Graphene (G) and atomic layers of hexagonal boron nitride (h-BN) are complementary two-dimensional materials, structurally very similar but with vastly different electronic properties. Recent studies indicate that h-BN atomic layers would be excellent dielectric layers to complement graphene electronics. Graphene on h-BN has been realized via peeling of layers from bulk material to create G/h-BN stacks. Considering that both these layers can be independently grown via chemical vapor deposition (CVD) of their precursors on metal substrates, it is feasible that these can be sequentially grown on substrates to create the G/h-BN stacked layers useful for applications. Here we demonstrate the direct CVD growth of h-BN on highly oriented pyrolytic graphite and on mechanically exfoliated graphene, as well as the large area growth of G/h-BN stacks, consisting of few layers of graphene and h-BN, via a two-step CVD process. The G/h-BN film is uniform and continuous and could be transferred onto different substrates for further characterization and device fabrication.

Polychlorinated biphenyls (PCBs) were not widely manufactured or used in China before they became the subject of international bans on production. Recent work has shown they have reached China associated with imported wastes, and that there are considerable unintentional sources of PCBs that have only recently been identified. As such, it was hypothesised that the source inventory and profile of PCBs may be different or unique in China, compared to countries where they were widely used and which have been widely studied. For the first time in this study we therefore undertook a complete analysis of 209 PCB congeners and assessed the contribution of unintentionally-produced PCBs (UP-PCBs) in the atmosphere of China, using polyurethane foam passive air samplers (PUF-PAS) deployed across a wide range of Chinese locations. ∑209 PCBs ranged from 9 to 6856 pg/m 3 (median: 95 pg/m 3 ) during three deployments in 2016-2017. PCB 11 was one of the most detected congeners, contributing 33±19% to ∑209 PCBs. The main sources to airborne PCBs in China were estimated and ranked as pigment/painting (34%), metallurgical industry/combustion (31%), e-waste (23%) and petrochemical/plastic industry (6%). For typical Aroclor-PCBs, e-waste source dominated (>50%). Results from our study indicate that UP-PCBs have become the controlling source in the atmosphere of China and an effective control strategy is urgently needed to mitigate emissions from multiple industrial sources.

Polychlorinated biphenyls (PCBs) are industrial organic contaminants identified as persistent, bioaccumulative, toxic (PBT), and subject to long-range transport (LRT) with global scale significance. This study focuses on a reconstruction and prediction for China of long-term emission trends of intentionally and unintentionally produced (UP) ∑PCBs (UP-PCBs, from the manufacture of steel, cement and sinter iron) and their re-emissions from secondary sources (e.g., soils and vegetation) using a dynamic fate model (BETR-Global). Contemporary emission estimates combined with predictions from the multimedia fate model suggest that primary sources still dominate, although unintentional sources are predicted to become a main contributor from 2035 for PCB-28. Imported e-waste is predicted to play an increasing role until 2020-2030 on a national scale due to the decline of intentionally produced (IP) emissions. Hypothetical emission scenarios suggest that China could become a potential source to neighboring regions with a net output of ∼0.4 t year by around 2050. However, future emission scenarios and hence model results will be dictated by the efficiency of control measures.