F100 Chemistry

Question:

1- What is the fading?

Why does that happen?

2- Two molecular structures that have been known to fade are the ones responsible for Methylene blue

Three conditions under which molecules begin to fade, and the chemical processes leading to fading. Other factors could also play a part in the process.

4. Is there a known reaction mechanism for molecules that fade? For example, studies have been done on the fading of Thiazole orange, DODC, and Methylene blue.

5 Describe the kinetics and effects of this fading process

6- Explain with figure how oxygen (singlet oxygen), can be used to explain photobleaching in biological stains.

7- The kinetic insights into Methylene blue’s mechanism for fading thiazole orange and Methylene blue

Answer:

The Causes of Color Fade and Its Effects

The garment’s molecular attractivity to the pigment loses its molecular affinity with the fabric, which can lead to color fading.

As a result of chemical reactions, the dye is incorporated with the fabric as a component of the fabric.

Photo fading can occur when the intensity of dyed materials is reduced by UV light sources.

It can also be described as the removal of excess energy or absorbed energy. The following are some ways that fading can occur:

Radiation emission, or the interaction between the phosphorescence and the fluorescence

Other possible causes of fading include photochemical (Oster and Wotherspoon 1957).

Radiation less transitions could also be caused by factors such as intersystem crossing or internal energy conversion.

A very low pH or high pH could also cause the breaking of the azo bonds, which could be an example process.

Jablonski Schem: This diagram shows the difference between phosphorescence & fluorescence, or in other words it can help explain the photochemistry behind textile dyes.

This diagram shows the crucial transition between electronic states of fiber molecules and dyes components.

The excited electronic states are created when the ground state molecules absorb the light (S0), and then the excited state molecules (S1 or S2).

As the excited states are short-lived, they tend to be shorter than those of the molecules that tend to remain at the ground state.

Photochemical reactions: The photochemical reactions that are most commonly derived from triplets generally result from those who live for 10s or less from 100ns.

The life expectancy of the excited singlet is much lower at 1-1000 ps.

Intersystem reactions might occur during the degradation reaction. This could lead to the molecule living for a shorter time than the excited singlet.

It is possible for the molecules to reach high vibrational levels, which could lead to an accelerated reaction.

Radiationless transitions are possible because of internal energy conversion, intersystem crossing or vibrational relaxation.

The diagram above shows the radiationless transition using wavy lines that could be macroscopically observable due to heat evolution.

Radiationless transition occurs due to the intersystem crossing or internal energy conversion. This can also be called the iso-energic or as no change in overall energie.

Radiation: This radiation is emitted from excited states at the lowest vibrational levels of ground state. It could also be called fluorescence.

The radiation that is emitted from the ground state, starting at the lowest triplet T, can be called phosphorescence.

Photochemical reactions: The triplet states are responsible for the most common photochemical reactions. They have a limited lifespan of between 10 s and 100ns.

The lives of the excited singlet state are between 1 and 1000ps. They also live much less than the lives of the ground state element, which is responsible for the efficient chemical reaction.

Condensed phase is formed when the excited singlet relaxes. This can lead to the loss of thermal energy to those singlets that were lowest excited, which in turn leads to insignificance in chemical reactions.

HD* singlet excited states are produced when a molecule absorbs light. They tend to be too brief-lived for conventional photochemical reaction.

Photo-oxidation using singlet oxygen: The triplet-triplet excitation with oxygen results in the triplet annihilation that produces the singlet oxygen. This will also cause the dye destruction.

Triplet-triplet destruction could also occur when the dye is excited to triplet state. This could lead to the production of singlet oxygen (scheme 2).

3HD* + 3O2 + HD + 1O2

1O2 + HD ——a Composition

Because of variations in singlet oxygen lifetimes, the efficient singlet oxygen generators are the copper (ii), phthalocyanine and the methyleneblue.

Molecules That Fade

Dimers, Methylene Blue, and aggregates with a sm211 amount of molecules are molecules that could be destroyed by the interaction of ultra-violate radiations or other chemical reactions.

“In relation to the basophilic staining wool fibers with Methylene Blue to reveal cortical differentiation,” the persistence of the initial staining intensity of the orthocortex has been questioned (Dong and al.

2011). It is possible to see a relationship between light intensity and fading rate, given the assumption that threshold intensity exists.

Conditions under which Molecules Fade

Fading is caused by excited single states. This happens when one of the molecules absorbs a photon that is too short-lived for conventional photochemical reactions.

Photo degradation is caused by the absorption of 1 out 100, 000 photons through the standard quantum. This results in textile dye fading.

Fading can be caused by the singletoxygen as dye molecules may undergo triplet-triplet destruction with oxygen having triplet ground states. This alternatively leads to the production of singletoxygen, which causes the dye to fade (Barka Abdennouri, Makhfouk 2011, Makhfouk).

The dye molecules might also fade due to superoxide.

Reaction Mechanism for Fading Molecules

These are the reactions that have been tested for molecules that disappear:

Reaction mechanisms and capacity-fading of the Tin nanoparticles in potassium ion batteries. The reaction of ozone and indigos results in the fading of natural organic colorsants. The mechanism for the photofading and formation of azo dyes within the Hydrazine (Franca Oliveira, Ferreira 2009).

Mechanism of TiO2-coated photoluminescent material.

Another study was focused on the reactive oxyzen spices causing capsanthin to fade in vitro.

Kinetics of the Fading Process

Here are some explanations for the kinetics behind fading:

Here’s a reaction

aA + —> CC + dD

The rate of reactions can be described as the change in concentration per unit time.

Reaction rate = D[A]/(a Dt] = D[B]/ (b Dt), = D[C]/[c Dt] = D[D]/[d Dt).

This is how you can define the relationship between instantaneous concentrations and the rate of reaction of reactants:

Rate of reaction = k[A]m[B]n

These are some of the relationships that have been established for different orders of reaction:

The order of the reaction —– Plot will give a straight line

Second order (m=2) —– [A]-1

First order (m=1) —– [A] vs. Time

Half-order (m=1/2 —– [A]1/2 Vs. Time

The dye is destroyed by excitation to triplet state.

Figure 1.

Source: Mowry & Ogren 1999

Copper and phthalocyanine are both methylene blues. However, their efficiency will depend on the solvent used due to variations in singlet oxygen lifespan.

Figure 2

Source: Mowry & Orgen 1999

Mechanism of Fading Of Thiazole Orange and Methylene Blue

The mechanisms of Methylene blue and thiazole orange fading can damage the cellulose which absorbs the visible spectrum’s energy intensive portion. Hence, it is also possible for general dyes to exhibit phototendering.

The dye-sensitised, oxidative degradation mechanism explains that hydrogen atoms are removed first by the excited dye molecule.

Photofading of textile dyes.

Review of Progress in Coloration and Related Topics 31(1), pp. 21-28.

Mowry S. and Ogren P.J. 1999.

Kinetics of methylene-blue reduction by ascorbic Acid.

Journal of chemical education, 7(7), p.970.

Ferreira, M.E.

Studies of the kinetics and equilibrium of methylene-blue adsorption by coffee grounds.

Dong, Y. Lu, B. Zang, S. Zhao, J. Wang, X., and Cai Q. (2011)

Adsorption onto SBA?15 allows for the removal of methylene from colored effluents.

Journal of Chemical Technology & Biotechnology 86(4) pp. 616-619.

Barka, N.; Abdennouri M.; Makhfouk M.E.

Biosorption of Scolymus hispanicus on Scolymus hispanicus enables the removal of Methylene Blue T and Eriochrome Black T in aqueous solutions. Kinetics, equilibrium, and thermodynamics.

Journal of the Taiwan Institute of Chemical Engineers 42(2), pp.320-326.

Oster, G., and Wotherspoon N., 1957.

Journal of the American Chemical Society, (79-18), pp.4836–4838.