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One-pot synthesis of palladium nanoparticles (PdNPs) has been achieved using calix[4]pyrrole hydrazide (MCPTH) as both reducing as well as capping agent. The synthetic procedure involves the use of environmentally benign water as solvent media. MCPTH-PdNPs have been characterized by using various analytical techniques. Transmission electron microscope analysis visualized the presence of well-dispersed and spherical Pd nanoparticles with an average dimension of 3–4 nm. Powder X-ray diffraction pattern portrayed the presence of face-centered cubic crystal structured PdNPs. A zeta potential value of − 26.2 mV suggests better stability of the nanoparticles. The heterogeneous catalytic activity of MCPTH-PdNPs was studied by probing the reduction of two carcinogenic azo dyes, namely, methylene blue and methyl orange in the presence of sodium borohydride. A remedial pathway for the process of dye degradation is proposed where the catalytic activity of Pd is faciled by the transfer of electrons from MCPTH to the metal centre. The mechanism for dye degradation is further substantiated by Density Functional Theory (DFT) calculations. The results of this work provide not only insight into fabrication of nanoparticles using calixarene platforms but also open new vistas to environmental remediation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Calix[4]pyrrole octahydrazide (CPOH) has been used as a reducing and stabilizing agent. [•] One pot method to produce water dispersible and stable (150days) CPOH-AuNPs. [•] CPOH-AuNps are selective and sensitive (1nM to 1μM) fluorescent sensors for Co(II). [•] Size 8nm and stable at neutral pH must find various biological/biomedical applications. [ABSTRACT FROM AUTHOR]

Newly synthesized Au nanoparticles (AuNPs) capped by calix[4]pyrrole tetrahydrazide (CPTH) has been explored for the colorimetric and fluorimetric detection of Pb(II) ions. The molecular modeling studies reveal the surface mediated properties of CPTH around AuNPs. It is observed that reduction of Au(III) to Au(0) occurs due to the presence of hydrazide groups of CPTH and charge transfer preferably through N atoms and carbonyl group. These interactions further govern the stability of the CPTH-AuNPs. The optical sensing of Pb(II) was carried out in water and the linear range of detection falls between 10 nM and 1 μM concentration range. Moreover, a concomitant pink-to-violet color change is observed providing a useful optical method of detecting Pb(II) in water. The mechanistic insights for the sensing of Pb(II) is based on the overarching hypothesis that Pb(II)ions disturbs the non-covalent interactions of the capping CPTH ligand around the Au° particles causing aggregation of CPTH-AuNPs. The aggregation of CPTH-AuNPs has been elucidated by TEM and DLS experiments. Also, the plausible binding behavior of CPTH-AuNPs with Pb(II) due to hydrogen bonding interactions through –NH groups is discussed. CPTH-AuNPs have also shown their utility for analysis of Pb(II) in industrial waste water and human serum samples. The ability of CPTH-AuNPs for its in vitro anti-oxidant activity and radical scavenging efficiencies has been studied. Thus, the present study suggests notable potential of supramolecular functionalized nanoparticles as a promising chemosensor for toxic ions and a beneficial tool for biomedical applications. [ABSTRACT FROM AUTHOR]