Selective Hydrogenation of Cinnamaldehyde, Furanic, and Aromatic Aldehydes over a Z-Scheme Heterojunction Photocatalyst Constituted of Pd NPs Supported on g-C₃N₄/ZnO Nanocomposite

Abstract

In this study, a Z-scheme heterojunction photocatalyst is fabricated by systematically manipulating and integrating g-C 3 N 4 and ZnO. The Z-scheme g-C 3 N 4(x) /ZnO (y) exhibits enhanced charge separation and migration, confirmed through photoluminescence (PL), time-correlated single-photon counting spectroscopy, and electrochemical impedance spectroscopy. Pd NPs, with an elevated work function and low Fermi energy level, are decorated onto the heterojunction, further amplifying charge separation, as revealed by ultraviolet photoelectron spectroscopy. The resulting Pd-decorated photocatalysts (Z%Pd@g-C 3 N 4(x) / ZnO (y) ) are evaluated for the selective reduction of α−β unsaturated compound, cinnamaldehyde. The catalysts with lower Pd NPs (0.5 or 1%) afford ∼100% yield for hydrocinnamaldehyde, while higher Pd NPs (3%Pd@g-C 3 N 4(0.73) /ZnO (0.27) ) afford ∼100% yield for hydrocinnamyl alcohol. Biomassderived furanic aldehydes afforded ring-reduced and side-chain-reduced products under different Pd loading, whereas no ringreduced products were obtained for the aromatic aldehydes. Interface interactions impact charge migration, leading to longer lifetimes for photogenerated charge pairs and improved separation of electrons and holes in photocatalytic processes. Characterizations and control experiments provide valuable insights into the structure−activity relationship, ultimately contributing to formulating a plausible reaction mechanism for photocatalytic reduction.

Advancing sustainable lignin valorisation: utilizing Z-scheme photocatalysts for efficient hydrogenolysis of lignin's β-O-4, α-O-4, and 4-O-5 linkages under ambient conditions

“…S17a†). 69 It induced upward band bending in CN and downward band bending in band edges of BMO near the interface (refer to Fig. 10a(i) and (ii)).…”

“…70–72 Upon incorporating Pd NPs into the heterojunction, the Fermi level of the CN/rGO/BMO(2 : 1) composite aligned with the Fermi level of Pd NPs at 5.12 eV vs. V ac . 69 It led to resifting of the Fermi level at 4.78 eV vs. V ac for 0.5%Pd@CN/rGO/BMO(2 : 1) and 4.93 eV vs. V ac for 5%CN/rGO/BMO(2 : 1) catalysts (Fig. S18b and c†).…”

“…68 The alignment of band edges between CN and BMO, as projected by MS, was observed. 69 Upon integration into a heterojunction material, the Fermi level of CN (4.58 eV vs. V ac ) underwent a reduction, while BMO's Fermi level (4.92 eV vs. V ac ) increased. This resulted in a new equilibrium at 4.72 eV vs. V ac , as obtained from the UPS analysis of CN/rGO/BMO(2 : 1) (Fig.…”

Heterogeneous photocatalytic valorization of lignocellulose biomass for chemical and fuel production via reductive pathways

“…Direct hydrogenation using molecular H 2 occurred in IPA as a solvent under irradiation with a 150 W white LED light. 84 The study showed selectivity modulation between BHMF and BHMTHF (a ring-reduced product) by adjusting the reaction time and Pd loading. Over 1% Pd@C 3 N 4(0.73) /ZnO (0.27) and 3% Pd@C 3 N 4(0.73) /ZnO (0.27) catalysts, 82% and 92% product selectivity were achieved for BHMF and BHMTHF, respectively, in 6 h and 8 h (Table 1, entries 20 and 21).…”