypyrrole (UFB-PPy), was synthesized for Cr(VI) removal from water in this paper. The structure of the UFB and UFB-PPy were characterized by SEM, EDS, FT-IR, BET, XPS and TG. The adsorption properties of UFB-PPy towards Cr(VI) were investigated by the effects of temperature, initial concentration of Cr(VI), interfering ions and contact time in batch experiments, the isothermal models (Langmuir, Freundlich and Temkin) and the kinetic models (Pseudo first-order kinetic, Pseudo second-order kinetic and Intra-particle diffusion models) were used to describe the adsorption behavior. The effects of the initial concentration and flow rate of the Cr(VI) solution in the column experiments were also studied, and the dynamic models (Yoon-Nelson, Adams-Bohart and Wolborska model) were applied to predict the adsorption performance. The Cr(VI) removal mechanism of UFB-PPy was revealed by studying the effect of pH on adsorption, testing of Cl^-, and analyzing the XPS. The results showed that UFB-PPy exhibited excellent adsorption properties for Cr(VI) both in batch and column adsorption. The possible adsorption mechanism involved electrostatic attraction, ion exchange and reduction. Conveniently, the chromium resources can be recovered with the form of high-purity Cr₂O₃ by simple calcination of Cr(VI)-captured UFB-PPy (UFB-PPy-Cr).

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).