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The B 6 Ca 2 and B 8 Ca 2 clusters adopt interesting inverse sandwich architectures, featuring a prolate B 6 (or perfect B 8) ring jammed with two capping Ca atoms. Both clusters show the high thermodynamic stability due to the double (σ and π) electronic delocalization. In present paper, we computationally studied the hydrogen storage of them. The results suggest that each Ca site in B 6 Ca 2 and B 8 Ca 2 clusters could store up six H 2 , yielding a gravimetric density of 14.2 wt% for B 6 Ca 2 and 12.6 wt% for B 8 Ca 2. The average adsorption energy for H 2 -adsorbed B 6 Ca 2 and B 8 Ca 2 complexes is within the scope of 0.12–0.15 eV per H 2 at w B97XD level, hinting that two clusters could reversibly store and release hydrogen, which is positively confirmed by the Born-Oppenheimer molecular dynamics simulations. Both B 6 Ca 2 and B 8 Ca 2 nanoclusters are feasible hydrogen storage media under the ambient condition. The B 6 Ca 2 and B 8 Ca 2 inverse sandwiches possess high-capacity hydrogen storage and release. Each Ca site can adsorb six H 2 , yielding a gravimetric density of 14.2 wt% for B 6 Ca 2 and 12.6 wt% for B 8 Ca 2. [Display omitted] • The B 6 Ca 2 and B 8 Ca 2 inverse sandwiches have the high thermostability with the double electronic delocalization. • The B 6 Ca 2 and B 8 Ca 2 inverse sandwiches exhibit the high-capacity hydrogen storage and release. • The gravimetric density is as high as 14.2 wt% for B 6 Ca 2 and 12.6 wt% for B 8 Ca 2. • The Ca-doped boron nanostructure can be used as hydrogen storage material. [ABSTRACT FROM AUTHOR]

An electrostatic self-assembly strategy for the preparation of graphene quantum dots (GQDs) attached to the surface of a glassy carbon electrode (GCE) has been developed. The GQDs were prepared by tuning the carbonization degree of citric acid and characterized by atomic force microscopy, transmission electron microscopy, Raman spectroscopy and UV–vis absorption spectroscopy. In addition, the electrochemical behaviours of hydroquinone (HQ) and catechol (CC) on the resulting modified electrodes were investigated. Under optimum conditions, the as-prepared GQDs modified electrode exhibited high electrochemical activity and good selectivity for the oxidation of HQ and CC, the linear ranges for HQ and CC were 4.0∼600 μM and 6.0∼400 μM respectively, and the detection limit was 0.40 μM and 0.75 μM, respectively. The modified electrode was also applied for the detection of real samples with satisfactory results. [ABSTRACT FROM AUTHOR]