Nitrogen-doped porous carbons by conversion of azo dyes especially in the case of tartrazineZhong Jie Zhanga,b, Chong Chenb, Peng Cuib,*, Xiang Ying Chenb,*aCollege of Chemistry I (A) is the discharge current;Dt (s) is the discharge time;DV (V) is the potential win- dow; and m (mg) is the mass of active materials loaded in working electrode.Specific energy density (E) and specific power density (P) derived from galvanostatic tests can be calculated from the equations:E ¼1 2CDV2P ¼E Dtwhere E (Wh kg?1) is the average energy density; C (F g?1) is thespecific capacitance;DV (V) is the potential window; P (W kg?1) is the average power density andDt (s) is the discharge time.3. Results and discussionThe component, crystallinity and purity of the carbon samples were studied by XRD technique. By direct carbonization of pure tartrazine at 800?C for 2 h under Ar flow, black product appears and the corresponding XRD pattern is shown in Fig. 2a, mainly consisting of carbon, orthorhombic Na2SO4(JCPDS Card No. 37-0808) and other unidentified substances. The formation of Na2SO4 originates from the reaction of sulfonate and sodium ions within the structure of tartrazine, and similar phenomenon also occurs in case of production of porous carbon from calcium lignosulfonate [16]. The product was subsequently washed with aqueous HCl so- lution and deionized water to remove any soluble/insolubleimpurities, resulting in the formation of relatively pure carbon, dominated as T-800-blank. The XRD pattern in Fig. 2b has one broad diffraction peak centering at ca. 24.9?, indicative feature of amorphous carbon and close to that of (002) plane of crystal graphite. Furthermore, one minor and indistinct diffraction peak locates at ca. 24.9?, approximately indexed as (10) plane [17]. On the other hand, when heating the mixture of tartrazine and Ca(OAc)2$H2O powder as 1:1/3:1 at 800?C, the product iscomposed of amorphous carbon and CaCO3, CaO etc. [18], which was washed with aqueous HCl solution and deionized water, eventually resulting in T-Ca-800-1:1/3:1. Their XRD patterns are shown in Fig. 2dee, incredibly close to that of T-800-blank. The shapes and sizes of the carbon samples wereinvestigated by FESEM technique. Fig. 3a shows the representative FESEM image of the T-800-blank sample, which consists of a large number of micrometer block particles with irregular shapes. With respect toT- Ca-800-1:1/3:1 samples, their FESEM images depicted in Fig. 3be d are somewhat similar to that of T-800-blank. Taking into account the self-carbonization/decomposition of tartrazine as well as the templating effect of calcium acetate at elevated temperatures, nanoscale porous structures are anticipated to happen within the carbonproducts, which will further be detected by the following N2 adsorption/desorption analysis. The empirical composition, functional groups on the surfaces, chemical state and electronic state of the elements toward the present carbons were determined by XPS technique, giving infor- mation concerning the outermost 3e4 nm surface layer carbon surface. Fig. 4a indicates the overall XPS survey spectra of the T- 800-blank and T-Ca-800-1:1/3:1 samples from0 to1400 eV. All the carbon samples consisting of C/N/O elements apparently reveal their purities after washing process. In addition, the relative in- tensities of C/N/O elements differentiate from each other, implying their different content in the products. The high resolution XPS spectra toward C1s are given in Fig. 4b, ranging from 280.5 to297.5 eV, which can be closely fitted into three main peaks locating at ca. 284.9, 285.8 and 288.3 eV, respectively. In details, the peak at ca. 284.9 eV is attributed to sp2C]C bond, evincing the graphitic nature [19]. The peak at ca. 285.8 eV might be due to sp3CeC bond [20] and/or CeN bond [21]. As for the one at ca. 288.3 eV, it can be incurred by eOeC]O bond [22]. Fig. 4c gives us the high resolution XPS spectra of O1s with the binding energy scope from 526.5 to 541.0 eV. All the O1s spectra arealmost the same and can be approximately fitted into three main peaks at ca. 531.4, 532.5 and 533.4 eV, respectively. Hereinto, the peak at ca. 531.4 eV owes to eC]O bond; the peak at ca. 532.5 eV is due to CeOeC/CeOH bond; and the one at ca. 533.4 eV can be ascribed to OeC]O bond [23]. Besides, the high resolution N1s1020304050607043.7O24.9O# ## ###(b)(a)Intensity (a.u.)2 Theta (deg.)1020304050607043.7o24.9o23.5oIntensity (a.u.)2 Theta (deg.)(e)(d)(c)Fig. 2. XRD patterns of the T-800-blank sample before (a) and after (b) being washed with aqueous HCl solution and deionized water to remove any unwanted impurities; as well as the comparative XRD patterns of the (c) T-800-blank; (d) T-Ca-800-1:1 and (e) T-Ca-800-3:1 samples. Notes: # ¼ orthorhombic Na2SO4(JCPDS Card No. 37-0808). The inset in the right XRD pattern is the approximate unit structure of amorphous carbon.Z.J. Zhang et al. / Journal of Power Sources 242 (2013) 41e4943spectra (393.0e410.0 。