Boosting the CO₂ capture and regeneration performance by nanographene@zinc oxide as novel green-synthesized nanocomposites

Increasing carbon dioxide (CO₂) emissions on a global scale necessitate the development of effective and sustainable solutions to combat climate change. This study examined in detail the CO₂ adsorption capacity and regeneration performance of the nanographene@zinc oxide (NG@ZnO-green) nanocomposite, produced using an environmentally friendly green synthesis method. While pure water was used as the solvent in the impregnation stage of the conventional production of the NG@ZnO nanocomposite, hemp stalk bio-extract was used instead in the green synthesis process. This bio-extract enabled more effective binding of ZnO to the NG surface, thus maximizing the interaction between NG and ZnO, resulting in a more homogeneous modification. SEM and TEM analyses revealed that the ZnO particles were densely and uniformly distributed on the NG surface. According to BET results, the NG@ZnO-green nanocomposite has a specific surface area of 705 m²/g, a total pore volume of 0.51 cm³/g, and a mean pore diameter of 4.97 nm. CO₂ adsorption tests were conducted at 298 K and 273 K under 1 bar pressure, and NG, NG@ZnO, and NG@ZnO-green exhibited CO₂ uptake capacities of 2.07–2.59 mmol/g, 4.56–5.43 mmol/g, and 5.95–6.99 mmol/g, respectively. This comparison revealed that the NG@ZnO-green nanocomposite exhibited significantly superior performance compared to both pure NG and conventionally synthesized NG@ZnO, confirming the effectiveness of the proposed green synthesis strategy. The isosteric heat of adsorption (Q_st), calculated using the Clausius–Clapeyron equation, indicated strong physical interactions between NG@ZnO-green and CO₂. Ten-cycle reuse tests revealed a high regeneration capacity for this nanocomposite, with a reuse efficiency of up to 95 %. All findings demonstrate that the environmentally friendly synthesis method developed using hemp-based bio-extract offers advantages not only in terms of sustainability but also in terms of CO₂ capture performance. Furthermore, this capacity exceeds that reported for many advanced adsorbents under similar conditions, demonstrating the material's technical and environmental superiority. The NG@ZnO-green nanocomposite stands out as a promising candidate for carbon capture technologies.