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•Porous self-templated N-doped carbon aerogel was prepared from banana flesh.•The specific surface area and pore distribution could be controlled by CO2 activation time.•The specific ...surface area and porous volume reached 1414.97 m2 g−1 and 0.746 cm3 g−1.•The specific capacitance reached 178.9 F g−1 at a current density of 1 A g−1.
N-doped porous carbon materials derived from eco-friendly, renewable and economical biomass resources have attracted interest for applications in supercapacitors due to their porous structures and physicochemical properties. However, controlling the pore structure remains difficult and there is a need to simplify the N-doping process. Herein, we report a porous self-templated N-doped carbon aerogel derived from banana flesh obtained through one-step carbonization followed by CO2 activation. The specific surface area and pore distribution of the carbon aerogels could be controlled by changing the CO2 activation time. A specific surface area and total pore volume of 1414.97 m2 g−1 and 0.746 cm3 g−1 were achieved. The results show that raw banana flesh provides the necessary N content, which only slightly decreased following activation from 3.25% to 2.25%. On the surface of the carbon aerogel we detected pyrrolic N and pyridinic N groups, which are known to contribute to pseudo-capacitance. Furthermore, the specific capacitance of the prepared carbon aerogel reached 178.9 F g−1 at a current density of 1 A g−1. The simple preparation method and excellent electrochemical performance show great potential for application of our porous self-templated N-doped carbon aerogel as an electrode in high performance supercapacitors.
Optimizing the structure of electrodes to decrease electrolyte transport resistance is essential for high electrochemical performance in supercapacitors. Here, we prepare ultralight carbon aerogels ...containing tubular structures and N-containing sandwich-like walls based on the natural structure of kapok fibers, by in-situ polymerization of pyrrole and carbonization. The resulting carbon aerogels are composed of microtubes with a diameter of 10 μm, an ultralow density of 6 mg cm−3, and also N-containing sandwich-like walls composed of pyridinic nitrogen, pyrrolic/pyridine nitrogen, and quaternary nitrogen/oxidized nitrogen. The unique tubular structure promotes transport of electrolyte, yielding higher electrochemical performance. Consequently, the tubular structure produces a 72 F g−1 increase in the capacitance compared with that of a cattail carbon aerogel without a tubular structure. The N-containing sandwich-like walls provide more active sites, greater pseudocapacitance, and increase the thickness of the microtube to protect the tubular structures from damage during carbonization. Specifically, the optimal sample has a specific capacitance of 274 F g−1 at a current density of 1 A g−1 with an energy density of 8.51 Wh kg−1, a superior rate capability, and excellent cycling stability with a capacitance retention of 97.7% after 4000 cycles.
•A novel carbon aerogel for supercapacitor electrodes is reported.•Tubular structure produces a 72 F g−1 increase in the specific capacitance.•The N-walls provide more active sites and protect the tubular structures from damage.•Carbon aerogel theoretically affords a maximized specific capacitance of 274 F g−1.
We prepared carbon aerogel/RuO2 composites with three-dimensional microtubes based on renewable natural kapok fibers by combining a NaClO2 pretreatment, CO2 activation and loading of RuO2 ...nanoparticles. The electrochemical performance of the material was optimized by tuning the carbonization temperature. The composite calcined at 800 °C for 2 h and activated by CO2 for 30 min possessed an integrated tubular structure and moderate pore size distribution. This composite material also showed highest specific capacitance of 433 F g−1 at a current density of 1 A g−1 with a capacitance retention of 91.5% for 2000 cycles in 3 M KOH solution in three-electrode system. The maximum energy density was 8.92 Wh kg−1 at 558.12 W kg−1 at a cell voltage of 1 V in 3.0 M KOH aqueous electrolyte in a symmetric device. We attribute the reversible capacity of the obtained bio-derived carbon aerogel/RuO2 composites to the high-speed flow of the electrolyte in the unique hollow tubular structure, the appropriate pore size distribution and the synergetic effect of the high capacitance of RuO2 and good stability of the carbon material.
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The introduction of a built-in electric field by using ferroelectric materials is an efficient way to modulate the carrier generation and transportation behavior of photocatalysts. Here, we propose a ...hydrothermal-synthesized Ag2O/BaTiO3 heterostructure composite, whose photocatalytic performance can be largely enhanced by a four-way coupling effect among piezoelectricity, pyroelectricity, semiconductor and photoexcitation, referred as the piezo/pyro-phototronic synergistic effect. The photoelectrochemical (PEC) test of Ag2O/BaTiO3 shows a high photocurrent density of 3.48 mA/cm2 at 1.5 VSCE, which is 1.5 and 1.3 times as high as that of pristine BaTiO3 and Ag2O, respectively, and the transient photocurrent density of the composite at 0.5 VSCE is 20 times higher than that of the pure BaTiO3. Under varying temperature field and ultrasonic excitation condition, the photocatalytic degradation efficiency of the Ag2O/BaTiO3 composite is enhanced greatly when compared to that under only light illumination condition. This enhancement can be attributed to the attraction and release process of photogenerated carriers during the varying temperature field and ultrasonic excitation cycling. These results indicate that the ferroelectric heterostructure composites can act as a promising photocatalyst in wastewater treatment field under different environmental conditions.
Photocatalytic performance of Ag2O/BaTiO3 can be enhanced by a four-way coupling effect among piezoelectricity, pyroelectricity, semiconductor and photoexcitation. Display omitted
•Micro-sized Ag2O/BaTiO3 heterostructure composite was obtained by chemical precipitation synthesis.•The piezo/pyro-phototronic synergistic effect improved the catalytic performance of the BaTiO3-based materials efficiently.•The attraction and release process of photogenerated carriers contributed to enhancement of the catalytic activity.•This work provides promising methods for utilizing ferroelectricity-driven catalysts in various conditions.
3D flower-like g-C
3
N
4
/TiO
2
composite microspheres (FCTCMs) were prepared by a simple solvothermal method and combined with a thermal treatment method. By controlling the amount of urea mixed ...with the 3D flower-like structure of TiO
2
microspheres (FTMs), FCTCMs with different g-C
3
N
4
loadings were prepared. Urea has two functions in the preparation process: one decomposes into gaseous substances during heat treatment at 550 °C to form g-C
3
N
4
in the gap between nanosheets of TiO
2
microspheres; and the other effectively protects the 3D flower-like structure of TiO
2
microspheres (FTMs). The results of XRD, TEM, FT-IR, SEM and XPS indicate that g-C
3
N
4
and TiO
2
were connected in a surface-to-surface manner. Its photocatalytic performance was characterized by the degradation of methyl orange and methylene blue solution. The results show that the photocatalytic performance of FCTCMs under visible light was as twice as FTMs. The transient photocurrent responses and EIS results also indicate the increase in the number of photogenerated electron–hole pairs produced by FCTCMs.
A carbon aerogel with porous structure was synthesized from bleached softwood kraft pulp (BSKP) via eco-friendly freezing-drying and carbonization steps. The obtained carbon aerogel exhibited a low ...density of 25.5 mg cm−3, high hydrophobicity with a water contact angle of 139.7° and good compressive properties. When used as an absorbent, the carbon aerogel could absorb 14 to 26 times its own weight in organic solvent and oil. Furthermore, the aerogel could be easily recovered and regenerated through burning, pressure recycling, and squeezing, and a high adsorption efficiency was maintained over a number of cycles. The use of biomass as a raw material, together with the excellent hydrophobicity and recyclability, make this carbon aerogel a suitable adsorbent for a variety of practical separation requirements.
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•Compressive carbon aerogels were successfully prepared from bleached softwood kraft pulp.•The carbon aerogels exhibited lightweight and hydrophobicity properties.•The carbon aerogels had high adsorption efficiency towards oil and organic liquids.•The carbon aerogels could be easily recovered and regenerate by burning, pressure recycling or squeezing.
A thick electrode with a high mass loading is one of the promising structural designs to improve the energy density of supercapacitors. However, the slow ion transport and sluggish charge kinetics ...caused by the increased electrode thickness are still major challenges toward high-performance energy storage devices. Herein, an all-cellulose-based carbon aerogel asymmetric supercapacitor (ACAS) device is successfully assembled by using a thin cellulose aerogel as a separator and cellulose carbon aerogel and RuO2/cellulose carbon aerogel as the ultrathick anode and cathode, respectively. Benefiting from the 3D hierarchical porous percolation network structure, both cellulose aerogel and carbon aerogel provide continuous pathways that are beneficial to the electrolyte penetration, thereby facilitating the rapid transport of ions and electrons. As a result, the assembled ACAS device achieves an ultrathickness (up to ∼2.3 mm), including the anode (up to 1.2 mm) and the cathode (up to 1.0 mm). Consequently, the ACAS device possesses a high volumetric capacitance of 6.18 F cm–3 and a high energy density (3.4 Wh L–1) with a maximum power density of 23 W L–1, which surpass values for the most-reported cellulose-based asymmetric supercapacitor. This work presents a design concept using renewable cellulose materials for the separator and thick electrodes in supercapacitors, which further facilitates the future application of sustainable and high-density energy storage devices.
•BiOCl nanosheets are immobilized by calcium alginate hydrogel through a simple crosslinking process.•BOC-CA hydrogel beads can float on the water surface.•The hydrogel beads show enhanced ...photocatalytic effect during the cycled ultraviolet irradiated degradation process.•The porous structure of the beads provides channels for the transport of ultraviolet induced OVs of BiOCl photocatalysts.•The hydrogel beads have excellent recovery rate and high photocatalytic efficiency over 24 degradation cycles.
Photo-induced oxygen vacancies (OVs) are widely introduced as active sites in BiOCl to improve photocatalytic performance. Herein, we propose a strategy to take advantage of OVs of BiOCl nanosheets, which are immobilized in the network of water-rich calcium alginate (CA) hydrogel beads. By modulating the porous structure of the hydrogel, the OVs irradiated by UV light on the surface of BiOCl can be rapidly diffused to the deep inner of the beads, and then they disappear after the beads are immersed into the water for hours, which further enables the regeneration of even better BiOCl-CA beads. This reactive cyclic channel in a water-rich environment improves the transport of photogenerated carriers and achieves excellent cyclic photocatalytic performance. This work not only improves the recovery efficiency of photocatalytic materials but also puts forward a new system of BiOCl based hydrogel beads that can be used repeatedly in wastewater treatment.
In this paper, the center hollow ZnO and TiO₂ nanotubes arrays were synthesized by chemical etching ZnO nanorods and sol-gel process assisted by ZnO nanorods templates, respectively. And the process ...concerning the formation of nanotubes was analyzed. Furthermore, as an application of the ZnO and TiO₂ nanotubes, dye-sensitized solar cells (DSSCs) based on them were successfully fabricated and the cell performances were characterized. The efficiency of DSSCs based on ZnO and TiO₂ nanotubes was 1.2% and 2.1%, respectively.
The photoelectrochemical (PEC) properties of BiVO4 are limited by the poor separation and transfer of photogenerated electron-hole pairs and easy recombination. Hence, we designed the ternary ...composite photoelectrode through the embedding of Ag in BiVO4/Cu2O p-n heterojunction and evaluated its PEC performance by degrading Rhodamine B (RhB) for the first time. As expected, the BiVO4/Ag/Cu2O photoelectrode among four of the BiVO4-based photoelectrodes achieved the highest photocurrent density (3.36 mA/cm2), which is about 8.6 times than pure BiVO4 photoelectrode (0.39 mA/cm2). Additionally, the resulting fabricated BiVO4/Ag/Cu2O composite as the working photoelectrode performs a highly efficient degradation of RhB molecules in water solution through PEC process (86% within 120 min), which is 2.8 times than pure BiVO4. It is noteworthy that the generation of built-in potential at the interface of BiVO4/Cu2O p-n heterojunction plays a crucial role in the carriers' separation efficiency. Meanwhile, the surface plasmon resonance (SPR) of Ag nanoparticles (NPs) displays a magnificent role in improving the PEC performance by hot-electrons injection (HET) and plasma resonance energy transfer (PRET) to metal semiconductors. This research may inspire a new design for the synergistic effect of p-n heterojunction and plasmon to enhance PEC properties of pollution degradation.
The ternary composite photoelectrode through the embedding of Ag in BiVO4/Cu2O p-n heterojunction was designed and evaluated its PEC performance by degrading Rhodamine B. The improved PEC performance of BiVO4/Ag/Cu2O due to the generation of built-in potential at the interface of BiVO4/Cu2O p-n heterojunction and the surface plasmon resonance of Ag. Display omitted
