Utilization of Electrocoagulated Sewage as a Photoelectrocatalyst for Water Splitting.

Electrocoagulation (EC) as a wastewater treatment process for the removal of pollutants has been demonstrated in numerous studies. However, proper management of solid waste generated after EC treatment is essential to minimize its environmental impact. Hence, more emphasis needs to be paid towards unused solid waste after EC treatment. The present study investigates the possibilities of utilizing waste released after the EC process as an electrocatalyst in the presence of sunlight. In this study, the sludge produced after domestic wastewater treatment by the EC process is collected and tested for water oxidation reaction under AM 1.5 illumination of simulated solar light. The sludge produced after EC treatment was characterized meticulously and confirmed to be the magnetite phase of iron oxide, which is used as a photoanode for photoelectrochemical (PEC) water splitting. The chemical composition of sludge is majorly dependent on the treatment time, which plays a crucial role in deciding the metal ions present in the sludge. After 30 min, which is the optimized time for EC treatment, sludge was studied as an efficient photoanode material. The band gap illumination of sludge (iron oxide) as working electrodes results in anodic current; the photocurrent appears at a bias of ca. 390 mV with respect to the flat-band potential. The PEC activity of waste is treatment-time dependent and decreases after reaching an optimal time of 30 min. A photocurrent density of 4.6 × 10-6 A cm-2 was found at the potential of 1.23 V (vs RHE) for sludge collected after 30 min of treatment time. It indicates that the sludge-derived photoanode has the potential to be an efficient component in PEC systems, contributing to the overall efficiency of water-splitting processes. Our experimental results show a new pathway of a "waste to energy" approach that aligns with the principles of circular economy and sustainable resource management.

Catalytic reduction of oxygen to water by non-heme iron complexes: exploring the effect of the secondary coordination sphere proton exchanging site.

In this study, we prepared non-heme FeIII complexes (1, 2, and 3) of an N4 donor set of ligands (H2L, Me2L, and BPh2L). 1 is supported by a monoanionic bispyridine-dioxime ligand (HL). In 2 and 3, the primary coordination sphere of Fe remained similar to that in 1, except that the oxime protons of the ligand were replaced with two methyl groups and a bridging -BPh2 moiety, respectively. X-ray structures of the FeII complexes (1a and 3a) revealed similar Fe-N distances; however, they were slightly elongated in 2a. The FeIII/FeII potential of 1, 2, and 3 appeared at -0.31 V, -0.25 V, and 0.07 V vs. Fc+/Fc, respectively, implying that HL and Me2L have comparable donor properties. However, BPh2L is more electron deficient than HL or Me2L. 1 showed electrocatalytic oxygen reduction reaction (ORR) activity in acetonitrile in the presence of trifluoroacetic acid (TFAH) as the proton source at Ecat/2 = -0.45 V and revealed selective 4e-/4H+ reduction of O2 to H2O. 1 showed an effective overpotential (ηeff) of 0.98 V and turnover frequency (TOFmax) of 1.02 × 103 s-1. Kinetic studies revealed a kcat of 2.7 × 107 M-2 s-1. Strikingly, 2 and 3 remained inactive for electrocatalytic ORR, which established the essential role of the oxime scaffolds in the electrocatalytic ORR of 1. Furthermore, a chemical ORR of 1 has been investigated using decamethylferrocene as the electron source. For 1, a similar rate equation was noted to that of the electrocatalytic pathway. A kcat of 6.07 × 104 M-2 s-1 was found chemically. Complex 2, however, underwent a very slow chemical ORR. Complex 3 chemically enhances the 4e-/4H+ reduction of O2 and exhibits a TOF of 0.24 s-1 and a kcat value of 2.47 × 102 M-1 s-1. Based on the experimental observations, we demonstrate that the oxime backbone of the ligand in 1 works as a proton exchanging site in the 4e-/4H+ reduction of O2. The study describes how the ORR is affected by the tuning of the ligand scaffold in a family of non-heme Fe complexes.

Green chemistry routed sugar press mud for (2D) ZnO nanostructure fabrication, mineral fortification, and climate-resilient wheat crop productivity.

Nanotechnology appears to be a promising tool to redefine crop nutrition in the coming decades. However, the crucial interactions of nanomaterials with abiotic components of the environment like soil organic matter (SOM) and carbon‒sequestration may hold the key to sustainable crop nutrition, fortification, and climate change. Here, we investigated the use of sugar press mud (PM) mediated ZnO nanosynthesis for soil amendment and nutrient mobilisation under moderately alkaline conditions. The positively charged (+ 7.61 mv) ZnO sheet-like nanoparticles (~ 17 nm) from zinc sulphate at the optimum dose of (75 mg/kg blended with PM (1.4% w/w) were used in reinforcing the soil matrix for wheat growth. The results demonstrated improved agronomic parameters with (~ 24%) and (~ 19%) relative increases in yield and plant Zn content. Also, the soil solution phase interactions of the ZnO nanoparticles with the PM-induced soil colloidal carbon (- 27.9 mv and diameter 0.4864 µm) along with its other components have influenced the soil nutrient dynamics and mineral ecology at large. Interestingly, one such interaction seems to have reversed the known Zn-P interaction from negative to positive. Thus, the study offers a fresh insight into the possible correlations between nutrient interactions and soil carbon sequestration for climate-resilient crop productivity.

Mechanistic insights into the electrolyte effects on the electrochemical nitrogen reduction reaction using copper hexacyanoferrate/f-MWCNT nano-composites.

Developing an efficient, selective, and stable electrocatalysis system for the electrocatalytic N2 reduction reaction (ENRR) is a promising strategy for the green and sustainable production of ammonia. The activity, selectivity, and stability of various electrocatalysts in different electrolyte solvents, mainly acidic and alkaline electrolytes, are commonly compared in the literature. However, a mechanistic insight into the effect of these electrolytes on ENRR activity is lacking. Herein we demonstrate that the acidity or alkalinity of the electrolyte is a key factor in determining the rate-limiting step and, by extension, the ENRR performance of an electrochemical setup for the electroproduction of ammonia. Our results from ex situ X-ray photoelectron, Raman, and FTIR spectroscopy analysis of the fresh and spent Cu-hexacyanoferrate Prussian blue analogue-decorated functionalized carbon nanotube (CuFe PBA/f-CNT) catalyst reveal that NH4+-species are more strongly adsorbed on the catalyst surface during the ENRR in acidic than in alkaline electrolytes. The results of our detailed rotating ring-disc electrode voltammetry studies suggest that the ENRR over CuFe PBA/f-CNT is mostly controlled by surface adsorption in an acidic electrolyte and by mass transport in an alkaline electrolyte. In situ Raman spectroscopy confirms this finding and shows that the leaching of Fe(CN)6 species from the CuFe PBA/f-CNT composite in an alkaline electrolyte greatly affects the ENRR performance. We believe that the work presented herein offers a new insight into the mechanistic aspects of the ENRR in different electrolyte systems and hence can prove very valuable for the development of effective ENRR electrode/electrolyte systems for practical applications.

The enhanced electrocatalytic performance of nanoscopic Cu6Pd12Fe12 heterometallic molecular box encaged cytochrome c.

Designing molecular cages for atomic/molecular scale guests is a special art used by material chemists to harvest the virtues of the otherwise vile idea known as "the cage". In recent years, there has been a notable surge in research investigations focused on the exploration and utilization of the distinct advantages offered by this art in the advancement of efficient and stable bio-electrocatalysts. This usually is achieved through encapsulation of biologically accessible redox proteins within specifically designed molecular cages and matrices. Herein, we present the first successful method for encaging cytochrome c (Cyt-c), a clinically significant enzyme system, inside coordination-driven self-assembled Cu6Pd12Fe12 heterometallic hexagonal molecular boxes (Cu-HMHMB), in order to create a Cyt-c@Cu-HMHMB composite. 1H NMR, FTIR, and UV-Vis spectroscopy, ICP-MS, TGA and voltammetric investigations carried out on the so-crafted Cyt-c@Cu-HMHMB bio-inorganic composite imply that the presented strategy ensures encaging of Cyt-c in a catalytically active, electrochemically stable and redox-accessible state inside the Cu-HMHMB. Cyt-c@Cu-HMHMB is demonstrated to exhibit excellent stability and electrocatalytic activity toward very selective, sensitive electrochemical sensing of nitrite exhibiting a limit of detection as low as 32 nanomolar and a sensitivity of 7.28 µA µM-1 cm-2. Importantly, Cyt-c@Cu-HMHMB is demonstrated to exhibit an excellent electrocatalytic performance toward the 4e pathway oxygen reduction reaction (ORR) with an onset potential of 0.322 V (vs. RHE) and a Tafel slope of 266 mV dec-1. Our findings demonstrate that Cu-HMHMB is an excellent matrix for Cyt-c encapsulation. We anticipate that the entrapment-based technique described here will be applicable to other enzyme systems and Cyt-c for various electrochemical and other applications.

Phase controlled green synthesis of wurtzite (P63mc) ZnO nanoparticles: interplay of green ligands with precursor anions, anisotropy and photocatalysis.

Green approaches for nanosynthesis often lack the precise control of synthetic outcomes, which is primarily due to the poorly defined reaction protocols. Herein, we investigated the use of lignocellulosic agro-waste, sugarcane press mud (PM), for the synthesis of ZnO nanoparticles using three different precursor salts and their further application in the photocatalytic degradation of rhodamine dyes. This approach resulted in the formation of ZnO nanoparticles with two different morphologies, i.e., sheet-like structure from the zinc sulphate and nitrate precursors, whereas sphere-like structures from zinc acetate. In all three cases, the wurtzite phase (P63mc) of ZnO nanoparticles remained consistent. Also, the ZnO nanoparticles were found to be positively charged ("ζ" = +8.81 to +9.22 mv) and nearly monodispersed, with a size and band gap in the range of ∼14-20 nm and 3.78-4.1 eV, respectively. Further, the potential photocatalytic activity of these nanoparticles was investigated under direct sunlight. At the same photocatalyst dose of 0.1 g L-1, the three ZnO nanoparticles showed varying efficiencies due to their shape anisotropy. The ZnO NPs from acetate salt (∼20 nm, sheet like) showed the highest dye degradation efficiency (90.03%) in 4.0 hours, indicating the role of the catalyst-dye interface in designing efficient photocatalysts.

A novel cobalt(ii) acetate complex bearing lutidine ligand: a promising electrocatalyst for oxygen evolution reaction.

Developing cost-effective electrocatalysts using earth-abundant metal as an alternative to expensive precious metal catalyst remains a key challenge for researchers. Several strategies are being researched/tested for making low-cost transition metal complexes with controlled electron-density and coordination flexibility around the metal center to enhance their catalytic activity. Herein, we report a novel lutidine coordinated cobalt(ii) acetate complex [(3,5-lutidine)2Co(OAc)2(H2O)2] (1) as a promising electrocatalyst for oxygen evolution reaction (OER). Complex 1 was characterized by FT-IR, elemental analysis, and single crystal X-ray diffraction data. The structure optimization of complex 1 was also done using DFT calculation and the obtained geometrical parameters were found to be in good agreement with the parameters obtained from the solid state structure obtained through single crystal X-ray diffraction data. Further, the molecular electrostatic potential (MEP) maps analysis of complex 1 observed electron rich centers that were found to be in agreement with the solid-state structure. It was understood that the coordination of lutidine as a Lewis base and acetate moiety as a flexible ligand will provide more coordination flexibility around the metal center to facilitate the catalytic reaction. Further, the electron rich centers around metal center will also support the enhancement of their catalytic activity. Complex 1 shows impressive OER activity, even better than the state-of-the-art IrO2 catalyst, in terms of turnover frequency (TOF: 0.05) and onset potential (1.50 V vs. RHE). The TOF for complex 1 is two and half times higher, while the onset potential is ca. 20 mV lower, than the benchmark IrO2 catalyst studied under identical conditions.

Favoring Product Desorption by a Tailored Electronic Environment of Oxygen Vacancies in SrTiO3 via Cr Doping for Enhanced and Selective Electrocatalytic CO2 to CO Conversion.

The electrochemical CO2 reduction reaction (ECO2RR) into value-added products is crucial to address the herculean task of CO2 mitigation. Several efforts are being made to develop active ECO2RR catalysts, targeting enhanced CO2 adsorption and activation. A rational design of ECO2RR catalysts with a facile product desorption step is seldom reported. Herein, ensuing the Sabatier principle, we report a strategy for an enhanced ECO2RR with a faradaic efficiency of 85% for CO production by targeting the product desorption step. The energy barrier for product desorption was lowered via a tailored electronic environment of oxygen vacancies (Ovac) in Cr-doped SrTiO3. The substitutional doping of Cr3+ for Ti4+ into the SrTiO3 lattice favors the generation of more Ovac and modifies the local electronic environment. Density functional theory analysis evinces the spontaneous dissociation of COOH# intermediates over Ovac and lower CO intermediate binding on Ovac reducing the energy demand for CO release due to Cr doping.

Two-Dimensional Tungsten Oxide/Selenium Nanocomposite Fabricated for Flexible Supercapacitors with Higher Operational Voltage and Their Charge Storage Mechanism.

The present work elaborates the high-energy-density, stable, and flexible supercapacitor devices (full-cell configuration with asymmetric setup) based on a two-dimensional tungsten oxide/selenium (2D WO3/Se) nanocomposite. For this, the 2D WO3/Se nanocomposite synthesized by a hydrothermal method followed by air annealing was coated on a flexible carbon cloth current collector and combined separately with both 0.1 M H2SO4 and 1-butyl-3-methyl imidazolium tetrafluoroborate room temperature ionic liquid (BmimBF4 RTIL) as electrolyte. Different physicochemical characterization techniques, viz., transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, are utilized for phase confirmation and morphology identification of the obtained samples. The electrochemical analysis was used to evaluate charge storage mechanism. The half-cell configuration (three electrode system) in 0.1 M H2SO4 shows a specific capacitance of 564 F g-1 at 6 A g-1 current density, whereas with ionic liquid as electrolyte, a higher specific capacitance of 1650 F g-1 was obtained at a higher current of 40 mA and working potential of 4 V. Importantly, the asymmetric flexible supercapacitor device with PVA-H2SO4 electrolyte shows a working voltage of 1.7 V. A specific capacitance of 858 mF g-1 is obtained for the asymmetric electrode system with an energy density of 47 mWh kg-1 and a power density of 345 mW kg-1 at a current density of 0.2 A g-1.

Supersensitive Detection of Anions in Pure Organic and Aqueous Media by Amino Acid Conjugated Ellman's Reagent.

The last few decades witnessed a remarkable advancement in the field of molecular anion receptors. A variety of anion binding motifs have been discovered, and large number of designer molecular anion receptors with high selectivity are being reported. However, anion detection in an aqueous medium is still a formidable challenge as evident from only a miniscule of synthetic systems available in the literature. We, herein, report 5,5'-dithio-bis(2-nitrobenzoic acid) (Ellman's reagent) appended with amino acids as supersensitive anion sensors that can detect F- and H2PO4- ions in both aqueous as well as organic media. Interestingly, the sensors showed a dual response to anions, viz., chromogenic response in organic medium and electrochemical response in aqueous solutions. Various spectroscopic techniques such as UV-vis and 1H NMR are used to investigate the binding studies in acetonitrile, whereas electrochemical methods such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) are employed to explore the anion binding in water. The host-guest complex stoichiometry and binding constants are calculated using the BindFit software. The geometry of host-guest complex has been optimized by the density functional theory (DFT) method. These molecules are versatile sensors since these function in both water and acetonitrile with extremely low limit of detection (LOD) up to 0.07 fM and limit of quantification (LOQ) up to 0.23 fM. To our knowledge, the present system is the first example of a sensor that can detect the lowest concentration of anions in water quantitatively. The minimalistic design strategy presented here opens up the innumerable possibilities for designing dual anion sensors in a one fell swoop.

Exploiting the unique specialty of hydrazone functionality: Synthesis of a highly sensitive UV-Vis active solvatochromic probe.

The unique physico-chemical attributes of the hydrazone functionality have been extensively studied for a diverse range of chemical, biological and analytical applications. The synthesis of a highly sensitive hydrazone based UV-Vis active solvatochromic probe that exhibits excellent sensitivity toward sensing of solvent polarity, microstructural changes and onset of micellization in aqueous systems was carried out. Specifically, synthesis of 2,4-dinitrophenyl-2-(2-nitrobenzylidene)hydrazone (DNPNBH), through an easy to carry, atom economical, one-pot single step approach via use of low-cost precursors viz. ortho-nitrobenzaldehyde and 2,4-dinitrophenyl hydrazine is presented. The UV-Vis absorption features of the synthesized hydrazone exhibit excellent sensitivity toward the polarity of its immediate microenvironment. The microenvironment polarity sensing potential of DNPNBH is demonstrated for some single solvent systems and DMF-Water mixture as a model binary solvent system and the results are supported by quantum mechanical calculations. Use of the DNPNBH as a probe (at concentrations many orders lower than required for conventional probes) to precisely reflect the onset of micellization and estimation of critical micelle concentration (CMC) of amphiphilic molecules (5.25 mM for SDS, 1.53 mM for CTAB and 0.055 mM for Brij56) in aqueous solutions is also demonstrated. The results clearly qualify the synthesized hydrazone as a highly sensitive UV-Vis probe that can be employed for reliable sensing of solvent polarity, composition dependence of physicochemical attributes in mixed solvent systems and the estimation of CMC of surfactant systems via spectrophotometry.

Development of Cuboidal KNbO3@α-Fe2O3 Hybrid Nanostructures for Improved Photocatalytic and Photoelectrocatalytic Applications.

Monophasic and hybrid nanostructures of KNbO3 and α-Fe2O3 have been prepared using a hydrothermal process for photoelectrocatalytic and photocatalytic applications. Powder X-ray diffraction studies showed the formation of KNbO3, α-Fe2O3, and KNbO3/α-Fe2O3 with average grain sizes of 18.3, 11.5, and 26.1 nm and Brunauer-Emmett-Teller (BET) specific surface areas of 4, 100, and 20 m2/gm, respectively. Under simulated solar irradiation, the as-prepared heterostructure shows enhanced photoelectrocatalytic oxygen evolution reaction (OER) activity compared to pristine KNbO3 and α-Fe2O3. Significant photocatalytic activity of as-synthesized KNbO3/α-Fe2O3 heterostructure photocatalyst was obtained for removal of methylene blue organic dye under visible light, and the percentage activity was found to be 11, 49, and 89% for KNbO3, α-Fe2O3, and KNbO3/α-Fe2O3 photocatalysts, respectively. The dielectric constant was found to be 250.2, 65.2, and 251.5 for KNbO3, α-Fe2O3, and KNbO3/α-Fe2O3 heterostructure, respectively, at 50 °C and 500 kHz frequency.

Mechanistic insight into the electrocatalytic performance of reduced graphene oxide supported palladium, silver and palladium-silver nanodeposits toward electro-dehalogenation of halocarbons in room temperature ionic liquids.

Herein, we report the results from our extensive voltammetric investigations designed to explore, assess and explain the electrocatalytic performance of reduced graphene oxide supported metal nano-deposits toward the electro-dehalogenation of halocarbons in room temperature ionic liquids (RTILs). Specifically, we investigated the electro-reductive dechlorination of the model halocarbon, carbon tetrachloride over glassy carbon electrode (GCE) and palladium-graphene (Pd-Gr), silver-graphene (Ag-Gr) and palladium-silver-graphene (PdAg-Gr) nanocomposites in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]). Analysis of the voltammetric data in light of Marcus-Hush formulation reveals that the electro-reductive cleavage of the C-Cl bond of CCl4 over GCE in [BMIM][NTf2] follows a sticky dissociative electron transfer (SDET) pathway. The significantly stronger interaction energy between electrogenerated Cl- and CCl3˙ (radical) fragments in RTILs makes electroreduction of CCl4 in [BMIM][NTf2] much easier than in organic solvents. The activation-driving force relationship for electro-catalytic dechlorination of CCl4 over Pd-Gr was observed to follow a modified sticky dissociative electron transfer model wherein apart from the ion-radical interaction, the adsorptive interaction of chlorinated species with the electrocatalytic surface needs to be taken into consideration to account for the apparent activation energy-driving force dependence. Interestingly the activation energy-driving force relationships for the electroreduction of CCl4 over Ag-Gr and PdAg-Gr were observed to fit a modified stepwise ET (MSET) pathway. In the MSET pathway, the adsorption and the implied free energy change of the electroreducible halocarbon significantly alter the solvent re-organization energy and the inherent barrier for the heterogeneous ET process. The adsorptive interaction and hence the electrocatalytic performance of PdAg-Gr were observed to be more than that observed for Ag-Gr. This is attributed to the Ag to Pd charge transfer in the PdAg-Gr nanodeposits. Our results besides underlining the positive influence of RTILs in facilitating the electroreductive detoxification of halocarbons, very well establish the mechanistic basis for the electrocatalytic performance of graphene based nanodeposits toward electrodehalogenation of halocarbons.

Transforming micelles into mixed micelles: a promising approach to tune the catalytic performance of imidazolium-based surface active ionic liquids toward degradation of rhodamine B.

Herein, we demonstrate that the catalytic performance of imidazolium-based surface-active ionic liquid (SAIL) micelles can be significantly enhanced through the addition of an appropriate type and amount of intelligently conceived amphiphile to form mixed micelles. Specifically, we show that the catalytic performance of 1-dodecyl-3-methyl imidazolium chloride (DDMIMCl) micelles toward the reductive degradation of rhodamine B (RhB), a carcinogenic dye extensively used in multiple industrial applications, can be appreciably boosted through addition of Brij56, a nonionic surfactant. Detailed kinetic investigations on the catalytic performance of pre- and post-micellar concentrations of DDMIMCl and its mixed micelles with Brij56 over various mole fractions, toward the reductive degradation of RhB, are presented. The data analyzed in light of Berezin's kinetic model suggest that the addition of Brij56 to DDMIMCl micelles significantly enhances their catalytic performance. The catalytic activity exhibited by the DDMIMCl-Brij56 (XBrij56 = 0.2) mixed micellar system is better than that reported for many state-of-the-art nanoparticle/homogenous catalysts. The results explained in light of Berezin's kinetic model are well supported by physico-chemical studies like conductometry, fluorimetry and dynamic light scattering. The presented results anticipate stimulation of extensive research activity for exploiting the mixed micellization approach as a novel avenue for modulating the catalytic performance of SAILs.

Exploring Burstein-Moss type effects in nickel doped hematite dendrite nanostructures for enhanced photo-electrochemical water splitting.

The Burstein-Moss (B-M) effect, which suggests that the optical band gap of degenerately doped semiconductors increases when all states close to the conduction band get populated due to shifting of an absorption edge to higher energy, is important, as it gives a chance to obtain different optical properties for the same material. Here, we report our observations of the similar shift in the optical band gap in NixFe2-xO3 nanocomposites as a function of composition with the help of cyclic voltammetry (CV) and XPS valence band (VB) position measurements. The conduction band edge (CBE) position of the NixFe2-xO3 nanocomposites as determined using CV was noted to move towards more negative potential with increasing Ni-concentration. A similar shift is also noted in the CBE estimated using XPS measurements (by subtracting the VB position from the optical band gap values). The observed shift in the optical band gap along with the CBE position gives the corresponding shift in the Fermi level, which is found to move closer to the CBE position, suggesting the observation of an effect similar to the B-M shift. Also, the extent of band bending estimated from the deviation of the CBE from the flat band potential (measured through Mott-Schottky plots) is found to increase with increasing Ni-concentration. Moreover, the Ni-composition has been observed to enhance the current density as well as to facilitate water splitting at a much lower onset potential compared to pure hematite. The NixFe2-xO3 nanocomposite with an 11 mol% Ni-composition shows the highest photo-electrochemical response with an almost ten times enhancement in the current density at 1.9 V vs. RHE in alkaline medium, as compared to the dark current. This enhanced performance is attributed to the improved charge separation and higher charge carrier density as a result of the higher extent of band bending in the NixFe2-xO3 nanocomposites.

Fermi level equilibration of Ag and Au plasmonic metal nanoparticles supported on graphene oxide.

For the first time, the process of Fermi level equilibration has been studied and compared for plasmonic metal nanoparticles (PMNPs) supported on conducting substrates i.e. graphene oxide (GO) sheets. The extent of Fermi level equilibration has been monitored by recording the changes in the position and intensity of the surface plasmon resonance (SPR) band of Ag and Au PMNPs supported on reduced graphene oxide (rGO). Ag PMNPs supported on rGO show larger variation in the SPR band position and intensity as compared to rGO supported Au PMNPs. The average shift in the chemical potential has been determined through the changes in the SPR band position for Ag, Ag@rGO, Au, and Au@rGO, which are approximately -1812 ± 70 mV, -171 ± 20 mV, -96 ± 8 mV and -29 ± 4 mV, respectively. The calculated values of the shift in chemical potential suggest that Ag and its rGO composite are more prone to Fermi level equilibration as compared to the Au and Au@rGO composite. The electrochemical (galvanostatic) charging/discharging (GCD) measurements also brace the observations from the chemical charging/discharging method with minor variations due to the measurements under two different conditions; particulate films in the case of the former versus the dispersed phase in the case of the latter. Moreover, the average capacitance associated with single nanoparticles (Ag and Au) is estimated using the capacitance values determined from GCD curves and the approximate number of nanoparticles determined from the quantity of PMNPs used in the deposited films for GCD measurements. These values are in close agreement with the quantized double layer capacitance values of monolayer protected clusters reported in the literature. A similar inference is also drawn from the enzyme-less glucose sensing activity of these nanostructures, where Ag and Ag@rGO show better activity in terms of lower values of the limit of detection (LOD) and the limit of quantification (LOQ).

Plant leaf extracts as photocatalytic activity tailoring agents for BiOCl towards environmental remediation.

The inducement of plant leaf extracts for the synthesis of various nanostructures has intrigued researchers across the earth to explore the mechanisms of biologically active compounds present in the plants. Herein, a green modified hydrolysis route has been employed for the synthesis of bismuth oxychloride i.e. BiOCl-N, BiOCl-T and BiOCl-A using plant extracts of Azadirachta indica (Neem), Ocimum sanctum (Tulsi), and Saraca indica (Ashoka), and; simultaneously, without plant extract (BiOCl-C), respectively. The as-prepared samples were examined by several microscopic and spectroscopic techniques which revealed that the biosynthesized BiOCl attained certain favorable features such as hierarchical nano-flower morphology, higher porosity, higher specific surface area and narrower band gap compared to BiOCl-C. The degradation of methyl orange (MO) and bisphenol A (BPA) using biosynthesized BiOCl were improved by 21.5% within 90 min and 18.2% within 600 min under visible light irradiation, respectively. The photocurrent response, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) studies indicated the effective inhibition of the electron-hole pair recombination and enhanced photocatalytic activity of the biosynthesized BiOCl.

Facile Green Synthesis of BiOBr Nanostructures with Superior Visible-Light-Driven Photocatalytic Activity.

Novel green bismuth oxybromide (BiOBr-G) nanoflowers were successfully synthesized via facile hydrolysis route using an Azadirachta indica (Neem plant) leaf extract and concurrently, without the leaf extract (BiOBr-C). The Azadirachta indica leaf extract was employed as a sensitizer and stabilizer for BiOBr-G, which significantly expanded the optical window and boosted the formation of photogenerated charge carriers and transfer over the BiOBr-G surface. The photocatalytic performance of both samples was investigated for the degradation of methyl orange (MO) and phenol (Ph) under the irradiation of visible light. The leaf extract mediated BiOBr-G photocatalyst displayed significantly higher photocatalytic activity when compared to BiOBr-C for the degradation of both pollutants. The degradation rate of MO and Ph by BiOBr-G was found to be nearly 23% and 16% more when compared to BiOBr-C under visible light irradiation, respectively. The substantial increase in the photocatalytic performance of BiOBr-G was ascribed to the multiple synergistic effects between the efficient solar energy harvesting, narrower band gap, high specific surface area, porosity, and effective charge separation. Furthermore, BiOBr-G displayed high stability for five cycles of photocatalytic activity, which endows its practical application as a green photocatalyst in the long run.

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.

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.