The fundamental challenge of adsorption-driven heterogeneous advanced oxidation processes (HAOPs) lies in the potential competition and interference between the adsorption and oxidation processes. In adsorption-driven HAOPs, a material with a high adsorption capacity is typically used to accumulate oxidants in water prior to initiating an advanced oxidation process. This issue arises because the adsorbent can also capture some of the target organic pollutants for degradation by HAOPs. This can lead to a reduction in the availability of pollutants for oxidation by the reactive oxygen species (ROS) generated during HAOP, ultimately suppressing the overall treatment efficiency. Additionally, the adsorption of dissolved organic matter (DOM) present in water can interfere with the generation and action of ROS, further diminishing the effectiveness of HAOP in pollutant degradation. To address this fundamental issue, it is crucial to carefully screen and optimize both the catalyst material and the operating conditions for HAOP. Balancing the adsorption capacity of a material with the requirements of interfacial oxidation for efficient pollutant degradation is the key to successful and effective wastewater treatment via adsorption-based HAOPs. Generally, recent study on HAOPs have focused on exploring novel catalysts [1]. As a guideline for understanding how catalysts affect the rate of chemical reactions, the classic Sabatier theory emphasizes the importance of interactions between catalysts and reactants on catalytic performance [2]. This suggests that the adhesion of reactants to the catalyst should be neither too weak nor too strong so that the active sites can be rapidly regenerated, accompanied by detachment of the formed products. Otherwise, the catalytic reactions will be largely hindered because of the “blocking” of active sites by strongly interacting reactants or weakly detached intermediates/products. Unfortunately, this paradigm is often overlooked in the development of HAOPs, in which the adsorption affinity to oxidants or/and contaminants is known to be the key step controlling catalytic performance. In addition, the intermediates generated during organic degradation may have low polarity and are likely adsorbed on the surface of the catalyst to cause undesirable deactivation.

Concerns about the heterogeneous or homogeneous reaction nature of HAOPs, especially Fenton catalysis, also remain elusive because of the challenge of revealing where adsorption interactions and catalysis reactions occur. However, recent studies [3], [4] of HAOPs have revealed that organic pollutants can be eliminated from water through oxidative coupling and polymerization pathways on catalyst surfaces through their translocation from the water phase to the solid phase, a process known as the direct oxidative transfer process (DOTP). This interesting point has been highlighted by Zhang and Yu [5], and the “adsorption-driven” mechanism is expected to promote DOTP. Typically, the polymerization must meet certain conditions. Free radicals are required to initiate aggregation to afford polymers with relatively large molecular weights. However, in many cases, the polymerization process does not occur because the molecular weight is not large enough during chain reactions. At this point, the adsorption process, which is associated with various significant factors, such as surface chemistry, surface area, pore size, and pore volume, is frequently either neglected or only superficially elucidated. For example, the adsorption process is related to polarity (e.g., “like dissolves like” theory) and surface hydropathy. In detail, the larger the contact angle is, the more the surface is covered by organic compounds. Moreover, the adsorption energy (E_ad) is widely used to explain differences in catalysis. A higher E_ad usually accounts for greater rates, which seems to differ from the Sabatier theory. Specifically, in our recent works, we determined that the higher E_ad of H₂O₂ on the surface activation site contributes to the highly efficient generation of radicals compared with that of the counterpart catalyst [6]. Notably, E_ad remains within the optimal range; if it exceeds the upper limit, the performance of the materials can be negatively affected. Therefore, a deeper understanding of the molecular-level interactions between oxidants/contaminants and catalyst surfaces is highly important for optimizing and practicing heterogeneous catalysis. We believe that the protocol should include the identification of specific adsorption sites (e.g., functional groups and microstructural features) and the elucidation of bonding mechanisms (e.g., surface complexation, hydrogen bonding, and π–π interactions). These interactions are critical because they not only facilitate the mass transfer of contaminants from the liquid phase to the solid phase of the catalyst but also determine the desorption of products from the catalyst surface. Recognizing the importance of these interactions underscores the need for a more comprehensive approach in HAOP research that integrates both catalytic action and adsorption dynamics to increase contaminant degradation efficiency under practical scenarios.

In practice, in many HAOP studies [7], [8], [9], researchers usually conduct adsorption equilibrium experiments (often lasting between 30 and 60 min) before the addition of oxidants, such as H₂O₂, peroxymonosulfate (PMS), peroxydisulfate (PDS), peracetic acid (PAA), high-valent metals (e.g., MnO_x), and nonmetals (e.g., IO₄⁻)). In some cases, the adsorption efficiencies of contaminants can reach as high as 40% to 50% before the implementation of catalytic degradation experiments [10], [11]. At this juncture, the necessity of adding an oxidant to break down contaminants and the adsorption function for oxidant activation or organic capture/detachment are not well explained, leaving the scientific basis for this step unclear. This practice raises a pivotal question regarding the material used: Is it primarily an “adsorbent” for capturing contaminants or a “catalyst” for chemical transformations? The distinction reveals high value, as it influences both the experimental approach and the interpretation of the results. Understanding whether these materials serve to adsorb and/or catalyze contaminants can significantly affect the design of pollution control strategies and the development of new materials for environmental cleanup. Therefore, the concept of adsorption-driven interfacial interactions is fundamental for understanding the specific mechanisms that influence the performance of HAOPs. Rather than the outer edge, these interactions are at the core and determine the efficiency and selectivity of HAOPs in removing contaminants from water and eliminating environmental pollutants. At the heart of this interaction is the principle that the adsorption of contaminants onto the surfaces of catalysts or adsorbents brings them into close proximity with reactive species, such as hydroxyl radicals, which are effective at degrading a wide range of organics. Contaminants with lower or higher adsorption capacities are less likely to be degraded, highlighting the critical role of suitable adsorption affinity in increasing the overall efficiency of HAOPs. Ideally, we can construct a composite catalyst with functional “dual active sites” to address the deactivation problem. One site is mainly responsible for the adsorption process, and the other is mainly responsible for the catalytic process. Given the short lifetime of hydroxyl radicals, the generation of nonradical species (e.g., singlet oxygen and high-valence metals) with much longer migration distances (∼μm) can improve the mass transfer between adsorption sites and catalysis sites [12]. Moreover, the surface area, porosity, and chemical functionality of the catalyst are also key parameters for the adsorption capacity/kinetics and catalytic reactivity. Researchers and engineers strive to optimize these properties through material screening and modification, aiming to increase the efficiency of contaminant adsorption and facilitate more effective degradation (Fig. 1).

On the other hand, interfacial interactions play an important role in the selective formation of reactive oxidation species in HAOPs, which provides an opportunity to target specific contaminants with diverse physicochemical properties. Different contaminants exhibit varying adsorption affinities to the surface of a given catalyst owing to their chemical structures, sizes, charges, and so forth. [13]. Consequently, understanding and controlling these interfacial interactions can lead to the selective removal of certain contaminants, which is especially crucial when dealing with complex waste streams containing mixtures of various pollutants and complex water matrices. Specifically, in addition to the material itself, the operational parameters of HAOPs, such as the pH, temperature, and concentration of reactive species, can also impact the efficacy of adsorption-driven interfacial interactions. For example, the pH of water can influence the ionization state of both the material surface and the contaminants, thereby affecting the adsorption capacity. Temperature variations can alter the adsorption isotherm and/or thermodynamics and degradation reaction kinetics, necessitating careful control to achieve optimal performance. In the broader context of water treatment and environmental remediation, understanding and leveraging adsorption-driven interfacial interactions are crucial for the development and optimization of HAOPs. By gaining deeper insights into these mechanisms, researchers can design more effective and selective processes, contributing significantly to the advancement of sustainable and efficient solutions for addressing water pollution and protecting environmental health.

Overall, the catalytic reaction can be optimized by balancing the rates of adsorption, reaction, and desorption on the catalyst surface. By controlling these factors, it is possible to maximize the efficiency of the reaction and the selective yield of the desired products and undesired byproducts. Attention should be given to determining the pivotal role of adsorption-driven interfacial interactions in enhancing the efficiency and selectivity of HAOPs. Analyzing the adsorption rate and substrate concentration on the catalyst surface after degradation is also suggested for understanding and optimizing catalytic processes. Factors such as the catalyst’s active sites, surface area, and pore structure coupled with the consideration of molecule size, polarity, and stability greatly affect the overall adsorption kinetics and isotherm. Techniques such as desorption analysis, surface characterization methods (e.g., X-ray photoelectron spectroscopy (XPS; liquid phase), atomic force microscope (AFM)), and advanced in situ characterization approaches (e.g. in situ Fourier transform infrared spectrometer (FTIR)) can help to estimate substrate concentrations and visualize distributions/changes on the material surface. Optimizing these parameters is vital for designing effective catalysts and enhancing industrial processes to address critical challenges in water treatment and environmental remediation.

This work was supported by the National Key Research and Development Program of China (2022YFC3205300) and the National Natural Science Foundation of China (22176124).