Electrochemical determination of free chlorine on pseudo-graphite electrode

CuO-ZIF-8 modified electrode surface as a new electrochemical sensing platform for detection of free chlorine in aqueous solution

This work has applied metal-organic frameworks (MOFs) with high adsorbability and catalytic activity to develop electrochemical sensors to determine free chlorine (free-Cl) concentrations in aqueous media. A zeolitic imidazolate frameworks, Zn(Hmim)2 (ZIF-8) has been synthesized and incorporated with CuO nanosheets to decorate a glassy carbon electrode (GCE) and provide a new sensor for free-Cl determination. The as-prepared ZIF-8 and CuO-ZIF-8 composites have been characterized by FESEM, EDX, XRD, and FT-IR analyses. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) utilized to characterize the CuO-ZIF-8/GC modified electrode electrochemically, demonstrated the ability of the sensor to measure free-Cl concentration. Using differential pulse voltammetry (DPV) and under the optimal conditions, the prepared CuO-ZIF-8/GC modified electrode showed a linear response in the 0.25-60 ppm range with a 12 ppb detection limit (LOD) for free-Cl concentration. Finally, the fabricated sensor was applied to analyze free-Cl from actual swimming pool water samples with promising 97.5 to 103.0% recoveries.

Cobalt-based metal-organic framework-functionalized graphene oxide modified electrode as a new electrochemical sensing platform for detection of free chlorine in aqueous solution

This work reports the profit of using a MOF compound for developing a sensitive electrochemical sensor to free chlorine detection in an aqueous solution. Co-MOF and FGO composites were synthesized and combined with the carbon paste (CP) to prepare an efficient electrochemical sensor with high sensing ability. The fabricated Co-MOF and FGO composites were characterized by SEM, EDX, FT-IR, and XRD techniques. Meanwhile, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were utilized to assess the electrochemical performance of the Co-MOF-FGO/CP modified electrode. Under the optimized condition, the amperometric detection showed that the reduction current of free chlorine increased linearly with a coefficient determination of 0.995 during its wide concentration range of 0.1-700 ppm. Also the detection limit (LOD) (S/N = 3) was 0.01 ppm. The selectivity of the sensor was tested with possible interferences, and satisfactory results were obtained. The proposed sensor was successfully used to determine the free chlorine in tap water and swimming pool water real samples. The results suggested that this proposed sensor could pave the way for developing the electrochemical sensor of free chlorine in aqueous media with MOFs.

Miniaturized 3D printed electrochemical platform with optimized Fibrous carbon electrode for non-interfering hypochlorite sensing

3D printing technology based electrochemical device can provide ease of fabrication, cost effectiveness, rapid detection and lower limit of detection. Herein, a novel, customized, portable and inexpensive 3D printed electrochemical device, has been presented. Fibrous carbon Toray paper, deposited with gold nanoparticles through electrodeposition, used as a working electrode which Further device was tested with 1 mM sodium hypochlorite using cyclic voltammetry (CV) and square wave voltammetry (SWV) in 0.1 M PBS. Hypochlorite has a pivotal role in supporting the growing chemical and paper industries and finds diverse uses in several clinical applications. It is primarily used for disinfecting food, water and surfaces. The scan rate study was carried out from 20 mVs^-1 to 250 mVs^-1 using cyclic voltammetry technique. The diffusion coefficient obtained from scan rate effect was 1.39 × 10^-6 cm²s^-1. The concentration range was evaluated with SWV technique, in a linear range of 0.6 μM-40 μM, with a detection limit of 0.7 μM. The device was further analyzed to ensure non-interference from co-existing chemicals like sodium chloride, potassium nitrate, sodium carbonate, sodium nitrite. Real sample analysis was done with sea, artificial sea and tap water with impressive recovery values. In summary, the developed working electrode can be customized and modified based on testing analyte; thus, the proposed device can be used for various other biochemical analytes.

Diamino group-functionalized Zr-based metal-organic framework for fluorescence sensing of free chlorine in the aqueous phase and Knoevenagel condensation

We developed a porous diamino group-functionalized Zr(IV) metal-organic framework (MOF). The synthesized MOF has a similar structure to DUT-52 (DUT = Dresden University of Technology), which has a face-centered cubic structure with an Fm3̄m space group. The synthesized material (DUT-52-(NH2)2-1) was solvent exchanged with methanol (MeOH) and activated at 100 °C overnight. Both the as-synthesized and activated materials (DUT-52-(NH2)2-1') are thermally stable until 300 °C. The Brunauer-Emmett-Teller (BET) surface area of DUT-52-(NH2)2-1' was found to be 413 m² g^-1. DUT-52-(NH2)2-1' showed a significant quenching of fluorescence response after coming in contact with free chlorine (ClO^-) in an aqueous medium. The selectivity of DUT-52-(NH2)2-1' towards ClO^- was not significantly hampered in the presence of any competitive ion. The limit of detection (LOD) value was found to be 0.08 μM in phosphate-buffered saline (PBS, pH = 7.4). DUT-52-(NH2)2-1' is recyclable and very sensitive towards ClO^-. Moreover, the paper strip method was developed for onsite identification of ClO^-. Furthermore, the catalytic activity of DUT-52-(NH2)2-1' was tested in the Knoevenagel condensation between benzaldehyde and cyanoacetamide. The experimental results clearly indicate that DUT-52-(NH2)2-1' exhibits high activity with very high selectivity towards condensation products. The solid was reusable three times with no decay in its activity, as evidenced by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM) and fourier transform infrared (FT-IR).

Biodegradable asparagine–graphene oxide free chlorine sensors fabricated using solution-based processing

A free chlorine-sensing biodegradable ink was made by functionalizing asparagine onto graphene oxide then deposited on an electrode. The sensor showed a sensitivity of 0.30 μA ppm−1, selectivity amid interfering ions, and low temperature dependence.

A reusable, reagent-less free chlorine sensor using gold thin film electrode

Free chlorine is widely used as a disinfectant in the water industry. Accurate monitoring of the residual free chlorine concentration in water cycles is critical to maintain public health safety. Here, we report on a thin gold film-based reusable and reagent-less free chlorine sensor. A gold thin film of 300 nm thickness was deposited on a polyimide tape, which was placed on a glass substrate and a simple Styrofoam adhesive tape was used to cover the film and expose 0.36 cm2 circular area as the sensing surface. The sensor showed a high sensitivity of 0.327 μA ppm-1, with a linear range of 0 to 6 ppm, and an accuracy of <0.1 ppm with high selectivity in the presence of commonly interfering ions. The sensor response time was 50 s with a negligible hysteresis of 0.06 ppm. The sensor showed very little change in output current in the pH range between 5.2 to 8.4, and temperature range of 20 to 30 °C. Therefore, the sensor operation is reagent-less, does not need frequent calibration, and showed consistent sensing performance with real water samples. The simple fabrication, ease-of-use and reliable sensing performance of the proposed sensor shows feasibility for mass-production and application in remote and resource-limited areas.