A Comparative Study of the Adsorption of Chloro- and Non-Chloro-Containing Organophosphorus Compounds on WO₃

Abstract

The adsorption of dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), and methyldichlorophosphate (MDCP) on monoclinic tungsten oxide (m-WO3) evacuated at various temperatures was investigated using infrared spectroscopy. DMMP is the most common molecule used for evaluating the performance of WO3 and other semiconducting metal oxide (SMO)-based sensors to phosphonate-based nerve agents. However, toxic nerve agents such as sarin differ from DMMP in that they contain a functional group (P−F in sarin) that can be readily hydrolyzed. It is shown that the adsorption of organophosphates that contain P−Cl groups differs from nonhalogenated simulants such as DMMP and TMP on WO3 surfaces. Specifically, the non-chlorinated simulants DMMP and TMP adsorb on the surface solely through the PO functionality with the surface water layer as well as the Lewis and Brønsted acid sites. The relative number of molecules bound on Lewis and Brønsted acid surface sites depends on the initial evacuation temperature of the WO3 surface. When MDCP adsorbs on WO3 through the PO bond, it is accompanied by the hydrolysis of P−Cl groups by water vapor or the adsorbed water layer leading to additional phosphate-like species on the surface. The infrared data suggests that a halogenated phosphate like MDCP is a better simulant molecule for studies aimed at understanding the role of water and hydrolysis in the response of metal oxide-based sensors to nerve agents.

Flower-like tungsten oxide particles: Synthesis, characterization and dimethyl methylphosphonate sensing properties

“…As observed in the low-frequency spectral region, the frequency of P O stretching mode, which occurs at 1276 cm −1 in gaseous phase, shifted to 1231 and 1253 cm −1 upon adsorption within the first minute, 45 and 23 cm −1 lower than those of gaseous DMMP. According to previous reports [17][18][19], the two positions are the evidence of the formation of two types of bonding between P O and WO 3 surface sites: adsorption via hydrogen bonding (1231 cm −1 ) and with surface Brønsted sites (1253 cm −1 ). Although a third adsorption mode (Lewis acid site adsorption) existed, as reported before [18,19], no evidence was observed in the current experiment.…”

“…According to previous reports [17][18][19], the two positions are the evidence of the formation of two types of bonding between P O and WO 3 surface sites: adsorption via hydrogen bonding (1231 cm −1 ) and with surface Brønsted sites (1253 cm −1 ). Although a third adsorption mode (Lewis acid site adsorption) existed, as reported before [18,19], no evidence was observed in the current experiment. It can be easily understood if we consider that the adsorption herein occurred at room temperature rather than at higher temperature as in the previous reports.…”

Adsorption of dimethyl methylphosphonate and trimethyl phosphate on calcium oxide: an ab initio study

“…Several studies were carried out to understand the mechanism of the adsorption and decomposition processes on such oxides as alumina-supported cerium oxide and iron co-impregnated oxide [31], manganese oxide [32], monoclinic tungsten oxide (m-WO 3 ) [33], cerium oxide, Fe 2 O 3 , silica [34][35][36][37][38], and TiO 2 [39][40][41][42]. The thermal oxidative decomposition study of DMMP on amorphous manganese oxide and Al 2 O 3 -supported manganese oxide catalyst has shown the DMMP oxidation to CO 2 [32].…”

“…The thermal oxidative decomposition study of DMMP on amorphous manganese oxide and Al 2 O 3 -supported manganese oxide catalyst has shown the DMMP oxidation to CO 2 [32]. The investigation of the adsorption of DMMP on monoclinic tungsten oxide has proven that DMMP simulant adsorbs on the surface solely through the P=O functionality with the surface water layer as well as the Lewis and Brönsted acid site [33]. DMMP on the alumina-supported cerium oxide decomposes by producing methanol and dimethyl ether [34].…”

Synthesis and characterization of porous WO 3 –SnO 2 nanomaterials: An infrared study of adsorbed pyridine and dimethyl methylphosphonate

“…Our studies provided a better understanding of the mode of interaction between the simulant molecule, dimethyl methylphosphonate (DMMP), and the WO 3 surface sites using FTIR spectroscopy [39][40][41][42]. Therein, the DMMP adsorbed on the surface was shown to decompose and poison the surface via the methylphosphate group at temperatures above 300°C.…”