Engineering at Subatomic Scale: Achieving Selective Catalytic Pathways via Tuning of the Oxidation States in Functionalized Single‐Atom Quantum Catalysts

Abstract

Regulating the catalytic pathways of single‐atom sites in single atom catalysts (SACs) is an exciting debate at the moment, which has redirected the research towards understanding and modifying the single‐atom catalytic sites through various strategies including altering the coordination environment of single atom for desirable outcomes as well as increasing their number. One useful aspect concerning the tunability of the catalytic pathways of SACs, which has been overlooked, is the oxidation state dynamics of the single atoms. In this study, iron single‐atoms (FeSA) with variable oxidation states, dependent on the precursors, are harnessed inside a nitrogen‐rich functionalized carbon quantum dots (CQDs) matrix via a facile one‐step and low‐temperature synthesis process. Dynamic electronic properties are imparted to the FeSAs by the simpler carbon dots matrix of CQDs in order to achieve the desired catalytic pathways of reactive oxygen species (ROS) generation in different environments, which are explored experimentally and theoretically for an in‐depth understanding of the redox chemistry that drives the alternative catalytic pathways in FeSA@CQDs. These alternative and oxidation state‐dependent catalytic pathways are employed for specific as well as cascade‐like activities simulating natural enzymes as well as biomarkers for the detection of cancerous cells.

Design of carbon dots as nanozymes to mediate redox biological processes

“…51 According to a large number of studies, the precursor is the key factor affecting the performance of CDs. [52][53][54] The effect of precursors on the properties of CDs may be related to their different structures, including the graphitization of conjugated domains and carbon cores, the functional groups attached to the surface, and the degree of functionalization during precursor carbonization. 31 Researchers synthesized CDs from various biologically active precursors to preserve some of the properties of the raw materials, such as carbon dots (J-CDs) obtained from Jujube fruit to treat cancer related anaemia (Fig.…”

Multi-enzyme mimics – cracking the code of subcellular cascade reactions and their potential biological applications

“…To eliminate the factor that CQDs might have some contribution in these activities, we also checked the performance of CQDs and found that CQDs in itself do not show any multi-nanozyme like activity except a very low POD-like activity. 123 Furthermore, the coordination environment also contributes in defining the catalytic properties of a nanozyme. The sites such as MX 2 , MX 3 , and MX 4 (M = metal and X = N, O, S, halogen), as shown in Fig.…”

“…For instance, while measuring the POD-like activity of Fe-based SACs by Zeb et al, the affinity for H 2 O 2 as a substrate was very low and the V max value was high while that of TMB as a substrate showed a lower V max value which led to the conclusion that the higher affinity of H 2 O 2 is an indication of the CAT-like activity of the nanozyme. 123 4.3. Deciphering the mechanisms of cascade reactions 4.3.1.…”

“…Xu and co-workers observed this phenomenon where the FeSA@CQDs-2 nanozyme generated H 2 O 2 at lower pH values while produced O 2 at higher pH values. 123 Similarly, a nanozyme could behave as POD at lower pH values, while it acts as CAT at pH 6.5 or at higher pH. Fe-based nanozymes such as Fe 3 O 4 along with many other materials such as PB, PBAs and SACs show this typical phenomenon due to the alteration of their redox potentials by changing the pH of the reaction medium.…”

“…Similarly, H 2 O 2 undergoes instant cleavage and generates H 2 O 2(ads) , such as in the case of doped graphene or single-atom catalysts because these catalysts have very high redox potential which can instantly oxidize H 2 O 2 into OH in an acidic medium 123,…”