Sulphonated Carbon Dots Synthesized Through a One‐Pot, Facile and Scalable Protocol Facilitates the Preparation of Renewable Precursors Using Glucose/Levulinic Acid

Abstract

Herein, we report the efficacy of Brønsted acid‐functionalized CDs in an enriched preparation of 5‐hydroxymethylfurfural (HMF) and ethyl levulinate (EL) energy fuel building‐block compounds. The cheap p‐toluenesulphonic acid was used as a precursor to prepare CD‐SO3H by employing a simple, one‐pot and scalable protocol. The high‐end analytical techniques endorsed the catalyst's higher acid density and minimum particle size characteristics. Its glucose reaction evaluation resulted in an 82 mol% HMF using glucose via dehydration. Similarly, it enabled an 85 mol% EL from levulinic acid via esterification under modest reaction conditions. It also promoted the synthesis of other varieties of alkyl levulinates (such as levulinic acid 1‐butyl and methyl esters) with a similar yield result. The recyclability study showed that it could be reused for up to 5 cycles. Overall, the catalytic setup represented an environmentally‐friendly and feasible method for process development.

Realizing Direct Conversion of Glucose to Furfurals with Tunable Selectivity Utilizing a Carbon Dot Catalyst with Dual Acids Controlled by a Biphasic Medium

“…A two-step protocol was followed for the preparation of carbon dot-sulfonic-iron (II) nanocomposite (Fe 2+ @SO3-CD) to expose both LA and BA sites. Briefly, first, the sulfonated acid-functionalized carbon dot (SO3H-CD) was synthesized using the low-cost, and benchtop chemical p-TSA [44]. Second, the iron metal was impregnated into SO3H-CD.…”

“…Our recent work demonstrated that the sulfonated carbon dot (SO3H-CD) is promising for HMF synthesis using glucose ascribed to its higher Brønsted acid sites [44]. For furfural synthesis, LA sites are favorable, based on the literature [23,54,55].…”

“…The comparative UV-vis spectra of Fe 2+ @SO3-CD (Fig. S1) and SO3H-CD [44] highlight that the former has an additional absorption peak at 275 nm, which belongs to the ligand to metal charge-transfer interaction (LMCT), based on the study by Li et al, who reported a similar effect of LMCT at 250 nm when synthesizing the Fe and O-Si nanocomposite [57]. However, the redshift (25 nm) in the wavelength is likely caused by the prevalent sulfonate environment around the Fe-O bond in Fe 2+ @SO3-CD.…”

“…In the past, various functionalized or metal-supported carbonaceous materials, such as graphene oxide, carbon nanotube, g-CN, carbon sphere, and activated carbon, have been exploited as heterogeneous catalysts for various organic transformations because of their cheap and easily available characteristics [34][35][36][37][38]. In recent years, the interest in exploring the applicability of the new class of low-cost carbon nanomaterial, i.e., photoluminescent carbon dots (CD) has increased among scientists because of its wide range of potential applications, including nanotherapeutics, [39] bioimaging, [40] sonocatalysis, [41] energy storage, [42] electronics, [43] and organic transformation reactions [44]. Moreover, it possesses low toxicity, high surface area, good stability, and strong quantum confinement properties.…”

“…We have recently demonstrated a method for simple one-step preparation of sulfonic acid functionalized CD using a cheaper p-TSA precursor. The protocol involved no solvent usage and interestingly, the catalyst exhibited effectiveness in glucose conversion [44]. The catalyst exposing the Brønsted acid (BA) sites established by the -SO3H groups outperformed the glucose dehydration to HMF and levulinic acid esterification to alkyl levulinate reactions.…”