No abstract

It has long been under debate whether the electron transport performance of graphene could be enhanced by the possible occurrence of van Hove singularities in grain boundaries. Here, we provide direct experimental evidence to confirm the existence of van Hove singularity states close to the Fermi energy in certain ordered grain boundaries using scanning tunneling microscopy. The intrinsic atomic and electronic structures of two ordered grain boundaries, one with alternative pentagon and heptagon rings and the other with alternative pentagon pair and octagon rings, are determined. It is firmly verified that the carrier concentration and, thus, the conductance around ordered grain boundaries can be significantly enhanced by the van Hove singularity states. This finding strongly suggests that a graphene nanoribbon with a properly embedded ordered grain boundary can be a promising structure to improve the performance of graphene-based electronic devices.

Doping with anion and cation impurities is an effective approach to tune the photoelectrochemical properties of TiO2. Here, we explore the Rh monodoping and (Rh + F) codoping effect on electronic structures and photocatalytic activities of anatase TiO2 by performing extensive density functional theory calculations. Upon Rh monodoping, the band gap of TiO2 can be effectively reduced. But this cationic dopant creates an unoccupied intermediate localized state within the band gap, which will act as photogenerated carrier recombination center, which reduces the photocatalytic efficiency. Fortunately, we find that the stable charge-compensated donor–acceptor pair (Rh + F) codoping in TiO2 can effectively reduce the band gap by forming a delocalized intermediate band within the band gap. Moreover, the band edge alignment in the (Rh + F) codoped TiO2 is desirable for water splitting. The calculated optical absorption curve of (Rh + F) codoped TiO2 verifies that it has significantly improved visible light absorption. These findings imply that the (Rh + F) codoped TiO2 is a promising visible light photocatalyst for water splitting.

Haematococcus pluvialis is an astaxanthin-rich microalga that can increase its astaxanthin production by salicylic acid (SA) or jasmonic acid (JA) induction. The genetic transcriptome details of astaxanthin biosynthesis were analyzed by exposing the algal cells to 25 mg/L of SA and JA for 1, 6 and 24 hours, plus to the control (no stress). Based on the RNA-seq analysis, 56,077 unigenes (51.7%) were identified with functions in response to the hormone stress. The top five identified subcategories were cell, cellular process, intracellular, catalytic activity and cytoplasm, which possessed 5600 (~9.99%), 5302 (~9.45%), 5242 (~9.35%), 4407 (~7.86%) and 4195 (~7.48%) unigenes, respectively. Furthermore, 59 unigenes were identified and assigned to 26 putative transcription factors (TFs), including 12 plant-specific TFs. They were likely associated with astaxanthin biosynthesis in Haematococcus upon SA and JA stress. In comparison, the up-regulation of differential expressed genes occurred much earlier, with higher transcript levels in the JA treatment (about 6 h later) than in the SA treatment (beyond 24 h). These results provide valuable information for directing metabolic engineering efforts to improve astaxanthin biosynthesis in H. pluvialis.