A modular photochemical reactor system comprises a plurality of fluidic modules (20) each having i) a central planar process fluid layer (30) and ii) two outer planar thermal control fluid layers (40) for containing flowing thermal control fluid and a plurality of illumination modules (50), the illumination modules (50) of said plurality each having a planar form with first and second major surfaces (52, 54) and each comprising at least a first array (60) of semiconductor emitters (70), said emitters (70) positioned to emit from or through the first major surface (52), wherein said first array (60) of semiconductor emitters (70) comprises at least a first emitter (72) and a second emitter (74), the first emitter (72) capable of emitting at a first center wavelength and the second emitter (74) capable of emitting at a second center wavelength, said first and second center wavelengths differing from each other.

A reaction chamber contains catalytic material(s). Tunable microwave source(s) each emit microwave radiation at corresponding time-varying microwave frequency(ies) or at simultaneous multiple different microwave frequencies. Microwave transmission element(s) irradiate the interior volume of the reaction chamber with the microwave radiation, emitted by the microwave source(s), that propagates along the transmission element(s) into the reaction chamber. The reaction chamber is characterized by a maximum temperature variation of a fixed-frequency, steady-state temperature spatial profile that results from irradiation of the reaction chamber by microwave radiation at a substantially fixed microwave frequency and at a reference microwave power level. Irradiation of the reaction chamber at the reference microwave power level by the microwave radiation with the time-varying microwave frequency(ies), or the simultaneous multiple different microwave frequencies, results in a multi-frequency temperature spatial profile having a maximum temperature variation less than the maximum temperature variation of the fixed-frequency, steady-state temperature spatial profile.

Systems and methods for eliminating carbon dioxide and capturing solid carbon are disclosed. By eliminating carbon dioxide gas, e.g., from an effluent exhaust stream of a fossil fuel fired electric power production facility, the inventive concepts presented herein represent an environmentally-clean solution that permanently eliminates greenhouse gases while at the same time producing captured solid carbon products that are useful in various applications including advanced composite material synthesis (e.g., carbon fiber, 3D graphene) and energy storage (e.g., battery technology). Capture of solid carbon during the disclosed process for eliminating greenhouse gasses avoids the inefficiencies and risks associated with conventional carbon dioxide sequestration. Colocation of the disclosed reactor with a fossil fuel fired power production facility brings to bear an environmentally beneficial, and financially viable approach for permanently capturing vast amounts of solid carbon from carbon dioxide gas and other greenhouse gases that would otherwise be released into Earth's biosphere.