Connecting Carbon Capture with Oceanic Biomass Production

The climate change believed by anthropogenic emission is not isolated but tightly coupled with other issues including biodiversity loss and ocean acidification etc., and in order to prevent the potential serious impacts, both political and technological methods are being tried for greenhouse mitigation. Dimming the income sunlight by some “geoengineering” approaches currently seem ruinously expensive and technically difficult, and would not prevent the increase of greenhouse gases (GHGs) in atmosphere and ocean acidification, so capturing carbon to reduce the environmental concentration of carbon dioxide (CO2) and promoting renewable energy development for the reduction of using fossil fuels are very necessary. Biofuels derived from natural and agricultural biomass could be deployed for power production and existing transportation needs. The current economics are more favorable for conversion of edible biomass into biofuels, which could spend plenty of freshwater and farmlands, compete with food supply, and create a “carbon debt” with local ecosystem destruction by deforestation to expand biofuel-crop production. So it is vital to develop processes for converting non-edible feedstock such as lignocellulose and microalgae into biofuels.
 Compared with lignocellulose, microalgae have higher growth rates, don’t need plenteous freshwater for irrigating, and can grow in the conditions that are not favorable for terrestrial biomass growth. The current limitation of microalgal biofuels is the microalgae cultivation cost, and to compensate the high cost of microalgal biofuels, three suggestions are propounded here. (i) Using ships as the platforms of cultivating microalgae, producing biofuels, and transporting feedstock and products on a large scale on subtropical oligotrophic oceans, where the ocean’s least productive waters are formed with compared peaceful surface condition and poor marine communities. (ii) Operating different kinds of oceanic biomass productions for high-value products to compensate the cost of microalgal biofuels. Different kinds of microalgae and macroalgae (seaweeds) could be cultivated for biofuels, chemicals, healthy food, and feed for breeding economic marine species to satisfy the accelerating demands for seafood supply and simultaneously mitigate the fast decline of wild stocks. (iii) Constituting financial subsidies to make CO2 as the feedstock of microalgae cultivation for free, and exact quantifying the carbon captured in biomass products and the CO2 reduction that these products would provide by displacing natural and nonrenewable carbon resources, to take part in the international carbon-credit trading markets and sell the offsets. In a word, this article mainly talks about trying to find a way that connect CO2 capture with renewable energy development, and partially combat against deforestation, loss of biodiversity, shortage of food, and decline of marine lives etc., if possible

Intrinsic Defects and Electronic Conductivity of TaON: First-Principles Insights

As a compound in between the tantalum oxide and nitride, the tantalum oxynitride TaON is expected to combine their advantages and act as an efficient visible-light-driven photocatalyst. In this letter, using hybrid functional calculations we show that TaON has different defect properties from the binary tantalum oxide and nitride: (i) instead of O or N vacancies or Ta interstitials, the $O_N$ antisite is the dominant defect, which determines its intrinsic n-type conductivity and the p-type doping difficulty; (ii) the $O_N$ antisite has a shallower donor level than O or N vacancies, with a delocalized distribution composed mainly of the Ta $5d$ orbitals, which gives rise to better electronic conductivity in the oxynitride than in the oxide and nitride. The phase stability analysis reveals that the easy oxidation of TaON is inevitable under O rich conditions, and a relatively O poor condition is required to synthesize stoichiometric TaON samples

Role of initial magnetic disorder: A time-dependent ab initio study of ultrafast demagnetization mechanisms.

Despite more than 20 years of development, the underlying physics of the laser-induced demagnetization process is still debated. We present a fast, real-time time-dependent density functional theory (rt-TDDFT) algorithm together with the phenomenological atomic Landau-Lifshitz-Gilbert model to investigate this problem. Our Hamiltonian considers noncollinear magnetic moment, spin-orbit coupling (SOC), electron-electron, electron-phonon, and electron-light interactions. The algorithm for time evolution achieves hundreds of times of speedup enabling calculation of large systems. Our simulations yield a demagnetization rate similar to experiments. We found that (i) the angular momentum flow from light to the system is not essential and the spin Zeeman effect is negligible. (ii) The phonon can play a role but is not essential. (iii) The initial spin disorder and the self-consistent update of the electron-electron interaction play dominant roles and enhance the demagnetization to the experimentally observed rate. The spin disorder connects the electronic structure theory with the phenomenological three-temperature model

Thermodynamic Oxidation and Reduction Potentials of Photocatalytic Semiconductors in Aqueous Solution

We introduce an approach to calculate the thermodynamic oxidation and reduction potentials of semiconductors in aqueous solution. By combining a newly-developed ab initio calculation for compound formation energy and band alignment with electrochemistry experimental data, this approach can be used to predict the stability of almost any compound semiconductor in aqueous solution. 30 photocatalytic semiconductors have been studied, and a graph (a simplified Pourbaix diagram) showing their valence/conduction band levels and oxidation/reduction potentials is produced. Based on this graph, we have studied the stabilities and trends against the oxidative and reductive photocorrosion for compound semiconductors. We found that, only metal oxides can be thermodynamically stable when used as the n-type photoanodes. All the non-oxides are unstable due to easy oxidation by the photogenerated holes, but they can be resistant to the reduction by electrons, thus stable as the p-type photocathodes