The development of effective approaches for the preparation of 0D quantum dots (QDs)/2D nanosheets (NSs) heterostructures, which have been proven to be favorable for heterogeneous catalysis, is ...highly desirable but remains a great challenge. Herein, 0D metal oxide nanocrystals–2D ultrathin g‐C3N4 nanosheets (Co3O4/CNNS) heterostructures are synthesized via a facile chemical reaction, followed by annealing in air. Ultrafine Co3O4 QDs (≈2.2–3.2 nm) are uniformly and tightly attached on the surface of g‐C3N4 nanosheets. Detailed characterization reveals that the specially designed unique 0D/2D structure is critical to the high photocatalytic performance for the degradation of tetracycline (TC) via peroxymonosulfate (PMS) activation. The optimal catalyst, namely, Co3O4/CNNS‐1100, exhibits excellent performance and ≈98.7% TC can be degraded under visible light irradiation. Moreover, TC degradation is almost completely insusceptible to several real water samples. Meanwhile, other dye pollutants can also be efficiently degraded by the Co3O4/CNNS‐1100/PMS/vis system. The quenching tests display that that the h+, ∙OH, O2∙−, and SO4∙− are responsible for TC removal. The improved photocatalytic performance can be attributed to the synergistic effect of the photocatalytic‐ and chemical‐processes in the PMS activation. This work gives an insight into the development of multifunctional 0D/2D nanocomposites for further potential applications which are not limited to environmental purification.
Co3O4 quantum dots are strongly coupled with graphitic carbon nitride nanosheets using an in situ growth strategy. Such structures efficiently prevent the aggregation of Co3O4 and permit efficient interfacial electrons transport (ascribed to the large contact area provided by the 0D–2D structure), synchronously the photocatalytic‐ and chemical‐processes, so to render enough active sites to make peroxymonosulfate activation persistent.
Clay minerals have been proposed for the potential retention of the high-level radioactive wastes in deep geological repositories. The retention of uranium (U(VI)) and europium (Eu(III)) onto ...well-characterized sepiolite was elucidated by using microscopic adsorption, spectroscopic techniques and surface complexation modeling. The results of macroscopic adsorption experiments showed that the uptake of U(VI) and Eu(III) onto sepiolite significantly increased with increasing pH 4.0–7.0, whereas the decrease adsorption of U(VI) at pH>7.0 and in the presence of carbonate (10−3mol/L) was attributed to the electrostatic repulsion. The chemical affinity of U(VI) with sepiolite was stronger than that of Eu(III) with sepiolite in terms of batch desorption tests. Based on the EXAFS spectra analysis, the interatomic distances of U–Si at ∼3.16Å was observed in U(VI)/sepiolite systems, which indicated that the inner-sphere surface species were coordinated on SiO4 tetrahedra via bidentate configuration. The U–C shell at ∼2.9Å in the presence of carbonate revealed the U(VI)-carbonate ternary complexes at sepiolite–water interface. The results from the three common surface complexation models (SCMs), including constant-capacitance model (CCM), diffuse-layer model (DLM), and triple-layer model (TLM), can give an excellent fit to the experimental data with the bidentate edge-sharing (E2, >SO2M(n−2)+), bidentate corner-sharing (C2, (>SO)2M(OH)2(n−4)+) and >SOMCO3(n−3)+ inner-sphere surface complexes in ambient environments. However, the second ternary surface complex >SOCO2M(n−1)+ was determined in the presence of carbonate. The findings presented in this study are significant toward the description and predication of fate and transport of radionuclides at the water–mineral interface in the natural environment.
With the development of Internet technology, the volume of data is increasing tremendously. To tackle with large-scale data, more and more applications choose to enlarge the storage capacity of ...users’ terminals with the help of cloud platforms. Before storing data to an untrusted cloud server, some measures should be adopted to guarantee the data security. However, the communication overhead will increase dramatically when users transmit files encrypted by a traditional encryption scheme. In this paper, we address the above problems by proposing a blockchain-based security architecture for distributed cloud storage, where users can divide their own files into encrypted data chunks, and upload those data chunks randomly into the P2P network nodes that provide free storage capacity. We customize a genetic algorithm to solve the file block replica placement problem between multiple users and multiple data centers in the distributed cloud storage environment. Numerical results show that the proposed architecture outperforms the traditional cloud storage architectures in terms of file security and network transmission delay. On average, the file loss rate based on the simulation assumptions utilized in this paper is close to 0% on our architecture while it’s nearly 100% and 71.66% on the architecture with single data center and the distributed architecture using genetic algorithm. Besides, with proposed scheme, the transmission delay on the proposed architecture is reduced by 39.28% and 76.47% on average on the user’s number and the number of file block replicas, respectively, in comparison to the architecture with single data center. Meanwhile, the transmission delay of file block replicas is also reduced by 41.36% on average than that on the distributed architecture using genetic algorithm.
Graphene has attracted multidisciplinary study because of its unique physicochemical properties. Herein, few-layered graphene oxide nanosheets were synthesized from graphite using the modified ...Hummers method, and were used as sorbents for the removal of Cd(II) and Co(II) ions from large volumes of aqueous solutions. The effects of pH, ionic strength, and humic acid on Cd(II) and Co(II) sorption were investigated. The results indicated that Cd(II) and Co(II) sorption on graphene oxide nanosheets was strongly dependent on pH and weakly dependent on ionic strength. The abundant oxygen-containing functional groups on the surfaces of graphene oxide nanosheets played an important role on Cd(II) and Co(II) sorption. The presence of humic acid reduced Cd(II) and Co(II) sorption on graphene oxide nanosheets at pH < 8. The maximum sorption capacities (C smax) of Cd(II) and Co(II) on graphene oxide nanosheets at pH 6.0 ± 0.1 and T = 303 K were about 106.3 and 68.2 mg/g, respectively, higher than any currently reported. The thermodynamic parameters calculated from temperature-dependent sorption isotherms suggested that Cd(II) and Co(II) sorptions on graphene oxide nanosheets were endothermic and spontaneous processes. The graphene oxide nanosheets may be suitable materials in heavy metal ion pollution cleanup if they are synthesized in large scale and at low price in near future.
A novel efficient Ag@AgCl/g-C3N4 plasmonic photocatalyst was synthesized by a rational in situ ion exchange approach between exfoliated g-C3N4 nanosheets with porous 2D morphology and AgNO3. The ...as-prepared Ag@AgCl-9/g-C3N4 plasmonic photocatalyst exhibited excellent photocatalytic performance under visible light irradiation for rhodamine B degradation with a rate constant of 0.1954 min–1, which is ∼41.6 and ∼16.8 times higher than those of the g-C3N4 (∼0.0047 min–1) and Ag/AgCl (∼0.0116 min–1), respectively. The degradation of methylene blue, methyl orange, and colorless phenol further confirmed the broad spectrum photocatalytic degradation abilities of Ag@AgCl-9/g-C3N4. These results suggested that an integration of the synergetic effect of suitable size plasmonic Ag@AgCl and strong coupling effect between the Ag@AgCl nanoparticles and the exfoliated porous g-C3N4 nanosheets was superior for visible-light-responsive and fast separation of photogenerated electron–hole pairs, thus significantly improving the photocatalytic efficiency. This work may provide a novel concept for the rational design of stable and high performance g-C3N4-based plasmonic photocatalysts for unique photochemical reaction.
Graphene oxide (GO) has attracted considerable attention because of its remarkable enhanced adsorption and multifunctional properties. However, the toxic properties of GO nanosheets released into the ...environment could lead to the instability of biological system. In aqueous phase, GO may interact with fine mineral particles, such as chloridion intercalated nanocrystallined Mg/Al layered double hydroxides (LDH–Cl) and nanocrystallined Mg/Al LDHs (LDH–CO3), which are considered as coagulant molecules for the coagulation and removal of GO from aqueous solutions. Herein the coagulation of GO on LDHs were studied as a function of solution pH, ionic strength, contact time, temperature and coagulant concentration. The presence of LDH–Cl and LDH–CO3 improved the coagulation of GO in solution efficiently, which was mainly attributed to the surface oxygen-containing functional groups of LDH–Cl and LDH–CO3 occupying the binding sites of GO. The coagulation of GO by LDH–Cl and LDH–CO3 was strongly dependent on pH and ionic strength. Results of theoretical DFT calculations indicated that the coagulation of GO on LDHs was energetically favored by electrostatic interactions and hydrogen bonds, which was further evidenced by FTIR and XPS analysis. By integrating the experimental results, it was clear that LDH–Cl could be potentially used as a cost-effective coagulant for the elimination of GO from aqueous solutions, which could efficiently decrease the potential toxicity of GO in the natural environment.
► The sulfonated graphene nanosheets were prepared and had high dispersion property in aqueous solution. ► The kinetic and thermodynamic adsorption of 1-naphthol on the sulfonated graphene nanosheets ...was studied. ► The sulfonated graphene nanosheets have the highest adsorption capacity of todays’ nanomaterials.
The sulfonated graphene nanosheets were prepared from graphene oxides. The kinetic and thermodynamic adsorption of 1-naphthol from aqueous solution on the sulfonated graphene nanosheets were investigated under ambient conditions. The results of 1-naphthol kinetic adsorption on sulfonated graphene indicated that the adsorption was inclined to stack on the surface of graphene nanosheets with low activation energy. The thermodynamic parameters calculated from the temperature dependent adsorption isotherms indicated that the adsorption was a spontaneous and endothermic process, and the adsorption was in good agreement with the theory of non-bonding interaction intensity. The adsorption capacities of 1-naphthol on sulfonated graphene nanosheets are ∼2.3
mmol/g at 293.15
K, and ∼6.4
mmol/g at 313.15 and 333.15
K, which are the highest adsorption capacity of todays’ nanomaterials. The results suggest that the sulfonated graphene nanosheets may be a promising suitable candidate for the preconcentration of 1-naphthol from large volume of aqueous solutions in real work in near future.
A kind of sulfonated graphene (around 3 nm thick) with high dispersion properties has been synthesized. It is demonstrated to adsorb persistent organic aromatic pollutants effectively from aqueous ...solutions. The adsorption capability of the prepared sulfonated graphene nanomaterials approaches ∼2.3–2.4 mmol g−1 for naphthalene and 1‐naphthol, which is one of the highest capabilities of today's nanomaterials. This highly effective adsorbent may be a promising candidate to remove aromatic chemicals from large volumes of aqueous solutions. It opens a new door for cost effective environmental pollution management with graphene in the near future.
A simple and green route was developed for the first time to produce fluorescent graphitic carbon nitride (F-g-C₃N₄) by hydrothermal treatment of bulk g-C₃N₄. The produced F-g-C₃N₄ dots have blue ...emission and a high quantum yield, and were applied as a very effective fluorescent probe for label-free selective and sensitive detection of Cu(2+) and Fe(3+) ions; the limits of detection were as low as 0.5 nM and 1.0 nM, respectively. By using sodium hexametaphosphate (SHPP) as a masking agent of Fe(3+), Cu(2+) was exclusively detected in the presence of Fe(3+) ions. Cu(2+) and Fe(3+) ions in real water samples were also detected successfully. This exceptional fluorescent performance makes the probes based on F-g-C₃N₄ dots attractive for highly sensitive detection of Cu(2+) and Fe(3+) ions in real water.
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•Water-soluble polyacrylamide coated-Fe3O4 magnetic composites were synthesized successfully.•PAM@Fe3O4 showed high efficient enrichment of U(VI) from wastewater.•The Qmax of U(VI) on ...PAM@Fe3O4 reached 220.9mg/g.•Amide groups on the surface of PAM@Fe3O4 facilitated U(VI) sorption.•The used PAM@Fe3O4 could be effectually regenerated.
In this study, polyacrylamide was coated onto Fe3O4 to prepare novel polyacrylamide coated-Fe3O4 magnetic composites (denoted as Fe3O4@PAM). The as-prepared composites were characterized by Fourier transferred infrared spectroscopy, X-ray diffraction, and thermo gravimetric analysis, and the results indicated that polyacrylamide was successfully coated on the surface of Fe3O4. And Fe3O4@PAM composites were applied as adsorbents to remove U(VI) from aqueous solutions and it could be separated by a simple magnetic separation method. The sorption isotherms were well fitted by the Langmuir sorption isotherms, and the maximum sorption capacity of Fe3O4@PAM for U(VI) at pH 5.0 was calculated to be 220.9mg/g. According to the XPS analysis of Fe3O4@PAM before and after U(VI) sorption, the nitrogen-containing functional groups on the surface of Fe3O4@PAM were responsible for U(VI) sorption. The U(VI) sorbed onto Fe3O4@PAM could be desorbed effectively in acid solutions, and the sorption capacity of regenerated sorbents could still maintain high level even after five cycles. The results showed that the Fe3O4@PAM composites were promising materials for the separation and enrichment of radionuclides from aqueous solution in environmental pollution cleanup.
