Renewable β-cyclodextrin (β-CD) was immobilized onto the surface of hybrid silica using ethylenediamine as linking groups to construct an adsorbent in water treatment (CD@Si), and the obtained CD@Si was characterized through FT-IR, XPS, EDX, contact angle measurement, TGA, solid-state ¹³C NMR, SEM, and XRD analyses. The effect of initial pH, contact time on the adsorption performance of CD@Si for p-nitrophenol, and the adsorption kinetics, adsorption isotherms, adsorption thermodynamics, reusability and adsorption mechanism were investigated systematically, which indicate that the adsorption of p-nitrophenol onto CD@Si is a very fast process. The adsorption equilibrium can be reached in 15 s with an acceptable equilibrium adsorption capacity of 69.6 mg g⁻¹ at pH 7.0, which is much faster than many reported adsorbents based on β-CD. The adsorption of p-nitrophenol onto CD@Si follows the pseudo-second-order model, obeys the Freundlich model, and is a feasible, spontaneous, and exothermic process which is more favorable at lower temperatures. And the formation of an inclusion complex and a hydrogen bond interaction are two origins of p-nitrophenol being adsorbed onto CD@Si. Additionally, CD@Si can be recycled and reused for at least five runs with an acceptable adsorption capacity, and is a very promising adsorbent for the fast adsorption of p-nitrophenol or its analogues from the aqueous phase. Additionally, this work also provides a strategy to increase the adsorption rate of adsorbents based on β-CD.

Photocatalysis is one of the most promising technologies to achieve efficient carbon dioxide reduction reaction (CO₂RR) under mild conditions. Herein, metalloporphyrin-based metal–organic frameworks (MOFs) with different metal centers, denoted as PCN-222, were utilized as visible-light photocatalysts for CO₂ reduction. Due to the combination of the conjugated planar macrocyclic structures of metalloporphyrins and the stable porous structures of MOFs, all PCN-222 materials exhibited excellent light-harvesting and CO₂-adsorbing abilities. Among the studied MOFs of varied metal centers (M = Pt, Fe, Cu, Zn, Mn), PCN-222(2H&Zn) exhibited the highest photocatalytic CO₂RR performance, with an average CO yield of 3.92 μmol g⁻¹ h⁻¹ without any organic solvent or sacrificial agent. Furthermore, this was three and seven times higher than that of PCN-222(Zn) (1.36 μmol g⁻¹ h⁻¹) and PCN-222(2H) (0.557 μmol g⁻¹ h⁻¹). The superior photocatalytic activity of PCN-222(2H&Zn) was attributed to its effective photoexcited electron–hole separation and transportation compared with other PCN-222(2H&M) materials. The obtained results indicate that Zn ions in the porphyrin’s center played an important role in the reaction of active sites for the adsorption–activation of CO₂. In addition, PCN-222(2H&Zn) showed the highest CO₂ selectivity (almost 100%) and stability. This work provides a clear guide for the design of efficient photocatalysts.