Highly efficient conversion of CO2 to cyclic carbonates with a binary catalyst system in a microreactor: intensification of “electrophile–nucleophile” synergistic effect

An intensification of the “electrophile–nucleophile” synergistic effect was achieved in a microreactor for the coupling reaction of CO₂ and epoxides mediated by the binary Al complex/ternary ammonium salt catalyst system. The microreactor technology is proven to be a powerful tool for the preparation of cyclic carbonates with an improved reaction rate and a wide substrate scope.

An intensification of the “electrophile–nucleophile” synergistic effect was achieved in a microreactor for the coupling reaction of CO₂ and epoxides mediated by the binary Al complex/ternary ammonium salt catalyst system.     

Self-assembly of the monohydroxy triterpenoid lupeol yielding nano-fibers,sheets and gel: environmental and drug delivery applications

Lupeol is a medicinally important naturally abundant triterpenoid having a 6–6–6–6–5 fused pentacyclic backbone and one polar secondary “–OH” group at the C3 position of the “A” ring. It was extracted from the dried outer bark of Bombax ceiba and its self-assembly properties were investigated in different neat organic as well as aquous-organic binary liquid mixtures. The triterpenoid having only one polar “–OH” group and a rigid lipophilic backbone self-assembled in neat organic non-polar liquids like n-hexane, n-heptane, n-octane and polar liquids like DMSO, DMF, DMSO–H₂O, DMF–H₂O, and EtOH–H₂O yielding supramolecular gels via formation of nano to micrometre long self-assembled fibrillar networks (SAFINs). Morphological investigation of the self-assemblies was carried out by field emission scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy, optical microscopy, concentration dependent FTIR and wide angle X-ray diffraction studies. The mechanical properties of the gels were studied by concentration dependent rheological studies in different solvents. The gels were capable of removing toxic micro-pollutants like rhodamine-B and 5,6-carboxyfluorescein as well as the toxic heavy metal Cr(vi) from contaminated water. Moreover release of the chemotherapeutic drug doxorubicin from a drug loaded gel in PBS buffer at pH 7.2 has also been demonstrated by spectrophotometry.

The monohydroxy triterpenoid lupeol forms gels in organic and aqueous organic liquids via self-assembly. The resulting supramolecular gels could be utilized for pollutant capture, drug entrapment and release applications.     

One-pot route to graft long-chain polymer onto silica nanoparticles and its application for high-performance poly(l-lactide) nanocomposites

A facile “one-pot” synthetic route to modify SiO₂ nanoparticles with long-chain polymer was developed. The structure and morphology of SiO₂ grafted with poly(l-lactide) (SiO₂-g-PLA) were characterized by FTIR, TGA, GPC, and TEM. Furthermore, a series of PLA/SiO₂-g-PLA nanocomposites were prepared with different nanofiller loadings, and their related performances were investigated. As an effective nucleating agent, the SiO₂-g-PLA had a positive effect to improve the crystallization rate and increase the crystallinity. Meanwhile, the PLA nanocomposites presented outstanding mechanical properties including excellent toughness and high stiffness. In addition, the PLA materials kept good transparency with less than 3 wt% nanofillers. Overall, this work provides a useful method for preparing high-performance polymer nanocomposites.

A facile “one-pot” synthetic route is used to modify SiO₂ nanoparticles with a long-chain polymer, and to prepare high-performance poly(l-lactide) nanocomposites.     

Molecularly imprinted polymers for selective adsorption of quinoline: theoretical and experimental studies

The effects of solvent on the synthesis of molecularly imprinted polymers (MIPs) for the selective adsorption of quinoline were evaluated in this work. The MIPs were synthesized by the “bulk” method using the quinoline molecule (IQ) as a template in different solvents, such as toluene (MIPT) and chloroform (MIPC). The adsorbents were characterized by thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and N₂ adsorption/desorption measurements. The influences of time, adsorbate concentration, and temperature on the adsorption of quinoline by MIPT and MIPC were evaluated. Maximum adsorption capacities (q_e) of 35.23 and 24.10 mg g⁻¹ were obtained for MIPT and MIPC, respectively. Thermodynamic studies indicate that occur physisorption and a spontaneous process (Δ_adsG° < 0) entropically directed. Finally, the highest selectivity and reusability of MIPC for quinoline adsorption was ascribed to the better interaction between the chloroform and monomer, which favors the formation of porous adsorbents with higher numbers of adsorption sites.

Molecularly imprinted polymers synthesized by a one-pot synthesis absorb quinoline efficiently and selectively.     

Effects of critical interfacial shear strength between a polymer matrix and carbon nanotubes on the interphase strength and Pukanszky's “B” interphase parameter

In this paper, the “B” interphase parameter in the Pukanszky model and interphase strength for polymer carbon nanotube (CNT) nanocomposites are expressed by the critical interfacial shear strength (τ_c) and interfacial shear strength (τ) between a polymer matrix and CNTs. A suggested model and a developed Pukanszky model for tensile strength of nanocomposites are combined to develop the equations for “B” and interphase strength. Many experimental data for various samples confirm the models. The impacts of all parameters on the “B” and interphase strength are explained to approve the developed equations. The contour plots display the same trends for the roles of all parameters in the “B” and interphase strength. Low “τ_c”, high “τ”, thin and large CNTs as well as a dense interphase are ideal to obtain the high levels for “B” and interphase strength. Among the studied parameters, CNT size largely controls the “B” and interphase strength, while the waviness and strength of CNTs play insignificant roles.

In this paper, the “B” interphase parameter in the Pukanszky model and interphase strength for polymer carbon nanotube (CNT) nanocomposites are expressed by the critical interfacial shear strength (τ_c) and interfacial shear strength (τ) between a polymer matrix and CNTs.     

A porous β-cyclodextrin-based terpolymer fluorescence sensor for in situ trinitrophenol detection

Permanent porosity plays a key role in fluorescent-based polymers with “on–off” emissive properties due to the role of guest adsorption at accessible fluorophore sites of the polymer framework. In particular, we report on the design of a porous fluorescent polymer (FL-PFP) composed of a covalently cross-linked ternary combination of β-cyclodextrin (β-CD), 4,4′-diisocyanato-3,3′-dimethyl biphenyl (DL) and tetrakis(4-hydoxyphenyl)ethene (TPE). The textural properties of FL-PFP were evaluated by the gas uptake properties using N₂ and CO₂ isotherms. The BET surface area estimates according to N₂ uptake ranged from 100–150 m² g⁻¹, while a lower range of values (20–30 m² g⁻¹) was estimated for CO₂ uptake. Model nitroarenes such as trinitrophenol (TNP) and nitrobenzene (NB) were shown to induce turn-off of the fluorescence emission of the polymer framework at concentrations near 50 nM with ca. 50% fluorescence quenching upon TNP adsorption and detection. The strong donor–acceptor interaction between the nitroarenes and the TPE reporter unit led to fluorescence quenching of FL-PFP upon nitroarene adsorption. The fluorescence lifetime (τ) for FL-PFP (τ = 3.82 ns) was obtained along with a quantum yield estimate of 0.399 relative to quinine sulphate. The β-CD terpolymer reported herein has significant potential for monitoring the rapid and controlled detection of nitroarenes (TNP and NB) in aquatic environments and other complex media.

Permanent porosity plays a key role in fluorescent-based polymers with “on–off” emissive properties due to the role of guest adsorption at accessible fluorophore sites of the polymer framework.     

A smart multi-functional coating based on anti-pathogen micelles tethered with copper nanoparticles via a biosynthesis method using l-vitamin C

A multi-functional anti-pathogen coating with “release-killing”, “contact-killing” and “anti-adhesion” properties was prepared from biocompatible polymer encapsulated chlorine dioxide (ClO₂) which protected the active ingredient from the outside environment. A slow sustained-release of ClO₂ from micelles over fifteen days was detected for long-term release-killing. Micelles only release ClO₂ on demand in minimum inhibitory concentrations. We prepared nanoparticles which were covalently clustered on micelle surfaces to improve contact-killing as well as to improve the stability of the micelle. Copper nanoparticles were generated using the biosynthesis method including l-vitamin C, which avoids the toxicity and allows for the preparation of copper nanoparticles in a green environment. Synergistic anti-pathogen activity could be generated by a combination of micelle released ClO₂ and ascorbic acid. In addition to release-killing and contact-killing, a pluronic polymer coated surface also provides an additional “anti-adhesion” property through its protein-repelling ability. In this research, the designed coating demonstrated a broad-spectrum of activity to kill drug-resistant bacteria, viruses and spores in short period of time. Based on scanning electron microscopy (SEM), transmission electron microscopy (TEM) and anti-oxidase assays, we found that the designed coatings killed the pathogens via bio-oxidation. We also carried out acute respiratory toxicity tests in this research. Analysis of blood samples, lung function and histopathological slices indicated that the synthesized micelles allowed a controlled and sustained release of ClO₂ to kill pathogens while maintaining an overall ClO₂ concentration in the air within a safe range.

A multi-functional anti-pathogen coating with “release-killing”, “contact-killing” and “anti-adhesion” properties was prepared from biocompatible polymer encapsulated chlorine dioxide (ClO₂) which protected the active ingredient from the outside environment.     

An environmentally sustainable plasticizer toughened polylactide

Cardanol (CD), derived from renewable natural cashew nutshell liquid, has been used as a new plasticizer for polylactide (PLA), to create blends which retain the environmentally friendly features of PLA. The differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM) results all reveal that PLA and CD show good miscibility at low CD content. CD significantly decreased the glass transition temperature and enhanced the crystallization ability of PLA, demonstrating good plasticizing efficiency with PLA. At 10 wt% CD, ultimate elongation and impact toughness increased to 472% and 9.4 kJ m⁻², respectively, which represented improvements of 31-fold and 2.6-fold over the corresponding measurements for neat PLA. The plasticization effect of CD was also demonstrated by the decreased melt complex viscosity and shear storage modulus at lower CD content for the blends when compared with neat PLA. Thus, the investigated CD presents an interesting candidate for a PLA plasticizer, meeting “double green” criteria. No cytotoxicity was found for the blends and hence they may be suitable for biomedical applications.

Cardanol, derived from renewable resources, exhibits good plasticizing efficiency for PLA, meeting “double green” criteria.     

Highly covalent molecular cage based porous organic polymer: pore size control and pore property enhancement

It remains a great challenge to effectively control the pore size in porous organic polymers (POPs) because of the disordered linking modes. Herein, we used organic molecular cages (OMCs), possessing the properties of fixed intrinsic cavities, high numbers of reactive sites and dissolvable processability, as building blocks to construct a molecular cage-based POP (TPP-pOMC) with high valency through covalent cross coupling reaction. In the formed TPP-pOMC, the originating blocking pore channels of TPP-OMC were “turned on” and formed fixed pore channels (5.3 Å) corresponding to the connective intrinsic cavities of cages, and intermolecular pore channels (1.34 and 2.72 nm) between cages. Therefore, TPP-pOMC showed significant enhancement in Brunauer–Emmett–Teller (BET) surface area and CO₂ adsorption capacity.

By utilizing the cage to framework strategy, the blocking pores of the cage itself were “turned on” to construct a highly covalent molecular cage based porous organic polymer.     

Thermally controlled biotransformation of glycyrrhizic acid via an asymmetric temperature-responsive polyurethane membrane

Separating a target product from a relatively complex bioreaction system is often difficult. In this work, a “smart” bioreaction system was developed by using the special characteristic of temperature-responsive polyurethane (TRPU). By combining solvent evaporation with a wet phase inversion technique, an asymmetric membrane consisting of an integral and dense skin layer supported by a porous sublayer was prepared from a thermally responsive polyurethane that experiences a sudden free volume increase upon heating through a phase transition temperature of 56 °C. Subsequently, the asymmetric TRPU membrane served as the carrier of an immobilized enzyme, wherein β-glucuronidase was multipoint-conjugated by using biotin and streptavidin on the porous sublayer. Then, the material-asymmetric TRPU membrane served jointly as the antennae as well as the actuator, which reversibly responds to temperature to switch (on–off) the access of the reactant glycyrrhizic acid (GL). Under the optimal temperature (40 °C) and pH (7.0) conditions, the immobilized β-glucuronidase contributed to almost 33% yield of glycyrrhetinic acid 3-O-mono-β-d-glucuronide (GAMG) of the isolated counterpart for the same concentration of substrate (250 mg L⁻¹) reaction for 24 h, while costing 1% of that of the isolated β-glucuronidase. Kinetic results showed that V_max and K_m values were 8.89 × 10³ mg L⁻¹ and 2.30 × 10³ mg L⁻¹ h⁻¹, respectively. The specific functional polymer-immobilized β-glucuronidase design serves as a bioreactor of GL into GAMG, as well as a separator deliberately irritated and controlled by temperature. This “smart” support material presents a potential facilitator for the separation of complex biotransformation reactions.

A “smart” bioreaction system was developed by using the special characteristic of a temperature-responsive polyurethane (TRPU). This “smart” support material presents a potential benefit of separation for complex biotransformation reactions.     

Facile synthesis of carbon nitride quantum dots as a highly selective and sensitive fluorescent sensor for the tetracycline detection

Enhanced blue fluorescent carbon nitride quantum dots (g-C₃N₄QDs) were synthesized by a simple solvothermal “tailoring” process from bulk g-C₃N₄ and analyzed by various characterization methods. The as-obtained g-C₃N₄QDs were successfully applied in the determination of tetracycline (TC) with a good linear relationship in the range of 0.23–202.70 μM. The proposed fluorescent sensor shows excellent stability, good repeatability, high selectivity and outstanding sensitivity to TC with a low detection limit of 0.19 μM. The fluorescence quenching mechanism of g-C₃N₄QDs with TC was mainly governed by static quenching and the inner filter effect. The method was successfully applied to monitor TC in tap water and milk powder samples.

The g-C₃N₄QDs were synthesized by a simple solvothermal “tailoring” process from bulk g-C₃N₄ which have a “strong quenching” behaviour in the presence of TC. The proposed fluorescent sensor has been successfully applied to detect TC in actual samples.     

Influence of molecular weight on molecular dynamics and dynamic rheology of polypropylene glycol filled with silica

Molecular weight strongly influences the molecular dynamics and rheological responses of nanocomposites, which is far from being well understood. Herein molecular dynamics and rheological behaviors of hydrophilic fumed silica filled unentangled polypropylene glycol (PPG) were investigated as a function of weight averaged molecular weight (M_w) of PPG and volume fraction (∅) of silica. It is shown that M_w does not affect the glassy layers surrounding the nanoparticles and the segmental dynamics of the mobile PPG phase. On the other hand, the mobile PPG phase in the highly filled nanocomposites exhibits an abnormal “more fragile” to “stronger” transition with increasing M_w. The reinforcement and thinning behaviors are stronger in lower-M_w nanocomposites with the “more fragile” mobile PPG phase. The results suggest that reinforcement of nanocomposites affects the dynamic fragility of the mobile phase of the matrix.

The mobile phase exhibits an abnormal “more fragile” to “stronger” transition with increasing molecular weight of polypropylene glycol in nanocomposites at high silica loadings, which significantly lowers the degrees of reinforcement and thinning.     

Structural,optical and electronic properties of Ni1−xCoxO in the complete composition range

Crystallographic and electronic structures of phase pure ternary solid solutions of Ni_1−xCo_xO (x = 0 to 1) have been studied using XRD, EXAFS and XAS measurements. The lattice parameter of the cubic rock-salt (RS) Ni_1−xCo_xO solid solutions increases linearly with increasing Co content and follows Vegard''s law, in the complete composition range. A linear increase in the bond lengths (Ni/Co–O, Ni–Ni and Ni–Co) with “x”, closely following the bond lengths determined from virtual crystal approximation (VCA), is observed, which implies that there is only a minimal local distortion of the lattice in the mixed crystal. The optical gap of the ternary solid solution determined from diffuse reflectivity measurements shows neither a linear variation with Co composition nor bowing, as observed in many ternary semiconductors. This trend in the variation of optical gaps is explained by probing the conduction band using XAS at the O K-edge. We have observed that the variation in the onset energy of the conduction band edge with “x” is very similar to the variation in the optical gap with “x”, thus clearly indicating the dominant role played by the conduction band position in determining the optical gap. The variation in the intensities of the pre-edge peak in the XANES spectra measured at Ni and Co K-edges, and the L_1/2 peak in XAS spectra measured at Ni and Co L-edges, is found to depend on the unoccupied O 2p-metal-(Ni/Co) 3d hybridized states and the bond lengths.

The optical gap of Ni_1−xCo_xO solid solutions neither varies linearly with Co composition nor shows any bowing in the complete composition range. The nature of this variation of the gap is governed by the position of conduction band edge.     

Transformation of ZIF-8 nanoparticles into 3D nitrogen-doped hierarchically porous carbon for Li–S batteries

Li–S batteries have been attracting increasing interest owing to their remarkable advantages of low cost, high theoretical capacity and high theoretical energy density. Nevertheless, the severe “shuttle effects” of lithium polysulfides have markedly limited the performance of the cells and further hindered their commercial applications. Herein, a novel scheme combining a transformation strategy with ammonia treatment was developed to fabricate ZIF-8-derived nitrogen-doped hierarchically porous carbon (NHPC/NH₃). When NHPC/NH₃ was used as a host of sulfur, the obtained S@NHPC/NH₃ cathode for Li–S cells presented an initial specific capacity of 1654 mA h g⁻¹ and an outstanding cycling stability with only 0.27% attenuation per cycle from the 30th cycle to 130th cycle. Together with the theoretical calculation, it was concluded that such excellent electrochemical performances should be attributed to the suppressed “shuttle effect” via both physical and chemical adsorption of lithium polysulfides in the optimized microporous structures with effective nitrogen doping sites as well as the improved kinetics owing to the abundant meso/macroporous structures.

A novel transformation strategy assisted with ammonia treatment was successfully developed to fabricate ZIF-8-derived nitrogen-doped hierarchically porous carbon (NHPC/NH₃).     

Correction: Synthesis and structural characterization of CO2-soluble oxidizers [Bu4N]BrO3 and [Bu4N]ClO3 and their dissolution in cosolvent-modified CO2 for reservoir applications

Correction for ‘Synthesis and structural characterization of CO₂-soluble oxidizers [Bu₄N]BrO₃ and [Bu₄N]ClO₃ and their dissolution in cosolvent-modified CO₂ for reservoir applications’ by Katherine L. Hull et al., RSC Adv., 2020, 10, 44973–44980, DOI: 10.1039/D0RA09563J.

The authors regret that the value for the solubility of [Bu₄N]BrO₃ in the last sentence of the Results and discussion section was given incorrectly.In the sentence beginning “Notably, the solubility of [Bu₄N]BrO₃ achieved…” on page 44978, the corrected sentence should read “Notably, the solubility of [Bu₄N]BrO₃ achieved (>0.12 wt%) with ethanol cosolvent significantly exceeds the typical concentrations utilized in the application (∼0.03 wt%)”.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Tantalum(v) 1,3-propanediolate β-diketonate solution as a precursor to sol–gel derived,metal oxide thin films

Correction for ‘Tantalum(v) 1,3-propanediolate β-diketonate solution as a precursor to sol–gel derived, metal oxide thin films’ by Christopher Beale et al., RSC Adv., 2020, 10, 13737–13748, DOI: 10.1039/D0RA02558E.

The authors regret that the plasma treatment and printing parameters were reported incorrectly in the subsection “Deposition on a-SiO₂ for UV/Vis spectrophotometry” in the Experimental section of the original article.Before printing, the substrate for both samples was subjected to an argon plasma treatment for 5 minutes (150 W, 0.6 mbar). The plasma power is now corrected to be the same as stated in the “Deposition on a-SiO₂ for Raman/XRD” subsection, where originally it was incorrectly stated that “the power was set slightly higher” for the Raman/XRD samples. For both the acetylacetone and benzoylacetone inks, the inks were printed on their respective substrates with a 75 μm drop pitch having dimensions of 400 × 220 drops to create a uniform layer.The correct section is as follows:     

‘Hairy’ root extracts as source for ‘green’ synthesis of silver nanoparticles and medical applications

The research was focused on the synthesis of silver nanoparticles (AgNPs) using extracts from the “hairy” root cultures of Artemisia tilesii Ledeb. and Artemisia annua L. The effect of operational parameters such as type of solvent, temperature of extraction, flavonoids concentration, and reducing power of the wormwood “hairy” root extracts on the particle size and yield of the resultant nanoparticles is reported for the first time. From the studied solvents, a water–ethanol mixture with a concentration of 70 vol% was found to be the best for the extraction of flavonoids from all “hairy” root cultures. The total flavonoid contents in A. annua and A. tilesii “hairy” root extracts were up to 80.0 ± 0.9 and 108 ± 4.4 mg RuE per g DW, respectively. Identification of flavonoids was confirmed by UPLC-ESI-UHR-Qq-TOF-MS analysis. Luteolin-7-β-d-glucopyranosid, isorhamnetin 3-O-glucoside, baicalein-7-O-glucuronide, apigenin-7-O-glucoside, quercetin, sitosterol, caffeoylquinic, galic, chlorogenic and caffeic acids were founded in the extracts. These extracts demonstrated the high reducing activities. Spherical, oval and triangular nanoparticles with effective sizes of 5–100 nm were observed. The TEM data revealed great differences in the shapes of NPs, obtained from the extracts from different root clones. The clustered and irregular NPs were found in the case of using ethanol extracts, mostly aggregated and having the size of 10–50 nm. The sizes of AgNPs decreased to 10–30 nm in the case of using aqueous extracts obtained at 80 °C. Biosynthesized AgNPs showed surface plasmon resonance in the range of 400–450 nm. The antimicrobial activity of the as-produced AgNPs was studied by disc diffusion method on Gram-positive (Staphylococcus aureus ATCC 25923 (F-49)), Gram-negative (Pseudomonas aeruginosa ATCC 27853 (F-51), Escherichia coli ATCC 25922 (F-50)) and Candida albicans ATCC 88-653 strains. It was found that the nanoparticles in some cases possessed the greater ability to inhibit microorganism growth compared to 1 mM AgNO₃ solution. The colloidal solutions of the obtained AgNPs were stable in the dark for 12 months at room temperature. Thus, the A. annua and A. tilesii “hairy” root extracts can be used for obtaining of bioactive AgNPs.

The research was focused on the synthesis of silver nanoparticles (AgNPs) using extracts from the “hairy” root cultures of Artemisia tilesii Ledeb. and Artemisia annua L.     

Photophysical properties and singlet oxygen generation of meso-iodinated free-base corroles

In order to study the effect of meso-iodination of free-base corroles on their photophysical character, we designed and synthesized a series of free-base corrole derivatives F10–OH (iodine-free), F10–OH–I (mono-iodo) and F10–OH–2I (di-iodo), with different substitution patterns at the meso-position as candidates for photodynamic therapy (PDT). We employed several optical spectroscopic techniques, including time-resolved spectroscopy from a femtosecond to microsecond and singlet oxygen luminescence to study the properties of excited singlet and triplet states, as well as the singlet oxygen quantum yields. The sub-picosecond internal conversion, ∼1 ps intramolecular vibrational energy redistribution, tens of ps vibrational cooling, are similar across the three corroles. The addition of one (F10–OH–I) and two iodine (F10–OH–2I) atoms to the remote aryl ring of triarylcorroles induces a 4.6-fold and 6.2-fold decrease in fluorescence quantum yields Φ_fl and a 2.2-fold and 4.9-fold increase in the time constant of intersystem crossing k_ISC. In addition, a slight increase in intersystem crossing quantum yields Φ_T was also observed from F10–OH to F10–OH–2I. It means the intersystem crossing is improved by the iodination, from F10–OH to F10–OH–2I, because of the heavy atom effect. However, the sample F10–OH–I, instead of F10–OH–2I, shows the highest singlet oxygen quantum yield Φ_Δ.

The effect of corrole macrocycle meso-iodination on its photophysical character.     

Effects of potassium additives on the combustion characteristics of graphite as a heating source of heat-not-burn tobacco

“Heat-not-burn” tobacco with an external heating source is a cleaner alternative to conventional cigarettes due to its lower emission of nicotine, CO and tar in the smoke, and graphite is a promising carbon heating source for a “heat-not-burn” tobacco product yet is not easy to be fired. This work aims to improve the combustion properties of graphite using potassium catalysts. Thermal gravimetric analysis is performed to investigate the combustion properties, and a first-order kinetic model is applied to describe the combustion process. Scanning electron microscopy is used to observe the surface morphology, and the mineral and elemental composition are investigated by powder X-ray diffraction and energy dispersive spectrometry, respectively. The results indicate that the potassium additives can significantly decrease the ignition temperature of the graphite samples by 51–124 °C, and the promotion effects are closely related to the potassium and oxygen content of the additives. Further kinetic analysis implies that K and O can decrease the activation energy required for the oxidation reactions by 45.1% from 194.5 to 106.8 kJ mol⁻¹, thereby improving the graphite combustion. Moreover, potassium can play the role of “O₂ transfer”, which can transfer atmospheric oxygen to support graphite combustion. K₂CO₃ is a suitable catalyst for graphite combustion, and the suggested addition amount is 0.88% in weight.

The ignition temperature of a graphite-heated heat-not-burn tobacco product can be significantly decreased by 120 °C with 0.88 wt% of K₂CO₃ additive.     

Thiol–ene coupling reaction achievement and monitoring by “in situ” UV irradiation NMR spectroscopy

In this study, the possibilities of a new “in situ” LED UV illumination NMR spectroscopic technique for performing an initiator-free thiol–ene “click” coupling reaction of an allyl-functionalized poly(allyl glycidyl ether) (PAGE) prepolymer with a number of mono- and di-oligo polyethylene glycol (PEG) thiols is demonstrated. The state-of-the-art setup constructed with LEDs as UV light sources that illuminate through optical fibers directly into an NMR testing tube at a fixed wavelength of 365 nm is appropriate for various polymeric materials and biologically active substances. The selected experimental protocol uses a series of periods of irradiation and dark periods, thus providing opportunities to conduct an effective thiol–ene “click” reaction and simultaneously study the kinetics of the photochemical reaction with the exposure time, as well as macromolecular association directly in a solution applying the whole types of NMR methods: from conventional ¹H or ¹³C NMR to diffusion NMR spectroscopy (DOSY). In addition, the molecular mass characteristics of the prepared copolymers were studied by gel-permeation chromatography (GPC). The observed differences in the reaction rates as well as in the size of species formed (the corresponding hydrodynamic radiuses R_h of aggregates) as a result of the coupling process of parent PAGE prepolymers and model PEG thiols were thoroughly discussed and the reaction pathway proposed.

An “In situ” LED UV illumination NMR setup for achievement of initiator-free coupling reactions of allyl-functionalized poly(allyl glycidyl ether) with polyethylene glycols thiols.