In this Account we have compiled a list of reliable bond energies that are based on a set of critically evaluated experiments. A brief description of the three most important experimental techniques for measuring bond energies is provided. We demonstrate how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.

Bond Dissociation Energies of Organic Molecules

Sulfate radical-based advanced oxidation processes (SR-AOPs) employing heterogeneous catalysts to generate sulfate radical (SO4 −) from peroxymonosulfate (PMS) and persulfate (PS) have been extensively employed for organic contaminant removal in water. This article aims to provide a state–of–the–art review on the recent development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on PMS activation. The hybrid heterogeneous catalyst/PMS systems integrated with other advanced oxidation technologies is also discussed. Several strategies for the identification of principal reactive radicals in SO4 −–oxidation systems are evaluated, namely (i) use of chemical probe or spin trapping agent coupled with analytical tools, and (ii) competitive kinetic approach using selective radical scavengers. The main challenges and mitigation strategies pertinent to the SR-AOPs are identified, which include (i) possible formation of oxyanions and disinfection byproducts, and (ii) dealing with sulfate produced and residual PMS. Potential future applications and research direction of SR-AOPs are proposed. These include (i) novel reactor design for heterogeneous catalytic system based on batch or continuous flow (e.g. completely mixed or plug flow) reactor configuration with catalyst recovery, and (ii) catalytic ceramic membrane incorporating SR-AOPs.

Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects

Intermolecular static and dynamic fluorescence quenching constants of eight coumarin derivatives by nucleobase derivatives have been determined in aqueous media. One common sequence of the quenching efficiency has been found for the nucleobases. The feasibility of a photoinduced electron transfer reaction for the nucleobase-specific quenching of fluorescent dyes is investigated by the calculation of the standard free energy changes with the Rehm−Weller equation. A complete set of one-electron redox potential data for the nucleobases are determined electrochemically in aprotic solvents for the first time, which are compared with values obtained by various other methods. Depending on the redox properties of the fluorescent dyes, the sequences of the quenching efficiencies can be rationalized by the orders of electrochemical oxidation potentials (vs NHE) of nucleosides (dG (+1.47 V) < dA < dC ≈ dT < U (≥ +2.39 V)) and reduction potentials (dG (< −2.76 V) < dA < dC < dT < U (−2.07 V)). The correlation between...

Nucleobase-specific quenching of fluorescent dyes. 1. nucleobase one-electron redox potentials and their correlation with static and dynamic quenching efficiencies

A high-efficient, low-cost, and eco-friendly catalyst is highly desired to activate peroxides for environmental remediation. Due to the potential synergistic effect between bimetallic oxides’ two different metal cations, these oxides exhibit superior performance in the catalytic activation of peroxymonosulfate (PMS). In this work, novel Mn1.8Fe1.2O4 nanospheres were synthesized and used to activate PMS for the degradation of bisphenol A (BPA), a typical refractory pollutant. The catalytic performance of the Mn1.8Fe1.2O4 nanospheres was substantially greater than that of the Mn/Fe monometallic oxides and remained efficient in a wide pH range from 4 to 10. More importantly, a synergistic effect between solid-state Mn and Fe was identified in control experiments with Mn3O4 and Fe3O4. Mn was inferred to be the primary active site in the surface of the Mn1.8Fe1.2O4 nanospheres, while Fe(III) was found to play a key role in the synergism with Mn by acting as the main adsorption site for the reaction substrates....

Degradation of Bisphenol A by Peroxymonosulfate Catalytically Activated with Mn1.8Fe1.2O4 Nanospheres: Synergism between Mn and Fe

How thiols and disulfides bind to gold surfaces to form self-assembled monolayers is a long-standing open question. In particular, determining the nature itself of the anchor groups and of their interaction with the metal is a priority issue, which has so far been approached only with oversimplified models. We present ab initio calculations of the adsorption configurations (dissociative and not) of methanethiol and dimethyl disulfide on Au(111) at low coverage, which are based on density functional theory using gradient-corrected exchange-correlation functionals. A complete characterization of their structure, binding energies, and type of bonding is obtained. It is established that dissociation is clearly favored for the disulfide with subsequent formation of strongly bound thiolates, in agreement with experimental evidence, whereas thiolates resulting from S−H bond cleavage in thiols can coexist with the adsorbed “intact” species and become favored if accompanied by the formation of molecular hydrogen.

Thiols and Disulfides on the Au(111) Surface: The Headgroup−Gold Interaction

Absolute rate constants for the reactions of the hydroxyl radical with benzene and toluene were measured within the temperature and pressure ranges 213 less than or equal to T less than or equal to 1150 K and 20 less than or equal to P less than or equal to 200 torr by using He, Ar, and SF/sub 6/ as diluent gases. To help elucidate the variations in reaction mechanism with temperature, we also studied OH reactions with deuterated benzene (C/sub 6/D/sub 6/) and with selectively deuterated toluenes (C/sub 6/H/sub 5/CD/sub 3/, C/sub 6/D/sub 5/CD/sub 3/, and C/sub 6/D/sub 5/CH/sub 3/). Three major reaction channels were characterized kinetically. At T less than or equal to 298 K, electrophilic addition of the OH radical to the aromatic ring is the dominant reactive pathway in all systems studied. At temperatures above 500 K, rapid decomposition of the thermalized adduct back to reactants diminishes the importance of the addition channel and leads to bimolecular reaction rate-constant values significantly lower than those measured near room temperature. At elevated temperatures, the ring hydrogen abstraction (for benzene) and side-chain hydrogen abstraction (for toluene) pathways are shown to be predominant. The measured bimolecular rate constants increase monotonically withmore » increases in temperature above 500 K, and kinetic separation of the two hydrogen abstraction modes for toluene is achieved.« less

Kinetics of the reactions of hydroxyl radical with benzene and toluene

Absolute rate coefficients for the reactions OH + H/sub 2/ ..-->.. H/sub 2/O + H (k/sub 1/) and OH + D/sub 2/ ..-->.. DHO + D (k/sub 2/) have been measured between 250 and 1050/sup 0/K by using the flash photolysis-resonance fluorescence technique. The adaptation of the flash photolysis-resonance fluorescence technique to high-temperature studies is described. The measured values of k/sub 1/ and k/sub 2/ exhibit non-Arrhenius behavior. k/sub 1/ and k/sub 2/ are best described by three-parameter functions, k/sub 1/(T) = (4.12 x 10/sup -19/)T/sup 2/ /sup 44/ exp(-1281/T) cm/sup 3/ molecule/sup -1/ s/sup -1/ and k/sub 2/(T) = (4.37 x 10/sup -15/)T/sup 1/ /sup 18/ exp(-2332/T) cm/sup 3/ molecule/sup -1/ s/sup -1/ over the entire temperature range 250 to 1050/sup 0/K. Alternatively, at low temperatures k/sub 1/ and k/sub 2/ can be described by Arrhenius expressions, k/sub 1/(T) = (4.9 +- 0.5) x 10/sup -12/ exp(-(1.99 +- 0.34) x 10/sup 3//T) cm/sup 3/ molecule/sup -1/ s/sup -1/ for 250 < T < 400/sup 0/K and k/sub 2/(T) = 1.21 +- 0.52) x 10/sup -11/ exp(-(2.67 +- 0.15) x 10/sup 3//T) cm/sup 3/ molecule/sup -1/ s/sup -1/ for 250 < T < 470/sup 0/K. The results are compared withmore » theoretical calculations based on an ab initio potential energy surface for reaction 1.« less

Kinetic study of the reaction of hydroxyl with hydrogen and deuterium from 250 to 1050 K

Time-resolved resonance fluorescence detection of Br( 2 P 3/2 ) atom disappearance or appearance following 266-nm laser flash photolysis of CF 2 Br 2 /H 2 S/H 2 /N 2 , CF 2 Br 2 /CH 3 SH/H 2 /N 2 , Cl 2 CO/H 2 S /HBr/N 2 , and CH 3 SSCH 3 /HBr/H 2 /N 2 mixtures has been employed to study the kinetics of the reactions Br( 2 P 3/2 )+H 2 S⇄SH+HBr

Temperature-dependent kinetics studies of the reactions bromine atom(2P3/2) + hydrogen sulfide .tautm. mercapto + hydrogen bromide and bromine atom(2P3/2) + methanethiol .tautm. methylthiol + hydrogen bromide. Heats of formation of mercapto and methylthio radicals

Time-resolved resonance fluorescence detection of Cl({sup 2}P{sub J}) following 266-nm laser flash photolysis of Cl{sub 2}CO/CH{sub 3}SCH{sub 3}(DMS)/N{sub 2} mixtures has been employed to study the kinetics of the title reaction over the temperature and pressure ranges 240-421 K and 3-700 Torr. The reaction is found to be very fast, occurring on essentially every Cl({sup 2}P{sub J}) + DMS encounter. The reaction rate increases with decreasing temperature and shows a significant pressure dependence. At 297 K, for example, the rate coefficient increases from a low-pressure limit value of approximately 1.8 x 10{sup {minus}10} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} to a value of (3.3 {+-} 0.5) x 10{sup {minus}10} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} at P = 700 Torr. A few experiments were carried out with CD{sub 3}SCD{sub 3} or C{sub 2}H{sub 5}SC{sub 2}H{sub 5} replacing DMS as the sulfide reactant; within experimental uncertainty, no dependence of the rate coefficient on the identity of the sulfide reactant was observed. In a separate study, time-resolved tunable diode laser spectroscopic detection of HCl has been coupled with 248-nm laser flash photolysis of Cl{sub 2}CO/DMS/CO{sub 2}/N{sub 2} mixtures to measure the HCl product yield from the title reaction as a function ofmore » pressure at T = 297 K. The HCl yield approaches unity as P {yields} 0 but decreases with increasing pressure to a value of {approximately}0.5 at P = 203 Torr. The yield experiments demonstrate that hydrogen abstraction is the dominant reaction mechanism in the low-pressure limit. With increasing pressure, stabilization of a (CH{sub 3}){sub 2}SCl adduct apparently becomes competitive with the hydrogen abstraction pathway. The potential role of the title reaction in marine atmospheric chemistry is discussed. 59 refs., 7 figs., 3 tabs.« less

Kinetic and mechanistic study of the reaction of atomic chlorine with dimethyl sulfide

The kinetics of the reactions CH3 + HBr, CD3 + HBr, CH3 + DBr, C2H5 + HBr, C2H5 + DBr, t-C4H9 + HBr, and t-C4H9 + DBr is studied as a function of temperature (257-430 K) and pressure (10-300 Torr of N2). Time-resolved resonance fluorescence detection of Br atom appearance following laser flash photolysis of RI was used in the experiments. Results show that the rates of all reactions increased as the temperature decreased.

J. M. Nicovich

Papers

Kinetics of the reactions of hydroxyl radical with benzene and toluene

Kinetic study of the reaction of hydroxyl with hydrogen and deuterium from 250 to 1050 K

Temperature-dependent kinetics studies of the reactions bromine atom(2P3/2) + hydrogen sulfide .tautm. mercapto + hydrogen bromide and bromine atom(2P3/2) + methanethiol .tautm. methylthiol + hydrogen bromide. Heats of formation of mercapto and methylthio radicals

Kinetic and mechanistic study of the reaction of atomic chlorine with dimethyl sulfide

Kinetics of the reactions of alkyl radicals with HBr and DBr