Rapid self-heating synthesis of Fe-based nanomaterial catalyst for advanced oxidation

Reconstructing the electron and spin structures of nanoscale iron sulfide through a biosurfactant layer towards radical-nonradical co-dominant regime

Radical-nonradical co-dominant pathways have become a hot topic in advanced oxidation, but achieving this on transition metal sulfides (TMS) remains challenging because their inherently higher electron and spin densities always induce radicals rather than nonradicals. Herein, a biosurfactant layer (BLR) was introduced to redistribute the electron and spin structure of nanoscale iron sulfide (FeS), which allowed both radical and nonradical to co-dominate the catalytic reaction. The resulting BLR-encased FeS hybrid (BLR@FeS) exhibited satisfactory removal efficiency (98.5 %) for hydrogen peroxide (H2O2) activation, outperforming both the constituent components [FeS (70.9 %) and BLR (86.2 %)]. Advanced characterizations showed that C, O, N-related sites (-CO and -NC) in BLR attracted electrons in FeS due to their strong electronegativity and electron-withdrawing capacity, which not only decreased electron density in FeS, but also resulted in a shift of the Fe/S sites from the high-spin to the medium-spin state. The reaction routes established by the BLR@FeS/H2O2 system maintained desirable stability against environmental interferences such as common inorganic anions, humic acid and changes in pH. Our study provides a state-of-the-art, molecule-level understanding of tunable co-dominant pathways and expands the targeted applications in the field of advanced oxidation.

Platinum-Ruthenium Bimetallic Nanoparticle Catalysts Synthesized Via Direct Joule Heating for Methanol Fuel Cells

Platinum-Ruthenium (PtRu) bimetallic nanoparticles are promising catalysts for methanol oxidation reaction (MOR) required by direct methanol fuel cells. However, existing catalyst synthesis methods have difficulty controlling their composition and structures. Here, a direct Joule heating method to yield highly active and stable PtRu catalysts for MOR is shown. The optimized Joule heating condition at 1000 °C over 50 microseconds produces uniform PtRu nanoparticles (6.32 wt.% Pt and 2.97 wt% Ru) with an average size of 2.0 ± 0.5 nanometers supported on carbon black substrates. They have a large electrochemically active surface area (ECSA) of 239 m2 g-1 and a high ECSA normalized specific activity of 0.295 mA cm-2. They demonstrate a peak mass activity of 705.9 mA mgPt -1 for MOR, 2.8 times that of commercial 20 wt.% platinum/carbon catalysts, and much superior to PtRu catalysts obtained by standard hydrothermal synthesis. Theoretical calculation results indicate that the superior catalytic activity can be attributed to modified Pt sites in PtRu nanoparticles, enabling strong methanol adsorption and weak carbon monoxide binding. Further, the PtRu catalyst demonstrates excellent stability in two-electrode methanol fuel cell tests with 85.3% current density retention and minimum Pt surface oxidation after 24 h.

Atomic-Level Engineered Cobalt Catalysts for Fenton-Like Reactions: Synergy of Single Atom Metal Sites and Nonmetal-Bonded Functionalities

Single atom catalysts (SACs) are atomic-level-engineered materials with high intrinsic activity. Catalytic centers of SACs are typically the transition metal (TM)-nonmetal coordination sites, while the functions of coexisting non-TM-bonded functionalities are usually overlooked in catalysis. Herein, the scalable preparation of carbon-supported cobalt-anchored SACs (CoCN) with controlled Co─N sites and free functional N species is reported. The role of metal- and nonmetal-bonded functionalities in the SACs for peroxymonosulfate (PMS)-driven Fenton-like reactions is first systematically studied, revealing their contribution to performance improvement and pathway steering. Experiments and computations demonstrate that the Co─N3C coordination plays a vital role in the formation of a surface-confined PMS* complex to trigger the electron transfer pathway and promote kinetics because of the optimized electronic state of Co centers, while the nonmetal-coordinated graphitic N sites act as preferable pollutant adsorption sites and additional PMS activation sites to accelerate electron transfer. Synergistically, CoCN exhibits ultrahigh activity in PMS activation for p-hydroxybenzoic acid oxidation, achieving complete degradation within 10 min with an ultrahigh turnover frequency of 0.38 min-1, surpassing most reported materials. These findings offer new insights into the versatile functions of N species in SACs and inspire rational design of high-performance catalysts in complicated heterogeneous systems.

Electrothermal mineralization of per- and polyfluoroalkyl substances for soil remediation

Per- and polyfluoroalkyl substances (PFAS) are persistent and bioaccumulative pollutants that can easily accumulate in soil, posing a threat to environment and human health. Current PFAS degradation processes often suffer from low efficiency, high energy and water consumption, or lack of generality. Here, we develop a rapid electrothermal mineralization (REM) process to remediate PFAS-contaminated soil. With environmentally compatible biochar as the conductive additive, the soil temperature increases to >1000 °C within seconds by current pulse input, converting PFAS to calcium fluoride with inherent calcium compounds in soil. This process is applicable for remediating various PFAS contaminants in soil, with high removal efficiencies ( >99%) and mineralization ratios ( >90%). While retaining soil particle size, composition, water infiltration rate, and cation exchange capacity, REM facilitates an increase of exchangeable nutrient supply and arthropod survival in soil, rendering it superior to the time-consuming calcination approach that severely degrades soil properties. REM is scaled up to remediate soil at two kilograms per batch and promising for large-scale, on-site soil remediation. Life-cycle assessment and techno-economic analysis demonstrate REM as an environmentally friendly and economic process, with a significant reduction of energy consumption, greenhouse gas emission, water consumption, and operation cost, when compared to existing soil remediation practices.

Revealing the Synergistic Effect of Cation and Anion Vacancies on Enhanced Fenton-Like Reaction: The Electron Density Modulation of O 2p-Co 3d Bands

Defect engineering is considered as a flexible and effective mean to improve the performance of Fenton-like reactions. Herein, a simple method is employed to synthesize Co3O4 catalysts with Co-O vacancy pairs (VP) for peroxymonosulfate (PMS) activation. Multi-scaled characterization, experimental, and simulation results jointly revealed that the cation vacancies-VCo contributed to enhanced conductivity and anion vacancies-VO provided a new active center for the 1O2 generation. Co3O4-VP can optimize the O 2p and Co 3d bands with the strong assistance of synergistic double vacancies to reduce the reaction energy barrier of the "PMS → Co(IV) = O → 1O2" pathway, ultimately triggering the stable transition of mechanism. Co3O4-VP catalysts with radical-nonradical collaborative mechanism achieve the synchronous improvement of activity and stability, and have good environmental robustness to favor water decontamination applications. This result highlights the possibility of utilizing anion and cation vacancy engineering strategies to rational design Co3O4-based materials widely used in catalytic reactions.

Advanced oxidation processes for water and wastewater treatment - Guidance for systematic future research

Advanced oxidation processes (AOPs) are a growing research field with a large variety of different process variants and materials being tested at laboratory scale. However, despite extensive research in recent years and decades, many variants have not been transitioned to pilot- and full-scale operation. One major concern are the inconsistent experimental approaches applied across different studies that impede identification, comparison, and upscaling of the most promising AOPs. The aim of this tutorial review is to streamline future studies on the development of new solutions and materials for advanced oxidation by providing guidance for comparable and scalable oxidation experiments. We discuss recent developments in catalytic, ozone-based, radiation-driven, and other AOPs, and outline future perspectives and research needs. Since standardized experimental procedures are not available for most AOPs, we propose basic rules and key parameters for lab-scale evaluation of new AOPs including selection of suitable probe compounds and scavengers for the measurement of (major) reactive species. A two-phase approach to assess new AOP concepts is proposed, consisting of (i) basic research and proof-of-concept (technology readiness levels (TRL) 1-3), followed by (ii) process development in the intended water matrix including a cost comparison with an established process, applying comparable and scalable parameters such as UV fluence or ozone consumption (TRL 3-5). Subsequent demonstration of the new process (TRL 6-7) is briefly discussed, too. Finally, we highlight important research tools for a thorough mechanistic process evaluation and risk assessment including screening for transformation products that should be based on chemical logic and combined with complementary tools (mass balance, chemical calculations).

Facet-Dependent Fe2O3/BiVO4(110)/BiVO4(010)/Fe2O3 Dual S-Scheme Photocatalyst as an Efficient Visible-Light-Driven Peroxymonosulfate Activator for Norfloxacin Degradation

A lack of eco-friendly, highly active photocatalyst for peroxymonosulfate (PMS) activation and unclear environmental risks are significant challenges. Herein, we developed a double S-scheme Fe2O3/BiVO4(110)/BiVO4(010)/Fe2O3 photocatalyst to activate PMS and investigated its impact on wheat seed germination. We observed an improvement in charge separation by depositing Fe2O3 on the (010) and (110) surfaces of BiVO4. This enhancement is attributed to the formation of a dual S-scheme charge transfer mechanism at the interfaces of Fe2O3/BiVO4(110) and BiVO4(010)/Fe2O3. By introducing PMS into the system, photogenerated electrons effectively activate PMS, generating reactive oxygen species (ROS) such as hydroxyl radicals (·OH) and sulfate radicals (SO4·-). Among the tested systems, the 20% Fe2O3/BiVO4/Vis/PMS system exhibits the highest catalytic efficiency for norfloxacin (NOR) removal, reaching 95% in 40 min. This is twice the catalytic efficiency of the Fe2O3/BiVO4/PMS system, 1.8 times that of the Fe2O3/BiVO4 system, and 5 times that of the BiVO4 system. Seed germination experiments revealed that Fe2O3/BiVO4 heterojunction was beneficial for wheat seed germination, while PMS had a significant negative effect. This study provides valuable insights into the development of efficient and sustainable photocatalytic systems for the removal of organic pollutants from wastewater.

Enzyme-triggered on-demand release of a H2O2-self-supplying CuO2@Fe3O4 nanoagent for enhanced chemodyamic antimicrobial therapy and wound healing

Nanoagents for chemodynamic therapy (CDT) hold a promising future in the field of antimicrobials, especially copper peroxide (CuO2) (CP) nanomaterials which have garnered significant attention due to their ability to self-supply H2O2. Nevertheless, the poor stability of CuO2 remains a critical challenge which restricts its practical application in the antibacterial field. In this study, an advanced nano-antimicrobial system HA-CP@Fe3O4 with enzyme-responsive properties is developed by coating hyaluronic acid (HA) on CuO2-loaded iron tetraoxide nanoparticles. The coating of HA not only stabilizes the CuO2 nanomaterials but also provides responsiveness towards the enzyme hyaluronidase, which is typically secreted by some bacteria. The outer layer of HA in HA-CP@Fe3O4 undergoes decomposition in the presence of hyaluronidase-secreting bacteria, resulting in the release of CuO2@Fe3O4. The released CuO2@Fe3O4 then self-supplies H2O2 and generates reactive oxygen species (ROS) within the infected microenvironment through Fenton and Russell effects, to ultimately achieve effective and precise antimicrobial activity. Simultaneously, the magnetic property provided by Fe3O4 allows the substance to be directed towards the infection site. Both in vitro and in vivo tests demonstrated that HA-CP@Fe3O4 exhibited excellent antimicrobial capabilities at low concentration (30 μg mL-1), exceptional biocompatibility and the ability to accelerate wound healing. The findings of this work offer a new and promising approach for targeted and precise CDT.

Synergistic effects of Fe-based nanomaterial catalyst on humic substances formation and microplastics mitigation during sewage sludge composting

In this study, a novel Fe-based nanomaterial catalyst (Fe0/FeS) was synthesized via a self-heating process and employed to explore its impact on the formation of humic substances and the mitigation of microplastics. The results reveal that Fe0/FeS exhibited a significant increase in humic acid content (71.01 mg kg-1). Similarly, the formation of humic substances resulted in a higher humification index (4.91). Moreover, the addition of Fe0/FeS accelerated the degradation of microplastics (MPs), resulting in a lower concentration of MPs (9487 particles/kg) compared to the control experiments (22792 particles/kg). Fe0/FeS significantly increased the abundance of medium-sized MPs (50-200 μm) and reduced the abundance of small-sized (10-50 μm) and large-sized MPs (>1000 μm). These results can be attributed to the Fe0/FeS regulating the ▪OH production and specific microorganisms to promote humic substance formation and the degradation of MPs. This study proposes a feasible strategy to improve composting characteristics and reduce contaminants.

Deep Oxidation of Chlorinated VOCs by Efficient Catalytic Peroxide Activation over Nanoconfined Co@NCNT Catalysts

The catalytic removal of chlorinated VOCs (CVOCs) in gas-solid reactions usually suffers from chlorine-containing byproduct formation and catalyst deactivation. AOP wet scrubber has recently attracted ever-increasing interest in VOC treatment due to its advantages of high efficiency and no gaseous byproduct emission. Herein, the low-valence Co nanoparticles (NPs) confined in a N-doped carbon nanotube (Co@NCNT) were studied to activate peroxymonosulfate (PMS) for efficient CVOC removal in a wet scrubber. Co@NCNT exhibited unprecedented catalytic activity, recyclability, and low Co ion leakage (0.19 mg L-1) for chlorobenzene degradation in a very wide pH range (3-11). The chlorobenzene removal efficiency was kept stable above 90% over Co@NCNT, much higher than that of nonconfined Co@NCNS (45%). The low-valence Co NPs achieved a continuous electron redox cycling (Co0/Co2+ → Co3+ → Co0/Co2+) and greatly promoted the O-O bond dissociation of PMS with the least energy (0.83 eV) inside the channel of Co@NCNT to form abundant HO• and SO4•-. Thus, the deep oxidation of chlorobenzene was achieved without any biphenyl byproducts from the coupling reaction. This study provided a new avenue for designing novel nanoconfined catalysts with outstanding activity, paving the way for the deep oxidation of CVOC waste gas via AOP wet scrubber.