Synergistic effects of hybrid n-doping on the thermoelectric performance and air-stability of water-processable single-walled carbon nanotubes.

Organic thermoelectrics (TEs) based on carbon nanotubes (CNTs) have attracted much attention with their inherent advantages, such as, earth-abundant elements, broad electronic tunability, and excellent mechanical compliance. However, the inferior TE performance and doping stability of n-type CNTs to those of p-type CNTs have been bottlenecks to establish CNT-based next-generation TEs. Herein, we report a hybrid n-doping method that improves the n-type TE performance and long-term air-stability of water-processable single-walled CNT (SWCNT) and carboxymethyl cellulose (CMC) composite. The hybrid n-doping process with polyethyleneimine (PEI) n-dopant contains primary addition and secondary immersion doping, which causes a simultaneous increase in electrical conductivity and Seebeck coefficient through efficient n-doping and surface energy filtering effect, respectively. Furthermore, the hybrid-doped films exhibit superior long-term stability by inhibiting the oxidation of SWCNT/CMC at nanoscale, which allows to ensure the initial power factor even after storing in ambient for a month. Finally, we successfully demonstrated hybrid-doped SWCNT/CMC-based TEGs with long-term stable output characteristics. This work can offer insights to develop efficient and air-stable n-type organic TE materials and devices.

Structural and Electronic Response of Multigap N-Doped In2Se3: A Prototypical Material for Broad Spectral Optical Devices.

The production of controlled doping in two-dimensional semiconductor materials is a challenging issue when introducing these systems into current and future technology. In some compounds, the coexistence of distinct crystallographic phases for a fixed composition introduces an additional degree of complexity for synthesis, chemical stability, and potential applications. In this work, we demonstrate that a multiphase In2Se3 layered semiconductor system, synthesized with three distinct structures─rhombohedral α and ß-In2Se3 and trigonal δ-In2Se3─exhibits chemical stability and well-behaved n-type doping. Scanning tunneling spectroscopy measurements reveal variations in the local electronic density of states among the In2Se3 structures, resulting in a compound system with electronic bandgaps that range from infrared to visible light. These characteristics make the layered In2Se3 system a promising candidate for multigap or broad spectral optical devices, such as detectors and solar cells. The ability to tune the electronic properties of In2Se3 through structural phase manipulation makes it ideal for integration into flexible electronics and the development of heterostructures with other materials.

High-Performance Bimetallic Electrocatalysts for Hydrogen Evolution Reaction Using N-Doped Graphene-Supported N-Co6Mo6C.

Hydrogen has garnered considerable attention as a promising energy source for addressing contemporary environmental degradation and energy scarcity challenges. Electrocatalytic water splitting for hydrogen production has emerged as an environmentally friendly and versatile method, offering high purity. However, the development of cost-effective electrocatalytic catalysts using abundant and inexpensive materials is crucial. In this study, we successfully synthesized nitrogen-doped Co6Mo6C supported on nitrogen-doped graphene (N-Co6Mo6C/NC). The catalyst exhibited high performance and durability in alkaline electrolytes (1.0 M KOH) for hydrogen evolution, showcasing an overpotential of 185 mV at a current density of 100 mA cm-2 and a Tafel slope of 80 mV dec-1. These findings present a novel avenue for the fabrication of efficient bimetallic carbide catalysts.

Microalgae realizes self N-doped biochar for heavy metal polluted sediment remediation.

Heavy metal contamination in sediment has become a significant global environmental challenge. Numerous studies have demonstrated the effectiveness of modified biochar to solve heavy metal contamination in sediment. However, the modification process with complex methods and expensive modifiers prevented its large-scale application. In this study, an N self-doped biochar was obtained by pyrolysis of Spirulina sp. (SBC). Meanwhile, the K2CO3 impregnation method was utilized to prepare Spirulina sp. biochar (KSBC), which demonstrated a higher specific surface area (874 m2/g) and richer O, N functional groups. The adsorption capacity of KSBC550-120 for Cu (Ⅱ), Zn (Ⅱ), and Cd (Ⅱ) was 57.9 ± 0.3 mg/g, 43.6 ± 0.7 mg/g, and 63.9 ± 0.6 mg/g, respectively. The adsorption process is primarily governed by chemical processes, mainly through ion exchange, surface complexation, dissolution-precipitation, electrostatic interactions, adsorption-reduction, and cation-π interactions. Moreover, utilizing KSBC550-120 for mixing or capping effectively reduced heavy metal concentrations in both the overlying and pore water of the sediments. 1.0 wt% KSBC550-120 with capping treatment significantly reduced the release of heavy metals from the sediment by 80.3-91.9%. This study provides effective theoretical support for re-utilizing waste algal residues and remediation of the heavy metal-contaminated river and lake sediments using microalgae biochar.

Engineering Three-Dimensional Interconnected Pores with Plentiful Edge Sites via a Confined Space for Enhanced Oxygen Reduction.

N-Doped carbon sheets based on edge engineering provide more opportunities for improving oxygen reduction reaction (ORR) active sites. However, with regard to the correlation between porous structural configurations and performances, it remains underexplored. Herein, a silica-assisted localized etching method was employed to create two-dimensional mesoporous carbon materials with customizable pore structures, abundant edge sites, and nitrogen functionalities. The mesoporous carbon exhibited superior electrocatalytic performance for the ORR compared to that of a 20 wt % Pt/C catalyst, achieving a half-wave potential of 0.88 V versus RHE, situating them in the leading level of the reported carbon electrocatalysts. Experimental data suggest that the edge graphitic nitrogen sites played a crucial role in the ORR process. The three-dimensional interconnected pores provided a high density of active sites for the ORR and facilitated the efficient transport of electrons. These unique properties make the carbon sheets a promising candidate for highly efficient air cathodes in rechargeable Zn-air batteries.

Isomers of n-Type Poly(thiophene-alt-co-thiazole) for Organic Thermoelectrics.

n-Type polythiophene represents a promising category of n-type polymer thermoelectric materials known for their straightforward structure and scalable synthesis. However, n-type polythiophene often suffers from a twisted backbone and poor stacking property when introducing high-density electron-withdrawing groups for a lower lowest unoccupied molecular orbital (LUMO) level, which is considered to be beneficial for n-doping efficiency. Herein, we developed two isomers of polythiophene derivatives, PTTz1 and PTTz2, by inserting thiazole units into the polythiophene backbone composed of thieno[3,4-c]pyrrole-4,6-dione (TPD) and thiophene-3,4-dicarbonitrile (2CNT). Although PTTz1 and PTTz2 share a similar polymer skeleton, they differ in thiazole configuration, with the nitrogen atoms of the thiazole units oriented toward TPD and 2CNT, respectively. The insertion of thiazole units significantly planarizes the polythiophene backbone while largely preserving low LUMO levels. Notably, PTTz2 exhibits a more coplanar backbone and closer π-stacking compared to PTTz1, resulting in a greatly enhanced electron mobility. Both PTTz1 and PTTz2 can be easily n-doped due to their deep LUMO levels. PTTz2 demonstrates superior thermoelectric performance, with an electrical conductivity of 50.3 S cm-1 and a power factor of 23.8 µW m-1 K-2, which is approximately double that of PTTz1. This study highlights the impact of the thiazole unit on n-type polythiophene derivatives and provides valuable guidelines for the design of high-performance n-type polymer thermoelectric materials.

n-Type Doping Effect of Anthracene-Based Cationic Dyes in Organic Electronics.

n-Type doping for improving the electrical characteristics and air stability of n-type organic semiconductors (OSCs) is important for realizing advanced future electronics. Herein, we report a selection method for an effective n-type dopant with an optimized structure and thickness based on anthracene cationic dyes with high miscibility induced by a molecular structure similar to that of OSCs. Among the doped OSCs evaluated, rhodamine B (RhoB)-doped OSC exhibits the highest density, a smallest roughness of 2.69 nm, a phase deviation of 0.85° according to atomic force microscopy measurements, and the highest electron mobility (µ), showing its high miscibility. Surface doping of RhoB affords the lowest contact resistance of 2.01 × 105 Ω cm compared to bulk and contact doping, resulting in an effective doping structure. The RhoB-doped OSC retains 81.63% of the original µ value of 6.13 × 10-2 cm2 V-1 s-1 after 15 days, whereas pristine OSC shows a lower µ of 2.33 × 10-2 cm2 V-1 s-1 and maintains only 4.41% of the original value after 15 days. Our findings demonstrate that this methodology is effective for the selection of a high-performance n-type dopant for OSCs toward the development of high-performance and air-stable n-type organic electronics.

Tuning (Photo)Electronic Properties of an Electron Deficient Porous Polymer via n-Doping with Tetrathiafulvalene.

Charge-transfer complex formation within the pores of porous polymers is an efficient way to tune their electronical properties. Introduction of electron accepting guests to the electron donating hosts to conduct their p-doping is intensively studied in this context. However, the vice versa scenario, n-doping by treating the electron deficient (i.e., n-type) porous polymers with electron donating dopants, is rare. In this work, synthesis of an n-type phenazine based conjugated microporous polymer and its exposure to strong electron donating tetrathiafulvalene (TTF) dopants are presented. The fundamental physical characterizations (e.g., elemental analysis, gas sorption) showed that the vacuum impregnation technique is a good approach to load the guest molecules inside the pores. Moreover, the formation of charge-transfer complexes between the phenazine building blocks of the polymeric network and TTF dopants are confirmed via spectral techniques such Fourier transform infra-red, UV-vis, steady-state/time-resolved photoluminescence, and transient absorbance spectroscopies. Effect of the doping to the electronical properties is monitored by employing photoelectrochemical measurements, which showed lower charge-transfer resistivity and nearly doubled photocurrents after the doping. The study is, therefore, an important advancement for the applicability of (n-type) porous polymeric materials in the field of photo(electro)catalysis and organic electronics.

Selective production of high-value fuel via catalytic upgrading of bio-oil over nitrogen-doped carbon-alumina hybrid supported cobalt catalysts.

Bio-oil derived from biomass fast pyrolysis can be upgraded to gasoline and diesel alternatives by catalytic hydrodeoxygenation (HDO). Here, the novel nitrogen-doped carbon-alumina hybrid supported cobalt (Co/NCAn, n = 1, 2.5, 5) catalyst is established by a coagulation bath technique. The optimized Co/NCA2.5 catalyst presented 100 % conversion of guaiacol, high selectivity to cyclohexane (93.6 %), and extremely high deoxygenation degree (97.3 %), respectively. Therein, the formation of cyclohexanol was facilitated by stronger binding energy and greater charge transfer between Co and NC which was unraveled by density functional theory calculations. In addition, the appropriate amount of Lewis acid sites enhanced the cleavage of the C-O bond in cyclohexanol, finally resulting in a remarkable selectivity for cyclohexane. Finally, the Co/NCA2.5 catalyst also exhibited excellent selectivity (93.1 %) for high heating value hydrocarbon fuel in crude bio-oil HDO. This work provides a theoretical basis on N dopants collaborating alumina hybrid catalysts for efficient HDO reaction.

Heteroatom doped biochar-aluminosilicate composite as a green alternative for the removal of hazardous dyes: Functional characterization and modeling studies.

In this work, a novel nitrogen-doped biochar bentonite composite was synthesized by a single-pot co-pyrolysis method. Batch studies were conducted to evaluate the performance of the developed composite in eliminating synthetic dyes from the aqueous matrix. Energy dispersive X-ray spectroscopy analysis and field emission scanning electron microscopy imaging confirmed the N doping and bentonite impregnation into biochar. X-ray photoelectron spectroscopy analysis revealed that the N atoms were doped interstitially into the carbon matrix of biochar in the form of pyridinic and pyrrolic nitrogen. Simultaneous heteroatom doping and bentonite impregnation reduced the specific surface area to 41.721 m2 g-1 but improved the adsorption capacity of biochar for dye adsorption. Further experimental studies depicted that simultaneous bentonite impregnation and N doping into the biochar matrix is beneficial for direct blue-6 (DB-6) and methylene blue (MB) removal and maximum adsorption capacities of 53.17 mg. g-1 and 41.33 mg. g-1 were obtained for MB and DB-6, respectively, at varying conditions. Adsorption energetics of the dyes with the developed composite portrayed the spontaneity of the process through negative ΔG values. The Langmuir and Freundlich isotherm models fitted the best for MB and DB-6 adsorption. The monolayer adsorption capacity and favourability factor for MB and DB-6 adsorption were calculated to be 54.15 mg. g-1 and 0.217, respectively from the best-fitted isotherms. Based on density functional theory calculations and spectroscopic studies, major interactions governing the adsorption were predicted to be charge-based interactions, π-π interactions, H-bonding, and Lewis acid-base interactions.