After carbon, hydrogen, and oxygen, nitrogen is the next most abundant element in the human body. Inorganic and organic compounds of nitrogen feature prominently in many biological and environmental, as well as industrial, processes. In nature, the inorganic compounds of nitrogen are controlled by a reaction cycle called the nitrogen cycle (Figure 1).1 The denitrification pathway in this cycle, that is, the conversion of nitrate to dinitrogen, is employed by certain bacteria to produce ATP anaerobically and gain energy for cell growth. All organisms use ammonia as one of the starting building blocks for the synthesis of amino acids, nucleotides, and many other important biological compounds. Nitric oxide is * Corresponding author. E-mail: m.koper@chem.leidenuniv.nl. † Present address: Energy research Centre of The Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands. ‡ Present address: Research, Development & Innovation, AkzoNobel Chemicals bv, Velperweg 76, P.O. Box 9300, 6800 SB Arnhem, The Netherlands. Chem. Rev. 2009, 109, 2209–2244 2209

Nitrogen cycle electrocatalysis.

This article reviews fundamental aspects of deposition, structure and electrochemistry of Prussian Blue and its analogues. Special attention is given to the metal hexacyanoferrates with potential analytical applications. Prussian Blue and its analogues as advanced sensing materials for nonelectroactive ions are discussed. In contrast to common ‘smart materials’, the sensitivity and selectivity of metal hexacyanoferrates to such ions is provided by thermodynamic background. Prussian Blue itself is recognized as the most advantageous low-potential transducer for hydrogen peroxide over all known systems. Both high sensitivity (ca. 1 A M−1 cm−2) and selectivity in relation to oxygen reduction are more than three orders of magnitude higher, than for platinum electrodes. Biosensors based on different transducing principles containing enzymes oxidases are compared, and the devices operated due to hydrogen peroxide detection with the Prussian Blue based transducer are shown to be the most advantageous ones. The future prospects of chemical and biological sensors based on metal hexacyanoferrates are outlined.

Prussian Blue and Its Analogues: Electrochemistry and Analytical Applications

This review focuses on the electrosynthesis, in situ characterization, and technological applications of Prussian blue analogues with the generic formula AhMk[Fe(CN)6]l·mH2O, where h, k, l, and m are stoichiometric numbers, A = alkali metal cation, and M is a transition metal. Six such metal hexacyanoferrate (MHCF) compounds derived from Cu, Pd, In, V, Co, and Ni are featured in this article against the backdrop of the Prussian blue parent compound itself and other related compounds. The use of cyclic voltammetry and complementary techniques including scanning probe microscopies, quartz crystal microgravimetry, and ac impedance spectroscopy, for studying the growth of MHCF films on targeted substrates, is discussed. Spectroelectrochemical in situ characterization of these films in the UV−visible and IR regions is then reviewed. Finally, the use of Prussian blue and its analogues in devices for displays and “smart” windows, photoimaging, environmental remediation, chemical/biological sensing, energy conver...

Metal Hexacyanoferrates: Electrosynthesis, in Situ Characterization, and Applications

Biomass-derived nitrogen-doped carbon quantum dots: highly selective fluorescent probe for detecting Fe3+ ions and tetracyclines.

The past decade has witnessed the emergence of carbon dots (c-dots), outshining other members of the carbon family because of their outstanding properties in fluorescence, cytocompatibility, photostability, electronic, mechanical and other chemical properties. This has resulted in an increasing number of applications in bioimaging, sensing, photovoltaic and medicine. Nature offers a wealth of exciting precursors that motivate constant persuasion of benign synthetic routes. Consequently, the past 5 years has seen a tremendous rise in green synthetic approaches of c-dots. This study reviews the journey of green c-dots by means of green sources of synthesis and their applications, with the major focus on various sensors and bioimaging probes.

Sustainable carbon-dots: recent advances in green carbon dots for sensing and bioimaging

Green synthesis of highly fluorescent carbon quantum dots from sugarcane bagasse pulp

Preparation and physicochemical characterization of cellulose nanocrystals from industrial waste cotton

A newly modified electrode was prepared by mechanical immobilization of copper hexacyanoferrate (CuHCF) on a graphite electrode. The modified electrode was characterized by cyclic voltammetric experiments. The effect of different background electrolytes, pHs and scan rates on the electrochemical behaviour of the electrode has been evaluated. In NH4Cl two reversible redox peaks were observed. The first redox peak corresponding to Cu+/Cu2+ is observed only in this medium. The second redox peak corresponds to the Fe(CN)6

 4–/Fe(CN)6

 3– couple. Both anodic peaks were used for catalytic oxidation of ascorbic acid. As the anodic current for catalytic oxidation was proportional to the amount of ascorbic acid, an analytical method was developed for the determination of ascorbic acid in commercial samples.

Characterization and application of an electrode modified by mechanically immobilized copper hexacyanoferrate

Copper hexacyanoferrate (CuHCF) modified graphite electrode prepared by mechanical immobilisation method has been used for the amperometric determination of sulphite, which can be extended for the determination of SO 2 in air after absorbing the pollutant in sodium hydroxide solution. This method is based upon the electrocatalytic oxidation of sulphite by the modified electrode. The pH of the medium for oxidation should be in the range of 3.5–8.0. The range of determination of SO 2 is from 5.1 to 30.7 ppm. The presence of H 2 S with SO 2 will interfere in the determination. This can be eliminated by precipitating H 2 S as CuS.

Chemically modified sensor for amperometric determination of sulphur dioxide

A chemically modified amperometric sensor was constructed by mechanically immobilizing cobalt hexacyanoferrate onto the surface of a paraffin impregnated graphite electrode (PIGE) The cyclic voltammogram of the electrode exhibited two reversible redox peaks corresponding to Co 2+ /Co 3+ and Fe(CN) 6 4− /Fe(CN) 6 3− reactions Thiosulphate was found to undergo electrocatalytic oxidation at a reduced overpotential with good sensitivity in a wider pH range at the modified electrode The sensor showed good stability and reproducibility Under optimal condition, the sensor showed a linear response for thiosulphate in the concentration range from 4×10 −5 to 48×10 −4  M with a correlation coefficient of 09972 and the detection limit was 18×10 −5  M (S/N=3) The sensor has been applied for the determination of thiosulphate in the photographic effluents

D. Ravi Shankaran

Papers

Green synthesis of highly fluorescent carbon quantum dots from sugarcane bagasse pulp

Preparation and physicochemical characterization of cellulose nanocrystals from industrial waste cotton

Characterization and application of an electrode modified by mechanically immobilized copper hexacyanoferrate

Chemically modified sensor for amperometric determination of sulphur dioxide

Amperometric sensor for thiosulphate based on cobalt hexacyanoferrate modified electrode