Molecular Dye-Sensitized Photocatalysis with Metal-Organic Framework and Metal Oxide Colloids for Fuel Production

Philip M Stanley,Julien Warnan

doi:10.3390/en14144260

Abstract

Colloidal dye-sensitized photocatalysis is a promising route toward efficient solar fuel production by merging properties of catalysis, support, light absorption, and electron mediation in one. Metal-organic frameworks (MOFs) are host materials with modular building principles allowing scaffold property tailoring. Herein, we combine these two fields and compare porous Zr-based MOFs UiO-66-NH2(Zr) and UiO-66(Zr) to monoclinic ZrO2 as model colloid hosts with co-immobilized molecular carbon dioxide reduction photocatalyst fac-ReBr(CO)3(4,4′-dcbpy) (dcbpy = dicarboxy-2,2′-bipyridine) and photosensitizer Ru(bpy)2(5,5′-dcbpy)Cl2 (bpy = 2,2′-bipyridine). These host-guest systems demonstrate selective CO2-to-CO reduction in acetonitrile in presence of an electron donor under visible light irradiation, with turnover numbers (TONs) increasing from ZrO2, to UiO-66, and to UiO-66-NH2 in turn. This is attributed to MOF hosts facilitating electron hopping and enhanced CO2 uptake due to their innate porosity. Both of these phenomena are pronounced for UiO-66-NH2(Zr), yielding TONs of 450 which are 2.5 times higher than under MOF-free homogeneous conditions, highlighting synergistic effects between supramolecular photosystem components in dye-sensitized MOFs.

Highlights

Solar fuel production has emerged as a pertinent possibility on route to address growing energy challenges and shift fossil fuel dependency toward sustainable sources [1]
The solvent was removed in vacuo and the residue was dissolved in minimal amounts of ethylene glycol dimethyl ether and added to hexane (100 mL) at 0 ◦C
The resulting powder was dissolved in water, filtered, and the filtrate was evaporated to give the crystalline product (0.120 mg, 0.143 mmol, 70% yield), matching literature characterizations [31]. 1H NMR (400 MHz, 300 K, DMSO-d6): δ = 8.87 (m, 4H), 8.80 (d, 3J = 8.3 Hz, 2H), 8.37 (d, 3J = 8.1 Hz, 2H), 8.19 (m, 4H), 8.00 (s, 2H), 7.79 (d, 3J = 5.6 Hz, 2H), 7.77 (d, 3J = 5.6 Hz, 2H), 7.58 (t, 3J = 6.5 Hz, 2H), 7.53 (t, 3J = 6.5 Hz, 2H) UiO-66-NH2(Zr) The synthesis was modified from a literature procedure [32]. 2-aminoterephthalic acid (0.186 g, 1.03 mmol, 1.00 eq.) and ZrCl4 (0.240 g, 1.03 mmol, 1.00 eq.) were dissolved in anhydrous N,N-dimethylformamide (DMF, 60 mL)

Summary

Introduction

Previous advances include molecular catalyst and dye engineering to improve catalytic parameters such as activity and selectivity on the one hand, as well as light harvesting and antenna effects on the other [4,5] Immobilizing such species to host materials can yield beneficial sustained performance, with dye-sensitized photocatalysis (DSP) emerging as a selected approach with distinct advantages [6,7]. This methodology bridges the fields of molecular (photo)catalysis and material chemistry by coupling a catalyst and a dye via co-anchoring onto a semiconductor particle—effectively employing the latter as a solid-state electron mediator and a scaffold [6]. This presents the question how dye-sensitized MOFs (DSMs) directly dcoyme-speanrseittizoedthMeirOcFosm(DmSoMnsly) duirseecdtlymceotmalpoaxriedteo-bthaeseirdcopmarmticolnelycouusnedtemrpeatratlsoixnidceo-lbloasidedal psoarlatirclfeueclopurnotedrupcatriotsni.n colloidal solar fuel production

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Discussion

Conclusion