One-step hyper-cross-linking of porous styrenic polymers using dichloroalkane cross-linkers to maintain hydrophobicity

Elucidating the enduring transformations in cellulose-based carbon nanofibers through prolonged isothermal treatment

This study investigates the conversion of highly acetylated sugarcane bagasse into high-modulus carbon nanofibers (CnNFs) with exceptional electrical conductivity. By electrospinning the bagasse into nanofibers with diameters ranging from 80 nm to 800 nm, a cost-effective CnNFs precursor is obtained. The study reveals the transformation of the cellulose crystalline structure into a stable antiparallel chain arrangement of cellulose II following prolonged isothermal treatment, leading to a remarkable 50 % increase in CnNFs recovery with carbon contents ranging from 80 % to 90 %. This surpasses the performance of any other reported biomass precursors. Furthermore, graphitization-induced shrinkage of CnNFs diameter results in significant growth of specific surface area and pore volume in the resulting samples. This, along with a highly ordered nanostructure and high crystallinity degree, contributes to an impressive tensile modulus of 9.592 GPa, surpassing that of most petroleum-based CnNFs documented in the literature. Additionally, the prolonged isothermal treatment influences the d002 value (measured at 0.414 nm) and CnNFs degree of crystallinity, leading to an enhancement in electrical conductivity. However, the study observes no size effect advantages on mechanical properties and electrical conductivity, possibly attributed to the potential presence of point defects in the ultrathin CnNFs. Overall, this research opens a promising and cost-effective pathway for converting sugarcane biomasses into high-modulus carbon nanofibers with outstanding electrical conductivity. These findings hold significant implications for the development of sustainable and high-performance materials for various applications, including electronics, energy storage, and composite reinforcement.

Graphene oxide enhances thermal stability and microwave absorption/regeneration of a porous polymer

Microwave regeneration of adsorbents offers several advantages over conventional regeneration methods; however, its application for microwave transparent adsorbents such as polymers is challenging. In this study, hypercrosslinked polymer/graphene oxide (GO) nanocomposites with large surface area and enhanced microwave absorption ability were synthesized. Polymers of 4, 4´-bis ((chloromethyl)-1, 1´-biphenyl- benzyl chloride) were hypercrosslinked through the Friedel-Crafts reactions. GO sheets were synthesized through the Hummer's method. Nanocomposites with different GO contents (1-8 wt%) were synthesized by solution mixing method. Thermogravimetry analysis revealed a large enhancement in the thermal stability of GO-filled nanocomposites compared to pristine polymer. N₂ adsorption isotherm analysis showed 7% and 10% reduction in BET surface area and total pore volume of the nanocomposite with 8 wt% GO. Compared to the pristine polymer, the dielectric constant and dielectric loss factor increased from 5 to 17 and 0.05-1.6, respectively, for the nanocomposites with 8 wt% GO. Microwave-assisted desorption of toluene from samples revealed more than 160 ºC and 4 times improvement in the desorption temperature and desorption efficiency, respectively, by addition of 4 wt% GO to the polymer. This study showed the important role of GO addition for efficient microwave-assisted regeneration of polymer adsorbents.

A hyper-cross-linked polymer derived from pitch as an efficient adsorbent for VOCs

Hyper-cross-linked polymers (HCPs) have been attracted widespread attention as adsorbents in recent years. A series of HCPs (HCP-1, HCP-2 and HCP-3) were synthesized via a Friedel-Crafts reaction using low-cross-linked pitch as precursor and dichloromethane (DCM) as cross-linking reagent and solvent. The prepared HCPs were characterized by N2 adsorption, Fourier transform infrared (FI-IR), Scanning electron microscopy (SEM), Thermogravimetric analysis (TGA) and static water contact angle. The resultant HCPs possess micro/meso pore structures and a high stability. The Brunauer-Emmett-Teller (BET) surface areas of HCP-1, HCP-2 and HCP-3 are 152 m2·g−1, 467 m2·g−1 and 447 m2·g−1, respectively. Their total pore volumes vary from 0.207 cm·g−1 to 0.545 cm3·g−1 and following the sequence of HCP-1<HCP-3<HCP-2. The FTIR spectra of HCPs suggests the DCM is successfully grafted onto the skeleton structure. Dynamic adsorption capacities of the prepared HCP-1, HCP-2 and HCP-3 were examined and the results show the adsorption properties of o-xylene on HCP-2 are significantly higher than that of the other HCPs. The adsorption amount of o-xylene on HCP-2 is 198.18 mg·g−1, which is higher than that of benzene, suggesting a strong adsorption selectivity for o-xylene over benzene. In addition, the effect of water vapor on the adsorption of o-xylene onto HCP-2 was investigated. The dynamic adsorption amount of o-xylene on HCP-2 decreases by 76.47% under the relative humidity (RH) of 30%, implying that the HCP-2 has poor hydrophobicity. The equilibrium adsorption capacity of o-xylene on HCP-2 shows a slight decline after five adsorption cycles.

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Effects of the Reaction Parameters and Light Hydrothermal Aging for Catalytic Combustion of Propane over Co-Mn-Ce Catalyst

A composite oxides’ Co-Mn-Ce catalyst was synthesized by a coprecipitation method, and the experiment was carried out to study the effects of reaction parameters and light hydrothermal aging on propane combustion over the Co-Mn-Ce catalyst. The influence of reaction temperature, propane concentration, oxygen concentration, water vapor, and hydrothermal aging was studied during the catalytic combustion of propane. The propane conversion significantly decreased by 10% when the propane concentration increased at 300°C and then further decreased from 80% to 40% as water vapor concentration increased from 0 to 10 vol.%. In addition, water vapor also prolonged the time required to reach equilibrium. After hydrothermal treatment, the catalyst obtained the lowest oxidation capacity of propane. Furthermore, the results of in situ DRIFTs and O2 temperature programmed desorption (O2-TPD) demonstrated that there were fewer oxygen species after hydrothermal aging, and carbonates were the main intermediates formed during the catalytic oxidation of propane.

Tailoring Nanoporous-Engineered Sponge Fiber Molecular Sieves with Ternary-Nested Architecture for Precise Molecular Separation

Polymeric fiber molecular sieves (PFMs) with ultrahigh surface areas, well-defined Murray's-law hierarchical nanoporous structures, and superior self-standing properties are of great interest for molecular-level separation applications. However, creating such PFMs has been proven extremely challenging. Herein, we report a cross-scale pore-forming strategy to create intriguing sponge fiber molecular sieves with hierarchical, tailorable, and molecularly defined nanoporosity by nanospace-confined chain-packing modulation at the molecular level. Robust secondary ultramicropores (<7 Å) and micropores (<2 nm) are in situ constructed in the macro/mesoporous skeletons of sponge fibers to realize a tunable pore size distribution. The resultant PFMs exhibit the integrated properties of ultrahigh surface area (860 m² g^-1), large pore volume (0.6 cm³ g^-1), self-standing properties, and excellent molecular sieving performance and are widely applied in acetophenone/phenyl ethanol separation, hydrogen peroxide purification, ethyl acetate separation, and CO₂ adsorption fields. The fabrication of such PFMs provides a feasible way for the design and development of polymeric fibrous sieves for molecular separation in large-scale chemical, energy, and environmental operation processes.

Online measurement of 1,2,4-trichlorobenzene as dioxin indicator on multi-walled carbon nanotubes

Polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) emission is one of main concerns for the secondary pollution of municipal solid waste incinerators (MSWI). For timely response to emission, 1,2,4-trichlorobenzene (1,2,4-TrClBz) as dioxin indicator can be monitored via online measurement techniques. In this study, multi-walled carbon nanotubes (MWCNTs) were investigated for their suitability as a 1,2,4-TrClBz sorbent for MSWI stack gas analysis. The tests include, batch adsorption, continuous adsorption-desorption of 1,2,4-TrClBz via thermal desorption coupled with gas chromatography (TD-GC-ECD), temperature and concentration stability of MWCNTs, and adsorption performance of the system. Thermogravimetric/derivative thermogravimetric (TGA/DTG) analysis reveals that MWCNTs has higher capacity in terms of weight loss (14.34%) to adsorb 1,2,4-TrClBz compared to Tenax TA (9.46%) and also shows fast desorption of adsorbate at temperature of 87 °C compared to Tenax TA (130 °C). Interestingly, carbon nanotubes and Tenax TA gave almost similar adsorption-desorption response, and from TD-GC-ECD analysis it was found that with increasing mass flow of 1,2,4-TrClBz (7.42 × 10^-6 - 44.52 × 10^-6 mg ml^-1) through sorbent traps, average peak areas increased from 2.86 ± 0.02 to 13.54 ± 0.26 for MWCNTs and 2.89 ± 0.02 to 13.38 ± 0.12 for Tenax TA, respectively. The stability of MWCNTs for temperature was 400 °C and for concentration of 1,2,4-TrClBz was 50 ppbv. However, regeneration of sorbent at 100 ppbv (1,2,4-TrClBz) was not possible. TD-GC-ECD system showed high adsorption performance with 3.86% and 3.59% relative standard deviation at 250 °C and 300 °C, respectively. Further Fourier Transform Infrared Spectroscopy (FTIR) analysis confirmed that adsorbate can be fully desorbed at 300 °C.

Novel amino-functionalized hypercrosslinked polymer nanoparticles constructed from commercial macromolecule polystyrene via a two-step strategy for CO2 adsorption

Commercial polymers have large cost advantage to drive HCPs to industrialize. The AHCPNPs using commercial PS as main block prove that it still has well-defined microporous structure, high specific surface area and extremely CO₂ capture capacity.

Nitrogen-Doped Hollow Copolymer Tube via Template-Free Asynchronous Polymerization with Highly Selective Separation of Hydrophilic Dipeptide for Enhancing Inhibitory Activity of Angiotensin Converting Enzyme

A N-doped hollow copolymer tube (NHCT) was fabricated via template-free one-pot asynchronous polymerization strategy. Discrepancies of monomer polymerization speed and their hydrophilic-hydrophobic interaction resulted in the assembly of a hollow tube having inner diameter and double wall thickness of ∼230 and 40 nm, respectively. The formation and growth mechanism of NHCT analyzed via advanced characterization revealed that the unique growth processes tuned a demarcating surface layer between inner (hydrophilic) and outer (hydrophobic) layers. The screening and recognition ability of NHCT were determined for two specific dipeptides (WW and RR) possessing great discrepancies in hydrophilicity and angiotensin converting enzyme inhibitory (ACE-I) activity. NHCT realized high adsorption capacity (1.57 mmol/g) and selectivity (∼1274) for hydrophilic dipeptide RR (low ACE-I activity) from the mixture of RR/WW. As a result, ACE-I activity for residual solution were enhanced about 4.1 times as compared to original solution from natural silkworm pupae protein hydrolysate. Awarding to these results and its facile and discerning ability, NHCT can be envisioned to be of great value for the separation of small functional peptides from a natural edible source.

Phenol adsorption and desorption with physically and chemically tailored porous polymers: Mechanistic variability associated with hyper-cross-linking and amination

Understanding phenol adsorption-desorption mechanisms allows adsorbent tailoring to improve capacity and adsorbent reuse. Amberlite™ XAD4, a commercial styrenic polymer that is convenient to physically and chemically modify, was functionalized with dimethylamine (DMA) or trimethylamine (TMA) and/or hyper-cross-linked with 1,2-dichloroethane. These modifications were applied to enhance individual and/or synergistic phenol adsorption mechanisms, including hydrogen bonding, electrostatic interactions, and π-π dispersion forces. While XAD4-DMA adsorbs more phenol at pH = 6, XAD4-TMA has 23% higher capacity at pH = 11 due to adsorbate deprotonation that increases electrostatic interactions. Combining hyper-cross-linking with amination maximizes adsorption capacity due to synergistic impacts associated with increased micropore volume and surface affinity. Amine groups reduce desorption efficiency by 6-94% due to stronger adsorbate-adsorbent interactions compared to π-π dispersion forces. Isobutanol, which forms hydrogen bonds, is the most efficient desorption solvent, followed by chloroform, which has the same polarity index but does not hydrogen bond. n-Hexane only desorbs phenol removed with π-π dispersion forces and is not appropriate to regenerate aminated polymers. 0.1 N NaOH is an environmentally benign solvent for regenerating as-received XAD4 and XAD4-DMA, but not XAD4-TMA. Understanding phenol adsorption mechanisms allows development of physiochemically modified polymers with increased phenol adsorption capacity and regeneration efficiency.