Effect of common low-molecular-weight organic acid on the photodegradation of sertraline by ferrihydrite.

Sertraline is one of the most commonly used antidepressant pharmaceuticals with ubiquitous distribution in the aqueous environment. However, the environmental behavior of sertraline in the co-presence of low-molecular-weight organic acid (LMWOA) and iron oxide mineral is still poorly understood. In this study, the photodegradation of sertraline was systematically investigated in a common photosensitizing system (ferrihydrite (Fh)-LMWOA). Six LMWOAs, including citrate acid (CA), tartrate acid (TA), malate acid (MA), lactate acid (LA), succinate acid (SA) and malonic acid (MOA) were chosen as the representatives. Our results implied that the different Fe3+ dissolution rates would lead to rather different sertraline degradation patterns following the order of Fh-CA > Fh-TA > Fh-MA > Fh-LA > Fh-SA > Fh-MOA. The reaction was initiated by the interaction between LMWOA and Fh via ligand-promoted-dissolution mechanism. Furthermore, the Fe3+ dissolution rates also showed a strong correlation with the metal-organic complexation constants, indicating that the photodegradation process is strongly related to the complexation ability of LMWOA with Fe3+. •OH, O2•- and CO2•- were detected, indicating that they contributed to the photodegradation of sertraline. •OH was demonstrated to be the dominant Reactive oxygen species (ROS) for the degradation of sertraline, and the detailed transformation pathways were proposed based on the product analysis and theoretical calculation. According to the ecological structure activity relationship estimation, the photodegradation products of sertraline possessed lower toxicity compared to the parent compound. These findings contribute to a more comprehensive understanding of the environmental fate of sertraline and evaluate its potential ecotoxicity in natural systems.

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.

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.

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.

Hydrolysis of Chloramphenicol Catalyzed by Clay Minerals under Nonaqueous Conditions.

Soil contamination with antibiotics has raised great environmental concerns, while the abiotic degradation of antibiotics on drought soil particles has been largely ignored. In this study, we examined the transformation of chloramphenicol (CAP) on phyllosilicates under nonaqueous conditions. A significant hydrolysis of CAP mediated by kaolinite occurred under moderate relative humidities (RH: 33-76%) with the half-lives of 10-20 days. By contrast, incubation with montmorillonite did not result in detectable degradation of CAP. Infrared and Raman spectroscopies together with density functional theory calculations suggested that the surface-catalyzed CAP hydrolysis was mainly attributed to the basal plane hydroxyl groups of kaolinite, which formed hydrogen-bond interactions with the carbonyl of CAP such that the hydrolysis activation energy of CAP was greatly reduced. Neither the Brønsted nor the Lewis acidity was the determinant for the hydrolysis reaction. The surface moisture content played an essential role in CAP hydrolysis. Specifically, water facilitated the mass transfer of CAP over the low-RH range, whereas excessive water competed for the reactive hydroxyl sites. These results highlight an important but long-overlooked abiotic transformation pathway for antibiotics in field soil, where the soil moisture is low and the microbial activity is suppressed.