Stoichiometry-grain size-specific capacitance interrelationships in nickel oxide.

Nickel oxide exhibits almost the highest theoretical specific capacitance (C s), which includes contributions from non-faradaic double layer charging and faradaic OH- adsorption. However, the realistic and tangible C s is due to the faradaic process, which can be influenced by chemical (i.e. stoichiometry) and structural (i.e. grain size) changes. Hence, it is necessary to investigate the interrelationships among chemical and structural features and charge storage capacity. Here, a non-stoichiometric nickel oxide (Ni x O) containing Ni2+ and Ni3+ was synthesized by a sol-gel method at 620, 720 and 920 °C using Ni(NO3)2·6H2O and citric acid. The grain size as estimated from X-ray diffraction increases from 55 to 194 nm with increase in the synthesis temperature. The stoichiometry measured through Ni2+ (or Ni3+) fraction from X-ray photoelectron spectroscopy also increases from 70.3 to 99.2 atom% with synthesis temperature. The C s due to faradaic OH- adsorption was estimated from cyclic voltammetry in 2 M KOH within -0.05 to +0.60 V vs. Hg/Hg2Cl2/KCl (sat. in water). This C s increases from 7.5 to 92.4 F g-1 with a decrease in the grain size and stoichiometry (increase in Ni3+) due to possibly the increased conductivity and NiOOH formation through OH- adsorption. The deviation from stoichiometry at lower grain size mainly stems from nickel vacancy accommodation, according to the thermodynamic model proposed here. The interrelationships among stoichiometry, grain size and the specific capacitance of nickel oxide are investigated.

Boron from net charge acceptor to donor and its effect on hydrogen uptake by novel Mg-B-electrochemically synthesized reduced graphene oxide.

Hydrogen uptake (H-uptake) is studied in ball milled Mg-B-electrochemically synthesized reduced graphene oxide (erGO) nanocomposites at PH2 ≈ 15 bar, ~ 320 °C. B/C (weight ratio): 0, ~ 0.09, ~ 0.36, ~ 0.90 are synthesized maintaining erGO≈10wt %. B occupies octahedral interstices within Mg unit cell-revealed by electron density maps. Persistent charge donations from Mg and B to C appear as Mg-C (~ 283.2 eV), B-C (~ 283.3-283.9 eV) interactions in C-1s core X-ray photoelectron spectroscopy (XPS) at all B/C. At B/C > 0.09, charge reception by B from Mg yields Mg-B interaction. This net charge acceptor role of B renders it electron-rich and does not alter Mg unit cell size significantly. Despite charge donation to both C and B, the Mg charge is < + 2, resulting in long incubation times (> 5 h) at B/C > 0.09. At B/C≈0.09 the minimal Mg-B interaction renders B a charge donor, resulting in Mg-B repulsion and Mg unit cell expansion. Mg-C peak shift to lower binding energies (C-1s XPS), decreases incubation time to ~ 2.25 h and enhances H-uptake kinetics. Various atomic interactions influence the reduction of incubation time in H-uptake and increase its kinetics in the order: (Mg → C; B → C)B/C≈0.09, B: donor > (Mg → C)B/C=0 > (ternary Mg → B → C)B/C>0.09, B: acceptor.

Efficacy and reusability of mixed-phase TiO2-ZnO nanocomposites for the removal of estrogenic effects of 17ß-Estradiol and 17α-Ethinylestradiol from water.

Photocatalytic removal of estrogenic compounds (ECs), 17ß-estradiol (E2), and 17α-ethinylestradiol (EE2) were assessed using a TiO2-ZnO nanocomposite (NC) over a range of initial EC concentration (Co; 10 mg/L - 0.05 mg/L). Photocatalytic removal was evaluated under UV and visible irradiation using 10 mg/L NC over 240 min duration. After 240 min, analysis using GCxGC TOF MS revealed 100% transformation at Co ≤ 1 mg/L and ≥25% transformation at Co ≤ 10 mg/L under visible irradiation. Degradation was accompanied by breakdown of the fused ring structure of E2, generating smaller molecular weight by-products which were subsequently mineralized as revealed through TOC removal. With UV photocatalysis, ~30% and ~20% mineralization was attained for E2 and EE2, respectively, for Co of 10 mg/L. Under visible irradiation, ~25% and ~10% mineralization was achieved for E2 and EE2, respectively. Estrogenicity variation was estimated using the E-screen assay conducted with estrogen receptor-positive MCF-7 breast cancer cells. Complete removal of estrogenicity of ECs was confirmed after 240 min of photocatalysis under UV and visible irradiation. FTIR spectroscopy-based analysis of the NC after E2 photocatalysis revealed the presence of sorbed organics. Desorption, followed by GC × GC TOF-MS analysis revealed these organics as by-products of photocatalysis. Desorption of sorbed organics followed by recalcination at 600 °C for 1 h regenerated the active sites on the NC, enabling its efficient reuse for 3 cycles under visible irradiation without loss in activity.

The dehydrogenation mechanism during the incubation period in nanocrystalline MgH2.

The dehydrogenation mechanism during the incubation period in nanocrystalline MgH2 (low α: converted metal fraction and dα/dt) and the reasons for the occurrence of the incubation period at 320, 350, and 400 °C were investigated. Pre-existing Mg crystallites can enhance Mg nucleation during the incubation period, as suggested by the estimated activation energy for nucleation (12 ± 2 kJ per mol H). The released H-atoms enter MgH2 as interstitials, as indicated by the MgH2 unit-cell contraction, resulting in increased equatorial Mg-H bond length, decreased charge-density distribution in the interstitial region, as observed from the charge-density maps, and decreased H-H distance in the {001} plane up to the midway of the incubation period. Eventually, hydrogen vacancies are created, as indicated by the red shift in the Eg and A1g peaks of Raman spectra. The high estimated activation energy for the growth of Mg (209 ± 8 kJ per mol H) renders it difficult and explains the reason for the presence of an incubation period.