One-pot synthesis of highly fluorescent amino-functionalized graphene quantum dots for effective detection of copper ions

In this work, a green and simple one-pot route was developed for the synthesis of highly fluorescent amino-functionalized graphene quantum dots (a-GQDs) via hydrothermal process without any further modification or surface passivation. We synthesized the a-GQDs using glucose as the carbon source and ammonium as a functionalizing agent without the use of a strong acid, oxidant, or other toxic chemical reagent. The as-obtained a-GQDs have a uniform size of 3–4 nm, high contents of amino groups, and show a bright green emission with high quantum yield of 32.8%. Furthermore, the a-GQDs show effective fluorescence quenching for Cu²⁺ ions which can serve as effective fluorescent probe for the detection of Cu²⁺. The fluorescent probe using the obtained a-GQDs exhibits high sensitivity and selectivity toward Cu²⁺ with the limit of detection as low as 5.6 nM. The mechanism of the Cu²⁺ induced fluorescence quenching of a-GQDs can be attributed to the electron transfer by the formation of metal complex between Cu²⁺ and the amino groups on the surface of a-GQDs. These results suggest great potential for the simple and green synthesis of functionalized GQDs and a practical sensing platform for Cu²⁺ detection in environmental and biological applications.     

第一性原理研究O和S掺杂的石墨相氮化碳(g-C_3N_4)_6量子点电子结构和光吸收性质

利用密度泛函和含时密度泛函理论研究了氧(O)和硫(S)原子掺杂的石墨相氮化碳(g-C_3N_4)_6量子点的几何、电子结构和紫外-可见光吸收性质.结果表明:掺杂后(g-C_3N_4)_6量子点杂质原子周围的C-N键长发生了一定的改变,最高电子占据分子轨道-最低电子未占据分子轨道(HOMO-LUMO)能隙显著减小.形成能的计算表明O原子取代掺杂的(g-C_3N_4)_6量子点体系更稳定,且O原子更易取代N3位点,而S原子更易取代N8位点.模拟的紫外-可见电子吸收光谱表明,O和S原子的掺杂改善了(g-C_3N_4)_6量子点的光吸收,使其吸收范围覆盖了整个可见光区域,甚至扩展到了红外区.而且适当的杂质浓度使(g-C_3N_4)_6量子点光吸收在强度和范围上都得到明显改善.通过O和S掺杂的比较,发现二者在可见光区对(g-C_3N_4)_6量子点的光吸收有相似的影响,然而在长波长区域二者的影响有明显差异.总体而言,O掺杂要优于S掺杂对(g-C_3N_4)_6量子点光吸收的影响.     

Ultrasonic-assisted magnetic solid phase extraction of morphine in urine samples by new imprinted polymer-supported on MWCNT-Fe3O4-NPs: Central composite design optimization

Multiwalled carbon nanotubes (MWCNTs) were magnetized with Fe₃O₄ nanoparticles (MWCNTs-Fe₃O₄-NPs) and subsequently coated by vinyl end groups (Vinyltrimethoxysilane). MWCNT-Fe₃O₄-NPs were used as support for a new morphine (MO) molecularly imprinted polymer (MWCNT-Fe₃O₄-NPs@MO-MIP) by surface imprinting polymerization method. The MWCNT-Fe₃O₄-NPs@MO-MIP was characterized by FTIR, VSM and SEM techniques and successfully used for determination of MO. Ultrasonic-assisted magnetic solid phase extraction followed by UV–vis spectrophotometer (UAMSPE-UV–vis) was investigated for MWCNT-Fe₃O₄-NPs@MO-MIP and compared with non-imprinted polymer (NIP) using batch method. Central composite design under response surface methodology was used for the evaluation of the effect of variables, individually, as well as their possible interaction effects on the adsorption process. The variables such as sonication time, MWCNT-Fe₃O₄-NPs@MO-MIP mass, initial concentration of MO and pH were investigated in this study. At optimum experimental conditions, UAMSPE-UV–vis method was exhibited a linear range of 0.8–8.7 mg L⁻¹ of the MO concentration with a detection limit of 0.18 mg L⁻¹. The relative standard deviation for the analyte was found to be lower than 2.32%. The MWCNT-Fe₃O₄-NPs@MO-MIP adsorption capacity was found to be 37.01 mg g⁻¹. The enrichment and preconcentration factors were found to be 107.01 and 98.21, respectively. The developed method was finally applied successfully to the determination of MO in urine and wastewater samples with the recoveries ranged from 96.40 to 105.6%.