The application of porous carbon microspheres derived from pure biomass in supercapacitors is restricted due to their limited reactive groups. MXene owns a combination of redox Faradic surface with ...good metallic conductivity and hydrophilicity, which assists to obtain high pseudocapacitance and energy density. Herein, Ti3C2Tx MXene was introduced to chitosan-based porous carbon microsphere (CPCM) to fabricated sandwich-like structure (CPCM/MXene) through electrostatic interaction. The Ti3C2Tx protected the spherical structure of CPCM. Meanwhile, CPCM hindered the reaggregation of Ti3C2Tx by inserting in the Ti3C2Tx layers, promoting the electrolyte migration kinetics. The synergistic effect endowed CPCM/MXene high specific capacitance of 362 F/g at current density of 0.5 A/g and acceptable cycling stability with 93.87% capacitance retention at a high current density of 10 A/g after 10,000 cycles. Furthermore, CPCM/MXene displayed a high energy density of 27.8 W/(h•kg) at 500.0 W/kg of power density. These satisfactory performances prove that combining Ti3C2Tx MXene nanosheets with porous carbon microspheres is a considering method to construct a new generation electrode material of supercapacitor.
For the high-valued utilization of hemicelluloses and for realizing the controllable synthesis of NPs, this paper's aim is to combine xylan, chitosan and nanometal materials at the same time. In this ...research study, firstly, propargyl xylan was synthesized via nucleophilic substitution reaction between xylan and propargyl bromide in NaOH solution. On the other hand, a tosyl group was introduced onto the 6th position of synthesized quaternized chitosan (QCS), and the azide group replaced the tosyl group to obtain 6-amido-QCS (QCS-N
). The synthesis conditions of the above reactions were optimized. Subsequently, the novel xylan-click-QCS polymer was obtained via click reaction between terminal alkyne groups on the xylan chains and azide groups on QCS. Then, AgNPs and AuNPs were synthesized by adopting the xylan-click-QCS polymer as the reducing and stabilizing agent, and the reaction conditions were optimized to obtain well-dispersed and highly stable nanoparticles. There were two kinds of Ag nanomaterials, with diameters of 10~20 nm and 2~5 nm, respectively, indicating the formation of Ag nanoclusters, except for Ag nanoparticles, in this reaction. The diameter of the synthesized AuNPs was 20~30 nm, which possessed a more uniform size distribution. The Ag nanoclusters with a smaller size (2~5 nm) could inhibit MCF-7 cell proliferation effectively, indicating their application potential in cancer therapy. The study gives a new approach to the high-value utilization of biopolymers.
Fluorescent sensors with single reading are generally subject to unpredictable disturbs from environmental and artificial factors. In order to overcome this barrier of detection reliability, a ...paper-based optical sensor with proportional fluorescence was established and further combined with a smartphone for visual, on-site and quantitative detection of Fe3+, which affects the color, smell and taste of water, and endangers the health of plants and animals. The ratio fluorescent probe was fabricated by rhodamine B and carbon quantum dots derived from xylan. The red fluorescence of rhodamine B was inert to Fe3+, which was referred to as background. And blue emitting carbon quantum dots functioned as signal report units, which would be quenched by Fe3+ and make the fluorescence of the ratio probe change from purple to red. The quantitative detection of Fe3+ was conducted by investigating the RGB value of fluorescent images with a smartphone. With the increase of Fe3+ concentration, the R/B (red/blue) value of the fluorescent paper gradually increased. The linear detection range was 10–180 μM, and the limit of detection was 198.2 nM. The application of ratio fluorescent paper with a smartphone provides a facile method for the rapid detection of ions.
Reduced graphene oxide (rGO) films suffer from low capacitance for inner unreduced oxygen functional groups, restacking of sheets and high contact resistance. Herein, carbon spheres derived from ...renewable xylan were added to graphene oxide with large sheet area to fabricate film by gelation and filtration, followed by in situ reduction for high-performance flexible supercapacitor. rGO film with transverse size about 13 μm showed a good specific capacitance of 967 mF/cm
2
at a scanning rate of 5 mV/s and increased to 1786 mF/cm
2
by in situ reducing its inner part, which generally remained oxidized due to outer hindering from hydrophobic graphene. Then, by hydrothermal carbonization of xylan and activation with KOH, activated carbon sphere (aXCS) was prepared, which had a diameter of 150–200 nm and a specific capacitance of 270 F/g. The aXCS acted as spacer and connector to avoid restacking of graphene sheets and decrease interlayer contact resistance, resulting 94% increase in capacitance performance from rGO film to aXCS/rGO film. Therefore, combined in situ reduction and enhancement through compositing aXCS, the final film (aXCS/rGO-AA) showed a boosted specific capacitance of 755 mF/cm
2
at 1 mA/cm
2
in double electrode system, power density of 22.5–2250 mW/cm
2
, and energy density of 11.88–25.2 mWh/cm
2
. Meanwhile, aXCS/rGO-AA had outstanding cycling stability that its specific capacitance maintained 108.7% after 10,000 cycles of charge–discharge, showing promising potential in wearable and portable electronics.
Graphical abstract
Copper sulfide nanoparticles (CuS NPs) have recently attracted extensive attention in various fields due to their excellent optical and electrical properties. However, CuS NPs are easy to agglomerate ...in their preparation on account of the high surface activity. In this study, uniform dispersion of CuS NPs were fabricated with corn stalk as a template and stabilizer, further CuS@corn stalk/chitin composite hydrogel was obtained by crosslinking with chitin. The results reveal that the CuS NPs were evenly dispersed into the composite hydrogels with a three-dimensional network structure, which were verified by the UV-vis spectrum, XRD, FT-IR spectra and SEM. In addition, the as-prepared composite hydrogel with the traits of peroxidase-like activity can convert H
O
into an extremely oxidative and toxic ·OH, which manifested good effects for photodegradation of RhB and antibacterial against
and
. Hence, the composite hydrogels could be used for photocatalytic treatment and sterilization of wastewater, which provides a new idea for the functional application of CuS NPs.
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A highly sensitive electrochemical sensor was developed through a one-pot green synthesis method for nitrite detection based on the electrochemical technique. Xylan-based carbon ...quantum dots (CQDs) were used as green in situ reducing agent to prepare CQDs capped gold nanoparticles (Au@CQDs). MXene of good electrical conductivity was used as the immobilized matrix to fabricate Au@CQDs-MXene nanocomposites with the advantages of good electrical conductivity and electrocatalysis. An electrochemical sensor for nitrite monitor was obtained by loading the Au@CQDs-MXene on a glassy carbon electrode. The sensor presents high sensitivity, good stability, wide linear range, and excellent selectivity due to the high catalytic activity of AuNPs and CQDs, the large specific surface area of MXene, and exceptional electrical conductivity of AuNPs and MXene. Under the optimal condition, the linear detection range of the sensor was from 1 μM to 3200 μM with a detection limit of 0.078 μM (S/N = 3), which was superior to most reported sensors using differential pulse voltammetry (DPV) method. Furthermore, this sensor was successfully applied to detect nitrite in tap water and salted vegetables with satisfactory recoveries. This modified electrocatalytic sensor shows a new pathway to fabricate nitrite detection sensor with feasibility for practical application.
Carbon spheres have emerged as a promising material in energy storage, but preparing carbon spheres from raw biomass in a cost-effective way still remains as a great challenge. Here, for the first ...time, we directly transformed bagasse to nitrogen-doped carbon sphere through hydrothermal carbonization. Before carbonization, bagasse and graphene oxide was fully dissolved in NaOH/urea aqueous system. In the process of hydrothermal carbonization, graphene oxide acted as template and accelerant, and urea was acted as nitrogen source. The diameter of the prepared carbon spheres was about 200 nm, which were distributed on the graphene sheets and acted as spacer to prevent aggregation of graphene sheets. The nitrogen-doped bagasse-based carbon spheres/reduced graphene oxide composite exhibited 3D interconnected structures with high electrical conductivity, large specific surface areas, and active nitrogen-doped sites. Applied as electrode material for supercapacitor, the composite showed a higher specific capacitance, rate capability and better cycling stability compared to some traditional carbon spheres, active carbon and reduced graphene oxide. The specific capacitance is 226.8 F g−1 at the current density of 0.5 A g−1, which still retains 83.9% after 10,000 cycles. After 10,000 cycles, the composite maintains 83.9% of the initial capacitance. Furthermore, the possible formation mechanism of nitrogen-doped bagasse-based carbon spheres/reduced graphene oxide composite was discussed. This study achieved full solubility of bagasse in NaOH/urea aqueous system, not only providing a promising way to convert lignocellulosic raw biomass into carbon spheres directly, but also proposing an emerging strategy for synthesizing high capacitive and stable biomass-based electrode material.
Bagasse was transformed to nitrogen-doped carbon spheres and used as supercapacitor electrodes, which is the high-value utilization of renewable resources.Illustration for the preparation of bagasse-based carbon spheres/RGO composite, and application as supercapacitor electrodes. Display omitted
•Carbon sphere was prepared in a direct and cost-effective way.•Raw biomass like bagasse was chose as carbon precursor.•Bagasse was firstly dissolved in NaOH/urea solution to form homogenous mixture.•Graphene oxide was used as template and accelerant.•Show better performance than those of many reported carbon spheres and porous carbon materials.
Concern about food safety triggers demand on rapid, accurate and on-site detection of foodborne pathogens. Among various fluorescent probes for detection, carbon dots (CDs) prepared by carbonization ...of carbon-rich raw materials show extraordinary performance for their excellent and tailorable photoluminescence property, as well as their facilely gained specificity by surface customization and modification. CDs-based fluorescent probes play a crucial role in many pathogenic bacteria sensing systems. In addition, microfluidic technology with characteristics of portability and functional integration is expected to combine with CDs-based fluorescent probes for point-of-care testing (POCT), which can further enhance the detection property of CDs-based fluorescent probes. Here, this paper reviews CDs-based bacterial detection methods and systems, including the structural modulation of fluorescent probes and pathogenic bacteria detection mechanisms, and describes the potential of combining CDs with microfluidic technology, providing reference for the development of novel rapid detection technology for pathogenic bacteria in food.
•Applications of CDs in detection of foodborne pathogen are systematically reviewed.•Fabrication and post-modification of CDs to construct fluorescent sensors are included.•Mechanisms of recognition and response towards pathogenic bacteria are summarized.•Potential combination of CDs with microfluidic systems is elaborated.
a high-sensitivity electrochemical sensor based on green synthesized Ag@CQDs-rGO nanocomposite has been developed to offer a new platform for the enhanced selectivity of dopamine detection.
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•Xylan was carbonized to prepare carbon quantum dots (CQDs)•AgNPs and rGO were greenly synthesized by CQDs as reducing agent and stabilizer.•An electrochemical sensor with Ag@CQDs-rGO nanocomposite was fabricated.•The detection range was from 0.1 to 300 μM and the limit of detection was 1.59 nM.•The sensor showed excellent DA detection capacity in real samples.
Although polysaccharide-based carbon quantum dots (CQDs) are widely used in the field of detection, most of the CQDs-based sensors only take advantage of their optical properties. In this work, considering the selectivity to target substance and reducibility of xylan-based CQDs, a high-sensitive sensor based on greenly synthesized CQDs-based nanocomposite was fabricated for dopamine (DA) detection. First, the CQDs prepared from xylan were used as the reductant and stabilizer to quickly synthesize silver nanoparticles (Ag NPs) and reduced graphene oxide (rGO), and then Ag@CQDs-rGO nanocomposite was obtained and loaded on glassy carbon electrode (GCE) to fabricate electrochemical sensor. The electrochemical sensing of DA is of great significance for studying and treating neurochemical diseases due to its potential feasibility in diagnostics. Under optimal conditions, the linear range for monitoring DA was from 0.1 to 300 μM with a limit of detection of 1.59 nM (S/N = 3). Finally, this sensor was successfully applied to detect DA in dopamine hydrochloride injection and bovine serum solution samples. The proposed strategy may broaden the application of polysaccharide-based CQDs and this sensor may provide a discriminative and sensitive analytical platform for DA clinical diagnostics and drug screening.
Fluorescent sensors with single reading are generally subject to unpredictable disturbs from environmental and artificial factors. In order to overcome this barrier of detection reliability, a ...paper-based optical sensor with proportional fluorescence was established and further combined with a smartphone for visual, on-site and quantitative detection of Fesup.3+, which affects the color, smell and taste of water, and endangers the health of plants and animals. The ratio fluorescent probe was fabricated by rhodamine B and carbon quantum dots derived from xylan. The red fluorescence of rhodamine B was inert to Fesup.3+, which was referred to as background. And blue emitting carbon quantum dots functioned as signal report units, which would be quenched by Fesup.3+ and make the fluorescence of the ratio probe change from purple to red. The quantitative detection of Fesup.3+ was conducted by investigating the RGB value of fluorescent images with a smartphone. With the increase of Fesup.3+ concentration, the R/B (red/blue) value of the fluorescent paper gradually increased. The linear detection range was 10–180 μM, and the limit of detection was 198.2 nM. The application of ratio fluorescent paper with a smartphone provides a facile method for the rapid detection of ions.
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