Actinometry_in_Photochemistry_Presentation (2).pptx

A presentation on actinometry instrument used in photochemistry

1. Actinometry in Photochemistry Measuring Light Intensity for Photochemical Applications - By : Aniket Singh

2. Introduction to Actinometry Actinometry is the technique used to measure the number of photons in a specific wavelength range. Used to determine the light intensity or photon flux in photochemical experiments. Actinometry allows for accurate quantification of light, ensuring reproducibility and efficiency of reactions. The device or chemical system used to measure the light intensity is called Actinometer.

3. History The first actinometer was invented by John Hershel in 1825 for the investigation of solar radiation in relation to meteorology research, based on temperature changes induced by absorption of light by a copper sulfate solution.

4. An actinometer instrument from the 1800s designed by Jules Violle and used to estimate the temperature of the Sun's surface.

5. QUANTUM YIELD AND ITS IMPORTANCE • The efficiency of a photochemical process is expressed in terms of Quantum Yield (Φ) which is defined as number of molecules reacting per quantum of light absorbed. • Critical for determining the efficiency of photochemical process. Φ = Number of molecules reacting in a given time Number of quantum of radiation absorbed in same time

6. Types of Actinometers • Chemical Actinometers : Chemical actinometers are devices used to measure the intensity of light based on photochemical reactions. 1. Ferrioxalate Actinometer: Fe(II) formation from Fe(III) under UV light. 2. Reinecke's Salt Actinometer: Involves photoreduction of Reinecke's Salt. 3. Uranyl oxalate Actinometer • Physical Actinometers: Physical actinometers measure light intensity through the detection of physical changes such as changes in electrical properties, temperature, or radiant power. - Photodiodes: Convert light into an electrical current. - Thermopiles: Measure temperature change caused by light absorption. - Photocell: Converts light energy into electrical energy

7. Instrumentation of Actinometer Light Source : Depending on the application, this could be a UV lamp, a visible light source, or a combination of light sources. Sample holder : Often a quartz cuvette or glass vessel that holds the chemical solution or device that undergo physical change. The material of the holder should be transparent to the light being measured. Chemical solution or measurement device: Detects and quantifies the chemical or physical changes in response to light. Detector: Measures the physical or chemical changes in the sample. Measurement and Data Acquisition System: Records and analyzes the data obtained from the detector. Calibration Standards: Provides known references for calibrating the actinometer and ensuring accurate measurements.

8. FERRIOXALATE actinometer Reaction : [Fe 3+ (C 2 O 4 ) 3 ] 3- h υ →[ Fe 2+ (C 2 O 4 ) 2 ] 2- + C 2 O 4 - [ Fe 3+ (C 2 O 4 ) 3 ] 3- + C 2 O 4 - → [ Fe 3+ (C 2 O 4 ) 3 ] 2- + (C 2 O 4 ) 2- [ Fe 3+ (C 2 O 4 ) 3 ] 2- → [ Fe 2+ (C 2 O 4 ) 3 ] 2- + 2CO 2 Procedure: 1. Prepare a standard ferrioxalate solution. 2. Expose to light for a fixed time. 3. Measure concentration of Fe(II) using spectrophotometry. 4. Calculate photon flux using known quantum yield. Advantages: Broad wavelength sensitivity, high quantum yield accuracy. Limitations: Sensitive to impurities and temperature variations.

9. Uranyl Oxalate Actinometer Reaction: Procedure: Dissolve uranyl oxalate in an appropriate solvent . Place the solution in a radiation chamber and expose it to the radiation source . After exposure, use spectroscopic methods to analyze the concentration of uranyl ions and/or oxalate ions . Use the measured changes in concentration to calculate the dose of radiation using calibration data. UO 2 2+ + hv → (UO 2 2+ ) * (UO 2 2+ ) * + oxalate → UO 2 2+ + CO 2 + CO + H 2 O

10. PHOTOCELL A device that detects light and converts light energy directly into electrical energy. A photocell consists of a photosensitive cathode and a collector anode enclosed in an evacuated bulb. Light quanta of energy greater than the threshold energy of metal causes ejection of electrons which are collected by anode and current flows in a circuit. The intensity of current generated will be linearly proportional to the incident light intensity.

11. THERMOPILES An electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series , or less commonly, in parallel. Thermophiles are thermocouples connected in series and generate E.M.F on heating.

12. Applications of Actinometry Photochemical Research: Quantify light source for accurate reaction rates. Climate Studies: Monitoring solar radiation to understand global warming trends. Weather forecasting: Measure solar and UV radiation to improve weather models and forecasts. Solar Observation: Measure solar radiation to study solar activity and its effects on Earth. Astronomical Research: Calibrate telescopes and instruments by measuring light intensity from celestial objects.

13. Challenges and Future Directions • Challenges: Sensitivity to experimental conditions, need precise calibration. • Future Developments: Advancements in sensor technology and new chemical actinometers . • Conclusion: Importance of actinometry in advancing photochemical research and applications.

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