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Ionic diodes have emerged repeatedly in the literature for gel interfaces, for nanopores and channels, for nano-/micro-fluidic systems, and for asymmetrically ionomer-covered microholes. Concentration polarisation is likely to be the key to understanding the diode function and the diode time constant diode, i.e. the time for approaching steady state following a potential/polarity switch. For frequencies higher than diode = 2f = (diode)-1, the polarization mechanism is too slow for ion current rectification. Below the frequency associated with the diode time constant, irreversibility in ion flow is induced and the diode switches between two resistive states at opposite potentials (“open” and “closed”). The irreversible flow of ions allows energy conversion from electrical to electrochemical. For energy conversion, two coupled ionic diodes are necessary driven by alternating current (AC) electricity to minimise driver electrode electrolysis and energy losses. Opportunities for AC-desalination and for electroosmotic water harvesting with coupled ionic diodes are discussed.

Piezo-polarized charges are generated on piezoelectric materials via the ultrasound effect. Positive synergy is achieved through sonolysis and electrochemical oxidation. Impressive degradation efficiency of sulfamethoxazole on FTO/BaZr(0.1)Ti(0.9)O3 electrode is observed.

Silver nanoparticles (AgNPs) were synthesized separately and loaded onto the expanded layers of exfoliated graphite (EG) to form a silver nanoparticle-exfoliated graphite nanocomposite (AgNPs-EG). The AgNPs-EG was compressed into a pellet (0.6 cm in diameter) and used to prepare an electrochemical sensor for bisphenol A (BPA) in standard samples and in thermal paper. The synthesized materials were characterized by ultraviolet-visible spectrophotometry, X-ray diffraction spectroscopy, scanning electron microscopy, and energy-dispersive X-ray. The electrochemical behavior of BPA on the AgNPs-EG sensor was investigated by cyclic voltammetry and square wave voltammetry. Under optimized experimental conditions, the oxidation peak current was linearly proportional to bisphenol A concentrations in the range from 5.0 to100 μM, with a coefficient of determination (R2 ) of 0.9981. The obtained limit of detection of the method was 0.23 μM. The fabricated sensor was able to overcome electrode fouling with good reproducibility (RSD = 2.62%, n = 5) by mechanical polishing of the electrode on emery paper. The proposed method was successfully applied to determine bisphenol A in thermal paper samples and demonstrated good accuracy of 93.1 to 113% recovery.

Ionic rectifier membranes or devices generate uni-directional ion transport to convert an alternating current (AC) ion current input into stored energy or direct current (DC) in the form of ion/salt gradients. Electrochemical experiments 80 years ago were conducted on biological membrane rectifier systems, but today a plethora of artificial ionic rectifier types has been developed and electroanalytical tools are employed to explore mechanisms and performance. This overview focuses on microscale ionic rectifiers with a comparison to nano- and macroscale ionic rectifiers. The potential is surveyed for applications in electrochemical analysis, desalination, energy harvesting, electrochemical synthesis, and in selective ion extraction.

This work is focused on the photocatalytic degradation of antibiotics ciprofloxacin and sulfamethoxazole in wastewater using a nanocomposite of tungsten trioxide (WO3) and carbon nanodots (CNDs). This material was prepared by doping tungsten trioxide (WO3) with carbon nanodots (CNDs) by hydrothermal technique. The structural, optical, morphological and photocatalytic properties of the CNDs-doped WO3 nanocomposite as well as an undoped WO3 nanorod were successfully characterized by TEM, XRD, Raman, FTIR, BET and UV–Vis DRS. The photocatalytic degradation performance, degradation kinetics and degradation patterns were followed by UV–Visible spectroscopy and ultra performance liquid chromatography coupled with mass spectrometry (UPLC-MS). The percentage removal of ciprofloxacin and sulfamethoxazole were higher with the WO3-CNDs than the pristine WO3 photocatalyst denoting the positive effect of doping. The percentage removal of the antibiotics when monitored by UPLC-MS was found to be higher than that of UV–Visible spectroscopy. The intermediate products and pathway were different with the doped and the undoped WO3 photocatalysts.

In this article, we report the simultaneous determination cholesterol (CL), ascorbic (AA) acid and uric acid (UA) at a carbon paste electrode (CPE) modified with copper oxide decorated reduced graphene (CuO-rGR), with 1-methyl-3-octylimidazolium tetrafluoroborate (1M3OIDTFB) as a binder. The electrode, CuO-rGR/1M3OIDTFB/CPE, showed remarkable sensitivities towards the determination of the analytes, and well defined and clearly separated oxidation peaks were obtained during their simultaneous analysis in a buffer solution at pH 7.4. The differences observed between their peaks potentials are as follows: 430 mV (between CL and AA), 270 mV (between AA and UA) and 700 mV (between CL and UA). The morphologies and structure properties of the CuO-rGR were investigated by FESEMD and EDAX methods. The CuO-rGR/1M3OIDTFB/CPE displayed linear response in the concentration ranges 0.04–300.0 μM, 0.04–240.0 μM and 0.4–400.0 μM for CL, AA and UA with the detection limits 9.0 nM, 9.0 nM and 0.08 μM, respectively. The CuO-rGR/1M3OIDTFB/CPE displayed high performance for the determination of CL, AA and UA in real samples.

Membrane materials with semipermeability for anions or for cations are of interest in electrochemical and nanofluidic separation and purification technologies. In this study, partially hydrolyzed polyacrylonitrile (phPAN) is investigated as a pH-switchable anion/cation conductor. When switching from anionic to cationic semipermeability, also the ionic current rectification effect switches for phPAN materials deposited asymmetrically onto a 5, 10, 20, or 40 μm diameter microhole in a 6 μm thick polyethylene-terephthalate (PET) film substrate. Therefore, ionic rectifier behavior can be tuned and used to monitor and characterize semipermeability. Effects of electrolyte type and concentration and pH (relative to the zeta potential at approximately 3.1) are investigated by voltammetry, chronoamperometry, and impedance spectroscopy. A computational model provides good qualitative agreement with the observed electrolyte concentration data. High rectification effects are observed for both cations (pH > 3.1) and anions (pH < 3.1) but only at relatively low ionic strengths.

A wide range of semiconductor photocatalysts have been used over the years in water treatment to eliminate toxic organic substances from wastewater. The quest for visible or solar light driven photocatalysts with striking merits such as wide range of applications, ease of preparation, tailored architecture that gives rise to improved performance, ability of dual existence as both p type or n type semiconductor, among others, presents copper(I) oxide as a promising photocatalyst. This paper reviews the recent applications of Cu2O in photocatalytic and photoelectrocatalytic treatment of water laden with organic pollutants such as dyes and pharmaceuticals. It covers the various modes of synthesis, morphologies and composites or heterostructures of Cu2O as found in the literature. Concluding remarks and future perspectives on the application of Cu2O are presented.

Development of electrochemical sensors for important drugs such nicotine (an addictive drug) is important for the society. This study reports the electrochemical detection of nicotine at a carbon nanofiber/poly (amidoamine) dendrimer modified glassy carbon electrode. The carbon nanofiber (CNF) modified GCE was prepared by drop-coating followed by the electrodeposition of generation 4 poly (amidoamine) succinamic acid dendrimer (PAMAM) to form the sensor - CNF-PAMAM GCE. Characterization of prepared materials and modified electrodes was carried out using Fourier transmission infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The CNF-PAMAM composite was confirmed by microscopy. A marked reduction in charge transfer resistance and increase in current of the CNF-PAMAM GCE in comparison to the bare electrode showed a synergic improvement electrochemical response because of the CNF-PAMAM nanocomposite. The CNF-PAMAM demonstrated an enhanced performance in the oxidation of nicotine in comparison to the bare GCE by shifting the anodic potential E

Toward the improvement of the application of heterogeneous electro-Fenton in water treatment, we report a new strategy of enhancing the immobilization of a magnetite nanoparticle catalyst on a carbon felt cathode. Exploiting the intrinsic ferrimagnetic properties of magnetite nanoparticles, magnet bars were used to attach the magnetite into the void spaces of the porous carbon felt (CF) cathode. The magnetite nanoparticles were prepared by coprecipitation with variations in the molar ratios of Fe

Electrodeposited bismuth ferrite (BiFeO3) thin films on fluorine-doped tin oxide (FTO) substrate were employed as photoanodes in the photoelectrocatalytic degradation of methylene blue. The BiFeO3 thin films electrodeposited for 300 s, 600 s, 1200 s, 1800 s and 3600 s were characterised with XRD, field emission scanning electron microscopy (FESEM) and UV–vis diffuse reflectance spectroscopy. SEM images displayed different morphology at different electrodeposition times which affects the photoelectrocatalytic (PEC) performances. The FESEM cross-sectional area was used to measure the thickness of the film. The optical properties showed that the band gaps of the photoanodes were increasing as the electrodeposition time increased. The photocurrent response obtained showed that all thin film photoanodes responded to visible light and lower charge transfer resistance (from electrochemical impedance spectroscopy studies) was observed with photoanodes electrodeposited at a shorter time compared to those at a longer time. The PEC application of the photoanode for the removal of methylene blue (MB) dye in water showed that the percentage degradation decreased with an increase in electrodeposition time with removal rates of 97.6% and 70% observed in 300 s and 3600 s electrodeposition time, respectively. The extent of mineralisation was measured by total organic carbon and reusability studies were carried out. Control experiments such as adsorption, photolysis, photocatalysis and electrocatalysis processes were also investigated in comparison with PEC. The electrodeposition approach with citric acid exhibited improved electrode stability while mitigating the problem of catalyst leaching or peeling off during the PEC process.

Solving high electrical-energy input for pollutants degradation is one of the core requirements for the practical application of photoelectrocatalytic (PEC) technology. Herein, we developed a self-driven dual-photoelectrode PEC system (TiO2 NNs-Co3O4) composed of a TiO2 nanoneedle arrays (TiO2 NNs) photoanode and Co3O4 photocathode for the first time. Under light-emitting-diode (LED) illumination, the bias-free TiO2 NNs-Co3O4 PEC system exhibited excellent PEC performance, with an internal bias as high as 0.19 V, achieving near complete degradation (99.62%) of sulfamethazine (SMT) with a pseudo-first-order rate constant of 0.042 min−1. The influences of solution pH, typical inorganic anions, natural organic matter, and initial SMT concentration on the PEC performance were investigated. Moreover, the main reactive oxygen species (h+, •OH, •O2−) in the dual-photoelectrode PEC system for SMT decomposition were elaborated. The practical application feasibility for efficient water purification of this unbiased PEC system was evaluated. It was proved that the TiO2 NNs photoanode provided a negative bias while the Co3O4 photocathode provided a positive bias for the photoanode, which made this system operate without external bias. This work elucidated the cooperative mechanism of photoelectrodes, providing guidance to develop a sustainable, efficient, and energy-saving PEC system for wastewater treatment.

Tremendous progress has been made in the aspect of material design, especially in nanomaterials fabrication over the past decades. And as such, the rapid development of nanomaterials through nanotechnology has opened up new avenues for their use in photoelectrochemical applications. Their unique characteristics at nano dimensions compared to their bulk counterparts make them very much attractive. Largely, optical properties and functionalities in emerging technologies, flexibility and semiconducting properties to mention a few make the use of nanomaterials indispensable for photoelectrochemical applications. Owing to this effect, the present chapter deals with the photoelectrochemical (PEC) application of nanomaterials in specific areas such as photoelectrochemical biosensing, hydrogen production via solar water splitting and photovoltaic devices. The chapter also addresses the progress in the utilization of the nanomaterials and illustrates the designs for their integration in biosensors, highly efficient and stable photoelectrode in PEC water splitting for hydrogen production and outstanding smart solar energy harvesting devices for third-generation photovoltaics.

The mineralization of tetracycline by electrochemical advanced oxidation processes (EAOPs) as well as the study of the toxicity of its intermediates and degradation products are presented. Electro-Fenton (EF), anodic oxidation (AO), and electro-Fenton coupled with anodic oxidation (EF/AO) were used to degrade tetracycline on carbon felt (cathode) and a sub-stoichiometric titanium oxide (Ti4O7) layer deposited on Ti (anode). As compared to EF and AO, the coupled EF/AO system resulted in the highest pollutant removal efficiencies: total organic carbon removal was 69 ± 1% and 68 ± 1%, at 20 ppm and 50 ppm of initial concentration of tetracycline, respectively. The effect of electrolysis current on removal efficiency, mineralization current efficiency, energy consumption, and solution toxicity of tetracycline mineralization were investigated for 20 ppm and 50 ppm tetracycline. The EF/AO process using a Ti4O7 anode and CF cathode provides low energy and high removal efficiency of tetracycline caused by the production of hydroxyl radicals both at the surface of the non-active Ti4O7 electrode and in solution by the electro-Fenton process at the cathodic carbon felt. Complete removal of tetracycline was observed from HPLC data after 30 min at optimized conditions of 120 mA and 210 mA for 20 ppm and 50 ppm tetracycline concentrations. Degradation products were elucidated, and the toxicity of the products were measured with luminescence using Microtox® bacteria toxicity test.

We report the photoelectrocatalysis of diclofenac sodium using a reactor consisting of Ag-BiVO

Towards nonconventional wastewater treatment methods for the degradation of organic pollutants in wastewater, a perovskite-based photoelectrochemical system was developed. Bismuth ferrite doped with lanthanum (La-BiFeO3, La-BFO) perovskite was synthesised through a hydrothermal method with low calcination temperature for the photoelectrochemical degradation of orange II dye and other cocktails of dyes. Photoanodes were prepared by the deposition of the perovskites on a fluorine-doped tin oxide (FTO) substrate. The photoanodes were characterised using XRD, FESEM, FTIR and UV-vis diffuse reflectance. The photoelectrochemical properties of the synthesised photoanodes were investigated with chronoamperometry and electrochemical impedance spectroscopy (including Mott–Schottky analysis). The results show that all La3+-doped BFO photoanodes exhibited a higher absorption edge in the visible light region than the undoped BFO. The photocurrent response of 10% La-BFO (the best performing electrode) exhibited a three times higher current response than the pure BFO. In addition, the electrode exhibited a good degradation efficiency of 84.2% within 120 min with applied bias potential of 2 V at a pH of 7. EIS studies showed a significant enhancement of the interfacial electron transfer of the charge carriers. The enhancements in electrode performances were attributed to the synergistic effect of the applied bias potential and the introduction of La3+ into the BFO matrix. This study therefore shows that the photoelectrocatalytic performance of BFO for water treatment can be improved by the introduction of perovskites-doping ions such as La3+.

Photoelectrocatalysis is a hybrid photon/electron-driven process that benefits from the synergistic effects of both processes to enhance and stabilize the generation of disinfecting oxidants. Photoelectrocatalysis is an easy to operate technology that can be scaled-up or scaled-down for various water treatment applications as low-cost decentralized systems. This review article describes the fundamentals of photoelectrocatalysis, applied to water disinfection to ensure access to clean water for all as a sustainable development goal. Advances in reactor engineering design that integrate light-delivery and electrochemical system requirements are presented, with a description of photo-electrode material advances, including doping, nano-decoration, and nanostructure control. Disinfection and cell inactivation are described using different model microorganisms such as E. coli, Mycobacteria, Legionella, etc., as well the fungus Candida parapsilosis, with relevant figures of merit. The key advances in the elucidation of bacterial inactivation mechanisms by photoelectrocatalytic treatments are presented and knowledge gaps identified. Finally, prospects and further research needs are outlined, to define the pathway towards the future of photoelectrocatalytic disinfection technologies.

The poisoning of pure platinum electrodes has propelled the improvement of platinum-based alloy catalysts. In this work, we report the application of exfoliated graphite electrode as an anode platform for binary platinum-based electrocatalysts for methanol oxidation in alkaline media. Platinum-based binary electrocatalysts comprising of Pt-Au and Pt-Pd nanoparticles on functionalized multi-walled carbon nanotubes (MWCNTs) support were synthesized via polyol process. The nanocomposite electrocatalysts (Pt-Au/fMWCNTs and Pt-Pd/fMWCNTs) were characterized by transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffractometer (XRD). The electrochemical activity of the Pt-Pd/fMWCNTs and the Pt-Au/fMWCNTs electrocatalysts was assessed utilizing cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in the presence of methanol. The nanoparticles were in the size regime of 3 to 5 nm and the XRD affirmed successful functionalization of the MWCNT and its impregnation with the binary Pt nanoparticles. The electrooxidation of methanol in alkaline conditions was seen with a high current density of about 26.1 mA cm−2 on Pt-Au/fMWCNTs and 13.52 mA cm−2 on Pt-Pd/fMWCNTs electrocatalysts deposited on exfoliated graphite working electrodes. The exfoliated graphite platform is a promising electrode for fuel cell application.

We demonstrate that ionic current rectification effects are observed with a film of negatively charged carbon nanofibers (CNFs) deposited as a film or mat onto a 10 μm diameter microhole in poly-ethylene-terephthalate (PET). CNFs are synthesized by using a chemical vapor deposition (CVD) method, followed by oxidation with hydrogen peroxide to introduce carboxyl moieties (providing negative surface charges). CNFs are characterized with transmission electron microscopy, scanning electron microscopy, elemental analysis, and zeta potential measurements. When drop-dried asymmetrically onto a 10 μm diameter cylindrical channel on a 6 μm thick PET substrate and placed as a membrane between two electrolyte compartments, ionic current rectification is observed. Effects of pH, ionic strength, and nature of electrolyte are investigated. Bipolar reactivity of iodide is demonstrated. Potential for future applications in water purification are discussed.