Applications of alkyl orthoesters as valuable substrates in organic transformations,focusing on reaction media

In this review we focus on applications of alkyl orthoesters as valuable and efficient substrates to perform various classes of two-component and multi-component organic reactions. The article has classified them according to two aspects, which are: (i) a focus on the reaction medium (solvent-free conditions, aqueous media, and organic solvents); and (ii) an examination of product structures. Reaction accomplishment under solvent-free conditions is an eco-friendly process with the absence of volatile toxic solvents, which puts it in line with green chemistry goals. Water is an interesting choice in organic transformations due to its inexpensiveness and safety. The authors hope their assessment will help chemists to attain new approaches for utilizing alkyl orthoesters in various organic synthetic methods. The review covers the corresponding literature up to the beginning of 2020.

In this review we focus on applications of alkyl orthoesters as valuable and efficient substrates to perform various classes of two-component and multi-component organic reactions.     

Preparation of cyclic imides from alkene-tethered amides: application of homogeneous Cu(ii) catalytic systems

A Cu-based homogeneous catalytic system was proposed for the preparation of imides from alkene-tethered amides. Here, O₂ acted as a terminal oxidant and a cheap and easily available oxygen source. The cleavage of C C bonds and the formation of C–N bonds were catalyzed by Cu(ii) salts with proper nitrogen-containing ligands under 100 °C. The synthesis approach has potential applications in pharmaceutical syntheses. Moreover, scaled-up experiments confirmed the practical applicability.

A catalytic system comprising Cu(ii) and a nitrogen-based ligand for the oxygenation and cyclization of alkene-tethered amides.     

A comparative study of 0D and 1D Ce-ZnO nanocatalysts in photocatalytic decomposition of organic pollutants

Nanosized zinc oxide is an intriguing material that can be applied in various fields. In this study, Ce doped ZnO nano-catalysts (Ce-ZnO) were synthesized by two different methods (i.e., hydrothermal (Ce-ZnO-HT) and polymer gel combustion (Ce-ZnO-CB) methods) to compare their photodegradation efficiency. The prepared material characteristics were investigated using XRD, SEM, TEM, FTIR, UV-Vis, PL, XPS, EDS, and BET. The bandgap of both nanoparticles (NPs) was 2.95 eV, despite the fact that the morphology of Ce-ZnO-HT NPs was 1D-rod-shaped and that of Ce-ZnO-CB NPs was 0D-spherical. However, the surface area and oxygen vacancy rate of Ce-ZnO-HT NPs were higher than those of Ce-ZnO-CB NPs. These differences are directly related to the photocatalytic activity of Ce-ZnO NPs. Accordingly, the results showed that photocatalytic efficiency was classified in the order Ce-ZnO-HT > Ce-ZnO-CB > pure ZnO, and the photocatalytic reaction rate constant of Ce-ZnO-HT used to decompose MB was 3.0 times higher than that of Ce-ZnO-CB. Interestingly, the photodegradation mechanism study revealed that hydroxyl radicals and holes were shown to be more important contributors to methyl blue degradation than photo-induced electrons and superoxide radical ions.

Ce doped ZnO nano-catalysts were synthesized by two different methods i.e., hydrothermal and polymer gel combustion method, to compare their photodegradation efficiency.     

Different transition metal combinations of LDH systems and their organic modifications as UV protecting materials for polypropylene (PP)

In this research, the use of layered double hydroxides (LDHs) as ultraviolet (UV) light-protecting additives for PP is explored. Different LDHs, such as ZnTi, ZnSn, ZnGa, ZnCr and CdCr LDHs, were prepared and their UV absorptions were characterized. The ZnTi LDHs showed higher UV absorption than the other four metallic combinations and were further organically modified with dodecylbenzene sodium sulfonate (SDBS) and lauric acid (LA). Nanocomposites of polypropylene (PP) with four different types of LDHs, ZnTi, ZnSn, ZnTi-SDBS and ZnTi-LA, were prepared at concentrations of 5%. The crystallinities and layered structures of all the metallic combinations of LDHs were characterized by wide angle X-ray spectroscopy (WAXS) and ultraviolet visible (UV-vis) absorption spectroscopy, and their crystal morphologies were studied by scanning electron microscopy (SEM). The decomposition and thermal properties of the nanocomposites and pure PP were analyzed by thermogravimetric analysis (TGA) and transmission electron microscopy (TEM) and by their photo-oxidation behavior. The addition of these organically modified and unmodified LDHs showed significant changes in the thermal decomposition of PP. The thermal stability of PP was increased to around 70 °C by the addition of SDBS-modified ZnTi LDHs (5% by weight), and an increase in induction time of about 300% was determined.

In this research, the use of layered double hydroxides (LDHs) as ultraviolet (UV) light-protecting additives for PP is explored.     

Nano ferrites (AFe2O4, A = Zn,Co, Mn,Cu) as efficient catalysts for catalytic ozonation of toluene

Nano ferrites (AFe₂O₄, A = Zn, Co, Mn, Cu) were supported on the surface of γ-Al₂O₃ support by hydrothermal synthesis to prepare a series of novel composite catalysts (AFe₂O₄/γ-Al₂O₃) for catalytic ozonation for elimination of high concentration toluene at ambient temperature. The characterization results showed that the high-purity nano-AFe₂O₄ particles were uniformly loaded on mesoporous γ-Al₂O₃. Further, it was confirmed that among the several catalysts prepared, the amount of oxygen vacancies (O_vs), Lewis acid sites (LAS), and Brønsted acid sites (BAS) of the ZnFe₂O₄/γ-Al₂O₃ catalyst were the highest. This meant that the ZnFe₂O₄/γ-Al₂O₃ catalyst had a strong adsorption capacity for toluene and ozone (O₃), and had a strong catalytic activity. When the temperature was 293 K and the space velocity was 1500 h⁻¹, the mol ratio of O₃ to toluene was 6, the degradation rate of toluene (600 mg m⁻³) can reach an optimum of 99.8%. The results of electron paramagnetic resonance (EPR) and Fourier infrared (FT-IR) proved superoxide radicals and hydroxyl radicals by catalytic ozonation. Moreover, the GC-MS analysis results indicated that the toluene degradation began with the oxidation of methyl groups on the benzene ring, eventually producing CO₂ and H₂O. After repeated experiments, the toluene degradation rate remained stable, and the residual content of O₃ in each litre of produced gas was less than 1 mg L⁻¹, thereby indicating that the ZnFe₂O₄/γ-Al₂O₃ catalyst had excellent reusability and showed great potential for the treatment of toluene waste gas.

Nano ferrites (AFe₂O₄, A = Zn, Co, Mn, Cu) were supported on the surface of γ-Al₂O₃ by hydrothermal synthesis to prepare a series of novel catalysts (AFe₂O₄/γ-Al₂O₃) for catalytic ozonation of high concentration toluene at ambient temperature.     

Sustained ex vivo skin antiseptic activity of chlorhexidine in poly(epsilon-caprolactone) nanocapsule encapsulated form and as a digluconate.

In this work, the sustained bactericidal activity of chlorhexidine base loaded poly(epsilon-caprolactone), PCL, nanocapsules against Staphylococcus epidermidis inoculated onto porcine ear skin was investigated. Drug loaded nanocapsules were prepared by the interfacial polymer deposition following solvent displacement method, then characterized by photon correlation spectroscopy, electrophoretic measurements, transmission and scanning electron microscopy. Antimicrobial activity of these colloidal carriers was evaluated (i) in vitro against eight strains of bacteria, and (ii) ex vivo against Staphylococcus epidermidis inoculated for 12 h onto porcine ear skin surface treated for 3 min either with 0.6% chlorhexidine base loaded or unloaded nanocapsules suspended in hydrogel, or 1% chlorhexidine digluconate aqueous solution. Chlorhexidine absorption into the stratum corneum (SC) was evaluated by the tape-stripping method. The results showed that chlorhexidine nanocapsules in aqueous suspension having a 200-300 nm size and a positive charge exhibited similar minimum inhibitory concentrations against several bacteria with chlorhexidine digluconate aqueous solution. Ex vivo, there was a significant reduction in the number of colony forming units (CFUs) from 3-min treated skin with chlorhexidine nanocapsule suspension (5 to <1 log(10)) compared to chlorhexidine digluconate solution (5 to 2.02 log(10)) after a 8-h artificial contamination. After a 12-h artificial contamination, both formulations failed to achieve a 5 log(10) reduction. Furthermore, from a 3-min treatment with an identical applied dose and a subsequent 12-h artificial contamination, a residual chlorhexidine concentration in the SC was found to be three-fold higher with chlorhexidine nanocapsule suspension than with chlorhexidine digluconate solution. Interestingly, nanocapsules were shown in porcine skin follicles. Consequently, a topical application of chlorhexidine base-loaded positively charged nanocapsules in an aqueous gel achieved a sustained release of bactericide against Staphylococcus epidermidis for at least 8 h. Enhancement of drug delivery by mediating a more direct and prolonged contact between the carrier and (i) bacteria, (ii) skin surface, and (iii) skin follicles was assumed.     

Synthesis of silver particles stabilized by a bifunctional SiHx–NHy–PMHS oligomer as recyclable nanocatalysts for the catalytic reduction of 4-nitrophenol

Bifunctional oligomers with both reducing and stabilizing functionalities were prepared and successfully applied to the preparation of silver colloids of around 2 nm size without employing a strong stabilizer such as S and P, which was quite difficult to achieve. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were performed to determine the morphology and particle size of the Ag colloids. UV-vis spectroscopy and X-ray absorption spectroscopy (XAS) were implemented to investigate the oxidation state of the Ag colloids. Synthesis parameters such as the density control of the ligating functionalities, the propinquity of the reducing and stabilizing groups, the extent of ligand stabilization and the reducing rates were found to have important effects on the formation and stabilization of Ag colloids. The as-synthesized Ag colloids were very stable even after being deposited on silica; then, they were subjected to calcination to get rid of the organics, which afforded Ag NPs (1.9–3.5 nm) on silica with narrow size distribution. These Ag NPs performed excellently in catalytic 4-nitrophenol reduction with conversion of up to 98% within 10 min. Furthermore, the Ag nanoparticles were quite stable and exhibited excellent reusability for seven successive reaction cycles without obvious decay. The straightforward synthesis of the ultra-small and stable Ag NPs has the potential for applications in the synthesis of other supported late transition metals.

A novel strategy using bifunctional SiH_x–NH_y–PMHS without using strong stabilizers was applied to synthesize Ag NPs of around 2 nm size.     

Efficient removal of Cu(ii) from aqueous systems using enhanced quantum yield nitrogen-doped carbon nanodots

The valorization of cellulose-based waste is of prime significance to green chemistry. However, the full exploitation of these lignocellulosic compounds to produce highly luminescent nanoparticles under mild conditions has not yet been achieved. In this context, we convert low-quality waste into value-added nanomaterials for the removal of Cu(ii) from wastewater. Carboxymethylcellulose (CMC), which was derived from empty fruit bunches, was selected for its high polymerization index to produce luminescent nitrogen-doped carbon dots (N-CDs) with the assistance of polyethylene glycol (PEG) as a dopant. The optimum N-CD sample with the highest quantum yield (QY) was characterized using various analytical techniques and the results show that the N-CDs have great crystallinity, are enriched with active sites and exhibit a long-shelf life with an enhanced QY of up to 27%. The influence of Cu²⁺ concentration, adsorbent (N-CDs) dosage, pH and contact time were investigated for the optimal adsorption of Cu²⁺. The experiments showed the rapid adsorption of Cu²⁺ within 30 min with a removal efficiency of over 83% under optimal conditions. The equilibrium isotherm investigation revealed that the fitness of the Langmuir isotherm model and kinetic data could be well explained by the pseudo-second order model. Desorption experiments proved that N-CDs can be regenerated successfully over five adsorption–desorption cycles owing to the ability of ascorbic acid (AA) to reduce the adsorbed nanocomplex into Cu⁺. The rapid adsorption property using low-cost materials identifies N-CDs as a superior candidate for water remedy.

Low value waste resources have been converted into value-added luminescence carbon dots for copper adsorption from contaminated water.     

One-pot synthesis of enhanced fluorescent copper nanoclusters encapsulated in metal–organic frameworks

The encapsulation of Cu nanoclusters (Cu NCs) in metal–organic frameworks (MOFs) would improve the properties of Cu NCs. So far, these composites were reported by a two-step synthesis process. In this work, a facile one-pot synthesis of hybridization of glutathione (GSH) protected Cu NCs (Cu NCs@GSH) and MOF-5 (Cu NCs@GSH/MOFs) composites was reported for the first time. The results of UV-vis, TEM, XPS and SEM proved Cu NCs@GSH were distributed homogeneously over the entire MOF structure. The fluorescence intensity of Cu NCs encapsulated in MOF-5 was enhanced about 35-fold owing to the confining scaffold of the MOF and the stability was extended from 3 days to 3 months. Cu NCs@GSH/MOFs composites exhibited strong orange fluorescence and the emissions could change between blue, orange and red as they were partially reversible in different pH environments. This one-pot synthetic strategy could be extended for the encapsulation of fluorescent Ag NCs in MOFs as well. As-prepared Cu NCs@GSH/MOF-5 composites had high stability, and were easily recycled by centrifugation in aqueous solution, therefore, it would be utilized to develop a reusable sensor for detection of metal ions in the future.

The encapsulation of Cu nanoclusters (Cu NCs) in metal–organic frameworks (MOFs) would improve the properties of Cu NCs.     

Poly(hydroxyethylaspartamide) derivatives as colloidal drug carrier systems.

Poly(hydroxyethylaspartamide) (PHEA) derivatives bearing at the polyaminoacidic backbone poly(ethyleneglycol) (2000 or 5000 Da) or both poly(ethyleneglycol) and hexadecylalkylamine as pendant moieties were investigated as polymeric colloidal drug carriers. The ability of the PHEA derivatives to solubilize hydrophobic drugs was investigated using paclitaxel, amphotericin B and methotrexate. The results demonstrated that the drug solubility depends on both macromolecule composition and drug physicochemical properties. In particular, PEG/hexadecylalkylamine co-grafting increased significantly the solubilization properties of PHEA for the considered drugs while the conjugation of PEG only did not endow PHEA with drug carrier properties. A stability study carried out with paclitaxel/PHEA-PEG(5000)-hexadecylalkylamine demonstrated that the drug/carrier system is characterized by physicochemical instability, which is strictly related to the incubation pH. However, the carrier was found to partially prevent drug degradation. Investigations performed using murine myeloid leukaemia NFS-60 cell line showed that paclitaxel loaded PHEA-PEG(5000)-hexadecylalkylamine possesses high pharmacological activity with IC(50) value of 22.3 ng/ml. Pharmacokinetic studies carried out by intravenous administration of paclitaxel loaded PHEA-PEG(5000)-hexadecylalkylamine to Balb/c mice demonstrated that the carrier modifies the in vivo paclitaxel fate. In particular, PHEA-PEG(5000)-hexadecylalkylamine prolonged the drug distribution and elimination phase of 6 and 17 times, respectively; in addition, it increased the systemic availability (AUC) by about 30 times.     

Impact of drying/wetting conditions on the binding characteristics of Cu(ii) and Cd(ii) with sediment dissolved organic matter

The biogeochemical processing of dissolved organic matter (DOM) in bottomland sediment under drying/wetting conditions regulates the environmental behavior of heavy metals. Although moisture is a critical factor, the structural characteristics of DOM and its reactivity with heavy metals under drying/wetting conditions are not well known. Herein, the response of DOM to drying/wetting conditions and its influence on the binding of Cu(ii) and Cd(ii) onto DOM were clarified via various multi-spectroscopic techniques. Ultraviolet-visible spectra (UV-Vis) showed that higher aromatic, hydrophobic, and molecular weight fractions were observed in sediment DOM under drying conditions than those under wetting conditions. The binding abilities for Cd(ii) with DOM under drying/wetting conditions are lower than those for Cu(ii). The stability constants between Cu(ii) and DOM were found to decrease under drying/wetting conditions; however, the binding capacities for Cu(ii) increased, especially under wetting conditions. Two-dimensional correlation spectroscopy based on Fourier-transform infrared (FTIR) and synchronous fluorescence spectra (SFS) showed that Cu(ii) and Cd(ii) have different binding sequences and binding sites and that Cu(ii) has more binding sites under drying and wetting conditions; however, Cd(ii) shows the opposite behavior. These results clearly demonstrate that the binding of sediment DOM with Cu(ii) is more prevalent and stable compared with Cd(ii) under drying and wetting conditions. Because of its relatively low binding capacity and binding stability, Cd(ii) can exhibit a high environmental hazard for migration and transformation with DOM due to water flow under wetting conditions. This study helps reveal the impact of drying/wetting conditions on the environmental behavior of heavy metals in bottomland wetlands.

The biogeochemical processing of dissolved organic matter (DOM) in bottomland sediment under drying/wetting conditions regulates the environmental behavior of heavy metals.     

Novel mesoporous Ag@SiO2 nanospheres as a heterogeneous catalyst with superior catalytic performance for hydrogenation of aromatic nitro compounds

Mesoporous core–shell structure Ag@SiO₂ nanospheres are constructed to prevent Ag nanoparticles from aggregation during the hydrogenation reaction. The prepared catalyst shows superior catalytic performance for hydrogenation of nitro compounds with 100% conversion and selectivity without any by-products, which also indicates good recycling performance for several times use.

Mesoporous core–shell structure Ag@SiO₂ nanospheres are constructed to prevent Ag nanoparticles from aggregation during the hydrogenation reaction.     

Modulation of the sustained delivery of myelopoietin (Leridistim) encapsulated in multivesicular liposomes (DepoFoam).

Myelopoietins (MPO) are novel chimeric growth factors containing IL-3 and G-CSF receptor agonists that enhance the biological properties of both cytokines. These cytokines, like many therapeutic proteins, clear rapidly from circulation and must be administered daily to provide efficacy. Therefore, a controlled and sustained delivery system comprised of a biocompatible and biodegradable matrix, would offer important therapeutic advantages in the clinic, such as significantly reducing dose frequency and providing efficacy without toxicity. We report here the encapsulation of Leridistim (a protein from the MPO family) in multivesicular liposomes (DepoFoam) for sustained delivery, and demonstrate that a single injection of DepoFoam-encapsulated Leridistim results in elevated neutrophil counts for 10 days, in contrast to only 2 days for un-encapsulated Leridistim. Moreover, varying the lipid content of the DepoFoam matrix modulated the duration of elevated neutrophils from 2-3 to 9-10 days. The encapsulated Leridistim was released in vivo from the multivesicular liposomes in a uniform manner, consistent with its pharmacodynamic duration. Finally, a reproducible pharmacodynamic effect was observed with several batches of a DepoLeridistim formulation, indicating consistency of the manufacturing process of the DepoFoam delivery system. The capability of altering the release rates by varying the lipid composition provides maximum flexibility for controlled delivery of cytokine therapeutics.     

Poly(ethylene glycol)-functionalized 3D covalent organic frameworks as solid-state polyelectrolytes

Existing lithium-ion-conducting covalent organic frameworks (COFs) are mainly two-dimensional, in which the one-dimensional channels are difficult to completely and uniformly stack in the same direction, particularly in the case of powdered COFs, resulting in the hindrance of ion transport at the grain boundary or at the interface of the powder contact. In this contribution, poly(ethylene glycol) (PEG)-functionalized three-dimensional COFs with 3D channels were successfully constructed for ion conduction in different directions, which is conducive to reducing the grain boundary and interface contact resistance. Combined with the coupling behaviour between the PEG chain segments and Li-ions, the 3D COF incorporated with LiTFSI achieves a high ionic conductivity of 3.6 × 10⁻⁴ S cm⁻¹ at 260 °C. The maximum operating temperature is higher than the boiling point of commercial organic electrolytes, indicating the excellent security of PEG-based COFs as Li-ion polyelectrolytes at high temperature.

Poly(ethylene glycol)-functionalized three-dimensional COFs with 3D channels were successfully constructed for ion conduction in different directions, which achieves a high ionic conductivity of 3.6 × 10⁻⁴ S cm⁻¹ at 260 °C.

Lithium-ion batteries (LIBs) are an indispensable energy storage system in contemporary society,^1–3 but most of them use liquid electrolytes, posing the risk of flammability, particularly in large-scale applications.^4,5 Solid electrolytes have been explored as ideal substitutes,^6–12 which commonly encompass ether polymeric- or ceramic-based electrolytes. Nonetheless, ceramic electrolytes still encounter large obstacles, such as instability, poor processability, and non-negligible grain boundary resistance.^8,13,14 Polymer electrolytes have higher stability and lower interfacial resistance, and are considered to be more promising polyelectrolyte materials. In particular, poly(ethylene glycol) (PEG)-based polymers, which are constructed by grafting PEG onto polymer chains, possess considerable ionic conductivity. However, they undergo a solid-to-liquid translation process with increasing temperature,¹⁵ which can easily cause a short circuit between the cathode and anode from the electrolyte draining, leading to acute safety risks. It is also laborious to expound the structure–property relationship between the ion-conducting pathways and ion conduction due to the structurally disordered character of PEG-based electrolytes.¹⁶Covalent organic frameworks (COFs) are a novel class of Li-ion conducting materials, which can acquire superior chemical, thermal and electrochemical stability through certain organic bonds or robust π–π stacking.^17–22 Compatible COFs can not only provide precisely tuned spatial pores for ion transport but also provide insight into the conduction mechanisms based on the long-range order.^23–26 The existing COF-based electrolytes are mainly divided into three categories: (i) COFs with non-electric neutral skeletons (Li-ion as the equilibrium cation), which need an external organic solvent to support ion transport, posing similar safety problems as organic liquid electrolytes;^27,28 (ii) COFs doped with PEG and lithium salt, in which the physically adsorbed PEG has a leakage risk;¹⁵ and (iii) PEG-functionalized COFs, of which the powder has anisotropy, resulting in disappointing ionic conductivity.^29–31 To the best of our knowledge, most of the existing Li-ion-conducting COFs are two dimensional, in which the one-dimensional channels can hardly be completely and uniformly stacked in the same direction, especially in the case of the powder-form COFs, which will lead to blockage of ion transport at the grain boundary or at the interface of the powder contact.In view of this, we have developed a self-assembly strategy to construct a PEG-functionalized three-dimensional COF, which has more ion transport paths in different directions that are beneficial to reducing the grain boundary and interface contact resistance experienced in the bulk condition. Distinct from amorphous bulk PEG, the grafted PEG constructs clear Li⁺-conducting routes in crystalline frameworks, which is beneficial to understanding the relationship between structure and ionic conduction. PEG with small molecular weight exhibits a liquid state at room temperature, but the hybrid materials consisting of short-chain PEG and COFs macroscopically present a solid state due to the confinement of the rigid skeleton of the COFs. The highest operating temperature can reach 260 °C along with a remarkable ionic conductivity of 3.6 × 10⁻⁴ S cm⁻¹. This temperature is higher than the boiling point of commercial organic electrolytes such as propylene carbonate (242 °C), diethyl carbonate (127 °C) and dimethyl carbonate (91 °C), indicating the excellent security of PEG-based COFs as Li-ion electrolytes.In this work, three types of PEG-functionalized COFs were synthesized under solvothermal conditions by the condensation of tetrakis(4-aminophenyl)methane with three aldehyde monomers with different lengths of PEG chains (Fig. 1a). The corresponding three-dimensional COFs, denoted as 3D-COF-PEG2, 3D-COF-PEG3 and 3D-COF-PEG6 hereafter, were produced as microcrystalline powders insoluble in common organic solvents. 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li were prepared by introducing LiTFSI into the COFs.Open in a separate windowFig. 1(a) A bottom-up strategy for the synthesis of COFs. (b) Observed PXRD patterns of 3D-COF-PEG2: experimental PXRD pattern (black line), Pawley-refined pattern (red line), calculated pattern (blue line), and their difference (green line). (c) dia topology structure of 3D-COF-PEG2.The crystallinity of the COFs was evaluated by PXRD, and due to the structural consistency of these samples, 3D-COF-PEG2 was taken out to build in Materials Studio. The PXRD pattern of 3D-COF-PEG2 with its simulated value is illustrated in Fig. 1b, showing that it possessed a dia topology with 5-fold interpenetration, and it could be observed that the obvious peaks at 4.24° along with few weaker peaks at 6.13° and 8.63° corresponded to the (220), (040) and (440) planes with the FDDD (70) space group. The negligible values of R_wp = 2.78% and R_p = 2.11% imply that the Pawley refinement of the 3D-COF-PE2 pattern coincides with the experimental pattern. There are no diffraction peaks after modification with LiTFSI (Fig. S1, ESI^†), which is due to the disordered LiTFSI and ion-coupled PEG chains in the channel. The three-dimensional compounds are connected by imine bonds, and the structures are shown in Fig. 1c.For the isomorphic compounds, the PXRD of the three samples are consistent (Fig. 2a). Their morphology reveals uneven spherical and elliptical shapes, as seen in the SEM images (Fig. 3). It could be seen that the maximum nitrogen adsorption values are 133, 102 and 101 cm³ g⁻¹ for 3D-COF-PEG2, 3D-COF-Open in a separate windowFig. 2(a) PXRD patterns, (b) N₂ adsorption, (c) TG plots and (d) DSC curves of 3D-COF-PEG2, 3D-COF-PEG3 and 3D-COF-PEG6. (e) IR plots of 3D-COF-PEG6 and 3D-COF-PEG6-Li. (f) ⁷Li solid NMR for LiTFSI, 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li.Open in a separate windowFig. 3(a–c) SEM patterns of 3D-COF-PEG2, 3D-COF-PEG3 and 3D-COF-PEG6, respectively. (d–f) SEM patterns of 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li, respectively.PEG3 and 3D-COF-PEG6, respectively, proving a more crowded situation in 3D-COF-PEG6 (Fig. 2b). After introducing LiTFSI, the adsorption amounts clearly drop to 71.0, 39.8 and 79.2 cm³ g⁻¹ for 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li, respectively (Fig. S2, ESI^†). The thermal stability and thermodynamics were also analysed. There is almost no weight loss before 400 °C for these COFs before or after introducing LiTFSI, demonstrating their remarkable thermal stability (Fig. 2c and S3, ESI^†). As seen in Fig. 2d, three COFs exhibit an endothermic peak at −11 °C in the measured temperature region, showing a segment movement behaviour, which is conducive to ionic conduction (Fig. S4, ESI^†). From the IR plots (Fig. 2e), it can be seen that there is a single v_as(COC) peak at 1103 cm⁻¹ for 3D-COF-PEG6, but it splits into two peaks for 3D-COF-PEG6-Li at 1109 cm⁻¹ and 1093 cm⁻¹ (Fig. 2e). This is similar to the other samples, implying an interaction between Li⁺ and the PEG chains (Fig. S5, ESI^†). The ⁷Li NMR peaks are located at −946 Hz, −1106 Hz, −1126 Hz and −1074 Hz for bulk LiTFSI, 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li, respectively, showing a unique chemical state of the Li-ions in the COFs (Fig. 2f).The ionic conductivity (σ) was calculated from the Nyquist plots versus different temperatures (Fig. 4a and S6–S8, ESI^†). The σ of 3D-COF-PEG2-Li is 8.5 × 10⁻⁹ S cm⁻¹ at 100 °C, 1.2 × 10⁻⁶ S cm⁻¹ at 180 °C and 1.2 × 10⁻⁵ S cm⁻¹ at 260 °C. 3D-COF-PEG3-Li exhibits higher ionic conductivity values of 3.4 × 10⁻⁸ S cm⁻¹ at 100 °C, 4.5 × 10⁻⁶ S cm⁻¹ at 180 °C, and 5.3 × 10⁻⁴ S cm⁻¹ at 260 °C. The ionic conductivity of 3D-COF-PEG6-Li is the highest, at 3.7 × 10⁻⁶ S cm⁻¹ at 100 °C, 7.0 × 10⁻⁵ S cm⁻¹ at 180 °C, and 3.6 × 10⁻⁴ S cm⁻¹ at 260 °C (Fig. 4b). Obviously, with an increase in the length of the PEG chain, the ionic conductivity climbs as well, because of which the longer PEG chain offers more coupling sites for lithium ions to facilitate the ionic conduction. Furthermore, the highest operating temperature (260 °C) is higher than the boiling point of commercial organic electrolytes such as propylene carbonate (242 °C), diethyl carbonate (127 °C), and dimethyl carbonate (91 °C), indicating the excellent safety of PEG-based COFs as Li-ion electrolytes. The long-term ionic conduction durability measurement of 3D-COF-PEG6-Li was also carried out at 200 °C for 42 h (Fig. 4c). It affords stable conductivity above ∼10⁻⁴ S cm⁻¹, demonstrating its prominent ionic conductivity retention. The activity energy value (E_a) is calculated to be around 0.49 eV for 3D-COF-PEG6-Li, which is smaller than those of 3D-COF-PEG2-Li and 3D-COF-PEG3-Li (0.78 eV and 0.79 eV, respectively) (Fig. 4d and S9, ESI^†), showing the lower Li⁺ conducting energy barrier in COF-PEG-B6-Li. With longer PEG chains, the coupling behaviour between ether bonds and lithium ions will be more frequent, which is one important cause of the decreased Li⁺ conduction barrier. As illustrated in Fig. 4e, the Li⁺ transference number is around 0.22 for COF-PEG-B6-Li at 100 °C, which is comparable to that of PEG-based polymer electrolytes. COFs introduced with LiTFSI also show high electrochemical stability, and they are all stable when the voltage is lower than 4 V, suggesting their compatibility with high voltage cathodes (Fig. 4e and S10, ESI^†).Open in a separate windowFig. 4(a) Nyquist plots of 3D-COF-PEG6-Li at 260 °C. (b) Ionic conductivity of 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li versus temperature from 100 °C to 260 °C. (c) Long-term ionic conducting durability test of 3D-COF-PEG6-Li at 200 °C. (d) Calculation of activation energy for 3D-COF-PEG2-Li, 3D-COF-PEG3-Li and 3D-COF-PEG6-Li. (e) Li⁺ transference number measurement of 3D-COF-PEG6-Li at 100 °C. (f) Linear sweep voltammograms (LSV) of 3D-COF-PEG6-Li at 100 °C.     

Carbon nanotube impregnated anthracite (An/CNT) as a superior sorbent for azo dye removal

Raw anthracite was impregnated with a minute amount of multi-walled carbon-nanotubes at a solid/solid ratio of 50 : 1 via calcination at 950 °C for 2 h to produce anthracite/carbon nanotube (An/CNT) composite with superior sorption efficiency. Both An/CNT composite and its precursor anthracite were characterized by XRD, SEM, FT-IR and BET surface area (S_BET). The removal efficiency of an azo dye methyl orange (MO) by the An/CNT composite was evaluated under different experimental parameters. The MO sorption isotherm data fitted to the Langmuir model well with an R² of 0.999 and a MO sorption capacity (q_max) of 416.7 mg g⁻¹. The distribution coefficient K_d decreases from 117.9 to 16.1 L g⁻¹ as the initial MO concentrations increased from 40 to 140 mg L⁻¹. The MO sorption kinetic data was well described by the pseudo-second-order equation with an R² of 1. The external (film) diffusion followed by intra-particle diffusion was the major driving process during the early stage of MO sorption. The electrostatic interaction between the oxygen- and nitrogen-bearing functional groups on the An/CNT surface and MO ions was the key controlling mechanism for the MO sorption process, particularly at pH < pH_PZC of the composite. Meanwhile, valuable contributions from Yoshida and dipole–dipole H bonding mechanisms can explain the MO sorption by the addressed composite, especially at pH > pH_PZC.

Raw anthracite was impregnated with a minute amount of multi-walled carbon-nanotubes at a solid/solid ratio of 50 : 1 via calcination at 950 °C for 2 h to produce anthracite/carbon nanotube (An/CNT) composite with superior sorption efficiency.     

A novel π-conjugated poly(biphenyl diimide) with full utilization of carbonyls as a highly stable organic electrode for Li-ion batteries

Organic carbonyl redox polymers, especially conjugated polyimides with multiple reversible redox centers have attracted considerable attention as electrode materials for organic Li-ion batteries. However, the low utilization of carbonyls hindered their potential applications in energy storage. Herein, a novel π-conjugated polyimide (PBPI) based on biphenyl diimide (BPI) containing two seven-membered imide rings is developed. PBPI is used as an anode material for organic Li-ion batteries, which show high conductivity and insolubility in the electrolyte and enable intercalation of four Li-ions per BPI unit, thus contributing to a reversible capacity of 136 mA h g⁻¹ at 100 mA g⁻¹ with coulombic efficiency close to 100%. Moreover, the battery based on PBPI manifested superior high-rate performance (65 mA h g⁻¹ at 2000 mA g⁻¹) as well as significant cycling stability (over 1600 cycles at 100 mA g⁻¹). Remarkably, the full redox-active site (C O) utilization of an aromatic diimide core to achieve its full potential applications is reported for the first time. This work provides a new strategy for developing redox π-conjugated polyimides and accommodation of more alkaline ions for high performance battery systems.

A novel π-conjugated polyimide based on the two seven-membered imide rings-containing BPI was reported, which be used as a highly stable anode electrode material with full utilization of carbonyls for the application organic Li-ion batteries.     

Molybdenum disulfide (MoS2) based photoredox catalysis in chemical transformations

Photoredox catalysis has been explored for chemical reactions by irradiation of photoactive catalysts with visible light, under mild and environmentally benign conditions. Furthermore, this methodology permits the activation of abundant chemicals into valuable products through novel mechanisms that are otherwise inaccessible. In this context, MoS₂ has drawn attention due to its excellent solar spectral response and its notable electrical, optical, mechanical and magnetic properties. MoS₂ has a number of characteristic properties like tunable band gap, enhanced absorption of visible light, a layered structure, efficient photon electron conversion, good photostability, non-toxic nature and quantum confinement effects that make it an ideal photocatalyst and co-catalyst for chemical transformations. Recently, MoS₂ has gained synthetic utility in chemical transformations. In this review, we will discuss MoS₂ properties, structure, synthesis techniques, and photochemistry along with modifications of MoS₂ to enhance its photocatalytic activity with a focus on its applications and future challenges.

Photoredox catalysis has been explored for chemical reactions by irradiation of photoactive catalysts with visible light, under mild and environmentally benign conditions.     

Palladium supported on mixed-metal–organic framework (Co–Mn-MOF-74) for efficient catalytic oxidation of CO

Successful monometallic and bimetallic metal–organic frameworks with different Co/Mn ratios have been synthesized under solvothermal conditions. The as-synthesized MOFs followed by deposition of Pd nanoparticles with 0.5 to 7 wt%. The XRD, BET, SEM, TEM, EDAX and FT-IR characterization results reveal that bimetallic MOFs and Pd nanoparticles were finely dispersed on the prepared MOFs surfaces. XRD results confirm the formation of the desire MOFs and show the high degree of dispersion of Pd nanoparticles. TEM images show that Pd nanoparticles are nano-sized with almost uniform shape. EDAX shows that Pd nanoparticles successfully loaded on Co_0.5–Mn_0.5-MOF-74 catalyst. CO oxidation as a model reaction was then used to assess the catalytic performance of the prepared catalysts. The catalytic activity results show enhancement in the catalytic activities of monometallic MOFs after introducing another metal in the same framework and show an excellent improvement in CO conversion after loading with Pd nanoparticles. Furthermore, the samples that contain Pd nanoparticles exhibits higher catalytic activities which raised with increasing the content of Pd nanoparticles.

Pd nanoparticles were loaded on Co_x–Mn_(1−x)-MOF-74. 5 wt% Pd@Co_0.5–Mn_0.5-MOF-74 was the most effective catalyst for CO oxidation. The prepared catalysts displayed excellent stability during CO oxidation without significant decrease in catalytic performance.