Nitrogen-doped biochar nanosheets facilitate charge separation of a Bi/Bi2O3 nanosphere with a Mott–Schottky heterojunction for efficient photocatalytic reforming of biomass

Abstract

Coupling a semimetal with a semiconductor on nitrogen-doped carbon for photocatalytic reforming of biomass-derived feedstocks into high value-added chemicals is of great significance; however, no success has been achieved to date. Here, uniformly dispersed Bi/Bi₂O₃ nanospheres with a Mott–Schottky heterojunction embedded on the nitrogen-doped biochar nanosheets (Bi/Bi₂O₃@N-BC) were developed and successfully used in photocatalytic biomass-reforming to lactic acid. A built-in electric field between the interfaces of Bi and Bi₂O₃ was constructed via the Schottky effect of the Bi/Bi₂O₃ heterojunction, resulting in the rapid separation/migration of electrons–holes; whereas the N-BC facilitates the adsorption of reactants and the mass transfer of products or by-products. The highest yield of lactic acid reached was 91.21%, and Bi/Bi₂O₃@N-BC displayed excellent stability, reusability and universality. The experimental results indicated that the contents of photoinduced h⁺, ˙O₂⁻, ˙OH and ¹O₂ increased with prolonging the visible-light irradiation time, and trapping tests suggested that ˙O₂⁻, ¹O₂ and h⁺ promoted the lactic acid production in turn, whereas ˙OH inhibited the reaction. A 1000-fold scale-up experiment showed that the economically and environmentally viable system has potential for application in the industrial production of lactic acid, and this work also provides an efficient strategy for the development of functional photocatalysts and photocatalytic biorefinery.