Surface Polymerization of Mo(VI) and W(VI) Anions on Hematite Revealed by in Situ Infrared Spectroscopy and DFT+U Theoretical Study

Abstract

The study of the interactions between dissolved Mo(VI) or W(VI) species and the surfaces of metal (hydr)oxides is relevant for two main areas: the optimization of the preparation of catalytic supports and the understanding of the environmental fate of these elements. For the latter, iron (hydr)oxides are the most important sinks for pollutants, and recently, their surface reactivity was the focus of many research works. In this work, we develop a joint approach, using in situ infrared spectroscopy and DFT simulations, to characterize the Mo(VI) and W(VI) species adsorbed on hematite (α-Fe 2 O 3 ). Surface sorbed polymers of tungstate and molybdate on hematite were identified for low pH and at high concentration of these elements, which is similar to the formation of polyoxometalates in solution phase. However, the surface speciation is different from the adsorption of polymolybdate or polytungstate already formed in solution and should be consistent with the growth of a surface polymer. For low concentrations/high pH conditions, the spectra are consistent with a monodentate surface complexation.

In Situ IR‐ATR Study of the Interaction of Nitrogen Heteroaromatic Compounds with HY Zeolites: Experimental and Theoretical Approaches

“…The method proposed by Davantès et al . was adapted to deposit the solid film of the sample onto the ATR crystal . Accordingly, a droplet of the concentrated suspension of the pretreated solid, with a granulometry less than 20 μm, was put on top of the IR‐ATR crystal and left to dry.…”

“…The method proposed by Davantès et al was adapted to deposit the solid film of the sample onto the ATR crystal. [28] Accordingly, a droplet of the concentrated suspension of the pretreated solid, with a granulometry less than 20 μm, was put on top of the IR-ATR crystal and left to dry. Thereafter, the deposited zeolites were dehydrated in situ under an argon flow of 30 ml.min À 1 at 473 K for 4 h. The MCM-41 film was studied without in situ activation because of its instability during the treatment.…”

“…In such cases, the characterization with IR-ATR spectroscopy opened a wide range of possibilities for in situ studies of liquidsolid adsorption. [26] Experimental setups concerning IR-ATR continuous flow, [27][28][29] batch cells, [30] and others have been adapted for studying the adsorption of probe molecules in the liquid phase, [26] as well as for homogeneous and heterogeneous catalytic processes and electrochemical studies. [31][32][33][34][35][36][37][38] In particular, Rivera et al performed pyridine adsorption in liquid phase over sol-gel films deposited over the ATR crystal solubilized in n-heptane and methanol.…”

A facile surface passivation of hematite photoanodes with molybdate overlayers for efficient PEC water oxidation

“…The molybdate in situ mediated hematite films were further characterized by SEM-EDXS to measure Mo/Fe ratios, and were named according to the actual Mo/Fe ratios. Samples mediated with varied concentrations of NaMoO 4 of 0.3, 0.45, 1.5, 3 mmol/L were referred to as Fe to the FeOOH [49], which would affect the crystallization of FeOOH. In our earlier study [50], the adsorption of phosphate groups (PO 4 3+ ) on the certain planes of FeOOH nuclei was also found to affect the growth of FeOOH, leading to the formation of an ultrathin nanocube-structured FeOOH film.…”

“…Then how does those surface molybdate affect the PEC performance? Actually, the surface polymerization of Mo(VI) on hematite has been well studied by in situ infrared spectroscopy and DFT+U theoretical analysis [49]. Molybdate on the surface of Fe 2 O 3 was DOI:10.1063/1674-0068/31/cjcp1806133 c ⃝2018 Chinese Physical Society observed in high concentration (∼1 mmol/L) whose growth starts from two dimensions, then in threedimension upon increasing its concentration.…”