Leveraging Carbon Quantum Dot Spacers as Dual Proton/Electron Boosters to Upgrade TiO2@Polydopamine Photocatalysts for pH-Resilient Conversion of O2 into H2O2.

Photocatalytic synthesis of H2O2 is a proton-coupled electron transfer (PCET) process, which is generally jeopardized by the kinetic mismatch between photogenerated electron transfer and proton supply. To address the challenge, here we proposed a new core-shell design of nanocomposite catalysts comprising of carbon quantum dot (CD)-topped TiO2 nanoparticles encapsulated by polydopamine (PDA) shells, which delivered stable catalytic activity across a pH range of 1-9, exhibiting a photocatalytic generation rate of H2O2 that reached 18.14 mmol g-1 h-1 in methanol and 8.66 mmol g-1 h-1 in water. This extraordinary, pH-tolerant photocatalytic generation of H2O2 was benefited from the innovative use of CDs, interspaced between the TiO2 cores and PDA shells, not only as a reservoir of protons to buffer the local acidic microenvironment but also as a proton/electron dual booster to sustain an excellent kinetic match between the proton and photogenerated electron transfer, thus enabling the O2 reduction to selectively proceed via two-electron reaction pathway over a wide pH span.