Grey Rutile TiO2 with Long-Term Photocatalytic Activity Synthesized Via Two-Step Calcination

Precursor- and waste-free synthesis of spark-ablated nanoparticles with enhanced photocatalytic activity and stability towards airborne organic pollutant degradation

Photocatalyst synthesis typically involves multiple steps, expensive precursors, and solvents. In contrast, spark ablation offers a simple process of electrical discharges in a gap between two electrodes made from a desirable material. This enables a precursor- and waste-free generation of pure metal oxide nanoparticles or mixtures of various compositions. This study presents a two-step method for the production of photocatalytic filters with deposited airborne MnOx, TiO2, and ZnO nanoparticles using spark ablation and calcination processes. The resulting MnOx and TiO2 filters demonstrated almost twice the activity with outstanding performance stability, as compared to sol-gel MnO2 and commercial TiO2. The introduced method is not only simple, precursor- and waste-free, and leads to superior performance for the case studied, but it also has future potential due to its versatility. It can easily produce mixed and doped materials with further improved properties, making it an interesting avenue for future research.

Co, Cu, Fe, and Ni Deposited over TiO2 and Their Photocatalytic Activity in the Degradation of 2,4-Dichlorophenol and 2,4-Dichlorophenoxyacetic Acid

Pure TiO2 synthesized by the sol-gel method and subsequently deposited at 5% by weight with Co, Cu, Fe, and Ni ions by the deposition–precipitation method were studied as photocatalysts. The nanomaterials were analyzed by SEM, TEM, UV-Vis DRS, DRX, Physisorption N2, and XPS. The SEM and TEM images present a semi-spherical shape with small agglomerations of particles and average size between 63 and 65 nm. UV-Vis results show that a reduction below 3.2 eV exhibits a redshift displacement and increment in the optical absorption of the nanoparticles promoting the absorption in the UV-visible region. XRD spectra and analysis SAED suggest the characteristic anatase phase in TiO2 and deposited materials according to JCPDS 21-1272. The specific surface area was calculated and the nanomaterial Ni/TiO2 (21.3 m2 g−1) presents a slight increment when comparing to TiO2 (20.37 m2g−1). The information generated by the XPS spectra present the deposition of metallic ions on the support and the presence of different valence states for each photocatalyst. The photocatalytic activity was carried out in an aqueous solution with 80 mg L−1 of 2,4-D or 2,4-DCP under UV light (285 nm) with 100 mg L−1 of each photocatalysts for 360 min. The nanomaterial that presented the best efficiency was Ni/TiO2, obtaining a degradation of 85.6% and 90.3% for 2,4-D and 2,4-DCP, respectively. Similarly, this material was the one that presented the highest mineralization, 68.3% and 86.5% for 2,4-D and 2,4-DCP, respectively. Photocatalytic reactions correspond to the pseudo-first-order Langmuir–Hinshelwood model.

Hydrogenated Amorphous Titania with Engineered Surface Oxygen Vacancy for Efficient Formaldehyde and Dye Removals under Visible-Light Irradiation

Hydrogenated crystalized TiO_2−x with oxygen vacant (O_V) doping has attracted considerable attraction, owing to its impressive photoactivity. However, amorphous TiO₂, as a common allotrope of titania, is ignored as a hydrogenated templet. In this work, hydrogenated amorphous TiO_2−x (HAm-TiO_2−x) with engineered surface O_V and high surface area (176.7 cm² g⁻¹) was first prepared using a unique liquid plasma hydrogenation strategy. In HAm-TiO_2−x, we found that O_V was energetically retained in the subsurface region; in particular, the subsurface O_V-induced energy level preferred to remain under the conduction band (0.5 eV) to form a conduction band tail and deep trap states, resulting in a narrow bandgap (2.36 eV). With the benefits of abundant light absorption and efficient photocarrier transportation, HAm-TiO_2−x coated glass has demonstrated superior visible-light-driven self-cleaning performances. To investigate its formaldehyde photodegradation under harsh indoor conditions, HAm-TiO_2−x was used to decompose low-concentration formaldehyde (~0.6 ppm) with weak-visible light (λ = 600 nm, power density = 0.136 mW/cm²). Thus, HAm-TiO_2−x achieved high quantum efficiency of 3 × 10⁻⁶ molecules/photon and photoactivity of 92.6%. The adsorption capabilities of O₂ (−1.42 eV) and HCHO (−1.58 eV) in HAm-TiO_2−x are both largely promoted in the presence of subsurface O_V. The surface reaction pathway and formaldehyde decomposition mechanism over HAm-TiO_2−x were finally clarified. This work opened a promising way to fabricate hydrogenated amorphous photocatalysts, which could contribute to visible-light-driven photocatalytic environmental applications.