Development and Characterization of Titanium Dioxide Gel with Encapsulated Bacteriorhodopsin for Hydrogen Production

Abstract

We study bacteriorhodopsin (BR) in its native purple membrane encapsulated within amorphous titanium dioxide, or titania, gels and in the presence of titania sol particles to explore this system for hydrogen production. Förster resonance energy transfer between BR and titanium dioxide sol particles was used to conclude that there is nanometer-scale proximity of bacteriorhodopsin to the titanium dioxide. The detection of BR-titania sol aggregates by fluorescence anisotropy and particle sizing indicated the affinity amorphous titania has for BR without the use of additional cross-linkers. UV-vis spectroscopy of BR-titania gels shows that methanol addition did not denature BR at a 25 mM concentration presence as a sacrificial electron donor. Additionally, confinement of BR in the gels significantly limited protein denaturation at higher concentration of added methanol or ethanol. Subsequently, titania gels fabricated through the sol-gel process using a titanium ethoxide precursor, water, and the addition of 25 mM methanol were used to encapsulate BR and a platinum reduction catalyst for the production of hydrogen gas under white light irradiation. The inclusion of 5 μM bacteriorhodopsin resulted in a hydrogen production rate of about 3.8 μmol hydrogen mL h, an increase of 52% compared to gels containing no protein. Electron transfer and proton pumping by BR in close proximity to the titania gel surface are feasible explanations for the enhanced production of hydrogen without the need to cross-link BR to the titania gel. This work sets the stage for further developments of amorphous, rather than crystalline, titania-encapsulated bacteriorhodopsin for solar-driven hydrogen production through water splitting.

Artificial Photosynthesis: Current Advancements and Future Prospects

“…These structures have been utilized in the development of solar cells, increasing their efficiency and representing a potential alternative for the development of energy conversion systems. bRs have also been used when functionalized with TiO 2 gel in the presence of platinum nanoparticles for hydrogen production [ 213 ]. Under these conditions, it was observed that bRs did not denature even in the presence of ethanol or methanol, and the hydrogen production from these hybrid structures was 52% higher than that observed in the absence of bR.…”

Green Catalysts: Applied and Synthetic Photosynthesis

“…Both the sensitizer and photon pumping activity of bR has been leveraged in heterogeneous and homogeneous catalytic systems for light driven hydrogen production. Crystalline [143] and amorphous [144] TiO2 suspensions combined with bR, a sacrificial reductant (e.g., methanol), and Pt catalyst can generate H2 under illumination with visible light. In a related study, Allam et al observed a more negative onset potential and increased photocurrent densities with bR coated TiO2 nanotube based photoanodes compared to the same electrodes without bR under photochemical conditions for solar water splitting [145].…”

PEDOT-Carbon Nanotube Counter Electrodes and Bipyridine Cobalt (II/III) Mediators as Universally Compatible Components in Bio-Sensitized Solar Cells Using Photosystem I and Bacteriorhodopsin

“…Both protein–pigment complexes have shown remarkable thermal stability and their structural, biochemical, and photophysical properties have been extensively studied [ 15 , 16 ]. Similarly, both PSI and bR have also been widely used in a variety of biotechnological applications, most notably in BSSCs [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ].…”