Stacked waveguide reactors with gradient embedded scatterers for high-capacity water cleaning.

We present a compact water-cleaning reactor with stacked layers of waveguides containing gradient patterns of optical scatterers that enable uniform light distribution and augmented water-cleaning rates. Previous photocatalytic reactors using immersion, external, or distributive lamps suffer from poor light distribution that impedes scalability. Here, we use an external UV-source to direct photons into stacked waveguide reactors where we scatter the photons uniformly over the length of the waveguide to thin films of TiO2-catalysts. We also show 4.5 times improvement in activity over uniform scatterer designs, demonstrate a degradation of 67% of the organic dye, and characterize the degradation rate constant.

Integrated hollow fiber membranes for gas delivery into optical waveguide based photobioreactors.

Compact algal reactors are presented with: (1) closely stacked layers of waveguides to decrease light-path to enable larger optimal light-zones; (2) waveguides containing scatterers to uniformly distribute light; and (3) hollow fiber membranes to reduce energy required for gas transfer. The reactors are optimized by characterizing the aeration of different gases through hollow fiber membranes and characterizing light intensities at different culture densities. Close to 65% improvement in plateau peak productivities was achieved under low light-intensity growth experiments while maintaining 90% average/peak productivity output during 7-h light cycles. With associated mixing costs of ∼ 1 mW/L, several magnitudes smaller than closed photobioreactors, a twofold increase is realized in growth ramp rates with carbonated gas streams under high light intensities, and close to 20% output improvement across light intensities in reactors loaded with high density cultures.

Engineered surface scatterers in edge-lit slab waveguides to improve light delivery in algae cultivation.

Most existing photobioreactors do a poor job of distributing light uniformly due to shading effects. One method by which this could be improved is through the use of internal wave-guiding structures incorporating engineered light scattering schemes. By varying the density of these scatterers, one can control the spatial distribution of light inside the reactor enabling better uniformity of illumination. Here, we compare a number of light scattering schemes and evaluate their ability to enhance biomass accumulation. We demonstrate a design for a gradient distribution of surface scatterers with uniform lateral scattering intensity that is superior for algal biomass accumulation, resulting in a 40% increase in the growth rate.

Redox mediated photocatalytic water-splitting in optofluidic microreactors.

While photocatalytic water-splitting is a promising alternative energy source, low photocatalytic efficiencies in the visible spectrum hinders its widespread deployment and commercialization. Although screening combinations of new materials and characterizing their reaction kinetics offers possible improvements to efficiency, current experiments are challenged by expensive bulky setups and slow recovery of particles downstream. Optofluidics is a good platform for screening Z-scheme catalysts cheaply and rapidly. By alleviating the problems of mass transport it can also potentially increase reaction rates and efficiencies. Here, we demonstrate a novel optofluidic device based on applying catalyst sol-gels on planar channels while measuring the reaction output by monitoring the depletion of the redox mediators. We use our setup to study the kinetics of the TiO(2)-Pt water-splitting reaction mediated by I(-)/IO(3)(-) redox pairs under different flow rates. In particular, for TiO(2)-Pt, we show ~2-fold improvements in reaction rates and efficiencies.