Herein, we proposed a simple method to measure the inner resistance of a photoelectrochemical (PEC) sensor. Three photoanodes, including TiO2 nanotubes array (TiO2 NTs), g-C3N4/TiO2 NTs and Mn3(BTC)2/g-C3N4/TiO2 NTs (BTC = 1,3,5-benzene- tricarboxylic acid), were chosen as the models. It was shown the change in inner resistance of the photoanode is the main factor for the photocurrent response in a PEC sensor. Under light excitation, the inner resistance of the photoanode is reduced remarkably, resulting in the increment in the photocurrent. The influence of the light intensity on the inner resistance is less than that on the photocurrent, due to the synchronous change in photovoltage. With increasing concentration of hole scavengers (e.g., H2O2, ascorbic acid), the steady inner resistances of the three photoanodes are decreased. In the PEC sensor with Mn3(BTC)2/g-C3N4/TiO2 NTs, the Mn3(BTC)2 layer is served as a size-exclusion filter to prevent the diffusion of molecules with size larger than the apertures in crystals, which improves the selectivity of the PEC sensor to smaller molecules (e.g., H2O2). The catalytic effect of Mn3(BTC)2 to H2O2 enhances the PEC response sensitivity to H2O2. Under optimized conditions, the reciprocal of the averaged steady effective inner resistance of Mn3(BTC)2/g-C3N4/TiO2 NTs is in a linear correlation with the logarithmic concentration of H2O2 in the range of 0.003 to 10 μM with a limit of detection of 1 nM. This PEC sensor was applied for H2O2 determination in exhaled breath condensate samples.Download high-res image (107KB)Download full-size image

•IL-rGO is used as a support for electrochemical deposition of AuNDs.•AuNDs shows superior electrochemical activity properties for iron.•Sandwich structured IL-rGO/AuNDs/Nafion modified electrode has been obtained successfully.•IL-rGO/AuNDs/Nafion modified electrode can be applied for iron determination in coastal waters.An effective and sensitive method for electrochemical determination of iron was reported, based on the ionic liquid-reduced graphene oxide (IL-rGO) supported gold nanodendrites (AuNDs). IL-rGO as a soft support could provide large specific surface area for AuNDs and make them smaller sizes and unique forms, which would benefit to the electrochemical reduction of iron. Nafion is employed as a cation exchange polymer in which IL-rGO and AuNDs can be tightly attached to the electrode surface. The proposed sandwich structured IL-rGO/AuNDs/Nafion modified electrode shows excellent electrochemical properties. The IL-rGO/AuNDs/Nafion modified electrode combined individual advantages as a whole and showed good responses for iron ions. Under the optimized conditions, the reduction peak currents of iron have a good linear relation with its concentrations ranging from 0.30 to 100 μmol L−1 with the detection limit of 35 nmol L−1. More importantly, this sandwich structured modified electrode had a good anti-interference ability and successfully applied in the determination of the total dissolved iron in coastal waters.

•This study is the first to conduct electroploymerization of ARS in RTILs.•BMIMBF4 was successfully mixed in polymeric ARS film.•PARS/BMIMBF4 film was tighter, smoother and better electrochemical property.•PARS/BMIMBF4/GCE showed superior performance for catechol determination.A novel modified electrode for voltammetric catechol determination was fabricated by electroploymerization of alizarin red S (ARS) onto a glassy carbon electrode (GCE) in one kind of room-temperature ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, BMIMBF4). The polymeric ARS/ionic liquid (PARS/BMIMBF4) film modified electrode was characterized by using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and electrochemical methods. The EDX, XPS and FTIR results indicated that PARS/BMIMBF4 film was successfully obtained. Compared with the GCE modified by electroploymerization of ARS in aqueous solution, the GCE modified by electroploymerization of ARS in BMIMBF4 showed smoother and more compact morphology for coating and better electroanalytical properties. Given the combined electrochemical activity of PARS and excellent conductivity of BMIMBF4, the PARS/BMIMBF4/GCE has been successfully used for catechol determination by differential pulse voltammetry (DPV) with a linear range of 0.10 to 500 μM. The sensitivity and detection limit are 42 nA/μM and 0.026 μM, respectively. The PARS/BMIMBF4 modified electrode was successfully applied to the determination of catechol in real water samples and may serve as a simple but high-performance sensor for the determination of some environmental pollutants.

Ten water-soluble ions (F−, Cl−, NO2−, NO3−, SO42−, K+, Na+, NH4+, Ca2+, and Mg2+) in PM2.5 samples were determined by capillary electrophoresis (CE) with a resonant capacitively coupled contactless conductive detector (RC4D). The main component of the background electrolyte (BGE) solution was 20 mM 2-morpholinoethanesulfonic acid (MES)/L-histidine (His) (pH = 6.1). The modifiers of 1.5 mM 18-crown-6 and 20 μM CTAB were added to the BGE for the separation of cations and anions, respectively. The limit of detection for the ten ions is in the range of 3–20 μg L−1. In the combination of dual-opposite end injection and end-to-end differential detection, simultaneous determination of the ten ions was performed in a BGE of 20 mM MES/His + 1.5 mM 18-crown-6 + 20 μM CTAB. A flow injection interface was employed for delay of sample injection without interrupting the electrophoresis. The negative peaks appeared in the early and later stages of electrophoresis increase the possibility of peak superposition in electropherograms. With two independent separation capillaries employed in end-to-end differential detection, simultaneous determination of anions and cations was performed with optimized BGE and better peak separation.

Ten water-soluble ions (F−, Cl−, NO2−, NO3−, SO42−, K+, Na+, NH4+, Ca2+, and Mg2+) in PM2.5 samples were determined by capillary electrophoresis (CE) with a resonant capacitively coupled contactless conductive detector (RC4D). The main component of the background electrolyte (BGE) solution was 20 mM 2-morpholinoethanesulfonic acid (MES)/L-histidine (His) (pH = 6.1). The modifiers of 1.5 mM 18-crown-6 and 20 μM CTAB were added to the BGE for the separation of cations and anions, respectively. The limit of detection for the ten ions is in the range of 3–20 μg L−1. In the combination of dual-opposite end injection and end-to-end differential detection, simultaneous determination of the ten ions was performed in a BGE of 20 mM MES/His + 1.5 mM 18-crown-6 + 20 μM CTAB. A flow injection interface was employed for delay of sample injection without interrupting the electrophoresis. The negative peaks appeared in the early and later stages of electrophoresis increase the possibility of peak superposition in electropherograms. With two independent separation capillaries employed in end-to-end differential detection, simultaneous determination of anions and cations was performed with optimized BGE and better peak separation.