Contact-electro-catalysis for the degradation of organic pollutants using pristine dielectric powders

Mechanochemistry has been studied for some time, but research on the reactivity of charges exchanged by contact-electrification (CE) during mechanical stimulation remains scarce. Here, we demonstrate that electrons transferred during the CE between pristine dielectric powders and water can be utilized to directly catalyze reactions without the use of conventional catalysts. Specifically, frequent CE at Fluorinated Ethylene Propylene (FEP) - water interface induces electron-exchanges, thus forming reactive oxygen species for the degradation of an aqueous methyl orange solution. Contact-electro-catalysis, by conjunction of CE, mechanochemistry and catalysis, has been proposed as a general mechanism, which has been demonstrated to be effective for various dielectric materials, such as Teflon, Nylon-6,6 and rubber. This original catalytic principle not only expands the range of catalytic materials, but also enables us to envisage catalytic processes through mechano-induced contact-electrification.

Research Progress on the Applications of Electrospun Nanofibers in Catalysis

During the last two decades, electrospinning has become a very popular technique for the fabrication of nanofibers due to its low cost and simple handling. Nanofiber materials have found utilization in many areas such as medicine, sensors, batteries, etc. In catalysis, these materials also present important advantages, since they present a low resistance to internal diffusion and a high surface area to volume ratio. These advantages are mainly due to the diameter–length proportion. A bibliographic analysis on the applications of electrospun nanofibers in catalysis shows that there are two important groups of catalysts that are being investigated, based on TiO2 and in carbon materials. The main applications found are in photo- and in electro-catalysis. The present study contributes by reviewing these catalytic applications of electrospun nanofibers and demonstrating that they are promising materials as catalysts, underlining some works to prove the advantages and possibilities that these materials have as catalysts. On one hand, the possibilities of synthesis are almost infinite, since with coaxial electrospinning quite complex nanofibers with different layers can be prepared. On the other hand, the diameter and other properties can be controlled by monitoring the applied voltage and other parameters during the synthesis, being quite reproducible procedures. The main advantages of these materials can be grouped in two: one related to their morphology, as has been commented, relative to their low resistance and internal diffusion, that is, their fluidynamic behavior in the reactor; the second group involves advantages related to the fact that the active phases can be nanoscaled and dispersed, improving the activity and selectivity in comparison with conventional catalytic materials with the same chemical composition.

Faradaic junction and isoenergetic charge transfer mechanism on semiconductor/semiconductor interfaces

Energy band alignment theory has been widely used to understand interface charge transfer in semiconductor/semiconductor heterojunctions for solar conversion or storage, such as quantum-dot sensitized solar cells, perovskite solar cells and photo(electro)catalysis. However, abnormally high open-circuit voltage and charge separation efficiency in these applications cannot be explained by the classic theory. Here, we demonstrate a Faradaic junction theory with isoenergetic charge transfer at semiconductor/semiconductor interface. Such Faradaic junction involves coupled electron and ion transfer, which is substantively different from the classic band alignment theory only involving electron transfer. The Faradaic junction theory can be used to explain these abnormal results in previous studies. Moreover, the characteristic of zero energy loss of charge transfer in a Faradaic junction also can provide a possibility to design a solar conversion device with a large open-circuit voltage beyond the Shockley-Queisser limit by the band alignment theory.

A Review of Electrical Assisted Photocatalytic Technologies for the Treatment of Multi-Phase Pollutants

This article reviews the fundamental theories and reaction mechanisms of photocatalytic technologies with the assistance of electrical field for degrading multi-phase pollutants. Photo(electro)catalysis including photocatalytic oxidation (PCO) and photoelectrocatalytic oxidation (PECO) have been a potential technologies applied for the treatment of organic and inorganic compounds in the wastewaters and waste gases, which has been treated as a promising technique by using semiconductors as photo(electro)catalysts to convert light or electrical energy to chemical energy. Combining photocatalytic processes with electrical field is an option to effectively decompose organic and inorganic pollutants. Although photocatalytic oxidation techniques have been used to decompose multi-phase pollutants, developing efficient advanced oxidation technologies (AOTs) by combining photocatalysis with electrical potential is urgently demanded in the future. This article reviews the most recent progress and the advances in the field of photocatalytic technologies combined with external electrical field, including the characterization of nano-sized photo(electro)catalysts, the degradation of multi-phase pollutants, and the development of electrical assisted photocatalytic technologies for the potential application on the treatment of organic and inorganic compounds in the wastewaters and waste gases. Innovative oxidation techniques regarding photo(electro)catalytic reactions with and without oxidants are included in this review article.

Evaluating the biological efficacy of a ballast water management system using filtration and electro-catalysis with an accurate definition of holding time

We employed a mesoscale experimental system and enriched natural plankton communities to investigate the efficacy of a type of ballast-water management system (BWMS) that uses a combination of filtration and electro-catalysis as the treatment technology. The water samples were collected immediately after treatment and at discharge to measure the biological efficiency of this BWMS. The main hydro chemical parameters, the TRO concentration and the plankton species composition before and after the ballast treatment process, were measured. After treatment, the concentration of TRO remained at a high level of 1.690 ± 0.573 (SD) mg/L. The biological efficacy of ballast water after treatment at holding times of 10 min, 20 min, 30 min, 40 min, and 50 min were measured. Holding time significantly impacted the biological efficacy. The discharged, treated water satisfied the D-2 standard of the International Maritime Organization (IMO) after 50 minutes of holding time.

Evaluating the contingency treatment performance of advanced electro-catalysis oxidation processes for marine bacteria in ballast water

Effects of ballast water (BW) treatment by Advanced Electro-Catalysis Oxidation Processes (AEOP) on abundance, activity, and diversity of marine bacteria were examined in a full-scale ballast water management system (BWMS) at Yangshan Port, Shanghai, China. Water samples were collected immediately after treatment and at discharge to evaluate the contingency treatment performance of the BWMS for bacteria. After treatment, the total viable count reduced to 0.7 × 104 CFU·mL−1, and both E. coli and enterococci decreased to 10 CFU·100 mL−1, satisfied the D-2 Standard of the International Maritime Organization (IMO). AEOP can be as an effective contingency reception facility. Sequencing of 16S rRNA gene amplicons demonstrated the declining trend in bacterial diversity, while the treatment did not completely eliminate the risk of bacterial dispersal, including potentially pathogenic bacteria, survived in treated and discharged samples. Bacterial diversity is of greater concern when evaluating effects of ballast water treatment on microorganisms, because the bacteria which can develop adaptive mechanisms to environmental change will have a greater potential for invasion in the new environment.

Conducting-Polymer Nanocomposites as Synergistic Supports That Accelerate Electro-Catalysis: PEDOT/Nano Co3O4/rGO as a Photo Catalyst of Oxygen Production from Water

This work describes how conducting polymer nanocomposites can be employed as synergistic supports that significantly accelerate the rate of electro-catalysis. The nanocomposite PEDOT/nano-Co3O4/rGO is discussed as an example in this respect, which is specific for photo electro-catalytic oxygen (O2) generation from water using light (PEDOT = poly (3,4-ethylenedioxythiophene; rGO = reduced graphene oxide). We show that the conducting polymer PEDOT and the conductive additive rGO may be used to notably amplify the rate of O2-generation from water by the nano catalyst, Co3O4. A composite film containing the precise molar ratio 7.18 (C; PEDOT):1 (Co):5.18 (C; rGO) exhibited high photocatalytic activity (pH 12) for the oxygen evolution reaction (OER) at 0.80 V (vs Ag/AgCl), with a current density of 1000 ± 50 μA/cm2 (including a photocurrent of 500 μA/cm2), achieved after >42 h of operation under illumination with a light of intensity 0.25 sun. By comparison, the best industrial catalyst, Pt, yielded a much lower 150 μA/cm2 under the same conditions. Oxygen gas was the sole product of the reaction.