Uranium standards in drinking water: An examination from scientific and socio-economic standpoints of India.

The detection of uranium in drinking water has ignited concerns among the public, regulators, and policymakers, particularly as around 1% of the 55,554 water samples in India have shown uranium levels surpassing the 60 µg/l guideline established by the Atomic Energy Regulatory Board (AERB) based on radiological toxicity. Further, the Bureau of Indian Standard (BIS), has given a limit of 30 µg/l, which is derived from World Health Organization (WHO) guidelines. Besides the chemical and radiological aspects associated with uranium, factors such as technological constraints in water purification, waste management, environmental factors, and socio-economic conditions significantly influence these guideline values, which are often overlooked. This manuscript explores the variations in approaches for establishing guideline values and highlights the uncertainties arising from dependence on various variables such as intake and usage patterns, inter- and intra-species distinctions, and epidemiological data. A critical analysis indicates that adherence to global guidelines may result in some undesirable environmental issues. By considering factors such as population dynamics, socio-economic conditions, and geological influences, we suggest that limit of 60 µg/l for uranium in drinking water is appropriate for India.

Evidence of the presence of SARS-CoV-2 virus in atmospheric air and surfaces of a dedicated COVID hospital.

The present study was conducted from July 1, 2020 to September 25, 2020 in a dedicated coronavirus disease 2019 (COVID-19) hospital in Delhi, India to provide evidence for the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus in atmospheric air and surfaces of the hospital wards. Swabs from hospital surfaces (patient's bed, ward floor, and nursing stations area) and suspended particulate matter in ambient air were collected by a portable air sampler from the medicine ward, intensive care unit, and emergency ward admitting COVID-19 patients. By performing reverse-transcriptase polymerase chain reaction (RT-PCR) for E-gene and RdRp gene, SARS-CoV-2 virus was detected from hospital surfaces and particulate matters from the ambient air of various wards collected at 1 and 3-m distance from active COVID-19 patients. The presence of the virus in the air beyond a 1-m distance from the patients and surfaces of the hospital indicates that the SARS-CoV-2 virus has the potential to be transmitted by airborne and surface routes from COVID-19 patients to health-care workers working in COVID-19 dedicated hospital. This warrants that precautions against airborne and surface transmission of COVID-19 in the community should be taken when markets, industries, educational institutions, and so on, reopen for normal activities.

Tuning of electron tunneling: a case study using BODIPY molecular layers.

Redox active π-conjugated organic molecules have shown the potential to be used as electronic components such as diode and memory elements. Here, we demonstrate that using simple surface chemistry, rectification characteristics can be tuned to reproducible negative differential resistance (NDR) with a very high peak-to-valley ratio (PVR) up to 1000 in 2,6-diethyl-4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indecene (BODIPY) grafted on Si. The change in properties is related to oxidation and reduction of BODIPY, which results in the change in resonant to non-resonant tunneling of electrons under bias. This has been explained by the ab initio molecular-orbital theoretical calculations.

Ruthenium based metallopolymer grafted reduced graphene oxide as a new hybrid solar light harvester in polymer solar cells.

A new class of pyridyl benzimdazole based Ru complex decorated polyaniline assembly (PANI-Ru) was covalently grafted onto reduced graphene oxide sheets (rGO) via covalent functionalization approach. The covalent attachment of PANI-Ru with rGO was confirmed from XPS analysis and Raman spectroscopy. The chemical bonding between PANI-Ru and rGO induced the electron transfer from Ru complex to rGO via backbone of the conjugated PANI chain. The resultant hybrid metallopolymer assembly was successfully demonstrated as an electron donor in bulk heterojunction polymer solar cells (PSCs). A PSC device fabricated with rGO/PANI-Ru showed an utmost ~6 fold and 2 fold enhancement in open circuit potential (Voc) and short circuit current density (Jsc) with respect to the standard device made with PANI-Ru (i.e., without rGO) under the illumination of AM 1.5 G. The excellent electronic properties of rGO significantly improved the electron injection from PANI-Ru to PCBM and in turn the overall performance of the PSC device was enhanced. The ultrafast excited state charge separation and electron transfer role of rGO sheet in hybrid metallopolymer was confirmed from ultrafast spectroscopy measurements. This covalent modification of rGO with metallopolymer assembly may open a new strategy for the development of new hybrid nanomaterials for light harvesting applications.

Fast Response and High Sensitivity of ZnO Nanowires-Cobalt Phthalocyanine Heterojunction Based H2S Sensor.

The room temperature chemiresistive response of n-type ZnO nanowire (ZnO NWs) films modified with different thicknesses of p-type cobalt phthalocyanine (CoPc) has been studied. With increasing thickness of CoPc (>15 nm), heterojunction films exhibit a transition from n- to p-type conduction due to uniform coating of CoPc on ZnO. The heterojunction films prepared with a 25 nm thick CoPc layer exhibit the highest response (268% at 10 ppm of H2S) and the fastest response (26 s) among all samples. The X-ray photoelectron spectroscopy and work function measurements reveal that electron transfer takes place from ZnO to CoPc, resulting in formation of a p-n junction with a barrier height of 0.4 eV and a depletion layer width of ∼8.9 nm. The detailed XPS analysis suggests that these heterojunction films with 25 nm thick CoPc exhibit the least content of chemisorbed oxygen, enabling the direct interaction of H2S with the CoPc molecule, and therefore exhibit the fastest response. The improved response is attributed to the high susceptibility of the p-n junctions to the H2S gas, which manipulates the depletion layer width and controls the charge transport.

Silicon-pyrene/perylene hybrids as molecular rectifiers.

We have synthesized two alkenyl (C-6 and C-11 chains) pyrenes and one alkenyl (C-11 chain) perylene as the σ-π systems, which were electro-grafted on H-terminated Si surfaces to form the respective monolayers. The I-V characteristics of the monolayers revealed pronounced rectification in forward bias with a maximum rectification ratio (RR) of 2.5 × 10(5) at 2.5 V for the C-6-pyrene 4b, 1000 at 1.5 V for the C-11-pyrene 4a and 3000-5000 at 1.75 V for the C-11-perylene 3. The higher RR of the devices containing 4b compared to those of 4a and 3 is possibly due to better alignment and packing of the 4b-monolayers on the Si substrate. The rectification was explained using the ab initio molecular-orbital calculations.

Ultrasensitive and selective detection of dopamine using cobalt-phthalocyanine nanopillar-based surface acoustic wave sensor.

A highly selective and sensitive surface acoustic wave (SAW) sensor of dopamine (DA) was developed by depositing cobalt phthalocyanine (CoPc) nanopillars on gold-coated sensing platform of SAW sensor. The developed biosensor presents a sensitivity of 1.6°/nM, has a low limit of detection (LOD) on the order of 0.1 nM, and imparts more selectivity toward DA, since the detection limit of the interfering ascorbic acid (AA) is as high as 1 mM. To understand the selectivity mechanisms of this sensor toward DA, density functional theory-based chemical calculations were carried out. Calculations suggest two different types of interactions: dative bond with a very strong character for DA-CoPc complexes, and significant ionic character in the case of AA-CoPc ones. The interaction energies, in liquid phase, were estimated to be equal to -81 kJ mol(-1) and -38 kJ mol(-1) for DA-CoPc and AA-CoPc complexes, respectively, therefore accounting for the selective detection of DA over AA using tandem CoPc nanopillar-based SAW sensor device. This work demonstrates a simple and efficient design of SAW sensors employing thin nanostructured CoPc biomolecular recognition layers for DA detection.

In situ diazonium-modified flexible ITO-coated PEN substrates for the deposition of adherent silver-polypyrrole nanocomposite films.

In this paper, we report a simple and versatile process of electrografting the aryl multilayers onto indium tin oxide (ITO)-coated flexible poly(ethylene naphthalate) (PEN) substrates using a diazonium salt (4-pyrrolylphenyldiazonium) solution, which was generated in situ from a reaction between the 4-(1H-pyrrol-1-yl)aniline precursor and sodium nitrite in an acidic medium. The first aryl layer bonds with the ITO surface through In-O-C and Sn-O-C bonds which facilitate the formation of a uniform aryl multilayer that is ∼8 nm thick. The presence of the aryl multilayer has been confirmed by impedance spectroscopy as well as by electron-transfer blocking measurements. These in situ diazonium-modified ITO-coated PEN substrates may find applications in flexible organic electronics and sensor industries. Here we demonstrate the application of diazonium-modified flexible substrates for the growth of adherent silver/polpyrrole nanocomposite films using surface-confined UV photopolymerization. These nanocomposite films have platelet morphology owing to the template effect of the pyrrole-terminated aryl multilayers. In addition, the films are highly doped (32%). This work opens new areas in the design of flexible ITO-conductive polymer hybrids.

Core/shell, protuberance-free multiwalled carbon nanotube/polyaniline nanocomposites via interfacial chemistry of aryl diazonium salts.

Highly uniform core-shell like multi-walled carbon nanotubes-polyaniline (MWCNT-PANI) nanocomposites were prepared in two steps (i) surface modification of MWCNTs with a 4-aminodiphenylamine group via in situ diazonium generation process; and (ii) polymerization of aniline onto surface modified MWCNTs. This functionalization helped to easily disperse the MWCNTs in acidic solutions; hence it is suitable for the chemical oxidative polymerization of aniline. It was found that MWCNT-PANI nano-composites with higher MWCNTs loading yield PANI chains with more quinoid units than the pure PANI, which results in significant improvement in the conductivity of the composites. This facile approach of synthesizing core-shell nanocomposites highlights the efficiency of the interfacial chemistry of aryl diazonium salts in generating conductive polymer/MWCNT nanocomposites with enhanced conductivity and high surface area.

One pot, single step, room temperature dielectrophoretic deposition of gold nanoparticles clusters on polyethylene terephthalate substrate.

The major challenge of plastic electronics is the deposition of gold nanoparticles (AuNPs) on flexible substrates at room temperature. Here, we show fast, single step, room temperature deposition of AuNPs on polyethylene terephthalate (PET) and biaxially oriented PET (BoPET) substrate by employing dielectrophoresis. The deposition has been carried out using two-electrode system, with BoPET (or PET) and metallic (Pt or stain steel) mesh, under an AC signal of 20 kHz and 20 V peak-to-peak (V(pp)) (signal for PET is 6 V(pp) and 6 kHz). In this method, we show how to deposit AuNPs on PET-like insulator by exploiting its polarization capability under an AC signal. The polarization of PET has been confirmed by change in the Raman spectra of the PET film under in situ AC signals. Furthermore, we show that using this dielectrophoretic deposition method, the PET films can be patterned by AuNPs at room temperature without any pre- and posttreatment.