ZnIn2S4 flowerlike microspheres embedded with carbon quantum dots for efficient photocatalytic reduction of Cr(VI)

Development of efficient heterostructured photocatalysts that respond to visible light remains a considerable challenge. We herein show the synthesis of ZnIn₂S₄/carbon quantum dot hybrid photocatalysts with flowerlike microspheres via a facile solvothermal method. The ZnIn₂S₄/carbon quantum dot flowerlike microspheres display enhanced photocatalytic and photoelectrochemical activity compared with that of pure ZnIn₂S₄. With a content of only 0.5 wt % carbon quantum dots, 93% of Cr(VI) is reduced under visible-light irradiation at 40 min. As a co-catalyst, the carbon quantum dots improve the light absorption and lengthen the lifetime of charge carriers, consequently enhancing the photocatalytic and photoelectrochemical activity.     

Structural engineering design of carbon dots for lubrication

Carbon dots (CDs) have opened up a new field of carbon nanomaterials and successively attracted increasing attention since their discovery in 2004. Owing to their ultrasmall size, tunable surface functional groups, excellent dispersibility, attractive stability, low toxicity, environmental friendliness, facile synthesis and low-cost precursors, CDs have been developed as green and promising friction-reducing and anti-wear materials in lubrication science, applied to energy conservation and extension of mechanical service life in recent years. However, there are few reviews focusing on the application of CDs in the important field of lubrication. In this review, we comprehensively summarize the development of CDs in lubrication for the first time. Firstly, three strategies for structural engineering design of CDs to improve their tribological characteristics are fully analyzed, in terms of size and shape control, surface modification and heteroatom doping. Secondly, the advance in lubrication application of CDs, including CDs as additives for lubricants, greases, gel and magnetorheological fluids as well as CDs as lubricating coatings, is systematically highlighted. Thirdly, the lubricating mechanisms of CDs as additives are introduced in detail. Furthermore, the remaining major challenges and opportunities for CDs in lubrication field are discussed and outlined.     

Capillary electrophoresis coupled to chemometrics for analysis of carbon dots in nanoparticles mixtures

Since their discovery in 2004, carbon dots (CDs) have attracted attention due to their intrinsic physicochemical properties and the easy synthesis from simple precursors. However, quantification of CDs in mixtures of nanoparticles with similar sizes and surface functionality is still a challenging issue for research applications or regulatory purposes. In this work, CDs and silver nanoparticles were first synthesized under alkaline conditions by using glucose as precursor and capping agent, respectively. Mixtures of these nanoparticles were made at micromolar range, without purification, and then analyzed by CE–DAD, using an electrolyte solution composed of 20 mM sodium borate and 20 mM SDS at pH 8.5, in a total time of <15 min. The three-way electrophoretic data were then decomposed by advanced chemometric models, parallel factor analysis and multivariate curve resolution–alternating least-squares. The explained variances for both models were 95.8% (parallel factor analysis) and 85.3% (multivariate curve resolution–alternating least-squares). In both cases, the quality of the results was verified by the root mean square standard deviation coefficient variation, which resulted lower than 5%, and no significant bias was observed at 95% of statistical confidence. Satisfactory prediction for CDs concentration was obtained with recovery values between 80.0% and 115%.     

Visible light induced efficient activation of persulfate by a carbon quantum dots (CQDs) modified γ-Fe2O3 catalyst

In this study, a carbon quantum dots modified maghemite catalyst (CQDs@γ-Fe₂O₃) has been synthesized by a one-step solvothermal method for efficient persulfate (PDS) activation under visible light irradiation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) characterization indicated that the formation of heterojunction structure between CQDs and γ-Fe₂O₃ effectively reduced the catalyst band gap (E_g), favoring the separation rate of electrons and holes, leading to remarkable efficient sulfamethoxazole (SMX) degradation as compared to the dark-CQDs@γ-Fe₂O₃/PDS and vis-γ-Fe₂O₃/PDS systems. The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe³⁺. Electron paramagnetic resonance (EPR) and radical scavenging experiments demonstrated that both OH and SO₄⁻ were generated in the reaction system, while OH was relatively more dominant than SO₄⁻ for SMX degradation. Finally, the reaction mechanism in the vis-CQDs@γ-Fe₂O₃/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle. CQDs would enrich the photo-generated electrons from γ-Fe₂O₃, causing efficient interfacial generation of surface-bond Fe²⁺ and reduction of adsorbed Fe³⁺. This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX.     

Photocatalytic degradation of amoxicillin by carbon quantum dots modified K2Ti6O13 nanotubes: Effect of light wavelength

Novel carbon quantum dots modified potassium titanate nanotubes (CQDs/K₂Ti₆O₁₃) composite was synthesized and exhibited high photocatalytic activity for degradation of amoxicillin under UV and visible lights with nine wavelengths. Better amoxicillin removal was achieved at lower wavelength irradiation due to its higher photo energy.     

Rational design of ternary NiS/CQDs/ZnIn2S4 nanocomposites as efficient noble-metal-free photocatalyst for hydrogen evolution under visible light

The NiS/CQDs nanocomposite (CQDs represents carbon quantum dots), with a mass ratio of NiS/CQDs to be 1.19:1 based on the ICP result, was obtained via a facile hydrothermal method from a mixture of CQDs, Ni(OAc)₂ and Na₂S. The self-assembly of ZnIn₂S₄ microspheres on the surface of NiS/CQDs was realized under microwave conditions to obtain a ternary NiS/CQDs/ZnIn₂S₄ nanocomposite. The as-obtained NiS/CQDs/ZnIn₂S₄ nanocomposite was fully characterized, and its photocatalytic hydrogen evolution under visible light irradiation was investigated. The ternary NiS/CQDs/ZnIn₂S₄ nanocomposite showed superior photocatalytic activity for hydrogen evolution than ternary CQDs/NiS/ZnIn₂S₄, which was obtained by deposition of NiS in the preformed CQDs/ZnIn₂S₄. The superior photocatalytic performance of ternary NiS/CQDs/ZnIn₂S₄ is ascribed to the introduction of CQDs, which act as a bridge to promote the vectorial transfer of photo-generated electrons from ZnIn₂S₄ to NiS. This result suggests that the rational design and fabrication of ternary CQDs-based systems are important for the efficient photocatalytic hydrogen evolution. This study provides a strategy for developing highly efficient noble-metal-free photocatalysts for hydrogen evolution using CQDs as a bridge to promote the charge transfer in the nanocomposite.     

Surface domain potential difference-mediated efficient charge separation on a defective ZnIn2S4 microsphere photocatalyst

Low-efficiency charge separation in metal sulfides is a major obstacle to realizing high photocatalytic performance. Herein, we propose the concept of a similar surface domain potential difference between adjacent microdomains with and without surface S vacancies on ZnIn₂S₄ to mediate charge separation. Defective ZnIn₂S₄ microspheres (DZISNPs) are prepared through a solvothermal method combined with a low-temperature hydrogenation surface engineering strategy. The as-prepared DZISNPs with a narrowed bandgap of 2.38 eV possess a large specific surface area of 178.5 m² g^?1, a pore size of 6.89 nm, and a pore volume of 0.36 cm³ g^?1, which further improves the visible light absorption. The resultant DZISNPs exhibit excellent visible light activity (2.15 mmol h^?1 g^?1), which is ～two-fold higher than that of the original DZISNP. The experimental results and DFT calculations reveal that the enhanced property can be a result of the surface S vacancy-induced surface domain potential difference, promoting the spatial separation of electrons and holes. Furthermore, the long-term stability of the DZISNPs indicates that the formation of surface S vacancies can inhibit the photocorrosion of ZnIn₂S₄. This strategy provides new insights for fabricating highly efficient and stable sulfide photocatalysts.     

Fabrication of ternary dual Z-Scheme AgI/ZnIn2S4/BiVO4 heterojunction photocatalyst with enhanced photocatalytic degradation of tetracycline under visible light

In this study, a novel ternary AgI/ZnIn₂S₄/BiVO₄(AZB) composite photocatalyst was successfully prepared by hydrothermal method and in-situ precipitation method. The as-synthesized samples were characterized by XRD, SEM, TEM, XPS and so on, and the photocatalytic activity was evaluated through photocatalytic degradation of tetracycline (TC) under visible light irradiation. When the molar ratio of Bi to Ag was 1:1, the degradation rate of TC can reach 91.44 % within 150 min. The AZB heterojunction demonstrated outstanding efficiency with the apparent reaction rate constants of 0.02118 min^?1 for TC removal, was 4.68, 3.27 and 3.27 times higher than that of pure BiVO₄, AgI and ZnIn₂S₄. Based on active species trapping experiments and ESR analysis, a dual Z-Scheme pathways among BiVO₄, AgI and ZnIn₂S₄ for effective separation of photogenerated charges was recommended. This work provided a promising insight for the design of ternary dual Z-scheme heterojunction with multilevel electron transfer to present greater photo-absorption, charge separation, and photodegradation for environmental decontamination.     

Facile one-pot synthesis of PEG-derived carbon dots with enhanced luminescence via L-cysteine-assisted S,N-doping

Carbon nanodots (C-dots) are promising photoluminescent nanomaterials for biomedical applications. Among them, PEG-derived C-dots demonstrate exceptional photoluminescence and passivation properties, making them particularly attractive for use in the biomedical field. In this article, we present the synthesis of photoluminescent S,N-doped PEG-derived carbon dots that are stable at ambient temperature and can be produced using an easy hydrothermal technique. To synthesize the carbon dots, the non-hazardous polymer polyethylene glycol (PEG) was used as the sole precursor rather than any other potentially hazardous compounds. The absence of L-cysteine in the reaction mixture resulted in carbon dots with no significant absorbance in the visible region but exhibited photoluminescence properties with a maximum excitation and emission at 343 and 452 nm, respectively. However, the addition of L-cysteine resulted in a visible absorbance and a red shift in both the maximum excitation and emission, at around 435 and 503 nm, respectively. The Fourier transform infrared spectroscopy (FTIR) analysis provided evidence for the presence of -SH, -SO₂, -NH₂, and CON-H bond stretching after the addition of L-cysteine, suggesting possible S,N-doping of the carbon dots, which likely caused the observed changes in photoluminescence properties. These findings contribute to the understanding of S,N-doping in carbon dots and highlight their potential applications in optoelectronics, sensing, and biomedical imaging.     

空心NiCo2S4纳米球助催化剂担载ZnIn2S4纳米片用于可见光催化制氢

纳米片与空心球上之间的合理界面调控是开发高效太阳能制氢光催化剂的潜在策略。在各类光催化材料中,金属硫化物由于具有相对较窄的带隙和优越的可见光响应能力而被广泛研究。ZnIn₂S₄是一种层状的三元过渡金属半导体光催化剂,其带隙可控(约2.4 eV)。在众多金属硫化物光催化剂中,ZnIn₂S₄引起了广泛兴趣。然而,单纯的ZnIn₂S₄光催化活性仍然相对较差,主要是因为光生载流子的复合率较高、迁移速率较慢。在半导体光催化剂上负载助催化剂是提升光催化剂性能的一种有效方法,因为它不仅可以加速光生电子和空穴的分离,而且还可以降低质子还原反应的活化能。作为一种三元过渡金属硫化物,NiCo₂S₄表现出较高的导电性、较低的电负性、丰富的氧化还原特性以及优越的电催化活性。这些特性表明,NiCo₂S₄可以作为光催化制氢的助催化剂,以加速电荷分离和转移。此外,NiCo₂S₄和ZnIn₂S₄都属于三元尖晶石的晶体结构,这可能有助于构建具有紧密界面接触的NiCo₂S₄/ZnIn₂S₄复合物,从而提高光催化性能。本文中,将超薄ZnIn₂S₄纳米片原位生长到非贵金属助催化剂NiCo₂S₄空心球上,形成具有强耦合界面和可见光吸收的NiCo₂S₄@ZnIn₂S₄分级空心异质结构光催化剂。最优NiCo₂S₄@ZnIn₂S₄复合样品(NiCo₂S₄含量：ca. 3.1%)的析氢速率高达78 μmol·h^-1,约是纳米片组装ZnIn₂S₄光催化剂析氢速率的9倍、约是1% (w, 质量分数)Pt/ZnIn₂S₄样品析氢速率的3倍。此外,该复合光催化剂在反应中表现出良好的稳定性。荧光和电化学测试结果表明,NiCo₂S₄空心球是一种有效的助催化剂,可促进光生载流子的分离和传输,并降低析氢反应的活化能。最后,提出了NiCo₂S₄@ZnIn₂S₄光催化析氢的可能反应机理。在NiCo₂S₄@ZnIn₂S₄复合光催化剂中,具有高导电性的NiCo₂S₄助催化剂可快速接受ZnIn₂S₄上的光生电子,用以还原质子生成氢气,而电子牺牲剂TEOA捕获光生空穴,进而完成光催化氧化还原循环。该研究有望为基于纳米片为次级结构的分级空心异质结光催化剂的设计合成及其光催化制氢研究提供一定的指导。     

pH and H2O2 dual-responsive carbon dots for biocatalytic transformation monitoring

Development of sensitive biosensors for biocatalytic transformations monitoring is in high demand but remains a great challenge. It is ascribed to the current strategies that focused on the single metabolite detection, which may bring about the relatively low sensitivity and false diagnosis result. Herein, we report the design and fabrication of novel carbon dots (CDs) with strong orange light emission, pH and H₂O₂ dual-responsive characteristics. The fluorescence quenching of CDs by H⁺ and H₂O₂ enables the highly sensitive detection of H⁺/H₂O₂-generating biocatalytic transformations. This is exemplified by the glucose oxidase-mediated catalytic oxidation reaction on glucose, in which H⁺ and H₂O₂ would be formed. As compared to the case in which glucose is present, significant fluorescence reduction is detected, and the fluorescence intensity is negatively proportional to glucose concentration. Thus, highly sensitive detection of glucose was readily achieved with a detection limit down to 10.18 nmol/L. The prepared CDs not only realize the highly sensitive detection of glucose, but also allows the probing other substances by changing the enzymes, thus providing a versatile platform, and demonstrating good potential to be used for biocatalytic transformations effective monitoring.     

Species,engineering and characterizations of defects in TiO2-based photocatalyst

This review gave a brief summary on the main species, engineering and characterizations of defects on the TiO₂-realted model photocatalyst.     

Supported carbon dots decorated with metallothionein for selective cadmium adsorption and removal

Carbon dots are prepared and immobilized onto spherical SiO_2 through a one-step thermal oxidation and then decorated with metallothionein(MT), a protein with high affinity towards thiophilic metals. The MT-carbon dots composites are characterized by means of FT-IR, SEM and TGA, giving rise to a MT loading amount of 823 μg g~(-1). The adsorption of cadmium by the composites is a fast process and follows Langmuir model. In comparison with native SiO_2, a 2- and 2.4-folds improvement on the static and dynamic adsorption capacity of the composites for cadmium are obtained, respectively. Moreover,the adsorption efficiency is not affected by the presence of other metals. Finally, the composites are successfully applied for the removal of cadmium in a series of environmental water samples.     

Exposed Zinc Sites on Hybrid ZnIn2S4@CdS Nanocages for Efficient Regioselective Photocatalytic Epoxide Alcoholysis

Photocatalytic epoxide alcoholysis through C−O bond cleavage and formation has emerged as an alternative to synthesizing anti-tumoral pharmaceuticals and fine chemicals. However, the lack of crucial evidence to interpret the interaction between reactants and photocatalyst surface makes it challenging for photocatalytic epoxide alcoholysis with both high activity and regioselectivity. In this work, we report the hierarchical ZnIn₂S₄@CdS photocatalyst for epoxide alcoholysis with high regioselectivity nearly 100 %. Mechanistic studies unveil that the precise activation switch on exposed Zn acid sites for C−O bond polarization and cleavage has a critical significance for achieving efficient photocatalytic performance. Furthermore, the establishment of Z-scheme heterojunction facilitates the interface charge separation and transfer. Remarkably, the underlying regioselective photocatalytic reaction pathway has been distinctly revealed.     

ZnIn2S4@CNO多级纳米片用于光催化分解水制氢和还原CO2（英文）

光催化分解水制氢和还原CO2是太阳能利用领域的研究热点,对清洁能源的转化具有重要意义.石墨相氮化碳(CN)作为一种非金属半导体,是一种非常有开发潜力的光催化材料.然而限于其聚合物本质,光催化效率仍有待进一步提高.原位非金属掺杂可以利用元素电子结构调控电荷分布,优化光生电荷传输性能.同时,半导体复合,尤其是2D层状复合结构的构筑,可充分发挥2D半导体的优势,合适的能带交错有利于光生电荷的传输,可在一定程度上加速催化反应的进行.本文首先以草酸为氧掺杂源,采用二步煅烧法合成氧掺杂氮化碳纳米片催化剂(CNO).在二次煅烧和氧掺杂共同作用下,增大了CN层间距和多孔性,颗粒尺寸减小,同时增强了对光的吸光性,拓展了可见光吸收范围.接下来采用一步水热合成法得到ZnIn2S4@CNO(ZC)复合材料,在可见光照射下通过分解水制氢和CO2还原反应对复合材料进行光催化还原性能评价.采用X射线衍射(XRD)、透射电镜(TEM)、X射线光电子能谱(XPS)、荧光光谱(PL)、光电化学测试等方法对ZC进行详细的结构表征和分析.XRD和XPS结果表明,经过一步直接水热可得到层状ZC复合材料,高倍TEM进一步证实二者形成均一的2D异质复合材料.N2-吸附-脱附曲线表明,复合材料具有较大的比表面积和均一的孔结构分布,主要得益于O掺杂CNO纳米片的多孔性结构.光电性质测试结果表明,相比于CNO,复合材料具有降低的荧光发射强度和延长的荧光寿命,表明复合产物显著抑制了光生电荷的复合.电化学测试进一步表明,复合异质结的构筑有利于光生载流子的产生,同时降低了界面电荷转移电阻,提高了电荷迁移速率.因此,多孔2D异质结构的构筑对促进CN基半导体光催化还原具有重要作用.在可见光照射下(λ>400 nm),复合材料表现出优异的光催化还原性能,且随着CNO含量的增加催化活性不断提高,其中ZC 40%(CNO质量比40%)具有最佳的催化活性,其产氢速率达188.4μmol/h,约是ZnIn2S4和CNO的2.1倍.同时,光催化还原CO2测试表明,复合材料具有显著提高的CO和CH4产率,其中CO为主要反应产物.ZC40%的CO产生速率为12.69μmol/h,分别是ZnIn2S4和CNO的2.2倍和14.0倍.对催化剂进行连续光反应,结果表明,复合催化剂具有优异的结构稳定性和活性稳定性,能够持续发生光还原反应制取H2和CO.     

氧化石墨烯量子点修饰氧掺杂多孔g-C3N4在光催化降解和抗菌中的应用（英文）

偶氮类合成色素具有遗传毒性、致癌性和致泻性,而食源性致病菌易引发细菌性感染和食物中毒事件,食品加工过程中产生的色素废水和致病菌废水若未经妥善处理就排入水体,会对水体及环境造成污染,废水中的偶氮类色素和致病菌还会通过食物链对人体健康产生威胁.因此,寻求更为高效、绿色、安全的处理技术和净化材料有效去除食品废水中高污染性和毒害性的偶氮类色素和致病菌显得尤为迫切.g-C3N4是一种具有可见光响应的有机半导体光催化材料,广泛应用于降解污染物、杀灭致病菌、催化有机反应等领域.然而,g-C3N4本身存在着比表面积小、光吸收性能差、光氧化能力低以及光生载流子迁移效率低等缺点,限制了其光催化性能.针对上述问题,我们对g-C3N4的空间和电子结构进行了设计,将形貌调控、元素掺杂和助催化剂修饰三种改性方法相结合,以获得兼具大比表面积、优异光吸收性能、强氧化能力以及快速光生载流子迁移能力的高活性g-C3N4基光催化体系.本文通过水热法制备了氧掺杂多孔氮化碳(PCNO),通过酸剥离法制备了氧化石墨烯量子点(ox-GQDs),最后通过自组装法将助催化剂ox-GQDs修饰到PCNO上,制备了ox-GQDs/PCNO复合光催化剂.零维的ox-GQDs可以通过氢键、π-π作用和化学键作用,与二维的PCNO实现紧密接触,均匀地分散在PCNO的表面和内部孔道上.由于ox-GQDs独特的上转换特性、电子捕获能力和过氧化物酶活性,ox-GQDs/PCNO复合光催化剂具有比PCNO更佳的光吸收性能、更高的电荷转移效率以及更强的光氧化能力.因此,ox-GQDs/PCNO复合材料在降解偶氮类色素和杀灭致病菌方面均表现出更为优异的可见光催化性能,活性最佳的复合材料ox-GQDs-0.2%/PCNO降解偶氮类色素苋菜红的速率常数约是PCNO的3.1倍,并且该材料能在可见光照射4 h内杀灭99.6%的大肠杆菌,远超过PCNO 31.9%的抗菌活性.另外,光生空穴、超氧自由基和羟基自由基被证实是ox-GQDs/PCNO体系在光催化反应中产生的活性物种,可以彻底矿化偶氮类色素并有效杀灭致病菌.本研究可以拓展g-C3N4基光催化剂在环境净化领域的应用前景,并为阐明ox-GQDs在复合光催化体系中的作用提供新的见解.     

Colorimetric and fluorimetric dual mode detection of Fe2+ in aqueous solution based on a carbon dots/phenanthroline system

In this work, green fluorescent carbon dots with a high relative quantum yield of 74.13% were synthesized by using one-pot hydrothermal hydrolysis of m-phenylenediamine (mPD) and PEG 1500 in H₂SO₄ solution at 180 ^°C for 10 h (mPD-CDs). In the presence of mPD-CDs, Fe²⁺ can form a complex with 1,10-phenanthroline (Fe(II) – phenanthroline) without interference from mPD-CDs, which has an absorption peak centered at 512 nm and its absorbance is sensitive to the concentration of Fe(II) – phenanthroline. Accordingly, a colorimetric method for the detection of Fe²⁺ was constructed with a limit of detection (LOD) of 2.98 μM. Moreover, the absorption spectrum of the Fe (II)-phenanthroline complex is overlapping with the excitation and emission spectra of mPD-CDs located at 440 and 516 nm, respectively, resulting in an inner filter effect (IFE) which is sensitive to the concentration of Fe(II) – phenanthroline. Correspondingly, a fluorimetric method for the detection of Fe²⁺ based on the mPD-CDs/phenanthroline system was built with a LOD as low as 0.59 μM. Therefore, colorimetric and fluorimetric dual mode detection of Fe²⁺ in aqueous solution can be achieved by a carbon dots/phenanthroline system.     

Field-portable ratiometric fluorescence imaging of dual-color label-free carbon dots for uranyl ions detection with cellphone-based optical platform

Under the public spotlight, uranyl (UO₂²⁺) ions has attracted considerable attention for the extreme radioactive and chemical toxicity to ourselves and our environment. Herein, we present a simple and effective ratiometric fluorescence imaging method for the visualizing and quantitative detection UO₂²⁺ ions by cellphone-based optical platform. The sensing solution was prepared by mixing label-free red carbon dots (r-CDs) and blue carbon dots (b-CDs) together with a fixed photoluminescence intensity ratio of 4:1. When UO₂²⁺ ions were added, the fluorescence of r-CDs can be selectively quenched, while the fluorescence of b-CDs remains stable without spectral changes. With the gradually increase the amounts of UO₂²⁺ ions, the different response of dual-color CDs resulted in a signification color evolution from deep red to dark purple under the ultraviolet (UV) light illumination. Then, a cellphone-based optical platform was constructed for directly imaging the color change of the samples, and the built-in Colorpicker APP quickly output the red, green and blue (RGB) channel values of these images within one second. Interesting, there was a linear relationship between the ratio of red and blue (R/B) channel values and UO₂²⁺ ions concentration from 0 μmol/L to 30.0 μmol/L (R² = 0.92804) with the detection limit of ∼8.15 μmol/L (signal-to-noise ratio of 3). In addition, the optical platform has also been applied to the quantification of UO₂²⁺ ions in tap water and river water sample. With the advantage of low-cost, portable, easy to operation, we anticipate that this method would greatly improve the accessibility of UO₂²⁺ ions detection even in resource-limited areas.     

pH and H2O2 dual-responsive carbon dots for biocatalytic transformation monitoring

Carbon dots with strong orange light emission, pH and H₂O₂ dual-responsive characteristics, were prepared and applied for probing enzyme-mediated biocatalytic transformations via the fluorescence quenching.     

Field-portable ratiometric fluorescence imaging of dual-color label-free carbon dots for uranyl ions detection with cellphone-based optical platform

Under the public spotlight, uranyl (UO₂²⁺) ions has attracted considerable attention for the extreme radioactive and chemical toxicity to ourselves and our environment. Herein, we present a simple and effective ratiometric fluorescence imaging method for the visualizing and quantitative detection UO₂²⁺ ions by cellphone-based optical platform. The sensing solution was prepared by mixing label-free red carbon dots (r-CDs) and blue carbon dots (b-CDs) together with a fixed photoluminescence intensity ratio of 4:1. When UO₂²⁺ ions were added, the fluorescence of r-CDs can be selectively quenched, while the fluorescence of b-CDs remains stable without spectral changes. With the gradually increase the amounts of UO₂²⁺ ions, the different response of dual-color CDs resulted in a signification color evolution from deep red to dark purple under the ultraviolet (UV) light illumination. Then, a cellphone-based optical platform was constructed for directly imaging the color change of the samples, and the built-in Colorpicker APP quickly output the red, green and blue (RGB) channel values of these images within one second. Interesting, there was a linear relationship between the ratio of red and blue (R/B) channel values and UO₂²⁺ ions concentration from 0 μmol/L to 30.0 μmol/L (R² = 0.92804) with the detection limit of ~8.15 μmol/L (signal-to-noise ratio of 3). In addition, the optical platform has also been applied to the quantification of UO₂²⁺ ions in tap water and river water sample. With the advantage of low-cost, portable, easy to operation, we anticipate that this method would greatly improve the accessibility of UO₂²⁺ ions detection even in resource-limited areas.