[en] Highlights: • Ag nanoparticle-decorated TiO₂ NWs were fabricated by a facile chemical method. • Ag-decorated TiO₂ NWs was used as photoanode for PEC water splitting. • The photoanode shows remarkable visible-light PEC water splitting performance. • Visible light PEC water splitting is attributed to SPR-mediated electron transfer. - Abstract: Here, we demonstrate that TiO₂ nanowires (NWs) can be significantly driven by visible light through the decoration with Ag nanoparticles (NPs) (Ag-decorated TiO₂ NWs). The Ag-decorated TiO₂ NWs show remarkably photoelectrochemical (PEC) water splitting performance under illumination with λ > 420 visible light due to surface plasmon resonance (SPR) of Ag NPs. In this work, low power of the used light source (100 mW/cm²) was not capable of heating the Ag-decorated TiO₂ nanowire photoanode enough to directly split water. In addition, under irradiation with λ > 420 nm visible light, no photocurrent was produced by TiO₂ nanowire photoanode indicates that electron transitions between valence band and conduction band do not take place in prepared anatase TiO₂ NWs. Meanwhile, the SPR energy (2.95–2.13 eV < 3.2 eV) is insufficient to excite TiO₂ NWs to generate electro-hole pairs through SPR-enhanced electromagnetic fields. Thus the remarkably visible-light-responsive PEC water splitting activity of Ag-decorated TiO₂ NWs is not attributed to local heating caused by SPR-mediated photothermal process, large enhancement of electromagnetic fields induced by SPR and scattering of resonant photons. We propose that the visible light PEC water splitting performance of Ag-decorated TiO₂ NWs is attributed to electron transfer from Ag NPs to the conduction band of TiO₂ NWs mediated by SPR. In addition, a Schottky barrier established at the interface of Ag NPs and TiO₂ NWs prevents these transferred electrons from returning to the Ag NPs and significantly retarded the recombination of electron-hole pairs in the Ag NPs, also contributing to visible-light-driven PEC water splitting performance. So the remarkably visible-light-driven PEC water splitting performance of Ag-decorated TiO₂ NWs is attributed to the synergistic effects of electron transfer mediated by SPR and the Schottky barrier between Ag NPs and TiO₂ NWs. The achieved Ag-decorated TiO₂ NWs can be added to these previously prepared TiO₂ photocatalysts mainly driven by SPR of Au NPs for the development of new visible light photocatalysts.

[en] MnI₂ is one of the important multiferroics materials with a layered, nearly two-dimensional (2D) structure due to van der Waals bonds. In this work, we developed physical vapor deposition and mechanical exfoliation methods to prepare 2D MnI₂ flakes on amorphous SiO₂ substrates. The morphologies, composition and structure properties of the 2D MnI₂ flakes were characterized by optical microscopy, atomic force microscopy, scanning electronic microscope and Raman spectroscopy. Furthermore, we systematically studied the degradation of the MnI₂ flakes. With h-BN and PMMA as protective materials, we improved the stability of the MnI₂ flakes and slow down the degradation process under moisture conditions. In this regard, we provided MnI₂ flakes as new 2D materials with effective protection, which may pave the way for the application of low dimensional multiferroics materials in the future. (paper)

[en] Highlights: • Water is scarce in the nine coal-fired energy bases of the north and west China. • The water footprint of coal and power production in the nine bases is evaluated. • The virtual water flow along with the energy products transfer is also analyzed. • Water stress in the energy bases is keeping increasing in the past and future. • The comprehensive countermeasures are proposed to ensure water and energy security. -- Abstract: In the past decades, the nine major energy bases in north and west China produced increasing amounts of coal and coal-fired power to meet rapidly growing energy demand. However, the poor water resources condition has become a bottleneck for sustainable development. In this study, the water footprint of coal and power production is evaluated, and the flow of virtual water arising from the transport of energy products is quantified. The results show that total coal and power production increased continuously from 2006 to 2015. The annual total water footprint was as much as 1.29 billion m³; it showed an initially increasing trend that peaked in 2013, after which it decreased. After 2013, the water footprint decreased primarily as a result of improvements in water-saving technologies. The results also indicate that increasing amounts of virtual water (as much as 0.87 billion m³ in 2015) embedded in energy products flowed from the north and west water deficient areas to the southeast water-rich areas of China, causing severe water scarcity in the major energy producing regions. Unfortunately, based on our estimates, water stress will continuously increase during the 13th Five-Year Plan period (2016–2020). This study finds that water-saving measures alone are not sufficient to relieve the water shortage and to guarantee water security. Comprehensive countermeasures, including an adjustment to the industrial structure, the physical transfer of water, regulation of the virtual water trade and policy and planning changes, are also necessary.

[en] Highlights: • Small volume of agricultural trade could lead to severe resources degradations. • Visible trade-offs are shown between water and land efficiencies for food. • Central Asia shows high potential of more food supply for feeding 387 million people. Besides posing soaring pressure on water and land resources, the ever-intensifying agricultural production redistributes these pressures trough increasingly intensive trade. Environmental consequences are complicated and unprecedented, and postulate thorough scrutiny. Little attention is paid to developing regions which are small nodes in terms of trade volume in global trade however of visible gaps in water and land productivities. Five Central Asian nations (CANs) have close trade activities with their neighbour China, but their agricultural production efficiency is strikingly low and the ecological environment is severely degraded. Here we evaluate, among CANs and China, the water and land footprints, virtual water and land trades, as well as potentials in enhancing water and land efficiency related to sixteen primary crop products, four primary animal products, and twelve derivative products production and trade over the period 2000–2014. We find that the blue water footprint and land footprint per unit product in CANs were up to 61- and 17-times higher than in China. Through enhancing water and land efficiency without further intervention in water and land endowments, the scenario for CANs shows an additional food supply for feeding 387 million people or half the starving population in the world.