Quantum yields of phenol and nitrate, produced by photodecomposition in aqueous solutions of NO2 - and HNO2 in the presence of benzene as scavenger for OH radicals, have been determined as a function of wavelength between 280 and 390 nm. The production of phenol was used to calculate primary OH quantum yields. For NO2 - photolysis at pH 6 Φ1(OH) was found to decrease with increasing wavelength from 0.069 ± 0.008 at 280 nm to 0.022 ± 0.004 at 390 nm, in agreement with previous data. The OH quantum yield Φ2(OH) for the photolysis of HNO2 at pH 2 was essentially constant over the entire wavelength range with Φ2 = 0.35 ± 0.02 (2σ). Quantum yields for NO3 - are comparable in magnitude to those of phenol, indicating that NO as primary product is largely oxidized to nitrate. The most likely conversion processes are reactions of NO with O2 - (pH 6), the latter resulting from the oxidation of benzene, to form peroxynitrous acid, which undergoes thermal decomposition, and of NO2 with HO2 (pH 2) to form peroxynitric acid, which reacts further with HNO2. The rate of NO3 - production decreases with time in the photolysis of NO2 -, whereas it increases in the photolysis of HNO2, and these features remain unexplained.

We present a new approach for modeling adsorption in metal-organic frameworks (MOFs) with unsaturated metal centers and apply it to the challenging propane/propylene separation in copper(II) benzene-1,3,5-tricarboxylate (CuBTC). We obtain information about the specific interactions between olefins and the open metal sites of the MOF using quantum mechanical density functional theory. A proper consideration of all the relevant contributions to the adsorption energy enables us to extract the component that is due to specific attractive interactions between the π-orbitals of the alkene and the coordinatively unsaturated metal. This component is fitted using a combination of a Morse potential and a power law function and is then included into classical grand canonical Monte Carlo simulations of adsorption. Using this modified potential model, together with a standard Lennard-Jones model, we are able to predict the adsorption of not only propane (where no specific interactions are present), but also of propylene (where specific interactions are dominant). Binary adsorption isotherms for this mixture are in reasonable agreement with ideal adsorbed solution theory predictions. We compare our approach with previous attempts to predict adsorption in MOFs with open metal sites and suggest possible future routes for improving our model.

Force-field based grand-canonical Monte Carlo simulations are used to investigate the acetylene and carbon dioxide uptake capacity, as well as the C(2)H(2)/CO(2) adsorption selectivity of three novel microporous materials: Magnesium formate, Cu(3)(btc)(2), and cucurbit[6]uril. Because no comparable computational studies of acetylene adsorption have been reported so far, the study focuses on systems for which experimental data are available to permit a thorough validation of the simulation results. The results for magnesium formate are in excellent agreement with experiment. The simulation predicts a high selectivity for acetylene over CO(2), which can be understood from a detailed analysis of the structural features that determine the affinity of Mg-formate towards C(2)H(2). For Cu(3)(btc)(2), preliminary calculations reveal the necessity to include the interaction of the sorbate molecules with the unsaturated metal sites, which is done by means of a parameter adjustment based on ab-initio calculations. In spite of the high C(2)H(2) storage capacity, the C(2)H(2)/CO(2) selectivity of this material is very modest. The simulation results for the porous organic crystal cucurbit[6]uril show that the adsorption characteristics that have been observed experimentally, particularly the very high isosteric heat of adsorption, cannot be understood when an ideal structure is assumed. It is postulated that structural imperfections play a key role in determining the C(2)H(2) adsorption behavior of this material, and this proposition is supported by additional calculations.

Metal–organic frameworks (MOFs) have shown tremendous potential for challenging gas separation applications, an example of which is the separation of olefins from paraffins. Some of the most promising MOFs show enhanced selectivity for the olefins due to the presence of coordinatively unsaturated metal sites, but accurate predictive models for such systems are still lacking. In this paper, we present results of a combined experimental and theoretical study on adsorption of propane, propylene, ethane, and ethylene in CuBTC, a MOF with open metal sites. We first propose a simple procedure to correct for impurities present in real materials, which in most cases makes experimental data from different sources consistent with each other and with molecular simulation results. By applying a novel molecular modeling approach based on a combination of quantum mechanical density functional theory and classical grand canonical Monte Carlo simulations, we are able to achieve excellent predictions of olefin adsorption, in much better agreement with experiment than traditional, mostly empirical, molecular models. Such an improvement in predictive ability relies on a correct representation of the attractive energy of the unsaturated metal for the carbon–carbon double bond present in alkenes. This approach has the potential to be generally applicable to other gas separations that involve specific coordination-type bonds between adsorbates and adsorbents.