Monoclinic hydromagnesite (Mg 5 (CO 3 ) 4 •(OH) 2 •4H 2 O) flower-like structures of 2-3 µm diameter have been synthesized at room temperature by a simple precipitation method without using any template, catalyst, or surfactant. The as-synthesized flowers were further calcined at various temperatures to prepare monodispersed, nanofibrous MgO microtubes of aspect ratio ∼15. Both the precursor flowers and the MgO microtubes formed were characterized by powder XRD, TG-DTA, FT-IR, SEM, EDAX, HR-TEM, SAED, BET analysis and photoluminescence (PL) studies. A plausible mechanism for the formation of cubic MgO microtubes from monoclinic hydromagnesite flowers is proposed. The as-synthesized nanofibrous MgO microtubes have shown intense green and red emission. The more defective MgO microtubes formed in N 2 atmosphere at 400 °C showed the highest PL intensity and surface area. An attempt has been made to correlate the lattice parameter and the PL intensity.

Solid solutions of GaN in ZnO (Zn 1-z Ga z )(O 1-x N x ) (x and z e 0.15) have been prepared by simple solution combustion method. Except for minor changes in the lattice contraction, no significant change in the Wurtzite structure was observed. Raman and secondary ion mass spectrometry results show the direct Zn-N and Ga-N bonds in (Zn 1-z Ga z )(O 1-x N x ). Visible light absorption and XPS results demonstrate that N 2p states of nitride occupy the states above the O 2p valence band, and hence a change in optical band gap reduction occurs to ∼2.5 eV from 3.37 eV for ZnO. Significant nitrogen fixation catalytic activity through NH 3 formation has been observed at ambient pressure on virgin (Zn 1-z Ga z )(O 1-x N x ) material, indicating its potential as a catalyst.

Two wet chemical methods, namely, wet etching (heterogeneous) and chemical precipitation (homogeneous), have been exploited for the formation of hierarchical ZnO architectures without any specific templates, catalysts, or capping agents. As-synthesized ZnO have been extensively characterized by X-ray diffraction, UV-visible absorbance studies, Fourier transform infrared analysis, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive analysis of X-rays, selected area electron diffraction, photoluminescence (PL), and textural analysis. Wet etching resulted in the formation of self-assembled hexagonal plates with a disordered superlattice-type texture and ultimately ended up in crystallites with highdefect concentration showing a red PL emission. Mechanistic aspects of the growth process in both the methods have been analyzed, and a rational explanation is presented for their observed morphologies. ZnO prepared by both methods have been tested for their photocatalytic water splitting abilities in producing H 2 . Crystalline, spectral, textural, and activity analyses have been carried out for commercial ZnO for a comparison. Pt loaded ZnO was used for the concurrent hydrogen generation and dinitrogen fixation yielding a maximum of 86 µmol of ammonia/(h/0.1 g of catalyst), thus achieving the activation of N 2 at room temperature and atmospheric pressure.

Polycrystalline gold nanowires were synthesized by a simple chemical reduction method using potassium oxalate as the reducing and capping agent along with polyvinylpyrrolidone (PVP) as the co-capping agent at room temperature. Different molar concentration ratios of HAuCl 4 and potassium oxalate were studied for the synthesis of Au nanowires. Kinetics studies for Au colloid formation were carried out using UV-vis spectroscopic technique for the various concentration ratios of the reactants. As the concentration of oxalate was increased, the rate of reduction as well as particle growth was found to increase. XRD and TEM analyses revealed the formation of polycrystalline Au nanowires with a preferential growth of the {111} facet. In the absence of PVP, no Au colloid was formed. Studies revealed that the formation of the Au nanowire was due to the bridging nature of the oxalate dianion. The formation of Pt nanowires further supported the role of oxalate when the same method was adopted for the synthesis of Pt nanowires without using PVP. A plausible mechanism was proposed for the formation of Au nanowires explaining the role of oxalate.

CdS nanorods along with nanostrips and plates have been prepared on a large scale by the solvothermal route using the precursor cadmium oxalate under mild conditions with ethylene glycol as the solvent and (NH4)2S as the sulfiding agent, without using catalysts, surfactants or template. The aspect ratio of the rods varied from 3 to 30. Characterization has been done by TEM, HR-TEM, EDX, HR-SEM, XRD, BET surface area, UV–vis absorption, photoluminescence and fluorescence studies. Photo-catalytic H2 production activity was tested with as-synthesized CdS, calcined CdS, noble metal loaded CdS and for bulk CdS. The nanorods being formed are used as such for H2 production. The as-synthesized CdS is found to have very good H2 production capacity compared to that of the bulk CdS. Upon Pt loading much enhanced activity was observed in the rate of hydrogen production.