Photodegradation of ciprofloxacin adsorbed in the intracrystalline space of montmorillonite

Predicting environmental risks of pharmaceutical residues by wastewater surveillance: An analysis based on pharmaceutical sales and their excretion data

Pharmaceutical residues are increasingly becoming a significant source of environmental water pollution and ecological risk. This study, leveraging official national pharmaceutical sales statistics, predicts the environmental concentrations of 33 typical pharmaceuticals in the Tianjin area. The results show that 52 % of the drugs have a PEC/MEC (Predicted Environmental Concentration/Measured Environmental Concentration) ratio within the acceptable range of 0.5-2, including atenolol (1.21), carbamazepine (1.22), and sulfamethoxazole (0.91). Among the selected drugs, tetracycline, ciprofloxacin, and acetaminophen had the highest predicted concentrations. The EPI (Estimation Programs Interface) biodegradation model, a tool from the US Environmental Protection Agency, is used to predict the removal efficiency of compounds in wastewater treatment plants. The results indicate that the EPI predictions are acceptable for macrolide antibiotics and β-blockers, with removal rates of roxithromycin, spiramycin, acetaminophen, and carbamazepine being 14.1 %, 61.2 %, 75.1 %, and 44.5 %, respectively. However, the model proved to be less effective for fluoroquinolone antibiotics. The ECOSAR (Ecological Structure-Activity Relationships) model was used to supplement the assessment of the potential impacts of drugs on aquatic ecosystems, further refining the analysis of pharmaceutical environmental risks. By combining the concentration and detection frequency of pharmaceutical wastewater, this study identified 9 drugs with significant toxicological risks and marked another 24 drugs as substances of potential concern. Additionally, this study provides data support for addressing pharmaceutical residues of priority concern in subsequent research.

Iron redox cycling in layered clay minerals and its impact on contaminant dynamics: A review

A majority of clay minerals contain Fe, and the redox cycling of Fe(III)/Fe(II) in clay minerals has been extensively studied as it may fuel the biogeochemical cycles of nutrients and govern the mobility, toxicity and bioavailability of a number of environmental contaminants. There are three types of Fe in clay minerals, including structural Fe sandwiched in the lattice of clays, Fe species in interlayer space and adsorbed on the external surface of clays. They exhibit distinct reactivity towards contaminants due to their differences in redox properties and accessibility to contaminant species. In natural environments, microbially driven Fe(III)/Fe(II) redox cycling in clay minerals is thought to be important, whereas reductants (e.g., dithionite and Fe(II)) or oxidants (e.g., peroxygens) are capable of enhancing the rates and extents of redox dynamics in engineered systems. Fe(III)-containing clay minerals can directly react with oxidizable pollutants (e.g., phenols and polycyclic aromatic hydrocarbons (PAHs)), whereas structural Fe(II) is able to react with reducible pollutants, such as nitrate, nitroaromatic compounds, chlorinated aliphatic compounds. Also structural Fe(II) can transfer electrons to oxygen (O₂), peroxymonosulfate (PMS), or hydrogen peroxide (H₂O₂), yielding reactive radicals that can promote the oxidative transformation of contaminants. This review summarizes the recent discoveries on redox reactivity of Fe in clay minerals and its links to fates of environmental contaminants. The biological and chemical reduction mechanisms of Fe(III)-clay minerals, as well as the interaction mechanism between Fe(III) or Fe(II)-containing clay minerals and contaminants are elaborated. Some knowledge gaps are identified for better understanding and modelling of clay-associated contaminant behavior and effective design of remediation solutions.

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.

Synthesis of Gum Arabic Magnetic Nanoparticles for Adsorptive Removal of Ciprofloxacin: Equilibrium, Kinetic, Thermodynamics Studies, and Optimization by Response Surface Methodology

Given the increasing risks that antibiotic abuse poses to microecology and human health, it is imperative to develop incredibly powerful adsorbents. This study investigated the use of environmentally sustainable polymeric nanocomposite based on gum arabic (GA) and magnetic nanoparticles (MNPs) synthesized via co-precipitation method to form gum arabic magnetitic nanoparticles (GA-MNPs) as an efficient adsorbent for ciprofloxacin (CIP) removal from aqueous solution. The physicochemical properties and morphology of the synthesized GA-MNPs were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Energy Dispersive X-Ray Analysis (EDX). The experiment was designed by response surface methodology (RSM) and the Central Composite Design (CCD) was utilized to optimize the operating variables: contact time (0–120 min), pH (3–10), adsorbent dosage (0.10–0.40 g/L), and concentration of adsorbate (5–100 mg/L). Results showed that 96.30% was the maximum percentage of CIP removed. The adsorption effect of the CIP molecule on the surface of the GA-MNPs was investigated using regression analysis and analysis of variance. Furthermore, Freundlich Isotherm and Pseudo Second order kinetic equations have the highest consistency with experimental investigations suggesting double-layer adsorption. This implies that chemisorption was the mechanism involved. In addition, the calculated thermodynamic parameters were postulating an exothermic and spontaneous method in nature. Owing to its adsorption selectivity and recyclability, GA-MNPs could be classified as an environmentally friendly, less expensive, and highly efficient promising adsorbent for remediation of CIP from aqueous solution.

Tetracycline removal enhancement with Fe-saturated nanoporous montmorillonite in a tripartite adsorption/desorption/photo-Fenton degradation process

The adsorption and photo-Fenton degradation of tetracycline (TC) over Fe-saturated nanoporous montmorillonite was analyzed. The synthesized samples were characterized using XRD, FTIR, SEM, and XRF analysis, and the adsorption and desorption of TC onto these samples, as well as the antimicrobial activity of TC during these processes, were analyzed at different pH. Initially, a set of adsorption/desorption experiments was conducted, and surprisingly, up to 50% of TC adsorbed was released from Mt structure. Moreover, the desorbed TC had strong antibacterial activity. Then, an acid treatment (for the creation of nanoporous layers) and Fe saturation of the montmorillonite were applied to improve its adsorption and photocatalytic degradation properties over TC. Surprisingly, the desorption of TC from modified montmorillonite was still high up to 40% of adsorbed TC. However, simultaneous adsorption and photodegradation of TC were detected and almost no antimicrobial activity was detected after 180 min of visible light irradiation, which could be due to the photo-Fenton degradation of TC on the modified montmorillonite surface. In the porous structures of modified montmorillonite high, ˙OH radicals were created in the photo-Fenton reaction and were measured using the Coumarin technique. The ˙OH radicals help the degradation of TC as proposed in an oxidation process. Surprisingly, more than 90% of antimicrobial activity of the TC decreased under visible light (after 180 min) when desorbed from nanoporous Fe-saturated montmorillonite compared to natural montmorillonite. To the best of our knowledge, this is the first time that such a high TC desorption rate from an adsorbent with the least residual antimicrobial activity is reported which makes nanoporous Fe-saturated montmorillonite a perfect separation substance of TC from the environment.

In silico toxicity evaluation for transformation products of antimicrobials, from aqueous photolysis degradation

This study investigates degradation processes of three antimicrobials in water (norfloxacin, ciprofloxacin, and sulfamethoxazole) by photolysis, focusing on the prediction of toxicity endpoints via in silico quantitative structure-activity relationship (QSAR) of their transformation products (TPs). Photolysis experiments were conducted in distilled water with individual solutions at 10 mg L^-1 for each compound. Identification of TPs was performed by means of LC-TOF-MS, employing a method based on retention time, exact mass fragmentation pattern, and peak intensity. Ten main compounds were identified for sulfamethoxazole, fifteen for ciprofloxacin, and fifteen for norfloxacin. Out of 40 identified TPs, 6 have not been reported in the literature. Based on new data found in this work, and TPs already reported in the literature, we have proposed degradation pathways for all three antimicrobials, providing reasoning for the identified TPs. QSAR risk assessment was carried out for 74 structures of possible isomers. QSAR predictions showed that all 19 possible structures of sulfamethoxazole TPs are non-mutagenic, whereas 16 are toxicant, 18 carcinogenic, and 14 non-readily biodegradable. For ciprofloxacin, 28 out of the 30 possible structures for the TPs are mutagenic and non-readily biodegradable, and all structures are toxicant and carcinogenic. All 25 possible norfloxacin TPs were predicted mutagenic, toxicant, carcinogenic, and non-readily biodegradable. Results obtained from in silico QSAR models evince the need of performing risk assessment for TPs as well as for the parent antimicrobial. An expert analysis of QSAR predictions using different models and degradation pathways is imperative, for a large variety of structures was found for the TPs.

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.

Montmorillonite promoted photodegradation of amlodipine in natural water via formation of surface complexes

The photolysis of amlodipine (AML) as a ubiquitous pollutant in natural water has been extensively studied. Montmorillonite (MMT), a major component of suspended particles in surface aquifers, plays key roles in the natural transportation and transformation of organic contaminants in the environment. However, literature has scarcely focused on whether and how suspended particles affect the phototransformation of AML. This study systematically investigated the phototransformation behavior of AML in MMT suspensions under simulated sunlight. The results obtained showed that MMT significantly enhanced the photolysis of AML. The photodegradation of AML in 0.05 g/L MMT suspension reached 92.2 % after 3 h irradiation under the simulated sunlight. The photodecomposition followed the pseudo-first-order kinetic with a rate constant of 0.803 h^-1 in the presence of 0.05 g/L MMT, which is about 19 times larger than that in the absence of MMT (0.0421 h^-1). Further mechanistic investigation suggested that MMT accelerated the photolysis of AML by the formation of surface complexes between cationic amino groups of AML and the negatively charged sites on MMT surface, which greatly facilitated light absorption and electron transfer for the production of cationic radical AML^+·. Meanwhile, the hydroxyl radicals generated by irradiated MMT also played an important role in the photocatalytic degradation of AML. The probable photodegradation pathways of AML in MMT suspension further supported the proposed mechanisms. The toxicity evaluation of phototransformation products of AML with ECOSAR program indicated that photolysis could reduce its potential threats. These findings reveal an important and previously overlooked phototransformation mechanisms of AML in the presence of MMT clays, which is of importance in assessing the environmental fate of other similar organic contaminants.

Visible-LED-light-driven photocatalytic degradation of ofloxacin and ciprofloxacin by magnetic biochar modified flower-like Bi2WO6: The synergistic effects, mechanism insights and degradation pathways

Bi₂WO₆ possesses good stability but poor photocatalytic activity under visible light. Herein, the coupling of Bi₂WO₆, Fe₃O₄ and biochar (Bi₂WO₆/Fe₃O₄/BC) was investigated to enhance the photocatalytic performance of Bi₂WO₆ through facile hydrothermal method, which almost completely degraded ofloxacin (OFL) and ciprofloxacin (CIP) within 30 min under energy-saving visible LED irradiation. The superior photocatalytic activity of Bi₂WO₆/Fe₃O₄/BC was ascribed to the stronger visible light adsorption capacity and the lower recombination of electron-hole pairs. O₂^- played a major role during the photocatalytic reaction. The characterization results suggested that the introduction of biochar avoided the agglomeration of Bi₂WO₆ microspheres and Fe₃O₄ nanoparticles, at the same time, the biochar participated in OFL and CIP photodegradation by consuming different oxygen-containing functional groups. In order to further evaluate the application potential of Bi₂WO₆/Fe₃O₄/BC, the effects of environment factors and the application in different actual water were carefully investigated. Various transformation products and the possible degradation pathways of OFL and CIP were analyzed based on high resolution mass spectrometry (HRMS) results, moreover, the toxicity evaluation results of Escherichia coli indicated these intermediates products were less toxic compared OFL and CIP. Overall, Bi₂WO₆/Fe₃O₄/BC can provide a potential way for the application of photocatalytic technology in ambient wastewater purification.

Water-soluble manganese porphyrins as good catalysts for cipro- and levofloxacin degradation: Solvent effect, degradation products and DFT insights

Synthetic manganese porphyrins (MnPs), in the presence of oxidants, were employed for the degradation of fluoroquinolone antibiotics. Ciprofloxacin (CIP) and levofloxacin (LEV) degradation by iodosylbenzene, iodobenzene diacetate, H₂O₂ and meta-chloroperbenzoic acid using water-soluble MnP catalysts yielded thirteen and nine products, respectively, seven of which have been proposed for the first time. The MnP catalysts have demonstrated the ability to degrade these antibiotics to a high degree (up to 100% degradation). The structures of the degradation products were proposed based on mass spectrometry analysis, and density functional theory calculations could confirm how the substituent moieties attached to the basic chemical structure of the fluoroquinolones influence the degradation reactions. CIP has been shown to be a more reactive substrate towards the porphyrinic catalysts tested because of its three-membered ring. However, the catalysts could almost completely degrade LEV, highlighting the ability of these porphyrins to act as catalysts to degrade environmental pollutants.

Combined first-principles calculations and experimental study on the photocatalytic mechanism of natural dolomite

Mineral-based photocatalysts have received great attention due to their low cost. In this study, the photocatalytic activity of natural dolomite and its mechanism were investigated based on designed experiments and first-principles calculations. The kinetic study showed that natural dolomite showed notable photocatalytic activity for the degradation of target compounds including methylene blue, diphenhydramine, and tetracycline. The EPR analysis demonstrated that O₂⁻˙, ˙OH, and ¹O₂ were produced in the dolomite system under simulated sunlight irradiation. The first-principles calculations indicated that the isomorphous substitution of Fe²⁺ for Mg²⁺ in the dolomite lattice led to the impurity levels appearing in the forbidden band, which caused a significant decrease of the band gap from 5.02 to 1.63 eV. As a result, natural dolomite could act as a semiconductor photocatalyst in photochemical reactions due to the substitution of Mg²⁺ by Fe²⁺. Under simulated sunlight irradiation, photogenerated electron–hole pairs in the natural dolomite were separated and transferred to the surface, and then formed reactive radicals through further reactions, thereby enhancing the degradation of target compounds. This research may contribute to the understanding of the photocatalytic activity of natural minerals.

Natural dolomite exhibits notable photocatalytic activity due to the isomorphous substitution of Fe²⁺ for Mg²⁺ in the lattice, implying that it can be used as a low-cost photocatalyst.

Conventional and emerging technologies for removal of antibiotics from wastewater

Antibiotics and pharmaceuticals related products are used to enhance public health and quality of life. The wastewater that is produced from pharmaceutical industries still contains noticeable amount of antibiotics, and this has remained one of the major environmental problems facing public health. The conventional wastewater remediation approach employed by the pharmaceutical industries for the antibiotics wastewater removal is unable to remove the antibiotics completely. Besides, municipal and livestock wastewater also contain unmetabolized antibiotics released by human and animal, respectively. The antibiotic found in wastewater leads to antibiotic resistance challenges, also emergence of superbugs. Currently, numerous technological approaches have been developed to remove antibiotics from the wastewater. Therefore, it was imperative to critically review the weakness and strength of these current advanced technological approaches in use. Besides, the conventional methods for removal of antibiotics such as Klavaroti et al., Homem and Santos also discussed. Although, membrane treatment is discovered as the ultimate choice of approach, to completely remove the antibiotics, while the filtered antibiotics are still retained on the membrane. This study found, hybrid processes to be the best solution antibiotics removal from wastewater. Nevertheless, real-time monitoring system is also recommended to ascertain that, wastewater is cleared of antibiotics.

Designing nanoarchitecture for environmental remediation based on the clay minerals as building block

Nanoarchitecture of hybrids materials based on clay minerals as nano building blocks for the environmental remediation is summarized with the emphasis on the utilization of layered clay minerals, especially smectite group of clay minerals, as nano building blocks for designing functional nanostructures for the adsorption of molecular contaminants from the environments. Smectites are well-known adsorbents of cationic contaminants, while surface modification of smectites with organoammonium ions has given hydrophobic and microporous characters to uptake nonionic organic contaminants from environments. Not only on the designed interactions between adsorbent-adsorbate for efficient and higher capacity adsorption, the states of the adsorbed nonionic organic compounds have been altered and varied by the modification of smectites as shown by the controlled release and specific catalytic reactions. The organically modified clays are classified from the nanoarchitecture, and the functions derived from the nanoarchitectures are discussed based on the structure-property relationship.

Adsorption of deoxynivalenol by pillared montmorillonite

Deoxynivalenol (DON) is found widely in foods and feeds that are contaminated with mildew and is one of the most harmful mycotoxins, threating not only human health but also impacting animal husbandry. Various physical, chemical and biological detoxification strategies have been applied in the past to reduce mycotoxin contamination. As a practical and economic method, addition of montmorillonite (Mt) offers the potential to eliminate mycotoxins, especially aflatoxin B1 (AFB₁) and zearalenone (ZEA). Our study aimed to control DON, for the first time, using environmentally friendly Mt, modified with aluminum, iron and titanium via a pillaring effect to enlarge interlayer spacing. The materials were characterized using XRD, FTIR, SEM, EDS and BET. Spacing of the pillared Mt layers was shown to exceed that of raw Mt and could be tuned using the pillaring reagents (Al, Fe and Ti, 0.01 to 2.00 eq. relative to the cation exchange capacity of Mt). Adsorption of DON by pillared Mt was investigated using UPLC-MSMS (at pH 2.0 and 6.8). The results demonstrated that the adsorption ratios of 1.00-Al-Mt, 0.50-Fe-Mt and 1.00-Ti-Mt were 23.6%, 14.7% and 23.4%, respectively at pH 2.0 and 27.1%, 21.8%, and 27.4% correspondingly at pH 6.8 when added at 1.0 mg, which is 3-4 times higher than raw Mt (6.3-6.8% at pH 2.0 and 7.3-8.1% at pH 6.8). It was also found that with increased addition of pillared Mt (2.5 mg), the adsorption ratio approached 35%. The time for reaching equilibrium was approximately 120 min. These results demonstrated that Mt after pillaring modifications with Al, Fe and Ti can have potential for the control of DON in foods and feeds.

Study of intermediate by-products and mechanism of the photocatalytic degradation of ciprofloxacin in water using graphitized carbon nitride nanosheets

The photocatalytic degradation of the antibiotic ciprofloxacin in water was carried out with nanosheets of graphitic carbon nitride (g-C₃N₄) as catalyst and visible light irradiation using low-power (4 × 10 W) white light LEDs. The aim of this study was to identify the intermediate by-products formed during the degradation and to propose a pathway for CIP degradation. To achieve this goal, photocatalytically degraded CIP solutions were analysed by liquid chromatography coupled to high-resolution mass spectrometry using a QTOF instrument. The accurate mass and the MS/MS data of the detected ions allowed us to determine the elementary composition of eight by-products and to propose the chemical structures for seven of them. Three of these by-products have been reported for the first time and the elementary composition of a fourth one that had been wrongly reported in the literature was accurately established. CIP degradation followed a pseudo-first order kinetics with a pseudo-first order kinetic constant of 0.035 min^-1. In addition, a study of the influence of several scavengers showed that only the presence of triethanolamine dramatically reduced the pseudo-first order kinetic constant (0.00072 min^-1), pointing out that the reactive species were the holes produced in the catalyst. Finally, the main pathway of CIP degradation seems to be the attack to the piperazine group by ·OH radicals, following heterocycle breakup and the subsequent loss of two of its carbon atoms as CO₂ molecules, and then defluorination, oxidation and cleavage of the cycles of this intermediate.

Sorption process of municipal solid waste biochar-montmorillonite composite for ciprofloxacin removal in aqueous media

This study evaluates a novel adsorbent for ciprofloxacin (CPX) removal from water using a composite derived from municipal solid waste biochar (MSW-BC) and montmorillonite (MMT). The composite adsorbent and pristine materials were characterized using powder X-Ray Diffraction (PXRD), Fourier-Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscope (SEM) before and after the adsorption. Batch experiments were conducted to study the mechanisms involved in the adsorption process. Ciprofloxacin sorption mechanisms were interpreted in terms of its pH-dependency and the distribution coefficients. The SEM images confirmed the successful binding of MMT onto the MSW-BC through flaky structure along with a porous morphology. Encapsulation of MMT onto MSW-BC was exhibited through changes in the basal spacing of MMT via PXRD analysis. Results from FTIR spectra indicated the presence of functional groups for both pristine materials and the composite that were involved in the adsorption reaction. The Hill isotherm model and pseudo-second-order and Elovich kinetic models fitted the batch sorption data, which explained the surface heterogeneity of the composite and cooperative adsorption mechanisms. Changes made to the MSW-BC through the introduction of MMT, enhanced the active sites on the composite adsorbent, thereby improving its interaction with ionizable CPX molecules giving high sorption efficiency.

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.

Biocompatible functionalisation of nanoclays for improved environmental remediation

Among the wide range of materials used for remediating environmental contaminants, modified and functionalised nanoclays show particular promise as advanced sorbents, improved dispersants, or biodegradation enhancers. However, many chemically modified nanoclay materials are incompatible with living organisms when they are used in natural systems with detrimental implications for ecosystem recovery. Here we critically review the pros and cons of functionalised nanoclays and provide new perspectives on the synthesis of environmentally friendly varieties. Particular focus is given to finding alternatives to conventional surfactants used in modified nanoclay products, and to exploring strategies in synthesising nanoclay-supported metal and metal oxide nanoparticles. A large number of promising nanoclay-based sorbents are yet to satisfy environmental biocompatibility in situ but opportunities are there to tailor them to produce "biocompatible" or regenerative/reusable materials.

Enhanced Phototransformation of Tetracycline at Smectite Clay Surfaces under Simulated Sunlight via a Lewis-Base Catalyzed Alkalization Mechanism

As an important class of soil minerals and a key constituent of colloidal particles in surface aquifers, smectite clays can strongly retain tetracyclines due to their large surface areas and high cation exchange capacities. However, the research on phototransformation of tetracyclines at smectite clay surfaces is rarely studied. Here, the phototransformation kinetics of tetracycline preadsorbed on two model smectite clays (hectorite and montmorillonite) exchanged with Na⁺, K⁺, or Ca²⁺ suspended in aqueous solution under simulated sunlight was compared with that of tetracycline dissolved in water using batch experiments. Adsorption on clays accelerated tetracycline phototransformation (half-lives shortened by 1.1-5.3 times), with the most significant effects observed for Na⁺-exchanged clays. Regardless of the presence or absence of clay, the phototransformation of tetracycline was facilitated by increasing pH from 4 to 7. Inhibition or enhancement of photolysis-induced reactive species combined with their measurement using scavenger/probe chemicals indicate that the facilitated production of self-photosensitized singlet oxygen (¹O₂) was the key factor contributing to the clay-enhanced phototransformation of tetracycline. As evidenced by the red shifts and the increased molar absorptivity in the UV-vis absorption spectra, the complexation of tetracycline with the negatively charged (Lewis base) sites on clay siloxane surfaces led to formation of the alkalized form, which has larger light absorption rate and is more readily to be oxidized compared to tetracycline in aqueous solution at equivalent pH. Our findings indicate a previously unrecognized, important phototransformation mechanism of tetracyclines catalyzed by smectite clays.