Qianwen Zheng

Synthesis of layered double hydroxides/graphene oxide nanocomposite as a novel high-temperature CO2 adsorbent

Abstract In this contribution, a novel high-temperature CO2 adsorbent consisting of Mg-Al layered double hydroxide (LDH) and graphene oxide (GO) nanosheets was prepared and evaluated. The nanocomposite-type adsorbent was synthesized based on the electrostatically driven self-assembly between positively charged Mg-Al LDH single sheet and negatively charged GO monolayer. The characteristics of this novel adsorbent were investigated using XRD, FE-SEM, HRTEM, FT-IR, BET and TGA. The results showed that both the CO2 adsorption capacity and the multicycle stability of LDH were increased with the addition of GO owing to the enhanced particle dispersion and stabilization. In particular, the absolute CO2 capture capacity of LDH was increased by more than twice by adding 6.54 wt% GO as support. GO appeared to be especially effective for supporting LDH sheets. Moreover, the CO2 capture capacity of the adsorbent could be further increased by doping with 15 wt% K2CO3. This work demonstrated a new approach for the preparation of LDH-based hybrid-type adsorbents for CO2 capture.

Synthesis of LiAl2-layered double hydroxides for CO2 capture over a wide temperature range

Although there are many reports on layered double hydroxide (LDH) derived CO2 adsorbents, none of them have studied the special case of LiAl2 LDHs. Here we report the first detailed investigation of the performance of LiAl2 LDHs as novel CO2 adsorbents. LiAl2 LDHs were synthesized using both traditional coprecipitation and gibbsite intercalation methods. All the materials were thoroughly characterized using XRD, SEM, TEM, FTIR, BET, and TGA. The CO2 capture performance of these LDHs were investigated as a function of charge compensating anions, Li/Al ratio in preparation solution, calcination temperature, adsorption temperature, and doping with K2CO3. The data indicated that LiAl2 LDHs derived compounds can be used as CO2 adsorbents over a wide temperature range (60–400 °C), with a CO2 capture capacity of 0.94 and 0.51 mmol g−1 at 60 and 200 °C, respectively. By doping LiAl2–CO3 LDH with 20 wt% K2CO3, the CO2 adsorption capacity was increased up to 1.27 and 0.83 mmol g−1 at 60 and 200 °C, respectively. CO2 adsorption–desorption cycling studies showed that both pure LiAl2 LDH and the K2CO3-promoted LiAl2 LDH had stable CO2 capture performance even after 22 cycles. Considering its high CO2 capture capacity and good cycling stability, LiAl2 LDH based novel CO2 adsorbents have significant potential for CO2 capture applications.

Unexpected highly reversible topotactic CO2 sorption/desorption capacity for potassium dititanate

Potassium dititanate (K2Ti2O5) was revealed to possess an unexpected, highly reversible CO2 sorption/desorption capacity at ca. 750 °C, which is promising as a high-temperature CO2 adsorbent for sorption enhanced hydrogen production (SEHP) processes. In contrast to numerous other adsorbents that are severely sintered during cycles at high temperatures, the CO2 sorption/desorption cycles over K2Ti2O5 exhibited a contrast particle size “break-down” process. The large K2Ti2O5 particles gradually breakdown into K2Ti2O5 nanofibers after 20 cycles, leading to a very stable CO2 sorption/desorption performance with very rapid kinetics. A reversible CO2 capture capacity as high as 7.2 wt% was achieved at 750 °C. Moreover, only 6 min is required for complete CO2 desorption at 750 °C, indicating that this adsorbent can be practically run with a simple pressure swing sorption scheme. Surprisingly, an interesting structure switching phenomenon between K2Ti2O5 and K2Ti4O9 caused by CO2 sorption and desorption was revealed. A detailed mechanism was proposed based on XRD, FTIR, SEM, HR-TEM, and SAED analyses and was further verified by density functional theory calculation. Considering its relatively high CO2 capture capacity, superior cycling stability, and excellent regeneration ability, we believe K2Ti2O5 offers significant potential as a practical, novel high-temperature CO2 adsorbent.

LDH/MgCO3 hybrid multilayer on an aluminium substrate as a novel high-temperature CO2 adsorbent

A LDH/MgCO3 hybrid multilayer thin film as a high-temperature CO2 adsorbent has been fabricated in situ on an aluminium foil/mesh substrate, which possesses high CO2 capture capacity (0.56 mmol g−1) and may offer practical advantages such as higher thermal and mechanical stability, and a more flexible solution for making robust solid porous structures.

Revealing how molten salts promote CO2 capture on CaO via an impedance study and sorption kinetics simulation

Electrochemical impedance spectroscopy analyses were utilised to explore the oxygen ion conductivity of alkali metal salts promoted CaO, which revealed that oxysalts, such as carbonate and sulfate with good ion conductivity, promote CO2 capture.