Hydrolysis of Chloramphenicol Catalyzed by Clay Minerals under Nonaqueous Conditions

Hydrothermal reduction and phase transformation of Fe(III) minerals induced by rice straw to improve the heterogeneous Fenton degradation of metolachlor

Heterogeneous Fenton technology is effective in degrading residual pesticides in soil, but the reduction of Fe(III) in the mineral structure presents a bottleneck. This study combined rice straw with Schwertmannite (Sch), ferrihydrite (Fh), and magnetite (Mag) via a hydrothermal process to obtain iron oxides-hydrothermal carbon composites (Sch@HTC, Fh@HTC, and Mag@HTC). Poor-crystallized Sch and Fh, which were more capable of accepting electrons compared to well-crystallized Mag, exhibited obvious phase transformation to highly active Fe(II)-mineral (humboldtine) via the combination of oxalic acid, an intermediate product, with reduced Fe(II), while Mag was hard to achieve. After hydrothermal treatment, all composites showed enhanced catalytic activity, which increased with the degree of phase transformation. Especially, Sch@HTC demonstrated the highest catalytic activity, degrading 85 % of metolachlor in soil within 24 hours, 2-10 times faster than the others. Surprisingly, the solid-phase Fe(II) in soil increased slightly after the Fenton reaction. Moreover, the in-situ fluorescence intensity of HO• in soil was continuously enhanced, and the effective utilization of H2O2 to HO• was improved. These results confirmed that HTC could provide electrons to Fe(III) during the hydrothermal process, facilitating the Fe(III)/Fe(II) redox cycle and sustaining reactive Fe(II), thus overcoming key challenges in heterogeneous Fenton catalysis.

Alkaline hydrolysis of 1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB) during spent sulfuric acid neutralization using lime

1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB) is the main byproduct of synthesizing an insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and requires environmental management and safe handling during disposal. This study introduces a lime neutralization method for treating TCTNB-containing spent sulfuric acid and systematically investigates the underlying hydrolysis mechanism using mass spectroscopy, Fourier transform infrared spectroscopy (FTIR) and Density functional theory (DFT) calculations. Our results demonstrated that TCTNB hydrolysis was significantly accelerated by increasing the pH from 10 to 12 and the temperature from 22 to 95 °C. The hydrolysis reactions proceeded via nucleophilic aromatic substitution, with preference for targeting the chlorine (Cl) groups of TCTNB over the nitro (NO2) groups due to the higher electrophilicity of Cl-attached carbon atoms. DFT calculations indicated 15 thermodynamically favorable substitution products; however, kinetic limitations caused by deprotonation of intermediates led to the formation of mono- and di-substituted products. Hirshfeld charge analysis and pKa calculations revealed that deprotonation decreased the electrophilicity of the benzene ring, increased energy barriers, and thus hindered further hydrolysis. Additionally, hydrolysis significantly reduced the ecotoxicity of TCTNB by weakening the electrophilicity of the benzene ring. Field tests confirmed that TCTNB in spent acid could be successfully treated with lime to produce non-hazardous and recyclable gypsum. These findings offer theoretical guidance for the safe disposal of TCTNB-containing spent acid and underscore alkaline hydrolysis with lime as a promising treatment strategy.

Performance and mechanism of CuFe2O4/2D-V to activate persulfate for levofloxacin removal

Supported catalysts have gradually become a research hotspot in the field of removing antibiotics from wastewater. In this study, CuFe2O4@2D-V composite catalyst was prepared by basic hydrothermal synthesis. Two-dimensional expanded vermiculite (2D-V) was prepared by high temperature and ultrasonic stripping to provide a loading platform for CuFe2O4 metal ions. The characterization of CuFe2O4@2D-V was analysis by SEM, XRD and EDS. Then, levofloxacin (LVX) was chosen as representative to investigate the catalytic performance of CuFe2O4@2D-V by persulfate (PMS) activation. The optimal preparation conditions of CuFe2O4@2D-V and operating parameters of activating PMS to remove LVX were also studied. The result showed that under the condition of CuFe2O4 loading 50 %, initial pH 9.2, LVX concentration 10 mg/L, catalyst concentration 0.5 g/L and PMS concentration of 0.3 mM, the removal efficiency and reaction rate of LVX could reach 89 % and 0.071 min-1, respectively. Meanwhile, the catalyst had a good stability and high reusability. Based on the analysis of intermediate products by LC-MS, three possible degradation pathways were proposed. Quenching experiments found that non-radical O21 dominated LVX degradation process. Also, the redox reaction between Cu (I)/Cu (II) and Fe (II)/Fe (III) played an important role in LVX removal process. This work might fill the gap in the application of vermiculite as a two-dimensional carrier, and provide further understanding for antibiotic wastewater treatment by metal based two-dimensional composite materials.

Spontaneous Abiotic Reduction of Arsenate to Arsenite Mediated by Structural Fe(II) Resulting from Abundant Oxygen Vacancy Clusters in Poorly Crystalline Ferrihydrite in Drought Environments

The reduction of As(V) to As(III) has been proposed as an undesirable process, increasing the mobility and toxicity of arsenic. Although most studies revealed that As(V) reduction occurs in the aqueous phase, it remains unclear whether abiotic As(V) reduction driven by minerals in drought environments also exists. In this study, we examined the transformation of As(V) to As(III) mediated by ferrihydrite during drying processes using high-resolution X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy analyses. The results revealed that nearly 40.8% of ferrihydrite-sorbed As(V) was transformed to As(III) after placing the As(V)-adsorbed ferrihydrite solids in a drought-tolerant environment for 7 days. As(V) reduction occurred under both oxic and anoxic conditions, with the reduction rate being higher in an anoxic atmosphere than in oxygen and air. Chemical analysis revealed the presence of structural Fe(II) in ferrihydrite, which was attributed to the abundance of oxygen vacancy clusters, as evidenced by positron annihilation lifetime (PAL) analysis. Fe L-edge XANES analysis and DFT calculations demonstrated that structural Fe(II) in dried ferrihydrite played a vital role in As(V) reduction, inducing electron transfer from Fe to As atoms. The findings of this study highlight a potentially important but long-overlooked As(V) reduction pathway at mineral surfaces under drought conditions in dried soils.

Molecular Insights into the Synergistic Inhibition of Microplastics-Derived Dissolved Organic Matter and Anions on the Transformation of Ferrihydrite

Ferrihydrite (Fh), as a ubiquitous iron (oxyhydr)oxide, plays an essential role in nutrient cycling and pollutant transformation due to its high surface area and diversified reaction sites. In the natural environment, Fh transformation could be easily influenced by coexisting components (particularly dissolved organic matter (DOM) and anions). As a new and important carbon source, microplastic-derived DOM (MP-DOM) directly or indirectly affects the morphology and fate of Fh, but limited knowledge exists about the combined effect of MP-DOM and anions on Fh transformation. Herein, this study elucidates the joint effects of polystyrene DOM (PS-DOM) and anions (such as Cl-, SO42-, and PO43-) on Fh transformation. Single anions (especially PO43-) were shown to inhibit the transformation of Fh to hematite (Hm) by hindering the dissolution and recrystallization of Fe(III). However, the inhibitory effect was strongly enhanced when PS-DOM and anions coexisted, which is attributed to their synergetic effects on inhibiting dissolution/recrystallization by occupying more active sites and hindering electron transfer. Furthermore, Fh transformation was predominantly controlled by PS-DOM, especially those containing high-unsaturation, high-oxidation-state, and O-rich phenolic compounds. These findings provide a new perspective on the significance of considering the joint effects of DOM and anions in evaluating the transformation of iron minerals.

Local Polarization Piezoelectric Electric Field Promoted Water Dissociation for Hydroxyl Radical Generation under Ambient Humidity Condition

Combining piezocatalysts with mechanical ball milling for dissociating water to generate hydroxyl radicals (·OH) offers unprecedented opportunities for energy conversion and environmental remediation. However, the in-depth insights into the relationship between water and local polarization piezoelectric electric field (LPPEF) are currently lacking, in particularly, the ·OH formation mechanism in ball milling driven piezocatalyst system is not systematically elucidated. To this end, the present work constructs a ball milling driven piezoelectric solid/liquid interface between piezoelectric Pb2B5O9Cl (PBOC) and different contents of water to investigate LPPEF initiated catalytic reaction. Results show that PBOC exhibits an excellent Tetrabromobisphenol A (TBBPA) degradation efficiency with a 68.94 and 12.43 times faster rate constant than traditional SiO2 and BaTiO3, respectively. Under ambient humidity condition, the lower energy barrier of water dissociation (0.23 eV) endows ·OH generation more energetically favorable than under the water-oversaturated condition (0.66 eV), and trace water magnifies the polarizability of [BO3] and [BO4] units in PBOC to initiate an enhanced LPPEF, thus it enhances the trapping of lone pairs electrons in trace adsorbed water by holes to contribute a higher yield of ·OH. This study constructs a highly correlated field-initiated electron transfer system that provides opportunities for promoting the performance of piezocatalytic materials.

Hydrolysis of p-Phenylenediamine Antioxidants: The Reaction Mechanism, Prediction Model, and Potential Impact on Aquatic Toxicity

While p-phenylenediamine antioxidants (PPDs) pose potential risks to aquatic ecosystems, their environmental persistence and transformation remain ambiguous due to the undefined nature of PPD C-N bond hydrolysis. Here, we investigated the hydrolysis patterns of PPDs by analyzing their hydrolysis half-lives, hydrolysis products around neutral pH (pH 6.0-7.7), and the role of atoms within the C-N bonds in PPDs. Hydrolysis preferentially targets the aromatic secondary amine N with the strongest proton affinity and the C atom of C-N with the highest nucleophilic-attack reactivity. The hydrolysis half-life (t1/2) shortens when the maximum proton affinity of N increases. These results are supported by theoretical calculations, demonstrating a hydrolysis reaction propelled by proton transfer from water to N and complemented by aromatic nucleophilic substitution of N in C-N by water hydroxyl. With the experimental results and the atom reactivity-based predictive model, the t1/2 around neutral pH for 60 PPDs (monitored in environment, commercially available, or under investigation) is determined, showing variations ranging from 2.2 h to 47 days. The model prediction of primary C-N hydrolysis is confirmed through typical PPDs. With the elucidated mechanism and developed model, this research provides new insights into PPD hydrolysis, underscoring its significance in delineating environmental impacts.

Water Vapor Condensation Triggers Simultaneous Oxidation and Hydrolysis of Organic Pollutants on Iron Mineral Surfaces

Increasing worldwide contamination with organic chemical compounds is a paramount environmental challenge facing humanity. Once they enter nature, pollutants undergo transformative processes that critically shape their environmental impacts and associated risks. This research unveils previously overlooked yet widespread pathways for the transformations of organic pollutants triggered by water vapor condensation, leading to spontaneous oxidation and hydrolysis of organic pollutants. These transformations exhibit variability through either sequential or parallel hydrolysis and oxidation, contingent upon the functional groups within the organic pollutants. For instance, acetylsalicylic acid on the goethite surface underwent sequential hydrolysis and oxidation that first hydrolyzed to salicylic acid followed by hydroxylation oxidation of the benzene moiety driven by the hydroxyl radical (•OH). In contrast, chloramphenicol underwent parallel oxidation and hydrolysis, forming hydroxylated chloramphenicol and 2-amino-1-(4-nitrophenyl)-1,3-propanediol, respectively. The spontaneous oxidation and hydrolysis occurred consistently on three naturally abundant iron minerals with the key factors being •OH production capacity and surface binding strength. Given the widespread presence of iron minerals on Earth's surface, these spontaneous transformation paths could play a role in the fate and risks of organic pollutants of health concerns.

A H2O2-free heterogeneous Fenton process for the degradation of lincomycin using natural structural iron-containing clay mineral and dimethoxyhydroquinone with in situ generated hydroxyl radicals

The heterogeneous Fenton process is a strategy for overcoming the greatest shortcomings of traditional homogeneous Fenton, i.e. the high generation of ferric hydroxide sludge and effectivity in a limited pH range. In this study, we constructed a heterogeneous Fenton system with natural iron-bearing clay mineral (nontronite) and dimethoxyhydroquinone (DMHQ) to degrade lincomycin (LCM) without the addition of H₂O₂. The degradation mechanism was derived from the hydroxyl radicals (^•OH) produced from the oxygenation of Fe(II) in nontronites, which was reduced by DMHQ. Acidic conditions and low concentrations of LCM were favourable for LCM degradation. When the solution pH increased from 3 to 7, the final LCM removal ratio decreased from 95 to 46%. However, LCM can still be degraded by 46% under neutral conditions and 20% at the LCM concentration of 500 μmol/L. The nontronite has good reusability, and the LCM degradation efficiency in the fourth cycle still exceeded 90% of the original efficiency. The degradation sites of LCM mainly occurred in the methyl thioether moiety and the aliphatic amine group on the pyrrolidine ring, with the final product of CO₂. This research presents a new eco-friendly and cost-effective method for the heterogenous Fenton process without external H₂O₂.

Dry-to-wet fluctuation of moisture contents enhanced the mineralization of chloramphenicol antibiotic

Due to livestock wastewater irrigation, soil is becoming one of the major sinks of antibiotics in the environment. Recently, it is getting recognized that a variety of minerals under low moisture conditions can induce strong catalytic hydrolysis to antibiotics. However, the relative importance and implication of soil water content (WC) for natural attenuation of soil residual antibiotics has not been well recognized. In order to explore the optimal moisture levels and the key soil properties dominating for the high catalytic hydrolysis activities of soils, this study collected 16 representative soil samples across China, and assessed their performances to degrade chloramphenicol (CAP) under different moisture levels. The results showed that the soils with low organic matter contents (< 20 g/kg) and high amounts of crystalline Fe/Al were particularly effective in catalyzing CAP hydrolysis when exposed to low WC (< 6%, wt/wt), leading to CAP hydrolysis half-lives of <40 d Higher WC greatly suppressed the catalytic activity of the soil. By utilizing this process, it is possible to integrate abiotic and biotic degradation to enhance the mineralization of CAP, attributing to that the hydrolytic products are more available for soil microorganisms. As expected, the soils experienced periodic dry-to-wet moisture conditions (i.e., the WC shifting from 1 to 5% to 20-35%, wt/wt) exhibited higher degradation and mineralization of ¹⁴C-CAP, in comparison with the constant wet treatment. Meanwhile, the bacterial community composition and the specific genera showed that the dry-to-wet fluctuation of soil WC relieved the antimicrobial stress to bacterial community. Our study verifies the critical role of soil WC in mediating the natural attenuation of antibiotics, and guides to remove antibiotics from both wastewater and soil.

Higher toxicity induced by co-exposure of polystyrene microplastics and chloramphenicol to Microcystis aeruginosa: Experimental study and molecular dynamics simulation

Antibiotics and microplastics (MPs) inevitably coexist in natural waters, but their combined effect on aquatic organisms is still ambiguous. This study investigated the individual and combined toxicity of chloramphenicol (CAP) and micro-polystyrene (mPS) particles to Microcystis aeruginosa by physiological biomarkers, related gene expression, and molecular dynamics simulation. The results indicated that both individual and joint treatments threatened algal growth, while combined toxicity was higher than the former. Photosynthetic pigments and gene expression were inhibited by single CAP and mPS exposure, but CAP dominated and aggravated photosynthetic toxicity in combined exposure. Additionally, mPS damaged cell membranes and induced oxidative stress, which might further facilitate the entry of CAP into cells during co-exposure. The synergistic effect of CAP and mPS might be explained by the common photosynthetic toxicity target of CAP and mPS as well as oxidative stress. Furthermore, the molecular dynamics simulation revealed that CAP altered conformations of photosynthetic assembly protein YCF48 and SOD enzyme, and competed for functional sites of SOD, thus disturbing photosynthesis and antioxidant systems. These findings provide useful insights into the combined toxicity mechanism of antibiotics and MPs as well as highlight the importance of co-pollutant toxicity in the aquatic environment.

Insight into the Photodegradation of Microplastics Boosted by Iron (Hydr)oxides

Iron (hydr)oxides as a kind of natural mineral actively participate in the transformation of organic pollutants, but there is a large knowledge gap in their impacts on photochemical processes of microplastics (MPs). This study is the first to examine the degradation of two ordinary plastic materials, polyethylene (PE) and polypropylene (PP), mediated by iron (hydr)oxides (goethite and hematite) under simulated solar light irradiation. Both iron (hydr)oxides significantly promoted the degradation of MPs (particularly PP) with a greater effect by goethite than hematite, related to hydroxyl radical (^•OH) produced by iron (hydr)oxides. Under light irradiation, the surface Fe(II) phase catalyzed the production of H₂O₂ and promoted the release of Fe²⁺, leading to the subsequent light-driven Fenton reaction which produced a large amount of ^•OH. As the iron (hydr)oxides were modified with NaF at various concentrations, the activity of the surface Fe(II) as well as the release of Fe²⁺ were greatly reduced, and thus the ^•OH formation and MP degradation were depressed remarkably. It is worth noting that the surface hydroxyl groups (especially ≡FeOH) affected the reaction kinetics of ^•OH by regulating the activity of Fe species. These findings unveil the distinct impacts and intrinsic mechanisms of iron (hydr)oxides in influencing the photodegradation of MPs.

Lewis Acid-Base Interaction Triggering Electron Delocalization to Enhance the Photodegradation of Extracellular Antibiotic Resistance Genes Adsorbed on Clay Minerals

The transformation of extracellular antibiotic resistance genes (eARGs) is largely influenced by their inevitable photodegradation in environments where they tend to be adsorbed by ubiquitous clay minerals instead of being in a free form. However, the photodegradation behaviors and mechanisms of the adsorbed eARGs may be quite different from those of the free form and still remain unclear. Herein, we found that kaolinite, a common 1:1-type clay, markedly enhanced eARG photodegradation and made eARGs undergo direct photodegradation under UVA. The decrease in the transformation efficiency of eARGs caused by photodegradation was also promoted. Spectroscopy methods combined with density functional theory calculations revealed that the Lewis acid-base interaction between P-O in eARGs and Al-OH on kaolinite delocalized electrons of eARGs, thus resulting in increased photon absorption ability of eARGs. This ultimately led to enhanced photodegradation of kaolinite-adsorbed eARGs. Additionally, divalent Ca²⁺ could reduce the Lewis acid-base interaction-mediated adsorption of eARGs by kaolinite, thereby weakening the enhanced photodegradation of eARGs caused by electron delocalization. In contrast, the 2:1-type clay montmorillonite without strong Lewis acid sites was unable to delocalize the electrons to enhance the photodegradation of eARGs. This work allowed us to better evaluate eARGs' fate and risk in real aqueous environments.

Facet effect of hematite on the hydrolysis of phthalate esters under ambient humidity conditions

Phthalate esters (PAEs) have been extensively used as additives in plastics and wallcovering, causing severe environmental contamination and increasing public health concerns. Here, we find that hematite nanoparticles with specific facet-control can efficiently catalyze PAEs hydrolysis under ambient humidity conditions, with the hydrolysis rates 2 orders of magnitude higher than that in water saturated condition. The catalytic performance of hematite shows a significant facet-dependence with the reactivity in the order {012} > {104} ≫ {001}, related to the atomic array of surface undercoordinated Fe. The {012} and {104} facets with the proper neighboring Fe-Fe distance of 0.34-0.39 nm can bidentately coordinate with PAEs, and thus induce much stronger Lewis-acid catalysis. Our study may inspire the development of nanomaterials with appropriate surface atomic arrays, improves our understanding for the natural transformation of PAEs under low humidity environment, and provides a promising approach to remediate/purify the ambient air contaminated by PAEs.

Humidity induces the formation of radicals and enhances photodegradation of chlorinated-PAHs on Fe(III)-montmorillonite

Chlorinated-PAHs (ClPAHs) are widely detected in the soil surface and atmospheric particles. However, the underlying mechanisms of their photodegradation are not well understood. In the present study, the formation of radicals on ClPAHs-contaminated clay minerals was quantitatively monitored via electron paramagnetic resonance (EPR) spectroscopy, and the impact of relative humidity (RH) was systematically explored. ClPAHs removal (> 75%) was attributed to electron transfer and •OH attack. The degradation easiness of ClPAHs follows: 2-ClNAP >2-ClANT >9-ClPHE >1-ClPYR. Light irradiation significantly improved the generation of reactive oxygen species (ROS, such as •OH and •O₂^-), and further generate a series of hydroxylated products of ClPAHs. Persistent free radicals (PFRs) were only detected on clay minerals contaminated with 2-ClANT and 1-ClPYR. RH 10-80%, the concentration of •OH and •O₂^- increased by 1.07 and 62.79 times respectively, which facilitated transformation of PFRs and ClPAHs degradation. The results of quantum chemical calculations indicate that the initial reaction of ClPAHs photodegradation is mediated by the substitution of •OH for chlorine groups. The present work implies that higher humidity may decrease the generation of PFRs on clay minerals and help mitigate the threats of PFRs and ClPAHs to human health.

The photodegradation processes and mechanisms of polyvinyl chloride and polyethylene terephthalate microplastic in aquatic environments: Important role of clay minerals

It is well known that microplastics (MPs) may experience weathering and aging under ultraviolet light (UV) irradiation, but it remains unclear if these processes are impacted by natural components, such as clay minerals. In this study, we systematically investigated the photodegradation behaviors of polyvinyl chloride (PVC) and poly (ethylene terephthalate) (PET), two utmost used plastics, in the presence of clay minerals (kaolinite and montmorillonite). The results demonstrated that the clay minerals, particularly kaolinite, significantly promoted the MPs photodegradation, and the aging of PET was more prominent. The photodegradation was the most distinct at pH 7.0, regardless of the presence or absence of the clay minerals. The results of electron paramagnetic resonance and inhibition experiments of reactive oxygen species indicated that the minerals, particularly kaolinite, remarkably facilitated production of •OH, which was the key species contributing to the photodegradation of MPs. Specifically, UV irradiation facilitated the photo-ionization of MPs, producing hydrated electrons and MP radical cations (MP⁺). The Lewis base sites prevalent on the clay siloxane surfaces could stabilize the MP radical cations and prevent their recombination with hydrated electrons, which promoted the generation of •OH under aerobic conditions, and facilitated the degradation of MP. Two-dimensional (2D) Fourier transformation infrared (FTIR) correlation spectroscopy (COS) analysis and ultra-high-performance liquid chromatography coupled to a Q Exactive Orbitrap HF mass spectrometer were used to identify the sequential changes of functional groups, and the degradation products of the MPs. This study improves our understanding on the aging of MPs in the complex natural environment.

Structure-dependent surface catalytic degradation of cephalosporin antibiotics on the aged polyvinyl chloride microplastics

Microplastics (MPs) have been recognized as a global concern due to their potential health effect, as MPs could adsorb and carry various pollutants in aquatic environment. In the present study, a new environmental behavior related to polyvinyl chloride microplastics (PVC-MPs) and the underlying mechanism were described. Our results showed that the photo-aged PVC-MPs could affect the transformation of cephalosporin antibiotics. For instance, the presence of altered PVC-MPs significantly accelerated the hydrolysis of cefazolin (CFZ), but exhibited negligible effect on the degradation of cephalexin (CFX). As indicated by in situ Fourier transform infrared spectra and theoretical calculations, hydrogen bonds could be formed between β-lactam carbonyl of CFZ and the oxygen-containing moieties on the aged PVC-MP surfaces. The hydrogen-bonding was able to significantly increase the positive atomic Mulliken charge on the β-lactam carbonyl carbon, thus narrowing the energy gap of CFZ hydrolysis and subsequently enhancing the disruption of β-lactam ring. While for CFX, instead of the β-lactam carbonyl, the amide amino group was involved in the hydrogen-bonding due to the structural difference. Therefore, in addition to increasing the adsorption capacity, the aged PVC-MPs could act as the catalyst to mediate the transformation of antibiotics. Our study would help improve the understanding for interactions between contaminants and MPs in natural environments.

Iron Minerals Mediated Interfacial Hydrolysis of Chloramphenicol Antibiotic under Limited Moisture Conditions

Iron minerals are important soil components; however, little information is available for the transformation of antibiotics on iron mineral surfaces, especially under limited moisture conditions. In this study, we investigated the catalytic performance of four iron minerals (maghemite, hematite, goethite, and siderite) for the hydrolysis of chloramphenicol (CAP) antibiotic at different moisture conditions. All the iron oxides could efficiently catalyze CAP hydrolysis with the half-lives <6 days when the surface water content was limited, which was controlled by the atmospheric relative humidity of 33-76%. Different minerals exhibited distinctive catalytic processes, depending on the surface properties. H-bonding or Lewis acid catalysis was proposed for surface hydrolytic reaction on iron oxides, which however was almost completely inhibited when the surface water content was >10 wt % due to the competition of water molecules for surface reactive sites. For siderite, the CAP hydrolysis was resistant to excessive surface water. A bidentate H-bonding interaction mechanism would account for CAP hydrolysis on siderite. The results of this study highlight the importance of surface moisture on the catalytic performance of iron minerals. The current study also reveals a potential degradation pathway for antibiotics in natural soil, which has been neglected before.

Surface catalyzed hydrolysis of chloramphenicol by montmorillonite under limited surface moisture conditions

Phyllosilicates possess high surface acidity under limited surface moisture conditions and are thus able to mediate the abiotic transformation of antibiotics. This route of abiotic transformation has long been ignored given that most of the studies carried out in aqueous phase. In this study, the catalytic performance of cation-exchanged montmorillonites (Mⁿ⁺-Mts) to the hydrolysis of chloramphenicol (CAP) was investigated under different moisture conditions. Montmorillonite exchanged with Fe³⁺ and Al³⁺ show the greatest catalytic activities. Multiple spectroscopic techniques and theoretical calculations indicate that the surface Brønsted- and Lewis-acid properties are sensitive to surface wetting. At lower moisture level (<10%, wt/wt), the strong Brønsted-acid catalysis predominates the hydrolysis of CAP. Attributing to the strong Lewis-acidities, Fe³⁺-Mt and Al³⁺-Mt could perform high catalytic activities over a wider moisture range (10- 100%, wt/wt). However, such hydrolysis reaction was almost suppressed at water content >400%. In addition, the presence of natural organic matter (NOM, 1%, wt/wt) had little impact on the catalytic activities of Fe³⁺-Mt and Al³⁺-Mt. The results of this study highlight the environmental significance of dry surface reaction by clay minerals as an effective abiotic transformation pathway to the elimination of antibiotics in natural field soil, which is commonly partly hydrated.

Catalytic degradation of micropollutant by peroxymonosulfate activation through Fe(III)/Fe(II) cycle confined in the nanoscale interlayer of Fe(III)-saturated montmorillonite

Low cost, green, regenerable catalyst for persulfate activation is the popularly concerned topic for the degradation of persistent organic micropollutants in drinking water. In this work, natural montmorillonite (MMT) saturated with Fe(III) ions was used to activate peroxymonosulfate (PMS) for the degradation of atrazine in raw drinking water. Results showed that the adsorption of atrazine was quickly completed within 1 min and the percentage degradation was finally increased up to 94.1% in 60 min. The d₀₀₁-spacing of MMT was enlarged to 2.91 nm at the most by Fe(III) saturation. Atrazine was adsorbed into the nanoscale interlayer of Fe(III)-saturated montmorillonite (Fe-MMT), where the Fe(III)/Fe(II) cycle was sustainably realized through the accelerated transformation of electrons between Fe(III) and PMS. Meanwhile, the in-situ generated Fe(II) accelerated the decomposition of PMS to further proceed the degradation of atrazine through the oxidation of HO• and SO₄•^- radicals. This nanoconfined effect of PMS activation by Fe(III) was further confirmed through the degradation of various micropollutants in the backgrounds of river water. The selective catalytic oxidation of micropollutants through PMS activation was attributed to the 2D mesoporous structure of Fe-MMT, inhibiting the interlayer adsorption of larger molecular backgrounds (humic acids etc.). Fe(III)-saturated montmorillonite (Fe-MMT) provided a feasible and scalable method of PMS activation by Fe(III) for the degradation of micropollutants in drinking water.