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A simple and sensitive spectrophotometric method for the quantification of sulfite at trace level has been proposed. The method is based on the change in the intensity of the color developed on reaction of sulfite with Rhodamine-B Phenyl hydrazide (RBPH) in aqueous micellar medium. The experimental conditions such as pH, concentration of RBPH and Tween 80 have been optimized and calibration plot has been constructed. The proposed method offers a wide linearity in the concentration range 0–15 ppm of sulfite. The limit of detection and limit of quantification were found to be 0.006 and 1.5 ppm respectively, with the regression co-efficient R2 = 0.992. The proposed method has been successfully applied to measure the trace level sulfite in food samples such as tomato ketchup, jam, dry grapes, sugar and wine. Comparison of the developed method with standard protocol showed good recoveries.

The elimination of volatile organic solvents in organic synthesis is the most important goal in “Green” chemistry. We report a simple, efficient and facile method for the addition of progargyl bromide to carbonyl compounds using Mg metal as a mediator under solvent-free conditions which could regioselectively generate homopropargyl alcohols efficiently in good to excellent yields. The procedure has advantages such as short reaction time, operationally simple, excellent product yields, high regioselectivity and organic solvent-free.

Minerals and elementary compounds of heavy metals are part of the ecosystem. Because of their high density and property to accumulate in stable forms, they are considered to be highly toxic to animals, plants and humans. Continuous mining activities and industrial effluents are the major sources which are adding toxic heavy metal ions into ecosystem and biota. Hence it is of utmost importance to quantify the levels of heavy metal ions in environmental and biological samples. On the other hand, it is equally important to remove the heavy metal ions and their compounds from the environmental and biological samples. That facilitates the environmental samples to be fit for using, consumption. In this regard, promising quantification methods such as electrochemical, spectrophotometric, naked eye sensing, test strips for spot analysis of heavy metal ions are considered for discussion. The main objective of this chapter is to give the overview of the most practiced quantification approaches available in the literature. Please note that reader cannot find the pin to pin publications regarding the same and that is not the aim of this book chapter.

The RGO/AuNPs/CS/ZnTCPP nanocomposites were successfully prepared with reduced graphene oxide (RGO) loaded with Au nanoparticles (AuNPs) existed in chitosan (CS) and water-soluble zinc meso-tetra (4-carboxylphenyl) porphyrin (ZnTCPP) by π-π nanoassembly method and were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), 1H NMR spectra and UV–vis absorption spectroscopy. The most important advantage of the RGO/AuNPs/CS/ZnTCPP nanocomposites was environmentally friendly. Indium tin oxide (ITO) electrode surface was modified with the RGO/AuNPs/CS/ZnTCPP nanocomposites exhibited a good photocurrent response at −0.2 V under whitelight of Xenon lamp illumination. The photocurrent response could be greatly increased by adding hydroquinone (HQ) to the solution. Electrons of ZnTCPP were excited from HOMO to LUMO by irradiating light. The photoexcited electrons injected into the RGO, and then transferred to AuNPs further to the ITO. Addition of HQ resulted in the enhanced photocurrent signal by acting as a sacrificial electron donor; Thereby scavenged the photogenerated holes of the excited ZnTCPP and oxidized to benzoquinone (BQ). Based on the above interaction, detection of HQ was developed by a novel photoelectrochemical (PEC) sensor (S/N = 3) with a linear range from 5 to 300 nmol/L (r = 0.997) and detection limit of 0.5 nmol/L. Proposed biosensor is simple, rapid and this was successfully applied for the quantification HQ in the real sample matrices.

How to improve the accuracy of target detection substance in low-content and complex of real sample, which is still a major challenge in the analysis field. There is no doubt that the internal standard method is the best choice in the analysis methods. The internal standard method of ECL strategy can furnish more accurate detection results in the changeable complex environment, and it can dispel the primary vaguest interference in the system through the self-calibration of two emission spectra. Herein, we effectually explored a strong and stable bimodal ECL system based on graphitic carbon nitride quantum dots (g-CNQDs) as single luminophore in the presence of double coreactants potassium persulfate (K2S2O8) and tetrabutylammonium bromide (TBAB) under the optimized conditions. ECL-1 at 2.82 V and ECL-2 at 1.73 V were observed when the potential was scanned between −3 and 3 V at the scan rate of 0.2 V·s–1. The ECL-1 was responding to the analyte, that is, ascorbic acid (AA) and the ECL-2 was not for a cert...

The design and synthesis of highly active hydrogen evolution reaction (HER) catalyst with strong stability is highly desirable and challenging. In this work, we followed simple two-step strategy to grow Nickel–Cobalt phosphide nanowires (NiCoP NWs) directly on the Ni foam (NF) by hydrothermal method. Catalytic current density of 10 mA cm −2 at an overpotential of 118 mV has been obtained. Prepared material exhibited long-term stability and nearly 100% Faradaic efficiency in 0.5 M H 2 SO 4 for HER. Ni and Co composite materials with amorphous structure are considered as better catalysts by exhibiting the higher activity. The results in this paper might promote further development of the advanced catalysts for special electrochemical properties and other devices.

In this study, graphene grafted Ag 3 PO 4 @AgBr (GO-Ag 3 PO 4 @AgBr) composite with enhanced photocatalytic performance was synthesized via in situ fabrication method. The synthesized composite was characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The GO-Ag 3 PO 4 @AgBr composite was exhibited higher activity than Ag 3 PO 4 @AgBr and bare Ag 3 PO 4 . The material characterization and the detailed study of the various parameters which affect the photocatalytic reaction, revealed that the enhanced catalytic activity is related to the surface electric property of the synthesized catalyst. The investigation of the energy band structure further considered as a reason for the enhancement of the multi-electron reaction. Furthermore, the effect of illuminated light on the catalytic performance was also investigated. The results indicated that simulated sunlight significantly affects the catalytic activity compared with visible light. In addition, the photocatalytic experimental conditions were tested, and sonication of the dye/catalyst reaction system for 10 min was selected to be the optimum condition to establish absorption – desorption equilibrium. This work could supply a new way to use natural sunlight to facilitate the practical application of photocatalysts in environment issues.

A simple strategy has been proposed for the covalent anchoring of cobalt hexacyanoferrate (CoHCF) particles on graphitic carbon substrate using p-phenylenediamine as a linker molecule. The covalent anchoring was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and electrochemical studies. A robust pellet electrode was fabricated using CoHCF particles modified graphitic carbon and it has been applied in the electrocatalytic oxidation of sulfite. The proposed sensor showed a linearity in the concentration range 4–128 μM of sulfite with a limit of detection (LOD) 1.7 μM and limit of quantification (LOQ) 5.8 μM. Proposed sensor has been successfully applied to measure sulfite levels from a variety of food sample matrices. The results obtained by the proposed electrochemical sensor have been compared with the iodimetric method.

An electrochemical sensor for dopamine (DA) has been developed based on the electrografting of 4-aminobenzene sulfonic acid (4-ABSA) onto the graphite pencil lead electrode (GPLE). The process of covalent anchoring and presence of 4-ABSA on the GPLE was studied using cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical behaviour of the sensor towards DA, ascorbic acid (AA), and uric acid (UA) was studied in detail in phosphate buffer of pH 7. After optimizing the various parameters that influence the differential pulse voltammetric (DPV) signal for DA, the sensor exhibited a linear response over the 0.5 – 10 μmol⋅L-1concentration range with a limit of detection, 0.095 μmol⋅L-1 (at an S/N of 3). The sensor can selectively quantify DA even in the presence of 1 mmol⋅L-1 AA. Distinct DPV signals were obtained for DA (at 0.191 mV vs. Ag/AgCl) and for UA (at 0.343 mV vs. Ag/AgCl). The sensor is highly selective, sensitive and stable. It was applied to the quantification of DA in injections and urine. Recovery studies were done by spiking both the real samples with a known quantity of DA.

Recent research suggests that transition metal phosphides (TMPs) are one of the most promising nobel-metal-free electrocatalysts for catalyzing the hydrogen evolution reaction. In this study, we report rectangular CoP nanosheet (NS) arrays on carbon cloth (CoP NS/CC) via a concise two-step synthetic method. The 3D rectangular CoP NS/CC with a three-dimensional porous and self-supported structure was fabricated via a hydrothermal method, followed by a low-temperature phosphidation treatment. Such 3D rectangular CoP NS/CC, as an HER electrocatalyst in acidic solution, exhibited high activity, good stability, and nearly 100% Faradaic efficiency (FE). The electrocatalyst requires an overpotential of 92, 112 and 195 mV to achieve current densities of 10, 20 and 100 mA cm−2, respectively, and maintain its catalytic stability for more than 50 h. In addition, the electrocatalyst works well in a neutral environment.

J- and H-aggregates of zinc tetraphenylporphyrin (ZnTPP) on carbon nanotube films (CNTFs) were prepared using the mixed solvent method. This resulted in completely different structures, such as the four-leaf clover and flower, on the CNTF, which were observed by recording SEM images. Characteristic changes in the electronic spectra of the ZnTPP monomer appeared when it underwent J- and H-aggregation. The measured photocurrent significantly varied for the same molecule when it was aggregated in two different ways on ITO and ITO/CNTF. The electron recombination resistance of the two aggregates, which was investigated using electrochemical impedance spectroscopy, was also different. The photocatalytic efficiency of the J- and H-aggregates was examined by performing methylene blue dye decoloration studies. In addition, a scanning electrochemical microscope was used to investigate the photoinduced charge transfer kinetics of the J- and H-aggregates at the electrode/electrolyte interface as a fresh attempt. The heterogeneous charge transfer constants for the J- and H-aggregates in the presence of light at varied intensities were calculated. Thereby, striking differences in the photophysical, photocatalytic, and photoelectrochemical properties of the J- and H-aggregates were visualized throughout our studies.

The cathodic electrochemiluminescence (ECL) behavior of meso-tetra(4-sulfonatophenyl)porphyrin (TSPP) with potassium peroxydisulfate (K2S2O8) as the coreactant in aqueous solution with strong and stable emission was exploited to determine Cu(2+) down to nanomolar concentration. Two possible reaction mechanisms have been proposed to understand the generation of ECL by the TSPP/K2S2O8 system. The effects of the concentration of TSPP and K2S2O8, pH of the medium, and scan rate on the ECL intensity were studied in detail. The ECL intensity was efficiently quenched by trace amounts of Cu(2+). This phenomenon was used to develop a new method, which can offer rapid, reliable, and selective detection of Cu(2+). Under the optimum conditions, plots of the ECL of the TSPP/K2S2O8 system versus the concentration of Cu(2+) are linear in the range of 5 to 160 nM with a detection limit of 1.56 nM (S/N = 3). The proposed ECL sensor was successfully applied for analysis of tap and river water samples. It is anticipated that TSPP could be a new class of promising luminescent agent for ECL sensors. Graphical Abstract A two-step cathodic elelctrochemiluminescence (ECL) behavior of TSPP/K2S2O8 system in the aqueous solution and Cu(2+) determination using the same.

In this paper, an easy carbon radicals reaction procedure is put forward to functionalized graphene-supported Pt–Pd bimetallic nanoparticles (NPs). To begin with, graphene was functionalized with carboxylic sodium electro-catalyst through method of π–π interaction, which could provide more binding sites for Pt–Pd NPs. Then a fast method of in-situ electrochemical reduction was developed to synthesize highly dispersed Pt–Pd NPs on functionalized graphene. The prepared nanocomposite was characterized by Raman spectroscopy, thermogravimetric analysis (TGA), Fourier transformed infrared spectrometry (FT-IR), scanning electron microscopy (SEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and electrochemical technique. The obtained nanocomposite shows much high catalytic activity and long-term stability towards methanol oxidation than that of Pt or Pd black. It was suggesting the synergetic effects of bimetallic NPs. Moreover, it demonstrates that the incorporation of the carbon radical reaction with electrochemical reduction method is a novel approach to functionalize graphene. Our study may provide a new insight into electro-oxidation of methanol on bimetallic material.

A simple amine embellished tube array was assembled at the liquid–liquid interface to study ion transfer behavior. Variation in the pH of the solution resulted in three different protonation states at the amino groups of the nanochannel, which in turn regulated ion transport, similar to the switching effect of ion channels in vivo.

Recombination of photogenerated electron-hole pairs is extremely limited in the practical application of photocatalysis toward solving the energy crisis and environmental pollution. A rational design of the cascade system (i.e., rGO/Bi2 WO6 /Au, and ternary composites) with highly efficient charge carrier separation is successfully constructed. As expected, the integrated system (rGO/Bi2 WO6 /Au) shows enhanced photocatalytic activity compared to bare Bi2 WO6 and other binary composites, and it is proved in multiple electron transfer (MET) behavior, namely a cooperative electron transfer (ET) cascade effect. Simultaneously, UV-vis/scanning electrochemical microscopy is used to directly identify MET kinetic information through an in situ probe scanning technique, where the "fast" and "slow" heterogeneous ET rate constants (Keff ) of corresponding photocatalysts on the different interfaces are found, which further reveals that the MET behavior is the prime source for enhanced photocatalytic activity. This work not only offers a new insight to study catalytic performance during photocatalysis and electrocatalysis systems, but also opens up a new avenue to design highly efficient catalysts in photocatalytic CO2 conversion to useful chemicals and photovoltaic devices.

Almost all life activities involve the process of multistep electron transfer (ET) which occurs on biomembrane. Metalloporphyrins (MTPPs) are a class of molecules which are closely related to life course. Here, the n-step (n = 1, 2) ET behaviors controlled by different metal ions in porphyrin cores were investigated by thin-layer cyclic voltammetry (TLCV). The bimolecular ET was reacted between the MTPP (M = Fe, Zn, Co, Cu, Ni) and Fe(CN)64– in nitrobenzene and aqueous phase, respectively, and the interface between nitrobenzene and aqueous phase was considered as a bionic membrane. The thin-layer theory, which has been revised, was used to calculate the kinetic constants for each step electron transfer reactions. It was shown that the kinetic data were affected dramatically by the different coordinated ions in porphyrin complexes.

The GO-COOH/AuNPs/ZnAPTPP nanocomposites were constructed using zinc monoamino porphyrin (ZnAPTPP) through π–π conjugation with carboxylated graphene oxide (GO-COOH) loaded with Au nanoparticles (AuNPs). Prepared materials were characterized by 1 H NMR spectra, UV–vis absorption spectroscopy and electrochemical impedance spectroscopy. ITO electrode surface was modified with the prepared nanocomposites showed a good photocurrent response when the bias potential, −0.1 V was applied. Nanocomposites modified ITO electrode exhibited good photo-response to the 4-nitrophenol (4-NP). ZnAPTPP were excited from HOMO to LUMO under light irradiation, the photoexcited electrons injected into the conduction band of GO-COOH, and then transferred to AuNPs further to the ITO. The presence of GO-COOH and AuNPs improved the separation of photogenerated charges due to their synergetic effect and excellent conductivity. Externally added 4-NP scavenges the photogenerated holes i.e. it acts as a sacrificial electron donor thereby it enhances the photocurrent of the system. Based on this interaction, a novel method for photoelectrochemical detection of 4-NP was developed with a linear range from 0.1 to 15 nmol/L (r = 0.996) and detection limit of 0.04 nmol/L (S/N = 3). Proposed method is simple and sensitive and this was successfully applied for the quantification 4-NP in river water sample matrices.

The novel membrane test strip of phenolphthalein hydrazide (PH)-polysulfone has been designed and demonstrated for Cu2+ ions detection. Before finding performance of membrane the studies with PH alone has been performed. Aqueous solutions of PH are colorless, but upon interaction with Cu2+ ions become pink (when 8.2 ≤ pH ≥ 12). The colorimetric change is initiated by the coordination of Cu2+ with PH as a polydentate ligand, opening the spirolactam ring that subsequently hydrolyses releasing phenolphthalein (P). Further membrane was preloaded with PH that could be used as a simple, low cost, and portable sensor for Cu2+ ions in environmental water samples. Given the detection limits of this sensor, a maximum response would warn the tester that Cu2+ concentrations were above safe drinking regulation values. Approximate concentrations can be determined via a color comparison chart. Different metal ions were tested in order to determine the chemodosimeters specificity, of the 12 tested ions only Hg2+ induced a similar molecular transformation (i.e., PH to P). The chemodosimeter allows the quantification of Cu2+ ions in the linear dynamic range of 0–22 μM. The Sandell sensitivity, limit of detection, limit of quantification, and relative standard deviation were found to be 0.276 μg/mL/cm2, 0.279 μM, 1.674 μM, and 0.682% respectively.

A new protocol toward the synthesis of cobalt nitroprusside (CoNP) coordination nanoparticles has been described based on drop-by-drop (DbD) method without using any additives. It was also prepared by sonication as well as bulk mixing methods for comparison purpose. The prepared complex was characterized by Infrared spectroscopy (FTIR), XRD and cyclicvoltammetry (CV) techniques. The CoNP complexes prepared by different synthetic approaches were used as modifier molecules to fabricate carbon paste electrodes (CPE's) toward electrochemical oxidation of sulfite. The experimental results revealed that the cobalt nitroprusside nanoparticles (n-CoNP) prepared by drop-by-drop method showed a considerable enhancement in the electrocatalytic activity when compared to its counterparts prepared by other approaches. Electrochemical behavior of the n-CoNP CPE was studied and used as an electrochemical sensor for the quantification of sulfite at trace level. It showed a linear response over the concentration range 1–5.9 × 10−5 M and 2–8 × 10−3 M of sulfite. The limit of detection and limit of quantification were found to be 0.4 × 10−5 M and 2.29 × 10−5 M respectively. The interference of various organic acids and inorganic ions commonly present in different food and water sample matrices were studied. The n-CoNP modified electrode was used for the quantification of sulfite in different food samples and the results were in good agreement with those obtained by the standard iodometric protocol.

A simple spectrophotometric method has been developed for the quantification of dissolved sulfide based on its reaction with ferric iron and the subsequent reaction of ferrous iron with 1-nitroso-2-naphthol in alkaline medium. The insoluble iron(II)-ligand complex has been solubilized in micellar medium using neutral surfactant which facilitates the non extraction step. The method obeys Beer’s law in the concentration range 0.5–8 μg in 10 mL of aqueous phase. The complex showed an absorption maximum at 710 nm with e value of 4.11 × 104 L/mol cm. The detection limit has been found to be 0.0036 μg/mL. The interference of common cations and anions has been studied and the proposed method has been successfully applied to determine the sulfide in different sewage water samples.

Iron nitroprusside (FeNP) particles have been synthesized from drop by drop (n-FeNP) and bulk mixing (BM) (b-FeNP) methods. FeNP particles obtained from both methods were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). n-FeNP particles were used in constructing modified carbon paste electrode (CPE), which has been further used for electrochemical studies. The effect of pH and electrolyte cation on the electrochemical behavior of n-FeNP modified CPE has been studied in detail. Oxidation of nitrite and reduction of peroxodisulfate reactions have been electrocatalyzed at two redox centers of n-FeNP modified CPE. Based on the electrochemical experiments conducted and Tafel plots, mechanism for both the reactions has been proposed. Both the analytes were estimated in soil and ground water samples using n-FeNP modified CPE and the results were validated with the help of standard methods.

Porphyrin is one of the most attractive molecules for its well known functions in biological and biomimetic systems because of their excellent stability, unique optical and electronic properties.Their electrochemical and photophysical properties make porphyrin derivatives combine with a complementary electron-accepting species to mimic the electron transport of biological process based on the formation of electron donor/acceptor(D/A) system.So Porphyrin compounds are widely employed as platform to recognize various species. Photoinduced charge transfer (PCT) plays a central role in biologically significant systems and in applications that harvest solar energy. The electron-rich macrocyclic compounds such as porphyrins have been widely used as biomimetic photosensitizing electron donor in these studies, since they absorb lights over wide wavelengths in the visible region and exhibit favorable redox potentials. Our group mainly focus on the PCT kinetics, electron transfer mechanisms of porphyrin and its derivarives. Scanning electrochemical microscopy (SECM), Electrochemical Impedance spectroscopy are the techniques that have been used extensively in our investigatios. Self-assembled monolayers (SAMs) of thiol-porphyrins with different alkyl chain length (H2TPPO(CH2)nSH, n=3, 6, 9 and 12)，thiol-derivatized tetraphenylporphyrin (SH-TPP) and cobalt tetraphenylporphyrin (SH-CoTPP) on gold electrode have been prepared and their structure, direct electron transfer (ET) process， electrochemical behaviors of a series of SH-Terminated-Functionalized Porphyrinswas studied by electrochemical impedance spectroscopy and SECM. SAMs of thiol-derivatized tetraphenylporphyrin on Gold electrodes was designed to detect H2PO4 -even in the presence of a 10-fold excess of other anions. Substituent effects of iron porphyrin complexes on the structures and kinetic processes have been studied. We developed a novel SECM model which provide a two-dimensional quantitative analysis on a heterogeneous electron transport (ET) process of a functionalized porpyrin by photoinduced ET at the ITO/liquid interface. Our liquid-liquid interface works include but not restricted to the following examples. Investigation of Ion Transport Traversing the “Ion Channels”, Consecutive electron transfer of metalloporphyrin species containing different substituents at the Liquid/Liquid Interface by thin-layer cyclic voltammetry, electrochemical properties of metalloporphyrin species at the Liquid/Liquid interface by switching substitutes on the porphyrin ring, current oscillatory phenomena based on Fe3+/Fe2+at the liquid/liquid interface. Potential electrochemical sensors have been developed for the anaytes which are of environmenal and biological significance. Few examples are, an electrochemical method for the detection of DNA damage by combining the layer-by-layer assembly film with adriamycin (ADM) as an electrochemical probe, recognition of -1,3-glucanase gene (Glu) specific sequence based on probe extension, electrochemical behavior of hydroquinone (HQ) was studied by cyclic voltammetry at a glassy carbon electrode (GCE) modified by a gel containing multi-walled carbon nanotubes (MWNTs) and room temperature ionic liquid (RTIL) of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6), investigation of the mechanism of the N-H migration in asymmetrical metal-free porphyrins, four porphyrins of electron-withdrawing or electron-donating substituent at the -position were studied theoretically visual colorimetric and electrochemical biosensor for porphyrin, Ag nanoparticles on functionalized graphene for an excellent electrochemical sensor of nitroaromatic compounds methyl-parathion pesticide, based on the advantages of porphyrin and porphyrin derivatives, we envisioned the introduction of the hydroxyphenyl-porphyrin into CNTs could enhance the sensitivity of the detection of explosives basedon the synergetic effects of porphyrin and CNTs.