**1. Introduction**

Titanium dioxide (TiO2) nanoparticles (NPs) exhibit interesting potential applications in various fields such as sensors, catalysts, optical filters, anti-reflection coatings, etc. [1]. These TiO2 NPs are widely used in personal care products such as cosmetics, toothpaste, and sunscreen lotions [2–4]. The properties such as stability and non-toxicity make them available for a wide range of applications [5]. In addition to the properties mentioned above, TiO2 is also widely studied due to its electronic, optical, and photocatalytic activity [6,7]. Incorporating with metal ions such as iron, copper, zinc, nickel, chromium has been well addressed, altering the structure, chemical composition, and optical properties of TiO2 [8,9]. Amongst all, iron is the favorable ion to replace Ti in TiO2 as it has the ionic radius of Fe3+ (0.64 Å) which is comparable with Ti4+ (0.68 Å). Thus, Fe3+ can replace Ti4+ comfortably in the crystal structure of TiO2 with some defects.

Moreover, Fe3+ incorporating in TiO2 improves the photocatalytic activity under visible light [10] and reduces the optical bandgap [11]. Moreover, Fe-doped TiO2 has applications in spintronic and magneto-optic devices [12]. Application of Fe-doped TiO2 in gas sensor and photocatalytic degradation prepared from ball milling method was

**Citation:** Ali, A.M.; Sayed, M.A.; Algarni, H.; Ganesh, V.; Aslam, M.; Ismail, A.A.; El-Bery, H.M. Synthesis, Characterization and Photoelectric Properties of Fe2O3 Incorporated TiO2 Photocatalyst Nanocomposites. *Catalysts* **2021**, *11*, 1062. https:// doi.org/10.3390/catal11091062

Academic Editors: Ioan Balint and Monica Pavel

Received: 6 August 2021 Accepted: 27 August 2021 Published: 31 August 2021

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successfully presented by Sunil et al. [13]. Hussain et al. has studied the electrical, optical, and magnetic properties of Fe-doped TiO2 nanotubes [14]. In the literature, there are a variety of approaches for synthesizing Fe-doped TiO2 NPs such as the hydrothermal method [10], thermal hydrolysis [15], wet-chemical synthesis [16], and sol-gel method [17]. The influence of annealing at different temperatures was also studied by Gareso et al. [18] using the co-precipitation method. Rodriguez and co-workers [19] used the sol-gel technique for the synthesis of Fe-incorporated TiO2 and observed a decrease in the optical bandgap from 3.3 eV to 2.9 eV with enhanced absorption in the visible region as the incorporating concentration of Fe increases. Fe-doped TiO2 NPs prepared by the hydrothermal method were applied as an efficient electron mediator for the fabrication of hydrazine chemical sensor using glassy carbon electrode [20] which proves to be a sensitive sensor. The sol-gel routed spin coating technique was employed to synthesize Fe-doped TiO2 NPs and observed that the optical transmittance is was decreased with increasing Fe dopant concentrations [21]. Here, we chose the sol-gel method to synthesize Fe2O3-doped TiO2 NPs in the presence of diethanolamine. This method is easy and cost-effective and can obtain a high degree of purity, homogeneity and small particle size at low temperatures. Despite TiO2 is considered one of the most extensively investigated photocatalysts due to its chemical and photostability, low cost and availability [22,23]. Still, it suffers from a high recombination rate of photogenerated charge carriers and low activity in visible light due to its wide bandgap (Eg). One of the strategies that can overcome this problem is the fabrication of heterostructure with another narrower Eg visible active semiconductor [24]. Band alignment (CB and VB) between semiconductor photocatalysts is crucial. Therefore, we chose hematite Fe2O3 as a visible active photocatalyst (Eg = ca. 2 eV) and combined it with TiO2 to form the composite and investigated. Formation of internal electric field upon light irradiation and Fermi energy level alignment between TiO2 and Fe2O3 will promote the separation of photogenerated electron-hole pairs. Therefore, TiO2–Fe2O3 heterostructures were applied in different photocatalytic-based applications for instance as an effective photoanode for water oxidation in photoelectrochemical cells (PEC) [25], photoreduction of Cr(VI) [26], and dye degradation [27]. Some of the applications use external bias to reduce the recombination rate, as in the case of PEC applications. In view of these important and potential applications, it is worthwhile to study the different properties of Fe-doped TiO2. Hence, in the present work, pure and doped TiO2 with different Fe2O3 contents were prepared by the sol-gel technique. The prepared samples were denoted as PT, 0.1F, 0.5F, and PF for pure TiO2 and Fe doped 0.1, 0.5, and pure Fe2O3, respectively. These materials were subjected to characterize for structural, morphological, optical, and photoelectrochemical properties.
