Nature provides an almost limitless supply of sources that inspire scientists to develop new materials with novel applications and less of an environmental impact. Recently, much attention has been ...focused on preparing natural‐product‐derived carbon dots (NCDs), because natural products have several advantages. First, natural products are renewable and have good biocompatibility. Second, natural products contain heteroatoms, which facilitate the fabrication of heteroatom‐doped NCDs without the addition of an external heteroatom source. Finally, some natural products can be used to prepare NCDs in ways that are very green and simple relative to traditional methods for the preparation of carbon dots from man‐made carbon sources. NCDs have shown tremendous potential in many fields, including biosensing, bioimaging, optoelectronics, and photocatalysis. This Review addresses recent progress in the synthesis, properties, and applications of NCDs. The challenges and future direction of research on NCD‐based materials in this booming field are also discussed.
On the dot: In this Review, methods for the preparation of natural‐product‐derived carbon dots (NCDs) are summarized. Then, the physical and optical properties of the NCDs are outlined, and finally, several applications of NCDs are noted, including their use in sensors, bioimaging, and solar cells and their use as catalysts.
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•Dye loaded MnO2 and chlorine intercalated g-C3N4 coupled nanocomposites were successfully prepared.•The composite showed enhanced visible light activities for the degradation of ...phenol and 2,4-chlorophenol.•The intercalated chlorine and coupled MnO2 plays important role in charge separation.•The enhanced activities are attributed to enhanced charge separation and conductivity and extended optical absorption.
It is very important to improve the photocatalytic activities of g-C3N4 as a metal free potential photocatalyst. Herein, we prepared chlorine intercalated dye loaded porous g-C3N4 coupled MnO2 to degrade highly toxic phenol and 2,4-dichlorophenol pollutants. The optimized nanocomposite degraded respectively 47 and 60% phenol and 2,4-dichlorophenol under visible light in one hour as compared to 7 and 9% degradation activity of bare g-C3N4. These enhanced degradation activities are attributed to the increased internal layer conductivity after the introduction of chlorine as inter-layer electron channels, improved charge separation due to the heterojunction formation when MnO2 is introduced as proper energy platform and extended optical absorption even to 650 nm after loading a proper amount of meso-Tetrakis(3,5-dihydroxyphenyl)N-confused porphyrin dye as visible light absorber as confirmed from photoluminescence spectra, amount of produced hydroxyl radicals and photoelectrochemical measurements. From trapping experiments, it has been confirmed that hydroxyl radicals are the major species responsible for the degradation of 2,4-DCP.
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► Carbon spheres with controllable sizes, good morphologies, and large numbers of oxygen-containing functional groups were prepared by hydrothermal approach. ► The sizes and surface ...morphologies of carbon spheres are controlled by the concentration of glucose solution, duration, reaction temperature, and second hydrothermal carbonization. ► The obtained carbon spheres as positive candidates for porous functional materials were activated by KOH. After activation, spherical carbon materials with perfect spherical shapes and developed structures were prepared.
Carbon spheres (CSs) with controllable sizes and rich in oxygen-containing groups were fabricated using a simple hydrothermal treatment of glucose. The effects of the hydrothermal parameters, including the concentration of glucose, reaction temperature, duration, and the second hydrothermal treatment were investigated. The obtained CSs were then activated using KOH for the eventual preparation of porous carbon spheres. A scanning electron microscope was used to characterize the morphology and size of the CSs. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to analyze the functional surface groups. N
2 adsorption–desorption isotherms were used to analyze the porous structure of the CS. The results revealed that the morphologies and size distribution of the CSs can be controlled by adjusting the experimental parameters. A hydrothermal temperature between 180 and 190
°C over 4–5
h was suitable for CS formation. Under these conditions, the size of the CS increased with the concentration of glucose. Mono-dispersed CSs with good morphologies and large numbers of oxygen-containing functional groups (primarily –OH and C
O) can be obtained using a 0.3
mol/L glucose solution that is hydrothermally treated at 190
°C for 4
h. The resulting CSs sizes were about 350
nm in diameter. After a second hydrothermal treatment, the sizes of CSs grew nearly 250
nm without damage to its morphology or broadening of their size distribution. Porous CSs with perfectly spherical shapes and fully developed structures (
S
BET
=
1282.8
m
2/g,
V
micro
=
0.44
cm
3/g) could then be obtained via KOH activation.
► Nanocrystalline cellulose was prepared by purely physical method of ultrasonication. ► Nanocrystalline cellulose was applied in reinforcing poly(vinyl alcohol) composites. ► Elaborate the role of ...ultrasonication in nanocrystalline cellulose preparation.
Rod-shaped nanocrystalline cellulose (NCC) was prepared from microcrystalline cellulose (MCC) using the purely physical method of high-intensity ultrasonication. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction was used for the characterization of the morphology and crystal structure of the material. The thermal properties were investigated using thermogravimetric analysis. The reinforcement capabilities of the obtained NCC were investigated by adding it to poly(vinyl alcohol) (PVA) via the solution casting method. The results revealed that the prepared NCC had a rod-shaped structure, with diameters between 10 and 20
nm and lengths between 50 and 250
nm. X-ray diffraction results indicated that the NCC had the cellulose I crystal structure similar to that of MCC. The crystallinity of the NCC decreased with increasing ultrasonication time. The ultrasonic effect was non-selective, which means it can remove amorphous cellulose and crystalline cellulose. Because of the nanoscale size and large number of free-end chains, the NCC degraded at a slightly lower temperature, which resulted in increased char residue (9.6–16.1%), compared with that of the MCC (6.2%). The storage modulus of the nanocomposite films were significantly improved compared with that of pure PVA films. The modulus of PVA with 8
wt.% NCC was 2.40× larger than that of pure PVA.
S-doped TiO2 photocatalyst with high visible light activity was prepared by acid catalyzed hydrolysis method using thiourea (TU) as sulfur source. The catalyst was characterized by DRS, XPS, XRD, ...FTIR, SEM and N2 adsorption. It was found that cation S6+ was homogeneously incorporated into the bulk phase of TiO2 and substitutes for some of the lattice titanium (Ti4+). Doped S can form a new band above the valence band and narrow the band-gap of the photocatalyst, giving rise to a second absorption edge in the visible light region. The activity of the catalyst was examined by photodegradation of phenol in aqueous solution under both artificial visible light and solar light irradiation. The activity of catalyst was found to be dependent on the doping amount of S and the maximum activity was observed when the catalyst was obtained by calcinated at 600 degrees C with the mass ratio of TU/TiO2=1. Too much of new-generated band-gap structures due to higher S-doping could act as recombination centers for electron-hole pairs. Catalyst with optimum S-doping exhibited the highest activity under both artificial light and solar irradiation for phenol degradation. In addition, doped S also beneficial for the better dispersion, large S(BET) and phase transformation retardation of TiO2.
•ZnO coupled g-C3N4 nanocomposites were successfully prepared.•Amorphous Al-O channels were introduced between the nanocomposites to improve charge transfer.•Au nanoparticles were loaded on the ...surface of the prepared nanocomposites to extend light absorption.•The nanocomposites imparted improved photoactivities as compared to bare samples for pollutants degradation.•The improved activities are due to the extended light absorption and enhanced charge transfer in the nanocomposites.
The increasing environmental pollution has triggered severe threat to life in the recent years. As for this, a novel amorphous aluminum oxide bridged ZnO and g-C3N4 nanocomposites were fabricated and loaded with gold nanoparticles. The samples were characterized and applied for the photodegradation of different chlorophenols under visible light irradiation. The optimized nanophotocatalyst showed extended photoactivities and 39, 45 and 58 % of 2-chlorophenol, 2,4-dichlrophenol and 2,4,6-trichlorphenol were respectively removed in one hour under visible light irradiation. These upgraded activities are attributed to the extended optical absorption due to the presence of Au nanoparticles and much better charge separation by inducting surface plasmon resonance excited electrons through Al-O bridged channels to the conduction bands of g-C3N4 and ZnO. The large surface area of the amorphous Al-O helps to adsorb and degrade more pollutant particles. The different photoactivities of the chlorophenols are attributed to the different charge densities in the aromatic ring in the presence of different number of chloro-groups. The major oxidizing agents in the photodegradation of different chlorophenols were different suggesting the different behaviour of these compounds toward oxidation. We hope that this study would provide an easy approach to deal with environmental pollution in future.
Wound dressings with high flexibility, mechanical strength, and porosity have received increasing attention. Herein, nanocomposite sponges of sodium alginate/graphene oxide (GO)/polyvinyl alcohol ...were prepared by a freeze-thawing cyclic process and freeze-dried molding. The properties of the sponges were investigated including morphology, mechanical properties, swelling, water vapor permeability, in vitro norfloxacin (NFX) release, antibacterial property, and biocompatibility as well as in vivo wound healing in a mouse model. A GO concentration of 1 wt% resulted in the sponges with a homogeneously porous and interconnected network structure, which exhibited suitable water absorption, breathability, and mechanical properties. Hemolysis tests indicated that the prepared sponges were non-hemolytic material. The CCK-8 assay demonstrated that the presence of an appropriate amount of GO could promote the cell proliferation. The sponges displayed excellent bioavailability of NFX, with a sustained release behavior and a strong inhibitory effect against both Escherichia coli and Staphylococcus aureus. The in vivo evaluations demonstrated that the sponges enhanced wound healing. Therefore, these novel nanocomposite sponges are promising candidates for wound healing applications.
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•The sponges (SPG) were prepared by a freeze-thawing method and freeze-dried technology.•The SPG exhibited uniform pore structure and excellent flexibility.•Graphene oxide improved biocompatibility of the SPG.•The SPG could be used as an excellent wound dressing for biomedical field.
A fluorescent probe for the determination of nitrite (NO2−) was fabricated by using green fluorescent nitrogen doped carbon dots (NCDs). The NCDs were synthesized via a one-pot hydrothermal ...carbonization of citric acid in the presence of p-phenylenediamine as the nitrogen source. The N content of the NCDs was high to 17.09% and consisted of a variety of functional groups on the NCDs surface, including sp2-hybridized CN, porphyrin C–N–C and amino N in N-(C) 3 or H–N-(C) 2 et al. N atoms were also doped within the framework of the NCDs. The almost monodisperse NCDs (average particle diameter = 3.67 nm) exhibited green photoluminescence (PL) with excitation/emission maxima of 360/505 nm. The PL of the NCDs was dependent on both excitation wavelength and solution pH. The NCDs showed a strong PL quenching response to NO2− under acidic conditions (pH = 2.5). The PL intensity of the NCDs was inversely proportional to the concentration of NO2− between 0.02 and 40 μM (R2 = 0.992), with a detection limit of 21.2 nM. The practical use of the nanoprobe for NO2− determination in food samples was also demonstrated, successfully. NCD-nitroso compounds formed because of reaction between the abundant amide groups on the surface of NCDs with the NO2−, which caused an inner filter effect and static PL quenching. Importantly, the NCDs had low cellular toxicity and were successfully used as a multicolor cellular imaging agent for Hepg2 cells.
One-pot hydrothermal synthesis of nitrogen doped carbon dots that emit green fluorescence and their applications for nitrite detection based on inner filter effect and static quenching and multicolor cellular imaging. Display omitted
•Nitrogen doped carbon dots (NCDs) were prepared by hydrothermal treatment of citric acid and p-phenylenediamine.•The NCDs showed selective and sensitive nitrite determination property.•The NCDs were successfully used to detect the content of nitrite in food samples.•The NCDs possessed high efficiency for multicolor cellular imaging.
Abstract
Sustainable afterglow room temperature phosphorescence (RTP) materials, especially afterglow RTP structural materials, are crucial but remain difficult to achieve. Here, an oxidation ...strategy is developed to convert lignin to afterglow materials with a lifetime of ~ 408 ms. Specifically, lignin is oxidized to give aromatic chromophores and fatty acids using H
2
O
2
. The aromatic chromophores are locked by a fatty acid-based matrix by hydrogen bonds, triggering enhanced spin orbit coupling and long afterglow emission. More interestingly, motivated by this discovery, an auto fabrication line is built to convert wood (natural structural materials) to wood with afterglow RTP emission (RTP wood) via in situ oxidation of naturally-occurring lignin located in the wood cell walls to oxidized lignin (OL). The as-prepared RTP wood exhibits great potential for the construction of sustainable afterglow furniture. With this research we provide a new strategy to promote the sustainability of afterglow RTP materials and structural materials.
Carbon spheres (CSs) with regular shapes (Ø 300–1200 nm) and numerous oxygen groups (–OH, C6H5–C=O, and C=O) were prepared by a simple glucose hydrothermal process. CSs were studied by x-ray powder ...diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, x-ray photoelectron spectra, and elemental analysis. Their size was directly proportional to temperature and glucose concentration. Their shape could be controlled by temperature and reaction time. To prepare CSs (Ø 300–800 nm) with regular shapes and smooth surfaces, temperature and reaction time in the range of 180–230 °C and 3–4 h, respectively, were optimal. The chemical properties of the CSs were affected by temperature. A phase transformation from amorphous to turbostratic structure took place at T > 230 °C. The number of oxygen groups decreased as the temperature increased, and T ≤ 230 °C were optimal to prepare oxygen-rich CSs. Comparison of oxygen contents and O/C ratios indicated a further carbonization, and the degree was directly related to temperature. A possible formation mechanism for the CSs is proposed.
