Sustainable chemical approaches to two-dimensional nanosheets and mesoporous platforms and catalysts
Authors:   , Ravula Sudhir 
Published: April 2021

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Green Chemistry, also called as Sustainable Chemistry, envisions minimum hazard to improve the efficiency and performance of materials while designing new chemical processes. In general, Green Chemistry is defined as " ... the utilization of a set of principles that reduces or eliminates the use or generation of hazardous substances in the design, manufacture, and application of chemical products."[1] In recent decades, there is widespread recognition of the need to adopt cleaner, sustainable practices to enhance the quality and control of commercial products through a knowledge based approach. The goal for the researchers in sustainable chemistry is to meet the objective without compromising the basic needs of future generations. Nanotechnology, much like Green Chemistry, has revolutionized the fundamentals of all fields, serving as a classic example for emerging products in science and technologies. Despite significant achievements involving nanomaterials, the hazardous chemicals and toxicities associated with them are not fully addressed, which causes a major impact on the environment. These phenomena were especially observed for the use of nanocatalysts. Several greener approaches were utilized to produce nanomaterials or nanoparticles, which avoids toxic reducing agents such as borohydrides or hydrazine. However, chemists need to develop simple and cost-effective approaches for sustainable nanocatalysts to meet global challenges. The overall focus of this doctoral dissertation has been paid to the synthesis, controlled surface modification, and functionalization of distinct types of nanoparticles and nanocomposites through sustainable chemical approaches for environmental and biological applications. As a two-dimensional material, molybdenum disulfide (MoS2) has drawn wide attention due to its fascinating properties and exciting application prospects. However, in order to access these properties, which lie within single- or few-layer nanosheets, the inter-sheet van der Waals interactions within the bulk material must be adequately disrupted to exfoliate MoS2 to atomic thicknesses. Chapter 2 present the sonication-assisted aqueous phase exfoliation of bulk MoS2 into dispersed single- or few-layer nanosheets using popular culinary hydrocolloids. In addition, the sterically stabilized nanosheets were successfully decorated with gold nanoparticles via an in-situ reduction by the hydrocolloids to yield plasmonic nanocomposites exhibiting excellent catalytic activity in 4-nitrophenol (4-NP) reduction. Chapter 3 describes one-pot aqueous photo-assisted route to produce tailored metal nanoparticles decorated aminoclay nanosheets. This method uses no heating or external reducing agent (e.g., NaBH4) nor is photocatalyst required. Finally, these nanohybrids were tested as a dual catalyst for 4-NP reduction or antimicrobial activity. Layered transition metal dichalcogenides (TMDs) have attracted increased attention due to their enhanced hydrogen evolution reaction (HER) performance. Chapter 4 accounts the successful synthesis of few-layered MoS2/rGO, SnS2/rGO, and (MoS2)x(SnO2)1-x/rGO nanohybrids anchored on reduced graphene oxide (rGO) through a facile hydrothermal reaction in the presence of ionic liquids (ILs) as stabilizing, delayering agents. Linear sweep voltammetry measurements reveal that incorporation of Sn into the ternary nanohybrids (as a discrete SnO2 phase) greatly reduces the overpotential by 90--130 mV relative to the MoS2 electrocatalyst. The hierarchical structures and large surface areas possessing exposed, active edge sites make few layered (MoS2)x(SnO2)1-x/rGO nanohybrids promising nonprecious metal electrocatalysts for the HER. Conventional ILs have detectable vapor pressures, however, they are still insignificant near ambient temperatures compared with traditional molecular solvents. In Chapter 5, a simple, straightforward, and reliable isothermal gravimetric measurements were conducted on various ILs, deep eutectic solvents (DES), polymeric ionic liquids, protic ionic liquids, and molecular solvents to estimate their vapor pressures with high accuracy. The vapor pressure of ILs and DESs are in the range of 0.1 - 30 Pa at 100 - 250 [degrees]C and 3 - 161 Pa at 60 - 160 [degrees]C, respectively. Moreover, our study elucidates the trends in vapor pressure and ionic constituent's role. Based on the vapor pressure data, an investigator can readily design specific fluids on the mode of applications. In Chapter 6 reports a template-free strategy to attain a hierarchically mesoporous carbon from the cyclotrimerization of alkyne-functionalized ionic liquids (AFILs) as carbon precursors paired with paramagnetic anions. Thus, the current AFILs are shown to be viable precursors to porous carbon materials with several interesting applications, including the sorption of dyes (cationic methylene blue (MB) and anionic thiazine red R (TRR)) from a contaminated aqueous stream and their subsequent degradation by employing the Fenton reaction. In particular, the mesoporous carbons were successfully applied as a selective adsorbent for separation of binary-dye mixtures (MB + TRR). Importantly, the Fe-AFILs@C can be easily removed from the aqueous solution after sorption process, and can be easily regenerated with a simple ethanol-washing step.