# Highly Active under VIS Light M/TiO\({}_{2}\) Photocatalysts Prepared by Single-Step Synthesis
## 1 Introduction
Au has been used to dope TiO\({}_{2}\) and has successfully improved its photocatalytic efficiency by almost 30% [14]. A V/Co/TiO\({}_{2}\) photocatalyst prepared by a sol-gel process has also been able to upgrade the degradation efficiency of TiO\({}_{2}\), as seen in the literature, by reducing the required irradiation time by 40% [15]. The use of Pt, as well as Au, have been investigated as possible dopants for TiO\({}_{2}\), with the positive result of a two-fold increase in the MB concentration that the photocatalysts can degrade in 1h of light exposure [16]. A nanocomposite Fe/TiO\({}_{2}\) photocatalyst has also been tested, while the performance of it revealed that the doped catalyst was able to perform better than pure TiO\({}_{2}\) due to a reduction in band gap energy of the Fe-TiO\({}_{2}\) composite to 1.45 eV [17]. The doping of TiO\({}_{2}\) with Ag, Sn, and Zn has been proven to enhance the photocatalytic efficiency of TiO\({}_{2}\) thin films, while Zn-doped TiO\({}_{2}\) films with a doping level of 5-mole percent exhibited the highest enhancement in photocatalytic properties [18]. On the other hand, the purity and nanostructure of the films are detrimental to efficient photocatalysts to suspend non-radiative recombination, according to numerous literature reports [19; 20; 21]. The addition of MnTiO\({}_{3}\) to TiO\({}_{2}\) has also been investigated in the literature and was found to be a good candidate for the removal of organic pollutants from industrial wastewater [22]. The addition of plasmonic metals (Au, Ag, and Cu) to TiO\({}_{2}\) has been researched, and the effect of pH on the photodegradation of MB has been documented. The improved photocatalytic performance observed is attributed to the altered electrical properties of the composite catalysts [23]. The study of the photocatalytic efficiency of Cu/TiO\({}_{2}\) nanocomposites, synthesized via atomic layer deposition (ALD), showed that the layer acted as a means of enhancing the photocatalytic activity of TiO\({}_{2}\) and the effect of the number of deposition cycles used was also investigated [24]. Another photocatalyst that has been studied in the literature is Cu/TiO\({}_{2}\) on SiO\({}_{2}\) substrate in order to facilitate nanoparticle formation. Nanoparticles were then studied to measure their efficiency in degrading MB when applied to building materials. The effect of Cu concentration on the catalyst performance was also studied, determining that there is an optimum level of doping (5 at.%) [25]. The use of MoS\({}_{2}\)/Cu/TiO\({}_{2}\) nanoparticles prepared through hydrolysis has been investigated and exhibited improved performance compared to pure TiO\({}_{2}\). This is due to a decrease in the band gap values, their smaller crystallite size, the increase in the O adsorption, and the favoring of the anatase phase against rutile [26]. In the literature, the synthesis of Cu/TiO\({}_{2}\)/MSM (mesoporous silica microsphere) has been studied, and the existence of an optimum concentration of Cu (0.1 wt%) has been documented [27]. The optimum concentration of copper could possibly depend on the structure and the properties of the matrix material, while the preparation or deposition approach also affects and determines the properties of the composite materials. Thus, sol-gel methods report different optima in comparison with the sputtering methods [28; 29]. Another metal that has recently been studied for potential employment as a doping agent in TiO\({}_{2}\) is Ag. A nanocomposite structure of Ag/TiO\({}_{2}\) synthesized via the use of plasma has been studied with respect to its property of activating the photodegradation of MB under solar light. An optimum amount of doping (2.0 mol.%) was observed, while it was also evidenced that Ag improved the photocatalytic properties of TiO\({}_{2}\)[30]. The synthesis of Ag/TiO\({}_{2}\) has also been studied when prepared through precipitation, and it resulted in an increase in the degradation efficiency in comparison to the pure TiO\({}_{2}\) catalyst.