18-Feb-2022: Tuning of properties of Gold-nanorods using DC electric field paves way for more efficient way of detecting food contamination
In a recent study, Indian researchers have found that properties of Gold-nanorods can be tuned by applying external forces for devising sensors that can detect trace amounts of molecules, paving the way for more efficient way of detecting food contamination.
Gold nanorods have unique plasmonic properties. They can be used as sensors in the detection of minute amounts of particles (femto-moles of molecules) and also in the fluorescent enhancement of low-quantum yield molecules. To be used as sensors, they needed to arrange the particles in 2D arrays.
W. Zaibudeen and Ranjini Bandyopadhyay from the Raman Research Institute, Bangalore, an autonomous institute of the Department of Science & Technology, Govt. of India, tried to enhance the domain sizes of the ordered nanorods by applying an electric field. They changed the field's direction and amplitude, which provided them control over the domain morphologies.
A colloidal droplet of gold nanorods (Au-NR) was placed in an electric field while it was evaporating. During this event, the nanorods formed an assembly which led to the formation of very minute and distinct structures or patterns. Observation of these structures helped the researchers to understand that these gold nanorods get pushed from the droplet’s centre to its edge due to the presence of an outward flow in the drop, resulting in the formation of the coffee stain-like patterns.
When these patterns were observed using a very powerful microscope, it was seen that, while most of the nanorods gathered along the outer edge of the ring, some particles remained in a scattered arrangement in the central part of the ring. This meant that there must have been a flow that counteracted the outward flow. This counter-flow occurred due to the Marangoni effect -- a phenomenon that results from the gradients in surface tension. This effect prevents the solid particles from depositing at the edge and hence prolongs the entire process. This work has been published in the journal ‘Soft Matter’ recently.
The research team studied how the Au-NRs react in the absence and presence of DC electric field. Multiple regions of homogeneously aligned Au-NR were detected in the absence of a DC electric field. When a DC electric field was applied perpendicular to the substrate, the Au-NRs at the outer coffee ring edge rotated and aligned along the applied field’s direction. However, in other regions of the coffee ring, the orientation of the Au-NR clusters was found to be insensitive to the presence of the electric field.
The scientists concluded that, by applying external forces, the properties of these nanorods can be tuned, leading to technological implications like devising sensors for detecting trace amounts of molecules.
31-Jan-2022: Indian scientists develop efficient and durable solar cells by tuning the length and porosity of nanorods
Indian Scientists have devised a new process for increasing the efficiency and stability of Titanium dioxide (TiO2) nanorods based on Perovskite Solar Cells (PSC). It will help develop solar cells with stable light-harvesting active layer.
Perovskite solar cells have become commercially attractive because of the potential of achieving even higher efficiencies and very low production costs. However, the challenge lies in its short- and long-term stability.
Scientists led by Dr. V. Ganapathy from International Advanced Research Centre for Powder Metallurgy and New Materials, an autonomous institute of the Department of Science & Technology (DST), Government of India, have increased the efficiency and stability of Titanium dioxide (TiO2) nanorods based Perovskite Solar Cells (PSC) by varying the length and porosity of the TiO2-Nanorods. They did this by establishing a correlation between the lengths of the TiO2-NR and the porosity of the electrode for the ambient processed PSCs.
The team explains that porosity of the electrode plays a vital role in perovskite infiltration and sensitization. The inter-pore distance between the two TiO2 nanorods determines the photo-electrode's porosity, and the porosity varies as the growth of the nanorod length increases.
“In this work, we had precise control over the length, porosity, and morphology of the TiO2-NR from compact film to nanostructured film.”
The team controlled nanostructures of the TiO2-NR by varying the concentration of the titania precursor and the growth time. The power conversion efficiency for nanorod-based PSCs was enhanced with variation in the length and porosity of the TiO2-NR. The interspacing between the TiO2-NR facilitated deep infiltration of the perovskite during the spin coating and is locally confined to the surface of the TiO2-NR. Due to the large pores present in the TiO2-NR photoelectrode, infiltration of small molecular HTM was also enhanced. The present work was published in the ‘Journal of Alloys and Compounds’,
The PSCs prepared with 350nm TiO2-NR exhibited better efficiency when compared with the conventional NP-TiO2. The similar thickness of NP-TiO2 based device exhibited less photocurrent value than NR-TiO2, which was attributed to the dense packing of 20nm TiO2 particles inhibiting the loading of perovskite. The high crystallinity of the TiO2-NR provided a low resistance to the flow of electrons in the Electron transport layer (ETL).
In the current work, apart from high efficiency, the crystalline structure of ETL also significantly influenced the stability of PSCs.
“The decomposition of perovskite absorber is a critical factor behind the performance degradation of PSCs. Given the similar nature of perovskite, enhanced stability of TiO2-NR PSC is attributed to slow ion migration across thermodynamically stable rutile TiO2-NR/MAPbI3 interface,” added Dr. V. Ganapathy.
3-Jun-2021: Nanorod based oxygen sensor working at room temperature can save lives in places like underground mines, higher altitudes
Indian Scientists have developed a nanorods-based oxygen sensor which works at room temperature with assistance of UV irradiation and can detect oxygen gas concentrations in places such as underground mines, at higher altitudes, inside aeroplanes and research labs.
Monitoring O2 concentration in very low ppm-level is of paramount importance, and a fast and selective oxygen sensor working at room temperature can save lives in places like underground mines, higher altitudes and improve the accuracy of numerous experiments being conducted in research labs.
A team of scientists led by Dr S. Angappane, a Scientist at the Centre for Nano and Soft Matter Sciences (CeNS), an autonomous research institute under the Department of Science & Technology, Government of India, have fabricated a metal oxide semiconductor (MOS) nanorods array-based oxygen sensor which works at room temperature with assistance of UV irradiation and can detect broad ppm range of oxygen gas concentrations. They used titanium oxide for the purpose and work, involving Hiran Jyothilal, Gaurav Shukla, Sunil Walia, and Bharath SP led by Dr S. Angappane, published in the journal Materials Research Bulletin.
The team showed that the sensor gives the best sensitivity with low power consumption and works at room temperature. The fabricated sensors exhibited response and recovery times of around 3 sec and 10 sec, respectively, at 1000 ppm. The sensor works in oxygen concentrations ranging from 25 ppm to 10 lakh ppm (100%) with good stability. The superior sensing property is attributed to the enhanced electrical conductivity, excitons (combination of an electron and a positive hole) created, and desorption of water molecules (released through surface) from the sensor surface by UV irradiation, facilitating increased interaction of oxygen molecules with chromium incorporated in titanium dioxide slanted nanorods array present in the sensor.
The CeNS team is further working on miniaturizing the sensor and its electronics interfacing with other gas sensors to fabricate a suitable electronic nose.
29-Oct-2021: Low-cost process developed of synthesizing silver Nano-wires at large scale
A team of Indian scientists and research students have developed a process for large-scale manufacturing of nano-materials (Silver nanowires) that can bring down the costs to less than one-tenth of the market price.
Synthesis of one-dimensional nanomaterials like nanowires, nanotubes, and so on in large quantities is a technologically challenging task and hence makes it an expensive material. Secondly, it is necessary to get uniform nanowire diameter range with a narrow variation in the length as it helps achieve uniform coating for touch screens or other conducting coating applications.
A process developed by Dr. Amol A. Kulkarni from CSIR-National Chemical Laboratory, Pune, can produce silver nanowires at the scale of 500 grams per day at the cost of 20$/gm when compared to 250$/gm to 400$/gm of market price.
It is an economical process of continuous flow manufacturing of functional nano-materials (silver nanowires) at a large scale with support from the Advanced Manufacturing Technologies Program of the Department of Science & Technology, Government of India.
The product manufactured consists of silver nanowires possessing excellent conductivity, which can be used in making conducting inks and coatings for display technologies and flexible electronics. A total of 5 national and international patents have also been filed for the novel process.
This is the first-ever continuous process for synthesizing a functional nanomaterial (Silver nanowires) efficiently with excellent product quality (aspect ratio of nanowires >1000) and at a very low cost (~20$/gm) on a large scale (500 g/day) with a footprint of the pilot plant not more than 6 sq. meters. The process is a simple, cost-effective, and scalable synthesis route when compared to existing batch manufacturing protocols that even generate a large amount of nanoparticles in suspension, which is not easy to separate from nanowires. The developed process has been tested at CSIR-NCL’s characterization facility and is in stage 8 of the Technology Readiness Level.
CSIR-NCL has licensed the process technology to Nanorbital Advanced Materials LLP (Ahmedabad) in November 2020 and has signed material transfer agreement with 3 more industries in 2021. Dr. Amol plans to further conduct testing of the developed nanomaterial in different display devices for transparent conducting applications as well as for printing of flexible electronics, including wearable electrodes.
This technology can make the Indian industries enter into the niche area of electronic chemicals and eventually open up new jobs.
5-Oct-2021: Scalable synthesis method developed of Nano-crystals with bright emission colours useful for LED
Indian researchers have developed a method that can help large scale synthesis of a special class of semiconductor nanocrystals. These nanocrystals called two-dimensional layered perovskite and perovskite nanocrystals, which have bright emission colours and are not affected by or corroded by the environment, are useful for both high colour purity and low-cost solution processability.
Nanomaterials have unique properties compared to their bulk counterpart as they exhibit bright emission and are useful for light-emitting diodes (LED) apart from several other applications in our day-to-day life. However, large-scale syntheses of such materials are challenging as the reaction mechanism, and kinetics of large-scale syntheses are often different from small-scale syntheses. Such large scale synthesis methods are necessary for industrial applications.
To this end, a group of researchers at the Centre for Nano and Soft Matter Sciences (CeNS), an autonomous research institute under the Department of Science and Technology (DST), have synthesized two-dimensional layered perovskite and perovskite nanocrystals by a method called sonochemical process that is often used for large scale synthesis. This process utilizes the principles of sonochemistry to make molecules undergo a chemical reaction with the application of powerful ultrasound radiation. This work has been published in the ‘Journal of Physical Chemistry C’.
The team tracked how these nanomaterials grow during the reaction. They controlled reaction parameters, such as time and temperature, to tune the dimensionality of these nanomaterials and their emission colours. The researchers showed that at an early stage of reaction, two-dimensional layered perovskites form, and they get converted to perovskite nanocrystals controllably. They also demonstrated a white-light-emitting diode with the mixture of these perovskites. Further works are in progress by the CeNS team to increase the stability of these nanomaterials.