Hydrolytic Stability Research Articles

A robust ultra-microporous cationic aluminum-based metal-organic framework with a flexible tetra-carboxylate linker

Al-based cationic metal-organic frameworks (MOFs) are uncommon. Here, we report a cationic Al-MOF, MIP-213(Al) ([Al18(μ2-OH)24(OH2)12(mdip)6]6Cl·6H2O) constructed from flexible tetra-carboxylate ligand (5,5'-Methylenediisophthalic acid; H4mdip). Its crystal structure was determined by the combination of three-dimensional electron diffraction (3DED) and high-resolution powder X-ray diffraction. The structure is built from infinite corner-sharing chains of AlO4(OH)2 and AlO2(OH)3(H2O) octahedra forming an 18-membered rings honeycomb lattice, similar to that of MIL-96(Al), a scarce Al-polycarboxylate defective MOF. Despite sharing these structural similarities, MIP-213(Al), unlike MIL-96(Al), lacks the isolated μ3-oxo-bridged Al-clusters. This leads to an ordered defective cationic framework whose charge is balanced by Cl- sandwiched between two Al-trimers at the corner of the honeycomb, showing strong interaction with terminal H2O coordinated to the Al-trimers. The overall structure is endowed by a narrow quasi-1D channel of dimension ~4.7 Å. The Cl- in the framework restrains the accessibility of the channels, while the MOF selectively adsorbs CO2 over N2 and possesses high hydrolytic stability.

Synthesis of new water treatment photocatalytic coatings with controllable functional properties based on the SrO-Bi2O3-SiO2 system that use the energy of solar radiation

This work is devoted to the study of water purification from organic pollutants using new environmentally safe photocatalysts capable of using solar insolation to oxidize organic pollutants. Most methods of creating photocatalysts allow obtaining them only in powder form, which limits their application in water treatment plants. In this regard, photocatalysts formed as coatings on the carrier surface may be more promising. This work contributes to solving the problem of developing a technologically concise and economical method of creating bismuth photocatalytic coatings with biological indifference and high light absorption efficiency (LAE) of solar irradiation. The developed cleaning material is a structurally organized system consisting of a ceramic carrier on which a photocatalytic coating is formed. The coating was formed by soaking the silicate carrier in a bismuth precursor solution (BPS) followed by drying and oxidative pyrolysis. The highest catalytic activity and LAE (58.3–60.3%) were observed for the materials obtained at 10–15% wt. bismuth in BPS. The highest hydrolytic stability was observed at 25% wt. bismuth in BPS. Strontium bismuthate SrBi7.65O13 was the dominant phase in the coating composition for the samples with the highest activity and LAE. Increasing the content of another photocatalytically active phase Bi4Si3O12 resulted in the LAE decreasing to 51.9%, providing greater hydrolytic stability of the material. The proposed method allows for flexibly controlling the properties of the obtained photocatalytic coatings, thus making possible to directionally create different types of materials to be applied in the field of wastewater treatment.

Chemically recyclable oxygen-protective polymers developed by ring-opening metathesis homopolymerization of cyclohexene derivatives

•Successful ring-opening metathesis polymerization of cyclohexene derivatives •Elaborate design of functional cyclohexene monomers to control ring strains •Facile thermodynamic control of polymerization and depolymerization for recycling •Chemically recyclable oxygen-protective polymers with high hydrolytic stability The ring-opening metathesis polymerization (ROMP) of six-membered cyclic olefins has been a long-standing challenge due to their low ring strain energies (RSEs). Here, we achieved the homopolymerization of cyclohexene derivatives to produce oxygen-enriched, chemically recyclable polymers. The polymerization was enabled by utilizing elaborately designed cyclohexene monomers to increase the ring strain energy. Specifically, the 1,2-diol groups of vicinal trans-cyclohexene-diols were converted to carbonate groups for highly efficient and controlled polymerization. The resulting polymers, which have fused cyclic carbonate groups on the backbone, were hydrolyzed to generate hydroxyl-group-enriched polymers with a well-defined 1,2-diol structure at every sixth carbon. Closed-loop recycling was demonstrated by ring-closing metathesis depolymerization (RCMD) back to vicinal trans-cyclohexene-diols. Open-loop recycling was also possible by oxidative cleavage of the 1,2-diol group of the polymers, producing industrially useful α,ω-dicarboxylic acids. The chemically recyclable and structurally well-defined 1,2-diol polymers have high hydrolytic stability and excellent oxygen-protective properties. The ring-opening metathesis polymerization (ROMP) of six-membered cyclic olefins has been a long-standing challenge due to their low ring strain energies (RSEs). Here, we achieved the homopolymerization of cyclohexene derivatives to produce oxygen-enriched, chemically recyclable polymers. The polymerization was enabled by utilizing elaborately designed cyclohexene monomers to increase the ring strain energy. Specifically, the 1,2-diol groups of vicinal trans-cyclohexene-diols were converted to carbonate groups for highly efficient and controlled polymerization. The resulting polymers, which have fused cyclic carbonate groups on the backbone, were hydrolyzed to generate hydroxyl-group-enriched polymers with a well-defined 1,2-diol structure at every sixth carbon. Closed-loop recycling was demonstrated by ring-closing metathesis depolymerization (RCMD) back to vicinal trans-cyclohexene-diols. Open-loop recycling was also possible by oxidative cleavage of the 1,2-diol group of the polymers, producing industrially useful α,ω-dicarboxylic acids. The chemically recyclable and structurally well-defined 1,2-diol polymers have high hydrolytic stability and excellent oxygen-protective properties.

Hydrolytic and thermal stability of urea‐formaldehyde resins based on tannin and betaine bio‐fillers

AbstractIn this work, betaine (trimethyl glycine) and tannin (complex biomolecules of polyphenolic nature) were used as bio‐fillers. Urea‐formaldehyde (UF) resin with a molar ratio of formaldehyde versus urea (FA/U) of 0.8 was synthesized in situ with tannin and betaine as bio‐fillers, to obtain UF resin with reduced free FA content and increased hydrolytic and thermal stability by the principles of sustainability. The samples TUF (with tannin) and BUF (with betaine) were characterized by using X‐ray diffraction analysis (XRD), non‐isothermal thermogravimetric analysis (TGA), and differential thermal analysis (DTA), supported by data from Fourier Transform Infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The percentage of free FA in modified BUF resin is 0.1%, while the percentage of free FA in tannin‐modified resin is 0.8%. The hydrolytic stability of the modified UF resins was determined by measuring the concentration of liberated FA in the modified UF resins, after acid hydrolysis. The modified BUF resin is hydrolytically more stable because the content of released FA is 3.6% compared to the modified TUF resin, where it was 7.4%. Based on the value for T5%, the more thermally stable resin is the modified TUF resin (T5% = 123.1°C), while the value of the T5% for the BUF resin is 83.1°C. This work showed how UF bio‐composite with reduced free FA content and increased hydrolytic and thermal stability can be obtained using tannin and betaine as bio‐fillers.

Study of Hydrolytic Enzymes Activity and Stability of the Isolated Yeast Close to Zygoascus hellenicus

Background: Lipase is one of the most well-known and essential biocatalysts in the de-tergent, food, and pharmaceutical industries. Microbial lipase sources such as yeasts are applicable due to their stability in harsh conditions. Objective: In this study, the effect of temperature, initial pH, and incubation time were investigated to improve the extracellular lipase production by yeast, named Zygoascus hellenicus strain MZ_574439 T. Methods: Strain MZ_574439 T has already been isolated and registered from Iran. In the current project, strain MZ_574439 T with 99% similarity to Z. hellenicus was isolated from water samples. Results: Our findings showed that the isolated strain has a remarkable difference from its close phy-logenetic species in the production of lipase and can produce extracellular lipase up to 7.2 U/ml while the Z. hellenicus has no ability of lipase production. The isolated strain was not able to pro-duce other hydrolytic enzymes. The enzyme activity results showed that the best activity for the iso-lated lipase is pH= 7 and 37°C. The best stability condition for the enzyme occurs at 50°C and pH =7. Conclusion: From the current study, it can be concluded that Z. hellenicus produces lipase. The li-pase enzyme production was optimized with different physiological conditions. Yeast extract could be a better source for maximum lipase production.

Designed Multifunctional Isopeptide for Enhanced Annexin A1 Biosensing Based on Peptide-Protein Interactions in Human Blood.

Specific peptide-protein interactions play an important role in biosensing systems based on functional peptides; however, the non-specific interactions with unrelated biomolecules and poor proteolytic stability restrict the clinical application of natural peptides. Here, we leveraged a self-designed multifunctional isopeptide (MISP) to construct an electrochemical biosensing platform for annexin A1 (ANXA1) detection in human blood. The MISP was designed to contain two parts: an antifouling cyclotide cyclo-C(EK)4 and a d-amino acid-containing carbohydrate-mimetic recognizing peptide IF-7 (D-IF7) connected by the isopeptide bond. We have discussed the properties of the cyclotide and illustrated its unique advantage over the natural linear antifouling peptides by molecular dynamics simulations, and the results were further confirmed by dissipative quartz crystal microbalance (QCM-D). In addition, through electrochemical experiments and fluorescence imaging experiments, we demonstrated that the MISP-based biosensor possessed excellent antifouling ability and proteinase hydrolysis stability. Interestingly, the assaying results of the MISP-biosensor were consistent with those of the commercial ANXA1 kits in a variety of healthy and ANXA1-upregulated clinical blood samples, and, more importantly, for the analysis of blood samples with lower ANXA1 expressions, the sensing capability of the biosensor was greatly superior to that of the kits because of the lower detection limit of the MISP-biosensor. This biosensing platform based on the designed MISP offers enormous potential for achieving accurate biomarker detection with robust operation in complex biological samples.

Upcycling Waste Polycarbonate to Poly(carbonate imine) Vitrimers with High Thermal Properties and Unprecedented Hydrolytic Stability

The global market for polycarbonate (PC) increases steadily because of its heat resistance, toughness, and optical transparency. To achieve sustainability, the waste polycarbonate (WPC) should be recycled. This work reports a 100% atom-efficiency upcycling of WPC to a WPC-derived aldehyde (WPC-CHO). Then, poly(carbonate imine) vitrimers (PCIs) based on the WPC-CHO and two aromatic diamines were prepared. Generally, polyimines can cleave in mild acidic conditions such as 0.1 M HCl(aq) and seldom show good thermal and tensile properties. The PCIs in this work showed good thermal and tensile properties and an unprecedented resistance toward acid hydrolysis. They can survive even immersing in a 5 M H2SO4 THF/H2O solution for 6 months. This unusual resistance toward acid hydrolysis expands the application of PCIs in an acidic environment. Small pieces of PCIs can be compression-molded into a newly formed polymer film at 240 °C. This thermal reprocessability demonstrates the vitrimer characteristic of the PCIs. The PCIs can be degraded through simultaneous aminolysis of carbonate and transimination of imine by hexylamine (HA) in a catalyst-free mild condition. Based on the aminolysis and transimination, we degraded the cross-linking network in the PCI-based carbon fiber-reinforced polymer (CFRP) and recovered undamaged carbon fiber. This environmentally friendly work will attract the attention of researchers who are interested in sustainability and circularity.

Development of hydrolytic stability screening methods for early drug discovery with high differentiation and predictive power

In early drug discovery, hydrolytic chemical stability is routinely assessed to ensure future developability of quality compounds and stability in in vitro test environments. When conducting high-throughput hydrolytic stability analyses as part of the compound risk assessment, aggressive conditions are typically applied to allow for faster screening. However, it can be challenging to extrapolate the real stability risk and to rank compounds due to over-estimating risk based on aggressive conditions and the narrow discriminative window. In this study, critical assay parameters including temperature, concentration, and detection technique were systematically assessed using selected model compounds, and the impact and interplay of these parameters on predictive power and prediction quality were evaluated. Improved data quality was achieved using high sample concentration and reduced temperature, combined with ultraviolet (UV) detection, while mass spectrometry (MS) detection was found to be a useful complementary detection technique. Therefore, a highly discriminative stability protocol with optimized assay parameters and experimental data quality is proposed. The optimized assay can provide early guidance on the potential stability risk of a drug molecule as well as enable more confident decision-making in compound design, selection, and development.

Liquid extraction of lithium using a mixture of alkyl salicylate and tri-n-octylphosphine oxide

Alkyl esters (C3-C8) of salicylic acid (HL) together with trioctylphosphine oxide (TOPO) were considered in order to find new lithium-selective extraction agents for liquid extraction. The hydrolytic stability of salicylic acid alkyl esters in lithium extraction processes from alkaline solutions was studied. Factors were found to reduce the hydrolysis of the extractant. Compositions of extractable alkali metals (Li, Na, K) complexes by a mixture of octyl ether of salicylic acid (HL8) with TOPO have been determined. The enthalpy values of the extraction reactions were calculated. Extraction isotherms were obtained and laboratory simulation of lithium extraction from alkaline multicomponent solutions using HL8-TOPO mixture as an extractant was performed.

The comparative study of biocomposites based on hydrochar and chitosan‐modified urea‐formaldehyde resins

AbstractTo provide new insight into the field of urea‐formaldehyde (UF) adhesives science, in this work, for the first time, UF resin was modified with hydrochar of spent mushroom substrate (HCUF) and chitosan (CHUF) to investigate the effect of these bio‐fillers on the hydrolytic and thermal stability of in situ prepared UF resins. The characterization of the modified UF biocomposites was performed using X‐ray diffraction analysis (XRD), Fourier transforms infrared spectroscopy (FTIR), non‐isothermal thermogravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA). Scanning electron micrographs (SEM) of the CHUF and HCUF biocomposites show a spherical structure that differs from each other because the surface of the CHUF biocomposite has pronounced pores that form a network structure. With its hydroxyl and amino groups, chitosan bonding to UF resin through hydrogen bonds, which is confirmed by FTIR analysis. The content of free FA in CHUF biocomposite is 0.06%, while that of HCUF is higher and amounts to 0.48%. The content of released FA in both modified UF biocomposites was similar (2.5% and 2.8% for CHUF and HCUF, respectively). The hydrolytic stability of CHUF is slightly higher compared to the HCUF biocomposite. Thermal analysis shows that the CHUF is thermally more stable because it starts to decompose at a slightly higher temperature than the HCUF biocomposite.

Tris(aminomethyl)phosphines and Their Copper(I) (Pseudo)halide Complexes with Aromatic Diimines-A Critical Retrospection.

Metal complexes feature a wide range of available geometries, diversified lability, controllable hydrolytic stability, and easily available rich redox activity. These characteristics, combined with the specific properties of coordinated organic molecules, result in many different mechanisms of biological action, making each of the myriads of the classes of metal coordination compounds unique. This focused review presents combined and systematized results of the studies of a group of copper(I) (pseudo)halide complexes with aromatic diimines and tris(aminomethyl)phosphines of a general formula [CuX(NN)PR3], where X = I- or NCS-, NN = 2,2'-bipyridyl, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline or 2,2'-biquinoline, and PR3 = air-stable tris(aminomethyl)phosphines. The structural and electronic properties of the phosphine ligands and luminescent complexes are discussed. The complexes with 2,9-dimethyl-1,10-phenanthroline, apart from being air- and water-stable, exhibit a very high in vitro antimicrobial activity against the Staphylococcus aureus and Candida albicans. Moreover, some of these complexes also show a strong in vitro antitumor activity against human ovarian carcinoma cell lines: MDAH 2774 and SCOV 3, CT26 (mouse colon carcinoma), and A549 (human lung adenocarcinoma) cell lines. The tested complexes are moderately able to induce DNA lesions through free radical processes, however the trends do not reflect observed differences in biological activity.

Benzoxazine-sulfur-Chitosan based freestanding beads: Synthesis, characterization, stability, and removal of mercury and oil

Environmentally benign dual-functional sorbents are desired for easy removal of various and variably located pollutants such as heavy toxic metal ions and crude oil from water. Herein, we have developed sorbents based on sustainable feedstocks using a facile methodology. Bulk copolymerization of biobased benzoxazine (C-fa, cardanol ‘C’ and furfurylamine ‘fa’) with elemental sulfur (S, industrial waste) proceeded in a single step (10 min) to form poly(benzoxazine-ran-sulfur). Bare chitosan (CS) beads and CS/poly(benzoxazine-ran-sulfur) composite beads are fabricated, and performance is analyzed. CS/poly(benzoxazine-ran-sulfur) beads reveal good mechanical and hydrolytic stability, and effectively remove crude oil (8-times the sorbent weight) with appreciable recyclability. These composite beads also demonstrated well-defined mercury ion uptake kinetics, along with a very high mercury ion capture capacity of 334.5 mg of mercury per gram of polymer as calculated from the Langmuir isotherm model and followed a pseudo-second-order kinetics. Designed waste-derived sorbents hold a great promise in tackling the diverse nature of pollutants essential for water purification.

Preparation, Characterization, and Properties of Alkali-Resistant and Hydrolysis-Resistant Silicone Surfactant

It is a challenge to research and develop silicon surfactants with good acid and alkali stability. In the present paper, methylpropenyl polyether modified nonionic silicone surfactant (MPNTS), an alkali-resistant and hydrolysis-resistant silicone surfactant, was synthesized by hydrosilylation of 1,1,1,3,5,5,5-heptamethyl trisiloxane (MDHM) and methylpropenyl polyether (EO(7)). The polyether segments are grafted onto the main chain of organosilicon heptamethyl trisiloxane at a molar ratio of 1:1.05 (n(Si-H):n(C=C)). To evidence product formation, the MPNTS were analyzed by FT-IR and 1H NMR spectroscopy. The surface tension of NPNTS is 18.68 mN/m, and the CMC value is 78 mg/L by a contact angle tester. MPTNS shows hydrolytic stability and maintains that it could keep surface activity after standing for 60 days at pH = 7–10. The compatibility performance analysis shows that MPNTS has good compatibility and synergy with cationic, anionic, and nonionic surfactants, and it reveals the application prospects in daily chemicals, agricultural adjuvants, and other products.

Fabrication and Comparative Properties of Sustainable Epoxy Methacrylate of Bisphenol-C-Jute/Treated Jute- Natural Fibers Sandwich Composites: Part-1

Epoxy methacrylate of bisphenol-C-jute/treated jute and their sandwich composites of white coir, brown coir, wild almond, bamboo, betel nut, and palmyra were prepared by a compression molding technique under 5MPa pressure and at room temperature for three h. The neat sample showed almost double tensile strength than its jute composite, while it is comparable for treated jute. The composites revealed substantially improved flexural strength compared to neat. The neat, jute/treated jute and their sandwich composites indicated good impact strength, pretty good Barcol hardness, and fairly good electric strength. The neat sample showed excellent volume resistivity, while jute/treated jute and their sandwich composites revealed reasonably good volume resistivity. The composites showed high water ingress tendency, excellent hydrolytic stability, and different diffusivity in different environments at 30oC. Water ingress trend was observed the same for all the composites in different environments, and it is H2SO4 > HCl >NaOH >H2O>NaCl. The sandwich composites may find their applications as low-cost housing and insulating materials and also for marine vessels.

Fabrication and Comparative Properties of Sustainable Epoxy Methacrylate of Bisphenol-C-Jute/Treated Jute- Natural Fibers Sandwich Composites: Part-2

Compression-molded epoxy methacrylate of bisphenol-C-jute/treated jute-banana/groundnut/ cane sugar/pineapple leaf/rice husk/wheat husk sandwich composites were fabricated under 5 MPa pressure at room temperature for 3 h. Alkali treated jute-natural fiber sandwich composites displayed considerably improved mechanical properties over untreated jute-natural fiber sandwich composites due to surface modification of the jute fibers. Both types of sandwich composites showed high water uptake tendency, excellent hydrolytic stability against acids, alkali, and salt solutions, and also a longer equilibrium time at 30oC. Alkali treated sandwich composites revealed a considerably lower water uptake tendency than untreated sandwich composites. Observed water uptake trend is H2SO4 > HCl >NaOH >H2O>NaCl.

Effect of montmorillonite activation method on formaldehyde content in urea-formaldehyde composites

In this paper, the synthesis of modified urea-formaldehyde (UF) composites with differently activated montmorillonite KSF (UF/KSF) was performed. Two types of montmorillonite (MMT) KSF were used: sample activated with sulfuric acid-KSF(H2SO4) and sample activated with acid and stirring-KSF(H2SO4+stirrer). In order to examine the effect of KSF activation mode on the thermal and hydrolytic stability of UF resins, thermogravimetric analysis (TGA) was performed, as well as A determination of the amount of liberated formaldehyde (FA) after acid hydrolysis. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis were used to characterize the samples of modified UF/KSF composites and differently activated KSF. Activation of KSF led to a decrease in its specific surface area (SSA) and to an increase in cation exchange capacity (CEC). SEM analysis showed that in the KSF(H2SO4+stirrer) sample, the layered microstructure was disrupted. Free formaldehyde was not detected in the sample of UF resin with KSF(H2SO4), and in the sample with KSF(H2SO4+stirrer) it was 0.06%. The UF/KSF(H2SO4) composite showed higher hydrolytic stability (3.9%) compared to UF/KSF(H2SO4+stirrer) (4.62%), but lower compared to the UF/KSF(inactive) (1.23%). TG analysis showed that the KSF(H2SO4) sample had better thermal stability than the KSF(H2SO4+stirrer) sample, but this did not contribute to the better thermal stability of UF/KSF(H2SO4) compared to UF/KSF(H2SO4+stirrer), both samples had a T5% value of 112 °C.

Linker mediated enhancement in reusability and regulation of Pb(II) removal mechanism of Cu-centered MOFs

Our study demonstrates improved hydrolytic stability of Cu-centered MOFs through linker selection, resulting in enhanced and selective Pb(II) removal with contrasting removal mechanisms. A simple one-pot solvothermal process was employed to synthesize Copper 1,3,5-Benzene-Tricarboxylic Acid (Cu-BTC) MOF, Copper Imidazolate (Cu-Im) MOF and Copper Nicotinic Acid (Cu-NA) MOF, respectively. The synthesis of these MOFs was confirmed using characterization techniques such as XPS, XRD, FTIR and ICP-OES. Water stability studies using experimental and modelling approaches demonstrated that substituting the 1,3,5-benzene-tricarboxylic acid linker with either imidazolate or nicotinic acid, enhanced the hydrostability of the Cu-centered MOF from under 2 h to over 48 h, while showing a high Pb(II) adsorption capacity of 492 mg g−1. This improved hydrostability was observed across acidic and basic pH and at elevated temperatures. The improved stability of Cu-Im significantly enhanced its reusability and showed Pb(II) adsorption for 3 cycles, with 99.5 % removal efficiency at the end of the 3rd cycle and a desorption efficiency of 92.7 %. The experimental data obtained were substantiated with modelling studies (density functional theory) to gain insights into the 2D structure of Cu-Im and compare the hydrolytic stability of Cu-BTC and Cu-Im. Cu-Im, when tested on textile effluent showed a Pb(II) removal efficiency of 99 % within 2 h of treatment. This study opens up the possibility of using linker selection and design as a strategy to enhance the hydrostability of Cu-centered MOFs and in the process improve its applicability for environmental remediation applications.

Diphosphoryl‐functionalized Polyoxometalates: Structurally and Electronically Tunable Hybrid Molecular Materials

AbstractHerein, we report the synthesis and characterization of a new class of hybrid Wells–Dawson polyoxometalate (POM) containing a diphosphoryl group (P2O6X) of the general formula [P2W17O57(P2O6X)]6−(X=O, NH, or CR1R2). Modifying the bridging unit X was found to impact the redox potentials of the POM. The ease with which a range of α‐functionalized diphosphonic acids (X=CR1R2) can be prepared provides possibilities to access diverse functionalized hybrid POMs. Compared to existing phosphonate hybrid Wells–Dawson POMs, diphosphoryl‐substituted POMs offer a wider tunable redox window and enhanced hydrolytic stability. This study provides a basis for the rational design and synthesis of next‐generation hybrid Wells–Dawson POMs.

Diphosphoryl-functionalized Polyoxometalates: Structurally and Electronically Tunable Hybrid Molecular Materials.

Herein, we report the synthesis and characterization of a new class of hybrid Wells-Dawson polyoxometalate (POM) containing a diphosphoryl group (P2 O6 X) of the general formula [P2 W17 O57 (P2 O6 X)]6- (X=O, NH, or CR1 R2 ). Modifying the bridging unit X was found to impact the redox potentials of the POM. The ease with which a range of α-functionalized diphosphonic acids (X=CR1 R2 ) can be prepared provides possibilities to access diverse functionalized hybrid POMs. Compared to existing phosphonate hybrid Wells-Dawson POMs, diphosphoryl-substituted POMs offer a wider tunable redox window and enhanced hydrolytic stability. This study provides a basis for the rational design and synthesis of next-generation hybrid Wells-Dawson POMs.

Biodegradable Preformed Particle Gel (PPG) Made of Natural Chitosan Material for Water Shut-Off Application.

Oil and gas extraction frequently produces substantial volumes of produced water, leading to several mechanical and environmental issues. Several methods have been applied over decades, including chemical processes such as in-situ crosslinked polymer gel and preformed particle gel, which are the most effective nowadays. This study developed a green and biodegradable PPG made of PAM and chitosan as a blocking agent for water shutoff, which will contribute to combating the toxicity of several commercially used PPGs. The applicability of chitosan to act as a crosslinker has been confirmed by FTIR spectroscopy and observed by scanning electron microscopy. Extensive swelling capacity measurements and rheological experiments were performed to examine the optimal formulation of PAM/Cs based on several PAM and chitosan concentrations and the effects of typical reservoir conditions, such as salinity, temperature, and pH. The optimum concentrations of PAM with 0.5 wt% chitosan were between 5-9 wt%, while the optimum chitosan amount with 6.5 wt% PAM was in the 0.25-0.5 wt% range, as these concentrations can produce PPGs with high swellability and sufficient strength. The swelling capacity of PAM/Cs is lower in high saline water (HSW) with a TDS of 67.2976 g/L compared with fresh water, which is related to the osmotic pressure gradient between the swelling medium and the PPG. The swelling capacity in freshwater was up to 80.37 g/g, while it is 18.73 g/g in HSW. The storage moduli were higher in HSW than freshwater, with ranges of 1695-5000 Pa and 2053-5989 Pa, respectively. The storage modulus of PAM/Cs samples was higher in a neutral medium (pH = 6), where the fluctuation behavior in different pH conditions is related to electrostatic repulsions and hydrogen bond formation. The increase in swelling capacity caused by the progressive increment in temperature is associated with the amide group's hydrolysis to carboxylate groups. The sizes of the swollen particles are controllable since they are designed to be 0.63-1.62 mm in DIW and 0.86-1.00 mm in HSW. PAM/Cs showed promising swelling and rheological characteristics while demonstrating long-term thermal and hydrolytic stability in high-temperature and high-salinity conditions.