The strong metal-support interaction (SMSI) in supported catalysts plays a dominant role in catalytic degradation, upgrading, and remanufacturing of environmental pollutants. Previous studies have shown that SMSI is crucial in supported catalysts\' activity and stability. However, for redox reactions catalyzed in environmental catalysis, the enhancement mechanism of SMSI-induced oxygen vacancy and electron transfer needs to be clarified. Additionally, the precise control of SMSI interface sites remains to be fully understood. Here we provide a systematic review of SMSI\'s catalytic mechanisms and control strategies in purifying gaseous pollutants, treating organic wastewater, and valorizing biomass solid waste. We explore the adsorption and activation mechanisms of SMSI in redox reactions by examining interfacial electron transfer, interfacial oxygen vacancy, and interfacial acidic sites. Furthermore, we develop a precise regulation strategy of SMSI from systematical perspectives of interface effect, crystal facet effect, size effect, guest ion doping, and modification effect. Importantly, we point out the drawbacks and breakthrough directions for SMSI regulation in environmental catalysis, including partial encapsulation strategy, size optimization strategy, interface oxygen vacancy strategy, and multi-component strategy. This review article provides the potential applications of SMSI and offers guidance for its controlled regulation in environmental catalysis.

Manganese dioxide (MnO2), renowned for its abundant natural crystal phases, emerges as a leading catalyst candidate for the degradation of pollutants. The relationship between its crystal phase and catalytic activity, particularly for periodate activation, has remained both ambiguous and contentious. This study delineates the influence of various synthetic MnO2 phase structures on their capabilities in catalyzing periodate-assisted pollutant oxidation. Five distinct MnO2 phase structures (α-, β-, γ-, δ-, and ε-MnO₂) were prepared and evaluated to activate periodate and degrade pollutants, following the sequence: α-MnO₂ > γ-MnO₂ > β-MnO₂ > ε-MnO₂ > δ-MnO₂. Through quenching experiments, electron paramagnetic resonance tests, and in situ electrochemical studies, we found an electron transfer-mediated process drive pollutant degradation, facilitated by a highly reactive metastable intermediate complex (MnO₂/PI*). Quantitative structure-activity relationship analysis further indicated that degradation efficiency is strongly associated with both the crystal phase and the Mn (IV) content, highlighting it as a key active site. Moreover, the α-MnO₂ phase demonstrated exceptional recycling stability, enabling an effective pollutant removal in a continuous flow packed-bed reactor for 168 h. Thus, α-MnO₂/PI proved highly effective in mineralizing organic pollutants and reducing their toxicities, highlighting its significant potential for environmental remediation.

Metal-organic frameworks (MOFs) show potential application in many domains, in which photochromic MOFs (PMOFs) have received enormous attention. Researchers mainly utilize photoactive ligands to build PMOFs. Recently, the mixed electron donating and accepting ligands strategies have also been used to construct PMOFs driven by the electron transfer between nonphotochromic moieties. However, the potential interligand competition inhibits the formation of PMOFs. Therefore, the exploration of single-ligand-guided assembly is conductive for building PMOFs. Considering the existing electron accepting and donating role of pyridyl and carboxyl, the pyridinecarboxyate derived from the fusion of pyridyl and carboxyl units may serve as single ligand to yield PMOFs. In this work, the coordination assembly of bipyridinedicarboxylate (2,2\'-bipyridine-4,4\'-dicarboxylic acid, H2bpdc; 1,10-phenanthroline-2,9-dicarboxylic acid, H2pda) and LaCl3 generate two PMOFs, [La(bpdc)(H2O)Cl] (1) and [La(pda)(H2O)2Cl]·2H2O (2). Both complexes feature dinuclear lanthanum as building blocks with differences in the connecting number of likers, in which 1 has (4,8)-connected topology and 2 exhibits sql topology. Their structural differences result in the diversities of photoresponsive functionalities. Compared with reported PMOFs built from photoactive ligands and mixed ligands, this study provides new available categories of single ligand for generating PMOFs and tuning the structure and photoresponsive properties via ligand substitution and external photostimulus.

Phenols are the widely detected contaminants in the aquatic environment. Pyrogenic carbon (PyC) can mediate phenols degradation, but the specific properties of PyC or phenols influencing this reaction remain unknown. The present study investigated the kinetic process and mechanism of removal of various phenols by different PyC in aqueous phase system. To avoid the impact of the accumulated degradation byproducts on the overall reaction, we conducted a short-term experiment, quantified adsorption and degradation, and obtained reaction rate constants using a two-compartment first-order kinetics model. The adsorption rate constants (ka) of phenols by PyC were 10-220 times higher than degradation rate constants (kd), and they were positively correlated. Interestingly, no correlation was found between kd and common PyC properties, including functional groups, electron transfer capacities, and surface properties. Phenols were primarily attacked by •OH in the adsorbed phase. But neither the instantly trapped •OH, nor the accumulated •OH could explain phenol degradation. Chemical redox titration revealed that the electron transfer parameters, such as the electron donating rate constant (kED) of PyC, correlated well with kd (r>0.87, P < 0.05) of phenols. Analysis of 13 phenols showed that Egap and ELUMO negatively correlated with their kd, confirming the importance of the electronic properties of phenols to their degradation kinetics. This study highlights the importance of PyC electron transfer kinetics parameters for phenols degradation and manipulation of PyC electron transfer rate may accelerate organic pollutant removal, which contributes to a deeper understanding of the environmental behavior and application of PyC systems.

The presence of organic phosphorus may influence the characteristics of Cr(VI) reduction and immobilization on Fe(II)-bearing clay minerals under anoxic conditions, as the organic phosphorus tends to bind strongly to clay minerals in soil. Herein, reduced nontronite (rNAu-2) was used to reduction of Cr(VI) in the presence of phytic acid (IHP) at neutral pH. With IHP concentration from 0 to 500 μM, Cr(VI) reduction decreased obviously (17.8%) within first 5 min, and then preferred to stagnate during 4-12 h (≥50 μM). After that, Cr(VI) was reduced continuously at a slightly faster rate. Density functional theory (DFT) calculations revealed that IHP primarily absorbed at the edge sites of rNAu-2 to form Fe-IHP complexes. X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and Fourier transform infrared spectroscopy (FTIR) results demonstrated that IHP hindered the ingress of CrO42- into the interlayer space of rNAu-2 and impeded their reduction by trioctahedral Fe(II) and Al-Fe(II) at basal plane sites in the initial stage. Additionally, Fe(II) extraction results showed that IHP promoted the electron from interior transfer to near-edge, but hindered it further transfer to surface, resulting in the inhibition on Cr(VI) reduction at edge sites during the later stage. Consequently, IHP inhibits the reduction and immobilization of Cr(VI) by rNAu-2. Our study offers novel insights into electron transfer pathways during the Cr(VI) reduction by rNAu-2 with coexisting IHP, thereby improve the understanding of the geochemical processes of chromium within the iron cycle in soil.

It is of great significance to develop an energy-efficient and external oxidant-free strategy for antibiotics removal. In this study, the novel light-dark tandem strategy was established to enhance tetracycline (TC) removal by bifunctional FeCu-doped carbon composites (FeCu@BC) derived from waste cotton fabrics. Interestingly, over 95 % TC was removed by FeCu@BC under light alone and dark alone in 10 min, with the same preferred conditions of pH 7.50 and 0.04 g/L catalyst dosage. Surprisingly, the enhanced mineralization efficiency of TC was achieved by the light-dark tandem without adjusting the parameters as 86.65 %, which was 1.13, 1.46 and 2.12 times higher than those of the dark-light tandem, light alone and dark alone, respectively. The mechanisms were elucidated as that 83.28 % direct degradation and 4.37 % indirect degradation under light while 47.63 % direct degradation and 24.16 % indirect degradation under darkness contributed for TC removal. The synergetic effects of persistent free radicals (PFRs) and FeCu interactions enabled FeCu@BC to work efficiently under both light and darkness, and light enhanced electron transfer between PFRs and FeCu interactions. Furthermore, energetic electrons stored in these active sites under light could be extracted to enhance electron transfer under subsequent darkness and the strongly catalytically active species initiated under light remained in action after cessation of light. Finally, high molecular TC was easily decomposed by energetic photo-catalysis and low molecular intermediates were mineralized under subsequent enhanced dark-catalysis to increase the mineralization efficiency. In general, this study provided an eco-friendly organics removal strategy and mechanisms insights based on the natural day-night cycle.

The efficiency of direct electron flow from electron donors to electron acceptors in redox reactions is significantly influenced by the spatial separation of these components. Geobatteries, a class of redox-active substances naturally present in soil-water systems, act as electron reservoirs, reversibly donating, storing, and accepting electrons. This capability allows the temporal and spatial decoupling of redox half-reactions, providing a flexible electron transfer mechanism. In this review, we systematically examine the critical role of geobatteries in influencing electron transfer and utilization in environmental biogeochemical processes. Typical redox-active centers within geobatteries, such as quinone-like moieties, nitrogen- and sulfur-containing groups, and variable-valent metals, possess the potential to repeatedly charge and discharge. Various characterization techniques, ranging from qualitative methods like elemental analysis, imaging, and spectroscopy, to quantitative techniques such as chemical, spectroscopic, and electrochemical methods, have been developed to evaluate this reversible electron transfer capacity. Additionally, current research on the ecological and environmental significance of geobatteries extends beyond natural soil-water systems (e.g., soil carbon cycle) to engineered systems such as water treatment (e.g., nitrogen removal) and waste management (e.g., anaerobic digestion). Despite these advancements, challenges such as the complexity of environmental systems, difficulties in accurately quantifying electron exchange capacity, and scaling-up issues must be addressed to fully unlock their potential. This review underscores both the promise and challenges associated with geobatteries in responding to environmental issues, such as climate change and pollutant transformation.

In recent years, there has been significant interest in photocatalytic technologies utilizing semiconductors and photosensitizers responsive to solar light, owing to their potential for energy and environmental applications. Current efforts are focused on enhancing existing photocatalysts and developing new ones tailored for environmental uses. Anthraquinones (AQs) serve as redox-active electron transfer mediators and photochemically active organic photosensitizers, effectively addressing common issues such as low light utilization and carrier separation efficiency found in conventional semiconductors. AQs offer advantages such as abundant raw materials, controlled preparation, excellent electron transfer capabilities, and photosensitivity, with applications spanning the energy, medical, and environmental sectors. Despite their utility, comprehensive reviews on AQs-based photocatalytic systems in environmental contexts are lacking. In this review, we thoroughly describe the photochemical properties of AQs and their potential applications in photocatalysis, particularly in addressing key environmental challenges like clean energy production, antibacterial action, and pollutant degradation. However, AQs face limitations in practical photocatalytic applications due to their low electrical conductivity and solubility-related secondary contamination. To mitigate these issues, the design and synthesis of graphene-immobilized AQs are highlighted as a solution to enhance practical photocatalytic applications. Additionally, future research directions are proposed to deepen the understanding of AQs\' theoretical mechanisms and to provide practical applications for wastewater treatment. This review aims to facilitate mechanistic studies and practical applications of AQs-based photocatalytic technologies and to improve understanding of these technologies.

Contact-electro-catalysis (CEC) usually uses polymer dielectrics as its catalysts under mechanical stimulation conditions, which although has a decent catalytic dye degradation effect still warrants performance improvement. A carrier separation promotion strategy based on an internal electric field by polarization can effectively improve ferroelectric material performance in photocatalysis and piezocatalysis. Therefore, carrier separation as a necessary process of CEC also can be promoted and is largely expected to improve CEC performance theoretically. However, the carrier separation enhancement by the internal electric field strategy has not been achieved in the CEC experiment yet, because of the difficulty of building an internal electric field in an inert polymer dielectric. Herein, a polytetrafluoroethylene (PTFE) dielectric was charged through an electret process, which was believed to establish an internal electric field for CEC catalysts proved by KPFM, XPS, and triboelectric nanogenerator voltage output analysis. The fastest degradation rate of methyl orange reached over 90% at 1.5 h, while the hydroxyl free radical (•OH) yield of the PTFE electret was nearly three times that of the original PTFE. Density functional theory (DFT) calculations verified that the potential barrier of interatomic electron transfer between PTFE and H2O was reduced by 37% under the internal electric field. The electret strategy used herein to optimize the PTFE catalyst provides a base for the use of other general plastics in CEC and facilitates the production of easily prepared, easily recyclable, and inexpensive polymer dielectric catalysts that can promote large-scale pollutant degradation via CEC.

In present work, blue carbon dots (b-CDs) were derived from ammonium citrate and guanidine hydrochloride, and red carbon dots (r-CDs) were stemmed from malonate, ethylenediamine and meso‑tetra (4-carboxyphenyl) porphin based on facile hydrothermal method. Eco-friendly ratiometric fluorescence probe was innovatively constructed to effectively measure Hg2+ utilizing b-CDs and r-CDs. The developed probe displayed two typical emission peaks at 450 nm from b-CDs and 650 nm from r-CDs under the excitation at 360 nm. Mercury ion has strong quenching effect on the fluorescence intensity at 450 nm due to the electron transfer process and the fluorescence change at 450 nm was used as the response signal, whereas the fluorescence intensity at 650 nm kept unchangeable which resulted from the chemical inertness between Hg2+ and r-CDs, serving as the reference signal in the sensing system. Under optimal circumstances, this probe exhibited an excellent linearity between the fluorescence response values of ΔF450/F650 and Hg2+ concentrations over range of 0.01-10 µmol/L, and the limit of detection was down to 5.3 nmol/L. Furthermore, this probe was successfully employed for sensing Hg2+ in practical environmental water samples with satisfied recoveries of 98.5%-105.0%. The constructed ratiometric fluorescent probe provided a rapid, environmental-friendly, reliable, and efficient platform for measuring trace Hg2+ in environmental field.