Highly ordered molecularly imprinted mesoporous silica for selective removal of bisphenol A from wastewater

Potential application of 2D nano-layered MXene in analysing and remediating endocrine disruptor compounds and heavy metals in water

With the advancement of technologies and growth of the economy, it is inevitable that more complex processes are deployed, producing more heterogeneous wastewater that comes from biomedical, biochemical and various biotechnological industries. While the conventional way of wastewater treatment could effectively reduce the chemical oxygen demand, pH and turbidity of wastewater, trace pollutants, specifically the endocrine disruptor compounds (EDCs) that exist in µg L-1 or ng L-1 have further hardened the detection and removal of these biochemical pollutants. Even in small amounts, EDC could interfere human's hormone, causing severe implications on human body. Hence, this review elucidates the recent insights regarding the effectiveness of an advanced 2D material based on titanium carbide (Ti3C2Tx), also known as MXene, in detecting and removing EDCs. MXene's highly tunable feature also allows its surface chemistry to be adjusted by adding chemicals with different functional groups to adsorb different kinds of EDCs for biochemical pollution mitigation. At the same time, the incorporation of MXene into sample matrices also further eases the analysis of trace pollutants down to ng L-1 levels, thereby making way for a more cleaner and comprehensive wastewater treatment. In that sense, this review also highlights the progress in synthesizing MXene from the conventional method to the more modern approaches, together with their respective key parameters. To further understand and attest to the efficacy of MXene, the limitations and current gaps of this potential agent are also accentuated, targeting to seek resolutions for a more sustainable application.

A Fusion of Molecular Imprinting Technology and Siloxane Chemistry: A Way to Advanced Hybrid Nanomaterials

Molecular imprinting technology is a well-known strategy to synthesize materials with a predetermined specificity. For fifty years, the "classical" approach assumed the creation of "memory sites" in the organic polymer matrix by a template molecule that interacts with the functional monomer prior to the polymerization and template removal. However, the phenomenon of a material's "memory" provided by the "footprint" of the chemical entity was first observed on silica-based materials nearly a century ago. Through the years, molecular imprinting technology has attracted the attention of many scientists. Different forms of molecularly imprinted materials, even on the nanoscale, were elaborated, predominantly using organic polymers to induce the "memory". This field has expanded quickly in recent years, providing versatile tools for the separation or detection of numerous chemical compounds or even macromolecules. In this review, we would like to emphasize the role of the molecular imprinting process in the formation of highly specific siloxane-based nanomaterials. The distinct chemistry of siloxanes provides an opportunity for the facile functionalization of the surfaces of nanomaterials, enabling us to introduce additional properties and providing a way for vast applications such as detectors or separators. It also allows for catalyzing chemical reactions providing microreactors to facilitate organic synthesis. Finally, it determines the properties of siloxanes such as biocompatibility, which opens the way to applications in drug delivery and nanomedicine. Thus, a brief outlook on the chemistry of siloxanes prior to the discussion of the current state of the art of siloxane-based imprinted nanomaterials will be provided. Those aspects will be presented in the context of practical applications in various areas of chemistry and medicine. Finally, a brief outlook of future perspectives for the field will be pointed out.

Competitive removal mechanism to simultaneously incarcerate bisphenol A, triclosan and 4-tert-octylphenol within beta-cyclodextrin crosslinked citric acid used for encapsulation in polypropylene membrane protected-micro-solid-phase extraction

Endocrine disrupting compounds (EDCs) are extensively found in the environment and severely impacting human health. In addressing this issue, the beta-cyclodextrin crosslinked citric acid (BCD-CA) had been previously employed in membrane-protected micro-solid phase extraction for sequestering EDCs from water medium; and the findings revealed that BCD-CA possessed a selectivity property. On that account, the potential of BCD-CA towards competitive adsorption of selected EDCs was investigated in terms of adsorption mechanism and selectivity property. Factors that affected the removal efficiencies such as sample pH, sorbent dosage, contact time and initial concentration were evaluated. The characterization results revealed that the carbon percentage of BCD-CA had increased by 2.04%, while the hydrogen percentage had reduced by 1.83%, signifying the successful crosslinking of BCD-CA. Besides, the amount of active BCD was calculated to be 3.2 × 10^-7 mol, while the amount of carboxyl group was 2.48 × 10^-5 mol per 4 mg of BCD-CA. Moreover, BCD-CA was stable in an aqueous medium with the zeta potential obtained at -36.5 mV and had a high-water retention capacity (∼150%). The competitive adsorption mechanism by BCD-CA with EDCs followed the pseudo-second-order kinetics and Freundlich isotherm, suggesting that the adsorption process was dominated by chemisorption on the heterogeneous surface of the adsorbent. Thermodynamic results revealed that adsorption of 4-tert-octylphenol had the most negative ΔG value, indicating most favorable to be adsorbed by BCD-CA as opposed to triclosan and bisphenol A, which was coherent with the apparent formation constant results. These unique properties manifested the practicality of BCD-CA as a selective adsorbent to detect and remove EDCs from the water medium.

Activation of persulfate by mesoporous silica spheres-doping CuO for bisphenol A removal

In the present work, mesoporous silica spheres-doping CuO (CuO/MSS) was prepared via a facile hydrothermal method. It acted as a peroxydisulfate (PDS) activator for the removal of bisphenol A (BPA). X-Ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) showed that CuO was successfully synthesized and silica spheres were doped in CuO. Nitrogen sorption isotherm showed that CuO/MSS, which had a high specific surface area and a narrow pore size distribution, exhibited a mesoporous structure. The effect of initial pH, PDS dosage, catalyst amount, and activation temperature was assessed. A removal efficiency of over 80% was observed after five consecutive cycles, suggesting the superior stability of the catalyst. X-ray photoelectron spectroscopy (XPS), radical quenching experiments, and electrochemical evaluation showed that BPA removal was dominated by the electron transfer among PDS, BPA, and the surface of CuO/MSS (non-radical pathway), while SO₄^·- and OH· radicals had a minor contribution (radical pathway). In addition, the degradation pathways of BPA were proposed according to the intermediates. Overall, this study indicates that CuO/MSS is a promising effective PDS activator to address the drawbacks of the classical Fenton process.

A descriptive and comparative analysis on the adsorption of PPCPs by molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) have aroused great attention as a new material for the removal or detection of pharmaceuticals and personal care products (PPCPs). However, it is not clear about the superiority and deficiency of MIPs in the process of removing or detecting PPCPs. Herein, we evaluated the performance of MIPs in the aspects of adsorption capacity, binding affinity, adsorption rate, and compatibility to other techniques, and proposed ways to improve its performance. Without regard to the selectivity of MIPs, for the PPCPs adsorption, MIPs surprisingly did not always perform better than the conventional adsorbents (non-imprinted polymers, biochar, activated carbon and resin), indicating that MIPs should be used where selectivity is crucial, for example recovery of specific PPCPs in an environmental sample extraction process. Compared to the traditional solid-phase extraction for PPCPs detection pretreatment, the usage of MIPs as substitute extraction agents could obtain high selectivity of specific substance, due to the uniformity and effectiveness of the specific sites. A promising development in the future would be to combine other simple and rapid quantitative technologies, such as electro/photochemical sensor and catalytic degradation, to realize rapid and sensitive detection of trace PPCPs.

Glycosyl imprinted mesoporous microspheres for the determination of glycopeptide antibiotics using ultra-high performance liquid chromatography coupled with tandem mass spectrometry

Glycopeptide antibiotics are critical weapons against serious Gram-positive resistant bacteria, and therefore the development of analytical methods for their determination is essential. In this work, with the aim of extending the scope of molecularly imprinted mesoporous materials to the recognition of large molecules such as proteins and peptides, we selected the glycosyl moiety of glycopeptide antibiotics as a template and synthesised a boronic acid functional monomer by click chemistry reaction to prepare glycosyl imprinted mesoporous microspheres. On the basis of boronate affinity, the template and the functional monomer formed a self-assembly structure that was incorporated into the silica framework during polymerisation. The removal of the glycosyl moiety created cavities with boronic acid groups covalently anchored to the pore walls of the glycosyl imprinted mesoporous microspheres. The resultant microspheres showed regular spherical shape, narrow size distribution and porous structure and exhibited high adsorption capability and fast adsorption kinetics. The size exclusion effect of the mesoporous structure prevents large molecules from entering the cavities, while the glycosyl imprinted cavities provide selectivity for glycopeptide antibiotics. The glycosyl imprinted mesoporous microspheres were employed to separate six glycopeptide antibiotics in serum samples, which were then determined using ultra-high performance liquid chromatography tandem mass spectrometry. The proposed method exhibited satisfactory linearity in the range of 0.1 to 20.0 μg/L, demonstrating great potential for the determination of glycopeptide antibiotics in serum samples.

Metal-Organic Gel-Modulated Synthesis of Hierarchically Porous Molecularly Imprinted Polymers for Efficient Removal of Sildenafil from Water

Molecularly imprinted polymers (MIPs) with high specific recognition capability are promising in environmental remediation. However, traditional MIPs usually show poor specific binding affinity toward templates in pure aqueous medium, thus greatly limiting their practical applications in wastewater treatment. Herein, we proposed a facile and versatile method to synthesize a water-compatible hierarchically porous MIP (HP-MIP), in which a metal-organic gel (MOG) was formed by in situ assembly and acted as a removable structural modulator. Remarkably, the integration of the MOG modulator and template imprinting defects significantly improved the specific template binding affinity of HP-MIP in water. The adsorption behavior of HP-MIP fitted well with the heterogeneous Freundlich isotherm, suggesting that HP-MIP possessed greater site heterogeneity to sildenafil than HP-NIP, which confirmed the efficiency of HP-MIP for the removal of sildenafil from water. This approach provides an important pathway to prepare water-compatible porous MIP for efficient removal of highly toxic organic pollutants from wastewater.

Exploring the Ability of Luminescent Metal Assemblies to Bind and Sense Anionic or Ionizable Analytes A Ru(phen)2bipy-Based Dizinc Complex for Bisphenol A (BPA) Recognition

The synthesis of a new Ru^II complex, in which the metal is coordinated by two 1,10-phenanthroline ligands and a 2,2′-bipyridyl unit linked, via methylene bridges in its 4 and 4′ positions, to two 1,4,7,10-tetraazacyclododecane (cyclen) macrocycles ([Ru(phen)₂L]²⁺) is reported. Protonation and Zn^II binding by [Ru(phen)₂L]²⁺ have been analyzed by potentiometric titration, evidencing the formation of mixed hetero-binuclear and hetero-trinuclear Zn^II/Ru^II complexes. These complexes were tested as bis-phenol A (BPA) binders. Only the dizinc complex with [Ru(phen)₂L]²⁺ is able to bind BPA in aqueous solution, affording a remarkably stable {Zn₂[Ru(phen)₂L]BPA(H₋₂)}⁴⁺ adduct at neutral pH, in which BPA is bound in its doubly deprotonated form to the two Zn^II ions. BPA binding was found to quench the luminescence emission of the Ru^II(phen)₂bipy core. Although the quenching effect is modest, this study demonstrates that appropriately designed dizinc complexes can be used for binding and optical sensing of BPA in water.