In the present study, we report the systematic investigation of the effect of chemical oxidation on the structure of single-walled carbon nanotubes (SWNTs) by using different oxidants. The oxidation procedure was characterized by using infrared spectroscopy and transmission electron microscopy (TEM). The SWNTs were produced by chemical vapor deposition (CVD) and oxidized with three kinds of oxidants: (1) nitric acid (2.6 M), (2) a mixture of concentrated sulfuric acid (98 wt %) and concentrated nitric acid (16 M) (v/v ) 3/1) and (3) KMnO 4 . The results reveal that the different functional groups can be introduced when the SWNTs are treated with different oxidants. Refluxing in dilute nitric acid can be considered as a mild oxidation for SWNTs, introducing the carboxylic acid groups only at those initial defects that already exist. The abundance of the carboxylic acid groups generated with this oxidant remained constant along with the treating time. In contrast, sonication of SWNTs in H 2 SO 4 /HNO 3 increased the incidence of carboxylic acid groups not only at initial defect sites but also at newly created defect sites along the walls of SWNTs. Compared to the two oxidants above, when KMnO 4 in alkali was used as the oxidant, which is relatively mild, different amounts of -OH, -CdO, and -COOH groups were introduced. The oxidation processes begin mainly with the oxidation of the initial defects that arise during the CVD growth of the SWNTs and are accompanied by processes that can be roughly divided into two steps: (1) the defect-generating step and (2) the defect-consuming step. Specifically, during the defect-generating step, the oxidants attack the graphene structure by electrophilic reactions and generate active sites such as -OH and -CdO. This step depends on the oxidant's ability to generate -C-OH groups and to transform them into -CdO groups. During the defect-consuming step, the graphene structure of the tube was destroyed by the oxidation of the generated active sites in step 1. The defect-consuming step mostly counts on the ability of the oxidant to etch/destroy the graphite-like structure around the already generated -CdO and their neighborhood groups.

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We reveal a new approach for forming a Ag-graded absorber to overcome the large open-circuit voltage deficit in (Cu,Ag)2ZnSn(S,Se)4 solar cells.

In this article, pure phase metastable wurtzite Cu 2 ZnSnS 4 (CZTS) nanocrystals (NCs) were synthesized by a facile one-pot method. When pure 1dodecanethiol (DDT) was used as the solvent, two coexisting CZTS phases (wurtzite and kesterite) were found. When an increased amount of oleylamine (OAm) was added to DDT, kesterite CZTS disappeared gradually, and the asobtained CZTS NCs became smaller and more uniform. When 0.5 mL of OAm was added, rice-like pure phase metastable wurtzite CZTS NCs were obtained. The factors, including amount of OAm, reaction temperature, reaction time, and concentration of precursors, which influence the morphology, size, and monodispersity of CZTS NCs, were studied in detail. The results showed OAm played an important role in the formation of the final pure phase metastable wurtzite NCs. Time-dependent experiments were performed to observe the growth of CZTS NCs. The final CZTS NCs evolved from spherical-like Cu 2 S NCs through rhombuslike intermediate shaped NCs to rice-like pure wurtzite CZTS NCs. On the basis of the detailed time-dependent shape and elemental composition evolutions, a possible asynchronous doping growth and formation mechanism was proposed. The optical and electrical properties of the pure wurtzite CZTS NCs were also investigated. The band gap of the rice-like CZTS is about 1.49 eV, which approaches the optimum value for solar photoelectric conversion. Meanwhile, the current−voltage characteristics and Hall effect measurement of the wurtzite CZTS NCs films indicated that rice-like CZTS NCs favored the electronic transmission and thus may induce the generation of photocurrent. Thus, the obtained wurtzite CZTS NCs are more suitable for using as absorber layer in low cost solar cells.

An ionic liquid/aqueous two-phase system based on the hydrophilic ionic liquid 1-butyl-3-methylimidazolium chloride (BmimCl) and K(2)HPO(4) has been employed for direct extraction of proteins from human body fluids for the first time. Proteins present at low levels were quantitatively extracted into the BmimCl-rich upper phase with a distribution ratio of about 10 between the upper and lower phase and an enrichment factor of 5. Addition of an appropriate amount of K(2)HPO(4) to the separated upper phase results in a further phase separation, giving rise to an improved enrichment factor of 20. FTIR and UV spectroscopy demonstrated that no chemical (bonding) interactions between the ionic liquid and the protein functional groups were identifiable, while no alterations of the natural properties of the proteins were observed. The partitioning of proteins in the two-phase system was assumed to have been facilitated by the electrostatic potential difference between the coexisting phases, as well as by salting out effects. The system could be applied successfully for the quantification of proteins in human urine after on-line phase separation in a flow system. The use of an ionic liquid, as a green solvent, offers clear advantages over traditional liquid-liquid extractions, in which the use of toxic organic solvents is unavoidable.

A new fabrication strategy of the graphene-coated solid-phase microextraction (SPME) fiber is developed. Graphite oxide was first used as starting coating material that covalently bonded to the fused-silica substrate using 3-aminopropyltriethoxysilane (APTES) as cross-linking agent and subsequently deoxidized by hydrazine to give the graphene coating in situ. The chemical bonding between graphene and the silica fiber improve its chemical stability, and the obtained fiber was stable enough for more than 150 replicate extraction cycles. The graphene coating was wrinkled and folded, like the morphology of the rough tree bark. Its performance is tested by headspace (HS) SPME of polycyclic aromatic hydrocarbons (PAHs) followed by GC/MS analysis. The results showed that the graphene-coated fiber exhibited higher enrichment factors (EFs) from 2-fold for naphthalene to 17-fold for B(b)FL as compared to the commercial polydimethylsioxane (PDMS) fiber, and the EFs increased with the number of condensed rings of PAHs. The strong adsorption affinity was believed to be mostly due to the dominant role of π-π stacking interaction and hydrophobic effect, according to the results of selectivity study for a variety of organic compounds including PAHs, the aromatic compounds with different substituent groups, and some aliphatic hydrocarbons. For PAHs analysis, the graphene-coated fiber showed good precision (<11%), low detection limits (1.52-2.72 ng/L), and wide linearity (5-500 ng/L) under the optimized conditions. The repeatability of fiber-to-fiber was 4.0-10.8%. The method was applied to simultaneous analysis of eight PAHs with satisfactory recoveries, which were 84-102% for water samples and 72-95% for soil samples, respectively.

Ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6), as a green solvent, was successfully used for the direct extraction of dsDNA. The extraction efficiency and the distribution coefficient values indicated that trace amounts of DNA at the levels of <5 ng microL-1 facilitate quantitative fast extraction, while proteins and metal species do not interfere. A total of 30% of the DNA in ionic liquid at approximately 20 ng microL-1 was back extracted into aqueous phase in phosphate-citrate buffer with a single-stage extraction. The extraction is demonstrated to be endothermic with an enthalpy of 34.3 kJ moL-1. The extraction mechanisms were proposed and verified by 31P NMR and FT-IR spectra. Interactions between cationic 1-butyl-3-methylimidazolium (Bmim+) and P-O bonds of phosphate groups in the DNA strands take place both in the dissolved BmimPF6 in aqueous phase and at the interface of the two phases. This interaction consequently led to the transformation of DNA conformations, along with a reduction of ethidium resonance light scattering at 510 nm, and a procedure for DNA quantification in ionic liquid was developed based on this observation.

Indium phosphide (InP) core/shell quantum dots (QDs) without intrinsic toxicity have shown great potential to replace the widely applied cadmium‐containing QDs in next‐generation commercial display and lighting applications. However, it remains challenging to synthesize InP core/shell QDs with high quantum yields (QYs), uniform particle size, and simultaneously thicker shell thickness to reduce nonradiative Förster resonant energy transfer (FRET). Here, thick InP‐Based QLEDs shell InP/GaP/ZnS//ZnS core/shell QDs with high stability, high QY (≈70%), and large particle size (7.2 ± 1.3 nm) are successfully synthesized through extending the growth time of shell materials along with the timely replenishment of shelling precursor. The existence of GaP interface layer minimizes the lattice mismatch and reduces interfacial defects. While thick ZnS shell, which suppresses the FRET between closely packed QDs, ensures high PL QY and stability. The robustness of such properties is demonstrated by the fabrication of green electroluminescent LEDs based on InP core/shell QDs with the peak external quantum efficiency and current efficiency of 6.3% and 13.7 cd A−1, respectively, which are the most‐efficient InP‐based green quantum dot light‐emitting diodes (QLEDs) till now. This work provides an effective strategy to further improve heavy‐metal‐free QLED performance and moves a significant step toward the commercial application of InP‐based electroluminescent device.