Construction of an OCP-ATR-FTIR Spectroscopy Device to In Situ Monitor the Interfacial Reaction of Contaminants: Competitive Adsorption of Cr(VI) and Oxalate on Hematite

Abstract

The comprehensive understanding of contaminant interfacial behavior strongly depends on the in situ characterization technique, which is still a great challenge. In this study, we constructed a device integrated with open-circuit potentialand attenuated total reflectance Fourier transform infrared (OCP-ATR-FTIR) spectroscopy to simultaneously monitor the electrochemical and infrared spectral information on the interfacial reaction for the process analysis, taking the competitive adsorption of hexavalent chromium (Cr­(VI)) and oxalate on hematite nanocubes (HNC) as an example. The synchronous OCP and infrared results revealed that Cr­(VI) interacted with HNC via bidentate binuclear inner-sphere coordination, accompanied by electron transfer from HNC to Cr­(VI), while oxalate was adsorbed on HNC through bidentate mononuclear side-on inner-sphere coordination with electron transfer from HNC to oxalate, and also outer-sphere coordination with negative charge accumulation. When oxalate was added to HNC with preadsorbed Cr­(VI), oxalate would occupy the inner-sphere adsorption sites and thus cause the detaching of preadsorbed Cr­(VI) from HNC. This study provides a promising in situ characterization technique for real-time interfacial reaction monitoring and also sheds light on the competitive adsorption mechanism of oxalate and Cr­(VI) on the mineral surface.

Rational Surface Oxidation Promoted Long-Term Cd(II) Removal Performance of Mackinawite (FeS)

“…The OCP method could sensitively reflect the direction and amount of charge transfer. When the mackinawite working electrode gains a positive charge or a loose negative charge, the OCP value will rise, and vice versa. ,, The pH change would also slightly affect the OCP value via the accumulation of H + or OH – on the surface of the mackinawite electrode. Interestingly, the OCP signal of FeS@FeO during Cd­(II) removal increased until 1.5 h but decreased during 1.5–2.5 h and increased again thereafter.…”

“…8 mg of FeS@FeO was added into 2 mL of H 2 O and ultrasonicated for 60 s to form the FeS@FeO ink; then, 10 μL of ink was drop-cast on the Au–Si prism and dried. The open circuit potential (OCP) measurement was performed in a two-electrode system, with a standard Ag/AgCl electrode in 0.05 mol L –1 sodium sulfate-filled Luggin capillary as the reference electrode. , The OCP signals were monitored by an electrochemical workstation (CHI760E, Chenhua, China). At regular time intervals, the samples were withdrawn for ex situ determination of the concentrations of dissolved iron, sulfide, and Cd­(II).…”

Highly selective urea electrooxidation coupled with efficient hydrogen evolution

“…To clarify the specific reaction pathways governed by the asymmetric Ni–O–Ti sites for the UOR, an in situ FTIR spectroscopy study was conducted 37 . Urea features ν (C = O) at 1670 cm –1 , δ (NH 2 ) at 1630 and 1600 cm –1 , and ν a (C⎓N) at 1466 cm –1 (Fig.…”