**1. Introduction**

Photocatalysis is an applicable technology to control the pollutants and contaminations that are released by industrial activity to the nature. The important feature of photocatalysis is that it is possible to replace the high-temperature reactions to eliminate contaminations with reactions that can take place at room temperature, hence, maintain fossil fuel for other purposes. Heterogeneous photocatalysis process implied a material (usually semiconductor) with a certain bandgap that can be activated by light (at certain wavelength). When the semiconductor crystal is subjected to light with a wavelength higher than the bandgap, electrons are normally activated and move from valance band to conduction band creating a positive hole instead, this process is called electron/hole separation. After formation of electron and holes, one of the two following situations might take place: a) recombination between the electron and holes or b) electron and holes reach the surface and activate an organic molecule on the surface of the semiconductor crystal, that is, electrons will participate in reduction process, while the holes participate in oxidation process. Several free radicals were detected as a result of photocatalytic process, notably hydroxyl radicals (• OH) and superoxide anions (O2 •− ). The formed radicals are participating in the continuous reactions with the adjacent organic molecules until total minimization. Therefore, the overall process can be summarized in four main steps: (a) adsorption of organic molecule on the surface of the semiconductor crystal, (b) electron/hole formation, (c) reaction between electron and/or holes with the adsorbed molecule, (d) over-reaction might take place, and (e) desorption of the products (**Figure 1**) [1].

According to Scopus®, in the last 10 years (between 2013 and 2022), the researchers in different fields reported their research results in photocatalysis in more than 66,262 papers (**Figure 2**). Out of these papers, 7850 papers reported the findings in the area of air purification. From these papers, only 1258 papers (only 1.8% of the total photocatalysis publications) discussed the utilization of photocatalysis to purify air from short-chain hydrocarbons. These statistics clearly show that the research in the field of air purification from hydrocarbons needs attention to be developed and improved. Hence, more efforts must be performed in this research area because a clean environment is one of the research strategic plans in most countries.

**Figure 1.** *The photocatalytic process over semiconductor crystals.*

#### **Figure 2.**

*The number of publications in the last 10 years of the photocatalysis research. The orange line represents the number of photocatalysis in hydrocarbon elimination area.*
