Catechol redox couple functionalized metal-organic framework UiO-66-NH2 as an efficient catalyst for chromium ion sensor in water samples

• Published in: Journal of cleaner production Vol. 374; p. 133731
• Main Authors: Ranjith Kumar, Deivasigamani, Karthik, Raj, Dhakal, Ganesh, Nguyen, Van Quang, Lee, Jintae, Shim, Jae-Jin
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 10.11.2022
• Subjects: Bronsted acidity; Catechol; Diazotization; Hexavalent chromium; UiO-66-NH2; UiO-66-NH2; Diazotization; Hexavalent chromium; Catechol; Bronsted acidity
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2022.133731

Hexavalent chromium (Cr6+) is a major toxic pollutant than the trivalent (Cr3+) in water, which is challenging for selective Cr6+ detection in an acidic medium. Zirconium-cluster (Zr6) metal-organic frameworks (MOFs) are highly stable in acid medium, and their three-dimensional structures enable facile access to target analytes. However, non-electroactive metals and linkers within MOFs limit their electrochemical applications. Therefore, the purpose of the present study is an innovative diazotization of redox-active functional moiety on the non-electroactive MOF to electroactive MOF for electrocatalytic applications. Present work, post-synthetically diazotized UiO-66-NH2 MOF with redox-active catechol form UiO-66-NN-φ(OH)2. Phenolic groups in as-prepared UiO-66-NN-φ(OH)2 were revealed as excellent redox couple that was effectively used as an electrocatalytic Cr6+ sensor. The pKa (Brønsted acidities) of the Zr-η3-OH and functional catechol were estimated. To improve redox current, electrochemically reduced graphene oxide (ERGO) was used as a substrate for UiO-66-NN-φ(OH)2 MOF with the surface coverage (τ) of 6.63 × 10−10 mol cm−2. In contrast, the τ value of UiO-66-NN-φ(OH)2/glassy carbon (GC) electrode was 2.12 × 10−11 mol cm−2. The temperature effect on the redox chemistry of UiO-66-NN-φ(OH)2@ERGO/GC C–OH and Cr6+ was examined. The UiO-66-NN-φ(OH)2@ERGO/GC electrode operates in a wide Cr6+ concentration range (0.062–962 μM) with excellent sensitivity (0.211 μA μM−1), a low limit of detection (0.06 μM), and high specificity and storage stability. Finally, the innovative new UiO-66-NN-φ(OH)2@ERGO/GC was applied to actual tap waters containing Cr6+ and exhibited a wide recovery range that traditional ICP-AES validated. [Display omitted] •The homogenous 100 nm octahedral morphology UiO-66-NH2 MOF was prepared.•The UiO-66-NN-φ(OH)2/ERGO revealed high surface coverage of 6.63 × 10−10 mol cm−2.•Brønsted acidities of Zr-η3-OH and linker–OH group pKa measured as 3.32 and 4.40.•The UiO-66-NN-φ(OH)2@ERGO/GC able to sense wide range Cr6+ (0.062–962 μM).•This electrode revealed high sensitivity (0.211 μA μM−1)), and low LOD (0.06 μM).