Metal Sulfide-Polymer Nanocomposites for Biomedical, Environmental and Forensic Applications

Abstract

Currently, mankind is facing the most challenging and solution demanding biomedical and environmental related issues. Florescence forensic detection is another important and relatively new field need to be addressed. Transition metal sulfide (TMS) polymer matrix nanocomposites (PMNCs) are significant materials to mitigate such problems because they show combination of tuneable nanoscopic and bulk properties. Polymers show good absorptivity, processability and long-term stability whereas, transition metal sulfide nanoparticles (NPs) possess excellent electronic, catalytic, optical, and magnetic properties. Organic polymers such as chitosan, polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) are good matrix materials for polymer matrix nanocomposite (PMNC). These polymers are not only used for toxic metal adsorption but can also be used a matrix material for NPs synthesis and stabilization due to their diverse polymeric structure and tremendous physicochemical properties. In this work, two types of TMS PMNCs i.e., CdS/CS/PVA and CuS/PVP have been synthesized by adopting two different strategies i.e., the in-situ polymer synthesis and dispersion in polymer matrix. Chitosan and PVA were used as a matrix material for CdS NPs and PVP is used as a matrix material for CuS NPs. CuS NPs were first synthesised by thermolysis of copper dithiocarbamate complex and then disperse in PVP matrix. The in-situ synthesis of cadmium sulfide (CdS) quantum dots (QDs) has been carried out using chitosan/poly(vinyl alcohol) matrix (CP). The CP matrix was crosslinked by tetraethyl orthosilicate (TEOS) and used as a medium for NPs synthesis. Different analytical techniques were used to confirm the formation of PMNCs. The synthesised material was characterized by FT-IR, XRD, SEM, TEM, UV-Visible and fluorescence spectroscopy. The SEM and TEM results indicated polymer-based stability due to capping effect on the particle surface. The XRD diffractograms showed that both CuS and CdS PMNCs have grown in typical hexagonal crystalline forms. The optical properties valuation of PMNCs by UV-Visible and fluorescence spectroscopy have approved their better absorption ability in UV-visible (CdS PMNCs) and (CuS PNMCs) NIR regions. The time-resolved PL and steady-state indicated the low electron-hole recombination rate in CdS NPs than the bulk CdS. Prepared CuS/PVP PMNCs are cost effective and body compatible so can be used as photothermal agent for healing deep cancer cells. These PMNCs efficiently kill MCF7 ii (Michigan Cancer Foundation-7) breast cancer cells (both in vivo and in vitro) under NIR irradiation by raising the temperature of tumour cells. Such materials can be used for the treatment of deep cancer as they can produce a heating effect using high wavelength and deeply penetrating NIR radiation. After characterization, CdS was tested as a photocatalyst for the reduction of 4 Nitrophenol (4-NP) to 4-Aminophenol (4-AP) in saturated aqueous sodium borohydride solution and Cr(VI) to Cr(III) in aqueous formic acid solution, with high efficiency and selectivity. The catalyst can reduce 4-NP to 4-AP in 14 min and Cr(VI) to Cr(III) in 10 min. The results reveal that CdS PMNCs (Bx/CdS) exhibit better catalytic efficiency towards Cr(VI) reduction (kapp= 0.984 min−1) as compared to 4-NP reduction (kapp= 0.894 min-1). The transformation of 4-NP to 4-AP on CdS follows pseudo-first order kinetics. CdS PMNCs i.e., CdS/CPx was also used for fluorescence detection of latent fingerprints (LFPs) with high resolution and visibility at transparent and coloured substrates. The CdS/CPx powders were used for the fluorescence detection of latent fingerprints (LFPs) on different substrates using super glue fuming, followed by powder dusting of QDs. The results revealed that CP not only stabilizes the CdS QDs but also imparts many useful properties, such as uniform size distribution of QDs. The developing mechanism suggested that selectivity attained towards the ridge of the fingermark is due to the affinity between polymer matrix and oily secretions of the LFPs. The designed nanohybrids have shown very high sensitivity toward LFPs and much effective for fluorescence detection in forensic investigation.