Fotosintezė ir Fotokatalizė

Algimantas Časas

Turinys:Fototsintezė:• Natūralus procesas• Reakcijos• NADPH• ATP• Calvin Cycle

Fotokatalizė:• Energetinei poreikiai, ištekliai• Procesų vartojimas praktikoje.• Degalų kūrimas• Aplinką valamčių įrenginių kūrimas

 

Fototsintezė

Natūralus procesas 

Fotosintezė vyksta tik tose ląstelėse, kuriose yra žalios plastidės – chloroplastai. Iš tokių ląstelių sudaryti lapai, todėl jie laikomi augalo fotosintezės organais. Taip pat jų yra kai kurių bakterijų ląstelių membranoje.

Fotosintezės schema

 

Fontosintezės reakcijos produktai

• NADPH• ATP

  

• Calvin Cycle

NADPH (Nikotinamidadenindinukleotido fosfatas)

2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2

Z schema

 

Model for the topology of chloroplast thylakoid membrane, and for the disposition within the chloroplast of the major intrinsic protein complexes, PSI, PSII, LHCII trimer, Cytochrome b6 f dimer andATPase. (Redrawn after Allen and Forsberg, 2001.)

ATP ADM AMP reakcija

                                 Adenozintrifosfato reakcija (ATP)

ATP + H2O → ADP + Pi ΔG˚ = −30.5 kJ/mol (−7.3 kcal/mol)ATP + H2O → AMP + PPi ΔG˚ = −45.6 kJ/mol (−10.9 kcal/mol)

                                          Adenozindifosfatas (ADP)

Adenozinmonofosfatas (AMP)          Fosfatas (Pi)

Pirofosfatas (PP i)

Calvin Ciklas

3 CO2 + 6 C21H29N7O17P3 + 5 H2O + 9 C10H16N5O13P3 → C3H5O3-PO32- + 2 H+ + 6 NADP+ + 9 C10H15N5O10P2 + 8 Pi

Video paaiškinimai, vizualizacijos

Fotosintezės šviesos reakcijos              Calvin Ciklas

Dirbtinė fotosintezės grandis

Reaction scheme for photosystem II (left) and the artificial system (right), with a comparison of the redox potentials (middle). The schematic figures are not drawn to scale.

Fotokatalizė

LBNL solar workshopJ. A. Turner, Science 285, 687 (1999)

LBNL solar workshop

Photoelectrochemical H2 generation

1.       Absorption of light near the surface of the semiconductor creates electron-hole pairs. 2.       Holes (minority carriers) drift to the surface of the semiconductor (the photo anode) where they react with water to produce oxygen: 2h+ + H2O -> ½ O2 (g) + 2H+ 3.       Electrons (majority carriers) are conducted to a metal electrode (typically Pt) where they combine with H+ ions in the electrolyte solution to make H2 :2e- + 2H+ -> H2 (g) 4.       Transport of H+ from the anode to the cathode through the electrolyte completes the electrochemical circuit. The overall reaction : 2h + H2O -> H2(g) + ½ O2 (g)

The Energy in Sunlight1.2 x 105 TW delivered to Earth

36,000 TW on land (world)2,200 TW on land (US)

Earth’s Ultimate Recoverable Resource

of oil3 Trillion (=Tera) Barrels

1.7 x 1022 Joules1.5 days of sunlight

San Francisco Earthquake(1906)

magnitude 7.81017 Joules

1 second of sunlight

Annual Human Production of Energy4.6 x 1020 Joules1 hour of sunlight

Solar Energy Utilization

Solar ElectricSolar Fuel

Solar Thermal

.0002 TW PV (world).00003 TW PV (US)

$0.30/kWh w/o storage

CO2

sugar

H2O

O2

NCO

NCH3

N

N

N

NHH

H

naturalphotosynthesis

artificialphotosynthesis

50 - 200 °Cspace, water

heating

500 - 3000 °Cheat engines

electricity generationprocess heat

1.5 TW electricity (world)$0.03-$0.06/kWh (fossil)

1.4 TW biomass (world)0.2 TW biomass sustainable (world)

~ 14 TW additional energy by 2050

0.006 TW (world)

11 TW fossil fuel (present use)

2 TW space and water heating (world)

H2O

O2CO2

H2, CH4CH3OH

e-

h+

Leveraging Photosynthesis for Efficient Energy Production

• photosynthesis converts ~ 100 TW of sunlight to sugars: nature’s fuel• low efficiency (< 0.3%) requires too much land area

Modify the biochemistry of plants and bacteria

- improve efficiency by a factor of 5–10 - produce a convenient fuel methanol, ethanol, H2, CH4

Scientific Challenges• understand and modify genetically controlled biochemistry that limits growth• elucidate plant cell wall structure and its efficient conversion to ethanol or other fuels • capture high efficiency early steps of photosynthesis to produce fuels like ethanol and H2 • modify bacteria to more efficiently produce fuels • improved catalysts for biofuels production

hydrogenase

2H+ + 2e- H2

switchgrass

10 µ

chlamydomonas moewusii

Solar-Powered Catalysts for Fuel Formation

artificial photosynthesisfuel from sunlight, H20, CO2H2, CH4, CH3OH, C2H5OH

Mn

MnMn

Mn

O

OO

O

OO

Mn

Mn

MnMn

O

OO

O

2H2O 4H+ + 4e-

cubanePSII

bacteria - hydrogenasecatalyst for

2 H+ + 2e- H2

plants - photosynthesis2H2O + hv → 4H+ + 4e- + O2

CO2 + H+ + e-→ carbohydrates (~ H6C12O6)bio inspired artificial water splitting

fuel production:

Tard et al, Nature 433, 610 (2005)Justice, Rauchfuss et al, J. Am. Chem. Soc.126, 13214 (2004)

Alper, Science 299, 1686 (2003)

Wu, Dismukes et al, Inorg, Chem 43, 5795 (2004)Ferreira, et al, Science 303: 1831 (2004).

Solar Fuels: Solving the Storage Problem

• Biomass < 0.3% efficient: too much land area Increase efficiency 5 - 10 times• Designer plants and bacteria for designer fuels:

H2, CH4, methanol and ethanol• Develop artificial photosynthesis

Energy Conversion Efficiency

conversion efficiency practical target chemical bonds > electrons 30% (fossil electricity) > 60% chemical bonds > motion 28% (gasoline engine) > 60% photovoltaics

photons > electrons 18% (market) / 28% (lab) > 60% photosynthesis

photons > chemical bonds 0.3% (biomass) > 20%

     solid state lighting

electrons > photons 5-25% > 50%

Hydrogen as an Energy Carrier

solarwindhydro

fossil fuelreforming

+carbon capture

nuclear/solar thermochemical

cyclesH2

gas orhydridestorage

automotivefuel cells

stationaryelectricity/heat

generation

consumerelectronics

H2O

production storage use in fuel cells

bio- and bio-inspired

H2

9M tons/yr

150 M tons/yr(light trucks and cars in 2040) 9.72 MJ/L

(2015 FreedomCAR Target)

4.4 MJ/L (Gas, 10,000 psi)8.4 MJ/L (LH2)

$3000/kW

$30/kW(Internal Combustion Engine)

$300/kWmass production

Solar Thermochemical Fuel Production

high-temperature hydrogen generation500 °C - 3000 °C

Scientific Challengeshigh temperature reaction kinetics of - metal oxide decomposition - fossil fuel chemistryrobust chemical reactor designs and materials

fossil fuelsgas, oil, coal

SolarReforming

SolarDecomposition

SolarGasification

CO2 , CSequestration

Solar H2

concentrated solar power

Solar ReactorMx Oy x M + y/2 O2

Hydrolyserx M + y H2O MxOy + y H2

H2

M

Mx Oy

Mx Oy

H2O

1/2 O2

concentratedsolar power

A. Streinfeld, Solar Energy, 78,603 (2005)

Predicting Catalysts for Hydrogen Production, Storage or Fuel-Cell Utilization

• There is a need for low-temperature, highly efficient and durable catalysts for large scale hydrogen production.

• New catalyst structures and compositions are now being predicted a priori using quantum chemistry and molecular dynamics.

• Single metallic layers of one metal embedded within a matrix of another metal produce low-energy hydrogen scission and recombination.

• Nickel within platinum can attach atomic hydrogen weakly like copper and gold, while dissociating molecular hydrogen rapidly like platinum and rhodium.

• This study may lead to breakthroughs in hydrogen production, storage and combustion in fuel cells.

Theoretical calculation of molecular hydrogen undergoing dissociation over near-surface alloys.

• Small purple spheres: hydrogen• Blue spheres: platinum atoms • Red spheres: nickel atoms • Bicolor blue and red spheres: platinum

atoms whose electronic properties have been dramatically altered by the underlying nickel.

J. Zhang, et al, Angew. Chem. Int Ed. 44, 2132 (2005)

Literatūra:

ŠVIESOS POVEIKIS ELEKTROCHEMINIAM PORĖTŲJŲ SLUOKSNIŲSUSIFORMAVIMUI ANT p-GaAs PADĖKLŲI. Šimkienė, R.-A. Bendorius, J. Sabataitytė, K. Naudžius, T. Puidokas, M. Treideris

Mimicking photosystem II reactions in artificial photosynthesis:Ru(II)-polypyridine photosensitisers linked to tyrosine andmanganese electron donorsLeif Hammarströma;, Licheng Sunb, Björn Åkermarkb, Stenbjörn Styring ca Department of Physical Chemistry, Uppsala University, Box 532, S-751 21 Uppsala, Swedenb Department of Organic Chemistry, Stockholm University, S-10691 Stockholm, Swedenc Department of Biochemistry, Centre for Chemistry and Chemical Engineering, Lund University, Box 124, S-22100 Lund, Sweden

http://en.wikipedia.org/wiki/Photosynthesis 

http://en.wikipedia.org/wiki/Photoelectrochemical_cell

http://www.youtube.com/

Royal Belgian Academy Councilof Applied ScienceHydrogen as an energy carrierApril 2006

Solar Fuel II: The Quest for CatalystsSunlight, leaves, and water can make clean energy. They can also make pretty pictures, as inthis cyanotype, also called a “sun print.”by H a rr y B . G r ay