Role of the chemical structure of ionic liquids in their ecotoxicity and reactivity towards Fenton oxidation

Direct growth of nano-worm-like Cu2S on copper mesh as a hierarchical 3D catalyst for Fenton-like degradation of an imidazolium room-temperature ionic liquid in water

The increasing consumption of room-temperature ionic liquids (RTILs) inevitably releases RTILs into the water environment, posing serious threats to aquatic ecology due to the toxicities of RTILs. Thus, urgent needs are necessitated for developing useful processes for removing RTILs from water, and 1-butyl-3-methylimidazolium chloride (C4mimCl), the most common RTIL, would be the most representative RTIL for studying the removal of RTILs from water. As advanced oxidation processes with hydrogen peroxide (HP) are validated as useful approaches for eliminating emerging contaminants, developing advantageous heterogeneous catalysts for activating HP is the key to the successful degradation of C4mim. Herein, a hierarchical structure is fabricated by growing Cu₂S on copper mesh (CSCM) utilizing CM as a Cu source. Compared to its precursor, CuO@CM, this CSCM exhibited tremendously higher catalytic activity for catalyzing HP to degrade C4mim efficiently because CSCM exhibits much more superior electrochemical properties and reactive sites, allowing CSCM to degrade C4mim rapidly. CSCM also exhibits a smaller E_a of C4mim elimination than all values in the literature. CSCM also shows a high capacity and stability for activating HP to degrade C4mim in the presence of NaCl and seawater. Besides, the mechanistic investigation of C4mim elimination by CSCM-activated HP has also been clarified and ascribed to OH and ¹O₂. The elimination route could also be examined and disclosed in detail through the quantum computational chemistry, confirming that CSCM is a useful catalyst for catalyzing HP to degrade RTILs.

New insights on the effects of ionic liquid structural changes at the gene expression level: Molecular mechanisms of toxicity in Daphnia magna

Knowledge on the molecular basis of ionic liquids' (ILs) ecotoxicity is critical for the development of these designer solvents as their structure can be engineered to simultaneously meet functionality performance and environmental safety. The molecular effects of ILs were investigated by using RNA-sequencing following Daphnia magna exposure to imidazolium- and cholinium-based ILs: 1-ethyl-3-methylimidazolium chloride ([C₂mim]Cl), 1-dodecyl-3-methylimidazolium chloride ([C₁₂mim]Cl) and cholinium chloride ([Chol]Cl)-; the selection allowing to compare different families and cation alkyl chains. ILs shared mechanisms of toxicity focusing e.g. cellular membrane and cytoskeleton, oxidative stress, energy production, protein biosynthesis, DNA damage, disease initiation. [C₂mim]Cl and [C₁₂mim]Cl were the least and the most toxic ILs at the transcriptional level, denoting the role of the alkyl chain as a driver of ILs toxicity. Also, it was reinforced that [Chol]Cl is not devoid of environmental hazardous potential regardless of its argued biological compatibility. Unique gene expression signatures could also be identified for each IL, enlightening specific mechanisms of toxicity.

Cation and anion effect on the biodegradability and toxicity of imidazolium- and choline-based ionic liquids

This work studies the effect of the cation and anion on the biodegradability and inhibition of imidazolium- and choline-based ionic liquids (ILs) using activated sludge. Six commercial ILs, formed by combination of 1-Butyl-3-methylimidazolium (Bmim⁺) and N,N,N-trimethylethanolammonium (Choline⁺) cations and chloride (Cl^-), acetate (Ac^-) and bis(trifluoromethanesulfonyl)imide (NTf₂^-) anions were evaluated, all representative counter-ions with markedly different toxicity and biodegradability. Inherent and fast biodegradability tests were used to evaluate both the microorganism inhibition and the IL biodegradability. In addition, the ecotoxicological response (EC₅₀) of the ILs was studied using activated sludge and Vibrio fischeri (Microtox® test). Bmim⁺ and NTf₂^- can be considered as non-biodegradable, whereas aerobic microorganisms easily degraded Choline⁺ and Ac^-. The biodegradation pattern of each cation/anion is nearly unaffected by counter-ion nature. Moreover, concentrations of CholineNTf₂ higher than 50 mg/L caused a partial inhibition on microbial activity, in good concordance with its low EC₅₀ (54 mg/L) measured by respiration inhibition test, which alerts on the negative environmental impact of NTf₂-containing ILs on the performance of sewage treatment plants.

Ionic liquid-based water treatment technologies for organic pollutants: Current status and future prospects of ionic liquid mediated technologies

Water scarcity motivated the scientific researcher to develop efficient technologies for the wastewater treatment for its reuse. Ionic liquids have been applied to many industrial and analytical separation processes, but their applications in the wastewater treatment, especially in the removal of organic pollutants, are still not well explored. Potential applications of ionic liquids include solvent extraction, solvent membrane technologies and ionic liquid-modified materials that are mainly used as adsorbents. Aforementioned technologies have been examined for the abatement of phenol, chloro- and nitrophenols, toluene, bisphenol A, phthalates, pesticides, dyes, and pharmaceuticals etc. Present review enlightens the application of different ionic liquids in wastewater treatment and suggests the versatility of ionic liquids in the development of rapid, effective and selective removal processes for the variety of organic pollutants. Implementation of ionic liquid based technologies for wastewater treatment have lots of challenges including the selection of non-hazardous ionic liquids, technological applications, high testing requirements for individual uses and scaling-up of the entire pollutant removal, disposal, and ionic liquid regeneration process. Toxicity assessment of water soluble ionic liquids (ILs) is the major issue due to the widespread application of ILs and hence more exposure of environment by ILs. The development of effective technologies for the recovery/treatment of wastewater contaminated with ILs is necessary from the environmental point of view. Furthermore, the cost factor is the major challenge associated with ionic liquid-based technologies.

Chronic toxicity of treated and untreated aqueous solutions containing imidazole-based ionic liquids and their oxydized by-products

In the present work, an experimental study is presented aimed at assessing the chronic toxicity of three imidazole-based ionic liquids, i.e. imidazole (IM), 1-methylimidazole (1MIM), 1-ethyl-3-methyl-imidazolium chloride (1E3MIM), and 1-butyl-3-methyl-imidazolium chloride (1B3MIM), generally considered as environmentally friendly surrogates of traditional industrial solvents. In this study Daphnia magna was used as test organism due to its wide application in the ecotoxicological literature of ionic liquids, monitoring both the cumulative survival of exposed organisms, and their reproductive parameters. The intracellular oxidative stress of daphnids was also assessed through the determination of Reactive Oxygen Species (ROS) and Catalase activity (CAT). The chronic toxicity of their oxidized by-products (BPs), generated by advanced oxidation treatment with UV₂₅₄/H₂O₂, was finally evaluated. Four generations of BPs were considered, each formed at reaction times higher than those required for the complete removal of the parent compounds. Results indicate that IM and 1MIM have a moderate chronic toxicity, which mainly affects reproductive parameters. On the contrary, 1E3MIM and 1B3MIM showed significantly higher chronic toxicity effects resulting in a significant increase in the mortality of exposed organisms compared to the controls. UV/H₂O₂ treatment of the compounds did not always reduce the observed effects, since the generated BPs have, in some cases, higher chronic toxicity than their corresponding parent compounds. Chronic toxic effects remained significant up to the fourth generation of BPs in the cases of 1E3MIM and 1B3MIM, whereas they were found to be negligible from the second generation of BPs in the case of IM and 1MIM. The results of oxidative stress measurements confirmed the previous findings, suggesting a potential risk for the aquatic ecosystem induced by the mentioned compounds and their BPs.

Removal of residual functionalized ionic liquids from water by ultrasound-assisted zero-valent iron/activated carbon

Numerous applications of ionic liquids (ILs) are often accompanied by the generation of aqueous wastes. Due to the high toxicity and poor biodegradability of ILs, effective chemical treatment is of great importance for their removal from aqueous solution. In this work, an ultrasound-assisted zero-valent iron/activated carbon (US-ZVI/AC) micro-electrolysis technique was used to degrade residual functionalized ILs, 1-butyl-3-methyl benzimidazolium bromide ([BMBIM]Br) and 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) in aqueous solution, and the degradation degree, degradation kinetics and possible degradation pathways were investigated. It was shown that the degradation of these functionalized ILs was highly efficient in the US-ZVI/AC system, and the degradation degree was as high as 96.1% and 92.9% in 110 min for [BMBIM]Br and [AMIM]Cl, respectively. The degradation of [BMBIM]Br could be described by the second-order kinetics model, and [BMBIM]⁺ was decomposed in two ways: (i) sequential cleavage of N-alkyl side chain of the cation produced three intermediates; (ii) the 2-positioned H atoms of the benzimidazolium ring were first oxidized, and then the imidazolium ring was opened. The degradation of [AMIM]Cl followed the first-order kinetics rule, and the 2,4,5-positioned H atoms of the imidazolium ring were oxidized to induce ring opening. In addition, the removal of total organic carbon was found to be >87%, which indicates that most of the ILs was mineralized in the degradation process. These results suggest that ultrasound-assisted ZVI/AC micro-electrolysis is highly effective for the removal of residual functionalized ILs from aqueous environment.

Removal of imidazolium-based ionic liquid by coupling Fenton and biological oxidation

In this work, we assessed the potential of combining Fenton´s reagent and biological oxidation for removing the imidazolium-based ionic liquid 1-Ethyl-3-methylimidazolium chloride (EmimCl). Fenton-like oxidation was conducted at variable H₂O₂ doses from 20 to 100% the stoichiometric value as calculated from the theoretical chemical oxygen demand (COD). The stoichiometric H₂O₂ dose afforded Total Organic Carbon (TOC) conversion and COD removal of 50 and 62%, respectively. Identifying the reaction by-products formed at low hydrogen peroxide doses allowed a plausible pathway for EmimCl oxidation to be proposed. The effluents from Fenton-like oxidation at substoichiometric H₂O₂ doses were less ecotoxic and more biodegradable than was the parent ionic liquid. The effluent from Fenton-like oxidation with the 60% H₂O₂ dose (TOC conversion ≅ 41%, COD removal ≅ 31%) was subsequently subjected to an effective biological treatment that allowed complete removal of the starting compound, increased its ecotoxicity to a low-moderate level and rendered it acceptably biodegradable. Biological oxidation was performed in 8-h and 12-h cycles in a sequencing batch reactor. Combining Fenton and biological oxidation of EmimCl afforded TOC conversion and COD removal of around 90%.

Heterogeneous electro-Fenton catalyst for 1-butylpyridinium chloride degradation

The application of the electro-Fenton process for organic compound mineralisation has been widely reported over the past years. However, operational problems related to the use of soluble iron salt as a homogeneous catalyst involve the development of novel catalysts that are able to operate in a wide pH range. For this purpose, polyvinyl alcohol-alginate beads, containing goethite as iron, were synthesised and evaluated as heterogeneous electro-Fenton catalyst for 1-butylpyridinium chloride mineralisation. The influence of catalyst dosage and pH solution on ionic liquid degradation was analysed, achieving almost total oxidation after 60 min under optimal conditions (2 g/L catalyst concentration and pH 3). The results showed good catalyst stability and reusability, although its effectiveness decreases slightly after three successive cycles. Furthermore, a plausible mineralisation pathway was proposed based on the oxidation byproducts determined by chromatographic techniques. Finally, the Microtox® test revealed notable detoxification after treatment which demonstrates high catalyst ability for pyridinium-based ionic liquid degradation by the electro-Fenton process.

Photostability and photocatalytic degradation of ionic liquids in water under solar light

The aim of this work is to study, (i) the photostability of different imidazolium and pyridinium ionic liquids (ILs) in water under solar light; and (ii) the photocatalytic degradation of those ILs in water with TiO₂ under solar light. The effects of the type of cation and anion as well as the length of the cationic chain of the imidazolium ILs have been analyzed. These imidazolium-based ILs show high solar stability, slightly decreasing as the length of the cationic chain increases. The anion plays a main role in the stability of ILs under solar light, decreasing in the case of hydrophobic anions. The kind of head group (pyridinium or imidazolium) or the presence of functional groups (allyl, OH) also influence the solar light stability. DFT calculations on the fundamental and excited electronic states of the ILs were carried out to obtain a deeper insight on their photostability. In the case of the photocatalytic degradation of the ILs, complete conversion was achieved for all the ILS tested but mineralization reached 80% at the most. The rate of degradation increased with the length of the alkyl chain while the anion showed little effect. The pyridinium-based IL tested was the easiest to breakdown.

The aim of this work is to study, (i) the photostability of different imidazolium and pyridinium ionic liquids (ILs) in water under solar light; and (ii) the photocatalytic degradation of those ILs in water with TiO₂ under solar light.

Kinetics of imidazolium-based ionic liquids degradation in aqueous solution by Fenton oxidation

In the last few years, several works dealing with Fenton oxidation of ionic liquids (ILs) have proved the capability of this technology for their degradation, achieving complete ILs removal and non-toxic effluents. Nevertheless, very little is known about the kinetics of this process, crucial for its potential application. In this work, the effect of several operating conditions, including reaction temperature (50-90 °C), catalyst load (10-50 mg L^-1 Fe³⁺), initial IL concentration (100-2000 mg L^-1), and hydrogen peroxide dose (10-200% of the stoichiometric amount for the complete IL mineralization) on 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) oxidation has been investigated. Under the optimum operating conditions (T = 90 °C; [Fe³⁺]₀ = 50 mg L^-1; [H₂O₂]₀ = 100% of the stoichiometric amount), the complete removal of [C₄mim]Cl (1000 mg L^-1) was achieved at 1.5-min reaction time. From the experimental results, a potential kinetic model capable to describe the removal of imidazolium-based ILs by Fenton oxidation has been developed. By fitting the proposed model to the experimental data, the orders of the reaction with respect to IL initial concentration, Fe³⁺ amount and H₂O₂ dose were found to be close to 1, with an apparent activation energy of 43.3 kJ mol^-1. The model resulted in a reasonable fit within the wide range of operating conditions tested in this work.

Removal of imidazolium- and pyridinium-based ionic liquids by Fenton oxidation

The oxidation of imidazolium (1-hexyl-3-methylimidazolium chloride, HmimCl) and pyridinium (1-butyl-4-methylpyridinium chloride, BmpyrCl) ionic liquids (ILs) by Fenton's reagent has been studied. Complete conversion was achieved for both ILs using the stoichiometric H₂O₂ dose at 70 °C, reaching final TOC conversion values around 45 and 55% for HmimCl and BmpyrCl, respectively. The decrease in hydrogen peroxide dose to substoichiometric concentrations (20-80% stoichiometric dose) caused a decrease in TOC conversion and COD removal and the appearance of hydroxylated oxidation by-products. Working at these substoichiometric H₂O₂ doses allowed the depiction of a possible degradation pathway for the oxidation of both imidazolium and pyridinium ILs. The first step of the oxidation process consisted in the hydroxylation of the ionic liquid by the attack of the ·OH radicals, followed by the ring-opening and the formation of short-chain organic acids, which could be partially oxidized up to CO₂ and H₂O. At H₂O₂ doses near stoichiometric values (80%), the resulting effluents showed non-ecotoxic behaviour and more biodegradable character (BOD₅/COD ratio around 0.38 and 0.58 for HmimCl and BmpyrCl, respectively) due to the formation of short-chain organic acids. Graphical abstract ᅟ.

Improved Monitoring of Aqueous Samples by the Concentration of Active Pharmaceutical Ingredients using Ionic-Liquid-based Systems

Fluoroquinolones (FQs) and Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are two classes of Active Pharmaceutical Ingredients (APIs), widespreadly used in human healthcare and as veterinary drugs, and that have been found throughout the water cycle in the past years. These two classes of APIs are commonly present in aqueous streams in concentrations ranging from ng.L-1 to µg.L-1. Despite such low concentrations, these contaminants tend to bioaccumulate, leading to serious environmental and health issues after chronic exposure. The low concentrations of FQs and NSAIDs in aqueous media also render their difficult identification and quantification, wich may result in an unefficient evaluation of their environmental impact and persistence. Therefore, the development of alternative pre-treatment techniques for their extraction and concentration from aqueous samples is a crucial requirement. In this work, liquid-liquid systems, namely ionic-liquid-based aqueous biphasic systems (IL-based ABS), were tested as simultaneous extraction and concentration platforms of FQs and NSAIDs. ABS composed of imidazolium-, ammonium- and phosphonium-based ILs and a citrate-based salt (C6H5K3O7) were evaluated for the single-step extraction and concentration of three FQs (ciprofloxacin, enrofloxacin and norfloxacin) and three NSAIDs (diclofenac, naproxen and ketoprofen) from aqueous samples. Outstanding one-step extraction efficiencies of APIs close to 100% were obtained. Furthermore, concentration factors of both FQs and NSAIDs were optimized by an appropriate manipulation of the phase-forming components compositions to tailor the volumes of the coexisting phases. Concentration factors of 1000-fold of both FQS and NSAIDs were obtained in a single-step, without reaching the saturation of the IL-rich phase. The concentration of APIs up to the mg.L-1 allowed their easy and straightforward identification and quantification by High-Performance Liquid Chromatography (HPLC) coupled to an UV detector, as shown either with model aqueous samples or real wastewater effluent samples.

Comparison of the effect of ionic liquids containing hexafluorophosphate and trifluoroacetate anions on the inhibition of growth and oxidative stress in spring barley and common radish

Ionic liquids are a group of chemical compounds with chemical properties that are of great interest to various fields of science and industry. However, commercial use of these substances raises concern because they may threaten the natural ecosystems. The present study used 2 types of (-)-menthol-containing imidazolium chiral ionic liquids: 1-[(1R,2S,5R)-(-)-menthoxymethyl]-3-methylimidazolium hexafluorophosphate [Im-Men][PF₆ ] and 1-[(1R,2S,5R)-(-)-menthoxymethyl]-3-methylimidazolium trifluoroacetate [Im-Men][CF₃ CO₂ ]. The effects of these compounds on growth and development of spring barley (Hordeum vulgare) and common radish (Raphanus sativus L. subvar. radicula Pers.) were investigated. The present study demonstrated that chiral ionic liquids produced a relatively high phytotoxicity, by shortening the plants' lengths and roots, thus causing a decline in the experimental plants' fresh weights. The investigated ionic liquids also led to a reduction in photosynthetic pigment levels, changes in hydrogen peroxide and malondialdehyde content, and changes in the activities of superoxide dismutase, catalase, and peroxidase in both plants. Changes in these enzymes were used to indicate oxidative stress levels in spring barley and common radish. It was demonstrated that imidazolium ionic liquid-induced phytotoxicity depended largely on the type of anion. The liquid [Im-Men][PF₆ ] exhibited higher toxicity toward spring barley and common radish seedlings. Common radish was more resistant to chiral ionic liquids. Environ Toxicol Chem 2017;36:2167-2177. © 2017 SETAC.

Environmental Impact of Ionic Liquids: Recent Advances in (Eco)toxicology and (Bio)degradability

This Review aims to integrate the most recent and pertinent data available on the (bio)degradability and toxicity of ionic liquids for global and critical analysis and on the conscious use of these compounds on a large scale thereafter. The integrated data will enable focus on the recognition of toxicophores and on the way the community has been dealing with them, with the aim to obtain greener and safer ionic liquids. Also, an update of the most recent biotic and abiotic methods developed to overcome some of these challenging issues will be presented. The review structure aims to present a potential sequence of events that can occur upon discharging ionic liquids into the environment and the potential long-term consequences.

Removal of herbicidal ionic liquids by electrochemical advanced oxidation processes combined with biological treatment

Recently a new group of ionic liquids (ILs) with herbicidal properties has been proposed for use in agriculture. Owing to the design of specific physicochemical properties, this group, referred to as herbicidal ionic liquids (HILs), allows for reducing herbicide field doses. Several ILs comprising phenoxy herbicides as anions and quaternary ammonium cations have been synthesized and tested under greenhouse and field conditions. However, since they are to be introduced into the environment, appropriate treatment technologies should be developed in order to ensure their proper removal and avoid possible contamination. In this study, didecyldimethylammonium (4-chloro-2-methylphenoxy) acetate was selected as a model HIL to evaluate the efficiency of a hybrid treatment method. Electrochemical oxidation or electro-Fenton was considered as a pretreatment step, whereas biodegradation was selected as the secondary treatment method. Both processes were carried out in current mode, at 10 mA with carbon felt as working electrode. The efficiency of degradation, oxidation and mineralization was evaluated after 6 h. Both processes decreased the total organic carbon and chemical oxygen demand (COD) values and increased the biochemical oxygen demand (BOD₅) on the COD ratio to a value close to 0.4, showing that the electrolyzed solutions can be considered as 'readily biodegradable.'

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine

Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in the form of ionic liquid species. The main aim of this Review is to attract a broad audience of chemical, biological, and medical scientists to study advantages of ionic liquid pharmaceutics. Overall, the discussed data highlight the importance of the research direction defined as "Ioliomics", studies of ions in liquids in modern chemistry, biology, and medicine.

Biodegradation, ecotoxicity and UV254/H2O2 treatment of imidazole, 1-methyl-imidazole and N,N'-alkyl-imidazolium chlorides in water

Imidazole-based compounds are used as reagents for the manufacturing of other compounds including imidazolium-based ionic liquids, which have been recently proposed as a green alternative to conventional solvents. Since some imidazole-based compounds have been demonstrated to be harmful to aquatic organisms, the removal of imidazole, 1-methylimidazole, 1-ethyl-3-methyl-imidazolium chloride and 1-butyl-3-methyl-imidazolium chloride from aqueous solutions was attempted by biological oxidation, direct UV₂₅₄ photolysis, and UV₂₅₄/H₂O₂ process at pH 5.5 and 8.5. Results showed that UV₂₅₄/H₂O₂ treatment is an effective tool for the removal of the selected compounds at both pHs. In fact, the kinetic constants of the reaction between the photogenerated HO radicals and the four target compounds, estimated by means of both numerical and competition kinetic method, range between 2.32·10⁹ M^-1 s^-1 and 5.52 ·10⁹ M^-1 s^-1. Moreover, an ecotoxicity assessment of the contaminated water before and after initial treatment without further processing was assessed by using two living aquatic organisms: Raphidocelis subcapitata and Daphnia magna. The results of this assessment not only corresponded closely to previous findings (in terms of EC₅₀ values) reported in the literature, but also indicated that, in some cases, UV₂₅₄/H₂O₂ oxidation by-products could be even more toxic than parent compounds.

Influence of the current density on the electrochemical treatment of concentrated 1-butyl-3-methylimidazolium chloride solutions on diamond electrodes

This paper focuses on the influence of the current density treatment of a concentrated 1-butyl-3-methylimidazolium chloride (BMImCl) solution on an electrochemical reactor with a boron-doped diamond (BDD) anode. The decrease in the total organic carbon (TOC) and the BMImCl concentration demonstrate the capability of BDD in oxidizing ionic liquids (ILs) and further mineralizing (to CO2 and NO3 (-)) more rapidly at higher current densities in spite of the reduced current efficiency of the process. Moreover, the presence of Cl(-) led to the formation of oxychlorinated anions (mostly ClO3 (-) and ClO4 (-)) and, in combination with the ammonia generated in the cathode from the nitrate reduction, chloramines, more intensely at higher current density. Finally, the analysis of the intermediates formed revealed no apparent influence of the current density on the BMImCl degradation mechanism. The current density presents therefore a complex influence on the IL treatment process that is discussed throughout this paper.