Polyelectrolyte‐controlled visible light catalytic reduction of nitrobenzene

Abstract

To study the effect of cationic polyelectrolytes on the photoreduction of nitrobenzene over TiO2, a sequence of synthetic cationic polyelectrolytes (SCPs) containing acrylamide (AAm) and 2‐(dimethylamino)ethyl acrylate methochloride (DAEA) using various AAm:DAEA molar ratios (50:50, 55:45, 60:40, 70:30, and 85:15) were synthesized and named as PEA, PEB, PEC, PED, and PEE, respectively. According to the obtained monomer reactivity ratios, the SCPs with a range from medium to high molecular weights (2.11×105 ≤ Mv ≤ 1.22 ×106 g/mol) were obtained. Then the influence of the SCPs and the other polyelectrolytes such as Zetag 7563 (a commercial grade of cationic polyelectrolyte) and poly(vinylsulfate) potassium salt (PVSK) as an anionic polyelectrolyte on the photoreduction of nitrobenzene over TiO2 under 400 nm LED irradiation was investigated. Zetag 7563 was not an appropriate polyelectrolyte to enhance the photoreduction of nitrobenzene due to its high Mv, and having high entanglement of polymer chains. By the addition of PVSK anionic polyelectrolyte, the conversion of nitrobenzene to aniline decreased; the PVSK has a probably greater tendency than nitrobenzene to be absorbed on the surface of TiO2 (PVSK reduces the adsorption of nitrobenzene on the surfaces of TiO2 due to the electrostatic interactions with TiO2). Simultaneous use of TiO2 with 0.01 g of PEB (with medium Mv and 4.4 meq/g charge density), led to an increase in the nitrobenzene photoreduction (95% conversion) in comparison with application of bare TiO2 (53% conversion). It supposes that the selection of appropriate SCPs can facilitate the access of reactants to each other and enhance the nitrobenzene photoreduction.