Selvakannan Periasamy

Controlling Core/Shell Formation of Nanocubic p-Cu2O/n-ZnO Toward Enhanced Photocatalytic Performance

p-Type Cu2O/n-type ZnO core/shell photocatalysts has been demonstrated to be an efficient photocatalyst as a result of their interfacial structure tendency to reduce the recombination rate of photogenerated electron-hole pairs. Monodispersed Cu2O nanocubes were synthesized and functioned as the core, on which ZnO nanoparticles were coated as the shells having varying morphologies. The evenly distributed ZnO decoration as well as assembled nanospheres of ZnO were carried out by changing the molar concentration ratio of Zn/Cu. The results indicate that the photocatalytic performance is initially increased, owing to formation of small ZnO nanoparticles and production of efficient p-n junction heterostructures. However, with increasing Zn concentration, the decorated ZnO nanoparticles tend to form large spherical assemblies resulting in decreased photocatalytic activity due to the interparticle recombination between the agglomerated ZnO nanoparticles. Therefore, photocatalytic activity of Cu2O/ZnO heterostructures can be optimized by controlling the assembly and morphology of the ZnO shell.

SERS and fluorescence-based ultrasensitive detection of mercury in water

The development of reliable and ultrasensitive detection marker for mercury ions (Hg2+) in drinking water is of great interest for toxicology assessment, environmental protection and human health. Although many Hg2+ detection methods have been developed, only few offer sensitivities below 1pM. Herein, we describe a simple histidine (H) conjugated perylene diimide (PDI) bolaamphiphile (HPH) as a dual-responsive optical marker to develop highly selective and sensitive probe as visible (sol-to-gel transformation), fluorescence and SERS-based Hg2+sensor platform in the water. Remarkably, HPH as a SERS marker supported on Au deposited monodispersed nanospheres monolayers (Au-MNM) of polystyrene offers an unprecedented selectivity and the best ever reported detection limit (LOD) of 60 attomolar (aM, 0.01 parts-per-quadrillion (ppq)) for Hg2+ in water. This is ten orders of magnitude lower than the United States Environmental Protection Agency (USEPA) tolerance limit of Hg2+ in drinking water (10nM, 2 ppb). This simple and effective design principle of host-guest interactions driven fluorescence and SERS-based detection may inspire the future molecular engineering strategies for the development of ultrasensitive toxic analyte sensor platforms.

Efficient Heterostructures of Ag@CuO/BaTiO3 for Low-Temperature CO2 Gas Detection: Assessing the Role of Nanointerfaces during Sensing by Operando DRIFTS Technique

Tetragonal BaTiO3 spheroids synthesized by a facile hydrothermal route using Tween 80 were observed to be polydispersed with a diameter in the range of ∼15-75 nm. Thereon, BaTiO3 spheroids were decorated with different percentages of Ag@CuO by wet impregnation, and their affinity toward carbon dioxide (CO2) gas when employed as sensitive layers in a microsensor was investigated. The results revealed that the metal nanocomposite-based sensor had an exceptional stability and sensitivity toward CO2 gas (6-fold higher response), with appreciable response and recovery times (<10 s) and higher repeatability (98%) and accuracy (96%) at a low operating temperature of 120 °C, compared to those of pure BaTiO3 and CuO. Such improved gas-sensing performances even at a very low concentration (∼700 ppm) is attributable to both the chemical and electrical contributions of Ag@CuO forming intermittent nanointerfaces with BaTiO3 spheroids, exhibiting unique structural stability. The CO2-sensing mechanism of CuO/BaTiO3 nanocomposite was studied by the diffuse reflectance infrared Fourier transform spectroscopy technique that established the reaction of CO2 with BaO and CuO to form the respective carbonate species that is correlated with the change in material resistance consequently monitored as sensor response.