Photoelectron Spectroscopic and Electronic Structure Studies of CH2O Bonding and Reactivity on ZnO Surfaces: Steps in the Methanol Synthesis Reaction

CO reductive oligomerization by a divalent thulium complex and CO2-induced functionalization

The divalent thulium complex [Tm(Cpttt)2] (Cpttt = 1,2,4-tris(tert-butyl)cyclopentadienyl) reacts with CO to afford selective CO reductive dimerization and trimerization into ethynediolate (C2) and ketenecarboxylate (C3) complexes, respectively. DFT calculations were...

Interaction of Zinc Oxide Clusters with Molecules Related to the Sulfur Vulcanization of Polyolefins (“Rubber”)

The vulcanization of rubber by sulfur is a large-scale industrial process that is only poorly understood, especially the role of zinc oxide, which is added as an activator. We used the highly symmetrical cluster Zn(4)O(4) (T(d)) as a model species to study the thermodynamics of the initial interaction of various vulcanization-related molecules with ZnO by DFT methods, mostly at the B3LYP/6-31+G* level. The interaction energy of Lewis bases with Zn(4)O(4) increases in the following order: CO<S(6)<C(2)H(4)<C(3)H(6)<Me(2)S(2)<1,4-C(5)H(8)<MeSH<Me(2)O<Me(2)S<Me(3)N<<CH(3)COO(-). The corresponding binding energies range from -57 to -262 kJ mol(-1). However, Brønsted acids react with the Zn(4)O(4) cluster with proton transfer from the ligand molecule to one of the oxygen atoms of Zn(4)O(4), and these reactions are all strongly exothermic [binding energies [kJ mol(-1)] in parentheses: H(2)O (-183), MeOH (-171), H(2)S (-245), MeSH (-230), C(3)H(6) (-121), and CH(3)COOH (-255)]. The important vulcanization accelerator mercaptobenzothiazole (C(7)H(5)NS(2), MBT) containing several donor sites reacts with the Zn(4)O(4) cluster with proton transfer from the NH group to one of the oxygen atoms of ZnO, and in addition the exocyclic thiono sulfur atom and the nitrogen atom coordinate to one and the same zinc atom, resulting in a binding energy of -247 kJ mol(-1). A second isomer of [(MBT)Zn(4)O(4)] with a strong O--HN hydrogen bond rather than a Zn--N bond is only slightly less stable (binding energy -243 kJ mol(-1)). The NH form of free MBT is 36 kJ mol(-1) more stable than the tautomeric SH form, while the sulfurized MBT derivative benzothiazolyl hydrodisulfide C(7)H(5)NS(3) (BtSSH) is most stable with the connectivity >CSSH.

Characterization of infrared chemical sensors modified with ZnO nanowires for the detection of volatile organic compounds

In this paper we describe the application and characterization of zinc oxide (ZnO) nanowires in an infrared (IR) chemical sensing system for the detection of volatile organic compounds (VOCs). Under suitable conditions, we grew ZnO nanowires on the surfaces of IR internal reflection elements (IREs) and obtained successful results for the detection of VOCs. ZnO nanowires offer a large surface area to effectively adsorb the examined species; the sensitivity of these IR sensing systems was increased by 3- to 15-fold after surface treatment with the ZnO nanowires. To explore the performance of this type of sensor, we correlated the morphologies of the ZnO nanowires grown on the surfaces of the IREs with the adsorption behavior observed during the sensing of the VOCs. To characterize the properties of the ZnO nanowires during the detection of VOCs having a range of functionalities, we classified the VOCs and examined their enrichment factors by comparing the IR signals detected in the presence and absence of the ZnO nanowires. Our results indicate that the ZnO nanowires exhibited better performance for the detection of aromatic-type VOCs than they did for non-aromatic compounds. For quantitative analyses, we examined several compounds for their responses toward varying quantities of injected VOCs. Our results indicate that the IREs treated with ZnO nanowires display acceptable linearity in their standard curves; the linear regression coefficients were higher than 0.995 for a range of volatile compounds.