Photocatalytic Hydrogen Production Performance of ZnCdS/CoWO4 Heterojunctions in the Reforming of Lignin Model Compounds

Abstract

Biomass reforming under mild conditions for synergistic hydrogen production, driven by renewable solar energy, has rapidly emerged as a promising strategy that not only enables the efficient reutilization of biomass but also facilitates the generation of high-purity hydrogen. In this work, ZnCdS (ZCS) nanoparticles and CoWO₄ (CW) nanocrystals were assembled via a solvothermal method to construct a ZCS/CW S-type heterojunction composite. The resultant materials' physicochemical characteristics were methodically described. With lignin model compounds (PP-ol) and sodium lignosulfonate as substrates, the ZnCdS/CoWO₄-10% catalyst demonstrated a significant generation of hydrogen activity, producing hydrogen at rates of 223.30 μmol·g^-1·h^-1 and 140.28 μmol·g^-1·h^-1, respectively, according to experimental results. The formation of heterojunctions endows composite photocatalysts with higher hydrogen evolution rates compared to single-component catalysts. This is attributed to energy band bending at the interface of the heterojunction, which facilitates efficient charge separation while maintaining strong redox capabilities. High-value compounds like phenol and acetophenone were formed when the oxidation products in the post-reaction lignin model compound solution were subsequently analyzed using high-performance liquid chromatography. Additionally, a convincing mechanism for the catalytic reaction was suggested. It is expected that this study will offer a viable route for the creation of effective photocatalytic materials, high-value organic waste transformation, and sustainable hydrogen production.

Keywords: heterojunction; hydrogen generation; photo-reforming; photocatalytic.

Figure 1

Diagram illustrating the synthesis process of the photocatalytic composite.

Figure 2

(a) Standard card patterns of ZCS and CW, (b) XRD patterns of samples.

Figure 3

SEM images of (a) ZnCdS, (b) CoWO₄, (c,d) SEM images of ZCS/CW-10%.

Figure 4

(a–c) TEM images of composite materials, (d) EDX elemental mapping.

Figure 5

Fine spectrum of (a) Zn 2p, (b) Cd 3d, (c) S 2p, (d) W 4f, (e) O 1s, (f) Co 2p.

Figure 6

(a) UV–Vis absorption spectra, (b) the relationship between (αhυ)² and (hυ), (c,d) Mott Schottky plots of ZCS and CW.

Figure 7

(a,b) ZCS, (c,d) CW, (e,f) ZCS/CW-10% nitrogen adsorption–desorption isotherms and pore size distribution curves.

Figure 8

CW, ZCS, ZCS/CW-10% of (a) Steady-state fluorescence spectra, (b) Transient photocurrent response, (c) Electrochemical impedance, (d) ESR test of ZCS/CW-10%.

Figure 9

(a) Hydrogen production rate graph, (b) Comparison of hydrogen production rates (the error bar represents the standard deviation, p < 0.05).

Figure 10

(a) HPLC spectra of the solution under different CW loadings, (b) Conversion rate and hydrogen production under different CW loadings.

Figure 11

(a) Photocatalytic hydrogen production cycling experiment conducted on the ZCS/CW-10% sample, (b) SEM and TEM profile of ZCS/CW-10% material after the reaction, (c) FT-IR pattern and (d) XRD pattern of the fresh and recycled photocatalyst.

Figure 12

(a) Hydrogen production rate graph, (b) Comparison of hydrogen production rates, (c) Comparison of hydrogen production rates of sodium sulfonate and model compounds for catalysts, (d) Photocatalytic hydrogen production cycle experiment conducted on the ZnCdS/CoWO₄-10% sample (the error bar in the (b) represents the standard deviation, p < 0.05).

Figure 13

Charge Transfer at the Interface Between ZCS and CW.

Figure 14

Method for the cleavage of C–O bonds in lignin model compounds under light irradiation.

Figure 15

Mechanism of hydrogen production from photocatalytic reforming of lignin model compounds by ZCS/CW-10%.