Post-synthesis Method Research Articles

Precise design of Cu-exchanged zeolites with diverse topologies via atomic layer deposition for boosting low-temperature NH3-SCR

Atomic layer deposition (ALD), as an advanced grafting technique, enables precise tailoring of the active sites using self-limiting growth at atomic level. The primary difficulties faced by this metal post-synthesis method are the low metal loading and expensive precursors due to the highly developed internal micropores of zeolite as a support. Cu(hfac)2 was deposited over zeolites with different topologies in order to clarify the matching principles as well as key factors between zeolites and ALD, and the method was applied for the first time to selective catalytic reduction (SCR) of NO by NH3. It was shown that Cu loading on EMC-2 zeolite can be reached to 1.58wt% after only twice cycles, and the Cu-EMC-2 exhibits excellent performance, achieving more than 90% NO conversion at 200-550 °C. The temperature-programmed reduction by hydrogen (H2-TPR) and electron paramagnetic resonance (EPR) demonstrated that Cu-based zeolites prepared by ALD were dominated by isolated Cu+ or [Cu(OH)]+ ions, which are combined with single Al sites. Kinetic diameter computation, molecular dynamic simulation, and X-ray photoelectron spectroscopy (XPS) together indicate that the copper precursors could successfully enter the zeolites with 12-member rings (MR), while having difficulty entering the zeolites with 10-MR or 8-MR because of pore diffusion limitation, making poorly dispersed copper ions on the zeolitic surface. This study guides how to improve metal precursor utilization and clarifies that the essentials in coupling ALD with zeolites is the pore structures or membered rings.

Sonochemical post-synthesis modification of Y zeolite with iron species

Faujasite is a zeolite that, when in a Y structure, is widely used as a catalyst to produce fuel by fluid catalytic cracking (FCC) and is recently being investigated for applications in sustainable processes. Hence, there is an increased interest in modifying Y zeolites with metals such as Fe to improve and optimize their catalytic properties. Several post-synthesis methods such as chemical vapor deposition, impregnation and ion exchange have been explored for the introduction of Fe. Nevertheless, these currently developed methods can be time-consuming and unable to selectively tune the Fe species. Therefore, this study explores the use of ultrasonic irradiation in a liquid state modification of a Fe-exchanged Y zeolite (FeY) in a buffer solution with different pH values (5 and 9) and oxidation states of Fe ions (ferrous and ferric) for the introduction of Fe species. At the tested ultrasonic modification conditions, the zeolitic structure was preserved with slight Si/Al ratio and pore structure adjustments in correlation with the introduced Fe species (ions, hydroxides and oxides). Setting the sonochemical method as a potential path for the search of reaction conditions for the design and fabrication of Fe-modified zeolitic materials with tuned properties for a wide range of applications.

Optimization of surface silanol groups in mesoporous SBA-15 and KIT-6 materials: Effects on APTES functionalization and CO2 adsorption

Hybrid mesoporous silicas are potentially reusable promising adsorbents for CO2 capture. Here SBA-15 and KIT-6 mesoporous silicas were synthetized by the sol-gel technique using a lower calcination temperature than the conventional one: 300 °C vs. 550 °C. This strategy aimed to maximize the surface hydroxyl group density and consequently, to improve functionalizing agent-loading performed by the post-synthesis grafting method. The as-obtained silica-based samples were then characterized and applied to CO2 capture. A correlation between chemical-textural properties and adsorption capacities of pure and modified materials was discussed. The calcined at 300 °C silica supports, SBA-15-300-1 and KIT-6-300-1, with high silanol group densities showed better adsorption capacities overall pressure range. It is worth highlighting that the KIT-6-300-1: APTES adsorbent had a good stability performance, showing a drop of around 8 % over the aging time of a year. While, the SBA-15-300-1: APTES solid presented an excellent recycled performance after 10 adsorption-desorption cycles, maintaining about 95 % of its initial capacity.

Ion exchange in semiconductor magic-size clusters.

As a crucial post-synthesis method, ion exchange allows for precise control over the composition, interface, and morphology of nanocrystals at the atomic scale, achieving material properties that are difficult to obtain with traditional synthesis techniques. In nanomaterial science, semiconductor magic-size clusters (MSCs), with their atomic-level precision and unique quantum confinement effects, serve as a bridge between molecules and nanocrystals. Despite this, research on ion exchange in MSCs is still in its infancy. This review introduces the principles of ion exchange and reactions in colloidal nanocrystals and MSCs, analyzing the importance and challenges of ion exchange in studying MSCs. This paper begins with a focus on the current research progress of cation and anion exchange in II-VI and III-V semiconductor MSCs. Then, the common methods for characterizing MSCs during the ion exchange process are discussed. Finally, the article envisions future research directions based on MSCs' ion exchange. Research on MSCs' ion exchange not only aids in designing MSCs with complex functionalities, but also plays an essential role in elucidating the ion exchange mechanisms in nanocrystals, providing new insights for the innovative design and synthesis of nanomaterials.

Hierarchical EMT structured zeolites as improved catalysts for glycerol dehydration

A fast and simple post-synthesis method for creating secondary mesoporosity in EMT zeolites was developed using an ammonium fluoride / cetyltrimethylammonium bromide (NH4F/CTAB) solution at low temperature with ultrasound irradiation. This strategy is shown to be highly effective for producing hierarchical EMT structured zeolites through the etching of both Si and Al species. The catalytic performance of these materials were assessed using glycerol dehydration as a reaction test, which is in addition a relevant reaction due to the high amounts of glycerol generated as a by-product of biodiesel production. The resulting hierarchical EMT structured zeolites exhibited improved catalytic activity and high selectivity towards acrolein (around 80 %). This innovative approach creates new opportunities for using hierarchical EMT structured zeolites in processes related with biodiesel manufacture.

Synthesis of UiO-66-Pyca-CuO by a Simple and Novel Method: MOF-based Metal Thin Film as Heterogeneous Catalysts for the Synthesis of α-Aminonitriles.

Metal-organic frameworks (MOFs), particularly UiO-66-NH2, are employed as catalysts in many industrial catalyst applications. As converting catalysts into thin film significantly increases their catalytic properties, we report a general approach to synthesizing MOF thin films (UiO-66-Pyca-CuO). First, functionalization of UiO-66-NH2 was done with 3-pyridine carboxaldehyde by the postsynthesis method, and then, UiO-66-Pyca was entangled on the surface of copper oxide nanoparticles with a modern strategy (MOF thin film). The morphology and structure of the synthesized UiO-66-Pyca-CuO were determined by using X-ray diffraction, Fourier transform infrared, field-emission scanning electron microscopy, energy-dispersive analysis of X-ray, inductively coupled plasma-mass spectrometry, elemental analyses of CHNOS, temperature-programmed desorption of ammonia, Brunauer-Emmett-Teller, and X-ray photoelectron spectroscopy. We studied the catalytic action of the UiO-66-Pyca-CuO thin film in the synthesis of α-aminonitriles via Strecker reaction. Our studies show that this catalysis can be a suitable catalyst in the synthesis of α-aminonitriles because of having advantages such as using the solvent being environmentally friendly, easy separation of the catalyst (only by picking up the MOF thin film from inside the solution), the reaction at room temperature, high yield, and reusability.

Design of Scaffolds Based on Zinc-Modified Marine Collagen and Bilberry Leaves Extract-Loaded Silica Nanoparticles as Wound Dressings.

In this study, wound dressings were designed using zinc-modified marine collagen porous scaffold as host for wild bilberry (WB) leaves extract immobilized in functionalized mesoporous silica nanoparticles (MSN). These new composites were developed as an alternative to conventional wound dressings. In addition to the antibacterial activity of classic antibiotics, a polyphenolic extract could act as an antioxidant and/or an anti-inflammatory agent as well. Wild bilberry leaves extract was prepared by ultrasound-assisted extraction in ethanol and its properties were evaluated by UV-Vis spectroscopy (radical scavenging activity, total amount of polyphenols, flavonoids, anthocyanins, and condensed tannins). The extract components were identified by HPLC, and the antidiabetic properties of the extract were evaluated via α-glucosidase inhibitory activity. Spherical MSN were modified with propionic acid or proline moieties by post-synthesis method and used as carriers for the WB leaves extract. The textural and structural features of functionalized MSN were assessed by nitrogen adsorption/desorption isotherms, small-angle XRD, SEM, TEM, and FTIR spectroscopy. The composite porous scaffolds were prepared by freeze drying of the zinc-modified collagen suspension containing WB extract loaded silica nanoparticles. The properties of the new composites demonstrated enhanced properties in terms of thermal stability of the zinc-collagen scaffold, without altering the protein conformation, and stimulation of NCTC fibroblasts mobility. The results of the scratch assay showed contributions of both zinc ions from collagen and the polyphenolic extract incorporated in functionalized silica in the wound healing process. The extract encapsulated in functionalized MSN proved enhanced biological activities compared to the extract alone: better inhibition of P. aeruginosa and S. aureus strains, higher biocompatibility on HaCaT keratinocytes, and anti-inflammatory potential demonstrated by reduced IL-1β and TNF-α levels. The experimental data shows that the novel composites can be used for the development of effective wound dressings.

"Cloth-to-Clothes-Like" Fabrication of Soft Actuators.

Inspired by adaptive natural organisms and living matter, soft actuators appeal to a variety of innovative applications such as soft grippers, artificial muscles, wearable electronics, and biomedical devices. However, their fabrication is typically limited in laboratories or a few enterprises since specific instruments, strong stimuli, or specialized operation skills are inevitably involved. Here a straightforward "cloth-to-clothes-like" method to prepare soft actuators with a low threshold by combining the hysteretic behavior of liquid crystal elastomers (LCEs) with the exchange reaction of dynamic covalent bonds, is proposed. Due to the hysteretic behavior, the LCEs (resemble "cloth") effectively retain predefined shapes after stretching and releasing for extended periods. Subsequently, the samples naturally become soft actuators (resemble "clothes") via the exchange reaction at ambient temperatures. As a post-synthesis method, this strategy effectively separates the production of LCEs and soft actuators. LCEs can be mass-produced in bulk by factories or producers and stored as prepared, much like rolls of cloth. When required, these LCEs can be customized into soft actuators as needed. This strategy provides a robust, flexible, and scalable solution to engineer soft actuators, holding great promise for mass production and universal applications.

Defective NH2-UiO-66 for effective Pb(II) removal: Facile fabrication strategy, performances and mechanisms

Defective NH2-UiO-66 adsorbent (named as NH2-UiO-66-SD) was successfully fabricated via post-synthesis method with the aid of both sodium carbonate anhydrous (Na2CO3) and diethylenetriaminepentaacetic acid (DTPA), in which the defective structure was confirmed by various characterizations. The as-obtained defective NH2-UiO-66-SD exhibited outstanding Pb(II) sorption capacity (172.21 ​mg ​g−1) and rapid diffusion rate (29.87 ​mg ​g−1 min−0.5) at room temperature with optimal pH being 5.47. The Pb(II) sorption behavior was conformed to pseudo-second-order kinetics and Langmuir model, demonstrating that the chemical sorption of the monolayer played a dominant model. As well, the thermodynamic parameters like standard Gibbs free energy change ΔGo (−31.21 ​kJ ​mol−1), standard enthalpy change ΔHo (12.79 ​kJ−1 ​mol−1) and standard entropy change ΔSo (146.73 ​J ​mol−1 ​K−1) revealed that the Pb(II) sorption process of NH2-UiO-66-SD was spontaneous, endothermic and disordered. Furthermore, the NH2-UiO-66-SD exhibited desirable desorption and recirculation performances (removal efficiencies >85 ​% in 5 runs) with ideal stability. Moreover, the Pb(II) sorption mechanism of NH2-UiO-66-SD mainly included the electrostatic attractions and coordinative interactions. Overall, this work offered an intriguing method of fabricating defective NH2-UiO-66 adsorbent, which vastly enhanced adsorption efficiency for toxic metal ions elimination from wastewater.

Regulation of acid/basic properties of Zr-Beta zeolite for efficient conversion of furfural to furfuryl alcohol

Zr-Beta zeolites with different acid/basic properties were prepared by hydrothermal and post-synthesis methods and subsequent alkaline treatment. The acid/basic properties of Zr-Beta zeolites were characterized by FT-IR spectra of hydroxyl region and probe molecule adsorption (CD3CN, pyridine and CHCl3). The effects of the acid/basic properties of Zr-Beta zeolites on the conversion of furfural (FUR) to furfuryl alcohol (FAL) via Meerwein-Ponndorf-Verley reduction were investigated and discussed. The results indicate that both Brønsted acid sites, including strong and weak Brønsted acid sites, and Lewis acid sites are effective for conversion of FUR, but high yield of FAL can only be obtained over Zr-Beta with sole Lewis acid sites of framework Zr due to the further conversion of FAL to furfuryl ether, angelica lactone and levulinate ester over Brønsted acid sites. Therefore, Al-free Zr-Beta(h) synthesized in fluoride media is more active and selective than the post-synthesized counterpart. Alkali (earth) metal cations modified Zr-Beta(h) can further eliminate weak Brønsted acid sites of silanols and at the same time generate basic sites. Thus, the activity and selectivity of Zr-Beta(h) are further enhanced. 99.5 % of FAL yield was obtained over Na-Zr-Beta(h) with 99.8 % of FUR conversion at 120 °C for 4 h.

Mechanochemistry-based liquid-assisted synthesis of hydrophobic Zr-Beta with high metal loading for Meerwein-Ponndorf-Verley reduction

Heteroatom-incorporated zeolite catalysts are critical for biomass utilization and feedstock valorization in green chemistry. Key features are adjustable acidity, high stability, and a tailored range of functionalities. However, an environmentally benign synthesis of zeolites with good crystallinity and especially with high levels of metal substitution into the lattice remains challenging. Here, we propose a mechanochemistry-based liquid-assisted method (MCLA) for Zr-incorporated Beta zeolites that is high yielding, facile and sustainable. Compared with the fluoride-mediated hydrothermal method, crystallization times were considerably shortened so that Si-Beta and Zr-Beta (Si/Zr 100) zeolites can be synthesized within 9 and 15 h, respectively. Using the MCLA route, Beta zeolites with Zr loading up to 10.4 wt% (Si/Zr 12.5) were obtained. The materials have excellent catalytic activity for Meerwein-Ponndorf-Verley reductions with much higher water tolerance compared to Zr-Beta prepared by the post-synthesis method. The hydrophobic nature of the MCLA-synthesized zeolites makes them particularly useful as catalysts for organic reactions.

Pure-red electroluminescence of quantum-confined CsPbI3 perovskite nanocrystals obtained by the gradient purification method

Pure-red emission light-emitting diodes (LEDs) are highly desirable for display and lighting applications. Here, we present a synergistic approach to fabricate pure-red emission LEDs based on quantum-confined CsPbI3 nanocrystals (NCs). By introducing ZnI2 acting as a co-precursor and passivating agent into the synthesis, and applying a gradient post-synthesis purification method allowing us to obtain size-selected fractions with precisely adjusted emission colors, we obtained uniform and small (about 6 nm), quantum-confined CsPbI3 NCs exhibiting high stability in ambient conditions and a superior photoluminescence quantum yield of up to 88%. These NCs exhibited the tendency to undergo oriented attachment, resulting in self-assembled superstructures with a pure-red emission at 629 nm. Importantly, partial recrystallization into fused superstructures led to removal of the insulating ligand barriers between NCs. LEDs based on the CsPbI3 NCs showed pure-red electroluminescence at 633 nm, with an external quantum efficiency of 14.7% and a luminance of over 1000 cd/m2. Our study reveals the mechanism behind the oriented attachment and assembly of small, quantum-confined CsPbI3 NCs, and contributes to the development of pure-red electroluminescent LEDs.

Composite Photocatalysts with Fe, Co, and Ni Oxides on Supports with Tetracoordinated Ti Embedded into Aluminosilicate Gel during Zeolite Y Synthesis.

Ti-aluminosilicate gels were used as supports for the immobilization of Fe, Co, and Ni oxides (5%) by impregnation and synthesis of efficient photocatalysts for the degradation of β-lactam antibiotics from water. Titanium oxide (1 and 2%) was incorporated into the zeolite network by modifying the gel during the zeolitization process. The formation of the zeolite Y structure and its microporous structure were evidenced by X-ray diffraction and N2 physisorption. The structure, composition, reduction, and optical properties were studied by X-ray diffraction, H2-TPR, XPS, Raman, photoluminescence, and UV-Vis spectroscopy. The obtained results indicated a zeolite Y structure for all photocatalysts with tetracoordinated Ti4+ sites. The second transitional metals supported by the post-synthesis method were obtained in various forms, such as oxides and/or in the metallic state. A red shift of the absorption edge was observed in the UV-Vis spectra of photocatalysts upon the addition of Fe, Co, or Ni species. The photocatalytic performances were evaluated for the degradation of cefuroxime in water under visible light irradiation. The best results were obtained for iron-immobilized photocatalysts. Scavenger experiments explained the photocatalytic results and their mechanisms. A different contribution of the active species to the photocatalytic reactions was evidenced.

Photoinduced patterning of oxygen vacancies to promote the ferroelectric phase of Hf0.5Zr0.5O2

Photoinduced reductions in the oxygen vacancy concentration were leveraged to increase the ferroelectric phase fraction of Hf0.5Zr0.5O2 thin-films. Modest (∼2−77 pJ/cm2) laser doses of visible light (488 nm, 2.54 eV) spatially patterned the concentration of oxygen vacancies as monitored by photoluminescence imaging. Local, tip-based, near-field, nanoFTIR measurements showed that the photoinduced oxygen vacancy concentration reduction promoted formation of the ferroelectric phase (space group Pca21), resulting in an increase in the piezoelectric response measured by piezoresponse force microscopy. Photoinduced vacancy tailoring provides, therefore, a spatially prescriptive, post-synthesis, and low-entry method to modify phase in HfO2-based materials.

Antibacterial performance effects of Ag NPs in situ loaded in MOFs nano-supports prepared by post-synthesis exchange method

The preparation of metal nanoparticles (NPs) on metal-organic frameworks (MOFs) has aroused great interest in the field of bacteriostasis. However, MOFs as nano-supports to form uniformly dispersed NPs loadings has still been in the exploratory stage. The use of Agx/Cu-BTC as nano-supports was investigated for the preparation of silver nanoparticles and their antibacterial activity. The post-synthetic exchange method was used to achieve the in situ loading of Ag NPs on copper(II) benzene-1,3,5-tricarboxylate (Cu-BTC) nano-supports and the Agx/Cu-BTC (x = 7, 14, 21 % molar ratio) were successful synthesized. The crystal structure characteristics and the physicochemical properties of the prepared materials were analyzed by SEM, EDS, FT-IR, XRD, XPS, TG, and BET. Using Bacillus subtilis as the experimental strain and Cu-BTC as the antibacterial activity standard, the antibacterial performance of Agx/Cu-BTC was evaluated using the minimum inhibitory concentration test and the Kirby-Bauer test. According to the reaction mechanism of related antibacterial materials, a reasonable mechanism explanation was given for the antibacterial effect of Ag NPs. All characterization results demonstrated that the preparation of Ag NPs using Cu-BTC as nano-supports did not destroy the structure of Cu-BTC. Agx/Cu-BTC still maintained the ortho-octahedral structure, which demonstrated the in situ preparation of Ag NPs was achieved. With the ratio of Ag NPs increased, the specific surface area became smaller, the average pore size became larger, and the thermal stability was enhanced. Agx/Cu-BTC showed significantly stronger antibacterial activity than Cu-BTC. Among the synthesized materials, Ag21/Cu-BTC showed the strongest antibacterial activity, which was due to the more adsorption of Ag NPs onto the cell wall, causing irregular pits and damaging the cell wall and cell membrane. As a result, the cell membrane permeability was altered, allowing more nutrients to flow out of the cell. Ag NPs entered the cell causing a significant increase in the level of reactive oxygen species (ROS), leading to cell damage or death. The higher the concentration of Ag NPs, the more Ag+ was released and the stronger the antibacterial activity. Overall, the in situ preparation of Ag NPs by MOFs nano-supports has the potential to enhance the antibacterial performance of Ag NPs, making them more effective in applications.

Phosphonate functionalized magnetic mesoporous silica for rare earth element recovery from citrate assisted solid waste extracts

The growing high demand of rare earth elements (REEs) has prompted extensive research on REE recovery from waste streams. This study reports the synthesis and evaluation of phosphonate-functionalized magnetic mesoporous silica (MMS-PP) for REE recovery from the acidic extracts of solid wastes. MMS-PP was synthesized using surfactant template and post-synthesis methods, and tested using simulated and real extraction solutions from citrate-assisted REE extracts from municipal solid waste incineration (MSWI) ash. The organic-inorganic hybrid MMS-PP was evaluated for La recovery from 50 mM simulated citrate extract, with the adsorption capacity of 13.5 mg/g compared to ∼2.5 mg/g for non-functionalized MMS. The MMS-PP material exhibited fast adsorption within 10 min, good La selectivity against competing Na+ and Ca2+, moderate selectivity against Al3+ and Fe3+, high recyclability over multiple adsorption-desorption cycles, and equivalent efficiency for La, Ce, Nd, and Y recovery. The MMS-PP material also demonstrated 70–95% REE recovery from real citrate extracts of MSWI ash, and the spent MMS-PP material can be regenerated and reused for multiple cycles. Functionalized mesoporous materials in combination with organic-ligand assisted extraction can potentially provide a green, effective, and tunable solid-liquid separation platform for REE recovery from complex solid waste streams.

Simple one-pot fabrication of durable superhydrophobic cotton wool using octadecyltrimethoxysilane modified silica-sol for oil-water separation

A fluorine-free superhydrophobic cotton is successfully fabricated using a simple and cost-effective one-pot synthesis method, employing octadecyltrimethoxysilane (ODTMS) as a modifying silane in a silica-sol. Unlike conventional techniques that utilise coupling agents or post-synthesis curing methods to enhance coating stability, this approach eliminates the need for extra chemicals thus saving time and reducing fabrication cost. The prepared cotton demonstrates remarkable superhydrophobicity, as evidenced by a water contact angle of 159°. Additionally, it exhibits exceptional durability and stability when exposed to harsh acidic and alkaline solutions, as well as during laundering test. Moreover, the cotton displays excellent oil–water separation efficiency (>99.0 %) and maintains consistent performance throughout 20 reuse cycles, highlighting its high reusability. Furthermore, the modified cotton is highly effective for separating oil-in-water emulsions, even for highly stable emulsions, achieving separation efficiencies above 90.0 %. The fabrication process is simple and environmentally safe, offering an economical and viable solution for industries handling oily wastewater. Overall, this fluorine-free superhydrophobic cotton presents a promising and cost-effective option for various industrial applications.

DMF promoted embedded of melamine inside HKUST-1 for efficient Hg(II) adsorption with regenerability

In response to the growing problem of Hg(II) pollution in water environment, highly efficient HKUST-1@melamine adsorbent for Hg(II) removal was synthesized by in-situ growth post-synthesis modification method. Under the regulation of DMF, melamine embedded inside the HKUST-1 pore, which guaranteed the high loading rate. Based on theoretical calculation, DMF lowered the energy barrier for melamine to enter the HKUST-1 pore (2.79 eV to 0.21 eV). Meanwhile, water stability and skeleton structure were also be strengthened. The –NH2 on melamine in the pores would coordinate with Hg(II), and the corresponding Eads of the composite with Hg(II) was calculated −3.49 eV, confirming the spontaneous adsorption reaction. Under the optimal conditions, HKUST-1@melamine showed the best adsorption of Hg(II) with a removal rate of 99.41 % within 90 min. The maximum adsorption capacity qm of 1557.38 mg/g, which was several times more than the existing MOF-based adsorbents. And the good selectivity and anti-interference realized the following practical application in real samples. In addition, the material achieved 85.3 % of qm after 4 regeneration cycles with 5 % thiourea. This research would provide a theoretical basis for rapid and efficient nanomaterials-based treatment of heavy metals pollution in water.

Ni-Cu and Ni-Co-Modified Fly Ash Zeolite Catalysts for Hydrodeoxygenation of Levulinic Acid to γ-Valerolactone.

Monometallic (Ni, Co, Cu) and bimetallic (Ni-Co, Ni-Cu) 10-20 wt.% metal containing catalysts supported on fly ash zeolite were prepared by post-synthesis impregnation method. The catalysts were characterized by X-ray powder diffraction, N2 physisorption, XPS and H2-TPR methods. Finely dispersed metal oxides and mixed oxides were detected after the decomposition of the impregnating salt on the relevant zeolite support. Via reduction intermetallic, NiCo and NiCu phases were identified in the bimetallic catalysts. The catalysts were studied in hydrodeoxygenation of lignocellulosic biomass-derived levulinic acid to γ-valerolactone (GVL) in a batch system by water as a solvent. Bimetallic, 10 wt.% Ni, and 10 wt.% Cu or Co containing fly ash zeolite catalysts showed higher catalytic activity than monometallic ones. Their selectivity to GVL reached 70-85% at about 100% conversion. The hydrogenation activity of catalysts was found to be stronger compared to their hydration ability; therefore, the reaction proceeds through formation of 4-hydroxy pentanoic acid as the only intermediate compound.

Adsorption of Pb(II) on covalent organic frameworks: Overlooked sorption sites formed in the post-synthetic modification process

The post-synthesis strategy is frequently employed to create functional covalent organic frameworks (COFs) for the removal of heavy metals. Different post-synthesis methods can yield structurally distinct side chains. However, the potential adsorption role of these side chains is often overlooked, even though they can provide efficient adsorption sites that significantly enhance the adsorption performance of functional COFs for targeted pollutants. In this study, two post-modification reactions were conducted to introduce functional groups into the original COFs, namely acetylene COFs and ethylene COFs (referred to as COFV1 and COFV2). This resulted in the synthesis of modified MCOFV1 and MCOFV2 with emerging triazole and thioether groups, respectively. Subsequently, these modified COFs were characterized and employed to investigate the influence of the newly formed structures on the adsorption of Pb(II). Density functional theory (DFT) calculations were carried out to explore the adsorption mechanism and the binding energies between COFs and Pb(II). The results indicate that after modification, the specific surface area of COFV1 and COFV2 decreased by 8.08 and 2.05 times, reaching 204.9 m2 g–1 for MCOFV1 and 587.5 m2 g−1 for MCOFV2. However, their Pb(II) equilibrium adsorption capacity significantly increased, with MCOFV1 achieving 52.1 mg/g (11.5 times higher than COFV1) and MCOFV2 achieving 31.1 mg/g (1.6 times higher than COFV2) based on the pseudo-first-order model. This indicates that the triazole group, which is produced in the post-modification reaction, demonstrates greater efficacy in the removal of Pb(II) as compared to the thioether group. This study reveals that efficient bifunctional groups can be formed through suitable post-modification methods, enhancing the adsorption performance of COFs in environmental remediation.