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The catalytic reduction of 4-nitrophenol to 4-aminophenol by using aqueous sodium borohydride (NaBH4) solution is the most widely used model reaction to evaluate the catalytic activity of nanoparticles (NPs). It is generally believed that NaBH4 is the hydrogen source for the −NO2 to −NH2 conversion. Water can also contribute hydrogen for the molecular conversion, but this potential hydrogen source has been overlooked since solvents are typically not involved in the chemical reactions. Surprisingly, through simple experiments using isotopic solvent (D2O) or reducer (NaBD4), we find that the reduction reaction cannot proceed without the presence of water or other protic solvents. The vibrational spectroscopic analysis of the final reduction products also confirms that the hydrogen atoms in this conversion originate from the protic solvent. Therefore, it is water (or any protic solvents) rather than the hydride reducer that provides the hydrogen for the formation of the 4-aminophenol product. A reaction mechanism for the hydride reduction of 4-nitrophenol is proposed according to this finding. This work highlights the critical role of protic solvents in heterogeneous catalysis and provides a new perspective for understanding interfacial reactions.

The activation of the carbon–halogen (C–X) bond is of great significance in chemical synthesis. Herein, we report on in situ surface-enhanced Raman spectroscopic monitoring of hot electron-induced C–X bond cleavage on noble metal nanoparticle (NP) monolayers. We find that the cleavage is closely related to the localized surface plasmon resonance on metal surfaces, which is simulated using the three-dimensional finite-difference time-domain method. Because of higher plasmonic activity, the dissociation of the C–X bond on 80 nm Ag NP monolayers is much faster than that on 40 nm Ag and 80 nm Au NP monolayers. By adding hole compensators for continuous generation of hot electrons, the reaction can be greatly improved, indicating that the plasmonic hot electrons are responsible for dehalogenation. Finally, the mechanism of hot electron-induced C–X bond cleavage with an intermediate of carbon radicals is proposed. This work provides new opportunities for C–X activation by using plasmonic metals which will benefit the highly efficient conversion of aryl halide compounds.

Selective oxidation of alcohols to aldehydes under mild conditions is important for the synthesis of high‐value‐added organic intermediates but still very challenging. For most of the thermal and photocatalytic systems, noble metal catalysts or harsh reaction conditions are required. Herein, the synthesis and use of Ag2S‐CdS p‐n nanojunctions as an efficient photocatalyst for selective oxidation of a series of aromatic alcohols to their corresponding aldehydes is reported. High quantum efficiencies (59.6% and 36.9% under 380 and 420 nm, respectively) are achieved in air atmosphere at room temperature. Photoluminescence and photo‐electrochemical tests show that the excellent performance is mainly due to the p‐n junction‐enhanced charge separation and transfer for the activation of both O2 (in air) and substrates. This study demonstrates the potential of p‐n junction in photocatalytic synthesis under mild conditions.

Deuteration has found important applications in synthetic chemistry especially for pharmaceutical developments. However, conventional deuteration methods using transition-metal catalysts or strong bases generally involve harsh reaction conditions, expensive deuterium source, insufficient efficiency, and poor selectivity. Herein, we report an efficient visible-light-driven dehalogenative deuteration of organic halides using plasmonic Au/CdS as photocatalyst and D2O as deuterium donor. Electron transfer from Au to CdS, which has been confirmed by surface-enhanced Raman spectroscopy, plays a decisive role for the plasmon-mediated dehalogenation. The deuteration is revealed to proceed via a radical pathway in which substrates are first activated by the photoinduced electron transfer to generate aryl radicals, and the radicals are further trapped by D2O to give deuterated products. Under visible-light irradiation, excellent deuteration efficiency is achieved with high functional group tolerance and a wide range of substrates at room temperature. Compared with bare CdS, the photocatalytic activity increases ∼18 times after the loading of plasmonic Au nanoparticles. This work sheds light on the interfacial charge transfer between plasmonic metals and semiconductors as an important criterion for rational design of visible-light photocatalysts.