Defa Wang

Hydroxyaldehydes are terminally differentiated building blocks and key intermediates for organic synthesis. Unsymmetric oxidation of α,ω-diols to aliphatic hydroxyaldehydes is rarely developed due to the tremendous difficulties and challenges to avoid overoxidation. Here, we disclose a heterogeneous photocatalytic approach with Pt-loaded TiO₂ as a photocatalyst to realize the semioxidation of α,ω-diols to aliphatic hydroxyaldehydes. 6-Hydroxyhexanal is produced via photocatalytic dehydrogenation of 1,6-hexanediol at a rate of ca. 21.7 g/m²/h with selectivity higher than 96% and simultaneous generation of stoichiometric amounts of H₂. The absence of aggressive oxygen-based radical species, appropriately controlled oxidation capacity of photogenerated holes, low affinity of hydroxyaldehyde for photocatalysts in the suitable acetonitrile solvent matrix, and fine-tuned reaction temperature ensure that the oxidation of 1,6-hexanediol terminates at 6-hydroxyhexanal. This work reports on a conceptual breakthrough in photocatalytic interface design for high-value-added molecular synthesis via controlled surface redox reactions.

Methylamine hydrochlorides (MACls) are important building blocks in organic synthesis, yet their conventional production requires energy-intensive, multistep processes. Herein, we report a photocatalytic strategy for the direct synthesis of MACls from methanol and ammonium chloride under mild conditions. A high MACls yield of 29.62 mmol·g^-1 is achieved within 4 h over Pd-decorated TiO₂ with oxygen vacancies, outperforming most previously reported photocatalytic C-N coupling systems. In situ spectroscopy, isotope effects, and theoretical studies reveal that methanol is initially oxidized to formaldehyde, a key intermediate that reacts with ammonium chloride via nucleophilic condensation and successive methylation to form C-N bonds, thereby yielding MACls. Photoexcitation enables both the thermodynamically and kinetically unfavorable methanol-to-formaldehyde conversion and drives stepwise methylation reactions, which are otherwise inactive in the dark. The cooperative interaction between Pd and oxygen vacancies promotes charge separation and methanol dehydrogenation, resulting in highly efficient MACls photosynthesis. This work advances mechanistic insights into photocatalytic C-N bond formation and presents a sustainable approach for producing value-added C-N compounds from simple C₁ and nitrogen feedstocks.

Constructing a heterojunction is considered one of the most effective strategies for enhancing photocatalytic activity. Herein, we employ Ta₃N₅ and tubular graphitic carbon nitride (TCN) to construct a Ta₃N₅/TCN van der Waals heterojunction via electrostatic self-assembly for enhanced photocatalytic H₂ production. SEM and TEM results show that Ta₃N₅ particles (~300 nm in size) are successfully anchored onto the surface of TCN. The light absorption capability of the Ta₃N₅/TCN heterojunction is between those of Ta₃N₅ and TCN. The strong interaction between Ta₃N₅ and TCN with different energy structures (Fermi levels) by van der Waals force renders the formation of an interfacial electric field to drive the separation and transfer of photogenerated charge carriers in the Ta₃N₅/TCN heterojunction, as evidenced by the photoluminescence (PL) and photoelectrochemical (PEC) characterization results. Consequently, the optimal Ta₃N₅/TCN heterojunction exhibits a remarkable H₂ production rate of 12.73 mmol g⁻¹ h⁻¹ under visible light irradiation, which is 3.3 and 16.8 times those of TCN and Ta₃N₅, respectively. Meanwhile, the cyclic experiment demonstrates excellent stability of the Ta₃N₅/TCN heterojunction upon photocatalytic reaction. Notably, the photocatalytic performance of 15-TaN/TCN outperforms the most previously reported CN-based and Ta₃N₅-based heterojunctions for H₂ production. This work provides a new avenue for the rational design of CN-based van der Waals heterojunction photocatalysts with enhanced photocatalytic activity.

The increased light absorption, reactive sites, CO ₂ adsorption/activation, and desorption energy barrier of CO* in Co/TiO ₂ –TiN synergistically account for the selective photothermocatalytic CO ₂ reduction into CH ₄ .

Visible-light-driven photocatalytic hydrogen production is one of the ideal green technologies for solar-to-chemical energy conversion. Carbon nitride (C₃N₄, CN) has been attracting extensive attention for its suitable band structure and stability, but the efficiency of photocatalytic hydrogen evolution is low due to insufficient visible-light absorption and rapid charge recombination. Herein, we develop a novel (F, K)-co-doped CN (FKCN) catalyst via a facile thermal polymerization approach using KOH-modified melamine and NH₄F as the dopant precursors. The FKCN catalyst demonstrates broadened light absorption, significantly enhanced charge separation, and excellent cyclic stability. And the optimal F_(0.15)K₍₆₎CN catalyst achieves a hydrogen evolution rate of as high as 3101.5 μmol g⁻¹ h⁻¹ (12-fold that of pristine CN) under visible-light irradiation (λ ≥ 420 nm), which is among the best element-doped CN photocatalysts. This work highlights the effectiveness of a multi-element doping strategy in designing CN-based photocatalysts for efficient hydrogen evolution.

The efficiency of CO₂ photoreduction is often limited by the low reactivity of CO₂ molecules and the rapid recombination of photogenerated charge carriers in most of the photocatalysts developed so far. In this study, we report a newly developed p-type Bi₂Te₃/SrTiO₃ (pBT/STO) nanocomposite for efficient CO₂ photoreduction. Upon light irradiation, the thermoelectric pBT with a strong light absorption capacity generates the photothermal effect favoring the activation of CO₂ molecules. Meanwhile, a temperature gradient formed in pBT induces a thermoelectric field via the Seebeck effect, which promotes the charge carriers’ separation/transfer. In addition, the excellent electric conductivity and large work function render pBT an efficient cocatalyst for further improving the charge carriers’ separation/transfer. Owing to the synergistic photothermoelectric (PTE) effect on activation of CO₂ molecules and promotion of charge separation/transfer, the efficiency of CO₂ photoreduction over pBT/STO is significantly enhanced. We achieve the highest CO evolution rate of 28.0 μmol·g_cat⁻¹·h⁻¹ over the optimal pBT(3)/STO, which is 12.8 times that of pure STO. This work suggests that a thermoelectric material and a semiconductor can be incorporated into a nanocomposite system for efficient CO₂ reduction via the synergistic photothermoelectric effect on activating the CO₂ molecules and promoting the charge carriers’ separation/transfer.

Photoreduction of CO₂ and H₂O into fuels and value‐added chemicals is an effective solution to address global energy issues. However, developing photocatalysts with high activity and selectivity remains a major challenge. Herein, we report Ag nanoparticles (NPs) loaded FeVO₄ (FVO) composite photocatalyst for highly efficient and selective photoreduction of CO₂ to CO. Under a 300 W Xe lamp irradiation, the optimal Ag₁‐FVO catalyst exhibits a CO yield of 255.4 μmol g⁻¹ h⁻¹ and a CO selectivity of 99.7 %, which are dramatically higher than those of pure FVO alone. The significantly enhanced photocatalytic performance could be attributed to Ag NPs on the surface of FVO, which improve the separation efficiency of photogenerated carriers and promote the adsorption/activation of CO₂ molecules. This study suggests that modification of semiconductor photocatalysts with Ag NPs is an effective method for enhancing the CO₂ photoreduction activity.

Photoreduction of CO₂ into value‐added chemicals and fuels is a promising green technology for solar‐to‐chemical conversion. Owing to the atomic utilization, unique metal‐support interaction, and unsaturated coordination active sites, single‐atom catalysts (SACs) have been attracting great attention in achieving high activity and selectivity of CO₂ photoreduction reactions. On the other hand, carbon nitride (C₃N₄) with abundant periodically unsaturated coordination of nitrogen atoms can serve as an excellent support for anchoring metal single atoms. In this context, extensive research efforts have been paid in C₃N₄‐based SACs for CO₂ photoreduction in recent years. In this review, we report the recent advances in C₃N₄ supported SACs for CO₂ photoreduction. We start from the introduction of synthetic strategies of various C₃N₄ supported metal SACs. Secondly, the main advanced characterization techniques and calculation methods for identifying the single‐atoms and their coordination environments of C₃N₄‐based SACs are summarized. Thirdly, some state‐of‐the‐art works on the rational design of C₃N₄‐based SACs and their applications in CO₂ photoreduction are introduced. Lastly, we briefly summarize the main challenges and propose important perspectives of C₃N₄‐based SACs in CO₂ photoreduction. This review is expected to provide some useful guidelines for the development of efficient and stable C₃N₄‐based SACs for CO₂ photoreduction.

As a promising technology to mitigate global carbon emissions, photothermal catalytic CO₂ reduction remains a great challenge in increasing the conversion efficiency and regulating the product selectivity. Herein, a series of phase‐separated Ni–Mo alloy catalysts for efficient photothermal CO₂ reduction with tunable CO selectivity is reported. With the increase of Mo content, the evolution rate and selectivity of CO increases. The optimal catalyst Ni₁Mo₁ achieves 32.1% CO₂ conversion with 98.0% of CO selectivity and 71.1 mmol g_cat⁻¹ h⁻¹ of CO evolution rate under a 300 W xenon lamp irradiation. Further increasing the Mo content reduces the CO evolution rate while maintaining the high CO selectivity. In the mechanistic study, it is revealed that the Ni–Mo alloy with an appropriate Ni/Mo ratio (e.g., Ni₁Mo₁) possesses a modified electronic structure with more negative d‐band center, which increases the light absorption, reduces the H₂ dissociation, and favors the CO desorption, thereby leading to efficient and selective photothermal reduction of CO₂ to CO. In this work, a viable strategy to design nickel‐based catalysts is provided for efficient and selective photothermal CO₂ reduction via composition‐mediated modification of electronic structure.

Modifying the polymeric carbon nitride (CN) with organic molecules is a promising strategy to enhance the photocatalytic activity. However, most previously reported works show that interchain embedding and edge grafting of the organic molecule can hardly be achieved simultaneously. Herein, we successfully synthesized organic molecule bifunctionalized CN (MBCN) through copolymerization of melon and sulfanilamide at a purposely elevated temperature of 550 °C. In MBCN, the edge grafted and interchain embedded benzene rings act as the electron‐donating group and charge‐transfer channel, respectively, rendering efficient photocatalytic H₂O₂ production. The optimal MBCN exhibits a significantly improved non‐sacrificial photocatalytic H₂O₂ generation rate (54.0 μmol g⁻¹ h⁻¹) from pure water, which is 10.4 times that of pristine CN. Experimental and density functional theory (DFT) calculation results reveal that the enhanced H₂O₂ production activity of MBCN is mainly attributed to the improved photogenerated charge separation/transfer and decreased formation energy barrier (▵G) from O²⁻ to the intermediate 1,4‐endoperoxide (⋅OOH). This work suggests that simultaneous formation of electron donating group and charge transfer channel via organic molecule bifunctionalization is a feasible strategy for boosting the photocatalytic activity of CN.