Project description:The photoreduction for hazardous Cr(VI) in industrial wastewater has been considered a "green" approach with low-cost and easy-to-go operation. SnS2 is a promising narrow bandgap photocatalyst, but its low charge carrier separation efficiency should be solved first. In this work, N-doped carbon quantum dots (CQDs) were prepared and loaded onto SnS2 nanoparticles via an in situ method. The resulting composite samples (NC@SnS2) were characterized, and their photocatalytic performance was discussed. SnS2 nanoparticles were obtained as hexagonal ones with a bandgap of 2.19 eV. The optimal doping level for NC@SnS2 was citric acid: urea:SnS2 = 1.2 mmol:1.8 mmol:3.0 mmol. It showed an average diameter of 40 nm and improved photocatalytic performance, compared to pure SnS2, following a pseudo-first-order reaction with a kinetic rate constant of 0.1144 min-1. Over 97% of Cr(VI) was photo-reduced after 30 min. It was confirmed that modification of SnS2 with CQDs can not only improve the light-harvesting ability but also stimulate the charge separation, which therefore can enhance the photoreactivity of SnS2 toward Cr(VI) reduction. The excellent stability of NC@SnS2 indicates that it is promising to be practically used in industrial wastewater purification.
Project description:The Maillard reaction involves a series of complex reactions; fluorescent compounds have been considered as vital intermediate products of the reaction. In this article, carbon dots (CDs) based on the Maillard reaction (MR-CDs) were prepared with L-tryptophan and D-glucose, and they had excellent photoluminescence stability. MR-CDs showed stable pH-dependence behavior and exhibited an excellent linear response to pH in the range of 4.0-7.5 and 7.5-13.0, respectively. Under the masking effect of sodium fluoride for Fe(III), MR-CDs showed excellent selectivity and sensitivity for Cr (VI). The linear range of Cr(VI) was 0.2-50 μM and the limit of detection was 20 nM. (S/N ≥ 3). Furthermore, MR-CDs were used to detect Cr(VI) in tap water samples. The recoveries were between 95.8% and 98.94%, and RSDs were less than 3.17%.
Project description:In recent years, carbon dots (CDs) are promising fluorescence probes for ions detection. In this paper, the CDs which are with an average diameter of 5.5 nm were synthesized through a simple one-step hydrothermal carbonization of ethylene diamine tetraacetic acid (EDTA) salt. The CDs have strong yellow photoluminescence (PL) with a maximum emission intensity at 550 nm under an excitation wavelength of 450 nm. As the electron transfer will occur between Cr (VI) and the CDs, yellow fluorescence was quenched after adding the Cr (VI) ions. The CDs probe allows the detection of Cr (VI) ions over a concentration range from 0 to 0.1 M (R 2 = 0.987) and the lower detection limit is 10-5 M. Simultaneously, the CDs show highly selectivity and stability toward the detection of Cr (VI) ions.
Project description:Due to its lethal effect on the human body and other creatures, Cr(VI) ions have attained widespread public attention, and an effective adsorbent for removing Cr(VI) ions is vital. Chitosan (CS)/cellulose nanocrystals grafted with carbon dots (CNCD) composite hydrogel with strong sorption ability and sensitive detection ability for Cr(VI) was formed. The cellulose nanocrystals (CN) offered a natural skeleton for assembling 3D porous structures, and then improved the sorption ability for Cr(VI); moreover, carbon dots (CD) acted as a fluorescent probe for Cr(VI) and provided Cr(VI) adsorption sites. With a maximum adsorption capacity of 217.8 mg/g, the CS/CNCD composite hydrogel exhibited efficient adsorption properties. Meanwhile, with a detection limit of 0.04 μg/L, this hydrogel was used for selective and quantitative detection of Cr(VI). The determination of Cr(VI) was based on the inner filter effect (IFE) and static quenching. This hydrogel retained its effective adsorption ability even after four repeated regenerations. Furthermore, the economic feasibility of the CS/CNCD composite hydrogel over activated carbon was confirmed using cost analysis. This study provided one new method for producing low-cost adsorbents with effective sorption and sensitive detection for Cr(VI).
Project description:The photocatalytic reduction of Cr(VI) is investigated over iron(III)-based metal-organic frameworks (MOFs) structured as MIL-88B. It is found that MIL-88B (Fe) MOFs, containing Fe3-?3-oxo clusters, can be used as photocatalyst for the reduction of Cr(VI) under visible light irradiation, which is due to the direct excitation of Fe3-?3-oxo clusters. The amine-functionalized MIL-88B (Fe) MOFs (denoted as NH2-MIL-88B (Fe)) shows much higher efficiency for the photocatalytic Cr(VI) reduction under visible-light irradiation compared with MIL-88B (Fe). It is revealed that in addition to the direct excitation of Fe3-?3-oxo clusters, the amine functionality in NH2-MIL-88B (Fe) can also be excited and then transferred an electron to Fe3-?3-oxo clusters, which is responsible for the enhanced photocatalytic activity for Cr(VI) reduction. The enhanced photocatalytic activity for Cr(VI) reduction is also achieved for other two amine-functionalized iron(III)-based MOFs (NH2-MIL-53 (Fe) and NH2-MIL-101 (Fe)).
Project description:Hydrolysed polyacrylamide (HPAM) is widely used in many industrial fields where its rheological properties play a leading role. Recent discovery of the reduction of HPAM's viscosity by adding carbon quantum dots (CQDs), however, is controversial to the established theories. By using all atom molecular dynamics simulation with an OPLS-AA force field, this study aims to provide detailed molecular insight into such an uncommon phenomenon. The dynamic structures of the HPAM chain in the presence or absence of CQDs were clearly captured from the molecular aspect. The results reveal that the adsorption of CQD reduces the gyration radius of the HPAM chain, and it is the corresponding hydration effect that leads to the reduction of the viscosity. The amide rather than the carboxylate group along the HPAM chain is dominant in terms of the interaction with the CQDs, and the driven atoms depend on the surface where the polymer is adsorbed.
Project description:Nitrogen-doped carbon quantum dots (NCQDs) were prepared from chitosan through a hydrothermal reaction. When ethanol precipitation was used as the purification method, a high product yield of 85.3% was obtained. A strong blue fluorescence emission with a high quantum yield (QY) of 6.6% was observed from the NCQD aqueous solution. Physical and chemical characteristics of the NCQDs were carefully investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Raman spectra, X-ray photoelectron spectroscopy (XPS), and transient fluorescence spectra. Experimental results showed that diameters of the NCQDs were in the range of 2-10 nm. The carbon quantum dots possess good water dispersibility and precipitation by ethanol. When used for metal ion detection, the detection limit of the NCQDs for Fe3+ was as low as 1.57 ?M. This work proposed a facile method to synthesize NCQDs from chitosan with high yield and demonstrated that carbon quantum dots derived from chitosan were promising for ion detection.
Project description:Quantum dots have innate advantages as the key component of optoelectronic devices. For white light-emitting diodes (WLEDs), the modulation of the spectrum and color of the device often involves various quantum dots of different emission wavelengths. Here, we fabricate a series of carbon quantum dots (CQDs) through a scalable acid reagent engineering strategy. The growing electron-withdrawing groups on the surface of CQDs that originated from acid reagents boost their photoluminescence wavelength red shift and raise their particle sizes, elucidating the quantum size effect. These CQDs emit bright and remarkably stable full-color fluorescence ranging from blue to red light and even white light. Full-color emissive polymer films and all types of high-color rendering index WLEDs are synthesized by mixing multiple kinds of CQDs in appropriate ratios. The universal electron-donating/withdrawing group engineering approach for synthesizing tunable emissive CQDs will facilitate the progress of carbon-based luminescent materials for manufacturing forward-looking films and devices.
Project description:Cr(VI) is considered as a priority pollutant, and its remediation has attracted increasing attention in the environmental area. In this study, the driving of pyrite-based Cr(VI) reduction by Acidithiobacillus ferrooxidans was systematically investigated. The results showed that pyrite-based Cr(VI) reduction was a highly proton-dependent process and that pH influenced the biological activity. The passivation effect became more significant with an increase in pH, and there was a decrease in Cr(VI) reduction efficiency. However, Cr(VI) reduction efficiency was enhanced by inoculation with A. ferrooxidans. The highest reduction efficiency was achieved in the biological system with a pH range of 1-1.5. Pyrite dissolution and reactive site regeneration were promoted by A. ferrooxidans, which resulted in the enhanced effect in Cr(VI) reduction. The low linear relevancy between pH and Cr(VI) dosage in the biological system indicated a complex interaction between bacteria and pyrite. Secondary iron mineral formation in an unfavorable pH environment inhibited pyrite dissolution, but the passivation effect was relieved under the activity of A. ferrooxidans due to S/Fe oxidization. The balance between Cr(VI) reduction and biological activity was critical for sustainable Cr(VI) reduction. Pyrite-based Cr(VI) remediation driven by chemoautotrophic acidophilic bacteria is shown to be an economical and efficient method of Cr(VI) reduction.
Project description:A transposon insertion mutant has been identified in a Desulfovibrio desulfuricans G20 mutant library that does not grow in the presence of 2 mM U(VI) in lactate-sulfate medium. This mutant has also been shown to be deficient in the ability to grow with 100 microM Cr(VI) and 20 mM As(V). Experiments with washed cells showed that this mutant had lost the ability to reduce U(VI) or Cr(VI), providing an explanation for the lower tolerance. A gene encoding a cyclic AMP (cAMP) receptor protein (CRP) was identified as the site of the transposon insertion. The remainder of the mre operon (metal reduction) contains genes encoding a thioredoxin, thioredoxin reductase, and an additional oxidoreductase whose substrate has not been predicted. Expression studies showed that in the mutant, the entire operon is downregulated, suggesting that the CRP may be involved in regulating expression of the whole operon. Exposure of the cells to U(VI) resulted in upregulation of the entire operon. CdCl(2), a specific inhibitor of thioredoxin activity, inhibits U(VI) reduction by washed cells and inhibits growth of cells in culture when U(VI) is present, confirming a role for thioredoxin in U(VI) reduction. The entire mre operon was cloned into Escherichia coli JM109 and the transformant developed increased U(VI) resistance and the ability to reduce U(VI) to U(IV). The oxidoreductase protein (MreG) from this operon was expressed and purified from E. coli. In the presence of thioredoxin, thioredoxin reductase, and NADPH, this protein was shown to reduce both U(VI) and Cr(VI), providing a mechanism for the cytoplasmic reduction of these metals.