Elucidating protonation pathways in CO2 photoreduction using the kinetic isotope effect.

The surge in anthropogenic CO2 emissions from fossil fuel dependence demands innovative solutions, such as artificial photosynthesis, to convert CO2 into value-added products. Unraveling the CO2 photoreduction mechanism at the molecular level is vital for developing high-performance photocatalysts. Here we show kinetic isotope effect evidence for the contested protonation pathway for CO2 photoreduction on TiO2 nanoparticles, which challenges the long-held assumption of electron-initiated activation. Employing isotopically labeled H2O/D2O and in-situ diffuse reflectance infrared Fourier transform spectroscopy, we observe H+/D+-protonated intermediates on TiO2 nanoparticles and capture their inverse decay kinetic isotope effect. Our findings significantly broaden our understanding of the CO2 uptake mechanism in semiconductor photocatalysts.

Boosting mineralized organic pollutants by using a sulfur-vacancy CdS photocatalyst.

Photocatalytic mineralization of organic pollutions and simultaneously converting CO2 to CO (tetracycline → CO2 → CO) represents a fascinating way to solve the environmental and energy crisis. This work demonstrates the excellent mineralization and CO2 reduction performance of S-vacancy CdS and reveals the high efficiency of the carbon self-recycling two-in-one photocatalytic system.

Water molecule switching heterogeneous proton-coupled electron transfer pathway.

Figuring out the specific pathway of semiconductor-mediated proton-coupled electron transfer (PCET) driven by light is essential to solar energy conversion systems. In this work, we reveal that the amount of adsorbed water molecules determines the photo-induced PCET pathway on the TiO2 surface through systematic kinetic solvent isotope effect (KSIE) experiments. At low water content (<1.7 wt%), the photo-induced single-proton/single-electron transfer on TiO2 nanoparticles follows a stepwise PT/ET pathway with the formation of high-energy H+/D+-O[double bond, length as m-dash]C or H+/D+-O-C intermediates, resulting in an inverse KSIE (H/D) ∼0.5 with t Bu3ArO· and KSIE (H/D) ∼1 with TEMPO in methanol-d 0/d 4 systems. However, at high water content (>2 wt%), the PCET reaction follows a concerted pathway with a lower energy barrier, leading to normal KSIEs (H/D) ≥ 2 with both reagents. In situ ATR-FTIR observation and DFT calculations suggest that water molecules' existence significantly lowers the proton/electron transfer energy barrier, which coincides with our experimental observations.

Fabricating acid-sensitive controlled PAA@Ag/AgCl/CN photocatalyst with reversible photocatalytic activity transformation.

Achieving the intelligent controllability of the photocatalyst to the surrounding environment is a very meaningful work. Here, the polyacrylic acid (PAA) modified Ag/AgCl-40/CN composite was constructed to achieve an intelligent response of pH value. PAA exhibits hydrophilic properties at high pH value, increasing the adsorption capacity to tetracycline (TC) molecules. The morphology of PAA from contracted state to diastolic state, releasing the Ag/AgCl-40/CN catalyst. In addition, PAA modified Ag/AgCl-40/CN can prevent the loss of AgCl. The g-C3N4 nanosheets (CN) as a carrier enhance the dispersibility of the AgCl particles. The LSPR effects of Ag nanoparticles produce more electrons acting on photocatalytic degradation. On the results of experiment, the degradation of TC by PAA@Ag/AgCl-40/CN shows an excellent degradation activity when the high pH value. Photoluminescence spectroscopy and photocurrent demonstrate that carrier separation efficiency of PAA@Ag/AgCl-40/CN is higher than CN and Ag/AgCl-40/CN. The detection of the main active substances •O2- and h+, revealing a reasonable mechanism for the PAA@Ag/AgCl-40/CN hybrid system. This work provides a procedure to obtain smart materials that can switch photocatalytic processes.

Construction of Heterogenous S-C-S MoS2/SnS2/r-GO Heterojunction for Efficient CO2 Photoreduction.

Photocatalytic reduction of CO2 by semiconductors is of great significance in generating value-added fuels. Here, we construct a novel S-C-S heterojunction constituted of MoS2/SnS2/r-GO by a simple solvothermal method. The prepared MoS2/SnS2/r-GO showed significant photoexcitation of photosensitive oxygen (ROS) by electron spin resonance spectroscopy, demonstrating that superoxide radicals (•O2-), pores, and hydroxyl radicals (•OH) are the main active species. The constructed S-C-S heterojunction has a multilevel electron transport mechanism and synergistic effect, which provides the possibility of producing more organic fuel. The photocatalytic materials were characterized by XRD, XPS, SEM, TEM, PL, etc. As a result, the atomic layer MoS2/SnS2/r-GO heterojunction exhibited a CO formation rate of 68.53 µmol g-1 h-1 and a CH4 formation rate of 50.55 µmol g-1 h-1, respectively. This work opens up new prospects for the formation of heterojunctions of chalcogenide transition-metal sulfides.