TiO2 exists naturally in three crystalline forms: anatase, rutile, brookite, and TiO2 (B). These polymorphs exhibit different properties and consequently different photocatalytic performances. This paper aims to clarify the differences between titanium dioxide polymorphs, and the differences in homophase, biphase, and triphase properties in various photocatalytic applications. However, homophase TiO2 has various disadvantages such as high recombination rates and low adsorption capacity. Meanwhile, TiO2 heterophase can effectively stimulate electron transfer from one phase to another causing superior photocatalytic performance. Various studies have reported the biphase of polymorph TiO2 such as anatase/rutile, anatase/brookite, rutile/brookite, and anatase/TiO2 (B). In addition, this paper also presents the triphase of the TiO2 polymorph. This review is mainly focused on information regarding the heterophase of the TiO2 polymorph, fabrication of heterophase synthesis, and its application as a photocatalyst.

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TiO2 material is composited with silica obtained from natural sand with indirect sonochemistry method. The addition of SiO2 increase the photocatalyst activity of TiO2 as an antibacterial against S. aureus and P. aeruginosa.

Heavy metals are non-biodegradable and have a high toxicity effect on microorganisms which makes their presence in the environment extremely dangerous. The method of handling heavy metal waste by photocatalysis techniques using TiO2/SiO2 composite showed a good performance in reducing harmful pollutants. In this study, SiO2 from Bengkulu beach sand, Indonesia, was used as a support material for TiO2 photocatalyst to remove Cr(VI) and Pb(II). SiO2 was obtained through leaching techniques using NaOH as a solvent. The TiO2/SiO2 composite photocatalyst was synthesized using a solvothermal method at 130 °C and then characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and a particle size analyzer (PSA). Based on the XRD diffractogram, the synthesized TiO2 showed the anatase structure while the SiO2 showed the amorphous structure. The Ti–O–Si bond is defined in the infrared (IR) spectra, which indicates that the relationship between TiO2 and SiO2 is a chemical interaction. The results of SEM and PSA characterizations show agglomerated spherical (round) particles with a mean particle size of 616.9 nm. The TiO2/SiO2 composite of 7:1 ratio showed the highest photocatalytic activity after 180 min of ultraviolet (UV) irradiation, with a concentration-decrease percentage of 93.77% and 93.55% for Cr(VI) and Pb(II), respectively.