Enhanced EDC removal from water through electron beam-mediated adsorber particle integration in microfiltration membranes

The existence of endocrine disrupting chemicals (EDCs) in water and wastewater gives rise to significant environmental concerns. Conventional treatment approaches demonstrate limited capacity for EDC removal. Thus, incorporation of advanced separation procedures becomes essential to enhance the efficiency of EDC removal. In this work, adsorber composite microfiltration polyethersulfone membranes embedded with divinyl benzene polymer particles were created. These membranes were designed for effectively removing a variety of EDCs from water. The adsorber particles were synthesized using precipitation polymerization. Subsequently, they were integrated into the membrane scaffold through a phase inversion process. The technique of electron beam irradiation was applied for the covalent immobilization of particles within the membrane scaffold. Standard characterization procedures were carried out (i.e., water permeance, contact angle, X-ray photoelectron spectroscopy and scanning electron microscopy) to gain a deep understanding of the synthesized membrane properties. Dynamic adsorption experiments demonstrated the excellent capability of the synthesized composite membranes to effectively remove EDCs from water. Particularly, among the various target molecules examined, testosterone stands out with the most remarkable enhancement, presenting an adsorption loading of 220 mg m-2. This is an impressive 26-fold increase in the adsorption when compared to the performance of the pristine membrane. Similarly, androst-4-ene-3,17-dione exhibited an 18-fold improvement in adsorption capacity in comparison to the pristine membrane. The composite membranes also exhibited significant adsorption capacities for other key compounds, including 17β-estradiol, equilin, and bisphenol-A. With the implementation of an effective regeneration procedure, the composite membranes were put to use for adsorption over three consecutive cycles without any decline in their adsorption capacity.

Synthesis of Modified Poly(vinyl Alcohol)s and Their Degradation Using an Enzymatic Cascade

Poly(vinyl alcohol) (PVA) is a water-soluble synthetic vinyl polymer with remarkable physical properties including thermostability and viscosity. Its biodegradability, however, is low even though a large amount of PVA is released into the environment. Established physical-chemical degradation methods for PVA have several disadvantages such as high price, low efficiency, and secondary pollution. Biodegradation of PVA by microorganisms is slow and frequently involves pyrroloquinoline quinone (PQQ)-dependent enzymes, making it expensive due to the costly cofactor and hence unattractive for industrial applications. In this study, we present a modified PVA film with improved properties as well as a PQQ-independent novel enzymatic cascade for the degradation of modified and unmodified PVA. The cascade consists of four steps catalyzed by three enzymes with in situ cofactor recycling technology making this cascade suitable for industrial applications.

Enzymatic degradation of polyethylene terephthalate nanoplastics analyzed in real time by isothermal titration calorimetry

Plastics are globally used for a variety of benefits. As a consequence of poor recycling or reuse, improperly disposed plastic waste accumulates in terrestrial and aquatic ecosystems to a considerable extent. Large plastic waste items become fragmented to small particles through mechanical and (photo)chemical processes. Particles with sizes ranging from millimeter (microplastics, <5 mm) to nanometer (nanoplastics, NP, <100 nm) are apparently persistent and have adverse effects on ecosystems and human health. Current research therefore focuses on whether and to what extent microorganisms or enzymes can degrade these NP. In this study, we addressed the question of what information isothermal titration calorimetry, which tracks the heat of reaction of the chain scission of a polyester, can provide about the kinetics and completeness of the degradation process. The majority of the heat represents the cleavage energy of the ester bonds in polymer backbones providing real-time kinetic information. Calorimetry operates even in complex matrices. Using the example of the cutinase-catalyzed degradation of polyethylene terephthalate (PET) nanoparticles, we found that calorimetry (isothermal titration calorimetry-ITC) in combination with thermokinetic models is excellently suited for an in-depth analysis of the degradation processes of NP. For instance, we can separately quantify i) the enthalpy of surface adsorption ∆_AdsH = 129 ± 2 kJ mol^-1, ii) the enthalpy of the cleavage of the ester bonds ∆_EBH = -58 ± 1.9 kJ mol^-1 and the apparent equilibrium constant of the enzyme substrate complex K = 0.046 ± 0.015 g L^-1. It could be determined that the heat production of PET NP degradation depends to 95% on the reaction heat and only to 5% on the adsorption heat. The fact that the percentage of cleaved ester bonds (η = 12.9 ± 2.4%) is quantifiable with the new method is of particular practical importance. The new method promises a quantification of enzymatic and microbial adsorption to NP and their degradation in mimicked real-world aquatic conditions.

Estradiol Removal by Adsorptive Coating of a Microfiltration Membrane

This work demonstrates the enhancement of the adsorption properties of polyethersulfone (PES) microfiltration membranes for 17β-estradiol (E2) from water. This compound represents a highly potent endocrine-disrupting chemical (EDC). The PES membranes were modified with a hydrophilic coating functionalized by amide groups. The modification was performed by the interfacial reaction between hexamethylenediamine (HMD) or piperazine (PIP) as the amine monomer and trimesoyl chloride (TMC) or adipoyl chloride (ADC) as the acid monomer on the surface of the membrane using electron beam irradiation. The modified membranes and the untreated PES membrane were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), water permeance measurements, water contact angle measurements, and adsorption experiments. Furthermore, the effects of simultaneous changes in four modification parameters: amine monomer types (HMD or PIP), acid monomer types (TMC or ADC), irradiation dosage (150 or 200 kGy), and the addition of toluene as a swelling agent, on the E2 adsorption capacity were investigated. The results showed that the adsorption capacities of modified PES membranes toward E2 are >60%, while the unmodified PES membrane had an adsorption capacity up to 30% for E2 under similar experimental conditions, i.e., an enhancement of a factor of 2. Next to the superior adsorption properties, the modified PES membranes maintain high water permeability and no pore blockage was observed. The highlighted results pave the way to develop efficient low-cost, stable, and high-performance adsorber membranes.

Fluorimetric high-throughput screening method for polyester hydrolase activity using polyethylene terephthalate nanoparticles

Biocatalysis has recently emerged as a powerful and eco-friendly technology in waste plastic recycling, especially for the widely used polyethylene terephthalate (PET). So far, however, a high-throughput screening assay specifically toward PET-hydrolyzing activity has rarely been applied. This hinders the identification of new polyester hydrolases and their variants with adequate activities fulfilling the requirements for industrial applications. This chapter describes the detailed procedure for assaying terephthalate as a major product of enzymatic PET hydrolysis in a 96-well microtiter plate format. Using PET nanoparticles derived readily from waste food packaging as a substrate, an active thermophilic PET hydrolase was clearly distinguished from an inactive variant by a Fenton chemistry-mediated fluorimetric detection. The assay uses enzymes in crude cell lysates, obtained by a simple freeze-thaw protocol. The experimental work validates the applicability of this method for screening mutant libraries of novel PET hydrolases and will thus facilitate the identification of promising variants useful for effective plastic waste recycling.

Biocatalytic Degradation Efficiency of Postconsumer Polyethylene Terephthalate Packaging Determined by Their Polymer Microstructures

Polyethylene terephthalate (PET) is the most important mass-produced thermoplastic polyester used as a packaging material. Recently, thermophilic polyester hydrolases such as TfCut2 from Thermobifida fusca have emerged as promising biocatalysts for an eco-friendly PET recycling process. In this study, postconsumer PET food packaging containers are treated with TfCut2 and show weight losses of more than 50% after 96 h of incubation at 70 °C. Differential scanning calorimetry analysis indicates that the high linear degradation rates observed in the first 72 h of incubation is due to the high hydrolysis susceptibility of the mobile amorphous fraction (MAF) of PET. The physical aging process of PET occurring at 70 °C is shown to gradually convert MAF to polymer microstructures with limited accessibility to enzymatic hydrolysis. Analysis of the chain-length distribution of degraded PET by nuclear magnetic resonance spectroscopy reveals that MAF is rapidly hydrolyzed via a combinatorial exo- and endo-type degradation mechanism whereas the remaining PET microstructures are slowly degraded only by endo-type chain scission causing no detectable weight loss. Hence, efficient thermostable biocatalysts are required to overcome the competitive physical aging process for the complete degradation of postconsumer PET materials close to the glass transition temperature of PET.

Deposition of exchange-coupled dinickel complexes on gold substrates utilizing ambidentate mercapto-carboxylato ligands

The chemisorption of magnetically bistable transition metal complexes on planar surfaces has recently attracted increased scientific interest due to its potential application in various fields, including molecular spintronics. In this work, the synthesis of mixed-ligand complexes of the type [NiII2L(L')](ClO4), where L represents a 24-membered macrocyclic hexaazadithiophenolate ligand and L' is a ω-mercapto-carboxylato ligand (L' = HS(CH2)5CO2- (6), HS(CH2)10CO2- (7), or HS(C6H4)2CO2- (8)), and their ability to adsorb on gold surfaces is reported. Besides elemental analysis, IR spectroscopy, electrospray ionization mass spectrometry (ESIMS), UV-vis spectroscopy, and X-ray crystallography (for 6 and 7), the compounds were also studied by temperature-dependent magnetic susceptibility measurements (for 7 and 8) and (broken symmetry) density functional theory (DFT) calculations. An S = 2 ground state is demonstrated by temperature-dependent susceptibility and magnetization measurements, achieved by ferromagnetic coupling between the spins of the Ni(II) ions in 7 (J = +22.3 cm-1) and 8 (J = +20.8 cm-1; H = -2JS1S2). The reactivity of complexes 6-8 is reminiscent of that of pure thiolato ligands, which readily chemisorb on Au surfaces as verified by contact angle, atomic force microscopy (AFM) and spectroscopic ellipsometry measurements. The large [Ni2L] tail groups, however, prevent the packing and self-assembly of the hydrocarbon chains. The smaller film thickness of 7 is attributed to the specific coordination mode of the coligand. Results of preliminary transport measurements utilizing rolled-up devices are also reported.

The critical zeta potential of polymer membranes: how electrolytes impact membrane fouling

The zeta potential of membrane surfaces and the resulting electrostatic interactions are determining factors of membrane fouling. This publication presents the impact of salt concentration and pH value on these interactions.

Particle adsorption on a polyether sulfone membrane: how electrostatic interactions dominate membrane fouling

This study presents a new method focussing on electrostatic interactions during fouling of microfiltration membranes.

Chemisorption of exchange-coupled [Ni2L(dppba)]+ complexes on gold by using ambidentate 4-(diphenylphosphino)benzoate co-ligands

A new strategy for the fixation of redox-active dinickel(II) complexes with high-spin ground states to gold surfaces was developed. The dinickel(II) complex [Ni2L(Cl)]ClO4 (1ClO4), in which L(2-) represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, reacts with ambidentate 4-(diphenylphosphino)benzoate (dppba) to form the carboxylato-bridged complex [Ni2L(dppba)](+), which can be isolated as an air-stable perchlorate [Ni2L(dppba)]ClO4 (2ClO4) or tetraphenylborate [Ni2L(dppba)]BPh4 (2BPh4) salt. The auration of 2ClO4 was probed on a molecular level, by reaction with AuCl, which leads to the monoaurated Ni(II)2Au(I) complex [Ni(II)2L(dppba)Au(I)Cl]ClO4 (3ClO4). Metathesis of 3ClO4 with NaBPh4 produces [Ni(II)2L(dppba)Au(I)Ph]BPh4 (4BPh4), in which the Cl(-) is replaced by a Ph(-) group. The complexes were fully characterized by ESI mass spectrometry, IR and UV/Vis spectroscopy, X-ray crystallography (2BPh4 and 4BPh4), cyclic voltammetry, SQUID magnetometry and HF-ESR spectroscopy. Temperature-dependent magnetic susceptibility measurements reveal a ferromagnetic coupling J = +15.9 and +17.9 cm(-1) between the two Ni(II) ions in 2ClO4 and 4BPh4 (H = -2 JS1S2). HF-ESR measurements yield a negative axial magnetic anisotropy (D<0), which implies a bistable (easy axis) magnetic ground state. The binding of the [Ni2L(dppba)]ClO4 complex to gold was ascertained by four complementary surface analytical methods: contact angle measurements, atomic-force microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry. The results indicate that the complexes are attached to the Au surface through coordinative Au-P bonds in a monolayer.