Hematite (α-Fe2O3)-based photoanodes offer great potential for use in solar hydrogen production as part of efforts to construct a sustainable and renewable energy economy based on photoelectrochemical (PEC) water splitting. A co-doping modification is of the utmost significance for improving PEC performance. To develop an efficient photoanode, a comprehensive grasp of co-dopants with diverse valence states is necessary. Herein, we describe a hydrothermal and dip-coating approach to the fabrication of Hf-doped Fe2O3 (Hf-HT) photoanodes co-doped with Be2+, Al3+, Si4+, and Nb5+ and evaluate the influence of each co-dopant on PEC performance. The PEC characteristic results revealed that Be2+ and Al3+ co-dopants enhanced surface charge separation efficiency, thus accelerating charge transfers at the photoanode–electrolyte interface. Meanwhile, the PEC performance of the Hf-HT photoanode co-doped with Nb did not significantly improve because of the thick Nb2O5 overlayer. However, the use of a Si4+ co-dopant improved the bulk properties of the photoanode. An optimized Hf-HT photoanode co-doped with Be achieved a photocurrent density of 1.98 mA/cm2 at 1.23 VRHE. This demonstrates that ex situ co-doping can have both positive and negative impacts on the PEC activity of photoelectrodes, and the co-dopants used to accomplish the desired outcomes should be considered in detail.

Hematite (α-Fe2O3)-based photoanodes offer great potential for use in solar hydrogen production as part of efforts to construct a sustainable and renewable energy economy based on photoelectrochemical (PEC) water splitting. A co-doping modification is of the utmost significance for improving PEC performance. To develop an efficient photoanode, a comprehensive grasp of co-dopants with diverse valence states is necessary. Herein, we describe a hydrothermal and dip-coating approach to the fabrication of Hf-doped Fe2O3 (Hf-HT) photoanodes co-doped with Be2+, Al3+, Si4+, and Nb5+ and evaluate the influence of each co-dopant on PEC performance. The PEC characteristic results revealed that Be2+ and Al3+ co-dopants enhanced surface charge separation efficiency, thus accelerating charge transfers at the photoanode–electrolyte interface. Meanwhile, the PEC performance of the Hf-HT photoanode co-doped with Nb did not significantly improve because of the thick Nb2O5 overlayer. However, the use of a Si4+ co-dopant improved the bulk properties of the photoanode. An optimized Hf-HT photoanode co-doped with Be achieved a photocurrent density of 1.98 mA/cm2 at 1.23 VRHE. This demonstrates that ex situ co-doping can have both positive and negative impacts on the PEC activity of photoelectrodes, and the co-dopants used to accomplish the desired outcomes should be considered in detail.

This study investigates the degradation of organophosphorus pesticides coupled with hydrogen (H2) production using titanium dioxide modified with fluoride and platinum (F−/TiO2@Pt). In the presence of dicrotophos (300 μM) under anoxic conditions, F−/TiO2@Pt achieved complete degradation and produced 17.87 μmol of H2 after 4 h. In contrast, only 42.4 μM, 92.4 μM, and 251.5 μM of dicrotophos were degraded using bare TiO2, F−/TiO2, and TiO2@Pt, respectively, with significantly lower or negligible H2 production (i.e., 6.60 μmol with TiO2@Pt and negligible amounts with bare TiO2 and F−/TiO2). The markedly enhanced degradation of dicrotophos and H2 generation by the dual surface modification with F− and Pt, compared to single-component modifications, is attributed to the synergistic action of F− and Pt in suppressing charge recombination and promoting electron transfer to H+. Beyond dicrotophos, F−/TiO2@Pt also exhibited superior degradation efficiency and H2 production compared to TiO2@Pt in the presence of various organophosphorus pesticides, including dichlorvos, trichlorfon, acephate, ethoprophos, methacrifos, and fenamiphos. Furthermore, F−/TiO2@Pt outperformed TiO2@Pt under all tested experimental conditions, including variations in F− concentration, catalyst dosage, Pt loading, and pH, except at pH 11.0. This study demonstrates an effective surface modification strategy for dual-function photocatalysis targeting organophosphorus pesticide degradation and H2 production.

The effect of oxalate on the degradation of ranitidine was investigated in the titanium dioxide (TiO2)/hydrogen peroxide (H2O2) system. The degradation of ranitidine proceeded more rapidly, with a 5.7-fold increase in the presence of oxalate. The oxalate-enhanced degradation is attributed to the higher production of hydroperoxyl radicals (HO2 ●) through the complexation of oxalate on the >TiIII (>TiIII(oxalate)n (2n−3)−), generated from inner-sphere electron transfer in the peroxo metal complexes (>TiIV−OOH). This was confirmed by measuring the time-dependent concentrations of HO2 ●, hydroxyl radicals (●OH), and H2O2 both with and without oxalate. The results of reactive oxygen species (ROS)-quenching experiments show that both HO2 ● and singlet oxygen (1O2) are primary oxidants in the TiO2/H2O2/oxalate system. The pseudo-first-order degradation rate constants (k) for ranitidine were higher with increasing TiO2 dosage (up to [TiO2] = 1.0 g/L) and H2O2 concentration but were optimal at [oxalate] = 1 mM. Although other chelating agents, such as citrate, acetate, and malonate, also showed a positive effect on the degradation of ranitidine in the TiO2/H2O2 system, oxalate exhibited the best performance. In addition, the extent of positive effect of oxalate in the TiO2/H2O2 system was much higher than that in the tungsten oxide (WO3)/H2O2 system.