Construction of durable superhydrophilic activated carbon fibers based material for highly-efficient oil/water separation and aqueous contaminants degradation

Selective removal of organic contaminants and ascorbic acid enhancement effect based on the magnetic Fe0/FeS2-doped carbon nanolayer

Developing highly effective iron-based catalyst to selectively remove organic contaminants has garnered considerable attention. Herein, a magnetic Fe0/FeS2-doped carbon nanolayer (S-Fe@NC) was synthesized through a straightforward one-step pyrolysis method, pyrolyzing a mixture composed of 4,6-dihydroxypyrimidine, trithiocyanuric acid, and FeCl3·6H2O. With the presence of PMS, S-Fe@NC demonstrated the ability to remove almost 100% bisphenol-A (50 μM) within 3 min, attributed to its excellent graphitization degree and high FeS2/Fe0 content. Furthermore, the S-Fe@NC catalyst demonstrated an impressive kobs value of 1.476 min-1, which surpassed the traditional Fenton system by 77 times and even exceeded the commercial Fe0 catalyst by 127 times. More importantly, the S-Fe@NC/PMS system succeeded in selectively removing organic contaminants based on the hydrophobic interaction between catalyst and contaminants. Besides, the result of electron paramagnetic resonance and the radical quenching experiments indicated that ·OH, SO4·-, 1O2, and O2·- were involved in the organic contaminants removal. Interestingly, after adding ascorbic acid (AA) to the S-Fe@NC/PMS system, more ROS could be generated to result in the kobs augmenting by 4.16 times (6.133 min-1), completely different from the common sense that AA was usually used as a radical quencher. Additionally, the magnetically separable catalyst also exhibited excellent reusability and broad pH adaptability (2.0-12.0). This study provided a valuable insight for developing highly selective and effective Fe-based catalyst for practical wastewater treatment.

A multifunctional Ag NPs/guar gum hydrogel as versatile platform for catalysts, antibacterial agents, and construction of oil-water separation interfaces

The frequently encountered wastewater contaminations, including soluble aromatic compound and dye pollutants, pathogenic bacteria, and insoluble oils, have resulted in significant environmental and human health issues. It poses a challenge to utilize identical materials for the treatment of complex wastewater. Herein, in this research, multifunctional Ag NPs/guar gum hybrid hydrogels were fabricated using a facile in situ reduction and self-crosslinking method for efficient remediation of complex wastewater. The Ag NPs/guar gum hybrid hydrogel showed remarkable remodeling, adhesive, and self-healing characteristics, which was favorable for its versatile applications. The combination of Ag NPs with the guar gum skeleton endowed the hybrid hydrogel with exceptional catalytic activity for reducing aromatic compounds and dye pollutants, as well as remarkable antibacterial efficacy against pathogenic bacteria. In addition, the Ag NPs/guar gum hybrid hydrogel could be employed to coat a variety of substrates, including cotton fabrics and stainless steel meshes. The hydrogel coated cotton fabrics and meshes presented superhydrophilicity/underwater superoleophobicity, excellent antifouling capacity, and outstanding recyclability, which could be successfully applied for efficient separation of oil-water mixtures. The findings of this work provide a feasible and cost-effective approach for the remediation of intricate wastewater.

Activated carbon fibers functionalized with superhydrophilic coated pDA/TiO2/SiO2 with photoluminescent self-cleaning properties for efficient oil-water separation

The adhesion of high-viscosity oil contamination poses limitations on three-dimensional (3D) materials' practical use in treating oilfield-produced water (OPW). In this study, we developed a hybrid pDA/TiO2/SiO2 coating (PTS) on the surface of hydrophilic activated carbon (ACF1) through a combination of dopamine (DA) polymerization, ethyl orthosilicate (TEOS) hydrolysis, and the condensation of TiO2 nanoparticles (NPs) with SiO2 NPs. This coating was designed for gravity-based oil-water separation. The inherent porosity and generous pore size of ACF1-PTS conferred it an ultra-high permeation flux (pure water flux of 3.72 × 105 L∙m-2∙h-1), allowing it to effectively separate simulated oil-water mixtures and oil-water emulsions while maintaining exceptional permeation flux and oil rejection efficiency. When compared to cleaning methods involving ethanol aqueous solutions and NaClO, ultraviolet (UV) illumination cleaning proved superior, enabling oil-contaminated ACF1-PTS to exhibit remarkable flux recovery efficiency and oil-removal capabilities during cyclic separation of actual OPW. Furthermore, the ACF1-PTS material demonstrated impressive stability and durability when exposed to acidic environments (acid, alkali, and salt), robust hydraulic washout conditions, and 25-cycle tests. This study offers valuable insights and research avenues for the development of highly efficient and environmentally friendly 3D oil-water separation materials for the actual treatment of OPW.

Super-amphiphilic graphene promotes peroxymonosulfate-based emulsion catalysis for efficient oil purification

Oil fractions containing highly toxic and hazardous organic contaminants can not only cause severe environmental disasters, but also an undesired waste of resources. Given the exceptional performance of persulfates in the removal of persistent and refractory organic pollutants from aqueous media, herein, a peroxymonosulfate-based Pickering emulsion catalytic (PPEC) system was constructed for the hazardous oil purification, using super-amphiphilic graphene as a solid emulsifier and a heterogeneous catalyst simultaneously. Combined detailed instrumental analysis with theoretical calculations, we find that the incorporation of pyridinic N and its oxide significantly facilitated the formation of super-amphiphilic graphene and successfully induced the formation of Pickering emulsion. In addition to stabilizing the PPEC system, super-amphiphilic graphene can also achieve efficient removal of Sudan III (simulated lipophilic organic pollutant) by activating peroxymonosulfate (PMS) to generate •O₂^- and ¹O₂. Results showed that 80 mg/L Sudan III (20 mL) could be fully degraded within 30 min using 10 mL 5 mmol PMS. More significantly, our proposed PPEC system also exhibited excellent property in the purification of practical waste engine oil. This study provides new insights into the purification and recovery of waste oil.

Layered double hydroxide/carbonitride heterostructure with potent combination for highly efficient peroxymonosulfate activation

Iron-based layered double hydroxides (LDHs) have drawn tremendous attention as a promising peroxymonosulfate (PMS) activators, but they still suffer from low efficiencies limited by electrostatic agglomeration and low electronic conductivity. Herein, a MgFeAl layered double hydroxide/carbonitride (LDH/CN) heterostructure was constructed via triggering the interlayer reaction of citric acid (CA) and urea. CA as a structure-directing agent regulated the interlayer anion of MgFeAl-LDH, which enabled an interfacial tuning in the process of coupling with CN. The obtained LDH/CN heterostructure, as an efficient PMS activator, achieved nearly 100% bisphenol A (BPA) removal rate in 10 min with high specific activity (0.146 L min^-1·m^-2). Electron paramagnetic resonance (EPR) tests, quenching experiments, electrochemical characterization and X-ray photoelectrons spectroscopy (XPS) tests were applied to clarify the mechanism of BPA degradation. The results unraveled that the activity of the catalyst originated from the heterostructure of LDH and CN with an efficient interfacial electron transfer, which promoted the fast generation of O₂^•- for rapid pollutant degradation. In addition, the catalyst exhibited excellent applicability in realistic wastewater. This work offered a rational strategy for forming a heterostructure catalyst with a fine interface engineering in actual environmental cleanup.

Direct Z-scheme heterojunction Bi/Bi2S3/α-MoO3 photoelectrocatalytic degradation of tetracycline under visible light

A hot research topic in visible-light-driven photoelectrocatalytic (PEC) oxidation technology is the development of superior photoanode materials. The design of the photoanode system with a direct Z-scheme charge transfer mechanism is crucial to achieving effective charge separation for sustainable photoelectrocatalysis. Here, a novel Bi/Bi2S3/α-MoO3 heterostructure was successfully assembled by a simple and feasible strategy. The direct Z-scheme heterogeneous formed between Bi2S3 and α-MoO3 has the advantages of low resistance, high optical response current and the surface plasmon resonance (SPR) effect of Bi nanoparticles (Bi NPs). Thus, the efficiency of photogenerated carrier separation and transfer is further enhanced, and the catalytic activity is significantly improved. It is impressive that the unique photoanode has achieved a maximum removal efficiency of 85.8% of tetracycline (TC) pollutants under visible light irradiation within 60 min and has excellent stability, which is expected to degrade antibiotics efficiently and environmentally in harsh environments. These characteristics give Bi/Bi2S3/α-MoO3 promising candidates for practical applications in antibiotic degradation.

Hygroscopic ramie fabrics for recovering highly viscous low sulfur fuel oil

Low sulfur fuel oils (LSFOs) with less than 0.5% sulfur content have been mandated for marine vessels by the International Maritime Organization since 2020. However, owing to the low dispersibility and high viscosity of LSFOs, their oceanic spills are difficult to clean using conventional response systems. In this study, we propose a superhydrophilic and hygroscopic ramie to clean spilled LSFO. To this end, a raw ramie fiber, which is intrinsically hydrophobic, was treated using a mild alkali to remove its waxy, rough, and gummy veneer and reveal a smooth surface. This substantially improved its hygroscopic nature, superhydrophilicity, and water-retention, while preserving its mechanical durability in dry and wet environments. The hygroscopic ramie exhibited underwater superoleophobicity and self-cleaning abilities against highly adhesive LSFOs. Two proofs-of-concept are demonstrated in this study-an oil-proof glove for maximizing oil repellency and a direct oil-scooping device for simple and continuous recovery of spilled oil with high efficiency.