Synergetic Oxidation of the Hydroxyl Radical and Superoxide Anion Lowers the Benzoquinone Intermediate Conversion Barrier and Potentiates Effective Aromatic Pollutant Mineralization

Temperature-induced atomic intrinsic sites evolution during waste dyeing sludge into the wealthy iron-based catalyst to sustainable decontamination

Although the worldwide spike in the production of dyeing sludge offers a tantalizing resource to be harnessed, effective waste-to-wealth strategies remain elusive due to its intricate toxic organic matter and metallic elements. Here, we developed a temperature-rebuilding strategy to transform discarded dyeing sludge into an iron-based catalyst with favorable charge transfer for the highly efficient and sustainable Fenton-like catalytic degradation of ppm-level contaminants in wash-tank water. Using X-ray diffraction, X-ray photoelectron spectroscopy, and synchrotron X-ray absorption spectroscopy, we could precisely track and identify the gradual formation of inherent sites (i.e., Fe2(SO4)3, FeOOH, and Fe1-xS) towards active sites (i.e., FeS and Fe0) at crystal, surface, and atomic levels. Benefiting from the reconstruction of iron sites, BC-800 effectively decomposed peroxymonosulfate into multiple radicals and nonradicals through electronic structure modulation, which enabled nearly 100 % degradation and over 60 % mineralization rate of common aromatic compounds within 30 min via ring-opening and dechlorination/substitution pathways. More delightedly, the BC-800 maintained excellent Fenton-like activity across a broad pH or multiple anions coexisted, and its device allowed extended parachlorophenol degradation for over 1 d. This work proposes a feasible "waste control by waste" approach to the reutilization of dyeing sludge, encouraging a potential solution for sustainable wastewater treatment.

Selective ·OH generation in Fenton-like reaction by dual sulfur coordination of iron organic frameworks

Traditional Fenton-like reaction simultaneously generates hydroxyl radical (·OH) and superoxide radical (·O2-) through Fe(Ⅲ)/Fe(Ⅱ) cycle, while ·OH with higher oxidation capacity is commonly consumed by ·O2-. Therefore, selective generation of ·OH but not ·O2- in Fenton-like reaction is highly desirable, but still remains challenging since it is hard to bypass Fe cycle process. This work constructed dual S coordination of Fe organic frameworks, i.e. S-Fe-MOFs, using ligand with mercaptan groups (-SH), which achieving 93.89 % selectivity of ·OH generation in Fenton-like reaction, much higher than that of Fe-MOFs without S-Fe coordination (48.65 %). Benefiting from selectivity of ·OH generation, Fenton-like activity of S-Fe-MOFs up to 0.36 min-1 using bisphenol A (BPA) as a probe, was 75 times than that of Fe-MOFs (0.0048 min-1). Dual S coordination could give rise to a symmetrical "push-pull" effect on OO bond of H2O2 by changing adsorption configuration from "end-on" to "side on" type that two O atoms in H2O2 adsorbed together on Fe sites, and thus resulting in one H2O2 split directly two ·OH. Differ from traditional ·OH generation pathway, this process not only bypasses electron transfer between Fe(Ⅱ)/Fe(Ⅲ) cycle but also avoids the electron loss of catalyst, endowing S-Fe-MOFs excellent stability in Fenton-like reaction. S-Fe-MOFs on fix-bed reactor maintained high efficiency towards BPA degradation in 12 h continuous flow in real water environment. This work provides new insight into designing catalyst to overcome the limitation of traditional Fenton-like reaction.

Mn/S diatomic sites in C3N4 to enhance O2 activation for photocatalytic elimination of emerging pollutants

Oxygen activation leading to the generation of reactive oxygen species (ROS) is essential for photocatalytic environmental remediation. The limited efficiency of O2 adsorption and reductive activation significantly limits the production of ROS when employing C3N4 for the degradation of emerging pollutants. Doping with metal single atoms may lead to unsatisfactory efficiency, due to the recombination of photogenerated electron-hole pairs. Here, Mn and S single atoms were introduced into C3N4, resulting in the excellent photocatalytic performances. Mn/S-C3N4 achieved 100% removal of bisphenol A, with a rate constant 11 times that of pristine C3N4. According to the experimental results and theoretical simulations, S-atoms restrict holes, facilitating the photo-generated carriers' separation. Single-atom Mn acts as the O2 adsorption site, enhancing the adsorption and activation of O2, resulting the generation of ROS. This study presents a novel approach for developing highly effective photocatalysts that follows a new mechanism to eliminate organic pollutants from water.

Constructing Tandem Fenton-like Reaction Systems Based on Structure Adaption to Boost Water Contaminant Mineralization Efficiency

Mineralization of emerging contaminants by using advanced oxidation processes (AOPs) is a desirable option to ensure water safety, but still challenged by the excessive chemical and/or energy input. Here, we conceptually proposed the tandem reaction system (TRS) of different reactive oxygen species (ROS) based on structure adaption of target contaminants. To construct a model TRS, we first realized highly selective generation of three classical ROS (1O2, HO⋅ and SO4⋅-) by peroxymonosulfate activation in an electrochemical Fenton-like system, where three replaceable Fe-centered cathodes were rationally designed as electronic mediator. The 1O2+SO4⋅--TRS exhibited nearly 100 % mineralization of sulfamethoxazole (SMX), whereas only 34.2 %, 56.2 % and 60.8 % for each of the single 1O2/HO⋅/SO4⋅--AOP systems. Mechanism exploration of SMX degradation in TRS evidenced that the initial reaction with 1O2 selectively destructed the sulfonamide bridge of SMX to form p-aminobenzenesulfonic acid, which will be vulnerable to sequent SO4⋅- attack to facilitate mineralization. Successful extendibility of 1O2+SO4⋅--TRS to other sulfonamide antibiotics and 1O2+HO⋅-TRS to phenolic and arylcarboxylic compounds, as well as the demonstration of 1O2+SO4⋅--TRS in treatment of three actual pharmaceutical wastewaters strongly support that TRS is a powerful and sustainable strategy to enhance the mineralization of emerging contaminants in water.

The photocatalytic wastewater hydrogen production process with superior performance to the overall water splitting

The utilization of a cost-free sacrificial agent is a novel approach to significantly enhance the efficiency of photocatalytic hydrogen (H2) production by water splitting. Wastewater contains various organic pollutants, which have the potential to be used as hole sacrificial agents to promote H2 production. Our studies on different pollutants reveals that not all pollutants can effectively promote H2 production. However, when using the same pollutants, not all photocatalysts achieved a higher H2 evolution rate than pure water. Only when the primary oxidizing active species of the photocatalyst are •OH radicals, which are generated by photogenerated holes, and when the pollutants are easily attacked and degraded by •OH radicals, can the production of H2 be effectively promoted. It is noteworthy that the porous brookite TiO2 photocatalyst exhibits a significantly higher H2 evolution rate in Reactive Red X-3B and Congo Red, reaching as high as 26.46 mmol⋅g-1⋅h-1 and 32.85 mmol⋅g-1 ⋅h-1, respectively, which is 2-3 times greater than that observed in pure water and is 10 times greater than most reported studies. The great significance of this work lies in the potential for efficient H2 production through the utilization of wastewater.

Localized heating coupling with radical oxidation eliminating antibiotic resistance genes (ARGs) in interfacial photothermal Fenton-like disinfection process

Conventional oxidative disinfection processes are inefficient in eliminating intracellular antibiotic resistance genes (iARGs) due to the barrier of the cell membrane and the competitive reaction of cellular constituents within antibiotic-resistant bacteria (ARB), resulting in the widespread prevalence of ARGs in recycled water. This study presented the first application of localized heating coupling with advanced oxidation to destroy the resistant Escherichia coli cells and improved subsequent iARGs (blaTEM-1) degradation in a novel photothermal Fenton-like disinfection process. The Fe-Mn@CNT microfiltration membrane, comprising carbon nanotubes wrapped with Fe and Mn nanoparticles (Fe-Mn@CNT), was employed as a nanomaterial for photothermal conversion and H2O2 activation. The highly efficient absorption of full-spectrum photons by CNTs enabled the Fe-Mn@CNT membrane to concentrate light to generate localized intense heat, resulting in the destruction of ARB nearby, and the subsequent release of iARGs. Interfacial heat favored Fe-Mn-induced H2O2 activation, leading to the production of more ·OH, which in turn promoted the oxidation for ARG degradation and ARB cell damage. The results of the acetylcysteine quenching experiments indicated that interfacial heating and radical oxidation-induced accumulation of intracellular reactive oxygen species contributed to the elimination of about 1-log iARGs through direct attack. The integrity of the cell membrane, the morphology of ARB and the variation of i/e ARG copy numbers were observed to reveal that the introduction of interfacial heating aggravated the cell lysis and accelerated the iARGs release, resulting in the inactivation of 7.27-log ARB and the elimination of 4.64-log iARGs and 2.23-log eARGs. Localized heating coupling with ·OH oxidation achieved a 143 % increase in iARGs removal compared to the conventional Fenton-like oxidation. The interfacial photothermal Fenton-like disinfection process exhibited remarkable material stability, robust disinfection performance, and effective suppression of horizontal gene transfer, underscoring its immense potential to mitigate the risk of ARG dissemination in reclaimed water systems.

Enhancing Fenton-like reaction mediating performance of covalent organic frameworks through porosity modification

Covalent organic framework (COF) catalytic photocatalysts mediating Fenton-like reactions have been applied to the treatment of organic dyes in printing and dyeing wastewater. However, the photocatalytic performance of original COF is often unsatisfactory. This study investigated the impact of porosity modification strategies on the performance of COF photocatalysts in mediating the removal of organic dyes via Fenton-like reaction. Porosity modification was achieved by increasing the concentration of acetic acid (HAc) catalyst during COF preparation. The modified TAPB-DMTA COF (12M COF) exhibited excellent adsorption and photocatalytic properties. The Fenton-like reaction mediated by 12M COF photocatalysis removed nearly 96% of malachite green (MG) within 20 min, with a rate constant of 0.091 min-1, which was 2.9 and 6.5 times higher than that of g-C3N4 and original COF under the same reaction conditions, respectively. Additionally, the modulation mechanism of porosity modification on COF photocatalysis was explored. The conduction band (CB) of COF was reduced from -0.14 eV to -0.38 eV after porosity modification, facilitating the generation of longer-lived O2•- in the reaction system, which was conducive to efficient MG removal. Anti-interference experiments showed that the photocatalytic Fenton-like reaction system based on 12 M COF was less affected by common anions, cations and dissolved organics, while maintaining a high MG removal rate in tap water, mid-water, secondary clarifier effluent and river water. In summary, porosity modification was an effective strategy to improve the catalytic performance of original COFs. This study presented an efficient metal-free photocatalyst modification strategy for the Fenton-like reaction while avoiding the production of toxic by-products during dye degradation.

Highly energy-efficient degradation of simulated dye wastewater by array type underwater bubble discharge plasma: Key factors identification and degradation pathways

The extensive use of dyes presents a significant safety concern for the reuse of water resources, highlighting the critical need for a rapid and efficient degradation method for dye mixtures in wastewater. This study introduces a degradation system based on an array type underwater bubble discharge plasma specifically designed to treat a dye mixture wastewater containing methylene blue (MB) and methyl violet 2B (MV2B). Analysis of the optical and electrical characteristics reveals that the device experiences minimal temperature increase, with the highest intensity of the band associated with N2 in the emission spectra, and discharges occurring predominantly during the rising and falling edges of a pulse cycle. Experimental results demonstrate that the most effective degradation efficiencies (MB = 94.83%, MV2B = 93.48%) are achieved at an initial dye concentration of 50 mg/L, a power supply frequency of 6 kHz, an air flow rate of 2.5 SLM and an initial electrical conductivity of 50 μS/cm. The degradation of dyes is primarily attributed to the demethylation process of O3(aq) and other species. Toxicity analysis indicates that the plasma degradation process significantly reduces the toxicity of the intermediate products of dyes. This study not only presents a novel approach for treating high concentration mixed dye wastewater, but also provides valuable insights for future research in this area.

Decolorization and degradation of crystal violet dye by electron beam radiation: Performance, degradation pathways, and synergetic effect with peroxymonosulfate

Ionizing radiation (mainly including gamma ray and electron beam) technology provides a more efficient and ecological option for dye-containing wastewater treatment, which is supported by its successful achievements in industrial-scale applications. However, the degradation pathway of triphenylmethane dyes by radiation technology is still unclear. In this study, crystal violet (CV) was selected as representative cationic triphenylmethane dye, the decolorization and degradation performance by electron beam radiation technology was systematically evaluated. The results showed that CV can be efficiently decolorized and mineralized by radiation, and its degradation kinetics followed the first-order kinetic model. The effect of inorganic anions and chelating agents commonly existed in dye-containing wastewater on CV decolorization and total organic carbon (TOC) removal was explored. Quenching experiments, density functional theory (DFT) calculation and high performance liquid chromatography mass spectrometry (HPLC-MS) analysis were employed to reveal CV decolorization and degradation mechanism and pathway, which mainly included N-demethylation, triphenylmethane chromophore cleavage, ring-opening of aromatic products and further oxidation to carboxylic acid, and mineralization to CO2 and H2O. Additionally, electron beam radiation/PMS process was explored to decrease the absorbed dose required for decolorization and degradation, and the synergetic effect of radiation with PMS was elucidated. More importantly, the findings of this study would provide the support for treating actual dyeing wastewater by electron beam radiation technology.

The effects of water, substrate, and intermediate adsorption on the photocatalytic decomposition of air pollutants over nano-TiO2 photocatalysts

The photocatalytic performance of nano-TiO2 photocatalysts in air pollutant degradation greatly depends on the adsorption of water, substrates, and intermediates. Especially under excessive humidity, substrate concentration, and intermediate concentration, the competitive adsorption of water, substrates, and intermediates can seriously inhibit the photocatalytic performance. In the past few years, extensive studies have been performed to investigate the influence of humidity, substrate concentration, and intermediates on the photocatalytic performance of TiO2, and significant advances have been made in the area. However, to the best of our knowledge, there is no review focusing on the effects of water, substrate, and intermediate adsorption to date. A comprehensive understanding of their mechanisms is key to overcoming the limited application of nano-TiO2 photocatalysts in the photocatalytic decomposition of air pollutants. In this review, the progress in experimental and theoretical fields, including a recent combination of photocatalytic experiments and adsorption and photocatalytic simulations by density functional theory (DFT), to explore the impact of adsorption of various reaction components on nano-TiO2 photocatalysts is comprehensively summarized. Additionally, the mechanism and broad perspective of the impact of their adsorption on the photocatalytic activity of TiO2 in air treatment are also critically discussed. Finally, several solutions are proposed to resolve the current problems related to environmental factors. In general, this review contributes a comprehensive perspective of water, substrate, and intermediate adsorption toward boosting the photocatalytic application of TiO2 nanomaterials.