A nano-silica–AgNPs composite material is proposed as a novel antifouling adsorbent for cost-effective and ecofriendly water purification. Fabrication of well-dispersed AgNPs on the nano-silica surface, designated as NSAgNP, has been achieved through protein mediated reduction of silver ions at ambient temperature for development of sustainable nanotechnology. The coated proteins on AgNPs led to the formation of stable NSAgNP and protected the AgNPs from oxidation and other ions commonly present in water. The NSAgNP exhibited excellent dye adsorption capacity both in single and multicomponent systems, and demonstrated satisfactory tolerance against variations in pH and dye concentration. The adsorption mainly occurred through electrostatic interaction, though π–π interaction and pore diffusion also contributed to the process. Moreover, the NSAgNP showed long-term antibacterial activity against both planktonic cells and biofilms of Gram-negative Escherichia coli and Pseudomonas aeruginosa. The antibacterial activity of AgNPs retarded the initial attachment of bacteria on NSAgNP and thus significantly improved the antifouling properties of the nanomaterial, which further inhibited biofilm formation. Scanning electron and fluorescence microscopic studies revealed that cell death occurred due to irreversible damage of the cell membrane upon electrostatic interaction of positively charged NSAgNP with the negatively charged bacterial cell membrane. The high adsorption capacity, reusability, good tolerance, removal of multicomponent dyes and E. coli from the simulated contaminated water and antifouling properties of NSAgNP will provide new opportunities to develop cost-effective and ecofriendly water purification processes.

A highly selective and efficient single molecular FRET based sensor has been developed for the ratiometric detection of Fe³⁺ in aqueous samples and live cells.

Novel bio-renewable castor oil based polyurethane (PU)–silica nanocomposite films were prepared using castor oil, 1,6-hexamethylene diisocyanate and dibutyltin dilaurate in tetrahydrofuran at room temperature. ATR-FTIR spectra confirm the formation of polyurethane and the presence of silica nanoparticles in the polyurethane matrix. The increase of Si nanoparticle content shifts the peak position of N–H and CO (both hydrogen and non-hydrogen bonded) groups present in the polyurethane structure. Furthermore, Raman spectra confirmed the urethane–amide interaction present in the polyurethane–silica nanocomposites. ²⁹Si CP/MAS NMR spectra evidence the formation and the presence of completely condensed SiO₂ species in the polyurethane nanocomposite films. The incorporation of silica nanoparticles increases the thermal stability of the above-mentioned polyurethane films, which can be seen from the increase in activation energy (E_a) values of the degradation process. The E_a values at two stages (T_max1 and T_max2) of the degradation process are 133, 139 and 157, 166 kJ mol⁻¹ for PU control and PU-5AMS (5 wt% amine modified silica nanoparticles), respectively. DSC results prove the interfacial interaction present between silica nanoparticles and the polyurethane hard segment, which decreases the melting temperature. Optical transmittance of the polyurethane films decreased with increasing silica content due to the scattering at the interfaces between the silica nanoparticles and polyurethane. It is interesting to note that the presence of silica nanoparticles gives reinforcement to polyurethane film, thereby increasing the storage modulus up to 24% for PU-5AMS. FE-SEM and HR-TEM images confirm the presence of silica nanoparticles in the polyurethane matrix.