Photocatalytic Conversion of Diluted CO₂ into Light Hydrocarbons Using Periodically Modulated Multiwalled Nanotube Arrays

Abstract

Solar-energy-driven conversion of CO 2 into hydrocarbon fuels can simultaneously generate chemical fuels to meet energy demand and mitigate rising CO 2 levels. The utilization of the clean and renewable solar power resource is, on a longterm basis, an essential component of solutions to address growing global energy demand, which is projected to be 40 TW by 2050. [1] This is because the solar energy received on the earths surface in one hour exceeds current total global energy demand. From the perspective of climate change, expansion of the current fossil fuel-based energy infrastructure to meet the projected energy demand is predicted to add 2986-7402 Gt of CO 2 to the atmosphere by 2100, resulting in a mean rise in global temperature of 2.4-4.5 8C. [2] Since the discovery of the photoreduction of carbon dioxide to form organic compounds using semiconductors by Fujishima and co-workers in 1979, [3] a growing interest in the development of catalysts that are capable of solar-based capture and storage of CO 2 has evolved. [4] Titanium dioxide, which is a cost-efficient, non-toxic and abundant n-type semiconductor, has been widely considered in the solar-driven reduction of CO 2 . Owing to its large band-gap energy of 3-3.2 eV, TiO 2 without doping or post-synthesis treatments can absorb only the ultraviolet portion of the solar spectrum. To narrow the band-gap of TiO 2 and improve its photocatalytic performance, strategies such as compositional doping or deliberately introducing disorder in crystalline TiO 2 are being investigated. [5] Herein, we demonstrate an approach that is able to achieve high-rate sunlight-driven conversion of diluted CO 2 to light hydrocarbons in which an optimized combination of a Cu-Pt coating and modulated-diameter TiO 2 nanotubes are used as the photocatalyst. We demonstrate at least a fourfold improvement in CO 2 conversion rates over prior art [6] by using a catalyst consisting of coaxial Cu-Pt bimetallic shells supported on a periodically modulated double-walled TiO 2 nanotube (PMTiNT) array core. The photocatalytic reaction occurs at room temperature and generates CH 4 , C 2 H 4 , and C 2 H 6 as reaction products. Under AM 1.5 one-sun illumination, using 99.9 % CO 2 , we obtained a hydrocarbon production rate of 3.51 mL g À1 h À1 or 574 nmol cm À2 h À1 . A key novelty is the effectiveness of our photocatalyst for the photoreduction of unconcentrated CO 2 . When the Cu 0.33 -Pt 0.67 /PMTiNT heterogeneous catalyst was utilized for the photoreduction of diluted CO 2 (0.998 % in N 2 ) at 25 8C, we found an average hydrocarbon production rate of 3.7 mL g À1 h À1 or 610 nmol cm À2 h À1 . The periodic modulation of the diameters of the nanotube arrays increased the surface area and improved the utilization of light while the bimetallic coating increased catalyst activity and specificity. Our version of a highly active CO 2 reduction system does not require reactant gases with high purities and could potentially be used to photocatalytically capture CO 2 directly from air or from flue gas...

Design and fabrication of semiconductor photocatalyst for photocatalytic reduction of CO2 to solar fuel

“…TiO 2 nanotubes [63,97,[186][187][188][189][190][191], nanofibers [192] and nanorods [168,169,193] exhibited a much better photocatalytic activity for CO 2 reduction than P25 or TiO 2 NPs. For instance, Fu et al [192] demonstrated that the TiO 2 nanofibers with a 2-h solvothermal treatment exhibited the highest activity for photocatalytic reduction of CO 2 to CH 4 , which was about 6 and 25 times higher than those of TiO 2 nanofibers without solvothermal treatment and P25, respectively, due to the enhanced CO 2 adsorption capacity and the improved charge separation.…”

“…The optimum mole ratio of H 2 O/CO 2 for CO 2 photoreduction over highly dispersed TiO 2 anchored on porous Vycor glass was found to be about 5 [295]. Recently, efficient high-rate sunlight-driven conversion of diluted CO 2 into light hydrocarbons in gas phase was also achieved by coupling coaxial Cu-Pt bimetallic coatings with these TiO 2 nanotube arrays as catalysts at room temperature [188]. Therefore, for the photocatalytic reduction of CO 2 by water vapor, control of CO 2 and H 2 O adsorption capacity of photocatalysts and the ratio of H 2 O to CO 2 is of great importance to optimize the photocatalytic activity and selectivity in future studies.…”

“…12. In another example, a bimetallic co-catalyst of Cu 0.33 -Pt 0.67 was loaded on the double-walled TiO 2 nanotube for the photoreduction of diluted CO 2 to CH 4 (1% in N 2 ), an average hydrocarbon production rate of 6.1 mmol m −2 h −1 was realized under AM 1.5 one-sun illumination [321]. However, the enhancement mechanism of bimetallic co-catalysts is still unclear.…”

From single to multiple TiO2 nanotubes layers: Analysis of the parameters which influence the growth

“…In fact, being characterized by both a large internal surface area and a geometric and structural order, during the years they have been used in many different fields such as catalysis [2][3], energy [4][5], sensing [6][7], biosensing [8] and biomedicine [9].…”

Photocatalytic Conversion of CO2Using ZnOSemiconductor by Hydrothermal Method

“…Although, photoreduction of CO 2 shows great potential [86][87], at present one of the greatest drawbacks is the low conversion efficiency due to some associated major factors which bound the efficiency: (i) mismatching between the absorption ability of semiconductor and the solar spectrum; (ii) poor charge transfer separation efficiency; (iii) low solubility of CO 2 molecule in water (approximately 33 mol in 1 ml of water at 100 kPa and room temperature); (iv) reverse reactions during reduction of CO 2 ; and (v) competition reaction of water reduction to hydrogen [88]. The solar spectrum consists of 4 % of the UV radiations and 43% visible region.…”