Strong Acid Research Articles

Cooperative α-C–H activation enabled quantitative and partial photooxidation of biomass-derived 5-hydroxymethylfurfural

Photocatalytic activation of C‒H bonds is versatile but challenging for undergoing oriented conversion processes. Herein, a spatially site-isolated heterojunction (ZS-Vs/ZIS) of ZnIn2S4 with strong Lewis acidity (ZIS) and ZnS with S-vacancy (ZS-Vs) is constructed for activating α-C‒H bond and forming •O2‒ to cleave the C‒H bond, respectively. ZS-Vs/ZIS displays outstanding performance in visible-light partial photooxidation of bio-based 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) in an unprecedented yield of 95.7% at 25 ºC. In-situ experiments and calculations reveal that Zn sites of ZIS serve as hole enrichment to adsorb HMF for α-C‒H activation via ligand-to-metal charge transfer. Shallow trap states introduced by S-vacancy in ZS-Vs act as an electron pool to realize directed O2 activation into •O2‒ for breaking pre-activated α-C‒H bond in HMF to exclusively give DFF. Moreover, ZS-Vs/ZIS has good recyclability and universality in the photooxidation of various alcohols to carbonyls (86.4‒95.6% yields). The synergistic C‒H activation/breaking strategy exhibits high potential in targeted photocatalytic transformations.

Generation of Bis(pentafluorophenyl)boron Enolates from Alkynes and Their Catalyst-Free Alkyne Coupling.

Carbon-carbon bond forming reactions are powerful synthetic tools for constructing organic molecular frameworks. In this study, strongly Lewis acidic bis(pentafluorophenyl)boron enolates were generated from alkynes through oxygen transfer from 2,6-dibromopyridine N-oxide using tris(pentafluorophenyl)borane [B(C6F5)3]. Boron enolates were highly reactive owing to the strong Lewis acidity of the boron centers, and thus immediately coupled with alkynes. N-Ethynylphthalimide reacted as an alkyne with 2,6-dibromopyridine N-oxide and B(C6F5)3 to form a semi-stable bis(pentafluorophenyl)boron enolate through the coordination of the carbonyl group to the boron center. This enolate underwent coupling with another alkyne.

Determination of pKa of triazolo[5,1-c][1,2,4]triazines in non-aqueous media by potentiometric titration

In this work, for the first time, an approach was suggested for determining the pKa of triazolo[5,1-c][1,2,4]triazine compounds in N,N-dimethylformamide using potentiometric titration. It was noted that change in system potential in the titration curves of triazolo[5,1-с][1,2,4]triazine are observed for compounds containing either H+ located at the nitrogen atom in position 1 or an –NH2 group. The calculated pKa values of the studied molecules correspond to the pKa values of moderately strong acids and are in the range of 2–8. The relationship was established between the acidity of the heterocyclic fragment and the presence of electron donor substituents. The obtained pKa values of the compounds correlate with the calculated possible deprotonation centers of the molecule. It was found that determining the acidity constants of substances is useful for clarifying the mechanisms of their transformations. The possibility of establishing a relationship between the structure of the compound, pKa, and probable biological activity was shown.

Peroxidation of methyl ethyl ketone catalyzed by UiO-66 and the thermal stability analysis

The synthesis of methyl ethyl ketone peroxide (MEKP) generally belongs to the homogeneous strong acid catalysed process. Acid is corrosive to the equipment, cannot be reused and thus has a large amount of wastewater to be post-treated and needs high treatment cost. The heterogeneous catalytic synthesis of organic peroxides is gaining more and more attention. In this study, methyl ethyl ketone peroxide was prepared from butanone oxidized by hydrogen peroxide and in the presence of UiO-66 as the catalyst. Under the conditions that the molar ratio of H2O2 to methyl ethyl ketone (MEK) is 2, the mass ratio of UiO-66 to MEK is 0.045, the reaction temperature is 30 °C, and the reaction time is 70 min, the active oxygen content of the product reaches 10.81 %, and the main products are methyl ethyl ketone peroxide and its oligomers. The thermal decomposition heat and activated energy are 748 J·g−1 and 101 kJ·mol−1 based on the thermogravimetric-differential scanning calorimetry (TG-DSC) determination. Finally, after four cycles, uio-66 still had 70.2 % yield, and XRD and FTIR after the cycles proved the good stability of the catalyst. The study provides a new way for the production of methyl ethyl ketone peroxide by heterogeneous catalytic oxidation.

Generation of Bis(pentafluorophenyl)boron Enolates from Alkynes and Their Catalyst‐Free Alkyne Coupling

Carbon‐carbon bond forming reactions are powerful synthetic tools for constructing organic molecular frameworks. In this study, strongly Lewis acidic bis(pentafluorophenyl)boron enolates were generated from alkynes through oxygen transfer from 2,6‐dibromopyridine N‐oxide using tris(pentafluorophenyl)borane [B(C6F5)3]. Boron enolates were highly reactive owing to the strong acidity of the boron centers, and thus immediately coupled with alkynes. N‐Ethynylphthalimide reacted as an alkyne with 2,6‐dibromopyridine N‐oxide and B(C6F5)3 to form a semi‐stable bis(pentafluorophenyl)boron enolate through the coordination of the carbonyl group to the boron center. This enolate underwent coupling with another alkyne.

Strong acid- and irradiation-resistant nitrogen-rich covalent organic polymers with high iodine adsorption capacity

The removal of radioactive iodine from nuclear waste is very important for the development of nuclear energy. Covalent organic polymers (COPs) have been widely investigated for iodine capture due to their simple operation, diverse structures, and abundant pores. However, the disposal of nuclear waste in a strongly acidic and radioactive environment is still a great challenge. Herein, three nitrogen-rich COPs were successfully designed and synthesized by Schiff-base polycondensation reactions. The high density of N atoms in triazines and imines enhanced the binding capacity of iodine molecules, with an optimal gas-phase iodine adsorption capacity of 4.98 g g−1 and a liquid-phase iodine adsorption capacity of 1224.6 mg g−1. The backbone structure of the hydrazone bond connection and the introduction of thiophene effectively enhanced the stability of the TZ-COPs. The adsorption performance of TZ-2 was maintained after 6 M HNO3 immersion and 100 kGy radiation irradiation, respectively. In addition, TZ-2 still has 92.32 % adsorption performance in five cycles, with excellent reversible regeneration ability. Therefore, this work is important for the preparation of nitrogen-rich COPs for the efficient and reversible removal of radioiodine from nuclear waste.

Calcination-Controlled Synthesis of Carbon Dots@MgF2 Composites with Yellow, White, and Ultraviolet-Blue Thermally Activated Delayed Fluorescence for Multilevel Information Encryption.

It is attractive but challenging to develop carbon dot (CD) based materials with tunable thermally activated delayed fluorescence (TADF), especially in the long wavelength region. Here, by simply calcinating the mixture of m-phenylenediamine and MgF2 at 300-500 °C, a series of CDs@MgF2 composites exhibiting yellow, white, and ultraviolet-blue TADF with high photoluminescence quantum yields of up to 37.6% are prepared. Photophysical studies reveal that the yellow TADF with long lifetimes of 810-1106ms originates from the surface emission centers of CDs, while the ultraviolet-blue TADF with short lifetimes of 266-379ms is related to the carbon core emission centers. The combination of yellow and ultraviolet-blue TADF in a single material triggers dynamic afterglow with time-dependent colors from white to yellow. The MgF2 matrix offers multiple confinement of CDs through a rigid network, strong space constraint, and robust covalent/hydrogen bonding, thus preventing the triplet excitations from non-radiative transitions. The electron-withdrawing fluorine atoms induce substantial spin-orbit coupling and reduce the singlet-triplet energy gap, consequently facilitating the reverse intersystem crossing to enhance TADF efficiency. Importantly, the CDs@MgF2 composites possess outstanding optical stability against water, organic solvents, strong acids, bases, and oxidants. The fascinating TADF features enable the successful demonstration of multilevel information encryption using CDs@MgF2.

Tuning CO2 Hydrogenation to Light Olefin Selectivity via Cu/Zn/Zr Supported on Modified SAPO‐34

AbstractTo alleviate CO2 emissions and reduce reliance on fossil fuels, a groundbreaking bifunctional catalyst system was introduced, which ingeniously merged CZZ with modified SAPO‐34 zeolite, to convert CO2 into light olefins. Different metals were impregnated into SAPO‐34 to form MeSAPO‐34 (Me = Zn, Zr, Mn) and the metal Zr content was altered. Furthermore, CZZ and MeSAPO‐34 was combined into CZZ/MeSAPO‐34 composite catalysts, which was used for CO2 hydrogenation. The MeSAPO‐34 and xZrSAPO‐34 catalysts were rigorously characterized by various techniques, revealing key physicochemical attributes. This innovative approach harnessed the synergistic effects between the metallic CZZ component and the modified zeolite to facilitate a series of reactions, effectively generating C2‐C4‐rich hydrocarbons. Benefiting from weak acid, higher oxygen vacancy concentration and interactions between components, the CZZ/ZrSAPO‐34 catalyst system has shown remarkable efficiency in enhancing the light olefin selectivity. The key aspects of this system are its ability to modulate surface acidity and oxygen vacancy concentration, thus creating favorable conditions for light olefin production via enhanced tandem reaction based on CO2 hydrogenation. This work enriches our insight into designing novel composite catalysts for promoting CO2 conversion and hence mitigating CO2 emissions.

Highly Conducting and Ultra-Stretchable Wearable Ionic Liquid-Free Transducer for Wireless Monitoring of Physical Motions.

Wearable strain transducers are poised to transform the field of healthcare owing to the promise of personalized devices capable of real-time collection of human physiological health indicators. For instance, monitoring patients' progress following injury and/or surgery during physiotherapy is crucial but rarely performed outside clinics. Herein, multifunctional liquid-free ionic elastomers are designed through the volume effect and the formation of dynamic hydrogen bond networks between polyvinyl alcohol (PVA) and weak acids (phosphoric acid, phytic acid, formic acid, citric acid). An ultra-stretchable (4600% strain), highly conducting (10 mScm-1), self-repairable (77% of initial strain), and adhesive ionic elastomer is obtained at high loadings of phytic acid (4:1 weight to PVA). Moreover, the elastomer displayed durable performances, with intact mechanical properties after a year of storage. The elastomer is used as a transducer to monitor human motions in a device comprising an ESP32-based development board. The device detected walking and/or running biomechanics and communicated motion-sensing data (i.e., amplitude, frequency) wirelessly. The reported technology can also be applied to other body parts to monitor recovery after injury and/or surgery and inform practitioners of motion biomechanics remotely and in real time to increase convalescence effectiveness, reduce clinic appointments, and prevent injuries.

The role of Lewis acidity in bis(β-diketonate)zirconium(IV) complexes as catalysts for the ring-opening polymerization of δ-valerolactone

Poly(δ-valerolactone) (PVL) is a polymer that has garnered significant researcher interest due to its intriguing features and prospective uses across numerous domains, particularly in medicine. This work aimed to assess the influence of the Lewis acidity of the bis(β-diketonate)Zr catalyst complex on the ring-opening polymerization of δ-valerolactone. The ligand in the compound contains an electron-donating group, specifically the methyl group (2a). Furthermore, electron-withdrawing groups employed include phenyl (2b–2c) and trifluoromethyl groups (2d). Characterization data indicate that PVL has been successfully synthesized with a bis(β-diketonate)Zr complex catalyst. The hierarchy of Lewis acid strength for the bis(β-diketonate)Zr complex is 2c > 2b > 2d ≫ 2a. The sequence of PVL DP from highest to lowest is 2b, 2c, 2d and 2a. Nonetheless, the elevated Lewis acidity of complex 2c does not provide PVL with the greatest degree of polymerization. The steric barrier of complex 2c, which contains two phenyl groups, is larger than that in complex 2b. Consequently, the coordination process of the nucleophilic monomer with the electrophilic zirconium central atom becomes increasingly difficult.

High-effective, convenient and environmental-friendly MOFs-chitosan-glyoxal composite film for ceftizoxime adsorption: Behavior and mechanisms

In this work, a novel PCN-222-chitosan-glyoxal (PCN@CSG22PCN@CSG: PCN-222-chitosan-glyoxal.) composite film was constructed by loading PCN-222 in chitosan substrate, and used for ceftizoxime adsorption. The results demonstrated that the PCN@CSG not only had excellent adsorption properties for ceftizoxime, but also maintained excellent structural properties in harsh environments (strong acids and alkalis), making it have good recycling performance. Specifically, the adsorption kinetics and isotherms investigation demonstrated that the adsorption process followed the pseudo-second-order kinetic model and Freundlich isotherm model respectively, indicating that it was a multilayer process mainly controlled by chemisorption. The PCN@CSG possesses excellent absorptive capacity of 561.7 mg·g−1 and reaches equilibrium rapidly within 60 min, which is attributed to the structural advantages of PCN-222 and chitosan. The amino, carboxyl and hydroxyl functional groups of PCN-222 provide numbers of active sites and cationic chitin greatly promoted the electrostatic adsorption with negative ceftizoxime. In addition, the PCN@CSG has the advantages of renewable and environment-friendly for the biodegradation of chitosan. After five consecutive adsorption-desorption cycles, the removal rate was still higher than 90 %, confirming the excellent reusability of PCN@CSG. This work provided a great prospect for the design and application of shaped-MOFs composite materials for the removal of cephalosporins in environmental water.

Heavier Diferrocenylpnictogenium Ions.

The synthesis, characterization and reactivity of the diferrocenylphosphenium ion [Fc2P]+ was extended to the heavier diferrocenylpnictogenium ions, [Fc2E]+ (E = As, Sb, Bi). The lighter diferrocenylnitrenium ion, [Fc2N]+, was detected by mass spectrometry, but could not be isolated. The molecular structures of [Fc2E]+ (E = P, As, Sb, Bi) reveal intramolecular coordination of the iron atoms, which counterbalance the electron deficiency of the pnictogens without affecting the strong Lewis acidities, which were determined according to the method of Gutmann and Beckett. The (electro-)chemical oxidation and reduction afforded the dications [Fc2E]2+ (E = P (unstable), As) and the neutral dipnictogens Fc2EEFc2 (E = P, As).

Superactivity of Bimetallic CuFeO2 Submicron Particles towards Selective Proteolysis, Depending on their Surface Hydroxyls.

Nano bimetallic oxides as nanoproteases have the great advantages in the heterogeneous hydrolysis of proteins. Here, we report that bimetallic delafossite CuFeO2 submicron particles (CuFeO2 SMPs) display a high protease activity towards selective cleavage of peptide bond involving hydrophobic residue at 25 °C. CuFeO2 SMPs have excellent regeneration performance with high structural stability. The strong Lewis acidity of Fe3+ and the strong nucleophilicity of Cu+ bound hydroxyl groups are both necessary for the high protease activity of CuFeO2 SMPs. Low-valent metal ion has a great advantage in that low-valent Cu+ bound hydroxyl has strong nucleophilicity, resulting in promotion of protein hydrolysis via high-efficient bimetallic catalysis. This study provides evidence that the protease activity of CuFeO2 SMPs depends on metal ion-bound hydroxyls on their surface. Our findings highlight that the valence of metal ions in artificial protease and their surface hydroxyls are two important factors that determine their catalytic efficiency.

Influence of surface properties of transition metal oxides for permanganate activation: Key role of Lewis acid sites

Permanganate (PM) activation to remove contaminants in aqueous solution has gained increasing interest, and effective approaches to enhance its oxidation ability are becoming one of the hot spots. Transition metal oxides (TMOs) stand out as the most potential catalysts, but have received little attention in this area until now. Their mechanism towards PM activation also remains controversial. In this study, a series of TMOs with diverse surface properties were synthesized, and their effectiveness was compared. It was observed that α-MnO2, NiO and Co3O4 exhibited significantly higher rates of degrading sulfadiazine, levofloxacin and phenol through PM activation than CeO2, α-Fe2O3 and CuO. A performance evolution depended on the surface Lewis acid (LA) strength was established, while a less consistent correlation was observed between the degradation rate and other surface properties. Based on electrochemical analysis and density functional theory calculations, the spontaneous adsorption of MnO4- anions on LA sites in TMOs with an increase in oxidation potential of PM was further confirmed. This research would deepen the understanding of PM activation mechanism, and offer new guidance in the design of more efficient catalysts.

Insights into the low-temperature rapid catalytic pyrolysis and remediation mechanism of weathered petroleum-contaminated saline-alkali soil using Beta zeolite

Pyrolysis technique is considered to have great potential in the remediation of petroleum-contaminated soil, but it still has difficulties such as high energy consumption for the degradation of complex petroleum hydrocarbons and the deterioration of soil quality after treatment. In this study, the low-temperature rapid catalytic pyrolysis was realized using Beta zeolite to assist in remediating weathered petroleum-contaminated saline-alkali soil. Under the action of Beta zeolite, the removal efficiency of petroleum hydrocarbons reached 81% after pyrolysis treatment for 10 min at 250 °C, which was reduced to regulatory standard. The pyrolysis behavior and mechanism revealed that the addition of Beta zeolite effectively reduced the activation energy of C-C and C-O bonds cleavage in petroleum hydrocarbon macromolecules due to the strong acidity of Beta, meanwhile the quality of recovered oil from pyrolysis was improved. Additionally, the analyses of soil physicochemical property indicated that the harmless graphitic C generated from the degradation of petroleum hydrocarbons increased the organic matter in the soil, and the addition of Beta zeolite enhanced soil water retention capacity and reduced the soil alkalinity, thus improving the ecological function of saline-alkali soil. This study provides a new strategy for the removal of organic pollutants under special soil media conditions.

Accumulation of coumaric acid is a key factor in tobacco continuous cropping obstacles.

Phenolic acids are believed to play a significant role in tobacco continuous cropping obstacles, but the strength and potential mechanisms of different phenolic acids remain unclear. This study evaluated the allelopathic effects of six phenolic acids that exhibited cumulative effects in our previous research. Different concentrations of phenolic acids with the strongest allelopathic effects were added to potting soil to explore their impacts on tobacco growth and physiological characteristics, as well as on soil chemical properties and microbial community structure. The results showed that coumaric acid exhibited the strongest direct allelopathic effect. Exogenous coumaric acid significantly reduced soil pH and shifted the soil microbial community from bacteria-dominated to fungi-dominated. Simultaneously, the abundance of bacteria related to nutrient utilization (e.g., Flavisolibacter, Methylobacterium) and fungi related to disease resistance (e.g., Fusicolla, Clonostachys) gradually decreased, along with a reduction in soil catalase, urease, invertase, and acid phosphatase activities. Leaf MDA levels increased continuously with higher concentrations of coumaric acid, while the root resistance hormone (jasmonic acid and the jasmonate-isoleucine complex) levels show the opposite trend. Coumaric acid may inhibit tobacco growth by influencing the physiological processes in tobacco plants directly and the broader soil microecological balance indirectly. This study provides theoretical guidance for precise mitigation of continuous cropping obstacles in future tobacco cultivation.

Hydro-chemical characterization of groundwater using multivariate statistics in Hawassa City, Southern Ethiopia

ABSTRACT This study characterized the hydro-chemical characteristics of groundwater for assessing the possibility of managed aquifer recharge in Hawassa City. A total of 48 water samples were taken from hand-dug wells and boreholes and examined to determine the water type, critical metrics, and key determinants of water quality. Multivariate statistical techniques such as hierarchical cluster, principal component, and linear discriminant analysis were used. The samples were divided into four variable groups and four case cluster groups. The results depicted the water hardness group (C1), soil salinity group (C2), weak and strong acids forming group (C3), and pollution indicator group (C4). Four water types were identified, Na–HCO3 and Ca–Na–HCO3 (87.5%), Ca–HCO3, and Na–Cl. Na–HCO3 was the dominant in hand-dug wells than in deep boreholes, which may account for evaporation or contaminations. Seven principal components with a cumulative variance of 78.58% were also formed. The first two, hardness and salinity, contributed 25.4 and 11.4% variance, respectively. In linear discriminate analysis, three discriminate functions with eight variables were generated, namely pH, K+, Na+, Ca2+, HCO3−, Cl−, BOD5, and COD. Thus, it is revealed that the decline in water quality attributed to natural and anthropogenic causes.

The Influence of Fluoride Ions on the Forms of Lanthanide Migration in Natural and Polluted Waters of the Lovozero Massif (The Kola Peninsula)

A comprehensive study (monitoring, thermodynamic modeling) of natural and anthropogenically polluted waters of the Lovozero Massif has been carried out. A thermodynamic study of the weathering of the Lovozero Massif within the “water-rock-atmosphere” system at a temperature of 5 °C showed that the elements contained in the rocks of the studied massif influence the formation of the chemical composition of natural waters. It has been established that an increase in the degree of “water-rock” interaction leads to an increase in the concentrations of F−, Cl−, SO42−, and HCO3− in the solution. This affects the mobility of lanthanum, cerium, and other elements due to the formation of complex compounds with them. The relatively high content of fluorine, phosphorus, and HCO3− (weak and medium acids) in the solution promotes the dissolution of silicates while Si, Al, and P are released into the solution. Monitoring of water from a flooded mine in which there is an increase in the degree of interaction of water with rock showed higher pH values for the concentrations of Na, HCO3−, F−, P, Al, Si, V, U, La, and Ce. The conclusions are relevant in the context of the use of groundwater for drinking water supply purposes. The obtained information is useful to evaluate the health of the population of the region under study.

Acid-Triggered Side Chain Cleavage Leads to Doped Conjugated Polymers of High Conductivity.

Cleavable side chain based conjugated polymers (CSCPs) represent a unique approach to offering solution processability with added benefits via the elimination of insulating side chains. This work highlights an optimally designed polythiophene-carboxylic acid based CSCP, POET-T2-COOH, which achieves a conductivity exceeding 350 S/cm in molecularly doped and side chain cleaved films, 100-100,000 times higher than three other structurally isomeric CSCPs. The high conductivity of POET-T2-COOH is accomplished via a new "cleavage with doping" methodology, synergistically combining a strong acid and a primary dopant. This hybrid method achieves the greatest conductivity in all isomeric CSCPs over conventional doping or cleavage techniques. The doped and side chain cleaved POET-T2-COOH displays a stable conductivity in inert atmospheres and a high work function of 5.3 eV, opening up new applications.

Niobium Pentoxide as an Acid Catalyst: An Overview

The global chemical industry is under increasing pressure to adopt more sustainable practices, as most chemical products exceed environmental safety limits. Given that chemical production largely relies on catalytic processes, the development of solid acid catalysts has become crucial for more sustainable production. Among these catalysts, niobium pentoxide stands out due to its strong acid sites, which remain active in the presence of water, and its stability under hydrothermal conditions. Recent studies have demonstrated that these solids maintain their catalytic activity even in the presence of strong bases, making them unique catalysts. This review explores the potential of niobium pentoxide as an acid catalyst, addressing advances in synthesis techniques, surface modifications, and combinations with other materials to enhance its catalytic performance in sustainable applications, such as biomass conversion and biofuel production, opening new pathways for the production of greener chemicals. Finally, the future perspectives of niobium pentoxide - based catalysts in green chemistry are discussed.