Saptak Rarotra | IIT Guwahati (original) (raw)

Papers by Saptak Rarotra

Physical review applied, Dec 5, 2018

Self-organization of large-area nanoscale patterns employing a single-step inexpensive process ca... more Self-organization of large-area nanoscale patterns employing a single-step inexpensive process can be crucial in the fabrication of low-cost but high-performance devices. In the present study, we employ the spin dewetting of a conductive polymer to fabricate an array of micro-to-nanoscale orderedheterojunctions (OHJ) to demonstrate the improvements in the key performance indicators of organic photovoltaic (OPV) devices in ambient conditions. For this purpose, the surface of a hole-collector polymer film [e.g., (poly-(2,3-dihydrothieno-1, 4-dioxin):poly-(styrene sulfonate) (PEDOT:PSS)], coated on a transparent conducting substrate, is decorated with physicochemical patterns of a self-assembled monolayer. Afterward, the electron donor polymer [e.g., poly (3-hexylthiophene-2,5-diyl) (P3HT)] is spin-dewetted into a large collection of digitized micro-and nanodroplets. A theoretical analysis of the governing equations with appropriate boundary conditions uncovers that the imbalance of centripetal, capillary, and van der Waals forces plays a major role in deciding the droplet spacing of the spin-dewetted morphologies. Further, simulations are performed to understand the effect of size and periodicity of the donor droplets inside the device architecture, which could lead to an enhanced current flow when compared with a planar heterojunction (PHJ) device composed of thin films. Subsequently, a detailed experimental analysis is performed to uncover the role of spin speed and the initial loading of the electron donor polymer into the solvent during spin casting on the size, periodicity, and density of the electron donor droplets on the hole-collector surface. Capping the optimally discretized P3HT droplet arrays with the electron-acceptor layer [e.g., ([6,6]-phenyl-C 61 butyric acid methyl ester (PCBM)] led to the formation of a highly corrugated donor-acceptor interface suitable for higher photon absorption, facile exciton generation, and improved exciton separation. The self-organized-large-scale-integration (SOLSI) of the spin-dewetted droplets at the charge-carrier donor-acceptor interface of the OPV-OHJ assemblage enables the enhancement by approximately 40% as compared to similar OPV-PHJ configurations. The enhanced photoconversion efficiency takes place via optimal separation of photon absorption and carrier collection pathways. The study uncovers the importance of developing high-density and large-area nanopatterns employing spin dewetting to develop process-intensified OPV-OHJ cells with improved performance at a lower fabrication cost.

Advanced Materials, Oct 10, 2021

Journal of nanostructure in chemistry, Jan 6, 2021

Carbon nanotube (CNT)-doped transparent conductive films (TCFs) is an encouraging option toward g... more Carbon nanotube (CNT)-doped transparent conductive films (TCFs) is an encouraging option toward generally utilized indium tin oxide-depended TCFs for prospective stretchable optoelectronic materials. Industrial specifications of TCFs involve not just with high electrical performance and transparency but also amidst environmental resistance and mechanical characteristic; those are usually excused within the research background. Though the optoelectronic properties of these sheets require to be developed to match the necessities of various strategies. While, the electrical stability of single-walled CNT TCFs is essentially circumscribed through the inherent resistivity of single SWCNTs and their coupling confrontation in systems. The main encouraging implementations, CNT-doped TCFs, is a substitute system during approaching electronics to succeed established TCFs, that utilize indium tin oxide. Here we review, a thorough summary of CNT-based TCFs including an overview, properties, history, synthesis protocol covering patterning of the films, properties and implementation. There is the attention given on the optoelectronic features of films and doping effect including applications for sophisticated purposes. Concluding notes are given to recommend a prospective investigation into this field towards real-world applicability.

Biomaterials and polymers horizon, Aug 1, 2022

COVID-19 has intensified human suffering, undermined the economy, turned the lives of billions of... more COVID-19 has intensified human suffering, undermined the economy, turned the lives of billions of people around the globe upside down, and significantly affected the health, economic, environmental, and social domains. This study aims to provide a comprehensive analysis of the impact of the COVID-19 outbreak on the ecological environment, the energy sector, society, and the economy and investigate the global preventive measures taken to reduce the transmission of COVID-19. This epidemic has caused severe demographic changes and unemployment, and economic activities have been shut down to save human lives. Transportation industries are most severely hit as global tourism has fallen to almost zero during these months. As a solution, financial institutes have introduced stimulus packages worth more than $6 trillion. However, restricted economic activities have also contributed to a cleaner environment. Here in this report, we have collected the literature based on the impacts of lockdown on (EEE); environment (such as; air pollution, water pollution, marine life, and wildlife, etc.), education (such as; positive drawbacks, and long-term effects) and economy (such as; GDP, street vendors, agriculture and food supply sector, and drug traffickers, etc.). Finally, we concluded our topic with affirmative and negative impacts of COVID-19 during the lockdown. To the best of our knowledge, this is a unique and one-of-its-kind review highlighting the essential impact of COVID-19 on the environment, education, and economy.

In this paper, we studied the effect of annealing of CdS nanoparticles that were prepared using c... more In this paper, we studied the effect of annealing of CdS nanoparticles that were prepared using chemical precipitation technique. The synthesized material were characterized using TEM and it was found the size of the CdS nanoparticles were ∼5 nm. The prepared nanoparticles were annealed using hot air oven at 120°C and microwave oven at 900 W for different amount of time in order to check the effect of annealing. It was found that the annealing of the nanoparticles has increased the optical absorbance and reduced the band gap of the material. Interestingly, microwave annealing enhanced the optical absorbance compared to the annealing using oven and the band gap of the material was found to be less in case of 60s microwave assisted annealing compared to the 3 hr hot-air oven treatment. Moreover, the time requirement for microwave annealing was significantly less than that of hot air oven annealing for obtaining similar optical characteristics. The study was also performed for CdS-TiO2 nanocomposites and a similar trend in band gap reduction was observed. This study of annealing will be helpful in tuning the band gap of the CdS and CdS-TiO2 nanocomposites for different optoelectronic applications.

Journal of Porous Materials, Jul 22, 2022

Journal of Material Cycles and Waste Management, Nov 24, 2021

Electrical and electronic equipment with axillaries at their end of life are considered as e-wast... more Electrical and electronic equipment with axillaries at their end of life are considered as e-waste. Utilization/reutilization of e-waste especially recovery of rare earth metals from e-waste has engrossed great attention in last decades. In this line, here we are reporting a process for utilizing spent lithium-ion mobile batteries as a source of Co metal ions (in the form of cobalt oxalate through acid leaching) for wZIF-67 (waste mobile battery-based ZIF) synthesis at certain experimental conditions. Afterward, a comparative analysis was carried out based on structure and properties between wZIF-67 [Co metal ions from waste mobile battery and 2-methylimdazole (Hm-im) based ZIF] and pZIF-67 [cobalt(II) nitrate hexahydrate-based ZIF 2-methylimdazole (Hm-im) based ZIF]. Our results indicated that, wZIF-67 has almost analogous features and is possibly utilized for gas storage and separation, sensing, catalysis and energy applications in future.

Scientific Reports

We report co-electrolysis of seawater and carbon dioxide (CO2) gas in a solar cell-integrated mem... more We report co-electrolysis of seawater and carbon dioxide (CO2) gas in a solar cell-integrated membraneless microfluidic reactor for continuous synthesis of organic products. The microfluidic reactor was fabricated using polydimethylsiloxane substrate comprising of a central microchannel with a pair of inlets for injection of CO2 gas and seawater and an outlet for removal of organic products. A pair of copper electrodes were inserted into microchannel to ensure its direct interaction with incoming CO2 gas and seawater as they pass into the microchannel. The coupling of solar cell panels with electrodes generated a high-intensity electrical field across the electrodes at low voltage, which facilitated the co-electrolysis of CO2 and seawater. The paired electrolysis of CO2 gas and seawater produced a range of industrially important organics under influence of solar cell-mediated external electric field. The, as synthesized, organic compounds were collected downstream and identified usi...

Journal of Porous Materials

Physical Review Applied, 2018

ELECTROPHORESIS, 2018

We explore the improvements in yield and conversion of a chemical reaction inside a twophase micr... more We explore the improvements in yield and conversion of a chemical reaction inside a twophase microfluidic reactor when subjected to an externally applied alternating current (AC) electric field. A computational fluid dynamic (CFD) framework has been developed to incorporate the descriptions of the two-phase flow, multicomponent transport and reaction, and the Maxwell's stresses generated at oil-water interface owing to the presence of the externally applied electric field. The CFD model ensures that the reactants are flown into a microchannel together with the oil and water phases before the reaction takes place at the interface and products diffuse back to the bulk phases. The study unveils that the variation in the intensity of the AC field helps in converting a two-phase stratified flow into an oil-inwater microemulsion composed of oil slugs, plugs or droplets. Importantly, the results also suggest that harnessing the vortices inside or outside these flow patterns helps in the improvement in mass transfer across the interface, which can be employed to improve the yield and conversion of a reaction. We have shown an example case of a pseudo-first order

Energy Technology, 2017

We report the design and development of a microfluidic electrolyzer for the continuous production... more We report the design and development of a microfluidic electrolyzer for the continuous production and in situ separation of hydrogen fuel. A series of photovoltaic cells were integrated with a microchannel to produce a high intensity electric field under direct solar illumination, which electrolyzed the sea water when flown in the microchannel. The rate of hydrogen production could be varied by tuning the electric field intensity or the flow rate of the sea water. Addition of an outlet near the cathode led to an in situ separation of hydrogen in the straight-channel electrolyzer. Hydrogen was also separated from oxygen using a Y-shaped electrolyzer where the electrodes were placed on the Y-arms. The power required for the proposed process was much lower than their macroscopic analogues because the smaller gap between the electrodes ensured a lower electrical resistance and high-intensity field inside the microchannel. A large scale integration of an array of such electrolyzers can lead to an economic, portable, continuous, and clean pathway to produce hydrogen under ambient condition.

Journal of Chemical & Engineering Data, 2015

ABSTRACT The present equilibrium study deals with the reactive extraction of 4-oxopentanoic acid ... more ABSTRACT The present equilibrium study deals with the reactive extraction of 4-oxopentanoic acid [levulinic acid] from an aqueous solution by N,N-dioctyloctan-1-amine [tri-n-octylamine (TOA)] at a constant concentration of 0.573 kmol·m–3 in a wide range of diluents such as [n-decane, decane-1-ol, n-decane + decane-1-ol (1:1 v/v), toluene, 4-methylpentan-2-one (MIBK), and dichloromethane (DCM)] at isothermal conditions ((298 ± 1) K). The physical extraction of levulinic acid with pure diluents is also carried out. The effect of acid concentration (0.10 mol·kg–1 to 0.75 mol·kg–1) and type of diluent on the recovery of levulinic acid from aqueous solution are determined. Mathematical modeling based on mass action law is used to estimate overall equilibrium constants (KE), stoichiometry of reaction, and individual equilibrium constants (K11 and K21) for 1:1 and 2:1 complexes between acid and TOA. Further, the experimentally determined distribution coefficients (KD) are correlated predicted ones by the linear solvation energy relationship (LSER) model based on solute–solvent interaction parameters. The extraction power of TOA increases in the order of DCM ≥ decan-1-ol > MIBK > n-decane + decan-1-ol (1:1 v/v) > toluene > n-decane with the highest extraction efficiency, 98.7 %.

Biomaterials and Polymers Horizon

Biomass Conversion and Biorefinery, 2021

Strengthening green alternative energy sources has been enforced due to hydrocarbon fuels’ conseq... more Strengthening green alternative energy sources has been enforced due to hydrocarbon fuels’ consequential harmful impacts. Climate change, economic enhancement, and energy security are motivating reasons behind the idea of expansion of biofuel production worldwide. Raw materials like lignocellulose have wide range of complex sugars in the form of cellulose (60–70%) and xylan (30–40%) which further by its hydrolysis and fermentation can be used to produce biofuels. Presently, naturally occurring xylanase enzyme is widely used as a natural resource for biofuel diligence to break down the second abundant β-1,4 xylan sugar into xylooligosaccharide, xylobiose, and xylose subunits. For larger scale, numerous approaches are required to improve or modify its thermostability, specificity, and enzyme activity along with its broad range of substrate to shorten the cost in biofuel production. Therefore, the present review provides a synopsis of present scenario of xylanase as a major participant in biofuel production, along with its various applications and factors affecting xylanase production. This present review provides evidence that narrates its presence in the production of biofuels such as bioethanol and biobutanol. Lastly, the present works discuss the major aspects of biofuel conversion efficiency.

Journal of Material Cycles and Waste Management

Nanostructured Materials for Photoelectrochemical Water Splitting