Polyethyleneimine-assisted formation of Ag-SiO2 hybrid microspheres for H2O2 sensing and SERS applications.

Herein, we report a simple, cost-effective, and eco-friendly approach for producing polyethyleneimine (PEI)-assisted silver nanoparticle-supported silica microspheres through evaporation-induced assembly (EIA). The silica-PEI microspheres obtained through EIA consisted of highly trapped PEI molecules owing to their electrosorption onto oppositely charged silica colloids. The trapped PEI molecules in the microspheres played a crucial role in linking silver ions to form silver ion-PEI complexes, which were then reduced to form silver nanoparticles. Further, the complex interactions between PEI and silica colloids led to enhanced porosity in the microspheres, enabling the efficient adsorption of Ag ions. The characterization of the Ag-SiO2 microspheres was carried out using various techniques, including field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and Fourier transform infrared (FTIR) spectroscopy, which confirmed the successful formation of Ag nanoparticles on microspheres, and a plausible formation mechanism is elucidated. The Ag-SiO2 microspheres exhibited good sensing properties for hydrogen peroxide (H2O2), with an estimated limit of detection of 1.08 mM and a sensitivity of 0.033 µA mM-1 mm-2. The microspheres were also used as a surface-enhanced Raman scattering (SERS) substrate, which demonstrated high sensitivity in detecting rhodamine 6G down to a concentration of 2 × 10-6 M. The present approach elucidates a promising alternative to conventional methods that face challenges, such as scalability issues, complex and cumbersome synthesis procedures, and the use of strong reducing agents. With the potential for industrial-level scalability, this method offers a viable strategy for producing Ag-SiO2 microspheres with possible applications in biomedical and sensing technologies.

Defect-Induced Adsorption Switching (p- to n- Type) in Conducting Bare Carbon Nanotube Film for the Development of Highly Sensitive and Flexible Chemiresistive-Based Methanol and NO2 Sensor.

Lightweight and flexible gas sensors are essentially required for the fast detection of toxic gases to pass on the early warning to deter accident situations caused by gas leakage. In view of this, we have fabricated a thin paper-like free-standing, flexible, and sensitive carbon nanotube (CNT) aerogel gas sensor. The CNT aerogel film synthesized by the floating catalyst chemical vapor deposition method consists of a tiny network of long CNTs and ∼20% amorphous carbon. The pores and defect density of the CNT aerogel film were tuned by heating at 700 °C to obtain a sensor film, which showed excellent sensitivity for toxic NO2 and methanol gas in the concentration range of 1-100 ppm with a remarkable limit of detection ∼90 ppb. This sensor has consistently responded to toxic gas even after bending and crumpling the film. Moreover, the film heat-treated at 900 °C showed a lower response with opposite sensing characteristics due to switching of the semiconductor nature of the CNT aerogel film to n-type from p-type. The annealing temperature-based adsorption switching can be related to a type of carbon defect in the CNT aerogel film. Therefore, the developed free-standing, highly sensitive, and flexible CNT aerogel sensor paves the way for a reliable, robust, and switchable toxic gas sensor.

Band gap and defect engineering of bismuth vanadate using La, Ce, Zr dopants to obtain a photoelectrochemical system for ultra-sensitive detection of glucose in blood serum.

Bismuth vanadate (BiVO4) is a promising photoactive material for the design of photoelectrochemical (PEC) analytical devices for the non-enzymatic detection of glucose. In this work, un-doped and La/Ce/Zr doped BiVO4 photo anodes were developed by spray pyrolysis coating to generate unique 2D hierarchical architectures using the facile ultrasonic spray coating technique without any complex pre or post-treatment. The influence of different dopants on the morphology and photoelectrochemical activity of BiVO4 coatings was investigated. X-ray diffraction, scanning electron microscopy, UV-vis optical absorbance, and positron annihilation techniques were used to evaluate the structure, defects, and optical properties of BiVO4 films. DFT simulation confirmed the Zr doping induced band gap reduction in the BiVO4 lattice. The Zr doping on the Bi site in BiVO4 lattice provided significantly low Bi and V-based defect density and a higher bulk diffusion length of charge pairs (4 times that of pristine) as well as charge transfer efficiency and this led to the foremost photocurrent for water splitting. The Zr-doped BiVO4 photo anode showed remarkable sensitivity in glucose sensing. The sensitivity and limit of detection of the Zr-doped BiVO4 PEC device towards glucose were 0.14 mA cm-2 mM-1 and 1.22 µM, respectively, in the concentration range of 1-7 mM. The system showed sensitive detection of glucose in blood serum. This is the first time that a 2D morphology electrode design consisting of Zr-doped BiVO4, which leads to exceptionally high sensitivity for glucose sensing, has been reported.

Optimizing metal-support interphase for efficient fuel cell oxygen reduction reaction catalyst.

The development of cost-effective and highly-efficient electro-catalysts is essential for the advancement of proton exchange membrane fuel cells (PEMFC). We present a novel nitrogen-sulphur co-doped carbon nanotubes-few layer graphene1D-2D hybrid support formed by partially exfoliating multiwall carbon nanotubes (PECNT), to improve interface bonding to catalyst nanoparticles. Detailed Raman spectroscopy and STEM-EDS analyses demonstrate that active sites on the co-doped hybrid support ensure both uniform distribution and improved bonding of the catalyst nanoparticles to the support. Electrochemical studies show that Pt nanoparticles decorated on nitrogen-sulphur co-doped PECNT (Pt/NS-PECNT) have higher electrochemical active surface area and mass activity accompanied by low H2O2 formation and improved positive half-wave potential, as compared to those decorated on co-doped rGO-incorporated PECNT hybrid structure (Pt/NS-(rGO-PECNT)). Fuel cell measurements demonstrate a higher power density for our novel (Pt/NS-PECNT) electro-catalyst when compared to both Pt/NS-(rGO + PECNT), and commercial Pt/C electro-catalyst. We demonstrate in this work that the interconnectivity between Pt-nanoparticles and the dopant or defect sites on the support play a crucial role in enhancing the ORR activity, fuel cell performance, and durability of the catalyst.

Tri-iodide reduction activity of ultra-small size PtFe nanoparticles supported nitrogen-doped graphene as counter electrode for dye-sensitized solar cell.

Efficient and cost effective counter electrode (CE) is pre-requisite for the commercialization of dye-sensitized solar cell (DSSC). Present work investigates ultra small size platinum-iron alloy nanoparticles dispersed over nitrogen-doped graphene (PtFe/NG) as an effective counter electrode for DSSC. Hereby we achieve low loading of Pt by alloying with Fe accompanied by superior electrocatalytic activity towards the iodide-triiodide (I-/I3-) mechanism. Enhancement in electrocatalytic performance of PtFe/NG has been shown by cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization analysis. PtFe/NG counter electrode exhibits higher power conversion efficiency (∼6.12%) with lower charge transfer resistance, which helps in faster diffusion of I-/I3- ions as compared to NG and Pt/NG counter electrodes. The increased electrocatalytic activity of PtFe/NG is due to the collective effect of intrinsic electronic effects by alloying, uniform dispersion of small PtFe alloy nanoparticles over nitrogen doped graphene, and additional catalytic sites offered by nitrogen-doped graphene.