On the capture of ultralow-level benzene in indoor environments: Experiments, modeling and molecular simulation

Targeted improvement of narrow micropores in porous carbon for enhancing trace benzene vapor removal: Revealing the adsorption mechanism via experimental and molecular simulation

Porous carbon materials are highly desirable for removing benzene due to their low energy for capture and regeneration. Research has demonstrated that narrow microporous volume is crucial for effective adsorption of benzene at ultra-low concentration. Unfortunately, achieving directional increase in the narrow microporous volume in porous carbon remains a challenge. Here, nitrogen-doped hydrothermal carbon was prepared using urea-assisted hydrothermal method, and then porous carbon (PUC800) was prepared by KOH activation. The resulting material had 180 % higher pore volume and 179 % higher surface area compared to non-nitrogen activation methods. Then, using mechanochemical (mechanical compaction and KOH activation) approach to produce PUC800-3T, which had a 30 % increase in pore volume and a 33 % increase in surface area compared to PUC800. PUC800-3T showed benzene adsorption capacity of 4.2 mmol g-1 at 1 Pa and 5.8 mmol g-1 at 5 Pa. Experimental and molecular simulation indicate that the benzene adsorption at 1 and 5 Pa is determined by pore volume of less than 0.8 and 0.9 nm, respectively. Density functional theory calculations provided insight into the CH⋯X (X = N/O) interactions drive benzene adsorption on the carbon framework. This work provides valuable theoretical and experimental support for designing, preparing, and applying adsorbents for trace removal of benzene vapor.

Research on nonsteady-state adsorption and regulation towards stabler adsorption for benzene over single-wall carbon materials

With the intention of separating benzene (C6H6) from indoor polluted air and collecting it in a cleaner way, it is promising of getting C6H6 adsorbed on activated carbon materials with outstanding physicochemical properties. In this study, how C6H6 is adsorbed over single-wall carbon materials and relevant adsorption processes are enhanced is thoroughly investigated via density functional theory (DFT). Especially, distinction between partial and whole effects of adsorbents on C6H6 adsorption, features of electron distribution across section of adsorption forms, and regulation mechanism of nonsteady-state adsorption for C6H6 are key points. According to calculation results, C6H6 molecules could be captured by pure single-wall carbon nanotube (CNT) through repulsive forces (quantified as 103.42 kJ/mol) from all quarters, which makes it stay in nonsteady-state adsorption forms and easily run into free state. Therefore, when external temperature increases from 0 to 300 K, molecular movement will be intense enough to help C6H6 break into another random positions instead of statistically remaining immobile. As for this problem, single-wall CNTs are modified through making defects and replacing some C atoms with N atoms, respectively. In this way, surficial electron distribution of modified adsorbents is regulated to tremendously cut down repulsive forces (quantified as 50.30 kJ/mol) and reverse nonsteady-state adsorption into near-equilibrium quasi-steady-state adsorption (single-side attraction near 100 kJ/mol). Therefore, this research would provide useful information for exploiting single-wall carbon materials as effective adsorbents of C6H6 in order to quickly achieve indoor air purification.

Trace removal of benzene vapour using double-walled metal-dipyrazolate frameworks

In principle, porous physisorbents are attractive candidates for the removal of volatile organic compounds such as benzene by virtue of their low energy for the capture and release of this pollutant. Unfortunately, many physisorbents exhibit weak sorbate-sorbent interactions, resulting in poor selectivity and low uptake when volatile organic compounds are present at trace concentrations. Herein, we report that a family of double-walled metal-dipyrazolate frameworks, BUT-53 to BUT-58, exhibit benzene uptakes at 298 K of 2.47-3.28 mmol g^-1 at <10 Pa. Breakthrough experiments revealed that BUT-55, a supramolecular isomer of the metal-organic framework Co(BDP) (H₂BDP = 1,4-di(1H-pyrazol-4-yl)benzene), captures trace levels of benzene, producing an air stream with benzene content below acceptable limits. Furthermore, BUT-55 can be regenerated with mild heating. Insight into the performance of BUT-55 comes from the crystal structure of the benzene-loaded phase (C₆H₆@BUT-55) and density functional theory calculations, which reveal that C-H···X interactions drive the tight binding of benzene. Our results demonstrate that BUT-55 is a recyclable physisorbent that exhibits high affinity and adsorption capacity towards benzene, making it a candidate for environmental remediation of benzene-contaminated gas mixtures.

A figure of merits-based performance comparison of various advanced functional nanomaterials for adsorptive removal of gaseous ammonia

The implementation of sustainable industrial development based on energy/cost-effective techniques with zero/low rate of pollutant emission is an ideal strategy for the proper management of a natural environment. Gaseous ammonia released from a variety of anthropogenic sources (e.g., agriculture, pharmaceuticals, commercial cleaning products, and refrigerant) is estimated to be as high as 150 million tons∙year^-1. To reduce the negative effects of atmospheric ammonia, the great utility of advanced functional nanomaterials (e.g., metal organic frameworks, covalent organic polymers, metal/metal oxide nanoparticles, and carbon nanostructures) has been recognized. To gain a better understanding of the sorptive removal potential of diverse materials, their performance has been evaluated based on the key performance merits (e.g., initial concentration, sorption capacity, and partition coefficient). Generally, the PC values can be applied to significantly estimate the contaminant adsorption potential of NMs via balancing the biased influences of operating parameters (e.g., initial concentration of pollutants) as perceived for the partitioning of compounds between aqueous phases at equilibrium (e.g., Henry's Law). Therefore, in this work, we have proposed the PC as a prosperous performance merit (in terms of heterogeneity of surface and strength of adsorption process) for the selection of high performance nano-adsorbents for gaseous ammonia. Moreover, the water stability, recyclability, economic aspects, and future perspectives have also been discussed for real-world applications of advanced nanomaterial against gaseous ammonia adsorption. The outcome of this evaluation will be expedient for the classification/selection of the most effectual and cost-effective options for mitigation of environmental pollutants like gaseous ammonia.