This paper aims to investigate the confined distance near the floor(0 similar to 28 mm) and wire size (the ratios of copper core diameter to entire wire diameter are: 6mm/8 mm,6mm/10 mm, 8mm/12 mm and 6mm/12 mm for type I, type II, type III and type IV, respectively) on the flame spread over polyethylene (PE) wires. It is indicated that, when the confined distance is relatively small, the extinction occurs for all types. The typical parameters of flame shape including of flame width, flame height and flame area, flame spread rate and mass loss rate with the increase of confined distance s can be separated into continuous growth stage and stable fluctuation stage. At the continuous growth stage, the flame area shows an exponential relationship with s as: A similar to s(5/2). And at the stable fluctuation stage, the flame width is larger than that at the unconfined condition accounting for a large portion. While, the flame height is always smaller than that in the unconfined case. In order to explicitly describe the heat transfer, the upward large main flame and downward small flame are firstly introduced in this paper. Correspondingly, the heat flux feedback of components to the preheating zone is established with the upward main flame flux (q) over dot(f)''((up)) [includes of (q) over dot(vf(up))'' + (q) over dot(rf(up))''], the downward small flame heat flux (q) over dot(f(down))'' [includes of (q) over dot(vf) (down)) ''+ (q) over dot(rf(down))''], the conductive heat flux (q) over dot(c)'' and the gypsum board heat flux (q) over dot(g)''. With the increase of s, q(f(down))'' shows an increasing and then decreasing trend, making it take a second role during heat flux feedback. Meanwhile, the analysis demonstrates that for the larger copper core (type III) and the smaller of PE thickness (type I), the ratio of heat flux of (q) over dot(f(down))/(q) over dot(f(up)) +(q) over dot(f(down)) will be increased, which will enhance the heat transfer effect of downward small flame.

Glutathione (GSH) has important physiological functions and has been implicated in several diseases. It is therefore of great physiological importance and clinical value to develop simple and efficient methods for measuring GSH levels. However, common used luminescent materials with short lifetimes inevitably generated background signal from the biological samples during light excitation. In this work, a GSH sensing method with ultralow background interference was developed using phosphorescent carbon dots (CDs). Introducing heteroatom and carbonyl group effectively activated the triplet state of phosphorescent CDs. Meanwhile, immobilization of CDs in SiO2 (CDs@SiO2) realized long-lived phosphorescent emission (lifetime of 1.54s) in aqueous dispersion. Manganese dioxide (MnO2) quenched the phosphorescence of CDs@SiO2 via inner filter effect and triplet energy transfer, yet the phosphorescence was restored when GSH was present. The phosphorescence was recorded when the excitation source was turned off, which successfully eliminated the background fluorescence of biological samples. The work presented here will promote the fabrication of bioprobes with low background.

The electrical wire fire often occurs in the confined space, making the flame spread behavior complex and the risk increase. In this paper, experimental and theoretical study on the flame spread over three types of polyethylene (PE) electrical wires under different side-confined distances (0 similar to 40 mm) and currents (0 similar to 60 A) was carried out. The ratios of copper diameter to entire wire diameter were 6mm/10 mm, 8mm/12 mm, and 6mm/12 mm for type I, type II and type III, respectively. The results show that, with the increase of s, the flame width and height, and flame spread rate will firstly increase to the maximum peaks at the position of s = 5 mm with attachment wall effect, and then gradually decrease to the values of the unconfined conditions. And with the increase of current, these parameters will gradually increase to the largest at I = 40 A and then decrease for I = 60 A, as the current effect changes from preheating to dripping acceleration. The firm correlation between preheating length delta(ph) and pressure difference Delta P is built, which demonstrates the smallest preheating length is at s = 5 mm with the maximum promotion of heat transfer by gypsum board. On the other hand, the generated Joule heat by the current will enhance the length of preheating, making it proportional to current. Meanwhile, it is found that, the dripping frequency influenced by the dripping mass rate, will increase with the current. The heat transfer components including of the solid conduction heat flux (q(joukte) and and (q) over dot(c)''), flame heat flux ((q) over dot(vf)'' and (q) over dot(rf)'') and gypsum board heat flux (q) over dot(rg)" and (q) over dot(vg)'') are quantitatively analyzed. Correspondingly, a heat transfer model over flame spread is established, which can well predict the flame spread rate. As the diameter of the wire is relatively small, the controlling heat transfer is the flame convective heat flux (q) over dot(vf)'' in this research. In addition, it is illustrated that, the heat flux of gypsum board (q) over dot(vg)" and (q) over dot(rg)'' will decrease with the increase of copper core diameter from type I of 6 mm to type II of 8 mm.While the solid conduction heat flux of copper (q) over dot(cg)'' +(q) over dot(joule)'' will decrease with the increase of thickness of PE from type I of 2 mm to type III of 3 mm. These findings can well give the understanding of heat transfer of flame spread over electrical wires with the effects of sidewall and current.

In this study, the flame merging and flame spread behaviors over two identical parallel electrical wires (the ratios of copper core diameter to entire wire diameter are: 6mm/10mm and 8mm/12mm for typeⅠand typeⅡ, respectively) were experimentally investigated under different wire spacings (3∼18mm) and confined distances(10∼30mm). The results show that the smaller confined distance D will promote the merging, making the wire spacing s increase for the fully merging. With the increase of D, the flame width and flame spread rate will increase.While the flame height will be stretched at smaller D. And is larger than that of single wire at the same D for different wire spacings.The interesting finding is that a pool fire is formed at the middle of the wire spacing when s and D are small, which will enhance the flame spread.The heat flux feedback of components including of the conductive heat flux , the first single flame heat flux , the second flame heat flux , the pool fire heat flux and the gypsum board heat flux are quantitatively analyzed. At the intermittent and non merging stages, the convective and radiative heat fluxes and will decrease largely due to the interaction weakened greatly. Based on the heat transfer analysis, a flame spread model is established, which can well predict the flame spread rate.These findings can give the useful suggestions on the layout design of electrical wires in confined space in buildings.

Development of inexpensive and environmentally friendly chemical sensors can help improve the global ecological environment and reduce pollutant emissions. In this work, asphaltene of coal liquefaction by-product was employed as the carbon source to fabricate carbon dots (CDs) by straightforward microwave radiation. The asphaltene-based CDs gave out blue emission under UV light excitation. Interestingly, the CDs are highly lipophilic because of its carbonized structure and insufficient hydrophilic groups. Based on these findings, an outstanding fluorescent sensor for 2,4,6-trinitrophenol (TNP) was developed by loading asphaltene-based CDs into polymeric micelles. The micelle formed by nonionic tri-block copolymers exhibited a hydrophobic inner cavity and hydrophilic surface. Due to the protection of the micelles, the emission of asphaltene-based CDs was enhanced by 2.89 times. But the fluorescence was significantly quenched by TNP through energy transfer and electron transfer mechanism, showing high sensitivity to TNP with a detection limit of 0.21 μM. The findings presented here provide a green method to synthesize fluorescent CDs and a promising strategy to design fluorescent probes.

Employing long-lived luminescent materials to design a chemical sensing platform can eliminate real-time excitation and background fluorescence. However, the realization of long-lived emissions in aqueous media was limited to transition-metal complexes, doped quantum dots, organic crystals, and inorganic persistent phosphors, which suffer from the drawbacks of large size, expensive elements, and poor dispersibility. In this work, phosphorescent carbon dots (CDs) were covalently immobilized in a silica matrix (CDs@SiO2) to achieve afterglow emission in an aqueous dispersion. CDs@SiO2 with long lifetime (∼1.6 s) was utilized as an energy donor to fabricate nonradiative energy transfer systems with various organic dyes through the surface micelle self-assembly method. Benefiting from the high energy transfer efficiency between CDs@SiO2 and organic dyes, multicolor afterglow emissions were successfully obtained in aqueous media. As a proof of concept, a ratiometric phosphorescent probe using CDs@SiO2 as a donor and Hg2+-responsive rhodamine derivative as an acceptor was designed. Hg2+ triggered the energy transfer process between the donor-acceptor pair, leading to the sensitive detection of Hg2+ ions. The work presented here provides opportunities to develop chemical sensors with low background interferences and easily recognizable signals.

Exploring the practical applications of luminescent carbon dots (CDs) plays an important role in analytical chemistry. In this study, maleic anhydride and polyethyleneimine derived phosphorescent CDs can generate oxidative singlet oxygen and superoxide radical under UV light irradiation. The o-phenylenediamine (OPD) was used as a chromogenic agent, which can be oxidized by singlet oxygen and superoxide radical to produce intense yellow color fluorescence. Furthermore, the CDs-photosensitized oxidation of OPD was inhibited by Cu2+ ions. Because the high affinity between glyphosate and Cu2+, CDs-photosensitized oxidation can take place when glyphosate is added into the Cu2+-mediated system. Utilizing the blue color fluorescence of CDs as internal standard, a ratiometric fluorescent method for glyphosate detection was established. The proposed method can be performed on a smartphone, which exhibits a satisfactory performance for detection of glyphosate residue in real samples rapidly, conveniently, and effectively.

Freeradicals and their induced oxidative damage in living organismsare related to many diseases. Natural substances with antioxidantcapacity are effective in scavenging free radicals, which could slowdown aging and prevent diseases. However, the existing methods forthe evaluation of antioxidant activity mostly required the use ofcomplex instruments and operations. In this work, we proposed a uniquemethod to determine the total antioxidant capacity (TAC) in real samplesthrough a photosensitization-mediated oxidation system. N- and P-dopedlong-lived phosphorescent carbon dots (NPCDs) were developed, whichexhibited the effective intersystem crossing from the singlet to thetriplet state under UV light irradiation. Mechanism study confirmedthat the energy of excited triplet state in NPCDs generated superoxideradicals and singlet oxygen through type I and type II photoreactions,respectively. On this basis, the quantitative determination of TACin fresh fruits was achieved using 3,3 ',5,5 '-tetramethylbenzidine(TMB) as a chromogenic bridge in the photosensitization-mediated oxidationsystem. This demonstration will not only provide a facile way to analyzeantioxidant capacity in practical samples but also broaden the applicationsof phosphorescent carbon dots.