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Materials-by-Design symbolizes the development of advanced materials with cost and time -effective experimentation. Here, we show the single and unique strategy of developing macroporous WO3 with different morphologies (nano to micro) using glycine as structure assisting agent. The developed structures were analyzed with various characterizing tools, and tested for practical application as acetone gas sensor (83.87% for 10 ppm). The morphological correlation with the sensitivity is described.

In the present communication, we have presented a high performance acetone sensor based on Pd loaded Sm doped SnO 2 nanomaterial. The (0.5, 1, 2 and 3) wt% Pd loaded 6 mol% Sm doped SnO 2 nanoparticles were prepared using a co-precipitation method. The characterization of samples was done by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FEG-SEM), Energy Dispersive Analysis by X-rays (EDAX), High Resolution-Transmission Electron Microscopy (HR-TEM) and Selective Area Electron Diffraction (SAED) techniques. The gas response studies such as sensitivity, selectivity and stability towards liquid petroleum gas, ammonia, ethanol and acetone were measured at 100 ppm concentrations. The results show that optimum Pd loading (2 wt%) results in smaller crystallite size (~3.1 nm), lower operating temperature (200 °C), higher gas response (94%),better selectivity, faster response (~3 s) and quicker recovery (~12 s) towards acetone.

Vertically aligned ZnO nanorods (ZNRs) arrays with various aspect ratios were deposited by using a simple and inexpensive hydrothermal route at relatively low temperature of 90 °C. The influence of hydroxide anion generating agents in the solution on the growth of ZNRs arrays was studied. Hexamethylenetetramine (HMTA) and ammonia were used as hydroxide anion generating agents while polyethyleneimine (PEI) as structure directing agent. The combined effect of these three agents plays a crucial role in the growth of ZNRs arrays with respect to their rod length and diameter, which controls the aspect ratio. The deposited ZNRs exhibited hexagonal wurtize crystal structure with preferred orientation along (002) plane. The highly crystalline nature and pure phase formation of ZNRs was confirmed from FT-Raman studies. The maximum gas response (R g /R a ) of 67.5 was observed for high aspect ratio ZNRs, deposited with combination of HMTA, ammonia as well as PEI. The enhancement in gas response can be attributed to high surface area (45 cm 2 /g) and desirable surface accessibility in high aspect ratio ZNRs. Fast response–recovery characteristics, especially a much quicker gas response time of 32 s and recovery time of 530 s were observed at 100 ppm NO 2 gas concentration.

Cu doped ZnO microballs were synthesized via oxalate assisted sonochemical route by using Zn(NO 3 ) 2 and Cu(NO 3 ) 2 as precursors. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis results demonstrate several nanosheets-like structures assembled to form microballs of 2–4 μm diameters. Room-temperature photoluminescence spectra (PL) show near band emission centered at ~390 nm. Absorbance spectra reveal red shift towards UV region on incorporation of Cu in ZnO. The as-synthesized products with extended light absorption exhibits excellent sunlight driven photodegradation ability towards Methylene blue (MB) and Rhodamine B (RhB) dyes.

One-dimensional single-crystalline h-WO3 nanorods have been synthesized by using a facile hydrothermal technique. Crystal structure, morphology evolution and thermal stability of the products are characterized by using X-ray Diffraction pattern, Scanning Electron Micrographs, Photoluminescence reflectance spectrum; UV–vis diffused reflectance spectral analysis and Raman techniques. The evolution and distribution of WO3 nanorods strongly depend on hydrothermal reaction temperature and time of reaction. Hydrothermal reaction temperature of 170 °C for 48 h ensures the formation of well-defined agglomerated WO3 nanorods. Gas response measurements reveal that WO3 sensor operating at 250 °C exhibits highest sensitivity towards NO2 with low cross sensitivity towards LPG, acetone and ammonia gas, which makes this material a competitive candidate for NO2 sensing applications. A possible adsorption and reaction model is proposed to illustrate formation of one dimensional nanostructure and gas sensing mechanism.

Hierarchical undoped, vanadium and tungsten doped ZnO nanostructures have been synthesized via a surfactant assisted hydrothermal method. The as-synthesized products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDAX), UV–visible spectroscopy, photoluminescence (PL) and particle size distribution (PSD) analysis. A possible growth mechanism of the various hierarchical ZnO nanostructures is proposed. Gas response of sensors fabricated from the as-prepared as well as V- and W-doped ZnO were systematically investigated for acetone, ethanol, methanol, formaldehyde, dimethylsulfoxide (DMSO), triethylamine (TEA), ammonia and ethylenediammine (EDA). Undoped ZnO showed ~80% sensitivity towards acetone while on V-doping the sensitivity enhanced up to 92%. In the W-doped ZnO response towards acetone suppressed while the response towards TEA enhanced. The doping and morphology of ZnO are probably responsible for such a difference in the gas response. UV–visible absorption results reveal that doping ZnO with tungsten shows red-shift of the absorption edge. The photoluminescence (PL) studies reveal a slight red-shift in UV emission in pure ZnO upon V- and W-doping, which is assumed to be associated with the different compress stress in the architectures.

A simple and robust synthesis approach to zinc based spinel ferrite (ZnFe 2 O 4 ) using the glycine combustion method is reported. The route utilizes divalent zinc nitrate (Zn(NO 3 ) 2 ·6H 2 O) and trivalent iron nitrate (Fe(NO 3 ) 3 ·9H 2 O) precursors in aqueous solution (distilled H 2 O). Glycine (NH 2 –CH 2 –COOH) acts as a fuel for the combustion process and subsequent ferrite (ZnFe 2 O 4 ) formation. As produced material powder was sintered at 700 °C in the pellet form and examined for LPG, acetone, ethanol and ammonia sensing properties in the temperature range of 200–450 °C. XRD and TEM analyses revealed the formation of single phase nanocrystalline material with crystallite size in the range of 25–30 nm. SEM analysis confirmed the coarse structural morphology due to auto-ignition during the combustion reaction. The produced ferrite showed maximum response to both acetone (57%) and LPG (54%) at operating temperatures of 250 °C and 375 °C, respectively. Further, the sensor showed decent stability and reproducibility towards LPG and acetone, over the period of 30 days, which was then decreased by 2% up to 45 days. The present study confirms that the as produced ZnFe 2 O 4 is a promising candidate for fabricating high performance sensors towards LPG and acetone sensing, in practice.

The sensors based on cerium oxide–zinc oxide (CeO 2 –ZnO) composites were fabricated by using thick-film screen printing of hydrothermally grown powders. The structural, morphological investigations were carried out by using XRD, FESEM and TEM and these studies revealed that the synthesized products were grown in high-density and possessed well-crystallinity. Furthermore, the gas responses were evaluated towards the ethanol, acetone, liquid petroleum gas (LPG) and ammonia gases. The 2 wt% CeO 2 –ZnO composite exhibited excellent response of 94% at 325 °C and better selectivity towards ethanol with low response and recovery time as compared to pure ZnO and can stand as reliable sensor element for ethanol sensor related applications.

Undoped and Lanthanum doped tin dioxide nanopowders were successfully synthesized by a chemical co-precipitation method. The TGA–DTA, XRD, TEM, SEM, EDAX, FTIR, Raman and UV–vis techniques were used to characterize various physico-chemical properties of samples. Thick films of functional material were prepared by using a screen printing technique and then sintered at 650 °C for 2 h. XRD analysis of all the samples revealed formation of single phase rutile type tetragonal structures which was further supported by Raman studies and FTIR measurements. The particle size of sintered SnO 2 was decreased with La doping, confirming the role of La as a grain growth inhibitor. Morphological studies revealed formation of porous structure useful for gas sensing application. Gas sensing characteristics were investigated towards various reducing gases such as liquefied petroleum gas (LPG), acetone (CH 3 COCH 3 ), ethanol (C 2 H 5 OH) and ammonia (NH 3 ). The maximum response was exhibited by 3 mol% La doped SnO 2 thick film towards acetone vapor at an operating temperature of 300 °C. The sensor exhibited quick response and recovery times which were 20 s and 48 s, respectively.

Nanocrystalline CoFe 2− x Ce x O 4 ferrites ( x =0, 0.04, 0.08) were synthesized by using the inexpensive, simple and eco - friendly molten-salt (M-S) method. Effects of Ce doping on the structural, morphological and gas sensing properties of the CoFe 2 O 4 ferrite were investigated. X-ray diffraction (XRD) analysis revealed the formation of spinel CoFe 2 O 4 . Transmission electron microscopy (TEM) investigations showed that the synthesized ferrite is made up of very fine spherical nanoparticles. Furthermore, the gas response of nanocrystalline ferrite materials was investigated in the temperature range of 200–450 °C toward the reducing gases like liquefied petroleum gas (LPG), acetone, ethanol and ammonia. The sensor response was found to be sensitive and selective toward acetone as compared to other reducing gases. It is observed that the addition of Ce (4 wt%) strongly influenced the response and the operating temperature of the sensor material and thus can serve as acetone-sensing sensors.

Hierarchical nanostructured ZnO with uniform flower-like morphology was obtained by using PEG-assisted low-temperature (120°C) hydrothermal route. These structures are formed by systematic assembly of nanosheets (10–25 nm thick) with dominant {2-1-10} planes. The products were characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman and photoluminescence (PL) spectroscopy. These nanostructures display a strong structure-induced photocatalytic performance. It is observed that a significant improvement takes place in the photodegradation of methylene blue as compared with other morphologies such as; spheres, vesicular and nanosheets.

Li doped and undoped γ - Fe 2 O 3 nanopowders have been synthesized at room temperature via simple method by using ethylene diamine as a precipitating agent. The influence of Li doping on the humidity sensing behavior was investigated by varying the doping concentration of Li (0.15, 0.30, 0.45 and 0.75 mol%). The results revealed that the Li doping was advantageous for tuning the response curves in the lower humidity region. The optimal content for Li doping was found to be 0.45 mol% for which the sensor showed more linear behavior with its potential for device application in comparison with the other samples.

Hierarchical zinc oxide nanostructures were successfully synthesized by facile hydrothermal and sonochemical routes using citrate and PEG as structure directing agents. The effect of precursor concentration and preparation methods on the formation of typical morphology was systematically studied under hydrothermal and sonochemical conditions. Different concentrations of zinc acetate, sodium citrate and NaOH under hydrothermal and sonochemical methods generate different hierarchical structures such as flower-like, cabbage-like, and ellipsoidal ball-like morphologies, depending on the preparation conditions. The as-prepared ZnO samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission election microscopy (TEM), photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and particle size distribution (PSD) analysis. Catalytic activities of the as-prepared samples were studied by photodegradation of Methylene blue.

Undoped and cerium (Ce) doped nanocrystalline copper ferrite (CuFe 2 O 4 ) materials were synthesized via the molten-salt (M-S) method. Effects of Ce doping on the structural, morphological and gas sensing properties of the CuFe 2 O 4 ferrite have been investigated. X-ray diffraction (XRD) analysis revealed the formation of spinel CuFe 2 O 4 . Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations showed that the synthesized ferrite is made up of very fine spherical nanoparticles. Moreover, the gas sensing properties of sintered samples were studied towards different reducing gases such as liquefied petroleum gas (LPG), acetone, ethanol and ammonia. The sample with 4% cerium doped CuFe 2 O 4 (Ce4) showed the maximum gas sensitivity (86%) towards LPG with fast response time of 5 s and good recovery time of 68 s.

ZnO and Zn 0.9 Cd 0.1 O powders were synthesized using a citrate gel combustion method. The citrate gel combustion process provides homogeneous and phase pure nanocrystalline powders through a single step exothermic reaction. The pellets of ZnO and Zn 0.9 Cd 0.1 O were sintered at 600 °C for 6 h and further used to study their structural, morphological, and gas response properties. The XRD and TEM study reveals formation of nanocrystaline powders for both compositions. The gas sensing properties of the pelletized sensor materials were studied at operating temperatures from 200 to 450 °C. It has been observed that gas response considerably depends upon the operating temperature and test gas species. The operating temperature of the ZnO sensor significantly decreased with addition of cadmium. The reproducibility and stability study of Zn 0.9 Cd 0.1 O confirmed its candidature for acetone sensor related applications.

Undoped and Ni, Ce-doped nanocrystalline tin oxide were synthesized by co-precipitation route. Doped as well as undoped SnO2 compositions revealed single phase structure without any impurity. The lattice constant of SnO2 increases and the grain size decreases with doping of Ni and Ce. The responses of the sensing elements are evaluated by measuring the resistance change upon exposure to various test gases such as liquid petroleum gas (LPG), acetone, ethanol and ammonia. In comparison to LPG, ethanol, and ammonia the response towards acetone vapor increases markedly on simultaneous doping of Ni and Ce. For acetone vapors with 500 ppm at 300 °C, the undoped SnO2 shows 31% response, while with individual Ni or Ce doping it increases to 38 and 60%, respectively, however with simultaneous doping of Ni and Ce there is a significant enhancement up to 92%. The results of gas sensing measurements reveal that the thick films deposited on alumina substrates using screen printing technique give selectively a high response of (87%) with fast recovery (∼1 min) towards 100 ppm acetone at 300 °C.

Nanocrystalline pristine and 0.5, 1.5 and 3.0 wt% Pd loaded SnO2 were synthesized by a facile co-precipitation route. These powders were screen-printed on alumina substrates to form thick films to investigate their gas sensing properties. The crystal structure and morphology of different samples were characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The 3.0 wt% Pd:SnO2 showed response of 85% toward 100 ppm of LPG at operating temperature of 250 °C with fast response (8 s) and quick recovery time (24 s). The high response toward LPG on Pd loading can be attributed to lowering of crystallite size (9 nm) as well as the role of Pd particles in exhibiting spill-over mechanism on the SnO2 surface. Also selectivity of 3.0 wt% Pd:SnO2 toward LPG was confirmed by measuring its response to other reducing gases like acetone (CH3COCH3), ethanol (C2H5OH) and ammonia (NH3) at optimum operating temperature.

The present investigation deals with the synthesis of nanostructured nickel ferrite (NiFe 2 O 4 ) and their liquid petroleum gas-sensing characteristics. The 15–20 nm size nickel ferrite has been synthesized at 700 °C by a simple molten-salt route using sodium chloride as grain growth inhibitor. These nanoparticles exhibit significantly high response towards liquid petroleum gas (LPG) in comparison with ethanol vapor, hydrogen sulfide, ammonia and hydrogen. The gas response towards various gases at their 200 ppm concentrations is investigated at 200–450 °C. Different characterization techniques have been employed, such as differential thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) to study the crystallite size, structure and morphology. The results suggest possibility of utilization of the nanostructured nickel ferrite, without addition of any precious metal ion, as the LPG detector.