A cheap, simple method of regulating the reduction products of plasmon-driven photochemical reactions at interfaces

Abstract

The application provides a cheap and simple method for regulating and controlling reduction products of photochemical reactions driven by plasmons at an interface, and belongs to the technical field of catalysis.The application can realize high selectivity and high efficiency of reduction of p-mercaptobenzoic acid (PMBA) molecules adsorbed on silver nanoparticles to generate thiophenol (TP), p-mercaptobenzaldehyde (PMBALD) or p-mercaptobenzyl alcohol (PMBALC) by adjusting excitation of localized surface plasmon resonance (LSPR) and the concentration of silver nitrate.In the method, the generation selectivity of TP, PMBALD or PMBALC is close to 100% by fine tuning the concentration of silver nitrate, and the generation selectivity of PMBALD or PMBALC is realized by regulating excitation power, excitation wavelength and excitation time of plasmon resonance (LSPR).

Description

TECHNICAL FIELD

[0001] The present application relates to a method for regulating the photochemical reduction product driven by plasmonic metal at the interface, in particular, a method for regulating the photochemical reaction driven by hot carriers generated by plasmons at the interface, and belongs to the field of catalysis technology. BACKGROUND

[0002] Carboxylic acids are readily available and cost-effective feedstocks for the production of high-value compounds such as aldehydes, alcohols, and decarboxylation products. Among these products, aldehydes are more attractive for their applications in the chemical industry. However, it is still a great challenge to reduce carboxylic acids to aldehydes with high selectivity. Traditionally, the direct reduction of carboxylic acids to aldehydes usually involves toxic solvents and high temperatures, which are not environmentally friendly. Recently, photocatalysis has been applied to the selective reduction of carboxylic acids. In particular, using localized surface plasmon resonance (LSPR), plasmonic photocatalysis has been used to reduce carboxylic acids under mild conditions. The direct electron transfer between the excited plasmonic catalyst and the reactant helps to generate intermediates of highly active radicals, resulting in high reaction selectivity.

[0003] However, only decarboxylation has been achieved in plasmonic-mediated carboxylic acid reduction. The plasmonic reduction of carboxylic acids to aldehydes and alcohols is still a great challenge and has not been reported so far. SUMMARY

[0004] The technical problem solved by the present application is that the present application can realize the high-selectivity and high-efficiency reduction of p-mercaptobenzoic acid (PMBA) molecules adsorbed on silver nanoparticles to produce thiophenol (TP), p-mercaptobenzaldehyde (PMBALD), or p-mercaptobenzyl alcohol (PMBALC) by adjusting the excitation of localized surface plasmon resonance (LSPR) and the concentration of silver nitrate. In the present method, the generation selectivity of TP, PMBALD, or PMBALC approaches 100% by fine-tuning the concentration of silver nitrate, and the generation selectivity of PMBALD or PMBALC is realized by regulating the excitation power, excitation wavelength, and excitation time of the excitation of localized plasmon resonance (LSPR). By adsorbing the reactant PMBA molecules on the surface of the plasmonic silver catalyst and selectively reducing the reactant molecules using the plasmonic effect, the catalytic process is observed using optical in-situ means, the mechanism of plasmonic-enhanced catalysis is elucidated, and the kinetics of selective reduction is explored.

[0005] In order to solve the above technical problems, the technical scheme provided by the present application is: a cheap and simple method for regulating and controlling the reduction product of the photochemical reaction driven by the interface plasmon, and a method for plasmonic metal-mediated photoreduction, wherein silver nanoparticles AgNPs with a diameter of 70 nm are self-assembled on the surface of a cover glass after polyvinylpyrrolidone PVP modification, the above structure is immersed in a p-mercaptobenzoic acid PMBA ethanol solution, the AgNPs and the p-mercaptobenzoic acid PMBA reactant molecules are adsorbed on the surface of the PVP-modified cover glass, the nanoparticle structure is uniformly distributed on the surface of the cover glass, and a structure basis for in-situ monitoring is provided, the reactant molecules are adsorbed on the plasmonic metal by forming a plasmonic metal-sulfur chemical bond, and then the ethanol solution is washed and the air gun is dried, so that a simple catalytic structure of the plasmonic metal adsorbed with the reactant probe molecules is obtained; the reaction of the p-mercaptobenzoic acid to benzene thiophenol, p-mercaptobenzaldehyde and p-mercaptobenzyl alcohol is monitored by in-situ Raman spectroscopy, and the plasmon-driven photoreduction reaction is effectively and simply selectively controlled on the catalytic structure by simply adding silver nitrate solution.

[0006] The specific method is as follows: the cleaned cover glass is immersed in PVP 10 g dissolved in ethanol 20 mL for one day, the excess PVP is washed with ultrapure water, and the air gun is dried.

[0007] 14. 85 mL of AgNP colloid is placed in a 50 mL clean centrifuge tube, a magnetic sub is placed in the centrifuge tube in advance, the rotation speed is set to 660 rpm, 150 muL of 1M NaCl is slowly added drop by drop, the cleaned cover glass is completely immersed in the solution, and adsorption is performed for 7 hours; finally, the above structure is immersed in a p-mercaptobenzoic acid ethanol solution for 2 minutes, the reactant p-mercaptobenzoic acid is adsorbed by forming a chemical bond between the plasmonic metal and sulfur, and then the ethanol solution is washed and the air gun is dried, so that a simple catalytic structure of the plasmonic metal adsorbed with the reactant probe molecules is obtained; and a SERS substrate is obtained.

[0008] Different concentrations of silver nitrate solution are added dropwise on the above SERS substrate to regulate and control the reduction reaction of p-mercaptobenzoic acid mediated by plasmons,

[0009] When the concentration of AgNO3 is zero, only benzene thiophenol TP is produced;

[0010] When the concentration of AgNO3 is 25-50 mM, only p-mercaptobenzaldehyde (PMBALD) is produced;

[0011] When the concentration of AgNO3 is 8-12.7 M, only p-mercaptobenzyl alcohol (PMBALC) is produced;

[0012] wherein the laser power of the localized surface plasmon resonance LSPR is 1.8 mW, the laser wavelength is fixed at 532 nm, and the laser irradiation time is 120 s.

[0013] Preferably, when the concentration of AgNO3 is increased to 25 mM, the production of TP is greatly inhibited, and the Raman signal of TP is hardly observed, while the signal of PMBALD appears in the SERS spectrum, indicating that PMBALD is formed in this case;

[0014] With further increase of the concentration of AgNO3 to 0.1-0.2 M, PMBALD molecules dominate the products of plasmonic-mediated PMBA reduction; in addition, a small amount of PMBALC is observed in the products, indicating that the production of PMBALD is high; further increasing the concentration of AgNO3 leads to a decrease in the production of PMBALD molecules;

[0015] When the concentration of AgNO3 is increased to a high value of 2-4 M, the production of PMBALD molecules is hardly observed; while the production of PMBALC molecules increases sharply, indicating that the production of PMBALC is favored at high AgNO3 concentration;

[0016] At a very high AgNO3 concentration of 8-12.7 M, the production of PMBALC reaches a maximum, and no other products are observed, indicating that the production of PMBALC is high, with a yield of 100%;

[0017] The reaction pathway of plasmonic-mediated PMBA reduction is closely related to the concentration of AgNO3, and high reaction selectivity can be achieved by precisely controlling the concentration of AgNO3 in the reaction system; in addition, by adjusting the concentration of AgNO3, high selectivity for the production of TP, PMBALD or PMBALC molecules can be achieved.

[0018] Preferably, under magnetic stirring, 20 mL of ultrapure water is added to a 100 mL three-necked flask, boiled in an oil bath at 120°C, and then 2 mL of 10 mM AgNO3 is added to the ultrapure water; after boiling the solution again, 0.8 mL of sodium citrate (1 wt%) is injected into the solution; after 1 hour of reaction, AgNP colloids are obtained, with 70 nm AgNPS particles dispersed in water called AgNP colloids.

[0019] Preferably, the excitation of LSPR generally affects the efficiency and / or selectivity of plasmonic-mediated chemical reactions to a great extent; with a fixed concentration of silver nitrate of 50 mM, a laser wavelength of 532 nm, and a laser irradiation time of 120 s, the laser power is changed from 0.16, 0.59, 1.8 to 2.2 mW, and the contribution of plasmonic effect to PMBA reduction is systematically studied;

[0020] At a low laser power of 0.16 mW, PMBALD molecules were produced without the production of PMBALC molecules;

[0021] After 70 s of laser irradiation, the production of PMBALD increased; the peak intensity at 1765 cm -1 was still not high, indicating that the yield of PMBALD was relatively low at this laser power;

[0022] When the laser power was increased to 0.59 mW, the increase in the peak intensity of PMBALD was significantly improved, indicating that the production of PMBALD molecules was much faster at the increased laser power; in addition, the SERS signal of PMBALC molecules was also observed at this laser power, indicating that the production of PMBALC was promoted;

[0023] With the further increase of the laser power to 1.8 mW, the production of both PMBALD and PMBALC molecules increased; higher laser power can lead to stronger LSPR, which can accelerate the plasmon-mediated reaction;

[0024] Further increasing the laser power to 2.2 mW led to a decrease in the production rate of PMBALD and PMBALC; the reduction of aldehyde to alcohol is usually an exothermic reaction, and the increase in temperature will inhibit this reaction thermodynamically.

[0025] Beneficial effects:

[0026] 1. A method for monitoring the plasmon-mediated reduction of p-mercaptobenzoic acid (PMBA) on plasmonic silver nanoparticles (AgNPs) using in-situ Raman spectroscopy. The presence of silver nitrate (AgNO3) inhibits the production of TP and new products of p-mercaptobenzaldehyde (PMBALD) and p-mercaptobenzyl alcohol (PMBALC) are observed. The excitation of LSPR and the presence of AgNO3 are crucial for the controlled reduction of PMBA to PMBALD and PMBALC. The selectivity of the reaction can be largely adjusted by the concentration of AgNO3. The present invention helps to deepen the understanding of plasmon-mediated reduction of carboxylic acid and provides a simple and effective method for controlling plasmon-mediated reduction of carboxylic acid.

[0027] 2、According to the inventors, LSPR can bring new reaction pathways and help to produce new products in photocatalytic reactions. Here, we propose that all aldehydes, alcohols and decarboxylation products can be produced through plasmon-mediated reduction of carboxylic acids, and the selectivity of products can be controlled. On the other hand, LSPR can also enhance the Raman scattering of nearby molecules, providing an effective method for monitoring plasmon-mediated chemical reactions. Raman scattering provides vibrational information of reactants, intermediates and products adsorbed on plasmonic nanocatalysts, which is conducive to qualitative and quantitative analysis of the reaction. Many catalytic reactions have been monitored, and the reaction mechanism has been studied using plasmon-enhanced Raman scattering (also known as surface-enhanced Raman scattering, SERS).

[0028] 3、The present application prepares a uniform and stable silver nanoparticle substrate sheet. The method does not involve toxic and harmful chemicals, and is simple and safe to operate. It provides sites for the adsorption of reactants p-mercaptobenzoic acid, allowing selective reduction to produce TP, PMBALD or PMBALC with a yield close to 100%.

[0029] 4、The present application drops silver nitrate (AgNO3) of different concentrations. Due to the hot carriers generated by the plasmonic effect, with the help of hot electrons generated by the plasma, Ag + can combine with oxygen atoms, and protons can combine with carbon atoms in carboxyl groups. Then, the oxygen atoms in the C=O double bond and the hydrogen atoms in the -OH group can be removed to produce an aldehyde group (in the PMBALD molecule). The aldehyde group can further combine with Ag + , protons and electrons. Finally, when the laser power of the local surface plasmon resonance LSPR is 1.8 mW, the laser wavelength is fixed at 532 nm, and the laser irradiation time is 120 s. PMBALC can be prepared. When the concentration of AgNO3 is 25-50 mM, only p-mercaptobenzaldehyde (PMBALD) is produced; when the concentration of AgNO3 is 8-12.7 M, only p-mercaptobenzyl alcohol (PMBALC) is produced.

[0030] 5、It is well known that AgNO3 is an electron sacrificial agent widely used in photocatalysis. In order to study the contribution of AgNO3 in plasmon-mediated PMBA reduction, we first replaced AgNO3 Figure 4 a) with KBrO3 and Na2S2O8 (50 mM) as electron sacrificial agents. When KBrO3 or Na2S2O8 is used as a sacrificial agent, the main product is still TP, and PMBALD is almost not produced Figure 4a) In addition, even if the reaction time is prolonged, PMBALC cannot be produced in both cases. These two cases are quite different from the case where AgNO3 is present. In the presence of KBrO3 or Na2S2O8, only TP is produced, and PMBALD or PMBALC is not observed. In contrast, in the presence of AgNO3, TP is no longer produced, and PMBALD is the main product. Therefore, silver nitrate can not only act as an electron sacrificial agent in the PMBA reduction process. AgNO3 also plays a unique role in the plasma-mediated reduction of PMBA to PMBALD or PMBALC. We ruled out the possible contribution of other nitrate salts (NaNO3, Ba(NO3)2) to replace AgNO3 in the reaction system. It was found that only TP was produced in the presence of other nitrate salts, and PMBALD was not produced. - Figure 4 b).

[0031] 6、To further investigate the role of plasmons, we systematically changed the laser wavelength. Changing this condition can change the local electromagnetic field near the plasmonic nanostructure. First we adjusted the laser wavelength to 532 nm and 633 nm respectively, without changing other conditions (laser power is 1.8 mW, laser irradiation time is 120 s, silver nitrate concentration is 50 mM). In order to further quantitative comparison, we calculated the peak intensity ratio (Iv -1 / Iv -1 ) at 1765 cm C＝O (assigned to C=O stretch) and 1079 cm CS (assigned to C-S stretch), which gives the process of PMBA reduction reaction. When we use 532 nm laser irradiation, this ratio increases rapidly. By fitting, we calculate the PMBALD generation rate at 532 nm is 0.1299 s -1 , which is about 3.93 times of the PMBALD generation rate at 633 nm (0.03308 s -1 ).

[0032] 7、The application provides a method for realizing high-selectivity reduction of carboxylic acid by using plasmon catalysis. The plasmon effect of AgNPs can selectively catalyze the PMBA reduction reaction, and high product conversion rate and selectivity are obtained, that is, aldehyde, alcohol and other reduction products are generated. Moreover, the plasmon-induced chemical reaction has the characteristics of simplicity and convenience, and the plasmon catalytic reaction can be carried out in aqueous solution or air, which solves the problems of low yield and harsh conditions in the current reduction method for generating alcohol and aldehyde.

[0033] ​8. This invention also utilizes in-situ Raman spectroscopy to study the reduction mechanism of carboxylic acids in situ. By using in-situ Raman spectroscopy as a monitoring method, the selective reduction reaction of PMBA molecules mediated by plasmon resonances was monitored in situ. These findings not only contribute to a deeper understanding of plasmon resonance-mediated chemical reactions but also provide theoretical support for the design of more efficient plasmon resonance catalysts. Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings.

[0035] Figure 1 This is a schematic diagram and characterization of the reaction system based on AgNPs. (a) Schematic diagram showing the reaction pathway of plasma-mediated selective reduction of PMBA. (b) XPS Ag 3d spectra of AgNPs before and after adsorption of PMBA molecules. (c) TEM high-angle ring dark-field image and EDS spectrum of AgNPs adsorbed by PMBA.

[0036] Figure 2 This section describes the typical plasma-mediated reduction process of PMBA molecules, monitored by in-situ SERS spectroscopy. (ac) Pathways of PMBA reduction to (a) TP, (b) PMBALD, and (c) PMBALC. (df) In-situ Raman spectra of plasma-mediated PMBA reduction to (d) TP, (e) PMBALD, and (f) PMBALC. (gi) δ CCC / γ CS γ C＝O / γ CS and γ CO / γ CS The time trajectories of the Raman intensity ratios represent the generation of (g)TP, (h)PMBALD, and (i)PMBALC, respectively.

[0037] Figure 3 The conversion of PMBALD to PMBALC is achieved through plasma-mediated PMBA reduction. (a) In-situ Raman spectra of PMBA reduction to PMBALD and PMBALC, indicating the conversion from PMBALD to PMBALC. (b) Time trajectory of PMBALD production (top), PMBALC production (middle), and PMBALC:PMBALD ratio (bottom).

[0038] Figure 4AgNO3 role in plasma-mediated selective reduction of PMBA. (a) Contribution of the electron sacrificial agent to the selective reduction of PMBA. (b) Contribution of the cation to the selective reduction of PMBA. Ba(N03)2 and NaN03 did not reduce PMBA to PMBALD, indicating that silver ions play a crucial role. (c) Effect of AgN03 concentration on plasma-mediated selective reduction of PMBA. The concentration of AgN03 was varied between 0 and 12.7 M. (d) Plasmonic-mediated TP, PMBALD, and PMBALC production at different concentrations of AgN03, the dotted line indicates the position y = 0.

[0039] Figure 5 Effect of laser power on plasma-mediated selective reduction of PMBA molecules. (a-d) Time traces of the peak intensity of PMBALD and PMBALC during plasma-mediated selective reduction of PMBA molecules at (a) 0.16, (b) 0.59, (c) 1.8, and (d) 2.2 mW laser power. The dotted line indicates the position y = 0. (e) Peak intensity of PMBALD and PMBALC after 120 s of plasma-mediated reduction of PMBA at different laser powers. (f) Intensity ratio of PMBALD and PMBALC after plasma-mediated reduction at different laser powers.

[0040] Figure 6 Schematic representation of the plasma-mediated selective reduction of PMBA molecules on AgNPs. DETAILED DESCRIPTION

[0041] Example 1

[0042] Construction of silver plasmonic system. AgNPs were synthesized according to the wet-chemical method. Briefly, 20 mL of ultrapure water was added to a 100 mL three-necked flask under magnetic stirring and boiled in an oil bath at 120 °C. Then, 2 mL of 10 mM AgN03 was added to the ultrapure water. After boiling the solution again, 0.8 mL of sodium citrate (1 wt%) was injected into the solution. After 1 h of reaction, AgNP colloids were obtained, with 70 nm AgNPs particles dispersed in water called AgNP colloids.

[0043] Example 2

[0044] Preparation of SERS substrate. The AgNPs, PMBA reactant molecules were adsorbed on the PVP modified glass slide surface, which made the nanoparticles structure uniformly distributed on the glass slide surface, providing a structural basis for in situ monitoring. The preparation method is as follows: the cleaned glass slide was soaked in PVP (10 g) dissolved in ethanol (20 mL) for one day, then the excess PVP was washed with ultrapure water and dried with an air gun. Take 14.85 mL of AgNP colloid in a 50 mL clean centrifuge tube, put a magnet in the centrifuge tube in advance, set the speed to 660 rpm, slowly add 150 μL of 1M NaCl drop by drop. Then immerse the cleaned glass slide completely in the solution, adsorb for 7 h. Finally, immerse the above structure in the p-mercaptobenzoic acid ethanol solution for 2 min, and the reactant p-mercaptobenzoic acid is adsorbed by the chemical bond formation between the plasmonic metal and sulfur, and the SERS substrate is obtained.

[0045] We also performed X-ray photoelectron spectroscopy (XPS) measurements. However, almost no shift of the Ag 3d peak was observed after the adsorption of PMBA molecules ( Figure 1 b), and almost no S2s peak was observed, which may be due to the small amount of adsorbed PMBA molecules. Then we used energy dispersive spectroscopy (EDS) mapping to confirm the successful adsorption of PMBA molecules on AgNPs. Obviously, the distribution of S element from PMBA molecules is highly consistent with the distribution of Ag element from AgNPs ( Figure 1 c), indicating the uniform adsorption of PMBA molecules on the surface of AgNPs. These results show that PMBA molecules are successfully adsorbed on the surface of AgNPs.

[0046] Example 3, adding different concentrations of silver nitrate solution to regulate plasmon-mediated p-mercaptobenzoic acid reduction reaction.

[0047] When the laser power is fixed at 1.8 mW, the laser wavelength is fixed at 532 nm, and the laser irradiation time is 120 s, we change the concentration of AgNO3, and study its contribution to the reduction rate and selectivity of PMBA.

[0048] When the concentration of AgNO3 is zero, only TP is produced, indicating that the production rate of TP is very high (up to 100%). When the concentration of AgNO3 increases to 25 mM, the production of TP is greatly inhibited, and almost no Raman signal of TP is observed. At the same time, the signal of PMBALD appears in the SERS spectrum, indicating that PMBALD is formed in this case. When the concentration of AgNO3 is 25-50 mM, only p-mercaptobenzaldehyde (PMBALD) is produced.

[0049] As the AgNO3 concentration further increased to 0.1–0.2 M, PMBALD molecules dominated the plasma-mediated PMBA reduction products. Furthermore, a small amount of PMBALC was observed in the products, indicating a high yield of PMBALD.

[0050] Further increasing the AgNO3 concentration led to a decrease in the production of PMBALD molecules. When the AgNO3 concentration increased to a high value of 2-4 M, almost no PMBALD molecule production was observed. However, the production of PMBALC molecules increased sharply, indicating that high AgNO3 concentrations favor the production of PMBALC.

[0051] At very high AgNO3 concentrations of 8–12.7 M, PMBALC yields reached their maximum, and no other products were observed, indicating that PMBALC yields were very high (up to 100%).

[0052] As attached Figure 4 As shown in Figure c. The above results clearly demonstrate that the plasma-mediated PMBA reduction reaction pathway is closely related to the concentration of AgNO3, and that high reaction selectivity can be achieved by precisely controlling the AgNO3 concentration in the reaction system. Furthermore, by adjusting the AgNO3 concentration, high selectivity can be achieved for the production of TP, PMBALD, or PMBALC molecules.

[0053] Example 4: The contribution of LSPR excitation to plasma-mediated PMBA reduction.

[0054] LSPR excitation typically significantly influences the efficiency and / or selectivity of plasma-mediated chemical reactions. Therefore, we fixed the silver nitrate concentration at 50 mM, the laser wavelength at 532 nm, and the laser irradiation time at 120 s, and systematically investigated the contribution of plasma effects to PMBA reduction by changing the laser power to 0.16, 0.59, 1.8, and 2.2 mW, respectively. Figure 5 As shown. At a low laser power of 0.16 mW, PMBALD molecules were produced, but no PMBALC molecules were produced. Furthermore, PMBALD production increased after 70 seconds of laser irradiation. Note that at ~1765 cm⁻¹... -1The peak intensity of PMBALD was still not high, indicating that the yield of PMBALD was relatively low at this laser power. When the laser power was increased to 0.59 mW, the increase of the peak intensity of PMBALD was significantly improved, indicating that the production of PMBALD molecules was much faster at the increased laser power. In addition, the SERS signal of PMBALC molecules was also observed at this laser power, indicating that the production of PMBALC was promoted. With the laser power further increased to 1.8 mW, the production of both PMBALD and PMBALC molecules was increased. These results are reasonable because higher laser power can lead to stronger LSPR, which can accelerate the plasmon-mediated reactions. However, further increasing the laser power to 2.2 mW led to the decreased production of PMBALD and PMBALC. It is well known that the reduction of aldehyde to alcohol is usually an exothermic reaction, and the increase of temperature can thermodynamically inhibit this reaction. Therefore, the decrease of reaction rate at high laser power of 2.2 mW can be due to the increase of local temperature. However, this change of local temperature cannot be measured in our lab. The above results indicate that the laser power of 1.8 mW is the optimal power for the production of PMBALD and PMBALC. As Figure 5 shown.

[0055] Example 5, Typical pathways of plasmon-mediated PMBA reduction.

[0056] In-situ surface-enhanced Raman spectroscopy (SERS) technique was used to monitor the plasmon-mediated PMBA reduction process on the PMBA-adsorbed AgNP substrates. The three products of TP, PMBALD and PMBALC can be produced through the plasmon-mediated PMBA reduction, and these reduction processes can be continuously monitored Figure 2 a-c).

[0057] Firstly, under the irradiation of 532 nm laser beam, PMBA molecules can be reduced to TP through decarboxylation process (pathway 1, Figure 2 a) with the extension of laser irradiation time, the surface-enhanced Raman scattering intensity gradually increases at 997 and 1021 cm -1 , which are due to the in-plane deformation of benzene ring and C-C stretching combination band (v CCC + δ CC ), and C-C stretching and C-H stretching combination band (v CC + δ CH ), respectively. This increase of intensity indicates the formation of TP molecules. Apparently, the intensity of these two peaks increases sharply within the first 5 s and reaches saturation quickly Figure 2 (g), indicating a fast decarboxylation reaction. Using the method shown in our previous report, the reaction rate within 5 s was determined to be ~0.099 s -1These results indicate that plasma AgNPs can drive the decarboxylation of PMBA molecules to rapidly form TP molecules through cleavage of C-C bonds. Similar observations have been reported in previous literature, indicating that both hot electrons and holes generated by plasma are involved in the decarboxylation reaction.

[0058] In addition to decarboxylation, plasma-mediated reduction of PMBA to PMBALD (pathway 2, Figure 2 b) can also be observed on PMBA-adsorbed AgNPs in the presence of 50 mM AgNO3. -1 Its intensity gradually increases within 100 s of laser irradiation Figure 2 e). This new peak can be attributed to C=O stretching (γ C＝O , indicating the formation of an aldehyde group and the direct generation of PMBALD molecules. In addition, the peak intensity at 1373 cm -1 , which is due to the rocking vibration of C-H in aldehyde, is significantly increased, which is double evidence of the formation of aldehyde (-CHO). To the best of our knowledge, this is the first report of plasma-mediated direct reduction of carboxyl (-COOH) to aldehyde group (-CHO) under in situ monitoring by SERS spectra.

[0059] If saturated AgNO3(12.7 M) is introduced into the plasma-mediated reduction, the carboxyl group in PMBA can be further reduced to a hydroxymethyl group (pathway 3, Figure 2 c), indicating the generation of PMBALC. With laser irradiation, a new SERS peak appears at 1056 cm -1 , which increases sharply in intensity within 1 s Figure 2 f). This peak can be related to C-O stretching vibration (γ CO , indicating the formation of a hydroxymethyl group and the generation of PMBALC molecules. The measured reaction rate is about 1.33 s -1 ( Figure 2 i), indicating that the reduction of PMBA to PMBALC is a very fast process. In addition, broad peaks appear at 788 and 901 cm -1 , with increased intensity. These two peaks are attributed to -CH2 vibration in the -CH2OH group, double confirming the formation of alcohol. To the best of our knowledge, this is the first report and in situ monitoring of plasma-mediated reduction of carboxyl to hydroxymethyl.

[0060] Example 6, Controllable plasma-mediated reduction of PMBALD to PMBALC

[0061] The obtained PMBALD can be further reduced to generate PMBALC on the surface of AgNPs.

[0062] Figure 3is the conversion of PMBALD to PMBALC in the plasma-mediated PMBA reduction. (a) In-situ Raman spectra of PMBA reduction to PMBALD and PMBALC, indicating the conversion from PMBALD to PMBALC. (b) Time trace of PMBALD production (top panel), PMBALC production (middle panel) and PMBALC:PMBALD ratio (bottom panel), the dotted line indicates the position y = 0. The bottom panel indicates that more PMBALC molecules are produced with laser irradiation, which means the conversion from PMBALD to PMBALC.

[0063] In the production of PMBALD, we prolonged the illumination period. The reduction process was monitored under 1.8 mW 532 nm laser beam irradiation. Within the first 150 s, the intensity of the broad Raman peak at ~1765 cm

[0064] ~1765 cm -1 (C=0 stretch, γ C＝O ) slowly increased, indicating the reduction of PMBA to PMBALD. After 150 s, a new Raman peak started to appear at ~1056 cm -1 (C-O stretch, γ CO ) with slowly increasing intensity Figure 3 a). This new Raman peak can be attributed to the C-O vibration in the -CH2OH group, indicating the production of PMBALC. Then, the intensity ratios of γ C＝O / γ CS and γ CO / γ CS were used to quantify the formation of PMBALD and PMBALC Figure 3 b).

[0065] Obviously, the peak intensity of the -CHO group increased sharply after laser irradiation, and the increase of the peak intensity gradually slowed down with further laser irradiation. In contrast, the peak intensity of the -CH2OH group increased slowly under laser irradiation. To more clearly show this difference, we plotted the peak intensity ratio of -CH2OH and -CHO group versus irradiation time Figure 3 b), which clearly shows the time lag of the formation of ethanol compared to aldehyde. These results indicate that the generation of ethanol follows the generation of aldehyde, indicating that ethanol is generated from aldehyde.

[0066] Example 7, Role of AgNO3 in the plasma-mediated PMBA reduction

[0067] Obviously, AgNO3 plays a crucial role in the plasma-mediated selective reduction of PMBA. In the absence of silver nitrate, only decarboxylation occurs. In the presence of silver nitrate, the decarboxylation is suppressed, and the reduction of PMBA to aldehyde and / or alcohol is the main reaction process.

[0068] It is well known that AgNO3is an electron sacrificial agent widely used in photocatalysis. To investigate the contribution of AgNO3in the plasma-mediated PMBA reduction, we first replaced AgNO3with the electron sacrificial agents of KBrO3and Na2S2O8(50 mM) Figure 4 a) When KBrO3or Na2S2O8as the sacrificial agent, the main product is still TP, and PMBALD is almost not produced Figure 4 a). Moreover, even with the extension of reaction time, PMBALC cannot be produced in both cases. These two cases are quite different from the case with AgNO3present. In the presence of KBrO3or Na2S2O8, only TP is produced, and no PMBALD or PMBALC is observed. In contrast, in the presence of AgNO3, TP is no longer produced, and PMBALD is the main product. Therefore, silver nitrate can not only act as an electron sacrificial agent in the PMBA reduction process. AgNO3also plays a unique role in the plasma-mediated PMBA reduction to PMBALD or PMBALC. To further reveal the role of AgNO3in the plasma-mediated PMBA reduction, the role of nitrate ions (NO3 - ) and silver ions (Ag + ) in the plasma-mediated PMBA reduction was investigated, respectively. First, we ruled out the possible contribution of NO3 - by replacing AgNO3with other nitrate salts (NaNO3, Ba(NO3)2) in the reaction system. It was found that only TP was produced without PMBALD Figure 4 b) in the presence of other nitrate salts. These results indicate that NO3 - is not the main contributor to the production of PMBALD or PMBALC. We speculate that Ag + plays a key role in the high-selective reduction of PMBA to PMBALD or PMBALC.

[0069] Example 8, Mechanism of Controlling the Reduction Product of Plasmon-Driven Photochemical Reactions at the Interface.

[0070] The above results show that the excitation of LSPR is crucial for the selective reduction of PMBA molecules. It is reported that the decarboxylation of PMBA to generate TP molecules involves hot electrons and hot holes. Obviously, the reduction of carboxylic acid to aldehyde and ethanol involves hot electrons. These hot electrons and hot holes can be provided by exciting LSPR on silver nanoparticles. Therefore, controlling the reduction of PMBA to TP, PMBALD, and / or PMBALC is apparently a plasma-mediated phenomenon. On the other hand, the presence of AgNO3is also a key to controlling the plasma-mediated PMBA reduction. In particular, Ag +plays a key role in the high selective reduction of PMBA to PMBALD and PMBALC. Different concentrations of AgNO3 can largely tune the selectivity of the plasma-mediated reduction of PMBA.

[0071] Based on the above results, we proposed a reaction mechanism. The mechanism of plasma-mediated decarboxylation of PMBA has been reported in the literature. In our case, the reduction of PMBA to TP follows the same reaction mechanism. When AgNO3 is introduced, Ag + may participate in the reaction, helping to produce PMBALD and PMBALC. As Figure 6 shown, with the help of hot electrons generated by plasma, Ag + can combine with oxygen atoms, and protons can combine with carbon atoms in the carboxyl group. Then, the oxygen atom in the C=O double bond and the hydrogen atom in the -OH group can be removed, producing an aldehyde group (in the PMBALD molecule). The aldehyde group can further combine with Ag + , protons, and electrons. Finally, the alcohol of PMBALC can be prepared. Therefore, only TP molecules are produced in the absence of AgNO3. In the presence of AgNO3, PMBALD and PMBALC molecules can be produced. Since more Ag + is involved in the production of PMBALC molecules, higher AgNO3 concentrations can be beneficial to the production of PMBALC.

[0072] Comparative Example 1

[0073] To further investigate the role of plasmons, we systematically changed the laser wavelength. Changing this condition can change the local electromagnetic field near the plasmonic nanostructure. First we adjusted the laser wavelength to 532 nm and 633 nm, respectively, without changing other conditions (laser power of 1.8 mW, laser irradiation time of 120 s, silver nitrate concentration of 50 mM). To make a quantitative comparison, we calculated the peak intensity ratio (Iv -1 / Iv -1 ) at 1765 cm C＝O (due to C=O stretching) and 1079 cm CS (due to C-S stretching) for the process of PMBA reduction reaction. When we used 532 nm laser irradiation, this ratio increased rapidly. By fitting, we calculated the PMBALD generation rate at 532 nm to be 0.1299 s -1 , which is about 3.93 times the PMBALD generation rate at 633 nm (0.03308 s -1 ).

[0074] The present application is not limited to the specific technical solutions described in the above embodiments, and any technical solution formed by equivalent replacement is within the protection scope of the present application.

Claims

1. A method for regulating the reduction products of a plasmon-driven photochemical reaction at an interface, characterized in that: A plasma-metal-mediated photoreduction method involves modifying a coverslip surface with polyvinylpyrrolidone (PVP) and then self-assembling 70 nm diameter silver nanoparticles (AgNPs). This structure is then immersed in an ethanol solution of p-mercaptobenzoic acid (PMBA). The adsorption of AgNPs and PMBA reactant molecules on the PVP-modified slide surface ensures a uniform distribution of the nanoparticle structure, providing a structural basis for in-situ monitoring. The reactant molecules are then adsorbed onto the plasma metal via plasma-metal-sulfur chemical bonds. After rinsing with ethanol solution and drying with an air gun, a plasma metal catalytic structure adsorbing reactant probe molecules is obtained. The reactions from p-mercaptobenzoic acid to thiophenol, p-mercaptobenzaldehyde, and p-mercaptobenzyl alcohol are monitored using in-situ Raman spectroscopy. Furthermore, the plasmon-driven photoreduction reaction can be selectively manipulated by adding silver nitrate solution to this catalytic structure. The specific method is as follows: Soak the cleaned glass slide in 10g of PVP dissolved in 20mL of ethanol for one day. Wash off the excess PVP with ultrapure water and dry with an air gun. Take 14.85mL of AgNP colloid into a clean 50mL centrifuge tube, place a magnetic ball in the tube beforehand, set the centrifuge speed to 660rpm, and slowly add 150μL of 1M NaCl drop by drop. Then completely immerse the cleaned glass slide in the solution and allow it to adsorb for 7 hours. Finally, soak the above structure in an ethanol solution of p-mercaptobenzoic acid for 2 minutes. Adsorb the reactant p-mercaptobenzoic acid through the chemical bonding between the plasma metal and sulfur. Rinse with ethanol solution and dry with an air gun to obtain a plasma metal catalytic structure that adsorbs the reactant probe molecules; thus, a plasma-enhanced Raman scattering (SERS) substrate is obtained. Different concentrations of silver nitrate solution were added to the above SERS substrate to regulate the plasmon-mediated reduction reaction of p-mercaptobenzoic acid. When the AgNO3 concentration is zero, only thiophenol TP is produced; When the AgNO3 concentration is 25-50mM, only p-mercaptobenzaldehyde (PMBALD) is produced. When the AgNO3 concentration is between 8 and 12.7 M, only p-mercaptobenzyl alcohol (PMBALC) is produced. The laser power for localized surface plasmon resonance (LSPR) was 1.8 mW, the laser wavelength was fixed at 532 nm, and the laser irradiation time was 120 s.

2. The method for reducing products by a plasmon-driven photochemical reaction at the interface according to claim 1, characterized in that: When the AgNO3 concentration was increased to 25 mM, the production of TP was greatly suppressed and almost no Raman signal of TP was observed. At the same time, the signal of PMBALD appeared in the SERS spectrum, indicating that PMBALD was formed under these conditions. As the AgNO3 concentration further increased to 0.1-0.2 M, PMBALD molecules dominated the plasma-mediated PMBA reduction products; in addition, a small amount of PMBALC was also observed in the products, indicating that the yield of PMBALD was high; further increasing the AgNO3 concentration led to a decrease in the production of PMBALD molecules. When the AgNO3 concentration increased to a high value of 2-4 M, almost no PMBALD molecules were produced; however, the production of PMBALC molecules increased sharply, indicating that high AgNO3 concentrations favor the production of PMBALC. At very high AgNO3 concentrations of 8–12.7 M, the yield of PMBALC reached its maximum, and no other products were observed, indicating that the yield of PMBALC was very high, with a yield of 100%. The plasma-mediated reduction of PMBA is closely related to the concentration of AgNO3, and high reaction selectivity can be achieved by precisely controlling the concentration of AgNO3 in the reaction system. In addition, high selectivity for TP, PMBALD, or PMBALC molecules can be achieved by adjusting the concentration of AgNO3.

3. The method for reducing products by a plasmon-driven photochemical reaction at the interface according to claim 1, characterized in that: Under magnetic stirring, 20 mL of ultrapure water was added to a 100 mL three-necked flask and boiled in an oil bath at 120 °C. Then, 2 mL of 10 mM AgNO3 was added to the ultrapure water. After boiling the solution again, 0.8 mL of sodium citrate (1 wt%) was injected into the solution. After reacting for 1 hour, AgNP colloids were obtained. AgNP particles with a diameter of 70 nm dispersed in water are called AgNP colloids.

4. The method for reducing products by a plasmon-driven photochemical reaction at the interface according to claim 1, characterized in that: With the silver nitrate concentration fixed at 50 mM, the laser wavelength at 532 nm, and the laser irradiation time at 120 s, the laser power was changed from 0.16, 0.59, and 1.8 to 2.2 mW, and the contribution of plasma effect to PMBA reduction was systematically studied. At a low laser power of 0.16mW, PMBALD molecules were generated, but PMBALC molecules were not generated. After 70 seconds of laser irradiation, the production of PMBALD increased; at 1765 cm⁻¹ -1 The peak intensity at that point is still not high, indicating that the yield of PMBALD is relatively low at this laser power. When the laser power was increased to 0.59 mW, the increase in the peak intensity of PMBALD was significantly improved, indicating that the generation of PMBALD molecules was much faster at the increased laser power; in addition, SERS signal of PMBALC molecules was also observed at this laser power, indicating that it promoted the generation of PMBALC. As the laser power was further increased to 1.8mW, the production of both PMBALD and PMBALC molecules increased; higher laser power can lead to stronger LSPR, which can accelerate plasma-mediated reactions. Further increasing the laser power to 2.2mW resulted in a decrease in the productivity of PMBALD and PMBALC.

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