Synchronized methylene blue removal using Fenton-like reaction induced by phosphorous oxoanion and submerged plasma irradiation process.

In this study, a combination of phosphorus (PP) oxoanions in a submerged plasma irradiation (SPI) system was used to enhance the removal efficiency of dyes from wastewater. The SPI system showed synergistic methylene blue removal efficiency, due to the plasma irradiation and Fenton-like oxidation. The ferrous ions released from the iron electrode in the SPI system under plasmonic conditions form complexes with the PP anions, which can then react with dissolved oxygen (O2) or hydrogen peroxide (H2O2) via Fenton-like reactions. The experimental results revealed that a sodium triphosphate (TPP) combined SPI system has a higher dye removal efficiency than a tetrasodium pyrophosphate (DP) or a sodium hexametaphosphate (HMP) combined SPI system under similar dissolved iron ion concentrations. To confirm the accuracy of the proposed removal mechanism via Fenton-like oxidation, it was compared to SPI systems under an oxygen environment (TPP/SPI/O2 (k = 0.0182 s-1)) and a nitrogen environment (TPP/SPI/N2 (k = 0.0062 s-1)). The results indicate that the hydroxyl radical (OH) in the TPP/SPI/O2 system is the major oxidant in methylene blue removal, because the dye degradation rates dramatically decreased with the addition of radical scavengers such as tert-butanol (k = 0.0023 s-1) and methanol (k = 0.0021 s-1). On the other hand, no change was observed in the methylene blue removal efficiency of the TPP/SPI/O2 system when it was subjected to a wide range of pHs (3-9). In addition, it was proved that this system could be used to eliminate six different commercial dyes. The results of this study indicated that the TPP/SPI/O2 system is a promising advanced oxidation approach for dye wastewater treatment.

Enhanced methylene blue oxidative removal by copper electrode-based plasma irradiation with the addition of hydrogen peroxide.

Submerged plasma irradiation (SPI)-based advanced oxidation processes have been studied for the oxidation of recalcitrant organic compounds because of their various physical and chemical properties. However, SPI technologies still have a few drawbacks such as relatively low efficiency for wastewater treatment and high energy consumption. In order to overcome these drawbacks, in this study, we proposed the combination of SPI and the Cu(II)-catalyzed Fenton-like system. The removal of methylene blue (MB) by the SPI system was significantly enhanced upon the addition of H2O2. The pseudo-first-order rate constants of MB removal increased with the increase of applied voltage. In addition, the optimum H2O2 dose and initial solution pH were 100 mM and 9, respectively. The reactive oxidants responsible for MB removal in copper electrode-based SPI/H2O2 systems are likely to be hydroxyl radicals (OH) or cupryl ion (Cu(III)), wherein Cu(III) is especially important. Furthermore, the copper electrode-based SPI/H2O2 system is a novel advanced oxidation process capable of oxidizing water recalcitrant and toxic organic pollutants at neutral pH.

Methylene blue removal by submerged plasma irradiation system in the presence of persulfate.

The submerged plasma irradiation (SPI) system is utilized in applications and implications of many environmental fields as an advanced oxidation technology (AOT). However, ramifications of the SPI-based technologies for water treatment are constrained by the different inadequacies. To overcome this matter, in this study, the influence of added persulfate such as peroxydisulfate (PDS) or peroxymonosulfate (PMS) on the removal efficiency of methylene blue (MB) in the SPI system was investigated. The SPI-PMS system was the most effective for MB removal. Also, the pseudo first order rate constants of MB degradation increased with the increase of persulfate dose, applied voltage, and initial solution pH values. The radical species responsible for both the PDS and PMS-activated systems are likely to be peroxomonosulfate radicals (i.e., SO5 (·-)), sulfate radicals (SO4 (·-)), and hydroxyl radicals ((·)OH). Additionally, the persulfate-based SPI system is a novel AOT capable of producing SO4 (·-)or (·)OH and oxidizing water pollutants at near neutral pH.

Isotherm and thermodynamic studies of Zn (II) adsorption on lignite and coconut shell-based activated carbon fiber.

The Zn (II) adsorption capacity of lignite and coconut shell-based activated carbon fiber (ACF) was evaluated as a function of initial Zn (II) concentration, temperature and contact time in batch adsorption process in this study. Adsorption uptake increased with initial Zn (II) concentration and temperature. Optimal contact time for the adsorption of Zn (II) ions onto lignite and coconut shell-based ACF was found to be 50 min. Removal percentage decreased from 88.0% to 78.54% with the increment in initial Zn (II) concentration from 5 to 50 mg L(-1). Equilibrium data fit well with Langmuir-I isotherm indicating homogeneous monolayer coverage of Zn (II) ions on the adsorbent surface. Maximum monolayer adsorption capacity of Zn (II) ions on ACF was found to be 9.43 mg g(-1). Surface morphology and functionality of ACF prior to and after adsorption were characterized by electron microscopy and infrared spectroscopy. Various thermodynamic parameters such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were evaluated.