Chemiresistive NH3 detection at sub-zero temperatures by polypyrrole- loaded Sn1-xSbxO2 nanocubes

Chemiresistive gas sensors operate mainly at high temperatures, primarily due to the need of energy for surface adsorption-desorption of analytes. As a result, the operating temperature of the chemiresistive sensors could be reduced only to room temperature. Hence, a plethora of sensing requirements at temperatures below ambient have remained outside the scope of chemiresistive materials. In this work, we have developed an antimony-doped SnO2 nanocube-supported expanded polypyrrole network that could detect low ppm ammonia gas (<= 20 ppm) at sub-zero temperatures with high response (similar to 4), selectivity, and short response and recovery times. The low temperature chemiresistive sensing has been explained in terms of the interplay of an extended conducting network of an in situ deposited polymer, effective transport properties of majority charge carriers and a loosely bound exciton-like electron-hole pair formation and breakage mechanism

Dopant-mediated surface charge imbalance for enhancing the performance of metal oxide chemiresistive gas sensors

Chemically pristine and untailored metal oxide-based gas sensors usually suffer the brunt of poor sensitivity and selectivity. Doping with a suitable element is an efficient strategy to overcome the above challenges. However, to date, the choice of the dopant has been made primarily on empirical basis. This reflects the existence of lack of a general understanding as to what defines the suitability of a dopant. Based on surface electronic state analyses in different cases of dopant-enhanced gas sensing by tin oxide-based systems, we could identify a correlation between the role of the dopant oxidation states for generating surface charge imbalance and improvement in their respective sensing performances. The above studies were then extended to 54 different cases of dopant-induced sensing improvement in metal oxide-based systems and a similar correlation was observed. Based on the above observations, a generalized picture has been drawn that categorically delineates the role of surface charge imbalance in improved gas sensing performance. The above understanding is expected to make the choice of dopant more specific, paving the way for the development of highly sensitive gas sensors

Band gap engineered Sn-doped bismuth ferrite nanoparticles for visible light induced ultrafast methyl blue degradation

Remediation of water pollution persists as major concern for scientists and industry. Various ceramic based nanomaterials have been used in efficient photocatalytic degradation of different industrial dyes. However, the major factors that restrict efficacy of these systems are requirement of UV source for activating dye degradation process, prolonged time for degradation and lower efficiency. This paves way to development of alternative material systems that can resolve above problems by not only ensuring maximum dye degradation in minimum time in presence of visible light but also reusability in several cycles. In this work, we report visible light driven photocatalytic degradation of methyl blue (MB) using Sn-doped bismuth ferrite (BFO) nanoparticles. Different concentrations (0, 1%, 1.5%, 2%) of Sn-doped BFO nanoparticles were synthesized using facile sol-gel methods. It was observed that 1.5% Sn-doped BFO nanoparticle exhibits highest photocatalytic activity towards MB degradation compared with pure and other doped BFO nanoparticles. 1.5% Sn-doped BFO nanoparticle de-lineates 70% dye degradation capability within 10 min of irradiation under visible light. 1.5% Sn-doped sample shows 99% degradation capability within 2 h of visible light irradiation while pristine BFO nanoparticles can degrade only 20% under identical conditions. Additionally, 1.5% Sn-doped BFO nanoparticles are also capable of degrading RhB, another important contaminant. The 1.5% Sn-doped BFO nanoparticle could be a promising photocatalyst for efficient degradation of industrial effluents having various dyes. The efficient dye degradation of 1.5% Sn doped BFO nanoparticle has been explained in terms of increased density of surface active sites evident from bulk structural analyses and greater probability of generation of electron-hole pairs on surface by virtue of reduced band gap. A theoretical modelling of band structure has been done to identify surface .OH ions as most effective species to promote dye degradation

Surface-analyte interaction as a function of topological polar surface area of analytes in metal (Cd, Al, Ti, Sn) sulfide, nitride and oxide based chemiresistive materials

Material surface - analyte interactions play important roles in numerous surface mediated processes including gas sensing. However, effects of topological polar surface area (TPSA) of target analytes on surface interactions during gas sensing have been so far largely disregarded. In this work, based on experimental observations on cross-sensitivity in cadmium sulfide (CdS) nanoparticle based room temperature gas sensor, we found that for reactions with similar Energy Rate of Surface Interaction (ERSI), unexpected quadratic correlation exists between sensing response of CdS and TPSA of analytes. From general understanding and as reported earlier in case of drug absorption through surface of membranes, it is expected that surface interactions would decrease with increasing TPSA of analytes. Our results imply that for certain TPSA range, sensor surface-analyte interactions actually increase with increasing TPSA before it finally starts decreasing. Further experiments on four other diverse material systems like AlN, SnO2, TiO2 (Anatase) and Vanadium-doped SnO2 showed similar trend, revealing generalized picture of TPSA dependence of sensor surface-analyte interactions. A physical explanation behind the parabolic relation has been provided based on electrostatic energy minimization of interacting polar fields. Above finding is anticipated to pave way to achieve improved surface interactions and highly selective sensing performances consecutively

Poly aniline (PANI) loaded hierarchical Ti1−xSbxO2 rutile phase nanocubes for selective room temperature detection of benzene vapor

Benzene is one of the aromatic yet hazardous hydrocarbons that are deceptive under their sweet odor. Even in low ppm concentration, benzene vapor in ambient surroundings have been proven to be a major human carcinogen, primarily responsible for leukemia. Often found along with traces of toluene and xylene which have similar molecular structures, selective detection of low concentration benzene, particularly at room temperature is a major challenge. In this work, using the idea that transition from uni-faceted to bi-faceted crystal growth shall induce a change in morphology from spherical to cubical; antimony doped rutile TiO2 nanocubes were synthesized and employed in benzene vapor detection. While the PANI loaded antimony doped (0.03) TiO2 nanocubes showed an enhanced 80% response to 2 ppm benzene in air at room temperature, it was selective (up to 7 times more) against 2 ppm toluene and xylene vapor. The sensors were highly stable against humidity and also reusable for a considerable span of time. The role of specificity in exposed cubical facet has been explained for eliminating cross-sensitivity in benzene detection phenomenon

Y and Al co-doped ZnO-nanopowder based ultrasensitive trace ethanol sensor: A potential breath analyzer for fatty liver disease and drunken driving detection

Excess ethanol in exhaled breath can be an indicator of intoxication and a biomarker for fatty liver disease. Herein, we report for the first time a highly sensitive and selective Al and Y co-doped ZnO nanopowder sensor for the detection of trace ethanol in exhaled breath. The nanopowder was synthesized by a facile sol-gel method and characterized by multiple sophisticated techniques, viz. XRD, XPS, FTIR, FESEM, EDX, BET surface area analysis, UV-Vis spectroscopy, photoluminescence, infrared imaging, and current-voltage (I-V) measurement. The developed sensors, especially 5% Y and 1% Al co-doped ZnO exhibited excellent n-type response to 1 ppm ethanol (62.8%). Further, appreciable selectivity to trace ethanol with respect to other interfering gases, viz. acetone, ammonia, CO, NO, NO2, formalin, acetylene, and saturated moisture was observed. Additionally, ul-trafast response (0.77 s) and recovery (8.1 s) time, good repeatability, and long-term stability for at least 10 months were observed. Satisfactory resolution between healthy breath, and simulated breath with ethanol vapor excess was obtained. The optimized sensor could be very suitable for both the detection of liver problem as well as commercial breath ethanol analyzer for drunken driving detection

Ferromagnetic Ni1-xVxO1-y Nano-Clusters for NO Detection at Room Temperature: A Case of Magnetic Field-Induced Chemiresistive

Surface modulation of functional nanostructures is an efficient way of improving gas sensing properties in chemiresistive materials. However, synthesis methods employed so far in achieving desired performances are cumbersome and energy intensive. Moreover, nano-engineering-induced magnetic properties of these materials which are expected to enhance sensing responses have not been utilized until now in improving their interaction with target gases. In particular for gasses with paramagnetic nature such as NO or NO2, the inherent magnetic property of the chemiresistor might assist in enabling superior sensing performance. In this work, vanadium-doped NiO nano-clusters with ferromagnetic behavior at room temperature have been synthesized by a simple and effective combination of soft chemical routes and employed in efficient and selective detection of paramagnetic NO gas. While NiO is typically anti-ferromagnetic, the nanoscale engineering of NiO-and V-doped NiO samples have been found to tune the inherent anti-ferromagnetic behavior into room-temperature ferromagnetism. Surface modification in terms of formation of nano-clusters led to an increased Brunauer- Emmett-Teller surface area of similar to 120 m2/g. The sample Ni0.636V0.364O has been observed to exhibit a selective and high response of similar to 98% to 1 ppm NO at room temperature with fast response (14 s) and recovery (95 s). The improved sensing response of this sample compared to other doped NiO variants could be explained in terms of lower remnant magnetic moment of the sample accompanied with higher excess negative charge at the surface. The sensing response of this sample was increased by 30% in the presence of an external magnetic field of 280 gauss, highlighting the importance of magnetic ordering in chemiresistive gas sensing between the magnetic sensor material and target analyte. This material stands as a potential gas sensor with excellent NO detection properties

Ammonia Sensing by Sn1-xVxO2 Mesoporous Nanoparticles

Chemiresistive gas sensing by metal oxide based materials has been usually explained in terms of surface chemistry and band structure modifications due to factors such as chemical composition, particle surface to volume ratio, material morphology, temperature, and surface oxygen vacancy. In this work, keeping parameters such as particle size, morphology, surface area, temperature, and surface oxygen vacancy fixed, we have for the first time attempted to delineate quantitatively the role of crystal structure and surface electronic states in improving gas sensing responses of doped nanosized metal oxide samples. While vanadium-doped tin oxide samples show a nearly 4-fold increase in 10 ppm ammonia sensing responses, the Sn0.696V0.304O2. sample shows similar to 1.2 times more sensing response as compared to Sn0.657V0.343O2. The ammonia sensing behavior has been found to be directly correlated to crystal structures and concentrations of various oxidation states of vanadium dopants present in the studied samples. Detailed comparative analysis of crystal and electronic structures of the samples has revealed the mechanism of enhancement in the ammonia sensing behavior of vanadium-doped tin oxides. It is expected that similar mechanisms might be responsible for enhancement in gas sensing properties of other metal oxide based systems

Effect of dopant oxidation states on enhanced low ppm CO sensing by copper doped zinc oxide

Chemiresistive gas sensing by functional ceramics, like semiconductor metal oxides have been so far explained in terms of parameters such as particle size, morphology, temperature, oxygen vacancies, surface charge imbalance and so on. However, the effects of oxidation states of dopants in shaping gas sensing behavior in chemiresistors have been largely ignored. In this work, the role of oxidation states of Cu dopants on improved CO sensing behaviour of ZnO has been categorically analyzed. In this process, a multi-fold enhanced and selective sensing response towards low ppm CO in comparison to pure zinc oxide has been achieved by n-type Cu doped Zinc Oxide. Extensive studies on surface electronic and bulk crystal structures have revealed that relative amount of Cu1+ and Cu2+ is the probable primary cause behind enhanced CO sensing response by Cu doped zinc oxide. Our results thus indicate that by modifying the relative amounts of different oxidation states of dopants, semi-conductor metal oxide systems may be tuned to show improved sensing response towards CO and other gases

pH-regulated hydrothermal synthesis and characterization of Sb4O5X2 (X = Br/Cl) and its use for the dye degradation of methyl orange both with and without light illumination

A pH-regulated hydrothermal synthesis method was employed to synthesize Sb4O5Br2 and Sb4O5Cl2 crystallites. Characterization is done by single crystal X-ray diffraction, powder X-ray diffraction, infra-red spectroscopy, scanning electron microscopy and DFT studies. The compounds crystallize in monoclinic symmetry with a P2(1)/c space group. Complete structural analysis of the Sb4O5Br2 compound by using single crystal X-ray diffraction data is performed for the first time and a comparative study with Sb4O5Cl2 is also discussed. The SEM study reveals that the surface morphology changes with the variation of pH for bromide compounds, whereas pH change does not affect the morphology of the chloride analogues. Electronic band structures of the synthesized oxyhalides were investigated in order to understand their catalytic effects in the dye degradation reactions in dark as well as sunlight conditions