The preparation and characterization of multifunctional ZnO 1-x N x (x e 0.15) via a simple solution combustion method is reported. ZnO 1-x N x exhibits visible light absorption, thermal stability, nanometer-/ micrometer-sized triangular particles, and catalytic properties. X-ray diffraction studies of ZnO 1-x N x demonstrate that the lattice oxygen in ZnO is replaced by nitrogen without any major change in the wurtzite structure; however, charge compensation occurs, because of interstitial Zn atoms, as well as oxygen vacancies. Microscopic studies reveal the dominance of nanometer-and micrometer-sized triangles of ZnO 1-x N x . UV-visible and Raman spectra indicate a midgap state, derived from N 2p states, and direct Zn-N interaction, respectively. Secondary ion mass spectrometry studies show the presence of N and ZnN species in the bulk and support the direct Zn-N interaction. Electron paramagnetic resonance (EPR) studies indicate the presence of a small amount of defects. Photocatalytic decomposition of rhodamine B, and anisole acylation at room temperature, highlights the effectiveness of ZnO 1-x N x to catalysis applications. The aforementioned multifunctional characteristics suggest that ZnO 1-x N x might be used in place of conventional ZnO for better control and that it might be explored for further applications in catalysis and optoelectronics.

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.

Indium and nitrogen codoping in ZnO leads to a solid solution of InN in ZnO with a composition of (Zn 1-z In z )(O 1-x N x ). A simple solution combustion method has been adopted to prepare the above materials in less than 10 min with metal nitrates as the metal ion source and urea as fuel. With reference to ZnO, significant increase in lattice parameters was observed with increasing In-content. However, the In 2 O 3 phase was observed along with InN for In content g10%. Optical absorption extended into the visible region, at least up to 550 nm, demonstrates an effective reduction of optical band gap due to the formation of solid solution. A new feature observed just above O 2p valence band in X-ray photoelectron spectroscopy (XPS) suggests the creation of N 2p states from InN; the N 1s core level XPS result too confirms nitride contribution. Raman spectroscopy and secondary ion mass spectrometry results show direct In-N, Zn-N, and In-N-Zn fragments in (Zn 1-z In z )(O 1-x N x ). Catalytic activity explored for oxidation of 2-butanol to ethyl methyl ketone demonstrates a high selectivity at 350 and 400°C. All of the above characteristics suggest the multifunctional nature of (Zn 1-z In z )(O 1-x N x ) and its potential for other applications.

The highly desirable combination of the visible light absorption properties of In1-xGaxN Quantum dots (QD) along with the multifunctionality of ZnO into a single integrated material was prepared for solar harvesting. This is the first report on InGaN QD integrated with ZnO (InGaN@ZnO), synthesized by a highly reproducible, simple combustion method in 15 min. Structural, microstructural and electronic integration of the nitride and oxide components of InGaN@ZnO was demonstrated by appropriate characterization methods. Self-assembly of InGaN QD is induced in growing nascent zinc oxo nanoclusters taking advantage of the common wurtzite structure and nitrogen incorporation at the expense of oxygen vacancies. Direct integration brings about a single phase structure exhibiting extensive visible light absorption and high photostability. InGaN@ZnO suggests synergistic operation of light harvesting and charge conducting components for solar H2 generation without using any co-catalyst or sacrificial agent, and a promising photocurrent generation at 0 V under visible light illumination. The present study suggests a direct integration of QD with the host matrix and is a potential method to realize the advantages of QDs.

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Simple solution combustion synthesis was adopted to synthesize ZnO–ZnS (ZSx) nanocomposites using zinc nitrate as an oxidant and a mixture of urea and thiourea as a fuel. A large thiourea/urea ratio leads to more ZnS in ZSx with heterojunctions between ZnS and ZnO and throughout the bulk; tunable ZnS crystallite size and textural properties are an added advantage. The amount of ZnS in ZSx can be varied by simply changing the thiourea content. Although ZnO and ZnS are wide band gap semiconductors, ZSx exhibits visible light absorption, at least up to 525 nm. This demonstrates an effective reduction of the optical band gap and substantial changes in its electronic structure. Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and secondary-ion mass spectrometry results show features due to ZnO and ZnS and confirm the composite nature with heterojunctions. The above mentioned observations demonstrate the multifunctional nature of ZSx. Bare ZSx exhibits a promising sunlight-driven photocatalytic activity for complete mineralization of endocrine disruptors such as 2,4-dichlorophenol and endosulphan. ZSx also exhibits photocurrent generation at no applied bias. Dye-sensitized solar cell performance evaluation with ZSx shows up to 4% efficiency and 48% incident photon conversion efficiency. Heterojunctions observed between ZnO and ZnS nanocrystallites in high-resolution transmission electron microscopy suggest the reason for effective separation of electron–hole pairs and their utilization.