Synthesis of Copper(I) Oxide Particles with Variable Color:Demonstrating Size-De

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Synthesis of Copper(I) Oxide Particles with Variable Color:Demonstrating Size-Dependent Optical Properties
Introduction Cluster based materials exhibit considerable advantages over bulk materials including surface features, electrostatic fields and reactivity that can differ and/or be varied as a function of both composition and cluster size. Nanocrystals formed from semiconductor materials with diameters of 1 – 30 nm are often referred to as quantum dots. Quantum dots are already in commercial use in sensors, LEDS and lasers including those used as readers for HD-DVD and Blu-ray high-definition DVDs. The spectral properties of quantum dots arise from a quantum confinement effect. When an electron in these semiconducting materials is excited into the conduction band a hole is created in the valence band. The physical distance between the location of the excited electron and the hole it came from is called the Bohr exciton radius (rB). In a bulk semiconductor crystal rB is small compared to the overall size of the crystal and the electron can migrate freely through the lattice. However, in the nanoscale quantum dot, rB is close to the diameter of particle and the electron is trapped in molecular orbitals rather than bands of orbitals. The energy spacing of these molecular orbitals depends on the number of atoms and hence the size of the crystal. Consequently, the excitation or absorption energy changes with the size of the quantum dot. As the dot gets bigger the absorption energy moves to lower frequency and the colour of light reflected changes from blue to red.
In this experiment you will synthesise micro- and nanosized copper(I) oxide particles with size-dependent optical properties by reducing alkaline copper(II)citrate complex (Benedict’s reagent) with glucose. The Cu2O particles varies from hundreds of nanometers to micrometers depending on concentrations of initial reagents and their colour varies from yellow to dark red, accordingly. Shown below are the electron-half-equations (a, b) and summary redox reaction (c) between copper(II) 25 ions and -hydroxy-ketone group of reducing sugars (e.g., fructose) in open-chain form. Redox reaction is activated by transformation of -hydroxy-ketone group to enediol via keto-enol tautomerization in alkali solutions. a) Oxidation: R1CH(OH)COR2 + 2 OH R1COCOR2 + 2 H2O + 2 e b) Reduction: 2Cu(in complex)2+ + 2 OH + 2 e Cu2O + H2O c) Summary: R1CH(OH)COR2 + 2Cu2+ + 4 OH R1COCOR2 + Cu2O + 3H2O
Question1: How do the measured wavelength maxima compare with the observed colours of the solutions?
Synthesis of Copper(I) Oxide Particles with Variable Color:Demonstrating Size-Dependent Optical Properties
Introduction Cluster based materials exhibit considerable advantages over bulk materials including surface features, electrostatic fields and reactivity that can differ and/or be varied as a function of both composition and cluster size. Nanocrystals formed from semiconductor materials with diameters of 1 – 30 nm are often referred to as quantum dots. Quantum dots are already in commercial use in sensors, LEDS and lasers including those used as readers for HD-DVD and Blu-ray high-definition DVDs. The spectral properties of quantum dots arise from a quantum confinement effect. When an electron in these semiconducting materials is excited into the conduction band a hole is created in the valence band. The physical distance between the location of the excited electron and the hole it came from is called the Bohr exciton radius (rB). In a bulk semiconductor crystal rB is small compared to the overall size of the crystal and the electron can migrate freely through the lattice. However, in the nanoscale quantum dot, rB is close to the diameter of particle and the electron is trapped in molecular orbitals rather than bands of orbitals. The energy spacing of these molecular orbitals depends on the number of atoms and hence the size of the crystal. Consequently, the excitation or absorption energy changes with the size of the quantum dot. As the dot gets bigger the absorption energy moves to lower frequency and the colour of light reflected changes from blue to red.
In this experiment you will synthesise micro- and nanosized copper(I) oxide particles with size-dependent optical properties by reducing alkaline copper(II)citrate complex (Benedict’s reagent) with glucose. The Cu2O particles varies from hundreds of nanometers to micrometers depending on concentrations of initial reagents and their colour varies from yellow to dark red, accordingly. Shown below are the electron-half-equations (a, b) and summary redox reaction (c) between copper(II) 25 ions and -hydroxy-ketone group of reducing sugars (e.g., fructose) in open-chain form. Redox reaction is activated by transformation of -hydroxy-ketone group to enediol via keto-enol tautomerization in alkali solutions. a) Oxidation: R1CH(OH)COR2 + 2 OH R1COCOR2 + 2 H2O + 2 e b) Reduction: 2Cu(in complex)2+ + 2 OH + 2 e Cu2O + H2O c) Summary: R1CH(OH)COR2 + 2Cu2+ + 4 OH R1COCOR2 + Cu2O + 3H2O
Question1: How do the measured wavelength maxima compare with the observed colours of the solutions?
Synthesis of Copper(I) Oxide Particles with Variable Color:Demonstrating Size-Dependent Optical Properties
Introduction Cluster based materials exhibit considerable advantages over bulk materials including surface features, electrostatic fields and reactivity that can differ and/or be varied as a function of both composition and cluster size. Nanocrystals formed from semiconductor materials with diameters of 1 – 30 nm are often referred to as quantum dots. Quantum dots are already in commercial use in sensors, LEDS and lasers including those used as readers for HD-DVD and Blu-ray high-definition DVDs. The spectral properties of quantum dots arise from a quantum confinement effect. When an electron in these semiconducting materials is excited into the conduction band a hole is created in the valence band. The physical distance between the location of the excited electron and the hole it came from is called the Bohr exciton radius (rB). In a bulk semiconductor crystal rB is small compared to the overall size of the crystal and the electron can migrate freely through the lattice. However, in the nanoscale quantum dot, rB is close to the diameter of particle and the electron is trapped in molecular orbitals rather than bands of orbitals. The energy spacing of these molecular orbitals depends on the number of atoms and hence the size of the crystal. Consequently, the excitation or absorption energy changes with the size of the quantum dot. As the dot gets bigger the absorption energy moves to lower frequency and the colour of light reflected changes from blue to red.
In this experiment you will synthesise micro- and nanosized copper(I) oxide particles with size-dependent optical properties by reducing alkaline copper(II)citrate complex (Benedict’s reagent) with glucose. The Cu2O particles varies from hundreds of nanometers to micrometers depending on concentrations of initial reagents and their colour varies from yellow to dark red, accordingly. Shown below are the electron-half-equations (a, b) and summary redox reaction (c) between copper(II) 25 ions and -hydroxy-ketone group of reducing sugars (e.g., fructose) in open-chain form. Redox reaction is activated by transformation of -hydroxy-ketone group to enediol via keto-enol tautomerization in alkali solutions. a) Oxidation: R1CH(OH)COR2 + 2 OH R1COCOR2 + 2 H2O + 2 e b) Reduction: 2Cu(in complex)2+ + 2 OH + 2 e Cu2O + H2O c) Summary: R1CH(OH)COR2 + 2Cu2+ + 4 OH R1COCOR2 + Cu2O + 3H2O
Question1: How do the measured wavelength maxima compare with the observed colours of the solutions?

Explanation / Answer

any given solution will absorb light of a particular wavelength (will be called as wavelength maximum) .

Each wavelength corresponds to a colour in the visible light spectrum.

The perceived color of the solution exhibits a kind of complementary relation with the color (wavelength) of the visible light absorbed.

For example:

if the solution appears to be blue then it implies that it is abosrbing all lights except blue and so it is exhibiting blue colour.

So if we plot a graph between transmittance and wavelength then it will show a maxima at the wavelenght corresponding to the wavelength of blue colour.

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