No abstract

Contrary to common expectations, the hydroxyl scavengers, carbonate and bicarbonate, are able to enhance the phototransformation by nitrate of a number of substituted phenols. Carbonate and bicarbonate, in addition to modifying the solution pH, are also able to induce a considerable formation of the carbonate radicals upon nitrate photolysis. The higher availability of less-reactive species than the hydroxyl radical would contribute to substantially enhance the photodegradation of the phenols/phenolates that are sufficiently reactive toward the carbonate radical. This phenomenon has a potentially important impact on the fate of the relevant compounds in surface waters. In contrast, the degradation of compounds that are not sufficiently reactive toward CO(3)(-*) is inhibited by carbonate and bicarbonate because of the scavenging of *OH.

This paper reports a simple model to describe the formation and reactivity of hydroxyl radicals in the whole column of surface freshwater systems. The model is based on empirical irradiation data and it is a function of the water chemical composition (the photochemically significant parameters Non-Purgeable Organic Carbon -NPOC-, nitrate, nitrite, carbonate and bicarbonate), the water body conformation best expressed as the average depth, and the water absorption spectrum in a simplified Lambert-Beer approach. The purpose is to derive the lifetime of dissolved molecules, due to the reaction with • OH, on the basis of their second-order rate constants with the hydroxyl radical. It is also proposed a simplified (and approximated) approach to simulate the absorption spectrum of water when the latter is not available, based on the value of the NPOC. Such a simulation can be useful when the model is adopted to describe a degradation scenario for a certain compound, without a direct link to a definite ecosystem. The model was applied to the lifetime of various pesticides in surface water bodies, and it suggested that the lifetime of a given compound can be very variable in different systems, even more than the lifetime of different compounds in the same water body. The variations of the chemical composition and of the depth of the water column are the main reasons for the reported finding.

The sunlight-driven fixation of CO 2 into valuable chemicals constitutes a promising approach toward environmental remediation and energy sustainability over traditional thermal-driven fixation. Consequently, in this article, we report a strategic design and utilization of Mg-centered porphyrin-based metal− organic framework (MOFs) having relevance to chlorophyll in green plants as a visible light-promoted highly recyclable catalyst for the effective fixation of CO 2 into value-added cyclic carbonates under ambient conditions. Indeed, the Mg-centered porphyrin MOF showed good CO 2 capture ability with a high heat of adsorption (44.5 kJ/mol) and superior catalytic activity under visible light irradiation in comparison to thermal-driven conditions. The excellent light-promoted catalytic activity of Mg−porphyrin MOF has been attributed to facile ligand-to-metal charge transfer transition from the photoexcited Mg−porphyrin unit (SBU) to the Zr 6 cluster which in turn activates CO 2 , thereby lowering the activation barrier for its cycloaddition with epoxides. The in-depth theoretical studies further unveiled the detailed mechanistic path of the light-promoted conversion of CO 2 into high-value cyclic carbonates. This study represents a rare demonstration of sunlight-promoted sustainable fixation of CO 2 , a greenhouse gas into value-added chemicals.

The capture and conversion of CO2 from direct air into value-added products under mild conditions represents a promising step towards environmental remediation and energy sustainability. Consequently, herein, we report application...

This works shows that the addition of phenol and 2-propanol as model organic compounds significantly decreases the direct photolysis quantum yield of 4-chloro-2-methylphenoxyacetic acid (MCPA) upon UVB irradiation in aqueous solution. Laser flash photolysis data suggest that 2-propanol is able to decrease the formation of the MCPA excited states under irradiation. A decrease from 0.54 to 0.34 of the photolysis quantum yield of the anionic form of MCPA (which prevails over the undissociated one in surface waters) could have a considerable impact on the MCPA lifetime in ecosystems where the direct photolysis is the main phototransformation pathway. In surface water bodies where the direct photolysis has comparable kinetics as the reaction with • OH, a decrease of the quantum yield would enhance the relative importance of the • OH pathway, which yields considerably less toxic intermediates than the direct photolysis.

Variable-tempera ture (5-300 K) susceptibility measurements carried out for the binuclear nickel(II) complexes of a tetraamino diphenol macrocyclic ligand (H2L) of compositions [Ni2L(H20 4), [Ni2L-(py)2](C104)2 (5), and [Ni2L^-02CCH2NH3)(H20)2](C104)2*2H20 (6) are reported. All the complexes behave antiferromagnetically, and the exchange parameter, J, varies in the following way: 1 (-17 cm"1), 2 (-21 cm-1), 3 (-29 cm-1), 4 (-50 cm*1), 5 (-67 cm-1), and 6 (-1 cm-'). The decrease in the value of J from 1 to 3 is attributed to the increase in tetragonal distortion around the metal centers. The change in stereochemistry of nickel(II) to the square pyramidal configuration leads to the significant decrease in the value of J for 4 and 5. The net effective exchange coupling constant of 6, in which two orthogonal superexchange pathways are involved, is very small. The X-ray structure of 2 has been determined. The complex crystallizes in the monoclinic space group P2\¡c with a = 10.091(1) A,b = 7.957(1) A, c = 24.569(3) Á, ß = 92.77(1)°, and Z -2. The structure was solved by direct methods and refined to R = 0.039 and J?w = 0.042. Complex 2 undergoes two reversible one-electron oxidation steps (£'i/2 = 0.90,1.05 V vs SCE, Pt/MeCN) with the formation of Ni(II)-Ni(III) and Ni(III)-Ni(III) species.

The rational design of efficient catalytic materials for conversion of carbon dioxide (CO 2 ), a greenhouse gas into valuable products has fascinated chemists ever since the advent of the area of green and sustainable catalysis. Herein, we report design of a bifunctional, 3D Zn-MOF, [Zn 3 (BINDI)(DATRZ) 2 (H 2 O) 2 ] n by utilizing a Lewis acidic Zn(II) ion, long-chain, rigid aromatic tetracarboxylate ligand, N,N′-bis(5-isophthalic acid)naphthalenediimide (BINDIH 4 ) and basic −NH 2 rich 3,5-diamino-1,2,4-triazole (DATRZ) linker. The Zn-MOF possesses a BET surface area of 1085.8 m 2 /g and a high density of CO 2 -philic −NH 2 groups lined in the 1D channels promoting selective and recyclable CO 2 adsorption with a high heat of interaction energy of 44.3 kJ/mol. The high surface area combined with the presence of Lewis acidic (LA) and basic sites rendered Zn-MOF an ideal bifunctional heterogeneous catalyst for efficient coupling of CO 2 with terminal/internal epoxides under eco-friendly, solvent-free, RT and atmospheric pressure (balloon) conditions. Interestingly, Zn-MOF showed excellent catalytic activity for fixation of CO 2 even from simulated flue gas/dilute CO 2 gas. Remarkably, Zn-MOF showed high recyclability for up to 10 cycles with retaining the framework stability and catalytic activity. Overall, this work demonstrates the rational integration of Lewis acidic and basic sites in a 3D framework for the efficient utilization of CO 2 under environment-friendly conditions.