Room-temperature chemiresistive ammonia sensors based on 2D MXenes and their hybrids: recent developments and future prospects.

Detection of ammonia (NH3) gas at room temperature is essential in a variety of sectors, including pollution monitoring, commercial safety and medical services, etc. Two-dimensional (2D) materials have emerged as fascinating candidates for gas-sensing applications due to their distinct properties. MXenes, a type of 2D transition metal carbides/nitrides/carbonotrides, have drawn the interest of researchers due to their high conductivity, large surface area, and changing surface chemistry. The review begins by describing the NH3 gas-detecting methods of 2D materials and then concentrates on MXene-based sensors, emphasising the benefits that MXenes provide in this context. The study also explains the prime factors involved in evaluating sensor performance, which include sensor response, sensitivity, selectivity, stability, charge transfer values, adsorption energy and response/recovery times. Subsequently, the review covers two main categories: pristine/intercalated MXenes and MXene-based hybrid materials. The review investigates the approaches for improving the sensing characteristics of pristine and intercalated MXenes by introducing MXene hybrids like MXene-metal oxide hybrids, MXene-transition metal dichalcogenides hybrid, MXene-other 2D materials hybrid, MXene-polymers and other hybrids and other MXene-derived materials. In summary, this review offers a thorough overview of current advancements and potential applications for room-temperature ammonia sensors based on 2D MXenes and their hybrids. In order to pave the way for future improvements in MXene-based gas-sensing technology for room temperature ammonia detection, the study concludes by outlining potential future scope and conclusions.

Antioxidant peptide nanohybrid: a new perspective to immobilize bioactive peptides from milk industry wastewater.

In this study, dairy industry wastewater was collected and used as a protein source. The proteins were converted into powder form using lyophilization. The proteins were digested using Bacillus subtilis (B. subtilis) NCIM 2724. The maximum degree of hydrolysis (DH) of protein was observed at pH of 7, 30 °C incubation temperature, 120 rpm shaking speed, and 96 h incubation. The tris-glycine sodium dodecyl sulfate-polyacrylamide (tris-glycine-SDS) gel electrophoresis showed the disappearance of large molecular weight proteins due to the proteolytic action of B. subtilis. The resulting digest was fractionated using a 3 kDa membrane filter. The antioxidant activity of the obtained fractions was evaluated. Antioxidant activity of digest and filtrate was found to be 12.78% (±0.040) and 49% (±0.025), respectively, at a concentration of 50 mg/mL. The 3 kDa filtrate was subjected to liquid chromatography-mass spectrometry (LCMS) analysis. Bioinformatics tools were used to predict the sequences of antioxidant peptides. Furthermore, the 3 kDa filtrate was used for the synthesis of antioxidant nanohybrid. Scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS) confirmed the nanohybrid formation and encapsulation of peptides. The antioxidant nanohybrid showed enhanced antioxidant activity compared to the free peptide solution. The dairy industry has a significant environmental impact due to high water use and waste generation. This study addresses an important issue of recycling protein-containing wastewater and the potential to be used for converting these proteins into antioxidant peptides. Such practices will help to reduce environmental impact and sustainably operate the industry.

Nitrogen dioxide gas-sensing properties of hydrothermally synthesized WO3 · nH2O nanostructures.

Nitrogen dioxide (NO2) has been identified as a serious air pollutant that threats to our environment, human life and world ecosystems. Therefore, detection of this air pollutant is crucial. Metal oxide semiconductor is one of the best approaches frequently used to detect NO2 at relatively low temperatures. Hydrated tungsten trioxide (WO3 · H2O), an n-type semiconductor, is regarded to be a promising material for fabricating gas sensors, which are widely used in environmental and safety monitoring. In this work, WO3 · nH2O nanoparticles have been synthesized using a polyfunctional surfactant-mediated hydrothermal approach in the addition of H2C2O4 and K2SO4 at a molar ratio of 1 : 1. This paper has also reported the effect of reaction temperature (120°C to 200°C) on morphological changes and gas-sensing performance. The characterization of these synthesized nanostructures was carried out by UV-Vis absorption spectroscopy, X-ray diffraction and field-emission scanning electron microscopy (FESEM). The UV absorption peak was obtained around 300 nm. FESEM analysis showed sheet-like structures come together to form flower-type morphology. The synthesized WO3 · nH2O flower-like structures was then used for NO2 gas-sensing application. The prepared sensors showed considerably better sensor response (R g/R a = 17.48) at 185°C for 25 ppm NO2.

Controlled synthesis of monodispersed ZnSe microspheres for enhanced photo-catalytic application and its corroboration using density functional theory.

The present work reports enhanced photocatalytic performance of highly crystalline, monodisperse ZnSe microspheres, synthesized by the size-selective, ETDA-assisted hydrothermal method. Systematic studies on time-dependent reaction kinetics and growth parameters indicate dependency of morphology and crystal structure on the volume % of EDTA and dependency of size on the volume % of hydrazine hydrate for ZnSe microspheres. X-ray diffraction studies confirm highly crystalline cubic zinc blende crystal structure with crystallite size in the range of 10-15 nm. Diffuse reflectance spectra show blue shift having a broad absorption peak between 415 and 425 nm, with a band gap of ∼2.6 eV from the K-M plot. Photoluminescence spectra show higher ratio of near band edge emission to deep level emission, confirming the decrease in defect related emission and depicting the higher crystallinity of ZnSe. Raman spectroscopy also confirms the crystalline and pure nature of ZnSe microspheres, from the observation of a high intensity dominant peak at 248 cm-1, attributed to longitudinal optical phonon scattering. Morphological analysis using FE-SEM and HRTEM shows monodispersed microspheres having size ∼2.5 µm, made up of small ZnSe nanocrystals with ∼10 nm size and with an interplanar spacing of ∼0.32 nm, corresponding to zinc blende ZnSe(111) planes. Brunauer-Emmett-Teller analysis indicates type-IV adsorption-isotherms and hysteresis loops, confirming the presence of mesopores on the surface of ZnSe microspheres controlling the diffusion rate of the catalyst. The degradation rate constant for methylene-blue using first-order reaction kinetics confirms improvement in photocatalytic activity by a factor of 7 to 13 times higher than that of bulk ZnSe, which is attributed to the controlled, well-defined morphology of spherical microstructures made up of small-sized ZnSe nanocrystals. Density functional theory based calculations support the preferential adsorption of EDTA at the Se site of the ZnSe(111) surface with an energy of -1.90 eV. The electronic-structure plot demonstrates semiconducting behaviour with a direct band gap of ∼1.51 eV. First-principles calculations confirm enhancement in the photocatalytic water splitting activity of the ZnSe(111) surface via adsorption of intermediates. The improvement in dye degradation can be attributed to the enhanced oxidation process through the formation of intermediates such as O* (-3.13 eV) and HO* (-2.57 eV) at the Se site of the ZnSe surface.

Self-assembly of soybean peroxidase nanohybrid for activity enhancement and dye decolorization: experimental and computational studies.

The soybean peroxidase (SBP) mediated nanohybrid [SBP-Cu3(PO4)2·3H2O] synthesis was carried out in the present study. The scanning electron microscopy (SEM) analysis showed a characteristic flower-like hierarchical structure of the SBP-nanohybrid. The mechanism of SBP-nanohybrid formation was elucidated using computational approaches. The predicted Cu2+ binding sites followed by molecular docking studies showed the two lowest energy (-4.4 kcal/mol and -3.56 kcal/mol) Cu2+ binding sites. These two binding sites are located at the opposite position and might be involved in the formation of SBP-nanohybrid assemblies. Further, these sites are different than the catalytic active site pocket of SBP, and may facilitate more substrate catalysis. Obtained computational results were confirmed by in-vitro guaiacol oxidations studies using SBP-nanohybrid. The effect of various parameters on SBP-nanohybrid activity was studied. The pH 7.2 was found optimum for SBP-nanohybrid activity. The enzyme activity increased with an increase in temperature up to 50 °C temperature and then decreased with an increase in temperature. Around ∼138% enhanced activity was recorded using SBP-nanohybrid compared to crude SBP. Also, the SBP-nanohybrid showed around 95% decolorization of methylene blue (MB) in 1 h and the MB degradation was confirmed by high-pressure liquid chromatography analysis (HPLC).Communicated by Ramaswamy H. Sarma.

Production of bioemulsifier by Acinetobacter species isolated from healthy human skin.

Six Acinetobacter sp. isolated from healthy human skin were checked for the production of bioemulsifier. Optimization studies indicated that Luria Bertani broth pH 7 supplemented with calcium chloride (1%) was the optimum medium. Temperature at 37 degrees C was optimum and inducer oils in the medium did not enhance bioemulsifier production. Partial purification of bioemulsifier and chemical analysis revealed that it is a proteoglycan with protein (53%), polysaccharide (43%) and lipid (2%). Maximum emulsification activity obtained was 400 EU/ml. Thin layer chromatography revealed the presence of mannose and rhamnose sugar and oleic and palmitic acids as parts of lipids. The yield obtained was 1.9 g / 1. Reconstitution studies revealed that the protein and polysaccharide fractions together display 94.55% of emulsification activity. It was also noted that the bioemulsifier was stable for 72 hr at 37 degrees C and displayed good cleaning property towards different oils. The partially purified bioemulsifier formed stable oil-in-water emulsions with plant oils.

Optimization of medium for lipase production by Acinetobacter haemolyticus from healthy human skin.

A lipase producing Acinetobacter haemolyticus TA106 was isolated from healthy human skin of tribal population. The maximum activity of 55 U/ml was observed after medium optimization using the "one variable at a time" and the statistical approaches. The optimal composition of the medium was determined as (% w/v or v/v): tryptone--1, yeast extract--0.5, sodium chloride-1, olive oil-1, Tween-80 1, manganese sulphate--5 mM, sucrose--1, pH-7. It was found that maximum production occurred in late log phase, i.e., after 72 h and at 200 rpm. From factorial design and statistical analysis, it was found that pH, temperature, salt, inoculum density and aeration significantly affected the lipase production. It was also noted that inoculum density of 3% (v/v), sucrose (1% w/v) and manganese sulphate (5 mM) displayed maximum lipase activity of 55 U/ml by conventional as well as statistical method. Optimization studies also indicated the increase in specific activity from 0.2 U/mg to 6.7 U/mg.