Insights into the Surface Complexation of Dimethylarsinic Acid on Iron (Oxyhydr)oxides from ATR-FTIR Studies and Quantum Chemical Calculations

Abstract

The surface chemistry of methylated arsenicals with ubiquitous geosorbents and industrial catalysts is poorly understood. These arsenic compounds pose both a health and an environmental risk in addition to being a challenge to the energy industry. We report herein a detailed spectroscopic analysis of the surface structure of dimethylarsinic acid (DMA) adsorbed on hematite and goethite using attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Spectra of adsorbed DMA, DMA(ads), were collected in situ as a function of pH and ionic strength, using both H(2)O and D(2)O at 298 K in flow mode. Experimental data were complemented with DFT calculations of geometries and frequencies of hydrated DMA-iron oxide clusters. Results indicate the simultaneous formation of inner- and outer-sphere complexes with distinct spectral components. Desorption behavior of DMA due to chloride and phosphate was studied as a function of time from the decrease in the absorbance of apparent spectral features. The impact of our studies on the environmental fate of DMA in geochemical environments and the design of technologies to reduce arsenic content in fuels are discussed.

Multiscale Assessment of Methylarsenic Reactivity in Soil. 2. Distribution and Speciation in Soil

“…At pH 6, the Fe-oxyhydroxide surface is positively charged, and MMA is negatively charged (CH 3 AsO 3 - ). It has reported that DMA and As V can form outer-sphere complexes with Fe/Al-oxyhydroxides [26-27]. Due to the similar molecular structures between As V , MMA, and DMA, it is possible that MMA also forms outer-sphere surface complex on the Fe-oxyhydroxide surface, contributing to the high sorption.…”

In situ ATR–FTIR and surface complexation modeling studies on the adsorption of dimethylarsinic acid and p-arsanilic acid on iron-(oxyhydr)oxides

“…The assignment of the spectral components observed in Fig. 1 has been discussed in detail in our recent publication reporting adsorption mechanism of DMA [34]. Briefly, the assignment of the observed frequencies was based on comparison with the spectra of bulk DMA in the liquid (pK a = 6.1) and solid acid and salt phases [37], desorption kinetics due to chloride and phosphate anions, and aided by frequency calculations on geometry-optimized clusters of DMA-iron oxide clusters.…”

“…3a and b for p-AsA are expressed in molecule cm À2 and molar ratios units using constants reported earlier [35]. The validity of this approach to quantifying S DMA and S p-AsA from spectral data was verified by bulk measurements of surface coverage from analysis of total arsenic using inductively coupled plasma atomic emission spectroscopy (ICP-AES) [34,35]. The quantification approach reported herein has the advantage of being an in situ cost-effective method (no chemical digestion is needed to release bonded arsenic).…”

“…This excellent body of published work highlighted the need for experiments on the surface chemistry of organoarsenicals. To date, the number of batch studies on the factors that affect the adsorption and desorption of organoarsenicals on Fe-, Al-and Ti-(oxyhydr)oxides [24][25][26][27][28][29][30][31][32][33] exceeds that of in situ surface sensitive measurements using techniques such as attenuated total internal reflection spectroscopy (ATR-FTIR) [30,[34][35][36] and X-ray absorption spectroscopy (XAS) [27,30]. Surface complexation models (SCMs) have been used to describe the adsorption of methylated arsenic species on hydrous iron oxide [25] and nanocrystalline titanium oxide [27].…”

Dissolution of realgar by Acidithiobacillus ferrooxidans in the presence and absence of zerovalent iron: Implications for remediation of iron-deficient realgar tailings

“…Small peaks at 793 cm -1 and 884 cm -1 were observed only in 2.0 g ZVI experiment, which were assigned to As-O-Fe complexes (Jia et al, 2007;Guan et al, 2008;Adamescu et al, 2010). The band at 1080 cm -1 was assigned to jarosite (Bigham and Nordstrom, 2000).…”