Pravin P. Ingole

In Situ Solid‐State Synthesis of a AgNi/g‐C3N4 Nanocomposite for Enhanced Photoelectrochemical and Photocatalytic Activity

A graphitic carbon nitride (g-C3 N4 ) polymer matrix was embedded with AgNi alloy nanoparticles using a simple and direct in situ solid-state heat treatment method to develop a novel AgNi/g-C3 N4 photocatalyst. The characterization confirms that the AgNi alloy particles are homogeneously distributed throughout the g-C3 N4 matrix. The catalyst shows excellent photoelectrochemical activity for water splitting with a maximum photocurrent density of 1.2 mA cm-2 , which is the highest reported for doped g-C3 N4 . Furthermore, a detailed experimental study of the photocatalytic degradation of Rhodamine B (RhB) dye using doped g-C3 N4 showed the highest reported degradation efficiency of approximately 95 % after 90 min. The electronic conductivity increased upon incorporation of AgNi alloy nanoparticles on g-C3 N4 and the material showed efficient charge carrier separation and transfer characteristics, which are responsible for the enhanced photoelectrochemical and photocatalytic performance under visible light.

Enhanced photoelectrochemical performance of electrodeposited hematite films decorated with nanostructured NiMnOx

In the present work, we report a novel nickel-manganese oxide (NiMnOx) decorated hematite (α-Fe2O3) photoanode for efficient water splitting in a photoelectrochemical (PEC) cell. The photoanodes are prepared by a two step electrodeposition process. NiMnOx loading on the hematite surface is varied by changing the electrodeposition time. The NiMnOx loaded α-Fe2O3 photoanodes are characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, UV-Vis absorption and photoluminescence spectroscopy. The results demonstrate that the NiMnOx decorated α-Fe2O3 photoanode exhibits excellent photoelectrochemical activity. The α-Fe2O3/NiMnOx photoanode, where NiMnOx was coated for 200 s, shows a maximum photocurrent of 2.35 mA cm−2 at an applied potential of 0.23 V vs. the Ag/AgCl reference electrode. There is a large shift in the onset potential towards the cathodic region also observed. The photoconversion efficiency is calculated which is around 0.85% at 0.23 V vs. Ag/AgCl. The superior PEC performance of NiMnOx decorated α-Fe2O3 photoanodes can be explained by a combined effect of better water oxidation on the hematite surface and efficient separation of photogenerated electron–hole pairs on its surface due to NiMnOx modification.

Citrate-stabilized Q-CdSe seed-mediated synthesis of silver nanoparticles: The role of citrate moieties anchored to the Q-CdSe surface

Here, we try to explore a new dimension/role for citrate molecules in the bound state, i.e. anchored to the surface of cadmium selenide quantum dots (Q-CdSe), in the synthesis of metal nanoparticles (MNPs). Being labile, the citrate molecule is considered a good candidate for the stabilization of semiconductor quantum dots (QDs) such as Q-CdSe that can be used for further functionalization/modification of the surface properties of the QDs. In its free/ionic form (i.e. not bound to the surface), it is well known for its role as a reducing as well as a capping agent in the synthesis of silver and gold MNPs. A simple strategy for the preparation of silver MNPs following the chemical reduction of silver ions that is mediated by citrate-stabilized Q-CdSe seeds without addition of an external reducing agent is presented. The citrate moieties anchored to the surface of Q-CdSe are found to play an important role in the chemical reduction of silver ions. The obtained product was analysed by spectroscopic, microscopic and structural characterization techniques such as surface plasmon resonance (SPR), transmission electron microscopy (TEM) and cyclic voltammetry. The characteristic redox behaviour observed in cyclic voltammograms (CVs) also supports the formation of Ag MNPs in the samples. Further, the impact of the reaction solution pH on the feasibility of silver ion reduction by Q-CdSe seeds resulting into the formation of Ag MNPs is also briefly discussed.

Probing the Crystal Structure, Composition-Dependent Absolute Energy Levels, and Electrocatalytic Properties of Silver Indium Sulfide Nanostructures.

The absolute electronic energy levels in silver indium sulfide (AIS) nanocrystals (NCs) with varying compositions and crystallographic phases have been determined by using cyclic voltammetry. Different crystallographic phases, that is, metastable cubic, orthorhombic, monoclinic, and a mixture of cubic and orthorhombic AIS NCs, were studied. The band gap values estimated from the cyclic voltammetry measurements match well with the band gap values calculated from the diffuse reflectance spectra measurements. The AIS nanostructures were found to show good electrocatalytic activity towards the hydrogen evolution reaction (HER). Our results clearly establish that the electronic and electrocatalytic properties of AIS NCs are strongly sensitive to the composition and crystal structure of AIS NCs. Monoclinic AIS was found to be the most active HER electrocatalyst, with electrocatalytic activity that is almost comparable to the MoS2 -based nanostructures reported in the literature, whereas cubic AIS was observed to be the least active of the studied crystallographic phases and compositions. In view of the HER activity and electronic band structure parameters observed herein, we hypothesize that the Fermi energy level of AIS NCs is an important factor that decides the electrocatalytic efficiency of these nanocomposites. The work presented herein, in addition to being the first of its kind regarding the composition and phase-dependence of electrochemical aspects of AIS NCs, also presents a simple solvothermal method for the synthesis of different crystallographic phases with various Ag/In molar ratios.

Probing Absolute Electronic Energy Levels in Hg-Doped CdTe Semiconductor Nanocrystals by Electrochemistry and Density Functional Theory

The absolute electronic energy levels in Hg-doped CdTe semiconductor nanocrystals (CdHgTe NCs) with varying sizes/volumes and Hg contents are determined by using cyclic voltammetry (CV) measurements and density functional theory (DFT) -based calculations. The electrochemical measurements demonstrate several distinct characteristic features in the form of oxidation and reduction peaks in the voltammograms, where the peak positions are dependent on the volume of CdHgTe NCs as well as on their composition. The estimated absolute electronic energy levels for three different volumes, namely 22, 119 and 187 nm(3) with 2.7±0.3 % of Hg content, show strong volume dependence. The volume-dependent shift in the characteristic reduction and oxidation peak potential scan can be attributed to the alteration in the energetic band positions owing to the quantum confinement effect. Moreover, the composition (Cd/Hg=98.3/1.7 and 97.0/3.0) -dependent alteration in the electronic energy levels of CdHgTe NCs for two different samples with similar volumes (ca. 124±5 nm(3) ) are shown. Thus obtained electronic energy level values of CdHgTe NCs as a function of volume and composition demonstrate good congruence with the corresponding absorption and emission spectral data, as well as with DFT-based calculations. DFT calculations reveal that incorporation of Hg into CdTe NCs mostly affects the energy levels of conduction band edge, whereas the valence band edge remains almost unaltered.

Effect of Electrochemical Charge Injection on the Photoluminescence Properties of CdSe Quantum Dot Monolayers Anchored to Oxide Substrates

Abstract The photoluminescence (PL) properties of TOPO capped CdSe quantum dots (Q-CdSe) monolayers deposited on indium tin oxide (ITO) substrates and incorporated into an electrochemical cell have been studied. In particular, the effect of electrochemical charge injection by combining the electrochemical set-up with fluorescence spectroscopy has been investigated. It was observed that when positive potentials are applied to the film in electrolyte solution, the PL is irreversibly quenched. However, the PL quenching observed after applying negative potentials to the substrate was reversible. In addition, the changes in the PL exhibit characteristic profiles at particular applied potentials. Voltammetric measurements were performed to further understand the possible origins of the specific PL changes as a function of applied potential. The results have the prospect to prove helpful in explaining the phenomenon of PL intermittency or blinking in semiconductor quantum dots.

n-Type Cu2O/α-Fe2O3 Heterojunctions by Electrochemical Deposition: Tuning of Cu2O Thickness for Maximum Photoelectrochemical Performance

Abstract Here, we report the enhanced photoelectrochemical performance of surface modified hematite thin films with n-type copper oxide nanostructures (Cu2O/Fe2O3) obtained through simple electrochemical deposition method. The thickness and amount of cuprous oxide layer were varied by simply changing the number of electrodeposition cycles (viz. 5, 10, 25, 50 and 100) in order to understand its thermodynamic and kinetic influence on the photoelectrochemical activity of the resultant nano-heterostructures. Structural and morphological characteristics of the obtained Cu2O/Fe2O3 films have been studied by absorption spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analysis. Electrochemical investigations such as linear sweep voltammetry, Mott–Schottky analysis, and electrochemical impedance spectroscopy suggested the formation of n-type Cu2O layers over the hematite films with varying charge-carrier densities, ranging from 0.56×1019 to 3.94×1019 cm−3, that varies with the number of cycles of electrochemical deposition. Besides, the thickness of deposited cuprous oxide layer is noted to alter the net electrochemical and photo-electrochemical response of the base material. An interesting, peak event was recorded for a particular thickness of the cuprous oxide layer (obtained after 25 cycles of electrochemical deposition) below and above which the efficiency of catalyst was impaired. The heterojunction obtained thus, followed well known Z-scheme and gave appreciable increment in the photocurrent response.

Biofabricated BiOI with enhanced photocatalytic activity under visible light irradiation

In the recent past, there has been a large-scale utilization of plant extracts for the synthesis of various photocatalysts. The biofabrication technology eliminates the usage of harmful chemicals and serves as an eco-friendly approach for environmental remediation. Herein, a comparative analysis between bismuth oxyiodide synthesized via Azadirachta indica (neem) leaf extract (BiOI-G) and without leaf extract (BiOI-C) has been envisaged. The BiOI-G and BiOI-C samples were characterized by spectral and microscopic techniques, which revealed that the Azadirachta indica assisted BiOI-G attained enhanced features over BiOI-C such as narrower band gap, large surface area, porosity, increased absorption range of visible light and effectual splitting of the photogenerated e−–h+ pairs. Benefiting from these enhanced features, BiOI-G degraded methyl orange (MO), rhodamine B (RhB), and benzotriazole (BT) at a significantly higher rate in comparison to BiOI-C. The degradation rate of MO, RhB and BT by BiOI-G was observed to be 1.3, 1.25 and 1.29 times higher in comparison to BiOI-C. Moreover, BiOI-G displayed high stability upto five cycles of the photocatalytic activity, which endow its effectiveness as a highly-efficient green photocatalyst.

PdAg Bimetallic Nanoalloy-Decorated Graphene: A Nanohybrid with Unprecedented Electrocatalytic, Catalytic, and Sensing Activities

Recent reports about the promising and tunable electrocatalytic activity and stability of nanoalloys have stimulated an intense research activity toward the design and synthesis of homogeneously alloyed novel bimetallic nanoelectrocatalysts. We herein present a simple one-pot facile wet-chemical approach for the deposition of high-quality bimetallic palladium-silver (PdAg) homogeneous nanoalloy crystals on reduced graphene (Gr) oxide sheets. Morphological, structural, and chemical characterizations of the so-crafted nanohybrids establish a homogeneous distribution of 1:1 PdAg nanoalloy crystals supported over reduced graphene oxide (PdAg-Gr). The PdAg-Gr nanohybrids exhibit outstanding electrocatalytic, catalytic, and electroanalytical performances. The PdAg-Gr samples were found to exhibit exceptional durability when subjected to repeated potential cycles or long-term electrolysis. In the CVs recorded for fuel cell reactions, viz. methanol oxidation reaction and oxygen reduction reaction, and for detoxification of environmental pollutants, viz. electroreduction of methyl iodide and chloroacetonitrile over PdAg-Gr with potential sweep rate of 25 mVs-1, the peak potentials were observed to be just -0.221, -0.297, (vs Ag/AgCl, 3 M KCl) -1.508, and -1.189 V (vs Fc+/Fc), respectively. The potential of PdAg-Gr nanohybrid for simultaneous and sensitive electrochemical sensing and estimation of hydroxybenzene isomers with very low detection limits (0.05 μM for hydroquinone, 0.06 μM for catechol, 6.7 nM for 4-aminophenol, and 13.7 nM for 2-aminophenol) is demonstrated. Additionally, PdAg-Gr was observed to offer excellent solution-phase catalytic performance in bringing about the reduction of notorious environmental pollutant 4-nitrophenol to pharmaceutically important 4-aminophenol with an apparent rate constant ( kapp) of 3.106 × 10-2 s-1 and a normalized rate constant ( knor) of 6.21 × 102 s-1 g-1. The presented synthetic scheme besides being high yielding, low cost, and easy to carry out results in the production of PdAg-Gr nanohybrids with stability and activity significantly better than most of the nanomaterials purposefully designed and testified so far by various groups.

Self-assembled AuNPs on sulphur-doped graphene: a dual and highly efficient electrochemical sensor for nitrite (NO2−) and nitric oxide (NO)

A simple strategy for the synthesis of self-assembled gold nanoparticles (AuNPs) on sulphur-doped graphene (S-Gr) to form AuNPs-S-Gr nanohybrids is presented. Structural, chemical and morphological characterization of AuNPs-S-Gr nanohybrids through UV-Vis spectroscopy, the X-ray diffraction technique (XRD), Raman spectroscopy, force field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) and electrochemical techniques establishes the AuNPs-S-Gr nanohybrid as a monolayer of AuNPs assembled on S-Gr. The lead underpotential deposition experiments ascertain that nano Au in AuNPs-S-Gr nanohybrids is better exposed for faradic processes than in citrate-stabilized AuNPs, with the faradic response in the former being dominated by the Au-(111) planes. The AuNPs-S-Gr nanohybrids are demonstrated to be electrochemically stable, reusable and with an excellent prospect for the sensitive and selective electrochemical detection of two biologically and environmentally important oxides of nitrogen viz. nitrite (NO2−) and nitric oxide (NO). The electrocatalytic electron transfer rate constants (kcat) of the AuNPs-S-Gr nanohybrid towards electro-oxidation of NO2− and NO were observed to be 0.98 (±0.03) × 105 M−1 s−1/2 and 0.51 (±0.02) × 104 M−1 s−1/2, respectively. The AuNPs-S-Gr nanohybrid was demonstrated to ensure selective and sensitive electrochemical quantification of NO2− and NO with a very high sensitivity (20766.17 and 21046.72 μA M−1 cm−2), a wide linear range (12.5–680.92 and 24.9–680.93 μM) and very low detection limits (0.003 and 0.009 μM), respectively. Importantly, the AuNPs-S-Gr nanohybrid exhibited appreciable selectivity towards the detection of NO2− and NO even in the presence of a very high concentration of common interfering ions. The stability and reproducibility of faradic signals for NO2− and NO detection at the AuNPs-S-Gr nanohybrid were found to be excellent for standard laboratory and real samples. The electrocatalytic activity and sensing results of the AuNPs-S-Gr nanohybrid for NO2− and NO are much better than those recently reported over surfaces purposefully designed for electrocatalytic oxidation and electrosensing of these analytes.