Integrating photocatalytic reduction of CO2 with selective oxidation of tetrahydroisoquinoline over InP–In2O3 Z-scheme p-n junction

The development of a facile strategy to construct stable hierarchal porous heterogeneous photocatalysts remains a great challenge for efficient CO2 reduction. Additionally, hole-trapping sacrificial agents (e.g., triethanolamine, triethylamine, and methanol) are mostly necessary, which produce useless chemicals, and thus cause costs/environmental concerns. Therefore, utilizing oxidation ability of holes to develop an alternative photooxidation reaction to produce value-added chemicals, especially coupled with CO2 photoreduction, is highly desirable. Here, an in situ partial phosphating method of In2O3 is reported for synthesizing InP–In2O3 p-n junction. A highly selective photooxidation of tetrahydroisoquinoline (THIQ) into value-added dihydroisoquinoline (DHIQ) is to replace the hole driven oxidation of typical sacrificial agents. Meanwhile, the photoelectrons of InP–In2O3 p-n junction can induce the efficient photoreduction of CO2 to CO with high selectivity and stability. The evolution rates of DHIQ and CO are 2 and 3.8 times higher than those of the corresponding In2O3 n-type precursor, respectively. In situ irradiated X-ray photoelectron spectroscopy and electron spin resonance are utilized to confirm that the direct Z-scheme mechanism of InP–In2O3 p-n junction accelerate the efficient separation of photocarriers.