| Summary: | Pd nanoparticles (PdNPs) were successfully deposited on the surface of Fe(III)-modified hydroxyapatite (HAp), which was subsequently used as a photocatalyst for simultaneous photocatalytic H<sub>2</sub> evolution and xylose conversion. The structural phase and morphology of the pristine HAp, FeHAp, and Pd@FeHAp were examined using XRD, SEM, and TEM instruments. At 20 °C, Pd@FeHAp provided a greater xylose conversion than pristine HAp and FeHAp, about 2.15 times and 1.41 times, respectively. In addition, lactic acid and formic acid production was increased by using Pd@FeHAp. The optimal condition was further investigated using Pd@FeHAp, which demonstrated around 70% xylose conversion within 60 min at 30 °C. Moreover, only Pd@FeHAp produced H<sub>2</sub> under light irradiation. To clarify the impact of Fe(III) doping in FeHAp and heterojunction between PdNPs and FeHAp in the composite relative to pure Hap, the optical and physicochemical properties of Pd@FeHAp samples were analyzed, which revealed the extraordinary ability of the material to separate and transport photogenerated electron-hole pairs, as demonstrated by a substantial reduction in photoluminescence intensity when compared to Hp and FeHAp. In addition, a decrease in electron trap density in the Pd@FeHAp composite using reversed double-beam photoacoustic spectroscopy was attributed to the higher photocatalytic activity rate. Furthermore, the development of new electronic levels by the addition of Fe(III) to the structure of HAp in FeHAp may improve the ability to absorb light by lessening the energy band gap. The photocatalytic performance of the Pd@FeHAp composite was improved by lowering charge recombination and narrowing the energy band gap. As a result, a newly developed Pd@FeHAp composite might be employed as a photocatalyst to generate both alternative H<sub>2</sub> energy and high-value chemicals.
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