Removal of methylene blue from aqueous solutions using an Fe2+ catalyst and in-situ H2O2 generated at gas diffusion cathodes

Floating sandwich-type electro-Fenton: A feasible process to remove micro-pollutants through adsorption enrichment and enhanced oxidation efficiency

To improve the removal efficiency of low-concentration organic pollutants and enhance the oxidation efficiency of electro-Fenton (EF) process, a floating sandwich-type EF system (N/(A)/D-EF) without aeration was constructed for the first time. This EF system electro-synthesized H₂O₂ through the floating natural air diffusion electrode (NADE) without aeration, and regenerated Fe(II) effectively by the activated carbon fiber (ACF) interlayer, which significantly enhanced the process oxidation capacity since its ^•OH yield was 8.7 times that of the conventional EF system. In addition, the ACF interlayer could adsorb and enrich micro-pollutants and the generated ^•OH directly oxidize the pollutants adsorbed on the ACF, which enabled regeneration of ACF and maintained removal stability in 20 consecutive experiments. The removal rate constant (k) of carbamazepine by N/(A)/D-EF process was 7.6 times and 2.1 times higher than that of conventional EF and ACF adsorption process, respectively. This process could efficiently remove mixed low-concentration organic pollutants (0.1 mg L^-1) in domestic sewage and lake water with rate constant 1.6-7.1 times that of the conventional EF process but lower energy consumption. Meanwhile, the N/(A)/D-EF process had a wider application range of sewage pH and conductivity, which was a promising process for removing low-concentration pollutants in wastewater.

Synthesis and application of gas diffusion cathodes in an advanced type of undivided electrochemical cell

This paper reports the oxidation of Remazol black B dye by employing iron ions catalyst based gas diffusion cathodes, (GDCs). A GDC was synthesized by using a layer of carbon black and iron ions catalyst for oxygen reduction to hydrogen peroxide. The results demonstrated around 97% decolorization of Remazol black-B dye for 50 min by iron ions catalyst based GDC. The degradation study was performed under electrogenerated hydrogen peroxide at a constant voltage of - 0.6 V vs Hg/HgSO4 in which the rate of degradation was correlated with hydrogen peroxide production. Overall, the GDC's found to be effective method to degrade the dyes via electro-Fenton.

Dual-mode immunoassay system based on glucose oxidase-triggered Fenton reaction for qualitative and quantitative detection of danofloxacin in milk

In this study, a novel colorimetric and fluorescent dual-mode ELISA based on glucose oxidase (GOx)-triggered Fenton reaction was developed for the qualitative and quantitative detection of danofloxacin (DAN). In this system, streptavidin-linked biotinylated anti-DAN-monoclonal antibody (SA-Bio-mAb) and biotinylated GOx (Bio-GOx) form the immune complex mAb-Bio-SA-Bio-GOx. In the absence of DAN, the mAb-Bio-SA-Bio-GOx would be immobilized by combining with coated DAN-BSA and catalyzed glucose to generate H₂O₂. The Fenton reaction between H₂O₂ and Fe²⁺ generated hydroxyl radicals, which oxidized the o-phenylenediamine to 2,3-diamino-phenazine. A dual-signal immunoassay with colorimetry and fluorescence as the signal readout was established. In the presence of DAN, DAN and DAN-BSA competed with Bio-mAb, decreasing the connection between immune complexes and DAN-BSA and finally resulting in lower signal of colorimetry and fluorescence. Under optimal conditions, the limit of detection of the fluorescence immunoassay was 0.337 ng/mL and was 5.24-fold lower than that of traditional ELISA. The colorimetric immunoassay cut-off value was 30 ng/mL in milk. The average recoveries of the method for milk samples that are spiked with different concentrations of DAN were 91.1 to 128.3%, with a coefficient of variation of 0.7 to 8.2%. These results of the method exhibited good agreement with those of liquid chromatography-tandem mass spectrometry system (LC-MS/MS) method. In brief, this work provides an improved screening strategy with high sensitivity and accuracy for the qualitative or quantitative detection of DAN in milk monitoring.

Removal of methylene blue dye from aqueous solutions by adsorption on levulinic acid-modified natural shells

This study has developed an innovative and environmentally friendly approach for the removal of methylene blue (MB) dye by natural shells (NShs) chemically modified with levulinic acid (LA). Almond shell (ASh), walnut shell (WSh), and apricot kernel shell (AKSh) were used as waste fillers. The adsorption behavior of MB onto the biosorbents was investigated with respect to parameters such as sorbent dosage (0.4-6 g/L), pH (3-10), initial dye concentration (10-500 mg/L), and temperature (25-65 °C). The biosorbents were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) analysis. The isotherm and kinetic adsorption data can be said to fit the Freundlich isotherm model and the pseudosecond-order model, respectively. The maximum adsorption capacity (q_max) of LA-modified walnut shell (LA-WSh), almond shell (LA-ASh), and apricot kernel shell (LA-AKSh) calculated by the Langmuir equation at 25 °C was 294.1, 270.2, and 180.0 mg/g, respectively. The results of thermodynamic analysis showed that adsorption was feasible, endothermic, and spontaneous.

Modifying graphite felt cathode by HNO3 or KOH to improve the degradation efficiency of electro-Fenton for landfill leachate

Based on graphite felt (GF), the cathode of an electro-Fenton (EF) system was modified by HNO₃ and KOH respectively to improve the degradation efficiency for actual landfill leachate. The results of Fourier transform infrared spectroscopy (FTIR) spectra, Boehm titration experiments, contact angle, scanning electron microscopy (SEM) and adsorption experiments illustrated that the surface of the modified GFs had more oxygen-containing functional (OG) groups, and possessed better hydrophilicity and larger specific surface area. In 180 min H₂O₂ electrogeneration experiments, the cumulative amount of H₂O₂ produced by unmodified GF (GF-0), HNO₃ modified GF (GF-1) and KOH modified GF (GF-2) was 526 mg/L, 891 mg/L and 823 mg/L respectively. In 180 min EF reaction, the removal rate of chemical oxygen demand (COD) in GF-0, GF-1 and GF-2 EF systems was 31.88%, 60.65% and 52.08% respectively; the removal rate of NH₄ ⁺-N in GF-0, GF-1 and GF-2 EF systems was 43.37%, 98.10% and 94.81% respectively. In addition, both the performance of GF-1 and GF-2 for Fe²⁺ regeneration was greatly enhanced, and GF-1 was superior to GF-2. The degradation efficiency for landfill leachate was enhanced obviously by employing the modified EF system, suggesting that the two modified cathodes have great potential in practical production.