In the process of methane (CH₄) oxidation to methanol (CH₃OH), CH₃OH is more easily oxidized than CH₄, resulting in inevitable peroxide phenomenon. In this work, we innovatively proposed a tandem reaction pathway to obtain a photocatalytic oxidation process of CH₄ with high activity and selectivity. This work confirms that the methyl hydrogen peroxide (CH₃OOH), the first product of CH₄ oxidation by H₂O₂, is then completely reduced to CH₃OH in an electron-rich environment. Under irradiation, H₂O₂ was excited into hydroxyl radicals (·OH) and hydroperoxyl radicals (·OOH) on brookite TiO₂ photocatalyst. The ·OH oxidized CH₄ to form methyl radicals (·CH₃), which then reacted with ·OOH to form CH₃OOH. CH₃OOH gained electrons on Pt nanoparticles (NPs) and was reduced to CH₃OH. At this point, low concentration of ·OH was difficult to further oxidize CH₃OH, so that it can exist stably. Under the conditions of room temperature (25 °C) and atmospheric pressure, the productivity of CH₃OH was 883 μmol/(g·h), which was 4 times more than the reported photocatalytic CH₄ oxidation system with the same reaction conditions, and the selectivity was 100% in liquid products (98.77% for all products). The photocatalyst showed excellent stability and maintained ＞ 85% product activity after 9 catalytic cycles. This work contributed to the development of highly efficient and selective CH₄ photooxidation system under mild conditions.

Partial oxidation of methane into primary oxidation products with high value remains a challenge. In this work, photocatalytic oxidation of methane (CH₄) with high methyl hydroperoxide (CH₃OOH) selectivity is achieved using pure titanium oxide (TiO₂) without any cocatalyst at room temperature and atmospheric pressure. The CH₃OOH production rate can reach up to 2050 ± 88 μmol·g⁻¹·h⁻¹ at pH ≈ 7.0 with 100% selectivity in the liquid product. The stable reaction cycle can reach more than 30 times. This low-cost system achieves superior CH₄ conversion activity and selectivity compared with similar work. The energy of hydrogen peroxide (H₂O₂) to adsorbed hydroperoxyl radical (*OOH) has a significantly lower reaction energy than conversion to adsorbed hydroxyl radical (*OH) on the (210) surface of the TiO₂. The *OOH preferentially combines with methyl radical (·CH₃) to form the most energetically favorable CH₃OOH. The mild oxidative environment of this system prevents the reduction of CH₃OOH to CH₃OH or over-oxidation of CH₄, which ensures the final CH₃OOH with high selectivity and stability. This work provided a low-cost but highly efficient method to achieve partial oxidation with superior selectivity, i.e., to convert CH₄ into high-value chemicals.

Photocatalytic water splitting (PWS) has attracted widespread attention as a sustainable method for converting solar to green hydrogen energy. So far PWS research has mainly focused on the development of artificial photocatalytic hydrogen production systems for pure water. It is more practically attractive to create systems for seawater, i.e., to reduce the cost of hydrogen production and make better use of naturally occurring water resources. Herein, brookite, anatase, and rutile TiO₂ nanoparticles are investigated as photocatalysts to explore the feasibility of such thought and have shown attractive hydrogen production performance under full solar spectrum without any sacrificial agent. It is worth noting that, brookite TiO₂, has more suitable band gap position and excellent photoelectric properties compared with anatase and rutile TiO₂, and has higher efficiency and stability in the process of hydrogen production. The photocatalytic hydrogen production rate of brookite TiO₂ can reach up to 1,476 μmol/g/h, the highest value reported for TiO₂-based systems and most other photocatalysts in seawater splitting under full spectrum. As the Cl⁻ ions in seawater go through a cycle of oxidation and reduction, no Cl₂ is detected in the solar hydrogen production from seawater.

Solar energy is an inexhaustible renewable energy source. Among the various methods for solar energy conversion, photocatalytic hydrogen (H₂) production is considered as one of the most promising ways. Since Fujishima pioneered this field in 1972, photocatalytic water splitting to produce H₂ has received widespread attention. Up to now, abundant semiconductor materials have been explored as photocatalysts for pure water splitting to produce H₂. However, photocatalytic seawater splitting is more in line with the concept of sustainable development, which can greatly alleviate the problem of limited freshwater resource. At present, only few studies have focused on the process of H₂ production by photocatalytic seawater splitting due to the complex composition of seawater and lack of suitable photocatalysts. In this review, we outline the most recent advances in photocatalytic seawater splitting. In particular, we introduce the H₂ production photocatalysts, underlying mechanism of ions in seawater on photocatalytic seawater splitting, current challenges and future potential advances for this exciting field.

The TiO₂-H₂O₂ system possesses excellent oxidation activity even under dark conditions. However, the mechanism of this process is unclear and inconsistent. In this work, the binary component system containing TiO₂ nanoparticles (NPs) with single electron-trapped oxygen vacancy (SETOV, V_O·) and H₂O₂ exhibit excellent oxidative performance for tetracycline, RhB, and MO even without light irradiation. We systematically investigated the mechanism for the high activity of the TiO₂-H₂O₂ under dark condition. Reactive oxygen species (ROS) induced from H₂O₂ play a significant role in improving the catalytic degradation activities. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) results firstly confirm that H₂O₂ is primarily activated by SETOVs derived from the TiO₂ NPs through direct contribution of electrons, producing both ·O₂^-/·OOH and ·OH, which are responsible for the excellent reactivity of TiO₂-H₂O₂ system. This work not only provides a new perspective on the role of SETOVs playing in the H₂O₂ activation process, but also expands the application of TiO₂ in environmental conservation.

Hierarchical TiO₂ photocatalysts with a one-dimensional heterojunction were synthesized via a facile template-free hydrothermal method. The TiO₂ photocatalysts were flower-like microspheres with a 3 μm diameter. The base structure of the flower-like microspheres was a uniform nanowire with a 10 nm diameter. Anatase films were evenly coated onto the surface of the rutile TiO₂ nanowires to form a one-dimensional core-shell base structure. This kind of one-dimensional heterojunction is conducive to the separation of charge carriers. In addition, the hierarchical TiO₂ microspheres possessed a good mesoporous structure with a high specific surface area of 260 m²/g. Thus, the light scattering and utilization efficiency were improved in this structure. The photocatalysts exhibited better performance in both photocatalytic oxidation and reduction reactions. Moreover, the novel TiO₂ photocatalysts displayed excellent stability in these reactions. This kind of hierarchical TiO₂ structure has never been reported in the literature. The hierarchical structure and one-dimensional heterojunction were vital to the increase in quantum efficiency. Therefore, these hierarchical TiO₂ photocatalysts have potential applications in the environmental and energy fields, such as in photocatalytic degradation, hydrogen production, Li-ion batteries, and dye-sensitized solar cells.