High yield of hydrogen peroxide on modified graphite felt electrode with nitrogen-doped porous carbon carbonized by zeolitic imidazolate framework-8 (ZIF-8) nanocrystals.

The aim of this work was to develop a new modified graphite felt (GF) as carbonaceous cathode for electro-Fenton (EF) application loaded with nitrogen-doped porous carbon (NPC) carbonized by zeolitic imidazolate framework-8 (ZIF-8) nanocrystals as carbon precursor. At initial pH 7, the highest generation rate of H2O2 was 0.74 mg h-1 cm-2 by applying 12.5 mA cm-2 by modified cathode, but in the same condition, the GF only had 0.067 mg h-1 cm-2. The production efficiency increased 10 times. Additionally, phenol (50 mg L-1) could be largely removed by NPC modified cathode, the mineralization ratio and TOC reached 100% and 82.61% at 120 min of optimization condition, respectively. The NPC cathode kept its stability after 5 cycles. The materials were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and linear sweep voltammetry (LSV). The results demonstrated that a homogenous NPC covered the carbon-based material GF. The existing graphitic-N and sp2 carbon of NPC promoted the electron transfer between carbon surface and oxygen molecules, as well as accelerated the oxygen reduction reaction (ORR) and the modified graphite felt had much higher electrocatalytic activity. In this work, several manufacturing parameters like the current, pH and load of NPC were optimized. The optimized design could improve the efficiency of new cathode with in situ electro-chemical production of H2O2 and significantly offer a potential material for degradation of organic pollutants.

Preparation of transition metal composite graphite felt cathode for efficient heterogeneous electro-Fenton process.

A composite graphite felt (GF) modified with transition metal was fabricated and used as cathode in heterogeneous electro-Fenton (EF) for methyl orange (MO) degradation. Characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), the morphology and surface physicochemical properties of the cathodes after modification were observed considerably changed. After loading metals, the current response became higher, the accumulation of H2O2 and the degradation efficiency of MO were improved. Under the same conditions, GF-Co had the highest catalytic activity for electro-reduction of O2 to H2O2 and MO degradation. At pH 3, 99 % of MO degradation efficiency was obtained using GF-Co after 120 min treatment and even at initial pH 9, 82 % of that was obtained. TOC removal efficiency reached 93.8 % using GF-Co at pH 3 after 120 min treatment while that was 12.3 % using GF. After ten-time runs, the mineralization ratio of the GF-Co was still 89.5 %, suggesting that GF-Co was very promising for wastewater treatment. The addition of isopropanol proved that ·OH played an important role in degradation of MO.

Heterogeneous electro-Fenton using modified iron-carbon as catalyst for 2,4-dichlorophenol degradation: influence factors, mechanism and degradation pathway.

Modified iron-carbon with polytetrafluoroethylene (PTFE) was firstly investigated as heterogeneous electro-Fenton (EF) catalyst for 2,4-dichlorophenol (2,4-DCP) degradation in near neutral pH condition. The catalyst was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), and the effects of some important operating parameters such as current intensity and pH on the 2,4-DCP degradation were investigated. After the catalyst modification with 20% PTFE, the degradation performance maintained well with much lower iron leaching, and at current intensity 100 mA, initial pH 6.7, catalyst loading 6 g/L, the degradation efficiency of 2,4-DCP could exceed 95% within 120 min treatment. Two-stage pseudo first-order kinetics of 2,4-DCP degradation was observed, including a slow anodic oxidation stage (first-stage) and much faster heterogeneous EF oxidation (second-stage), in which the automatic drop of pH in the first-stage initiated the Fe(2+) release from micro-electrolysis and thus benefited to the subsequent EF reaction. Aromatic intermediates such as 3,5-dichlorocatechol, 4,6-dichlororesorcinol and 2-chlorohydroquinone were detected by GC-MS. Oxalic acid, acetic acid, formic acid and Cl(-) were quantified by ion chromatograph. Based on these analysis as well as the detection of H2O2 and OH, a possible mechanism and degradation pathway for 2,4-DCP were proposed. This work demonstrated that such a heterogeneous EF using cheap modified Fe-C catalyst was promising for organic wastewater treatment in initial neutral pH condition.

Recent updates on electrochemical degradation of bio-refractory organic pollutants using BDD anode: a mini review.

Boron-doped diamond (BDD) is playing an important role in environmental electrochemistry and has been successfully applied to the degradation of various bio-refractory organic pollutants. However, the review concerning recent progress in this research area is still very limited. This mini-review updated recent advances on the removal of three kinds of bio-refractory wastewaters including pharmaceuticals, pesticides, and dyes using BDD electrode. It summarized the important parameters in three electrochemical oxidation processes, i.e., anodic oxidation (AO), electro-Fenton (EF), and photoelectro-Fenton (PEF) and compared their different degradation mechanisms and behaviors. As an attractive improvement of PEF, solar photoelectro-Fenton using sunlight as UV/vis source presented cost-effectiveness, in which the energy consumption for enrofloxacin removal was 0.246 kWh/(g TOC), which was much lower than that of 0.743 and 0.467 kWh/(g TOC) by AO and EF under similar conditions. Finally the existing problems and future prospects in research were suggested.