The substantial increase of the atmospheric CO2 concentration over the last few decades has steered toward research on direct air capture (DAC). DAC is one of the mobile-source carbon capture and storage (CCS) processes that is variant from the conventional point-source CCS in terms of easing the CO2 concentration levels and promoting negative carbon emission. We propose here a sustainable material based on the quaternization of bamboo fiber and the implication in DAC. The quaternized bamboo cellulose could adsorb CO2 at a medium relative humidity (RH) of 60–80%, with the efficiency of quaternary ammonium groups over 0.65. The CO2 capacity at higher RH strikingly decreased, which indicates the moisture-swing characteristics, and that was further validated by a desorption ratio of 0.70 under humid gas purge. The unique phenomenon that a dry atmosphere (e.g., RH < 20%) is not favored by adsorption was revealed and could be attributed to the hydrophobic feature of the sorbent inherited from natural lignocellulose. The results suggest that quaternized cellulose with a low cost may open up new possibilities for the utilization of moisture-swing CO2 adsorbents in damp circumstances.
Oval caves have recently been discovered in the Bashuihe granite pluton of Laoshan Mountain, China. Oval caves typically occur in alkaline granites. This study conducted microthermometry and stable isotope analysis of quartz inclusions from oval caves and host rocks from the Bashuihe pluton to reconstruct the diagenetic evolutionary history of the Laoshan area. The temperature measurement results indicated a homogenisation temperature range from 162.5 to 261.6°C (mean 203.9°C), a salinity range of 2.1–8.3 wt% (mean 5.07 wt%), and a density range of 0.8–0.98 g/cm3 (mean 0.90 g/cm3), indicating a low-temperature, low-salinity, and low-density fluid. The emplacement depth ranged from 2.73 km to 4.43 km, indicating medium-shallow granite. A hydrogen and oxygen isotope analysis ( , ) revealed that the diagenetic fluids of the Bashuihe pluton represented a mixed hydrothermal solution composed of meteoric water and magmatic water. The results of a whole rock, H–O isotopes, rare earth element, and high field strength element analysis on the Laoshan alkali granites suggest significant hydrothermal activity in the late stage of magmatism. Primary oval caves in the Bashuihe pluton most likely evolved in the following sequence: fluid was enriched in the late diagenetic stage, diagenetic minerals crystallised under low temperature and pressure conditions, the crystallisation rate accelerated, and the magma condensed rapidly. Moreover, the increase in magma fluid enabled the movement and convergence of fluid. The accumulated fluid and volatiles occupied more space, and rapid magma condensation trapped the accumulated fluid and volatiles in the pluton, forming the oval granite cave. This research provides a crucial theoretical reference for the development and utilisation of underground space and engineering buildings in granite regions.
Ni-MgO dual function materials (DFMs) show promise for integrated CO2 sorption and methanation. To improve CO2 sorption capacity, Ni-MgO DFMs are promoted with alkali metal nitrates. However, the high catalyst reduction temperature will result in high energy consumption, huge temperature gap between reduction (∼650 °C) and CO2 sorption and methanation (∼300 °C), and the loss of alkali metal nitrates. In this work, we prepared a Ni/CeO2 catalyst and investigated the effect of reduction temperature on its structure–property relationships in CO2 methanation, aiming to lower the reduction temperature to an isothermal level that matches CO2 methanation. Results indicated that the reduction temperature fell from over 650 to 300 °C, and Ni/CeO2 reduced at 300 °C featured high CO2 conversion (72.7%) and CH4 selectivity (98.9%). The CO2 methanation activity of Ni/CeO2 declined significantly when the reduction temperature exceeded 400 °C. The formation of more oxygen vacancy defects due to the interaction between NiO and CeO2 promoted the reduction of NiO species at lower temperatures. The declined CO2 methanation activity at high reduction temperatures was ascribed to the consumption of oxygen vacancies in catalyst reduction, and less defects were available for CO2 activation and methanation. An alkali metal nitrate promoted MgO adsorbent was physically mixed with Ni/CeO2 to construct (Li-Na-K)NO3-MgO-Ni/CeO2-phy DFMs for integrated CO2 sorption and methanation. The DFMs could be facilely reduced at 300 °C, and this has made it possible to realize the isothermal operation of catalyst reduction and CO2 sorption and methanation in integrated CO2 capture and utilization (ICCU). The (Li-Na-K)NO3-MgO-Ni/CeO2-phy DFMs reduced at 300 °C exhibited an impressive CO2 uptake of 2.74 mmol CO2/g DFMs and a great CH4 yield of 1.10 mmol CH4/g DFMs, and they could be a promising alternative to Ru-based DFMs with respect to their comparable CO2 sorption capacity and methanation activity and minimized cost of raw materials.
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