Here, we report the luminescence based sensing of trace amounts of nitroaromatic explosive organic compounds. The luminescence emission of nanosized spinel oxide ZnCr2O4 with high chemical and thermal stabilities has been used as a potential probe to detect such organic explosives. Low temperature solution combustion synthesized ZnCr2O4 oxide with an average particle size of ∼9 nm exhibits strong luminescence emission at 410 nm upon excitation at 260 nm in an aqueous suspension. The presence of nitroaromatics in ZnCr2O4 suspension dramatically suppresses the luminescence emission providing an opportunity to detect it quantitatively. The detection limit for 2,4,6-trinitrophenol (TNP) is as low as 23 ppb. A number of organic compounds have been investigated for a comprehensive understanding. The astonishing sensitivity of ZnCr2O4 nanoparticles towards nitro explosives is appealing for sensing application. A plausible explanation of such luminescence quenching has been ascribed to a two-fold mechanism. The underling mechanism is further substantiated by a similar study on ZnO nanoparticles.

We report an experimental study for the structural and magnetic properties of highly pure LaFe 0.5 Mn 0.5 O 3 perovskite phase. The impurity free LaFe 0.5 Mn 0.5 O 3 has been prepared by sol-gel technique at 500 °C and annealed at different temperatures up to 1000 °C. Previous works on LaFe 0.5 Mn 0.5 O 3 revealed presence of secondary phases along with contradicting magnetic properties. Such as, Bhame et al (2005 Phys. Rev. B 72 054426-7) reported the superparamagnetic or spin-glass like behavior for 200 °C treated sample that persisted even at 700 °C sample. However, Wei et al (2012 Mater. Chem. Phys. 136 755-61) claimed room temperature ferromagnetism in all the samples annealed in the range of 600 °C-700 °C where the saturation magnetization decreases with the increase in temperature. These contradicting results lead us to revisit the effect of annealing temperature on the magnetic properties of LaFe 0.5 Mn 0.5 O 3 . We noticed a gradual increase in magnetization with increase in annealing temperatures without any signature of long range spin ordering for pure single phase samples. The increased magnetic moment with annealing temperatures has been attributed to the suppression of surface contribution of disordered spin. The low temperature magnetic behaviors can be explained by the interacting cluster glass behavior for the pristine as well as for 1000 °C annealed samples.

We report the low temperature synthesis of nanosized CaCu 3-x Mn x Ti 4-x Mn x O 12 (x = 0, 0.5 and 1.0) quadruple perovskites and their magnetic, dielectric and catalytic performance towards CO oxidation and methanol steam reforming (MSR). Our investigations reveal the pronounced effects of particle size and chemical substitution on all the physical properties reported here. The manganese doped samples exhibit remarkable change in magnetic properties, where antiferromagnetic pristine phase converted to ferrimagnetic phase for x = 1. The dielectric constant values of the cold-pressed nanosized perovskites are~10 3 and follows Maxwell-Wagner type relaxation. This value is about 100 fold lower than that of the bulk samples that has been ascribed to the effect of particle size and the absence of nano-twinning in the material as revealed from HRTEM studies. The doping of manganese further reduces the magnitude of dielectric value, which is the chemical effect. Mndoped samples show greater catalytic activity compared to the pristine sample towards CO oxidation due to a synergistic CuÀMn interaction. The catalytic performance of these oxides for MSR reaction is intriguing. Although the catalyst undergoes decomposition in the MSR atmosphere causing a decrease in methanol conversion during time-on-stream (TOS) tests, the activity can be regenerated by in-situ or ex-situ annealing in air. The notable catalytic activity and reversibility between pristine and decomposed form are very interesting.

Facile synthesis of Al-doped CaCu3Ti4O12 quadruple perovskite has been reported and it is projected to be a promising candidate for Schottky barrier diode application and a methanol steam reforming catalyst for hydrogen generation.

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