Humidity activated ultra-selective room temperature gas sensor based on W doped MoS2/RGO composites for trace level ammonia detection.

The lack of highly efficient, cost effective and stable ammonia gas sensors functionable at room temperature even in extreme humid environments poses significant challenge for the future generation gas sensors. The prime factors that impede the development of such next generation gas sensors are the strong interference of humidity and sluggish selectivity. Herein, we fabricated tungsten doped molybdenum disulphide/reduced graphene oxide composite by an in-situ hydrothermal method to exploit the adsorption, dissolution (solubility), ionization and transmission process of ammonia and thereby to effectuate its trace level detection even in indispensable humid environments. The protype based on 5 at.% Tungsten doped MoS2/RGO (W5) gas sensor exhibited 3.8-fold increment in its response to 50 ppm of ammonia when the relative humidity varied from 20 % to 70 % with ultra-high selectivity at room temperature. The as prepared gas sensor revealed a practical detection limit down to 1 ppm with a substantial response and rapid recovery time. Furthermore, W5 gas sensor exhibited a 42-fold increment in response to 50 ppm of ammonia relative to its pristine (MoS2/RGO) MG composite with a RH of 70 %. The proton hopping mechanism accountable for such an enormous enhancement in ammonia sensing and its potential for breath sensor are briefly annotated.

Electronic sensitization enhanced p-type ammonia gas sensing of zinc doped MoS2/RGO composites.

Zinc (Zn) doping induced synergetic effects of defects engineering and heterojunction in Molybdenum disulphide/Reduced graphene oxide (MoS2/RGO) effectively enhances the p-type Volatile organic compounds (VOC) gas sensing traits and helps in tailoring the over dependence on noble metals for surface sensitization. Through this work, we have successfully prepared Zn doped MoS2 grafted on RGO employing an in-situ hydrothermal method. Optimal doping concentration of Zn dopants in the MoS2 lattice triggered more active sites on the basal plane of MoS2 with the aid of defects promoted by the zinc dopants. Effective intercalation of RGO further boost up the exposed surface area of Zn doped MoS2 for further interaction of ammonia gas molecules. Besides, smaller crystallite size brought out by 5% Zn dopants aids in efficient charge transfer across the heterojunctions that further amplifies the ammonia sensing traits with a peak response of 32.40% along with a response time of 21.3 s and recovery time of 44.90 s. The as prepared ammonia gas sensor exhibited excellent selectivity and repeatability. The obtained results reveal that transition metal doping into the host lattice proves to be a promising approach for VOC sensing characteristics of p-type gas sensors and gives insight about the importance of dopants and defects for the development of highly efficient gas sensors in the future.

Investigation on hydrogen bonds and conformational changes in protein/polysaccharide/ceramic based tri-component system.

The main attention of present work is to study the molecular level interactions in the interface of biocomposite to increase their applicability. A specific kind of molecular interaction namely, hydrogen bonds play a vital role in deciding composite property. In this study, we construct a tri-component system based on silk fibroin/sodium alginate/hydroxyapatite by varying protein and polysaccharide proportions using in-situ co-precipitation method. The Fourier Transfer Infrared (FTIR) prediction state that prepared composite exhibit inter-(OH⋯N, OH⋯O, OH⋯π) and intra-(OH⋯OH) molecular hydrogen bonds and their strength are varied in accordance with composition of composite. During composite preparation, conformational changes from the random coil to ß-sheet structure through intermediate ß-turns exist within the protein molecule that is confirmed by vibrational spectra. The crystallographic profile and morphology of HAP were greatly influenced by virtue of polymer matrix. Simulated body fluid (SBF) immersion study shows that biodegradation and swelling ratio are correlated with type of hydrogen bond and secondary structure of protein. Moreover, the in-vitro biomineralization, cytotoxicity and antibacterial activity of composite were analysed in detail.