We investigated the effects of supercritical-CO2 treatment on the pore structure and consequent H2 adsorption behavior of single-walled carbon nanohorns (SWCNHs) and SWCNH aggregates. High-resolution transmission electron microscopy and adsorption characterization techniques were employed to elucidate the alterations in the SWCNH morphology and aggregate pore characteristics induced by supercritical-CO2 treatment. Our results confirm that supercritical-CO2 treatment reduces the interstitial pore surface area and volume of SWCNH aggregates, notably affecting the adsorption of N2 (77 K), CO2 (273 K), and H2 (77 K) gasses. The interstitial porosity strongly depends on the supercritical-CO2 pressure. Supercritical-CO2 treatment softens the individual SWCNHs and opens the core of SWCNH aggregates, producing a partially orientated structure with interstitial ultramicropores. These nanopores are formed by the diffusion and intercalation of CO2 molecules during treatment. An increase in the amount of H2 adsorbed per interstitial micropore of the supercritically modified SWCNHs was observed. Moreover, the increase in the number and volume of ultramicropores enable the selective adsorption of H2 and CO2 molecules. This study reveals that supercritical-CO2 treatment can modulate the pore structure of SWCNH aggregates and provides an effective strategy for tailoring the H2 adsorption properties of nanomaterials.

탄소중립을 달성하기 위해 이산화탄소를 포집, 활용, 저장하는 CCUS (carbon capture, utilization, and storage) 기 술이 주목받고 있다. 본 연구에서는 광물 탄산화 공정을 통해 이산화탄소를 탄산염으로 고정하고, 이를 전이금속 탄산염 기반 리튬이온배터리 (LIB) 음극재로 적용하였다. CO2를 탄산염으로 고정후, 이를 이용해 FeCO3를 제작하고, rGO와 PVP와 복합 화하여 음극활물질에 적용하였다. rGO는 전기전도도를 높이고 입자의 응집을 방지해 부피 팽창을 완화했으며, PVP는 계면 활성제로서 입자 표면을 안정화하여 구조적 안정성을 강화하였다. FeCO3-PVP-rGO 복합체 기반한 음극재에 대한 전기화학 테스트를 진행한 결과, FeCO3/rGO 복합체는 1,620 mA/g의 전류 밀도에서 50 사이클 이후에도 400 mAh/g의 용량을 유지하 였다. 본 연구는 CO2를 고부가가치 배터리 소재로 전환하여 차세대 에너지 저장 기술에 기여할 가능성을 시사한다.

Among the products of the electrocatalytic reduction of carbon dioxide (CO2RR), CO is currently the most valuable product for industrial applications. However, poor stability is a significant obstacle to CO2RR. Therefore, we synthesized a series of bimetallic organic framework materials containing different ratios of tungsten to copper using a hydrothermal method and used them as precursors. The precursors were then subjected to pyrolysis at 800 °C under argon gas, and the M-N bimetallic sites were formed after 2 h. Loose porous structures favorable for electrocatalytic reactions were finally obtained. The material could operate at lower reduction potentials than existing catalysts and obtained higher Faraday efficiencies than comparable catalysts. Of these, the current density of WCu-C/N (W:Cu = 3:1) could be stabilized at 7.9 mA ‧ cm-2 and the FE of CO reached 94 % at a hydrogen electrode potential of -0.6 V (V vs. RHE). The novel materials made with a two-step process helped to improve the stability and selectivity of the electrocatalytic reduction of CO2 to CO, which will help to promote the commercial application of this technology.

Schlumbergera truncata absorbs CO2 through its mature phylloclades during the night, and can use a substantial amount of CO2 without requiring ventilation. This study investigated the growth and photosynthetic responses of S. truncata ‘Red Candle’ at two CO2 levels—ambient (≈ 400 μmol･mol-1) and elevated (≈ 1000 μmol･mol-1). At 0–8 weeks after treatment (WAT), width and length of mature phylloclade and length of immature phylloclade did not differ significantly among the CO2 treatments. At 4–8 WAT, number of branches and phylloclades were significantly greater in plants grown under ambient CO2 than those under elevated CO2. Net CO2 uptake was highest in mature phylloclades of plants grown under ambient and elevated CO2 regimes at night, at 2.51 and 1.30 μmol·CO2·m-2·s-1, respectively. However, no statistically significant variation was observed at 6 WAT, and stomatal conductance was significantly affected only by CO2 uptake time at 6 and 8 WAT. Water-use efficiency of mature and immature phylloclades at night increased with increase in CO2 levels (r = 0.7462 and 0.9312, respectively). At 123 days after treatment, plants grown under elevated CO2 had 82.7 floral buds, compared to 72.1 buds in those under ambient CO2. However, this difference was not statistically significant. Moreover, S. truncata grown under elevated CO2 exhibited decreased growth and photosynthesis, whereas the number of floral buds did not exhibit any significant differences among the treatments.

Artificial photosynthesis harnesses clean and sustainable solar power to catalyze the conversion of CO2 and H2O molecules into valuable chemicals and O2. This sustainable approach combines energy conversion with environmental pollution control. Non-oxide photocatalysts with broad visible-light absorption and suitable band structures, hold immense potential for CO2 conversion. Nevertheless, they still face numerous challenges in practical applications, particularly in CO2 conversion with H2O. Surface modification and functionalization play the significant role in improving the activity of non-oxide photocatalysts. Multifarious strategies, such as cocatalyst loading, surface regulation, doping engineering, and heterostructure construction, have been explored to optimize light harvesting, bandgap driving force, electron–hole pairs separation/transfer, CO2 adsorption, activation, and catalysis processes. This review summarizes recent progress in surface modification strategies for non-oxide photocatalysts and discusses their enhancement mechanisms for efficient CO2 conversion. These insights are expected to guide the design of high-performance non-oxide photocatalyst systems.

CO2 photocatalytic reduction is a carbon–neutral renewable energy technology. However, this technology is restricted by the low utilization of photocatalytic electrons. Therefore, to improve the separation efficiency of photogenerated carriers and enhance the performance of CO2 photocatalytic reduction. In this paper, g-C3N4/Pd composite with Schottky junction was synthesized by using g-C3N4, a two-dimensional material with unique interfacial effect, as the substrate material in combination with the co-catalyst Pd. The composite of Pd and g-C3N4 was tested to have a strong localized surface plasmon resonance effect (LSPR), which decreased the reaction barriers and improved the electron utilization. The combination of reduced graphene oxide (rGO) created a π–π conjugation effect at the g-C3N4 interface, which shortened the electron migration path and further improved the thermal electron transfer and utilization efficiency. The results show that the g-C3N4/ rGO/Pd (CRP) exhibits the best performance for photocatalytic reduction of CO2, with the yields of 13.57 μmol g− 1 and 2.73 μmol g− 1 for CO and CH4, respectively. Using the in situ infrared test to elucidate the intermediates and the mechanism of g-C3N4/rGO/Pd (CRP) photocatalytic CO2 reduction. This paper provides a new insight into the interface design of photocatalytic materials and the application of co-catalysts.