A Robust Flow-Through Platform for Organic Contaminant Removal

Fe-doped g-C3N4 with duel active sites for ultrafast degradation of organic pollutants via visible-light-driven photo-Fenton reaction: Insight into the performance, kinetics, and mechanism

The photo-Fenton process provides a sustainable and cost-effective strategy for removing refractory organic contaminants in wastewater. Herein, a high-efficient Fe-doped g-C3N4 photocatalyst (Fe@CN10) with a unique 3D porous mesh structure was prepared by one-pot thermal polymerization for ultrafast degradation of azo dyes, antibiotics, and phenolic acids in heterogeneous photo-Fenton systems under visible light irradiation. Fe@CN10 exhibited a synergy between adsorption-degradation processes due to the co-existence of Fe3C and Fe3N active sites. Specifically, Fe3C acted as an adsorption site for pollutant and H2O2 molecules, while Fe3N acted as a photocatalytic active site for the high-efficient degradation of MO. Resultingly, Fe@CN10 showed a photocatalytic degradation rate of MO up to 140.32 mg/L min-1. The dominant ROS contributed to the removal of MO in the photo-Fenton pathway was hydroxyl radical (•OH). Surprisingly, as the key reactive species, singlet oxygen (1O2) generated from superoxide radical (•O2-) also efficiently attacked MO in a photo-self-Fenton pathway. Additionally, sponge/Fe@CN10 was prepared and filled in the continuous flow reactors for nearly 100% degradation of MO over 150 h when treating artificial organic wastewater. This work provided a facile route to prepare highly-active Fe-doped photocatalysts and develop a green photocatalytic system for wastewater treatment in the future.

Removal of Gaseous Hydrogen Sulfide by a FeOCl/H2O2 Wet Oxidation System

The removal of gaseous hydrogen sulfide using FeOCl/H₂O₂ was studied. The effects of the FeOCl dosage, the H₂O₂ concentration, the reaction temperature, and the gas flow rate on the removal of H₂S were investigated. The reaction products were analyzed, and the characterization of FeOCl was carried out by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy. Furthermore, radical quenching experiments were carried out using butylated hydroxytoluene, isopropanol, and benzoquinone. It was found that the H₂S removal rate for a H₂S gas concentration of 160 ppm reached 85.6% when bubbling through 100 mL of an aqueous solution containing FeOCl (1 g/L) and H₂O₂ (0.33 mol/L) at 293 K with a flow rate of 135 mL/min. Although the dissolution of chlorine in FeOCl was found to result in reduced catalytic performance, the activity was restored after soaking the catalyst in concentrated hydrochloric acid (37%) and subsequent calcination. The mechanism of H₂S removal was also discussed, and it was found that this process was controlled by H₂S diffusion. FeOCl was found to activate H₂O₂ and produce radicals, such as ^•OH and ^•O₂ ^-, resulting in the formation of a water film rich in radicals on the FeOCl surface. Following the diffusion of H₂S into the water film, it underwent oxidation by radicals to produce SO₄ ^2-. Overall, the catalyst and the product can be effectively separated.

An Eco-friendly Iron Cathode Electro-Fenton System Coupled With a pH-Regulation Electrolysis Cell for p-nitrophenol Degradation

The high consumption of salt reagents and strict pH control are still bottlenecks for the full-scale application of the Fenton reaction. In this work, a novel eco-friendly iron cathode electrochemical Fenton (ICEF) system coupled with a pH-regulation divided electrolysis cell was developed. In a pH-regulation divided electrolysis system, the desired pH for an effective Fenton reaction and for a neutral treated media could be obtained by H₂O splitting into H⁺ and OH⁻ at the anode and cathode, respectively. In an ICEF system, an iron plate was used as the cathode to inhibit the release of iron ions and promote the reduction of Fe³⁺ to Fe²⁺. It was found that when a potential of 1.2 V/SCE was applied on the iron cathode, 98% of p-nitrophenol was removed in the combined system after 30 min with continuously adding 200 mg/L of H₂O₂. Meanwhile, a COD and TOC removal efficiency of 79 and 60% was obtained, respectively. In this case, the conductivity just slightly increased from 4.35 to 4.37 mS/cm, minimizing the increase of water salinity, as compared with the conventional Fenton process. Generally, this combined system was eco-friendly, energy-efficient, and has the potential of being a promising technology for the removal of bio-refractory organic pollutants from wastewaters.

Self-Perpetuating Carbon Foam Microwave Plasma Conversion of Hydrocarbon Wastes into Useful Fuels and Chemicals

White wastes (unseparated plastics, face masks, textiles, etc.) pose a serious challenge to sustainable human development and the ecosystem and have recently been exacerbated due to the surge in plastic usage and medical wastes from COVID-19. Current recycling methods such as chemical recycling, mechanical recycling, and incineration require either pre-sorting and washing or releasing CO₂. In this work, a carbon foam microwave plasma process is developed, utilizing plasma discharge to generate surface temperatures exceeding ∼3000 K in a N₂ atmosphere, to convert unsorted white wastes into gases (H₂, CO, C₂H₄, C₃H₆, CH₄, etc.) and small amounts of inorganic minerals and solid carbon, which can be buried as artificial "coal". This process is self-perpetuating, as the new solid carbon asperities grafted onto the foam's surface actually increase the plasma discharge efficiency over time. This process has been characterized by in situ optical probes and infrared sensors and optimized to handle most of the forms of white waste without the need for pre-sorting or washing. Thermal measurement and modeling show that in a flowing reactor, the device can achieve locally extremely high temperatures, but the container wall will still be cold and can be made with cheap materials, and thus, a miniaturized waste incinerator is possible that also takes advantage of intermittent renewable electricity.