High-yield and nitrogen self-doped hierarchical porous carbon from polyurethane foam for high-performance supercapacitors

Catalytic Upgrading of Plastic Wastes into High-Value Carbon Nanomaterials: Synthesis and Applications

The surge in waste plastics has placed a serious burden on the global ecosystem. Traditional recycling methods are insufficient to handle the growing volume of plastic waste, highlighting the urgent demand for innovative recycling technologies. Transforming plastics into high-value carbon nanomaterials is a simple and efficient resource recovery strategy, especially effective for handling mixed or hard-to-separate plastic waste. This method not only simplifies the sorting of discarded plastics but also offers significant advantages in recovery efficiency and processing convenience. This review systematically summarized various technologies for converting plastics into carbon nanomaterials, focusing on the catalytic mechanisms of different conversion methods. We also analyzed how various catalysts, catalytic temperatures, and metal-support interactions affect the yield and quality of carbon nanomaterials. Additionally, the potential applications of carbon nanomaterials in environmental remediation, energy storage, and catalysis are also evaluated. The ongoing challenges and future research directions in this field are critically discussed, which will ultimately facilitate more effective resource recovery from plastics and contribute to the realization of a circular economy. We believe that this review will inspire more creativity in designing such win-win reaction systems to realize a "waste treat waste" concept.

N-doped porous carbon derived from different lignocellulosic biomass models for high-performance supercapacitors: the role of lignin, cellulose and hemicellulose

Biomass-derived porous carbon (PC) has been widely studied in the field of supercapacitors due to its low cost, sustainability and developed pore structure, but how to screen the precursors of high-performance PC is still a major difficulty. Herein, six lignocellulosic biomass models based on different compositions were innovatively constructed and prepared into high-performance PC by a synergistic activation-doping strategy. The results show that the synergistic activation-doping strategy has a certain universality for biomass models. Meanwhile, cellulose and hemicellulose mainly contribute to the formation of micropores, resulting in high specific surface area (SSA), specific capacitance and energy density. While lignin provides some micropores and most mesopores for PC, which enables PC to exhibit excellent rate and cycling performance. Specifically, the MF prepared from the biomass model constructed based on wheat bran has the optimized specific capacitance (474 F g-1 at 1 A g-1), due to its largest SSA (2773 m2 g-1) and high proportion of micropores (76.6%). At 5 A g-1, the coulombic efficiency during 5000 cycles is maintained at 98.8-99.4%, and the final capacity retention is 95.89%. Impressively, an aqueous symmetric supercapacitor based on MF assembled in 1 M Na2SO4 electrolyte delivers an energy density of 27.66 Wh kg-1 at a power density of 82.03 W kg-1. This study provides a reference for the precursor screening of high-performance PC at the composition level, and also contributes an operational idea for PC performance regulation.

Microenvironment modulation of interpenetrating-type hierarchical porous foam carbon by mild-homogeneous activation for H2 storage and CO2 capture under ambient pressure

Currently, carbon-based porous materials for hydrogen (H2) storage and carbon dioxide (CO2) capture are mostly applied at higher pressures (30-300 bar). However, applications for H2 storage and CO2 capture under ambient pressure conditions are significant for the development of portable, household, and miniaturized H2 energy technologies. This demands a higher standard for the interface microenvironment of adsorbents. Derived from polyurethane foams (PUFs) solid waste, the hierarchical porous foam carbon with interpenetrating-type pore structures exhibits high specific surface area (SBET = 1753 m2/g), abundant oxygen and nitrogen functional groups, and a hierarchical nanopore structure (VUltra = 0.232 cm3/g, VMicro = 0.628 cm3/g and VMeso = 0.186 cm3/g) through the mild-homogeneous sonication-assisted activation process. Under the limited adsorption of pore interface microenvironment composed by hierarchical nanopore structure and dipole-induced interaction (H(Ⅱ)-H(Ⅰ)···N/O and O(Ⅱ) = C(Ⅰ) = O(Ⅱ)···N/O), it exhibits an excellent H2 storage density (2.92 wt% at 77 K, 1 bar) and CO2 capture capacity (5.28 mmol/g at 298 K, 1 bar). This research approach can serve as a reference for the dual-functional design of porous foam carbon, and promote the development of adsorption materials for CO2 capture and energy gas storage under ambient conditions.

Multi-heteroatom-doped porous carbon with high surface adsorption energy of potassium derived from biomass waste for high-performance supercapacitors

Sustainable and renewable biomass-derived porous carbon (BPC) have garnered considerable attention owing to their low cost, high specific surface area, and outstanding electrochemical performance. However, the subpar energy density severely restricts the applications of BPC in high-energy-density devices. Herein, a high-surface-area porous carbon with multiple heteroatoms doping was derived from rapeseed meals by hydrothermal carbonization and high-temperature activation. The rapeseed meal-derived activated carbon (RMAC) exhibits a remarkable surface area of 3291 m2 g-1 and is doped with nitrogen (1.05 at.%), oxygen (7.4 at.%), phosphorus (0.31 at.%), and sulfur, resulting in an impressive specific capacitance of 416 F g-1 at 1 A g-1. Furthermore, even after 10,000 cycles, the optimized RMAC-800 electrode maintains 92 % of its initial capacitance, attesting to its exceptional performance. Through comprehensive density functional theory (DFT) calculations, the elements O, N, P, and S can significantly enhance the electron negativity and density, improving the adsorption and diffusion of K+ to attain a high capacitance. To assess the RMAC-800's practical performance, an asymmetric supercapacitor with 1 M [BMIM]BF4/AN electrolyte was produced that delivered a high energy density of 195.94 Wh kg-1 at a power density of 1125 W kg-1. Thus, we propose an eco-friendly strategy for producing BPC materials with outstanding electrochemical performance for supercapacitors.

In situ N, O co-doped porous carbon derived from antibiotic fermentation residues as electrode material for high-performance supercapacitors

With the widespread use of antibiotics, the safe utilization of waste antibiotic fermentation residues has become an urgent issue to be resolved. In this study, in situ N, O co-doped porous carbon was prepared using fresh oxytetracycline fermentation residue under the mild activation of the green activator K2CO3. The optimal sample exhibited a 3D grid carbon skeleton structure, excellent specific surface area (SBET = 948 m2 g-1), and high nitrogen and oxygen content (N = 3.42 wt%, O = 14.86 wt%). Benefiting from its developed morphology, this sample demonstrated excellent electrochemical performance with a high specific capacitance of 310 F g-1 at a current density of 0.5 A g-1 in the three-electrode system. Moreover, it exhibited superior cycling stability with only a 5.32% loss of capacity after 10 000 cycles in 6 M KOH aqueous electrolyte. Furthermore, the symmetric supercapacitor prepared from it exhibited a maximum energy density of 7.2 W h kg-1 at a power density of 124.9 W kg-1, demonstrating its promising application prospects. This study provided a green and facile process for the sustainable and harmless treatment of antibiotic fermentation residues.

Distribution, migration, and removal of N-containing products during polyurethane pyrolysis: A review

Due to the wide applications of polyurethane (PU), production is constantly increasing, accounting for 8% of produced plastics. PU has been regarded as the 6th most used polymer in the world. Improper disposal of waste PU will result in serious environmental consequences. The pyrolysis of polymers is one of the most commonly used disposal methods, but PU pyrolysis easily produces toxic and harmful nitrogen-containing substances due to its high nitrogen content. This paper reviews the decomposition pathways, kinetic characteristics, and migration of N-element by product distribution during PU pyrolysis. PU ester bonds break to produce isocyanates and alcohols or decarboxylate to produce primary amines, which are then further decomposed to MDI, MAI, and MDA. The nitrogenous products, including NH3, HCN, and benzene derivatives, are released by the breakage of C-C and C-N bonds. The N-element migration mechanism is concluded. Meanwhile, this paper reviews the removal of gaseous pollution from PU pyrolysis and discusses the removal mechanism in depth. Among the catalysts for pollutant removal, CaO has the most superior catalytic performance and can convert fuel-N to N2 by adsorption and dehydrogenation reactions. At the end of the review, new challenges for the utilization and high-quality recycling of PU are presented.

Upcycling of thermosetting polymers into high-value materials

Thermosetting polymers, a large class of polymers featuring excellent properties, have been widely used and play an irreplaceable role in our life. Nevertheless, they are arduous to be recycled or reused on account of their permanently cross-linked networks, and the main recycling approaches used currently include energy recovery through incineration, utilization as fillers after mechanical grinding, and pyrolysis, which only reclaim a small fraction or partial value of thermosetting polymers and their downstream materials. In this minireview, we provide an overview of the efforts undertaken towards upcycling thermosetting polymers in recent years. The research progress on physical upcycling, carbonization, solvolysis and vitrimerization of thermoset waste to high-value materials, including oil-water separation materials, 3D printable materials, functional carbon materials (supercapacitors, photothermal conversion materials, and catalytic materials), additives, emulsifiers, biolubricants, and vitrimers, are summarized and discussed. Perspectives on the future development of the art of upcycling thermosets are also provided.

Synthesis of CNT@CoS/NiCo Layered Double Hydroxides with Hollow Nanocages to Enhance Supercapacitors Performance

One of the key factors to improve electrochemical properties is to find exceptional electrode materials. In this work, the nickel-cobalt layered double hydroxide (CNT@CoS/NiCo-LDH) with the structure of a hollow nanocage was prepared by etching CNT@CoS with zeolitic imidazolate framework-67 (ZIF-67) as a template. The results show that the addition of nickel has a great influence on the structure, morphology and chemical properties of materials. The prepared material CNT@CoS/NiCo-LDH-100 (C@CS/NCL-100) inherited the rhombic dodecahedral shape of ZIF-67 well and the CNTs were evenly interspersed among the rhombic dodecahedrons. The presence of CNTs improved the conductivity and surface area of the samples. The C@CS/NCL-100 demonstrates a high specific capacitance of 2794.6 F·g^-1 at 1 A·g^-1. Furthermore, as an assemble device, the device of C@CS/NCL-100 as a positive electrode exhibits a relatively high-energy density of 35.64 Wh·kg^-1 at a power density of 750 W·kg^-1 Further, even at the high-power density of 3750 W·kg^-1, the energy density can still retain 26.38 Wh·kg^-1. Hence, the superior performance of C@CS/NCL-100 can be ascribed to the synergy among CNTs, CoS and NiCo LDH, as well as the excellent three-dimensional structure obtained by used ZIF-67 as a template.