Enhanced Mass Transfer of Ozone and Emerging Pollutants through a Gas-Solid-Liquid Reaction Interface for Efficient Water Decontamination

Machine Learning-Assisted Molecular Structure Embedding for Accurate Prediction of Emerging Contaminant Removal by Ozonation Oxidation

Ozone has demonstrated high efficacy in depredating emerging contaminants (ECs) during drinking water treatment. However, traditional quantitative structure-activation relationship (QSAR) models often fall short in effectively normalizing and characterizing diverse molecular structures, thereby limiting their predictive accuracy for the removal of various ECs. This study uses embedded molecular structure vectors generated by a graph neural network (GNN), combined with functional group prompts, as inputs to a feedforward neural network. A data set of 28 ECs and 542 data points, representing diverse molecular structures and physiochemical properties, was built to predict the residual rate of ECs (REC) in ozonation oxidation. Compared to traditional QSAR models, the GNN-based molecular structure embedded methods significantly improve prediction accuracy. The resulting KANO-EC model achieved an R2 of 0.97 for REC, demonstrating its ability to capture complex structural features. Moreover, KANO-EC maintains exceptional interpretability, elucidating key functional groups (e.g., carbonyls, hydroxyls, aromatic rings, and amines) involved in the oxidation mechanism. This study presents the KANO-EC model as a novel approach for predicting the ozonation removal efficiency of current and potential ECs. The model also provides valuable insights for developing efficient control strategies for ensuring the long-term safety and sustainability of drinking water supplies.

Nanochanneling and Local Crystallization Engineering Accelerate Multiphase Single-Atom Catalysis for Rapid Water Decontamination

Precise engineering of single-atom catalysts (SACs) with optimal hierarchical structures and favorable local chemical environments remains a significant challenge to cater for multiphase heterogeneous processes. Here, we develop a universal strategy for synthesizing channel-digging microspherical SACs that markedly enhance gas-liquid-solid mass transfer and fine-tune the thermodynamics of catalytic ozonation. By catalytically graphitizing carbon microspheres and selectively etching amorphous carbon domains via mild combustion, we fabricate cross-linked hierarchical graphitic nanochannels confining transition metal (e.g., Co, Cr, Mn, Fe, Ni) single atoms (TMCSs-Air). This nanoenvironment engineering increases interfacial ozone (O3) mass transfer by 3.2-fold and directs O3 adsorption from a conventional "end-on" to a bidental "side-on" configuration. The enhanced inter-orbital electronic interactions lower the O3 activation barrier and form highly oxidizing surface-confined O3 (*O3). Consequently, the CoCSs-Air catalyst achieves a 3.6-fold higher ozone utilization efficiency and a 4.2-fold greater turnover frequency (TOF = 1580 min-1) compared with pristine Co-doped carbon microspheres (CoCSs). Technical and economic evaluations further confirm the feasibility of TMCSs-Air nanoreactors in treating real-world petrochemical wastewater, highlighting its broader potential in overcoming gas diffusion barriers and tuning reaction pathways for multiphase heterogeneous catalysis.

Mass Transfer-Enhanced Photothermal Membranes with Synergistic Light Utilization for High-Turbidity Wastewater Purification

The photo-Fenton process faces significant limitations in treating high-turbidity, colored wastewater due to light attenuation and impurity interference (blocked mass transfer). To address these issues, we developed a suspended photothermal Fenton membrane by loading a photothermal catalyst on a hydrophobically modified cotton filter paper, enabling precise suspension 1 mm below the water surface. This design achieved 89.49 % light utilization and high chemical oxygen demand (COD) removal, even in wastewater with extreme chromaticity (10 multiples) and turbidity (703 NTU). The enhanced photothermal conversion accelerated molybdenum co-catalyzed Fenton reactions and improved peroxymonosulfate (PMS) activation, maintaining over 90 % phenol removal for 15 days. Mechanistic simulations revealed improved mass transfer of reactive oxygen species (ROS) and pollutants at the solid-liquid interface, with PMS diffusion identified as the rate-limiting step. The membrane resisted fouling from suspended solids and maintained stable operation in soil-containing solutions for 10 days. This innovative approach offers an efficient solution for degrading pollutants in dark-colored, high-turbidity wastewater, overcoming traditional process limitations.

Carbonaceous materials in structural dimensions for advanced oxidation processes

Carbonaceous materials have attracted extensive research and application interests in water treatment owing to their advantageous structural and physicochemical properties. Despite the significant interest and ongoing debates on the mechanisms through which carbonaceous materials facilitate advanced oxidation processes (AOPs), a systematic summary of carbon materials across all dimensions (0D-3D nanocarbon to bulk carbon) in various AOP systems remains absent. Addressing this gap, the current review presents a comprehensive analysis of various carbon/oxidant systems, exploring carbon quantum dots (0D), nanodiamonds (0D), carbon nanotubes (1D), graphene derivatives (2D), nanoporous carbon (3D), and biochar (bulk 3D), across different oxidant systems: persulfates (peroxymonosulfate/peroxydisulfate), ozone, hydrogen peroxide, and high-valent metals (Mn(VII)/Fe(VI)). Our discussion is anchored on the identification of active sites and elucidation of catalytic mechanisms, spanning both radical and nonradical pathways. By dissecting catalysis-related factors such as sp2/sp3 C, defects, and surface functional groups that include heteroatoms and oxygen groups in different carbon configurations, this review aims to provide a holistic understanding of the catalytic nature of different dimensional carbonaceous materials in AOPs. Furthermore, we address current challenges and underscore the potential for optimizing and innovating water treatment methodologies through the strategic application of carbon-based catalysts. Finally, prospects for future investigations and the associated bottlenecks are proposed.

Environmental applications of metal-organic framework-based three-dimensional macrostructures: a review

Metal-organic frameworks (MOFs) hold considerable promise for environmental remediation owing to their exceptional performance and distinctive structure. Nonetheless, the practical implementation of MOFs encounters persistent technical hurdles, notably susceptibility to loss, challenging recovery, and potential environmental toxicity arising from the fragility, insolubility, and poor processability of MOFs. MOF-based three-dimensional macrostructures (3DMs) inherit the advantageous attributes of the original MOFs, such as ultra-high specific surface area, tunable pore size, and customizable structure, while also incorporating the intriguing characteristics of bulk materials, including hierarchical structure, facile manipulation, and structural flexibility. Consequently, they exhibit rapid mass transfer and exceptional practicality, offering extensive potential applications in environmental remediation. This review presents a comprehensive overview of recent advancements in utilizing MOF-based 3DMs for environmental remediation, encompassing their fascinating characteristics, preparation strategies, and characterization methods, and highlighting their exceptional performance in pollutant adsorption, catalysis, and detection. Furthermore, existing challenges and prospects are presented to advance the utilization of MOF-based materials across various domains, particularly in environmental remediation.

Micro and nanobubbles-assisted advanced oxidation processes for water decontamination: The importance of interface reactions

Micro and nanobubbles (MNBs), as an efficient and convenient method, have been widely used in water treatment. Composed of gas and water, MNBs avoid directly introducing potential secondary pollutants. Notably, MNBs exhibit significant advantages through interface reactions in assisting AOPs. They overcome barriers like low mass transfer coefficients and limited reactive sites, and shorten the distance between pollutants and oxidants, achieving higher pollutant removal efficiency. However, there is a lack of systematic summary and in-depth discussion on the fundamental mechanisms of MNBs-assisted AOPs. In this critical review, the characteristics of MNBs related to water treatment are outlined first. Subsequently, the recent applications, performance, and mechanisms of MNBs-assisted AOPs including ozone, plasma, photocatalytic, and Fenton oxidation are overviewed. We conclude that MNBs can improve pollutant removal mainly by enhancing the utilization of reactive oxygen species (ROS) generated by AOPs due to the effective interface reactions. Furthermore, we calculated the electrical energy per order of reaction (EE/O) parameter of different MNBs-assisted AOPs, suggesting that MNBs can reduce the total energy consumption in most of the tested cases. Finally, future research needs/opportunities are proposed. The fundamental insights in this review are anticipated to further facilitate an in-depth understanding of the mechanisms of MNBs-assisted AOPs and supply critical guidance on developing MNBs-based technologies for water treatment.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Efficient photoelectrocatalytic degradation of pollutants over hydrophobic carbon felt loaded with Fe-doped porous carbon nitride via direct activation of molecular oxygen

Developing a photoelectric cathode capable of efficiently activating molecular oxygen to degrade pollutants is a coveted yet challenging goal. In pursuit of this, we synthesize a Fe doped porous carbon nitride catalyst (Fe-CN) using an ionothermal strategy and subsequently loaded it on the hydrophobic carbon felt (CF) to fabricate the Fe-CN/CF photoelectric cathode. This cathode benefits from the synergistic effects between the porous CN support and the highly dispersed Fe species, which enhance O2 absorption and activation. Additionally, the hydrophobic CF serves as a gas diffusion layer, accelerating O2 mass transfer. These features enable the Fe-CN/CF cathode to demonstrate notable photoelectrocatalytic (PEC) degradation efficiency. Specifically, under optimal conditions (cathodic bias of -0.3 VAg/AgCl, pH 7, and a catalyst loading of 3 mg/cm2), the system achieves a 76.4% removal rate of tetracycline (TC) within 60 min. The general application potential of this system is further underscored by its ability to remove approximately 98% of 4-chlorophenol (4-CP) and phenol under identical conditions. Subsequent investigations into the active species and degradation pathways reveal that 1O2 and h+ play dominant role during the PEC degradation process, leading to gradually breakdown of TC into less toxicity, smaller molecular intermediates. This work presents a straightforward yet effective strategy for constructing efficient PEC systems that leverage molecular oxygen activation to degrade pollutants.

3D Carbon Microspheres with a Maze-Like Structure and Large Mesopore Tunnels Built From Rapid Aerosol-Confined Coherent Salt/Surfactant Templating

Hierarchically porous carbons with tailor-made properties are essential for applications wherein rich active sites and fast mass transfer are required. Herein, a rapid aerosol-confined salt/surfactant templating approach is proposed for synthesizing hierarchically porous carbon microspheres (HPCMs) with a maze-like structure and large mesopore tunnels for high-performance tri-phase catalytic ozonation. The confined assembly in drying microdroplets is crucial for coherent salt (NaCl) and surfactant (F127) dual templating without macroscopic phase separation. The HPCMs possess tunable sizes, a maze-like structure with highly open macropores (0.3-30 µm) templated from NaCl crystal arrays, large intrawall mesopore tunnels (10-45 nm) templated from F127, and rich micropores (surface area >1000 m2 g-1 ) and oxygen heteroatoms originated from NaCl-confined carbonization of phenolic resin. The structure formation mechanism of the HPCMs and several influencing factors on properties are elaborated. The HPCMs exhibit superior performance in gas-liquid-solid tri-phase catalytic ozonation for oxalate degradation, owing to their hierarchical pore structure for fast mass transfer and rich defects and oxygen-containing groups (especially carbonyl) for efficient O3 activation. The reactive oxygen species responsible for oxalate degradation and the influences of several structure parameters on performance are discussed. This work may provide a platform for producing hierarchically porous materials for various applications.