Electrochemical behaviour of pesticides at bare and nylon 6,6-modified solid electrodes in differential pulse cathodic stripping voltammetry

The study of the voltammetric behaviour of five types of pesticides, namely paraquat dichloride, metsulfuron-methyl, lindane, chlorothalonil and glyphosate were carried out. The electrodes used were hanging mercury drop electrode (HMDE), glassy carbon electrode (GCE), HB pencil electrode (HBPE), boron doped diamond electrode (BDDE) and screen printed electrode (SPE). Due to the toxicity of mercury and to improve the detectivity for the determination of these pesticides, nylon-6,6 was used as modifier to modify the electrodes to produce nylon-6,6-modified glassy carbon electrode (Nyl-MGCE), nylon-6,6-modified HB pencil electrode (Nyl- MHBPE), nylon-6,6-modified boron doped diamond electrode (Nyl-MBDDE), and nylon-6,6-modified screen printed electrode (Nyl-MSPE). All measurements were performed using differential pulse cathodic stripping voltammetry technique (DPCSV) vs. Ag/AgCl (3.0 M KCl). Experimental parameters such as pH of Britton- Robinson buffer (BRB), accumulation time, accumulation potential and initial potential were optimized for the pesticides determination. Linear calibration plots for the paraquat dichloride and metsulfuron-methyl were obtained with the limit of detection (LOD) value of 3.66 × 10-8 M and 8.86 × 10?8 M, respectively on HMDE. The detectivity of DPCSV with nylon-6,6-modified solid electrodes were more effective compared to bare solid electrodes, where the LOD values for paraquat dichloride were 2.75 × 10-8 M (GCE), 6.42 × 10-9 M (Nyl-MGCE), 2.37 × 10-8 M (HBPE), 1.33 × 10-8 M (Nyl-MHBPE), 2.52 × 10-8 M (SPE), 1.05 × 10-8 M (Nyl- MSPE), 2.86 × 10-8 M (BDDE), and 1.54 × 10-8 M (Nyl-MBDDE). The novel sensors, Nyl-MSPE and Nyl-MHBPE were utilized for lindane and chlorothalonil analysis, and the LODs obtained were 4.26 × 10-8 M and 2.13 × 10-8 M, respectively. Efforts to study the electroactivity behaviour of metsulfuron-methyl and glyphosate were unsuccessful at all types of working electrodes that have been assessed in this study except HMDE for metsulfuron-methyl. There was no significant interfering metal ions effect found for voltammetric determination on the selected pesticides. Approximately 90% recovery was achieved for pesticides analyses. It can be concluded that the proposed DPCSV methods with nylon-6,6- modified solid electrodes were efficiently applied in this study and verified in real water samples analysis. The proposed DPCSV methods were also comparatively selective and have good coefficient of determination (R2 = 0.995)

Leachability of heavy metals from cement mortar bricks modified with water treatment alum sludge

Leachability profiles of aluminium (Al), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn) from raw drinking water treatment sludge (WTS), laboratory produced sludge and WTS-cement solidified bricks (CMWTS) were studied to determine the potential of reusing WTS in brick manufacturing. The leachability of the heavy metals was investigated using the extraction method. Leach Tests were performed on WTS obtained from the Semanggar Water Treatment Plant, Kota Tinggi, Johore, Malaysia; laboratory produced sludge, and CMWTS produced using the solidification-stabilization (S/S) technique. Structural identity, chemical composition, effectiveness of the solidification-stabilization (S/S) technique and strengths of bricks were also investigated. Surface and other physicochemical properties were studied using FESEM, SEM, BET-surface area analyzer, XRD, FTIR, TOC, compressive strength test and TG analyzer. Leach tests showed that some heavy metals were leached out from samples in acidic solution but very low levels of heavy metals were leached in water and basic conditions and indicating that the WTS was safe for reuse. When the WTS was solidified in cement mortar, the compressive strength of the bricks increased with increasing curing time, pH of the curing solution and amount of WTS added. However, a reduction of compressive strength was observed at 20% WTS in the CMWTS bricks. It can be concluded that WTS has the potential for reuse in brick manufacturing as the addition of up to 20% WTS in cement mortar produced bricks with good strength properties as well as reduced leachability of the selected heavy metals from WTS

Characterization of alum sludge for reuse and disposal

The properties of spent drinking water treatment sludge (WTS) were investigated to determine its physical and chemical properties. WTS was obtained from the Semanggar Water Treatment Plant, Kota Tinggi, Johore, Malaysia. Bulk density, particle density, porosity, surface area, particle size, moisture content, ash content, chemical composition, leachability of heavy metals, pH and the total organic carbon (TOC) were determined. Surface and other physicochemical properties were also studied using the scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD), TGA, FTIR, BET single point surface area analyzer, and TOC analyzer. Results showed that the particle size, bulk density and particle density of WTS were 2-5 μm, 0.831 ± 0.061 g/cm3 and 2.66 ± 0.029 g/cm3, respectively. The porosity was 68-69% with surface of 38.92 m2/g and ash content of 67%, reflecting the high TOC of 1440.37±14.71. The sludge contained 29% moisture and showed a pH value of 4.28 in solution. Analysis of acid digest indicated a high content of Al and Fe. The WTS were shown to leach very low levels of selected heavy metals

Novel electrochemical sensor based on nylon 6,6-modified graphite HB pencil electrode for chlorothalonil determination by differential pulse cathodic stripping voltammetry

Mercury-based electrode was the choice of electrode material for many years, and it has been extensively used in voltammetry studies. Nonetheless, alternative electrode materials are highly preferred in voltammetry studies due to the toxicity of mercury. This work introduces a novel green sensor, nylon 6,6-modified graphite HB pencil electrode (Nyl-MHBPE) as electrochemical method for chlorothalonil determination by differential pulse cathodic stripping voltammetry (DPCSV). The Nyl-MHBPE was significantly improved electroactivity towards the reduction of chlorothalonil, under the optimal conditions (at pH 8.0). It was clearly observed that nylon 6,6 revealed as an efficient modifier for enhancing stripping signal for voltammetric analysis. Moreover, the developed sensor showed great feature such as a remarkably low detection limit in nanomolar level (0.94 × 10−8 M) with a linear range from 1 to 26 × 10−7 M. It presented excellent repeatability with high sensitivity and selectivity. Besides, analysis of chlorothalonil in real water samples was successfully carried out with good recovery values (92.5–103%) and relative standard deviation (RSD) values < 2.2%. The performance of Nyl-MHBPE was also compared to bare pencil electrode (HBPE). Another significant feature of this work is that the conductivity properties of the Nyl-MHBPE were superior as compared to hanging mercury drop electrode (HMDE). The present study provides admirable merits that make the Nyl-MHBPE selected as a promising electrochemical sensor to perform routine analysis of chlorothalonil

Nylon 6,6 modified screen printed carbon electrodes as electrochemical sensors for rapid chlorothalonil determination in water samples using differential pulse cathodic stripping voltammetry

A newly developed electrochemical sensor for chlorothalonil based on nylon 6,6 film deposited onto screen printed electrode (SPE) with electrochemical modulation of pH at the electrode/solution interface was studied for the first time. Differential pulse cathodic stripping voltammetry (DPCSV) was used to carry out the electrochemical and analytical studies. Experimental parameters such as accumulation potential, initial potential, accumulation time and pH of Britton-Robinson buffer have been optimized. Chlorothalonil gave optimum analytical signal in a medium of 0.04 M Britton-Robinson buffer at pH 6.0. A well-defined reduction peak was observed, at Ep= −0.851 and −0.938 V vs. Ag/AgCl (3.0 M KCl) for both bare SPE and modified SPE, respectively. The peak currents of modified SPE were significantly increased as compared to bare SPE. At the modified SPE, a linear relationship between the peak current and chlorothalonil concentration was obtained in the range from 0.1 to 2.8 × 10−6 M with a detection limit of 1.53 × 10−8 M (S/N= 3). The practical applicability of the newly developed method has been demonstrated on analyses of real water samples. The newly developed sensor shows good reproducibility with RSD of 3.92%. The nylon 6,6 modified SPE showed itself as promising sensor with good selectivity for chlorothalonil determination

Green sensors for voltammetric determination of lindane in water samples using bare and nylon 6,6 modified pencil electrodes

Lindane, an insecticide, was determined using the differential pulse cathodic stripping voltammetry technique on bare and nylon 6,6 modified pencil electrodes. Experimental parameters, such as pH, accumulation time, accumulation potential and initial potential, were optimized. A well-defined peak of lindane was found for both electrodes which was identified at −0.338 V and −0.350 V, respectively. pHs of 8.0 and 7.0 were chosen as the optimum pHs due to a good stripping signal of the reduction peak for both bare and nylon 6,6 modified pencil electrodes. There were no significant interfering ion effects on the electroanalysis of lindane. The limits of determination for bare and nylon 6,6 modified pencil electrodes were 2.13 × 10−8 M and 3.81 × 10−8 M. The nylon 6,6 modified pencil electrode exhibited a significant increase in the stripping response toward lindane determination as compared to the bare pencil electrode. Water samples were prepared by spiking known concentrations of lindane and the recovery value achieved at both bare and nylon 6,6 modified pencil electrodes was ≥95.3% with RSDs ≤ 3.22%. Ultimately, the proposed methods were relatively selective and highly sensitive and exhibited good precision